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Escobar F, Friis S, Adly N, Brinkwirth N, Gomis-Tena J, Saiz J, Klaerke DA, Stoelzle-Feix S, Romero L. Experimentally validated modeling of dynamic drug-hERG channel interactions reproducing the binding mechanisms and its importance in action potential duration. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2024; 254:108293. [PMID: 38936153 DOI: 10.1016/j.cmpb.2024.108293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Revised: 06/09/2024] [Accepted: 06/16/2024] [Indexed: 06/29/2024]
Abstract
BACKGROUND AND OBJECTIVE Assessment of drug cardiotoxicity is critical in the development of new compounds and modeling of drug-binding dynamics to hERG can improve early cardiotoxicity assessment. We previously developed a methodology to generate Markovian models reproducing preferential state-dependent binding properties, trapping dynamics and the onset of IKr block using simple voltage clamp protocols. Here, we test this methodology with real IKr blockers and investigate the impact of drug dynamics on action potential prolongation. METHODS Experiments were performed on HEK cells stably transfected with hERG and using the Nanion SyncroPatch 384i. Three protocols, P-80, P0 and P 40, were applied to obtain the experimental data from the drugs and the Markovian models were generated using our pipeline. The corresponding static models were also generated and a modified version of the O´Hara-Rudy action potential model was used to simulate the action potential duration. RESULTS The experimental Hill plots and the onset of IKr block of ten compounds were obtained using our voltage clamp protocols and the models generated successfully mimicked these experimental data, unlike the CiPA dynamic models. Marked differences in APD prolongation were observed when drug effects were simulated using the dynamic models and the static models. CONCLUSIONS These new dynamic models of ten well-known IKr blockers constitute a validation of our methodology to model dynamic drug-hERG channel interactions and highlight the importance of state-dependent binding, trapping dynamics and the time-course of IKr block to assess drug effects even at the steady-state.
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Affiliation(s)
- Fernando Escobar
- Centro de Innovación e Investigación en Bioingeniería, Universitat Politècnica de València, Valencia, Spain
| | | | | | | | - Julio Gomis-Tena
- Centro de Innovación e Investigación en Bioingeniería, Universitat Politècnica de València, Valencia, Spain
| | - Javier Saiz
- Centro de Innovación e Investigación en Bioingeniería, Universitat Politècnica de València, Valencia, Spain
| | - Dan A Klaerke
- Department of Pathobiology, University of Copenhagen, Copenhagen, Denmark
| | | | - Lucia Romero
- Centro de Innovación e Investigación en Bioingeniería, Universitat Politècnica de València, Valencia, Spain.
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2
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El Harchi A, Hancox JC. hERG agonists pose challenges to web-based machine learning methods for prediction of drug-hERG channel interaction. J Pharmacol Toxicol Methods 2023; 123:107293. [PMID: 37468081 DOI: 10.1016/j.vascn.2023.107293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 05/23/2023] [Accepted: 07/12/2023] [Indexed: 07/21/2023]
Abstract
Pharmacological blockade of the IKr channel (hERG) by diverse drugs in clinical use is associated with the Long QT Syndrome that can lead to life threatening arrhythmia. Various computational tools including machine learning models (MLM) for the prediction of hERG inhibition have been developed to facilitate the throughput screening of drugs in development and optimise thus the prediction of hERG liabilities. The use of MLM relies on large libraries of training compounds for the quantitative structure-activity relationship (QSAR) modelling of hERG inhibition. The focus on inhibition omits potential effects of hERG channel agonist molecules and their associated QT shortening risk. It is instructive, therefore, to consider how known hERG agonists are handled by MLM. Here, two highly developed online computational tools for the prediction of hERG liability, Pred-hERG and HergSPred were probed for their ability to detect hERG activator drug molecules as hERG interactors. In total, 73 hERG blockers were tested with both computational tools giving overall good predictions for hERG blockers with reported IC50s below Pred-hERG and HergSPred cut-off threshold for hERG inhibition. However, for compounds with reported IC50s above this threshold such as disopyramide or sotalol discrepancies were observed. HergSPred identified all 20 hERG agonists selected as interacting with the hERG channel. Further studies are warranted to improve online MLM prediction of hERG related cardiotoxicity, by explicitly taking into account channel agonism as well as inhibition.
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Affiliation(s)
- Aziza El Harchi
- School of Physiology and Pharmacology and Neuroscience, Biomedical Sciences Building, The University of Bristol, University Walk, Bristol BS8 1TD, UK.
| | - Jules C Hancox
- School of Physiology and Pharmacology and Neuroscience, Biomedical Sciences Building, The University of Bristol, University Walk, Bristol BS8 1TD, UK
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Zünkler BJ, Wos-Maganga M, Bohnet S, Kleinau A, Manns D, Chatterjee S. Intracellular Binding of Terfenadine Competes with Its Access to Pancreatic ß-cell ATP-Sensitive K + Channels and Human ether-à-go-go-Related Gene Channels. J Membr Biol 2023; 256:63-77. [PMID: 35763054 PMCID: PMC9884252 DOI: 10.1007/s00232-022-00252-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 06/02/2022] [Indexed: 02/07/2023]
Abstract
Most blockers of both hERG (human ether-à-go-go-related gene) channels and pancreatic ß-cell ATP-sensitive K+ (KATP) channels access their binding sites from the cytoplasmic side of the plasma membrane. It is unknown whether binding to intracellular components competes with binding of these substances to K+ channels. The whole-cell configuration of the patch-clamp technique, a laser-scanning confocal microscope, and fluorescence correlation spectroscopy (FCS) were used to study hERG channels expressed in HEK (human embryonic kidney) 293 cells and KATP channels from the clonal insulinoma cell line RINm5F. When applied via the pipette solution in the whole-cell configuration, terfenadine blocked both hERG and KATP currents with much lower potency than after application via the bath solution, which was not due to P-glycoprotein-mediated efflux of terfenadine. Such a difference was not observed with dofetilide and tolbutamide. 37-68% of hERG/EGFP (enhanced green-fluorescent protein) fusion proteins expressed in HEK 293 cells were slowly diffusible as determined by laser-scanning microscopy in the whole-cell configuration and by FCS in intact cells. Bath application of a green-fluorescent sulphonylurea derivative (Bodipy-glibenclamide) induced a diffuse fluorescence in the cytosol of RINm5F cells under whole-cell patch-clamp conditions. These observations demonstrate the presence of intracellular binding sites for hERG and KATP channel blockers not dialyzable by the patch-pipette solution. Intracellular binding of terfenadine was not influenced by a mutated hERG (Y652A) channel. In conclusion, substances with high lipophilicity are not freely diffusible inside the cell but steep concentration gradients might exist within the cell and in the sub-membrane space.
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Affiliation(s)
- Bernd J Zünkler
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany.
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Mendelssohnstr. 1, 38106, Braunschweig, Germany.
| | - Maria Wos-Maganga
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Stefanie Bohnet
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Anne Kleinau
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Detlef Manns
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Shivani Chatterjee
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
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4
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Jiang H, Zhang S, Lu W, Yang F, Bi X, Ma W, Wei Z. In silico assessment of pharmacotherapy for carbon monoxide induced arrhythmias in healthy and failing human hearts. Front Physiol 2022; 13:1018299. [DOI: 10.3389/fphys.2022.1018299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2022] [Accepted: 11/16/2022] [Indexed: 11/17/2022] Open
Abstract
Background: Carbon monoxide (CO) is gaining increased attention in air pollution-induced arrhythmias. The severe cardiotoxic consequences of CO urgently require effective pharmacotherapy to treat it. However, existing evidence demonstrates that CO can induce arrhythmias by directly affecting multiple ion channels, which is a pathway distinct from heart ischemia and has received less concern in clinical treatment.Objective: To evaluate the efficacy of some common clinical antiarrhythmic drugs for CO-induced arrhythmias, and to propose a potential pharmacotherapy for CO-induced arrhythmias through the virtual pathological cell and tissue models.Methods: Two pathological models describing CO effects on healthy and failing hearts were constructed as control baseline models. After this, we first assessed the efficacy of some common antiarrhythmic drugs like ranolazine, amiodarone, nifedipine, etc., by incorporating their ion channel-level effects into the cell model. Cellular biomarkers like action potential duration and tissue-level biomarkers such as the QT interval from pseudo-ECGs were obtained to assess the drug efficacy. In addition, we also evaluated multiple specific IKr activators in a similar way to multi-channel blocking drugs, as the IKr activator showed great potency in dealing with CO-induced pathological changes.Results: Simulation results showed that the tested seven antiarrhythmic drugs failed to rescue the heart from CO-induced arrhythmias in terms of the action potential and the ECG manifestation. Some of them even worsened the condition of arrhythmogenesis. In contrast, IKr activators like HW-0168 effectively alleviated the proarrhythmic effects of CO.Conclusion: Current antiarrhythmic drugs including the ranolazine suggested in previous studies did not achieve therapeutic effects for the cardiotoxicity of CO, and we showed that the specific IKr activator is a promising pharmacotherapy for the treatment of CO-induced arrhythmias.
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Delayed Ventricular Repolarization and Sodium Channel Current Modification in a Mouse Model of Rett Syndrome. Int J Mol Sci 2022; 23:ijms23105735. [PMID: 35628543 PMCID: PMC9147596 DOI: 10.3390/ijms23105735] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Revised: 05/13/2022] [Accepted: 05/17/2022] [Indexed: 02/01/2023] Open
Abstract
Rett syndrome (RTT) is a severe developmental disorder that is strongly linked to mutations in the MECP2 gene. RTT has been associated with sudden unexplained death and ECG QT interval prolongation. There are mixed reports regarding QT prolongation in mouse models of RTT, with some evidence that loss of Mecp2 function enhances cardiac late Na current, INa,Late. The present study was undertaken in order to investigate both ECG and ventricular AP characteristics in the Mecp2Null/Y male murine RTT model and to interrogate both fast INa and INa,Late in myocytes from the model. ECG recordings from 8-10-week-old Mecp2Null/Y male mice revealed prolongation of the QT and rate corrected QT (QTc) intervals and QRS widening compared to wild-type (WT) controls. Action potentials (APs) from Mecp2Null/Y myocytes exhibited longer APD75 and APD90 values, increased triangulation and instability. INa,Late was also significantly larger in Mecp2Null/Y than WT myocytes and was insensitive to the Nav1.8 inhibitor A-803467. Selective recordings of fast INa revealed a decrease in peak current amplitude without significant voltage shifts in activation or inactivation V0.5. Fast INa 'window current' was reduced in RTT myocytes; small but significant alterations of inactivation and reactivation time-courses were detected. Effects of two INa,Late inhibitors, ranolazine and GS-6615 (eleclazine), were investigated. Treatment with 30 µM ranolazine produced similar levels of inhibition of INa,Late in WT and Mecp2Null/Y myocytes, but produced ventricular AP prolongation not abbreviation. In contrast, 10 µM GS-6615 both inhibited INa,Late and shortened ventricular AP duration. The observed changes in INa and INa,Late can account for the corresponding ECG changes in this RTT model. GS-6615 merits further investigation as a potential treatment for QT prolongation in RTT.
