Endothelin in human congestive heart failure

Clinical implications of cardiac (123)I-meta-iodobenzylguanidine scintigraphy and cardiac natriuretic peptides in patients with heart disease

The purpose of this study was to evaluate whether or not cardiac sympathetic nerve activity, using (123)I-meta-iodobenzylguanidine ((123)I-MIBG) imaging, and cardiac natriuretic peptides (atrial and brain, ANP and BNP) were independent predictors of cardiac events, and, if so, which was the stronger predictor. Planar (123)I-MIBG images were obtained from 62 patients with heart disease. Plasma ANP and BNP levels, left ventricular ejection fraction (LVEF) by echocardiography, serum total cholesterol and triglyceride were measured. (123)I-MIBG was assessed as the heart-to-mediastinum (H/M) ratio of the delayed image and the washout rate (WoR) from the early to the delayed image. Patients were followed up for an average of 16.2 months, and 12 of 62 patients had cardiac events. Patients with events had significantly lower LVEF and H/M ratio compared with those without events. They had significantly higher WoR, ANP and BNP. By multivariate Cox proportional hazard analysis, (123)I-MIBG (H/M or WoR), ANP and BNP were independent predictors for cardiac events. Event-free survival using a Kaplan-Meier model, with a threshold value of 2.0 for H/M and 45% for WoR, showed that patients with H/M<2.0 and/or WoR>45% had a significantly poorer prognosis. These results suggest that (123)I-MIBG imaging and cardiac natriuretic peptides are useful tools for the evaluation of patients with heart disease, and that cardiac sympathetic nerve activity is a stronger predictor of cardiac events.

Endothelin antagonism with bosentan: current status and future perspectives

Endothelin receptor antagonists have been proposed for the treatment of a variety of disorders in which the endothelins may act as pathogenic mediators, such as hypertension, congestive heart failure, and cerebral vasospasm. Bosentan is a nonpeptide competitive antagonist, which can be a good tool for studying the endothelin system. It is specific for the endothelin system and blocks the actions of endothelin at both mammalian receptors (A and B). Bosentan has recently moved into Phase III clinical trial. This review will attempt to overview the experimental and clinical effects of bosentan.

Altered expression of endothelin receptors in failing human left ventricles

BACKGROUND

Endothelin signaling is activated in failing human hearts, and may contribute to progressive myocardial dysfunction and remodeling. However, the behavior of endothelin receptor systems (ET(A) and ET(B)) in failing human hearts is not well understood.

METHODS AND RESULTS

(125)[I]-endothelin-1 binding assays conducted in the presence of a non-hydrolyzable guanine nucleotide to uncouple agonist binding demonstrated that membranes prepared from nonfailing left ventricles (LVs) exhibit a mixed pattern of ET(A) ( approximately 60%) and ET(B) ( approximately 40%) receptor protein expression. Chronic LV failure from either idiopathic dilated (IDC) or ischemic (ISC) cardiomyopathy was accompanied by a significant (P<0.001) increase in ET(A) receptor density, to approximately 80% of the total population, and a significant (P<0.02) decrease in ET(B) receptor density. Ribonuclease protection assays demonstrated an increase in ET(A) mRNA abundance in IDC and ISC LVs, and a significant (P<0.04) increase in ET(B) mRNA abundance in ISC LVs. Enzyme-linked immunoabsorbent assays demonstrated a significant increase in tissue immunoreactive endothelin-1 concentration in IDC (P=0.01) and in IDC+ISC LVs (P=0.02), but receptor subtype protein or mRNA level was not significantly correlated with tissue ET-1 across all LVs. In situ reverse-transcription polymerase chain reaction in LV sections demonstrated that in both failing and nonfailing LVs the ET(A) gene is expressed in cardiac myocytes, vascular smooth muscle and endothelium; the ET(B) gene is expressed in cardiac myocytes, fibroblasts and endothelium; and the prepro-endothelin-1 gene is expressed in myocytes and interstitial cells.

CONCLUSIONS

In chronically failing human LVs, ET(A) receptor density is increased to become the dominant subtype while ET(B) receptor density is decreased. The ET(A), but not the ET(B) density change is accompanied by cognate regulation of mRNA abundance. Both receptor genes and prepro-endothelin-1 are expressed in cardiac myocytes. Finally, based on a lack of correlation with endothelin-1 tissue levels, it is unlikely that the failure-related changes in ET(A) and ET(B) receptor protein and mRNA expression result from homologous regulation by agonist exposure.

Endothelial dysfunction in chronic heart failure: clinical and therapeutic implications

Chronic heart failure is a complex clinical syndrome in which abnormal vascular endothelial function has been shown to occur at both the experimental and clinical levels. Alterations in endothelial function may contribute to the increased vasomotor tone and to the vascular remodeling process observed in patients with chronic heart failure. Reduced shear stress, increased activity of the various vasoconstricting neurohormonal systems, and increased levels of proinflammatory cytokines promote endothelial dysfunction in chronic heart failure. This article summarizes the major mechanisms implicated in the pathophysiology of abnormal endothelial function in chronic heart failure, as well as the novel therapeutic interventions aimed at reducing endothelial dysfunction in patients with the syndrome.

Association between plasma endothelin-1 levels and Cheyne-Stokes respiration in patients with congestive heart failure

STUDY OBJECTIVES

Elevated plasma endothelin-1 (ET-1) levels have been reported in association with hypoxia and congestive heart failure (CHF). Furthermore, Cheyne-Stokes respiration-central sleep apnea (CSR-CSA) has been found to correlate with the degree of pulmonary hypertension and the severity of CHF; however, the association between ET-1 levels and CSR-CSA has not been investigated previously.

SETTING

Veterans Affairs Medical Center.

INTERVENTIONS

We studied 46 consecutive patients with CHF (left ventricular function < or = 40%) who underwent right-heart catheterization and overnight polysomnography. Thirty-nine patients completed the study. Sixteen patients (41%) had CSR-CSA, 5 patients (13%) had obstructive apnea, and 18 patients (46%) had no sleep-disordered breathing. Circulating plasma ET-1 levels were assayed in patients with CSR-CSA and in patients with no sleep-disordered breathing using commercially available enzyme-linked immunosorbent assay kits.

RESULTS

ET-1 levels were significantly elevated in patients with CSR-CSA (mean +/- SD, 5.4 +/- 1.3 pg/mL) compared to those without central apnea (3.9 +/- 1.1 pg/mL; p < 0.01), and correlated with mean pulmonary artery pressure (r = 0.66, p < 0.01), pulmonary capillary wedge pressure (r = 0.56, p < 0.03), and central apnea frequency (r = 0.66, p < 0.01). In multivariate analysis, the severity of CSR-CSA was the only variable independently associated with plasma ET-1.

CONCLUSIONS

We conclude that elevated plasma ET-1 levels are linked to the severity of CSR-CSA. Whether ET-1 represents an important pathogenic factor in CSR-CSA or marker of its occurrence requires further evaluation.

