Dietary supplementation with vitamins C and E inhibits in vitro oxidation of lipoproteins

The oxidative modification of lipoproteins has been implicated in atherogenesis, suggesting a protective role of circulating antioxidants. Vitamin C (ascorbic acid, 1 g/day) and vitamin E (dl alpha-tocopheryl acetate, 800 IU/day) were administered to healthy female and male volunteers. Lipoproteins with density < 1.063 g/mL were isolated from serum before and after vitamin supplementation and incubated with copper (Cu) or mononuclear cells (MC) plus Cu. Administration of vitamins C and E together to 4 subjects for 10 days resulted in a 57% (range 40-72%) decrease in Cu-catalyzed production of thiobarbituric acid reactive substances (TBARS) under the following conditions of assay: incubation times of 0-8 hours, Cu concentrations of 0-10 microM lipoprotein protein concentrations of 0.1-0.5 mg/mL. Decreases in other parameters of lipoprotein oxidation, i.e,, electrophoretic mobility, production of conjugated dienes and modification of amino groups, were also observed. Vitamin E administration alone produced a 52% inhibition and vitamin C alone a 15% inhibition of TBARS formation. Vitamins C and E supplementation resulted in a 78% decrease in the susceptibility of lipoproteins to MC-mediated oxidation. There was a strong inverse correlation (r = -0.64, p < 0.0007) between vitamin E levels in the lipoproteins and TBARS production in samples from 12 subjects administered vitamins C and E. In 3 individuals vitamin E levels remained low and in 2 of these subjects there was no effect of vitamins C and E administration on TBARS production. These results suggest a protective role of antioxidant vitamins and significant individual variability in response.