sodium 4,4-dimethyl-2,5-dioxoimidazolidin-1-ide

Repeated dose toxicity: oral

Administrative data

Endpoint:

repeated dose toxicity: oral

Remarks:

combined repeated dose and carcinogenicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study performed to GLP and guideline.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1994

Report date:

1994

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

other: EPA 83-5

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

5,5-dimethylhydantoin

EC Number:

201-051-3

EC Name:

5,5-dimethylhydantoin

Cas Number:

77-71-4

IUPAC Name:

5,5-dimethylimidazolidine-2,4-dione

Constituent 2

Reference substance name:

dimethylhydantoin

IUPAC Name:

dimethylhydantoin

Details on test material:

- Name of test material (as cited in study report): 5,5 diemthylhydantoin
- Structural formula attached as image file (if other than submission substance): see Data Matrix attachment in Section 13 for DMH structural formula
- Physical state: white crystalline solid
- Stability under test conditions: stable for the duration of the study

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Testing lab
- Age at study initiation: 8 weeks at start of dosing
- Weight at study initiation: Males: 224-282 g - Females: 147-198 g
- Housing: stainless steel cages
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 3 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°F): 66-77
- Humidity (%): 40-70
- Air changes (per hr): 10 room air changes per hour.
- Photoperiod: 12 hours per day with fluorescent lightning.

Administration / exposure

Route of administration:

oral: feed

Vehicle:

other: Basal diet (Ground Purina Certified rodent Chow)

Details on oral exposure:

DIET PREPARATION
- Rate of preparation of diet: Fresh diet was prepared and offered to the animals each week.
- Mixing appropriate amounts with (Type of food): A concentrated premix was prepared by direct addition of DMH to ground rodent feed, milled in a ball mill for 1 hour and then mixed for 1 hour in a Hobart mixer to ensure homogenous distribution of the test substance in the diet. The test diets were prepared by appropriate dilutions of the concentrated premix or higher diet concentration and were mixed in a Hobart mixer for 15 minutes. Dietary concnetrations were not adjusted for percent active ingredeint of the test substance, as received was >99%.
- Storage temperature of food: Prepared diets were stored in closed polyethylene containers at room temperature until fed to the animals.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

DMH was analyzed in the rodent diet using HPLC.
The dosages obtained in terms of test substance consumed for the 100, 300, and 1000 mg/kg/day groups ranged from 88.9 to 112.2, 265.3 to 342.5, and 896.9 to 1132.4 mg/kg/day for the males and 90.9 to 117.6, 269.0 to 347.7, and 908.8 to 1147.9 mg/kg/day for the females respectively.

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

7 days per week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
100 mg/kg/day
Basis:
nominal in diet

Doses / concentrations 2

Remarks:

Doses / Concentrations:
300 mg/kg/day
Basis:
nominal in diet

Doses / concentrations 3

Remarks:

Doses / Concentrations:
1000 mg/kg/day
Basis:
nominal in diet

No. of animals per sex per dose:

60/sex/dose level

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale: Prior to initiation of the chronic study, the potential for DMH to produce toxicity in rats was evaluated in a 14-day dietary dose range-finding study. In the range finding study rats were exposed to DMH in the diet at concentrations of 0, 7000, 14000 or 20000 ppm for 14 days. These dietary concentrations corresponded to approximate mean intake levels of 571, 1157 and 1663 mg/kg/day for males and 596, 1160, and 1717 mg/kg/day for females respectively. Measured parameters included food consumption, body weights and body weight gains and gross pathology. There were no treatmnet related effects observed and DMH was considered to be palatable and not toxic to rats when administered in the diet at concentrations as high as 20000 ppm. Based on this information, the limit dose of 1000 mg/kg was selected as the target dosage level for the high dose group for the chronic study.

Examinations

Observations and examinations performed and frequency:

CLINICAL OBSERVATIONS: Yes
- Time schedule: clinical signs were checked twice daily, detailed clinical observations were performed once each week.

MORTALITY: Yes
- Time schedule: Twice daily

BODY WEIGHT: Yes
- Time schedule for examinations: weekly for the first 14 weeks of the study and every other week thereafter.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: weekly for the first 14 weeks of the study and every other week thereafter.

