Recent progress in phospholipase A₂ research: from cells to animals to humans

Evidence for distinct mechanisms of uptake and antitumor activity of secretory phospholipase A2 responsive liposome in prostate cancer

Secretory phospholipase A(2) (sPLA(2)) cleave phospholipids at sn-2 ester bonds, releasing lysophospholipids and fatty acids, and are over expressed in several pathologies, including inflammation, arthritis, sepsis and breast and prostate cancers. Herein we evaluated the therapeutic activity of liposomes engineered to be responsive to different sPLA(2) isoforms compared to clinically used long-circulating (pegylated) sterically stabilized liposomes (SSL) in vitro and in vivo, and assessed differences in roles of sPLA(2) in the mechanism of uptake and delivery of these nanoparticles. Exposing sPLA(2) responsive liposomes (SPRL) to sPLA(2) increased the release of intraluminal entrapped contents in a time-dependent manner that was inhibited by the sPLA(2) inhibitor LY3117273. Treatment of prostate cancer cells with doxorubicin encapsulated in SSL and SPRL resulted in cytotoxicity in LNCaP, DU-145 and PC-3 cells lines comparable to free drug. Interestingly, cytotoxicity was not altered by sPLA(2) inhibition. Tracking of drug and liposome delivery using fluorescence microscopy and flow cytometry, we demonstrated that drug uptake was liposome-dependent, as encapsulation of doxorubicin in SPRL resulted in 1.5 to 2-fold greater intracellular drug levels compared to SSL. Liposome uptake was cell-dependent and did not correlate to doxorubicin uptake; however, doxorubicin uptake was generally greatest in PC-3 cells, followed by DU-145 cells and then LNCaP cells. In almost all cases, uptake of one of our formulations, SPRL-E, was greater than SSL. The therapeutic activity of SPRL in vivo was demonstrated using a mouse xenograft model of human prostate cancer, which showed that doxorubicin entrapped within SPRL decreased tumor growth compared to SSL, suggesting that SPRL are more effective at slowing tumor growth than a SSL formulation similar to the FDA approved DOXIL™. Collectively, these data show the therapeutic activity of SPRL compared to SSL, yield insights into the mechanisms of action of these nanoparticles and suggest that SPRL could be useful for treatment of other pathologies that over express sPLA(2).

Mechanism-based inhibition of iPLA2β demonstrates a highly reactive cysteine residue (C651) that interacts with the active site: mass spectrometric elucidation of the mechanisms underlying inhibition

The multifaceted roles of calcium-independent phospholipase A2β (iPLA2β) in numerous cellular processes have been extensively examined through utilization of the iPLA2-selective inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one (BEL). Herein, we employed accurate mass/high resolution mass spectrometry to demonstrate that the active site serine (S465) and C651 of iPLA2β are covalently cross-linked during incubations with BEL demonstrating their close spatial proximity. This cross-link results in macroscopic alterations in enzyme molecular geometry evidenced by anomalous migration of the cross-linked enzyme by SDS-PAGE. Molecular models of iPLA2β constructed from the crystal structure of iPLA2α (patatin) indicate that the distance between S465 and C651 is approximately 10 Å within the active site of iPLA2β. Kinetic analysis of the formation of the 75 kDa iPLA2β-BEL species with the (R) and (S) enantiomers of BEL demonstrated that the reaction of (S)-BEL with iPLA2β was more rapid than for (R)-BEL paralleling the enantioselectivity for the inhibition of catalysis by each inhibitor with iPLA2β. Moreover, we demonstrate that the previously identified selective acylation of iPLA2β by oleoyl-CoA occurs at C651 thereby indicating the importance of active site architecture for acylation of this enzyme. Collectively, these results identify C651 as a highly reactive nucleophilic residue within the active site of iPLA2β which is thioesterified by BEL, acylated by oleoyl-CoA, and located in close spatial proximity to the catalytic serine thereby providing important chemical insights on the mechanisms through which BEL inhibits iPLA2β and the topology of the active site.

Proinflammatory and immunoregulatory roles of eicosanoids in T cells

Eicosanoids are inflammatory mediators primarily generated by hydrolysis of membrane phospholipids by phospholipase A2 to ω-3 and ω-6 C20 fatty acids that next are converted to leukotrienes (LTs), prostaglandins (PGs), prostacyclins (PCs), and thromboxanes (TXAs). The rate-limiting and tightly regulated lipoxygenases control synthesis of LTs while the equally well-controlled cyclooxygenases 1 and 2 generate prostanoids, including PGs, PCs, and TXAs. While many of the classical signs of inflammation such as redness, swelling, pain, and heat are caused by eicosanoid species with vasoactive, pyretic, and pain-inducing effects locally, some eicosanoids also regulate T cell functions. Here, we will review eicosanoid production in T cell subsets and the inflammatory and immunoregulatory functions of LTs, PGs, PCs, and TXAs in T cells.

Mast cells: from lipid droplets to lipid mediators

LDs (lipid droplets) are metabolically highly active intracellular organelles. The lipid and protein profiles of LDs are cell-type-specific, and they undergo dynamic variation upon changes in the physiological state of a cell. It is well known that the main function of the LDs in adipocytes is to ensure energy supply and to maintain lipid homoeostasis in the body. In contrast, LDs in inflammatory cells have been implicated in eicosanoid biosynthesis, particularly under inflammatory conditions, thereby enabling them to regulate immune responses. Human mast cells are potent effector cells of the innate immune system, and the triacylglycerol (triglyceride) stores of their cytoplasmic LDs have been shown to contain large amounts of arachidonic acid, the main precursor of pro-inflammatory eicosanoids. In the present review, we discuss the current knowledge about the formation and function of LDs in inflammatory cells with specific emphasis on arachidonic acid and eicosanoid metabolism. On the basis of findings reported previously and our new observations, we propose a model in which lipolysis of LD-triacylglycerols provides arachidonic acid for lipid mediator generation in human mast cells.

