Modelling the effects of chloroquine on KCNJ2-linked short QT syndrome

The Kir2.1E299V mutation increases atrial fibrillation vulnerability while protecting the ventricles against arrhythmias in a mouse model of short QT syndrome type 3

AIMS

Short QT syndrome type 3 (SQTS3) is a rare arrhythmogenic disease caused by gain-of-function mutations in KCNJ2, the gene coding the inward rectifier potassium channel Kir2.1. We used a multidisciplinary approach and investigated arrhythmogenic mechanisms in an in-vivo model of de-novo mutation Kir2.1E299V identified in a patient presenting an extremely abbreviated QT interval and paroxysmal atrial fibrillation.

METHODS AND RESULTS

We used intravenous adeno-associated virus-mediated gene transfer to generate mouse models, and confirmed cardiac-specific expression of Kir2.1WT or Kir2.1E299V. On ECG, the Kir2.1E299V mouse recapitulated the QT interval shortening and the atrial-specific arrhythmia of the patient. The PR interval was also significantly shorter in Kir2.1E299V mice. Patch-clamping showed extremely abbreviated action potentials in both atrial and ventricular Kir2.1E299V cardiomyocytes due to a lack of inward-going rectification and increased IK1 at voltages positive to -80 mV. Relative to Kir2.1WT, atrial Kir2.1E299V cardiomyocytes had a significantly reduced slope conductance at voltages negative to -80 mV. After confirming a higher proportion of heterotetrameric Kir2.x channels containing Kir2.2 subunits in the atria, in-silico 3D simulations predicted an atrial-specific impairment of polyamine block and reduced pore diameter in the Kir2.1E299V-Kir2.2WT channel. In ventricular cardiomyocytes, the mutation increased excitability by shifting INa activation and inactivation in the hyperpolarizing direction, which protected the ventricle against arrhythmia. Moreover, Purkinje myocytes from Kir2.1E299V mice manifested substantially higher INa density than Kir2.1WT, explaining the abbreviation in the PR interval.

CONCLUSION

The first in-vivo mouse model of cardiac-specific SQTS3 recapitulates the electrophysiological phenotype of a patient with the Kir2.1E299V mutation. Kir2.1E299V eliminates rectification in both cardiac chambers but protects against ventricular arrhythmias by increasing excitability in both Purkinje-fiber network and ventricles. Consequently, the predominant arrhythmias are supraventricular likely due to the lack of inward rectification and atrial-specific reduced pore diameter of the Kir2.1E299V-Kir2.2WT heterotetramer.

The network of cardiac KIR2.1: its function, cellular regulation, electrical signaling, diseases and new drug avenues

The functioning of the human heart relies on complex electrical and communication systems that coordinate cardiac contractions and sustain rhythmicity. One of the key players contributing to this intricate system is the KIR2.1 potassium ion channel, which is encoded by the KCNJ2 gene. KIR2.1 channels exhibit abundant expression in both ventricular myocytes and Purkinje fibers, exerting an important role in maintaining the balance of intracellular potassium ion levels within the heart. And by stabilizing the resting membrane potential and contributing to action potential repolarization, these channels have an important role in cardiac excitability also. Either gain- or loss-of-function mutations, but also acquired impairments of their function, are implicated in the pathogenesis of diverse types of cardiac arrhythmias. In this review, we aim to elucidate the system functions of KIR2.1 channels related to cellular electrical signaling, communication, and their contributions to cardiovascular disease. Based on this knowledge, we will discuss existing and new pharmacological avenues to modulate their function.

Antiviral and anti-inflammatory drugs to combat COVID-19: Effects on cardiac ion channels and risk of ventricular arrhythmias

Introduction: Drugs with no indication for the treatment of cardiovascular diseases (e.g., drugs employed to treat COVID-19) can increase the risk of arrhythmias. Of interest, a six-fold increase in the number of arrhythmic events was reported in patients with severe COVID-19. In this study, we reviewed (i) the pro-arrhythmic action of drugs given to patients with COVID-19 infection, and (ii) the effects of inflammatory cytokines on cardiac ion channels and possible generation of arrhythmias.

