Pyrene lipids as markers of peroxidative processes in different regions of low and high density lipoproteins

Abstract

Three different pyrene derivatives, pyrene decanoyl phosphatidylcholine (P 10PC), pyrene dodecanoyl sulfatide (P 12CS) and cholesteryl pyrenyl hexanoate (P 6Chol), were used to follow lipid peroxidation in low and high density lipoproteins. Probe-labelled lipoproteins were subjected to Cu 2+ catalyzed peroxidation. In all cases the fluorescence of the probes progressively decreased due to the involvement of pyrene in the peroxidative reaction. Thus, we used the fluorescence decrease of P 6Chol to monitor the lipid peroxidation in the hydrophobic core of LDL and HDL, and that of the amphipatic probes, P 10PC and P 12CS, to follow lipid peroxidation in the envelope of both lipoproteins. The possibility of following lipid peroxidation in individual lipoprotein regions could lead to more detailed information on the oxidative modifications that play an important role in the altered cholesterol homeostasis involved in the formation of atherosclerotic lesions. No differences were observed in the peroxidation kinetics of the hydrophobic core of HDL and LDL monitored with P 6Chol. On the contrary kinetics obtained with P 10PC and P 12CS demonstrated the HDL envelope to be more susceptible to Cu 2+-dependent lipid peroxidation than that of the LDL. This could be due to a greater radical generating capacity of the HDL envelope and can be explained on the basis of low vitamin E levels and large amounts of polyunsaturated fatty acids esterified on phospholipids determined in HDL, and on literature evidence that indicates HDL as the principal vehicle of circulating plasma lipid peroxides.