Improvement in left ventricular remodeling by the endothelial nitric oxide synthase enhancer AVE9488 after experimental myocardial infarction

Increase in parasympathetic tone by pyridostigmine prevents ventricular dysfunction during the onset of heart failure

Heart failure (HF) is characterized by elevated sympathetic activity and reduced parasympathetic control of the heart. Experimental evidence suggests that the increase in parasympathetic function can be a therapeutic alternative to slow HF evolution. The parasympathetic neurotransmission can be improved by acetylcholinesterase inhibition. We investigated the long-term (4 wk) effects of the acetylcholinesterase inhibitor pyridostigmine on sympathovagal balance, cardiac remodeling, and cardiac function in the onset of HF following myocardial infarction. Myocardial infarction was elicited in adult male Wistar rats. After 4 wk of pyridostigmine administration, per os, methylatropine and propranolol were used to evaluate the cardiac sympathovagal balance. The tachycardic response caused by methylatropine was considered to be the vagal tone, whereas the bradycardic response caused by propranolol was considered to be the sympathetic tone. In conscious HF rats, pyridostigmine reduced the basal heart rate, increased vagal, and reduced sympathetic control of heart rate. Pyridostigmine reduced the myocyte diameter and collagen density of the surviving left ventricle. Pyridostigmine also increased vascular endothelial growth factor protein in the left ventricle, suggesting myocardial angiogenesis. Cardiac function was assessed by means of the pressure-volume conductance catheter system. HF rats treated with pyridostigmine exhibited a higher stroke volume, ejection fraction, cardiac output, and contractility of the left ventricle. It was demonstrated that the long-term administration of pyridostigmine started right after coronary artery ligation augmented cardiac vagal and reduced sympathetic tone, attenuating cardiac remodeling and left ventricular dysfunction during the progression of HF in rats.

Xenon and isoflurane reduce left ventricular remodeling after myocardial infarction in the rat

BACKGROUND

Xenon and isoflurane are known to have cardioprotective properties. We tested the hypothesis that these anesthetics positively influence myocardial remodeling 28 days after experimental perioperative myocardial infarction and compared their effects.

METHODS

A total of 60 male Sprague-Dawley rats were subjected to 60 min of coronary artery occlusion and 120 min of reperfusion. Prior to ischemia, the animals were randomized for the different narcotic regimes (0.6 vol% isoflurane, 70 vol% xenon, or intraperitoneal injection of s-ketamine). Acute injury was quantified by echocardiography and troponin I. After 4 weeks, left ventricular function was assessed by conductance catheter to quantify hemodynamic compromise. Cardiac remodeling was characterized by quantification of dilatation, hypertrophy, fibrosis, capillary density, apoptosis, and expression of fetal genes (α/β myosin heavy chains, α-skeletal actin, periostin, and sarco/endoplasmic reticulum Ca2+-ATPase).

RESULTS

Whereas xenon and isoflurane impeded the acute effects of ischemia-reperfusion on hemodynamics and myocardial injury at a comparable level, differences were found after 4 weeks. Xenon in contrast to isoflurane or ketamine anesthetized animals demonstrated a lower remodeling index (0.7 ± 0.1 vs. 0.9 ± 0.3 and 1.0 ± 0.3g/ml), better ejection fraction (62 ± 9 vs. 49 ± 7 and 35 ± 6%), and reduced expression of β-myosin heavy chain and periostin. The effects on hypertrophy, fibrosis, capillary density, and apoptosis were comparable.

CONCLUSIONS

Compared to isoflurane and s-ketamine, xenon limited progressive adverse cardiac remodeling and contractile dysfunction 28 days after perioperative myocardial infarction.

Inhibition of TGF-β1 by eNOS gene transfer provides cardiac protection after myocardial infarction

Objective

Endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) have been implicated in protection against myocardial ischemia injury. This study was designed to explore a new method of therapy for myocardial injury by eNOS gene transfection.

Methods

A rat model of myocardial infarction (MI) was established by left anterior descending (LAD) coronary artery ligation. eNOS gene in an adenovirus vector was delivered locally into the rat heart and hemodynamic parameters were examined after 3 weeks, Matrix metalloproteinase-2 and 9 (MMP-2, MMP-9) mRNA were measured by reverse transcription polymerase chain reaction (RT-PCR), and the protein levels of eNOS, caspase-3, and transforming grouth factor β₁ (TGF-β₁) were determined by western blot assay.

Results

eNOS gene transfer significantly reduced cardiomyocyte apoptosis and improved cardiac function. In addition, eNOS significantly reduced the mRNA levels of MMP-2 and MMP-9. In the eNOS gene transfected group, the activation of caspase-3 and TGF-β₁ were decreased. However, the protection was reversed by administration of the NOS inhibitor, N(ω)-nitro-l-arginine methyl ester (L-NAME).

Conclusion

These results demonstrate that the eNOS provides cardiac protection after myocardial infarction injury through inhibition of cardiac apoptosis and collagen deposition, and suppression of TGF-β₁.

Angiogenesis in the infarcted myocardium

SIGNIFICANCE

Proangiogenic therapy appeared a promising strategy for the treatment of patients with acute myocardial infarction (MI), as de novo formation of microvessels, has the potential to salvage ischemic myocardium at early stages after MI, and is also essential to prevent the transition to heart failure through the control of cardiomyocyte hypertrophy and contractility.

