Complexity of inducible nitric oxide synthase: cellular source determines benefit versus toxicity

Immunotoxicity of legacy and alternative per- and polyfluoroalkyl substances on zebrafish larvae

Hexafluoropropylene oxide dimer acid (HFPO-DA) and perfluoroethylcyclohexane sulfonate (PFECHS) are increasingly used as alternatives for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). However, their immunotoxicity and underlying molecular mechanisms remain poorly understood. Here, to assess immunotoxic effects, zebrafish embryos were exposed to environmentally relevant concentrations of PFOA, PFOS, HFPO-DA, and PFECHS for four days. Results revealed that all four per- and polyfluoroalkyl substances (PFAS) resulted in decreased heart rate and spontaneous movement, and induced oxidative stress in zebrafish larvae. Notably, HFPO-DA exhibited more severe oxidative stress than PFOA. Immune dysfunction was observed, characterized by elevated cytokine, complement factor, nitric oxide, and neutrophil content, along with a significant decrease in lysozyme content. Transcriptomic analysis revealed the activation of Toll-like receptor (TLR)/NOD-like receptor (NLR)/RIG-I-like receptor (RLR) and associated downstream genes, indicating their pivotal role in PFAS-induced immunomodulation. Molecular docking simulations demonstrated stable interactions between PFAS and key receptors (TLR2, NOD2 and RIG-I). Overall, HFPO-DA and PFECHS exhibited immunotoxic effects in zebrafish larvae similar to legacy PFAS, providing important information for understanding the toxic mode of action of these emerging alternatives.

Neutrophils are indispensable for adverse cardiac remodeling in heart failure

Persistent immune activation contributes significantly to left ventricular (LV) dysfunction and adverse remodeling in heart failure (HF). In contrast to their well-known essential role in acute myocardial infarction (MI) as first responders that clear dead cells and facilitate subsequent reparative macrophage polarization, the role of neutrophils in the pathobiology of chronic ischemic HF is poorly defined. To determine the importance of neutrophils in the progression of ischemic cardiomyopathy, we measured their production, levels, and activation in a mouse model of chronic HF 8 weeks after permanent coronary artery ligation and large MI. In HF mice, neutrophils were more abundant both locally in failing myocardium (more in the border zone) and systemically in the blood, spleen, and bone marrow, together with increased BM granulopoiesis. There were heightened stimuli for neutrophil recruitment and trafficking in HF, with increased myocardial expression of the neutrophil chemoattract chemokines CXCL1 and CXCL5, and increased neutrophil chemotactic factors in the circulation. HF neutrophil NETotic activity was increased in vitro with coordinate increases in circulating neutrophil extracellular traps (NETs) in vivo. Neutrophil depletion with either antibody-based or genetic approaches abrogated the progression of LV remodeling and fibrosis at both intermediate and late stages of HF. Moreover, analogous to murine HF, the plasma milieu in human acute decompensated HF strongly promoted neutrophil trafficking. Collectively, these results support a key tissue-injurious role for neutrophils and their associated cytotoxic products in ischemic cardiomyopathy and suggest that neutrophils are potential targets for therapeutic immunomodulation in this disease.

Effects of the interaction of Notch and TLR4 pathways on inflammation and heart function in septic heart

We investigated the role of the interaction between the Notch and Toll-like receptor 4 (TLR4) pathways in septic myocardial injury. The sepsis model was induced in rats with lipopolysaccharide (LPS). Rats were divided into control, LPS, LPS + TAK242 ((6R)-6-[N-(2-chloro-4-fluorophenyl)sulfamoyl]cyclohex-1-ene-1-carboxylate) and LPS + DAPT (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-s-phenylglycinetbutylester) groups. Heart function was evaluated with a Cardiac Doppler ultrasound. Myocardial morphological changes were detected by hematoxylin-eosin staining (H&E). Apoptosis was assessed by a TUNEL assay. The mRNA and protein levels were detected with real-time PCR, Western blot, and immunohistochemistry analysis. We found that heart function in the LPS + TAK242 group was significantly improved, but not in the LPS + DAPT group. LPS + TAK242 had a lower level of degeneration and necrosis of cardiomyocytes and inflammatory cell infiltration, as well as lower apoptosis and caspase-3 expression than the LPS group. Compared with the LPS group, the inflammatory cell infiltration was reduced in the LPS + DAPT group, while the degeneration and necrosis of cardiomyocytes were not obviously improved. Additionally, the expression levels of tumor necrosis factor-α and Interleukin-6, the protein contents of Notch intracellular domain and Hes1, and the P65 nuclear factor kappa-B (NF-κB) to P-P65 NF-κB ratio in LPS + TAK242 group and LPS + DAPT group were significantly lower than those in LPS group. Conclusively, the interaction between TLR4 and Notch signaling pathways enhances the inflammatory response in the septic heart by activating NF-κB. Blocking the TLR4 pathway with TAK242 can improve heart dysfunction and myocardial damage in sepsis, while blocking the Notch pathway with DAPT cannot effectively prevent heart dysfunction and myocardial damage in sepsis.

Whole body periodic acceleration (pGz) improves endotoxin induced cardiomyocyte contractile dysfunction and attenuates the inflammatory response in mice

Sepsis-induces myocardial contractile dysfunction. We previously showed that whole body periodic acceleration (pGz), the sinusoidal motion of the supine body head-foot ward direction significantly improves survival and decreases microvascular permeability in a lethal model of sepsis. We tested the hypothesis that pGz improves LPS induced cardiomyocyte contractile dysfunction and decreases LPS pro-inflammatory cytokine response when applied pre- or post-treatment. Isolated cardiomyocytes were obtained from mice that received LPS who had been pre-treated with pGz for three days (pGz-LPS) or control. Peak shortening (PS), maximal velocity of shortening (+dL/dt), and relengthening (-dL/dt) as well as diastolic intracellular calcium concentration ([Ca⁺²]_d), sodium ([Na⁺]_d), reactive oxygen species (ROS), and cardiac troponin (cTnT) production were measured. LPS decreased PS, +dL/dt, and -dL/dt, by 37%, 41% and 35% change respectively (p < 0.01), increased [Ca⁺²]_d, [Na⁺]_d, ROS, and cTnT by 343%, 122%, 298%, and 610% change respectively (p < 0.01) compared to control. pGz pre-treatment attenuated the parameters mentioned above. In a separate cohort, the effects of a lethal dose of LPS on protein expression of nitric oxide synthases (iNOS, eNOS, nNOS), pro- and anti-inflammatory cytokines in hearts of mice was studied in pre-treated with pGz for three days prior to LPS (pGz-LPS) and post-treated with pGz 30 min after LPS (LPS-pGz) were determined. LPS increased expression of early and late iNOS and decreased expression of eNOS, phosphorylated eNOS (p-eNOS), and nNOS. Both pre- and post-treatment with pGz markedly reduced early and late pro-inflammatory surge. Therefore, pre- and post-treatment with pGz improves LPS-induced cardiomyocyte dysfunction, decreases iNOS expression, and increases cytoprotective eNOS and nNOS, with decreased pro-inflammatory response. Such results have potential for translation to benefit outcomes in human sepsis.

Hepatocellular iNOS protects liver from NASH through Nrf2-dependent activation of HO-1

Multiple molecular events are involved in non-alcoholic steatohepatitis (NASH). There is no consensus on the role of inducible nitric oxide synthase (iNOS) in the progression of NASH. The present study therefore investigated the role of iNOS in NASH pathogenesis using bone marrow-transplanted iNOS chimeric mice under high-fat diet (HFD) conditions. The chimeric mice were fed a HFD for 16 wk, and primary hepatocytes were stimulated with oleic acid (OA). The molecular mechanisms underlying the role of iNOS in NASH were investigated. Marked hepatic steatosis and injury observed in the HFD mice and OA-stimulated hepatocytes were reduced by hepatocyte-derived iNOS. Mechanistically, iNOS upregulated heme oxygenase 1 (HO-1) by augmenting nuclear factor erythroid 2-related factor 2 (Nrf-2) binding to the HO-1 gene promoter. In conclusion, hepatocyte-derived iNOS may play a protective role against the progression of NASH by upregulating HO-1 through Nrf-2. Upregulation of hepatocellular iNOS may represent a potentially new therapeutic paradigm to combat NASH.

Hepatocellular iNOS protects liver from ischemia/reperfusion injury through HSF1-dependent activation of HSP70

Although the role of inducible nitric oxide synthase (iNOS) in hepatic ischemia/reperfusion (I/R) injury remains controversial and confusing, with both harmful and beneficial effects in animal studies, the mechanism of these incongruous actions remains unclear. In the current study, we generated bone marrow chimeric mice with hepatocyte-restricted expression of iNOS. Chimeric mice and primary hepatocytes were subjected to I/R or anoxia/reoxygenation stimulation, respectively. The role of iNOS in liver I/R injury and the underlying molecular mechanisms were investigated. Hepatocyte-derived iNOS resulted in hepatoprotection from I/R injury, as well as in vitro experiments. Mechanistically, iNOS upregulates Heat shock protein (HSP) 70 by augmenting heat shock factor 1 (HSF1) binding to the HSP70 gene promoter. Importantly, inhibition of HSP70 partly reversed the iNOS overexpression-mediated hepatoprotection. The present findings demonstrate that hepatocellular iNOS protects from hepatic I/R injury through the HSF1-dependent activation of the HSP70. The upregulation of hepatocellular iNOS may offer a promising strategy for protecting against I/R injury.

