Molecular cloning of a non-isopeptide-selective human endothelin receptor

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.

C-type natriuretic peptide (CNP)/guanylate cyclase B (GC-B) system and endothelin-1(ET-1)/ET receptor A and B system in human vasculature

To assess the physiological and clinical implications of the C-type natriuretic peptide (CNP)/guanylyl cyclase B (GC-B) system in the human vasculature, we have examined gene expressions of CNP and its receptor, GC-B, in human vascular endothelial cells (ECs) and smooth muscle cells (SMCs) and have also compared the endothelin-1(ET-1)/endothelin receptor-A (ETR-A) and endothelin receptor-B (ETR-B) system in human aortic ECs (HAECs) and vascular SMCs (HSMCs) in vitro. We also examined these gene expressions in human embryonic stem (ES)/induced pluripotent stem cell (iPS)-derived ECs and mural cells (MCs). A little but significant amount of mRNA encoding CNP was detected in both human ES-derived ECs and HAECs. A substantial amount of GC-B was expressed in both ECs (iPS-derived ECs and HAECs) and SMCs (iPS-derived MCs and HSMCs). ET-1 was expressed solely in ECs. ETR-A was expressed in SMCs, while ETR-B was expressed in ECs. These results indicate the existence of a vascular CNP/GC-B system in the human vascular wall, indicating the evidence for clinical implication of the CNP/GC-B system in concert with the ET-1/ETR-A and ETR-B system in the human vasculature.

Loss of endothelin type B receptor function improves insulin sensitivity in rats

High salt intake (HS) is associated with obesity and insulin resistance. ET-1, a peptide released in response to HS, inhibits the actions of insulin on cultured adipocytes through ET-1 type B (ETB) receptors; however, the in vivo implications of ETB receptor activation on lipid metabolism and insulin resistance is unknown. We hypothesized that activation of ETB receptors in response to HS intake promotes dyslipidemia and insulin resistance. In normal salt (NS) fed rats, no significant difference in body mass or epididymal fat mass was observed between control and ETB deficient rats. After 2 weeks of HS, ETB-deficient rats had significantly lower body mass and epididymal fat mass compared to controls. Nonfasting plasma glucose was not different between genotypes; however, plasma insulin concentration was significantly lower in ETB-deficient rats compared to controls, suggesting improved insulin sensitivity. In addition, ETB-deficient rats had higher circulating free fatty acids in both NS and HS groups, with no difference in plasma triglycerides between genotypes. In a separate experiment, ETB-deficient rats had significantly lower fasting blood glucose and improved glucose and insulin tolerance compared to controls. These data suggest that ET-1 promotes adipose deposition and insulin resistance via the ETB receptor.

The Glucagon-Like Peptide-1 Receptor Agonist Liraglutide Improves Hypoxia-Induced Pulmonary Hypertension in Mice Partly via Normalization of Reduced ETB Receptor Expression

The glucagon-like peptide-1 receptor (GLP-1R) agonist liraglutide is an incretin hormone mimetic used in the treatment of diabetes. However, the effects of liraglutide on pulmonary hypertension (PH) and pulmonary endothelin (ET) system are unknown. Eight-week-old C57BL6/J mice were injected liraglutide or vehicle for 5 weeks. One week after injection, the mice were exposed to either room air (normoxia) or chronic hypoxia (10 % O2) for 4 weeks. The right ventricular systolic pressure (RVSP) was significantly higher in hypoxia + vehicle group than in normoxia + vehicle group. ET-1 mRNA expression in the lungs was comparable among all the groups. ETB mRNA and protein expression in the lungs was significantly lower in hypoxia + vehicle group than in normoxia + vehicle group. The above changes were normalized by liraglutide treatment. The expression of phospho-eNOS and phospho-AMPK proteins in the lungs was significantly higher in hypoxia + liraglutide group than in normoxia + vehicle group. We demonstrated for the first time that liraglutide effectively improved RVSP and RV hypertrophy in hypoxia-induced PH mice by activating eNOS through normalization of impaired ETB pathway and augmentation of AMPK pathway. Therefore, GLP-1R agonists can be promising therapeutic agents for PH.

SCF-KIT signaling induces endothelin-3 synthesis and secretion: Thereby activates and regulates endothelin-B-receptor for generating temporally- and spatially-precise nitric oxide to modulate SCF- and or KIT-expressing cell functions

We demonstrate that SCF-KIT signaling induces synthesis and secretion of endothelin-3 (ET3) in human umbilical vein endothelial cells and melanoma cells in vitro, gastrointestinal stromal tumors, human sun-exposed skin, and myenteric plexus of human colon post-fasting in vivo. This is the first report of a physiological mechanism of ET3 induction. Integrating our finding with supporting data from literature leads us to discover a previously unreported pathway of nitric oxide (NO) generation derived from physiological endothelial NO synthase (eNOS) or neuronal NOS (nNOS) activation (referred to as the KIT-ET3-NO pathway). It involves: (1) SCF-expressing cells communicate with neighboring KIT-expressing cells directly or indirectly (cleaved soluble SCF). (2) SCF-KIT signaling induces timely local ET3 synthesis and secretion. (3) ET3 binds to ETBR on both sides of intercellular space. (4) ET3-binding-initiated-ETBR activation increases cytosolic Ca²⁺, activates cell-specific eNOS or nNOS. (5) Temporally- and spatially-precise NO generation. NO diffuses into neighboring cells, thus acts in both SCF- and KIT-expressing cells. (6) NO modulates diverse cell-specific functions by NO/cGMP pathway, controlling transcriptional factors, or other mechanisms. We demonstrate the critical physiological role of the KIT-ET3-NO pathway in fulfilling high demand (exceeding basal level) of endothelium-dependent NO generation for coping with atherosclerosis, pregnancy, and aging. The KIT-ET3-NO pathway most likely also play critical roles in other cell functions that involve dual requirement of SCF-KIT signaling and NO. New strategies (e.g. enhancing the KIT-ET3-NO pathway) to harness the benefit of endogenous eNOS and nNOS activation and precise NO generation for correcting pathophysiology and restoring functions warrant investigation.

