Exploring the interplay between extracellular pH and Dronedarone's pharmacological effects on cardiac function.

Dronedarone (DRN) is a clinically used drug to mitigate arrhythmias with multichannel block properties, including the sodium channel Nav1.5. Extracellular acidification is known to change the pharmacological properties of several antiarrhythmic drugs. Here, we explore how modification in extracellular pH (pHe) shapes the pharmacological profile of DRN upon Nav1.5 sodium current (INa) and in the ex vivo heart preparation. Embryonic human kidney cells (HEK293T/17) were used to transiently express the human isoform of Nav1.5 α-subunit. Patch-Clamp technique was employed to study INa. Neurotoxin-II (ATX-II) was used to induce the late sodium current (INaLate). Additionally, ex vivo Wistar male rat preparations in the Langendorff system were utilized to study electrocardiogram (ECG) waves. DRN preferentially binds to the closed state inactivation mode of Nav1.5 at pHe 7.0. The recovery from INa inactivation was delayed in the presence of DRN in both pHe 7.0 and 7.4, and the use-dependent properties were distinct at pHe 7.0 and 7.4. However, the potency of DRN upon the peak INa, the voltage dependence for activation, and the steady-state inactivation curves were not altered in both pHe tested. Also, the pHe did not change the ability of DRN to block INaLate. Lastly, DRN in a concentration and pH dependent manner modulated the QRS complex, QT and RR interval in clinically relevant concentration. Thus, the pharmacological properties of DRN upon Nav1.5 and ex vivo heart preparation partially depend on the pHe. The pHe changed the biological effect of DRN in the heart electrical function in relevant clinical concentration.

Cardiotoxicity of pyrethroids: molecular mechanisms and therapeutic options for acute and long-term toxicity.

Pyrethroids (PY) are synthetic pesticides used in many applications ranging from large-scale agriculture to household maintenance. Their classical mechanisms of action are associated with binding to the sodium channel of insect neurons, disrupting its inactivation, ensuring their use as insecticides. However, PY can also lead to toxicity in vertebrates, including humans. In most toxicological studies, the impact of PY on heart function is neglected. Acute exposure to a high dose of PY causes enhancement of the late sodium current (INaL), which impairs the action potential waveform and can cause severe cardiac arrhythmias. Moreover, long-term, low-dose exposure to PY displays oxidative stress in the heart, which could induce tissue remodeling and impairment. Isolated and preliminary evidence supports that, for acute exposure to PY, an antiarrhythmic therapy with ranolazine (an INaL blocker), can be a promising therapeutic approach. Besides, heart tissue remodeling associated with low doses and long-term exposure to PY seems to benefit from antioxidant therapy. Despite significant leaps in understanding the mechanical details of PY intoxication, currently, few studies are focusing on the heart. In this review, we present what is known and what are the gaps in the field of cardiotoxicity induced by PY.

Experimental hypothyroidism induces cardiac arrhythmias and ranolazine reverts and prevents the phenotype.

AIMS: Hypothyroidism is associated with an increased risk of cardiovascular disease and enhanced susceptibility to arrhythmias. In our investigation, we evaluated the potential involvement of late sodium current (INa,late) in cardiac arrhythmias in an experimental murine model of hypothyroidism. MAIN METHODS: Male Swiss mice were treated with methimazole (0.1 % w/vol, during 21 days) to induce experimental hypothyroidism before ECG, action potential (AP) and intracellular Ca2+ dynamics were evaluated. Susceptibility to arrhythmia was measured in vitro and in vivo. KEY FINDINGS: The results revealed that hypothyroid animals presented ECG alterations (e.g. increased QTc) with the presence of spontaneous sustained ventricular tachycardia. These changes were associated with depolarized resting membrane potential in isolated cardiomyocytes and increased AP duration and dispersion at 90 % of the repolarization. Aberrant AP waveforms were related to increased Ca2+ sparks and out-of-pace Ca2+ waves. These changes were observed in a scenario of enhanced INa,late. Interestingly, ranolazine, a clinically used blocker of INa,late, restored the ECG alterations, reduced Ca2+ sparks and aberrant waves, decreased the in vitro events and the severity of arrhythmias observed in isolated cardiomyocytes from hypothyroid animals. Using the in vivo dobutamine + caffeine protocol, animals with hypothyroidism developed catecholaminergic bidirectional ventricular tachycardia, but pre-treatment with ranolazine prevented this. SIGNIFICANCE: We concluded that animals with hypothyroidism have increased susceptibility to developing arrhythmias and ranolazine, a clinically used blocker of INa,late, is able to correct the arrhythmic phenotype.

