Secreted phospholipases A2 induce the expression of chemokines in microvascular endothelium

COVID-19, Blood Lipid Changes, and Thrombosis

Although there is increasing evidence that oxidative stress and inflammation induced by COVID-19 may contribute to increased risk and severity of thromboses, the underlying mechanism(s) remain to be understood. The purpose of this review is to highlight the role of blood lipids in association with thrombosis events observed in COVID-19 patients. Among different types of phospholipases A₂ that target cell membrane phospholipids, there is increasing focus on the inflammatory secretory phospholipase A₂ IIA (sPLA₂-IIA), which is associated with the severity of COVID-19. Analysis indicates increased sPLA₂-IIA levels together with eicosanoids in the sera of COVID patients. sPLA₂ could metabolise phospholipids in platelets, erythrocytes, and endothelial cells to produce arachidonic acid (ARA) and lysophospholipids. Arachidonic acid in platelets is metabolised to prostaglandin H2 and thromboxane A₂, known for their pro-coagulation and vasoconstrictive properties. Lysophospholipids, such as lysophosphatidylcholine, could be metabolised by autotaxin (ATX) and further converted to lysophosphatidic acid (LPA). Increased ATX has been found in the serum of patients with COVID-19, and LPA has recently been found to induce NETosis, a clotting mechanism triggered by the release of extracellular fibres from neutrophils and a key feature of the COVID-19 hypercoagulable state. PLA2 could also catalyse the formation of platelet activating factor (PAF) from membrane ether phospholipids. Many of the above lipid mediators are increased in the blood of patients with COVID-19. Together, findings from analyses of blood lipids in COVID-19 patients suggest an important role for metabolites of sPLA₂-IIA in COVID-19-associated coagulopathy (CAC).

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.

Mechanism of rutaecarpine on ethanol-induced acute gastric ulcer using integrated metabolomics and network pharmacology

This study was aimed to explore the mechanism of rutaecarpine (RUT) on ethanol-induced gastric ulcer (GU) in mice by integrated approaches. At first, the efficacy was determined through the macroscopic and microscopic state of stomach tissue and the expression levels of GU-related factors. Then, the serum metabolomics method based on UPLC-Q-TOF/MS was used to explore the specific metabolites and metabolic pathways. Finally, the upstream key protein targets of these specific metabolites were analyzed by network pharmacology and verified by PCR to explore the potential mechanism. RUT alleviated the histological and pathological damage of gastric tissue caused by ethanol, and could remarkably ameliorate the level of GU-related factors. Subsequently, a total of 7 potential metabolites involved in 9 metabolic pathways were identified by metabolomics analysis. Then, a 'component-targets-metabolites' interaction network was constructed, and therefore 4 key target proteins (PLA2G1B, PDE5A, MIF and SRC) that may regulate the specific metabolites were obtained. This case was further verified by the results of PCR. ALL the above results strongly demonstrated that RUT exerted a gastroprotective effect against GU. And it is the first time to combine metabolomics combined with network pharmacology to elucidate the mechanism of RUT on GU, which may be related to the regulation of energy metabolism, oxidative stress, and inflammation, and these pathways may be regulated through the upstream protein PLA2G1B, PDE5A, MIF and SRC.

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

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

Inhibitory Effect of Pelargonidin on Secretory Group IIA Phospholipase A2

The expression of secretory group IIA phospholipase A2 (sPLA2-IIA) has been shown to be elevated in various inflammatory diseases, and lipopolysaccharide (LPS) up-regulates the expression of sPLA2-IIA in human umbilical vein endothelial cells (HUVECs). Pelargonidin (PEL) is a well-known red pigment found in plants, and has been reported as having important biological activities that are potentially beneficial for human health. Here, PEL was examined for its effects on the expression and activity of sPLA2-IIA in HUVECs and mouse. Post treatment of cells or mouse with PEL inhibited LPS-induced expression and activity of sPLA2-IIA. Therefore, these results suggest that PEL inhibited LPS mediated expression of sPLA2-IIA.

