Enzymatic activity and immunoreactivity of extracellular phospholipase A2 in inflammatory synovial fluids

Modulation of immunity by the secreted phospholipase A2 family

Among the phospholipase A2 (PLA2 ) superfamily, which typically catalyzes the sn-2 hydrolysis of phospholipids to yield fatty acids and lysophospholipids, the secreted PLA2 (sPLA2 ) family contains 11 isoforms in mammals. Individual sPLA2 s have unique enzymatic specificity toward fatty acids and polar heads of phospholipid substrates and display distinct tissue/cellular distributions, suggesting their distinct physiological functions. Recent studies using knockout and/or transgenic mice for a full set of sPLA2 s have revealed their roles in modulation of immunity and related disorders. Application of mass spectrometric lipidomics to these mice has enabled to identify target substrates and products of individual sPLA2 s in given tissue microenvironments. sPLA2 s hydrolyze not only phospholipids in the plasma membrane of activated, damaged or dying mammalian cells, but also extracellular phospholipids such as those in extracellular vesicles, microbe membranes, lipoproteins, surfactants, and dietary phospholipids, thereby exacerbating or ameliorating various diseases. The actions of sPLA2 s are dependent on, or independent of, the generation of fatty acid- or lysophospholipid-derived lipid mediators according to the pathophysiological contexts. In this review, we make an overview of our current understanding of the roles of individual sPLA2 s in various immune responses and associated diseases.

Half is enough: Oxidized lysophospholipids as novel bioactive molecules

Studies in the last decade have established the roles of oxidized phospholipids as modulators of various cellular processes, from inflammation and immunity to cell death. Oxidized lysophospholipids, formed through the activity of phospholipases and oxidative enzymes and lacking an acyl chain in comparison with parent phospholipids, are now emerging as novel bioactive lipid mediators. Their detection and structural characterization have been limited in the past due to low amounts and the complexity of their biosynthetic and removal pathways, but recent studies have unequivocally demonstrated their formation under inflammatory conditions. The involvement of oxidized lysophospholipids in immune regulation classifies them as damage-associated molecular patterns (DAMPs), which can promote sterile inflammation and contribute to autoimmune and chronic diseases as well as aging-related diseases. Their signaling pathways are just beginning to be revealed. As the first publications indicate that oxidized lysophospholipids use the same receptors as pathogen-associated molecular patterns (PAMPs), it is likely that the inhibition of signaling pathways activated by oxidized lysophospholipids would affect innate immunity per se. On the other hand, inhibition or modulation of their enzymatic formation, which would not interfere with the response to pathogens, might be beneficial and is potentially a promising new field of research.

Old but New: Group IIA Phospholipase A2 as a Modulator of Gut Microbiota

Among the phospholipase A₂ (PLA₂) superfamily, the secreted PLA₂ (sPLA₂) family contains 11 mammalian isoforms that exhibit unique tissue or cellular distributions and enzymatic properties. Current studies using sPLA₂-deficient or -overexpressed mouse strains, along with mass spectrometric lipidomics to determine sPLA₂-driven lipid pathways, have revealed the diverse pathophysiological roles of sPLA₂s in various biological events. In general, individual sPLA₂s exert their specific functions within tissue microenvironments, where they are intrinsically expressed through hydrolysis of extracellular phospholipids. Recent studies have uncovered a new aspect of group IIA sPLA₂ (sPLA₂-IIA), a prototypic sPLA₂ with the oldest research history among the mammalian PLA₂s, as a modulator of the gut microbiota. In the intestine, Paneth cell-derived sPLA₂-IIA acts as an antimicrobial protein to shape the gut microbiota, thereby secondarily affecting inflammation, allergy, and cancer in proximal and distal tissues. Knockout of intestinal sPLA₂-IIA in BALB/c mice leads to alterations in skin cancer, psoriasis, and anaphylaxis, while overexpression of sPLA₂-IIA in Pla2g2a-null C57BL/6 mice induces systemic inflammation and exacerbates arthritis. These phenotypes are associated with notable changes in gut microbiota and fecal metabolites, are variable in different animal facilities, and are abrogated after antibiotic treatment, co-housing, or fecal transfer. These studies open a new mechanistic action of this old sPLA₂ and add the sPLA₂ family to the growing list of endogenous factors capable of affecting the microbe–host interaction and thereby systemic homeostasis and diseases.

