Pioglitazone attenuates atrial remodeling and vulnerability to atrial fibrillation in alloxan-induced diabetic rabbits

The Many Facets of PPAR-γ Agonism in Obesity and Associated Comorbidities: Benefits, Risks, Challenges, and Future Directions

PURPOSE OF REVIEW

Obesity is strongly associated with cardiometabolic disorders and certain malignancies, emphasizing the key role of adipose tissue in human health. While incretin mimetics have shown effectiveness in glycemic control and weight loss, a holistic strategy for combating obesity and associated comorbidities remains elusive. This review explores peroxisome proliferator-activated receptor gamma (PPAR-γ) agonism as a potential therapeutic approach, highlighting its benefits, addressing its limitations, and outlining future directions for developing more effective treatment strategies.

RECENT FINDINGS

Both natural and synthetic PPAR-γ agonists hold significant therapeutic potential as insulin sensitizers, while also demonstrating anti-inflammatory properties and playing a critical role in regulating lipid metabolism. However, the clinical use of natural agonists is limited by poor bioavailability, while synthetic agents like thiazolidinediones are associated with adverse effects, including fluid retention, weight gain, and bone loss. Current research is focused on developing modified, tissue-specific PPAR-γ agonists, as well as dual PPAR-α/PPAR-γ agonists, with improved safety profiles to mitigate these side effects. Nanotechnology-based drug delivery systems also hold promise for enhancing bioavailability and therapeutic efficacy. Furthermore, the transformative potential of machine learning and artificial intelligence offers opportunities to accelerate advancements in this field. PPAR-γ agonists exhibit significant potential in addressing metabolic syndrome, cardiovascular disease, and cancer. However, their clinical use is restricted by safety concerns and suboptimal pharmacokinetics. Innovations in modified PPAR-γ agonists, nanotechnology-based delivery systems, and computational tools hold promise for creating safer and more effective therapeutic options for obesity and its associated disorders.

Mitochondrial Dysfunction in Atrial Fibrillation: The Need for a Strong Pharmacological Approach

Despite great progress in treating atrial fibrillation (AF), especially with the development of increasingly effective invasive techniques for AF ablation, many unanswered questions remain regarding the pathogenic mechanism of the arrhythmia and its prevention methods. The development of AF is based on anatomical and functional alterations in the cardiomyocyte resulting from altered ionic fluxes and cardiomyocyte electrophysiology. Electric instability and electrical remodeling underlying the arrhythmia may result from oxidative stress, also caused by possible mitochondrial dysfunction. The role of mitochondrial dysfunction in the pathogenesis of AF is not yet fully elucidated; however, the reduction in AF burden after therapeutic interventions that improve mitochondrial fitness tends to support this concept. This selected review aims to summarize the mechanisms of mitochondrial dysfunction related to AF and the current pharmacological treatment options that target mitochondria to prevent or improve the outcome of AF.

Metabolic remodelling in atrial fibrillation: manifestations, mechanisms and clinical implications

Atrial fibrillation (AF) is a continually growing health-care burden that often presents together with metabolic disorders, including diabetes mellitus and obesity. Current treatments often fall short of preventing AF and its adverse outcomes. Accumulating evidence suggests that metabolic disturbances can promote the development of AF through structural and electrophysiological remodelling, but the underlying mechanisms that predispose an individual to AF are aetiology-dependent, thus emphasizing the need for tailored therapeutic strategies to treat AF that target an individual's metabolic profile. AF itself can induce changes in glucose, lipid and ketone metabolism, mitochondrial function and myofibrillar energetics (as part of a process referred to as 'metabolic remodelling'), which can all contribute to atrial dysfunction. In this Review, we discuss our current understanding of AF in the setting of metabolic disorders, as well as changes in atrial metabolism that are relevant to the development of AF. We also describe the potential of available and emerging treatment strategies to target metabolic remodelling in the setting of AF and highlight key questions and challenges that need to be addressed to improve outcomes in these patients.

Effect of different hypoglycemic drugs and insulin on the risk of new-onset atrial fibrillation in people with diabetes: a network meta-analysis

OBJECTIVE

Diabetes is considered a significant risk factor for the development of atrial fibrillation/flutter (AF/AFL). However, there is still insufficient evidence to determine the varying effects of different hypoglycemic drugs (HDs) on the incidence of new-onset AF/AFL in diabetic patients. To address this gap, we conducted a network meta-analysis to investigate whether various HDs have different effects on the risk of new-onset AF/AFL compared with insulin.

METHOD

We conducted a comprehensive search in PubMed, EMBASE, Cochrane Library, and Web of Science to identify all clinical trials investigating the association between various HDs or insulin and incident AF/AFL up until April 1, 2024. Bayesian random-effects model was used for network meta-analysis, and the results were expressed as relative risk (RR) and 95% confidence interval (CI).

RESULT

After searching 2070 articles, a total of 12 studies (2,349,683 patients) were included in the network meta-analysis. The treatment regimen comprised insulin and 8 HDs hypoglycemic drugs, which are sodium-dependent glucose transporters 2 inhibitor (SGLT2i), glucagon-like peptide 1 receptor agonist (GLP-1RA), dipeptidyl peptidase 4 inhibitors (DPP4i), metformin (Met), sulfonylureas (SU), non-sulfonylureas (nSU), thiazolidinedione (TZD) and α-glycosidase inhibitors (AGI). The use of SGLT2i [RR 0.23, 95%CI (0.11, 0.49)], GLP-1RA [RR 0.28, 95%CI (0.13, 0.57)], and DPP4i [RR 0.34, 95%CI (0.17, 0.67)] demonstrated significant efficacy in reducing the incidence of new-onset AF/AFL when compared to insulin. When HDs were compared in pairs, SGLT2i is more effective than Met [RR 0.35, 95% CI (0.19, 0.62)], SU (RR 0.27, 95% CI (0.14, 0.51)], nSU [RR 0.28, 95% CI (0.08, 0.95)], TZD [RR 0.34, 95% CI (0.17, 0.7)], GLP-1RA is more effective Met [RR 0.42, 95% CI (0.25, 0.71)], SU (RR 0.33, 95% CI (0.18, 0.6)], TZD [RR 0.41, 95% CI (0.21, 0.82)], while Met[RR 1.98, 95% CI (1.23, 3.23)], SU [RR 2.54, 95% CI (1.46, 4.43)], TZD [RR 2.01, 95% CI (1.05, 3.79)] was not as effective as DPP4i.

