Related Experiment Video
Updated: Feb 21, 2026

A Phenotyping Regimen for Genetically Modified Mice Used to Study Genes Implicated in Human Diseases of Aging
Published on: July 14, 2016
N-Acetyltransferase 2 Genotype-Dependent N-Acetylation of Hydralazine in Human Hepatocytes
Cecily E Allen1, Mark A Doll1, David W Hein2
1Department of Pharmacology and Toxicology and James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, Kentucky.
Abstract:
Hydralazine is used in the treatment of essential hypertension and is under investigation for epigenetic therapy in the treatment of neoplastic and renal diseases. N-acetyltransferase (NAT) 2 exhibits a common genetic polymorphism in human populations. After recombinant expression in yeast, human NAT2 exhibited an apparent Lineweaver-Burk constant (K-m) value (20.1 ± 8.8 μM) for hydralazine over 20-fold lower than the apparent K-m value (456 ± 57 μM) for recombinant human NAT1 (P = 0.0016). The apparent Vmax value for recombinant human NAT1 (72.2 ± 17.9 nmol acetylated/min/mg protein) was significantly (P = 0.0245) lower than recombinant human NAT2 (153 ± 15 nmol acetylated/min/mg protein), reflecting 50-fold higher clearance for recombinant human NAT2. Hydralazine NAT activities exhibited a robust acetylator gene dose response in cryopreserved human hepatocytes both in vitro and in situ. Hydralazine NAT activities in vitro differed significantly with respect to NAT2 genotype at 1000 (P = 0.0319), 100 (P = 0.002), and 10 μM hydralazine (P = 0.0029). Hydralazine NAT activities differed significantly (P < 0.001) among slow acetylator hepatocytes, (NAT2*5B/*5B > NAT2*5B/*6A > NAT2*6A/*6A). The in situ hydralazine N-acetylation rates differed significantly with respect to NAT2 genotype after incubation with 10 (P = 0.002) or 100 µM (P = 0.0015) hydralazine and were higher after incubation with 100 μM (10-fold) than with 10 μM (4.5-fold) hydralazine. Our results clearly document NAT2 genotype-dependent N-acetylation of hydralazine in human hepatocytes, suggesting that hydralazine efficacy and safety could be improved by NAT2 genotype-dependent dosing strategies.
Related Concept Videos
Phase II Reactions: Acetylation Reactions
The substrates for acetylation are typically drugs or their metabolites with an amino, sulfonamide, or hydrazine functional group. Acetylation can occur at several points in the drug molecule, including primary, secondary, and...
Pharmacogenetics of Phase II Enzymes: N-acetyltransferase, Thiopurine S-methyltransferase, UDP-glucuronosyltransferase
Phase II Reactions: Sulfation and Conjugation with α-Amino Acids
Pharmacogenetics of Drug Targets: β₂-Adrenergic Receptors, Apo E, Thymidylate Synthase
Pharmacogenetic Phenotypes: Alterations in Pharmacokinetics, Drug Targets and Biologic Milieu
Phase II Reactions: Glucuronidation