Cell-specific regulation of iNOS by AMP-activated protein kinase in primary rat hepatocytes

BACKGROUND

AMP-activated protein kinase (AMPK) regulates several metabolic pathways in hepatocytes that are critical to the hepatic response to sepsis and shock. Induction of nitric oxide synthesis is an important response to sepsis, inflammation and shock and many of the stimuli that upregulate inducible nitric oxide synthase (iNOS) also activate AMPK. AMPK inhibits nitric oxide (NO) production in skeletal and cardiac muscle cells, but the role of AMPK in regulating iNOS expression in hepatocytes has not been determined.

MATERIALS AND METHODS

Primary cultured rat hepatocytes were preincubated with an AMPK inhibitor, AMPK activators, or transfected with AMPK siRNA before being treated with the proinflammatory cytokines interleukin-1β (IL-1β) and interferon-γ (IFNγ). The hepatocyte cell lysate and culture supernatants were collected for Western blot analysis and Griess assay.

RESULTS

IL-1β and IFNγ markedly upregulated iNOS expression and AMPK phosphorylation. IL-1β + IFNγ-induced NO production and iNOS expression were significantly decreased in hepatocytes treated with the AMPK inhibitor compound C and AMPK knockdown by AMPK siRNA. Cytokine-induced iNOS expression was increased by AMPK activators 1-oxo-2-(2H-pyrrolium-1-yl)-1H-inden-3-olate, AMPK signaling activator III and AICA-riboside. Compound C upregulated Akt and c-Jun N-terminal kinase phosphorylation but decreased IκBα phosphorylation. AICA-riboside exerted opposite effects on these signaling pathways in hepatocytes.

CONCLUSIONS

In contrast to other cell types, AMPK increased IL-1β + IFNγ-induced NO production and iNOS expression through the Akt, c-Jun N-terminal kinase, and NF-κΒ signaling pathways in primary hepatocytes. These data suggest that AMPK-altering medications used clinically may have subsequent effects on iNOS expression and proinflammatory signaling pathways.

Cardiac hyporesponsiveness in severe sepsis is associated with nitric oxide-dependent activation of G protein receptor kinase

G protein-coupled receptor kinase isoform 2 (GRK2) has a critical role in physiological and pharmacological responses to endogenous and exogenous substances. Sepsis causes an important cardiovascular dysfunction in which nitric oxide (NO) has a relevant role. The present study aimed to assess the putative effect of inducible NO synthase (NOS2)-derived NO on the activity of GRK2 in the context of septic cardiac dysfunction. C57BL/6 mice were submitted to severe septic injury by cecal ligation and puncture (CLP). Heart function was assessed by isolated and perfused heart, echocardiography, and β-adrenergic receptor binding. GRK2 was determined by immunofluorescence and Western blot analysis in the heart and isolated cardiac myocytes. Sepsis increased NOS2 expression in the heart, increased plasma nitrite + nitrate levels, and reduced isoproterenol-induced isolated ventricle contraction, whole heart tension development, and β-adrenergic receptor density. Treatment with 1400W or with GRK2 inhibitor prevented CLP-induced cardiac hyporesponsiveness 12 and 24 h after CLP. Increased labeling of total and phosphorylated GRK2 was detected in hearts after CLP. With treatment of 1400W or in hearts taken from septic NOS2 knockout mice, the activation of GRK2 was reduced. 1400W or GRK2 inhibitor reduced mortality, improved echocardiographic cardiac parameters, and prevented organ damage. Therefore, during sepsis, NOS2-derived NO increases GRK2, which leads to a reduction in β-adrenergic receptor density, contributing to the heart dysfunction. Isolated cardiac myocyte data indicate that NO acts through the soluble guanylyl cyclase/cGMP/PKG pathway. GRK2 inhibition may be a potential therapeutic target in sepsis-induced cardiac dysfunction.

NEW & NOTEWORTHY The main novelty presented here is to show that septic shock induces cardiac hyporesponsiveness to isoproterenol by a mechanism dependent on nitric oxide and mediated by G protein-coupled receptor kinase isoform 2. Therefore, G protein-coupled receptor kinase isoform 2 inhibition may be a potential therapeutic target in sepsis-induced cardiac dysfunction.

Leukocyte iNOS is required for inflammation and pathological remodeling in ischemic heart failure

In the failing heart, iNOS is expressed by both macrophages and cardiomyocytes. We hypothesized that inflammatory cell-localized iNOS exacerbates left ventricular (LV) remodeling. Wild-type (WT) C57BL/6 mice underwent total body irradiation and reconstitution with bone marrow from iNOS^-/- mice (iNOS^-/-c) or WT mice (WTc). Chimeric mice underwent coronary ligation to induce large infarction and ischemic heart failure (HF), or sham surgery. After 28 days, as compared with WTc sham mice, WTc HF mice exhibited significant (p < 0.05) mortality, LV dysfunction, hypertrophy, fibrosis, oxidative/nitrative stress, inflammatory activation, and iNOS upregulation. These mice also exhibited a ~twofold increase in circulating Ly6C^hi pro-inflammatory monocytes, and ~sevenfold higher cardiac M1 macrophages, which were primarily CCR2^- cells. In contrast, as compared with WTc HF mice, iNOS^-/-c HF mice exhibited significantly improved survival, LV function, hypertrophy, fibrosis, oxidative/nitrative stress, and inflammatory activation, without differences in overall cardiac iNOS expression. Moreover, iNOS^-/-c HF mice exhibited lower circulating Ly6C^hi monocytes, and augmented cardiac M2 macrophages, but with greater infiltrating monocyte-derived CCR2⁺ macrophages vs. WTc HF mice. Lastly, upon cell-to-cell contact with naïve cardiomyocytes, peritoneal macrophages from WT HF mice depressed contraction, and augmented cardiomyocyte oxygen free radicals and peroxynitrite. These effects were not observed upon contact with macrophages from iNOS^-/- HF mice. We conclude that leukocyte iNOS is obligatory for local and systemic inflammatory activation and cardiac remodeling in ischemic HF. Activated macrophages in HF may directly induce cardiomyocyte contractile dysfunction and oxidant stress upon cell-to-cell contact; this juxtacrine response requires macrophage-localized iNOS.

Hydrogen sulfide inhibits high glucose-induced NADPH oxidase 4 expression and matrix increase by recruiting inducible nitric oxide synthase in kidney proximal tubular epithelial cells

High-glucose increases NADPH oxidase 4 (NOX4) expression, reactive oxygen species generation, and matrix protein synthesis by inhibiting AMP-activated protein kinase (AMPK) in renal cells. Because hydrogen sulfide (H₂S) inhibits high glucose-induced matrix protein increase by activating AMPK in renal cells, we examined whether H₂S inhibits high glucose-induced expression of NOX4 and matrix protein and whether H₂S and NO pathways are integrated. High glucose increased NOX4 expression and activity at 24 h in renal proximal tubular epithelial cells, which was inhibited by sodium hydrosulfide (NaHS), a source of H₂S. High glucose decreased AMPK phosphorylation and activity, which was restored by NaHS. Compound C, an AMPK inhibitor, prevented NaHS inhibition of high glucose-induced NOX4 expression. NaHS inhibition of high glucose-induced NOX4 expression was abrogated by N(ω)-nitro-l-arginine methyl ester, an inhibitor of NOS. NaHS unexpectedly augmented the expression of inducible NOS (iNOS) but not endothelial NOS. iNOS siRNA and 1400W, a selective iNOS inhibitor, abolished the ameliorative effects of NaHS on high glucose-induced NOX4 expression, reactive oxygen species generation, and, matrix laminin expression. Thus, H₂S recruits iNOS to generate NO to inhibit high glucose-induced NOX4 expression, oxidative stress, and matrix protein accumulation in renal epithelial cells; the two gasotransmitters H₂S and NO and their interaction may serve as therapeutic targets in diabetic kidney disease.

