Clinical trials of endothelin antagonists in heart failure: publication is good for the public health

Is endothelin targeting finally ready for prime time?

The endothelin family of peptides has long been recognized as a physiological regulator of diverse biological functions and mechanistically involved in various disease states, encompassing, among others, the cardiovascular system, the kidney, and the nervous system. Pharmacological blockade of the endothelin system, however, has encountered strong obstacles in its entry into the clinical mainstream, having obtained only a few proven indications until recently. This translational gap has been attributable predominantly to the relevant side effects associated with endothelin receptor antagonism (ERA), particularly fluid retention. Of recent, however, an expanding understanding of the pathophysiological processes involving endothelin, in conjunction with the development of new antagonists of endothelin receptors or adjustment of their doses, has driven a flourish of new clinical trials. The favorable results of some of them have extended the proven indications for ET targeting to a variety of clinical conditions, including resistant arterial hypertension and glomerulopathies. In addition, on the ground of strong preclinical evidence, other studies are ongoing to test the potential benefits of ERA in combination with other treatments, such as sodium-glucose co-transporter 2 inhibition in fluid retentive states or anti-cancer therapies in solid tumors. Furthermore, antibodies providing long-term blockade of endothelin receptors are under testing to overcome the short half-life of most small molecule endothelin antagonists. These efforts may yet bring new life to the translation of endothelin targeting strategies in clinical practice.

Current and future strategies for targeting the endothelin pathway in cardiovascular disease

The first endothelin (ET)-1 receptor antagonist was approved for clinical use over 20 years ago, but to date this class of compounds has been limited to treating pulmonary arterial hypertension, a rare disease. Translational research over the last 5 years has reignited interest in the ET system as a therapeutic target across the spectrum of cardiovascular diseases including resistant hypertension, microvascular angina and post-coronavirus disease 2019 conditions. Notable developments include approval of a new ETA receptor antagonist and, intriguingly, combining the actions of ETA and an angiotensin II type 1 receptor antagonist within the same novel small molecule. Combinations of ET receptor blockers with other drugs, including phosphodiesterase-5 inhibitors and sodium-glucose co-transporter-2 antagonists, may drive synergistic benefits with the prospect of alleviating side effects. These new therapeutic strategies have the potential to dramatically widen the scope of indications targeting the ET-1 pathway.

Signaling cascades in the failing heart and emerging therapeutic strategies

Chronic heart failure is the end stage of cardiac diseases. With a high prevalence and a high mortality rate worldwide, chronic heart failure is one of the heaviest health-related burdens. In addition to the standard neurohormonal blockade therapy, several medications have been developed for chronic heart failure treatment, but the population-wide improvement in chronic heart failure prognosis over time has been modest, and novel therapies are still needed. Mechanistic discovery and technical innovation are powerful driving forces for therapeutic development. On the one hand, the past decades have witnessed great progress in understanding the mechanism of chronic heart failure. It is now known that chronic heart failure is not only a matter involving cardiomyocytes. Instead, chronic heart failure involves numerous signaling pathways in noncardiomyocytes, including fibroblasts, immune cells, vascular cells, and lymphatic endothelial cells, and crosstalk among these cells. The complex regulatory network includes protein-protein, protein-RNA, and RNA-RNA interactions. These achievements in mechanistic studies provide novel insights for future therapeutic targets. On the other hand, with the development of modern biological techniques, targeting a protein pharmacologically is no longer the sole option for treating chronic heart failure. Gene therapy can directly manipulate the expression level of genes; gene editing techniques provide hope for curing hereditary cardiomyopathy; cell therapy aims to replace dysfunctional cardiomyocytes; and xenotransplantation may solve the problem of donor heart shortages. In this paper, we reviewed these two aspects in the field of failing heart signaling cascades and emerging therapeutic strategies based on modern biological techniques.

