Pioglitazone attenuates inflammatory atrial fibrosis and vulnerability to atrial fibrillation induced by pressure overload in rats

Indoxyl Sulfate and Its Potential Role in Mineralocorticoid Receptor Transactivation in Chronic Kidney Disease

BACKGROUND

The uremic toxin indoxyl sulfate (IS) is an important factor in chronic kidney disease (CKD) progression. Inhibitors of the renin-angiotensin system and add-on therapy with mineralocorticoid receptor (MR) antagonists can help reduce proteinuria and suppress CKD progression. However, the association between IS and MR activation remains unknown.

MATERIALS AND METHODS

 In vivo experiments utilized the 5/6 nephrectomy model to assess mineralocorticoid receptor (MR) activation in chronic kidney disease (CKD). The clinical parameters and immunohistochemical analysis of IS and MR proteins were investigated. In vitro experiments involved transfecting COS-7 cells with MR expression plasmids and MR response element-luciferase reporter plasmids. The cells were then treated with aldosterone (10⁻¹⁰ mol/L), indoxyl sulfate (IS, 500 μmol/L), and α-lipoic acid (10⁻³ mol/L). MR transcriptional activity was investigated by luciferase assays, and protein levels were measured by Western blotting.

RESULTS

In the 5/6 nephrectomy model, the serum IS concentration was significantly increased; however, the plasma aldosterone levels were decreased. Immunohistochemistry showed that the expression of IS protein increased in injured tubular cells in the 5/6 nephrectomy group compared with that in the sham group. Furthermore, evaluations of serial kidney sections revealed that the expression site of IS protein was colocalized with the distal nephron, where the expression of MR protein was observed. MR-mediated transcriptional activity in COS-7 cells was increased in an aldosterone concentration-dependent manner. IS increased MR-mediated transcriptional activity and protein levels with and without aldosterone, and α-lipoic acid attenuated this increase.

CONCLUSIONS

IS could enhance MR transactivation by increasing MR protein levels through oxidative stress in CKD rats, indicating that treatment with MR antagonists and antioxidants may play a permissive role in inhibiting IS-induced CKD progression.

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.

Integrative bioinformatics analysis reveals STAT2 as a novel biomarker of inflammation-related cardiac dysfunction in atrial fibrillation

Atrial fibrillation (AF) is a common critical cause of stroke and cardiac dysfunction worldwide with lifetime risks. Viral infection and inflammatory response with myocardial involvement may lead to an increase in AF-related mortality. To dissect the potential sequelae of viral infection in AF patients, especially the coronavirus disease 2019 (COVID-19), based on AF and COVID-19 databases from Gene Expression Omnibus, weighted gene co-expression network analysis was used to identify key genes in heart tissues and peripheral blood mononuclear cells. Here, HSCT, PSMB9, STAT2, and TNFSF13B were identified as common risk genes of AF and COVID-19 patients. Correlation analysis of these genes with AF and COVID-19 showed a positive disease relevance. silencing of STAT2 by small interfering RNA significantly rescued SARS-CoV-2 XBB1.5 pseudovirus-induced cardiac cell contraction dysfunction in vitro. In conclusion, we identified STAT2 may be a novel biomarker of inflammation-related cardiac dysfunction in AF.

Diabetes mellitus and atrial fibrillation-from pathophysiology to treatment

Type 2 diabetes mellitus (T2DM) is a leading risk factor for cardiovascular complications around the globe and one of the most common medical conditions. Atrial fibrillation (AF) is the most common supraventricular arrhythmia, with a rapidly increasing prevalence. T2DM has been closely associated with the risk of AF development, identified as an independent risk factor. Regarding cardio-vascular complications, both AF and T2DM have been linked with high mortality. The underlying pathophysiology has not been fully determined yet; however, it is multifactorial, including structural, electrical, and autonomic pathways. Novel therapies include pharmaceutical agents in sodium-glucose cotransporter-2 inhibitors, as well as antiarrhythmic strategies, such as cardioversion and ablation. Of interest, glucose-lowering therapies may affect the prevalence of AF. This review presents the current evidence regarding the connection between the two entities, the pathophysiological pathways that link them, and the therapeutic options that exist.

Treatment of type 2 diabetes patients with heart conditions

INTRODUCTION

While type 2 diabetes mellitus (T2DM) increases the risk of cardiac complications, diabetes treatment choices may increase or decrease the rates of cardiac events. In the present review, we comprehensively discussed the treatment options of diabetic subjects with cardiac conditions.

AREAS COVERED

Current evidence related to diabetes treatment in cardiac situations has been reviewed. Clinical trials and meta-analyses on cardiac safety of anti-diabetic medicines are discussed. Treatment choices with proven benefits and those at least without associated increased cardiac risk were drawn from clinical trials; meta-analyses and cardiac safety studies in the recent medical literature were the basis of the suggestions in the present review.

EXPERT OPINION

We can suggest that hypoglycemia and extreme hyperglycemia should be avoided in acute ischemic heart conditions. Certain diabetic treatment options, especially sodium-glucose cotransporter-2 (SGLT2) inhibitors, can reduce overall cardiovascular mortality and hospitalization due to heart failure. Therefore, we suggest that physicians should choose SGLT2 inhibitors as the first-line treatment option in diabetic patients with heart failure or those who have a high risk of heart failure development. T2DM increases the risk of atrial fibrillation (AF), and metformin and pioglitazone seem to reduce the risk of AF in diabetic population.

Atrial Fibrillation and Diabetes Mellitus: Dangerous Liaisons or Innocent Bystanders?

Atrial fibrillation (AF) is the most common arrhythmia in adults and diabetes mellitus (DM) is a major risk factor for cardiovascular diseases. However, the relationship between both pathologies has not been fully documented and new evidence supports the existence of direct and independent links. In the myocardium, a combination of structural, electrical, and autonomic remodeling may lead to AF. Importantly, patients with AF and DM showed more dramatic alterations than those with AF or DM alone, particularly in mitochondrial respiration and atrial remodeling, which alters conductivity, thrombogenesis, and contractile function. In AF and DM, elevations of cytosolic Ca²⁺ and accumulation of extra cellular matrix (ECM) proteins at the interstitium can promote delayed afterdepolarizations. The DM-associated low-grade inflammation and deposition/infiltration of epicardial adipose tissue (EAT) enforce abnormalities in Ca²⁺ handling and in excitation-contraction coupling, leading to atrial myopathy. This atrial enlargement and the reduction in passive emptying volume and fraction can be key for AF maintenance and re-entry. Moreover, the stored EAT can prolong action of potential durations and progression from paroxysmal to persistent AF. In this way, DM may increase the risk of thrombogenesis as a consequence of increased glycation and oxidation of fibrinogen and plasminogen, impairing plasmin conversion and resistance to fibrinolysis. Additionally, the DM-associated autonomic remodeling may also initiate AF and its re-entry. Finally, further evidence of DM influence on AF development and maintenance are based on the anti-arrhythmogenic effects of certain anti-diabetic drugs like SGLT2 inhibitors. Therefore, AF and DM may share molecular alterations related to Ca²⁺ mobility, mitochondrial function and ECM composition that induce atrial remodeling and defects in autonomic stimulation and conductivity. Likely, some specific therapies could work against the associated cardiac damage to AF and/or DM.

