Metformin therapy confers cardioprotection against the remodeling of gap junction in tachycardia-induced atrial fibrillation dog model

Effects of Zinc Combined with Metformin on Zinc Homeostasis, Blood-Epididymal Barrier, and Epididymal Absorption in Male Diabetic Mice

Diabetes increases the likelihood of germ cell damage, hypogonadism, and male infertility. Diabetes leads to lower zinc (Zn) levels, an important micronutrient for maintaining male fertility, and zinc deficiency can lead to decreased male fertility through multiple mechanisms. The aim of this study was to investigate the effect of combined metformin and zinc administration on epididymis in diabetic mice; 10 of 50 male mice were randomly selected as the control group (group C), and the remaining 40 mice were randomly divided into untreated diabetes group (group D), diabetes + zinc group (group Z), diabetes + metformin group (group M), and diabetes + metformin + zinc group (group ZM) with 10 mice each. Diabetic mice in group Z received oral zinc (10 mg/kg) once daily for 4 weeks; diabetic mice in group M received oral metformin (200 mg/kg) once daily for 4 weeks; diabetic mice in group ZM received oral metformin and zinc once daily for 4 weeks; and groups C and D received the same amount of sterile water by gavage. Overnight fasted mice were sacrificed, and blood samples, mouse epididymides, and sperm were collected for further experiments. In group D, fasting blood glucose and insulin resistance index increased significantly, semen quality, serum insulin, and testosterone decreased, and epididymal structure was disordered. In group D, epididymal tissue zinc, free zinc ions in the caput, and cauda of epididymis and zinc transporter (ZnT2) decreased significantly, while ZIP12, metallothionein (MT), and metal transcription factor (MTF1) increased significantly. In addition, the expressions of blood-epididymal barrier (BEB)-related molecules (including ZO-1 β-catenin and N-cadherin) and aquaporins (AQPs, including AQP3, AQP9, and AQP11) in the epididymis of mice in group D were significantly decreased. In addition, compared with groups D, Z, and M, in the ZM group, the expression of BEB-related molecules (including ZO-1, β-catenin, and N-cadherin) and aquaporins (AQP3, AQP9, and AQP11) in epididymis tissue were significantly increased, and sperm motility and serum testosterone were significantly increased. It was concluded that male diabetic mice have a disturbed epididymal structure and decreased semen quality by causing an imbalance in epididymal zinc homeostasis, BEB, and impaired absorptive function. The combination of zinc and metformin is an effective and safe alternative treatment and provides additional benefits over metformin alone.

Gap junctions in polycystic ovary syndrome: Implications for follicular arrest

Gap junctions are specialized intercellular conduits that provide a direct pathway between neighboring cells, which are involved in numerous physiological processes, such as cellular differentiation, cell growth, and metabolic coordination. The effect of gap junctional hemichannels in folliculogenesis is particularly obvious, and the down-regulation of connexins is related to abnormal follicle growth. Polycystic ovary syndrome (PCOS) is a ubiquitous endocrine disorder of the reproductive system, affecting the fertility of adult women due to anovulation. Exciting evidence shows that gap junction is involved in the pathological process related to PCOS and affects the development of follicles in women with PCOS. In this review, we examine the expression of connexins in follicular cells of PCOS and figure out whether such communication could have consequences for PCOS women. While along with results from clinical and related animal studies, we summarize the mechanism of connexins involved in the pathogenesis of PCOS.

Metformin reduces new-onset atrial fibrillation risk rather than atrial fibrillation burden in type 2 diabetes patients: A case-control study

Background

The effects of metformin on atrial fibrillation (AF) in type 2 diabetes patients remain unclear. We aimed to explore the effects of metformin on AF, including new-onset AF and AF burden, in type 2 diabetes patients with pacemakers.

Methods and results

This retrospective study included a total of 227 patients. Based on the presence of paroxysmal AF, the patients were divided into a paroxysmal AF group (n = 80) and a non-AF group (n = 147). In the non-AF group, a significant association was observed between metformin use and a lower risk of new-onset AF in multivariable Cox hazards models (hazard ratio [HR]: 0.36; 95 % confidence interval [CI]: 0.14-0.91; p = 0.0311*) when adjusted for age, sex, body mass index (BMI), drinking, smoking, left atrial dimension, creatinine, complications, and drugs. In the paroxysmal AF group, univariable analysis indicated no association between the AF burden and metformin use (p = 0.817). Furthermore, when adjusted for metformin use, age, sex, BMI, drinking, smoking, cardiovascular disease, myocardial infarction, heart failure, stroke, and ejection fraction in multivariable Cox hazards models, we found a lower proportion of major adverse cardiovascular events (MACEs) both in the total (HR: 0.28; 95 % CI: 0.1-0.82; p = 0.0202*) and the non-AF group (HR: 0.19; 95 % CI: 0.05-0.79; p = 0.0223*) compared to that in the AF group (HR: 0.31; 95 % CI: 0.02-4.41; p = 0.3879).

