Secretory phospholipase A2-potentiated inducible nitric oxide synthase expression by macrophages requires NF-kappa B activation

Thymopentin improves the survival of septic mice by promoting the production of 15-deoxy-prostaglandin J2 and activating the PPARγ signaling pathway

Sepsis, a systemic inflammatory response syndrome (SIRS) caused by infection, is a major public health concern with limited therapeutic options. Infection disturbs the homeostasis of host, resulting in excessive inflammation and immune suppression. This has prompted the clinical use of immunomodulators to balance host response as an alternative therapeutic strategy. Here, we report that Thymopentin (TP5), a synthetic immunomodulator pentapeptide (Arg-Lys-Asp-Val-Tyr) with an excellent safety profile in the clinic, protects mice against cecal ligation and puncture (CLP)-induced sepsis, as shown by improved survival rate, decreased level of pro-inflammatory cytokines and reduced ratios of macrophages and neutrophils in spleen and peritoneum. Regarding mechanism, TP5 changed the characteristics of LPS-stimulated macrophages by increasing the production of 15-deoxy-Δ^12,14 -prostaglandin J2 (15-d-PGJ2). In addition, the improved effect of TP5 on survival rates was abolished by the peroxisome proliferator-activated receptor γ (PPARγ) antagonist GW9662. Our results uncover the mechanism of the TP5 protective effects on CLP-induced sepsis and shed light on the development of TP5 as a therapeutic strategy for lethal systemic inflammatory disorders.

A Potential Role of Phospholipase 2 Group IIA (PLA2-IIA) in P. gingivalis-Induced Oral Dysbiosis

Porphyromonas gingivalis is an oral pathogen with the ability to induce oral dysbiosis and periodontal disease. Nevertheless, the mechanisms by which P. gingivalis could abrogate the host-microbe symbiotic relationship leading to oral dysbiosis remain unclear. We have recently demonstrated that P. gingivalis specifically increased the antimicrobial properties of oral epithelial cells, through a strong induction of the expression of PLA₂-IIA in a mechanism that involves activation of the Notch-1 receptor. Moreover, gingival expression of PLA₂-IIA was significantly increased during initiation and progression of periodontal disease in non-human primates and interestingly, those PLA₂-IIA expression changes were concurrent with oral dysbiosis. In this chapter, we present an innovative hypothesis of a potential mechanism involved in P. gingivalis-induced oral dysbiosis and inflammation based on our previous observations and a robust body of literature that supports the antimicrobial and proinflammatory properties of PLA₂-IIA as well as its role in other chronic inflammatory diseases.

Cytotoxic effect of methanolic extract, alkaloid and terpenoid fractions of Stachys pilifera against HT-29 cell line

Stachys pilifera (S. pilifera) Benth (Lamiaceae) is used in traditional medicine to treat a variety of diseases. Despite some reports on the antitumor effects of some species of this genus, anticancer activity of S. pilifera has not been yet reported. Here, we examined the cytotoxic effect and cell death mechanisms of methanolic extract of S. pilifera and its alkaloid and terpenoid fractions on the HT-29 colorectal cell line. HT-29 cells were cultivated and then incubated in the methanolic extract of S. pilifera and its fractions at various concentrations for 24 h. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Morphology of cells was evaluated by contrast microscopy. Furthermore, effects of the tested extract and fractions were tested on some regulators of cell death and proliferation such as caspase-8, caspase-9, nuclear factor-κB (NF-κB), and nitric oxide (NO). Cisplatin was used as positive control. The estimated IC₅₀ values of the methanolic extract, alkaloid and terpenoid fractions, and cisplatin against HT29 cell after 24 h were determined to be 612, 48.12, 46.44, and 4.02 μg/mL, respectively. Morphological changes such as plasma membrane blebbing, cell size reduction, and apoptotic bodies were observed in cells faced with the extract and fractions. S. pilifera extract and its fractions induced apoptosis through inhibition of NF-κB, NO, and activation of caspase-8 and caspase-9. Data showed considerable cytotoxic and antiproliferative effects of S. plifera on colorectal cell line through induction of apoptosis. These findings provide a basis for the therapeutic potential of S. pilfera in the treatment of colon cancer.

