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Persson F, Andersson B, Duker G, Jacobson I, Carlsson L. Functional effects of the late sodium current inhibition by AZD7009 and lidocaine in rabbit isolated atrial and ventricular tissue and Purkinje fibre. Eur J Pharmacol 2006; 558:133-43. [PMID: 17198698 DOI: 10.1016/j.ejphar.2006.11.040] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2006] [Revised: 11/17/2006] [Accepted: 11/27/2006] [Indexed: 11/19/2022]
Abstract
AZD7009 (tert-Butyl-2-(7-[(2S)-3-(4-cyanophenoxy)-2-hydroxypropyl]-9-oxa-3,7-diazabicyclo[3.3.1]non-3-yl)ethylcarbamate) is an antiarrhythmic agent that increases atrial refractoriness, shows high antiarrhythmic efficacy and has low proarrhythmic potential. This study was primarily undertaken to determine the effects of AZD7009 on the late sodium current and to examine the impact of late sodium current inhibition on action potential duration in various myocardial cells. AZD7009 inhibited the late sodium current in Chinese Hamster Ovary K1 (CHO K1) cells expressing hNa(v)1.5 with an IC(50) of 11+/-2 microM. The late sodium current in isolated rabbit atrial and ventricular myocytes was also concentration dependently inhibited by AZD7009. Action potentials were recorded during exposure to 5 microM E-4031 (1-[2-(6-methyl-2pyridyl)ethyl]-4-(4-methylsulfonyl aminobenzoyl)piperidine), a compound that selectively inhibits the rapid delayed rectifier potassium current (I(Kr)), and to E-4031 in combination with AZD7009 or lidocaine in rabbit atrial and ventricular tissue and Purkinje fibres. In Purkinje fibres, but not in ventricular tissue, AZD7009 and lidocaine attenuated the E-4031-induced action potential duration prolongation. In atrial cells, AZD7009, but not lidocaine, further prolonged the E-4031-induced action potential duration. E-4031 induced early afterdepolarisations (EADs) in Purkinje fibres, EADs that were totally suppressed by AZD7009 or lidocaine. In conclusion, excessive action potential duration prolongation induced by E-4031 was attenuated by AZD7009 and lidocaine in rabbit Purkinje fibre, but not in atrial or ventricular tissue, most likely by inhibiting the late sodium current. Furthermore, the opposite effect by AZD7009 on action potential duration in atrial tissue suggests that AZD7009, in addition to inhibiting I(Kr), also inhibits other repolarising currents in the atria.
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Lu HR, Vlaminckx E, Van de Water A, Rohrbacher J, Hermans A, Gallacher DJ. In-vitro experimental models for the risk assessment of antibiotic-induced QT prolongation. Eur J Pharmacol 2006; 553:229-39. [PMID: 17054943 DOI: 10.1016/j.ejphar.2006.09.035] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2006] [Revised: 09/06/2006] [Accepted: 09/12/2006] [Indexed: 11/27/2022]
Abstract
The prolongation of the ventricular repolarization and proarrhythmic effects (Torsade de Pointes: TdP) of five reference antibiotics were compared in four in-vitro models. 1. Using the patch clamp technique on the human ether-a-gogo-related gene (HERG) current, the rank order for blockade of the HERG-current (IC(50)) was: sparfloxacin (44 microM)>telithromycin=moxifloxacin=erythromycin (+/-100 microM). 2. Assessing their effects on action potential duration (APD(90)) and incidence of early afterdepolarizations in isolated rabbit Purkinje fibers, the rank order was: sparfloxacin>moxifloxacin>telithromycin>erythromycin (prolongation of APD(90) at 100 microM: 83%, 48%, 33% and 17% from baseline compared to +5% with solvent, P<0.05, respectively). 3. Assessing the drug effects on the APD(60), triangulation, reverse use-dependency, and instability in isolated Langendorff-perfused rabbit hearts, the rank order was: moxifloxacin>erythromycin>sparfloxacin>telithromycin. 4. Assessing their torsadogenic potentials (scores of effects on QT-interval, peak of the T wave to end of T wave: T(p-e), T(p-e)/QT ratio, R wave on T wave (R on T) and TdP in isolated rabbit left ventricular wedge preparations, the rank order for their TdP risk score was: sparfloxacin>erythromycin>moxifloxacin>telithromycin. Additional experiments with grepafloxacin indicate that the rank order to detect grepafloxacin-induced long QT was the wedge preparation>the Purkinje fiber>HERG>the isolated heart, where the isolated heart was unable to detect grepafloxacin-induced APD prolongation. The present study demonstrates that the first three in-vitro models can be used to assess the ability of antibiotic compounds to delay ventricular repolarization. However, with respect to their known clinical effects on QT and TdP incidence, the wedge preparation appears to be more predictive and suitable for detecting torsadogenic action of antibiotics.
