Registration Dossier
Registration Dossier
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EC number: 204-617-8 | CAS number: 123-31-9
Carcinogenicity
Administrative data
Description of key information
Fischer 344 rat, males, 103 w gavage (5 d/w) at doses of 0, 25 and 50 mg/kg bw/d, combined carcinogenicity and chronic toxicity study similar to OECD Guideline 453: NOAEL 25 mg/kg bw/d, LOAEL 50 mg/kg bw/d (decreased body weight, increased severity of chronic progressive nephropathy, significant increase of renal tubuli adenoma; renal findings as sex- and species-specific effect of no toxicological relevance for human risk assessment) (Kari et al., 1992; NTP, 1989)
HQ has been classified in Carcinogenicity Category 2 (suspected human carcinogen) according to C&L of the GHS. However, the indications that HQ may cause carcinogenic effects in humans are rather questionable as the critical evaluation of the total evidence from the cancer bioassays and epidemiological studies together with more recent reevaluations of the carcinogenic potential of HQ as well as recent studies on the mechanisms of the induction of renal neoplasms show. Additionally, principally HQ was found to inhibit the neoplastic responses of other carcinogenic compounds, and to show no tumor promoting activity. Toxicokinetic studies demonstrated a significant metabolic capacity of humans for the detoxification of HQ and an existing background exposure to HQ, e.g. from food or endogenous production. HQ was not found to exert a genotoxic activity in vivo under exposure conditions relevant for human exposure although a genotoxic potential principally exists. Consequently, in this special case a threshold approach seems to be justified and a DNEL for repeated dose toxicity can be derived.
Key value for chemical safety assessment
Carcinogenicity: via oral route
Link to relevant study records
- Endpoint:
- carcinogenicity: oral
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- not specified
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- comparable to guideline study with acceptable restrictions
- Remarks:
- Compared to the criteria of a Guideline carcinogenesis bioassay this study shows the following restrictions: single dose group with reduced animal number of 30 males and 30 females, limited documentation of test conditions and test results, no historical control data for neoplastic and non-neoplastic lesions reported; study results acceptable for evaluation as key study
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to other study
- Qualifier:
- no guideline followed
- Principles of method if other than guideline:
- Neoplastic and non-neoplastic histopathological lesions were evaluated after chronic application of a single dose of hydroquinone. Further, clinical signs, survival, body weight gain, food and water consumption, and weights of liver and kidneys were examined. Foci of cellular alteration in liver were evaluated quantitatively.
- GLP compliance:
- not specified
- Species:
- rat
- Strain:
- B6C3F1
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River Japan, Inc., Atsugi
- Age at study initiation: 6 w
- Weight at study initiation: not specified
- Fasting period before study: no
- Housing: 5 per cage
- Diet: powdered diet MF, Oriental Yeast Co., Ltd., Tokyo, ad libitum
- Water: tap water ad libitum
- Acclimation period: 1 w
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +- 2
- Humidity (%): 60 +- 10
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12 / 12 - Route of administration:
- oral: feed
- Details on exposure:
- DIET PREPARATION
- Rate of preparation of diet (frequency): twice a month
- Mixing appropriate amounts with (Type of food): powdered diet
- Storage temperature of food: no data - Analytical verification of doses or concentrations:
- not specified
- Duration of treatment / exposure:
- 96 w
- Frequency of treatment:
- daily
- Post exposure period:
- no
- Remarks:
- Doses / Concentrations:
0, 0.8%
Basis:
nominal in diet - Remarks:
- Doses / Concentrations:
0, 1046 mg/kg bw/d in male rats, 1486 mg/kg bw/d in female rats
Basis:
actual ingested
calculated from food consumption - No. of animals per sex per dose:
- 30
- Control animals:
- yes, plain diet
- Details on study design:
- - Dose selection rationale: same dose used in prior studies with HQ and analogs
- Observations and examinations performed and frequency:
- CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: twice daily
BODY WEIGHT: Yes
- Time schedule for examinations: weekly for the first 14 w, once every 4 weeks thereafter
FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Time schedule for examinations: over a two-day period before weighing
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes
WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: over a two-day period before weighing
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: No
CLINICAL CHEMISTRY: No
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No - Sacrifice and pathology:
- GROSS PATHOLOGY: Yes, complete gross necropsy; organ weights of liver and kidneys
HISTOPATHOLOGY: Yes
Tissues examined in all rats: aorta, adrenal glands, epididymis/prostrate/testes, seminal vescicles or ovaries/uterus, esophagus, eyes, gross lesions, Harderian gland, heart, kidneys, liver, lungs, mammary gland, lymph nodes, pancreas, parathyroid glands, pituitary gland, salivary glands, skin, small and large intestines, spleen, skeletal muscle, stomach, thymus, thyroid gland, tongue, trachea, urinary bladder, vagina. - Other examinations:
- Quantitative evaluation of foci of cellular alteration in the liver: by color image processor (Spicca-II, Nippon Avionics Co., Ltd., Tokyo) (no further data given, criteria of evaluation not specified)
- Statistics:
- Analysis of variance, Student's t-test for significant differences between mean values; incidences of histopathologic lesions by tw-sided Fisher's exact propability test; severity of non-neoplastic lesion development by the Mann-Whitney test
- Clinical signs:
- no effects observed
- Mortality:
- no mortality observed
- Body weight and weight changes:
- effects observed, treatment-related
- Food consumption and compound intake (if feeding study):
- no effects observed
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- no effects observed
- Ophthalmological findings:
- not examined
- Haematological findings:
- not examined
- Clinical biochemistry findings:
- not examined
- Urinalysis findings:
- not examined
- Behaviour (functional findings):
- not examined
- Organ weight findings including organ / body weight ratios:
- effects observed, treatment-related
- Gross pathological findings:
- effects observed, treatment-related
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Histopathological findings: neoplastic:
- effects observed, treatment-related
- Details on results:
- Effects in the single dose group:
BODY WEIGHT AND WEIGHT GAIN
Males: Body weight gain was lower in dosed males compared to controls from ca. week 2 on. However, a maximum of weight was observed at week 66 with values of ca. 46 and 43 g in controls and HQ-treated males, which was followed by a decrease of body weight in both groups up to final body weights of 37 +- 6 g and 38 +- 5 g. Consequently, body weights of control males fell by about 20% and those of dosed males by about 12% during the last 30 weeks of the study (effect not discussed by the authors, no data on food consumption available).
Females: Body weight gain was lower in dosed females compared to controls from ca. week 10 until the end of the study. Final body weights in controls and HQ-treated females were 47 +- 7 g and 34 +- 5 g, decrease of 28% statistically significant with P<0.01
FOOD CONSUMPTION
Both sexes: reported to be comparable to controls, however, no data are specified
ORGAN WEIGHTS (for details see Table 1)
Females: statistically significant increases of relative liver and kidney weights, P<0.01
Evaluation: There were no correlating histopathological findings as increased incidences of hyperplasia in kidneys or livers of female mice.
GROSS PATHOLOGY
Both sexes: small nodular lesions (< 1 mm in size) in the forestomach lumen of many mice
HISTOPATHOLOGY: NON-NEOPLASTIC (for details see Table 2)
KIDNEYS:
Males: no chronic nephropathy, no indication of alpha-2µ-globulin nephropathy (unpublished data)
LIVER:
Males: statistically significant increases in dosed compared to control males of incidences of centrilobular hypertrophy, 26% vs. 0%, P<0.01, and of incidences of foci of cellular alteration 47% vs. 14%, P<0.05
FORESTOMACH:
Both sexes: statistically significant increases of forestomach hyperplasia with P<0.01: males 37% vs. 4%, females 47% vs. 10%
HISTOPATHOLOGY: NEOPLASTIC (for details see Table 2)
KIDNEYS:
Males: significantly increased incidences of renal tubular hyperplasia (30% vs. 0%), P<0.01; no significant increase of renal tubular adenomas (10% vs. 0%, dosed vs. control males)
LIVER:
Males: statistically significant increases in dosed compared to control males of hepatocellular adenoma, 47% vs. 22%, P<0.05
EVALUATION: The increased incidence of renal tubular hyperplasia was considered to be biologically significant by the authors of the study, since spontaneous appearance of renal neoplastic lesions in this mouse strain is very rare. Since there was no indication of renal toxicity or of alpha-2µ-globulin nephropathy a different mechanism must be considered. The enhanced development of altered liver foci and hepatocellular adenomas in male mice is an effect that has also been observed after application of other phenolic antioxidants.
HISTORICAL CONTROL DATA (no data specified)
OTHER FINDINGS
Quantitative evaluation of foci of cellular alteration: significant increase in dosed rats compared to control values with P<0.05 in males of the number of foci per cm2 liver, P<0.05; various types of liver foci such as basophilic, eosinophilic and clear cell - Relevance of carcinogenic effects / potential:
- This study was not performed according to existing guidelines and standards for carcinogenicity studies. As there is only a single dose group it is not possible to make any conclusions on dose-response-relationships both for non-neoplastic and neoplastic effects. Dose selection was not based on dose range finding studies but is a dose used in previous toxicological examinations with hydroquinone. The animal number per test group and sex of 30 was distinctly lower than the standard of 50. Consequently, for the evaluation of neoplastic effects only 30 hydroquinone-treated mice per sex were available in total on contrast to 150 (3 dose groups with 50 mice each) in a guideline study, and so the probability to detect rarely occurring neoplasms is distinctly reduced in this study. In the publication, tumour incidences are only specified for the kidney, the liver and the forestomach, and there are no historical control incidences of the investigating laboratory given. Consequently, the study is of limited reliability for an assessment of the carcinogenic potential of hydroquinone.
In male mice exposed to a dose of 1046 mg/kg bw/d via diet for 96 weeks, there was a significant increase of the incidence of hepatocellular adenoma compared to the concurrent control group (47% vs. 22%), whereas the incidence of hepatocellular carcinoma was slightly decreased in the dosed males (20% vs. 26%). No statistical evaluation of the combined incidences of hepatocellular adenoma or carcinoma was presented. The increased incidence of adenoma correlated with statistically significantly increased indicences of foci of cellular alteration and of liver hypertrophy. The enhanced development of these preneoplastic and neoplastic lesions is an effect that has also been observed after application of other phenolic antioxidants suggesting a structure-activity-relationship. The increased incidence of forestomach hyperplasia indicates a local irritant effect of hydroquinone that was also observed in high incidence after gavage application of a dose of 400 mg/kg bw to female B6C3F1 mice for 13 weeks (NTP, 1989). Consequently, the tested dose of 1046 mg/kg bw/d is considered to be in the range of the maximum tolerable dose (MTD).
There was no indication of a neoplastic effect in female mice exposed to a dose of 1486 mg/kg bw/d via diet for 96 weeks. At this dose the final body weight of female mice was significantly reduced compared to control females by 28% indicating that this dose was in the range of the maximum tolerable dose (MTD). This is also confirmed by the increased incidence of forestomach hyperplasia indicating a local irritant effect of hydroquinone that was also observed in high incidence after gavage application of a dose of 400 mg/kg bw to female B6C3F1 mice for 13 weeks (NTP, 1989). - Dose descriptor:
- NOAEL
- Sex:
- male/female
- Basis for effect level:
- other: only a single dose tested
- Remarks on result:
- not determinable
- Remarks:
- no NOAEL identified. Effect type:toxicity
- Dose descriptor:
- dose level:
- Effect level:
- 1 046 mg/kg bw/day (actual dose received)
- Sex:
- male
- Basis for effect level:
- other: renal tubular hyperplasia, liver hypertrophy, forestomach hyperplasia
- Remarks on result:
- other: Effect type: toxicity
- Dose descriptor:
- dose level:
- Effect level:
- 1 486 mg/kg bw/day (actual dose received)
- Sex:
- female
- Basis for effect level:
- other: statistically significant reduction of final body weight and increase of relative kidney and liver weights, forestomach hyperplasia
- Remarks on result:
- other: Effect type: toxicity
- Dose descriptor:
- dose level:
- Effect level:
- 1 046 mg/kg bw/day (actual dose received)
- Sex:
- male
- Basis for effect level:
- other: increased incidence of liver adenomas
- Remarks on result:
- other: Effect type: carcinogenicity
- Dose descriptor:
- NOEL
- Effect level:
- 1 486 mg/kg bw/day (actual dose received)
- Sex:
- female
- Basis for effect level:
- other: no increased tumour incidences
- Remarks on result:
- other: Effect type: carcinogenicity
- Conclusions:
- In male mice exposed to a dose of 1046 mg/kg bw/d via diet for 96 weeks, there was a significant increase of the incidence of hepatocellular adenoma compared to the concurrent control group.
There was no indication of a neoplastic effect in female mice exposed to a dose of 1486 mg/kg bw/d via diet for 96 weeks. - Executive summary:
Hydroquinone was continuously fed to groups of 30 male and 30 female B6C3F1 mice for 96 weeks at a single food concentration of 0.8% corresponding to doses of 1,046 mg/kg bw/d in males and 1,486 mg/kg bw/d in females (no guideline conditions). Control groups received plain diet. Mortality, clinical sign, body weight gain, and food and water consumption were recorded. Mice were sacrificed after 96 weeks for complete gross necropsy, determination of kidney and liver weights and comprehensive histopathological examination. Additionally, a quantitative evaluation of foci of cellular alteration in the liver was made (criteria of evaluation not specified). Details of the histopathological examination are only given for the findings in kidneys, livers and the forestomach.
There were no significant differences in survival between dose and control group, and no compound-related clinical signs. Male mice showed increasing body weights both in dosed and control mice only up to study week 66. Thereafter, body weights of control males fell by about 20% and those of dosed males by about 12% during the last 30 weeks of the study so that final body weights of dosed and control males were comparable (no data on food consumption, effect not discussed by the authors). In female mice, a statistically significant decrease (P<0.01) of final body weight of 28% compared to control females was found while food consumption was not affected and body weights increased continuously in dosed and control females up to the end of study. Female mice showed statistically significant increases of relative liver and kidney weights (P<0.01). Small nodular lesions were grossly visible in the forestomach lumen of mice of both sexes.
In hydroquinone-treated males, significantly increased incidences of renal tubular hyperplasia (30% vs. 0%, P<0.01) were observed with no significant increase of renal tubular adenomas (10% vs. 0%, dosed vs. control males).The increased incidence of renal tubular hyperplasia was considered to be biologically significant by the authors of the study, since spontaneous appearance of renal neoplastic lesions in this mouse strain is very rare. As there was no indication of renal toxicity or of alpha-2µ-globulin nephropathy a different mechanism must be considered. Also in males, there were statistically significant increases of incidences of centrilobular hypertrophy (26% vs. 0%) and of foci of cellular alteration (47% vs. 14%), of hepatocellular adenoma (47% vs. 22%, dosed vs. control males, P<0.05). In both sexes, forestomach hyperplasia was statistically significantly increased (males 37% vs. 4%, females 47% vs. 10%, P<0.01 dosed vs. controls), indicating a local irritant effect of hydroquinone that had also been observed in high incidence in another study with gavage application (NTP, 1989).
In male mice exposed to a dose of 1046 mg/kg bw/d via diet for 96 weeks, there was a significant increase of the incidence of hepatocellular adenoma compared to the concurrent control group. There was no indication of a neoplastic effect in female mice exposed to a dose of 1486 mg/kg bw/d (maximum tolerable dose) via diet for 96 weeks.
- Endpoint:
- carcinogenicity: oral
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- not specified
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- comparable to guideline study with acceptable restrictions
- Remarks:
- Compared to the criteria of a Guideline carcinogenesis bioassay this study shows the following restrictions: single dose group with reduced animal number of 30 males and 30 females, limited documentation of test conditions and test results, no historical control data for neoplastic and non-neoplastic lesions reported; study results acceptable for evaluation as key study
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to other study
- Qualifier:
- no guideline followed
- Principles of method if other than guideline:
- Neoplastic and non-neoplastic histopathological lesions were evaluated after chronic application of a single dose of hydroquinone. Further, clinical signs, survival, body weight gain, food and water consumption, and weights of liver and kidneys were examined. Foci of cellular alteration in liver were evaluated quantitatively.