Association between antidiabetic drugs and the incidence of atrial fibrillation in patients with type 2 diabetes: A nationwide cohort study in South Korea

BACKGROUND

Although diabetes is a risk factor for atrial fibrillation (AF), studies on the AF risk according to the antidiabetic drugs are lacking. This study evaluated the effects of antidiabetic drugs on AF incidence in Korean patients with type 2 diabetes.

METHODS

We included 2,515,468 patients with type 2 diabetes from the Korean National Insurance Service database without a history of AF who underwent health check-ups between 2009 and 2012. Newly diagnosed AF incidence was recorded until December 2018 according to the main antidiabetic drug combinations used in the real world.

RESULTS

Of the patients included (mean age, 62 ± 11 years; 60 % men), 89,125 were newly diagnosed with AF. Metformin (MET) alone (hazard ratio [HR] 0.959, 95 % CI 0.935-0.985) and MET combination therapy (HR < 1) significantly decreased the risk of AF compared to the no-medication group. The antidiabetic drugs consistently showing a protective effect against AF incidence were MET (HR 0.977, 95 % CI 0.964-0.99) and thiazolidinedione (TZD; HR 0.926, 95 % CI 0.898-0.956), even after adjusting for various factors. Moreover, this protective effect was more remarkable with MET and TZD combination therapy (HR 0.802, 95 % CI 0.754-0.853) than with other drug combinations. In the subgroup analysis, the preventive effect of MET and TZD treatment against AF remained consistent, regardless of age, sex, duration, and diabetes severity.

CONCLUSION

The combination therapy of MET and TZD is the most effective antidiabetic drug for preventing AF in patients with type 2 diabetes.

Research Progress of Myocardial Fibrosis and Atrial Fibrillation

With the aging population and the increasing incidence of basic illnesses such as hypertension and diabetes (DM), the incidence of atrial fibrillation (AF) has increased significantly. AF is the most common arrhythmia in clinical practice, which can cause heart failure (HF) and ischemic stroke (IS), increasing disability and mortality. Current studies point out that myocardial fibrosis (MF) is one of the most critical substrates for the occurrence and maintenance of AF. Although myocardial biopsy is the gold standard for evaluating MF, it is rarely used in clinical practice because it is an invasive procedure. In addition, serological indicators and imaging methods have also been used to evaluate MF. Nevertheless, the accuracy of serological markers in evaluating MF is controversial. This review focuses on the pathogenesis of MF, serological evaluation, imaging evaluation, and anti-fibrosis treatment to discuss the existing problems and provide new ideas for MF and AF evaluation and treatment.

Peroxisome Proliferator-Activated Receptor-γ Agonist Attenuates Vocal Fold Fibrosis in Rats via Regulation of Macrophage Activation

Macrophages aid in wound healing by changing their phenotype and can be a key driver of fibrosis. However, the contribution of macrophage phenotype to fibrosis following vocal fold injury remains unclear. Peroxisome proliferator-activated receptor-γ (PPARγ) is expressed mainly by macrophages during early wound healing and regulates the macrophage phenotype. This study aimed to evaluate the effects of pioglitazone (PIO), a PPARγ agonist, on the macrophage phenotype and fibrosis following vocal fold injury in rats. PIO was injected into the rat vocal folds on days 1, 3, 5, and 7 after injury, and the vocal fold lamina propria was evaluated on days 4 and 56 after injury. Moreover, THP-1-derived macrophages were treated with PIO, and the expression of proinflammatory cytokines under lipopolysaccharide/interferon-γ stimulation was analyzed. PIO reduced the expression of Ccl2 both in vivo and in vitro. Furthermore, PIO decreased the density of inducible nitric oxide synthase⁺ CD68⁺ macrophages and inhibited the expression of fibrosis-related factors on day 4 after injury. On day 56 after injury, PIO inhibited fibrosis, tissue contracture, and hyaluronic acid loss in a PPARγ-dependent manner. These results indicate that PPARγ activation could inhibit accumulation of inflammatory macrophages and improve tissue repair. Taken together, these findings imply that inflammatory macrophages play a key role in vocal fold fibrosis.

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.

Effect of obesity and epicardial fat/fatty infiltration on electrical and structural remodeling associated with atrial fibrillation in a novel canine model of obesity and atrial fibrillation: A comparative study

BACKGROUND

How obesity and epicardial fat influence atrial fibrillation (AF) is unknown.

METHODS

To investigate the effect of obesity/epicardial fat on the AF substrate, we divided 20 beagle dogs of normal weight into four groups (n = 5 each): one of the four groups (Obese-rapid atrial pacing [RAP] group) served as a novel canine model of obesity and AF. The other three groups comprised dogs fed a standard diet without RAP (Control group), dogs fed a high-fat diet without RAP (Obese group), or dogs fed a standard diet with RAP (RAP group). All underwent electrophysiology study, and hearts were excised for histopathologic and fibrosis-related gene expression analyses.

RESULTS

Left atrial (LA) pressure was significantly higher in the Obese group than in the Control, RAP, and Obese-RAP groups (23.4 ± 6.9 vs. 11.4 ± 2.1, 11.9 ± 6.4, and 13.5 ± 2.9 mmHg; p = .005). The effective refractory period of the inferior PV was significantly shorter in the RAP and Obese-RAP groups than in the Control group (p = .043). Short-duration AF was induced at greatest frequency in the Obese-RAP and Obese groups (p < .05). Epicardial fat/Fatty infiltration was greatest in the Obese-RAP group, and greater in the Obese and RAP groups than in the Control group. %interstitial fibrosis/fibrosis-related gene expression was significantly greater in the Obese-RAP and RAP groups (p < .05).

CONCLUSIONS

Vulnerability to AF was associated with increased LA pressure and increased epicardial fat/fatty infiltration in our Obese group, and with increased epicardial fat/fibrofatty infiltration in the RAP and Obese-RAP groups. These may explain the role of obesity/epicardial fat in the pathogenesis of AF.

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.

