Molecular heterogeneity of platelet-activating factor (PAF) in rat glandular stomach determined by gas chromatography/mass spectrometry. PAF molecular species changes upon water-immersion stress

Quantitative determination of major platelet activating factors from human plasma

Platelet activating factor (PAF) is a potent lipid mediator that is involved in many important biological functions, including platelet aggregation and neuronal differentiation. Although an ELISA assay has been used to measure PAF levels, it cannot distinguish between its isoforms. To achieve this, liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been used instead. However, isobaric lysophosphatidylcholine (lyso PC), which is often present in large amounts in complex biological samples and has similar retention times in many LC conditions, can affect the accurate measurement of PAF. The present study examined the fragmentation behavior of major PAF and lyso PC during various MS/MS conditions. Fragment ions at m/z 184 and at m/z 104 were abundantly observed from MS/MS of lyso PCs. PAF provided a dominant fragment ion at m/z 184, but a fragment ion at m/z 104 was almost never produced, regardless of the collision energy. Thus, the two fragment ions at m/z 184 and m/z 104 were used to accurately measure PAF levels. First, the fragment ion at m/z 184 and the retention time of PAF in LC-MS/MS were used to identify and quantitate PAF. However, if there were small retention time shifts, which are common in multiple sample runs, and lipid composition in a sample is very complicated, the fragment ion at m/z 104 was used to confirm whether the fragment ion at m/z 184 belonged to PAF. This novel method accurately determined the major PAF (C16:0 PAF, C18:0 PAF, and C18:1 PAF) levels in human plasma.

Bioactive products of phospholipid oxidation: isolation, identification, measurement and activities

There is considerable evidence to suggest that oxidation of LDL plays an important role in atherogenesis. Polyunsaturated fatty acids, a major oxidative target, are present as phospholipids in the outer core of the lipoprotein particle. Studies from several laboratories have shown an increase in the levels of phospholipid oxidation products in atherosclerotic lesions and of antibodies to oxidized phospholipids in mice and humans with lesions. Significantly, phospholipid oxidation products have been demonstrated (in vitro) to selectively activate processes in vascular wall cells that may contribute to atherogenesis. This review discusses activities, methods for isolation, identification and measurement of bioactive phospholipids. Past studies suggest that defined and relatively simple current technologies allow identification of bioactive phospholipid oxidation products and measurement of their levels in tissue.

Effects of growth temperature on the fatty acid composition of the free-living nematode Caenorhabditis elegans

The effects of growth temperature on the fatty acid compositions of the phosphatidylcholine (PC), phosphatidylethanolamine (PE), and total lipid (TL) fractions of the free-living nematode Caenorhabditis elegans were investigated. A reduction in growth temperature from 25 to 15 degrees C caused the proportions of eicosapentaenoic acid (20:5n-3) to increase from 23.6 to 32.5% in the PC, from 7.4 to 10.8% in the PE, and from 12.9 to 19.9% in the TL fractions. Conversely, the levels of dihomo-gamma-linolenic acid (20:3n-6) and arachidonic acid (20:4n-6) in these phospholipid fractions and the TL fraction both decreased with decreasing growth temperature. Analysis of the positional distribution of fatty acids in the PC fraction revealed that the change in the composition of C20 polyunsaturated fatty acid was obvious in position sn-2. Lowering the growth temperature induced an increase in the level of the diacyl subclass of PE from 58% at 25 degrees C to 71% at 15 degrees C, with a concomitant decrease in the levels of the alkylacyl and alkenylacyl subclass of PE of C. elegans. These changes observed in the phospholipids of C. elegans might be one mechanism for adaptation to low temperature.

