Sodium methanethiolate

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:

experimental study

Adequacy of study:

key study

Study period:

April 1999

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1999

Report date:

1999

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

no

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Sodium methanethiolate

EC Number:

225-969-9

EC Name:

Sodium methanethiolate

Cas Number:

5188-07-8

Molecular formula:

CH4S.Na

IUPAC Name:

sodium methylsulfanide

Details on test material:

Test article name : Sodium methylmercaptide
Origin: Elf Aquitaine production, Lacq
Batch: 9901-03935

Test animals

Species:

mouse

Strain:

other: OF1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Species: Mouse Strain: Swiss Ico, OF1 (IOPS Caw)
- Source: Iffa Crédo, l'Arbresle, France
- Age: ca. 5 week old
- Weight at dosing: no data
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Housing: up to 5 per cage in polycarbonate cages  
- Diet: AO4C pelleted maintenance diet, ad libitum
- Water: filtered tap water freely available at all times
- Temperature: 21 +/-2°C
- Humidity: 30-70%
- Air changes: 12 cycles/hour
- Photoperiod: 12 hour light/dark cycle

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

Distilled water

Details on exposure:

A preliminary toxicity test was performed to define the dose-levels to be used for the cytogenetic study. In the main study, three groups of five male and five female mice received two oral treatments of SODIUM METHYLMERCAPTIDE at dose-levels of 12.5, 25 or 50 mg/kg/day (10 mL/kg bw ) , at a 24-hour interval. One group of five males and five females received the vehicle (distilled water) under the same experimental conditions, and acted as control group. One group of five males and five females received the positive control test substance (cyclophosphamide) once by oral route at the dose-level of 50 mg/kg. The animals of the treated and vehicle control groups were killed 24 hours after the last treatment and the animals of the positive control group were killed 24 hours after the single treatment.

Duration of treatment / exposure:

Two oral treatment at 24-hour interval

Post exposure period:

24 hours

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 12.5, 25 and 50 mg/kg/d
Basis:

No. of animals per sex per dose:

- Range-finding test - 3 groups of 3 animals/sex/group
- Micronucleus assay - 4 groups of 5 (controls +/-, low and mid dose) or 8 (high dose) animals/sex/group

Control animals:

yes, concurrent vehicle

Positive control(s):

Cyclophosphamide (50 mg/kg bw, 10 mL/kg bw , single oral administration)

Examinations

Tissues and cell types examined:

Bone marrow

Details of tissue and slide preparation:

Bone marrow smears were prepared. For each animal, the number of the micronucleated polychromatic erythrocytes (MPE) was counted in 2000 polychromatic erythrocytes. The polychromatic (PE) and normochromatic (NE) erythrocyte ratio was established by scoring a total of 1000 erythrocytes (PE+NE).

Evaluation criteria:

For a result to be considered positive, a statistically significant increase in the frequency of MPE must be demonstrated when compared to the concurrent vehicle control group. Reference to historical data, or other considerations of biological relevance was also taken into account in the evaluation of data obtained.

Statistics:

When there was no significant within-group heterogeneity, using the heterogeneity chi-square test value (Lovell et al., 1989), the frequencies of MPE in each treated group was compared with those in the concurrent vehicle control groups by using a 2 x 2 contingency table to determine the qui2 value (Lovell et al., 1989).
When there was significant within-group heterogeneity, then that group was compared with the control group using a non-parametric analysis, the Mann-Whitney test (Schwartz, 1969).
The student "t" test was used for the PE/NE ratio comparison.
Probability values of p < 0.05 was considered as significant.

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Toxicity:

yes

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

All the dose-levels were expressed in terms of active material taking into account a 32.8% active material content in the supplied test substance.

PRELIMINARY TOXICITY TEST In order to select the top dose-level for the cytogenetic study, 500, 100, and 50 mg/kg/day were tested.  At 500 mg/kg/day, all the treated animals (three males and three females) died 2 minutes following the first treatment. At 100 mg/kg/day, the three treated males showed sedation, lateral recumbency and dyspnea 2 minutes following the first treatment. Two minutes later, 1/3 males was found dead and sedation was noted in the surviving animals. No second treatment was performed at this dose-level. At 50 mg/kg/day, 1/3 males was found dead 24 hours after the second treatment, and reddish discharge was noted in the mouth area of this animal. No clinical signs and no mortality related to the test substance were noted in females at this dose-level.

