3,3-bis[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-1,5-divinyltrisiloxane

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

7th of January 2020 to ...

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

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

3,3-bis[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-1,5-divinyltrisiloxane

EC Number:

262-061-1

EC Name:

3,3-bis[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-1,5-divinyltrisiloxane

Cas Number:

60111-54-8

Molecular formula:

C16H36O4Si5

IUPAC Name:

tetraethenyldimethylsilyl silicate

Test material form:

liquid

Test animals

Species:

rat

Strain:

Crj: CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc., Raleigh, NC
- Females nulliparous and non-pregnant: Yes
- Age at study initiation: approximately 7 weeks
- Weight at study initiation: Between 171 and 307 grams
- Fasting period before study: No
- Housing: 2-3 animals of the same sex and same dosing groups were housed together in polycarbonate, solid-bottom cages containing appropriate bedding material (Bed-O-Cobs® or other suitable material).
- Diet: PMI Nutrition International, LLC Certified Rodent LabDiet 5002, ad libitum. Access to diet was restricted during the conduct of the functional observational battery (FOB) and motor activity (MA) assessments.
- Water: Municipal tap water, treated by reverse osmosis and ultraviolet irradiation, ad libitum.
- Acclimation period: At least 7 days.

DETAILS OF FOOD AND WATER QUALITY: Analysis of the nutritional components and environmental contaminants were provided by the supplier and available at the Testing Facility. Periodic analysis of the water was also performed and available at the Testing Facility. It was considered that there are no known contaminants in the water or the feed that could interfere with the outcome of the study.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20°C - 26°C
- Humidity (%): 30 - 70%
- Air changes (per hr): Not specified
- Photoperiod (hrs dark / hrs light): 12 hours light and 12 hours dark

IN-LIFE DATES: Not specified

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: Dosing formulations were prepared on a weight to volume basis at appropriate concentrations to meet dose level requirements.

VEHICLE
- Justification for use and choice of vehicle: The vehicle was selected in consultation with the sponsor based on the test item’s characteristics.
- Concentration in vehicle: 0, 25, 75, 250 mg/mL
- Amount of vehicle: 4 mL/kg
- Lot/batch no.: 2IH0387
- Purity: Not specified

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

During the first dose samples preparation and the last preparation, duplicate dose formulation samples were obtained from each dose level group for concentration analysis. The samples were analysed by gas chromatography (GC) method using flame ionization detection (FID). Mean sample concentration within 100% ± 15% of theoretical concentration. Each individual sample concentration result was within or equal to ± 20%.
Prestart homogeneity investigation was included on the samples and collected from various levels (top, middle and bottom) of the low and high dose groups. As the test item was shown to be homogenous, samples were not collected during the study for the investigation of homogeneity. Stability and resuspension homogeneity of the test substance formulations were not assessed as it has previously been shown that the test substance formulations were stable and homogenous over the range of concentrations used in the study.

Duration of treatment / exposure:

90 days

Frequency of treatment:

Once daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/kg bw/day (nominal)

Remarks:

Control group

Doses / concentrations 2

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

Low dose group

Doses / concentrations 3

Dose / conc.:

300 mg/kg bw/day (nominal)

Remarks:

Middle dose group

Doses / concentrations 4

Dose / conc.:

1 000 mg/kg bw/day (nominal)

Remarks:

High dose group

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: The doses were based on the results of a previous dose range finding study (Charles River Laboratories, 2020a). In the study, the test substance was administered to 5 male and female rats by oral gavage for 14 consecutive days at doses of 0, 100, 500 and 1000 mg/kg bw/day in corn oil. On day 14, a slightly lower mean body weight (5%) was noted in the 1000 mg/kg bw/day group males. This correlated with a lower cumulative body weight gain (28%, Day 1 to 14) and minimally lower food consumption (8%) over the course of the study compared to the control group. Males in the 500 mg/kg bw/day dose group had slightly lower cumulative body weight gain (12%, Day 1 to 14) and minimally lower food consumption (5%) compared to controls. There were no effects noted in females. Based on these findings, dose levels of 100, 300, and 1000 mg/kg bw/day were selected for the main study with the aim of inducing toxic effects but not death or severe suffering in the highest dose tested.
- Rationale for animal assignment: randomised (based on mean body weight)
- Fasting period before blood sampling for clinical biochemistry: At least 8 hours although not more than 24 hours.
- Rationale for selecting satellite groups: 5 animals/sex from the control and high dose group were selected as satellite groups.
- Post-exposure recovery period in satellite groups: 28 days of recovery
- Section schedule rationale: randomised