- GLP compliance:
- not specified
- Species:
- rat
- Strain:
- Fischer 344
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River Japan, Inc., Atsugi
- Age at study initiation: 6 w
- Weight at study initiation: not specified
- Fasting period before study: no
- Housing: 5 per cage
- Diet: powdered diet MF, Oriental Yeast Co., Ltd., Tokyo, ad libitum
- Water: tap water ad libitum
- Acclimation period: 1 w
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +- 2
- Humidity (%): 60 +- 10
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12 / 12 - Route of administration:
- oral: feed
- Details on exposure:
- DIET PREPARATION
- Rate of preparation of diet (frequency): twice a month
- Mixing appropriate amounts with (Type of food): powdered diet
- Storage temperature of food: no data - Analytical verification of doses or concentrations:
- not specified
- Duration of treatment / exposure:
- 104 w
- Frequency of treatment:
- daily
- Post exposure period:
- no
- Remarks:
- Doses / Concentrations:
0, 0.8%
Basis:
nominal in diet - Remarks:
- Doses / Concentrations:
0, 351 mg/kg bw/d in male rats, 368 mg/kg bw/d in female rats
Basis:
actual ingested
calculated from food consumption - No. of animals per sex per dose:
- 30
- Control animals:
- yes, plain diet
- Details on study design:
- - Dose selection rationale: same dose used in prior studies with HQ and analogs
- Observations and examinations performed and frequency:
- CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: twice daily
BODY WEIGHT: Yes
- Time schedule for examinations: weekly for the first 14 w, once every 4 weeks thereafter
FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Time schedule for examinations: over a two-day period before weighing
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes
WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: over a two-day period before weighing
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: No
CLINICAL CHEMISTRY: No
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No - Sacrifice and pathology:
- GROSS PATHOLOGY: Yes, complete gross necropsy; organ weights of liver and kidneys
HISTOPATHOLOGY: Yes
Tissues examined in all rats: aorta, adrenal glands, epididymis/prostrate/testes, seminal vescicles or ovaries/uterus, esophagus, eyes, gross lesions, Harderian gland, heart, kidneys, liver, lungs, mammary gland, lymph nodes, pancreas, parathyroid glands, pituitary gland, salivary glands, skin, small and large intestines, spleen, skeletal muscle, stomach, thymus, thyroid gland, tongue, trachea, urinary bladder, vagina. - Other examinations:
- Quantitative evaluation of foci of cellular alteration in the liver: by color image processor (Spicca-II, Nippon Avionics Co., Ltd., Tokyo) (no further data given, criteria of evaluation not specified)
- Statistics:
- Analysis of variance, Student's t-test for significant differences between mean values; incidences of histopathologic lesions by tw-sided Fisher's exact propability test; severity of non-neoplastic lesion development by the Mann-Whitney test
- Clinical signs:
- no effects observed
- Mortality:
- no mortality observed
- Body weight and weight changes:
- effects observed, treatment-related
- Food consumption and compound intake (if feeding study):
- no effects observed
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- no effects observed
- Ophthalmological findings:
- not examined
- Haematological findings:
- not examined
- Clinical biochemistry findings:
- not examined
- Urinalysis findings:
- not examined
- Behaviour (functional findings):
- not examined
- Organ weight findings including organ / body weight ratios:
- effects observed, treatment-related
- Gross pathological findings:
- effects observed, treatment-related
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Histopathological findings: neoplastic:
- effects observed, treatment-related
- Details on results:
- Effects in the single dose group:
BODY WEIGHT AND WEIGHT GAIN
Body weight decreased from week 18 on; final body weights of controls and HQ-treated groups: males 438 +- 38 g, 422 +- 44 g, decrease by 4%, ; females 306 +- 42 g, 283 +- 28 g, decrease by 7.5%, significantly different from control females, P<0.05; statistically significant reduction of body weight gain compared to controls in both males and females (no data and P-values specified)
ORGAN WEIGHTS (for details see Table 1)
Males: statistically significant increases of absolute and relative liver and kidney weights
Females: statistically significant increase of relative kidney weight
GROSS PATHOLOGY
Males: increased granular appearance or indentation of kidneys
HISTOPATHOLOGY: NON-NEOPLASTIC (for details see Table 2)
KIDNEYS:
Males: chronic nephropathy both in controls and doses male rats, however, with higher severity in HQ-treated males; significantly increased incidence compared to control males, P<0.01; increased incidence of epithelial hyperplasia in the renal papilla, significantly different from control males, P<0.05
Females: only slight nephropathy, significantly increased incidence compared to control females, P<0.01
Evaluation: Epithelial hyperplasia in the renal papilla was considered to be component of advanced chronic nephropathy. As there were no indications of alpha-2µ-globulin nephropathy (unpublished data), a different mechanism for the development of renal adenomas has to be considered.
LIVER:
Males: significant reduction in bile duct hyperplasia in dosed compared to control males, P<0.05
HISTOPATHOLOGY: NEOPLASTIC (for details see Table 2)
Males: significantly increased incidences of renal tubular hyperplasia (100% vs. 3%) and of renal tubular adenomas (47% vs. 0%) compared to control males, both with P<0.01
HISTORICAL CONTROL DATA (no data specified)
OTHER FINDINGS
Quantitative evaluation of foci of cellular alteration: significant reduction in dosed rats compared to control values with P<0.05 in males and P<0.01 in females, mostly foci of basophilic character - Relevance of carcinogenic effects / potential:
- This study was not performed according to existing guidelines and standards for carcinogenicity studies. As there is only a single dose group it is not possible to make any conclusions on dose-response-relationships both for non-neoplastic and neoplastic effects. Dose selection was not based on dose range finding studies but is a dose used in previous toxicological examinations with hydroquinone. The animal number per test group and sex of 30 was distinctly lower than the standard of 50. Consequently, only 30 hydroquinone-treated rats per sex were available for evaluation of neoplastic effects in total and so the probability to detect rarely occurring neoplasms is distinctly reduced in this study. There are no tumour incidences published except those of renal tubuli adenoma and hepatocellular carcinoma, and there are no historical control incidences of the investigating laboratory given. Consequently, the study is of limited reliability for an assessment of the carcinogenic potential of hydroquinone.
In male Fischer 344 rats statistically significantly increased incidences of renal tubular adenoma (47% vs. 0% in control males), of renal tubular hyperplasia (100% vs. 3% in control males) and of epithelial hyperplasia in the renal papilla (37% vs. 6%) were found at the dietary dose of 351 mg/kg bw/d. The authors of the study considered the epithelial hyperplasia in the renal papilla to be a component of the observed advanced chronic nephropathy, whereas a different unknown mechanism for the development of renal tubular hyperplasia and adenomas was considered as there were no indications of alpha-2µ-globulin nephropathy (unpublished data). There was no significant decrease of final body weight in male rats (-4%), however, the significantly increased incidence of chronic nephropathy (80% in dosed vs. 57% in controls) indicated that the dosing was close to the maximal tolerable dose (MTD).
In female Fischer 344 rats there were no increased incidences of neoplastic findings at the dietary dose of 368 mg/kg bw/d. This dose is considered to be close to the maximal tolerable dose (MTD) as a significant decrease of final body weight by 7.5% was observed compared to control females. - Dose descriptor:
- NOAEL
- Sex:
- male/female
- Basis for effect level:
- other: only a single dose tested
- Remarks on result:
- not determinable
- Remarks:
- no NOAEL identified. Effect type:toxicity
- Dose descriptor:
- dose level:
- Effect level:
- 351 mg/kg bw/day (actual dose received)
- Sex:
- male
- Basis for effect level:
- other: reduction of final body weight and increase of liver and kidney weights, increased chronic nephropathy
- Remarks on result:
- other: Effect type: toxicity
- Dose descriptor:
- dose level:
- Effect level:
- 368 mg/kg bw/day (actual dose received)
- Sex:
- female
- Basis for effect level:
- other: statistically significant reduction of final body weight and increase of relative kidney weight
- Remarks on result:
- other: Effect type: toxicity
- Dose descriptor:
- dose level:
- Effect level:
- 351 mg/kg bw/day (actual dose received)
- Sex:
- male
- Basis for effect level:
- other: histopathology
- Remarks on result:
- other: Effect type: other: chronic nephropathy and induction of renal tubular hyperplasia and adenoma
- Dose descriptor:
- NOEL
- Effect level:
- 368 mg/kg bw/day (actual dose received)
- Sex:
- female
- Basis for effect level:
- other: no increased tumour incidences
- Remarks on result:
- other: Effect type: carcinogenicity
- Conclusions:
- In male Fischer 344 rats a statistically significantly increased incidence of renal tubular adenoma was found at the dietary dose of 351 mg/kg bw/d which was accompanied by an increased incidence of renal tubular hyperplasia. A mechanism independent of alpha-2µ-globulin nephropathy was assumed.
In female Fischer 344 rats there were no increased incidences of neoplastic findings at the dietary dose of 368 mg/kg bw/d. - Executive summary:
Hydroquinone was continuously fed to groups of 30 male and 30 female F344 rats for 104 weeks at a single food concentration of 0.8% corresponding to doses of 351 mg/kg bw/d in males and 368 mg/kg bw/d in females. Control groups received plain diet. Mortality, clinical signs, body weight gain, and food and water consumption were recorded. Rats were sacrificed after 104 weeks for complete gross necropsy, determination of kidney and liver weights and comprehensive histopathological examination. Additionally, a quantitative evaluation of foci of cellular alteration in the liver was made (criteria of evaluation not specified). Details of the histopathological examination are only given for the findings in kidneys and livers.
There were no significant differences in survival between dose and control group, and no compound-related clinical signs. Decreased body weight in the absence of affected food consumption was observed in both sexes from week 18 on resulting in decreased final body weights (-4% in males, significant decrease of -7.5% in females). Males showed statistically significant increases of absolute and relative liver and kidney weights, in females a significant effect existed only for relative kidney weight. Increased granular appearance or indentation of kidneys was found during gross necropsy.
In hydroquinone-treated males, chronic nephropathy appeared with higher severity and significantly increased incidence compared to control males (80% vs. 57%, P<0.01), which was also associated with a significantly increased incidence of epithelial hyperplasia in the renal papilla (P<0.05). Further, significantly increased incidences of renal tubular hyperplasia (100% vs. 3%) and of renal tubular adenomas (47% vs. 0%) existed in dosed males compared to control males (P<0.01). In female rats, a significant increase of the incidence of chronic nephropathy compared to control females (27% vs. 3%, P<0.05) was seen, however, effects were only graded as slight. Renal tubular hyperplasia was observed in 7% of female rats only. Renal tubular hyperplasias were composed of tubules with stratified epithelial cells which partially or fully filled the tubular lumina, often with cystic forms. Renal tubular adenoma also exhibited cystic or solid forms, in both cases being composed of relatively uniform epithelial cells with clear or pale basophilic cytoplasm and round nuclei with prominent nucleoli. A mechanism independent of alpha-2µ-globulin nephropathy was assumed. In contrast, in the livers, a significant reduction in bile duct hyperplasia was found in dosed compared to control males (P<0.05) as well as a significant decrease of the number of altered liver foci per cm2 liver tissue in rats of both sexes (P<0.05 in males, P<0.01 in females).
There were no increased incidences of neoplastic findings in female rats under the conditions of this assay.
- Endpoint:
- carcinogenicity: oral
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- from August 1982 to August 1984
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- comparable to guideline study with acceptable restrictions
- Remarks:
- Similar to guideline study with acceptable restrictions: only 2 instead of 3 dose groups, no data on food consumption; hematology and clinical chemistry examinations only at 15 mo, no urinalysis data
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to other study
- Qualifier:
- equivalent or similar to guideline
- Guideline:
- OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
- Deviations:
- yes
- Remarks:
- (only 2 instead of 3 dose groups, no data on food consumption; hematology and clinical chemistry examinations only at 15 mo, no urinalysis data)
- GLP compliance:
- not specified
- Species:
- mouse
- Strain:
- B6C3F1
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, NY, USA
- Age at study initiation: males 8-9 w , females 9-10 w
- Fasting period before study: no
- Housing: 5 per cage
- Diet: NIH 07 rat ration (Zeigler Bros. Inc., Gardner, PA, USA) ad libitum
- Water: tap water ad libitum
- Acclimation period: males 18 d, females 26 d
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 - 27 °C (65 - 80 °F)
- Humidity (%): 40 - 79
- Air changes (per hr): 6 - 13 room air changes per hr
- Photoperiod (hrs dark / hrs light): 12/12 - Route of administration:
- oral: gavage
- Vehicle:
- water
- Details on exposure:
- PREPARATION OF DOSING SOLUTIONS: appropriate amount of hydroquinone dissolved in deionised water by stirring with a magnetic stir bar; maximum storage time 21 d at room temperature in the dark in amber serum vials with Teflon-lined seals, sparged with argon or nitrogen before sealing
VEHICLE
- Concentration in vehicle: 5, 10 mg/mL
- Amount of vehicle (if gavage): 10 mL/kg - Analytical verification of doses or concentrations:
- yes
- Details on analytical verification of doses or concentrations:
- UV spectroscopy of acetonitrile extracts at 295 nm or methanol extracts at 293 nm; analyzed concentrations (data from 10 samples each): mean 4.88, range 4.72 - 5.09 mg/mL; mean 9.78, range 9.39 – 10.25 mg/mL; variation considered to be in acceptable range; stability investigations by HPLC after 21 days of storage of the dosing solution at room temperature in the dark indicated no notable decrease of hydroquinone concentration
- Duration of treatment / exposure:
- 65 or 103 w
- Frequency of treatment:
- 5 d/w
- Post exposure period:
- 24 h for interim sacrifice, about 2 w for terminal sacrifice
- Dose / conc.:
- 0 mg/kg bw/day (actual dose received)
- Dose / conc.:
- 50 mg/kg bw/day (actual dose received)
- Dose / conc.:
- 100 mg/kg bw/day (actual dose received)
- No. of animals per sex per dose:
- 64 or 65 males, 65 females (including 10 for 65 w treatment)
- Control animals:
- yes, concurrent vehicle
- Details on study design:
- - Dose selection rationale: based on 13 week range-finding toxicity study (see separate endpoint study record in Section 7.5.1)
- Observations and examinations performed and frequency:
- Observations and examinations performed and frequency
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: 2 times per day
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: 2 times per day
BODY WEIGHT: Yes
- Time schedule for examinations: at initiation of dosing, weekly thereafter for 13 weeks, and monthly for the rest of the study period
FOOD CONSUMPTION: No
WATER CONSUMPTION: No
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: Yes, at 15 mo
Investigated parameters: leukocytes, lymphocytes, segmented neutrophiles, monocytes, eosinophils, atypical lymphocytes, atypical mononuclear cells, bands, hematocrit, hemoglobin, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, mean cell volume, erythrocytes, reticulocytes
CLINICAL CHEMISTRY: Yes, at 15 mo
Investigated parameters: albumin, alkaline phosphatase, alanine aminotransferase, blood urea nitrogen, creatinine, sorbitol dehydrogenase, total protein
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No - Sacrifice and pathology:
- GROSS PATHOLOGY: Yes, all animals
ORGAN WEIGHTS: Yes, at 15 mo and 2 y
HISTOPATHOLOGY: Yes
Tissues examined in high-dose mice and controls: adrenal glands, brain, caecum, colon, duodenum, epididymis/prostrate/testes or ovaries/uterus, esophagus, gallbladder, gross lesions and tissue masses, heart, ileum, jejunum, kidneys, liver, lungs and mainstem bronchi, mammary gland, mandibular or mesenteric lymph nodes, nasal cavity and turbinates, pancreas, parathyroid glands, pituitary gland, rectum, salivary glands, skin, spleen, sternebrae and vertebrae including marrow, stomach, thymus, thyroid gland, trachea, and urinary bladder
Tissues examined in low-dose male mice: adrenal glands, gross lesions, liver, spleen, thyroid gland
Tissues examined in low-dose female mice: gross lesions, liver, lungs, ovaries, salivary glands, thyroid gland - Statistics:
- Survival probabilities estimated by product-limit procedure of Kaplan and Meier (1958), statistical analysis by methods of Cox (1972) and Tarone (1975);
Statistical significance of organ weights, hematological and clinical chemistry data analyzed by Dunn's test (Dunn, 1964) or Shirley's test (Shirley, 1977);
Data on tumor incidences analyzed by life-table analysis, logistic regression, Fisher's exact test, and Cochran-Armitage trend test - Clinical signs:
- no effects observed
- Mortality:
- no mortality observed
- Body weight and weight changes:
- effects observed, treatment-related
- Food consumption and compound intake (if feeding study):
- not examined
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- not examined
- Ophthalmological findings:
- not examined
- Haematological findings:
- no effects observed
- Clinical biochemistry findings:
- no effects observed
- Urinalysis findings:
- not examined
- Behaviour (functional findings):
- not examined
- Organ weight findings including organ / body weight ratios:
- effects observed, treatment-related
- Gross pathological findings:
- no effects observed
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Histopathological findings: neoplastic:
- effects observed, treatment-related
- Details on results:
- CLINICAL SIGNS AND MORTALITY
No significant differences in survival were observed between any groups of either sex; no compound-related clinical signs
BODY WEIGHT AND WEIGHT GAIN (for details see Table 1)
100 mg/kg: mean body weights of male mice 5-8% lower between week 93 and 104; mean body weight of female mice 5-8% lower between week 20 to 44 and 10-14% lower between week 45 and 104
HAEMATOLOGY (data from 15 mo interim sacrifice group, for details see Table 2)
100 mg/kg: male mice showed significant increases of hematocrit and erythrocytes
Evaluation: Significant changes of hematocrit and erythrocytes were only found in males and are therefore considered to be of negligible biological significance.
