Hydroquinone

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from June 26 1981 to September 28 1981

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study meets basic scientific principles as a range-finding subchronic toxicity study, sufficient documentation of test conditions and test results

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Toxicity and carcinogenicity of hydroquinone in F344/N rats and B6C3F1 mice.

Author:

Kari FW, Bucher J, Eustis SL, Haseman JK, Huff JE

Year:

1992

Bibliographic source:

Food Chem Toxicol 30, 737 - 747

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1989

Report date:

1989

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

13-week range-finding toxicity study investigating mortality, clinical signs and body weights and selected organ weights, as well as gross necropsy and histopathology

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Hydroquinone

EC Number:

204-617-8

EC Name:

Hydroquinone

Cas Number:

123-31-9

Molecular formula:

C6H6O2

IUPAC Name:

hydroquinone

Details on test material:

- Name of test material (as cited in study report): hydroquinone
- Physical state: colourless, crystalline solid
- Analytical purity: > 99%
- Purity test date:
- Lot/batch No.: 56978
- Stability under test conditions: 2 weeks when stored in the dark at temperatures of up to 60 °C
- Storage condition of test material: bulk material was stored at 25 °C under nitrogen or argon and periodic characterization by infrared or ultravioloet spectroscopy and oxidative titration indicated no deterioration over the course of the studies

Test animals

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, Portage, MI, USA
- Age at study initiation: 7-8 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: 22 d

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19 - 24 °C (66 - 76 °F)
- Humidity (%): 44 - 84
- Air changes (per hr): 10 - 12 room air changes per hr
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: appropriate amount of hydroquinone mixed with appropriate amount of corn oil; suspensions homogenized in Polytron homogenizer; air removed under vacuum, solutions sealed under argon; maximum storage time 11 d at room temperature in the dark in amber serum vials with Teflon-lined seals

VEHICLE
- Justification for use and choice of vehicle (if other than water): solubility
- Concentration in vehicle: 5, 10, 20, 40, and 80 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:

Method: UV spectroscopy of acetonitrile extracts at 295 nm or methanol extracts at 293 nm; analyzed concentrations were in the range between 90 and 110 % of the nominal concentration before start of dosing and between 96 and 101 % ca. 8 weeks later; variation of analyzed concentrations dependant on layer (top, middle or bottom) of the dosing mixture where the sample was taken, variation considered to be in acceptable range

Duration of treatment / exposure:

13 w

Frequency of treatment:

5 d/w

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 25, 50, 100, 200, or 400 mg/kg bw/d
Basis:
actual ingested

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: based on 14-day range-finding toxicity study (see separate endpoint study record)

Examinations

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

FOOD CONSUMPTION: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes, all animals

ORGAN WEIGHTS: Liver

HISTOPATHOLOGY: Yes
Tissues examined in all vehicle controls and dosed rats receiving 200 or 400 mg/kg, and animals dying before end of the study: adrenal glands, brain, colon, esophagus, gross lesions and tissue masses, heart, kidneys, liver, lungs and mainstem bronchi, mammary gland, mandibular or mesenteric lymph nodes, pancreas, parathyroid glands, pituitary gland, prostrate/testes or ovaries/uterus, salivary glands, skin, small intestine, spinal cord, spleen, sternebrae and vertebrae including marrow, stomach, thymus, thyroid gland, trachea, and urinary bladder.
Tissues examined in 100 mg/kg-group: liver, kidneys, and stomach of male rats, and kidneys of female rats

Statistics:

Statistical significance of liver weights by Dunn's test (Dunn, 1964) or Shirley's test (Shirley, 1977)

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

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:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY
400 mg/kg: mortality 10/10 males (N=8 in week 2, N=1 each in week 7 and 13), and 10/10 females (N=2 in week 1 and 2 each, N=1 in week 4 and 6, N=2 in week 5 and 7); tremors and convulsions observed in all rats immediately after dosing and preceding death, clear orange fluid or orange staining around the nose in most cases
200 mg/kg: mortality 0/10 males, and 3/10 females in week 11; clinical signs: lethargy in male rats after 10 w of dosing and in all female rats for the duration of the study, females exhibited tremors and sometimes convulsions immediately after dosing, clear orange fluid or orange staining around the nose in most cases
No effects at doses up to 100 mg/kg

BODY WEIGHT AND WEIGHT GAIN
Females: similar to controls in all dose groups, final body weight 97 to 100 % of control value
Males: final body weight significantly decreased from 50 mg/kg up (no data for food consumption available): 99, 95, 92, and 91% of control value at 25, 50, 100, and 200 mg/kg

ORGAN WEIGHTS (For details see Table 1)
Absolute liver weights: significant decreases in males from 25 to 200 mg/kg in combination with decreased body weight from 50 to 200 mg/kg; significant increase in females from 50 to 200 mg/kg without effect on body weight
Relative liver weights: significant decreases in males from 25 to 100 mg/kg; significant increase in females from 50 to 200 mg/kg
Evaluation: The toxicological significance of the changes of liver weights is questionable, as effects were opposed in male and female rats and there were no corresponding histopathological findings. Additionally, decreased liver weights in male rats of the 50 to 200 mg/kg-groups occurred with a simultaneous decrease of body weight.

