Ranolazine improves oxidative stress and mitochondrial function in the atrium of acetylcholine-CaCl2 induced atrial fibrillation rats

Empagliflozin protects the heart from atrial fibrillation in rats through inhibiting the NF-κB/HIF-1α regulatory axis and atrial remodeling

Atrial fibrillation (AF) is the most common form of sustained cardiac arrhythmia. The current study aimed to investigate the potential of empagliflozin (EMPA) to protect against acetylcholine (ACh)/calcium chloride (CaCl2)-induced AF in rats and elucidate the possible underlying mechanism of action. Rats were randomly assigned to five groups, as follows: CTRL group: received 1 ml/kg isotonic saline; AF group: received 1 ml/kg induction mixture of ACh/CaCl2 (60 µg ACh and 10 mg CaCl2 per ml); EMPA group: received 30 mg/kg EMPA; AF + EMPA10 group: received the induction mixture concurrent with 10 mg/kg EMPA; AF + EMPA30 group: received the induction mixture concurrent with 30 mg/kg EMPA. Our results showed that EMPA administration inhibited the AF-related electrocardiographic abnormalities and decreased the serum brain natriuretic peptide levels. EMPA treatment maintained the cardiac redox balance, as indicated by reduced levels of the lipid peroxidation biomarker malonaldehyde while enhancing the antioxidant glutathione levels. Moreover, EMPA markedly repressed ACh/CaCl2-induced C-reactive protein, tumor necrosis factor, and interleukin-6 production. Interestingly, EMPA administration strongly suppressed cardiac transforming growth factor beta1, collagen type I, and alpha-smooth muscle actin expression levels in the AF rats. These results were consistent with our histopathological findings, which revealed the ameliorative effect of EMPA on AF-induced inflammatory and fibrotic lesions. Mechanistically, EMPA dose-dependently downregulated nuclear factor-kappa B (NF-κB) and hypoxia-inducible factor (HIF)-1α expressions. Besides, it attenuated the pro-apoptotic active caspase-3 while augmenting the anti-apoptotic B-cell lymphoma 2 expressions. Furthermore, EMPA dose-dependently suppressed cardiac phosphatidylinositol 3-kinase (PI3K)/Akt signaling. In conclusion, this study demonstrates that EMPA intervention, within AF induction, protects against ACh/CaCl2-induced AF in rats, exerting powerful antioxidant, anti-inflammatory, anti-fibrotic, and anti-apoptotic effects. These effects are mainly mediated through the targeting of the NF-κB/HIF-1α regulatory axis in a dose-dependent manner.

Halofuginone ameliorates the susceptibility to atrial fibrillation by activating the PI3K/Akt signaling pathway

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice. Halofuginone (HF) exerts beneficial effects on organ fibrosis, periodontitis, and cancer. However, the effect of HF against AF remains unknown. During the induction of AF, the rats were intragastrically administered HF (5 mg/kg and 10 mg/kg) daily for 7 consecutive days. Cardiac function was evaluated through echocardiographic analysis. The presence of pathological changes and interstitial fibrosis in the left atrial tissues were investigated. Intracellular Ca2+ homeostasis and mitochondrial function in atrial tissues were evaluated. The activation of the PI3K/Akt signaling pathway was examined, and an allosteric Akt inhibitor, MK-2206, was applied to confirm the involvement of the PI3K/Akt signaling pathway in the protection against AF by HF. The administration of HF resulted in a prolongation of the atrial effective refractory period (AERP), a reduction in both the duration and inducibility of AF, and a decrease in atrial weight, heart weight, atrial weight/body weight ratio, and heart weight/body weight ratio in rats with AF. In addition, the administration of HF resulted in a reduction in left atrial diameter (LAD) and an increase in left ventricular internal diameter diastolic (LVIDd), ejection fraction (EF), and fractional shortening (FS), while having no effect on left ventricular internal diameter systolic (LVIDs). The pathological changes and cardiac fibrosis observed in rats with AF were mitigated by HF. Moreover, HF enhanced mitochondrial function, suppressed cardiomyocyte apoptosis, and activated the PI3K/Akt pathway in AF rats. Furthermore, the protective effect against AF was also observed in an in vitro model. The effects of HF on fibrosis markers, intracellular Ca2+ homeostasis, mitochondrial function, and cardiac apoptosis were blocked by MK-2206. HF alleviated the susceptibility to AF in vivo and in vitro via the activation of the PI3K/Akt signaling pathway.

Restoring the Autonomic Balance in an Atrial Fibrillation Rat Model by Electroacupuncture at the Neiguan Point

OBJECTIVES

Autonomic nervous activity imbalance plays an important role in atrial fibrillation (AF). AF can be treated by acupuncture at the Neiguan point (PC6), but the mechanism remains elusive. Here, we investigated autonomic nervous system activity in electroacupuncture (EA) at PC6 in a rat AF model.

MATERIAL AND METHODS

In this study, we established a rat AF model via tail vein injection with ACh-CaCl2 for ten consecutive days with or without EA at PC6. AF inducibility and heart rate variability (HRV) were assessed by electrocardiogram. Next, we completed in vivo recording of the activity of cervical sympathetic and vagal nerves, respectively. Finally, the activities of brain regions related to autonomic nerve regulation were assessed by c-Fos immunofluorescence and multichannel recording.

RESULTS

EA at PC6 decreased AF inducibility and prevented changes in HRV caused by ACh-CaCl2 injection. Meanwhile, EA at PC6 reversed the increased sympathetic and decreased vagal nerve activity in AF rats. Furthermore, EA treatment downregulated increased c-Fos expression in brain regions, including paraventricular nucleus, rostral ventrolateral medulla, and dorsal motor nucleus of the vagus in AF, while c-Fos expression in nucleus ambiguus was upregulated with EA.

CONCLUSION

The protective effect of EA at PC6 on AF is associated with balance between sympathetic and vagal nerve activities.

Barium Chloride-Induced Cardiac Arrhythmia Mouse Model Exerts an Experimental Arrhythmia for Pharmacological Investigations

AIM

Cardiac arrhythmias are among the most important pathologies that cause sudden death. The exploration of new therapeutic options against arrhythmias with low undesirable effects is of paramount importance.

METHODS

However, the convenient and typical animal model for screening the potential lead compound becomes a very critical modality, particularly in anti-arrhythmia. In this study, mice were intraperitoneally (i.p.) injected with BaCl2, CaCl2, and adrenaline to induce arrhythmia, and simultaneously compared with BaCl2-induced rats.

RESULTS

Electrocardiogram (ECG) showed that the majority of mice repeatedly developed ventricular bigeminy, ventricular tachycardia (VT), and ventricular fibrillation (VF) after BaCl2-injection as seen in rats. The ECG of mice developed ventricular bigeminy and VT after CaCl2 and AT after adrenaline i.p. injection. Additionally, acute cardiac arrhythmia after BaCl2 i.p. injection could be reverted by drugs (lidocaine and amiodarone) administration. Additionally, the different routes of administration for various chemical-induced arrhythmia in both mice and rats were also retrieved from PubMed and summarized. Comparing this approach with previous studies after the literature review reveals that arrhythmia of BaCl2-induced i.p. mice is compatible with the induction of other routes.

CONCLUSIONS

This study brings an alternative experimental model to investigate antiarrhythmic theories and provides a promising approach to discovering new interventions for acute arrhythmias.

Targeting Nrf2/HO-1 and NF-κB/TNF-α signaling pathways with empagliflozin protects against atrial fibrillation-induced acute kidney injury in rats

A bidirectional relationship exists between atrial fibrillation (AF) and kidney function. Uncontrolled AF may lead to kidney injury, whereas renal dysfunction may contribute to AF initiation and maintenance. This study aimed to investigate the protective effect of the sodium glucose cotransporter-2 inhibitor empagliflozin (EMPA) on acute kidney injury (AKI) associated with AF induced by acetylcholine and calcium chloride (ACh/CaCl2) in rats and elucidate the potential underlying mechanism. Rats were randomly divided as follows: control (CTRL) group: administered vehicles only; AF group: intravenously injected 1 ml/kg of an ACh/CaCl2 mixture for seven days to induce AF; EMPA group: orally administered EMPA (30 mg/kg) for seven days; AF+EMPA10 and AF+EMPA30 groups: co-administered the induction mixture and EMPA (10 and 30 mg/kg, respectively) for seven days. Our results showed that EMPA (10 and 30 mg/kg) effectively maintained kidney function and demonstrated a significant antioxidant potential. EMPA also suppressed AF-induced renal tubulointerstitial injury and fibrotic changes concurrently with reducing renal levels of the pro-inflammatory cytokines tumour necrosis factor-α (TNF-α) and interleukin-6, as well as the pro-fibrotic marker transforming growth factor beta-1 and collagen type I. Mechanistically, EMPA boosted nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) renal tissue expression while repressing nuclear factor kappa B (NF-κB) activation. In addition, these beneficial effects of EMPA on kidneys were concurrent with its ability to effectively inhibit AF-related electrocardiographic changes, reduce incidence and duration of AF episodes, and markedly suppress serum B-type natriuretic peptide and C-reactive protein levels. In conclusion, EMPA protected against AKI associated with AF induced by ACh/CaCl2 in rats through simultaneous modulation of the Nrf2/HO-1 and the NF-κB/TNF-α signaling pathways, exerting antioxidant, anti-inflammatory, and anti-fibrotic effects.

