Subcellular mechanisms of endothelin action in vascular system

The Anti-Atherosclerotic Effects of Endothelin Receptor Antagonist, Bosentan, in Combination with Atorvastatin-An Experimental Study

Bosentan, an endothelin receptor antagonist (ERA), has potential anti-atherosclerotic properties. We investigated the complementary effects of bosentan and atorvastatin on the progression and composition of the atherosclerotic lesions in diabetic mice. Forty-eight male ApoE-/- mice were fed high-fat diet (HFD) for 14 weeks. At week 8, diabetes was induced with streptozotocin, and mice were randomized into four groups: (1) control/COG: no intervention; (2) ΒOG: bosentan 100 mg/kg/day per os; (3) ATG: atorvastatin 20 mg/kg/day per os; and (4) BO + ATG: combined administration of bosentan and atorvastatin. The intra-plaque contents of collagen, elastin, monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-a (TNF-a), matrix metalloproteinases (MMP-2, -3, -9), and TIMP-1 were determined. The percentage of lumen stenosis was significantly lower across all treated groups: BOG: 19.5 ± 2.2%, ATG: 12.8 ± 4.8%, and BO + ATG: 9.1 ± 2.7% compared to controls (24.6 ± 4.8%, p < 0.001). The administration of both atorvastatin and bosentan resulted in significantly higher collagen content and thicker fibrous cap versus COG (p < 0.01). All intervention groups showed lower relative intra-plaque concentrations of MCP-1, MMP-3, and MMP-9 and a higher TIMP-1concentration compared to COG (p < 0.001). Importantly, latter parameters presented lower levels when bosentan was combined with atorvastatin compared to COG (p < 0.05). Bosentan treatment in diabetic, atherosclerotic ApoE-/- mice delayed the atherosclerosis progression and enhanced plaques' stability, showing modest but additive effects with atorvastatin, which are promising in atherosclerotic cardiovascular diseases.

Potentiation of P2X3 receptor mediated currents by endothelin-1 in rat dorsal root ganglion neurons

Endothelin-1 (ET-1), an endogenous vasoconstrictor, has been known as a pro-nociceptive agent involved in multitude of pain. ET-1 acts on endothelin receptors on vascular endothelial cells, sensitizes release of ATP, which then acts on P2X3 receptors on nociceptors and results in mechanical hyperalgesia. Both endothelin receptors and P2X3 receptors are present in primary sensory neuron, where it remains unclear whether there is an interaction between them. Herein, we reported that ET-1 potentiated the electrophysiological activity of P2X3 receptors in rat dorsal root ganglia (DRG) neurons. ET-1 concentration-dependently increased α,β-methylene-ATP (α,β-meATP)-evoked inward currents, which were mediated by P2X3 receptors. ET-1 shifted the α,β-meATP concentration-response curve upwards, with an increase of 34.38 ± 4.72% in the maximal current response to α,β-meATP in the presence of ET-1. ET-1 potentiation of α,β-meATP-evoked currents was voltage-independent. ET-1 potentiated P2X3 receptor-mediated currents through endothelin-A receptors (ET_AR), but not endothelin-B receptors (ET_BR). ET-1 potentiation was supressed by blockade of intracellular G-protein or protein kinase C (PKC) signaling. Moreover, there is a synergistic effect on mechanical allodynia induced by intraplantar injection of ET-1 and α,β-meATP in rats. Pharmacological blockade of P2X3 receptors also alleviated ET-1-induced mechanical allodynia. These results suggested that ET-1 sensitized P2X3 receptors in primary sensory neurons via an ET_AR and PKC signaling pathway. Our data provide evidence that cutaneous ET-1 induced mechanical allodynia not only by increasing the release of ATP from vascular endothelial cells, but also by sensitizing P2X3 receptors on nociceptive DRG neurons.

Endothelin-1 enhances acid-sensing ion channel currents in rat primary sensory neurons

Endothelin-1 (ET-1), an endogenous vasoactive peptide, has been found to play an important role in peripheral pain signaling. Acid-sensing ion channels (ASICs) are key sensors for extracellular protons and contribute to pain caused by tissue acidosis. It remains unclear whether an interaction exists between ET-1 and ASICs in primary sensory neurons. In this study, we reported that ET-1 enhanced the activity of ASICs in rat dorsal root ganglia (DRG) neurons. In whole-cell voltage-clamp recording, ASIC currents were evoked by brief local application of pH 6.0 external solution in the presence of TRPV1 channel blocker AMG9810. Pre-application with ET-1 (1−100 nM) dose-dependently increased the proton-evoked ASIC currents with an EC₅₀ value of 7.42 ± 0.21 nM. Pre-application with ET-1 (30 nM) shifted the concentration–response curve of proton upwards with a maximal current response increase of 61.11% ± 4.33%. We showed that ET-1 enhanced ASIC currents through endothelin-A receptor (ET_AR), but not endothelin-B receptor (ET_BR) in both DRG neurons and CHO cells co-expressing ASIC3 and ET_AR. ET-1 enhancement was inhibited by blockade of G-protein or protein kinase C signaling. In current-clamp recording, pre-application with ET-1 (30 nM) significantly increased acid-evoked firing in rat DRG neurons. Finally, we showed that pharmacological blockade of ASICs by amiloride or APETx2 significantly alleviated ET-1-induced flinching and mechanical hyperalgesia in rats. These results suggest that ET-1 sensitizes ASICs in primary sensory neurons via ET_AR and PKC signaling pathway, which may contribute to peripheral ET-1-induced nociceptive behavior in rats.

Drug-likeness prediction of chemical constituents isolated from Chinese materia medica Ciwujia

ETHNOPHARMACOLOGICAL RELEVANCE

Ciwujia (CWJ), one of the most commonly used Chinese materia medicas (CMMs), is derived from the roots, rhizomes, and stems of Acanthopanax senticosus harms (AS). CWJ has been used for the treatment of various central nervous system (CNS) and peripheral system diseases. Drug-likeness prediction can help to analyze the absorption, distribution, metabolism, and excretion (ADME) processes of the compounds in CWJ, as well as their potential therapeutic and toxic effects, which is of significance in the confirmation of the active material bases of CWJ.

MATERIALS AND METHODS

The ADME properties of the compounds were calculated through web based PreADMET program and ACD/I-Lab 2.0. The potential therapeutic and toxicity targets of these compounds were screened by the ChemQuery tool in DrugBank and T3DB.

RESULTS

14/39 compounds had moderate or good oral bioavailability (OB). 29/39 compounds bound weakly to the plasma proteins. 18/39 compounds might pass across the blood-brain barrier (BBB). Most of these compounds showed low renal excretion ability. 25/39 compounds had 99 structurally similar drugs and 158 potential therapeutic targets. Additionally, 17/39 compounds had 53 structurally similar toxins and 126 potential toxicity targets.

