Role of endothelins in congestive heart failure

Up-regulation of heme oxygenase-1 after infarct initiation reduces mortality, infarct size and left ventricular remodeling: experimental evidence and proof of concept

BACKGROUND

Up-regulation of HO-1 by genetic manipulation or pharmacological pre-treatment has been reported to provide benefits in several animal models of myocardial infarction (MI). However, its efficacy following MI initiation (as in clinical reality) remains to be tested. Therefore, this study investigated whether HO-1 over-expression, by cobalt protoporphyrin (CoPP) administered after LAD ligation, is still able to improve functional and structural changes in left ventricle (LV) in a rat model of 4-week MI.

METHODS

A total of 144 adult male Wistar rats were subjected to either left anterior coronary artery ligation or sham-operation. The effect of CoPP treatment (5 mg/kg i.p. at the end of the surgical session and, then, once a week for 4 weeks) was evaluated on the basis of survival, electro- and echocardiography, plasma levels of B-type natriuretic peptide (BNP), endothelin-1 and prostaglandin E2, coronary microvascular reactivity, MI size, LV wall thickness and vascularity. Besides, the expression of HO-1 and connexin-43 in different LV territories was assessed by western blot analysis and immunohistochemistry, respectively.

RESULTS

CoPP induced an increased expression of HO-1 protein with >16 h delay. CoPP treatment significantly reduced mortality, MI size, BNP concentration, ECG alterations, LV dysfunction, microvascular constriction, capillary rarefaction and restored connexin-43 expression as compared to untreated MI. These functional and structural changes were paralleled by increased HO-1 expression in all LV territories. HO activity inhibition by tin-mesoporphyrin abolished the differences between CoPP-treated and untreated MI animals.

CONCLUSIONS

This is the first report demonstrating the putative role of pharmacological induction of HO-1 following coronary occlusion to benefit infarcted and remote territories, leading to better cardiac function in a 4-week MI outcome.

Inotropes for the management of acute heart failure patients with renal dysfunction. Still an option?

INTRODUCTION

Renal dysfunction is highly prevalent in patients with acute heart failure (AHF). These patients are more vulnerable in worsening of kidney function and have also higher mortality rates.

AREAS COVERED

Recent developments in the understanding of bidirectional interaction between heart and kidney are reviewed in the context of the potential impact of inotropes on renal function. Key clinical trials reporting the use of inotropes in AHF patients with renal dysfunction are discussed in this review.

EXPERT OPINION

Inotropes may be indicated on a short-term basis and under close monitoring in AHF with renal dysfunction mostly in cases of low output heart failure that can provoke renal hypoperfusion. Dopamine administration with low dose of i.v. furosemide has been recently compared with high dose of i.v. furosemide alone, demonstrating lower rates of worsening renal function and electrolyte disturbances. Moreover, small clinical trials have shown that the novel inodilator levosimendan seems to be superior to dobutamine or placebo in improving renal function in patients with acutely decompensated heart failure. The impact of novel inotropes on kidney function is still unclear. Randomized clinical trials are required in order to identify the role of inotropes in the management and/or prevention of acute cardiorenal syndrome.

Therapeutic options for the management of the cardiorenal syndrome

Patients with heart failure often present with impaired renal function, which is a predictor of poor outcome. The cardiorenal syndrome is the worsening of renal function, which is accelerated by worsening of heart failure or acute decompensated heart failure. Although it is a frequent clinical entity due to the improved survival of heart failure patients, still its pathophysiology is not well understood, and thus its therapeutic approach remains controversial and sometimes ineffective. Established therapeutic strategies, such as diuretics and inotropes, are often associated with resistance and limited clinical success. That leads to an increasing concern about novel options, such as the use of vasopressin antagonists, adenosine A1 receptor antagonists, and renal-protective dopamine. Initial clinical trials have shown quite encouraging results in some heart failure subpopulations but have failed to demonstrate a clear beneficial role of these agents. On the other hand, ultrafiltration appears to be a more promising therapeutic procedure that will improve volume regulation, while preserving renal and cardiac function. Further clinical studies are required in order to determine their net effect on renal function and potential cardiovascular outcomes. Until then, management of the cardiorenal syndrome remains quite empirical.

