Lysophosphatidylcholine stimulates the release of arachidonic acid in human endothelial cells

Lysophosphatidylcholine (lyse-PC) is a product of phosphatidylcholine hydrolysis by phospholipase A(2) (PLA(2)) and is present in cell membranes, oxidized lipoproteins, and atherosclerotic tissues. It has the ability to alter endothelial functions and is regarded as a causal agent in atherogenesis. In this study, the modulation of arachidonate release 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 stearoyl (C-18:0) groups elicited the enhancement of arachidonate release, while other lysolipids such as lysophosphatidylethanolamine, lysophosphatidylserine, lysophosphatidylinositol, or lysophosphatidate were relatively ineffective. Lyse-PC-induced arachidonate release was decreased by treatment of cells with PLA(2) inhibitors such as para-bromophenacyl bromide and arachidonoyl trifluoromethyl ketone. Furthermore, arachidonate release was attenuated in cells grown in the presence of antisense oligodeoxynucleotides that specifically bind cytosolic PLA(2) mRNA. Treatment of cells with lyse-PC resulted in a translocation of PLA(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 PKC (staurosporine and Ro31-8220) or a specific inhibitor of mitogen-activated protein kinase/extracellular regulated kinase kinase (PD098059). Taken together, the results of this study show that lyse-PC caused the elevation of cellular Ca2+ and the activation of PKC, which stimulated cytosolic PLA(2) in an indirect manner and resulted in an enhanced release of arachidonate.