RECENT ADVANCES

Exciting preclinical studies evaluating proangiogenic therapies for MI have prompted the initiation of numerous clinical trials based on protein or gene transfer delivery of growth factors and administration of stem/progenitor cells, mainly from bone marrow origin. Nonetheless, these clinical trials showed mixed results in patients with acute MI.

CRITICAL ISSUES

Even though methodological caveats, such as way of delivery for angiogenic growth factors (e.g., protein vs. gene transfer) and stem/progenitor cells or isolation/culture procedure for regenerative cells might partially explain the failure of such trials, it appears that delivery of a single growth factor or cell type does not support angiogenesis sufficiently to promote cardiac repair.

FUTURE DIRECTIONS

Optimization of proangiogenic therapies might include stimulation of both angiogenesis and vessel maturation and/or the use of additional sources of stem/progenitor cells, such as cardiac progenitor cells. Experimental unraveling of the mechanisms of angiogenesis, vessel maturation, and endothelial cell/cardiomyocyte cross talk in the ischemic heart, analysis of emerging pathways, as well as a better understanding of how cardiovascular risk factors impact endogenous and therapeutically stimulated angiogenesis, would undoubtedly pave the way for the development of novel and hopefully efficient angiogenesis targeting therapeutics for the treatment of acute MI.

Identification of free nitric oxide radicals in rat bone marrow: implications for progenitor cell mobilization in hypertension

Nitric oxide (NO) has been implicated in matrix metallopeptidase 9 (MMP9)-dependent mobilization of hematopoietic stem and progenitor cells from bone marrow (BM). However, direct measurement of NO in the BM remained elusive due to its low in situ concentration and short lifetime. Using NO spin trapping and electron paramagnetic resonance (EPR) spectroscopy we give the first experimental confirmation of free NO radicals in rodent BM. NO production was quantified and attributed to enzymatic activity of NO synthases (NOS). Although endothelial NOS (eNOS) accounts for most (66%) of basal NO, we identified a significant contribution (23%) from inducible NOS (iNOS). Basal NO levels closely correlate with MMP9 bioavailability in BM of both hypertensive and control rats. Our observations support the hypothesis that inadequate mobilization of BM-derived stem and progenitor cells in hypertension results from impaired NOS/NO/MMP9 signalling in BM, a condition that may be corrected with pharmacological intervention.

AVE3085 protects coronary endothelium from the impairment of asymmetric dimethylarginine by activation and recoupling of eNOS

PURPOSE

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of eNOS and it is recognized as a risk factor for endothelial dysfunction in cardiovascular diseases. We investigated the effect of AVE3085, a newly developed transcription enhancer of eNOS, on ADMA-induced endothelial dysfunction in coronary arteries with underlying mechanisms explored.

METHODS

Porcine coronary small arteries (diameter 600-800 μm) were studied in a myograph for endothelium-dependent relaxation to bradykinin and endothelium-independent relaxation to sodium nitroprusside. Protein expressions of eNOS and phosphorylated-eNOS (p-eNOS(Ser1177) and p-eNOS(Thr495)), and nitrotyrosine formation were determined by Western blot. NO release was directly measured with a NO microsensor. Productions of O(2) (.-) and peroxynitrite (ONOO(-)) were determined by lucigenin- and luminol- enhanced chemiluminescence respectively.

RESULTS

Exposure to ADMA significantly decreased the bradykinin-induced vasorelaxation and reduced the protein expression of p-eNOS(Ser1177) whereas increased the expression of p-eNOS(Thr495) and nitrotyrosine. Pre-incubation with AVE3085 restored the bradykinin-induced relaxation, reversed the decrease of p-eNOS(Ser1177), and lowered the level of p-eNOS(Thr495) and nitrotyrosine. NO release in response to bradykinin was significantly reduced by ADMA and such reduction was restored by AVE3085. AVE3085 also prevented the elevation of O (2) (.-) and ONOO(-) levels in coronary arteries exposed to ADMA.

CONCLUSIONS

AVE3085 prevents ADMA-induced endothelial dysfunction in coronary arteries. The protective effect of AVE3085 may be attributed to increased NO production resulting from enhanced eNOS activation, and decreased oxidative stress that involves inhibition of O (2) (.-) generation by eNOS recoupling. The present study suggested the therapeutic potential of AVE3085 in endothelial dysfunction in cardiovascular disorders.

Nitric oxide modulation as a therapeutic strategy in heart failure

Nitric oxide (NO) is recognized as one of the most important cardiovascular signaling molecules, with multiple regulatory effects on myocardial and vascular tissue as well as on other tissues and organ systems. With the growth in understanding of the range and mechanisms of NO effects on the cardiovascular system, it is now possible to consider pharmaceutical interventions that directly target NO or key steps in NO effector pathways. This article reviews aspects of the cardiovascular effects of NO, abnormalities in NO regulation in heart failure, and clinical trials of drugs that target specific aspects of NO signaling pathways.

