Myocardial calcium-independent nitric oxide synthase activity is present in dilated cardiomyopathy, myocarditis, and postpartum cardiomyopathy but not in ischaemic or valvar heart disease

Leukocyte iNOS is required for inflammation and pathological remodeling in ischemic heart failure

In the failing heart, iNOS is expressed by both macrophages and cardiomyocytes. We hypothesized that inflammatory cell-localized iNOS exacerbates left ventricular (LV) remodeling. Wild-type (WT) C57BL/6 mice underwent total body irradiation and reconstitution with bone marrow from iNOS^-/- mice (iNOS^-/-c) or WT mice (WTc). Chimeric mice underwent coronary ligation to induce large infarction and ischemic heart failure (HF), or sham surgery. After 28 days, as compared with WTc sham mice, WTc HF mice exhibited significant (p < 0.05) mortality, LV dysfunction, hypertrophy, fibrosis, oxidative/nitrative stress, inflammatory activation, and iNOS upregulation. These mice also exhibited a ~twofold increase in circulating Ly6C^hi pro-inflammatory monocytes, and ~sevenfold higher cardiac M1 macrophages, which were primarily CCR2^- cells. In contrast, as compared with WTc HF mice, iNOS^-/-c HF mice exhibited significantly improved survival, LV function, hypertrophy, fibrosis, oxidative/nitrative stress, and inflammatory activation, without differences in overall cardiac iNOS expression. Moreover, iNOS^-/-c HF mice exhibited lower circulating Ly6C^hi monocytes, and augmented cardiac M2 macrophages, but with greater infiltrating monocyte-derived CCR2⁺ macrophages vs. WTc HF mice. Lastly, upon cell-to-cell contact with naïve cardiomyocytes, peritoneal macrophages from WT HF mice depressed contraction, and augmented cardiomyocyte oxygen free radicals and peroxynitrite. These effects were not observed upon contact with macrophages from iNOS^-/- HF mice. We conclude that leukocyte iNOS is obligatory for local and systemic inflammatory activation and cardiac remodeling in ischemic HF. Activated macrophages in HF may directly induce cardiomyocyte contractile dysfunction and oxidant stress upon cell-to-cell contact; this juxtacrine response requires macrophage-localized iNOS.

β-Adrenergic signaling and response to pressure overload in transgenic mice with cardiac-specific overexpression of inducible NO synthase

The role of iNOS induction in the context of cardiac hypertrophy and heart failure is still not fully understood. We have used transgenic mice with cardiac specific overexpression of iNOS (tg-iNOS) to investigate the consequences of high level NO formation on cardiac function in vivo and the response to chronic pressure overload. Conductance manometry was used to analyze cardiac function of wild type (WT) and tg-iNOS mice under basal conditions and β-adrenergic stimulation. To investigate the influence of iNOS on cardiac function in hypertrophied hearts, transversal aortic constriction was performed. Despite a high level of cardiac NO formation tg-iNOS mice showed almost normal LV function under basal conditions. The cardiac response to β-adrenergic stimulation, however, was completely abolished. Acute NOS inhibition led to an instantaneous recovery of the inotropic response to catecholamines in tg-iNOS mice. Chronic pressure overload induced a similar extent of cardiac hypertrophy in WT and tg-iNOS hearts. LV function, however, was more compromised in tg-iNOS hearts as revealed by a decreased contractility and cardiac output.

IN CONCLUSION

a high level of cardiac NO formation does not induce heart failure per se but severely enhances the functional depression in response to pressure overload. This effect could be due to the tonic impairment of the cardiac β-adrenergic response.

Gene transfer as a strategy to achieve permanent cardioprotection I: rAAV-mediated gene therapy with inducible nitric oxide synthase limits infarct size 1 year later without adverse functional consequences

The ultimate goal of prophylactic gene therapy is to confer permanent protection against ischemia. Although gene therapy with inducible nitric oxide synthase (iNOS) is known to protect against myocardial infarction at 3 days and up to 2 months, the long-term effects on myocardial ischemic injury and function are unknown. To address this issue, we created a recombinant adeno-associated viral vector carrying the iNOS gene (rAAV/iNOS), which enables long-lasting transgene expression. The ability of rAAV/iNOS to direct the expression of functional iNOS protein was confirmed in COS-7 cells before in vivo gene transfer. Mice received injections in the anterior LV wall of rAAV/LacZ or rAAV/iNOS; 1 year later, they underwent a 30-min coronary occlusion (O) and 4 h of reperfusion (R). iNOS gene transfer resulted in elevated iNOS protein expression (+3-fold vs. the LacZ group, n = 6; P < 0.05) and iNOS activity (+4.4-fold vs. the LacZ group, n = 6; P < 0.05) 1 year later. Infarct size (% of risk region) was dramatically reduced at 1 year after iNOS gene transfer (13.5 ± 2.2%, n = 12, vs. 41.7 ± 2.9%, n = 10, in the LacZ group; P < 0.05). The infarct-sparing effect of iNOS gene therapy at 1 year was as powerful as that observed 24 h after ischemic preconditioning (six 4-min O/4-min R cycles) (19.3 ± 2.3%, n = 11; P < 0.05). Importantly, compared with the LacZ group (n = 11), iNOS gene transfer (n = 10) had no effect on LV dimensions or function for up to 1 year (at 1 year: FS 34.5 ± 2.0 vs. 34.6 ± 2.6%, EF 57.0 ± 2.0 vs. 59.7 ± 2.9%, LVEDD 4.3 ± 0.1 vs. 4.2 ± 0.2 mm, LVESD 2.8 ± 0.1 vs. 2.9 ± 0.2 mm) (echocardiography). These data demonstrate, for the first time, that rAAV-mediated iNOS gene transfer affords long-term, probably permanent (1 year), cardioprotection without adverse functional consequences, providing a strong rationale for further preclinical testing of prophylactic gene therapy.

Heart failure treatment in the intensive care unit in children

Although pediatric heart failure is generally a chronic, progressive disorder, recovery of ventricular function may occur with some forms of cardiomyopathy. Guidelines for the management of chronic heart failure in adults and children have recently been published by the International Society for Heart and Lung Transplantation the American College of Cardiology, and the American Heart Association. The primary aim of heart failure therapy is to reduce symptoms, preserve long-term ventricular performance, and prolong survival primarily through antagonism of the neurohormonal compensatory mechanisms. Because some medications may be detrimental during an acute decompensation, physicians who manage these patients as inpatients must be knowledgeable about the medications and therapeutic goals of chronic heart failure treatment. Understanding the mechanisms of chronic heart failure may foster improved understanding of the treatment of decompensated heart failure.

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.

Hormones and postpartum cardiomyopathy

Prolactin, a hormone fundamental for lactation, was recently shown to mediate postpartum cardiomyopathy, a life-threatening disease in late-term and lactating mothers. The detrimental effect of prolactin results from myocardial upregulation of cathepsin-D, which in turn cleaves prolactin to a 16 kDa fragment (vasoinhibin) with anti-angiogenic and pro-apoptotic properties that impair developing cardiac vasculature.

