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The biased apelin receptor agonist, MM07, reverses Sugen/hypoxia-induced pulmonary arterial hypertension as effectively as the endothelin antagonist macitentan. Front Pharmacol 2024; 15:1369489. [PMID: 38655187 PMCID: PMC11035786 DOI: 10.3389/fphar.2024.1369489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Accepted: 03/26/2024] [Indexed: 04/26/2024] Open
Abstract
Introduction: Pulmonary arterial hypertension (PAH) is characterised by endothelial dysfunction and pathological vascular remodelling, resulting in the occlusion of pulmonary arteries and arterioles, right ventricular hypertrophy, and eventually fatal heart failure. Targeting the apelin receptor with the novel, G protein-biased peptide agonist, MM07, is hypothesised to reverse the developed symptoms of elevated right ventricular systolic pressure and right ventricular hypertrophy. Here, the effects of MM07 were compared with the clinical standard-of-care endothelin receptor antagonist macitentan. Methods: Male Sprague-Dawley rats were randomised and treated with either normoxia/saline, or Sugen/hypoxia (SuHx) to induce an established model of PAH, before subsequent treatment with either saline, macitentan (30 mg/kg), or MM07 (10 mg/kg). Rats were then anaesthetised and catheterised for haemodynamic measurements, and tissues collected for histopathological assessment. Results: The SuHx/saline group presented with significant increases in right ventricular hypertrophy, right ventricular systolic pressure, and muscularization of pulmonary arteries compared to normoxic/saline controls. Critically, MM07 was as at least as effective as macitentan in significantly reversing detrimental structural and haemodynamic changes after 4 weeks of treatment. Discussion: These results support the development of G protein-biased apelin receptor agonists with improved pharmacokinetic profiles for use in human disease.
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Inducible apelin receptor knockdown reduces differentiation efficiency and contractility of hESC-derived cardiomyocytes. Cardiovasc Res 2023; 119:587-598. [PMID: 36239923 PMCID: PMC10064845 DOI: 10.1093/cvr/cvac065] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 04/04/2022] [Accepted: 04/12/2022] [Indexed: 11/14/2022] Open
Abstract
AIMS The apelin receptor, a G protein-coupled receptor, has emerged as a key regulator of cardiovascular development, physiology, and disease. However, there is a lack of suitable human in vitro models to investigate the apelinergic system in cardiovascular cell types. For the first time we have used human embryonic stem cell-derived cardiomyocytes (hESC-CMs) and a novel inducible knockdown system to examine the role of the apelin receptor in both cardiomyocyte development and to determine the consequences of loss of apelin receptor function as a model of disease. METHODS AND RESULTS Expression of the apelin receptor and its ligands in hESCs and hESC-CMs was determined. hESCs carrying a tetracycline-inducible short hairpin RNA targeting the apelin receptor were generated using the sOPTiKD system. Phenotypic assays characterized the consequences of either apelin receptor knockdown before hESC-CM differentiation (early knockdown) or in 3D engineered heart tissues as a disease model (late knockdown). hESC-CMs expressed the apelin signalling system at a similar level to the adult heart. Early apelin receptor knockdown decreased cardiomyocyte differentiation efficiency and prolonged voltage sensing, associated with asynchronous contraction. Late apelin receptor knockdown had detrimental consequences on 3D engineered heart tissue contractile properties, decreasing contractility and increasing stiffness. CONCLUSIONS We have successfully knocked down the apelin receptor, using an inducible system, to demonstrate a key role in hESC-CM differentiation. Knockdown in 3D engineered heart tissues recapitulated the phenotype of apelin receptor down-regulation in a failing heart, providing a potential platform for modelling heart failure and testing novel therapeutic strategies.
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Abstract
Preventing SARS-CoV-2 infection by modulating viral host receptors, such as angiotensin-converting enzyme 2 (ACE2)1, could represent a new chemoprophylactic approach for COVID-19 that complements vaccination2,3. However, the mechanisms that control the expression of ACE2 remain unclear. Here we show that the farnesoid X receptor (FXR) is a direct regulator of ACE2 transcription in several tissues affected by COVID-19, including the gastrointestinal and respiratory systems. We then use the over-the-counter compound z-guggulsterone and the off-patent drug ursodeoxycholic acid (UDCA) to reduce FXR signalling and downregulate ACE2 in human lung, cholangiocyte and intestinal organoids and in the corresponding tissues in mice and hamsters. We show that the UDCA-mediated downregulation of ACE2 reduces susceptibility to SARS-CoV-2 infection in vitro, in vivo and in human lungs and livers perfused ex situ. Furthermore, we reveal that UDCA reduces the expression of ACE2 in the nasal epithelium in humans. Finally, we identify a correlation between UDCA treatment and positive clinical outcomes after SARS-CoV-2 infection using retrospective registry data, and confirm these findings in an independent validation cohort of recipients of liver transplants. In conclusion, we show that FXR has a role in controlling ACE2 expression and provide evidence that modulation of this pathway could be beneficial for reducing SARS-CoV-2 infection, paving the way for future clinical trials.
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Expanding the apelin receptor pharmacological toolbox using novel fluorescent ligands. Front Endocrinol (Lausanne) 2023; 14:1139121. [PMID: 36967803 PMCID: PMC10034064 DOI: 10.3389/fendo.2023.1139121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 02/24/2023] [Indexed: 03/11/2023] Open
Abstract
INTRODUCTION The apelin receptor binds two distinct endogenous peptides, apelin and ELA, which act in an autocrine/paracrine manner to regulate the human cardiovascular system. As a class A GPCR, targeting the apelin receptor is an attractive therapeutic strategy. With improvements in imaging techniques, and the stability and brightness of dyes, fluorescent ligands are becoming increasingly useful in studying protein targets. Here, we describe the design and validation of four novel fluorescent ligands; two based on [Pyr1]apelin-13 (apelin488 and apelin647), and two based on ELA-14 (ELA488 and ELA647). METHODS Fluorescent ligands were pharmacologically assessed using radioligand and functional in vitro assays. Apelin647 was validated in high content imaging and internalisation studies, and in a clinically relevant human embryonic stem cell-derived cardiomyocyte model. Apelin488 and ELA488 were used to visualise apelin receptor binding in human renal tissue. RESULTS All four fluorescent ligands retained the ability to bind and activate the apelin receptor and, crucially, triggered receptor internalisation. In high content imaging studies, apelin647 bound specifically to CHO-K1 cells stably expressing apelin receptor, providing proof-of-principle for a platform that could screen novel hits targeting this GPCR. The ligand also bound specifically to endogenous apelin receptor in stem cell-derived cardiomyocytes. Apelin488 and ELA488 bound specifically to apelin receptor, localising to blood vessels and tubules of the renal cortex. DISCUSSION Our data indicate that the described novel fluorescent ligands expand the pharmacological toolbox for studying the apelin receptor across multiple platforms to facilitate drug discovery.
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Apelin is expressed throughout the human kidney, is elevated in chronic kidney disease & associates independently with decline in kidney function. Br J Clin Pharmacol 2022; 88:5295-5306. [PMID: 35748053 PMCID: PMC9796317 DOI: 10.1111/bcp.15446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 06/13/2022] [Accepted: 06/15/2022] [Indexed: 01/02/2023] Open
Abstract
AIMS Chronic kidney disease (CKD) is common and cardiovascular disease (CVD) is its commonest complication. The apelin system is a potential therapeutic target for CVD but data relating to apelin in CKD are limited. We examined expression of the apelin system in human kidney, and investigated apelin and Elabela/Toddler (ELA), the endogenous ligands for the apelin receptor, in patients with CKD. METHODS Using autoradiography, immunohistochemistry and enzyme-linked immunosorbent assay, we assessed expression of apelin, ELA and the apelin receptor in healthy human kidney, and measured plasma apelin and ELA in 155 subjects (128 patients with CKD, 27 matched controls) followed up for 5 years. Cardiovascular assessments included blood pressure, arterial stiffness (pulse wave velocity) and brachial artery flow-mediated dilation. Surrogate markers of endothelial function (plasma asymmetric dimethylarginine and endothelin-1) and inflammation (C-reactive protein and interleukin-6) were measured. RESULTS The apelin system was expressed in healthy human kidney, throughout the nephron. Plasma apelin concentrations were 60% higher in women than men (6.48 [3.62-9.89] vs. 3.95 [2.02-5.85] pg/mL; P < .0001), and increased as glomerular filtration rate declined (R = -0.41, P < .0001), and albuminuria rose (R = 0.52, P < .0001). Plasma apelin and ELA were associated with vascular dysfunction. Plasma apelin associated independently with a 50% decline in glomerular filtration rate at 5 years. CONCLUSION We show for the first time that the apelin system is expressed in healthy human kidney. Plasma apelin is elevated in CKD and may be a potential biomarker of risk of decline in kidney function. Clinical studies exploring the therapeutic potential of apelin agonism in CKD are warranted.
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Endothelin-1 is increased in the plasma of patients hospitalised with Covid-19. J Mol Cell Cardiol 2022; 167:92-96. [PMID: 35339512 PMCID: PMC8941861 DOI: 10.1016/j.yjmcc.2022.03.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 02/25/2022] [Accepted: 03/19/2022] [Indexed: 12/03/2022]
Abstract
Virus induced endothelial dysregulation is a well-recognised feature of severe Covid-19 infection. Endothelin-1 (ET-1) is the most highly expressed peptide in endothelial cells and a potent vasoconstrictor, thus representing a potential therapeutic target. ET-1 plasma levels were measured in a cohort of 194 Covid-19 patients stratified according to the clinical severity of their illness. Hospitalised patients, including those who died and those developing acute myocardial or kidney injury, had significantly elevated ET-1 plasma levels during the acute phase of infection. The results support the hypothesis that endothelin receptor antagonists may provide clinical benefit for certain Covid-19 patients.
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Differential expression in humans of the viral entry receptor ACE2 compared with the short deltaACE2 isoform lacking SARS-CoV-2 binding sites. Sci Rep 2021; 11:24336. [PMID: 34934117 PMCID: PMC8692523 DOI: 10.1038/s41598-021-03731-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Accepted: 12/02/2021] [Indexed: 12/13/2022] Open
Abstract
ACE2 is a membrane protein that regulates the cardiovascular system. Additionally, ACE2 acts as a receptor for host cell infection by human coronaviruses, including SARS-CoV-2 that emerged as the cause of the on-going COVID-19 pandemic and has brought unprecedented burden to economy and health. ACE2 binds the spike protein of SARS-CoV-2 with high affinity and shows little variation in amino acid sequence meaning natural resistance is rare. The discovery of a novel short ACE2 isoform (deltaACE2) provides evidence for inter-individual differences in SARS-CoV-2 susceptibility and severity, and likelihood of developing subsequent 'Long COVID'. Critically, deltaACE2 loses SARS-CoV-2 spike protein binding sites in the extracellular domain, and is predicted to confer reduced susceptibility to viral infection. We aimed to assess the differential expression of full-length ACE2 versus deltaACE2 in a panel of human tissues (kidney, heart, lung, and liver) that are implicated in COVID-19, and confirm ACE2 protein in these tissues. Using dual antibody staining, we show that deltaACE2 localises, and is enriched, in lung airway epithelia and bile duct epithelia in the liver. Finally, we also confirm that a fluorescently tagged SARS-CoV-2 spike protein monomer shows low binding at lung and bile duct epithelia where dACE2 is enriched.
