Modulating effects of halogenated compounds on the metabolic detoxification of catechol estrogens and mammary carcinogenesis

通过测定双酚A及其氯代衍生物2-(3-氯-4-羟基苯基)-2-(4-羟基苯基)丙烷(3-ClBPA)和2，2-二(3-氯-4-羟基苯基)丙烷(3，3‘-diClBPA)与人雌激素受体-α和-β(ER-α和ER-β)的相对结合亲和力和对去卵巢雌性大鼠的促子宫作用，评价了双酚A及其氯化衍生物的雌激素样活性。双酚A及其氯化衍生物与17β-雌二醇竞争结合人ERA和ER-β蛋白。每天给动物注射50和100 mg/kg双酚A或其氯化衍生物，可显著增加子宫湿重和子宫内膜面积。本研究结果表明，3-氯双酚A和3，3‘-二氯双酚A对雌激素受体α的亲和力高于双酚A，但两种氯化双酚A在去卵巢雌性SD大鼠体内的雌激素样活性与双酚A相似。17β-雌二醇(E_2)和雌酮(E_1)是两种主要的内源性雌激素，在人体内代谢为邻苯二酚类雌激素(CES)。儿茶酚-O-甲基转移酶(COMT)介导的O-甲基化与酶促葡萄糖醛酸化和/或硫酸盐化结合在一起，有效地灭活了CES。我们发现，BPA及其氯化衍生物在体外对COMT介导的CES的O-甲基化几乎没有影响。但3-ClBPA对人UGT2B7介导的4-羟基-E_1葡萄糖醛酸化反应的抑制作用呈浓度依赖性。我们的研究结果表明，3-ClBPA，而不是BPA或3，3‘-diClBPA，在体外可以抑制人UGT2B7介导的4-羟基雌激素的葡萄糖醛酸化反应，并抑制这种结合酶在培养的MCF-7细胞中的表达。

The estrogenic activity of bisphenol A (BPA) and its chlorinated derivatives, 2-(3-chloro-4-hydroxyphenyl) -2-(4-hydroxyphenyl) propane (3-ClBPA) and 2,2-bis(3-chloro-4-hydroxyphenyl)propane (3,3'-diClBPA) was assessed by determining their relative binding affinity for the human estrogen receptor-α and -β (ERα and ERβ) and also their uterotrophic activity in ovariectomized female rats. BPA and its chlorinated derivatives were active in competing with [^3H] 17β-estradiol for their binding to the human ERa and ERβ proteins. Treatment of animals with 50 and 100 mg/kg/day of BPA or its chlorinated derivatives caused a significant increase in the uterine wet weight and the endometrial area. The results of our present study demonstrated that the affinities of 3-ClBPA and 3,3'-diClBPA for ERα were higher than the affinity of BPA, although the in vivo estrogenic activity of the two chlorinated BPAs in ovariectomized female Sprague-Dawley rats appeared to be comparable to that of BPA.17β-Estradiol (E_2) and estrone (E_1), two major endogenous estrogens, are metabolized to catechol estrogens (CEs, i.e., 2- and 4-hydroxy-F_2/E_1) in humans. CEs are effectively deactivated by the catechol-O-methyltransferase (COMT)-mediated O-methylation coupled with enzymatic glucuronidation and/or sulfation. We found that BPA and its chlorinated derivatives had little or no effect on the COMT-mediated O-methylation of CEs in vitro. However, 3-ClBPA inhibited the human UGT2B7-mediated glucuronidation of 4-hydroxy-E_1 in a concentration-dependent manner. The results of our study showed that 3-ClBPA, but not BPA or 3,3'-diClBPA, inhibited the human UGT2B7-mediated glucuronidation of 4-hydroxyestrogens in vitro, and it also inhibited the expression of this conjugating enzyme in cultured MCF-7 cells.