Nitric oxide provokes tumor necrosis factor-alpha expression in adult feline myocardium through a cGMP-dependent pathway

Modulation of Inflammatory Cytokine Production in Human Monocytes by cGMP and IRAK3

Interleukin-1 receptor-associated kinase-3 (IRAK3) is a critical checkpoint molecule of inflammatory responses in the innate immune system. The pseudokinase domain of IRAK3 contains a guanylate cyclase (GC) centre that generates small amounts of cyclic guanosine monophosphate (cGMP) associated with IRAK3 functions in inflammation. However, the mechanisms of IRAK3 actions are poorly understood. The effects of low cGMP levels on inflammation are unknown, therefore a dose–response effect of cGMP on inflammatory markers was assessed in THP-1 monocytes challenged with lipopolysaccharide (LPS). Sub-nanomolar concentrations of membrane permeable 8-Br-cGMP reduced LPS-induced NFκB activity, IL-6 and TNF-α cytokine levels. Pharmacologically upregulating cellular cGMP levels using a nitric oxide donor reduced cytokine secretion. Downregulating cellular cGMP using a soluble GC inhibitor increased cytokine levels. Knocking down IRAK3 in THP-1 cells revealed that unlike the wild type cells, 8-Br-cGMP did not suppress inflammatory responses. Complementation of IRAK3 knockdown cells with wild type IRAK3 suppressed cytokine production while complementation with an IRAK3 mutant at GC centre only partially restored this function. Together these findings indicate low levels of cGMP form a critical component in suppressing cytokine production and in mediating IRAK3 action, and this may be via a cGMP enriched nanodomain formed by IRAK3 itself.

bFGF alleviates diabetes-associated endothelial impairment by downregulating inflammation via S-nitrosylation pathway

Protein S-nitrosylation is a reversible protein modification implicated in both physiological and pathophysiological regulation of protein function. However, the relationship between dysregulated S-nitrosylation homeostasis and diabetic vascular complications remains incompletely understood. Here, we demonstrate that basic fibroblast growth factor (bFGF) is a key regulatory link between S-nitrosylation homeostasis and inflammation, and alleviated endothelial dysfunction and angiogenic defects in diabetes. Subjecting human umbilical vein endothelial cells (HUVECs) to hyperglycemia and hyperlipidemia significantly decreased endogenous S-nitrosylated proteins, including S-nitrosylation of inhibitor kappa B kinase β (IKKβ^C179) and transcription factor p65 (p65^C38), which was alleviated by bFGF co-treatment. Pretreatment with carboxy-PTIO (c-PTIO), a nitric oxide scavenger, abolished bFGF-mediated S-nitrosylation increase and endothelial protection. Meanwhile, nitrosylation-resistant IKKβ^C179S and p65^C38S mutants exacerbated endothelial dysfunction in db/db mice, and in cultured HUVECs subjected to hyperglycemia and hyperlipidemia. Mechanistically, bFGF-mediated increase of S-nitrosylated IKKβ and p65 was attributed to synergistic effects of increased endothelial nitric oxide synthase (eNOS) and thioredoxin (Trx) activity. Taken together, the endothelial protective effect of bFGF under hyperglycemia and hyperlipidemia can be partially attributed to its role in suppressing inflammation via the S-nitrosylation pathway.

Targets of cGMP/cGKI in Cardiac Myocytes

The 3',5'-cyclic guanosine monophosphate (cGMP)-dependent protein kinase type I (cGKI aka PKGI) is a major cardiac effector acting downstream of nitric oxide (NO)-sensitive soluble guanylyl cyclase and natriuretic peptides (NPs), which signal through transmembrane guanylyl cyclases. Consistent with the wide distribution of the cGMP-generating guanylyl cyclases, cGKI, which usually elicits its cellular effects by direct phosphorylation of its targets, is present in multiple cardiac cell types including cardiomyocytes (CMs). Although numerous targets of cGMP/cGKI in heart were identified in the past, neither their exact patho-/physiological functions nor cell-type specific roles are clear. Herein, we inform about the current knowledge on the signal transduction downstream of CM cGKI. We believe that better insights into the specific actions of cGMP and cGKI in these cells will help to guide future studies in the search for predictive biomarkers for the response to pharmacological cGMP pathway modulation. In addition, targets downstream of cGMP/cGKI may be exploited for refined and optimized diagnostic and therapeutic strategies in different types of heart disease and their causes. Importantly, key functions of these proteins and particularly sites of regulatory phosphorylation by cGKI should, at least in principle, remain intact, although upstream signaling through the second messenger cGMP is impaired or dysregulated in a stressed or diseased heart state.

Arginase 1 promotes retinal neurovascular protection from ischemia through suppression of macrophage inflammatory responses

The lack of effective therapies to limit neurovascular injury in ischemic retinopathy is a major clinical problem. This study aimed to examine the role of ureohydrolase enzyme, arginase 1 (A1), in retinal ischemia-reperfusion (IR) injury. A1 competes with nitric oxide synthase (NOS) for their common substrate l-arginine. A1-mediated l-arginine depletion reduces nitric oxide (NO) formation by NOS leading to vascular dysfunction when endothelial NOS is involved but prevents inflammatory injury when inducible NOS is involved. Studies were performed using wild-type (WT) mice, global A1^+/− knockout (KO), endothelial-specific A1 KO, and myeloid-specific A1 KO mice subjected to retinal IR injury. Global as well as myeloid-specific A1 KO mice showed worsened IR-induced neuronal loss and retinal thinning. Deletion of A1 in endothelial cells had no effect, while treatment with PEGylated (PEG) A1 improved neuronal survival in WT mice. In addition, A1^+/− KO mice showed worsened vascular injury manifested by increased acellular capillaries. Western blotting analysis of retinal tissue showed increased inflammatory and necroptotic markers with A1 deletion. In vitro experiments showed that macrophages lacking A1 exhibit increased inflammatory response upon LPS stimulation. PEG-A1 treatment dampened this inflammatory response and decreased the LPS-induced metabolic reprogramming. Moreover, intravitreal injection of A1 KO macrophages or systemic macrophage depletion with clodronate liposomes increased neuronal loss after IR injury. These results demonstrate that A1 reduces IR injury-induced retinal neurovascular degeneration via dampening macrophage inflammatory responses. Increasing A1 offers a novel strategy for limiting neurovascular injury and promoting macrophage-mediated repair.

