Hydroxytrimethylsilane

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

17 April 2013 to 19 November 2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2014

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Hydroxytrimethylsilane

EC Number:

213-914-1

EC Name:

Hydroxytrimethylsilane

Cas Number:

1066-40-6

Molecular formula:

C3H10OSi

IUPAC Name:

hydroxytrimethylsilane

Test material form:

other: liquid

Details on test material:

- Name of test material (as cited in study report): Trimethylsilanol

Test animals

Species:

rat

Strain:

other: Sprague-Dawley:Crl:CD IGS

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Germany
- Age at study initiation: 12 weeks
- Weight at study initiation: 230 to 316g
- Fasting period before study: no
- Housing: In groups of three to five animals in Makrolon type-4 cages with wire mesh tops up to the day of mating and afterwards individually in Makrolon type-3 cages with wire mesh tops with sterilized standard softwood bedding (‘Lignocel’) with paper enrichment (ISO-BLOX).
- Diet (ad libitum): Pelleted standard Harlan Teklad 2018C
- Water (ad libitum): community tap water
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18.2 - 23.5
- Humidity (%): 27.2 - 70.3
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 22 April 2013 To: 23 May 2013

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Trimethylsilanol was weighed into a glass beaker on a tared precision balance and the vehicle (corn oil) was added. Using an appropriate homogenizer, a homogeneous suspension was pre-pared. Separate formulations were prepared for each concentration.
Dose formulations were divided into daily aliquots.
Homogeneity of the test item in the vehicle was maintained during the daily administration period using a magnetic stirrer.

VEHICLE
- Concentration in vehicle: 0, 10, 30, 90 mg/mL
- Amount of vehicle: 5 mL/kg

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

On the first treatment day samples from the control group as well as three samples (top, middle and bottom) of about 1 g of each concentration were taken prior to dosing for analysis of concentration and homogeneity. Samples of about 1 g of each concentration were taken from the middle only to confirm the stability (4 hrs at room temperature and 8 days in refrigerator). During the last week of the treatment, samples were taken from the middle to confirm concentration. The aliquots for analysis of dose formulations were frozen (-20 ± 5 °C) and delivered on dry ice to the person responsible for formulation analysis and stored there at -20 ± 5 °C until analysis.

The samples were analyzed by Headspace GC-Method The test item was used as the analytical standard.

Duplicates were taken of all samples and were stored.

Details on mating procedure:

- Impregnation procedure: cohoused
- M/F ratio per cage: 1:1
- Length of cohabitation: until evidence of copulation observed
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: vaginal plug or sperm in vaginal smear referred to as day 0 post coitum
- Any other deviations from standard protocol: no

Duration of treatment / exposure:

Day 6 to Day 20 post coitum

Frequency of treatment:

daily

Duration of test:

21 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

50 mg/kg bw/day

Doses / concentrations 2

Dose / conc.:

150 mg/kg bw/day

Doses / concentrations 3

Dose / conc.:

450 mg/kg bw/day

No. of animals per sex per dose:

22 female

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: The dose levels were selected based on a previous dose range-finding toxicity study in Sprague Dawley rats using dose levels of 0, 50, 150 and 600/400 mg/kg bw/day.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: 3 times daily during treatment

BODY WEIGHT: Yes
- Time schedule for examinations: daily

FOOD CONSUMPTION: Yes
- Time schedule for examinations: recorded at 3-day intervals, days 0-3, 3-6, 6-9, 9-12, 12-15, 15-18 and 18-21 post coitum
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/animal/day: Yes

WATER CONSUMPTION: No
- Time schedule for examinations:

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 21
- liver weight recorded

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 statistical methods were used to analyze food consumption, body weights, reproduction and skeletal examination data:

• Means and standard deviations of various data were calculated and included in the report.

• The Dunnett-test (many to one t-test) based on a pooled variance estimate was applied if the variables could be assumed to follow a normal distribution for the comparison of the treated groups and the control groups for each sex.

• The Steel-test (many-one rank test) was applied instead of the Dunnett-test when the data could not be assumed to follow a normal distribution.

• Fisher's exact-test was applied if the variables could be dichotomized without loss of information.

Historical control data:

Data from test facility derived during 1992 to 2003 included

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
At 450 mg/kg bw/day clinical signs related to treatment with the test item were observed such as uncoordinated movement and/or decreased activity and/or prostrate appearance in all animals after dosing. The severity of these signs were slight to moderate (grade 1 or 2) throughout the study and one animal showed no recovery by the next morning of treatment. Statistically significantly decreased mean food consumption, body weight, body weight gain and corrected body weight gain were affected by the treatment with the test item and were considered to be adverse maternal toxic effects.

