Concomitant Block of the Rapid (I(Kr)) and Slow (I(Ks)) Components of the Delayed Rectifier Potassium Current is Associated With Additional Drug Effects on Lengthening of Cardiac Repolarization

Anti-malarial drugs: Mechanisms underlying their proarrhythmic effects

Malaria remains the leading cause of parasitic death in the world. Artemisinin resistance is an emerging threat indicating an imminent need for novel combination therapy. Given the key role of mass drug administration, it is pivotal that the safety of anti-malarial drugs is investigated thoroughly prior to widespread use. Cardiotoxicity, most prominently arrhythmic risk, has been a concern for anti-malarial drugs. We clarify the likely underlying mechanisms by which anti-malarial drugs predispose to arrhythmias. These relate to disruption of (1) action potential upstroke due to effects on the sodium currents, (2) action potential repolarisation due to effects on the potassium currents, (3) cellular calcium homeostasis, (4) mitochondrial function and reactive oxygen species production and (5) cardiac fibrosis. Together, these alterations promote arrhythmic triggers and substrates. Understanding these mechanisms is essential to assess the safety of these drugs, stratify patients based on arrhythmic risk and guide future anti-malarial drug development.

Risk Assessment of Drug-Induced Long QT Syndrome for Some COVID-19 Repurposed Drugs

The risk-benefit ratio associated with the use of repurposed drugs to treat severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2)-related infectious coronavirus disease 2019 (COVID-19) is complicated because benefits are awaited, not proven. A thorough literature search was conducted to source information on the pharmacological properties of 5 drugs and 1 combination (azithromycin, chloroquine, favipiravir, hydroxychloroquine, remdesivir, and lopinavir/ritonavir) repurposed to treat COVID-19. A risk assessment of drug-induced long QT syndrome (LQTS) associated with COVID-19 repurposed drugs was performed and compared with 23 well-known torsadogenic and 10 low torsadogenic risk compounds. Computer calculations were performed using pharmacokinetic and pharmacodynamic data, including affinity to block the rapid component of the delayed rectifier cardiac potassium current (I_Kr ) encoded by the human ether-a-go-go gene (hERG), propensity to prolong cardiac repolarization (QT interval) and cause torsade de pointes (TdP). Seven different LQTS indices were calculated and compared. The US Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) database was queried with specific key words relating to arrhythmogenic events. Estimators of LQTS risk levels indicated a very high or moderate risk for all COVID-19 repurposed drugs with the exception for azithromycin, although cases of TdP have been reported with this drug. There was excellent agreement among the various indices used to assess risk of drug-induced LQTS for the 6 repurposed medications and 23 torsadogenic compounds. Based on our results, monitoring of the QT interval shall be performed when some COVID-19 repurposed drugs are used, as such monitoring is possible for hospitalized patients or with the use of biodevices for outpatients.

Sevoflurane Alleviates Reperfusion Arrhythmia by Ameliorating TDR and MAPD90 in Isolated Rat Hearts after Ischemia-Reperfusion

Objective

To investigate the effect of sevoflurane on the monophasic action potentials (MAPs) in isolated rat hearts after ischemia-reperfusion.

Methods

Twenty-four healthy SD male rats, weighing 280–320 g, were randomly divided into three groups after successful preparation of a Langendorff isolated heart perfusion model with a stabilization period perfusion of 15 min with Krebs–Henseleit (K–H) fluid (n = 8): the control group (group A, continuously perfused with K–H fluid for 105 min), the ischemia-reperfusion group (group B, continuously perfused with K–H fluid for 15 min, and then exposed to 60 min of global ischemia induced by Thomas solution followed by 30 min of reperfusion), and the sevoflurane group (group C, K–H fluid contained 1.0 MAC sevoflurane, and other procedures were same as in group B). Heart rate (HR) and MAPs including time course (MAPD₅₀ or MAPD₉₀) of the epicardium (Epi) and endocardium (Endo) were recorded at the time of balance perfusion for 15 min (T₀), continuous perfusion for 15 min (T₁), reperfusion for 15 min/continuous perfusion for 105 min (T₂), and reperfusion for 30 min/continuous perfusion for 120 min (T₃), and the transmural dispersion of repolarization (TDR) was calculated. The incidence of arrhythmia, time for restoration of spontaneous heart beat, and duration of arrhythmia were recorded during the period of reperfusion.