Exenatide reduces atrial fibrillation susceptibility by inhibiting hKv1.5 and hNav1.5 channels

Exenatide, a promising cardioprotective agent, protects against cardiac structural remodeling and diastolic dysfunction. Combined blockade of sodium and potassium channels is valuable for managing atrial fibrillation (AF). Here, we explored whether exenatide displayed anti-AF effects by inhibiting human Kv1.5 and Nav1.5 channels. We used the whole-cell patch-clamp technique to investigate the effects of exenatide on hKv1.5 and hNav1.5 channels expressed in human embryonic kidney 293 cells and studied the effects of exenatide on action potential (AP) and other cardiac ionic currents in rat atrial myocytes. Additionally, an electrical mapping system was used to explore the effects of exenatide on electrical properties and AF activity in isolated rat hearts. Finally, a rat AF model, established using acetylcholine and calcium chloride, was employed to evaluate the anti-AF potential of exenatide in rats. Exenatide reversibly suppressed IKv1.5 with IC50 of 3.08 μM, preferentially blocked the hKv1.5 channel in its closed state, and positively shifted the voltage-dependent activation curve. Exenatide also reversibly inhibited INav1.5 with IC50 of 3.30 μM, negatively shifted the voltage-dependent inactivation curve, and slowed its recovery from inactivation with significant use-dependency at 5 and 10 Hz. Furthermore, exenatide prolonged AP duration and suppressed the sustained K+ current (Iss) and transient outward K+ current (Ito), but without inhibition of L-type Ca2+ current (ICa,L) in rat atrial myocytes. Exenatide prevented AF incidence and duration in rat hearts and rats. These findings demonstrate that exenatide inhibits IKv1.5 and INav1.5in vitro and reduces AF susceptibility in isolated rat hearts and rats.

Efficacy of nicorandil and ranolazine in prevention of contrast-induced nephropathy in patients with mild-to-moderate renal dysfunction: a randomized controlled trial

INTRODUCTION

Contrast-induced nephropathy (CIN) is a common complication after percutaneous coronary intervention (PCI). There is conflicting evidence regarding efficacy of nicorandil in CIN prevention. With respect to ranolazine, there is physiological possibility as well as data in animal study regarding its protective effect against CIN; there is, however, no human data till date.

AIM AND OBJECTIVES

To assess the efficacy of nicorandil and ranolazine in preventing CIN. The secondary endpoint was to measure difference in postprocedure acute kidney injury (AKI) incidence across groups. Also, patients were followed up till 6 months for major adverse events.

MATERIAL AND METHODS

This single-center randomized controlled study included 315 patients of coronary artery disease with mild-to-moderate renal dysfunction undergoing elective PCI. Eligible patients were assigned to either nicorandil (n = 105), ranolazine (n = 105) or control group (n = 105) in 1 : 1 : 1 ratio by block randomization. All enrolled patients were given intravenous sodium chloride at rate of 1.0 mL/kg/h (0.5 mL/kg/h for patients with left ventricular ejection fraction <45%) from 6 h before procedure till 12 h after procedure. Iso-osmolar contrast agent (iodixanol) was used for all patients. In addition to hydration, patients in nicorandil group received oral nicorandil (10 mg, 3 times/d) and those in ranolazine group received oral ranolazine (1000 mg, 2 times/d) 1 day before procedure and for 2 days after PCI. Patients in control group received only hydration.

RESULTS

Total number of CIN was 34 (10.7%), which included 19 (18.1%) in control, 8 (7.6%) in nicorandil and 7 (6.6%) in ranolazine group. There was significant association of CIN reduction across groups ( P  = 0.012). On pairwise comparison also, there was significant benefit across control and ranolazine as well as control and nicorandil ( P  < 0.025). There was numerically higher incidence of AKI in controls; the difference, however, did not reach statistical significance after applying Bonferroni correction ( P  = 0.044). Over 6-month follow-up, adverse events were similar across groups.

CONCLUSION

While this study adds to existing literature that supports role for nicorandil in CIN prevention, the efficacy of ranolazine in protecting against CIN has been demonstrated in humans for the first time.

Oxidative Stress, Inflammation, and Mitochondrial Dysfunction: A Link between Obesity and Atrial Fibrillation

The adipose tissue has long been thought to represent a passive source of triglycerides and fatty acids. However, extensive data have demonstrated that the adipose tissue is also a major endocrine organ that directly or indirectly affects the physiological functions of almost all cell types. Obesity is recognized as a risk factor for multiple systemic conditions, including metabolic syndrome, type 2 diabetes mellitus, sleep apnea, cardiovascular disorders, and many others. Obesity-related changes in the adipose tissue induce functional and structural changes in cardiac myocytes, promoting a wide range of cardiovascular disorders, including atrial fibrillation (AF). Due to the wealth of epidemiologic data linking AF to obesity, the mechanisms underlying AF occurrence in obese patients are an area of rich ongoing investigation. However, progress has been somewhat slowed by the complex phenotypes of both obesity and AF. The triad inflammation, oxidative stress, and mitochondrial dysfunction are critical for AF pathogenesis in the setting of obesity via multiple structural and functional proarrhythmic changes at the level of the atria. The aim of this paper is to provide a comprehensive view of the close relationship between obesity-induced oxidative stress, inflammation, and mitochondrial dysfunction and the pathogenesis of AF. The clinical implications of these mechanistic insights are also discussed.

Neuroprotective effect of ranolazine improves behavioral discrepancies in a rat model of scopolamine-induced dementia

Background

Ranolazine (Rn), an antianginal agent, acts in the central nervous system and has been used as a potential treatment agent for pain and epileptic disorders. Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases and the leading factor in dementia in the elderly.

Aim

We examined the impact of Rn on scopolamine (Sco)-induced dementia in rats.

Methods

Thirty-two albino male rats were divided into four groups: control, Rn, Sco, and Rn + Sco.

Results

A significant decrease in the escape latency in the Morris water maze test after pre-treatment with Rn explained better learning and memory in rats. Additionally, Rn significantly upregulated the activities of the antioxidant enzymes in the treated group compared to the Sco group but substantially reduced acetylcholinesterase activity levels in the hippocampus. Moreover, Rn dramatically reduced interleukin-1 β (IL-1β) and IL-6 and upregulated the gene expression of brain-derived neurotrophic factor (BDNF). Furthermore, in the Sco group, the hippocampal tissue's immunohistochemical reaction of Tau and glial factor activating protein (GFAP) was significantly increased in addition to the upregulation of the Caspase-3 gene expression, which was markedly improved by pre-treatment with Rn. The majority of pyramidal neurons had large vesicular nuclei with prominent nucleoli and appeared to be more or less normal, reflecting the all-beneficial effects of Rn when the hippocampal tissue was examined under a microscope.

Conclusion

Our findings indicated that Rn, through its antioxidative, anti-inflammatory, and anti-apoptotic effects, as well as the control of the expression of GFAP, BDNF, and Tau proteins, has a novel neuroprotective impact against scopolamine-induced dementia in rats.

Anti-inflammatory reprogramming of microglia cells by metabolic modulators to counteract neurodegeneration; a new role for Ranolazine

Microglia chronic activation is a hallmark of several neurodegenerative diseases, including the retinal ones, possibly contributing to their etiopathogenesis. However, some microglia sub-populations have anti-inflammatory and neuroprotective functions, thus making arduous deciphering the role of these cells in neurodegeneration. Since it has been proposed that functionally different microglia subsets also rely on different metabolic routes, we hypothesized that modulating microglia metabolism might be a tool to enhance their anti-inflammatory features. This would have a preventive and therapeutic potential in counteracting neurodegenerative diseases. For this purpose, we tested various molecules known to act on cell metabolism, and we revealed the anti-inflammatory effect of the FDA-approved piperazine derivative Ranolazine on microglia cells, while confirming the one of the flavonoids Quercetin and Naringenin, both in vitro and in vivo. We also demonstrated the synergistic anti-inflammatory effect of Quercetin and Idebenone, and the ability of Ranolazine, Quercetin and Naringenin to counteract the neurotoxic effect of LPS-activated microglia on 661W neuronal cells. Overall, these data suggest that using the selected molecules -also in combination therapies- might represent a valuable approach to reduce inflammation and neurodegeneration while avoiding long term side effects of corticosteroids.

