Endothelial dysfunction limits the antihypertrophic action of bradykinin in rat cardiomyocytes

The opposing roles of NO and oxidative stress in cardiovascular disease

Nitric oxide (NO) plays a pivotal role in the maintenance of cardiovascular homeostasis. A reduction in the bioavailability of endogenous NO, manifest as a decrease in the production and/or impaired signaling, is associated with many cardiovascular diseases including hypertension, atherosclerosis, stroke and heart failure. There is substantial evidence that reactive oxygen species (ROS), generated predominantly from NADPH oxidases (Nox), are responsible for the reduced NO bioavailability in vascular and cardiac pathologies. ROS can compromise NO function via a direct inactivation of NO, together with a reduction in NO synthesis and oxidation of its receptor, soluble guanylyl cyclase. Whilst nitrovasodilators are administered to compensate for the ROS-mediated loss in NO bioactivity, their clinical utility is limited due to the development of tolerance and resistance and systemic hypotension. Moreover, efforts to directly scavenge ROS with antioxidants has had limited clinical efficacy. This review outlines the therapeutic utility of NO-based therapeutics in cardiovascular diseases and describes the source and impact of ROS in these pathologies, with particular focus on the interaction with NO. Future therapeutic approaches in the treatment of cardiovascular diseases are highlighted with a focus on nitroxyl (HNO) donors as an alternative to traditional NO donors and the development of novel Nox inhibitors.

Unexpected anti-hypertrophic responses to low-level stimulation of protease-activated receptors in adult rat cardiomyocytes

Activators of protease-activated receptors PAR-1 and PAR-2 such as thrombin and synthetic hexapeptides promote hypertrophy of isolated neonatal cardiomyocytes at pathological concentrations. Since PAR-activating proteases often show dual actions at low vs. high concentrations, the potential hypertrophic effects of low-level PAR activation were examined. In H9c2 cardiomyoblasts, messenger RNA (mRNA) expression of the hypertrophic marker atrial natriuretic peptide (ANP) was significantly increased only by higher concentrations of thrombin, trypsin or the synthetic PAR-2 agonist SLIGRL. The dual PAR-1/PAR-2 agonist SFLLRN did not influence basal ANP mRNA expression in H9c2 cells. Low concentration of thrombin or trypsin (up to 0.1 U/mL) or of the synthetic ligands SFLLRN and SLIGRL (1 μM); however, all suppressed ANP mRNA expression stimulated by angiotensin II (Ang II). The PAR-1 selective ligand TFLLRN exerted a comparable effect as SFLLRN. In adult rat cardiomyocytes, protein synthesis determined by [(3)H]phenylalanine incorporation was not increased by various PAR agonists at concentrations tenfold lower than conventionally used to study PAR function in vitro (10 μM for SFLLRN or SLIGRL, 0.1 U/mL for thrombin or trypsin). The positive control endothelin-1 (ET-1, 60 nM) however significantly increased protein synthesis in adult rat cardiomyocytes. Addition of low concentrations of PAR agonists to cardiomyocytes treated with ET-1 or Ang II suppressed [(3)H]phenylalanine incorporation induced by the hypertrophic stimuli. The inhibitory effect of SFLLRN effect was partially reversed by the PAR-1 antagonist RWJ56110. These findings suggest that physiological concentrations of PAR activators may suppress hypertrophy, in contrast to the pro-hypertrophic effects evident at high concentrations. PAR-1 and PAR-2 may dynamically control cardiomyocyte growth, with the net effect critically dependent upon local agonist concentrations. The precise significance of proposed concept of bimodal PAR function in cardiomyocytes remains to be defined, particularly in vivo where hemodynamic and other regulatory factors may counteract or mask the direct cellular actions described here.

Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Cardiovascular disease is the primary cause of morbidity and mortality among the diabetic population. Both experimental and clinical evidence suggest that diabetic subjects are predisposed to a distinct cardiomyopathy, independent of concomitant macro- and microvascular disorders. 'Diabetic cardiomyopathy' is characterized by early impairments in diastolic function, accompanied by the development of cardiomyocyte hypertrophy, myocardial fibrosis and cardiomyocyte apoptosis. The pathophysiology underlying diabetes-induced cardiac damage is complex and multifactorial, with elevated oxidative stress as a key contributor. We now review the current evidence of molecular disturbances present in the diabetic heart, and their role in the development of diabetes-induced impairments in myocardial function and structure. Our focus incorporates both the contribution of increased reactive oxygen species production and reduced antioxidant defenses to diabetic cardiomyopathy, together with modulation of protein signaling pathways and the emerging role of protein O-GlcNAcylation and miRNA dysregulation in the progression of diabetic heart disease. Lastly, we discuss both conventional and novel therapeutic approaches for the treatment of left ventricular dysfunction in diabetic patients, from inhibition of the renin-angiotensin-aldosterone-system, through recent evidence favoring supplementation of endogenous antioxidants for the treatment of diabetic cardiomyopathy. Novel therapeutic strategies, such as gene therapy targeting the phosphoinositide 3-kinase PI3K(p110α) signaling pathway, and miRNA dysregulation, are also reviewed. Targeting redox stress and protective protein signaling pathways may represent a future strategy for combating the ever-increasing incidence of heart failure in the diabetic population.

HNO/cGMP-dependent antihypertrophic actions of isopropylamine-NONOate in neonatal rat cardiomyocytes: potential therapeutic advantages of HNO over NO

Nitroxyl (HNO) is a redox congener of NO. We now directly compare the antihypertrophic efficacy of HNO and NO donors in neonatal rat cardiomyocytes and compare their contributing mechanisms of actions in this setting. Isopropylamine-NONOate (IPA-NO) elicited concentration-dependent inhibition of endothelin-1 (ET1)-induced increases in cardiomyocyte size, with similar suppression of hypertrophic genes. Antihypertrophic IPA-NO actions were significantly attenuated by l-cysteine (HNO scavenger), Rp-8-pCTP-cGMPS (cGMP-dependent protein kinase inhibitor), and 1-H-(1,2,4)-oxodiazolo-quinxaline-1-one [ODQ; to target soluble guanylyl cyclase (sGC)] but were unaffected by carboxy-PTIO (NO scavenger) or CGRP8-37 (calcitonin gene-related peptide antagonist). Furthermore, IPA-NO significantly increased cardiomyocyte cGMP 3.5-fold (an l-cysteine-sensitive effect) and stimulated sGC activity threefold, without detectable NO release. IPA-NO also suppressed ET1-induced cardiomyocyte superoxide generation. The pure NO donor diethylamine-NONOate (DEA-NO) reproduced these IPA-NO actions but was sensitive to carboxy-PTIO rather than l-cysteine. Although IPA-NO stimulation of purified sGC was preserved under pyrogallol oxidant stress (in direct contrast to DEA-NO), cardiomyocyte sGC activity after either donor was attenuated by this stress. Excitingly IPA-NO also exhibited acute antihypertrophic actions in response to pressure overload in the intact heart. Together these data strongly suggest that IPA-NO protection against cardiomyocyte hypertrophy is independent of both NO and CGRP but rather utilizes novel HNO activation of cGMP signaling. Thus HNO acutely limits hypertrophy independently of NO, even under conditions of elevated superoxide. Development of longer-acting HNO donors may thus represent an attractive new strategy for the treatment of cardiac hypertrophy, as stand-alone and/or add-on therapy to standard care.

The soluble guanylyl cyclase activator bay 58-2667 selectively limits cardiomyocyte hypertrophy

BACKGROUND

Although evidence now suggests cGMP is a negative regulator of cardiac hypertrophy, the direct consequences of the soluble guanylyl cyclase (sGC) activator BAY 58-2667 on cardiac remodeling, independent of changes in hemodynamic load, has not been investigated. In the present study, we tested the hypothesis that the NO(•)-independent sGC activator BAY 58-2667 inhibits cardiomyocyte hypertrophy in vitro. Concomitant impact of BAY 58-2667 on cardiac fibroblast proliferation, and insights into potential mechanisms of action, were also sought. Results were compared to the sGC stimulator BAY 41-2272.

METHODS

Neonatal rat cardiomyocytes were incubated with endothelin-1 (ET(1), 60nmol/L) in the presence and absence of BAY 41-2272 and BAY 58-2667 (0.01-0.3 µmol/L). Hypertrophic responses and its triggers, as well as cGMP signaling, were determined. The impact of both sGC ligands on basal and stimulated cardiac fibroblast proliferation in vitro was also determined.

