Evaluation of the estrogenic effects of legume extracts containing phytoestrogens.

Seven legume extracts containing phytoestrogens were analyzed for estrogenic activity. Methanol extracts were prepared from soybean (Glycine max L.), green bean (Phaseolus vulgaris L.), alfalfa sprout (Medicago sativa L.), mung bean sprout (Vigna radiata L.), kudzu root (Pueraria lobata L.), and red clover blossom and red clover sprout (Trifolium pratense L.). Extracts of kudzu root and red clover blossom showed significant competitive binding to estrogen receptor beta (ERbeta). Estrogenic activity was determined using an estrogen-dependent MCF-7 breast cancer cell proliferation assay. Kudzu root, red clover blossom and sprout, mung bean sprout, and alfalfa sprout extracts displayed increased cell proliferation above levels observed with estradiol. The pure estrogen antagonist, ICI 182,780, suppressed cell proliferation induced by the extracts, suggesting an ER-related signaling pathway was involved. The ER subtype-selective activities of legume extracts were examined using transiently transfected human embryonic kidney (HEK 293) cells. All seven of the extracts exhibited preferential agonist activity toward ERbeta. Using HPLC to collect fractions and MCF-7 cell proliferation, the active components in kudzu root extract were determined to be the isoflavones puerarin, daidzin, genistin, daidzein, and genistein. These results show that several legumes are a source of phytoestrogens with high levels of estrogenic activity.