1,1,3,3-tetramethyldisiloxane

Toxicity to reproduction

Administrative data

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

10-06-2008 to 12-08-2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2009

Report date:

2009

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Dimethylsilanediol

EC Number:

213-915-7

EC Name:

Dimethylsilanediol

Cas Number:

1066-42-8

Molecular formula:

C2H8O2Si

IUPAC Name:

dimethylsilanediol

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Inc, NC
- Age at study initiation: Minimum nine weeks
- Weight at study initiation: Males: 231.5 to 255.7 g ; Females: 167.0 to 198.8 g
- Fasting period before study: No
- Housing: Individually in suspended wire-mesh cages. Pregnant females were housed in shoebox-type cages.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: Five days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.19-23.24
- Humidity (%): 50-67
- Air changes (per hr): 13.3
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 15-06-2008 To: 25-02-2009

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:DMSD was ground to a fine powder using a mortar and pestle. Dosing solutions were prepared by weighing the appropriate amount of the test substance into a tared container and adding the appropriate amount of corn oil to yield the desired dose level. Solutions were prepared every seven days, based on the stability of the test substance in corn oil.

VEHICLE
- Justification for use and choice of vehicle (if other than water): Most appropriate based on physical and chemical properties of test substance.
- Concentration in vehicle: Not given
- Amount of vehicle (if gavage): Total volume 5ml//kg
- Lot/batch no. (if required): 117K0127
- Purity: No data, used as provided.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: Up to two weeks
- Proof of pregnancy: vaginal plug / sperm in vaginal smear referred to as day 0 of pregnancy
- Further matings after two unsuccessful attempts: no, not required
- After successful mating each pregnant female was caged (how): individually in shoe-box type cage

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

A GC/FID method was used to verify concentration, stability and homogeneity of the test substance in corn oil. Concentration verification was conducted for the initial dose preparations.

Duration of treatment / exposure:

Toxicity group males and females were treated for 28 and 29 days, respectively. Reproductive phase females were treated to post-partum day 3.

Frequency of treatment:

Daily

Details on study schedule:

Not applicable as screening study.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

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

Doses / concentrations 2

Dose / conc.:

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

Doses / concentrations 3

Dose / conc.:

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

Doses / concentrations 4

Dose / conc.:

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

No. of animals per sex per dose:

Ten females in toxicity group; ten females in reproductive toxicity group; ten males to determine reproductive and toxicological endpoints.

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on the results of a range-finding study.
- Rationale for animal assignment (if not random): Random

Positive control:

None

Examinations

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Once before first dose, and then weekly. Skin, fur, eyes, mucous membranes, occurrence of secretions and excretions and autonomic ctivity (lacrimation, piloerection, pupil size, unusual respiratory pattern). Changes in gait, posture and response to handling as well as the presence of clonic or tonic movements, stereotypies (for example excessive grooming and repetitive circling), difficult or prolonged parturition or bizarre behaviour (such as self mutilation, walking backwards) were recorded.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were determined beginning with randomisation into the test groups, on the first day of dosing, at least weekly thereafter, and on the day of sacrifice. During gestation, the reproductive females were weighed on gestation days 0, 7, 14 and 20, within 24 hours of parturition, and on post-partum day four.

FOOD CONSUMPTION: For males, feeder weights were taken on days 1, 8 and 15 during the pre-mating period. For reproductive group females, feeder weights were taken on days 1, 8, 15, and on gestation days 0, 7, 14, 20 and on post-partum days 0 and 4.

OTHER: The duration of gestation was calculated from day 0 gestation for each female. From gestation day 20 after evidence of mating, pregnant animals were checked at least three times daily (twice daily on weekends and holidays) for evidence of parturition. If difficulties were observed, progress of the parturition process was monitored.

Oestrous cyclicity (parental animals):

Not applicable - screening study

Sperm parameters (parental animals):

Parameters examined in male parental animals: testis weight, epididymis weight, prostate gland weight

Litter observations:

STANDARDISATION OF LITTERS
- Performed on day 4 postpartum: Not applicable - screening study

PARAMETERS EXAMINED
The following parameters were examined in offspring: number and sex of pups, stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain, physical or behavioural abnormalities, other:]


GROSS EXAMINATION OF DEAD PUPS:
[no / yes, for external and internal abnormalities; possible cause of death was/was not determined for pups born or found dead.]

