Inhaled NO accelerates restoration of liver function in adults following orthotopic liver transplantation

Sodium nitrite therapy attenuates the hypertensive effects of HBOC-201 via nitrite reduction

Hypertension secondary to scavenging of NO remains a limitation in the use of HBOCs (haemoglobin-based oxygen carriers). Recent studies suggest that nitrite reduction to NO by deoxyhaemoglobin supports NO signalling. In the present study we tested whether nitrite would attenuate HBOC-mediated hypertension using HBOC-201 (Biopure), a bovine cross-linked, low-oxygen-affinity haemoglobin. In a similar way to unmodified haemoglobin, deoxygenated HBOC-201 reduced nitrite to NO with rates directly proportional to the extent of deoxygenation. The functional importance of HBOC-201-dependent nitrite reduction was demonstrated using isolated aortic rings and a murine model of trauma, haemorrhage and resuscitation. In the former, HBOC-201 inhibited NO-donor and nitrite-dependent vasodilation when oxygenated. However, deoxygenated HBOC-201 failed to affect nitrite-dependent vasodilation but still inhibited NO-donor dependent vasodilation, consistent with a model in which nitrite-reduction by deoxyHBOC-201 counters NO scavenging. Finally, resuscitation using HBOC-201, after trauma and haemorrhage, resulted in mild hypertension ( approximately 5-10 mmHg). Administration of a single bolus nitrite (30-100 nmol) at the onset of HBOC-201 resuscitation prevented hypertension. Nitrite had no effect on mean arterial pressure during resuscitation with LR (lactated Ringer's solution), suggesting a role for nitrite-HBOC reactions in attenuating HBOC-mediated hypertension. Taken together these data support the concept that nitrite can be used as an adjunct therapy to prevent HBOC-dependent hypertension.

Clamping techniques and protecting strategies in liver surgery

The use of vascular occlusion during liver resection is still a matter of debate. The aim of this review was to assess the advantages and disadvantages of portal triad occlusion as a protective strategy during elective liver resection and liver transplantation. Newer strategies such as pharmacological preconditioning are also discussed. A systematic literature search was conducted to detect randomized controlled trials assessing the effectiveness and safety of portal triad clamping, ischaemic preconditioning and pharmacological preconditioning during liver surgery. Vascular clamping cannot be systematically recommended. When used, portal triad clamping is associated with a tendency towards reduced blood loss and blood transfusion without having an impact on morbidity. Intermittent clamping appears to be better tolerated than continuous clamping, especially in patients with chronic liver disease. Ischaemic preconditioning before continuous portal triad clamping reduces reperfusion injury after warm ischaemia, particularly in steatotic patients. Ischaemic preconditioning has unclear effects in transplantation and there is currently no evidence to support or refute the use of ischaemic preconditioning in the donor. There are emerging alternative conditioning strategies, including the use of volatile anaesthetics, which may provide new and easily applicable therapeutic options to protect the liver.

Nitric oxide mechanism of protection in ischemia and reperfusion injury

In 1992 nitric oxide (NO) was declared molecule of the year by Science magazine, and ever since research on this molecule continues to increase. Following this award, NO was shown to be a mediator/protector of ischemia and reperfusion injury in many organs, such as the heart, liver, lungs, and kidneys. Controversy has existed concerning the actual protective effects of NO. However, literature from the past 15 years seems to reinforce the consensus that NO is indeed protective. Some of the protective actions of NO in ischemia and reperfusion are due to its potential as an antioxidant and anti-inflammatory agent, along with its beneficial effects on cell signaling and inhibition of nuclear proteins, such as NF-kappa B and AP-1. New therapeutic potentials for this drug are also continuously emerging. Exogenous NO and endogenous NO may both play protective roles during ischemia and reperfusion injury. Sodium nitroprusside and nitroglycerin have been used clinically with much success; though only recently have they been tested and proven effective in attenuating some of the injuries associated with ischemia and reperfusion. NO inhalation has, in the past, mostly been used for its pulmonary effects, but has also recently been shown to be protective in other organs. The potential of NO in the treatment of ischemic disease is only just being realized. Elucidation of the mechanism by which NO exerts its protective effects needs further investigation. Therefore, this paper will focus on the mechanistic actions of NO in ischemia and reperfusion injury, along with the compound's potential therapeutic benefits.

