Acute and short-term effects of the nonpeptide endothelin-1 receptor antagonist bosentan in humans

Gαq protein carboxyl terminus imitation polypeptide GCIP-27 improves cardiac function in chronic heart failure rats

Background

Gαq protein carboxyl terminus imitation polypeptide (GCIP)-27 has been shown to alleviate pathological cardiomyocyte hypertrophy induced by various factors. Pathological cardiac hypertrophy increases the morbidity and mortality of cardiovascular diseases while it compensates for poor heart function. This study was designed to investigate the effects of GCIP-27 on heart function in rats with heart failure induced by doxorubicin.

Methods and Results

Forty-eight rats were randomly divided into the following six groups receiving vehicle (control), doxorubicin (Dox), losartan (6 mg/kg, i.g.) and three doses of GCIP-27 (10, 30, 90 μg/kg; i.p., bid), respectively. Heart failure was induced by Dox, which was administered at a 20 mg/kg cumulative dose. After 10 weeks of treatment, we observed that GCIP-27 (30, 90 μg/kg) significantly increased ejection fraction, fraction shortening, stroke volume and sarcoplasmic reticulum Ca²⁺ ATPase activity of Dox-treated hearts. Additionally, GCIP-27 decreased myocardial injury, heart weight index and left ventricular weight index, fibrosis and serum cardiac troponin-I concentration in Dox-treated mice. Immunohistochemistry, western blotting and real-time PCR experiments indicated that GCIP-27 (10–90 μg/kg) could markedly upregulate the protein expression of myocardial α-myosin heavy chain (MHC), Bcl-2, protein kinase C (PKC) ε and phosphorylated extracellular signal-regulated kinase (p-ERK) 1/2 as well as the mRNA expression of α-MHC, but downregulated the expression of β-MHC, Bax and PKC βII, and the mRNA expression levels of β-MHC in Dox-treated mice. It was also found that GCIP-27 (30, 90 μg/L) decreased cell size and protein content of cardiomyocytes significantly in vitro by comparison of Dox group.

Conclusions

GCIP-27 could effectively ameliorate heart failure development induced by Dox. PKC–ERK1/2 signaling might represent the underlying mechanism of the beneficial effects of GCIP-27.

Modulation by endothelin-1 of spontaneous activity and membrane currents of atrioventricular node myocytes from the rabbit heart

Background

The atrioventricular node (AVN) is a key component of the cardiac pacemaker-conduction system. Although it is known that receptors for the peptide hormone endothelin-1 (ET-1) are expressed in the AVN, there is very little information available on the modulatory effects of ET-1 on AVN electrophysiology. This study characterises for the first time acute modulatory effects of ET-1 on AVN cellular electrophysiology.

Methods

Electrophysiological experiments were conducted in which recordings were made from rabbit isolated AVN cells at 35–37°C using the whole-cell patch clamp recording technique.

Results

Application of ET-1 (10 nM) to spontaneously active AVN cells led rapidly (within ∼13 s) to membrane potential hyperpolarisation and cessation of spontaneous action potentials (APs). This effect was prevented by pre-application of the ET_A receptor inhibitor BQ-123 (1 µM) and was not mimicked by the ET_B receptor agonist IRL-1620 (300 nM). In whole-cell voltage-clamp experiments, ET-1 partially inhibited L-type calcium current (I_Ca,L) and rapid delayed rectifier K⁺ current (I_Kr), whilst it transiently activated the hyperpolarisation-activated current (I_f) at voltages negative to the pacemaking range, and activated an inwardly rectifying current that was inhibited by both tertiapin-Q (300 nM) and Ba²⁺ ions (2 mM); each of these effects was sensitive to ET_A receptor inhibition. In cells exposed to tertiapin-Q, ET-1 application did not produce membrane potential hyperpolarisation or immediate cessation of spontaneous activity; instead, there was a progressive decline in AP amplitude and depolarisation of maximum diastolic potential.

Conclusions

Acutely applied ET-1 exerts a direct modulatory effect on AVN cell electrophysiology. The dominant effect of ET-1 in this study was activation of a tertiapin-Q sensitive inwardly rectifying K⁺ current via ET_A receptors, which led rapidly to cell quiescence.

Bosentan and the endothelin system in congestive heart failure

The endothelin system appears to play an important role in the pathophysiology of congestive heart failure (CHF). Endothelin receptor antagonists represent a novel class of agents that are being evaluated for their potential benefits in treating various cardiovascular disorders. Bosentan is an orally active endothelin receptor antagonist that has been studied for the treatment of CHF. Early clinical experience with bosentan has confirmed some benefits on hemodynamic parameters in patients with CHF. Its role in slowing the progression of the disease and improving survival remains to be elucidated.

Future pharmacologic agents for treatment of heart failure in children

The addition of new agents to the armamentarium of treatment options for heart failure in pediatric patients is exciting and challenging. Administration of these therapies to pediatric patients will require careful scrutiny of the data and skilled application. Developmental changes in drug metabolism, excretion, and distribution are concerning in pediatric patients, and inappropriate evaluation of these parameters can have disastrous results. Manipulation of the neurohormonal pathways in heart failure has been the target of most recently developed pharmacologic agents. Angiotensin receptor blockers (ARBs), aldosterone antagonists, beta-blockers, and natriuretic peptides are seeing increased use in pediatrics. In particular, calcium sensitizing agents represent a new frontier in the treatment of acute decompensated heart failure and may replace traditional inotropic therapies. Endothelin receptor antagonists have shown benefit in the treatment of pulmonary hypertension, but their use in heart failure is still debatable. Vasopressin antagonists, tumor necrosis factor inhibitors, and neutral endopeptidase inhibitors are also targeting aspects of the neurohormonal cascade that are currently not completely understood. The future of pharmacologic therapies will include pharmacogenomic studies on new and preexisting therapies for pediatric heart failure. The education and skill of the practitioner when applying these agents in pediatric heart failure is of utmost importance.

