Conditional neuronal nitric oxide synthase overexpression impairs myocardial contractility

Nitric oxide/reactive oxygen species generation and nitroso/redox imbalance in heart failure: from molecular mechanisms to therapeutic implications

Adaptation of the heart to intrinsic and external stress involves complex modifications at the molecular and cellular levels that lead to tissue remodeling, functional and metabolic alterations, and finally to failure depending upon the nature, intensity, and chronicity of the stress. Reactive oxygen species (ROS) have long been considered as merely harmful entities, but their role as second messengers has gradually emerged. At the same time, our comprehension of the multifaceted role of nitric oxide (NO) and the related reactive nitrogen species (RNS) has been upgraded. The tight interlay between ROS and RNS suggests that their imbalance may implicate the impairment in physiological NO/redox-based signaling that contributes to the failing of the cardiovascular system. This review initially provides basic concepts on the role of nitroso/oxidative stress in the pathophysiology of heart failure with a particular focus on sources of ROS/RNS, their downstream targets, and endogenous modulators. Then, the role of NO/redox regulation of cardiomyocyte function, including calcium homeostasis, electrogenesis, and insulin signaling pathways, is described. Finally, an overview of old and emerging therapeutic opportunities in heart failure is presented, focusing on modulation of NO/redox mechanisms and discussing benefits and limitations.

Nitric oxide and calcium signaling regulate myocardial tumor necrosis factor-α expression and cardiac function in sepsis

Myocardial tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is a critical inducer of myocardial dysfunction in sepsis. The purpose of this review is to summarize the mechanisms through which TNF-alpha production is regulated in cardiomyocytes in response to lipopolysaccharide (LPS), a key pathogen-associated molecular pattern (PAMP) in sepsis. These mechanisms include Nox2-containing NAD(P)H oxidase, phospholipase C (PLC)gamma1, and Ca2+ signaling pathways. Activation of these pathways increases TNF-alpha expression via activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). Conversely, activation of c-Jun NH2-terminal kinase 1 (JNK1) negatively regulates TNF-alpha production through inhibition of ERK1/2 and p38 MAPK activity. Interestingly, endothelial nitric oxide synthase (eNOS) promotes TNF-alpha expression by enhancing p38 MAPK activation, whereas neuronal NOS (nNOS) inhibits TNF-alpha production by reducing Ca2+-dependent ERK1/2 activity. Therefore, the JNK1 and nNOS inhibitory pathways represent a "brake" that limits myocardial TNF-alpha expression in sepsis. Further understanding of these signal transduction mechanisms may lead to novel pharmacological therapies in sepsis.

Neuronal NOS is dislocated during muscle atrophy in amyotrophic lateral sclerosis

Previously, we demonstrated that neuronal nitric oxide synthase (nNOS) is activated and promotes muscle atrophy in skeletal muscle during tail suspension, a model of unloading and denervation. Here, we examined patients with amyotrophic lateral sclerosis (ALS) and mutant (H46R) SOD1 transgenic (Tg) mice model using immunohistochemistry, Western blotting and real time PCR. We found cytoplasmic nNOS staining of angulated muscle fibers in patients with ALS. We also examined mutant SOD1 Tg mice and found cytoplasmic nNOS staining even before the onset of clinical muscle atrophy. In the Tg mice, nNOS was largely extracted with 100 mM NaCl and barely detected in the pellet fraction, suggesting fragile anchoring of nNOS to the sarcolemma. We also showed an elevated expression of atrogin-1, key molecules in muscle atrophy at the end stage. A common nNOS dislocation/atrogin-1/muscle atrophy pathway among tail suspension, denervation and ALS is suggested. nNOS modulation therapy may be beneficial in several types of muscle atrophy.

Conditional overexpression of neuronal nitric oxide synthase is cardioprotective in ischemia/reperfusion

BACKGROUND

We previously demonstrated that conditional overexpression of neuronal nitric oxide synthase (nNOS) inhibited L-type Ca2+ channels and decreased myocardial contractility. However, nNOS has multiple targets within the cardiac myocyte. We now hypothesize that nNOS overexpression is cardioprotective after ischemia/reperfusion because of inhibition of mitochondrial function and a reduction in reactive oxygen species generation.

METHODS AND RESULTS

Ischemia/reperfusion injury in wild-type mice resulted in nNOS accumulation in the mitochondria. Similarly, transgenic nNOS overexpression caused nNOS abundance in mitochondria. nNOS translocation into the mitochondria was dependent on heat shock protein 90. Ischemia/reperfusion experiments in isolated hearts showed a cardioprotective effect of nNOS overexpression. Infarct size in vivo was also significantly reduced. nNOS overexpression also caused a significant increase in mitochondrial nitrite levels accompanied by a decrease of cytochrome c oxidase activity. Accordingly, O(2) consumption in isolated heart muscle strips was decreased in nNOS-overexpressing nNOS(+)/αMHC-tTA(+) mice already under resting conditions. Additionally, we found that the reactive oxygen species concentration was significantly decreased in hearts of nNOS-overexpressing nNOS(+)/αMHC-tTA(+) mice compared with noninduced nNOS(+)/αMHC-tTA(+) animals.

CONCLUSION

We demonstrated that conditional transgenic overexpression of nNOS resulted in myocardial protection after ischemia/reperfusion injury. Besides a reduction in reactive oxygen species generation, this might be caused by nitrite-mediated inhibition of mitochondrial function, which reduced myocardial oxygen consumption already under baseline conditions.

