Mesitylene

Genetic toxicity: in vivo

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 from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP status unknown, near guideline study, published in peer reviewed literature, minor restrictions in design and/or reporting but otherwise adequate for assessment

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1998

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

yes

Remarks:

positive control substance tested only in males (not considered to affect scientific validity)

GLP compliance:

not specified

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Reference substance 001

Cas Number:

95-63-6

Molecular formula:

C9-H12

Constituent 2

Reference substance name:

1,,2,4-trimethylbenzene

IUPAC Name:

1,,2,4-trimethylbenzene

Constituent 3

Reference substance name:

pseudocumene

IUPAC Name:

pseudocumene

Details on test material:

Obtained from Fluka

Test animals

Species:

mouse

Strain:

Balb/c

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 9 weeks
- Weight at study initiation: Approximately 23 g

ENVIRONMENTAL CONDITIONS - not reported

IN-LIFE DATES: Not reported

Administration / exposure

Route of administration:

intraperitoneal

Vehicle:

- Vehicle(s)/solvent(s) used: mineral oil

Duration of treatment / exposure:

Dose preparations were injected i.p. with each dose divided into two equal parts and given at a 24 hour interval. Two stage model of the experiments was used. In the 1st one, 1 mL mineral oil or test substance at a dose equal to 80% of LD50 was dosed to males. In the 2nd, males received doses equal to 40 and 80% of LD50 and females 80% of LD50.

Frequency of treatment:

Two i.p. injections, 24 hours apart

Post exposure period:

Bone marrow samples were collected 30, 48 and 72 hours after the first injection

Doses / concentrations

Remarks:

Doses / Concentrations:
2000, 3280, 4000 mg/kg
Basis:
nominal conc.

No. of animals per sex per dose:

0 mg/kg (solvent control - mineral oil) - 8 male and 4 female; 2000 mg/kg - 12 male; 3280 mg/kg - 12 female; 4000 mg/kg - 23 male

Control animals:

yes, concurrent vehicle

Positive control(s):

mitomycin C;
- Route of administration: not reported
- Doses / concentrations: 2.5 mg/kg; 0 mg/kg (solvent control - distilled water)

Examinations

Tissues and cell types examined:

Bone marrow polychromatic erythrocytes (NCEs)

Details of tissue and slide preparation:

CRITERIA FOR DOSE SELECTION: not reported
DETAILS OF SLIDE PREPARATION: bone marrow samples were collected from each mouse 30, 48 and 72 hours after 1st injection and 4 bone marrow smears were prepared from each mouse

METHOD OF ANALYSIS: 1000 polychromatic erythrocytes (PCEs) per mouse were analysed for the number of micronucleated cells (mPCEs). The ratio of PCEs to mPCEs was determined by counting both cell types until the level of 200 NCEs was reached.

Evaluation criteria:

A test substance was considered genotoxic if the test substance induced a statistically significant and reproducible increase in the number of mPCEs for at least one of the study points.

Statistics:

One way analysis of variance with multiple comparison test by Domański, 1979

Results and discussion

Test results

Key result

Sex:

male/female

Genotoxicity:

negative

Toxicity:

yes

Vehicle controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RESULTS OF DEFINITIVE STUDY
- Induction of micronuclei (for Micronucleus assay): No induction at 30, 48 or 72 hours after dosing
- Ratio of PCE/NCE (for Micronucleus assay): In males, the highest dose (4000 mg/kg: 80% of LD50) induced a statistically significant decrease in the PCEs to NCEs
ratio (the cytotoxicity index was 0.68 at 72 hours, compared with 0.95 in the control male mice. The study performed on females using the equivalent of 80% of LD50 (3280 mg/kg) revealed that the animals survived but at the same time these doses were found not to induce cytotoxicity on bone marrow cells.

Any other information on results incl. tables

Induction of micronuclei in PCEs in mice

Dose	Number and sex	% mPCEs			ratio PCEs : mPCEs
		harvest time (hours)			harvest time (hours)
		30	48	72	30	48	72
Pseudocumene
1 ml mineral oil	8 male		0.18 ± 0.07			0.95
	4 female		0.23 ± 0.05			0.95
2000 mg/kg	12 male	0.15 ± 0.10	0.18 ± 0.10	0.20 ± 0.08	1.18	1.02	1.02
3280 mg/kg	12 female	0.23 ± 0.05	0.18 ± 0.05	0.13 ± 0.05	0.98	1.01	0.85
4000 mg/kg #	23male	0.23 ± 0.10	0.16 ± 0.08	0.16 ± 0.07	1.16	0.74	0.68*
Mitomycin C (positive control)
1 ml distilled water	4 male			0.15 ± 0.05			1.37
2.5 mg/kg	12 male	4.15 ± 0.38*	4.22 ± 0.35*	1.25 ± 0.15*	0.71*	0.48*	0.14*
* p ≥ 0.05 data for males treated at 80% LD50 and mineral oil expressed as mean values ± S.D. for 2-stage experiments # only 7 mice surviving at 72 hours

Applicant's summary and conclusion

Conclusions:

Interpretation of results: negative
Negative micronucleus response in polychromatic erythrocytes of the bone marrow

Executive summary:

Pseudocumene was tested in the in vivo micronucleus assay using bone marrow cells of the Imp:Balvb/c mouse. There was no effect on the frequency of micronucleated polychromatic erythrocytes.