Melatonin increases susceptibility to atrial fibrillation in obesity via Akt signaling impairment in response to lipid overload

Motor protein KIF5B inhibition as a novel strategy of controlled reperfusion against myocardial ischemia/reperfusion injury

Metabolic dysregulation triggered by nutrient influx at reperfusion onset induces reactive oxygen species (ROS) burst and cellular injury, contributing to the detrimental effects observed in ischemia/reperfusion (I/R) injury. Thus, implementing controlled reperfusion emerges as a superior cardioprotective strategy to alleviate reperfusion injury. Kinesin KIF5B transports GLUT4- and CD36-containing vesicles to the plasma membrane, facilizing the import of glucose and fatty acids into cells, suggesting a role in controlled reperfusion. Herein, we aim to investigate its specific role in myocardial I/R injury. By genetic and pharmacological modulation of KIF5B, we investigated its role in myocardial I/R injury both in vivo and in vitro. During reperfusion, a coordinated inhibition of metabolism-related genes and KIF5B expression occurred, probably mitigating the metabolic stress encountered as a compensatory mechanism. Genetic inhibition of KIF5B using AAV9-shRNA attenuated myocardial I/R injury, as evidenced by reduced infarct size, decreased cardiac biomarkers, and reduced cell apoptosis. Additionally, KIF5B inhibition mitigated post-reperfusion oxidative stress and arrhythmias. Mechanistically, concurrent decrease in CD36 membrane translocation following KIF5B ablation post-reperfusion was confirmed by immunofluorescence double staining, and siRNA knockdown of Kif5b inhibited fatty acids uptake in isolated primary neonatal rat cardiomyocytes. Intraperitoneal administration of rose bengal lactone (RBL, 1 mg/kg), a selective inhibitor of KIF5B, was shown to confer cardioprotective effects against myocardial I/R injury. Our findings demonstrate that the inhibition of KIF5B, as a novel strategy of controlled reperfusion, provides cardioprotection against myocardial I/R injury, and highlights the clinical potential of its inhibitor, RBL, to ameliorate reperfusion injury.

Succinate predisposes mice to atrial fibrillation by impairing mitochondrial function via SUCNR1/AMPK axis

Atrial fibrillation (AF), a major public health concern, is associated with high rates of death and disability. Mitochondrial dysfunction has emerged as a key contributor to the pathophysiology of AF. Succinate, an essential Krebs cycle metabolite, is often elevated in the circulation of patients at risk for AF. However, its exact role in AF pathogenesis is still not well understood. To explore the association linking succinate overload and AF, we first established AF-susceptible mouse models of obesity and diabetes, confirming that circulating succinate levels were significantly elevated in these AF-prone mice. Next, we assessed AF vulnerability and atrial remodeling in succinate-treated mice (2 %/5 % for 7 weeks) or isolated primary atrial cells (0.5 mM for 24 h). Our results demonstrated that succinate overload increased AF susceptibility in mice and triggered adverse atrial remodeling, characterized by left atrial dilation, connexins lateralization, ion channel disturbances, and fibrosis. Moreover, succinate compromised atrial mitochondrial structure, leading to increased oxidative stress. Mechanistically, succinate overload upregulated the expression of its cognate receptor SUCNR1 (succinate receptor 1) and decreased AMPK (AMP-activated protein kinase) phosphorylation both in vitro and in vivo. AICAR (AMPK activator) maintained mitochondrial health to mitigate remodeling in succinate-exposed cells and prevented succinate-induced AF in obese and diabetic mice. In conclusion, succinate overload enhances AF vulnerability and atrial remodeling by impairing AMPK signaling and mitochondrial function. Succinate, therefore, represents an underappreciated contributor to AF pathogenesis and a potential biomarker.

Melatonin lessens the susceptibility to atrial fibrillation in sleep deprivation by ameliorating Ca2+ mishandling in response to mitochondrial oxidative stress

BACKGROUND

The antiarrhythmic effect of melatonin(MLT) has been demonstrated in several studies; however, this hypothesis has recently been contested. Our research seeks to determine if exogenous MLT supplementation can reduce atrial fibrillation (AF) susceptibility due to sleep deprivation (SD) by addressing Ca2+ mishandling and atrial mitochondrial oxidative stress.

METHODS

Adult rats received daily MLT or vehicle injections and were exposed to a modified water tank. We evaluated MLT's impact on AF susceptibility by analyzing atrial electrical and structural changes, calcium handling, and oxidative stress markers. Techniques used included electrophysiological recording, echocardiography, optical mapping, histopathology, and molecular assays to understand MLT's protective effects against sleep deprivation-induced AF.