Enhancing extracellular vesicles for therapeutic treatment of arthritic joints

Extracellular vesicles are small membrane-derived packages of information that are released from virtually all cell types. These nano-packages contain regulatory material including proteins, lipids, mRNA and microRNA and are a key mechanism of paracellular communication within a given microenvironment. Encompassed with a lipid bilayer, these organelles have been attributed numerous roles in regulating both physiological and pathological functions. Herein, we describe the role of EVs in the context of Rheumatoid and Osteoarthritis and explore how they could be harnessed to treat inflammatory and degenerative joint conditions. These structures offer a promising therapeutic strategy for treating musculoskeletal diseases due to their bioactive content, stability, small size and intrinsic ability to enter the avascular cartilage, a notoriously challenging tissue to target. We also discuss how EVs can be manipulated to load therapeutic cargo or present additional targeting moieties to enhance their beneficial actions and tissue regenerative properties.

Mann T, Bastard K, F. Scott K, Church WB. Structural and Functional Aspects of Targeting the Secreted Human Group IIA Phospholipase A2

Human group IIA secretory phospholipase A₂ (hGIIA) promotes the proliferation of cancer cells, making it a compelling therapeutic target, but it is also significant in other inflammatory conditions. Consequently, suitable inhibitors of hGIIA have always been sought. The activation of phospholipases A₂ and the catalysis of glycerophospholipid substrates generally leads to the release of fatty acids such as arachidonic acid (AA) and lysophospholipid, which are then converted to mediator compounds, including prostaglandins, leukotrienes, and the platelet-activating factor. However, this ability of hGIIA to provide AA is not a complete explanation of its biological role in inflammation, as it has now been shown that it also exerts proinflammatory effects by a catalysis-independent mechanism. This mechanism is likely to be highly dependent on key specific molecular interactions, and the full mechanistic descriptions of this remain elusive. The current candidates for the protein partners that may mediate this catalysis-independent mechanism are also introduced in this review. A key discovery has been that selective inhibition of the catalysis-independent activity of hGIIA is achieved with cyclised derivatives of a pentapeptide, FLSYK, derived from the primary sequence of hGIIA. The effects of hGIIA on cell function appear to vary depending on the pathology studied, and so its mechanism of action is complex and context-dependent. This review is comprehensive and covers the most recent developments in the understanding of the many facets of hGIIA function and inhibition and the insight they provide into their clinical application for disease treatment. A cyclic analogue of FLSYK, c2, the most potent analogue known, has now been taken into clinical trials targeting advanced prostate cancer.

Synergy between 15-lipoxygenase and secreted PLA2 promotes inflammation by formation of TLR4 agonists from extracellular vesicles

Damage-associated endogenous molecules induce innate immune response, thus making sterile inflammation medically relevant. Stress-derived extracellular vesicles (stressEVs) released during oxidative stress conditions were previously found to activate Toll-like receptor 4 (TLR4), resulting in expression of a different pattern of immune response proteins in comparison to lipopolysaccharide (LPS), underlying the differences between pathogen-induced and sterile inflammation. Here we report that synergistic activities of 15-lipoxygenase (15-LO) and secreted phospholipase A₂ (sPLA₂) are needed for the formation of TLR4 agonists, which were identified as lysophospholipids (lysoPLs) with oxidized unsaturated acyl chain. Hydroxy, hydroperoxy, and keto products of 2-arachidonoyl-lysoPI oxidation by 15-LO were identified by mass spectrometry (MS), and they activated the same gene pattern as stressEVs. Extracellular PLA₂ activity was detected in the synovial fluid from rheumatoid arthritis and gout patients. Furthermore, injection of sPLA₂ promoted K/BxN serum-induced arthritis in mice, whereby ankle swelling was partially TLR4 dependent. Results confirm the role of oxidized lysoPL of stressEVs in sterile inflammation that promotes chronic diseases. Both 15-LO and sPLA₂ enzymes are induced during inflammation, which opens the opportunity for therapy without compromising innate immunity against pathogens.