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In vitro metabolism of synthetic Elabela/Toddler (ELA-32) peptide in human plasma and kidney homogenates analyzed with mass spectrometry and validation of endogenous peptide quantification in tissues by ELISA. Peptides 2021; 145:170642. [PMID: 34455010 PMCID: PMC8484864 DOI: 10.1016/j.peptides.2021.170642] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 08/17/2021] [Accepted: 08/20/2021] [Indexed: 12/31/2022]
Abstract
BACKGROUND Elabela/Toddler (ELA) is a novel endogenous ligand of the apelin receptor, whose signalling has emerged as a therapeutic target, for example, in cardiovascular disease and cancer. Shorter forms of ELA-32 have been predicted, including ELA-21 and ELA-11, but metabolism and stability of ELA-32 in humans is poorly understood. We, therefore, developed an LC-MS/MS assay to identify ELA-32 metabolites in human plasma and tissues. METHOD Human kidney homogenates or plasma were incubated at 37 °C with ELA-32 and aliquots withdrawn over 2-4 h into guanidine hydrochloride. Proteins were precipitated and supernatant solid-phase extracted. Peptides were extracted from coronary artery, brain and kidney by immunoprecipitation or solid-phase extraction following acidification. All samples were reduced and alkylated before analysis on an Orbitrap mass spectrometer in high and nano flow mode. RESULTS The half-life of ELA-32 in plasma and kidney were 47.2 ± 5.7 min and 44.2 ± 3 s, respectively. Using PEAKS Studio and manual data analysis, the most important fragments of ELA-32 with potential biological activity identified were ELA-11, ELA-16, ELA-19 and ELA-20. The corresponding fragments resulting from the loss of C-terminal amino acids were also identified. Endogenous levels of these peptides could not be measured, as ELA peptides are prone to oxidation and poor chromatographic peaks. CONCLUSIONS The relatively long ELA plasma half-life observed and identification of a potentially more stable fragment, ELA-16, may suggest that ELA could be a better tool compound and novel template for the development of new drugs acting at the apelin receptor.
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Human embryonic stem cell-derived cardiomyocyte platform screens inhibitors of SARS-CoV-2 infection. Commun Biol 2021; 4:926. [PMID: 34326460 PMCID: PMC8322398 DOI: 10.1038/s42003-021-02453-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 07/15/2021] [Indexed: 11/09/2022] Open
Abstract
Patients with cardiovascular comorbidities are more susceptible to severe infection with SARS-CoV-2, known to directly cause pathological damage to cardiovascular tissue. We outline a screening platform using human embryonic stem cell-derived cardiomyocytes, confirmed to express the protein machinery critical for SARS-CoV-2 infection, and a SARS-CoV-2 spike-pseudotyped virus system. The method has allowed us to identify benztropine and DX600 as novel inhibitors of SARS-CoV-2 infection in a clinically relevant stem cell-derived cardiomyocyte line. Discovery of new medicines will be critical for protecting the heart in patients with SARS-CoV-2, and for individuals where vaccination is contraindicated.
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Plasma levels of apelin are reduced in patients with liver fibrosis and cirrhosis but are not correlated with circulating levels of bone morphogenetic protein 9 and 10. Peptides 2021; 136:170440. [PMID: 33171278 PMCID: PMC7883214 DOI: 10.1016/j.peptides.2020.170440] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 10/06/2020] [Accepted: 11/01/2020] [Indexed: 12/24/2022]
Abstract
BACKGROUND The peptide apelin is expressed in human healthy livers and is implicated in the development of hepatic fibrosis and cirrhosis. Mutations in the bone morphogenetic protein receptor type II (BMPR-II) result in reduced plasma levels of apelin in patients with heritable pulmonary arterial hypertension. Ligands for BMPR-II include bone morphogenetic protein 9 (BMP9), highly expressed in liver, and BMP10, expressed in heart and to a lesser extent liver. However, it is not known whether reductions in BMP9 and/or BMP10, with associated reduction in BMPR-II signalling, correlate with altered levels of apelin in patients with liver fibrosis and cirrhosis. METHODS Plasma from patients with liver fibrosis (n = 14), cirrhosis (n = 56), and healthy controls (n = 25) was solid-phase extracted using a method optimised for recovery of apelin, which was measured by ELISA. RESULTS Plasma apelin was significantly reduced in liver fibrosis (8.3 ± 1.2 pg/ml) and cirrhosis (6.5 ± 0.6 pg/ml) patients compared with controls (15.4 ± 2.0 pg/ml). There was no obvious relationship between apelin and BMP 9 or BMP10 previously measured in these patients. Within the cirrhotic group, there was no significant correlation between apelin levels and disease severity scores, age, sex, or treatment with β-blockers. CONCLUSIONS Apelin was significantly reduced in plasma of patients with both early (fibrosis) and late-stage (cirrhosis) liver disease. Fibrosis is more easily reversible and may represent a potential target for new therapeutic interventions. However, it remains unclear whether apelin signalling is detrimental in liver disease or is beneficial and therefore, whether an apelin antagonist or agonist have clinical use.
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The G Protein Biased Small Molecule Apelin Agonist CMF-019 is Disease Modifying in Endothelial Cell Apoptosis In Vitro and Induces Vasodilatation Without Desensitisation In Vivo. Front Pharmacol 2021; 11:588669. [PMID: 33716722 PMCID: PMC7944139 DOI: 10.3389/fphar.2020.588669] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Accepted: 12/02/2020] [Indexed: 12/13/2022] Open
Abstract
Signaling through the apelin receptor is beneficial for a number of diseases including pulmonary arterial hypertension. The endogenous small peptides, apelin and elabela/toddler, are downregulated in pulmonary arterial hypertension but are not suitable for exogenous administration owing to a lack of bioavailability, proteolytic instability and susceptibility to renal clearance. CMF-019, a small molecule apelin agonist that displays strong bias towards G protein signaling over β-arrestin (∼400 fold), may be more suitable. This study demonstrates that in addition to being a positive inotrope, CMF-019 caused dose-dependent vasodilatation in vivo (50 nmol 4.16 ± 1.18 mmHg, **p < 0.01; 500 nmol 6.62 ± 1.85 mmHg, **p < 0.01), without receptor desensitization. Furthermore, CMF-019 rescues human pulmonary artery endothelial cells from apoptosis induced by tumor necrosis factor α and cycloheximide (5.66 ± 0.97%, **p < 0.01) by approximately 50% of that observable with rhVEGF (11.59 ± 1.85%, **p < 0.01), suggesting it has disease-modifying potential in vitro. CMF-019 displays remarkable bias at the apelin receptor for a small molecule and importantly recapitulates all aspects of the cardiovascular responses to the endogenous ligand, [Pyr1]apelin-13, in vivo. Additionally, it is able to protect human pulmonary artery endothelial cells from apoptosis, suggesting that the beneficial effects observed with apelin agonists extend beyond hemodynamic alleviation and address disease etiology itself. These findings support CMF-019 as a G protein biased small molecule apelin agonist in vitro and in vivo that could form the basis for the design of novel therapeutic agents in chronic diseases, such as, pulmonary arterial hypertension.
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Apelin peptides linked to anti-serum albumin domain antibodies retain affinity in vitro and are efficacious receptor agonists in vivo. Basic Clin Pharmacol Toxicol 2020; 126 Suppl 6:96-103. [PMID: 30901161 DOI: 10.1111/bcpt.13227] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 03/14/2019] [Indexed: 12/18/2022]
Abstract
The apelin receptor is a potential target in the treatment of heart failure and pulmonary arterial hypertension where levels of endogenous apelin peptides are reduced but significant receptor levels remain. Our aim was to characterise the pharmacology of a modified peptide agonist, MM202, designed to have high affinity for the apelin receptor and resistance to peptidase degradation and linked to an anti-serum albumin domain antibody (AlbudAb) to extend half-life in the blood. In competition, binding experiments in human heart MM202-AlbudAb (pKi = 9.39 ± 0.09) bound with similar high affinity as the endogenous peptides [Pyr1 ]apelin-13 (pKi = 8.83 ± 0.06) and apelin-17 (pKi = 9.57 ± 0.08). [Pyr1 ]apelin-13 was tenfold more potent in the cAMP (pD2 = 9.52 ± 0.05) compared to the β-arrestin (pD2 = 8.53 ± 0.03) assay, whereas apelin-17 (pD2 = 10.31 ± 0.28; pD2 = 10.15 ± 0.13, respectively) and MM202-AlbudAb (pD2 = 9.15 ± 0.12; pD2 = 9.26 ± 0.03, respectively) were equipotent in both assays, with MM202-AlbudAb tenfold less potent than apelin-17. MM202-AlbudAb bound to immobilised human serum albumin with high affinity (pKD = 9.02). In anaesthetised, male Sprague Dawley rats, MM202-AlbudAb (5 nmol, n = 15) significantly reduced left ventricular systolic pressure by 6.61 ± 1.46 mm Hg and systolic arterial pressure by 14.12 ± 3.35 mm Hg and significantly increased cardiac contractility by 533 ± 170 mm Hg/s, cardiac output by 1277 ± 190 RVU/min, stroke volume by 3.09 ± 0.47 RVU and heart rate by 4.64 ± 2.24 bpm. This study demonstrates that conjugating an apelin mimetic peptide to the AlbudAb structure retains receptor and in vivo activity and may be a new strategy for development of apelin peptides as therapeutic agents.
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Development and validation of an LC-MS/MS method for detection and quantification of in vivo derived metabolites of [Pyr 1]apelin-13 in humans. Sci Rep 2019; 9:19934. [PMID: 31882594 PMCID: PMC6934825 DOI: 10.1038/s41598-019-56157-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 11/22/2019] [Indexed: 12/15/2022] Open
Abstract
[Pyr1]apelin-13 is the predominant apelin peptide isoform in the human cardiovascular system and plasma. To date, few studies have investigated [Pyr1]apelin-13 metabolism in vivo in rats with no studies examining its stability in humans. We therefore aimed to develop an LC-MS/MS method for detection and quantification of intact [Pyr1]apelin-13 and have used this method to identify the metabolites generated in vivo in humans. [Pyr1]apelin-13 (135 nmol/min) was infused into six healthy human volunteers for 120 minutes and blood collected at time 0 and 120 minutes after infusion. Plasma was extracted in the presence of guanidine hydrochloride and analysed by LC-MS/MS. Here we report a highly sensitive, robust and reproducible method for quantification of intact [Pyr1]apelin-13 and its metabolites in human plasma. Using this method, we showed that the circulating concentration of intact peptide was 58.3 ± 10.5 ng/ml after 120 minutes infusion. We demonstrated for the first time that in humans, [Pyr1]apelin-13 was cleaved from both termini but the C-terminal was more susceptible to cleavage. Consequently, of the metabolites identified, [Pyr1]apelin-13(1-12), [Pyr1]apelin-13(1-10) and [Pyr1]apelin-13(1-6) were the most abundant. These data suggest that apelin peptides designed for use as cardiovascular therapeutics, should include modifications that minimise C-terminal cleavage.