Diabetes and Endocrine Disorders (Hyperthyroidism/Hypothyroidism) as Risk Factors for Atrial Fibrillation

Risk factors including cardiometabolic and endocrine disorders have a significant impact on atrial remodeling causing atrial fibrillation (AF). Diabetes mellitus and hyperthyroidism are strong independent risk factors for AF and worsen outcomes of rhythm control strategies. An early diagnosis and intervention for these risk factors combined with rhythm control strategies may improve the overall cardiovascular mortality and morbidity. This review summarizes the current state of knowledge about the AF risk factors diabetes mellitus and thyroid disease, and discusses the impact of the modification of these risk factors on primary and secondary prevention of AF.

Atrial Fibrillation and Diabetes Mellitus: JACC Review Topic of the Week

Diabetes mellitus is one of the most common chronic medical conditions, and is a risk factor for the development of atrial fibrillation (AF). The presence of diabetes in patients with AF is associated with increased symptom burden and increased cardiovascular and cerebrovascular mortality. The pathophysiology of diabetes-related AF is not fully understood, but is related to structural, electrical, electromechanical, and autonomic remodeling. This paper reviews the complex interaction between diabetes and AF, and explores its effect on the prevention and treatment of AF.

MFGE8 attenuates Ang-II-induced atrial fibrosis and vulnerability to atrial fibrillation through inhibition of TGF-β1/Smad2/3 pathway

Atrial fibrillation (AF) is characterized by potentiated growth of atrial fibroblasts and excessive deposition of the extracellular matrix. Atrial fibrosis has emerged as a hallmark of atrial structural remodeling linked to AF. Nonetheless, the specific mechanism underlying the progression of atrial fibrosis to AF is still largely unknown. MFGE8 (milk fat globule-EGF factor 8) is a soluble glycoprotein associated with many human diseases. Recently, a number of studies revealed that MFGE8 plays a crucial role in heart disease. Yet, MFGE8 regulation and function in the process of atrial fibrosis and vulnerability to AF remain unexplored. In this study, we found that the expression of MFGE8 was downregulated in the atriums of patients with AF compared with individuals without AF. In addition, the expression of MFGE8 was lower in atriums of angiotensin II (Ang-II)-stimulated rats as compared with the sham group. In vitro, silencing of MFGE8 by small interfering RNA significantly increased Ang-II-induced atrial fibrosis, whereas administration of recombinant human MFGE8 (rhMFGE8) attenuated the atrial fibrosis. Moreover, we found that the activated TGF-β1/Smad2/3 pathway after Ang-II treatment was significantly potentiated by the MFGE8 knockdown but inhibited by rhMFGE8 in vitro. Inhibition of integrin β3 which is the receptor for MFGE8, suppressed the TGF-β1/Smad2/3 activating effects of the MFGE8 knockdown in Ang-II-treated rat atrial fibroblasts. Finally, we administered rhMFGE8 to rats; it attenuated atrial fibrosis and remodeling and further reduced AF vulnerability induced by Ang-II, indicating that MFGE8 might have the potential both as a novel biomarker and as a therapeutic target in atrial fibrosis and AF.

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.

CYP2J2/EET reduces vulnerability to atrial fibrillation in chronic pressure overload mice

Growing evidence has well established the protective effects of CYP2J2/EET on the cardiovascular system. The aim of the present study was to determine whether CYP2J2/EET has a preventive effect on atrial fibrillation (AF) and to investigate the underlying mechanisms. Wild‐type mice were injected with or without AAV9‐CYP2J2 before abdominal aortic constriction (AAC) operation. After 8 weeks, compared with wild‐type mice, AAC mice display higher AF inducibility and longer AF durations, which were remarkably attenuated with AAV9‐CYP2J2. Also, AAV9‐CYP2J2 reduced atrial fibrosis area and the deposit of collagen‐I/III in AAC mice, accompanied by the blockade of TGF‐β/Smad‐2/3 signalling pathways, as well as the recovery in Smad‐7 expression. In vitro, isolated atrial fibroblasts were administrated with TGF‐β1, EET, EEZE, GW9662, SiRNA Smad‐7 and pre‐MiR‐21, and EET was demonstrated to restrain the differentiation of atrial fibroblasts largely dependent on Smad‐7, due to the inhibition of EET on MiR‐21. In addition, increased inflammatory cytokines, as well as activated NF‐κB pathways induced by AAC surgery, were also significantly blunted by AAV9‐CYP2J2 treatment. These effects of CYP2J2/EET were partially blocked by GW9662, the antagonist of PPAR‐γ. In conclusion, this study revealed that CYP2J2/EET ameliorates atrial fibrosis through modulating atrial fibroblasts activation by disinhibition of MiR‐21 on Smad‐7, and attenuates atrial inflammatory response by repressing NF‐κB pathways, reducing the vulnerability to AF, and CYP2J2/EET exerts its role at least partially through PPAR‐γ activation. Our findings might provide a novel upstream therapeutic strategy for AF.

CTRP9 Ameliorates Atrial Inflammation, Fibrosis, and Vulnerability to Atrial Fibrillation in Post-Myocardial Infarction Rats

Background

Inflammation and fibrosis play an important role in the pathogenesis of atrial fibrillation (AF) after myocardial infarction (MI). CTRP9 (C1q/tumor necrosis factor‐related protein‐9) as a secreted glycoprotein can reverse left ventricle remodeling post‐MI, but its effects on MI‐induced atrial inflammation, fibrosis, and associated AF are unknown.

Methods and Results

MI model rats received adenoviral supplementation of CTRP9 (Ad‐CTRP9) by jugular‐vein injection. Cardiac function, inflammatory, and fibrotic indexes and related signaling pathways, electrophysiological properties, and AF inducibility of atria in vivo and ex vivo were detected in 3 or 7 days after MI. shCTRP9 (short hairpin CTRP9) and shRNA were injected into rat and performed similar detection at day 5 or 10. Adverse atrial inflammation and fibrosis, cardiac dysfunction were induced in both MI and Ad‐GFP (adenovirus‐encoding green fluorescent protein)+MI rats. Systemic CTRP9 treatment improved cardiac dysfunction post‐MI. CTRP9 markedly ameliorated macrophage infiltration and attenuated the inflammatory responses by downregulating interleukin‐1β and interleukin‐6, and upregulating interleukin‐10, in 3 days post‐MI; depressed left atrial fibrosis by decreasing the expressions of collagen types I and III, α‐SMA, and transforming growth factor β1 in 7 days post‐MI possibly through depressing the Toll‐like receptor 4/nuclear factor‐κB and Smad2/3 signaling pathways. Electrophysiologic recordings showed that increased AF inducibility and duration, and prolongation of interatrial conduction time induced by MI were attenuated by CTRP9; moreover, CTRP9 was negatively correlated with interleukin‐1β and AF duration. Downregulation of CTRP9 aggravated atrial inflammation, fibrosis, susceptibility of AF and prolonged interatrial conduction time, without affecting cardiac function.