Cardiac electrophysiological effects of nitric oxide

Nitric oxide (NO) synthetized by essentially all cardiac cell types plays a key role in the regulation of cardiac function. Recent evidence shows that NO modulates the activity of cardiac ion channels implicated in the genesis of the cardiac action potential and exerts anti-arrhythmic properties under some circumstances. We review the effects of NO on cardiac ion channels and the signalling pathways, including cGMP-dependent (protein kinase G and cGMP-regulated phosphodiesterases) and cGMP-independent mechanisms (S-nitrosylation and direct effects on G proteins) and finally the role of NO in the genesis of cardiac arrhythmias during ischemia-reperfusion, heart failure, long QT syndrome, atrial fibrillation, and sudden cardiac death.

Nitric oxide synthases in the pathogenesis of cardiovascular disease: lessons from genetically modified mice

Nitric oxide (NO) is produced in almost all tissues and organs, exerting a variety of biological actions under both physiological and pathological conditions. NO is synthesized by three distinct NO synthase (NOS) isoforms (neuronal, inducible, and endothelial NOS), all of which are expressed in the human cardiovascular system. Although the regulatory roles of NOSs in cardiovascular diseases have been described in pharmacological studies with selective and non-selective NOS inhibitors, the specificity of the NOS inhibitors continues to be an issue of debate. To overcome this issue, genetically engineered animals have been used. All types of NOS gene-deficient animals, including singly, doubly, and triply NOS-deficient mice, and various types of NOS gene-transgenic (TG) animals, including conditional and non-conditional TG mice bearing endothelium-specific or cardiomyocyte-specific overexpression of each NOS gene, have thus been developed. The roles of individual NOS isoforms as well as the entire NOS system in the cardiovascular system have been extensively investigated in those mice, providing pivotal insights into an understanding of the pathophysiology of NOSs in human cardiovascular diseases. Based on studies with the murine NOS genetic models, this review briefly summarizes the latest knowledge of NOSs and cardiovascular diseases.

Inotropic response of cardiac ventricular myocytes to beta-adrenergic stimulation with isoproterenol exhibits diurnal variation: involvement of nitric oxide

RATIONALE

Although >10% of cardiac gene expression displays diurnal variations, little is known of their impact on excitation-contraction coupling.

OBJECTIVE

To determine whether the time of day affects excitation-contraction coupling in rat ventricles.

METHODS AND RESULTS

Left ventricular myocytes were isolated from rat hearts at 2 opposing time points, corresponding to the animals resting or active periods. Basal contraction and [Ca(2+)](i) was significantly greater in myocytes isolated during the resting versus active periods (cell shortening 12.4+/-0.3 versus 11.0+/-0.2%; P<0.05 and systolic [Ca(2+)](i) 422+/-12 versus 341+/-9 nmol/L; P<0.01. This corresponded to a greater sarcoplasmic reticulum (SR) Ca(2+) load (672+/-20 versus 551+/-13 nmol/L P<0.001). The increase in systolic [Ca(2+)](i) in response to isoproterenol (>3 nmol/L) was also significantly greater in resting versus active period myocytes, reflecting a greater SR Ca(2+) load at this time. This diurnal variation in response of Ca(2+)-homeostasis to isoproterenol translated to a greater incidence of arrhythmic activity in resting period myocytes. Inhibition of neuronal NO synthase during stimulation with isoproterenol, further increased systolic [Ca(2+)](i) and the percentage of arrhythmic myocytes, but this effect was significantly greater in active period versus resting period myocytes. Quantitative RT-PCR analysis revealed a 2.65-fold increase in neuronal NO synthase mRNA levels in active over resting period myocytes (P<0.05).

CONCLUSIONS

The threshold for the development of arrhythmic activity in response to isoproterenol is higher during the active period of the rat. We suggest this reflects a reduction in SR Ca(2+) loading and a diurnal variation in neuronal NO synthase signaling.

Neuronal nitric oxide synthase protects against myocardial infarction-induced ventricular arrhythmia and mortality in mice

BACKGROUND

Neuronal nitric oxide synthase (nNOS) is expressed in cardiomyocytes and plays a role in regulating cardiac function and Ca2+ homeostasis. However, the role of nNOS in cardiac electrophysiology after myocardial infarction (MI) is unclear. We hypothesized that nNOS deficiency increases ventricular arrhythmia and mortality after MI.

METHODS AND RESULTS

MI was induced in wild-type (WT) or nNOS(-/-) mice by ligation of the left coronary artery. Thirty-day mortality was significantly higher in nNOS(-/-) compared with WT mice. Additionally, nNOS(-/-) mice had impaired cardiac function 2 days after MI. Telemetric ECG monitoring showed that compared with WT, nNOS(-/-) mice had significantly more ventricular arrhythmias and were more likely to develop ventricular fibrillation after MI. Treatment with the L-type Ca2+ channel blocker verapamil reduced the incidence of arrhythmia and ventricular fibrillation in nNOS(-/-) mice after MI. To assess the role of nNOS in Ca2+ handling, patch-clamp and Ca2+ fluorescence techniques were used. Ca2+ transients and L-type Ca2+ currents were higher in nNOS(-/-) compared with WT cardiomyocytes. Additionally, nNOS(-/-) cardiomyocytes exhibited significantly higher systolic and diastolic Ca2+ over a range of pacing frequencies. Treatment with the NO donor S-nitroso N-acetyl-penicillamine decreased Ca2+ transients and L-type Ca2+ current in both nNOS(-/-) and WT cardiomyocytes. Furthermore, S-nitrosylation of Ca2+ handling proteins was significantly decreased in nNOS(-/-) myocardium after MI.

