Inhibitory effect of isoflavones on peroxynitrite-mediated low-density lipoprotein oxidation

Peroxynitrite, a potent oxidant formed in vivo from the reaction of nitric oxide with superoxide, can mediate low-density liprotein (LDL) oxidation which is thought to increase the risk of atherosclerosis. This study investigates the inhibitory effect of the isoflavones, genistein and daidzein, together with their glycosidic forms, genistin and daidzin, on the peroxynitrite-mediated LDL oxidation and nitration of tyrosine. Genistein and daidzein were observed to dose-dependently inhibit peroxynitrite-mediated LDL oxidation, while their glucoside conjugates showed less activity. Moreover, all the isoflavones used in this study were found to be potent peroxynitrite scavengers, preventing the nitration of tyrosine. The ability of the isoflavones at 50 microM to decrease the tyrosine nitration induced by peroxynitrite (1 mM) was in the ratios of genistein (49%), daidzein (40%), daidzin (41%) and genistin (42%) when compared to the control (tyrosine incubated only with peroxynitrite). These results suggest that an intake of isoflavones could contribute to protecting against cardiovascular diseases and chronic inflammatory diseases.