Entry-into-humans study with tezosentan, an intravenous dual endothelin receptor antagonist

The purpose of this study was to investigate the tolerability, pharmacokinetics, and pharmacodynamics of ascending doses of tezosentan, an IV dual endothelin receptor antagonist, during first administration in humans. Tezosentan infused at doses of 5, 20, 50, 100, 200, 400, and 600 mg for 1 h was administered to sequential groups of six male subjects in a randomized, placebo-controlled, double-blind design. Recording of vital signs, electrocardiogram, adverse events, and clinical laboratory parameters monitored tolerability and safety. Blood samples were collected frequently for pharmacokinetic determinations and measurement of plasma endothelin-1 concentrations. Tezosentan was well tolerated at all dose levels. Headache was the most frequently reported adverse event and occurred at a higher incidence than with placebo at doses of > or = 100 mg. No clinically relevant changes in vital signs, electrocardiographic, or clinical laboratory parameters occurred. Plasma concentrations of tezosentan rapidly approached steady state and could be described by a two-compartment model. The volume of distribution at steady state (approximately 16 l) and the clearance (approximately 30 l/h) were considered independent of dose, in view of the wide dose range explored. A pronounced and rapid disposition phase (half-life 6 min), accounting for the major part of the elimination, was followed by a slower phase (half-life 3 h), probably caused by distribution from tissues. Endothelin-1 concentrations increased in a dose- and concentration-dependent fashion and returned slowly to baseline after termination of the infusion. Tezosentan warrants further clinical development in view of its tolerability and pharmacokinetic profile, which appears advantageous for application in emergency situations.

The role of endothelin in the pathogenesis of heart failure

In fewer than than 15 years since its discovery, endothelin is now recognized as playing a central role in the pathogenesis of chronic heart failure. This review examines the signaling pathways and mechanism of action of endothelin in relation to the studies that have elucidated this role. Early investigations observed that the endothelin system is markedly upregulated in heart failure, whereas others demonstrated that endothelin is the most potent vasoconstrictor. However, it has multiple other actions, including mediating pathologic hypertrophy and fibrosis of both ventricular and vascular tissues, acting as a proarrhythmic, and potentiating the effects of other neurohormones. Endothelin receptor antagonists were developed to investigate the hypothesis that these adverse effects could be prevented and experimental studies showed promise in this regard. Clinical studies to date have not fulfilled this promise. Further analysis of these trials will hopefully provide insight into these disparate findings and guidance for future investigations.

New therapeutics for chronic heart failure

Traditionally, clinicians have viewed heart failure either as a problem of excessive salt and water retention caused by abnormalities of renal blood flow, or as a hemodynamic problem associated with a reduced cardiac output and excessive peripheral vasoconstriction. Recently, clinicians have begun to adopt a neurohormonal model in which heart failure progresses because of the toxic effects of endogenous biological systems that become activated in heart failure. We review the rationale for existing heart failure therapies and discuss the reasoning behind the development of some emerging therapies.

Pharmacokinetics and pharmacodynamics of tezosentan, an intravenous dual endothelin receptor antagonist, following chronic infusion in healthy subjects

AIMS

The purpose of this study was to investigate the tolerability, pharmacokinetics, and pharmacodynamics of tezosentan, an intravenous dual endothelin receptor antagonist, during chronic infusions in healthy male subjects.

METHODS

Tezosentan was infused at a rate of 100 mg h(-1) for 6 h (study A, six subjects) and at a rate of 5 mg h(-1) for 72 h (study B, eight subjects). Both studies had a randomized, placebo-controlled, double-blind design. Tolerability and safety were monitored by the recording of vital signs, ECG, adverse events and clinical laboratory parameters. Blood samples were collected frequently for pharmacokinetic determinations and measurement of plasma endothelin-1 concentrations.

RESULTS

In both studies tezosentan was well tolerated with headache the most frequently reported adverse event (incidence of 75-100% for tezosentan and 50% for placebo). Plasma concentrations of tezosentan rapidly approached steady state (3000 and 125 ng ml(-1) in study A and B, respectively) and did not change upon prolonged infusion. A two-compartment model could describe its pharmacokinetic profile. The half-lives of the two disposition phases were approximately 0.10 and 3.2 h. Endothelin-1 concentrations increased rapidly 11- and 2-fold compared with pre-dose values in study A and B, respectively, during infusion of tezosentan and did not change during the 72 h infusion.

CONCLUSIONS

On the basis of these results, dose finding studies with tezosentan in acute heart failure can be initiated in the dose range 5-100 mg h(-1).

Endothelin receptor antagonists in cardiology clinical trials

Endothelin-1 (ET-1) is enhanced and has been demonstrated to be a prognostic marker in patients with advanced stages of heart failure, acute ischaemic syndromes, myocardial infarction and pulmonary hypertension. Activation of the endothelin (ET) system is associated with adverse haemodynamic consequences in patients with congestive heart failure and results in coronary vasoconstriction in patients with coronary artery disease (CAD). Moreover, ET-1 raises blood pressure, induces vascular and myocardial hypertrophy and acts as the natural counterpart of nitric oxide (NO), which exerts vasodilating, antithrombotic and antiproliferative effects. This article reviews recently completed and ongoing clinical trials examining the effects of ET receptor antagonists in patients with heart failure, CAD, arterial hypertension and pulmonary hypertension.

Endothelin antagonists and heart failure

Chronic heart failure (CHF) is characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance, reduced exercise tolerance, and dyspnea. Despite considerable progress in the treatment of CHF, especially in targeting activated neurohumoral systems, mortality in these patients remains high. Therefore, new treatment approaches are warranted. Endothelin-1 (ET-1) plasma levels are elevated in CHF and correlate with both hemodynamic severity and symptoms. Plasma levels of ET-1 are strong independent predictors of mortality in CHF. Combined ET(A/B) selective ET(A) receptor antagonists have been evaluated in patients with CHF showing impressive hemodynamic improvements. These results indicate that ET receptor antagonists indeed have a potential to improve hemodynamics, symptoms, and potentially prognosis in patients with CHF, which still carries a high mortality.

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.

Diagnostic and therapeutic potential of the endothelin system in patients with chronic heart failure

There is now considerable evidence to support a role for the endothelin (ET) system in the pathogenesis and progression of chronic heart failure (CHF). As such, the potential exists for this system to be useful in both diagnosis (by measurement of peptide levels in plasma and other body fluids) and treatment (by pharmacological blockade) of this condition. Plasma levels of endothelin-1 (ET-1) are elevated in CHF and the magnitude of elevation correlates with disease severity. ET-1 levels in plasma predict subsequent mortality in patients with CHF. ET-1 may also contribute to symptoms associated with CHF, such as exercise intolerance. In the diagnosis of CHF, plasma levels of ET-1 appear to be a less powerful discriminator between patients with mild disease and control subjects with normal ventricular function on multivariate analyses, compared to brain natriuretic peptide (BNP), or its N-terminal fragment. ET-1 concentrations are also elevated in the saliva of patients with CHF and may represent an alternative approach to assessment of the status of the ET system in these patients. Specific ET receptor antagonists (both mixed and ET(A)-selective) have been developed. Studies with these agents in animal models of CHF have demonstrated beneficial effects via both haemodynamic and non-haemodynamic pathways. A number of short-term clinical studies have been performed demonstrating improvements in haemodynamic parameters without neurohormonal activation. Long-term clinical studies with ET receptor antagonists are currently underway to definitively test the impact of blockade of this system on mortality and major cardiovascular endpoints. Endothelin converting enzyme (ECE) inhibitors represent an alternative strategy of ET blockade, and early data from animal models suggest these agents may be of clinical utility, either alone or, more likely, in combination with other zinc metallopeptidases.

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.