Granulosa cell endothelin-2 expression is fundamental for ovulatory follicle rupture

Ovulation is dependent upon numerous factors mediating follicular growth, vascularization, and ultimately oocyte release via follicle rupture. Endothelin-2 (EDN2) is a potent vasoconstrictor that is transiently produced prior to follicle rupture by granulosa cells of periovulatory follicles and induces ovarian contraction. To determine the role of Edn2 expression, surgical transplant and novel conditional knockout mice were super-ovulated and analyzed. Conditional knockout mice utilized a new iCre driven by the Esr2 promoter to selectively remove Edn2. Follicle rupture and fertility were significantly impaired in the absence of ovarian Edn2 expression. When ovaries of Edn2KO mice were transplanted in wild type recipients, significantly more corpora lutea containing un-ovulated oocytes were present after hormonal stimulation (1.0 vs. 5.4, p = 0.010). Following selective ablation of Edn2 in granulosa cells, Esr2-Edn2KO dams had reduced oocytes ovulated (3.8 vs. 16.4 oocytes/ovary) and smaller litters (4.29 ± l.02 vs. 8.50 pups/dam). However, the number of pregnancies per pairing was not different and the reproductive axis remained intact. Esr2-Edn2KO ovaries had a higher percentage of antral follicles and fewer corpora lutea; follicles progressed to the antral stage but many were unable to rupture. Conditional loss of endothelin receptor A in granulosa cells also decreased ovulation but did not affect fecundity. These data demonstrate that EDN2-induced intraovarian contraction is a critical trigger of normal ovulation and subsequent fecundity.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.

Distinct ETA receptor binding mode of macitentan as determined by site directed mutagenesis

The competitive endothelin receptor antagonists (ERA) bosentan and ambrisentan, which have long been approved for the treatment of pulmonary arterial hypertension, are characterized by very short (1 min) occupancy half-lives at the ET_A receptor. The novel ERA macitentan, displays a 20-fold increased receptor occupancy half-life, causing insurmountable antagonism of ET-1-induced signaling in pulmonary arterial smooth muscle cells. We show here that the slow ET_A receptor dissociation rate of macitentan was shared with a set of structural analogs, whereas compounds structurally related to bosentan displayed fast dissociation kinetics. NMR analysis showed that macitentan adopts a compact structure in aqueous solution and molecular modeling suggests that this conformation tightly fits into a well-defined ET_A receptor binding pocket. In contrast the structurally different and negatively charged bosentan-type molecules only partially filled this pocket and expanded into an extended endothelin binding site. To further investigate these different ET_A receptor-antagonist interaction modes, we performed functional studies using ET_A receptor variants harboring amino acid point mutations in the presumed ERA interaction site. Three ET_A receptor residues significantly and differentially affected ERA activity: Mutation R326Q did not affect the antagonist activity of macitentan, however the potencies of bosentan and ambrisentan were significantly reduced; mutation L322A rendered macitentan less potent, whereas bosentan and ambrisentan were unaffected; mutation I355A significantly reduced bosentan potency, but not ambrisentan and macitentan potencies. This suggests that – in contrast to bosentan and ambrisentan - macitentan-ET_A receptor binding is not dependent on strong charge-charge interactions, but depends predominantly on hydrophobic interactions. This different binding mode could be the reason for macitentan's sustained target occupancy and insurmountable antagonism.

Proximal nephron

The kidney plays a fundamental role in maintaining body salt and fluid balance and blood pressure homeostasis through the actions of its proximal and distal tubular segments of nephrons. However, proximal tubules are well recognized to exert a more prominent role than distal counterparts. Proximal tubules are responsible for reabsorbing approximately 65% of filtered load and most, if not all, of filtered amino acids, glucose, solutes, and low molecular weight proteins. Proximal tubules also play a key role in regulating acid-base balance by reabsorbing approximately 80% of filtered bicarbonate. The purpose of this review article is to provide a comprehensive overview of new insights and perspectives into current understanding of proximal tubules of nephrons, with an emphasis on the ultrastructure, molecular biology, cellular and integrative physiology, and the underlying signaling transduction mechanisms. The review is divided into three closely related sections. The first section focuses on the classification of nephrons and recent perspectives on the potential role of nephron numbers in human health and diseases. The second section reviews recent research on the structural and biochemical basis of proximal tubular function. The final section provides a comprehensive overview of new insights and perspectives in the physiological regulation of proximal tubular transport by vasoactive hormones. In the latter section, attention is particularly paid to new insights and perspectives learnt from recent cloning of transporters, development of transgenic animals with knockout or knockin of a particular gene of interest, and mapping of signaling pathways using microarrays and/or physiological proteomic approaches.

Slow receptor dissociation kinetics differentiate macitentan from other endothelin receptor antagonists in pulmonary arterial smooth muscle cells

Two endothelin receptor antagonists (ERAs), bosentan and ambrisentan, are currently approved for the treatment of pulmonary arterial hypertension (PAH), a devastating disease involving an activated endothelin system and aberrant contraction and proliferation of pulmonary arterial smooth muscle cells (PASMC). The novel ERA macitentan has recently concluded testing in a Phase III morbidity/mortality clinical trial in PAH patients. Since the association and dissociation rates of G protein-coupled receptor antagonists can influence their pharmacological activity in vivo, we used human PASMC to characterize inhibitory potency and receptor inhibition kinetics of macitentan, ambrisentan and bosentan using calcium release and inositol-1-phosphate (IP₁) assays. In calcium release assays macitentan, ambrisentan and bosentan were highly potent ERAs with K_b values of 0.14 nM, 0.12 nM and 1.1 nM, respectively. Macitentan, but not ambrisentan and bosentan, displayed slow apparent receptor association kinetics as evidenced by increased antagonistic potency upon prolongation of antagonist pre-incubation times. In compound washout experiments, macitentan displayed a significantly lower receptor dissociation rate and longer receptor occupancy half-life (ROt_1/2) compared to bosentan and ambrisentan (ROt_1/2∶17 minutes versus 70 seconds and 40 seconds, respectively). Because of its lower dissociation rate macitentan behaved as an insurmountable antagonist in calcium release and IP₁ assays, and unlike bosentan and ambrisentan it blocked endothelin receptor activation across a wide range of endothelin-1 (ET-1) concentrations. However, prolongation of the ET-1 stimulation time beyond ROt_1/2 rendered macitentan a surmountable antagonist, revealing its competitive binding mode. Bosentan and ambrisentan behaved as surmountable antagonists irrespective of the assay duration and they lacked inhibitory activity at high ET-1 concentrations. Thus, macitentan is a competitive ERA with significantly slower receptor dissociation kinetics than the currently approved ERAs. Slow dissociation caused insurmountable antagonism in functional PASMC-based assays and this could contribute to an enhanced pharmacological activity of macitentan in ET-1-dependent pathologies.