A novel anti-inflammatory role for secretory phospholipase A2 in immune complex-mediated arthritis

Phospholipase A₂ (PLA₂) catalyses the release of arachidonic acid for generation of lipid mediators of inflammation and is crucial in diverse inflammatory processes. The functions of the secretory PLA₂ enzymes (sPLA₂), numbering nine members in humans, are poorly understood, though they have been shown to participate in lipid mediator generation and the associated inflammation. To further understand the roles of sPLA₂ in disease, we quantified the expression of these enzymes in the synovial fluid in rheumatoid arthritis and used gene-deleted mice to examine their contribution in a mouse model of autoimmune erosive inflammatory arthritis. Contrary to expectation, we find that the group V sPLA₂ isoform plays a novel anti-inflammatory role that opposes the pro-inflammatory activity of group IIA sPLA₂. Mechanistically, group V sPLA₂ counter-regulation includes promotion of immune complex clearance by regulating cysteinyl leukotriene synthesis. These observations identify a novel anti-inflammatory function for a PLA₂ and identify group V sPLA₂ as a potential biotherapeutic for treatment of immune-complex-mediated inflammation.

sPLA2-IIa is an inflammatory mediator when the ocular surface is compromised

sPLA2-IIa is an enzyme at high concentration in tears that has been known as an innate barrier of the ocular surface against microbial infection. sPLA2-IIa and other enzymes in the same protein family are known to hydrolyze fatty acids resulting in the generation of free arachidonic acid (AA) and lysophospholipids, which are the precursors of pro-inflammatory lipid mediators, such as PGE(2). sPLA2-IIa has been shown to be an inflammatory mediator in non-ocular inflammatory diseases such as rheumatoid arthritis (RA). It was also found to be increased in the tears of the patients with dry eye disease, chronic blepharitis and contact lens intolerance. However, the role of sPLA2-IIa in chronic ocular surface inflammation has yet to be determined. In the current study, we examined the potential role of sPLA2-IIa in inflammation of ocular surface diseases. Our results show that the activity of sPLA2-IIa was significantly increased in tears from dry eye disease patients compared with that from normal subjects. Also, sPLA2-IIa stimulated the production of PGE(2) in ocular surface epithelial cell cultures. The stimulating effect was markedly enhanced when the cells or tissues were pre-compromised with TNF-alpha, IL-1beta or desiccation. Furthermore, sPLA2-IIa stimulated inflammatory cytokine production in the ocular surface epithelial cell cultures in vitro. To our knowledge, this is the first report regarding the role of sPLA2-IIa as an inflammatory mediator in ocular surface inflammation. These findings indicate that sPLA2-IIa may play an important role in chronic ocular surface inflammation, especially when the ocular surface is compromised.

Role of crotoxin, a phospholipase A2 isolated from Crotalus durissus terrificus snake venom, on inflammatory and immune reactions

BACKGROUND

Crotoxin (CTX) is a potent neurotoxin from Crotalus durissus terrificus snake venom (CdtV) composed of two subunits: one without catalytic activity (crotapotin), and a basic phospolipase A2. Recent data have demonstrated that CdtV or CTX inhibit some immune and inflammatory reactions.

AIM

The aim of this paper was to investigate the mechanisms involved in these impaired responses.

MATERIALS AND METHODS

Male Swiss mice were bled before and at different intervals of time after subcutaneous injection of CTX or bovine serum albumin (BSA) (control animals). The effect of treatments on circulating leukocyte mobilisation and on serum levels of interleukin (IL)-6, IL-10, interferon (IFN)-gamma and corticosterone were investigated. Spleen cells from treated animals were also stimulated in vitro with concanavalin A to evaluate the profile of IL-4, IL-6, IL-10 or IFN-gamma secretion. Cytokine levels were determined by immunoenzymatic assay and corticosterone levels by radioimmunoassay. To investigate the participation of endogenous corticosteroid on the effects evoked by CTX, animals were treated with metyrapone, an inhibitor of glucocorticoid synthesis, previous to CTX treatment.

