Biosynthesis of platelet activating factor and 1-O-acyl analogues by endothelial cells.

Mass spectrometric procedures have been used to measure 1-O-alkyl-2-O-acetyl-glycero-3-phosphocholine (PAF) and a structural analogue, 1-O-acyl-2-O-acetyl-glycero-3-phosphocholine, biosynthesis in stimulated human umbilical vein endothelial cells (HUVEC). The primary species of acetylated glycerophosphocholine detected were of the 1-O-acyl type, rather than PAF. The amounts of PAF synthesized were much less than reported in earlier studies. In addition, mass spectrometric procedures were used to profile the molecular species of glycerophosphocholine in HUVEC and to determine those species which have arachidonate in the sn-2 position. The pattern of the occurrence of arachidonate in the sn-2 position is very similar to the pattern of synthesis of the acetylated glycerophosphocholines. These results suggest that 1-O-acyl-2-O-acetyl-glycero-3-phosphocholines may have significant but unappreciated biological activities. These results also support the view that glycerophosphocholine molecular species which have arachidonate esterified at the sn-2 position are the immediate precursors for the hydrolysis-acetylation steps which result in the synthesis of sn-2 acetylated glycerophosphocholines, including PAF.