The Lipoic Acid Analogue 1,2-Diselenolane-3-pentanoic Acid Protects Human Low Density Lipoprotein against Oxidative Modification Mediated by Copper Ion

1,2-Diselenolane-3-pentanoic acid, in which the sulfur atoms of α-lipoic acid are replaced with selenium, displayed markedly different antioxidant properties when compared to α-lipoic acid. 1,2-Diselenolane-3-pentanoic acid was unable to inhibit protein oxidative modification of human low density lipoprotein (LDL) and bovine serum albumin induced by copper ion or hydroxyl radical, whereas α-lipoic acid showed significant protection. However, 1,2-diselenolane-3-pentanoic acid was able to inhibit the formation of lipid peroxidation products in LDL after oxidation by copper, while α-lipoic acid did not. Hence the diselenium compound exerts its effects in a lipophilic environment whilst lipoic acid exerts its effects in a hydrophilic environment. These differences in antioxidant activities of the two compounds may be explained, at least in part, by their differing partition coefficients.