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Abstract
Oxidative modification of low-density lipoprotein (oxLDL) plays a pathogenic role in atherogenesis. Classical antioxidants such as l -ascorbic acid can inhibit formation of oxLDL. f -Keto-carboxylates such as pyruvate and congeners also display antioxidant properties in some cell-free and intact cell systems. We tested the hypothesis that pyruvate or f -keto-glutarate may function as antioxidants with respect to LDL incubated with 5 or 10 w M Cu 2+ alone or in combination with THP-1-derived macrophages. f -Hydroxy-carboxylates ( l -lactate), linear aliphatic mono-carboxylates (acetate/caprylate) and l -ascorbic acid served as controls. The oxLDL formation was ascertained by electrophoretic mobility and oxLDL cytotoxicity was judged by macrophage viability and thiobarbituric acid reactive substances (TBARS) formation. Cu 2+ alone was not cytotoxic but increased electrophoretic mobility of cell-free LDL, stimulating TBARS. Millimolar pyruvate, f -keto-glutarate, or micromolar l -ascorbic acid partially inhibited oxLDL formation, while f -hydroxy-carboxylate or the aliphatic mono-carboxylates had no measurable antioxidant properties in cell-free LDL. Co-culture of LDL with macrophages and Cu 2+ augmented TBARS release and resulted in 95% macrophage death. Pyruvate improved macrophage viability with 5 w M Cu 2+ up to 60%. l -Ascorbic acid ( S 100 w M) protected macrophages up to 80%. When S 100 w M l -ascorbic acid was combined with pyruvate, oxLDL formation and macrophage death were fully prevented. Thus, f -keto-carboxylates, but not physiological f -hydroxy-carboxylates or aliphatic mono-carboxylates qualify as antioxidants in LDL systems. Since f -keto-carboxylates enhanced the antioxidant power of l -ascorbic acid, our findings may have implications for strategies attenuating atherosclerosis.