Sustained nitric oxide synthesis contributes to immunopathology in ongoing myocarditis attributable to interleukin-10 disorders

Ongoing coxsackievirus B3 (CVB3) myocarditis is characterized by persistence of viral RNA and chronic inflammation primarily mediated by macrophages and T cells. Activated macrophages produce anti-viral effector molecules comprising reactive nitrogen intermediates; however, reactive nitrogen intermediates also contribute to host tissue damage. Controlled activation of macrophages depends on interferon (IFN)-gamma and interleukin (IL)-10. To evaluate mechanisms involved in CVB3-induced pathogenesis of myocarditis, we determined the relationship of inducible nitric-oxide synthase (iNOS) mRNA expression with IFN-gamma and IL-10 secretion during CVB3 infection in different mouse strains. We found in susceptible A.BY/SnJ mice that develop ongoing myocarditis, a low and delayed IFN-gamma secretion and highly diminished IL-10 production compared with resistant C57BL/6 mice. Consequently, iNOS mRNA synthesis was delayed but clearly prolonged in susceptible mice. IL-10 gene-deficient mice confirmed the regulatory role of IL-10 in the outcome of CVB3 myocarditis. These mice did not establish a persistent cardiac infection and revealed IFN-gamma secretion kinetics similar to resistant mice but showed a slightly elongated cardiac iNOS mRNA expression resulting in extended myocarditis. We conclude that coordinated secretion of IFN-gamma and IL-10 is crucial for the effective resolution of CVB3 myocarditis. Moreover, lack of regulatory IL-10 leads to uncontrolled iNOS mRNA production, thus contributing to ongoing myocardial injury.

Increased nitration of sarcoplasmic reticulum Ca2+-ATPase in human heart failure

BACKGROUND

Reduced sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a isoform) activity is a major determinant of reduced contractility in heart failure. Ca2+-ATPase inactivation can occur through SERCA2a nitration. We therefore investigated the role of SERCA2a nitration in heart failure.

METHODS AND RESULTS

We measured SERCA2a levels and nitrotyrosine levels in tissue from normal and failing human hearts using Western blots. We found that nitrotyrosine levels in idiopathic dilated cardiomyopathic (DCM) hearts were almost double those of control hearts in age-matched groups. Nitrotyrosine was dominantly present in a single protein with the molecular weight of SERCA2a, and immunoprecipitation confirmed that the protein recognized by the nitrotyrosine antibody was SERCA2a. There was a positive correlation between the time to half relaxation and the nitrotyrosine/SERCA2a content (P<0.01) in myocytes isolated from control and DCM hearts. In experiments with isolated SR vesicles from porcine hearts, we also showed that the Ca pump is inactivated by peroxynitrite exposure, and inactivation was prevented by protein kinase A pretreatment.

CONCLUSIONS

We conclude that SERCA2a inactivation by nitration may contribute to Ca pump failure and hence heart failure in DCM.

Deficiency of iNOS does not attenuate severe congestive heart failure in mice

Inducible nitric oxide synthase (iNOS) has been implicated in the pathophysiology of congestive heart failure (CHF). Given the extensive evidence supporting this concept, we hypothesized that iNOS deficiency (iNOS−/−) would attenuate the severity of CHF in mice. Mice were subjected to permanent occlusion [myocardial infarction (MI)] of the proximal left anterior descending coronary artery to produce CHF. Cardiac function was assessed in vivo using echocardiography and ultraminiature ventricular pressure catheters. Sham wild-type ( n = 17), sham iNOS−/− ( n = 8), MI wild-type ( n = 56), and MI iNOS−/− ( n = 48) mice were subjected to MI (or sham MI) and followed for 1 mo. Deficiency of iNOS did not alter survival during CHF compared with wild type (35% vs. 32%, P = not significant). Furthermore, fractional shortening and cardiac output were not significantly different between wild-type (9.6 ± 2.0% and 441 ± 20 μl·min−1·g−1) and iNOS−/− (9.8 ± 1.3% and 471 ± 26 μl·min−1·g−1) mice. The extent of cardiac hypertrophy and pulmonary edema was also similar between wild-type and iNOS−/− mice. None of the indexes demonstrated any significant differences between iNOS−/− and wild-type mice subjected to MI. These findings indicate that deficiency of iNOS does not significantly affect severe CHF in mice after MI.

Expression of inducible nitric oxide synthase is increased in patients with heart failure due to ischemic disease

The objective of the present study was to determine the relationship between nitric oxide synthases (NOS) and heart failure in cardiac tissue from patients with and without cardiac decompensation. Right atrial tissue was excised from patients with coronary artery disease (CAD) and left ventricular ejection fraction (LVEF) <35% (N = 10), and from patients with CAD and LVEF >60% (N = 10) during cardiac surgery. NOS activity was measured by the conversion of L-[H(3)]-arginine to L-[H(3)]-citrulline. Gene expression was quantified by the competitive reverse transcription-polymerase chain reaction. Both endothelial NOS (eNOS) activity and expression were significantly reduced in failing hearts compared to non-failing hearts: 0.36 +/- 0.18 vs 1.51 +/- 0.31 pmol mg-1 min-1 (P < 0.0001) and 0.37 +/- 0.08 vs 0.78 +/- 0.09 relative cDNA absorbance at 320 nm (P < 0.0001), respectively. In contrast, inducible NOS (iNOS) activity and expression were significantly higher in failing hearts than in non-failing hearts: 4.00 +/- 0.90 vs 1.54 +/- 0.65 pmol mg-1 min-1 (P < 0.0001) and 2.19 +/- 0.27 vs 1.43 +/- 0.13 cDNA absorbance at 320 nm (P < 0.0001), respectively. We conclude that heart failure down-regulates both eNOS activity and expression in cardiac tissue from patients with LVEF <35%. In contrast, iNOS activity and expression are increased in failing hearts and may represent an alternative mechanism for nitric oxide production in heart failure due to ischemic disease.

Mitochondrial respiratory abnormalities in patients with end-stage congenital heart disease

BACKGROUND

Nitric oxide (NO) binds to mitochondrial cytochrome oxidase to decrease myocardial oxygen consumption (MVO(2)). This regulation is disrupted in heart failure (HF) due to reduced NO. The present objective was to evaluate NO-mediated regulation of mitochondrial respiration in the myocardium of patients with congenital heart disease (CHD) and cardiomyopathy (CMP).

METHODS

MVO(2) was measured in vitro in explanted human myocardium obtained at transplantation. Seven patients had CHD (5 cyanotic, 2 acyanotic), and 11 had non-ischemic CMP. The effects of the following on MVO(2) were measured: kinin-dependent endothelial NO synthase (eNOS) agonists, bradykinin, ramiprilat and amlodipine; NO donors, nitroglycerin and S-nitroso-N-acetylpenicillamine (SNAP) (10(-7) to 10(-4) mol/liter); and NOS inhibitor, N(omega)-nitro-L-arginine methylester (L-NAME).

