Genistein, the dietary-derived angiogenesis inhibitor, prevents LDL oxidation and protects endothelial cells from damage by atherogenic LDL

There is now growing evidence that the oxidative modification of LDL plays a potential role in atherosclerosis. In this study, genistein, a compound derived from a soy diet with a flavonoid chemical structure (4',5,7-trihydroxyisoflavone), which was found to inhibit angiogenesis, has been evaluated for its ability to act as an LDL antioxidant and a vascular cell protective agent against oxidized LDL. The results showed that genistein was able to inhibit the oxidation of LDL in the presence of copper ions or superoxide/nitric oxide radicals as measured by thiobarbituric acid-reactive substance formation, alteration in electrophoretic mobility, and lipid hydroperoxides. Bovine aortic endothelial cell-and human endothelial cell-mediated LDL oxidation was also inhibited in the presence of genistein. The 7-O-glucoside of genistein, genistin, was much less effective in inhibiting LDL oxidation in the cell-free and cell-mediated lipoprotein-oxidating systems. Incubating human endothelial cells in the absence or presence of genistein and challenging the cells with already oxidized lipoprotein revealed that in addition to its antioxidative potential during LDL oxidating processes, genistein effectively protected the vascular cells from damage by oxidized lipoproteins. The tyrosine kinase inhibitor genistein was found to block upregulation of two tyrosine-phosphorylated proteins of 132 and 69 kDa in endothelial cells induced by oxidized LDL. Parallel experiments with the inactive analogue daidzein, however, showed that the cytoprotective effect of the isoflavones seems not to be dependent on tyrosine phosphorylation. Our findings will support the suggested and documented beneficial action of a soy diet in preventing chronic vascular diseases and early atherogenic events.