Inhibitory Effect of Zingerone on Secretory Group IIA Phospholipase A2

The expression of secretory group IIA phospholipase A2 (sPLA2-IIA) has been shown to be elevated in various inflammatory diseases, and lipopolysaccharide (LPS) up-regulates the expression of sPLA2-IIA in human umbilical vein endothelial cells (HUVECs). Zingerone (ZGR), a phenolic alkanone isolated from ginger, has been reported to have various pharmacological activities. Here, we examined the effects of ZRG on the expression and activity of sPLA2-IIA in LPS-activated HUVECs and in mouse models of endotoxemia and sepsis. Treatment of cells or mice with ZRG inhibited LPS-induced expression and activity of sPLA2-IIA. In addition, ZRG suppressed LPS-mediated activation of cytosolic phospholipase A2 (cPLA2) and extracellular signal-regulated kinase (ERK) 1/2. These results suggest that ZRG inhibits LPS-mediated activation of sPLA2-IIA expression by suppressing cPLA2 and ERK 1/2.

Molecular dynamics simulations reveal structural insights into inhibitor binding modes and functionality in human Group IIA phospholipase A2

Human Group IIA phospholipase A₂ (hGIIA) promotes inflammation in immune-mediated pathologies by regulating the arachidonic acid pathway through both catalysis-dependent and -independent mechanisms. The hGIIA crystal structure, both alone and inhibitor-bound, together with structures of closely related snake-venom-derived secreted phospholipase enzymes has been well described. However, differentiation of biological and nonbiological contacts and the relevance of structures determined from snake venom enzymes to human enzymes are not clear. We employed molecular dynamics (MD) and docking approaches to understand the binding of inhibitors that selectively or nonselectively block the catalysis-independent mechanism of hGIIA. Our results indicate that hGIIA behaves as a monomer in the solution environment rather than a dimer arrangement that is in the asymmetric unit of some crystal structures. The binding mode of a nonselective inhibitor, KH064, was validated by a combination of the experimental electron density and MD simulations. The binding mode of the selective pentapeptide inhibitor FLSYK to hGIIA was stipulated to be different to that of the snake venom phospholipases A₂ of Daboia russelli pulchella (svPLA₂ ). Our data suggest that the application of MD approaches to crystal structure data is beneficial in evaluating the robustness of conclusions drawn based on crystal structure data alone. Proteins 2017; 85:827-842. © 2016 Wiley Periodicals, Inc.

Inhibitory Effect of FXa on Secretory Group IIA Phospholipase A2

It is well known that the expression level of secretory group IIA phospholipase A2 (sPLA2-IIA) is elevated in inflammatory diseases and lipopolysaccharide (LPS) upregulates the expression of sPLA2-IIA in human umbilical vein endothelial cells (HUVECs). Activated factor X (FXa) is an important enzyme in the coagulation cascade responsible for thrombin generation, and it influences cell signaling in various cell types by activating protease-activated receptors (PARs). Here, FX or FXa was examined for its effects on the expression and activity of sPLA2-IIA in HUVECs and mouse. Prior treatment of cells or mouse with FXa inhibited LPS-induced expression and activity of sPLA2-IIA via interacting with FXa receptor (effective cell protease receptor-1, EPR-1). And FXa suppressed the activation of cytosolic phospholipase A2 (cPLA2) and extracellular signal-regulated kinase (ERK) 1/2 by LPS. Therefore, these results suggest that FXa may inhibit LPS-mediated expression of sPLA2-IIA by suppression of cPLA2 and ERK 1/2.

Inhibitory effect of polyozellin on secretory group IIA phospholipase A2

The expression of secretory group IIA phospholipase A2 (sPLA2-IIA) is enhanced by development of inflammatory disorders. In this study, sPLA2-IIA expression was induced in the lipopolysaccharide (LPS)-stimulated human umbilical vein endothelial cells and mice to evaluate the effect of polyozellin. Polyozellin, a major constituent of a Korea edible mushroom Polyozellus multiplex, has been known to exhibit the biological activities such as anti-oxidative and anti-inflammatory effects. Polyozellin remarkably suppressed the LPS-mediated protein expression and activity of sPLA2-IIA via inhibition of phosphorylation of cytosolic phospholipase A2 and extracellular signal-regulated kinase 1/2. These results demonstrated that polyozellin might play an important role in the modulation of sPLA2-IIA expression and activity in response to the inflammatory diseases.

Novel insight into drug repositioning: Methylthiouracil as a case in point

Drug repositioning refers to the development of existing drugs for new indications. These drugs may have (I) failed to show efficacy in late stage clinical trials without safety issues; (II) stalled in the development for commercial reasons; (III) passed the point of patent expiry; or (IV) are being explored in new geographic markets. Over the past decade, pressure on the pharmaceutical industry caused by the 'innovation gap' owing to rising development costs and stagnant product output have become major reasons for the growing interest in drug repositioning. Companies that offer a variety of broad platforms for identifying new indications have emerged; some have been successful in building their own pipelines of candidates with reduced risks and timelines associated with further clinical development. The business models and platforms offered by these companies will be validated if they are able to generate positive proof-of-concept clinical data for their repositioned compounds. This review describes the strategy of biomarker-guided repositioning of chemotherapeutic drugs for inflammation therapy, considering the repositioning of methylthiouracil (MTU), an antithyroid drug, as a potential anti-inflammatory reagent.