Pharmacotherapy for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a disabling, progressive disease. The past decade has seen an explosion in the available therapies for the management of PAH. Choosing appropriate pharmacotherapy can be a daunting task for the practitioner, as no head-to-head comparisons between drugs have been published. This article aims to assist the practitioner in developing an evidence-based, rational pharmacologic treatment algorithm for the management of patients with PAH. Currently approved pharmacotherapy and the pivotal trials that led to approval for the respective agents are reviewed. Common dilemmas in the treatment of PAH for which strong evidence is lacking are discussed.

Endothelin ET(B) receptors are involved in the relaxation to the pig urinary bladder neck

AIMS

The involvement of endothelin receptors in the contraction of the lower urinary tract smooth muscle is well established. There is scarce information, however, about endothelin receptors mediating relaxation of the bladder outlet region. The current study investigates the possible existence of endothelin ET(B) receptors involved in the relaxation of pig bladder neck.

METHODS

ET(B) receptor expression was determined by immunohistochemistry and urothelium-denuded bladder neck strips were mounted in organ baths for isometric force recording.

RESULTS

ET(B) -immunoreactivity (ET(B) -IR) was observed within nerve fibers among smooth muscle bundles and urothelium. BQ3020 (0.01-300 nM), an ET(B) receptor agonist, produced concentration-dependent relaxations which were reduced by BQ788, an ET(B) receptor antagonist, and by inhibitors of protein kinase A (PKA) and large (BK(Ca) )- or small (SK(Ca) )-conductance Ca(2+) -activated K(+) channels. Pretreatment with BK(Ca) or SK(Ca) channel inhibitors plus PKA blocking did not cause further inhibition compared with that exerted by inhibiting BK(Ca) or SK(Ca) channels only. BQ3020-induced relaxation was not modified by blockade of either nitric oxide (NO) synthase, guanylyl cyclase, cyclooxygenase (COX) or of intermediate-conductance Ca(2+) -activated-(IK(Ca) ), ATP-dependent-(K(ATP) ), or voltage-gated-(K(v) ) K(+) channels. Under non-adrenergic non-cholinergic (NANC) conditions, electrical field stimulation (0.5-16 Hz) evoked frequency-dependent relaxations, which were reduced by BQ788 and potentiated by threshold concentrations of BQ3020.

CONCLUSIONS

These results suggest that BQ3020 produces relaxation of the pig bladder neck via activation of muscle endothelin ET(B) receptors, NO/cGMP- and COX-independent-, cAMP-PKA pathway-dependent-mechanisms, and involving BK(Ca) and SK(Ca) channel activation. ET(B) receptors are also involved in the NANC inhibitory neurotransmission.

Darusentan, a selective endothelin A receptor antagonist, for the oral treatment of resistant hypertension

Resistant hypertension is defined as failure to lower blood pressure to target when a patient adheres to the maximum tolerated doses of three antihypertensive drugs including a diuretic. Notwithstanding the wide availability of several antihypertensive agents and the continued recommendation of dietary and lifestyle modifications, the prevalence of resistant hypertension remains high and is expected to increase thus underscoring the need for potential new treatment modalities in resistant hypertension. Endothelin-1 is a long-lasting potent vasoconstrictor and plays a key role in cardiovascular haemostasis. Endothelin mediates its biological activity in humans through the endothelin A and B receptors. The clinical experience and the evidence for therapy with darusentan in resistant systemic hypertension are reviewed. The leading journals that publish basic science and clinical research in the area of cardiovascular diseases and PubMed were scanned. While results from early clinical studies suggested that darusentan might emerge as new treatment option in patients with resistant hypertension, results from recent studies suggests that darusentan appears unlikely to find its way in the armamentarium for treatment of resistant hypertension.

Mechanisms involved in the effects of endothelin-1 in pig prostatic small arteries

Since endothelin-1 (ET-1) is involved in prostatic disorders, the current study investigated the mechanisms underlying the ET-1-induced effects in pig prostatic small arteries. The experiments were performed in rings mounted in microvascular myographs containing physiological saline solution at 37oC for isometric force recordings. On basal tension, ET-1 (0.1-30 nM) evoked concentration-dependent contractions, which were enhanced by endothelium removal. ET-1 contractions were inhibited by blockade of endothelin ETA and ETB receptors, extracellular Ca2+ removal and blockade of voltage-dependent (L-type)- and non-voltage-dependent-Ca2+ channels. On endothelium intact rings precontracted with noradrenaline, the ETB endothelin receptor agonist BQ3020 promoted a concentration-dependent relaxation which was reduced by blockade of ETB receptors, nitric oxide synthase, guanylyl cyclase and prostanoids synthesis. Endothelium removal abolished its relaxant response and unmasked a BQ3020-induced contraction. Tetraethylammonium and 4-aminopyridine, blockers of non-selective K+ channels and voltage-dependent K+ (Kv) channels, respectively, inhibited the relaxations to BQ3020. Iberiotoxin, apamin and glibenclamide, blockers of large and small Ca2+-activated- and ATP-dependent- K+ channels, respectively, failed to modify these responses. These data suggest that ET-1 promotes contraction of pig prostatic small arteries by activating vascular smooth muscle contractile endothelin ETA and ETB receptors coupled to extracellular Ca2+ entry, via voltage-dependent (L-type)- and non-voltage-dependent Ca2+ channels, also being due to intracellular Ca2+ mobilization. In addition, a population of endothelial ETB receptors mediates vasorelaxation via NO-cGMP pathway, vasodilator cyclooxygenase product(s) and Kv channels.

The cardiovascular physiology and pharmacology of endothelin-1

One year after the discovery in 1980 that the endothelium was obligatory for acetylcholine to relax isolated arteries, it was clearly shown that the endothelium could also promote contraction. In 1988, Dr Yanagisawa's group identified endothelin-1 (ET-1) as the first endothelium-derived contracting factor. The circulating levels of this short (21 amino acids) peptide were quickly determined in humans and it was reported that in most cardiovascular diseases, circulating levels of ET-1 were increased and ET-1 was then recognized as a likely mediator of pathological vasoconstriction in human. The discovery of two receptor subtypes in 1990, ET(A) and ET(B), permitted optimization of bosentan, which entered clinical development in 1993, and was offered to patients with pulmonary arterial hypertension in 2001. In this report, we discuss the physiological and pathophysiological role of endothelium-derived ET-1, the pharmacology of its two receptors, focusing on the regulation of the vascular tone and as much as possible in humans. The coronary bed will be used as a running example, but references to the pulmonary, cerebral, and renal circulation will also be made. Many of the cardiovascular complications associated with aging and cardiovascular risk factors are initially attributable, at least in part, to endothelial dysfunction, particularly dysregulation of the vascular function associated with an imbalance in the close interdependence of NO and ET-1, in which the implication of the ET(B) receptor may be central.

