2,5-di-tert-pentylhydroquinone

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

18 November - 2 December 1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: No deviations reported. The study fully meets the reported guidelines.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1992

Report date:

1992

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: EPA (40 CFR Part 792)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Details on test material:

- Name of test material (as cited in study report): Santovar A
- Substance type: white powder
- Physical state: solid
- Analytical purity: 98%
- Impurities (identity and concentrations): not mentioned
- Lot/batch No.: NOA027
- Expiration date of the lot/batch: 06-1992
- Stability under test conditions: yes, verified
- Storage condition of test material: room temperature
- Other: stability, homogeneity and dose of the tested substance are verified

Test animals

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc.
- Age at study initiation: females - 12 weeks
- Weight at study initiation: females - 227 - 276g
- Fasting period before study: not mentioned
- Housing: individually in stainless steel cages
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 11 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 -26
- Humidity (%): 40 - 70
- Air changes (per hr): not mentioned
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: prepared once weekly, daily aliquots were stored refrigerated.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Prestudy analytical chemistry evaluations indicated that Santovar A was homogeneous and stable in corn oil for up to eight days when stored refrigerated. Analysis of dosing preparations resulted in average test article recoveries ranging from 99.2 to 103.0% indicating that the mixtures were accurately prepared.

Details on mating procedure:

No details mentioned.

Duration of treatment / exposure:

From gestation day 6 - 15.

Frequency of treatment:

Once daily

Duration of test:

Until gestation day 20

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 20, 70, 175 mg/kg/day
Basis:
actual ingested

No. of animals per sex per dose:

25 females

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: based on range finding study (3044.226)

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: twice daily and one half and two hours after dosing

BODY WEIGHT: Yes
- Time schedule for examinations: 0, 6, 9, 12, 16, and 20 days.

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

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: thoracic, abdominal and pelvic cavities. Uterus in detail

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: No

Statistics:

Continuous maternal and fetal data, including body weights, body weight gain, food consumption, number of fetuses, implantation sites and corpora lutea, were analyzed by one-way analysis of variance (ANOVA) followed by Dunnett's test. The Mann-Whitney U test was used to compare post-implantation loss and resorptions. Fetal sex ratios were analyzed using the Chi-Square test. Fisher's Exact test was used to analyze the incidence and number of fetal malformations and variations utilzing the dam (litter) as the experimental unit. All analyses were two-tailed with a minimum signifcance level of 5%.

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

The toxicity was characterized by an increase in the incidence of reddish colored vaginal discharge and post-dose salivation at the 70.0 mg/kg/day.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

not specified

Maternal developmental toxicity

Number of abortions:

not specified

Pre- and post-implantation loss:

not specified

Total litter losses by resorption:

not specified

Early or late resorptions:

not specified

Dead fetuses:

not specified

Changes in pregnancy duration:

not specified

Changes in number of pregnant:

not specified

Other effects:

not specified

Details on maternal toxic effects:

Maternal toxic effects:yes
Details on maternal toxic effects:
Oral administration of Santovar A produced slight maternal toxicity at the 70.0 mg/kg/ day level and substantial maternal toxicity at the 175.0 mg/kg/day level. The toxicity was characterized by an increase in the incidence of reddish colored vaginal discharge and post-dose salivation at the 70.0 mg/kg/day level and more frequent and severe clinical signs, body weight loss and reduced food consumption at the 175.0 mg/kg/day level.

Effect levels (maternal animals)

1

Key result

Dose descriptor:

NOEL

Effect level:

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

Basis for effect level:

other: maternal toxicity

2

Key result

Dose descriptor:

NOAEL

Effect level:

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

Basis for effect level:

other: maternal toxicity

3

Key result

Dose descriptor:

NOEL

Effect level:

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

Basis for effect level:

other: developmental toxicity

Maternal abnormalities

Key result

Abnormalities:

effects observed, treatment-related

Localisation:

vagina

Results (fetuses)

Fetal body weight changes:

effects observed, treatment-related

Description (incidence and severity):

Mean fetal body weight was slightly, but statistically reduced at the 175.0 mg/kg/day level when compared to the control group.

Reduction in number of live offspring:

not specified

Changes in sex ratio:

not specified

Changes in litter size and weights:

not specified

Changes in postnatal survival:

not specified

External malformations:

not specified

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Slight, nonstatistical increases in the incidence of skull anomalies and 7th cervical ribs were observed in the 175.0 mg/kg/day group.