Conclusion

In type 2 diabetes patients with pacemakers, metformin reduced the probability of new-onset AF instead of addressing the AF burden. Furthermore, metformin therapy decreased the incidence of MACEs in type 2 diabetes patients without AF.

GLP-1 receptor agonists and myocardial metabolism in atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Many medical conditions, including hypertension, diabetes, obesity, sleep apnea, and heart failure (HF), increase the risk for AF. Cardiomyocytes have unique metabolic characteristics to maintain adenosine triphosphate production. Significant changes occur in myocardial metabolism in AF. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been used to control blood glucose fluctuations and weight in the treatment of type 2 diabetes mellitus (T2DM) and obesity. GLP-1RAs have also been shown to reduce oxidative stress, inflammation, autonomic nervous system modulation, and mitochondrial function. This article reviews the changes in metabolic characteristics in cardiomyocytes in AF. Although the clinical trial outcomes are unsatisfactory, the findings demonstrate that GLP-1 RAs can improve myocardial metabolism in the presence of various risk factors, lowering the incidence of AF.

Antiarrhythmic effects of metformin

Atrial fibrillation/flutter (AF) is a major public health problem and is associated with stroke, heart failure, dementia, and death. It is estimated that 20%-30% of Americans will develop AF at some point in their life. Current medications to prevent AF have limited efficacy and significant adverse effects. Newer and safer therapies to prevent AF are needed. Ventricular arrhythmias are less prevalent than AF but may have significant consequences including sudden cardiac death. Metformin is the most prescribed, first-line medication for treatment of diabetes mellitus (DM). It decreases hepatic glucose production but also reduces inflammation and oxidative stress. Experimental studies have shown that metformin improves metabolic, electrical, and histologic risk factors associated with AF and ventricular arrhythmias. Furthermore, in large clinical observational studies, metformin has been associated with a reduced risk of AF in people with DM. These data suggest that metformin may have antiarrhythmic properties and may be a candidate to be repurposed as a medication to prevent cardiac arrhythmias. In this article, we review the clinical observational and experimental evidence for the association between metformin and cardiac arrhythmias. We also discuss the potential antiarrhythmic mechanisms underlying this association. Repurposing a well-tolerated, safe, and inexpensive medication to prevent cardiac arrhythmias has significant positive public health implications.

Protective effects of metformin in various cardiovascular diseases: Clinical evidence and AMPK-dependent mechanisms

Metformin, a well-known AMPK agonist, has been widely used as the first-line drug for treating type 2 diabetes. There had been a significant concern regarding the use of metformin in people with cardiovascular diseases (CVDs) due to its potential lactic acidosis side effect. Currently growing clinical and preclinical evidence indicates that metformin can lower the incidence of cardiovascular events in diabetic patients or even non-diabetic patients beyond its hypoglycaemic effects. The underlying mechanisms of cardiovascular benefits of metformin largely involve the cellular energy sensor, AMPK, of which activation corrects endothelial dysfunction, reduces oxidative stress and improves inflammatory response. In this minireview, we summarized the clinical evidence of metformin benefits in several widely studied cardiovascular diseases, such as atherosclerosis, ischaemic/reperfusion injury and arrhythmia, both in patients with or without diabetes. Meanwhile, we highlighted the potential AMPK-dependent mechanisms in in vitro and/or in vivo models.

Epicardial fat and atrial fibrillation: the perils of atrial failure

Obesity is a heterogeneous condition, characterized by different phenotypes and for which the classical assessment with body mass index may underestimate the real impact on cardiovascular (CV) disease burden. An epidemiological link between obesity and atrial fibrillation (AF) has been clearly demonstrated and becomes even more tight when ectopic (i.e. epicardial) fat deposition is considered. Due to anatomical and functional features, a tight paracrine cross-talk exists between epicardial adipose tissue (EAT) and myocardium, including the left atrium (LA). Alongside-and even without-mechanical atrial stretch, the dysfunctional EAT may determine a pro-inflammatory environment in the surrounding myocardial tissue. This evidence has provided a new intriguing pathophysiological link with AF, which in turn is no longer considered a single entity but rather the final stage of atrial remodelling. This maladaptive process would indeed include structural, electric, and autonomic derangement that ultimately leads to overt disease. Here, we update how dysfunctional EAT would orchestrate LA remodelling. Maladaptive changes sustained by dysfunctional EAT are driven by a pro-inflammatory and pro-fibrotic secretome that alters the sinoatrial microenvironment. Structural (e.g. fibro-fatty infiltration) and cellular (e.g. mitochondrial uncoupling, sarcoplasmic reticulum fragmentation, and cellular protein quantity/localization) changes then determine an electrophysiological remodelling that also involves the autonomic nervous system. Finally, we summarize how EAT dysfunction may fit with the standard guidelines for AF. Lastly, we focus on the potential benefit of weight loss and different classes of CV drugs on EAT dysfunction, LA remodelling, and ultimately AF onset and recurrence.

