Variability in α-tocopherol antioxidant activity in the core and surface layers of low- and high-density lipoproteins

Abstract

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 (25-500 μM) before lipoprotein separation. The incorporation of α-tocopherol in LDL and HDL presents a progressive, time- dependent increase up to 200 μM α-tocopherol, then a plateau up to 500 μM. 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.