Correlation of inducible nitric oxide synthase (iNOS) inhibition with TNF-α, caspase-1, FasL and TLR-3 in pathogenesis of rabies in mouse model

The role of inflammatory cytokines such as interleukin-1α/β (IL-1α/β), IL-6, IL-10, tumour necrosis factor-alpha (TNF-α), interferons, nitric oxide (NO) and inducible nitric oxide synthase (iNOS) in pathogenesis of rabies is being actively pursued. Presently, levels of certain immune molecules in pathogenesis of rabies in mice have been investigated. CVS strain of rabies infection resulted in early increase in iNOS, TNF-α, caspase-1, Fas ligand (FasL) and toll-like receptor-3 (TLR-3) mRNA levels in brain, and nitric oxide levels in serum. The severity of clinical signs and microscopic lesions largely correlated with NO levels. Aminoguanidine (AG; iNOS inhibitor) decreased NO production with delay in development of clinical signs and increase in survival time. Prolonged survival time correlated with reduced viral load evident by real-time PCR, reduced fluorescent signals of rabies antigen in brain and reduced immunohistochemistry signals in neuronal cytoplasm. These parameters suggested that nitric oxide did influence the rabies virus replication. Inhibition of iNOS by AG administration led to decreased expression of TNF-α, caspase-1, FasL and TLR-3 mRNA levels suggesting that increase in NO levels in rabies virus infection possibly contributed to development of disease through inflammation, apoptosis and immune-evasive mechanisms.

Tumor Necrosis Factor - Alpha Is Essential for Angiotensin II-Induced Ventricular Remodeling: Role for Oxidative Stress

The functional crosstalk between angiotensin II (Ang II) and tumor necrosis factor (TNF)-α has been shown to cause adverse left ventricular remodeling and hypertrophy in hypertension. Previous studies from our lab showed that mice lacking TNF-α (TNF-α^-/-) have attenuated hypertensive response to Ang II; however, the signaling mechanisms involved are not known. In this study, we investigated the signaling pathways involved in the Ang II and TNF-α interaction. Chronic Ang II infusion (1μg/kg/min, 14 days) significantly increased cardiac collagen I, collagen III, CTGF and TGF-β mRNA and protein expression in wild-type (WT) mice, whereas these changes were decreased in TNF-α^-/- mice. TNF-α^-/- mice with Ang II infusion showed reduced myocardial perivascular and interstitial fibrosis compared to WT mice with Ang II infusion. In WT mice, Ang II infusion increased reactive oxygen species formation and the expression of NADPH oxidase subunits, indicating increased oxidative stress, but not in TNF-α^-/- mice. In addition, treatment with etanercept (8 mg/kg, every 3 days) for two weeks blunted the Ang II-induced hypertension (133±4 vs 154±3 mmHg, p<0.05) and cardiac hypertrophy (heart weight to body weight ratio, 4.8±0.2 vs 5.6±0.3, p<0.05) in WT mice. Furthermore, Ang II-induced activation of NF-κB, p38 MAPK, and JNK were reduced in both TNF-α^-/- mice and mice treated with etanercept. Together, these findings indicate that TNF-α contributes to Ang II-induced hypertension and adverse cardiac remodeling, and that these effects are associated with changes in the oxidative stress dependent MAPK/TGF-β/NF-κB pathway. These results may provide new insight into the mechanisms of Ang II and TNF-α interaction.

TNFα in myocardial ischemia/reperfusion, remodeling and heart failure

TNFα is crucially involved in the pathogenesis and progression of myocardial ischemia/reperfusion injury and heart failure. The formation and release of TNFα and its downstream signal transduction cascade following activation of its two receptor subtypes are characterized. Myocardial TNFα and TNF receptor activation have an ambivalent role in myocardial ischemia/reperfusion injury and protection from it. Excessive TNFα expression and subsequent cardiomyocyte TNF receptor type 1 stimulation induce contractile dysfunction, hypertrophy, fibrosis and cell death, while a lower TNFα concentration and subsequent cardiomyocyte TNF receptor type 2 stimulation are protective. Apart from its concentration and receptor subtype, the myocardial action of TNFα depends on the duration of its exposure and its localization. While detrimental during sustained ischemia, TNFα contributes to ischemic preconditioning protection, no matter whether it is the first, second or third window of protection, and both TNF receptors are involved in the protective signal transduction cascade. Finally, the available clinical attempts to antagonize TNFα in cardiovascular disease, notably heart failure, are critically discussed.

Nitric oxide affects IL-6 expression in human peripheral blood mononuclear cells involving cGMP-dependent modulation of NF-κB activity

Interleukin 6 (IL-6) and nitric oxide (NO) are important mediators of the inflammatory response. We report that in human peripheral blood mononuclear cells (PBMCs), NO exerts a biphasic effect on the expression of IL-6. Using sodium nitroprusside (SNP) and S-nitrosoglutathione (GSNO) as NO-donating compounds, we observed that both mRNA and protein levels of IL-6 increased at lower (≤10μM) and decreased at higher (>100μM) concentrations of NO donors. Changes in the expression of IL-6 correlated with changes in the activity of NF-κB, which increased at lower and decreased at higher concentrations of both NO donors as shown by the electrophoretic mobility shift assay (EMSA). The effects of NO on NF-κB activity were cGMP-dependent because they were reversed in the presence of ODQ, the inhibitor of soluble guanylyl cyclase (sGC), and KT5823, the inhibitor of cGMP-dependent protein kinase (PKG). Moreover, the membrane permeable analog of cGMP (8-Br-cGMP) mimicked the effect of the NO donors. These observations show that NO, depending on its concentration, may act in human PBMCs as a stimulator of IL-6 expression involving the sGC/cGMP/PKG pathway.

Nitric oxide and calcium signaling regulate myocardial tumor necrosis factor-α expression and cardiac function in sepsis

Myocardial tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is a critical inducer of myocardial dysfunction in sepsis. The purpose of this review is to summarize the mechanisms through which TNF-alpha production is regulated in cardiomyocytes in response to lipopolysaccharide (LPS), a key pathogen-associated molecular pattern (PAMP) in sepsis. These mechanisms include Nox2-containing NAD(P)H oxidase, phospholipase C (PLC)gamma1, and Ca2+ signaling pathways. Activation of these pathways increases TNF-alpha expression via activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). Conversely, activation of c-Jun NH2-terminal kinase 1 (JNK1) negatively regulates TNF-alpha production through inhibition of ERK1/2 and p38 MAPK activity. Interestingly, endothelial nitric oxide synthase (eNOS) promotes TNF-alpha expression by enhancing p38 MAPK activation, whereas neuronal NOS (nNOS) inhibits TNF-alpha production by reducing Ca2+-dependent ERK1/2 activity. Therefore, the JNK1 and nNOS inhibitory pathways represent a "brake" that limits myocardial TNF-alpha expression in sepsis. Further understanding of these signal transduction mechanisms may lead to novel pharmacological therapies in sepsis.

