Clinical effects of endothelin receptor antagonism with bosentan in patients with severe chronic heart failure: results of a pilot study

Bosentan

IMPORTANCE TO THE FIELD

Pulmonary arterial hypertension (PAH) is a morbid condition with high mortality if left untreated. Bosentan is an effective treatment option for group 1 pulmonary arterial hypertension. Bosentan improves exercise tolerance and functional class and delays the time to clinical worsening in these patients. Investigation is ongoing to determine its efficacy in other groups of pulmonary hypertension.

AREAS COVERED IN THIS REVIEW

This review provides a background on endothelin activity in PAH, as a rationale for the use of bosentan in this disease. It also presents evidence from key clinical trials of bosentan and discusses future directions in the study of bosentan to help the clinician better understand the role of bosentan in PAH management.

WHAT THE READER WILL GAIN

i) An understanding of the rationale for using endothelin receptor antagonists in treating PAH; ii) an understanding of the clinical evidence to support bosentan for the treatment of PAH; and iii) an understanding of how to use bosentan optimally in the treatment of PAH.

TAKE HOME MESSAGE

Bosentan is an effective and safe treatment for patients with PAH. Patients with suspected PAH should be evaluated carefully as the use of bosentan in non-group 1 pulmonary hypertension is still being investigated. Patients on bosentan should be monitored with monthly liver transaminase testing. Coadministration with other drugs should be reviewed carefully as drug-drug interactions may be important.

Development of pulmonary arterial hypertension in women: interplay of sex hormones and pulmonary vascular disease

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature, ultimately resulting in right heart failure and death. This disease is strongly predominant in females, although little is known regarding how sex influences disease development. Recent developments highlighting the importance of estrogen metabolites in both animal models and human disease have substantially increased our understanding of PAH in women. This review will focus on general knowledge of PAH, translational and basic science data regarding sex hormones in the pulmonary vasculature and on clinical issues that are particular to women with PAH. Future directions for study include the influence of sex hormones on right ventricular responses, improving the understanding of the influence of estrogen exposure in human disease and the study of dehydroepiandrosterone in basic science and human disease.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Pulmonary hypertension in heart failure

BACKGROUND

Pulmonary hypertension occurs in 60% to 80% of patients with heart failure and is associated with high morbidity and mortality.

METHODS AND RESULTS

Pulmonary artery pressure correlates with increased left ventricular end-diastolic pressure. Therefore, pulmonary hypertension is a common feature of heart failure with preserved as well as reduced systolic function. Pulmonary hypertension is partially reversible with normalization of cardiac filling pressures. Pulmonary vasculature remodeling and vasoconstriction create a second component, which does not reverse immediately, but has been shown to improve with vasoactive drugs and especially with left ventricular assist devices.

CONCLUSION

Many drugs used for idiopathic pulmonary arterial hypertension are being considered as treatment options for heart failure-related pulmonary hypertension. This is of particular significance in the heart transplant population. Randomized clinical trials with interventions targeting heart failure patients with elevated pulmonary artery pressure would be justified.

Current treatment options for early management in acute decompensated heart failure

Acute decompensated heart failure (ADHF) is a common syndrome that precedes over 100,000 hospitalizations in Canada per year (with length of stay in excess of six to eight days), making this the most costly disorder for patients older than 65 years of age. Over 85% of ADHF patients present with shortness of breath and exhibit evidence of volume overload. These findings may be variable in elderly patients, which complicates diagnosis. In fact, even in experienced centres, diagnostic accuracy is less than 80%. Despite advances in the treatment of chronic heart failure, meaningful improvements in outcomes associated with ADHF are very few. The basic assessment and treatments have not changed (early parenteral diuretics, electrocardiographic and oxygen saturation monitoring, supplemental oxygen administration). The introduction of measurement of natriuretic peptides in those in whom the diagnosis is uncertain may reduced the error rate by over 50%. The use of vasodilator therapy in the absence of cardiogenic shock can lead to earlier amelioration of symptoms, especially in those who do not respond to initial diuretics. Repeated monitoring of vital signs, body weight, electrolytes and creatinine levels is essential to minimize the risk of side effects of treatments. Noninvasive ventilation may reduce the need for endotracheal intubation in patients with severe ADHF and hypoxia at rest. Once the initial phase of heart failure treatment is completed, then the clinician should begin to focus on maximization of chronic heart failure therapy and discharge planning.

