Inhibitors of phospholipase promote apoptosis of human endothelial cells

In order to understand the signal transduction system that regulates Apoptosis of human umbilical vein endothelial cells (HUVEC), we investigated the effects of inhibitors of the activity of phospholipases. All three tested inhibitors of Phospholipase A2 (PLA2), namely, manoalide, 3-(4-octadecyl)benzoylacrylic acid (OBAA), and oleyoxyethylphosphorylcholine (OOPC), induced apoptotic cell death of HUVEC. After 16 h of treatment, almost all of the cells had disintegrated into apoptotic bodies, and DNA ladders characteristic of apoptotic cell death were clearly observed upon analysis of DNA on Agarose gels. The release of arachidonic acid from the cells that had been treated with manoalide, OBAA or OOPC (at the same concentrations as those at which these compounds induced Apoptosis) was inhibited. We also studied the effects of two inhibitors of phosphatidylinositol-specific Phospholipase C (PLC), U73122, and compound 48/80. Both compounds promoted the Apoptosis of HUVEC. After 16 h of treatment, few cells remained intact, and DNA fragmentation was clearly detectable after only 12 h. Quantitation of inositol released from cells treated with U73122 and compound 48/80 showed that the release of inositol was blocked. By contrast, U73343, a similar aminosteroid that does not inactivate PLC, had no such effects. Our results suggest that PLA2 and phosphatidylinositol-specific PLC might be involved in the signaling pathway of Apoptosis in HUVEC, and that the metabolism of arachidonic acid and of inositol might play important roles in the present apoptotic signal-transduction system.