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Torres-Jácome J, Tejeda-Chávez HR, Rodríguez-Menchaca AA, Sánchez-Chapula JA, Navarro-Polanco RA. The D3-dopaminergic agonist 7-hydroxy-dipropylaminotetralin (7-OH-DPAT) increases cardiac action potential duration and blocks human ether-a-go-go-related gene K+ channel. J Cardiovasc Pharmacol 2006; 47:656-62. [PMID: 16775504 DOI: 10.1097/01.fjc.0000211753.47067.cc] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The D3-dopaminergic agonist (+/-) 7-hydroxy-dipropylaminotetralin (7-OH-DPAT) prolonged cycle length and action potential duration, depolarized maximum diastolic potential, and reduced the upstroke velocity of the action potential of rabbit sinoatrial node cells. These effects were not mediated by D3-dopaminergic receptors. In cat Purkinje fibers, the drug increased action potential duration. In voltage-clamped cat ventricular myocytes, 7-OH-DPAT blocked the rapid component of the delayed rectifier potassium current, IKr. This effect was corroborated in experiments studying the effect of the drug on human Ether-a-go-go-related Gene channels expressed in Xenopus oocytes and in HEK293 cells. We conclude that the direct electrophysiologic effects of 7-OH-DPAT on cardiac tissues are caused by the blockade of the rapid component of the delayed rectifier potassium current, IKr.
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Fedida D, Orth PMR, Hesketh JC, Ezrin AM. The role of late I and antiarrhythmic drugs in EAD formation and termination in Purkinje fibers. J Cardiovasc Electrophysiol 2006; 17 Suppl 1:S71-S78. [PMID: 16686685 DOI: 10.1111/j.1540-8167.2006.00386.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Multiple components of cardiac Na current play a role in determining electrical excitation in the heart. Recently, the role of nonequilibrium components in controlling cardiac action potential plateau duration, and their importance in regulating the occurrence of afterdepolarizations and arrhythmias have garnered more attention. In particular, late Na current (late I(Na)) has been shown to be important in LQT2 and LQT3 arrhythmias. Class III agents like dofetilide, clofilium, and sotalol, which can all cause a drug-induced form of LQT2, significantly lengthen action potential duration at 50% and 90% repolarization in isolated rabbit Purkinje fibers, and can initiate the formation of early afterdepolarizations, and extra beats. These actions can lead to the development of a serious ventricular tachycardia, torsades de pointes, in animal models and patients. However, pretreatment with agents that block late I(Na), like lidocaine, mexiletine, and RSD1235, a novel mixed ion channel blocker for the rapid pharmacologic conversion of atrial fibrillation, significantly attenuates the prolonging effects of Class III agents or those induced by ATX-II, a specific toxin that delays Na channel inactivation and amplifies late I(Na) greatly, mimicking LQT3. The Na channel block caused by lidocaine and RSD1235 can be through the open or inactivated states of the channel, but both equivalently inhibit a late component of Na current (I(Na)), recorded at 22 degrees C using whole-cell patch clamp of Nav 1.5 expressed in HEK cells. These protective actions of lidocaine, mexiletine, and RSD1235 may result, at least in part, from their ability to inhibit late I(Na) during action potential repolarization, and inhibition of the inward currents contributing to EAD and arrhythmia formation.
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Alakhras M, Baldari D, El‐Sherif N, Turitto G. Location and clinical implications of high-degree atrioventricular block during dipyridamole infusion: a case report. Ann Noninvasive Electrocardiol 2006; 7:174-6. [PMID: 12049688 PMCID: PMC7027632 DOI: 10.1111/j.1542-474x.2002.tb00158.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
We describe a patient with bifascicular block, who developed transient high-degree atrioventricular block during dipyridamole infusion. This patient was subsequently found to have significant His-Purkinje disease at electrophysiology study, and underwent permanent pacemaker implantation. Spontaneous atrioventricular block was documented during follow-up. This case report raises the issue of dipyridamole safety in patients with intraventricular conduction defects, and contributes an additional mechanism to the possible explanation of dipyridamole-induced atrioventricular block.
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Vassalle M, Bocchi L, Du F. A slowly inactivating sodium current (INa2) in the plateau range in canine cardiac Purkinje single cells. Exp Physiol 2006; 92:161-73. [PMID: 17053038 DOI: 10.1113/expphysiol.2006.035279] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The action potential of Purkinje fibres is markedly shortened by tetrodotoxin, suggesting the possibility that a slowly inactivating sodium current might flow during the plateau. The aim of the present experiments was to investigate, in canine cardiac Purkinje single cells by means of a whole cell patch clamp technique, whether a sodium current slowly inactivates at less negative potentials and (if so) some of its distinctive characteristics. The results showed that a 500 ms depolarizing step from a holding potential of -90 mV to -50 mV induced the fast inward current I(Na) (labelled here I(Na1)). With steps to -40 mV or less negative values, a slowly decaying component (tentatively labelled here I(Na2)) appeared, which peaked at -30 to -20 mV and decayed slowly and incompletely during the 500 ms steps. The I(Na2) was present also during steps to -10 mV, but then the transient outward current (I(to)) appeared. When the holding potential (V(h)) was decreased to -60 to -50 mV, I(Na2) disappeared even if a small I(Na1) might still be present. Tetrodotoxin (30 mum), lignocaine (100 mum) and cadmium (0.2 mm; but not manganese, 1 mm) blocked I(Na2). During fast depolarizing ramps, the rapid inactivation of I(Na1) was followed by a negative slope region. During repolarizing ramps, a region of positive slope was present, whereas I(Na1) was absent. At less negative values of V(h), the amplitude of the negative and positive slopes became gradually smaller. Gradually faster ramps increased the magnitude of the negative slope, and tetrodotoxin (30 mum) reduced or abolished it. Thus, Purkinje cells have a slowly decaying inward current owing to Na(+) entry (I(Na2)) that is different in several ways from the fast I(Na1) and that appears important for the duration of the plateau.