Efficacy and safety of atrasentan in patients with cardiovascular risk and early atherosclerosis

Endothelin plays an important role in the pathogenesis of atherosclerosis. The aim of the study was to evaluate the safety and hemodynamic and metabolic responses to 6 months treatment with atrasentan, the selective endothelin-A receptor antagonist. Seventy-two patients with multiple cardiovascular risk factors and nonobstructive coronary artery disease on coronary angiogram were randomly assigned in a double-blind manner to atrasentan or placebo. Mean aortic blood pressure decreased from 92+/-10 to 80+/-10 mm Hg (P<0.001) in the atrasentan group and did not change in the placebo group (93+/-10 and 92+/-11 mm Hg; P=0.84). The difference between the groups was significant (P<0.001). No effect on heart rate was observed. In a subgroup of patients not treated with angiotensin-converting enzyme inhibitor, creatinine level decreased in the atrasentan versus the placebo group (P=0.011). Fasting glucose (P=0.026), glycosylated hemoglobin level (P=0.041), triglyceride l (P=0.013), lipoprotein-A (P=0.046), and uric acid levels (P=0.048) decreased significantly in the atrasentan group compared with the placebo group. No progression of angiographic coronary disease was observed. The most common adverse effects with atrasentan were nasal stuffiness, headache, and edema. In conclusion, 6 months of treatment with atrasentan results in a reduction of blood pressure and improvement in glucose and lipid metabolism. These findings suggest the beneficial role of atrasentan in the treatment of hypertension and metabolic syndrome.

Traditional and novel approaches to management of heart failure: successes and failures

Although considerable progress has been made in the pharmacologic and device management of chronic heart failure in recent decades, heart failure patients continue to remain symptomatic, with high hospitalization and mortality rates. A number of novel agents, including endothelin antagonists and tumor-necrosis factor blockers, have recently failed to improve the clinical outcomes of patients with heart failure. Have we reached a ceiling in preventing the progression of the disease? This article reviews successes and late-stage clinical trial disappointments in the treatment of patients with heart failure. Furthermore, the article discusses how agents that have beneficial effects in heart failure also generally attenuate or reverse ventricular remodeling, whereas the newer agents that have failed to improve clinical outcomes either had no effect on remodeling or have been associated with adverse remodeling.

Pulmonary hypertension in older adults

Pulmonary hypertension is a frequently encountered problem in older patients. True idiopathic pulmonary arterial hypertension can also be seen and requires careful exclusion in older patients. Institution of therapies must be tempered with an appreciation of individual comorbidities and functional limitations that may affect patients' ability to comply and benefit from the complex treatments available for pulmonary arterial hypertension. This article reviews the existing data on the various forms of pulmonary hypertension presenting in older patients and on appropriate therapy in this challenging population.

Clinical and Hemodynamic Effects of Bosentan Dose Optimization in Symptomatic Heart Failure Patients with Severe Systolic Dysfunction, Associated with Secondary Pulmonary Hypertension – A Multi-Center Randomized Study

OBJECTIVE

To evaluate the effects of bosentan on echo-derived hemodynamic measurements, and clinical variables in symptomatic heart failure (HF) patients.