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: The health condition of the animals was recorded at least once a day, 0.5 - 3 hours post-dosing, preferably at the same time each day. Twice daily all animals were observed for morbidity and mortality except on days of receipt and necropsy where the frequency was at least once daily.
- Cage side observations checked in table were included: morbidity, mortality, health condition of the animals

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed clinical observations were conducted once prior to the first dosing, then weekly (± 2 days) during the treatment and recovery periods, and on the day of the scheduled necropsies. Detailed clinical observations included examination of posture, convulsions/tremors, biting, palpebral (eyelid) closure, faeces consistency, ease of removal from cage, ease of handling animal in hand, lacrimation/chromodacryorrhea, salivation, piloerection, fur appearance, palpebral closure, respiratory rate/character, red/crusty deposits, mucous membranes/eye/skin colour, eye prominence and muscle tone.

BODY WEIGHT: Yes
- Time schedule for examinations: once prior to the first dosing, then weekly (± 2 days) during the treatment and recovery periods, on the day prior to the first day of scheduled necropsies and on the day of the scheduled necropsies.

FOOD CONSUMPTION AND COMPOUND INTAKE: Yes
- Food consumption was measured once weekly (± 2 days) during the treatment and recovery periods.

FOOD EFFICIENCY: No

WATER CONSUMPTION AND COMPOUND INTAKE: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: before the first administration and in the last week of the treatment period as well as at the end of the recovery period in the recovery animals.
- Dose groups that were examined: all animals.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: At the end of treatment and recovery period as part of the sacrifice of the animals.
- Anaesthetic used for blood collection: Not specified
- Animals fasted: Yes, at least for 8 hours but not more than 24 hours.
- How many animals: All surviving animals.
- Parameters checked in table were examined: Yes, see table 1.
- Other: Blood was taken from the venipuncture from the jugular vein. Anticoagulant K2EDTA was added.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: At the end of treatment and recovery period as part of the sacrifice of the animals.
- Animals fasted: Yes, at least for 8 hours but not more than 24 hours.
- How many animals: All surviving animals.
- Parameters checked in table were examined: Yes, see table 1

URINALYSIS: Yes
- Time schedule for collection of urine: Collected overnight
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes, at least for 8 hours but not more than 24 hours.
- Parameters checked in table were examined: Yes, see table 1

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: During the final week of test substance administration (week 13) and near the end of the recovery period (week 17).
- Dose groups that were examined: All animals in the main study and the recovery group.
- Battery of functions tested:
Open field observations: Time to first step (seconds), mobility, gait, convulsions/tremors, gait score, arousal, bizarre/stereotypic behaviour, rearing. backing, grooming, urination/defecation.
Sensory observations: Approach response, touch response, startle response, tail pinch response, olfactory orientation, pupil response, eyeblink response, forelimb extension, hindlimb extension, air righting reflex.
Neuromuscular observations: Hindlimb extensor strength, grip strength hind and forelimb, rotarod performance, hindlimb foot splay.
Physiological observations: Catalepsy, body temperature, body weight.