Conflicting effects of nitric oxide and oxidative stress in chronic heart failure: potential therapeutic strategies

Chronic heart failure (CHF) is characterized by decreased nitric oxide (NO) bioavailability. In addition, the beneficial NO turns to be deleterious when it reacts with superoxide anion, leading to peroxynitrite formation. Numerous experimental and clinical studies have reported increased production of reactive oxygen species (superoxide, hydrogen peroxide, hydroxyl radical) both in animals and patients with CHF. Moreover, there are indicative data suggesting mechanisms associated with endothelial dysfunction in states of CHF, mainly attributed to decreased NO bioavailability and enhanced inactivation of the latter. Thus, such molecules appear to be potential targets in patients with CHF. These patients are strong candidates to receive a variety of therapeutic agents, some of which have known antioxidant effects. Classic treatment with statins or angiotensin converting enzyme inhibitors has been found to be beneficial in restoring NO and improving myocardial function and structure. Other agents such as sildenafil and b-blockers along with novel agents such as NO synthase transcription enhancers have been proved to be also beneficial, but their use for such a purpose is still controversial. Approaches using more-effective antioxidants or targeting myocardial oxidant-producing enzymes and oxidative or nitrosative stress might be promising strategies in the future.

Therapeutic effect of enhancing endothelial nitric oxide synthase (eNOS) expression and preventing eNOS uncoupling

Nitric oxide (NO) produced by the endothelium is an important protective molecule in the vasculature. It is generated by the enzyme endothelial NO synthase (eNOS). Similar to all NOS isoforms, functional eNOS transfers electrons from nicotinamide adenine dinucleotide phosphate (NADPH), via the flavins flavin adenine dinucleotide and flavin mononucleotide in the carboxy-terminal reductase domain, to the heme in the amino-terminal oxygenase domain. Here, the substrate L-arginine is oxidized to L-citrulline and NO. Cardiovascular risk factors such as diabetes mellitus, hypertension, hypercholesterolaemia or cigarette smoking reduce bioactive NO. These risk factors lead to an enhanced production of reactive oxygen species (ROS) in the vessel wall. NADPH oxidases represent major sources of this ROS and have been found upregulated in the presence of cardiovascular risk factors. NADPH-oxidase-derived superoxide avidly reacts with eNOS-derived NO to form peroxynitrite (ONOO(-)). The essential NOS cofactor (6R-)5,6,7,8-tetrahydrobiopterin (BH(4) ) is highly sensitive to oxidation by this ONOO(-). In BH(4) deficiency, oxygen reduction uncouples from NO synthesis, thereby converting NOS to a superoxide-producing enzyme. Among conventional drugs, compounds interfering with the renin-angiotensin-aldosterone system and statins can reduce vascular oxidative stress and increase bioactive NO. In recent years, we have identified a number of small molecules that have the potential to prevent eNOS uncoupling and, at the same time, enhance eNOS expression. These include the protein kinase C inhibitor midostaurin, the pentacyclic triterpenoids ursolic acid and betulinic acid, the eNOS enhancing compounds AVE9488 and AVE3085, and the polyphenolic phytoalexin trans-resveratrol. Such compounds enhance NO production from eNOS also under pathophysiological conditions and may thus have therapeutic potential.

Tackling endothelial dysfunction by modulating NOS uncoupling: new insights into its pathogenesis and therapeutic possibilities

Endothelial nitric oxide synthase (eNOS) serves as a critical enzyme in maintaining vascular pressure by producing nitric oxide (NO); hence, it has a crucial role in the regulation of endothelial function. The bioavailability of eNOS-derived NO is crucial for this function and might be affected at multiple levels. Uncoupling of eNOS, with subsequently less NO and more superoxide generation, is one of the major underlying causes of endothelial dysfunction found in atherosclerosis, diabetes, hypertension, cigarette smoking, hyperhomocysteinemia, and ischemia/reperfusion injury. Therefore, modulating eNOS uncoupling by stabilizing eNOS activity, enhancing its substrate, cofactors, and transcription, and reversing uncoupled eNOS are attractive therapeutic approaches to improve endothelial function. This review provides an extensive overview of the important role of eNOS uncoupling in the pathogenesis of endothelial dysfunction and the potential therapeutic interventions to modulate eNOS for tackling endothelial dysfunction.

Soluble epoxide hydrolase inhibition improves myocardial perfusion and function in experimental heart failure

The study addressed the hypothesis that soluble epoxide hydrolase (sEH) inhibition, which increases cardiovascular protective epoxyeicosatrienoic acids (EETs), exerts beneficial effects in an established chronic heart failure (CHF) model. In CHF rats, left ventricular (LV) function, perfusion and remodeling were assessed using MRI and invasive hemodynamics after 42-day (starting 8 days after coronary ligation) and delayed 3-day (starting 47 days after coronary ligation) treatments with the sEH inhibitor AUDA (twice 0.25 mg/day). Delayed 3-day and 42-day AUDA increased plasma EETs demonstrating the effective inhibition of sEH. Delayed 3-day and 42-day AUDA enhanced cardiac output without change in arterial pressure, thus reducing total peripheral resistance. Both treatment periods increased the slope of the LV end-systolic pressure-volume relation, but only 42-day AUDA decreased LV end-diastolic pressure, relaxation constant Tau and the slope of the LV end-diastolic pressure-volume relation, associated with a reduced LV diastolic volume and collagen density. Delayed 3-day and, to a larger extent, 42-day AUDA increased LV perfusion associated with a decreased LV hypoxia-inducible factor-1alpha. Both treatment periods decreased reactive oxygen species level and increased reduced-oxidized glutathione ratio. Finally, MSPPOH, an inhibitor of the EET-synthesizing enzyme cytochrome epoxygenases, abolished the beneficial effects of 3-day AUDA on LV function and perfusion. Augmentation of EET availability by pharmacological inhibition of sEH increases LV diastolic and systolic functions in established CHF. This notably results from short-term processes, i.e. increased LV perfusion, reduced LV oxidative stress and peripheral vasodilatation, but also from long-term effects, i.e. reduced LV remodeling.