At 150 mg/kg bw/day, maternal animals showed slight (grade 1) signs observed as uncoordinated movement immediately after dosing, with recovery by the next morning for all animals. Slight decrease in maternal food intake was noted on the first week of treatment. Associated mean body weights and body weight gains were also statistically significantly decreased from early until middosing period. However, all of these effects were transient, of slight severity and considered unlikely to indicate any substantial impairment of maternal pregnancy.

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
The mean fetal body weight was statistically significantly lower at 450 mg/kg bw/day and was considered to be related to the treatment with the test item. In correlation with the lower fetal weights a slight delay in ossification was noted in the high dose group (450 mg/kg bw/day). An increased incidence of long or interrupted costal cartilages or long ventral plate indicated a slight disturbance in development at this dose level.

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Lower fetal weight, delayed ossification and increased incidence of some cartilaginous variations at 450 mg/kg/day.

Fetal abnormalities

Abnormalities:

effects observed, treatment-related

Overall developmental toxicity

Developmental effects observed:

yes

Lowest effective dose / conc.:

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

Treatment related:

yes

Relation to maternal toxicity:

developmental effects as a secondary non-specific consequence of maternal toxicity effects

Any other information on results incl. tables

Table 1: Results for Formulation Analysis

Dose Group	Sample taken from	Nominal Conc (mg/mL)	Actual Conc (mg/mL)	Relative to Nominal (%)	Mean (%)
Control	vehicle	0.0	ND	-	-
2	top middle bottom	10.0 10.0 10.0	9.273 9.830 9.721	92.7 98.3 97.2	96.1
3	top middle bottom	30.0 30.0 30.0	31.61 29.51 29.25	105.4 98.4 97.5	100.4
4	top middle bottom	90.0 90.0 90.0	89.91 90.59 90.59	99.9 100.7 100.7	100.4

ND = not detected

In addition, the test item was found to be stable in application formulations when kept four hours at room temperature and eight days at in the refrigerator (5 ± 3 °C) due to recoveries which met the variation limit of 10% from the time-zero (homogeneity) mean value.

Table 2 - Summary of Performance of Mated Females

Group Dose (mg/kg bw/day)	1 (0)	2 (50)	3 (150)	4 (450)
Female numbers	1 - 22	23 - 44	45 - 66	67 - 88
Number of mated females	22	22	22	22
Non-pregnant females (A)	1	0	1	1
Number of pregnant females	21	22	21	21
Number of females with live fetuses at termination*	21	22	21	21

*    Only dams with at least one live fetus at caesarean section were used for the calculations of food consumption, body weight gain and corrected body weight gain data.

(A) Female no. 10 from group 1 (control), female no. 57 from group 3 and female no. 79 from group 4 were not pregnant.

Applicant's summary and conclusion

Conclusions:

Administration of trimethylsilanol by oral gavage to Sprague-Dawley rats from Day 6 to 20 of pregnancy at 0, 50, 150 or 450 mg/kg/day resulted in clinical signs and reduced food consumption and body weight gain in dams at 150 and 450 mg/kg/day. The effects on food consumption and body weight were considered to be adverse at 450 mg/kg/day, therefore the maternal NOAEL was considered to be 150 mg/kg/day. Reduced fetal weight, delayed ossification and increased incidence of some cartilaginous variations were noted in fetuses at 450 mg/kg/day and considered to be adverse, therefore the fetal NOAEL was considered to be 150 mg/kg/day.

Executive summary:

Based on the results of this study, the NOEL (No-Observed-Effect-Level) for maternal effects was 50 mg/kg bw/day trimethylsilanol due to clinical signs, reduced food consumption and body weights of dams at 150 and 450 mg/kg bw/day. However, the NOAEL (No-Observed-Adverse-Effect-Level) for maternal effect was 150 mg/kg bw/day trimethylsilanol due to reduced corrected body weight gains indicating maternal toxicity at 450 mg/kg bw/day. The NOAEL for fetal developmental toxicity was 150 mg/kg bw/day based on the statistically significantly reduced fetal weights at the dose level of 450 mg/kg bw/day and the delayed ossification and the increased incidence of some cartilaginous variations of the fetuses which suggested a disturbance in development at 450 mg/kg bw/day.