Effects of LDL Lipids on Activity of Group IIA Secretory Phospholipase A2

Effects of phosphatidylcholine, oxidized phosphatidylcholine, sphyngomyelin, cholesterol, and cholesterol esters incorporated in LDL on activity of group IIA secretory phospholipase A2 from human cardiac myxoma were studied. Liposomes containing radioisotope-labeled phosphatidylethanolamine served as the substrate for group IIA secretory phospholipase A2. Oxidized phosphatidylcholine significantly stimulated activity of group IIA secretory phospholipase A2, while phosphatidylcholine in the same concentrations did not modify enzyme activity. Sphyngomyelin incorporated in LDL inhibited group IIA secretory phospholipase A2 activity. Cholesterol and cholesterol esters virtually did not modify enzyme activity. The results indicate that LDL phospholipids and their oxidized forms can be involved in regulation of group IIA secretory phospholipase A2. Study of the mechanisms regulating the proinflammatory group IIA secretory phospholipase A2 can promote the development of new approaches to the diagnosis and treatment of inflammatory processes.