LYSOPHOSPHATIDYLCHOLINE STIMULATES THE RELEASE OF ARACHIDONIC-ACID INHUMAN ENDOTHELIAL-CELLS

Lysophosphatidylcholine (lyse-PC) is a product of phosphatidylcholine hydrolysis by phospholipase A(2) (PLA(2)) and is present in cell membr anes, oxidized lipoproteins, and atherosclerotic tissues. It has the a bility to alter endothelial functions and is regarded as a causal agen t in atherogenesis. In this study, the modulation of arachidonate rele ase by lyse-PC in human umbilical vein endothelial cells was examined. Incubation of endothelial cells with lyse-PC resulted in an enhanced release of arachidonate in a time-and concentration dependent manner. Maximum arachidonate release was observed at 10 min of incubation with 50 mu M lyse-PC. Lyse-PC species containing palmitoyl (C-16:0) or ste aroyl (C-18:0) groups elicited the enhancement of arachidonate release , while other lysolipids such as lysophosphatidylethanolamine, lysopho sphatidylserine, lysophosphatidylinositol, or lysophosphatidate were r elatively ineffective. Lyse-PC-induced arachidonate release was decrea sed by treatment of cells with PLA(2) inhibitors such as para-bromophe nacyl bromide and arachidonoyl trifluoromethyl ketone. Furthermore, ar achidonate release was attenuated in cells grown in the presence of an tisense oligodeoxynucleotides that specifically bind cytosolic PLA(2) mRNA. Treatment of cells with lyse-PC resulted in a translocation of P LA(2) activity from the cytosolic to the membrane fractions of cells. Lyse-PC induced a rapid influx of Ca2+ from the medium into the cells, with a simultaneous enhancement of protein kinase C (PKC) activity in the membrane fractions. The lyse-PC-induced arachidonate release was attenuated when cells were preincubated with specific inhibitors of PK C (staurosporine and Ro31-8220) or a specific inhibitor of mitogen-act ivated protein kinase/extracellular regulated kinase kinase (PD098059) . Taken together, the results of this study show that lyse-PC caused t he elevation of cellular Ca2+ and the activation of PKC, which stimula ted cytosolic PLA(2) in an indirect manner and resulted in an enhanced release of arachidonate.