Late Sodium Current Inhibitors as Potential Antiarrhythmic Agents

Sodium-glucose cotransporter-2 inhibitors and the risk of atrial fibrillation in patients with type 2 diabetes: a population-based cohort study

AIMS

Sodium-glucose cotransporter-2 inhibitors (SGLT-2is) have a direct cardiac effect that is likely to be independent of its glucose lowering renal effect. Previous research has shown that SGLT2-is mitigate heart failure and prevent arrhythmic cardiac death. Our objective is to determine whether SGLT-2is reduce atrial fibrillation (AF) in comparison to other second-to third-line antidiabetic drugs in type 2 diabetes.

METHODS AND RESULTS

We conducted a population-based, new-user active comparator cohort study using data from the UK Clinical Practice Research Datalink. We identified a cohort of patients initiating a new antidiabetic drug class between January 2013 and September 2020. This cohort included patients initiating their first ever non-insulin antidiabetic drug, as well as those who switched to or added-on an antidiabetic drug class not previously used in their treatment history. Individuals with a diagnosis of AF or atrial flutter at any time before cohort entry were excluded. Cox regression analysis with time-dependent covariates was used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) of AF comparing SGLT-2-is with other second-line to third-line antidiabetic drugs. Stratified analyses were performed according to sex, diabetes duration (<5 or ≥ 5 years), body mass index (BMI), HbA1c, and presence of heart failure.The cohort comprised 142 447 patients. SGLT-2is were associated with a statistically significant reduced hazard of AF compared to other second-line to third-line antidiabetic drugs (adjusted HR: 0.77 [95% CI: 0.68-0.88]). This reduced risk was present in both sexes but was more prominently among women (adjusted HRwomen: 0.60 [95% CI: 0.45-0.79]; HRmen: 0.85 [95% CI: 0.73-0.98]; P-value interaction: 0.012). There was no evidence for effect modification when stratifying on duration of diabetes, BMI, HbA1c, or presence of heart failure.

CONCLUSION

SGLT-2is were associated with a reduced risk of AF in patients with type 2 diabetes compared to other second-line to third-line antidiabetic drugs. This reduced risk occurs in both sexes but more prominently among women.

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.

Exploring novel insights into the molecular mechanisms underlying Bisphenol A-induced toxicity: A persistent threat to human health

Bisphenol A (BPA) is a ubiquitous industrial chemical used in the production of polycarbonate plastics and epoxy resins, found in numerous consumer products. Despite its widespread use, its potential adverse health effects have raised significant concerns. This review explores the molecular mechanisms and evidence-based literature underlying BPA-induced toxicities and its implications for human health. BPA is an endocrine-disrupting chemical (EDC) which exhibits carcinogenic properties by influencing various receptors, such as ER, AhR, PPARs, LXRs, and RARs. It induces oxidative stress and contributes to cellular dysfunction, inflammation, and DNA damage, ultimately leading to various toxicities including but not limited to reproductive, cardiotoxicity, neurotoxicity, and endocrine toxicity. Moreover, BPA can modify DNA methylation patterns, histone modifications, and non-coding RNA expression, leading to epigenetic changes and contribute to carcinogenesis. Overall, understanding molecular mechanisms of BPA-induced toxicity is crucial for developing effective strategies and policies to mitigate its adverse effects on human health.

Ion channel dysfunction and fibrosis in atrial fibrillation: Two sides of the same coin

BACKGROUND

Atrial fibrillation (AF) is a common heart rhythm disorder that is associated with an increased risk of stroke and heart failure (HF). Initially, an association between AF and ion channel dysfunction was identified, classifying the pathology as a predominantly electrical disease. More recently it has been recognized that fibrosis and structural atrial remodeling play a driving role in the development of this arrhythmia also in these cases.

PURPOSE

Understanding the role of fibrosis in genetic determined AF could be important to better comprise the pathophysiology of this arrhythmia and to refine its management also in nongenetic forms. In this review we analyze genetic and epigenetic mechanisms responsible for AF and their link with atrial fibrosis, then we will consider analogies with the pathophysiological mechanism in nongenetic AF, and discuss consequent therapeutic options.

Ion channel trafficking implications in heart failure

Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.

Ventricular Tachycardia Due to Triggered Activity: Role of Early and Delayed Afterdepolarizations

Most forms of sustained ventricular tachycardia (VT) are caused by re-entry, resulting from altered myocardial conduction and refractoriness secondary to underlying structural heart disease. In contrast, VT caused by triggered activity (TA) is unrelated to an abnormal structural substrate and is often caused by molecular defects affecting ion channel function or regulation of intracellular calcium cycling. This review summarizes the cellular and molecular bases underlying TA and exemplifies their clinical relevance with selective representative scenarios. The underlying basis of TA caused by delayed afterdepolarizations is related to sarcoplasmic reticulum calcium overload, calcium waves, and diastolic sarcoplasmic reticulum calcium leak. Clinical examples of TA caused by delayed afterdepolarizations include sustained right and left ventricular outflow tract tachycardia and catecholaminergic polymorphic VT. The other form of afterpotentials, early afterdepolarizations, are systolic events and inscribe early afterdepolarizations during phase 2 or phase 3 of the action potential. The fundamental defect is a decrease in repolarization reserve with associated increases in late plateau inward currents. Malignant ventricular arrhythmias in the long QT syndromes are initiated by early afterdepolarization-mediated TA. An understanding of the molecular and cellular bases of these arrhythmias has resulted in generally effective pharmacologic-based therapies, but these are nonspecific agents that have off-target effects. Therapeutic efficacy may need to be augmented with an implantable defibrillator. Next-generation therapies will include novel agents that rescue arrhythmogenic abnormalities in cellular signaling pathways and gene therapy approaches that transfer or edit pathogenic gene variants or silence mutant messenger ribonucleic acid.