Endothelin and heart failure

The availability of potent and orally active nonpeptide endothelin (ET) receptor antagonists has generated a host of information on the pathophysiological role of ET-1 in a number of preclinical models including hypertension, renal failure, heart failure and pulmonary hypertension. Convincing data are available to show that ET-1 receptor antagonists are beneficial in humans as far as reversal of deranged systemic and regional hemodynamics associated with CHF and pulmonary hypertension. As in other disease areas, the issue of whether ET(A)-selective or ET(A/B) antagonists are more suited for CHF treatment remains unresolved. ET(B) receptors may mediate some critical processes in the kidney such as sodium and water excretion in addition to releasing vasodilator substances such as NO and prostacyclin from endothelial cells. In heart failure and chronic renal diseases, preservation of ET(B)-mediated responses in the kidney and pulmonary endothelium might be beneficial. On the other hand, blockade of ET(B)-mediated vasoconstriction, smooth muscle cell proliferation and fibrosis by ET(B) antagonists might be beneficial. In clinical trials so far, the hemodynamic effects of mixed antagonists of ET receptors and ET(A) selective antagonists seem equivalent.

Endothelin A receptor antagonists in congestive heart failure: blocking the beast while leaving the beauty untouched?

Congestive heart failure (CHF) is a disease process characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance and reduced exercise tolerance and dyspnea. Thus, mediators involved in the control of myocardial function and vascular tone may be involved in its pathophysiology. The family of endothelins (ET) consists of four closely related peptides, ET-1, ET-2, ET-3, and ET-4, which cause vasoconstriction, cell proliferation, and myocardial effects through activation of ET(A) receptors. In contrast, endothelial ET(B) receptors mediate vasodilation via release of nitric oxide and prostacyclin. In addition, ET(B) receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Thus, infusion of an ET(A) receptor antagonist into the brachial artery in healthy humans leads to vasodilation whereas infusion of an ET(B) receptor antagonist causes vasoconstriction. ET-1 plasma levels are elevated in CHF and correlate both with the hemodynamic severity and with symptoms. Plasma levels of ET-1 and its precursor, big ET-1, are strong independent predictors of death in patients after myocardial infarction and with CHF. ET-1 contributes to increased systemic and pulmonary vascular resistance, vascular dysfunction, myocardial ischemia, and renal impairment in CHF. Selective ET(A) as well as combined ET(A/B) receptor antagonists have been studied in patients with CHF showing impressive hemodynamic improvements (i.e. reduced peripheral vascular and pulmonary resistance as well as increased cardiac output). These results indicate that ET receptor antagonists indeed have a potential to improve hemodynamics, symptoms, and potentially prognosis of CHF which still carries a high mortality.

Pharmacodynamics and pharmacokinetics of omapatrilat in heart failure

The purpose of this study was to determine the pharmacodynamics and pharmacokinetics of omapatrilat, administered orally (25 mg) or intravenously (10 mg) in 19 New York Heart Association class II and class III congestive heart failure (CHF) patients versus 17 healthy controls matched for age, race, gender, and weight. The plasma concentrations of atrial natriuretic peptide (ANP) increased by approximately 20% and 30% in CHF and control subjects, respectively, at 4 hours after intravenous or oral omapatrilat administration. Similar elevation in the cyclic guanosine monophosphate concentration (25% to 35%) and ANP urinary excretion (21 ng/24 h to 22 ng/24 h) was seen in all treatment groups after omapatrilat administration. Angiotensin-converting enzyme activity was > 90% inhibited at 4 hours after dosing and remained approximately 60% to 70% inhibited at 24 hours after dosing. The levels of endothelin-1 and endothelin-2 remained unchanged after oral or intravenous administration of omapatrilat. The maximal reduction in seated blood pressure compared with baseline was similarfor CHF and control subjects. Clinical pharmacokinetic parameters were similar in both groups after intravenous dosing, but maximum concentration and area under the concentration-time curve were elevated in CHF patients compared with controls after oral dosing. Omapatrilat was well tolerated; differences in systemic exposure and metabolism between CHF patients and controls did not appear to be clinically significant.

Potential role of endothelin receptor antagonists in the setting of cardiopulmonary bypass: relevance to myocardial performance

The ET system is activated in cardiac surgical setting as evidenced by elevated systemic and myocardial ET-1 levels after coronary bypass grafting surgery which requires hypothermic cardioplegic arrest and cardiopulmonary bypass. Increased ET-1 may influence a number of clinical parameters in this setting. First, ET-1 may directly modulate myocardial contractile performance in the early postoperative period resulting in LV dysfunction and a complex postoperative course. Second, elevated ET-1 levels may exacerbate increased pulmonary vascular resistance and contribute to the development of transient pulmonary hypertension following bypass. Finally, augmented postoperative ET-1 levels could contribute to changes in the caliber and flow of vascular conduits used for coronary bypass. In this review, a current perspective on the ET system in the setting of cardiopulmonary bypass grafting surgery is provided and the potential use of ET receptor antagonists in this setting is discussed.

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.

Randomized trial of phosphodiesterase inhibitors versus catecholamines in patients with acutely decompensated heart failure

Increased neurohormone and cytokine concentrations are associated with adverse outcome in patients with congestive heart failure, so minimizing these increases may improve outcome, even in the acute phase of decompensated heart failure. The present study was designed to test the hypothesis that phosphodiesterase inhibitors, but not catecholamines, could favorably affect neurohormone and cytokine profiles in patients with acutely decompensated heart failure. Twenty-nine patients underwent monitoring using a Swan-Ganz catheter and were randomly allocated to receive phosphodiesterase inhibitors (PDEI group, n=19) or catecholamines (CA group, n=10). Pulmonary capillary wedge pressure decreased significantly in both groups and cardiac output showed a slight, but not statistically significant increase, in both groups. There was a significant decrease in plasma brain natriuretic peptide concentration in the PDEI group, but not in the CA group, whereas plasma interleukin-6 concentration increased in the CA group, but not in the PDEI group. Phosphodiesterase inhibitors favorably affect neurohormone and cytokine concentrations in patients with acutely decompensated heart failure.

The pregnancy hormone relaxin is a player in human heart failure

Human congestive heart failure is characterized by complex neurohumoral activation associated with the up-regulation of vasoconstricting and salt-retaining mediators and the compensatory rise of counter-regulatory hormones. In the present study, we provide the first evidence that relaxin (RLX), known as a pregnancy hormone, represents a potential compensatory mediator in human heart failure: plasma concentrations of RLX and myocardial expression of the two RLX genes (H1 and H2) correlate with the severity of disease and RLX responds to therapy. The failing human heart is a relevant source of circulating RLX peptides, and myocytes as well as interstitial cells produce RLX. Elevation of ventricular filling pressure up-regulates RLX expression and the hormone acts as a potent inhibitor of endothelin 1, the most powerful vasoconstrictor in heart failure. Furthermore, RLX modulates effects of angiotensin II, another crucial mediator. Our data identify RLX as a new player in human heart failure with potential diagnostic and therapeutic relevance.