Trim44 facilitates the migration and invasion of human lung cancer cells via the NF-κB signaling pathway

BACKGROUND

Trim44 is an important member of the tripartite motif-containing protein (TRIM) family. Recent research reported that Trim44 might play an important role in tumorigenesis, although its role in non-small cell lung cancer (NSCLC) and the related mechanisms is not yet known.

METHODS

In this study we analyzed 30 pairs of NSCLC tumors and the matched adjacent normal tissue to define the relationship between Trim44 and NSCLC tumors. The function of Trim44 in cell migration and invasion was determined by overexpression of Trim44 in normal bronchial epithelial cell line 16HE or knockdown of Trim44 in A549 cells, respectively. Whether Trim44-mediated NF-κB signaling activation was involved in Trim44-mediated promotion of lung cancer was tested by q-PCR analysis and cell migration and invasion assay using PDTC, an inhibitor of NF-κB.

RESULTS

We found that Trim44 was upregulated in NSCLC tumors (14/30 cases; 46.7%). Furthermore, Trim44 was upregulated in many NSCLC cell lines, especially in A549 and H441. Moreover, Trim44 significantly enhanced cell migration and invasion ability, which was related to increased CXCR6 and matrix metalloproteinase 9 (MMP9). Knockdown of Trim44 in A549 cells by siRNA showed a diminished effect in cell migration and invasion. Further investigation revealed that blocking the NF-κB signaling pathway using PDTC, an inhibitor of NF-κB, reversed the expression of CXCR6 and MMP9, and alleviated the promotion of migration and invasion mediated by Trim44.

CONCLUSIONS

Our data suggest that Trim44 promotes NSCLC development through activation of NF-κB signaling via upregulating CXCL16 and MMP9 expression.

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.

Acute phase reactants as novel predictors of cardiovascular disease

Acute phase reaction is a systemic response which usually follows a physiological condition that takes place in the beginning of an inflammatory process. This physiological change usually lasts 1-2 days. However, the systemic acute phase response usually lasts longer. The aim of this systemic response is to restore homeostasis. These events are accompanied by upregulation of some proteins (positive acute phase reactants) and downregulation of others (negative acute phase reactants) during inflammatory reactions. Cardiovascular diseases are accompanied by the elevation of several positive acute phase reactants such as C-reactive protein (CRP), serum amyloid A (SAA), fibrinogen, white blood cell count, secretory nonpancreatic phospholipase 2-II (sPLA2-II), ferritin, and ceruloplasmin. Cardiovascular disease is also accompanied by the reduction of negative acute phase reactants such as albumin, transferrin, transthyretin, retinol-binding protein, antithrombin, and transcortin. In this paper, we will be discussing the biological activity and diagnostic and prognostic values of acute phase reactants with cardiovascular importance. The potential therapeutic targets of these reactants will be also discussed.

Inhibitory effect of thrombin on the expression of secretory group IIA phospholipase A₂

It is well known that the expression level of secretory group IIA phospholipase A(2) (sPLA(2)-IIA) is elevated in inflammatory diseases and lipopolysaccharide (LPS) up-regulates the expression of sPLA(2)-IIA in human umbilical vein endothelial cells (HUVECs). Recently, lower concentration thrombin could elicit anti-inflammatory responses in HUVECs. Here, the effects of lower concentration thrombin on the expression of sPLA(2)-IIA in LPS-stimulated HUVECs were investigated. Prior treatment of cells with thrombin (25-75 pM) inhibited LPS-induced sPLA(2)-IIA expression by activating its receptor, protease-activated receptor-1 (PAR-1). And pretreatment of cells with either PI3-kinase inhibitor (LY294002) or cholesterol depleting agent (methyl-β-cyclodextrin, MβCD) abolished the inhibitory activity of thrombin against sPLA(2)-IIA expression. Therefore, these results suggest that PAR-1 activation by lower concentration thrombin inhibited LPS mediated expression of sPLA(2)-IIA by PAR-1 and PI3-kinase-dependent manner in lipid raft on the HUVECs.