Naringin exerts antiarrhythmic effects by inhibiting channel currents in mouse cardiomyocytes

INTRODUCTION

Naringin, a flavonoid extracted from citrus plants, has a variety of biological effects. Studies have shown that increasing the consumption of flavonoid-rich foods can reduce the incidence of cardiac arrhythmia. Naringin has been reported to have beneficial cardiovascular effects and thus can be used to prevent cardiovascular diseases, but the electrophysiological mechanism through which it prevents arrhythmias has not been elucidated. This study was conducted to investigate the effect of naringin on the transmembrane ion channel currents in mouse ventricular myocytes and the antiarrhythmic effect of this compound on Langendorff-perfused mouse hearts.

METHODS

Action potentials (APs) and ionic currents were recorded in isolated ventricular myocytes using the whole-cell patch-clamp technique. Anemone toxin II (ATX II) and CaCl2 were used to induce early afterdepolarizations (EADs) and delayed afterdepolarizations (DADs), respectively. Electrocardiogram (ECG) recordings were conducted in Langendorff-perfused mouse hearts with a BL-420F biological signal acquisition and analysis system.

RESULTS

At the cellular level, naringin shortened the action potential duration (APD) of ventricular myocytes and decreased the maximum depolarization velocity (Vmax) of APs.Naringin inhibited the L-type calcium current (ICa.L) and ATX II enhanced the late sodium current (INa.L) in a concentration-dependent manner with IC50 values of 508.5 μmol/L (n = 9) and 311.6 μmol/L (n = 10), respectively. In addition, naringin also inhibited the peak sodium current (INa·P) and delayed the rectifier potassium current (IK) and the transient outward potassium current (Ito). Moreover, naringin reduced ATX II-induced APD prolongation and EADs and had a significant inhibitory effect on CaCl2-induced DADs as well. At the organ level, naringin reduced the incidence of ventricular tachycardia (VT) and ventricular fibrillation (VF) induced by ATX II and shortened the duration of both in isolated hearts.

CONCLUSION

Naringin can inhibit the occurrence of EADs and DADs at the cellular level; furthermore, it can inhibit INa.L, ICa.L, INa·P, IK, and Ito in ventricular myocytes. Naringin also inhibits arrhythmias induced by ATX II in hearts. By investigating naringin with this electrophysiological method for the first time, we determined that this flavonoid may be a multichannel blocker with antiarrhythmic effects.

Store-Operated Ca2+ Entry as a Putative Target of Flecainide for the Treatment of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a genetic disorder that may lead patients to sudden cell death through the occurrence of ventricular arrhythmias. ACM is characterised by the progressive substitution of cardiomyocytes with fibrofatty scar tissue that predisposes the heart to life-threatening arrhythmic events. Cardiac mesenchymal stromal cells (C-MSCs) contribute to the ACM by differentiating into fibroblasts and adipocytes, thereby supporting aberrant remodelling of the cardiac structure. Flecainide is an Ic antiarrhythmic drug that can be administered in combination with β-adrenergic blockers to treat ACM due to its ability to target both Nav1.5 and type 2 ryanodine receptors (RyR2). However, a recent study showed that flecainide may also prevent fibro-adipogenic differentiation by inhibiting store-operated Ca2+ entry (SOCE) and thereby suppressing spontaneous Ca2+ oscillations in C-MSCs isolated from human ACM patients (ACM C-hMSCs). Herein, we briefly survey ACM pathogenesis and therapies and then recapitulate the main molecular mechanisms targeted by flecainide to mitigate arrhythmic events, including Nav1.5 and RyR2. Subsequently, we describe the role of spontaneous Ca2+ oscillations in determining MSC fate. Next, we discuss recent work showing that spontaneous Ca2+ oscillations in ACM C-hMSCs are accelerated to stimulate their fibro-adipogenic differentiation. Finally, we describe the evidence that flecainide suppresses spontaneous Ca2+ oscillations and fibro-adipogenic differentiation in ACM C-hMSCs by inhibiting constitutive SOCE.

Potential favorable action of sodium-glucose cotransporter-2 inhibitors on sudden cardiac death: a brief overview

The primary pharmacological action of sodium-glucose co-transporter 2 (SGLT2) inhibitors is to inhibit the reabsorption of glucose and sodium ions from the proximal tubules of the kidney and to promote urinary glucose excretion. Notably, several clinical trials have recently demonstrated potent protective effects of SGLT2 inhibitors in patients with heart failure (HF) or chronic kidney disease (CKD), regardless of the presence or absence of diabetes. However, the impact of SGLT2 inhibitors on sudden cardiac death (SCD) or fatal ventricular arrhythmias (VAs), the pathophysiology of which is partly similar to that of HF and CKD, remains undetermined. The cardiorenal protective effects of SGLT2 inhibitors have been reported to include hemodynamic improvement, reverse remodeling of the failing heart, amelioration of sympathetic hyperactivity, correction of anemia and impaired iron metabolism, antioxidative effects, correction of serum electrolyte abnormalities, and antifibrotic effects, which may lead to prevent SCD and/or VAs. Recently, as possible direct cardiac effects of SGLT2 inhibitors, not only inhibition of Na⁺/H⁺ exchanger (NHE) activity, but also suppression of late Na⁺ current have been focused on. In addition to the indirect cardioprotective mechanisms of SGLT2 inhibitors, suppression of aberrantly increased late Na⁺ current may contribute to preventing SCD and/or VAs via restoration of the prolonged repolarization phase in the failing heart. This review summarizes the results of previous clinical trials of SGLT2 inhibitors for prevention of SCD, their impact on the indices of electrocardiogram, and the possible molecular mechanisms of their anti-arrhythmic effects.

