Role of nitric oxide in heart failure

The benefit effects of nitric oxide (NO) donors in acute heart failure have led to the development of vasodilators as treatment of chronic heart failure. However, the mechanisms involved in the effects of NO are complex and still discussed. In chronic heart failure, the eNOS downregulation in vascular endothelium explains the alteration of endothelial function. In addition, in the myocardium, cytokines induce the expression of inducible nitric oxide synthase (iNOS) which increase NO production by myocytes and surrounding cells. This excess of NO production, associated with anion superoxide synthesis, limits the inotropic properties of catecholamines and exert proapoptotic effects. The role of NO donors in heart failure treatment is still controversial but by reducing preload they improve patient's symptoms. Beside blockade of the renin-angiotensin system, the angiotensin converting enzyme inhibitors act via the inhibition of bradykinin degradation which increase NO levels. Finally, vascular endothelial NO expression is improved by exercise training and participates in the improvement of exercise capacity in patients with chronic heart failure involved in cardiac readaptation program.     

Arrhythmia and neuronal/endothelial myocyte uncoupling in hyperhomocysteinemia

Elevated levels of homocysteine (Hcy) known as hyperhomocysteinemia (HHcy) are associated with arrhythmogenesis and sudden cardiac death (SCD). Hcy decreases constitutive neuronal and endothelial nitric oxide (NO), and cardiac diastolic relaxation. Hcy increases the iNOS/NO, peroxynitrite, mitochondrial NADPH oxidase, and suppresses superoxide dismutase (SOD) and redoxins. Hcy activates matrix metalloproteinase (MMP), disrupts connexin-43 and increases collagen/elastin ratio. The disruption of connexin-43 and accumulation of collagen (fibrosis) disrupt the normal pattern of cardiac conduction and attenuate NO transport from endothelium to myocyte (E-M) causing E-M uncoupling, leading to a pro-arrhythmic environment. The goal of this review is to elaborate the mechanism of Hcy-mediated iNOS/NO in E-M uncoupling and SCD. It is known that Hcy creates arrhythmogenic substrates (i.e. increase in collagen/elastin ratio and disruption in connexin-43) and exacerbates heart failure during chronic volume overload. Also, Hcy behaves as an agonist to N-methyl-D-aspartate (NMDA, an excitatory neurotransmitter) receptor-1, and blockade of NMDA-R1 reduces the increase in heart rate-evoked by NMDA-analog and reduces SCD. This review suggest that Hcy increases iNOS/NO, superoxide, metalloproteinase activity, and disrupts connexin-43, exacerbates endothelial-myocyte uncoupling and cardiac failure secondary to inducing NMDA-R1.     

Inducible NO synthase activity in blood vessels and heart: new insight into cell origin and consequences

Induction of the inducible form of nitric oxide synthase (iNOS) in the vascular and cardiac tissue by several inflammatory stimuli may result in the production of large amounts of nitric oxide (NO) for a sustained period. Recent data obtained in the rat aorta in which iNOS was induced by lipopolysaccharide (LPS) have demonstrated that adventitial cells represent the main site of NO production. Adventitial-derived NO can exert an immediate down-regulatory effect on smooth muscle contraction (via activation of the cyclic GMP pathway) but may also initiate longer lasting effects through the formation of NO stores within the medial layer. One candidate for such NO stores are dinitrosyl non-heme iron complexes. Low molecular weight thiols interact with preformed NO stores and promote vasorelaxation by a cyclic GMP-independent mechanism involving the activation of potassium channels. In the heart, the induction of iNOS is involved in delayed protection against ischemia-reperfusion-induced functional damages. Recent data obtained with monophosphoryl lipid A, a non-toxin derivative of LPS, strongly suggest that iNOS-derived NO in the rat heart does not act as an immediate mediator of the cardioprotection but rather as a trigger of long-term protective mechanisms. Thus, the present data reveal the important role of adventitial cells as a site of iNOS expression and activity in intact blood vessels. The induction of adaptive mechanisms in the heart and the formation of releasable NO stores in blood vessels are examples of long-term consequences of iNOS induction. These new information are relevant for a better understanding of the circumstances in which NO overproduction by iNOS may play either a beneficial or deleterious role in these tissues.     