Group V secreted phospholipase A2 contributes to LPS-induced leukocyte recruitment

Secreted phospholipases A(2) (sPLA(2)s) are well known for their contribution in the biosynthesis of inflammatory eicosanoids. These enzymes also participate in the inflammatory process by regulating chemokine production and protein expression of adhesion molecules. The majority of sPLA(2) isoforms are up-regulated by proinflammatory stimuli such as bacterial lipopolysaccharide (LPS), which predominantly increases the expression of group V sPLA(2) (sPLA(2)-V). Furthermore, it has recently been shown that sPLA(2)-V is a critical messenger in the regulation of cell migration during allergic airway responsiveness. Herein, we investigated the effect of sPLA(2)-V on LPS-mediated leukocyte recruitment and its capacity to modulate adhesion molecule expression. We conducted our study in the murine air pouch model, using sPLA(2)-V null mice (sPLA(2)-V(-/-)) and control wild-type (WT) littermates. We observed that LPS (1 microg/ml)-mediated leukocyte emigration in sPLA(2)-V(-/-) was attenuated by 52% and 86% upon 6 and 12 h of treatment respectively, as compared to WT mice. In WT mice, treatment with the cell-permeable sPLA(2) inhibitor (12-epi-scalaradial; SLD) reduced LPS-mediated leukocyte recruitment by 67%, but had no additional inhibitory effect in sPLA(2)-V(-/-) mice. Protein analyses from the air pouch skin were carried out upon LPS-challenge, and the expression of intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 were both significantly reduced in sPLA(2)-V(-/-) mice as compared to control WT mice. Together, our data demonstrate the role of sPLA(2)-V in LPS-induced ICAM-1 and VCAM-1 protein overexpression and leukocyte recruitment, supporting the contribution of sPLA(2)-V in the development of inflammatory innate immune responses.

Group V phospholipase A2 mediates barrier disruption of human pulmonary endothelial cells caused by LPS in vitro

We examined the functional role of 14-kD secretory group V phospholipase A(2) (gVPLA(2)) on the barrier function of pulmonary endothelial cells (ECs) after LPS activation in vitro. Expression of gVPLA(2) was elicited by 20 ng/ml LPS as demonstrated by increased (1) mRNA, (2) protein content, and (3) cell surface expression of gVPLA(2) within 4 hours. The effect of LPS on EC barrier function was measured by transendothelial monolayer electrical resistance (TER). LPS increased permeability across EC monolayers at 2-3 hours, and was sustained for 10 hours or more. Blockade of gVPLA(2) with mouse monoclonal 3G1 (MCL-3G1) monoclonal antibody directed against gVPLA(2) inhibited EC barrier dysfunction elicited by LPS in a time- and concentration-dependent manner; control IgG had no effect on TER. Like LPS, exogenous gVPLA(2) caused increased EC permeability in a time- and concentration-dependent manner; neither gIIaPLA(2), a close homolog of gVPLA(2), nor W31A, an inactive mutant of gVPLA(2), caused a decrease in EC TER. Immunofluorescence analysis revealed comparable F-actin stress fiber and intercellular gap formation for ECs treated with either gVPLA(2) or LPS. Treatment with gVPLA(2) disrupted vascular endothelial-cadherin junctional complexes on ECs. Coincubation of ECs with MCL-3G1 substantially attenuated the structural changes caused by gVPLA(2) or LPS. We demonstrate that (1) gVPLA(2) is constitutively expressed in ECs and is up-regulated after LPS activation, (2) endogenously secreted gVPLA(2) from ECs after LPS increases EC permeability through F-actin and junctional complex rearrangement, and (3) inhibition of endogenous gVPLA(2) from ECs is sufficient to block disruption of the EC barrier function after LPS in vitro.

Lung mast cells are a source of secreted phospholipases A2

BACKGROUND

Secreted phospholipases A(2) (sPLA(2)s) are released in plasma and other biologic fluids of patients with inflammatory, autoimmune, and allergic diseases.

OBJECTIVE

We sought to evaluate sPLA(2) activity in the bronchoalveolar lavage fluid (BALF) of asthmatic patients and to examine the expression and release of sPLA(2)s from primary human lung mast cells (HLMCs).

METHODS

sPLA(2) activity was measured in BALF and supernatants of either unstimulated or anti-IgE-activated HLMCs as hydrolysis of oleic acid from radiolabeled Escherichia coli membranes. Expression of sPLA(2)s was examined by using RT-PCR. The release of cysteinyl leukotriene (LT) C(4) was measured by means of enzyme immunoassay.