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: prior to first exposure and following study period of 104 weeks.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at 6, 12, 18 and 24 months
- How many animals: 15/sex/group
- Parameters examined: Haematocrit, haemoglobin concentration, erythrocyte count, total and differential leukocyte count, platelet count, reticulocyte count, mean corpuscular volume, mean corpuscular haemogoblin, mean corpuscular haemoglobin concentration.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at 6, 12, 18 and 24 months
- How many animals: 15/sex/group
- Parameters examined: sodium, potassium, chloride, calcium, phosphorus, glucose (fasting), total cholesterol, urea nitrogen, total bilirubin, direct bilirubin, indirect bilirubin, creatinine, total protein, albumin, globulin, A/G ratio, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma glutamyl transpeptidase, creatine kinase.

URINALYSIS: Yes
- Time schedule for collection of urine: at 6, 12, 18 and 24 months
- How many animals: 15/sex/group
- Parameters examined: colour and appearance, volume, specific gravity, pH, protein, glucose, ketones, bilirubin, blood, urobilinogen, microscopic elements.

Sacrifice and pathology:

GROSS PATHOLOGY AND HISTOPATHOLOGY: Yes
- On all surviving animals
- Performed on high dose group and control group
Organs: brain, spinal cord, pituitary, thyroid, parathyroid, thymus, oesophagus, salivary glands, stomach, small and large intestines, liver, pancreas, kidneys, adrenals, spleen, heart, trachea, lungs, aorta, uterus, vagina, mammary gland, prostate, testes, epididymis, seminal vesicles, urinary bladder, lymph nodes, sciatic nerve, sternum, femur, skin, skeletal muscle (thigh), eyes.
- Performed on low and intermediate dose groups: Kidneys, pituitary gland and all gross lesions and mammary glands of female rats.

Other examinations:

Organ weights: Yes
from all surviving animals
Liver, kidneys, adrenals, testes, ovaries, spleen, brain, heart.

Statistics:

Levene’s test for equality of variances, analysis of variance (ANOVA) and tests (when F value from ANOVA was significant).
Non-parametric data were evaluated using Kruskal-Wallis test followed by the Mann-Whitney U test when appropriate.
Two untreated controls were included in the study in order to collect data that would provide information regarding the range of normal or control values for the parameters evaluated in the study. These data were used as an aid in the identification of false positive statistical citations as well as confirmation of true treatment-related effects. Based on the independent manner in which the animals were handled and the data collected, it was not considered appropriate to combine the data from the two control groups for the purposes of comparing the combined control data to those from the treated groups.

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):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

effects observed, treatment-related

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS
The number of animals with urine stains tended to be increased in the high dose males and all dose groups of females. The number of females observed as unkept was increased in all dose group female rats which generally paralleled the number of animals that die. Therefore the higher incidence of these findings was not considered to indicate an effect of the test substance on the overall well being of the animals.

MORTALITY
The mean survival time for rats from the 1000mg/kg/day group (626 days for males and 647 days for females) was lower than the control groups (668 to 659 days for males and 669 to 703 days for females). This difference was only statistically significant for males.

BODY WEIGHT GAIN
Although generally not statistically significant slight decreases (~5 to 10%) in mean absolute body weight of animals in the high dose group of both sexes were observed during the last 2 to 3 months of the study.

FOOD CONSUMPTION AND COMPOUND INTAKE
No effects.

OPHTHALMOSCOPIC EXAMINATION
The incidence of several findings increased with age but were not considered to be effects of the test substance.

HAEMATOLOGY
No effects

CLINICAL CHEMISTRY
No effects

URINALYSIS
No effects
GROSS PATHOLOGY No effects
ORGAN WEIGHTS
No effects

HISTOPATHOLOGY: NEOPLASTIC
The incidences of mammary gland tumors (adenomas, fibroadenomas and carcinomas) was slightly increased in the high dose group of female rats although these were not statistically significant therefore the slight increase was attributed to random biologic variation.

Effect levels

Dose descriptor:

NOAEL

Effect level:

300 mg/kg diet

Sex:

male/female

Basis for effect level:

other: Based upon the equivocal decreases in body weight and survival for animals in the high dose group.

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Based upon the equivocal decreases in body weight and survival for animals in the high dose group, the No-Observable-Effect Level (NOEL) for systemic toxicity is considered to be at least 300 mg/kg/day but may be as high as 1000 mg/kg/day. The NOAEL is therefore 300 mg/kg/day.

Executive summary:

This study has been performed on DMH (Dimethyl Hydantoin) and has been used for read-across purposes.

Based upon the equivocal decreases in body weight and survival for animals in the high dose group, the No-Observable-Effect Level (NOEL) for systemic toxicity is considered to be at least 300 mg/kg/day but may be as high as 1000 mg/kg/day. The NOAEL is therefore 300 mg/kg/day.