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 l ipoprotein (LDL) with combinations of alpha-tocopherol and beta-carote ne would exert on LDL oxidation and attempt to define the nature of th e effects. Methods: Human plasma was pooled and alpha-tocopherol and b eta-carotene was added in a four-by-four design resulting in the enric hment of LDL with alpha-tocopherol and beta-carotene in varying concen trations. Enriched and control LDL was oxidized in Cu2+ mediated oxida tion system and resistance of LDL to oxidation was determined by lag t ime, thiobarbituric acid reactive substances (TEARS) activity, and rat e of oxidation. Results: Increasing LDL alpha-tocopheroI concentration had a linear relationship with lag time and a negative correlation wi th rate of oxidation. LDL beta-carotene concentration was linearly cor related with the rate of LDL oxidation and beta-carotene loss, and exp onentially related to TEARS concentration. Conclusions: These results support earlier findings for the protective effect of alpha-tocopherol against LDL oxidation, and suggest that beta-carotene participates as a prooxidant in the oxidative degradation of LDL under these conditio ns. Since high levels of alpha-tocopherol did not mitigate the prooxid ative effect of beta-carotene, these result indicate that increased LD L beta-carotene may cancel the protective qualities of alpha-tocophero l.