Methods: We conducted a literature search on the drugs with purported or demonstrated efficacy against COVID-19 disease, emphasizing the mechanisms by which anti-COVID-19 drugs and inflammatory cytokines interfere with cardiac ion channels.

Results:Antibiotics (azithromycin), antimalarials (hydroxychloroquine, chloroquine), antivirals (ritonavir/lopinavir, atazanavir), and some of the tyrosine kinase inhibitors (vandetanib) could induce long QT and increase risk for ventricular arrhythmias. The pro-arrhythmic action results from drug-induced inhibition of Kv11.1 (hERG) channels interfering with the repolarizing potassium IKr currents, leading to long QT and increased risk of triggered arrhythmias. At higher concentrations, these drugs may interfere with IKs, IK1, and/or Ito potassium currents, and even inhibit sodium (INa) and calcium (ICa) currents, inducing additional cardiac toxicity. Ibrutinib, an inhibitor of Bruton’s TK, increased the incidence of atrial fibrillation and ventricular tachycardia associated with a short QT interval. Inflammatory cytokines IL-6 and TNF-α inhibit IKr and Ito repolarizing potassium currents. High levels of inflammatory cytokines could contribute to the arrhythmic events. For remdesivir, favipiravir, dexamethasone, tocilizumab, anakinra, baricitinib, and monoclonal antibodies (bamlanivimab, etesevimab, and casirivimab), no evidence supports significant effects on cardiac ion channels, changes in the QT interval, and increased risk for ventricular arrhythmias.

Conclusion: This study supports the concept of hERG channel promiscuity. Different drug classes given to COVID-19 patients might delay repolarization, and increase the risk of ventricular arrhythmias. The presence of comorbid pro-arrhythmic disease states, and elevated levels of pro-arrhythmic cytokines, could increase the risk of ventricular arrhythmias. Discontinuation of nonessential drugs and correction of electrolyte abnormalities could prevent severe ventricular arrhythmias. Altogether, the most effective therapies against COVID-19 (remdesivir, dexamethasone, monoclonal antibodies) lack pro-arrhythmic activity.

Cardioprotection of an IK1 channel agonist on L-thyroxine induced rat ventricular remodeling

Downregulation of inward rectifier potassium (I_K1) channel is a hallmark in cardiac hypertrophy and failure. The cardioprotection of zacopride (a selective I_K1 agonist) and underlying mechanisms were investigated in L-thyroxine (T4) or Triiodothyronine (T3)-induced cardiac remodeling. In the in vivo study, adult male Sprague-Dawley (SD) rats were randomly divided into control, L-thyroxine, L-thy+zacopride, and L-thy+zacopride+chloroquine (an I_K1 antagonist) groups. Echocardiography, histopathology, TUNEL assay, western blotting and confocal imaging for intracellular Ca²⁺ fluorescence were performed. In the in vitro study, zacopride and nifedipine (a LTCC blocker) were used to compare their effects on Kir2.1, SAP97, autophagy, and [Ca²⁺]_i in H9C2 (2-1) cardiomyocytes. Zacopride treatment attenuated L-thyroxine- or T3 induced cardiac remodeling and dysfunction which manifested as cardiac hypertrophy and collagen deposition, dilated ventricle, decreased ejection fraction (EF), increased cardiomyocytes apoptosis, hyper-activation of CaMKII and PI3K/Akt/mTOR signaling, decreased cardiac autophagy, and increased expression of integrin β3. The cardioprotection of zacopride is strongly associated with the upregulation of I_K1, SAP97, and [Ca²⁺]_i homeostasis in cardiomyocytes. I_K1 antagonist chloroquine or BaCl₂ reversed these effects. Nifedipine could attenuate intracellular Ca²⁺ overload with no significant effects on I_K1, SAP97, and autophagy. This study showed that zacopride could improve cardiac remodeling via facilitating Kir2.1 forward trafficking, and negatively regulating calcium-activated and PI3K/Akt/mTOR signalings, in an I_K1-dependent manner.