RESULTS

eNOS agonists caused a smaller decrease in MVO(2) in CHD compared with CMP patients. Changes in MVO(2) at the highest dose in CHD vs CMP were, respectively: bradykinin, -22 +/- 7% vs: -30 +/- 5% (p < 0.05); ramiprilat, -17 +/- 8% vs -26 +/- 2%, (p < 0.001); and amlodipine, -5 +/- 7% vs -29 +/- 6% (p < 0.001). L-NAME attenuated the effect of bradykinin, ramiprilat and amlodipine in both groups, confirming that the drug effect was secondary to eNOS activation. Nitroglycerin and SNAP also caused smaller decreases in MVO(2) in CHD vs CMP (NTG -16 +/- 6% vs -37 +/- 4%, SNAP -37 +/- 4% vs -49 +/- 3%, [p < 0.01]), suggesting altered mitochondrial function in CHD.

CONCLUSIONS

Abnormal regulation of MVO(2) in end-stage CMP may be secondary to reduced endogenous NO availability and can be reversed by the use of NO agonists. In end-stage CHD, this abnormality may be related in part to abnormal mitochondrial function.

Myocyte Nitric Oxide Synthase 2 Contributes to Blunted β-Adrenergic Response in Failing Human Hearts by Decreasing Ca 2+ Transients

BACKGROUND

Human heart failure (HF) usually exhibits blunted response to beta-adrenergic receptor (AR) stimulation. Here, we examined whether expression of nitric oxide synthase-2 (NOS2, or inducible NOS) contributes to this loss of inotropic reserve in human HF.

METHODS AND RESULTS

Failing human hearts were obtained at transplantation. Contraction and [Ca2+]i measurements were performed in isolated cardiac myocytes and trabeculae. In HF myocytes and muscle, isoproterenol (ISO), a beta-AR agonist, led to small inotropic and lusitropic responses. Specific inhibition of NOS2 by aminoguanidine (AG) or L-NIL dramatically increased the ISO-induced inotropy and lusitropy, such that the ISO+AG response in HF approached that seen with ISO alone in nonfailing human myocytes or muscles. Ca2+ transient data directly paralleled these results, indicating that altered cellular Ca2+ handling is responsible. In nonfailing human hearts, NOS2 inhibition had no effects. In addition, NOS2 inhibition also had no effect in 30% of failing hearts, but in these myocytes and muscles, the ISO response alone was similar to that of nonfailing hearts. In line with these functional findings, NOS2 protein expression measured by Western blotting was induced in HF when AG/L-NIL had a functional effect but not when AG/L-NIL had no effect on contractility and Ca2+ transients.

CONCLUSIONS

NOS2 expression strongly limited ISO-induced increases in contraction, twitch Delta[Ca2+]i, and lusitropy in trabeculae and isolated myocytes from failing human hearts. Thus, the beta-AR hyporesponsiveness in human HF is mediated in large part by NO (or related congeners) produced within cardiac myocytes via NOS2.

Myoglobin protects the heart from inducible nitric-oxide synthase (iNOS)-mediated nitrosative stress

The role of inducible nitric-oxide synthase (iNOS) in the pathogenesis of heart failure is still a matter of controversy. In contrast to early reports favoring a contribution of iNOS because of the negative inotropic and apoptotic potential of NO, more recent clinical and experimental data question a causative role. Here we report that transgenic mice with cardiac specific iNOS-overexpression and concomitant myoglobin-deficiency (tg-iNOS+/myo-/-) develop signs of heart failure with cardiac hypertrophy, ventricular dilatation, and interstitial fibrosis. In addition, reactivation of the fetal gene expression program typical for heart failure occurs. The structural and molecular changes are accompanied by functional depression such as reduced contractility, ejection fraction, and cardiac energetics. Our findings indicate that excessive cardiac NO formation can cause heart failure; however, under normal circumstances myoglobin constitutes the important barrier that efficiently protects the heart from nitrosative stress.

Effect of the Asp298 variant of endothelial nitric oxide synthase on survival for patients with congestive heart failure

BACKGROUND

Significant variation exists within the endothelial nitric oxide synthase (NOS3) gene that may influence cardiovascular risk. The Asp298 variant of NOS3 has a shorter half-life in endothelial cells. Given the importance of nitric oxide in the heart failure syndrome, we evaluated the effect of this variant on event-free survival in a population with systolic dysfunction.

METHODS AND RESULTS

Four hundred sixty-nine patients (72% male, 49% ischemic; mean age, 56+/-12 years) with systolic dysfunction (left ventricular ejection fraction < or =0.45) were enrolled in a study of Genetic Risk Assessment of Cardiac Events (GRACE). The polymorphism in exon 7 of NOS3, a G-T transition at position 894 that results in a Glu to Asp amino acid substitution for codon 298, was genotyped and subjects were followed prospectively to the end point of death or heart transplantation. Event-free survival was compared on the basis of the presence (group 1, n=266) or absence (group 2, n=203) of the Asp298 variant. Event-free survival was significantly poorer in patients with the Asp298 variant (percent event-free survival group 1 at 1/2/3 years=78/65/54; group 2=82/72/64, P=0.03). In subset analysis, the adverse impact of the Asp298 variant was primarily in patients with nonischemic cardiomyopathy (group 1=82/73/63; group 2=87/79/71, P=0.03) and was not apparent among patients with ischemic heart disease (group 1=75/59/47; group 2=74/62/54, P=0.71).

CONCLUSIONS

For patients with heart failure caused by systolic function, the Asp298 variant of NOS3 is associated with poorer event-free survival, particularly in patients with nonischemic cardiomyopathy.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Nitric oxide, cell death, and heart failure

Strong evidence links cardiomyocyte loss to the pathology of some forms of heart failure. Both necrotic and apoptotic modes of cell death have been invoked as the mechanism underlying progressive cardiomyocyte dropout. Nitric oxide (NO) has received particular attention as a candidate reactive oxygen intermediate that influences not only cardiac function, but also cell death elicited by both apoptotic and necrotic mechanisms. NO is produced by resident cardiac cells under stress, and is produced in large quantities by activated immune cells that infiltrate the injured heart. A review of the literature, however, reveals that the actions of NO on apoptotic cell death are complex, especially in the context of heart disease, and that the practical contribution of NO to cell death in heart disease is yet to be defined.

