Nitric oxide: does it play a role in the heart of the critically ill?

Coronary vascular growth matches IGF-1-stimulated cardiac growth in fetal sheep

As loss of contractile function in heart disease could often be mitigated by increased cardiomyocyte number, expansion of cardiomyocyte endowment paired with increased vascular supply is a desirable therapeutic goal. Insulin-like growth factor 1 (IGF-1) administration increases fetal cardiomyocyte proliferation and heart mass, but how fetal IGF-1 treatment affects coronary growth and function is unknown. Near-term fetal sheep underwent surgical instrumentation and were studied from 127 to 134 d gestation (term = 147 d), receiving either IGF-1 LR3 or vehicle. Coronary growth and function were interrogated using pressure-flow relationships, an episode of acute hypoxia with progressive blockade of adenosine receptors and nitric oxide synthase, and by modeling the determinants of coronary flow. The main findings were that coronary conductance was preserved on a per-gram basis following IGF-1 treatment, adenosine and nitric oxide contributed to hypoxia-mediated coronary vasodilation similarly in IGF-1-treated and Control fetuses, and the relationships between coronary flow and blood oxygen contents were similar between groups. We conclude that IGF-1-stimulated fetal myocardial growth is accompanied by appropriate expansion and function of the coronary vasculature. These findings support IGF-1 as a potential strategy to increase cardiac myocyte and coronary vascular endowment at birth.

Rosuvastatin and retinoic acid may act as 'pleiotropic agents' against β-adrenergic agonist-induced acute myocardial injury through modulation of multiple signalling pathways

Cardiovascular disorders constitute the principal cause of deaths worldwide and will continue as the major disease-burden by the year 2060. A significant proportion of heart failures occur because of use and misuse of drugs and most of the investigational agents fail to achieve any clinical relevance. Here, we investigated rosuvastatin and retinoic acid for their "pharmacological pleiotropy" against high dose β-adrenergic agonist (isoproterenol)-induced acute myocardial insult. Rats were pretreated with rosuvastatin and/or retinoic acid for seven days and the myocardial injury was induced by administering isoproterenol on the seventh and eighth day. After induction, rats were anaesthetized for electrocardiography, then sacrificed and different samples were collected/stored for various downstream assays. Myocardial injury with isoproterenol resulted in increased cardiac mass, decreased R-wave amplitude, increased QRS and QT durations; elevated levels of cardiac markers like cTnI, CK-MB, ALT and AST; increased lipid peroxidation, protein carbonylation and tissue nitric oxide levels; decreased endogenous antioxidants like SOD, CAT, GR, GST, GPx and total antioxidant activity; increased inflammatory markers like TNF-α and IL-6; decreased the mRNA expression of Nrf2 and Bcl-2; increased the mRNA expression of Bax, eNOS and iNOS genes. Pretreatment with rosuvastatin and/or retinoic acid mitigated many of the above biochemical and pathological alterations. Our results demonstrate that rosuvastatin and retinoic acid exert cardioprotective effects and may act as potential agents in the prevention of β-adrenergic agonist-induced acute myocardial injury in rats. Cardioprotective potential of rosuvastatin and retinoic acid could be attributed to their influence on the redox pathways, immunomodulation, membrane stability, Nrf2 preservation, iNOS and Bax expression levels. Thus, they may act directly or indirectly at various steps, the breakpoints, in the pathophysiological cascade responsible for cardiac injury. Our study gives insights about the pharmacological pleiotropism of rosuvastatin and retinoic acid.

Deceased donor hyperglycemia and liver graft dysfunction

CONTEXT

Hyperglycemia is common in deceased donors, and provokes numerous adverse events in hepatocytic mitochondria.

OBJECTIVE

To determine whether hyperglycemia in deceased donors is associated with graft dysfunction after orthotopic liver transplant.