CLINICAL CHEMISTRY (data from 15 mo interim sacrifice group, for details see Table 2)
100 mg/kg: male mice showed showed significant increases of total protein and serum albumin, of serum alkaline phosphatase and of sorbitol dehydrogenase; female mice showed significant increases of total protein and serum albumin, whereas a significantly lower activity was observed for alanine aminotransferase and sorbitol dehydrogenase
Evaluation: The statistically significant effects in general represented only slight changes. Changes in enzyme activites were contrary in both sexes. Therfore the observed changes of clinical chemistry are considered to be of negligible biological significance.
ORGAN WEIGHTS (for details see Table 1)
100 mg/kg: both sexes showed significant increases of relative liver weights after 103 w of administration, whereas at interim sacrifice after 65 w liver weights of both males and females, and brain and kidney weights of females showed significant increases
50 mg/kg: male mice showed a significant increase of relative liver weight after 103 w, females showed a significant increase of relative kidney weight after 65 w
HISTOPATHOLOGY: NON-NEOPLASTIC (for details see Table 3)
LIVER 65-week interim sacrifice:
50 and 100 mg/kg, male mice: increased incidences of diffuse centrilobular fatty change, diffuse cytomegaly, occasional syncytial cells (multinucleated hepatocytes)
LIVER 105-week sacrifice:
100 mg/kg, male mice: increased incidence of anisokaryosis (variation in size of hepatocyte nuclei), syncitial alteration (hepatocytes with more than 5 nuclei per cell), and foci of cellular alteration (basophilic foci) compared to vehicle controls
Evaluation: Centrilobular fatty change and cytomegaly were observed at the 65-week interim sacrifice but not at the terminal sacrifice. This may be explained by the fact that after the 65-week administration necropsy occurred within 24 hrs after the last dose, whereas dosing was stopped 2 weeks before necropsy in the 2 year study. Presumably, fatty change and cytomegaly were reversible after cessation of hydroquinone administration.
HISTOPATHOLOGY: NEOPLASTIC (incidences given for vehicle control, 50 mg/kg, 100 mg/kg; for details see Table 3)
LIVER 105-week sacrifice:
Preneoplastic foci of cellular alteration: increased incidences in dosed males with 2/55, 5/54, 11/55; similar incidences in control and dosed females with 2/55, 6/55, 3/55
Hepatocellular adenoma: significant increase of incidences in dosed mice with no dose-relationship: males 9/55, 21/54, 20/55; females 2/55, 15/55, 12/55
Hepatocellular carcinoma: decreased incidences in dosed male mice with a dose-dependant trend: 13/55, 11/54, 7/55; inicidences in female mice similar to controls
Adenoma or carcinoma combined: no dose-response-relationship; no significant increase in dosed male mice: 20/55, 29/54, 25/55; significant increase in dosed female mice: 3/55, 16/55, 13/55
Evaluation: Foci of cellular alteration and hepatocellular adenomas form a morphologic continuum. Adenomas are larger than foci, e.g. involve several or more hepatocellular lobules, and exhibit loss of lobular architecture, with alteration in growth pattern of the hepatic plates, and greater cellular atypia. Increased incidences of adenoma in dosed male mice were offset by decreases of incidences of carcinoma. Consequently, combined incidences of adenoma or carcinoma in dosed males were not significantly different from the vehicle control group. Incidences were within the range of historical control data with up to 58%. However, in dosed female mice, incidences of adenomas, and combined incidences of adenoma or carcinoma were significantly increased each and were higher than the upper range of historical control incidences of 20%. There was no dose-response relationship as incidences were higher at 50 mg/kg compared to the high dose of 100 mg/kg. Hepatocellular neoplasms were evaluated to represent some evidence of carcinogenicity in female mice.
THYROID GLAND 105-week sacrifice:
Follicular cell hyperplasia: increased in dosed males and females compared to vehicle controls (hyperplasia also seen in 2 high-dose females at interim sacrifice)
Adenoma or carcinoma combined: dose-related marginal increase in dosed females 5%, 9%, 13%
Evaluation: As the combined incidences of adenomas or carcinomas of the thyroid gland were within the upper range of historicol controls of 15% this effect was not assessed as carcinogenic evidence.
HISTORICAL CONTROL DATA (compiled in footnote to Table 3) - Relevance of carcinogenic effects / potential:
- Deviating from OECD Guideline 453 only two groups had been dosed in this NTP study. As the investigated dose range reached the minimally toxic dose based on decreases of body weight gain, these two dose groups are considered to be sufficient for an investigation of the carcinogenic potential of hydroquinone.
In the thyroid gland of female mice, a dose-related marginal increase of combined adenoma or carcinoma was observed (5%, 9%, 13% in vehicle control, 50 and 100 mg/kg-dose group). However, these combined incidences were within the upper range of historicol controls of 15% so that this effect was not assessed as carcinogenic evidence.
The NTP concluded that some evidence of carcinogenic activity of hydroquinone was demonstrated in female B6C3F1 mice as both the incidences of hepatocellular adenoma (4%, 27%, and 22% in vehicle control, 50 and 100 mg/kg-dose group), and combined incidences of hepatocellular adenoma or carcinoma (5%, 29%, and 24%) were significantly increased compared to the vehicle control group, and additionally were higher than the upper range of historical control incidences of 20%. There was no dose-response relationship as incidences were higher at 50 mg/kg compared to the high dose of 100 mg/kg.
However, a later analysis of incidences of hepatic adenomas by Whysner et al. (1995) judged this finding to be equivocal as there was no dose-dependance in the NTP study, and in another study (Shibata et al., 1991) there was no finding of increased liver neoplasms in female B6C3F1 mice (see separate endpoint study records).
In contrast, increased incidences of hepatocellular adenoma in dosed male mice (16%, 39% and 36% in vehicle control, 50 and 100 mg/kg-dose group) were offset by decreases of incidences of hepatocellular carcinoma (24%, 20% and 13%). Consequently, combined incidences of hepatocellular adenoma or carcinoma in dosed males were not significantly different from the vehicle control group (36%, 54%, 45%). Combined incidences of adenoma or carcinoma were within the range of historical control data with up to 58% for these liver neoplasias. There were no other significantly increased incidences of neoplasias in male mice, so that the NTP concluded on no evidence of carcinogenic activity for male B6C3F1 mice under the conditions of the study. - Dose descriptor:
- LOAEL
- Effect level:
- 100 mg/kg bw/day (actual dose received)
- Sex:
- male/female
- Basis for effect level:
- other: body weight, organ weights, histopathology (liver, males only)
- Remarks on result:
- other: Effect type: toxicity
- Dose descriptor:
- NOEL
- Effect level:
- 50 mg/kg bw/day (actual dose received)
- Sex:
- male
- Basis for effect level:
- other: no increased incidences of neoplastic changes
- Remarks on result:
- other: Effect type: carcinogenicity
- Dose descriptor:
- dose level:
- Effect level:
- >= 50 mg/kg bw/day (actual dose received)
- Sex:
- female
- Basis for effect level:
- other: increased incidence of hepatocellular adenomas
- Remarks on result:
- other: Effect type: carcinogenicity
- Conclusions:
- Under the conditions of the 2-year gavage study, the NTP concluded on some evidence of carcinogenic activity of hydroquinone in female B6C3F1 mice, as shown by significant increases of hepatocellular adenoma, adenomas or carcinomas combined. There was no evidence of carcinogenicity in males.
- Executive summary:
Hydroquinone was administered to groups of 65 male and 65 female B6C3F1 mice for 103 weeks on 5 days per week via gavage at doses of 0, 50, and 100 mg/kg bw/d (vehicle water). The study protocol was similar to OECD Guideline 453 with several minor deviations. There were only 2 instead of 3 dose groups, and food consumption and urinalysis were not examined. Hematology and clinical chemistry examinations were performed at a single timepoint after 65 w of dosing in subgroups of 10 mice of each sex and dose. Mice were sacrificed for gross and histopathological examination at about 66 w (N=10) and 104 to 105 w (N=55) after start of dosing.
There were no significant differences in survival between any groups of either sex and no compound-related clinical signs. There were no biologically significant changes of haematological or clinical chemistry parameters. Toxicity was indicated at 100 mg/kg by decreases of body weights in males (5-8% lower than those of vehicle controls between weeks 93-104), and in females (5-8% lower between week 20-44, 10-14% lower between week 45-104). Relative brain weights (at 100 mg/kg) and kidney weights (at 50 and 100 mg/kg) showed significant increases in female mice at the interim sacrifice only and were considered to be of negligible biological significance. Significant increases of relative liver weights were found at 100 mg/kg in both sexes after 65 and 103 w of administration, and at 50 mg/kg in males after 103 w. Centrilobular fatty change and cytomegaly were observed in male mice at the 65-week interim sacrifice but not at the terminal sacrifice. This may be explained by the fact that after the 65-week administration necropsy occurred within 24 hrs after the last dose, whereas dosing was stopped 2 weeks before necropsy in the 2 year study. Presumably, fatty change and cytomegaly were reversible after cessation of hydroquinone administration. Findings in livers of male mice at 100 mg/kg after 105 w were characterized by increased incidences of anisokaryosis (variation in size of hepatocyte nuclei), syncitial alteration (hepatocytes with more than 5 nuclei per cell), and foci of cellular alteration (basophilic foci) compared to incidences in vehicle controls. Increased incidences of adenoma in both dose groups of males were offset by decreased incidences of carcinoma. Consequently, combined incidences of adenoma or carcinoma in dosed males were not significantly different from the vehicle control group. However, in dosed female mice, both incidences of adenomas, and combined incidences of adenoma or carcinoma were significantly increased (For detailed discussion see Section 7.7).
Under the conditions of the NTP study, the LOAEL for non-neoplastic chronic toxicity was 100 mg/kg bw/d in male and female mice (based on body weight reduction, organ weight effects and liver histopathology in males). There was no evidence of carcinogenic activity in male B6C3F1 mice. According to NTP criteria some evidence of carcinogenicity was demonstrated in female mice at 50 and 100 mg/kg bw/d by findings of increased incidences of hepatocellular adenoma, and adenoma or carcinoma combined.
- Endpoint:
- carcinogenicity: oral
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- study well documented, meets generally accepted scientific principles, acceptable for assessment
- Remarks:
- Publication meets basic scientific principles as a reevaluation and mechanistic study of neoplastic findings, well-documented and acceptable as key study
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to other study
- Qualifier:
- equivalent or similar to guideline
- Guideline:
- OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
- Version / remarks:
- Reevaluation based on citeria of the Society of Toxicologic Pathologists (STP) and of the International Agency for Research on Cancer (IARC)
- Deviations:
- not applicable
- Principles of method if other than guideline:
- Reevaluation of renal histopathology of the NTP cancer bioassay with emphasis on evaluation of incidences, severity and location of chronic progressive nephropathy and proliferative lesions in the rat kidney
- GLP compliance:
- not specified
- Species:
- rabbit
- Strain:
- Fischer 344
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, NY, USA
- Age at study initiation: males 7-8 w , females 8-9 w
- Fasting period before study: no
- Housing: 5 per cage
- Diet: NIH 07 rat ration (Zeigler Bros. Inc., Gardner, PA, USA) ad libitum
- Water: tap water ad libitum
- Acclimation period: males 21 d, females 28 d
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 - 27 °C (65 - 80 °F)
- Humidity (%): 40 - 79
- Air changes (per hr): 6 - 13 room air changes per hr
- Photoperiod (hrs dark / hrs light): 12/12 - Route of administration:
- oral: gavage
- Vehicle:
- water
- Details on exposure:
- PREPARATION OF DOSING SOLUTIONS: appropriate amount of hydroquinone dissolved in deionised water by stirring with a magnetic stir bar; maximum storage time 21 d at room temperature in the dark in amber serum vials with Teflon-lined seals, sparged with argon or nitrogen before sealing
VEHICLE
- Concentration in vehicle: 5, 10 mg/mL
- Amount of vehicle (if gavage): 5 mL/kg - Analytical verification of doses or concentrations:
- yes
- Details on analytical verification of doses or concentrations:
- UV spectroscopy of acetonitrile extracts at 295 nm or methanol extracts at 293 nm; analyzed concentrations (data from 10 samples each): mean 4.88, range 4.72 - 5.09 mg/mL; mean 9.78, range 9.39 – 10.25 mg/mL; variation considered to be in acceptable range; stability investigations by HPLC after 21 days of storage of the dosing solution at room temperature in the dark indicated no notable decrease of hydroquinone concentration
- Duration of treatment / exposure:
- 65 or 103 w
- Frequency of treatment:
- 5 d/w
- Post exposure period:
- Sacrifice in w 66
- Remarks:
- Doses / Concentrations:
0, 25, 50 mg/kg bw/d for male rats after 103 w of dosing, and 0 and 50 mg/kg after 65 w of dosing
Basis:
actual ingested - Remarks:
- Doses / Concentrations:
0, 50 mg/kg bw/d for female rats after 103 w of dosing
Basis:
actual ingested - No. of animals per sex per dose:
- 64 or 65 males, 65 females (including 10 for 65 w treatment)
- Control animals:
- yes, concurrent vehicle
- Details on study design:
- - Dose selection rationale: based on 13 week range-finding toxicity study (see separate endpoint study record)
- Observations and examinations performed and frequency:
- Data to be found in Endpoint study record: Carcino oral gavage rat (V2) 1992 Kari
- Sacrifice and pathology:
- GROSS PATHOLOGY: Data to be found in Endpoint study record: Carcino oral gavage rat (V2) 1992 Kari
HISTOPATHOLOGY: Yes
Reexamination of hematoxylin and eosin-stained kidney sections from the NTP cancer bioassay based on following criteria:
Zones of kidney (based on Young and Wilson, 1964):
zone 1, cortex; zone 2, outer stripe of outer medulla; zone 3, inner stripe of outer medulla; zone 4, inner medulla; zone 5, papilla
Grading of CPN (Chronic Progressive Nephropathy) according to semi-quantitative system based on lesion pathogenesis (Hard, unpublished data):
minimal, mild, low-moderate, high-moderate: increasing numbers of discrete focal lesions of basophilic tubules with thickened basement membranes in the cortex and hyaline casts in the cortex and/or medulla
severe: extension and coalescence of the foci into contiguous areas
end-stage: involvement of almost all of the outer zones of the kidney with very little or no normal-staining parenchyma remaining
Characterization of proliferative lesions following the criteria of the Society of Toxicologic Pathologists (STP) and of the International Agency for Research on Cancer (IARC):
- simple tubule hyperplasia: increase in the number of epithelial cells in which the single-cell layer is retained
- atypical tubule hyperplasia: complex proliferation of the lining beyond the normal single-cell layer but within the structure of a single nephron; absence of vascular ingrowth
- incipient renal tubule adenoma: very early borderline adenoma confined to a single solid basophilic lobule or to a mildly dilated tubule with complex lining
- renal tubule adenoma: epithelial proliferation beyond the well-defined structure of an individual tubule and extending into two or more lobules; presence of neovascularization; usually small neoplasms with absence of areas of hemorrhage and necrosis
- renal tubule carcinoma: more extended neoplasma with presence of areas of hemorrhage and necrosis
Additional observations:
Small tubule regeneration (STR): small basophilic profiles of epithelium in atrophic areas of CPN suggestive of new tubule regeneration varying from short lengths of simple tubules to irregular or convoluted basophilic tubules, sometimes also as complex tubule aggregates - Statistics:
- Survival rates grouped by CPN grade and dose estimated through the Kaplan-meier product limit lifetable method (Kaplan and Meier, 1958)
Evaluation of statistical significances: difference between pairs of survival distributions evaluated through log rank test, association between CPN grade and dose and the number of proliferative lesions by CPN grade through 2 x 2 frequency table analysis followed by chi-square test of association, increase in the number of rats with small tubule regeneration through chi-square test for trend - Clinical signs:
- effects observed, treatment-related
- Mortality:
- mortality observed, treatment-related
- Body weight and weight changes:
- not specified
- Food consumption and compound intake (if feeding study):
- not examined
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- not examined
- Ophthalmological findings:
- not examined
- Haematological findings:
- not examined
- Clinical biochemistry findings:
- not examined
- Urinalysis findings:
- not examined
- Behaviour (functional findings):
- not examined
- Organ weight findings including organ / body weight ratios:
- not examined
- Gross pathological findings:
- not examined
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Histopathological findings: neoplastic:
- effects observed, treatment-related
- Description (incidence and severity):
- A slight increase of renal tubule adenoma was observed with incidences of 0/44, 3/49 (including one very early adenoma), and 7/51 (including three very early adenomas) at 0, 25 and 50 mg/kg bw/d.