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6
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Huang M, Liao Z, Li X, Yang Z, Fan X, Li Y, Zhao Z, Lang S, Cyganek L, Zhou X, Akin I, Borggrefe M, El-Battrawy I. Effects of Antiarrhythmic Drugs on hERG Gating in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes From a Patient With Short QT Syndrome Type 1. Front Pharmacol 2021; 12:675003. [PMID: 34025432 PMCID: PMC8138577 DOI: 10.3389/fphar.2021.675003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 04/26/2021] [Indexed: 12/17/2022] Open
Abstract
Aims: The short QT syndrome type 1 (SQT1) is linked to hERG channel mutations (e.g., N588K). Drug effects on hERG channel gating kinetics in SQT1-cells have not been investigated. Methods: This study used hiPSC-CMs of a healthy donor and a SQT1-patient carrying the N588K mutation and patch clamp to examine the drug effects on hERG channel gating kinetics. Results: Ajmaline, amiodarone, ivabradine, flecainide, quinidine, mexiletine and ranolazine inhibited the hERG channel current (IKr) less strongly in hiPSC-CMs from the SQTS1-patient (SQT1-hiPSC-CMs) comparing with cells from the healthy donor (donor-hiPSC-CMs). Quinidine and mexiletine reduced, but ajmaline, amiodarone, ivabradine and ranolazine increased the time to peak of IKr similarly in SQT1-hiPSC-CMs and donor-hiPSC-CMs. Although regarding the shift of activation and inactivation curves, tested drugs showed differential effects in donor- and SQT1-hiPSC-CMs, quinidine, ajmaline, ivabradine and mexiletine but not amiodarone, flecainide and ranolazine reduced the window current in SQT1-hiPSC-CMs. Quinidine, ajmaline, ivabradine and mexiletine differentially changed the time constant of recovery from inactivation, but all of them increased the time constant of deactivation in SQT1-hiPSC-CMs. Conclusion: The window current-reducing and deactivation-slowing effects may be important for the antiarrhythmic effect of ajmaline, ivabradine, quinidine and mexiletine in SQT1-cells. This information may be helpful for selecting drugs for treating SQT1-patients with hERG channel mutation.
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Affiliation(s)
- Mengying Huang
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany
| | - Zhenxing Liao
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,North Sichuan Medical College, Nanchong, China
| | - Xin Li
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,College of Medical Technology, Chengdu University of Traditional Chinese Medicine, Chengdu, China
| | - Zhen Yang
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,North Sichuan Medical College, Nanchong, China
| | - Xuehui Fan
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, China
| | - Yingrui Li
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany
| | - Zhihan Zhao
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany
| | - Siegfried Lang
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,DZHK (German Center for Cardiovascular Research), Partner Sites, Heidelberg-Mannheim and Göttingen, Mannheim, Germany
| | - Lukas Cyganek
- DZHK (German Center for Cardiovascular Research), Partner Sites, Heidelberg-Mannheim and Göttingen, Mannheim, Germany.,Stem Cell Unit, Clinic for Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany
| | - Xiaobo Zhou
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, China.,DZHK (German Center for Cardiovascular Research), Partner Sites, Heidelberg-Mannheim and Göttingen, Mannheim, Germany
| | - Ibrahim Akin
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,DZHK (German Center for Cardiovascular Research), Partner Sites, Heidelberg-Mannheim and Göttingen, Mannheim, Germany
| | - Martin Borggrefe
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,DZHK (German Center for Cardiovascular Research), Partner Sites, Heidelberg-Mannheim and Göttingen, Mannheim, Germany
| | - Ibrahim El-Battrawy
- First Department of Medicine, Faculty of Medicine, University Medical Centre Mannheim (UMM), University of Heidelberg, Mannheim, Germany.,DZHK (German Center for Cardiovascular Research), Partner Sites, Heidelberg-Mannheim and Göttingen, Mannheim, Germany
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7
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Kistamás K, Hézső T, Horváth B, Nánási PP. Late sodium current and calcium homeostasis in arrhythmogenesis. Channels (Austin) 2020; 15:1-19. [PMID: 33258400 PMCID: PMC7757849 DOI: 10.1080/19336950.2020.1854986] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The cardiac late sodium current (INa,late) is the small sustained component of the sodium current active during the plateau phase of the action potential. Several studies demonstrated that augmentation of the current can lead to cardiac arrhythmias; therefore, INa,late is considered as a promising antiarrhythmic target. Fundamentally, enlarged INa,late increases Na+ influx into the cell, which, in turn, is converted to elevated intracellular Ca2+ concentration through the Na+/Ca2+ exchanger. The excessive Ca2+ load is known to be proarrhythmic. This review describes the behavior of the voltage-gated Na+ channels generating INa,late in health and disease and aims to discuss the physiology and pathophysiology of Na+ and Ca2+ homeostasis in context with the enhanced INa,late demonstrating also the currently accessible antiarrhythmic choices.
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Affiliation(s)
- Kornél Kistamás
- Department of Physiology, Faculty of Medicine, University of Debrecen , Debrecen, Hungary
| | - Tamás Hézső
- Department of Physiology, Faculty of Medicine, University of Debrecen , Debrecen, Hungary
| | - Balázs Horváth
- Department of Physiology, Faculty of Medicine, University of Debrecen , Debrecen, Hungary
| | - Péter P Nánási
- Department of Physiology, Faculty of Medicine, University of Debrecen , Debrecen, Hungary.,Department of Dental Physiology, Faculty of Dentistry, University of Debrecen , Debrecen, Hungary
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8
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Inhibitory Effectiveness of Gomisin A, a Dibenzocyclooctadiene Lignan Isolated from Schizandra chinensis, on the Amplitude and Gating of Voltage-Gated Na + Current. Int J Mol Sci 2020; 21:ijms21228816. [PMID: 33233411 PMCID: PMC7700137 DOI: 10.3390/ijms21228816] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2020] [Revised: 11/18/2020] [Accepted: 11/19/2020] [Indexed: 12/12/2022] Open
Abstract
Gomisin A (Gom A), a lignan isolated from Schisandra chinensis, has been reported produce numerous biological activities. However, its action on the ionic mechanisms remains largely unanswered. The present experiments were undertaken to investigate the possible perturbations of Gom A or other related compounds on different types of membrane ionic currents in electrically excitable cells (i.e., pituitary GH3 and pancreatic INS-1 cells). The exposure to Gom A led to the differential inhibition of peak and end-pulse components of voltage-gated Na+ current (INa) in GH3 cells with effective IC50 of 6.2 and 0.73 μM, respectively. The steady-state inactivation curve of INa in the presence of Gom A was shifted towards a more hyperpolarized potential. However, neither changes in the overall current-voltage relationship nor those for the gating charge of the current were demonstrated. The application of neither morin (10 μM) nor hesperidin (10 μM) perturbed the strength of INa, while sesamine could suppress it. However, in the continued presence of Gom A, the addition of sesamine failed to suppress INa further. Gom A also effectively suppressed the strength of persistent INa activated by long ramp voltage command, and further application of tefluthrin effectively attenuated Gom A-mediated inhibition of the current. The presence of Gom A mildly inhibited erg-mediated K+ current, while a lack of change in the amplitude of hyperpolarization-activated cation current was observed in its presence. Under cell-attached current recordings, the exposure to Gom A resulted in the decreased firing of spontaneous action currents with a minimal change in AC amplitude. In pancreatic INS-1 cells, the presence of Gom A was also noticed to inhibit peak and end-pulse components of INa differentially with the IC50 of 5.9 and 0.84 μM, respectively. Taken together, the emerging results presented herein provide the evidence that Gom A can differentially inhibit peak and sustained INa in endocrine cells (e.g., GH3 and INS-1 cells).
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9
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Ratte A, Wiedmann F, Kraft M, Katus HA, Schmidt C. Antiarrhythmic Properties of Ranolazine: Inhibition of Atrial Fibrillation Associated TASK-1 Potassium Channels. Front Pharmacol 2019; 10:1367. [PMID: 32038227 PMCID: PMC6988797 DOI: 10.3389/fphar.2019.01367] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 10/28/2019] [Indexed: 12/03/2022] Open
Abstract
Background: Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and one of the major causes of cardiovascular morbidity and mortality. Despite good progress within the past years, safe and effective treatment of AF remains an unmet clinical need. The anti-anginal agent ranolazine has been shown to exhibit antiarrhythmic properties via mainly late INa and IKr blockade. This results in prolongation of the atrial action potential duration (APD) and effective refractory period (ERP) with lower effect on ventricular electrophysiology. Furthermore, ranolazine has been shown to be effective in the treatment of AF. TASK-1 is a two-pore domain potassium (K2P) channel that shows nearly atrial specific expression within the human heart and has been found to be upregulated in AF, resulting in shortening the atrial APD in patients suffering from AF. We hypothesized that inhibition TASK-1 contributes to the observed electrophysiological and clinical effects of ranolazine. Methods: We used Xenopus laevis oocytes and CHO-cells as heterologous expression systems for the study of TASK-1 inhibition by ranolazine and molecular drug docking simulations to investigate the ranolazine binding site and binding characteristics. Results: Ranolazine acts as an inhibitor of TASK-1 potassium channels that inhibits TASK-1 currents with an IC50 of 30.6 ± 3.7 µM in mammalian cells and 198.4 ± 1.1 µM in X. laevis oocytes. TASK-1 inhibition by ranolazine is not frequency dependent but shows voltage dependency with a higher inhibitory potency at more depolarized membrane potentials. Ranolazine binds within the central cavity of the TASK-1 inner pore, at the bottom of the selectivity filter. Conclusions: In this study, we show that ranolazine inhibits TASK-1 channels. We suggest that inhibition of TASK-1 may contribute to the observed antiarrhythmic effects of Ranolazine. This puts forward ranolazine as a prototype drug for the treatment of atrial arrhythmia because of its combined efficacy on atrial electrophysiology and lower risk for ventricular side effects.
