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Abstract
PURPOSE OF REVIEW This article aims to review the current and upcoming treatment options of primary muscle channelopathies including the non-dystrophic myotonias and periodic paralyses. RECENT FINDINGS The efficacy of mexiletine in the treatment of myotonia is now supported by two randomised placebo-controlled trials, one of which utilised a novel aggregated n-of-1 design. This has resulted in licencing of the drug via orphan drug status. There is also good evidence that mexiletine is well tolerated and safe in this patient group without the need for intensive monitoring. A range of alternative antimyotonic treatment options include lamotrigine, carbamazepine and ranolazine exist with variable evidence base. In vitro studies have shown insight into reasons for treatment failure of some medications with certain genotypes opening the era of mutation-specific therapy such as use of flecainide. In the periodic paralyses, the ability of MRI to distinguish between reversible oedema and irreversible fatty replacement makes it an increasingly useful tool to guide and assess pharmacological treatment. Unfortunately, the striking efficacy of bumetanide in hypokalaemic periodic paralysis animal models was not replicated in a recent pilot study in humans. SUMMARY The treatment of skeletal muscle channelopathies combines dietary and lifestyle advice together with pharmacological interventions. The rarity of these conditions remains a barrier for clinical studies but the example of the aggregated n-of-1 trial of mexiletine shows that innovative trial design can overcome these hurdles. Further research is required to test efficacy of drugs shown to have promising characteristics in preclinical experiments such as safinamide, riluzule and magnesium for myotonia or bumetanide for hypokalaemic periodic paralysis.
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Affiliation(s)
- Nantaporn Jitpimolmard
- Queen Square Centre for Neuromuscular Diseases, UCL Queen Square Institute of Neurology, UCL, London, UK
- Rehabilitation Medicine Department, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - Emma Matthews
- Queen Square Centre for Neuromuscular Diseases, UCL Queen Square Institute of Neurology, UCL, London, UK
- Atkinson-Morley Neuromuscular Centre, St George’s University Hospitals Foundation Trust, London, UK
| | - Doreen Fialho
- Queen Square Centre for Neuromuscular Diseases, UCL Queen Square Institute of Neurology, UCL, London, UK
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Hoppe K, Chaiklieng S, Lehmann-Horn F, Jurkat-Rott K, Wearing S, Klingler W. Preclinical pharmacological in vitro investigations on low chloride conductance myotonia: effects of potassium regulation. Pflugers Arch 2020; 472:1481-1494. [PMID: 32748018 DOI: 10.1007/s00424-020-02410-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2019] [Revised: 05/24/2020] [Accepted: 05/26/2020] [Indexed: 12/20/2022]
Abstract
In myotonia, reduced Cl- conductance of the mutated ClC-1 channels causes hindered muscle relaxation after forceful voluntary contraction due to muscle membrane hyperexcitability. Repetitive contraction temporarily decreases myotonia, a phenomena called "warm up." The underlying mechanism for the reduction of hyperexcitability in warm-up is currently unknown. Since potassium displacement is known to reduce excitability in, for example, muscle fatigue, we characterized the role of potassium in native myotonia congenita (MC) muscle. Muscle specimens of ADR mice (an animal model for low gCl- conductance myotonia) were exposed to increasing K+ concentrations. To characterize functional effects of potassium ion current, the muscle of ADR mice was exposed to agonists and antagonists of the big conductance Ca2+-activated K+ channel (BK) and the voltage-gated Kv7 channel. Effects were monitored by functional force and membrane potential measurements. By increasing [K+]0 to 5 mM, the warm-up phenomena started earlier and at [K+]0 7 mM only weak myotonia was detected. The increase of [K+]0 caused a sustained membrane depolarization accompanied with a reduction of myotonic bursts in ADR mice. Retigabine, a Kv7.2-Kv7.5 activator, dose-dependently reduced relaxation deficit of ADR myotonic muscle contraction and promoted the warm-up phenomena. In vitro results of this study suggest that increasing potassium conductivity via activation of voltage-gated potassium channels enhanced the warm-up phenomena, thereby offering a potential therapeutic treatment option for myotonia congenita.