- Details on results:
- MORTALITY
small marginally significant decrease in survival of males: control vs. low-dose, P = 0.04; control vs. high-dose, P=0.06
HISTOPATHOLOGY: NON-NEOPLASTIC
No evidence of compound-induced nephrotoxicity in parenchyma unaffected by CPN absence of single-cell death in renal tubules, degenerative change and karyomegaly. No evidence of compound-induced alpha-2µ-globulin nephropathy: no hyaline droplet accumulation in proximal tubules or other characteristic changes
Evaluation of chronic progressive nephropathy (CPN) (detailed compilation in Table 1)
- 50 mg/kg males, 2 y study: clear enhancement of CPN; of the rats surviving into the last 10 w of the study 49% had endstage CPN and 40% had severe CPN; onset of end-stage disease involved rats at an earlier age (first case after 86 w, and 8 of the 20 cases before 100 w
Statistical significant increases of CPN grades severe vs. end-stage: 50 mg/kg vs. control, P = 0.001; 50 mg/kg vs. 25 mg/kg, P = 0.001
- 50 mg/kg males, 66 w : borderline statistical significant increase of CPN grades low-moderate vs. high-moderate, P = 0.06
Additional observations (detailed compilation in Table 2):
Small tubule regeneration (STR): in areas of severe and end-stage CPN; statistically significant increase in STR associated with severe and end-stage CPN with increasing dose, P = 0.0004
HISTOPATHOLOGY: NEOPLASTIC
Reevaluation of proliferative lesions in renal tissue sections of male rats from the NTP report (detailed compilation in Table 2):
25 mg/kg: NTP diagnosis of originally 4 adenomas changed to 2 adenomas and 1 incipient adenoma, additional diagnosis of 2 foci of atypical tubule hyperplasia
50 mg/kg: NTP diagnosis of originally 8 adenomas changed to 4 adenomas (including 1 cystadenoma) and 3 incipient adenomas and 14 foci of atypical tubule hyperplasia (in 11 rats)
Localization of adenomas and atypical tubule hyperplasia: outer stripe of outer medulla (OSOM; zone 2), junction of cortex and OSOM or in mid- to deep cortex (zone 1); all in rats with severe or end-stage CPN and within areas of spontaneous CPN alteration
Statistical significant increase of combined lesions of atypical hyperplasia or adenomas for end-stage versus severe CPN, P = 0.01; no significant increase for 50 mg/kg – vs. 25 mg/kg-group, P = 0.10 - Relevance of carcinogenic effects / potential:
- Deviating from OECD Guideline 453 only two groups had been dosed in the original NTP study. As the investigated dose range reached the minimally toxic dose based on decreases of body weight gain and borderline significant decreases of survival, these two dose groups are considered to be sufficient for an investigation of the carcinogenic potential of hydroquinone.
A slight increase of renal tubule adenoma was observed with incidences of 0/44, 3/49 (including one very early adenoma), and 7/51 (including three very early adenomas) at 0, 25 and 50 mg/kg bw/d. Observed renal adenomas are considered to be of little relevance for humans, as a minimal renal tumour response is linked to an interaction with a rodent-specific spontaneous renal disease. - Conclusions:
- The reevaluation of kidney histopathology from the NTP study suggested that the renal tumours were associated with an advanced state of chronic progressive nephropathy (CPN) in the male rats. Further, hydroquinone not only exacerbated spontaneous CPN in male rats at a dose of 50 mg/kg bw/d, but also exerted a stimulatory effect on the proliferative potential of the advanced stages of CPN at both 25 and 50 mg/kg, leading to an increased frequency of renal adenomas through this indirect mechanism. Consequently, these findings may have little relevance for humans, as a minimal renal tumour response is linked to an interaction with a rodent-specific spontaneous renal disease.
- Executive summary:
A reevaluation of the renal histopathology of the NTP cancer bioassay on hydroquinone was performed with emphasis on evaluation of incidences, severity and location of chronic progressive nephropathy (CPN) and proliferative lesions in the rat kidney. Characterization of proliferative lesions followed the criteria of the Society of Toxicologic Pathologists (STP) and of the International Agency for Research on Cancer (IARC) differentiating between simple tubule hyperplasia, atypical tubule hyperplasia, incipient renal tubule adenoma, and renal tubule adenoma and carcinoma. Grading of CPN was performed according to a semi-quantitative system based on lesion pathogenesis (Hard, unpublished data) with six different grades minimal, mild, low-moderate, high-moderate, severe and end-stage. Further small basophilic profiles of epithelium in atrophic areas of CPN suggestive of new tubule regeneration were observed. Kidney sections from the following dose groups were evaluated: male rats all dose groups of the 2 year study and the control and 50 mg/kg group of the 66 week interim sacrifice, female rats the control and 50 mg/kg group of the 2 year study.
There was no evidence of HQ-induced nephrotoxicity or alpha-2µ-globulin nephropathy. Hydroquinone exposure in male rats at 50 mg/kg in the 2 year study produced a statistically significant increase in the grade of CPN. At 0, 25, and 50 mg/kg, 0/44, 4/49, and 15/51 male rats had either atypical tubule hyperplasias or adenomas. All were located in the outer stripe of the medulla (OSOM), the junction of cortex and OSOM, or in the cortex within areas of severe or endstage CPN and were statistically associated with CPN grade. The reevaluation of proliferative lesions in male rat renal tissue sections deviated from the original NTP diagnosis. At 25 mg/kg, the diagnosis of originally 4 adenomas changed to 2 adenomas and 1 incipient adenoma with additional diagnosis of 2 foci of atypical tubule hyperplasia. At 50 mg/kg, instead of originally 8 adenomas the diagnosis was 4 adenomas (including 1 cystadenoma) and 3 incipient adenomas, and 14 foci of atypical tubule hyperplasia (in 11 rats).
Consequently, hydroquinone not only exacerbated spontaneous CPN in male rats at a dose of 50 mg/kg bw/d, but also exerted a stimulatory effect on the proliferative potential of the advanced stages of CPN at both 25 and 50 mg/kg, leading to an increased frequency of renal adenomas through this indirect mechanism. As a minimal renal tumour response is linked to an interaction with a rodent-specific spontaneous renal disease, these findings may have little relevance for humans.
- Endpoint:
- carcinogenicity: oral
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- from September 1982 to September 1984
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- comparable to guideline study with acceptable restrictions
- Remarks:
- Similar to guideline study with acceptable restrictions: only 2 instead of 3 dose groups, no data on food consumption; hematology and clinical chemistry examinations only at 15 mo, no urinalysis data
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to other study
- Qualifier:
- equivalent or similar to guideline
- Guideline:
- OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
- Deviations:
- yes
- Remarks:
- (only 2 instead of 3 dose groups, no data on food consumption; hematology and clinical chemistry examinations only at 15 mo, no urinalysis data)
- GLP compliance:
- not specified
- Species:
- rat
- Strain:
- Fischer 344
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, NY, USA
- Age at study initiation: males 7-8 w , females 8-9 w
- Fasting period before study: no
- Housing: 5 per cage
- Diet: NIH 07 rat ration (Zeigler Bros. Inc., Gardner, PA, USA) ad libitum
- Water: tap water ad libitum
- Acclimation period: males 21 d, females 28 d
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 - 27 °C (65 - 80 °F)
- Humidity (%): 40 - 79
- Air changes (per hr): 6 - 13 room air changes per hr
- Photoperiod (hrs dark / hrs light): 12/12 - Route of administration:
- oral: gavage
- Vehicle:
- water
- Details on exposure:
- PREPARATION OF DOSING SOLUTIONS: appropriate amount of hydroquinone dissolved in deionised water by stirring with a magnetic stir bar; maximum storage time 21 d at room temperature in the dark in amber serum vials with Teflon-lined seals, sparged with argon or nitrogen before sealing
VEHICLE
- Concentration in vehicle: 5, 10 mg/mL
- Amount of vehicle (if gavage): 5 mL/kg - Analytical verification of doses or concentrations:
- yes
- Details on analytical verification of doses or concentrations:
- UV spectroscopy of acetonitrile extracts at 295 nm or methanol extracts at 293 nm; analyzed concentrations (data from 10 samples each): mean 4.88, range 4.72 - 5.09 mg/mL; mean 9.78, range 9.39 – 10.25 mg/mL; variation considered to be in acceptable range; stability investigations by HPLC after 21 days of storage of the dosing solution at room temperature in the dark indicated no notable decrease of hydroquinone concentration
- Duration of treatment / exposure:
- 65 or 103 w
- Frequency of treatment:
- 5 d/w
- Post exposure period:
- about 1 w until sacrifice
- Dose / conc.:
- 0 mg/kg bw/day (actual dose received)
- Dose / conc.:
- 25 mg/kg bw/day (actual dose received)
- Dose / conc.:
- 50 mg/kg bw/day (actual dose received)
- No. of animals per sex per dose:
- 64 or 65 males, 65 females (including 10 for 65 w treatment)
- Control animals:
- yes, concurrent vehicle
- Details on study design:
- - Dose selection rationale: based on 13 week range-finding toxicity study (see separate endpoint study record in Section 7.5.1)
- Observations and examinations performed and frequency:
- Observations and examinations performed and frequency
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: 2 times per day
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: 2 times per day
BODY WEIGHT: Yes
- Time schedule for examinations: at initiation of dosing, weekly thereafter for 13 weeks, and monthly for the rest of the study period
FOOD CONSUMPTION: No
WATER CONSUMPTION: No
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: Yes, at 15 mo
Investigated parameters: leukocytes, lymphocytes, segmented neutrophiles, monocytes, eosinophils, atypical lymphocytes, atypical mononuclear cells, bands, hematocrit, hemoglobin, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, mean cell volume, erythrocytes, reticulocytes
CLINICAL CHEMISTRY: Yes, at 15 mo
Investigated parameters: albumin, alkaline phosphatase, alanine aminotransferase, blood urea nitrogen, creatinine, sorbitol dehydrogenase, total protein
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No - Sacrifice and pathology:
- GROSS PATHOLOGY: Yes, all animals
ORGAN WEIGHTS: Yes, at 15 mo and 2 y
HISTOPATHOLOGY: Yes
Tissues examined in all rats (except for preputial gland and thyroid gland for low dose male rats): adrenal glands, brain, caecum, colon, duodenum, epididymis/prostrate/testes or ovaries/uterus, esophagus, gross lesions and tissue masses, heart, ileum, jejunum, kidneys, liver, lungs and mainstem bronchi, mammary gland, mandibular or mesenteric lymph nodes, nasal cavity and turbinates, pancreas, parathyroid glands, pituitary gland, preputial or clitoral gland, rectum, salivary glands, skin, spleen, sternebrae and vertebrae including marrow, stomach, thymus, thyroid gland, trachea, and urinary bladder - Statistics:
- Survival probabilities estimated by product-limit procedure of Kaplan and Meier (1958), statistical analysis by methods of Cox (1972) and Tarone (1975);
Statistical significance of organ weights, hematological and clinical chemistry data analyzed by Dunn's test (Dunn, 1964) or Shirley's test (Shirley, 1977);
Data on tumor incidences analyzed by life-table analysis, logistic regression, Fisher's exact test, and Cochran-Armitage trend test - Clinical signs:
- no effects observed
- Mortality:
- no mortality observed
- Body weight and weight changes:
- effects observed, treatment-related
- Food consumption and compound intake (if feeding study):
- not examined
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- not examined
- Ophthalmological findings:
- not examined
- Haematological findings:
- effects observed, treatment-related
- Clinical biochemistry findings:
- no effects observed
- Urinalysis findings:
- not examined
- Behaviour (functional findings):
- not examined
- Organ weight findings including organ / body weight ratios:
- effects observed, treatment-related
- Gross pathological findings:
- no effects observed
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Histopathological findings: neoplastic:
- effects observed, treatment-related
- Details on results:
- CLINICAL SIGNS AND MORTALITY
No significant differences in survival were observed between any groups of either sex; no compound-related clinical signs
BODY WEIGHT AND WEIGHT GAIN (for details see Table 1)
50 mg/kg: mean body weights of male rats 5-9% lower between week 73 and 93, and 10-13% lower between week 94 and 104; mean body weight of female rats within 4% of those of the vehicle controls throughout the studies
25 mg/kg: mean body weights of male rats 5-9% lower between week 89 and 104; mean body weight of female rats within 4% of those of the vehicle controls throughout the studies
HAEMATOLOGY (data from 15 mo interim sacrifice group, for details see Table 2)
50 mg/kg: female mice showed slight but significant decreases of hematocrit, hemoglobin concentration and erythrocytes (P<0.05)
25 mg/kg: male mice showed slight but significant increase of lymphocytes
Evaluation: Significant changes of hematocrit, hemoglobin concentration and erythrocytes in female rats are consistent with mild regenerative anemia and reported toxicity of hydroquinone toward bone marrow. In males, a significant increase of lymphocytes was only observed at the low dose and is considered to be of negligible biological significance.
CLINICAL CHEMISTRY (data from 15 mo interim sacrifice group, for details see Table 2)
50 mg/kg: male mice showed slight but significant decrease of serum alkaline phosphatase
25 mg/kg: female mice showed significant increase of serum alkaline phosphatase
Evaluation: Statistically significant changes were singular effects in one sex at a single dose and are considered to be of negligible biological significance.
ORGAN WEIGHTS (for details see Table 1)
50 mg/kg: male rats showed significant increases of relative brain, kidney, and liver weights after 103 w of administration, and significant increases of relative kidney weights after 65 w of administration
HISTOPATHOLOGY: NON-NEOPLASTIC
65-week interim sacrifice:
25 and 50 mg/kg, male rats: treatment-related increased severity of nephropathy (for details see Table 3)
104-week sacrifice:
50 mg/kg, male rats: increased severity of nephropathy compared to vehicle controls (for details see Table 3). Advanced renal disease characterized by varied degrees of degeneration and regeneration of tubular epithelium, atrophy and dilatation of some tubules, hyaline casts in the tubular lumina, glomerulosclerosis, interstitial fibrosis, and chronic inflammation, cysts (dilated tubules in the renal cortex), and increased papillary hyperplasia of the transitional epithelium overlying the renal papillae
HISTOPATHOLOGY: NEOPLASTIC
65-week interim sacrifice:
Incidence of lesions in female rats (vehicle control, 25 mg/kg, 50 mg/kg):
PITUITARY GLAND: Hyperplasia 3/10, 1/10, 0/10; Adenomas 3/10, 3/10, 1/10;
treatment-related decreased incidences of hyperplasia or neoplasia (for details see Table 4)
104-week sacrifice: (for details see Table 5)
Incidence of lesions in male rats (vehicle control, 25 mg/kg, 50 mg/kg):
RENAL TUBULI: Hyperplasia 0/55, 0/55, 2/55
Adenoma 0/55, 4/55, 8/55; significant increase at 50 mg/kg
Evaluation: Slight dose-related increase of renal tubule adenoma with a statistically significant increase at 50 mg/kg bw/d. The incidence in both dose groups was higher than the highest observed incidence in historical untreated controls of 3/50.
ADRENAL GLAND: Benign or malignant pheochromocytomas (combined): 14/55, 19/48, 22/55
Evaluation: Pheochromocytomas not considered to be treatment-related because the increased incidences were marginally significant and were within the range of historical control incidences. Additionally, the finding was not supported by observations from the 15-month interim sacrifice.
PITUITARY GLAND: Adenomas 13/54, 9/54, 5/54, significant negative trend, significant decrease at 50 mg/kg
Evaluation: Negative trend not considered to be treatment-related because results of the pairwise comparison between the high dose and vehicle control groups was only marginally significant, and the incidence of adenomas and carcinomas (combined) was within the historical control range for untreated controls.
Incidence of lesions in female rats (vehicle control, 25 mg/kg, 50 mg/kg):
MONONUCLEAR CELL LEUKEMIA: 9/55, 15/55, 22/55; positive trend, significant, dose-dependant increase at 25 and 50 mg/kg
Evaluation: Positive trend and a significant, dose-dependant increase of mononuclear cell leukemia together with increased incidences compared to vehicle control were evaluated to point a treatment-related effect.
