Effect of antioxidants alone and in combination with monounsaturated fatty acid-enriched diets on lipoprotein oxidation

Previous studies have demonstrated that compared with more buoyant LDL, dense LDL (D-LDL) is more susceptible to oxidation and less readily protected from oxidation by antioxidant enrichment. However, diets enriched in monounsaturated fatty acids (MUFAs) appear particularly effective in protecting D-LDL from oxidation. We therefore evaluated in 12 non-insulin dependent diabetes mellitus subjects the effects of supplementation with α- tocopherol (1600 IU/d) and probucol (1 g/d) alone and in combination with an MUFA-enriched diet on LDL and LDL subtraction susceptibility to oxidation and monocyte release of superoxide anion. Subjects received either α-tocopherol or probucol for 4 months, and during the fourth month both groups also received an MUFA-enriched diet. α-Tocopherol levels were significantly increased in LDL and LDL subtractions (P<.05) after 3 months of supplementation. MUFA-enriched diets led to further increases in α- tocopherol in LDL fractions in the α-tocopherol group as well as in those receiving probucol. In the α-tocopherol-supplemented group, lag times were increased significantly (1.6- to 2.0-fold) for all LDL fractions, although the absolute increase was least for D-LDL. Although probucol supplementation increased lag times of LDL and LDL subtractions three- to fourfold, D-LDL was still more readily oxidized. In both the α-tocopherol- and probucol- supplemented groups the benefit of adding MUFA-enriched diets was greatest for D-LDL, with further increases in lag time of 26% and 18%, respectively. Neither antioxidant supplementation nor the addition of an MUFA-enriched diet reduced unstimulated or phorbol ester-stimulated monocyte superoxide anion production. These data demonstrate the markedly different effects that antioxidants and diet may have on different LDL subtractions, which may be particularly important in individuals with non-insulin-dependent diabetes mellitus, who frequently have increased amounts of D-LDL.