Plasma endothelin-1 levels in idiopathic dilated cardiomyopathy

Role of Vasoactive Hormone-Induced Signal Transduction in Cardiac Hypertrophy and Heart Failure

Heart failure is the common concluding pathway for a majority of cardiovascular diseases and is associated with cardiac dysfunction. Since heart failure is invariably preceded by adaptive or maladaptive cardiac hypertrophy, several biochemical mechanisms have been proposed to explain the development of cardiac hypertrophy and progression to heart failure. One of these includes the activation of different neuroendocrine systems for elevating the circulating levels of different vasoactive hormones such as catecholamines, angiotensin II, vasopressin, serotonin and endothelins. All these hormones are released in the circulation and stimulate different signal transduction systems by acting on their respective receptors on the cell membrane to promote protein synthesis in cardiomyocytes and induce cardiac hypertrophy. The elevated levels of these vasoactive hormones induce hemodynamic overload, increase ventricular wall tension, increase protein synthesis and the occurrence of cardiac remodeling. In addition, there occurs an increase in proinflammatory cytokines and collagen synthesis for the induction of myocardial fibrosis and the transition of adaptive to maladaptive hypertrophy. The prolonged exposure of the hypertrophied heart to these vasoactive hormones has been reported to result in the oxidation of catecholamines and serotonin via monoamine oxidase as well as the activation of NADPH oxidase via angiotensin II and endothelins to promote oxidative stress. The development of oxidative stress produces subcellular defects, Ca2+-handling abnormalities, mitochondrial Ca2+-overload and cardiac dysfunction by activating different proteases and depressing cardiac gene expression, in addition to destabilizing the extracellular matrix upon activating some metalloproteinases. These observations support the view that elevated levels of various vasoactive hormones, by producing hemodynamic overload and activating their respective receptor-mediated signal transduction mechanisms, induce cardiac hypertrophy. Furthermore, the occurrence of oxidative stress due to the prolonged exposure of the hypertrophied heart to these hormones plays a critical role in the progression of heart failure.

Endogenous ET-1 promotes ANP secretion through activation of COX2-L-PGDS-PPARγ signaling in hypoxic beating rat atria

Endothelin-1 (ET-1) is a potent stimulus for the secretion of atrial natriuretic peptide (ANP) and hypoxia stimulates the release of ET-1, which is involved in the regulation of atrial ANP secretion. However, the precise mechanism of endogenous ET-1 in the regulation of hypoxia-induced ANP secretion is unclear. Therefore, this study aimed to investigate the mechanism of hypoxia-induced endogenous ET-1 regulation of ANP secretion in isolated perfused hypoxic beating rat atria. The results of this study showed that acute hypoxia significantly stimulated ET-1 release and upregulated the expression of its type A as well as type B receptors (ETA and ETB receptors). Endogenous ET-1 induced by hypoxia markedly upregulated the expression of cyclooxygenase 2 (COX2) through activation of its two receptors, leading to an increase in lipocalin-type prostaglandin D synthase (L-PGDS) expression and prostaglandin D2 (PGD2) production. L-PGDS-derived PGD2 activated peroxisome proliferator-activated receptor γ (PPARγ), ultimately promoting hypoxia-induced ANP secretion. Conversely, L-PGDS-derived PGD2 may in turn regulate L-PGDS expression by a nuclear factor erythroid-2-related factor 2 (NRF2)-mediated feedback mechanism. These results indicate that endogenous ET-1 induced by hypoxia promotes hypoxia-induced ANP secretion by activation of COX2-L-PGDS-PPARγ signaling in beating rat atria. In addition, the positive feedback loop between L-PGDS-derived PGD2 and L-PGDS expression induced by hypoxia is part of the mechanism of hypoxia-induced ANP secretion by endogenous ET-1.

Endothelin and the heart in health and diseases

Endothelin-1 (ET-1), a 21-amino acid peptide, was initially identified in 1988 as a potent vasoconstrictor and pressor substance isolated from the culture supernatant of porcine aortic endothelial cells. From human genomic DNA analysis, two other family peptides, ET-2 and ET-3, were found. They showed different effects and distribution, suggesting that each peptide may play separate roles in different organs. In the heart, ET-1 also causes positive inotropic and chronotropic responses and hypertrophic activity of the cardiomyocytes. ETs act via activation of two receptor subtypes, ET_A and ET_B receptors, both of which are coupled to various GTP-binding proteins depending on cell types. Endogenous ET-1 may be involved in progression of various cardiovascular diseases. ET antagonists are currently used clinically in the treatment for patients with pulmonary hypertension, and are considered to have further target diseases as heart failure, cardiac hypertrophy and other cardiac diseases, renal diseases, systemic hypertension, and cerebral vasospasm.

Endothelin-1 critically influences cardiac function via superoxide-MMP9 cascade

We have generated low-expressing and high-expressing endothelin-1 genes (L and H) and have bred mice with four levels of expression: L/L, ∼20%; L/+, ∼65%; +/+ (wild type), 100%; and H/+, ∼350%. The hypomorphic L allele can be spatiotemporally switched to the hypermorphic H allele by Cre-loxP recombination. Young adult L/L and L/+ mice have dilated cardiomyopathy, hypertension, and increased plasma volumes, together with increased ventricular superoxide levels, increased matrix metalloproteinase 9 (Mmp9) expression, and reduced ventricular stiffness. H/+ mice have decreased plasma volumes and significantly heavy stiff hearts. Global or cardiomyocyte-specific switching expression from L to H normalized the abnormalities already present in young adult L/L mice. An epithelial sodium channel antagonist normalized plasma volume and blood pressure, but only partially corrected the cardiomyopathy. A superoxide dismutase mimetic made superoxide levels subnormal, reduced Mmp9 overexpression, and substantially improved cardiac function. Genetic absence of Mmp9 also improved cardiac function, but increased superoxide remained. We conclude that endothelin-1 is critical for maintaining normal contractile function, for controlling superoxide and Mmp9 levels, and for ensuring that the myocardium has sufficient collagen to prevent overstretching. Even a modest (∼35%) decrease in endothelin-1 gene (Edn1) expression is sufficient to cause cardiac dysfunction.

Old and newer biomarkers in heart failure: from pathophysiology to clinical significance

Heart failure is a complex disease in which a careful clinical examination and the measurement of cardiac function may not always be sufficient for making a correct diagnosis. Measuring plasma levels of natriuretic peptides may assist in this process, also offering a good tool for accurate risk stratification. Other alternative biomarkers may give insight into the different pathways of heart failure genesis and pathophysiology, and may help to identify those patients with overt heart failure and a more adverse outcome, or distinguish between those at risk of developing heart failure. Despite a high number of potentially useful biomarkers, only a few will likely be introduced routinely into clinical practice. However, a multi-marker approach might increase the diagnostic accuracy and it might identify different phenotypes of heart failure patients who might benefit from individualized therapy in the future.

Prunellae Spica Extract Contains Antagonists for Human Endothelin Receptors

Endothelin-1 (ET-1) is a powerful vasoconstrictor that contributes to blood pressure elevation. The biological effects of ETs are mediated by two receptors, namely, endothelin type A receptor (ETAR) and endothelin type B receptor (ETBR). Chinese herbal medicines (CHM) with antagonist activity for these two receptors were screened by establishing stable clones of CHO-K1 cells expressing high levels of human ETAR and ETBR, namely CHO-ETAR and CHO-ETBR.The aqueous extract of Prunellae Spica (P1) inhibited the binding of 125I-ET-1 to ETAR and ETBR in CHO-ETAR and CHO-ETBR cells, respectively. P1 suppressed the ET-1-induced mobilization of intracellular Ca2+ . Through the alcohol fractionation of P1, the antagonists of human ETAR and ETBR were found to belong to different, separable ingredients and the antagonist of ETAR is more soluble in alcohol. The two antagonists were also effective in the test on human primary cells, HASMC and HUVEC. P1 successfully prevented the development of ET-1-associated hypertension in rats without further purification. These results indicate the presence of anti-hypertensive ingredients in P. Spica extract, at least through the inactivation of ETAR and/or ETBR.