CONCLUSION

SGLT-2i, GLP-1RA, and DPP4i showed a superior efficacy in reducing the risk of new-onset AF/AFL compared to insulin therapy.

Diabetes status, genetic susceptibility, and incident arrhythmias: A prospective cohort study of 457,151 participants

AIMS

The association of diabetes onset age and duration with incident arrhythmias remains unclear. This study evaluates the association of diabetes onset age and duration with incident arrhythmias and assesses modifications by the genetic predisposition to atrial fibrillation (AF).

METHODS

We included 457,151 participants from the UK Biobank study. Multivariable Cox regression models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) were used for the association between diabetes status, genetic predisposition, and risk of incident arrhythmias. The polygenic risk score (PRS) for AF comprised 142 single-nucleotide variants.

RESULTS

Over 12 years of follow-up, we documented 23,518 AF, 9079 bradyarrhythmia, 9280 conduction system diseases, 3358 supraventricular arrhythmias, and 3095 ventricular arrhythmias. Compared with non-diabetes, the risks of AF increased by 19%, 25%, and 36% for those with diabetes durations <5, 5-9, and ≥10 years, respectively. After multivariate adjustment, with the increase in diabetes onset age, the HRs of outcomes were gradually attenuated. The multivariable-adjusted HRs (95% CI) of diabetes for AF were 1.46 (1.24-1.71) in early middle age (<55 years), 1.21 (1.12-1.30) in late middle age (55-64 years), and 1.15 (1.06-1.24) in the elderly population (≥65 years). A significant interaction between diabetes status and AF-PRS for incident AF was observed (P for interaction <0.001). The same trends were observed for the other arrhythmias.

CONCLUSIONS

Diabetes was associated with higher risks of incident arrhythmias, and younger age at onset of diabetes was significantly associated with higher risk of subsequent arrhythmias.

Adipose Triglyceride Lipase Deficiency Aggravates Angiotensin II-Induced Atrial Fibrillation by Reducing Peroxisome Proliferator-Activated Receptor α Activation in Mice

Atrial fibrillation (AF) is a main risk factor for cerebrovascular diseases but lacks precision therapy. Adipose triglyceride lipase (ATGL) is a key enzyme involved in the intracellular degradation of triacylglycerol and plays an important role in lipid and energy metabolism. However, the role of ATGL in the regulation of AF remains unclear. In this study, AF was induced by infusion of angiotensin II (Ang II, 2000 ng/kg/min) for 3 weeks in male ATGL knockout (KO) mice and age-matched C57BL/6 wild-type mice. The atrial volume was measured by echocardiography. Atrial fibrosis, inflammatory cells, and superoxide production were detected by histologic examinations. The results showed that ATGL expression was significantly downregulated in the atrial tissue of the Ang II-infused mice. Moreover, Ang II-induced increase in the inducibility and duration of AF, atrial dilation, fibrosis, inflammation, and oxidative stress in wild-type mice were markedly accelerated in ATGL KO mice; however, these effects were dramatically reversed in the ATGL KO mice administered with peroxisome proliferator-activated receptor (PPAR)-α agonist clofibric acid. Mechanistically, Ang II downregulated ATGL expression and inhibited PPAR-α activity, activated multiple signaling pathways (inhibiting kappa B kinase α/β-nuclear factor-κB, nicotinamide adenine dinucleotide phosphate oxidase, and transforming growth factor-β1/SMAD2/3) and reducing Kv1.5, Cx40, and Cx43 expression, thereby contributing to atrial structural and electrical remodeling and subsequent AF. In summary, our results indicate that ATGL KO enhances AF inducibility, possibly through inhibiting PPAR-α activation and suggest that activating ATGL might be a new therapeutic option for treating hypertensive AF.

Adipogenic Signaling Promotes Arrhythmia Substrates before Structural Abnormalities in TMEM43 ARVC

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic disorder of desmosomal and structural proteins that is characterized by fibro-fatty infiltrate in the ventricles and fatal arrhythmia that can occur early before significant structural abnormalities. Most ARVC mutations interfere with β-catenin-dependent transcription that enhances adipogenesis; however, the mechanistic pathway to arrhythmogenesis is not clear. We hypothesized that adipogenic conditions play an important role in the formation of arrhythmia substrates in ARVC. Cardiac myocyte monolayers co-cultured for 2-4 days with mesenchymal stem cells (MSC) were derived from human-induced pluripotent stem cells with the ARVC5 TMEM43 p.Ser358Leu mutation. The TMEM43 mutation in myocyte co-cultures alone had no significant effect on impulse conduction velocity (CV) or APD. In contrast, when co-cultures were exposed to pro-adipogenic factors for 2-4 days, CV and APD were significantly reduced compared to controls by 49% and 31%, respectively without evidence of adipogenesis. Additionally, these arrhythmia substrates coincided with a significant reduction in IGF-1 expression in MSCs and were mitigated by IGF-1 treatment. These findings suggest that the onset of enhanced adipogenic signaling may be a mechanism of early arrhythmogenesis, which could lead to personalized treatment for arrhythmias associated with TMEM43 and other ARVC mutations.

