Interleukin-13 inhibits inducible nitric oxide synthase expression in human mesangial cells

Pro- and anti-inflammatory cytokines in cutaneous leishmaniasis: a review

Cutaneous leishmaniasis (CL) is caused by different species of the genus Leishmania. Pro- and anti-inflammatory cytokines play different roles in resistance/susceptibility and the immunopathogenesis of Leishmania infection. The balance and dynamic changes in cytokines may control or predict clinical outcome. T helper 1 (Th1) inflammatory cytokines (especially interferon-γ, tumor necrosis factor-α and interleukin-12) are the crucial factors in the initiation of protective immunity against L. major infection, whereas T helper 2 cytokines including IL-5, IL-4, and IL-13 facilitate the persistence of parasites by downregulating the Th1 immune response. On the other hand, aggravation of inflammatory reactions leads to collateral tissue damage and formation of ulcer. For this reason, immunity system such as T regulatory cells produce regulatory cytokines such as transforming growth factor-β and IL-10 to inhibit possible injures caused by increased inflammatory responses in infection site. In this article, we review the role of pro- and anti-inflammatory cytokines in the immunoprotection and immunopathology of CL.

IL-13 Neutralization Modulates Function of Type II Polarized Macrophages in vivo in a Murine T-Cell Lymphoma

IL-13 is a Th2 cytokine that suppresses the effector function and alters the phenotype and function of macrophages switching to alternatively activated or type II polarized macrophages. The type II polarized macrophages or M2 phenotype differ from normal macrophages greatly in terms of receptor expression, cytokine and NO production, that show tumor promoting function rather than tumoricidal function of classically activated macrophages. The chemokines CCL-22 and CCL-17 produced by either tumor cells or alternatively activated macrophages attract Th2 cells preferentially, which increase the local concentration of Th2 cytokines including IL-13 that further skewed the normal phenotype of macrophages at the site of the tumor micro-environment. Therefore, it is possible to restore the phenotype and function of alternatively activated macrophages by eliminating or blocking the activities of these cytokines. In the present investigation, we show that by blocking the activity/signaling of one of its major constituents IL-13, the iNOS expression and correspondingly NO production increases. The observation signifies its efficacy towards a novel approach for cancer therapy by modulating the function of tumor-associated macrophages (TAM) in vivo for the first time.

Interleukin-13 inhibits cytokines synthesis by blocking nuclear factor-κB and c-Jun N-terminal kinase in human mesangial cells

Objective

Monocytes/macrophages, proinflammatory cytokines and chemokines are important in the pathogenesis of glomerulonephritis. Interleukin (IL) -13 has been shown to exert potent anti-inflammatory properties. This study was designed to investigate the effect of IL-13 on the expression of proinflammatory cytokines, chemokines and profibrogenic cytokines and the involved molecular mechanism in cultured human mesangial cells (HMCs).

Methods

The expressions of proinflammatory cytokines, chemokines and profibrogenic cytokines were determined by ribonuclease protection assay (RPA). Activity of nuclear factor-kappa B (NF-κB) and activator protein-1 (AP-1) was examined by electrophoretic mobility shift assay (EMSA). NF-κB subunit p65 nuclear transportation and c-Jun N-terminal kinase (JNK) activity were assayed by immunoblot.

Results

Recombinant IL-13 inhibited tumor necrosis factor-α (TNF-α), IL-1α, IL-1β, monocyte chemoattractant protein-1 (MCP-1), IL-8, and transforming growth factor-β1 (TGF-β1) mRNA expressions in a dose-dependent manner. Lipopolysacchorides (LPS) dramatically increased NF-κB DNA binding activity of HMCs, which was inhibited by IL-13 in a dose-dependent manner. LPS-activated NF-κB contained p50 and p65 dimers, but not c-Rel subunit. IL-13 blocked LPS-induced NF-κB subunit p65. LPS stimulated JNK/AP-1 activation, which was inhibited by IL-13 in a dose-dependent manner.

Conclusion

IL-13 inhibits proinflammatory cytokines, chemokines, and profibrogenic cytokines synthesis by blocking NF-κB and JNK/AP-1 activation. These observations point to the importance of IL-13 in the modulation of inflammatory processes in the renal glomerulus.

Transcriptional suppression of cytokine-induced iNOS gene expression by IL-13 through IRF-1/ISRE signaling

IL-13 has been reported as one of the major down-regulators of iNOS expression in various tissues and cells. The molecular mechanism of iNOS suppression by IL-13 remains unclear, especially at the transcriptional stage. In this study, we found that IL-13 inhibited the expression of iNOS mRNA, protein, and NO product in a concentration-dependent manner for cytokine-stimulated rat hepatocytes. The most effective dose for IL-13 inhibitory effect is approximately 5 ng/ml. IL-13 also decreased the rat iNOS transcriptional activity by promoter analysis, but had no effect on iNOS mRNA stability. By using TranSignal Protein/DNA Combo Array, we identified cytokine-stimulated IRF-1/ISRE binding that was decreased by the addition of IL-13. Gel shift assay confirmed that IL-13 reduced the IRF-1/ISRE binding at nucleotides -913 to -923 of the rat iNOS promoter. Western blot revealed that IL-13 diminished the relative amount of IRF-1 protein translocated to the nucleus. Our data demonstrate that IL-13 down-regulates the cytokine-induced iNOS transcription by decreasing iNOS specific IRF-1/ISRE binding activity.