Vascular gene expression in mice overexpressing human endothelin-1 targeted to the endothelium

Endothelin (ET)-1 plays an important pathophysiological role in several vascular diseases including hypertension and atherosclerosis. Transgenic mice overexpressing human preproET-1 selectively in the endothelium (eET-1) exhibit vascular injury in the absence of blood pressure elevation. ET-1 overexpression may induce vascular injury by inducing changes in gene expression. To understand mechanisms whereby ET-1 induces vascular damage, vascular gene expression profiling was performed using DNA microarrays. RNA from mesenteric arteries of male and female young (6-7 wk) and mature (6-8 mo) eET-1 and wild-type (WT) mice was isolated, and changes in gene expression were determined by genome-wide expression profiling using Illumina microarray and FlexArray software. Data were analyzed using a relaxed and a stringent statistical approach. The gene lists were compared and analyzed as well with Ingenuity Pathway Analysis. The most common change was an increase in the expression of lipid metabolism genes. Four of these genes were validated by qPCR, cyp51, dgat2, and scd1 genes in young and elovl6 in both young and mature male mice, supporting a role of ET-1 in atherosclerosis. To test the hypothesis that ET-1 participates in mechanisms leading to atherosclerosis, we crossed eET-1 with atherosclerosis-prone apoE(-/-) mice to determine whether ET-1 overexpression exacerbates high-fat diet (HFD)-induced atherosclerosis using oil red O staining of descending thoracic aorta. HFD increased lipid plaques by 3-, 27-, and 86-fold in eET-1, apoE(-/-), and crossed mice, respectively, vs. WT. This suggests that increased endothelial ET-1 expression results in early changes in gene expression in the vascular wall that enhance lipid biosynthesis and accelerate progression of atherosclerosis.

Endothelin receptors: what's new and what do we need to know?

Receptors are at the heart of how a molecule transmits a signal to a cell. Two receptor classes for endothelin (ET) are recognized, the ET(A) and ET(B) receptors. Intriguing questions have arisen in the field of ET receptor pharmacology, physiology, and function. For example, a host of pharmacological studies support the interaction of the ET(A) and ET(B) receptor in tissues (veins, arteries, bronchus, arterioles, esophagus), but yet few have been able to demonstrate direct ET(A)/ET(B) receptor interaction. Have we modeled this interaction wrong? Do we have a truly selective ET(A) receptor agonist such that we could selectively stimulate this important receptor? What can we learn from the recent phylogenic studies of the ET receptor family? Have we adequately addressed the number of biological molecules with which ET can interact to exert a biological effect? Recent mass spectrometry studies in our laboratory suggest that ET-1 interacts with other hereto unrecognized proteins. Biased ligands (ligands at the same receptor that elicit distinct signaling responses) have been discovered for other receptors. Do these exist for ET receptors and can we take advantage of this possibility in drug design? These and other questions will be posed in this minireview on topics on ET receptors.

Role of endothelin receptors on basal and endothelin-1-stimulated lung myofibroblast proliferation