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Affiliation(s)
- Antonius Ratte
- Department of Cardiology, University of Heidelberg, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany.,HCR, Heidelberg Centre for Heart Rhythm Disorders, University of Heidelberg, Heidelberg, Germany
| | - Felix Wiedmann
- Department of Cardiology, University of Heidelberg, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany.,HCR, Heidelberg Centre for Heart Rhythm Disorders, University of Heidelberg, Heidelberg, Germany
| | - Manuel Kraft
- Department of Cardiology, University of Heidelberg, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany.,HCR, Heidelberg Centre for Heart Rhythm Disorders, University of Heidelberg, Heidelberg, Germany
| | - Hugo A Katus
- Department of Cardiology, University of Heidelberg, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany.,HCR, Heidelberg Centre for Heart Rhythm Disorders, University of Heidelberg, Heidelberg, Germany
| | - Constanze Schmidt
- Department of Cardiology, University of Heidelberg, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany.,HCR, Heidelberg Centre for Heart Rhythm Disorders, University of Heidelberg, Heidelberg, Germany
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10
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Al-Owais MM, Hettiarachchi NT, Kirton HM, Hardy ME, Boyle JP, Scragg JL, Steele DS, Peers C. A key role for peroxynitrite-mediated inhibition of cardiac ERG (Kv11.1) K + channels in carbon monoxide-induced proarrhythmic early afterdepolarizations. FASEB J 2017; 31:4845-4854. [PMID: 28743763 PMCID: PMC5636698 DOI: 10.1096/fj.201700259r] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Accepted: 07/05/2017] [Indexed: 12/20/2022]
Abstract
Exposure to CO causes early afterdepolarization arrhythmias. Previous studies in rats have indicated that arrhythmias arose as a result of augmentation of the late Na+ current. The purpose of the present study was to examine the basis for CO-induced arrhythmias in guinea pig myocytes in which action potentials (APs) more closely resemble those of human myocytes. Whole-cell current- and voltage-clamp recordings were made from isolated guinea pig myocytes as well as from human embryonic kidney 293 (HEK293) cells that express wild-type or a C723S mutant form of ether-a-go-go-related gene (ERG; Kv11.1). We also monitored the formation of peroxynitrite (ONOO-) in HEK293 cells fluorimetrically. CO-applied as the CO-releasing molecule, CORM-2-prolonged the APs and induced early afterdepolarizations in guinea pig myocytes. In HEK293 cells, CO inhibited wild-type, but not C723S mutant, Kv11.1 K+ currents. Inhibition was prevented by an antioxidant, mitochondrial inhibitors, or inhibition of NO formation. CO also raised ONOO- levels, an effect that was reversed by the ONOO- scavenger, FeTPPS [5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrinato-iron(III)], which also prevented the CO inhibition of Kv11.1 currents and abolished the effects of CO on Kv11.1 tail currents and APs in guinea pig myocytes. Our data suggest that CO induces arrhythmias in guinea pig cardiac myocytes via the ONOO--mediated inhibition of Kv11.1 K+ channels.-Al-Owais, M. M., Hettiarachchi, N. T., Kirton, H. M., Hardy, M. E., Boyle, J. P., Scragg, J. L., Steele, D. S., Peers, C. A key role for peroxynitrite-mediated inhibition of cardiac ERG (Kv11.1) K+ channels in carbon monoxide-induced proarrhythmic early afterdepolarizations.
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Affiliation(s)
- Moza M Al-Owais
- Division of Cardiovascular and Diabetes Research, Leeds Institute of Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom; and
| | - Nishani T Hettiarachchi
- Division of Cardiovascular and Diabetes Research, Leeds Institute of Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom; and
| | - Hannah M Kirton
- Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Matthew E Hardy
- Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - John P Boyle
- Division of Cardiovascular and Diabetes Research, Leeds Institute of Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom; and
| | - Jason L Scragg
- Division of Cardiovascular and Diabetes Research, Leeds Institute of Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom; and
| | - Derek S Steele
- Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Chris Peers
- Division of Cardiovascular and Diabetes Research, Leeds Institute of Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom; and
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11
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Li Z, Dutta S, Sheng J, Tran PN, Wu W, Chang K, Mdluli T, Strauss DG, Colatsky T. Improving the In Silico Assessment of Proarrhythmia Risk by Combining hERG (Human Ether-à-go-go-Related Gene) Channel-Drug Binding Kinetics and Multichannel Pharmacology. Circ Arrhythm Electrophysiol 2017; 10:e004628. [PMID: 28202629 DOI: 10.1161/circep.116.004628] [Citation(s) in RCA: 114] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 01/19/2017] [Indexed: 11/16/2022]
Abstract
BACKGROUND The current proarrhythmia safety testing paradigm, although highly efficient in preventing new torsadogenic drugs from entering the market, has important limitations that can restrict the development and use of valuable new therapeutics. The CiPA (Comprehensive in vitro Proarrhythmia Assay) proposes to overcome these limitations by evaluating drug effects on multiple cardiac ion channels in vitro and using these data in a predictive in silico model of the adult human ventricular myocyte. A set of drugs with known clinical torsade de pointes risk was selected to develop and calibrate the in silico model. METHODS AND RESULTS Manual patch-clamp data assessing drug effects on expressed cardiac ion channels were integrated into the O'Hara-Rudy myocyte model modified to include dynamic drug-hERG channel (human Ether-à-go-go-Related Gene) interactions. Together with multichannel pharmacology data, this model predicts that compounds with high torsadogenic risk are more likely to be trapped within the hERG channel and show stronger reverse use dependency of action potential prolongation. Furthermore, drug-induced changes in the amount of electronic charge carried by the late sodium and L-type calcium currents was evaluated as a potential metric for assigning torsadogenic risk. CONCLUSIONS Modeling dynamic drug-hERG channel interactions and multi-ion channel pharmacology improves the prediction of torsadogenic risk. With further development, these methods have the potential to improve the regulatory assessment of drug safety models under the CiPA paradigm.
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Affiliation(s)
- Zhihua Li
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD.
| | - Sara Dutta
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Jiansong Sheng
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Phu N Tran
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Wendy Wu
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Kelly Chang
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Thembi Mdluli
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - David G Strauss
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
| | - Thomas Colatsky
- From the Division of Applied Regulatory Science, Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD
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12
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Pre- and Delayed Treatments With Ranolazine Ameliorate Ventricular Arrhythmias and Nav1.5 Downregulation in Ischemic/Reperfused Rat Hearts. J Cardiovasc Pharmacol 2016; 68:269-279. [DOI: 10.1097/fjc.0000000000000412] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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13
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Yang PC, Moreno JD, Miyake CY, Vaughn-Behrens SB, Jeng MT, Grandi E, Wehrens XHT, Noskov SY, Clancy CE. In silico prediction of drug therapy in catecholaminergic polymorphic ventricular tachycardia. J Physiol 2015; 594:567-93. [PMID: 26515697 PMCID: PMC4784170 DOI: 10.1113/jp271282] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Accepted: 10/22/2015] [Indexed: 01/31/2023] Open
Abstract
Key points The mechanism of therapeutic efficacy of flecainide for catecholaminergic polymorphic ventricular tachycardia (CPVT) is unclear. Model predictions suggest that Na+ channel effects are insufficient to explain flecainide efficacy in CPVT. This study represents a first step toward predicting therapeutic mechanisms of drug efficacy in the setting of CPVT and then using these mechanisms to guide modelling and simulation to predict alternative drug therapies.
Abstract Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterized by fatal ventricular arrhythmias in structurally normal hearts during β‐adrenergic stimulation. Current treatment strategies include β‐blockade, flecainide and ICD implementation – none of which is fully effective and each comes with associated risk. Recently, flecainide has gained considerable interest in CPVT treatment, but its mechanism of action for therapeutic efficacy is unclear. In this study, we performed in silico mutagenesis to construct a CPVT model and then used a computational modelling and simulation approach to make predictions of drug mechanisms and efficacy in the setting of CPVT. Experiments were carried out to validate model results. Our simulations revealed that Na+ channel effects are insufficient to explain flecainide efficacy in CPVT. The pure Na+ channel blocker lidocaine and the antianginal ranolazine were additionally tested and also found to be ineffective. When we tested lower dose combination therapy with flecainide, β‐blockade and CaMKII inhibition, our model predicted superior therapeutic efficacy than with flecainide monotherapy. Simulations indicate a polytherapeutic approach may mitigate side‐effects and proarrhythmic potential plaguing CPVT pharmacological management today. Importantly, our prediction of a novel polytherapy for CPVT was confirmed experimentally. Our simulations suggest that flecainide therapeutic efficacy in CPVT is unlikely to derive from primary interactions with the Na+ channel, and benefit may be gained from an alternative multi‐drug regimen. The mechanism of therapeutic efficacy of flecainide for catecholaminergic polymorphic ventricular tachycardia (CPVT) is unclear. Model predictions suggest that Na+ channel effects are insufficient to explain flecainide efficacy in CPVT. This study represents a first step toward predicting therapeutic mechanisms of drug efficacy in the setting of CPVT and then using these mechanisms to guide modelling and simulation to predict alternative drug therapies.
