Type II nitric oxide synthase activity is cardio-protective in experimental sepsis

Role of Oxidative Stress and Mitochondrial Dysfunction in Sepsis and Potential Therapies

Sepsis is one of the most important causes of death in intensive care units. Despite the fact that sepsis pathogenesis remains obscure, there is increasing evidence that oxidants and antioxidants play a key role. The imbalance of the abovementioned substances in favor of oxidants is called oxidative stress, and it contributes to sepsis process. The most important consequences are vascular permeability impairment, decreased cardiac performance, and mitochondrial malfunction leading to impaired respiration. Nitric oxide is perhaps the most important and well-studied oxidant. Selenium, vitamin C, and 3N-acetylcysteine among others are potential therapies for the restoration of redox balance in sepsis. Results from recent studies are promising, but there is a need for more human studies in a clinical setting for safety and efficiency evaluation.

Metabolomic profiling of amines in sepsis predicts changes in NOS canonical pathways

RATIONALE

Nitric oxide synthase (NOS) is a biomarker/target in sepsis. NOS activity is driven by amino acids, which cycle to regulate the substrate L-arginine in parallel with cycles which regulate the endogenous inhibitors ADMA and L-NMMA. The relationship between amines and the consequence of plasma changes on iNOS activity in early sepsis is not known.

OBJECTIVE

Our objective was to apply a metabolomics approach to determine the influence of sepsis on a full array of amines and what consequence these changes may have on predicted iNOS activity.

METHODS AND MEASUREMENTS

34 amino acids were measured using ultra purification mass spectrometry in the plasma of septic patients (n = 38) taken at the time of diagnosis and 24-72 hours post diagnosis and of healthy volunteers (n = 21). L-arginine and methylarginines were measured using liquid-chromatography mass spectrometry and ELISA. A top down approach was also taken to examine the most changed metabolic pathways by Ingenuity Pathway Analysis. The iNOS supporting capacity of plasma was determined using a mouse macrophage cell-based bioassay.

MAIN RESULTS

Of all the amines measured 22, including L-arginine and ADMA, displayed significant differences in samples from patients with sepsis. The functional consequence of increased ADMA and decreased L-arginine in context of all cumulative metabolic changes in plasma resulted in reduced iNOS supporting activity associated with sepsis.

CONCLUSIONS

In early sepsis profound changes in amine levels were defined by dominant changes in the iNOS canonical pathway resulting in functionally meaningful changes in the ability of plasma to regulate iNOS activity ex vivo.

Preadmission Use of Calcium Channel Blockers and Outcomes After Hospitalization With Pneumonia: A Retrospective Propensity-Matched Cohort Study

In sepsis, an overwhelming immune response, as mediated by the release of various inflammatory mediators, can lead to shock, multiple organ damage, and even death. Pneumonia is the leading cause of sepsis. In animal septic models, sepsis could induce uncontrolled calcium (Ca) leaking, raising cytosolic Ca to a toxic level, causing irreversible cellular injuries and organ failure. All types of calcium channel blockers (CCBs), by inhibiting Ca influx, have been shown to decrease overall mortality in various septic animal models. However, to our best knowledge, no clinical study had been conducted to investigate the beneficial effect(s) of CCBs in sepsis. We conducted a retrospective propensity-matched cohort study after screening 2214 patients hospitalized for pneumonia from year 2012 to 2014 at our institution. We identified 387 preadmission CCB users and 387 nonusers by propensity score matching. Logistic regression analysis was then used to determine the association between preadmission CCB use and outcomes in pneumonia. Our study showed that the odds for development of severe sepsis was significantly lower in the CCB user group [odds ratio (OR), 0.466; 95% confidence interval (CI), 0.311-0.697; P = 0.002]. Preadmission CCB use was associated with a lower risk of contracting bacteremia (OR, 0.498; 95% CI, 0.262-0.99; P = 0.0327), lower risk of acute respiratory insufficiency (OR, 0.573; 95% CI, 0.412-0.798; P = 0.001), lower risk of intensive care unit admission (OR, 0.602; 95% CI, 0.432-0.840; P = 0.0028). In conclusion, our study suggested preadmission CCB use was associated with a reduction in the risks of development of respiratory insufficiency, bacteremia, and severe sepsis in patients admitted to the hospital with pneumonia.

