New treatment options for late Na current, arrhythmias, and diastolic dysfunction

Piscidin-1 regulates lipopolysaccharide-induced intracellular calcium, sodium dysregulation, and oxidative stress in atrial cardiomyocytes

Lipopolysaccharide (LPS) triggers an inflammatory response, causing impairment of cardiomyocyte Ca2+ and Na + regulation. This study aimed to determine whether piscidin-1 (PCD-1), an antimicrobial peptide, improves intracellular Ca2+ and Na + regulation in LPS-challenged atrial cardiomyocytes. Rabbit atrial cardiomyocytes were enzymatically isolated from the left atria. Patch-clamp ionic current recording, intracellular Ca2+ monitoring using Fluo-3, and detection of cytosolic reactive oxygen species production were conducted in control, LPS-challenged, and LPS + PCD-1-treated atrial cardiomyocytes. LPS-challenged cardiomyocytes showed shortened durations of action potential at their 50% and 90% repolarizations, which was reversed by PCD-1 treatment. LPS-challenged cardiomyocytes showed decreased L-type Ca2+ channel currents and larger Na+/Ca2+ exchange currents compared to controls. While LPS did not affect the sodium current, an enhanced late sodium current with increased cytosolic Na+ levels was observed in LPS-challenged cardiomyocytes. These LPS-induced alterations in the ionic current were ameliorated by PCD-1 treatment. LPS-challenged cardiomyocytes displayed lowered Ca2+ transient amplitudes and decreased Ca2+ stores and greater Ca2+ leakage in the sarcoplasmic reticulum compared to the control. Exposure to PCD-1 attenuated LPS-induced alterations in Ca2+ regulation. The elevated reactive oxygen species levels observed in LPS-challenged myocytes were suppressed after PCD-1 treatment. The protein levels of NF-κB and IL-6 increased following LPS treatment. Decreased sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2a protein levels were observed in LPS-challenged cardiomyocytes. PCD-1 modulates LPS-induced alterations in inflammatory and Ca2+ regulatory protein levels. Our results suggest that PCD-1 modulates LPS-induced alterations in intracellular Ca2+ and Na + homeostasis, reactive oxygen species production, and the NF-κB inflammatory pathway in atrial cardiomyocytes.

NaV1.8 as Proarrhythmic Target in a Ventricular Cardiac Stem Cell Model

The sodium channel NaV1.8, encoded by the SCN10A gene, has recently emerged as a potential regulator of cardiac electrophysiology. We have previously shown that NaV1.8 contributes to arrhythmogenesis by inducing a persistent Na+ current (late Na+ current, INaL) in human atrial and ventricular cardiomyocytes (CM). We now aim to further investigate the contribution of NaV1.8 to human ventricular arrhythmogenesis at the CM-specific level using pharmacological inhibition as well as a genetic knockout (KO) of SCN10A in induced pluripotent stem cell CM (iPSC-CM). In functional voltage-clamp experiments, we demonstrate that INaL was significantly reduced in ventricular SCN10A-KO iPSC-CM and in control CM after a specific pharmacological inhibition of NaV1.8. In contrast, we did not find any effects on ventricular APD90. The frequency of spontaneous sarcoplasmic reticulum Ca2+ sparks and waves were reduced in SCN10A-KO iPSC-CM and control cells following the pharmacological inhibition of NaV1.8. We further analyzed potential triggers of arrhythmias and found reduced delayed afterdepolarizations (DAD) in SCN10A-KO iPSC-CM and after the specific inhibition of NaV1.8 in control cells. In conclusion, we show that NaV1.8-induced INaL primarily impacts arrhythmogenesis at a subcellular level, with minimal effects on systolic cellular Ca2+ release. The inhibition or knockout of NaV1.8 diminishes proarrhythmic triggers in ventricular CM. In conjunction with our previously published results, this work confirms NaV1.8 as a proarrhythmic target that may be useful in an anti-arrhythmic therapeutic strategy.

Role of ranolazine in heart failure: From cellular to clinic perspective

Ranolazine was approved by the US Food and Drug Administration as an antianginal drug in 2006, and has been used since in certain groups of patients with stable angina. The therapeutic action of ranolazine was initially attributed to inhibitory effects on fatty acids metabolism. As investigations went on, however, it developed that the main beneficial effects of ranolazine arise from its action on the late sodium current in the heart. Since late sodium currents were discovered to be involved in various heart pathologies such as ischemia, arrhythmias, systolic and diastolic dysfunctions, and all these conditions are associated with heart failure, ranolazine has in some way been tested either directly or indirectly on heart failure in numerous experimental and clinical studies. As the heart continuously remodels following any sort of severe injury, the inhibition by ranolazine of the underlying mechanisms of cardiac remodeling including ion disturbances, oxidative stress, inflammation, apoptosis, fibrosis, metabolic dysregulation, and neurohormonal impairment are discussed, along with unresolved issues. A projection of pathologies targeted by ranolazine from cellular level to clinical is provided in this review.