Differential expression of vasoactive mediators in microparticle-challenged lungs of chickens that differ in susceptibility to pulmonary arterial hypertension

Pulmonary hypertension syndrome (PHS; ascites) in fast growing meat-type chickens (broilers) is characterized by the onset of idiopathic pulmonary arterial hypertension (IPAH) leading to right-sided congestive heart failure and terminal ascites. Intravenous microparticle (MP) injection is a tool used by poultry geneticists to screen for the broilers that are resistant (RES) or susceptible (SUS) to IPAH in a breeding population. MPs occlude pulmonary arterioles and initiate focal inflammation, causing local tissues and responding leukocytes to release vasoactive mediators such as serotonin (5-HT), endothelin-1 (ET-1), and nitric oxide (NO). RT-PCR was used to examine the differences between RES and SUS broilers in terms of gene expression of ET-1, ET receptor types A and B (ET(A) and ET(B)), the serotonin transporter (SERT), serotonin receptors (5-HT(1A), 5-HT(2A), 5-HT(1B), 5-HT(2B)), endothelial NO synthase (eNOS), and inducible NOS (iNOS) in the lungs of these broilers before (0 h) and after (2, 6, 12, 24, and 48 h) MP injection. In SUS broilers MP injection elicited higher (P < 0.05) pulmonary expression of 5-HT(1A), 5-HT(2B), and ET-1, which promote vasoconstriction and proliferation of pulmonary arterial smooth muscle cells (PASMC). In RES broilers the MP injection elicited higher expression of eNOS, iNOS, and ET(B), which promote vasodilation and inhibit PASMC proliferation. These observations support the hypothesis that the resistance of broiler chickens to IPAH may be due to the higher expression of vasoactive mediators that favor enhanced vasodilation and attenuated vasoconstriction during MP injection challenges to the pulmonary vasculature.

Improved myocardial protection in the failing heart by selective endothelin-A receptor blockade

OBJECTIVE

Ischemia/reperfusion injury caused by cardioplegic arrest is still a major challenge in patients with reduced left ventricular function. We investigated the effect of chronic versus acute administration of the selective endothelin-A receptor antagonist (ERA) TBC-3214Na during ischemia/reperfusion in failing hearts.

METHODS

Male Sprague-Dawley rats underwent coronary ligation. Three days after myocardial infarction (MI), 19 randomly assigned animals (ERA chronic) were administered TBC-3214Na continuously with their drinking water, 29 MI rats received placebo, and 3 rats died during the observation period. Six weeks after infarction, hearts were evaluated in a blood-perfused working heart model during 60 minutes of ischemia and 30 minutes of reperfusion. In 14 MI rats, TBC-3214Na (ERA acute) was added to the cardioplegic solution during ischemia. Thirteen MI rats served as control.

RESULTS

At a similar infarct size, postischemic recovery of cardiac output (ERA chronic: 91% +/- 10%, ERA acute: 86% +/- 11% vs control: 52% +/- 15%; P < .05) and external heart work (ERA chronic: 90% +/- 10%, ERA acute: 85% +/- 13% vs control: 51% +/- 17%; P < .05) was significantly enhanced in both TBC-3214Na-treated groups whereas recovery of coronary flow was only improved in ERA acute rats (ERA acute: 121% +/- 23% vs ERA chronic: 75% +/- 13%; control: 64% +/- 15%; P < .05). Blood gas measurements showed enhanced myocardial oxygen delivery and consumption with acute TBC-3214Na therapy. Additionally, high-energy phosphates (phosphocreatine) were significantly higher and transmission electron microscopy revealed less ultrastructural damage under acute TBC-3214Na administration.

CONCLUSION

Acute endothelin-A receptor blockade is superior to chronic blockade in attenuating ischemia/reperfusion injury in failing hearts. Therefore, acute endothelin-A receptor blockade might be an interesting option for patients with heart failure undergoing cardiac surgery.

Endothelin receptor B-mediated induction of c-jun and AP-1 in response to shear stress in human endothelial cellsThis article is one of a selection of papers published in the special issue (part 2 of 2) on Forefronts in Endothelin

In vivo, endothelial cells are constantly exposed to shear stress by flowing blood. Short-term exposure of endothelial cells to shear stress has been shown to induce endothelin-1 release. It is currently unknown, however, whether this shear stress-dependent endothelin-1 release affects the expression and activity of transcription factors. In this study, primary cultures of human endothelial cells from the umbilical vein were exposed to laminar shear stress in a cone-and-plate viscometer. Laminar shear stress for 30 min induced a 2-fold increase in mRNA expression of c-jun , but not c-fos, in human endothelial cells. Blockade of endothelin receptor subtype B (ETB) with BQ788 prevented this shear stress-dependent induction of c-jun expression. The induction of c-jun by shear stress involved protein kinase C and endothelial NO synthase. In addition, exposure of endothelial cells to arterial laminar shear stress for 1 h increased the binding of transcription factor AP-1 to its consensus sequence by 1.7-fold in electrophoretic mobility shift assays. This induction was also mediated by an ETB-dependent pathway. Supershift analysis supports an AP-1 complex containing c-jun, but not c-fos, in human endothelial cells. In conclusion, our data suggest endothelin-1-mediated induction of c-jun expression and activation of AP-1 (possibly as a c-jun homodimer) by laminar shear stress in human endothelial cells.

Method for diagnosis of a disease involving an anti-endothelin receptor antibody

BACKGROUND

Endothelin (ET) is a potent vasoconstrictor peptide with profibrotic, promitotic, and proinflammatory effects. Elevated levels of ET or inappropriate activation of ET receptors are believed to contribute to the pathogenesis of various disorders, including cardiovascular and autoimmune diseases and allograft rejection.

OBJECTIVE

The pathogenetic significance of activating anti-ET receptor autoantibodies and their diagnostic usefulness are addressed.

METHODS

PubMed and EMBASE searches were performed for '(activating) endothelin receptor (auto)antibodies' and '(activating) angiotensin receptor (auto)antibodies'.

RESULTS/CONCLUSION

While activating angiotensin receptor autoantibodies have been detected in several acute and chronic disorders, published data for a corresponding role of ET receptor antibodies are currently lacking. Thus, their diagnostic and prognostic value needs to be confirmed.

New insights into the causes and therapy of cerebral vasospasm following subarachnoid hemorrhage

Cerebral vasospasm lingers as the leading preventable cause of death and disability in patients who experience aneurysmal subarachnoid hemorrhage. Despite the potentially devastating consequences of cerebral vasospasm, the mechanisms behind it are incompletely understood. Nitric oxide, endothelin-1, bilirubin oxidation products and inflammation appear to figure prominently in its pathogenesis. Therapies directed at many of these mechanisms are currently under investigation and hold significant promise for an ultimate solution to this substantial problem.

