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Toxicological information

Repeated dose toxicity: oral

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Administrative data

Endpoint:
sub-chronic toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1971
Report date:
1971

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)
Deviations:
yes
Remarks:
no information on the analytical examination of doses, ophthalmoscopic and neurobehavioural examination not performed
GLP compliance:
no
Limit test:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
ε-caprolactam
EC Number:
203-313-2
EC Name:
ε-caprolactam
Cas Number:
105-60-2
Molecular formula:
C6H11NO
IUPAC Name:
azepan-2-one

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Broekman Institute, Stiphout, The Netherlands
- Mean weight at study initiation: male 42.6 g, female 41.2 g
- Housing: 5 per cage
- Diet (e.g. ad libitum): test compound was thoroughly mixed into the stock diet
- Water (e.g. ad libitum): tap water



Administration / exposure

Route of administration:
oral: feed
Details on oral exposure:
DIET PREPARATION
- The following percentage composition of stock diet was used:
yellow maize 29.5, brewer's yeast 3, whole wheat 36, grass meal 3, soyabean-oil meal 10, soyabean oil 3, meat scraps 4, vitamin preparations 0.5, fish meal 8, trace mineralized salt 0.5, dried whey 2, and calcium phosphate 0.5. The test compound was thoroughly mixed into the stock diet by means of a modified meat cutter (Stefan).
- Rate of preparation of diet (frequency): The diets were freshly prepared once a fortnight
Analytical verification of doses or concentrations:
not specified
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
continuously
Doses / concentrationsopen allclose all
Dose / conc.:
0.05 other: % (nominal in diet)
Remarks:
29 mg/kg bw in males and 35 mg/kg bw in females (actual ingested)
Dose / conc.:
0.1 other: % (nominal in diet)
Remarks:
60 mg/kg bw in males and 70 mg/kg bw in females (actual ingested)
Dose / conc.:
0.25 other: % (nominal in diet)
Remarks:
146 mg/kg bw in males and 170 mg/kg bw in females (actual ingested)
Dose / conc.:
0.5 other: % (nominal in diet)
Remarks:
296 mg/kg bw in males and 342 mg/kg bw in females (actual ingested)
Dose / conc.:
1 other: % (nominal in diet)
Remarks:
592 mg/kg bw in males and 704 mg/kg bw in females (actual ingested)
No. of animals per sex per dose:
10
Control animals:
yes, concurrent no treatment
Details on study design:
- Dose selection rationale: The toxicity of caprolactam (CAP) was examined in a range-finding test with weanling albino rats fed the test substance at dietary levels of 0, 0.2, 1 and 5 % for 28 days. CAP at levels of 5 % and 1 % in the diet caused growth depression and increased liver and kidney weights. Histopathological changes in liver and kidney were observed in the 5 % group in both sexes. In the 1 % group slight histopathological changes were observed only in the kidneys of males. On the basis of the present results 1% CAP is expected to be an effect level in a sub-chronic (90-day) toxicity study.

Examinations

Observations and examinations performed and frequency:
DETAILED CLINICAL OBSERVATIONS: Yes

BODY WEIGHT: Yes
- Time schedule for examinations: weekly


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- 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


HAEMATOLOGY: Yes
- Time schedule for collection of blood: 13 week
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: all
- Parameters checked: haemoglobin, packed cell volume, red blood cell counts and total and differential white blood cell counts


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at the end of experiment
- Animals fasted: No data
- How many animals: all
- Parameters checked: glutamic-pyruvic transaminase (SGPT), glutamic-oxalacetic transaminase (SGOT), alkaline phosphatase (SAP), total serum
protein, albumin and albumin-globulin ratio


URINALYSIS: Yes
- Time schedule for collection of urine: 13 week
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters checked: appearance, pH, glucose, albumin, occult blood, ketones and microscopy of the sediment


Sacrifice and pathology:
GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
Other examinations:
The following organs were weighed: heart, kidneys, spleen, liver, brain, testicles/ovaries, thymus, pituitary, thyroids and adrenals

