Increased oxidation resistance of atherogenic plasma lipoproteins at high vitamin E levels in non-vitamin E supplemented men

Abstract

The oxidative modification of human low density lipoprotein (LDL) has been widely investigated. However, there are no data concerning the oxidation susceptibility of combined very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein fraction, although all of them are atherogenic and contain antioxidants such as α-tocopherol. We investigated the oxidation susceptibility and oxidation resistance of VLDL + LDL (including IDL) fraction by induction with CuCl 2 and its relation to plasma α-tocopherol concentration and lipid standardised α-tocopherol concentration in 406 non-vitamin E-supplemented men from eastern Finland. Even thought we did not give oral vitamin E or any other antioxidant supplementation to our study participants, we observed a significant, consistent relationship between measurements of oxidation resistance and plasma content of vitamin E. In the multivariate regression model, a high plasma content of vitamin E or lipid standardised vitamin E concentration were the most important determinants of lag time to maximal oxidation rate (standardised regression coefficient = 0.244, P < 0.0001 for vitamin E and 0.211, P < 0.0001 for lipid standardised vitamin E). After statistical adjustment for age, use of cigarettes, hypolipidemic medication (yes vs. no), month of the measurements, plasma concentrations of total ascorbic acid (ascorbic acid + dehydroascorbic acid), β-carotene and phospholipids, serum concentrations of LDL cholesterol and triglycerides and dietary intake of linoleic acid, the lag time to maximal oxidation rate was 10% (95% C.I. 6.0–13.5%) longer in men in the highest fifth than in the lowest fifth of plasma vitamin E content ( P < 0.0001 for trend). When the fifths of lipid standardised vitamin E were compared, the lag time to maximal oxidation rate was 6% (95% C.I. 1.8–10.1%) longer in men in the highest than in the lowest fifth ( P < 0.0001 for trend). Our data suggest that α-tocopherol is an important antioxidant preventing the in vitro oxidation of VLDL + LDL fraction even in non-supplemented subjects.