Role of cytosolic phospholipase A(2) in cytokine-stimulated prostaglandin release by human gallbladder cells

Eicosanoids are involved in gallbladder inflammation, epithelial water tran sport, and mucous secretion. Phospholipase A(2) enzymes liberate arachidoni c acid from membrane phospholipids for the synthesis of eicosanoids. The pu rpose of this study was to determine the effect of selective cytoplasmic an d secretory phospholipase A(2) inhibitors on basal and stimulated arachidon ic acid and prostaglandin E-2 release in gallbladder cells. Western immunob lotting was employed to evaluate both cytosolic and secretory phospholipase A(2) enzymes in human gallbladder cells. Cells were incubated for 22 hours with H-3 labeled arachidonic acid. Arachidonic acid and prostaglandin E-2 release was then measured in the supernate after 2 hours of exposure to hum an interleukin-1 beta, alone or after pretreatment for 1 hour with the inhi bitors. Unstimulated gallbladder cells express both 85 kDa cytosolic and 14 kDa secretory phospholipase A(2). The 85 kDa phospholipase A(2) was induce d by interleukin-1 beta, whereas there was no apparent change in secretory phospholipase A(2) enzyme concentrations. Both the secretory phospholipase A(2) inhibitor p-bromophenylacyl bromide and the cytosolic phospholipase A( 2) inhibitor arachidonyl trifluoromethyl ketone decreased basal and interle ukin-1 beta-stimulated arachidonic acid release. inn contrast, only inhibit ion of cytosolic phospholipase A(2) led to a decrease in interleukin-1 beta -stimulated prostaglandin E-2 release. Basal and interleukin-1 beta-stimula ced arachidonic acid release appears to be the result of the activity of bo th cytosolic and secretory phospholipase A(2). Interleukin-1 beta-stimulate d prostaglandin E-2 release appears to be dependent on the activity of cyto solic phospholipase A(2).