Endothelin receptor antagonists

Endothelin receptor antagonists (ERAs) have been developed to block the effects of endothelin-1 (ET-1) in a variety of cardiovascular conditions. ET-1 is a powerful vasoconstrictor with mitogenic or co-mitogenic properties, which acts through the stimulation of 2 subtypes of receptors [endothelin receptor subtype A (ETA) and endothelin receptor subtype B (ETB) receptors]. Endogenous ET-1 is involved in a variety of conditions including systemic and pulmonary hypertension (PH), congestive heart failure (CHF), vascular remodeling (restenosis, atherosclerosis), renal failure, cancer, and cerebrovascular disease. The first dual ETA/ETB receptor blocker, bosentan, has already been approved by the Food and Drug Administration for the treatment of pulmonary arterial hypertension (PAH). Trials of endothelin receptor antagonists in heart failure have been completed with mixed results so far. Studies are ongoing on the effects of selective ETA antagonists or dual ETA/ETB antagonists in lung fibrosis, cancer, and subarachnoid hemorrhage. While non-peptidic ET-1 receptor antagonists suitable for oral intake with excellent bioavailability have become available, proven efficacy is limited to pulmonary hypertension, but it is possible that these agents might find a place in the treatment of several cardiovascular and non-cardiovascular diseases in the coming future.

Aldosterone breakthrough during ras blockade: A role for endothelins and their antagonists?

Activation of the renin-angiotensin system (RAS), with ensuing aldosterone excess, detrimentally affects outcome in patients with hypertension and heart failure (HF). RAS blockade with angiotensin (Ang) 1-converting enzyme inhibitors (ACEIs) or Ang II type 1 receptor blockers (ARBs) is beneficial in such conditions. However, aldosterone secretion can persist despite these treatments. Hence, mechanisms besides Ang II acquire the role of aldosterone secretagogue. The RALES and EPHESUS studies have shown that this aldosterone "escape" or "breakthrough" is an important factor, because it is a determinant of outcome in HF patients. Endothelin (ET)-1, which stimulates aldosterone secretion via both A (ETA) and B (ETB) receptor subtypes, and which is increased in HF, is a candidate for the "aldosterone breakthrough." Moreover, the novel ET peptide ET-1(1-31) is involved in adrenocortical growth. Therefore, findings suggesting a role for the ET-1 system as an aldosterone secretagogue, along with the potential usefulness of endothelin antagonists for the prevention of "aldosterone breakthrough," are discussed.

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.

New pharmacological strategies in chronic heart failure

Diuretics, ACE inhibitors and betablockers form the cornerstone of pharmacological treatment of chronic heart failure (CHF), while angiotensin receptor blockers are gaining ground. However, despite optimal treatment CHF remains a syndrome with poor prognosis. For this reason, a large number of new agents have been developed as add-on treatment over the last few years. Vasopeptidase inhibitors, moxonidine, endothelin antagonists, vasopressin antagonists, and selective aldosterone antagonists, are some of the new agents that were designed to interfere with different neurohormonal pathways. Immunomodulating agents, growth hormone, caspase inhibitors, adrenomedullin, and erythropoietin have different modes of action, which in general are less understood. Although most of the agents exhibited efficacy in preclinical trials, the clinical results have not always been similarly positive. The results of trials involving vasopeptidase inhibitors, endothelin antagonists, immunomodulating agents, and growth hormone have been disappointing. Other compounds like caspase inhibitors, adrenomedullin, and vasopressin antagonists are still at the early stages of development. Currently, the two most promising agents seem to be erythropoietin and the selective aldosterone receptor blocker eplerenone. In the present article an overview of new pharmacological developments for CHF is given, and the clinical value of these developments is discussed.

The role of endothelin receptor antagonists in cardiovascular pharmacotherapy

Endothelin (ET) is a hormone produced predominantly by endothelial cells which has been recognised to play a significant role in the development of several cardiovascular disease states. In order to combat the deleterious effects of ET, several ET-receptor antagonists (ETRA) are currently in clinical development. The agents developed thus far inhibit the actions of ET through either selective inhibition of the ET(A) receptors or non-selective inhibition of both ET(A) and ET(B) receptors. However, due to the differing proportions of the two receptor subtypes in various tissues, animal models and pathologies, it remains a matter of debate whether receptor selective agents impart significant clinical benefits over non-selective agents. This paper seeks to briefly summarise the important preclinical and clinical effects that have been reported in the literature and will attempt to provide a rationale for the use of both types of ETRAs in the treatment of both systemic and pulmonary hypertension as well as chronic heart failure (CHF).

The pharmacology of bosentan

This article describes the pharmacological properties and the overall preclinical and clinical profiling of bosentan (Ro 47-0203), a non-peptide endothelin receptor antagonist with oral activity. Bosentan is a combined and competitive antagonist of both ETA and ETB receptors that is selective for the endothelin system. In vitro and in vivo, bosentan potently antagonises the vascular response elicited by the endothelins. Preclinical efficacy is demonstrated in a variety of pathological models including pulmonary and essential hypertension, renal failure of ischaemic and nephrotic origin and cerebral vasospasm following subarachnoid haemorrhage. Effects are particularly marked in experimental models of heart failure (HF) where bosentan acts as a potent vasodilator that improves overall left ventricular performance. After chronic treatment, bosentan also improves survival in rats with HF. As a result of the first encouraging clinical results that show pulmonary and systemic vasodilation, long-term studies are ongoing in the treatment of congestive heart failure (CHF).

Endothelin and pulmonary arterial hypertension

BACKGROUND AND OBJECTIVES

Pulmonary arterial hypertension (PHT) is a potentially fatal disease. The purpose of this article is to review the current knowledge of the role played by endothelin (ET) in PHT and the relevant drug regimens used in the treatment of this condition.