Metformin Reduces Potassium Currents and Prolongs Repolarization in Non-Diabetic Heart

Metformin is the first choice drug for the treatment of type 2 diabetes due to positive results in reducing hyperglycaemia and insulin resistance. However, diabetic patients have higher risk of ventricular arrhythmia and sudden cardiac death, and metformin failed to reduce ventricular arrhythmia in clinical trials. In order to explore the mechanisms responsible for the lack of protective effect, we investigated in vivo the effect of metformin on cardiac electrical activity in non-diabetic rats; and in vitro in isolated ventricular myocytes, HEK293 cells expressing the hERG channel and human induced pluripotent stem cells derived cardiomyocytes (hIPS-CMs). Surface electrocardiograms showed that long-term metformin treatment (7 weeks) at therapeutic doses prolonged cardiac repolarization, reflected as QT and QTc interval duration, and increased ventricular arrhythmia during the caffeine/dobutamine challenge. Patch-clamp recordings in ventricular myocytes isolated from treated animals showed that the cellular mechanism is a reduction in the cardiac transient outward potassium current (Ito). In vitro, incubation with metformin for 24 h also reduced Ito, prolonged action potential duration, and increased spontaneous contractions in ventricular myocytes isolated from control rats. Metformin incubation also reduced IhERG in HEK293 cells. Finally, metformin incubation prolonged action potential duration at 30% and 90% of repolarization in hIPS-CMs, which is compatible with the reduction of Ito and IhERG. Our results show that metformin directly modifies the electrical behavior of the normal heart. The mechanism consists in the inhibition of repolarizing currents and the subsequent decrease in repolarization capacity, which prolongs AP and QTc duration.

Piezo1 Participated in Decreased L-Type Calcium Current Induced by High Hydrostatic Pressure via. CaM/Src/Pitx2 Activation in Atrial Myocytes

Hypertension is a major cardiovascular risk factor for atrial fibrillation (AF) worldwide. However, the role of mechanical stress caused by hypertension on downregulating the L-type calcium current (I_Ca,L), which is vital for AF occurrence, remains unclear. Therefore, the aim of the present study was to investigate the role of Piezo1, a mechanically activated ion channel, in the decrease of I_Ca,L in response to high hydrostatic pressure (HHP, one of the principal mechanical stresses) at 40 mmHg, and to elucidate the underlying pathways. Experiments were conducted using left atrial appendages from patients with AF, spontaneously hypertensive rats (SHRs) treated with valsartan (Val) at 30 mg/kg/day and atrium-derived HL-1 cells exposed to HHP. The protein expression levels of Piezo1, Calmodulin (CaM), and Src increased, while that of the L-type calcium channel a1c subunit protein (Cav1.2) decreased in the left atrial tissue of AF patients and SHRs. SHRs were more vulnerable to AF, with decreased I_Ca,L and shortened action potential duration, which were ameliorated by Val treatment. Validation of these results in HL-1 cells in the context of HHP also demonstrated that Piezo1 is required for the decrease of I_Ca,L by regulating Ca²⁺ transient and activating CaM/Src pathway to increase the expression of paired like homeodomain-2 (Pitx2) in atrial myocytes. Together, these data demonstrate that HHP stimulation increases AF susceptibility through Piezo1 activation, which is required for the decrease of I_Ca,Lvia. the CaM/Src/Pitx2 pathway in atrial myocytes.

Molecular Insights in Atrial Fibrillation Pathogenesis and Therapeutics: A Narrative Review

