METABOLIC-ACTIVATION OF HETEROCYCLIC AROMATIC-AMINES CATALYZED BY HUMAN ARYLAMINE N-ACETYLTRANSFERASE ISOZYMES (NAT1 AND NAT2) EXPRESSED IN SALMONELLA-TYPHIMURIUM

Heterocyclic aromatic amines formed during the cooking of meat and meat-derived products can be activated to reactive metabolites which bind to DNA, induce mutations and cause tumors in animals. A principal route of metabolic activation is N-oxidation to hydroxylamines, and their subsequent activation by acetyltransferase-catalyzed O-acetylation. We have used mutagenicity assays to study O-acetylation of heterocyclic arylhydroxylamines by the two isozymes of human N-acetyltransferase, NAT1 and NAT2, expressed in Salmonella typhimurium. N-Acetylation was also examined, using an HPLC method. In addition, Salmonella strains with endogenous acetyltransferase and lacking this activating activity were used. Hydroxylamines of nine heterocyclic aromatic amines, IQ, isoIQ, MeIQ, MeIQx, NI, PhIP, Glu-P-1, Glu-P-2, and Trp-P-2 were generated in situ by rat liver S9 mix. The strains expressing human NAT1 and lacking acetyltransferase activity showing little or no ability to activate these substrates. The strains expressing human NAT2 and Salmonella acetyltransferase supported to different extents the activation of all the compounds except PhIP and Trp-P-2. N-Acetylation of IQ, MeIQx and PhIP was slow or not detectable, In conclusion, human NAT2 but not NAT1 can O-acetyIate heterocyclic hydroxylamines. NAT2 probably plays a key role in the genotoxic effects of the above heterocyclic amines except for PhIP and Trp-P-2, which have NAT2-independent mutagenic activity.