Tadalafil Integrates Nitric Oxide-Hydrogen Sulfide Signaling to Inhibit High Glucose-induced Matrix Protein Synthesis in Podocytes

Diabetes-induced kidney cell injury involves an increase in matrix protein expression that is only partly alleviated by current treatment, prompting a search for new modalities. We have previously shown that hydrogen sulfide (H2S) inhibits high glucose-induced protein synthesis in kidney podocytes. We tested whether tadalafil, a phosphodiesterase 5 inhibitor used to treat erectile dysfunction, ameliorates high glucose stimulation of matrix proteins by generating H2S in podocytes. Tadalafil abrogated high glucose stimulation of global protein synthesis and matrix protein laminin γ1. Tadalafil inhibited high glucose-induced activation of mechanistic target of rapamycin complex 1 and laminin γ1 accumulation in an AMP-activated protein kinase (AMPK)-dependent manner. Tadalafil increased AMPK phosphorylation by stimulating calcium-calmodulin kinase kinase β. Tadalafil rapidly increased the expression and activity of the H2S-generating enzyme cystathionine γ-lyase (CSE) by promoting its translation. dl-Propargylglycine, a CSE inhibitor, and siRNA against CSE inhibited tadalafil-induced AMPK phosphorylation and abrogated the tadalafil effect on high glucose stimulation of laminin γ1. In tadalafil-treated podocytes, we examined the interaction between H2S and nitric oxide (NO). N(ω)-Nitro-L-arginine methyl ester and 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one, inhibitors of NO synthase (NOS) and soluble guanylyl cyclase, respectively, abolished tadalafil induction of H2S and AMPK phosphorylation. Tadalafil rapidly augmented inducible NOS (iNOS) expression by increasing its mRNA, and siRNA for iNOS and 1400W, an iNOS blocker, inhibited tadalafil stimulation of CSE expression and AMPK phosphorylation. We conclude that tadalafil amelioration of high glucose stimulation of synthesis of proteins including matrix proteins in podocytes requires integration of the NO-H2S-AMPK axis leading to the inhibition of high glucose-induced mechanistic target of rapamycin complex 1 activity and mRNA translation.

Cardiac NO signalling in the metabolic syndrome

It is well documented that metabolic syndrome (i.e. a group of risk factors, such as abdominal obesity, elevated blood pressure, elevated fasting plasma glucose, high serum triglycerides and low cholesterol level in high-density lipoprotein), which raises the risk for heart disease and diabetes, is associated with increased reactive oxygen and nitrogen species (ROS/RNS) generation. ROS/RNS can modulate cardiac NO signalling and trigger various adaptive changes in NOS and antioxidant enzyme expressions/activities. While initially these changes may represent protective mechanisms in metabolic syndrome, later with more prolonged oxidative, nitrosative and nitrative stress, these are often exhausted, eventually favouring myocardial RNS generation and decreased NO bioavailability. The increased oxidative and nitrative stress also impairs the NO-soluble guanylate cyclase (sGC) signalling pathway, limiting the ability of NO to exert its fundamental signalling roles in the heart. Enhanced ROS/RNS generation in the presence of risk factors also facilitates activation of redox-dependent transcriptional factors such as NF-κB, promoting myocardial expression of various pro-inflammatory mediators, and eventually the development of cardiac dysfunction and remodelling. While the dysregulation of NO signalling may interfere with the therapeutic efficacy of conventional drugs used in the management of metabolic syndrome, the modulation of NO signalling may also be responsible for the therapeutic benefits of already proven or recently developed treatment approaches, such as ACE inhibitors, certain β-blockers, and sGC activators. Better understanding of the above-mentioned pathological processes may ultimately lead to more successful therapeutic approaches to overcome metabolic syndrome and its pathological consequences in cardiac NO signalling.

Working with nitric oxide and hydrogen sulfide in biological systems

Nitric oxide (NO) and hydrogen sulfide (H2S) are gasotransmitter molecules important in numerous physiological and pathological processes. Although these molecules were first known as environmental toxicants, it is now evident that that they are intricately involved in diverse cellular functions with impact on numerous physiological and pathogenic processes. NO and H2S share some common characteristics but also have unique chemical properties that suggest potential complementary interactions between the two in affecting cellular biochemistry and metabolism. Central among these is the interactions between NO, H2S, and thiols that constitute new ways to regulate protein function, signaling, and cellular responses. In this review, we discuss fundamental biochemical principals, molecular functions, measurement methods, and the pathophysiological relevance of NO and H2S.

Nitric oxide synthase regulation of cardiac excitation-contraction coupling in health and disease

Significant advances in our understanding of the ability of nitric oxide synthases (NOS) to modulate cardiac function have provided key insights into the role NOS play in the regulation of excitation-contraction (EC) coupling in health and disease. Through both cGMP-dependent and cGMP-independent (e.g. S-nitrosylation) mechanisms, NOS have the ability to alter intracellular Ca(2+) handling and the myofilament response to Ca(2+), thereby impacting the systolic and diastolic performance of the myocardium. Findings from experiments using nitric oxide (NO) donors and NOS inhibition or gene deletion clearly implicate dysfunctional NOS as a critical contributor to many cardiovascular disease states. However, studies to date have only partially addressed NOS isoform-specific effects and, more importantly, how subcellular localization of NOS influences ion channels involved in myocardial EC coupling and excitability. In this review, we focus on the contribution of each NOS isoform to cardiac dysfunction and on the role of uncoupled NOS activity in common cardiac disease states, including heart failure, diabetic cardiomyopathy, ischemia/reperfusion injury and atrial fibrillation. We also review evidence that clearly indicates the importance of NO in cardioprotection. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Interaction of inducible nitric oxide synthase with rac2 regulates reactive oxygen and nitrogen species generation in the human neutrophil phagosomes: implication in microbial killing

AIMS

Present study explores importance of inducible nitric oxide synthase (iNOS) and its interaction with Rac2 in reactive oxygen species (ROS)/reactive nitrogen species (RNS) generation, protein-nitration and in microbial killing by neutrophils.

RESULTS

The iNOS transcript and protein were constitutively present in human as well as in mice neutrophils. iNOS protein was found in cytosol, granules containing elastase and gelatinase, and in other subcellular organelles in resting human neutrophils. After phagocytosis of bovine serum albumin (BSA) coated beads, both human and mice neutrophils showed significant elevation in superoxide radicals, nitric oxide (NO), ROS/RNS and consequent BSA nitration. These responses were significantly reduced in presence of iNOS, NADPH oxidase (NOX), myeloperoxidase or Rac inhibitors, as well as in iNOS, Nox2 and Rac2 silenced human or iNOS-knockout mice neutrophils. Complex formed on interaction of iNOS with Rac2 coprecipitated with anti-Rac2, predominantly in cytosol in resting human neutrophils, while iNOS-Rac2 complex translocated to phagosomes after phagocytosis. This was accompanied by generation of superoxide radicals, NO, ROS/RNS and consequent BSA-nitration. Importance of Rac2 in iNOS mediated NO formation and microbial killing was confirmed by pretreatment of mice with Rac inhibitor, NSC23766 that significantly abrogated NO release and microbial killing in vivo.

INNOVATION

Present study highlights previously undefined role of Rac2-iNOS interaction, in translocation of iNOS to phagosomal compartment and consequent NO, superoxide radicals, ROS/RNS generation, BSA nitration and microbial killing.

CONCLUSIONS

Altogether results obtained demonstrate the role of iNOS in NO and ROS/RNS generation, after phagocytosis of coated latex beads by human polymorphonuclear neutrophils. These studies imply functional importance of iNOS and its interaction with Rac2 in pathogen killing by the neutrophils.

Temporal determination of lung NO system and COX-2 upregulation following ischemia-reperfusion injury

BACKGROUND

Pulmonary ischemia-reperfusion (IR) is a biopathological event detectable in several clinical conditions, including lung transplantation, cardiopulmonary bypass, resuscitation, and pulmonary embolism. The understanding behind the activation of various inflammatory mediators regulating the apoptotic pathways remains largely unknown. We investigated the temporal expression of endothelial nitric oxide (eNOS), inducible (iNOS), and cyclooxygenase-2 (COX-2) proteins following lung-IR injury.

METHODS

Lung IR was induced in anesthetized rats. One hour ischemia was performed by clamping the left hilum. eNOS, iNOS, and COX-2 levels in the bronchoalveolar lavage (BAL) were measured at different time points after restoring lung perfusion in conjunction with histological changes and cellular apoptosis.

RESULTS

BAL-eNOS levels were increased as early as 3 hours post IR, attaining the highest values (5.5 U/mL) at 3 hours, compared to non-IR values (2.8 U/mL). BAL-iNOS increased at 3-hour post-IR (3 U/mL). iNOS reached the highest levels at 24 hours (4.5 U/mL) as compared to nonischemic lungs (1.8 U/mL). COX-2 peaked at 12 hours (.025 U/mL) compared to 3, 24, and 48 hours. Highest apoptotic rates were detected at 12 and 48 hours following IR.

CONCLUSIONS

The time-associated involvement of eNOS, iNOS, and COX-2 enzymes during the evolution of IR injury may point to an early reaction of the NOSs system versus the COX-2. Similar patterns of enzymatic activity were previously shown in the context of lung IR injury. This temporal activation may indicate an involvement of eNOS in an early reparative response, and possibly the late-pathological response, mediated by the coinduction of iNOS-COX-2.

cGMP-dependent protein kinases (cGK)

cGMP-dependent protein kinases (cGK) are serine/threonine kinases that are widely distributed in eukaryotes. Two genes-prkg1 and prkg2-code for cGKs, namely, cGKI and cGKII. In mammals, two isozymes, cGKIα and cGKIβ, are generated from the prkg1 gene. The cGKI isozymes are prominent in all types of smooth muscle, platelets, and specific neuronal areas such as cerebellar Purkinje cells, hippocampal neurons, and the lateral amygdala. The cGKII prevails in the secretory epithelium of the small intestine, the juxtaglomerular cells, the adrenal cortex, the chondrocytes, and in the nucleus suprachiasmaticus. Both cGKs are major downstream effectors of many, but not all, signalling events of the NO/cGMP and the ANP/cGMP pathways. cGKI relaxes smooth muscle tone and prevents platelet aggregation, whereas cGKII inhibits renin secretion, chloride/water secretion in the small intestine, the resetting of the clock during early night, and endochondral bone growth. This chapter focuses on the involvement of cGKs in cardiovascular and non-cardiovascular processes including cell growth and metabolism.

