Genotoxicity of 1,3-dithiane and 1,4-dithiane in the CHO/SCE assay and the Salmonella/microsomal test

1,3-Dithiane and 1,4-dithiane are the sulfur-containing Maillard reaction products (MRPs) which have been found in boiled beef extracts. In this study the genotoxicity of these products was examined using the Salmonella/microsomal test and the CHO/SCE assay. 1,3-Dithiane showed a potent direct-acting mutagenicity toward S. typhimurium TA98 and TA100, but 1,4-dithiane had a lower mutagenicity toward both tester strains. Both compounds were shown to be non-mutagenic with hepatic metabolic activation with the exception of 1,3-dithiane toward strain TA100. To compare the mutagenic potential of 1,3-dithiane and 1,4-dithiane with other types of MRPs, 24 MRPs were examined for their mutagenicity to S. typhimurium TA98 and TA100 in the presence or absence of S9 mix. 2,6-Dimethylpyrazine, furan, 2-acetylpyrrole, and thiazole were shown to be mutagenic. However, these four MRPs exhibited a lower mutagenicity in TA98 than 1,3-dithiane and 1,4-dithiane. Furthermore, SCE frequencies in CHO cells were very significantly induced by 1,3-dithiane in the absence of S9 mix, but the SCE-inducing capability of 1,3-dithiane was reduced or even disappeared with metabolic activation. 1,4-Dithiane did not significantly induce SCE frequencies in the presence or absence of S9 mix. Thus, we concluded that 1,3-dithiane was a potent mutagenic MRP in the Salmonella/microsomal test, whereas it was a weak SCE inducer in the CHO/SCE assay.