Phospholipase A2 gene expression and activity in histologically normal ileal mucosa and in Crohn's ileitis

PLA2-Triggered Activation of Cyclosporine-Phospholipid Prodrug as a Drug Targeting Approach in Inflammatory Bowel Disease Therapy

Oral medication with activity specifically at the inflamed sites throughout the gastrointestinal tract and limited systemic exposure would be a major advance in our therapeutic approach to inflammatory bowel disease (IBD). For this purpose, we have designed a prodrug by linking active drug moiety to phospholipid (PL), the substrate of phospholipase A₂ (PLA₂). PLA₂ expression and activity is significantly elevated in the inflamed intestinal tissues of IBD patients. Since PLA₂ enzyme specifically hydrolyses the sn-2 bond within PLs, in our PL-based prodrug approach, the sn-2 positioned FA is replaced with cyclosporine, so that PLA₂ may be exploited as the prodrug-activating enzyme, releasing the free drug from the PL-complex. Owing to the enzyme overexpression, this may effectively target free cyclosporine to the sites of inflammation. Four PL-cyclosporine prodrugs were synthesized, differing by their linker length between the PL and the drug moiety. To study the prodrug activation, a novel enzymatically enriched model was developed, the colonic brush border membrane vesicles (cBBMVs); in this model, tissue vesicles were produced from colitis-induced (vs. healthy) rat colons. PLA₂ overexpression (3.4-fold) was demonstrated in diseased vs. healthy cBBMVs. Indeed, while healthy cBBMVs induced only marginal activation, substantial prodrug activation was evident by colitis-derived cBBMVs. Together with the PLA₂ overexpression, these data validate our drug targeting strategy. In the diseased cBBMVs, quick and complete activation of the entire dose was obtained for the 12-carbon linker prodrug, while slow and marginal activation was obtained for the 6/8-carbon linkers. The potential to target the actual sites of inflammation and treat any localizations throughout the GIT, together with the extended therapeutic index, makes this orally delivered prodrug approach an exciting new therapeutic strategy for IBD treatment.

Prodrug-Based Targeting Approach for Inflammatory Bowel Diseases Therapy: Mechanistic Study of Phospholipid-Linker-Cyclosporine PLA2-Mediated Activation

Therapeutics with activity specifically at the inflamed sites throughout the gastrointestinal tract (GIT) would be a major advance in our therapeutic approach to inflammatory bowel disease (IBD). We aimed to develop the prodrug approach that can allow such site-specific drug delivery. Currently, using cyclosporine as a drug of choice in IBD is limited to the most severe cases due to substantial systemic toxicities and narrow therapeutic index of this drug. Previously, we synthesized a series of a phospholipid-linker-cyclosporine (PLC) prodrugs designed to exploit the overexpression of phospholipase A₂ (PLA₂) in the inflamed intestinal tissues, as the prodrug-activating enzyme. Nevertheless, the extent and rate of prodrug activation differed significantly. In this study we applied in-vitro and modern in-silico tools based on molecular dynamics (MD) simulation, to gain insight into the dynamics and mechanisms of the PLC prodrug activation. We aimed to elucidate the reason for the significant activation change between different linker lengths in our prodrug design. Our work reveals that the PLC conjugate with the 12-carbon linker length yields the optimal prodrug activation by PLA₂ in comparison to shorter linker length (6-carbons). This optimized length efficiently allows cyclosporine to be released from the prodrug to the active pocket of PLA₂. This newly developed mechanistic approach, presented in this study, can be applied for future prodrug optimization to accomplish optimal prodrug activation and drug targeting in various conditions that include overexpression of PLA₂.

Gut microbiota: sculptors of the intestinal stem cell niche in health and inflammatory bowel disease

Intestinal epithelium represents a dynamic and diverse cellular system that continuously interacts with gut commensals and external cues. Intestinal stem cells, which lie at the heart of epithelial renewal and turnover, proliferate to maintain a steady stem cell population and differentiate to form functional epithelial cell types. This rather sophisticated assembly-line is maintained by an elaborate micro-environment, sculpted by a myriad of host and gut microbiota-derived signals, forming an intestinal stem cell niche. This complex, yet crucial signaling niche undergoes dynamic changes during homeostasis and chronic intestinal inflammation. Inflammatory bowel disease refers to a chronic inflammatory response toward pathogenic or commensal microbiota, in a genetically susceptible host. Compositional and functional alterations in gut microbiota are pathognomonic of IBD.The present review highlights the modulatory role of gut microbiota on the intestinal stem cell niche during homeostasis and inflammatory bowel disease. We discuss the mechanisms of direct action of gut commensals (through microbiota-derived or microbiota-influenced metabolites) on ISCs, followed by their effects via other epithelial and immune cell types.

