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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Study period:
August 2019 through November 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 guideline
Qualifier:
according to
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Version / remarks:
25 June 2018
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Department of Health of the Government of the United Kingdom
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Details on test material:
- Purity: 99.8%
- Batch number: H05217M044
- Appearance: Colorless liquid

Test animals

Species:
rat
Strain:
other: Crl:CD(SD)
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River (UK) Ltd.
- Age at study initiation: 70 to 79 days old
- Weight at study initiation: 231 to 294 g
- Fasting period before study:
- Housing: Housed up to 4 animals per cage during acclimazation; housed one stock male and one female during mating; individually housed during gestation. Cages comprised of a polycarbonate body with a stainless steel mesh lid. Solid (polycarbonate) bottom cages were used during the acclimatization and gestation periods.
- Diet: SDS VRF1 Certified pelleted diet (manufactured in Witham, Essex, England), available ad libitum
- Water: Water from the public, available ad libitum
- Acclimation period: Six days before commencement of pairing

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 40-70
- Air changes (per hr): at least 15 air changes/hour
- Photoperiod (hrs dark / hrs light): 12 hours light : 12 hours dark

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
other: Dried and de-acidified corn oil
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: The required amount of test item was added to the required volume of vehicle. The formulation was stirred using a magnetic stirrer under a fume hood until uniformly mixed and then transferred to final containers, via syringe, while magnetically stirring. A series of formulations at the required concentrations were prepared by dilution of individual weighing of the test item in ascending order of concentration.

VEHICLE
- Preparation of vehicle: 50% silica, 25% aluminum oxide neutral and 25% aluminum oxide activated acidic (40g, 20g and 20g respectively per liter of oil) were mixed. The dry mixture was placed in a vented oven set to 250 ºC overnight or for at least eight hours. The oil and dry materials were mixed in a suitable container, using a stir bar on a magnetic stirring plate, for at least two hours under a nitrogen purge and then allowed to dry to room temperature. The oil and dry materials mix was allowed to settle for a minimum of 30 minutes. The oil was filtered with 0.22 µm cellulose acetate filter system with vacuum to remove the alumina and silica.
- Amount of vehicle (if gavage): 4 mL/kg body weight.
Analytical verification of doses or concentrations:
yes
Remarks:
The mean concentrations of formulation samples taken from the first and last preparation were within 3% of the nominal concentration, confirming the accuracy of formulation. The difference from mean remained within 3%, confirming precise analysis.
Details on analytical verification of doses or concentrations:
Before commencement of treatment, the suitability of the proposed mixing procedures was determined and specimen formulations at 1 and 250 mg/mL were analyzed to assess the stability and homogeneity of the test item in the liquid matrix. Stability was confirmed as one day at ambient temperature (15 to 25 ºC) and fifteen days at refrigerated temperature (2 to 8 ºC).

Samples of each of the first and last preparation formulations were analyzed for achieved concentration of the test item.
Details on mating procedure:
- Impregnation procedure: cohoused
- M/F ratio per cage: 1:1
- Verification of same strain and source of both sexes: yes; a colony of stud males was maintained specifically for the purpose of mating; these animals were not part of the study and were maintained as stock animals.
- Proof of pregnancy: evidence of vaginal plug and sperm in vaginal smear referred to as day 0 of pregnancy
Duration of treatment / exposure:
From Day 6 to Day 19 (inclusive) after mating
Frequency of treatment:
Daily
Doses / concentrationsopen allclose all
Dose / conc.:
100 mg/kg bw/day (actual dose received)
Dose / conc.:
300 mg/kg bw/day (actual dose received)
Dose / conc.:
1 000 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
20 females per dose
Control animals:
yes, concurrent no treatment

Examinations

Maternal examinations:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Animals were inspected visually at least twice daily for evidence of ill-health or reaction to treatment. Cages were inspected daily for evidence of animal ill-health amongst the occupant(s).

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed observations were recorded daily during the treatment period at the following times in relation to dose administration: pre-dose observation; one to two hours after completion of dosing; as late as possible in the working day. A detailed physical examination was performed on each animal on Days 0, 5, 12, 18 and 20 after mating to monitor general health.

BODY WEIGHT: Yes
- Time schedule for examinations: The weight of each adult was recorded on Days 0, 3 and 6-20 after mating.

FOOD CONSUMPTION: Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: See Table 1

OTHER: A thyroid hormone analysis was performed on all animals, which occurred as scheduled termination. Animals were no fasted. Samples were analyzed for serum thyroxine (T4) and triiodothyronine (T3) levels, as well as thyroid-stimulating hormone (TSH).
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: Yes: half per litter
Statistics:
The following sequence of statistical tests was used for body weight, gravid uterus weight, food consumption, corpora lutea, implantations, pre/post implantation loss, live young, sex ratio - percentage male, placental, litter and fetal weights and organ weight data:

A parametric analysis was performed if Bartlett's test for variance homogeneity was not significant at the 1% level. For pre-treatment data, analysis of variance was used to test for any group differences. Where this was significant (p<0.05) inter group comparisons using t-tests, with the error mean square from the one-way analysis of variance, were made. For all other analyses the F1 approximate test was applied. If the F1 approximate test for monotonicity of dose-response was not significant at the 1% level, Williams' test for a monotonic trend was applied. If the F1 approximate test was significant, suggesting that the dose response was not monotone, Dunnett's test was performed instead.