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Affiliation(s)
- Kerstin Hoppe
- Department of Anesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital Frankfurt, Goethe University Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
- Department of Anesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital of Wuerzburg, Oberduerrbacher Str. 6, 97080, Wuerzburg, Germany.
| | - Sunisa Chaiklieng
- Division of Neurophysiology in the Center of Rare Diseases, Ulm University, Albert Einstein Allee 23, 89081, Ulm, Germany
- Faculty of Public Health, Khon Kaen University, Muang Khon Kaen, Thailand
| | - Frank Lehmann-Horn
- Department of Anesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital of Wuerzburg, Oberduerrbacher Str. 6, 97080, Wuerzburg, Germany
| | - Karin Jurkat-Rott
- Universtiy Medical Center Ulm, Division of Experimental Anesthesiology, Albert-Einstein-Allee 23, 89081, Ullm, Germany
| | - Scott Wearing
- Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, 4059, Australia
- Department of Conservative and Rehabilitation Orthopedics, Faculty of Sport and Health Science, Technical University of Munich, Gerog-Brauchle-Ring 60/62, Munich, Germany
| | - Werner Klingler
- Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, 4059, Australia
- Department of Anesthesiology, Intensive Care Medicine and Pain Therapy, SRH Clinincs, Hohenzollernstraße 40, 72488, Sigmaringen, Germany
- Department of Conservative and Rehabilitation Orthopedics, Faculty of Sport and Health Science, Technical University of Munich, Gerog-Brauchle-Ring 60/62, Munich, Germany
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Nam TS, Zhang J, Chandrasekaran G, Jeong IY, Li W, Lee SH, Kang KW, Maeng JS, Kang H, Shin HY, Park HC, Kim S, Choi SY, Kim MK. A zebrafish model of nondystrophic myotonia with sodium channelopathy. Neurosci Lett 2020; 714:134579. [PMID: 31669315 DOI: 10.1016/j.neulet.2019.134579] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2019] [Revised: 10/07/2019] [Accepted: 10/21/2019] [Indexed: 11/17/2022]
Abstract
Nondystrophic myotonias are disorders of Na+ (Nav1.4 or SCN4A) and Cl- (CLCN1) channels in skeletal muscles, and frequently show phenotype heterogeneity. The molecular mechanism underlying their pathophysiology and phenotype heterogeneity remains unclear. As zebrafish models have been recently exploited for studies of the pathophysiology and phenotype heterogeneity of various human genetic diseases, a zebrafish model may be useful for delineating nondystrophic myotonias. Here, we generated transgenic zebrafish expressing a human mutant allele of SCN4A, referred to as Tg(mylpfa:N440K), and needle electromyography revealed increased number of myotonic discharges and positive sharp waves in the muscles of Tg(mylpfa:N440K) than in controls. In addition, forced exercise test at a water temperature of 24 °C showed a decrease in the distance moved, time spent in and number of visits to the zone with stronger swimming resistance. Finally, a forced exercise test at a water temperature of 18 °C exhibited a higher number of dive-bombing periods and drifting-down behavior than in controls. These findings indicate that Tg(mylpfa:N440K) is a good vertebrate model of exercise- and cold-induced human nondystrophic myotonias. This zebrafish model may contribute to provide insight into the pathophysiology of myotonia in sodium channelopathy and could be used to explore a new therapeutic avenue.
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Affiliation(s)
- Tai-Seung Nam
- Department of Neurology, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea
| | - Jun Zhang
- Department of Biomedical Sciences, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea
| | | | - In Young Jeong
- Department of Biomedical Sciences, Korea University, Ansan, 15355, Republic of Korea
| | - Wenting Li
- Department of Biomedical Sciences, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea
| | - So-Hyun Lee
- Department of Biomedical Sciences, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea
| | - Kyung-Wook Kang
- Department of Neurology, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea
| | - Jin-Soo Maeng
- Research Group of Bioprocess Engineering, Korea Food Research Institute, Wanju-gun, 55365, Republic of Korea; Center for Convergent Research of Emerging Virus Infection, Korea Institute of Chemical Technology, Daejeon, 34114, Republic of Korea
| | - Hyuno Kang
- Korea Basic Science Institute, Gwangju Center, Gwangju, 61186, Republic of Korea
| | - Hee-Young Shin
- Department of Biomedical Sciences, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea
| | - Hae-Chul Park
- Department of Biomedical Sciences, Korea University, Ansan, 15355, Republic of Korea
| | - Sohee Kim
- Department of Robotics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, 42988, Republic of Korea.
| | - Seok-Yong Choi
- Department of Biomedical Sciences, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea.
| | - Myeong-Kyu Kim
- Department of Neurology, Chonnam National University Medical School, Gwangju, 61469, Republic of Korea.