Endothelial factors after selective retrograde coronary venous bypass under different pressures

BACKGROUND

Selective retrograde coronary venous bypass (SRCVB) may be a promising treatment for patients with advanced coronary artery disease (CAD). The aim of this study is to investigate the effect of SRCVB on plasma endothelial factor levels in dog myocardial ischemic model, and explore the possible mechanisms.

METHODS

24 crossbreed dogs were randomly divided into three groups: (1) control group; (2) SRCVB group with 60 mmHg perfusion pressure; (3) SRCVB group with 90 mmHg perfusion pressure. The posterior descending coronary artery (PDA) was ligated in all groups, and SRCVB was performed in the last two groups. The levels of plasma nitric oxide (NO) and endothelin (ET) at different time points were determined in each group. In SRCVB groups, ink and imaging agent were injected to the heart through SVG graft for assessment of vein perfusion.

RESULTS

At the acute period, there were significant increase in the plasma levels of NO and decrease in ET in SRCVB 90 mmHg group compared with the control (P < 0. 01), and a further improvement were found in SRCVB 60 mmHg group (P < 0. 01). The ink or imaging agent was found in the myocardial tissue and flowed back to right atrium through contralateral coronary vein.

CONCLUSIONS

SRCVB with low level of perfusion pressure could provide effective perfusion for ischemic myocardium and alleviate the myocardial endothelial cell injury. It may be a new therapeutic strategy for severe CAD.

Endothelial nitric oxide synthase enhancer reduces oxidative stress and restores endothelial function in db/db mice

AIMS

Endothelial dysfunction is caused by reduced nitric oxide (NO) bioavailability and/or over-produced reactive oxygen species (ROS). The present study investigated a vascular benefit of AVE3085, an endothelial nitric oxide synthase (eNOS) enhancer, in preserving endothelial function in diabetic mice and the mechanisms involved.

METHODS AND RESULTS

Male db/db and db/m(+) mice were orally administered AVE3085 for 7 days (10 mg kg(-1) day(-1)). Vascular reactivity of arteries was studied via myography under both isometric and isobaric conditions. ROS levels in aortas were determined using dihydroethidium fluorescence dye and electron paramagnetic resonance spin trapping. Chronic treatment with AVE3085 reduced blood pressure, enhanced endothelium-dependent relaxations (EDR) to acetylcholine in aortas, mesenteric, and renal arteries, lowered oxidative stress, and augmented the attenuated flow-dependent dilatation in mesenteric resistance arteries from db/db mice. Incubation of aortas from C57BL/6J mice in high glucose (30 mmol L(-1)) culture medium for 48 h impaired EDR and elevated ROS generation, and these effects were reversed by co-treatment with AVE3085 (1 µmol L(-1)). Benefits of AVE3085 were abolished by the transcription inhibitor actinomycin D, the NOS inhibitor N(G)-nitro-L-arginine methyl ester, and in eNOS(-/-) mice. NO production in primary endothelial cells from mouse aortas was detected with a NO-sensitive fluorescence dye. Protein expression was assayed by western blotting. Treatment with AVE3085 enhanced NO production in endothelial cells and eNOS expression in aortas.

CONCLUSION

AVE3085 ameliorates endothelial dysfunction in db/db mice through increased NO bioavailability, which reduces oxidative stress in the vascular wall. Targeting eNOS and NO production may be a promising approach to combat diabetic vasculopathy.

Critical role of the nitric oxide/reactive oxygen species balance in endothelial progenitor dysfunction

Endothelial injury and dysfunction are critical events in the pathogenesis of cardiovascular disease. During these processes, an impaired balance of nitric oxide bioavailability and oxidative stress is mechanistically involved. Circulating angiogenic cells (including early and late outgrowth endothelial progenitor cells (EPC)) contribute to formation of new blood vessels, neovascularization, and homeostasis of the vasculature, and are highly sensitive for misbalance between NO and oxidative stress. We here review the role of the endothelial nitric oxide synthase and oxidative stress producing enzyme systems in EPC during cardiovascular disease. We also focus on the underlying molecular mechanisms and potential emerging drug- and gene-based therapeutic strategies to improve EPC function in cardiovascular diseased patients.

Repeated sauna therapy attenuates ventricular remodeling after myocardial infarction in rats by increasing coronary vascularity of noninfarcted myocardium

Repeated sauna therapy (ST) increases endothelial nitric oxide synthase (eNOS) activity and improves cardiac function in heart failure as well as peripheral blood flow in ischemic limbs. The present study investigates whether ST can increase coronary vascularity and thus attenuate cardiac remodeling after myocardial infarction (MI). We induced MI by ligating the left coronary artery of Wistar rats. The rats were placed in a far-infrared dry sauna at 41°C for 15 min and then at 34°C for 20 min once daily for 4 wk. Cardiac hemodynamic, histopathological, and gene analyses were performed. Despite the similar sizes of MI between the ST and non-ST groups (51.4 ± 0.3 vs. 51.1 ± 0.2%), ST reduced left ventricular (LV) end-diastolic (9.7 ± 0.4 vs. 10.7 ± 0.5 mm, P < 0.01) and end-systolic (8.6 ± 0.5 vs. 9.6 ± 0.6 mm, P < 0.01) dimensions and attenuated MI-induced increases in LV end-diastolic pressure. Cross-sectional areas of cardiomyocytes were smaller in ST rats and associated with a significant reduction in myocardial atrial natriuretic peptide mRNA levels. Vascular density was reduced in the noninfarcted myocardium of non-ST rats, and the density of cells positive for CD31 and for α-smooth muscle actin was decreased. These decreases were attenuated in ST rats compared with non-ST rats and associated with increases in myocardial eNOS and vascular endothelial growth factor mRNA levels. In conclusion, ST attenuates cardiac remodeling after MI, at least in part, through improving coronary vascularity in the noninfarcted myocardium. Repeated ST might serve as a novel noninvasive therapy for patients with MI.