CONCLUSIONS

Deficiency in nNOS increases ventricular arrhythmia and mortality after MI in mice. The antiarrhythmic effect of nNOS involves inhibition of L-type Ca2+ channel activity and regulation of Ca2+ handling proteins via S-nitrosylation.

S-Nitrosylation of cardiac ion channels

Nitric oxide (NO) exerts ubiquitous signaling via posttranslational modification of cysteine residues, a reaction termed S-nitrosylation. Important substrates of S-nitrosylation that influence cardiac function include receptors, enzymes, ion channels, transcription factors, and structural proteins. Cardiac ion channels subserving excitation-contraction coupling are potentially regulated by S-nitrosylation. Specificity is achieved in part by spatial colocalization of ion channels with nitric oxide synthases (NOSs), enzymatic sources of NO in biologic systems, and by coupling of NOS activity to localized calcium/second messenger concentrations. Ion channels regulate cardiac excitability and contractility in millisecond timescales, raising the possibility that NO-related species modulate heart function on a beat-to-beat basis. This review focuses on recent advances in understanding of NO regulation of the cardiac action potential and of the calcium release channel ryanodine receptor, which is crucial for the generation of force. S-Nitrosylation signaling is disrupted in pathological states in which the redox state of the cell is dysregulated, including ischemia, heart failure, and atrial fibrillation.

The role of nitric oxide in myocardial repair and remodeling

Nitric oxide (NO) plays a crucial role in many aspects of the pathophysiology of heart failure. NO is a double-edged sword; NO inhibits ischemia/reperfusion (I/R) injury, represses inflammation, and prevents left ventricular (LV) remodeling, whereas excess NO and co-existence of reactive oxygen species (ROS) with NO are injurious. The failing heart is exposed to not only oxidative stress by a plethora of humoral factors and inflammatory cells but also nitrosative stress. Activation of nitric oxide synthase (NOS) of any isoforms, [i.e., endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS)], concomitant with oxidative stress results in NOS uncoupling, leading to further oxidative/nitrosative stress. Indiscriminate removal of oxidative stress is not an effective means to prevent this detrimental process, because oxidative stress is necessary for an adaptive mechanism for cell survival against noxious stimuli. Therefore, removal of ROS in a site-specific manner or inhibition of the source of injurious ROS without affecting redox-sensitive survival signal transduction pathways represents a promising approach to elicit the beneficial effect of NO. Recent emerging pharmacological tools and regular exercise inhibit ROS generation in the proximity of NOSs, thereby increasing bioavailable NO and exerting cardioprotection against I/R injury and LV remodeling.

Genetic variation in NOS1AP is associated with sudden cardiac death: evidence from the Rotterdam Study

Common variation within the nitric oxide-1 synthase activator protein (NOS1AP) locus is strongly related to QT interval, a sudden cardiac death (SCD) risk factor. A recent report describes common variation in NOS1AP associated with SCD in a US population of European ancestry. The objective of the current study was to obtain additional evidence by investigating the association between NOS1AP variants and SCD in the prospective population-based Rotterdam Study. The study population consisted of 5974 European ancestry subjects, aged 55 years and older, genotyped on Illumina arrays. SCD was defined according to European Society of Cardiology guidelines. Smoking, body mass index, diabetes mellitus, hypertension, heart failure and myocardial infarction were used as covariates in Cox proportional hazard models. Results were combined with reported evidence using inverse-variance weighted meta-analysis. Two hundred and eight (109 witnessed) cases of SCD occurred during a mean follow-up of 10.4 years. Within the Rotterdam Study alone, no significant associations were observed. Upon pooling of results with existing data, we observed strengthening of existing evidence for rs16847549 (US data HR = 1.31, P = 0.0024; Rotterdam Study HR = 1.18, P = 0.16; joint HR = 1.26, P = 0.0011). When the case definition in the Rotterdam Study was restricted to witnessed SCD, association of rs16847549 with SCD became stronger (joint P = 0.00019) and additionally the association between rs12567209 and SCD gained significance (US data HR = 0.57, P = 0.0035; Rotterdam Study HR = 0.69, P = 0.23; joint HR = 0.60, P = 0.0018). In conclusion, this study provided additional evidence for association between genetic variation within NOS1AP and SCD. The mechanism by which this effect is exerted remains to be elucidated.