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Lu HR, Vlaminckx E, Van de Water A, Gallacher DJ. Calmodulin antagonist W-7 prevents sparfloxacin-induced early afterdepolarizations (EADs) in isolated rabbit purkinje fibers: importance of beat-to-beat instability of the repolarization. J Cardiovasc Electrophysiol 2006; 17:415-22. [PMID: 16643366 DOI: 10.1111/j.1540-8167.2006.00420.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION The occurrence of early afterdepolarizations (EADs) has been related to the incidence of torsades de pointes in drug-induced long QT (LQT). The generation of EADs may be facilitated by Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase). METHODS AND RESULTS In the present study, we investigated a possible involvement of Ca(2+)/Calmodulin dependent protein kinase in the generation of sparfloxacin-induced EADs in isolated rabbit Purkinje fibers by means of a calmodulin antagonist W-7. EADs were evident in 8 of the 10 preparations perfused with sparfloxacin at 1 x 10(-4) M and stimulated at 0.2 Hz. The induction of EADs by sparfloxacin was associated with a large prolongation of the duration of the action potential (APD), an increase in the triangulation, and the short-term instability of the repolarization. CaM kinase blockade with the calmodulin antagonist W-7 inhibited sparfloxacin-induced EADs in a concentration-dependent manner (EADs were induced in 3 of 10, 1 of 10, and 0 of 8 preparations in the presence of W-7 at 5 x 10(-7) M, 5 x 10(-6) M, and 5 x 10(-5) M, respectively; P < 0.01 at 5 x 10(-6) M and 5 x 10(-5) M). The inhibition of sparfloxacin-induced EADs by W-7 at 5 x 10(-7) M and 5 x 10(-6) M was associated with a significant decrease in the beat-to-beat instability but not associated with a significant shortening of the APD and reduction of V(max). CONCLUSION The present findings support the hypothesis that CaM kinase may be a proarrhythmic signaling molecule and demonstrate that CaM kinase may be involved in the generation of EADs in drug-induced LQT and enhanced beat-to-beat instability of repolarization is essential for the genesis of EADs in rabbit in vitro.
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Hanson LA, Bass AS, Gintant G, Mittelstadt S, Rampe D, Thomas K. ILSI-HESI cardiovascular safety subcommittee initiative: Evaluation of three non-clinical models of QT prolongation. J Pharmacol Toxicol Methods 2006; 54:116-29. [PMID: 16843688 DOI: 10.1016/j.vascn.2006.05.001] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Accepted: 04/14/2006] [Indexed: 10/24/2022]
Abstract
INTRODUCTION Drugs that delay cardiac repolarization pose potential safety risks to patients and cause serious regulatory concern because of the link between QT interval prolongation and the potentially fatal arrhythmia torsades de pointes (TdP). Predicting which drugs will cause TdP is an inexact and difficult science. The utility of non-clinical assays was not well understood due in part to variability in methods, species, and consistency in the assays reported in the literature. The Health and Environmental Sciences Institute of the International Life Sciences Institute (ILSI/HESI) outlined a set of studies to determine how well selected commonly used non-clinical assays identified compounds known to cause TdP and prolong QT interval in humans. METHODS Compounds known to prolong ventricular repolarization and compounds considered safe by years of clinical use were tested in three assays: HERG ionic current, Purkinje fiber repolarization, and in vivo QT studies in conscious telemeterized dogs. RESULTS The data from each of these assays demonstrate that compounds that may pose a proarrhythmia risk for patients can be distinguished from those that are considered safe. DISCUSSION Taken collectively, the in-vitro and in-vivo preclinical results can be integrated to develop an accurate preclinical risk assessment to support clinical safety.
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Bottino D, Penland RC, stamps A, Traebert M, Dumotier B, Georgiva A, Helmlinger G, Lett GS. Preclinical cardiac safety assessment of pharmaceutical compounds using an integrated systems-based computer model of the heart. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2006; 90:414-43. [PMID: 16321428 DOI: 10.1016/j.pbiomolbio.2005.06.006] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Blockade of the delayed rectifier potassium channel current, I(Kr), has been associated with drug-induced QT prolongation in the electrocardiogram and life-threatening cardiac arrhythmias. However, it is increasingly clear that compound-induced interactions with multiple cardiac ion channels may significantly affect QT prolongation that would result from inhibition of only I(Kr) [Redfern, W.S., Carlsson, L., et al., 2003. Relationships between preclinical cardiac electrophysiology, clinical QT interval prolongation and torsade de pointes for a broad range of drugs: evidence for a provisional safety margin in drug development. Cardiovasc. Res. 58(1), 32-45]. Such an assessment may not be feasible in vitro, due to multi-factorial processes that are also time-dependent and highly non-linear. Limited preclinical data, I(Kr) hERG assay and canine Purkinje fiber (PF) action potentials (APs) [Gintant, G.A., Limberis, J.T., McDermott, J.S., Wegner, C.D., Cox, B.F., 2001. The canine Purkinje fiber: an in vitro model system for acquired long QT syndrome and drug-induced arrhythmogenesis. J. Cardiovasc. Pharmacol. 37(5), 607-618], were used for two test compounds in a systems-based modeling platform of cardiac electrophysiology [Muzikant, A.L., Penland, R.C., 2002. Models for profiling the potential QT prolongation risk of drugs. Curr. Opin. Drug. Discov. Dev. 5(1), 127-35] to: (i) convert a canine myocyte model to a PF model by training functional current parameters to the AP data; (ii) reverse engineer the compounds' effects on five channel currents other than I(Kr), predicting significant IC(50) values for I(Na+), sustained and I(Ca2+), L-type , which were subsequently experimentally validated; (iii) use the predicted (I(Na+), sustained and I(Ca2+), L-type) and measured (I(Kr)) IC(50) values to simulate dose-dependent effects of the compounds on APs in endocardial, mid-myocardial, and epicardiac ventricular cells; and (iv) integrate the three types of cellular responses into a tissue-level spatial model, which quantifiably predicted no potential for the test compounds to induce either QT prolongation or increased transmural dispersion of repolarization in a dose-dependent and reverse rate-dependent fashion, despite their inhibition of I(Kr) in vitro.