High-Density Lipoprotein (HDL) Counter-Regulates Serum Amyloid A (SAA)-Induced sPLA2-IIE and sPLA2-V Expression in Macrophages

Human serum amyloid A (SAA) has been demonstrated as a chemoattractant and proinflammatory mediator of lethal systemic inflammatory diseases. In the circulation, it can be sequestered by a high-density lipoprotein, HDL, which carries cholesterol, triglycerides, phospholipids and apolipoproteins (Apo-AI). The capture of SAA by HDL results in the displacement of Apo-AI, and the consequent inhibition of SAA’s chemoattractant activities. It was previously unknown whether HDL similarly inhibits SAA-induced sPLA₂ expression, as well as the resultant HMGB1 release, nitric oxide (NO) production and autophagy activation. Here we provided compelling evidence that human SAA effectively upregulated the expression and secretion of both sPLA₂-IIE and sPLA₂-V in murine macrophages, which were attenuated by HDL in a dose-dependent fashion. Similarly, HDL dose-dependently suppressed SAA-induced HMGB1 release, NO production, and autophagy activation. In both RAW 264.7 cells and primary macrophages, HDL inhibited SAA-induced secretion of several cytokines (e.g., IL-6) and chemokines (e.g., MCP-1 and RANTES) that were likely dependent on functional TLR4 signaling. Collectively, these findings suggest that HDL counter-regulates SAA-induced upregulation and secretion of sPLA₂-IIE/V in addition to other TLR4-dependent cytokines and chemokines in macrophage cultures.

Role of pancreatic β-cell death and inflammation in diabetes

Apoptosis of pancreatic β-cells is the final step in the development of type 1 diabetes (T1D), leading to critically diminished β-cell mass and contributing to the onset of hyperglycaemia. The spontaneous apoptosis of pancreatic β-cells during pancreas ontogeny also induces cell death-associated inflammation, stimulates antigen-presenting cells and sensitizes naïve diabetogenic T cells. The role of pancreatic β-cell death in type 2 diabetes (T2D) is less clear. In the preclinical period of T2D, hyperinsulinaemia and β-cell hyperplasia develop to compensate for insulin resistance, which is clearly seen in animal models of T2D. For the development of overt T2D, relative insulin deficiency is critical in addition to insulin resistance. Insulin deficiency could be due to β-cell dysfunction and/or decreased β-cell mass. Pancreatic β-cell apoptosis due to lipid injury (lipoapoptosis), endoplasmic reticulum (ER) stress or JNK activation could contribute to the decreased β-cell mass in T2D. Activation of inflammasomes by lipid injury, ER stress, human islet amyloid polypeptide, hyperglycaemia or autophagy insufficiency could also lead to β-cell death or dysfunction. Thus, β-cell death and cell death-associated inflammation through innate immune receptors could be important in both T1D and T2D.

Transglutaminase 2 and phospholipase A₂ interactions in the inflammatory response in human Thp-1 monocytes

Several experimental approaches have demonstrated that transglutaminase 2 (TG2) increased activity is involved in monocyte activation and inflammatory response. Preliminary results also demonstrate a TG-mediated post-translational modification of phospholipase A2 (PLA2), which catalyzes the release of arachidonic acid from its lipid storage sites. The control of PLA2-mediated production of eicosanoids has been found to be of great benefit for inflammatory disease treatment. However, the identification of the mechanisms of PLA2 activation is a very complex issue, because of the presence of multiple PLA2 forms. The aim of this study was to characterize the interactions between TG2 and sPLA2 in LPS-stimulated THP-1 cells, which were treated with TPA to induce early differentiated macrophage-type model. We demonstrated that increases in TG2 enzyme activity and protein expression may be considered an early event in monocyte/macrophage activation by LPS. Under these conditions, TG2 protein was co-immunoprecipitated with PLA2 by monoclonal antibody directed against the secretory form of the enzyme (sPLA2-V). Concomitantly, the PLA2 enzyme activity increased in TPA-treated cells exposed to LPS; these high levels of enzyme activity were significant reduced by R283, a site-specific inhibitor of TG2. Moreover, confocal laser scanning microscopy analysis of double-immunostained cytochemical specimens confirmed a co-localization of BAPA-labeled proteins and sPLA2-V in LPS-treated cells. These findings give evidence of a complex TG2/sPLA2-V, suggesting the possibility that sPLA2-V is a substrate for TG2. These results demonstrated that TG2 increases produced a sustained activation of PLA2 activity, suggesting a functional interaction between these enzymes in the regulation of inflammatory response.