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Affiliation(s)
- Pei-Chi Yang
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Jonathan D Moreno
- Division of Cardiology, Department of Medicine, Barnes-Jewish Hospital, Washington University in St Louis, St Louis, MO, USA
| | - Christina Y Miyake
- Cardiovascular Research Institute, Department of Molecular Physiology & Biophysics, Department of Medicine, Cardiology, Baylor College of Medicine, Houston, TX, USA
| | | | - Mao-Tsuen Jeng
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Eleonora Grandi
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Xander H T Wehrens
- Cardiovascular Research Institute, Department of Molecular Physiology & Biophysics, Department of Medicine, Cardiology, Baylor College of Medicine, Houston, TX, USA.,Department of Pediatrics, Texas Children's Hospital, Baylor College of Medicine, and the Cardiovascular Research Institute, Houston, TX, USA
| | - Sergei Y Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, Alberta, Canada
| | - Colleen E Clancy
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
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14
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Yu Z, van Veldhoven JPD, Louvel J, ’t Hart IME, Rook MB, van der Heyden MAG, Heitman LH, IJzerman AP. Structure–Affinity Relationships (SARs) and Structure–Kinetics Relationships (SKRs) of Kv11.1 Blockers. J Med Chem 2015; 58:5916-29. [DOI: 10.1021/acs.jmedchem.5b00518] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Zhiyi Yu
- Division
of Medicinal Chemistry, Leiden Academic Centre for Drug Research, Leiden University, 2300 RA Leiden, The Netherlands
| | - Jacobus P. D. van Veldhoven
- Division
of Medicinal Chemistry, Leiden Academic Centre for Drug Research, Leiden University, 2300 RA Leiden, The Netherlands
| | - Julien Louvel
- Division
of Medicinal Chemistry, Leiden Academic Centre for Drug Research, Leiden University, 2300 RA Leiden, The Netherlands
| | - Ingrid M. E. ’t Hart
- Division
of Medicinal Chemistry, Leiden Academic Centre for Drug Research, Leiden University, 2300 RA Leiden, The Netherlands
| | - Martin B. Rook
- Department of Medical Physiology, Division Heart & Lungs, University Medical Centre Utrecht, 3584 CM Utrecht, The Netherlands
| | - Marcel A. G. van der Heyden
- Department of Medical Physiology, Division Heart & Lungs, University Medical Centre Utrecht, 3584 CM Utrecht, The Netherlands
| | - Laura H. Heitman
- Division
of Medicinal Chemistry, Leiden Academic Centre for Drug Research, Leiden University, 2300 RA Leiden, The Netherlands
| | - Adriaan P. IJzerman
- Division
of Medicinal Chemistry, Leiden Academic Centre for Drug Research, Leiden University, 2300 RA Leiden, The Netherlands
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15
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Poulet C, Wettwer E, Grunnet M, Jespersen T, Fabritz L, Matschke K, Knaut M, Ravens U. Late Sodium Current in Human Atrial Cardiomyocytes from Patients in Sinus Rhythm and Atrial Fibrillation. PLoS One 2015; 10:e0131432. [PMID: 26121051 PMCID: PMC4485891 DOI: 10.1371/journal.pone.0131432] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Accepted: 06/01/2015] [Indexed: 12/19/2022] Open
Abstract
Slowly inactivating Na+ channels conducting “late” Na+ current (INa,late) contribute to ventricular arrhythmogenesis under pathological conditions. INa,late was also reported to play a role in chronic atrial fibrillation (AF). The objective of this study was to investigate INa,late in human right atrial cardiomyocytes as a putative drug target for treatment of AF. To activate Na+ channels, cardiomyocytes from transgenic mice which exhibit INa,late (ΔKPQ), and right atrial cardiomyocytes from patients in sinus rhythm (SR) and AF were voltage clamped at room temperature by 250-ms long test pulses to -30 mV from a holding potential of -80 mV with a 100-ms pre-pulse to -110 mV (protocol I). INa,late at -30 mV was not discernible as deviation from the extrapolated straight line IV-curve between -110 mV and -80 mV in human atrial cells. Therefore, tetrodotoxin (TTX, 10 μM) was used to define persistent inward current after 250 ms at -30 mV as INa,late. TTX-sensitive current was 0.27±0.06 pA/pF in ventricular cardiomyocytes from ΔKPQ mice, and amounted to 0.04±0.01 pA/pF and 0.09±0.02 pA/pF in SR and AF human atrial cardiomyocytes, respectively. With protocol II (holding potential -120 mV, pre-pulse to -80 mV) TTX-sensitive INa,late was always larger than with protocol I. Ranolazine (30 μM) reduced INa,late by 0.02±0.02 pA/pF in SR and 0.09±0.02 pA/pF in AF cells. At physiological temperature (37°C), however, INa,late became insignificant. Plateau phase and upstroke velocity of action potentials (APs) recorded with sharp microelectrodes in intact human trabeculae were more sensitive to ranolazine in AF than in SR preparations. Sodium channel subunits expression measured with qPCR was high for SCN5A with no difference between SR and AF. Expression of SCN8A and SCN10A was low in general, and lower in AF than in SR. In conclusion, We confirm for the first time a TTX-sensitive current (INa,late) in right atrial cardiomyocytes from SR and AF patients at room temperature, but not at physiological temperature. While our study provides evidence for the presence of INa,late in human atria, the potential of such current as a target for the treatment of AF remains to be demonstrated.
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Affiliation(s)
- Claire Poulet
- Department of Pharmacology and Toxicology, Medical Faculty, TU Dresden, Dresden, Germany
| | - Erich Wettwer
- Department of Pharmacology and Toxicology, Medical Faculty, TU Dresden, Dresden, Germany
| | - Morten Grunnet
- Danish Arrhythmia Research Centre, University of Copenhagen, Copenhagen, Denmark
| | - Thomas Jespersen
- Danish Arrhythmia Research Centre, University of Copenhagen, Copenhagen, Denmark
| | - Larissa Fabritz
- Centre for Cardiovascular Sciences, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Klaus Matschke
- Clinic for Cardiac Surgery, Heart Center Dresden, Dresden, Germanymailto
| | - Michael Knaut
- Clinic for Cardiac Surgery, Heart Center Dresden, Dresden, Germanymailto
| | - Ursula Ravens
- Department of Pharmacology and Toxicology, Medical Faculty, TU Dresden, Dresden, Germany
- * E-mail:
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16
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Trenor B, Gomis-Tena J, Cardona K, Romero L, Rajamani S, Belardinelli L, Giles WR, Saiz J. In silico assessment of drug safety in human heart applied to late sodium current blockers. Channels (Austin) 2015; 7:249-62. [PMID: 23696033 DOI: 10.4161/chan.24905] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Drug-induced action potential (AP) prolongation leading to Torsade de Pointes is a major concern for the development of anti-arrhythmic drugs. Nevertheless the development of improved anti-arrhythmic agents, some of which may block different channels, remains an important opportunity. Partial block of the late sodium current (I(NaL)) has emerged as a novel anti-arrhythmic mechanism. It can be effective in the settings of free radical challenge or hypoxia. In addition, this approach can attenuate pro-arrhythmic effects of blocking the rapid delayed rectifying K(+) current (I(Kr)). The main goal of our computational work was to develop an in-silico tool for preclinical anti-arrhythmic drug safety assessment, by illustrating the impact of I(Kr)/I(NaL) ratio of steady-state block of drug candidates on "torsadogenic" biomarkers. The O'Hara et al. AP model for human ventricular myocytes was used. Biomarkers for arrhythmic risk, i.e., AP duration, triangulation, reverse rate-dependence, transmural dispersion of repolarization and electrocardiogram QT intervals, were calculated using single myocyte and one-dimensional strand simulations. Predetermined amounts of block of I(NaL) and I(Kr) were evaluated. "Safety plots" were developed to illustrate the value of the specific biomarker for selected combinations of IC(50)s for I(Kr) and I(NaL) of potential drugs. The reference biomarkers at baseline changed depending on the "drug" specificity for these two ion channel targets. Ranolazine and GS967 (a novel potent inhibitor of I(NaL)) yielded a biomarker data set that is considered safe by standard regulatory criteria. This novel in-silico approach is useful for evaluating pro-arrhythmic potential of drugs and drug candidates in the human ventricle.
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17
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Sossalla S, Wallisch N, Toischer K, Sohns C, Vollmann D, Seegers J, Lüthje L, Maier LS, Zabel M. Effects of ranolazine on torsades de pointes tachycardias in a healthy isolated rabbit heart model. Cardiovasc Ther 2015; 32:170-7. [PMID: 24785406 PMCID: PMC4285941 DOI: 10.1111/1755-5922.12078] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
PURPOSE Torsades de pointes (TdP) tachycardias are triggered, polymorphic ventricular arrhythmias arising from early afterdepolarizations (EADs) and increased dispersion of repolarization. Ranolazine is a new agent which reduces pathologically elevated late INa but also IKr . Aim of this study was to evaluate the effects of ranolazine in a validated isolated Langendorff-perfused rabbit heart model. METHODS TdP was reproducibly induced with d-sotalol (10(-4) mol/L) and low potassium (K) (1.0 mmol/L for 5 min, pacing at CL 1000 ms). In 10 hearts, ECG and 8 epi- and endocardial monophasic action potentials were recorded. Action potential duration (APD) was measured at 90% repolarization and dispersion defined as APD max-min. RESULTS D-sotalol prolonged APD90 and increased dispersion of APD90 , simultaneously causing EADs and induction of TdP. The combination of d-sotalol and two concentrations of ranolazine did not increase dispersion of ventricular APD90 as compared to vehicle. Ranolazine at 5 μmol/L did not cause additional induction of EADs and/or TdP but also did not significantly suppress arrhythmogenic triggers. The higher concentration of ranolazine (10 μmol/L) in combination with d-sotalol caused further prolongation of APD90 , at the same time reduction in APD90 dispersion. In parallel, the incidence of EADs was reduced and an antitorsadogenic effect was seen. CONCLUSIONS In the healthy isolated rabbit heart (where late INa is not elevated), ranolazine does not cause proarrhythmia but exerts antiarrhythmic effects in a dose-dependent manner against d-sotalol/low K-induced TdP. This finding-despite additional APD prolongation-supports the safety of a combined use of both drugs and merits clinical investigation.
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Affiliation(s)
- Samuel Sossalla
- Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Göttingen, Germany; DZHK (German Center for Cardiovascular Research), Göttingen, Germany
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18
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Chae YJ, Lee HJ, Jeon JH, Kim IB, Choi JS, Sung KW, Hahn SJ. Effects of donepezil on hERG potassium channels. Brain Res 2014; 1597:77-85. [PMID: 25498859 DOI: 10.1016/j.brainres.2014.11.057] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 11/04/2014] [Accepted: 11/27/2014] [Indexed: 11/26/2022]
Abstract
Donepezil is a potent, selective inhibitor of acetylcholinesterase, which is used for the treatment of Alzheimer's disease. Whole-cell patch-clamp technique and Western blot analyses were used to study the effects of donepezil on the human ether-a-go-go-related gene (hERG) channel. Donepezil inhibited the tail current of the hERG in a concentration-dependent manner with an IC50 of 1.3 μM. The metabolites of donepezil, 6-ODD and 5-ODD, inhibited the hERG currents in a similar concentration-dependent manner; the IC50 values were 1.0 and 1.5 μM, respectively. A fast drug perfusion system demonstrated that donepezil interacted with both the open and inactivated states of the hERG. A fast application of donepezil during the tail currents inhibited the open state of the hERG in a concentration-dependent manner with an IC50 of 2.7 μM. Kinetic analysis of donepezil in an open state of the hERG yielded blocking and unblocking rate constants of 0.54 µM(-1)s(-1) and 1.82 s(-1), respectively. The block of the hERG by donepezil was voltage-dependent with a steep increase across the voltage range of channel activation. Donepezil caused a reduction in the hERG channel protein trafficking to the plasma membrane at low concentration, but decreased the channel protein expression at higher concentrations. These results suggest that donepezil inhibited the hERG at a supratherapeutic concentration, and that it did so by preferentially binding to the activated (open and/or inactivated) states of the channels and by inhibiting the trafficking and expression of the hERG channel protein in the plasma membrane.