Ações Transmurais Inotrópicas e Antiarrítmicas da Ranolazina em um Modelo Celular da Síndrome do QT Longo Tipo 3 / Inotropic and Antiarrhythmic Transmural Actions of Ranolazine in a Cellular Model of Type 3 Long QT Syndrome

Resumo A Ranolazina (RANO), conhecida na clínica como Ranexa, é um fármaco que previne a arritmia cardíaca através da inibição da corrente de sódio tardia (INaT). Um gradiente de voltagem transmural do canal Nav1.5 encontra-se na parede ventricular esquerda do coração. Assim, investigamos os efeitos da RANO em cardiomiócitos saudáveis e em modelo celular da Síndrome do QT longo tipo 3 (SQTL tipo 3). Usamos células isoladas do endocárdio (ENDO) e do epicárdio (EPI) e um software de medição com detecção de bordas por vídeo e microscopia de fluorescência para monitorar os transientes de cálcio. A RANO (0,1, 1, 10 e 30 uM, a 25OC) em uma série de frequências de estimulação teve impacto pouco significativo sobre ambos os tipos de células, mas a RANO (30uM) a 35OC minimizou o encurtamento dos sarcômeros em ~21% para células do endocárdio. Em seguida, para simular a SQTL tipo 3, as células do ENDO e EPI foram expostas à toxina ATX-II da anêmona do mar, que aumenta a INaT. As arritmias celulares induzidas por ATX-II foram suprimidas com o uso da RANO (30 µM) a 35OC. Com base nesses resultados, podemos concluir que a RANO tem um impacto pouco significativo sobre o encurtamento dos sarcômeros de células saudáveis do ENDO e EPI. Além disso, ela suprime as arritmias induzidas por INaT para níveis semelhantes nas células do ENDO e EPI.

Abstract Ranolazine (RANO) prevents cardiac arrhythmia by blocking the late sodium current (INaL). A transmural gradient of Nav1.5 is found in the left ventricular wall of the heart. Thus, we investigated the effects of RANO in healthy cardiomyocytes and in a cellular model of type 3 long QT syndrome (LQT3). We used isolated endocardium (ENDO) and epicardium (EPI) cells and a video edge detection system and fluorescence microscopy to monitor calcium transients. RANO (0.1, 1, 10 and 30 uM, at 25oC) at a range of pacing frequencies showed a minor impact on both cell types, but RANO at 30uM and 35oC for ENDO cells attenuated sarcomere shortening by~21%. Next, to mimic LQT3, we exposed ENDO and EPI cells to anemone toxin II (ATX-II), which augments INaL. Cellular arrhythmias induced by ATX-II were abrogated by RANO (30 µM) at 35oC. Based on our results we can conclude that RANO has a minor impact on sarcomere shortening of healthy ENDO and EPI cells and it abrogates arrhythmias induced by INaLto a similar level in ENDO and EPI cells.

Ranolazine reduces repolarization heterogeneity in symptomatic patients with diabetes and non-flow-limiting coronary artery stenosis.