Secretory Phospholipase A2 Inhibition Attenuates Adhesive Properties of Esophageal Barrett's Cells

BACKGROUND

Gastroesophageal reflux and Barrett's esophagus are significant risk factors for the development of esophageal adenocarcinoma. Group IIa secretory phospholipase A₂ (sPLA₂) catalyzes the production of various proinflammatory metabolites and plays a critical role in promoting reflux-induced inflammatory changes within the distal esophagus. We hypothesized that inhibition of sPLA₂ in human Barrett's cells would attenuate adhesion molecule expression via decreased activation of nuclear factor kappa B (NF-κB) and decrease cell proliferation, possibly mitigating the invasive potential of Barrett's esophagus.

MATERIALS AND METHODS

Normal human esophageal epithelial cells (HET1A) and Barrett's cells (CPB) were assayed for baseline sPLA₂ expression. CPB cells were treated with a specific inhibitor of sPLA₂ followed by tumor necrosis factor-α. Protein expression was evaluated using immunoblotting. Cell proliferation was assessed using an MTS cell proliferation assay kit. Statistical analysis was performed using the Student's t-test or analysis of variance, where appropriate.

RESULTS

CPB cells demonstrated higher baseline sPLA₂ expression than HET1A cells (P = 0.0005). Treatment with 30 μM sPLA₂ inhibitor significantly attenuated intercellular adhesion molecule-1 (P = 0.004) and vascular cell adhesion molecule-1 (P < 0.0001) expression as well as decreased NF-κB activation (P = 0.002). sPLA₂ inhibition decreased cell proliferation in a dose-dependent manner (P < 0.001 for 15, 20, and 30 μM doses).

CONCLUSIONS

sPLA₂ inhibition in human Barrett's cells decreases cellular adhesive properties and NF-κB activation as well as decreases cell proliferation, signifying downregulation of the inflammatory response and possible attenuation of cellular malignant potential. These findings identify sPLA₂ inhibition as a potential chemopreventive target for premalignant lesions of the esophagus.

Possible Involvement of Intracellular Calcium-Independent Phospholipase A2 in the Release of Secretory Phospholipases from Mast Cells-Increased Expression in Ileal Mast Cells of Crohn's Disease

Increased activity of secretory phospholipases A₂ (sPLA₂) type-II was previously observed in ileum of Crohn’s disease (CD). Our aims were to explore the involvement of calcium-independent (i)PLA₂β in the release of sPLA₂s from the human mast cell (MC) line (HMC-1) and investigate expressions of cytosolic (c)PLA₂α, iPLA₂β, sPLA₂-IIA and sPLA₂-V in MCs of CD ileum. The release of sPLA₂ was investigated in HMC-1 by immunocytochemistry and ELISA. The expression intensities of PLA₂s in mucosal MCs, and the proportion of PLA₂-positive MCs, were investigated in normal ileum and in ileum from patients with CD by immunohistochemistry. The calcium ionophore-stimulated release of sPLA₂-IIA and sPLA₂-V from HMC-1 was reduced by the iPLA₂-inhibitor bromoenol lactone. All four PLA₂s were detectable in mucosal MCs, both in normal ileum and in CD, but the proportion of iPLA₂β-containing mucosal MCs and the expression intensity of sPLA₂-IIA was increased in CD. Results indicate that iPLA₂β is involved in the secretion of sPLA₂s from HMC-1, and suggest that iPLA₂β-mediated release of sPLA₂ from intestinal MCs may contribute to CD pathophysiology. Ex vivo studies on isolated mucosal mast cells are however needed to clarify the precise role of MC PLA₂s in the inflammatory processes of CD.

Computational modeling and in-vitro/in-silico correlation of phospholipid-based prodrugs for targeted drug delivery in inflammatory bowel disease

Targeting drugs to the inflamed intestinal tissue(s) represents a major advancement in the treatment of inflammatory bowel disease (IBD). In this work we present a powerful in-silico modeling approach to guide the molecular design of novel prodrugs targeting the enzyme PLA₂, which is overexpressed in the inflamed tissues of IBD patients. The prodrug consists of the drug moiety bound to the sn-2 position of phospholipid (PL) through a carbonic linker, aiming to allow PLA₂ to release the free drug. The linker length dictates the affinity of the PL-drug conjugate to PLA₂, and the optimal linker will enable maximal PLA₂-mediated activation. Thermodynamic integration and Weighted Histogram Analysis Method (WHAM)/Umbrella Sampling method were used to compute the changes in PLA₂ transition state binding free energy of the prodrug molecule (∆∆G^tr) associated with decreasing/increasing linker length. The simulations revealed that 6-carbons linker is the optimal one, whereas shorter or longer linkers resulted in decreased PLA₂-mediated activation. These in-silico results were shown to be in excellent correlation with experimental in-vitro data. Overall, this modern computational approach enables optimization of the molecular design of novel prodrugs, which may allow targeting the free drug specifically to the diseased intestinal tissue of IBD patients.