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals after 28 days treatment
- Maternal animals: All surviving animals on day 4 post-partum (toxicity group after 29 days treatment)


GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.


HISTOPATHOLOGY / ORGAN WEIGHTS
The tissues indicated in Table 2 of Section 7.5.1 were prepared for microscopic examination and weighed, respectively.

Postmortem examinations (offspring):

SACRIFICE
- The F1 offspring on post-partum day 4.

GROSS NECROPSY
- Gross necropsy consisted of an external examination only.

HISTOPATHOLOGY / ORGAN WEIGTHS: Not conducted

Statistics:

See section 7.5.1

Reproductive indices:

Each litter was examined as soon as possible after delivery to determine the number and sex of the pups, the number of pups alive, number of dead pups, runts, and the presence of any gross abnormalities. Pups were counted and sexed and litter weights were taken within 24 hours of parturition and on day 4 post-partum. The day parturition was observed as complete was considered day 0 post-partum. Any abnormal behavior of the offspring was recorded.

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Abdominal soiling and urogenital soiling were significant abnormal observations in the reproductive group females at 500 mg/kg bw/day.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

All but one animal survived to their scheduled necropsy. The animal that died was euthanised following a dosing injury.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

There were no statistically significant differences across exposure groups for mean body weights. There were no statistically significant differences in body weight gain for the reproductive females in any of the treatment groups during any of the measured intervals. There were no differences in the average daily food consumption.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

There were no differences in the average daily food consumption across treatment groups for the reproductive females group or the toxicity female group for any of the measured time periods. In the male group there was a significant difference across treatment groups in week 2, however, there was not a significant difference between control and any of the treatment groups for that week.

Food efficiency:

not specified

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

There were no significant differences noted in the other hematology values or hematology differential data across groups for either sex. No toxicological significance is assigned at this time to any statistically identified differences in hematology parameters since the findings were within or slightly below historical control ranges for this laboratory and the findings did not correlate with a pathological outcome.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

There were dose-related decreases in male and female alkaline phosphatase and total bilirubin values as well as a dose related decrease in male aspartate aminotransferease values. No toxicologic significance was assigned to any statistically identified differences in clinical pathology since findings were within or slightly below historical control ranges for this laboratory and the findings did not correlate with a pathological outcome.

Urinalysis findings:

not specified

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

No statistically significant differences between the control and treatment groups in either sex at the treated time point for all the FOB ranked tests, except for an increase in defecation (males) at 500 mg/kg bw/day at a significance of p <0.05. There was no dose response associated with this effect, nor did it correlate with any change in the other neurobehavioral tests conducted on the same animals. There were no statistically significant differences between either male or female treatment groups and their respective controls for the FOB continuous test and motor activity. There were no treatment-related changes associated with dimethylsilanediol administration on rat neurobiological function as evaluated with FOB and motor activity parameters.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Liver: Males
There were two primary liver findings in male rats. In the liver of male rats, the incidence of centrilobular hypertrophy was significantly increased (p <0.01) in 250 and 500 mg/kg bw/day groups (8/10 animals in each group) over control. The increased incidence of centrilobular hypertrophy identified correlates with the statistically significant increase in relative liver weight observed for these groups. This is a common effect of xenobiotic administration and is considered an adaptive change.

Additionally, there was minimal to moderate brown pigment accumulation in and around bile ducts, with associated bile duct hyperplasia and chronic inflammation in 9/10 high-dose males. Under polarised light some pigment accumulations show birefringence. The finding was split into three components and recorded as 1) brown pigment, 2) periportal chronic inflammation, and 3) bile duct hyperplasia associated with brown pigment accumulation. The severity of the inflammatory and bile duct hyperplasia components generally closely matched the pigment accumulation. The brown pigment was not observed in control animals, at lower dose levels, or in female rats. Periportal chronic inflammation (9/10 animals), hyperplasia in the bile ducts associated with brown pigment accumulation (8/10 animals), and brown pigment accumulation (9/10 animals) showed significant increase in incidence (p<0.01) over control only in the 500 mg/kg/day group. For these microscopic findings in the liver, there were no significant shifts in severity across treatment groups.