Pharmacogenetic effect of an endothelin-1 haplotype on response to bucindolol therapy in chronic heart failure

BACKGROUND

Beta-blocker therapy has become a mainstay therapy for the over 5 million patients with chronic heart failure in the United States. Variation in clinical response to beta-blockers is a well-known phenomenon and may be because of genetic differences between patients. We hypothesized that variation in genes of the endothelin system mediate the clinical response to beta-blockers in heart failure.

METHODS

Single nucleotide polymorphisms (SNPs) in six endothelin system genes were genotyped in 309 heart failure patients in a randomized trial of bucindolol versus placebo therapy. We adjusted for multiple comparisons and tested for association between genotype and time to two prospective endpoints.

RESULTS

Nine SNPs were sufficiently common to undergo statistical analysis. The SNPs had no significant effect on prospective outcomes in the placebo group, or on the primary endpoint of time to death in either arm. Two SNPs (IVS-4 G/A and Lys198Asn) in the endothelin-1 gene, however, predicted time to the combined endpoint of heart failure hospitalization or all-cause death in bucindolol-treated patients. The alleles at these SNPs were in tight linkage disequilibrium appearing on either of two complementary haplotypes. A 'dose-response' trend was observed, with participants carrying the rarer haplotype having the highest hazard ratios as compared to the relative 'protective' effect of the common haplotype.

CONCLUSION

A common endothelin-1 gene haplotype may be a pharmacogenetic predictor of a favorable clinical response to beta-blocker therapy in heart failure patients. The existence of a less common 'high-risk' haplotype could identify a subpopulation of heart failure patients destined to respond poorly to beta-blocker therapies.

Direct comparison of selective endothelin A and non-selective endothelin A/B receptor blockade in chronic heart failure

OBJECTIVE

To investigate the potential differential effects of selective endothelin (ET) A and dual ET-A/B receptor blockade in patients with chronic heart failure.

METHODS

Nine patients with chronic heart failure (New York Heart Association class II-III) each received intravenous infusions of BQ-123 alone (selective ET-A blockade) and combined BQ-123 and BQ-788 (dual ET-A/B blockade) in a randomised, placebo controlled, three way crossover study.

RESULTS

Selective ET-A blockade increased cardiac output (maximum mean (SEM) 33 (12)%, p < 0.001) and reduced mean arterial pressure (maximum -13 (4)%, p < 0.001) and systemic vascular resistance (maximum -26 (8)%, p < 0.001), without changing heart rate (p = 0.38). Dual ET-A/B blockade significantly reduced the changes in all these haemodynamic variables compared with selective ET-A blockade (p < 0.05). Selective ET-A blockade reduced pulmonary artery pressure (maximum 25 (7)%, p = 0.01) and pulmonary vascular resistance (maximum 72 (39)%, p < 0.001). However, there was no difference between these effects and those seen with dual ET-A/B blockade. Unlike selective ET-A blockade, dual ET-A/B blockade increased plasma ET-1 concentrations (by 47 (4)% with low dose and 61 (8)% with high dose, both p < 0.05).

CONCLUSIONS

While there appeared to be similar reductions in pulmonary pressures with selective ET-A and dual ET-A/B blockade, selective ET-A blockade caused greater systemic vasodilatation and did not affect ET-1 clearance. In conclusion, there are significant haemodynamic differences between selective ET-A and dual ET-A/B blockade, which may determine responses in individual patients.

Comparison of selective ETAand ETBreceptor antagonists in patients with chronic heart failure

BACKGROUND

The vasoconstrictor action of endothelin-1 (ET-1) is mediated through ET(A) and ET(B) receptor subtypes on vascular smooth muscle. ET(B) receptors are also present on the vascular endothelium where they mediate vasodilation. Animal studies suggest that the ET(B) receptor also acts as a clearance receptor for endothelin.

AIMS

To investigate the effects of a selective ET(A) and a selective ET(B) receptor antagonist alone and in combination on haemodynamics and circulating concentrations of ET-1 in patients with chronic heart failure.

RESULTS

Infusion of BQ-123 (n=10), a selective ET(A) receptor antagonist, led to systemic vasodilation and did not change plasma ET-1 concentrations (1.38+/-0.82 to 1.38+/-0.91 fmol/ml, ns). Infusion of BQ-788 (n=8) led to systemic vasoconstriction with a rise in plasma ET-1 (1.84+/-1.06 to 2.73+/-0.99 fmol/ml, p<0.01). The addition of BQ-123 to BQ-788 led to systemic and pulmonary vasodilation with no further increase in plasma ET-1 concentrations (2.80+/-1.14 to 2.90+/-1.20 fmol/ml, ns).

CONCLUSION

The rise in plasma ET-1 concentrations in response to selective blockade of ET(B) receptors and the associated adverse haemodynamic effects suggest that ET(B) receptors have a role in the clearance of ET-1 in man and that their blockade may not be advantageous for patients with heart failure.

Endothelin receptor antagonists in heart failure: current status and future directions

Experimental evidence suggests that endothelin substantially contributes to left ventricular remodelling and progression of heart failure. Plasma endothelin (ET)-1 levels are increased in patients with heart failure, independent of the aetiology, and correlate with the severity of the disease. Furthermore, tissue endothelin levels and endothelin receptors are upregulated in myocardium from animals and humans with heart failure. In several experimental models of left ventricular remodelling and/or heart failure, treatment with nonselective ET-A and -B as well as selective ET-A antagonists exerted beneficial cardiovascular effects. In patients with heart failure, short-term studies of treatment with endothelin antagonists demonstrated an improvement of haemodynamic parameters; however, long-term treatment with these drugs did not significantly improve combined morbidity/mortality endpoints. Furthermore, in the recently completed Endothelin-A Receptor Antagonist Trial in Heart Failure (EARTH) trial in patients with chronic heart failure, the selective ET-A receptor antagonist darusentan did not significantly affect left ventricular remodelling as assessed by cardiac magnetic resonance imaging. Potential reasons for the lack of beneficial effects of long-term treatment with ET antagonists in patients with heart failure include the following. Firstly, adverse effects on left ventricular healing have been observed when endothelin antagonist therapy was introduced early after myocardial infarction in rats. Secondly, the role of the ET-B receptor in the pathophysiology of heart failure and remodelling processes has not been clearly defined. Finally, for the detection of improvement in left ventricular remodelling, a study needs to be conducted in patients with recent myocardial infarction and signs of heart failure.