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Affiliation(s)
- Yun Ju Chae
- Department of Physiology, College of Medicine, The Catholic University of Korea, Seoul 137-701, 222 Banpo-daero, Seocho-gu, Korea
| | - Hong Joon Lee
- Department of Pharmacology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea
| | - Ji Hyun Jeon
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea
| | - In-Beom Kim
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea
| | - Jin-Sung Choi
- College of Pharmacy, Integrated Research Institute of Pharmaceutical, The Catholic University of Korea, 43-1 Yeokgok 2-dong, Wonmi-gu, Bucheon, Gyeonggi-do, Korea
| | - Ki-Wug Sung
- Department of Pharmacology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea
| | - Sang June Hahn
- Department of Physiology, College of Medicine, The Catholic University of Korea, Seoul 137-701, 222 Banpo-daero, Seocho-gu, Korea.
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19
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Patanè S. HERG-targeted therapy in both cancer and cardiovascular system with cardiovascular drugs. Int J Cardiol 2014; 176:1082-5. [DOI: 10.1016/j.ijcard.2014.07.129] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Accepted: 07/26/2014] [Indexed: 01/16/2023]
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20
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Late sodium current (INaL) in pancreatic β-cells. Pflugers Arch 2014; 467:1757-68. [DOI: 10.1007/s00424-014-1613-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 09/01/2014] [Accepted: 09/08/2014] [Indexed: 12/20/2022]
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21
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Peters CH, Sokolov S, Rajamani S, Ruben PC. Effects of the antianginal drug, ranolazine, on the brain sodium channel Na(V)1.2 and its modulation by extracellular protons. Br J Pharmacol 2014; 169:704-16. [PMID: 23472826 DOI: 10.1111/bph.12150] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Revised: 01/17/2013] [Accepted: 02/10/2013] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND AND PURPOSE Ranolazine is an antianginal drug currently approved for treatment of angina pectoris in the United States. Recent studies have focused on its effects on neuronal channels and its possible therapeutic uses in the nervous system. We characterized how ranolazine affects the brain sodium channel, Na(V)1.2, and how its actions are modulated by low pH. In this way, we further explore ranolazine's potential as an anticonvulsant and its efficacy in conditions like those during an ischaemic stroke. EXPERIMENTAL APPROACH We performed whole-cell patch-clamp experiments on the voltage-gated sodium channel, Na(V)1.2. Experiments were performed with extracellular solution titrated to either pH 7.4 or pH 6.0 before and after ranolazine perfusion. KEY RESULTS Ranolazine accelerates onset and slows recovery of fast and slow inactivation. Ranolazine increases the maximum probability of use-dependent inactivation and reduces macroscopic and ramp sodium currents at pH 7.4. pH 6.0 reduced the slowing of fast inactivation recovery and inhibited use-dependent block by ranolazine. In the presence of ranolazine, the time constants of slow inactivation recovery and onset were significantly increased at pH 6.0 relative to pH 7.4 with 100 μM ranolazine. CONCLUSIONS AND IMPLICATIONS Our work provides novel insights into the modulation of brain sodium channel, Na(V)1.2, by ranolazine. We demonstrate that ranolazine binds Na(V)1.2 in a state-dependent manner, and that the effects of ranolazine are slowed but not abolished by protons. Our results suggest that further research performed on channels with epilepsy-causing mutations may prove ranolazine to be an efficacious therapy.
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Affiliation(s)
- C H Peters
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada.
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22
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FRAGAKIS NIKOLAOS, KOSKINAS KONSTANTINOSC, VASSILIKOS VASSILIOS. Ranolazine as a Promising Treatment Option for Atrial Fibrillation: Electrophysiologic Mechanisms, Experimental Evidence, and Clinical Implications. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2014; 37:1412-20. [DOI: 10.1111/pace.12486] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2014] [Revised: 06/29/2014] [Accepted: 06/30/2014] [Indexed: 11/28/2022]
Affiliation(s)
- NIKOLAOS FRAGAKIS
- Third Department of Cardiology; Hippokrateion Hospital; Aristotle University Medical School; Thessaloniki Greece
| | - KONSTANTINOS C. KOSKINAS
- Third Department of Cardiology; Hippokrateion Hospital; Aristotle University Medical School; Thessaloniki Greece
| | - VASSILIOS VASSILIKOS
- Third Department of Cardiology; Hippokrateion Hospital; Aristotle University Medical School; Thessaloniki Greece
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23
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Ranolazine inhibition of hERG potassium channels: drug-pore interactions and reduced potency against inactivation mutants. J Mol Cell Cardiol 2014; 74:220-30. [PMID: 24877995 PMCID: PMC4121676 DOI: 10.1016/j.yjmcc.2014.05.013] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Revised: 05/14/2014] [Accepted: 05/19/2014] [Indexed: 01/06/2023]
Abstract
The antianginal drug ranolazine, which combines inhibitory actions on rapid and sustained sodium currents with inhibition of the hERG/IKr potassium channel, shows promise as an antiarrhythmic agent. This study investigated the structural basis of hERG block by ranolazine, with lidocaine used as a low potency, structurally similar comparator. Recordings of hERG current (IhERG) were made from cell lines expressing wild-type (WT) or mutant hERG channels. Docking simulations were performed using homology models built on MthK and KvAP templates. In conventional voltage clamp, ranolazine inhibited IhERG with an IC50 of 8.03 μM; peak IhERG during ventricular action potential clamp was inhibited ~ 62% at 10 μM. The IC50 values for ranolazine inhibition of the S620T inactivation deficient and N588K attenuated inactivation mutants were respectively ~ 73-fold and ~ 15-fold that for WT IhERG. Mutations near the bottom of the selectivity filter (V625A, S624A, T623A) exhibited IC50s between ~ 8 and 19-fold that for WT IhERG, whilst the Y652A and F656A S6 mutations had IC50s ~ 22-fold and 53-fold WT controls. Low potency lidocaine was comparatively insensitive to both pore helix and S6 mutations, but was sensitive to direction of K+ flux and particularly to loss of inactivation, with an IC50 for S620T-hERG ~ 49-fold that for WT IhERG. Docking simulations indicated that the larger size of ranolazine gives it potential for a greater range of interactions with hERG pore side chains compared to lidocaine, in particular enabling interaction of its two aromatic groups with side chains of both Y652 and F656. The N588K mutation is responsible for the SQT1 variant of short QT syndrome and our data suggest that ranolazine is unlikely to be effective against IKr/hERG in SQT1 patients. hERG K+ channels regulate cardiac action potential repolarization. The molecular basis of hERG block by ranolazine and structurally related lidocaine was studied. S6 Y652A and F656A mutations affected greatly ranolazine but not lidocaine binding. T623 and S624 residues may directly interact with ranolazine but not lidocaine. N588K and S620T attenuated inactivation mutants had reduced sensitivity to both drugs.
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Remme CA, Wilde AAM. Targeting sodium channels in cardiac arrhythmia. Curr Opin Pharmacol 2013; 15:53-60. [PMID: 24721654 DOI: 10.1016/j.coph.2013.11.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 11/26/2013] [Accepted: 11/28/2013] [Indexed: 12/15/2022]
Abstract
Cardiac voltage-gated sodium channels are responsible for proper electrical conduction in the heart. During acquired pathological conditions and inherited sodium channelopathies, altered sodium channel function causes conduction disturbances and ventricular arrhythmias. Although the clinical, genetic and biophysical characteristics of cardiac sodium channel disease have been extensively studied, limited progress has been made in the development of treatment strategies targeting sodium channels. Classical non-selective sodium channel blockers have only limited clinical applicability, while more selective inhibitors of the late sodium current constitute a more promising treatment option. Because of our insufficient understanding of their complexity and subcellular diversity, other specific therapeutic targets for modulating sodium channels remain elusive. The current status and future potential of targeting sodium channels in cardiac arrhythmias are discussed.
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Affiliation(s)
- Carol Ann Remme
- Department of Clinical and Experimental Cardiology, Academic Medical Center, University of Amsterdam, The Netherlands.
| | - Arthur A M Wilde
- Department of Clinical and Experimental Cardiology, Academic Medical Center, University of Amsterdam, The Netherlands
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Ayon RJ, Fernandez RA, Yuan JXJ. Mutant hERG channel traffic jam. Focus on "Pharmacological correction of long QT-linked mutations in KCNH2 (hERG) increases the trafficking of Kv11.1 channels stored in the transitional endoplasmic reticulum". Am J Physiol Cell Physiol 2013; 305:C916-8. [PMID: 23986200 DOI: 10.1152/ajpcell.00256.2013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Ramon J Ayon
- Division of Pulmonary, Critical Care, Sleep and Allergy Medicine, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois; Institute for Personalized Respiratory Medicine, University of Illinois at Chicago, Chicago, Illinois; Department of Pharmacology, University of Illinois at Chicago, Chicago, Illinois; and Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois
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Moreno JD, Yang PC, Bankston JR, Grandi E, Bers DM, Kass RS, Clancy CE. Ranolazine for congenital and acquired late INa-linked arrhythmias: in silico pharmacological screening. Circ Res 2013; 113:e50-e61. [PMID: 23897695 DOI: 10.1161/circresaha.113.301971] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
RATIONALE The antianginal ranolazine blocks the human ether-a-go-go-related gene-based current IKr at therapeutic concentrations and causes QT interval prolongation. Thus, ranolazine is contraindicated for patients with preexisting long-QT and those with repolarization abnormalities. However, with its preferential targeting of late INa (INaL), patients with disease resulting from increased INaL from inherited defects (eg, long-QT syndrome type 3 or disease-induced electric remodeling (eg, ischemic heart failure) might be exactly the ones to benefit most from the presumed antiarrhythmic properties of ranolazine. OBJECTIVE We developed a computational model to predict if therapeutic effects of pharmacological targeting of INaL by ranolazine prevailed over the off-target block of IKr in the setting of inherited long-QT syndrome type 3 and heart failure. METHODS AND RESULTS We developed computational models describing the kinetics and the interaction of ranolazine with cardiac Na(+) channels in the setting of normal physiology, long-QT syndrome type 3-linked ΔKPQ mutation, and heart failure. We then simulated clinically relevant concentrations of ranolazine and predicted the combined effects of Na(+) channel and IKr blockade by both the parent compound ranolazine and its active metabolites, which have shown potent blocking effects in the therapeutically relevant range. Our simulations suggest that ranolazine is effective at normalizing arrhythmia triggers in bradycardia-dependent arrhythmias in long-QT syndrome type 3 as well tachyarrhythmogenic triggers arising from heart failure-induced remodeling. CONCLUSIONS Our model predictions suggest that acute targeting of INaL with ranolazine may be an effective therapeutic strategy in diverse arrhythmia-provoking situations that arise from a common pathway of increased pathological INaL.