METHODS

A detailed search via MEDLINE (PubMed) was performed by using PHT and ET as the key terms.

RESULTS

PHT could be a primary or a secondary diagnosis associated with various heart and lung diseases. PHT appears during the late stage of systemic sclerosis and may complicate other systemic diseases such as systemic lupus erythematosus. The vascular endothelium and activation of various mediators and growth factors such as the ET system are thought to play a crucial role in the development of this condition. The pathologic process progresses very rapidly from vasoconstriction to widespread pulmonary vascular obstruction. The use of high doses of calcium channel blockers is of limited value. Life-long anticoagulant therapy is recommended for the treatment of PHT. Currently, the drug being used in PHT therapy is continuous central-venous prostacyclin infusion. Prostacyclin is a strong vasodilator with antiaggregate and antifibrotic properties and has the potential to reduce endothelial injury and to induce vasculature remodeling. This treatment results in improved functional status and increased life span. Unfortunately, its use is accompanied by various side effects, technical difficulties, and high cost. The role of other therapeutic modalities (inhaled prostacyclin, subcutaneous treprostinil, oral beraprost, sildenafil) in vascular remodeling, and the improvement in functional capacity and survival of patients with PHT, are currently under investigation. Bosentan, administered orally, is a recently developed active ET receptor antagonist. It is a promising new therapeutic tool in the treatment of PHT because of its potent vasodilator, antiproliferative, and vascular remodeling activity.

CONCLUSIONS

The revolutionary conceptual shift in understanding the pathogenesis of PHT from a vasoconstrictive process to a vasoproliferative one, has led to a modification in the treatment of this disease from the use of vasodilators to the use of drugs with antiproliferative and vascular remodeling activity. Until now, prostacyclin was the only drug of this type available for the treatment of PHT. ET blockade seems to be a reasonable and potential therapeutic option.

Bosentan

Bosentan is the first endothelin (ET) receptor antagonist approved by the Food and Drug Administration for the management of pulmonary arterial hypertension (PAH). In patients with World Health Organization Class III and IV PAH, bosentan has demonstrated improvement in dyspnea and exercise tolerance. ET also plays an important role in the pathophysiology of different vascular diseases. Therefore, bosentan also may have the potential to alter the outcome of many other diseases, such as heart failure, hypertension, ischemic heart disease, and renal disease, as well as cerebrovascular disorders. Because of the rarity and the poor prognosis of patients with PAH, as well as the requirement of close monitoring of bosentan (due to its potential of causing liver dysfunction and its teratogenic effects), bosentan is currently available only through a special access program and is distributed by certain selected pharmacies. Patients who are receiving bosentan should be taught to recognize early signs and symptoms of liver dysfunction and possible pregnancy. In addition, bosentan is not only a substrate but also an inducer of CYP3A4 and CYP2C9. Therefore, it is anticipated that numerous drug interactions may occur. Patients should be advised to consult their physicians or pharmacists should they need to consume other prescription or nonprescription medications.

The role of oxidative stress in the pathophysiology of cerebrovascular lesions in Alzheimer's disease

Alzheimer's disease (AD) and stroke are two leading causes of age-associated dementia. A rapidly growing body of evidence indicates that increased oxidative stress from reactive oxygen radicals is associated with the aging process and age-related degenerative disorders such as atherosclerosis, ischemia/reperfusion, arthritis, stroke, and neurodegenerative diseases. New evidence has also indicated that vascular lesions are a key factor in the development of AD. This idea is based on a positive correlation between AD and cardiovascular and cerebrovascular diseases such as arterio- and atherosclerosis and ischemia/reperfusion injury. In this review we consider recent evidence supporting the existence of an intimate relationship between oxidative stress and vascular lesions in the pathobiology of AD. We also consider the opportunities for therapeutic interventions based on the molecular pathways involved with these causal relationships.

Endothelin in health and disease: endothelin receptor antagonists in the management of pulmonary artery hypertension

Endothelin (ET) has been identified as playing a fundamental role in many disease processes. Therapeutic efforts at interrupting ET's pathologic effects have focused on endothelin receptor antagonists (ERAs), of which two, bosentan and sitaxsentan, have been evaluated for the treatment of both primary and secondary pulmonary arterial hypertension (PAH). We discuss the multiple actions of ET, its role in various disease states, and the effects of ET receptor stimulation and blockade. Current classification and management of PAH are reviewed, along with the promise of greatly improved treatment generated by recent and ongoing clinical trials using ERAs.

Endothelin-1 and endothelin receptor antagonists as potential cardiovascular therapeutic agents

Endothelin (ET)-1 is an endothelium-derived peptide with potent vasoconstrictor and proliferative properties. The ET system is activated in several cardiovascular disease states associated with functional and structural vascular changes, including hypertension and heart failure. The two ET receptor subtypes are known as ET(A)R and ET(B)R. The former is located mainly on vascular smooth muscle cells and is responsible for mediating vasoconstriction and proliferation. The latter is present predominantly on endothelial cells and mediates vasorelaxation as well as ET-1 clearance. Activation of smooth muscle ET(B)R causes vasoconstriction. Selective ET(A)R antagonists as well as nonselective ET(A)R-ET(B)R antagonists have been developed. Studies with animal models and early-phase clinical trials provided strong evidence that these agents are effective in the treatment of heart failure, essential hypertension, pulmonary hypertension, and atherosclerosis. However, the complexity of biologic effects mediated by two different receptor subtypes complicates therapy with selective versus nonselective ET receptor antagonists. In addition to subtype selectivity and potency, changes in receptor subtype distribution under different pathologic conditions and different patient populations will play a crucial role in the evaluation of these potentially therapeutic drugs.