METHODS

Charts on 572 liver transplants performed at the Cleveland Clinic between January 2005 and October 2010 were reviewed. The primary measure was time-weighted averages of donors' glucose measurements. Liver graft dysfunction was defined as (1) primary nonfunction as indicated by death or retransplant or (2) liver graft dysfunction as indicated by an aspartate amino transferase level greater than 2000 U/L or prothrombin time greater than 16 seconds during the first postoperative week. The relationship of interest was estimated by using a multivariable logistic regression.

RESULTS

The incidence of graft dysfunction was 25%. No significant relationship was found between the range of donor glucose measurements and liver graft dysfunction after donor characteristics were adjusted for (P= .14, Wald test, adjusted odds ratio [95% CI] for liver graft dysfunction corresponding to a relative doubling in time-weighted average for donor glucose of 1.43 [0.89-2.30]). The results thus do not suggest that strict glucose control in donors is likely to improve graft quality.

Comparative study of the cardioprotective effects of local and remote preconditioning in ischemia/reperfusion injury

AIMS

Though the cardioprotective effects of local or remote preconditioning have been estimated, it is still unclear which of them is more reliable and provides more cardioprotection. The present investigation was directed to compare, in one study, the cardioprotective effects of different cycles of local or remote preconditioning in ischemia/reperfusion (I/R)-induced electrophysiological, biochemical and histological changes in rats.

MAIN METHODS

Rats were randomly assigned into 10 groups. Groups 1 and 2 were normal and I/R groups, respectively. Other groups were subjected to 1, 2, 3, 4 cycles of local or remote preconditioning before myocardial I/R (40 min/10 min). Heart rate and ventricular arrhythmias were recorded during I/R progress. At the end of reperfusion, plasma creatine kinase-MB (CK-MB) activity and total nitrate/nitrite (NO(x)) were determined. In addition, lactate, adenine nucleotides, thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and myeloperoxidase (MPO) activity were estimated in the heart left ventricle. Histological examination was also performed to visualize the protective cellular effects of the effective cycle of local or remote preconditioning.

KEY FINDINGS

In general, local preconditioning was more effective than remote preconditioning in reducing ventricular arrhythmias, CK-MB release, lactate accumulation and elevated MPO activity as well as preserving adenine nucleotides. Concerning the most effective group in each therapy, 3 cycles of local preconditioning provided more cardioprotection than that of remote preconditioning in the histological examination.

SIGNIFICANCE

Despite being invasive, local preconditioning provided more effective cardioprotection than remote preconditioning in ameliorating the overall electrophysiological, biochemical and histological changes.

Pharmacological preconditioning with nicorandil and pioglitazone attenuates myocardial ischemia/reperfusion injury in rats

The present investigation was designed to study the cardioprotective effects of nicorandil and pioglitazone preconditioning in myocardial ischemia/reperfusion-induced hemodynamic, biochemical and histological changes in rats. Oral doses of nicorandil (3 or 6 mg/kg) and pioglitazone (10 or 20mg/kg) were administered once daily for 5 consecutive days. Rats were then subjected to myocardial ischemia/reperfusion (40 min/10 min). Heart rate and ventricular arrhythmias were recorded during ischemia/reperfusion progress. At the end of reperfusion, plasma creatine kinase-MB activity and total nitrate/nitrite were determined. In addition, lactate, adenine nucleotides, thiobarbituric acid reactive substances, reduced glutathione and myeloperoxidase activity were estimated in the heart left ventricle. Finally, histological examination was performed to visualize the protective cellular effects of different pretreatments. Nicorandil (3 or 6 mg/kg) was effective in attenuating the ischemia/reperfusion-induced ventricular arrhythmias, creatine kinase-MB release, lactate accumulation and oxidative stress. Nicorandil (3 mg/kg) was more effective in improving the energy production and lowering the elevated myeloperoxidase activity. Both doses of pioglitazone (10 or 20 mg/kg) were equally effective in reducing lactate accumulation and completely counteracting the oxidative stress. Pioglitazone (10 mg/kg) was more effective in improving energy production and reducing ventricular arrhythmias, plasma creatine kinase-MB release and total nitrate/nitrite. It seems that selective mitochondrial K(ATP) channel opening by lower doses of nicorandil and pioglitazone in the present study provided more cardioprotection against ventricular arrhythmias and biochemical changes induced by ischemia/reperfusion. Histological examination revealed also better improvement by the lower dose of nicorandil than that of pioglitazone.