Measurement of IL-13-induced iNOS-derived gas phase nitric oxide in human bronchial epithelial cells

Exhaled nitric oxide (NO) is altered in numerous diseases including asthma, and is thought broadly to be a noninvasive marker of inflammation. However, the precise source of exhaled NO has yet to be identified, and the interpretation is further hampered by significant inter-subject variation. Using fully differentiated normal human bronchial epithelial (NHBE) cells, we sought to determine (1) the rate of NO release (flux, pl.s(-1.)cm(-2)) into the gas; (2) the effect of IL-13, a prominent mediator of allergic inflammation, on NO release; and (3) inter-subject/donor variability in NO release. NHBE cells from three different donors were cultured at an air-liquid interface and stimulated with different concentrations of IL-13 (0, 1, and 10 ng/ml) for 48 h. Gas phase NO concentrations in the headspace over the cells were measured using a chemiluminescence analyzer. The basal NO flux from the three donors (0.05 +/- 0.03) is similar in magnitude to that estimated from exhaled NO concentrations, and was significantly increased by IL-13 in a donor-specific fashion. The increase in NO release was strongly correlated with inducible nitric oxide synthase (iNOS) gene and protein expression. There was a trend toward enhanced production of nitrate relative to nitrite as an end product of NO metabolism in IL-13-stimulated cells. NO release from airway epithelial cells can be directly measured. The rate of release in response to IL-13 is strongly dependent on the individual donor, but is primarily due to the expression of iNOS.

Targeted histone H4 acetylation via phosphoinositide 3-kinase- and p70s6-kinase-dependent pathways inhibits iNOS induction in mesangial cells

The inducible nitric oxide synthase (iNOS) gene plays an important role in the response to and propagation of injury in glomerular mesangial cells. Although several cis and trans regulatory factors have been characterized, epigenetic regulation of the iNOS gene has not been considered extensively. In this report, we explored the role of histone acetylation in interleukin (IL)-1β-mediated iNOS induction in cultured murine mesangial cells. Treatment of cells with the histone deacetylase inhibitor trichostatin A (TSA, 200 nM) resulted in a time-dependent, selective increase in histone H4 acetylation. TSA treatment of cells stably transfected with an iNOS promoter-luciferase construct inhibited IL-1β induction of endogenous nitric oxide and iNOS protein production and iNOS promoter-luciferase activity. Chromatin immunoprecipitation assays revealed that, under basal conditions, acetylated histone H4 associated with the region −978 to −710 of the iNOS promoter, a region rich in gene control elements and that IL-1β significantly increased this binding, which was further accentuated by cotreatment with TSA. Blockade of the phosphoinositide 3-kinase pathway with LY-294002 or the p70s6-kinase pathway with rapamycin in the presence of TSA and IL-1β inhibited389Thr phosphorylation of p70s6 kinase, promoted binding of acetylated histone H4 to the iNOS promoter, and further suppressed iNOS protein expression and iNOS promoter activity. Thus TSA diminishes IL-1β-induced iNOS transcription through phosphoinositide 3-kinase- and p70s6 kinase-dependent pathways that increase site-specific histone H4 acetylation at the −978 to −710 region of the iNOS promoter. This novel epigenetic control mechanism extends the network of regulatory controls governing NO production in mesangial cells.

Antithrombotic agents in the treatment of severe sepsis

Sepsis, a systemic inflammatory syndrome, is a response to infection and when associated with multiple organ dysfunction is termed severe sepsis. It remains a leading cause of mortality in the critically ill. The response to the invading microorganisms may be considered as a balance between a pro-inflammatory and an anti-inflammatory reaction. While an inadequate pro-inflammatory reaction and a strong anti-inflammatory response could lead to overwhelming infection and the death of the patient, a strong and uncontrolled pro-inflammatory response, manifested by the release of pro-inflammatory mediators may lead to microvascular thrombosis and multiple organ failure. Endotoxin triggers sepsis via the release of various mediators such as tumour necrosis factor-alpha and interleukin-1 (IL-1). These cytokines activate the complement and coagulation systems, release adhesion molecules, prostaglandins, leukotrienes, reactive oxygen species and nitric oxide. Other mediators involved in the sepsis syndrome include IL-1, -6 and -8; arachidonic acid metabolites; platelet activating factor; histamine; bradykinin; angiotensin; complement components and vasoactive intestinal peptide. These pro-inflammatory responses are counteracted by IL-10. Most of the trials targeting the different mediators of the pro-inflammatory response have failed due to a lack of correct definition of sepsis. Understanding the exact pathophysiology of the disease will enable more advanced treatment options. Targeting the coagulation system with various anticoagulant agents including, activated protein C, and tissue factor pathway inhibitor (TFPI) is a rational approach. Many clinical trials have been conducted to evaluate these agents in severe sepsis. While trials on antithrombin and TFPI were not so successful, the double-blind, placebo-controlled, Phase III trial of recombinant human activated Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) was successful, creating a significant decrease in mortality when compared to the placebo group. A better understanding of the pathophysiologic mechanism of severe sepsis will provide better treatment options, and combination antithrombotic treatment may provide a multipronged approach for the treatment of severe sepsis.