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Abi-Gerges N, Small BG, Lawrence CL, Hammond TG, Valentin JP, Pollard CE. Gender differences in the slow delayed (IKs) but not in inward (IK1) rectifier K+ currents of canine Purkinje fibre cardiac action potential: key roles for IKs, beta-adrenoceptor stimulation, pacing rate and gender. Br J Pharmacol 2006; 147:653-60. [PMID: 16314855 PMCID: PMC1751338 DOI: 10.1038/sj.bjp.0706491] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2005] [Revised: 09/06/2005] [Accepted: 10/05/2005] [Indexed: 11/09/2022] Open
Abstract
As the beagle dog is a commonly used preclinical species to test the effects of new drugs on cardiac repolarisation and Purkinje fibres have become an established in vitro preparation to assess the effects of these new drugs on action potential duration (APD), the main aim of this study was therefore to evaluate the relative contribution of the inward (I(K1)) and slow delayed (I(Ks)) rectifier cardiac K(+) currents to action potential repolarisation in beagle Purkinje fibres under three different experimental conditions: (i) selective block of I(K1) with BaCl(2), (ii) selective block of I(Ks) with (-) chromanol 293B under basal conditions and (iii) selective block of I(Ks) during beta-adrenoceptor stimulation. Furthermore, the dependence of this contribution on gender and pacing rate was investigated. Microelectrode techniques were employed to measure APD in Purkinje fibres from adult female and male dogs. At stimulation rates of 3.33, 1.0 and 0.2 Hz, the degree of prolongation of APD evoked by BaCl(2) (10 microM) was comparable in fibres from female and male dogs. At the same stimulation rates, 10 microM (-) chromanol 293B did not change the APD in fibres from female and male dogs. During beta-adrenoceptor stimulation with 0.1 microM isoproterenol, an APD prolonging effect of (-) chromanol 293B was detected. In the presence of isoproterenol, action potentials in fibres from male dogs get shorter when changing the stimulation rate from 1.0 to 0.2 Hz, while the opposite is seen in fibres from female dogs. This alteration was completely reversed by (-) chromanol 293B. In conclusion, our findings confirm that beta-adrenoceptor stimulation is one condition where there may be an increased role of I(Ks) in action potential repolarisation. Gender differences in the autonomic modulation of I(Ks) could be a contributing factor to the reported increased susceptibility of female hearts to arrhythmias.
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Orth PMR, Hesketh JC, Mak CKH, Yang Y, Lin S, Beatch GN, Ezrin AM, Fedida D. RSD1235 blocks late INa and suppresses early afterdepolarizations and torsades de pointes induced by class III agents. Cardiovasc Res 2006; 70:486-96. [PMID: 16545351 DOI: 10.1016/j.cardiores.2006.01.026] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2005] [Revised: 12/31/2005] [Accepted: 01/27/2006] [Indexed: 10/25/2022] Open
Abstract
OBJECTIVE RSD1235 is a novel antiarrhythmic drug with atria-selective electrophysiological actions on Na(+) and K(+) currents. The mechanism for its protection of ventricular repolarization was assessed by its action on Purkinje fibers, and by block of late sodium current active during repolarization. Further, RSD1235's ability to reverse the pro-arrhythmic actions of the class III agents dofetilide and clofilium was assessed in isolated Purkinje fibers and an in vivo model of torsades de pointes (TdP). METHODS Action potential and early after-depolarization (EAD) recordings were made from in situ and isolated rabbit Purkinje fibers at 37 degrees C using floating sharp microelectrodes; late I(Na) was recorded using a whole-cell patch clamp technique of Nav1.5 expressed in HEK cells at 22 degrees C; In vivo, anesthetized methoxamine-sensitized rabbits were used to test the ability of RSD1235 to suppress clofilium-induced TdP. RESULTS RSD1235 (0.5-30 microM) had minor dose-dependent effects on action potential duration (APD) at 50% and 90% repolarization in Purkinje fibers, but pre-treatment significantly attenuated the APD-prolonging effects of dofetilide (300 nM). EADs induced by 300 nM dofetilide were terminated by 30 microM RSD1235 in all experiments (n=7). RSD1235 blocked a late component of Na current (I(Na)), which can produce inward currents contributing to EAD formation. RSD1235 pre-treatment (1 micromol/kg/min) or acute infusions prevented/terminated TdP induced by clofilium in 8 of 9 rabbits, and reduced the duration of TdP episodes from 71 +/- 23 s in control to 17 +/- 7 and 14 +/- 14 s at infusion rates of 0.3 and 1.0 micromol/kg/min, respectively (n = 9, p < 0.001). CONCLUSION RSD1235 itself has minor actions on repolarization in Purkinje fibers, but can reverse the AP-prolonging actions of class III agents and terminate arrhythmias in a model of TdP. We suggest that these protective actions of RSD1235 may result, at least in part, from its ability to inhibit late I(Na) during action potential repolarization.