Conclusions

CTRP9 is effective at attenuating atrial inflammation and fibrosis, possibly via its inhibitory effects on the Toll‐like receptor 4/nuclear factor‐κB and Smad2/3 signaling pathways, and may be an original upstream therapy for AF in early phase of MI.

Atrial fibrillation and its arrhythmogenesis associated with insulin resistance

Background

Insulin resistance (IR) is considered as a risk factor for atrial fibrillation (AF) even before diabetes develops. The pathophysiology and underlying mechanism are largely unclear.

Methods

We investigated the corresponding mechanism in two IR models of rats fed 15-week high-fat (HFa) and high-fructose/cholesterol (HFr) diets. AF was evaluated and induced by burst atrial pacing. Isolated atrial myocytes were used for whole-cell patch clamp and calcium assessment. Ex vivo whole heart was used for optical mapping. Western blot and immunofluorescence were used for quantitative protein evaluation.

Results

Both HFa and HFr rat atria were vulnerable to AF evaluated by burst atrial pacing. Isolated atrial myocytes from HFa and HFr rats revealed significantly increased sarcoplasmic reticulum calcium content and diastolic calcium sparks. Whole-heart mapping showed prolonged calcium transient duration, conduction velocity reduction, and repetitive ectopic focal discharge in HFa and HFr atria. Protein analysis revealed increased TGF-β1 and collagen expression; increased superoxide production; abnormal upregulation of calcium-homeostasis-related proteins, including oxidized CaMKIIδ, phosphorylated-phospholamban, phosphorylated-RyR-2, and sodium-calcium exchanger; and increased Rac1 activity in both HFa and HFr atria. We observed that inhibition of CaMKII suppressed AF in both HF and HFr diet-fed rats. In vitro palmitate-induced IR neonatal cardiomyocytes and atrial fibroblasts expressed significantly more TGF-β1 than did controls, suggesting paracrine and autocrine effects on both myocytes and fibroblasts.

Conclusions

IR engenders both atrial structural remodeling and abnormal intracellular calcium homeostasis, contributing to increased AF susceptibility. The inhibition of CaMKII may be a potential therapeutic target for AF in insulin resistance.

Tongguan capsule-derived herb reduces susceptibility to atrial fibrillation by inhibiting left atrial fibrosis via modulating cardiac fibroblasts

Tongguan capsule is a compound Chinese medicine used to treat ischaemic heart diseases. This study aimed to investigate whether Tongguan capsule-derived herb (TGD) has a preventive effect on atrial fibrillation (AF) in post-myocardial infarction (MI) rats and to determine the underlying mechanisms. MI was induced by ligation of the left anterior descending coronary artery. TGD was administered to the post-MI rats over a 4-week period. The TGD-treated rats had lower rates of AF inducibility and shorter AF durations than the MI rats. TGD improved the left atrial (LA) conduction velocity and homogeneity. It reduced the fibrosis-positive areas and the protein levels of collagen types I and III in the left atrium. In vitro, it inhibited the expression of collagen types I and III by inhibiting the proliferation, migration, differentiation and cytokine secretion of cardiac fibroblasts (CFs). In conclusion, the current study demonstrated that TGD reduces susceptibility to AF and improves LA conduction function in rats with post-MI by inhibiting left atrial fibrosis and modulating CFs. Targeting the CF population may be a novel antiarrhythmic therapeutic approach.

MD1 Deficiency Promotes Inflammatory Atrial Remodelling Induced by High-Fat Diets

BACKGROUND

Myeloid differentiation protein 1 (MD1) is expressed in various tissues, including the heart. However, the role of MD1 in obesity-related atrial remodelling remains incompletely understood. Here, this study intends to determine the regulatory role and underlying mechanisms of MD1 in obesity-related atrial remodelling.

METHODS

A high-fat diet (HFD) feeding was performed in 6-week-old MD1-knockout (MD1-KO) mice and wild-type (WT) littermates for 20 weeks. Morphological, biochemical, functional, histological, and electrophysiological studies were conducted at the age of 26 weeks.

RESULTS

Our results revealed that the MD1 expression levels were downregulated in the atrium of the HFD-fed induced obesity mice. An increase in body weight, glucose intolerance, hyperlipidemia, and adverse atrial remodelling, such as atrial inflammation and fibrosis, were induced by HFD feeding in WT mice. Vulnerability to atrial fibrillation (AF) was also significantly increased by HFD feeding in WT mice. In addition, these adverse effects caused by HFD-fed induced obesity were further exaggerated in MD1-KO mice compared with WT mice. Mechanistically, MD1-KO activated TLR4/NF-κB signaling pathways, which led to atrial remodelling in mice fed by HFD by increasing the phosphorylation of p65 and IκBα.

CONCLUSIONS

Our data suggested that MD1 deficiency played an important role in accelerating the development of inflammatory atrial fibrosis and increasing vulnerability to AF in mice with HFD-fed induced obesity, providing an essential target for improving HFD-induced atrial remodelling.

Antihyperglycemic drugs use and new-onset atrial fibrillation: A population-based nested case control study

Currently, the potential risk of atrial fibrillation associated with antihyperglycemic drug use has been a topic of considerable interest. However, it remains uncertain whether different classes of antihyperglycemic drug therapy are associated with the risk of atrial fibrillation risk. Here, we investigated the association between different classes of antihyperglycemic drugs and new-onset atrial fibrillation (NAF). A case-matched study was performed based on the National Health Insurance Program in Taiwan. Patients who had NAF were considered the NAF group and were matched in a 1:4 ratio with patients without NAF, who were assigned to the non-NAF group. Patients were matched according to sex, age, diabetes mellitus duration, index date, and Charlson Comorbidity Index score. We used multivariate logistic regression controlling for potential confounders to examine the association between different classes of antihyperglycemic drug use and the risk of NAF. Overall, we identified 2,882 cases and 11,528 matched controls for the study. After adjusting for sex, age, comorbidities, and concurrent medications, users of biguanides or thiazolidinediones were at a lower risk of developing NAF when compared with non-users (odds ratio [OR] 0.81, 95% confidence interval [CI] 0.71-0.95 and OR 0.72, 95% CI 0.63-0.83, respectively). In contrast, users of insulin were at a higher risk of developing NAF than were non-users (OR 1.19, 95% CI 1.06-1.35). Sulfonylureas, glinides, α-glucosidase inhibitors, and dipeptidyl peptidase-4 inhibitors were not associated with developing the risk of NAF. In conclusion, the use of biguanides or thiazolidinediones may be associated with a low risk of NAF, whereas insulin may be associated with a significant increase in the risk of NAF in patients with type 2 diabetes mellitus during long-term follow-up. Further prospective randomized studies should investigate which specific class of antihyperglycemic drug treatment for diabetes mellitus can prevent or postpone NAF.

