Differential binding with ERalpha and ERbeta of the phytoestrogen-rich plant Pueraria mirifica.

Variations in the estrogenic activity of the phytoestrogen-rich plant, Pueraria mirifica, were determined with yeast estrogen screen (YES) consisting of human estrogen receptors (hER) hERalpha and hERbeta and human transcriptional intermediary factor 2 (hTIF2) or human steroid receptor coactivator 1 (hSRC1), respectively, together with the beta-galactosidase expression cassette. Relative estrogenic potency was expressed by determining the beta-galactosidase activity (EC(50)) of the tuber extracts in relation to 17beta-estradiol. Twenty-four and 22 of the plant tuber ethanolic extracts interacted with hERalpha and hERbeta, respectively, with a higher relative estrogenic potency with hERbeta than with hERalpha. Antiestrogenic activity of the plant extracts was also determined by incubation of plant extracts with 17beta-estradiol prior to YES assay. The plant extracts tested exhibited antiestrogenic activity. Both the estrogenic and the antiestrogenic activity of the tuber extracts were metabolically activated with the rat liver S9-fraction prior to the assay indicating the positive influence of liver enzymes. Correlation analysis between estrogenic potency and the five major isoflavonoid contents within the previously HPLC-analyzed tuberous samples namely puerarin, daidzin, genistin, daidzein, and genistein revealed a negative result.