Prostanoids suppress the coronary vasoconstrictor influence of endothelin after myocardial infarction

Myocardial infarction (MI) is associated with endothelial dysfunction resulting in an imbalance in endothelium-derived vasodilators and vasoconstrictors. We have previously shown that despite increased endothelin (ET) plasma levels, the coronary vasoconstrictor effect of endogenous ET is abolished after MI. In normal swine, nitric oxide (NO) and prostanoids modulate the vasoconstrictor effect of ET. In light of the interaction among NO, prostanoids, and ET combined with endothelial dysfunction present after MI, we investigated this interaction in control of coronary vasomotor tone in the remote noninfarcted myocardium after MI. Studies were performed in chronically instrumented swine (18 normal swine; 13 swine with MI) at rest and during treadmill exercise. Furthermore, endothelial nitric oxide synthase (eNOS) and cyclooxygenase protein levels were measured in the anterior (noninfarcted) wall of six normal and six swine with MI. eNOS inhibition with N(ω)-nitro-L-arginine (L-NNA) and cyclooxygenase inhibition with indomethacin each resulted in coronary vasoconstriction at rest and during exercise, as evidenced by a decrease in coronary venous oxygen levels. The effect of l-NNA was slightly decreased in swine with MI, although eNOS expression was not altered. Conversely, in accordance with the unaltered expression of cyclooxygenase-1 after MI, the effect of indomethacin was similar in normal and MI swine. L-NNA enhanced the vasodilator effect of the ET(A/B) receptor blocker tezosentan but exclusively during exercise in both normal and MI swine. Interestingly, this effect of L-NNA was blunted in MI compared with normal swine. In contrast, whereas indomethacin increased the vasodilator effect of tezosentan only during exercise in normal swine, indomethacin unmasked a coronary vasodilator effect of tezosentan in MI swine both at rest and during exercise. In conclusion, the present study shows that endothelial control of the coronary vasculature is altered in post-MI remodeled myocardium. Thus the overall vasodilator influences of NO as well as its inhibition of the vasoconstrictor influence of ET on the coronary resistance vessels were reduced after MI. In contrast, while the overall prostanoid vasodilator influence was maintained, its inhibition of ET vasoconstrictor influences was enhanced in post-MI remote myocardium.

Modulating endothelial nitric oxide synthase: a new cardiovascular therapeutic strategy

The pathogenesis of many cardiovascular diseases is associated with reduced nitric oxide (NO) bioavailability and/or increased endothelial NO synthase (eNOS)-dependent superoxide formation. These findings support that restoring and conserving adequate NO signaling in the heart and blood vessels is a promising therapeutic intervention. In particular, modulating eNOS, e.g., through increasing the bioavailability of its substrate and cofactors, enhancing its transcription, and interfering with other modulators of eNOS pathway, such as netrin-1, has a high potential for effective treatments of cardiovascular diseases. This review provides an overview of the possibilities for modulating eNOS and how this may be translated to the clinic in addition to describing the genetic models used to study eNOS modulation.

Pathogenetic role of eNOS uncoupling in cardiopulmonary disorders

The homodimeric flavohemeprotein endothelial nitric oxide synthase (eNOS) oxidizes l-arginine to l-citrulline and nitric oxide (NO), which acutely vasodilates blood vessels and inhibits platelet aggregation. Chronically, eNOS has a major role in the regulation of blood pressure and prevention of atherosclerosis by decreasing leukocyte adhesion and smooth muscle proliferation. However, a disturbed vascular redox balance results in eNOS damage and uncoupling of oxygen activation from l-arginine conversion. Uncoupled eNOS monomerizes and generates reactive oxygen species (ROS) rather than NO. Indeed, eNOS uncoupling has been suggested as one of the main pathomechanisms in a broad range of cardiovascular and pulmonary disorders such as atherosclerosis, ventricular remodeling, and pulmonary hypertension. Therefore, modulating uncoupled eNOS, in particular eNOS-dependent ROS generation, is an attractive therapeutic approach to preventing and/or treating cardiopulmonary disorders, including protective effects during cardiothoracic surgery. This review provides a comprehensive overview of the pathogenetic role of uncoupled eNOS in both cardiovascular and pulmonary disorders. In addition, the related therapeutic possibilities such as supplementation with the eNOS substrate l-arginine, volatile NO, and direct NO donors as well as eNOS modulators such as the eNOS cofactor tetrahydrobiopterin and folic acid are discussed in detail.

Cytosolic phospholipase A2alpha contributes to blood pressure increases and endothelial dysfunction under chronic NO inhibition

OBJECTIVE

Nitric oxide (NO) is an important modulator of cardiovascular function. In this study, we examined whether cytosolic phospholipase A2α (cPLA2α), an initial enzyme in the arachidonic acid pathway, is involved in blood pressure (BP) elevation in a murine model of chronic NO inhibition.

