Drug development for treatment of cardiac arrhythmias: targeting the gap junctions

Abstract

EDITORIAL FOCUSDrug development for treatment of cardiac arrhythmias: targeting the gap junctionsAndrew L. Wit, and Heather S. DuffyAndrew L. Wit, and Heather S. DuffyPublished Online:01 Jan 2008https://doi.org/10.1152/ajpheart.01031.2007This is the final version - click for previous versionMoreSectionsPDF (50 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat reentrant excitation (12) is likely the most important mechanism for serious life-threatening arrhythmias. Traditionally, a major focus of antiarrhythmic drug development has been to explore the actions of drugs designed to block conduction in reentrant pathways(s). During the latter part of the 20th century, numerous new drugs were introduced clinically. Their major targets were and still are sarcolemmal ion channels (mainly Na+, Ca2+, and K+), reducing current flow to prolong refractoriness and to slow or block conduction (23). The overall experience with the lack of uniform efficacy of these antiarrhythmic drugs suggests that there is a missing factor that is important for successful pharmacological therapy of reentrant arrhythmias. Although the role of intercellular communication through gap junctions has long been known to be an important factor governing conduction properties (24), it was not considered as a major target for antiarrhythmic drug development during this time. It was not until the important studies of Spach et al. (32, 33) beginning in the 1980s on anisotropic propagation that the significance of intercellular coupling as a cause of reentry rose to a level of prominence. Therefore, it became logical to test the concept that drugs acting on gap junctions might have antiarrhythmic actions (35). Our approach, and that of others working in this area at that time (early 1990s), was to elucidate the effects of blocking gap junctional conductance on reentrant excitation (3, 4, 22). Although there were no drugs available that had a specific blocking effect on cell coupling, some chemicals that decreased gap junctional conductance, such as heptanol (3, 4, 22, 34), were used as model drugs. We showed that a preferential slowing of conduction and eventual conduction block caused by heptanol stopped anisotropic reentry in a rabbit model (22). Another approach that we took was to increase intracellular calcium to block gap junctions and reentrant excitation with the L-type cardiac-specific calcium current “enhancer” Bay Y 5959 (5). These studies indicated that the block of gap junction function can be antiarrhythmic. In contrast, rotigaptide, a drug specifically developed to target gap junctions for the treatment of arrhythmias, enhances coupling (8, 11, 17). The studies described in the article published in this issue of the American Journal of Physiology-Heart and Circulatory Physiology by Kjolbye et al. (16) from the laboratory of Rosenbaum show how enhanced coupling may have an important antiarrhythmic effect.Rotigaptide development can be traced to a group of peptides with antiarrhythmic properties [originally named the antiarrhythmic peptides (AAPs)] that were discovered in the early 1980s (1, 8, 17). Rotigaptide has been shown to improve conduction and decrease conduction block in experimental acute ischemia caused by coronary occlusion in the canine heart (36). In the current study by Kjolbye et al. (16) in this issue, it was shown that rotigaptide abolished ischemia-induced discordant alternans and prevented the occurrence of ventricular fibrillation that is associated with it (16).The Rosenbaum laboratory (25) has been at the forefront of investigation on how T-wave alternans is related to sudden cardiac death; this group has provided strong evidence that it arises from alternation of repolarization of the transmembrane ventricular muscle action potential (25). Action potential duration in some regions of the heart may alternate in a long-short-long pattern, while other regions alternate in a short-long-short pattern (spatially discordant alternans). However, since the flow of current among cells during the repolarization phase of ventricular muscle action potentials tends to suppress large repolarization gradients, such alternans is promoted by a decrease in cell coupling (25). In