The role of group IIA secretory phospholipase A2 (sPLA2-IIA) as a biomarker for the diagnosis of sepsis and bacterial infection in adults-A systematic review

INTRODUCTION

This paper investigates the role of Group II Secretory Phospholipase A2 (sPLA2-IIA) as a biomarker for the diagnosis of sepsis and bacterial infection in adults. Sepsis and bacterial infection are common problems encountered by patients in the hospital and often carry adverse outcomes if not managed early.

METHODS

Two independent reviewers conducted a comprehensive search using Ovid MEDLINE published from years 1993 to 2016 and SCOPUS published from year 1985 to 2017 to screen for relevant studies. The main inclusion criteria included adult subjects, patients with suspected or confirmed signs of infection and relevant outcomes which looked into the role of sPLA2-IIA in detecting the presence of sepsis and bacterial infection in the subjects.

RESULTS AND DISCUSSION

Four studies met the inclusion criteria. SPLA2-IIA was found to be effective in detecting the presence of sepsis and bacterial infection in adults. The levels of serum sPLA2-IIA also correlated well with the presence of sepsis and bacterial infection.

CONCLUSION

This systematic review highlights the role of sPLA2-IIA as a reliable tool to diagnose sepsis and bacterial infection in adult patients. Nonetheless, further studies should be done in the future to provide more compelling evidence on its application in the clinical setting.

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.

Potential role of protease-activated receptor-2-stimulated activation of cytosolic phospholipase A(2) in intestinal myofibroblast proliferation: Implications for stricture formation in Crohn's disease

BACKGROUND AND AIMS

Myofibroblast hyperplasia contributes to muscularis mucosae thickening and stricture formation in Crohn's disease (CD). Protease-activated receptor-2 (PAR-2) and cytosolic phospholipase A(2) (cPLA(2)) are known regulators of cell growth, but their significance in intestinal myofibroblast proliferation remain to be elucidated. The principle aims of the present study were to investigate if PAR-2 is expressed in the expanded muscularis mucosa in ileal CD specimens, if inflammatory cytokines may stimulate PAR-2 expression in intestinal myofibroblasts, and if PAR-2 and cPLA(2) may regulate intestinal myofibroblast growth.

METHODS

Immunohistochemistry was used for detection of PAR-2 in ileal CD specimens. Studies on PAR-2 expression, PLA(2) activation and cell growth were performed in a human intestinal myofibroblast cell line, CCD-18Co. PAR-2 expression was investigated by RT-PCR and immunocytochemistry. PLA(2) activity was analyzed by quantification of released (14)C-arachidonic acid ((14)C-AA). Cell growth was examined by (3)H-thymidine incorporation and cell counting.

RESULTS

The thickened muscularis mucosae of the CD specimens showed strong PAR-2 expression. In cultured myofibroblasts, tumor necrosis factor-α (TNF-α) up-regulated PAR-2 mRNA and protein, and potentiated PAR-2-stimulated (14)C-AA release by two known PAR-2 activators, trypsin and SLIGRL-NH(2). The release of (14)C-AA was dependent on cPLA(2). Trypsin stimulated the proliferation of serum-starved cells, and inhibition of cPLA(2) reduced normal cell growth and abolished the growth-promoting effect of trypsin.

CONCLUSIONS

The results suggest that PAR-2-mediated cPLA(2) activation might be of importance in intestinal myofibroblast proliferation. The results also point to the possibility that PAR-2 up-regulation by inflammatory cytokines, like TNF-α, may modulate this effect.

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.

Distinct isoforms of phospholipase A2 mediate the ability of Salmonella enterica serotype typhimurium and Shigella flexneri to induce the transepithelial migration of neutrophils

Salmonella spp. and Shigella spp. are responsible for millions of cases of enteric disease each year worldwide. While these pathogens have evolved distinct strategies for interacting with the human intestinal epithelium, they both induce significant proinflammatory responses that result in massive transepithelial migration of neutrophils across the intestinal mucosa. It has previously been shown with Salmonella enterica serotype Typhimurium that the process of neutrophil transmigration is mediated in part by the secretion of hepoxilin A(3) (HXA(3); 8-hydroxy-11,12-epoxy-eicosatetraenoic acid), a potent neutrophil chemoattractant, from the apical surface of infected model intestinal epithelium. This study confirms that HXA(3) is also secreted in response to infection by Shigella flexneri, that it is produced by a pathway involving 12/15-lipoxygenase (12/15-LOX), and that S. enterica serovar Typhimurium and S. flexneri share certain elements in the mechanism(s) that underlies the otherwise separate signal transduction pathways that are engaged to induce polymorphonuclear leukocyte (PMN) transepithelial migration (protein kinase C and extracellular signal-regulated kinases 1 and 2, respectively). PMN transepithelial migration in response to infection with S. flexneri was dependent on 12/15-LOX activity, the enzyme responsible for the initial metabolism of arachidonic acid to HXA(3). Probing further into this pathway, we also found that S. enterica serovar Typhimurium and S. flexneri activate different subtypes of phospholipase A(2), a critical enzyme involved in the liberation of arachidonic acid from cellular membranes. Thus, although S. enterica serovar Typhimurium and S. flexneri utilize different mechanisms for triggering the induction of PMN transepithelial migration, we found that their reliance on 12/15-LOX is conserved, suggesting that enteric pathogens may ultimately stimulate similar pathways for the synthesis and release of HXA(3).