Nitric oxide production is maintained in exercising swine with chronic left ventricular dysfunction

Left ventricular (LV) dysfunction caused by myocardial infarction (MI) is accompanied by endothelial dysfunction, most notably a loss of nitric oxide (NO) availability. We tested the hypothesis that endothelial dysfunction contributes to impaired tissue perfusion during increased metabolic demands as produced by exercise, and we determined the contribution of NO to regulation of regional systemic, pulmonary, and coronary vasomotor tone in exercising swine with LV dysfunction produced by a 2- to 3-wk-old MI. LV dysfunction resulted in blunted systemic and coronary vasodilator responses to ATP, whereas the responses to nitroprusside were maintained. Exercise resulted in blunted systemic and pulmonary vasodilator responses in MI that resembled the vasodilator responses in normal (N) swine following blockade of NO synthase with N(omega)-nitro-L-arginine (L-NNA, 20 mg/kg iv). However, L-NNA resulted in similar decreases in systemic (43 +/- 3% in N swine and 49 +/- 4% in MI swine), pulmonary (45 +/- 5% in N swine and 49 +/- 4% in MI swine), and coronary (28 +/- 4% in N and 35 +/- 3% in MI) vascular conductances in N and MI swine under resting conditions; similar effects were observed during treadmill exercise. Selective inhibition of inducible NO synthase with aminoguanidine (20 mg/kg iv) had no effect on vascular tone in MI. These findings indicate that while agonist-induced vasodilation is already blunted early after myocardial infarction, the contribution of endothelial NO synthase-derived NO to regulation of vascular tone under basal conditions and during exercise is maintained.

Cardiac-specific overexpression of inducible nitric oxide synthase does not result in severe cardiac dysfunction

Nitric oxide (NO), a potent regulator of myocardial contractility, has been implicated in the development of heart failure; however, no study exists describing the relation between expression of inducible nitric oxide synthase (iNOS), formation of NO in vivo, and cardiac contractility. We have therefore generated transgenic (TG) mice overexpressing iNOS under the cardiospecific alpha-myosin heavy chain (alpha-MHC) promoter. In vitro, iNOS activity in hearts of two transgenic lines was 260- to 400-fold above controls (wild type [WT]), but TG mice were viable and appeared normal. Ventricular mass/body weight ratio did not differ; heart rate and cardiac output as well as mean arterial blood pressure were decreased by 10%. NO(x) levels of hearts and blood of TG mice were 2.5- and 2-fold above WT controls, respectively. In the isolated heart, release of the NO oxidation products nitrate and nitrite, an index of in vivo NOS activity, was 40-fold over WT. However, cardiac hemodynamics and levels of ATP and phosphocreatine were unaltered. The high iNOS activity was associated with reduced cardiac L-arginine in TG hearts to only 15% of the WT, indicating limited substrate availability, whereas L-citrulline was 20-fold elevated. Our findings demonstrate that the heart can tolerate high levels of iNOS activity without detrimental functional consequences. The concept that iNOS-derived NO is the triggering factor in the pathomechanism leading to heart failure therefore needs to be reevaluated.

Elevated interleukin-1beta in pericardial fluid of patients with ischemic heart disease

BACKGROUND

Inflammatory cytokines may play an important role in the pathogenesis of atherosclerosis and heart failure. We have previously demonstrated that long-term treatment with interleukin (IL)-1beta in the coronary artery and myocardium promotes coronary arteriosclerosis and impairs cardiac function, respectively. The cytokines in pericardial fluid may reflect the extent of coronary atherosclerosis and may also directly promote the atherosclerotic process. This study was designed to examine the significance of cytokine concentrations in pericardial fluid of patients with cardiovascular disease.

METHODS

We measured concentrations of 10 major cytokines in the pericardial fluid of 56 consecutive patients obtained during open heart surgery, 27 with ischemic heart disease (IHD group), 21 with valvular heart disease (VHD group) and eight with congenital heart disease (CHD group).

RESULTS

The pericardial concentrations of IL-1beta (pg/ml) were significantly higher in the IHD group (60 +/- 15) than in the VHD (29 +/- 5) or the CHD group (26 +/- 4) (P < 0.05 both). There was no significant difference in pericardial concentrations of other cytokines among the three groups. In the IHD group, the IL-1beta concentrations were significantly elevated in patients who had undergone emergency operations or in those with unstable angina.

CONCLUSIONS

These results suggest that pericardial concentrations of IL-1beta may reflect the extent of ischemic heart disease and that elevated IL-1beta concentrations in pericardial fluid may also directly promote the process of coronary atherosclerosis.

Nitric oxide: not just a negative inotrope

Nitric oxide (NO) appears to play a role in modulating cardiac function in both health and disease. Early studies in isolated rodent cardiac myocytes demonstrated a depressant effect of NO supplied by NO donors (exogenous) as well as NO generated within myocytes (endogenous). There is increasing evidence for a functional NO generating system within the human myocardium, which appears upregulated in certain disease states. Induction of the high output nitric oxide synthase isoform (iNOS) has been demonstrated in the failing myocardium, though its functional significance remains unproven. More recently published data have contradicted the notion that NO acts solely as a negative inotrope demonstrating positive inotropy in both isolated rodent and human ventricular myocytes in response to a range of NO donors. Different NO donors have different NO release kinetics and generate a range of NO species (NO., NO+ and NO-) which may interact at a number of subcellular targets. The observed response of any cardiac preparation to an NO donor represents the net effect of activation of different effector targets and may explain the contradictory reported effects of NO. To realise the therapeutic potential of NO will require specific targeting at a subcellular level.

Ets-1 is involved in transcriptional regulation of the chick inducible nitric oxide synthase gene in embryonic ventricular myocytes

In order to elucidate roles of Ets family of transcription factors in transcriptional activation of inducible nitric oxide synthase (iNOS) genes, we analyzed the chick iNOS gene expression in cultured chick embryonic ventricular myocytes (CEVM). Deletional analysis and site-directed mutagenesis demonstrated that both the Ets/PEA3 site (-221 to -216 bp) and the kappaB site (-101 to -93 bp) of the 5'-flanking region of the chick iNOS gene were involved in the maximal activation of the lipopolysaccharide (LPS)-induced expression of the reporter (luciferase) gene, although the proximal kappaB site played the more essential role. Electrophoretic mobility shift assay revealed that LPS augmented the nuclear protein bindings to the Ets/PEA3 as well as kappaB motifs. Ets-1, one of the Ets proteins, was suggested to be bound to the Ets/PEA3 oligonucleotide. By Northern blot analysis, LPS was shown to induce iNOS mRNA in CEVM, along with a preceding increase in the levels of c-ets-1 mRNA. Ets-1 may be involved in the iNOS gene transcription in CEVM, presumably through interacting with the NF-kappaB.

The role of interleukin-1 in the failing heart

The prevalence of congestive heart failure and its continued poor prognosis despite presently available therapeutic options emphasize the importance of pursuing the observations suggesting an important role for an immunomodulatory approach to decompensated cardiac failure. Furthermore, there are several pieces of background information that suggest that cytokines like IL-1 may play a significant role in the pathogenesis of several forms of myocardial dysfunction. Although it seems clear that IL-1 is not acting alone under circumstances of myocardial injury, but in concert with other pro-inflammatory molecules and their effectors, we believe that continued investigations into the cytokine hypothesis will ultimately increase the understanding of how pro-inflammatory molecules influence myocardial function and how the modulation of such factors may improve the myocardial response to injury. The specific observations that emphasize the importance of pursuing a substantive role for IL-1 in this process are: (1) IL-1 is elevated in several cardiac disease states, (2) IL-1 is produced by myocardial cells themselves in response to injury, (3)The alterations in gene expression seen in response IL-1 resembles in many ways the phenotype of the failing heart, and (4) The co-localization of the IL-1 response with that of several previously described negative transcriptional regulators (making them potential targets for therapeutic manipulation).

