Activation of ETB receptors regulates the abundance of ET-1 mRNA in vascular endothelial cells

Endothelial dysfunction and inflammation in patients with non-obstructive coronary arteries

Aim To determine levels of markers for endothelial dysfunction and inflammation, endothelin-1, E-selectin, and tumor necrosis factor α (TNF-α) in patients with ischemic heart disease (IHD) and non-obstructive and obstructive coronary artery (CA) disease.Material and methods This study included 32 patients with verified IHD and non-obstructive (main group, n=19) and obstructive (comparison group, n=13) CA disease. Endothelial dysfunction was diagnosed by photoplethysmography and videocapillaroscopy. Serum concentrations of endothelin-1, E-selectin, and TNF- α were measured in all patients.Results Patients with non-obstructive CA disease showed a tendency towards more pronounced endothelial dysfunction (alternative stiffness index, 7.8 m /s [6.35; 9.08]; reflection index, 36.95 % [23.4; 52.65]; capillary density following reactive hyperemia, 54.33 cap /mm2 [48.92; 75.83]; capillary density following venous occlusion, 74.33 cap /mm2 [67.83; 93.00]) compared to the comparison group (alternative stiffness index, 9.05 m/s [7.08; 10.58]; reflection index, 28.25 % [23.35; 53.75]; capillary density following reactive hyperemia, 66.83 cap /mm2 [50.83; 78.67]; capillary density following venous occlusion, 87.0 cap /mm2 [77.58; 78.67]), although statistically significant differences were not found. Concentration of endothelin-1 was significantly higher in the IHD group with non-obstructive CA disease (0.45 ng/ml [0.28;0.65]) compared to patients with CA atherosclerotic stenosis (0.35 ng/ml [0.25; 0.38], p=0.035). Concentrations of E-selectin did not significantly differ between the groups (main group, 21.1 ng/ml [18.45; 35.03]; comparison group, 28.55 ng/ml [19.08; 35.01], p=0.29). In both groups, concentrations of TNF-α did not exceed the lower threshold of sensitivity (<2.3 pg/ml).Conclusion Endothelial dysfunction and increased endothelin-1 in patients with non-obstructive CA disease along with inflammation may additionally contribute to the pathogenesis of IHD in the absence of hemodynamically significant CA stenoses. Too low level of TNFα in both groups prevented us from using it as a diagnostic marker. Further study is needed that would include a greater number of patients and a search for alternative markers.

Induction of endothelium-dependent constriction of mesenteric arteries in endotoxemic hypotensive shock

BACKGROUND AND PURPOSE

Effective management of hypotension refractory to vasoconstrictors in severe sepsis is limited. A new strategy to ameliorate endotoxemic hypotension by inducing endothelium-dependent constriction of large arteries was assessed.

EXPERIMENTAL APPROACH

Endotoxemia in rats was induced by injection of LPS (10 mg·kg(-1), i.v.). Haemodynamics were measured in vivo, reactivity of isolated mesenteric arteries by myography and expression of proteins and enzyme activities by immunohistochemistry, biochemistry and molecular biology.

KEY RESULTS

Six hours after LPS, the hypotension was promptly reversed following injection (i.v. or i.p.) of oroxylin-A (OroA) . In isolated LPS-treated but not normal mesenteric arteries, OroA (1-10 μM) induced endothelium-dependent, sustained constriction, blocked by endothelin-1 (ET-1) receptor antagonists. OroA further enhanced LPS-induced expression of endothelin-converting enzyme, ET-1 mRNA and proteins and ET-1 release, OroA also enhanced phosphorylation of Rho-associated protein kinase (ROCK) and reversed LPS-induced suppression of RhoA activities in smooth muscle of arteries with endothelium. Activated- phosphorylation of smooth muscle ROCK was blocked by ET-1-receptor antagonists and ROCK inhibitors. Moreover, OroA post-treatment suppressed, via inhibiting NF-κB activation, inducible NOS expression and circulating NO.

