Effects of tea catechins on the ERE-regulated estrogenic activity

Tea catechins exert many biological effects, including anticancer and antibacterial activities. Also, it is reported that some plant flavonoids exhibit estrogenic activity. In this study, we investigated estrogenic or antiestrogenic activities of catechins in HeLa cells transiently transfected with an estrogen response element (ERE)-regulated luciferase reporter and an estrogen receptor (ER) ct or ERP expression vector. Catechins alone did not induce luciferase (luc) activity in either of the ERs. Addition of 17 beta -estradiol (E-2) plus epicatechin gallate (ECG) or epigallocatechin gallate (EGCG) at 5 x 10(-6) M resulted in significant decreases in the ER alpha -mediated luc activity compared with that of E-2 alone. On the contrary, lower concentrations significantly increased the E-2-induced luc activity. Similar effects were observed with tamoxifen. The ER beta -mediated estrogenic activities were stimulated by catechins. In conclusion, some catechins, particularly EGCG, were antiestrogenic for ER alpha at higher doses, and co-estrogenic for ER alpha at lower doses and for ER beta. The lower doses were found in human plasma after tea-drinking. In addition, some catechins may be antiendocrine disrupters because they suppressed bisphenol A-induced luc activities.