Shou M, Korzekwa K R, Krausz K W, Buters J T, Grogan J, Goldfarb I, Hardwick J P, Gonzalez F J, Gelboin H V
Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Mol Carcinog. 1996 Dec;17(4):241-9. doi: 10.1002/(SICI)1098-2744(199612)17:4<241::AID-MC8>3.0.CO;2-G.
7,12-Dimethylbenz[a]anthracene (DMBA), a potent carcinogen, requires metabolic activation by cytochrome P450s (P450s) to electrophilic metabolites that result in DNA modification, mutagenicity, and carcinogenicity. In this study, we used eight human forms, four rodent forms, and one rabbit form of P450 expressed from recombinant vaccinia or baculovirus vectors to define their specificity for metabolizing DMBA. Of the eight human P450s, 1A1 was the most active (specific activity = 14.7 nmol/min/nmol of P450) in total metabolism of DMBA and showed approximately 6- to 33-fold more activity than other P450s, 2B6, 2C9, and 1A2 were also capable of metabolizing DMBA (2.0-2.5 nmol/min/nmol of P450), whereas 2C8, 2E1, 3A4, and 3A5 exhibited relatively low activities. Among animal P450s, mouse 1A1 exhibited activity similar to that of human 1A1 and had 5.0- to 37-fold more activity than other rodent and rabbit P450s. In regard to enzyme regioselectivity, most human and rodent P450s predominantly formed the 8,9-diol, but human 2B6 and rat 2B1 preferentially formed the 5,6-diol. In the production of monohydroxymethyl metabolites, all the enzymes yielded more 7-hydroxymethyl-12-methylbenz[a]anthracene (7HOM12MBA) than 12-hydroxymethyl-7-methylbenz[a]anthracene (7M12HOMBA), except for human 1A1, which presented the reverse selectivity. Human liver microsomes from 10 organ donors were shown to metabolize DMBA and in most circumstances generated the metabolic profile DMBA trans-8,9-dihydrodiol > 7HOM12MBA > or = DMBA trans-5,6-dihydrodiol > or = 7,12-dihydroxymethylbenz[a]anthracene > 7M12HOMBA > DMBA trans-3,4-dihydrodiol. Thus, the combined activity of hepatic microsomal 2C9, 1A2, and 2B6 may contribute to the metabolic activation and the metabolism of DMBA in normal human liver.
7,12 - 二甲基苯并[a]蒽（DMBA）是一种强效致癌物，需要细胞色素P450（P450）将其代谢活化为亲电代谢产物，这些代谢产物会导致DNA修饰、致突变性和致癌性。在本研究中，我们使用了从重组痘苗病毒或杆状病毒载体表达的8种人类P450形式、4种啮齿动物P450形式和1种兔P450形式，以确定它们代谢DMBA的特异性。在8种人类P450中，1A1在DMBA的总代谢中活性最高（比活性 = 14.7 nmol/分钟/ nmol P450），其活性比其他P450（2B6、2C9和1A2）高约6至33倍，2B6、2C9和1A2也能够代谢DMBA（2.0 - 2.5 nmol/分钟/ nmol P450），而2C8、2E1、3A4和3A5表现出相对较低的活性。在动物P450中，小鼠1A1表现出与人类1A1相似的活性，其活性比其他啮齿动物和兔P450高5.0至37倍。关于酶的区域选择性，大多数人类和啮齿动物P450主要生成8,9 - 二醇，但人类2B6和大鼠2B1优先生成5,6 - 二醇。在单羟甲基代谢产物的生成中，除了人类1A1表现出相反的选择性外，所有酶生成的7 - 羟甲基 - 12 - 甲基苯并[a]蒽（7HOM12MBA）都比12 - 羟甲基 - 7 - 甲基苯并[a]蒽（7M12HOMBA）多。来自10名器官供体的人肝微粒体显示能够代谢DMBA，并且在大多数情况下产生的代谢谱为：DMBA反式 - 8,9 - 二氢二醇 > 7HOM12MBA > 或 = DMBA反式 - 5,6 - 二氢二醇 > 或 = 7,12 - 二羟甲基苯并[a]蒽 > 7M12HOMBA > DMBA反式 - 3,4 - 二氢二醇。因此，肝微粒体2C9、1A2和2B6的联合活性可能有助于正常人类肝脏中DMBA的代谢活化和代谢。