Females:
In the liver, the incidence of centrilobular hypertrophy was significantly increased (p <0.01) in the 250 and 500 mg/kg bw/day female toxicity groups. The increased incidence of centrilobular hypertrophy identified correlates with the statistically significant increase in relative liver weight observed for these groups. This is a common effect of xenobiotic administration and is considered an adaptive change.

For liver periportal vacuolization, only the 500 mg/kg bw/day toxicity female group was significantly (p <0.02) increased in incidence over the control group. Comparison of the graded animals only showed a significant increase in severity grade across treatment groups for liver vacuolization in females. It is generally but not universally held that this finding in and of itself is not considered adverse unless severe.

Thyroid Gland:
Both the 250 and 500 mg/kg bw/day male toxicity groups (8/10 and 9/10 animals, respectively) had significantly increased incidence (p <0.01) of thyroid gland follicular hypertrophy than did the control group and the comparison of the graded animals showed a significant increase in severity grade across treatment groups. Hypertrophy of the thyroid follicular epithelium is a common secondary response to increased thyroid hormone catabolism due to up-regulation of hepatic microsomal enzymes in response to xenobiotic administration. The rat is particularly sensitive to this effect due to the species’ lack of a protective carrier protein, thyroid binding globulin.

Prostate Gland
The 500 mg/kg bw/day group had a statistically significant increase in incidence (p <0.05) in chronic inflammation of the prostate gland over that seen in the control group. Chronic inflammation of the prostate gland is a fairly common spontaneous finding. This finding is not considered to be attributable to test article administration, particularly since the two most severe instances occurred in rats administered 0 and 50 mg/kg bw/day

Lung
In the lungs of males rats, there was an increasing trend in the observed incidence of pulmonary histiocytosis (aggregates of foamy macrophages). For histocytosis in the lungs there were no pair wise significant differences between any treated group and control. This is a very common spontaneous finding and there was no clear increase in severity associated with dosage. This finding is not considered to be attributable to test article administration.

Histopathological findings: neoplastic:

not examined

Other effects:

not examined

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

Description (incidence and severity):

None of the pair wise comparisons showed a difference between a treated group and control when adjusting for the litter size. The litter size was a significant contributor to explaining any differences in endpoints. There were no treatment-related effects apparent for any of the reproductive endpoints: gestation length, litter size, litter weight, ratio live births/litter size, litter sex ratio, number of implantation sites, number of corpora lutea, mating and fertility indices.

Effect levels (P0)

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

histopathology: non-neoplastic

Target system / organ toxicity (P0)

Critical effects observed:

yes

Lowest effective dose / conc.:

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

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

not specified

Results: F1 generation

General toxicity (F1)

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Food efficiency:

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Sexual maturation:

not examined

Anogenital distance (AGD):

not examined

Nipple retention in male pups:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

not examined

Histopathological findings:

not examined

Developmental neurotoxicity (F1)

Behaviour (functional findings):

not examined

Developmental immunotoxicity (F1)

Developmental immunotoxicity:

not examined

Details on results (F1)

None of the pair wise comparisons showed a difference between a treated group and control when adjusting for the litter size. The litter size was a significant contributor to explaining any differences in endpoints. There were no treatment-related effects apparent for any of the reproductive endpoints: gestation length, litter size, litter weight, ratio live births/litter size, litter sex ratio, number of implantation sites, number of corpora lutea, mating and fertility indices.

Effect levels (F1)

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

>= 500 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No trteatment-related effects observed

Target system / organ toxicity (F1)

Critical effects observed:

no

Overall reproductive toxicity

Reproductive effects observed:

no

Any other information on results incl. tables

See Section 7.5.1 for effects on toxicity group males and females in more detail, including results tables for key findings.

Applicant's summary and conclusion

Conclusions:

In the combined repeated dose toxicity study with the reproduction / developmental toxicity screening test with dimethylsilanediol, conducted according to OECD Test Guideline 422 and in compliance with GLP, the NOAEL for general systemic toxicity was 250 mg/kg bw/day based on hepatic brown pigment accumulation in and around the bile ducts, with associated bile duct hyperplasia and chronic inflammation at 500 mg/kg bw/day, and ≥500 mg/kg bw/day for reproductive and developmental toxicity.