Inflammatory responses after endothelin B (ETB) receptor activation in human monocytes: new evidence for beneficial anti-inflammatory potency of ETB-receptor antagonism

Endothelin (ET) stimulates potent ETA/ETB receptors important in the pathogenesis of pulmonary arterial hypertension (PAH) and fibrosis. Though therapy with ET-receptor antagonists is well established uncertainty exists whether selective ETA or dual ETA/ETB-receptor antagonism is superior in PAH. The objective of this study was to further elucidate the pro-inflammatory effects of ET-1 on ETB receptors in cultured human monocytes (10(5)/20 h) compared with non-specific stimulation with LPS in vitro and to define the antagonizing effects of bosentan, a dual ETA/ETB-receptor antagonist, on inflammatory mediator production. We further hypothesized that ETB-receptor antagonism reduces the requirement of PGE2 to control inflammatory mediator production. Activation of the monocyte ETB subtype by ET (1 ng/ml) concentration-dependently stimulated TNF-alpha (744%) >PGE2 (570%) > IL-1 beta (112%) and had no effect on 5-lipoxygenase metabolism. Compared with ET a different profile of IL-1 beta >TNF-alpha >PGE2 was induced by LPS. ETB-receptor antagonism attenuated ET- and LPS-responses in monocytes, in particular of TNF-alpha and PGE2 to a similar extend (40%) that were only demonstrable following LPS at therapeutic plasma concentrations of bosentan and had no effect on IL-1 beta. Inhibition of ETB receptors in LPS-stimulated monocytes by bosentan was responded with suppression of PGE2 and increased production of leukotrienes indicating strong effects in the cyclooxygenase pathway that is known to control cellular ET transcription. These data suggest an important signaling pathway between ET-induced cytokine production following ETB-receptor activation with no further control of ET transcription by PGE2 required following ETB receptor antagonism. Therefore, in states of inflammation increased ETB-receptor expression and activation mediated by elevated ET concentrations may be an underestimated mechanism, which warrants the application of combined ETA/ETB-receptor antagonists.

Role of endothelin-1 receptor antagonists in vasoconstriction mediated by endothelin and other vasoconstrictors in human internal mammary artery

BACKGROUND

The action of antagonists for endothelin type A (ET(A)) and type B (ET(B)) on the vasoconstriction mediated by various vasoconstrictors in the human bypass grafts have not been well-defined. We studied the role of antagonists for both ET(A) and ET(B) receptors in vasoconstriction mediated by endothelin-1 and other vasoconstrictors in the human internal mammary artery (IMA).

METHODS

Isolated IMA rings (n = 192, taken from 49 patients) were studied in organ bath for the interaction between endothelin-1, angiotensin II, U46619, and potassium chloride and the antagonist for ET(A) (BQ-123) or ET(B) (BQ-788).

RESULTS

Significant relaxations were observed by BQ-123 (agonist: endothelin-1, 84.9 +/- 7.9%; angiotensin II, 45.5 +/- 5.1%; and U46619, 30.7 +/- 5.7%) or BQ-788 (agonist: endothelin-1, 66.5 +/- 11.3%; angiotensin II, 38.9 +/- 4.2%; and U46619, 30.8 +/- 4.0%), but not to potassium chloride-induced precontraction. Incubation of IMA with BQ-123 or BQ-123 + BQ-788 significantly shifted the concentration-contraction curve to endothelin-1 rightward (p < 0.05 vs control) with effective concentration causing 50% of maximal response (EC50) (-7.59 +/- 0.04 or -7.81 +/- 0.05 vs -8.47 +/- 0.05 log M in the control, p < 0.001), whereas BQ-788 alone did not affect the contraction curve (p = 1.0 vs control). In contrast, none of the endothelin-1 inhibitors and the combination demonstrated significant depression effects on angiotensin II, U46619, or potassium chloride-induced contraction.

CONCLUSIONS

The present study demonstrates the role of ET(A) and ET(B) antagonists in the endothelin-1-mediated contraction in the human IMA and indicates the dominant role of ET(A) receptors. Although these effects are specific to endothelin-1, cross-action between endothelin-1 and angiotensin II exists. These findings provide useful knowledge for the future development of the clinical antispastic protocol in coronary bypass surgery.

Endogenous Endothelin in Human Coronary Vascular Function

Endothelin 1 mediates coronary vasoconstriction and endothelial dysfunction via endothelin receptor type A (ET A ) activation. However, the effects of selective endothelin receptor type B (ET B ) and combined ET A+B receptor blockade on coronary vasomotion are unknown. We measured coronary vascular tone and endothelium-dependent and -independent vasomotor function before and after selective infusion of BQ-788 (an ET B receptor antagonist) or combined infusion of BQ-788+BQ-123 (an ET A antagonist) into unobstructed coronary arteries of 39 patients with coronary atherosclerosis or risk factors undergoing cardiac catheterization. BQ-788 did not affect epicardial diameter but constricted the microcirculation ( P <0.0001), increased coronary sinus endothelin, and reduced nitrogen oxide levels. In contrast, BQ-123+BQ-788 dilated epicardial ( P <0.0001) and resistance ( P =0.022) arteries. Responses to acetylcholine and sodium nitroprusside were unaffected by BQ-788 alone. Epicardial endothelial dysfunction improved after BQ-123+BQ-788 ( P =0.007). Coronary microvascular responses to acetylcholine and sodium nitroprusside were unaffected by BQ-123+BQ-788. We conclude that selective ET B receptor antagonism causes coronary microvascular constriction, without affecting epicardial tone or endothelial function, via reduced endothelin clearance and NO availability. Combined ET A+B blockade dilates coronary conduit and resistance vessels and improves endothelial dysfunction of the epicardial coronary arteries. Thus, endogenous endothelin, predominantly via ET A receptor stimulation, contributes to basal constrictor tone and endothelial dysfunction, whereas ET B activation mediates vasodilation in human coronaries. Our data suggest that selective ET A blockade may have greater therapeutic potential than nonselective agents, particularly for treatment of endothelial dysfunction in atherosclerosis.