Conductance Changes of Na+ Channels during the Late Na+ Current Flowing under Action Potential Voltage Clamp Conditions in Canine, Rabbit, and Guinea Pig Ventricular Myocytes

Late sodium current (I_Na,late) is an important inward current contributing to the plateau phase of the action potential (AP) in the mammalian heart. Although I_Na,late is considered as a possible target for antiarrhythmic agents, several aspects of this current remained hidden. In this work, the profile of I_Na,late, together with the respective conductance changes (G_Na,late), were studied and compared in rabbit, canine, and guinea pig ventricular myocytes using the action potential voltage clamp (APVC) technique. In canine and rabbit myocytes, the density of I_Na,late was relatively stable during the plateau and decreased only along terminal repolarization of the AP, while G_Na,late decreased monotonically. In contrast, I_Na,late increased monotonically, while G_Na,late remained largely unchanged during the AP in guinea pig. The estimated slow inactivation of Na⁺ channels was much slower in guinea pig than in canine or rabbit myocytes. The characteristics of canine I_Na,late and G_Na,late were not altered by using command APs recorded from rabbit or guinea pig myocytes, indicating that the different shapes of the current profiles are related to genuine interspecies differences in the gating of I_Na,late. Both I_Na,late and G_Na,late decreased in canine myocytes when the intracellular Ca²⁺ concentration was reduced either by the extracellular application of 1 µM nisoldipine or by the intracellular application of BAPTA. Finally, a comparison of the I_Na,late and G_Na,late profiles induced by the toxin of Anemonia sulcata (ATX-II) in canine and guinea pig myocytes revealed profound differences between the two species: in dog, the ATX-II induced I_Na,late and G_Na,late showed kinetics similar to those observed with the native current, while in guinea pig, the ATX-II induced G_Na,late increased during the AP. Our results show that there are notable interspecies differences in the gating kinetics of I_Na,late that cannot be explained by differences in AP morphology. These differences must be considered when interpreting the I_Na,late results obtained in guinea pig.

Ranolazine exerts atrial antiarrhythmic effects in a rat model of monocrotaline-induced pulmonary hypertension

Atrial arrhythmias are a hallmark of heart diseases. The antiarrhythmic drug ranolazine with multichannel blocker properties is a promising agent to treat atrial arrhythmias. We therefore used the rat model of monocrotaline-induced pulmonary-hypertension to assess whether ranolazine can reduce the incidence of ex vivo atrial arrhythmias in isolated right atrium. Four-week-old Wistar rats were injected with 50 mg/kg of monocrotaline, and isolated right atrium function was studied 14 days later. The heart developed right atrium and right ventricular hypertrophy, and the ECG showed an increased P wave duration and QT interval, which are markers of the disease. Moreover, monocrotaline injection caused enhanced chronotropism and faster kinetics of contraction and relaxation in isolated right atrium. Additionally, in a concentration-dependent manner, ranolazine showed chronotropic and ionotropic effects upon isolated right atrium, with higher potency in the control when compared with experimental model. Using a burst pacing protocol, the isolated right atrium from the monocrotaline-treated animals was more susceptible to develop arrhythmias, and ranolazine was able to attenuate the phenotype. Thus, we concluded that the rat model of monocrotaline-induced pulmonary-hypertension develops right atrium remodelling, which increased the susceptibility to present ex vivo atrial arrhythmias, and the antiarrhythmic drug ranolazine ameliorated the phenotype.

Inhibition of late sodium current via PI3K/Akt signaling prevents cellular remodeling in tachypacing-induced HL-1 atrial myocytes

An aberrant late sodium current (I_Na,Late) caused by a mutation in the cardiac sodium channel (Na_v1.5) has emerged as a contributor to electrical remodeling that causes susceptibility to atrial fibrillation (AF). Although downregulation of phosphoinositide 3-kinase (PI3K)/Akt signaling is associated with AF, the molecular mechanisms underlying the negative regulation of I_Na,Late in AF remain unclear, and potential therapeutic approaches are needed. In this work, we constructed a tachypacing-induced cellular model of AF by exposing HL-1 myocytes to rapid electrical stimulation (1.5 V/cm, 4 ms, 10 Hz) for 6 h. Then, we gathered data using confocal Ca²⁺ imaging, immunofluorescence, patch-clamp recordings, and immunoblots. The tachypacing cells displayed irregular Ca²⁺ release, delayed afterdepolarization, prolonged action potential duration, and reduced PI3K/Akt signaling compared with controls. Those detrimental effects were related to increased I_Na,Late and were significantly mediated by treatment with the I_Na,Late blocker ranolazine. Furthermore, decreased PI3K/Akt signaling via PI3K inhibition increased I_Na,Late and subsequent aberrant myocyte excitability, which were abolished by I_Na,Late inhibition, suggesting that PI3K/Akt signaling is responsible for regulating pathogenic I_Na,Late. These results indicate that PI3K/Akt signaling is critical for regulating I_Na,Late and electrical remodeling, supporting the use of PI3K/Akt-mediated I_Na,Late as a therapeutic target for AF.