CONCLUSION

Our study suggests that these compounds have a certain drug-likeness potentials, which are also likely to be the material bases of CWJ. These results may provide a reference for the safe use of CWJ and the expansion of its application scope.

Comparative safety and tolerability of endothelin receptor antagonists in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a condition that leads to progressive right heart failure and death unless recognized and treated early. Endothelin, a potent endogenous vasoconstrictor, has been identified as an important mediator of PAH. Endothelin receptor antagonists (ERAs) have been associated with an improvement in exercise capacity and time to clinical worsening in patients with Group 1 PAH, and three different ERAs are currently approved for use in this population: bosentan, ambrisentan, and macitentan. While all three ERAs are generally well-tolerated, they each have important adverse effects that need to be recognized and monitored. In particular, they may cause anemia, peripheral edema, and mild cardiac, respiratory, neurologic, and gastrointestinal adverse effects to varying degrees. Although bosentan increases a patient's risk of developing liver transaminitis, ambrisentan and macitentan do not appear to confer the same risk of hepatotoxicity at this time. Important drug-drug interactions, particularly involving other drugs metabolized via the cytochrome P450 pathway, are important to recognize when prescribing ERAs. In this review, we provide a brief overview of the current state of knowledge as it relates to the adverse effect profiles, tolerability, and drug-drug interactions of this class of medication as informed by the results of randomized clinical trials, drug surveillance programs, and regulatory agencies.

Endothelin contributes to blunted renal autoregulation observed with a high-salt diet

Autoregulation of renal blood flow (RBF) is an essential function of the renal microcirculation that has been previously shown to be blunted by excessive dietary salt. Endogenous endothelin 1 (ET-1) is increased following a high-salt (HS) diet and contributes to the control of RBF but the differential effects of ET-1 on renal microvessel autoregulation in response to HS remain to be established. We hypothesized that a HS diet increases endothelin receptor activation in normal Sprague-Dawley rats and blunts autoregulation of RBF. The role of ET-1 in the blunted autoregulation produced by a HS diet was assessed in vitro and in vivo using the blood-perfused juxtamedullary nephron preparation and anesthetized rats, respectively. Using highly selective antagonists, we observed that blockade of either ETA or ETB receptors was sufficient to restore normal autoregulatory behavior in afferent arterioles from HS-fed rats. Additionally, normal autoregulatory behavior was restored in vivo in HS-fed rats by simultaneous ETA and ETB receptor blockade, whereas blockade of ETB receptors alone showed significant improvement of normal autoregulation of RBF. Consistent with this observation, autoregulation of RBF in ETB receptor-deficient rats fed HS was similar to both ETB-deficient rats and transgenic control rats on normal-salt diets. These data support the hypothesis that endogenous ET-1, working through ETB and possibly ETA receptors, contributes to the blunted renal autoregulatory behavior in rats fed a HS diet.

Evidence for the endothelin system as an emerging therapeutic target for the treatment of chronic pain

Many people worldwide suffer from pain and a portion of these sufferers are diagnosed with a chronic pain condition. The management of chronic pain continues to be a challenge, and despite taking prescribed medication for pain, patients continue to have pain of moderate severity. Current pain therapies are often inadequate, with side effects that limit medication adherence. There is a need to identify novel therapeutic targets for the management of chronic pain. One potential candidate for the treatment of chronic pain is therapies aimed at modulating the vasoactive peptide endothelin-1. In addition to vasoactive properties, endothelin-1 has been implicated in pain transmission in both humans and animal models of nociception. Endothelin-1 directly activates nociceptors and potentiates the effect of other algogens, including capsaicin, formalin, and arachidonic acid. In addition, endothelin-1 has been shown to be involved in inflammatory pain, cancer pain, neuropathic pain, diabetic neuropathy, and pain associated with sickle cell disease. Therefore, endothelin-1 may prove a novel therapeutic target for the relief of many types of chronic pain.

Endothelin antagonists in hypertension and kidney disease

The endothelin (ET) system seems to play a pivotal role in hypertension and in proteinuric kidney disease, including the micro- and macro-vascular complications of diabetes. Endothelin-1 (ET-1) is a multifunctional peptide that primarily acts as a potent vasoconstrictor with direct effects on systemic vasculature and the kidney. ET-1 and ET receptors are expressed in the vascular smooth muscle cells, endothelial cells, fibroblasts and macrophages in systemic vasculature and arterioles of the kidney, and are associated with collagen accumulation, inflammation, extracellular matrix remodeling, and renal fibrosis. Experimental evidence and recent clinical studies suggest that endothelin receptor blockade, in particular selective ETAR blockade, holds promise in the treatment of hypertension, proteinuria, and diabetes. Concomitant blockade of the ETB receptor is not usually beneficial and may lead to vasoconstriction and salt and water retention. The side-effect profile of ET receptor antagonists and relatively poor antagonist selectivity for ETA receptor are limitations that need to be addressed. This review will discuss what is currently known about the endothelin system, the role of ET-1 in the pathogenesis of hypertension and kidney disease, and summarize literature on the therapeutic potential of endothelin system antagonism.

The possible potential therapeutic targets for drug induced gingival overgrowth

Gingival overgrowth is a side effect of certain medications. The most fibrotic drug-induced lesions develop in response to therapy with phenytoin, the least fibrotic lesions are caused by cyclosporin A, and the intermediate fibrosis occurs in nifedipine-induced gingival overgrowth. Fibrosis is one of the largest groups of diseases for which there is no therapy but is believed to occur because of a persistent tissue repair program. During connective tissue repair, activated gingival fibroblasts synthesize and remodel newly created extracellular matrix. Proteins such as transforming growth factor (TGF), endothelin-1 (ET-1), angiotensin II (Ang II), connective tissue growth factor (CCN2/CTGF), insulin-like growth factor (IGF), and platelet-derived growth factor (PDGF) appear to act in a network that contributes to the development of gingival fibrosis. Since inflammation is the prerequisite for gingival overgrowth, mast cells and its protease enzymes also play a vital role in the pathogenesis of gingival fibrosis. Drugs targeting these proteins are currently under consideration as antifibrotic treatments. This review summarizes recent observations concerning the contribution of TGF-β, CTGF, IGF, PDGF, ET-1, Ang II, and mast cell chymase and tryptase enzymes to fibroblast activation in gingival fibrosis and the potential utility of agents blocking these proteins in affecting the outcome of drug-induced gingival overgrowth.

[Pulmonary hypertension: from molecular pathophysiology to haemodynamic abnormalities]

Pulmonary hypertension (PH) is a complex disorder resulting from many etiologies that cause disturbances of normal pulmonary haemodynamics. Recent breakthroughs have led to a better understanding of the pathophysiology of the disease. In PH, haemodynamic disturbances are closely linked to structural changes and excessive remodeling of pulmonary vessels, leading to progressive narrowing of the pulmonary vascular lumen. Imbalances between pulmonary vasoconstrictors and vasodilators on the one hand, and factors favoring cell proliferation and apoptosis on the other hand, probably account for most cases of PH. This review aims to update readers with the current knowledge on the molecular physiopathology of PH and how this can progress the therapeutic of this disorder.