Resistance to endotoxic shock in mice lacking natriuretic peptide receptor-A

Background and purpose:

Excessive production of nitric oxide (NO) by inducible NO synthase (iNOS) is thought to underlie the vascular dysfunction, systemic hypotension and organ failure that characterize endotoxic shock. Plasma levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are raised in animal models and humans with endotoxic shock and correlate with the associated cardiovascular dysfunction. Since both NO and natriuretic peptides play important roles in cardiovascular homeostasis via activation of guanylate cyclase-linked receptors, we used mice lacking natriuretic peptide receptor (NPR)-A (NPR1) to establish if natriuretic peptides contribute to the cardiovascular dysfunction present in endotoxic shock.

Experimental approach:

Wild-type (WT) and NPR-A knockout (KO) mice were exposed to lipopolysaccharide (LPS) and vascular dysfunction (in vitro and in vivo), production of pro-inflammatory cytokines, and iNOS expression and activity were evaluated.

Key results:

LPS-treated WT animals exhibited a marked fall in mean arterial blood pressure (MABP) whereas NPR-A KO mice maintained MABP throughout. LPS administration caused a greater suppression of vascular responses to the thromboxane-mimetic U46619, ANP, acetylcholine and the NO-donor spermine-NONOate in WT versus NPR-A KO mice. This differential effect on vascular function was paralleled by reduced pro-inflammatory cytokine production, iNOS expression and activity (plasma [NO_x] and cyclic GMP).

Conclusions and implications:

These observations suggest that NPR-A activation by natriuretic peptides facilitates iNOS expression and contributes to the vascular dysfunction characteristic of endotoxic shock. Pharmacological interventions that target the natriuretic peptide system may represent a novel approach to treat this life-threatening condition.

Nitric oxide permits hypoxia-induced lymphatic perfusion by controlling arterial-lymphatic conduits in zebrafish and glass catfish

The blood and lymphatic vasculatures are structurally and functionally coupled in controlling tissue perfusion, extracellular interstitial fluids, and immune surveillance. Little is known, however, about the molecular mechanisms that underlie the regulation of bloodlymphatic vessel connections and lymphatic perfusion. Here we show in the adult zebrafish and glass catfish (Kryptopterus bicirrhis) that blood-lymphatic conduits directly connect arterial vessels to the lymphatic system. Under hypoxic conditions, arterial-lymphatic conduits (ALCs) became highly dilated and linearized by NO-induced vascular relaxation, which led to blood perfusion into the lymphatic system. NO blockage almost completely abrogated hypoxia-induced ALC relaxation and lymphatic perfusion. These findings uncover mechanisms underlying hypoxia-induced oxygen compensation by perfusion of existing lymphatics in fish. Our results might also imply that the hypoxia-induced NO pathway contributes to development of progression of pathologies, including promotion of lymphatic metastasis by modulating arterial-lymphatic conduits, in the mammalian system.

Silencing the myotrophin gene by RNA interference leads to the regression of cardiac hypertrophy

Myotrophin-induced activation of NF-kappaB has been shown to be associated with cardiac hypertrophy (CH) that progresses to heart failure (HF). In the present study, we examined the cause-and-effect relationship between myotrophin and NF-kappaB activation using small hairpin RNA (shRNA) against myotrophin both in vitro (using neonatal rat myocytes) and in vivo [using myotrophin transgenic (Myo-Tg) mice, which overexpress myotrophin in the heart, develop CH, and gradually progress to HF]. Among several lentiviral vectors expressing myotrophin shRNAs, L-sh-109 showed the best silencing effect at both the mRNA (155.3 +/- 5.9 vs. 32.5 +/- 5.5, P < 0.001) and protein levels associated with a significant reduction of atrial natriuretic factor (ANF) and NF-kappaB. In vivo, when L-sh-109 was delivered directly into the hearts of 10-wk-old Myo-Tg mice, we observed a significant regression of cardiac mass (8.0 vs. 5.7 mg/g, P < 0.001) and myotrophin gene expression (54.5% over untreated Myo-Tg mice, P < 0.001) associated with a reduction in ANF and NF-kappaB signaling components. Our data suggest that using RNA interference to silence the myotrophin gene prevents NF-kappaB activation, associated with an attenuation of CH. This strategy could be an excellent therapeutic means for the treatment of CH and HF.

Nuclear co-translocation of myotrophin and p65 stimulates myocyte growth. Regulation by myotrophin hairpin loops

Myotrophin, a 12-kDa ankyrin repeat protein, stimulates protein synthesis and cardiomyocyte growth to initiate cardiac hypertrophy by activating the NF-kappaB signaling cascade. We found that, after internalization into myocytes, myotrophin cotranslocates into the nucleus with p65 to stimulate myocyte growth. We used structure-based mutations on the hairpin loops of myotrophin to determine the effect of the loops on myotrophin and p65 localization, induction of protein synthesis, and cardiac hypertrophy. Loop mutants, most prominently glutamic acid 33-->alanine (E33A), stimulated protein synthesis much less than wild type. Myotrophin-E33A internalized into myocytes but did not translocate into the nucleus and failed to promote nuclear translocation of p65. In addition, two cardiac hypertrophy marker genes, atrial natriuretic factor and beta-myosin heavy chain, were not up-regulated in E33A-treated cells. Myotrophin-induced myocyte growth and initiation of hypertrophy thus require nuclear co-translocation of myotrophin and p65, in a manner that depends crucially on the myotrophin hairpin loops.

Prevention of cardiac hypertrophy and heart failure by silencing of NF-kappaB

Activation of the nuclear factor (NF)-kappaB signaling pathway may be associated with the development of cardiac hypertrophy and its transition to heart failure (HF). The transgenic Myo-Tg mouse develops hypertrophy and HF as a result of overexpression of myotrophin in the heart associated with an elevated level of NF-kappaB activity. Using this mouse model and an NF-kappaB-targeted gene array, we first determined the components of NF-kappaB signaling cascade and the NF-kappaB-linked genes that are expressed during the progression to cardiac hypertrophy and HF. Second, we explored the effects of inhibition of NF-kappaB signaling events by using a gene knockdown approach: RNA interference through delivery of a short hairpin RNA against NF-kappaB p65 using a lentiviral vector (L-sh-p65). When the short hairpin RNA was delivered directly into the hearts of 10-week-old Myo-Tg mice, there was a significant regression of cardiac hypertrophy, associated with a significant reduction in NF-kappaB activation and atrial natriuretic factor expression. Our data suggest, for the first time, that inhibition of NF-kappaB using direct gene delivery of sh-p65 RNA results in regression of cardiac hypertrophy. These data validate NF-kappaB as a therapeutic target to prevent hypertrophy/HF.