Interactions between nitric oxide and lipid oxidation pathways: implications for vascular disease

Nitric oxide ((.)NO) signaling pathways and lipid oxidation reactions are of central importance in both the maintenance of vascular homeostasis and the progression of vascular disease. Because both of these pathways involve free radical species that can also react together at extremely fast rates, convergent interactions between these pathways are expected. Biochemical and cell biology studies have defined multiple interactions of (.)NO with oxidizing lipids that could lead to either vascular protection or potentiation of inflammatory vascular injury. For example, low levels of (.)NO generated by endothelial nitric oxide synthase can terminate propagating lipid radicals and inhibit lipoxygenases, reactions that would be protective. Alternatively, if generated at elevated levels, for example, after inducible nitric oxide synthase expression in inflammation, (.)NO can be converted to prooxidant species, such as peroxynitrite (ONOO(-)) and nitrogen dioxide ((.)NO(2)), that can potentiate inflammatory injury to vascular cells. Finally, both enzymatic and nonenzymatic lipid oxidation reactions can influence (.)NO bioactivity by directly scavenging (.)NO or altering the induction and catalytic activity of nitric oxide synthase enzymes. In this review, we summarize the biochemical interactions between (.)NO and lipid oxidation reactions and discuss the recognized and potential roles of these reactions in the vasculature.

Molecular Aspects of Myocarditis

Myocarditis is an acquired form inflammatory heart muscle disease, manifested as acute and chronic conditions. While many etiologies have been reported, the most common cause of this disease is infection, primarily viral. Typically, the specific causative agent(s) and mechanism(s) are elusive. Over the past several years, various new findings have added to our understanding of myocarditis. These include the identification of adenoviruses as important causative agents, a new receptor protein likely to play an important role in the virulence of certain agents affecting the myocardium, and the effect of viruses on the cardiac cytoskeleton. This report reviews the current understanding of myocarditis, proposes a hypothesis about the long-term sequelae, and suggests possible new therapeutic strategies.

The role of tumor necrosis factor alpha in the pathophysiology of congestive heart failure

A variety of clinical and experimental investigations have suggested that tumor necrosis factor alpha (TNF-alpha) may play a role in the pathophysiology of heart failure. Serum levels of TNF-alpha are elevated in patients with heart failure, and both cardiac and infiltrating cells of the myocardium can produce this proinflammatory cytokine. Both cardiac myocytes and nonmyocytes also express receptors for TNF-alpha, and experimental studies on isolated cells, muscles, and transgenic models demonstrate the ability of TNF-alpha to recapitulate functional and biochemical alterations resembling that observed in human congestive heart failure. The intracellular pathways affected by TNF-alpha include production of ceramide and an alteration in calcium metabolism. Recent studies in both animal models and clinical investigations suggest that anti-TNF-alpha therapies may limit the pathophysiologic consequences of congestive heart failure.

A prospective study of plasma nitrates following human heart transplantation-relevance to myocardial function

BACKGROUND

Nitric oxide (NO) has been shown to affect myocardial function in positive and negative inotropic ways. Expression of inducible nitric oxide synthase and release of nitric oxide into the circulation has been associated with acute rejection in animal studies. The role of NO and the associated myocardial dysfunction seen during acute rejection in humans has not been adequately defined. In a prospective sequential study, we have studied the relationship between plasma nitrate and biopsy-proven acute rejection, and systolic and diastolic function after heart transplantation.

METHODS

Biopsies were performed weekly and then fortnightly up to 12 weeks after transplantation and on clinical indication of rejection in 37 patients. Plasma nitrates were obtained on the morning of each biopsy (total 341). An echocardiogram was performed immediately prior to each biopsy in which the systolic parameters, ejection fraction (EF) and fractional shortening (fs), and the diastolic parameters, isovolumetric relaxation time (IVRT), mitral valve pressure half-time (MVPHT), mitral valve deceleration time (MVDT), e:a ratio, and a wave duration, were measured.

RESULTS

Plasma-nitrate level showed no significant correlation with the systolic parameters, EF or fs, or with changes in EF or fs. No significant correlation was found between plasma-nitrate level and the diastolic parameters IVRT, MVPHT, MVDT, mitral valve a wave duration, or e:a ratio.

CONCLUSIONS

This study has shown no correlation between plasma nitrate and impaired systolic or diastolic function after heart transplantation. Instead there was a weak trend for elevated nitrate to be associated with better systolic function.

Peripartum cardiomyopathy: analysis of clinical outcome, left ventricular function, plasma levels of cytokines and Fas/APO-1

OBJECTIVES

1) To evaluate the outcome of patients with peripartum cardiomyopathy (PPC) on current treatment for heart failure, 2) to assess the circulating plasma levels of cytokines and Fas receptors and 3) to identify predictors of prognosis.

BACKGROUND

Previous studies in patients with PPC were done when angiotensin-converting enzyme (ACE) inhibitors and beta-adrenergic blocking agents were not routinely used in heart failure. Inflammatory cytokines play an important role in the pathogenesis and progression of heart failure of other etiologies. However, there is a paucity of data regarding cytokine expression in patients with PPC. Plasma concentrations of Fas receptors (an apoptosis-signalling receptor) have not been reported in this population.

METHODS

We followed prospectively 29 consecutive black women with PPC. All patients were treated with diuretics, digoxin, enalapril and carvedilol. Echocardiograms were performed at baseline and after six months of treatment. Cytokine and soluble Fas/APO-1 plasma levels were measured at baseline.

RESULTS

Tumor necrosis factor-alpha, interleukin-6 and Fas/APO-1 levels were significantly elevated in the study patients compared with 20 healthy volunteers. Eight patients died. sFas/APO-1 levels were significantly higher in patients who died compared with survivors (8.98 +/- 4.5 vs. 5.33 +/- 3 U/ml, respectively, p = 0.02). At six months, ejection fraction improved from 26.7 +/- 10 to 42.7 +/- 16%, p = 0.00003, with an increment of more than 10 U in 10 patients (28.1 +/- 4 to 51.9 +/- 8%, p = 0.000008).

CONCLUSIONS

Cytokine and sFas levels are elevated in patients with PPC. Despite treatment with ACE inhibitors and beta-blockers, mortality remains high. However, in 34% of the patients, left ventricular function almost completely normalized.

Inhibition of nitric oxide synthesis improves left ventricular contractility in neonatal pigs late after cardiopulmonary bypass

BACKGROUND

Following neonatal open heart surgery a nadir occurs in left ventricular function six to 12 hours after cardiopulmonary bypass. Although initiated by intraoperative events, little is known about the mechanisms involved.

OBJECTIVE

To evaluate the involvement of nitric oxide in this late phase dysfunction in piglets.