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Apelin-36-[L28A] and Apelin-36-[L28C(30kDa-PEG)] peptides that improve diet induced obesity are G protein biased ligands at the apelin receptor. Peptides 2019; 121:170139. [PMID: 31472173 PMCID: PMC6838674 DOI: 10.1016/j.peptides.2019.170139] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 08/21/2019] [Accepted: 08/26/2019] [Indexed: 11/30/2022]
Abstract
BACKGROUND Apelin signalling pathways have important cardiovascular and metabolic functions. Recently, apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)], were reported to function independent of the apelin receptor in vivo to produce beneficial metabolic effects without modulating blood pressure. We aimed to show that these peptides bound to the apelin receptor and to further characterise their pharmacology in vitro at the human apelin receptor. METHODS [Pyr1]apelin-13 saturation binding experiments and competition binding experiments were performed in rat and human heart homogenates using [125I]apelin-13 (0.1 nM), and/or increasing concentrations of apelin-36, apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] (50pM-100μM). Apelin-36 and its analogues apelin-36-[F36A], apelin-36-[L28A], apelin-36-[L28C(30kDa-PEG)], apelin-36-[A28 A13] and [40kDa-PEG]-apelin-36 were tested in forskolin-induced cAMP inhibition and β-arrestin assays in CHO-K1 cells heterologously expressing the human apelin receptor. Bias signaling was quantified using the operational model for bias. RESULTS In both species, [Pyr1]apelin-13 had comparable subnanomolar affinity and the apelin receptor density was similar. Apelin-36, apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] competed for binding of [125I]apelin-13 with nanomolar affinities. Apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] inhibited forskolin-induced cAMP release, with nanomolar potencies but they were less potent compared to apelin-36 at recruiting β-arrestin. Bias analysis suggested that these peptides were G protein biased. Additionally, [40kDa-PEG]-apelin-36 and apelin-36-[F36A] retained nanomolar potencies in both cAMP and β-arrestin assays whilst apelin-36-[A13 A28] exhibited a similar profile to apelin-36-[L28C(30kDa-PEG)] in the β-arrestin assay but was more potent in the cAMP assay. CONCLUSIONS Apelin-36-[L28A] and apelin-36-[L28C(30kDa-PEG)] are G protein biased ligands of the apelin receptor, suggesting that the apelin receptor is an important therapeutic target in metabolic diseases.
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A novel cyclic biased agonist of the apelin receptor, MM07, is disease modifying in the rat monocrotaline model of pulmonary arterial hypertension. Br J Pharmacol 2019; 176:1206-1221. [PMID: 30710493 PMCID: PMC6468262 DOI: 10.1111/bph.14603] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 01/10/2019] [Accepted: 01/23/2019] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND AND PURPOSE Apelin is an endogenous vasodilatory and inotropic peptide that is down-regulated in human pulmonary arterial hypertension, although the density of the apelin receptor is not significantly attenuated. We hypothesised that a G protein-biased apelin analogue MM07, which is more stable than the endogenous apelin peptide, may be beneficial in this condition with the advantage of reduced β-arrestin-mediated receptor internalisation with chronic use. EXPERIMENTAL APPROACH Male Sprague-Dawley rats received either monocrotaline to induce pulmonary arterial hypertension or saline and then daily i.p. injections of either MM07 or saline for 21 days. The extent of disease was assessed by right ventricular catheterisation, cardiac MRI, and histological analysis of the pulmonary vasculature. The effect of MM07 on signalling, proliferation, and apoptosis of human pulmonary artery endothelial cells was investigated. KEY RESULTS MM07 significantly reduced the elevation of right ventricular systolic pressure and hypertrophy induced by monocrotaline. Monocrotaline-induced changes in cardiac structure and function, including right ventricular end-systolic and end-diastolic volumes, ejection fraction, and left ventricular end-diastolic volume, were attenuated by MM07. MM07 also significantly reduced monocrotaline-induced muscularisation of small pulmonary blood vessels. MM07 stimulated endothelial NOS phosphorylation and expression, promoted proliferation, and attenuated apoptosis of human pulmonary arterial endothelial cells in vitro. CONCLUSION AND IMPLICATIONS Our findings suggest that chronic treatment with MM07 is beneficial in this animal model of pulmonary arterial hypertension by addressing disease aetiology. These data support the development of G protein-biased apelin receptor agonists with improved pharmacokinetic profiles for use in human disease.
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New drugs and emerging therapeutic targets in the endothelin signaling pathway and prospects for personalized precision medicine. Physiol Res 2018; 67:S37-S54. [PMID: 29947527 DOI: 10.33549/physiolres.933872] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
During the last thirty years since the discovery of endothelin-1, the therapeutic strategy that has evolved in the clinic, mainly in the treatment of pulmonary arterial hypertension, is to block the action of the peptide either at the ET(A) subtype or both receptors using orally active small molecule antagonists. Recently, there has been a rapid expansion in research targeting ET receptors using chemical entities other than small molecules, particularly monoclonal antibody antagonists and selective peptide agonists and antagonists. While usually sacrificing oral bio-availability, these compounds have other therapeutic advantages with the potential to considerably expand drug targets in the endothelin pathway and extend treatment to other pathophysiological conditions. Where the small molecule approach has been retained, a novel strategy to combine two vasoconstrictor targets, the angiotensin AT(1) receptor as well as the ET(A) receptor in the dual antagonist sparsentan has been developed. A second emerging strategy is to combine drugs that have two different targets, the ET(A) antagonist ambrisentan with the phosphodiesterase inhibitor tadalafil, to improve the treatment of pulmonary arterial hypertension. The solving of the crystal structure of the ET(B) receptor has the potential to identify allosteric binding sites for novel ligands. A further key advance is the experimental validation of a single nucleotide polymorphism that has genome wide significance in five vascular diseases and that significantly increases the amount of big endothelin-1 precursor in the plasma. This observation provides a rationale for testing this single nucleotide polymorphism to stratify patients for allocation to treatment with endothelin agents and highlights the potential to use personalized precision medicine in the endothelin field.
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Detection of Atherosclerotic Inflammation by 68Ga-DOTATATE PET Compared to [ 18F]FDG PET Imaging. J Am Coll Cardiol 2017; 69:1774-1791. [PMID: 28385306 PMCID: PMC5381358 DOI: 10.1016/j.jacc.2017.01.060] [Citation(s) in RCA: 281] [Impact Index Per Article: 40.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 01/04/2017] [Accepted: 01/20/2017] [Indexed: 10/25/2022]
Abstract
BACKGROUND Inflammation drives atherosclerotic plaque rupture. Although inflammation can be measured using fluorine-18-labeled fluorodeoxyglucose positron emission tomography ([18F]FDG PET), [18F]FDG lacks cell specificity, and coronary imaging is unreliable because of myocardial spillover. OBJECTIVES This study tested the efficacy of gallium-68-labeled DOTATATE (68Ga-DOTATATE), a somatostatin receptor subtype-2 (SST2)-binding PET tracer, for imaging atherosclerotic inflammation. METHODS We confirmed 68Ga-DOTATATE binding in macrophages and excised carotid plaques. 68Ga-DOTATATE PET imaging was compared to [18F]FDG PET imaging in 42 patients with atherosclerosis. RESULTS Target SSTR2 gene expression occurred exclusively in "proinflammatory" M1 macrophages, specific 68Ga-DOTATATE ligand binding to SST2 receptors occurred in CD68-positive macrophage-rich carotid plaque regions, and carotid SSTR2 mRNA was highly correlated with in vivo 68Ga-DOTATATE PET signals (r = 0.89; 95% confidence interval [CI]: 0.28 to 0.99; p = 0.02). 68Ga-DOTATATE mean of maximum tissue-to-blood ratios (mTBRmax) correctly identified culprit versus nonculprit arteries in patients with acute coronary syndrome (median difference: 0.69; interquartile range [IQR]: 0.22 to 1.15; p = 0.008) and transient ischemic attack/stroke (median difference: 0.13; IQR: 0.07 to 0.32; p = 0.003). 68Ga-DOTATATE mTBRmax predicted high-risk coronary computed tomography features (receiver operating characteristics area under the curve [ROC AUC]: 0.86; 95% CI: 0.80 to 0.92; p < 0.0001), and correlated with Framingham risk score (r = 0.53; 95% CI: 0.32 to 0.69; p <0.0001) and [18F]FDG uptake (r = 0.73; 95% CI: 0.64 to 0.81; p < 0.0001). [18F]FDG mTBRmax differentiated culprit from nonculprit carotid lesions (median difference: 0.12; IQR: 0.0 to 0.23; p = 0.008) and high-risk from lower-risk coronary arteries (ROC AUC: 0.76; 95% CI: 0.62 to 0.91; p = 0.002); however, myocardial [18F]FDG spillover rendered coronary [18F]FDG scans uninterpretable in 27 patients (64%). Coronary 68Ga-DOTATATE PET scans were readable in all patients. CONCLUSIONS We validated 68Ga-DOTATATE PET as a novel marker of atherosclerotic inflammation and confirmed that 68Ga-DOTATATE offers superior coronary imaging, excellent macrophage specificity, and better power to discriminate high-risk versus low-risk coronary lesions than [18F]FDG. (Vascular Inflammation Imaging Using Somatostatin Receptor Positron Emission Tomography [VISION]; NCT02021188).
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D Atherosclerotic inflammation imaging using 68ga-dotatate pet vs. 18f-fdg pet: a prospective clinical sudy with molecular and histological validation. BRITISH HEART JOURNAL 2017. [DOI: 10.1136/heartjnl-2017-311726.235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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[Pyr 1]Apelin-13 (1-12) Is a Biologically Active ACE2 Metabolite of the Endogenous Cardiovascular Peptide [Pyr 1]Apelin-13. Front Neurosci 2017; 11:92. [PMID: 28293165 PMCID: PMC5329011 DOI: 10.3389/fnins.2017.00092] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 02/10/2017] [Indexed: 01/21/2023] Open
Abstract
Aims: Apelin is a predicted substrate for ACE2, a novel therapeutic target. Our aim was to demonstrate the endogenous presence of the putative ACE2 product [Pyr1]apelin-13(1–12) in human cardiovascular tissues and to confirm it retains significant biological activity for the apelin receptor in vitro and in vivo. The minimum active apelin fragment was also investigated. Methods and Results: [Pyr1]apelin-13 incubated with recombinant human ACE2 resulted in de novo generation of [Pyr1]apelin-13(1–12) identified by mass spectrometry. Endogenous [Pyr1]apelin-13(1–12) was detected by immunostaining in human heart and lung localized to the endothelium. Expression was undetectable in lung from patients with pulmonary arterial hypertension. In human heart [Pyr1]apelin-13(1–12) (pKi = 8.04 ± 0.06) and apelin-13(F13A) (pKi = 8.07 ± 0.24) competed with [125I]apelin-13 binding with nanomolar affinity, 4-fold lower than for [Pyr1]apelin-13 (pKi = 8.83 ± 0.06) whereas apelin-17 exhibited highest affinity (pKi = 9.63 ± 0.17). The rank order of potency of peptides to inhibit forskolin-stimulated cAMP was apelin-17 (pD2 = 10.31 ± 0.28) > [Pyr1]apelin-13 (pD2 = 9.67 ± 0.04) ≥ apelin-13(F13A) (pD2 = 9.54 ± 0.05) > [Pyr1]apelin-13(1–12) (pD2 = 9.30 ± 0.06). The truncated peptide apelin-13(R10M) retained nanomolar potency (pD2 = 8.70 ± 0.04) but shorter fragments exhibited low micromolar potency. In a β-arrestin recruitment assay the rank order of potency was apelin-17 (pD2 = 10.26 ± 0.09) >> [Pyr1]apelin-13 (pD2 = 8.43 ± 0.08) > apelin-13(R10M) (pD2 = 8.26 ± 0.17) > apelin-13(F13A) (pD2 = 7.98 ± 0.04) ≥ [Pyr1]apelin-13(1–12) (pD2 = 7.84 ± 0.06) >> shorter fragments (pD2 < 6). [Pyr1]apelin-13(1–12) and apelin-13(F13A) contracted human saphenous vein with similar sub-nanomolar potencies and [Pyr1]apelin-13(1–12) was a potent inotrope in paced mouse right ventricle and human atria. [Pyr1]apelin-13(1–12) elicited a dose-dependent decrease in blood pressure in anesthetized rat and dose-dependent increase in forearm blood flow in human volunteers. Conclusions: We provide evidence that ACE2 cleaves [Pyr1]apelin-13 to [Pyr1]apelin-13(1–12) and this cleavage product is expressed in human cardiovascular tissues. We have demonstrated biological activity of [Pyr1]apelin-13(1–12) at the human and rodent apelin receptor in vitro and in vivo. Our data show that reported enhanced ACE2 activity in cardiovascular disease should not significantly compromise the beneficial effects of apelin based therapies for example in PAH.