the current study (16), discordant alternans was produced by rapid pacing in the presence of ischemia, a pathological event that reduces the coupling among myocardial cells (18). The link between discordant alternans and reentrant arrhythmias is that discordant alternans creates large gradients of refractoriness of sufficient magnitude to cause unidirectional conduction block and reentry. Rotigaptide, by enhancing cell coupling, attenuated discordant alternans, abolishing the gradients of refractoriness, thereby preventing the occurrence of fibrillation (16).The mechanism of the antiarrhythmic effect of rotigaptide on gap junctions is unique; it is proposed to be prevention of dephosphorylation of connexin 43 (Cx43), the principle gap junction protein in ventricular myocardium (2, 16). Cx43 is known to be regulated by phosphorylation (19). In ventricular myocytes after ischemia, loss of the P2 band that is indicative of phosphorylated Cx43 protein in standard Western blots has been described previously (13). Although this has been termed a “dephosphorylation,” it is actually a change in the individual phosphorylated residues within the carboxy-terminal domain of Cx43 (19, 31). Two of the residues that lose their phosphates during an ischemic event are Ser297 and Ser368. These dephosphorylation events have been shown to be blocked by rotigaptide (2). Thus, the loss of the P0 band, or so-called dephosphorylated species, in the study by Kjølbye et al. (16) (termed a “hyperphosphorylation” of Cx43) caused by rotigaptide is likely a maintenance of the phosphorylation of these two key serine residues. This becomes important when trying to determine the exact molecular mechanism of the action of rotigaptide. Knowing which residues are phosphorylated can lead to an understanding of the underlying kinases involved and an understanding of the specificity of the result. This remains to be worked out. Drug action on kinases in other tissues might lead to unspecified adverse effects.As a result of this study and the previous ones on rotigaptide cited above, it appears that the concept of increasing gap junction conductance as an antiarrhythmic intervention is an excellent one and rotigaptide studies may pave the way for the eventual development of an effective drug to prevent life-threatening cardiac arrhythmias. However, there are several issues that must be considered relating to this line of drug development. 1) The proposed mechanism of action of rotigaptide is prevention of dephosphorylation of Cx43 that accompanies acute metabolic stress such as that accompanying myocardial ischemia. However, the role of dephosphorylation of Cx43 in other pathological situations with diminished gap junction coupling not involving metabolic stress is unknown. Therefore, a drug that targets dephosphorylation might not be effective in these conditions (10, 26, 28, 29, 30). In addition, the role of phophorylation state in controlling conductance of gap junctions formed by other connexins is unknown, for example, Cx40 a major connexin in the atria that may be involved in atrial fibrillation. 2) Gap junction remodeling accompanies some chronic diseases such as myopathies and chronic ischemic heart disease (10, 26, 27, 28, 29, 30). Remodeling includes a decrease in number of gap junction connections resulting from the interruption of communication between cells by fibrosis (32, 33) and downregulation of Cx43 formation or trafficking to the intercalated disk. Another feature of remodeling in some situations is lateralization of gap junctions where there is deposition of increased amounts of Cx on lateral membranes of myocytes (27). This deposition may represent movement of Cx43 out of the intercalated disk, decreasing gap junctions in the disk leading to uncoupling (9). For reasons that are not yet understood, lateralization can be associated with slow conduction and block and be a primary cause of reentry (27, 37). In the situation in which there is a significant decrease in the quantity of gap junctions and/or lateralization, increasing gap junction conductance might not be an effective means of improving conduction. Since there are many fewer connections in remodeled myocardium than in normal myocardium, blocking the few remaining gap junctions might be a more effective way of stopping reentry. Spear et al. (34) have shown that heptanol can cause conduction block in regions of nonuniform anisotropy in infarct border zones in concentrations that have little effect on conduction in normal ventricular muscle. 