METABOLIC-ACTIVATION AND DEACTIVATION OF ARYLAMINE CARCINOGENS BY RECOMBINANT HUMAN NAT1 AND POLYMORPHIC NAT2 ACETYLTRANSFERASES

A genetic polymorphism at the NAT2 gene locus, encoding for polymorphi c N-acetyltransferase (NAT2), segregates individuals into rapid, inter mediate or slow acetylator phenotypes. Both rapid and slow acetylator phenotypes have been associated with increased incidence of cancer in certain target organs related to arylamine exposure, suggesting a role for acetylation in both the activation and deactivation of arylamine carcinogens. A second gene (NAT1) encodes for a different acetyltransf erase isozyme (NAT1) that is not subject to the classical acetylation polymorphism. In order to assess the relative ability of NAT1 and NAT2 to activate and deactivate arylamine carcinogens, we tested the capac ity of recombinant human NAT1 and NAT2, expressed in Escherichia coli XA90 strains DMG100 and DMG200 respectively, to catalyze the N-acetyla tion (deactivation) and 0-acetylation (activation) of a variety of car bocyclic and heterocyclic arylamine carcinogens. Both NAT1 and NAT2 ca talyzed the N-acetylation of each of the 17 arylamines tested. Rates o f N-acetylation by NAT1 and NAT2 were considerably lower for heterocyc lic arylamines such as 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), particularly those (e.g. IQ) with steric hindrance to the exocyclic am ino group. For carbocyclic arylamines such as 4-aminobiphenyl and beta -naphthylamine, the apparent affinity was significantly (P < 0.05) hig her for NAT2 than NAT1. NAT1/NAT2 activity ratios and clearance calcul ations suggest a significant role for the polymorphic NAT2 in the N-ac etylation of carbocyclic arylamine carcinogens. Both NAT1 and NAT2 cat alyzed acetyl coenzyme A-dependent O-acetylation of N-hydroxy-2-aminof luorene and N-hydroxy-4-aminobiphenyl to yield DNA adducts. NAT1 catal yzed paraoxon-resistant, intramolecular N,O-acetyl-transferase-mediate d activation of N-hydroxy-2-acetylamino-fluorene and N-hydroxy-4-acety laminobiphenyl at low rates; catalysis by NAT2 was not readily detecta ble in the presence of paraoxon. In summary these studies strongly sug gest that the human acetylation polymorphism influences both the metab olic activation (O-acetylation) and deactivation (N-acetylation) of ar ylamine carcinogens via polymorphic expression of NAT2. These findings lend mechanistic support for human epidemiological studies suggesting associations between both rapid and slow acetylator phenotype and can cers related to arylamine exposure.