Dose-Dependent Effects of Genistein and Daidzein on Protein Metabolism in Porcine Myotube Cultures

This study was conducted to investigate whether the isoflavones genistein and daidzein, which are components of soy-based diets, and the estrogen 17 beta-estradiol affect differentiation and protein metabolism of porcine skeletal muscle cells in vitro. Serum-free porcine myotube cultures expressing the estrogen receptors ER alpha and ER beta were treated with various concentrations of genistein, daidzein, or 17 beta-estradiol for 26 In. The degree of differentiation by creatine phosphokinase activity was not altered by treatment. At 100 mu mol/L both genistein and daidzein caused decreases in protein amount due to cell loss. In addition, 100 mu mol/L genistein reduced protein synthesis rate of the surviving cells (P < 0.05) measured as [H-3]-phenylaianine incorporation. Interestingly, genistein (0.1 mu mol/L), daidzein (10, 100 mu mol/L), and 17 beta-estradiol (0.1, 1 nmol/L) slightly reduced protein degradation (P < 0.05). The results suggest that both genistein and daidzein affect protein metabolism in a close-dependent manner and that estrogenic actions may play a role in decreasing protein degradation in porcine skeletal muscle.