RESULTS

Marked alterations on peripheral leukocyte distribution, characterised by a drop in the number of lymphocytes and monocytes and an increase in the number of neutrophils, were observed after CTX injection. No such alteration was observed in BSA-treated animals. Increased levels of IL-6, IL-10 and corticosterone were also detected in CTX-injected animals. IFN-gamma levels were not modified after treatments. In contrast, spleen cells obtained from CTX-treated animals and stimulated with concanavalin A secreted less IL-10 and IL-4 in comparison with cells obtained from control animals. Metyrapone pretreatment was effective only to reverse the neutrophilia observed after CTX administration.

CONCLUSIONS

Our results suggest that CTX may contribute to the deficient inflammatory and immune responses induced by crude CdtV. CTX induces endogenous mechanisms that are responsible, at least in part, for these impaired responses.

Type IIA secretory phospholipase A2 up-regulates cyclooxygenase-2 and amplifies cytokine-mediated prostaglandin production in human rheumatoid synoviocytes

Human type IIA secretory phospholipase A2 (sPLA2-IIA) is induced in association with several immune-mediated inflammatory conditions. We have evaluated the effect of sPLA2-IIA on PG production in primary synovial fibroblasts from patients with rheumatoid arthritis (RA). At concentrations found in the synovial fluid of RA patients, exogenously added sPLA2-IIA dose-dependently amplified TNF-alpha-stimulated PGE2 production by cultured synovial fibroblasts. Enhancement of TNF-alpha-stimulated PGE2 production in synovial cells was accompanied by increased expression of cyclooxygenase (COX)-2 and cytosolic phospholipase A2 (cPLA2)-alpha. Blockade of COX-2 enzyme activity with the selective inhibitor NS-398 prevented both TNF-alpha-stimulated and sPLA2-IIA-amplified PGE2 production without affecting COX-2 protein induction. However, both sPLA2-IIA-amplified PGE2 production and enhanced COX-2 expression were blocked by the sPLA2 inhibitor LY311727. Colocalization studies using triple-labeling immunofluorescence microscopy showed that sPLA2-IIA and cPLA2-alpha are coexpressed with COX-2 in discrete populations of CD14-positive synovial macrophages and synovial tissue fibroblasts from RA patients. Based on these findings, we propose a model whereby the enhanced expression of sPLA2-IIA by RA synovial cells up-regulates TNF-alpha-mediated PG production via superinduction of COX-2. Therefore, sPLA2-IIA may be a critical modulator of cytokine-mediated synovial inflammation in RA.

Basic residues of human group IIA phospholipase A2 are important for binding to factor Xa and prothrombinase inhibition comparison with other mammalian secreted phospholipases A2

Human secreted group IIA phospholipase A2 (hGIIA) was reported to inhibit prothrombinase activity because of binding to factor Xa. This study further shows that hGIIA and its catalytically inactive H48Q mutant prolong the lag time of thrombin generation in human platelet-rich plasma with similar efficiency, indicating that hGIIA exerts an anticoagulant effect independently of phospholipid hydrolysis under ex vivo conditions. Charge reversal of basic residues on the interfacial binding surface (IBS) of hGIIA leads to decreased ability to inhibit prothrombinase activity, which correlates with a reduced affinity for factor Xa, as determined by surface plasmon resonance. Mutation of other surface-exposed basic residues, hydrophobic residues on the IBS, and His48, does not affect the ability of hGIIA to inhibit prothrombinase activity and bind to factor Xa. Other basic, but not neutral or acidic, mammalian secreted phospholipases A2 (sPLA2s) exert a phospholipid-independent inhibitory effect on prothrombinase activity, suggesting that these basic sPLA2s also bind to factor Xa. In conclusion, this study demonstrates that the anticoagulant effect of hGIIA is independent of phospholipid hydrolysis and is based on its interaction with factor Xa, leading to prothrombinase inhibition, even under ex vivo conditions. This study also shows that such an interaction involves basic residues located on the IBS of hGIIA, and suggests that other basic mammalian sPLA2s may also inhibit blood coagulation by a similar mechanism to that described for hGIIA.

