Effect of oral supplementation with D-alpha-tocopherol on the vitamin E content of human low density lipoproteins and resistance to oxidation.

Twelve clinically healthy subjects participated in a vitamin E supplementation study. Eight were given daily dosages of 150, 225, 800, or 1200 IU RRR-alpha-tocopherol for 21 days (two persons per dose) and four received placebo. Prior, during, and after the supplementation period, alpha-tocopherol, gamma-tocopherol, and carotenoids were determined in plasma and low density lipoprotein (LDL).

Role of vitamin E in preventing the oxidation of low-density lipoprotein.

The fatty acid composition, antioxidants, and the oxidation resistance of the low-density lipoproteins (LDL) from a number of different donors were determined. The oxidation resistance of LDL, as determined in vitro by the duration of the lag-phase in copper ion-induced oxidation, did not correlate with the alpha-tocopherol content of the LDL. By supplementating plasma with vitamin E, the alpha-tocopherol content of LDL could be increased from approximately 9 to 30 mol/mol LDL and also the oxidative resistance increased nearly linearly with increasing alpha-tocopherol content.

Antioxidants and resistance against oxidation of porcine LDL subfractions.

The objective of this study was to determine the level of antioxidants, the content of fatty acids and peroxidation products, and the resistance against oxidation of native porcine LDL1 and LDL2. There were no significant differences in the fatty acid distribution of both native low density lipoprotein (LDL) subfractions, which was similar to that of human LDL. The total amount of alpha- and gamma-tocopherol of pig LDL was significantly lower than in human LDL, and beta-carotene, lycopene, and retinyl esters were totally absent.

Continuous monitoring of in vitro oxidation of human low density lipoprotein.

The kinetics of the oxidation of human low density lipoprotein (LDL) can be measured continuously by monitoring the change of the 234 nm diene absorption. The time-course shows three consecutive phases, a lag-phase during which the diene absorption increases only weakly, a propagation phase with a rapid increase of the diene absorption and finally a decomposition phase. The increase of the dienes is highly correlated with the increase of MDA or lipid hydroperoxides.