Neuromodulation therapy for atrial fibrillation

Atrial fibrillation has a multifactorial pathophysiology influenced by cardiac autonomic innervation. Both sympathetic and parasympathetic influences are profibrillatory. Innovative therapies targeting the neurocardiac axis include catheter ablation or pharmacologic suppression of ganglionated plexi, renal sympathetic denervation, low-level vagal stimulation, and stellate ganglion blockade. To date, these therapies have variable efficacy. As our understanding of atrial fibrillation and the cardiac nervous system expands, our approach to therapeutic neuromodulation will continue evolving for the benefit of those with AF.

Antiarrhythmic and Inotropic Effects of Selective Na+/Ca2+ Exchanger Inhibition: What Can We Learn from the Pharmacological Studies?

Life-long stable heart function requires a critical balance of intracellular Ca²⁺. Several ion channels and pumps cooperate in a complex machinery that controls the influx, release, and efflux of Ca²⁺. Probably one of the most interesting and most complex players of this crosstalk is the Na⁺/Ca²⁺ exchanger, which represents the main Ca²⁺ efflux mechanism; however, under some circumstances, it can also bring Ca²⁺ into the cell. Therefore, the inhibition of the Na⁺/Ca²⁺ exchanger has emerged as one of the most promising possible pharmacological targets to increase Ca²⁺ levels, to decrease arrhythmogenic depolarizations, and to reduce excessive Ca²⁺ influx. In line with this, as a response to increasing demand, several more or less selective Na⁺/Ca²⁺ exchanger inhibitor compounds have been developed. In the past 20 years, several results have been published regarding the effect of Na⁺/Ca²⁺ exchanger inhibition under various circumstances, e.g., species, inhibitor compounds, and experimental conditions; however, the results are often controversial. Does selective Na⁺/Ca²⁺ exchanger inhibition have any future in clinical pharmacological practice? In this review, the experimental results of Na⁺/Ca²⁺ exchanger inhibition are summarized focusing on the data obtained by novel highly selective inhibitors.

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 (I_Na,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 I_Na,late. Interestingly, ranolazine, a clinically used blocker of I_Na,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 I_Na,late, is able to correct the arrhythmic phenotype.

Use of sodium-glucose cotransporter-2 inhibitors and the risk for sudden cardiac arrest and for all-cause death in patients with type 2 diabetes mellitus

AIMS

Sodium-glucose cotransporter-2 inhibitors (SGLT-2is) are antidiabetic agents that can have direct cardiac effects by impacting on cardiac ion transport mechanisms that control cardiac electrophysiology. We studied the association between SGLT-2i use and all-cause mortality and the risk of sudden cardiac arrest (SCA) in patients with type 2 diabetes.

METHODS

Using data from the UK Clinical Practice Research Datalink, a cohort study among patients initiating a new antidiabetic drug class on or after January 2013 through September 2020 was conducted. A Cox regression with time-dependent covariates was performed to estimate the hazard ratios (HRs) of SCA and all-cause mortality comparing SGLT-2is with other second- to third-line antidiabetic drugs. Stratified analyses were performed according to sex, diabetes duration (<5 or ≥5 years), and the presence of cardiovascular disease.

RESULTS

A total of 152 591 patients were included. Use of SGLT-2i was associated with a reduced HR of SCA when compared with other second- to third-line antidiabetic drugs after adjustment for common SCA risk factors, although this association marginally failed to reach statistical significance [HR: 0.62, 95% confidence interval (95% CI): 0.38-1.01]. The HR of all-cause mortality associated with SGLT-2i use when compared with other second- to third-line antidiabetics was 0.43 (95% CI: 0.39-0.48) and did not vary by sex, diabetes duration, or the presence of cardiovascular disease. SGLT-2i use remained associated with lower all-cause mortality in patients without concomitant insulin use (HR: 0.56, 95% CI: 0.50-0.63).

CONCLUSION

SGLT-2i use was associated with reduced all-cause mortality in patients with type 2 diabetes. The association between use of SGLT-2i and reduced risk of SCA was not statistically significant.

Aging-associated susceptibility to stress-induced ventricular arrhythmogenesis is attenuated by tetrodotoxin

Aging is associated with increased prevalence of life-threatening ventricular arrhythmias, but mechanisms underlying higher susceptibility to arrhythmogenesis and means to prevent such arrhythmias under stress are not fully defined. We aimed to define differences in aging-associated susceptibility to ventricular fibrillation (VF) induction between young and aged hearts. VF induction was attempted in isolated perfused hearts of young (6-month) and aged (24-month-old) male Fischer-344 rats by rapid pacing before and following isoproterenol (1 μM) or global ischemia and reperfusion (I/R) injury with or without pretreatment with low-dose tetrodotoxin, a late sodium current blocker. At baseline, VF could not be induced; however, the susceptibility to inducible VF after isoproterenol and spontaneous VF following I/R was 6-fold and 3-fold higher, respectively, in old hearts (P < 0.05). Old animals had longer epicardial monophasic action potential at 90% repolarization (APD₉₀; P < 0.05) and displayed a loss of isoproterenol-induced shortening of APD₉₀ present in the young. In isolated ventricular cardiomyocytes from older but not younger animals, 4-aminopyridine prolonged APD and induced early afterdepolarizations (EADs) and triggered activity with isoproterenol. Low-dose tetrodotoxin (0.5 μM) significantly shortened APD without altering action potential upstroke and prevented 4-aminopyridine-mediated APD prolongation, EADs, and triggered activity. Tetrodotoxin pretreatment prevented VF induction by pacing in isoproterenol-challenged hearts. Vulnerability to VF following I/R or catecholamine challenge is significantly increased in old hearts that display reduced repolarization reserve and increased propensity to EADs, triggered activity, and ventricular arrhythmogenesis that can be suppressed by low-dose tetrodotoxin, suggesting a role of slow sodium current in promoting arrhythmogenesis with aging.

