Stimulus-specific induction of phospholipid and arachidonic acid metabolism in human neutrophils

Abstract

Abstract. Phospholipid remodeling resulting in arachidonic acid (AA) release and metabolism in human neutrophils stimulated by calcium ionophore A23187 has been extensively studied, while data obtained using physiologically relevant stimuli is limited. Opsonized zymosan and immune complexes induced stimulus-specific alterations in lipid metabolism that were different from those induced by A23187.[3H]AA release correlated with activation of phospholipase A2 (PLA2) but not with cellular activation as indicated by superoxide generation. The latter correlated more with calcium-dependent phospholipase C (PLC) activation and elevation of cellular diacylglycerol (DAG) levels. When cells that had been allowed to incorporate [3H]AA were stimulated with A23187, large amounts of labeled AA was released, most of which was metabolized to 5-HETE and leukotriene B4. Stimulation with immune complexes also resulted in the release of [3H]AA but this released radiolabeled AA was not metabolized. In contrast, stimulation with opsonized zymosan induced no detectable release of [3H]AA.Analysis of [3H]AA-labeled lipids in resting cells indicated that the greatest amount of label was incorporated into the phosphatidylinositol (PI) pool, followed closely by phosphatidylcholine and phosphatidylserine, while little [3H]AA was detected in the phosphatidylethanolamine pool. During stimulation with A23187, a significant decrease in labeled PI occurred and labeled free fatty acid in the pellet increased. With immune complexes, only a small decrease was seen in labeled PI while the free fatty acid in the pellets was unchanged. In contrast, opsonized zymosan decreased labeled PI, and increased labeled DAG. Phospholipase activity in homogenates from human neutrophils was also assayed. A23187 and immune complexes, but not zymosan, significantly enhanced PLA2 activity in the cell homogenates. On the other hand, PLC activity was enhanced by zymosan and immune complexes. Stimulated increases in PLC activity correlated with enhanced superoxide generation induced by the stimulus.T I V A T I O S of neutrophils is intimately linked to changes in phospholipid metabolism (40,43,44). Released arachidonic acid (AA)' from membrane phospholipids (PLs) provides a substrate for the formation of bioactive lipids that can modulate cell responses (4, 33, 34). Additionally, nonmetabolized AA has been shown to activate the neutrophil NADPH oxidase (2, 15). It is also possible that phospholipid remodeling resulting in the release of AA and/or the formation of lysophospholipids may be a method of altering cell membrane fluidity during signal transduction (36). Crucial cell functions (i.e., phagocytosis, carrier-mediated transport, membrane-bound enzymes) can be altered by fatty acid enrichment (21,22,31,39).1. Abbreviations used in this paper: AA, arachidonic acid; DAG, diacylglycerol; LTB4, leukotriene B4; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PI, phosphatidylinositol; PL, phospholipid; PLA2, phospholipase A:; PLase, phospholipase; PLC, phospholipase...

Phospholipase A2: Its Usefulness in Laboratory Diagnostics

“…The initial step in formation of these inflammatory mediators in human PMN involves PLA 2 -catalyzed hydrolysis of cellular PLs. 190,191 A soluble PLA 2 stored in granules of PMNs is released into the extracellular space in response to phagocytic, antigenic, or chemotactic stimuli. [192][193][194][195][196] Alkylglycerols have been suggested to play a role in modulating the production of lipid mediators of inflammation by priming PLA 2 , 5-lipoxygenase, and acetyltransferase activation in PMN.…”

Arachidonic acid release in rabbit neutrophils

“…Many different cell types, including the neutrophilic polymorphonuclear leucocytes (neutrophils), release arachidonic acid in response to stimulation. The fatty acid is then metabolized to generate one or more biologically active eicosanoids such as prostaglandins, thromboxanes and leukotrienes (Lands & Samuelsson, 1968;Hirata et al, 1979;Billah et al, 1980;Corey et al, 1980;Rubin et al, 1981;Feinstein & Sha'afi, 1983;Flower, 1985;Alonso et al, 1986;Burch et al, 1986;Pollock et al, 1986;Smith & Waite, 1986;Godfrey et al, 1987). Although the steps involved in the release of arachidonic acid from membrane phospholipids after cell stimulation are complex and not fully understood, the main step involves the action of phospholipase A2 (PLA2).…”

Effects of various drugs on superoxide generation, arachidonic acid release and phospholipase A2 in polymorphonuclear leukocytes.

“…The only known exception is phorbol myristate acetate (PMA) which is a potent protein kinase C activator, but does not stimulate AA release (12,13). Very recent studies have presented a stimulus-specific in duction of the AA metabolism in terms of the activations of the cellular phospholipases (14). Furthermore, it has been demonstrated that the reaction products of phospholipase A2 could be responsible for the initiation of the respiratory burst of PMNs (12,15,16).…”