CONCLUSIONS AND IMPLICATIONS

Reversal of endotoxemic hypotensive by OroA was due to release of endothelial ET-1, upregulated by LPS, from mesenteric arteries, inducing prompt and sustained vasoconstriction via activation of vascular smooth muscle RhoA/ROCK-pathway. In late endotoxemia, OroA-induced vasoconstriction was partly due to decreased circulating NO. Activation of endothelium-dependent constriction in large resistance arteries and suppression of systemic inflammation offer new strategies for acute management of endotoxemic hypotensive shock.

Clinical pharmacokinetics and pharmacodynamics of the endothelin receptor antagonist macitentan

Pulmonary arterial hypertension (PAH) is a progressive disease of the lung vascular system, which leads to right-sided heart failure and ultimately death if untreated. Treatments to regulate the pulmonary vascular pressure target the prostacyclin, nitric oxide, and endothelin (ET) pathways. Macitentan, an oral, once-daily, dual ET_A and ET_B receptor antagonist with high affinity and sustained receptor binding is the first ET receptor antagonist to show significant reduction of the risk of morbidity and mortality in PAH patients in a large-scale phase III study with a long-term outcome. Here we present a review of the available clinical pharmacokinetic, pharmacodynamic, pharmacokinetic/pharmacodynamic relationship, and drug–drug interaction data of macitentan in healthy subjects, patients with PAH, and in special populations.

Pharmacokinetic and pharmacodynamic evaluation of macitentan , a novel endothelin receptor antagonist for the treatment of pulmonary arterial hypertension

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a chronic disorder of the pulmonary vasculature characterized by elevated mean pulmonary arterial pressure eventually leading to right-sided heart failure and premature death. Macitentan is an oral, once-daily, dual endothelin (ET)A and ETB receptor antagonist with high affinity and sustained receptor binding that was approved in the USA, Europe, Canada, and Switzerland for the treatment of PAH.

AREAS COVERED

This review discusses the pharmacokinetics (PK) and pharmacodynamics (PD) of macitentan and its drug interaction potential based on preclinical and clinical data.

EXPERT OPINION

Up to date, macitentan is the only registered treatment for PAH that significantly reduced morbidity and mortality as a combined endpoint in a long-term event-driven study. The safety profile of macitentan is favorable with respect to hepatic safety and edema/fluid retention and may be better than that of other ET receptor antagonists such as bosentan and ambrisentan. The PK profile supports a once-a-day dosing regimen. Macitentan has limited interactions with other drugs. Based on these characteristics macitentan is an important new addition to the treatment of PAH.

Microenvironmental stimuli affect Endothelin-1 signaling responsible for invasiveness and osteomimicry of bone metastasis from breast cancer

The present study was undertaken to clarify the function(s) of Endothelin-1 and its receptors ETAR and ETBR in osteolytic-bone metastasis from breast cancer, and their regulation by hepatocyte and transforming growth factors (HGF, TGF-β) and hypoxia. The aim was to evaluate the adaptability of bone metastasis to microenvironmental stimuli through Endothelin-1-mediated epithelial-mesenchymal transition (EMT), or the reverse process MET, and through osteomimicry possible key features for bone colonization. We compared low (MCF-7) and high (MDA-MB231) invasive-breast carcinoma cells, and 1833-bone metastatic clone, with human pair-matched primary breast-carcinomas and bone metastases. Parental MDA-MB231 and the derived 1833-clone responded oppositely to the stimuli. In 1833 cells, TGF-β and hypoxia increased Endothelin-1 release, altogether reducing invasiveness important for engraftment, while Endothelin-1 enhanced MDA-MB231 cell invasiveness. The Endothelin-1-autocrine loop contributed to the cooperation of intracellular-signaling pathways and extracellular stimuli triggering MET in 1833 cells, and EMT in MDA-MB231 cells. Only in 1833 cells, HGF negatively influenced transactivation and release of Endothelin-1, suggesting a temporal sequence of these stimuli with an initial role of HGF-triggered Wnt/β-catenin pathway in metastatization. Then, Endothelin-1/ETAR conferred MET and osteomimetic phenotypes, with Runt-related transcription factor 2 activation and metalloproteinase 9 expression, contributing to colonization and osteolysis. Findings with human pair-matched primary ductal carcinomas and bone metastases gave a translational significance to the molecular study. Endothelin-1, ETAR and ETBR correlated with the acquisition of malignant potential, because of high expression already in the in situ carcinoma. These molecular markers might be used as predictive index of aggressive behavior and invasive/metastatic phenotype.

