Shou M, Krausz K W, Gonzalez F J, Gelboin H V
Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Arch Biochem Biophys. 1996 Apr 1;328(1):201-7. doi: 10.1006/abbi.1996.0161.
The metabolic activation of the potent carcinogen dibenzo[a,h]anthracene (DB[a,h]A) was investigated with recombinant human cytochrome P450 enzymes 1A2, 2B6, 2C8, 2C9, 2E1, 3A3, 3A4, and 3A5 expressed in hepatoma G2 cells and with 14 different human liver microsomes. Three dihydrodiols, three phenols, and one diphenol were formed and separated by high-performance liquid chromatography and identified by UV absorption and mass spectra. Of all P450s tested, 1A2 and 2C9 were the most active and 2B6 was moderately active in the rate of total DB[a,h]A metabolism (2.5- to 12-fold greater activity than that for other P450s). The trans-3,4-dihydrodiol, generally recognized as a precursor of the ultimate carcinogenic 3,4-diol-1,2-epoxides, was produced most actively by 2C9, then 1A2 and 2B6. The values of enzymatic kinetics (K(m) and V(max)) indicated that 2C9 had the highest catalytic efficiency (V(max)/K(m) = 9.7) in the formation of 3,4-dihydrodiol, in contrast to 1A2 (5.9) and 2B6 (4.4). 1A2 had the highest activity toward production of the 1,2-dihydrodiol, which is considered to be a weakly carcinogenic metabolite. Although specific activities of human liver microsomes in overall metabolism of DB[a,h]A markedly differed between individuals, metabolic patterns were observed similar to that generated from 1A2. Since human 1A1, a predominant enzyme for metabolism of polycyclic aromatic hydrocarbons, is not significantly expressed in the liver, hepatic microsomal 2C9, 1A2, and 2B6 all probably contribute to the metabolic activation of DB[a,h]A.
利用在肝癌G2细胞中表达的重组人细胞色素P450酶1A2、2B6、2C8、2C9、2E1、3A3、3A4和3A5以及14种不同的人肝微粒体，对强效致癌物二苯并[a,h]蒽（DB[a,h]A）的代谢活化进行了研究。通过高效液相色谱法形成并分离出三种二氢二醇、三种酚和一种双酚，并通过紫外吸收和质谱进行鉴定。在所有测试的P450中，1A2和2C9在总DB[a,h]A代谢速率方面活性最高，2B6活性中等（活性比其他P450高2.5至12倍）。反式-3,4-二氢二醇通常被认为是最终致癌的3,4-二醇-1,2-环氧化物的前体，其生成最活跃的是2C9，其次是1A2和2B6。酶动力学值（K(m)和V(max)）表明，2C9在形成3,4-二氢二醇方面具有最高的催化效率（V(max)/K(m)=9.7），相比之下1A2为5.9，2B6为4.4。1A2对生成1,2-二氢二醇的活性最高，1,2-二氢二醇被认为是一种弱致癌代谢物。尽管人肝微粒体在DB[a,h]A整体代谢中的比活性在个体之间存在显著差异，但观察到的代谢模式与1A2产生的代谢模式相似。由于人1A1（多环芳烃代谢的主要酶）在肝脏中表达不显著，肝微粒体中的2C9、1A2和2B6可能都有助于DB[a,h]A的代谢活化。
