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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
At least 28 days
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP, using a closely related test substance.
Cross-reference
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2008

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: OECD TG 422
Deviations:
no
GLP compliance:
yes (incl. certificate)
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories
- Age at study initiation: 11-12 weeks.
- Weight at study initiation: Males: 341 g to 418 g; Toxicity phase females:231 g to 282 g ; Reproductive phase females: 218 g to 280 g
- Fasting period before study: None
- Housing: F0 animals were housed individually in clean, stainless steel wire mesh cages suspended above cage board. The cage-board was changed at least 3 times per week. The males and reproductive phase females were paired for mating in the home cage of the male. Following positive evidence of mating, the males were housed in suspended wire mesh cages until the scheduled necropsy, and the females were transferred to plastic maternity cages with nesting material, ground corncob bedding
- Use of restrainers for preventing ingestion (if dermal): yes/no
- Diet (e.g. ad libitum): Ad libitum except during exposure periods, FOB and fasting period prior to blood sampling.
- Water (e.g. ad libitum): Ad libitum except during exposure periods, FOB and fasting period prior to blood sampling.
- Acclimation period: The males and reproductive phase females were housed for an acclimation period of 16 days prior to the first day of treatment. The toxicity phase females were housed for an acclimation period of 23 days prior to the first day of treatment.


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22± 3
- Humidity (%): 50± 20
- Air changes (per hr): At least 10
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 3 April 2008 To: 31 May 2008

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Vehicle:
unchanged (no vehicle)
Details on exposure:
Trimethylsilanol was generated for exposure as a vapor using a bubbler-type vaporization system located within a heated containment box. Nitrogen flowed into the inlet stem of a gas washing bottle containing an appropriate quantity of test article and bubbled through a fritted disc at the bottom of the bottle in order to create vapors of the test article. The concentrated vapors were piped to the heated chamber inlet where the concentration was reduced by mixing with chamber ventilation air. The control group was exposed to clean, filtered air.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Actual exposure concentrations within each chamber were measured at approximately 35 minute intervals during each daily exposure period by a validated gas chromatographic method. Exposure atmosphere samples were delivered to the gas chromatograph from the approximate middle of each chamber by a pump and multi-port sampling valve. At least 1 standard was analyzed each day prior to exposure to confirm gas chromatographic calibration.
Homogeneity and temporal stability of the exposure concentrations were evaluated during the method development phase of the study. Four test locations and a reference location were used for these determinations. The test locations were top rear, top front, bottom rear and bottom front. Samples were collected and analyzed on the GC as rapidly as possible by alternating from the reference location to a test location. The measured concentration was calculated as a percent difference for each position from the reference location. Homogeneity was performed in triplicate for each test article exposure chamber.
Details on mating procedure:
- M/F ratio per cage: 1/1
- Length of cohabitation: Until evidence of mating.
- Proof of pregnancy: vaginal copulatory plug or the presence of sperm following a vaginal lavage defined as Day 0.
- Females with no evidence of mating or that failed to deliver were housed in plastic maternity cages until post-cohabitation or post-mating day 25.
- After successful mating each pregnant female was caged (how): plastic maternity cages with nesting material, ground corncob bedding.
Duration of treatment / exposure:
Six hours per day, seven days per week.
Frequency of treatment:
Daily
Duration of test:
Males and reproductive phase females were exposed daily for at least 14 days prior to mating and continuing throughout mating for a minimum of 34 days (males) or through gestation day 20 (reproductive phase females). Toxicity phase females were exposed daily for a minimum of 28 days.
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0, 61, 303 and 602 ppm (males), 0, 61, 304 and 604 ppm (toxicity phase females) and 0, 61, 304 and 603 ppm (reproductive phase females)
Basis:
analytical conc.
Remarks:
Doses / Concentrations:
0, 60, 300 and 600 ppm
Basis:
nominal conc.
No. of animals per sex per dose:
Ten
Control animals:
other: Filtered air only