Postreperfusion syndrome during liver transplantation for cirrhosis: outcome and predictors

During orthotopic liver transplantation (OLT), a marked decrease in blood pressure following unclamping of the portal vein and liver reperfusion is frequently observed and is termed postreperfusion syndrome (PRS). The predictive factors and clinical consequences of PRS are not fully understood. The goal of this study was to identify predictors of PRS and morbidity/mortality associated with its occurrence during OLT in patients with cirrhosis. During a 3-year period, all consecutive OLT procedures performed in patients with cirrhosis were studied. Exclusion criteria were OLT for acute liver failure, early retransplantation, combined liver/kidney transplantation, and living-donor related transplantation. PRS was defined as a decrease in the mean arterial pressure of more than 30% of the value observed in the anhepatic stage, for more than 1 minute during the first 5 minutes after reperfusion of the graft. Transplantation was performed with preservation of the inferior vena cava with or without temporary portocaval shunt. Associations between PRS and donor and recipient demographic data, recipient operative and postoperative outcomes were tested with bivariate statistics. Independent predictors of PRS were determined in multivariable logistic regression analysis. Of the 75 patients included in the study, 20 patients (25%) developed PRS. In a multivariable analysis, absence of a portocaval shunt [odds ratio (95% confidence interval) = 4.42 (1.18-17.6)] and duration of cold ischemia [odds ratio (95% confidence interval) = 1.34 (1.07-1.72)] were independent predictors of PRS. Patients who experienced PRS displayed more postoperative renal failure and lower early (<15 days after OLT) survival (80% versus 96%; P = 0.04). In conclusion, the absence of portocaval shunt and the duration of cold ischemia were independent predictors of intraoperative PRS. PRS was associated with significant adverse postoperative outcome. These results provide realistic clinical targets to improve patient outcome after OLT for cirrhosis.

Prolonged exposure to inhaled nitric oxide transiently modifies tubular function in healthy piglets and promotes tubular apoptosis

AIM

Inhaled nitric oxide (iNO) is a selective pulmonary vasodilator. We hypothesized that those piglets exposed to prolonged iNO react with a modified renal function.

METHODS

Randomized, placebo-controlled exposure to 40 p.p.m. iNO (30 h) in piglets (n = 20). Plasma and urine were sampled during three periods (first and second 12 h periods, and finally a 6 h period). We measured urine volumes, plasma and urine electrolytes (UNa, UK, UCl), plasma creatinine and urea. We calculated creatinine clearance (Ccr), and fractional excretions of sodium and potassium (FENa, FEK) and urinary excretions of electrolytes (UENa, UEK, UECl). Haemodynamic data were recorded and renal tubular apoptosis detected.

RESULTS

For the first 12 h, certain parameters significantly increased in the iNO group (mean +/- SD): UNa (mmol L(-1)), 87.7 (+/-35.0) vs. 39.3 (+/-22.9), UCl (mmol L(-1)) 80.4 (+/-32.8) vs. 48.0 (+/-26.7), FENa (%) 2.1 (+/-0.8) vs. 0.7 (+/-0.5), FEK (%) 31.7 (+/-7.0) vs. 20.7 (+/-12.3), as well as UENa (mmol) 61.0 (+/-21.1) vs. 27.6 (+/-17.9) and UECl (mmol) 57.3 (24.5) vs. 37.6 (29.0). These changes were absent in the second and third periods of the study. Significant differences in percentage of apoptotic cell nuclei in the renal cortex and medulla were found after iNO exposure: 39% vs. 15%.

CONCLUSION

Exposure to 40 p.p.m. iNO in healthy anaesthetized piglets has a transient natriuretic effect that disappears after 12 h. We also found evidence of renal tubular apoptosis promotion after 30 h of iNO.

