Variability in α-Tocopherol Antioxidant Activity in the Core and Surface Layers of Low-and High-Density Lipoproteins

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The effect of α-tocopherol enrichment of low- and high-density lipoproteins on Cu²⁺-catalyzed lipid peroxidation in the hydrophobic core and in the hydrophilic envelope of lipoproteins was investigated by using two pyrene derivatives, namely, cholesteryl pyrenyl hexanoate (P₆Chol) and pyrene dodecanoyl sulfatide (P₁₂CS). The progressive decrease in fluorescence of P₆Chol was used to monitor lipid peroxidation in the core of LDL and HDL, whereas that of P₁₂CS was used to follow lipid peroxidation in the envelope of both lipoproteins. α-Tocopherol enrichment of LDL and HDL was obtained by incubating blood plasma at 37°C with different concentrations of the vitamin (25-500μM) before lipoprotein separation. The incorporation of α-tocopherol in LDL and HDL presents a progressive, time-dependent increase up to 200μM α-tocopherol, then a plateau up to 500μM. In the envelopes, the added tocopherol causes a great decrease in the rate of peroxidation and a dramatic increase in the latency phase in both lipoproteins. In the cores the lengthening of latency phase resulting from α-tocopherol enrichment was by far greater in LDL than in HDL, and the decrease in the rate of peroxidation in both lipoproteins was less than in the envelopes.