3) Even in acute ischemia where increasing gap junction conductance has been shown to stop reentrant tachyarrhythmias, the effects on eventual infarct size must be considered. It has been shown that the so-called “kiss of death” action of gap junctions causes cells coupled to damaged regions in many different kinds of tissues to die in clusters via the passage of apoptotic signals from the damaged region through Cx43 gap junction channels (6, 21). The reduction of intercellular coupling by decreasing gap junction conductance is a response of the myocardium to limit the damage caused by an insult such as a coronary occlusion (7). Studies looking at myocardial infarct size in a mouse model have shown that decreasing the levels of Cx43 via knockout of one allele in murine hearts (Cx43+/−) caused a decrease in infarct size in this model (14). It thus may be of importance to determine overall infarct size in models where rotigaptide is used as an antiarrhythmic agent after coronary artery occlusion since to limit infarct size the effective intervention may be to decrease phosphorylation and gap junction conductance (20).REFERENCES1 Aonuma S, Kohama Y, Akai K, Iwasaki S. Studies on heart. II Further effects of bovine ventricle protein (BVP) and antiarrhythmic peptide (AAP) on myocardial cells in culture. Chem Pharm Bull 28: 3340–3346, 1980.Crossref | PubMed | ISI | Google Scholar2 Axelsen LN, Stahlhut M, Mohammed S, Larsen BD, Nielsen MS, Holstein-Rathlou NH, Andersen S, Jensen ON, Hennan JK, Kjolbye AL. Identification of ischemia-regulated phosphorylation sites in connexin43: A possible target for the antiarrhythmic peptide analogue rotigaptide (ZP123). J Mol Cell Cardiol 40: 790–798, 2006.Crossref | PubMed | ISI | Google Scholar3 Balke CW, Lesh MD, Spear JF, Kadish A, Levine JH, Moore EN. Effects of cellular uncoupling on conduction in anisotropic canine ventricular myocardium. Circ Res 63: 879–892, 1988.Crossref | PubMed | ISI | Google Scholar4 Brugada J, Mont L, Boersma L, Kirchhof C, Allessie MA. Differential effects of heptanol, potassium, and tetrodotoxin on reentrant ventricular tachycardia around a fixed obstacle in anisotropic myocardium. Circulation 84: 1307–1318, 1991.Crossref | PubMed | ISI | Google Scholar5 Cabo C, Schmitt H, Wit AL. New mechanism of antiarrhythmic drug action: increasing L-type calcium current prevents reentrant ventricular tachycardia in the infarcted canine heart. Circulation 102: 2417–2425, 2000.Crossref | PubMed | ISI | Google Scholar6 Cusato K, Bosco A, Rozental R, Guimaraes CA, Reese BE, Linden R, Spray DC. Gap junctions mediate bystander cell death in developing retina. J Neurosci 23: 6413–6422, 2003.Crossref | PubMed | ISI | Google Scholar7 De Mello WC. Effect of intracellular injection of cAMP on the electrical coupling of mammalian cardiac cells. Biochem Biophys Res Commun 119: 1001–1007, 1984.Crossref | PubMed | ISI | Google Scholar8 Dhein S, Manicone N, Muller A, Gerwin R, Ziskoven U, Irankhahi A, Minke C, Klaus W. A new synthetic antiarrhythmic peptide reduces dispersion of epicardial activation recovery interval and diminishes alterations of epicardial activation patterns induced by regional ischemia. A mapping study. Naunyn Schmiedebergs Arch Pharmacol 350: 174–184, 1994.PubMed | ISI | Google Scholar9 Duffy HS, Albala A, Mutsaers N, Wit AL. Remodeling of intercalated disks in infarct border zone causes slow transverse conduction by deposition of non functional connexin43 in lateral myocytes membranes (Abstract). Heart Rhythm 4, Suppl S, P02–15, 2007.Crossref | Google Scholar10 Dupont E, Matsushita T, Kaba RA, Vozzi C, Coppen SR, Khan N, Kaprielian R, Yacoub MH, Severs NJ. Altered connexin expression in human congestive heart failure. J Mol Cell Cardiol 33: 359–371, 2001.Crossref | PubMed | ISI | Google Scholar11 Eloff BC, Gilat E, Wan X, Rosenbaum DS. Pharmacological modulation of cardiac gap junctions to enhance cardiac conduction: evidence supporting a novel target for antiarrhythmic therapy. Circulation 108: 3157–3163, 2003.Crossref | PubMed | ISI | Google Scholar12 Hoffman