Cardiac hypertrophy: mechanisms and therapeutic opportunities

Cardiac hypertrophy and heart failure are major causes of morbidity and mortality in Western societies. Many factors have been implicated in cardiac remodeling, including alterations in gene expression in myocytes, cardiomyocytes apoptosis, cytokines and growth factors that influence cardiac dynamics, and deficits in energy metabolism as well as alterations in cardiac extracellular matrix composition. Many therapeutic means have been shown to prevent or reverse cardiac hypertrophy. New concepts for characterizing the pathophysiology of cardiac hypertrophy have been drawn from various aspects, including medical therapy and gene therapy, or use of stem cells for tissue regeneration. In this review, we focus on various types of cardiac hypertrophy, defining the causes of hypertrophy, describing available animal models of hypertrophy, discussing the mechanisms for development of hypertrophy and its transition to heart failure, and presenting the potential use of novel promising therapeutic strategies derived from new advances in basic scientific research.

Nitric oxide production is a proximal signaling event controlling exercise-induced mRNA expression in human skeletal muscle

Previous studies have described the magnitude and time course by which several genes are regulated within exercising skeletal muscle. These include interleukin-6 (IL-6), interleukin-8 (IL-8), heme oxygenase-1 (HO-1), and heat shock protein-72 (HSP72), which are involved in secondary signaling and preservation of intracellular environment. However, the primary signaling mechanisms coupling contraction to transcription are unknown. We hypothesized that exercise-induced nitric oxide (NO) production is an important signaling event for IL-6, IL-8, HO-1, and HSP72 expression in muscle. Twenty healthy males participated in the study. By real-time PCR, mRNA levels for 11 genes were determined in thigh muscle biopsies obtained 1) before and after 2 h knee extensor exercise without (control) and with concomitant NO synthase inhibition (nitro-L-arginine methyl ester, L-NAME, 5 mg x kg(-1)); or 2) before and after 2 h femoral artery infusion of the NO donor nitroglycerin (NTG, 1.5 microg x kg(-1) x min(-1)). L-NAME caused marked reductions in exercise-induced expression of 4 of 11 mRNAs including IL-6, IL-8, and HO-1. IL-6 protein release from the study leg to the circulation increased in the control but not in the L-NAME trial. NTG infusion significantly augmented expression of the mRNAs attenuated by L-NAME. These findings advance the novel concept that NO production contributes to regulation of gene expression in muscle during exercise. Subsequently, we sought evidence for involvement of AMP-activated kinase or nuclear factor kappa B, but found none.

NO-cGMP and TNF-alpha counter regulatory system in blood: understanding the mechanisms leading to myocardial dysfunction and failure

One of the major conceptual advances in the understanding of the pathogenesis of heart failure has been the insight that myocardial dysfunction and heart failure may progress as the result of the sustained over-expression of nitric oxide (NO) metabolites locally and in blood modulated by inducible nitric oxide synthase (iNOS). This by virtue of their deleterious effects is sufficient to contribute to disease progression by provoking left ventricular (LV) remodeling, hypertrophy and progressive LV dysfunction. Recently, tumor necrosis factor-alpha (TNF-alpha) has also been identified in this setting of heart failure. Analogous to the situation with NO, the over-expression of TNF-alpha is sufficient to contribute to disease progression in heart failure phenotype. Although important interactions between TNF-alpha and the NO have been recognized in the cardiovascular system for over a decade, the nature and importance of the interactions between these biologically active molecules in cardiac hypertrophy has become apparent only in the recent times. Therefore, we focused on the prevailing updated evidence which suggests that there is a functionally significant cross-regulation between NO and TNF-alpha signaling in blood thus playing a part in cardiac hypertrophy and failure. The discussions presented here will have a bearing on the therapeutic potential via inhibitors of these pathways in reducing cardiomyocyte hypertrophy and the LV dysfunction.

Nitric oxide stimulates cyclooxygenase-2 in cultured cTAL cells through a p38-dependent pathway

To examine the interaction of nitric oxide (NO) and cyclooxygenase (COX-2) and the signaling pathway involved, primary cultured rabbit cortical thick ascending limb (cTAL) were used. In these cells, immunoreactive COX-2 and vasodilatory prostaglandins were increased by a NO donor, S-nitros- N-acetylpenicillamine (SNAP; 2.5 ± 0.3-fold control, n = 6, P < 0.01). SNAP increased expression of phosphorylated p38 (pp38; 2.4 ± 0.3-fold control; n = 5; P < 0.01), which was inhibited by the p38 inhibitor SB-203580 (1.3 ± 0.1-fold control, n = 5, P < 0.01). SB-203580 inhibited SNAP-induced COX-2 expression [1.4 ± 0.2-fold control, n = 6, not significant (NS) vs. control] and levels of PGE2significantly. In cTAL cells transfected with a luciferase reporter driven by the wild-type mouse COX-2 promoter, SNAP stimulated luciferase activity, which was reversed by SB-203580 (control vs. SNAP vs. SNAP + SB-203580: 1.4 ± 0.2-, 8.3 ± 1.4-, and 0.4 ± 0.1-fold control, respectively, n = 4, P < 0.01). Electrophoretic mobility shift assay indicated that SNAP stimulated nuclear factor (NF)-κB binding activity in cTAL that was also inhibited by the p38 inhibitor. SNAP was not able to stimulate a mutant COX-2 promoter construct that is not activated by NF-κB (0.9 ± 0.1, 1.2 ± 0.1, and 1.0 ± 0.2 respectively, n = 4, NS). Low chloride increased COX-2 expression (2.7 ± 0.4-fold control, n = 6, P < 0.01) and pp38 expression (2.8 ± 0.3-fold; n = 5, P < 0.01), which were reversed by the specific NO synthase (NOS) inhibitor 7-nitroindazole. Administration of a low-salt diet increased immunoreactive COX-2 and neuronal NOS (nNOS) in the macula densa and surrounding cTAL of kidneys of wild-type mice but did not significantly elevate COX-2 expression in nNOS−/−mice. In summary, these studies indicate that, in cTAL, NO can increase COX-2 expression in cTAL and macula densa through p38-dependent signaling pathways via activation of NF-κB.

The role of NO in macrophage dysfunction at early stage after burn injury

AIM

To explore the role of nitric oxide (NO) in macrophage dysfunction at early stage after burn injury.