Activin Receptor-Like Kinase 4 Haplodeficiency Mitigates Arrhythmogenic Atrial Remodeling and Vulnerability to Atrial Fibrillation in Cardiac Pathological Hypertrophy

Background Activin receptor-like kinase 4 ( ALK 4) is highly expressed in mammal heart. Atrial fibrillation ( AF ) is closely related to ventricular pressure overload. Because pressure overload increases atrial pressure and leads to atrial remodeling, it would be informative to know whether ALK 4 exerts potential effects on atrial remodeling and AF vulnerability in a pressure-overload model. Methods and Results Wild-type littermates and ALK 4+/- mice were subjected to abdominal aortic constriction or a sham operation. After 4 or 8 weeks, echocardiographic and hemodynamic measurements were performed, and inducibility of AF was tested. The hearts were divided into atria and ventricles and then were fixed in formalin for staining, or they were weighted and snap-frozen for quantitative real-time polymerase chain reaction and Western blot analysis. Compared with wild-type littermates, ALK 4+/- mice demonstrated a similar extent of atrial hypertrophy but significantly suppressed atrial fibrosis at 8 weeks post-abdominal aortic constriction. ALK 4 haplodeficiency partially blocked abdominal aortic constriction-induced upregulation of monocyte chemotactic protein 1 and interleukin-6, and the increased chemotaxin of macrophages. ALK 4 haplodeficiency also blunted a reduction of connexin 40 and redistribution of connexin 43 from the intercalated disk to the lateral membranes, thereby improving localized conduction abnormalities. Meanwhile, ALK 4 haplodeficiency inhibited abdominal aortic constriction-induced decreased INa, ICa-L and IK1 densities as well as the accompanying action potential duration shortening. Mechanistically, ALK 4 haploinsufficiency resulted in the suppression of Smad2/3 activity in this model. Conclusions Our results demonstrate that ALK 4 haplodeficiency ameliorates atrial remodeling and vulnerability to AF in a pressure-overload model through inactivation of the Smad2/3 pathway, suggesting that ALK 4 might be a potential therapeutic target in combating pressure overload-induced AF .

Atrial overexpression of microRNA-27b attenuates angiotensin II-induced atrial fibrosis and fibrillation by targeting ALK5

Atrial fibrosis influences atrial fibrillation (AF) development by transforming growth factor beta 1 (TGF-β1)/Smad pathway. Although microRNAs are implicated in the pathogenesis of various diseases, information regarding the functional role of microRNAs in atrial dysfunction is limited. In the present study, we found that microRNA-27b (miR-27b) was the dominant member of miR-27 family expressed in left atrium. Moreover, the expression of miR-27b was significantly reduced after angiotensin II (AngII) infusion. Masson's trichrome staining revealed that delivery of miR-27b adeno-associated virus to left atrium led to a decrease in atrial fibrosis induced by AngII. The increased expression of collagen I, collagen III, plasminogen activator inhibitor type 1 and alpha smooth muscle actin was also inhibited after miR-27b upregulation. In isolated perfused hearts, miR-27b restoration markedly attenuated AngII-induced increase in interatrial conduction time, AF incidence and AF duration. Furthermore, our data evidence that miR-27b is a novel miRNA that targets ALK5, a receptor of TGF-β1, through binding to the 3' untranslated region of ALK5 mRNA. Ectopic miR-27b suppressed luciferase activity and expression of ALK5, whereas inhibition of miR-27b increased ALK5 luciferase activity and expression. Additionally, miR-27b inhibited AngII-induced Smad-2/3 phosphorylation without altering Smad-1 activity. Taken together, our study demonstrates that miR-27b ameliorates atrial fibrosis and AF through inactivation of Smad-2/3 pathway by targeting ALK5, suggesting miR-27b may play an anti-fibrotic role in left atrium and function as a novel therapeutic target for the treatment of cardiac dysfunction.

MicroRNA-30c suppresses the pro-fibrogenic effects of cardiac fibroblasts induced by TGF-β1 and prevents atrial fibrosis by targeting TGFβRII

Atrial fibrosis serves as an important contributor to atrial fibrillation (AF). Recent data have suggested that microRNA-30c (miR-30c) is involved in fibrotic remodelling and cancer development, but the specific role of miR-30c in atrial fibrosis remains unclear. The purpose of this study was to investigate the role of miR-30c in atrial fibrosis and its underlying mechanisms through in vivo and in vitro experiments. Our results indicate that miR-30c is significantly down-regulated in the rat abdominal aortic constriction (AAC) model and in the cellular model of fibrosis induced by transforming growth factor-β1 (TGF-β1). Overexpression of miR-30c in cardiac fibroblasts (CFs) markedly inhibits CF proliferation, differentiation, migration and collagen production, whereas decrease in miR-30c leads to the opposite results. Moreover, we identified TGFβRII as a target of miR-30c. Finally, transferring adeno-associated virus 9 (AAV9)-miR-30c into the inferior vena cava of rats attenuated fibrosis in the left atrium following AAC. These data indicate that miR-30c attenuates atrial fibrosis via inhibition of CF proliferation, differentiation, migration and collagen production by targeting TGFβRII, suggesting that miR-30c might be a novel potential therapeutic target for preventing atrial fibrosis.

Matrine reduces susceptibility to postinfarct atrial fibrillation in rats due to antifibrotic properties

This study aimed to investigate whether matrine could prevent atrial fibrillation (AF) after myocardial infarction by reducing left atrial fibrosis, and to determine the underlying mechanisms in isolated cardiac fibroblasts (CFs). Five weeks after MI, matrine-treated rats had lower rates of AF inducibility and shorter AF duration than MI rats. Matrine improved the left atrial conduction velocity and homogeneity. Matrine decreased the fibrosis positive areas and the protein levels of type I collagen and type III collagen in the left atrium. Matrine inhibited CFs differentiation to myofibroblasts and the expression of transforming growth factor-beta 1 and matrix metalloproteinase 9. In vitro, matrine inhibited the CFs proliferation, migration, differentiation, and secretion ability. These in vitro and in vivo data demonstrated that matrine has the potential to reduce susceptibility to AF after MI due, at least in part, to reduced atrial fibrosis via inhibiting CFs proliferation, migration, differentiation, and secretion ability.