Results

HR in group B and group C was lower at T₂ and T₃ than that in group A, while that in group B was significantly lower than that in group A at T₂ and T₃, and HR in group C was higher than that in group B at T₂ and T₃ (P < 0.05). There was no difference of TDR in each group at T₀ and T₁ (P > 0.05), while TDR in group B was increased at T₂ and T₃ compared with that in group C and group A (P < 0.05). TDR in group C was decreased compared with that in group B at T₂ and T₃ (P < 0.05), while there was no such difference between group C and group A (P > 0.05). The time for restoration of spontaneous heart beat and duration of arrhythmia in group C were shorter than those in group B (P < 0.05), while cardiac arrhythmia scores in group B were higher than those in group C (P < 0.05). There was no difference of MAPD₅₀ in each group (P > 0.05). The MAPD₉₀ in group B was much longer than that in other groups at T₂ and T₃ (P < 0.05), while there was no such difference between group C and group A (P > 0.05). The prolonged MAPD₉₀ at T₂ and T₃ in group B strikingly differed from that at T₀ and T₁ (P < 0.05). Nevertheless, there was no such difference in other groups at different time points (P > 0.05).

Conclusion

Sevoflurane alleviates reperfusion arrhythmia induced by myocardial ischemia-reperfusion through the shortening of MPAD₉₀ in isolated rat hearts.

α-Lipoic acid protects against arsenic trioxide-induced acute QT prolongation in anesthetized guinea pigs

Clinical use of arsenic trioxide (As₂O₃), which can induce the remission of relapsed or refractory acute promyelocytic leukemia, is often limited because of its cardiotoxicity. Symptoms of cardiotoxicity include acute cardiac conduction disturbances, such as QT prolongation. The present study was undertaken to evaluate the effects of α-lipoic acid (LA) on acute As₂O₃-induced ECG abnormalities (QTc interval prolongation) in anesthetized guinea pigs. Intravenous injection of As₂O₃ in guinea pigs caused QTc interval prolongation, which was significantly attenuated by co-treatment with LA (0.35, 3.5 and 35 mg/kg) in a dose-dependent manner. In isolated guinea pig cardiomyocytes, the decrease in IKs current induced by As₂O3 (1 μM) was rapidly restored to the basal level by the addition of LA (10 μM). Consistent with this finding, the As₂O₃-induced QTc interval prolongation was also improved rapidly by post-treatment with LA in guinea pigs. Electrospray ionization time-of-flight mass spectrometry analysis detected an expected peak of arsenic-LA complex in vitro, indicating that LA and As₂O3 form a new compound in vivo. In addition, pre-treatment with a chelating agent, British anti-Lewisite (BAL, 3.5 or 35 mg/kg), also attenuated the As₂O₃-induced QTc interval prolongation. In this study, co- and post-treatments with LA and pre-treatment with BAL ameliorated As₂O₃-induced acute QT prolongation in anesthetized guinea pigs. Because LA and probably BAL may bind to As₂O₃, these agents may exert protective effects through their chelating activity. Further studies are needed to determine whether LA is beneficial as a prophylactic or rescue agent for acute promyelocytic leukemia patients treated with As₂O₃.

Lengthening of cardiac repolarization in isolated guinea pigs hearts by sequential or concomitant administration of two IKr blockers

Block of I(Kr) is of major concern in drug safety. The objective of this study was to assess prolongation of cardiac repolarization during the combined use of two I(Kr) blockers when administered concomitantly or sequentially. (1) When isolated hearts from male guinea pigs were perfused concomitantly with two I(Kr) blockers, prolongation of monophasic action potential duration measured at 90% (MAPD(90)) was less than the summation of effects observed for each drug perfused alone. (2) In sequential administration, when ketoconazole or erythromycin was perfused first, they antagonized MAPD(90)-prolonging effects of domperidone. This effect was absent when domperidone or dofetilide was perfused first. Patch-clamp experiments confirmed that the order of sequential perfusion impacts the decrease in HERG tail amplitude. In conclusion, this study does not support the concept that potentiation of drug effects is observed during the combined administration of two I(Kr) blockers. Furthermore, order of administration of two I(Kr) blockers together may be an important factor in drug-induced long QT syndrome.