CRF2 receptors are highly expressed in the human cardiovascular system and their cognate ligands urocortins 2 and 3 are potent vasodilators

1. Systemic infusions of urocortin 1 produce a decrease in mean arterial pressure. This effect may be mediated by a direct action on novel corticotropin-releasing factor type 2 (CRF(2)) receptors predicted to be expressed in blood vessels and the heart. Our objectives were to determine the presence of CRF(2) receptors in the human cardiovascular system using the selective radioligand [(125)I]antisauvagine 30. We also investigated the potential functional roles of novel CRF(2) ligands in the regulation of vascular tone in human arteries in vitro. 2. Radioligand binding techniques were used to characterise the CRF(2) receptor. [(125)I]antisauvagine 30 bound specifically, saturably, reversibly and with high affinity to CRF(2) receptors in human left ventricle (K(D) 0.21+/-0.03 nm, B(MAX) 0.80+/-0.18 fmol mg(-1) protein), and no change in receptor density or affinity was observed in the dilated cardiomyopathy group. 3. Autoradiographical studies revealed highly localised binding of [(125)I]antisauvagine 30 to intramyocardial blood vessels. Binding sites were also detected in the myocardium and in the medial layer of internal mammary arteries. 4. In endothelium-denuded human internal mammary artery in vitro, all peptides tested produced a potent and sustained vasodilator response reversing endothelin-1-induced constrictions (10 nm) (urocortin 1: pD(2) 8.39+/-0.32, E(MAX) 46+/-7.7%; urocortin 2: pD(2) 8.27+/-0.17, E(MAX) 60+/-8.5%; urocortin 3: pD(2) 8.61+/-0.25, E(MAX) 61+/-7.2%; CRF: pD(2) 8.28+/-0.27, E(MAX): 40+/-10%). 5. We have demonstrated the presence of CRF(2) receptors in the human cardiovascular system and a direct, endothelium-independent vasodilator action of urocortins 2 and 3, which may counter-balance the centrally mediated pressor effects of CRF and urocortin 1.

Endothelin upregulates the expression of vasopressin V2 mRNA in the inner medullary collecting duct of the rat

Recent studies in our laboratory have demonstrated that bosentan, a mixed endothelin ET(A)/ET(B) receptor antagonist, prevented the upregulation of the arginine vasopressin (AVP) V(2) receptor in the inner medullary collecting duct (IMCD) of cardiomyopathic hamsters. These results suggested that endothelin-1 (ET-1) is involved in the upregulation of AVP V(2) receptors. Studies were performed to detect the effect of ET-1 on the expression of AVP V(2) receptors and the ET receptor mediating these effects within the IMCD of the rat. Rat IMCD tissue was isolated and incubated with the following: ET-1, or ET-1 in combination with ET(A) and ET(B) receptor antagonists BQ-123 and BQ-788, respectively, and sarafotoxin c (S6c), an ET(B) receptor-specific agonist. Tissue samples were then analyzed using quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and Western blotting. ET-1 treatment resulted in increased V(2) mRNA from a control level of 186.8 +/- 15.0 amol/microg total RNA to 430.7 +/- 49.0 amol/microg total RNA (P <.003). ET-1/ET(A) treatment resulted in no significant decrease in V(2) mRNA expression 335.0 +/- 38.0 amol/microg total RNA. Whereas ET-1/ET(B), and ET-1/ET(B)/ET(A) treatment resulted in V(2) mRNA approaching control 256.0 +/- 15.0 amol/microg total RNA, and 215.6 +/- 42.3 amol/microg total RNA. However, ET-3 treatment produced no significant changes in V(2) receptor mRNA expression. Sarafotoxin treatment corroborated both the ET-1 and ET receptor antagonist data, demonstrating striking significant increases in V(2) receptor mRNA and protein expression. S6c treatment increased V(2) mRNA expression from a control level of 199 +/- 17.3 amol/microg total RNA to 284.3 +/- 42.1 amol/microg total RNA (P < 05). Western blotting revealed that changes in V(2) mRNA expression in the various treatment conditions were similar to changes in protein expression. Overall, these data indicate that in the IMCD ET-1 increases AVP V(2) receptor expression and these changes are mediated by the ET(B) receptor.

Elevation of plasmatic endothelin in patients with heart failure

BACKGROUND

Endothelin 1 is an autocrine and paracrine factor with vasoconstrictive, mitogenic, and inotropic activities in vascular and cardiac muscles. Its elevation has been reported in patients with chronic heart failure and its production may be conditioned by activation of other neurohumoral factors that are stimulated by the disease.

METHODS

The objective of this study was to correlate level of endothelin (ET) with echocardiographic, clinical, and biochemical markers and to determine its role as an independent marker of severity. We included patients with congestive heart failure in whom echocardiographic evaluation had been done and serum markers measured. Serum endothelin 1 levels were determined by radioimmunoassay (RIA). Correlation between endothelin concentration, echocardiographic parameters, potentially confounding factors, and severity of heart failure was made.

RESULTS

Patients with symptomatic heart failure and longer time of evolution had higher levels of endothelin unrelated to levels of troponin T, tumor necrosis factor, and atrial natriuretic peptide. There were no differences in levels of endothelin, independently of the etiology of cardiac failure.

CONCLUSIONS

These results support the idea that endothelin plays an important independent role in the physiopathology of heart failure. It may be a severity marker and an attractive therapeutic target.

Plasma endothelin-1 levels and clinical correlates in patients with chronic heart failure

BACKGROUND

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide, and patients with chronic heart failure (CHF) are reported to have high plasma ET-1 levels. The aim of this study was to investigate the relation between plasma ET-1 levels and clinical correlates in patients with CHF. The effects of maximal exercise on plasma ET-1 levels were also investigated.

METHODS

Plasma concentrations of ET-1, norepinephrine, and atrial and brain natriuretic peptide (ANP and BNP) both at rest and after maximal cardiopulmonary exercise test were determined in 100 patients with CHF (60 +/- 12 years, New York Heart Association [NYHA] class I-III, left ventricular ejection fraction [LVEF]=36 +/- 8%, peak oxygen uptake [VO2] = 18.2 +/- 5.0 mL/min/kg) and 27 controls.

RESULTS

Patients with NYHA class II and III CHF had higher ET-1 levels (controls, NYHA class I, II, III: 2.1 +/- 0.6, 2.1 +/- 1.0, 2.6 +/- 0.9, 3.4 +/- 0.8 pg/mL, analysis of variance P <.0001). Maximal exercise did not alter ET-1 levels in controls or in each CHF subgroup. When all CHF patients were analyzed together, cardiothoracic ratio (P<.01), peak VO2 (P<.001), plasma norepinephrine (P<.01), plasma ANP (P<.01), and plasma BNP (P<.001) were significantly related with resting ET-1 levels on univariate analysis. Multivariate analysis revealed peak VO2 and plasma BNP levels showed an independent and significant relationship with the resting plasma ET-1 levels.

CONCLUSIONS

Resting ET-1 levels were increased in symptomatic patients with CHF, and maximal exercise did not increase ET-1 levels. Peak VO2 and plasma BNP levels were independently associated with resting plasma ET-1 levels in patients with CHF.

Aerobic exercise training reduces plasma endothelin-1 concentration in older women

Endothelial function deteriorates with aging. On the other hand, exercise training improves the function of vascular endothelial cells. Endothelin-1 (ET-1), which is produced by vascular endothelial cells, has potent constrictor and proliferative activity in vascular smooth muscle cells and, therefore, has been implicated in regulation of vascular tonus and progression of atherosclerosis. We previously reported significantly higher plasma ET-1 concentration in middle-aged than in young humans, and recently we showed that plasma ET-1 concentration was significantly decreased by aerobic exercise training in healthy young humans. We hypothesized that plasma ET-1 concentration increases with age, even in healthy adults, and that lifestyle modification (i.e., exercise) can reduce plasma ET-1 concentration in previously sedentary older adults. We measured plasma ET-1 concentration in healthy young women (21-28 yr old), healthy middle-aged women (31-47 yr old), and healthy older women (61-69 yr old). The plasma level of ET-1 significantly increased with aging (1.02 +/- 0.08, 1.33 +/- 0.11, and 2.90 +/- 0.20 pg/ml in young, middle-aged, and older women, respectively). Thus plasma ET-1 concentration was markedly higher in healthy older women than in healthy young or middle-aged women (by approximately 3- and 2-fold, respectively). In healthy older women, we also measured plasma ET-1 concentration after 3 mo of aerobic exercise (cycling on a leg ergometer at 80% of ventilatory threshold for 30 min, 5 days/wk). Regular exercise significantly decreased plasma ET-1 concentration in the healthy older women (2.22 +/- 0.16 pg/ml, P < 0.01) and also significantly reduced their blood pressure. The present study suggests that regular aerobic-endurance exercise reduces plasma ET-1 concentration in older humans, and this reduction in plasma ET-1 concentration may have beneficial effects on the cardiovascular system (i.e., prevention of progression of hypertension and/or atherosclerosis by endogenous ET-1).