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Elabela/Toddler Is an Endogenous Agonist of the Apelin APJ Receptor in the Adult Cardiovascular System, and Exogenous Administration of the Peptide Compensates for the Downregulation of Its Expression in Pulmonary Arterial Hypertension. Circulation 2017; 135:1160-1173. [PMID: 28137936 PMCID: PMC5363837 DOI: 10.1161/circulationaha.116.023218] [Citation(s) in RCA: 166] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 01/17/2017] [Indexed: 01/15/2023]
Abstract
Supplemental Digital Content is available in the text. Background: Elabela/toddler (ELA) is a critical cardiac developmental peptide that acts through the G-protein–coupled apelin receptor, despite lack of sequence similarity to the established ligand apelin. Our aim was to investigate the receptor pharmacology, expression pattern, and in vivo function of ELA peptides in the adult cardiovascular system, to seek evidence for alteration in pulmonary arterial hypertension (PAH) in which apelin signaling is downregulated, and to demonstrate attenuation of PAH severity with exogenous administration of ELA in a rat model. Methods: In silico docking analysis, competition binding experiments, and downstream assays were used to characterize ELA receptor binding in human heart and signaling in cells expressing the apelin receptor. ELA expression in human cardiovascular tissues and plasma was determined using real-time quantitative polymerase chain reaction, dual-labeling immunofluorescent staining, and immunoassays. Acute cardiac effects of ELA-32 and [Pyr1]apelin-13 were assessed by MRI and cardiac catheterization in anesthetized rats. Cardiopulmonary human and rat tissues from PAH patients and monocrotaline- and Sugen/hypoxia-exposed rats were used to show changes in ELA expression in PAH. The effect of ELA treatment on cardiopulmonary remodeling in PAH was investigated in the monocrotaline rat model. Results: ELA competed for binding of apelin in human heart with overlap for the 2 peptides indicated by in silico modeling. ELA activated G-protein– and β-arrestin–dependent pathways. We detected ELA expression in human vascular endothelium and plasma. Comparable to apelin, ELA increased cardiac contractility, ejection fraction, and cardiac output and elicited vasodilatation in rat in vivo. ELA expression was reduced in cardiopulmonary tissues from PAH patients and PAH rat models, respectively. ELA treatment significantly attenuated elevation of right ventricular systolic pressure and right ventricular hypertrophy and pulmonary vascular remodeling in monocrotaline-exposed rats. Conclusions: These results show that ELA is an endogenous agonist of the human apelin receptor, exhibits a cardiovascular profile comparable to apelin, and is downregulated in human disease and rodent PAH models, and exogenous peptide can reduce the severity of cardiopulmonary remodeling and function in PAH in rats. This study provides additional proof of principle that an apelin receptor agonist may be of therapeutic use in PAH in humans.
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Smooth Muscle Endothelin B Receptors Regulate Blood Pressure but Not Vascular Function or Neointimal Remodeling. Hypertension 2016; 69:275-285. [PMID: 28028193 PMCID: PMC5222555 DOI: 10.1161/hypertensionaha.115.07031] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Revised: 01/02/2016] [Accepted: 11/30/2016] [Indexed: 01/06/2023]
Abstract
Supplemental Digital Content is available in the text. The role of smooth muscle endothelinB (ETB) receptors in regulating vascular function, blood pressure (BP), and neointimal remodeling has not been established. Selective knockout mice were generated to address the hypothesis that loss of smooth muscle ETB receptors would reduce BP, alter vascular contractility, and inhibit neointimal remodeling. ETB receptors were selectively deleted from smooth muscle by crossing floxed ETB mice with those expressing cre-recombinase controlled by the transgelin promoter. Functional consequences of ETB deletion were assessed using myography. BP was measured by telemetry, and neointimal lesion formation induced by femoral artery injury. Lesion size and composition (day 28) were analyzed using optical projection tomography, histology, and immunohistochemistry. Selective deletion of ETB was confirmed by genotyping, autoradiography, polymerase chain reaction, and immunohistochemistry. ETB-mediated contraction was reduced in trachea, but abolished from mesenteric veins, of knockout mice. Induction of ETB-mediated contraction in mesenteric arteries was also abolished in these mice. Femoral artery function was unaltered, and baseline BP modestly elevated in smooth muscle ETB knockout compared with controls (+4.2±0.2 mm Hg; P<0.0001), but salt-induced and ETB blockade–mediated hypertension were unaltered. Circulating endothelin-1 was not altered in knockout mice. ETB-mediated contraction was not induced in femoral arteries by incubation in culture medium or lesion formation, and lesion size was not altered in smooth muscle ETB knockout mice. In the absence of other pathology, ETB receptors in vascular smooth muscle make a small but significant contribution to ETB-dependent regulation of BP. These ETB receptors have no effect on vascular contraction or neointimal remodeling.
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Chemerin Elicits Potent Constrictor Actions via Chemokine-Like Receptor 1 (CMKLR1), not G-Protein-Coupled Receptor 1 (GPR1), in Human and Rat Vasculature. J Am Heart Assoc 2016; 5:JAHA.116.004421. [PMID: 27742615 PMCID: PMC5121526 DOI: 10.1161/jaha.116.004421] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Circulating levels of chemerin are significantly higher in hypertensive patients and positively correlate with blood pressure. Chemerin activates chemokine-like receptor 1 (CMKLR1 or ChemR23) and is proposed to activate the "orphan" G-protein-coupled receptor 1 (GPR1), which has been linked with hypertension. Our aim was to localize chemerin, CMKLR1, and GPR1 in the human vasculature and determine whether 1 or both of these receptors mediate vasoconstriction. METHODS AND RESULTS Using immunohistochemistry and molecular biology in conduit arteries and veins and resistance vessels, we localized chemerin to endothelium, smooth muscle, and adventitia and found that CMKLR1 and GPR1 were widely expressed in smooth muscle. C9 (chemerin149-157) contracted human saphenous vein (pD2=7.30±0.31) and resistance arteries (pD2=7.05±0.54) and increased blood pressure in rats by 9.1±1.0 mm Hg at 200 nmol. Crucially, these in vitro and in vivo vascular actions were blocked by CCX832, which we confirmed to be highly selective for CMKLR1 over GPR1. C9 inhibited cAMP accumulation in human aortic smooth muscle cells and preconstricted rat aorta, consistent with the observed vasoconstrictor action. Downstream signaling was explored further and, compared to chemerin, C9 showed a bias factor=≈5000 for the Gi protein pathway, suggesting that CMKLR1 exhibits biased agonism. CONCLUSIONS Our data suggest that chemerin acts at CMKLR1, but not GPR1, to increase blood pressure. Chemerin has an established detrimental role in metabolic syndrome, and these direct vascular actions may contribute to hypertension, an additional risk factor for cardiovascular disease. This study provides proof of principle for the therapeutic potential of selective CMKLR1 antagonists.
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Endothelin ETA receptors predominate in chronic thromboembolic pulmonary hypertension. Life Sci 2016; 159:104-110. [PMID: 26874031 PMCID: PMC5000546 DOI: 10.1016/j.lfs.2016.02.036] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 01/21/2016] [Accepted: 02/09/2016] [Indexed: 12/15/2022]
Abstract
AIMS Endothelin-1 levels are raised in chronic thromboembolic pulmonary hypertension. Our aim in this study was to identify the presence of endothelin receptors in patients with CTEPH by analysing tissue removed at pulmonary endarterectomy. MAIN METHODS Pulmonary endarterectomy tissue cross-sections were analysed using autoradiography with [(125)I]-ET-1 using ligands selective for ETA or ETB to determine sub-type distribution. The precise cellular localisation of ETA and ETB receptors was determined using selective antisera to both sub-types and compared with haematoxylin and eosin, Elastic Van Gieson and smooth muscle actin labelled sections. KEY FINDINGS Two patterns of ET-1 binding were found. In sections with frequent recanalised channels, ET-1 bound to the smooth muscle cells surrounding the channels. In sections where there was less organised thrombus with no obvious re-canalisation, minimal ET-1 binding was observed. Some contractile type smooth muscle cells not associated with recanalised channels and diffusely spread throughout the PEA material were associated with ET receptor antibody binding on immunohistochemistry. There was a greater expression of the ETA receptor type in the specimens. SIGNIFICANCE The presence of ET-1 receptors in the chronic thrombus in proximal CTEPH suggests ET-1 could act not only on the distal vasculopathy in the unobstructed vessels but may also stimulate smooth muscle cell proliferation within chronic clot. The abundance of ET receptors within the tissue provides evidence that the ET pathway is involved in the pathology of chronic thrombus reorganisation leading to CTEPH providing a rationale for the repurposing of ET receptor antagonists in the treatment of this condition.
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Cardiac action of the first G protein biased small molecule apelin agonist. Biochem Pharmacol 2016; 116:63-72. [PMID: 27475715 PMCID: PMC5012889 DOI: 10.1016/j.bcp.2016.07.018] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Accepted: 07/25/2016] [Indexed: 11/19/2022]
Abstract
Apelin peptide analogues displaying bias towards G protein signalling pathways have beneficial cardiovascular actions compared with the native peptide in humans in vivo. Our aim was to determine whether small molecule agonists could retain G protein bias. We have identified a biased small molecule, CMF-019, and characterised it in vitro and in vivo. In competition radioligand binding experiments in heart homogenates, CMF-019 bound to the human, rat and mouse apelin receptor with high affinity (pKi=8.58±0.04, 8.49±0.04 and 8.71±0.06 respectively). In cell-based functional assays, whereas, CMF-019 showed similar potency for the Gαi pathway to the endogenous agonist [Pyr(1)]apelin-13 (pD2=10.00±0.13 vs 9.34±0.15), in β-arrestin and internalisation assays it was less potent (pD2=6.65±0.15 vs 8.65±0.10 and pD2=6.16±0.21 vs 9.28±0.10 respectively). Analysis of these data demonstrated a bias of ∼400 for the Gαi over the β-arrestin pathway and ∼6000 over receptor internalisation. CMF-019 was tested for in vivo activity using intravenous injections into anaesthetised male Sprague-Dawley rats fitted with a pressure-volume catheter in the left ventricle. CMF-019 caused a significant increase in cardiac contractility of 606±112mmHg/s (p<0.001) at 500nmol. CMF-019 is the first biased small molecule identified at the apelin receptor and increases cardiac contractility in vivo. We have demonstrated that Gαi over β-arrestin/internalisation bias can be retained in a non-peptide analogue and predict that such bias will have the therapeutic benefit following chronic use. CMF-019 is suitable as a tool compound and provides the basis for design of biased agonists with improved pharmacokinetics for treatment of cardiovascular conditions such as pulmonary arterial hypertension.