Aliskiren, exendin-4, and insulin: their impact on endothelin receptor subtype(s) regulation/binding in type 1 diabetic rat hearts

This study focuses on the impact of aliskiren and (or) glucagon-like peptide-1 analogue on the binding affinity/regulation of endothelin-1 (ET-1) to its receptor subtypes A (ETAR) and B (ETBR) at the level of the coronary endothelium and the cardiomyocytes in a type-1 diabetic rat model. Seven groups were used: (i) normal rats, (ii) rats with induced diabetes, (iii) rats with induced diabetes that were treated with insulin, (iv) rats with induced diabetes that were treated with exendin-4, (v) rats with induced diabetes that were treated with aliskiren, (vi) rats with induced diabetes that were co-treated with insulin plus aliskiren, and (vii) rats with induced diabetes that were co-treated with exendin-4 plus aliskiren. Heart perfusion with [125I]-ET-1 was employed to estimate ET-1 binding affinity (τ = 1/K–n) to ETAR and ETBR at the level of the coronary endothelium and the cardiomyocytes. Plasma ET-1 levels were measured using enzyme immunoassay, whereas densities of ETAR and ETBR were detected using Western blot. No significance differences were detected in the τ of ETAR and ETBR between normal and diabetic in cardiomyocytes and the coronary endothelium. Exendin-4 normalized the τ value for ETAR and ETBR on coronary endothelium, while aliskiren normalized it on cardiomyocytes. Furthermore, ETAR and ETBR densities were normalized with monotreatments of aliskiren and exendin-4, compared with up-regulated ETAR and down-regulated ETBR band densities in the diabetic animals. Our data indicate that aliskiren alleviates diabetes-associated hypertrophy in type 1 diabetes mellitus.

Intracrine endothelin signaling evokes IP3-dependent increases in nucleoplasmic Ca²⁺ in adult cardiac myocytes

Endothelin receptors are present on the nuclear membranes in adult cardiac ventricular myocytes. The objectives of the present study were to determine 1) which endothelin receptor subtype is in cardiac nuclear membranes, 2) if the receptor and ligand traffic from the cell surface to the nucleus, and 3) the effect of increased intracellular ET-1 on nuclear Ca(2+) signaling. Confocal microscopy using fluorescently-labeled endothelin analogs confirmed the presence of ETB at the nuclear membrane of rat cardiomyocytes in skinned-cells and isolated nuclei. Furthermore, in both cardiac myocytes and aortic endothelial cells, endocytosed ET:ETB complexes translocated to lysosomes and not the nuclear envelope. Although ETA and ETB can form heterodimers, the presence or absence of ETA did not alter ETB trafficking. Treatment of isolated nuclei with peptide: N-glycosidase F did not alter the electrophoretic mobility of ETB. The absence of N-glycosylation further indicates that these receptors did not originate at the cell surface. Intracellular photolysis of a caged ET-1 analog ([Trp-ODMNB(21)]ET-1) evoked an increase in nucleoplasmic Ca(2+) ([Ca(2+)]n) that was attenuated by inositol 1,4,5-trisphosphate receptor inhibitor 2-aminoethoxydiphenyl borate and prevented by pre-treatment with ryanodine. A caged cell-permeable analog of the ETB-selective antagonist IRL-2500 blocked the ability of intracellular cET-1 to increase [Ca(2+)]n whereas extracellular application of ETA and ETB receptor antagonists did not. These data suggest that 1) the endothelin receptor in the cardiac nuclear membranes is ETB, 2) ETB traffics directly to the nuclear membrane after biosynthesis, 3) exogenous endothelins are not ligands for ETB on nuclear membranes, and 4) ETB associated with the nuclear membranes regulates nuclear Ca(2+) signaling.