METHOD

Peritoneal macrophages were isolated and cultured from early stage burnt mice. NO production and inducible NO synthase (iNOS) expression in the macrophages were checked by the Greiss method and real-time PCR (TaqMan), respectively. l-Arginine, the substrate of NO producing, or N-monomethyl-l-arginine (l-NMMA), a competing blocker of NOS was administered to the culture, the changes of NO, TNF-alpha and PGE2 productions were measured, additionally the changes of the iNOS, TNF-alpha and COX-2 expression were assayed by real-time PCR. After that, the effects of l-arginine and l-NMMA were determined on burnt macrophage influencing the proliferation of normal splenic lymphocytes.

RESULT

A large amount of NO was produced by macrophages from post burn hour 6 (6PBH) with a high level of iNOS expression. l-Arginine could increase NO production in a dosage-dependent manner, while l-NMMA attenuated NO production, but neither could affect iNOS expression. Moreover, l-arginine enhanced productions of both the latter produced TNF-alpha and PGE2 from burnt macrophages, and the expressions of TNF-alpha and COX-2 were improved significantly, while l-NMMA did reverse ways. It was found that macrophages from post burn hour 24 mice could inhibit Con A-stimulated normal splenic lymphocytes dramatically, l-NMMA could decrease this function significantly, but l-arginine could not influence the suppression.

CONCLUSION

Our experiment indicated NO derived from burnt macrophage played a vital role in macrophage producing excessive TNF-alpha and PGE2, and suppressing lymphocyte function at early stage after burn injury.

Nitrosative stress and transcription

Low NO concentrations synthesized by constitutively expressed NO synthases act on several signaling pathways activating transcription factors (TF), such as NF-kappaB or AP-1, and thereby influence gene expression. In contrast, during inflammatory reactions the inducible NO synthase produces NO for prolonged periods of time. The resulting nitrosative stress directly affects redox-sensitive TF like NF-kappaB, AP-1, Oct-1, c-Myb, or zinc finger-containing TF, but also additional mechanisms have been identified. Nitrosative stress in some cases induces expression of TF (AP-1, p53), indirectly modulates activity or stability of TF (HIF-1, p53) or their inhibitors (NF-kappaB), or modulates accessibility of promoters via increased DNA methylation or histone deacetylation. Depending on the promoter the result is induced, increased, decreased or even totally inhibited expression of various target genes. In unstimulated cells nitrosative stress increases NF-kappaB- or AP-1-dependent transcription, while in activated cells nitrosative stress rather abolishes NF-kappaB- or AP-1-dependent transcription. Sometimes the oxygen concentration also is of prime importance, since under normoxic conditions nitrosative stress activates HIF-1-dependent transcription, while under hypoxic conditions nitrosative stress leads to inhibition of HIF-1-dependent transcription. This review summarizes what is known about effects of physiological NO levels as well as of nitrosative stress on transcription.

Expression of inducible nitric oxide synthase is increased in patients with heart failure due to ischemic disease

The objective of the present study was to determine the relationship between nitric oxide synthases (NOS) and heart failure in cardiac tissue from patients with and without cardiac decompensation. Right atrial tissue was excised from patients with coronary artery disease (CAD) and left ventricular ejection fraction (LVEF) <35% (N = 10), and from patients with CAD and LVEF >60% (N = 10) during cardiac surgery. NOS activity was measured by the conversion of L-[H(3)]-arginine to L-[H(3)]-citrulline. Gene expression was quantified by the competitive reverse transcription-polymerase chain reaction. Both endothelial NOS (eNOS) activity and expression were significantly reduced in failing hearts compared to non-failing hearts: 0.36 +/- 0.18 vs 1.51 +/- 0.31 pmol mg-1 min-1 (P < 0.0001) and 0.37 +/- 0.08 vs 0.78 +/- 0.09 relative cDNA absorbance at 320 nm (P < 0.0001), respectively. In contrast, inducible NOS (iNOS) activity and expression were significantly higher in failing hearts than in non-failing hearts: 4.00 +/- 0.90 vs 1.54 +/- 0.65 pmol mg-1 min-1 (P < 0.0001) and 2.19 +/- 0.27 vs 1.43 +/- 0.13 cDNA absorbance at 320 nm (P < 0.0001), respectively. We conclude that heart failure down-regulates both eNOS activity and expression in cardiac tissue from patients with LVEF <35%. In contrast, iNOS activity and expression are increased in failing hearts and may represent an alternative mechanism for nitric oxide production in heart failure due to ischemic disease.

Regulation of the human tumor necrosis factor-alpha promoter by angiotensin II and lipopolysaccharide in cardiac fibroblasts: different cis-acting promoter sequences and transcriptional factors

We recently showed that angiotensin (ANG) II as well as mechanical stretch stimulated production of tumor necrosis factor (TNF) in cardiac fibroblasts. Presently, we examined the molecular mechanisms by which ANGII and lipopolysaccharide (LPS) upregulate TNF-alpha gene expression. In neonatal rat cardiac fibroblasts, increased transcription of TNF-alpha mRNA was detected as luciferase activity associated with activity of the TNF-alpha promoter. Progressive deletion from this promoter located the LPS-responsive region between -200 and -120 bp from the transcription initiation site, while the sequence between -120 and -70 bp was required for ANGII-induced expression. Next, we examined which cis-acting sequences in the TNF-alpha promoter region were essential for induction of TNF-alpha transcription. Competition analysis by electrophoretic mobility shift assay with and without specific antibodies showed that LPS increased binding of Sp1 and Sp3 to the Sp1-binding site, while Egr-1 was unimportant. With ANGII, binding of ATF-2/c-jun to the CRE site was required for TNF-alpha gene induction; neither Ets nor NF-kappaB was essential. Mutation analysis confirmed that response to LPS relied upon the Sp1 site in the TNF-alpha promoter, while the CRE-binding site was essential for stimulation by ANGII. We concluded that since TNF-alpha gene expression is transcriptionally activated by ANGII or LPS in cardiac fibroblasts via different cis-acting sequences in the TNF-alpha promoter and different transcriptional factors, mechanisms inducing TNF production differ between heart failure or cardiac hypertrophy and infectious disease.

Macrophage endothelial nitric-oxide synthase autoregulates cellular activation and pro-inflammatory protein expression

Expression of inducible nitric-oxide (NO) synthase (iNOS) and "high-output" production of NO by macrophages mediates many cytotoxic actions of these immune cells. However, macrophages have also been shown to express a constitutive NOS isoform, the function of which remains obscure. Herein, bone marrow-derived macrophages (BMDMØs) from wild-type and endothelial NOS (eNOS) knock-out (KO) mice have been used to assess the role of this constitutive NOS isoform in the regulation of macrophage activation. BMDMØs from eNOS KO animals exhibited reduced nuclear factor-kappaB activity, iNOS expression, and NO production after exposure to lipopolysaccharide (LPS) as compared with cells derived from wild-type mice. Soluble guanylate cyclase (sGC) was identified in BMDMØs at a mRNA and protein level, and activation of cells with LPS resulted in accumulation of cyclic GMP. Moreover, the novel non-NO-based sGC activator, BAY 41-2272, enhanced BMDMØ activation in response to LPS, and the sGC inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one attenuated activation. These observations provide the first demonstration of a pathophysiological role for macrophage eNOS in regulating cellular activation and suggest that NO derived from this constitutive NOS isoform, in part via activation of sGC, is likely to play a pivotal role in the initiation of an inflammatory response.