Synthesis of mixed-chain phosphatidylcholines including coumarin fluorophores for FRET-based kinetic studies of phospholipase A(2) enzymes

Phospholipase A2 (PLA2) enzymes catalyze the hydrolysis of the sn-2 ester linkage of glycerophospholipids to produce fatty acids and lysophospholipids. A significant number of mammalian phospholipases comprise a family of secreted PLA2 enzymes, found in specific tissues and cellular locations, exhibiting unique enzymatic properties and distinct biological functions. Development of new real-time spectrofluorimetric PLA2 assays should facilitate the kinetic characterization and mechanistic elucidation of the isozymes in vitro, with the potential applicability to detect and measure catalytic PLA2 activity in tissues and cellular locations. Here we report a new synthesis of double-labeled phosphatidylcholine analogs with chain-terminal reporter groups including coumarin fluorophores for fluorescence resonance energy transfer (FRET)-based kinetic studies of PLA2 enzymes. The use of coumarin derivatives as fluorescent labels provides reporter groups with substantially decreased size compared to the first generation of donor-acceptor pairs of fluorescent phospholipids. The key advantage of the design is to interfere less with the physicochemical properties of the acyl chains, thereby improving the substrate quality of the synthetic probes. In order to assess the impact of the fluorophore substituents on the catalytic hydrolysis and on the phospholipid packing in the lipid-water interface of the assay, we used the experimentally determined specific activity of bee-venom phospholipase A2 as a model for the secretory PLA2 enzymes. Specifically, the rate of PLA2 hydrolysis of the coumarin labeled phosphatidylcholine analogs was less than three times slower than the natural substrate dipalmitoyl phosphatidylcholine (DPPC) under the same experimental conditions. Furthermore, variation of the mole fraction of the synthetic phosphatidylcholine vs. that of the natural DPPC substrate showed nearly ideal mixing behavior in the phospholipid-surfactant aggregates of the assay. The synthesis provides a rapid and efficient method for preparation of new synthetic phosphatidylcholines with the desired target structures for enzymatic and physicochemical studies.

The actions and metabolism of lysophosphatidylinositol, an endogenous agonist for GPR55

Lysophosphatidylinositol (LPI) is a subspecies of lysophospholipid and is assumed to be not only a degradation product of phosphatidylinositol (PI), but also a bioactive lysophospholipid mediator. However, not much attention has been directed toward LPI compared to lysophosphatidic acid (LPA), since the receptor for LPI has not been identified. During screening for an agonist for the orphan G protein coupled receptor GPR55, we identified LPI, 2-arachidonoyl LPI in particular, as an agonist for GPR55. Our efforts to identify an LPI receptor facilitated research on LPI as a lipid messenger. In addition, we also found that DDHD1, previously identified as phosphatidic acid-preferring phospholipase A1, was one of the synthesizing enzymes of 2-arachidonoyl LPI. Here, we summarized the background for discovering the LPI receptor, and the actions/metabolism of LPI. We also referred to the biosynthesis of PI, a 1-stearoyl-2-arachidonoyl species, since the molecule is the precursor of 2-arachidonoyl LPI. Furthermore, we discussed physiological and/or pathophysiological processes involving LPI and GPR55, including the relevance of LPI-GPR55 and cannabinoids, since GPR55 was previously postulated to be another cannabinoid receptor. Although there is no doubt that GPR55 is the LPI receptor, we should re-consider whether or not GPR55 is in fact another cannabinoid receptor.

Selective inhibition of human group IIA-secreted phospholipase A2 (hGIIA) signaling reveals arachidonic acid metabolism is associated with colocalization of hGIIA to vimentin in rheumatoid synoviocytes

Human group IIA secreted phospholipase A2 (hGIIA) promotes tumor growth and inflammation and can act independently of its well described catalytic lipase activity via an alternative poorly understood signaling pathway. With six chemically diverse inhibitors we show that it is possible to selectively inhibit hGIIA signaling over catalysis, and x-ray crystal structures illustrate that signaling involves a pharmacologically distinct surface to the catalytic site. We demonstrate in rheumatoid fibroblast-like synoviocytes that non-catalytic signaling is associated with rapid internalization of the enzyme and colocalization with vimentin. Trafficking of exogenous hGIIA was monitored with immunofluorescence studies, which revealed that vimentin localization is disrupted by inhibitors of signaling that belong to a rare class of small molecule inhibitors that modulate protein-protein interactions. This study provides structural and pharmacological evidence for an association between vimentin, hGIIA, and arachidonic acid metabolism in synovial inflammation, avenues for selective interrogation of hGIIA signaling, and new strategies for therapeutic hGIIA inhibitor design.

Lymphoid tissue phospholipase A2 group IID resolves contact hypersensitivity by driving antiinflammatory lipid mediators

PLA2G2D ameliorates skin inflammation through mobilizing pro-resolving lipid mediators.

Resolution of inflammation is an active process that is mediated in part by antiinflammatory lipid mediators. Although phospholipase A₂ (PLA₂) enzymes have been implicated in the promotion of inflammation through mobilizing lipid mediators, the molecular entity of PLA₂ subtypes acting upstream of antiinflammatory lipid mediators remains unknown. Herein, we show that secreted PLA₂ group IID (PLA2G2D) is preferentially expressed in CD11c⁺ dendritic cells (DCs) and macrophages and displays a pro-resolving function. In hapten-induced contact dermatitis, resolution, not propagation, of inflammation was compromised in skin and LNs of PLA2G2D-deficient mice (Pla2g2d^−/−), in which the immune balance was shifted toward a proinflammatory state over an antiinflammatory state. Bone marrow-derived DCs from Pla2g2d^−/− mice were hyperactivated and elicited skin inflammation after intravenous transfer into mice. Lipidomics analysis revealed that PLA2G2D in the LNs contributed to mobilization of a pool of polyunsaturated fatty acids that could serve as precursors for antiinflammatory/pro-resolving lipid mediators such as resolvin D1 and 15-deoxy-Δ^12,14-prostaglandin J₂, which reduced Th1 cytokine production and surface MHC class II expression in LN cells or DCs. Altogether, our results highlight PLA2G2D as a “resolving sPLA₂” that ameliorates inflammation through mobilizing pro-resolving lipid mediators and points to a potential use of this enzyme for treatment of inflammatory disorders.

The involvement of phospholipases A2 in asthma and chronic obstructive pulmonary disease

The increased morbidity, mortality, and ineffective treatment associated with the pathogenesis of chronic inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD) have generated much research interest. The key role is played by phospholipases from the A2 superfamily: enzymes which are involved in inflammation through participation in pro- and anti-inflammatory mediators production and have an impact on many immunocompetent cells. The 30 members of the A2 superfamily are divided into 7 groups. Their role in asthma and COPD has been studied in vitro and in vivo (animal models, cell cultures, and patients). This paper contains complete and updated information about the involvement of particular enzymes in the etiology and course of asthma and COPD.

