1-O-hexadec-1'-enyl-2-acetyl-sn-glycero-3-phosphocholine and its biological activity

Identification of plasmenylethanolamine as a major component of the phospholipids of strain DM 28c of Trypanosoma cruzi

A novel phospholipid has been purified from strain Dm 28c of Trypanosoma cruzi, and characterized by fast atom bombardment mass spectrometry and nuclear magnetic resonance spectroscopy as a plasmenylethanolamine with a hexadec-l-enyl group in the sn-1 position and an approximately equimolar mixture of octadecenoate and octadecadienoate esterified to the sn-2 hydroxyl. The purified plasmenylethanolamine reacted positively when probed with sera from patients with chronic Chagas' disease. Since plasmenylethanolamines of similar structure are abundant in mammalian cardiac and neuronal tissues, cross reactions between these epitopes may be a factor in the mechanism of autoimmune pathology in the chronic phase of Chagas' disease.

Composition of ether-linked sub-classes of glycerophospholipids in clones with a different metastatic potential isolated from a murine fibrosarcoma line (T3 cells)

An increase of ether-linked sub-classes of choline and ethanolamine glycerophospholipids has been shown in different types of tumor cells, and correlated with some of their specific biological parameters. In the present study, we examined the composition of ether-linked lipids in a series of clones with a different lung-colonizing potential isolated in our laboratory from a highly metastatic fibrosarcoma line (T3 cells). We found good correlation between the metastatic potential of T3 isolates and increased proportions of both alkylacyl and alkenylacyl subclasses in choline glycerophospholipids (CGP). Moreover, propagation of a weakly metastatic T3 clone in tissue culture led to the emergence of a sub-clone which expressed high metastatic potential together with a high level of alkylacyl and alkenylacyl CGP. No differences were found in the alkylacyl and alkenylacyl-ethanolamine glycerophospholipids (EGP) between the strongly and weakly metastatic T3 clones. We discuss the accumulation of alkylacyl and alkenylacyl CGP in metastatic cells for its possible role in metastatic diffusion by generation of platelet-activating factor (PAF).

Evidence for production of platelet-activating factor by yeast Saccharomyces cerevisiae cells

Various yeast strains were screened for platelet-activating factor (PAF) production. High PAF production was found mainly in the strains of Saccharomyces genus. Yeast PAF showed a typical platelet aggregation pattern, which was inhibited by specific PAF antagonists, such as CV-3988, CV-6209 and L-652731. The main molecular species of yeast PAF were identified as 1-palmitoleoyl-, -palmitoyl-, -oleoyl- and -stearoyl-2-acetyl-sn-glycero-3-phosphocholines (16:1, 16:0, 18:1 and 18:0 acylPAFs) and 1-hexadecenyl- and hexadecyl-2-acetyl-sn-glycero-3-phosphocholines (16:1 and 16:0 PAFs), by mass spectrometry. PAF formation in yeast cells increased at the middle stationary phase of growth.

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.

Platelet-activating factor and related acetylated lipids as potent biologically active cellular mediators

Platelet-activating factor (PAF or 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is the most potent lipid mediator yet discovered. It is known to stimulate a wide span of biological responses ranging from aggregation and degranulation of platelets and neutrophils to a variety of cellular effects involving the stimulation of chemotaxis; chemokinesis; superoxide formation; protein phosphorylation; activation of protein kinase C, arachidonic acid, and phosphoinositide metabolites; glycogenolysis; and tumor necrosis factor production. Obviously, with such a diversity of biological activities, it is not surprising that PAF has been considered to be a key component in numerous diseases related to hypersensitivity and inflammatory responses. Evidence has also been presented for the role of PAF in physiological processes, particularly those involving reproduction and fetal development. Furthermore, because of its potent hypotensive action, PAF has been implicated as a contributing factor in blood pressure regulation. PAF is produced by two independent enzymatic pathways. The remodeling route involves the structural modification of a membrane lipid (1-alkyl-2-acyl-sn-glycero-3-phosphocholine) by replacement of the acyl moiety with an acetate group. An alternate route is the de novo synthesis of PAF from an O-alkyl analogue of a lysophosphatidic acid that requires a reaction sequence of acetylation, dephosphorylation, and phosphocholine addition steps. Hypersensitivity and other pathophysiological reactions are thought to be caused by activation of the remodeling pathway, whereas the de novo route is believed to be the source of endogenous levels of PAF required for physiological functions. Inactivation of PAF occurs when the acetate group is hydrolyzed by an acetylhydrolase that is present in both extra- and intracellular compartments, although the catalytic activity of the two forms of acetylhydrolase are identical, some of their properties differ. The control of PAF metabolism is very complex, but acetylhydrolase, Ca2+, phosphorylation/dephosphorylation of enzymes, and fatty acids (especially polyunsaturates) appear to be important regulatory factors. Specific PAF receptors have clearly been demonstrated on several different types of cells, and although the mechanism of PAF actions is poorly understood, it appears that the PAF/receptor-induced responses are closely associated with the signal transduction process; both G proteins and adenyl cyclase appear to be involved. Because significant quantities of PAF are often retained within certain cells, the possibility of PAF serving as an intracellular mediator has also been proposed.

Development of a novel scintillation proximity radioimmunoassay for platelet-activating factor measurement: comparison with bioassay and GC/MS techniques

A novel, facile and sensitive scintillation proximity radioimmunoassay (SPRIA) for quantitation of PAF has been developed. No separation of antibody bound [3H]PAF from free [3H]PAF is required as the assay employs protein A - coated fluomicrospheres (beads containing scintillant). The assay system was suitable for the quantitation of 0.03 to 2 pmol of 1-hexadecyl-2-acetyl-sn-glycero-3- phosphocholine. The cross-reactivity was high with 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine but was very low with PAF analogs such as 1-alkyl- and 1-acyl-2-lyso-sn-glycero-3-phosphocholine, 1-acyl-2-acetyl-sn-glycero-3-phosphocholine, and 1-alk-1'-enyl-2-acetyl-sn-glycero-3-phosphocholine. The specificity of SPRIA was higher than that of bioassay (platelet degranulation assay). PAF receptor antagonists (L-652,731, WEB2086, and FR900452) at up to 10 nmol per tube had no affect on the SPRIA. These observations indicate that the specificity of the PAF antibody is quite different from that of the platelet receptor. The values obtained using SPRIA for the measurement of PAF produced in polymorphonuclear leukocytes with stimuli are comparable to those obtained by SIM/GC/MS analysis.