Comparison of 1-O-alkyl-, 1-O-alk-1'-enyl-, and 1-O-acyl-2-acetyl-sn-glycero-3-phosphoethanolamines and -3-phosphocholines as agonists of the platelet-activating factor family

Four naturally occurring platelet-activating factor (PAF) analogs, 1-alk-1'-enyl-2-acetyl-sn-glycero-3-phosphocholine, 1-hexadecanoyl-2-acetyl-sn-glycero-3-phosphocholine, 1-octadecanoyl-2-acetyl-sn-glycero-3-phosphocholine, and 1-alkyl-2-acetyl-sn-glycero-3-phosphoethanolamine, stimulated human neutrophils (PMN) to mobilize Ca2+, degranulate, and produce superoxide anion. They were, respectively, 5-, 300-, 500-, and 4000-fold weaker than PAF in each assay; inhibited PMN-binding of [3H]PAF at concentrations paralleling their biological potencies; and showed sensitivity to the inhibitory effects of PAF antagonists. PAF and the analogs, moreover, desensitized PMN responses to each other but not to leukotriene B4 and actually increased (or primed) PMN responses to N-formyl-MET-LEU-PHE. Finally, 5-hydroxyeicosatetraenoate-enhanced PMN responses to PAF and the analogs without enhancing the actions of other stimuli. It stereospecifically raised each analog's potency by as much as 100-fold and converted a fifth natural analog, 1-alk-1'-enyl-2-acetyl-sn-glycero-3-phosphoethanolamine from inactive to a weak stimulator of PMN. PAF and its analogs thus represent a structurally diverse family of cell-derived phospholipids which can activate, prime, and desensitize neutrophils by using a common, apparently PAF receptor-dependent mechanism.

Phospholipids from the free-living nematode Caenorhabditis elegans

The phospholipid and the fatty chain compositions of diacyl, alkylacyl and alkenylacyl glycerophospholipids of the free-living nematode, Caenorhabditis elegans, were investigated. The phospholipids were comprised of 54.5% ethanolamine glycerophospholipid (EGP), 32.3% choline glycerophospholipid (CGP), 8.1% sphingomyelin and 5.1% others. The most abundant fatty acid in CGP was eicosapentaenoic acid (20:5n-3). The fatty acids in CGP were more unsaturated than those in EGP. Alkenylacyl and alkylacyl subclasses accounted for 1.0 and 2.6%, respectively, of CGP and 14.0 and 19.6%, respectively, of EGP. At least 80% of the alkenyl and alkyl groups were 18:0 chains and the remaining were odd numbered chains. The potential presence of platelet-activating factor (PAF) was examined by bioassay, but PAF-like activity was not detected in the extracts of this nematode.

Modulation by drugs acting on the autonomic nervous system of platelet-activating factor in the stomach of rats

Platelet-activating factor (PAF), an ether linked choline glycerophospholipid, is a potent initiator of diverse physiological and pathological processes. We have reported that gastric endogenous PAF levels were reduced and the contents of each of its molecular species changed during water-immersion stress in rats (Sugatani J et al., FASEB J 3: 65-70, 1989 and Sugatani J et al., Lipids 26: 1347-1353, 1991). In this study, we determined the effects of autonomic drugs on the level of gastric PAF, its molecular heterogeneity and formation of gastric erosions in unstressed rats and those subjected to water-immersion stress. Atropine, an anticholinergic drug, suppressed both the stress-induced changes and development of gastric lesions. 6-Hydroxydopamine-induced sympathectomy induced a small decrease in the gastric PAF levels and the addition of stress further decreased the PAF levels and development of gastric lesions. Carbamylcholine induced a transient decrease in the gastric PAF level of normal rats, which was not associated with gastric erosion formation. In contrast, the endogenous gastroprotective factor dopamine evoked transient dose- and time-dependent increases in the gastric PAF levels. These observations indicate that cholinergic muscarinic-receptor activation in rats led to decreases in gastric PAF levels and a prolonged and marked decrease in its level was associated with the development of gastric lesions, and that dopamine increases gastric PAF levels. Gastric endogenous PAF levels are closely associated with the autonomic nervous system and should be considered further in investigations of gastric function.