The effect of Sirt1 deficiency on Ca2+ and Na+ regulation in mouse ventricular myocytes

This study addressed the hypothesis that cardiac Sirtuin 1 (Sirt1) deficiency alters cardiomyocyte Ca²⁺ and Na⁺ regulation, leading to cardiac dysfunction and arrhythmogenesis. We used mice with cardiac‐specific Sirt1 knockout (Sirt1^−/−). Sirt1^flox/flox mice were served as control. Sirt1^−/− mice showed impaired cardiac ejection fraction with increased ventricular spontaneous activity and burst firing compared with those in control mice. The arrhythmic events were suppressed by KN93 and ranolazine. Reduction in Ca²⁺ transient amplitudes and sarcoplasmic reticulum (SR) Ca²⁺ stores, and increased SR Ca²⁺ leak were shown in the Sirt1^−/− mice. Electrophysiological measurements were performed using patch‐clamp method. While L‐type Ca²⁺ current (I_{Ca, L}) was smaller in Sirt1^−/− myocytes, reverse‐mode Na⁺/Ca²⁺ exchanger (NCX) current was larger compared with those in control myocytes. Late Na⁺ current (I_{Na, L}) was enhanced in the Sirt1^−/− mice, alongside with elevated cytosolic Na⁺ level. Increased cytosolic and mitochondrial reactive oxygen species (ROS) were shown in Sirt1^−/− mice. Sirt1^−/− cardiomyocytes showed down‐regulation of L‐type Ca²⁺ channel α1c subunit (Cav1.2) and sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a), but up‐regulation of Ca²⁺/calmodulin‐dependent protein kinase II and NCX. In conclusions, these findings suggest that deficiency of Sirt1 impairs the regulation of intracellular Ca²⁺ and Na⁺ in cardiomyocytes, thereby provoking cardiac dysfunction and arrhythmogenesis.

Selective inhibition of physiological late Na+ current stabilizes ventricular repolarization

The physiological role of cardiac late Na+ current ( INa) has not been well described. In this study, we tested the hypothesis that selective inhibition of physiological late INa abbreviates the normal action potential (AP) duration (APD) and counteracts the prolongation of APD and arrhythmic activities caused by inhibition of the delayed rectifier K+ current ( IKr). The effects of GS-458967 (GS967) on the physiological late INa and APs in rabbit isolated ventricular myocytes and on the monophasic APs and arrhythmias in rabbit isolated perfused hearts were determined. In ventricular myocytes, GS967 and, for comparison, tetrodotoxin concentration dependently decreased the physiological late INa with IC50 values of 0.5 and 1.9 µM, respectively, and significantly shortened the APD measured at 90% repolarization (APD90). A strong correlation between inhibition of the physiological late INa and shortening of APD by GS967 or tetrodotoxin ( R2 of 0.96 and 0.97, respectively) was observed. Pretreatment of isolated myocytes or hearts with GS967 (1 µM) significantly shortened APD90 and monophasic APD90 and prevented the prolongation and associated arrhythmias caused by the IKr inhibitor E4031 (1 µM). In conclusion, selective inhibition of physiological late INa shortens the APD, stabilizes ventricular repolarization, and decreases the proarrhythmic potential of pharmacological agents that slow ventricular repolarization. Thus, selective inhibition of late INa may constitute a generalizable approach to stabilize ventricular repolarization and suppress arrhythmogenicity associated with conditions whereby AP or QT intervals are prolonged.

NEW & NOTEWORTHY The contribution of physiological late Na+ current in action potential duration (APD) of rabbit cardiac myocytes was estimated. The inhibition of this current prevented the prolongation of APD in rabbit cardiac myocytes, the prolongation of monophasic APD, and generation of arrhythmias in rabbit isolated hearts caused by delayed rectifier K+ current inhibition.

Ranolazine therapy in drug-refractory ventricular arrhythmias

AIMS

Ranolazine is an antiischemic and antianginal agent, but experimental and preclinical data provided evidence of additional antiarrhythmic properties. The aim of this study was to evaluate the safety and efficacy of ranolazine in reducing episodes of ventricular arrhythmias in patients with recurrent antiarrhythmic drug-refractory ventricular arrhythmias or with chronic angina.