Maintaining carotid flow by shunting during carotid endarterectomy diminishes the inflammatory response mediating ischaemic brain injury

OBJECTIVES

to assess whether shunting during carotid reconstruction affects the release of inflammatory mediators from the ipsilateral hemisphere.

MATERIALS AND METHODS

a catheter was placed in the ipsilateral jugular bulb during carotid endarterectomy (CEA) in 20 patients. Eight patients with ICBP (internal carotid backpressure) <40 mmHg received a shunt during CEA and 12 patients with ICBP >40 mmHg were operated upon without a shunt. Four patients with a carotid body tumour were used as controls. Blood was taken from the catheter as well as from the radial artery; before clamping, 5, 15, 30 min after clamping and 5 min after declamping. The oxygen extraction (AVO(2)) was calculated. Plasma concentrations of interleukin-1beta (IL-1beta), phospholipase A(2)(PLA(2)), thromboxane B(2)(TXB(2)), 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) and prostaglandin E(2)(PGE(2)) were measured by enzyme-linked immunosorbent assay (ELISA) technique.

RESULTS

all patients had a normal postoperative course except for one patient in the no-shunt group, who suffered a stroke 1 h later due to occlusion of the endarterectomy site. The AVO(2)extraction increased during clamping in patients operated upon without a shunt (p <0.05). This increase was partly recovered to pre-clamp levels 5 min after reperfusion. The extraction remained stable in the non-shunted patients and the control group. The increased extraction in the non-shunted group correlated with increased levels of IL-1beta during clamping ( p <0.05) and reperfusion ( p <0.01). PLA(2)also increased during reperfusion in the non-shunted group ( p <0.05). An increased ratio between TXB(2)and 6-keto-PGF1alpha was noted during clamping ( p <0.05) and further increased during reperfusion. The levels of PGE(2)remained stable in both CEA groups. The PLA(2)levels, as well as TXB(2), 6-keto-PGF1alpha and PGE(2)levels, remained unchanged during the procedure in the control group.

CONCLUSIONS

there is a metabolic response to carotid cross-clamping when no shunt is used. However, the clinical significance of this is unclear, since there were no intraoperative strokes.

Structure-based design of a new class of anti-inflammatory drugs: secretory phospholipase A(2) inhibitors, SPI

Human non-pancreatic secretory phospholipase A(2) (hnps-PLA(2)) is a group IIA enzyme that is massively over-expressed in a variety of severe inflammatory diseases. The enzyme degrades membrane phospholipids and it has been hypothesized that this activity can lead to a loss of tissue and organ integrity and function. This report overviews efforts directed toward the identification and clinical evaluation of a new class of anti-inflammatory drugs that specifically targets and inhibits the catalytic site of this hydrolytic enzyme. To achieve this goal, structure-based drug design was applied to a lead molecule identified by random high volume screening. Through an iterative process consisting of X-ray structure determination followed by inhibitor modification and testing, the lead compound was improved more than 6000-fold. Detailed information learned from earlier X-ray studies of stable substrate mimics aided this inhibitor improvement process. The optimized drug candidate, LY315920/S-5920, is currently undergoing phase II clinical evaluation. The outcome of studies such as these will define with greater clarity the pathological role of hnps-PLA(2) in human inflammatory diseases.

Phospholipase A2: its usefulness in laboratory diagnostics

Phospholipase A2 (PLA2) is an enzyme that catalyzes the hydrolysis of membrane phospholipids. This article reviews the source and structure of PLA2, the involvement of the enzyme in various biological and pathological phenomena, and the usefulness of PLA2 assays in laboratory diagnostics. Of particular importance is the role of PLA2 in the cellular production of mediators of inflammatory response to various stimuli. Assays for PLA2 activity and mass concentration are discussed, and the results of enzyme determinations in plasma from patients with different pathological conditions are presented. The determination of activity and mass concentration in plasma is particularly useful in the diagnosis and prognosis of pancreatitis, multiple organ failure, septic shock, and rheumatoid arthritis. A very important result is the demonstration that PLA2 is an acute phase protein, like CRP. Indeed, there is a close correlation between PLA2 mass concentration and CRP levels in several pathological conditions. Although the determination of C-reactive protein is much easier to perform and is routinely carried out in most clinical laboratories, the assessment of PLA2 activity or mass concentration has to be considered as a reliable approach to obtain a deeper understanding of some pathological conditions and may offer additional information concerning the prognosis of several disorders.