Hemodynamic effects of bosentan in patients with chronic heart failure

A role of the potent and long-acting vasoconstrictor peptide endothelin-1 and the pathophysiology of chronic human heart failure has been postulated based upon indirect evidence such as elevated plasma endothelin-1 levels and their with the degree of hemodynamic impairment. The advent of specific of endothelin-1 receptor antagonists has provided the opportunity not only to directly evaluate its pathophysiological role but also to assess its potential role as a new approach to heart failure therapy. This brief review summarizes the evidence linking endothelin-1 to the pathophysiology of chronic heart failure and the clinical results obtained in patients during acute, intravenous and more prolonged, oral administration with bosentan, a mixed ET(A)/ET(B)-receptor antagonist. Bosentan acutely and during short-term oral therapy markedly improved hemodynamics in patients in addition to standard heart failure therapy, including an ACE-inhibitor. These effects were associated with a reduced responsiveness of the renin-angiotensin system to diuretic therapy and reduced basal plasma aldosterone levels. Although the hemodynamic and neurohumoral profile of short-term bosentan therapy looks promising for the treatment of patients with chronic heart failure appropriate trials will have to be performed to document clinical benefit during long-term therapy. Finally, the question remains open whether mixed endothelin-1 receptor antagonists like bosentan will have similar effects as compared to antagonists which block the ET(A) receptor only.

Clinical experience with endothelin receptor antagonists in chronic heart failure

Both ET(A) selective and dual, ET(A/B), receptor antagonists have favourable short- and longer-term haemodynamic actions in patients with acute and chronic heart failure. Their effect on neurohumoral measures is not yet fully determined. Two moderately large, medium-duration studies have examined the effect of dual ET(A/B) receptor antagonists on clinical status, reaching conflicting conclusions. One large scale, long-term, morbidity mortality evaluation is underway with bosentan.

The endothelin-aldosterone axis and cardiovascular diseases

The results of the Randomized Aldactone Evaluation Study (RALES) and of several experimental studies have indicated that excess aldosterone detrimentally affects cardiovascular morbidity and mortality by acting through both classical and non-classical mineralocorticoid receptors. The effects mediated through classical mineralocorticoid receptors entail enhanced sodium and water reabsorption, potassium loss and hypokalaemia, congestion, increased vascular resistance and hypertension. Those occurring through non-classical mineralocorticoid receptors located on myofibroblasts comprise cardiac hypertrophy and fibrosis, which may be due to a direct effect of aldosterone on collagen synthesis. Data obtained in primary aldosteronism patients demonstrated left ventricular hypertrophy, as well as changes in left ventricular filling that can be accounted for by cardiac fibrosis. Available clinical data indicate that in a considerable proportion of congestive heart failure (CHF) patients treated with angiotensin converting enzyme (ACE) inhibitors, aldosterone secretion can escape from blockade of the renin-angiotensin system, thus suggesting that additional mechanisms, besides angiotensin II, can play an important role in the regulation of aldosterone secretion. Compelling evidence indicates that endothelin (ET)-1 is overtly increased in severe CHF and thus is a likely candidate for the aldosterone 'escape' phenomenon in CHF. Endothelin-1 is expressed in the adrenal cortex, together with its receptor subtypes A (ETA) and B (ETB), and directly stimulates aldosterone secretion in different species, in humans by acting via both ETA and ETB receptor subtypes. Moreover, we have recently found that the novel endothelin peptide ET-1 (1-31), by acting as an ETA agonist, can also be involved in the regulation of growth of the adrenal cortex, as well as in the pathogenesis of Conn's adenoma. In this paper, we review the findings suggesting a relationship between activation of the ET-1 system, enhanced aldosterone secretion and cardiac fibrosis and discuss the implications of endothelin antagonism for cardiovascular disease.

Endothelin receptor antagonists and cardiovascular diseases of aging

Our understanding of the role of the endothelin system in human cardiovascular physiology and pathophysiology has evolved very rapidly since the initial description of its constituent parts in 1988. Endothelin-1 (ET-1) is the predominant endothelin isoform in the human cardiovascular system and has potent vasoconstrictor, mitogenic and antinatriuretic properties which have implicated it in the pathophysiology of a number of cardiovascular diseases. The effects of ET-1 have been shown to be mediated by 2 principal endothelin receptor subtypes: ET(A) and ET(B). The development of a range of peptidic and nonpeptidic endothelin receptor antagonists represents an exciting breakthrough in human cardiovascular therapeutics. Two main classes of endothelin receptor antagonist have been developed for possible human therapeutic use: ET(A)-selective and nonselective antagonists. Extensive laboratory and clinical research with these agents has highlighted their promise in various cardiovascular diseases. Randomised, placebo-controlled clinical trials have yielded very encouraging results in patients with hypertension and chronic heart failure with more preliminary data suggesting a possible role in the treatment and prevention of atherosclerosis and stroke. Much more research is needed, however, before endothelin receptor antagonists can be considered for clinical use.

Differential effects of angiotensin II versus endothelin-1 inhibitions in hypertrophic left ventricular myocardium during transition to heart failure

BACKGROUND

In view of their mutual crosstalk, the roles of angiotensin II (Ang II) and endothelin-1 (ET-1) in the myocardium are assumed to be synergistic and supplemental.