Enhancement of YD spin relaxation by the CaMn4 cluster in photosystem II detected at room temperature: a new probe for the S-cycle

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

Increased L-arginine uptake and inducible nitric oxide synthase activity in aortas of rats with heart failure

L-Arginine crosses the cell membrane primarily through the system y(+) transporter. The aim of this study was to investigate the role of L-arginine transport in nitric oxide (NO) production in aortas of rats with heart failure induced by myocardial infarction. Tumor necrosis factor-alpha levels in aortas of rats with heart failure were six times higher than in sham rats (P < 0.01). L-Arginine uptake was increased in aortas of rats with heart failure compared with sham rats (P < 0.01). Cationic amino acid transporter-2B and inducible (i) nitric oxide synthase (NOS) expression were increased in aortas of rats with heart failure compared with sham rats (P < 0.05). Aortic strips from rats with heart failure treated with L-arginine but not D-arginine increased NO production (P < 0.05). The effect of L-arginine on NO production was blocked by L-lysine, a basic amino acid that shares the same system y(+) transporter with L-arginine, and by the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Treatment with L-lysine and L-NAME in vivo decreased plasma nitrate and nitrite levels in rats with heart failure (P < 0.05). Our data demonstrate that NO production is dependent on iNOS activity and L-arginine uptake and suggest that L-arginine transport plays an important role in enhanced NO production in heart failure.     

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

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

Inducible nitric oxide synthase in heart tissue and nitric oxide in serum of Trypanosoma cruzi-infected rhesus monkeys: association with heart injury

Background

The factors contributing to chronic Chagas'' heart disease remain unknown. High nitric oxide (NO) levels have been shown to be associated with cardiomyopathy severity in patients. Further, NO produced via inducible nitric oxide synthase (iNOS/NOS2) is proposed to play a role in Trypanosoma cruzi control. However, the participation of iNOS/NOS2 and NO in T. cruzi control and heart injury has been questioned. Here, using chronically infected rhesus monkeys and iNOS/NOS2-deficient (Nos2 ^−/−) mice we explored the participation of iNOS/NOS2-derived NO in heart injury in T. cruzi infection.

Methodology

Rhesus monkeys and C57BL/6 and Nos2 ^−/− mice were infected with the Colombian T. cruzi strain. Parasite DNA was detected by polymerase chain reaction, T. cruzi antigens and iNOS/NOS2⁺ cells were immunohistochemically detected in heart sections and NO levels in serum were determined by Griess reagent. Heart injury was assessed by electrocardiogram (ECG), echocardiogram (ECHO), creatine kinase heart isoenzyme (CK-MB) activity levels in serum and connexin 43 (Cx43) expression in the cardiac tissue.

Results

Chronically infected monkeys presented conduction abnormalities, cardiac inflammation and fibrosis, which resembled the spectrum of human chronic chagasic cardiomyopathy (CCC). Importantly, chronic myocarditis was associated with parasite persistence. Moreover, Cx43 loss and increased CK-MB activity levels were primarily correlated with iNOS/NOS2⁺ cells infiltrating the cardiac tissue and NO levels in serum. Studies in Nos2 ^−/− mice reinforced that the iNOS/NOS2-NO pathway plays a pivotal role in T. cruzi-elicited cardiomyocyte injury and in conduction abnormalities that were associated with Cx43 loss in the cardiac tissue.

Conclusion

T. cruzi-infected rhesus monkeys reproduce features of CCC. Moreover, our data support that in T. cruzi infection persistent parasite-triggered iNOS/NOS2 in the cardiac tissue and NO overproduction might contribute to CCC severity, mainly disturbing of the molecular pathway involved in electrical synchrony. These findings open a new avenue for therapeutic tools in Chagas'' heart disease.     

Effects of iNOS-related NO on hearts exposed to liposoluble iron

Inducible nitric oxide synthase (iNOS) protects heart against ischemia/reperfusion injury. However, it is unknown whether the beneficial effects of iNOS are mediated by the interaction of NO with radical oxygen species (ROS). To address this issue, we examined the effects of liposoluble iron-induced ROS generation in isolated perfused hearts from rats treated with lipopolysaccharide (LPS). LPS administration (10 mg/kg, i.p., 6 h before heart removal) induced iNOS expression and increased NO production as indicated by a 3-fold elevation of nitrite level in coronary effluents relative to control hearts. An enhanced expression of hemeoxygenase 1 protein was also observed in septic hearts compared to control. Iron-induced perfusion and contractile deficits were ameliorated by LPS with more important coronary than myocardial benefits. In iron-loaded hearts, oxidative stress as measured by the 2,3 dihydroxybenzoic acid/salicylic acid concentration ratio in cardiac tissue was 23% lower in septic than in control heart although the difference did not reach significance. In addition, the presence of the NO synthase inhibitor N-nitro-L-arginine in the perfusion medium totally blocked NO production but did not reverse the protective effects of LPS. The results indicate that LPS protects from iron-induced cardiac dysfunction by mechanisms independent on ex vivo NO production and suggest that NO acts as a trigger rather than a direct mediator of the cardioprotective effects of LPS in heart exposed to iron.     