Increased expression of human type IIa secretory phospholipase A2 antigen in arthritic synovium

OBJECTIVE

To determine the localisation and level of expression of human type IIa secretory phospholipase A2 (sPLA2) in the synovium of rheumatoid arthritis (RA), osteoarthritis (OA), and non-arthritic (NA) patients and to examine the relation between sPLA2 and histological features of inflammation.

METHODS

Immunoperoxidase staining using the anti-sPLA2 monoclonal antibody 9C1 was performed on frozen sections of knee synovium of 10 RA, 10 OA, and 10 NA patients. sPLA2 positive cells were scored on a scale of 0-3 in 10 fields of a representative tissue section from each case. Double labelling immunofluorescence confocal microscopy with antibodies to CD14 or CD45 and 9C1 was used to determine cell type specificity. Inflammation was assessed by semiquantitative scoring of lining layer thickness and mononuclear cell infiltrates (MC) and a cumulative inflammation score, generated by summing the two parameters. Scores in each group were compared using non-parametric statistical analysis.

RESULTS

sPLA2 was localised to endothelium (EC), vascular smooth muscle (VSM), and mast cells (M) in all tissue sections. In RA and OA sections, staining was seen in both macrophage-like and fibroblast-like cells in the synovial lining layer (LL) and subsynovial lining layer (SLL). Perineural cells stained positively. Subintimal lymphoid aggregates (LA) were negative in all sections. The RA group showed significantly greater staining in extravascular synovial tissue (median 3.6, range 1.5-6.0) than the OA (median 1.95, range 0-5.3) or NA (median 0, range 0-5.9) groups (p < 0.05). LL staining was significantly higher in RA than both OA and NA sections (p < 0.05). The OA group showed a trend to higher staining scores than the NA group that did not reach significance. There was a significant correlation between the sPLA2 staining score and inflammation score within the RA patient group (p < 0.05).

CONCLUSIONS

The synovium is a site of increased expression of sPLA2 antigen in both RA and OA relative to NA. Its presence in both fibroblast and macrophage-like cells in the LL and SLL of synovial tissue in RA and OA, but not NA, indicates that the enzyme is specifically induced in these regions in both conditions with expression in the LL being particularly characteristic of RA. The widespread expression of sPLA2 in synovium suggests it is likely to play a significant part in synovial pathology.

Quantitation of human tissue and immune cell type II 14 kDa phospholipase A2 by enzyme immunoassay

The metabolism of arachidonic acid into inflammatory mediators (e.g. prostaglandin, leukotrienes) is dependent upon the rate-limiting enzyme phospholipase A(2). Localization and quantification of type II 14 kDa phospholipase A(2) (PLA(2)) in cells or tissue preparations has historically been accomplished through activity measurements, a process that can provide variable results due to interference by exogenous substances with hydrolysis assessment. Others have reported on the use of sandwich enzyme immunoassays (EIA) to measure 14 kDa PLA(2) by mass in serum and exudate fluids, e.g. synovial fluid. Herein, we report the utilization of a human recombinant type II 14 kDa PLA(2) sandwich EIA to directly measure cell or tissue-residing 14 kDa PLA(2). It is known that type II 14 kDa PLA(2) resists acid treatment, and this technique was applied to cell fractions which liberated the enzyme from cellular membrane components prior to quantitation by EIA. Two human immune cell populations were assessed and shown to contain measurable levels of 14 kDa PLA(2). Neutrophil or monocyte cytosolic fractions contained no measurable levels whereas the respective 100 000g particulate fractions contained 2.6+/-0.8 pg (neutrophil) and 2.1+/-0.6 pg (monocyte) 14 kDa PLA(2)/mug protein. Human placenta cytosolic fractions contained no measurable levels while 100 000g particulate contained approximately 25 ng 14 kDa PLA(2)/mg protein. This EIA, in conjunction with acid extraction, provides an easy and reproducible assay to identify and quantify this enzyme in cells and whole tissues, expanding our ability to study the relationship of this enzyme to inflammatory processes.