Regulation of nitrite transport in red blood cells by hemoglobin oxygen fractional saturation

Allosteric regulation of nitrite reduction by deoxyhemoglobin has been proposed to mediate nitric oxide (NO) formation during hypoxia. Nitrite is predominantly an anion at physiological pH, raising questions about the mechanism by which it enters the red blood cell (RBC) and whether this is regulated and coupled to deoxyhemoglobin-mediated reduction. We tested the hypothesis that nitrite transport by RBCs is regulated by fractional saturation. Using human RBCs, nitrite consumption was faster at lower fractional saturations, consistent with faster reactions with deoxyheme. A membrane-based regulation was suggested by slower nitrite consumption with intact versus lysed RBCs. Interestingly, upon nitrite addition, intracellular nitrite concentrations attained a steady state that, despite increased rates of consumption, did not change with decreasing oxygen tensions, suggesting a deoxygenation-sensitive step that either increases nitrite import or decreases the rate of nitrite export. A role for anion exchanger (AE)-1 in the control of nitrite export was suggested by increased intracellular nitrite concentrations in RBCs treated with DIDS. Moreover, deoxygenation decreased steady-state levels of intracellular nitrite in AE-1-inhibited RBCs. Based on these data, we propose a model in which deoxyhemoglobin binding to AE-1 inhibits nitrite export under low oxygen tensions allowing for the coupling between deoxygenation and nitrite reduction to NO along the arterial-to-venous gradient.

Therapeutic antioxidant medical gas

Medical gases are pharmaceutical gaseous molecules which offer solutions to medical needs and include traditional gases, such as oxygen and nitrous oxide, as well as gases with recently discovered roles as biological messenger molecules, such as carbon monoxide, nitric oxide and hydrogen sulphide. Medical gas therapy is a relatively unexplored field of medicine; however, a recent increasing in the number of publications on medical gas therapies clearly indicate that there are significant opportunities for use of gases as therapeutic tools for a variety of disease conditions. In this article, we review the recent advances in research on medical gases with antioxidant properties and discuss their clinical applications and therapeutic properties.

Myocardial protection by nitrite: evidence that this reperfusion therapeutic will not be lost in translation

The circulating anion nitrite (NO(2)(-)), previously thought to be an inert product of nitric oxide (NO) oxidation, has now been identified as an important storage reservoir of bioavailable NO in the blood and tissues. Reduction of NO(2)(-) to NO over the physiologic pH and oxygen gradient by deoxyhemoglobin, myoglobin, xanthine oxidoreductase, and by nonenzymatic acidic disproportionation has been demonstrated to confer cytoprotection against ischemia-reperfusion injury in the heart, liver, brain, and kidney. Here, we review the mechanisms that have been established to regulate hypoxic NO(2)(-) reduction to NO, analyze the preclinical and clinical evidence supporting NO(2)(-)-mediated cytoprotection after ischemia-reperfusion injury, and examine the therapeutic potential of NO(2)(-) for cardiovascular disease. Evidence is accumulating that suggests NO(2)(-) has surmounted many of the direct challenges to reperfusion therapeutics summarized by the National Heart, Lung, and Blood Institute Working Group in "Myocardial protection at a crossroads: the need for translation into clinical therapy." In this context, we discuss important considerations in designing human clinical trials to test the efficacy of NO(2)(-) in the setting of ischemia-reperfusion injury, with particular attention to the study of ST-segment elevation myocardial infarction.

Ischemic preconditioning of the liver: a few perspectives from the bench to bedside translation

Utilization of ischemic preconditioning to ameliorate ischemia/reperfusion injury has been extensively studied in various organs and species for the past two decades. While hepatic ischemic preconditioning in animals has been largely beneficial, translational efforts in the two clinical contexts--liver resection and decreased donor liver transplantation--have yielded mixed results. This review is intended to critically examine the translational data and identify some potential reasons for the disparate clinical results, and highlight some issues for further studies.