Risk stratification of cardiac arrhythmias and sudden cardiac death in type 2 diabetes mellitus patients receiving insulin therapy: A population-based cohort study

INTRODUCTION

Metabolic abnormalities may exacerbate the risk of adverse outcomes in patients with type 2 diabetes mellitus. The present study aims to assess the predictive value of HbA1c and lipid variability on the risks of sudden cardiac death (SCD) and incident atrial fibrillation (AF).

METHODS

The retrospective observational study consists of type 2 diabetic patients prescribed with insulin, who went to publicly funded clinics and hospitals in Hong Kong between January 1, 2009 and December 31, 2009. Variability in total cholesterol, low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol (HDL-C), triglyceride, and HbA1c were assessed through their SD and coefficient of variation. The primary outcomes were incident (1) ventricular tachycardia/ventricular fibrillation, actual or aborted SCD and (2) AF.

RESULTS

A total of 23 329 patients (mean ± SD age: 64 ± 14 years old; 51% male; mean HbA1c 8.6 ± 1.3%) were included. On multivariable analysis, HbA1c, total cholesterol, LDL-C and triglyceride variability were found to be predictors of SCD (p < .05).

CONCLUSION

HbA1c and lipid variability were predictive of SCD. Therefore, poor glucose control and variability in lipid parameters in diabetic patients are associated with aborted or actual SCD. These observations suggest the need to re-evaluate the extent of glycemic control required for outcome optimization.

Pioglitazone Inhibits Diabetes-Induced Atrial Mitochondrial Oxidative Stress and Improves Mitochondrial Biogenesis, Dynamics, and Function Through the PPAR-γ/PGC-1α Signaling Pathway

Background: Oxidative stress contributes to adverse atrial remodeling in diabetes mellitus. This remodeling can be prevented by the PPAR-γ agonist pioglitazone via its antioxidant and anti-inflammatory effects. In this study, we examined the molecular mechanisms underlying the protective effects of pioglitazone on atrial remodeling in a rabbit model of diabetes. Methods: Rabbits were randomly divided into control, diabetic, and pioglitazone-treated diabetic groups. Echocardiographic, hemodynamic, and electrophysiological parameters were measured. Serum PPAR-γ levels, serum and tissue oxidative stress and inflammatory markers, mitochondrial morphology, reactive oxygen species (ROS) production rate, respiratory function, and mitochondrial membrane potential (MMP) levels were measured. Protein expression of the pro-fibrotic marker TGF-β1, the PPAR-γ coactivator-1α (PGC-1α), and the mitochondrial proteins (biogenesis-, fusion-, and fission-related proteins) was measured. HL-1 cells were transfected with PGC-1α small interfering RNA (siRNA) to determine the underlying mechanisms of pioglitazone improvement of mitochondrial function under oxidative stress. Results: The diabetic group demonstrated a larger left atrial diameter and fibrosis area than the controls, which were associated with a higher incidence of inducible atrial fibrillation (AF). The lower serum PPAR-γ level was associated with lower PGC-1α and higher NF-κB and TGF-β1 expression. Lower mitochondrial biogenesis (PGC-1α, NRF1, and TFAM)-, fusion (Opa1 and Mfn1)-, and fission (Drp1)-related proteins were detected. Mitochondrial swelling, higher mitochondrial ROS, lower respiratory control rate, and lower MMP were observed. The pioglitazone group showed a reversal of structural remodeling and a lower incidence of inducible AF, which were associated with higher PPAR-γ and PGC-1α. The pioglitazone group had lower NF-κB and TGF-β1 expression levels, whereas biogenesis-, fusion-, and fission-related protein expression was higher. Further, mitochondrial structure and function were improved. In HL-1 cells, PGC-1α siRNA transfection blunted the effect of pioglitazone on Mn-SOD protein expression and MMP collapse in H2O2-treated cells. Conclusion: Diabetes mellitus induces adverse atrial structural, electrophysiological remodeling, and mitochondrial damage and dysfunction. Pioglitazone prevented these abnormalities through the PPAR-γ/PGC-1α pathway.

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.

Rethinking pioglitazone as a cardioprotective agent: a new perspective on an overlooked drug

Since 1985, the thiazolidinedione pioglitazone has been widely used as an insulin sensitizer drug for type 2 diabetes mellitus (T2DM). Although fluid retention was early recognized as a safety concern, data from clinical trials have not provided conclusive evidence for a benefit or a harm on cardiac function, leaving the question unanswered. We reviewed the available evidence encompassing both in vitro and in vivo studies in tissues, isolated organs, animals and humans, including the evidence generated by major clinical trials. Despite the increased risk of hospitalization for heart failure due to fluid retention, pioglitazone is consistently associated with reduced risk of myocardial infarction and ischemic stroke both in primary and secondary prevention, without any proven direct harm on the myocardium. Moreover, it reduces atherosclerosis progression, in-stent restenosis after coronary stent implantation, progression rate from persistent to permanent atrial fibrillation, and reablation rate in diabetic patients with paroxysmal atrial fibrillation after catheter ablation. In fact, human and animal studies consistently report direct beneficial effects on cardiomyocytes electrophysiology, energetic metabolism, ischemia–reperfusion injury, cardiac remodeling, neurohormonal activation, pulmonary circulation and biventricular systo-diastolic functions. The mechanisms involved may rely either on anti-remodeling properties (endothelium protective, inflammation-modulating, anti-proliferative and anti-fibrotic properties) and/or on metabolic (adipose tissue metabolism, increased HDL cholesterol) and neurohormonal (renin–angiotensin–aldosterone system, sympathetic nervous system, and adiponectin) modulation of the cardiovascular system. With appropriate prescription and titration, pioglitazone remains a useful tool in the arsenal of the clinical diabetologist.