Association between Empagliflozin Use and Electrocardiographic Changes

Empagliflozin, a sodium-glucose transporter 2 inhibitor, has been shown to bind to late sodium channels in mice cardiomyocytes. We sought to investigate the electrocardiographic (ECG) features associated with empagliflozin use in patients with diabetes mellitus. We compared ECG features of 101 patients before and after initiation of empagliflozin and found that empagliflozin was associated with a significant increase in QRS duration among diabetes patients with heart failure.

Endocrine-Disrupting Effects of Bisphenol A on the Cardiovascular System: A Review

Currently, the plastic monomer and plasticizer bisphenol A (BPA) is one of the most widely used chemicals. BPA is present in polycarbonate plastics and epoxy resins, commonly used in food storage and industrial or medical products. However, the use of this synthetic compound is a growing concern, as BPA is an endocrine-disrupting compound and can bind mainly to estrogen receptors, interfering with different functions at the cardiovascular level. Several studies have investigated the disruptive effects of BPA; however, its cardiotoxicity remains unclear. Therefore, this review’s purpose is to address the most recent studies on the implications of BPA on the cardiovascular system. Our findings suggest that BPA impairs cardiac excitability through intracellular mechanisms, involving the inhibition of the main ion channels, changes in Ca²⁺ handling, the induction of oxidative stress, and epigenetic modifications. Our data support that BPA exposure increases the risk of developing cardiovascular diseases (CVDs) including atherosclerosis and its risk factors such as hypertension and diabetes. Furthermore, BPA exposure is also particularly harmful in pregnancy, promoting the development of hypertensive disorders during pregnancy. In summary, BPA exposure compromises human health, promoting the development and progression of CVDs and risk factors. Further studies are needed to clarify the human health effects of BPA-induced cardiotoxicity.

Moricizine prevents atrial fibrillation by late sodium current inhibition in atrial myocytes

Background

Enhanced late sodium current (INaL) is reportedly related to an increased risk of atrial fibrillation (AF). Moricizine, as a widely used anti-arrhythmia drug for suppressing ventricular tachycardia, has also been shown to prevent paroxysmal AF. However, the mechanism of its therapeutic effect remains poorly understood.

Methods

Angiotensin II (Ang II) was induced in C57Bl/6 mice (male wild-type) for 4 weeks to increase the susceptibility of AF, and acetylcholine-calcium chloride was used to induce AF. The whole-cell patch-clamp technique was used to detect INaL from isolated atrial myocytes. The expression of proteins in atrial of mice and HL-1 cells were examined by Western-blot.

Results

The results showed that moricizine significantly inhibited Ang II-mediated atrial enlargement and reduced AF vulnerability. We found that the densities of INaL were enhanced in Ang II-treated left and right atrial cardiomyocytes. Simultaneously, the Ang II-induced increase in INaL currents density was alleviated by the administration of moricizine, and no alteration in Nav1.5 expression was observed. In normal isolated atrial myocytes, moricizine significantly reduced Sea anemone toxin II (ATX II)-enhanced INaL density with a reduction of peak sodium currents. In addition, moricizine reduced the Ang II-induced upregulation of phosphorylated calcium/calmodulin-dependent protein kinase-II (p-CaMKII) in both the left and right atria. In HL-1 cells, moricizine also reduced the upregulation of p-CaMKII with Ang II and ATX II intervention, respectively.

Conclusions

Our results indicate that Ang II enhances the INaL via activation of CaMKII. Moricizine inhibits INaL and reduces CaMKII activation, which may be one of the mechanisms of moricizine suppression of AF.

Fibroblast growth factor homologous factors serve as a molecular rheostat in tuning arrhythmogenic cardiac late sodium current

Voltage-gated sodium (Nav1.5) channels support the genesis and brisk spatial propagation of action potentials in the heart. Disruption of NaV1.5 inactivation results in a small persistent Na influx known as late Na current (I Na,L), which has emerged as a common pathogenic mechanism in both congenital and acquired cardiac arrhythmogenic syndromes. Here, using low-noise multi-channel recordings in heterologous systems, LQTS3 patient-derived iPSCs cardiomyocytes, and mouse ventricular myocytes, we demonstrate that the intracellular fibroblast growth factor homologous factors (FHF1-4) tune pathogenic I Na,L in an isoform-specific manner. This scheme suggests a complex orchestration of I Na,L in cardiomyocytes that may contribute to variable disease expressivity of NaV1.5 channelopathies. We further leverage these observations to engineer a peptide-inhibitor of I Na,L with a higher efficacy as compared to a well-established small-molecule inhibitor. Overall, these findings lend insights into molecular mechanisms underlying FHF regulation of I Na,L in pathophysiology and outline potential therapeutic avenues.