THYROID GLAND: C-cell adenomas or carcinomas (combined) 13/55, 4/54, 8/55; significant decrease at 25 mg/kg
HISTORICAL CONTROL DATA (compiled in footnote to Table 5) - Relevance of carcinogenic effects / potential:
- Deviating from OECD Guideline 453 only two groups had been dosed in this NTP study. As the investigated dose range reached the minimally toxic dose based on decreases of body weight gain, these two dose groups are considered to be sufficient for an investigation of the carcinogenic potential of hydroquinone.
The NTP concluded that some evidence of carcinogenic activity of hydroquinone was demonstrated in male rats by a slight dose-related increase of renal tubule adenoma (observed incidences of 0/55, 4/55, and 8/55 at 0, 25 and 50 mg/kg bw/d) with a statistically significant increase at 50 mg/kg bw/d. The incidence in both dose groups was higher than the highest observed incidence in historical untreated controls of 3/50. However, a later reevaluation of Hard et al., 1997, discussed that these renal adenomas are considered to be of little relevance for humans, as a minimal renal tumour response is linked to a substance-specific interaction with a rodent-specific spontaneous renal disease.
The NTP considered the increase of incidences of benign or malignant pheochromocytomas of the adrenal gland (combined: 14/55, 19/48, 22/55 at 0, 25 and 50 mg/kg bw/d) in male rats not to be treatment-related because the increased incidences were marginally significant and were within the range of historical control incidences of up to 32/49.
The NTP concluded that some evidence of carcinogenic activity of hydroquinone was demonstrated in female rats by a positive trend and a significant, dose-dependant increase of mononuclear cell leukemia at 25 and 50 mg/kg compared to controls (9/55, 15/55, 22/55). The incidences in both dose groups exceeded the historical means observed in untreated or water gavage vehicle controls (19% and 25%, respectively). Further, the incidence in the high dose group of 40% exceeded the control incidences in all but one of the 46 studies with almost 2,300 untreated or water gavage control female F344 rats. However, a later analysis of leukaemia incidences by Whysner et al., 1995, judged this finding to be unrelated to treatment based on historical control incidences, and on the absence of an increase of leukaemia incidence in male rats or mice of both sexes, and the absence of an increase in any sex of rats in another study (Shibata et al., 1991). - Dose descriptor:
- LOAEL
- Effect level:
- 50 mg/kg bw/day (actual dose received)
- Sex:
- male
- Basis for effect level:
- other: body weight, organ weights, histopathology (nephropathy)
- Remarks on result:
- other: Effect type: toxicity
- Dose descriptor:
- LOAEL
- Effect level:
- 50 mg/kg bw/day (actual dose received)
- Sex:
- female
- Basis for effect level:
- other: haematology
- Remarks on result:
- other: Effect type: toxicity
- Dose descriptor:
- dose level:
- Effect level:
- 50 mg/kg bw/day (actual dose received)
- Sex:
- male
- Basis for effect level:
- other: increased incidence of renal tubule adenomas; effect level based on evaluation of the NTP
- Remarks on result:
- other: Effect type: carcinogenicity
- Dose descriptor:
- dose level:
- Effect level:
- >= 25 mg/kg bw/day (actual dose received)
- Sex:
- female
- Basis for effect level:
- other: increased incidence of mononuclear cell leukemia according to evaluation of the NTP
- Remarks on result:
- other: Effect type: carcinogenicity
- Conclusions:
- Under the conditions of the 2-year gavage study, the NTP concluded on some evidence of carcinogenic activity of hydroquinone in male and female F344 rats, as shown by marked increases of renal tubular cell adenoma in males, and increases of mononuclear cell leukaemia in females.
- Executive summary:
Hydroquinone was administered to groups of 65 male and 65 female F344 rats for 103 weeks on 5 days per week via gavage at doses of 0, 25, and 50 mg/kg bw/d (vehicle water). The study protocol was similar to OECD Guideline 453 with several minor deviations. There were only 2 instead of 3 dose groups, and food consumption and urinalysis were not examined. Hematology and clinical chemistry examinations were performed at a single timepoint after 65 w of dosing in subgroups of 10 rats of each sex and dose. Rats were sacrificed for gross and histopathological examination at about 66 w (N=10) and 104 w (N=55) after start of dosing.
There were no significant differences in survival between any groups of either sex and no compound-related clinical signs. Toxicity was indicated in male rats at 50 mg/kg by decreases of body weights between weeks 73 and 104 (5-13% lower than those of vehicle controls). Mean body weights of low-dose male rats was 5-9% lower between week 89 and 104. Mean body weight of female rats was within 4% of those of the vehicle controls throughout the studies. Slight significant decreases of hematocrit, hemoglobin concentration and erythrocytes (90% of values of the vehicle control) in female rats at 50 mg/kg were consistent with mild regenerative anemia but may be within the range of biological variation. Additionally, male rats showed no treatment related changes of haematological parameters so that the effect in females is considered to be of negligible biological significance. There was no effect of treatment on clinical chemistry parameters in any sex, or on organ weights or non-neoplastic histopathological findings in female rats. Male rats of the 50 mg/kg-group showed significant increases of relative brain and liver weights combined with decreased body weight after 103 w of administration. In absence of histopathological findings these organ weight changes are considered to be of questionable biological significance. Significant increases of relative kidney weights in male rats of the high-dose group occurred after 65 and 103 w of administration together with chronic renal disease. Advanced renal disease was characterized by varied degrees of degeneration and regeneration of tubular epithelium, atrophy and dilatation of some tubules, hyaline casts in the tubular lumina, glomerulosclerosis, interstitial fibrosis, and chronic inflammation, cysts (dilated tubules in the renal cortex), and increased papillary hyperplasia of the transitional epithelium overlying the renal papillae. Additionally, in male rats kidneys showed a slight increase of the incidences of renal tubuli hyperplasia in the high-dose group (0/55, 0/55, 2/55), and a dose-related increase of the incidences of renal tubuli adenoma (0/55, 4/55, 8/55; significant increase at 50 mg/kg). In female rats a significant dose-dependant increase of mononuclear cell leukaemia was found at 25 and 50 mg/kg (incidences 9/55, 15/55, 22/55). Increases of incidences of benign or malignant pheochromocytomas (combined) in adrenal glands of males (14/55, 19/48, 22/55) as well as a significant negative trend of adenomas in the pituitary gland of males (13/54, 9/54, 5/54) were considered to be unrelated to treatment because changes were marginally significant and incidences were within the range of historical controls. C-cell adenomas or carcinomas (combined) of the thyroid gland showed a significant decrease in 25 mg/kg female rats only (13/55, 4/54, 8/55).
The LOAEL for non-neoplastic chronic toxicity was 50 mg/kg bw/d in male rats (based on body weight reduction and nephropathy) and in female rats (haematological findings). According to NTP criteria some evidence of carcinogenicity was demonstrated by findings of renal tubule adenomas in male rats at 50 mg/kg bw/d and by increased incidences of mononuclear cell leukemia in female rats at 25 and 50 mg/kg bw/d.
Referenceopen allclose all
Table 1: Final body, liver and kidney weights after chronic feeding of 0.8% hydroquinone
Sex |
Group |
No. of surviving animals |
Final body weigth (g) |
Liver weight |
Kidney weight |
||
Absolute (g) |
Relative (%) |
Absolute (g) |
Relative (%) |
||||
Male |
Control |
22 |
37±6 |
2.11±0.86 |
5.81±2.57 |
0.66±0.11 |
1.78±0.28 |
HQ |
27 |
38±5 |
2.12±0.65 |
5.75±2.21 |
0.68±0.06 |
1.81±0.17 |
|
Female |
Control |
26 |
47±7 |
1.65±0.28 |
3.60±1.02 |
0.48±0.04 |
1.05±0.20 |
HQ |
26 |
34±5 ** |
1.76±0.53 |
5.27±1.74 ** |
0.49±0.06 |
1.48±0.28 ** |
|
Statistically significantly different from the corresponding control value: ** P<0.01
Table 2: Incidences of non-neoplastic and neoplastic lesions in the kidneysa and livers after chronic feeding of 0.8% hydroquinone
Site |
Lesion |
No of rats with lesions (%) |
|||
Males |
Females |
||||
Control |
HQ |
Control |
HQ |
||
Kidneys |
Pyelonephritis |
2/28 (7%) |
0/30 (0%) |
0/29 (0%) |
0/30 (0%) |
Interstitial nephritis |
0/28 (0%) |
0/30 (0%) |
0/29 (0%) |
1/30 (3%) |
|
Cyst |
0/28 (0%) |
2/30 (7%) |
0/29 (0%) |
1/30 (3%) |
|
Epithelial hyperplasia, tubuli |
0/28 (0%) |
9/30 (30%) ** |
0/29 (0%) |
0/30 (0%) |
|
Adenoma, tubuli |
0/28 (0%) |
3/30 (10%) |
0/29 (0%) |
0/30 (0%) |
|
Liver |
Hypertrophy |
0/28 (0%) |
26/30 (67%) ** |
0/29 (0%) |
3/30 (10%) |
Foci of cellular alteration |
4/28 (14%) |
14/30 (47%) * |
0/29 (0%) |
2/30 (7%) |
|
Hepatocellular adenoma |
6/28 (22%) |
14/30 (47%) * |
0/29 (0%) |
1/30 (3%) |
|
Hepatocellular carcinoma |
7/28 (26%) |
6/30 (20%) |
1/29 (3%) |
0/30 (0%) |
|
Forestomach |
Hyperplasia |
1/28 (4%) |
11/30 (37%) ** |
3/29 (10%) |
14/30 (47%) ** |
Squamous cell carcinoma |
0/28 (0%) |
1/30 (3%) |
0/29 (0%) |
1/30 (3%) |
|
Statistically significantly different from the corresponding control value: * P<0.05; ** P<0.01
a Description of kidney lesions:
Renal tubular hyperplasia : tubules with stratified epithelial cells which partially or fully filled the tubular lumina, often with cystic forms
Renal tubular adenoma: cystic or solid forms, in both cases being composed of relatively uniform epithelial cells with clear or pale basophilic cytoplasm and round nuclei with prominent nucleoli
Table 3: Quantitative data for foci of cellular alteration in the liver of rats after chronic feeding of 0.8% hydroquinone
Sex |
Group |
Number |
Number of foci of cellular alteration |
|
Total |
Number/cm2 of liver tissue |
|||
Male |
Control |
28 |
6 |
0.37±1.10 |
HQ |
30 |
23 |
1.16±1.54 * |
|
Female |
Control |
29 |
1 |
0.07±0.39 |
HQ |
30 |
3 |
0.13±0.44 |
|
Table 1: Final body, liver and kidney weights after chronic feeding of 0.8% hydroquinone
Sex |
Group |
No. of surviving animals |
Final body weigth (g) |
Liver weight |
Kidney weight |
||
Absolute (g) |
Relative (%) |
Absolute (g) |
Relative (%) |
||||
Male |
Control |
24 |
438±38 |
8.08±4.89 |
1.86±1.15 |
2.02±1.21 |
0.47±0.28 |
HQ |
22 |
422±44 |
12.07±1.13 ** |
2.89±0.37 ** |
3.42±0.52 ** |
0.82±0.16 ** |
|
Female |
Control |
22 |
306±42 |
7.24±1.46 |
2.38±0.38 |
1.86±0.10 |
0.62±0.09 |
HQ |
22 |
283±28 * |
7.31±1.03 |
2.62±0.55 |
1.91±0.08 |
0.68±0.06 * |
|
Statistically significantly different from the corresponding control value: * P<0.05; ** P<0.01
Table 2: Incidences of non-neoplastic and neoplastic lesions in the kidneysa and livers after chronic feeding of 0.8% hydroquinone
Site |
Lesion |
Severity |
No of rats with lesions (%) |
|||
Males |
Females |
|||||
Control |
HQ |
Control |
HQ |
|||
Kidneys |
Chronic nephropathy |
slight |
17/30 (57%) |
10/30 (33%) |
1/30 (3%) |
8/30 (27%) |
moderate |
0/30 (0%) |
9/30 (30%) |
0/30 (0%) |
0/30 (0%) |
||
severe |
0/30 (0%) |
5/30 (17%) |
0/30 (0%) |
0/30 (0%) |
||
Chronic nephropathy total incidence |
17/30 (57%) |
24/30 (80%) ** |
1/30 (3%) |
8/30 (27%) ** |
||
Epithelial hyperplasia, papilla |
2/30 (6%) |
11/30 (37%) * |
0/30 (0%) |
0/30 (0%) |
||
Epithelial hyperplasia, tubuli |
1/30 (3%) |
30/30 (100%) ** |
0/30 (0%) |
2/30 (7%) |
||
Adenoma, tubuli |
0/30 (0%) |
14/30 (47%) ** |
0/30 (0%) |
0/30 (0%) |
||
Liver |
Bile duct hyperplasia |
8/30 (27%) |
1/30 (3%) * |
0/30 (0%) |
1/30 (3%) |
|
Foci of cellular alteration |
21/30 (70%) |
14/30 (47%) |
22/30 (73%) |
19/30 (63%) |
||
Hyperplastic nodule |
2/30 (7%) |
1/30 (3%) |
2/30 (7%) |
2/30 (7%) |
||
Hepatocellular carcinoma |
1/30 (3%) |
1/30 (3%) |
0/30 (0%) |
1/30 (3%) |
||
Statistically significantly different from the corresponding control value: * P<0.05; ** P<0.01
a Description of kidney lesions:
Renal tubular hyperplasia : tubules with stratified epithelial cells which partially or fully filled the tubular lumina, often with cystic forms
Renal tubular adenoma: cystic or solid forms, in both cases being composed of relatively uniform epithelial cells with clear or pale basophilic cytoplasm and round nuclei with prominent nucleoli
Table 3: Quantitative data for foci of cellular alteration in the liver of rats after chronic feeding of 0.8% hydroquinone
Sex |
Group |
Number |
Number of foci of cellular alteration |
|
Total |
Number/cm2 of liver tissue |
|||
Male |
Control |
30 |
50 |
1.18±1.17 |
HQ |
30 |
25 |
0.57±0.69 * |
|
Female |
Control |
30 |
171 |
4.38±4.12 |
HQ |
30 |
47 |
1.38±1.37 ** |
|
Table 1: Body weights and relative organ weights after 65 and 103 w of gavage (mean±standard error)