The inter-chamber differences in the contractile function between left and right atrial cardiomyocytes in atrial fibrillation in rats

Introduction

The left and right atria (LA, RA) work under different mechanical and metabolic environments that may cause an intrinsic inter-chamber diversity in structure and functional properties between atrial cardiomyocytes (CM) in norm and provoke their different responsiveness to pathological conditions. In this study, we assessed a LA vs. RA difference in CM contractility in paroxysmal atrial fibrillation (AF) and underlying mechanisms.

Methods

We investigated the contractile function of single isolated CM from LA and RA using a 7-day acetylcholine (ACh)-CaCl2 AF model in rats. We compared auxotonic force, sarcomere length dynamics, cytosolic calcium ([Ca2+]i) transients, intracellular ROS and NO production in LA and RA CM, and analyzed the phosphorylation levels of contractile proteins and actin-myosin interaction using an in vitro motility assay.

Results

AF resulted in more prominent structural and functional changes in LA myocardium, reducing sarcomere shortening amplitude, and velocity of sarcomere relengthening in mechanically non-loaded LA CM, which was associated with the increased ROS production, decreased NO production, reduced myofibrillar content, and decreased phosphorylation of cardiac myosin binding protein C and troponin I. However, in mechanically loaded CM, AF depressed the auxotonic force amplitude and kinetics in RA CM, while force characteristics were preserved in LA CM.

Discussion

Thus, inter-atrial differences are increased in paroxysmal AF and affected by the mechanical load that may contribute to the maintenance and progression of AF.

A Polypyrrole-Polycarbonate Polyurethane Elastomer Alleviates Cardiac Arrhythmias via Improving Bio-Conductivity

Myocardial fibrosis, resulting from myocardial infarction (MI), significantly alters cardiac electrophysiological properties. As fibrotic scar tissue forms, its resistance to incoming action potentials increases, leading to cardiac arrhythmia, and eventually sudden cardiac death or heart failure. Biomaterials are gaining increasing attention as an approach for addressing post-MI arrhythmias. The current study investigates the hypothesis that a bio-conductive epicardial patch can electrically synchronize isolated cardiomyocytes in vitro and rescue arrhythmic hearts in vivo. A new conceived biocompatible, conductive, and elastic polyurethane composite bio-membrane, referred to as polypyrrole-polycarbonate polyurethane (PPy-PCNU), is developed, in which solid-state conductive PPy nanoparticles are distributed throughout an electrospun aliphatic PCNU nanofiber patch in a controlled manner. Compared to PCNU alone, the resulting biocompatible patch demonstrates up to six times less impedance, with no conductivity loss over time, as well as being able to influence cellular alignment. Furthermore, PPy-PCNU promotes synchronous contraction of isolated neonatal rat cardiomyocytes and alleviates atrial fibrillation in rat hearts upon epicardial implantation. Taken together, epicardially-implanted PPy-PCNU could potentially serve as a novel alternative approach for the treatment of cardiac arrhythmias.

Angiotensin-receptor blocker losartan alleviates atrial fibrillation in rats by downregulating frizzled 8 and inhibiting the activation of WNT-5A pathway

Atrial fibrillation (AF) is a common arrhythmia. Angiotensin-receptor blocker (ARB) is related to AF treatment. This study explored the mechanism of ARB in AF. AF rat models were established by Ach-CaCl2 mixed solution injection. Rats were treated with ARB by gavage and injected with pcDNA3.1-based frizzled homolog 8 (FZD8) overexpression plasmids (oe-FZD8) through the tail vein. The 12-lead electrocardiogram was recorded by biological signal acquisition and processing system and AF duration was recorded, and atrial effective refractory period (AERP) was monitored by electrophysiology. Atrial fibrosis degree, FZD8 messenger RNA and protein levels, collagen I, collagen III, transforming growth factor β1 (TGF-β1), fibronectin, α smooth muscle actin (α-SMA), WBT-5B, and p-JNK1/2 levels, interleukin 1 β (IL-1β) and interleukin 6 (IL-6) levels were detected by Masson staining, reverse transcription quantitative polymerase chain reaction, western blot assay, immunohistochemistry, and enzyme-linked immunosorbent assay. ACh-CaCl2-induced AF rats showed a large area of fused necrosis, abnormal collagen fibre proliferation, high atrial fibrosis degree, and increased atrial fibrosis area in atrial interstitium, elevated collagen I, collagen III, TGF-β1, fibronectin, α-SMA, IL-1β, and IL-6 levels, whereas these trends were averted by ARB treatment. FZD8 was highly expressed in AF rat myocardium. ARB repressed FZD8 expression, prolonged AERP and reduced AF incidence. FZD8 overexpression annulled the effects of ARB on improving AF rat myocardial fibrosis. ARB inactivated the WNT-5A pathway by suppressing FZD8. ARB inactivated the WNT-5A pathway by silencing FZD8, therefore, alleviating AF rat atrial fibrosis.

KCa3.1 Promotes Proinflammatory Exosome Secretion by Activating AKT/Rab27a in Atrial Myocytes during Rapid Pacing

Purpose

The aim of this study was to investigate the role of the medium-conductance calcium-activated potassium channel (KCNN4, KCa3.1) in the secretion of proinflammatory exosomes by atrial myocytes.

Methods

Eighteen beagles were randomly divided into the sham group (n = 6), pacing group (n = 6), and pacing+TRAM-34 group (n = 6). Electrophysiological data, such as the effective refractory period, atrial fibrillation (AF) induction, and AF duration, were collected by programmed stimulation. Atrial tissues were subjected to hematoxylin and eosin, Masson's trichrome, and immunofluorescence staining. The expression of KCa3.1 and Rab27a was assessed by immunohistochemistry and western blotting. The downstream signaling pathways involved in KCa3.1 were examined by rapid pacing or overexpressing KCNN4 in HL-1 cells.

Results

Atrial rapid pacing significantly induced electrical remodeling, inflammation, fibrosis, and exosome secretion in the canine atrium, while TRAM-34 (KCa3.1 blocker) inhibited these changes. Compared with those in control HL-1 cells, the levels of exosome markers and inflammatory factors were increased in pacing HL-1 cells. Furthermore, the levels of CD68 and iNOS in macrophages incubated with exosomes derived from HL-1 cells were higher in the pacing-exo group than in the control group. More importantly, KCa3.1 regulated exosome secretion through the AKT/Rab27a signaling pathway. Similarly, inhibiting the downstream signaling pathway of KCa3.1 significantly inhibited exosome secretion.

Conclusions

KCa3.1 promotes proinflammatory exosome secretion through the AKT/Rab27a signaling pathway. Inhibiting the KCa3.1/AKT/Rab27a signaling pathway reduces myocardial tissue structural remodeling in AF.

Effect of miR-499-5p/SOX6 axis on atrial fibrosis in rats with atrial fibrillation

Atrial fibrosis is involved in the progression of atrial fibrillation (AF). miR-499-5p is the most downregulated microRNA in arrhythmogenic cardiomyopathy hearts. Sry-related high-mobility-group box 6 (SOX6) is associated with apoptosis, inflammatory responses, and fibrosis. This study investigated the mechanism of miR-499-5p in ameliorating AF rats by regulating SOX6. AF rat models were established by injecting Ach-CaCl₂ mixture, and the rats were treated with Lv-miR-499-5p/oe-SOX6/si-SOX6 before modeling. AF duration was recorded using electrocardiogram. miR-499-5p and SOX6 expression levels in the myocardium were determined by reverse transcription-quantitative polymerase chain reaction. The binding of miR-499-5p and SOX6 was validated. The atrial fibrosis degree and cardiomyocyte apoptosis were assessed using the Masson and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining methods. Levels of SOX6, atrial fibrosis markers (collage I/α-SMA/TGFβ1), cell cycle-related proteins (p21/CDC25/Cyclin B1), and cell senescence markers (SA-β-gal/γ-H2AX) were measured using Western blotting and immunohistochemistry. miR-499-5p was downregulated and SOX6 was upregulated in AF rats. miR-499-5p overexpression shortened the AF duration, alleviated atrial fibrosis, and decreased collage I/α-SMA/TGFβ1. miR-499-5p targeted SOX6 to ameliorate atrial fibrosis. AF rats exhibited increased p21/CDC25/Cyclin B1/SA-β-gal/γ-H2AX levels and raised cardiomyocyte apoptosis. SOX6 silencing downregulated p21 and alleviated cardiomyocyte cycle arrest, cell senescence, and apoptosis in AF rats. Shortly, miR-499-5p suppresses atrial fibrosis and cardiomyocyte senescence by targeting SOX6 and downregulating p21, thus mitigating AF in rats.