Inhibition of extracellular release of proinflammatory secretory phospholipase A2 (sPLA2) by sulfasalazine: a novel mechanism of anti-inflammatory activity

Sulfasalazine is widely used in rheumatoid arthritis and inflammatory bowel diseases. The mechanisms of its activity have not been elucidated. In leukocytes, sulfasalazine and its analogue, CL 42A, inhibited the formation of leukotrienes and possibly of the second messenger compounds at the level of phospholipase C. Partial inhibition of interleukin-lbeta (IL-1beta), IL-6 and tumor necrosis factor-alpha (TNF-alpha) was also found. Since the synthesis of eicosanoids is induced by phospholipase A2 and since secretory phospholipase A2 (sPLA2) is proinflammatory, we investigated the impact of sulfasalazine and related compounds on mRNA, protein synthesis, and release of sPLA2 from osteoblasts. Sulfasalazine and CL 42A markedly inhibited extracellular release of sPLA2. The impact of sulfasalazine was evident at 50 microM (P < 0.001) and maximal at 400 microM, and that of CL 42A at 10 microM (P < 0.001) and 200 microM, respectively. Split products of sulfasalazine, 5-aminosalicylic acid (400 microM) and sulfapyridine (400 microM), had no impact. The effect of sulfasalazine and CL 42A was evident regardless of whether the cells were stimulated with IL-1beta/TNF-alpha, lipopolysaccharide/forskolin, or dibutyryl-cAMP. Sulfasalazine and CL 42A did not alter the level of sPLA2 mRNA. Exposure of stimulated fetal rat calvaria osteoblasts (FRCO) to sulfasalazine did not show accumulation of the intracellular sPLA2 protein as tested by western blot; however, enzymatic activity of PLA2 in disrupted cells was definitely increased. Thus, the impact is on the post-transcriptional release of sPLA2 rather than on the synthesis. There was also an increase in the extracellular release of prostaglandin E2 from FRCO exposed to sulfasalazine or to CL 42A. In contrast, sulfasalazine had no effect on the extracellular release of gelatinase from the cells or on mRNA of cytosolic PLA2 or cyclooxygenase 2. We conclude that the anti-inflammatory activity of sulfasalazine may be related, in part, to the selective inhibition of the extracellular release of proinflammatory sPLA2.

The synovial-like membrane at the bone interface in loose total hip replacements contains high levels of extracellular group II phospholipase A2

Progressive lysis of bone in loose total hip replacement has been ascribed to the capacity of the synovial-like membrane present at the bone interface to produce prostaglandin E2 and cytokines such as tumor necrosis factor (TNF alpha). Phospholipase A2 (PLA2) produces rate limiting precursor i.e. arachidonic acid in the biosynthesis of various types of biologically active lipids including prostaglandins. It has been shown that extracellular human group II phospholipase A2 is present in large amount in synovial fluid of patients with synovitis and that the expression of this enzyme is under the control of cytokines such as TNF alpha. Furthermore, the human extracellular enzyme has been also shown to induce in an experimental animal model to cause disruption of a synovial like membrane without increasing prostaglandin production. Here we have evaluated PLA2 and TNF alpha levels in the supernatant of homogenate of the synovial-like membrane present at the bone interface retrieved from six patients with a loose non septic failed total hip replacement. In all the membranes examined were found high levels of both TNF alpha (856 +/- 211 units/ml) and extracellular phospholipase A2 (2616 +/- 862 ng/ml). These findings suggest that extracellular PLA2 may play a major role in the process that cause disruption of the membrane at the bone-prosthesis interface.

