Role of the human N -acetyltransferase 2 genetic polymorphism in metabolism and genotoxicity of 4, 4′-methylenedianiline

4, 4′-Methylenedianiline (MDA) is used extensively as a curing agent in the production of elastomers and is classified as reasonably anticipated to be a humancarcinogen based on sufficient evidence in animal experiments. Human N-acetyltransferase1 (NAT1) and 2 (NAT2) catalyze the N- acetylationof aromatic aminesand NAT2 is subjected to a common genetic polymorphism in humanpopulations separating individuals into rapid, intermediate, and slow acetylatorphenotypes. Although MDA is known to undergo N- acetylationto mono- and di- acetylmetabolites, very little is known regarding whether this metabolism is subject to the NAT2 genetic polymorphism. We investigated the N- acetylationof MDA by recombinant humanNAT1, NAT2, genetic variants of NAT2, and cryoplateable human hepatocytesobtained from rapid, intermediate and slow acetylators. MDA N- acetylationwas catalyzed by both recombinant humanNAT1 and NAT2 exhibiting a fivefold higher affinity for humanNAT2. N- acetylationof MDA was acetylatorgenotype dependent as evidenced via its N- acetylationby recombinant humanNAT2 genetic variants or by cryoplateable human hepatocytes. MDA N- acetylationto the mono- acetylor di- acetyl-MDA was highest in rapid, lower in intermediate, and lowest in slow acetylator human hepatocytes. MDA-induced DNA damage in the human hepatocyteswas dose-dependent and also acetylatorgenotype dependent with highest levels of DNA damage in rapid, lower in intermediate, and lowest in slow acetylator human hepatocytesunder the same MDA exposure level. In summary, the N- acetylationof MDA by recombinant humanNAT2 and cryopreserved human hepatocytessupport an important role for the NAT2 genetic polymorphism in modifying MDA metabolism and genotoxicity and potentially carcinogenic risk.