Protective effect of low-intensity treadmill exercise against acetylcholine-calcium chloride-induced atrial fibrillation in mice

Atrial fibrillation (AF) is the most common supraventricular arrhythmia, and it corresponds highly with exercise intensity. Here, we induced AF in mice using acetylcholine (ACh)-CaCl₂ for 7 days and aimed to determine the appropriate exercise intensity (no, low, moderate, high) to protect against AF by running the mice at different intensities for 4 weeks before the AF induction by ACh-CaCl₂. We examined the AF-induced atrial remodeling using electrocardiogram, patch-clamp, and immunohistochemistry. After the AF induction, heart rate, % increase of heart rate, and heart weight/body weight ratio were significantly higher in all the four AF groups than in the normal control; highest in the high-ex AF and lowest in the low-ex (lower than the no-ex AF), which indicates that low-ex treated the AF. Consistent with these changes, G protein-gated inwardly rectifying K⁺ currents, which were induced by ACh, increased in an exercise intensity-dependent manner and were lower in the low-ex AF than the no-ex AF. The peak level of Ca²⁺ current (at 0 mV) increased also in an exercise intensity-dependent manner and the inactivation time constants were shorter in all AF groups except for the low-ex AF group, in which the time constant was similar to that of the control. Finally, action potential duration was shorter in all the four AF groups than in the normal control; shortest in the high-ex AF and longest in the low-ex AF. Taken together, we conclude that low-intensity exercise protects the heart from AF, whereas high-intensity exercise might exacerbate AF.

Sodium butyrate protects against oxidative stress in high-fat-diet-induced obese rats by promoting GSK-3β/Nrf2 signaling pathway and mitochondrial function

Sodium butyrate (NaB), obtained by fermenting dietary fiber via intestinal microflora, was recently shown to improve the activity of some antioxidant enzymes in vivo. This study aims to investigate the term changes of mitochondrial energy metabolism and redox homeostasis in skeletal muscles and clarify the regulatory mechanism and dose effect of NaB on skeletal muscle. Male Sprague-Dawley rats were divided into the control group, obesity-prone (OP) group and obesity-resistant (OR) group based on the gain of body weight after 8 weeks' of feeding high-fat diet (HFD), followed by sacrificing rats at the end of 20th week. NaB intervention (12 weeks) could effectively reduce the body weight of rats in the OP and OR groups. NaB also mediated upregulation of antioxidant enzyme activity and GSH/GSSG ratio, while reducing reactive oxygen species (ROS) levels and malondialdehyde (MDA) content. At the molecular level, NaB upregulated Pi3k, Nrf2, Nqo-1, and Ho-1, but downregulated Gsk-3β mRNA expression by regulating the Nrf2 antioxidant pathway to enhance tissue antioxidant capacity. At the same time, NaB intervention significantly upregulated Glut4, Irs-1, Pdx1, and MafA, expression in gastrocnemius muscles of OP and OR rats, and elevated insulin secretion and muscle insulin sensitivity. Thus, NaB activates antioxidant pathway, improves the antioxidant capacity of obese rat tissues and promotes glucose metabolism. PRACTICAL APPLICATIONS: This study found that obesity-prone and obesity-resistant rats have differences in mitochondrial redox homeostasis and energy metabolism in tissues. Meanwhile, sodium butyrate can effectively promote muscle protein synthesis, increase insulin sensitivity, and promote glucose metabolism in obesity rats. Thus, sodium butyrate supplementation or increasing intestinal butyrate production (e.g., by consuming foods rich in dietary fiber) is a potential means of improving the body's glucose metabolism and obesity profile.

Ranolazine Counteracts Strength Impairment and Oxidative Stress in Aged Sarcopenic Mice

Sarcopenia is defined as the loss of muscle mass associated with reduced strength leading to poor quality of life in elderly people. The decline of skeletal muscle performance is characterized by bioenergetic impairment and severe oxidative stress, and does not always strictly correlate with muscle mass loss. We chose to investigate the ability of the metabolic modulator Ranolazine to counteract skeletal muscle dysfunctions that occur with aging. For this purpose, we treated aged C57BL/6 mice with Ranolazine/vehicle for 14 days and collected the tibialis anterior and gastrocnemius muscles for histological and gene expression analyses, respectively. We found that Ranolazine treatment significantly increased the muscle strength of aged mice. At the histological level, we found an increase in centrally nucleated fibers associated with an up-regulation of genes encoding MyoD, Periostin and Osteopontin, thus suggesting a remodeling of the muscle even in the absence of physical exercise. Notably, these beneficial effects of Ranolazine were also accompanied by an up-regulation of antioxidant and mitochondrial genes as well as of NADH-dehydrogenase activity, together with a more efficient protection from oxidative damage in the skeletal muscle. These data indicate that the protection of muscle from oxidative stress by Ranolazine might represent a valuable approach to increase skeletal muscle strength in elderly populations.

Hybrid nanogenerator based closed-loop self-powered low-level vagus nerve stimulation system for atrial fibrillation treatment

Atrial fibrillation is an "invisible killer" of human health. It often induces high-risk diseases, such as myocardial infarction, stroke, and heart failure. Fortunately, atrial fibrillation can be diagnosed and treated early. Low-level vagus nerve stimulation (LL-VNS) is a promising therapeutic method for atrial fibrillation. However, some fundamental challenges still need to be overcome in terms of flexibility, miniaturization, and long-term service of bioelectric stimulation devices. Here, we designed a closed-loop self-powered LL-VNS system that can monitor the patient's pulse wave status in real time and conduct stimulation impulses automatically during the development of atrial fibrillation. The implant is a hybrid nanogenerator (H-NG), which is flexible, light weight, and simple, even without electronic circuits, components, and batteries. The maximum output of the H-NG was 14.8 V and 17.8 μA (peak to peak). In the in vivo effect verification study, the atrial fibrillation duration significantly decreased by 90% after LL-VNS therapy, and myocardial fibrosis and atrial connexin levels were effectively improved. Notably, the anti-inflammatory effect triggered by mediating the NF-κB and AP-1 pathways in our therapeutic system is observed. Overall, this implantable bioelectronic device is expected to be used for self-powerability, intelligentization, portability for management, and therapy of chronic diseases.

miR-29b ameliorates atrial fibrosis in rats with atrial fibrillation by targeting TGFβRΙ and inhibiting the activation of Smad-2/3 pathway

OBJECTIVE

Atrial fibrillation (AF) is a major cause of stroke with lifetime risks. microRNAs (miRNAs) are associated with AF attenuation, yet the mechanism remains unknown. This study investigated the functional mechanism of miR-29b in atrial fibrosis in AF.

METHODS

The AF rat model was established by a 7-day intravenous injection of Ach-CaCl₂ mixture. AF rats were injected with adeno-associated virus (AAv)-miR-29b and TGFβRΙ overexpression plasmid. AF duration was recorded by electrocardiogram. Atrial fibrosis was observed by Masson staining. Expressions of COL1A1, COL3A1, TGFβRΙ, TGFβΙ, miR-29b and Smad-2/3 pathway-related proteins in atrial tissues were detected by RT-qPCR and Western blot. Binding sites of miR-29b and TGFβRΙ were predicted and their target relationship was verified by dual-luciferase reporter assay.

RESULTS

miR-29b was poorly expressed and expressions of COL1A1, COL3A1, TGFβRΙ, and TGFβ1 were increased in atrial tissues of AF rats. miR-29b overexpression alleviated atrial fibrosis, reduced expressions of COL1A1, COL3A1, and TGFβ1, and shortened AF duration in AF rats. TGFβRΙ was highly expressed in atrial tissues of AF rats. miR-29b targeted TGFβRΙ. TGFβRΙ overexpression overcame the improving effect of miR-29b overexpression on AF. miR-29b overexpression decreased ratios of p-Smad-2/3 and Smad-2/3 and inhibited the Smad-2/3 pathway.

