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Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Study period:
10th September 2019 to 16th Dec 2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2020
Report date:
2020

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Version / remarks:
June, 2018
Deviations:
no
Qualifier:
according to guideline
Guideline:
EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)
Version / remarks:
August, 1998
Deviations:
not specified
GLP compliance:
yes
Limit test:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane
EC Number:
219-863-1
EC Name:
2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane
Cas Number:
2554-06-5
Molecular formula:
C12H24O4Si4
IUPAC Name:
2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-1,3,5,7,2,4,6,8-tetroxatetrasilocane

Test animals

Species:
rat
Strain:
Sprague-Dawley
Remarks:
Crl:CD(SD)
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories, Inc., Raleigh, NC
- Age at study initiation: 10-12 weeks old
- Weight at study initiation: 200-250 g (Gestation day 0).
- Fasting period before study: not specified
- Housing: Animals were individually housed in clean, solid-bottom cages with appropriate bedding and equipped with an automatic watering valve.
- Diet: Certified Rodent LabDiet 5002 meal, ad libitum
- Water: tap water, ad libitum
- Acclimation period: 2-6 days.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 to 26 °C
- Humidity (%): 30 to 70%
- Air changes (per hr): ≥10 per hour
- Photoperiod (hrs dark / hrs light): 12 hours light /12 hours dark
- Other: 100 % fresh air with no air recirculation was maintained.

IN-LIFE DATES: not specified

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
corn oil
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: Preparation occurred approximately weekly with an adequate amount of each formulation dispensed into daily aliquots. These aliquots were stored in a room with controls set to maintain a temperature between 18 to 24°C and protected from light until use.

VEHICLE
- Justification for use and choice of vehicle: the vehicle has been selected as suggested by the sponsor based on the test item's characteristics and testing guideline. The selected vehicle was corn oil.
- Concentration in vehicle: 0; 6.25; 25; 100 mg/mL
- Amount of vehicle: 4 mL/kg
- Lot/batch no.: 2IC0148, 1IG1538, and 2IH0387
- Purity: not specified
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Duplicate sets of samples (1.0 mL) for concentration analysis were collected twice during the study for all dose levels. Concentration results were considered acceptable if mean sample concentration results were within or equal to ± 15% of theoretical concentration.

Duplicate sets of samples (1.0 mL) for homogeneity analysis were collected once during the study from low dose and high dose groups. Homogeneity results were considered acceptable if the relative standard deviation of the mean concentration was ≤ 10% and if mean sample concentration results were within or equal to ± 15% of theoretical concentration.

Stability analysis was not performed since the test substance formulations have been previously shown to be stable over the range of concentrations used for this study for at least 8 days.

Analyses were performed by gas chromatography method using flame ionization detection using a validated analytical procedure.
Details on mating procedure:
Time-mated females were received from Charles River Laboratories on gestation days 1, 2, 3 or 4.
Duration of treatment / exposure:
From gestation day 6 to 20.
Frequency of treatment:
Single daily dose
Duration of test:
From Gestation day 6 to 20.
Doses / concentrationsopen allclose all
Dose / conc.:
0 mg/kg bw/day (nominal)
Remarks:
Control
Dose / conc.:
25 mg/kg bw/day (nominal)
Remarks:
Low dose (LD)
Dose / conc.:
100 mg/kg bw/day (nominal)
Remarks:
Middle dose (MD)
Dose / conc.:
400 mg/kg bw/day (nominal)
Remarks:
High dose (HD)
No. of animals per sex per dose:
25 females per group.
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: The dose selection was based on two previous dose range finding studies. The highest dose of 400 mg/kg bw/day was targeted to cause reduced body weight gains and feed consumption although not causing death or any obvious suffering. The lower doses were selected to provide dose response data for any observed toxicity and to establish a NOAEL value.
In a dose range-finding study, the test substance was administered to 5 male and 5 female (nonpregnant) Sprague Dawley rats per dose group via oral gavage for up to 14 consecutive days at dose levels of 0, 100, 300, 500, and 1000 mg/kg bw/day. All animals in the 1000 mg/kg bw/day group were euthanized in extremis on Day 8 following significant body weight losses in treated males during the first week of dosing. Mean body weights for the males was 15.9% lower and for females it was 5.2% lower than the concurrent control groups on Day 7. All other animals survived to the scheduled euthanasia. Test substance-related body weight losses or lower body weight gains, with corresponding lower food consumption, were generally noted for males and females in the 500 mg/kg bw/day group throughout the dosing period (Days 1–14), resulting in lower mean body weights than the control groups on Day 14. Lower body weight gains were also noted for males at 300 mg/kg bw/day and females at 100 and 300 mg/kg bw/day during Days 1–7, without corresponding lower food consumption or effects on mean body weights. Test substance-related increased liver weights (absolute and normalised) were noted in all test substance-treated males and females at the day 8/15 terminal necropsy. There were no correlations to differences in serum chemistry parameters.
In a dose range-finding prenatal developmental toxicity study, the test substance was administered to 5 pregnant Sprague Dawley females per dose group via oral gavage from Gestation Days 6–20 at dose levels of 0, 200, 400, and 600 mg/kg bw/day. 5 Females in the 400 and 600 mg/kg bw/day dose groups had decreased body weights gains (19% and 39%,respectively) and feed consumption (9% and 13%, respectively) over the Gestation Days 6–21 treatment period, which resulted in body weight decreases of 7% and 13%, respectively, on Gestation Day 21. All treated groups had increased absolute liver weights. A higher mean litter proportion of postimplantation loss (19.6% per litter) was noted in the 600 mg/kg bw/day group compared to the control group (3.2% per litter). A corresponding lower mean number of viable fetuses (8.5 per dam) was also observed in this group compared to the control group (12.6 per dam). The differences in this group were primarily attributed to 1 female, with 42.9% postimplantation loss and only 4 viable foetuses. Intrauterine survival was unaffected by test substance administration at dosage levels of 200 and 400 mg/kg bw/day.
- Rationale for animal assignment: randomised.