Nitric oxide at a low concentration protects murine macrophage RAW264 cells against nitric oxide-induced death via cGMP signaling pathway

1. We investigated the cytoprotective effect of low-dose nitric oxide (NO) on NO-induced cell death in mouse macrophage-like cell line RAW264. 2. Sodium nitroprusside (SNP), an NO donor, at a high concentration (4 mM) released cytochrome c from mitochondria and induced death in RAW264 cells. Acetyl-L-aspartyl-L-glutamyl-L-valyl-L-aspart-1-al (Ac-DEVD-CHO, 100-200 microM), a caspase-3 inhibitor, attenuated the SNP-induced cell death in a concentration-dependent manner. 3. Pretreatment with 100 microM SNP for 24 h, which had no effect on cell viability, attenuated the cell death and reduced cytochrome c release from mitochondria to the cytosol induced by 4 mM SNP. 4. LY83583 (1-3 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 30-100 microM), soluble guanylate cyclase inhibitors, negated the protective effect of the 100 microM SNP pretreatment. 5. Pretreatment with 1 mM dibutylyl guanosine-3',5'-cyclic monophosphate (DBcGMP), a cell-permeable guanosine-3',5'-cyclic monophosphate (cGMP) analogue, for 24 h inhibited both cytochrome c release and cell death induced by SNP. 6. Protein kinase G inhibitor KT5823 (10 microM) significantly reduced the cytoprotective effects of low-dose SNP and DBcGMP. 7. These results indicate that low-dose NO protects RAW264 cells from NO-induced apoptosis through cGMP production and activation of protein kinase G.

VEGF165 transfection decreases postischemic NF-kappa B-dependent myocardial reperfusion injury in vivo: role of eNOS phosphorylation

Endothelial nitric oxide synthase (eNOS) phosphorylation increases nitric oxide formation, for example, after VEGF stimulation. We investigated whether nitric oxide formed after overexpression of VEGF or of phosphomimetic eNOS (S1177D) affects PMN-induced myocardial detriment after ischemia and reperfusion. Pigs (n=8 per group) were subjected to percutaneous liposome-based gene transfer by retroinfusion of the anterior interventricular vein 48 h before LAD occlusion (60 min) and reperfusion (24 h). Thereafter, regional myocardial function was assessed as subendocardial segment shortening (SES), and infarct size was determined. Tissue from the infarct region, the noninfarcted area at risk, and a control region was analyzed for NF-kappaB activation (EMSA), tumor necrosis factor (TNF)-alpha, and E-selectin mRNA and infiltration of polymorphonuclear neutrophils (PMN). L-NAME was applied in one group of VEGF-transfected animals. NF-kappaB activition, PMN infiltration in the infarct region, and AAR were reduced after transfection of VEGF or eNOS S1177D, but not after VEGF+L-NAME coapplication. Infarct size decreased, whereas SES improved after either VEGF or eNOS S1177D transfection, an effect inhibited by L-NAME coapplication. Retroinfusion of liposomal VEGF cDNA reduces NF-kappaB-dependent postischemic inflammation and subsequent myocardial reperfusion injury, an effect mediated at least in part by enhanced eNOS phosphorylation.

Nitric oxide: a key regulator of myeloid inflammatory cell apoptosis

Apoptosis of inflammatory cells is a critical event in the resolution of inflammation, as failure to undergo this form of cell death leads to increased tissue damage and exacerbation of the inflammatory response. Many factors are able to influence the rate of apoptosis in neutrophils, eosinophils, monocytes and macrophages. Among these is the signalling molecule nitric oxide (NO), which possesses both anti- and proapoptotic properties, depending on the concentration and flux of NO, and also the source from which NO is derived. This review summarises the differential effects of NO on inflammatory cell apoptosis and outlines potential mechanisms that have been proposed to explain such actions.

Endothelial nitric-oxide synthase enhances lipopolysaccharide-stimulated tumor necrosis factor-alpha expression via cAMP-mediated p38 MAPK pathway in cardiomyocytes

The purpose of this study was to investigate the role of endothelial nitric-oxide synthase (eNOS), cAMP, and p38 MAPK in tumor necrosis factor-alpha (TNF-alpha) expression induced by lipopolysaccharide (LPS). LPS dose- and time-dependently induced phosphorylation of p38 MAPK and TNF-alpha expression in neonatal mouse cardiomyocytes. TNF-alpha expression was preceded by p38 MAPK phosphorylation, and selective inhibition of p38 MAPK abrogated LPS-induced TNF-alpha expression. Deficiency in eNOS decreased basal and LPS-stimulated TNF-alpha expression in cardiomyocytes. NOS inhibitor l-NAME attenuated LPS-induced p38 MAPK phosphorylation and TNF-alpha production in wild-type cardiomyocytes, whereas NO donor 2,2'-(hydroxynitrosohydrazono)bis-ethanamine (DETA-NO) (2 microm) or overexpression of eNOS by adenoviral gene transfer restored the response of eNOS(-/-) cardiomyocytes to LPS. These effects of NO were mediated through cAMP-dependent pathway based on the following facts. First, deficiency in eNOS decreased basal levels of intracellular cAMP, and DETA-NO elevated intracellular cAMP levels in eNOS(-/-) cardiomyocytes. Second, a cAMP analogue 8-Br-cAMP mimicked the effect of NO in eNOS(-/-) cardiomyocytes. Third, either inhibition of cAMP or cAMP-dependent protein kinase attenuated LPS-stimulated p38 MAPK phosphorylation and TNF-alpha production in wild-type cardiomyocytes. In conclusion, eNOS enhances LPS-stimulated TNF-alpha expression in cardiomyocytes. Activation of p38 MAPK is essential in LPS-stimulated TNF-alpha expression. Moreover, the effects of NO on LPS-stimulated TNF-alpha expression are mediated through cAMP/cAMP-dependent protein kinase-dependent p38 MAPK pathway in neonatal cardiomyocytes.

The role of anticytokine therapy in heart failure: recent lessons from preclinical and clinical trials?