Application period |
Parameter |
Dose groups males |
Dose groups females |
||||
Vehicle control |
50 mg/kg |
100 mg/kg |
Vehicle control |
50 mg/kg |
100 mg/kg |
||
65 w |
Body weight (g) |
45.6±1.26 |
44.9±1.34 |
46.9±1.01 |
46.7±2.51 |
42.4±2.54 |
40.6±1.17 |
Brain * |
10.6±0.41 |
11.0±0.33 |
10.2±0.21 |
10.7±0.48 |
12.2±0.74 |
12.6±0.35a |
|
Kidney * |
18.0±0.63 |
19.6±0.41 |
19.2±0.57 |
11.2±0.30 |
13.1±0.44b |
13.3±0.26b |
|
Liver * |
44.6±2.32 |
52.5±5.35 |
54.8±3.88b |
40.5±0.95 |
40.9±1.15 |
45.2±1.25b |
|
103 w |
Number of animals weighed |
33 |
36 |
36 |
37 |
39 |
36 |
Body weight |
44.0±0.76 |
43.0±0.72 |
42.0 ±0.95 |
50.7±1.65 |
51.5±1.46 |
47.8±1.24 |
|
Brain * |
11.7±0.21 |
11.9±0.22 |
12.1±0.28 |
10.7±0.40 |
10.5±0.38 |
11.0±0.29 |
|
Kidney * |
11.8±0.38 |
11.7±0.23§ |
12.4±0.32 |
7.5±0.44# |
7.4±0.31 |
7.3±0.22 |
|
Liver * |
67.2±4.80 |
76.4±4.82a§ |
70.0±3.17a |
52.0±3.22# |
52.0±2.65 |
55.1±2.68a |
|
* relative organ weights as mg of organ per g body weight;§N=35 mice weighed;#N=36 mice weighed
Statistically significant increased compared to vehicle control: a p<0.05, b p<0.0.1
Table 2: Overview of statistically significant haematological and clinical chemical parameters in the 65-week gavage studies of hydroquinone
Affected sex |
Endpoint |
Parameter |
Dose group |
||
Vehicle control |
50 mg/kg |
100 mg/kg |
|||
Male |
Hematology |
Hematocrit (%) |
36.5±2.38 |
39.5±1.27 |
41.3±1.17a |
Erythrocytes (106/µL) |
7.3±0.52 |
8.0±0.29 |
8.3±0.28a |
||
Clinical chemistry |
Total protein (g/dL) |
5.2±0.04 |
5.4±0.15 |
5.9±0.23b |
|
Albumin (g/dL) |
3.3±0.05 |
3.5±0.08 |
3.8±0.15b |
||
Alkaline phosphatase (IU/L) |
38.4±2.34 |
38.8±1.41 |
50.0±3.92a |
||
Sorbitol dehydrogenase (SU/mL) |
35.8±1.24 |
35.6±2.05 |
43.0±1.79b |
||
Female |
Clinical chemistry |
Total protein (g/dL) |
5.3±0.07 |
5.5±0.12 |
5.7±0.05b |
Albumin (g/dL) |
3.5±0.06 |
3.6±0.10 |
3.9±0.04b |
||
Alanine aminotransferase (IU/L) |
38.9±6.62 |
31.6±6.19 |
23.7±1.33b |
||
Sorbitol dehydrogenase (SU/mL) |
35.6±1.09 |
33.7±1.37 |
32.4±0.73a |
||
statistically different from vehicle control: a p<0.05, b p<0.0.1
Table 3: Number of mice with selected lesions in the liver and thyroid gland in the 65 w and 103 w gavage study of hydroquinone
Application period |
Site of lesion |
Type of lesion |
Dose groups males |
Dose groups females |
||||
Vehicle control |
50 mg/kg |
100 mg/kg |
Vehicle control |
50 mg/kg |
100 mg/kg |
|||
65 w |
Number of animals examined |
10 |
10 |
10 |
10 |
10 |
10 |
|
Liver |
Diffuse centrilobular fatty change |
1 |
0 |
7 |
0 |
0 |
0 |
|
Diffuse fatty change |
0 |
0 |
0 |
1 |
3 |
0 |
||
Diffuse cytomegaly |
0 |
8 |
10 |
0 |
0 |
0 |
||
Syncytial cells |
1 |
1 |
4 |
0 |
0 |
0 |
||
Basophilic focus |
0 |
0 |
1 |
0 |
0 |
0 |
||
Clear cell focus |
0 |
0 |
0 |
0 |
0 |
1 |
||
Hepatocellular adenoma |
1 |
1 |
4 |
0 |
1 |
0 |
||
Hepatocellular carcinoma |
2 |
1 |
1 |
0 |
0 |
0 |
||
Hepatocellular adenoma or carcinoma |
3 |
2 |
4 |
0 |
1 |
0 |
||
Thyroid gland |
Hyperplasia |
0 |
0 |
0 |
0 |
0 |
2 |
|
103 w |
Liver |
Number of animals examined |
55 |
54 |
55 |
55 |
55 |
55 |
Anisokaryosis |
0/55 (0%) |
2/54 (4%) |
12/55 (22%) |
n.s. |
n.s. |
n.s. |
||
Syncytial alteration |
5/55 (9%) |
3/54 (6%) |
25/55 (45%) |
n.s. |
n.s. |
n.s. |
||
Basophilic focus |
2/55 (4%) |
5/54 (9%) |
11/55 (20%) |
2/55 (4%) |
6/55 (11%) |
3/55 (5%) |
||
Hepatocellular adenoma |
9/55 (16%) |
21/54 (39%) |
20/55 (36%) |
2/55 (4%) |
15/55 (27%) |
12/55 (22%) |
||
Hepatocellular carcinoma |
13/55 (24%) |
11/54 (20%) |
7/55 (13%) |
1/55 (2%) |
2/55 (4%) |
2/55 (4%) |
||
Hepatocellular adenoma or carcinoma a |
20/55 (36%) |
29/54 (54%) |
25/55 (45%) |
3/55 (5%) |
16/55 (29%) |
13/55 (24%) |
||
Thyroid gland |
Number of animals examined |
55 |
53 |
54 |
55 |
55 |
55 |
|
Hyperplasia |
5/55 (9%) |
15/53 (28%) |
19/54 (35%) |
13/55 (24%) |
47/55 (85%) |
45/55 (82%) |
||
Adenoma |
2/55 (4%) |
1/53 (2%) |
2/54 (4%) |
3/55 (5%) |
5/55 (9%) |
6/55 (11%) |
||
Carcinoma |
0/55 (0%) |
0/53 (0%) |
0/54 (0%) |
0/55 (0%) |
0/55 (0%) |
1/55 (2%) |
||
Adenoma or carcinoma b |
2/55 (4%) |
1/53 (2%) |
2/54 (4%) |
3/55 (5%) |
5/55 (9%) |
7/55 (13%) |
||
Historical incidences in control groups (means±SD):
a male mice: water vehicle controls: 106/347 (31±6 %); untreated controls 609/2,032 (30±8%);
female mice: water vehicle controls: 29/348 (8±5 %); untreated controls 184/2,032 (9±5%)
b female mice: water vehicle controls 10/337 (3±2%); untreated controls 49/1,937 (3±3%)
Table 1: Distribution of CPN grade after gavage application for 2 years or 65 weeks
Duration of study |
Dose group (mg/kg) |
Sex |
Total number graded for CPNa |
Number of rats according to CPN grades |
|||||
Minimal |
Mild |
Low-moderate |
High-moderate |
Severe |
End-stage |
||||
2 y including spontaneous deaths |
0 |
Male |
44 |
0 |
0 |
2 |
20 |
20 |
2 |
25 |
Male |
49 |
2 |
2 |
2 |
20 |
21 |
2 |
|
50 |
Male |
51 |
0 |
2 |
2 |
11 |
16 |
20 |
|
0 |
Female |
53 |
4 |
6 |
15 |
27 |
1 |
0 |
|
50 |
Female |
46 |
2 |
7 |
18 |
15 |
1 |
3 |
|
66 w sacrifice |
0 |
Male |
10 |
0 |
0 |
6 |
4 |
0 |
0 |
50 |
Male |
10 |
0 |
0 |
1 |
9 |
0 |
0 |
|
aexcludes rats in which CPN grades were not evaluated due to autolysis
Table 2: Overview of proliferative kidney lesions (non-neoplastic and neoplastic) in kidney tissue sections from the NTP study
Dose group |
Total number of rats examined |
NTP diagnosis |
Reevaluation of adenoma diagnosed in NTP report (incidences of grades of CPN) |
Additional diagnoses during the reevaluation (incidences of grades of CPN) |
||||
Adenoma |
Adenoma |
Incipient adenoma |
Foci of atypical tubule hyperplasia |
Other |
Foci of atypical tubule hyperplasia |
Small tubule regeneration |
||
0 mg/kg |
44 |
0 |
0 |
0 |
0 |
0 |
0 |
8 (7 s 1 es) |
25 mg/kg |
49 |
4 |
2 (s, es) |
1 (s) |
0 |
1 lesion not related to renal origina (l-m) |
2 (s) |
16 (14 s, 2 es) |
50 mg/kg |
51 |
8 |
4 including 1 cystadenoma (1 s, 3 es) |
3 (2 s, 1 es) |
1 (s) |
13 foci in 11 rats (2 s, 9 es) |
27 (7 s, 20 es) |
|
Grades of CPN: l-m = low-moderate, s = severe, es = end-stage
a possibly a metastasis of a mesothelioma
Table 1: Body weights and relative organ weights after 65 and 103 w of gavage (mean ± standard error)
Application period |
Parameter |
Dose groups males |
Dose groups females |
||||
Vehicle control |
25 mg/kg |
50 mg/kg |
Vehicle control |
25 mg/kg |
50 mg/kg |
||
65 w |
Body weight (g) |
492±9.6 |
504±8.1 |
466±10.3 |
312±11.6 |
307±8.1 |
303±7.9 |
Brain* |
4.4±0.07 |
4.2±0.10 |
4.6±0.10 |
6.3±0.18 |
6.1±0.17 |
6.3±0.17 |
|
Kidney* |
6.2±0.12 |
6.6±0.20 |
6.8±0.14b |
6.6±0.52 |
6.0±0.19 |
6.0±0.12 |
|
Liver* |
33.6±0.65 |
33.7±0.78 |
36.8±1.29 |
29.8±1.16 |
30.8±0.79 |
31.6±0.73 |
|
103 w |
Number of animals weighed |
27 |
18 |
18 |
39 |
27 |
31 |
Body weight (g) |
464±9.2 |
434±8.5a |
402±11.9b |
337±7.1 |
360±13.1 |
330±7.4 |
|
Brain* |
4.9±0.11 |
5.2±0.12a |
5.6±0.18b |
5.9±0.16 |
5.6±0.17 |
6.0±0.15 |
|
Kidney* |
4.5±0.12 |
4.7±0.14 |
6.6±0.59b |
3.9±0.11 |
3.7±0.12 |
4.0±0.10 |
|
Liver* |
46.6±2.09 |
47.6±2.76 |
53.9±3.04a |
37.2±0.96 |
38.1±1.25 |
41.2±1.71 |
|
* relative organ weights as mg of organ per g body weight
Statistically significant increased compared to vehicle control: a p<0.05, b p<0.0.1
Table 2: Overview of statistically significant haematological and clinical chemical parameters in the 65-week gavage studies of hydroquinone (mean ± standard error)
Affected sex |
Endpoint |
Parameter |
Dose group |
||
Vehicle control |
25 mg/kg |
50 mg/kg |
|||
Male |
Hematology |
Lymphocytes (1,000 µL) |
1.2±0.14 |
1.8±0.15a |
1.9±0.37 |
Clinical chemistry |
Alkaline phosphatase (IU/L) |
139±4.7 |
133±5.1 |
132±17.6a |
|
Female |
Hematology |
Hematocrit (%) |
40.2±0.69 |
38.9±0.89 |
36.0±1.70a |
Hemoglobin (g/dL) |
14.8±0.27 |
14.3±0.26 |
13.4±0.62a |
||
Erythrocytes (106/µL) |
7.3±0.13 |
7.1±0.15 |
6.5±0.40a |
||
Clinical chemistry |
Alkaline phosphatase (IU/L) |
119±11.2 |
150±4.6a |
142±5.9 |
|
a statistically different from vehicle control with P<0.05
Table 3: Number of rats with indicated severity of nephropathy in the 65 w and 103 w gavage study of hydroquinone
Application period |
Severity |
Dose groups males |
Dose groups females |
||||
Vehicle control |
25 mg/kg |
50 mg/kg |
Vehicle control |
25 mg/kg |
50 mg/kg |
||
65 w |
No nephropathy |
0 |
0 |
0 |
4 |
5 |
3 |
minimal |
0 |
0 |
0 |
4 |
1 |
3 |
|
mild |
10 |
5 |
4 |
1 |
4 |
4 |
|
moderate |
0 |
5 |
6 |
1 |
0 |
0 |
|
103 w |
Number of rats examined |
55 |
55 |
55 |
55 |
55 |
55 |
No nephropathy |
2 |
3 |
0 |
8 |
8 |
9 |
|
minimal |
3 |
1 |
3 |
47 * |
47 * |
46 * |
|
mild |
12 |
12 |
5 |
||||
moderate |
26 |
31 |
15 |
||||
marked |
12 |
8 |
32 |
||||
* no grading of severity of nephropathy for female rats of the 2 year study
Table 4: Number of rats with hyperplastic or neoplastic lesions in the pituitary gland in the 65 w and 103 w gavage study of hydroquinone
Application period |
Site of lesion |
Type of lesion |
Dose groups males |
Dose groups females |
||||
Vehicle control |
25 mg/kg |
50 mg/kg |
Vehicle control |
25 mg/kg |
50 mg/kg |
|||
Number of animals examined |
10 |
10 |
10 |
10 |
10 |
10 |
||
65 w |
Pars distalis |
Hyperplasia |
1 |
3 |
1 |
3 |
1 |
0 |
Adenoma |
1 |
0 |
2 |
3 |
3 |
1 |
||
Carcinoma |
0 |
0 |
0 |
1 |
0 |
0 |
||
Pars intermedia |
Adenoma |
0 |
0 |
0 |
1 |
0 |
0 |
|
103 w |
Number of animals examined |
54 |
54 |
54 |
54 |
54 |
54 |
|
Pars distalis |
Hyperplasia |
12 |
14 |
11 |
28 |
22 |
26 |
|
Adenoma |
13 |
9 |
5a |
23 |
21 |
16 |
||
Carcinoma |
0 |
1 |
0 |
1 |
1 |
0 |
||
Adenoma or carcinoma |
13 |
10 |
5a |
24 |
22 |
16 |
||
amarginally significant decrease (P=0.038); however, incidence of adenomas and carcinomas (combined) of 9% is within the historical
control range of 5-54%
Table 5: Overview of statistically significant neoplastic findings in rats after 103 w of gavage application
Affected sex |
Site of lesion |
Type of lesion |
Parameter |
Dose group |
||
Vehicle control |
25 mg/kg |
50 mg/kg |
||||
Male |
Kidney, tubuli |
Hyperplasiae |
Overall rates |
0/55 (0%) |
0/55 (0%) |
2/55 (4%) |
Adenomaa, f |
Overall rates |
0/55 (0%) |
4/55 (7%) |
8/55 (15%) |
||
Terminal rates |
0/27 (0%) |
2/18 (11%) |
5/18 (28%) |
|||
Day of first observation |
392 |
598 |
||||
Logistic regression tests |
P=0.003 |
P=0.069 |
P=0.003 |
|||
Female |
Hemopoietic system |
Mononuclear leukaemiab |
Overall rates |
9/55 (16%) |
15/55 (27%) |
22/55 (40%) |
Terminal rates |
4/40 (10%) |
6/27 (22%) |
11/32 (34%) |
|||
Day of first observation |
553 |
576 |
492 |
|||
Logistic regression tests |
P=0.004 |
P=0.129 |
P=0.006 |
|||
Life table tests |
P=0.003 |
P=0.048 |
P=0.003 |
|||
Male |
Pituitary gland, |
Hyperplasia |
Overall rates |
12/54 (22%) |
14/54 (26%) |
11/54 (20%) |
Adenoma |
Overall rates |
13/54 (24%) |
9/54 (17%) |
5/54 (9%) |
||
Terminal rates |
6/27 (22%) |
3/17 (18%) |
1/18 (6%) |
|||
Day of first observation |
459 |
466 |
598 |
|||
Logistic regression tests |
P=0.031N |
P=0.303N |
P=0.038N |
|||
Carcinoma |
Overall rates |
0/54 (0%) |
1/54 (2%) |
0/54 (0%) |
||
Adenoma or carcinomac |
Overall rates |
13/54 (24%) |
10/54 (19%) |
5/54 (9%) |
||
Terminal rates |
6/27 (22%) |
3/17 (18%) |
1/18 (6%) |
|||
Day of first observation |
459 |
466 |
598 |
|||
Logistic regression tests |
P=0.033N |
P=0.392N |
P=0.038N |
|||
Male |
Adrenal gland |
Pheochromocytoma malignant |
Overall rates |
1/55 (2%) |
2/48 (4%) |
3/55 (5%) |
Pheochromocytoma benign |
Overall rates |
9/55 (16%) |
14/48 (29%) |
13/55 (24%) |
||
Bilateral pheochromo-cytoma benign |
Overall rates |
4/55 (7%) |
3/48 (6%) |
6/55 (11%) |
||
Pheochromocytoma combinedd |
Overall rates |
14/55 (25%) |
19/48 (40%) |
22/55 (40%) |
||
statistically significant findings
Historical incidences in control groups:
a Renal tubuli adenoma: water vehicle controls total 1/298 (0.3±0.8%), range 0/50 to 1/50; untreated controls total 9/1,928 (0.5±1%), range 0/50 to 3/50
b Mononuclear leukaemia: water vehicle controls total 75/299 (25±15%), range 4/50 to 23/49; untreated controls total 383/1,983 (19±7%), range 3/50 to 15/49
c Pituitary gland, adenoma or carcinoma: water vehicle controls 126/295 (43±12%); untreated controls 459/1,830 (25±10%)
d Adrenal gland, pheochromocytoma combined: water vehicle controls total 121/299 (40±16%), range 5/50 to 28/50; untreated controls total 489/1,915 (26±14%), range 3/50 to 32/49
Description of histopathological findings in renal tubules of male rats:
e Hyperplasia was characterized by tubules with stratified epithelial cells that partially filled the tubular lumina.
f Renal tubular adenoma were identified during microscopic examination but not by gross necropsy. Tubular adenomas were characterized by discrete masses of epithelial cells arranged in solid clusters or nests separated by a scant stroma. In a few tumors, some of the cells exhibited poorly defined tubular formation that blended with the solid areas. The epithelial cells were relatively uniform with pale basophilic cytoplasm and round nuclei with prominent nucleoli.