The complex role of iNOS in acutely rejecting cardiac transplants

This review summarizes the evidence for a detrimental role of nitric oxide (NO) derived from inducible NO synthase (iNOS) and/or reactive nitrogen species such as peroxynitrite in acutely rejecting cardiac transplants. In chronic cardiac transplant rejection, iNOS may have an opposing beneficial component. The purpose of this review is primarily to address issues related to acute rejection, which is a recognized risk factor for chronic rejection. The evidence for a detrimental role is based upon strategies involving nonselective NOS inhibitors, NO neutralizers, selective iNOS inhibitors, and iNOS gene deletion in rodent models of cardiac rejection. The review is presented in the context of the impact on various components, including graft survival, histological rejection, and cardiac function, which may contribute to the process of graft rejection in toto. Possible limitations of each strategy are discussed in order to understand better the variance in published findings, including issues related to the potential importance of cell localization of iNOS expression. Finally, the concept of a dual role for NO and its downstream product, peroxynitrite, in rejection vs immune regulation is discussed.     

Trypanosoma cruzi: Effect of the absence of 5-lipoxygenase (5-LO)-derived leukotrienes on levels of cytokines, nitric oxide and iNOS expression in cardiac tissue in the acute phase of infection in mice

Leukotrienes are important mediators of inflammatory responses. In this study, we investigated the effect of the absence of 5-lipoxygenase (5-LO)-derived leukotrienes on levels of cytokines, nitric oxide (NO) and iNOS expression in cardiac tissue of mice infected with Trypanosoma cruzi, the agent of Chagas’ disease. NO is a key mediator of parasite killing in mice experimentally infected with T. cruzi, and previous studies have suggested that leukotrienes, such as LTB₄, induces NO synthesis in T. cruzi-infected macrophages and plays a relevant role in the killing of parasite in a NO-dependent manner. We therefore investigated whether leukotrienes would have a similar role in vivo in controlling the parasite burden by regulating NO activity. We have made the striking observation that absence of 5-LO-derived leukotrienes results in increased NO and IL-6 production in the plasma with a concomitant decrease in the expression of iNOS in the cardiac tissue on day 12 after T. cruzi infection. These findings indicate that endogenous leukotrienes are important regulators of NO activity in the heart and therefore influence the cardiac parasite burden without exerting a direct action on IL-6 production in the acute phase of infection with T. cruzi.     

Co-induction of nitric oxide and tetrahydrobiopterin synthesis in the myocardium in vivo

Induction of the inducible isoform of nitric oxide (NO) synthase (iNOS) in the myocardium is implicated as a mechanism in the development of cardiac depression in immune activated states associated with an enhanced release of cytokines, such as septic shock. We evaluated the in vivo synthesis of NO and tetrahydrobiopterin (BH4), a cofactor of NOS, in the heart tissue using a model of LPS injection in rats (LPS: 10 mg/kg, i.v.). In control rats, iNOS activity or iNOS mRNA in the heart was negligible. Three hours after LPS administration, a marked induction of iNOS mRNA and activity was observed in the heart. A significant increase in BH4 content and GTP cyclohydrolase mRNA abundance was also observed in the heart from LPS-treated rats. Our results demonstrate induction of NO synthesis and parallel increase in BH4 concentration in the heart of rats after LPS treatment in vivo and may provide molecular evidence responsible for the increased production of BH4 which may up-regulate iNOS activity in the heart in vivo. (Mol Cell Biochem 166: 177-181, 1997)     

iNOS in cardiac myocytes plays a critical role in death in a murine model of hypertrophy induced by calcineurin