Axonal protection achieved by blockade of sodium/calcium exchange in a new model of ischemia in vivo

Ischemic white matter injury has been relatively little studied despite its importance to the outcome of stroke. To aid such research a new rat model has been developed in vivo and used to assess whether blockade of the sodium/calcium exchanger is effective in protecting central axons from ischemic injury. Vasoconstrictive agent endothelin-1 was injected into the rat spinal cord to induce ischemia. KB-R7943 or SEA0400 was administered systemically to block the operation of the sodium/calcium exchanger. Endothelin-1 caused profound reduction of local blood perfusion and resulted in a prompt loss of axonal conduction. Whereas recovery of conduction following vehicle administration was only to 10.5 ± 9% of baseline (n = 8) 4.5 h after endothelin-1 injection, recovery following KB-R7943 (30 mg/kg, i.a.) administration was increased to 35 ± 9% of baseline (n = 6; P < 0.001). SEA0400 (30 mg/kg, i.a.) was also protective (33.2 ± 6% of baseline, n = 4; P < 0.001). Neither drug improved conduction by diminishing the severity of the ischemia. The protective effect of KB-R7943 persisted for at least 3 days after ischemia, as it improved axonal conduction (76.3 ± 11% for KB-R7943 vs. 51.0 ± 19% for vehicle; P < 0.01) and reduced lesion area (55.6 ± 15% for KB-R7943 vs. 77.9 ± 9% for vehicle; P < 0.01) at this time. In conclusion, a new model of white matter ischemia has been introduced suitable for both structural and functional studies in vivo. Blocking the sodium/calcium exchanger protects central axons from ischemic injury in vivo.

Contribution of Ras farnesyl transferase, MAP kinase and cytochrome P-450 metabolites to endothelin-1 induced hypertension

Endothelin 1 (ET-1) is vasoactive peptide that acts via ET-A receptors coupling inducing vascular smooth muscle cell proliferation and contraction. ET-1 is involved in the development and maintenance of hypertension. Aim of this study was to determine the contribution of Ras farnesyl transferase, mitogen activated protein kinase (MAP kinase) and cytochrome P¬450 (CYP450) metabolites to ET-1 induced hypertension. ET-1 (5 pmol/kg per minute) was chronically infused into to the jugular vein by use of mini-osmotic pump for 9 days in male Sprague-Dawley rats. Mean arterial blood pressure (MABP) in ET-1-treated rats was 154±2 mm Hg (hypertensive rats) compared with 98±3 mm Hg in control (normotensive) rats. Infusion of Ras farnesyl transferase inhibitor FPTIII (138 ng/min), MAP kinase inhibitor PD-98059 (694 ng/min) and CYP450 inhibitor 17-ODYA (189 ng/min) significantly attenuated MABP to 115±2.5 mm Hg, 109±3 mm Hg and 118±1.5 mm Hg, respectively. These results suggest that CYP-450 metabolites and Ras/MAP kinase pathway contribute to the development of ET-1 induced hypertension. Further investigation has to be done to confirm whether activation of RAS/MAP kinase pathway by arachidonic acid metabolites plays an important role in the development of ET-1 induced hypertension.

Regulation of the Pulmonary Circulation in the Fetus and Newborn

During the development of the pulmonary vasculature in the fetus, many structural and functional changes occur to prepare the lung for the transition to air breathing. The development of the pulmonary circulation is genetically controlled by an array of mitogenic factors in a temporo-spatial order. With advancing gestation, pulmonary vessels acquire increased vasoreactivity. The fetal pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility. At birth, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. The striking hemodynamic differences in the pulmonary circulation of the fetus and newborn are regulated by various factors and vasoactive agents. Among them, nitric oxide, endothelin-1, and prostaglandin I2 are mainly derived from endothelial cells and exert their effects via cGMP, cAMP, and Rho kinase signaling pathways. Alterations in these signaling pathways may lead to vascular remodeling, high vasocontractility, and persistent pulmonary hypertension of the newborn.

Endothelin

Endothelin-1 is the most potent vasoconstrictor agent currently identified, and it was originally isolated and characterized from the culture media of aortic endothelial cells. Two other isoforms, termed endothelin-2 and endothelin-3, were subsequently identified, along with structural homologues isolated from the venom of Actractapis engaddensis known as the sarafotoxins. In this review, we will discuss the basic science of endothelins, endothelin-converting enzymes, and endothelin receptors. Only concise background information pertinent to clinical physician is provided. Next we will describe the pathophysiological roles of endothelin-1 in pulmonary arterial hypertension, heart failure, systemic hypertension, and female malignancies, with emphasis on ovarian cancer. The potential intervention with pharmacological therapeutics will be succinctly summarized to highlight the exciting pre-clinical and clinical studies within the endothelin field. Of note is the rapid development of selective endothelin receptor antagonists, which has led to an explosion of research in the field.

Endothelin-1 induced vascular smooth muscle cell proliferation is mediated by cytochrome p-450 arachidonic acid metabolites

Endothelins (ETs) are a family of three peptides (ET-1, ET-2, ET-3) that are implicated in the physiological control of vascular smooth muscle cell (VSMC) and myocardial contractility and growth. ET-1 is vasoactive peptide that acts via ET-A receptors coupling inducing vascular smooth muscle cell contraction. ET-1 is involved in the development and maintenance of hypertension. Aim of this study was to investigate whether ET-1 can induce vascular smooth muscle cell proliferation through arachidonic acid (AA) metabolites formed via cytochrome P¬450 (CYP-450). VSMC proliferation was measured by [3H]thymidine incorporation in cultured cells treated by ET-1 (10 to l00 nmol/L) in presence of different inhibitors of CYP-450 (17-ODYA 5 μmol/L), lipoxygenase (LO) (baicalein 20 μmol/L) and cyclooxygenase (COX) (indomethacin 5 μmol/L). ET-1 (10 to 100 nmol/L) induced VSMC proliferation and this effect was attenuated by CYP-450 inhibitor (17-ODYA) and lipoxygenase (LO) inhibitor (baicalein) but not by cyclooxygenase (COX) inhibitor (indomethacin). CYP-450 and LO metabolites of AA, 20-hydroxyeicosatetraenoic acid (HETE) and 12-HETE increased [3H]thymidine incorporation in VSMC. Inhibitors of MAP kinase (PD-98059 50 μmol/L) and cPLA2 (MAFP 50 μmol/L) attenuated ET-1 as well as 20-HETE induced VSMC proliferation. These results suggest AA metabolites via CYP-450 mediates ET-1 induce VSMC proliferation.