Gelam Honey Inhibits the Production of Proinflammatory, Mediators NO, PGE(2), TNF-α, and IL-6 in Carrageenan-Induced Acute Paw Edema in Rats

Natural honey is well known for its therapeutic value and has been used in traditional medicine of different cultures throughout the world. The aim of this study was to investigate the anti-inflammatory effect of Malaysian Gelam honey in inflammation-induced rats. Paw edema was induced by a subplantar injection of 1% carrageenan into the rat right hind paw. Rats were treated with the nonsteroidal anti-inflammatory drug (NSAID) Indomethacin (10 mg/kg, p.o.) or Gelam honey at different doses (1 or 2 g/kg, p.o.). The increase in footpad thickness was considered to be edema, which was measured using a dial caliper. Plasma and paw tissue were collected to analyze the production of inflammatory mediators, such as NO, PGE₂, TNF-α, and IL-6, as well as iNOS and COX-2. The results showed that Gelam honey could reduce edema in a dose-dependent fashion in inflamed rat paws, decrease the production of NO, PGE₂, TNF-α, and IL-6 in plasma, and suppress the expression of iNOS, COX-2, TNF-α, and IL-6 in paw tissue. Oral pretreatment of Gelam honey at 2 g/kg of body weight at two time points (1 and 7 days) showed a significantly decreased production of proinflammatory cytokines, which was similar to the effect of the anti-inflammatory drug Indomethacin (NSAID), both in plasma and tissue. Thus, our results suggest that Gelam honey has anti-inflammatory effects by reducing the rat paw edema size and inhibiting the production of proinflammatory mediators. Gelam honey is potentially useful for treating inflammatory conditions.

Interplay of endothelial and inducible nitric oxide synthases modulates the vascular response to ischaemia-reperfusion in the rabbit lung

AIM

Lung ischaemia-reperfusion induces nitric oxide synthesis and reactive nitrogen species, decreasing nitric oxide bioavailability. We hypothesized that in the ventilated lung, this process begins during ischaemia and intensifies with reperfusion, contributing to ischaemia-reperfusion-induced pulmonary vasoconstriction. The aim was to determine whether ischaemia-reperfusion alters inducible and endothelial nitric oxide synthase expression/activity, reactive nitrogen species generation, and nitric oxide bioavailability, potentially affecting pulmonary perfusion.

METHODS

Ischaemia-reperfusion was induced for various times in anesthetized rabbits with ventilated lungs by reversibly occluding the right pulmonary artery and initiating reperfusion. Nitric oxide synthase activity/expression and phosphorylation, reactive nitrogen species generation and total nitrate/nitrite were determined in lung tissue.

RESULTS

Inducible nitric oxide synthase expression and activity, and reactive nitrogen species formation coincided with increased pulmonary vascular resistance during reperfusion and increased with ischaemia duration, further increasing after 2-h reperfusion. Total nitrate/nitrite also increased with ischaemia but decreased after 2-h reperfusion. Pre-treatment with an inducible nitric oxide synthase inhibitor (1400W; Cayman Chemical Company, Ann Arbor, MI, USA) attenuated inducible nitric oxide synthase activity, reactive nitrogen species generation and pulmonary vascular resistance, but did not affect total nitrate/nitrite. Endothelial nitric oxide synthase expression was unchanged by ischaemia-reperfusion; however, its phosphorylation on serine 1177 and dephosphorylation on threonine 495 was uncoupled, suggesting decreased endothelial nitric oxide synthase activity. 1400W prevented uncoupling of endothelial nitric oxide synthase phosphorylation, maintaining its activity during reperfusion.

CONCLUSION

Ischaemia-reperfusion up-regulates inducible nitric oxide synthesis and/activity, which coincides with reduced endothelial nitric oxide synthase activity as suggested by its uncoupling and may contribute to ischaemia-reperfusion-induced pulmonary vasoconstriction.

Toll-like receptor 4 stimulation initiates an inflammatory response that decreases cardiomyocyte contractility

Toll-like receptors (TLRs) have been identified as primary innate immune receptors for the recognition of pathogen-associated molecular patterns by immune cells, initiating a primary response toward invading pathogens and recruitment of the adaptive immune response. TLRs, especially Toll-like receptor 4 (TLR4), can also be stimulated by host-derived molecules and are expressed in the cardiovascular system, thus acting as a possible key link between cardiovascular diseases and the immune system. TLR4 is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia. We used wild-type (WT) mice, TLR4-deficient (TLR4-knockout [ko]) mice, and chimeras that underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the heart (TLR4-ko/WT) and the immunohematopoietic system (WT/TLR4-ko). Following lipopolysaccharide (LPS) challenge (septic shock model) or coronary artery ligation, myocardial ischemia (MI) model, we found WT/TLR4-ko mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of interleukin-1β and tumor necrosis factor-α, and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. The cardiac function of TLR4-ko or WT/TLR4-ko mice was less affected by LPS and demonstrated reduced suppression by MI compared with WT. These results suggest that TLR4 expressed in the cardiomyocytes plays a key role in this acute phenomenon.

Nitric oxide in asthma physiopathology

Asthma is a chronic inflammatory airway disease characterized by allergen-induced airway hyperresponsiveness, airway inflammation, and remodeling. Nitric oxide (NO) derived from constitutive and inducible enzymes affects many aspects of asthma physiopathology. Animal in vivo studies have indicated that inhibition of iNOS may play a central role in the modulation of these features, particularly extracellular matrix remodeling. Additionally, increases in iNOS-derived NO, observed in asthmatic patients, may lead to an increase in peroxynitrite and an imbalance of oxidant and antioxidant pathways. In addition, endogenous nitric oxide produced by constitutive enzymes may protect against the remodeling of the lung. Therefore, nitric oxide donors and/or iNOS inhibitors may have therapeutic potential in asthma treatment and can also be used with corticosteroids to counteract airway remodeling. This paper focuses on the pathophysiological role of nitric oxide, mainly derived from inducible isoforms, in the various pathologic mechanisms of allergic asthma and the importance of nitric oxide and/or arginase inhibitors in asthma treatment.

Postconditioning attenuates myocardial injury by reducing nitro-oxidative stress in vivo in rats and in humans

In the present study, we hypothesized that postcon (postconditioning) confers cardioprotection in vivo by reducing the production of ONOO- (peroxynitrite) and nitro-oxidative stress subsequent to the inhibition of the iNOS (inducible NO synthase). Patients with AMI (acute myocardial infarct) were randomly assigned to undergo percutaneous coronary intervention without (control) or with ischaemic postcon by three episodes of 30-s inflation and 30-s deflation of the angioplasty balloon. Animal models of MI/R (myocardial ischaemia/reperfusion) injury were induced in rats by occluding the left coronary artery for 40 min followed by 4-h reperfusion. Rats were randomized to receive vehicle, postcon (three cycles of 10-s reperfusion and 10-s coronary re-occlusion preceding full reperfusion), the selective iNOS inhibitor 1400W or postcon plus 3-morpholinosydnonimine (an ONOO- donor). Postcon in patients reduced iNOS activity in white blood cells, decreased plasma nitrotyrosine, a fingerprint of ONOO- and an index of nitro-oxidative stress, and improved cardiac function (P<0.01 compared with control). In rats, postcon reduced post-ischaemic myocardial iNOS activity and nitrotyrosine formation, reduced myocardial infarct size (all P<0.05 compared with control) and improved cardiac function. Administration of 1400W resembled, whereas 3-morpholinosydnonimine abolished, the effects of postcon. In conclusion, reduction in ONOO--induced nitro-oxidative stress subsequent to the inhibition of iNOS represents a major mechanism whereby postcon confers cardioprotection in vivo.