Glycemic and lipid variability for predicting complications and mortality in diabetes mellitus using machine learning

INTRODUCTION

Recent studies have reported that HbA1c and lipid variability is useful for risk stratification in diabetes mellitus. The present study evaluated the predictive value of the baseline, subsequent mean of at least three measurements and variability of HbA1c and lipids for adverse outcomes.

METHODS

This retrospective cohort study consists of type 1 and type 2 diabetic patients who were prescribed insulin at outpatient clinics of Hong Kong public hospitals, from 1st January to 31st December 2009. Standard deviation (SD) and coefficient of variation were used to measure the variability of HbA1c, total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglyceride. The primary outcome is all-cause mortality. Secondary outcomes were diabetes-related complications.

RESULT

The study consists of 25,186 patients (mean age = 63.0, interquartile range [IQR] of age = 15.1 years, male = 50%). HbA1c and lipid value and variability were significant predictors of all-cause mortality. Higher HbA1c and lipid variability measures were associated with increased risks of neurological, ophthalmological and renal complications, as well as incident dementia, osteoporosis, peripheral vascular disease, ischemic heart disease, atrial fibrillation and heart failure (p <  0.05). Significant association was found between hypoglycemic frequency (p <  0.0001), HbA1c (p <  0.0001) and lipid variability against baseline neutrophil-lymphocyte ratio (NLR).

CONCLUSION

Raised variability in HbA1c and lipid parameters are associated with an elevated risk in both diabetic complications and all-cause mortality. The association between hypoglycemic frequency, baseline NLR, and both HbA1c and lipid variability implicate a role for inflammation in mediating adverse outcomes in diabetes, but this should be explored further in future studies.

Left atrial fibrosis in atrial fibrillation: Mechanisms, clinical evaluation and management

Atrial fibrillation (AF), the commonest arrhythmia, shows associations with various disease conditions. Mounting evidence indicates that atrial fibrosis is an important part of the arrhythmogenic substrate, with an essential function in the generation of conduction abnormalities that underlie the transition from paroxysmal to persistent AF, which in turn contributes to AF perpetuation. Left atrial (LA) fibrosis is considered a possible major factor and predictor in AF treatment. The present review provides insights into LA fibrosis’ association with AF. The information is focused on clinical aspects and mechanisms, clinical evaluating methods that evaluate fibrosis changes and examining possible options for the prevention of atrial fibrosis.

Effect of antidiabetic drugs on the risk of atrial fibrillation: mechanistic insights from clinical evidence and translational studies

Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation (AF), which is the most common sustained arrhythmia and is associated with substantial morbidity and mortality. Advanced glycation end product and its receptor activation, cardiac energy dysmetabolism, structural and electrical remodeling, and autonomic dysfunction are implicated in AF pathophysiology in diabetic hearts. Antidiabetic drugs have been demonstrated to possess therapeutic potential for AF. However, clinical investigations of AF in patients with DM have been scant and inconclusive. This article provides a comprehensive review of research findings on the association between DM and AF and critically analyzes the effect of different pharmacological classes of antidiabetic drugs on AF.

PPAR Gamma: From Definition to Molecular Targets and Therapy of Lung Diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that regulate the expression of genes related to lipid and glucose metabolism and inflammation. There are three members: PPARα, PPARβ or PPARγ. PPARγ have several ligands. The natural agonists are omega 9, curcumin, eicosanoids and others. Among the synthetic ligands, we highlight the thiazolidinediones, clinically used as an antidiabetic. Many of these studies involve natural or synthetic products in different pathologies. The mechanisms that regulate PPARγ involve post-translational modifications, such as phosphorylation, sumoylation and ubiquitination, among others. It is known that anti-inflammatory mechanisms involve the inhibition of other transcription factors, such as nuclear factor kB(NFκB), signal transducer and activator of transcription (STAT) or activator protein 1 (AP-1), or intracellular signaling proteins such as mitogen-activated protein (MAP) kinases. PPARγ transrepresses other transcription factors and consequently inhibits gene expression of inflammatory mediators, known as biomarkers for morbidity and mortality, leading to control of the exacerbated inflammation that occurs, for instance, in lung injury/acute respiratory distress. Many studies have shown the therapeutic potentials of PPARγ on pulmonary diseases. Herein, we describe activities of the PPARγ as a modulator of inflammation, focusing on lung injury and including definition and mechanisms of regulation, biological effects and molecular targets, and its role in lung diseases caused by inflammatory stimuli, bacteria and virus, and molecular-based therapy.

The Potential Effects of Aliskiren on Atrial Remodeling Induced by Chronic Intermittent Hypoxia in Rats

Purpose

Atrial remodeling takes part in the pathogenesis of atrial fibrillation (AF). Aliskiren, as a direct renin inhibitor, has been shown to exert protective effects against arrhythmia. The aim of this study was to investigate the potential role of aliskiren in atrial remodeling in a chronic intermittent hypoxia (CIH) rat model.

Methods

A total of 45 Sprague–Dawley rats were randomly assigned into three groups (n=15 per group): control group; CIH group; and CIH with aliskiren (CIH-A) group. CIH and CIH-A rats were subjected to CIH for 6 h per day for 4 weeks. Atrial fibrosis was evaluated using Masson’s trichrome staining. Electrophysiological tests were conducted in the isolated perfused hearts to assess the atrial effective refractory period and inducibility of AF. Atrial ionic remodeling was measured using the whole-cell patch-clamp technique, and Western blotting and real-time quantitative polymerase chain reactionwere performed to evaluate changes in ion channels.