Sex-Specific Effects of Prenatal Hypoxia on the Cardiac Endothelin System in Adult Offspring

Fetal hypoxia, a major consequence of complicated pregnancies, impairs offspring cardiac tolerance to ischemia/reperfusion (I/R) insult, however, the mechanisms remain unknown. Endothelin-1 (ET-1) signaling through the endothelin A receptors (ET_A) is associated with cardiac dysfunction. We hypothesized that prenatal hypoxia exacerbates cardiac susceptibility to I/R via increased ET-1 and ET_A levels, while ET_A inhibition ameliorates this. Pregnant Sprague-Dawley rats were exposed to normoxia (21% O₂) or hypoxia (11% O₂) on gestational days 15-21. Offspring were aged to 4 months, and hearts were aerobically perfused or subjected to ex vivo I/R, with or without pre-infusion with an ET_A antagonist (ABT-627). ET-1 levels were assessed with ELISA in aerobically perfused and post-I/R left ventricles (LV). ET_A and ET_B levels were assessed by Western blotting in non-perfused LV. As hypothesized, ABT-627 infusion tended to improve post-I/R recovery in hypoxic females (p=0.0528), however, surprisingly, ABT-627 prevented post-I/R recovery only in the hypoxic males (p<0.001). ET-1 levels were increased in post-I/R LV in both sexes regardless of the prenatal exposure (p<0.01). ET_A expression was similar among all groups, while ET_B (isoform C) levels were decreased in prenatally hypoxic females (p<0.05). In prenatally hypoxic males, ET_A signaling may be essential for tolerance to I/R, while in prenatally hypoxic females, ET_A may contribute to cardiac dysfunction. Our data illustrate that understanding the prenatal history has critical implications for treatment strategies in adult chronic diseases.

Structural heart defects associated with ETB mutation, a cause of Hirschsprung disease

BACKGROUND

HSCR, a colonic neurocristopathy affecting 1/5000 births, is suggested to associate with cardiac septal defects and conotruncal malformations. However, we question subtle cardiac changes maybe more commonly present due to multi-regulations by HSCR candidate genes, in this instance, ETB. To investigate, we compared the cardiac morphology and quantitative measurements of sl/sl rat to those of the control group.

METHODS

Eleven neonatal rats were generated from heterozygote (ETB+/-) crossbreeding. Age and bodyweight were recorded at time of sacrifice. Diffusion-staining protocols with 1.5% iodine solution was completed prior to micro-CT scanning. All rats were scanned using an in vivo micro-CT scanner, Caliper Quantum FX, followed by two quality-control scans using a custom-built ex vivo micro-CT system. All scans were reviewed for gross cardiac dysmorphology. Micro-CT data were segmented semi-automatically post-NLM filtering for: whole-heart, LV, RV, LA, RA, and aortic arch. Measurements were taken with Drishti. Following image analysis, PCR genotyping of rats was performed: five sl/sl rats, three wildtype, and three heterozygotes. Statistical comparisons on organ volume, growth rate, and organ volume/bodyweight ratios were made between sl/sl and the control group.

RESULTS

Cardiac morphology and constituents were preserved. However, significant volumetric reductions were recorded in sl/sl rats with respect to the control: whole heart (38.70%, p value = 0.02); LV (41.22%, p value = 0.01), RV (46.15%, p value = 0.02), LA (44.93%, p value = 0.06), and RA (39.49%, p value = 0.02). Consistent trend was observed in growth rate (~ 20%) and organ-volume/bodyweight ratios (~ 25%). On the contrary, measurements on aortic arch demonstrated no significant difference among the two groups.

