Oxidative Changes Associated with β-Carotene and α-Tocopherol Enrichment of Human Low-Density Lipoproteins

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Abstract
Objective: To determine what effects enrichment of human low-density lipoprotein (LDL) with combinations of α-tocopherol and β-carotene would exert on LDL oxidation and attempt to define the nature of the effects. Methods: Human plasma was pooled and α-tocopherol and β-carotene was added in a four-by-four design resulting in the enrichment of LDL with α-tocopherol and β-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 α-tocopherol concentration had a linear relationship with lag time and a negative correlation with rate of oxidation. LDL β-carotene concentration was linearly correlated with the rate of LDL oxidation and β-carotene loss, and exponentially related to TBARS concentration. Conclusions: These results support earlier findings for the protective effect of α-tocopherol against LDL oxidation, and suggest that β-carotene participates as a prooxidant in the oxidative degradation of LDL under these conditions. Since high levels of α-tocopherol did not mitigate the prooxidative effect of β-carotene, these result indicate that increased LDL β-carotene may cancel the protective qualities of α-tocopherol.