Endothelin-1 Concentrations in Pericardial Fluid Are More Elevated in Patients with Ischemic Heart Disease Than in Patients With Nonischemic Heart Disease

There is epidemiologic evidence that the prognosis of patients with nonischemic heart failure is better than that for patients with ischemic heart failure. In addition, studies have revealed that patients with ischemic heart failure show a poorer response to medical therapy. However, the pathophysiologic difference between ischemic and nonischemic heart disease is unclear. To clarify this point, we measured atrial natriuretic peptide, brain natriuretic peptide, angiotensin II, endothelin (ET)-1. interleukin-1beta interleukin-6. tumor necrosis factor (TNF)-alpha soluble TNF receptor I, and soluble TNF receptor II concentrations in plasma and pericardial fluid in patients with ischemic or nonischemic heart disease undergoing cardiac surgery. The pericardial ET-1 concentration in patients with ischemic heart disease was statistically greater than that in patients with nonischemic heart disease (about 1.5-fold), although no difference was found in the plasma ET-1 concentration. These findings suggest that the production and secretion of ET-1 from the myocardium in patients with ischemic heart disease are augmented to a greater extent than in patients with nonischemic heart disease. This result may lead to a greater understanding of the pathophysiology of ischemic heart disease.

Urocortin has cell-proliferative effects on cardiac non-myocytes

Urocortin (Ucn) is a member of the corticotropin-releasing hormone (CRH)-related peptides that has been reported to have cardiac inotropic and hypertrophic effects. In addition, Ucn mRNA was expressed in cardiac myocytes (MCs) and Ucn was suggested to have cardioprotective effects. Recently, it was reported that Ucn mRNA was expressed in cardiac non-myocytes (NMCs). Based on these facts, Ucn is assumed to affect not only MCs but also NMCs in an autocrine fashion. The present study was designed to elucidate a pathophysiological role of Ucn on NMCs. NMCs were prepared by the discontinuous Percoll gradient and adhesion method. Ucn increased [(3)H]-thymidine uptake into NMCs. Ucn also enhanced endothelin-1-induced increase of [(3)H]-thymidine uptake into NMCs. Effects of Ucn on [(3)H]-thymidine uptake into NMCs were significantly abolished by the protein kinase A inhibitor, H89 (10(-5) M), but not by a competitive antagonist of CRH receptors, astressin (10(-5) M). Ucn also increased intracellular cAMP accumulation more potently than CRH on a molar basis. Finally, both MCs and NMCs also secreted Ucn. Together with the recent findings, at least in NMCs, these data suggest that Ucn could exert its own actions via the cAMP signaling pathway, but not through known CRH type 2 receptors, in an autocrine fashion. In conclusion, the present study indicated that Ucn was secreted not only from MCs but also from NMCs and that the primary source of Ucn acting on heart was the heart itself. On the other hand, Ucn could proliferate NMCs as well as MCs, suggesting that Ucn could be involved in cardiac hypertrophy and fibrosis, i.e., cardiac remodeling, in spite of its putative cardioprotective actions.

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.

Treatment of heart failure in patients with diabetes mellitus

Patients with diabetes mellitus have an increased morbidity and mortality from cardiovascular disease. Both coronary artery disease and congestive heart failure (CHF) are largely responsible for the increased cardiovascular adverse events in patients with diabetes. This review discusses the pathophysiology of CHF, the mechanisms of left ventricular (LV) dysfunction and the neurohormonal mechanisms involved in both LV dysfunction and CHF. Diabetes with and without hypertension is an important cause of LV dysfunction and CHF. Diabetes may be responsible for the metabolic and ultrastructural causes of LV dysfunction, while hypertension may be responsible for the marked fibrotic changes that are found. Experimental induction of diabetes in animals has shed light on the biochemical and ultrastructural changes seen. The role of insulin to reverse both metabolic and structural changes is reviewed both from experimental data and with the limited amount of clinical data available. The therapy of CHF in patients with diabetes is similar to that of patients without diabetes, with therapy directed toward the use of beta-blockers and angiotensin converting enzyme (ACE) inhibitors. As the morbidity and mortality are higher in patients with diabetes, several studies have pointed out the importance of this subgroup where the opportunity to make a significant clinical impact exists. A significant opportunity exists to reduce morbidity and mortality with beta-blockers and ACE inhibitors when ischaemia and CHF are both present. However, studies in patients diabetes have been limited to post hoc subgroup analyses and rarely as predefined subgroups. Clinical trials involving patients with diabetes with and without hypertension and LV dysfunction are clearly needed in the future to adequately address the needs of this high risk subgroup.

Endothelin-1 stimulates cardiomyocyte injury during mitochondrial dysfunction in culture

To understand the pathophysiological role of endothelin-1 in the failing heart, we constructed a cellular mitochondrial impairment model and demonstrated the effect of endothelin-1. Primary cultured cardiomyocytes from neonatal rats were pretreated with rotenone, a mitochondrial complex I inhibitor, and the cytotoxic effect of endothelin-1 on the cardiomyocytes was demonstrated. Rotenone gradually decreased the pH of the culture medium with incubation time and caused slight cell injury. Endothelin-1 markedly enhanced the effect of rotenone that decreased the pH of the medium and enhanced cellular injury. The enhancement of the decrease in pH and cell injury induced by endothelin-1 was counteracted by the endothelin ET(A) receptor antagonist BQ123 or by maintaining the pH of the medium by the addition of 50 mM HEPES. Endothelin-1 markedly increased the uptake of 2-deoxyglucose and lactic acid production when the cardiomyocytes were pretreated with rotenone. These findings suggest that the stimulation of glucose uptake and anaerobic glycolysis followed by the increase in lactic acid accumulation in cardiomyocytes under the condition of mitochondrial impairment may be involved, at least in part, in the cellular injury by endothelin-1. Moreover, these findings suggest the possibility that the effect of endothelin-1 on myocardium is reversed by the condition of the mitochondria, and endogenous endothelin-1 may deteriorate cardiac failure with mitochondrial dysfunction. This may contribute to clarify the beneficial effect of endothelin receptor blockade in improving heart failures.

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.

beta-Adrenergic and endothelin receptor interaction in dilated human cardiomyopathic myocardium

BACKGROUND

Although end-stage dilated cardiomyopathy (DCM) is characterized by defects in beta-adrenergic receptor (beta-AR) activity and increased endothelin-1 (ET-1), possible interactions between these 2 systems remain to be defined. Accordingly, the goal of this study was to determine the effects of ET receptor activation on beta-AR signaling through measurement of cyclic adenosine monophosphate (cAMP) in normal and DCM myocardium.