BF, Rosen MR. Cellular mechanisms for cardiac arrhythmias. Circ Res 49: 1–15, 1981.Crossref | PubMed | ISI | Google Scholar13 Huang XD, Sandusky GE, Zipes DP. Heterogeneous loss of connexin43 protein in ischemic dog hearts. J Cardiovasc Electrophysiol 10: 79–91, 1999.Crossref | PubMed | ISI | Google Scholar14 Kanno S, Kovacs A, Yamada KA, Saffitz JE. Connexin43 as a determinant of myocardial infarct size following coronary occlusion in mice. J Am Coll Cardiol 41: 681–686, 2003.Crossref | PubMed | ISI | Google Scholar15 Kaprielian RR, Gunning M, Dupont E, Sheppard MN, Rothery SM, Underwood R, Pennell DJ, Fox K, Pepper J, Poole-Wilson PA, Severs NJ. Downregulation of immunodetectable connexin43 and decreased gap junction size in the pathogenesis of chronic hibernation in the human left ventricle. Circulation 97: 651–660, 1998.Crossref | PubMed | ISI | Google Scholar16 Kjolbye AL, Dikshteyn MS, Eloff BC, Deschenes I, Rosenbaum DS. Maintenance of intercellular coupling by the antiarrhythmic peptide rotigaptide suppresses arrhythmogenic discordant alternans. Am J Physiol Heart Circ Physiol (November 2, 2007) doi: 10.1152/ajpheart.01089. 2006.Google Scholar17 Kjolbye AL, Knudsen CB, Jepsen T, Larsen BD, Petersen JS. Pharmacological characterization of the new stable antiarrhythmic peptide analog Ac-d-Tyr-d-Pro-d-Hyp-Gly-d-Ala-Gly-NH2 (ZP123): in vivo and in vitro studies. J Pharmacol Exp Ther 306: 1191–1199, 2003.Crossref | PubMed | ISI | Google Scholar18 Kleber AG, Riegger CB, Janse MJ. Electrical uncoupling and increase of extracellular resistance after induction of ischemia in isolated, arterially perfused rabbit papillary muscle. Circ Res 61: 271–279, 1987.Crossref | PubMed | ISI | Google Scholar19 Lampe PD, Lau AF. The effects of connexin phosphorylation on gap junctional communication. Int J Biochem Cell Biol 36: 1171–1186, 2004.Crossref | PubMed | ISI | Google Scholar20 Lee TM, Chou TF. Troglitazone administration limits infarct size by reduced phosphorylation of canine myocardial connexin43 proteins. Am J Physiol Heart Circ Physiol 285: H1650–H1659, 2003.Link | ISI | Google Scholar21 Mesnil M, Piccoli C, Tiraby G, Willecke K, Yamasaki H. Bystander killing of cancer cells by herpes simplex virus thymidine kinase gene is mediated by connexins. Proc Natl Acad Sci USA 93: 1831–1835, 1996.Crossref | PubMed | ISI | Google Scholar22 Nassif G, Dillon SM, Rayhill S, Wit AL. Reentrant circuits and the effects of heptanol in a rabbit model of infarction with a uniform anisotropic epicardial border zone. J Cardiovasc Electrophysiol 4: 112–133, 1993.Crossref | PubMed | ISI | Google Scholar23 Nattel S. The molecular and ionic specificity of antiarrhythmic drug actions. J Cardiovasc Electrophysiol 10: 272–282, 1999.Crossref | PubMed | ISI | Google Scholar24 Page E. Cardiac Gap Junctions. New York: Raven Press, 1992, p. 1003–1048.Google Scholar25 Pastore JM, Girouard SD, Laurita KR, Akar FG, Rosenbaum DS. Mechanism linking T-wave alternans to the genesis of cardiac fibrillation. Circulation 99: 1385–1394, 1999.Crossref | PubMed | ISI | Google Scholar26 Peters NS, Green CR, Poole-Wilson PA, Severs NJ. Reduced content of connexin43 gap junctions in ventricular myocardium from hypertrophied and ischemic human hearts. Circulation 88: 864–875, 1993.Crossref | PubMed | ISI | Google Scholar27 Peters NS, Wit AL. Gap junction remodeling in infarction: does it play a role in arrhythmogenesis? J Cardiovasc Electrophysiol 11: 488–490, 2000.Crossref | PubMed | ISI | Google Scholar28 Sepp R, Severs NJ, Gourdie RG. Altered patterns of cardiac intercellular junction distribution in hypertrophic cardiomyopathy. Heart 76: 412–417, 1996.Crossref | PubMed | ISI | Google Scholar29 Severs NJ, Dupont E, Coppen SR, Halliday D, Inett E, Baylis D, Rothery S. Remodelling of gap junctions and connexin expression in heart disease. Biochim Biophys Acta 1662: 138–148, 2004.Crossref | PubMed | ISI | Google Scholar30 Smith JH, Green CR, Peters NS, Rothery S, Severs NJ. Altered patterns of gap junction distribution in ischemic heart disease. An immunohistochemical study of human myocardium using laser scanning confocal microscopy. Am J Pathol 139: 801–821, 1991.PubMed | ISI | Google Scholar31 Solan JL, Lampe PD. Key connexin 43 phosphorylation events regulate the gap junction life cycle. J