The role of endothelin-1 in the pathogenesis of idiopathic pulmonary fibrosis

The endothelin system participates in a number of critical biologic pathways, including normal wound healing. In addition, emerging basic science, and animal and human data all suggest that endothelin-1 (EDN1, also known as ET-1) is a potentially important contributor in the pathobiology of fibrosing disorders, including those that affect the lung. For example, EDN1 drives fibroblast activation, proliferation, as well as differentiation into myofibroblasts - processes that lead to excessive collagen deposition. Patients with idiopathic pulmonary fibrosis (IPF) have increased levels of EDN1 in both their bronchoalveolar lavage fluid and lung tissue. Beyond this, rodent models suggest that endothelin receptor antagonists can limit bleomycin-induced lung fibrosis. This suggests a biologic rationale for the blockade of EDN1 to limit the evolution of lung fibrosis in humans. Initial results from a trial examining the efficacy of a dual endothelin receptor antagonist suggest that this approach may delay disease progression in a subset of patients with IPF.

Ambrisentan for the treatment of pulmonary arterial hypertension

Ambrisentan is an endothelin receptor antagonist (ERA) that was recently approved for treatment of pulmonary arterial hypertension (PAH). Endothelin (ET) is a potent vasoconstrictor with mitogenic, hypertrophic and pro-inflammatory properties that is upregulated in pulmonary hypertensive diseases. The biologic effects of ET are mediated by 2 cell surface receptors termed ET_A and ET_B. ET_A mediates the vasoconstrictor effect of ET on vascular smooth muscle, whereas ET_B is expressed primarily on vascular endothelial cells where it induces nitric oxide synthesis and acts to clear ET from the circulation. Ambrisentan is the first ET_A selective ERA approved for use in the US. Recently published clinical trials in patients with PAH demonstrate improvement in functional capacity and pulmonary hemodynamics similar to other ET_A selective and non-selective ERAs. Its once daily dosing and lower incidence of serum aminotransferase elevation offer potential advantages over other ERAs, but further experience with this agent is needed to fully understand its long-term efficacy and safety. This review discusses the endothelin family of proteins and receptors and their role in the pathophysiology of pulmonary hypertensive diseases. It also examines the development process, safety profile and clinical trials that have resulted in ambrisentan being approved for treatment of PAH.

[Treatment of pulmonary hypertension associated with connective tissue disease]

Pulmonary hypertension is the most ominous complication of connective tissue diseases and its treatment has been a big challenge to clinicians. Vasodilators including epoprostenol (prostacyclin), bosentan (endothelin-receptor antagonist), and a sildenafil (phosphodiesterase type 5 inhibitor) have recently become available in Japan. These vasodilators may improve exercise tolerance, hemodynamics, activities of daily life, and the life span. In this article, we review an endothelin-receptor antagonist and phosphodiesterase type 5 inhibitor recently approved as treatment modalities for pulmonary hypertension in Japan.

Phosphorylation of Ser166 in RGS5 by protein kinase C causes loss of RGS function

RGS5 is a member of regulators of G protein signaling (RGS) proteins that attenuate heterotrimeric G protein signaling by functioning as GTPase-activating proteins (GAPs). We investigated phosphorylation of RGS5 and the resulting change of its function. In 293T cells, transiently expressed RGS5 was phosphorylated by endogenous protein kinases in the basal state. The phosphorylation was enhanced by phorbol 12-myristate 13-acetate (PMA) and endothelin-1 (ET-1), and suppressed by protein kinase C (PKC) inhibitors, H7, calphostin C and staurosporine. These results suggest involvement of PKC in phosphorylation of RGS5. In in vitro experiments, PKC phosphorylated recombinant RGS5 protein at serine residues. RGS5 protein phosphorylated by PKC showed much lower binding capacity for and GAP activity toward Galpha subunits than did the unphosphorylated RGS5. In cells expressing RGS5, the inhibitory effect of RGS5 on ET-1-induced Ca(2+) responses was enhanced by staurosporine. Mass spectrometric analysis of the phosphorylated RGS5 revealed that Ser166 was one of the predominant phosphorylation sites. Substitution of Ser166 by aspartic acid abolished the binding capacity to Galpha subunits and the GAP activity, and markedly reduced the inhibitory effect on ET-1-induced Ca(2+) responses. These results indicate that phosphorylation at Ser166 of RGS5 by PKC causes loss of the function of RGS5 in G protein signaling. Since this serine residue is conserved in RGS domains of many RGS proteins, the phosphorylation at Ser166 by PKC might act as a molecular switch and have functional significance.

Endothelin-1 and its receptors ET(A) and ET(B) in drug-induced gingival overgrowth

BACKGROUND

The purpose of this study was to study the expression of endothelin-1 (ET-1) and its receptors ETA and ETB in normal human gingiva and cyclosporin-induced gingival fibroblasts.

METHODS

Gingival samples were collected from eight normal healthy individuals, eight patients with periodontitis, and eight patients with cyclosporin A (CsA)-induced gingival overgrowth. Total RNA was extracted from tissue samples, and reverse transcriptase-polymerase chain reaction was performed for ET-1, ETA, and ETB. ET-1 protein was estimated from the tissues by enzyme-linked immunosorbent assay. The expression of ET-1 and its receptors was also examined in gingival fibroblast cells treated with CsA.

RESULTS

ET-1 mRNA expression was significantly higher in patients with CsA-induced gingival overgrowth (P <0.001) than in patients with periodontitis and the controls. ETA mRNA was expressed more than the ETB in all examined samples. In human gingival fibroblasts, ET-1 expression was increased with CsA incorporation compared to controls (P <0.001).

CONCLUSION

These results suggest that CsA can modulate the expression of ET-1 in gingival fibroblasts and CsA-induced gingival overgrowth.

Identification of novel genes associated with dominant follicle development in cattle

Follicle development is regulated by the interaction of endocrine and intrafollicular factors, as well as by numerous intracellular pathways, which involves the transcription of new genes, although not all are known. The aim of the present study was to determine the expression of a set of unknown genes identified by bovine cDNA microarray analysis in theca and granulosa cells of dominant and subordinate follicles, collected at a single stage of the first follicular wave using quantitative real-time polymerase chain reaction. Differences were further examined at three stages of the follicular wave (emergence, selection and dominance) and bioinformatics tools were used to identify these originally unknown sequences. The suggested name function and proposed role for the novel genes identified are as follows: MRPL41 and VDAC2, involved in apoptosis (dominant follicle development); TBC1D1 stimulates cell differentiation (growth associated with dominant follicle selection and development); STX7, promotes phagocytosis of cells (subordinate follicle regression); and SPC22 and EHD3, intracellular signalling (subordinate follicle regression). In conclusion, we have identified six novel genes that have not been described previously in ovarian follicles that are dynamically regulated during dominant follicle development and presumably help mediate intracellular signalling, cell differentiation, apoptosis and phagocytosis, events critical to follicular development.

