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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
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant, guideline study, available as unpublished report, fully adequate for assessment
Cross-referenceopen allclose all
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1990
Report Date:
1990

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
Principles of method if other than guideline:
not applicable
GLP compliance:
yes (incl. certificate)
Type of assay:
micronucleus assay

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): MRD-89-360
- Physical state: Colourless gas
- Analytical purity: Considered 100% pure
- Storage condition of test material: Room temperature

Test animals

Species:
mouse
Strain:
B6C3F1
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories, Inc., Shaver Road, Portage, Michigan 49081, USA
- Age at study initiation: approx. 6-7 weeks
- Weight at study initiation: 20-26 g (Day -2)
- Assigned to test groups randomly: no (using a computer generated, body weight sorting program)
- Housing: Individually in suspended stainless steel cages.
- Diet: Purina Certified Rodent Chow #5002 (pellets) (Ralston Purina Company) ad libitum (except during exposure)
- Water: Mains water ad libitum (except during exposure)
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 68-76°F
- Humidity: 40-70%
- Air changes (per hr): Not reported
- Photoperiod: 12hrs dark / 12hrs light

IN-LIFE DATES: From: 29 November 1989 To: 1 December 1990

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
The test material was delivered from a cylinder via a pressure regulator to a 1/4" coil of copper tubing submerged in a slightly heated water bath. The test material volatilised within the copper coil, entered a regulator to reduce pressure, and the resulting vapours were metered to the exposure chambers. The exposure chambers operated at an exhaust flow rate of 200 L/min, providing 1 air change every 5 mins and a theoretical equilibration time (T99) of 23 mins. The test and control groups were each contained in 1m3 stainless steel and glass chambers.

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography
- Samples taken from breathing zone: yes
Duration of treatment / exposure:
2 days
Frequency of treatment:
6 hours/day
Post exposure period:
1 day
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
1000, 3260, 10000 ppm
Basis:
other: target exposure concentrations
Remarks:
Doses / Concentrations:
1076, 3269, 10042 ppm
Basis:
analytical conc.
No. of animals per sex per dose:
10 males per group
Control animals:
yes, sham-exposed
Positive control(s):
MRD-89-362 (1,3 butadiene)
- Route of administration: inhalation
- Doses / concentrations: 1000 ppm

Examinations

Tissues and cell types examined:
polychromatic erythrocytes of the bone marrow of B6C3F1 mice
Details of tissue and slide preparation:
TREATMENT AND SAMPLING TIMES: Animals were killed approximately 24 hours after second exposure period. Immediately after death, both femurs were removed. The bone marrow was then removed and suspended in foetal bovine serum. After the suspension was centrifuged, the pellet was resuspended and smears were prepared (two slides per animal).

DETAILS OF SLIDE PREPARATION: Slides were stained using acridine orange

Evaluation criteria:
Polychromatic erythrocytes (PCE), normochromatic erythrocytes (NCE) and micronuclei identified by stain. Additional criteria for scoring micronuclei are a circular appearance and a diameter between 1/20 and 1/5 of the cell's diameter. 1000 polychromatic erythrocytes (PCE) from each animal were examined for micronuclei, and the ratio of PCE's to NCE's was determined for each animal by counting 1000 erythrocytes (PCE's and NCE's).
Statistics:
Statistical analysis included calculation of means and standard deviations of the micronuclei data and a test of equality of group means by a standard one way analysis of variance at each time period. When the ANOVA was significant, comparisons of control to dosed group means were by Duncan's Multiple Range Test. A standard regression analysis was performed to test for a dose response. Residuals from the ANOVA were analyzed for normality by Wilk's Criterion. The residuals were normally distributed (at the 0.01 level of significance) in more than 25% of the analyses. Therefore nonparametric analyses were not performed.

Results and discussion

Test results
Sex:
male
Genotoxicity:
negative
Negative controls valid:
yes
Positive controls valid:
yes
Additional information on results:
Positive and negative controls gave the expected results. A statistically significant decrease in the percentages of polychromatic erythrocytes (a measure of toxicity) was also observed.

Any other information on results incl. tables

none

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): negative
Isobutylene (2-methylpropene) was negative in the mouse bone-marrow micronucleus test.
Executive summary:

Mice were exposed to isobutylene (2-methylpropene) at target concentrations up to 10000 ppm (22948 mg/m3) for 2 days (6 hours/day). A statistically significant increase in micronucleus formation in mouse bone marrow was not observed therefore isobutylene was not clastogenic in mouse bone marrow. Positive and negative control compounds gave the expected results indicating that the method was robust.