Proliferation of myofibroblasts (MYF) contributes to numerous lung disorders. Endothelin-1 (ET-1) production is increased in various lung diseases and could contribute to lung remodelling. The respective roles of ETA and ETB receptors (ETA-R, ETB-R) and the role of endogenous ET-1 production by lung MYF on proliferation of MYF remain uncertain. Rat lung MYF were isolated and 3H-thymidine and 3H-leucine incorporation assays were completed in the presence of a selective ETA-R antagonist, a selective ETB-R antagonist, or a combination of both. Receptor expression was evaluated by confocal imaging, and ET-1 levels were measured by ELISA. Confocal microscopy revealed abundant ETA-R and ETB-R expression on lung MYF. ET-1 (10 nmol/L) stimulated MYF proliferation and protein synthesis through PI3-kinase and p38 pathways. Although neither selective ETA-R blockade (BQ-123, 1 micromol/L) nor selective ETB-R blockade (BQ-788, 1 micromol/L) alone inhibited proliferation or protein synthesis, their combination almost completely abolished ET-1 mitogenic effect. Surprisingly, basal MYF proliferation was increased by selective blockade of either ETA-R or ETB-R alone, but not by dual blockade. ET-1 levels were not affected by the antagonists. Our findings indicate that both the ETA-R and the ETB-R regulate basal and stimulated lung MYF proliferation and suggest possible interactions between the receptors.

Endothelin-1 regulates cardiac L-type calcium channels via NAD(P)H oxidase-derived superoxide

It has been shown that reactive oxygen species (ROS) are involved in the intracellular signaling response to G-protein coupled receptor stimuli in vascular smooth muscle cells and in neurons. In the present study, we tested the hypothesis that NAD(P)H oxidase-derived ROS are involved endothelin-1 (ET-1)-induced L-type calcium channel activation in isolated cardiac myocytes. ET-1 (10 nM) induced a 2-fold increase in L-type calcium channel open-state probability (NPo). This effect of ET-1 was abolished by the ET(A) receptor antagonist cyclo(D-Trp-D-Asp-Pro-D-Val-Leu) [BQ-123 (1 microM)] but was not altered in the presence of an ET(B) receptor antagonist N-cis-2,6-dimethylpiperidinocarbonyl-b-tBu-Ala-D-Trp(1-methoxycarbonyl)-D-Nle-OH [BQ-788 (1 microM)]. Pretreatment of cells with the ROS scavenger tempol (100 microM), polyethylene glycol-superoxide dismutase (SOD, 25 U/ml), or the NAD(P)H-oxidase inhibitor gp91ds-tat ([H]RKKRRQRRR-CSTRIRRQL[NH(3)]) (5 microM) significantly attenuated ET-1-induced increases in calcium channel NPo. Tempol, SOD, and gp91ds-tat alone had no effect on basal calcium channel activity. In addition, ET-1 significantly increased NAD(P)H oxidase activity and elevated intracellular superoxide levels in cultured cardiac myocytes. The superoxide generator, xanthine-xanthine oxidase (10 mM, 20 mU/ml), also increased calcium channel NPo in cardiac myocytes, mimicking the effect of ET-1. These observations provide the first evidence that ET-1 induces the activation of L-type Ca(2+) channels via stimulation of NAD(P)H-derived superoxide production in cardiac myocytes.

Nonselective ETA/ETB-receptor blockade increases systemic blood pressure of Bio 14.6 cardiomyopathic hamstersThis article is one of a selection of papers published in the special issue (part 1 of 2) on Forefronts in Endothelin

To examine the role of endothelin ETA and ETB receptors in congestive heart failure due to cardiomyopathy, the effect of chronic treatment with selective ETA- and ETB-receptor antagonists (atrasentan and A-192621, respectively), alone and in combination, was assessed on functional and biochemical parameters of 52-week-old Bio 14.6 cardiomyopathic hamsters. Compared with control animals, cardiomyopathic hamsters treated for 9 weeks with atrasentan showed no variation in MAP; however, selective ETB- and combined nonselective ETA- and ETB-receptor antagonists increased systemic blood pressure. After selective ETB-receptor blockade, plasma endothelin levels were augmented. Importantly, this increase was highly enhanced (more than 8-fold) by concomitant ETA-receptor antagonism. Furthermore, the left ventricle : body weight ratio of cardiomyopathic hamsters treated with A-192621, alone or in combination with atrasentan, was significantly increased. On the other hand, decreased left ventricular end-diastolic pressure was observed in cardiomyopathic hamsters after selective ETA- or combined nonselective ETA/ETB-receptor antagonism, while only selective ETA-receptor blockade reduced left ventricular endothelin levels. Our results suggest that, in congestive heart failure, ETB receptors are essential to limit circulating endothelin levels, which may argue for improved cardiac benefits after long-term treatment with highly selective ETA-receptor antagonists.