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Wang C, Zhang YJ, Wang YL, Xu YF, Liu S, Chen ZY, Liu LL. Effect of dipfluzine on delayed afterdepolarizations and triggered activity induced by isoprenaline in human atrial fibers. YAO XUE XUE BAO = ACTA PHARMACEUTICA SINICA 2006; 41:184-7. [PMID: 16671553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
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Aubert M, Osterwalder R, Wagner B, Parrilla I, Cavero I, Doessegger L, Ertel EA. Evaluation of the Rabbit Purkinje Fibre Assay as an in vitro Tool for Assessing the Risk of Drug-Induced Torsades de Pointes in Humans. Drug Saf 2006; 29:237-54. [PMID: 16524323 DOI: 10.2165/00002018-200629030-00007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
BACKGROUND The issue of drug-induced QT interval prolongation and torsades de pointes represents a major concern for pharmaceutical development. In this investigation, we examined the value of the isolated rabbit Purkinje fibre as an in vitro action potential (AP) assay to predict the potential of drugs to induce these undesirable adverse effects. METHODS First, we categorised the proarrhythmic risk of 26 medicinal products based on proportional reporting ratios for these two adverse events recorded in a US FDA database (Spontaneous Reporting System/Adverse Event Reporting System). Second, we measured drug effects on AP in rabbit Purkinje fibres. Finally, the results of the two analyses were compared to evaluate the predictive value of the in vitro assay. RESULTS Analysis of the clinical data classified the drugs into 14 positive, 7 negative and 5 questionable for proarrhythmic risk. Based on in vitro electrophysiological profiles, the drugs were grouped into four categories: (i) profile 1 drugs prolong repolarisation without slowing depolarisation; (ii) profile 2 drugs prolong repolarisation and also slow depolarisation; (iii) profile 3 drugs shorten repolarisation; and (iv) profile 4 drugs are without effects. All 14 clinical-positive drugs fell into profiles 1 or 2 (prolongers) with low safety margins (except probucol, which showed no effect, probably because of its low solubility). Clinical-negative drugs belonged mostly to profiles 3 or 4 (non-prolongers) [except clemastine and amlodipine, which were prolongers but had large safety margins]. Clinical-questionable drugs either did not prolong or prolonged slightly but produced additional electrophysiological effects opposing prolongation. CONCLUSION The rabbit Purkinje fibre is a valuable assay for evaluating the proarrhythmic liability of pharmaceuticals as it can reveal complex electrophysiological profiles that modulate repolarisation delay.
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Ducroq J, Printemps R, Le Grand M. Additive effects of ziprasidone and d,l-sotalol on the action potential in rabbit Purkinje fibres and on the hERG potassium current. J Pharmacol Toxicol Methods 2005; 52:115-22. [PMID: 15922632 DOI: 10.1016/j.vascn.2005.04.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
INTRODUCTION Ziprasidone, an atypical antipsychotic has been shown to be devoid of cardiac adverse effects in spite of its propensity to prolong the QT-interval via a hERG current inhibition. However, the effects of ziprasidone on the action potential (AP) parameters have not been published yet. Moreover, very little information is available concerning pharmacodynamic interactions between ziprasidone and other hERG channel blockers. Thus, we investigated the putative interaction between ziprasidone and D,L-sotalol on the hERG channels at therapeutic concentrations and their consequences on the action potential prolongation. METHODS AP were recorded at 1 and 0.2 Hz. Increasing concentrations of ziprasidone (0.01-10 micromol/L) were successively superfused for 30 min alone or in D,L-sotalol 10 micromol/L pre-treated fibres. Moreover, the effects of ziprasidone, alone or in association with d,l-sotalol, were investigated on the hERG current. RESULTS Ziprasidone (1-10 microM) induced a concentration and reverse frequency-dependent increase in APD(90) (APD(90): +27% and +36%, respectively at 1 Hz and +50% and +70%, respectively at 0.2 Hz) due to a hERG current blockade (IC50: 0.24 micromol/L). A pre-treatment with D,L-sotalol 10 micromol/L led to an increase in APD(90) of +23% at 1 Hz, stable at 66+/-4 min. In these pre-treated fibres, ziprasidone (1 and 10 micromol/L) induced an additional AP prolongation (APD(90): +16% and +18%, respectively at 1 Hz) as compared to D,L-sotalol pre-treatment. Moreover, D,L-sotalol did not interact with the pharmacological profile of ziprasidone on the hERG channel. CONCLUSION The present study demonstrates that ziprasidone induces an AP prolongation due to its propensity to block the hERG channel. Moreover, ziprasidone and d,l-sotalol, superfused concomitantly exhibit additive effects on the AP duration since they do not interact as competitors for the hERG channel.