METHODS AND RESULTS

Myocardial sarcolemmal preparations were prepared from normal human (n = 6), dilated cardiomyopathic (n = 10), and ischemic cardiomyopathic (ICM, n = 10) tissue. Basal cAMP production was measured in the presence of ET-1 alone (10(-6) to 0(-9) mol/L) as well as after (-)isoproterenol (10(-6) to 10(-2) mol/L) or forskolin (0.05 to 30.0 micromol/L) stimulation. beta-AR and ET receptor profiles were determined by radiolabeled ligand assays. ET-1 inhibited basal cAMP production in all preparations in a concentration-dependent manner. However, beta-AR-stimulated cAMP production by either isoproterenol or forskolin was not significantly affected by ET-1. beta-AR receptor density was reduced, and a selective reduction of the ET(B) receptor occurred in both forms of DCM.

CONCLUSIONS

Under basal conditions, ET receptor stimulation reduced cAMP levels, which may influence contractility, particularly with DCM.

Pathophysiology of chronic heart failure

Heart failure is a changing paradigm. The hemodynamic model, which served our needs well from the 1950s through the early 1980s, has now been largely abandoned, except for the management of decompensated patients in the hospital. The pathophysiology is exceedingly complex and involves structural changes, such as loss of myofilaments, apoptosis and disorganization of the cytoskeleton, as well as disturbances in Ca(2+) homeostasis, alteration in receptor density, signal transduction, and collagen synthesis. A more contemporary working hypothesis is that heart failure is a progressive disorder of left ventricular remodeling, usually resulting from an index event, that culminates in a clinical syndrome characterized by impaired cardiac function and circulatory congestion. This change in the framework of our understanding of the pathophysiology of heart failure is predicated on the results of numerous clinical trials conducted during the past 20 years. New therapies are now evolving that are designed to inhibit neuroendocrine and cytokine activation, whereas drugs specifically designed to heighten cardiac contractility and "unload" the left ventricle have proven to be unhelpful in long-term management of patients with chronic heart failure. However, the hemodynamic model is still relevant for patients in the hospital with decompensated heart failure, where positive inotropic drugs and vasodilators are still widely used. The modern treatment of chronic heart failure is now largely based on the neurohormonal hypothesis, which states that neuroendocrine activation is important in the progression of heart failure and that inhibition of neurohormones is likely to have long-term benefit with regard to morbidity and mortality. Thus, the evolution of treatment for chronic heart failure as a result of clinical trials has provided much enlightenment for our understanding of the fundamental biology of the disorder, a reversal of the usual flow of information from basic science to clinical investigation.

A novel pharmacological action of ET-1 to prevent the cytotoxicity of doxorubicin in cardiomyocytes

We previously reported that cardiomyocytes produce endothelin (ET)-1 and that the tissue level of ET-1 markedly increased in failing hearts in rats with chronic heart failure. Because the level of plasma ET-1 also increased progressively in patients with breast cancer who received doxorubicin (Dox; Adriamycin), which possesses cardiotoxicity, we hypothesized that ET-1 plays a role in the pathophysiology of cardiomyocytes injured by Dox. In this study, we investigated the effect of ET-1 on the cytotoxicity of Dox in primary cultured neonatal rat cardiomyocytes. The results showed that ET-1 effectively attenuated Dox-induced acute cardiomyocyte cytotoxicity (24-h incubation with Dox) evaluated by in vitro cell toxicity assay [3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay and lactate dehydrogenase release]. The cytoprotective effect of ET-1 was mediated via ET(A) receptors, because pretreatment with the ET(A)-receptor antagonist BQ123 completely suppressed the cytoprotective effect of ET-1, whereas the ET(B)-receptor antagonist BQ788 did not. The cytoprotective effect of ET-1 was abolished by pretreatment with cycloheximide or staurosporine. These results suggest that a protein molecule(s), which is synthesized de novo by the stimulation of protein kinase pathway, is involved in the cytoprotective effect of ET-1. ET-1 increased the expression of an endogenous antioxidant, manganese superoxide dismutase (Mn-SOD), in the cardiomyocytes, as demonstrated by a Western blotting analysis. Pretreatment with an antisense oligodeoxyribonucleotide of Mn-SOD markedly attenuated the cytoprotective effect of ET-1 on the Dox-induced cytotoxicity. However, under conditions of prolonged incubation with Dox (48 h), ET-1 did not affect Dox-induced cardiomyocyte cytotoxicity in culture. These results suggest that ET-1 prevents the early phase of Dox-induced cytotoxicity via the upregulation of the antioxidant Mn-SOD through ET(A) receptors in cultured cardiomyocytes.

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.

Effects of imidapril on endothelin-1 and ACE gene expression in failing hearts of salt-sensitive hypertensive rats

The renin-angiotensin system and endothelin are important regulators of the cardiovascular system. Although increased production of endothelin-1 (ET-1) is reported in patients with heart failure, the detailed mechanism remains to be determined. To elucidate the relationship between the renin-angiotensin system and ET-1 in hypertensive heart failure, we evaluated the effects of long-term treatment with imidapril, an angiotensin converting enzyme (ACE) inhibitor, on preproET-1, endothelin A receptor (ETAR), and ACE mRNA expression in the left ventricle and evaluated these in relation to myocardial remodeling in the failing heart of Dahl salt-sensitive (DS) hypertensive rats fed a high salt diet. In DS rats fed an 8% NaCl diet after the age of 6 weeks, a stage of concentric left ventricular hypertrophy at 11 weeks (DSLVH) was followed by a distinct stage of left ventricular failure with chamber dilatation at 18 weeks (DSHF). Imidapril (DSHF-IM, n = 8, 1 mg/kg/day, subdepressor dose) or vehicle (DSHF-V, n = 8) was given from stage DSLVH to DSHF for 7 weeks, and age-matched (18 weeks) Dahl salt-resistant rats fed the same diet served as the control group (DR-C, n = 8). In both groups, blood pressure was similar and significantly higher than in DR-C. Markedly increased left ventricular end-diastolic diameter and reduced fractional shortening in DSHF-V was significantly ameliorated in DSHF-IM using transthoracic echocardiography. The preproET-1, ETAR, and ACE mRNA levels in the left ventricle were significantly increased in DSHF-V compared with DR-C, and significantly suppressed in DSHF-IM compared with DSHF-V. DSHF-V demonstrated a significant increase in the wall-to-lumen ratio and perivascular fibrosis in coronary arterioles, and myocardial fibrosis, with all these parameters being significantly improved by imidapril. In conclusion, myocardial remodeling and heart failure in DS rats fed a high salt diet were significantly ameliorated by a subdepressor dose of imidapril, which may be attributable to a decrease in ET-1 mRNA expression and angiotensin II in the left ventricle.