Clinical review: Prevention and therapy of vasospasm in subarachnoid hemorrhage

Vasospasm is one of the leading causes of morbidity and mortality following aneurysmal subarachnoid hemorrhage (SAH). Radiographic vasospasm usually develops between 5 and 15 days after the initial hemorrhage, and is associated with clinically apparent delayed ischemic neurological deficits (DID) in one-third of patients. The pathophysiology of this reversible vasculopathy is not fully understood but appears to involve structural changes and biochemical alterations at the levels of the vascular endothelium and smooth muscle cells. Blood in the subarachnoid space is believed to trigger these changes. In addition, cerebral perfusion may be concurrently impaired by hypovolemia and impaired cerebral autoregulatory function. The combined effects of these processes can lead to reduction in cerebral blood flow so severe as to cause ischemia leading to infarction. Diagnosis is made by some combination of clinical, cerebral angiographic, and transcranial doppler ultrasonographic factors. Nimodipine, a calcium channel antagonist, is so far the only available therapy with proven benefit for reducing the impact of DID. Aggressive therapy combining hemodynamic augmentation, transluminal balloon angioplasty, and intra-arterial infusion of vasodilator drugs is, to varying degrees, usually implemented. A panoply of drugs, with different mechanisms of action, has been studied in SAH related vasospasm. Currently, the most promising are magnesium sulfate, 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors, nitric oxide donors and endothelin-1 antagonists. This paper reviews established and emerging therapies for vasospasm.

Endothelin receptor antagonism in pulmonary arterial hypertension--a role for selective ET(A) inhibition?

BACKGROUND

Pulmonary arterial hypertension (PAH) develops from an abnormal interaction between the endothelium and smooth muscle cells in the pulmonary arteries and is characterized by a progressive increase in pulmonary vascular resistance resulting from vascular remodeling, vasoconstriction, and cellular proliferation. A rapidly progressive disease with limited therapeutic options, PAH may progress to right ventricular failure and death. Endothelin (ET-1), a potent vasoconstrictor, has vascular remodeling properties that contribute to the acceleration of the disease. ET-1 predominantly binds to two receptors, endothelin-A (ET(A)) and endothelin-B (ET(B)) receptors. ET(A) receptors are found on smooth muscle cells only and, when activated, induce vasoconstriction and cellular proliferation. ET(B) receptors on smooth muscle cells, when activated, cause vasoconstriction, whereas those on endothelial cells produce vasodilation and clear circulating ET-1. Therefore, a clinically important question arises as to whether selective ET(A) receptor antagonism is superior to nonselective dual-receptor antagonism in the treatment of PAH.

SCOPE

To review clinical trials that studied safety and efficacy of various endothelin receptor antagonists (ETRAs) for the treatment of PAH and address the rationale for the use of either a nonselective or a selective ETRA.

FINDINGS

Nonselective blockade of both ET receptors with the ETRA bosentan has demonstrated benefit in PAH, as have sitaxsentan and ambrisentan, two investigational agents with more selectivity for the ET(A) receptor. Data from placebo-controlled studies and long-term, open-label studies suggest that all ETRAs have similar efficacy, though there is some evidence suggesting that selective ETRAs may have a safer profile.

CONCLUSION

Both selective and nonselective ETRAs have proven to be efficacious in treatment of PAH patients, and selective ETRAs may have a slightly safer profile. However, because PAH is a rare disease and trials have relatively small numbers of patients, it is difficult to quantify the magnitude of the difference between the different agents.

Acute administration of 17beta-estradiol reduces endothelin-1 release during pacing-induced ischemia

OBJECTIVES

To assess whether acute administration of 17beta-estradiol reduces pacing-induced cardiac release of endothelin-1 in female menopausal patients with coronary artery disease.

BACKGROUND

Endothelin-1 is a potent vasoactive peptide which plays a pathogenetic role in myocardial ischemia and adverse clinical events in patients with coronary artery disease. Estrogens decrease plasma levels of endothelin-1 and improve stress-induced myocardial ischemia in menopausal women with coronary artery disease.

METHODS

Twenty-two postmenopausal women with angiographically proven coronary artery entered a randomized, double blinded, placebo-controlled study. Patients were sampled into the coronary sinus and aorta for endothelin-1 at baseline and after incremental pacing. After baseline study, patients were randomized to receive either sublingual 17beta-estradiol (1 mg) or placebo and underwent the sampling protocol 20 min thereafter.

RESULTS

17Beta-estradiol but not placebo improved the time of onset of myocardial ischemia during pacing. The coronary sinus plasma levels of endothelin-1 were significantly reduced by estradiol administration but not by placebo, at each step of pacing protocol. The maximum reduction of endothelin-1 was noted at peak pacing (-0.18 ng/l; -0.09, -0.3; 95% CI). No changes in endothelin-1 were noted in patients allocated to placebo (-0.002 ng/l; -0.06, -0.01; 95% CI). Similarly, aorto-coronary sinus difference of endothelin-1 was significantly influenced by 17beta-estradiol administration but not by placebo.

CONCLUSION

Acute administration of 17beta-estradiol reduces pacing-induced cardiac release of endothelin-1 in postmenopausal women with coronary artery disease. This result may be related to the anti-ischemic or to a primary direct effect of the hormone upon myocyte release of the peptide, and may contribute to its anti-ischemic effect.

CONDENSED ABSTRACT

To assess effect of acute 17beta-estradiol administration on pacing-induced cardiac release of endothelin-1, we studied 22 female menopausal patients with coronary artery diseases. In a randomized, double-blinded, placebo-controlled study, patients were randomized to receive either sublingual 17beta-estradiol (1 mg) or placebo. Aortic and coronary sinus plasma endothelin-1 levels were evaluated at baseline, during incremental atrial pacing, and at peak pacing before and after the sublingual administration of either 17beta-estradiol or placebo. The time to the onset of myocardial ischemia during pacing was significantly increased by 17beta-estradiol vs. placebo. Moreover, coronary sinus endothelin-1 levels at peak pacing and aortic-coronary sinus changes were significantly improved by the administration of 17beta-estradiol but not by placebo. Acute administration of 17beta-estradiol reduces pacing-induced cardiac release of endothelin-1 in postmenopausal women with coronary artery disease.