Irx5 and transient outward K+ currents contribute to transmural contractile heterogeneities in the mouse ventricle

Previous studies have established that fast transmural gradients of transient outward K⁺ current (I_to,f) correlate with regional differences in action potential (AP) profile and excitation-contraction coupling (ECC) with high I_to,f expression in the epimyocardium (EPI) being associated with short APs and low contractility and vice versa. Herein, we investigated the effects of disrupted I_to,f gradient on contractile properties using mouse models of Irx5 knockout (Irx5-KO) for selective I_to,f elevation in the endomyocardium (ENDO) of the left ventricle (LV) and Kcnd2 ablation (K_V4.2-KO) for selective I_to,freduction in the EPI. Irx5-KO mice exhibited decreased global LV contractility in association with reductions in cell shortening and Ca²⁺ transient amplitudes in isolated ENDO but not EPI cardiomyocytes. Moreover, transcriptional profiling revealed that the primary effect of Irx5 ablation on ECC-related genes was to increase I_to,f gene expression (i.e. Kcnd2 and Kcnip2) in the ENDO, but not the EPI. Indeed, K_V4.2-KO mice showed selective increases in cell shortening and Ca²⁺ transients in isolated EPI cardiomyocytes, leading to enhanced ventricular contractility and mice lacking both Irx5 and Kcnd2 displayed elevated ventricular contractility comparable to K_V4.2-KO mice. Our findings demonstrate that the transmural electromechanical heterogeneities in the healthy ventricles depend on the Irx5-dependent I_to,f gradients. These observations provide a useful framework for assessing the molecular mechanisms underlying the alterations in contractile heterogeneity seen in the diseased heart.

Characteristics of Bisphenol Cardiotoxicity: Impaired Excitability, Contractility, and Relaxation

Bisphenol a (BPA) is a high production volume chemical that is frequently used to manufacture epoxy resins and polycarbonate plastics. BPA-containing products are now pervasive, and as a result, biomonitoring studies report widespread exposure in > 90% of adults, adolescents, and children. Both epidemiological and experimental studies have reported associations between BPA exposure and adverse cardiovascular health outcomes. With increasing concerns regarding BPA exposure, a few structurally similar bisphenol chemicals have been introduced as replacements, including bisphenol s (BPS) and bisphenol f (BPF). In accordance with the recently established "Key characteristics of cardiovascular toxicants", we reviewed the literature to highlight the immediate effects of bisphenol chemicals on (1) cardiac excitability, and (2) contractility and relaxation. BPA inhibits key cardiac ion channels, impairs cardiac excitability, and acts as a more potent inhibitor as compared to BPF and BPS. Through the inhibition of calcium current, some studies report that bisphenol chemicals can act as negative inotropic agents. Yet, others suggest that low dose exposures may increase contractility and precipitate triggered arrhythmias via the phosphorylation of key calcium handling proteins. Accordingly, we propose additional considerations for future work to comprehensively address the cardiac safety profile of BPA, as compared to replacement chemicals.

Late Sodium Current of the Heart: Where Do We Stand and Where Are We Going?

Late sodium current has long been linked to dysrhythmia and contractile malfunction in the heart. Despite the increasing body of accumulating information on the subject, our understanding of its role in normal or pathologic states is not complete. Even though the role of late sodium current in shaping action potential under physiologic circumstances is debated, it’s unquestioned role in arrhythmogenesis keeps it in the focus of research. Transgenic mouse models and isoform-specific pharmacological tools have proved useful in understanding the mechanism of late sodium current in health and disease. This review will outline the mechanism and function of cardiac late sodium current with special focus on the recent advances of the area.

Linked biaromatic compounds as cardioprotective agents

Cardiovascular diseases (CVDs) are widespread in the modern world, and their number is constantly growing. For a long time, CVDs have been the leading cause of morbidity and mortality worldwide. Drugs for the treatment of CVD have been developed almost since the beginning of the 20th century, and a large number of effective cardioprotective agents of various classes have been created. Nevertheless, the need for the design and development of new safe drugs for the treatment of CVD remains. Literature data indicate that a huge number of cardioprotective agents of various generations and mechanisms correspond to a single generalized pharmacophore model containing two aromatic nuclei linked by a linear linker. In this regard, we put forward a concept for the design of a new generation of cardioprotective agents with a multitarget mechanism of action within the indicated pharmacophore model. This review is devoted to a generalization of the currently known compounds with cardioprotective properties and corresponding to the pharmacophore model of biaromatic compounds linked by a linear linker. Particular attention is paid to the history of the creation of these drugs, approaches to their design, and analysis of the structure-action relationship within each class.

Late sodium current and calcium homeostasis in arrhythmogenesis

The cardiac late sodium current (INa,late) is the small sustained component of the sodium current active during the plateau phase of the action potential. Several studies demonstrated that augmentation of the current can lead to cardiac arrhythmias; therefore, INa,late is considered as a promising antiarrhythmic target. Fundamentally, enlarged INa,late increases Na+ influx into the cell, which, in turn, is converted to elevated intracellular Ca2+ concentration through the Na+/Ca2+ exchanger. The excessive Ca2+ load is known to be proarrhythmic. This review describes the behavior of the voltage-gated Na+ channels generating INa,late in health and disease and aims to discuss the physiology and pathophysiology of Na+ and Ca2+ homeostasis in context with the enhanced INa,late demonstrating also the currently accessible antiarrhythmic choices.