METHODS AND RESULTS

In the phase of compensated left ventricular (LV) hypertrophy of Dahl salt-sensitive rats, Ang II peptide and the ACE mRNA in the LV were increased by 1.6- and 3.8-fold, respectively. In contrast, ET-1 peptide and the preproET-1 mRNA remained unchanged. In subsequent congestive heart failure (CHF), Ang II and ACE mRNA did not show further increases. But ET-1 and the mRNA were increased de novo by 5.3- and 4.1-fold, respectively. In ascending aorta-banded rats, the local activations of Ang II and ET-1 also showed a differential time course between LV hypertrophy and CHF. Long-term treatments of Dahl salt-sensitive rats with temocapril (an ACE inhibitor) and with bosentan (a mixed ET receptor blocker) equally improved long-term survival. Temocapril reduced the LV/body weight ratio and ameliorated LV fractional shortening. Conversely, although bosentan equally improved fractional shortening, it did not reduce the increase in LV mass. Combined treatment with these 2 drugs further ameliorated the animal's survival without additional decreases in systolic pressure.

CONCLUSIONS

The pathophysiological roles in the myocardium during the transition to CHF differ qualitatively between Ang II and ET-1. Thus, long-term therapy with a combination of ACE inhibition and ET antagonism may provide a new approach for heart failure in humans.

Chronic endothelin-1 blockade reduces sympathetic nerve activity in rabbits with heart failure

Endothelin-1 (ET-1) is elevated in chronic heart failure (CHF). In this study, we determined the effects of chronic ET-1 blockade on renal sympathetic nerve activity (RSNA) in conscious rabbits with pacing-induced CHF. Rabbits were chronically paced at 320–340 beats/min for 3–4 wk until clinical and hemodynamic signs of CHF were present. Resting RSNA and arterial baroreflex control of RSNA were determined. Responses were determined before and after the ET-1 antagonist L-754,142 (a combined ETA and ETB receptor antagonist, n = 5) was administered by osmotic minipump infusion (0.5 mg · kg−1 · h−1 for 48 h). In addition, five rabbits with CHF were treated with the specific ETA receptor antagonist BQ-123. Baseline RSNA (expressed as a percentage of the maximum nerve activity during sodium nitroprusside infusion) was significantly higher (58.3 ± 4.9 vs. 27.0 ± 1.0, P < 0.001), whereas baroreflex sensitivity was significantly lower in rabbits with CHF compared with control (3.09 ± 0.19 vs. 6.04 ± 0.73, P < 0.001). L-754,142 caused a time-dependent reduction in arterial pressure and RSNA in rabbits with CHF. In addition, BQ-123 caused a reduction in resting RSNA. For both compounds, RSNA returned to near control levels 24 h after removal of the minipump. These data suggest that ET-1 contributes to sympathoexcitation in the CHF state. Enhancement of arterial baroreflex sensitivity may further contribute to sympathoinhibition after ET-1 blockade in heart failure.

Endothelin and endothelin receptor antagonism in heart failure

Endothelin (ET)-1 is a potent vasoconstrictor with growth promoting and mitogenic properties associated with various cardiovascular diseases (CVD) and has been found to be an important protagonist in congestive heart failure (CHF). The introduction of ET-1 receptor antagonists into the arena of clinical research has amplified our understanding of the ET system: the first human trials with acute and chronic inhibition of the ET system have shown promising results and confirm the findings from experimental models. The availability of oral compounds such as bosentan has raised the hope that these novel drugs might become a new therapeutic class of agents for the treatment of CVD and, in particular, of CHF. The question, however, remains whether the beneficial effects observed so far in patients with CHF go beyond simple hemodynamic improvements and whether these compounds improve long-term survival in these patients.

The role of endothelins and their receptors in heart failure

Endothelin (ET) is a peptide composed of 21 amino acids, derived from a larger precursor, the big-endothelin, by action of the endothelin-converting enzyme (ECE) family; three isoforms of endothelin, named ET-1, ET-2 and ET-3, have been identified. Endothelin-1 is generated mainly by vascular endothelial cells and exerts various important biological actions, mediated by two receptor subtypes, ET-A and ET-B, belonging to the G protein-coupled family that have been identified in various human tissues such as the cardiac tissue. Endothelin-1 is a potent vasoconstrictive agent, has inotropic and mitogenic actions, modulates salt and water homeostasis and plays an important role in the maintenance of vascular tone and blood pressure in healthy subjects. Endothelin-1, as well as ET-A and ECE-1, also has an important role in cardiovascular development, as observed by the variety of abnormalities related to neural crest-derived tissues in mouse embryos deficient of a member of the ET-1/ECE-1/ET-A pathway. Various evidence indicates that endogenous endothelin-1 may contribute to the pathophysiology of conditions associated with sustained vasoconstriction, such as heart failure. In heart failure, elevated circulating levels of both endothelin-1 and big-endothelin-1 are observed; in failing hearts an activation of the endothelin system is found: tissue level of ET-1 is increased with respect to non-failing hearts as well as receptor density, due mainly to an upregulation of the ET-A subtype, the prevalent receptor subclass in cardiac tissue. Finally, studies in both humans and animal models of cardiovascular disease show that inhibition of the endothelin function (anti-endothelin strategy) is associated with an improvement of haemodynamic conditions; these observations indicate that endothelin receptor antagonists or endothelin-converting enzyme inhibitors may constitute a novel and potentially important class of agents for the treatment of this disease.

Endothelin-receptor antagonists: current and future perspectives

Despite much effort over recent years to design and develop endothelin-receptor antagonists, these compounds are far from becoming new drug entities. This article will review preclinical data on select endothelin-receptor antagonists as well as clinical data on bosentan, the only molecule currently in Phase III clinical trials. Though efficacious, bosentan is less potent than the angiotensin converting enzyme (ACE) inhibitor, enalapril, in patients with hypertension. We will therefore discuss the possible reason(s) for this low potency, the consequences thereof, and a few therapeutic areas where endothelin-receptor antagonists could find better use.