Results

CIH induced obvious collagen deposition, and the abnormal fibrosis was significantly attenuated by aliskiren. The inducibility of AF was increased significantly in the CIH group compared with the control and CIH-A groups (23±24.5% vs 2.0±4.2% vs 5.0±7.0%, respectively; P<0.05). Compared with the control group, the densites of the calcium current (I_CaL) and sodium current (I_Na) were reduced significantly in the CIH group (I_CaL: −3.16±0.61 pA/pF vs −7.13±1.98 pA/pF; I_Na: −50.97±8.71 pA/pF vs −132.58±25.34 pA/pF, respectively; all P<0.05). Following intervention with aliskiren, the reductions in I_CaL and I_Na were significantly improved, and the ionic modeling changes assessed at the mRNA and protein levels were also significantly improved.

Conclusion

CIH could alter atrial modeling and subsequently promote the occurrence and development of AF, which could be attenuated by treatment with aliskiren.

Atrial remodeling and atrial fibrillation in acquired forms of cardiovascular disease

Atrial fibrillation (AF) is prevalent in common conditions and acquired forms of heart disease, including diabetes mellitus (DM), hypertension, cardiac hypertrophy, and heart failure. AF is also prevalent in aging. Although acquired heart disease is common in aging individuals, age is also an independent risk factor for AF. Importantly, not all individuals age at the same rate. Rather, individuals of the same chronological age can vary in health status from fit to frail. Frailty can be quantified using a frailty index, which can be used to assess heterogeneity in individuals of the same chronological age. AF is thought to occur in association with electrical remodeling due to changes in ion channel expression or function as well as structural remodeling due to fibrosis, myocyte hypertrophy, or adiposity. These forms of remodeling can lead to triggered activity and electrical re-entry, which are fundamental mechanisms of AF initiation and maintenance. Nevertheless, the underlying determinants of electrical and structural remodeling are distinct in different conditions and disease states. In this focused review, we consider the factors leading to atrial electrical and structural remodeling in human patients and animal models of acquired cardiovascular disease or associated risk factors. Our goal is to identify similarities and differences in the cellular and molecular bases for atrial electrical and structural remodeling in conditions including DM, hypertension, hypertrophy, heart failure, aging, and frailty.

Role of ion channels in chronic intermittent hypoxia-induced atrial remodeling in rats

AIMS

Atrial remodeling, including structural and electrical remodeling, is considered as the substrate in the development of atrial fibrillation (AF). Structural remodeling mainly involves atrial fibrosis, and electrical remodeling is closely related to the changes of ion channels in atrial myocytes. In this study, we aimed to investigate the changes of ion channels in atrial remodeling induced by CIH in rats, which provide the explication for the mechanisms of AF.

MATERIALS AND METHODS

80 male Sprague-Dawley rats were randomized into two groups: Control and CIH group (n = 40). CIH rats were subjected to CIH 8 h/d for 30 days. Atrial epicardial conduction velocity, conduction inhomogeneity and AF inducibility were examined. Masson's trichrome staining was used to evaluate the extent of atrial fibrosis, and the expression levels of ion channel subunits were measured by RT-qPCR, Western blot, and IHC, respectively. The remaining 40 rats were used for whole-cell patch clamp experiments. Action potential, I_Na, I_Ca-L, I_to were recorded and compared between two groups.

KEY FINDINGS

CIH rats showed increased AF inducibility, atrial interstitial collagen deposition, APD, expression levels of RyR2, p-RyR2, CaMKII, p-CaMKII, and decreased atrial epicardial conduction velocity, expression levels of Na_v1.5, Ca_v1.2, K_v1.5, K_v4.2, K_v4.3 compared to the Control rats, and the current density of I_Na, I_Ca-L, I_to were significantly decreased in CIH group.

SIGNIFICANCE

We observed significant atrial remodeling induced by CIH in our rat model, which was characterized by changes in ion channels. These changes may be the mechanisms of CIH promoting AF.

Effect of Dapagliflozin on Atrial Fibrillation in Patients With Type 2 Diabetes Mellitus

Background:

Atrial fibrillation (AF) and atrial flutter (AFL) are associated with both diabetes mellitus and its related comorbidities, including hypertension, obesity, and heart failure (HF). SGLT2 (sodium-glucose cotransporter 2) inhibitors have been shown to lower blood pressure, reduce weight, have salutary effects on left ventricular remodeling, and reduce hospitalization for HF and cardiovascular death in patients with type 2 diabetes mellitus. We therefore investigated whether SGLT2 inhibitors could also reduce the risk of AF/AFL.

Methods:

DECLARE-TIMI 58 (Dapagliflozin Effect on Cardiovascular Events–Thrombolysis in Myocardial Infarction 58) studied the efficacy and safety of the SGLT2 inhibitor dapagliflozin versus placebo in 17 160 patients with type 2 diabetes mellitus and either multiple risk factors for atherosclerotic cardiovascular disease (n=10 186) or known atherosclerotic cardiovascular disease (n=6974). We explored the effect of dapagliflozin on the first and total number of AF/AFL events in patients with (n=1116) and without prevalent AF/AFL using Cox and negative binomial models, respectively. AF/AFL events were identified by search of the safety database using MedDRA preferred terms (“atrial fibrillation,” “atrial flutter”).