Arrhythmogenic Remodeling in the Failing Heart

Chronic heart failure is a clinical syndrome with multiple etiologies, associated with significant morbidity and mortality. Cardiac arrhythmias, including ventricular tachyarrhythmias and atrial fibrillation, are common in heart failure. A number of cardiac diseases including heart failure alter the expression and regulation of ion channels and transporters leading to arrhythmogenic electrical remodeling. Myocardial hypertrophy, fibrosis and scar formation are key elements of arrhythmogenic structural remodeling in heart failure. In this article, the mechanisms responsible for increased arrhythmia susceptibility as well as the underlying changes in ion channel, transporter expression and function as well as alterations in calcium handling in heart failure are discussed. Understanding the mechanisms of arrhythmogenic remodeling is key to improving arrhythmia management and the prevention of sudden cardiac death in patients with heart failure.

Cardioprotection by SGLT2 Inhibitors-Does It All Come Down to Na+?

Sodium-glucose co-transporter 2 inhibitors (SGLT2i) are emerging as a new treatment strategy for heart failure with reduced ejection fraction (HFrEF) and—depending on the wistfully awaited results of two clinical trials (DELIVER and EMPEROR-Preserved)—may be the first drug class to improve cardiovascular outcomes in patients suffering from heart failure with preserved ejection fraction (HFpEF). Proposed mechanisms of action of this class of drugs are diverse and include metabolic and hemodynamic effects as well as effects on inflammation, neurohumoral activation, and intracellular ion homeostasis. In this review we focus on the growing body of evidence for SGLT2i-mediated effects on cardiac intracellular Na⁺ as an upstream mechanism. Therefore, we will first give a short overview of physiological cardiomyocyte Na⁺ handling and its deterioration in heart failure. On this basis we discuss the salutary effects of SGLT2i on Na⁺ homeostasis by influencing NHE1 activity, late I_Na as well as CaMKII activity. Finally, we highlight the potential relevance of these effects for systolic and diastolic dysfunction as well as arrhythmogenesis.

Electrical Features of the Diabetic Myocardium. Arrhythmic and Cardiovascular Safety Considerations in Diabetes

Diabetes is a chronic metabolic disease characterized by hyperglycemia in the absence of treatment. Among the diabetes-associated complications, cardiovascular disease is the major cause of mortality and morbidity in diabetic patients. Diabetes causes a complex myocardial dysfunction, referred as diabetic cardiomyopathy, which even in the absence of other cardiac risk factors results in abnormal diastolic and systolic function. Besides mechanical abnormalities, altered electrical function is another major feature of the diabetic myocardium. Both type 1 and type 2 diabetic patients often show cardiac electrical remodeling, mainly a prolonged ventricular repolarization visible in the electrocardiogram as a lengthening of the QT interval duration. The underlying mechanisms at the cellular level involve alterations on the expression and activity of several cardiac ion channels and their associated regulatory proteins. Consequent changes in sodium, calcium and potassium currents collectively lead to a delay in repolarization that can increase the risk of developing life-threatening ventricular arrhythmias and sudden death. QT duration correlates strongly with the risk of developing torsade de pointes, a form of ventricular tachycardia that can degenerate into ventricular fibrillation. Therefore, QT prolongation is a qualitative marker of proarrhythmic risk, and analysis of ventricular repolarization is therefore required for the approval of new drugs. To that end, the Thorough QT/QTc analysis evaluates QT interval prolongation to assess potential proarrhythmic effects. In addition, since diabetic patients have a higher risk to die from cardiovascular causes than individuals without diabetes, cardiovascular safety of the new antidiabetic drugs must be carefully evaluated in type 2 diabetic patients. These cardiovascular outcome trials reveal that some glucose-lowering drugs actually reduce cardiovascular risk. The mechanism of cardioprotection might involve a reduction of the risk of developing arrhythmia.

Bisphenol S and bisphenol F are less disruptive to cardiac electrophysiology, as compared to bisphenol A

Bisphenol A (BPA) is a high-production volume chemical used to manufacture consumer and medical-grade plastic products. Due to its ubiquity, the general population can incur daily environmental exposure to BPA, while heightened exposure has been reported in intensive care patients and industrial workers. Due to health concerns, structural analogues are being explored as replacements for BPA. This study aimed to examine the direct effects of BPA on cardiac electrophysiology compared with recently developed alternatives, including BPS (bisphenol S) and BPF (bisphenol F). Whole-cell voltage-clamp recordings were performed on cell lines transfected to express the voltage-gated sodium channel (Nav1.5), L-type voltage-gated calcium channel (Cav1.2), or the rapidly activating delayed rectifier potassium channel (hERG). Cardiac electrophysiology parameters were measured using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) and intact, whole rat heart preparations. BPA was the most potent inhibitor of fast/peak (INa-P) and late (INa-L) sodium channel (IC50= 55.3, 23.6 µM, respectively), L-type calcium channel (IC50= 30.8 µM) and hERG channel current (IC50= 127 µM). Inhibitory effects on L-type calcium channels were supported by microelectrode array recordings, which revealed a shortening of the extracellular field potential (akin to QT interval). BPA and BPF exposures slowed atrioventricular (AV) conduction and increased AV node refractoriness in isolated rat heart preparations, in a dose-dependent manner (BPA: +9.2% 0.001 µM, +95.7% 100 µM; BPF: +20.7% 100 µM). BPS did not alter any of the cardiac electrophysiology parameters tested. Results of this study demonstrate that BPA and BPF exert an immediate inhibitory effect on cardiac ion channels, while BPS is markedly less potent. Additional studies are necessary to fully elucidate the safety profile of bisphenol analogues on the heart.