DESIGN

Piglets aged 2 to 3 weeks (4-5 kg) underwent cardiopulmonary bypass (1 h) and cardioplegic arrest (0.5 h) and then remained ventilated with inotropic support. Twelve hours after bypass, while receiving dobutamine (5 microg/kg/min), the left ventricular response to non-selective nitric oxide synthase inhibition (l-N(G)-monomethylarginine (l-NMMA)) was evaluated using load dependent and load independent indices (E(es), the slope of the end systolic pressure-volume relation; M(w), the slope of the stroke work-end diastolic volume relation; [dP/dt(max)](edv), the slope of the dP/dt(max)-end diastolic volume relation), derived from left ventricular pressure-volume loops generated by conductance and microtip pressure catheters.

RESULTS

10 pigs received 7.5 mg l-NMMA intravenously and six of these received two additional doses (37.5 mg and 75 mg). E(es) (mean (SD)) increased with all three doses, from 54.9 (40.1) mm Hg/ml (control) to 86.3 (69.5) at 7.5 mg, 117.9 (65.1) at 37.5 mg, and 119 (80.4) at 75 mg (p < 0.05). At the two highest doses, [dP/dt(max)](edv) increased from 260.8 (209.3) (control) to 470.5 (22.8) at 37.5 mg and 474.1 (296.6) at 75 mg (p < 0.05); and end diastolic pressure decreased from 16.5 (5.6) mm Hg (control) to 11.3 (5.0) at 37.5 mg and 11.4 (4.9) at 75 mg (p < 0. 05).

CONCLUSIONS

In neonatal pigs 12 hours after cardiopulmonary bypass with ischaemic arrest, low dose l-NMMA improved left ventricular function, implying that there is a net deleterious cardiac action of nitric oxide at this time.

Inducible nitric oxide synthase and tumor necrosis factor in animal models of myocardial necrosis induced by coronary artery ligation or isoproterenol injection

BACKGROUND

Increased expression of inducible nitric oxide synthase (iNOS) has been described in humans with cardiomyopathies. Most animal models of ischemia-induced heart failure use the surgical ligation of coronary arteries. However, studies of iNOS expression in these models may be confounded by a robust immune response because of the surgical procedure itself leading to iNOS expression in the heart, as well as in other tissues.

METHODS AND RESULTS

iNOS expression was studied in adult male rats injected subcutaneously with either 250 mg/kg of isoproterenol (ISO) or vehicle on 2 consecutive days. This approach induces diffuse myocardial necrosis and leads to the development of a dilated cardiomyopathy. Hearts from ISO-injected animals harvested at 6 weeks had evidence of apical and subendocardial scarring. These hearts showed a 9.6-fold (left ventricle [LV], P = .004) and an 11.9-fold (right ventricle, P = .002) increase in the expression of tumor necrosis factor (TNF), and a 6.8-fold increase (LV, P = .0183) in iNOS messenger RNA compared with vehicle-injected controls. iNOS protein also was detectable by immmunoprecipitation in left ventricular muscle from ISO-injected animals, as well as by immunohistochemical analysis.

CONCLUSION

Expression of TNF and iNOS in the heart is increased in an experimental model of dilated cardiomyopathy that minimizes the confounding effects of surgery, supporting a role for the activation of innate immunity signaling pathways in the pathogenesis of heart failure.

Induction of myocardial nitric oxide synthase by Coxsackie B3 virus in mice

BACKGROUND

Inducible nitric oxide synthase (iNOS) expression is regulated by cytokines. This study investigated whether Coxsackie group B virus (CVB) myocarditis resulted in an environment suitable for induction of NOS in the murine heart.

MATERIALS AND METHODS

Myocardium was removed from mice infected with CVB3 and from controls. Histology, reverse transcriptase polymerase reaction (RT-PCR) for murine iNOS, NOS enzyme activity and immunohistochemistry were assessed.

RESULTS

Histology revealed severe myocarditis 7 days after infection with CVB3 but not in controls. RT-PCR using primers for murine iNOS detected iNOS mRNA in infected mice but not in controls. Calcium-independent NOS activity increased by day 5 after infection with a peak at day 7. Calcium-dependent NOS activity was present throughout, with a trend to lower levels during peak calcium-independent activity. Immunohistochemistry revealed iNOS to be localized to inflammatory cells rather than to myocytes.

CONCLUSION

This study demonstrates the development of calcium-independent NOS activity and de novo gene transcription for iNOS in the murine myocardium in response to CVB3 infection. The nitric oxide produced at such high output may act at times as part of the immune defence as an antiviral agent and may be toxic to host tissue.

Lipocortin-1 preserves myocardial responsiveness to beta-adrenergic stimulation in rat papillary muscle

1. During septic shock, myocardial contractile dysfunction is accompanied by the release of cytokines and enhanced production of nitric oxide, and the contractile dysfunction is prevented by glucocorticoids. 2. Myocardial dysfunction was induced in vitro by incubation of rat papillary muscle for 15 h with endotoxin (lipopolysaccharide, LPS) and interferon-gamma (IFN-gamma). 3. Both baseline contractile function and inotropic responsiveness to isoprenaline were markedly reduced by the combination of LPS plus IFN-gamma. 4. Lipocortin-1 (LC-1) is induced by glucocorticoids, and LC-1(2-26), its N-terminal fragment, protected the papillary muscle inotropic responsiveness to isoprenaline, but did not affect the decline in baseline contractile function induced by LPS plus IFN-gamma. 5. The mechanisms of this protective action need to be explored further, but LC-1 may prove to be a novel cardioprotective agent for the management of septic shock.

The inducible nitric oxide synthase in vascular and cardiac tissue

Expression of the inducible form of nitric oxide synthase (iNOS) has been reported in a variety of cardiovascular diseases. The resulting high output nitric oxide (NO) formation, besides the level of iNOS expression, depends also on the expression of the metabolic pathways providing the enzyme with substrate and cofactor. NO may trigger short and long term effects which are either beneficial or deleterious, depending on the molecular targets with which it interacts. These interactions are governed by local factors (like the redox state). In the cardiovascular system, the major targets involve not only guanylyl cyclase, but also other haem proteins, protein thiols, iron-non-haem complexes, and superoxide anion (forming peroxynitrite). The latter has several intracellular targets and may be cytotoxic, despite the existence of endogenous defence mechanisms. These interactions may either trigger NO effects or represent releasable NO stores, able to buffer NO and prolong its effects in blood vessels and in the heart. Besides selectively inhibiting iNOS, a number of other therapeutic strategies are conceivable to alleviate deleterious effects of excessive NO formation, including peroxynitrite (ONOO-) scavenging and inhibition of metabolic pathways triggered by ONOO-. When available, these approaches might have the advantage to preserve beneficial effects of iNOS induction. Counteracting vascular hyper-responsiveness to endogenous vasoconstrictor agonists in septic shock, or inducing cardiac protection against ischaemia-reperfusion injury are examples of such beneficial effects of iNOS induction.