Transgenic overexpression of calcineurin (CN/Tg) in mouse cardiac myocytes results in hypertrophy followed by dilation, dysfunction, and sudden death. Nitric oxide (NO) produced via inducible NO synthase (iNOS) has been implicated in cardiac injury. Since calcineurin regulates iNOS expression, and since phenotypes of mice overexpressing iNOS are similar to CN/Tg, we hypothesized that iNOS is pathogenically involved in cardiac phenotypes of CN/Tg mice. CN/Tg mice had increased serum and cardiac iNOS levels. When CN/Tg-iNOS(-/-) and CN/Tg mice were compared, some phenotypes were similar: extent of hypertrophy and fibrosis. However, CN/Tg-iNOS(-/-) mice had improved systolic performance (P < 0.001) and less heart block (P < 0.0001); larger sodium current density and lower serum TNF-alpha levels (P < 0.03); and less apoptosis (P < 0.01) resulting in improved survival (P < 0.0003). To define tissue origins of iNOS production, chimeric lines were generated. Bone marrow (BM) from wild-type or iNOS(-/-) mice was transplanted into CN/Tg mice. iNOS deficiency restricted to BM-derived cells was not protective. Calcineurin activates the local production of NO by iNOS in cardiac myocytes, which significantly contributes to sudden death, heart block, left ventricular dilation, and impaired systolic performance in this murine model of cardiac hypertrophy induced by the overexpression of calcineurin.     

Effects of simulated microgravity on nitric oxide level in cardiac myocytes and its mechanism

The depression of cardiac contractility induced by space microgravity is an important issue of aerospace medicine research, while its precise mechanism is still unknown. In the present study, we explored effects of simulated microgravity on nitric oxide (NO) level, inducible nitric oxide synthase (iNOS) expression and related regulative mechanism using electron spin resonance (ESR) spectroscopy, immunocytochemistry and in situ hybridization. We found a remarkable increase of NO level and up-regulation of iNOS and iNOS mRNA expression in rat cardiac myocytes under simulated microgravity. Staurosporine (a nonselective protein kinase inhibitor), calphostin C (a selective protein kinase C inhibitor), partially inhibited the effect of simulated microgravity. Thus regulative effect of simulated microgravity on iNOS expression is mediated at least partially via activation of protein kinase C. These results indicate that NO system in cardiac myocytes is sensitive to simulated microgravity and may play an important role in the depression of cardiac contractility induced by simulated microgravity.     

Nitrosative stress leads to protein glutathiolation, increased s-nitrosation, and up-regulation of peroxiredoxins in the heart

Nitric oxide (NO) is produced by different isoforms of nitric oxide synthases (NOSs) and operates as a mediator of important cell signaling pathways, such as the cGMP signaling cascade. Another mechanism by which NO exerts biological effects is mediated through S-nitrosation of target proteins. To explore thiol-based protein modifications in a situation of defined nitrosative stress, we used a transgenic mouse model with cardiac specific overexpression of inducible nitric oxide synthase (iNOS) and concomitant myoglobin deficiency (iNOS(+)/myo(-/-)). In comparison with the wild type hearts, protein glutathiolation detected by immunoblotting was significantly enhanced in iNOS(+)/myo(-/-) hearts, whereas protein S-nitrosation as measured by the biotin switch assay and two-dimensional PAGE revealed that nearly all of the detected proteins ( approximately 60) remained unchanged with the exception of three proteins. Tandem mass spectrometry revealed these proteins to be peroxiredoxins (Prxs), which are known to possess peroxidase activity, whereby hydrogen peroxide, peroxynitrite, and a wide range of organic hydroperoxides are reduced and detoxified. Immunoblotting with specific antibodies revealed up-regulation of Prx VI in the iNOS(+)/myo(-/-) hearts, whereas expression of Prx II and Prx III remained unchanged. Furthermore, the analysis of the cardiac S-nitrososubproteome identified several new proteins possibly being involved in NO-signaling pathways. Our data indicate that S-nitrosation and glutathiolation of cardiac proteins may contribute to the phenotype of NO-induced heart failure. The up-regulation of antioxidant proteins like Prx VI appears to be an additional mechanism to antagonize an excess of reactive oxygen/nitrogen species. Furthermore, S-nitrosation of Prxs may serve a new function in the signaling cascade of nitrosative stress.     