Effects of long-term treatment with nonselective endothelin receptor antagonist, TAK-044, on remodeling of cardiovascular system with sustained volume overload

To assess the role of endothelin-1 (ET-1) on cardiovascular remodeling, nonselective endothelin-receptor antagonist TAK-044 was administered for the long term to rabbits with or without arteriovenous (A-V) shunt formation. Six weeks after sham operation (n = 12) or carotid-jugular shunt formation (n = 21), TAK-044 (30 mg/day) or saline was infused subcutaneously using osmotic mini pumps for another 6 weeks. Twelve weeks after operation, left ventricular (LV) diameter was enlarged with the presence of an A-V shunt; however, the levels of LV diameter and arterial pressure or the postmortem weight of LVs of shunt rabbits were similar between saline and TAK-044 groups. A linear relation of the luminal diameter and the medial cross-sectional area of the left and right carotid arteries was similar between shunt + saline and shunt + TAK-044 groups. In saline groups, myocardial ET-1 levels were higher in shunt than in sham rabbits (217+/-22 vs. 136+/-19 pg/g tissue; p < 0.01 between rabbit groups) without changes in plasma ET-1 concentrations during saline infusion for 6 weeks. Differences in plasma ET-1 levels before and 6 weeks after the administration of TAK-044 were 0.32+/-0.78 and 0.16+/-0.28 pg/ml (NS between periods) in shunt and sham groups, respectively. In TAK-044 groups, myocardial ET-I levels 12 weeks after operation were similarly lower in both sham (105+/-7.4 pg/g tissue) and shunt rabbits (126+/-9.2 pg/g tissue) than in those with saline administration; however, the plasma ET-1 concentrations were increased significantly 6 weeks after TAK-044 administration by 5.0+/-0.6-fold and 3.5 +/-0.3-fold (p < 0.01) of the levels 6 weeks after operation in shunt and sham groups (NS between groups), respectively. Accordingly, myocardial but not plasma ET-1 levels were increased by a long-term burden of volume overload and were attenuated by a long-term administration of TAK-044 without altering drastically the hemodynamics or vascular remodeling. These results suggest that endogenous ET-1 does not play a major role in the compensatory stage of cardiovascular remodeling in the present volume-overload model.

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.

Inhibition by calcium antagonism of circulating and renal endothelin in experimental congestive heart failure

Endothelin (ET) is a potent vasoconstrictor and sodium-regulating peptide whose tissue and plasma concentrations are increased in congestive heart failure (CHF). ET may mediate its vasoconstrictor and sodium-regulatory actions secondary to an increase in intracellular calcium. Calcium influx may augment ET synthesis. Although felodipine, a dihydropyridine calcium-channel antagonist, is effective in reducing vascular resistance in generalized vasoconstriction, its actions in CHF on circulating and local tissue ET remain undefined. The current studies were designed to determine the modulating actions of felodipine (oral, 40 mg/day for 7 days; n = 6) in an experimental canine model of CHF produced by chronic thoracic inferior vena caval constriction (TIVCC) compared with normal (n = 7) and TIVCC-alone (n = 7) dogs. We hypothesized that felodipine would decrease circulating and renal ET. Plasma ET was significantly increased in TIVCC compared with normal dogs (26 +/- 0. 5 vs. 12 +/- 0.7 pg/ml, P < 0.05) and was markedly decreased by felodipine compared with TIVCC alone (14 +/- 3 vs. 26 +/- 0.5 pg/ml, P < 0.05). Renal ET immunohistochemical staining demonstrated the presence of ET in normal kidney, which was markedly increased in renal cortex and medulla in TIVCC dogs. Renal cortical and medullary ET staining densities were markedly decreased with felodipine compared with those with TIVCC alone. In the TIVCC + felodipine group, cardiovascular hemodynamics also was markedly improved compared with the TIVCC-alone group [systemic vascular resistance: 27 +/- 2 vs. 44 +/- 3 resistance units (RU), P < 0.05; pulmonary vascular resistance: 3.3 +/- 0.1 vs. 5.7 +/- 0.4 RU, P < 0.05; cardiac output: 2.9 +/- 0.2 vs. 1.7 +/- 0.1 l/min, P < 0.05]. This study demonstrates important modulating inhibitory actions of felodipine on renal and plasma ET in an experimental model of CHF.

Endothelin-1 activates p38 mitogen-activated protein kinase via endothelin-A receptor in rat myocardial cells

In myocardial cells (MCs), endothelin-1 (ET-1) exerts various effects such as hypertrophy, and causes cellular injury. Long-term treatment with an endothelin-A (ET(A)) receptor antagonist improves the survival of rats with heart failure, suggesting that myocardial endothelin system contributes to the progression of heart failure. p38 mitogen-activated kinase (MAPK) is a member of the MAPK family and activated by several forms of environmental stresses. We show here the effect of ET-1 on p38 MAPK activation and the role of ET-1-activated p38 MAPK on morphological changes in MCs. ET-1-stimulated p38 MAPK phosphorylation was detectable within 2 min and maximal at 5 min and was concentration dependent. The maximum effect was obtained at 10 nM. An ET(A) receptor antagonist, BQ-123, but not an endothelin-B receptor antagonist, BQ-788, inhibited these reactions. A p38 MAPK inhibitor, SB203580, failed to inhibit the morphological changes associated with ET-1-induced myocardial cell hypertrophy. These results indicate that p38 MAPK is activated by ET-1 but does not contribute to the development of ET-1-induced myocardial cell hypertrophy.

Role of endothelin in deterioration of heart failure due to cardiomyopathy in hamsters: increase in endothelin-1 production in the heart and beneficial effect of endothelin-A receptor antagonist on survival and cardiac function

BACKGROUND

We previously reported that chronic endothelin (ET) receptor blockade ameliorated the survival rate and cardiac hemodynamics in rats with chronic heart failure (CHF) due to myocardial infarction. However, it remains unclear whether ET-1 is involved in the pathophysiology of cardiomyopathy, which is one of the major causes of CHF. Accordingly, we investigated the production of ET-1 in the heart and the effect of chronic ETA receptor blockade on survival rate and cardiac function in the Bio 14.6 hamster, which is an idiopathic model of CHF caused by cardiomyopathy.

METHODS AND RESULTS

We used 52-week-old Bio 14.6 cardiomyopathic hamsters and age-matched F1b normal hamsters. The expression of preproET-1 mRNA and the ET-1 level in the hearts were markedly higher in the cardiomyopathic hamsters than in the normal hamsters. The cardiomyopathic hamsters showed severe CHF, illustrated by lower left ventricular (LV) +dP/dt/Pmax and right ventricular (RV) +dP/dt/Pmax and by higher LV end-diastolic pressure (EDP), RVEDP, and central venous pressure compared with the normal hamsters. Long-term (9 weeks) treatment with an ETA antagonist (TA-0201, 1.3 mg. kg-1. d-1) markedly increased survival of cardiomyopathic hamsters (untreated, 16%; TA-0201-treated, 65.2%; P<0.001). After 6 weeks of treatment, LV +dP/dt/Pmax and RV +dP/dt/Pmax were significantly higher and LVEDP and RVEDP were lower in the TA-0201-treated group than in the untreated group, suggesting that chronic TA-0201 treatment effectively prevented deterioration of cardiac dysfunction.

CONCLUSIONS

In the cardiomyopathic hamsters with CHF, the production of ET-1 in the heart was markedly increased, and chronic ETA receptor blockade greatly ameliorated survival and cardiac dysfunction. These results suggest that ET-1 plays an important role in the deterioration of CHF caused by cardiomyopathy, and ETA antagonists may exert therapeutic effects in CHF due to cardiomyopathy.

Pathophysiology of endothelin in the cardiovascular system

In this article, we review the basic pharmacological and biochemical features of endothelin and the pathophysiological roles of endothelin in cardiovascular diseases. Development of receptor antagonists has accelerated the pace of investigations into the pathophysiological roles of endogenous endothelin-1 in various diseases, e.g. chronic heart failure, renal diseases, hypertension, cerebral vasospasm, and pulmonary hypertension. In chronic heart failure, the expression of endothelin-1 and its receptors in cardiomyocytes is increased, and treatment with an endothelin receptor antagonist improves survival and cardiac function. Endothelin receptor antagonists also improve other cardiovascular diseases. These results suggest that the interference with endothelin pathway either by receptor blockade or by inhibition of endothelin converting enzyme may provide novel therapeutic drugs strategies for multiple disease states.