A Comparison of Phenomenologic Growth Laws for Myocardial Hypertrophy

The heart grows in response to changes in hemodynamic loading during normal development and in response to valve disease, hypertension, and other pathologies. In general, a left ventricle subjected to increased afterload (pressure overloading) exhibits concentric growth characterized by thickening of individual myocytes and the heart wall, while one experiencing increased preload (volume overloading) exhibits eccentric growth characterized by lengthening of myocytes and dilation of the cavity. Predictive models of cardiac growth could be important tools in evaluating treatments, guiding clinical decision making, and designing novel therapies for a range of diseases. Thus, in the past 20 years there has been considerable effort to simulate growth within the left ventricle. While a number of published equations or systems of equations (often termed "growth laws") can capture some aspects of experimentally observed growth patterns, no direct comparisons of the various published models have been performed. Here we examine eight of these laws and compare them in a simple test-bed in which we imposed stretches measured during in vivo pressure and volume overload. Laws were compared based on their ability to predict experimentally measured patterns of growth in the myocardial fiber and radial directions as well as the ratio of fiber-to-radial growth. Three of the eight laws were able to reproduce most key aspects of growth following both pressure and volume overload. Although these three growth laws utilized different approaches to predict hypertrophy, they all employed multiple inputs that were weakly correlated during in vivo overload and therefore provided independent information about mechanics.

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

BACKGROUND/AIMS

Recent evidence indicates that peroxisome proliferator-activated receptor (PPAR)-γ activators exert anti-inflammatory and antioxidant actions. However, the underlying mechanisms by which these agents prevent atrial remodeling in diabetes are not completely elucidated. We sought to investigate the potential effects of pioglitazone, a PPAR-γ activator, on atrial remodeling and atrial fibrillation (AF) inducibility in diabetic rabbits.

METHODS

Alloxan-induced diabetic rabbits were randomly divided into three groups: diabetes only, diabetes treated with low-dose pioglitazone (4 mg/day/kg), or diabetes treated with high-dose pioglitazone (8 mg/day/kg) (n=24 for each group). A total of 24 healthy rabbits served as controls. Eight weeks later, hemodynamic, echocardiographic, and electrophysiological parameters were recorded. Left atrial whole-cell patch-clamp studies, histological examination, and Western blot analysis were also performed.

RESULTS

In the DM group (6/8 vs 1/8, P<.05), higher AF inducibility, increased amount of fibrosis, lower INa , and higher ICaL were observed in the DM group compared to controls. Western blot analysis showed that DM increased the expression of extracellular signal-regulated kinase 2 (ERK2), phosphorylation ERK, transforming growth factor beta-1, Toll-like receptor 4, nuclear factor-κB p50, and heat-shock protein 70. All of these electrophysiological, histological, ion current density, and protein expression changes were all reduced by pioglitazone.

CONCLUSION

Pioglitazone attenuates diabetes-induced structural and electrophysiological remodeling in the atria, thereby reducing the vulnerability to AF.

Oxidative stress and inflammation as central mediators of atrial fibrillation in obesity and diabetes

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in humans. Several risk factors promote AF, among which diabetes mellitus has emerged as one of the most important. The growing recognition that obesity, diabetes and AF are closely intertwined disorders has spurred major interest in uncovering their mechanistic links. In this article we provide an update on the growing evidence linking oxidative stress and inflammation to adverse atrial structural and electrical remodeling that leads to the onset and maintenance of AF in the diabetic heart. We then discuss several therapeutic strategies to improve atrial excitability by targeting pathways that control oxidative stress and inflammation.

Antihyperglycemic drugs use and new-onset atrial fibrillation in elderly patients

BACKGROUND

Antihyperglycemic drugs have been linked to new-onset atrial fibrillation (NAF). However, the effect of the different classes of antihyperglycemic drugs on the development of NAF in elderly patients has not been well studied. In this study, we investigated the association between different classes of antihyperglycemic drugs and NAF in elderly patients.

MATERIALS AND METHODS

This was a nested case-control study performed using the database of National Health Insurance programme in Taiwan. Each participant aged 65 years and older who were NAF from 2005 to 2012 were assigned to the NAF group, whereas case was sex-, age-, diabetes duration-, index date-matched, and Charlson Comorbidity Index score-matched randomly selected participant without NAF were assigned to the non-NAF group. Multivariable logistic regression model was used for the estimation of odds ratios (ORs) and 95% confidence intervals (CIs) of NAF associated with use of different classes of antihyperglycemic agents. Nonusers served as the reference group.

RESULTS

We identified 1958 cases and 7832 controls. The risk of NAF after adjusting for sex, age, comorbidities and concurrent medication was higher among the users of insulin than among the nonusers (OR, 1·58; 95% CI, 1·37-1·82). Patients who took dipeptidyl peptidase 4 inhibitors were at lower risk of developing NAF than the nonusers (OR, 0·65; 95% CI, 0·45-0·93).

CONCLUSIONS

In this population, use of dipeptidyl peptidase 4 inhibitor was associated with a low risk of NAF. Insulin use was associated with a significant increase in the risk of NAF during the long-term follow-up.

Thiazolidinedione use and atrial fibrillation in diabetic patients: a meta-analysis

BACKGROUND

Accumulating evidence suggests that thiazolidinediones (TZDs) may exert protective effects in atrial fibrillation (AF). The present meta-analysis investigated the association between TZD use and the incidence of AF in diabetic patients.

METHODS

Electronic databases were searched until December 2016. Of the 346 initially identified records, 3 randomized clinical trials (RCTs) and 4 observational studies with 130,854 diabetic patients were included in the final analysis.

RESULTS

Pooled analysis of the included studies demonstrated that patients treated with TZDs had approximately 30% lower risk of developing AF compared to controls [odds ratio (OR): 0.73, 95% confidence interval (CI): 0.62 to 0.87, p = 0.0003]. This association was consistently observed for both new onset AF (OR =0.77, p = 0.002) and recurrent AF (OR =0.41, p = 0.002), pioglitazone use (OR =0.56, p = 0.04) but not rosiglitazone use (OR =0.78, p = 0.12). The association between TZD use and AF incidence was not significant in the pooled analysis of three RCTs (OR =0.77, 95% CI = 0.53-1.12, p = 0.17), but was significantly in the pooled analysis of the four observational studies (OR =0.71, p = 0.0003).

CONCLUSIONS

This meta-analysis suggests that TZDs may confer protection against AF in the setting of diabetes mellitus (DM). This class of drugs can be used as upstream therapy for DM patients to prevent the development of AF. Further large-scale RCTs are needed to determine whether TZDs use could prevent AF in the setting of DM.