Expression of cytosolic and group X secretory phospholipase A(2) genes in human colorectal adenocarcinomas

Gene expression of cytosolic phospholipase A(2) (cPLA(2)) and protein level of secretory PLA(2) group X (sPLA(2)-X) are upregulated in human colorectal cancer and provide cyclooxygenase-2 (COX-2) with arachidonic acid, resulting in increased levels of PGE(2). Mutated ras-genes are suggested to be involved in the regulatory pathway of cPLA(2) in lung cancer cells. We analysed the gene expression of cPLA(2) and sPLA(2)-X in 42 and 38 primary colorectal tumours, respectively, with and without K-ras mutations. We found an up-regulation of cPLA(2) mRNA but the induction in tumour tissues does not correlate with Ras-gene mutations. Moreover, our results cannot consistently reflect an overexpression of sPLA(2)-X gene in colorectal cancer tissues.

Pancreatic phospholipase A2 from the small intestine is a secretin-releasing factor in rats

A secretin-releasing activity exists in the upper small intestine and pancreatic juice in the rat and the dog. Group I pancreatic phospholipase A2 (PLA2) in canine pancreatic juice and porcine pancreatic PLA2 stimulate the release of secretin from both STC-1 cells and a secretin-producing cell (S cell)-enriched preparation isolated from rat duodenal mucosa. We investigated the distribution and release of pancreatic PLA2-like immunoreactivity in the gastrointestinal tract and the role of PLA2 on the release of secretin and pancreatic exocrine secretion in response to duodenal acidification in anesthetized rats. PLA2-like immunoreactivity was detected in the mucosa throughout the gastrointestinal tract. High concentrations of PLA2 were found in both the small intestine and the pancreas. Duodenal acidification significantly increased the release of PLA2 from the upper small intestine (385% over basal secretion). Intravenous infusion of an anti-PLA2 serum (anti-PLA2) dose-dependently inhibited the release of secretin and pancreatic exocrine secretion in response to duodenal acid perfusion. Preincubation of the concentrate of intestinal acid perfusate (10-fold) from donor rats with the anti-PLA2 significantly suppressed its stimulation of secretin release and pancreatic exocrine secretion in recipient rats. We conclude that pancreatic PLA2 also functions as a secretin-releasing factor in the small intestine that mediates acid-stimulated release of secretin in rats.

Presence of group IIa secretory phospholipase A2 in mast cells and macrophages in normal human ileal submucosa and in Crohn's disease

Secretory group IIa phospholipase A2 (PLA2-II) is an important regulator of proinflammatory lipid mediator production and may play a role in ileal inflammation in Crohn's disease. The enzyme has previously only been detected in epithelial Paneth cells. However, one characteristic feature of Crohn's disease is the transmural inflammation. Full thickness ileal sections from nine patients with Crohn's disease, and histologically normal sections from patients with colonic cancer (n=7) and chronic severe constipation (n=1) as controls, were used in this study. PLA2-II-positive cells were detected by immunofluorescence and in situ hybridization. Metachromatic staining and esterase staining were used to identify mast cells and macrophages, respectively. It was shown that mast cells and macrophages in the ileal submucosa in both patients and controls showed positive PLA2-II staining. The number of PLA2-II-labeled cells that did not react with metachromasia, e.g. macrophages, was significantly greater in inflamed Crohn's disease compared to controls. This is, to our knowledge, the first study that has described the presence in healthy, while presence and upregulation of PLA2-II-positive cells in inflamed human ileal submucosa. Our findings suggest a proinflammatory potential for secretory PLA2-II in submucosa, while proinflammatory stimulation of mast cells and macrophages in vitro has shown that the enzyme is responsible for delayed prostaglandin formation.

