Registration Dossier

Administrative data

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1980-11-26 to 1981-09-28
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
It was not compliant with GLP.

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
1982
Report Date:
1982
Reference Type:
publication
Title:
Genotoxicity studies on selected organosilicon compounds: in vivo assays.
Author:
Isquith, A. et al.
Year:
1988
Bibliographic source:
Food Chem Toxicol 26: 263-266

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)
Deviations:
yes
Remarks:
only male animals used. Number of cells counted for determination of mitotic index not indicated - probably ca. 100, should be 1000
Principles of method if other than guideline:
The test was performed according to the Rodent Bone Marrow Cytogenetic Assay as recommended by the Ad Hoc Committee on Chromosome Methodologies in Mutagen Testing (Toxicology and Applied Pharm 22: 269-275, 1972) with modifications per the EPA Gene-Tox Program Cytogenetics Committee (12/3 to 12/5, 1980, Washington D.C.).
GLP compliance:
not specified
Type of assay:
chromosome aberration assay

Test material

Reference
Name:
Unnamed
Type:
Constituent

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS

- Age at study initiation: 14 - 16 weeks

- Weight at study initiation: 250 - 280 g for range finding. 290 - 430 g for cytogenetic study

- Housing: 6 per cage

- Diet (e.g. ad libitum): Charles River Agway

ENVIRONMENTAL CONDITIONS

- Temperature (°C): 68 ± 3 F

- Humidity (%): approx 50

Administration / exposure

Route of administration:
intraperitoneal
Vehicle:
- Vehicle(s)/solvent(s) used: paraffin oil

- Lot/batch no. (if required): A7M02

- Purity: Laboratory Grade
Duration of treatment / exposure:
single treatment
Frequency of treatment:
Single IP injection
Post exposure period:
6, 24 and 48 hours
Doses / concentrationsopen allclose all
Dose / conc.:
255 mg/kg bw/day (nominal)
Dose / conc.:
515 mg/kg bw/day (nominal)
Dose / conc.:
1 030 mg/kg bw/day (nominal)
No. of animals per sex per dose:
5 males/dose
Control animals:
yes, concurrent vehicle
Positive control(s):
cyclophosphamide, positive control agent, was included in the 24-hour group.  

- Route of administration: IP Injection

- Doses / concentrations: 22 mg/kg bw

Examinations

Tissues and cell types examined:
Bone marrow from femur
Details of tissue and slide preparation:
CRITERIA FOR DOSE SELECTION: Based on two range finding studies conducted to determine the maximum dose the animals could tolerate.


Range finding studies: Range finding study 1: Animals Injected intraperitoneally with 1676, 504, 168 and 50 mg/kg and observed once a day for 7 days for signs of toxicity. Range finding study 2: 10 animals injected with 3911, 1825, 521, 183 and 52 mg/kg. In main study animals were sacrificed at 6, 24 and 48 hours


DETAILS OF SLIDE PREPARATION: Approximately 4 slides were prepared for each animal.  The chromosomes were prepared by standard methods and Giemsa stained.


TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields):
6h group: Stock solution of 321 mg/ml; volumes injected were 1.0, 0.5 and 0.25 ml, resulting in the following doses calculated from body weight: 1030 mg/kg +/- 3.2%; 515 mg/kg +/- 5.6%; 255 mg/kg +/- 1.2%

24 hour group: animals were injected with 1.0 or 0.5 ml of 321 mg/ml stock solution, or 1.0 ml of 91 mg/ml stock solution, resulting in the following doses calculated from body weight: 1030 mg/kg +/- 0.8%; 515 mg/kg +/- 5.6%; 255 mg/kg +/- 3.1%

48 hour group: animals were injected with 1.0 or 0.45 ml of 426 mg/ml stock solution, or 1 ml of 102 mg/ml stock solution. This resulted in the following doses calculated from body weight: 1030 mg/kg +/- 3.1%; 515 mg/kg +/- 9.3%; 255 mg/kg +/- 2.4%

METHOD OF ANALYSIS: metaphase cells analysed by projecting the negatives with a darkroom enlarger onto a white counter

OTHER:
Evaluation criteria:
In general, a minimum of 100 metaphase cells from each animal were scored for incidence of chromosomal aberrations.
Statistics:
Statistical methods: Chi2 test for comparison of expected and observed distribution of the number of breaks; Wilcoxon test was used as a nonparametric test.

Results and discussion

Test results
Key result
Sex:
male
Genotoxicity:
negative
Remarks:
on mitotic index
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: Exp 1: 1676, 504, 168, 50 mg/kg. Exp 2: 3911, 1825, 521, 183, 52 mg/kg

- Clinical signs of toxicity in test animals: No deaths observed in initial study. In second study 3 of 10 animals dosed with 3911 mg/kg died, while all the other animals survived till terminal sacrifice.

- Harvest times: 7 days exp 1, 14 days exp 2.

- High dose with and without activation: 1676 exp 1, 3911 exp 2

RESULTS OF DEFINITIVE STUDY

See table 1

Any other information on results incl. tables

Negative controls: frequencies of breaks were 0.54%, 2.49% and 1.47% at sacrifice at 6, 24 and 48 hours respectively.

Table 1:Results of chromosome analysis in rat bone marrow cells: test substance (total number of aberrations observed)

 

Low dose (255 mg/kg bw)

Mid dose (515 mg/kg bw)

High dose (1030 mg/kg bw)

Sampling time (h)

6

24

48

6

24

48

6

24

48

Number of cells evaluated

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

 500 approx

Toxicity,specify effects

 

 

 

 

 

 

 

 

 

Chromosome aberrations

Gaps

6

11

3

3

6

25

 2

 12

 14

Breaks

 5

 2

 9

 10

 15

 6

 5

 6

 7

Other aberrations

 0

 0

 0

 0

 0

 0

 0

 0

Mitotic index (% range)

 2 – 5

2 - 5

1 - 4

 2 - 4

 2 - 5

 4 - 7

 1 - 6

 3 - 5

 2 - 5

Polyploidy

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

Endo reduplication

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

N.R

 N.R = Not Reported

Table 2 Results of chromosome analysis in rat bone marrow cells: control substances (total number of aberrations observed)

 

Vehicle control

Positive control

Sampling time (h)

6

24

48

48

Number of cells evaluated

 500 approx

 450 approx

 500 approx

 250 approx

Chromosome aberrations

Gaps

6

19

15

ND

 

Breaks

3

12

8

145

 

Other aberrations

0

0

0

4 quad, 6 tri, 5 del

Mitotic index (% range)

 

2-7

1-4

3-4

2-4

 N.R = Not Reported

quad = quadriradial tri = triradial del = deletion

Applicant's summary and conclusion

Conclusions:
Hexamethyldisiloxane has been tested for the induction of chromosome aberrations in rat bone marrow cells in a valid study conducted according to a protocol that is similar to OECD 475. There was no evidence of induction of chromosomal damage in the bone marrow cells of rats following intraperitoneal injection. The test substance is considered to be non-clastogenic (negative for the induction of chromosome aberrations) in rat bone marrow cells under the conditions of the test.