Pharmacology and therapeutic potential of pattern recognition receptors

Pharmacologists have used pathogen-associated molecular patterns (PAMPs), such as lipopolysaccharide (LPS) for decades as a stimulus for studying mediators involved in inflammation and for the screening of anti-inflammatory compounds. However, in the view of immunologists, LPS was too non-specific for studying the mechanisms of immune signalling in infection and inflammation, as no receptors had been identified. This changed in the late 1990s with the discovery of the Toll-like receptors. These 'pattern recognition receptors' (PRRs) were able to recognise highly conserved sequences, the so called pathogen associated molecular patterns (PAMPs) present in or on pathogens. This specificity of particular PAMPs and their newly defined receptors provided a common ground between pharmacologists and immunologists for the study of inflammation. PRRs also recognise endogenous agonists, the so called danger-associated molecular patterns (DAMPs), which can result in sterile inflammation. The signalling pathways and ligands of many PRRs have now been characterised and there is no doubt that this rich vein of research will aid the discovery of new therapeutics for infectious conditions and chronic inflammatory disease.

Systemic use of selective iNOS inhibitor 1400W or non-selective NOS inhibitor l-NAME differently affects systemic nitric oxide formation after oral Porphyromonas gingivalis inoculation in mice

OBJECTIVE

Nitric oxide synthase (NOS) inhibitors are reported to protect against the local tissue damage in gingivitis and periodontal disease by reducing nitroxidative stress during inflammation, but their systemic effects are not well investigated.

DESIGN

NOS inhibitors systemic effects were investigated in a murine chronic oral inoculation model using live Porphyromonas gingivalis ATCC 33277 (0.3 ml; 10(9)cfu/ml) or sterile broth (0.3 ml). Organ nitric oxide (NO) and plasma nitrite/nitrate (NOx) were determined in mice treated with non-selective NOS inhibitor l-NAME (50mg/kg/24h i.p.) or selective iNOS inhibitor 1400W (10mg/kg/6h i.p.) for the last 5 days of the experiment. Differences between groups were evaluated by nonparametric Wilcoxon's rank-sum one-sided two-sample test and the results compared to those obtained from sham-treated (sterile broth) sham-inoculated animals (water for injection i.p./6h).

RESULTS

Repeated ingestion of P. gingivalis resulted in generalized production of NO in organs and NOx in plasma, the levels of both typically being reduced in P. gingivalis-inoculated-1400W-treated mice, whilst the use of l-NAME was largerly ineffective, even promoting NO/NOx formation. Application of either inhibitor to sham-inoculated animals enhanced NO/NOx formation, due only in part to the repeated i.p. injections.

CONCLUSIONS

The systemic use of 1400W or l-NAME differently affects systemic nitric oxide formation in mice orally challenged with P. gingivalis, but the sequelae of such an intervention should be evaluated further.

Identification and characterization of a dysfunctional cardiac myocyte phenotype: role of bacteria, Toll-like receptors, and endothelin

Cardiac myocyte dysfunction is clearly identified as underlying the acute heart failure associated with bacterial infection, as well as the chronic syndrome following cardiac damage, but the mechanisms leading to dysfunction in each case are not fully established. It is thought that local hormones such as endothelin 1 (ET-1) can increase the risk of heart failure in acute or chronic conditions. In the current study, we characterize myocytes as populations and identify a novel phenotype of the ventricular cardiac myocyte that does not contract appropriately on electrical stimulation. The noncontractile cardiac myocytes were viable and had normal calcium transients. The proportion of noncontractile cardiac myocytes was increased by bacteria (gram-positive Staphylococcus aureus or gram-negative Escherichia coli). Using selective ligands or myocytes from genetically modified mice, we established that the effects of S. aureus were mediated by Toll-like receptor 2/6 and of E. coli by Toll-like receptor 4. The transition to the noncontractile phenotype was strongly inhibited by ETA antagonism but unaffected by inhibition of NOS, suggesting that ET-1 and not NO mediates this phenomenon. These results are the first to describe the characteristics of this noncontractile phenotype and the mechanisms of its induction by bacteria. Description of the myocyte population, instead of effects only on individual cells, will be more relevant to the prediction of the depression of cardiac function.

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.