CONCLUSION

Despite the presence of normal morphology, significant cardiac growth retardation was detected in sl/sl rat, supporting the likely association of cardiac anomalies with HSCR, at least in ETB-/- subtype. Structural reduction was likely due to a combination of failure to thrive from enteric dysfunction, alterations to CaNCC colonization, and importantly coronary hypoperfusion from elevated ET-1/ETA-mediated hypervasoconstriction. Little correlation was detected between aortic arch development and sl/sl rat, supporting minor ETB role in large vessels. Although further clinical study is warranted, HSCR patients may likely require cardiac assessment in view of potential congenital cardiac defects.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

Endothelins in cardiovascular biology and therapeutics

Cardiovascular disease is a major contributor to global morbidity and mortality and is the common end point of many chronic diseases. The endothelins comprise three structurally similar peptides of 21 amino acids in length. Endothelin 1 (ET-1) and ET-2 activate two G protein-coupled receptors - endothelin receptor type A (ET_A) and endothelin receptor type B (ET_B) - with equal affinity, whereas ET-3 has a lower affinity for ET_A. ET-1 is the most potent vasoconstrictor in the human cardiovascular system and has remarkably long-lasting actions. ET-1 contributes to vasoconstriction, vascular and cardiac hypertrophy, inflammation, and to the development and progression of cardiovascular disease. Endothelin receptor antagonists have revolutionized the treatment of pulmonary arterial hypertension. Clinical trials continue to explore new applications of endothelin receptor antagonists, particularly in treatment-resistant hypertension, chronic kidney disease and patients receiving antiangiogenic therapies. Translational studies have identified important roles for the endothelin isoforms and new therapeutic targets during development, in fluid-electrolyte homeostasis, and in cardiovascular and neuronal function. Novel pharmacological strategies are emerging in the form of small-molecule epigenetic modulators, biologics (such as monoclonal antibodies for ET_B) and possibly signalling pathway-biased agonists and antagonists.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

Challenges in pulmonary hypertension associated with left heart disease

Introduction: Pulmonary hypertension (PH) secondary to left-sided heart disease (Group 2 PH) is a frequent complication of heart failure (HF) and is a heterogeneous phenotypic disorder that worsens exercise capacity, increases risk for hospitalization and survival independent of left ventricular ejection fraction (LVEF) or stage of HF. Areas covered: In this review, an update of the current knowledge and some potential challenges about the pathophysiology and treatments of group 2 PH in patients with HF of either preserved or reduced ejection fraction are provided. Also, this review discusses the epidemiology and provides hints for the optimal evaluation and diagnosis of these patients to prevent misclassification of their pulmonary hypertension. Expert opinion: There are many of areas lacking knowledge and understanding in the field of pulmonary hypertension associated to left heart disease (PH-LHD) that should be addressed in the future. Further research should be performed, in terms of pathobiology, and understanding the predisposition (genetic susceptibility and contributing factors) of the different phenotypes of this disorder. More clinical trials targeting new therapeutic options and specific PH therapies are warranted to help this increasing important patient group as the current guidelines recommend to only treat the underlying left-sided heart disease.

The Role of G Protein-Coupled Receptors in the Right Ventricle in Pulmonary Hypertension

Pressure overload of the right ventricle (RV) in pulmonary arterial hypertension (PAH) leads to RV remodeling and failure, an important determinant of outcome in patients with PAH. Several G protein-coupled receptors (GPCRs) are differentially regulated in the RV myocardium, contributing to the pathogenesis of RV adverse remodeling and dysfunction. Many pharmacological agents that target GPCRs have been demonstrated to result in beneficial effects on left ventricular (LV) failure, such as beta-adrenergic receptor and angiotensin receptor antagonists. However, the role of such drugs on RV remodeling and performance is not known at this time. Moreover, many of these same receptors are also expressed in the pulmonary vasculature, which could result in complex effects in PAH. This manuscript reviews the role of GPCRs in the RV remodeling and dysfunction and discusses activating and blocking GPCR signaling to potentially attenuate remodeling while promoting improvements of RV function in PAH.