METHOD

Multi- center, double-blind, randomized (2:1), placebo-controlled study comparing bosentan (8-125 mg b.i.d.) to placebo in patients with New York Heart Association class IIIb-IV HF, left ventricular ejection fraction <35% and systolic pulmonary artery pressure (SPAP) >40 mm Hg. Primary and secondary endpoints were change from baseline to 20 weeks in SPAP and cardiac index, respectively. Safety endpoints were treatment emergent adverse events (AEs), change in body weight, hemoglobin, hematocrit, systolic blood pressure and diuretic use.

RESULTS

Ninety-four patients enrolled: 60 to bosentan, 34 to placebo. There was no significant difference between the 2 arms in SPAP change (0.1 +/- 11.5 mm Hg , 95% confidence limit (CL) -5.4 to 5.2, p = 0.97), cardiac index shift (0.12 +/- 0.45, 95% CL -0.09 to 0.33 , p = 0.24 ) or any of the other 22 echocardiographic measurements obtained. Therapy-duration was longer in the placebo arm, while more patients in the bosentan arm experienced adverse and serious AEs.

CONCLUSION

In HF patients with left ventricular dysfunction and secondary pulmonary hypertension, bosentan did not provide any measurable hemodynamic benefit, and was associated with more frequent AEs, requiring drug discontinuation.

Baseline and Serial Neurohormones in Patients With Congestive Heart Failure Treated With and Without Bucindolol: Results of the Neurohumoral Substudy of the Beta-Blocker Evaluation of Survival Study (BEST)

BACKGROUND

Serial neurohormones may serve as markers of efficacy of congestive heart failure (CHF) therapy. We measured serial plasma big-endothelin (Big-ET), ET-1, N-terminal atrial natriuretic peptide, and brain natriuretic peptide (BNP) in 206 patients randomized to bucindolol or placebo in Beta-Blocker Evaluation of Survival Trial (BEST).

METHODS AND RESULTS

Neurohormones were measured at baseline and 3 and 12 months. At baseline, BNP and Big-ET levels were greater in New York Heart Association (NYHA) Class IV than in Class III patients (median 122 pg/mL versus 447 pg/mL, P = .001; and 20.0 pg/mL versus 9.9 pg/mL, P = .003), and in patients with left ventricular ejection fraction (LVEF) < or = 20% compared with LVEF > 20% (median 211 pg/mL versus 99.1 pg/mL; and 12.9 pg/mL versus 8.0 pg/mL, both P = .003). Big-ET and BNP were the strongest predictors of the composite end point of CHF hospitalization or death. LVEF at 12 months correlated inversely with 12-month BNP levels (r = -0.41, P = .0001). Bucindolol had no effect on neurohormones except that bucindolol treated patients had lower Big-ET levels at 3 months than patients receiving placebo (median 9.1 pg/mL versus 10.9 pg/mL, P = .05). A decline in ET-1 was associated with increased risk of the composite endpoint.

CONCLUSIONS

Lack of effect of bucindolol on natriuretic peptide levels appears consistent with its overall lack of efficacy in BEST.

Right ventricular failure complicating heart failure: pathophysiology, significance, and management strategies

Right heart failure most commonly results from the complication of left heart failure (systolic or nonsystolic dysfunction) or pulmonary hypertension. Over the past decade, greater attention has been paid to the role of right ventricular failure in the morbidity and mortality associated with cardiomyopathy and pulmonary hypertension. The right ventricle is distinct from the left ventricle not only in its spatial localization, but also in its response to increased afterload and signaling mechanisms. This article discusses the role of right ventricular failure in the setting of heart failure as well as the clinical diagnosis and management of right ventricular failure.

