1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Remarks:

Type of genotoxicity: chromosome aberration

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995-04-18 to 1995-05-03

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Version / remarks:

1981

Deviations:

yes

Remarks:

1000 cells examined for PCE/NCE

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane

EC Number:

241-881-3

EC Name:

1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane

Cas Number:

17955-88-3

Molecular formula:

C15H38O2Si3

IUPAC Name:

2,2,4,6,6-pentamethyl-4-octyl-3,5-dioxa-2,4,6-trisilaheptane

Test material form:

other: liquid

Test animals

Species:

mouse

Strain:

other: Crl: CD1 (ICR)BR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, United States
- Age at study initiation: 8 weeks old
- Weight at study initiation: 27.0-36.1 and 21.8-27.1 g for males and females, respectively
- Assigned to test groups randomly: [no/yes, under following basis: ]
- Fasting period before study:
- Housing: The animals were housed 7 per cage during quarantine and 3 to 5 during randomization.
- Diet: commercial diet, ad libitum
- Water: water, ad libitum
- Acclimation period: 7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°F): 72 +/- 6 °F
- Humidity (%): 55 +/- 15 %
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

intraperitoneal

Vehicle:

- Vehicle(s)/solvent(s) used: the test substance was administered undiluted, however saline was used as a vehicle control
- Lot/batch no. (if required): C271379

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: 501, 1670, 2756, 3925 and 5010 mg/kg were administered to 3 males and 3 females per dose by intraperitoneal injections for the dose selection study. All animals were examined daily for signs of toxicity or mortality during the 3-day study period.

Duration of treatment / exposure:

72 hours

Frequency of treatment:

Intraperitoneal injections were made at 24, 48 and 72 hours

Post exposure period:

Test animals and vehicle control animals were euthanised at 24, 48 and 72 hours after dosing for extraction of the bone marrow. Positive control animals were euthanised at 24 hours after dosing.

Doses / concentrations

Remarks:

Doses / Concentrations:
1253, 2505, 5010 mg/kg bw
Basis:
actual ingested

No. of animals per sex per dose:

Test group: 5 males and 5 females per dose

Control animals:

yes, concurrent vehicle

Positive control(s):

cyclophosphamide
- Justification for choice of positive control(s): no data
- Route of administration: oral gavage
- Doses / concentrations: 80 mg/kg bw

Examinations

Tissues and cell types examined:

Bone marrow

Details of tissue and slide preparation:

CRITERIA FOR DOSE SELECTION: Based on the results from dose range-finding study the maximum tolerated dose was concluded to be 5000 mg/kg bw and the chosen doses for the main study were 1253, 2505, 5010 mg/kg bw.

TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields): Dosed were administered at 24, 48 and 72 hours. Samples were obtained at 24, 48 and 72 hours.

DETAILS OF SLIDE PREPARATION: The marrow was flushed from the bone and transferred to centrifuge tubes containing 3-5 mL bovine serum. Following centrifugation to pellet the tissue, the supernatant was removed by aspiration and portions of the pellet were spread on slides and air dried. The slides were fixed in methanol, and stained in May-Grunwald solution followed by Giemsa. The air-dried slides were coverslipped using Depex mounting medium.

METHOD OF ANALYSIS: The slides were scored for micronuclei and the polychromatic erythrocyte (PCE) to normochromatic erythrocyte (NCE) cell ratio. 1000 PCE were scored per animal. The frequency of micronucleated cells was expressed as percent micronucleated cells based on the total PCEs present in the scored optic field. The normal frequency of micronuclei in this strain is approximately 0.0-0.4 %. The frequency of PCEs versus NCEs was determined by scoring the number of PCEs and NCEs observed in the optic fields while scoring the first 1000 erythrocytes.

Evaluation criteria:

A test article that induced neither a statistically significant dose response nor a statistically significant and reproducible increase at one dose lever was considered negative.

Statistics:

- ANOVA was performed on the proportion of cells with micronuclei per animal
- Tukey's Studentized range test was used at each harvest time to determine which dose groups were significantly different from the control group

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Toxicity:

no effects

Vehicle controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RESULTS OF RANGE-FINDING STUDY
- Dose range: 501, 1670, 2756, 3925 and 5010 mg/kg bw
- Clinical signs of toxicity in test animals: all animals appeared normal immediately after dosing and throughout the 3-day study period
- Evidence of cytotoxicity in tissue analyzed: the PCE/NCE ratio was unchanged in treated animals.
- Other: Based on the results the maximum tolerated dose was concluded to be 5000 mg/kg bw

RESULTS OF DEFINITIVE STUDY
- Induction of micronuclei (for Micronucleus assay): no significant increase in micronucleated PCEs was observed in any of the test animals at any of the harvest times.
- Ratio of PCE/NCE (for Micronucleus assay): mean PCE/NCE ration males 0.62; man PCE/NCE ratio female 0.53
- Appropriateness of dose levels and route: yes
- Statistical evaluation: no statistically significant increase in micronucleated cells in bone marrow polychromatic erythrocytes was observed.

Any other information on results incl. tables

Table 1: Summary of results on micronucleus data

Treatment	Dose	Harvest time (hours)	Total % of micronucleated PCEs mean of 1000 per animal	Mean ratio PCE/NCE
				Males	Females
Vehicle	Saline	24	0.02	0.66	0.55
		48	0.01	0.62	0.60
		72	0.01	0.51	0.57
Positive control	CP 80 mg/kg bw	24	2.18	0.63	0.58
Test substance	1253 mg/kg bw	24	0.03	0.79	0.43
		48	0.00	0.61	0.46
		72	0.00	0.48	0.56
	2505 mg/kg bw	24	0.05	0.63	0.53
		48	0.02	0.55	0.61
		72	0.02	0.56	0.55
	5010 mg/kg bw	24	0.04	0.67	0.65
		48	0.02	0.84	0.45
		72	0.00	0.51	0.53

CP: cyclophosphamide

Applicant's summary and conclusion

Conclusions:

Interpretation of results: negative
1,1,1,3,5,5,5-Heptamethyl-3-octyltrisiloxane has been tested for ability to induce micronuclei in mouse bone marrow polychromatic erythrocytes, conducted according to OECD TG 474 with acceptable restrictions, and in compliance with GLP (CHV, 1995). No increase in the number of micronuclei was observed when test substance was administered by intraperitonal injection up to limit concentration. No toxicity to bone marrow was observed when evaluated by the ratio of polychromatic erythrocytes to normochromatic erythrocytes. Appropriate solvent and positive controls were included and gave expected results. It is concluded that the test substance is negative for the induction of micronuclei under the conditions of this study.