In summary, over a decade of investigation has demonstrated the pathophysiologic importance of TNF in the development and progression of cardiac dilatation and heart failure. Although the signaling pathways that regulate the cardiac production of TNF have not yet been identified and the potential benefits of TNF expression to the heart are not understood, the benefits of anticytokine therapy in animal models is marked. Unfortunately, these salutary effects in the laboratory have not transitioned to the bedside. To accomplish the translational portion of the cytokine story, we must identify the point in time during the transition from compensated to decompensated heart failure in which TNF is expressed. In addition, we must better understand the role that other down-stream and non-TNF-dependent cytokines play in the development of heart failure. Not all patients are the same; therefore, we must pursue clinical trials that will allow us to elucidate the optimal degree of TNF inhibition, identify the patients who are most likely to respond to TNF inhibition, and determine what the true, long-term effects of TNF inhibition may be. Finally, we must recognize that inflammatory activities can exist in tissues and organs in the absence of TNF. Thus, anticytokine strategies alone might not be effective in ameliorating the signs and symptoms of heart failure. It is hoped that the failure of recent studies to demonstrate salutary benefits in patients with class II to IV heart failure will not diminish enthusiasm for the long-term potential of anticytokine therapy.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Relation of tissue Doppler-derived myocardial velocities to serum levels and myocardial gene expression of tumor necrosis factor-alpha and inducible nitric oxide synthase in patients with ischemic cardiomyopathy having coronary artery bypass grafting

We evaluated the relation of segmental and annular tissue Doppler (TD) velocities to serum levels and myocardial gene expression of tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide (NOS2) in humans. Seven patients with coronary artery disease underwent echocardiographic examination including TD imaging, along with transmural endomyocardial biopsies (2 biopsies per patient for a total of 14 specimens) at the time of bypass surgery. The specimens were analyzed for the number of mRNA copies of TNF-alpha and NOS2. In addition, serum levels of TNF-alpha and nitrite were determined before and after surgery. Normal segments (n = 7) had fewer numbers of mRNA copies of both TNF-alpha (54.6 vs 6.5, p = 0.002) and NOS2 (3,093 +/- 486 vs 661 +/- 259, p <0.001) than dysfunctional segments (n = 7). Peak systolic velocity (Sm) (13.3 +/- 1.4 vs 4.9 +/- 1.6 cm/s, p = 0.002) and early diastolic velocity (Em) (16.5 +/- 2.7 vs 8.8 +/- 1.3 cm/s, p = 0.02) were significantly higher in normal segments. A significant correlation was present among Em, Sm, and the number of mRNA copies of TNF-alpha and NOS2 at baseline and during infusion of dobutamine (r range -0.72 to -0.92, p <0.01 for all). Likewise, significant relations were present between the changes in serum cytokine levels and changes in the mitral annulus diastolic velocity, E/Ea ratio, and end-diastolic wall stress (r range 0.75 to 0.88, p </=0.05 for all). In conclusion, Sm and Em are strongly dependent on the regional levels of cytokine gene expression, which are known to have negative inotropic and lusitropic effects when overexpressed.

Increased nitric oxide in proportion to the severity of heart failure in patients with dilated cardiomyopathy: close correlation of tumor necrosis factor-alpha with systemic and local production of nitric oxide

Recent studies have demonstrated that proinflammatory cytokines induce large amounts of nitric oxide (NO) and that the amount increases in patients with congestive heart failure (CHF). There are, however, few reports regarding the relationships between NO production, cytokines and the severity of heart failure, so the plasma concentrations of nitrite and nitrate (NOx), tumor necrosis factor-alpha (TNF-alpha) and brain natriuretic peptide (BNP) were measured in 43 patients with CHF caused by dilated cardiomyopathy and 26 age- and sex-matched normal control subjects. Forearm blood flow (FBF) was measured using plethysmography during infusions of acetylcholine and nitroglycerin and after the administration of the NO synthesis inhibitor L-NMMA (N(G)-monomethyl-L-arginine). Plasma concentrations of both NOx and TNF-alpha were significantly higher in the patient group than in the control group (p<0.001) and correlated closely with BNP concentrations (p<0.001). There was a positive relationship between NOx and TNF-alpha concentrations (r=0.80, p<0.001). Administration of L-NMMA significantly reduced FBF in both groups, and the percent change in FBF from baseline correlated significantly with TNF-alpha concentrations (r=0.63, p<0.001). The FBF response to acetylcholine was depressed in the patient group and correlated inversely with TNF-alpha concentrations. The FBF response to nitroglycerin did not correlate with TNF-alpha concentrations. The findings indicate that the concentrations of NO and TNF-alpha in patients with CHF increase in proportion to the severity of heart failure, and that TNF-alpha plays a role in the enhanced systemic and local production of NO.

Endotoxin stress-response in cardiomyocytes: NF-kappaB activation and tumor necrosis factor-alpha expression

Although tumor necrosis factor (TNF)-alpha is implicated in numerous cardiac pathologies, the intracellular events leading to its production by heart cells are largely unknown. The goal of the present study was to identify the role of the transcription factor nuclear factor (NF)-kappaB in this process. Among the many inducers of TNF-alpha expression in myeloid cells, only lipopolysaccharide (LPS) led to its induction in cultured neonatal myocytes. LPS also activated the NF-kappaB pathway, as evidenced by the degradation of the inhibitory protein IkappaB and the appearance of NF-kappaB-binding complexes in nuclear extracts. Furthermore, inhibitors of NF-kappaB activation, such as lactacystin, MG132, and pyrrolidine dithiocarbamate, were found to completely block the production of TNF-alpha in response to LPS stimulation, indicating a requirement of NF-kappaB for TNF-alpha expression. However, interleukin-1beta and phorbol 12-myristate 13-acetate also activated NF-kappaB but did not evoke TNF-alpha expression, revealing that this factor is not sufficient for cytokine production. Detailed examination of the NF-kappaB cascade revealed that cardiac cells displayed a unique pattern of IkappaB degradation in response to LPS, with IkappaBbeta but not IkappaBalpha being degraded upon stimulation. Additionally, two specific p65-containing DNA-binding complexes were observed in the nuclear extracts of neonatal cardiomyocytes: an inducible complex that is necessary for TNF-alpha expression and a constitutive species. Taken together, these results reveal that NF-kappaB is not only involved in cytokine production but also may be linked to other pathways that subserve a constitutive, protective mechanism for the heart cell.