Modulation of neutrophil apoptosis by murine pulmonary microvascular endothelial cell inducible nitric oxide synthase

Neutrophils contribute significantly to ALI (acute lung injury) through adhesion to pulmonary microvascular endothelial cells (PMEC), trans-PMEC migration and alveolar infiltration. Trans-PMEC migration delays expression of neutrophil apoptosis, which promotes intra-alveolar neutrophil survival and neutrophil mediated ALI. We assessed the role of neutrophil vs PMEC inducible nitric oxide (NO) synthase (iNOS) in modulating neutrophil apoptosis. Apoptosis of wild-type vs iNOS-/- neutrophils was quantified by microscopy and FACS annexin-V binding. In a murine model of ALI, neutrophils isolated by BAL(broncho-alveolar lavage) from iNOS-/- mice had increased expression of apoptosis after 24h culture ex vivo than wild-type neutrophils (15.2±3.3 vs 3.0±0.4%, mean±sd, p<0.01). Apoptosis rates of isolated bone marrow iNOS+/+ vs iNOS-/- neutrophils were similar under basal and LPS/IFN-γ stimulation, and following LPS/IFN-γ-stimulated trans-PMEC migration. Apoptosis of both iNOS+/+ and iNOS-/- neutrophils was inhibited by trans-PMEC migration only across iNOS+/+ PMEC (1.6±0.3 and 1.5±0.3%, respectively; p<0.05 for each vs non-migrated neutrophils) but not across iNOS-/- PMEC (4.3±1 and 3.1±0.6%, respectively). PMEC iNOS-dependent inhibition of neutrophil apoptosis was independent of changes in neutrophil caspase-3 activity. We conclude that PMEC iNOS, but not neutrophil iNOS, has an important inhibitory effect on neutrophil apoptosis during trans-PMEC neutrophil migration, which is independent of caspase-3 activity. Further studies will define the mechanism of PMEC iNOS-dependent inhibition of neutrophil apoptosis and assess the potential relevance of this phenomenon in human neutrophils and ALI.

Cardiomyocyte Toll-like receptor 4 is involved in heart dysfunction following septic shock or myocardial ischemia

Toll-like receptors are expressed in immune cells and cardiac muscle. We examined whether the cardiac Toll-like receptor 4 (TLR4) is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia (MI). We used wild type mice (WT), TLR4 deficient (TLR4-ko) mice and chimeras that underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the heart (TLR4-ko/WT) and the immunohematopoietic system (WT/TLR4-ko). Mice were injected with lipopolysaccharide (LPS) (septic shock model) or subjected to coronary artery ligation (MI model) and tested in vivo and ex vivo, for function, histopathology proinflammatory cytokine and TLR4 expression. WT mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of IL-1 beta and TNF-alpha and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. TLR4 deficient mice sustained significantly smaller infarctions as compared to control mice at comparable areas at risk. The cardiac function of TLR4-ko mice was not affected by LPS and demonstrated reduced suppression by MI compared to WT. Chimeras deficient in myocardial TLR4 were resistant to suppression induced by LPS and the heart function was less depressed, compared to the TLR4-ko, following MI in the acute phase (4h). In contrast, hearts of chimeras deficient in immunohematopoietic TLR4 expression were suppressed both by LPS and MI, exhibiting increased myocardial cytokine levels, similar to WT mice. We concluded that cardiac function of TLR4-ko mice and chimeric mice expressing TLR4 in the immunohematopoietic system, but not in the heart, revealed resistance to LPS and reduced cardiac depression following MI, suggesting that TLR4 expressed by the cardiomyocytes themselves plays a key role in this acute phenomenon.

Generation of NO by bystander human CD8 T cells augments allogeneic responses by inhibiting cytokine deprivation-induced cell death

Nitric oxide (NO), generated by inducible NO synthase (iNOS) in bystander human CD8 T cells, augments the accumulation of allogeneically activated human CD8 T cells in vitro and in vivo. Here, we report that iNOS-derived NO does not affect T-cell proliferation but rather inhibits cell death of activated human CD8 T cells after activation by allogeneic endothelial cells in culture. Exogenous NO did not affect activation-induced cell death of human CD8 T cells but specifically reduced death of activated T cells due to cytokine deprivation. NO-mediated inhibition of T-cell death did not involve cGMP signaling, and NO did not affect the expression of Bcl-2-related proteins known to regulate cytokine deprivation-induced cell death. However, NO inhibited the activity of caspases activated as a consequence of cytokine deprivation in activated T cells. This protective effect correlated with S-nitrosylation of caspases and was phenocopied by z-VAD.fmk and z-LEHD.fmk, pharmacological inhibitors of caspases. In summary, our findings indicate that NO augments the accumulation of activated human T cells principally by inhibiting cytokine deprivation-induced cell death through S-nitrosylation of caspases.

Mechanical ventilation during experimental sepsis increases deposition of advanced glycation end products and myocardial inflammation

Introduction

Increasing evidence links advanced glycation end products (AGE) including N^ε-(carboxymethyl)lysine (CML) to the development of heart failure. Accumulation of AGE leads to myocardial inflammation, which is considered as one of the possible mechanisms underlying sepsis-induced cardiac dysfunction. We hypothesized that mechanical ventilation (MV) augmented sepsis-induced myocardial CML deposition and inflammation.

Methods

Sepsis was induced using a modified cecal ligation and perforation (CLP) technique in 36 male adult Sprague Dawley rats. Rats were randomized to four hours of MV with low tidal volume (LTV: 6 ml/kg, PEEP 5 cmH₂O, n = 10) or high tidal volume (HTV: 15 ml/kg, PEEP 3 cmH₂O, n = 10) 24 hours after the induction of sepsis. Eight rats served as septic, non-ventilated controls and eight as non-septic, non-ventilated controls. After 28 hours all rats were killed. The number of extravascular polymorphonuclear (PMN) leucocytes, macrophages, and lymphocytes was measured as the number of positive cells/mm². The number of CML positive endothelial cells were semi-quantified based upon an intensity score. The CML intensity score was correlated with the number of inflammatory cells to study the association between CML depositions and inflammation.

Results

Gas exchange was comparable between the ventilated groups. Sepsis induced a significant increase in CML deposition in both ventricles that was significantly augmented by MV compared with non-ventilated septic controls (left ventricle 1.1 ± 1.0 vs 0.7 ± 0.1, P = 0.030; right ventricle 2.5 ± 0.5 vs 0.6 ± 0.1, P = 0.037), irrespective of ventilatory strategy. In the right ventricle there was a non-significant tendency towards increased CML deposition in the HTV group compared with septic, non-ventilated controls (1.0 ± 0.1 vs 0.7 ± 0.09, P = 0.07). Sepsis induced a significant increase in the number of macrophages and PMNs compared with non-ventilated septic controls that was augmented by MV, irrespective of ventilatory strategy. CML deposition was significantly correlated with the number of macrophages and PMNs in the heart.

Conclusions

Sepsis induces CML deposition in the heart with a predominant right ventricular inflammation that is significantly augmented by MV, irrespective of the ventilatory strategy.

Hindlimb ischemia/reperfusion-induced remote injury to the small intestine: role of inducible nitric-oxide synthase-derived nitric oxide

Systemic inflammatory response syndrome, as a consequence of ischemia/reperfusion (I/R), negatively influences the function of the affected organs. The objective of this study was to assess the role of nitric oxide (NO) in remote intestinal inflammatory response elicited by hindlimb I/R. To this end, C57BL/6 (wild type; WT) and inducible nitric-oxide synthase (iNOS)-deficient mice were subjected to bilateral hindlimb ischemia (1 h) followed by 6 h of reperfusion. Some WT mice were injected with iNOS inhibitor N-[3-(aminomethyl)benzyl] acetamidine (1400W) (5 mg/kg s.c.) immediately before reperfusion, and proinflammatory response was assessed 6 h later. Hindlimb I/R resulted in dysfunction of the small intestine as assessed by the increase in permeability [blood-to-lumen clearance of Texas Red-dextran (molecular mass 3 kDa)] and an increase in the luminal levels of tumor necrosis factor (TNF)-alpha protein and nitrate/nitrite (NO(2)(-)/NO(3)(-)). The above-mentioned changes were accompanied by up-regulation of the proinflammatory phenotype in the mucosa of small intestine with respect to 1) an increase in TNF-alpha and iNOS protein expression, 2) leukocyte accumulation, 3) formation of edema, 4) an increase in leukocyte rolling/adhesion in the submucosal microvasculature, and 5) activation of transcription factor nuclear factor-kappaB and up-regulation of adhesion molecule expression. Interestingly, the most profound changes with respect to intestinal dysfunction were found in jejunum and ileum, whereas duodenum was affected the least. Interfering with iNOS activity (1400W and iNOS-deficient mice) significantly attenuated hindlimb I/R-induced inflammatory response and dysfunction of the small intestine with respect to the above-mentioned markers of inflammation. The obtained results indicate that hindlimb I/R induces remote inflammatory response in the small intestine through an iNOS-derived NO-dependent mechanism.

Activated protein C improves lipopolysaccharide-induced cardiovascular dysfunction by decreasing tissular inflammation and oxidative stress

BACKGROUND

Recombinant human activated Protein C (APC) is used as an adjunctive therapeutic treatment in septic shock. APC seemingly acts on coagulation-inflammation interaction but also by decreasing proinflammatory gene activity, thus inhibiting subsequent production of proinflammatory cytokines, NO and NO-induced mediators, reactive oxygen species production and leukocyte-endothelium interaction. The hemodynamic effects of APC on arterial pressure and cardiac function are now well established in animal models. However, the specific effects of APC on heart and vessels have never been studied.

OBJECTIVES

To investigate the potential protective properties of therapeutic ranges of APC on a rat endotoxic shock model in terms of anti-inflammatory and cytoprotective pathways.