Evaluation and Management of Right-Sided Heart Failure: A Scientific Statement From the American Heart Association

Background and Purpose:

The diverse causes of right-sided heart failure (RHF) include, among others, primary cardiomyopathies with right ventricular (RV) involvement, RV ischemia and infarction, volume loading caused by cardiac lesions associated with congenital heart disease and valvular pathologies, and pressure loading resulting from pulmonic stenosis or pulmonary hypertension from a variety of causes, including left-sided heart disease. Progressive RV dysfunction in these disease states is associated with increased morbidity and mortality. The purpose of this scientific statement is to provide guidance on the assessment and management of RHF.

Methods:

The writing group used systematic literature reviews, published translational and clinical studies, clinical practice guidelines, and expert opinion/statements to summarize existing evidence and to identify areas of inadequacy requiring future research. The panel reviewed the most relevant adult medical literature excluding routine laboratory tests using MEDLINE, EMBASE, and Web of Science through September 2017. The document is organized and classified according to the American Heart Association to provide specific suggestions, considerations, or reference to contemporary clinical practice recommendations.

Results:

Chronic RHF is associated with decreased exercise tolerance, poor functional capacity, decreased cardiac output and progressive end-organ damage (caused by a combination of end-organ venous congestion and underperfusion), and cachexia resulting from poor absorption of nutrients, as well as a systemic proinflammatory state. It is the principal cause of death in patients with pulmonary arterial hypertension. Similarly, acute RHF is associated with hemodynamic instability and is the primary cause of death in patients presenting with massive pulmonary embolism, RV myocardial infarction, and postcardiotomy shock associated with cardiac surgery. Functional assessment of the right side of the heart can be hindered by its complex geometry. Multiple hemodynamic and biochemical markers are associated with worsening RHF and can serve to guide clinical assessment and therapeutic decision making. Pharmacological and mechanical interventions targeting isolated acute and chronic RHF have not been well investigated. Specific therapies promoting stabilization and recovery of RV function are lacking.

Conclusions:

RHF is a complex syndrome including diverse causes, pathways, and pathological processes. In this scientific statement, we review the causes and epidemiology of RV dysfunction and the pathophysiology of acute and chronic RHF and provide guidance for the management of the associated conditions leading to and caused by RHF.

Kidney involvement in systemic sclerosis: From pathogenesis to treatment

Among all possible systemic sclerosis internal organ complications, kidney involvement is frequently neglected or underestimated, except for the life-threatening scleroderma renal crisis. Fortunately, this severe clinical presentation is nowadays better controlled with available treatments, in particular angiotensin-converting enzyme inhibitors, and this has led to a reduction in its short- and longer-term mortality. Pathogenetic determinants are not well understood and many different other kidney involvements are possible in systemic sclerosis, including proteinuria, albuminuria, reduction of renal filtration, autoantibodies-related glomerulonephritis, and drug-related side effects. Different serological and radiological methods of evaluations are nowadays available, some representing promising diagnostic tool and prognostic outcome measure. Except for angiotensin-converting enzyme inhibitors in scleroderma renal crisis, no other treatment is currently recommended for treatment of kidney involvement in systemic sclerosis. For this reason, further studies are necessary to investigate its prognostic impact, in particular in combination with other systemic sclerosis-related internal organ manifestations. This review summarizes current available literature on kidney involvement in systemic sclerosis.

Neurohormonal Blockade in Heart Failure

A key feature of chronic heart failure (HF) is the sustained activation of endogenous neurohormonal systems in response to impaired cardiac pumping and/or filling properties. The clinical use of neurohormonal blockers has revolutionised the care of HF patients over the past three decades. Drug therapy that is active against imbalance in both the autonomic and renin-angiotensin-aldosterone systems consistently reduces morbidity and mortality in chronic HF with reduced left ventricular ejection fraction and in sinus rhythm. This article provides an assessment of the major neurohormonal systems and their therapeutic blockade in patients with chronic HF.