Roles of secretory phospholipases A(2) in inflammatory diseases and trauma

Six distinct secretory small molecular weight phospholipases A(2) (PLA(2)) have been cloned and characterized from human tissues. Two of them, pancreatic group IB PLA(2) (PLA(2)-IB) and synovial-type group IIA PLA(2) (PLA(2)-IIA) have been studied as to their association to various inflammatory diseases. PLA(2)-IB is a digestive enzyme synthesized by pancreatic acinar cells. In acute pancreatitis, which is characterized by destruction of pancreatic tissue, PLA(2)-IB is released into the circulation, but its role in pancreatic and other tissue damage is still hypothetical. The concentration of PLA(2)-IIA increases in blood plasma in generalized inflammatory response resulting from infections, chronic inflammatory diseases, acute pancreatitis, trauma and surgical operations. PLA(2)-IIA is synthesized in a number of gland cells and is present in cellular secretions on mucosal surfaces including Paneth cells of intestinal mucosa, prostatic gland cells and seminal plasma, and lacrimal glands and tears. PLA(2)-IIA is expressed in hepatoma-derived cells in vitro and hepatocytes in vivo. PLA(2)-IIA is regarded as an acute phase protein and seems to function as an antibacterial agent especially effective against Gram-positive bacteria. Other putative functions in the inflammatory reaction include hydrolysis of cell membrane phospholipids and release of arachidonic acid for prostanoid synthesis.

Group IIA phospholipase A2 mediates lung injury in intestinal ischemia-reperfusion

OBJECTIVE

To assess the mechanistic role of group IIA phospholipase A2 (PLA2) in the process of local and distant organ injury after intestinal ischemia-reperfusion.

SUMMARY BACKGROUND DATA

Intestinal ischemia-reperfusion produces lung injury by a mechanism that involves PLA2 activation, but it is unclear which isozyme is responsible for this phenomenon. Group IIA PLA2, one of the secreted forms of PLA2, is known to play a pivotal role in a variety of inflammatory reactions.

METHODS

Rats underwent 45 minutes of superior mesenteric artery occlusion in the presence and absence of pretreatment with group IIA PLA2 inhibitor, S-5920/LY315920Na (20 mg/kg, subcutaneously, 30 minutes before clamping). At 2 hours of reperfusion, intestinal and lung leak was assessed by 125I-albumin tissue/blood ratio, and liver injury was estimated by serum alanine aminotransferase. PLA2 activities in tissues and sera were quantitated by phosphatidyl-glycerol/sodium cholate mixed micelle assay. PLA2 activities in tissues were also measured after in vitro preincubation with EDTA, S-5920/LY315920Na, or antirat group IIA PLA2 antibody.

RESULTS

Intestinal ischemia-reperfusion provoked intestinal leak, liver injury, and lung leak, whereas tissue PLA2 activity was decreased in the intestine, unchanged in the liver, and increased in the lung. Serum PLA2 activities were increased in the portal and systemic circulation during ischemia. Pretreatment with S-5920/LY315920Na eliminated PLA2 activities in all tissues and sera and only abolished lung leak. The in vitro experiment revealed that most of the intestinal and lung PLA2 activities were inhibited by EDTA, S-5920/LY315920Na, and antirat group IIA PLA2 antibody, but hepatic PLA2 activity was not.

CONCLUSION

Intestinal ischemia-reperfusion appears to produce lung injury by a mechanism that involves group IIA PLA2 activation. Intestinal ischemia-reperfusion is likely to promote intestinal and hepatic injury independent of group IIA PLA2.

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.

Gene expression of group II phospholipase A2 in intestine in Crohn's disease

OBJECTIVE

Phospholipase A2 (PLA2) has been suggested to play an important role in the pathogenesis of inflammatory bowel diseases. Our aim was to identify cells that express group II phospholipase A2 (PLA2-II) at the mRNA and enzyme protein levels in the intestine in Crohn's disease.

METHODS

Tissue samples were obtained from the intestine of 20 patients with Crohn's disease (seven operated and 13 colonoscopied) and from eight control patients without inflammatory diseases. The samples were studied by immunohistochemistry for PLA2-II enzyme protein and in situ hybridization for PLA2-II mRNA.

RESULTS

PLA2-II protein and mRNA were detected in the Paneth cells of the small intestinal mucosa in all patients and controls. PLA2-II protein and mRNA were found in the columnar epithelial cells of the small intestinal mucosa in six of eight and eight of eight patients with Crohn's ileitis, respectively. In the eight control patients PLA2-II protein and mRNA were not found in these cells (p = 0.007 and p < 0.001, respectively). Metaplastic Paneth cells, which consistently contained PLA2-II mRNA, were found in the colonic mucosa in five of six patients with Crohn's colitis and of one of eight control patients (p = 0.026). The columnar epithelial cells of the colonic mucosa contained PLA2-II protein in three of six and PLA2-II mRNA in six of six patients with Crohn's colitis, whereas the protein was found in these cells in none of eight of the controls (p = 0.055) and the mRNA in only one of eight (p = 0.005) controls.

CONCLUSIONS

In Crohn's disease, Paneth cells and columnar epithelial cells of the small and large intestinal mucosa synthesize PLA2-II at the site of active inflammation.

