Cirsimaritin Contributes to the Estrogenic Activity of Cirsium japonicum var. maackii through the Activation of Estrogen Receptor α

Phytoestrogens are naturally occurring plant‐derived chemicals that exert female hormone‐like activities similar to those of endogenous estrogens. The purpose of this study was to quantitate the estrogenic activity of six chemical constituents (apigenin, hispidulin, cirsimaritin, cirsimarin, pectolinarin, and linarin) of Cirsium japonicum var. maackii using several in vitro assays. Reporter gene activation by each compound was examined using a human breast cancer (MCF‐7) cell‐based transactivation assay. Proliferative activity was also examined using MCF‐7 cells. Reporter gene activation in MCF‐7 cells by cirsimaritin was significantly suppressed by co‐administration of the estrogen receptor (ER) antagonist ICI 182,780, indicating that cirsimaritin is an ER agonist. Under experimental conditions simulating postmenopausal syndrome ( i.e ., a low concentration of estrogen), cirsimaritin exerted beneficial effects on MCF‐7 cells by increasing estrogenic activity. These results suggest that cirsimaritin is an effective estrogenic compound that can improve postmenopausal symptoms.