Patatin-related phospholipase pPLAIIIδ increases seed oil content with long-chain fatty acids in Arabidopsis

The release of fatty acids from membrane lipids has been implicated in various metabolic and physiological processes, but in many cases, the enzymes involved and their functions in plants remain unclear. Patatin-related phospholipase As (pPLAs) constitute a major family of acyl-hydrolyzing enzymes in plants. Here, we show that pPLAIIIδ promotes the production of triacylglycerols with 20- and 22-carbon fatty acids in Arabidopsis (Arabidopsis thaliana). Of the four pPLAIIIs (α, β, γ, δ), only pPLAIIIδ gene knockout results in a decrease in seed oil content, and pPLAIIIδ is most highly expressed in developing embryos. The overexpression of pPLAIIIδ increases the content of triacylglycerol and 20- and 22-carbon fatty acids in seeds with a corresponding decrease in 18-carbon fatty acids. Several genes in the glycerolipid biosynthetic pathways are up-regulated in pPLAIIIδ-overexpressing siliques. pPLAIIIδ hydrolyzes phosphatidylcholine and also acyl-coenzyme A to release fatty acids. pPLAIIIδ-overexpressing plants have a lower level, whereas pPLAIIIδ knockout plants have a higher level, of acyl-coenzyme A than the wild type. Whereas seed yield decreases in transgenic plants that ubiquitously overexpress pPLAIIIδ, seed-specific overexpression of pPLAIIIδ increases seed oil content without any detrimental effect on overall seed yield. These results indicate that pPLAIIIδ-mediated phospholipid turnover plays a role in fatty acid remodeling and glycerolipid production.

Mast cell maturation is driven via a group III phospholipase A2-prostaglandin D2-DP1 receptor paracrine axis

Microenvironment-based alterations in phenotypes of mast cells influence the susceptibility to anaphylaxis, yet the mechanisms underlying proper maturation of mast cells toward an anaphylaxis-sensitive phenotype are incompletely understood. Here we report that PLA2G3, a mammalian homolog of anaphylactic bee venom phospholipase A2, regulates this process. PLA2G3 secreted from mast cells is coupled with fibroblastic lipocalin-type PGD2 synthase (L-PGDS) to provide PGD2, which facilitates mast-cell maturation via PGD2 receptor DP1. Mice lacking PLA2G3, L-PGDS or DP1, mast cell-deficient mice reconstituted with PLA2G3-null or DP1-null mast cells, or mast cells cultured with L-PGDS-ablated fibroblasts exhibited impaired maturation and anaphylaxis of mast cells. Thus, we describe a lipid-driven PLA2G3-L-PGDS-DP1 loop that drives mast cell maturation.

Identification of novel phospholipase A2 group IX members in metazoans

Sequence homologues of the bacterium Streptomyces violaceoruber and sea anemone Nematostella vectensis PLA2 pfam09056 members were identified in several bacteria, fungi and metazoans illustrating the evolution of this PLA2 sub-family. Comparison of their molecular structures revealed that bacteria and fungi members are part of the GXIV of PLA2s while metazoan representatives are similar with GIX PLA2 of the marine snail Conus magus. Members of GXIV and GIX PLA2s show modest overall sequence similarity (21-35%) but considerable motif conservation within the putative Ca(2+)-binding, catalytic sites and cysteine residue positions which are essential for enzyme function. GXIV PLA2s of bacteria and fungi typically contain four cysteine residues composing two intramolecular disulphide bonds. GIX PLA2 homologues were identified in cnidarians and molluscs and in a single tunicate but appear to be absent from other metazoan genomes. The mature GIX PLA2 deduced peptides contain up to ten cysteine residues capable of forming five putative disulphide bonds. Three disulphide bonds were identified in GIX PLA2s, two of which correspond to those localized in GXIV PLA2s. Phylogenetic analysis demonstrates that metazoan GIX PLA2s cluster separate from the bacterial and fungal GXIV PLA2s and both pfam09056 members form a group separate from the prokaryote and eukaryote GXIIA PLA2 pfam06951. Duplicate PLA2 pfam09056 genes were identified in the genomes of sea anemone N. vectensis and oyster Crassostrea gigas suggest that members of this family evolved via species-specific duplication events. These observations indicate that the newly identified metazoan pfam09056 members may be classified as GIX PLA2s and support the idea of the common evolutionary origin of GXIV and GIX PLA2 pfam09056 members, which emerged early in bacteria and were maintained in the genomes of fungi and selected extant metazoan taxa.

A distal enhancer controls cytokine-dependent human cPLA2α gene expression

Specific control of group IVA cytosolic phospholipase A2 (cPLA2α or PLA2G4A) expression modulates arachidonic acid production, thus tightly regulating the downstream effects of pro- and anti-inflammatory eicosanoids. The significance of this pathway in human disease is apparent in a range of pathologies from inflammation to tumorigenesis. While much of the regulation of cPLA2α has focused on posttranslational phosphorylation of the protein, studies on transcriptional regulation of this gene have focused only on proximal promoter regions. We have identified a DNase I hypersensitive site encompassing a 5' distal enhancer element containing a highly conserved consensus AP-1 site involved in transcriptional activation of cPLA2α by interleukin (IL)-1β. Chromatin immunoprecipitation (ChIP), knockdown, knockout, and overexpression analyses have shown that c-Jun acts both in a negative and positive regulatory role. Transcriptional activation of cPLA2α occurs through the phosphorylation of c-Jun in conjunction with increased association of C/EBPβ with the distal novel enhancer. The association of C/EBPβ with the transcriptional activation complex does not require an obvious DNA binding site. These data provide new and important contributions to the understanding of cPLA2α regulation at the transcriptional level, with implications for eicosanoid metabolism, cellular signaling, and disease pathogenesis.

Emerging targets in lipid-based therapy

The use of prostaglandins and NSAIDS in the clinic has proven that lipid mediators and their associated pathways make attractive therapeutic targets. When contemplating therapies involving lipid pathways, several basic agents come to mind. There are the enzymes and accessory proteins that lead to the metabolism of lipid substrates, provided through diet or through actions of lipases, the subsequent lipid products, and finally the lipid sensors or receptors. There is abundant evidence that molecules along this lipid continuum can serve as prognostic and diagnostic indicators and are in fact viable therapeutic targets. Furthermore, lipids themselves can be used as therapeutics. Despite this, the vernacular dialog pertaining to "biomarkers" does not routinely include mention of lipids, though this is rapidly changing. Collectively these agents are becoming more appreciated for their respective roles in diverse disease processes from cancer to preterm labor and are receiving their due appreciation after decades of ground work in the lipid field. By relating examples of disease processes that result from dysfunction along the lipid continuum, as well as examples of lipid therapies and emerging technologies, this review is meant to inspire further reading and discovery.