G protein-coupled receptor signalling in the cardiac nuclear membrane: evidence and possible roles in physiological and pathophysiological function

G protein-coupled receptors (GPCRs) play key physiological roles in numerous tissues, including the heart, and their dysfunction influences a wide range of cardiovascular diseases. Recently, the notion of nuclear localization and action of GPCRs has become more widely accepted. Nuclear-localized receptors may regulate distinct signalling pathways, suggesting that the biological responses mediated by GPCRs are not solely initiated at the cell surface but may result from the integration of extracellular and intracellular signalling pathways. Many of the observed nuclear effects are not prevented by classical inhibitors that exclusively target cell surface receptors, presumably because of their structures, lipophilic properties, or affinity for nuclear receptors. In this topical review, we discuss specifically how angiotensin-II, endothelin, β-adrenergic and opioid receptors located on the nuclear envelope activate signalling pathways, which convert intracrine stimuli into acute responses such as generation of second messengers and direct genomic effects, and thereby participate in the development of cardiovascular disorders.

ETA and ETB receptors are expressed in vascular adventitial fibroblasts

The adventitia has been recognized to play important roles in vascular oxidative stress, remodeling, and contraction. We recently demonstrated that adventitial fibroblasts are able to express endothelin (ET)-1 in response to ANG II. However, it is unclear whether ET-1 receptors are expressed in the adventitia. We therefore investigated the expression and roles of both ET(A) and ET(B) receptors in collagen synthesis and ET-1 clearance in adventitial fibroblasts. Adventitial fibroblasts were isolated and cultured from the mouse thoracic aorta by the explant method. Cultured cells were treated with ANG II (100 nmol/l) or ET-1 (10 pM) in the presence or absence of the ANG II type 1 receptor antagonist losartan (100 μM), the ET-1 receptor antagonists BQ-123 (ET(A) receptor, 1 μM) and BQ-788 (ET(B) receptor, 1 μM), and the ET(B) receptor agonist sarafotoxin 6C (100 nM). ET-1 peptide levels were determined by ELISA, whereas ET(A), ET(B), and collagen levels were determined by Western blot analysis. ANG II increased ET-1 peptide levels in a time-dependent manner. ANG II increased ET(A) and ET(B) receptor protein levels as well as collagen in a similar fashion. ANG II-induced collagen was reduced while in the presence of BQ-123, suggesting a role for the ET(A) receptor in the regulation of the extracellular matrix. ANG II treatment in the presence of BQ-788 significantly increased ET-1 peptide levels. Conversely, the ET(B) receptor agonist sarafotoxin 6C significantly decreased ET-1 peptide levels. These data implicate a role for the ET(B) receptor in the clearance of the ET-1 peptide. In conclusion, both ET(A) and ET(B) receptors are expressed in adventitial fibroblasts, which paves the ground for the biological significance of adventitial ET-1. The ET(A) receptor subtype mediates collagen I expression, whereas the ET(B) receptor subtype may play a protective role through increasing the clearance of the ET-1 peptide.

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.

Endothelium-derived endothelin-1

One year after the revelation by Dr. Furchgott 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 acid) 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 tagged as "a bad guy." The discovery of two receptor subtypes in 1990, ET(A) and ET(B), permitted optimization of the first dual ET-1 receptor antagonist in 1993 by Dr. Clozel's team, who entered clinical development with bosentan, which was offered to patients with pulmonary arterial hypertension in 2001. The revelation of Dr. Furchgott opened a Pandora's box with ET-1 as one of the actors. In this brief review, we will discuss the physiological and pathophysiological role of endothelium-derived ET-1 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 in this review because it is the most susceptible to endothelial dysfunction, but references to the 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 nitric oxide and ET-1.

Endothelium in pharmacology: 30 years on

In this issue, BJP is proud to publish an Endothelium Themed Section to celebrate the life of Robert F. Furchgott, who died on May 19th 2009. It is 30 years since he discovered endothelium-derived relaxant factor and a decade since he was awarded the Nobel Prize for this work. His discovery has led to an array of new therapeutic targets. The themed section includes three reviews on the pathophysiology of the endothelium and the drug targets that this presents, four research papers and three commentaries on research. This themed section also forms the nucleus of an online Virtual Issue that collects in one place further reviews and research papers on the topic of the 'Endothelium' that BJP and our sister journal BJCP have published in the past year, and that should help researchers and students to find the latest work in this field.