A phase II study of bosentan, a dual endothelin receptor antagonist, as monotherapy in patients with stage IV metastatic melanoma

There is no effective systemic therapy for disseminated metastatic melanoma. Data suggest that endothelin may play a role in pathophysiology of melanoma and that the dual endothelin receptor antagonist bosentan may have anti-tumor activity. This multicenter, open-label, single-arm, prospective, proof-of-concept study assessed the effects of bosentan monotherapy (500 mg oral tablets, bid) on tumor response in patients with stage IV metastatic melanoma. Patients were treated until disease progression, death or serious adverse event leading to premature study drug discontinuation. Tumor response was assessed at 6-weekly intervals using the Response Evaluation Criteria in Solid Tumors (RECIST). Among the 35 patients included in this study with stage IV metastatic melanoma, 21 (60%) were stage M1C, 10 (29%) stage M1B and 4 (11%) stage M1A (American Joint Committee on Cancer [AJCC] classification). Nine patients (26%) had received prior therapy for stage IV melanoma. Disease stabilization was observed in 6 of the 32 patients analyzed per protocol at week 6 with confirmatory evaluation at week 12, 5 of whom were still stable at > or =24 weeks. Of the 6 patients with disease stabilization, 2 were stage M1A, 1 was stage M1B and the remaining 3 were stage M1C. Partial or complete response was not observed. Progressive disease was observed in 17 (49%) patients at week 12 and in 25 (71%) patients at the end of the study (data base closure). The most frequent adverse events were typical for the underlying disease or known to be associated with bosentan: headache (43%), fatigue (34%), nausea (31%), back pain (23%) and abnormal hepatic function (23%). Bosentan might have benefit in disease stabilization in certain patients with metastatic melanoma and deserves further investigation in combination with other anticancer drugs.

Pulmonary Hypertension Associated with Left-Sided Heart Disease

Pulmonary hypertension (PH) denotes a poor prognosis in patients with left-sided heart disease. No study has demonstrated long-term benefit from PH drugs such as prostanoids, endothelin antagonists, and phosphodiesterase-5 inhibitors. In some cases, cautious use of PH drugs may be indicated. However, theoretic and practical concerns limit any formal recommendations.

Pulmonary Arterial Hypertension

The first description of the circulation of blood through the lungs has been attributed to Ibn Nafis (1210–1288).1 The concept was rediscovered by Michael Servetus, a Spanish physician during the Renaissance (1511–1553) and recorded, oddly enough, in two pages of his religious treatise, Christianismi Restitutio (1553).2 The definitive exposition of the pulmonary circulation was made by William Harvey in DeMotu Cordis (1628).3 The first observation of the pulmonary capillaries was first reported by Marcellus Malpighi (1661).4 Heart catheterization in humans, driven by a desire to obtain the perfect mixed venous specimen and measure cardiac output, was first performed in 1929 by the German urologist Forssmann,5 using a ureteral catheter to access his own right atrium. Over a decade later, Cournand and Richards at Columbia University in New York subsequently used right heart catheterization to record pulmonary artery pressure (PAP) in patients with shock and secondary forms of pulmonary hypertension (PHT). For these accomplishments, which were inspired by an interest in the pulmonary circulation and PHT related to mitral stenosis, Forssmann, Cournand, and Richards received the Nobel Prize in 1956.

Combination Therapy With Sildenafil and Bosentan Reverts Severe Pulmonary Hypertension and Allows Heart Transplantation: Case Report

INTRODUCTION

Severe pulmonary hypertension with no response to vasodilators on an acute hemodynamic study is a contraindication to cardiac transplantation. The development of oral pulmonary vasodilators improves the prognosis in these patients. We present the case of a patient whose admission to the waiting list for cardiac transplantation was possible after 6 months of combination therapy with Sildenafil and Bosentan.

CASE REPORT

The patient was a 50-year-old man with severe dilated alcohol-induced cardiomyopathy. A pretransplantation study, including a right hemodynamic analysis, revealed irreversible pulmonary hypertension, with 59 mm Hg mean pulmonary artery pressure and 6.4 Wood IU pulmonary vascular resistance, with no response to acute vasodilators with nitric oxide or prostacyclin. Initially, heart transplantation was not possible and the patient started treatment with oral Sildenafil. After 6 months there was no improvement in echocardiographic or hemodynamic parameters, and combination therapy with Bosentan was started. With the combination therapy, the patient progressively improved clinically and hemodynamically, the pressures becoming normal at the sixth month, at which time he was included on the waiting list for a heart transplantation. Eight months later he received a graft with a good posttransplantation course, no right ventricular failure in the acute phase, and absence of pulmonary hypertension on echocardiogrphic and invasive studies.