RESULTS

We now demonstrate that BAY 58-2667 (0.01-0.3 µmol/L) elicited concentration-dependent antihypertrophic actions, inhibiting ET(1)-mediated increases in cardiomyocyte 2D area and de novo protein synthesis, as well as suppressing ET(1)-induced cardiomyocyte superoxide generation. This was accompanied by potent increases in cardiomyocyte cGMP accumulation and activity of its downstream signal, vasodilator-stimulated phosphoprotein (VASP), without elevating cardiomyocyte cAMP. In contrast, submicromolar concentrations of BAY 58-2667 had no effect on basal or stimulated cardiac fibroblast proliferation. Indeed, only at concentrations ≥10 µmol/L was inhibition of cardiac fibrosis seen in vitro. The effects of BAY 58-2667 in both cell types were mimicked by BAY 41-2272.

CONCLUSIONS

Our results demonstrate that BAY 58-2667 elicits protective, cardiomyocyte-selective effects in vitro. These actions are associated with sGC activation and are evident in the absence of confounding hemodynamic factors, at low (submicromolar) concentrations. Thus this distinctive sGC ligand may potentially represent an alternative therapeutic approach for limiting myocardial hypertrophy.

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.

Lack of association between aortic sclerosis and left ventricular hypertrophy in elderly subjects

BACKGROUND

The presence of aortic sclerosis has been associated with increased LV mass, particularly in hypertensive subjects. However, aortic sclerosis has also been associated with endothelial dysfunction, which may provide stimuli for development of left ventricular hypertrophy independent of afterload. Thus, we have sought to determine whether aortic sclerosis is a determinant of increased left ventricular mass in a non-hypertensive cohort of aging subjects.

METHODS

79 subjects, mean age 68 ± 6 years, without existing cardiovascular disease or previous antihypertensive therapy were studied. LV volumes were calculated from the short axis stack of cardiac MRI and LV mass was indexed to height(2.7). The presence of aortic sclerosis was assessed with echocardiography using backscatter from the aortic valve (AV(BS)) and visual scoring. Plasma asymmetric dimethylarginine levels and vascular responses to salbutamol were used to assess endothelial function. ANCOVA was used to test the relationship between LV mass index and afterload. Univariate and multivariate analyses were performed to find determinants of increased LV mass.

RESULTS

15 (19%) of subjects had aortic sclerosis on the basis of AV(BS); none had aortic valve areas <1.5 cm(2). There was no significant difference in LV mass between subjects with and without aortic sclerosis. While LV mass was directly related to systolic blood pressure, this relationship was independent of the presence/absence of aortic sclerosis. On multivariate analysis, significant correlates of increased LV mass were male gender, systolic blood pressure and increased BMI, but not presence of aortic sclerosis.

CONCLUSIONS

In this aging normotensive population free of established cardiovascular disease, aortic sclerosis is not associated with left ventricular hypertrophy.

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.

Direct isolation, culture and transplant of mouse skeletal muscle derived endothelial cells with angiogenic potential

BACKGROUND

Although diseases associated with microvascular endothelial dysfunction are among the most prevalent illnesses to date, currently no method exists to isolate pure endothelial cells (EC) from skeletal muscle for in vivo or in vitro study.

METHODOLOGY

By utilizing multicolor fluorescent-activated cell sorting (FACS), we have isolated a distinct population of Sca-1(+), CD31(+), CD34(dim) and CD45(- )cells from skeletal muscles of C57BL6 mice. Characterization of this population revealed these cells are functional EC that can be expanded several times in culture without losing their phenotype or capabilities to uptake acetylated low-density lipoprotein (ac-LDL), produce nitric oxide (NO) and form vascular tubes. When transplanted subcutaneously or intramuscularly into the tibialis anterior muscle, EC formed microvessels and integrated with existing vasculature.

CONCLUSION

This method, which is highly reproducible, can be used to study the biology and role of EC in diseases such as peripheral vascular disease. In addition this method allows us to isolate large quantities of skeletal muscle derived EC with potential for therapeutic angiogenic applications.

Tissue kallikrein and kinin infusion rescues failing myocardium after myocardial infarction

BACKGROUND

Tissue kallikrein is a serine proteinase that generates the vasoactive kinin peptide, which produces vasodilatory, angiogenic, and antiapoptotic effects. In this study, we investigated the effect of a stable supply of kallikrein and kinin on ventricular remodeling and blood vessel growth in rats after myocardial infarction.

