Methylthiouracil

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

Salmonella mutagenicity tests: V. Results from the testing of 311 chemicals

Author:

Zeiger E et al.

Year:

1992

Bibliographic source:

Environ Mol Mutagen 19; Suppl 21:2-141

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Bacterial cultures were grown overnight at 37C with shaking in Oxoid 2 broth supplemented wiht biotin (0.8 ug/ml) and histidine (40ug/ml). For metabolic activation S-9 Aroclor 1254-induced, male Sprague-Dawley rat and Syrian hamster livers were used. The top agar was added and poured onto surface of petri dishes containing Vogel-Bonner medium. Histidine-independent colonies arising on these plates were counted following two days incubation at 37C. Plates were machine counted. The test chemical was initially tested in the preincubation test at half-log dose intervals up to a dose tha elicited toxicity, or to a dose immedelately below on the was toxic in the preliminary toxicity procedure. Test item was tested as triplicates. Concurrent solvent and positive controls were run at each trial.

GLP compliance:

not specified

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

Methylthiouracil

EC Number:

200-252-3

EC Name:

Methylthiouracil

Cas Number:

56-04-2

Molecular formula:

C5H6N2OS

IUPAC Name:

methylthiouracil

Test material form:

solid: crystalline

Specific details on test material used for the study:

6-Methyl-2-thiouracil, CAS nro.56-04-2. Supplier: Aldric. Analyzed purity 99%.

Method

Species / strain

Species / strain 1

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Species / strain 2

Species / strain / cell type:

S. typhimurium TA 1538

Test concentrations with justification for top dose:

10,33, 100, 333, 1000, 333, 10000 ug/plate. Bacterial toxicity was used as a selection of top dose

Vehicle / solvent:

DMSO

Controls

Untreated negative controls:

yes

Remarks:

DMSO

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

9-aminoacridine

sodium azide

methylmethanesulfonate

mitomycin C

other: 4-nitro-o-phenylenediamine

Details on test system and experimental conditions:

The initial test of a chemical was done without activation and with 10% S-9. If a positive result was obtained, the postitive trials were repeated. If trials were negative the chemical was retested without S-9 and with 30% S-9. Tf all trials were negative, no further testing was performed.

Evaluation criteria:

Individual trials were judged mautgenic, weakly mutagenic, questionable or nonmutagenic, depending on the magnitude of His+ revertants, and the shape of the dose-response. A trial was considered questionable if the dose-response was judged insufficientrly high to support a call of weakly mutagenic, if only a single dose was elevated over the control, or if a weak increase was not dose-related. The distinctions betweem a questionable response and a nonmutagenic or weakly mutagenic response, and between a weak mutagenic response, and betweem and between a weak mutagenic respons and mutagenic respons are highlty subjective. It was not necessary for a response to reach two-fold over nackground for a trial to be judged mutagenic.
A chemical was judged mutagenic or weakly mutagenic if it produced a reproducible, dose-related response over hte solvent control, under a single metabolic activation condition, in replicate trials. A chemical was judged questionable if the results of individual trials were not reproducible, if increases in His+ revertants did not meet the criteria for a weakly mutagenic response, or if only single doses produceed increases in His+ revertants in repeated trials. Chemicals were judged nonmutagenic if they did not meet the criteria for a mutagenic or questionable response.

Results and discussion

Test results

Test results 1

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

not specified

Genotoxicity:

not determined

Cytotoxicity / choice of top concentrations:

not determined

Test results 2

Key result

Species / strain:

S. typhimurium TA 97

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Test results 3

Key result

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Test results 4

Key result

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Test results 5

Key result

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Applicant's summary and conclusion

Conclusions:

In Salmonella mutation test with methylthiouracil no revertant mutations was observed.

Executive summary:

Salmonella mutation test was performed using strains TA 97, TA 97, TA 100 and TA 1535 with concentrations 10, 33, 100, 33, 1000, 3333, and 10 000 ug/plate.

Compared to the solvent control no two-fold or more in number of revertant clones were observed in any strains and concentrations tested.