Computer Modeling of the Heart for ECG Interpretation—A Review

Computer modeling of the electrophysiology of the heart has undergone significant progress. A healthy heart can be modeled starting from the ion channels via the spread of a depolarization wave on a realistic geometry of the human heart up to the potentials on the body surface and the ECG. Research is advancing regarding modeling diseases of the heart. This article reviews progress in calculating and analyzing the corresponding electrocardiogram (ECG) from simulated depolarization and repolarization waves. First, we describe modeling of the P-wave, the QRS complex and the T-wave of a healthy heart. Then, both the modeling and the corresponding ECGs of several important diseases and arrhythmias are delineated: ischemia and infarction, ectopic beats and extrasystoles, ventricular tachycardia, bundle branch blocks, atrial tachycardia, flutter and fibrillation, genetic diseases and channelopathies, imbalance of electrolytes and drug-induced changes. Finally, we outline the potential impact of computer modeling on ECG interpretation. Computer modeling can contribute to a better comprehension of the relation between features in the ECG and the underlying cardiac condition and disease. It can pave the way for a quantitative analysis of the ECG and can support the cardiologist in identifying events or non-invasively localizing diseased areas. Finally, it can deliver very large databases of reliably labeled ECGs as training data for machine learning.

In silico models for evaluating proarrhythmic risk of drugs

Safety evaluation of drugs requires examination of the risk of generating Torsade de Pointes (TdP) because it can lead to sudden cardiac death. Until recently, the QT interval in the electrocardiogram (ECG) has been used in the evaluation of TdP risk because the QT interval is known to be associated with the development of TdP. Although TdP risk evaluation based on QT interval has been successful in removing drugs with TdP risk from the market, some safe drugs may have also been affected due to the low specificity of QT interval-based evaluation. For more accurate evaluation of drug safety, the comprehensive in vitro proarrhythmia assay (CiPA) has been proposed by regulatory agencies, industry, and academia. Although the CiPA initiative includes in silico evaluation of cellular action potential as a component, attempts to utilize in silico simulation in drug safety evaluation are expanding, even to simulating human ECG using biophysical three-dimensional models of the heart and torso under the effects of drugs. Here, we review recent developments in the use of in silico models for the evaluation of the proarrhythmic risk of drugs. We review the single cell, one-dimensional, two-dimensional, and three-dimensional models and their applications reported in the literature and discuss the possibility of utilizing ECG simulation in drug safety evaluation.

Role of If Density on Electrical Action Potential of Bio-engineered Cardiac Pacemaker: A Simulation Study

Due to the inevitable drawbacks of the implantable electrical pacemaker, the biological pacemaker was believed to be an alternative therapy for heart failure. Previous experimental studies have shown that biological pacemaker could be produced by genetically manipulating non-pacemaking cardiac cells by suppressing the inward rectifier potassium current (I_K1) and expressing the hyperpolarization- activated current (I_f). However, the role of I_f in such bio-engineered pacemaker is not clear. In this study, we simulated the action potential of biological pacemaker cells by manipulating I_f-I_K1 parameters (i.e., inhibiting I_K1 as well as incorporating I_f) to analyze possible mechanisms by which different I_f densities control pacemaking action potentials. Our simulation results showed different pacing mechanism between the bioengineered pacemaking cells with and without I_f. In addition, it was shown that a greater I_f density might result in a slower pacing frequency, and excessive of it might produce an early-afterdepolarizations-like action potential due to a sudden release of calcium from sarcoplasmic reticulum into the cytoplasm. This study indicated that when I_K1 was significantly suppressed, incorporating I_f may not enhance the pacing ability of biological pacemaker, but lead to abnormal dynamics of intracellular ionic concentration, increasing risks of dysrhythmia in the heart.