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Champeroux P, Viaud K, El Amrani AI, Fowler JSL, Martel E, Le Guennec JY, Richard S. Prediction of the risk of Torsade de Pointes using the model of isolated canine Purkinje fibres. Br J Pharmacol 2005; 144:376-85. [PMID: 15655517 PMCID: PMC1576014 DOI: 10.1038/sj.bjp.0706070] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Torsade de Pointes (TdP) is a well-described major risk associated with various kinds of drugs. However, prediction of this risk is still uncertain both in preclinical and clinical trials. We tested 45 reference compounds on the model of isolated canine Purkinje fibres. Of them, 22 are clearly associated and/or labelled with a risk of TdP, and 13 others are drugs with published clinical evidence of QT prolongation, with only one or two exceptional cases of TdP. The 10 remaining drugs are without reports of TdP and QT prolongation. The relevance of different indicators such as APD(90) increase, reverse use dependency, action potential triangulation or effect on V(max) was evaluated by comparison with available clinical data. Finally, a complex algorithm called TDPscreen and based on two subalgorithms corresponding to particular electrophysiological patterns was defined. This latter algorithm enabled a clear separation of drugs into three groups: (A) drugs with numerous or several reports (>2 cases) of TdP, (B) drugs causing QT prolongation and/or TdP only, the latter at a very low frequency (< or =2 cases), (C) drugs without reports of TdP or QT prolongation. The use of such an algorithm combined with a database accrued from reference compounds with available clinical data is suggested as a basis for testing new candidate drugs in the early stages of development for proarrhythmic risk prediction.
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Choi BH, Ha KC, Park JA, Jung YJ, Kim JC, Lee GI, Choi HS, Kang YJ, Chae SW, Kwak YG. Regional differences of superoxide dismutase activity enhance the superoxide–induced electrical heterogeneity in rabbit hearts. Basic Res Cardiol 2005; 100:355-64. [PMID: 15870956 DOI: 10.1007/s00395-005-0531-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Revised: 03/14/2005] [Accepted: 04/05/2005] [Indexed: 11/28/2022]
Abstract
During myocardial ischemia and the subsequent reperfusion, free radicals are important intermediates of the cellular damage and rhythm disturbances. We examined the effects of superoxide radicals or hydrogen peroxide (H(2)O(2)) on the action potentials in isolated rabbit Purkinje fibers, atrial muscle and ventricular muscle. Reactive oxygen species (ROS) donors such as adriamycin, xanthine/xanthine oxidase and menadione induced prolongation of APD(90) in Purkinje fibers. Menadione (30 microM), the most specific superoxide radical donor, prolonged the action potential duration at 90% repolarization (APD(90)) by 17% in Purkinje fibers, whereas it shortened the APD by 57% in ventricular muscle, and it did not affect the atrial APD. All these menadione-induced effects were completely blocked by 2,2,6,6-tetramethyl- 1-peperadinyloxy, a superoxide radical scavenger. Superoxide dismutase (SOD) activity was lowest in Purkinje fibers, it was moderate in atrial muscle and highest in ventricular muscle. H(2)O(2) shortened the APDs of all three cardiac tissues in a concentration-dependent manner. These results suggest that the different electrical responses to O(2) ([Symbol: see text]-) in different cardiac regions may result from the regional differences in the SOD activity, thereby enhancing the regional electrical heterogeneity.
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Lee FY, Wei J, Wang JJ, Liu HW, Shih TC, Lin CI. Electromechanical properties of Purkinje fiber strands isolated from human ventricular endocardium. J Heart Lung Transplant 2005; 23:737-44. [PMID: 15366435 DOI: 10.1016/s1053-2498(03)00230-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
BACKGROUND Abnormalities in the regulation of intracellular Ca2+ were observed in cardiac cells obtained from failing human hearts. However, the electromechanical properties and pharmacologic responses of human ventricular Purkinje fibers have not been well characterized. METHODS Strands of free-running Purkinje fibers and/or trabecular muscle fibers with a diameter of around 1.5 mm were removed from the endocardial surface of ventricles obtained from 16 transplant recipient hearts. Action potential (AP) was detected by conventional microelectrode techniques and twitch force by a force-displacement transducer. RESULTS The human Purkinje fiber strands as revealed by histologic examination were composed of Purkinje cells and the surrounding ventricular muscle cells. In well-polarized Purkinje fibers (mean +/- SE of maximum diastolic potential [MDP] = -85 +/- 1 mV) showing fast-response AP (Phase 0 Vmax >100 V/sec), the cardiotonic agents isoproterenol and strophanthidin (1 to 2 micromol/liter) accelerated the slope of diastolic depolarization and induced delayed afterdepolarization but not spontaneous APs. Steady-state contraction and the post-rest potentiation of contraction (PRPC) were similar in both Purkinje fibers and ventricular muscles, but inotropic agents induced tachyarrhythmia only in Purkinje fibers. In partially depolarized Purkinje fibers (MDP <-70 mV) with slow-response AP, isoproterenol and/or strophanthidin readily induced automatic and triggered rhythms. CONCLUSIONS Accumulation of excessive cytosolic Ca2+ in the presence of cardiotonic agents could lead to tachyarrhythmias in Purkinje fibers, but rarely in ventricular muscles of failing human hearts.