Enrasentan improves survival, limits left ventricular remodeling, and preserves myocardial performance in hypertensive cardiac hypertrophy and dysfunction

Evidence suggests that endothelin receptor antagonists may have therapeutic potential for the chronic treatment of heart failure. In the current study, the effects of an orally active mixed endothelin-A/endothelin-B (ETA /ETB ) receptor antagonist (enrasentan) were assessed in a model of cardiac hypertrophy and dysfunction (spontaneously hypertensive stroke prone rats) maintained on a high-salt/high-fat diet. Echocardiography was used to quantify cardiac performance and left ventricular dimensions. Enrasentan (1,200 and 2,400 parts per million in the high-salt/high-fat diet) had no significant effects on body weight and systolic blood pressure. However, increases in heart rate were not observed in the enrasentan-treated groups at 12 weeks (p < 0.05). Enrasentan-treated groups exhibited significantly improved survival (90-95% vs. 30% [control rats] at 18 weeks; p < 0.001). Enrasentan treatments also increased stroke volume (at 8, 12, and 16 weeks) and cardiac index (at 8 and 16 weeks) 33-50% and 45-63%, respectively. Enrasentan treatments reduced the relative wall thickness (14-27% at 8 and 12 weeks), ratio of left ventricular mass to body weight (20% at 12 weeks), and ratio of terminal heart weight to body weight (16-23%, p < 0.05). Finally, circulating aldosterone concentration (54-57%) and proANF fragment (33%) were reduced in enrasentan-treated groups (54-57% and 33%, respectively). Mixed ETA /ETB receptor antagonism improves cardiac performance and attenuates ventricular remodeling and premature mortality in an aggressive hypertension model.

Impact of cardiac transplantation on molecular pathology of ET-1, VEGF-C, and mitochondrial metabolism and morphology in dilated versus ischemic cardiomyopathic patients

Little is known about the long-term impact of cardiac transplantation on activity and modifications of endothelin (ET)-1 system, vascular endothelial growth factor (VEGF), and mitochondrial metabolism and morphology in patients with ischemic cardiomyopathy (ICM) versus dilated cardiomyopathy (DCM). Messenger RNA (mRNA) expression levels of ET-1, endothelin converting enzyme (ECE)-1, VEGF-C, carnitine palmitoyltransferase (CPT)-1, and carnitine acetyltransferase (CARAT), as well as the number of normal, edematous, and degenerated mitochondria were assessed in left ventricular biopsies of 21 patients with DCM and 20 with ICM (New York Heart Association class III-IV) before and up to 3 months after cardiac transplantation. Cardiac samples of donated, nonfailing hearts served as controls (n=10). In cardiac biopsies of both ICM and DCM patients, ET-1, VEGF-C, CPT-1, and CARAT mRNA were up-regulated, whereas ECE-1 mRNA was down-regulated (P<0.05). Degenerated mitochondria had the highest number in both groups, followed by normal and edematous mitochondria. After cardiac transplantation, in ICM patients impaired gene expression levels decreased to, or below, normal levels, and the number of normal mitochondria increased (P<0.05). In implanted hearts of DCM patients, however, up-regulated ET-1 transcript levels persisted and the number of normal mitochondria decreased, whereas the number of degenerated mitochondria increased (P<0.05), and edematous mitochondria remained unchanged in number. These results show that cardiac transplantation corrects the impaired hemodynamic and echocardiographic parameters in both groups, whereas in DCM, the molecular pathology of ET-1 system and mitochondria persists. Therefore, it is more likely that these changes are the cause rather than a consequence of DCM.

Role of endogenous endothelin on coronary flow in health and disease

The role of the endothelium in the control of coronary flow has been demonstrated. Results of recent studies, both on animals and on humans, suggest that endogenous endothelin also plays an important role in basal coronary tone. Disease processes such as ischaemia-reperfusion injury, congestive heart failure, hypertension and atherosclerosis may be contributed to by an imbalance in, or excess of, release of endothelin. With the discovery of newer endothelin antagonists and endothelin converting enzyme inhibitors, especially with fewer hepatic side effects, there is the potential for much future research into novel therapeutic management of these common cardiovascular disorders.

Characterization of effects of endothelin-1 on the L-type Ca2+ current in human atrial myocytes

The effects of endothelin-1 (ET-1) on the L-type Ca2+ current (I(Ca)) were examined in whole cell patch-clamped human atrial myocytes. Depending on the initial current density, ET-1 (10 nM) increased the amplitude of I(Ca) by 99 +/- 7% or decreased it by 33 +/- 2%. The stimulatory effect predominated on current of low density (2.3 +/- 0.2 pA/pF), whereas I(Ca) of higher density (5.8 +/- 0.3 pA/pF) was inhibited by ET-1. After I(Ca) stimulation by 1 microM isoproterenol, ET-1 always inhibited the current by 32 +/- 7% (P < 0.05), an effect that was suppressed by pretreating myocytes with pertussis toxin. Atrial natriuretic peptide (ANP) inhibited I(Ca) (41 +/- 3%) by reducing intracellular cAMP concentration. In ANP-treated myocytes, the stimulatory effect of ET-1 on I(Ca) predominated (52 +/- 7%). The inhibitory effect of ET-1 on I(Ca) was blocked by the ET(A) antagonist BQ-123, whereas the stimulatory effect was suppressed by the ET(B) agonist BQ-788. We conclude that ET-1 has opposite effects on I(Ca) depending on the baseline amplitude of current, and both subtype ET receptors are implicated in the signal transduction pathways.

Endothelin mediates the altered renal hemodynamics associated with experimental congestive heart failure

Congestive heart failure (CHF) is commonly associated with renal dysfunction. The goal of the current study was to evaluate the role of endothelin in the renal dysfunction of experimental CHF by using tezosentan, a potent dual endothelin receptor antagonist. Rats were subjected to coronary artery ligation. Cardiac and renal hemodynamics were assessed after 3-5 weeks, when CHF had developed. Compared with control rats, CHF rats had significantly higher left ventricular end-diastolic pressure (LVEDP), lower mean arterial pressure, and reduced dP/dt(max). CHF rats had severe renal vasoconstriction, as assessed by increased renal vascular resistance (RVR, p < 0.001), decreased renal plasma flow (RPF, p < 0.001), and glomerular filtration rate (GFR, p < 0.001). Filtration fraction rose (p < 0.001). Urine flow rate and sodium excretion were markedly lower. Acute administration of tezosentan induced a marked decrease in LVEDP without change of dP/dt(max) and heart rate. Tezosentan decreased RVR (-43%, p < 0.001) and increased RPF and GFR. Filtration fraction decreased slightly. Tezosentan also increased urine flow rate and sodium excretion. These findings demonstrate that endothelin at least partly mediates the altered renal hemodynamics associated with experimental CHF. Dual endothelin receptor blockade could be useful for the improvement of both cardiac and renal function in CHF.

Functional role of endogenous endothelin-1 in congestive heart failure treated with angiotensin II receptor antagonist

Interactions between angiotensin (ANG) II and endothelin (ET)-1 receptor transduction pathways have been unclear in congestive heart failure (CHF). Therefore the objects of this study are, in CHF, whether production of ET-1 is modulated by ANG II and/or whether hemodynamic effects of endogenous ET-1 are modulated by ANG II. Twelve dogs were randomly assigned to two groups: untreated (n = 6) and treated with ANG II type 1 (AT1) receptor antagonist (TCV116, 1.5 mg/kg/d) (n = 6). After rapid ventricular pacing (240 bpm) for 4 weeks, plasma and cardiac ET-1 levels were compared between the two groups. Acute hemodynamic effects of a nonspecific ET(A&B) receptor antagonist, TAK044 (3 mg/kg plus 3 mg/kg/h i.v.) were examined in both groups by a conductance catheter and a micromanometer. After 4 weeks of pacing, plasma and cardiac tissue ET-1 levels were elevated in both groups to a similar degree. In the group treated with TCV116, TAK044 produced an increase in stroke volume and a decrease in total systemic resistance; heart rate was unchanged. The time constant of left ventricular (LV) relaxation was significantly decreased. The slope of LV end-systolic pressure-volume relation (E(ES)) was increased (p < 0.05), indicating an increased LV contractility. Thus endogenous ET-1 produces an arterial vasoconstriction and impairs LV contractility and relaxation in CHF with AT1 receptor antagonism. These hemodynamic responses to TAK044 in CHF treated with TCV116 were similar in untreated CHF. These results suggest that the production of ET-1 and the cardiac effects of endogenous ET-1 in CHF may be unaffected by ANG II acting through AT1 receptors.

