Metabolic Modulation of Estrogenicity of Endocrine Disrupting Chemicals by Cytochrome P450 in Human and Rat Livers

内分泌干扰物（EDCs）是由异种代谢酶如肝微粒体细胞色素P450 （P450）代谢的。为了对雌激素性EDCs进行精确的风险评估，应考虑其雌激素性的代谢调节。因此，我们利用半乳糖苷酶报告试验，利用表达人雌激素受体的重组酵母，研究了包括大豆异黄酮（如染料木素）在内的雌激素性EDCs与人肝脏S9和大鼠肝脏S9或微粒体孵育是否会导致代谢失活或雌激素性激活。4-叔辛基酚、4-壬基酚和染料木素与大鼠肝脏S9孵育，代谢失活了它们的雌激素活性。相比之下，双酚A （BPA）与大鼠肝脏S9和人肝脏S9孵育后，其雌激素原性比含有灭活S9的对照提高了数倍。BPA的代谢激活需要微粒体和细胞质组分，这表明除了P450外，还涉及另一个因子。通过LC/MS分析初步确定活性代谢物为异丙烯酚二聚体。另一方面，染料木黄酮的弱雌激素4′-甲氧基衍生物生物茶素A在大鼠肝脏S9或微粒体中主要转化为活性代谢物染料木黄酮，导致雌激素增强。这些结果清楚地表明，由P450等外源代谢酶催化的雌激素性EDCs的代谢转化引起了其雌激素性的显著调节。

Endocine disrupting chemicals (EDCs) are metabolized by xenobiotic metabolizing enzymes such as hepatic microsomal cytochrome P450 (P450). In order to make a precise risk assessment of estrogenic EDCs, metabolic modulation of their estrogenicity should be taken into account. Therefore, we investigated whether the incubation of estrogenic EDCs including soygean isoflavones such as genistein with human liver S9 and rat liver S9 or microsomes results in metabolic inactivation or activation of estrogenicity using a galactosidase reporter assay with recombinant yeast expressing human estrogen receptor. By incubation of 4-tert-octylphenol and 4-nonylphenol as well as genistein with rat liver S9, their estrogenic activities were metabolically inactivated. In contrast, the estrogenicity of bisphenol A (BPA) was increased several times by incubation with rat liver S9 as well as human liver S9 compared with those of the controls containing the inactivated S9. This metabolic activation of BPA required both microsomal and cytosolic fractions, indicating an involvement of another factor(s) in addition to P450. The structural feature of an active metabolite was tentatively suggested to be a dimer of isopropenyl phenol by LC/MS analysis. On the other hand, biochanin A, a weak estrogenic 4' -methoxy derivative of genistein, was predominantly converted to genistein, an active metabolite, with rat liver S9 or microsomes, resulting in an increase of estrogenicity. These results clearly demonstrated that the metabolic conversion of estrogenic EDCs catalyzed with xenobiotic metabolizing enzymes such as P450 caused a marked modulation of their estrogenicity.