CONCLUSION

miR-29b might mitigate atrial fibrosis in AF rats by targeting TGFβRΙ and inhibiting the Smad-2/3 pathway.

Enhancing Fatty Acids Oxidation via L-Carnitine Attenuates Obesity-Related Atrial Fibrillation and Structural Remodeling by Activating AMPK Signaling and Alleviating Cardiac Lipotoxicity

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in clinical setting. Its pathogenesis was associated with metabolic disorder, especially defective fatty acids oxidation (FAO). However, whether promoting FAO could prevent AF occurrence and development remains elusive. In this study, we established a mouse model of obesity-related AF through high-fat diet (HFD) feeding, and used l-carnitine (LCA, 150 mg/kg⋅BW/d), an endogenous cofactor of carnitine palmitoyl-transferase-1B (CPT1B; the rate-limiting enzyme of FAO) to investigate whether FAO promotion can attenuate the AF susceptibility in obesity. All mice underwent electrophysiological assessment for atrial vulnerability, and echocardiography, histology and molecular evaluation for AF substrates and underlying mechanisms, which were further validated by pharmacological experiments in vitro. HFD-induced obese mice increased AF vulnerability and exhibited apparent atrial structural remodeling, including left atrial dilation, cardiomyocyte hypertrophy, connexin-43 remodeling and fibrosis. Pathologically, HFD apparently leads to defective cardiac FAO and subsequent lipotoxicity, thereby evoking a set of pathological reactions including oxidative stress, DNA damage, inflammation, and insulin resistance. Enhancing FAO via LCA attenuated lipotoxicity and lipotoxicity-induced pathological changes in the atria of obese mice, resulting in restored structural remodeling and ameliorated AF susceptibility. Mechanistically, LCA activated AMPK/PGC1α signaling both in vivo and in vitro, and pharmacological inhibition of AMPK via Compound C attenuated LCA-induced cardio-protection in palmitate-treated primary atrial cardiomyocytes. Taken together, our results demonstrated that FAO promotion via LCA attenuated obesity-mediated AF and structural remodeling by activating AMPK signaling and alleviating atrial lipotoxicity. Thus, enhancing FAO may be a potential therapeutic target for AF.

miR-425-5p is negatively associated with atrial fibrosis and promotes atrial remodeling by targeting CREB1 in atrial fibrillation

BACKGROUND

Progression of atrial fibrosis is vital for atrial remodeling in atrial fibrillation (AF). The main objective of the present study was to explore the association between miR-425-5p and atrial fibrosis as well as the resultant impact on atrial remodeling in AF.

METHODS

Firstly, miRNAs sequencing and quantitative real-time polymerase chain reaction was used to screen and verify the miRNAs expression level in plasma and atrial tissue in AF patients. The left atrial fibrosis was evaluated with the left atrial low voltage area by using left atrial voltage matrix mapping. Cell counting kit-8 was used to detect fibroblasts proliferation. The AF mouse model was established using acetylcholine-CaCl2 injection for 7 days. Target gene prediction software, luciferase assay, and western blotting were employed to confirm the direct targets of miR-425-5p.

RESULTS

Firstly, we demonstrated that miR-425-5p was downregulated in plasma and atrial tissue among the patients who suffered from AF. We then confirmed that the plasma's miR-425-5p level was negatively correlated with left atrial fibrosis in persistent AF, and catheter ablation could restore the decreased plasma miR-425-5p. Besides, receiver operating characteristic curve analysis revealed the miR-425-5p not only could differentiate AF from healthy control wit area under the curve (AUC) 0.921, but also discriminated persistent AF from paroxysmal AF with AUC 0.888. Furthermore, downregulation of miR-425-5p could promote atrial remodeling, and overexpression of miR-425-p could improve atrial remodeling and decrease susceptibility to atrial fibrillation. Finally, CREB1 was verified to be a direct target for miR-425-5p.

CONCLUSIONS

Our findings suggested that miR-425-5p could serve as novel atrial fibrosis biomarker and contributed to atrial remodeling in AF.

miR‑101a‑3p overexpression prevents acetylcholine‑CaCl2‑induced atrial fibrillation in rats via reduction of atrial tissue fibrosis, involving inhibition of EZH2

Atrial fibrillation (AF), a clinically common heart arrhythmia, can result in left ventricular hypofunction, embolism and infarction. MicroRNA (miR)‑101a‑3p is lowly expressed in atrial tissues of patients with AF, but its role in AF remains unknown. In the present study, an AF model in rats was established via intravenous injection of acetylcholine (Ach)‑CaCl2. The downregulation of miR‑101a‑3p and upregulation of enhancer of zeste 2 homolog 2 (EZH2) were observed in AF model rats, indicating the involvement of miR‑101a‑3p and EZH2 in AF development. To study the effect of miR‑101a‑3p on AF in vivo, AF model rats were intramyocardially injected with lentivirus expressing miR‑101a‑3p. Electrocardiogram analysis identified that miR‑101a‑3p overexpression restored disappeared P wave and R‑R interphase changes in Ach‑CaCl2‑induced rats. Overexpression of miR‑101a‑3p also increased the atrial effective refractory period, reduced AF incidence and shortened duration of AF. Histological changes in atrial tissues were observed after H&E and Masson staining, which demonstrated that miR‑101a‑3p reduced atrial remodeling and fibrosis in AF model rats. Moreover, EZH2 expression was downregulated in atrial tissues by miR‑101a‑3p induction. Immunohistochemistry for collagen Ⅰ and collagen III revealed a reduction in atrial collagen synthesis following miR‑101a‑3p overexpression in AF model rats. Additionally, miR‑101a‑3p lowered the expression of pro‑fibrotic biomarkers, including TGF‑β1, connective tissue growth factor, fibronectin and α‑smooth muscle actin. The luciferase reporter assay results also indicated that EZH2 was a target gene of miR‑101a‑3p. Taken together, it was found that miR‑101a‑3p prevented AF in rats possibly via inhibition of collagen synthesis and atrial fibrosis by targeting EZH2, which provided a potential target for preventing AF.

CXCL12/CXCR4 axis as a key mediator in atrial fibrillation via bioinformatics analysis and functional identification

Atrial fibrillation (AF) is an increasingly prevalent arrhythmia with significant health and socioeconomic impact. The underlying mechanism of AF is still not well understood. In this study, we sought to identify hub genes involved in AF, and explored their functions and underlying mechanisms based on bioinformatics analysis. Five microarray datasets in GEO were used to identify the differentially expressed genes (DEGs) by Robust Rank Aggregation (RRA), and hub genes were screened out using protein-protein interaction (PPI) network. AF model was established using a mixture of acetylcholine and calcium chloride (Ach-CaCl2) by tail vein injection. We totally got 35 robust DEGs that mainly involve in extracellular matrix formation, leukocyte transendothelial migration, and chemokine signaling pathway. Among these DEGs, we identified three hub genes involved in AF, of which CXCL12/CXCR4 axis significantly upregulated in AF patients stands out as one of the most potent targets for AF prevention, and its effect on AF pathogenesis and underlying mechanisms were investigated in vivo subsequently with the specific CXCR4 antagonist AMD3100 (6 mg/kg). Our results demonstrated an elevated transcription and translation of CXCL12/CXCR4 axis in AF patients and mice, accompanied with the anabatic atrial inflammation and fibrosis, thereby providing the substrate for AF maintenance. Blocking its signaling via AMD3100 administration in AF model mice reduced AF inducibility and duration, partly ascribed to decreased atrial inflammation and structural remodeling. Mechanistically, these effects were achieved by reducing the recruitment of CD3+ T lymphocytes and F4/80+ macrophages, and suppressing the hyperactivation of ERK1/2 and AKT/mTOR signaling in atria of AF model mice. In conclusion, this study provides new evidence that antagonizing CXCR4 prevents the development of AF, and suggests that CXCL12/CXCR4 axis may be a potential therapeutic target for AF.

