Genistein and other isoflavones found in soybeans inhibit estrogen metabolism in salmonid fish

Abstract

The study was conducted to test the hypothesis that genistein, an isoflavone found in high concentrations in soybeans, inhibits hepatic and renal estrogen metabolism in salmonid fish. Liver and kidney tissues of rainbow trout ( Oncorhyncus mykiss), Atlantic salmon ( Salmo salar), and lake trout ( Salvelinus namaycush) were incubated in vitro with radiolabelled estradiol-17β (E2) in the presence of various doses of genistein. The cultures were extracted to remove unmetabolized E2 and neutral E2 metabolites, and the production of water-soluble (conjugated) E2 metabolites was quantified by liquid scintillation counting. High doses (1 and 10 μM) of genistein inhibited E2 metabolism in the liver and kidney of Atlantic salmon and rainbow trout, and in the liver of lake trout. At 1 μM, daidzein, glycitein, and a mix of genistein/daidzein/glycitein at a ratio typically found in soybeans (1.3:1:0.2), all inhibited estrogen metabolism in the liver of rainbow trout, but had no effect on the kidney. The results suggest that the inhibition of hepatic and renal E2 metabolism may be, at least in part, a mechanism mediating the estrogenic effects of isoflavones in salmonid fish.