Activation of human inflammatory cells by secreted phospholipases A2

Unraveling snake venom phospholipase A2: an overview of its structure, pharmacology, and inhibitors

Snake bite is a neglected disease that affects millions of people worldwide. WHO reported approximately 5 million people are bitten by various species of snakes each year, resulting in nearly 1 million deaths and an additional three times cases of permanent disability. Snakes utilize the venom mainly for immobilization and digestion of their prey. Snake venom is a composition of proteins and enzymes which is responsible for its diverse pharmacological action. Snake venom phospholipase A2 (SvPLA2) is an enzyme that is present in every snake species in different quantities and is known to produce remarkable functional diversity and pharmacological action like inflammation, necrosis, myonecrosis, hemorrhage, etc. Arachidonic acid, a precursor to eicosanoids, such as prostaglandins and leukotrienes, is released when SvPLA2 catalyzes the hydrolysis of the sn-2 positions of membrane glycerophospholipids, which is responsible for its actions. Polyvalent antivenom produced from horses or lambs is the standard treatment for snake envenomation, although it has many drawbacks. Traditional medical practitioners treat snake bites using plants and other remedies as a sustainable alternative. More than 500 plant species from more than 100 families reported having venom-neutralizing abilities. Plant-derived secondary metabolites have the ability to reduce the venom's adverse consequences. Numerous studies have documented the ability of plant chemicals to inhibit the enzymes found in snake venom. Research in recent years has shown that various small molecules, such as varespladib and methyl varespladib, effectively inhibit the PLA2 toxin. In the present article, we have overviewed the knowledge of snake venom phospholipase A2, its classification, and the mechanism involved in the pathophysiology of cytotoxicity, myonecrosis, anticoagulation, and inflammation clinical application and inhibitors of SvPLA2, along with the list of studies carried out to evaluate the potency of small molecules like varespladib and secondary metabolites from the traditional medicine for their anti-PLA2 effect.

Lipidomic analysis reveals altered lipid profiles of gingival tissues with periodontitis

AIM

The role of lipids in periodontitis has not been well studied. Thus, this study aimed to explore periodontitis-associated lipid profile changes and identify differentially expressed lipid metabolites in gingival tissues.

MATERIALS AND METHODS

Gingival tissues from 38 patients with periodontitis (periodontitis group) and 38 periodontally healthy individuals (control group) were collected. A UHPLC-QTOF-MS-based non-targeted metabolomics platform was used to identify and compare the lipid profiles of the two groups. The distribution and expression of related proteins were subsequently analyzed via immunohistochemistry to further validate the identified lipids.

RESULTS

Lipid profiles significantly differed between the two groups, and 20 differentially expressed lipid species were identified. Lysophosphatidylcholines (lysoPCs), diacylglycerols (DGs), and phosphatidylethanolamines (PEs) were significantly upregulated, while triacylglycerols (TGs) were downregulated in the periodontitis group. Moreover, the staining intensity of ABHD5/CGI-58, secretory phospholipase A2 (sPLA2), and sPLA2-IIA was significantly stronger in the gingival tissues of patients with periodontitis than in those of healthy controls.

CONCLUSIONS

LysoPCs, DGs, and PEs were significantly upregulated, whereas TGs were downregulated in gingival tissues of patients with periodontitis. Correspondingly, the immunohistochemical staining of ABHD5/CGI-58, sPLA2, and sPLA2-IIA in gingival tissues was consistent with the downstream production of lipid classes (lysoPCs, TGs, and DGs).

Inflammatory Effects of Bothrops Phospholipases A2: Mechanisms Involved in Biosynthesis of Lipid Mediators and Lipid Accumulation

Phospholipases A₂s (PLA₂s) constitute one of the major protein groups present in the venoms of viperid and crotalid snakes. Snake venom PLA₂s (svPLA₂s) exhibit a remarkable functional diversity, as they have been described to induce a myriad of toxic effects. Local inflammation is an important characteristic of snakebite envenomation inflicted by viperid and crotalid species and diverse svPLA₂s have been studied for their proinflammatory properties. Moreover, based on their molecular, structural, and functional properties, the viperid svPLA₂s are classified into the group IIA secreted PLA₂s, which encompasses mammalian inflammatory sPLA₂s. Thus, research on svPLA₂s has attained paramount importance for better understanding the role of this class of enzymes in snake envenomation and the participation of GIIA sPLA₂s in pathophysiological conditions and for the development of new therapeutic agents. In this review, we highlight studies that have identified the inflammatory activities of svPLA₂s, in particular, those from Bothrops genus snakes, which are major medically important snakes in Latin America, and we describe recent advances in our collective understanding of the mechanisms underlying their inflammatory effects. We also discuss studies that dissect the action of these venom enzymes in inflammatory cells focusing on molecular mechanisms and signaling pathways involved in the biosynthesis of lipid mediators and lipid accumulation in immunocompetent cells.

Exposure to PM2.5 during pregnancy causes lung inflammation in the offspring: Mechanism of action of mogrosides

Epidemiological and toxicological studies have demonstrated that exposure to fine particulate matter (PM2.5) during pregnancy is harmful to the tissues of the offspring. However, the mechanism by which PM2.5 exposure causes lung damage in the offspring or potential dietary therapy for this condition remains unclear. Mogrosides (MGs) are derived from the traditional plant Siraitia grosvenorii and are used medicinally, where they can moisten the lungs and relieve coughing. In this study, pregnant rats were exposed to PM2.5 by intratracheal instillation and treated with MGs by gavage to model the effect of PM2.5 in the offspring and the interventional effect of MGs on lung tissue. We then used transcriptomics, metabolomics, and RT-qPCR as tools to look for metabolite and genetic changes in the offspring. We found that when compared to the control group, the mRNA levels of the inflammatory mediator Pla2g2d and the metabolites lysophosphatidylcholines (LysoPCs) and arachidonic acid (AA) were up-regulated in the lung tissues of PM2.5 group. In contrast, these inflammatory changes were restored after treatment with MGs during pregnancy. In addition, the levels of AA, LPC 15:0 and LPC 18:0 were elevated in the PM2.5 group compared with control group. This increase was inhibited by co-administration of MGs. The change of PGA1 was adverse. In conclusion, even a relatively low exposure to PM2.5 in rats during pregnancy produces inflammation in the lungs of the male offspring, and an intervention with MGs could significantly alleviate this effect. Furthermore, Pla2g2d may represent a potential target for MGs resulting in the improvement of PM2.5-induced lung injury.

Role of human group IIA secreted phospholipase A2 in malaria pathophysiology: Insights from a transgenic mouse model

We previously showed that injection of recombinant human group IIA secreted phospholipase A₂ (hGIIA sPLA₂) to Plasmodium chabaudi-infected mice lowers parasitaemia by 20%. Here, we show that transgenic (TG) mice overexpressing hGIIA sPLA₂ have a peak of parasitaemia about 30% lower than WT littermates. During infection, levels of circulating sPLA₂, enzymatic activity and plasma lipid peroxidation were maximal at day-14, the peak of parasitaemia. Levels of hGIIA mRNA increased in liver but not in spleen and blood cells, suggesting that liver may contribute as a source of circulating hGIIA sPLA₂. Before infection, baseline levels of leukocytes and pro-inflammatory cytokines were higher in TG mice than WT littermates. Upon infection, the number of neutrophils, lymphocytes and monocytes increased and were maximal at the peak of parasitaemia in both WT and TG mice, but were higher in TG mice. Similarly, levels of the Th1 cytokines IFN-γ and IL-2 increased in WT and TG mice, but were 7.7- and 1.7-fold higher in TG mice. The characteristic shift towards Th2 cytokines was observed during infection in both WT and TG mice, with increased levels of IL-10 and IL-4 at day-14. The current data are in accordance with our previous in vitro findings showing that hGIIA kills parasites by releasing toxic lipids from oxidized lipoproteins. They further show that hGIIA sPLA₂ is induced during mouse experimental malaria and has a protective in vivo role, lowering parasitaemia by likely releasing toxic lipids from oxidized lipoproteins but also indirectly by promoting a more sustained innate immune response.

