Arachidonic acid is released by phospholipase A 2 and converted into hundreds of distinct bioactive mediators by a variety of cyclooxygenases (COX), lipoxygenases (LO), and cytochrome P450s. Because of the size and diversity of the eicosanoid class of signaling molecules produced, a thorough and systematic investigation of these biological processes requires the simultaneous quantitation of a large number of eicosanoids in a single analysis. We have developed a robust liquid chromatography/tandem mass spectrometry method that can identify and quantitate over 60 different eicosanoids in a single analysis, and we applied it to agoniststimulated RAW264.7 murine macrophages. Fifteen different eicosanoids produced through COX and 5-LO were detected either intracellularly or in the media following stimulation with 16 different agonists of Toll-like receptors (TLR), G protein-coupled receptors, and purinergic receptors. No significant differences in the COX metabolite profiles were detected using the different agonists; however, we determined that only agonists creating a sustained Ca 2؉ influx were capable of activating the 5-LO pathway in these cells. Synergy between Ca 2؉ and TLR pathways was detected and discovered to be independent of NF-B-induced protein synthesis. This demonstrates that TLR induction of protein synthesis and priming for enhanced phospholipase A 2 -mediated eicosanoid production work through two distinct pathways.

Cyclooxygenase (COX) has two isoforms, COX-1 and -2, which catalyze the key step in the conversion of cellular arachidonic acid into prostaglandins. In recent years, interest in COX-2 has significantly increased since it has been a target for the development of specific non-steroidal anti-inflammatory drugs. We report that COX-2 expression is up-regulated in phorbol ester (phorbol myristate acetate, PMA)-differentiated human U937 macrophage-like cells stimulated with lipopolysaccharide (LPS), whereas COX-1 is not up-regulated. We show that the LPS-induced up-regulation of COX-2 depends on the activity of the Mg ؉2 -dependent phosphatidic acid phosphohydrolase 1 (PAP-1). Inhibition of PAP-1 by bromoenol lactone, propranolol, or ethanol resulted in a decrease in LPS-induced COX-2 mRNA transcript production, COX-2 protein expression, and prostaglandin E 2 release from U937 macrophages. To ensure that these results did not arise because of PMA treatment of the U937 cells, similar experiments were conducted with the P388D 1 cell line, which does not require PMA differentiation. LPS increased the levels of endogenous cellular diacylglycerol (DAG) within 2 min of stimulation. This increase was observed to be sensitive to the PAP-1 inhibitors. Furthermore, phosphatidic acid phosphohydrolase activity assays showed that the bromoenol lactone-sensitive PAP-1 activity was translocated from the cytosolic fraction to the membrane fraction within 2 min of LPS exposure. Finally, DAG add-back experiments demonstrate that LPS-induced COX-2 expression is enhanced by the addition of exogenous DAG.

A series of 2-oxoamides based on dipeptides and pseudodipeptides were synthesized and their activities toward two human intracellular phospholipases A 2 (GIVA cPLA 2 and GVIA iPLA 2 ) and one human secretory phospholipase A 2 (GV sPLA 2 ) were evaluated. Derivatives containing a free carboxyl group are selective GIVA cPLA 2 inhibitors. A derivative based on the ethyl ester of an ether pseudodipeptide is the first 2-oxoamide, which preferentially inhibits GVIA iPLA 2 . The effect of 2-oxoamides on the generation of arachidonic acid from RAW 264.7 macrophages was also studied and it was found that selective GIVA cPLA 2 inhibitors preferentially inhibited cellular arachidonic acid release; one pseudodipeptide gave an IC 50 value of 2 μM.

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Group IVA phospholipase A2 (GIVA PLA2) catalyzes the release of arachidonic acid (AA) from the sn-2 position of glycerophospholipids. AA is then further metabolized into terminal signaling molecules including numerous prostaglandins. We have now demonstrated the involvement of phosphatidic acid phosphohydrolase 1 (PAP-1) and protein kinase C (PKC) in the Toll-like receptor-4 (TLR-4) activation of GIVA PLA2. We also studied the effect of PAP-1 and PKC on Ca+2 induced and synergy enhanced GIVA PLA2 activation. We observed that the AA release induced by exposure of RAW 264.7 macrophages to the TLR-4 specific agonist Kdo2-Lipid A is blocked by the PAP-1 inhibitors bromoenol lactone (BEL) and propranolol as well as the PKC inhibitor Ro 31-8220; however these inhibitors did not reduce AA release stimulated by Ca+2 influx induced by the P2X7 purinergic receptor agonist ATP. Additionally, stimulation of cells with diacylglycerol (DAG), the product of PAP-1 mediated hydrolysis, initiated AA release from unstimulated cells as well as restored normal AA release from cells treated with PAP-1 inhibitors. Finally, neither PAP-1 nor PKC inhibition reduced GIVA PLA2 synergistic activation by stimulation with Kdo2–Lipid A and ATP.