METHODS AND RESULTS

cPLA2α gene-deficient mice (cPLA2α-/-) and wild-type mice (WT) were administered the NO synthesis inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) for 4 weeks. Before treatment, BP was comparable in both groups; it increased significantly in the WT but not in the cPLA2α-/- after treatment. Bone marrow transplantation experiments showed that cPLA2α in blood cells and plasma eicosanoid concentrations were not involved in BP elevation by L-NAME treatment. Activation of cPLA2α and subsequent production of eicosanoids in the aortic endothelium but not in aortic smooth muscle cell, heart, or kidney was observed after L-NAME treatment. Aortic ring assays revealed that endothelial function was comparable in both groups of mice before treatment. L-NAME treatment disturbed endothelial function in WT but not in cPLA2α-/-.

CONCLUSIONS

These results suggest that endothelial cPLA2α may play a principal role in L-NAME-induced hypertension and may be a target molecule for maintaining endothelial function under NO inhibition.

Modulating the nitric oxide - cyclic GMP pathway in the pressure-overloaded left ventricle and group II pulmonary hypertension

Group II pulmonary hypertension (PH) commonly occurs in the setting of a pressure-overloaded left ventricle (LV) which is also conducive to the development of heart failure with preserved ejection fraction. Population trends and a high prevalence of underlying causative conditions, such as essential hypertension or aortic stenosis, have increased the awareness of the pressure-overloaded LV and associated group II pulmonary hypertension. Patients often exhibit poor exercise tolerance and signs of heart failure indistinguishable from systolic heart failure; but effective medical treatments in this area have been lacking. Recent preclinical work has shed light on how the down-regulated nitric oxide - cyclic GMP pathway (within the myocardium and pulmonary vasculature) contributes to the pathophysiology of these associated conditions. This article will discuss the impact of the nitric oxide - cyclic GMP pathway on the pathogenesis of the pressure-overloaded LV and group II pulmonary hypertension, and will also introduce the potential therapeutic value of modulating this pathway.

Nitric oxide pathway in hypertrophied heart: new therapeutic uses of nitric oxide donors

Left ventricular hypertrophy (LVH) is regarded as a complication common to a number of cardiovascular diseases, including hypertension, myocardial infarction and ischaemia associated with coronary artery disease. Initially LVH is a compensatory mechanism, but in the long term cardiac hypertrophy predisposes individuals to heart failure, myocardial infarction and sudden death. Alteration of the nitric oxide (NO) pathway is believed to play an important role in the haemodynamically overloaded heart and pathological cardiac remodelling. Although re-establishment of the physiological NO pathway could be considered an important therapeutic target, the use of conventional nitrates is limited in the clinical setting by the development of tissue resistance and tolerance and by the shortage of large-scale clinical trials unequivocally confirming the beneficial impact of NO donors on cardiovascular morbidity and mortality. The aim of this review is to present current therapeutic options for dealing with changes in the L-arginine-NO pathway. The most promising therapeutic approach is represented by a new neutral sugar organic nitrate, LA-419, the thiol group of which seems to protect NO from degradation, thereby increasing its bioavailability. In a model of aortic stenosis-induced pressure overload, LA-419 has been found to restore the complete NO signalling cascade and reduce left ventricular remodelling, but without restoring the original pressure gradient, indicating a possible direct antiproliferative effect. Future studies are needed to confirm this therapeutic benefit in other animal models of hypertension and in the clinical setting.

Increased cytochrome P4502E1 expression and altered hydroxyeicosatetraenoic acid formation mediate diabetic vascular dysfunction: rescue by guanylyl-cyclase activation

OBJECTIVE

We investigated the mechanisms underlying vascular endothelial and contractile dysfunction in diabetes as well as the effect of HMR1766, a novel nitric oxide (NO)-independent activator of soluble guanylyl cyclase (sGC).

RESEARCH DESIGN AND METHODS

Two weeks after induction of diabetes by streptozotocin, Wistar rats received either placebo or HMR1766 (10 mg/kg twice daily) for another 2 weeks; thereafter, vascular function was assessed.

RESULTS

Endothelial function and contractile responses were significantly impaired, while vascular superoxide formation was increased in the aortae from diabetic versus healthy control rats. Using RNA microarrays, cytochrome P4502E1 (CYP2E1) was identified as the highest upregulated gene in diabetic aorta. CYP2E1 protein was significantly increased (16-fold) by diabetes, leading to a reduction in levels of the potent vasoconstrictor 20-hydroxy-eicosatetraenoic acid (20-HETE). Induction of CYP2E1 expression in healthy rats using isoniazide mimicked the diabetic noncontractile vascular response while preincubation of aortae from STZ-diabetic rats in vitro with 20-HETE rescued contractile function. Chronic treatment with the sGC activator HMR1766 improved NO sensitivity and endothelial function, reduced CYP2E1 expression and superoxide formation, enhanced 20-HETE levels, and reversed the contractile deficit observed in the diabetic rats that received placebo.

CONCLUSIONS

Upregulation of CYP2E1 is essentially involved in diabetic vascular dysfunction. Chronic treatment with the sGC activator HMR1766 reduced oxidative stress, decreased CYP2E1 levels, and normalized vasomotor function in diabetic rats.

Aminoethyl nitrate--the novel super nitrate?