Sepsis and the heart

Septic shock, the most severe complication of sepsis, accounts for approximately 10% of all admissions to intensive care. Our understanding of its complex pathophysiology remains incomplete but clearly involves stimulation of the immune system with subsequent inflammation and microvascular dysfunction. Cardiovascular dysfunction is pronounced and characterized by elements of hypovolaemic, cytotoxic, and distributive shock. In addition, significant myocardial depression is commonly observed. This septic cardiomyopathy is characterized by biventricular impairment of intrinsic myocardial contractility, with a subsequent reduction in left ventricular (LV) ejection fraction and LV stroke work index. This review details the myocardial dysfunction observed in adult septic shock, and discusses the underlying pathophysiology. The utility of using the regulatory protein troponin for the detection of myocardial dysfunction is also considered. Finally, options for the management of sepsis-induced LV hypokinesia are discussed, including the use of levosimendan.

Insulin inhibits tumor necrosis factor-alpha induction in myocardial ischemia/reperfusion: role of Akt and endothelial nitric oxide synthase phosphorylation

OBJECTIVES

Intensive insulin therapy with tight glucose control is known to result in reduced morbidity and mortality in inflammation-related critical illness. Tumor necrosis factor (TNF)-alpha induction in myocardial infarction may trigger inflammation and have detrimental effects on cardiomyocytes. This study was designed to investigate whether insulin attenuates TNF-alpha induction in acute myocardial ischemia/reperfusion (MI/R) and the underlying signaling mechanisms.

DESIGN

Randomized experimental study.

SETTING

Research laboratory.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Anesthetized rats were subjected to MI/R (30 mins/3 hrs) and were treated with saline, glucose-insulin-potassium, or glucose-potassium infusion (4 mL/kg/hr intravenously). In vitro study was performed on cultured cardiomyocytes subjected to simulated ischemia/reperfusion (SI/R).

MEASUREMENTS AND MAIN RESULTS

In vivo treatment with glucose-insulin-potassium, but not glucose-potassium, significantly attenuated inflammatory response as evidenced by decreased TNF-alpha induction and myocardial myeloperoxidase activity, with concurrent reduction in creatine kinase activity and myocardial infarction compared with those in control rats. In cultured cardiomyocytes subjected to SI/R, insulin reduced TNF-alpha induction and increased Akt and endothelial nitric oxide synthase (eNOS) phosphorylation and subsequent nitric oxide (NO) production. Inhibition of insulin-stimulated NO production using either the PI3K inhibitor wortmannin or the NOS inhibitor L-NAME blocked TNF-alpha reduction afforded by insulin. Furthermore, the suppression on TNF-alpha by either insulin or TNF-alpha neutralizing antibody improved viability and reduced apoptosis of cardiomyocytes subjected to SI/R.

CONCLUSIONS

Our data showed that insulin inhibits ischemia/reperfusion-induced TNF-alpha production through the Akt-activated and eNOS-NO-dependent pathway in cardiomyocytes. The anti-inflammatory property elicited by insulin may contribute to its cardioprotective and prosurvival effects in the critically ill.

