The alpha-tocopherol, ascorbic acid, and rutin inhibit synergistically the copper-promoted LDL oxidation and the cytotoxicity of oxidized LDL to cultured endothelial cells

Low-density lipoproteins (LDL) mildly oxidized by copper ions or UV radiations exhibit a cytotoxic effect to cultured endothelial cells. Rutin, a polyphenolic flavonoid, ascorbic acid, and alpha-tocopherol were able to inhibit the peroxidation of LDL and their subsequent cytotoxicity. The mixture of the three compounds (rutin/ascorbic acid/alpha-tocopherol, 4/4/1) exhibited a supra-additive antioxidant effect. The inhibition of the cytotoxic effect was well correlated with that of TBARS formation. Another important conclusion is that these antioxidants were able to prevent directly at the cellular level the cytotoxic effect of oxidized LDL, since cells preincubated with them were protected against the cytotoxic effect of previously oxidized LDL. The protective effect of antioxidants was limited because of their own toxicity. The antioxidant mixture permitted a maximal cytoprotective effect with relatively lower concentrations to be obtained and the cytotoxicity of high concentrations to be avoided. In conclusion, rutin, ascorbic acid, and alpha-tocopherol constitute two lines of defense in protecting cells against injury owing to oxidation of LDL (1) at the LDL level, by inhibiting the LDL oxidation and the subsequent cytotoxicity, and (2) at the cellular level, by protecting the cells directly, i.e., by increasing their resistance against the cytotoxic effect of oxidized LDL.