Results

Ames bacterial reverse-mutation assay

Results obtained with different concentrations of 2-amino-4-methylhiazole in the mutagenicity assay, using TA 1537, TA 1535, TA 98, TA 100, TA 102 strains of S. typhymurium, and E. coli KMWP2p 101 are shown in Tables 3 – 6. It was observed that 2-amino-4-methylthiazole did not show mutagenic effects , both with and without metabolic activation.

At the same time, sulfamethylthiazole at high concentrations ( from 5.000 to 0.450 mg/plate) showed inhibition on the five strains of Salmonella typhymurium and E. coli KMWP2p 101, whereas at low concentrations ( from 0.1350 to 0.011 mg/plate ) did not show mutagenic effects, both with and without metabolic activation.

Discussion

4-methylthiazol-2-ylamine (CAS 1603-91-4) was previously tested only on Salmonella typhimurium TA 100 and K. pneumonia without metabolic activation. The substance was mutagen in K. pneumonia, while it was not mutagen in S. typhimurium TA 100 ( 6 ); this mutagenic activity was found only at high mmole/l (50 and 20).

Other structural analogue compounds are: aminothiazole (CAS 96-50-4), 2-amino-5-methylthiazole (CAS 7304-71-7), and 3-methylisothiazol-5- amine (CAS 24340-76-9); for these compounds there are some studies regarding mutagenic properties.

Aminothiazole was mutagen on K. pneumonia but not with S. typhimurium TA 100 without metabolic activation ( 6 ); in other experiments it was mutagen in S. typhimurium strains TA 98 and TA 1538 with metabolic activation ( 7 ) and not mutagen in other S. typhimurium strains both with and without metabolic activation ( 7 ). Aminothiazole was mutagen in L 5178Y TK +/- cells both with and without metabolic activation ( 7 ).

For 2-amino-5-methylthiazole no data are reported in the literature. However, the substance was notified in accordance with Directive 67/548/CEE and data on its genotoxic activity had been generated in accordance with regulatory program (8). The authors studied the bacterial reverse mutation assay (Ames test) according to OECD Guideline 471; they concluded that 2-amino-5-methylthiazole is clearly negative in 3 strains of S. typhymurium whereas a weak mutagen response in 2 other genotypically different strains could not be ruled out definitively. A mutagenic risk is unlikely because of the marginal response and the required high concentrations.

3-Methylisothiazol-5-amine was mutagen in S. typhimurium TA 98 and TA 1538 with metabolic activation and not mutagen in other S. typhimurium strains both with and without metabolic activation ( 7 ).

Our results demonstrate that 4-methylthiazol-2-ylamine is not mutagen in the five strains of S. typhimurium and E. coli KMWP2p 101; it seems that the presence of methyl group in position 2 allows to obtain less or not mutagenic compounds as it appears when the methyl group is in the position 5.

Regarding N’1–(4 methylthiazol-2-yl) sulphanilamide no data have been collected about its mutagenic potential. Our data on five S. typhimurium strains and E. coli KMWP2p 101 demonstrate that this sulphamidic drug is not mutagen.

Similar compound sulphathiazole (CAS 72-14-0) was not mutagen in S. typhimurium TA 97, TA 98, TA 100, TA 1535, TA 1537 and TA 1538 with and without metabolic activation ( 9 ). Researches performed with a DNA-cell-binding (DCB) assay demonstrate that sulphathiazole is positive in the (DCB) assay performed in E. coli with metabolic activation ( 9 ). However this test is an old test for mutagenic assay and now it is not utilized.

Sulphathiazole is confirmed to be not mutagen in L5178Y TK+/- cells both with and without metabolic activation ( 10 ).

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10. Seifried, H., E., Seifried, R., M., Clarke, J., J., Junghans, T., B., and San R., H., C., (2006). A compilation of two decades of mutagenicity test results with the Ames Salmonella typhimurium and L 5178Y mouse lymphoma cell mutation assays. Chem. Res. Toxicol. 19: 627-644.