Oxidative changes associated with beta-carotene and alpha-tocopherol enrichment of human low-density lipoproteins.

OBJECTIVE: To determine what effects enrichment of human low-density lipoprotein (LDL) with combinations of alpha-tocopherol and beta-carotene would exert on LDL oxidation and attempt to define the nature of the effects. METHODS: Human plasma was pooled and alpha-tocopherol and beta-carotene was added in a four-by-four design resulting in the enrichment of LDL with alpha-tocopherol and beta-carotene in varying concentrations. Enriched and control LDL was oxidized in Cu2+ mediated oxidation system and resistance of LDL to oxidation was determined by lag time, thiobarbituric acid reactive substances (TBARS) activity, and rate of oxidation. RESULTS: Increasing LDL alpha-tocopherol concentration had a linear relationship with lag time and a negative correlation with rate of oxidation. LDL beta-carotene concentration was linearly correlated with the rate of LDL oxidation and beta-carotene loss, and exponentially related to TBARS concentration. CONCLUSIONS: These results support earlier findings for the protective effect of a-tocopherol against LDL oxidation, and suggest that beta-carotene participates as a prooxidant in the oxidative degradation of LDL under these conditions. Since high levels of alpha-tocopherol did not mitigate the prooxidative effect of beta-carotene, these result indicate that increased LDL beta-carotene may cancel the protective qualities of alpha-tocopherol.

Blood antioxidants changes in young women following beta-carotene depletion and repletion.

OBJECTIVE: This study was undertaken to investigate the relationship between beta-carotene intake and biochemical indices of antioxidant status in the blood of nine premenopausal women ages 18 to 42. METHODS: Nine healthy adult women were fed a low beta-carotene diet for 68 days. They were repleted with the same diet supplemented with beta-carotene (15 mg beta-carotene) for 28 days. During the last week of the study, they received an additional mixed carotenoid supplement. Indices of blood antioxidant status were measured on days 1, 29, 36, 43, 50, 64, 71, 92, and 99. RESULTS: We found significant increases of erythrocyte conjugated dienes between the 71st and 99th day of the study; increases of glutathione (GSH) peroxidase (GP) on day 43 and day 92 compared to a decrease on day 29; and decreases of GSH reductase throughout the treatment period. Erythrocyte catalase activities seemed to parallel GP activities. Erythrocyte oxidized glutathione (GSSG) levels were depressed both after beta-carotene depletion and repletion. beta-Carotene depletion/repletion had no effect on plasma vitamin E or GSH levels. Platelet GSH levels were depressed after beta-carotene depletion followed by elevated GSH levels after beta-carotene repletion. CONCLUSION: A diet low in beta-carotene and adequate in all other nutrients, including vitamin A, resulted in altered erythrocyte and platelet antioxidant indices; however, it had little impact on plasma GSH or vitamin E levels in young healthy women. Our results are consistent with the suggestion that carotenes may be important in the prevention of oxidative damage.