Contractile regulation by overexpressed ETArequires intact T tubules in adult rat ventricular myocytes

Endothelin (ET)-1 regulates the contractility and growth of the heart by binding G protein-coupled receptors of the ET type A receptor (ETA)/ET type B (ETB) receptor family. ETA, the predominant ET-1 receptor subtype in myocardium, is thought to localize preferentially within cardiac T tubules, but the consequences of mislocalization are not fully understood. Here we examined the effects of the overexpression of ETAin conjunction with T-tubule loss in cultured adult rat ventricular myocytes. In adult myocytes cultured for 3 to 4 days, the normally robust positive inotropic effect (PIE) of ET-1 was lost in parallel with T-tubule degeneration and a decline in ETAprotein levels. In these T tubule-compromised myocytes, an overexpression of ETAusing an adenoviral vector did not rescue the responsiveness to ET-1, despite the robust expression in the surface sarcolemma. The inclusion of the actin polymerization inhibitor cytochalasin D (CD) during culture prevented gross morphological changes including a loss of T tubules and a rounding of intercalated discs, but CD alone did not rescue the responsiveness to ET-1 or prevent ETAdownregulation. The rescue of a normal PIE in 3- to 4-day cultured myocytes required both an increased expression of ETAand intact T tubules (preserved with CD). Therefore, the activation of ETAlocalized in T tubules was associated with a strong PIE, whereas the activation of ETAin surface sarcolemma was not. The results provide insight into the pathological cardiac conditions in which ETAis upregulated and T-tubule morphology is altered.

Inhibition of basal and stimulated release of endothelin-1 from guinea pig tracheal epithelial cells in culture by beta 2-adrenoceptor agonists and cyclic AMP enhancers

The effects of cyclic AMP-related compounds and beta adrenoceptor agonists on the basal and lipopolysaccharide (LPS)-stimulated release of endothelin-1 (ET-1) from guinea-pig tracheal epithelial cells (GPTEpCs) in culture were studied. Forskolin (a potent activator of adenylyl cyclase), 8-bromo-cyclic AMP (a cyclic AMP analogue), salbutamol and salmeterol (two beta 2-adrenoceptor agonists), were used to increase cyclic AMP levels. Cultured GPTEpCs released ET-1 continuously over a 24 h incubation period. The values reached 1,938 +/- 122 pg/mg of total cell proteins after 24 h. LPS (10 microg/ml) significantly stimulated the release of ET-1 by 1.6- to 1.8-fold, up to 1,262 +/- 56 pg/mg total cell proteins after an 8 h incubation period. Compound 8-bromo-cyclic AMP (10(-5), 10(-4) and 10(-3) M) reduced the basal release of ET-1 from GPTEpCs by up to 31% (P < 0.01) and the LPS stimulated release by up to 42% (P < 0.05), after an 8 h incubation period. Forskolin (10(-6), 10(-5) and 10(-4) M) also inhibited the basal release of ET-1 by up to 28% (P < 0.05) and LPS-stimulated release of ET-1 by up to 50% (P < 0.05), after an 8 h incubation period. At the concentration of 10(-5) M, forskolin increased cyclic AMP levels in GPTEpCs by 17-fold (P < 0.001) in the medium, 15 min after the beginning of the incubation. Salbutamol (10(-8) to 10(-6) M) had no effect on the basal production and release of ET-1 after 8 h. Conversely, this short acting beta 2-adrenoceptor agonist significantly reduced LPS-mediated increase of ET-1 production by up to 55% (P < 0.05) after an 8 h incubation period. Salmeterol (10(-9) M to 10(-5) M) inhibited basal and LPS-stimulated production and release of ET-1 after an 8 h incubation period (between 44 and 51%, P < 0.01). Both salbutamol and salmeterol (10(-6) M) increase cyclic AMP levels by five- and twofold, respectively (P < 0.05). In summary, these observations indicate that beta 2-adrenoceptor agonists or cyclic AMP enhancers can modulate both basal and more markedly, the enhanced production of ET-1 from LPS-activated guinea pig airway EpCs. In addition, these compounds increase cyclic AMP levels in the cells. It is suggested that there is a correlation between cyclic AMP increase and inhibition of ET-1 release by guinea pig airway EpCs. Since ET-1 production was shown to be elevated in asthmatic subjects and in patients suffering from other inflammatory lung disorders, the inhibition of its production by beta adrenoceptor agonists, such as salbutamol and salmeterol, could be added to their therapeutical benefits.