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Biliczki P, Acsai K, Virág L, Tálosi L, Jost N, Biliczki A, Papp JG, Varró A. Cellular electrophysiological effect of terikalant in the dog heart. Eur J Pharmacol 2005; 510:161-6. [PMID: 15763239 DOI: 10.1016/j.ejphar.2004.12.040] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Revised: 12/21/2004] [Accepted: 12/24/2004] [Indexed: 11/29/2022]
Abstract
The cellular mechanism of action of terikalant, an investigational antiarrhythmic agent known to block the inward rectifier and other potassium currents, has not yet been fully clarified. The aim of the present study was therefore to analyse the in vitro electrophysiological effects of terikalant in canine isolated ventricular muscle and Purkinje fibers by applying the standard microelectrode technique. The effects of terikalant on the duration of action potential at a stimulation cycle length of 1000 ms and on the maximum upstroke velocity of the action potential in right ventricular papillary muscle were examined at 1, 2.5, 10, and 20 microM concentrations. Terikalant significantly prolonged the action potential duration measured both at 50% and 90% of repolarization in concentration-dependent manner. The maximum upstroke velocity of the action potential was unaffected at 1 and 2.5 microM concentrations. However, this parameter was significantly reduced at 10 and 20 microM concentrations of terikalant. In Purkinje fibers terikalant (2.5 microM) also produced a marked action potential lengthening effect. Frequency dependence (cycle length of 300-5000 ms) of the action potential lengthening effect of terikalant was studied at a concentration of 2.5 microM. Prolongation of the duration of action potential occurred in a reverse frequency-dependent manner both in papillary muscle and Purkinje fibers, with a more pronounced frequency-dependence observed in Purkinje fibers. The onset kinetics of the terikalant (10 microM) induced block of the maximum upstroke velocity of the action potential was rapid (0.6+/-0.1 beat(-1), n=6) like that of Class I/B antiarrhythmics, and the offset (recovery) kinetics of the drug (2956+/-696 ms, n=6) best resembled that of Class I/A antiarrhythmic drugs. It was concluded that terikalant, unlike pure Class III antiarrhythmic drugs, has combined mode of action by lengthening repolarization and blocking the inward sodium current in a use-dependent manner.
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Sheridan RD, Turner SR, Cooper GJ, Tattersall JEH. Effects of seven drugs of abuse on action potential repolarisation in sheep cardiac Purkinje fibres. Eur J Pharmacol 2005; 511:99-107. [PMID: 15792777 DOI: 10.1016/j.ejphar.2005.02.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2004] [Revised: 02/04/2005] [Accepted: 02/09/2005] [Indexed: 10/25/2022]
Abstract
Seven drugs of abuse have been examined for effects on the action potential in sheep isolated cardiac Purkinje fibres. Phencyclidine (5 microM) induced a significant increase (30.7%) in action potential duration at 90% repolarisation (APD(90)). Similarly, 10 microM 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') induced a significant increase in APD(90) of 12.1%. Although Delta(9)-tetrahydrocannabinol (0.1 microM) induced a small, but statistically significant, 4.8% increase in APD(90), no effects were observed at 0.01 or 1 microM. Cocaethylene (10 microM) induced a significant shortening of APD(90) (-23.8%). Cocaine (up to 1 microM), (+)-methamphetamine ('Speed'; up to 5 microM), and the heroin metabolite, morphine (up to 5 microM), had no statistically significant effects. The possible significance of these findings is discussed in the context of other recognised cardiac effects of the tested drugs.
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Shin WH, Kim EJ. The Different Effects of Phenothiazines on Cardiac Action Potential Duration. Basic Clin Pharmacol Toxicol 2005; 96:143-5. [PMID: 15679478 DOI: 10.1111/j.1742-7843.2005.pto960209.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Carnes CA, Geisbuhler TP, Reiser PJ. Age-dependent changes in contraction and regional myocardial myosin heavy chain isoform expression in rats. J Appl Physiol (1985) 2004; 97:446-53. [PMID: 15220325 DOI: 10.1152/japplphysiol.00439.2003] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The goals of this study were to measure the relative levels of the alpha- and beta-isoforms of myosin heavy chain (MHC-alpha and MHC-beta, respectively) in multiple, specific regions of the adult rat heart and to determine whether age-dependent changes in isoform levels in different regions are uniform. Relative amounts of MHC-alpha and MHC-beta were determined in right and left atria and left ventricular (LV) Purkinje fibers (PF), papillary muscles, trabeculae, and endo-, mid-, and epicardial regions at 2, 5, 10, 16, and 21 mo. PFs contained substantial amounts of myosin and were striated and capable of generating force and shortening on activation. Levels of MHC-beta increased in all LV compartments with age, especially between 2 and 5 mo. There was more MHC-beta in PFs than other LV sites. There were regional differences in the level of MHC-beta throughout the LV at all ages, and the rates of change within regions differed. Ca(2+)-activated tension in PFs and trabeculae was compared at 2 and 22 mo. PF tension was less than trabecula tension, and this difference may be explained by differences in MHC content. V(max) and tension-generating ability in PFs decreased with age. Maximal tension generated by trabeculae did not change during aging. A large proportion of the increase in the level of MHC-beta that is normally associated with aging occurs at a relatively early age in rat LV. PFs, with their small diameters and short diffusion distance, should be considered for skinned multicellular myocardial studies.