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Hawash AA, Voss AA, Rich MM. Inhibiting persistent inward sodium currents prevents myotonia. Ann Neurol 2017; 82:385-395. [PMID: 28833464 PMCID: PMC5639374 DOI: 10.1002/ana.25017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 07/28/2017] [Accepted: 08/13/2017] [Indexed: 12/20/2022]
Abstract
OBJECTIVE Patients with myotonia congenita have muscle hyperexcitability due to loss-of-function mutations in the ClC-1 chloride channel in skeletal muscle, which causes involuntary firing of muscle action potentials (myotonia), producing muscle stiffness. The excitatory events that trigger myotonic action potentials in the absence of stabilizing ClC-1 current are not fully understood. Our goal was to identify currents that trigger spontaneous firing of muscle in the setting of reduced ClC-1 current. METHODS In vitro intracellular current clamp and voltage clamp recordings were performed in muscle from a mouse model of myotonia congenita. RESULTS Intracellular recordings revealed a slow afterdepolarization (AfD) that triggers myotonic action potentials. The AfD is well explained by a tetrodotoxin-sensitive and voltage-dependent Na+ persistent inward current (NaPIC). Notably, this NaPIC undergoes slow inactivation over seconds, suggesting this may contribute to the end of myotonic runs. Highlighting the significance of this mechanism, we found that ranolazine and elevated serum divalent cations eliminate myotonia by inhibiting AfD and NaPIC. INTERPRETATION This work significantly changes our understanding of the mechanisms triggering myotonia. Our work suggests that the current focus of treating myotonia, blocking the transient Na+ current underlying action potentials, is an inefficient approach. We show that inhibiting NaPIC is paralleled by elimination of myotonia. We suggest the ideal myotonia therapy would selectively block NaPIC and spare the transient Na+ current. Ann Neurol 2017;82:385-395.
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Affiliation(s)
- Ahmed A Hawash
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
| | - Andrew A Voss
- Department of Biology, Wright State University, Dayton, OH
| | - Mark M Rich
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
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Ginanneschi F, Mignarri A, Lucchiari S, Ulzi G, Comi GP, Rossi A, Dotti MT. Neuromuscular excitability changes produced by sustained voluntary contraction and response to mexiletine in myotonia congenita. Neurophysiol Clin 2017; 47:247-252. [PMID: 28153715 DOI: 10.1016/j.neucli.2017.01.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 01/03/2017] [Indexed: 02/02/2023] Open
Abstract
OBJECTIVE To investigate the cause of transient weakness in myotonia congenita (MC) and the mechanism of action of mexiletine in reducing weakness. METHODS The changes in neuromuscular excitability produced by 1min of maximal voluntary contractions (MVC) were measured on the amplitude of compound muscle action potentials (CMAP) in two patients with either recessive or dominant MC, compared to control values obtained in 20 healthy subjects. Measurements were performed again in MC patients after mexiletine therapy. RESULTS Transient reduction in maximal CMAP amplitude lasting several minutes after MVC was evident in MC patients, whereas no change was observed in controls. Mexiletine efficiently reduced this transient CMAP depression in both patients. DISCUSSION Transient CMAP depression following sustained MVC may represent the electrophysiological correlate of the weakness clinically experienced by the patients. In MC, the low chloride conductance could induce self-sustaining action potentials after MVC, determining progressive membrane depolarization and a loss of excitability of muscle fibers, thus resulting in transient paresis. Mexiletine may prevent conduction block due to excessive membrane depolarization, thus reducing the transient CMAP depression following sustained MVC.
