Supplementation with vitamin E but not beta-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-alpha-tocopherol (vitamin E) and beta-carotene and of smoking on the resistance of LDL against copper-mediated oxidation. Six healthy nonsmoking volunteers ingested 1,000 IU/day D,L-alpha-tocopherol acetate for 7 days. After vitamin E ingestion concentrations of alpha-tocopherol in plasma and LDL increased 3.0- and 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 alpha-tocopherol content of LDL and the increase in resistance time were highly correlated (rs = 0.89, p = 0.014). Eight weeks after termination of the vitamin E intake, alpha-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 beta-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 alpha-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 beta-carotene resulted in a 16.6- and 5.0-fold increase of LDL beta-carotene and total carotenoid content, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)