Endothelin-1 expression correlates with atypical histological features in mammary phyllodes tumours

BACKGROUND AND AIMS

Endothelin-1 expression is increased in infiltrating duct carcinoma and is associated with larger tumour size, higher histological grade and lymphovascular permeation. This has not been evaluated in phyllodes tumours, which are uncommon fibroepithelial lesions with potential for local recurrences or distant metastasis. While the grading of phyllodes tumours depends on a combination of histological parameters, prediction of their behaviour remains difficult.

METHOD

A large series of 461 phyllodes tumours (291 benign, 115 borderline malignant and 55 frankly malignant) were evaluated for endothelin-1 expression in both the epithelial cells and stromal cells by immunohistochemistry; results were correlated with the tumour grade.

RESULTS

For benign phyllodes tumours, the epithelial staining of endothelin was negative, weak, moderate and strong in 6%, 26%, 15% and 53% of cases respectively; results were 4%, 18%, 19% and 59% respectively for borderline and 6%, 18%, 6% and 70% respectively for frankly malignant tumours. For the stromal staining, the negative, weak, moderate and strong staining was 32%, 19%, 18% and 31% respectively for benign phyllodes, 24%, 13%, 10% and 53% respectively for borderline and 8%, 16%, 17% and 59% respectively for frankly malignant tumours. There was correlation between epithelial and stromal staining, and the stromal staining correlated with histological features of stromal cellularity, stromal cell nuclear pleomorphism, margin status and stromal overgrowth.

CONCLUSION

These observations suggest a close relationship between the epithelial and stromal elements in phyllodes tumours; endothelin may play a significant role in the malignant progression of phyllodes tumours.

Signaling pathways involving the sodium pump stimulate NO production in endothelial cells

The cardiac steroid ouabain, a known inhibitor of the sodium pump (Na+, K+ -ATPase), has been shown to release endothelin from endothelial cells when used at concentrations below those that inhibit the pump. The present study addresses the question of which signaling pathways are activated by ouabain in endothelial cells. Our findings indicate that ouabain, applied at low concentrations to human umbilical cord endothelial cells (HUAECs), induces a reaction cascade that leads to translocation of endothelial nitric oxide synthase (eNOS) and to activation of phosphatidylinositol 3-kinase (PI3K). These events are followed by phosphorylation of Akt (also known as protein kinase B, or PKB) and activation of eNOS by phosphorylation. This signaling pathway, which results in increased nitric oxide (NO) production in HUAECs, is inhibited by the PI3K-specific inhibitor LY294002. Activation of the reaction cascade is not due to endothelin-1 (ET-1) binding to the ET-1 receptor B (ETB), since application of the ETB-specific antagonist BQ-788 did not have any effect on Akt or eNOS phosphorylation. The results shown here indicate that ouabain binding to the sodium pump results in the activation of the proliferation and survival pathways involving PI3K, Akt activation, stimulation of eNOS, and production of NO in HUAECs. Together with results from previous publications, the current investigation implies that the sodium pump is involved in vascular tone regulation.

Dual role of macrophages in tumor growth and angiogenesis

During the neoplastic progression, macrophages as well as dendritic and NK cells are attracted into the tumor site and initiate the immune response against transformed cells. They activate and present tumor antigens to T cells, which are then activated to kill tumor cells. However, tumor cells are often capable of escaping the immune machinery. As the immune surveillance is not sufficient anymore, tumor-associated macrophages contribute to tumor progression. It is notable that tumor-associated macrophages promote the proliferation of tumor cells directly by secreting growth factors. They also participate in tumor progression by acting on endothelial cells and thus promoting the neovascularization of the tumor. Tumor-associated macrophages are indeed key protagonists during angiogenesis and promote each step of the angiogenesis cascade.

Difference in the characteristics of ETA-receptor-stimulated response between rat small pulmonary and renal arteries

We investigated the difference in the characteristics of endothelin-1 (ET-1)-induced contraction and the responses of intracellular Ca(2+) concentration ([Ca(2+)](i)) between rat small pulmonary artery and renal artery. ET-1 (30 nM) failed to elicit any contraction in renal arteries pretreated with 3 microM BQ-123, an ETA blocker. However, in the pulmonary artery a combination of BQ-123 and BQ-788, an ETB blocker (5 microM each), only partially inhibited the ET-1-induced contraction (by 25%). To focus on the ETA receptor, in the presence of 5 microM BQ-788, nitric oxide donors (sodium nitroprusside and (+/-)-S-nitroso-N-acetylpenicillamine) and forskolin reduced both the ET-1-induced contraction and increase in [Ca(2+)](i) in both pulmonary and renal arteries. However, the effects were stronger in the renal than in the pulmonary artery. ET-1-induced increase in [Ca(2+)](i) was only partially attenuated by 10 microM verapamil (to 81% of control) in pulmonary arteries but was reduced to 56.1% of control in renal arteries. Our results provide evidence that ET-1 may activate ET receptor(s) insensitive to both BQ-123 and BQ-788 in rat small pulmonary artery, at least under these conditions. Furthermore, the effects of relaxants such as L-type Ca(2+) channel blocker and nitric oxide donors on the ET-1-induced contraction were studied.

Endothelin-1 promotes cell survival in renal cell carcinoma through the ET(A) receptor

Endothelin-1 (ET-1) is a potent vasoconstrictor that has been shown to significantly impact many benign and malignant tissues by signaling through its two cognate receptors: ET(A) and ET(B). As ET-1 has a role in both normal and diseased kidney, we initiated studies to investigate endothelin axis expression and function in renal cell carcinoma (RCC). In this study, relatively high levels of ET-1 were detected in all six human RCC cell lines investigated. RT-PCR and Southern analyses revealed that all six RCC cell lines expressed ET(A) receptor mRNA, while 3/6 cell lines also expressed ET(B) mRNA. High affinity ET-1 binding occurred in all but one RCC cell line and quantitative RT-PCR demonstrated ET(A) mRNA expression in all six cell lines. Methylation of the ET(B) promoter (EDNRB) in 4/6 RCC cell lines was observed, suggesting a mechanism for repressed ET(B) expression. Moreover, methylation occurred in 32/48 of renal tumors and in 27/55 of histologically normal adjacent tissue samples studied, while no methylation was evident in any normal tissue isolated from nephrectomy or at autopsy. Functionally, ET-1 significantly inhibited paclitaxel-induced apoptosis in RCC cells through binding ET(A) with the ET-1 signaling mediated via the PI3-kinase/Akt pathway. Collectively, these data support the therapeutic targeting of the ET(A) receptor as a novel treatment strategy for RCC.