Serum amyloid A protein enhances the activity of secretory non-pancreatic phospholipase A2

The acute-phase proteins serum amyloid A protein (SAA) and secretory phospholipase A2 (sPLA2) are simultaneously expressed during inflammatory conditions. SAA associates with high-density lipoprotein (HDL) altering its physicochemical composition. We found that purified acute-phase SAA, but not the constitutive form, markedly enhances the lipolytic activity of sPLA2 in a dose-related manner with phosphatidylcholine/lysophosphatidylcholine or phosphatidylethanolamine/lysophosphatidylethanolamine liposomal substrates. Normal HDL was found to reduce activity of sPLA2 in a dose-dependent manner, but when acute-phase HDL containing 27% SAA was tested, it enhanced sPLA2 activity. Immunopurified monospecific antibodies against SAA completely abolished the enhancing activity of SAA and acute-phase HDL. Given the central role of HDL in lipoprotein metabolism, the interaction between HDL, SAA and sPLA2 may account for changes detected in lipoprotein metabolism during the acute phase.

Increased group II phospholipase A2 in colonic mucosa of patients with Crohn's disease and ulcerative colitis

The immunochemical protein content of group II phospholipase A2 (PLA2) and PLA2 enzymatic activity were measured for colonic mucosal biopsy samples obtained from patients with either Crohn's disease of the colon or ulcerative colitis, and control patients without inflammatory bowel disease. Immunoreactive group II PLA2 (IR-PLA2 II) content and PLA2 activity in actively inflamed colonic mucosa of Crohn's disease patients were significantly higher than those in inactively inflamed mucosa of Crohn's disease patients and the colonic mucosa of controls. IR-PLA2 II content and PLA2 activity in severely inflamed mucosa of ulcerative colitis patients were significantly higher than those in the colonic mucosa of the controls. Mucosal PLA2 enzymatic activity was closely correlated with mucosal IR-PLA2 II content in patients with Crohn's disease and ulcerative colitis. These results suggest that an increase in PLA2 enzymatic activity in inflamed colonic mucosa of Crohn's disease and ulcerative colitis was mainly attributed to increased protein content of group II PLA2, and that an increase in mucosal group II PLA2 may be involved in the pathogenesis of intestinal inflammation of Crohn's disease and ulcerative colitis.

Sequence specific inhibition of human type II phospholipase A2 enzyme activity by phosphorothioate oligonucleotides

Phosphorothioate oligonucleotides were identified which directly inhibited human type II phospholipase A2 (PLA2) enzyme activity in a sequence specific manner. The minimum pharmacophore common to all oligonucleotides which inhibited PLA2 enzyme activity consisted of two sets of three or more consecutive guanosine residues in a row. These oligonucleotides appear to form G quartets resulting in the formation of oligonucleotide aggregates. Additionally, a phosphorothioate backbone was required to be effective inhibitors of type II PLA2. The activity of one oligodeoxynucleotide, IP 3196 (5'-GGGTGGGTATAGAAGGGCTCC-3') has been characterized in more detail. IP 3196 inhibited PLA2 enzyme activity when the substrate was presented in the form of a phospholipid bilayer but not when presented in the form of a mixed micelle with anionic detergents. Human type II PLA2 was 50-fold more sensitive to inhibition by IP 3196 than venom and pancreatic type I enzymes. These data demonstrate that phosphorothioate oligonucleotides can specifically inhibit human type II PLA2 enzyme activity in a sequence specific manner.

Group II phospholipase A2 in synovial fluid and serum in acute arthritis

Increased catalytic activity of synovial-type (group II) phospholipase A2 (syn-PLA2), has been associated with cartilage erosions in rheumatoid arthritis and osteoarthritis. The catalytic activity of phospholipase A2 and the concentration of syn-PLA2 were measured in a prospective study in synovial fluid (SF) samples from 66 patients with acute knee joint effusion. The median (range) of the concentration of syn-PLA2 in SF was 210 micrograms/l (80-1480 micrograms/l) in culture-positive septic arthritis, 460 micrograms/l (270-1040 micrograms/l) in reactive arthritis, 780 micrograms/l (120-2710 micrograms/l) in osteoarthritis and 230 micrograms/l (80-1400 micrograms/l) in traumatic joint effusions. High concentrations of syn-PLA2 are found also in SF of patients with arthritides not expected to lead to permanent destruction of cartilage.