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Toxicological information

Genetic toxicity: in vivo

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Administrative data

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
experimental study
Adequacy of study:
key study
Study period:
27 October 1987 - 03 January 1988
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1988
Report Date:
1988

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
GLP compliance:
yes (incl. certificate)
Type of assay:
micronucleus assay

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): isobutyltriethoxysilane

- Physical state: clear colourless liquid

- Storage condition of test material: in closed bottles (hydrolysis by humidity)

Test animals

Species:
mouse
Strain:
CD-1
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River UK, Limited Margate, Kent, England
- Weight at study initiation: 22-24 grams
- Assigned to test groups randomly: yes
- Fasting period before study: overnight prior to dosing and for two hours after dosing
- Housing: Each group of 2 or 5 mice was kept in a plastic disposable cage
- Diet: Labsure LAD 1 rodent breeding diet, ad libitum
- Water: tap water, ad libitum
- Acclimation period: ca. 4 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22
- Air changes (per hr): 30
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
- Vehicle(s)/solvent(s) used: corn oil
Details on exposure:
The isobutyltriethoxysilane treated groups were dosed with varying dose volumes up to a maximum administrable volume of 10 ml/kg bodyweight. The negative control compound, corn oil, was dosed at the standard dose volume of 10ml/kg bodyweight. Mitomycin C, the positive control compound was dosed at the standard dose volume of 20 ml/kg bw. The animals were deprived of diet overnight prior to and for two hours after oral dosing.
Duration of treatment / exposure:
Single exposure.
Frequency of treatment:
Single administration.
Post exposure period:
Five males and five females from the vehicle control and test compound groups were sacrificed 24, 48 and 72 hours after dosing. The positive control group was sacrificed 24 hours after dosing.
Doses / concentrations
Dose / conc.:
8 800 mg/kg bw (total dose)
Remarks:
preliminary toxicity study
No. of animals per sex per dose:
15M, 15F - negative control
15+4* M, 15+4* F - isobutyltriethoxysilane
5M, 5F - positive control
Control animals:
yes
Positive control(s):
mitomycin C

- Route of administration: gavage
- Doses / concentrations: 20 ml/kg bw

Examinations

Tissues and cell types examined:
bone marrow
Details of tissue and slide preparation:
CRITERIA FOR DOSE SELECTION: From the results obtained in the preliminary toxicity study, a dosage of 8800 mg/kg bw was chosen for the micronucleus test.

TREATMENT AND SAMPLING TIMES (in addition to information in specific fields): Following dosing the animals were examined regularly, and any mortalities or clinical signs of reaction to the test compound were recorded. Five males and five females from the negative control and test compound groups were sacrificed 24, 48 and 72 hours after dosing. The positive control group were sacrificed 24 hours after dosing. The animals were killed by cervical dislocation and both femurs dissected out from each animal. The femurs were cleared of tissue and one epiphysis removed from each bone.

DETAILS OF SLIDE PREPARATION: A direct bone marrow smear was made onto a slide containing a drop of calf serum. One smear was made from each femur. The prepared smears were air-dried and fixed in methanol (>10 minutes) and air dried. After rinsing in buffered distilled water (pH 6.8) the smears were air-dried and stained for 10 minutes in 10% Giemsa. Following rinsing in distilled water, the smears were differentiated in buffered distilled water (pH6.8) for 10n minutes. After air-drying, the smears were mounted with cover slips using DPX.

METHOD OF ANALYSIS: The stained smears were examined by light microscopy to determine the incidence of micronucleated cells per 1000 polychromatic erythrocytes per animal. The ratio of polychromatic to normochromatic erythrocytes for each animal was assessed by examination of at least 1000 erythrocytes.

Statistics:
The test substance did not cause any statistically significant increases in the number of micronucleated polychromatic erythrocytes at any of the three kill times - p>0.05 using Wilcoxons' sum of ranks test.

Results and discussion

Test results
Key result
Sex:
male/female
Genotoxicity:
negative
Toxicity:
no effects
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
RESULTS OF RANGE-FINDING STUDY
- Dose range: 880-8800 mg/kg
- Clinical signs of toxicity in test animals: none


RESULTS OF DEFINITIVE STUDY
- Induction of micronuclei (for Micronucleus assay): At all sampling times, mice treated with the test material showed no significant increase in the frequency of micronucleated polychromatic erythrocytes. However, at the 48 hour sampling time, a small but statistically significant decrease in the ratio of polychromatic to normochromatic erythrocytes was observed. However no other decreases were observed at any other sampling time and therefore this decrease is not considered to be of sufficient magnitude to indicate bone marrow cell toxicity.
- Ratio of PCE/NCE (for Micronucleus assay): The test substance did not cause any statistically significant increases in the number of micronucleated polychromatic erythrocytes. Mitomycin (positive control) caused large, highly significant increases (p<0.001) in the frequency of micronucleated polychromatic erythrocytes.

Any other information on results incl. tables

Table 1:Summary of results of in vivo micronucleus test with group totals/means for the entire experiment and results of statistical analysis

Kill

Compound & Dosage

Ratio p/n

Incidence mnp

Incidence mnn

Mean

P

Mean 0/00

P

Total 0/00

 24h

 Negative control

Isobutyltriethoxysilane(8800 mg/kg)

Mitomycin C (12 mg/kg)

0.749

0.657

0.451

-

0.157

0.014

0.3

0.3

32.4

-

0.616

<0.01

0.3

0.0

1.5

48h

 Negative control

Isobutyltriethoxysilane(8800 mg/kg)

0.831

0.619

-

0.038

0.0

0.3

-

0.241

0.2

0.1

 72h

 Negative control

Isobutyltriethoxysilane(8800 mg/kg)

0.933

0.831

-

0.095

0.1

0.2

-

0.370

0.2

0.2

P           Result of statistical analysis usingWilcoxon’ssum of ranks test (1-sided probabilities)      

p/n        Ratio of polychromatictionormochromaticerythrocytes

mnp     number of micronucleated polychromatic erythrocytes observed

mnn     number of micronucleated normochromaticerythrocytes observed

0/00     number per thousand cells           

Applicant's summary and conclusion

Conclusions:
Triethoxyisobutylsilane has been tested for the induction of micronuclei in mice according to OECD TG 471 and under GLP conditions. No evidence was seen of a test substance related increase in the incidence of micronucleated polychromatic erythrocytes in mice bone marrow. The ratio of normochromatic to polychromatic erythrocytes was not affected by the test substance indicating lack of toxicity to bone marrow cells. It is concluded that the test substance does not cause damage to chromosomes under the conditions of the test.