Roles of Immune Cells in Hereditary Angioedema

Hereditary angioedema (HAE) is a rare genetic disease, characterized by recurrent and unexpected potentially life-threatening mucosal swelling. HAE may be further classified into HAE with C1‐inhibitor deficiency (C1‐INH‐HAE) and HAE with normal C1‐INH activity (nlC1‐INH‐HAE), mostly due to mutations leading to increased vascular permeability. Recent evidence implicates also the innate and adaptive immune responses in several aspects of angioedema pathophysiology. Monocytes/macrophages, granulocytes, lymphocytes, and mast cells contribute directly or indirectly to the pathophysiology of angioedema. Immune cells are a source of vasoactive mediators, including bradykinin, histamine, complement components, or vasoactive mediators, whose concentrations or activities are altered in both attacks and remissions of HAE. In turn, through the expression of various receptors, these cells are also activated by a plethora of molecules. Thereby, activated immune cells are the source of molecules in the context of HAE, and on the other hand, increased levels of certain mediators can, in turn, activate immune cells through the engagement of specific surface receptors and contribute to vascular endothelial processes that lead to hyperpemeability and tissue edema. In this review, we summarize recent developments in the putative involvement of the innate and adaptive immune system of angioedema.

Diclofenac N-Derivatives as Therapeutic Agents with Anti-Inflammatory and Anti-Cancer Effect

A series of diclofenac N-derivatives (2, 4, 6, 8c, 9c, 10a-c) were synthesized in order to test their anti-cancer and anti-inflammatory effects. The anticarcinogen activity has been assayed against three cancer cell lines: HT29, human colon cancer cells; Hep-G2, human hepatic cells; and B16-F10, murine melanoma cells. First, we determined the cytotoxicity of the different compounds, finding that the most effective compound was compound 8c against all cell lines and both compounds 4 and 6 in human Hep-G2 and HT29 cell lines. Compounds 4 and 8c were selected for the percentage of apoptosis determination, cell cycle distribution, and mitochondrial membrane potential measure because these products presented the lowest IC₅₀ values in two of the three cancer cell lines assayed (B16-F10 and HepG2), and were two of the three products with lowest IC₅₀ in HT29 cell line. Moreover, the percentages of apoptosis induction were determined for compounds 4 and 8c, showing that the highest values were between 30 to 60%. Next, the effects of these two compounds were observed on the cellular cycle, resulting in an increase in the cell population in G2/M cell cycle phase after treatment with product 8c, whereas compound 4 increased the cells in phase G0/G1, by possible differentiation process induction. Finally, to determine the possible apoptosis mechanism triggered by these compounds, mitochondrial potential was evaluated, indicating the possible activation of extrinsic apoptotic mechanism. On the other hand, we studied the anti-inflammatory effects of these diclofenac (DCF) derivatives on lipopolysaccharide (LPS) activated RAW 264.7 macrophages-monocytes murine cells by inhibition of nitric oxide (NO) production. As a first step, we determined the cytotoxicity of the synthesized compounds, as well as DCF, against these cells. Then, sub-cytotoxic concentrations were used to determine NO release at different incubation times. The greatest anti-inflammatory effect was observed for products 2, 4, 8c, 10a, 10b, and 9c at 20 µg·mL^-1 concentration after 48 h of treatment, with inhibition of produced NO between 60 to 75%, and a concentration that reduces to the 50% the production of NO (IC_{50 NO}) between 2.5 to 25 times lower than that of DCF. In this work, we synthesized and determined for the first time the anti-cancer and anti-inflammatory potential of eight diclofenac N-derivatives. In agreement with the recent evidences suggesting that inflammation may contribute to all states of tumorigenesis, the development of these new derivatives capable of inducing apoptosis and anti-inflammatory effects at very low concentrations represent new effective therapeutic strategies against these diseases.

Macrophage-polarizing stimuli differentially modulate the inflammatory profile induced by the secreted phospholipase A2 group IA in human lung macrophages

In this study we investigated the effects of snake venom Group IA secreted phospholipase A₂ (svGIA) on the release of inflammatory and angiogenic mediators from human lung macrophages (HLMs). HLMs were incubated with lipopolysaccharide (LPS) or svGIA with or without macrophage-polarizing stimuli (IL-4, IL-10, IFN-γ or the adenosine analogue NECA). M2-polarizing cytokines (IL-4 and IL-10) inhibited TNF-α, IL-6, IL-12, IL-1β, CXCL8 and CCL1 release induced by both LPS and svGIA. IL-4 inhibited also the release of IL-10. IFN-γ reduced IL-10 and IL-12 and increased CCL1 release by both the LPS and svGIA-stimulated HLMs, conversely IFN-γ reduced IL-1β only by svGIA-stimulated HLMs. In addition, IFNγ promoted TNF-α and IL-6 release from svGIA-stimulated HLMs to a greater extent than LPS. NECA inhibited TNF-α and IL-12 but promoted IL-10 release from LPS-stimulated HLMs according to the well-known effect of adenosine in down-regulating M1 activation. By contrast NECA reduced TNF-α, IL-10, CCL1 and IL-1β release from svGIA-activated HLM. IL-10 and NECA increased both LPS- and svGIA-induced vascular endothelial growth factor A (VEGF-A) release. By contrast, IL-10 reduced angiopoietin-1 (ANGPT1) production from activated HLMs. IFN-γ and IL-4 reduced VEGF-A and ANGPT1 release from both LPS- and svGIA-activated HLMs. Moreover, IL-10 inhibited LPS-induced ANGPT2 production. In conclusion, we demonstrated a fine-tuning modulation of svGIA-activated HLMs differentially exerted by the classical macrophage-polarizing cytokines.

Polymorphism of Secretary PLA2G2A Gene Associated with Its Serum Level in Type2 Diabetes Mellitus Patients in Northern Iran

BACKGROUND

Inflammation may occur in Type2 diabetes mellitus. sPLA2 is among the factors that contribute to the activation of pathways involved in inflammation. Several agents affect serum sPLA2 level, one of which is genetic diversity.

OBJECTIVE

The current study was performed to determine whether there is a relationship between sPLA2 gene (-763C > G) polymorphism and circulating sPLA2 level in patients with Type 2 diabetes.

METHODS

DNA was extracted from blood samples and used for the amplification of sPLA2 gene using ARMS-PCR.

RESULTS

A statistical analysis using SPSS (version 16) revealed a significant correlation between -763C > G sPLA2 gene polymorphisms and the disease incidence in patients with T2DM. Among the three possible genotypes (GG, CC, and CG), CG genotype was found to have a higher frequency(53%) in T2DM patients. GG and CC genotypes frequencies were 20 and 27%, respectively. In healthy individuals, the frequencies of CC, GG, and GC genotypes were 77, 9.8% and 13.2%, respectively). Patients with genotype GG had the highest level of sPLA2. We showed that C>G polymorphism at position- 763 is associated with a high level of sPLA2 in both T2DM patients and healthy individuals. The average of sPLA2 circulating level was (170.48± 84.90), (106.62 ± 74.31), in patients and normal individuals, respectively.

CONCLUSION

Our findings show that sPLA2 serum level is significantly higher in patients with T2DM disease than that in healthy individuals.

