Estrogenic effects of ethanol and ether extracts of propolis.

Propolis obtained from honeybee hives has been used in Oriental folk medicine as an anti-inflammatory, anti-carcinogenic, or immunomodulatory agent. The potential estrogenic activity of propolis was investigated in vitro using the MCF-7 human breast cancer cell proliferation, human estrogen receptor (hER) binding and yeast-based steroid receptor transcription, and in vivo using the immature rat uterotrophic effect. Treatments with ethanol extract of propolis (EEP) and ether extract of propolis (REP) enhanced MCF-7 cell proliferation in concentrations ranging from 0.8 to 4 microg/ml. Both EEP and REP competed for binding of [3H]17beta-estradiol to the hER with IC(50) values of 9.14 and 9.72 microg/ml, respectively. In yeast estrogen receptor transcription assay, both EEP and REP were found to be estrogenic with EC(50) values of 9.48, and 8.55 microg/ml, respectively. Animals treated with EEP or REP for 4 days (500-1000 mg/kg per day, s.c.) exhibited significant dose-dependent increases in uterine wet weight. However, in the yeast androgen and progesterone receptor transcription assays, either EEP or REP was found not to be active. The results suggest that propolis produces estrogenic effects through activation of estrogen receptors.