Phospholipases of mineralization competent cells and matrix vesicles: roles in physiological and pathological mineralizations

The present review aims to systematically and critically analyze the current knowledge on phospholipases and their role in physiological and pathological mineralization undertaken by mineralization competent cells. Cellular lipid metabolism plays an important role in biological mineralization. The physiological mechanisms of mineralization are likely to take place in tissues other than in bones and teeth under specific pathological conditions. For instance, vascular calcification in arteries of patients with renal failure, diabetes mellitus or atherosclerosis recapitulates the mechanisms of bone formation. Osteoporosis—a bone resorbing disease—and rheumatoid arthritis originating from the inflammation in the synovium are also affected by cellular lipid metabolism. The focus is on the lipid metabolism due to the effects of dietary lipids on bone health. These and other phenomena indicate that phospholipases may participate in bone remodelling as evidenced by their expression in smooth muscle cells, in bone forming osteoblasts, chondrocytes and in bone resorbing osteoclasts. Among various enzymes involved, phospholipases A₁ or A₂, phospholipase C, phospholipase D, autotaxin and sphingomyelinase are engaged in membrane lipid remodelling during early stages of mineralization and cell maturation in mineralization-competent cells. Numerous experimental evidences suggested that phospholipases exert their action at various stages of mineralization by affecting intracellular signaling and cell differentiation. The lipid metabolites—such as arachidonic acid, lysophospholipids, and sphingosine-1-phosphate are involved in cell signaling and inflammation reactions. Phospholipases are also important members of the cellular machinery engaged in matrix vesicle (MV) biogenesis and exocytosis. They may favour mineral formation inside MVs, may catalyse MV membrane breakdown necessary for the release of mineral deposits into extracellular matrix (ECM), or participate in hydrolysis of ECM. The biological functions of phospholipases are discussed from the perspective of animal and cellular knockout models, as well as disease implications, development of potent inhibitors and therapeutic interventions.

Dietary omega-3 PUFA and health: stearidonic acid-containing seed oils as effective and sustainable alternatives to traditional marine oils

The daily consumption of dietary omega-3 PUFA is recommended by governmental agencies in several countries and by a number of health organizations. The molecular mechanisms by which these dietary PUFA affect health involve the enrichment of cellular membranes with long-chain 20- and 22-carbon omega-3 PUFA that impacts tissues by altering membrane protein functions, cell signaling, and gene expression profiles. These changes are recognized to have health benefits in humans, especially relating to cardiovascular outcomes. Cellular membrane enrichment and health benefits are associated with the consumption of long-chain omega-3 PUFA found in marine oils, but are not generally linked with the consumption of alpha-linolenic acid, the 18-carbon omega-3 PUFA found in plant seed oils. However, the supply of omega-3 PUFA from marine sources is limited and may not be sustainable. New plant-derived sources of omega-3 PUFA like stearidonic acid-soy oil from genetically modified soybeans and Ahiflower oil from Buglossoides arvensis seeds that are enriched in the 18-carbon omega-3 PUFA stearidonic acid are being developed and show promise to become effective as well as sustainable sources of omega-3 PUFA. An example of changes in tissue lipid profiles associated with the consumption of Ahiflower oil is presented in a mouse feeding study.

Secretory phospholipase A2 in dromedary tears: a host defense against staphylococci and other gram-positive bacteria

The best known physiologic function of secreted phospholipase A2 (sPLA2) group IIA (sPLA2-IIA) is defense against bacterial infection through hydrolytic degradation of bacterial membrane phospholipids. In fact, sPLA2-IIA effectively kills Gram-positive bacteria and to a lesser extent Gram-negative bacteria and is considered a major component of the eye's innate immune defense system. The antibacterial properties of sPLA2 have been demonstrated in rabbit and human tears. In this report, we have analyzed the bactericidal activity of dromedary tears and the subsequently purified sPLA2 on several Gram-positive bacteria. Our results showed that the sPLA2 displays a potent bactericidal activity against all the tested bacteria particularly against the Staphylococcus strains when tested in the ionic environment of tears. There is a synergic action of the sPLA2 with lysozyme when added to the bacteria culture prior to sPLA2. Interestingly, lysozyme purified from dromedary tears showed a significant bactericidal activity against Listeria monocytogene and Staphylococcus epidermidis, whereas the one purified from human tears displayed no activity against these two strains. We have also demonstrated that Ca(2+) is crucial for the activity of dromedary tear sPLA2 and to a less extent Mg(2+) ions. Given the presence of sPLA2 in tears and intestinal secretions, this enzyme may play a substantial role in innate mucosal and systemic bactericidal defenses against Gram-positive bacteria.

Interactions of PLA2-s from Vipera lebetina, Vipera berus berus and Naja naja oxiana venom with platelets, bacterial and cancer cells

Secretory phospholipasesA₂ (sPLA₂s) form a large family of structurally related enzymes widespread in nature. Herein, we studied the inhibitory effects of sPLA₂s from Vipera lebetina (VLPLA₂), Vipera berus berus (VBBPLA₂), and Naja naja oxiana (NNOPLA₂) venoms on (i) human platelets, (ii) four different bacterial strains (gram-negative Escherichia coli and Vibrio fischeri; gram-positive Staphylococcus aureus and Bacillus subtilis) and (iii) five types of cancer cells (PC-3, LNCaP, MCF-7, K-562 and B16-F10) in vitro. sPLA₂s inhibited collagen-induced platelet aggregation: VBBPLA₂ IC₅₀ = 0.054, VLPLA₂ IC₅₀ = 0.072, NNOPLA₂ IC₅₀ = 0.814 μM. p-Bromophenacylbromide-inhibited sPLA₂ had no inhibitory action on platelets. 36.17 μM VBBPLA₂ completely inhibited the growth of gram-positive Bacillus subtilis whereas no growth inhibition was observed towards gram-negative Escherichia coli. The inhibitory action of sPLA₂s (~0.7 μM and ~7 μM) towards cancer cells depended on both venom and cell type. VBBPLA₂ (7.2 μM) inhibited significantly the viability of K-562 cells and the cell death appeared apoptotic. The sPLA₂s exhibited no inhibitory effect towards LNCaP cells and some effect (8%–20%) towards other cells. Thus, already sub-μM concentrations of sPLA₂s inhibited collagen-induced platelet aggregation and from the current suite of studied svPLA₂s and test cells, VBBPLA₂ was the most growth inhibitory towards Bacillus subtilis and K-562 cells.