Robert F. Furchgott, Nobel laureate (1916-2009)--a personal reflection

Robert F. Furchgott, pharmacologist and joint winner of the Nobel Prize for Medicine or Physiology (1998) died on the 12th of May 2009 aged 92. By unlocking the astonishingly diverse biological actions of nitric oxide, Furchgott leaves behind a rich legacy that has both revolutionized our understanding of human physiology and stimulated new and exciting opportunities for drug development in a wide range of pathological conditions. In this article, William Martin, who worked with Furchgott for 2 years (1983-1985), following the exciting discovery of endothelium-derived relaxing factor/nitric oxide, pays tribute to his close friend and colleague.

NF-kappaB activation, dependent on acetylation/deacetylation, contributes to HIF-1 activity and migration of bone metastatic breast carcinoma cells

Here, we show that NF-kappaB-HIF-1 interaction contributed to breast cancer metastatic capacity by means of an incomplete epithelial/mesenchymal transition and influencing migration, as shown in 1833 (human) and 4T1 (mouse) metastatic cells after different stimuli. The 1833 and the transforming growth factor-beta1-exposed 4T1 cells showed both epithelial (E-cadherins) and mesenchymal (N-cadherins and vimentin) markers, and common mechanisms contributed to the retention of certain epithelial characteristics and the control of migration. The complex NF-kappaB-HIF-1 reciprocal regulation and the enhanced c-Jun expression played a functional role in exacerbating the invasiveness of 1833 cells after p50/p65 transfection and of 4T1 cells exposed to transforming growth factor-beta1. Twist expression seemed to exert a permissive role also regulating epithelial/mesenchymal transition markers. After c-Src wild-type (Srcwt) transfection, c-Src-signal transducer overexpression in 1833 cells increased HIF-1 transactivating activity and invasiveness, and changed E-cadherin/N-cadherin ratio versus mesenchymal phenotype. The transcription factor pattern and the motile phenotype of metastatic 1833 cells were influenced by p65-lysine acetylation and HDAC-dependent epigenetic mechanisms, which positively regulated basal NF-kappaB and HIF-1 activities. However, HDAC3 acted as a corepressor of NF-kappaB activity in parental MDA-MB231 cells, thus explaining many differences from the derived 1833 clone, including reduced HIF-1alpha and c-Jun expression. Invasiveness was differently affected by HDAC knockdown in 1833 and MDA-MB231 cells. We suggest that acetylation/deacetylation are critical in establishing the bone-metastatic gene signature of 1833 cells by regulating the activity of NF-kappaB and HIF-1, and further clarify the epigenetic control of transcription factor network in the motile phenotype of 1833 cells.

The mating response cascade does not modulate changes in the steady-state level of target mRNAs through control of mRNA stability

Many extracellular signals trigger changes in gene expression by altering the steady-state level of target transcripts. This modulation of transcript levels is typically ascribed to changes in transcription of target genes; however, there are numerous examples of changes in mRNA processing and stability that contribute to the overall change in transcript levels following signalling pathway activation. The alpha-factor-stimulated mating pathway in Saccharomyces cerevisiae is a receptor-operated MAP kinase cascade that results in increased levels of a large number of target mRNA transcripts when stimulated acutely. A previous study identified many of the transcripts modulated in response to alpha-factor and argued, based on genetic studies, that the response occurred solely at the level of gene transcription (Roberts et al., 2000). We directly examined whether enhanced mRNA stability contributes to the increase in the steady-state level of alpha-factor target transcripts by exploiting a temperature-sensitive RNA Polymerase II mutant, a Ste12 transcription factor import mutant, and tet-regulated synthetic mating factor minigene reporters. Examination of a panel of alpha-factor-responsive transcripts reveals no change in mRNA stability in response to alpha-factor stimulation, providing direct evidence that this signal transduction pathway in S. cerevisiae does not function through modulating transcript stability.