Necroptosis is required for atrial fibrillation and involved in aerobic exercise-conferred cardioprotection

Necroptosis, a novel programmed cell death, plays a critical role in the development of fibrosis, yet its role in atrial fibrillation (AF) remains elusive. Mounting evidence demonstrates that aerobic exercise improves AF-related symptoms and quality of life. Therefore, we explored the role of necroptosis in AF pathogenesis and exercise-conferred cardioprotection. A mouse AF model was established either by calcium chloride and acetylcholine (CaCl₂ -Ach) administration for 3 weeks or high-fat diet (HFD) feeding for 12 weeks, whereas swim training was conducted 60 min/day, for 3-week duration. AF susceptibility, heart morphology and function and atrial fibrosis were assessed by electrophysiological examinations, echocardiography and Masson's trichrome staining, respectively. Both CaCl₂ -Ach administration and HFD feeding significantly enhanced AF susceptibility (including frequency and duration of episodes), left atrial enlargement and fibrosis. Moreover, protein levels of necroptotic signaling (receptor-interacting protein kinase 1, receptor-interacting protein kinase 3, mixed lineage kinase domain-like protein and calcium/calmodulin-dependent protein kinase II or their phosphorylated forms) were markedly elevated in the atria of AF mice. However, inhibiting necroptosis with necrostatin-1 partly attenuated CaCl₂ -Ach (or HFD)-induced fibrosis and AF susceptibility, implicating necroptosis as contributing to AF pathogenesis. Finally, we found 3-week swim training inhibited necroptotic signaling, consequently decreasing CaCl₂ -Ach-induced AF susceptibility and atrial structural remodeling. Our findings identify necroptosis as a novel mechanism in AF pathogenesis and highlight that aerobic exercise may confer benefits on AF via inhibiting cardiac necroptosis.

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.

Differences in energy metabolism and mitochondrial redox status account for the differences in propensity for developing obesity in rats fed on high-fat diet

Obesity is a metabolic disease that is accompanied by oxidative stress. Mitochondrial dysfunction is closely associated with the occurrence and development of obesity. However, it is unclear if there are differences in mitochondrial redox homeostasis and energy metabolism between obesity-prone (OP) and obesity-resistant (OR) individuals and if these differences account for the different susceptibilities to developing obesity. The present study aimed to compare the regulation of energy metabolism between OP and OR rats during high-fat diet (HFD)-induced oxidative stress. Male Sprague Dawley rats were randomly divided into the control group and the HFD group. The HFD group was further divided into the OP and OR groups based on body weight gain (upper 1/3 for OP; lower 1/3 for OR) after eight weeks on HFD. Rats were sacrificed at the 8th and 20th week, and serum and organs were collected. At 8 weeks, HFD decreased mitochondrial antioxidant enzyme activity and increased the production of ROS in the OP rats, which was accompanied by unusual mitochondrial oxidative phosphorylation, reduced mitochondrial membrane potential (MMP), and decreased ATP production. When the feeding period was extended beyond the 8 weeks, the energy expenditure of the OP rats reduced further, resulting in elevated blood lipids and glucose levels and increased body weight. In contrast, the OR rats had higher mitochondrial antioxidant enzyme activity and normal redox homeostasis throughout the period, which was beneficial in energy utilization and ATP production. Thus, the increase in energy expenditure in the OR rats reduced the HFD-induced weight gain. Mitochondrial function and antioxidant defense might be involved in the different propensities for developing obesity. Consequently, the ability of OR rats to resist obesity may be attributed to their ability to maintain mitochondrial function and redox balance.

Ranolazine alleviates contrast-associated acute kidney injury through modulation of calcium independent oxidative stress and apoptosis

This study investigates the role of ranolazine in contrast-associated acute kidney injury (CA-AKI) and potential mechanisms. For in vivo studies, mouse models of CA-AKI and control mice were treated with ranolazine or vehicle. Blood urea nitrogen (BUN) and serum creatinine were detected by spectrophotometry. Anti-T-cell immunoglobulin and mucin domain 1 (TIM 1) and anti-lipocalin 2 antibody (LCN2) were detected by immunofluorescence. Hemodynamic parameters were detected via invasive blood pressure measurement and renal artery color doppler ultrasound, capillary density was measured by CD31 immunofluorescence, vascular permeability assay was performed by Evans blue dye. The expressions of oxidative stress and apoptotic markers were measured and analyzed by immunofluorescence and western blotting. For in vitro studies, intracellular calcium concentration of HUVECs was measured with Fluo 3-AM under confocal microscopy. Results show that compared with control mice, serum BUN, creatinine, TIM 1 and LCN2 levels were elevated in CA-AKI mice, but this effect was alleviated by ranolazine-pretreatment. Safe doses of ranolazine (less than 64 mg/kg) had no significant effect on overall blood pressure, but substantially improved renal perfusion, reduced contrast-induced microcirculation disturbance, improved renal capillary density and attenuated renal vascular permeability in ranolazine-pretreated CA-AKI mice. Mechanistically, ranolazine markedly down-regulated oxidative stress and apoptosis markers compared to CA-AKI mice. Intracellularly, ranolazine attenuated calcium overload in HUVECs. These results indicate that ranolazine alleviates CA-AKI through modulation of calcium independent oxidative stress and apoptosis.

The seasonal profile of proliferation and apoptosis in the prostate gland of the wild ground squirrel (Spermophilus dauricus)

The seasonal cycle of growth and regression in the prostate gland of wild ground squirrel provide a unique research model to understand the morphological changes of prostate glands. Our previous studies showed that the local production of dihydrotestosterone could affect the morphology and function of the prostate gland in either an autocrine or paracrine manner. In the present study, we attempted to gain more insight into this process by investigating the expression of key factors implicated in cell proliferation, apoptosis, and the cell cycle, including mechanistic target of rapamycin (mTOR), cyclin-D2, p21, p27 and retinoblastoma 1 (pRB). Morphological and histological observations confirmed that the prostate increased significantly in both size and weight during the breeding season. Positive immunostaining for proliferating cell nuclear antigen (PCNA) was mainly localized to the prostate epithelial cells during the breeding season, which is significantly higher in the prostate gland during the breeding season (2470 ± 81/mm²) than that in the nonbreeding season (324 ± 54/mm²). However, there was no significant difference in the prostate gland when compared between the breeding and nonbreeding seasons, with regards to TUNEL staining. Moreover, cell cycle regulators were mainly localized to the epithelial cells, including mTOR, cyclin-D2, p21, p27 and pRB. the immunostaining of mTOR and cyclin D2 were stronger during the breeding season, whereas the immunostaining of p27 and pRB were stronger during the nonbreeding season. The mRNA expression levels of mTOR, cyclin D2, and PCNA, were higher during the breeding season while those of p27 and p21 were higher during the nonbreeding season. Collectively, this study profiled the distinct expression pattern of key cell cycle regulators throughout the breeding and nonbreeding seasons. Collectively, these factors may play important roles in regulating the seasonal growth and regression of the prostatic epithelium in the wild ground squirrel.

Hemodynamic Instability in Heart Failure Intensifies Age-Dependent Cognitive Decline

This review attempts to examine two key elements in the evolution of cognitive impairment in the elderly who develop heart failure. First, major left side heart parts can structurally and functionally deteriorate from aging wear and tear to provoke hemodynamic instability where heart failure worsens or is initiated; second, heart failure is a major inducer of cognitive impairment and Alzheimer's disease in the elderly. In heart failure, when the left ventricular myocardium of an elderly person does not properly contract, it cannot pump out adequate blood to the brain, raising the risk of cognitive impairment due to the intensification of chronic brain hypoperfusion. Chronic brain hypoperfusion originates from chronically reduced cardiac output which progresses as heart failure worsens. Other left ventricular heart parts, including atrium, valves, myocardium, and aorta can contribute to the physiological shortfall of cardiac output. It follows that hemodynamic instability and perfusion changes occurring from the aging heart's blood pumping deficiency will, in time, damage vulnerable brain cells linked to specific cognitive regulatory sites, diminishing neuronal energy metabolism to a level where progressive cognitive impairment is the outcome. Could cognitive impairment progress be reversed with a heart transplant? Evidence is presented detailing the errant hemodynamic pathways leading to cognitive impairment during aging as an offshoot of inefficient structural and functional heart parts and their contribution to heart failure.

