Non-β-Blocking Carvedilol Analog, VK-II-86, Prevents Ouabain-Induced Cardiotoxicity

Abstract

Background: It has been shown that carvedilol and its non β-blocking analog, VK-II-86, inhibit spontaneous Ca 2+ release from the sarcoplasmic reticulum (SR). The aim of this study is to determine whether carvedilol and VK-II-86 suppress ouabain-induced arrhythmogenic Ca 2+ waves and apoptosis in cardiac myocytes. Methods and Results: Rat cardiac myocytes were exposed to toxic doses of ouabain (50 µmol/L). Cell length (contraction) was monitored in electrically stimulated and non-stimulated conditions. Ouabain treatment increased contractility, frequency of spontaneous contractions and apoptosis compared to control cells. Carvedilol (1 µmol/L) or VK-II-86 (1 µmol/L) did not affect ouabain-induced inotropy, but significantly reduced the frequency of Ca 2+ waves, spontaneous contractions and cell death evoked by ouabain treatment. This antiarrhythmic effect was not associated with a reduction in Ca 2+ calmodulin-dependent protein kinase II (CaMKII) activity, phospholamban and ryanodine receptor phosphorylation or SR Ca 2+ load. Similar results could be replicated in human cardiomyocytes derived from stem cells and in a mathematical model of human myocytes. Conclusions: Carvedilol and VK-II-86 are effective to prevent ouabain-induced apoptosis and spontaneous contractions indicative of arrhythmogenic activity without affecting inotropy and demonstrated to be effective in human models, thus emerging as a therapeutic tool for the prevention of digitalis-induced arrhythmias and cardiac toxicity.

A carvedilol analogue, VK‐II‐86, prevents hypokalaemia‐induced ventricular arrhythmia through novel multi‐channel effects

“…Pretreatment with dantrolene and VK-II-86, both previously shown to inhibit RyR2 (Gonano et al, 2018;Maxwell et al, 2012;Suetomi et al, 2011;Uchinoumi et al, 2010;Zhou et al, 2011) We found a significant depolarization of the RMP in the ventricular AP for both murine and canine ventricular tissues and cells. This contrasts with previous studies reporting that hypokalaemia results in hyperpolarization of RMP (Aronsen et al, 2015;Bouchard et al, 2004;Tazmini et al, 2020).…”

“…VK-II-86 caused a slight reduction in peak density of I Ca in 4 mM [K + ], so an investigation of ionotropic effects would be prudent. A previous study of VK-II-86 in rat cardiomyocytes demonstrated no effect of VK-II-86 on cell ionotropy, in the presence of ouabain(Gonano et al, 2018).The ability of VK-II-86 to prevent the hypokalaemia-induced reduction of I K1 is a functionally important feature of the drug. The inward component of I K1 stabilizes the RMP and its outward component contributes to terminal repolarization of the action potential F I G U R E 7 In canine ventricular cardiomyocytes, hypokalaemic conditions increase L-type Ca 2+ current (LTCC) density and accelerate channel recovery from inactivation.…”

“…Dantrolene's ability to prevent Ca 2+ ‐mediated arrhythmias through RyR2 inhibition has been demonstrated in rabbits with heart failure (Maxwell et al, 2012) and in mice carrying catecholaminergic polymorphic ventricular tachycardia (CPVT) mutations (Suetomi et al, 2011; Uchinoumi et al, 2010). VK‐II‐86 has also been shown to be anti‐arrhythmic in CPVT mice, (Zhou et al, 2011) and rats overdosed with digoxin (Gonano et al, 2018). VK‐II‐86 prevented Ca 2+ waves in rats without affecting SR Ca 2+ load or levels of phosphorylated or oxidized CaMKII, phospholamban or RyR2, suggesting direct inhibition of RyR2 (Gonano et al, 2018).…”

Cellular Mechanisms Underlying the Low Cardiotoxicity of Istaroxime

“…We have previously shown that digitalis‐induced cardiotoxicity involves CaMKII‐dependent phosphorylation of the cardiac ryanodine receptors, 8 , 16 leading to increased diastolic SR Ca 2+ release, which is visualized as an increased number of sparks and waves. In particular, we previously showed that both the inhibition of cardiac isoform of ryanodine receptors mediated spontaneous SR Ca 2+ release and of the mitochondrial Ca 2+ uniporter can prevent ouabain‐induced cardiomyocyte death, 16 suggesting that increased SR Ca 2+ release, and Ca 2+ transference to mitochondria, plays a role in ouabain‐induced cardiomyocyte death. Based on this concept, herein we compared the capacity of ouabain and istaroxime to promote CaMKII activation and to increase Ca 2+ spark and wave frequency, and we observed that, in fact, all these events were enhanced by ouabain but not by istaroxime.…”

“…Cells were evaluated morphologically, being classified as viable or nonviable according to their length‐to‐width ratio (>3 were considered viable). 8 , 16 From each culture, which was considered as an n=1, at least 8 photographs per group were taken to count and classify the cells. All data of cell viability are expressed as percentage of the total number of cells.…”