DESIGN

Laboratory investigation.

SETTING

University medical center research laboratory.

INTERVENTIONS

Rats were exposed to lipopolysaccharide (LPS) (10 mg/Kg intravenous). Endotoxic shock was treated with infusion of saline with or without APC (33 microg/kg/h) during 4 hrs. Hemodynamic parameters were continuously assessed and measurements of muscle oxygen partial pressures, NO and superoxide anion (O2(-)) by spin trapping, of NF-kappaB, metalloproteinase-9 (MMP-9) and inducible NO synthase (iNOS) by Western blotting, as well as leukocyte infiltration and MMP-9 activity were performed at both the heart and aorta level (tissue).

MAIN RESULTS

APC partially prevented the reduction of blood pressure induced by LPS and improved both vascular hyporeactivity and myocardial performance. This was associated with a decreased up-regulation of NF-kappaB, iNOS and MMP-9. LPS-induced tissue increases in NO and O2(-) production were decreased by APC. Furthermore, APC decreased tissue leukocyte infiltration/activation as assessed by a decrease in myeloperoxidase and matrix metalloproteinase 9 activity.

CONCLUSIONS

These data suggest that APC improves cardiovascular function: 1) by modulating the endotoxin induced-proinflammatory/prooxidant state, 2) by decreasing endothelial/leukocyte interaction and 3) by favoring stabilization of the extracellular matrix.

cGMP regulated protein kinases (cGK)

cGMP-dependent protein kinases (cGK) are serine/threonine kinases that are widely distributed in eukaryotes. Two genes--prkg1 and prkg2--code for cGKs, namely cGKI and cGKII. In mammals, two isozymes, cGKIalpha and cGKIbeta, are generated from the prkg1 gene. The cGKI isozymes are prominent in all types of smooth muscle, platelets, and specific neuronal areas such as cerebellar Purkinje cells, hippocampal neurons, and the lateral amygdala. The cGKII prevails in the secretory epithelium of the small intestine, the juxta-glomerular cells, the adrenal cortex, the chondrocytes, and in the nucleus suprachiasmaticus. Both cGKs are major downstream effectors of many, but not all signalling events of the NO/cGMP and the ANP/cGMP pathways. cGKI relaxes smooth muscle tone and prevents platelet aggregation, whereas cGKII inhibits renin secretion, chloride/water secretion in the small intestine, the resetting of the clock during early night, and endochondreal bone growth. cGKs are also modulators of cell growth and many other functions.

Role of blood- and tissue-associated inducible nitric-oxide synthase in colonic inflammation

There is evidence that inducible nitric-oxide synthase (iNOS)-derived NO contributes to the pathophysiology of intestinal inflammation. The aims of this study were to assess the role of iNOS in the development of dextran sodium sulfate (DSS)-induced colonic inflammation and to define the contribution of tissue-specific iNOS expression to this inflammatory response. Study groups included: 1) wild-type (WT) mice; 2) WT=>WT bone marrow chimeras with normal iNOS function; 3) WT=>iNOS-/- chimeras (with functional blood cell iNOS, but iNOS-deficient tissue); 4) iNOS-/-=>WT chimeras (with iNOS-deficient blood cells, but normal tissue iNOS activity); and 5) iNOS-deficient mice. In WT mice and WT=>WT chimeras, DSS-induced colonic inflammation was characterized by bloody diarrhea and a high disease activity index. However, WT=>iNOS-/- and iNOS-/-=>WT chimeras and iNOS-/- mice exhibited an attenuated disease activity index, with parallel changes in histopathology. Colonic myeloperoxidase (MPO) was comparably elevated in DSS-treated WT mice (30.1+/-1.7) and WT=>WT chimeras (29.0+/-1), whereas MPO was significantly reduced in iNOS-/- mice and iNOS-/-=>WT chimeras (9.5+/-1.7 and 15.6+/-2.2, respectively). WT=>iNOS-/- chimeras exhibited the lowest MPO activity (3.7+/-0.6). Our findings implicate both blood cell- and tissue-derived iNOS in DSS-induced colonic inflammation, with tissue-associated iNOS making a larger contribution to the recruitment of inflammatory cells.

EFFECTS OF COMBINING INDUCIBLE NITRIC OXIDE SYNTHASE INHIBITOR AND RADICAL SCAVENGER DURING PORCINE BACTEREMIA

Complex interactions of nitric oxide and other free radicals have been implicated in the pathogenesis of sepsis and organ dysfunction. We hypothesized that simultaneous inducible nitric oxide synthase inhibition (L-N6-[1-iminoethyl]-lysine [L-NIL]) and neutralization of superoxide (O2-) (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl [Tempol]) would protect from detrimental consequences of long-term, volume-resuscitated, hyperdynamic porcine bacteremia. In this prospective, randomized, controlled experimental study, 16 anesthetized, mechanically ventilated and instrumented pigs were exposed to 24 h of continuous infusion of live Pseudomonas aeruginosa. After 12 h of hyperdynamic sepsis, animals were randomized to receive either vehicle (control, n = 8) or combination of L-NIL and Tempol (n = 8). Systemic and hepatosplanchnic hemodynamics, oxygen exchange, metabolism, ileal mucosal microcirculation and tonometry, oxidative stress and coagulation parameters were assessed before, 12, 18, and 24 h of P. aeruginosa infusion. Combined treatment inhibited sepsis-induced increase in plasma nitrate/nitrite, 8-isoprostane, and thiobarbituric acid reactive species concentrations, prevented hypotension, and reversed hyperdynamic circulation. Despite lower intestinal macrocirculation, combined regimen attenuated the otherwise progressive deterioration in ileal mucosal microcirculation and prevented mucosal acidosis. Treatment substantially attenuated mesenteric and hepatic venous acidosis, preserved sepsis-induced impairment of hepatosplanchnic redox state, and prevented the development of renal dysfunction. Finally, coinfusion of L-NIL and Tempol largely attenuated the sepsis-induced rise in plasma von Willebrand factor and thrombin-antithrombin complexes. Thus, hemodynamic, microcirculatory, metabolic, renal, and coagulation data indicate that combining inducible inhibition with cell permeable O2(-) radical scavenger afforded significant protection in porcine sepsis, thus suggesting an important interactive role of O2(-) and nitric oxide in mediating organ dysfunction.

Infiltration of inflammatory cells plays an important role in matrix metalloproteinase expression and activation in the heart during sepsis

Septicemia is an emerging pathological condition involving, among other effects, refractory hypotension and heart dysfunction. Here we have investigated the contribution of resident nonmyocytic cells to heart alterations after lipopolysaccharide administration. These cells contributed to the rapid infiltration of additional inflammatory cells that enhance the onset of heart disease through the release of inflammatory mediators. Early activation of resident monocytic cells played a relevant role on the infiltration process, mainly of major histocompatibility complex class II- and CD11b-positive cells. This infiltration was significantly impaired in animals lacking the nitric-oxide synthase-2 (NOS-2) gene or after pharmacological in-hibition of NOS-2 or cylooxygenase-2, suggesting a significant contribution of nitric oxide and prostanoids to the infiltration process. Under these conditions, the expression of NOS-2 and cylooxygenase-2 in the whole organ was attenuated because cardiomyocytes failed to express these enzymes. However, cardiomyocytes expressed and activated matrix metalloproteinase-9 through mechanisms regulated, at least in part, by nitric oxide and prostaglandins in an additive way. These results directly link the inflammatory response in the heart and extracellular matrix remodeling by the matrix metalloproteinases released by the cardiomyocytes, suggesting that activation and recruitment of inflammatory cells to the heart is a major early event in cardiac dysfunction promoted by septicemia.

Systemic NO production during (septic) shock depends on parenchymal and not on hematopoietic cells: in vivo iNOS expression pattern in (septic) shock

Septic shock is the leading cause of death in noncoronary intensive care units and the 10th leading cause of death overall. Several lines of evidence support an important role for the vasodilator NO in hypotension, a hallmark of septic shock. However, NO may also positively or negatively regulate inflammation, apoptosis, and oxidative stress. These dual effects of NO may relate to its isoform specific production but also to differences in cellular and/or temporal expression. Via bone marrow transplantations, we examined the contribution of hematopoietic cells to the dramatically elevated NO levels seen in (septic) shock. Surprisingly, hematopoietic cells are not responsible at all for the production of circulating NO after systemic tumor necrosis factor or lipopolysaccharide challenge and contribute only marginally in a bacteremic (Salmonella) model of septic shock. Immunohistochemistry identified the nonhematopoietic sources of NO as hepatocytes, paneth cells, and intestinal and renal epithelial cells. In contrast, during granulomatous Bacillus Calmette-Guérin inflammation, the hematopoietic cell population represents the sole source of systemic NO. These mouse data demonstrate that, in contrast to the general conjecture, the dramatically elevated levels of NO during (septic) shock are not produced by hematopoietic cells such as monocytes/macrophages but rather by parenchymal cells in liver, kidney and gut.

