Aspirin induces non-enzymatic formation of platelet-activating factor from lyso platelet-activating factor

Non-enzymatic platelet-activating factor formation by acetylated proteins

Substantial amounts of platelet-activating factor (PAF 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine), the potent phospholipid mediator of allergic and inflammatory reactions, are formed upon incubation of acetylated low-density lipoprotein, acetylated bovine serum albumin (BSA) and acetylated apolipoprotein A-I with 1-0-hexadecyl-sn-glycero-3-phosphocholine (lyso-PAF). Acetylated BSA produced 0.3 nmol PAF/mg of protein after a 6 h incubation period with 40 microM lyso-PAF. The transfer of acetate bound to acetylated proteins to lyso-PAF was non-enzymatic. Chemical PAF formation by acetylated proteins, involved in lipid metabolism and transport, could lead to complication of inflammatory and allergic events.

Lipid acetylation reactions and the metabolism of platelet-activating factor

In this review properties of lipid acetyltransferase enzymes are outlined. The three activities of interest are lyso PAF acetyltransferase (acetyl CoA: 1-alkyl-sn-glycero-3-phosphocholine acetyltransferase), AGP acetyltransferase (acetyl CoA: 1-alkyl sn-glycero-3-phosphate acetyltransferase) and a transacetylase activity that can transfer acetyl groups from PAF to lipid acceptors in the formation of 1-alkenyl-2-acetyl-sn-glycero-3-phosphoethanolamine and N-acetyl sphingosine (C2 ceramide). This review focuses on the role of acetyltransferases and transacetylases within the metabolism of platelet-activating factor and specifically addresses characteristics of the enzymes, including subcellular localization, substrate selectivity, and enzymatic regulation.