RESULTS

Phospholipase A(2) (PLA(2)) activity was higher in the BALF of asthmatic patients than in the control group. BALF PLA(2) activity was blocked by the sPLA(2) inhibitors dithiothreitol and Me-Indoxam but not by the cytosolic PLA(2) inhibitor AZ-1. HLMCs spontaneously released a PLA(2) activity that was increased on stimulation with anti-IgE. This PLA(2) activity was blocked by dithiothreitol and Me-Indoxam but not by AZ-1. HLMCs constitutively express mRNA for group IB, IIA, IID, IIE, IIF, III, V, X, XIIA, and XIIB sPLA(2)s. Anti-IgE did not modify the expression of sPLA(2)s. The cell-impermeable inhibitor Me-Indoxam significantly reduced (up to 40%) the production of LTC(4) from anti-IgE-stimulated HLMCs.

CONCLUSIONS

sPLA(2) activity is increased in the airways of asthmatic patients. HLMCs express multiple sPLA(2)s and release 1 or more of them when activated by anti-IgE. The sPLA(2)s released by mast cells contribute to LTC(4) production by acting in an autocrine fashion. Mast cells can be a source of sPLA(2)s in the airways of asthmatic patients.

Ceramide elevates 12-hydroxyeicosatetraenoic acid levels and upregulates 12-lipoxygenase in rat primary hippocampal cell cultures containing predominantly astrocytes

We report, exogenous addition of ceramide significantly increases 12-hydroxyeicosatetraenoic acid [12-(S)-HETE] levels, in a dose-dependent manner. 12-(S)-HETE levels, in 20, 30 and 40microM ceramide exposed rat primary hippocampal cell cultures containing predominantly astrocytes and few neurons and other glial cells (the cultured hippocampal cells were predominantly astrocytes amounting to over 99% of total cells with few neurons and other glial cells) amounted to 207, 260 and 408% of the controls, respectively. However, dihydroceramide, an inactive analog of ceramide did not alter the levels of 12-(S)-HETE. Ceramide also increased the mRNA and protein expression, and activity of 12-lipoxygease (12-LOX) needed for the synthesis of 12(S)-HETE. These results indicate a possible link between ceramide and 12-LOX pathway. However, ceramide did not alter expression of 5-lipoxygenase (5-LOX), another member of the lipoxygenase family. However, ceramide upregulated expression of cytosolic phospholipase-A(2) (cPLA(2)) and cyclooxygenase-2 (COX-2). Further, ceramide caused a significant increase in the levels of reactive oxygen species (ROS). Ceramide-mediated generation of ROS was inhibited by baicalien but not by indomethacin. In addition, ceramide treated cells exhibited increased mRNA expression of DNA damage induced transcript3 (Ddit3). This report which demonstrate induction of pro-carcinogenic 12-LOX pathway by an anticancer ceramide, may be relevant to cancer biologists studying drug resistant tumors and devising potent anticancer therapeutic strategies to treat drug resistant tumors. These results indicate possibility of 12-LOX involvement in ceramide-mediated generation of ROS and cellular oxidative stress. Induction of 12-LOX pathway by ceramide may have implications in understanding pathophysiology of neurodegenerative diseases involving ROS generation and inflammation.

Secretory PLA2 inhibitor indoxam suppresses LDL modification and associated inflammatory responses in TNFalpha-stimulated human endothelial cells

BACKGROUND AND PURPOSE

Secretory phospholipase A2 (sPLA2) is implicated in atherosclerosis, although the effects of specific sPLA2 inhibitors have not been studied. We investigated the effects of the indole analogue indoxam on low-density lipoprotein (LDL) modification by sPLA2 enzymes of different types and on the associated inflammatory responses in human umbilical vein endothelial cells (HUVEC).

EXPERIMENTAL APPROACH

LDL modification was assessed by measuring the contents of two major molecular species of lysophosphatidylcholine (LPC) using electrospray ionization-liquid chromatography/mass spectrometry. The proinflammatory activity of the modified LDL was evaluated by determining monocyte chemoattractant protein-1 (MCP-1) mRNA expression and transcriptional factor nuclear factor-kappaB (NF-kappaB) activity in HUVEC.