Altered Metabolism of Phospholipases, Diacylglycerols, Endocannabinoids, and N-Acylethanolamines in Patients with Mastocytosis

Background

Mastocytosis is a condition characterized by the expansion and accumulation of mast cells (MCs) in various organs. The symptoms are related to the increased release of MC-derived mediators that exert local and distant effects. MCs are a source and target of phospholipase enzymes (PLs), which catalyze the cleavage of membrane phospholipids releasing lipid mediators (e.g., diacylglycerols (DAGs) and the endocannabinoid (EC) 2-arachidonoylglycerol (2-AG)). To date, there are no data on the role of these lipid mediators in mastocytosis. Here, we analyzed plasma levels of PLA₂, PLC, DAG, ECs, and EC-related N-acylethanolamines in patients with mastocytosis.

Methods

In 23 patients with mastocytosis and 23 healthy individuals, we measured plasma PLA₂ and PLC activities, DAG, 2-AG, anandamide (AEA), palmitoylethanolamide (PEA), and oleoylethanolamide (OEA).

Results

Plasma PLA₂ and PLC activities were increased in mastocytosis patients compared to controls. Concentrations of DAG (18:1 20:4 and 18:0 20:4), two second messengers produced by PLC, were higher in mastocytosis compared to controls, whereas the concentrations of their metabolite, 2-AG, were not altered. AEA was decreased in mastocytosis patients compared to controls; by contrast, AEA congener, PEA, was increased. PLA₂ and PLC activities were increased only in patients with mediator-related symptoms. Moreover, PLC activity was positively correlated with disease severity and tryptase concentrations. By contrast, AEA was negatively correlated with tryptase concentrations.

Conclusions

PLs and some lipid mediators are altered in patients with mastocytosis. Our results may pave the way for investigating the functions of these mediators in the pathophysiology of mastocytosis and provide new potential biomarkers and therapeutic targets.

Evaluation of a ketogenic diet for improvement of neurological recovery in individuals with acute spinal cord injury: a pilot, randomized safety and feasibility trial

Study design

Longitudinal, randomized study.

Objectives

(1) Test the safety and feasibility of a ketogenic diet (KD) intervention in the acute stages of spinal cord injury (SCI), (2) assess the effects of a KD on neurological recovery, and (3) identify potential serum biomarkers associated with KD-induced changes in neurological recovery.

Setting

Acute care and rehabilitation facility.

Methods

The KD is a high-fat, low-carbohydrate diet that includes ≈70-80% total energy as fat. Seven participants with acute complete and incomplete SCI (AIS A-D) were randomly assigned to KD (n = 4) or standard diet (SD, n = 3). Neurological examinations, resting energy expenditure analysis, and collection of blood for evaluation of circulating ketone levels were performed within 72 h of injury and before discharge. Untargeted metabolomics analysis was performed on serum samples to identify potential serum biomarkers that may explain differential responses between groups.

Results

Our pilot findings primarily demonstrated that KD is safe and feasible to be administered in acute SCI. Furthermore, upper extremity motor scores were higher (p < 0.05) in the KD vs. SD group and an anti-inflammatory lysophospholipid, lysoPC 16:0, was present at higher levels, and an inflammatory blood protein, fibrinogen, was present at lower levels in the KD serum samples vs. SD serum samples.

Conclusion

Taken together, these preliminary results suggest that a KD may have anti-inflammatory effects that may promote neuroprotection, resulting in improved neurological recovery in SCI. Future studies with larger sample size are warranted for demonstrating efficacy of KD for improving neurological recovery.

Phospholipase A2 catalysis and lipid mediator lipidomics

Phospholipase A₂ (PLA₂) enzymes are the upstream regulators of the eicosanoid pathway liberating free arachidonic acid from the sn-2 position of membrane phospholipids. Free intracellular arachidonic acid serves as a substrate for the eicosanoid biosynthetic enzymes including cyclooxygenases, lipoxygenases, and cytochrome P450s that lead to inflammation. The Group IVA cytosolic (cPLA₂), Group VIA calcium-independent (iPLA₂), and Group V secreted (sPLA₂) are three well-characterized human enzymes that have been implicated in eicosanoid formation. In this review, we will introduce and summarize the regulation of catalytic activity and cellular localization, structural characteristics, interfacial activation and kinetics, substrate specificity, inhibitor binding and interactions, and the downstream implications for eicosanoid biosynthesis of these three important PLA₂ enzymes.

Secreted Phospholipases A2 in Hereditary Angioedema With C1-Inhibitor Deficiency

Background

Hereditary angioedema (HAE) caused by deficiency (type I) or dysfunction (type II) of the C1 inhibitor protein (C1-INH-HAE) is a disabling, potentially fatal condition characterized by recurrent episodes of swelling. We have recently found that patients with C1-INH-HAE have increased plasma levels of vascular endothelial growth factors and angiopoietins (Angs), which have been associated with vascular permeability in several diseases. Among these and other factors, blood endothelial cells and vascular permeability can be modulated by extracellular or secreted phospholipases A₂ (sPLA₂s).

Objective

We sought to investigate the enzymatic activity and biological functions of sPLA₂ in patients with C1-INH-HAE.

Methods

sPLA₂s enzymatic activity was evaluated in the plasma from 109 adult patients with C1-INH-HAE and 68 healthy donors in symptom-free period and attacks. Plasma level of group IIA sPLA₂ (hGIIA) protein was measured in selected samples. The effect of C1-INH-HAE plasma on endothelial permeability was examined in vitro using a vascular permeability assay. The role of hGIIA was determined using highly specific sPLA₂ indole inhibitors. The effect of recombinant hGIIA on C1-INH activity was examined in vitro by functional assay.

Results

Plasma sPLA₂ activity and hGIIA levels are increased in symptom-free C1-INH-HAE patients compared with controls. sPLA₂ activity negatively correlates with C1-INH protein level and function. C1-INH-HAE plasma increases endothelial permeability in vitro, and this effect is partially reverted by a specific hGIIA enzymatic inhibitor. Finally, recombinant hGIIA inhibits C1-INH activity in vitro.

Conclusion

sPLA₂ enzymatic activity (likely attributable to hGIIA), which is increased in C1-INH-HAE patients, can promote vascular permeability and impairs C1-INH activity. Our results may pave the way for investigating the functions of sPLA₂s (in particular, hGIIA) in the pathophysiology of C1-INH-HAE and may inform the development of new therapeutic targets.

A Review of Chronic Musculoskeletal Pain: Central and Peripheral Effects of Diclofenac

Diclofenac is widely used to manage chronic inflammatory and degenerative joint diseases such as osteoarthritis (OA), rheumatoid arthritis (RA), ankylosing spondylitis, and extra-articular rheumatism. Its various mechanisms of action make it particularly effective in treating nociceptive pain, but it is also an alternative for treating spinal and chronic central pain. Osteoarthritis and rheumatoid arthritis are the most frequently encountered arthritic conditions in adults. The management of nociceptive pain requires a sequential hierarchical approach, with the initial NSAID treatment being characterized by the replacement of one drug with another, or complete discontinuation usually because of insufficient pain control. OA- and RA-related pain is complex and multifactorial, and due to physiological interactions between the signaling of the central and peripheral nervous systems. The mechanisms of action of diclofenac make it particularly effective in treating both nociceptive pain and chronic central pain. This review underlines the mechanisms of diclofenac involved in chronic and acute joint pain, the most relevant adverse events.