Differential roles of endothelin-1 in the development of secondary pulmonary hypertension in patients with left heart failure with or without acute exacerbation

BACKGROUND

The aim of this study was to investigate the contribution of endothelin-1 (ET-1) to the development of secondary pulmonary hypertension (PH) in patients with left heart failure (HF).

METHODS AND RESULTS

The subjects were 40 patients with left HF with (group 1; n = 20) and without (group 2; n = 20) acute exacerbation. Before treatment, the ET-1 level in the pulmonary capillary wedge region was three times greater in patients of group 2 than group 1, although there was no significant difference in mean pulmonary artery pressure (mPAP) or pulmonary vascular resistance index (PVRI) between the two groups. Also, the ET-1 level significantly correlated with mPAP and PVRI for both groups, but with different slopes of the regression lines. After treatment of group 1, the extent of reduction in the ET-1 level significantly correlated with that in mPAP and in PVRI, whereas the ET-1 level itself correlated with mPAP, with the regression lines approximating those of group 2.

CONCLUSIONS

Our findings suggest that ET-1 may have differential roles in the development of secondary PH in patients with left HF with or without acute exacerbation.

Endogenous plasma endothelin concentrations and coronary circulation in patients with mild dilated cardiomyopathy

OBJECTIVE

To determine whether increased plasma concentrations of endothelin-1 (ET-1) and big endothelin (BET) play a role in the regulation of coronary circulation in patients with idiopathic dilated cardiomyopathy (IDCM).

SETTING

Tertiary referral centre for cardiac diseases.

PATIENTS

Fourteen patients (eight male/six female; mean (SD) age 59 (9) years) with IDCM (ejection fraction 36 (9)%) and five normotensive subjects (two male/three female; age 52 (7) years) serving as controls were studied.

METHODS

Functional status was classified according to New York Heart Association (NYHA) class. Endogenous ET-1 and BET plasma concentrations from the aorta and the coronary sinus were determined by radioimmunoassay. Coronary blood flow, using the inert chromatographic argon method, myocardial oxygen consumption, and coronary sinus oxygen content under basal conditions were determined.

RESULTS

In the aorta, mean (SD) concentrations of ET-1 (IDCM 0.76 (0.25) v controls 0.31 (0.06) fmol/ml; p = 0.002) and BET (IDCM 3.58 (1.06) v controls 2.11 (0.58) fmol/ml; p = 0.014) were increased in patients with IDCM. Aortic ET-1 concentrations correlated positively with NYHA class (r = 0. 731; p < 0.001), myocardial oxygen consumption (r = 0.749; p < 0. 001), and coronary blood flow (r = 0.645; p = 0.003), but inversely with coronary sinus oxygen content (r = -0.633; p = 0.004), which was significantly decreased in IDCM patients (IDCM 4.68 (1.05) v controls 6.70 (1.06) vol%; p = 0.003).

CONCLUSIONS

The coronary circulation in patients with IDCM is exposed to an increased endothelin load. ET-1 concentrations correlate with functional deterioration. A decrease of the coronary sinus content of oxygen suggests a mismatch between coronary blood flow and metabolic demand. Thus, ET-1 might be a marker of a disequilibrium between myocardial oxygen demand and coronary blood flow in IDCM.

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 and von Willebrand factor as parameters of endothelial function in idiopathic dilated cardiomyopathy: different stimuli for release before and after heart transplantation?

BACKGROUND

Congestive heart failure (CHF) and heart transplantation (HTX) are characterized by endothelial dysfunction as indicated by elevation of markers of endothelial function, including endothelin and von Willebrand factor (vWF). However, previous studies included both patients with idiopathic dilated cardiomyopathy and ischemic heart disease; the latter condition shows endothelial dysfunction, per se. The 2 endothelial factors have different origin and may provide different information about endothelial dysfunction in CHF and after HTX caused by idiopathic dilated cardiomyopathy.

METHODS

We investigated plasma endothelin and vWF, the relation between these 2 factors, and determinants of endothelin and vWF plasma levels in 32 healthy controls, 25 patients with CHF, and 22 patients who had HTX; both conditions were caused by idiopathic dilated cardiomyopathy.

RESULTS

Plasma endothelin was elevated in CHF (6.8 +/- 3.4 pg/mL) and after HTX (6.1 +/- 2.1) compared with healthy controls (4.0 +/- 1.0, P <.0001 for both). VWF was also elevated in CHF (1.6 +/- 0.6 U/mL) and after HTX (2.6 +/- 1.0) compared with healthy controls (1.0 +/- 0.5, P <.0001 for both). VWF was increased after HTX compared with CHF (P <.001), in contrast to similar endothelin levels in CHF and after HTX. Plasma endothelin and vWF correlated in both CHF (r = 0.65, P <.001) and HTX (r = 0.66, P <. 001) but not in controls. In CHF, New York Heart Association functional class was an independent determinant of vWF (P <.0001) and furosemide dose of endothelin (P <.0001). In cardiac transplant recipients, plasma albumin was an independent determinant of vWF (P <.01), and plasma sodium and furosemide dose were independent determinants of endothelin (P <.01).

CONCLUSIONS

Plasma endothelin and vWF were directly correlated in both CHF and after HTX caused by idiopathic dilated cardiomyopathy. However, the production of the 2 factors appeared to be stimulated by different mechanisms and provided different information about endothelial function, as indicated by the different determinants and different response to heart transplantation.

Dilated cardiomyopathy: changing pathophysiological concepts and mechanisms of dysfunction

Experimental observations made over the past two decades have led to a profound shift in the conceptual paradigms about the syndrome of heart failure and dilated cardiomyopathy. As a consequence, heart failure is currently considered a complex disease and is not merely characterized by hemodynamic disturbances. It is now believed that the syndrome is governed and impelled by neurohormonal imbalances and intracardiac paracrine processes. The latter processes are mediated by activated cardiac endothelial cells and cytokines, creating a state of cardiac maladaption and leading to disease progression. Therapeutic interventions such as operative left ventricular volume reduction or mitral valve reconstruction should therefore no longer be solely interpreted in terms of hemodynamics (i.e., symptomatic improvements). Effects on neurohormonal, endothelial, and cytokine activities should be taken equally into account.

Changes of neurohumoral parameters and endothelin-1 in response to exercise in patients with mild to moderate congestive heart failure

Plasma endothelin levels are increased in patients with moderate and severe CHF. Conflicting data exist about the endothelin-1 (ET) level in patients with mild to moderate CHF and the effect of maximal exercise on plasma ET levels.

METHODS AND RESULTS

We determined the plasma levels of ET and various neurohumoral parameters in 93 patients with CHF in functional class II and III of the NYHA classification at rest and after maximal bicycle exercise. Baseline ET level was increased compared to an age-matched healthy volunteer group (6.95+/-0.31 vs 3.29+/-0.17 pg/ml, mean+/-S.E.M., P<0.05), without significant differences between NYHA class II and III patients. Maximal exercise did not increase the ET level. In contrast, the neurohumoral parameters were significantly increased with maximal exercise. In conclusion, plasma levels of ET are increased in patients with mild to moderate CHF. However, no further increase in response to exercise was observed. Thus, it is highly unlikely that exercise capacity may be limited by ET-mediated peripheral vasoconstriction.

