Hammons G J, Guengerich F P, Weis C C, Beland F A, Kadlubar F F
Cancer Res. 1985 Aug;45(8):3578-85.
Hepatic N-oxidation and aryl ring oxidation are generally regarded as critical activation and detoxification pathways for arylamine carcinogenesis. In this study, we examined the in vitro hepatic metabolism of the carcinogens, 2-aminofluorene (2-AF) and 2-naphthylamine (2-NA), and the suspected carcinogen, 1-naphthylamine (1-NA), using high-pressure liquid chromatography. Hepatic microsomes from rats, dogs, and humans were shown to catalyze the N-oxidation of 2-AF and of 2-NA, but not of 1-NA; and the rates of 2-AF N-oxidation were 2- to 3-fold greater than the rates of 2-NA N-oxidation. In each species, rates of 1-hydroxylation of 2-NA and 2-hydroxylation of 1-NA were comparable and were 2- to 5-fold greater than 6-hydroxylation of 2-NA or 5- and 7-hydroxylation of 2-AF. Purified rat hepatic monooxygenases, cytochromes P-450UT-A, P-450UT-H, P-450PB-B, P-450PB-D, P-450BNF-B, and P-450ISF/BNF-G but not P-450PB-C or P-450PB/PCN-E, catalyzed several ring oxidations as well as the N-oxidation of 2-AF. Cytochromes P-450PB-B, P-450BNF-B, and P-450ISF/BNF-G were most active; however, only cytochrome P-450ISF/BNF-G, the isosafrole-induced isozyme, catalyzed the N-oxidation of 2-NA. The purified porcine hepatic flavin-containing monooxygenase, which was known to carry out the N-oxidation of 2-AF, was found to catalyze only ring oxidation of 1-NA and 2-NA. No activity for 1-NA N-oxidation was found with any of the purified enzymes. These data support the hypothesis that 1-NA is probably not carcinogenic. Furthermore, carcinogenic arylamines appear to be metabolized similarly in humans and experimental animals and perhaps selectively by a specific form of hepatic cytochrome P-450. Enzyme mechanisms accounting for the observed product distributions were evaluated by Hückel molecular orbital calculations on neutral, free radical, and cation intermediates. A reaction pathway is proposed that involves two consecutive one-electron oxidations to form a paired substrate cation-enzyme hydroxyl anion intermediate that collapses to ring and N-hydroxy products.
肝脏N-氧化和芳环氧化通常被认为是芳胺致癌作用的关键激活和解毒途径。在本研究中，我们使用高压液相色谱法检测了致癌物2-氨基芴（2-AF）和2-萘胺（2-NA）以及疑似致癌物1-萘胺（1-NA）的体外肝脏代谢情况。结果显示，大鼠、狗和人类的肝脏微粒体可催化2-AF和2-NA的N-氧化，但不能催化1-NA的N-氧化；2-AF的N-氧化速率比2-NA的N-氧化速率高2至3倍。在每个物种中，2-NA的1-羟基化速率和1-NA的2-羟基化速率相当，且比2-NA的6-羟基化速率或2-AF的5-和7-羟基化速率高2至5倍。纯化的大鼠肝脏单加氧酶，细胞色素P-450UT-A、P-450UT-H、P-450PB-B、P-450PB-D、P-450BNF-B和P-450ISF/BNF-G，但不包括P-450PB-C或P-450PB/PCN-E，可催化几种环氧化以及2-AF的N-氧化。细胞色素P-450PB-B、P-450BNF-B和P-450ISF/BNF-G活性最高；然而，只有异黄樟素诱导的同工酶细胞色素P-450ISF/BNF-G可催化2-NA的N-氧化。已知可进行2-AF N-氧化的纯化猪肝脏含黄素单加氧酶，被发现仅催化1-NA和2-NA的环氧化。在任何纯化酶中均未发现1-NA N-氧化活性。这些数据支持了1-NA可能不具有致癌性的假设。此外，致癌芳胺在人类和实验动物中的代谢方式似乎相似，并且可能由肝脏细胞色素P-450的特定形式选择性代谢。通过对中性、自由基和阳离子中间体进行休克尔分子轨道计算，评估了解释观察到的产物分布的酶机制。提出了一种反应途径，该途径涉及两个连续的单电子氧化，以形成成对的底物阳离子-酶羟基阴离子中间体，该中间体分解为环和N-羟基产物。