Mast Cells Play an Important Role in the Pathogenesis of Hyperglycemia-Induced Atrial Fibrillation

BACKGROUND AND OBJECTIVES

Recently, it was reported that mast cells (MCs) could underlie the mechanisms of several cardiovascular diseases. However, the role of MCs in diabetes-induced atrial fibrillation (AF) has not been notably investigated. We tested the hypothesis that MC deficiency attenuates hyperglycemia-induced AF in mice.

METHODS AND RESULTS

Mast cell-deficient W/W(v)  mice, and congenic +/+ littermates (WT) were divided into either the vehicle (VEH)-injection group or the streptozotocin (STZ)-injection group (MCKO-VEH, MCKO-STZ, WT-VEH, and WT-STZ groups). On day 28 of our studies, we observed that (1) STZ-induced hyperglycemia increased MC infiltration in the left atrium (LA) in WT mice (P < 0.01), (2) atrium isolated from the WT-STZ group showed inhomogeneous interstitial fibrosis, abundant infiltration of macrophages, and enhanced apoptosis compared to the WT-VEH group (P < 0.01, P < 0.01, P < 0.05, respectively). However, the changes observed in the WT-STZ group were significantly attenuated in the MCKO-STZ mice. In addition, we observed that (3) messenger RNA levels of tumor necrosis factor-α, monocyte chemoattractant protein-1, interleukin-1β, transforming growth factor-β, and collagen-1 in the LA were increased in the WT-STZ group, but not in the MCKO-STZ group, (4) STZ-induced hyperglycemia increased AF induction and prolonged interatrial conduction time in the WT mice, which were not observed in the MCKO mice, and that (5) hyperglycemia-enhanced atrial production of reactive oxygen species (ROS) was equally observed in the WT and MCKO mice.

CONCLUSIONS

Our results suggest that MCs contribute to the pathogenesis of hyperglycemia-induced AF via enhancement of inflammation and fibrosis.

High-fat diet increases vulnerability to atrial arrhythmia by conduction disturbance via miR-27b

BACKGROUND

Lifestyle-related diseases, such as obesity and dyslipidemia are important risk factors for atrial fibrillation (AF). However, the underlying mechanism linking these diseases and AF has not been fully investigated.

METHODS

Adult male mice were fed a high-fat diet (HFD) or vehicle (NC) for 2 months. Electrocardiography and in vivo electrophysiological study were performed. Mice were then sacrificed for quantification of mRNA, microRNA, and protein in atria, in addition to histological analysis. Conduction velocity (CV) in right atrium was measured by optical mapping in Langendorff perfused hearts. Cultured atrial cardiomyocytes were treated with palmitate with or without a specific microRNA inhibitor. Twelve hours after stimulation, cells were lysed, and subjected to analysis with qPCR and Western blotting.

RESULTS

HFD mice showed prolonged P wave duration, increased inducibility of sustained atrial tachycardia, and reduced atrial CV than NC mice. HFD mice also showed increased expression in inflammatory cytokines, whereas fibrotic area and signals relating fibrosis were not changed. HFD mice demonstrated reduced expression of Cx40 in mRNA and protein levels, and its lateralized expression in atria. MicroRNA array analysis revealed that miR-27b expression was up-regulated in HFD mice, and luciferase assay confirmed the direct interaction between miR-27b and Cx40 3'UTR. In palmitate-stimulated atrial cardiomyocytes, miR-27b up-regulation and Cx40 down-regulation were observed, while expression of inflammatory cytokines was not altered. Inhibition of miR-27b with antisense oligonucleotides reversed the alteration caused by palmitate stimulation.

CONCLUSION

HFD may increase the vulnerability to atrial arrhythmia by down-regulation of Cx40 via miR-27b, rather than fibrosis, which is independent of inflammation.

Role of Indoxyl Sulfate as a Predisposing Factor for Atrial Fibrillation in Renal Dysfunction

Background

Renal dysfunction is a major risk factor for atrial fibrillation (AF). The uremic toxin indoxyl sulfate may contribute to the progression of cardiac fibrosis and AF substrate in renal dysfunction.

Methods and Results

Male Sprague–Dawley rats were assigned randomly to the following groups: 5/6 nephrectomy (5/6Nx) with vehicle, 5/6Nx with AST‐120, sham procedure with vehicle, and sham procedure with AST‐120. Vehicle and AST‐120 were administered for 4 weeks. Serum levels of IS were significantly increased in 5/6Nx groups. Expression of malondialdehyde, an indicator of oxidative stress, was upregulated in the left atrium of 5/6Nx groups and was accompanied by an increase in expression of NADPH oxidase 2 and 4. Monocyte‐mediated inflammatory signals such as CD68, monocyte chemoattractant protein 1, and vascular cell adhesion molecule 1 were also upregulated in 5/6Nx groups. Interstitial fibrosis was promoted heterogeneously, and expression of profibrotic indicators such as transforming growth factor β1, α‐smooth muscle actin, and collagen type 1 was upregulated in left atrium tissue of 5/6Nx groups. In cultured atrial fibroblasts, incubation with IS upregulated expression of the markers of oxidative stress, inflammation, and profibrotic factors. These results suggest the direct effects of IS on the progression of AF substrate. AF was consistently and invariably induced by atrial extrastimuli in 5/6Nx groups in electrophysiological experiments. AST‐120 treatment significantly alleviated renal dysfunction–induced oxidative stress, inflammation, and atrial fibrosis and, consequently, attenuated AF inducibility.

Conclusions

Indoxyl sulfate facilitates atrial fibrosis and AF and thus is a novel therapeutic target for prevention of renal dysfunction–induced AF.

Splenectomy exacerbates atrial inflammatory fibrosis and vulnerability to atrial fibrillation induced by pressure overload in rats: Possible role of spleen-derived interleukin-10

BACKGROUND

The spleen is important for cardiac remodeling induced by myocardial infarction. However, the role of the spleen in inflammatory atrial fibrosis induced by pressure overload is unknown.

OBJECTIVE

The purpose of this study was to investigate whether splenectomy (SPX) attenuates or exacerbates pressure overload-induced atrial inflammatory fibrosis and vulnerability to atrial fibrillation (AF) in rats.

METHODS

Male Sprague-Dawley rats (6 weeks old) were divided into Sham+Sham, Sham+SPX, abdominal aortic constriction (AAC)+Sham, and AAC+SPX groups, and were evaluated for inflammation, fibrosis, and AF on days 2, 4, 14, and 28.