Membr Biol. Epub ahead of print July 15, 2007.ISI | Google Scholar32 Spach MS, Barr RC. Effects of cardiac microstructure on propagating electrical waveforms. Circ Res 86: E23–28, 2000.Crossref | PubMed | ISI | Google Scholar33 Spach MS, Heidlage JF, Dolber PC, Barr RC. Electrophysiological effects of remodeling cardiac gap junctions and cell size: experimental and model studies of normal cardiac growth. Circ Res 86: 302–311, 2000.Crossref | PubMed | ISI | Google Scholar34 Spear JF, Balke CW, Lesh MD, Kadish AH, Levine JL, Moore EN. Effect of cellular uncoupling by heptanol on conduction in infarcted myocardium. Circ Res 66: 202–217, 1990.Crossref | PubMed | ISI | Google Scholar35 Wit AL. Anisotropic Reentry: A Model of Arrhythmias That May Necessitate a New Approach to Antiarrhythmic Drug Development. Boston, MA: Kluwer Academic, 1989, p. 199–213.Google Scholar36 Xing D, Kjolbye AL, Nielsen MS, Petersen JS, Harlow KW, Holstein-Rathlou NH, Martins JB. ZP123 increases gap junctional conductance and prevents reentrant ventricular tachycardia during myocardial ischemia in open chest dogs. J Cardiovasc Electrophysiol 14: 510–520, 2003.Crossref | PubMed | ISI | Google Scholar37 Yao JA, Hussain W, Patel P, Peters NS, Boyden PA, Wit AL. Remodeling of gap junc annel function in epicardial border zone of healing canine infarcts. Circ Res 92: 437–443, 2003.Crossref | PubMed | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: A. L. Wit Department of Pharmacology and The Center for Molecular Therapeutics, College of Physicians & Surgeons of Columbia University, 630 W. 168th St. New York, New York 10032 (e-mail: [email protected]) Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByConnexin 43 participates in atrial electrical remodelling through colocalization with calcium channels in atrial myocytes4 October 2021 | Clinical and Experimental Pharmacology and Physiology, Vol. 49, No. 1Interrupting Burn-Induced Changes in Serum Acute Response Markers via Connexin 32 Gap Junction Inhibition and Neutralization at the Liver2 June 2017 | Nano LIFE, Vol. 07, No. 02Effect of lysophosphatidic acid on the immune inflammatory response and the connexin 43 protein in myocardial infarction9 March 2016 | Experimental and Therapeutic Medicine, Vol. 11, No. 5Peptides and peptide-derived molecules targeting the intracellular domains of Cx43: Gap junctions versus hemichannelsNeuropharmacology, Vol. 75Current and Emerging Antiarrhythmic Drug Therapy for Ventricular Tachycardia20 February 2013 | Cardiology and Therapy, Vol. 2, No. 1Gap Junctions, Slow Conduction, and Ventricular Tachycardia After Myocardial InfarctionJournal of the American College of Cardiology, Vol. 60, No. 12The connexin43 carboxyl terminus and cardiac gap junction organizationBiochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 1818, No. 8Gap junction inhibition prevents drug-induced liver toxicity and fulminant hepatic failure15 January 2012 | Nature Biotechnology, Vol. 30, No. 2Enhanced PKCε mediated phosphorylation of connexin43 at serine 368 by a carboxyl-terminal mimetic peptide is dependent on injury28 October 2014 | Channels, Vol. 5, No. 3A Peptide Mimetic of the Connexin43 Carboxyl Terminus Reduces Gap Junction Remodeling and Induced Arrhythmia Following Ventricular InjuryCirculation Research, Vol. 108, No. 6Antiarrhythmic therapy in atrial fibrillationPharmacology & Therapeutics, Vol. 128, No. 1Improving cardiac gap junction communication as a new antiarrhythmic mechanism: the action of antiarrhythmic peptides27 November 2009 | Naunyn-Schmiedeberg's Archives of Pharmacology, Vol. 381, No. 3The ECG Recognition and Treatment of Antiarrhythmic DrugsTHE JOURNAL OF JAPAN SOCIETY FOR CLINICAL ANESTHESIA, Vol. 30, No. 4Cardiac Gap Junctions: A New Target for New Antiarrhythmic Drugs: Gap Junction Modulators6 January 2010Safety Pharmacology and Regulatory Issues in the Development of Antiarrhythmic Medications6 January 2010New Pharmacological Agents for ArrhythmiasCirculation: Arrhythmia and Electrophysiology, Vol. 2, No. 5 More from this issue > Volume 294Issue 1January 2008Pages H16-H18 Copyright & PermissionsCopyright © 2008 by the American Physiological Societyhttps://doi.org/10.1152/ajpheart.01031.2007PubMed17890421History Published online 1 January 2008 Published in print 1 January 2008 Metrics