Results:

Dapagliflozin reduced the risk of AF/AFL events by 19% (264 versus 325 events; 7.8 versus 9.6 events per 1000 patient-years; hazard ratio [HR], 0.81 [95% CI, 0.68–0.95]; P =0.009). The reduction in AF/AFL events was consistent regardless of presence or absence of a history of AF/AFL at baseline (previous AF/AFL: HR, 0.79 [95% CI, 0.58–1.09]; no AF/AFL: HR, 0.81 [95% CI, 0.67–0.98]; P for interaction 0.89). Similarly, presence of atherosclerotic cardiovascular disease (HR, 0.83 [95% CI, 0.66–1.04]) versus multiple risk factors (HR, 0.78 [95% CI, 0.62–0.99]; P for interaction 0.72) or a history of HF (HF: HR, 0.78 [95% CI, 0.55–1.11]; No HF: HR, 0.81 [95% CI, 0.68–0.97]; P for interaction 0.88) did not modify the reduction in AF/AFL events observed with dapagliflozin. Moreover, there was no effect modification by sex, history of ischemic stroke, glycated hemoglobin A 1c , body mass index, blood pressure, or estimated glomerular filtration rate (all P for interaction >0.20). Dapagliflozin also reduced the total number (first and recurrent) of AF/AFL events (337 versus 432; incidence rate ratio, 0.77 [95% CI, 0.64–0.92]; P =0.005).

Conclusions:

Dapagliflozin decreased the incidence of reported episodes of AF/AFL adverse events in high-risk patients with type 2 diabetes mellitus. This effect was consistent regardless of the patient’s previous history of AF, atherosclerotic cardiovascular disease, or HF.

Registration:

URL: https://www.clinicaltrials.gov ; Unique identifier: NCT01730534.

Epicardial Adipose Tissue Inflammation Can Cause the Distinctive Pattern of Cardiovascular Disorders Seen in Psoriasis

Psoriasis is a systemic inflammatory disorder that can target adipose tissue; the resulting adipocyte dysfunction is manifest clinically as the metabolic syndrome, which is present in ≈20%-40% of patients. Epicardial adipose tissue inflammation is likely responsible for a distinctive pattern of cardiovascular disorders consisting of 1) accelerated coronary atherosclerosis leading to myocardial infarction, 2) atrial myopathy leading to atrial fibrillation and thromboembolic stroke, and 3) ventricular myopathy leading to heart failure with a preserved ejection fraction. If cardiovascular inflammation drives these risks, then treatments that focus on blood pressure, lipids, and glucose will not ameliorate the burden of cardiovascular disease in patients with psoriasis, especially in those who are young and have severe inflammation. Instead, interventions that alleviate systemic and adipose tissue inflammation may not only minimize the risks of atrial fibrillation and heart failure but may also have favorable effects on the severity of psoriasis. Viewed from this perspective, the known link between psoriasis and cardiovascular disease is not related to the influence of the individual diagnostic components of the metabolic syndrome.

Role of NLRP3-Inflammasome/Caspase-1/Galectin-3 Pathway on Atrial Remodeling in Diabetic Rabbits

Both diabetes mellitus (DM) and atrial fibrillation (AF) are usually associated with enhanced inflammatory response. The effect of the "NACHT, LRR and PYD domain containing protein 3" (NLRP3)-inflammasome/caspase-1/galectin-3 pathway and the potential benefits of NLRP3-inflammasome inhibitor glibenclamide (GLB) on atrial remodeling in the DM state are still unknown. Here, we demonstrated that higher AF inducibility and conduction inhomogeneity, slower epicardial conduction velocity, and increased amount of fibrosis in diabetic rabbits as against normal ones were markedly reduced by GLB. Atrial caspase-1 activity as well as serum IL-1β and IL-18 levels were elevated in diabetic animals but suppressed by GLB. Moreover, GLB decreased the DM-induced protein expression enhancement of NLRP3, Gal-3, TGF-β1, and CaV1.2 according to western blot analysis. Summarily, our findings indicate that the NLRP3-inflammasome/caspase-1/Gal-3 signaling pathway is related to the pathogenesis of AF in the diabetic state. NLRP3-inflammasome inhibitor GLB prevents AF inducibility and moderates atrial structural remodeling in DM.

Atrial Fibrillation and Heart Failure With Preserved Ejection Fraction in Patients With Nonalcoholic Fatty Liver Disease

The most common causes of chronic liver disease in the developed world-nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH)-are the hepatic manifestations of an insulin-resistant state that is linked to visceral adiposity and systemic inflammation. NAFLD and NASH lead to an expansion of epicardial adipose tissue and the release of proinflammatory adipocytokines that cause microcirculatory dysfunction and fibrosis of the adjoining myocardium, resulting in atrial fibrillation as well as heart failure with a preserved ejection fraction (HFpEF). Inflammatory changes in the left atrium lead to electroanatomical remodeling; thus, NAFLD and NASH markedly increase the risk of atrial fibrillation. Simultaneously, patients with NAFLD or NASH commonly show diastolic dysfunction or latent HFpEF. Interventions include 1) weight loss by caloric restriction, bariatric surgery, or intensive exercise, and 2) drugs that ameliorate fat-mediated inflammation in both the liver and heart (eg, statins, metformin, sodium-glucose cotransporter 2 inhibitors, glucagon-like peptide-1 receptor agonists, and pioglitazone). Patients with NAFLD or NASH commonly have an inflammation-related atrial and ventricular myopathy, which may contribute to symptoms and long-term outcomes.