Endothelin receptor antagonists

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

SOX10, in combination with Sp1, regulates the endothelin receptor type B gene in human melanocyte lineage cells

Waardenburg syndrome (WS) is an auditory-pigmentary disorder that exhibits varying combinations of sensorineural hearing loss and abnormal pigmentation of the hair and skin. WS type 4 (WS4), a subtype of WS, is characterized by the presence of the aganglionic megacolon and is associated with mutations in the gene encoding either endothelin 3, endothelin receptor type B (EDNRB), or Sry-box 10 (SOX10). Here, we provide evidence that SOX10 regulates the expression of EDNRB gene in human melanocyte-lineage cells, as judged by RNA interference and chromatin immunoprecipitation analyses. Human melanocytes preferentially express the EDNRB transcripts derived from the conventional EDNRB promoter. SOX10 transactivates the EDNRB promoter through the cis-acting elements, the two CA-rich sequences and the GC box. Moreover, a transcription factor Sp1 enhances the degree of the SOX10-mediated transactivation of the EDNRB promoter through these cis-acting elements. Furthermore, we have shown that the EDNRB promoter is heavily methylated in HeLa human cervical cancer cells, lacking EDNRB expression, but not in melanocytes and HMV-II melanoma cells. The expression of EDNRB became detectable in HeLa cells after treatment with a demethylating reagent, 5'-aza-2'-deoxycytidine, which was further enhanced in the transformed cells over-expressing SOX10. We therefore suggest that SOX10, alone or in combination with Sp1, regulates transcription of the EDNRB gene, thereby ensuring appropriate expression level of EDNRB in human melanocytes.

Significance of plasma nitric oxide/endothelial-1 ratio for prediction of coronary artery disease

Vascular tone is regulated by vasodilators and vasoconstrictors. Endothelin-1 (ET-1) is the predominant vasoconstrictor peptide that constricts vascular smooth muscle, whereas nitric oxide (NO) is the primary vasodilator peptide that relaxes vascular smooth muscle. In this study, the authors examined whether NO/ET-1 ratio is a useful marker for detecting coronary artery disease (CAD), by comparison with evaluation based on vascular endothelial (VE) function. They measured plasma NOX and ET-1 by using ENO-200 and radioimmunoassay, in 38 subjects with normal (NL) coronary arteries (NL group; mean age, 60 +/-12 years) and 25 subjects with CAD (CAD group; mean age, 69 +/- 6 years). VE function (randomized endothelium-dependent [D] and endothelium-independent [I] VE function) was assessed by measuring brachial artery (BA) diameter by using high-resolution ultrasound (7.5 MHz). Soon after these procedures, symptom-limited exercise testing was performed. There were no statistically significant differences in serum lipid concentrations or VED function between the groups. However, the CAD group had a significantly lower NO/ET-1 ratio (1.2 +/- 1.1 vs 2.7 +/- 2.2, p < 0.01) and BA diameter after sublingual nitroglycerin (VEID function: 6 +/- 7% vs 10 +/- 4%, p < 0.05). As expected, the ST segment and treadmill exercise duration were significantly lower in the CAD group. Sensitivity and specificity for detecting CAD by plasma NO/ET-1 ratio (> or =2 .0) were 90% and 85%, respectively; sensitivity and specificity for detecting CAD by ST depression (> or =1 mm) were 80% and 78%, respectively. The present results suggest that plasma NO/ET-1 ratio is a useful biological marker for predicting CAD.

The pharmacology of bosentan

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

Endothelins in bone cancer metastases

Most evidence indicates that osteoblastic bone metastases are due to tumor-produced factors that stimulate the osteoblast. This review supports a causal role for ET-1. Based on our results, we propose a model to explain the tumor cell and bone interactions that are responsible for the osteoblastic response (Figure 2). Tumor cells housed in bone produce factors, such as ET-1, stimulate osteoblast activity. This results in the abundant and disorganized new bone formation that is characteristic of osteoblastic metastases. The effects of ET-1 to stimulate bone formation are mediated by ETA receptors on the osteoblast. ETA receptor inhibition successfully blocked osteoblastic bone metastases in a mouse model. These receptor antagonists are currently in clinical trials for advanced prostate cancer and bone metastases (Stephenson, 2001; Carducci et al., 2002; 2003). Therefore, the molecular mechanisms responsible for osteoblastic metastases are complex and involve bi-directional interactions between tumor cells and bone. Elucidation of the interactions at a molecular level can identify therapeutic targets for osteoblastic metastases. Although ET-1 and ETA receptors are potential targets for this devastating complication of cancer (Remuzzi et al., 2003), they are certainly not the only ones. The rapid pace of metastasis research, will not only expand our therapeutic armamentarium against bone metastases, but will also provide insight into achieving the ultimate goal: the prevention of cancer metastases to bone.

Endothelin receptor blockers in cardiovascular disease

The endothelin (ET) system is comprised of 4 active ETs, with ET-1 being the predominant isoform in the cardiovascular system. Because of the potent vasoconstricting and mitogenic effects of ET-1 and its involvement in various cardiovascular diseases, blockade of the ET receptor has received considerable attention. ET receptor antagonism has been demonstrated to be beneficial in patients with pulmonary hypertension. The nonselective ET receptor antagonist bosentan improves exercise capacity and increases time to clinical worsening in patients with pulmonary arterial hypertension. The selective ET A receptor antagonist sitaxsentan also improves hemodynamics and exercise capacity in patients with pulmonary arterial hypertension. Results with ET receptor antagonists in congestive heart failure have been disappointing. Although some studies have suggested benefit, larger studies have been neutral. The use of ET receptor antagonists for other conditions has not been fully explored. Future studies with the use of ET receptor antagonists as part of a multidrug regimen are also needed.

Endothelium-dependency of yohimbine-induced corpus cavernosum relaxation

Development and maintenance of penile erection requires the relaxation of the smooth muscle cells in the cavernous bodies and is essentially mediated by nitric oxide (NO). The penile flaccid state is conversely maintained by the alpha adrenergic neuroeffector system and by other vasoconstrictors, such as endothelin-1 (ET-1). In this study we examined the mechanisms involved in yohimbine-induced relaxation in human and rabbit corpora cavernosa (CC). We essentially found that yohimbine not only blocks contractions induced by adrenergic agonists, but also by non-adrenergic substances, such as ET-1. This effect was unrelated to antagonism at the level of ET receptors, because yohimbine did not affect ET-1-induced increase in intracellular calcium in isolated CC cells. Conversely, our data suggest that yohimbine counteracts ET-1-induced contractions by interfering with NO release from the endothelium. In fact, yohimbine-induced CC relaxation was inhibited by the mechanical removing of the endothelium and by blocking NO formation or signalling via guanylate cyclase and cGMP formation. Conversely, yohimbine activity was strongly increased by inhibiting cGMP degradation. In an experimental model of hypogonadism, performed on rabbits by chronic treatment with a long-lasting GnRH agonist, the relaxant yohimbine activity was also decreased, but completely restored by androgen supplementation. This effect was evident only in preparations in which the main source of NO was present (endothelium) or in which NO formation was not impaired by L-NAME. Our data indicate that the relaxant effect of yohimbine is both endothelium and androgen-dependent. This might justify the lack of efficacy of this drug in treatment of some form of organic erectile dysfunction.