Nitric oxide and nitric oxide synthase isoforms in the normal, hypertrophic, and failing heart

Nitric oxide (NO) produced in the heart by nitric oxide synthase (NOS) is a highly reactive signaling molecule and an important modulator of myocardial function. NOS catalyzes the conversion of L: -arginine to L: -citrulline and NO but under particular circumstances reactive oxygen species (ROS) can be formed instead of NO (uncoupling). In the heart, three NOS isoforms are present: neuronal NOS (nNOS, NOS1) and endothelial NOS (eNOS, NOS3) are constitutively present enzymes in distinct subcellular locations within cardiomyocytes, whereas inducible NOS (iNOS, NOS2) is absent in the healthy heart, but its expression is induced by pro-inflammatory mediators. In the tissue, NO has two main effects: (i) NO stimulates the activity of guanylate cyclase, leading to cGMP generation and activation of protein kinase G, and (ii) NO nitrosylates tyrosine and thiol-groups of cysteine in proteins. Upon nitrosylation, proteins may change their properties. Changes in (i) NOS expression and activity, (ii) subcellular compartmentation of NOS activity, and (iii) the occurrence of uncoupling may lead to multiple NO-induced effects, some of which being particularly evident during myocardial overload as occurs during aortic constriction and myocardial infarction. Many of these NO-induced effects are considered to be cardioprotective but particularly if NOS becomes uncoupled, formation of ROS in combination with a low NO bioavailability predisposes for cardiac damage.

Nitric oxide synthases and cardiovascular diseases: insights from genetically modified mice

Nitric oxide (NO) is produced in almost all tissues and organs, exerting a variety of biological actions under both physiological and pathological conditions. NO is synthesized by 3 distinct NO synthase (NOS) isoforms (neuronal, inducible, and endothelial NOS), all of which are expressed in the human cardiovascular system. The regulatory roles of NOSs in cardiovascular diseases have been described in pharmacological studies with selective and non-selective NOS inhibitors. However, the specificity of the NOS inhibitors continues to be an issue of debate. To overcome this issue, genetically engineered animals have been used. All types of NOS gene-deficient (knockout: KO) animals, including singly, doubly, and triply NOS-KO mice, and various types of NOS gene-transgenic (TG) animals, including conditional and non-conditional TG mice bearing endothelium-specific or cardiomyocyte-specific overexpression of each NOS gene, have thus far been developed. The roles of individual NOS isoforms, as well as the entire NOS system, in the cardiovascular system have been extensively investigated in those mice, and the results provide pivotal insights into the pathophysiology of NOSs in human cardiovascular diseases. Based on studies with murine NOS genetic models, this review summarizes the latest knowledge of NOSs and cardiovascular diseases.

The heart is an early target of anthrax lethal toxin in mice: a protective role for neuronal nitric oxide synthase (nNOS)

Anthrax lethal toxin (LT) induces vascular insufficiency in experimental animals through unknown mechanisms. In this study, we show that neuronal nitric oxide synthase (nNOS) deficiency in mice causes strikingly increased sensitivity to LT, while deficiencies in the two other NOS enzymes (iNOS and eNOS) have no effect on LT-mediated mortality. The increased sensitivity of nNOS-/- mice was independent of macrophage sensitivity to toxin, or cytokine responses, and could be replicated in nNOS-sufficient wild-type (WT) mice through pharmacological inhibition of the enzyme with 7-nitroindazole. Histopathological analyses showed that LT induced architectural changes in heart morphology of nNOS-/- mice, with rapid appearance of novel inter-fiber spaces but no associated apoptosis of cardiomyocytes. LT-treated WT mice had no histopathology observed at the light microscopy level. Electron microscopic analyses of LT-treated mice, however, revealed striking pathological changes in the hearts of both nNOS-/- and WT mice, varying only in severity and timing. Endothelial/capillary necrosis and degeneration, inter-myocyte edema, myofilament and mitochondrial degeneration, and altered sarcoplasmic reticulum cisternae were observed in both LT-treated WT and nNOS-/- mice. Furthermore, multiple biomarkers of cardiac injury (myoglobin, cardiac troponin-I, and heart fatty acid binding protein) were elevated in LT-treated mice very rapidly (by 6 h after LT injection) and reached concentrations rarely reported in mice. Cardiac protective nitrite therapy and allopurinol therapy did not have beneficial effects in LT-treated mice. Surprisingly, the potent nitric oxide scavenger, carboxy-PTIO, showed some protective effect against LT. Echocardiography on LT-treated mice indicated an average reduction in ejection fraction following LT treatment in both nNOS-/- and WT mice, indicative of decreased contractile function in the heart. We report the heart as an early target of LT in mice and discuss a protective role for nNOS against LT-mediated cardiac damage.

Erythropoietin protects the heart from ventricular arrhythmia during ischemia and reperfusion via neuronal nitric-oxide synthase

Erythropoietin (EPO) is a potent cardioprotective agent in models of myocardial ischemia and reperfusion (I/R). It has been suggested recently that EPO may also reduce ventricular arrhythmia after I/R. The present study investigated the role of neuronal nitric oxide synthase (nNOS) on the antiarrhythmic effects of EPO. EPO treatment increased nNOS expression in isolated neonatal mouse ventricular myocytes. Cotreatment with the phosphatidylinositol 3 (PI3)-kinase inhibitor, LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride], or treatment of cardiomyocytes infected with a dominant negative adenovirus targeted to Akt1 (ADV-dnAkt1) blocked the effects of EPO on nNOS expression, suggesting that EPO regulates nNOS expression via PI3-kinase and Akt. To examine the in vivo antiarrhythmic effects of EPO, wild-type (WT) and nNOS(-/-) mice were anesthetized and, after a baseline measurement, subjected to myocardial I/R to provoke ventricular arrhythmias. Pretreatment with EPO 24 h before ischemia increased nNOS expression and significantly reduced the number of premature ventricular contractions (PVCs) and the incidence of ventricular tachycardia (VT) in WT mice. In contrast, treatment with EPO had no effect on PVCs or the incidence of VT in nNOS(-/-) mice. Furthermore, EPO treatment after ischemia significantly reduced the threshold dose of cesium chloride (CsCl) to induce VT. We conclude that EPO via nNOS protects the heart from spontaneous and CsCl-induced ventricular arrhythmia during myocardial I/R.