Brief periods of nitric oxide inhalation protect against myocardial ischemia-reperfusion injury

BACKGROUND

Prolonged breathing of nitric oxide reduces myocardial ischemia-reperfusion injury, but the precise mechanisms responsible for the cardioprotective effects of inhaled nitric oxide are incompletely understood.

METHODS

The authors investigated the fate of inhaled nitric oxide (80 parts per million) in mice and quantified the formation of nitric oxide metabolites in blood and tissues. The authors tested whether the accumulation of nitric oxide metabolites correlated with the ability of inhaled nitric oxide to protect against cardiac ischemia-reperfusion injury.

RESULTS

Mice absorbed nitric oxide in a nearly linear fashion (0.19 +/- 0.02 micromol/g x h). Breathing nitric oxide rapidly increased a broad spectrum of nitric oxide metabolites. Levels of erythrocytic S-nitrosothiols, N-nitrosamines, and nitrosyl-hemes increased dramatically within 30 s of commencing nitric oxide inhalation. Marked increases of lung S-nitrosothiol and liver N-nitrosamine levels were measured, as well as elevated cardiac and brain nitric oxide metabolite levels. Breathing low oxygen concentrations potentiated the ability of inhaled nitric oxide to increase cardiac nitric oxide metabolite levels. Concentrations of each nitric oxide metabolite, except nitrate, rapidly reached a plateau and were similar after 5 and 60 min. In a murine cardiac ischemia-reperfusion injury model, breathing nitric oxide for either 5 or 60 min before reperfusion decreased myocardial infarction size as a fraction of myocardial area at risk by 31% or 32%, respectively.

CONCLUSIONS

Breathing nitric oxide leads to the rapid accumulation of a variety of nitric oxide metabolites in blood and tissues, contributing to the ability of brief periods of nitric oxide inhalation to provide cardioprotection against ischemia-reperfusion injury. The nitric oxide metabolite concentrations achieved in a target tissue may be more important than the absolute amounts of nitric oxide absorbed.

Molecular mediators of liver ischemia and reperfusion injury: a brief review

Ischemia and reperfusion injury is a dynamic process that involves multiple organ systems in various clinical states including transplantation, trauma, and surgery. Research into this field has identified key molecular and signaling players that mediate, modulate, or augment cellular, tissue, and organ injury during this disease process. Further elucidation of the molecular mechanisms should provide the rationale to identify much-needed novel therapeutic options to prevent or ameliorate organ damage due to ischemia and reperfusion in clinics.

The functional nitrite reductase activity of the heme-globins

Hemoglobin and myoglobin are among the most extensively studied proteins, and nitrite is one of the most studied small molecules. Recently, multiple physiologic studies have surprisingly revealed that nitrite represents a biologic reservoir of NO that can regulate hypoxic vasodilation, cellular respiration, and signaling. These studies suggest a vital role for deoxyhemoglobin- and deoxymyoglobin-dependent nitrite reduction. Biophysical and chemical analysis of the nitrite-deoxyhemoglobin reaction has revealed unexpected chemistries between nitrite and deoxyhemoglobin that may contribute to and facilitate hypoxic NO generation and signaling. The first is that hemoglobin is an allosterically regulated nitrite reductase, such that oxygen binding increases the rate of nitrite conversion to NO, a process termed R-state catalysis. The second chemical property is oxidative denitrosylation, a process by which the NO formed in the deoxyhemoglobin-nitrite reaction that binds to other deoxyhemes can be released due to heme oxidation, releasing free NO. Third, the reaction undergoes a nitrite reductase/anhydrase redox cycle that catalyzes the anaerobic conversion of 2 molecules of nitrite into dinitrogen trioxide (N(2)O(3)), an uncharged molecule that may be exported from the erythrocyte. We will review these reactions in the biologic framework of hypoxic signaling in blood and the heart.