Vascular protection by dietary polyphenols

Consumption of polyphenol-rich foods, such as fruits and vegetables, and beverages derived from plants, such as cocoa, red wine and tea, may represent a beneficial diet in terms of cardiovascular protection. Indeed, epidemiological studies demonstrate a significant inverse correlation between polyphenol consumption and cardiovascular risk. Among the numerous plausible mechanisms by which polyphenols may confer cardiovascular protection, improvement of the endothelial function and inhibition of angiogenesis and cell migration and proliferation in blood vessels have been the focus of recent studies. These studies have indicated that, in addition to and independently from their antioxidant effects, plant polyphenols (1) enhance the production of vasodilating factors [nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and prostacyclin] and inhibit the synthesis of vasoconstrictor endothelin-1 in endothelial cells; and (2) inhibit the expression of two major pro-angiogenic factors, vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP-2) in smooth muscle cells. The mechanisms of these effects involve: (1) in endothelial cells, increased Ca(2+) level and redox-sensitive activation of the phosphoinositide 3 (PI3)-kinase/Akt pathway (leading to rapid and sustained activation of nitric oxide synthase and formation of EDHF) and enhanced expression of nitric oxide synthase; and (2) in smooth muscle cells, both redox-sensitive inhibition of the p38 mitogen-activated protein kinase (p38 MAPK) pathway activation (leading to inhibition of platelet-derived growth factor (PDGF)-induced VEGF gene expression) and redox-insensitive mechanisms (leading to inhibition of thrombin-induced MMP-2 formation). The current evidence suggests that all these mechanisms are triggered by polyphenols with specific structures, although the structural requirements may be different from one effect to the other, and that they all contribute to the vasoprotective, anti-angiogenic, anti-atherogenic, vasorelaxant and anti-hypertensive effects of acute or chronic administration of plant polyphenols found in vivo in animals and in patients.

The endothelin system and its role in acute myocardial infarction

Immediately after an acute myocardial infarction (AMI) or in models of ischemia-reperfusion injury, cardiac endothelin (ET) system is markedly activated, and plasma levels of ET are increased. In the heart, expression of the main components of the ET system (ET-1 peptide, both receptor subtypes ETA and ETB, though not endothelin converting enzyme) are increased both at the gene level and protein level, in the viable myocardium, and--even more substantially--in the necrotic area. Despite these conspicuous abnormalities, the role of ET in this setting remains unclear. In the absence of human data, most short-term studies in animals (in terms of hours to up to 8 days post-AMI) and in the reperfused ischemic heart, have found beneficial effects of ET receptor blockade on survival rate, incidence of arrhythmias, cardiac function, and morphology. In contrast, many studies in which a long-term ET inhibition was started immediately post-infarction and the late effects were examined in animals with ensuing chronic heart failure (14-100 days postinfarction), adverse effects were also observed, such as scar thinning, further ventricular dilation, or even a worse survival rate. It appears that the ET system plays a dual role during the early post-AMI period. At present, it is not clear whether the short-term beneficial effects or long-term adverse effects of ET receptor blockade would prevail. Acute use of short-acting ET receptor antagonists in patients with AMI complicated by an acute heart failure is an attractive possibility that also remains to be investigated.