COMPARISON OF THE EFFECTS OF DIETARY VITAMIN-E ON IN-VIVO AND IN-VITRO PARAMETERS OF LIPID-PEROXIDATION IN THE RABBIT

This study has investigated the effect of dietary vitamin E on markers of antioxidant status. Four groups of rabbits received diets containi ng 30 energy percent (en%) total fat (7.8 en% contributed by linoleic acid) for 12 weeks. D,1-alpha tocopheryl acetate was added to the diet s to obtain a range of vitamin E concentrations (49, 114, 179, or 775 tocopherol equivalents per kg diet). Increased vitamin E concentration s were demonstrated in plasma lipoproteins and erythrocyte membranes f ollowing supplementation, and dietary effects on lipid peroxidation we re investigated by (i) monitoring a fluorescent parinaric acid probe i ncorporated into erythrocyte membranes in vivo, (ii) determination of malondialdehyde and oxysterols in plasma, and (iii) investigation of t he susceptibility of low density lipoprotein (LDL) to copper-induced c onjugated diene formation in vitro. No effects of vitamin E were obser ved on parinaric acid oxidation in vivo or on the accumulation of lipi d peroxidation products in plasma, but the resistance of LDL to oxidat ion in vitro increased significantly as vitamin E was supplemented to the diets. Our results demonstrate that under these dietary conditions (7.8 en% linoleic acid) increasing the vitamin E content of plasma an d erythrocytes approximately two-fold does not reduce the level of lip id peroxidation in vivo, indicating sufficient antioxidant capacity on the lowest vitamin E diet. In contrast, LDL became more resistant to an extreme oxidative stress applied in vitro. The relevance of these a ssays to currently proposed mechanisms of atherosclerosis is discussed .