Table 6: Number of female rats with various stages of mononuclear cell leukemia after 103 w of gavage application
Stage |
Vehicle control |
25 mg/kg |
50 mg/kg |
1 |
0 |
2 |
1 |
2 |
4 |
5 |
7 |
3 |
5 |
8 |
14 |
Total |
9 |
15 |
22 |
Stage 1: probably not a contributory cause of death; stage 2: probable contributory cause of death; stage 3: probable cause of death
Endpoint conclusion
- Endpoint conclusion:
- adverse effect observed
- Dose descriptor:
- NOAEL
- 25 mg/kg bw/day
- Study duration:
- chronic
- Species:
- rat
- Quality of whole database:
- There were 2 carcinogenicity studies showing kidney adenomas in male F344 rats. The other neoplastic or non-neoplastic findings were not consistent between studies or genders.
Carcinogenicity: via inhalation route
Endpoint conclusion
- Endpoint conclusion:
- no study available
Carcinogenicity: via dermal route
Endpoint conclusion
- Endpoint conclusion:
- no adverse effect observed
Justification for classification or non-classification
HQ has been classified in Carcinogenicity Category 2 (suspected human carcinogen) according to C&L of the GHS based on the presence of renal tubular adenomas and hyperplasia in male Fischer F344 rats. Numerous mechanistic investigations have indicated that the likely mechanism is related to exacerbation of Chronic Progressive Nephropathy which seems to occur with a particular sensitivity in Fischer F344 male rats, possibly related to a higher kidney exposure to toxic metabolites in that rat strain, but not related to direct DNA damage nor to DNA adducts. This was supported by the lack of DNA binding activity in kidneys, and by negative results in in vivo TGR assay in mice and in vivo Comet assay in F344 rats. The mechanism of action identified in Fischer F344 rats is not relevant to human. A more severe classification is therefore not justified. As the in vivo comet assay showed also no genotoxic activity in the male gonads, as a reliable surrogate of germ cells, a DNEL for threshold effects is derived for the risk assessment.
Additional information
With HQ two long-term studies with oral application in F344 rats and B6C3F1 mice have been performed by NTP (1989) and Shibata et al. (1991).
Studies with rats:
In the NTP study (1989), HQ was administered to male and female F344 rats over 103 weeks on 5 days per week via gavage at doses of 0, 25, and 50 mg/kg bw/d (vehicle water). The study protocol was similar to OECD Guideline 453 with several minor deviations (only 2 instead of 3 dose groups, food consumption and urinalysis not examined). In the study performed by Shibata et al. (1991), male and female F344 rats were dosed continuously with 0 or 0.8 % HQ via diet (m: ca. 351 mg/kg; f: ca. 368 mg/kg) over 104 w. In this study only tumour incidences for renal adenomas and hepatocellular carcinomas were given and only one dose was tested. Therefore, it is not possible to make any conclusions concerning dose-response-relationship. The individual data are summarized in the Tables 1 and 2.
Table 1: Long-term studies with F344 rats
Dose Application Duration |
Results |
Reference |
0, 25 or 50 mg/kg via gavage on 5 d/w over 103 w |
males: 50 mg/kg: slight, but statistically significant increased incidences of renal adenomas (0/55, 4/55, 8/55)* females: >= 25 mg/kg: statistically significant increased incidences of mononuclear cell leukaemia (9/55, 15/55 and 22/55 [16, 27 or 40 %]) |
NTP (1989); Kari et al. (1992) |
0 or 0.8 % via diet over 104 w (m: ca. 351 mg/kg; f: ca. 368 mg/kg) |
males: 351 mg/kg: statistically significant increased incidences of renal adenomas (0/30 and 14/30 [0 or 47 %]) females: no indication for carcinogenic effects |
Shibata et al. (1991) |
* re-evaluated data (Hard et al., 1997): 0/44, 2/49 and 4/51
NTP (1989) / Kari et al. (1992): Kidneys of males showed slightly increased incidences of renal tubular hyperplasia in the high-dose group (0/55, 0/55, 2/55), and dose-related increased incidences of renal tubular adenomas. Chronic renal disease was diagnosed in the high-dose group after 65 and 103 w of administration, and in the low-dose group only at the 66-week interim sacrifice. In females a significant dose-dependent increase of mononuclear cell leukaemia was found at >= 25 mg/kg.
Shibata et al. (1991): In treated males, the finding of significantly increased incidences of renal tubular hyperplasia (100 % vs. 3 % in controls) and of renal tubular adenomas (47 % vs. 0 % in controls) was associated with an exacerbation of chronic nephropathy.
Studies with mice:
In the NTP study (1989), HQ was administered to male and female B6C3F1 mice for 103 weeks on 5 days per week via gavage at doses of 0, 50, and 100 mg/kg bw/d (vehicle water). The study protocol was similar to OECD Guideline 453 with several minor deviations (only 2 instead of 3 dose groups, food consumption and urinalysis not examined). In the study performed by Shibata et al. (1991), male and female B6C3F1 mice were dosed continuously with 0 or 0.8 % HQ via diet (m: ca. 1046 mg/kg; f: ca. 1486 mg/kg) over 96 weeks. In this study only tumour incidences for kidneys, liver and forestomach were given and only one dose was tested. Therefore, it is not possible to make any conclusions concerning dose-response-relationship.
Table 2: Long-term studies with B6C3F1 mice
Dose Application Duration |
Results |
Reference |
0, 50 or 100 mg/kg via gavage on 5 d/w over 103 w |
males: no indication for carcinogenic effects females: >= 50 mg/kg: statistically significant increased incidences (no dose-response relationship) of hepatocellular adenomas (2/55, 15/55 and 12/55 [4, 27 or 22 %]) and of combined incidences of hepatocellular adenomas or carcinomas (3/55, 16/55 and 13/55 [5, 29 or 24 %]) |
NTP (1989); Kari et al. (1992) |
0 or 0.8 % via diet over 96 w (m: ca. 1046 mg/kg; f: ca. 1486 mg/kg) |
males: 1046 mg/kg: statistically significant increased incidences of hepatocellular adenomas (6/28 and 14/30 [22 or 47 %]); no statistical evaluation given concerning combined incidences of hepatocellular adenomas or carcinomas females: no indication for carcinogenic effects |
Shibata et al. (1991) |
NTP (1989) / Kari et al. (1992): In both dose groups of males, increased incidences ofhepatocellularadenomas were offset by decreased incidences ofhepatocellularcarcinomas so that the combined incidences ofhepatocellularadenomas or carcinomas were not significantly different from the vehicle control group. However, in dosed females, both incidences ofhepatocellularadenomas and of combined incidences ofhepatocellularadenomas or carcinomas were significantly increased.
Shibata et al. (1991): In treated mice of both sexes small nodular lesions were grossly visible in the forestomach lumen, which was associated with a statistically significant increase of forestomach hyperplasia (m: 37 % vs. 4 % in controls; f: 47 % vs. 10 % in controls), indicating a local irritant effect of HQ that had also been observed in high incidence in the NTP study with gavage application. In treated males, significantly increased incidences of renal tubular hyperplasia (30 vs. 0 % in controls) were observed without a significant increase of renal tubular adenomas (10 % vs. 0 % in controls). There was no indication of alpha-2µ-globulin nephropathy. In dosed males, there was a significant increased incidence of hepatocellular adenomas compared to controls together with significant increased incidences of centrilobular hypertrophy (26 % vs. 0 %) and of foci of cellular alteration (47 % vs. 14 %). In contrast, there was a single case (3 %) of liver adenomas in HQ-treated females and no increase of altered liver foci. Principally, the applied doses appear to be very high as in a 13-week gavage study with B6C3F1 mice a dose of 200 mg/kg bw induced increased lethality (NTP, 1989; see section 7.5).
Evaluation of the interaction of renal non-neoplastic and neoplastic lesions
Studies with long-term exposure of F344 rats to HQ indicated the simultaneous appearance of neoplastic and non-neoplastic changes in the kidney (see Table 3).
Table 3: Comparison of the incidences of renal adenomas and CPN in 2-year studies with F344 rats
Dose |
Sex |
Rats graded (n) |
Number of rats according to CPN grades |
|||||
|
|
|
Renal adenomas |
Minimal |
Mild |
Low- to High-Moderate |
Severe |
End-stage |
Data from NTP (1989) and Kari et al. (1992): 2 year study (gavage on 5 d/w over 103 w) |
||||||||
0 |
M |
44 |
0/44 |
0 |
0 |
22 |
20 |
2 |
25 |
M |
49 |
2/49 |
2 |
2 |
22 |
21 |
2 |
50 |
M |
51 |
4/51 |
0 |
2 |
13 |
16 |
20 |
0 |
F |
53 |
0/55* |
4 |
6 |
42 |
1 |
0 |
50 |
F |
46 |
0/55* |
2 |
7 |
33 |
1 |
3 |
Interim sacrifice (w 66) |
||||||||
0 |
m |
10 |
|
0 |
0 |
10 |
0 |
0 |
50 |
m |
10 |
|
0 |
0 |
10 |
0 |
0 |
|
|
|
|
|
|
|
|
|
Data from Shibata et al.(1991): 0 or 0.8 % via diet over 104 w (m: ca. 351 mg/kg; f: ca. 368 mg/kg) |
||||||||
0 |
M |
30 |
0 |
|
17 |
0 |
0 |
|
351 |
M |
30 |
14 |
|
10 |
9 |
5 |
|
0 |
F |
30 |
0 |
|
1 |
0 |
0 |
|
368 |
F |
30 |
0 |
|
8 |
0 |
0 |
|
* Data from NTP (1989) and Kari et al. (1982)
In the NTP study, high-dosed male rats showed both significant increases of relative kidney weights and increased severity of CPN compared to vehicle controls after 65 and 103 w, while in the low-dose group an increased severity of CPN occurred at the 66-week interim sacrifice only. Advanced renal disease was characterized by varied degrees of degeneration and regeneration of tubular epithelium, atrophy and dilatation of some tubules, hyaline casts in the tubular lumen, glomerulosclerosis, interstitial fibrosis, and chronic inflammation, cysts (dilated tubules in the renal cortex), and increased papillary hyperplasia of the transitional epithelium overlying the renal papillae. Additionally, in male rats kidneys showed a slight increase of the incidences of renal tubuli hyperplasia in the high-dose group (0, 0 and 3.6 %), and a dose-related increase of the incidences of renal tubuli adenomas (0, 7.3 and 14 %; significant increase at 50 mg/kg). There was no indication of renal lesions in female rats (NTP, 1989; Kari et al., 1992).
In the study of Shibata et al. (1991), CPN in treated male F344 rats appeared with higher severity and significantly increased incidence compared to control males (80 % vs. 57 %), which was also associated with a significantly increased incidence of epithelial hyperplasia in the renal papilla. Further, significantly increased incidences of renal tubular hyperplasia (100 % vs. 3 %) and of renal tubular adenomas (47 % vs. 0 %) existed in dosed males vs. controls. In female rats, a significantly increased incidence of CPN compared to control females (27 % vs. 3 %) was seen, but effects were only graded as slight. Renal tubular hyperplasia was observed in 7 % of female rats only, and there were no adenomas. Renal tubular hyperplasia was composed of tubules with stratified epithelial cells which partially or fully filled the tubular lumen, often with cystic forms. Renal tubular adenoma also exhibited cystic or solid forms, in both cases being composed of relatively uniform epithelial cells with clear or pale basophilic cytoplasm and round nuclei with prominent nucleoli.
Re-evaluation of renal lesions
Hard et al. (1997) published a re-evaluation of the renal histopathology of the NTP cancer bioassay on HQ with emphasis on evaluation of incidences, severity and location of CPN and of proliferative non-neoplastic and neoplastic lesions. Characterization of proliferative lesions followed the criteria of the Society of Toxicologic Pathologists (STP) and of the International Agency for Research on Cancer (IARC). There was no evidence of HQ-induced nephrotoxic changes or of alpha-2µ-globulin nephropathy. At terminal sacrifice high-dose males exhibited a statistically significant increase in the grade of CPN. Of the rats surviving into the last 10 w of the study, 49 % had end-stage CPN and 40 % had severe CPN. The re-evaluation of proliferative lesions deviated from the original NTP diagnoses, as at 25 mg/kg the diagnosis of originally 4 adenomas changed to 2 adenomas and 1 incipient adenoma with additional diagnosis of 2 foci of atypical tubule hyperplasia and at 50 mg/kg, instead of originally 8 adenomas the diagnosis was 4 adenomas (including 1 cystadenoma) and 3 incipient adenomas, and 14 foci of atypical tubule hyperplasia (in 11 rats). At 0, 25, and 50 mg/kg, 0/44, 4/49, and 15/51 male rats had either atypical tubule hyperplasia or adenomas, all being in the outer stripe of the medulla(OSOM), the junction of cortex and OSOM, or in the cortex within areas of severe or endstage CPN,and being statistically associated with CPN grade. Consequently, HQ not only exacerbated spontaneous CPN in high-dose male F344 rats, but also exerted a stimulatory effect on the proliferative potential of the advanced stages of CPN at both doses leading to an increased frequency of renal adenomas through this indirect mechanism. As a minimal renal tumour response is linked to an interaction with a rodent-specific spontaneous renal disease, these findings may have little relevance for humans.
A further reanalysis of renal findings was published by Whysner et al. (1995). The finding of renal adenomas appearing in HQ-treated male Fischer 344 rats but not in control groups or in dosed female rats was consistent between the two studies. The higher incidence in the study of Shibata was discussed to be explainable by the use of a larger daily dose administered by diet on 7 days per week compared to a 5 days per week gavage in the NTP study. In the NTP study, an increase in the severity of CPN was found to be related to treatment with HQ only in male rats with almost all of the adenomas and hyperplastic lesions appearing within foci of CPN. In the NTP study, there was no indication of CPN in female rats. In the Shibata study, CPN of a slight degree was increased in HQ-exposed female rats (27 % vs. 3 % in controls), whereas 17 %, 30 % and 33 % of male rats exhibited severe, moderate and slight degrees of CPN, respectively. No data of the locations of CPN and possible interactions with renal tumours are available for this study. There was no evidence of HQ-induced alpha-2µ-globulin nephropathy in either study.
Specific investigations on the mechanisms of the nephrotoxic action of HQ after acute to subchronic oral application (see IUCLID Section 7.9.3) show a strain- and species-specific susceptibility of male F344 rats. Renal lesions induced by exposure to HQ or by the critical metabolite 2,3,5-TriGSylHQ are characterized by tubular cell necrosis followed by cell regeneration. Cell proliferation distal to the site of toxicity was absent. Thus renal cell proliferation presumably is an attempt to compensate for proximal tubular cell loss rather than representing a direct mitogenic effect of HQ. The site-selectivity of nephrotoxicity at the outer stripe of the outer medulla (OSOM, corresponding to S3M segment of the nephron or P3 region) may be a consequence of the susceptibility of this area to oxidative stress, and to the high concentrations of gamma-glutamyl transpeptidase (GGT) in proximal tubular cells. Mechanistically, nephrotoxicity and hyperplasia in the kidney induced by HQ administration could predispose the male F344 rats to kidney tumour formation by an interaction with regenerative cell proliferation associated with CPN. This mode of tumour formation is not expected to operate in the absence of the renal disease process or at subtoxic exposure levels (Boatman et al., 1992, 1993, 1996; English et al., 1994; Peters et al., 1997).
Measurement of levels of 8-hydroxydeoxyguanosine adducts and of HQ-specific or BQ-specific DNA adducts in kidneys of HQ treated F344 rats indicated that hydroquinone does not induce oxidative DNA damage or covalent binding to DNA after multiple gavage doses (see Section 6.6: English et al., 1994, 1997).
In total, as also recently discussed by McGregor (2007),the increased incidence of renal adenomas in HQ-dosed male F344 rats, which is dependent onthe specific susceptibility of this strain and species to the nephrotoxic action of HQ and to the spontaneous development of CPN, does not represent a risk for humans to develop renal cancer.
Re-evaluation of hepatic lesions
In a critical evaluation, Whysner et al. (1995) pointed out that the findings of hepatic adenomas in mice were not consistent between the two bioassays (NTP, 1989; Shibata of al., 1991; see Table 4).
No increases of hepatocellular carcinomas were seen in either study in any sex. In the NTP study, compared to controls, HQ-treated male mice showed no significant change of total liver cancer incidence (adenomas and carcinomas combined) while high-dose males exhibited a lower incidence than low-dose males. Although, in both dose groups, the incidence of liver adenomas showed a similar, statistically significant increase in adenomas, the incidence of liver carcinomas was lower than in the vehicle controls. This means, in the presence of HQ there was a higher incidence of both altered liver foci and benign liver neoplasms while a simultaneous shift from malignant to benign liver tumours occurred in male mice compared to controls. In female mice, the NTP reported a statistically significantly increased incidence of adenomas and of adenomas and carcinomas combined for both dose groups. These incidences showed an inverse dose-relationship, as it had also been found in male mice in the same study. Based on these findings, the NTP concluded on some evidence of carcinogenic activity of HQ in female B6C3F1 mice.
