Dual effects of daidzein on chicken hepatic vitellogenin II expression and estrogen receptor-mediated transactivation in vitro

Two in vitro systems were employed to delineate the estrogenic activity of daidzein (Da), alone or in combination with high or low concentrations of estrogen in two cell types possessing different estrogen-receptor (ER) isoforms, ER alpha and/or ER beta: (1) vitellogenin II (VTG), the egg yolk precursor protein and the endpoint biomarker for estrogenicity, in chicken primary hepatocytes, and (2) CHO-K1 cells transiently co-transfected with ER alpha or ER beta and estrogen-response elements (ERE) linked to a luciferase reporter gene. Da (100 mu M) alone induced VTG mRNA expression in chicken hepatocytes, albeit with much less potency compared to estradiol (E-2). Da exhibited different effects in the presence of 1 mu M and 10 mu M E-2. At a concentration of 100 mu M, Da enhanced 1 mu M E-2-induced VTG transcription by 2.4-fold, but significantly inhibited 10 mu M E-2-induced VTG mRNA expression in a dose-dependent fashion from 1 to 100 mu M. Tamoxifen completely blocked the estrogenic effect of daidzein, alone or in combination with 1 mu M of E-2, but did not influence its anti-estrogenic effect on 10 mu M E-2-induced VTG mRNA expression. Furthermore, neither E-2 nor daidzein, alone or in combination, affected ER alpha mRNA expression, yet all the treatments significantly up-regulated ER mRNA expression in chicken hepatocytes. E-2 effectively triggered estrogen-response elements (ERE)-driven reporter gene transactivation in CHO-K1 cells expressing ER alpha or ER beta and showed much greater potency with ER alpha than with ER beta. In contrast, daidzein was 1000 times more powerful in stimulating ER beta- over ER alpha-mediated transactivation. Daidzein, in concentrations ranging from 5 nM to 50 mu M, did not affect ER beta-mediated transactivation induced by 1 nM E-2, but it significantly inhibited ER beta-mediated transactivation induced by 10 nM E-2 at 500 nM. Despite the tremendous difference in sensitivity between the two in vitro systems, daidzein exhibited greater potency as an estrogen-antagonist for ER beta-mediated activity. (C) 2009 Elsevier Inc. All rights reserved.