Transport and peripheral bioactivities of nitrogen oxides carried by red blood cell hemoglobin: role in oxygen delivery

The biology of NO (nitric oxide) is poorly explained by the activity of the free radical NO ((.)NO) itself. Although (.)NO acts in an autocrine and paracrine manner, it is also in chemical equilibrium with other NO species that constitute stable stores of NO bioactivity. Among these species, S-nitrosylated hemoglobin (S-nitrosohemoglobin; SNO-Hb) is an evolved transducer of NO bioactivity that acts in a responsive and exquisitely regulated manner to control cardiopulmonary and vascular homeostasis. In SNO-Hb, O(2) sensing is dynamically coupled to formation and release of vasodilating SNOs, endowing the red blood cell (RBC) with the capacity to regulate its own principal function, O(2) delivery, via regulation of blood flow. Analogous, physiological actions of RBC SNO-Hb also contribute to central nervous responses to blood hypoxia, the uptake of O(2) from the lung to blood, and baroreceptor-mediated control of the systemic flow of blood. Dysregulation of the formation, export, or actions of RBC-derived SNOs has been implicated in human diseases including sepsis, sickle cell anemia, pulmonary arterial hypertension, and diabetes mellitus. Delivery of SNOs by the RBC can be harnessed for therapeutic gain, and early results support the logic of this approach in the treatment of diseases as varied as cancer and neonatal pulmonary hypertension.

Role of oxidative stress in experimental sepsis and multisystem organ dysfunction

Massive increase in radical species can lead to oxidative stress, promoting cell injury and death. This review focuses on experimental evidence of oxidative stress in critical illnesses, sepsis and multisystem organ dysfunction. Oxidative stress could negatively affect organ injury and thus overall survival of experimental models. Based on this experimental evidence, we could improve the rationale of supplementation of antioxidants alone or in combination with standard therapies aimed to reduce oxidative stress as novel adjunct treatment in critical care.

Zur Funktion des β3-Adrenozeptors am Herzen: Signaltransduktion, inotroper Effekt und therapeutischer Ausblick

Beta-adrenergic stimulation is an important regulatory mechanism of cardiac function. Next to beta1- and beta2-adrenoceptors, the expression of a third beta-adrenoceptor population, the beta3-adrenoceptor, has recently been evidenced in the human heart. Stimulation of cardiac beta3-adrenoceptors leads to a decrease in contractility via a release of nitric oxide (NO). In this context, different molecular mechanisms of endothelial nitric oxide synthase (eNOS) activation have been uncovered to occur as a consequence of beta3-adrenergic stimulation. In both nonfailing and failing myocardium, beta3-adrenergic stimulation may have a protective effect against excessive chatecolaminergic stimulation as it occurs during somatic and mental stress and during heart failure. For this reason, the beta3-adrenoceptor is discussed as a possible target for the pharmacological therapy of heart failure.

Glucose, insulin and myocardial ischaemia

PURPOSE OF REVIEW

The importance of glucose metabolism and insulin therapy during myocardial ischaemia is increasingly being investigated. Insulin is used to achieve a tight glucose control or as part of glucose-insulin-potassium therapy. We have reviewed (1) the physiological and physiopathological consequences of hyperglycaemia focusing on potential machanisms of myocardial ischaemia, (2) the effects of insulin on vascular tone, on the release of free fatty acids, on inflammatory pathways, on the switch of energy source and on apoptosis, and (3) clinical data reporting the effects of intensive insulin therapy and glucose-insulin-potassium solutions during myocardial ischaemia and ischaemic heart failure.

RECENT FINDINGS

In addition to its known toxic cellular effects, hyperglycaemia increases the activity of inducible nitric oxide synthase and promotes inflammation. Conversely insulin exerts anti-inflammatory and anti-apoptotic effects. Glucose-insulin-potassium solutions could improve survival after acute myocardial infarction or after surgery, according to recent meta-analyses, but confirmation of these data is eagerly awaited.

SUMMARY

Hyperglycaemia is toxic, while insulin is beneficial during acute myocardial ischaemia. Some recent evidence confirms a substantial benefit of insulin administered either alone to achieve a tight glucose control or as a component of glucose-insulin-potassium therapy. Further research is needed to confirm that tendency and to define the threshold of tight glucose control.

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.