KEY RESULTS

Indoxam dose-dependently inhibited palmitoyl- and stearoyl-LPC production in LDL incubated with snake venom sPLA2 (IC50 1.2 microM for palmitoyl-LPC, 0.8 microM for stearoyl-LPC). MCP-1 mRNA expression and NF-kappaB activity were enhanced by venom sPLA2-treated LDL, which was completely suppressed by indoxam but not by thioetheramide-PC, a competitive sPLA2 inhibitor. Indoxam also suppressed LPC production in LDL treated with human synovial type IIA sPLA2. Tumour necrosis factor alpha (TNFalpha) increased type V sPLA2 expression in HUVEC. Indoxam dose-dependently suppressed LPC production in native and glycoxidized LDL treated with TNFalpha-stimulated HUVEC. Indoxam suppressed MCP-1 mRNA expression and NF-kappaB activity in TNFalpha-stimulated HUVEC incubated with native or glycoxidized LDL.

CONCLUSIONS AND IMPLICATIONS

Indoxam prevented sPLA2-induced LPC production in native and glycoxidized LDL as well as LDL-induced inflammatory activity in HUVEC. Our results suggest that indoxam may be a potentially useful anti-atherogenic agent.

Signaling events involved in cytokine and chemokine production induced by secretory phospholipase A2 in human lung macrophages

Secretory phospholipases A(2) (sPLA(2)) are enzymes released during inflammatory reactions. These molecules activate immune cells by mechanisms either related or unrelated to their enzymatic activity. We examined the signaling events activated by group IA (GIA) and group IB (GIB) sPLA(2) in human lung macrophages leading to cytokine/chemokine production. sPLA(2) induced the production of cytokines (TNF-alpha, IL-6 and IL-10) and chemokines (CCL2, CCL3, CCL4 and CXCL8), whereas no effect was observed on IL-12, CCL1, CCL5 and CCL22. sPLA(2) induced the phosphorylation of the MAPK p38 and ERK1/2, and inhibition of these kinases by SB203580 and PD98059, respectively, reduced TNF-alpha and CXCL8 release. Suppression of sPLA(2) enzymatic activity by a site-directed inhibitor influenced neither cytokine/chemokine production nor activation of MAPK, whereas alteration of sPLA(2) secondary structure suppressed both responses. GIA activated the phosphatidylinositol 3-kinase (PI3 K)/Akt system and a specific inhibitor of PI3 K (LY294002) reduced sPLA(2)-induced release of TNF-alpha and CXCL8. GIA promoted phosphorylation and degradation of IkappaB and inhibition of NF-kappaB by MG-132 and 6-amino-4-phenoxyphenylethylamino-quinazoline suppressed the production of TNF-alpha and CXCL8. These results indicate that sPLA(2) induce the production of cytokines and chemokines in human macrophages by a non-enzymatic mechanism involving the PI3 K/Akt system, the MAPK p38 and ERK1/2 and NF-kappaB.

Upregulation of group IB secreted phospholipase A(2) and its M-type receptor in rat ANTI-THY-1 glomerulonephritis

Treatment of rat glomerular mesangial cell (GMC) cultures with pancreatic secreted phospholipase A(2) (sPLA(2)-IB) results in an enhanced expression of sPLA(2)-IIA and COX-2, possibly via binding to its specific M-type sPLA(2) receptor. In the current study, we have investigated the expression and regulation of sPLA(2)-IB and its receptor during glomerulonephritis (GN). In vivo we used the well-established rat model of anti-Thy 1.1 GN (anti-Thy 1.1-GN) to study the expression of sPLA(2)-IB and the M-type sPLA(2) receptor by immunohistochemistry. In addition, in vitro we determined the interkeukin (IL)-1beta-regulated mRNA and protein expression in primary rat glomerular mesangial and endothelial cells as well as in rat peripheral blood leukocytes (PBLs). Shortly after induction of anti-Thy 1.1-GN, sPLA(2)-IB expression was markedly upregulated in the kidney at 6-24 h. Within glomeruli, the strongest sPLA(2)-IB protein expression was detected on infiltrated granulocytes and monocytes. However, at the same time, the M-type receptor was also markedly upregulated on resident glomerular cells. In vitro, the most prominent cytokine-stimulated secretion of sPLA(2)-IB was observed in monocytes isolated from rat PBLs. Treating glomerular endothelial cells (GECs) with cytokines elicited only weak sPLA(2)-IB expression, but treatment of these cells with exogenous sPLA(2)-IB resulted in a marked expression of the endogenous sPLA(2)-IB. Mesangial cells did not express sPLA(2)-IB at all. The M-type sPLA(2) receptor protein was markedly upregulated on cytokine-stimulated mesangial and endothelial cells as well as on lymphocytes and granulocytes. During anti-Thy 1.1 rat GN, sPLA(2)-IB and the M-type sPLA(2) receptor are induced as primary downstream genes stimulated by inflammatory cytokines. Subsequently, both sPLA(2)-IB and the M-type sPLA(2) receptor are involved in the autocrine and paracrine amplification of the inflammatory process in different resident and infiltrating cells.

