ABSTRACT
Hydroxychloroquine (HCQ), clinically established in antimalarial and autoimmune therapy, recently raised cardiac arrhythmogenic concerns when used alone or with azithromycin (HCQ+AZM) in Covid-19. We report complementary, experimental, studies of its electrophysiological effects. In patch clamped HEK293 cells expressing human cardiac ion channels, HCQ inhibited IKr and IK1 at a therapeutic concentrations (IC50s: 10 ± 0.6 and 34 ± 5.0 µM). INa and ICaL showed higher IC50s; Ito and IKs were unaffected. AZM slightly inhibited INa, ICaL, IKs, and IKr, sparing IK1 and Ito. (HCQ+AZM) inhibited IKr and IK1 (IC50s: 7.7 ± 0.8 and 30.4 ± 3.0 µM), sparing INa, ICaL, and Ito. Molecular induced-fit docking modeling confirmed potential HCQ-hERG but weak AZM-hERG binding. Effects of µM-HCQ were studied in isolated perfused guinea-pig hearts by multielectrode, optical RH237 voltage, and Rhod-2 mapping. These revealed reversibly reduced left atrial and ventricular action potential (AP) conduction velocities increasing their heterogeneities, increased AP durations (APDs), and increased durations and dispersions of intracellular [Ca2+] transients, respectively. Hearts also became bradycardic with increased electrocardiographic PR and QRS durations. The (HCQ+AZM) combination accentuated these effects. Contrastingly, (HCQ+AZM) and not HCQ alone disrupted AP propagation, inducing alternans and torsadogenic-like episodes on voltage mapping during forced pacing. O'Hara-Rudy modeling showed that the observed IKr and IK1 effects explained the APD alterations and the consequently prolonged Ca2+ transients. The latter might then downregulate INa, reducing AP conduction velocity through recently reported INa downregulation by cytosolic [Ca2+] in a novel scheme for drug action. The findings may thus prompt future investigations of HCQ's cardiac safety under particular, chronic and acute, clinical situations.
ABSTRACT
The macrolide antibiotic azithromycin (AZM) is widely used for respiratory infections and has been suggested to be a possible treatment for the Coronavirus Disease of 2019 (COVID-19). However, AZM-associated QT interval prolongation and arrhythmias have been reported. Integrated mechanistic information on AZM actions on human ventricular excitation and conduction is lacking. Therefore, this study was undertaken to investigate the actions of AZM on ventricular cell and tissue electrical activity. The O'Hara- Virag-Varro-Rudy dynamic (ORd) model of human ventricular cells was modified to incorporate experimental data on the concentration-dependent actions of AZM on multiple ion channels, including INa, ICaL, IKr, IKs, IK1 and INaL in both acute and chronic exposure conditions. In the single cell model, AZM prolonged the action potential duration (APD) in a concentration-dependent manner, which was predominantly attributable to IKr reduction in the acute condition and potentiated INaL in the chronic condition. High concentrations of AZM also increased action potential (AP) triangulation (determined as an increased difference between APD30 and APD90) which is a marker of arrhythmia risk. In the chronic condition, the potentiated INaL caused a modest intracellular Na + concentration accumulation at fast pacing rates. At the 1D tissue level, the AZM-prolonged APD at the cellular level was reflected by an increased QT interval in the simulated pseudo-ECG, consistent with clinical observations. Additionally, AZM reduced the conduction velocity (CV) of APs in the acute condition due to a reduced INa, and it augmented the transmural APD dispersion of the ventricular tissue, which is also pro-arrhythmic. Such actions were markedly augmented when the effects of chronic exposure of AZM were also considered, or with additional IKr block, as may occur with concurrent use of other medications. This study provides insights into the ionic mechanisms by which high concentrations of AZM may modulate ventricular electrophysiology and susceptibility to arrhythmia.