Effects of verapamil and nifedipine on different parameters in lipopolysaccharide-induced septic shock

Septic shock has a high mortality rate due to the hypotension and circulatory disorder that occurs during its pathogenesis. Recently, humoral factors such as cytokines and nitric oxide became important in the complex pathophysiology of septic shock because there is a close relationship between the determined levels of these humoral factors and the responses to the therapy and survival periods. Verapamil and nifedipine are calcium channel blockers commonly used in the pharmacotherapy of cardiovascular disorders. In the present study these drugs were investigated in the rat septic shock model. In vivo hemodynamic parameters were recorded using a data acquisition system in endotoxin-induced septic shock in rats. The animals were followed for 5 h and blood pressure, rectal temperature, and ECG were recorded. Blood samples were collected at 1 h and 5 h time points after the injection of endotoxin, and serological samples were stored at -25 degrees C. Subsequently, tumor necrosis factor-alpha, interleukin-10 (enzyme-linked immunosorbent assay), and nitrite (Griess reagent) were determined in these serological samples. Significant correlations were observed between these humoral factors and the disordered hemodynamic factors. A reversal of changes was observed in the levels of serum cytokines, nitrite levels, and hemodynamic parameters with verapamil and nifedipine preadministration (P<0.05). Additionally, superoxide dismutase (SOD), catalase, and malondialdehyde (MDA) were determined in livers obtained from these animals at the end of the experiments, and these results were compared to hemodynamic parameters and cytokines. Nifedipine and verapamil increased the levels of MDA and SOD but did not change catalase activity.

Early pharmacological preconditioning by erythropoietin mediated by inducible NOS and mitochondrial ATP-dependent potassium channels in the rat heart

Administration of recombinant human erythropoietin (rhEPO) is known to induce protection against cardiac ischaemia injury improving functional recovery and reducing apoptosis. But the underlying mechanisms are not elucidated. We determined the role of nitric oxide synthases (NOS) as well as ATP-dependent (K(ATP)) and calcium-activated (K(Ca)) potassium channels in the early cardioprotection induced by rhEPO. Wistar male rats were divided into two experimental groups treated by rhEPO (5,000 IU/kg, i.p.) or saline (control group). One hour later, rats were anaesthetized, hearts isolated, retrogradely perfused and submitted to a 30-min no-flow global ischaemia followed by 120 min of reperfusion sequence. Cardiac functional recovery (left ventricular developed pressure, LVDP) was significantly higher in the group treated by rhEPO (LVDP at 30 min reperfusion: 71.7 +/- 2.3 mmHg) compared with the control group (57.4 +/- 5.8 mmHg). We observed the same significant effect on its derivative (dP/dt). The rhEPO-induced improvement in ventricular function was abolished by perfusion prior to ischaemia with either N-nitro-l-arginine methyl ester (l-NAME, a nonspecific NOS inhibitor) or N-(3-(aminomethyl)benzyl)acetamidine (1,400W, a specific inducible NOS inhibitor) or 5-hydroxydecanoic acid (5HD, a mitochondrial K(ATP) channel blocker) but not with paxilline (a K(Ca) channel inhibitor). Thus, in vivo rhEPO administration provides early preconditioning against ischaemic injury in the isolated perfused rat heart that is dependent on iNOS and mitochondrial K(ATP) channels.