Do most patients with obesity or type 2 diabetes, and atrial fibrillation, also have undiagnosed heart failure? A critical conceptual framework for understanding mechanisms and improving diagnosis and treatment

Obesity and diabetes can lead to heart failure with preserved ejection fraction (HFpEF), potentially because they both cause expansion and inflammation of epicardial adipose tissue and thus lead to microvascular dysfunction and fibrosis of the underlying left ventricle. The same process also causes an atrial myopathy, which is clinically evident as atrial fibrillation (AF); thus, AF may be the first manifestation of HFpEF. Many patients with apparently isolated AF have latent HFpEF or subsequently develop HFpEF. Most patients with obesity or diabetes who have AF and exercise intolerance have increased left atrial pressures at rest or during exercise, even in the absence of diagnosed HFpEF. Among patients with AF, those who also have latent HFpEF have increased risk for systemic thromboembolism and death. The identification of HFpEF in patients with obesity or diabetes alters the risk-to-benefit relationship of commonly prescribed treatments. Bariatric surgery and statins can ameliorate AF and reduce the risk for HFpEF. Conversely, antihyperglycaemic drugs that promote adipogenesis or cause sodium retention (insulin and thiazolidinediones) may increase the risk for heart failure in patients with an underlying ventricular myopathy. Patients with obesity and diabetes who undergo catheter ablation for AF are at increased risk for AF recurrence and for post-ablation increases in pulmonary venous pressures and worsening heart failure, especially if HFpEF coexists. Therefore, AF may be the earliest indicator of HFpEF in patients with obesity or type 2 diabetes, and recognition of HFpEF alters the management of these patients.

Inhibitory effect of alpinetin on IL-6 expression by promoting cytosine methylation in CpG islands in the IL-6 promoter region

Background

Alpinetin is a flavonoid which exerts antibacterial and anti‐inflammatory functions. In order to prove that the induced methylation is an important mechanism for alpinetin in regulating the expression of inflammatory factor Interleukin‐6 (IL‐6), we detected the dinucleotide methylation status of CpG islands in the IL‐6 promoter region and IL‐6 level after treatment of RAW246.7 murine macrophages with alpinetin.

Methods

After RAW246.7 murine macrophages were treated with alpinetin, alpinetin + GW9662 (the peroxisome proliferator‐activated receptor (PPAR) antagonist), and alpinetin + DNA methyltransferase 3 alpha (DNMT3A) siRNA for 96 hr, CpG islands were analyzed using time‐of‐flight mass spectrophotometry (TOF‐MS) and bisulfite sequencing polymerase chain reaction (BSP). Dinucleotide methylation status of the CpG islands in the IL‐6 promoter region was analyzed by methylation‐specific Polymerase Chain Reaction (PCR). IL‐6 level was detected using the enzyme‐linked immunosorbent assay (ELISA) method. Pearson's correlation analysis was conducted to test for potential correlation between the methylation status of CpG islands in the IL‐6 promoter region and IL‐6 level in RAW 246.7 cells.

Results

Alpinetin promoted dinucleotide methylation status of two CpG islands in the IL‐6 promoter region stretching 500–2500 bp upstream of the transcriptional start site (TSS) (p < .05). This promoting effect was more significant for the CpG island stretching 500–1500 bp long. The methylation ratio of dinucleotide at this position was significantly inversely correlated with the level of IL‐6 (p < .05). PPAR antagonist GW9662 and interference of DNMT3A could reverse both the alpinetin‐induced methylation and inhibitory effects on IL‐6 expression.

Conclusion

Alpinetin could induce dinucleotide methylation status of CpG islands in the IL‐6 promoter region by activating methyltransferase, thus inhibiting IL‐6 expression in murine macrophages.

Lifestyle modifications for treatment of atrial fibrillation

The management of atrial fibrillation (AF) has focused on anticoagulation, rhythm control and ventricular rate control. Recently, a fourth pillar of AF management has been incorporated recognising the importance of risk factor management (RFM). There are several risk factors that contribute to the development and progression of AF, these include traditional risk factors such as age, hypertension, heart failure, diabetes and valvular heart disease. However, increasingly it is recognised that obesity, sleep apnoea, hyperlipidaemia, smoking, alcohol, physical inactivity, genetics, aortic stiffness are associated with the development of AF. Importantly, several of these risk factors are modifiable. We have seen the evolution of RFM programmes which have demonstrated promising results. Indeed, the evidence is now so compelling that major clinical guidelines strongly advocate that aggressive treatment of these risk factors as a key component of AF management. Patients with AF who comprehensively managed their risk factors demonstrate greater reduction in symptoms, AF burden, more successful ablations and improved outcomes with greater AF freedom. In this article, we will review the evidence for the association between cardiac risk factors and AF and assess the burgeoning evidence for improved AF outcomes associated with aggressive cardiac RFM.

Mechanism of electrical remodeling of atrial myocytes and its influence on susceptibility to atrial fibrillation in diabetic rats

AIMS

To explore the atrial electrical remodeling and the susceptibility of atrial fibrillation (AF) in diabetic rats.

MATERIALS AND METHODS

Zucker diabetic fatty (ZDF) rats were chosen as diabetic animal model, and age-matched non-diabetic littermate Zucker lean (ZL) rats as control. AF susceptibility was determined by electrophysiological examination. The current density of I_to, I_Kur and I_Ca-L were detected by whole-cell patch-clamp technique, and ion channel protein expression in atrial tissue and HL-1 cells treated with advanced glycation end products (AGE) was analyzed by western blotting.

KEY FINDINGS

Diabetic rats had significantly enlarged left atria and evenly thickened ventricular walls, hypertrophied cells and interstitial fibrosis in atrial myocardium, increased AF susceptibility, and prolonged AF duration after atrial burst stimulation. Compared with atrial myocytes isolated from ZL controls, atrial myocytes isolated from ZDF rats had prolonged action potential duration, decreased absolute value of resting membrane potential level and current densities of I_to, I_Kur and I_Ca-L. The ion channel protein (Kv4.3, Kv1.5 and Cav1.2) expression in atrium tissue of ZDF rats and HL-1 cells treated with high concentration AGE were significantly down-regulated, compared with controls.