Examinations

Maternal examinations:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily, in the morning and in the afternoon.
- Cage side observations checked included: The general health/mortality and moribundity was recorded.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: During the dosing period, observations were done once prior to dosing and once 1–2 hours postdose.

BODY WEIGHT: Yes
- Time schedule for examinations: on gestation day 0 and thereafter, daily during days 5-21.

FOOD CONSUMPTION AND COMPOUND INTAKE: Yes
- Food consumption was quantitatively measured on Gestation Days 5–21 (daily).

WATER CONSUMPTION AND COMPOUND INTAKE: No

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 21
- Organs examined: Animals were subjected to a complete necropsy examination, which included evaluation of the thoracic, abdominal, and pelvic cavities with their associated organs and tissues. The liver, thyroid gland and kidneys were weighed at necropsy for all scheduled euthanasia animals. Paired organs were weighed together. Tissues were collected from liver, kidneys, thyroid gland and all gross lesions. The thyroid gland from all females was embedded in paraffin, sectioned, mounted on glass slides, and stained with haematoxylin and eosin. The thyroid gland was examined microscopically from all females in all groups.

Thyroid hormones: Yes
- Blood samples for thyroid hormone analyses were collected (prior to noon in order to avoid diurnal fluctuations in thyroid hormone levels) via a jugular vein into tubes without anticoagulant on GD 21. The blood samples were analysed for triiodothyronine (total T3), thyroxine (total T4) and thyroid-stimulating hormone (TSH).
Ovaries and uterine content:
The ovaries and uterine content were 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
- Other: the placentae were also examined.
Fetal examinations:
- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: approximately one half per litter
- Skeletal examinations: Yes: approximately one half per litter (those not used for soft tissue examinations)
- Head examinations: Yes: approximately one half per litter (those used in soft tissue examinations)
Statistics:
All statistical tests were conducted at the 5% significance level. All pairwise comparisons were conducted using two sided tests and were reported at the 1% and 5% levels.
Numerical data collected on scheduled occasions for the listed variables were analysed as indicated by sex and occasion or by litter. Mean, standard deviation, percentage, and/or incidence were reported whenever possible.
Indices:
No data
Historical control data:
yes, for the background incidence of fetal malformations and developmental variations (from Charles River Laboratories).