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Affiliation(s)
- Jonathan D Moreno
- Tri-Institutional MD-PhD Program, Weill Cornell Medical College/The Rockefeller University/Sloan-Kettering Cancer Institute, New York, New York, USA, 10021
| | - Pei-Chi Yang
- Department of Pharmacology, University of California, Davis, Genome Building Rm 3503, Davis, CA 95616-8636
| | - John R Bankston
- Department of Pharmacology Columbia University College of Physicians and Surgeons 630 W. 168th St. New York, NY 10032, USA
| | - Eleonora Grandi
- Department of Pharmacology, University of California, Davis, Genome Building Rm 3503, Davis, CA 95616-8636
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Genome Building Rm 3503, Davis, CA 95616-8636
| | - Robert S Kass
- Department of Pharmacology Columbia University College of Physicians and Surgeons 630 W. 168th St. New York, NY 10032, USA
| | - Colleen E Clancy
- Department of Pharmacology, University of California, Davis, Genome Building Rm 3503, Davis, CA 95616-8636
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Smith JL, Reloj AR, Nataraj PS, Bartos DC, Schroder EA, Moss AJ, Ohno S, Horie M, Anderson CL, January CT, Delisle BP. Pharmacological correction of long QT-linked mutations in KCNH2 (hERG) increases the trafficking of Kv11.1 channels stored in the transitional endoplasmic reticulum. Am J Physiol Cell Physiol 2013; 305:C919-30. [PMID: 23864605 DOI: 10.1152/ajpcell.00406.2012] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
KCNH2 encodes Kv11.1 and underlies the rapidly activating delayed rectifier K(+) current (IKr) in the heart. Loss-of-function KCNH2 mutations cause the type 2 long QT syndrome (LQT2), and most LQT2-linked missense mutations inhibit the trafficking of Kv11.1 channels. Drugs that bind to Kv11.1 and block IKr (e.g., E-4031) can act as pharmacological chaperones to increase the trafficking and functional expression for most LQT2 channels (pharmacological correction). We previously showed that LQT2 channels are selectively stored in a microtubule-dependent compartment within the endoplasmic reticulum (ER). We tested the hypothesis that pharmacological correction promotes the trafficking of LQT2 channels stored in this compartment. Confocal analyses of cells expressing the trafficking-deficient LQT2 channel G601S showed that the microtubule-dependent ER compartment is the transitional ER. Experiments with E-4031 and the protein synthesis inhibitor cycloheximide suggested that pharmacological correction promotes the trafficking of G601S stored in this compartment. Treating cells in E-4031 or ranolazine (a drug that blocks IKr and has a short half-life) for 30 min was sufficient to cause pharmacological correction. Moreover, the increased functional expression of G601S persisted 4-5 h after drug washout. Coexpression studies with a dominant-negative form of Rab11B, a small GTPase that regulates Kv11.1 trafficking, prevented the pharmacological correction of G601S trafficking from the transitional ER. These data suggest that pharmacological correction quickly increases the trafficking of LQT2 channels stored in the transitional ER via a Rab11B-dependent pathway, and we conclude that the pharmacological chaperone activity of drugs like ranolazine might have therapeutic potential.
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Affiliation(s)
- Jennifer L Smith
- Center for Muscle Biology, Department of Physiology, University of Kentucky, Lexington, Kentucky
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Late sodium current inhibition in acquired and inherited ventricular (dys)function and arrhythmias. Cardiovasc Drugs Ther 2013; 27:91-101. [PMID: 23292167 DOI: 10.1007/s10557-012-6433-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The late sodium current has been increasingly recognized for its mechanistic role in various cardiovascular pathologies, including angina pectoris, myocardial ischemia, atrial fibrillation, heart failure and congenital long QT syndrome. Although relatively small in magnitude, the late sodium current (I(NaL)) represents a functionally relevant contributor to cardiomyocyte (electro)physiology. Many aspects of I(NaL) itself are as yet still unresolved, including its distribution and function in different cell types throughout the heart, and its regulation by sodium channel accessory proteins and intracellular signalling pathways. Its complexity is further increased by a close interrelationship with the peak sodium current and other ion currents, hindering the development of inhibitors with selective and specific properties. Thus, increased knowledge of the intricacies of the complex nature of I(NaL) during distinct cardiovascular conditions and its potential as a pharmacological target is essential. Here, we provide an overview of the functional and electrophysiological effects of late sodium current inhibition on the level of the ventricular myocyte, and its potential cardioprotective and anti-arrhythmic efficacy in the setting of acquired and inherited ventricular dysfunction and arrhythmias.
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Abstract
To date, research on the human ether-a-go-go related gene (hERG) has focused on this potassium channel's role in cardiac repolarization and Long QT Syndrome (LQTS). However, growing evidence implicates hERG in a diversity of physiologic and pathological processes. Here we discuss these other functions of hERG, particularly their impact on diseases beyond cardiac arrhythmia.
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Frommeyer G, Kaiser D, Uphaus T, Kaese S, Osada N, Rajamani S, Belardinelli L, Breithardt G, Eckardt L, Milberg P. Effect of ranolazine on ventricular repolarization in class III antiarrhythmic drug-treated rabbits. Heart Rhythm 2012; 9:2051-8. [PMID: 23044390 DOI: 10.1016/j.hrthm.2012.08.029] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2012] [Indexed: 11/16/2022]
Abstract
BACKGROUND Ranolazine exhibits a synergistic effect in combination with class III drugs to suppress atrial fibrillation. OBJECTIVE To investigate whether a combination therapy affects repolarization and provokes ventricular tachyarrhythmias (VT) in a sensitive model of proarrhythmia. METHODS Thirty-seven rabbits were assigned to 3 groups and fed with amiodarone (50 mg/kg/d; n = 10) or dronedarone (50 mg/kg/d; n = 10) over a period of 6 weeks. A third group was used as control (n = 17). After obtaining baseline data in Langendorff-perfused control hearts, sotalol (100 μM) was administered in this group. Thereafter, ranolazine (10 μM) was additionally infused on top of amiodarone, dronedarone, or sotalol. RESULTS Chronic treatment with amiodarone or dronedarone as well as sotalol significantly increased action potential duration at 90% repolarization (APD(90)). Additional treatment with ranolazine further increased APD(90) in amiodarone- and dronedarone-pretreated hearts but not in sotalol-treated hearts. Ranolazine increased postrepolarization refractoriness as compared with amiodarone or dronedarone alone owing to a marked effect on the refractory period. In contrast to amiodarone and dronedarone, acute application of sotalol increased dispersion of repolarization (P < .05). Additional treatment with ranolazine did not further increase spatial or temporal dispersion. After lowering extracellular [K(+)] in bradycardic hearts, no proarrhythmia occurred in amiodarone- or dronedarone-treated hearts whereas 11 of 17 sotalol-treated hearts showed early afterdepolarizations and subsequent polymorphic VT. Additional treatment with ranolazine reduced the number of VT episodes in sotalol-treated hearts and did not cause proarrhythmia in combination with amiodarone or dronedarone. CONCLUSIONS Application of ranolazine on top of class III drugs does not cause proarrhythmia despite a marked effect on ventricular repolarization. The effect of ranolazine on the repolarization reserve is associated with the lack of effect on early afterdepolarizations and dispersion of repolarization.
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Affiliation(s)
- Gerrit Frommeyer
- Division of Electrophysiology, Department of Cardiovascular Medicine, University of Münster, Münster, Germany
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18β-Glycyrrhetinic acid preferentially blocks late Na current generated by ΔKPQ Nav1.5 channels. Acta Pharmacol Sin 2012; 33:752-60. [PMID: 22609834 DOI: 10.1038/aps.2012.22] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
AIM To compare the effects of two stereoisomeric forms of glycyrrhetinic acid on different components of Na(+) current, HERG and Kv1.5 channel currents. METHODS Wild-type (WT) and long QT syndrome type 3 (LQT-3) mutant ΔKPQ Nav1.5 channels, as well as HERG and Kv1.5 channels were expressed in Xenopus oocytes. In addition, isolated human atrial myocytes were used. Two-microelectrode voltage-clamp technique was used to record the voltage-activated currents. RESULTS Superfusion of 18β-glycyrrhetinic acid (18β-GA, 1-100 μmol/L) blocked both the peak current (I(Na,P)) and late current (I(Na,L)) generated by WT and ΔKPQ Nav1.5 channels in a concentration-dependent manner, while 18α-glycyrrhetinic acid (18α-GA) at the same concentrations had no effects. 18β-GA preferentially blocked I(Na,L) (IC(50)=37.2 ± 14.4 μmol/L) to I(Na,P) (IC(50)=100.4 ± 11.2 μmol/L) generated by ΔKPQ Nav1.5 channels. In human atrial myocytes, 18β-GA (30 μmol/L) inhibited 47% of I(Na,P) and 87% of I(Na,L) induced by Anemonia sulcata toxin (ATX-II, 30 nmol/L). Superfusion of 18β-GA (100 μmol/L) had no effects on HERG and Kv1.5 channel currents. CONCLUSION 18β-GA preferentially blocked the late Na current without affecting HERG and Kv1.5 channels.