Specific role of neuronal nitric-oxide synthase when tethered to the plasma membrane calcium pump in regulating the beta-adrenergic signal in the myocardium

The cardiac neuronal nitric-oxide synthase (nNOS) has been described as a modulator of cardiac contractility. We have demonstrated previously that isoform 4b of the sarcolemmal calcium pump (PMCA4b) binds to nNOS in the heart and that this complex regulates beta-adrenergic signal transmission in vivo. Here, we investigated whether the nNOS-PMCA4b complex serves as a specific signaling modulator in the heart. PMCA4b transgenic mice (PMCA4b-TG) showed a significant reduction in nNOS and total NOS activities as well as in cGMP levels in the heart compared with their wild type (WT) littermates. In contrast, PMCA4b-TG hearts showed an elevation in cAMP levels compared with the WT. Adult cardiomyocytes isolated from PMCA4b-TG mice demonstrated a 3-fold increase in Ser(16) phospholamban (PLB) phosphorylation as well as Ser(22) and Ser(23) cardiac troponin I (cTnI) phosphorylation at base line compared with the WT. In addition, the relative induction of PLB phosphorylation and cTnI phosphorylation following isoproterenol treatment was severely reduced in PMCA4b-TG myocytes, explaining the blunted physiological response to the beta-adrenergic stimulation. In keeping with the data from the transgenic animals, neonatal rat cardiomyocytes overexpressing PMCA4b showed a significant reduction in nitric oxide and cGMP levels. This was accompanied by an increase in cAMP levels, which led to an increase in both PLB and cTnI phosphorylation at base line. Elevated cAMP levels were likely due to the modulation of cardiac phosphodiesterase, which determined the balance between cGMP and cAMP following PMCA4b overexpression. In conclusion, these results showed that the nNOS-PMCA4b complex regulates contractility via cAMP and phosphorylation of both PLB and cTnI.

Common variation in NOS1AP and KCNH2 genes and QT interval duration in young adults. The Cardiovascular Risk in Young Finns Study

BACKGROUND

Common genetic variants in the nitric oxide synthase 1 adaptor protein gene (NOS1AP) and in the HERG potassium channel gene (KCNH2) have been associated with cardiac repolarization in middle-aged and elderly subjects.

AIM

We examined the relation between these variants and QT interval duration in a population of healthy young adults.

METHODS

We measured QT interval duration and genotyped rs10494366 T>G (NOS1AP gene, n=1,842) and rs1805123 A>C (KCNH2 gene, n=1,894) in subjects aged 24-39 years.

RESULTS

The NOS1AP variant was significantly related with heart rate-corrected QT interval duration (QTc). Additive regression model adjusting for age, sex, systolic blood pressure, body mass index, alcohol use, and smoking indicated that the G allele was associated with a 3.2 ms (95% confidence interval (CI) 1.7-4.6 ms, P<0.0001) increase in QTc interval duration for each additional copy. The KCNH2 variant was not significantly related with QTc interval duration in the study sample.

CONCLUSION

These findings provide evidence from a population of healthy young adults that a common variation in the NOS1AP gene influences cardiac repolarization within the normal physiological range. Further studies are warranted to investigate the effects of this variant on sudden cardiac death and ventricular arrhythmias.

A common NOS1AP genetic polymorphism is associated with increased cardiovascular mortality in users of dihydropyridine calcium channel blockers

AIM

Recently, a polymorphism in the NOS1AP gene (rs10494366), a regulator of neuronal nitric oxide synthase (nNOS), was associated with QTc prolongation. Both nNOS and calcium channel blockers (CCBs) regulate intracellular calcium levels and have an important role in cardiovascular homeostasis. The aim was to investigate whether this polymorphism is associated with cardiovascular mortality in users of CCBs.

METHODS

The data from the Rotterdam study, a population-based closed cohort study of Caucasian individuals of > or =55 years of age, were used. We identified 1113 participants in the Rotterdam Study who were prescribed CCBs for the first time between 1991 and 2005. All-cause and cardiovascular mortality was assessed in participants who were prescribed CCBs with different NOS1AP rs10494366 genotypes using Cox proportional hazard models.

RESULTS

In participants starting on dihydropyridine CCBs (amlodipine, nifedipine and others) all-cause mortality (n = 79) risks were higher in participants with the TG [hazard ratio (HR) 2.57, 95% confidence interval (CI) 1.24, 5.34] or the GG genotype (HR 3.18, 95% CI 1.18, 8.58) than in participants with the referent TT genotype. Cardiovascular mortality (n = 54) risks were 3.51 (95% CI 1.41, 8.78) for the TG genotype and 6.00 (95% CI 1.80, 20.0) for the GG genotype. No differences in all-cause mortality or cardiovascular mortality were seen in participants starting with the nondihydropyridine CCBs verapamil or diltiazem.