Long-term use of most organic nitrates is limited by development of tolerance, induction of oxidative stress and endothelial dysfunction. In this issue of the BJP, Schuhmacher et al. characterized a novel class of organic nitrates with amino moieties (aminoalkyl nitrates). Aminoethyl nitrate was identified as a novel organic mononitrate with high potency but devoid of induction of mitochondrial oxidative stress. Cross-tolerance to nitroglycerin or the endothelium-dependent agonist acetylcholine after in vivo treatment was not observed. Like all nitrates, aminoethyl nitrate induced vasorelaxation by activation of soluble guanylate cyclase. Thus, in contrast to the prevailing view, high potency in an organic nitrate is not necessarily accompanied by induction of oxidative stress or endothelial dysfunction. This work from Daiber's group is an important step forward in the understanding of nitrate bioactivation, tolerance phenomena and towards the development of better organic nitrates for clinical use.

Cardioselective nitric oxide synthase 3 gene transfer protects against myocardial reperfusion injury

Nitric oxide modulates the severity of myocardial ischemia-reperfusion (I/R) injury. We investigated whether cardioselective nitric oxide synthase 3 (NOS3) gene transfer could confer myocardial protection against I/R injury in pigs and examined potential molecular mechanisms. I/R injury was induced by balloon occlusion of the left anterior descending artery for 45 min followed by 4 or 72 h reperfusion. Hemodynamic and pathological changes were measured in pigs in the absence (n = 11) or presence of prior intracoronary retroinfusion of human NOS3 (AdNOS3, 5 x 10(10) PFU, n = 13) or control vector (AdRR5, 5 x 10(10) PFU, n = 11). Retrograde NOS3 gene transfer selectively increased NOS3 expression and NO bioavailability in the area at risk (AAR) without changing endogenous NOS isoform expression. At 4 h R, LV systolic (dP/dt(max)) and diastolic (dP/dt(min)) function was better preserved in AdNOS3- than in AdRR5-injected pigs (2,539 +/- 165 vs. 1,829 +/- 156 mmHg/s, and -2,781 +/- 340 vs. -2,062 +/- 292 mmHg/s, respectively, P < 0.05 for both). Myocardial infarct size (% AAR) was significantly smaller in AdNOS3 than in control and AdRR5 and associated with a significantly greater reduction in cardiac myeloperoxidase activity, a marker of neutrophil infiltration. The latter effects were sustained at 72 h R in a subset of pigs (n = 7). In the AAR, intercellular endothelial adhesion molecule-1 expression and cardiomyocyte apoptosis were significantly lower in AdNOS3. In conclusion, single myocardial NOS3 retroinfusion attenuates I/R injury, and causes a sustained reduction in myocardial infarct size and inflammatory cell infiltration. Gene-based strategies to increase NO bioavailability may have therapeutic potential in myocardial I/R.

Exploiting cGMP-based therapies for the prevention of left ventricular hypertrophy: NO* and beyond

Left ventricular hypertrophy (LVH), an increased left ventricular (LV) mass, is common to many cardiovascular disorders, initially developing as an adaptive response to maintain myocardial function. In the longer term, this LV remodelling becomes maladaptive, with progressive decline in LV contractility and diastolic function. Indeed LVH is recognised as an important blood-pressure independent predictor of cardiovascular morbidity and mortality. The clinical efficacy of current treatments for LVH is reduced, however, by their tendency to slow disease progression rather than induce its reversal, and thus the development of new therapies for LVH is paramount. The signalling molecule cyclic guanosine-3',5'-monophosphate (cGMP), well-recognised for its role in regulating vascular tone, is now being increasingly identified as an important anti-hypertrophic mediator. This review is focused on the various means by which cGMP can be stimulated in the heart, such as via the natriuretic peptides, to exert anti-hypertrophic actions. In particular we address the limitations of traditional nitric oxide (NO*) donors in the face of the potential therapeutic advantages offered by novel alternatives; NO* siblings, ligands of the cGMP-generating enzymes, soluble (sGC) and particulate guanylyl cyclases (pGC), and phosphodiesterase inhibitors. Further impact of cGMP within the cardiovascular system is also discussed with a view to representing cGMP-based therapies as innovative pharmacotherapy, alone or concurrent with standard care, for the management of LVH.

The eNOS enhancer AVE 9488: a novel cardioprotectant against ischemia reperfusion injury

Nitric oxide (NO) is an important regulator of vascular and myocardial function. Cardiac ischemia/reperfusion injury is reduced in mice overexpressing endothelial NO synthase (eNOS) suggesting cardioprotection by eNOS. Novel pharmacological substances, so called eNOS enhancers, upregulate eNOS expression and thereby increase NO production. We tested the effects of the eNOS enhancer AVE 9488 on cardiac ischemia/reperfusion injury in vivo in mice. After treatment with the eNOS enhancer AVE 9488 (30 mg/kg/day) or placebo for one week mice underwent 30 min of coronary artery ligation and 24 h of reperfusion in vivo. Ischemia-reperfusion damage was significantly reduced in mice treated with the eNOS enhancer when compared to placebo treated mice (infarct/area at risk 65.4 +/- 4.1 vs. 36.9 +/- 4.0%, placebo vs. eNOS enhancer, P = 0.0002). The protective effect was blunted in eNOS knockout mice treated with the eNOS enhancer (infarct/area at risk 64.1 +/- 6.2%, eNOS knockout + eNOS enhancer vs. WT + eNOS enhancer, P = ns). Reactive oxygen species were significantly reduced in mice treated with the eNOS enhancer as indicated by significantly lower malondialdehyde-thiobarbituric acid levels (placebo vs. eNOS enhancer, 3.2 +/- 0.5 vs. 0.8 +/- 0.07 micromol/l, P = 0.0003). Thus pharmacological interventions addressed to increase eNOS-derived NO production constitute a promising therapeutic approach to prevent myocardial ischemia/reperfusion injury.

