Modulation of Estrogenic Activity in Estrogen Receptor α and β by Flavinoids in Women’s Health Botanicals

Menopausal women have been choosing natural alternatives over conventional hormone treatments to manage their symptoms, partly due to a reported increase in risk of breast carcinogenesis from hormone therapy that consists of conjugated estrogens and medroxyprogesterone. The popular botanicals-hops, red clover, licorice, and epimedium-are some of the dietary supplements used to alleviate these symptoms, which include hot flashes and night sweats. They contain phytoestrogens-compounds that behave like estrogens-known as flavonoids and isoflavonoids. These activate estrogen receptors (ER) α and β when consumed. ERα activity includes cellular proliferation, while ERβ attenuates this ERα-induced function, thus regulating proliferation. ERβ is also suggested to have a chemoprotective role in vivo. We hypothesized that botanicals containing ERβ-preferential (iso)flavonoids may be able to provide ERβ-related protective benefits by counterbalancing ERα proliferation. In this study, the initial aims included optimizing estrogenic screening assays to identify ERβ-preferential (iso)flavonoids present in select botanicals. Using bioassay-guided fractionation, 8-prenylapigenin (8-PA) was isolated from the tested licorice extract and identified as a potent ERβ-preferential agonist with nanomolar EC50 values. Secondly, a structure activity relationship (SAR) study was conducted to identify (iso)flavonoid structures that favor ERβ-preferential activity. Notable (iso)flavonoids analyzed included 8-prenylnaringenin, 8-prenylapigenin, apigenin, naringenin, genistein, 8-prenylgenistein. Results showed that prenylation on the 8-position of the A-ring of flavonoids increased overall estrogenic activity, and when combined with C2-C3 unsaturation on the C-ring, this resulted in an increase in ERβ potency. In contrast, this same prenylation on isoflavonoids resulted in a decrease in overall estrogenic activity, while the absence of prenylation with C2-C3 unsaturation on the C-ring increased ERβ-preferential potency. Select women’s health botanicals are used for menopausal symptoms, and these induce ERα activity when consumed. However, if they contain ERβ-preferential (iso)flavonoids, these may contribute chemoprotective benefits through ERβ activity that attenuates ERα-induced proliferation, reducing the risk of breast carcinogenesis. These botanicals may offer a beneficial safety profile, while providing potential health benefits.