Hypermethylation of the inducible nitric-oxide synthase gene promoter inhibits its transcription

Exuberant generation of nitric oxide (NO) by inducible nitric-oxide synthase (iNOS) can cause unintended injury to host cells during glomerulonephritis and other inflammatory diseases. Although much is known about the mechanisms of iNOS induction, few transcriptional repression mechanisms have been found. We explored the role of cytosine methylation in the regulation of iNOS transcription. Treatment of mesangial cells with DNA methylation inhibitors augmented cytokine induction of endogenous NO production and iNOS protein levels, as well as iNOS promoter activity. In a corresponding manner, in vitro methylation of the murine iNOS promoter was sufficient to silence its activity in mesangial cells. In contrast, antisense knockdown of DNA methyltransferase-3b expression and activity increased iNOS promoter activity and nitrite production. Bisulfite treatment and sequencing analysis of the iNOS promoter identified methylation of cytosines framing an enhancer element at -879/-871. In vitro methylation inhibited binding of NFkappaB p50 to this element, and deletion of the element resulted in relief of transcriptional repression. These results provide evidence for a unique molecular mechanism involved in transcriptional regulation of iNOS gene expression.

Inhibition of matrix metalloproteinases by chemically modified tetracyclines in sepsis

Sepsis precipitates a systemic inflammatory stimulus that causes systemic release of cytokines and sequestration of polymorphonuclear neutrophils, resulting in degranulation of matrix metalloproteinases (MMPs), which causes extracellular matrix basement membrane degradation. One of the important anti-inflammatory properties of tetracyclines is their ability to inhibit MMPs. In this study, we focused on the regulation of MMPs in sepsis and their reduction by treatment with nonantimicrobial chemically modified tetracyclines (CMTs), which retain their anti-inflammatory activity. Sepsis was induced by cecal ligation and puncture (CLP) method. At 24 h and 1 h before CLP, some rats received CMT-3 (25 mg/kg), another group of rats received hydroxamate (H; an inhibitor of MMP; 25 mg/kg), and untreated rats received saline by gavage. At 0 h, 0.5 h, 1.5 h, and 24 h after CLP, blood and liver samples were collected. Plasma and liver MMP-9 by zymography and Western immunoblotting, plasma nitric oxide by measuring nitrate level, plasma glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) by enzymatic method, and liver gelatinase by radiolabeled gelatin lysis assay and 24 h mortality were determined. Plasma MMP-9 (92 kDa), nitrate, and GOT and GPT levels were elevated compared with the time 0 level and reached peak at 1.5 h CLP and remained high for 24 h. Both CMT-3 and H treatment reduced GOT,GPT, 92-kDa gelatinase, and nitrate levels throughout the 24 h. CMT-3 and H are equally effective in sepsis treatment. The 24-h mortality for CLP rats was 30%, whereas pretreatment with CMT-3 and H resulted in 0% mortality. Hepatic MMP-9 and gelatinase activity increased significantly after CLP, and pretreatment with CMT-3 and H inhibited these expressions. These results indicate the beneficial effect of CMT-3 in preventing the increase in GOT, GPT, NO, MMP-9, gelatinase activity, and the ensuing septic shock.

Isoprenylation of RhoB is necessary for its degradation. A novel determinant in the complex regulation of RhoB expression by the mevalonate pathway

Statins improve vascular functions by mechanisms independent from their cholesterol-lowering effect. Rho GTPases are emerging as key targets for the vascular effects of statins. RhoB is a short-lived, early-response inducible protein involved in receptor endocytosis, apoptosis, and gene expression. Here we show that statins regulate RhoB expression by acting at multiple levels. Simvastatin increased RhoB protein levels by 8- to 10-fold. This effect was related to a depletion of isoprenoid intermediates, as deduced from the observation that several metabolites of the cholesterol biosynthetic pathway, namely, mevalonate and geranylgeranyl-pyrophosphate, attenuated simvastatin-induced RhoB up-regulation. Moreover, prenyltransferase inhibitors mimicked simvastatin effect. Cholesterol supplementation did not prevent simvastatin-elicited up-regulation but increased RhoB levels per se. Simvastatin moderately augmented RhoB transcript levels, but markedly impaired the degradation of RhoB protein, which accumulated in the cytosol in its non-isoprenylated form. Inhibition of RhoB isoprenylation was apparently required for simvastatin-induced up-regulation, because levels of an isoprenylation-deficient RhoB mutant were not affected by simvastatin. Moreover, this mutant was found to be markedly more stable than the wild-type protein. These results show that RhoB isoprenylation is necessary for rapid turnover of this protein and identify a novel link between the cholesterol biosynthetic pathway and the regulation of G-protein expression.

Signal transducers and activators of transcription 3 (STAT3) inhibits transcription of the inducible nitric oxide synthase gene by interacting with nuclear factor kappaB

