Bioactivation of the human carcinogen aristolochic acid

Aristolochic acids are potent human carcinogens; the role of phase II metabolism in their bioactivation is unclear. Accordingly, we tested the ability of the partially reduced metabolites, N-hydroxyaristolactams (AL-NOHs), and their N-O-sulfonated and N-O-acetylated derivatives to react with DNA to form aristolactam-DNA adducts. AL-NOHs displayed little or no activity in this regard while the sulfo- and acetyl compounds readily form DNA adducts, as detected by ³²P-postlabeling analysis. Mouse hepatic and renal cytosols stimulated binding of AL-NOHs to DNA in the presence of adenosine 3'-phosphate 5'-phosphosulfate (PAPS), but not of acetyl-CoA. Using Time of Flight (TOF) LC/MS, AL-I-NOH formed the sulfated compound in the presence of PAPS and certain human sulfotransferases, SULT1B1 >>> SULT1A2 > SULT1A1 >>> SULT1A3. The same pattern of SULT reactivity was observed when AL-I-NOH was incubated with these enzymes and PAPS and the reaction was monitored by formation of aristolactam-DNA adducts. In the presence of human NAD(P)H:quinone oxidoreductase, the ability of AA-I to bind DNA covalently was increased significantly by addition of PAPS and SULT1B1. We conclude from these studies that AL-NOHs, formed following partial nitroreduction of aristolochic acids, serve as substrates for SULT1B1, producing N-sulfated esters which, in turn, are converted to highly active species that react with DNA and, potentially, cellular proteins, resulting in the genotoxicity and nephrotoxicity associated with ingestion of aristolochic acids by humans.