Phospholipase A2 activation in human neutrophils requires influx of extracellular Ca2+ and leukotriene B4

Abstract

We have demonstrated that phospolipase A2 (PLA2) activation in human neutrophils requires both the influx of extracellular Ca2+ and leukotriene B4 (LTB4). Surprisingly, the eicosanoids (LTB4 and its omega-oxidation products) formed were quantitatively very similar in both thapsigargin (Thap)- and A-23187-stimulated neutrophils. In contrast, Thap had very little effect on the activation of PLA2 when 5-lipoxygenase (5-LO) was blocked by BW755C or MK-886, whereas A-23187 caused a substantial activation. The lack of PLA2 activation in Thap-stimulated neutrophils results from the inhibition of LTB4 formation in the presence of 5-LO inhibitors. It appears that A-23187 activates both LTB4-dependent and -independent PLA2, whereas Thap activates LTB4-dependent PLA2. Experiments with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid demonstrated that activation of Thap-sensitive PLA2 and 5-LO requires the influx of Ca2+. Neither the transient elevation of cytosolic Ca2+ from intracellular stores nor the sustained Ca2+ influx alone without LTB4 appears sufficient to cause the activation of LTB4-dependent PLA2. We suggest that the activation of LTB4-dependent PLA2 involves 1) a sustained elevation of cytosolic Ca2+ coupled to the influx of extracellular Ca2+ and 2) a coupling between LTB4 and its receptor. We conclude that LTB4-dependent PLA2 plays an important role in the poststimulatory formation of lipid mediators such as prostaglandins, leukotrienes, and platelet-activating factor.

Cytosolic phospholipase A2 alpha inhibitor, pyrroxyphene, displays anti-arthritic and anti-bone destructive action in a murine arthritis model

“…In human rheumatoid arthritis, PLA 2 activity and levels of LTB 4 and PGE 2 in the synovial fluid have shown a good correlation [35]. LTB 4 is known to positively stimulate the activation of PLA2 [36,37], and its importance in the pathogenesis of collagen-induced arthritis in mice has been confirmed by us [18] and another research group [22]. Indomethacin was reported to have a slight inhibitory effect in collageninduced arthritis [21], and COX-2 knockout mice did not develop collagen-induced arthritis [38].…”

Reactive oxidants regulate membrane repolarization and store-operated uptake of calcium by formyl peptide-activated human neutrophils

“…The efficiency of these Ca 2+ clearance mechanisms is potentiated by NADPH oxidase-mediated membrane depolarization which prevents influx of extracellular Ca 2+ [21]. Given the well- [22] and activation of β2-integrins [23]. Moreover, refilling of stores enables the cells to reinitiate Ca 2+ -dependent inflammatory responses on reexposure to a Ca 2+ -mobilizing stimulus.…”

Formation of 8‐iso‐PGF2α and thromboxane A2 by stimulation with several activators of phospholipase A2 in the isolated human umbilical vein

“…Elevated intracellular calcium activates PLA 2 and PLC followed by stimulation of arachidonic acid metabolism, whose intermediates also generate free radicals ( Kuehl et al ., 1980 ; Kontos et al ., 1985 ). All substances used activate PLs by calcium mobilization and subsequent eicosanoid release ( Benbarek et al ., 1999 ; Kajiyama et al ., 1990 ; Reddy et al ., 1995 ; Cherouny et al ., 1988 ; Vercellotti et al ., 1991 ; Rao et al ., 1995 ; Schoenberg, 1997 ). Liu & Li (1995) proposed that formation of reactive oxygen species and arachidonic acid metabolites initiate feedback loops in which formation of one leads to generation of the others.…”

“…Mediators such as bradykinin (BK) and histamine or oxygen free radicals and catecholamines are involved in inflammation and cardiovascular diseases ( Vane & Ferreira, 1978 ; Jean & Bodinier, 1994 ; Kopin, 1989 ). It is well known that BK, histamine, noradrenaline (NA), the divalent cation ionophore A 23187 and hydrogen peroxide (H 2 O 2 ) activate phospholipase A 2 (PLA 2 ) by calcium‐mobilization followed by an increased release of eicosanoids ( Pace‐Asciak & Rangraj, 1977 ; Cherouny et al ., 1988 ; Rao et al ., 1995 ; Schoenberg, 1997 ; Kajiyama et al ., 1990 ; Reddy et al ., 1995 ; Kennedy et al ., 1996 ; Förstermann et al ., 1984 ; Weigel et al ., 1991 ; Juan, 1979 ; Juan & Sametz, 1980 ; Sametz & Juan, 1982 ).…”