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MESH Headings
- Amino Acids, Branched-Chain/chemistry
- Amino Acids, Branched-Chain/metabolism
- Amino Acids, Branched-Chain/pharmacokinetics
- Amino Acids, Branched-Chain/pharmacology
- Animals
- Apelin
- Apelin Receptors
- Benzimidazoles/chemistry
- Benzimidazoles/metabolism
- Benzimidazoles/pharmacokinetics
- Benzimidazoles/pharmacology
- Binding Sites
- Binding, Competitive
- CHO Cells
- Cardiotonic Agents/chemistry
- Cardiotonic Agents/metabolism
- Cardiotonic Agents/pharmacokinetics
- Cardiotonic Agents/pharmacology
- Cricetulus
- Half-Life
- Heart Ventricles/drug effects
- Heart Ventricles/metabolism
- Humans
- Intercellular Signaling Peptides and Proteins/agonists
- Intercellular Signaling Peptides and Proteins/chemistry
- Intercellular Signaling Peptides and Proteins/metabolism
- Intercellular Signaling Peptides and Proteins/pharmacology
- Male
- Mice
- Models, Molecular
- Molecular Docking Simulation
- Myocardial Contraction/drug effects
- Random Allocation
- Rats
- Rats, Sprague-Dawley
- Receptors, G-Protein-Coupled/agonists
- Receptors, G-Protein-Coupled/chemistry
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/metabolism
- Recombinant Proteins/chemistry
- Recombinant Proteins/metabolism
- Structural Homology, Protein
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Characterization of [¹²⁵I]GLP-1(9-36), a novel radiolabeled analog of the major metabolite of glucagon-like peptide 1 to a receptor distinct from GLP1-R and function of the peptide in murine aorta. Life Sci 2014; 102:134-8. [PMID: 24641952 DOI: 10.1016/j.lfs.2014.03.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Revised: 01/29/2014] [Accepted: 03/04/2014] [Indexed: 12/26/2022]
Abstract
AIMS Glucagon-like peptide 1 (GLP-1) is an insulin secretagogue, released in response to meal ingestion and efficiently lowers blood glucose in Type 2 diabetic patients. GLP-1(7-36) is rapidly metabolized by dipeptidyl peptidase IV to the major metabolite GLP-1(9-36)-amide, often thought to be inactive. Inhibitors of this enzyme are widely used to treat diabetes. Our aim was to characterize the binding of GLP-1(9-36) to native mouse tissues and to cells expressing GLP1-R as well as to measure functional responses in the mouse aorta compared with GLP-1(7-36). MAIN METHODS The affinity of [(125)I]GLP-1(7-36) and [(125)I]GLP-1(9-36) was measured in mouse tissues by saturation binding and autoradiography used to determine receptor distribution. The affinity of both peptides was compared in binding to recombinant GLP-1 receptors using cAMP and scintillation proximity assays. Vasoactivity was determined in mouse aortae in vitro. KEY FINDINGS In cells expressing GLP-1 receptors, GLP-1(7-36) bound with the expected high affinities (0.1 nM) and an EC50 of 0.07 nM in cAMP assays but GLP-1(9-36) bound with 70,000 and 100,000 fold lower affinities respectively. In contrast, in mouse brain, both labeled peptides bound with a single high affinity, with Hill slopes close to unity, although receptor density was an order of magnitude lower for [(125)I]GLP-1(9-36). In functional experiments both peptides had similar potencies, GLP-1(7-36), pD2=7.40 ± 0.24 and GLP-1(9-36), pD2=7.57 ± 0.64. SIGNIFICANCE These results suggest that GLP-1(9-36) binds and has functional activity in the vasculature but these actions may be via a pathway that is distinct from the classical GLP-1 receptor and insulin secretagogue actions.
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The CCR5 chemokine receptor mediates vasoconstriction and stimulates intimal hyperplasia in human vessels in vitro. Cardiovasc Res 2014; 101:513-21. [PMID: 24323316 PMCID: PMC3928001 DOI: 10.1093/cvr/cvt333] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 11/28/2013] [Accepted: 11/29/2013] [Indexed: 11/22/2022] Open
Abstract
AIMS The chemokine receptor CCR5 and its inflammatory ligands have been linked to atherosclerosis, an accelerated form of which occurs in saphenous vein graft disease. We investigated the function of vascular smooth muscle CCR5 in human coronary artery and saphenous vein, vascular tissues susceptible to atherosclerosis, and vasospasm. METHODS AND RESULTS CCR5 ligands were vasoconstrictors in saphenous vein and coronary artery. In vein, constrictor responses to CCL4 were completely blocked by CCR5 antagonists, including maraviroc. CCR5 antagonists prevented the development of a neointima after 14 days in cultured saphenous vein. CCR5 and its ligands were expressed in normal and diseased coronary artery and saphenous vein and localized to medial and intimal smooth muscle, endothelial, and inflammatory cells. [(125)I]-CCL4 bound to venous smooth muscle with KD = 1.15 ± 0.26 nmol/L and density of 22 ± 9 fmol mg(-1) protein. CONCLUSIONS Our data support a potential role for CCR5 in vasoconstriction and neointimal formation in vitro and imply that CCR5 chemokines may contribute to vascular remodelling and augmented vascular tone in human coronary artery and vein graft disease. The repurposing of maraviroc for the treatment of cardiovascular disease warrants further investigation.
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Modulation of endothelin receptors in the failing right ventricle of the heart and vasculature of the lung in human pulmonary arterial hypertension. Life Sci 2014; 118:391-6. [PMID: 24582810 PMCID: PMC4288792 DOI: 10.1016/j.lfs.2014.02.020] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 01/08/2014] [Accepted: 02/11/2014] [Indexed: 01/08/2023]
Abstract
AIMS In pulmonary arterial hypertension (PAH), increases in endothelin-1 (ET-1) contribute to elevated pulmonary vascular resistance which ultimately causes death by right ventricular (RV) heart failure. ET antagonists are effective in treating PAH but lack efficacy in treating left ventricular (LV) heart failure, where ETA receptors are significantly increased. The aim was to quantify the density of ETA and ETB receptors in cardiopulmonary tissue from PAH patients and the monocrotaline (MCT) rat, which recapitulates some of the pathophysiological features, including increased RV pressure. MAIN METHODS Radioligand binding assays were used to quantify affinity, density and ratio of ET receptors. KEY FINDINGS In RV from human PAH hearts, there was a significant increase in the ratio of ETA to ETB receptors compared with normal hearts. In the RV of the MCT rat, the ratio also changed but was reversed. In both human and rat, there was no change in LV. In human PAH lungs, ETA receptors were significantly increased in the medial layer of small pulmonary arteries with no change detectable in MCT rat vessels. SIGNIFICANCE Current treatments for PAH focus mainly on pulmonary vasodilatation. The increase in ETA receptors in arteries provides a mechanism for the beneficial vasodilator actions of ET antagonists. The increase in the ratio of ETA in RV also implicates changes to ET signalling although it is unclear if ET antagonism is beneficial but the results emphasise the unexploited potential for therapies that target the RV, to improve survival in patients with PAH.
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Selective deletion of endothelin B receptors from vascular smooth muscle does not inhibit neointimal lesion formation. Life Sci 2013. [DOI: 10.1016/j.lfs.2014.01.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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12 Pharmacology of Human ETA and ETB Receptor Signalling VIA G-Protein and Beta-Arrestin Pathways. BRITISH HEART JOURNAL 2012. [DOI: 10.1136/heartjnl-2012-302951.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Defining the affinity and receptor sub-type selectivity of four classes of endothelin antagonists in clinically relevant human cardiovascular tissues. Life Sci 2012; 91:681-6. [PMID: 22634326 DOI: 10.1016/j.lfs.2012.05.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Revised: 05/04/2012] [Accepted: 05/08/2012] [Indexed: 12/30/2022]
Abstract
AIMS We have compared the endothelin receptor subtype affinity (K(D)) and selectivity of four structural classes of antagonists (peptide, sulphonamide-based, carboxylic acid-based, myceric acid-based) in human cardiovascular tissues to determine whether these are predicted by values reported for human cloned receptors. Additionally, affinities (K(B)) for these antagonists, determined in ET-1-mediated vasoconstriction assays in human blood vessels, were used to identify discrepancies between K(B) and K(D) determined in the same tissues. MAIN METHODS Competition binding experiments were carried out in sections of human left ventricle, coronary artery and homogenates of saphenous vein to determine K(D) values for structurally different ET(A)-selective (FR139317, BMS 182874, S97-139, sitaxentan, ambrisentan) and mixed (PD142893, Ro462005, bosentan, L-749329, SB209670) antagonists. Schild-derived values of antagonist affinity were obtained in vascular functional studies. KEY FINDINGS When compared with previously reported data in human cloned endothelin receptors, those antagonists reported to be ET(A)-selective exhibited even greater ET(A) selectivity in human ventricle (BMS 182874, sitaxentan, ambrisentan) that expressed both receptor subtypes. Those antagonists reported to have <100 fold selectivity in cloned receptors (PD142893, Ro-462005, bosentan, SB209670, L-749329) did not distinguish between receptor subtypes in human left ventricle. For antagonists where we determined affinity in vascular functional and binding assays (Ro462005, bosentan, BMS 182874, L-749329, SB209670) there was no correlation between the degree of discrepancy in K(B) and K(D) and structural class. SIGNIFICANCE For an antagonist to retain ET(A)-selectivity in vivo it may be necessary to identify those compounds that have at least 1000 fold ET(A):ET(B) selectivity in in vitro assays.
