N-acetyltransferase 2 acetylator genotype-dependent N-acetylation of 4-aminobiphenyl in cryopreserved human hepatocytes.

Arylamine N-acetyltransferases are xenobiotic-metabolizing enzymes responsible for detoxification of many drugs and carcinogens. Two N-acetyltransferase proteins (NAT1 and NAT2) are expressed in humans and they both N-acetylate aromatic amine carcinogens such as 4-aminobiphenyl. Arylamines such as 4-aminobiphenyl represent a large class of chemical carcinogens. Exposure to 4-aminobiphenyl occurs in the chemical, dye and rubber industries as well as in hair dyes, paints, and cigarette smoke. NAT2 is subject to a genetic polymorphism resulting in rapid, intermediate and slow acetylator phenotypes. We investigated the role of the NAT2 genetic polymorphisms on the N-acetylation of 4-aminobiphenyl in cryopreserved human hepatocytes in which NAT2 genotype and deduced phenotype were determined. Differences in sulfamethazine (selectively N-acetylated via NAT2) and 4-aminobiphenyl (N-acetylated by both NAT1 and NAT2) N-acetylation rates among rapid, intermediate, and slow NAT2 acetylator genotypes were tested for significance by one-way analysis of variance. In vitro 4-aminobiphenyl N-acetyltransferase activities differed significantly between rapid, intermediate and slow acetylators at 10 µM (P = 0.0102) or 100 µM (P = 0.0028). N-acetylation of 4-aminobiphenyl in situ also differed significantly between human hepatocytes from rapid, intermediate, and slow acetylators at 10 µM (P = 0.0015) and 100 µM (P = 0.0216). A gene dose-response relationship was exhibited as intermediate acetylators catalyzed 4-aminobiphenyl N-acetylation both in vitro and in situ at rates arithmetically between rapid and slow acetylators. In conclusion, N-acetylation of 4-aminobiphenyl is NAT2 genotype-dependent in human hepatocytes. These results suggest refinement of the exposure limit and safety for arylamine carcinogens according to NAT2 genotype.