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Parikh A, Mantravadi R, Kozhevnikov D, Roche MA, Ye Y, Owen LJ, Puglisi JL, Abramson JJ, Salama G. Ranolazine stabilizes cardiac ryanodine receptors: a novel mechanism for the suppression of early afterdepolarization and torsades de pointes in long QT type 2. Heart Rhythm 2012; 9:953-60. [PMID: 22245792 DOI: 10.1016/j.hrthm.2012.01.010] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Indexed: 12/19/2022]
Abstract
BACKGROUND Ranolazine (Ran) is known to inhibit multiple targets, including the late Na(+)current, the rapid delayed rectifying K(+)current, the L-type Ca(2+)current, and fatty acid metabolism. Functionally, Ran suppresses early afterdepolarization (EADs) and torsades de pointes (TdP) in drug-induced long QT type 2 (LQT2) presumably by decreasing intracellular [Na(+)](i) and Ca(2+)overload. However, simulations of EADs in LQT2 failed to predict their suppression by Ran. OBJECTIVE To elucidate the mechanism(s) whereby Ran alters cardiac action potentials (APs) and cytosolic Ca(2+)transients and suppresses EADs and TdP in LQT2. METHODS The known effects of Ran were included in simulations (Shannon and Mahajan models) of rabbit ventricular APs and Ca(2+)transients in control and LQT2 models and compared with experimental optical mapping data from Langendorff rabbit hearts treated with E4031 (0.5 μM) to block the rapid delayed rectifying K(+)current. Direct effects of Ran on cardiac ryanodine receptors (RyR2) were investigated in single channels and changes in Ca(2+)-dependent high-affinity ryanodine binding. RESULTS Ran (10 μM) alone prolonged action potential durations (206 ± 4.6 to 240 ± 7.8 ms; P <0.05); E4031 prolonged action potential durations (204 ± 6 to 546 ± 35 ms; P <0.05) and elicited EADs and TdP that were suppressed by Ran (10 μM; n = 7 of 7 hearts). Simulations (Shannon but not Mahajan model) closely reproduced experimental data except for EAD suppression by Ran. Ran reduced open probability (P(o)) of RyR2 (half maximal inhibitory concentration = 10 ± 3 μM; n = 7) in bilayers and shifted half maximal effective concentration for Ca(2+)-dependent ryanodine binding from 0.42 ± 0.02 to 0.64 ± 0.02 μM with 30 μM Ran. CONCLUSIONS Ran reduces P(o) of RyR2, desensitizes Ca(2+)-dependent RyR2 activation, and inhibits Ca(i) oscillations, which represents a novel mechanism for its suppression of EADs and TdP.
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Affiliation(s)
- Ashish Parikh
- Department of Bioengineering, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA
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Moreno JD, Clancy CE. Pathophysiology of the cardiac late Na current and its potential as a drug target. J Mol Cell Cardiol 2011; 52:608-19. [PMID: 22198344 DOI: 10.1016/j.yjmcc.2011.12.003] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Revised: 11/30/2011] [Accepted: 12/07/2011] [Indexed: 12/19/2022]
Abstract
A pathological increase in the late component of the cardiac Na(+) current, I(NaL), has been linked to disease manifestation in inherited and acquired cardiac diseases including the long QT variant 3 (LQT3) syndrome and heart failure. Disruption in I(NaL) leads to action potential prolongation, disruption of normal cellular repolarization, development of arrhythmia triggers, and propensity to ventricular arrhythmia. Attempts to treat arrhythmogenic sequelae from inherited and acquired syndromes pharmacologically with common Na(+) channel blockers (e.g. flecainide, lidocaine, and amiodarone) have been largely unsuccessful. This is due to drug toxicity and the failure of most current drugs to discriminate between the peak current component, chiefly responsible for single cell excitability and propagation in coupled tissue, and the late component (I(NaL)) of the Na(+) current. Although small in magnitude as compared to the peak Na(+) current (~1-3%), I(NaL) alters action potential properties and increases Na(+) loading in cardiac cells. With the increasing recognition that multiple cardiac pathological conditions share phenotypic manifestations of I(NaL) upregulation, there has been renewed interest in specific pharmacological inhibition of I(Na). The novel antianginal agent ranolazine, which shows a marked selectivity for late versus peak Na(+) current, may represent a novel drug archetype for targeted reduction of I(NaL). This article aims to review common pathophysiological mechanisms leading to enhanced I(NaL) in LQT3 and heart failure as prototypical disease conditions. Also reviewed are promising therapeutic strategies tailored to alter the molecular mechanisms underlying I(Na) mediated arrhythmia triggers.
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Affiliation(s)
- Jonathan D Moreno
- Tri-Institutional MD-PhD Program, Weill Cornell Medical College/The Rockefeller University/Sloan-Kettering Cancer Institute, New York, NY 10021, USA
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Tamargo J, Caballero R, Delpón E. Ranolazine: an antianginal drug with antiarrhythmic properties. Expert Rev Cardiovasc Ther 2011; 9:815-27. [PMID: 21809962 DOI: 10.1586/erc.11.91] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Ranolazine is an agent approved for the symptomatic treatment of chronic stable angina that inhibits the late inward sodium current (I(NaL)). I(NaL) amplitude is increased under several pathological conditions, including increased oxidative stress, myocardial ischemia, cardiac hypertrophy, heart failure, long-QT syndrome variant 3 and atrial fibrillation. Experimental and preliminary clinical evidence suggests that ranolazine may represent a new therapeutic strategy in the treatment of a broad spectrum of cardiac arrhythmias. This article reviews the role of the I(NaL) and provides an update on experimental and clinical evidence supporting the efficacy and safety of ranolazine across a broad spectrum of arrhythmias.
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Affiliation(s)
- Juan Tamargo
- Department of Pharmacology, School of Medicine, Universidad Complutense, 28040 Madrid, Spain.
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Kahlig KM, Lepist I, Leung K, Rajamani S, George AL. Ranolazine selectively blocks persistent current evoked by epilepsy-associated Naν1.1 mutations. Br J Pharmacol 2011; 161:1414-26. [PMID: 20735403 DOI: 10.1111/j.1476-5381.2010.00976.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Mutations of SCN1A, the gene encoding the pore-forming subunit of the voltage-gated sodium channel Na(V) 1.1, have been associated with a spectrum of genetic epilepsies and a familial form of migraine. Several mutant Na(V) 1.1 channels exhibit increased persistent current due to incomplete inactivation and this biophysical defect may contribute to altered neuronal excitability in these disorders. Here, we investigated the ability of ranolazine to preferentially inhibit increased persistent current evoked by mutant Na(V) 1.1 channels. EXPERIMENTAL APPROACH Human wild-type (WT) and mutant Na(V) 1.1 channels were expressed heterologously in human tsA201 cells and whole-cell patch clamp recording was used to assess tonic and use-dependent ranolazine block. KEY RESULTS Ranolazine (30 µM) did not affect WT Na(V) 1.1 channel current density, activation or steady-state fast inactivation but did produce mild slowing of recovery from inactivation. Ranolazine blocked persistent current with 16-fold selectivity over tonic block of peak current and 3.6-fold selectivity over use-dependent block of peak current. Similar selectivity was observed for ranolazine block of increased persistent current exhibited by Na(V) 1.1 channel mutations representing three distinct clinical syndromes, generalized epilepsy with febrile seizures plus (R1648H, T875M), severe myoclonic epilepsy of infancy (R1648C, F1661S) and familial hemiplegic migraine type 3 (L263V, Q1489K). In vitro application of achievable brain concentrations (1, 3 µM) to cells expressing R1648H channels was sufficient to suppress channel activation during slow voltage ramps, consistent with inhibition of persistent current. CONCLUSIONS AND IMPLICATIONS Our findings support the feasibility of using selective suppression of increased persistent current as a potential new therapeutic strategy for familial neurological disorders associated with certain sodium channel mutations.
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Affiliation(s)
- Kristopher M Kahlig
- Department of Pharmacology, Vanderbilt University, Nashville, TN 37232-0275, USA
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Kim HJ, Ahn HS, Choi JS, Choi BH, Hahn SJ. Effects of Ranolazine on Cloned Cardiac Kv4.3 Potassium Channels. J Pharmacol Exp Ther 2011; 339:952-8. [DOI: 10.1124/jpet.111.184176] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
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Antzelevitch C, Burashnikov A, Sicouri S, Belardinelli L. Electrophysiologic basis for the antiarrhythmic actions of ranolazine. Heart Rhythm 2011; 8:1281-90. [PMID: 21421082 DOI: 10.1016/j.hrthm.2011.03.045] [Citation(s) in RCA: 178] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2011] [Accepted: 03/11/2011] [Indexed: 12/19/2022]
Abstract
Ranolazine is a Food and Drug Administration-approved antianginal agent. Experimental and clinical studies have shown that ranolazine has antiarrhythmic effects in both ventricles and atria. In the ventricles, ranolazine can suppress arrhythmias associated with acute coronary syndrome, long QT syndrome, heart failure, ischemia, and reperfusion. In atria, ranolazine effectively suppresses atrial tachyarrhythmias and atrial fibrillation (AF). Recent studies have shown that the drug may be effective and safe in suppressing AF when used as a pill-in-the pocket approach, even in patients with structurally compromised hearts, warranting further study. The principal mechanism underlying ranolazine's antiarrhythmic actions is thought to be primarily via inhibition of late I(Na) in the ventricles and via use-dependent inhibition of peak I(Na) and I(Kr) in the atria. Short- and long-term safety of ranolazine has been demonstrated in the clinic, even in patients with structural heart disease. This review summarizes the available data regarding the electrophysiologic actions and antiarrhythmic properties of ranolazine in preclinical and clinical studies.