Treatment of advanced group 2 PH

Pulmonary hypertension (PH) frequently occurs in patients with left heart disease (LHD), including heart failure with reduced and preserved ejection fraction and valvular heart disease. PH in patients with LHD is associated with worse outcomes making it an attractive target of therapy. Despite the strong rational for treatment, no clear benefits from treating with pulmonary arterial hypertension specific therapies in patients with PH from LHD have been found in clinical trials and some studies have demonstrated harm. Therefore, PH in the setting of LHD should be managed with optimal medical and surgical treatment of LHD and identification and treatment of comorbidities that could contribute to PH. Additionally, significant PH is a contraindication to heart transplantation and, in select patients with left heart failure, left ventricular unloading with prolonged inotrope infusion or left ventricular assist device implantation may successfully reduce pulmonary artery pressures and facilitate transplantation.

Modulation of endothelin receptors in the failing right ventricle of the heart and vasculature of the lung in human pulmonary arterial hypertension

AIMS

In pulmonary arterial hypertension (PAH), increases in endothelin-1 (ET-1) contribute to elevated pulmonary vascular resistance which ultimately causes death by right ventricular (RV) heart failure. ET antagonists are effective in treating PAH but lack efficacy in treating left ventricular (LV) heart failure, where ETA receptors are significantly increased. The aim was to quantify the density of ETA and ETB receptors in cardiopulmonary tissue from PAH patients and the monocrotaline (MCT) rat, which recapitulates some of the pathophysiological features, including increased RV pressure.

MAIN METHODS

Radioligand binding assays were used to quantify affinity, density and ratio of ET receptors.

KEY FINDINGS

In RV from human PAH hearts, there was a significant increase in the ratio of ETA to ETB receptors compared with normal hearts. In the RV of the MCT rat, the ratio also changed but was reversed. In both human and rat, there was no change in LV. In human PAH lungs, ETA receptors were significantly increased in the medial layer of small pulmonary arteries with no change detectable in MCT rat vessels.

SIGNIFICANCE

Current treatments for PAH focus mainly on pulmonary vasodilatation. The increase in ETA receptors in arteries provides a mechanism for the beneficial vasodilator actions of ET antagonists. The increase in the ratio of ETA in RV also implicates changes to ET signalling although it is unclear if ET antagonism is beneficial but the results emphasise the unexploited potential for therapies that target the RV, to improve survival in patients with PAH.

The role of the paracrine/autocrine mediator endothelin-1 in regulation of cardiac contractility and growth

Endothelin-1 (ET-1) is a critical autocrine and paracrine regulator of cardiac physiology and pathology. Produced locally within the myocardium in response to diverse mechanical and neurohormonal stimuli, ET-1 acutely modulates cardiac contractility. During pathological cardiovascular conditions such as ischaemia, left ventricular hypertrophy and heart failure, myocyte expression and activity of the entire ET-1 system is enhanced, allowing the peptide to both initiate and maintain maladaptive cellular responses. Both the acute and chronic effects of ET-1 are dependent on the activation of intracellular signalling pathways, regulated by the inositol-trisphosphate and diacylglycerol produced upon activation of the ET(A) receptor. Subsequent stimulation of protein kinases C and D, calmodulin-dependent kinase II, calcineurin and MAPKs modifies the systolic calcium transient, myofibril function and the activity of transcription factors that coordinate cellular remodelling. The precise nature of the cellular response to ET-1 is governed by the timing, localization and context of such signals, allowing the peptide to regulate both cardiomyocyte physiology and instigate disease.

LINKED ARTICLES

This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Clinical trials with endothelin receptor antagonists: what went wrong and where can we improve?