METHODS

Seventeen implantable cardioverter defibrillator (ICD) recipients, who had experienced a worsening of their ventricular arrhythmia burden, and 12 ICD recipients with angina were enrolled. Patients were followed up for 6 months after the addition of ranolazine (postranolazine). Data were compared with before its administration (preranolazine).

RESULTS

In the Arrhythmias group, a significant reduction was found in the median number of ventricular tachycardia episodes per patient (4 vs. 0, P = 0.01), and in ICD interventions in terms of both antitachycardia pacing (2 vs. 0, P = 0.04) and shock delivery (2 vs. 0, P = 0.02) after the addition of ranolazine. Moreover, fewer patients experienced episodes of nonsustained ventricular tachycardia (71 vs. 41%, P = 0.04), ventricular tachycardia (76 vs. 24%, P = 0.01), ICD antitachycardia pacing (47 vs. 18%, P = 0.02), and ICD shocks (47 vs. 6%, P = 0.03). In the Angina group, none of the patients developed major ventricular arrhythmias while on ranolazine treatment. No adverse effects were observed.

CONCLUSION

In this small study, ranolazine proved to be effective, well tolerated, and safe in reducing ventricular arrhythmia episodes and ICD interventions in patients with recurrent antiarrhythmic drug-refractory events. In addition, none of the patients with chronic angina developed major ventricular arrhythmias.

Ranolazine Attenuates the Electrophysiological Effects of Myocardial Stretch in Langendorff-Perfused Rabbit Hearts

PURPOSE

Mechanical stretch is an arrhythmogenic factor found in situations of cardiac overload or dyssynchronic contraction. Ranolazine is an antianginal agent that inhibits the late Na (+) current and has been shown to exert a protective effect against arrhythmias. The present study aims to determine whether ranolazine modifies the electrophysiological responses induced by acute mechanical stretch.

METHODS

The ventricular fibrillation modifications induced by acute stretch were studied in Langendorff-perfused rabbit hearts using epicardial multiple electrodes under control conditions (n = 9) or during perfusion of the late Na(+) current blocker ranolazine 5 μM (n = 9). Spectral and mapping techniques were used to establish the ventricular fibrillation dominant frequency, the spectral concentration and the complexity of myocardial activation in three situations: baseline, stretch and post-stretch.

RESULTS

Ranolazine attenuated the increase in ventricular fibrillation dominant frequency produced by stretch (23.0 vs 40.4 %) (control: baseline =13.6 ± 2.6 Hz, stretch = 19.1 ± 3.1 Hz, p < 0.0001; ranolazine: baseline =  1.4 ± 1.8 Hz, stretch =14.0 ± 2.4 Hz, p < 0.05 vs baseline, p < 0.001 vs control). During stretch, ventricular fibrillation was less complex in the ranolazine than in the control series, as evaluated by the lesser percentage of complex maps and the greater spectral concentration of ventricular fibrillation. These changes were associated to an increase in the fifth percentile of VV intervals during ventricular fibrillation (50 ± 8 vs 38 ± 5 ms, p <  .01) and in the wavelength of the activation (2.4 ± 0.3 vs 1.9 ± 0.2 cm, p < 0.001) under ranolazine.

CONCLUSIONS

The late inward Na(+) current inhibitor ranolazine attenuates the electrophysiological effects responsible for the acceleration and increase in complexity of ventricular fibrillation produced by myocardial stretch.

Contribution of the late sodium current to intracellular sodium and calcium overload in rabbit ventricular myocytes treated by anemone toxin

Pathological enhancement of late Na+ current ( INa) can potentially modify intracellular ion homeostasis and contribute to cardiac dysfunction. We tested the hypothesis that modulation of late INa can be a source of intracellular Na+ ([Na+]i) overload. Late INa was enhanced by exposing rabbit ventricular myocytes to Anemonia sulcata toxin II (ATX-II) and measured using whole cell patch-clamp technique. [Na+]i was determined with fluorescent dye Asante NaTRIUM Green-2 AM. Pacing-induced changes in the dye fluorescence measured at 37°C were more pronounced in ATX-II-treated cells than in control (dye washout prevented calibration). At 22–24°C, resting [Na+]i was 6.6 ± 0.8 mM. Treatment with 5 nM ATX-II increased late INa 8.7-fold. [Na+]i measured after 2 min of electrical stimulation (1 Hz) was 10.8 ± 1.5 mM and 22.1 ± 1.6 mM ( P < 0.001) in the absence and presence of 5 nM ATX-II, respectively. Inhibition of late INa with GS-967 (1 μM) prevented Na+i accumulation. A strong positive correlation was observed between the late INa and the pacing-induced increase of [Na+]i ( R2 = 0.88) and between the rise in [Na+]i and the increases in cytosolic Ca2+ ( R2 = 0.96). ATX-II, tetrodotoxin, or GS-967 did not affect [Na+]i in quiescent myocytes suggesting that late INa was solely responsible for triggering the ATX-II effect on [Na+]i. Experiments with pinacidil and E4031 indicate that prolongation of the action potential contributes to as much as 50% of the [Na+]i overload associated with the increase in late INa caused by ATX-II. Enhancement of late INa can cause intracellular Na+ overload in ventricular myocytes.