Systemic, pulmonary, and renal hemodynamic effects of endothelin ET(A/B)-receptor blockade in patients with maintained left ventricular function

Endothelin-1 (ET-1) regulates vascular tone in congestive heart failure and modulates renal function. Its role in patients with normal left ventricular (LV) function and its renal effects are unclear. Cardiac and renal hemodynamics were studied in 24 patients with normal LV function and coronary arteries after single-dose, double-blind, randomized administration of TAK-044 (25, 50, or 100 mg, i.v.), an ET(A/B)-receptor antagonist, or placebo. Hemodynamics were monitored using Swan-Ganz and arterial catheters, and ET levels were measured. Renal function was assessed by clearance techniques. In the absence of a dose-response relation, TAK-044 patients were analyzed as a single group. Most hemodynamic effects occurred during the first 4 h. TAK-044 reduced mean arterial (-9.3 mm Hg, p < 0.001), pulmonary (-1.8 mm Hg, p = 0.01), and pulmonary capillary wedge pressure (-1.6 mm Hg, p < 0.001) between 30 min and 4 h. Mean reduction in systemic vascular resistance was 279 dyne/s/cm2 (p < 0.001), whereas heart rate increased 6.1 beats/min (p < 0.001) and cardiac index by 0.37 L/m2 (p = 0.01). Stroke volume index, right atrial pressure, and pulmonary vascular resistance did not change. TAK-044 increased renal plasma flow in proportion to the increase in cardiac output (+119 ml/min, 4 h after TAK-044; p < 0.05) and ET-1 levels (2.5-fold; p < 0.05). No serious side effects were noted. In patients with normal cardiac function, ET-receptor blockade causes vasodilation and reduces systemic but not pulmonary vascular resistance and increases cardiac index and renal plasma flow.

Modulation of in vivo cardiac hypertrophy with insulin-like growth factor-1 and angiotensin-converting enzyme inhibitor: relationship between change in myosin isoform and progression of left ventricular dysfunction

OBJECTIVES

Supplemental myocardial hypertrophy induced by insulin-like growth factor (IGF)-1 may prevent transition from hypertrophy to heart failure under chronic mechanical overload.

BACKGROUND

Several studies have suggested that IGF-1 treatment may be beneficial in chronic heart failure. In addition, recent studies indicated that the amount of alpha-myosin heavy chain (MHC) plays a significant hemodynamic role in large animals including humans.

METHODS

We treated Dahl salt-sensitive hypertensive rats on a long-term basis with IGF-1. The effects were compared with those produced by treatment using a sub-antihypertensive dose of temocapril, an angiotensin-converting enzyme (ACE) inhibitor. At 11 weeks, when these rats displayed compensated left ventricular hypertrophy (LVH), they were randomized to three groups: 1) IGF group (3 mg/kg/day); 2) temocapril group (1 mg/kg/day); and 3) vehicle (control) group.

RESULTS

After 15 weeks, the control rats showed left ventricular (LV) enlargement and severe LV dysfunction and rapidly died of pulmonary congestion (mean survival time: 16.8+/-0.5 weeks). The survival time was significantly shortened (15.6+/-0.3 weeks) in the IGF-1 group but significantly prolonged (19.5+/-0.6 weeks) in the temocapril group. The rats in the IGF-1 group showed accelerated LV dilation and dysfunction. Of the several parameters investigated, it was found that the relative amounts of MHC isoforms differed among the three groups. The alpha-MHC mRNA level was decreased by 52% (p<0.01) in the IGF group, while it increased by 58% (p<0.01) in the temocapril group compared with the control group. These changes were related to the progression of LV dysfunction.

CONCLUSIONS

Supplemental myocardial hypertrophy with long-term IGF-1 treatment may not be beneficial if concentric LVH already exists. Our data suggest that IGF-1 may not protect myocardial performance when its hypertrophic effect aggravates the reduction of alpha-MHC. By contrast, the ACE inhibitor may improve myocardial function and prognosis by preventing the down-regulation of this isoform.

Prognostic value of hemodynamic vs big endothelin measurements during long-term IV therapy in advanced heart failure patients

STUDY OBJECTIVE

To compare hemodynamics and plasma big endothelin levels in patients awaiting heart transplantation who are receiving continuous IV therapy, and to establish their respective potency for predicting future cardiac events.

DESIGN

A randomized, prospective trial of ambulatory continuous treatment with IV prostaglandin E(1) (PGE(1)) vs dobutamine. A subanalysis was conducted of all patients who completed 4 weeks of follow-up in regard to treatment effects on hemodynamics and big endothelin plasma levels.

PATIENTS

Thirty-two listed heart transplant candidates who were refractory to oral treatment, 21 patients who were receiving PGE(1), and 11 patients receiving dobutamine.

MEASUREMENTS AND RESULTS

Hemodynamics and plasma big endothelin levels were measured at baseline and after 4 weeks. The cardiac index increased significantly (PGE(1) group, 1.7 +/- 0.4 vs 2.5 +/- 0.6 L/min/m(2); dobutamine group, 1.8 +/- 0.3 vs 2.3 +/- 0.6 L/min/m(2); p < 0.05), whereas the systemic vascular resistance index (SVRI) decreased significantly only in the PGE(1) group (3,352 +/- 954 vs 2,178 +/- 519 dyne. s. cm(-5)/m(2); p < 0. 05). The plasma big endothelin level decreased significantly (PGE(1) group, 7.6 +/- 3.1 vs 4.7 +/- 2.6 fmol/mL; dobutamine group, 6.5 +/- 3.7 vs 5.0 +/- 2.6 fmol/mL; p < 0.01 for the time effect). Plasma big endothelin (beta = 0.393; chi(2) = 10.8; p = 0.001) and SVRI (beta = 0.003; chi(2) = 6.9; p < 0.01), both measured after 4 weeks of continuous treatment, were the only independent predictors of future outcome.

CONCLUSION

Continuous treatment over 4 weeks with either PGE(1) or dobutamine in patients awaiting heart transplantation yields an improved hemodynamic state accompanied by a reduction of increased big endothelin levels. Plasma big endothelin measured after 4 weeks of continuous therapy provides prognostic information about future outcome.