In the early 1990s, within three years of cloning of endothelin receptors, orally active endothelin receptor antagonists (ERAs) were tested in humans and the first clinical trial of ERA therapy in humans was published in 1995. ERAs were subsequently tested in clinical trials involving heart failure, pulmonary arterial hypertension, resistant arterial hypertension, stroke/subarachnoid hemorrhage and various forms of cancer. The results of most of these trials - except those for pulmonary arterial hypertension and scleroderma-related digital ulcers - were either negative or neutral. Problems with study design, patient selection, drug toxicity, and drug dosing have been used to explain or excuse failures. Currently, a number of pharmaceutical companies who had developed ERAs as drug candidates have discontinued clinical trials or further drug development. Given the problems with using ERAs in clinical medicine, at the Twelfth International Conference on Endothelin in Cambridge, UK, a panel discussion was held by clinicians actively involved in clinical development of ERA therapy in renal disease, systemic and pulmonary arterial hypertension, heart failure, and cancer. This article provides summaries from the panel discussion as well as personal perspectives of the panelists on how to proceed with further clinical testing of ERAs and guidance for researchers and decision makers in clinical drug development on where future research efforts might best be focused.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.

Pulmonary hypertension associated with left heart disease: characteristics, emerging concepts, and treatment strategies

Left heart disease (LHD) represents the most common causes of pulmonary hypertension (PH). Whether caused by systolic or diastolic dysfunction or valvular heart disease, a hallmark of PH associated with LHD is elevated left atrial pressure. In all cases, the increase in left atrial pressure causes a passive increase in pulmonary pressure. In some patients, a superimposed active component caused by pulmonary arterial vasoconstriction and vascular remodeling may lead to a further increase in pulmonary arterial pressure. When present, PH is associated with a worse prognosis in patients with LHD. In addition to local abnormalities in nitric oxide and endothelin production, gene modifiers such as serotonin polymorphisms may be associated with the pathogenesis of PH in LHD. Optimizing heart failure regimens and corrective valve surgery represent the cornerstone of the treatment of PH in LHD. Recent studies suggest that sildenafil, a phosphodiesterase-5 inhibitor, is a promising agent in the treatment of PH in LHD. Unloading the left ventricle with circulatory support may also reverse severe PH in patients with end-stage heart failure allowing candidacy to heart transplantation.

What we may expect from biomarkers in heart failure

A profusion of circulating candidate biomarkers in heart failure is currently being investigated. Although all will advance our insight into the pathophysiology of heart failure, their potential clinical utility will depend on satisfaction of three key criteria. Assays must be accessible, reliable, and affordable. Secondly, the marker must provide information about cardiac function and prognosis not otherwise available. Finally, measurement of the marker must demonstrably lead to improved management and better clinical outcomes. Despite many promising candidates requiring fuller investigation, currently, only the natriuretic peptides satisfy these requirements.

Endothelin: 20 years from discovery to therapy

Since its identification as an endothelial cell-derived vasoconstrictor peptide in 1988, endothelin-1, the predominant member of the endothelin peptide family, has received considerable interest in basic medical science and in clinical medicine, which is reflected by more than 20 000 scientific publications on endothelin research in the past 20 years. The story of endothelin is unique as the gene sequences of endothelin receptors and the first receptor antagonists became available within only 4 years of the identification of the peptide sequence. The first clinical study in patients with congestive heart failure was published only 3 years thereafter. Yet, despite convincing experimental evidence of a pathogenetic role for endothelin in development, cell function, and disease, many initial clinical studies on endothelin antagonism were negative. In many of these studies, study designs or patient selection were inadequate. Today, for diseases such as pulmonary hypertension, endothelin antagonist treatment has become reality in clinical medicine, and ongoing clinical studies are evaluating additional indications, such as renal disease and cancer. Twenty years after the discovery of endothelin, its inhibitors have finally arrived in the clinical arena and are now providing us with new options to treat disease and prolong the lives of patients. Possible future indications include resistant arterial hypertension, proteinuric renal disease, cancer, and connective tissue diseases.