Activation of human inflammatory cells by secreted phospholipases A2

Secreted phospholipases A(2) (sPLA(2)s) are enzymes detected in serum and biological fluids of patients with various inflammatory, autoimmune and allergic disorders. Different isoforms of sPLA(2)s are expressed and released by human inflammatory cells, such as neutrophils, eosinophils, T cells, monocytes, macrophages and mast cells. sPLA(2)s generate arachidonic acid and lysophospholipids thus contributing to the production of bioactive lipid mediators in inflammatory cells. However, sPLA(2)s also activate human inflammatory cells by mechanisms unrelated to their enzymatic activity. Several human and non-human sPLA(2)s induce degranulation of mast cells, neutrophils and eosinophils and activate exocytosis in macrophages. In addition some, but not all, sPLA(2) isoforms promote cytokine and chemokine production from macrophages, neutrophils, eosinophils, monocytes and endothelial cells. These effects are primarily mediated by binding of sPLA(2)s to specific membrane targets (heparan sulfate proteoglycans, M-type, N-type or mannose receptors) expressed on effector cells. Thus, sPLA(2)s may play an important role in the initiation and amplification of inflammatory reactions by at least two mechanisms: production of lipid mediators and direct activation of inflammatory cells. Selective inhibitors of sPLA(2)-enzymatic activity and specific antagonists of sPLA(2) receptors are current being tested for pharmacological treatment of inflammatory and autoimmune diseases.

Cytosolic phospholipase A2 inhibition attenuates ischemia-reperfusion injury in an isolated rat lung model

BACKGROUND

Arachidonic acid metabolites and platelet-activating factor (PAF) are potentially involved in ischemia-reperfusion (IR) lung injury. A key enzyme regulating their metabolism is cytosolic phospholipase A2 (cPLA2). Arachidonyl trifluoromethyl ketone (AACOCF3) is reported to be a potent cPLA2 inhibitor. In the present study, we hypothesized that pharmacological inhibition of cPLA2 might ameliorate IR lung injury.

METHODS

To test the hypothesis, we examined the effects of AACOCF3 in an isolated rat lung model. Three groups were defined (n=6, each): in the vehicle group, lungs were perfused for 2 hours without an ischemic period. In the ischemic groups, 20 mg/kg of AACOCF3 (AACOCF3 group) or saline (control group) was i.v. administered 15 min before lung harvest. Lungs were flushed with LPD solution, cold-stored 18 hours, and reperfused for 2 hours.

RESULTS

IR increased cPLA2 activity mainly via alveolar macrophages, sPLA2 activity, thromboxane and leukotriene formation, and the expression of PAF receptor, whereas AACOCF3 treatment significantly reduced all of these. Compared to the vehicle group, the wet-to-dry ratio, proteins in BAL, and MPO activity increased significantly by twofold, fourfold, and threefold, respectively. Furthermore, the PO2 dropped from 615.7+/-31.2 to 452.1+/-30.9 mmHg at the end of reperfusion (P<0.001). AACOCF3 treatment maintained the PO2 at a level similar to the vehicle group throughout reperfusion and reduced significantly the alveolar-capillary leakage, edema formation, and neutrophil extravasation.

CONCLUSION

Pharmacological inhibition of the cPLA2 cascade decreases bioactive lipid formation and attenuates IR-induced lung injury.

Pancreatic phospholipase A2 contributes to lung injury in experimental meconium aspiration