Examinations

Maternal examinations:
CAGE SIDE AND DETAILED CLINICAL OBSERVATIONS: Yes
All rats were observed twice daily for moribundity and mortality. Individual clinical observations were recorded daily. Once prior to the initiation of exposure, on the first day of exposure and on a weekly basis throughout the study, all rats were observed outside the home cage in a standard arena and evaluated for changes in gait, posture and response to handling, as well as the presence of clonic or tonic movements, stereotypies or bizarre behavior. Observations were conducted prior to test article exposure during the treatment period and were not performed on the day of Functional Observational Battery (FOB) assessments. Animals visible in the exposure chamber were also observed for signs of toxicity at the mid-point of exposure (3 hours following beginning of exposure) and any positive findings were recorded. All animals were observed for signs of toxicity approximately 1 hour following the exposure period.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual male and toxicity phase female body weights were recorded weekly, beginning 1 week prior to test article exposure, on the first day of exposure and weekly thereafter until the scheduled euthanasia. Body weights were also recorded for the toxicity phase animals assigned to FOB and locomotor activity assessments on the days of these evaluations. Individual reproductive phase female body weights were recorded weekly, beginning 1 week prior to test article exposure, on the first day of exposure and on a weekly basis thereafter until evidence of copulation was observed. Once evidence of mating was observed, reproductive phase female body weights were recorded on gestation days 0, 4, 7, 11, 14, 17 and 20 and on lactation days 1 and 4.

FOOD CONSUMPTION:
Individual food consumption was recorded on the corresponding weekly body weight days until pairing. Once evidence of mating was observed, reproductive phase female food consumption was recorded on gestation days 0, 4, 7, 11, 14, 17 and 20 and on lactation days 1 and 4.

WATER CONSUMPTION: No

POST-MORTEM EXAMINATIONS: Yes
- Females that delivered were euthanized on lactation day 4; the number of former implantation sites and corpora lutea were recorded. Females that failed to deliver were euthanized on post mating day 25 (females with evidence of mating) or post-cohabitation day 25 (females with no evidence of mating).
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.


Ovaries and uterine content:
The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: No data
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: No data
- Number of late resorptions: No data
Fetal examinations:
On PND 4, surviving F1 pups were euthanized via an intraperitoneal injection of sodium pentobarbital and necropsied with emphasis on developmental morphology. Organs and tissues with gross lesions were preserved in 10% neutral-buffered formalin for possible future histopathologic examination. All carcasses were then discarded. Histopathologic examination was deemed unnecessary during consultation between the study director and the sponsor.
Statistics:
Analyses were conducted using two-tailed tests (except as noted otherwise) for minimum significance levels of 1% and 5%, comparing each test article-treated group to the control group by sex. Each mean was presented with the standard deviation, standard error and the number of animals used to calculate the mean. Data obtained from nongravid females were excluded from statistical analyses following the mating period. Where applicable, the litter was used as the experimental unit. Parental mating, fertility, conception and copulation indices were analyzed using the Chi square test with Yates’ correction factor. Mean body weights (weekly, gestation and lactation), body weight changes and food consumption, precoital intervals, offspring body weights and body weight changes, gestation length, numbers of corpora lutea and implantation sites, number of pups born, live litter size on PND 0, unaccounted-for sites, absolute and relative organ weights, clinical pathology values (except gamma glutamyltransferase) and FOB data values were subjected to a parametric one way analysis of variance (ANOVA) to determine intergroup differences. If the ANOVA revealed statistically significant (p<0.05) intergroup variance, Dunnett's test was used to compare the test article-exposed groups to the control group. FOB parameters that yielded scalar or descriptive data and qualitative histopathological findings in the test article exposed groups were compared to the control group using Fisher’s Exact test. Mean litter proportions (% per litter) of males at birth and postnatal survival, as well as gamma glutamyltransferase values, were subjected to the Kruskal-Wallis nonparametric ANOVA to determine intergroup differences. If the ANOVA revealed statistically significant (p<0.05) intergroup variance, Dunn’s test was used to compare the test article-exposed groups to the control group.
Historical control data:
Mentioned in draft report, but not provided yet. Update when final report is available.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:no effects

Details on maternal toxic effects:
No test substance-related adverse toxicologically significant effects were observed in the dams.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOAEL
Effect level:
>= 600 ppm (nominal)
Basis for effect level:
other: maternal toxicity
Dose descriptor:
NOAEL
Effect level:
>= 600 ppm (nominal)
Basis for effect level:
other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
No test substance-related adverse toxicologically significant effects were observed in the pups.