Regulatory effects of the JAK3/STAT1 pathway on the release of secreted phospholipase A₂-IIA in microvascular endothelial cells of the injured brain

Background

Secreted phospholipase A₂-IIA (sPLA₂-IIA) is an inducible enzyme released under several inflammatory conditions. It has been shown that sPLA₂-IIA is released from rat brain astrocytes after inflammatory stimulus, and lipopolysaccharide (LPS) and nitric oxide (NO) have been implicated in regulation of this release. Here, brain microvascular endothelial cells (BMVECs) were treated with LPS to uncover whether sPLA₂-IIA was released, whether nitric oxide regulated this release, and any related signal mechanisms.

Methods

Supernatants were collected from primary cultures of BMVECs. The release of sPLA₂-IIA, and the expression of inducible nitric oxide synthase (iNOS), phospho-JAK3, phospho-STAT1, total JAK3 and STAT1, β-actin, and bovine serum albumin (BSA) were analyzed by Western blot or ELISA. NO production was calculated by the Griess reaction. sPLA₂ enzyme activity was measured with a fluorometric assay. Specific inhibitors of NO (L-NAME and aminoguanidine, AG), JAK3 (WHI-P154,WHI), STAT1 (fludarabine, Flu), and STAT1 siRNA were used to determine the involvement of these molecules in the LPS-induced release of sPLA₂-IIA from BMVECs. Nuclear STAT1 activation was tested with the EMSA method. The monolayer permeability of BMVECs was measured with a diffusion assay using biotinylated BSA.

Results

Treatment of BMVECs with LPS increased the release of sPLA₂-IIA and nitrite into the cell culture medium up to 24 h. Pretreatment with an NO donor, sodium nitroprusside, decreased LPS-induced sPLA₂-IIA release and sPLA₂ enzyme activity, and enhanced the expression of iNOS and nitrite generation after LPS treatment. Pretreatment with L-NAME, AG, WHI-P154, or Flu notably reduced the expression of iNOS and nitrite, but increased sPLA₂-IIA protein levels and sPLA₂ enzyme activity. In addition, pretreatment of the cells with STAT1 siRNA inhibited the phosphorylation of STAT1, iNOS expression, and nitrite production, and enhanced the release of sPLA₂-IIA. Pretreatment with the specific inhibitors of NOS, JAK2, and STAT3 decreased the permeability of BMVECs. In contrast, inhibition of sPLA₂-IIA release increased cell permeability. These results suggest that sPLA₂-IIA expression is regulated by the NO-JAK3-STAT1 pathway. Importantly, sPLA₂-IIA augmentation could protect the LPS-induced permeability of BMVECs.

Conclusion

Our results demonstrate the important action of sPLA₂-IIA in the permeability of microvascular endothelial cells during brain inflammatory events. The sPLA₂ and NO pathways can be potential targets for the management of brain MVEC injuries and related inflammation.

Secreted phospholipases A(2): A proinflammatory connection between macrophages and mast cells in the human lung

Secretory phospholipases A(2) (sPLA(2)) are an emerging class of mediators of inflammation. These enzymes accumulate in plasma and other biological fluids of patients with inflammatory, autoimmune and allergic diseases. sPLA(2)s are secreted at low levels in the normal airways and tend to increase during inflammatory lung diseases (e.g. bronchial asthma, chronic obstructive pulmonary disease, interstitial lung fibrosis, and sarcoidosis) as the result of plasma extravasation and/or local production. Such immune resident cells as macrophages and mast cells can be a source of sPLA(2)s in the lung. However, these cells are also targets for sPLA(2)s that sustain the activation programs of macrophages and mast cells with mechanism related to their enzymatic activity as well as to their capacity to interact with surface molecules (e.g., heparan sulfate proteoglycans, M-type receptor, mannose receptor). Recent evidence suggests that mast cells are a better source of extracellular sPLA(2)s than macrophages. On the other hand, macrophages appear to be a preferential target for sPLA(2)s. Anatomical association between macrophages and mast cells in the airways suggest that sPLA(2)s released by mast cells may activate in a paracrine fashion several macrophage functions relevant to the modulation of lung inflammation. Thus, sPLA(2)s may play a major role in inflammatory lung diseases by acting as a proinflammatory connection between macrophages and mast cells.