Antioxidant activity by a synergy of redox-sensitive mitochondrial phospholipase A2 and uncoupling protein-2 in lung and spleen

Mitochondrial uncoupling protein-2 (UCP2) has been suggested to participate in the attenuation of the reactive oxygen species production, but the mechanism of action and the physiological significance of UCP2 activity remain controversial. Here we tested the hypothesis that UCP2 provides feedback downregulation of oxidative stress in vivo via synergy with an H2O2-activated mitochondrial calcium-independent phospholipase A2 (mt-iPLA2). Tert-butylhydroperoxide or H2O2 induced free fatty acid release from mitochondrial membranes as detected by gas chromatography/mass spectrometry, which was inhibited by r-bromoenol lactone (r-BEL) but not by its stereoisomer s-BEL, suggesting participation of mt-iPLA2γ isoform. Tert-butylhydroperoxide or H2O2 also induced increase in respiration and decrease in mitochondrial membrane potential in lung and spleen mitochondria from control but not UCP2-knockout mice. These data suggest that mt-iPLA2γ-dependent release of free fatty acids promotes UCP2-dependent uncoupling. Upon such uncoupling, mitochondrial superoxide formation decreased instantly also in the s-BEL presence, but not when mt-iPLA2 was blocked by R-BEL and not in mitochondria from UCP2-knockout mice. Mt-iPLA2γ was alternatively activated by H2O2 produced probably in conjunction with the electron-transferring flavoprotein:ubiquinone oxidoreductase (ETFQOR), acting in fatty acid β-oxidation. Palmitoyl-d,l-carnitine addition to mouse lung mitochondria, respiring with succinate plus rotenone, caused a respiration increase that was sensitive to r-BEL and insensitive to s-BEL. We thus demonstrate for the first time that UCP2, functional due to fatty acids released by redox-activated mt-iPLA2γ, suppresses mitochondrial superoxide production by its uncoupling action. In conclusion, H2O2-activated mt-iPLA2γ and UCP2 act in concert to protect against oxidative stress.

The leukotrienes: immune-modulating lipid mediators of disease

The leukotrienes are important lipid mediators with immune modulatory and proinflammatory properties. Classical bioactions of leukotrienes include chemotaxis, endothelial adherence, and activation of leukocytes, chemokine production, as well as contraction of smooth muscles in the microcirculation and respiratory tract. When formed in excess, these compounds play a pathogenic role in several acute and chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. An increasing number of diseases have been linked to inflammation implicating the leukotrienes as potential mediators. For example, recent investigations using genetic, morphological, and biochemical approaches have pointed to the involvement of leukotrienes in cardiovascular diseases including atherosclerosis, myocardial infarction, stroke, and abdominal aortic aneurysm. Moreover, new insights have changed our previous notion of leukotrienes as mediators of inflammatory reactions to molecules that can fine-tune the innate and adaptive immune response. Here, we review the most recent understanding of the leukotriene cascade with emphasis on recently identified roles in immune reactions and pathophysiology.

Eicosanoids in metabolic syndrome

Chronic persistent inflammation plays a significant role in disease pathology of cancer, cardiovascular disease, and metabolic syndrome (MetS). MetS is a constellation of diseases that include obesity, diabetes, hypertension, dyslipidemia, hypertriglyceridemia, and hypercholesterolemia. Nonalcoholic fatty liver disease (NAFLD) is associated with many of the MetS diseases. These metabolic derangements trigger a persistent inflammatory cascade, which includes production of lipid autacoids (eicosanoids) that recruit immune cells to the site of injury and subsequent expression of cytokines and chemokines that amplify the inflammatory response. In acute inflammation, the transcellular synthesis of antiinflammatory eicosanoids resolve inflammation, while persistent activation of the autacoid-cytokine-chemokine cascade in metabolic disease leads to chronic inflammation and accompanying tissue pathology. Many drugs targeting the eicosanoid pathways have been shown to be effective in the treatment of MetS, suggesting a common linkage between inflammation, MetS and drug metabolism. The cross-talk between inflammation and MetS seems apparent because of the growing evidence linking immune cell activation and metabolic disorders such as insulin resistance, dyslipidemia, and hypertriglyceridemia. Thus modulation of lipid metabolism through either dietary adjustment or selective drugs may become a new paradigm in the treatment of metabolic disorders. This review focuses on the mechanisms linking eicosanoid metabolism to persistent inflammation and altered lipid and carbohydrate metabolism in MetS.

Age-related changes in the response of intestinal cells to 1α,25(OH)2-vitamin D3

The hormonally active form of vitamin D(3), 1α,25(OH)(2)-vitamin D(3), acts in intestine, its major target tissue, where its actions are of regulatory and developmental importance: regulation of intracellular calcium through modulation of second messengers and activation of mitogenic cascades leading to cell proliferation. Several causes have been postulated to modify the hormone response in intestinal cells with ageing, among them, alterations of vitamin D receptor (VDR) levels and binding sites, reduced expression of G-proteins and hormone signal transduction changes. The current review summarizes the actual knowledge regarding the molecular and biochemical basis of age-impaired 1α,25(OH)(2)-vitamin D(3) receptor-mediated signaling in intestinal cells. A fundamental understanding why the hormone functions are impaired with age will enhance our knowledge of its importance in intestinal cell physiology.

Mechanism of fatty-acid-dependent UCP1 uncoupling in brown fat mitochondria

Mitochondrial uncoupling protein 1 (UCP1) is responsible for nonshivering thermogenesis in brown adipose tissue (BAT). Upon activation by long-chain fatty acids (LCFAs), UCP1 increases the conductance of the inner mitochondrial membrane (IMM) to make BAT mitochondria generate heat rather than ATP. Despite being a member of the family of mitochondrial anion carriers (SLC25), UCP1 is believed to transport H(+) by an unusual mechanism that has long remained unresolved. Here, we achieved direct patch-clamp measurements of UCP1 currents from the IMM of BAT mitochondria. We show that UCP1 is an LCFA anion/H(+) symporter. However, the LCFA anions cannot dissociate from UCP1 due to hydrophobic interactions established by their hydrophobic tails, and UCP1 effectively operates as an H(+) carrier activated by LCFA. A similar LCFA-dependent mechanism of transmembrane H(+) transport may be employed by other SLC25 members and be responsible for mitochondrial uncoupling and regulation of metabolic efficiency in various tissues.

