Preferential hydrolysis of oxidized phospholipids by peritoneal fluid of rats treated with casein.

1-Palmitoyl-2-azelaoyl-PC, which is one of the possible cytotoxic products generated by the oxyhemoglobin-induced lipid peroxidation of 1-palmitoyl-2-linoleoyl-PC, was found to be efficiently hydrolyzed by the peritoneal fluid of rats treated with casein. The rate of hydrolysis of 1-palmitoyl-2-azelaoyl-PC was approx. 15-fold higher than that observed with 1-palmitoyl-2-linoleoyl-PC. When 1-palmitoyl-2-linoleoyl-PC pretreated with oxyhemoglobin was incubated with the peritoneal fluid, oxidized products of PC were hydrolyzed more efficiently than the intact 1-palmitoyl-2-linoleoyl-PC. When 1-[(1-)14C]palmitoyl-2-azelaoyl-PC was incubated with the peritoneal fluid, radiolabeled lysoPC was formed, whereas radiolabeled neutral lipids were not formed, indicating that the hydrolytic activity was of the 'phospholipase A2' type. We previously found and purified an extracellular phospholipase A2 (Chang, H.W. et al. (1987) J. Biochem. 102, 147-154) in the peritoneal fluid of rats injected intraperitoneally with casein. Hydrolysis of 1-palmitoyl-2-azelaoyl-PC by this purified phospholipase A2 was as low as that of 1-palmitoyl-2-linoleoyl-PC. These two phospholipase A2 activities showed different pH optima and Ca2+ requirements. The present phospholipase A2 activity, which preferentially hydrolyzes oxidized products of PC, may play an important role in detoxification or repair of damaged membrane in inflamed sites.