Gaseous nitrogen oxide promotes human lung cancer cell line A549 migration, invasion, and metastasis via iNOS-mediated MMP-2 production

Gaseous nitrogen oxide (gNO) is an important indoor and outdoor air pollutant. Many studies have indicated gNO causes lung tissue damage by its oxidation properties and free radicals. However, there are considerably few data on the association between lung cancer and gNO exposure. The purpose of this study was to examine whether gNO could contribute to the process of malignant progression of lung cancer. The results of wound-healing assay and in vitro transwell assay revealed that gNO-induced dose and time dependently the migration and invasion of A549 cells, a human lung cancer cell line, under noncytotoxic concentrations. gNO was able to induce release of NO from A549 cells, an effect that was mediated via the activation of inducible nitric oxide synthases (iNOS), but not constitutive isoforms, during the same treatment period. An increased expression of matrix metalloproteinase (MMP) and a coincided reduction in repress tissue inhibitors of metalloprotease-2 were observed upon the treatment of gNO. The gNO-mediated MMP-2 induction appeared to be a consequence of nuclear factor kappa B and activation protein-1 activation, because that their DNA binding activity was enhanced by gNO. All these influences of gNO were efficiently repressed by the pretreatment of a NOS inhibitor (N(G)-nitro-L-arginine methyl ester). Using a mouse model, we showed that gNO promoted A549 metastasis to the lung through a mechanism involving the iNOS-dependent MMP-2 activity. Our data imply that gNO exposure, which in turn led to iNOS activation and the enhancement of MMP-mediated cellular events, was related to lung cancer development.

Activation of toll-like receptor 4 modulates vascular endothelial growth factor synthesis through prostacyclin-IP signaling

In this study, we show that activation of toll-like receptor (TLR)4 by lipopolysaccharide (LPS) induces cyclooxygenase-2 (COX-2) expression, which results in prostaglandin (PG)I2 formation in macrophages. The LPS-stimulated COX-2 expression and PGI2 release were accompanied by production of the potent angiogenic cytokine, vascular endothelial growth factor (VEGF), and these effects were suppressed by NS-398, which is a COX-2 inhibitor. Direct addition of iloprost (an analogue of PGI2) for IP receptor also induced the production of VEGF, whereas DP, FP, and TP receptor agonists did not. Inhibition of IP protein expression by micro interfering RNA blocked LPS-induced VEGF production. Additionally, macrophages transiently caused Akt phosphorylation after stimulation with LPS, and inhibition of Akt phosphorylation blocked the production of VEGF and COX-2 expression in response to LPS. Overall, this study demonstrated that engagement of TLR4 with LPS induces production of PGI2 via Akt and generates VEGF through IP receptor.

Crystallization and preliminary X-ray crystallographic analysis of the heterodimeric crotoxin complex and the isolated subunits crotapotin and phospholipase A2

Crotoxin, a potent neurotoxin from the venom of the South American rattlesnake Crotalus durissus terrificus, exists as a heterodimer formed between a phospholipase A(2) and a catalytically inactive acidic phospholipase A(2) analogue (crotapotin). Large single crystals of the crotoxin complex and of the isolated subunits have been obtained. The crotoxin complex crystal belongs to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 38.2, b = 68.7, c = 84.2 A, and diffracted to 1.75 A resolution. The crystal of the phospholipase A(2) domain belongs to the hexagonal space group P6(1)22 (or its enantiomorph P6(5)22), with unit-cell parameters a = b = 38.7, c = 286.7 A, and diffracted to 2.6 A resolution. The crotapotin crystal diffracted to 2.3 A resolution; however, the highly diffuse diffraction pattern did not permit unambiguous assignment of the unit-cell parameters.

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.

Scalaradial Inhibition of Epidermal Growth Factor Receptor-Mediated Akt Phosphorylation Is Independent of Secretory Phospholipase A2

The marine natural product 12-epi-scalaradial (SLD) is a specific secretory phospholipase A(2) (sPLA(2)) inhibitor. However, little is known about whether this compound has other pharmacological effects. Here, we revealed a novel effect of SLD on epidermal growth factor receptor (EGFR)-mediated Akt phosphorylation. SLD dose- and time-dependently inhibited epidermal growth factor (EGF)-stimulated Akt phosphorylation, which is required for Akt activation. SLD also blocked the EGF-stimulated membrane translocation of 3-phosphoinositide-dependent protein kinase 1 and inhibited phosphatidylinositol 3-kinase activity. This inhibition is specific for SLD because other phospholipase inhibitors, including sPLA(2) inhibitor thioetheramide-phosphatidylcholine, cytosolic PLA(2) inhibitor arachidonyl trifluoromethyl ketone, cytosolic PLA(2) and Ca(2+)-independent PLA(2) inhibitor methyl arachidonyl fluorophosphonate, phospholipase C inhibitor U73122, and cyclooxygenases inhibitor indomethacin, failed to inhibit EGF-stimulated Akt phosphorylation. Furthermore, arachidonic acid, the main sPLA(2)-catalyzed metabolite, was not able to rescue SLD inhibition of EGF-stimulated Akt phosphorylation. Overexpression of group IIA or group X sPLA(2) did not reverse the inhibitory effect of SLD on Akt phosphorylation, either. Our results demonstrate that SLD inhibits EGFR-mediated Akt phosphorylation, and this novel effect of SLD is independent of sPLA(2).