The dual endothelin receptor antagonist tezosentan acutely improves hemodynamic parameters in patients with advanced heart failure

BACKGROUND

Endothelin-1, a potent vasoconstrictor, is elevated in congestive heart failure and is postulated to play a major role in the pathogenesis of the disease. Endothelin receptor antagonism may be a specific therapeutic approach. This study was designed to determine the effective dosage range, hemodynamic effects, and tolerability of tezosentan, an intravenous dual endothelin receptor antagonist, in patients with advanced heart failure.

METHODS

This randomized, double-blind, placebo-controlled multicenter trial enrolled 38 patients with symptomatic stable heart failure (New York Heart Association class III, left ventricular ejection fraction <35%) undergoing right heart catheterization. Patients were equally randomized to a 4-hour intravenous infusion of placebo or tezosentan in ascending doses (5, 20, 50, and 100 mg over 1 hour each). Angiotensin-converting enzyme inhibitors and diuretics were withheld 24hours before the study. Hemodynamics were measured during and for 4 hours after the infusion.

RESULTS

Compared with placebo, tezosentan treatment produced a significant increase in cardiac index (treatment difference 0.59 L/min/m(2), P =.0001) and decreases in pulmonary and systemic vascular resistances (P </=.01) without changes in heart rate. Consistently greater decreases in pulmonary capillary wedge pressure, mean right atrial pressure, and pulmonary and arterial pressures with tezosentan did not reach statistical significance. Hemodynamic changes were dose dependent with maximal effects at 20 and 50 mg per hour. Tezosentan was well tolerated. Despite increased endothelin-1 concentrations, hemodynamic rebound was not observed.

CONCLUSION

Tezosentan rapidly and dose dependently improved hemodynamics. The favorable effects on cardiac index and pulmonary and systemic vascular resistances without changes in heart rate may be beneficial in the treatment of acute heart failure.

Chelerythrine and genistein inhibit the endothelin-1-induced increase in myofilament Ca(2+) sensitivity in rabbit ventricular myocytes

We performed experiments to elucidate the cellular mechanism for the biphasic inotropic response to endothelin-1 of single rabbit ventricular myocytes loaded with a fluorescent dye, acetoxymethylester of indo-1. Endothelin-1 at 10 nM elicited a biphasic inotropic effect: a transient decrease in cell shortening and Ca(2+) transients followed by an increase in cell shortening without significant elevation of peak Ca(2+) transients. The selective endothelin ET(A) receptor antagonist FR139317 (2(R)-[2(R)-[2(S)-[(1-hexahydro-1H-azepinyl)]carbonyl]amino-4-methylpentanoyl]amino-3-[3-(1-methyl-1H-indolyl)propionyl]amino-3-(2-pyridyl)propionic acid) at 1 microM abolished the biphasic effect of endothelin-1 on cell shortening and Ca(2+) transients. The selective protein kinase C inhibitor chelerythrine at 1 microM and the tyrosine kinase inhibitor genistein at 5 microM inhibited the endothelin-1-induced increase in cell shortening without significantly affecting Ca(2+) transients and the transient decrease in cell shortening and Ca(2+) transients. The present results indicate that both protein kinase C and tyrosine kinase may contribute to the increase in myofilament Ca(2+) sensitivity induced by endothelin-1, whereas the decrease in Ca(2+) transients induced by endothelin-1 may be mediated by a signalling pathway different from that involved in the increase in cardiac contractility in rabbit ventricular myocytes.

Increased extraction of endothelin-1 across the failing human heart

In this study we compared the transcardiac gradient of plasma endothelin-1 in patients with normal ventricular function and in those with congestive heart failure. We documented a significant reduction in the plasma levels of endothelin-1 across the failing human heart, an effect not seen in patients with normal left ventricular function.

Nonselective endothelin receptor antagonist initiated soon after the onset of myocardial infarction may deteriorate 24-hour survival

To investigate the effects of endothelin blockade initiated immediately after the onset of myocardial infarction on survival and left ventricular remodeling, treatment with the nonselective receptor antagonist TAK-044 (n = 22) or saline (n = 19) for 3 weeks was initiated immediately after coronary ligation in rats. The 24-h survival rate was significantly lower in the TAK-044 group than in the saline group. The systolic blood pressure 24 h after the onset of myocardial infarction was similar in the saline and TAK-044 groups, although it was significantly lower in the TAK-044 group during the 3-week protocol. Heart weight/tibial length was significantly increased in the TAK-044 group compared with the saline group. As all deaths in the TAK-044 group occurred within 24 h after myocardial infarction, we performed additional experiments using a separate group of rats 12-16 h after myocardial infarction. Plasma and myocardial endothelin-1 levels were significantly increased, and a bolus injection of TAK-044 significantly reduced left ventricular dP/dtmax in these rats that had had a myocardial infarction compared with sham-operated rats. Endothelin receptor blockade initiated immediately after the onset of myocardial infarction may deteriorate acute-phase survival and left ventricular remodeling. Inhibition of the positive inotropic action of endothlin-1 may partially explain the increased 24-h mortality.

Endothelin receptor antagonists in congestive heart failure: a new therapeutic principle for the future?

Congestive heart failure (CHF) is characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance and reduced exercise tolerance and dyspnea. Thus, mediators involved in the control of myocardial function and vascular tone may be involved in its pathophysiology. The family of endothelins (ET) consists of four closely related peptides, ET-1, ET-2, ET-3 and ET-4, which cause vasoconstriction, cell proliferation and myocardial effects through activation of ETA receptors. In contrast, endothelial ETB receptors mediate vasodilation via release of nitric oxide and prostacyclin. In addition, ETB receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Thus, infusion of an ETA-receptor antagonist into the brachial artery in healthy humans leads to vasodilation, whereas infusion of an ETB-receptor antagonist causes vasoconstriction. Endothelin-1 plasma levels are elevated in CHF and correlate both with hemodynamic severity and symptoms. Plasma levels of ET-1 and its precursor, big ET-1, are strong independent predictors of death after myocardial infarction as well as in CHF. Endothelin-1 contributes to increased systemic and pulmonary vascular resistance, vascular dysfunction, myocardial ischemia and renal impairment in CHF. Selective ETA, as well as combined ETA/B-receptor antagonists, have been studied in patients with CHF, and their use has shown impressive hemodynamic improvement (i.e., reduced peripheral vascular and pulmonary resistance as well as increased cardiac output). These results indicate that ET-receptor antagonists, indeed, have a potential to improve hemodynamics, symptoms and, potentially, prognosis in patients with CHF, which still carries a high mortality.

