CAFFEINE-DERIVED N-NITROSO COMPOUNDS .3. MUTAGENICITY IN SALMONELLA-TYPHIMURIUM AND IN-VITRO INDUCTION OF DNA SINGLE-STRAND BREAKS IN RAT HEPATOCYTES BY MONONITROSOCAFFEIDINE AND DINITROSOCAFFEIDINE

Mutagenesis in S. typhimurium and in vitro induction of DNA single-str and breaks in primary rat hepatocytes (DNA-SSB) have been investigated for two new N-nitroso compounds, mononitrosocaffeidine (MNC) and dini trosocaffeidine (DNC). Mononitrosamidocaffeidine (MNAC) and tert.-(but yloxy)carbonyl-mononitrosamidocaffeidine (t-BOC-MNAC), both nitrosated derivatives of caffeidine with nitrosation at methylcarboxamide-N onl y, were also similarly studied. MNC, an asymmetric nitrosamine, failed to show mutagenicity in any of the tester strains used, and also did not induce DNA-SSB in rat hepatocytes. DNC, having both N-nitrosamide and N-nitrosamine groups in the molecule, showed direct mutagenicity i n TA100, TA1535 and TA102. The mutagenic potential of the compound was found to increase on S9 activation. However, it was non-mutagenic in TA98 and TA1537. DNC also exhibited a high potential for inducing alka li-labile DNA-SSB in rat hepatocytes (70-78% C-T value) and was cytoto xic at concentrations over 0.1 mumole/ml. Both MNC and DNC were found to produce formaldehyde on S9 activation. MNAC was not mutagenic direc tly but showed weak mutagenicity on metabolic activation, whereas t-BO C-MNAC was mutagenic both with and without S9 activation in TA100, TA1 535 and TA102. t-BOC-MNAC was more cytotoxic to hepatocytes than MNAC, though both caused DNA-SSB to the same extent (62% C-T value). On the basis of the presented data it is inferred that while DNC is a direct -acting mutagen in TA100, TA1535 and TA102 due to the presence of a re active N-methylnitrosamido group, its mutagenic potential is greatly e nhanced in the presence of S9 possibly due to the synergistic influenc e of an activated N-methylnitrosamino group in the molecule. Additiona lly, the study shows a qualitative consistency between Salmonella muta genicity, genotoxicity in hepatocytes and the reactivity of the methyl group at the nitrosamido-N in nitrosated caffeidine compounds.