Prolific generation of NO by inducible nitric oxide synthase (iNOS) can cause unintended injury to host cells during glomerulonephritis and other inflammatory diseases. While much is known about the mechanisms of iNOS induction, few transcriptional repressors have been found. We explored the role of signal transducers and activators of transcription 3 (STAT3) proteins in interleukin (IL)-1beta- and lipopolysaccharide (LPS)+interferon (IFN)-gamma-mediated iNOS induction in murine mesangial cells. Both stimuli induced rapid phosphorylation of STAT3 and sequence-specific STAT3 DNA-binding activity. Supershift assays with a STAT3 element probe demonstrated that nuclear factor kappaB (NF-kappaB) p65 and p50 complexed with STAT3 in the DNA-protein complex. The direct interaction of STAT3 and NF-kappaB p65 was verified in vivo by co-immunoprecipitation and in vitro by pull-down assays with glutathione S-transferase-NF-kappaB p65 fusion protein and in vitro -translated STAT3alpha. Overexpression of STAT3 dramatically inhibited IL-1beta- or LPS+IFN-gamma-mediated induction of iNOS promoter-luciferase constructs that contained the wild-type iNOS promoter or ones harbouring mutated STAT-binding elements. In tests of indirect inhibitory effects of STAT3, overexpression of STAT3 dramatically inhibited the activity of an NF-kappaB-dependent promoter devoid of STAT-binding elements without affecting NF-kappaB DNA-binding activity. Thus STAT3, via direct interactions with NF-kappaB p65, serves as a dominant-negative inhibitor of NF-kappaB activity to suppress indirectly cytokine induction of the iNOS promoter in mesangial cells. These results provide a new model for the termination of NO production by activated iNOS following exposure to pro-inflammatory stimuli.

Mediators of injury in lupus nephritis

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of autoantibodies and the development of immune complex glomerulonephritis. Lupus nephritis (LN) remains a leading cause of morbidity and mortality in SLE. As a result, defining pathogenetic mediators in LN remains a major research effort. Progression to LN in SLE is dependent on the host breaking immune tolerance and forming autoantibodies that deposit in the kidney. A variety of predisposing factors in the host must then be present for this event to result in renal pathology. In this article, the authors review recent reports that advance our understanding of LN disease mediators, from autoantibody production and immune complex deposition to end stage fibrosis.

Histone deacetylases augment cytokine induction of the iNOS gene

The inducible nitric oxide synthase (iNOS) gene plays an important role in renal diseases. Transcription is the principal mode of regulation. This study explores the role of acetylation in cytokine-mediated iNOS induction in cultured murine mesangial cells and RAW 264.7 cells. Nitric oxide production was measured by the Griess reaction. The activity of the iNOS promoter and a nuclear factor-kappa B (NF-kappa B) element promoter were assessed in transient transfection assays. Gel shift and supershift assays were used to identify NF-kappa B in nuclear extracts. Protein-protein interactions were assayed by co-immunoprecipitation and GST pull-down assays. Treatment with the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) and overexpression of HDAC isoforms were used to assess the impact of acetylation status on iNOS and NF-kappa B element promoter activity. TSA inhibited induction of endogenous NO production and iNOS as well as NF-kappa B element promoter activity in response to interleukin-1 beta (IL-1 beta) or lipopolysaccharide (LPS) + interferon-gamma (IFN-gamma) in both cell types without altering NF-kappa B DNA binding activity. Overexpression of specific HDAC isoforms enhanced cytokine induction of both the iNOS and the NF-kappa B element promoter. HDAC2 and NF-kappa B p65 co-immunoprecipitated from mesangial cell nuclear extracts, and in vitro translated HDAC2 specifically interacted with an NF-kappa B p65 GST fusion protein. Hyperacetylation diminishes cytokine induction of iNOS transcription activity, at least partially, by limiting the functional efficacy of NF-kappa B. The specific recruitment of HDAC2 to NF-kappa B at target promoters and the consequent effects on acetylation status may play an important role in regulating iNOS as well as other NF-kappa B-dependent genes involved in inflammation.

Inhibition of inducible NO synthase by TH2 cytokines and TGF beta in rheumatoid arthritic synoviocytes: effects on nitrosothiol production

The aim of this study was to compare the effects on NO production of IL-4, IL-10, and IL-13 with those of TGF-beta. RA synovial cells were stimulated for 24 h with IL-1 beta (1 ng/ml), TNF-alpha (500 pg/ml), IFN-gamma (10(-4)IU/ml) alone or in combination. Nitrite was determined by the Griess reaction, S-nitrosothiols by fluorescence, and inducible NO synthase (iNOS) by immunofluorescence and fluorescence activated cell sorter analysis (FACS). In other experiments, IL-4, IL-10, IL-13, and TGF beta were used at various concentrations and were added in combination with proinflammatory cytokines. The addition of IL-1 beta, TNF-alpha, and IFN-gamma together increased nitrite production: 257.5 +/- 35.8 % and S-nitrosothiol production : 413 +/- 29%, P < 0.001. None of these cytokines added alone had any significant effect. iNOS synthesis increased with NO production. IL-4, IL-10, IL-13, and TGF beta strongly decreased the NO production caused by the combination of IL-1 beta, TNF-alpha, and IFN-gamma. These results demonstrate that stimulated RA synoviocytes produce S-nitrosothiols, bioactive NO* compounds, in similar quantities to nitrite. IL-4, IL-10, IL-13, and TGF-beta decrease NO production by RA synovial cells. The anti-inflammatory properties of these cytokines may thus be due at least in part to their effect on NO metabolism.