The role of ANG II and endothelin-1 in exercise-induced diastolic dysfunction in heart failure

The diastolic dysfunction present at rest in congestive heart failure (CHF) is exacerbated during exercise (Ex). Increases in circulating ANG II and endothelin-1 (ET-1) during Ex may contribute to this response. We assessed the effect of Ex on circulating plasma levels of ANG II and ET-1 and left ventricular (LV) dynamics before and after pacing-induced CHF at rest and during Ex in nine conscious, instrumented dogs. Before CHF, there were modest increases in circulating levels of ANG II (but not ET-1) during Ex. LV diastolic performance was enhanced during Ex with decreases in the time constant of LV relaxation (tau), LV end-systolic volume (V(ES)), and LV minimum pressure with a downward shift of the LV early diastolic portion of the pressure-volume (P-V) loop. This produced an increase in peak LV filling rate without an increase in mean left atrial (LA) pressure. After CHF, the resting values of ANG II and ET-1 were elevated and increased to very high levels during Ex. After CHF, mean LA pressure, tau, and LV minimum pressure were elevated at rest and increased further during Ex. Treatment with L-754,142, a potent ET-1 antagonist, or losartan, an ANG II AT(1)-receptor blocker, decreased these abnormal Ex responses in CHF more effectively than an equally vasodilatory dose of sodium nitroprusside. Combined treatment with both ANG II- and ET-1-receptor blockers was more effective than either agent alone. We conclude that in CHF, circulating ANG II and ET-1 increase to very high levels during Ex and exacerbate the diastolic dysfunction present at rest.

Biphasic inotropic response to endothelin-1 in the presence of various concentrations of norepinephrine in dog ventricular myocardium

The present study was undertaken to investigate the interaction between endothelin-1 (ET-1) and norepinephrine (NE) on contractile regulation in dog ventricular myocardium. ET-1 alone did not elicit any inotropic response in isolated dog ventricular trabeculae (37 degrees C, 0.5 Hz). In the presence of NE at a high concentration (10(-7) M), ET-1 (10(-8) M) elicited a long-lasting negative inotropic effect, while in the presence of NE at a moderate concentration (3 x 10(-8) M) it produced a biphasic inotropic effect: a sustained positive inotropic effect subsequent to a short-lasting negative inotropic effect. In the presence of a lower concentration (10(-9) M) that affected scarcely the basal force of contraction, ET-1 produced a pronounced positive inotropic effect in association with negative lusitropic and negative clinotropic effects in a concentration-dependent manner subsequent to a small transient negative inotropic effect. The presented results indicate that not only the extent, but also the quality of the inotropic response to ET-1 is determined by the level of NE in the biophase. The crosstalk of ET-1 with NE may play a crucial role in pathophysiological regulation of cardiac contractility in intact dog ventricular myocardium.

Acute effects of endothelin-1 and TAK-044 (ET(A) and ET(B) receptor antagonist) in rats with dilated cardiomyopathy

The hemodynamic effects of endothelin (ET)-1 and TAK-044 (ET(A) and ET(B) receptor antagonist) were studied in a rat model of dilated cardiomyopathy after autoimmune myocarditis. Six weeks after immunization, survived Lewis rats (30/43 = 70%) were randomly allocated into five groups to be given 0, 0.3, 3, 30 and 60 mg/kg/day (groups F0, F0.3, F3, F30 and F60; each group, n = 4) of TAK-044 using an osmotic pump subcutaneously. Age-matched normal Lewis rats (n = 26) were also randomly divided into four groups to be given 0, 0.3, 3 and 30 mg/kg/day (groups N0, N0.3, N3 and N30; each group, n = 4). ET-1 concentrations in plasma and myocardium were measured, and immunohistochemical detection of ET-1 in the left ventricle from the remaining rats (groups F and N) was performed. After administration of TAK-044 for 7 days, 2, 4, 11, 21 and 42 ng/min ET-1 every 20 min was infused using a pump, and the change in mean arterial pressure of each group during the infusion was examined. The plasma and myocardial ET-1 concentrations were significantly higher in group F than group N (12.3 +/- 1.5 vs. 5.4 +/- 0.2 pg/ml and 426 +/- 31 vs. 98 +/- 6 pg/g tissue; both p < 0.01). Strong positive signals for ET-1 were found to be widely distributed in the left ventricular myocardium of both groups of rats. Although the ET-1-induced increase in the mean arterial pressure was abolished in group N30, the maximal dose of ET-1 produced a 34% increase in the mean arterial pressure in group F30. Even in group F60, ET-1-induced hypertension was blocked incompletely. These results indicate that the heart may be a major ET-1-producing organ, and a higher dose of ET-1 antagonist is needed to block the effect of ET-1 in rats with dilated cardiomyopathy.

Increased sensitivity of vascular smooth muscle to nitric oxide in dilated cardiomyopathy of Syrian hamsters (Bio TO-2 strain)

We assessed the evolution with time of the responsiveness of three vascular beds in dilated cardiomyopathic hamsters of the Bio TO-2 strain. Eight cardiomyopathic hamsters and 8 control hamsters were investigated at 180 and 300 days of age. Thoracic aorta and mesenteric and renal artery rings were studied in isolated organ baths. Cumulative concentration-response relations to phenylephrine, acetylcholine, sodium nitroprusside, and angiotensin II were established for each ring. Maximum effect (Emax) and concentration inducing 50% of Emax (EC50) were determined from each concentration-response curve and pD2 was calculated as -log(EC50). Compared with control hamsters, in cardiomyopathic hamsters, Emax of phenylephrine was not modified in aorta, whereas it was significantly lower in mesenteric (-6% and -33% at 180 and 300 days, respectively) and renal (-17% and -24%) arteries. Emax of acetylcholine was significantly higher in aorta (+57% and +30%), mesenteric (+42% and +34%), and renal (+168% and +70%) arteries. Emax of sodium nitroprusside was significantly higher in aorta (+26% and +16%) and tended to be higher in mesenteric (+25% and +23%) and renal (+27% and +10%) arteries. Emax of angiotensin II was not modified in aorta and tended to be lower in mesenteric artery at 300 days. The pD2 of phenylephrine was significantly increased in aorta and the pD2 of sodium nitroprusside was significantly increased in aorta and renal artery. In conclusion, in dilated cardiomyopathic hamsters, endothelium-dependent and -independent vasodilations are enhanced early, demonstrating increased sensitivity of vascular smooth muscle to nitric oxide. This abnormality may be involved in the decreased responsiveness to phenylephrine and angiotensin II.

The role of angiotensin II and TGF-beta on the progression of chronic allograft nephropathy

Chronic allograft nephropathy is the most prevalent cause of graft dysfunction and failure. Its pathogenesis and treatment remains poorly defined. The calcineurin inhibitors, cyclosporine and tacrolimus, may play a role in the progressive loss of renal function in patients with chronic allograft nephropathy. This effect may be either related to the direct stimulation of profibrogenic cytokines such as transforming growth factor (TGF-β) or indirect mechanisms, through increases in blood pressure or alterations in either carbohydrate or lipid metabolism. Experimental studies have demonstrated that angiotensin-converting enzyme inhibitors (ACE-I) and angiotensin II receptor blockers (ARBs) can attenuate cyclosporine-mediated increases in TGF-β production in renal tissue. Clinical studies have demonstrated that either cyclosporine or tacrolimus dose reduction may help reduce the rate of loss of renal function in patients with chronic allograft nephropathy. Moreover, other studies have demonstrated that a chronic reduction in the dose of cyclosporine in transplant patients can reduce serum TGF-β levels. Treatment with an ARB can normalise the plasma levels of TGF-β in renal transplant patients receiving cyclosporine. All these observations suggest that there may be a role of cyclosporine, and possibly tacrolimus, in worsening chronic allograft nephropathy through their effects on the renin-angiotensin-aldosterone system (RAAS) and TGF-β production.

