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Toxicological information

Genetic toxicity: in vivo

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Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
See endpoint summary for justification of read-across.
Cross-reference
Reason / purpose:
read-across source
Reference
Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1982-04-21 to 1982-05-14
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
The deviations are that only 1000 cells were scored compared with 2000 in current guideline.
Reference:
Composition 0
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
Deviations:
yes
Remarks:
1000 cells scored
Principles of method if other than guideline:
Micronucleus test in vivo: Matter and Schmid, 1971, Mut. Res. 12: 417-425.
GLP compliance:
yes
Type of assay:
micronucleus assay
Test material information:
Composition 1
Species:
rat
Strain:
Sprague-Dawley
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS

- Source: Spartan Research Laboratories, Inc. Harlet, MI

- Weight at study initiation: 100 to 175 grams

- Housing: Animals housed individually

- Diet (e.g. ad libitum): PURINA Rodent Laboratory Chow (ad libitum)

- Water (e.g. ad libitum): ad libitum
Route of administration:
inhalation
Vehicle:
- Vehicle(s)/solvent(s) used: air

- Concentration of test material in vehicle: 100 ppm
Details on exposure:
TYPE OF INHALATION EXPOSURE: nose only

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION

- Exposure apparatus: specially constructed glass chamber

- System of generating particulates/aerosols: vapours were generated by bubbling clean, dry air through the liquid test material
Duration of treatment / exposure:
4 hour(s)
Frequency of treatment:
Single 4 hour exposure
Post exposure period:
30 hours
Dose / conc.:
100 ppm (nominal)
No. of animals per sex per dose:
5 animals per dose level
Control animals:
yes, concurrent no treatment
Positive control(s):
triethylenemelamine

- Route of administration: split-dose intraperitoneal injection (0 and 24 hours)

- Doses / concentrations: 0.5 mg/kg/dose
Tissues and cell types examined:
Animals were exposed to the test article by acute inhalation. They were sacrificed, the bone marrow is extracted and smear preparations made and stained. Polychromatic erythrocytes are scored for micronuclei under the microscope. Both positive and negative (solvent) controls are used in each experiment.
Details of tissue and slide preparation:
At sacrifice the adhering soft tissue and epiphyses of both tibiae were removed. The marrow was aspirated from the bone and transferred to centrifuge tubes containing 5 ml fetal calf serum (one tube for each animal). Following centrifugation to pellet the tissue, the supernatant was drawn off and portions of the pellet was spread on slides and air-dried. The slides were then stained in May-Gruenwald Solution and Giemsa. A thousand polychromatic erythrocytes (PCEs) per animal were scored. The frequency of micronucleated was expressed as percent micronucleated cells based on the total PCEs present in the scored optic field.
Evaluation criteria:
In the normal animal, the normocytes/PCE's is approximately 2. If an agent inhibits the proliferation of erythroblasts the proportion of PCE's is generally reduced. If the agent promotes chromosome breakage or acts as a spindle poison, generally the proportion of red normocytes increases.
Statistics:
Mean normocyte and polychromatic erythrocytes calculated as well as ratio of normocytes to PCE's. Student T-test was used to confirm no difference between the PCE MN count for study groups A(treated) and D(control).
Sex:
female
Genotoxicity:
negative
Toxicity:
yes
Vehicle controls valid:
yes
Negative controls valid:
yes
Positive controls valid:
yes
Additional information on results:
RESULTS OF RANGE-FINDING STUDY

- Dose range: 100 ppm

- Clinical signs of toxicity in test animals: To ensure that the Micronucleus Assay was performed on animals exposed to a lethal concentration of the test material (Group A), a second group of animals (Group B) was simultaneously exposed to the chemical via inhalation as a positive control for lethality. The data demonstrates that both groups (A&B) was exposed to a lethal concentration of the test material. All five animals in Group B experienced weight loss and died within the 14 day observation period. At autopsy all five animals showed extensive lung damage with haemorrhage and atelectasis. Animals exposed via inhalation to the test material all showed slight to moderate evidence of lung damage in the form of petechial haemorrhage and focal atelectasis. Some evidence of kidney congestion was noted in several animals. No abnormal pathology was evident in either the positive control (C) or negative control (D) groups.

- Evidence of cytotoxicity in tissue analyzed: The ratio of normocytes to PCE's obtained with both the test material treatment (Group A = 10.64) and the negative control (Group D = 10.28) closely approximate the normal expected ratio and were fairly consistent. The mean normocyte count from the positive control group was elevated (Group C = 19.4) indicating that the animals responded to a known clastogen (chromosome breaking agent). This same trend verified by the increase in percentage of micronucleated PCEs in the positive control group.

- Harvest times: Group A (Treatment group): 30 hours after exposure. Group C (Positive Control): 30 hours. Group D (Negative Control): 30 hours.

- High dose: 100 ppm

RESULTS OF DEFINITIVE STUDY

- Induction of micronuclei (for Micronucleus assay): Within normal range for all groups

- Ratio of PCE/NCE (for Micronucleus assay): Within normal range for all groups

- Statistical evaluation: Comparison of the study groups by Student T-test using a SAS computer program confirms there is no difference between the mean PCE micronucleus count for study groups A and D (test article and negative control) (<.0001) while the positive control is definitely positive (p>0.5) compared to the former groups.

 The following table indicates that the animals responded to the positivecontrol substance. Both normocytes/PCE **  ratio and % of micronucleated PCEs weresignificantly increased in the positive control group when compared to test material-treated group.

Table 3 : Mean Results of in vivo micronucleus test with mouse bone marrow

 

Test Group

(A)

Positive Control (C)

Negative Control (D)

Number of cells evaluated

1000

1000

1000

Sampling time (h)

30h

30h

30h

Number of erythrocytes

Normocytes / Field

10.64

19.4

10.28

PCE / Field

4.36

4.56

4.36

Micronuclei / 1000 PCE

6.8

39.2

5.6

Ratio of erythro­cytes

Normochromatic / polychromatic

2.52

4.38

2.39

% Micronucleated PCE

0.68

3.92

0.56

 

Conclusions:
Interpretation of results (migrated information): negative
Under test conditions, trimethoxysilane did not induce chromosome breakage or act
as a spindle poison in the rodent micronucleus assay even
when animals were exposed to lethal concentrations. There is no evidence from this study that the mechanism of kill at
toxic levels of exposure involves genotoxicity. The test substance is non-mutagenic in Sprague-Dawley rats in this mammalian micronucleus assay.

Data source

Materials and methods

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: liquid

Results and discussion

Test results
Sex:
female
Genotoxicity:
negative
Toxicity:
yes
Remarks on result:
other: Micronucleus assay

Applicant's summary and conclusion