OXIDATION OF PHOSPHATIDYLCHOLINE LIPOSOMES IN AQUEOUS DISPERSIONS INDUCED BY COPPER AND IRON

The oxidations of phosphatidylcholine liposomes in aqueous dispersions induced by copper and iron have been studied aiming specifically at elucidating the action of copper ion in the chain initiation of the oxidation of liposomal membranes. Both copper(II) and iron(III) ions induced steady oxidations and the addition of t-butyl hydroperoxide enhanced the rate of oxidation. The reduction of hydroperoxides present initially in the liposomes by triphenylphosphine markedly reduced the rate of oxidation. The rate of oxidation induced by copper(II) ion was proportional to the first power of phosphatidylcholine concentration and to the half power of both copper(II) ion and t-butyl hydroperoxide concentrations, suggesting that the oxidation was initiated by the oxygen radicals formed in the decomposition of hydroperoxide by copper(II) and copper(I) ions. The anionic dipalmitoylphosphatidic acid added into the liposomes enhanced the rate of oxidation induced by metal ions, whereas the addition of cationic octadecylamine showed little effect on the rate of oxidation.