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
In this OECD test guideline 422 screening study, which was conducted to GLP, test substance-related effects were limited to changes in hematology (lower eosinophil and lymphocyte counts for males) and serum chemistry (higher alanine aminotransferase for males and toxicity phase females) at 600 ppm. These changes occurred in the absence of correlating histologic changes and were not considered adverse. There were no effects on development of offspring. Therefore, under the conditions of this screening study, an exposure level of 600 ppm was considered to be the no-observed-adverse-effect level (NOAEL) for trimethylsilanol. It is considered appropriate to use this result in support of the developmental toxicity endpoint for chlorodimethylsilane as this substance is hydrolysed very rapidly in the presence of moisture to dimethylsilanol and hydrogen chloride, and the toxicity of di- and tri-methylsilanol are expected to be similar. Since chlorodimethylsilane is hydrolysed to dimethylsilane and hydrogen chloride, additional local irritation can be expected due to the acidic nature of the HCl.
Executive summary:

Three groups of Crl:CD(SD) rats, each group consisting of 10 males, 10 toxicity phase females and 10 reproductive phase females, were exposed via whole-body inhalation to vapor atmospheres of the test article, trimethylsilanol, 6 hours/day, 7 days/week.  Target exposure concentrations were 60, 300 and 600 parts per million (ppm).  A concurrent control group was exposed to filtered air on a comparable regimen. F0 males and reproductive phase females were exposed daily for 14 days prior to mating, throughout the mating period and continuing through the day prior to euthanasia (males) or gestation day 20 (reproductive phase females). F0 reproductive phase females with no evidence of mating or that failed to deliver were exposed through post-mating or post-cohabitation day 24 (the day prior to euthanasia) for a total of 52 consecutive days. F0 toxicity phase females were exposed for 28 consecutive days.

All animals were observed twice daily for mortality and moribundity. Clinical observations, body weights and food consumption were recorded at appropriate intervals.  Functional observational battery (FOB) and locomotor activity data were recorded for all males and toxicity phase females prior to initiation of exposure for each sex (baseline evaluation) and near the end of exposure. F0 males were euthanized following completion of the mating period and F0 toxicity phase females were euthanized following 28 days of exposure. Clinical pathology evaluations (hematology and serum chemistry) were performed on all F0 males and toxicity phase females at necropsy. Complete necropsies were conducted on all F0 males and toxicity phase females, and selected organs were weighed; selected tissues in the control and high‑exposure groups were examined microscopically.

All F0 reproductive phase females were allowed to deliver and rear their pups until lactation day 4. F1clinical observations and body weights were recorded on postnatal days (PND) 1 and 4. Reproductive phase dams and pups were euthanized and examined on lactation day/PND 4.

One F0 toxicity phase female in the 300 ppm group was found dead on study day 35, the day of scheduled necropsy.  While the cause of death for this female was not determined, there were no mortalities in the 600 ppm group.  Therefore, this mortality at 300 ppm was not attributed to test article exposure.  All other toxicity phase females and all F0males and reproductive phase females survived to the scheduled necropsies.  There were no test article-related macroscopic findings or effects on organ weights.There were no remarkable clinical observations noted at any exposure level.  Mean body weights, body weight gains and food consumption for males and females at all exposure levels were similar to the control group for all phases.  There were no test article-related effects on FOB parameters, including home cage, handling, open field, sensory, neuromuscular or physiological observations and no effects on locomotor activity patterns for males and toxicity phase females.  No remarkable shifts in the pattern of habituation occurred during locomotor activity assessments in any of the test article‑exposed groups when the F0 males and toxicity phase females were evaluated prior to the initiation of exposure or during the study week 4 evaluation.

Decreased mean eosinophil and lymphocyte counts were noted for the 600 ppm group F0 males.  In addition, increased mean alanine aminotransferase values were noted for F0 males and toxicity phase females in the 600 ppm group when compared with the control group.  Although these changes were considered test article‑related, they were not considered adverse in the absence of correlating histopathology.

Mean mating, fertility and copulation/conception indices for all exposure concentrations were similar to the control group.  Mean gestation lengths, postnatal survival and F1 body weights were similar to the control group.  There were no test article-related macroscopic findings observed for pups.

Test article-related effects were limited to changes in hematology (lower eosinophil and lymphocyte counts for males) and serum chemistry (higher alanine aminotransferase for males and toxicity phase females) at 600 ppm.  These changes occurred in the absence of correlating histologic changes and were not considered adverse.  Therefore, under the conditions of this screening study, an exposure level of 600 ppm was considered to be the no-observed-adverse-effect level (NOAEL) for reproductive, systemic and neonatal toxicity of trimethylsilanol when administered via whole-body inhalation exposure to Crl:CD(SD) rats. It is considered appropriate to use this result in support of the developmental toxicity endpoint for chlorodimethylsilane as this substance is hydrolysed very rapidly in the presence of moisture to dimethylsilanol and hydrogen chloride, and the toxicity of di- and tri-methylsilanol are expected to be similar. Since chlorodimethylsilane is hydrolysed to dimethylsilane and hydrogen chloride, additional local irritation can be expected due to the acidic nature of the HCl.