Expression and activity of pulmonary endothelin converting enzyme in heart failure: relation to endothelin biosynthesis and receptor distribution

BACKGROUND

Although reduced pulmonary clearance of endothelin-1 (ET-1) has been suggested to contribute to increased circulating levels in congestive heart failure (CHF), the regulation of the pulmonary ET system with CHF remains to be defined. Accordingly, the aim of the present study is to investigate the expression and activity of the ET system with the development of CHF.

METHODS AND RESULTS

Pulmonary tissue samples were collected from pigs with pacing CHF (240 bpm, 3 wks, n = 10) and controls (n = 10). The pulmonary messenger RNA (mRNA) and protein levels of endothelin converting enzyme-1 (ECE-1) subisoforms, ET-1, and ET receptor profiles were determined. The gene expression of ET-1 precursor, ECE-1a, and ET(A) was upregulated 4-, 3-, and 2-fold, respectively, with CHF. Pulmonary tissue ET-1 was increased to 13 +/- 2 fmol/mg protein from control values of 5 +/- 1 fmol/mg protein (P <.05), and ECE-1 activity was augmented from 3,264 +/- 665 fmol/mg protein in control animals to 14,073 +/- 654 fmol/mg protein per hour in CHF animals (P <.05). The ET(B) receptor density decreased, whereas ET(A) receptors were increased in CHF, indicating a shift in the ET(A) to ET(B) ratio.

CONCLUSIONS

Both the increased synthesis and the decreased clearance of ET-1 via ET(B) receptors may contribute to the increased systemic and pulmonary ET-1 levels in CHF.

Plasma endothelin concentrations in hypertension

The endothelins comprise a family of potent vasoconstricting peptides. Endothelin-1 appears to be the predominant isoform produced by the vascular endothelium, acting mainly in a paracrine fashion on vascular smooth muscle cells to cause vasoconstriction. It also has a range of other local actions--in the kidney, in the nervous system and on other hormone systems--that could, potentially, play a part in the genesis of hypertension. The association of raised plasma endothelin concentrations in human hypertension has caused much interest, but the literature is not consistent. Given the generally low plasma concentration of the endothelins, and their mainly paracrine actions, it remains unclear whether plasma endothelin has a functional role in hypertension. Additionally, problems remain with the measurement of plasma endothelin that raise doubts about the validity of conclusions drawn from these measurements.

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.

Therapeutic potential for endothelin receptor antagonists in cardiovascular disorders

The endothelins are synthesized in vascular endothelial and smooth muscle cells, as well as in neural, renal, pulmonal, and inflammatory cells. These peptides are converted by endothelin-converting enzymes (ECE-1 and -2) from 'big endothelins' originating from large preproendothelin peptides cleaved by endopeptidases. Endothelin (ET)-1 has major influence on the function and structure of the vasculature as it favors vasoconstriction and cell proliferation through activation of specific ET(A) and ET(B) receptors on vascular smooth muscle cells. In contrast, ET(B )receptors on endothelial cells cause vasodilation via release of nitric oxide (NO) and prostacyclin. Additionally, ET(B) receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Indeed, ET-1 contributes to the pathogenesis of important disorders as arterial hypertension, atherosclerosis, and heart failure. In patients with atherosclerotic vascular disease (as well as in many other disease states), ET-1 levels are elevated and correlate with the number of involved sites. In patients with acute myocardial infarction, they correlate with 1-year prognosis. ET receptor antagonists have been widely studied in experimental models of cardiovascular disease. In arterial hypertension, they prevent vascular and myocardial hypertrophy. Experimentally, ET receptor blockade also prevents endothelial dysfunction and structural vascular changes in atherosclerosis due to hypercholesterolemia. In experimental myocardial ischemia, treatment with an ET receptor antagonist reduced infarct size and prevented left ventricular remodeling after myocardial infarction. Most impressively, treatment with the selective ET(A) receptor antagonist BQ123 significantly improved survival in an experimental model of heart failure. In many clinical conditions, such as congestive heart failure, both mixed ET(A/B )as well as selective ET(A) receptor antagonism ameliorates the clinical status of patients, i.e. symptoms and hemodynamics. A randomized clinical trial showed that a mixed ET(A/B) receptor antagonist effectively lowered arterial blood pressure in patients with arterial hypertension. In patients with primary pulmonary hypertension or pulmonary hypertension related to scleroderma, treatment with a mixed ET(A/B) receptor antagonist resulted in an improvement in exercise capacity. ET receptor blockers thus hold the potential to improve the outcome in patients with various cardiovascular disorders. Randomized clinical trials are under way to evaluate the effects of ET receptor antagonism on morbidity and mortality.

alpha-atrial natriuretic peptide, cyclic guanosine monophosphate, and endothelin in plasma as markers of myocardial depression in human septic shock

OBJECTIVE

To assess the value of alpha-atrial natriuretic peptide (alpha-ANP), second messenger cyclic guanosine monophosphate (cGMP,) and endothelin as markers of myocardial depression in septic shock.

DESIGN

Prospective observational study.

SETTING

Medical intensive care unit (ICU) of a university hospital.

PATIENTS

Fourteen consecutive patients with septic shock and arterial and pulmonary artery catheters in place.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables and plasma levels of alpha-ANP, cGMP, and endothelin were measured every 6 hrs for 3 days after admission. Eight patients died from shock in the ICU. The nadir left ventricular stroke work index (LVSWI) was below 35 g/m2 in all patients, and the median peak circulating alpha-ANP (n < 68 pg/mL) was 276 pg/mL (range, 79-1056), the median peak cGMP (n < 2.1 ng/mL) was 8.1 ng/mL (range, 3.2-29.7), and the median peak endothelin (n < 5.3 pg/mL) was 15.5 pg/mL (range, 8.5-33.9), supranormal in all patients. Outcome groups differed in the course of cardiac index and LVSWI, which were lower in nonsurvivors despite similar filling pressures and more intensive inotropic treatment (p < .01). The course of alpha-ANP, cGMP, and endothelin plasma levels also differed between groups, with higher levels in nonsurvivors (p < .05). As for pooled data, the mean daily or nadir LVSWI inversely related to mean daily or peak alpha-ANP, cGMP, and endothelin levels, respectively (p < .05). The area under the receiver operating characteristic curve for myocardial depression (LVSWI < 35 g/m2) was for alpha-ANP and endothelin 0.77, and for cGMP 0.85 (p < .01). The optimum cutoff values for alpha-ANP, cGMP, and endothelin were 172 pg/mL, 4.5 ng/mL, and 10.0 pg/mL, respectively. The sensitivity for myocardial depression of alpha-ANP, cGMP, and endothelin was 68%, 77%, and 72%, and the specificity was 82%, 93%, and 69%, respectively.

CONCLUSIONS

Circulating alpha-ANP, endothelin, and, particularly, cGMP may be markers of the myocardial depression of human septic shock, which is associated with mortality.