CONCLUSION

Combinations of an oral pulmonary vasodilator with diverse action mechanisms may represent an alternative for patients with irreversible pulmonary hypertension who do not respond to monotherapy.

Effect of endothelins on the cardiovascular system

Endothelins (ETs) exert a persistent constrictor effect on the vessels via an increase in intracellular Ca2+ concentration due to the activation of Na+/H+ and Na+/Ca2+ exchangers of the vascular smooth muscle fibres. They also produce a transient dilator effect via the activation of endothelial nitric oxide synthase mediated by protein kinase B/Akt. ETA and ETB2 receptors are involved in vasoconstriction, whereas transient vasodilatation depends on the activation of ETB1 receptors. Depending on animal species and experimental conditions, ETs can also play a role in cardiac muscle contraction and induce either an increase or a decrease in contractility. It is likely that only ETA, and not ETB, receptors are involved in the ET-induced increase in myocardial contractility. As in the case of vasoconstriction, this inotropic effect depends on an increase in intracellular Ca2+ concentration induced by Na+/H+ and Na+/Ca2+ exchangers. Activation of the Na+/H+ exchanger is stimulated by protein kinase C, which is activated by diacylglycerol released in response to ET activity. It has also been proposed that the positive inotropic effect can occur without the contribution of the Na+/Ca2+ exchanger, if the cell alkalinisation produced by the Na/H exchanger improves myofibrillar Ca2+ sensitivity. A reduction in contractility has been attributed to the involvement of the Gi protein/protein kinase G pathway or to the activation of protein kinase C without an increase in intracellular Ca2+ concentration or in myofibrillar Ca2+ sensitivity. The chronic effect of ETs on the myocardium results in hypertrophy and prevention of apoptosis, two processes that are together responsible for the contradictory effect of ETs in heart failure.

Endothelial-cardiomyocyte interactions in cardiac development and repair

Communication between endothelial cells and cardiomyocytes regulates not only early cardiac development but also adult cardiomyocyte function, including the contractile state. In the normal mammalian myocardium, each cardiomyocyte is surrounded by an intricate network of capillaries and is next to endothelial cells. Cardiomyocytes depend on endothelial cells not only for oxygenated blood supply but also for local protective signals that promote cardiomyocyte organization and survival. While endothelial cells direct cardiomyocytes, cardiomyocytes reciprocally secrete factors that impact endothelial cell function. Understanding how endothelial cells communicate with cardiomyocytes will be critical for cardiac regeneration, in which the ultimate goal is not simply to improve systolic function transiently but to establish new myocardium that is both structurally and functionally normal in the long term.

The problem of polypharmacy in heart failure

Improvements in the medical therapy for chronic heart failure have led to a dramatic decrease in the morbidity and mortality of patients with heart failure over the past two decades. This improvement has been gained at the expense of an increasing number of potent drugs that heart failure patients have to take chronically. Because heart failure forms the end-stage of different cardiovascular diseases and their predisposing risk factors, patients need drug treatment not only for heart failure itself but also for related conditions. Even more, because most heart failure patients are elderly, a number of unrelated, noncardiovascular diseases become apparent, which further increase the number of pharmaceutical substances with which heart failure patients are treated. The resulting polypharmacy leads to problems including economic burden, patient compliance, and most importantly, partly unpredictable drug interactions. This article reviews the existing data concerning some of these problems, to provide an aid for choosing the appropriate drugs in heart failure patients and minimizing the patient's risk.