The chemopreventive role of ursodeoxycholic acid in azoxymethane-treated rats: suppressive effects on enhanced group II phospholipase A2 expression in colonic tissue

Great interest has been focused on the chemoprevention of colonic carcinogenesis by oral administration of ursodeoxycholic acid (UDCA) because its administration reportedly reduces the incidence of colon cancer in animal experiments. To elucidate the precise role of UDCA in the chemoprevention of azoxymethane-induced colon carcinogenesis, we examined the expression levels of group II phospholipase A2 in the colonic tissue of UDCA-treated and untreated rats and correlated the levels with the findings of aberrant crypt foci, putative preneoplastic lesions. Twelve weeks after azoxymethane exposure, the total number of aberrant crypt foci in 0.4% UDCA-fed rats and 1% UDCA-fed rats was significantly decreased compared to the untreated animals. The mucosal concentrations of PGE2 and 6-keto PGF1alpha were significantly lower in the UDCA-treated rats than in untreated rats. In correlation with lowering, the enhanced activity, protein mass and mRNA levels of group II phospholipase A2 were significantly attenuated in the UDCA-treated animals. The chemopreventive role of UDCA in colon carcinogenesis may lie in its modulation of the arachidonate metabolism in colonic mucosa.

Selective Inhibitors of Cytosolic or Secretory Phospholipase A2 Block TNF-Induced Activation of Transcription Factor Nuclear Factor-κB and Expression of ICAM-1

TNF signaling mechanisms involved in activation of transcription factor NF-κB were studied in the human keratinocyte cell line HaCaT. We show that TNF-induced activation of NF-κB was inhibited by the well-known selective inhibitors of cytosolic phospholipase A2 (cPLA2): the trifluoromethyl ketone analogue of arachidonic acid (AACOCF3) and methyl arachidonyl fluorophosphate. The trifluoromethyl ketone analogue of eicosapentaenoic acid (EPACOCF3) also suppressed TNF-induced NF-κB activation and inhibited in vitro cPLA2 enzyme activity with a similar potency as AACOCF3. The arachidonyl methyl ketone analogue (AACOCH3) and the eicosapentanoyl analogue (EPACHOHCF3), which both failed to inhibit cPLA2 enzyme activity in vitro, had no effect on TNF-induced NF-κB activation. TNF-induced NF-κB activation was also strongly reduced in cells stimulated in the presence of the secretory PLA2 (sPLA2) inhibitors 12-epi-scalaradial and LY311727. Addition of excess arachidonic acid suppressed the inhibitory effect of 12-epi-scalaradial and LY311727. Moreover, both methyl arachidonyl fluorophosphate and 12-epi-scalaradial blocked TNF-mediated enhancement of expression of ICAM-1. Activation of NF-κB by IL-1β was markedly less sensitive to both cPLA2 and sPLA2 inhibitors. The results indicate that both cPLA2 and sPLA2 may be involved in the TNF signal transduction pathway leading to nuclear translocation of NF-κB and to NF-κB-activated gene expression in HaCaT cells.

Modulation of K+ channels by arachidonic acid in T84 cells. II. Activation of a Ca(2+)-independent K+ channel

We used single-channel recording techniques to identify and characterize a large-conductance, Ca(2+)-independent K+ channel in the colonic secretory cell line T84. In symmetric potassium gluconate, this channel had a linear current-voltage relationship with a single-channel conductance of 161 pS. Channel open probability (Po) was increased at depolarizing potentials. Partial substitution of bath K+ with Na+ indicated a permeability ratio of K+ to Na+ of 25:1. Channel Po was reduced by extracellular Ba2+. Event-duration analysis suggested a linear kinetic model for channel gating having a single open state and three closed states: C3<-->C2<-->C1<-->O. Arachidonic acid (AA) increased the Po of the channel, with an apparent stimulatory constant (Ks) of 1.39 microM. Neither channel open time (O) nor the fast closed time (C1) was affected by AA. In contrast, AA dramatically reduced mean closed time by decreasing both C3 and C2. The cis-unsaturated fatty acid linoleate increased Po also, whereas the saturated fatty acid myristate and the trans-unsaturated fatty acid elaidate did not affect Po. This channel is activated also by negative pressure applied to the pipette during inside-out recording. Thus we determined the effect of the stretch-activated channel blockers amiloride and Gd3+ on the K+ channel after activation by AA. Amiloride (2 mM) on the extracellular side reduced single-channel amplitude in a voltage-dependent manner, whereas Gd3+ (100 microM) had no effect on channel activity. Activation of this K+ channel may be important during stimulation of Cl- secretion by agonists that use AA as a second messenger (e.g., vasoactive intestinal polypeptide, adenosine) or during the volume regulatory response to cell swelling.