Discriminant biomarkers of acute respiratory distress syndrome associated to H1N1 influenza identified by metabolomics HPLC-QTOF-MS/MS platform

Acute respiratory distress syndrome (ARDS) is a serious complication of influenza A (H1N1) virus infection. Its pathogenesis is unknown and biomarkers are lacking. Untargeted metabolomics allows the analysis of the whole metabolome in a biological compartment, identifying patterns associated with specific conditions. We hypothesized that LC-MS could help identify discriminant metabolites able to define the metabolic alterations occurring in patients with influenza A (H1N1) virus infection that developed ARDS. Serum samples from patients diagnosed with 2009 influenza A (H1N1) virus infection with (n = 25) or without (n = 32) ARDS were obtained on the day of hospital admission and analyzed by LC-MS/MS. Metabolite identification was determined by MS/MS analysis and analysis of standards. The specificity of the patterns identified was confirmed in patients without 2009 influenza A(H1N1) virus pneumonia (15 without and 17 with ARDS). Twenty-three candidate biomarkers were found to be significantly different between the two groups, including lysophospholipids and sphingolipids related to inflammation; bile acids, tryptophan metabolites, and thyroxine, related to the metabolism of the gut microflora. Confirmation results demonstrated the specificity of major alterations occurring in ARDS patients with influenza A (H1N1) virus infection.

Restoring pulmonary surfactant membranes and films at the respiratory surface

Pulmonary surfactant is a complex of lipids and proteins assembled and secreted by the alveolar epithelium into the thin layer of fluid coating the respiratory surface of lungs. There, surfactant forms interfacial films at the air-water interface, reducing dramatically surface tension and thus stabilizing the air-exposed interface to prevent alveolar collapse along respiratory mechanics. The absence or deficiency of surfactant produces severe lung pathologies. This review describes some of the most important surfactant-related pathologies, which are a cause of high morbidity and mortality in neonates and adults. The review also updates current therapeutic approaches pursuing restoration of surfactant operative films in diseased lungs, mainly through supplementation with exogenous clinical surfactant preparations. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Group V Secreted Phospholipase A2 Induces the Release of Proangiogenic and Antiangiogenic Factors by Human Neutrophils

Secreted phospholipases A₂ (sPLA₂s) are extracellular enzymes that catalyze the release of free fatty acids and lysophospholipids from membrane phospholipids and also bind to different receptors (e.g., PLA₂R1 or integrins). To date, 12 mammalian sPLA₂s have been identified, which play a critical role in pathophysiological processes including inflammation and cancer. sPLA₂s activate immune cells such as human neutrophils (PMNs) by enzymatic activity- or receptor-mediated mechanisms. In addition, human PMNs synthesize and store human group V (hGV) and human group X (hGX) sPLA₂s in their granules, but only the former is released upon cellular activation. We investigated the effects of sPLA₂s on the release of proangiogenic and antiangiogenic factors by PMNs. We found that exogenous hGV and hGX sPLA₂s induce the release of vascular endothelial growth factor (VEGF)-A, angiopoietin 1 (Ang1), and CXCL8/IL-8. Only hGV induces the secretion of the antiangiogenic isoform of VEGF-A, namely, VEGF-A_165b. While the release of VEGF-A, Ang1, and CXCL8/IL-8 was likely mediated by hGV enzymatic activity and/or binding to PLA₂R1 and heparan sulfate proteoglycans, the release of VEGF-A_165b requires the interaction with α_Vβ₃ and α₄β₁ integrins. We also provide evidence that endogenous hGV released by N-formyl-met-leu-phe (fMLF)-activated PMNs is involved in the release of angiogenic factors. The translational relevance of these data is supported by our findings that hGV expression is increased in human samples of lung cancer which are infiltrated by PMNs. Overall, our results suggest that the hGV-neutrophil axis may play a relevant role in the modulation of cancer-related inflammation and angiogenesis.

Inhibitory effects of bee venom and its components against viruses in vitro and in vivo

Bee venom (BV) from honey bee (Apis Melifera L.) contains at least 18 pharmacologically active components including melittin (MLT), phospholipase A₂ (PLA₂), and apamin etc. BV is safe for human treatments dose dependently and proven to possess different healing properties including antibacterial and antiparasitidal properties. Nevertheless, antiviral properties of BV have not well investigated. Hence, we identified the potential antiviral properties of BV and its component against a broad panel of viruses. Co-incubation of non-cytotoxic amounts of BV and MLT, the main component of BV, significantly inhibited the replication of enveloped viruses such as Influenza A virus (PR8), Vesicular Stomatitis Virus (VSV), Respiratory Syncytial Virus (RSV), and Herpes Simplex Virus (HSV). Additionally, BV and MLT also inhibited the replication of non-enveloped viruses such as Enterovirus-71 (EV-71) and Coxsackie Virus (H3). Such antiviral properties were mainly explained by virucidal mechanism. Moreover, MLT protected mice which were challenged with lethal doses of pathogenic influenza A H1N1 viruses. Therefore, these results provides the evidence that BV and MLT could be a potential source as a promising antiviral agent, especially to develop as a broad spectrum antiviral agent.

Insulin resistance in prepubertal obese children correlates with sex-dependent early onset metabolomic alterations

Background:

Insulin resistance (IR) is usually the first metabolic alteration diagnosed in obese children and the key risk factor for development of comorbidities. The factors determining whether or not IR develops as a result of excess body mass index (BMI) are still not completely understood.

Objectives:

This study aimed to elucidate the mechanisms underpinning the predisposition toward hyperinsulinemia-related complications in obese children by using a metabolomic strategy that allows a profound interpretation of metabolic profiles potentially affected by IR.

Methods:

Serum from 60 prepubertal obese children (30 girls/30 boys, 50% IR and 50% non-IR in each group, but with similar BMIs) were analyzed by using liquid chromatography–mass spectrometry, gas chromatography–mass spectrometry and capillary electrophoresis–mass spectrometry following an untargeted metabolomics approach. Validation was then performed on a group of 100 additional children with the same characteristics.

Results:

When obese children with and without IR were compared, 47 metabolites out of 818 compounds (P<0.05) obtained after data pre-processing were found to be significantly different. Bile acids exhibit the greatest changes (that is, approximately a 90% increase in IR). The majority of metabolites differing between groups were lysophospholipids (15) and amino acids (17), indicating inflammation and central carbon metabolism as the most altered processes in impaired insulin signaling. Multivariate analysis (OPLS-DA models) showed subtle differences between groups that were magnified when females were analyzed alone.

Conclusions:

Inflammation and central carbon metabolism, together with the contribution of the gut microbiota, are the most altered processes in obese children with impaired insulin signaling in a sex-specific fashion despite their prepubertal status.

Molecular and cellular mechanisms linking inflammation to insulin resistance and β-cell dysfunction

Obesity is a major public health problem worldwide, and it is associated with an increased risk of developing type 2 diabetes. It is now commonly accepted that chronic inflammation associated with obesity induces insulin resistance and β-cell dysfunction in diabetic patients. Obesity-associated inflammation is characterized by increased abundance of macrophages and enhanced production of inflammatory cytokines in adipose tissue. Adipose tissue macrophages are suggested to be the major source of local and systemic inflammatory mediators such as tumor necrosis factor α, interleukin (IL)-1β, and IL-6. These cytokines induce insulin resistance in insulin target tissues by activating the suppressors of cytokine signaling proteins, several kinases such as c-Jun N-terminal kinase, IκB kinase β, and protein kinase C, inducible nitric oxide synthase, extracellular signal-regulated kinase, and protein tyrosine phosphatases such as protein tyrosine phosphatase 1B. These activated factors impair the insulin signaling at the insulin receptor and the insulin receptor substrates levels. The same process most likely occurs in the pancreas as it contains a pool of tissue-resident macrophages. High concentrations of glucose or palmitate via the chemokine production promote further immune cell migration and infiltration into the islets. These events ultimately induce inflammatory responses leading to the apoptosis of the pancreatic β cells. In this review, the cellular and molecular players that participate in the regulation of obesity-induced inflammation are discussed, with particular attention being placed on the roles of the molecular players linking inflammation to insulin resistance and β-cell dysfunction.