Cellular mechanisms for the treatment of chronic heart failure: the nitric oxide- and adenosine-dependent pathways

Accumulated evidence suggests that several drugs proven to improve survival in patients with chronic heart failure (CHF) enhance endogenous nitric oxide (NO)- and/or adenosine-dependent pathways. Indeed, we and others have demonstrated that: i) antagonists of either renin-angiotensin-aldosterone or beta-adrenergic systems enhance NO-dependent pathways; ii) although carvedilol and amlodipine belong to different drug classes, both of them can increase cardiac adenosine levels; iii) increased adenosine levels by dipyridamole are associated with the improvement of CHF. Interestingly, both NO and adenosine have multifactorial beneficial actions in cardiovascular systems. First of all, both of them induce vasodilation and decrease myocardial hypercontractility, which may contribute to a reduction in the severity of myocardial ischaemia. Both adenosine and NO are also involved in cardioprotection attributable to acute and late phases of ischaemic preconditioning, respectively. Secondly, they can modulate the neurohormonal systems that contribute to the progression of CHF. Thus, we propose that enhancement of endogenous NO and/or adenosine as potential therapeutic targets in a new strategy for the treatment for CHF.

The role of nitric oxide in anthracycline toxicity and prospects for pharmacologic prevention of cardiac damage

Anthracycline antibiotics are potent antitumor agents whose activity is severely limited by a cumulative dose-dependent chronic cardiotoxicity that results from the summation of multiple biochemical pathways of cellular damage, which ultimately yields to disruption of myocardiocyte integrity and loss of cardiac function. Nitric oxide (NO) is a key molecule involved in the pathophysiology of heart; dysregulation of activity of NO synthases (NOSs) and of NO metabolism seems to be a common feature in various cardiac diseases. The contribution of NO to anthracycline cardiac damage is suggested by evidence demonstrating anthracycline-mediated induction of NOS expression and NO release in heart and the ability of NOSs to promote anthracycline redox cycling to produce reactive oxygen species (ROS), including O2-* and H2O2. Overproduction of ROS and NO yields to reactive nitrogen species, particularly the powerful oxidant molecule peroxynitrite (ONOO-), which may produce the marked reduction of cardiac contractility. This review focuses on the anthracycline-mediated deregulation of NO network and presents an unifying viewpoint of the main molecular mechanisms involved in the pathogenesis of anthracycline cardiotoxicity, including iron, free radicals, and novel mechanistic notions on cardiac ceramide signaling and apoptosis. The data presented in the literature encourage the development of strategies of pharmacological manipulation of NO metabolism to be used as a novel approach to the prevention of cardiotoxicity induced by anthracyclines.

Nitric oxide and cardiac function: ten years after, and continuing

Nitric oxide (NO) is produced from virtually all cell types composing the myocardium and regulates cardiac function through both vascular-dependent and -independent effects. The former include regulation of coronary vessel tone, thrombogenicity, and proliferative and inflammatory properties as well as cellular cross-talk supporting angiogenesis. The latter comprise the direct effects of NO on several aspects of cardiomyocyte contractility, from the fine regulation of excitation-contraction coupling to modulation of (presynaptic and postsynaptic) autonomic signaling and mitochondrial respiration. This multifaceted involvement of NO in cardiac physiology is supported by a tight molecular regulation of the three NO synthases, from cellular spatial confinement to posttranslational allosteric modulation by specific interacting proteins, acting in concert to restrict the influence of NO to a particular intracellular target in a stimulus-specific manner. Loss of this specificity, such as produced on excessive NO delivery from inflammatory cells (or cytokine-stimulated cardiomyocytes themselves), may result in profound cellular disturbances leading to heart failure. Future therapeutic manipulations of cardiac NO synthesis will necessarily draw on additional characterization of the cellular and molecular determinants for the net effect of this versatile radical on the cardiomyocyte biology.