Disruption of the actin cytoskeleton regulates cytokine-induced iNOS expression

Interleukin-1beta (IL-1beta) induces the inducible nitric oxide synthase (iNOS), resulting in the release of nitric oxide (NO) from glomerular mesangial cells. In this study, we demonstrated that disruption of F-actin formation by sequestration of G-actin with the toxin latrunculin B (LatB) dramatically potentiated IL-1beta-induced iNOS protein expression in a dose-dependent manner. LatB by itself had little or no effect on iNOS expression. Staining of F-actin with nitrobenzoxadiazole (NBD)-phallacidin demonstrated that LatB significantly impaired F-actin stress fiber formation. Jasplakinolide (Jasp), which binds to and stabilizes F-actin, suppressed iNOS expression enhanced by LatB. These data strongly suggest that actin cytoskeletal dynamics regulates IL-1beta-induced iNOS expression. We demonstrated that LatB decreases serum response factor (SRF) activity as determined by reporter gene assays, whereas Jasp increases SRF activity. The negative correlation between SRF activity and iNOS expression suggests a negative regulatory role for SRF in iNOS expression. Overexpression of a dominant negative mutant of SRF increases the IL-1beta-induced iNOS expression, providing direct evidence that SRF inhibits iNOS expression.

Posttranscriptional regulation of human iNOS by the NO/cGMP pathway

Nitric oxide (NO) and cGMP may exert positive or negative effects on inducible NO synthase (iNOS) expression. We have explored the influence of the NO/cGMP pathway on iNOS levels in human mesangial cells. Inhibition of NOS activity during an 8-h stimulation with IL-1beta plus tumor necrosis factor (TNF)-alpha reduced iNOS levels, while NO donors amplified iNOS induction threefold. However, time-course studies revealed a subsequent inhibitory effect of NO donors on iNOS protein and mRNA levels. This suggests that NO may contribute both to iNOS induction and downregulation. Soluble guanylyl cyclase (sGC) activation may be involved in these effects. Inhibition of sGC attenuated IL-1beta/TNF-alpha-elicited iNOS induction and reduced NO-driven amplification. Interestingly, cGMP analogs also modulated iNOS protein and mRNA levels in a biphasic manner. Inhibition of transcription unveiled a negative posttranscriptional modulation of the iNOS transcript by NO and cGMP at late times of induction. Supplementation with 8-bromo-cGMP (8-BrcGMP) reduced iNOS mRNA stability by 50%. These observations evidence a complex feedback regulation of iNOS expression, in which posttranscriptional mechanisms may play an important role.

The involvement of tyrosine kinases, cyclic AMP/protein kinase A, and p38 mitogen-activated protein kinase in IL-13-mediated arginase I induction in macrophages: its implications in IL-13-inhibited nitric oxide production

In macrophages, L-arginine can be used by NO synthase and arginase to form NO and urea, respectively. Therefore, activation of arginase may be an effective mechanism for regulating NO production in macrophages through substrate competition. Here, we examined whether IL-13 up-regulates arginase and thus reduces NO production from LPS-activated macrophages. The signaling molecules involved in IL-13-induced arginase activation were also determined. Results showed that IL-13 increased arginase activity through de novo synthesis of the arginase I mRNA and protein. The activation of arginase was preceded by a transient increase in intracellular cAMP, tyrosine kinase phosphorylation, and p38 mitogen-activated protein kinase (MAPK) activation. Exogenous cAMP also increased arginase activity and enhanced the effect of IL-13 on arginase induction. The induction of arginase was abolished by a protein kinase A (PKA) inhibitor, KT5720, and was down-regulated by tyrosine kinase inhibitors and a p38 MAPK inhibitor, SB203580. However, inhibition of p38 MAPK had no effect on either the IL-13-increased intracellular cAMP or the exogenous cAMP-induced arginase activation, suggesting that p38 MAPK signaling is parallel to the cAMP/PKA pathway. Furthermore, the induction of arginase was insensitive to the protein kinase C and p44/p42 MAPK kinase inhibitors. Finally, IL-13 significantly inhibited NO production from LPS-activated macrophages, and this effect was reversed by an arginase inhibitor, L-norvaline. Together, these data demonstrate for the first time that IL-13 down-regulates NO production through arginase induction via cAMP/PKA, tyrosine kinase, and p38 MAPK signalings and underline the importance of arginase in the immunosuppressive activity of IL-13 in activated macrophages.

Nitric oxide production and inducible nitric oxide synthase expression in peritoneal macrophages of cirrhotic patients

The present study assessed whether peritoneal macrophages isolated from cirrhotic patients produce nitric oxide (NO) and express NO synthase type II (NOS II) mRNA and protein. Patients with cirrhosis and ascites without peritonitis or with unresolved or resolved spontaneous bacterial peritonitis (SBP) were studied. Following paracentesis, ascites NO(2)(-) + NO(3)(-) content (NOx) was measured. Peritoneal macrophages from ascites were seeded on well plates, and NO(2)(-) in the medium was determined. NOx was higher in patients with unresolved or resolved SBP than in cirrhotic patients without peritonitis. Macrophages of patients with SBP or resolved SBP produced NO(2)(-) after 30 hours in culture, but those obtained from patients without peritonitis did not. Reverse-transcription polymerase chain reaction (RT-PCR) and immunocytochemical analysis revealed the presence of a clear signal for NOS II mRNA and protein in macrophages of SBP patients, regardless of whether or not the infection subsided. Therefore, peritoneal macrophages isolated from cirrhotic patients with unresolved or resolved SBP produce NO and express the NOS II mRNA and protein, suggesting that NOS II may contribute to the control of SBP, or to its associated pathology, in human cirrhosis.