Endothelin-1: a new target of therapeutic intervention for the treatment of heart failure

Endothelin-1 has been appreciated in animals and humans as a potential target for inhibition in patients with acutely decompensated congestive heart failure (CHF), as well as patients with a chronic low-output state. There has been intense interest in determining the effects of endothelin-1 on the cardiovascular system. Elevated plasma levels of endothelin-1 in patients with CHF portend a poorer prognosis than similar patients without elevated levels. Endothelin-1 levels correlate inversely with maximum oxygen consumption, and inhibition of the myocardial endothelin pathway in rats with CHF improves survival. An association between endothelin-1 and the development of CHF has recently been supported. Selectively inhibiting the endothelin A receptors in dogs with CHF produced hemodynamic improvement. Similarly, in rabbits, a structural advantage was demonstrated. Benefits in cardiac remodeling have been demonstrated in several models of CHF by nonselectively antagonizing endothelin receptors. In human trials using nonselective endothelin-1 inhibitors, researchers have demonstrated hemodynamic benefit and improvement in cardiac function in patients with decompensated CHF. Inhibition of endothelin-1 in patients with CHF appears to have potential therapeutic value, and ongoing clinical trials will further investigate the safety, efficacy, and role of this new potential therapeutic target for the treatment of CHF.

Regulation of ET: pulmonary release of ET contributes to increased plasma ET levels and vasoconstriction in CHF

Endothelin (ET) contributes to the increased systemic vascular resistance and elevated cardiac filling pressures seen in congestive heart failure (CHF). We investigated to what extent ET-mediated vasoconstriction in CHF occurs through an endocrine action of elevated plasma ET or by an autocrine/paracrine mechanism related to induction of vascular ET gene expression. Three weeks of pacing (225 beats/min) induced a marked release of ET-1 from the pulmonary circulation with a sixfold elevation of arterial plasma ET in CHF pigs compared with sham-operated pigs. Arterial plasma ET was the strongest and only independent predictor of systemic vascular resistance. In contrast, vascular preproET-1 and ET-receptor mRNA expression were unaltered or decreased in CHF pigs and did not correlate with indexes of vascular tone. However, myocardial preproET-1 mRNA expression increased twofold in CHF pigs. PreproET-2 and preproET-3 mRNAs were not detectable in cardiovascular tissues. In conclusion, plasma ET was markedly increased because of an augmented release from the pulmonary circulation during CHF, and arterial plasma ET correlated with systemic vascular resistance. The absence of ET induction in the peripheral vasculature suggests that ET increases vascular tone during CHF by an endocrine, not an autocrine/paracrine, mechanism.

Therapy with the nonpeptide endothelin receptor antagonist 97-139 in a murine model of congestive heart failure: reduction of cardiac mass and myofiber hypertrophy

Endothelin-1 (ET-1) is a potent vasoconstrictor. This peptide exerts numerous effects on the heart, including regulation of cardiomyocyte growth during hypertrophy. The effects of the structurally novel, nonpeptide, ET-1-selective, competitive antagonist (ETA) 97-139 were investigated in mice with congestive heart failure (CHF) and myocardial hypertrophy. Morphological and microscopical analyses were conducted on day 56 after viral inoculation following 28 day treatment with 99-139. Eight week-old DBA2 mice were intraperitoneally inoculated with encephalomyocarditis virus at a dose of 500 pfu/mouse. The 30 mice were divided into two groups--an ETA treated group and an untreated group. Heart weight (HW) in the infected group was significantly (p < 0.05) increased compared to that in the uninfected group. HW and the HW/body weight (BW) ratio were significantly (p < 0.05) reduced in the ETA treated group compared with the untreated group (HW; 127.7 +/- 6.2 mg vs 144.3 +/- 4.2 mg, HW/BW; 4.9 +/- 0.9 x 10(-3) vs 5.4 +/- 0.5 x 10(-3)). Myofiber diameter in the ETA treated group was significantly reduced compared with the untreated group (12.1 +/- 1.5 microm vs 14.3 +/- 1.9 microm). These results suggest the ET-1 receptor antagonist 97-139 has an effect on the reduction of cardiac mass and myofiber hypertrophy, and that 97-139 may be a useful agent for CHF due to viral myocarditis.

Effects of long-term therapy with bosentan on the progression of left ventricular dysfunction and remodeling in dogs with heart failure

OBJECTIVES

In this study, we examined the effects of long-term therapy with bosentan on the progression of LV dysfunction and remodeling in dogs with moderate HF.

BACKGROUND

Acute intravenous administration of bosentan, a mixed endothelin-1 type A and type B receptor antagonist, was shown to improve left ventricular (LV) function in patients and dogs with heart failure (HF).

METHODS

Left ventricular dysfunction was induced by multiple, sequential intracoronary microembolizations in 14 dogs. Embolizations were discontinued when LV ejection fraction (EF) was between 30% and 40%. Dogs were randomized to three months of therapy with bosentan (30 mg/kg twice daily, n = 7) or no therapy at all (control, n = 7).

RESULTS

In untreated dogs, EF decreased from 35 +/- 1% before initiating therapy to 29 +/- 1% at the end of three months of therapy (p = 0.001), and LV end-diastolic volume (EDV) and end-systolic volume (ESV) increased (EDV: 71 +/- 3 vs. 84 +/- 8 ml, p = 0.08; ESV: 46 +/- 2 vs. 60 +/- 6 ml, p = 0.03). By contrast, in dogs treated with bosentan, EF tended to increase from 34 +/- 2% before initiating therapy to 39 +/- 1% at the end of three months of therapy (p = 0.06), and EDV and ESV decreased (EDV: 75 +/- 3 vs. 71 +/- 4 ml, p = 0.05; ESV: 48 +/- 2 vs. 43 +/- 3 ml, p = 0.01). Furthermore, compared with untreated dogs, dogs treated with bosentan showed significantly less LV cardiomyocyte hypertrophy and LV volume fraction of interstitial fibrosis.