Endothelial nitric oxide synthase increases in left atria of dogs with pacing-induced heart failure

In congestive heart failure (CHF) the alterations in cardiac NO synthase (NOS) isoforms activity and expression are incompletely documented and the chamber specificity of these changes is unknown. We studied plasma nitrate-nitrite (NO-x), atrial, and ventricular NOS activities and protein expression (Western blot and densitometric analysis) in nonpaced control dogs and in dogs paced for 2 or 21 days into CHF. Plasma NO-x rose significantly after 7 and 21 days of pacing, whereas creatinine levels remained unchanged. In control dogs Ca2+-dependent NOS activity in left atria was double that of right or left ventricular activity. In paced animals the activity increased only in the atria after 21 but not 2 days of pacing. Levels of endothelial NOS (eNOS) protein were enhanced in the left atria but not ventricles after 21 days of pacing because of a greater quantity of the 150-kDa but not the 135-kDa eNOS. Ca2+-independent NOS activity was undetectable in any cardiac tissue. The specific upregulation of eNOS in the left atria suggests that NO production may be enhanced to counterbalance hypertrophy that develops during pacing-induced CHF.

Influence of nitric oxide on vascular, metabolic, and contractile responses to dobutamine in in situ canine hearts

The left anterior descending coronary arteries of 30 anesthetized, open-chest dogs were perfused via an extracorporeal circuit. Coronary blood flow (CBF), myocardial oxygen consumption (MVO2), and segmental shortening (SS) were measured. Studies were performed with coronary perfusion pressure (CPP) or CBF constant. With CPP constant, effects of intracoronary (IC) infusions of dobutamine (2.5, 5.0, or 10.0 microg/min) were evaluated alone (control) and after inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine methyl ester (L-NAME). With CBF constant, a NO donor (sodium nitroprusside [SNP] 80 microg/min IC) or nitroglycerin [NTG] 40 microg/min IC) or a releaser of endogenous NO (acetylcholine [ACh]; 20 microg/ min IC) was infused along with dobutamine. Increases in CBF during dobutamine and isoproterenol were compared before and after blockade of beta1-adrenergic receptors with atenolol. Dobutamine caused proportional, dose-dependent increases in CBF, MVO2, and SS, which were not altered by L-NAME. Administration of the NO donors or ACh during dobutamine markedly decreased CPP, but only ACh also reduced SS and MVO2. These latter effects persisted after L-NAME. Atenolol blunted increases in CBF by dobutamine more than those by isoproterenol. We conclude that endogenous NO did not modulate the coronary vasodilation or the increases in myocardial contractility and MVO2 during dobutamine. In addition, neither SNP nor NTG altered myocardial contractility or MVO2 in dobutamine-stimulated myocardium, whereas ACh had a negative inotropic effect in dobutamine-stimulated myocardium that was independent of NO.

IMPLICATIONS

Endogenous nitric oxide (NO) did not modulate increases in coronary blood flow, myocardial contractility, or myocardial oxygen consumption during intracoronary infusions of dobutamine. The NO donors sodium nitroprusside and nitroglycerin had no effect on contractility or oxygen consumption in dobutamine-stimulated myocardium. Acetylcholine had negative inotropic effect in dobutamine-stimulated myocardium that was independent of NO.

Increased expression of constitutive nitric oxide synthase III, but not inducible nitric oxide synthase II, in human heart failure

OBJECTIVES

The purpose of the present study was to examine the expression of the endothelial-type nitric oxide synthase (NOS III) and the inducible-type NOS (NOS II) in human myocardium and their regulation in heart failure from patients with different etiologies.

BACKGROUND

In heart failure, plasma levels of nitrates were found to be elevated. However, data on myocardial NOS expression in heart failure are conflicting.

METHODS

Using RNase protection analysis and Western blotting, the expression of NOS III and NOS II was investigated in ventricular myocardium from nonfailing (NF) hearts (n=5) and from failing hearts of patients with idiopathic dilated cardiomyopathy (dCMP, n=14), ischemic cardiomyopathy (iCMP, n=9) or postmyocarditis cardiomyopathy (mCMP, n=7). Furthermore, immunohistochemical studies were performed to localize NOS III and NOS II within the ventricular myocardium.

RESULTS

In failing human hearts, NOS III mRNA levels were increased to 180% in dCMP, 200% in iCMP and to 210% in mCMP as compared to NF hearts. Similarly, in Western blots (using constitutively expressed beta-tubulin as a reference) NOS III protein expression was increased about twofold in failing compared to NF hearts. Immunohistochemical studies with a selective antibody to NOS III showed no obvious differences in the staining of the endothelium of cardiac blood vessels from NF and failing human hearts. However, NOS III-immunoreactivity in cardiomyocytes was significantly more intense in failing compared to NF hearts. Low expression of NOS II mRNA was detected in only 2 of 30 failing human hearts and was not found in NF hearts. Inducible-type NOS protein was undetectable in either group.

CONCLUSIONS

We conclude that the increased NOS III expression in the ventricular myocardium of failing human hearts may contribute to the contractile dysfunction observed in heart failure and/or may play a role in morphologic alterations such as hypertrophy and apoptosis of cardiomyocytes.

Expression, activity and functional significance of inducible nitric oxide synthase in the failing human heart

OBJECTIVES

The study was designed to evaluate the functional impact of nitric oxide (NO) generation within the myocardium on cardiac contraction in the failing human heart.

BACKGROUND

Heart failure is associated with activation of cytokines and expression of inducible nitric oxide synthase (NOS II), which generates NO from L-arginine. Nitric oxide has been shown to modulate myocardial performance, raising the possibility that cardiac generation of NO by NOS II modulates cardiac contraction in the failing human heart.

METHODS

Left ventricular (LV) tissue of 24 patients with end-stage heart failure was obtained during cardiac transplantation. Gene expression of NOS II and endothelial NO-synthase (NOS III) was quantified by competitive reverse transcription-polymerase chain reaction and compared to tissues of five nonfailing donor hearts. Nitric oxide synthase II activity was determined by citrulline assay and related to changes in force of contraction induced by the beta-adrenergic agonist isoproterenol, NO-donors and/or N-mono-methyl-L-arginine (L-NMMA), an inhibitor of NOS.

RESULTS

While NOS III mRNA was reduced in failing hearts, NOS II mRNA was increased in failing LV tissue and correlated with NOS II activity. High NOS II activity was associated with early relaxation and impaired responsiveness to beta-adrenergic stimulation, that is, the inotropic response to isoproterenol in failing hearts was inversely related to NOS II activity (r=0.61, p < 0.005). Nitric oxide donors or L-NMMA did not affect myocardial performance in failing hearts at baseline. However, L-NMMA enhanced the positive inotropic response to beta-adrenergic stimulation in failing hearts with high NOS II activity. Nitric oxide donors attenuated the isoproterenol-induced increase in force of contraction of failing hearts.

CONCLUSIONS

Cardiac production of NO by NOS II attenuates the positive inotropic effects of beta-adrenergic stimulation and hastens relaxation in failing human hearts.