GROSS PATHOLOGY
400 mg/kg: 4/10 males and 5/10 females red-to-brown perioral staining; 1/10 males and 2/10 females reddened mucosa in the stomach; 1/10 males meningeal hemorrhage
200 mg/kg: 2/10 males intra-abdominal bleeding; 1/10 females blood in the stomach, 2/10 females perioral staining
up to 100 mg/kg: no findings

HISTOPATHOLOGY: NON-NEOPLASTIC
Inflammation and epithelial hyperplasia of the forestomach: at 200 mg/kg in 4/10 males and 1/10 females, mild to moderate severity
Toxic nephropathy with tubular cell degeneration and regeneration in the renal cortex: at 200 mg/kg in 7/10 males and 6/10 females, at 100 mg/kg in 1/10 females; moderate to marked severity in males and minimal to mild severity in females; no indications for alpha2µ-globulin nephrotoxic syndrome (no hyaline droplet formation, no granular casts, no linear mineralization)
up to 50 mg/kg: no findings
Evaluation: The findings in the forestomach are indicative of a local irritant action in the forestomach due to bolus application via gavage.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

50 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

2

Dose descriptor:

LOAEL

Effect level:

100 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: kidney lesions in females

3

Dose descriptor:

LOAEL

Effect level:

100 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: reduced body weight

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 1: Liver weights and terminal body weights after 13-week gavage of hydroquinone (mean±standard error)

Sex	Dose (mg/kg)	Number weighed	Necropsy body weight (g)	Absolute liver weight (mg)	Relative liver weight (mg/g)
Male	0	10	367±7.1	15,708±652	42.9±1.77
	25	10	365±3.4	12,319±342^b	33.7±0.76^b
	50	10	347± 5.6^b	12,331±490^b	35.5±1.41^a
	100	10	338±6.2^b	11,227±271^b	33.2±0.69^b
	200	10	333±5.3^b	13,653±456^b	40.9±1.06
Female	0	10	201±3.4	6,845±218	34.0±0.68
	25	10	202±2.4	6,924±203	34.2± 0.93
	50	10	200±2.8	7,611±247^a	38.0±1.06^b
	100	10	195±2.9	7,551±224^a	38.8±1.12^b
	200	7	196±3.1	7,990±110^b	40.9±0.89^b

Statistically different from control group: ^a p<0.05; ^b p<0.01

Applicant's summary and conclusion

Conclusions:

When applied on 5 days per week for 13 weeks by gavage, hydroquinone at doses of 50 mg/kg and below had negligible effects in rats. Because of deaths, reductions in body weight gain, and forestomach and kidney lesions at doses of 100 mg/kg bw/d and up, doses selected for the 2-year studies with rats were 25 and 50 mg/kg bw/d.

Executive summary:

Hydroquinone was administered to groups of 10 male and 10 female F344 rats for 13 weeks on 5 days per week via gavage at doses of 0, 25, 50, 100, 200 and 400 mg/kg bw/d (vehicle corn oil) as a range-finding toxicity study for a subsequent 2-year study. Investigated endpoints were mortality, clinical signs, body weights and selected organ weights, as well as gross necropsy and a comprehensive histopathology of tissues.

At 400 mg/kg, all rats died, mostly within the first 7 weeks of the study with tremors and convulsions preceding death. At 200 mg/kg, 3/10 females died in week 11, and lethargy was observed in male rats after 10 w of dosing and in all female rats during the whole dosing period. Female rats exhibited tremors and sometimes convulsions immediately after dosing. Final body weights were similar to controls in all dose groups of females, whereas in males final body weights were decreased by 8% and 9% at 100 and 200 mg/kg, respectively (no data for food consumption available). Gross pathology findings in the 400 and 200 mg/kg-groups were red-to-brown perioral staining in 11/40 rats and single cases of reddened mucosa or blood in the stomach, intra-abdominal bleeding, and meningeal hemorrhage. Inflammation and epithelial hyperplasia of the forestomach were seen at 200 mg/kg in 4/10 males and 1/10 females, indicating a local irritant action of HQ in the forestomach due to bolus application via gavage. Toxic nephropathy, characterized by tubular cell degeneration and regeneration in the renal cortex, was seen at 200 mg/kg in 7/10 males and 6/10 females, and at 100 mg/kg in 1/10 females. Subchronic administration of hydroquinone at doses of 50 mg/kg and below had negligible effects in rats resulting in a NOAEL of 50 mg/kg bw/d and a LOAEL of 100 mg/kg bw/d.