To investigate the role of pancreatic (group I) secretory PLA2 (sPLA2-I) in the pathogenesis of meconium aspiration syndrome, human particulate meconium or its supernatant either before or after extraction of PLA2-I was insufflated into rat lungs. In addition, the pulmonary effects of intra-tracheal human and bovine PLA2-I were studied. Lungs with saline instillation served as controls. Intrapulmonary particulate meconium (both before and after PLA2-I extraction), unlike meconium supernatant, resulted in markedly elevated lung tissue PLA2 catalytic activity and human PLA2-I concentrations when compared with controls. On the other hand, tissue concentrations of the group II PLA2 remained unchanged in all meconium lungs. Pulmonary PLA2-I concentrations further correlated positively with lung injury scores. Instillation of meconium-derived human PLA2-I, at a concentration of one-third of that in particulate meconium, did not raise PLA2 activity or concentrations of PLA2-I or PLA2-II in the lung tissue from the control level, but still resulted in significantly elevated lung wet/dry ratio and injury score. In contrast, insufflation of bovine pancreatic PLA2 increased the lung tissue enzyme activity and wet/dry ratio from the control level, but had no effect on the type II PLA2 concentration or lung injury score. Our data thus indicate that human pancreatic PLA2, introduced in high amounts within aspirated meconium especially in particulate form, is a potent inducer of lung tissue inflammatory injury.

Secretory phospholipases A2 in inflammatory and allergic diseases: not just enzymes

Secretory phospholipases A(2) (sPLA(2)s) are molecules released in plasma and biologic fluids of patients with systemic inflammatory, autoimmune, and allergic diseases. Several sPLA(2) isoforms are expressed and released by such human inflammatory cells as neutrophils, eosinophils, basophils, T cells, monocytes, macrophages, and mast cells. Certain sPLA(2)s release arachidonic acid, thereby providing the substrate for the biosynthesis of proinflammatory eicosanoids. However, there are other mechanisms by which sPLA(2)s might participate in the synthesis of lipid mediators. Interestingly, sPLA(2)s activate inflammatory cells through mechanisms unrelated to their enzymatic activity. Several sPLA(2)s induce degranulation of mast cells and eosinophils and activate exocytosis in macrophages. Furthermore, sPLA(2)s promote cytokine and chemokine production from macrophages, neutrophils, eosinophils, monocytes, and endothelial cells. Some of these effects are mediated by the binding of sPLA(2)s to specific receptors expressed on effector cells. Thus sPLA(2)s might play important roles in the initiation and amplification of the inflammatory reaction. Selective inhibitors of sPLA(2)s and specific antagonists of sPLA(2) receptors might prove useful in the treatment of allergic and autoimmune diseases, such as bronchial asthma and rheumatoid arthritis.

Identification of genes differentially expressed in rat alveolar type I cells

Although approximately 98% of the internal surface area of the lung is lined by alveolar type I cells, little is known about the functions of this cell type. Using freshly isolated rat type I and type II cells, we created a subtraction library by suppression subtractive hybridization to identify genes differentially expressed by type I cells. We identified twelve genes of known function that are differentially expressed by type I cells. Differential expression of all 12 genes was confirmed by Northern blotting; we confirmed differential expression by immunocytochemistry for 3 genes for which suitable antibodies were available. Most of the genes code for proteins that are multifunctional. From the known functions of these genes, we infer that type I cells may play a role in the maintenance of normal alveolar homeostasis and protection from injury, lung development and remodeling, host defense, tumor/growth suppression, and surfactant metabolism, among other functions.

Secretory phospholipases A2 as multivalent mediators of inflammatory and allergic disorders

Phospholipases A(2) (PLA(2)s) are enzymes responsible for mobilization of fatty acids, including arachidonic acid (AA), from phospholipids. These enzymes are classified as high-molecular-weight cytosolic PLA(2)s (cPLA(2)s) and low-molecular-weight secretory PLA(2)s (sPLA(2)s). There is increasing evidence that large quantities of sPLA(2)s are released in the plasma of patients with systemic inflammatory and autoimmune diseases. In addition, high levels of sPLA(2)s can be detected at sites of allergic inflammation including the upper airways of patients with rhinitis and the lower airways of patients with asthma. These extracellular enzymes play an important role in inflammation by releasing AA, which can be subsequently converted to proinflammatory prostaglandins and leukotrienes. Generation of AA mediated by sPLA(2)s occurs through different mechanisms, including (1) the direct hydrolysis of outer cell membrane phospholipids, (2) internalization and transfer of sPLA(2)s to intracellular pools of phospholipids enriched in AA, and (3) activation of cPLA(2)s. In addition, sPLA(2)s induce degranulation and production of cytokines and chemokines from a variety of cells involved in inflammatory and immune responses. These effects are exerted by mechanisms that are independent of the enzymatic activity and are mediated by the interaction of sPLA(2)s with specific or promiscuous membrane receptors. Therefore, sPLA(2)s may have an important role in inflammatory and allergic reactions by activating multiple mechanisms within inflammatory and immune cells, leading to the production of eicosanoids, cytokines and chemokines.