BQ-788, a selective endothelin ET(B) receptor antagonist

We describe characteristics of a selective endothelin (ET) ET(B) receptor antagonist, BQ-788 [N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine], which is widely used to demonstrate the role of endogenous or exogenous ETs in vitro and in vivo. In vitro, BQ-788 potently and competitively inhibited (125)I-labeled ET-1 binding to ET(B) receptors in human Girrardi heart cells (hGH) with an IC(50) of 1.2 nM, but only poorly inhibited the binding to ET A receptors in human neuroblastoma cell line SK-N-MC cells (IC(50), 1300 nM). In isolated rabbit pulmonary arteries, BQ-788 showed no agonistic activity up to 10 microM and competitively inhibited the vasoconstriction induced by an ET(B)-selective agonist (pA(2), 8.4). BQ-788 also inhibited several bioactivities of ET-1, such as bronchoconstriction, cell proliferation, and clearance of perfused ET-1. Thus, it is confirmed that BQ-788 is a potent, selective ET(B) receptor antagonist. In vivo, in conscious rats, BQ-788, 3 mg/kg/h, i.v., completely inhibited a pharmacological dose of ET-1- or sarafotoxin6c (S6c) (0.5 nmol/kg, i.v.)-induced ET(B) receptor-mediated depressor, but not pressor responses. Furthermore, BQ-788 markedly increased the plasma concentration of ET-1, which is considered an index of potential ET(B) receptor blockade in vivo. In Dahl salt-sensitive hypertensive (DS) rats, BQ-788, 3 mg/kg/h, i.v., increased blood pressure by about 20 mm Hg. It is reported that BQ-788 also inhibited ET-1-induced bronchoconstriction, tumor growth and lipopolysaccharide-induced organ failure. These data suggest that BQ-788 is a good tool for demonstrating the role of ET-1 and ET(B) receptor subtypes in physiological and/or pathophysiological conditions.

Role of endothelin in cardiovascular disease

Endothelins are a family of peptides, which comprises endothelin-1 (ET-1), endothelin-2 (ET-2) and endothelin-3 (ET-3), each containing 21 amino-acids. ET-1 is a peptide secreted mostly by vascular endothelial cells, the predominant isoform expressed in vasculature and the most potent vasoconstrictor currently known. ET-1 also has inotropic, chemotactic and mitogenic properties. In addition, it influences salt and water homeostasis through its effects on the renin-angiotensin-aldosterone system (RAAS), vasopressin and atrial natriuretic peptide and stimulates the sympathetic nervous system. The overall action of endothelin is to increase blood pressure and vascular tone. Therefore, endothelin antagonists may play an important role in the treatment of cardiac, vascular and renal diseases associated with regional or systemic vasoconstriction and cell proliferation, such as essential hypertension, pulmonary hypertension, chronic heart failure and chronic renal failure. Long-term anti-endothelin therapy may improve symptoms and favourably alter the progression of heart failure. Endothelin appears to participate in induction and progression of sclerotic renal changes, leading to progression to end-stage renal disease. Anti-endothelin therapy might offer additional benefits in the prevention of progression of chronic renal failure in addition to the known benefits of RAAS inhibition. Clinical trials have demonstrated potentially important benefits of endothelin antagonists for patients with essential hypertension, pulmonary hypertension and heart failure. Further studies are necessary to determine the role of anti-endothelin therapy in the treatment of cardiovascular diseases and determine the different roles of selective receptor antagonism vs. mixed ET(A/B)-receptor antagonism in human diseases.

Increased expression of endothelin receptors in human cirrhosis--relationship with splanchnic hemodynamics

The purpose of the present study was to assess the correlation that likely exists among increased portal pressure (Pp), portal blood flow quantity (Qp) and ETA and ETB receptor mRNA expression in human cirrhosis. In situ hybridization and reverse-transcription polymerase chain reactions (RT-PCR) were performed to determined the expression of ETA and ETB receptor mRNA in liver tissues from traumatic subjects (n = 10) and cirrhotic patients (n = 15) in whom hepatic hemodynamic values were measured. The expression of the two transcripts was significantly higher in liver samples of cirrhotic patients than in those obtained from traumatic subjects. It has shown that ETA receptor mRNA predominantly located in hepatic stellate cells (HSCs) and vascular smooth muscle cells of intrahepatic arteries and portal veins, ETB receptor mRNA in HSCs, sinusoidal endothelial cells and Kuppfer cells. There was a highly significant direct relationship between ETA and ETB receptor mRNA and Pp and Qp in cirrhotic patients. It suggests that liver paracrine endothelin system may be overactivated in human cirrhosis accompanied with increased expression of ETA and ETB receptor mRNA which may play an important role in the pathogenesis and maintenance of splanchnic hyperdynamics.

Endothelin-1 production by prostate cancer cell lines is up-regulated by factors involved in cancer progression and down-regulated by androgens

BACKGROUND

Recent data demonstrate that endothelin-1 (ET-1) concentration increases in plasma of men with advanced, hormone-refractory prostate adenocarcinoma. In addition, ET-1 is involved in osteblastic remodelling and new bone formation, suggesting a role for this vasoactive peptide in the metastatic progression of prostate cancer to the bone.

METHODS

We investigated the regulation of ET-1 expression in androgen-sensitive and insensitive prostate cancer cell lines by androgens and several factors involved in progression of prostate cancer (EGF) and bone remodelling (TGFbeta-1, IL1-alpha and IGF-1).

RESULTS

Northern analysis and radio immunoassay demonstrated that all the ET-1 pathways are tuned off in the androgen-sensitive LNCaP cell line when compared to the androgen-insensitive PC-3 and DU145. In PC-3 cells transfected with a full-length androgen receptor expression vector (PC-3-AR), treatment with androgens reduced gene expression and secretion of ET-1 without affecting the gene expression of ET-3. Collectively, these data support a role for androgens in the regulation of ET-1 production by prostate adenocarcinoma cells. In PC-3 and DU145 cells, ET-1 gene expression and secretion were up-regulated by TGFbeta-1, EGF and IL1-alpha, whereas IGF-1 was ineffective. Conversely, none of the treatments affected ECE-1 or ET-3 gene expression.

CONCLUSIONS

In conclusion, ET-1 production by prostate adenocarcinoma cells is down-regulated by androgens and up-regulated by factors involved in tumour progression indicating a role for this peptide in the biology of prostate cancer. In view of the role exerted by ET-1 in the process of bone metastasis, our data suggest the use of ET-1 receptor antagonists in the treatment of advanced prostate cancer.