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Microarray, qPCR, and KCNJ5 sequencing of aldosterone-producing adenomas reveal differences in genotype and phenotype between zona glomerulosa- and zona fasciculata-like tumors. J Clin Endocrinol Metab 2012; 97:E819-29. [PMID: 22442279 DOI: 10.1210/jc.2011-2965] [Citation(s) in RCA: 132] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
CONTEXT Aldosterone-producing adenomas (APA) are heterogeneous. The recent finding of somatic KCNJ5 mutations suggests a genetic explanation. OBJECTIVES The objectives of this study were the following: 1) to compare transcriptional profiles in APA and adjacent adrenal gland (AAG); 2) to test whether gene expression profile clusters with different cell histology; and 3) to measure the frequency of KCNJ5 mutations and determine the genotype-phenotype relationship. DESIGN/SETTING The design of the study included laboratory analyses of 46 unselected APA. PATIENTS The patients in this study had primary hyperaldosteronism with unilateral APA. INTERVENTIONS The objectives of this study were the following: 1) Illumina beadchip analysis of RNA from eight paired APA-AAG; 2) a blinded review of cell histology for 46 APA; 3) laser capture microdissection of zona glomerulosa (ZG) and zona fasciculata (ZF) cells; and 4) sequencing of KCNJ5 in 46 APA. MAIN OUTCOME MEASURES The main outcome measures of this study were the following: 1) a difference in gene expression profile and a correlation with histological markers of ZF; 2) a frequency of KCNJ5 mutations and phenotypic comparisons of wild type with mutant APA. RESULTS The results of the study were the following: 1) a cluster analysis of microarray data separated APA from AAG. APA at opposite ends of the APA cluster had an approximately 800-fold difference in CYP17A1 mRNA expression, whereas histology showed 0% ZF-like cells in one vs. 100% in the other. A heat map ranking APA by CYP17A1 expression correctly predicted several genes (e.g. KCNK1, SLC24A3) to be enriched in laser capture microdissection samples of ZG; 2) known or novel mutations of KCNJ5 were found in 20 of 46 consecutive APA [43% (95% confidence interval [CI] (29, 58)%)]. The APA with KCNJ5 gene mutations were larger compared with tumors harboring the wild type, 1.63 [95% CI (1.37, 1.88)] vs. 1.14 [0.97, 1.30] cm (P = 0.0013), had predominantly ZF-like cells, and their CYP17A1 (log(2)-fold change) was higher than in wild type: -0.96 [95% CI (-0.07, -1.85)] vs. -2.54 [-1.61, -3.46], (P = 0.017). CONCLUSIONS KCNJ5 mutations are common in APA, particularly those arising from ZF. The long-recognized heterogeneity among APA may have a genetic basis.
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Comparison of human ETA and ETB receptor signalling via G-protein and β-arrestin pathways. Life Sci 2012; 91:544-9. [PMID: 22480514 DOI: 10.1016/j.lfs.2012.03.021] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Revised: 03/05/2012] [Accepted: 03/08/2012] [Indexed: 02/04/2023]
Abstract
AIMS To determine the pharmacology of ET(A)- and ET(B)-mediated β-arrestin recruitment and compare this to established human pharmacology of these receptors to identify evidence for endothelin receptor biased signalling and pathway specific blockade by antagonists. MAIN METHODS The ability of ET-1, ET-2, ET-3, sarafotoxin 6b and sarafotoxin 6c to activate ET(A) and ET(B)-mediated β-arrestin recruitment was determined in CHO-K1 cells. Affinities were obtained for ET(A) selective (BQ123, sitaxentan, ambrisentan), ET(B) selective (BQ788) and mixed (bosentan) antagonists using ET-1 and compared to affinities obtained in competition experiments in human heart and by Schild analysis in human saphenous vein. Agonist dependence of affinities was compared for BQ123 and BQ788 in the ET(A) and ET(B) β-arrestin assays respectively. KEY FINDINGS For β-arrestin recruitment, order of potency was as expected for the ET(A) (ET-1≥ET-2>>ET-3) and ET(B) (ET-1=ET-2=ET-3) receptors. However, at the ET(A) receptor sarafotoxin 6b and ET-3 were partial agonists. Antagonism of ET peptides by selective and mixed antagonists appeared non-competitive. BQ123, but not BQ788, exhibited agonist-dependent affinities. Bosentan was significantly more effective an inhibitor of β-arrestin recruitment mediated by ET(A) compared to the ET(B) receptor. In the ET(A) vasoconstrictor assay, ET-1, ET-2 and S6b were equipotent, full agonists and antagonists tested behaved in a competitive manner, although affinities were lower than predicted from the competition binding experiments in left ventricle. SIGNIFICANCE These data suggest that the pharmacology of ET(A) and ET(B) receptors linked to G-protein- and β-arrestin mediated responses was different and bosentan appeared to show bias, preferentially blocking ET(A) mediated β-arrestin recruitment.
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Comparison of endothelin receptors in normal versus cirrhotic human liver and in the liver from endothelial cell-specific ETB knockout mice. Life Sci 2012; 91:716-22. [PMID: 22365955 DOI: 10.1016/j.lfs.2012.02.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Revised: 01/20/2012] [Accepted: 02/03/2012] [Indexed: 01/06/2023]
Abstract
AIMS Endothelin (ET) antagonists show promise in animal models of cirrhosis and portal hypertension. The aim was to pharmacologically characterise the expression of endothelin receptors in human liver, hepatic artery and portal vein. MAIN METHODS Immunofluorescence staining, receptor autoradiography and competition binding assays were used to localise and quantify ET receptors on hepatic parenchyma, hepatic artery and portal vein in human cirrhotic or normal liver. Additional experiments were performed to determine the affinity and selectivity of ET antagonists for liver ET endothelin receptors. An endothelial cell ET(B) knockout murine model was used to examine the function of sinusoid endothelial ET(B) receptors. KEY FINDINGS ET(B) receptors predominated in normal human liver and displayed the highest ratio (ET(B):ET(A) 63:47) compared with other peripheral tissues. In two patients examined, liver ET(B) expression was up-regulated in cirrhosis (ET(B):ET(A) 83:17). Both sub-types localised to the media of normal portal vein but ET(B) receptors were downregulated fivefold in the media of cirrhotic portal vein. Sinusoid diameter was fourfold smaller in endothelial cell ET(B) knockout mice. The liver morphology of ET(B) knockout mice was markedly different to normal murine liver, with loss of the wide spread sinusoidal pattern. In the knockout mice, sinusoids were reduced in both number and absolute diameter, while large intrahepatic veins were congested with red blood cells. SIGNIFICANCE These data support a role for the ET system in cirrhosis of the liver and suggest that endothelial ET(B) blockade may cause sinusoidal constriction which may contribute to hepatotoxicity associated with some endothelin antagonists.
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Cellular localization of receptors using antibodies visualized by light and dual labeling confocal microscopy. Methods Mol Biol 2012; 897:239-60. [PMID: 22674169 DOI: 10.1007/978-1-61779-909-9_12] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Immunocytochemistry can be used to visualize the binding of specific site-directed antisera to receptors in tissue sections and permits the precise identification of cell types expressing a particular receptor when viewed using a conventional light microscope or by confocal microscopy. Protocols are also described for the dual labeling of cells in the same section using primary antisera raised in two different species (one to the receptor of interest, the second to an immunogen such as a cell-specific marker or the endogenous ligand) with the corresponding secondary antisera conjugated to different fluorescent dyes.The technique has a range of applications. Subtypes of receptors can be identified and distinguished prior to the development of selective agonists or antagonists, which is particularly important for mapping orphan receptors, where the identity of the endogenous ligand in not yet known. The deletion of genes encoding receptors, particularly in mice, has emerged as a powerful tool in understanding the role of a specific receptor in physiological processes. Receptor immunocytochemistry can be used to analyze the resulting phenotype in whole body sections of mice without preselection of the tissue to be studied.
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Abstract
Radioligand binding is widely used to characterize receptors and determine their anatomical distribution, particularly the superfamily of seven transmembrane-spanning G protein-coupled receptors for both established transmitters such as endothelin-1 and an increasing number of orphan receptors recently paired with their cognate ligands. Three types of assay are described. In saturation experiments, tissue sections, cultured cells, or homogenates are incubated with an increasing concentration of a radiolabeled ligand, which can be a labeled analog of a naturally occurring transmitter, hormone, or synthetic drug. Analysis using iterative nonlinear curve-fitting programs, such as KELL, measures the affinity of the labeled ligand for a receptor (equilibrium dissociation constant, K ( D )), receptor density (B (max)), and Hill slope (nH). The affinity and selectivity of an unlabeled ligand to compete for the binding of a fixed concentration of a radiolabeled ligand to a receptor are determined using a competition binding assay. Kinetic assays measure the rate of association to or dissociation from a receptor from which a kinetic K ( D ) may be derived. Quantitative autoradiography and image analysis is a sensitive technique to detect low levels of radiolabeled ligands and determine the anatomical distribution of receptors in sections that retain the morphology of the tissue. The measurement of bound radioligand within discrete regions of autoradiographical images using -computer-assisted image analysis is described.
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Inotropic action of the puberty hormone kisspeptin in rat, mouse and human: cardiovascular distribution and characteristics of the kisspeptin receptor. PLoS One 2011; 6:e27601. [PMID: 22132116 PMCID: PMC3222648 DOI: 10.1371/journal.pone.0027601] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Accepted: 10/20/2011] [Indexed: 01/05/2023] Open
Abstract
Kisspeptins, the ligands of the kisspeptin receptor known for its roles in reproduction and cancer, are also vasoconstrictor peptides in atherosclerosis-prone human aorta and coronary artery. The aim of this study was to further investigate the cardiovascular localisation and function of the kisspeptins and their receptor in human compared to rat and mouse heart. Immunohistochemistry and radioligand binding techniques were employed to investigate kisspeptin receptor localisation, density and pharmacological characteristics in cardiac tissues from all three species. Radioimmunoassay was used to detect kisspeptin peptide levels in human normal heart and to identify any pathological changes in myocardium from patients transplanted for cardiomyopathy or ischaemic heart disease. The cardiac function of kisspeptin receptor was studied in isolated human, rat and mouse paced atria, with a role for the receptor confirmed using mice with targeted disruption of Kiss1r. The data demonstrated that kisspeptin receptor-like immunoreactivity localised to endothelial and smooth muscle cells of intramyocardial blood vessels and to myocytes in human and rodent tissue. [125I]KP-14 bound saturably, with subnanomolar affinity to human and rodent myocardium (KD = 0.12 nM, human; KD = 0.44 nM, rat). Positive inotropic effects of kisspeptin were observed in rat, human and mouse. No response was observed in mice with targeted disruption of Kiss1r. In human heart a decrease in cardiac kisspeptin level was detected in ischaemic heart disease. Kisspeptin and its receptor are expressed in the human, rat and mouse heart and kisspeptins possess potent positive inotropic activity. The cardiovascular actions of the kisspeptins may contribute to the role of these peptides in pregnancy but the consequences of receptor activation must be considered if kisspeptin receptor agonists are developed for use in the treatment of reproductive disorders or cancer.
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Endothelial cell-specific ETB receptor knockout: autoradiographic and histological characterisation and crucial role in the clearance of endothelin-1. Can J Physiol Pharmacol 2011; 88:644-51. [PMID: 20628430 DOI: 10.1139/y10-041] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Inactivation of endothelin B receptors (ETB), either through selective pharmacological antagonism or genetic mutation, increases the circulating concentration of endothelin-1 (ET-1), suggesting ETB plays an important role in clearance of this peptide. However, the cellular site of ETB-mediated clearance has not yet been determined. We have used a novel mouse model of endothelial cell-specific knockout (KO) of ETB (EC ETB(-/-)) to evaluate the relative contribution of EC-ETB to the clearance of ET-1. Phenotypic evidence of EC-specific ETB KO was confirmed by immunocytochemistry and autoradiography. Binding of the radiolabelled selective ETB ligand BQ3020 was significantly and selectively decreased in EC-rich tissues of EC ETB(-/-) mice, including the lung, liver, and kidney. By contrast, ETA binding was unaltered. RT-PCR confirmed equal expression of ET-1 in tissue from EC ETB(-/-) mice and controls, despite increased concentration of plasma ET-1 in EC ETB(-/-). Clearance of an intravenous bolus of [(125)I]ET-1 was impaired in EC ETB(-/-) mice. Pretreatment with the selective ETB antagonist A192621 impaired [(125)I]ET-1 clearance in control animals to a similar extent, but did not further impair clearance in EC ETB(-/-) mice. These studies suggest that EC-ETB are largely responsible for the clearance of ET-1 from the circulation.