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:
no effects observed
Description (incidence and severity):
No test substance-related clinical observations were noted at the daily examinations at any dosage level. Observations noted in the test substance-treated groups occurred infrequently, at similar frequencies in the control group, and/or in a manner that was not dose related. No clinical observations were noted 1-2 hours postdosing at any dosage level. With the exception of 1 female in the control group, all females were gravid.
Dermal irritation (if dermal study):
not examined
Mortality:
no mortality observed
Description (incidence):
All females in the control, 25, 100, and 400 mg/kg bw/day groups survived to the scheduled necropsy on gestation days 21.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Mean maternal body weight losses were noted in the 400 mg/kg bw/day group following the initiation of dosing (gestation days 6–7 and 7–8), resulting in a statistically significant mean body weight loss in this group during gestation days 6–9. The only other statistically significant difference from the control group was a lower mean body weight gain in the 400 mg/kg bw/day group during gestation days 20–21. Although mean body weight gains in the 400 mg/kg/day group were generally comparable to the control during the remainder of the treatment period (gestation days 9–12, 12–15, and 15–21), the initial decrement resulted in a non-statistically significantly lower (11.4%) mean body weight gain in this group when the overall treatment period (gestation days 6–21) was evaluated.
Mean absolute body weights in the 400 mg/kg bw/day group were statistically significantly (6.1% and 5.7%) lower than the control group on gestation days 8 and 9. Thereafter, mean absolute body weight were generally comparable to the control group throughout the treatment period. However, mean corrected body weight and mean corrected body weight gain were statistically significantly (6.4% and 28.7%, respectively) lower in the 400 mg/kg bw/day group compared to the control group. The body weight effects in this group were considered test substance related and adverse.
Mean maternal body weights, body weight gains, corrected body weights, corrected body weight gains in the 25 and 100 mg/kg bw/day groups were unaffected by test article administration. Differences from the control group were slight and not statistically significant.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
In the 400 mg/kg bw/day dose group, lower mean food consumption (33.5% compared to control) was observed during gestation days 6-9. No other differences in the other dose groups occurred when compared to the control group.
Food efficiency:
not specified
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
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
Mean absolute liver weights in the 25, 100, and 400 mg/kg bw/day groups were statistically significantly higher (12.4% to 29.2%) than the control group. These effects were considered test substance related. A statistically significantly higher (9.6%) mean absolute kidneys weight was also noted in the 400 mg/kg bw/day group compared to the control group; this finding was not considered test substance related due to the magnitude of the change. No other statistically significant differences were noted at any dosage level.
Gross pathological findings:
no effects observed
Description (incidence and severity):
At the scheduled necropsy on gestation day 21, no test substance-related internal findings were observed at dosage levels of 25, 100, and 400 mg/kg bw/day. Macroscopic findings observed in the test substance-treated groups occurred infrequently, at similar frequencies in the control group, and/or in a manner that was not dose-related.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
no effects observed
Description (incidence and severity):
There were no test substance-related histologic changes in the thyroid gland. All histologic changes were considered to be incidental findings or related to some aspect of experimental manipulation other than administration of the test substance. There was no test substance-related alteration in the prevalence, severity, or histologic character of those incidental tissue alterations.
Histopathological findings: neoplastic:
no effects observed
Other effects:
effects observed, treatment-related
Description (incidence and severity):
Statistically significantly lower mean T3 (44.4%) and T4 (38.5%) concentrations were noted in the 400 mg/kg bw/day group compared to the control group. In addition, statistically significantly higher (58.9% to 76.8%) mean TSH concentrations were noted in the 25, 100, and 400 mg/kg bw/day groups compared to the control group, albeit in a manner that was not clearly dose responsive and there was no corresponding test substance-related or dose-responsive change in mean T3 and T4 concentrations in the 25 and 100 mg/kg bw/day groups. These findings were considered test substance-related, but not adverse, due to lack of effects on the thyroid gland weight and histopathology.

Maternal developmental toxicity

Number of abortions:
no effects observed
Pre- and post-implantation loss:
no effects observed
Total litter losses by resorption:
no effects observed
Early or late resorptions:
no effects observed
Dead fetuses:
no effects observed
Changes in pregnancy duration:
no effects observed
Changes in number of pregnant:
no effects observed
Other effects:
no effects observed
Description (incidence and severity):
The mean numbers of corpora lutea was comparable to the control group.
Details on maternal toxic effects:
Intrauterine survival was unaffected by test substance administration at all dosage levels. Parameters evaluated included postimplantation loss, live litter size, and foetal sex ratios. Mean numbers of corpora lutea and implantation sites and the mean litter proportions of pre-implantation loss were similar across all groups.