Zaprinast, an inhibitor of cGMP-selective phosphodiesterases, enhances the secretion of TNF-alpha and IL-1beta and the expression of iNOS and MHC class II molecules in rat microglial cells

Proinflammatory cytokines produced by activated glial cells may in turn augment the immune/inflammatory reactions of glial cells through autocrine and paracrine routes. The NO/cGMP signaling represents one of the reactions of activated glial cells. We investigated whether the production of proinflammatory cytokines by glial cells is affected by NO-dependent downstream cGMP signaling. In primary cultures of mixed astrocytes and microglial cells, zaprinast (0.1 mM), an inhibitor of cGMP-selective phosphodiesterases, enhanced the basal and LPS (1.0 microg/ml)-induced secretion of TNF-alpha and IL-1beta. Zaprinast also enhanced NO production induced by LPS or IFN-gamma (100 U/ml), and in microglial cell cultures, but not in astrocyte cultures, zaprinast enhanced the basal and the IFN-gamma-induced production of the cytokines, TNF-alpha and IL-1beta, and of NO. This upregulation by zaprinast was partially inhibited by KT5823 (1.0 microM), an inhibitor of protein kinase G. The LPS-induced production of TNF-alpha, IL-1beta, and NO was inhibited by ODQ (50 microM), an inhibitor of soluble guanylyl cyclase, and by KT5823. Immunohistochemical analysis of mixed glial cell cultures showed that LPS/IFN-gamma-induced iNOS expression and the enhanced expression of iNOS by zaprinast were restricted to microglial cells. Zaprinast enhanced the IFN-gamma (200 U/ml)-induced expression of MHC Class II molecules in astrocytes and microglial cells in mixed cultures, but did not enhance this IFN-gamma-induced expression in pure astrocytes, which lacked paracrine TNF-alpha from microglial cells. Summarizing, zaprinast, which is associated with cGMP/protein kinase G signaling, may augment central immune/inflammatory reactions, possibly via the increased production of TNF-alpha and IL-1beta by activated microglial cells.

Is nitric oxide overproduction the target of choice for the management of septic shock?

Sepsis is a heterogeneous class of syndromes caused by a systemic inflammatory response to infection. Septic shock, a severe form of sepsis, is associated with the development of progressive damage in multiple organs, and is a leading cause of patient mortality in intensive care units. Despite important advances in understanding its pathophysiology, therapy remains largely symptomatic and supportive. A decade ago, the overproduction of nitric oxide (NO) had been discovered as a potentially important event in this condition. As a result, great hopes arose that the pharmacological inhibition of NO synthesis could be developed into an efficient, mechanism-based therapeutic approach. Since then, an extraordinary effort by the scientific community has brought a deeper insight regarding the feasibility of this goal. Here we present in summary form the present state of knowledge of the biological chemistry and physiology of NO. We then proceed to a systematic review of experimental and clinical data, indicating an up-regulation of NO production in septic shock; information on the role of NO in septic shock, as provided by experiments in transgenic mice that lack the ability to up-regulate NO production; effects of pharmacological inhibitors of NO production in various experimental models of septic shock; and relevant clinical experience. The accrued evidence suggests that the contribution of NO to the pathophysiology of septic shock is highly heterogeneous and, therefore, difficult to target therapeutically without appropriate monitoring tools, which do not exist at present.

Nuclear factor kappa-B and the heart

Nuclear factor kappa-B (NFkappaB), a redox-sensitive transcription factor regulating a battery of inflammatory genes, has been indicated to play a role in the development of numerous pathological states. Activation of NFkappaB induces gene programs leading to transcription of factors that promote inflammation, such as leukocyte adhesion molecules, cytokines, and chemokines, although some few substances with possible anti-inflammatory effects are also NFkappaB regulated. The present article reviews basic regulation of NFkappaB and its activation, cell biological effects of NFkappaB activation and the role of NFkappaB in apoptosis. Evidence involving NFkappaB as a key factor in the pathophysiology of ischemia-reperfusion injury and heart failure is discussed. Although activation of NFkappaB induces pro-inflammatory genes, it has lately been indicated that the transcription factor is involved in the signaling of endogenous myocardial protection evoked by ischemic preconditioning. A possible role of NFkappaB in the development of atherosclerosis and unstable coronary syndromes is discussed. Nuclear factor kappa-B may be a new therapeutic target for myocardial protection.

Reduced sensitivity of inducible nitric oxide synthase-deficient mice to chronic colitis

BACKGROUND

Overproduction of nitric oxide by the inducible form of nitric oxide synthase (iNOS) has been implicated in colitis. Different authors have postulated both toxic and protective effects of nitric oxide (NO) in the pathophysiology of active inflammation. The objective of this study was to examine the role of iNOS in experimental chronic colitis using iNOS-deficient mice.

METHODS

For induction of colitis, mice received three cycles of 2% of dextran sodium sulfate (DSS) (M.W. 40,000) treatment in drinking water. The degree of colonic inflammation, leukocyte infiltration, and the expression of cell adhesion molecules were determined. INOS expression and nitrotyrosine were also determined by immunohistochemistry.

RESULTS

After DSS treatment, a moderate colitis with marked cell infiltration was observed. Intense expression of iNOS was observed on infiltrating cells as well as on the colonic mucosal epithelium in these animals. In the iNOS-deficient mice, tissue damage was significantly diminished. No iNOS or nitrotyrosine staining was found in iNOS-deficient mice. The number of infiltrating cells and the expression of mucosal adressin cell adhesion molecule-1 were significantly attenuated in the DSS-treated colon of iNOS-deficient mice.

CONCLUSION

Induction of iNOS seems to act as a critical toxic effector molecule in the pathogenesis of chronic colonic inflammation.

Blockade of the natriuretic peptide receptor guanylyl cyclase-A inhibits NF-kappaB activation and alleviates myocardial ischemia/reperfusion injury

Acute myocardial infarction (AMI) remains the leading cause of death in developed countries. Although reperfusion of coronary arteries reduces mortality, it is associated with tissue injury. Endothelial P-selectin-mediated infiltration of neutrophils plays a key role in reperfusion injury. However, the mechanism of the P-selectin induction is not known. Here we show that infarct size after ischemia/reperfusion was significantly smaller in mice lacking guanylyl cyclase-A (GC-A), a natriuretic peptide receptor. The decrease was accompanied by decreases in neutrophil infiltration in coronary endothelial P-selectin expression. Pretreatment with HS-142-1, a GC-A antagonist, also decreased infarct size and P-selectin induction in wild-type mice. In cultured endothelial cells, activation of GC-A augmented H2O2-induced P-selectin expression. Furthermore, ischemia/reperfusion-induced activation of NF-kappaB, a transcription factor that is known to promote P-selectin expression, is suppressed in GC-A-deficient mice. These results suggest that inhibition of GC-A alleviates ischemia/reperfusion injury through suppression of NF-kappaB-mediated P-selectin induction. This novel, GC-A-mediated mechanism of ischemia/reperfusion injury may provide the basis for applying GC-A blockade in the clinical treatment of reperfusion injury.