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Abstract
BACKGROUND AND PURPOSE The aim of this study was to determine whether the apelin/APJ system is altered in human cardiovascular disease by investigating whether the expression of apelin or its receptor is altered at the protein level. EXPERIMENTAL APPROACH Radioligand binding studies were used to determine apelin receptor density in human cardiac tissues. Apelin peptide levels in cardiovascular tissues were determined by radioimmunoassay. In vitro pharmacology was used to assess vasoactive properties of apelin in human coronary artery. Localization of apelin and its receptor in coronary artery was determined using immunohistochemistry. KEY RESULTS Apelin receptor density was significantly decreased in left ventricle from patients with dilated cardiomyopathy or ischaemic heart disease compared with controls, but apelin peptide levels remained unchanged. Apelin was up-regulated in human atherosclerotic coronary artery and this additional peptide localized to the plaque, colocalizing with markers for macrophages and smooth muscle cells. Apelin potently constricted human coronary artery. CONCLUSIONS AND IMPLICATIONS We have detected changes in the apelin/APJ system in human diseased cardiac and vascular tissue. The decrease in receptor density in heart failure may limit the positive inotropic actions of apelin, contributing to contractile dysfunction. The contribution of the increased apelin levels in atherosclerotic coronary artery to disease progression remains to be determined. These data suggest a potential role for the apelin/APJ system in human cardiovascular disease.
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Expression and vasoconstrictor function of anorexigenic peptides neuromedin U-25 and S in the human cardiovascular system. Cardiovasc Res 2008; 81:353-61. [PMID: 18987052 DOI: 10.1093/cvr/cvn302] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS Neuromedin U-25 (NMU-25), a brain-gut peptide with anorexigenic actions, was paired with the G-protein-coupled receptors NMU1 and NMU2 in 2000. NMU-25 elicited a potent hypertensive effect in rats but little is known about its cardiovascular effects in humans. We examined the hypothesis that NMU fulfils the criteria for controlling vascular reactivity within the human cardiovascular system. METHODS AND RESULTS The radioligand [125I]-NMU-25 demonstrated specific, saturable, and high affinity (K(D) = 0.26 +/- 0.06 nM) binding in the human left ventricle and coronary artery, and quantitative reverse transcription-polymerase chain reaction revealed that mRNA encoding NMU1 predominated in these tissues. NMU-25-like immunoreactivity was detected in human plasma, left ventricle, coronary artery, saphenous vein, and epicardial adipose tissue, and both NMU-25 and a related peptide, neuromedin S (NMS), were identified by high-performance liquid chromatography in the left ventricle. NMU receptor and peptide were localized to endothelial cells, with the receptor also present on vascular smooth muscle cells. NMU-25 was a potent vasoconstrictor of isolated rings of human coronary and mammary artery and saphenous vein. Compared with NMU-25, NMS had a significantly reduced maximum response in saphenous vein, and the Arg165Trp variant of NMU-25, associated with childhood-onset obesity, was without effect. NMU-25 precursor mRNA was upregulated in the left ventricle from patients with dilated cardiomyopathy and ischaemic heart disease. CONCLUSION We have detected the expression of both NMU receptor and peptide in human cardiovascular tissues and have shown that NMU-25 and NMS act as potent vasoconstrictors in human vascular beds.
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Immunocytochemical localization of the urotensin-II receptor, UT, to rat and human tissues: relevance to function. Peptides 2008; 29:735-42. [PMID: 17905478 DOI: 10.1016/j.peptides.2007.08.021] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2007] [Revised: 08/14/2007] [Accepted: 08/14/2007] [Indexed: 02/07/2023]
Abstract
We have examined whether differential expression of UT receptors in cardiovascular tissues from rats and humans may account for the diverse vascular actions reported for urotensin-II. We found UT immunoreactivity ubiquitously expressed in arterial and venous smooth muscle and cardiomyocytes in both species, however, compared to human, levels of UT immunoreactivity in rat vascular endothelial cells was below the level for detection. In rat skeletal muscle cells UT receptor localized to the sarcolemma, a pattern comparable to that for isoforms of nitric oxide synthase suggesting that urotensin-II mediated hindquarter vasodilatation may involve release of nitric oxide from skeletal muscle fibers.
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Kisspeptins: a multifunctional peptide system with a role in reproduction, cancer and the cardiovascular system. Br J Pharmacol 2007; 151:1143-53. [PMID: 17519946 PMCID: PMC2189831 DOI: 10.1038/sj.bjp.0707295] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Orphan G-protein-coupled receptors that have recently been paired with their cognate ligand are an often untapped resource for novel drug development. The KISS1 receptor (previously designated GPR54) has been paired with biologically active cleavage peptides of the KiSS-1 gene product, the kisspeptins (KP). The focus of this review is the emerging pharmacology and physiology of the KP. Genetic linkage analysis in humans revealed that mutations in KISS1 (GPR54, AXOR12 or hOT7T175) result in idiopathic hypogonadotrophic hypogonadism and knockout mouse studies confirmed this finding. Identification of KISS1 (GPR54) as a molecular switch for puberty subsequently led to the discovery that KP activate the GnRH cascade. Prior to the role of KISS1 (GPR54) in puberty being described, KP had been shown to be inhibitors of tumour metastasis across a range of cancers. Subsequently the mechanism of this inhibition has been suggested to be via altered cell motility and adhesiveness. PCR detected highest expression of KP and KISS1 (GPR54) in placenta, and changes in KP levels throughout pregnancy and expression in trophoblasts suggests a role in placentation. Placentation and metastasis are invasive processes that require angiogenesis. Investigation of KISS1 (GPR54) and KP in vasculature revealed discrete localisation of KISS1 (GPR54) to blood vessels prone to atherosclerosis and a potent vasoconstrictor action. A role for KP has also been shown in whole body homeostasis. KP are multifunctional peptides and further investigation is required to fully elucidate the complex pathways regulated by these peptides and how these pathways integrate in the whole body system.
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Kisspeptins are novel potent vasoconstrictors in humans, with a discrete localization of their receptor, G protein-coupled receptor 54, to atherosclerosis-prone vessels. Endocrinology 2007; 148:140-7. [PMID: 17023533 DOI: 10.1210/en.2006-0818] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The G protein-coupled receptor GPR54 (also designated KISS1) is activated by cleavage products of the KiSS1 protein, the kisspeptins (KP), to act as a molecular switch for puberty. Additionally, KP are potent inhibitors of tumor metastasis and play a role in placentation, both processes involving angiogenesis. Our aim was to investigate whether GPR54 and KP are expressed within normal and diseased human vasculature and what their functional role may be. RT-PCR screening of human blood vessels revealed a discrete localization of GPR54 mRNA in smooth muscle of vessels with the same developmental origins, aorta, coronary artery, and umbilical vein, a pattern confirmed by immunocytochemistry and radioligand binding. Novel ligand [(125)I]KP-13 exhibited saturable and high-affinity binding in aorta smooth muscle sections (dissociation constant K(D) = 0.2 +/- 0.03 nM), and using confocal microscopy, we found colocalization of receptor and peptide to vascular endothelial cells and to the atherosclerotic plaque of coronary artery. RIA detected 13.04 +/- 2.94 and 20.50 +/- 5.00 fmol/g KP in human coronary artery and aorta, respectively. KP-10, KP-13, and KP-54 acted as vasoconstrictors with comparable potency and efficacy in isolated rings of coronary artery (negative logarithm of the EC(50) and maximal response, respectively, as follows: KP-10, 7.89 +/- 0.24 and 33.7 +/- 17.0; KP-13, 8.66 +/- 0.88 and 35.1 +/- 7.9; KP-54, 8.86 +/- 1.11 and 25.7 +/- 5.5) and umbilical vein (negative logarithm of the EC(50) and maximal response, respectively, as follows: KP-10, 8.44 +/- 022 and 24.3 +/- 3.7; KP-13, 8.43 +/- 0.88 and 28.4 +/- 8.6; KP-54, 8.93 +/- 0.39 and 36.9 +/- 5.2). In conclusion, we have detected expression of both peptide and receptor in aorta, coronary artery, and umbilical vein and have shown for the first time that the KP are vasoconstrictors in humans, suggesting a previously undescribed role for GPR54 and KP in the cardiovascular system.
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Characterization of the snake venom ligand [125I]-DNP binding to natriuretic peptide receptor-A in human artery and potent DNP mediated vasodilatation. Br J Pharmacol 2006; 149:838-44. [PMID: 17043672 PMCID: PMC2014690 DOI: 10.1038/sj.bjp.0706924] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND AND PURPOSE The natriuretic peptides, ANP and BNP, modulate vascular smooth muscle tone in human conduit arteries. Surprisingly, the natriuretic peptide receptor-A (NPR-A) has not been visualized using radioligand binding in these vessels. A new member of this peptide family, Dendroaspis natriuretic peptide (DNP) identified from snake venom, has been proposed to be present in human plasma and endothelial cells. Also, recently a novel radioligand, [(125)I]-DNP, has been characterized as selective for NPR-A in human heart. EXPERIMENTAL APPROACH Our aims were to investigate expression and function of NPR-A receptors in human mammary artery using [(125)I]-DNP to quantify receptor density, immunocytochemistry to delineate the cellular distribution of the receptor and in vitro pharmacology to compare DNP induced vasodilatation to that of ANP. KEY RESULTS Saturable, sub-nanomolar affinity [(125)I]-DNP binding was detected to smooth muscle of mammary artery, with receptor density of approximately 2 fmol mg(-1) protein, comparable to that of other vasoactive peptides. NPR-A immunoreactivity was localised to vascular smooth muscle cells and this was confirmed with fluorescence dual labelling. NPR-A expression was not detected in the endothelium. Like ANP, DNP fully reversed the constrictor response to ET-1 in endothelium intact or denuded mammary artery, with comparable nanomolar potencies. CONCLUSIONS AND IMPLICATIONS This is the first characterization of NPR-A in human mammary artery using [(125)I]-DNP and we provide evidence for the presence of receptor protein on vascular smooth muscle cells, but not endothelial cells. This implies that the observed vasodilatation is predominantly mediated via direct activation of smooth muscle NPR-A.
