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

ABSTRACT

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.