1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane

Toxicity to reproduction: other studies

Administrative data

Endpoint:

toxicity to reproduction: other studies

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20.11.2006 to 28.09.2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2007

Report date:

2007

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD 440: Uterotrophic Bioassay in Rodents

Deviations:

yes

Remarks:

(inhalation is not a recommended route of administration; only one concentration was tested)

Principles of method if other than guideline:

The objective of the study was to evaluate the potential estrogenic and anti-estrogenic effects of octamethyltrisiloxane using ovariectomized adult Sprague-Dawley rats in the rodent uterotrophic assay (RUA).

GLP compliance:

yes

Type of method:

in vivo

Test material

Test material information

Constituent 1

Reference substance name:

Reference substance 002

Cas Number:

107-51-7

Constituent 2

Reference substance name:

Octamethyltrisiloxane

EC Number:

203-497-4

EC Name:

Octamethyltrisiloxane

Cas Number:

107-51-7

Molecular formula:

C8H24O2Si3

IUPAC Name:

octamethyltrisiloxane

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles Rivers Laboratories Inc (Portage, MI)
- Age at study initiation: 6 weeks (at the time of ovariectomization - surgery performed by the supplier) ; 62 days at start of exposure
- Weight at study initiation: Females: 251g (at the time of randomization, one day prior to study start)
- Fasting period before study: no
- Housing: individually housed in suspended wire-mesh cages above fecal pans contained Bed-O'Cobs bedding
- Use of restrainers for preventing ingestion (if dermal): not applicable
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: quarantine 7 days; acclimation at least 14 days following surgery; chamber acclimation 4 days prior to start of exposure

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.0 -22.9
- Humidity (%): 35-57
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12:12

IN-LIFE DATES: From: 6-Dec-2006 To: 15-Mar-2007

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: clean air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 2000-litre stainless steel and glass rochester-stye inhalation chambers and stainless steel exposure caging (4 layers of 20 compartments; rotated daily
- Method of holding animals in test chamber: cage
- Source and rate of air: Chamber: building air supply passed through HEPA and activated charcoal filters; Test article carrier: compressed air passed through a series of filters;
- System of generating particulates/aerosols: J-tube vaporization
- Temperature, humidity, pressure in air chamber: 20.8-25.2°C; 42.5-64.6% humidity
- Air change rate: 10-15 air changes of chamber volume per hour
- Method of particle size determination: no data
- Treatment of exhaust air: no data

TEST ATMOSPHERE
- Brief description of analytical method used: automated sampling system analysed by gas chromatography and flame ionization detection and each chamber was evaluated at least once per hour during the exposure period.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Test atmosphere: automated sampling system analysed by gas chromatography and flame ionization detection and each chamber was evaluated at least once per hour during the exposure period.

Positive (genistein and 17-alpha-ethinyl estradiol) and negative (ICI 182,780) controls - analytical analysis of solutions by HPLC

Duration of treatment / exposure:

Six hours

Frequency of treatment:

Daily

Duration of test:

Three days

Doses / concentrations

Dose / conc.:

3 500 ppm

Remarks:

target

No. of animals per sex per dose:

Eight

Control animals:

other: corn oil, subcutaneously... (see attached file)

Details on study design:

The potential estrogenic and anti-estrogenic activity of octamethyltrisiloxane was studied in Sprague Dawley rats using the rodent uterotrophic assay. Ovariectomized rats were exposed to 3500 ppm octamethyltrisiloxane for 6 hours/day for 3 days. Additional groups of animals were treated subcutaneously with 17alpha-ethinyl estradiol (EE) (0.3, 1.0 or 3.0 µg/kg bw/day) or genistein (10, 25, 50 mg/kg bw/day) followed by whole body inhalation exposure to filtered air for 6 hours/day for three consecutive days. A final group of animals was given a combination of the estrogen receptor antagonist ICI 182,780 (3 mg/kg bw/day) and EE (3.0 µg/kg bw/day) for comparison as a positive control. All animals were necropsied following the last exposure on the day 3 and the uterus removed and weighed with and without uterine fluid.