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Fluconazole inhibits hERG K(+) channel by direct block and disruption of protein trafficking. Eur J Pharmacol 2010; 650:138-44. [PMID: 20951697 DOI: 10.1016/j.ejphar.2010.10.010] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2010] [Revised: 09/15/2010] [Accepted: 10/03/2010] [Indexed: 11/21/2022]
Abstract
Fluconazole, a commonly used azole antifungal drug, can induce QT prolongation, which may lead to Torsades de Pointes and sudden death. To investigate the arrhythmogenic side effects of fluconazole, we studied the effect of fluconazole on human ether-a-go-go-related gene (hERG) K(+) channels (wild type, Y652A and F656C) expressed in human embryonic kidney (HEK293) cells using a whole-cell patch clamp technique, Western blot analysis and confocal microscopy. Fluconazole inhibited wild type hERG currents in a concentration-dependent manner, with a half-maximum block concentration (IC(50)) of 48.2±9.4μM. Fluconazole did not change other channel kinetics (activation and steady-state inactivation) of hERG channel. Mutations in drug- binding sites (Y652A or F656C) of the hERG channel significantly attenuated the hERG current blockade by fluconazole. In addition, fluconazole inhibited the trafficking of hERG protein by Western blot analysis and confocal microscopy, respectively. These findings indicate that fluconazole may cause acquired long QT syndrome (LQTS) via a direct inhibition of hERG current and by disrupting hERG protein trafficking, and the mutations Y652 and F656 may be obligatory determinants in inhibition of hERG current for fluconazole.
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Fink M, Noble D. Pharmacodynamic effects in the cardiovascular system: the modeller's view. Basic Clin Pharmacol Toxicol 2010; 106:243-9. [PMID: 20470255 DOI: 10.1111/j.1742-7843.2009.00534.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Cardiovascular disease, and the cardiovascular side effects of drugs, are essentially multifactorial problems involving interactions between many proteins, dependent on highly organized cell, tissue and organ structures. This is one reason why the side effects of drugs are often unanticipated. It is impossible to unravel such problems without using a systems approach, i.e. focussing on processes, not just molecular components. This inevitably involves modelling as the interactions require quantitative analysis. Modelling is a tool of analysis aimed at understanding, first, and predicting, eventually. We illustrate these principles using modelling of the heart. Models of the cardiac myocyte have benefited from several decades of interaction between experimentation and simulation. They are now sufficiently detailed to have been of use in the development of new drug compounds like ranolazine and ivabradine. With the help of cardiac modelling, we have also been able to unravel the mechanisms underlying the beneficial effect of sodium calcium exchange block for long QT syndrome (LQTS) 2 and LQTS3 patients. Detailed models of the interaction between ion channels and blocking agents provide the basis for modelling drug action from basic principles and predict changes in the inhomogeneous tissue of the heart. We demonstrate that mathematical models are beneficial for unravelling the complex interactions of pharmacodynamics in the heart. Embedding these detailed biophysical cellular scale models into anatomically correct models of the ventricle geometry will enable reconstructions of Torsades de Pointes arrhythmias and of fibrillation, providing a mechanism for linking detailed cellular scale experimental data to clinical applications.
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Affiliation(s)
- Martin Fink
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
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Estacion M, Waxman SG, Dib-Hajj SD. Effects of ranolazine on wild-type and mutant hNav1.7 channels and on DRG neuron excitability. Mol Pain 2010; 6:35. [PMID: 20529343 PMCID: PMC2898769 DOI: 10.1186/1744-8069-6-35] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Accepted: 06/08/2010] [Indexed: 12/19/2022] Open
Abstract
Background A direct role of sodium channels in pain has recently been confirmed by establishing a monogenic link between SCN9A, the gene which encodes sodium channel Nav1.7, and pain disorders in humans, with gain-of-function mutations causing severe pain syndromes, and loss-of-function mutations causing congenital indifference to pain. Expression of sodium channel Nav1.8 in DRG neurons has also been shown to be essential for the manifestation of mutant Nav1.7-induced neuronal hyperexcitability. These findings have confirmed key roles of Nav1.7 and Nav1.8 in pain and identify these channels as novel targets for pain therapeutic development. Ranolazine preferentially blocks cardiac late sodium currents at concentrations that do not significantly reduce peak sodium current. Ranolazine also blocks wild-type Nav1.7 and Nav1.8 channels in a use-dependent manner. However, ranolazine's effects on gain-of-function mutations of Nav1.7 and on DRG neuron excitability have not been investigated. We used voltage- and current-clamp recordings to evaluate the hypothesis that ranolazine may be effective in regulating Nav1.7-induced DRG neuron hyperexcitability. Results We show that ranolazine produces comparable block of peak and ramp currents of wild-type Nav1.7 and mutant Nav1.7 channels linked to Inherited Erythromelalgia and Paroxysmal Extreme Pain Disorder. We also show that ranolazine, at a clinically-relevant concentration, blocks high-frequency firing of DRG neurons expressing wild-type but not mutant channels. Conclusions Our data suggest that ranalozine can attenuate hyperexcitability of DRG neurons over-expressing wild-type Nav1.7 channels, as occurs in acquired neuropathic and inflammatory pain, and thus merits further study as an alternative to existing non-selective sodium channel blockers.
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Affiliation(s)
- Mark Estacion
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
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A novel mechanism for the treatment of angina, arrhythmias, and diastolic dysfunction: inhibition of late I(Na) using ranolazine. J Cardiovasc Pharmacol 2010; 54:279-86. [PMID: 19333133 DOI: 10.1097/fjc.0b013e3181a1b9e7] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Inhibition of the persistent or late Na current (INa) using ranolazine (Ranexa) represents a novel mechanism of action that was approved in the United States in 2006 and only recently in the European Union for use in patients with stable angina pectoris. In general, myocardial ischemia is associated with reduced adenosine triphosphate fluxes and decreased energy supply, resulting in severe disturbances of intracellular ion homeostasis in cardiac myocytes. In the recent years, increased late INa was suggested to contribute to this phenomenon by elevating intracellular Na concentration with subsequent rise in diastolic Ca levels by means of the sarcolemmal Na-Ca exchange system. Ranolazine, a specific inhibitor of late INa, reduces Na influx and hence ameliorates disturbed Na and Ca homeostasis. This is associated with a symptomatic improvement of angina in patients unlike other antianginal drugs without affecting heart rate or systemic blood pressure as shown in placebo-controlled studies. Therefore, ranolazine is a useful new option for patients with chronic stable angina not only as an add-on therapy. New clinical and experimental studies even point to potential antiarrhythmic effects, beneficial effects in diastolic heart failure, and under hyperglycemic conditions. In the present article, the relevant pathophysiological concepts for the role of late INa inhibition are reviewed and the most recent data from basic studies and clinical trials are summarized.
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Chen BS, Lo YC, Peng H, Hsu TI, Wu SN. Effects of ranolazine, a novel anti-anginal drug, on ion currents and membrane potential in pituitary tumor GH(3) cells and NG108-15 neuronal cells. J Pharmacol Sci 2009; 110:295-305. [PMID: 19609066 DOI: 10.1254/jphs.09018fp] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
Ranolazine, a piperazine derivative, is currently approved for the treatment of chronic angina. However, its ionic mechanisms in other types of cells remain unclear, although it is thought to be a selective blocker of late Na(+) current. This study was conducted to evaluate the possible effects of ranolazine on Na(+) current (I(Na)), L-type Ca(2+) current (I(Ca,L)), inwardly rectifying K(+) current (I(K(IR))), delayed-rectifier K(+) current (I(K(DR))), and Ca(2+)-activated K(+) current (I(K(Ca))) in pituitary tumor (GH(3)) cells. Ranolazine depressed the transient and late components of I(Na) with different potencies. This drug exerted an inhibitory effect on I(K(IR)) with an IC(50) value of 0.92 microM, while it slightly inhibited I(K(DR)) and I(K(Ca)). It shifted the steady-state activation curve of I(K(IR)) to more positive potentials with no change in the gating charge of the channel. Ranolazine (30 microM) also reduced the activity of large-conductance Ca(2+)-activated K(+) channels in HEK293T cells expressing alpha-hSlo. Under current-clamp conditions, low concentrations (e.g., 1 microM) of ranolazine increased the firing of action potentials, while at high concentrations (>or=10 microM), it diminished the firing discharge. The exposure to ranolazine also suppressed I(Na) and I(K(IR)) effectively in NG108-15 neuronal cells. Our study provides evidence that ranolazine could block multiple ion currents such as I(Na) and I(K(IR)) and suggests that these actions may contribute to some of the functional activities of neurons and endocrine or neuroendocrine cells in vivo.
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Affiliation(s)
- Bing-Shuo Chen
- Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Taiwan
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Wu L, Rajamani S, Li H, January CT, Shryock JC, Belardinelli L. Reduction of repolarization reserve unmasks the proarrhythmic role of endogenous late Na(+) current in the heart. Am J Physiol Heart Circ Physiol 2009; 297:H1048-57. [PMID: 19592609 DOI: 10.1152/ajpheart.00467.2009] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Reduction of repolarization reserve increases the risk of arrhythmia. We hypothesized that inhibition of K(+) current (I(K)) to decrease repolarization reserve would unmask the proarrhythmic role of endogenous, physiological late Na(+) current (late I(Na)). Monophasic action potentials (MAP) and 12-lead electrocardiogram were recorded from female rabbit isolated hearts. To block I(K) and reduce repolarization reserve, E-4031, 4-aminopyridine, and BaCl(2) were used; to block endogenous late I(Na), tetrodotoxin (TTX) and ranolazine were used. E-4031 (1-60 nM) concentration-dependently prolonged MAP duration (MAPD(90)) and increased duration of the T wave from T(peak) to T(end) (T(peak)-T(end)), transmural dispersion of repolarization (TDR), and beat-to-beat variability (BVR) of MAPD(90). E-4031 caused spontaneous and pause-triggered polymorphic ventricular tachycardia [torsade de pointes (TdP)]. In the presence of 60 nM E-4031, TTX (0.6-3 muM) and ranolazine (5-10 muM) shortened MAPD(90), decreased TDR, BVR, and T(peak)-T(end) (n = 9-20, P < 0.01), and abolished episodes of TdP. In hearts treated with BaCl(2) or 4-aminopyridine plus E-4031, TTX (0.6-3 muM) shortened MAPD(90) and decreased T(peak)-T(end). Ranolazine could not reverse the effect of E-4031 to inhibit human ether-a-go-go-related gene (HERG) K(+) current; thus, the reversal by ranolazine of effects of E-4031 was likely due to inhibition of late I(Na) and not to antagonism of the HERG-blocking action of E-4031. We conclude that endogenous, physiological late I(Na) contributes to arrhythmogenesis in hearts with reduced repolarization reserve. Inhibition of this current partially reverses MAPD prolongation and abolishes arrhythmic activity caused by I(K) inhibitors.
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Affiliation(s)
- Lin Wu
- Pharmacological Sciences, Gilead Sciences, Palo Alto, California 94304, USA
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