A non-parametric analysis was performed if Bartlett's test was still significant at the 1% level following both logarithmic and square-root transformations. Forpre-treatment data, Kruskal-Wallis’ test was used to test for any group differences. Where this was significant (p<0.05) inter group comparisons using Wilcoxon rank sum tests were made. For all other analyses the H1 approximate test, the non-parametric equivalent of the F1 test described above, was applied. If the H1 approximate test for monotonicity of dose-response was not significant at the 1% level, Shirley's test for a monotonic trend was applied. If the H1 approximate test was significant, suggesting that the dose-response was not monotone, Steel's test was performed instead.

For organ weight data, analysis of covariance was performed using terminal body weight as covariate, unless non-parametric methods were applied.
Indices:
Pre-implantation loss (%) = ((Number of copora lutea - Number of implantations)/Number of corpora lutea) X 100
Post-implantation loss (%) = ((Number of copora lutea - Number of implantations)/Number of implantations) X 100
Historical control data:
Historical Control data was included and used for the evaluation of both fetal and litter incidences.

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:
no effects observed
Dermal irritation (if dermal study):
not examined
Mortality:
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
effects observed, non-treatment-related
Description (incidence and severity):
At 1000 mg/kg bw/day group mean food consumption was slightly lower, and attained statistical significance, during Days 6-18 of gestation when compared with the group mean food consumption of the control group.
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
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
The mean gravid uterine weight for females treated with triethoxy(methyl)silane was comparable to the mean gravid uterine weight from the control females, as was adjusted body weight gain.

The weight of the liver was higher in females treated with 1000 mg/kg bw/day when compared with the controls (136% of the controls, respectively) and slightly higher in females receiving 300 mg/kg bw/day (109% of the controls, respectively). The weight of the thyroids and parathyroids were higher in females receiving 1000 mg/kg bw/day triethoxy(methyl)silane (129% of the controls, respectively). The weight changes stated above all attained statistical significance.
Gross pathological findings:
no effects observed
Neuropathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
In the thyroids, minimal/slight follicular cell hypertrophy was seen in all treated groups, with a clear relationship to dose. The hypertrophy was considered to account for the statistically significant higher than control group mean bodyweight adjusted thyroid weights for females that received 1000 mg/kg bw/day. This effect is likely secondary to the increase in TSH, which is a compensatory feedback mechanism to increase thyroid hormone production by the thyroid gland and part of a homeostatic response by the hypothalamic-pituitary-thyroid axis.
Histopathological findings: neoplastic:
not examined
Other effects:
effects observed, treatment-related
Description (incidence and severity):
The analysis of serum TSH concentrations performed at scheduled termination on Day 20 of gestation revealed that the TSH level at 1000 mg/kg bw/day was found to be statistically significantly higher compared to the control group at the 0.1% (p < 0.001) level.

There was a decrease in T4 and T3 concentration in females receiving 1000 mg/kg bw/day triethoxy(methyl)silane, both were found to be statistically significantly lower compared to the control group at the 0.1% (p < 0.001) level.

It was concluded that there was an effect of triethoxy(methyl)silane on serum T3, T4 and TSH concentrations in pregnant rats at a dose level of 1000 mg/kg bw/day, administered via oral gavage. It is possible that the change in TSH and thyroid hormones were secondary to liver enzyme induction and enhanced metabolism and clearance of thyroid hormones, which is consistent with increased liver weights.

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:
not examined

Effect levels (maternal animals)

Key result
Dose descriptor:
NOAEL
Effect level:
1 000 mg/kg bw/day (actual dose received)
Based on:
test mat.
Basis for effect level:
other: No adverse effects observed

Maternal abnormalities

Key result
Abnormalities:
no effects observed

Results (fetuses)

Fetal body weight changes:
no effects observed
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
Skeletal malformations:
effects observed, non-treatment-related
Description (incidence and severity):
At 1000 mg/kg bw/day there was a slight increase in incidence of cranial interparietal fissure(s) compared to concurrent control and was outside historical control data range. In isolation and at such low incidence this was not considered adverse.
Visceral malformations:
effects observed, non-treatment-related
Description (incidence and severity):
At 1000 and 300 mg/kg bw/day there was a slight increase in the incidence of partially undescended thymus compared to concurrent control but was within historical control data range and therefore considered unrelated to treatment. This is a transient stage in fetal development and therefore not considered adverse.
Other effects:
not examined

Effect levels (fetuses)

Key result
Dose descriptor:
NOAEL
Effect level:
1 000 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: no adverse effects observed

Fetal abnormalities

Key result
Abnormalities:
no effects observed

Overall developmental toxicity

Key result
Developmental effects observed:
no

Applicant's summary and conclusion

Conclusions:
Based on the results of this study, no adverse effects on development of offspring were observed up to and including 1000 mg/kg bw/day, the highest dose tested.