Interactions between nitric oxide and arachidonic acid in lung epithelial cells: possible roles for peroxynitrite and superoxide

This study investigated interactions between nitric oxide synthesis and phospholipase A2 (PLA2) activation in lung epithelial cells. Nitrite formation, inducible nitric oxide synthase expression, and [3H]arachidonic acid (AA) release were determined following treatment with: (1) the nitric oxide synthase inhibitors N(G)-nitro-L-arginine methyl esther (L-NAME) and aminoguanidine; (2) arachidonyl trifluoromethyl ketone (AACOCF3), a specific cytosolic PLA2 inhibitor; (3) S-morpholinosydnonimine (SIN-1), a nitric oxide donor which provokes peroxynitrite formation; (4) trolox, a free radical scavenger, and (5) the AA release agonists calcium ionophore, phorbol 12-myristate 13-acetate, and sodium vanadate. The results demonstrated that (1) L-NAME and aminoguanidine inhibited agonist-induced AA release by 40 and 65%, respectively; (2) AACOCF3 inhibited nitrite formation and inducible nitric oxide synthase expression in a dose-dependent manner; (3) SIN-1, together with AA release agonists, significantly increased the AA output, and (4) trolox counteracted the SIN-1 effects. Our results demonstrate cross talk between nitric oxide synthase and PLA(2) pathways, with a possible intermediary role for peroxynitrite and superoxide.

Group IB Secretory Phospholipase A2 Stimulates CXC Chemokine Ligand 8 Production via ERK and NF-κB in Human Neutrophils

Although the level of group IB secretory phospholipase A(2) (sPLA(2)-IB) has been reported to be up-regulated during inflammatory response, the role of sPLA(2)-IB on the regulation of inflammation and immune responses has not been fully elucidated. In this study, we found that sPLA(2)-IB stimulates the expression and secretion of CXCL8 without affecting other proinflammatory cytokines, such as IL-1beta or TNF alpha in human neutrophils. The induction of CXCL8 secretion by sPLA(2)-IB occurs at both the transcription and translational levels and correlates with activation of NF-kappaB. Moreover, the NF-kappaB inhibitors pyrrolidinedithiocarbamate, dexamethasone, or sulfasalazine were found to prevent CXCL8 production by sPLA(2)-IB in human neutrophils. In addition, the signaling events induced by sPLA(2)-IB included activation of the MAPK ERK and an increase in intracellular Ca(2+), which are both required for CXCL8 production. The exogenous addition of sPLA(2)-IB did not induce arachidonic acid release from human neutrophils, and the inactivation of sPLA(2)-IB by EGTA did not affect CXCL8 production by sPLA(2)-IB in human neutrophils. Taken together, we suggest that sPLA(2)-IB plays a role in the modulation of inflammatory and immune responses via the sPLA(2) receptor, by inducing CXCL8 in human neutrophils.

Antiarthritic effect of bee venom: Inhibition of inflammation mediator generation by suppression of NF-?B through interaction with the p50 subunit

OBJECTIVE

To investigate the molecular mechanisms of the antiarthritic effects of bee venom (BV) and melittin (a major component of BV) in a murine macrophage cell line (Raw 264.7) and in synoviocytes obtained from patients with rheumatoid arthritis.

METHODS

We evaluated the antiarthritic effects of BV in a rat model of carrageenan-induced acute edema in the paw and in a rat model of chronic adjuvant-induced arthritis. The inhibitory effects of BV and melittin on inflammatory gene expression were measured by Western blotting, and the generation of prostaglandin E(2) (PGE(2)) and nitric oxide (NO) and the intracellular calcium level were assayed. NF-kappaB DNA binding and transcriptional activity were determined by gel mobility shift assay or by luciferase assay. Direct binding of BV and melittin to the p50 subunit of NF-kappaB was determined with a surface plasmon resonance analyzer.