CONCLUSIONS

In dogs with moderate HF, long-term therapy with bosentan prevents the progression of LV dysfunction and attenuates LV chamber remodeling. The findings support the use of mixed endothelin-1 receptor antagonists as adjuncts to the long-term treatment of HF.

Role of endothelin-1 in myocardial failure

Endothelin-1 (ET-1) is a potent molecule produced throughout the cardiovascular system; it can exert important effects on both the structure and function of vascular smooth muscle cells and cardiac myocytes. ET-1 appears to play a central role in the physiological regulation of cardiovascular function, particularly in the vasculature. The known actions of ET-1 and the demonstration that plasma ET-1 is elevated in patients with heart failure has raised the possibility that this molecule could play a role in the pathophysiology of heart failure. This thesis has been supported and furthered by studies in animal models of heart failure that demonstrate the salutary, short-term effects of ET-1 receptor antagonists on hemodynamic function, as well as improved ventricular remodeling and survival with long-term administration. Early clinical trials with these ET receptor blockers have demonstrated systemic vasodilation. Long-term trials to determine the effects of ET-1 blockade on symptoms and survival are under way.

Discovery and synthesis of (S)-3-[2-(3,4-dimethoxyphenyl)ethoxy]-2- (4,6-dimethylpyrimidin-2-yloxy)-3,3-diphenylpropionic acid (LU 302872), a novel orally active mixed ET(A)/ET(B) receptor antagonist

Structural variation of the endothelin A-selective antagonist (S)-3-methoxy-2-(4,6-dimethoxypyrimidin-2-yloxy)-3, 3-diphenylpropionic acid (LU 135252) led to analogues which retain ET(A) affinity but exhibit substantial ET(B) affinity as well. The most active derivative obtained is (S)-3-[2-(3, 4-dimethoxyphenyl)ethoxy]-2-(4,6-dimethylpyrimidin-2-yloxy)- 3, 3-diphenylpropionic acid (LU 302872), which can be prepared in enantiomerically pure form in eight steps via an acid-catalyzed transetherification. It has a K(i) = 2.15 nM for binding to the ET(A) receptor and a K(i) = 4.75 nM for binding to the ET(B) receptor, is orally available, and antagonizes the big ET-induced blood pressure increase in rats and the big ET-induced bronchospasm in guinea pigs each time at a dose of 10 mg/kg.

Novel neuropeptides in the pathophysiology of heart failure: adrenomedullin and endothelin-1

The clinical success of neurohumoral manipulation by ACE inhibitors and beta blockers in heart failure has led to new therapeutic approaches. New neurohumoral factors are now viewed as offering the potential for treatment interventions. Not only do we consider blocking the production of deleterious hormones, but also, more recently, consideration has been given to augmenting the actions of factors with potentially beneficial actions. Hopefully such manipulation of ADM and ET-1 can result in further improvement in the well-being of heart failure patients.

Endothelin in heart failure

Congestive heart failure is a complex disease that results from pumping failure of the cardiac muscle and adaptational processes of the cardiovascular system to correct for the reduced blood supply to the organism. It is associated with increased vasoconstriction and impaired vasodilation in response to physical activity. The elevated vasoconstrictor tone is caused by the activation of compensatory mechanisms including the sympathetic nervous system and stimulation of the release of neurohormones like angiotensin II, catecholamines, and vasopressin. Furthermore, the vascular endothelium is importantly involved in the regulation of vascular tone as it releases a variety of vasoactive substances that act locally and systemically. In congestive heart failure, there is a marked imbalance between the diminished release or the increased inactivation of vasodilators on the one hand, ie, nitric oxide, and the elevated production, release, or reduced inactivation of vasoconstrictors such as endothelin-1 on the other hand. In addition to its very potent vasoconstrictor effects, endothelin-1 possesses antinatriuretic and mitogenic properties that are a common feature of substances that are involved in development of the deleterious consequences that render congestive heart failure a lethal disease. The spectrum of action of the endothelin system and the advent of specific antagonists for its receptors have made this system a very interesting target for clinical research and possibly for future therapeutic approaches.

Pulmonary and systemic responses to exogenous endothelin-1 in patients with left ventricular dysfunction

Plasma levels of immunoreactive endothelin-1 (ET-1) are elevated in chronic heart failure (CHF) and have been reported to correlate closely with pulmonary hemodynamic measurements. We investigated the effects of exogenous ET-1 on the pulmonary vasculature in patients with left ventricular systolic dysfunction (LVD), with or without overt heart failure. ET-1 was infused at 1, 5, and 15 pmol/min into a distal pulmonary artery of 10 patients with LVD. Hemodynamics were measured by a thermodilution catheter and arterial line. Intravascular Doppler and local pulmonary angiography were used to assess local pulmonary blood flow in the first four patients. Systemic hemodynamic changes occurred with ET-1 infusion in a dose-dependent fashion. Mean arterial pressure (100 +/- 8-107 +/- 11 mm Hg; p < 0.01) and systemic vascular resistance (1,699 +/- 375-2,033 +/- 427 dynes/s/cm-5; p < 0.001) rose, whereas the cardiac index fell from 2.43 +/- 0.53 to 2.20 +/- 0.491/min/m2 (p < 0.002). However, mean pulmonary artery pressure (21 +/- 7 mm Hg) and pulmonary vascular resistance (151 +/- 43-147 +/- 43 dynes/s/cm-5) did not change. Exogenous ET-1, when infused into patients with LVD, causes systemic but not pulmonary vasoconstriction.