Prostaglandins as PPARγ Modulators in Adipogenesis

Adipocytes and fat cells play critical roles in the regulation of energy homeostasis. Adipogenesis (adipocyte differentiation) is regulated via a complex process including coordinated changes in hormone sensitivity and gene expression. PPARγ is a ligand-dependent transcription factor and important in adipogenesis, as it enhances the expression of numerous adipogenic and lipogenic genes in adipocytes. Prostaglandins (PGs), which are lipid mediators, are associated with the regulation of PPARγ function in adipocytes. Prostacyclin promotes the differentiation of adipocyte-precursor cells to adipose cells via activation of the expression of C/EBPβ and δ. These proteins are important transcription factors in the activation of the early phase of adipogenesis, and they activate the expression of PPARγ, which event precedes the maturation of adipocytes. PGE₂ and PGF_2α strongly suppress the early phase of adipocyte differentiation by enhancing their own production via receptor-mediated elevation of the expression of cycloxygenase-2, and they also suppress the function of PPARγ. In contrast, PGD₂ and its non-enzymatic metabolite, Δ¹²-PGJ₂, activate the middle-late phase of adipocyte differentiation through both DP2 receptors and PPARγ. This paper focuses on potential roles of PGs as PPARγ modulators in adipogenesis and regulators of obesity.

The expression of phospholipase A2 group X is inversely associated with metastasis in colorectal cancer

Among the secretory phospholipase A2s (sPLA2), sPLA2 group X (PLA2GX) has the most potent hydrolyzing activity toward phosphatidylcholine, and has recently been shown to be implicated in chronic inflammatory diseases. The aim of the present study was to investigate PLA2GX expression in colorectal cancer (CRC) and its correlation with patient clinicopathological features. The present study comprises a series of 158 patients who underwent surgical resection for primary CRC. PLA2GX expression in CRC tissues was examined by immunohistochemistry and compared with patient clinicopathological findings and survival. A total of 64% of the tumors expressed PLA2GX at high levels. Statistical analysis revealed that PLA2GX expression was inversely correlated with hematogenous metastasis (P=0.005). In the subgroup analysis, left-sided tumors with high PLA2GX expression showed an inverse correlation with lymph node metastasis (P=0.018) and hematogenous metastasis (P=0.017). Patients with high PLA2GX expression tended to have a longer disease-specific survival compared with those with low PLA2GX expression in left-sided, but not right-sided, CRC (P=0.08). In light of the present results, we suggest that PLA2GX has an inhibitory effect on the progression of CRC.

In silico and in vitro characterization of phospholipase A₂ isoforms from soybean (Glycine max)

At the present, no secreted phospholipase A₂ (sPLA₂) from soybean (Glycine max) was investigated in detail. In this work we identified five sequences of putative secreted sPLA₂ from soybean after a BLAST search in G. max database. Sequence analysis showed a conserved PA2c domain bearing the Ca²⁺ binding loop and the active site motif. All the five mature proteins contain 12 cysteine residues, which are commonly conserved in plant sPLA₂s. We propose a phylogenetic tree based on sequence alignment of reported plant sPLA₂s including the novel enzymes from G. max. According to PLA₂ superfamily, two of G. max sPLA₂s are grouped as XIA and the rest of sequences as XIB, on the basis of differences found in their molecular weights and deviating sequences especially in the N- and C-terminal regions of the isoenzymes. Furthermore, we report the cloning, expression and purification of one of the putative isoenzyme denoted as GmsPLA₂-XIA-1. We demonstrate that this mature sPLA₂ of 114 residues had PLA₂ activity on Triton:phospholipid mixed micelles and determine the kinetic parameters for this system. We generate a model based on the known crystal structure of sPLA₂ from rice (isoform II), giving first insights into the three-dimensional structure of folded GmsPLA₂-XIA-1. Besides describing the spatial arrangement of highly conserved pair HIS-49/ASP-50 and the Ca⁺² loop domains, we propose the putative amino acids involved in the interfacial recognition surface. Additionally, molecular dynamics simulations indicate that calcium ion, besides its key function in the catalytic cycle, plays an important role in the overall stability of GmsPLA₂-XIA-1 structure.

Autoproteolytic Activation of a Symbiosis-regulated Truffle Phospholipase A2

Fungal phospholipases are members of the fungal/bacterial group XIV secreted phospholipases A(2) (sPLA(2)s). TbSP1, the sPLA(2) primarily addressed in this study, is up-regulated by nutrient deprivation and is preferentially expressed in the symbiotic stage of the ectomycorrhizal fungus Tuber borchii. A peculiar feature of this phospholipase and of its ortholog from the black truffle Tuber melanosporum is the presence of a 54-amino acid sequence of unknown functional significance, interposed between the signal peptide and the start of the conserved catalytic core of the enzyme. X-ray diffraction analysis of a recombinant TbSP1 form corresponding to the secreted protein previously identified in T. borchii mycelia revealed a structure comprising the five α-helices that form the phospholipase catalytic module but lacking the N-terminal 54 amino acids. This finding led to a series of functional studies that showed that TbSP1, as well as its T. melanosporum ortholog, is a self-processing pro-phospholipase A(2), whose phospholipase activity increases up to 80-fold following autoproteolytic removal of the N-terminal peptide. Proteolytic cleavage occurs within a serine-rich, intrinsically flexible region of TbSP1, does not involve the phospholipase active site, and proceeds via an intermolecular mechanism. Autoproteolytic activation, which also takes place at the surface of nutrient-starved, sPLA(2) overexpressing hyphae, may strengthen and further control the effects of phospholipase up-regulation in response to nutrient deprivation, also in the context of symbiosis establishment and mycorrhiza formation.

Phospholipase signalling networks in cancer

Phospholipases (PLC, PLD and PLA) are essential mediators of intracellular and intercellular signalling. They can function as phospholipid-hydrolysing enzymes that can generate many bioactive lipid mediators, such as diacylglycerol, phosphatidic acid, lysophosphatidic acid and arachidonic acid. Lipid mediators generated by phospholipases regulate multiple cellular processes that can promote tumorigenesis, including proliferation, migration, invasion and angiogenesis. Although many individual phospholipases have been extensively studied, how phospholipases regulate diverse cancer-associated cellular processes and the interplay between different phospholipases have yet to be fully elucidated. A thorough understanding of the cancer-associated signalling networks of phospholipases is necessary to determine whether these enzymes can be targeted therapeutically.