CONCLUSION

The minor G allele of rs10494366 in the NOS1AP gene is associated with increased all-cause and cardiovascular mortality in Caucasian users of dihydropyridine CCBs. The mechanism underlying the observed association is unknown.

Fluvastatin reduces pulmonary vein spontaneous activity through nitric oxide pathway

INTRODUCTION

Pulmonary veins (PVs) are the most important focus for the generation of atrial fibrillation. The HMG-CoA reductase inhibitors (statins) can reduce the occurrence of atrial fibrillation. The purposes of this study were to evaluate whether statins may inhibit the PV arrhythmogenic activity to prevent atrial arrhythmias from PVs and to investigate the link between fluvastatin, nitric oxide synthase (NOS) activity, mechanical activity, and electrical activity.

METHODS

Conventional microelectrodes and Western blot were used to record the electrical activity, diastolic tension, contractility and expression of Akt, endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and phosphorylated Akt and eNOS before and after the administration of fluvastatin in rabbit PVs or atria.

RESULTS

Fluvastatin decreased the PV spontaneous activity, diastolic tension, and contractility, but did not change the action potential duration or resting membrane potential. The effects of fluvastatin on the PV firing rate and diastolic tension were attenuated in the presence of L-NAME (100 microM), wortmannin (100 nM), and ODQ (3 microM). Fluvastatin (1 muM) increased the phosphorylated Akt and eNOS, but did not change the total Akt or eNOS in the PVs and atria. In contrast, fluvastatin (1 microM) decreased the total nNOS in the PVs and atria.

CONCLUSIONS AND IMPLICATIONS

Fluvastatin produced nitric oxide through the PI3kinase/Akt pathway, thus reducing the PV vascular diastolic tension and PV spontaneous activity. These results may contribute to the beneficial effects of statins.

Nitric oxide signaling and the regulation of myocardial function

Nitric oxide, which is produced endogenously within cardiac myocytes by three distinct isoforms of nitric oxide synthase, is a key regulator of myocardial function. This review will focus on the regulation of myocardial function by each nitric oxide synthase isoform during health and disease, with a specific emphasis on the proposed end-targets and signaling pathways.

Cardiomyocyte Overexpression of Neuronal Nitric Oxide Synthase Delays Transition Toward Heart Failure in Response to Pressure Overload by Preserving Calcium Cycling

Background— Defects in cardiomyocyte Ca 2+ cycling are a signature feature of heart failure (HF) that occurs in response to sustained hemodynamic overload, and they largely account for contractile dysfunction. Neuronal nitric oxide synthase (NOS1) influences myocyte excitation-contraction coupling through modulation of Ca 2+ cycling, but the potential relevance of this in HF is unknown.

Methods and Results— We generated a transgenic mouse with conditional, cardiomyocyte-specific NOS1 overexpression (double-transgenic [DT]) and studied cardiac remodeling, myocardial Ca 2+ handling, and contractility in DT and control mice subjected to transverse aortic constriction (TAC). After TAC, control mice developed eccentric hypertrophy with evolution toward HF as revealed by a significantly reduced fractional shortening. In contrast, DT mice developed a greater increase in wall thickness ( P <0.0001 versus control+TAC) and less left ventricular dilatation than control+TAC mice ( P <0.0001 for both end-systolic and end-diastolic dimensions). Thus, DT mice displayed concentric hypertrophy with fully preserved fractional shortening (43.7±0.6% versus 30.3±2.6% in control+TAC mice, P <0.05). Isolated cardiomyocytes from DT+TAC mice had greater shortening, intracellular Ca 2+ transients, and sarcoplasmic reticulum Ca 2+ load ( P <0.05 versus control+TAC for all parameters). These effects could be explained, at least in part, through modulation of phospholamban phosphorylation status.

Conclusions— Cardiomyocyte NOS1 may be a useful target against cardiac deterioration during chronic pressure-overload–induced HF through modulation of calcium cycling.

Constitutive nitric oxide synthases in the heart from hypertrophy to failure

1. Endogenous myocardial nitric oxide (NO) may modulate the transition from adaptive to maladaptive hypertrophy leading to heart failure. This review summarizes the information on the interrelations between the precise localization of NO synthases (NOS) and their regulatory functions within different compartments of the heart. 2. In rodent models of pressure overload or myocardial infarction, the three NOS isoforms (NOS1, NOS2, NOS3) were shown to play a neutral, protective, or even adverse role in myocardial remodelling, depending on the NOS activity, the location of each NOS and their regulators. 3. The analysis of conditions that modulate the expression of NOS1 and NOS3 in the heart according to physiopathological situations, indicated that, beside the level of total NOS activity, unique changes in NO compartmentation secondary to NOS1 or NOS3 subcellular location might be involved in the development of cardiac hypertrophy and failure. 4. Thus, different circuits in NO-signalling pathways in myocardium might be activated and this principle is a key to understand contradictions existing in NO biology in the heart. Unravelling the mechanisms behind the NO, NOS and cardiac function is still an ongoing challenge.