METHODS AND RESULTS

At 1 week after coronary artery ligation, tissue kallikrein or kinin was infused through a minipump for 4 weeks. At 5 weeks after myocardial infarction, kallikrein and kinin infusion significantly improved cardiac contractility and reduced diastolic dysfunction without affecting systolic blood pressure. Kallikrein and kinin infusion significantly increased capillary density in the noninfarcted region. Kallikrein and kinin infusion also reduced heart weight/body weight ratio, cardiomyocyte size, and atrial natriuretic peptide and brain natriuretic peptide expression in the noninfarcted area. Moreover, kallikrein and kinin infusion inhibited interstitial collagen deposition, collagen fraction volume, and collagen I and collagen III mRNA levels, transforming growth factor (TGF)-beta1 and plasminogen activator inhibitor-1 expression, and Smad2 phosphorylation. The effects of kallikrein and kinin on cardiac remodeling were associated with increased nitric oxide levels and reduced NADPH oxidase expression and activity, superoxide formation, and malondialdehyde levels. Furthermore, in cultured cardiac fibroblasts, kinin inhibited angiotensin II-stimulated TGF-beta1 production, and the effect was blocked by icatibant.

CONCLUSION

These results indicate that a subdepressor dose of kallikrein or kinin can restore impaired cardiac function in rats with postinfarction heart failure by inhibiting hypertrophy and fibrosis and promoting angiogenesis through increased nitric oxide formation and suppression of oxidative stress and TGF-beta1 expression.

Putative roles of kinin receptors in the therapeutic effects of angiotensin 1-converting enzyme inhibitors in diabetes mellitus

The role of endogenous kinins and their receptors in diabetes mellitus is being confirmed with the recent developments of molecular and genetic animal models. Compelling evidence suggests that the kinin B(2) receptor is organ-protective and partakes to the therapeutic effects of angiotensin 1-converting enzyme inhibitors (ACEI) and angiotensin AT(1) receptor antagonists. Benefits derive primarily from vasodilatory, antihypertensive, antiproliferative, antihypertrophic, antifibrotic, antithrombotic and antioxidant properties of kinin B(2) receptor activation. Mechanisms include the formation of nitric oxide and prostacyclin and the inhibition of NAD(P)H oxidase activity involving classical and novel signalling pathways. Kinin B(2) receptor also ameliorates insulin resistance by increasing glucose uptake and supply, and by inducing glucose transporter-4 translocation either directly or through phosphorylation of insulin receptor. The kinin B(1) receptor, which is induced by the cytokine network, growth factors and hyperglycaemia, mediates hyperalgesia, vascular hyperpermeability and leukocytes infiltration in diabetic animals. However, emerging data highlight reno- and cardio-protective effects mediated by kinin B(1) receptor under chronic ACEI therapy in diabetes mellitus. Thus, the Janus-faced of kinin receptors needs to be taken into account in future drug development. For instance, locally acting kinin B(1)/B(2) receptor agonists if used in a safe therapeutic window may represent a more rationale strategy in the prevention and management of diabetic complications. Because kinin B(2) receptor antagonists may further increase insulin resistance, the persisting dogma that restricts the development of kinin receptor analogues to antagonists (that is still relevant to abrogate pain and inflammation) needs to be revisited.

B-type natriuretic peptide prevents acute hypertrophic responses in the diabetic rat heart: importance of cyclic GMP

Stimulation of cardiomyocyte guanosine 3',5'-cyclic monophosphate (cyclic GMP) via endothelial-derived nitric oxide (NO) is an important mechanism by which bradykinin and ACE inhibitors prevent hypertrophy. Endothelial NO dysfunction and cardiac hypertrophy are morbid features of diabetes not entirely prevented by ACE inhibitors. In cardiomyocyte/endothelial cell cocultures, bradykinin efficacy is abolished by high-glucose-induced endothelial NO dysfunction. We now demonstrate that antihypertrophic actions of natriuretic peptides, which stimulate cyclic GMP independently of NO, are preserved in cardiomyocytes despite high-glucose-induced endothelial dysfunction. Further, streptozotocin-induced diabetes significantly impairs the effectiveness of acute antihypertrophic strategies in isolated rat hearts. In hearts from citrate-treated control rats, angiotensin II-stimulated [(3)H]phenylalanine incorporation and atrial natriuretic peptide and beta-myosin heavy chain mRNA expression were prevented by B-type natriuretic peptide (BNP), bradykinin, the ACE inhibitor ramiprilat, and the neutral endopeptidase inhibitor candoxatrilat. These antihypertrophic effects were accompanied by increased left ventricular cyclic GMP. In age-matched diabetic hearts, the antihypertrophic and cyclic GMP stimulatory actions of bradykinin, ramiprilat, and candoxatrilat were absent. However, the blunting of hypertrophic markers and accompanying increases in cyclic GMP stimulated by BNP were preserved in diabetes. Thus BNP, which increases cyclic GMP independently of NO, is an important approach to prevent growth in the diabetic myocardium, where endothelium-dependent mechanisms are compromised.