Novel bioactive glycerol-based lysophospholipids: new data -- new insight into their function

Based on the results of research conducted over last two decades, lysophospholipids (LPLs) were observed to be not only structural components of cellular membranes but also biologically active molecules influencing a broad variety of processes such as carcinogenesis, neurogenesis, immunity, vascular development or regulation of metabolic diseases. With a growing interest in the involvement of extracellular lysophospholipids in both normal physiology and pathology, it has become evident that those small molecules may have therapeutic potential. While lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) have been studied in detail, other LPLs such as lysophosphatidylglycerol (LPG), lysophosphatidylserine (LPS), lysophosphatidylinositol (LPI), lysophosphatidylethanolamine (LPE) or even lysophosphatidylcholine (LPC) have not been elucidated to such a high degree. Although information concerning the latter LPLs is sparse as compared to LPA and S1P, within the last couple of years much progress has been made. Recently published data suggest that these compounds may regulate fundamental cellular activities by modulating multiple molecular targets, e.g. by binding to specific receptors and/or altering the structure and fluidity of lipid rafts. Therefore, the present review is devoted to novel bioactive glycerol-based lysophospholipids and recent findings concerning their functions and possible signaling pathways regulating physiological and pathological processes.

Lipidomics analysis of mesenteric lymph after trauma and hemorrhagic shock

BACKGROUND

After trauma and hemorrhagic shock (T/HS), a variety of inflammatory mediators enter the systemic circulation through mesenteric lymph ducts, leading to acute lung injury and multiple-organ dysfunction syndrome. Recent studies have demonstrated that post-HS mesenteric lymph (PHSML) activates polymorphonuclear leukocytes (PMNs) and causes vascular endothelial cell and red blood cell dysfunction. Furthermore, PHSML contains proinflammatory mediators, such as biologically active lipids. The purpose of this study was to identify the lipid mediators in PHSML and plasma by liquid chromatography/electrospray ionization mass spectrometry and then estimate the biologic activities of the identified lipids on PMNs.

METHODS

PHSML was collected from male Sprague-Dawley rats undergoing trauma (laparotomy) plus HS (40 mm Hg, 30 minutes) or sham shock (SS). The lipids in PHSML and plasma were extracted using the methods of Bligh and Dyer, and liquid chromatography/electrospray ionization mass spectrometry was performed. The biologic activities (superoxide production and elastase release) of identified lipids on human PMNs were tested.

RESULTS

Phosphatidylcholine, lysophosphatidylcholine (LPC), phosphatidylethanolamine, lysophosphatidylethanolamine (LPE), and sphingomyelin were detected in the PHSML. Furthermore, linoleoyl, arachidonoyl, and docosahexaenoyl LPCs and LPEs significantly increased in the PHSML of the T/HS group as compared with those of the T/SS group. In the plasma, arachidonoyl and docosahexaenoyl LPCs of the T/HS group also significantly increased in comparison with that of the T/SS group. Linoleoyl and arachidonoyl LPCs and LPEs showed the priming activity on N-formyl-methionyl-leucyl-phenylalanine-activated PMNs. The elastase release was also induced by linoleoyl and arachidonoyl LPCs.

CONCLUSION

Mesenteric lymph after T/HS contains biologically active lipids, such as LPCs and LPEs with polyunsaturated fatty acids, which may be involved in the pathogenesis of acute lung injury/multiple-organ dysfunction syndrome.

Group IVA phospholipase A₂ optimizes ovulation and fertilization in rodents through induction of and metabolic coupling with prostaglandin endoperoxide synthase 2

Female mice lacking group IVA phospholipase A(2) (Pla2g4a(-/-)) have a smaller litter size, which is due, in part, to defective implantation. We examined PLA(2)G4A dependence of the processes of ovulation and fertilization. Following induction of ovulation by equine chorionic gonadotropin (eCG)/human CG (hCG) treatment and mating, ovulation and fertilization rates were reduced significantly in Pla2g4a(-/-) mice as compared to wild-type littermates. Human CG triggered robust ovarian prostaglandin (PG) E(2) production in the preovulatory period that was significantly attenuated in Pla2g4a(-/-) mice. Human CG transiently enhanced ovarian expression of PLA(2)G4A and prostaglandin endoperoxide synthase 2 (PTGS2) in wild-type mice. This PTGS2 induction was decreased in Pla2g4a(-/-) mice and also in immature rats treated with the PLA(2)G4A inhibitor, archidonyl trifluoromethyl ketone. A close spatiotemporal association of PLA(2)G4A with PTGS2 was found in mouse and rat preovulatory follicles examined by immunohistochemistry. Less association was observed with 4 other forms of PLA(2). Our data strongly suggest that PLA(2)G4A amplifies hCG induction of PTGS2 and colocalizes with the induced PTGS2, thus contributing to robust PG production required for optimal ovulation and fertilization in rodents.

Mediator lipidomics in acute inflammation and resolution

Acute inflammation is an indispensable host response to foreign challenges or tissue injury. In healthy conditions, inflammatory processes are self-limiting and self-resolving, suggesting the existence of endogenous mechanisms for the control of inflammation and resolution. A comprehensive understanding of the cellular and molecular events of a well-orchestrated inflammatory response is required, and recent studies have uncovered the roles of endogenous lipid mediators derived from polyunsaturated fatty acids (i.e. lipoxins, resolvins, protectins) in controlling the resolution of inflammation. This review presents recent advances in understanding the formation and action of these mediators, especially focusing on the LC-MS/MS-based lipidomics approach and the emerging roles of eosinophils and eosinophil-derived lipid mediators in controlling acute inflammation and resolution.

