Selective acylation of lyso platelet activating factor by arachidonate in human neutrophils

Human polymorphonuclear leukocytes (PMN) incubated with 1-O-[³H]alkyl-2-acetyl-sn-glycero-3-phosphocholine (1-[³H]alkyl-2-acetyl-GPC; platelet activating factor) inactivated the compund by removing the acetyl group and replacing it with a long chain acyl residue. The nature of the acyl group added at the 2-position of the 1-O-[³H]alkyl-2-acyl-GPC formed was examined by argentation chromatography and by reverse phase high performance liquid chromatography. A striking selectivity for arachidonate was observed in the acylation reaction. The major labled component of the starting material was the 1-O-hexadecyl-linked species; high performance liquid chromatography analysis revealed that 75 to 80% of this component was acylated by arachidonate. Similarly, based on argentation thin layer chromatography, approximately 80% of the total starting material was acylated by tetraenoic acyl residues. The incorporation of 1-O-[³H]alkyl-2-lyso-GPC into 1-O-alkyl-2-acyl-GPC by the PMN was compared; no difference in the acylation pattern was observed with the 2-acetyl and 2-lyso precursors. Thus, activation of the PMN does not appear to be required to elicit the selectivity for arachidonate. When labeled 1-palmitoyl-2-lyso-GPC was compared in the system under the same conditions, it was also preferentially acylated by arachidonate; thus, it is not clear at this time whether or not the selectivity for arachidonate is physiologically limited to platelet activating factor. Our findings suggest a close relationship exists between the metabolism of platelet activating factor and arachidonate in human PMN.