Susceptibility for hydroperoxide formation of phosphatidylcholine and phosphatidylethanolamine in liposomes

To compare the peroxidative susceptibilities of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in liposomes, multilamellar vesicles (MLVs) were prepared with equimolar L-alpha-dilinoleoyl PC (DLPC) and L-alpha-dilinoleoyl PE (DLPE), and with soya PC and soya PE having a uniform constituent fatty acids. The hydroperoxide formation at 37 degrees C in the presence of a water-soluble radical initiator was examined by chemiluminescence-high-performance liquid chromatography (CL-HPLC), and the effect of heterogeneous distribution of PC and PE on peroxidation was investigated. No difference was found between the hydroperoxidation of PC and PE in MLVs systems, except that soya PC was more susceptible to peroxidation than soya PE in the L-alpha-dipalmitoyl PC (DPPC)-based liposomes. No correlation was found between the amount of phospholipids distributed in the external leaflet of MLVs and hydroperoxide formation. This result suggested that the unsaturation of constituent fatty acids in phospholipids is more important than the difference in the polar head group of phospholipids regarding their peroxidizabilities in liposomes.