SOYBEAN ISOFLAVONOIDS AND THEIR METABOLIC PRODUCTS INHIBIT IN-VITRO LIPOPROTEIN OXIDATION IN SERUM

Isoflavonoids are compounds present in many legumes, but are derived i n the human diet mainly from soybeans and various soybean-based food p roducts. The major isoflavonoids occurring in soy are the glycosides o f genistein and daidzein. The metabolic products of genistein metaboli sm in humans have not been clearly shown. The two main products of dai dzein metabolism in human appear to be equal and O-demethylangolensin. Increasing evidence suggests that oxidative modification to low-densi ty lipoprotein is involved in atherogenesis, and that natural antioxid ants that prevent or inhibit oxidative damage to low-density lipoprote in may beneficially influence atherogenesis. In the present experiment s, the effects of genistein and daidzein, and the daidzein metabolites equol and O-desmethylangolensin on Cu2+-induced oxidation of lipoprot eins in serum were examined. Three concentrations of each compound (0. 1 mu M, 1 mu M, 10 mu M) were tested for antioxidant activity in six i ndividual serum samples. All compounds tested inhibited lipoprotein ox idation. The minimum concentration for significant inhibition was 1 mu M for genistein and daidzein (P <0.05), and 0.1 mu M equol and O-desm ethylangolensin (P <0.05). Equol and O-desmethylangolensin were more p otent inhibitors of in vitro lipoprotein oxidation in serum than the t wo major dietary isoflavonoids. This study has demonstrated that soybe an isoflavonoids and metabolic products of daidzein metabolism inhibit lipoprotein oxidation is vitro. Human intervention studies are needed to determine if these compounds can influence oxidation in vivo. (C) Elsevier Science Inc. 1996