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Toxicological information

Genetic toxicity: in vivo

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Administrative data

Endpoint:
in vivo mammalian cell study: DNA damage and/or repair
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2004
Report Date:
2004

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 486 (Unscheduled DNA Synthesis (UDS) Test with Mammalian Liver Cells in vivo)
GLP compliance:
yes (incl. certificate)
Type of assay:
unscheduled DNA synthesis

Test material

Reference
Name:
Unnamed
Type:
Constituent

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS

- Age at study initiation: Males 8 weeks / Females 9 - 12 weeks


TEST ANIMALS
- Source: Chales River
- Age at study initiation: Males 8 weeks / Females 9 - 12 weeks
- Assigned to test groups randomly: yes
- Fasting period before study: no
- Housing: 2 same sex animals in stainless steel cages in sealed chambers
- Diet: ad libitum, except during exposure periods
- Water: ad libitum, except during exposure periods
- Acclimation period: 5days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22
- Humidity (%): 30-70%
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12

Administration / exposure

Route of administration:
inhalation
Vehicle:
- Vehicle(s)/solvent(s) used: air
Details on exposure:
TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION

- Exposure apparatus: 2200 L, stainless steel chambers equipped with glass doors

- Source and rate of air: Compressed air (40l/min)

- System of generating particulates/aerosols: Vapours generated by heating round-bottom flask containing test article

- Air flow rate: 380 l/min

Duration of treatment / exposure:
6 hours/day for 7 days
Frequency of treatment:
daily for 7 consecutive treatments
Doses / concentrations
Dose / conc.:
160 ppm (nominal)
Remarks:
highest that can be prepared consistently based on vapour pressure
No. of animals per sex per dose:
6

Control animals:
yes, concurrent vehicle
Positive control(s):
2-acetylaminofluorene

- Route of administration: Oral gavage

- Doses / concentrations: 100 mg/kg b.w.

Examinations

Tissues and cell types examined:
hepatocytes
Details of tissue and slide preparation:
CRITERIA FOR DOSE SELECTION:


TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields): All animals were observed for mortality/moribundity twice daily during the 7 day exposure period, prior to and following exposure. Body weights were taken on the first day of the acclimatization period and on exposure days 1, 4 and 7.

DETAILS OF SLIDE PREPARATION: Primary hepatocytes were obtained by liver perfusion and cultures were established and exposed for 4 hours to 3HTdR, which is incorporated if UDS occurs. Cells were fixed to coverslips, which were contained in the culture dishes, and prepared for silver grain counting (autoradiography)

METHOD OF ANALYSIS: At least two slides/animal and 50 cells/slide were evaluated. The nuclear and cytoplasmic grain counts, as well as, the net grain counts (nuclear minus cytoplasmic grains) were reported separately.
Evaluation criteria:
A test item is classified as positive if the mean number of net grains is higher than five per nucleus at one of the test points. A group average between 0 and 5 net grains is considered a marginal response.
Statistics:
Student's t-test for body weights; Mann-Whitney test for analysis of micronucleated polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE).

Results and discussion

Test results
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:
The mean nominal concentration for the groups exposed to D5 (Groups 2, 5, 8 and 11) was 164.1 ± 3.2 ppm. The mean
analytical concentration for the same groups was 156.4 ± 3.1 ppm, thus, 4.7% lower than the mean nominal concentration.

There were no unscheduled deaths or clinical signs observed during the course of the study. There were no statistically
significant differences in body weight between the treatment and the control groups.

The viability of the hepatocytes was not substantially affected by the in vivo treatment with the test item at any
of the treatment periods. The interindividual variations obtained for the numbers and the viabilities of the isolated
hepatocytes were in the range of the laboratory's historical control.

The test item did not induce any UDS in the hepatocytes of the treated animals as compared to the current vehicle
controls. Neither the nuclear grains nor the resulting net grains were distinctly enhanced due to the in vivo treatment
of the animals with the test item. Therefore, the net grain values obtained after treatment with the test item were
consistently negative. In addition, no substantial shift to higher values was obtained in the percentage distributions
of the nuclear grain counts.

In vivo treatment with 2-AAF revealed distinct increases in the number of nuclear and net grain counts.

Any other information on results incl. tables

Table 1 Mean net grains per nucleus

Treatment

Net grains per nucleus (males)

Net grains per nucleus (females)

Period

5/6 hours

16 hours

5/6 hours

16 hours

Air control

-9.57

-14.80

-6.51

-12.85

160 ppm D5

-9.72

-13.16

-7.26

-11.83

Positive control

45.65

17.99

34.27

13.41

Applicant's summary and conclusion

Conclusions:
Decamethylcyclopentasiloxane has been tested according to OECD 486 and in compliance with GLP in an inhalation study in rat. No test substance related induction of unscheduled DNA synthesis in the hepatocytes of treated rats relative to the vehicle was observed. Appropriate positive control substance was used and gave expected results. it is concluded that the test substance is negative for the induction of unscheduled DNA synthesis in rat hepatocytes under the conditions of the test.