Acute antihypertrophic actions of bradykinin in the rat heart: importance of cyclic GMP

The antihypertrophic action of angiotensin (Ang)-converting enzyme (ACE) inhibitors in the heart is attributed in part to potentiation of bradykinin. Bradykinin prevents hypertrophy of cultured cardiomyocytes by releasing nitric oxide (NO) from endothelial cells, which increases cardiomyocyte guanosine 3'5'-cyclic monophosphate (cyclic GMP). It is unknown whether cyclic GMP is essential for the action of bradykinin, or whether findings in isolated cardiomyocytes apply in whole hearts, in the presence of other cell types and mechanical/dynamic activity. We now examine the contribution of cyclic GMP to the antihypertrophic action of bradykinin in cardiomyocytes and perfused hearts. In adult rat isolated cardiomyocytes cocultured with bovine aortic endothelial cells, the inhibitory action of bradykinin (10 micromol/L) against Ang II (1 micromol/L)-induced [3H]phenylalanine incorporation was abolished by the soluble guanylyl cyclase inhibitor [1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L). In Langendorff-perfused rat hearts, Ang II (10 nmol/L)-induced increases in [3H]phenylalanine incorporation and atrial natriuretic peptide mRNA expression were prevented by bradykinin (100 nmol/L), the NO donor sodium nitroprusside (3 micromol/L), and the ACE inhibitor ramiprilat (100 nmol/L). The acute antihypertrophic action of bradykinin was accompanied by increased left ventricular cyclic GMP, and the ramiprilat effect was attenuated by HOE 140 (1 micromol/L, a B2-kinin receptor antagonist) or [1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (100 nmol/L). In conclusion, bradykinin exerts a direct inhibitory action against the acute hypertrophic response to Ang II in rat isolated hearts, and elevation of cardiomyocyte cyclic GMP may be an important antihypertrophic mechanism used by bradykinin and ramiprilat in the heart.

Bradykinin inhibits serum-depletion-induced apoptosis of human vascular endothelial cells by inducing nitric oxide via calcium ion kinetics

Vascular endothelial cells play important roles in atherogenesis, and bradykinin is associated with atherosclerosis. The effect of bradykinin on apoptosis in human umbilical vein endothelial cells (HUVECs) was investigated, with a focus on Ca2+ kinetics and nitric oxide production. In serum-free conditions, the number of apoptotic cells increased in a time-dependent manner, but this increase was inhibited by bradykinin in a dose-dependent manner. The apoptosis inhibited by bradykinin was reduced by nitric oxide inhibitor N(G)-monomethyl-L-arginine (L-NMMA) and consequently restored by combined treatment with L-NMMA and L-arginine. Bradykinin increased influx of extracellular Ca2+, generation of inositol 1,4,5-trisphosphate, and release of Ca2+ from intracellular storage sites, thus increasing the total intracellular Ca2+ concentration ([Ca2+]i). Bradykinin increased nitric oxide production, which was inhibited by L-NMMA and restored by combined treatment with L-NMMA and L-arginine. Sodium nitroprusside (SNP) dose-dependently increased nitric oxide production and inhibited apoptosis; however, 10(-5) M SNP did not inhibit apoptosis. Caspase-3 inhibitor, acetyl-Asp-Met-Gln-Asp-aldehyde, enhanced bradykinin-induced inhibition of apoptosis but did not effect bradykinin-induced nitric oxide production. These findings suggest that bradykinin inhibits serum-depletion-induced apoptosis in HUVECs by enhancing nitric oxide production via an increase in [Ca2+]i.