Immune Cells and Metabolism

Low-grade inflammation in the obese AT (AT) and the liver is a critical player in the development of obesity-related metabolic dysregulation, including insulin resistance, type 2 diabetes and non-alcoholic steatohepatitis (NASH). Myeloid as well as lymphoid cells infiltrate the AT and the liver and expand within these metabolic organs as a result of excessive nutrient intake, thereby exacerbating tissue inflammation. Macrophages are the paramount cell population in the field of metabolism-related inflammation; as obesity progresses, a switch takes place within the AT environment from an M2-alternatively activated macrophage state to an M1-inflammatory macrophage-dominated milieu. M1-polarized macrophages secrete inflammatory cytokines like TNF in the obese AT; such cytokines contribute to insulin resistance in adipocytes. Besides macrophages, also CD8+ T cells promote inflammation in the AT and the liver and thereby the deterioration of the metabolic balance in adipocytes and hepatocytes. Other cells of the innate immunity, such as neutrophils or mast cells, interfere with metabolic homeostasis as well. On the other hand, eosinophils or T-regulatory cells, the number of which in the AT decreases in the course of obesity, function to maintain metabolic balance by ameliorating inflammatory processes. In addition, eosinophils and M2-polarized macrophages may contribute to "beige" adipogenesis under lean conditions; beige adipocytes are located predominantly in the subcutaneous AT and have thermogenic and optimal energy-dispensing properties like brown adipocytes. This chapter will summarize the different aspects of the regulation of homeostasis of metabolic tissues by immune cells.

Lipidome and transcriptome profiling of pneumolysin intoxication identifies networks involved in statin-conferred protection of airway epithelial cells

Pneumonia remains one of the leading causes of death in both adults and children worldwide. Despite the adoption of a wide variety of therapeutics, the mortality from community-acquired pneumonia has remained relatively constant. Although viral and fungal acute airway infections can result in pneumonia, bacteria are the most common cause of community-acquired pneumonia, with Streptococcus pneumoniae isolated in nearly 50% of cases. Pneumolysin is a cholesterol-dependent cytolysin or pore-forming toxin produced by Streptococcus pneumonia and has been shown to play a critical role in bacterial pathogenesis. Airway epithelium is the initial site of many bacterial contacts and its barrier and mucosal immunity functions are central to infectious lung diseases. In our studies, we have shown that the prior exposure to statins confers significant resistance of airway epithelial cells to the cytotoxicity of pneumolysin. We decided to take this study one step further, assessing changes in both the transcriptome and lipidome of human airway epithelial cells exposed to toxin, statin or both. Our current work provides the first global view in human airway epithelial cells of both the transcriptome and the lipid interactions that result in cellular protection from pneumolysin.

Effect of azithromycin on the LPS-induced production and secretion of phospholipase A2 in lung cells

Azithromycin is a member of macrolides, utilized in the treatment of infections. Independently, these antibiotics also possess anti-inflammatory and immunomodulatory properties. Phospholipase A2 isotypes, which are implicated in the pathophysiology of inflammatory lung disorders, are produced by alveolar macrophages and other lung cells during inflammatory response and can promote lung injury by destructing lung surfactant. The aim of the study was to investigate whether in lung cells azithromycin can inhibit secretory and cytosolic phospholipases A2, (sPLA2) and (cPLA2), respectively, which are induced by an inflammatory trigger. In this respect, we studied the lipopolysaccharide (LPS)-mediated production or secretion of sPLA2 and cPLA2 from A549 cells, a cancer bronchial epithelial cell line, and alveolar macrophages, isolated from bronchoalveolar lavage fluid of ARDS and control patients without cardiopulmonary disease or sepsis. Pre-treatment of cells with azithromycin caused a dose-dependent decrease in the LPS-induced sPLA2-IIA levels in A549 cells. This inhibition was rather due to reduced PLA2G2A mRNA expression and secretion of sPLA2-IIA protein levels, as observed by western blotting and indirect immunofluorescence by confocal microscopy, respectively, than to the inhibition of the enzymic activity per se. On the contrary, azithromycin had no effect on the LPS-induced production or secretion of sPLA2-IIA from alveolar macrophages. The levels of LPS-induced c-PLA2 were not significantly affected by azithromycin in either cell type. We conclude that azithromycin exerts anti-inflammatory properties on lung epithelial cells through the inhibition of both the expression and secretion of LPS-induced sPLA2-IIA, while it does not affect alveolar macrophages.

20(S)-Protopanaxatriol inhibits release of inflammatory mediators in immunoglobulin E-mediated mast cell activation

Background

Antiallergic effect of 20(S)-protopanaxatriol (PPT), an intestinal metabolite of ginseng saponins, was investigated in guinea pig lung mast cells and mouse bone marrow-derived mast cells activated by a specific antigen/antibody reaction.

Methods

Increasing concentrations of PPT were pretreated 5 min prior to antigen stimulation, and various inflammatory mediator releases and their relevant cellular signaling events were measured in those cells.

Results

PPT dose-dependently reduced the release of histamine and leukotrienes in both types of mast cells. Especially, in activated bone marrow-derived mast cells, PPT inhibited the expression of Syk protein, cytokine mRNA, cyclooxygenase-1/2, and phospholipase A₂ (PLA₂), as well as the activities of various protein kinase C isoforms, mitogen-activated protein kinases, PLA₂, and transcription factors (nuclear factor-κB and activator protein-1).

Conclusion

PPT reduces the release of inflammatory mediators via inhibiting multiple cellular signaling pathways comprising the Ca²⁺ influx, protein kinase C, and PLA₂, which are propagated by Syk activation upon allergic stimulation of mast cells.

Bacillus thuringiensis membrane-damaging toxins acting on mammalian cells

Bacillus thuringiensis is widely used as a biopesticide in forestry and agriculture, being able to produce potent species-specific insecticidal toxins and considered nonpathogenic to other animals. More recently, however, repeated observations are documenting the association of this microorganism with various infectious diseases in humans, such as food-poisoning-associated diarrheas, periodontitis, bacteremia, as well as ocular, burn, and wound infections. Similar to B. cereus, B. thuringiensis produces an array of virulence factors acting against mammalian cells, such as phosphatidylcholine- and phosphatidylinositol-specific phospholipase C (PC-PLC and PI-PLC), hemolysins, in particular hemolysin BL (HBL), and various enterotoxins. The contribution of some of these toxins to B. thuringiensis pathogenicity has been studied in animal models of infection, following intravitreous, intranasal, or intratracheal inoculation. These studies lead to the speculation that the activities of PC-PLC, PI-PLC, and HBL are responsible for most of the pathogenic properties of B. thuringiensis in nongastrointestinal infections in mammals. This review summarizes data regarding the biological activity, the genetic basis, and the structural features of these membrane-damaging toxins.

Taiwan cobra phospholipase A2 suppresses ERK-mediated ADAM17 maturation, thus reducing secreted TNF-α production in human leukemia U937 cells

The goal of this study was to explore the signaling pathway regulating the processing of proADAM17 into ADAM17 in Taiwan cobra phospholipase A2 (PLA2)-treated human leukemia U937 cells. PLA2 induced reactive oxygen species (ROS)-elicited p38 MAPK activation and ERK inactivation in U937 cells. Catalytically inactive bromophenacylated PLA2 (BPB-PLA2) and PLA2 mutants evoked Ca(2+)-mediated p38 MAPK activation, and the level of phosphorylated ERK remained unchanged. PLA2 treatment reduced mature ADAM17 expression and secreted TNF-α (sTNF-α) production. Co-treatment of SB202190 (p38 MAPK inhibitor) and catalytically inactive PLA2 increased ERK phosphorylation, ADAM17 maturation and sTNF-α production. Nevertheless, mRNA levels of ADAM17 and TNF-α were insignificantly altered after PLA2 and SB202190/BPB-PLA2 treatment. ADAM17 activity assay and knock-down of ADAM17 revealed that ADAM17 was involved in sTNF-α production. Restoration of ERK activation increased the processing of proADAM17 into ADAM17 in PLA2-treated cells, while inactivation of ERK reduced ADAM17 maturation in untreated and SB202190/BPB-PLA2-treated cells. Removal of cell surface heparan sulfate abrogated PLA2 and SB202190/BPB-PLA2 effect on ADAM17 maturation. Taken together, the present data reveal that PLA2 suppresses ERK-mediated ADAM17 maturation, thus reducing sTNF-α production in U937 cells. Moreover, the binding with heparan sulfate is crucial for the PLA2 effect.

