Oral administration of Brazilian propolis exerts estrogenic effect in ovariectomized rats
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Propolis, a natural product derived from plants by honeybees, is a mixture of several hundred chemicals, including flavonoids, coumaric acids, and caffeic acids, some of which show estrogen-like activity. In this study, the estrogenic activity of crude ethanolic extract of Brazilian propolis was determined using several <i>in vitro</i> and <i>in vivo</i> assays. Propolis was found to bind to human estrogen receptors (ERs). Furthermore, propolis induced the expression of estrogen-responsive genes in ER-positive MCF-7 and Ishikawa cells. These <i>in vitro</i> assays suggest that propolis exerts estrogenic activity; therefore, <i>in vivo</i> experiments were conducted using ovariectomized rats. Oral administration of propolis (55 or 550 mg/kg/day for 3 days) significantly increased uterine wet weight and luminal epithelium thickness in comparison with the corresponding values in the corn oil-treated control group. Moreover, propolis induced ductal cell proliferation in the mammary glands. These effects were completely inhibited by full ER antagonist ICI 182,780, confirming that the effects of propolis are mediated by the ER. Our data show that oral intake of propolis induces estrogenic activity in ER-expressing organs <i>in vivo</i> and suggest that Brazilian propolis is a useful dietary source of phytoestrogens and a promising treatment for postmenopausal symptoms.
- The Journal of Toxicological Sciences
The Journal of Toxicological Sciences 40(2), 235-242, 2015
The Japanese Society of Toxicology