Neuronal phospholipid deacylation is essential for axonal and synaptic integrity

Recessively-inherited deficiency in the catalytic activity of calcium-independent phospholipase A2-beta (iPLA2β) and neuropathy target esterase (NTE) causes infantile neuroaxonal dystrophy and hereditary spastic paraplegia, respectively. Thus, these two related phospholipases have non-redundant functions that are essential for structural integrity of synapses and axons. Both enzymes are expressed in essentially all neurons and also have independent roles in glia. iPLA2β liberates sn-2 fatty acid and lysophospholipids from diacyl-phospholipids. Ca(2+)-calmodulin tonically-inhibits iPLA2β, but this can be alleviated by oleoyl-CoA. Together with fatty acyl-CoA-mediated conversion of lysophospholipid to diacyl-phospholipid this may regulate sn-2 fatty acyl composition of phospholipids. In the nervous system, iPLA2β is especially important for the turnover of polyunsaturated fatty acid-associated phospholipid at synapses. More information is required on the interplay between iPLA2β and iPLA2-gamma in deacylation of neuronal mitochondrial phospholipids. NTE reduces levels of phosphatidylcholine (PtdCho) by degrading it to glycerophosphocholine and two free fatty acids. The substrate for NTE may be nascent PtdCho complexed with a phospholipid-binding protein. Protein kinase A-mediated phosphorylation enhances PtdCho synthesis and may allow PtdCho accumulation by coordinate inhibition of NTE activity. NTE operates primarily at the endoplasmic reticulum in neuronal soma but is also present in axons. NTE-mediated PtdCho homeostasis facilitates membrane trafficking and this appears most critical for the integrity of axon terminals in the spinal cord and hippocampus. For maintenance of peripheral nerve axons, iPLA2β activity may be able to compensate for NTE-deficiency but not vice-versa. Whether agonists acting at neuronal receptors modulate the activity of either enzyme remains to be determined. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

Conservation of group XII phospholipase A2 from bacteria to human

Vertebrate group XII phospholipases A(2) (GXII PLA(2), conserved domain pfam06951) are proteins with unique structural and functional features within the secreted PLA(2) family. In humans, two genes (GXIIA PLA(2) and GXIIB PLA(2)) have been characterised. GXIIA PLA(2) is enzymatically active whereas GXIIB PLA(2) is devoid of catalytic activity. Recently, putative homologues of the vertebrate GXII PLA(2)s were described in non-vertebrates. In the current study a total of 170 GXII PLA(2) sequences were identified in vertebrates, invertebrates, non-metazoan eukaryotes, fungi and bacteria. GXIIB PLA(2) was found only in vertebrates and the searches failed to identify putative GXII PLA(2) homologues in Archaea. Comparisons of the predicted functional domains of GXII PLA(2)s revealed considerable structural identity within the Ca(2+)-binding and the catalytic sites among the various organisms suggesting that functional conservation may have been retained across evolution. The preservation of GXII PLA(2) family members from bacteria to human indicates that they have emerged early in evolution and evolved via gene/genome duplication events prior to Eubacteria. Gene duplicates were identified in some invertebrate taxa suggesting that species-specific duplications occurred. The analysis of the GXII PLA(2) homologue genome environment revealed that gene synteny and gene order are preserved in vertebrates. Conservation of GXII PLA(2)s indicates that important functional roles involved in species survival and were maintained across evolution and may be dependent on or independent of the enzyme's phospholipolytic activity.

MAP-kinase regulated cytosolic phospholipase A2 activity is essential for production of infectious hepatitis C virus particles

Hepatitis C virus (HCV) has infected around 160 million individuals. Current therapies have limited efficacy and are fraught with side effects. To identify cellular HCV dependency factors, possible therapeutic targets, we manipulated signaling cascades with pathway-specific inhibitors. Using this approach we identified the MAPK/ERK regulated, cytosolic, calcium-dependent, group IVA phospholipase A2 (PLA2G4A) as a novel HCV dependency factor. Inhibition of PLA2G4A activity reduced core protein abundance at lipid droplets, core envelopment and secretion of particles. Moreover, released particles displayed aberrant protein composition and were 100-fold less infectious. Exogenous addition of arachidonic acid, the cleavage product of PLA2G4A-catalyzed lipolysis, but not other related poly-unsaturated fatty acids restored infectivity. Strikingly, production of infectious Dengue virus, a relative of HCV, was also dependent on PLA2G4A. These results highlight previously unrecognized parallels in the assembly pathways of these human pathogens, and define PLA2G4A-dependent lipolysis as crucial prerequisite for production of highly infectious viral progeny.

The human genome encodes more than 30 phospholipase A2s. These enzymes cleave fatty acids at the C2 atom of phosphoglycerides and thus modulate membrane properties. Among all PLA2s only PLA2G4A, which is recruited to perinuclear membranes by Ca²⁺ and activated by extracellular stimuli via the mitogen activated protein kinase pathway, specifically cleaves lipids with arachidonic acid. Metabolism of arachidonic acid yields prostaglandins and leukotriens, important lipid mediators of inflammation. We show that inhibition of PLA2G4A produces aberrant HCV particles and that infectivity is rescued by addition of arachidonic acid. Our results suggest that a specific lipid (arachidonic acid) is essential for production of highly infectious HCV progeny, likely by creating a membrane environment conducive for efficient incorporation of crucial host and viral factors into the lipid envelope of nascent particles. Strikingly, PLA2G4A is also essential for production of highly infectious Dengue Virus (DENV) particles but not for vesicular stomatitis virus (VSV). These observations argue that HCV and DENV which unlike VSV produce particles at intracellular membranes usurp a common host factor (PLA2G4A) for assembly of highly infectious progeny. These findings open new perspectives for antiviral intervention and highlight thus far unrecognized parallels in the assembly pathway of HCV and DENV.

Inhibitors of Cytosolic Phospholipase A2α as Anti-inflammatory Drugs

Arachidonic acid derivatives, like prostaglandins and leukotrienes, as well as the alkyl-ether phospholipid platelet-activating factor (PAF) are highly active substances with diverse biological actions. Elevated levels of these lipid mediators in response to a variety of stimuli have been implicated in the pathology of many inflammatory diseases. The rate-limiting step in the generation of prostaglandins, leukotrienes and PAF, respectively, is the cleavage of the sn-2-ester of membrane phospholipids by a phospholipase A2 (PLA2). Among the superfamily of PLA2 enzymes, cytosolic PLA2α (cPLA2α, also referred to as group IVA PLA2) is thought to play the primary role in this biochemical reaction. Therefore, inhibition of cPLA2α activity is an attractive approach to the control of inflammatory disorders.

In this chapter the main groups of cPLA2α inhibitors are described and the problems associated with the development of clinical active drug candidates are discussed. Furthermore, in-vivo data obtained with such compounds in pre-clinical animal models of inflammation will be presented.