The prevalence of atrial fibrillation (AF) is bound to increase globally in the following years, affecting the quality of life of millions of people, increasing mortality and morbidity, and beleaguering health care systems. Increasingly effective therapeutic options against AF are the constantly evolving electroanatomic substrate mapping systems of the left atrium (LA) and ablation catheter technologies. Yet, a prerequisite for better long-term success rates is the understanding of AF pathogenesis and maintenance. LA electrical and anatomical remodeling remains in the epicenter of current research for novel diagnostic and treatment modalities. On a molecular level, electrical remodeling lies on impaired calcium handling, enhanced inwardly rectifying potassium currents, and gap junction perturbations. In addition, a wide array of profibrotic stimuli activates fibroblast to an increased extracellular matrix turnover via various intermediaries. Concomitant dysregulation of the autonomic nervous system and the humoral function of increased epicardial adipose tissue (EAT) are established mediators in the pathophysiology of AF. Local atrial lymphomononuclear cells infiltrate and increased inflammasome activity accelerate and perpetuate arrhythmia substrate. Finally, impaired intracellular protein metabolism, excessive oxidative stress, and mitochondrial dysfunction deplete atrial cardiomyocyte ATP and promote arrhythmogenesis. These overlapping cellular and molecular alterations hinder us from distinguishing the cause from the effect in AF pathogenesis. Yet, a plethora of therapeutic modalities target these molecular perturbations and hold promise in combating the AF burden. Namely, atrial selective ion channel inhibitors, AF gene therapy, anti-fibrotic agents, AF drug repurposing, immunomodulators, and indirect cardiac neuromodulation are discussed here.

Mitochondrial Dysfunction in Atrial Fibrillation-Mechanisms and Pharmacological Interventions

Despite the enormous progress in the treatment of atrial fibrillation, mainly with the use of invasive techniques, many questions remain unanswered regarding the pathomechanism of the arrhythmia and its prevention methods. The development of atrial fibrillation requires functional changes in the myocardium that result from disturbed ionic fluxes and altered electrophysiology of the cardiomyocyte. Electrical instability and electrical remodeling underlying the arrhythmia may result from a cellular energy deficit and oxidative stress, which are caused by mitochondrial dysfunction. The significance of mitochondrial dysfunction in the pathogenesis of atrial fibrillation remains not fully elucidated; however, it is emphasized by the reduction of atrial fibrillation burden after therapeutic interventions improving the mitochondrial welfare. This review summarizes the mechanisms of mitochondrial dysfunction related to atrial fibrillation and current pharmacological treatment options targeting mitochondria to prevent or improve the outcome of atrial fibrillation.

Effects of metformin on atrial and ventricular arrhythmias: evidence from cell to patient

Metformin has been shown to have various cardiovascular benefits beyond its antihyperglycemic effects, including a reduction in stroke, heart failure, myocardial infarction, cardiovascular death, and all-cause mortality. However, the roles of metformin in cardiac arrhythmias are still unclear. It has been shown that metformin was associated with decreased incidence of atrial fibrillation in diabetic patients with and without myocardial infarction. This could be due to the effects of metformin on preventing the structural and electrical remodeling of left atrium via attenuating intracellular reactive oxygen species, activating 5′ adenosine monophosphate-activated protein kinase, improving calcium homeostasis, attenuating inflammation, increasing connexin-43 gap junction expression, and restoring small conductance calcium-activated potassium channels current. For ventricular arrhythmias, in vivo reports demonstrated that activation of 5′ adenosine monophosphate-activated protein kinase and phosphorylated connexin-43 by metformin played a key role in ischemic ventricular arrhythmias reduction. However, metformin failed to show anti-ventricular arrhythmia benefits in clinical trials. In this review, in vitro and in vivo reports regarding the effects of metformin on both atrial arrhythmias and ventricular arrhythmias are comprehensively summarized and presented. Consistent and controversial findings from clinical trials are also summarized and discussed. Due to limited numbers of reports, further studies are needed to elucidate the mechanisms and effects of metformin on cardiac arrhythmias. Furthermore, randomized controlled trials are needed to clarify effects of metformin on cardiac arrhythmias in human.

New methodological approaches to atrial fibrillation drug discovery

INTRODUCTION

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice and rhythm control using pharmacological agents is required in selected patients. Nonetheless, current medication is only modestly efficacious and associated with significant cardiovascular and systemic side effects. More efficacious and safe drugs are required to restore and maintain sinus rhythm in patients with AF.

AREAS COVERED

In this review, several potential drug targets are discussed including trans-membrane ion channels, intracellular calcium signaling, gap junction signaling, atrial inflammation and fibrosis, and the autonomic nervous system. New tools and methodologies for AF drug development are also reviewed including gene therapy, genome-guided therapy, stem cell technologies, tissue engineering, and optogenetics.

EXPERT OPINION

In recent decades, there has been an increased understanding of the underlying pathogenesis of AF. As a result, there is a gradual paradigm shift from focusing only on trans-membrane ion channel inhibition to developing therapeutic agents that target other underlying arrhythmogenic mechanisms. Gene therapy and genome-guided therapy are emerging as novel treatments for AF with some success in proof-of-concept studies. Recent advances in stem cell technology, tissue engineering, and optogenetics may allow more effective in-vitro drug screening than conventional methodologies.