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MESH Headings
- Adrenomedullin/pharmacology
- Amino Acid Sequence
- Atrial Natriuretic Factor/pharmacology
- Calcitonin Gene-Related Peptide/pharmacology
- Dose-Response Relationship, Drug
- Elapid Venoms/metabolism
- Elapid Venoms/pharmacology
- Fluorescent Antibody Technique, Indirect
- Guanylate Cyclase/analysis
- Guanylate Cyclase/drug effects
- Guanylate Cyclase/metabolism
- Humans
- Immunohistochemistry
- In Vitro Techniques
- Intercellular Signaling Peptides and Proteins
- Ligands
- Mammary Arteries/chemistry
- Mammary Arteries/drug effects
- Mammary Arteries/metabolism
- Microscopy, Confocal
- Models, Biological
- Molecular Sequence Data
- Muscle, Smooth, Vascular/chemistry
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Peptides/metabolism
- Peptides/pharmacology
- Protein Binding
- Radiopharmaceuticals/metabolism
- Receptors, Atrial Natriuretic Factor/analysis
- Receptors, Atrial Natriuretic Factor/drug effects
- Receptors, Atrial Natriuretic Factor/metabolism
- Vasodilation/drug effects
- Vasodilator Agents/metabolism
- Vasodilator Agents/pharmacology
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Regional heterogeneity in the haemodynamic responses to urotensin II infusion in relation to UT receptor localisation. Br J Pharmacol 2006; 147:612-21. [PMID: 16314853 PMCID: PMC1751348 DOI: 10.1038/sj.bjp.0706503] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The aim of the study was to measure regional haemodynamic responses to 6 h infusions of human urotensin II (hUII), to identify possible mediators of the effects observed, and to relate the findings to the distribution of urotensin II receptors (UT receptors). Male, Sprague-Dawley rats had pulsed Doppler flow probes and intravascular catheters implanted for measurement of regional haemodynamics in the conscious, freely moving state. Infusions of saline (0.4 ml h(-1)) or hUII (30, 300 and 3,000 pmol kg(-1) h(-1)) were given i.v. for 6 h, and the effects of pretreatment with indomethacin (5 mg kg(-1) h(-1)), N(G)-nitro-L-arginine methyl ester (L-NAME, 3 mg kg(-1) h(-1)) or propranolol (1 mg kg(-1); 0.5 mg kg(-1) h(-1)) on responses to hUII (300 pmol kg(-1) h(-1) for 6 h) were assessed. Cellular localisation of UT receptor-like immunoreactivity was determined in relevant tissues. hUII caused dose-dependent tachycardia and hindquarters vasodilatation, accompanied by a slowly developing rise in blood pressure. Haemodynamic effects of hUII were attenuated by propranolol or L-NAME and abolished by indomethacin. UT receptor-like immunoreactivity was detected in skeletal and vascular smooth muscle. The findings indicate that in conscious rats, infusions of hUII cause vasodilatation, which, of the vascular beds monitored, is selective for the hindquarters and dependent on cyclooxygenase products and nitric oxide. The pressor effect of hUII under these conditions is likely to be due to an increase in cardiac output, possibly due to a positive inotropic effect. UT receptor-like immunoreactivity present in skeletal muscle is consistent with the haemodynamic pattern.
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MESH Headings
- Adrenergic beta-Antagonists/pharmacology
- Animals
- Blood Pressure
- Cyclooxygenase Inhibitors/pharmacology
- Dose-Response Relationship, Drug
- Enzyme Inhibitors/pharmacology
- Heart Rate
- Hemodynamics/drug effects
- Hindlimb
- Indomethacin/pharmacology
- Infusions, Intravenous
- Male
- Muscle, Skeletal/blood supply
- Muscle, Skeletal/drug effects
- Muscle, Skeletal/metabolism
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- NG-Nitroarginine Methyl Ester/pharmacology
- Nitric Oxide Synthase/antagonists & inhibitors
- Nitric Oxide Synthase/metabolism
- Propranolol/pharmacology
- Rats
- Rats, Sprague-Dawley
- Receptors, G-Protein-Coupled/drug effects
- Receptors, G-Protein-Coupled/metabolism
- Regional Blood Flow
- Urotensins/administration & dosage
- Urotensins/pharmacology
- Vasodilation
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Novel snake venom ligand dendroaspis natriuretic peptide is selective for natriuretic peptide receptor-A in human heart: downregulation of natriuretic peptide receptor-A in heart failure. Circ Res 2006; 99:183-90. [PMID: 16778132 DOI: 10.1161/01.res.0000232322.06633.d3] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The natriuretic peptides are considered to be cardioprotective; however, their receptors have not been identified in human myocardium using radiolabeled analogs. Dendroaspis natriuretic peptide (DNP) has been recently identified as a new member of this peptide family and is thought to be less susceptible to enzymatic degradation. Therefore, we have developed the novel radiolabeled analog [125I]-DNP and used this to localize high-affinity (K(D)=0.2 nmol/L), saturable, specific binding sites in adult human heart (n=6) and coronary artery (n=8). In competition binding experiments, atrial natriuretic peptide and brain type natriuretic peptide had greater affinity for [125I]-DNP binding sites than C-type natriuretic peptide and the natriuretic peptide receptor (NPR)-C ligand, cANF. This rank order of potency suggested binding of [125I]-DNP was specific to NPR-A. Messenger RNA encoding NPR-A was identified in left ventricle and coronary artery smooth muscle, and expression was confirmed by immunocytochemical studies at the protein level. In addition, fluorescence dual labeling immunocytochemistry localized NPR-A protein to cardiomyocytes, endocardial endothelial cells, and smooth muscle of intramyocardial vessels. Importantly, we demonstrated a significant downregulation in the density of NPR-A in heart and coronary artery of patients with ischemic heart disease that may explain, in part, the attenuated natriuretic peptide response reported in this patient group.
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Quantification of endothelin receptor subtypes in peripheral tissues reveals downregulation of ET(A) receptors in ET(B)-deficient mice. Exp Biol Med (Maywood) 2006; 231:741-5. [PMID: 16740991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/09/2023] Open
Abstract
We have previously shown that in homozygous endothelin (ET)(B)-/- deficient mice, ET(A) receptor density is significantly downregulated in the brain by 45%. In these mice, plasma ET-1 levels are elevated. Our aim was to use quantitative autoradiography to establish the distribution of ET receptor subtypes in peripheral tissues from wild-type mice and to measure the density of the ET(A) subtype in ET(B)-/- knockout animals. Our second aim was to test whether deletion of ET(B) receptors, which is associated with elevated plasma levels of ET-1, would also reduce ET(A) expression in the periphery. In longitudinal sections from wild-type mice, the highest densities of ET(A) receptors localized to major organs including the ventricle of the heart, lung, and liver parenchyma. High densities of ET(A) receptors were detected in the smooth muscle layer of the vasculature such as intrarenal vessels as well as the smooth muscle layer and epithelial cells of the gastrointestinal tract. In these tissues, the ET(A) subtype was more abundant, representing between 60% and 100% of the ET receptors. ET(B) receptors predominated in the medulla of kidney, with high densities also localizing to glomeruli within the cortex and to the sinusoids from the liver. Lower densities of ET(B) receptors were also present in the lung, heart, liver, and the smooth muscle layer of the gastrointestinal tract. In ET(B)-/- knockout mice, ET(B) receptors were not detected as expected by either ligand binding or immunocytochemistry. The pattern of ET(A) receptor distribution in the ET(B)-/- knockout mice was similar to the controls, but the density of ET(A) receptors was significantly reduced in the lung by 39%. Diminished responses to the endogenous agonist after repeated stimulation are an important feature of G-protein signaling, preventing potential damage to the overstimulated cell, and it is likely that downregulation occurs in response to higher circulating levels of ET-1.
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Endothelin-mediated vasoconstriction in early atherosclerosis is markedly increased in ApoE-/- mouse but prevented by atorvastatin. Exp Biol Med (Maywood) 2006; 231:806-12. [PMID: 16741003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/09/2023] Open
Abstract
We have discovered that endothelin-1 (ET-1) vasoconstriction is significantly enhanced in aortas of young (8-16-week-old) apolipoprotein E-deficient (ApoE-/-) mice devoid of atherosclerotic lesions (maximum response expressed as a percentage of the mean response to 100 mM KCl (E(MAX)) = 55.7% +/- 19.5% KCl, n = 5) compared to age-matched C57BL/6/J control animals (E(MAX) = 12.6% +/- 2.5% KCl, n = 8), indicating that alterations in the endothelin system may contribute to disease progression, at least in this animal model. There was no difference in the potency of ET-1 to contract aorta from the two groups (C57BL/6/J pD2 = 8.74 +/- 0.30; ApoE-/- pD2 = 8.50 +/- 0.15, P > 0.05). This increased response was specific to ET-1, as it was not observed with phenylephrine or U46619, nor was it due to a non-receptor mediated increase in contractile sensitivity, as there was no change in response to KCl between the two groups. [125I]ET-1 bound with subnanomolar affinity (K(D)) to aorta (K(D) = 0.018 +/- 0.002 nM, n = 4) and, with an order of magnitude lower affinity, to heart (K(D) = 0.47 +/- 0.05, n = 5) of C57BL/6/J mice with binding densities (B(MAX)) of 9.3 +/- 2.4 fmol mg(-1)protein and 100 +/- 14 fmol mg(-1) protein, respectively. Alterations in vascular reactivity to ET-1 could not be explained by increased endothelin receptor density or affinity, as these were not altered in aorta (K(D) = 0.011 +/- 0.003 nM; B(MAX) = 10.1 +/- 3.9 fmol mg(-1), n = 4) and heart (K(D) = 0.43 +/- 0.04 nM; B(MAX) = 115 +/- 26 fmol mg(-1), n == 6) of ApoE-/- animals. The ratio of ET(A) to ET(B) receptors in heart of control and ApoE-/- mice was similar, comprising 89% and 85% ET(A) receptors, respectively. In isolated aorta from ApoE-/- mice on the Western diet, which more closely resembled more advanced stages of the disease in man, the augmented ET-1 vasoconstrictor response was maintained (E(MAX) = 25.2% +/- 6.8% KCl, n = 9); however, it was completely prevented in animals that had received 10 weeks of oral atorvastatin (30 mg kg(-1) day(-1)) (E(MAX) = 4.0% +/- 1.5% KCl, n = 5), a concentration that was chosen because it did not affect plasma cholesterol and triglyceride levels. Therefore, this protective prevention of enhanced ET-1 vasoconstriction in ApoE-/- mice by atorvastatin was independent of its lipid-lowering properties.
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Radioligand-binding and molecular-imaging techniques for the quantitative analysis of established and emerging orphan receptor systems. Methods Mol Biol 2005; 306:93-120. [PMID: 15867465 DOI: 10.1385/1-59259-927-3:093] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
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49
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Immunocytochemical localization of receptors using light and confocal microscopy with application to the phenotypic characterization of knock-out mice. Methods Mol Biol 2005; 306:155-72. [PMID: 15867468 DOI: 10.1385/1-59259-927-3:155] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
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50
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Abstract
Autoradiographical images of whole body sections from control mice (29 +/- 3 days old) revealed high ETA densities within the cardiovascular system, with ETB receptors predominating in the kidney. A similar distribution of ETA receptors was found in ETB-deficient mice (25 +/- 2 days old) but the density was reduced in peripheral tissues including the heart and vessels. ETB receptors were not detected in any animal, confirming gene deletion. In the central nervous system, ETA receptors localized to the cerebral vasculature of controls, with lower levels in brain regions including the molecular layer of the cerebellum. The highest ETB densities were also in the cerebellum, but to the granular layer. A similar pattern of ETA binding was detected in brain regions from knockout animals but the density was reduced. BQ3020 competed biphasically for [I]-endothelin-1 binding to control brains: KDETB = 9.3 +/- 5.4 nM, Bmax = 48.7 +/- 5.8 fmol/mg protein; KDETA = 2.1 +/- 0.8 microM, Bmax = 32.7 +/- 6.3. In knockout mice, only ETA receptors could be detected (KDETA = 1.9 +/- 0.7 microM) and the receptor density (18.2 +/- 1.9 fmol/mg protein) was significantly reduced by 45%. These results reveal deletion of the ETB subtype is associated with a reduction in both central and peripheral ETA number, and may reflect an unsuspected role for ETB receptors in regulating development or expression of the ETA subtype.
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