Neurohormonal regulation of myocardial cell apoptosis during the development of heart failure

Adult cardiac myocytes are terminally differentiated cells that are no longer able to divide. Accumulating data support the idea that apoptosis in these cells is involved in the transition from cardiac compensation to decompensated heart failure. Since a number of neurohormonal factors are activated in this state, these factors may be involved in the positive and negative regulation of apoptosis in cardiac myocytes. beta1-Adrenergic receptor and angiotensin type 1 receptor pathways, nitric oxide and natriuretic peptides are involved in the induction of apoptosis in these cells, while alpha1- and beta2-adrenergic receptor and endothelin-1 type A receptor pathways and gp130-related cytokines are antiapoptotic. The myocardial protection of the latter is mediated, at least in part, through mitogen-activated protein kinase-dependent pathways, compatible with the findings in other cell types. In contrast, signaling pathways leading to apoptosis in cardiac myocytes are distinct from those in other cell types. The cAMP/PKA pathway induces apoptosis in cardiac myocytes and blocks apoptosis in other cell types. The p300 protein, a coactivator of p53, mediates apoptosis in fibroblasts but appears to play a protective role in differentiated cardiac myocytes. The inhibition of myocardial cell apoptosis in heart failure may be achieved by directly blocking apoptosis signaling pathways or by modulating neurohormonal factors involved in their regulation. These may provide novel therapeutic strategies in some forms of heart failure.

The effect of angiotensin II on mitogen-activated protein kinase in human cardiomyocytes

The role of angiotensin II (Ang II)-receptors on mitogen-activated protein kinase (MAPK) activation in cardiomyocytes remains controversial. Therefore, the current study was designed to investigate the actions of AT(1)- and AT(2)-receptors on Ang II-induced extracellular signal-regulated kinase (ERK), p38 and the c-Jun N-terminal kinase (JNK) MAPK activities in human cardiomyocytes. Human cardiac tissue was obtained from open-heart surgery (n=6). The cardiac tissue was minced and incubated in the special tissue culture system for 24 hours in the absence or presence of Ang II (10(-7) M). These studies were repeated with the AT(1)-receptor antagonist losartan (10(-6) M) or the AT(2)-receptor antagonist PD-123319 (10(-6) M). Immunohistochemical staining and Western blot analysis with phospho-antibodies were performed to determine ERK, JNK and p38 activities. Ang II increased ERK and p38 activities in human cardiomyocytes. The effects of Ang II were abolished by losartan and enhanced by PD-123319. Co-incubation with both losartan and PD-123319 resulted in a decrease of ERK and p38 activities in cardiomyocytes. The immunohistochemical staining of JNK showed no significant differences between Ang II alone, Ang II plus losartan and Ang II plus PD-123319 groups. In conclusion, Ang II has a potent effect on ERK and p38 MAPK activities in cardiomyocytes, by acting through AT(1)-receptors. This effect of Ang II is modified by AT(2)-receptors. Therefore, Ang II, via AT(1)- and AT(2)-receptor stimulation, has a distinct effect on MAPK activity in cardiomyocytes.

Temporal endothelin dynamics of the myocardial interstitium and systemic circulation in cardiopulmonary bypass

OBJECTIVE

Increased systemic levels of the bioactive peptide endothelin 1 during and after cardioplegic arrest and cardiopulmonary bypass have been well documented. However, endothelin 1 is synthesized locally, and therefore myocardial endothelin 1 production during and after cardiopulmonary bypass remains unknown.

METHODS

Pigs (n = 11) were instrumented for cardiopulmonary bypass, and cardioplegic arrest was initiated. Myocardial interstitial and systemic arterial levels of endothelin 1 were measured before cardiopulmonary bypass, throughout bypass and cardioplegic arrest (90 minutes), and up to 90 minutes after separation from bypass. Myocardial interstitial endothelin 1 was determined by microdialysis and radioimmunoassay.

RESULTS

Baseline myocardial endothelin 1 levels were higher than systemic endothelin 1 levels (25.6 +/- 6.7 vs 8.3 +/- 1.1 fmol/mL, P <.05). With the onset of bypass, myocardial endothelin 1 increased by 327% +/- 92% from baseline (P <.05), which preceded the increase in systemic endothelin 1 levels.

CONCLUSION

Myocardial compartmentalization of endothelin 1 exists in vivo. Cardiopulmonary bypass and cardioplegic arrest induce temporal differences in endothelin 1 levels within the myocardial interstitium and systemic circulation, which, in turn, may influence left ventricular function in the postbypass period.

Improvement of renal dysfunction in rats with chronic heart failure after myocardial infarction by treatment with the endothelin A receptor antagonist, LU 135252

OBJECTIVE

To investigate the role of an activated endothelin system in the renal dysfunction observed in chronic heart failure after myocardial infarction.

METHODS

In rats with heart failure after myocardial infarction and in sham-operated animals (Sham), we investigated the effect on renal function of long-term oral treatment with the selective endothelin A (ETA) receptor antagonist, LU 135252 (30 mg/kg per day; groups MI/LU and Sham/LU) or placebo (groups MI/P, Sham/P). Only animals with extensive myocardial infarction (at least 46% of the left ventricle) were included in the study. Infarct size was matched between groups MI/P and MI/LU. Endogenous creatinine clearance, fractional sodium excretion, and plasma and urinary concentrations of endothelin were determined 12 weeks after myocardial infarction.

RESULTS

Endogenous creatinine clearance was significantly lower in group MI/P than in group Sham/P (MI/P: 0.64 +/- 0.05, Sham/P: 0.81 +/- 0.04 ml/min per 100 g body weight; P= 0.01 (means +/- SEM)). Treatment with LU 135252 completely prevented the decline in creatinine clearance in rats with chronic myocardial infarction (MI/LU: 0.98 +/- 0.21; Sham/LU: 0.83 +/- 0.10). Fractional sodium and protein excretion did not differ among the four groups. Group MI/P had a marked increase in plasma endothelin concentrations, which was not affected by treatment with LU 135252. Urinary endothelin excretion was significantly lower in group MI/P than in group Sham/P. In the treatment groups, no difference could be observed between animals that had suffered myocardial infarction and the sham-operated group, although LU 135252 markedly increased the urinary excretion of endothelin.

CONCLUSION

Our data demonstrate a restoration of impaired renal function in chronic ischaemic heart failure by treatment with the selective ETA receptor antagonist, LU 135252. These results offer a promising therapeutic option for the treatment of renal insufficiency in patients with chronic heart failure.

Endothelin-1 as a protective factor against beta-adrenergic agonist-induced apoptosis in cardiac myocytes

OBJECTIVES

The purpose of this study was to investigate the regulation of beta-adrenergic agonist-induced apoptosis by endothelin-1 (ET-1) in cardiac myocytes.

BACKGROUND

Numerous hormonal factors including norepinephrine and ET-1 are activated in patients with heart failure. These factors may be involved in the positive and negative regulation of myocardial cell apoptosis observed in failing hearts. Recently, it has been shown that norepinephrine can induce myocardial cell apoptosis via a beta-adrenergic receptor-dependent pathway.

METHODS

Primary cardiac myocytes were prepared from neonatal rats. These cells were stimulated with the beta-adrenergic agonist isoproterenol (ISO) in the presence or absence of ET-1.

RESULTS

The administration of 10(-7) mol/liter of ET-1 completely blocked Iso-induced apoptosis. An endothelin type A receptor antagonist, FR139317, negated the inhibitory effect of ET-1 on apoptosis, while the endothelin type B receptor antagonist BQ788 did not show such a negation. Endothelin-1 also inhibited apoptosis induced by a membrane-permeable cAMP analogue (8-Br-cAMP), which bypassed Gi. The effect of ET-1 was neutralized by an MEK-1-specific inhibitor (PD098059), a phosphatidylinositol 3'-kinase inhibitor (wortmannin) and its downstream pp70 S6-kinase inhibitor, rapamycin.

CONCLUSIONS

These findings suggest that ET-1 represents a protective factor against myocardial cell apoptosis in heart failure and that this effect is mediated mainly through endothelin type A receptor-dependent pathways involving multiple downstream signalings in cardiac myocytes.