RESULTS

BV (0.8 and 1.6 mug/kg) reduced the effects of carrageenan- and adjuvant-induced arthritis. This reducing effect was consistent with the inhibitory effects of BV (0.5, 1, and 5 mug/ml) and melittin (5 and 10 mug/ml) on lipopolysaccharide (LPS; 1 mug/ml)-induced expression of cyclooxygenase 2, cytosolic phospholipase A(2), inducible NO synthase, generation of PGE(2) and NO, and the intracellular calcium level. BV and melittin prevented LPS-induced transcriptional and DNA binding activity of NF-kappaB via the inhibition of IkappaB release and p50 translocation. BV (affinity [K(d)] = 4.6 x 10(-6)M) and melittin (K(d) = 1.2 x 10(-8)M) bound directly to p50.

CONCLUSION

Target inactivation of NF-kappaB by directly binding to the p50 subunit is an important mechanism of the antiarthritic effects of BV.

Role of nitric oxide in myotoxic activity induced by crotoxin in vivo

This study was aimed to determine the role of nitric oxide on the skeletal myotoxic activity induced by crotoxin, the major component of the venom of Crotalus durissus terrificus. Rats were treated with N(G)-nitro-L-arginine methyl ester (L-NAME), a non-selective inhibitor of nitric oxide synthase or vehicle for 4 days, and on the 5th day received an intramuscular injection of crotoxin into the tibialis anterior muscle. Rats were also treated with aminoguanidine bicarbonate salt or 7-nitroindazole, inhibitors of the inducible and neuronal isoforms of nitric oxide synthase, respectively, for 4 days and on the 5th day injected with crotoxin. All treated groups were sacrificed 24 h after injection of crotoxin. Tibialis anterior and soleus muscles were removed, frozen and stored in liquid nitrogen. Histological sections were stained with toluidine blue and assayed for acid phosphatase. The results show that L-NAME significantly minimizes myonecrosis induced by crotoxin and both aminoguanidine and 7-nitroindazole partially prevented myonecrosis induced by crotoxin. Based on the present results we conclude that nitric oxide is a very important intracellular signaling molecule that mediates crotoxin myotoxic activity.

Regulation of the Expression of Inducible Nitric Oxide Synthase

Nitric oxide (NO), generated by the inducible isoform of nitric oxide synthase (iNOS), has been described to have beneficial microbicidal, antiviral, antiparasital, immunomodulatory, and antitumoral effects. However, aberrant iNOS induction at the wrong place or at the wrong time has detrimental consequences and seems to be involved in the pathophysiology of several human diseases. iNOS is primarily regulated at the expression level by transcriptional and post-transcriptional mechanisms. iNOS expression can be induced in many cell types with suitable agents such as bacterial lipopolysaccharides (LPS), cytokines, and other compounds. Pathways resulting in the induction of iNOS expression may vary in different cells or different species. Activation of the transcription factors NF-kappaB and STAT-1alpha, and thereby activation of the iNOS promoter, seems to be an essential step for iNOS induction in most cells. However, at least in the human system, also post-transcriptional mechanism are critically involved in the regulation of iNOS expression. The induction of iNOS can be inhibited by a wide variety of immunomodulatory compounds acting at the transcriptional levels and/or post-transcriptionally.

Biological effects of group IIA secreted phosholipase A(2)

Group IIA secreted phospholipase A(2) (sPLA(2)-IIA) is the most abundant element in human tissues of a large family of low molecular weight phospholipases A(2), which shows properties different from those displayed by the cytosolic phospholipase A(2) involved in the release of arachidonic acid. sPLA(2)-IIA behaves as a ligand for a group of receptors inside the C-type multilectin mannose receptor family and also interacts with heparan sulfate proteoglycans such as glypican, the dermatan/chondroitin sulfate-rich decorin, and the chondroitin sulfate-rich versican, thus being able to internalize to specific compartments within the cell and producing biological responses. This review provides a short summary of the biological actions of sPLA(2)-IIA on intracellular signaling pathways.

Selenium deficiency increases the expression of inducible nitric oxide synthase in RAW 264.7 macrophages: role of nuclear factor-kappaB in up-regulation

