Cao K, Devanesan P D, Ramanathan R, Gross M L, Rogan E G, Cavalieri E L
Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805, USA.
Chem Res Toxicol. 1998 Aug;11(8):917-24. doi: 10.1021/tx9702300.
Oxidation of catechol estrogens (CE) leads to the reactive electrophilic CE quinones. Reaction of CE-3,4-quinones with DNA has been implicated in tumor initiation. One pathway to prevent this reaction is conjugation of CE quinones with glutathione (GSH). Four CE, 4-hydroxy estrone (4-OHE1), 4-hydroxyestradiol (4-OHE2), 2-OHE1, and 2-OHE2, were conjugated with GSH after oxidation catalyzed by horseradish peroxidase (HRP), lactoperoxidase (LP), or rat liver microsomal cytochrome P450. This reaction is a free-radical chain autoxidation that produces very high yields of products. Six mono-GSH conjugates, 4-OHE1(E2)-2-SG, 2-OHE1(E2)-1-SG, and 2-OHE1(E2)-4-SG, and four di-GSH conjugates, 4-OHE1(E2)-1,2-bisSG and 2-OHE1(E2)-1,4-bisSG, were identified and quantified. These di-GSH conjugates were also obtained quantitatively from oxidation of mono-GSH conjugates by the same enzymes. HRP and LP gave very similar product profiles. Phenobarbital- and 3-methylcholanthrene-induced microsomes with either NADPH or cumene hydroperoxide as cofactor oxidized 4-OHE2 to form similar amounts of GSH conjugates. Enzymatic oxidation of 2-OHE1(E2) in the presence of GSH produced more 2-OHE1(E2)-4-SG than the 1-isomer. This contrasts with the direct reaction of E1(E2)-2,3-Q and GSH, in which the 1-isomer is formed more abundantly than the 4-isomer (Cao, K., Devanesan, P. D., Ramanathan, R., Gross, M. L., Rogan, E. G., and Cavalieri, E. L. (1998) Chem. Res. Toxicol. 11, 909-916). Competitive enzymatic oxidation of equimolar 4-OHE2 and 2-OHE2 in the presence of an equimolar amount of GSH yielded more 2-OHE2 conjugates than 4-OHE2 conjugates, despite E2-3,4-Q being more reactive with GSH than E2-2,3-Q. These results suggest that 2-OHE2 is a better substrate than 4-OHE2 in the catalytic oxidation to quinones, despite the greater reactivity of E2-3,4-Q, compared to E2-2,3-Q, with GSH.
儿茶酚雌激素（CE）的氧化会生成具有反应活性的亲电CE醌。CE - 3,4 - 醌与DNA的反应被认为与肿瘤起始有关。防止这种反应的一种途径是CE醌与谷胱甘肽（GSH）结合。在辣根过氧化物酶（HRP）、乳过氧化物酶（LP）或大鼠肝微粒体细胞色素P450催化氧化后，四种CE，即4 - 羟基雌酮（4 - OHE1）、4 - 羟基雌二醇（4 - OHE2）、2 - OHE1和2 - OHE2，与GSH结合。该反应是一种自由基链式自氧化反应，产物产率非常高。鉴定并定量了六种单GSH结合物，即4 - OHE1（E2）- 2 - SG、2 - OHE1（E2）- 1 - SG和2 - OHE1（E2）- 4 - SG，以及四种双GSH结合物，即4 - OHE1（E2）- 1,2 - bisSG和2 - OHE1（E2）- 1,4 - bisSG。这些双GSH结合物也可通过相同酶对单GSH结合物的氧化定量获得。HRP和LP产生的产物谱非常相似。用苯巴比妥和3 - 甲基胆蒽诱导的微粒体，以NADPH或氢过氧化异丙苯作为辅助因子，将4 - OHE2氧化形成相似量的GSH结合物。在GSH存在下，2 - OHE1（E2）的酶促氧化产生的2 - OHE1（E2）- 4 - SG比1 - 异构体更多。这与E1（E2）- 2,3 - Q和GSH的直接反应形成对比，在该直接反应中，1 - 异构体的生成量比4 - 异构体更多（曹，K.，德瓦内桑，P. D.，拉马纳坦，R.，格罗斯，M. L.，罗根，E. G.，和卡瓦列里，E. L.（1998年）《化学研究毒理学》11，909 - 91）。在等摩尔量的GSH存在下，对等摩尔的4 - OHE2和2 - OHE2进行竞争性酶促氧化，尽管E2 - 3,4 - Q与GSH的反应性比E2 - 2,3 - Q更高，但产生的2 - OHE2结合物比4 - OHE2结合物更多。这些结果表明，尽管E2 - 3,4 - Q与GSH的反应性比E2 - 2,3 - Q更高，但在催化氧化为醌的过程中，2 - OHE2比4 - OHE2是更好的底物。