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Masumiya H, Saito M, Ito M, Matsuda T, Noguchi K, Iida-Tanaka N, Tanaka H, Shigenobu K. Lack of action potential-prolonging effect of terfenadine on rabbit myocardial tissue preparations. Biol Pharm Bull 2004; 27:131-5. [PMID: 14709917 DOI: 10.1248/bpb.27.131] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of terfenadine, an antiallergic drug also known for its QT-prolonging and arrhythmogenic activities, on the action potential of isolated myocardial tissue preparations from rabbits were examined with microelectrode techniques. In the Purkinje fibers and atrium, terfenadine concentration dependently decreased the maximum rate of rise (+.V(max)) without affecting other action potential parameters. In the ventricle, terfenadine had little effect on action potential configuration. In the sinoatrial node, terfenadine 20 microM prolonged cycle length mainly through inhibition of +.V(max). Terfenadine 1 microM completely inhibited the human ether a go-go-related gene (HERG) channel current expressed in HEK293 cells in the same experimental solution as in microelectrode experiments. The lack of terfenadine effect on the action potential duration suggests that there are drugs for which the HERG channel inhibitory action underlying in vivo QT prolongation cannot be evaluated based on their action potential-prolonging activity in isolated myocardial tissue preparations.
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Abi-Gerges N, Small BG, Lawrence CL, Hammond TG, Valentin JP, Pollard CE. Evidence for gender differences in electrophysiological properties of canine Purkinje fibres. Br J Pharmacol 2004; 142:1255-64. [PMID: 15265803 PMCID: PMC1575188 DOI: 10.1038/sj.bjp.0705880] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Women are more prone to develop torsades de pointes, a rare life-threatening polymorphic ventricular tachycardia, than are men during administration of medicines that have the potential to block I(Kr) (rapid delayed rectifier cardiac K(+) current) and to prolong the QT interval. Blockade of I(Kr), hypokalaemia and extreme bradycardia were used to evaluate whether there are gender differences in cardiac repolarisation in canine Purkinje fibres (PFs). Microelectrode techniques were employed to measure action potential (AP) parameters in PFs from adult female and male dogs. Under control conditions, fibres from female animals in normal or low K(+) conditions exhibited significantly longer AP durations at 50% (APD(50)) and 90% (APD(90)) of repolarisation as compared with APDs of fibres from male animals. Gender-related difference to rate adaptation was also present in APD(90) of fibres from female animals compared to males. At a stimulation rate of 0.2 Hz, but not at 1.0 Hz, dofetilide elicited a significantly higher increase in APD(90), incidence of early afterdepolarisations, triggered and sustained-triggered activities (TAs) in fibres from female animals compared to males in either normal or low K(+) conditions. The sustained TAs were reversed by raising the concentration of [K(+)](0) in Purkinje preparations from both male (one out of one) and female (12 out of 12) dogs. In conclusion, our data provide experimental evidence pointing to gender differences in canine AP repolarisation. PFs from female dogs can be used in safety pharmacology studies as a sensitive model for evaluating the potential proarrhythmic events in vitro of a new medicinal product.
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Van Bogaert PP, Pittoors F. Use-dependent blockade of cardiac pacemaker current (If) by cilobradine and zatebradine. Eur J Pharmacol 2004; 478:161-71. [PMID: 14575801 DOI: 10.1016/j.ejphar.2003.08.083] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The action of the bradycardiac agents, cilobradine (DK-AH269) and zatebradine (UL-FS49), on the cardiac pacemaker current (If) was investigated on short Purkinje fibres from sheep hearts, using the two-microelectrode voltage-clamp technique, and on isolated rabbit sino-atrial cells with the patch clamp technique. These drugs reduce dose dependently the amplitude of the If, without modifying either the voltage dependence or the kinetics of channel activation. When voltage-clamp pulse trains were applied, cilobradine induced a use-dependent blockade of If that was stronger and faster than that with zatebradine. Recovery from blockade during prolonged hyperpolarization was significantly faster with zatebradine. Presumably, both drugs block the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel by gaining access to a binding site within the open channel pore, and are removed from the blocking site by strong hyperpolarization with large inward If through the open channel. Cilobradine, compared to zatebradine blocks If more effectively and faster in both preparations. Consequently cilobradine strongly reduces the pacemaker diastolic depolarization rate and the cell's firing frequency.
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Martin RL, McDermott JS, Salmen HJ, Palmatier J, Cox BF, Gintant GA. The utility of hERG and repolarization assays in evaluating delayed cardiac repolarization: influence of multi-channel block. J Cardiovasc Pharmacol 2004; 43:369-79. [PMID: 15076220 DOI: 10.1097/00005344-200403000-00007] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Drug-induced delayed cardiac repolarization is a recognized risk factor for proarrhythmia and is associated with block of IKr (the potassium current encoded by the human ether-a- go-go-related gene [hERG]). To evaluate the utility of 2 in vitro assays widely used to assess delayed repolarization, we compared the effects of haloperidol and 9 structurally diverse drugs in a hERG and repolarization (canine Purkinje fiber action potential duration [APD]) assay over wide concentrations. Despite potent hERG current block (IC50 = 0.174 microM), haloperidol elicited a bell-shaped concentration-response relationship for APD prolongation, with lesser prolongation (and reduced plateau height) observed with concentrations eliciting maximal hERG block, consistent with multi-channel block at higher concentrations. Consistent with this hypothesis, APD prolongation with the specific IKr blocker dofetilide was a) reduced by concomitant administration of nifedipine (calcium current block) and b) reversed by lidocaine (late sodium current block). Additional studies demonstrated prominent (>50%) hERG inhibition with most (9/10) drugs despite wide APD changes (158% prolongation - 16% shortening), consistent with multi-channel block. The poor correlation between hERG and repolarization assays suggests that the hERG assay oversimplifies drug effects on the complex repolarization process for drugs demonstrating multi-channel block and that neither assay alone adequately predicts proarrhythmic risk.
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