Wenxin Keli Regulates Mitochondrial Oxidative Stress and Homeostasis and Improves Atrial Remodeling in Diabetic Rats

Mitochondrial dysfunction and oxidative stress play an important role in the pathogenesis of both atrial fibrillation (AF) and diabetes mellitus (DM). Wenxin Keli (WXKL), an antiarrhythmic traditional Chinese medicine, has been shown to prevent cardiac arrhythmias through modulation of cardiac ion channels. This study tested the hypothesis that WXKL can improve atrial remodeling in diabetic rats by restoring mitochondrial function. Primary atrial fibroblasts of neonatal SD rats were divided into four groups: control, hydrogen peroxide (H₂O₂), H₂O₂+WXKL 1 g/L, and H₂O₂+WXKL 3 g/L groups. Intracellular mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and mitochondrial oxygen consumption were measured. SD male rats were randomly divided into three groups: control, DM, and DM+WXKL groups. Rats in the DM+WXKL group were treated with daily gavage of WXKL at 3 g/kg. After eight weeks, echocardiography, hemodynamic examination, histology, electrophysiology study, mitochondrial respiratory function, and western blots were assessed. H₂O₂ treatment led to increased ROS and decreased intracellular MMP and mitochondrial oxygen consumption in primary atrial fibroblasts. WXKL improved the above changes. DM rats showed increased atrial fibrosis, greater left atrial diameter, lower atrial conduction velocity, higher conduction heterogeneity, higher AF inducibility, and lower mitochondrial protein expression, and all these abnormal changes except for left atrial diameter were improved in the DM+WXKL group. WXKL improves atrial remodeling by regulating mitochondrial function and homeostasis and reducing mitochondrial ROS in diabetic rats.

Arnebiae Radix prevents atrial fibrillation in rats by ameliorating atrial remodeling and cardiac function

ETHNOPHARMACOLOGICAL RELEVANCE

Arnebiae Radix, a common herbal medicine in China, is often utilized to treat blood-heat syndrome and has been reported to exert an effect on the heart.

AIM OF THE STUDY

The combination of acetylcholine (Ach) and CaCl₂ has been widely used to induce atrial fibrillation (AF) in animals. However, whether Arnebiae Radix displays any preventive action on Ach-CaCl₂ induced AF in rats remains uncertain. In our study, we attempted to investigate the protective effects of Arnebiae Radix on Ach-CaCl₂ induced AF compared to amiodarone, which was employed as the positive control.

MATERIALS AND METHODS

To establish the AF model, SD rats were treated with a mixture of 0.1 mL/100 g Ach-CaCl₂ (60 μg/mL Ach and 10 mg/mL CaCl₂) by tail vein injection for 7 days. Rats were also given a gavage of Arnebiae Radix (0.18 g/mL) one week before or concurrently with the establishment of the AF model. At the end of the experimental period, the induction, duration and timing of AF were monitored using electrocardiogram recordings. Left atrial tissues were stained to observe the level of fibrosis. Electrophysiological measurements were used to examine atrial size and function.

RESULTS

In Ach-CaCl₂-induced AF rats, Arnebiae Radix decreased AF induction, duration and susceptibility to AF. In addition, Arnebiae Radix significantly reduced atrial fibrosis and inhibited atrial enlargement induced by Ach-CaCl₂. Moreover, there was an apparent improvement in cardiac function in the Arnebiae Radix-treated group.

CONCLUSIONS

Our findings indicate that Arnebiae Radix treatment can attenuate Ach-CaCl₂-induced atrial injury and serve as an effective therapeutic strategy for the treatment of AF in the future.

Remodeling of myocardial energy and metabolic homeostasis in a sheep model of persistent atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common progressive cardiac arrhythmia and is often associated with rapid contraction in both atria and ventricles. The role of atrial energy and metabolic homeostasis in AF progression is under-investigated.

OBJECTIVES

To determine the remodeling of energy metabolism during persistent AF and the effect of eplerenone (EPL), an aldosterone inhibitor, on metabolic homeostasis.

METHODS

A nonsustained atrial pacing sheep model was developed to simulate the progression of AF from paroxysmal to persistent. Metabolomic and proteomic analyses at termination of the experiment were used to analyze atrial tissues obtained from sheep in sham, sugar pill (SP) and EPL-treated groups.

RESULTS

Proteomic analysis indicated that compared to the sham group, in SP group, fatty acid (FA) synthesis, FA oxidation, tricarboxylic acid (TCA) cycle processes and amino acids (AAs) transport and metabolism were reduced, while glycolytic processes were increased. In metabolomic analysis, the levels of intermediate metabolites of the glycolytic pathways, including 2-phosphoglyceric acid (2 PG), 1,3-bisphosphoglyceric acid (1,3 PG), and pyruvate, HBP (uridine diphosphate-N-acetylglucosamine, UDP-GlcNAc), TCA (citrate) and AAs were greater while the levels of the majority of lipid classes, including phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylglycerol (PG), glycerophosphoglycerophosphates (PGP), glycerophosphoinositols (PI) and glycerophosphoserines (PS), were decreased in the atria of SP group than in those of sham group. EPL-pretreatment decreased the expression of glut4 and increased the content of acylcarnitines and lipids, such as lyso phospholipids, phospholipids and neutral lipids.

CONCLUSION

In the metabolic remodeling during AF, glucose and lipid metabolism were up- and down-regulated, respectively, to sustain TCA cycle anaplerosis. EPL partialy reversed the metabolic shifting.

Inhibition of PI3Kinase-α is pro-arrhythmic and associated with enhanced late Na+ current, contractility, and Ca2+ release in murine hearts

BACKGROUND

Phosphoinositide 3-kinase α (PI3Kα) is a proto-oncogene with high activity in the heart. BYL719 (BYL) is a PI3Kα-selective small molecule inhibitor and a prospective drug for advanced solid tumors. We investigated whether acute pharmacological inhibition of PI3Kα has pro-arrhythmic effects.

METHODS & RESULTS

In isolated wild-type (WT) cardiomyocytes, pharmacological inhibition of PI3Kα (BYL719) increased contractility by 28%, Ca²⁺ release by 20%, and prolonged action potential (AP) repolarization by 10-15%. These effects of BYL719 were abolished by inhibition of reverse-mode Na⁺/Ca²⁺ exchanger (NCX) (KB-R7943) or by inhibition of late Na⁺ current (I_Na-L) (ranolazine). BYL719 had no effect on PI3Kα-deficient cardiomyocytes, suggesting BYL719 effects were PI3Kα-dependent and mediated via NCX and I_Na-L. I_Na-L was suppressed by activation of PI3Kα, application of exogenous intracellular PIP3, or ranolazine. Investigation of AP and Ca²⁺ release in whole heart preparations using epicardial optical mapping showed that inhibition of PI3Kα similarly led to prolongation of AP and enhancement of Ca²⁺ release. In hearts of PI3Kα-deficient mice, β-adrenergic stimulation in the presence of high Ca²⁺ concentrations and 12-Hz burst pacing led to delayed afterdepolarizations and ventricular fibrillation. In vivo, administration of BYL719 prolonged QT interval [QT_cF (Fridericia) increased by 15%] in WT, but not in PI3Kα-deficient mice.

CONCLUSIONS

Pharmacological inhibition of PI3Kα is arrhythmogenic due to activation of I_Na-L leading to increased sarcoplasmic reticulum Ca²⁺ load and prolonged QT interval. Therefore, monitoring of cardiac electrical activity in patients receiving PI3K inhibitors may provide further insights into the arrhythmogenic potential of PI3Ka inhibition.

Ranolazine: Multifaceted Role beyond Coronary Artery Disease, a Recent Perspective

Ranolazine is a piperazine derivative approved as an antianginal. Primarily used as a second-line antianginal in stable coronary artery disease. Ranolazine blocks the late Na + current and prevents the rise of cytosolic calcium. It decreases myocardial wall tension and improves coronary blood flow. Ranolazine is effective in atrial fibrillation (AF) as an adjunct to electrical or pharmacological cardioversion. It can be used in combination with amiodarone or dronedarone. It has also been used in AF arising after coronary artery bypass grafting surgery. Role of ranolazine is also being evaluated in pulmonary arterial hypertension, diastolic dysfunction, and chemotherapy-induced cardiotoxicity. Ranolazine has some anti-glycemic effect and has shown a reduction of hemoglobin A1c in multiple trials. The antianginal effect of ranolazine has also been seen to be more in patients with diabetes compared to those without diabetes. Ranolazine is being evaluated in patients with the peripheral arterial disease with intermittent claudication and hypertrophic cardiomyopathy. Pilot studies have shown that ranolazine may be beneficial in neurological conditions with myotonia. The evidence-base on the use of ranolazine in various conditions is rapidly increasing with results of further trials eagerly awaited. Accumulating evidence may see ranolazine in routine clinical use for many conditions beyond its traditional role as an antianginal.

