Endothelial degradation of extracellular lyso-phosphatidylcholine

Abstract

Formation of lysophospholipids, including lyso-phosphatidylcholine (lysoPC), is enhanced during oxidation of low-density lipoprotein, in ischaemic tissue and under inflammatory conditions. Besides being potentially cytotoxic, extracellular lysoPC induces changes in several properties of vascular endothelial cells. These include expression of endothelial adhesion molecules and interference with the endothelial production of nitrogen monoxide, prostacyclin and growth factors. One way of controlling the concentration of extracellular lysoPC is by the action of lysophospholipases, which degrade lysoPC into a free fatty acid and glycerophosphocholine. We therefore tested whether vascular endothelial cells have the ability to degrade extracellular lysoPC. Monolayers of primary cultures of human umbilical vein endothelial cells degraded an average of 84+/-24 nmol lysoPC/10(6) cells/2 h. By comparison, monocytes degraded 9.7+/-3.7 nmol lysoPC/10(6) cells/2 h, and erythrocytes and platelets < 1 nmol lysoPC/10(6) cells/2 h. The ability of endothelial cells to degrade extracellular phospholipids (diacylphosphatidyl choline) was found to be relatively low (9.5+/-6.4 nmol/10(6) cells/2 h). Triacylglycerol hydrolase activity was just above detection level. In conclusion, endothelial cells seem to degrade extracellular lysoPC effectively. This endothelial property may be important in controlling plasma and tissue levels of extracellular lysoPC as well as in the interaction between lysoPC and the vascular endothelium.