Role of endothelin axis in progression to aggressive phenotype of prostate adenocarcinoma

BACKGROUND

Mitogenic and anti-apoptotic actions of endothelin-1 (ET-1) are mediated through endothelin A (ET(A)) receptors. We investigated endothelin receptor expression in increasingly aggressive phenotype and in vivo effects of combination therapy using ET(A) antagonist with paclitaxel.

METHODS

Dunning prostate cancer cells ranged in aggressiveness from non-tumorigenic G, to tumorigenic, non-metastatic AT-1, and to tumorigenic and metastatic MLL. Binding assays were performed alongside Q-PCR to assess receptor density. MLL xenografts were treated with vehicle, atrasentan, paclitaxel, and paclitaxel+atrasentan.

RESULTS

Saturation binding assays demonstrated endothelin receptor density of MLL and AT-1 cells seven- and threefold higher than G cells, respectively. Q-PCR showed 9- and 4.5-fold greater ET(A) mRNA expression in MLL and AT-1 than G cells, respectively and no endothelin receptor B (ET(B)) expression. Combination therapy had significant effect on reduction of tumor volume than paclitaxel or atrasentan alone.

CONCLUSIONS

ET(A) expression increases in aggressive prostate carcinoma. ET(A) blockade combined with paclitaxel may reduce tumor growth in advanced prostate carcinoma.

Involvement of extracellular Ca2+ influx through voltage-independent Ca2+ channels in endothelin-1 function

This article reviews the types and roles of voltage-independent Ca(2+) channels involved in the endothelin-1 (ET-1)-induced functional responses such as vascular contraction, cell proliferation, and intracellular Ca(2+)-dependent signaling pathways and discusses the molecular mechanisms for the activation of voltage-independent Ca(2+) channels by ET-1. ET-1 activates some types of voltage-independent Ca(2+) channels, such as Ca(2+)-permeable nonselective cation channels (NSCCs) and store-operated Ca(2+) channels (SOCC). Extracellular Ca(2+) influx through these voltage-independent Ca(2+) channels plays essential roles in ET-1-induced vascular contraction, cell proliferation, activation of epidermal growth factor receptor tyrosine kinase, regulation of proline-rich tyrosine kinase, and release of arachidonic acid. The experiments using various constructs of endothelin receptors reveal the importance of G(q) and G(12) families in activation of these Ca(2+) channels by ET-1. These findings provide a potential therapeutic mechanism of a functional interrelationship between G(q)/G(12) proteins and voltage-independent Ca(2+) channels in the pathophysiology of ET-1, such as in chronic heart failure, hypertension, and cerebral vasospasm.

Endothelins in breast tumour cell invasion

Endothelins are a family of small, structurally related, vasoactive peptides that have a great number of physiological roles in many tissues. The 'endothelin axis' consists of three 21 amino acid peptides (ET-1, ET-2 and ET-3), two G-protein-coupled receptors (ET-RA and ET-RB), and two activating peptidases or endothelin-converting enzymes (ECE-1 and ECE-2). There is increased expression of the endothelin axis in invasive breast cancer compared to the normal breast or non-invasive neoplastic tissue. Endothelin expression is associated with invading regions of tumours in patient biopsies and is more common in tumours with high histological grade and lymphovascular invasion, and there is increased systemic endothelin in patients with lymph node metastases compared to those without lymph node involvement. Stimulation of breast tumour cell lines with endothelins leads to an invasive phenotype in vitro. Over-expression of the endothelins and their receptors is insufficient to induce an invasive phenotype in benign cells, yet expression by tumour cells leads to markedly increased invasive ability indicating that endothelins act in concert with other factors--both autocrine and paracrine--including cytokines, matrix metalloproteinases and the activation of tumour-associated macrophages. The association between endothelins, poor prognosis and invasion may mean that the endothelin axis is a valid therapeutic target for the treatment of invasive breast cancer. This review summarises our current knowledge of endothelins in breast cancer invasion and discusses the potential further directions of such research as well as the possibility of anti-endothelin-based therapy of breast cancer.

Function and survival of dendritic cells depend on endothelin-1 and endothelin receptor autocrine loops

The biologic effects of endothelin-1 (ET-1) are not limited to its potent vasoconstricting activity. The endothelin receptors, ETA and ETB, have differential tissue and functional distributions. Here we showed that dendritic cells (DCs), the major antigen-presenting cells in the adaptive limb of the immune system, produce large amounts of ET-1 and significantly increase the expression of endothelin receptors upon maturation. Selective blockade of the ETA receptor significantly reduced expression of the mature DC marker CD83, decreased the production of the immunostimulatory cytokine interleukin-12, down-regulated DC ability to stimulate T cells, and promoted DC apoptosis. Selective ETB receptor blockade, on the other hand, resulted in increased expression of CD83 and improved DC survival. Therefore, ET-1/ETA/ETB autocrine/paracrine loops on DCs appear to be essential for the normal maturation and function of human DCs, presenting a unique target for immunomodulatory therapies.

Historical review: Endothelin

Endothelin (ET) is a potent vasoconstrictive peptide that was isolated initially from the conditioned medium of cultured endothelial cells. In 1988, details of the isolation and identification, amino acid sequence, cDNA sequence and pharmacology of ET were published. Subsequently, ET isoforms, ET receptors and endothelin-converting enzyme (ECE) were cloned. Because ET was thought to be important in cardiovascular homeostasis, many investigators focused on the physiological and pathophysiological significance of ET. Accordingly, ET receptor antagonists and ECE inhibitors have been developed rapidly, mostly for the treatment of cardiovascular diseases. The field of molecular biology has provided valuable information about ET, including evidence that the ET system plays important roles in the early development of the neural crest and, thus, in the formation of organs. These results now present new avenues of ET research.

Atrial natriuretic peptide and endothelin-3 target renal sodium-glucose cotransporter

Atrial natriuretic peptide (ANP) and endothelin (ET) are endogenous vasoactive factors that exert potent diuretic and natriuretic actions. We have previously shown that ANP and ET-3 act through an NO pathway to inhibit the sodium-glucose cotransporter (SGLT) in the intestine [Gonzalez Bosc LV, Elustondo PA, Ortiz MC, Vidal NA. Effect of atrial natriuretic peptide on sodium-glucose cotransport in the rat small intestine. Peptides 1997; 18: 1491-5; Gonzalez Bosc LV, Majowicz MP, Ortiz MC, Vidal NA. Effects of endothelin-3 on intestinal ion transport. Peptides 2001; 22: 2069-75.]. Here we address the role of ANP and ET-3 on SGLT activity in renal proximal tubules. In rat renal cortical brush border membranes (BBV), fluorescein isothiocianate (FITC) labeling revealed a specific 72-kD peptide that exhibits increased FITC labeling in the presence of Na+ and D-glucose. Using alpha-14C-methylglucose active uptake, rat BBV were shown to possess SGLT activity with an affinity constant (K(0.5) approximately 2.4 mM) that is consistent with the expression of the low-affinity, high-capacity SGLT2 isoform. SGLT2 activity in these preparations is dramatically inhibited by ANP and ET-3. This inhibition is independent of changes in membrane lipids and is mimicked by the cGMP analogue, 8-Br-cGMP, suggesting the involvement of cGMP/PKG pathways. These results are the first demonstration that both ANP and ET-3 inhibit rat cortical renal SGLT2 activity, and suggest a novel mechanism by which these vasoactive substances modulate hydro-saline balance at the proximal tubular nephron level.

