Low-Densit Lipoprotein Oxidation

Background. Data continue to accumulate supporting a proatherogenic role for oxidized low-density lipoprotein (Ox-LDL). Antioxidant micronutrients such as ascorbate, a-tocopherol, and beta carotene, levels of which can be favorably manipulated by dietary measures without side effects, could be a safe approach in inhibiting LDL oxidation. In fact, in vitro studies have shown that all three antioxidants can inhibit LDL oxidation. The present study was undertaken to ascertain both the safety and antioxidant effect of combined supplementation with a-tocopherol, ascorbate, and beta carotene on LDL oxidation. Methods and Results. The effect of combined supplementation with a-tocopherol (800 IU/d) plus ascorbate (1.0 g/d) and beta carotene (30 mg/d) on copper-catalyzed LDL oxidation was tested in a randomized, placebo-controlled study in two groups of 12 male subjects over a 3-month period. Blood samples for the lipoprotein profile, antioxidant levels, and LDL isolation were obtained at baseline and at 3 months. Neither placebo nor combined antioxidant therapy resulted in any side effects or exerted an adverse effect on the plasma lipoprotein profile. Compared with placebo, combined antioxidant therapy resulted in a significant increase in plasma ascorbate and lipid standardized a-tocopherol and beta carotene levels (2.6-, 4.1-, and 16.3-fold, respectively). At baseline, there were no significant differences in the time course curves and kinetics of LDL oxidation as evidenced by the thiobarbituric acid reacting substances (TBARS) assay and the formation of conjugated dienes. However, at 3 months, combined supplementation resulted in a twofold prolongation of the lag phase and a 40% decrease in the oxidation rate. The combined antioxidant group was also compared with a group that received 800 IU of a-tocopherol only. Although the combined antioxidant group had significantly higher ascorbate and beta carotene levels than the group supplemented with a-tocopherol alone, there were no significant differences between the two groups with respect to LDL oxidation kinetics. Conclusions. Combined supplementation with ascorbate, beta carotene, and tr-tocopherol is not superior to high-dose cy-tocopherol alone in inhibiting LDL oxidation. Hence, a-tocopherol therapy should be favored in future coronary prevention trials involving antioxidants. (Circulation. 1993;88:2780-2786.)