Histological study of right ventricle-pulmonary artery valved conduit implantation (RPVC) in dogs with pulmonic stenosis

We examined whether right ventricle-pulmonary artery valved conduit (RPVC) implantation can overcome the disadvantages of current procedures for pulmonic stenosis (PS). We histologically evaluated the feasibility of RPVC using a homograft in PS model dogs. Eight dogs underwent pulmonary artery banding (PAB) and then 12 weeks later were assigned to PAB (n=4) or PAB+RPVC (n=4) groups. Dogs in the PAB group received no treatment throughout the experimental period, whereas the PAB+RPVC group underwent RPVC. At 1 year after PAB, hearts and conduits were explanted from euthanized dogs and histologically evaluated. The ratios (%) of myocardial fibrosis on right ventricle (RV) epicardial, median and endocardial layers were significantly lower in the PAB+RPVC, than in the PAB group. The ratio of myocardial fibrosis on left ventricular (LV) epicardial and endocardial layers were significantly lower in the PAB+RPVC, than in the PAB group. Neo-intimal thickness in the anastomosis areas of the Denacol and PAB+RPVC groups was 42.77 +/- 30.19 and 88.30 +/- 27.24 microm, respectively, with no significant differences between the groups. Calcification and neo- intima hypertrophy were not obvious in the valve area. Immunohistological staining showed that the internal surface of the anastomosis and intermediate areas were positive for endothelial cells. We concluded that RPVC using a bioprosthetic graft can apparently overcome the disadvantages of current procedures for pulmonic stenosis.

Inhibition of platelet activation in rats with severe congestive heart failure by a novel endothelial nitric oxide synthase transcription enhancer

AIMS

Increased risk of thrombo-embolic events in congestive heart failure (CHF) has been attributed to a hypercoagulable state including vascular endothelial dysfunction and reduced bioavailability of nitric oxide (NO) as well as platelet activation. We investigated whether treatment with a novel endothelial NO synthase (eNOS)-transcription enhancer positively modulates systemic NO bioavailability and reduces platelet activation in rats with CHF.

METHODS AND RESULTS

After experimental myocardial infarction, male Wistar rats were treated with either placebo or the eNOS-transcription enhancer, AVE9488 (25 ppm/day) for 10 weeks. In rats with severe CHF (left ventricular end-diastolic pressure >15 mmHg), platelet vasodilator-stimulated phosphoprotein (VASP)-phosphorylation reflecting the integrity of the NO/cGMP pathway was significantly reduced (mean immunofluorescence at Ser(157): Sham, 61.4 +/- 9.1; CHF-Placebo, 37.4 +/- 4.9; P < 0.05; Ser(239): Sham, 18.1 +/- 2.5; CHF-Placebo, 13.2 +/- 0.6; P < 0.05). Platelet surface expression of P-selectin and glycoprotein 53 were increased in CHF rats compared with sham-operated animals. Chronic treatment with AVE9488 significantly enhanced platelet VASP-phosphorylation in CHF rats (Ser(157): 70.4 +/- 16.2; Ser(239): 19.3 +/- 1.8). In parallel, platelet surface expression of P-selectin and glycoprotein 53 was reduced in the treatment group.

CONCLUSION

Platelet activation was evident in CHF rats. Therapy with the eNOS-transcription enhancer, AVE9488, reduced platelet activation in parallel to normalization of platelet NO bioavailability.

Potential novel pharmacological therapies for myocardial remodelling

Left ventricular (LV) remodelling remains an important treatment target in patients after myocardial infarction (MI) and chronic heart failure (CHF). Accumulating evidence has supported the concept that beneficial effects of current pharmacological treatment strategies to improve the prognosis in these patients, such as angiotensin-converting enzyme (ACE) inhibition, angiotensin type 1 receptor blocker therapy, and beta-blocker therapy, are related, at least in part, to their effects on LV remodelling and dysfunction. However, despite modern reperfusion therapy after MI and optimized treatment of patients with CHF, LV remodelling is observed in a substantial proportion of patients and is associated with an adverse clinical outcome. These observations call for novel therapeutic strategies to prevent or even reverse cardiac remodelling. Recent insights from experimental studies have provided new targets for interventions to prevent or reverse LV remodelling, i.e. reduced endothelial nitric oxide (NO) synthase-derived NO availability, activation of cardiac and leukocyte-dependent oxidant stress pathways, inflammatory pathway activation, matrix-metalloproteinase activation, or stem cell transfer and delivery of novel paracrine factors. An important challenge in translating these observations from preclinical studies into clinical treatment strategies relates to the fact that clinical studies are designed on top of established pharmacological therapy, whereas most experimental studies have tested novel interventions without concomitant drug regimens such as ACE inhibitors or beta-blockers. Therefore, animal studies may overestimate the effect of potential novel treatment strategies on LV remodelling and dysfunction, since established pharmacological therapies may act, in part, via identical or similar signalling pathways. Nevertheless, preclinical studies provide essential information for identifying potential novel targets, and their potential drawbacks, and are required for developing novel clinical treatment strategies to prevent or reverse LV remodelling and dysfunction.