Smith Graeme B J, Bend John R, Bedard Leanne L, Reid Ken R, Petsikas Dimitri, Massey Thomas E
Department of Pharmacology and Toxicology, Queen's University Kingston, Ontario, Canada.
Drug Metab Dispos. 2003 Sep;31(9):1134-41. doi: 10.1124/dmd.31.9.1134.
The contributions of different enzymes to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) biotransformation were assessed in human lung microsomes prepared from peripheral lung specimens obtained from seven subjects. Metabolite formation was expressed as a percentage of total recovered radioactivity from [5-3H]NNK and its metabolites per milligram of protein per minute. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol was the major metabolite formed in the presence of an NADPH-generating system, with production ranging from 0.5186 to 1.268%/mg of protein/min, and total NNK bioactivation (represented by the sum of the four alpha-carbon hydroxylation endpoint metabolites) ranged from 0.002100 to 0.005685% alpha-hydroxylation/mg of protein/min. Overall, production of bioactivation metabolites was greater than that of detoxication (i.e., N-oxidation) products. Based on total bioactivation, subjects could be classified as high or low NNK bioactivators. In the presence of an NADPH-generating system, microsomal formation of the endpoint metabolite 1-(3-pyridyl)-1-butanone-4-carboxylic acid (keto acid) was consistently higher than that of all other alpha-carbon hydroxylation endpoint metabolites. Contributions of cytochrome p450 (p450) enzymes to NNK oxidation were demonstrated by NADPH dependence, inhibition by carbon monoxide, and inhibition by the nonselective p450 inhibitors proadifen hydrochloride (SKF-525A) and 1-aminobenzotriazole (ABT), particularly in lung microsomes from high bioactivators. At 5.0 mM, ABT inhibited total NNK bioactivation by 54 to 100%, demonstrating the importance of ABT-sensitive enzyme(s) in human pulmonary NNK bioactivation. Contributions of CYP2A6 and/or CYP2A13, as well as CYP2B6, to NNK bioactivation were also suggested by selective chemical and antibody inhibition in lung microsomes from some subjects. It is likely that multiple p450 enzymes contribute to human pulmonary microsomal NNK bioactivation, and that these contributions vary between individuals.
在从7名受试者的外周肺组织标本制备的人肺微粒体中，评估了不同酶对4-(甲基亚硝胺基)-1-(3-吡啶基)-1-丁酮(NNK)生物转化的贡献。代谢物的形成以每分钟每毫克蛋白质中[5-³H]NNK及其代谢物的总回收放射性的百分比表示。在存在NADPH生成系统的情况下，4-(甲基亚硝胺基)-1-(3-吡啶基)-1-丁醇是主要形成的代谢物，生成量范围为0.5186至1.268%/毫克蛋白质/分钟，总NNK生物活化作用(由四种α-碳羟基化终产物的总和表示)范围为0.002100至0.005685%α-羟基化/毫克蛋白质/分钟。总体而言，生物活化代谢物的生成量大于解毒(即N-氧化)产物的生成量。根据总生物活化作用，受试者可分为高或低NNK生物活化剂。在存在NADPH生成系统的情况下，终产物代谢物1-(3-吡啶基)-1-丁酮-4-羧酸(酮酸)的微粒体形成始终高于所有其他α-碳羟基化终产物。细胞色素P450(P450)酶对NNK氧化的贡献通过对NADPH的依赖性、一氧化碳的抑制作用以及非选择性P450抑制剂盐酸丙胺卡因(SKF-525A)和1-氨基苯并三唑(ABT)的抑制作用得到证明，特别是在高生物活化剂的肺微粒体中。在5.0 mM时，ABT抑制总NNK生物活化作用54%至100%，证明了ABT敏感酶在人肺NNK生物活化中的重要性。一些受试者肺微粒体中的选择性化学和抗体抑制作用也表明了CYP2A6和/或CYP2A13以及CYP2B6对NNK生物活化的贡献。多种P450酶可能参与人肺微粒体NNK生物活化作用，并且这些贡献在个体之间存在差异。