CYTOGENETIC TEST No clinical signs and no mortality were observed in the animals of both sexes given 12.5, 25 or 50 mg/kg/day. For both males and females, the mean values of MPE as well as the PE/NE ratio in the groups treated with the test substance, were equivalent to those of the vehicle group and no significant difference was noted. The mean values of MPE as well as the PE/NE ratio for the vehicle and positive controls were consistent with the historical data. Cyclophosphamide induced a highly significant increase (p<0.001) in the frequency of MPE, indicating the sensitivity of the test system. The study was therefore considered valid.

Any other information on results incl. tables

Results of the Cytogenetic Test:  24 hr after the last administration, mean (SD)

mg/kg/day	0	12.5	25	50	+Ctrl
Males
MPE/1000 PE	1.6 (0.8)	0.9 (0.7)	1.9 (1.3)	1.4 (0.8)	38.0 (11.5)
PE/NE ratio	1.4 (0.7)	0.9 (0.3)	1.1 (0.4)	1.0 (0.1)	0.9 (0.3)
Females
MPE/1000 PE	1.1 (0.8)	1.0 (0.9)	1.3 (1.2)	1.5 (1.2)	30.9 (4.3)
PE/NE ratio	0.8 (0.3)	0.8 (0.1)	1.2 (0.6)	0.8 (0.5)	0.8 (0.4)

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): negative
SODIUM METHYLMERCAPTIDE does not induce damage to the chromosomes or the mitotic apparatus of mice bone marrow cells after two oral administrations, at a 24-hour interval, at the dose-levels of 12.5, 25 or 50 mg/kg/day.

Executive summary:

Sodium methylmercaptide was tested in a Mammalian Erythrocyte Micronucleus Test, according to the OECD n° 474 Guideline and EC 92/69/EEC B.12 guidelines in compliance with the Principles of Good Laboratory Practice.

A preliminary toxicity test was performed to define the dose-levels to be used for the cytogenetic study. In the main study, three groups of five male and five female Swiss Ico: OF1 (IOPS Caw) mice received two oral treatments of sodium methylmercaptide at dose-levels of 12.5, 25 or 50 mg/kg/day, at a 24-hour interval. One group of five males and five females received the vehicle (distilled water) under the same experimental conditions, and acted as control group. One group of five males and five females received the positive control test substance (cyclophosphamide) once by oral route at the dose-level of 50 mg/kg. The animals of the treated and vehicle control groups were killed 24 hours after the last treatment and the animals of the positive control group were killed 24 hours after the single treatment. Bone marrow smears were then prepared. For each animal, the number of the micronucleated polychromatic erythrocytes (MPE) was counted in 2000 polychromatic erythrocytes. The polychromatic (PE) and normochromatic (NE) erythrocyte ratio was established by scoring a total of 1000 erythrocytes (PE + NE).

The top dose-level for the cytogenetic test was selected according to the criteria specified in the international guidelines; since toxic effects were noted in the preliminary test, the top dose-level was based on the toxicity level, such that a higher dose-level was expected to induce lethality. Consequently, 50 mg/kg/day was selected as the top dose-level. The two other dose-levels were 25 and 12.5 mg/kg/day. For both males and females, the mean values of MPE as well as the PE/NE ratio in the groups treated with the test substance, were equivalent to those of the vehicle group and no significant difference was noted. The mean values of MPE as well as the PE/NE ratio for the vehicle and positive controls were consistent with the historical data. Cyclophosphamide induced a highly significant increase (p < 0.001) in the frequency of MPE, indicating the sensitivity of the test system.

Sodium methylmercaptide does not induce damage to the chromosomes or the mitotic apparatus of mice bone marrow cells after two oral administrations, with a 24-hour interval, at the dose-levels of 12.5, 25 or 50 mg/kg/day.