Negative Regulation by Phosphatidylinositol 3-Kinase of Inducible Nitric Oxide Synthase Expression in Macrophages

Triggering of the macrophage cell line RAW 264.7 with LPS promotes a transient activation of phosphatidylinositol 3-kinase (PI3-kinase). Incubation of activated macrophages with wortmannin and LY294002, two inhibitors of PI3-kinase, increased the amount of inducible nitric oxide synthase (iNOS) and the synthesis of nitric oxide. Treatment with wortmannin promoted a prolonged activation of NF-κB in LPS-treated cells as well as an increase in the promoter activity of the iNOS gene as deduced from transfection experiments using a 1.7-kb fragment of the 5′ flanking region of the iNOS gene. Cotransfection of cells with a catalytically active p110 subunit of PI3-kinase impaired the responsiveness of the iNOS promoter to LPS stimulation, whereas transfection with a kinase-deficient mutant of p110 maintained the up-regulation in response to wortmannin. These results indicate that PI3-kinase plays a negative role in the process of macrophage activation and suggest that this enzyme might participate in the mechanism of action of antiinflammatory cytokines.

Dual effect of nitric oxide donors on cyclooxygenase-2 expression in human mesangial cells

Nitric oxide (NO) is emerging as a key regulator of gene expression, capable of playing either positive or negative roles. The results of this study indicate that NO exerts a dual effect on cyclooxygenase-2 (COX-2) expression in human mesangial cells (HMC). Treatment of HMC with NO synthase inhibitors attenuated interleukin-1beta (IL-1beta/tumor necrosis factor-alpha (TNF-alpha)-elicited COX-2 protein and mRNA expression, suggesting a positive role of endogenous NO on COX-2 induction. However, NO donors (sodium nitroprusside [SNP] and S-nitroso-N-acetylpenicillamine [SNAP]) amplified cytokine-elicited COX-2 expression at early time points of treatment (up to 8 h for mRNA and up to 24 h for protein expression), but were inhibitory at later times. Oligonucleotide decoy experiments confirmed the importance of nuclear factor kappaB (NF-kappaB) activation for COX-2 induction by IL-1beta/TNF-alpha. Treatment with N(G)-nitro-L-arginine methyl ester (L-NAME) did not affect initial activation of NF-kappaB by IL-1beta/TNF-alpha, but unveiled an inhibitory effect of NO generation on NF-kappaB activity after 4 h. In HMC supplemented with SNP, cytokine-induced NF-kappaB activation was potentiated at early times of induction (5 to 15 min), but inhibited at later times (1 to 4 h), suggesting a dual effect of NO donors on NF-kappaB activation. Interestingly, IkappaBalpha protein levels followed a reciprocal pattern of expression: IkappaBalpha levels were lower at early times of induction in NO donor-supplemented cells; however, after 1 h of treatment, IkappaBalpha levels became higher than in cells treated only with cytokines. In the presence of SNP, cytokine-elicited IkappaBalpha mRNA induction was initially delayed, but was amplified at later times. These changes in IkappaBalpha expression could contribute to the dual effects of NO donors on NF-kappaB activation and COX-2 expression in HMC.

Regulation of cyclooxygenase-2 expression in human mesangial cells--transcriptional inhibition by IL-13

Activated mesangial cells may play an important part in glomerulonephritis. Cytokines can modulate the release of prostanoids by human mesangial cells (HMC). We have investigated the effects of pro-inflammatory stimuli on COX-2 expression in HMC and its potential modulation by interleukin (IL)-13. HMC released increased amounts of prostaglandin E2 (PGE2) after treatment with several combinations of IL-1 beta, tumor necrosis factor (TNF)-alpha and/or lipopolysaccharide. Increases in PGE2 correlated with the induction of COX-2 protein expression. The accumulation of PGE2 elicited by a combination of IL-1 beta/TNF-alpha correlated closely with the temporal pattern of COX-2 protein expression, which reflected the induction of COX-2 mRNA. IL-13 inhibited IL-1 beta/TNF-alpha-elicited PGE2 production, as well as COX-2 protein and mRNA expression in a concentration-dependent fashion. With 50 ng.mL-1 IL-13 these parameters were inhibited by 90, 80 and 84%, respectively. In HMC transfected with the 5' regulatory region of the COX-2 gene, IL-13 suppressed cytokine-induced promoter activation. Our results suggest that COX-2 expression is a major target for IL-13-mediated abrogation of prostaglandin release by HMC and support that this process takes place by transcriptional inhibition of the COX-2 gene.

Expression of inducible nitric oxide synthase activity in human colon epithelial cells: modulation by T lymphocyte derived cytokines

BACKGROUND

Nitric oxide (NO) synthesis and inducible nitric oxide synthase (iNOS) expression are increased in colonic biopsy specimens from patients with ulcerative colitis, but the cellular source of NO production is not known.

AIMS

To examine the distribution of iNOS in human colonic mucosa and to explore the ability of T lymphocyte derived cytokines to regulate iNOS expression and activity in human colonic epithelial cells.

METHODS

iNOS expression was examined using immunohistochemistry in colonic biopsy samples from 12 patients with ulcerative colitis and three with infectious colitis and compared with 10 normal controls. In vitro iNOS expression and activity were determined in HT-29 cell cultures; nitrite levels were measured using a fluorescent substrate, iNOS mRNA expression by northern blot analysis, and iNOS protein expression by western blot analysis.