Endothelin-1 increases 2-arachidonoyl glycerol (2-AG) production in astrocytes

Astrocytes play an important role in neuroprotective responses. Recent studies indicate that endothelin-1, a neuropeptide upregulated during brain injury, increases levels of the endocannabinoid anandamide, a lipid with neuroprotective properties, in astrocytes in primary cultures. However, whether this neuropeptide also alters levels of 2-arachidonoyl glycerol (2-AG), the most abundant endocannabinoid in the CNS, in astrocytes remains unknown. In addition, 2-AG levels in astrocytes have never been measured. In this report we use chemical ionization gas chromatography/mass spectrometry to quantify picomole amounts of 2-AG in primary cultures of mouse astrocytes. We also demonstrate that endothelin-1 increases 2-AG production by 5-fold in these cells, a response that requires extracellular calcium and endothelin-1(A) receptor engagement. Immunocytochemistry showed that although cultured mouse neurons and microglia express cannabinoid receptors, cultured astrocytes do not. The data suggest that endothelin-1 modulates 2-AG production in astrocytes and that this endocannabinoid may participate in paracrine signaling toward neurons and microglia.

Role of endothelins in congestive heart failure

Despite major advances in conventional medical therapy, patients with heart failure continue to experience significant morbidity and mortality. Endothelin-1 (ET-1) is a potent vasocontrictor and mitogenic peptide that is activated in heart failure. There is increasing experimental and clinical evidence in support of an important role of ET-1 in the pathophysiology of heart failure. Manipulation of the activity of ET-1, especially using endothelin receptor blockers, has allowed for the further elucidation of the role of this neurohormonal system and development of novel therapeutic strategies in heart failure. Published clinical studies of these agents to date have involved relatively small numbers of patients with severe heart failure, followed for a relatively short period of time, and have mainly examined surrogate endpoints. Large-scale trials that address to hard clinical outcomes are ongoing and their results forthcoming. A key question that remains concerns whether selective ETA or dual ETA-ETB receptor blockade will be more effective.

Endothelin-1-induced arachidonic acid release by cytosolic phospholipase A2 activation in rat vascular smooth muscle via extracellular signal-regulated kinases pathway

The present study investigates whether endothelin-1 (ET-1), like noradrenaline (NA), stimulates the release of arachidonic acid (AA) via cytosolic phospholipase A2 (cPLA2) in rat tail artery. In tail artery segments labelled with [3H]AA, ET-1-induced AA release in a concentration-dependent manner with an EC50 of 1.3 nM. The effect of ET-1 was inhibited by bosentan and was insensitive to BQ788, suggesting the involvement of ETA receptor. The stimulation of AA release induced by ET-1 was prevented by arachydonyl trifluoromethyl ketone (AACOCF3), a selective inhibitor of cPLA2 and not by RHC80267, a diacylglycerol lipase inhibitor. Furthermore, PD98059, inhibitor of mitogen-activated protein kinase kinase (MEK) cascade and calphostin C, a protein kinase C (PKC) inhibitor, prevented the stimulation of AA release induced by ET-1 and NA. Immunoblotting of the cytosolic fraction of rat tail arteries stimulated with ET-1 or NA showed an increase in extracellular signal-regulated kinases (ERKs) phosphorylation and this effect was abolished by calphostin C treatment. These findings show that in rat tail artery ET-1 and NA induce a sequential activation of protein kinase C and extracellular signal-regulated kinases that results in stimulation of AA release via cPLA2 activation. This may represent a general pathway by which G-proteins coupled receptors stimulate AA release and its metabolites in vascular smooth muscle.

Endothelin-1 as a target for therapeutic intervention in prostate cancer

The endothelins, a family of potent vasoconstricting peptides, have been implicated in the pathophysiology of advanced prostate cancer. Two endothelin receptors, ET-A and ET-B are found in normal prostate tissue. Malignant prostate cells are notable for the loss of ET-B receptors and increased levels of endothelin-1 [ET-1]; this distortion of the endothelin system may be a significant factor in the progression of prostate cancer. Proposed roles for endothelin in prostate cancer include growth promotion, apoptosis inhibition, bone formation, and stimulation of nociceptive receptors. ET-1 can act alone as a mitogen, but its effects are greatest as a comitogen with a variety of growth factors, including basic fibroblast growth factor, insulin-like growth factors, and platelet derived growth factor. Although their exact functions are unclear, ET-1, in conjunction with vascular endothelial growth factor, appears to play a major role in tumor angiogenesis. By a variety of methods, ET-1 alters the balance of osteoblast and osteoclasts to the favor new bone formation that is characteristic of metastatic disease. Several studies indicate that the refractory pain of metastatic cancer is related to the direct nociceptive effects ET-1. These findings suggest that ET receptors are promising therapeutic targets for pharmacologic intervention. Early clinical trials indicate that the ET-A receptor antagonist used in prostate cancer is reasonably well tolerated with mild but pervasive symptoms related to ET-1's vasoconstrictive effects. Results of ongoing clinical trials are eagerly awaited in order to see if the hypothetical promise of ET antagonism will result in clinical success.

Vascular effects of poly-N-acetylglucosamine in isolated rat aortic rings

BACKGROUND

[corrected] Poly-N-acetylglucosamine (p-GlcNAc) is a secretion of marine diatoms that is known to be useful in controlling bleeding. As a component of promoting hemostasis, p-GlcNAc is thought to exert vasoconstrictor effects in arteries. The present study was undertaken to determine whether p-GlcNAc induced a significant vasoconstrictor effect and, if so, what the mechanism of this effect might be.

MATERIALS AND METHODS

We examined vascular effects of p-GlcNAc on isolated aortic rings obtained from Sprague-Dawley rats. The rings were suspended in organ baths and precontracted with U46619, a thromboxane A2 mimetic.

