Cellular mechanisms underlying the low cardiotoxicity of Istaroxime

RACIOPPI, MARÍA FLORENCIA; BURGOS, JUAN IGNACIO; MORELL, MALENA; VILA PETROFF, MARTÍN GERARDO; GONANO, LUIS ALBERTO

Congreso; Reunión anual de sociedades de biociencias; 2020

Pharmacological Na+/K+ ATPase (NKA) inhibition induces Ca2+ calmodulin dependent kinase II (CaMKII)-dependent cardiomyocyte death and arrhythmias. Istaroxime is a novel inhibitor of NKA with low risk of Ca2+ triggered arrhythmias due to its additional capacity to accelerate Ca2+ uptake via sarcoplasmic reticulum Ca2+ ATPase (SERCA). We aim to test if therapeutic concentrations of istaroxime impact cardiomyocyte viability and to gain insight into its mechanisms.2 µM ouabain and 10 µM istaroxime promoted an equivalent inotropic effect by perfusing rat ventricular myocytes and measuring cell shortening (T test. n= 15 and 23 respectively).Cell viability was evaluated by morphological parameters after 24 hours of culture at 37ºC in the absence and presence of 2 µM ouabain and 10 µM istaroxime (percentages of cell viability: Control 52 ± 2.5%; Ouabain 2 µM 33 ± 3%; Istaroxime 10 µM 46 ± 3% respectively. ANOVA with Tukey post-test. n=7 per group).The apoptotic index BAX/BCL-2 and CAMKII activity were quantified by western blot in homogenates of rat cardiomyocytes incubated during 1 hour in control, ouabain 2 µM or istaroxime 10 µM. In contrast to ouabain, istaroxime did not promote significant CaMKII activation or cardiomyocyte apoptosis (ANOVA with tukey post-test. N=4 per group)We explored diastolic Ca2+ release by confocal microscopy in Fluo4 loaded myocytes after incubation with the indicated drugs. In contrast to ouabain, istaroxime did not significantly increase Ca2+ spark and wave frequency, but increased the proportion of aborted Ca2+ waves. This lower Ca2+ wave incidence remains present in cells from PLB-KO mice, suggesting that relief on PLB-dependent SERCA inhibition is not the only mechanism underlying istaroxime`s low arrhythmogenesis as previously suggested.We conclude that istaroxime reaches a significant inotropic effect without inducing CaMKII-dependent cardiomyocyte death, and new insights are provided to explain low arrhytmogenesis.