The nitric oxide scavenger cobinamide profoundly improves survival in a Drosophila melanogaster model of bacterial sepsis

Septic shock has an extremely high mortality rate, with approximately 200,000 people dying from sepsis annually in the U.S. The high mortality results in part from severe hypotension secondary to high serum NO concentrations. Reducing NO levels should be beneficial in sepsis, but NOS inhibitors have had a checkered history in animal models, and one such agent increased mortality in a clinical trial. An alternative approach to reduce NO levels in sepsis is to use an NO scavenger, which should leave sufficient free NO for normal physiological functions. Using a well-established model of bacterial sepsis in Drosophila melanogaster, we found that cobinamide, a B(12) analog and an effective NO scavenger in vitro, dramatically improved fly survival. Cobinamide augmented the effect of an antibiotic and was beneficial even in immune-deficient flies. Cobinamide's mechanism of action appeared to be from reducing NO levels and improving cardiac function.

Cardiomyocyte-Specific Overexpression of NO Synthase-3 Protects Against Myocardial Ischemia-Reperfusion Injury

OBJECTIVE

The protective effect of NO synthase-3 (eNOS)-derived NO in limiting myocardial ischemia-reperfusion (MI-R) injury is well established. We reported previously that systemic genetic overexpression of eNOS attenuates MI-R injury. The purpose of the current study was to investigate tissue-specific genetic overexpression of the human eNOS gene.

METHODS AND RESULTS

To accomplish this, we used 2 distinct murine models of transgenic overexpression, a cardiomyocyte-specific eNOS overexpresser (CS eNOS-Tg) under the control of the alpha-myosin heavy chain promoter, and a systemic eNOS transgenic mouse (SYS eNOS-Tg) under control of the native eNOS promoter with an upstream endothelial enhancer element. Mice were subjected to 30 or 45 minutes of left coronary artery ischemia and 24 or 72 hours of reperfusion. CS eNOS-Tg mice displayed significantly decreased infarct size beyond that of mice with systemic overexpression. Additionally, CS eNOS-Tg mice exhibited better preservation of cardiac function compared with SYS eNOS-Tg mice after myocardial infarction.

CONCLUSIONS

These results provide evidence that site-specific targeting of eNOS gene therapy may be more advantageous in limiting MI-R injury and subsequent cardiac dysfunction.

Is there a role for cardiomyocyte toll-like receptor 4 in endotoxemia?

Lipopolysaccharide (LPS) is thought to be an important molecule in myocardial depression in sepsis. Toll-like receptor 4 (TLR4), the lipopolysaccharide receptor, is known to underlie these responses. Because TLR4 is expressed on both cardiac myocytes and immune cells, it is unclear as to which cell type is responsible for myocyte depression. In this article, we present evidence that the early response is likely related to TLR4 on immune cells and most likely macrophages, whereas the more delayed response may involve various immune cells as well as myocytes.

Plgf−/−eNos−/−mice show defective angiogenesis associated with increased oxidative stress in response to tissue ischemia

Neo-angiogenesis is a complex phenomenon modulated by the concerted action of several molecular factors. We have generated a congenic line of knockout mice carrying null mutations of both placental growth factor (PlGF) and endothelial nitric oxide synthase (eNOS), two genes that play a pivotal role in the regulation of pathological angiogenesis. In the present study, we describe the phenotype of this new experimental animal model after surgically induced hind-limb ischemia. Plgf-/-, eNos-/-, Plgf-/- eNos-/-, and wild-type C57BL/6J mice were studied. Plgf-/- eNos-/- mice showed the most severe phenotype: self-amputation, and death occurred in up to 47% of the animals studied; in ischemic legs, capillary density was severely reduced; macrophage infiltration and oxidative stress increased as compared to the other groups of animals. These changes were associated with an up-regulation of both inducible NOS (iNOS) expression and vascular endothelial growth factor (VEGF) protein levels in ischemic limbs, and to an increased extent of protein nitration. Our results demonstrate that the deletion of these two genes, Plgf, which acts in synergism with VEGF, and eNos, a downstream mediator of VEGF, determines a significant change in the vascular response to an ischemic stimulus and that oxidative stress within the ischemic tissue represents a crucial factor to maintain tissue homeostasis.

Nitric oxide-modulating agents for gastrointestinal disorders

Almost 20 years after the identification of the biological role of nitric oxide (NO), the full therapeutic potential of novel agents that mimic the activity of NO or interfere with its synthesis has yet to be realised for utilities involving the gastrointestinal tract. New utilities for classical NO donors, which were used as vasodilators for decades, in the treatment of motility disorders have been explored and a product for treating anal fissure was recently launched. New classes of compounds incorporating a NO-donating moiety into standard non-steroidal anti-inflammatory drugs, the NO-non-steroidal anti-inflammatory drugs (NO-NSAIDs) or COX-inhibiting nitric oxide donors (CINODs) have also been developed. These have been shown to exhibit reduced gastrointestinal injury in experimental models, and reports on their efficacy and safety in Phase I and II studies are now available. Modulation of the inducible NO synthase isoform that generates excessive NO that can lead to subsequent cytotoxic moieties, such as peroxynitrite, may have therapeutic possibilities in a range of inflammatory diseases of the gut. Likewise, agents that promote the decomposition of peroxynitrite or removal of its other component, superoxide, may also prove to be of use. Further targets for pharmaceutical exploitation are likely to come from both genomic and molecular insights into the processes that regulate the NO system.

Receptor for Advanced-Glycation End Products

Background— The beneficial effects of reperfusion therapies have been limited by the amount of ischemic damage that occurs before reperfusion. To enable development of interventions to reduce cell injury, our research has focused on understanding mechanisms involved in cardiac cell death after ischemia/reperfusion (I/R) injury. In this context, our laboratory has been investigating the role of the receptor for advanced-glycation end products (RAGE) in myocardial I/R injury.

Methods and Results— In this study we tested the hypothesis that RAGE is a key modulator of I/R injury in the myocardium. In ischemic rat hearts, expression of RAGE and its ligands was significantly enhanced. Pretreatment of rats with sRAGE, a decoy soluble part of RAGE receptor, reduced ischemic injury and improved functional recovery of myocardium. To specifically dissect the impact of RAGE, hearts from homozygous RAGE-null mice were isolated, perfused, and subjected to I/R. RAGE-null mice were strikingly protected from the adverse impact of I/R injury in the heart, as indicated by decreased release of LDH, improved functional recovery, and increased adenosine triphosphate (ATP). In rats and mice, activation of the RAGE axis was associated with increases in inducible nitric oxide synthase expression and levels of nitric oxide, cyclic guanosine monophosphate (cGMP), and nitrotyrosine.

Conclusions— These findings demonstrate novel and key roles for RAGE in I/R injury in the heart. The findings also demonstrate that the interaction of RAGE with advanced-glycation end products affects myocardial energy metabolism and function during I/R.

Cellular and molecular mechanisms underlying LPS-associated myocyte impairment

Recently we reported that Toll-like receptor 4 (TLR4)-positive immune cells of unknown identity were responsible for the LPS-induced depression of cardiac myocyte shortening. The aim of this study is to identify the TLR4-positive cell type that is responsible for the LPS-induced cardiac dysfunction. Neither neutrophil depletion alone nor mast cell deficiency had any impact on the impairment of myocyte shortening during LPS treatment. In contrast, LPS-treated, macrophage-deficient mice demonstrated a partial reduction in shortening compared with saline-treated, macrophage-deficient mice. Because the removal of macrophages could only partially restore myocyte shortening, we also investigated the effects of removing both neutrophils and macrophages on myocyte shortening. Interestingly, endotoxemic, neutrophil-depleted, and macrophage-deficient mice had completely restored myocyte shortening. Because both macrophages and neutrophils can produce nitric oxide (NO) and TNF-α, we examined LPS-treated inducible NO synthase knockout (iNOSKO) mice and TNF receptor (TNFR)-deficient mice. Eliminating both TNFR1 and TNFR2 was required to restore myocyte shortening during LPS treatment, whereas iNOS deficiency had no effect. These data suggest that macrophages and to a lesser degree neutrophils cause cardiac impairment, presumably via TNF-α.