Cloning, chromosomal mapping, and expression of a novel human secretory phospholipase A2

Secretory phospholipases A2 (sPLA2s) represent a rapidly expanding family of structurally related enzymes found in mammals as well as in insect and snake venoms. In this report, a cDNA coding for a novel sPLA2 has been isolated from human fetal lung, and its gene has been mapped to chromosome 16p13.1-p12. The mature sPLA2 protein has a molecular mass of 13.6 kDa, is acidic (pI 5.3), and made up of 123 amino acids. Key structural features of the sPLA2 include: (i) a long prepropeptide ending with an arginine doublet, (ii) 16 cysteines located at positions that are characteristic of both group I and group II sPLA2s, (iii) a C-terminal extension typical of group II sPLA2s, (iv) and the absence of elapid and pancreatic loops that are characteristic of group I sPLA2s. Based on these structural properties, this sPLA2 appears as a first member of a new group of sPLA2s, called group X. A 1.5-kilobase transcript coding for the human group X (hGX) sPLA2 was found in spleen, thymus, and peripheral blood leukocytes, while a less abundant 0.8-kilobase transcript was detected in the pancreas, lung, and colon. When the hGX sPLA2 cDNA was expressed in COS cells, sPLA2 activity preferentially accumulated in the culture medium, indicating that hGX sPLA2 is an actively secreted enzyme. It is maximally active at physiological pH and with 10 mM Ca2+. hGX sPLA2 prefers phosphatidylethanolamine and phosphatidylcholine liposomes to those of phosphatidylserine.

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.

Flavonoids as phospholipase A2 inhibitors: importance of their structure for selective inhibition of group II phospholipase A2

The inhibitory effect of the plant flavonoid, rutin, on group I phospholipase A2 (PLA2-I) from porcine pancreas and Naja naja, and on group II phospholipase A2 (PLA2-II) from Vipera russelli and Crotalus atrox was investigated. Rutin efficiently inhibited PLA2-II from both Vipera russelli and Crotalus atrox but was only a weak inhibitor of PLA2-I from porcine pancreas and Naja naja. The lack of strong inhibition of pancreatic PLA2-I was not due to contaminating proteins in the enzyme preparation, since the same weak inhibition was obtained against pancreatic PLA2 purified to homogeneity as judged by two-dimensional gel electrophoresis. Rutin also efficiently inhibited human PLA2-II from synovial fluid but was only a weak inhibitor of human PLA2-I from pancreatic juice, suggesting that rutin is a selective PLA2-I from porcine pancreas. The results obtained indicate that the hydroxyl group in 5-position as well as the double bond and the double-bonded oxygen in the oxane ring are all important for the overall ability of flavonoids to inhibit PLA2 activity, and that the hydroxyl groups in 3'- and 4'- position are required for selective inhibition of PLA2-II.

Compartmentalisation and characteristics of a Ca2+-dependent phospholipase A2 in human colon mucosa

The biochemical properties of the phospholipase A2 (PLA2) found in the 100,000 x g centrifugate cytosol or particulate fractions of human colonic mucosa have been investigated using both deoxycholate-solubilized and Escherichia coli (E. coli) phospholipids as substrates. PLA2 activity was present in both subcellular fractions and the profiles of biochemical activites were similar. Activity in the particulate fraction was approximately twofold greater than the cytosol fraction when expressed on the basis of protein concentration. The PLA2 is Ca2+ dependent and using EGTA-regulated buffers cytosolic or particulate fraction activity was similar at both 10 microm or 10 mm Ca2+ concentrations. Using deoxycholate-phospholipid micelles as substrate a small but statistically significant twofold preference for glycero-phosphatidylcholine bearing sn-2-arachidonate compared with sn-2-oleate was seen, but this preference was not noted using arachidonate or oleate labelled E. coli membranes. Dithiothreitol (10 mM) reduced colon mucosal cytosol PLA2 activity significantly by 63.5 +/- 1.90% in cytosol and by 30.54 +/- 1.27% in microsomes using micelles as substrate or by 84.3 +/- 2.30% in cytosol and by 69.33 +/- 11.30% in microsomes using oleate-labelled E. coli as substrates. Warming at 57 degrees C reduced activity significantly by 35.0 +/- 5.80% in microsomes and by 40.0 +/- 7.08% in cytosol. Acid treatment increased PLA2 activity to 148 +/- 16.3% in microsomes and 145 +/- 18.6% in cytosol. When mucosal preparations were subjected to heparin-Sepharose chromatography, it bound tightly and eluted in the same position on a salt gradient as authentic human group II PLA2. Further purification by gel-permeation chromatography gave activity in the 14 kDa region of the elution profile. These features have many of the characteristics expected of a 14 kDa isoform of PLA2 but exhibit activity at concentrations of Ca2+ that are relevant in the intracellular environment and may participate in cellular lipid metabolism.

