Catechol estrogen 4-hydroxyequilenin is a substrate and an inhibitor of catechol-O-methyltransferase.
Catechol estrogen 4-hydroxyequilenin is a substrate and an inhibitor of catechol-O-methyltransferase.
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儿茶酚雌激素 4-羟基马萘雌酮是儿茶酚-O-甲基转移酶的底物和抑制剂。
DOI：
10.1021/tx0340549
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Bolton,JudyL
中科院分区：
文献类型：
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作者：
Yao,Jiaqin;Li,Yan;Chang,Minsun;Wu,Huaping;Yang,Xiaofeng;Goodman,JulieE;Liu,Xuemei;Liu,Hong;Mesecar,AndrewD;VanBreemen,RichardB;Yager,JamesD;Bolton,JudyL
Redox and/or electrophilic metabolites formed during estrogen metabolism may play a role in estrogen carcinogenesis. 4-Hydroxyequilenin (4-OHEN) is the major phase I catechol metabolite of the equine estrogens equilenin and equilin, which are components of the most widely prescribed estrogen replacement formulation, Premarin. Previously, we have found that 4-OHEN rapidly autoxidized to ano-quinone in vitro and caused toxic effects such as the inactivation of human detoxification enzymes. 4-OHEN has also been shown to be a substrate for catechol-O-methyltransferase (COMT) in human breast cancer cells. In the present study, we demonstrated that 4-OHEN was not only a substrate of recombinant human soluble COMT in vitro with aKmof 2.4 μM andkcatof 6.0 min-1but it also inhibited its own methylation by COMT at higher concentrations in the presence of the reducing agent dithiothreitol. In addition, 4-OHEN was found to be an irreversible inhibitor of COMT-catalyzed methylation of the endogenous catechol estrogen 4-hydroxyestradiol with aKiof 26.0 μM and ak2of 1.62 × 10-2s-1. 4-OHEN in vitro not only caused the formation of intermolecular disulfide bonds as demonstrated by gel electrophoresis, but electrospray ionization mass spectrometry and matrix-assisted laser desorption ionization time-of-flight mass spectrometry also showed that 4-OHEN alkylated multiple residues of COMT. Peptide mapping experiments further indicated that Cys33 in recombinant human soluble COMT was the residue most likely modified by 4-OHEN in vitro. These data suggest that inhibition of COMT methylation by 4-OHEN might reduce endogenous catechol estrogen clearance in vivo and further enhance toxicity.