CAPON modulates cardiac repolarization via neuronal nitric oxide synthase signaling in the heart

Congenital long- or short-QT syndrome may lead to life-threatening ventricular tachycardia and sudden cardiac death. Apart from the rare disease-causing mutations, common genetic variants in CAPON, a neuronal nitric oxide synthase (NOS1) regulator, have recently been associated with QT interval variations in a human whole-genome association study. CAPON had been unsuspected of playing a role in cardiac repolarization; indeed, its physiological role in the heart (if any) is unknown. To define the biological effects of CAPON in the heart, we investigated endogenous CAPON protein expression and protein-protein interactions in the heart and performed electrophysiological studies in isolated ventricular myocytes with and without CAPON overexpression. We find that CAPON protein is expressed in the heart and interacts with NOS1 to accelerate cardiac repolarization by inhibition of L-type calcium channel. Our findings provide a rationale for the association of CAPON gene variants with extremes of the QT interval in human populations.

Deficient ryanodine receptor S-nitrosylation increases sarcoplasmic reticulum calcium leak and arrhythmogenesis in cardiomyocytes

Altered Ca(2+) homeostasis is a salient feature of heart disease, where the calcium release channel ryanodine receptor (RyR) plays a major role. Accumulating data support the notion that neuronal nitric oxide synthase (NOS1) regulates the cardiac RyR via S-nitrosylation. We tested the hypothesis that NOS1 deficiency impairs RyR S-nitrosylation, leading to altered Ca(2+) homeostasis. Diastolic Ca(2+) levels are elevated in NOS1(-/-) and NOS1/NOS3(-/-) but not NOS3(-/-) myocytes compared with wild-type (WT), suggesting diastolic Ca(2+) leakage. Measured leak was increased in NOS1(-/-) and NOS1/NOS3(-/-) but not in NOS3(-/-) myocytes compared with WT. Importantly, NOS1(-/-) and NOS1/NOS3(-/-) myocytes also exhibited spontaneous calcium waves. Whereas the stoichiometry and binding of FK-binding protein 12.6 to RyR and the degree of RyR phosphorylation were not altered in NOS1(-/-) hearts, RyR2 S-nitrosylation was substantially decreased, and the level of thiol oxidation increased. Together, these findings demonstrate that NOS1 deficiency causes RyR2 hyponitrosylation, leading to diastolic Ca(2+) leak and a proarrhythmic phenotype. NOS1 dysregulation may be a proximate cause of key phenotypes associated with heart disease.

Effects of sex differences on constitutive nitric oxide synthase expression and activity in response to pressure overload in rats

Clinical studies have documented sex differences in left ventricular (LV) hypertrophy patterns, but the mechanisms are so far poorly defined. This study aimed to determine whether 1) severe pressure overload altered expression and/or activity of cardiac constitutive nitric oxide synthase (NOS1 and NOS3) and 2) these changes were modulated according to sex. Analyses were performed 0.4–20 wk after thoracic aortic constriction (TAC) in male and female Wistar rats. Male rats with TAC exhibited early signs of cardiac dysfunction, as shown by echocardiographic and LV end-diastolic pressure measurements, whereas females with TAC exhibited higher LV hypertrophy (+96% vs. males at 20 wk; P < 0.05). After TAC, cardiac NOS1 expression was rapidly induced (0.4 wk) and stable afterward in males ( P < 0.05 vs. sham groups), whereas it was delayed in females. Accordingly, specific NOS1 activity was increased by 2 wk in male rats with TAC (+122%; P < 0.001 vs. sham groups) and only by 20 wk in females (+220%; P < 0.001 vs. sham groups). NOS1 activity was correlated with NOS1 level. Regarding cardiac NOS3, expression was unaffected by TAC, and the decrease in activity observed at early and late times in male and female rats with TAC, respectively, is shown to be related to NOS3 allosteric regulator caveolin-1 level. The data demonstrated a unique sex-dependent regulation of the constitutive NOSs in response to TAC in rats; such a difference might play a role in the sex-dependent adaptability of the heart in response to pressure overload.

Sympathetic control of heart rate in nNOS knockout mice

Inhibition of neuronal nitric oxide synthase (nNOS) in cardiac postganglionic sympathetic neurons leads to enhanced cardiac sympathetic responsiveness in normal animals, as well as in animal models of cardiovascular diseases. We used isolated atria from mice with selective genetic disruption of nNOS (nNOS(-/-)) and their wild-type littermates (WT) to investigate whether sympathetic heart rate (HR) responses were dependent on nNOS. Immunohistochemistry was initially used to determine the presence of nNOS in sympathetic [tyrosine hydroxylase (TH) immunoreactive] nerve terminals in the mouse sinoatrial node (SAN). After this, the effects of postganglionic sympathetic nerve stimulation (1-10 Hz) and bath-applied norepinephrine (NE; 10(-8)-10(-4) mol/l) on HR were examined in atria from nNOS(-/-) and WT mice. In the SAN region of WT mice, TH and nNOS immunoreactivity was virtually never colocalized in nerve fibers. nNOS(-/-) atria showed significantly reduced HR responses to sympathetic nerve activation and NE (P < 0.05). Similarly, the positive chronotropic response to the adenylate cyclase activator forskolin (10(-7)-10(-5) mol/l) was attenuated in nNOS(-/-) atria (P < 0.05). Constitutive NOS inhibition with L-nitroarginine (0.1 mmol/l) did not affect the sympathetic HR responses in nNOS(-/-) and WT atria. The paucity of nNOS in the sympathetic innervation of the mouse SAN, in addition to the attenuated HR responses to neuronal and applied NE, indicates that presynaptic sympathetic neuronal NO does not modulate neuronal NE release and SAN pacemaking in this species. It appears that genetic deletion of nNOS results in the inhibition of adrenergic-adenylate cyclase signaling within SAN myocytes.