Gene expression of group II phospholipase A2 in intestine in ulcerative colitis

BACKGROUND

It has been suggested that phospholipase A2 (PLA2) has an essential role in the pathogenesis of inflammatory bowel diseases.

AIMS

This study aimed at identifying cells in intestinal and mesenteric tissue samples that might express group II phospholipase A2 (PLA2-II) at the mRNA and enzyme protein levels in patients with ulcerative colitis. PATIENTS AND TISSUE SAMPLES: Tissue samples were obtained from the intestine, mesentery, skeletal muscle, and subcutaneous fat of six patients who underwent panproctocolectomy for severe ulcerative colitis. Mucosal biopsy specimens were obtained from the colon of another group of six patients with ulcerative colitis during routine diagnostic colonoscopies. Tissues from six patients without intestinal inflammatory diseases served as controls.

METHODS

Tissue samples were studied by light microscopy, immunohistochemistry for PLA2-II enzyme protein, and in situ hybridisation and northern hybridisation for PLA2-II mRNA.

RESULTS

PLA2-II mRNA and PLA2-II protein were detected in metaplastic Paneth cells in six patients and in the columnar epithelial cells of colonic mucosa in four out of six patients with active ulcerative colitis. Positive findings were less numerous in patients with mild ulcerative colitis. Only two out of six control patients had a weak positive signal for PLA2-II mRNA and one of these two patients had a weak positive immunoreaction for PLA2-II in columnar epithelial cells in the colonic mucosa. None of the control patients had metaplastic Paneth cells.

CONCLUSIONS

Metaplastic Paneth cells and colonic epithelial cells synthesise PLA2-II in ulcerative colitis. The activity of the PLA2-II synthesis seems to be related to the degree of inflammation in the diseased bowel.

Zinc (Zn2+) binds to and stimulates the activity of group I but not group II phospholipase A2

Phospholipase A2 plays an important part in the generation of inflammatory lipid mediators and so it is of major interest to understand functional distinctions between structurally similar forms of phospholipase A2. In the present study, the influence of zinc (Zn2+) on the activity of group I and group II phospholipase A2 was examined in vitro. It appeared that Zn2+ (0.04-1 x 10(-3)M) increased group I phospholipase A2 activity from porcine pancreas and rat lung whereas the activity of group II phospholipase A2 from Crotalus atrox and Vipera russelli was unaffected. The presence of Cd2+ of Hg2+ (0.8-5 x 10(-3)M) also increased group I pancreatic phospholipase A2 activity while no augmentation was found with Cr2+, Fe2+ or Mg2+. The selective stimulation of group I phospholipase A2 by Zn2+ corresponded to a binding of these phospholipases A2 to a zinc-affinity column, while group II phospholipase A2 was not bound. Furthermore, the PLA2 activity in bronchoalveolar lavage fluid from rat was stimulated by Zn2+. These results indicate that Zn2+ binds to and increases the activity of group I, but not group II phospholipase A2. This difference in Zn(2+)-binding may be used to discriminate between group I and group II phospholipase A2 and to separate the enzymes from each other in complex biological materials. The possibility that activation of group I phospholipase A2 in the lung is important in zinc-induced metal fume fever is implied.

Cyclooxygenase-1 and cyclooxygenase-2 gene expression in human colorectal adenocarcinomas and in azoxymethane induced colonic tumours in rats

Increased prostaglandin E2 synthesis is considered important in both human and experimental colon carcinogenesis. It is not known, however, which cyclooxygenase isoenzyme is involved. The aim of this study was to compare the content of mRNA for cyclooxygenase-1 and cyclooxygenase-2 in colorectal cancers with the content in normal colonic specimens. Fifteen human colorectal adenocarcinomas, 35 azoxymethane induced colonic tumours from rats, and specimens of normal colon were analysed by reverse transcription and polymerase chain reaction (RT-PCR). It was found that cyclooxygenase-1 and cyclooxygenase-2 mRNA were increased in azoxymethane induced colonic tumours, compared with specimens taken adjacent to the tumours or from the macroscopically normal intestine distant from the tumours. Cyclooxygenase-1 and cyclooxygenase-2 mRNA were increased in specimens from the macroscopically normal intestine of azoxymethane treated animals, compared with colonic specimens from saline treated rats. Cyclooxygenase-2 mRNA, but not cyclooxygenase-1 mRNA, was increased in human colorectal cancers, compared with the adjacent mucosa or macroscopically normal mucosa distant from the tumours. The results suggest that cyclooxygenase-2 is involved in the increased prostaglandin E2 synthesis in colonic cancers, and that activation of this isoenzyme is an early event in colon carcinogenesis. However, cyclooxygenase-1 may also be involved, at least in experimental colon carcinogenesis.