Epidemiology of heart failure with preserved ejection fraction

The prevalence of heart failure (HF) and its subtype, HF with preserved ejection fraction (HFpEF), is on the rise due to aging of the population. HFpEF is convergence of several pathophysiological processes, which are not yet clearly identified. HFpEF is usually seen in association with systemic diseases, such as diabetes, hypertension, atrial fibrillation, sleep apnea, renal and pulmonary disease. The proportion of HF patients with HFpEF varies by patient demographics, study settings (cohort vs. clinical trial, outpatient clinics vs. hospitalised patients) and cut points used to define preserved function. There is an expanding body of literature about prevalence and prognostic significance of both cardiovascular and non-cardiovascular comorbidities in HFpEF patients. Current therapeutic approaches are targeted towards alleviating the symptoms, treating the associated comorbid conditions, and reducing recurrent hospital admissions. There is lack of evidence-based therapies that show a reduction in the mortality amongst HFpEF patients; however, an improvement in exercise tolerance and quality of life is seen with few interventions. In this review, we highlight the epidemiology and current treatment options for HFpEF.

Therapeutic interventions for heart failure with preserved ejection fraction: A summary of current evidence

Heart failure with preserved ejection fraction (HFPEF) is common and represents a major challenge in cardiovascular medicine. Most of the current treatment of HFPEF is based on morbidity benefits and symptom reduction. Various pharmacological interventions available for heart failure with reduced ejection fraction have not been supported by clinical studies for HFPEF. Addressing the specific aetiology and aggressive risk factor modification remain the mainstay in the treatment of HFPEF. We present a brief overview of the currently recommended therapeutic options with available evidence.

Ranolazine improves diastolic function in spontaneously hypertensive rats

Diastolic dysfunction can lead to heart failure with preserved ejection fraction, for which there is no effective therapeutic. Ranolazine has been reported to reduce diastolic dysfunction, but the specific mechanisms of action are unclear. The effect of ranolazine on diastolic function was examined in spontaneously hypertensive rats (SHRs), where left ventricular relaxation is impaired and stiffness increased. The objective of this study was to determine whether ranolazine improves diastolic function in SHRs and identify the mechanism(s) by which improvement is achieved. Specifically, to test the hypothesis that ranolazine, by inhibiting late sodium current, reduces Ca(2+) overload and promotes ventricular relaxation and reduction in diastolic stiffness, the effects of ranolazine or vehicle on heart function and the response to dobutamine challenge were evaluated in aged male SHRs and Wistar-Kyoto rats by echocardiography and pressure-volume loop analysis. The effects of ranolazine and the more specific sodium channel inhibitor tetrodotoxin were determined on the late sodium current, sarcomere length, and intracellular calcium in isolated cardiomyocytes. Ranolazine reduced the end-diastolic pressure-volume relationship slope and improved diastolic function during dobutamine challenge in the SHR. Ranolazine and tetrodotoxin also enhanced cardiomyocyte relaxation and reduced myoplasmic free Ca(2+) during diastole at high-stimulus rates in the SHR. The density of the late sodium current was elevated in SHRs. In conclusion, ranolazine was effective in reducing diastolic dysfunction in the SHR. Its mechanism of action, at least in part, is consistent with inhibition of the increased late sodium current in the SHR leading to reduced Ca(2+) overload.

New Insights Into Diastolic Dysfunction and Heart Failure With Preserved Ejection Fraction

As the population ages, the incidence of patients presenting for surgical procedures with diastolic dysfunction and heart failure with preserved ejection fraction will rise. This review will discuss the most current and relevant information on the pathophysiology, treatment, and perioperative management of these patients.

Management of myocardial ischemia. Is ranolazine needed? For all or some patients with myocardial ischemia?

This editorial refers to 'Should ranolazine be used for all patients with ischemic heart disease or only for symptomatic patients with stable angina or for those with refractory angina pectoris? A critical appraisal' by U Thadani also published in this issue.