BACKGROUND: Experimental evidence suggests that ranolazine decreases susceptibility to ischemia-induced arrhythmias independent of effects on coronary artery blood flow. OBJECTIVE: In symptomatic diabetic patients with non-flow-limiting coronary artery stenosis with diffuse atherosclerosis and/or microvascular dysfunction, we explored whether ranolazine reduces T-wave heterogeneity (TWH), an electrocardiographic (ECG) marker of arrhythmogenic repolarization abnormalities shown to predict sudden cardiac death. METHODS: We studied all 16 patients with analyzable ECG recordings during rest and exercise tolerance testing before and after 4 weeks of ranolazine in the double-blind, crossover, placebo-controlled RAND-CFR trial (NCT01754259). TWH was quantified without knowledge of treatment assignment by second central moment analysis, which assesses the interlead splay of T waves in precordial leads about a mean waveform. Myocardial blood flow (MBF) was measured by positron emission tomography. RESULTS: At baseline, prior to randomization, TWH during rest was 54 ± 7 µV and was not altered following placebo (47 ± 6 µV, p = .47) but was reduced by 28% (to 39 ± 5 µV, p = .002) after ranolazine. Ranolazine did not increase MBF at rest. Exercise increased TWH after placebo by 49% (to 70 ± 8 µV, p = .03). Ranolazine did not reduce TWH during exercise (to 75 ± 16 µV), and there were no differences among the groups (p = .95, ANOVA). TWH was not correlated with MBF at rest before (r2  = .07, p = .36) or after ranolazine (r2  = .23, p = .06). CONCLUSIONS: In symptomatic diabetic patients with non-flow-limiting coronary artery stenosis with diffuse atherosclerosis and/or microvascular dysfunction, ranolazine reduced TWH at rest but not during exercise. Reduction in repolarization abnormalities appears to be independent of alterations in MBF.

Eleclazine, an inhibitor of the cardiac late sodium current, is superior to flecainide in suppressing catecholamine-induced ventricular tachycardia and T-wave alternans in an intact porcine model.

BACKGROUND: The capacity of catecholamines to induce ventricular tachycardia (VT) is well documented. OBJECTIVE: The effectiveness of the novel cardiac late sodium inhibitor eleclazine in suppressing catecholamine-induced VT in a large animal model was compared with that of flecainide. METHODS: In 13 closed-chest anesthetized Yorkshire pigs, spontaneous VT and surges in T-wave alternans (TWA) level measured using the Modified Moving Average method were induced by epinephrine (2.0 µg/kg, i.v., bolus over 1 minute). Effects of eleclazine (0.3 mg/kg, i.v., infused over 15 minutes; n = 6) or flecainide (1 mg/kg, i.v., bolus over 2 minutes followed by 1 mg/kg/hr, i.v., for 1 hour; n = 7) on VT incidence and TWA level were measured from right intraventricular electrogram recordings. RESULTS: Epinephrine reproducibly elicited hemodynamically significant spontaneous VT in all 13 pigs and increased TWA level by 33-fold compared to baseline (P < .001). Eleclazine reduced the incidence of epinephrine-induced ventricular premature beats and couplets by 51% (from 31.3 ± 1.91 to 15.2 ± 5.08 episodes; P = .038) and the incidence of 3- to 7-beat VT by 56% (from 10.8 ± 3.45 to 4.7 ± 3.12 episodes; P = .004). Concurrently, the drug reduced the peak epinephrine-induced TWA level by 64% (from 217 ± 22.2 to 78 ± 15.3 µV; P < .001). Flecainide also reduced the incidence of epinephrine-induced ventricular premature beats and couplets by 53% (from 40.4 ± 6.37 to 19.0 ± 2.73 episodes; P = .024) but did not affect the incidence of VT (from 15.0 ± 3.08 to 11.6 ± 2.93 episodes; P = .29) or the peak TWA level (from 207 ± 30.6 to 172 ± 26.2 µV; P = .34). CONCLUSION: Selective inhibition of cardiac late sodium current with eleclazine is more effective than flecainide in reducing catecholamine-induced VT and TWA in an intact porcine model.

Inhibition of the cardiac late sodium current with eleclazine protects against ischemia-induced vulnerability to atrial fibrillation and reduces atrial and ventricular repolarization abnormalities in the absence and presence of concurrent adrenergic stimulation.