Effect levels (maternal animals)

Dose descriptor:
NOAEL
Effect level:
100 mg/kg bw/day
Based on:
test mat.
Basis for effect level:
body weight and weight gain

Maternal abnormalities

Abnormalities:
effects observed, treatment-related
Localisation:
other: Body weight
Description (incidence and severity):
Decreased body weight at 400 mg/kg bw/day

Results (fetuses)

Fetal body weight changes:
effects observed, treatment-related
Description (incidence and severity):
Mean foetal body weights (male, female, and combined sexes) in the 400 mg/kg bw/day group were statistically significantly lower (14.9% to 16.2%) than the concurrent control group. The values were also below the respective minimum mean values in the Charles River Ashland developmental historical control data (version 2019.01). Therefore, the lower mean foetal body weights in this group were considered test substance-related and adverse. Mean foetal body weights in the 25 and 100 mg/kg bw/day groups were unaffected by test substance administration.
Reduction in number of live offspring:
no effects observed
Changes in sex ratio:
no effects observed
Changes in litter size and weights:
no effects observed
Changes in postnatal survival:
no effects observed
External malformations:
no effects observed
Description (incidence and severity):
No test substance-related external malformations were observed in foetuses in this study. One foetus in the 100 mg/kg bw/day group had a small left eye bulge and one foetus in the 25 mg/kg bw/day group had a cleft palate (entire length). In the absence of a dose response, these malformations were not considered test substance-related.
No external developmental variations were observed in foetuses in this study.
Skeletal malformations:
effects observed, treatment-related
Description (incidence and severity):
No test substance-related foetal malformations were observed at any dosage levels.
In the 25 mg/kg bw/day, one female was observed with split palatine plates, corresponding to cleft palate noted externally. However, this was considered as not test-item related in the absence of a dose response occurring.
At 400 mg/kg bw/day, test substance-related skeletal developmental variations were noted. They included the findings of delayed ossification which correspond to the lower foetal weights in the same group and were considered nonadverse as they were expected to resolve over time.
Visceral malformations:
no effects observed
Description (incidence and severity):
No test substance-related visceral malformations were observed in foetuses in this study. One foetus in the 400 mg/kg bw/day group had a retroesophageal right subclavian artery; however, this was noted for a single foetus, the mean litter proportion was not statistically significant compared to the control group, and the value was within the Charles River Ashland developmental historical control data range. Therefore, this malformation was not considered test substance-related. No test substance-related visceral developmental variations were observed in foetuses in the study. Findings observed in the test substance-treated groups were noted infrequently, similarly in the control group, were not observed in a dose related manner, the differences in the mean litter proportions were not statistically significant compared to the concurrent control group, and/or the values were within the ranges of the Charles River Ashland developmental historical control data.
Other effects:
effects observed, treatment-related
Description (incidence and severity):
A statistically significant shorter mean absolute anogenital distance (11.3%) was noted in the 400 mg/kg bw/day group males compared to the control group; however, mean anogenital distance relative to the cube root of the body weight in these males was only 6.3% lower than the control group and not statistically significant. Because the mean anogenital distance in this group was only slightly shorter than noted in the control group and was not statistically significant when normalized to body weight, the difference in mean absolute anogenital distance in the 400 mg/kg bw/day group males was considered secondary to the lower mean foetal body weights. Mean absolute and relative anogenital distances for female foetuses in this group were comparable to the control group. Mean anogenital distances in the 25 and 100 mg/kg bw/day groups were comparable to the control group.

Effect levels (fetuses)

Dose descriptor:
NOAEL
Effect level:
100 mg/kg bw/day
Based on:
test mat.
Sex:
male/female
Basis for effect level:
fetal/pup body weight changes

Fetal abnormalities

Abnormalities:
effects observed, treatment-related
Localisation:
other: Foetal body weights
Description (incidence and severity):
Lower mean foetal body weights at 400 mg/kg bw/day dose group.

Overall developmental toxicity

Developmental effects observed:
yes
Lowest effective dose / conc.:
400 mg/kg bw/day
Treatment related:
yes
Relation to maternal toxicity:
not specified
Dose response relationship:
yes
Relevant for humans:
yes

Any other information on results incl. tables

Overall developmental toxicity:

Lowest effective dose / concentration: 400 mg/kg bw/day. Relation to maternal toxicity: uncertain at this time if the developmental effects are a secondary non-specific consequence of maternal toxicity effects.

Applicant's summary and conclusion

Conclusions:
In an oral prenatal developmental toxicity study, conducted according to OECD Test Guideline 414 and in compliance with GLP, a maternal and prenatal development NOAEL was determined to be 100 mg/kg bw/day based on lower maternal and foetal body weights at 400 mg/kg bw/day.