RESULTS

p-GlcNAc produced a concentration-dependent vasoconstriction over the range of 14 to 100 microg/ml. At a concentration of 100 microg/ml, p-GlcNAc significantly contracted aortic rings by 133 +/- 20 mg of developed force (P < 0.01). Neither a deacetylated derivative of p-GlcNAc nor a structurally related macromolecule, chitin, contracted rat aortic rings, indicating a specificity for p-GlcNAc. The vasoconstriction to p-GlcNAc was totally abolished in deendothelialized rat aortic rings, suggesting that an endothelial component is essential to the vasoconstriction. Pretreatment with the endothelin ET(A) receptor antagonist, JKC-301 (0.5 and 1 microM), significantly diminished p-GlcNAc-induced vasoconstriction by 57 to 61% (P < 0.01). However, p-GlcNAc did not significantly diminish nitric oxide release from rat aortic endothelium.

CONCLUSION

These results provide evidence that p-GlcNAc significantly contracts isolated rat aortic rings via an endothelium-dependent mechanism, partly via enhancement of endothelin-1 release from endothelial cells.

Involvement of oxidative stress in NF-kappaB activation in endothelial cells treated by photodynamic therapy

In human endothelial cells ECV 304 and HMEC-1 photosensitized by pyropheophorbide-a methylester (PPME) in sublethal conditions transcription factor Nuclear Factor kappa B (NF-kappaB) activation takes place for several hours. Activated NF-kappaB was functional because it stimulated the transcriptional activation of either a transfected reporter gene or the endogenous gene encoding interleukin (IL)-8. Concomitant with NF-kappaB activation, inhibitor of NF-kappaB alpha (IkappaB alpha) was degraded during photosensitization and IkappaB beta, p100, p105 and IkappaB epsilon were slightly modified. Reactive oxygen species (ROS) were shown to be crucial intermediates in the activation because antioxidants strongly decreased NF-kappaB activation. Using both a fluorescent probe and isotope substitution, it was shown that ROS, and especially singlet oxygen (1O2), were important in the activation process. Because NF-kappaB activation in the presence of ROS was suspected to proceed through a pathway independent of the IkappaB kinases (IKK), we demonstrated that the IKK were indeed not activated by photosensitization but required an intact tyrosine residue at position 42 on IkappaB alpha, suggesting the involvement of a tyrosine kinase in the activation process. This was further reinforced by the demonstration that herbimycin A, a tyrosine kinase inhibitor, prevented NF-kappaB activation by photosensitization but not by TNF alpha, a cytokine known to activate NF-kappaB through an IKK-dependent mechanism.

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

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

Effects of endothelin-3 on intestinal ion transport

We investigated the effects of endothelin 3 (ET-3) on electrolyte transport in rat small intestine using a voltage clamp technique in Ussing's chamber. ET-3 diminished potential difference (PD) and short circuit current (Isc). ET-3 did not affect PD or Isc in low Na(+) and/or D-glucose-free medium. Phloridzine (an inhibitor of sodium-glucose cotransporter [SGLT1]) pretreatment abolished the effect of ET-3 on Isc. Methylene blue (a soluble guanylate cyclase inhibitor) or N-nitro-L-arginine methyl ester (a NOS inhibitor) pretreatment delayed the effect of ET-3 on PD and Isc. ET-3 enhanced NOS activity on enterocytes and systemic NO production. Then, ET-3 could inhibit SGLT1 with the participation of NO.

Endothelin receptor subtype A blockade selectively reduces pulmonary pressure after cardiopulmonary bypass

BACKGROUND

The bioactive peptide endothelin-1 is elevated during and after cardiopulmonary bypass and exerts cardiovascular effects through its 2 receptor subtypes, endothelin-1A and endothelin-1B. Increased endothelin-1A receptor stimulation after cardiopulmonary bypass can cause increased pulmonary vascular resistance and modulate myocardial contractility. However, whether and to what degree selective endothelin-1A blockade influences these parameters in the postbypass setting is not completely understood.

OBJECTIVES

Our objective was to measure left ventricular function and hemodynamics in a porcine model of cardiopulmonary bypass after selective blockade of endothelin-1A.

METHODS

Adult pigs (n = 23) underwent 90 minutes of cardiopulmonary bypass and were randomized 30 minutes after bypass to receive a selective endothelin-1A antagonist (TBC 11251, 10 mg/kg; n = 13) or saline vehicle (n = 10).

RESULTS

After bypass and before randomization, pulmonary vascular resistance rose nearly 4-fold, and left ventricular preload recruitable stroke work fell to one third of baseline values (both P <.05). In the vehicle group pulmonary vascular resistance continued to rise, and preload recruitable stroke work remained reduced. However, after endothelin-1A blockade, the rise in pulmonary vascular resistance was significantly blunted compared with that in the vehicle group. Moreover, the reduction in pulmonary vascular resistance with endothelin-1A blockade was achieved without a significant change in systemic perfusion pressures.

CONCLUSIONS

The present study demonstrated that increased activity of the endothelin-1A receptor likely contributes to alterations in pulmonary vascular resistance in the postbypass setting. Selective endothelin-1A blockade may provide a means to selectively decrease pulmonary vascular resistance without significant effects on systemic hemodynamics.

Role of endothelin-1 receptors in healthy anaesthetized rabbits

1. Many diseases are associated with elevated endothelin (ET)-1 plasma concentrations. In order to understand the consequence of this elevation, in the present study the effects of exogenous ET-1 on the entire organsim were investigated, in particular with respect to the role of ETA and ETB receptors in the cardiovascular system. In open-chest rabbits, left ventricular (LV) pressure (LVPmax, LVPed), dP/dtmax and dP/dtmin were recorded in ejecting and isovolumically beating hearts to determine cardiac function. In addition, heart rate (HR), aortic pressure (AoP) and aortic flow (AoF) were measured. Total peripheral resistance (TPR) was calculated from mean AoP and AoF. 2. In the first series of experiments (n = 11), ET-1 (0.5 nmol/kg; bolus) produced a non-significant reduction in HR. Systolic function, in terms of AoF, LVPmax and dP/dtmax, was improved; for example, LVPmax was increased significantly (69 +/- 10 vs 106 +/- 20 mmHg for control and ET-1, respectively; P < 0.05). Similarly, early relaxation (dP/dtmin) was improved. In parallel, TPR rose significantly (0.25+/-0.07 vs 0.35+/-0.1 mmHg/min per mL for control and ET-1, respectively; P < 0.05). Isovolumic measurements showed corresponding responses. 3. In the second series of experiments (n = 7), animals were pretreated with an ETA receptor antagonist (330 nmol/min per kg FR 139317). After ETA receptor blockade, the administration of ET-1 had no significant effect on cardiac function or vasomotion. 4. In the third series of experiments (n = 6), animals were pretreated with an ETB receptor antagonist (10 nmol/min per kg BQ 788). In this series of experiments, the effects of ET-1 on cardiac function and vasomotion were the same as in the first series of experiments, except for the effect on HR, which decreased by 35% after ET-1. 5. In our experimental model, exogenous ET-1 exerted a clear-cut positive inotropic effect, together with the anticipated peripheral vasoconstriction via ETA receptors.