BACKGROUND: Myocardial ischemia carries dual risk for initiating atrial and ventricular arrhythmias that can be exacerbated by adrenergic stimulation. OBJECTIVE: The purpose of this study was to investigate whether selective inhibition of the cardiac late sodium current (INa) with eleclazine decreases susceptibility to ischemia-induced atrial fibrillation (AF) and atrial and ventricular repolarization abnormalities before and after epinephrine infusion. METHODS: In chloralose-anesthetized, open-chest, male Yorkshire pigs (n = 12), atrial and ventricular ischemia was induced by partial occlusion of the left circumflex coronary artery proximal segment to reduce flow by 75%. Epinephrine (0.5 µg/kg IV bolus over 1 minute; n = 6) was infused before and at 2 hours after eleclazine (0.9 mg/kg IV bolus over 15 minutes). RESULTS: Left circumflex coronary artery occlusion significantly increased ventricular dispersion of repolarization (T-wave alternans [TWA] by 861%, T-wave heterogeneity by 286%, Tpeak-Tend interval by 74%) and atrial repolarization alternans (TWAa) by 2850% and lowered AF threshold by 65%. Eleclazine reduced the ischemia-induced surge in TWA by 81% (P = .007), T-wave heterogeneity by 23% (P = .035), and Tpeak-Tend by 28% (P = .014), suppressed the ischemia-induced surge in atrial TWAa by 64% (P = .002), and reduced the ischemia-induced fall in AF threshold to 20%. It shortened baseline QT interval by 6% (P <.001), JT interval by 8% (P <.001), and atrial action potential duration (PTa) by 8% (P = .002). Similar beneficial effects of eleclazine were observed after epinephrine infusion without reducing contractility (P = .054). CONCLUSION: Selective inhibition of cardiac late INa with eleclazine confers dual protection against vulnerability to ischemia-induced AF and reduces atrial and ventricular repolarization abnormalities before and during adrenergic stimulation without negative inotropic effects.

Eleclazine, a new selective cardiac late sodium current inhibitor, confers concurrent protection against autonomically induced atrial premature beats, repolarization alternans and heterogeneity, and atrial fibrillation in an intact porcine model.

BACKGROUND: The cardiac late sodium current (INa) has been increasingly implicated in the initiation of atrial fibrillation (AF). Eleclazine (formerly known as GS-6615) is a new selective late INa inhibitor and is undergoing clinical testing for the treatment of cardiac arrhythmias. OBJECTIVE: We tested whether late INa inhibition by eleclazine confers protection against atrial premature beats (APBs) and AF. METHODS: In closed-chest anesthetized Yorkshire pigs, epinephrine (2.0 µg/kg, intravenous, bolus over 1 minute) was administered alone to induce APBs (n = 6) or in combination with intrapericardial acetylcholine (0.5-4 mL of 12.5 mM solution) to induce spontaneous AF (n = 11). Effects of eleclazine (0.3 and 0.9 mg/kg, intravenous, over 15 minutes) on APBs and AF were determined. RESULTS: Epinephrine-induced APBs were reduced >3-fold (P < .04) after eleclazine (0.9 mg/kg) infusion. The combined administration of epinephrine and acetylcholine resulted in AF in all animals tested, which was invariably preceded by APBs. Eleclazine pretreatment suppressed AF in all 7 animals in at least 1 test episode during the 60- to 150-minute observation period (P = .04). The plasma eleclazine level at 120 minutes was 828 ± 45.8 nM, within exposure range evaluated clinically. Eleclazine shortened ventricular QT and atrial PTa intervals by 7% (P < .001 for both) and reduced atrial repolarization alternans (P = .003) and heterogeneity (P = .021) without attenuation of the inotropic response to catecholamine (P = .56). The drug inhibited the enhanced late INa of single atrial myocytes with a potency of 736 ± 67 nM. CONCLUSION: Selective cardiac late INa inhibition with eleclazine suppresses autonomically mediated atrial repolarization alternans and heterogeneity, APBs, and AF in an intact porcine model.