Neurohumoral activation and progression of heart failure: hypothetical and clinical considerations

The model for heart failure has changed radically over the past 20 years. No longer a simple hemodynamic paradigm of pump dysfunction, heart failure is now characterized as a complex clinical syndrome with release of many neurohormones and cytokines, which are believed to be most responsible for progression of disease. This change in our understanding of the pathophysiology of heart failure has important therapeutic implications. Drugs designed to influence the myocardial contractile state have been found over the past few decades to have either a neutral or an adverse effect on long-term survival, whereas agents designed to block the renin-angiotensin-aldosterone and other neurohormonal systems have proved to be remarkably effective treatment. Recently, drugs designed to block excessive sympathetic nervous system activity have been demonstrated in well-controlled studies to be safe and effective forms of therapy for heart failure. Carvedilol, a nonselective beta-adrenergic blocker with alpha1-blocking and antioxidant properties, is associated with prevention of progression of heart failure as manifested by improvement in left ventricular (LV) function, reduction in heart size, and improved survival in patients with New York Heart Association functional Class II and III symptoms. This improvement is observed equally in patients with ischemic and non-ischemic heart failure. It is tempting to speculate that beta-adrenergic blockers prevent the progression of heart failure by reducing LV mass and LV chamber size. In essence, carvedilol, and perhaps other beta-adrenergic blockers, appear to abrogate relentless LV remodeling which is typically associated with progression of heart failure. The combination of angiotensin-converting enzyme inhibitors and beta-adrenergic blockers may be particularly effective in this regard, although more data on beta-adrenergic blockers in patients with advanced heart failure are needed. Data from experimental heart failure animal models also suggest that endothelin (ET) subtype A (ET(A)) receptor blockers have the potential to lessen the pace of progressive LV remodeling. As our understanding of the neuroendocrine response to diminished cardiac performance improves, novel and even more imaginative neurohormonal and cytokine antagonists are likely to emerge as important new treatments for both hypertension and heart failure.

Endothelin as a regulator of cardiovascular function in health and disease

The endothelins are a family of endothelium-derived peptides that possess characteristically sustained vasoconstrictor properties. Endothelin-1 appears to be the predominant member of the family generated by vascular endothelial cells. In addition to its direct vascular effects, endothelin-1 has inotropic and mitogenic properties, influences homeostasis of salt and water, alters central and peripheral sympathetic activity and stimulates the renin-angiotensin-aldosterone system. Studies with endothelin receptor antagonists have indicated that endothelin-1 probably has complex opposing vascular effects mediated through vascular smooth muscle and endothelial ET(A) and ET(B)receptors. Endogenous generation of endothelin-1 appears to contribute to maintenance of basal vascular tone and blood pressure through activation of vascular smooth muscle ET(A)receptors. At the same time, endogenous endothelin-1 acts through endothelial ET(B) receptors to stimulate formation of nitric oxide tonically and to oppose vasoconstriction. In view of the multiple cardiovascular actions of endothelin-1, there has been much interest in its contribution to the pathophysiology of hypertension. Results of most studies suggest that generation of, or sensitivity to, endothelin-1 is no greater in hypertensive than it is in normotensive subjects. Nonetheless, the deleterious vascular effects of endogenous endothelin-1 may be accentuated by reduced generation of nitric oxide caused by hypertensive endothelial dysfunction. It also appears likely that endothelin participates in the adverse cardiac and vascular remodelling of hypertension, as well as in hypertensive renal damage. Irrespective of whether vascular endothelin activity is increased in hypertension, anti-endothelin agents do produce vasodilatation and lower blood pressure in hypertensive humans. There is more persuasive evidence for increased endothelin-1 activity in secondary forms of hypertension, including pre-eclampsia and renal hypertension. Endothelin-1 also appears to play an important role in pulmonary hypertension, both primary and secondary to diseases such as chronic heart failure. The hypotensive effects of endothelin converting enzyme inhibitors and endothelin receptor antagonists should be useful in the treatment of hypertension and related diseases. Development of such agents will increase knowledge of the physiological and pathological roles of the endothelins, and should generate drugs with novel benefits.

Expression of endothelin-1 and endothelin-converting enzyme-1 mRNAs and proteins in failing human hearts

Accumulating evidence suggests that endogenous endothelin-1 (ET-1) may contribute to the development of heart failure. In this study we determined sites of ET-1 synthesis and production in the failing human myocardium by immunohistochemistry and in situ hybridization for ET-1 and endothelin-converting enzyme-1 (ECE-1). Myocardial tissues were obtained from 19 patients with heart failure and from four noncardiac patients as controls. In both failing and nonfailing hearts, apparent immunoreactivity for ET-1 and ECE-1 was consistently seen in cardiac myocytes. Endothelial cells of intramyocardial coronary arteries and veins had only weak or focal ET-1 and apparent ECE-1 immunoreactivities. On the other hand, in situ hybridization showed strong signals for ET-1 and ECE-1 mRNAs in vascular endothelial cells but a lesser intensity of signals in cardiac myocytes. Apparent immunoreactivity and strong hybridization signals for both ET-1 and ECE-1 were seen in macrophages, which were abundant in infarcted regions of ischemic cardiomyopathy and in myocardium of septic patients but were rare in healthy hearts. These results suggest that, in failing human heart, vascular endothelial cells and macrophages rather than cardiac myocytes appear to be the principal ET-1 synthetic sites, although ET-1 peptides are abundantly present in cardiac myocytes of both failing and nonfailing hearts. Endogenous ET-1 may play a pathophysiologic role in human heart failure.

PD156707: a potent antagonist of endothelin-1 in human diseased coronary arteries and vein grafts

We have determined the ability of the endothelin A (ETA)-selective antagonist PD156707 to block constrictor ET-1 responses in blood vessels from the diseased human heart. ET-1 potently contracted nonatherosclerotic coronary arteries from patients with cardiomyopathy (pD2 = 7.96 +/- 0.15; n = 6), atherosclerotic coronary arteries from patients with ischemic heart disease (pD2 = 8.26 +/- 0.20; n = 4), and saphenous vein grafts that had developed "atherosclerotic" disease after coronary artery bypass (pD2 = 8.41 +/- 0.09; n = 6). PD156707 (100 nM) antagonized the vasoconstrictor response to ET-1 in each of the three preparations, with estimated pA2 values of 7.91 +/- 0.20, 8.05 +/- 0.14, and 8.07 +/- 0.02, respectively. These data suggest that the upregulation of ETB receptors that has been reported in human atherosclerotic coronary arteries does not contribute significantly to the ET-1-mediated constrictor response in these vessels in vitro.

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.

Predictors of myocardial dysfunction in human immunodeficiency virus-infected patients

BACKGROUND

Some of the most frequent manifestations of heart involvement in human immunodeficiency virus (HIV) infection include right and left ventricular dysfunction. The pathogenesis remains obscure.

METHODS AND RESULTS

This prospective clinical and echocardiographic study involved 181 patients at all stages of HIV infection. We tested a set of clinical variables using a backward logistic regression model to assess their ability to independently predict the presence of ventricular dysfunction. The presence of pulmonary infections (all etiologies mixed) was the only variable independently associated with isolated right ventricular dysfunction (odds ratio = 4.08; P = .02). Signs suggestive of pulmonary arterial hypertension were present in 71% of the patients with right ventricular dilation. History of previous opportunistic infections (all etiologies mixed) (odds ratio = 10.9; P = .0026) and time since the diagnosis of acquired immunodeficiency syndrome more than 12 months (odds ratio = 6.6; P = .03) were the only two independent predictors of left ventricular dysfunction.

CONCLUSIONS

Isolated right ventricular dysfunction may be secondary to pulmonary hypertension caused by repetitive pulmonary infections and not to primary myocardial disease. The aggressive treatment of opportunistic infections may become an important element of heart failure prophylaxis in HIV infection because they may be associated with left ventricular dysfunction.