The inducible isoform of nitric oxide synthase (iNOS) is implicated in atherosclerosis, malignancy, rheumatoid arthritis, tissue and reperfusion injuries. A key determinant of the pro-oxidant versus protective effects of NO is the underlying redox status of the tissue. Selenoproteins, such as glutathione peroxidases (GPxs) and thioredoxin reductases, are key components of cellular defence and promote optimal antioxidant/oxidant balance. In this study, we have investigated the relationship between Se status, iNOS expression and NO production in Se-deficient and Se-supplemented RAW 264.7 macrophage cell lines. The cellular GPx activity, a measure of Se status, was 17-fold lower in Se-deficient RAW 264.7 cells and the total cellular oxidative tone, as assessed by flow cytometry with 2',7'-dichlorodihydrofluorescein diacetate, was higher in the Se-deficient cells than the Se-supplemented cells. Upon lipopolysaccharide (LPS) stimulation of these cells in culture, we found significantly higher iNOS transcript and protein expression levels with an increase in NO production in Se-deficient RAW 264.7 cells than the Se-supplemented cells. Electrophoretic mobility-shift assays, nuclear factor-kappaB (NF-kappaB)-luciferase reporter assays and Western blot analyses indicate that the increased expression of iNOS in Se deficiency could be due to an increased activation and consequent nuclear localization of the redox-sensitive transcription factor NF-kappaB. These results suggest an inverse relationship between cellular Se status and iNOS expression in LPS-stimulated RAW 264.7 cells and provide evidence for the beneficial effects of dietary Se supplementation in the prevention and/or treatment of oxidative-stress-mediated inflammatory diseases.

Nitric oxide production by a murine macrophage cell line (RAW264.7) stimulated with lipopolysaccharide from Actinobacillus actinomycetemcomitans

The aim of this study was to determine whether Actinobacillus actinomycetemcomitans lipopolysaccharide (LPS-A. actinomycetemcomitans) could stimulate a murine macrophage cell line (RAW264.7 cells) to produce nitric oxide (NO). The cells were treated with LPS-A. actinomycetemcomitans or Escherichia coli LPS (LPS-Ec) for 24 h. The effects of N(G)-monomethyl-L-arginine (NMMA), polymyxin B and cytokines (IFN-gamma, TNF-alpha, IL-4 and IL-12) on the production of NO were also determined. The role of protein tyrosine kinase, protein kinase C and microtubulin organization on NO production were assessed by incubating RAW264.7 cells with genistein, bisindolylmaleide and colchicine prior to LPS-A. actinomycetemcomitans stimulation, respectively. NO levels from the culture supernatants were determined by the Griess reaction. The results showed that LPS-A. actinomycetemcomitans stimulated NO production by RAW264.7 cells in a dose-dependent manner, but was slightly less potent than LPS-Ec. NMMA and polymyxin B blocked the production of NO. IFN-gamma and IL-12 potentiated but IL-4 depressed NO production by LPS-A. actinomycetemcomitans-stimulated RAW264.7 cells. TNF-alpha had no effects on NO production. Genistein and bisindolylmalemaide, but not colchicine, reduced the production of NO in a dose-dependent mechanism. The results of the present study suggest that A. actinomycetemcomitans LPS, via the activation of protein tyrosine kinase and protein kinase C and the regulatory control of cytokines, stimulates NO production by murine macrophages.

Secretory phospholipases A2 induce cytokine release from blood and synovial fluid monocytes

Secretory phospholipases A2 (sPLA2) are released in the blood of patients with various inflammatory diseases and exert proinflammatory activities by releasing arachidonic acid (AA), the precursor of eicosanoids. We examined the ability of four sPLA2 to activate blood and synovial fluid monocytes in vitro. Monocytes were purified from blood of healthy donors or from synovial fluid of patients with rheumatoid arthritis by negative immunoselection and by adherence to plastic dishes, respectively. The cells were incubated with group IA, IB, IIA and III sPLA2 and the release of TNF-alpha, IL-6 and IL-12 was determined by ELISA. Group IA, IB and IIA sPLA2 induced a concentration-dependent release of TNF-alpha and IL-6 from blood monocytes. These sPLA2 activated IL-12 production only in monocytes preincubated with IFN-gamma. Group IA and IIA sPLA2 also induced TNF-alpha and IL-6 release from synovial fluid monocytes. TNF-alpha and IL-6 release paralleled an increase in their mRNA expression and was independent from the capacity of sPLA2 to mobilize AA. These results indicate that sPLA2 stimulate cytokine release from blood and synovial fluid monocytes by a mechanism at least partially unrelated to their enzymatic activity. This effect may concur with the generation of AA in the proinflammatory activity of sPLA2 released during inflammatory diseases.