Initial experience with bosentan therapy in patients considered ineligible for heart transplantation because of severe pulmonary hypertension

BACKGROUND

Pre-operative elevated pulmonary vascular resistance (PVR) has been associated with increased right ventricular failure and mortality after heart transplantation. The aim of this study was to assess the efficacy of bosentan, an oral endothelin-receptor antagonist, to reduce PVR in patients considered ineligible for heart transplantation because of severe pulmonary hypertension.

METHODS

Seven patients with end-stage congestive heart failure and considered ineligible for heart transplantation because of severe pulmonary hypertension (PVR>2.5 Wood units after nitroprusside infusion) were included in the study. They received bosentan 62.5 mg b.i.d. for four wk and 125 mg b.i.d. thereafter. Right heart catheterization was repeated after six wk of therapy.

RESULTS

After six wk of bosentan therapy, there was a significant decrease in PVR (6.0 +/- 2 vs. 3.8 +/- 2 Wood units, before vs. after bosentan; p = 0.02), in PVR during nitroprusside infusion (3.3 +/- 1 vs. 2.1 +/- 1 Wood units, before vs. after bosentan; p = 0.02) and in diastolic pulmonary artery pressure (33 +/- 7 vs. 23 +/- 7 mmHg, before vs. after bosentan; p = 0.04). No significant adverse events were observed. After bosentan therapy, five patients had PVR<or=2.5 Wood units. They were included in the waiting list and all five had a successful heart transplantation, although two of them required bosentan after surgery.

CONCLUSIONS

In patients considered ineligible for heart transplantation because of high PVR, bosentan therapy significantly reduced PVR. These data suggest that therapy with endothelin-receptor blockers might be useful to identify a subgroup of patients with high PVR who can benefit from heart transplantation.

Cardiovascular endothelins: essential regulators of cardiovascular homeostasis

The endothelin (ET) system consists of 3 ET isopeptides, several isoforms of activating peptidases, and 2 G-protein-coupled receptors, ETA and ETB, that are linked to multiple signaling pathways. In the cardiovascular system, the components of the ET family are expressed in several tissues, notably the vascular endothelium, smooth muscle cells, and cardiomyocytes. There is general agreement that ETs play important physiological roles in the regulation of normal cardiovascular function, and excessive generation of ET isopeptides has been linked to major cardiovascular pathologies, including hypertension and heart failure. However, several recent clinical trials with ET receptor antagonists were disappointing. In the present review, the authors take the stance that ETs are mainly and foremost essential regulators of cardiovascular function, hence that antagonizing normal ET actions, even in patients, will potentially do more harm than good. To support this notion, we describe the predominant roles of ETs in blood vessels, which are (indirect) vasodilatation and ET clearance from plasma and interstitial spaces, against the background of the subcellular mechanisms mediating these effects. Furthermore, important roles of ETs in regulating and adapting heart functions to different needs are addressed, including recent progress in understanding the effects of ETs on diastolic function, adaptations to changes in preload, and the interactions between endocardial-derived ET-1 and myocardial pump function. Finally, the potential dangers (and gains) resulting from the suppression of excessive generation or activity of ETs occurring in some cardiovascular pathological states, such as hypertension, myocardial ischemia, and heart failure, are discussed.

Endothelins: Pathophysiology and treatment implications in chronic heart failure

Less than 20 years after its discovery, endothelin is recognized as playing a central role in the pathogenesis of chronic heart failure. Endothelin is not only one of the most potent known vasoconstrictors; it also has multiple other actions. It mediates pathologic hypertrophy and fibrosis of both ventricular and vascular tissues, it potentiates the effects of other neurohormones, and it acts as a proarrhythmic. Endothelin receptor antagonists have been developed to investigate the hypothesis that these adverse effects could be prevented, and experimental studies showed promise in this regard. Clinical studies have confirmed the ability of these new agents to improve hemodynamics, but beneficial effects on clinical outcomes have been more difficult to demonstrate. Further analysis of the data from these trials, as well as other ongoing studies, may provide insight into these disparate findings and guidance for future investigations.