Overexpression of miR-27b-3p Targeting Wnt3a Regulates the Signaling Pathway of Wnt/β-Catenin and Attenuates Atrial Fibrosis in Rats with Atrial Fibrillation

MicroRNAs (miRNAs) are regarded as a potential method for the treatment of atrial fibrillation (AF) although its molecular mechanism remains unknown. We found in our previous study that the level of peripheral blood miR-27b-3p and the expression of atrial tissue CX43 were both significantly downregulated in AF patients. In the present study, we propose and test this hypothesis that overexpression of miR-27b-3p attenuates atrial fibrosis, increases CX43 expression, and regulates the signaling pathway of Wnt/β-Catenin by targeting Wnt3a. miR-27b-3p overexpression was induced by rat tail vein injection of adeno-associated virus. Two weeks after transfection of adeno-associated virus, the rat AF model was established by tail vein injection of acetylcholine- (ACh-) CaCl₂ for 7 days, and 1 ml/kg was injected daily. The incidence and duration of AF were recorded with an electrocardiogram. Cardiac function was monitored by cardiac ultrasound. Serum cardiac enzyme was detected by ELISA. The expression of atrial miR-27b-3 and Wnt3a was assayed by quantitative RT-PCR. Atrial fibrosis was determined by Masson's trichrome staining. Expression of atrial Collagen-I and Collagen-III was tested by the immunohistochemical method. Expression of CX43 was measured by immunofluorescence. The expression of Collagen-I, a-SMA, Collagen-III, TGF-β1, CX43, Wnt3a, β-Catenin, and p-β-Catenin was assayed by western blot. Our results showed that miR-27b-3p overexpression could reduce the incidence and duration of AF, alleviate atrial fibrosis, increase atrial CX43 expression, and decrease the expression of Collagen-I, a-SMA, Collagen-III, TGF-β1, Wnt3a, and p-β-Catenin. In addition, the results of luciferase activity assay showed that Wnt3a is a validated miR-27b-3p target in HEK 293T cells. Our results provide a new evidence that miR-27b-3p regulates the signaling pathway of Wnt/β-Catenin by targeting Wnt3a, which may play an important role in the development of atrial fibrosis and AF.

Atrial Fibrillation Is Associated With Impaired Atrial Mitochondrial Energetics and Supercomplex Formation in Adults With Type 2 Diabetes

OBJECTIVES

Type 2 diabetes mellitus is a chronic progressive disease that is associated with increased risk for cardiovascular diseases and with impaired mitochondrial metabolism in cardiac and skeletal muscles. Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is associated with significant morbidity and mortality. Type 2 diabetes is also one of the prevalent concomitant diseases in patients with AF. During AF, myocardial energy demand is high due to electrical activity. To date, however, very little is known about the effects of AF on atrial muscle mitochondrial energetics. We hypothesized that preexisting fibrillation or type 2 diabetes impacts atrial mitochondrial energetics and electron transport chain supercomplexes.

METHODS

Atrial appendages were collected from patients who had consented and who had and did not have preexisting AF and were undergoing coronary artery bypass graft surgery. Mitochondrial functional analyses were conducted in permeabilized myofibers using high-resolution respirometry.

RESULTS

Results show impaired complex I and II function in addition to impaired electron transport chain supercomplex assembly in patients with diabetes and AF compared to patients with diabetes but without AF. There were no differences in mitochondrial content in atrial muscle between the groups. There was a strong trend for increased oxidative damage (protein carbonyls) in patients with diabetes and AF compared to patients with diabetes but without AF.

CONCLUSIONS

Overall, findings suggest impaired mitochondrial function in AF and type 2 diabetes.

Xanthine Oxidase Inhibitor Allopurinol Prevents Oxidative Stress-Mediated Atrial Remodeling in Alloxan-Induced Diabetes Mellitus Rabbits

Background

There are several mechanisms, including inflammation, oxidative stress and abnormal calcium homeostasis, involved in the pathogenesis of atrial fibrillation. In diabetes mellitus (DM), increased oxidative stress may be attributable to higher xanthine oxidase activity. In this study, we examined the relationship between oxidative stress and atrial electrical and structural remodeling, and calcium handling abnormalities, and the potential beneficial effects of the xanthine oxidase inhibitor allopurinol upon these pathological changes.

Methods and Results

Ninety rabbits were randomly and equally divided into 3 groups: control, DM, and allopurinol‐treated DM group. Echocardiographic and hemodynamic assessments were performed in vivo. Serum and tissue markers of oxidative stress and atrial fibrosis, including the protein expression were examined. Atrial interstitial fibrosis was evaluated by Masson trichrome staining. I_CaL was measured from isolated left atrial cardiomyocytes using voltage‐clamp techniques. Confocal microscopy was used to detect intracellular calcium transients. The Ca²⁺ handling protein expression was analyzed by Western blotting. Mitochondrial‐related proteins were analyzed as markers of mitochondrial function. Compared with the control group, rabbits with DM showed left ventricular hypertrophy, increased atrial interstitial fibrosis, oxidative stress and fibrosis markers, I_CaL and intracellular calcium transient, and atrial fibrillation inducibility. These abnormalities were alleviated by allopurinol treatment.

Conclusions

Allopurinol, via its antioxidant effects, reduces atrial mechanical, structural, ion channel remodeling and mitochondrial synthesis abnormalities induced by DM‐related increases in oxidative stress.

Ca2+/calmodulin-dependent kinase II-dependent regulation of atrial myocyte late Na+ current, Ca2+ cycling, and excitability: a mathematical modeling study

Atrial fibrillation (AF) affects more than three million people per year in the United States and is associated with high morbidity and mortality. Both electrical and structural remodeling contribute to AF, but the molecular pathways underlying AF pathogenesis are not well understood. Recently, a role for Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) in the regulation of persistent "late" Na⁺ current ( I_Na,L) has been identified. Although I_Na,L inhibition is emerging as a potential antiarrhythmic strategy in patients with AF, little is known about the mechanism linking I_Na,L to atrial arrhythmogenesis. A computational approach was used to test the hypothesis that increased CaMKII-activated I_Na,L in atrial myocytes disrupts Ca²⁺ homeostasis, promoting arrhythmogenic afterdepolarizations. Dynamic CaMKII activity and regulation of multiple downstream targets [ I_Na,L, L-type Ca²⁺ current, phospholamban, and the ryanodine receptor sarcoplasmic reticulum Ca²⁺-release channel (RyR2)] were incorporated into an existing well-validated computational model of the human atrial action potential. Model simulations showed that constitutive CaMKII-dependent phosphorylation of Na_v1.5 and the subsequent increase in I_Na,L effectively disrupt intracellular atrial myocyte ion homeostasis and CaMKII signaling. Specifically, increased I_Na,L promotes intracellular Ca²⁺ overload via forward-mode Na⁺/Ca²⁺ exchange activity, which greatly increases RyR2 open probability beyond that observed for CaMKII-dependent phosphorylation of RyR2 alone. Increased I_Na,L promotes atrial myocyte repolarization defects (afterdepolarizations and alternans) in the setting of acute β-adrenergic stimulation. We anticipate that our modeling efforts will help identify new mechanisms for atrial Na_V1.5 regulation with direct relevance for human AF. NEW & NOTEWORTHY Here, we present a novel computational model to study the effects of late Na⁺ current ( I_Na,L) in human atrial myocytes. Simulations predict that I_Na,L promotes intracellular accumulation of Ca²⁺, with subsequent dysregulation of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) signaling and ryanodine receptor 2-mediated Ca²⁺ release. Although I_Na,L plays a small role in regulating atrial myocyte excitability at baseline, CaMKII-dependent enhancement of the current promoted arrhythmogenic dynamics. Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/camkii-dependent-regulation-of-atrial-late-sodium-current-and-excitability/ .

Cardiac metabolism - A promising therapeutic target for heart failure

Both heart failure with reduced ejection fraction (HFrEF) and with preserved ejection fraction (HFpEF) are associated with high morbidity and mortality. Although many established pharmacological interventions exist for HFrEF, hospitalization and death rates remain high, and for those with HFpEF (approximately half of all heart failure patients), there are no effective therapies. Recently, the role of impaired cardiac energetic status in heart failure has gained increasing recognition with the identification of reduced capacity for both fatty acid and carbohydrate oxidation, impaired function of the electron transport chain, reduced capacity to transfer ATP to the cytosol, and inefficient utilization of the energy produced. These nodes in the genesis of cardiac energetic impairment provide potential therapeutic targets, and there is promising data from recent experimental and early-phase clinical studies evaluating modulators such as carnitine palmitoyltransferase 1 inhibitors, partial fatty acid oxidation inhibitors and mitochondrial-targeted antioxidants. Metabolic modulation may provide significant symptomatic and prognostic benefit for patients suffering from heart failure above and beyond guideline-directed therapy, but further clinical trials are needed.