The contribution of UDP-glucuronosyltransferase 1A9 on CYP1A2-mediated genotoxicity by aromatic and heterocyclic amines

The importance of environmental and dietary arylamines, and heterocyclic am ines in the etiology of human cancer is of growing interest, These pre-carc inogens are known to undergo bioactivation by cytochrome P450 (CYP)-directe d oxidation, which then become substrates for the UDP-glucuronosyl-transfer ases (UGTs). Thus, glucuronidation may contribute to the elimination of CYP -mediated reactive intermediate metabolites, preventing a toxic event, In t his study, human UGTs were analyzed for their ability to modulate the mutag enic actions of N-hydroxy-arylamines formed by CYP1A2. Studies with recombi nant human UGT1A1, UGT1A3, UGT1A4 UGT1A6, UGT1A7, UGT1A8, UGT1A9, UGT1A10, UGT2B4, UGT2B7 and UGT2B15 expressed in heterologous cell culture confirmed that UGT1A9 glucuronidated the mutagenic arylamines N-hydroxy-2-acetylamin ofluorene (N-hydroxy-2AAF) and 2-hydroxyamino-1-methyl-6-phenylimidazo (4,5 -b)pyridine (N-hydroxy-PhIP). To examine the mutagenic potential of these a gents, a genotoxicity assay was employed using Salmonella typhimurium NM200 9, a bacterial strain expressing the umuC SOS response gene fused to a beta -galactosidase reporter lacZ gene. DNA modification results in the inducti on of the umuC gene and subsequent enhancement of P-galactosidase activity, Both N-hydroxy-2AAF and N-hydroxy-PhIP stimulated a dose-dependent increas e in bacterial P-galactosidase activity, In addition, the procarcinogens 2A AF and PhIP were efficiently bioactivated to bacterial mutagens when incuba ted with Escherichia coli membranes expressing CYP1A2 and NADPH reductase, CYP1A2 generated 2AAF- and PhIP-mediated DNA damage, but only the action of N-hydroxy-2AAF was blocked by expressed UGT1A9, These results indicate tha t UGT1A9 can control the outcome of a genotoxic response, The results also indicate that while a potential toxicant such as N-hydroxy-PhIP can serve a s substrate for glucuronidation, its biological actions can exceed the capa city of the detoxification pathway to prevent the mutagenic episode.