IMMUNOLOGY: No

OTHER: Thyroid Hormone Sample Analysis
- Time schedule for examinations: On the day prior to scheduled necropsy and on the day prior to recovery necropsy.
- Method of analysis: For total T3 and T4 analysis, hormone samples were analysed using a validated UHP-LCMS/MS assay. For thyroid stimulating hormone (TSH) analysis, hormone samples were analysed using a validated Luminex Bead-Based (TSH) assay.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 2 & 3)

HISTOPATHOLOGY: Yes (see table 3)

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, unless otherwise noted. For body weight, body weight gains, food consumption, haematology, coagulation, clinical chemistry, urinalysis, organ weights and organ weight relative to body/brain weight used Levene's test. The groups were compared using an overall one-way ANOVA F-test if Levene’s test was not significant or the Kruskal-Wallis test if it was significant. If the overall F-test or Kruskal-Wallis test was found to be significant, then pairwise comparisons were conducted using Dunnett’s or Dunn’s test, respectively. Datasets with 2 groups were compared using a Dunnett’s test equivalent to t-test in Nevis 2012 tables) or Dunn’s test (equivalent to Wilcoxon Rank-Sum test in Nevis 2012 tables). Functional observation battery data, motor activity data, TSH and T3/T4 used the statistical method WTDMS: The groups were compared using an overall one-way ANOVA F-test. If the overall F-test was found to be significant, then pairwise comparisons were conducted using Dunnett’s test. The motor activity ambulatory and total counts data were statistically analysed using SAS Software and/or SAS. All statistical tests were conducted at the 5% significance level and all pairwise comparisons were performed using two-sided tests.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Description (incidence and severity):

There were no test substance related clinical observations. All clinical observations in the test substance treated groups were noted with similar incidence in the control group, were limited to single animals, were not noted in a dose related manner, and/or were common findings for laboratory rats of this age and strain.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One female animal in the 1000 mg/kg bw/day group was found dead on Day 63. No gross lesions could be found at necropsy. Congestion of the adrenal gland, kidney, lung, mandibular lymph node, ovary, thymus and uterus was noted, however, attributed to post/perimortem changes. The cause of death was not determined, although, the effects were not considered as test substance related.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

Body weights were unaffected by test substance administration. There were no statistically significant differences when the control and test substance treated groups were compared.

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

Food consumption was unaffected by test substance administration. However, some statistically significant differences were observed when the control and test substance-treated groups were compared. However, the differences in food consumption were considered to be due to biological variability and not test substance-related since there was no dose response.

Food efficiency:

not examined

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No ophthalmic lesions indicative of toxicity were observed in any of the test substance treated groups. All findings observed were typical in prevalence and appearance for laboratory rats of this age and strain.

Haematological findings:

no effects observed

Description (incidence and severity):

There were no test substance-related effects observed in the haematology parameters, including the coagulation parameters.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

Clinical chemistry parameters were unaffected by the test substance administration. Any differences, regardless of statistical significance, were not considered test substance-related based on their general overlap of individual mean values with the range of concurrent control, and/or were of a magnitude of change commonly observed in rats under similar study conditions.

Urinalysis findings:

no effects observed

Description (incidence and severity):

Urinalysis parameters were unaffected by the test substance administration. Any differences in urine parameters were not considered test substance related based on their general overlap of individual mean values with the range of concurrent control and/or were of a magnitude of change commonly observed in rats under similar study conditions.

Behaviour (functional findings):

effects observed, non-treatment-related

Description (incidence and severity):

Open field observations, sensory observations, neuromuscular observations and physiological observations were unaffected by test substance administration as no statistically significant difference occurred compared to the control group on weeks 13 and 17 evaluations.
No test substance-related effects were observed in the locomotor activity in any of the animals. However, a statistically significant lower ambulatory count was observed in high dose recovery females on week 17 (towards the end of recovery period) for the 0-10 minutes interval. However, no other indications of reduced activity occurred on weeks 13 or 17 therefore the incident was regarded as not test substance-related.

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

In the 1000 mg/kg bw/day male group, mean absolute brain weight was lower than the mean control brain weight. However, this was only observed in one sex, lacked histologic correlations and was within the historical control database range of values. Therefore, the effect was not observed as test substance related. Other isolated organ weight values that were statistically different from their respective controls occurred. Although, no patterns, trends or correlating data could be established to suggest these values were toxicologically relevant. Thus, the organ weight differences observed were considered incidental and/or related to difference of sexual maturity and unrelated to administration of the test substance.