Secreted phospholipase A2 is increased in meconium-stained amniotic fluid of term gestations: potential implications for the genesis of meconium aspiration syndrome

BACKGROUND

Meconium-stained amniotic fluid (MSAF) represents the passage of fetal colonic content into the amniotic cavity. Meconium aspiration syndrome (MAS) is a complication that occurs in a subset of infants with MSAF. Secreted phospholipase A2 (sPLA2) is detected in meconium and is implicated in the development of MAS. The purpose of this study was to determine if sPLA2 concentrations are increased in the amniotic fluid of women in spontaneous labor at term with MSAF.

MATERIALS AND METHODS

This was a cross-sectional study of patients in spontaneous term labor who underwent amniocentesis (n = 101). The patients were divided into two study groups: (1) MSAF (n = 61) and (2) clear fluid (n = 40). The presence of bacteria and endotoxin as well as interleukin-6 (IL-6) and sPLA2 concentrations in the amniotic fluid were determined. Statistical analyses were performed to test for normality and bivariate analysis. The Spearman correlation coefficient was used to study the relationship between sPLA2 and IL-6 concentrations in the amniotic fluid.

RESULTS

Patients with MSAF have a higher median sPLA2 concentration (ng/mL) in amniotic fluid than those with clear fluid [1.7 (0.98-2.89) versus 0.3 (0-0.6), p < 0.001]. Among patients with MSAF, those with either microbial invasion of the amniotic cavity (MIAC, defined as presence of bacteria in the amniotic cavity), or bacterial endotoxin had a significantly higher median sPLA2 concentration (ng/mL) in amniotic fluid than those without MIAC or endotoxin [2.4 (1.7-6.0) versus 1.7 (1.3-2.5), p < 0.05]. There was a positive correlation between sPLA2 and IL-6 concentrations in the amniotic fluid (Spearman Rho = 0.3, p < 0.05).

CONCLUSION

MSAF that contains bacteria or endotoxin has a higher concentration of sPLA2, and this may contribute to induce lung inflammation when meconium is aspirated before birth.

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.

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.

The expression of genes encoding for COX-2, MPO, iNOS, and sPLA2-IIA in patients with recurrent depressive disorder

BACKGROUND

There is evidence that inflammation, oxidative and nitrosative stress (IO&NS) play a role in the pathophysiology of depression. There are also data indicating altered inflammatory gene expression in depressive disorder and that genetic variants of IO&NS genes are associated with increased risk of the disease in question. The aim of this study was to explore mRNA expression of four IO&NS genes PTGS2, MPO, NOS2A, and PLA2G2A coding respectively: cyclooxygenase-2 (COX-2), myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS) and secretory phospholipase A2 type IIA (sPLA2-IIA).

METHOD

Expression of the mRNA was determined using quantitative real-time PCR, in peripheral blood cells of patients with recurrent depressive disorder (rDD) and normal controls.

RESULTS

The mRNA expressions of the genes encoding for COX-2, MPO, iNOS and sPLA2-IIA were significantly increased in the peripheral blood cells of depressed patients versus controls.

LIMITATIONS

Patients were treated with antidepressants.

CONCLUSION

Our results indicate and may confirm the role of peripheral IO&NS pathways in the pathophysiology of depression. The results represent a promising way to investigate biological markers of depression.

Gene expression signatures differ with extent of atherosclerosis in monkey iliac artery

OBJECTIVE

The aim of this study was to evaluate global gene expression patterns in the common iliac arteries of monkeys with a varied extent of atherosclerosis.

METHODS

The left common iliac artery was removed from ovariectomized cynomolgus monkeys (n = 12) after 6.5 years of consuming a diet containing fat and cholesterol at levels comparable with those consumed in Western populations. Arterial gene expression was analyzed using DNA microarray and real-time reverse transcription-polymerase chain reaction.

RESULTS

Significant differential expression of 986 genes was observed in iliac arteries containing moderate to large atherosclerotic plaques compared with normal/minimally affected reference group arteries. Atherosclerosis-associated genes included cytokines, chemokines, components of signal transduction pathways, and transcriptional activators and repressors, as well as other functional categories. Real-time reverse transcription-polymerase chain reaction confirmed a differential expression of genes chosen from a variety of functional categories. Specifically, the expression of genes for estrogen receptor-1, claudin 11, and brain heart protocadherin 7 was reduced, whereas the expression of genes for apolipoprotein E, growth differentiation factor 15, superoxide dismutase-2, SET domain bifurcated 2, phospholipase A2 group IIA, phospholipase A2 group VII, and ring finger protein 149 was increased in atherosclerotic arteries.

CONCLUSIONS

The gene expression environment in arteries containing atherosclerotic plaques is profoundly different from that of relatively unaffected arteries and reflects the cellular and molecular complexity of atherosclerosis and associated arterial remodeling processes.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Phospholipase A2 mediates apolipoprotein-independent uptake of chylomicron remnant-like particles by human macrophages

Apolipoprotein E-receptor-mediated pathways are the main routes by which macrophages take up chylomicron remnants, but uptake may also be mediated by receptor-independent routes. To investigate these mechanisms, triacylglycerol (TG) accumulation induced by apolipoprotein-free chylomicron remnant-like particles (CRLPw/o) in human monocyte-derived macrophages was evaluated. Macrophage TG content increased about 5-fold after incubation with CRLPw/o, and this effect was not reduced by the inhibition of phagocytosis, macropinocytosis, apolipoprotein E function, or proteoglycan bridging. The role of lipases, including lipoprotein lipase, cholesteryl ester hydrolase, and secretory (sPLA2) and cytosolic phospholipase A2, was studied using [³H]TG-labelled CRLPw/o. Total cell radioactivity after incubation with [³H]TG CRLPw/o was reduced by 15–30% by inhibitors of lipoprotein lipase and cholesteryl ester hydrolase and by about 45% by inhibitors of sPLA2 and cytosolic PLA₂ . These results suggest that macrophage lipolytic enzymes mediate the internalization of postprandial TG-rich lipoproteins and that sPLA₂ and cytosolic PLA2, play a more important role than extracellular lipoprotein lipase-mediated TG hydrolysis.

Group V secretory phospholipase A2 plays a pathogenic role in myocardial ischaemia-reperfusion injury

AIMS

Group V secretory phospholipase A(2) (sPLA(2)-V) is highly expressed in the heart. This study examined (i) the role of sPLA(2)-V in myocardial ischaemia-reperfusion (I/R) injury and (ii) the cooperative action of sPLA(2)-V and cytosolic PLA(2) (cPLA(2)) in myocardial I/R injury, using sPLA(2)-V knockout (sPLA(2)V(-/-)) mice.