Heterogeneous expression and activity of endothelial and inducible nitric oxide synthases in end-stage human heart failure: their relation to lesion site and beta-adrenergic receptor therapy

BACKGROUND

Recent reports have suggested that excessive amounts of endogenous NO may contribute to the myocardial dysfunction and injury in heart failure. In the present report, we investigate the cellular expression and activity of endothelial (eNOS) and inducible (iNOS) NO synthase in failing human hearts with special reference to the underlying lesion and drug therapy.

METHODS AND RESULTS

Myocardial tissues were obtained from 28 failing human hearts with various pathogeneses and 4 nonfailing hearts as controls. Only weak or focal expression of both eNOS and iNOS was seen in ventricles of nonfailing hearts. In failing hearts, immunoreactivity and hybridization signals for eNOS were increased only in cardiac myocytes of subendocardial areas. Signals for iNOS in cardiac myocytes were consistently seen in heart failure of various pathogeneses and were apparent in both infarcted and noninfarcted regions of ischemic cardiomyopathy. Apparent signals for iNOS were also seen in infiltrating macrophages in infarcted regions of ischemic cardiomyopathy, myocarditis, and septic hearts. The expression of eNOS but not iNOS in the myocytes was intimately associated with beta-adrenergic therapy before the operation, being more abundant in patients on beta-blockers compared with diminished presence in patients on beta-agonists. In contrast to immunohistochemical data, iNOS activity was more variable than constitutive NOS activity and correlated significantly with the density of infiltrating macrophages.

CONCLUSIONS

These results suggest that whereas increased eNOS and/or iNOS expression in failing cardiac myocytes may in general contribute to myocardial dysfunction, myocyte injury or death associated with inflammatory lesions may be caused in part by abundant iNOS expression within infiltrating macrophages rather than cardiac myocytes.

Role of nitric oxide and peroxynitrite in the cytokine-induced sustained myocardial dysfunction in dogs in vivo

Studies in vitro suggested that inflammatory cytokines could cause myocardial dysfunction. However, the detailed mechanism for the cytokine-induced myocardial dysfunction in vivo remains to be examined. We thus examined this point in our new canine model in vivo, in which microspheres with and without IL-1beta were injected into the left main coronary artery. Left ventricular ejection fraction (LVEF) was evaluated by echocardiography for 1 wk. Immediately after the microsphere injection, LVEF decreased to approximately 30% in both groups. While LVEF rapidly normalized in 2 d in the control group, it was markedly impaired in the IL-1beta group even at day 7. Pretreatment with dexamethasone or with aminoguanidine, an inhibitor of inducible nitric oxide synthase, prevented the IL-1beta-induced myocardial dysfunction. Nitrotyrosine concentration, an in vivo marker of the peroxynitrite production by nitric oxide and superoxide anion, was significantly higher in the myocardium of the IL-1beta group than in that of the control group or the group cotreated with dexamethasone or aminoguanidine. There was an inverse linear relationship between myocardial nitrotyrosine concentrations and LVEF. These results indicate that IL-1beta induces sustained myocardial dysfunction in vivo and that nitric oxide produced by inducible nitric oxide synthase and the resultant formation of peroxynitrite are substantially involved in the pathogenesis of the cytokine-induced sustained myocardial dysfunction in vivo.

Molecular cloning and expression of inducible nitric oxide synthase in chick embryonic ventricular myocytes

OBJECTIVE

Inducible nitric oxide synthase (iNOS) has been implicated to contribute to myocardial dysfunction in various settings, but considerable species differences have been noted in the levels of iNOS expression and its function in several tissues. The aim of this study was to elucidate evolutional changes in myocardial iNOS expression and function.

METHODS

An iNOS cDNA clone was isolated by RT-PCR from the 10-day old cultured chick embryonic ventricular myocytes stimulated with 10 micrograms/ml of lipopolysaccharide. Expression of the iNOS mRNA was analyzed with Northern blot analysis and RNase protection assay. The iNOS activity was estimated from conversion rates of L-arginine to L-citrulline and intracellular cGMP contents were measured with radioimmunoassay. Furthermore, both [Ca2+]i (fluorescent dye indo-1) and cell contraction (video motion detector) were simultaneously recorded.

RESULTS

Aside from the primer sequences, the insert (1026 bp) of the cDNA clone showed 66.4% identity at the deduced amino acid level to the human iNOS cDNAs. Northern blot analysis revealed that chicken iNOS mRNA of approximately 4.5 kb was induced by lipopolysaccharide within 6 h in the cultured myocytes. RNase protection assay also showed that lipopolysaccharide provoked 14.6 +/- 5.1-fold increases (n = 6, p < 0.05) in the iNOS mRNA signals within 6 h. The iNOS activity (+300%, P < 0.05) as well as the intracellular cGMP contents (+75%, P < 0.01) were significantly augmented in the lipopolysaccharide-stimulated cells. Both the cell contraction and [Ca2+]i were significantly reduced after the administration of a large amount (10 mM) of L-arginine in the myocytes pretreated with both lipopolysaccharide and NG-monomethyl-L-arginine (100 microM).

CONCLUSION

As like as the nucleotide and amino acid sequences, the myocardial effects of the iNOS may also be evolutionary conserved.

Increased sensitivity to nitric oxide synthase inhibition in patients with heart failure: potentiation of beta-adrenergic inotropic responsiveness

BACKGROUND

We previously showed that cardiac nitric oxide (NO) inhibits the positive inotropic response to beta-adrenergic stimulation in humans with left ventricular (LV) dysfunction. Whether this effect is specific to heart failure per se or is a generalized feature of normal human myocardium is unknown. We therefore tested the hypothesis that inhibition of cardiac NO potentiates the positive inotropic response to beta-adrenergic stimulation in patients with symptomatic LV failure but not in subjects with normal LV function.

METHODS AND RESULTS

We studied 11 patients with LV failure due to idiopathic dilated cardiomyopathy and 7 control subjects with normal LV function. The beta-adrenergic agonist dobutamine was infused via a peripheral vein before and during concurrent intracoronary artery infusion of acetylcholine, which activates the agonist-coupled isoforms of NO synthase, and N(G)-monomethyl-L-arginine, which inhibits all isoforms of NO synthase. Changes in contractility were assessed by measuring the peak rate of rise of LV pressure (+dP/dt). Dobutamine increased +dP/dt by 40+/-6% and 73+/-14% in patients with heart failure and control subjects, respectively. Acetylcholine inhibited the +dP/dt response to dobutamine to a similar degree in patients with heart failure and control subjects (-39 +/- 8% and -31 +/- 4%, respectively; P=NS). Infusion of N(G)-monomethyl-L-arginine potentiated the +dP/dt response to dobutamine by 51+/-15% (P=.01 versus dobutamine) in patients with heart failure but had no effect in control subjects (-6 +/- 4%; P=NS versus dobutamine; P=.0002 versus heart failure patients).

CONCLUSIONS

Inhibition of cardiac NO augments the positive inotropic response to beta-adrenergic receptor stimulation in patients with heart failure due to idiopathic dilated cardiomyopathy but not in control subjects with normal LV function.