Structural identification of phosphatidylcholines having an oxidatively shortened linoleate residue generated through its oxygenation with soybean or rabbit reticulocyte lipoxygenase

Abstract

Phosphatidylcholines (PCs) with platelet-activating factor (PAF)-like biological activities are known to be generated by fragmentation of the sn-2-esterified polyunsaturated fatty acyl group. The reaction is free radical-mediated and triggered by oxidants such as metal ions, oxyhemoglobin, and organic hydroperoxides. In this study, we characterized the PAF-like phospholipids produced on reaction of PC having a linoleate group with lipoxygenase enzymes at low oxygen concentrations. When the oxidized PCs were analyzed by gas chromatography–mass spectrometry, two types of oxidatively fragmented PC were detected. One PC had an sn-2-short chain saturated or unsaturated acyl group (C8–C13) with an aldehydic terminal; the abundant species were PCs with C9 and C13. The other PC had a short chain saturated acyl group (C6–C9) with a methyl terminal, and the most predominant species was PC with C8. When the extracts of oxidation products were subjected to catalytic hydrogenation, PCs having saturated acyl groups (C6–C14) were detected; the most abundant was C12 species. The less regiospecific formation of PAF-like lipids suggests that they were generated by oxidative fragmentation of PC hydroperoxides formed by non-stereoselective oxygenation of the alkyl radical of esterified linoleate that escaped from the active centers of lipoxygenases. One of the PAF-like PC with an aldehydic terminal was found to be bioactive; it inhibited the production of nitric oxide induced by lipopolysaccharide and interferon-γ in vascular smooth muscle cells from rat aorta.

Keywords

• platelet-activating factor
• phosphatidylcholine hydroperoxide
• free radical
• lipid peroxidation
• gas chromatography–mass spectrometry
• nitric oxide production