SIGNIFICANCE

The atrial electrical remodeling induced by hyperglycemia contributed to the increased AF susceptibility in diabetic rats.

Disease-treatment interactions in the management of patients with obesity and diabetes who have atrial fibrillation: the potential mediating influence of epicardial adipose tissue

Both obesity and type 2 diabetes are important risk factors for atrial fibrillation (AF), possibly because they both cause an expansion of epicardial adipose tissue, which is the source of proinflammatory adipocytokines that can lead to microvascular dysfunction and fibrosis of the underlying myocardium. If the derangement of epicardial fat adjoins the left atrium, the result is an atrial myopathy, which is clinically manifest as AF. In patients with AF, there is a close relationship between epicardial fat volume and the severity of electrophysiological abnormalities in the adjacent myocardial tissues, and epicardial fat mass predicts AF in the general population. The expansion of epicardial adipose tissue in obesity and type 2 diabetes may also affect the left ventricle, impairing its distensibility and leading to heart failure with a preserved ejection fraction (HFpEF). Patients with obesity or type 2 diabetes with AF often have HFpEF, but the diagnosis may be missed, if dyspnea is attributed to increased body mass or to the arrhythmia. The expected response to the treatment for obesity, diabetes or AF may be influenced by their effects on epicardial inflammation and the underlying atrial and ventricular myopathy. Bariatric surgery and metformin reduce epicardial fat mass and ameliorate AF, whereas insulin promotes adipogenesis and cardiac fibrosis, and its use is accompanied by an increased risk of AF. Rate control strategies for AF may impair exercise tolerance, because they allow for greater time for ventricular filling in patients who cannot tolerate volume loading because of cardiac fibrosis and HFpEF. At the same time, both obesity and diabetes decrease the expected success rate of rhythm control strategies for AF (e.g., electrical cardioversion or catheter ablation), because increased epicardial adipose tissue volumes and cardiac fibrosis are important determinants of AF recurrence following these procedures.

The Association Between Diabetes Mellitus and Atrial Fibrillation: Clinical and Mechanistic Insights

A number of clinical studies have reported that diabetes mellitus (DM) is an independent risk factor for Atrial fibrillation (AF). After adjustment for other known risk factors including age, sex, and cardiovascular risk factors, DM remains a significant if modest risk factor for development of AF. The mechanisms underlying the increased susceptibility to AF in DM are incompletely understood, but are thought to involve electrical, structural, and autonomic remodeling in the atria. Electrical remodeling in DM may involve alterations in gap junction function that affect atrial conduction velocity due to changes in expression or localization of connexins. Electrical remodeling can also occur due to changes in atrial action potential morphology in association with changes in ionic currents, such as sodium or potassium currents, that can affect conduction velocity or susceptibility to triggered activity. Structural remodeling in DM results in atrial fibrosis, which can alter conduction patterns and susceptibility to re-entry in the atria. In addition, increases in atrial adipose tissue, especially in Type II DM, can lead to disruptions in atrial conduction velocity or conduction patterns that may affect arrhythmogenesis. Whether the insulin resistance in type II DM activates unique intracellular signaling pathways independent of obesity requires further investigation. In addition, the relationship between incident AF and glycemic control requires further study.

Urinary Biomarkers of Oxidative Stress in Atrial Fibrillation

There is increasing evidence from molecular studies to support the role of inflammation and increased oxidative stress that produce structural and electrical atrial remodeling to produce Atrial Fbrillation (AF). Oxidative damage to cardiomyocytes yields chemical substances that are secreted in urine. These substances can serve as biomarkers that can be measured, potentially allowing clinicians to quantify oxidative damage to the heart.

Alogliptin prevents diastolic dysfunction and preserves left ventricular mitochondrial function in diabetic rabbits

Background

There are increasing evidence that left ventricle diastolic dysfunction is the initial functional alteration in the diabetic myocardium. In this study, we hypothesized that alogliptin prevents diastolic dysfunction and preserves left ventricular mitochondrial function and structure in diabetic rabbits.

Methods

A total of 30 rabbits were randomized into control group (CON, n = 10), alloxan-induced diabetic group (DM, n = 10) and alogliptin-treated (12.5 mg/kd/day for 12 weeks) diabetic group (DM-A, n = 10). Echocardiographic and hemodynamic studies were performed in vivo. Mitochondrial morphology, respiratory function, membrane potential and reactive oxygen species (ROS) generation rate of left ventricular tissue were assessed. The serum concentrations of glucagon-like peptide-1, insulin, inflammatory and oxidative stress markers were measured. Protein expression of TGF-β1, NF-κB p65 and mitochondrial biogenesis related proteins were determined by Western blotting.

Results

DM rabbits exhibited left ventricular hypertrophy, left atrial dilation, increased E/e′ ratio and normal left ventricular ejection fraction. Elevated left ventricular end diastolic pressure combined with decreased maximal decreasing rate of left intraventricular pressure (− dp/dtmax) were observed. Alogliptin alleviated ventricular hypertrophy, interstitial fibrosis and diastolic dysfunction in diabetic rabbits. These changes were associated with decreased mitochondrial ROS production rate, prevented mitochondrial membrane depolarization and improved mitochondrial swelling. It also improved mitochondrial biogenesis by PGC-1α/NRF1/Tfam signaling pathway.

Conclusions

The DPP-4 inhibitor alogliptin prevents cardiac diastolic dysfunction by inhibiting ventricular remodeling, explicable by improved mitochondrial function and increased mitochondrial biogenesis.