Subcellular mechanisms underlying the low cardiotoxicity of istaroxime.

RACIOPPI, MARIA FLORENCIA; GONANO, LUIS ALBERTO; BURGOS, JUAN IGNACIO; MORELL, MALENA

Mar del Plata

Congreso; Congreso de la Sociedad Argentina de Fiosiología; 2019

SAFIS

Pharmacological inhibition of sodium/potassium ATPase (NKA) with digitalis improves cardiac contractility but also promote diastolic Ca2+ waves. We have demonstrated that acute exposure to high doses of digitalis induces CaMKII-dependent phosphorylation of RyR2 and Ca2+ related arrhythmias. In parallel, we showed that low ?therapeutic? doses of digitalis activate CaMKII-dependent apoptosis in ventricular cardiomyocytes.Istaroxime has a dual effect which combines NKA inhibition with sarcoplasmic reticulum (SR)-Ca2+ uptake acceleration due to SERCA-PLB dissociation. This peculiar combination makes istaroxime an inotropic-lusitropic agent with lower arrhytmogenic potential compared to digitalis compounds. However, the impact of istaroxime on cardiomyocyte viability and apoptosis has never been addressed. Our hypothesis is that istaroxime can reach a significant inotropic response with lower induction of CaMKII-dependent cardiomyocyte apoptosis and lower occurrence of arrhythmogenic Ca2+ release during diastole.To investigate this, mouse ventricular cardiomyocytes were paced at 1 Hz and superfused with Hepes-buffer at in the presence of ouabain 2 µM or istaroxime 10 µM, detecting that both promoted a similar increase in cell shortening. We also measured SR Ca2+ waves in Fluo-4 loaded cells to confirm if, after 1 hour of incubation, istaroxime is less arrhytmogenic than ouabain. On average, 2 µM ouabain-treated cells presented a significantly higher Ca2+ waves frequency compared to 10 µM istaroxime-treated cells (0,135±0,020 and 0,061±0,013 waves/min respectively. n= 23 per group). Cardiomyocytes were cultured for 24 hours at 37ºC and we observed a significant reduction in cell viability accompanied by an increase in caspase-3 activity in ouabain-treated cells. Interestingly, 10 µM and even 20 µM istaroxime did not significantly affect cell viability and caspase-3 activity compared to control without drugs (n=5 cultures per group). We conclude that istaroxime is less cardiotoxic than ouabain, suggesting its potential benefit for the treatment of chronic heart failure.