Use of a hanging-weight system for liver ischemic preconditioning in mice

Ischemic preconditioning (IP) represents a powerful experimental strategy to identify novel molecular targets to attenuate hepatic injury during ischemia. As a result, murine studies of hepatic IP have become an important field of research. However, murine IP is technically challenging, and experimental details can alter the results. Therefore, we systematically tested a novel model of hepatic IP by using a hanging-weight system for portal triad occlusion. This system has the benefit of applying intermittent hepatic ischemia and reperfusion without manipulation of a surgical clamp or suture, thus minimizing surgical trauma. Systematic evaluation of this model revealed a close correlation of hepatic ischemia time with liver damage as measured by alanine (ALT) and aspartate (AST) aminotransferase serum levels. Using different numbers of IP cycles and times intervals, we found optimal liver protection with four cycles of 3 min ischemia/3 min reperfusion as measured by ALT, AST, lactate dehydrogenase, and interleukin-6. Similarly, ischemia-associated increases in hepatic infarct size, neutrophil infiltration, and histological injury were maximally attenuated with the above regimen. To demonstrate transcriptional consequences of liver IP, we isolated RNA from preconditioned liver and confirmed transcriptional modulation of known target genes (equilibrative nucleoside transporters, acute-phase complement genes). Taken together, these studies confirm highly reproducible liver injury and protection by IP when using the hanging-weight system for hepatic ischemia and intermittent reperfusion. Further studies of murine IP may consider this technique.

SNO-hemoglobin is not essential for red blood cell-dependent hypoxic vasodilation

The coupling of hemoglobin sensing of physiological oxygen gradients to stimulation of nitric oxide (NO) bioactivity is an established principle of hypoxic blood flow. One mechanism proposed to explain this oxygen-sensing-NO bioactivity linkage postulates an essential role for the conserved Cys93 residue of the hemoglobin beta-chain (betaCys93) and, specifically, for S-nitrosation of betaCys93 to form S-nitrosohemoglobin (SNO-Hb). The SNO-Hb hypothesis, which conceptually links hemoglobin and NO biology, has been debated intensely in recent years. This debate has precluded a consensus on physiological mechanisms and on assessment of the potential role of SNO-Hb in pathology. Here we describe new mouse models that exclusively express either human wild-type hemoglobin or human hemoglobin in which the betaCys93 residue is replaced with alanine to assess the role of SNO-Hb in red blood cell-mediated hypoxic vasodilation. Substitution of this residue, precluding hemoglobin S-nitrosation, did not change total red blood cell S-nitrosothiol abundance but did shift S-nitrosothiol distribution to lower molecular weight species, consistent with the loss of SNO-Hb. Loss of betaCys93 resulted in no deficits in systemic or pulmonary hemodynamics under basal conditions and, notably, did not affect isolated red blood cell-dependent hypoxic vasodilation. These results demonstrate that SNO-Hb is not essential for the physiologic coupling of erythrocyte deoxygenation with increased NO bioactivity in vivo.

Chronic sodium nitrite therapy augments ischemia-induced angiogenesis and arteriogenesis

Chronic tissue ischemia due to defective vascular perfusion is a hallmark feature of peripheral artery disease for which minimal therapeutic options exist. We have reported that sodium nitrite therapy exerts cytoprotective effects against acute ischemia/reperfusion injury in both heart and liver, consistent with the model of bioactive NO formation from nitrite during ischemic stress. Here, we test the hypothesis that chronic sodium nitrite therapy can selectively augment angiogenic activity and tissue perfusion in the murine hind-limb ischemia model. Various therapeutic doses (8.25-3,300 mug/kg) of sodium nitrite or PBS were administered. Sodium nitrite significantly restored ischemic hind-limb blood flow in a time-dependent manner, with low-dose sodium nitrite being most effective. Nitrite therapy significantly increased ischemic limb vascular density and stimulated endothelial cell proliferation. Remarkably, the effects of sodium nitrite therapy were evident within 3 days of the ischemic insult demonstrating the potency and efficacy of chronic sodium nitrite therapy. Sodium nitrite therapy also increased ischemic tissue nitrite and NO metabolites compared to nonischemic limbs. Use of the NO scavenger carboxy PTIO completely abolished sodium nitrite-dependent ischemic tissue blood flow and angiogenic activity consistent with nitrite reduction to NO being the proangiogenic mechanism. These data demonstrate that chronic sodium nitrite therapy is a recently discovered therapeutic treatment for peripheral artery disease and critical limb ischemia.