Visceral malformations:

not specified

Other effects:

not specified

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes
Details on embryotoxic / teratogenic effects:
Mean fetal body weight was slightly, but statistically reduced at the 175.0 mg/kg/day level when compared to the control group. Slight, nonstatistical increases in the incidence of skull anomalies and 7th cervical ribs were observed in the 175.0 mg/kg/day group.

Effect levels (fetuses)

Key result

Dose descriptor:

NOEL

Effect level:

70 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

not specified

Basis for effect level:

fetal/pup body weight changes

Fetal abnormalities

Key result

Abnormalities:

not specified

Overall developmental toxicity

Key result

Developmental effects observed:

not specified

Lowest effective dose / conc.:

20 mg/kg bw/day

Treatment related:

yes

Any other information on results incl. tables

The increase in reddish colored vaginal discharge did not result in adverse effects in rats (e.g. no change in spontanious abortions, in litter size etc). Post-dose salivation is not considered adverse. Therefore the reviewer considers 70 mg/kg bw/day as a NOAEL.

Applicant's summary and conclusion

Conclusions:

Sprague-Dawley rats were treated with 0, 20, 70, and 175 mg/kg 2,5-Di-t-pentylhydroquinone once daily during gestation days 6-15. Based on the results of this study, a dosage level of 20.0 mg/kg/day was considered a no-observed-effect level (NOEL) for maternal toxicity and a dosage level of 70.0 mg/kg/day was considered a NOEL for developmental toxicity. Santovar A at a dosage level of 175.0 mg/kg/day produced substantial maternal toxicity with minimal developmental toxicity.

Executive summary:

This study was performed to detect and evaluate the potential embryotoxic or teratogenic effects of Santovar A when administered orally to pregnant rats during the period of major organogenesis. The study design consisted of a vehicle control and three treatment groups. Each group contained twenty-five mated female Sprague-Dawley rats. The test article was mixed with corn oil and administered at dosage levels of 20.0, 70.0 and 175.0 mg/kg/day from gestation day 6 through gestation day 15. All doses were given at a constant volume of 5 ml/kg. Control animals were administered corn oil under the same experimental conditions and at an equivalent dose volume. The animals were observed daily for clinical signs of toxicity. Body weights and food consumption were measured on gestation days 0, 6, 9, 12, 16 and 20. All females were euthanized on gestation day 20 and subjected to cesarean section. Fetuses were individually weighed, sexed and examined for external, visceral and skeletal abnormalities.

 

Oral administration of Santovar A produced slight maternal toxicity at the 70.0 mg/kg/day level and substantial maternal toxicity at the 175.0 mg/kg/ day level.

The toxicity was characterized by an increase in the incidence of reddish colored vaginal discharge and post-dose salivation at the 70.0 mg/kg/day level and more frequent and severe clinical signs, body weight loss and reduced food consumption at the 175.0 mg/kg/day level. No adverse clinical signs were observed in the 20.0 mg/kg/day group. Similarly, no treatment-related differences in mean body weights, body weight gain or food consumption were observed at the 20.0 or 70.0 mg/kg/day levels. Mean fetal body weight was slightly, but statistically reduced at the 175.0 mg/kg/day level when compared to the control group. All other cesarean section parameters were comparable among the groups. No apparent treatment-related malformations or developmental variations were observed at the 20.0 or 70.0 mg/kg/day levels. Slight, non-statistical increases in the incidence of skull anomalies and 7th cervical ribs were observed in the 175.0 mg/kg/day group. The number of litters with sternebra(e) #5 and/or #6 unossifed was also statistically increased at this level when compared to the control group. The number of litters in the control group with unossifed sternebrae in this study is unusually low when compared to SLS historical control data.

Therefore, it is not clear if the increase in the number of litters with sternebra(e) #5 and/or #6 unossified at the 175.0 mg/kg/day level in this study was spontaneous or associated with the reduced fetal body weights observed at this level.

 

Based on the results of this study, a dosage level of 20.0 mg/kg/day was considered a no-observed-effect level (NOEL) for maternal toxicity and a dosage level of 70.0 mg/kg/day was considered a NOEL for developmental toxicity.

Santovar A at a dosage level of 175.0 mg/kg/day produced substantial maternal toxicity with minimal developmental toxicity.