RESULTS

No iNOS expression was detected (10 of 10) in non-inflamed mucosa derived from normal controls. In 11 of 12 cases of newly diagnosed ulcerative colitis, iNOS protein was expressed in the epithelial cells, while no other positive cells were found in the lamina propria. Similar iNOS labelling was found in colonic biopsy samples from patients with infectious colitis in the acute phase, but when re-examined in samples from patients in total remission, no iNOS staining was observed. Both interleukin (IL)-13 and IL-4, but not IL-10, are potent inhibitors of iNOS expression and activity induced by an optimal combination of cytokines, namely IL-1 alpha, tumour necrosis factor alpha and interferon gamma.

CONCLUSIONS

The data suggest that the epithelium is the major source of iNOS activity in ulcerative colitis and that IL-13 and IL-4 may act as intrinsic regulators of NO generation in intestinal inflammation.

Interleukin-13 counteracts suppression induced by interleukin-1beta of glucose metabolism but not of insulin secretion in rat pancreatic islets

The cytokine interleukin-1beta (IL-1beta) has been postulated to be involved in beta-cell destruction in IDDM. It has also been suggested that this action by IL-1beta is mediated by nitric oxide (NO) generation. Recently it has been reported that Th2-cell promoting cytokines e.g. interleukin-4 (IL-4) and interleukin-13 (IL-13) can reduce NO formation from activated macrophaghes after cytokine activation. In the present study we examined the effect of IL-13 on IL-1beta suppression of islet function. For this purpose rat pancreatic islets were cultured in medium RPMI 1640 + 10% fetal calf serum and exposed for 42 h to human IL-13 (0. 0.1, 1 and 10 ng/ml) in the presence or absence of human IL-1beta (25 U/ml) during the last 24 h of culture. IL-13 alone did not affect any islet functions during prolonged exposure. The highest concentration of IL-13 counteracted IL-1beta suppression of islet glucose oxidation, but not insulin release. Moreover, IL-13 failed to reduce IL-1beta stimulated NO production, as measured by medium nitrite levels. Acute exposure to IL-13 caused a slight stimulation of islet insulin secretion. When IL-4 (10 ng/ml) was combined with IL-13 no synergistic action of the two cytokines was observed in the counteraction of IL-1beta mediated changes. In conclusion, the present study showed that IL-13 could partially prevent IL-1beta induced inhibition of the glucose metabolism, and this effect appeared to be unrelated to NO levels. So far it has not been possible to demonstrate in vitro that Th2-cell promoting cytokines such as IL-4 and IL-13 can effectively reduce cytokine-induced NO from islet cells, as has been reported for macrophages. However, it cannot be excluded that Th2-cell promoting cytokines can be effective in reducing a Th1-cell mediated anti-beta-cell response in vivo.

Arginase activity is modulated by IL-4 and HOArg in nephritic glomeruli and mesangial cells

Arginase shares a common substrate, L-arginine, with nitric oxide synthase (NOS). Both enzymes are active at inflammatory sites. To understand regulation of arginase and its relationship to nitric oxide (NO) production, we studied effects of NG-hydroxy-L-arginine (HOArg) and interleukin-4 (IL-4) on urea and NO2- synthesis by glomeruli during rat immune glomerulonephritis and compared these with macrophages and glomerular mesangial cells (MC). In nephritic glomeruli, elicited macrophages, and MC stimulated with IL-1 and adenosine 3',5'-cyclic monophosphate agonists, increased arginase and induced NOS activity was found. Urea production was inhibited by HOArg and increased by IL-4. NO inhibition [NG-monomethyl-L-arginine (L-NMMA)] increased arginase activity in nephritic glomeruli and macrophages but not MC. NO2- synthesis was inhibited by L-NMMA and IL-4. It was increased with HOArg under conditions of NO inhibition. In contrast, in normal glomeruli and basal MC, where there was no induced NO synthesis, IL-4 had no effect on arginase activity, whereas HOArg consistently reduced it in glomeruli only. Type II arginase (Arg II) mRNA was detected in normal glomeruli; nephritic glomeruli expressed both Arg I and Arg II mRNAs. This is the first demonstration of arginase modulation in glomeruli and MC and of the expression of arginase isoforms in glomeruli. The differential responses to two endogenous compounds generated by inflammation suggest this may be part of coordinated regulation of arginase and inducible NOS in immune injury, whereby arginase is inhibited during high-output NO production and stimulated with NO suppression. This, together with control of arginase and NOS isoforms, may be important in controlling the balance of inflammatory and repair mechanisms.

Tetrahydrobiopterin modulates cyclooxygenase-2 expression in human mesangial cells

Tetrahydrobiopterin (BH4) biosynthetic pathways are stimulated under inflammatory conditions. The newly synthesized BH4 serves as a cofactor for optimal activity of inducible nitric oxide synthase (NOS2). In human mesangial cells (HMC), BH4 is also a limiting factor for NOS2 expression. In this study we show that BH4 availability can also play a modulatory role in the expression of cyclooxygenase 2 (COX-2) in HMC. Supplementing HMC with the BH4 donor sepiapterin potentiated IL-1beta/TNF-alpha-induced COX-2 expression by approximately 2-fold. This effect was abolished by methotrexate. In contrast, the NOS inhibitor L-NAME and the soluble guanylate cyclase inhibitor ODQ did not block sepiapterin amplification of COX-2 expression. Moreover, sepiapterin was found to modulate the tyrosine phosphorylation of several cellular substrates, an early event which occurred well before the induction of NOS2 could be evidenced. These findings suggest a role for BH4 in the modulation of mesangial cell responses to pro-inflammatory stimuli.