Results and discussion

Results of examinations

Clinical signs:
no effects observed
Description (incidence and severity):
No abnormalities of condition or behaviour were observed.
Mortality:
no mortality observed
Description (incidence):
During the course of the experiment no deaths occurred.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Slight growth depression occurred at the 1.0 % feeding level in both sexes. This growth depession was only biologically relevant in males (15 and 11% at week 2 and 4).
Food consumption and compound intake (if feeding study):
no effects observed
Description (incidence and severity):
Decreased food consumption was observed at the highest feeding level in both sexes during week 2, 3 and 4. At 0.5 % food consumption was relatively low in week 2 and 3 in both sexes. Towards the end of the experiment food consumption was comparable in all groups.
Food efficiency:
effects observed, treatment-related
Description (incidence and severity):
Food efficiency in males at the highest feeding level was slightly lower than in the other test groups. The food efficiency figure obtained in control males was low, probably as a result of relatively low body weights at week 4 which had disappeared not until week 10.
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
no effects observed
Description (incidence and severity):
Haematological data showed no distinct differences between groups. Total leucocytes count was increased in males of some experimental groups, but there was no trend towards higher average leucocytes counts with an increase of Caprolactam in the diet.
Clinical biochemistry findings:
no effects observed
Description (incidence and severity):
No significant differences occurred in serum enzyme values amongst the various groups.
Urinalysis findings:
no effects observed
Description (incidence and severity):
The results of the urine analyses showed no changes in the composition of the urine which could be attributed to the feeding of Caprolactam.
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
The relative weight of the kidneys and testicles were increased (25 and 18%) at 1.0 % in males. The relative weight of the liver was increased in both sexes (19% in males and 14% in females) at 1.0 %. All other organ weights of test groups were comparable with the control values. The mathematically significantly decreased heart weight of females at 0.5 % is not considered of toxicological importance, because it was not observed at the 1.0 % level.
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
At autopsy, the kidneys of male rats showed a pale-greenish discolouration at the highest dose level. Other gross changes attributable to the ingestion of Caprolactam were not seen.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
At microscopic examination pathological changes related to the ingestion of Caprolactam were found in the kidneys of males only. These changes consisted of hyaline-droplet degeneration of the proximal convoluted tubules in the kidneys of nearly all male rats at 0.1 % Caprolactam and above. Its degree was distinctly dose-related. The swollen epithelial cells of these tubules showed a granular cytoplasm,caused by large accumulations of tiny droplets of precipitated proteinaceous material. The droplets stained deeply red with Azan. At the 0.05 % level these changes were completely absent.
The other abnormalities were about equally distributed amongst test and control animals. The pathological examinations indicate that the ingestion of Caprolactam at levels of 0.1 % and above is nephrotoxic for male rats of this particular strain (SD).

Effect levels

open allclose all
Dose descriptor:
NOAEL
Effect level:
29 mg/kg bw/day (actual dose received)
Sex:
male
Basis for effect level:
other: hyaline-droplet degeneration of the proximal convoluted tubules in the kidneys
Dose descriptor:
NOEL
Effect level:
342 mg/kg bw/day (actual dose received)
Sex:
female
Basis for effect level:
other: liver weight

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
Based on hyaline-droplet degeneration of the proximal convoluted tubules in the kidneys, the NOAEL for males was found to be 29 mg/kg bw/day.
In females, the NOAEL was 342 mg/kg bw based on increase in relative liver weights.
The findings in male kidneys are supposed to be of no relevance for other species including humans (Haschek and Rousseaux, Fundamentals of Toxicologic Pathology, Academic Press, 1996). Therefore, CAP does not require any classification.
Executive summary:

A study similar to the OECD Guideline 408 was performed. A distinct gender variance in systemic toxicity of CAP was observed in this 90 day continuous feeding study with Sprague-Dawley rats.

Various dietary levels up to 1.0 % resulted in distinct ill effects as shown by growth depression, decreased food intake and increased weights of the liver at 1.0 % in both sexes.

In males discoloration of the kidneys and increased relative weights of kidneys and testicles at 1.0 % and microscopically changes of the kidneys at 0.1 % and above was observed. The kidneys of male rats are more susceptible to Caprolactam than those of females. Possibly a relationship exists between the presence of this type of degeneration in males only and the well-known higher urinary protein excretion in male rats than in females (Sellers et al. Am. J. Physiol. 163; 662-667, 1950).

Based on hyaline-droplet degeneration of the proximal convoluted tubules in the kidneys, the NOAEL for males was found to be 29 mg/kg bw/day.

In females, the NOAEL was 342 mg/kg bw based on increase in relative liver weights.

The findings in male kidneys are supposed to be of no relevance for other species including humans (Haschek and Rousseaux, Fundamentals of Toxicologic Pathology, Academic Press, 1996). Therefore, CAP does not require any classification.