In the recovery group, isolated organ weight values were statistically different from their respective controls. Mean ovary/oviduct weights (absolute and relative to terminal body weight and brain weight) were higher in the 1000 mg/kg bw/day female group than in controls, however, lacked histologic and gross correlations and were not present at the terminal euthanasia. Additionally, mean testis weight (relative to brain weight) was higher in the 1000 mg/kg bw/day male group than in the control group. Nevertheless, this was not evident in absolute weight or weight relative to terminal body weight, lacked gross/histologic correlates and was not observed at the terminal euthanasia. Additionally, no other patterns, trends, or correlating data was established to suggest these values were toxicologically relevant. Thus, the organ weight differences observed were considered incidental and/or related to difference of sexual maturity and unrelated to the administration of the test substance.

Gross pathological findings:

no effects observed

Description (incidence and severity):

No test substance-related effects were observed in any dose groups.

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

Adrenal glands: minimal to moderate adrenal cortical vacuolation was noted in 6 out of 10 males i n the 1000 mg/kg bw/day group and mild to moderate cortical vacuolation in 3 out of 10 males in the 300 mg/kg bw/day group. Females in either group were not affected. Minimal or mild cortical hypertrophy y was noted in 2 out of 10 males in the 1000 mg/kg bw/day group and minimal to moderate hypertrophy was noted in 5 out of 10 males in the 300 mg/kg bw/day group. There were no instances in the control group males. Low incidences of cortical hypertrophy were present in control and treated group females, although, this did not rise above background levels. Adrenal cortical vacuolation and hypertrophy are common incidental findings and due to the low severity and lack of other histologic changes were considered non-adverse in this study.
Lungs: The lungs were examined as potential target tissues due to the presence of mixed inflammation in the 1000 mg/kg bw/day group males and females at the terminal euthanasia. Evaluation of low- and middle dose groups at the terminal euthanasia and control and high-dose groups at the recovery euthanasia revealed that minimal to moderate infiltration and inflammation occurred at low levels across control and treated groups. This was characterised by mixed cell, mononuclear, histiocytic or granulomatous reactions. All findings were considered a spectrum of effects most likely secondary to accidental inhalation of vehicle or test substance during gavage or related to some other aspect of the experimental procedure. There was no clear dose relationship in incidence or severity of the findings and therefore, considered as incidental and not test substance related.

Histopathological findings: neoplastic:

no effects observed

Other effects:

effects observed, non-treatment-related

Description (incidence and severity):

No test substance-related effects were observed in the total amount of T3, T4, or TSH. However, statistically significantly lower T4 was noted in the 300 and 1000 mg/kg bw/day group males on day 90. Upon review, it was noted that the control value was artificially elevated due to the value in a single male. When this male was excluded, the values for the 300 and 1000 mg/kg bw/day group males were consistent with the concurrent control group. Therefore, this difference was not considered as test substance-related.
Additionally, statistically significantly higher T4 was noted in the 1000 mg/kg bw/day group females on day 118. This difference was attributed to a lower mean concurrent control value due to 3 control females with individual values below 20000 pg/mL and not a test substance-related effect. Furthermore, individual TSH samples across all groups were noted as result unobtainable (RU). These samples often had a high replicate variability and therefore, did not produce an acceptable result across the 3 separate occasions of analysis. The variability was considered to be due to a suspected matrix effect.

There were no test substance-related effects on the oestrous cycle for females at any dose level when evaluated prior to the terminal necropsy.

Effect levels

Key result

Dose descriptor:

NOAEL

Effect level:

>= 1 000 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse effects observed

Target system / organ toxicity

Critical effects observed:

no

Applicant's summary and conclusion

Conclusions:

In a repeated dose 90-day oral toxicity study, conducted according to OECD Test Guideline 408 and in compliance with GLP, the NOAEL for systemic effects was concluded to be ≥1000 mg/kg bw/day based on no adverse effects observed up to the highest dose tested.