Autoxidative Glycosylation and Possible Involvement of Peroxides and Free Radicals in LDL Modification by Glucose

It has been postulated that the etiology of the complications of diabetes involves oxidative stress, perhaps as a result of hyperglycemia. Consistent with this hypothesis, it has been shown that glucose, under physiological conditions, produces oxidants that possess reactivity similar to the hydroxyl free radical. These oxidants hydroxylate benzoic acid, fragment protein, and induce peroxidation in phosphatidylcholine liposomes and low-density lipoprotein (LDL) when LDL is incubated with hyperglycemic levels of glucose in vitro. These reactions are accelerated by transition metals and inhibited by a metal-chelating agent. The atherosclerotic potential of LDL in diabetes mellitus is often discussed in terms of protein glycosylation, which may affect cellular interactions. Our studies demonstrate, however, that peroxidative reactions also accompany LDL glycosylation in vitro. Peroxidative modification of LDL has also been implicated in LDL atherogenicity. Our studies indicate that glycosylation and peroxidation occur concomitantly in LDL modified by glucose in vitro and may both contribute to the behavioral changes of this lipoprotein.