METHODS AND RESULTS

Myocardial I/R injury was created by 1 h ligation of the left anterior descending coronary artery, followed by 24 h of reperfusion. The sPLA(2)V(-/-) mice had a 44% decrease in myocardial infarct size, a preservation of echocardiographic LV function (%fractional shortening: 40 ± 3.5 vs. 21 ± 4.6, respectively), and lower content of leucotriene B(4) (LTB(4)) and thromboxane B(2) (TXB(2)) (40 and 37% lower, respectively) in the ischaemic myocardium after I/R compared with wild-type (WT) mice. Intraperitoneal administration of AACOCF3 or MAFP, inhibitors of cPLA(2) activity, decreased myocardial infarct size and myocardial content of LTB(4) and TXB(2) in both genotyped mice. The decrease in myocardial infarct size and content of LTB(4) and TXB(2) after cPLA(2) inhibitor administration was greater in WT mice than in sPLA(2)V(-/-) mice. I/R increased phosphorylation of extracellular signal-related kinase 1/2, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinases in the ischaemic myocardium in association with cPLA(2) phosphorylation. The I/R-induced increase in the phosphorylation of p38 and cPLA(2) was less in sPLA(2)-V(-/-) mice than in WT mice. Pretreatment with the p38 inhibitor SB202190 suppressed an increase in cPLA(2) phosphorylation after I/R in WT mice.

CONCLUSION

sPLA(2)-V plays an important role in the pathogenesis of myocardial I/R injury partly in concert with the activation of cPLA(2).

2-aminohydroxamic acid derivatives as inhibitors of Bacillus cereus phosphatidylcholine preferred phospholipase C PC-PLC(Bc)

Phosphatidylcholine preferring phospholipase C (PC-PLC) is an important enzyme that plays a key role in a variety of cellular events and lipid homoeostases. Bacillus cereus phospholipase C (PC-PLC(Bc)) has antigenic similarity with the elusive mammalian PC-PLC, which has not thus far been isolated and purified. Therefore the discovery of inhibitors of PC-PLC(Bc) is of current interest. Here, we describe the synthesis and biological evaluation of a new type of compounds inhibiting PC-PLC(Bc). These compounds have been designed by evolution of previously described 2-aminohydroxamic acid PC-PLC(Bc) inhibitors that block the enzyme by coordination of the zinc active site atoms present in PC-PLC(Bc) [Gonzalez-Roura, A.; Navarro, I.; Delgado, A.; Llebaria, A.; Casas, J. Angew. Chem. Int. Ed.2004, 43, 862]. The new compounds maintain the zinc coordinating groups and possess an extra trimethylammonium function, linked to the hydroxyamide nitrogen by an alkyl chain, which is expected to mimic the trimethylammonium group of the phosphatidylcholine PC-PLC(Bc) substrates. Some of the compounds described inhibit the enzyme with IC(50)'s in the low micromolar range. Unexpectedly, the most potent inhibitors found are those that possess a trimethylammonium group but have chemically blocked the zinc coordinating functionalities. The results obtained suggest that PC-PLC(Bc) inhibition is not due to the interaction of compounds with the phospholipase catalytic zinc atoms, but rather results from the inhibitor cationic group recognition by the PC-PLC(Bc) amino acids involved in choline lipid binding.

AtsPLA2-alpha nuclear relocalization by the Arabidopsis transcription factor AtMYB30 leads to repression of the plant defense response

The hypersensitive response (HR), characterized by a rapid and localized cell death at the inoculation site, is one of the most efficient resistance reactions to pathogen attack in plants. The transcription factor AtMYB30 was identified as a positive regulator of the HR and resistance responses during interactions between Arabidopsis and bacteria. Here, we show that AtMYB30 and the secreted phospholipase AtsPLA(2)-alpha physically interact in vivo, following the AtMYB30-mediated specific relocalization of AtsPLA(2)-alpha from cytoplasmic vesicles to the plant cell nucleus. This protein interaction leads to repression of AtMYB30 transcriptional activity and negative regulation of plant HR. Moreover, Atspla(2)-alpha mutant plants are more resistant to bacterial inoculation, whereas AtsPLA(2)-alpha overexpression leads to decreased resistance, confirming that AtsPLA(2)-alpha is a negative regulator of AtMYB30-mediated defense. These data underline the importance of cellular dynamics and, particularly, protein translocation to the nucleus, for defense-associated gene regulation in plants.

Acyl chain-dependent effect of lysophosphatidylcholine on endothelial prostacyclin production

Previously we identified palmitoyl-lysophosphatidylcholine (16:0 LPC), linoleoyl-LPC (18:2 LPC), arachidonoyl-LPC (20:4 LPC), and oleoyl-LPC (18:1 LPC) as the most prominent LPC species generated by the action of endothelial lipase (EL) on high-density lipoprotein. In the present study, the impact of those LPC on prostacyclin (PGI(2)) production was examined in vitro in primary human aortic endothelial cells (HAEC) and in vivo in mice. Although 18:2 LPC was inactive, 16:0, 18:1, and 20:4 LPC induced PGI(2) production in HAEC by 1.4-, 3-, and 8.3-fold, respectively. LPC-elicited 6-keto PGF1α formation depended on both cyclooxygenase (COX)-1 and COX-2 and on the activity of cytosolic phospholipase type IVA (cPLA2). The LPC-induced, cPLA2-dependent (14)C-arachidonic acid (AA) release was increased 4.5-fold with 16:0, 2-fold with 18:1, and 2.7-fold with 20:4 LPC, respectively, and related to the ability of LPC to increase cytosolic Ca(2+) concentration. In vivo, LPC increased 6-keto PGF(1α) concentration in mouse plasma with a similar order of potency as found in HAEC. Our results indicate that the tested LPC species are capable of eliciting production of PGI(2), whereby the efficacy and the relative contribution of underlying mechanisms are strongly related to acyl-chain length and degree of saturation.

Diclofenac: an update on its mechanism of action and safety profile

BACKGROUND

Diclofenac is a proven, commonly prescribed nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-inflammatory, and antipyretic properties, and has been shown to be effective in treating a variety of acute and chronic pain and inflammatory conditions. As with all NSAIDs, diclofenac exerts its action via inhibition of prostaglandin synthesis by inhibiting cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) with relative equipotency. However, extensive research shows the pharmacologic activity of diclofenac goes beyond COX inhibition, and includes multimodal and, in some instances, novel mechanisms of action (MOA).

DATA SOURCES

Literature retrieval was performed through PubMed/MEDLINE (through May 2009) using combinations of the terms diclofenac, NSAID, mechanism of action, COX-1, COX-2, and pharmacology. Reference citations resulting from publications identified in the literature search were reviewed when appropriate.

METHODS

This article reviews the established, putative, and emerging MOAs of diclofenac; compares the drug's pharmacologic and pharmacodynamic properties with other NSAIDs to delineate its potentially unique qualities; hypothesizes why it has been chosen for further recent formulation enhancement; and evaluates the potential effect of its MOA characteristics on safety.

DISCUSSION

Research suggests diclofenac can inhibit the thromboxane-prostanoid receptor, affect arachidonic acid release and uptake, inhibit lipoxygenase enzymes, and activate the nitric oxide-cGMP antinociceptive pathway. Other novel MOAs may include the inhibition of substrate P, inhibition of peroxisome proliferator activated receptor gamma (PPARgamma), blockage of acid-sensing ion channels, alteration of interleukin-6 production, and inhibition of N-methyl-D-aspartate (NMDA) receptor hyperalgesia. The review was not designed to compare MOAs of diclofenac with other NSAIDs. Additionally, as the highlighted putative and emerging MOAs do not have clinical data to demonstrate that these models are correct, further research is necessary to ascertain if the proposed pathways will translate into clinical benefits. The diversity in diclofenac's MOA may suggest the potential for a relatively more favorable profile compared with other NSAIDs.

