Shou M, Korzekwa K R, Brooks E N, Krausz K W, Gonzalez F J, Gelboin H V
Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Carcinogenesis. 1997 Jan;18(1):207-14. doi: 10.1093/carcin/18.1.207.
The metabolic activation of estrone (E1), a potent estrogen was investigated using recombinant human cytochrome P450 enzymes, 1A2, 2B6, 2C8, 2C9, 2C9R144C, 2E1, 3A4, 3A5 and liver microsomes from 14 human organ donors. At least five products of E1 were detected and quantitated by HPLC and gas chromatography-mass spectrometry (GC-MS). Among these metabolites, 16alpha-OH-E1, 2-OH-E1 and 4-OH-E1, which are believed to be associated with estrogen carcinogenesis in animals, were definitively identified. Of all P450s examined, 1A2 and 3A4 exhibited the highest activities with turnovers of 3.4 and 2.5 nmol/min/nmol P450 for the total metabolism of E1, respectively, while 3A5, 2C9 and 2C9R144C showed moderate activities. 2B6, 2E1 and 2C8 did not produce any significant amount of products. 1A2 formed almost exclusively the 2-OH-E1 at a rate of 3.3 nmol/min/nmol but 3A4 preferentially formed the metabolite X1 (an unknown hydroxylation product) and 16alpha-OH-E1. Kinetic characterization showed that the Km values of 1A2, 3A4 and 3A5 were 14, 95 and 64 microM and Vmax were 5.43, 0.68 and 0.35 min(-1), respectively. All human liver microsomes were capable of metabolizing estrone and a 4-fold variation was seen between individuals. The relative amount of metabolites formed was generally 2-OH-E1 > metabolite X1 > 4-OH-E1 > 16alpha-OH-E1 > metabolite X2. 3A4/5 enzyme complex was assessed by inhibitory monoclonal antibody specific for 3A4/5 to contribute 60-88% to the formation of individual metabolites in human liver except for 2-OH-E1 (3%). The formation of 2-OH-E1 and 16alpha-OH-E1 by 14 human liver microsomes was significantly correlated with caffeine 3-demethylation supported by 1A2 (r2 = 0.87) and with testosterone 6beta-hydroxylation by 3A4 (r2 = 0.66), respectively. Thus the metabolic patterns exhibited by human liver are likely due to the combined activities of the P450 1A2 and 3A4 enzymes.
使用重组人细胞色素P450酶1A2、2B6、2C8、2C9、2C9R144C、2E1、3A4、3A5以及来自14位人体器官捐赠者的肝微粒体，对强效雌激素雌酮（E1）的代谢活化进行了研究。通过高效液相色谱法（HPLC）和气相色谱 - 质谱联用仪（GC - MS）检测并定量了至少五种E1的产物。在这些代谢产物中，明确鉴定出了16α - 羟基 - E1、2 - 羟基 - E1和4 - 羟基 - E1，据信它们与动物体内雌激素致癌作用有关。在所检测的所有细胞色素P450中，1A2和3A4对E1的总代谢表现出最高活性，周转率分别为3.4和2.5 nmol/分钟/ nmol细胞色素P450，而3A5、2C9和2C9R144C表现出中等活性。2B6、2E1和2C8未产生任何显著量的产物。1A2几乎仅以3.3 nmol/分钟/ nmol的速率生成2 - 羟基 - E1，但3A4优先生成代谢产物X1（一种未知的羟基化产物）和16α - 羟基 - E1。动力学特征表明，1A2、3A4和3A5的米氏常数（Km）值分别为14、95和64 μM，最大反应速度（Vmax）分别为5.43、0.68和0.35分钟⁻¹。所有人体肝微粒体都能够代谢雌酮，个体之间存在4倍的差异。形成的代谢产物的相对量通常为2 - 羟基 - E1＞代谢产物X1＞4 - 羟基 - E1＞16α - 羟基 - E1＞代谢产物X2。通过对3A4/5特异的抑制性单克隆抗体评估3A4/5酶复合物，其对人体肝脏中除2 - 羟基 - E1（3%）外的各代谢产物形成的贡献为60 - 88%。14个人体肝微粒体形成2 - 羟基 - E1和16α - 羟基 - E1分别与1A2支持的咖啡因3 - 去甲基化（r² = 0.87）和3A4支持的睾酮6β - 羟基化（r² = 0.66）显著相关。因此，人体肝脏表现出的代谢模式可能是由于细胞色素P450 1A2和3A4酶的联合活性所致。
