PEROXIDATION OF EGG-YOLK PHOSPHATIDYLCHOLINE LIPOSOMES BY HYPOCHLOROUS ACID

The powerful neutrophil-derived oxidant hypochlorous acid HOCl/OCl- is assumed to contribute to tissue injury in a number of pathological st ates accompanied by massive accumulation of neutrophils. The productio n of malondialdehyde to indicate lipid peroxidation was studied in egg yolk phosphatidylcholine liposomes upon treatment with NaOCl as a sou rce for hypochlorous acid. Its accumulation was inhibited by alpha-toc opherol and butylated hydroxytoluene. Singlet oxygen, hydroxyl radical s or superoxide anion radicals derived from direct reactions of hypoch lorous acid seem not to be involved in initiation of lipid peroxidatio n because the malondialdehyde accumulation was unaffected by hydrogen peroxide, catalase, superoxide dismutase, ferrous sulphate or ferric c hloride. Double bonds of fatty acid residues seem to be the primary ta rget for NaOCl. Their number is continuously diminished in liposomes ( 2 mg lipids/ml) after incubation with increasing amounts of NaOCl at 3 7 degrees C for 40 min as detected by two independent methods (iodine bromide reduction and H-1-NMR spectroscopy). A 1:1 molar ratio between the loss of double bonds and NaOCl added was found only at low NaOCl concentrations. Then double bonds are decreased with a lower efficienc y. A continuous increase of lipid peroxidation products was only obser ved up to 0.5-0.7 mmol/l NaOCl. The yield of lipid hydroperoxides kept constant at higher NaOCl concentrations. However, diene conjugates an d malondialdehyde exhibit a maximum at 0.7-1 mmol/l or 0.5 mmol/l NaOC l, respectively, while the concentration of these products decreases a t higher doses of NaOCl. The decrease of malondialdehyde was more pron ounced than for diene conjugates. These results were discussed from th e background that at minimum two (diene conjugates) or three (malondia ldehyde) double bonds in a fatty acid residue are necessary for format ion of lipid peroxidation products.