Mitochondrial dysfunction and oxidative stress in the pathogenesis of alcohol- and obesity-induced fatty liver diseases

Fatty liver disease associated with chronic alcohol consumption or obesity/type 2 diabetes has emerged as a serious public health problem. Steatosis, accumulation of triglyceride in hepatocytes, is now recognized as a critical "first-hit" in the pathogenesis of liver disease. It is proposed that steatosis "primes" the liver to progress to more severe liver pathologies when individuals are exposed to subsequent metabolic and/or environmental stressors or "second-hits." Genetic risk factors can also influence the susceptibility to and severity of fatty liver disease. Furthermore, oxidative stress, disrupted nitric oxide (NO) signaling, and mitochondrial dysfunction are proposed to be key molecular events that accelerate or worsen steatosis and initiate progression to steatohepatitis and fibrosis. This review article will discuss the following topics regarding the pathobiology and molecular mechanisms responsible for fatty liver disease: (1) the "two-hit" or "multi-hit" hypothesis, (2) the role of mitochondrial bioenergetic defects and oxidant stress, (3) the interplay between NO and mitochondria in fatty liver disease, (4) genetic risk factors and oxidative stress-responsive genes, and (5) the feasibility of antioxidants for treatment.

DETANO and nitrated lipids increase chloride secretion across lung airway cells

We investigated the cellular mechanisms by which nitric oxide (NO) increases chloride (Cl-) secretion across lung epithelial cells in vitro and in vivo. Addition of (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1, 2-diolate (DETANONOate [DETANO];1-1,000 microM) into apical compartments of Ussing chambers containing Calu-3 cells increased short-circuit currents (I(sc)) from 5.2 +/- 0.8 to 15.0 +/- 2.1 microA/cm(2) (X +/- 1 SE; n = 7; P < 0.001). NO generated from two nitrated lipids (nitrolinoleic and nitrooleic acids; 1-10 microM) also increased I(sc) by about 100%. Similar effects were noted across basolaterally, but not apically, permeabilized Calu-3 cells. None of these NO donors increased I(sc) in Calu-3 cells pretreated with 10 microM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (an inhibitor of soluble guanylyl cyclase). Scavenging of NO either prevented or reversed the increase of I(sc). These data indicate that NO stimulation of soluble guanylyl cyclase was sufficient and necessary for the increase of I(sc) via stimulation of the apical cystic fibrosis transmembrane regulator (CFTR). Both Calu-3 and alveolar type II (ATII) cells contained CFTR, as demonstrated by in vitro phosphorylation of immunoprecipitated CFTR by protein kinase (PK) A. PKGII (but not PKGI) phosphorylated CFTR immuniprecipitated from Calu-3 cells. Corresponding values in ATII cells were below the threshold of detection. Furthermore, DETANO, 8-Br-cGMP, or 8-(4-chlorophenylthio)-cGMP (up to 2 mM each) did not increase Cl- secretion across amiloride-treated ATII cells in vitro. Measurements of nasal potential differences in anesthetized mice showed that perfusion of the nares with DETANO activated glybenclamide-sensitive Cl- secretion. These findings suggest that small concentrations of NO donors may prove beneficial in stimulating Cl- secretion across airway cells without promoting alveolar edema.

The nitrate-nitrite-nitric oxide pathway in physiology and therapeutics

The inorganic anions nitrate (NO3-) and nitrite (NO2-) were previously thought to be inert end products of endogenous nitric oxide (NO) metabolism. However, recent studies show that these supposedly inert anions can be recycled in vivo to form NO, representing an important alternative source of NO to the classical L-arginine-NO-synthase pathway, in particular in hypoxic states. This Review discusses the emerging important biological functions of the nitrate-nitrite-NO pathway, and highlights studies that implicate the therapeutic potential of nitrate and nitrite in conditions such as myocardial infarction, stroke, systemic and pulmonary hypertension, and gastric ulceration.