Arrhythmogenic and antiarrhythmic actions of late sustained sodium current in the adult human heart

Late sodium current (late INa) inhibition has been proposed to suppress the incidence of arrhythmias generated by pathological states or induced by drugs. However, the role of late INa in the human heart is still poorly understood. We therefore investigated the role of this conductance in arrhythmias using adult primary cardiomyocytes and tissues from donor hearts. Potentiation of late INa with ATX-II (anemonia sulcata toxin II) and E-4031 (selective blocker of the hERG channel) slowed the kinetics of action potential repolarization, impaired Ca2+ homeostasis, increased contractility, and increased the manifestation of arrhythmia markers. These effects could be reversed by late INa inhibitors, ranolazine and GS-967. We also report that atrial tissues from donor hearts affected by atrial fibrillation exhibit arrhythmia markers in the absence of drug treatment and inhibition of late INa with GS-967 leads to a significant reduction in arrhythmic behaviour. These findings reveal a critical role for the late INa in cardiac arrhythmias and suggest that inhibition of this conductance could provide an effective therapeutic strategy. Finally, this study highlights the utility of human ex-vivo heart models for advancing cardiac translational sciences.

Utility of Normalized TdP Score System in Drug Proarrhythmic Potential Assessment: A Blinded in vitro Study of CiPA Drugs

Drugs that prolong QT may cause torsade de pointes (TdP). However, translation of nonclinical assessment of QT prolongation or hERG channel, targeted by QT-prolonging drugs, into clinical TdP risk has been insufficient to date. In this blinded study, we confirmed the utility of a Normalized TdP Score System in predicting drug-induced TdP risks among 34 drugs, including 28 with low, intermediate, and high TdP risks under the Comprehensive In Vitro Proarrhythmia Assay (CiPA) initiative plus six compounds with names blinded to the investigators, using the rabbit ventricular wedge assay. Concentration-dependent TdP scores were determined by drug-induced changes in QT, T_p-e , and proarrhythmias. Disclosure of the names and testing concentrations was made after completion of the experiments and report to the sponsors. Drugs' normalized TdP scores were calculated thereafter based on their respective free clinical maximum concentration (C_max ). Drugs' normalized TdP scores were calculated and ranked for 33 drugs, excluding 1 investigational drug, and the TdP risks of the 28 CiPA drugs were correctly distinguished according to their respective categories of low, intermediate, and high TdP risks under the CiPA initiative. Accordingly, we are able to propose the cutoff values of the normalized TdP scores at 1 × C_max : ≤ 0, > 0 to < 0.65 and ≥ 0.65, respectively, for low, intermediate, and high risk. This blinded study supports utility of our Normalized TdP Score System in predicting drug-induced TdP risks in 33 drugs, including 28 used for characterization of other assays under the CiPA initiative. However, these results need to be replicated in other laboratories.

Targeting Cardiac Metabolic Pathways: A Role in Ischemic Management

Among the vast number of noncommunicable diseases encountered worldwide, cardiovascular diseases accounted for about 17.8 million deaths in 2017 and ischemic heart disease (IHD) remains the single-largest cause of death in countries across all income groups. Because conventional medications are not without shortcomings and patients still refractory to these medications, scientific investigation is ongoing to advance the management of IHD, and shows a great promise for better treatment modalities, but additional research can warrant improvement in terms of the quality of life of patients. Metabolic modulation is one promising strategy for the treatment of IHD, because alterations in energy metabolism are involved in progression of the disease. Therefore, the purpose of this review was to strengthen attention toward the use of metabolic modulators and to review the current level of knowledge on cardiac energy metabolic pathways.

Xanthine oxidase inhibitor allopurinol improves atrial electrical remodeling in diabetic rats by inhibiting CaMKII/NCX signaling

AIMS

Atrial fibrillation (AF) is a common arrhythmia which is associated with higher risk of stroke, heart failure and all-cause mortality. Abnormal Ca²⁺ handling in diabetes mellitus (DM) can cause delayed depolarization involved with increased NCX activity. Complicated mechanisms are involved in atrial remodeling, of which CaMKII may be a key node signal. Therefore, we intend to explore whether CaMKII activation induces atrial electrical remodeling by regulating NCX expression in this study.

MAIN METHODS

Adult male SD rats were used to establish a diabetic rat model, divided into three groups: the control group, DM group and allopurinol group. Hemodynamic and ECG indicators were recorded, after which electrophysiological studies were conducted. The protein expression of CaMKII, p-CaMKII, XO, MnSOD and NCX was measured by Western blot and immunohistochemistry. H&E and Masson staining were applied for observing myocardial fibrosis. HL-1 cells were cultured for the measurement of ROS generation.

KEY FINDINGS

The arrangement of atrial myocytes was disordered and the collagen volume fraction of the atrium tissue was elevated in the DM group compared with the control group, and improved by allopurinol. Higher incidence of inducible AF, reduced conduction velocity and higher conduction inhomogeneity were observed in diabetic rats. These electrophysiological abnormalities were accompanied by higher oxidative stress and protein expression of p-CaMKII and NCX. Allopurinol prevented the development of these abnormal changes.

SIGNIFICANCE

Allopurinol can improve atrial electrical remodeling by inhibiting CaMKII activity and protein expression of NCX. These data indicate xanthine oxidase inhibition can reduce oxidative stress and ameliorate atrial electrical remodeling.