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.

Simultaneously produced superoxide/nitric oxide radicals (y c3 2 /NO c ) could form peroxynitrite (OONO 3 ) which has been found to cause atherogenic, i.e. oxidative modification of LDL. Aromatic hydroxylation and nitration of the aspirin metabolite salicylate by OONO 3 has been reported. Therefore we tested if salicylate may be able to protect LDL from oxidation by y c3 2 /NO c by scavenging the OONO 3 reactive decomposition products. When LDL was exposed to simultaneously produced y c3 2 /NO c using the sydnonimine SIN-1, salicylate exerted an inhibitory effect on LDL oxidation as measured by TBARS and lipid hydroperoxide formation and alteration in electrophoretic mobility of LDL. The cytotoxic effect of SIN-1 pre-oxidised LDL to endothelial cells was also diminished when salicylate was present during SIN-1 treatment of LDL. Spectrophotometric analysis revealed that salicylate was converted to dihydroxybenzoic acid (DHBA) derivatives in the presence of SIN-1. 2,3-and 2,5-DHBA were even more effective to protect LDL from oxidation by y

Lipoprotein(a) (Lp(a)) is a complex of low density lipoprotein (LDL) with apolipoprotein (apo) (a). To examine the size distribution of Lp(a). plasma was separated by fast flow gel filtration and Lp(a):B complexes were determmed in the eluate by enzyme immunoassays, in which detection was performed with monoclonal antibodies specific for apoB. Lp(a):B particles displayed apparent molecular masses (M,) of 2 x 10h to at least 10 x 106. Lp(a) size isoforms differed by the expression of apoB epitopes and their interaction with cultured human skin fibroblasts. LDL was more effective in inhibiting bmding, uptake, and degradation of low M, Lp(a) than of high M, Lp(a). In contrast, Glu-plasminogen. a?-macroglobulin and tissue-type plasminogen activator were more effective in competing for the cellular degradation of high M, Lp(a) than of low M, Lp(a). Ligand blotting revealed that Lp(a) bound to the low density hpoprotein receptor. the low density lipoprotem receptor-related protein/a,-macroglobulin receptor (LRP) and to two other endosomal membrane proteins. We propose that the LDL receptor preferentially internalizes low A4, Lp(a), whereas LRP may have a role in the clearance of high A4, Lp(a).

Hyperglycemia has been assumed to be responsible for oxidative stress in diabetes. In this respect, glucose autoxidation and advanced glycation end products (AGE) may play a causal role in the etiology of diabetic complications as e.g. atherosclerosis. There is now growing evidence that the oxidative modification of LDL plays a potential role in atherogenesis. Glucose derived oxidants have been shown to peroxidise LDL. In the present study, genistein, a compound derived from soy with a flavonoid chemical structure (4', 5, 7-trihydroxyisoflavone) has been evaluated for its ability to act as an antioxidant against the atherogenic modification of LDL by glucose autoxidation radical products. Daidzein, (4',7-dihydroxyisoflavone) an other phytoestrogen of soy, was tested in parallel. Genistein--in contrast to daidzein--effectively prevented the glucose mediated LDL oxidation as measured by thiobarbituric acid-reactive substance formation (TBARS), alteration in electrophoretic mobility, lipid hydroperoxides and fluorescence quenching of tryptophan residues of the lipoprotein. In addition the potential of glucose-oxidized LDL to increase tissue factor (TF) synthesis human endothelial cells (HUVEC) was completely inhibited when genistein was present during LDL oxidative modification by glucose. Both phytoestrogens did not influence the nonenzymatic protein glycation reaction as measured by the in vitro formation of glycated LDL. As the protective effect of genistein on LDL atherogenic modification was found at glucose/genistein molar ratios which may occur in vivo, our findings support the suggested beneficial action of a soy diet in preventing chronic vascular diseases and early atherogenic events.

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