Genetic Heterogeneity Between theNAT2*5BandNAT2*7BSlow Acetylator NAT2 Alleles Towards theN-acetylation of Hydralazine and Isoniazid

Abstract ID 100370 Poster Board 236 N-acetyltransferase 2 (NAT2) exhibits a common genetic polymorphism in human populations. NAT2 genetic polymorphisms result from single nucleotide polymorphisms (SNPs) associated with allelic variations which confer differences in the N-acetylation of many arylamine and hydrazine drugs and xenobiotics. The frequency of NAT2 genetic variants differs with ethnicity. The NAT2*4 allele is the reference allele associated with rapid acetylators. The NAT2*5B allele is a slow acetylator allele common in individuals of European ancestry while the NAT2*7B allele is a slow acetylator allele common in individuals of Asian ancestry. Although both NAT2*5B and NAT2*7B alleles are associated with slow acetylator phenotype, recent studies reported higher levels of N-acetylation towards arylamine carcinogens when catalyzed by NAT2*7B versus NAT2*5B. The purpose of the current study was to investigate the catalytic activity of NAT2*5B and NAT2*7B towards the N-acetylation of the commonly used hydrazine drugs hydralazine and isoniazid. Chinese hamster ovary (CHO) cell lysates stably transfected with human recombinant CYP1A2 and NAT2*4, NAT2*5B or NAT2*7B were incubated with hydralazine or isoniazid (10–1000 μM), and acetyl coenzyme A (300 – 1000 μM) at 37°C for 60 minutes. The amount of the acetylated products was determined following separation and quantitation by high performance liquid chromatography. Data was analyzed using one way ANOVA followed by a Tukey's post-hoc test. NAT2 catalytic activity towards the N-acetylation of hydralazine in NAT2*4 cells was about 2-fold higher (p< 0.001) than in NAT2*5B cell line, which was about 3-fold higher (p< 0.001) than the NAT2*7B cell line. NAT2 catalytic activity towards the N-acetylation of 100 μM isoniazid in NAT2*4 cells was about 4-fold higher (p< 0.05) than NAT2*5B cell line while there was no detectable activity in the NAT2*7B cell line. With 1000 μM isoniazid, NAT2 catalytic activity in NAT2*4 cells was about 4-and 5-fold higher (p< 0.001) than in NAT2*5B and NAT2*7B cell lines, respectively. These results confirm genetic heterogenicity within the slow NAT2 genotype. Furthermore, the present study documents differences between hydrazine drugs such as hydralazine and isoniazid versus arylamine carcinogens in the relative N-acetylation capacity catalyzed by NAT2*5B and NAT2*7B. Genetic heterogeneity within the slow acetylator phenotype is an important consideration for NAT2 genotype-guided isoniazid and hydralazine dosing strategies. NIH funding: P20-GM113226, P42-ES023716 & P30-ES030283