Group X secretory phospholipase A2 negatively regulates adipogenesis in murine models

Studies in vitro indicate that group X secretory phospholipase A(2) (GX sPLA(2)) potently releases arachidonic acid (AA) and lysophosphatidylcholine from mammalian cell membranes. To define the function of GX sPLA(2) in vivo, our laboratory recently generated C57BL/6 mice with targeted deletion of GX sPLA(2) (GX(-/-) mice). When fed a normal rodent diet, GX(-/-) mice gained significantly more weight and had increased adiposity compared to GX(+/+) mice, which was not attributable to alterations in food consumption or energy expenditure. When treated with adipogenic stimuli ex vivo, stromal vascular cells isolated from adipose tissue of GX(-/-) mice accumulated significantly more (20%) triglyceride compared to cells from GX(+/+) mice. Conversely, overexpression of GX sPLA(2), but not catalytically inactive GX sPLA(2), resulted in a significant 50% reduction in triglyceride accumulation in OP9 adipocytes. The induction of genes encoding adipogenic proteins (PPARγ, SREBP-1c, SCD1, and FAS) was also significantly blunted by 50-80% in OP9 cells overexpressing GX sPLA(2). Activation of the liver X receptor (LXR), a nuclear receptor known to up-regulate adipogenic gene expression, was suppressed in 3T3-L1 and OP9 cells when GX sPLA(2) was overexpressed. Thus, hydrolytic products generated by GX sPLA(2) negatively regulate adipogenesis, possibly by suppressing LXR activation.

[The role of adipokines and insulin resistance in the pathogenesis of nonalcoholic fatty liver disease]

Nonalcoholic fatty liver disease (NAFLD) develops in 17-33% of the population of developed countries. The incidence of NAFLD is constantly growing due to the increasing prevalence of obesity. It is estimated that one third of subjects with NAFLD suffer from nonalcoholic steatohepatitis (NASH) and 15% of them develop liver cirrhosis within a five-year period. In recent years this important complication of obesity became the subject of numerous studies. It, the pathogenesis of NAFLD is still unclear. A key role in the development of this disease was attributed to insulin resistance. Hormones and cytokines produced by adipose tissue called adipokines may be a link between obesity, insulin resistance, and NAFLD. However, it is well known that increased levels of adipokines such as TNF-alpha, IL-6, and resistin and a decreased level of adiponectin augment inflammation in the liver. Further studies are necessary to explain the roles of leptin, visfatin, retinol binding protein-4, omentin, and vaspin in the pathogenesis of NAFLD. The aim this paper is to introduce new areas of study on the pathogenesis of NAFLD.

Group X secretory phospholipase A2 regulates the expression of steroidogenic acute regulatory protein (StAR) in mouse adrenal glands

We developed C57BL/6 mice with targeted deletion of group X secretory phospholipase A(2) (GX KO). These mice have approximately 80% higher plasma corticosterone concentrations compared with wild-type (WT) mice under both basal and adrenocorticotropic hormone (ACTH)-induced stress conditions. This increased corticosterone level was not associated with increased circulating ACTH or a defect in the hypothalamic-pituitary axis as evidenced by a normal response to dexamethasone challenge. Primary cultures of adrenal cells from GX KO mice exhibited significantly increased corticosteroid secretion compared with WT cells. Conversely, overexpression of GX secretory phospholipase A(2) (sPLA(2)), but not a catalytically inactive mutant form of GX sPLA(2), significantly reduced steroid production 30-40% in Y1 mouse adrenal cell line. This effect was reversed by the sPLA(2) inhibitor, indoxam. Silencing of endogenous M-type receptor expression did not restore steroid production in GX sPLA(2)-overexpressing Y1 cells, ruling out a role for this sPLA(2) receptor in this regulatory process. Expression of steroidogenic acute regulatory protein (StAR), the rate-limiting protein in corticosteroid production, was approximately 2-fold higher in adrenal glands of GX KO mice compared with WT mice, whereas StAR expression was suppressed in Y1 cells overexpressing GX sPLA(2). Results from StAR-promoter luciferase reporter gene assays indicated that GX sPLA(2) antagonizes StAR promoter activity and liver X receptor-mediated StAR promoter activation. In summary, GX sPLA(2) is expressed in mouse adrenal glands and functions to negatively regulate corticosteroid synthesis, most likely by negatively regulating StAR expression.

Production of vascular endothelial growth factors from human lung macrophages induced by group IIA and group X secreted phospholipases A2

Angiogenesis and lymphangiogenesis mediated by vascular endothelial growth factors (VEGFs) are main features of chronic inflammation and tumors. Secreted phospholipases A(2) (sPLA(2)s) are overexpressed in inflammatory lung diseases and cancer and they activate inflammatory cells by enzymatic and receptor-mediated mechanisms. We investigated the effect of sPLA(2)s on the production of VEGFs from human macrophages purified from the lung tissue of patients undergoing thoracic surgery. Primary macrophages express VEGF-A, VEGF-B, VEGF-C, and VEGF-D at both mRNA and protein level. Two human sPLA(2)s (group IIA and group X) induced the expression and release of VEGF-A and VEGF-C from macrophages. Enzymatically-inactive sPLA(2)s were as effective as the active enzymes in inducing VEGF production. Me-Indoxam and RO092906A, two compounds that block receptor-mediated effects of sPLA(2)s, inhibited group X-induced release of VEGF-A. Inhibition of the MAPK p38 by SB203580 also reduced sPLA(2)-induced release of VEGF-A. Supernatants of group X-activated macrophages induced an angiogenic response in chorioallantoic membranes that was inhibited by Me-Indoxam. Stimulation of macrophages with group X sPLA(2) in the presence of adenosine analogs induced a synergistic increase of VEGF-A release and inhibited TNF-alpha production through a cooperation between A(2A) and A(3) receptors. These results demonstrate that sPLA(2)s induce production of VEGF-A and VEGF-C in human macrophages by a receptor-mediated mechanism independent from sPLA(2) catalytic activity. Thus, sPLA(2)s may play an important role in inflammatory and/or neoplastic angiogenesis and lymphangiogenesis.

Taiwan cobra phospholipase A2-elicited JNK activation is responsible for autocrine fas-mediated cell death and modulating Bcl-2 and Bax protein expression in human leukemia K562 cells

Phospholipase A(2) (PLA(2)) from Naja naja atra venom induced apoptotic death of human leukemia K562 cells. Degradation of procaspases, production of tBid, loss of mitochondrial membrane potential, Bcl-2 degradation, mitochondrial translocation of Bax, and cytochrome c release were observed in PLA(2)-treated cells. Moreover, PLA(2) treatment increased Fas and FasL protein expression. Upon exposure to PLA(2), activation of p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun NH(2)-terminal kinase) was found in K562 cells. SB202190 (p38 MAPK inhibitor) pretreatment enhanced cytotoxic effect of PLA(2) and led to prolonged JNK activation, but failed to affect PLA(2)-induced upregulation of Fas and FasL protein expression. Sustained JNK activation aggravated caspase8/mitochondria-dependent death pathway, downregulated Bcl-2 expression and increased mitochondrial translocation of Bax. SP600125 (JNK inhibitor) abolished the cytotoxic effect of PLA(2) and PLA(2)-induced autocrine Fas death pathway. Transfection ASK1 siRNA and overexpression of dominant negative p38alpha MAPK proved that ASK1 pathway was responsible for PLA(2)-induced p38 MAPK and JNK activation and p38alpha MAPK activation suppressed dynamically persistent JNK activation. Downregulation of FADD abolished PLA(2)-induced procaspase-8 degradation and rescued viability of PLA(2)-treated cells. Taken together, our results indicate that JNK-mediated autocrine Fas/FasL apoptotic mechanism and modulation of Bcl-2 family proteins are involved in PLA(2)-induced death of K562 cells.