Phosphatidylcholine metabolism in human endothelial cells: modulation by phosphocholine

Phosphatidylcholine is the principal phospholipid in mammalian tissues, and a major source for the production of arachidonic acid. In this study, the effect of exogenous phosphocholine, a precursor of phosphatidylcholine biosynthesis, on the metabolism of phosphatidylcholine in human umbilical vein endothelial cells was investigated. Incubation of endothelial cells with exogenous phosphocholine at concentrations of 1 to 5 mM was found to inhibit choline uptake and its subsequent incorporation into phosphatidylcholine. Phosphocholine appeared to inhibit choline uptake in a competitive manner. Since phosphatidylcholine is metabolized mainly by the action of phospholipase A₂, with the release of arachidonic acid and other fatty acids, the effect of phosphocholine on arachidonic acid release in endothelial cells was also examined. The induction of arachidonic acid release by ATP was enhanced in cells treated with 1 mM phosphocholine. In vitro assays of phospholipase A₂ activity in cells incubated with phosphocholine, however, did not produced any significant change in the activity of this enzyme. The results of this study show that phosphocholine modulates the biosynthesis and catabolism of phosphatidylcholine in an indirect manner.