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

内分泌干扰物（Endocine disrupting chemicals，EDCs）是由外源性代谢酶如肝微粒体细胞色素P450（P450）代谢的。为了对雌激素性内分泌干扰物进行准确的风险评估，应考虑其雌激素活性的代谢调节。因此，我们研究了雌激素内分泌干扰物，包括大豆异黄酮，如染料木素与人肝S9和大鼠肝S9或微粒体的孵育是否导致代谢失活或激活的雌激素活性，使用半乳糖苷酶报告基因分析与重组酵母表达人雌激素受体。将4-叔辛基酚、4-壬基酚和染料木黄酮与大鼠肝S_9孵育，它们的雌激素活性被代谢失活。与此相反，双酚A（BPA）的雌激素活性增加了几倍，通过与大鼠肝S9以及人肝S9孵育相比，含有灭活S9的对照。BPA的这种代谢活化需要微粒体和细胞溶质组分，表明除P450外还涉及另一种因子。通过LC/MS分析，初步认为活性代谢产物的结构特征为异丙烯基苯酚的二聚体。另一方面，鹰嘴豆芽素A是染料木黄酮的弱雌激素4' -甲氧基衍生物，在大鼠肝S9或微粒体中主要转化为活性代谢物染料木黄酮，导致雌激素活性增加。这些结果清楚地表明，外源性代谢酶如P450催化的雌激素样内分泌干扰物的代谢转化引起其雌激素活性的显着调节。

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.