Effects of nonselective endothelin-1 receptor antagonism on cardiac mast cell-mediated ventricular remodeling in rats

The objective of this study was to investigate the effect a nonselective endothelin-1 (ET-1) receptor antagonist (bosentan) had on the acute myocardial remodeling process including left ventricular (LV) mast cells and matrix metalloproteinase (MMP) activity secondary to volume overload. Additionally, we investigated the overall functional outcome of preventative endothelin receptor antagonism during 14 days of chronic volume overload. LV tissue from sham-operated (Sham), untreated-fistula (Fist), and bosentan (100 mg.kg(-1).day(-1))-treated animals (Fist + Bos) was analyzed for mast cell density, MMP activity, and myocardial collagen volume fraction at 1 and 5 days after the creation of an aortocaval fistula. When compared with untreated fistulas, bosentan treatment prevented the marked increase in LV mast cell density at 1 day postfistula (3.1 +/- 0.3 vs. 1.3 +/- 0.3 LV mast cells/mm2, Fist vs. Fist + Bos, P <or= 0.01). Additionally, the substantial increase in MMP-2 activation in the untreated fistula at 1 day was prevented following bosentan treatment (1.6 +/- 0.3 vs. 0.9 +/- 0.1 arbitrary activity units, Fist vs. Fist + Bos, P <or= 0.01). The marked decrease in collagen volume fraction seen in the Fist group (1.4 +/- 0.1 vs. 0.8 +/- 0.1% myocardial tissue, Sham vs. Fist, P <or= 0.01) was significantly attenuated following bosentan treatment at both the 1- and 5-day time points. Lastly, a 2-wk preventative treatment with bosentan resulted in significant attenuation of the increase in LV end-systolic and -diastolic volumes compared with those in untreated fistula hearts. In summary, nonselective ET-1 antagonism prevents the acute increases in cardiac mast cell density and MMP activation induced secondary to chronic volume overload. By preventing these events, ET-1 antagonism was efficacious in attenuating ventricular dilatation and limiting the development of structural and functional deficits in the first 2 wk of chronic volume overload. Accordingly, these results are the first to demonstrate that cardiac mast cells are responsive to the endogenous endothelin system in vivo. Another novel finding from this study is that chronic nonspecific endothelin antagonism may inadvertently potentiate ET-1-mediated signaling.

Pathogenesis of chronic heart failure: change of dominating paradigm

The review considers literature data reflecting the evolution of views on pathogenesis of chronic heart failure. Connection of revision of a dominating paradigm of pathogenesis at every stage of development of cardiology with changes in approaches to therapy of chronic heart failure is analyzed.

Approach to patients with heart failure and pulmonary hypertension

Pulmonary hypertension (PH), defined as a mean pulmonary artery pressure greater than 25 mm Hg, is not a diagnosis, but rather the physiologic consequence of the interaction between pulmonary blood flow, pulmonary vascular impedance, and downstream pulmonary venous pressure. The diagnosis and appropriate treatment of PH in patients with or without heart failure (HF) requires an understanding of the underlying pathogenesis, whether it be due to increased pulmonary venous pressure, increased pulmonary vascular resistance (PVR), increased pulmonary blood flow, or a combination thereof. Furthermore, an explanation for the underlying cause must also be sought. For example, a rise in pulmonary venous pressure may relate primarily to an increase in left ventricular end-diastolic pressure in a patient with a known cardiomyopathy; however, it may be complicated by severe mitral regurgitation. Similarly, an increased PVR may reflect reactive changes in the pulmonary vasculature due to long-standing pulmonary venous hypertension, concomitant hypoxemia/hypercapnia, or it may be the harbinger of chronic thromboembolic disease. It is imperative that reversible causes of PH be considered. Although most often diagnosed by Doppler echocardiography, full hemodynamic characterization of PH requires right heart catheterization to measure biventricular filling pressures and PVR. Integration of invasive pulmonary hemodynamics with an assessment of right ventricular function is essential to appreciate the clinical and prognostic significance of PH of an individual patient. Right heart catheterization is not practically feasible in all patients with HF and PH; however, at a minimum it should be performed in patients with a Doppler-estimated pulmonary artery pressure greater than 60 mm Hg, those who present clinically with predominant right HF, significant mitral valve disease, and in particular, patients with impaired right ventricular function.