Group IIA secretory phospholipase A(2) stimulates inducible nitric oxide synthase expression via ERK and NF-kappaB in macrophages

The mammalian group IIA secretory phospholipase A(2) (sPLA(2)) is believed to play an important role in inflammation and cell injury. The present study underlines the importance of group IIA sPLA(2) in the regulation of iNOS. Treatment of cells with sPLA(2) induced protein expression and mRNA accumulation of iNOS in a dose-dependent manner. The pretreatment of cells with rho-BPB or SCA, selective sPLA(2) inhibitors, inhibited sPLA(2)-induced iNOS expression. sPLA(2) stimulated the simultaneous activation of two classes of mitogen-activated protein kinases ERK and JNK, but did not stimulate p38 MAPK. PD98059, a selective MEK inhibitor, inhibited sPLA(2)-induced nitrite production and iNOS expression as well as ERK phosphorylation. In addition, pretreatment of rho-BPB or SCA also resulted in inhibition of sPLA(2)-induced ERK phosphorylation. The sPLA(2) signaling mechanisms involving the activation of transcription factor NF-kappaB were studied in the same cells. That stimulation of cells with sPLA(2) caused NF-kappaB activation in a time-dependent manner was shown by the detection of NF-kappaB-specific DNA-protein binding and by IkappaBalpha degradation. sPLA(2)-induced NF-kappaB activation was prevented in the presence of rho-BPB. Furthermore, the NF-kappaB inhibitor PDTC suppressed sPLA(2)-induced nitrite production and iNOS expression as well as IkappaBalpha degradation. The results strongly suggest that group IIA sPLA(2) induces iNOS in macrophages and that this induction occurs through ERK and NF-kappaB.

Functional coupling between secretory and cytosolic phospholipase A2 modulates tumor necrosis factor-alpha- and interleukin-1beta-induced NF-kappa B activation

Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta are potent activators of the transcription factor NF-kappaB, induced during inflammatory conditions. We have previously shown that both secretory and cytosolic phospholipase A(2) (PLA(2)) are involved in TNF-alpha- and IL-1beta-induced NF-kappaB activation. In this study, we have addressed the mechanism of PLA(2) involvement with respect to downstream arachidonic acid (AA) metabolites and the functional coupling between PLA(2)s mediating NF-kappaB activation. We show that in addition to inhibitors of secretory and cytosolic PLA(2)s, 5-lipoxygenase inhibitors attenuate TNF-alpha- and IL-1beta-stimulated NF-kappaB activation. Exogenous addition of leukotriene B(4) (LTB(4)) restored NF-kappaB activation reduced by 5-lipoxygenase inhibitors or an LTB(4) receptor antagonist, thus identifying LTB(4) as a mediator in signaling to NF-kappaB. TNF-alpha- and IL-1beta-induced AA release from cellular membranes was accompanied by phosphorylation of cytosolic PLA(2). Inhibitors of secretory PLA(2) and of 5-lipoxygenase/LTB(4) functionality markedly reduced AA release and nearly completely abolished cytosolic PLA(2) phosphorylation. This demonstrates that secretory PLA(2), through 5-lipoxygenase metabolites, is an essential upstream regulator of cytosolic PLA(2) and AA release. Our results therefore suggest the existence of a functional link between secretory and cytosolic PLA(2) in cytokine-activated keratinocytes, providing a molecular explanation for the participation of both secretory and cytosolic PLA(2) in arachidonic acid signaling and NF-kappaB activation in response to proinflammatory cytokines.

Phosphatidylcholine-specific phospholipase C and D in stimulation of RAW264.7 mouse macrophage-like cells by lipopolysaccharide

The purpose of these studies was to identify the role of phospholipases in the activation of macrophages by lipopolysaccharide (LPS). Tricyclodecan-9-yl-xanthogenate (D609), an inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC); butanol, an inhibitor of phosphatidylcholine phospholipase D (PC-PLD); and propranolol, an inhibitor of phosphatidate phosphohydrolase, were used in the study. Treatment of RAW264.7 murine macrophage-like cells with LPS resulted in expression of inducible nitric oxide synthase and tumor necrosis factor-alpha. The expression was partially inhibited by D609, butanol, or propranolol and was completely blocked by the combination of D609 and butanol. RAW264.7 cells constitutively produced low basal levels of diacylglycerol and phosphatidic acid; production of both was significantly increased after stimulation with LPS, reaching a peak in 2-3 min and remaining elevated after 30 min. In LPS-induced RAW264.7 cells, diacylglycerol was suppressed by each of the three inhibitors alone and almost abolished by D609 plus butanol or D609 plus propranolol. Phosphatidic acid was reduced to basal level by butanol after LPS stimulation for 2.5 min and by butanol plus D609 after LPS stimulation for 2.5 or 10 min. Taken together, these data indicate that activation of RAW264.7 cells by LPS can be mediated by the activities of both PC-PLC and PC-PLD.