Interaction of Phytoestrogens with Estrogen Receptors α and β (II)

We investigated the estrogenic activities of isoflavone derivatives in competition binding assays with human estrogen receptor (hER) α or hER β protein, and in a gene expression assay using a yeast system. Coumestrol binds as strongly as 17β-estradiol to both hERs. Biochanin A, 5-OMe-genistein, formononetin, and tectorigenin bind well to hER β, but significant binding to hER α is only observed with 5-OMe-genistein, formononetin and tectorigenin. The binding of 7-OMe-genistein and irisolidone is poor to both receptors. Among the glucosides, sissotorin binds both receptors and the binding is stronger than genistin. Coumestrol induces transcription as strongly as genistein. Tectorigenin also induces transcription with both hERs. Though biochanin A, 5-OMe-genistein, 7-OMe-genistein, irisolidone and formononetin slightly induce transcription with hER β, they act as antagonists in the induction of transcription by 17β-estradiol. The results show that methylation or glucosidation of isoflavones generally inhibits their phytoestrogenic activities.