Statistics:

ANOVA, Dunnet's test. SAS version 9.1.3 (2006) statically significant probabilities were reported for p-values of <0.05, <0.02 and <0.01

Results and discussion

Effect levels

Key result

Dose descriptor:

NOAEC

Effect level:

>= 3 500 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: 3500 ppm is equivalent to 33.9 mg/l. No uterotrophic effects at this exposure concentration (the only level tested).

Observed effects

There were no unscheduled deaths during the study. There were no clinical signs of toxicity and no effects on body weight. The EE and genistein treatment resulted in the anticipated increase in absolute uterine wet and blotted weight. There was a significant increase in uterine wet and blotted weight at all doses (p<0.01). The wet and blotted uterine weights of the octamethyltrisiloxane-treated group were not significantly increased over the corn oil control group. When the uterine weights, both wet and blotted were normalised to terminal body weight, the EE and genistein treatments showed a significant increase over corn oil control values at all doses (p<0.01). The normalised uterine weights of the octamethyltrisiloxane-treated group were not significantly increased over the control group. The luminal and glandular epithelial cell height was significantly increased for all doses of EE and genistein (p<0.01). Octamethyltrisiloxane, did not result in any significant increase in either luminal or glandular epithelial cell height. Group 8, the combination of the pure anti-estrogen ICI with EE demonstrated complete antagonism of the EE estrogenic effects as expected. Cotreatment of EE and octamethyltrisiloxane did not result in any significant decrease in the absolute or relative (wet or blotted) uterine weights or epithelial cell heights compared to the treatment of Group 4, EE at 3 µg/kg bw/day.

Applicant's summary and conclusion

Conclusions:

In a uterotrophic assay conducted using a protocol comparable to OECD test guideline 440 and to GLP (reliability score 1), exposure to 3500 ppm (equivalent to 33.9 mg/l) octamethyltrisiloxane did not result in any increase in wet or blotted uterine weight or changes to the epithelial cell height. When EE and octamethyltrisiloxane were given in combination there were no anti-estrogenic effects observed in the wet or blotted uterine weights or in the epithelial cell heights.

Executive summary:

In a rodent uterotropic assay (comparable with OECD Guideline 440), groups of 8 ovariectomized female Sprague Dawley rats were exposed to an atmospheric concentration of 3500 ppm octamethyltrisiloxane for 6 hours/day for three days. Concurrent groups of animals were treated subcutaneously with the positive controls - ethinyl estradiol (EE; 0.3, 1.0 or 3.0 µg/kg bw/day) and genistein (Gen; 10, 25 or 50 mg/kg bw/day bw/day) - or vehicle control (corn oil), followed by 6 -hour whole body exposure to filtered air for three consecutive days. In order to study the anti-estrogenic effect of octamethyltrisiloxane, further groups were exposed to the anti-estrogenic agent (ICI 182,780; 3 mg/kg bw/day) plus EE at 3 µg/kg bw/day or octamethlytrisiloxane at 3500 ppm plus EE at 3 µg/kg bw/day. All animals were necropsied following the last 6 -hour exposure on day 3 and the uterus removed and weighed with and without uterine fluid. Uterine luminal and glandular epithelial cell heights were determined by microscopic examination.

 

As expected, the positive controls EE and genistein resulted in significant dose-related increases in absolute and relative uterine weights and increases in uterine glandular and luminal cell height. Octamethyltrisiloxane was without effect on these parameters when compared to the corn oil control group.

 

Similarly, octamethyltrisiloxane exhibited no anti-estrogenic effect when co-administered with EE as uterine relative and absolute weights or glandular or luminal epithelial cell heights were unaffected when compared to EE administered alone. The positive control (ICI 182,780 plus EE) showed an anti-estrogenic effect.

In conclusion, octamethyltrisiloxane did not induce estrogenic or anti-estrogenic effects in the rodent uterotrophic assay following inhalation exposure of rats at 3500 ppm.