RESULTS

On day 4, an AAC-induced rise in interleukin-10 (IL-10) level was observed in the spleen, serum, and left atrium (LA), with SPX showing inhibitory effects in the latter 2 instances. In addition, AAC-induced M2 macrophage recruitment into the LA was decreased by SPX, as determined by immunofluorescence labeling (P <.05). On day 28, AAC-induced heterogeneous interstitial fibrosis of the LA was enhanced by SPX (P <.05). Electrophysiologic recordings revealed that the duration of AF and prolongation of interatrial conduction time induced by AAC were increased by SPX (P < .01 and P <.05, respectively). Furthermore, in the AAC+SPX group, the number of macrophages infiltrating into the LA on day 2 was marginal, but increased on day 28 relative to the AAC+Sham group. IL-10 administration attenuated the AAC-induced atrial remodeling that was aggravated by SPX.

CONCLUSION

The study results suggest that SPX exacerbates AAC-induced inflammatory atrial fibrosis and increases vulnerability to AF after 4 weeks, likely because of depletion of spleen-derived IL-10.

Diabetes mellitus and atrial fibrillation: Pathophysiological mechanisms and potential upstream therapies

Diabetes mellitus (DM) represents one of the most important risk factors for atrial fibrillation (AF) while AF is a strong and independent marker of overall mortality and cardiovascular morbidity in diabetic patients. Autonomic, electrical, electromechanical, and structural remodeling, including oxidative stress, connexin remodeling and glycemic fluctuations seem to be implicated in AF pathophysiology in the setting of DM. The present review highlights the association between DM and AF, provides a comprehensive overview of the responsible pathophysiological mechanisms and briefly discusses potential upstream therapies for DM-related atrial remodeling.

Pioglitazone improves potassium channel remodeling induced by angiotensin II in atrial myocytes

BACKGROUND

It has been demonstrated that atrial electrical remodeling contributes toward atrial fibrillation (AF) maintenance, and that angiotensin II (AngII) is involved in the pathogenesis of atrial electrical remodeling. Peroxisome proliferator activated receptor-γ (PPAR-γ) agonists have been shown to inhibit atrial electrical remodeling, but the underlying mechanisms are poorly understood. In the present study we investigated the regulating effects of PPAR-g agonist on AngII-induced potassium channel remodeling in atrial myocytes.

MATERIAL/METHODS

Whole-cell patch-clamp technique was used to record transient outward potassium current (Ito), ultra-rapid delayed rectifier potassium (Ikur), and inward rectifier potassium current (Ik1). Real-time PCR was used to assess potassium channel subunit mRNA expression.

RESULTS

Compared with the control group, AngII reduced Ito and Ikur current density as well as amplified Ik1 current density, which were partially prevented by pioglitazone. Furthermore, pioglitazone alleviated the downregulation of Ito subunit (Kv 4.2) and Ikur subunit (Kv 1.5), as well as the upregulation of Ik1 subunit (Kir 2.1 and Kir 2.2) mRNA expression stimulated by AngII.

CONCLUSIONS

These results suggest that pioglitazone exhibits a beneficial effect on AngII-induced potassium channel remodeling. PPAR-γ agonists may be potentially effective up-stream therapies for AF.

Diabetes mellitus and atrial remodeling: mechanisms and potential upstream therapies

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice, and its prevalence has increasing substantially over the last decades. Recent data suggest that there is an increased risk of AF among the patients with diabetes mellitus (DM). However, the potential molecular mechanisms regarding DM-related AF and diabetic atrial remodeling are not fully understood. In this comprehensive review, we would like to summarize the potential relationship between diabetes and atrial remodeling, including structural, electrical, and autonomic remodeling. Also, some upstream therapies, such as thiazolidinediones, probucol, ACEI/ARBs, may play an important role in the prevention and treatment of AF. Therefore, large prospective randomized, controlled trials and further experimental studies should be challengingly continued.

Pioglitazone inhibits angiotensin II-induced atrial fibroblasts proliferation via NF-κB/TGF-β1/TRIF/TRAF6 pathway

The exact mechanisms underlying inhibitory effects of pioglitazone (Pio) on Angiotensin II (AngII)-induced atrial fibrosis are complex and remain largely unknown. In the present study, we examined the effect of Pio on AngII-induced mice atrial fibrosis in vivo and atrial fibroblasts proliferation in vitro. In vivo study showed that AngII infusion induced atrial fibrosis and increased expressions of Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF) and tumor necrosis factor receptor associated factor 6 (TRAF6) in mice models. However, those effects could be attenuated by Pio (P<0.01). As for in vitro experiment, Pio suppressed AngII-induced atrial fibroblasts proliferation via nuclear factor-κB/transforming growth factor-β1/TRIF/TRAF6 signaling pathway in primary cultured mice atrial fibroblasts (P<0.01). In conclusion, suppression of Pio on AngII-induced atrial fibrosis might be related to its inhibitory effects on above signaling pathway.

Rosiglitazone attenuates atrial structural remodeling and atrial fibrillation promotion in alloxan-induced diabetic rabbits

INTRODUCTION

The pleiotropic effects of glitazones may favorably affect atrial remodeling. We sought to investigate the effects of peroxisome proliferator-activated receptor-γ (PPAR-γ) activator rosiglitazone on atrial structural remodeling and atrial fibrillation (AF) promotion in alloxan-induced diabetic rabbits.

METHODS

Twenty alloxan-induced diabetic rabbits were randomly divided into two groups (10 animals in each group), namely the diabetic rosiglitazone group (treated with rosiglitazone 2 mg/day/kg for 4 weeks) and the nontreated diabetic group, while 10 additional healthy rabbits served as controls. Moreover, isolated Langendorff-perfused rabbit hearts were used to evaluate atrial electrophysiological parameters and vulnerability to AF, examined by burst pacing. Histological examination was also performed, whereas plasma oxidative stress and inflammatory biomarkers were measured.

RESULTS

The duration of induced AF was significantly prolonged in the alloxan-induced diabetic rabbits compared with controls (1.6 ± 0.4 s vs. 0 s; P < 0.05). Rosiglitazone treatment significantly reduced the duration of induced AF in the treated rabbits (1.6 ± 0.4 s vs. 1.2 ± 0.05 s; P < 0.05). Moreover, rosiglitazone attenuated atrial structural remodeling reducing the interatrial activation time (35.4 ± 12.1 ms vs. 24.2 ± 10.8 ms, P < 0.05; control 23.3 ± 10.4 ms) and the atrial interstitial fibrosis as well (collagen volume fraction: 5.6 ± 3.9% vs. 2.4 ± 2.1%, P < 0.05; control 1.6 ± 0.8%). Rosiglitazone increased plasma superoxide dismutase (SOD) activity and, on the other hand, decreased malondialdehyde (MDA), hs-C-reactive protein, and tumor necrosis factor-α levels.

CONCLUSION

Rosiglitazone attenuates arrhythmogenic atrial structural remodeling and AF promotion in alloxan-induced diabetic rabbits. Also, it seems to modulate oxidative stress and inflammation in this experimental model.