Nitric oxide in renal health and disease

Nitric oxide (NO) is a labile radical gas that is widely acclaimed as one of the most important molecules in biology. Through covalent modifications of target proteins and redox reactions with oxygen and superoxide radical and transition metal prosthetic groups, NO plays a critical role in many vital biological processes, including the control of vascular tone, neurotransmission, ventilation, hormone secretion, inflammation, and immunity. Moreover, NO has been shown to influence a host of fundamental cellular functions, such as RNA synthesis, mitochondrial respiration, glycolysis, and iron metabolism. NO is formed from L-arginine by NO synthases (NOSs), a family of related enzymes encoded by separate unlinked genes. The different NOS isozymes exhibit disparate tissue and intrarenal distributions and are governed by unique regulatory mechanisms. In the kidney, NO participates in several vital processes, including the regulation of glomerular and medullary hemodynamics, the tubuloglomerular feedback response, renin release, and the extracellular fluid volume. While NO serves beneficial roles as a messenger and host defense molecule, excessive NO production can be cytotoxic, the result of NO's reaction with reactive oxygen and nitrogen species, leading to peroxynitrite anion formation, protein tyrosine nitration, and hydroxyl radical production. Indeed, NO may contribute to the evolution of several commonly encountered renal diseases, including immune-mediated glomerulonephritis, postischemic renal failure, radiocontrast nephropathy, obstructive nephropathy, and acute and chronic renal allograft rejection. Moreover, impaired NO production has been implicated in the pathogenesis of volume-dependent hypertension. This duality of NO's beneficial and detrimental effects has created extraordinary interest in this molecule and the need for a detailed understanding of NO biosynthesis.

Activation of phosphatidylinositol 3-kinase by interleukin-13. An inhibitory signal for inducible nitric-oxide synthase expression in epithelial cell line HT-29

The human colonic epithelial cell line HT-29 can be induced by a combination of the cytokines interleukin (IL)-1alpha, tumor necrosis factor alpha, and interferon-gamma to express the inducible form of nitric-oxide synthase (iNOS; Kolios, G., Brown, Z., Robson, R., Robertson, D. A. F., & Westwick, J. (1995) Br. J. Pharmacol. 116, 2866-2872). IL-13 is a potent inhibitor of cytokine-induced iNOS mRNA expression and nitric oxide generation in HT-29 cells via an unknown mechanism. We report here that in HT-29 cells, IL-13 induces a concentration and time-dependent increase in the formation of the lipid products of phosphatidylinositol (PtdIns) 3-kinase, namely phosphatidylinositol (3,4)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate. IL-13 also induces a parallel concentration and time-dependent increase in the in vitro lipid kinase activity present in immunoprecipitates of the p85 regulatory subunit of PtdIns 3-kinase. In addition, we also demonstrate that IL-13 stimulates the tyrosine phosphorylation of the adaptor molecule insulin receptor substrate 1, which may facilitate receptor coupling to PtdIns 3-kinase. Both the increases in D-3 phosphatidylinositol lipids and the increased in vitro lipid kinase activity of p85 immunoprecipitates were inhibited by wortmannin and LY294002. Inhibition of the PtdIns 3-kinase activity was paralleled by a reversal of the ability of IL-13 to inhibit iNOS mRNA expression and nitrite generation in HT-29 cells. These data demonstrate that the activation of PtdIns 3-kinase by IL-13 is a key signal that is responsible for the inhibition of iNOS transcription in activated epithelial cells.

Repression of inducible nitric oxide synthase and cyclooxygenase-2 by prostaglandin E2 and other cyclic AMP stimulants in J774 macrophages

The enhanced nitric oxide (NO) and prostaglandin (PG) generation of activated macrophages is controlled by glucocorticoid-sensitive inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively. Negative feedback regulation of iNOS expression by the products of both pathways has been suggested, but their effects on COX-2 expression have not been examined. We hae investigated the effect of E- and l-series prostaglandins that activate adenylate cyclase (AC), forskolin (a direct activator of AC), and other agents that influence the cyclicAMP/cyclicGMP systems on the ability of E. coli endotoxin (lipopolysaccharide, LPS) to induce iNOS and COX-2 in the murine macrophage cell line J774. After a 2-hr pretreatment before adding endotoxin, PGE2, PGI2, forskolin, IBMX (isobutylmethylxanthine, a cyclicAMP/cyclicGMP phosphodiesterase inhibitor), 8-bromo cyclicAMP, and arachidonic acid itself all inhibited the expression of both iNOS and COX-2 (as shown by Western blotting) and reduced NO release and COX activity, whereas PGF2 alpha and 8-bromo cyclic GMP were only weakly effective. The effects of PGE2, PGI2, and forskolin were enhanced by cotreatment with IBMX. The suppression of LPS-induced iNOS induction by PGE2 was functionally significant, in that it protected against the mild cytotoxicity of the NO generated in response to endotoxin. These results provide the first direct evidence for the feedback regulatory suppression of COX-2 induction by a PG-driven cAMP-mediated process, and show that the modulation of iNOS and COX-2 induction shares common features. They also suggest that such modulation is normally held in check by high phosphodiesterase activity within these cells.