Modulation of cardiac contraction, relaxation and rate by the endothelial nitric oxide synthase (eNOS): lessons from genetically modified mice

The modulatory role of endothelial nitric oxide synthase (eNOS) on heart contraction, relaxation and rate is examined in light of recent studies using genetic deletion or overexpression in mice under specific conditions. Unstressed eNOS-/- hearts in basal conditions exhibit a normal inotropic and lusitropic function, with either decreased or unchanged heart rate. Under stimulation with catecholamines, eNOS-/- mice predominantly show a potentiation in their beta-adrenergic inotropic and lusitropic responsiveness. A similar phenotype is observed in beta 3-adrenoceptor deficient mice, pointing to a key role of this receptor subtype for eNOS coupling. The effect of eNOS on the muscarinic cholinergic modulation of cardiac function probably operates in conjunction with other NO-independent mechanisms, the persistence of which may explain the apparent dispensability of this isoform for the effect of acetylcholine in some eNOS-/- mouse strains. eNOS-/- hearts submitted to short term ischaemia-reperfusion exhibit variable alterations in systolic and diastolic function and infarct size, while those submitted to myocardial infarction present a worsened ventricular remodelling, increased 1 month mortality and loss of benefit from ACE inhibitor or angiotensin II type I receptor antagonist therapy. Although non-conditional eNOS gene deletion may engender phenotypic adaptations (e.g. ventricular hypertrophy resulting from chronic hypertension, or upregulation of the other NOS isoforms) potentially confounding the interpretation of comparative studies, the use of eNOS-/- mice has undoubtedly advanced (and will probably continue to improve) our understanding of the complex role of eNOS (in conjunction with the other NOSs) in the regulation of cardiac function. The challenge is now to confirm the emerging paradigms in human cardiac physiology and hopefully translate them into therapy.

Heat shock proteins and their role in heart injury

Heat shock protein (HSP) synthesis arises transiently as a tool to protect cellular homeostasis after exposure to heat and a wide spectrum of stressful and potentially deleterious stimuli. HSPs are "molecular chaperones" that recognize and form a complex with incorrectly folded or denatured proteins, which ultimately leads to correct folding, compartmentalization, or degradation. Accumulating evidence has implicated HSPs as mediators of myocardial protection, particularly in experimental models of ischemia and reperfusion injury. Impaired myocardial performance, which results from many factors, including hypoxia, is one of the main mechanisms responsible for heart failure in the critically ill patient. In this setting, different protective functions have been attributed to HSPs, which include repairing ion channels, restoring redox balance, interacting with nitric oxide-induced protection, inhibiting proinflammatory cytokines, and preventing apoptosis pathway activation. On this basis, novel therapeutic strategies by means of promising pharmacologic interventions and/or gene transfection techniques are being investigated for their potential to enhance HSP expression by myocardial cells, with the goal of improving the outcome of the critically ill patient.

The nitric oxide pathway in the cardiovascular system

The present review analyzes the role nitric oxide (NO) plays in the homeostasis of the cardiovascular system. By regulating vascular smooth muscle cell and myocyte contractility, myocardial oxygen consumption and renal tubular transport, this simple molecule plays a central role in the control of vascular tone, cardiac contractility and short and long term regulation of arterial pressure. Fifteen years ago, all we knew about NO is that it had very similar properties as those of endothelium-derived relaxing factor and that its action was probably mediated by cGMP. An enormous amount of knowledge has since been amassed on the biochemical pathways that NO follows from the moment it is synthesized from L-arginine until the physiological or pathological actions take place in the effector cells. This review intends to organize this knowledge in a fashion that is easy to understand. We will dissect the NO pathway in different steps, focusing on the physiological and pathophysiological actions of the isoenzymes which synthesize NO, the molecules involved in this synthesis such as caveolins, protein kinases and cofactors, the situations in which endogenous inhibitors of NO synthase are formed from L-arginine instead of NO, the way in which NO exerts its physiological actions through cGMP-dependent protein kinases and finally, the pathological routes NO may follow when the oxidative status of the cell is high.