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Affiliation(s)
- Federica Ginanneschi
- Department of Medical, Surgical and Neurological Sciences, Neurology-Neurophysiology Unit, University of Siena, Policlinico Le Scotte, Viale Bracci 1, 53100 Siena, Italy.
| | - Andrea Mignarri
- Department of Medical, Surgical and Neurological Sciences, Neurology-Neurophysiology Unit, University of Siena, Policlinico Le Scotte, Viale Bracci 1, 53100 Siena, Italy
| | - Sabrina Lucchiari
- Dino Ferrari Centre, Neuroscience Section, Department of Pathophysiology and Transplantation (DEPT), University of Milan, Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Gianna Ulzi
- Dino Ferrari Centre, Neuroscience Section, Department of Pathophysiology and Transplantation (DEPT), University of Milan, Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Giacomo P Comi
- Dino Ferrari Centre, Neuroscience Section, Department of Pathophysiology and Transplantation (DEPT), University of Milan, Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Alessandro Rossi
- Department of Medical, Surgical and Neurological Sciences, Neurology-Neurophysiology Unit, University of Siena, Policlinico Le Scotte, Viale Bracci 1, 53100 Siena, Italy
| | - Maria Teresa Dotti
- Department of Medical, Surgical and Neurological Sciences, Neurology-Neurophysiology Unit, University of Siena, Policlinico Le Scotte, Viale Bracci 1, 53100 Siena, Italy
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Novak KR, Norman J, Mitchell JR, Pinter MJ, Rich MM. Sodium channel slow inactivation as a therapeutic target for myotonia congenita. Ann Neurol 2015; 77:320-32. [PMID: 25515836 DOI: 10.1002/ana.24331] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2014] [Revised: 12/01/2014] [Accepted: 12/07/2014] [Indexed: 01/21/2023]
Abstract
OBJECTIVE Patients with myotonia congenita have muscle hyperexcitability due to loss-of-function mutations in the chloride channel in skeletal muscle, which causes spontaneous firing of muscle action potentials (myotonia), producing muscle stiffness. In patients, muscle stiffness lessens with exercise, a change known as the warmup phenomenon. Our goal was to identify the mechanism underlying warmup and to use this information to guide development of novel therapy. METHODS To determine the mechanism underlying warmup, we used a recently discovered drug to eliminate muscle contraction, thus allowing prolonged intracellular recording from individual muscle fibers during induction of warmup in a mouse model of myotonia congenita. RESULTS Changes in action potentials suggested slow inactivation of sodium channels as an important contributor to warmup. These data suggested that enhancing slow inactivation of sodium channels might offer effective therapy for myotonia. Lacosamide and ranolazine enhance slow inactivation of sodium channels and are approved by the US Food and Drug Administration for other uses in patients. We compared the efficacy of both drugs to mexiletine, a sodium channel blocker currently used to treat myotonia. In vitro studies suggested that both lacosamide and ranolazine were superior to mexiletine. However, in vivo studies in a mouse model of myotonia congenita suggested that side effects could limit the efficacy of lacosamide. Ranolazine produced fewer side effects and was as effective as mexiletine at a dose that produced none of mexiletine's hypoexcitability side effects. INTERPRETATION We conclude that ranolazine has excellent therapeutic potential for treatment of patients with myotonia congenita.
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Affiliation(s)
- Kevin R Novak
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
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Feldman DH, Lossin C. The Nav channel bench series: Plasmid preparation. MethodsX 2014; 1:6-11. [PMID: 26150927 PMCID: PMC4472833 DOI: 10.1016/j.mex.2014.01.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 01/09/2014] [Indexed: 12/12/2022] Open
Abstract
Research involving recombinant voltage-gated sodium (Nav) channels has unique challenges. Multiple factors contribute, but undoubtedly at the top of the list is these channels' DNA instability. Once introduced into bacterial hosts, Nav channel plasmid DNA will almost invariably emerge mutagenized and unusable, unless special conditions are adopted. This is particularly true for Nav1.1 (gene name SCN1A), Nav1.2 (SCN2A), and Nav1.6 (SCN8A), but less so for Nav1.4 (SCN4A) and Nav1.5 (SCN5A) while other Nav channel isoforms such as Nav1.7 (SCN9A) lie in between. The following recommendations for Nav plasmid DNA amplification and preparation address this problem. Three points are essential:•Bacterial propagation using Stbl2 cells at or below 30 °C.•Bias toward slow-growing, small bacterial colonies.•Comprehensive sequencing of the entire Nav channel coding region.
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Affiliation(s)
- Daniel H Feldman
- Department of Neurology, University of California - Davis, United States
| | - Christoph Lossin
- Department of Neurology, University of California - Davis, United States
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