Oxidation of fluorescent glycero- and sphingophospholipids in human plasma lipoproteins: Alkenylacyl subclasses are preferred targets

Objectives: Oxidation of polyunsaturated fatty acids in lipoproteins is supposed to play a crucial role at the early stages of atherogenesis. The polyunsaturated lipids (PUFAs) become oxidized and, thus, the degree and rate of lipid oxidation depend on their concentration and, probably, on the lipid moiety to which they are attached. Design and methods: To determine the relative oxidation susceptibilities of sphingo- and glycerolipid-bound fatty acyl chains, we used fluorescent analogs of the respective compounds, in which one natural fatty acyl chain was replaced by fluorescent diphenylhexatriene propionic acid. Results: Oxidation susceptibilities of the fluorescent acyl chains in the presence of Cu²⁺ or AAPH depended, in general, on the phospholipid to which they were bound and the lipoprotein. Phospholipids were oxidized faster in HDL than in LDL or Lp(a). Plasmalogens were more susceptible to oxidation than phosphatidylcholine and sphingomyelin. Conclusion: Thus, HDL and plasmalogens may be considered as preferred targets of lipid oxidation before the bulk of polyunsaturated phospholipids (mainly phosphatidylcholine) in LDL is subject to free radical attack.