Oral administration of geranylgeranylacetone blunts the endothelial dysfunction induced by ischemia and reperfusion in the rat heart

It has been shown that geranylgeranylacetone (GGA) protects heart against ischemia/reperfusion injury via enhanced heat shock protein 72 (HSP72) expression in rats. In the present study, we investigated the protective effect of GGA on ischemia/reperfusion-induced endothelial dysfunction. Rats were given oral GGA (GGA group) or vehicle (CON group), and 24 hours later their hearts were removed and placed in the Langendorff apparatus for 30-minute low-flow ischemia followed by 30-minute reperfusion. GGA improved the postischemic functional recovery (P < 0.01), which was abolished by N-nitro-L-arginine methyl ester (L-NAME, NO synthase inhibitor). NO production during both ischemia and reperfusion were increased in the GGA group, and the acetylcholine (ACh)-induced (endothelium-dependent) vasodilation, measured as the percentage decrease in coronary perfusion pressure after ischemia/reperfusion (14.9 +/- 1.3%), was preserved as compared with that in the CON group (7.9 +/- 1.4%). LY294002, a phosphatidylinositol 3 (PI3) kinase inhibitor, abolished the protective effects of GGA on endothelial-dependent coronary vasodilation and NO production, whereas Y27632 (Rho kinase inhibitor) increased endothelium-dependent coronary vasodilation and NO production in CON group toward the level seen in GGA group. The amount of adrenomedullin in the coronary effluent at basal condition was lower in the GGA group than in the CON group (P < 0.05), and during both ischemia and reperfusion there was no difference in the amount of adrenomedullin between the GGA and CON groups. In addition, no difference was observed in the amount of endothelin-1 between the GGA and CON groups. These results indicate that GGA attenuates the ischemia/reperfusion-induced coronary endothelial dysfunction, which may contribute to its cardioprotective effect. The PI3 kinase and/or Rho kinase pathways appear to be involved in this process, whereas adrenomedullin and endothelin-1 are not necessary for the GGA-induced cardioprotection.

Anti-inflammatory effect of augmented nitric oxide production in chronic lung infection

Chronic infection of the lungs with Pseudomonas aeruginosa complicates many long-term lung diseases including cystic fibrosis, bronchiectasis, chronic obstructive lung disease, and mechanical ventilation. In acute inflammatory lung diseases, increased nitric oxide synthase (NOS-2) expression leads to excess nitric oxide (NO) production, resulting in the production of reactive nitrogen intermediates, which contribute to tissue damage. In contrast, the contribution of NO to pulmonary damage in chronic Pseudomonas infection of the lung has not been directly examined and is unclear. Although NOS-2 expression is increased in this condition, NO production is not abnormally elevated. It was hypothesized that chronic infection of the airways does not cause increased NO production but, in contrast, leads to inappropriately low NO concentrations that are pro-inflammatory. A rodent model of chronic airway infection was used to examine the effects on lung damage of augmenting or inhibiting NO production after airway infection with P. aeruginosa was well established. Three days post-infection, L-arginine, which augments NO production, or L-NAME, an inhibitor of NO production, was administered in drinking water. Lung damage was assessed 12 days later. L-arginine treatment reduced tissue damage, inhibited neutrophil recruitment, and reduced the pro-inflammatory cytokine interleukin (IL)-1beta. Treatment with L-NAME caused loss of alveolar walls, greater vascular damage, and increased levels of the pro-inflammatory cytokine IL-6. Thus, in chronic airway infection, inhibition of NO production worsened lung damage, whereas augmenting NO ameliorated this damage. This is the first demonstration that augmenting endogenous NO production in chronic infective lung disease caused by P. aeruginosa is anti-inflammatory. Given that infection with this organism complicates many chronic lung diseases, most notoriously cystic fibrosis, these findings have important clinical implications.

In Vivo Nitric Oxide Production and iNOS Expression in X-Ray Irradiated Mouse Skin

Inducible nitric oxide synthase (iNOS) and NO have been suggested to be involved in acute radiation response in tissues such as the liver, intestine, colon, and brain. However, direct measurement of NO and iNOS in ionizing radiation-induced skin inflammatory reactions is not reported yet. We show here for the first time, by in vivo experiments, that X-ray irradiated mouse skin generates NO with concomitant expression of iNOS at both the mRNA and protein levels. When irradiated at 50 Gy, iNOS mRNA appeared at day 8 post-irradiation, whereas iNOS protein could be detected only at day 14. No iNOS protein was detectable however for the mice receiving 5 or 15 Gy irradiation, even at day 14. Skin inflammatory reactions were observed at day 8 post-irradiation as an increase in skin thickness, which increased further by day 14. Histological observations showed acute inflammatory responses. The parallel relationship between iNOS induction and the onset of skin inflammatory reactions suggests the involvement of iNOS and NO in the skin damage. Immunohistochemical staining showed the localization of iNOS at skin erosion areas, exudate and infiltrating cells. Taken together, these findings suggest that iNOS induction and NO production in X-irradiated skin are relatively early events in skin inflammatory reactions and are probably secondary rather than primary reactions of irradiation.

Function of cGMP-Dependent Protein Kinases as Revealed by Gene Deletion

Over the past few years, a wealth of biochemical and functional data have been gathered on mammalian cGMP-dependent protein kinases (cGKs). In mammals, three different kinases are encoded by two genes. Mutant and chimeric cGK proteins generated by molecular biology techniques yielded important biochemical knowledge, such as the function of the NH2-terminal domains of cGKI and cGKII, the identity of the cGMP-binding sites of cGKI, and the substrate specificity of the enzymes. Genetic approaches have proven especially useful for the analysis of the biological functions of cGKs. Recently, some of the in vivo targets and mechanisms leading to changes in neuronal adaptation, smooth muscle relaxation and growth, intestinal water secretion, bone growth, renin secretion, and other important functions have been identified. These data show that cGKs are signaling molecules involved in many biological functions.

Recent advances in the understanding of the role of nitric oxide in cardiovascular homeostasis

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. To date, 3 distinct NOS isoforms have been identified: neuronal NOS (NOS1), inducible NOS (NOS2), and endothelial NOS (NOS3). Biochemically, NOS consists of a flavin-containing reductase domain, a heme-containing oxygenase domain, and regulatory sites. NOS catalyse an overall 5-electron oxidation of one Nomega-atom of the guanidino group of L-arginine to form NO and L-citrulline. NO exerts a plethora of biological effects in the cardiovascular system. The basal formation of NO in mitochondria by a mitochondrial NOS seems to be one of the main regulators of cellular respiration, mitochondrial transmembrane potential, and transmembrane proton gradient. This review focuses on recent advances in the understanding of the role of enzyme and enzyme-independent NO formation, regulation of NO bioactivity, new aspects of NO on cardiac function and morphology, and the clinical impact and perspectives of these recent advances in our knowledge on NO-related pathways.

Is non-insulin dependent glucose uptake a therapeutic alternative? Part 1: physiology, mechanisms and role of non insulin-dependent glucose uptake in type 2 diabetes

Several decades of research for treating type 2 diabetes have yielded new drugs but the actual experience with the available oral antidiabetic compounds clearly shows that therapeutic needs are not matched. This highlights the urgent need for exploring other pathways. All cell types have the capacity to take up glucose independently of insulin, whereby basal but also hyperglycaemia-promoted glucose supply is ensured. Although poorly explored, insulin-independent glucose uptake might nevertheless represent a therapeutic target, as an alternative to the clear limits of actual drug treatments. This review not only critically examines some major pathways not requiring insulin (although they may be influenced by the hormone) but importantly, this analysis extends to the clinical applicability of these potential therapeutic principles by also considering their predictable tolerability for long-term therapy. In particular vascular safety (the ultimate problem linked with diabetes) will be envisaged because of the ubiquitous distribution of glucose transporters and some linked mechanisms. Several mechanisms can be identified which do not require insulin for their functioning. The first part of this review deals with the description, the regulation and the limits of some mechanisms representing potential pharmacological targets capable of having a highly significant impact on glucose uptake. These selected topics are: a) unmasking and/or activation of glucose transporters in cell plasma membranes, b) insulin mimetics acting at postreceptor level, c) activation of AMPK, d) increasing nitric oxide and e) increasing glucose-6P and glycogen stores.

Comparison of effects of nitric oxide synthase (NOS) inhibitors on plasma nitrite/nitrate levels and tissue NOS activity in septic organs

An excessive production of nitric oxide (NO) by NO synthase (NOS) is considered to contribute to circulatory disturbance, tissue damage, and refractory hypotention, which are often observed in septic disorders. It is anticipated that a selective inducible NOS (iNOS) inhibitor with excellent pharmacokinetics may be potentially effective as a novel and potent therapeutic intervention in sepsis. We examined whether or not a selective iNOS inhibitor shows iNOS selectivity at the tissue level, when administered systemically. The effects of four NOS inhibitors on plasma nitrite/nitrate (NOx) and tissue NOS levels were compared in major organs (lungs, liver, heart, kidneys, and brain) 6 hr after the injection of E. coli lipopolysaccharide (LPS) into male Wistar-King rats. The rats treated with the three iNOS inhibitors (N-(3-(aminomethyl)benzyl)acetamidine (1400W), (1 S, 5 S, 6 R, 7 R )-2-aza-7-chloro-3-imino-5-methylbicyclo [4.1.0] heptane hydrochloride (ONO-1714), and aminoguanidine) administered 1 hr after LPS injection, showed dose-dependent decreases in plasma NOx levels and NOS activity in the lungs. The non-selective NOS inhibitor (N(G)-methyl-L-arginine (L-NMMA)) had an effect only at the maximum dose. The differences in in vitro iNOS selectivity among these drugs did not correlate with iNOS selectivity at the tissue level. The relationship between plasma NOx levels and NOS activity in the lungs showed a linear relationship with or without the NOS inhibitors. In conclusion, the iNOS selectivity of these drugs does not seem to differ at the tissue level. Plasma NOx levels may be a useful indicator of lung NOS activity.