Nitric Oxide Scavenging by the Cobalamin Precursor Cobinamide

Nitric oxide (NO) is an important signaling molecule, and a number of NO synthesis inhibitors and scavengers have been developed to allow study of NO functions and to reduce excess NO levels in disease states. We showed previously that cobinamide, a cobalamin (vitamin B12) precursor, binds NO with high affinity, and we now evaluated the potential of cobinamide as a NO scavenger in biologic systems. We found that cobinamide reversed NO-stimulated fluid secretion in Drosophila Malpighian tubules, both when applied in the form of a NO donor and when produced intracellularly by nitricoxide synthase. Moreover, feeding flies cobinamide markedly attenuated subsequent NO-induced increases in tubular fluid secretion. Cobinamide was taken up efficiently by cultured rodent cells and prevented NO-induced phosphorylation of the vasodilator-stimulated phosphoprotein VASP both when NO was provided to the cells and when NO was generated intracellularly. Cobinamide appeared to act via scavenging NO because it reduced nitrite and nitrate concentrations in both the fly and mammalian cell systems, and it did not interfere with cGMP-induced phosphorylation of VASP. In rodent and human cells, cobinamide exhibited toxicity at concentrations > or =50 microM with toxicity completely prevented by providing equimolar amounts of cobalamin. Combining cobalamin with cobinamide had no effect on the ability of cobinamide to scavenge NO. Cobinamide did not inhibit the in vitro activity of either of the two mammalian cobalamin-dependent enzymes, methionine synthase or methylmalonyl-coenzyme A mutase; however, it did inhibit the in vivo activities of the enzymes in the absence, but not presence, of cobalamin, suggesting that cobinamide toxicity was secondary to interference with cobalamin metabolism. As part of these studies, we developed a facile method for producing and purifying cobinamide. We conclude that cobinamide is an effective intra- and extracellular NO scavenger whose modest toxicity can be eliminated by cobalamin.

Activation of acid sphingomyelinase and its inhibition by the nitric oxide/cyclic guanosine 3',5'-monophosphate pathway: key events in Escherichia coli-elicited apoptosis of dendritic cells

Depletion of dendritic cells (DCs) via apoptosis contributes to sepsis-induced immune suppression. The mechanisms leading to DC apoptosis during sepsis are not known. In this study we report that immature DCs undergo apoptosis when treated with high numbers of Escherichia coli. This effect was mimicked by high concentrations of LPS. Apoptosis was accompanied by generation of ceramide through activation of acid sphingomyelinase (A-SMase), was prevented by inhibitors of this enzyme, and was restored by exogenous ceramide. Compared with immature DCs, mature DCs expressed significantly reduced levels of A-SMase, did not generate ceramide in response to E. coli or LPS, and were insensitive to E. coli- and LPS-triggered apoptosis. However, sensitivity to apoptosis was restored by addition of exogenous A-SMase or ceramide. Furthermore, inhibition of A-SMase activation and ceramide generation was found to be the mechanism through which the immune-modulating messenger NO protects immature DCs from the apoptogenic effects of E. coli and LPS. NO acted through formation of cGMP and stimulation of the cGMP-dependent protein kinase. The relevance of A-SMase and its inhibition by NO/cGMP were confirmed in a mouse model of LPS-induced sepsis. DC apoptosis was significantly higher in inducible NO synthase-deficient mice than in wild-type animals and was significantly reduced by treatment ex vivo with NO, cGMP, or the A-SMase inhibitor imipramine. Thus, A-SMase plays a central role in E. coli/LPS-induced DC apoptosis and its inhibition by NO, and it might be a target of new therapeutic approaches to sepsis.

Endothelin-1-mediated coronary vasoconstriction deteriorates myocardial depression in hearts isolated from lipopolysaccharide-treated rats: Interaction with nitric oxide

1. The aim of the present study was to evaluate the contribution of disturbance of coronary perfusion to myocardial depression in hearts isolated from lipopolysaccharide (LPS)-treated rats and to investigate the involvement of endothelin (ET)-1 and nitric oxide (NO). 2. Rats were treated with LPS (10 mg/kg, i.p.) and, 4 h later, plasma ET-1 concentrations were measured by radioimmunoassay and hearts were excised for perfusion at a constant perfusion flow. The selective ETA receptor antagonist BQ-123, in the absence or presence of aminoguanidine, a specific inhibitor of inducible NO synthase, was given 15 min before LPS challenge. Coronary perfusion pressure (CPP) and measures of myocardial contractile function were recorded. 3. In hearts isolated from LPS-treated rats, there was a marked increase in CPP that was abolished by pretreatment with BQ-123. In parallel, an increase in plasma ET-1 concentrations was seen in these rats. Lipopolysaccharide also induced decreases in left ventricular developed pressure (LVDP), the product of LVDP and heart rate and maximal rate of rise/fall of left ventricular pressure (+/- dP/dtmax). Single treatment with BQ-123 or aminoguanidine attenuated LPS-induced myocardial depression. However, when these two drugs were given simultaneously, myocardial depression elicited by LPS was blocked significantly. 4. Endothelin-1-mediated coronary vasoconstriction, together with NO, contributes to myocardial depression in hearts isolated from LPS-treated rats.