In the study of Shibata et al. (1991), at a distinctly higher dose of 1046 mg/kg bw/d administered via feeding for 96 w, male mice demonstrated a statistically significant increase (P<0.05) in adenomas at the single dose tested together with a slight decrease in carcinomas. In contrast, no increases in either adenomas or carcinomas existed for female mice at a distinctly higher dose of 1486 mg/kg bw/d.
Importantly, liver adenomas and carcinomas are tumours known to occur with a high background incidence in B6C3F1 mice. Historical incidences in male B6C3F1 mice derived from NTP studies are up to 44% for adenomas and up to 58% for adenomas or carcinomas, combined (N=2032) in untreated mice of this strain, and up to 20% and 38%, respectively, in water gavage vehicle controls (N=347). Consequently, in both studies, liver tumour incidences in HQ-treated male mice were all within the upper range of historical incidences specified by NTP (NTP, 1989) for untreated controls of up to 58% (N=2032). Historical incidences in female B6C3F1 mice derived from NTP studies are up to 18% for adenomas and up to 20% for adenomas or carcinomas combined (N=2032) in untreated mice of this strain, and up to 12% and 14%, respectively, in water gavage vehicle controls (N=347). In female mice of the NTP study the observed maximal incidences of liver tumours were in the low dose group, with 27% for adenomas and 29% for combined adenomas or carcinomas, respectively, and were higher than the upper range of historical controls. This finding is contrasted with a single case (3%) of liver adenomas in HQ-treated females in the study of Shibata, which were exposed to a distinctly higher dose.
Based on the overall evidence from cancer bioassays with B6C3F1 mice and F344 rats, or from human exposure experience (see below), there is no indication that the liver is a target of a possible neoplastic action of HQ. In male mice, liver tumour incidences were within historical control ranges and were not dose-related. In female mice, there was no increase of liver tumours in one study and in the other study the total liver tumour incidence decreased from 29% to 24% from the low dose to the high dose, without associated reduced survival. Additionally, liver histopathology in rats demonstrated a significant reduction in bile duct hyperplasia in dosed compared to control males (P<0.05) as well as a significant reduction of the number of altered liver foci per cm2 liver tissue in both sexes (P<0.05 in males, P<0.01 in females) (data of Shibata et al., 1991).
Table 4: Overview on incidences of liver neoplasia and altered liver foci in mice after long-term treatment with HQ
Sex |
Dose (mg/kg bw/d) |
Basophilic foci (%) |
Eosinophilic foci (%) |
Adenomas (%) |
Hepatocellular carcinomas (%) |
Adenomas or hepatocellular carcinomas (%) |
Reference |
Male |
0 |
2/55 (4) |
4/55 (7) |
9/55 (16) |
13/55 (24) |
20/55 (36) |
NTP (1989); Kari et al. (1992)**** |
50 |
5/54 (9) |
2/55 (4) |
21/54 (39)* |
11/54 (20) |
29/54 (54) |
||
100 |
11/55 (20) |
1/55 (2) |
20/55 (36)** |
7/55 (13) |
25/55 (45) |
||
|
|
Altered foci (%) |
|
|
|
|
|
Male |
0 |
4/28 (14) |
6/28 (22) |
7/28 (26) |
|
Shibata et al. (1991)***** |
|
1046 |
14/30 (47)** |
14/30 (47)** |
6/30 (20) |
|
|||
|
|
|
|
|
|
|
|
Female |
0 |
2/55 (4) |
1/55 (2) |
2/55 (4) |
1/55 (2) |
3/55 (6) |
NTP (1989); Kari et al. (1992)**** |
50 |
6/55 (11) |
2/55 (4) |
15/55 (27)*** |
2/55 (4) |
16/55 (29)*** |
||
100 |
3/55 (5) |
0/55 (0) |
12/55 (22)* |
2/55 (4) |
13/55 (24)* |
||
|
|
Altered foci (%) |
|
|
|
|
|
Female |
0 |
0/29 (0) |
0/29 (0) |
1/29 (3) |
|
Shibata et al. (1991)***** |
|
1486 |
2/30 (7) |
1/30 (3)** |
0/30 (0) |
|
|||
* significantly
different, P<0.01;** significantly different,
P<0.05;*** significantly different, P<0.001;****administered
by gavage on
5 d/w for 103 w;*****administered via diet on 7 d/w for 96 w
Re-evaluation of mononuclear cell leukaemia
NTP (1989) concluded that there is some evidence of leukaemia in female rats at a dose level of >= 25 mg/kg (dosing via gavage on 5 d/w over 103 w). However, in a critical re-evaluation the finding of mononuclear cell leukaemia only in female rats from one study at an incidence within historical control incidences, was judged to be unrelated to HQ exposure (Whysner et al., 1995).
Both in controls and in dosed male rats high rates of mononuclear cell leukaemia were found, which are not indicating an effect due to HQ exposure. Although the high-dose group of females exhibited a statistically significant increased incidence of this neoplasm compared to controls (incidences 16 %, 27 %, 40 %), incidences were still within the range of historical controls from NTP studies (up to 31 % in untreated controls, N=1983, up to 47 % in water gavage vehicle controls, N=299). Furthermore, no increase in leukaemia incidence was found in either sex of F344 rats in the study of Shibata (personal communication cited in Whysner et al., 1995) even though the dose in this study was 10-times that of the NTP study when calculated on a daily basis. In addition, in the two studies with mice (NTP, 1989; Shibata et al., 1991) there was no increased incidence of leukaemia or lymphoma. Analysis of the incidence of spontaneous tumour in NTP studies later showed mononuclear cell leukemia to be among the highest rates of spontaneous neoplasms in Fischer F344 rats, and were found related to housing and dietary conditions (Haseman et al., Toxicol. Pathol., 26(3):428-441, 1998). The relevance to human cancer risk of this neoplasm commonly observed in aged F344 rats is debated (Williams et al., Principles of testing carcinogenic activity, in: Principles and Method of Toxicology, Fifth edition, Ed. A.W. Hayes, pp. 1265 -1316, 2007; Thomas et al., Toxicol. Sci. 99:3 -19, 2007).
HUMAN EXPERIENCE
A retrospective study was performed in a well-characterized 1942-1990 cohort of 879 workers (858 men and 21 women) employed principally in the manufacture and use of HQ at a large chemical plant comprising 22,895 person-years of exposure during the 50-year observation period. Mean duration of tenure in a HQ environment was 13.7 years, mean follow-up from first exposure was 26.8 years; 2205 person-years (10%) were represented by subjects with ages of >= 65 years. From 1949-1990 average exposure concentrations ranged from 0.1 to 6.0 mg/m3for HQ dust and less than 0.1 to 0.3 mg/m3for benzoquinone vapour. 20% of cohort members had presumably experienced higher exposures to HQ dust, e.g. up to 35 mg/m3in the packaging area, at the period up to 1949, before measures to reduce exposure had been installed. Causes of mortality were followed up to 1991 and were compared with vital statistics from the general population of the State of Tennessee, and to an occupational reference group of 30,000 hourly wage personnel employed at Kodak's Rochester facilities from 1964 to 1992, few of whom had potential HQ exposure.
There was no evidence of excess mortality in the investigated cohort. In contrast, the number of deaths from all causes of death, and from all forms of malignant cancer was statistically significantly below expectation compared with both general population and occupational controls. There was also a lower than expected death rate from circulatory diseases. Additionally, there were fewer than expected deaths from respiratory cancer, non-malignant pulmonary diseases, and genitourinary system illness, including nephrotoxicity. There was no evidence of a dose-relationship with respect to lifetime exposure or latency. This study did not support the findings of animal cancer bioassays showing an increased prevalence of predominately benign neoplasms of the kidney and liver and of mononuclear cell leukaemia in F344 rats or B6C3F1 mice (Kari et al., 1992; NTP 1989; Shibata et al., 1991). In the cohort of HQ workers, cancer mortality was not statistically significantly different from expectation, and no liver tumour or leukaemia deaths were observed. The two observed cases of malignant kidney tumours (1.3 expected, no significant effect) were confounded by an excessive smoking history, which is recognized as major cause of renal cancer in humans, and by workplace exposure to other chemicals (Key study: Pifer et al., 1995).
A cohort of 837 Danish lithographers, born in 1933 - 1942, was followed in the Danish Cancer Register from 1974 to 1989. Information on exposure to organic solvents and other chemicals is only available from questionnaires (no quantitative data). About 200 of the cohort members reported an exposure to HQ from photochemicals besides a lot of other chemicals. Due to the insufficient characterisation of the existing exposures, the study can be only be used as supporting information. There was no indication of an increased cancer incidence in the kidneys or the liver or of leukaemia in the total cohort including the subcohort with HQ-exposure. A discussed association between HQ exposure and appearance of malignant melanoma in lithographers is considered to be highly questionable as only two of the five melanoma cases reported exposure to HQ. Further, location of the melanoma at the trunk was not at the primary site of dermal contact with HQ during manual photo processing, and possible confounding factors contributing to the development of malignant melanoma, as exposure to a multitude of other chemicals, life-style and sun-exposure had not been controlled in the study (Supporting study: Nielsen et al., 1996).
Based on these epidemiological studies in HQ-exposed workers there are no indications, that kidneys, livers, or blood system are specific target organs of a possible carcinogenic effect of HQ, even at the elevated exposure levels of the early years of HQ production before 1950. This is in accordance with the known high metabolic capacity of humans for detoxification of HQ, which results in distinctly lower levels of possibly reactive critical metabolites compared to rats (see IUCLID Section 7.1.1).
SUPPORTING INFORMATION FROM OTHER EXPERIMENTAL STUDIES RELATED TO CARCINOGENICITY
HQ was found to show no tumor promoting activity in the urinary bladder, liver, forestomach and glandular stomach of F344 rats, in the liver of Wistar rats, and in the pancreas, liver and gallbladder of Syrian Golden hamsters when, after treatment with site-specific initiators, HQ was fed at concentrations of 0.05 to 2% for up to 51 weeks depending on the corresponding test protocols (for details see Table). Investigations included histopathological examination of hyperplastic and neoplastic lesions as wells as assays for cell proliferative activity (DNA synthesis). In the kidney of Wistar rats, HQ treatment enhanced formation of renal tumors after initiation with N-ethyl-N-hydroxyethyl-nitrosamine. In contrast, HQ was found to inhibit tumor formation in liver or pancreas initiated by treatment with DEN or BOP, respectively (Supporting studies: Hirose et al., 1989; Kurata et al., 1990; Maryama et al., 1991; Okazaki et al., 1993; Williams et al., 2007). There were no early proliferative responses in forestomachs of F344 rats or Syrian Golden hamsters after feeding of 0.5% HQ for 20 w or 0.8% HQ for 8 w (Hirose et al., 1986; Shibata et al., 1990). HQ was inactive in two short-term liver foci assays on enhancement of GST positive foci in male F344 rats after initiation with AAF or DEN (Hasegawa and Ito, 1992; Williams et al., 2007) while a weak enhancement of GGT-positive liver foci was reported in male Sprague-Dawley rats after initiation with DEN. In this study, HQ alone induced no altered liver foci. HQ-induced GSH depletion and cytotoxicity were events found to be critical for development of the altered liver foci (Stenius et al., 1989).
After dermal treatment of female Swiss mice with 5 mg HQ, 3 times weekly, for 368 d, there were no skin papilloma or skin carcinoma. Inhibition of the carcinogenic effect of BaP after coadministration of HQ was reflected in a cocarcinogenesis assay by skin tumor incidences decreased by at least 50%. Also HQ showed no promoting activity on mouse skin after intiation with BaP (Van Duuren et al., 1976).
Table 5: Overview on further studies related to carcinogenicity (all studies with Reliability 2)
Endpoints |
Animals |
Treatment |
Test result |
Reference |
Tumor promotion in urinary bladder |
F344 rats |
Initiation: 0.05% BBN in drinking water for 4 w, Control: without BBN treatment but exposure to HQ |
Neg |
Kurata et al., 1990 |
Tumour promotion in kidney and liver |
Wistar Crj rat |
Initiation: 0.3% EHEN in drinking water for 3 w Control: without EHEN treatment but exposure to HQ |
Neg: in liver Pos: in kidney (enhancement of EHEN-induced renal tumours) |
Okazaki et al., 1993 |
Tumor promotion in liver Short-term liver foci (GST pos foci) assay with and without initiation with AAF |
F344 rats |
Initiation: 3 mg/kg AAF by gavage 3 times a week for 12 w from week 1 to 13 |
Neg: no effect of HQ alone Inhibition of AAF-induced effects |
Williams et al., 2007 |
Tumor promotion in liver Short-term liver foci (GST pos foci) assay after initiation with DEN |
F344 rats |
Initiation: 200 mg/kg DEN / hepatectomy |
Neg: |
Hasegawa and Ito, 1992 |
Tumor promotion in liver Short-term liver foci (GGT pos foci) assay without and with initiation with DEN |
Sprague-Dawley rat |
Initiation: 30 mg/kg DEN i.p. / hepatectomy Initiation: 30 mg/kg DEN i.p. / hepatectomy Controls: treated with HQ alone |
Neg: no effect of HQ alone
Pos: |
Stenius et al., 1989 |
Tumour promotion in pancreas, liver and gallbladder |
Syrian Golden hamsters |
Initiation: 70 mg/kg BOPtwice Control: only HQ in diet |
Neg: pancreas Neg: liver and gallbladder no significant changes |
Maryama et al., 1991 |
Early proliferative changes in forestomach
|
Syrian Golden hamsters |
0.5% HQ in diet for 20 w |
Neg |
Hirose et al., 1986 |
Tumour promotion in forestomach and glandular stomach |
F344 rat |
Initiation: 150 mg/kg MNNG by gavage Control: only HQ in diet |
Neg |
Hirose et al., 1989 |
Early proliferative changes in forestomach |
F344 rat |
0.8% HQ in diet for 8 w |
Neg |
Shibata et al., 1990 |
Carcinogenicity skin |
Swiss mice ICR/Ha |
Dermal treatment |
Neg |
Van Duuren et al., 1976 |
Cocarcinogenic activity on skin |
Swiss mice ICR/Ha |
Dermal treatment |
Inhibition of carcinogenic effects of BaP |
|
Tumor promotion skin |
Swiss mice ICR/Ha |
Dermal treatment |
Neg |
AAF: acetylaminofluorene; BaP: benzo[a]pyrene; BBN: N-butyl-N-(4-hydroxybutyl)nitrosamine; BOP: N-nitroso-bis(2-oxopropyl)amine;
EHEN: N-ethyl-N-hydroxyethyl-nitrosamine; MNNG: N-methyl-N’-nitro-N-nitrosoguanidine; TBMP: 2-tert-buty-4-methylphenol
CONCLUSIONS
HQ has been classified in Carcinogenicity Category 2 (suspected human carcinogen) according to C&L of the GHS, mainly based on the kidney tumors observed in male F344 rats. However, the indications that HQ may cause carcinogenic effects in humans are rather questionable as the critical evaluation of the total evidence from the cancer bioassays and epidemiological studies together with more recent reevaluations of the carcinogenic potential of HQ as well as recent studies on the mechanisms of the induction of renal neoplasms. Additionally, principally HQ was found to inhibit the neoplastic responses of other carcinogenic compounds, and to show no tumor promoting activity. Toxicokinetic studies demonstrated a significant metabolic capacity of humans for the detoxification of HQ and an existing background exposure to HQ, e.g. from food or endogenous production. HQ was not found to exert a genotoxic activity in vivo under exposure conditions relevant for human exposure. Consequently, in this special case a threshold approach seems to be justified and a DNEL for repeated dose toxicity can be derived.
Justification for selection of carcinogenicity via oral route endpoint:
Renal tubular hyperplasia and renal tubular adenomas were reported in male F344 rats in 2 different carcinogenicity studies, via oral gavage or in the feed. Numerous mechanistic investigations have indicated that the likely mechanism is related to exacerbation of Chronic Progressive Nephropathy which seems to occur with a particular sensitivity in Fischer F344 male rats, possibly related to a higher kidney exposure to toxic metabolites in that rat strain, but not related to direct DNA damage. This was comforted by negative results in in vivo TGR assay in mice and in vivo Comet assay in F344 rats. This mechanism of action is not relevant to human. As the in vivo comet assay also showed no genotoxic activity in the germ cells, a DNEL for threshold effects is derived for the risk assessment.
Justification for selection of carcinogenicity via dermal route endpoint:
No carcinogenic effects observed in mice following dermal treatment, and no cocarcinogenic effects or tumor promoting effects.
Carcinogenicity: via oral route (target organ): urogenital: kidneys
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