Ischemic, genetic and pharmacological origins of cardiac arrhythmias: the contribution of the Quebec Heart Institute

Research in the field of basic electrophysiology at the Quebec Heart Institute (Laval Hospital, Quebec City, Quebec) has evolved since its beginning in the 1990s. Interests were focused on cardiac arrhythmias induced by drugs, allelic variants and metabolic factors produced during ischemia. The results have contributed to the creation of new standards in drug development, more specifically, testing all new drugs for their potential effects on cardiac potassium currents, which could produce life-threatening proarrhythmic effects. In a French-Canadian population, three heterozygous single nucleotide polymorphisms in hK(v)1.5, a gene encoding for a major atrial repolarizing current, were found. These variants affect the expression level of the hK(v)1.5 channel and change the inactivation process in the presence of its accessory beta subunit. Because these effects could shorten atrial action potential, their presence was tested in postcoronary bypass patients and a higher prevalence was found in patients with postoperative atrial fibrillation. Finally, three potentially proarrhythmic factors characteristic of ischemia were identified: pH decrease; oxygen free radicals, which both increase the flow of K(+) ions through human ether-a-go-go-related gene and hK(v)1.5, producing a reduction in action potential duration, frequently leading to cardiac arrhythmias; and lysophosphatidylcholine, a metabolite involved in the production of cardiac arrhythmias early during ischemia that was shown to be a major cause of electrical uncoupling. Over the past decade, the Quebec Heart Institute has provided a significant amount of original data in the field of basic cardiac electrophysiology, specifically concerning arrhythmias originating from pharmacological agents, genetic background and cardiac ischemia.

Blockade of IKs by HMR 1556 increases the reverse rate-dependence of refractoriness prolongation by dofetilide in isolated rabbit ventricles

1. The rate-dependent contributions of the rapid and slow components of the cardiac delayed rectifier K+ current (IKr and IKs, respectively) to repolarization are not fully understood. It is unclear whether the addition of IKs block will attenuate reverse rate-dependence seen after IKr block. 2. The individual and combined electrophysiological effects of selective IKr and IKs blockers, dofetilide and HMR 1556, respectively, were evaluated using Langendorff-perfused rabbit hearts. Monophasic action potential duration at 90% repolarization (MAPD90) and ventricular effective refractory period (VERP) were determined at cycle lengths (CLs) of 200-500 ms (at 50 ms intervals). 3. Dofetilide (1-100 nM) prolonged MAPD90 in a concentration-dependent manner (P < 0.001, n = 6) with reverse rate-dependence (P < 0.0001). In contrast, HMR 1556 (10-240 nM) alone did not prolong MAPD90. However, in the presence of 7.5 nM dofetilide, HMR 1556 (100 nM) increased the extent of reverse rate-dependence by further prolonging MAPD90 at CLs of 400, 450 and 500 ms (P < 0.05, n = 9) and, to a lesser extent, at shorter CLs (e.g. by 17 +/- 4 ms at CL 500 vs 2 +/- 3 ms at CL 200 ms). 4. Effects of dofetilide and HMR 1556 on VERP were similar to those on MAPD90. The slope of the VERP vs CL relation was steeper after the combination (0.081 +/- 0.013) than after dofetilide alone (0.028 +/- 0.018, P < 0.01, n = 9). 5. Blockade of rabbit IKs increased reverse rate-dependence of IKr block.

Characterization of binding site of closed-state KCNQ1 potassium channel by homology modeling, molecular docking, and pharmacophore identification

This investigation was performed to assess the importance of interaction in the binding of blockers to KCNQ1 potassium using molecular modeling. This work could be considered made up by three main steps: (1) the construction of closed-state structure of KCNQ1 through homology modeling; (2) the automated docking of three blockers: IKS-142, L-735821, and BMS-IKS, using DOCK program; (3) the generation and validation of pharmacophore for KCNQ1 ligands using Catalyst/HypoGen. The obtained results highlight the hydrophobic or aromatic residues involved in S6 transmembrane domain and the base of the pore helix of KCNQ1, confirming the mutagenesis data and pharmacophore model, and giving new suggestions for the rational design of novel KCNQ1 ligands.

The pharmacophore hypotheses of IKr potassium channel blockers: novel class III antiarrhythmic agents

Predictive pharmacophore models were developed for a large series of I(Kr) potassium channel blockers as class III antiarrhythmic agents using HypoGen in Catalyst software. The pharmacophore hypotheses were generated using a training set consisting of 34 compounds carefully selected from documents. Their biological data, expressed as IC(50), spanned from 1.5 nM to 2.8 mM with 7 orders difference. The most predictive hypothesis (Hypo1), consisting of four features (one positive ionizable feature, two aromatic rings and one hydrophobic group), had a best correlation coefficient of 0.825, a lowest rms deviation of 1.612, and a highest cost difference (null cost-total cost) of 77.552, which represents a true correlation and a good predictivity. The hypothesis Hypo1 was then validated by a test set consisting of 21 compounds and by a cross-validation of 95% confidence level with randomizing the data using CatScramble program. Accordingly, our model has strong predictivity to identify structural diverse I(Kr) potassium channel blockers with desired biological activity by virtual screening