Supplementation With Vitamin E but Not j3-Carotene In Vivo Protects Low Density Lipoprotein From Lipid Peroxidation In Vitro Effect of Cigarette Smoking

Several lines of evidence suggest that oxidatively modified low density lipoprotein (LDL) is atherogenic and that antioxidants may protect LDL against oxidation. In addition, cigarette smoking is known to induce oxidant stress. We have examined the effect of ingestion of the antioxidants D,L-ar-tocopherol (vitamin E) and 0-carotene and of smoking on the resistance of LDL against copper-mediated oxidation. Six healthy nonsmoking volunteers ingested 1,000 IU/day D,L-a-tocopherol acetate for 7 days. After vitamin E ingestion concentrations of or-tocopherol in plasma and LDL increased 3.0and 2.4-fold, respectively. Simultaneously, the oxidation resistance of LDL was elevated significantly (+41%), and the rate of oxidation was decreased significantly (—19%). The increase in o-tocopherol content of LDL and the increase in resistance time were highly correlated (r,=0.89, p=0.014). Eight weeks after termination of the vitamin E intake, o-tocopherol concentrations in plasma and LDL and oxidation resistance of LDL had returned to baseline values. In smokers (n=46), plasma levels of vitamin C (—26%) and concentrations of 0-carotene (—44%, —43%) and total carotenoids (—23%, —29%) in plasma and LDL, respectively, were significantly lower compared with nonsmokers (n=23). No differences were found in o-tocopherol content of LDL and the susceptibility of LDL to lipid peroxidation in both groups. Supplementation of a group of smokers in a 14-week randomized, double-blind, placebo-controlled intervention trial with ^-carotene resulted in a 16.6and 5.0-fold increase of LDL /^-carotene and total carotenoid content, respectively. Similar increases were found in plasma without changes in other vitamins. Comparison of the changes in the length of the resistance time between the /J-carotene group (R=23) and the placebo group (n=23) showed no significant differences. We conclude that Ingestion of vitamin E strongly protects LDL against oxidative modification, whereas ^-carotene is not effective, and that smoking does not alter the oxidation resistance of LDL. (Arteriosclerosis and Thrombosis 1992;12:554-562)