Effects of simulated microgravity on nitric oxide level in cardiac myocytes and its mechanism

Prolonged exposure to space microgravity results in cardiovascular deconditioning and the depression of cardiac contractility, while its mechanism is still unknown[1]. Thus study about ef-fects of microgravity on cardiac myocytes and related mechanism is an important issue in space medicine. It would also contribute to understanding effects of mechanical signal on signal transduction in cardiac myocytes and pathology of related diseases. Nitric oxide (NO) is a universal signal molecular in ce…     

Late preconditioning induced by NO donors, adenosine A1 receptor agonists, and delta1-opioid receptor agonists is mediated by iNOS

Although ischemia-induced late preconditioning (PC) is known to be mediated by inducible nitric oxide (NO) synthase (iNOS), the role of this enzyme in pharmacologically induced late PC remains unclear. We tested whether targeted disruption of the iNOS gene abrogates late PC elicited by three structurally different NO donors [diethylenetriamine/NO (DETA/NO), nitroglycerin (NTG), and S-nitroso-N-acetyl-penicillamine (SNAP)], an adenosine A1 receptor agonist [2-chloro-N6-cyclopentyladenosine (CCPA)], and a delta1-opioid receptor agonist (TAN-670). The mice were subjected to a 30-min coronary occlusion followed by 24 h of reperfusion. In iNOS knockout (iNOS-/-) mice, infarct size was similar to wild-type (WT) controls, indicating that iNOS does not modulate infarct size in the absence of PC. Pretreatment of WT mice with DETA/NO, NTG, SNAP, TAN-670, or CCPA 24 h before coronary occlusion markedly reduced infarct size. In iNOS-/- mice, however, the late PC effect elicited by DETA/NO, NTG, SNAP, TAN-670, and CCPA was completely abrogated. Furthermore, in WT mice pretreated with TAN-670 or CCPA, the selective iNOS inhibitor 1400W also abolished the delayed PC properties of these drugs; 1400W had no effect in WT mice. These data demonstrate that iNOS plays an obligatory role in NO donor-induced, adenosine A1 receptor agonist-induced, and delta1-opioid receptor agonist-induced late PC, underscoring the critical role of this enzyme as a common mediator of cardiac adaptations to stress.     

Molecular and pharmacological approaches to inhibiting nitric oxide after burn trauma

Whereas controversial, several studies have suggested that nitric oxide (NO) alters cardiac contractility via cGMP, peroxynitrite, or poly(ADP ribose) synthetase (PARS) activation. This study determined whether burn-related upregulation of myocardial inducible NO synthase (iNOS) and NO generation contributes to burn-mediated cardiac contractile dysfunction. Mice homozygous null for the iNOS gene (iNOS knockouts) were obtained from Jackson Laboratory. iNOS knockouts (KO) as well as wild-type mice were given a cutaneous burn over 40% of the total body surface area by the application of brass probes (1 x 2 x 0.3 cm) heated to 100 degrees C to the animals' sides and back for 5 s (iNOS/KO burn and wild-type burn). Additional groups of iNOS KO and wild-type mice served as appropriate sham burn groups (iNOS/KO sham and wild-type sham). Cardiac function was assessed 24 h postburn by perfusing hearts (n = 7-10 mice/group). Burn trauma in wild-type mice impaired cardiac function as indicated by the lower left ventricular pressure (LVP, 67 +/- 2 mmHg) compared with that measured in wild-type shams (94 +/- 2 mmHg, P < 0.001), a lower rate of LVP rise (+dP/dtmax, 1,620 +/- 94 vs. 2,240 +/- 58 mmHg/s, P < 0.001), and a lower rate of LVP fall (-dP/dtmax, 1,200 +/- 84 vs. 1,800 +/- 42 mmHg/s, P < 0.001). Ventricular function curves confirmed significant contractile dysfunction after burn trauma in wild-type mice. Burn trauma in iNOS KO mice produced fewer cardiac derangements compared with those observed in wild-type burns (LVP: 78 +/- 5 mmHg; +dP/dt: 1,889 +/- 160 mmHg/s; -dP/dt: 1,480 +/- 154 mmHg/s). The use of a pharmacological approach to inhibit iNOS (aminoguanidine, given ip) in additional wild-type shams and burns confirmed the iNOS KO data. Whereas the absence of iNOS attenuated burn-mediated cardiac contractile dysfunction, these experiments did not determine the contribution of cardiac-derived NO versus NO generated by immune cells. However, our data indicate a role for NO in cardiac dysfunction after major trauma.