Differential role of S-nitrosylation and the NO-cGMP-PKG pathway in cardiac contractility

The role of nitric oxide (NO) in cardiac contractility is complex and controversial. Several NO donors have been reported to cause positive or negative inotropism. NO can bind to guanylate cyclase, increasing cGMP production and activating PKG. NO may also directly S-nitrosylate cysteine residues of specific proteins. We used the isolated rat heart preparation to test the hypothesis that the differential inotropic effects depend on the degree of NO production and the signaling recruited. SNAP (S-nitroso-N-acetylpenicillamine), a NO donor, increased contractility at 0.1, 1 and 10 microM. This effect was independent of phospholamban phosphorylation, was not affected by PKA inhibition with H-89 (N-[2((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide), but it was abolished by the radical scavenger Tempol (4-hydroxy-[2,2,4,4]-tetramethyl-piperidine-1-oxyl). However, at 100 microM SNAP reduced contractility, effect reversed to positive inotropism by guanylyl cyclase blockade with ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), and abolished by PKG inhibition with KT5823, but not affected by Tempol. SNAP increased tissue cGMP at 100 microM, but not at lower concentrations. Consistently, a cGMP analog also reduced cardiac contractility. Finally, SNAP at 1 microM increased the level of S-nitrosylation of various cardiac proteins, including the ryanodine receptor. This study demonstrates the biphasic role for NO in cardiac contractility in a given preparation; furthermore, the differential effect is clearly ascribed to the signaling pathways involved. We conclude that although NO is highly diffusible, its output determines the fate of the messenger: low NO concentrations activate redox processes (S-nitrosylation), increasing contractility; while the cGMP-PKG pathway is activated at high NO concentrations, reducing contractility.

17beta-estradiol regulates constitutive nitric oxide synthase expression differentially in the myocardium in response to pressure overload

Estrogens [E(2)] exert direct and indirect effects that can modulate the development of cardiac disease. However, the precise mechanisms that are involved remain undefined. Our objective was to investigate whether E(2) affected the activity and expression of constitutive nitric oxide synthase (NOS) isoforms (NOS3 and NOS1) in cardiac hypertrophy induced by thoracic aortic constriction (TAC). Ovariectomized (Ovx) and nonovariectomized Wistar rats were subjected to TAC. Ovx animals received E(2) or placebo 3 wk after surgery for 11 wk. Afterward cardiac function and degree of left ventricular hypertrophy were assessed by echocardiography. NOS activity and expression were studied by biochemical techniques. TAC led to significant left ventricular hypertrophy (>90%) irrespective of hormonal status. Cardiac performance declined more in TAC+Ovx (-20%, P < 0.015) than in the two other TAC groups [TAC and TAC+Ovx+E(2)]. Total NOS activity decreased significantly in the Ovx groups. In response to TAC, total NOS activity increased whatever the E(2) status. Specific NOS3 activity dramatically decreased in the Ovx groups (-55%, P < 0.009) and was unaltered by TAC. By using coimmunoprecipitation assays, we showed that NOS3/caveolin-1 complexes negatively regulated NOS3 activity as a function of E(2) status. On the other hand, NOS1 expression and activity were markedly increased in hypertrophied myocardium (P < 0.003), irrespective of E(2) status. This study demonstrates a differential regulation of NOS expression and activity in response to pressure overload and E(2) status, the former being mainly involved in the induction of NOS1, whereas the latter regulated NOS3 activity and in turn cardiac function.

Atrial Glutathione Content, Calcium Current, and Contractility

Atrial fibrillation (AF) is characterized by decreased L-type calcium current (I(Ca,L)) in atrial myocytes and decreased atrial contractility. Oxidant stress and redox modulation of calcium channels are implicated in these pathologic changes. We evaluated the relationship between glutathione content (the primary cellular reducing moiety) and I(Ca,L) in atrial specimens from AF patients undergoing cardiac surgery. Left atrial glutathione content was significantly lower in patients with either paroxysmal or persistent AF relative to control patients with no history of AF. Incubation of atrial myocytes from AF patients (but not controls) with the glutathione precursor N-acetylcysteine caused a marked increase in I(Ca,L). To test the hypothesis that glutathione levels were mechanistically linked with the reduction in I(Ca,L), dogs were treated for 48 h with buthionine sulfoximine, an inhibitor of glutathione synthesis. Buthionine sulfoximine treatment resulted in a 24% reduction in canine atrial glutathione content, a reduction in atrial contractility, and an attenuation of I(Ca,L) in the canine atrial myocytes. Incubation of these myocytes with exogenous glutathione also restored I(Ca,L) to normal or greater than normal levels. To probe the mechanism linking decreased glutathione levels to down-regulation of I(Ca), the biotin switch technique was used to evaluate S-nitrosylation of calcium channels. S-Nitrosylation was apparent in left atrial tissues from AF patients; the extent of S-nitrosylation was inversely related to tissue glutathione content. S-Nitrosylation was also detectable in HEK cells expressing recombinant human cardiac calcium channel subunits following exposure to nitrosoglutathione. S-Nitrosylation may contribute to the glutathione-sensitive attenuation of I(Ca,L) observed in AF.