RESULTS

Our findings indicate that MLT treatment effectively mitigates SD-induced AF, safeguards against atrial structural alterations, diminishes mitochondrial oxidative stress and normalizes calcium dynamics. Notably, MLT corrected calcium transient duration (CaD), action potential duration (APD), and conduction heterogeneity, shortened calcium transient refractoriness, and improved arrhythmogenic atrial alternans and spatially discordant alternans, thereby lowering the arrhythmogenic potential of the atria during sleep deprivation. In terms of mechanisms, MLT prevents SD-induced activation of ROS/CaMKII in atrial cardiomyocytes, reversing calcium transient refractoriness and inhibiting arrhythmogenic alternans.

CONCLUSIONS

MLT significantly decreases the susceptibility to SD-induced AF by ameliorating mitochondrial oxidative stress and Ca2+ mishandling. These findings suggest a potential therapeutic application of MLT as an antiarrhythmic intervention for SD-related AF and underscore the need for further investigation, including clinical studies, to validate these mechanisms.

Long-term glucosamine supplementation aggravates atrial fibrillation susceptibility by impairing AMPK signaling

AIMS

Glucosamine, a widely used dietary supplement, has been linked to potential cardiovascular risks, including atrial fibrillation (AF). This study aimed to investigate the effects of long-term glucosamine supplementation on AF susceptibility and the underlying mechanisms.

MATERIALS AND METHODS

C57BL/6 J mice were treated with low-dose (15 mg/kg/day) or high-dose (250 mg/kg/day) glucosamine via drinking water for 6 weeks. AF susceptibility was assessed through transesophageal electrical stimulation. Atrial remodeling was characterized through electrophysiological and echocardiography studies, histological analysis, and molecular examination. AMP-activated protein kinase (AMPK) activator 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) was used to validation the underlying mechanism in mice and isolated neonatal atrial cardiomyocytes.

KEY FINDINGS

Long-term high-dose glucosamine supplementation increased AF susceptibility in mice, as indicated by an elevated AF incidence and duration. Glucosamine induced notable electrical remodeling, evidenced by intra-atrial conduction slowing (P wave duration, amplitude, and area), likely attributable to reduced conduction velocity, as confirmed by two-dimensional electrical mapping. Structural remodeling including increased left atrial weight, cardiomyocyte hypertrophy and fibrosis was evident in the atria of glucosamine-treated mice, despite unaffected cardiac function. Mechanistically, glucosamine suppressed atrial AMPK signaling, leading to lipid and glycogen accumulation. Intriguingly, despite impaired atrial AMPK signaling, high-dose glucosamine improved systemic insulin sensitivity. Pharmacological activation of AMPK with AICAR mitigated glucosamine-induced AF susceptibility and associated pathological changes both in vivo and in vitro.

SIGNIFICANCE

Our findings demonstrate that long-term glucosamine supplementation enhances AF susceptibility, potentially by impairing atrial AMPK signaling, underscoring the importance of caution in the utilization of glucosamine.

Exploring Anti-Inflammatory Treatment as Upstream Therapy in the Management of Atrial Fibrillation

Inflammation has been widely recognized as one of the major pathophysiological drivers of the development of atrial fibrillation (AF), which works in tandem with other risk factors of AF including obesity, diabetes, hypertension, and heart failure (HF). Our current understanding of the role of inflammation in the natural history of AF remains elusive; however, several key players, including the NLRP3 (NLR family pyrin domain containing 3) inflammasome, have been acknowledged to be heavily influential on chronic inflammation in the atrial myocardium, which leads to fibrosis and eventual degradation of its electrical function. Nevertheless, our current methods of pharmacological modalities with reported immunomodulatory properties, including well-established classes of drugs e.g., drugs targeting the renin-angiotensin-aldosterone system (RAAS), statins, and vitamin D, have proven effective in reducing the overall risk of developing AF, the onset of postoperative atrial fibrillation (POAF), and reducing overall mortality among patients with AF. This might bring hope for further progress in developing new treatment modalities targeting cellular checkpoints of the NLRP3 inflammasome pathway, or revisiting other well-known anti-inflammatory drugs e.g., colchicine, vitamin C, nonsteroidal anti-inflammatory drugs (NSAIDs), glucocorticosteroids, and antimalarial drugs. In our review, we aim to find relevant upstream anti-inflammatory treatment methods for the management of AF and present the most current real-world evidence of their clinical utility.

ANXA1-FPR2 axis mitigates the susceptibility to atrial fibrillation in obesity via rescuing AMPK activity in response to lipid overload

Atrial fibrillation (AF) is the most prevalent arrhythmia in clinical practice, and obesity serves as a significant risk factor for its development. The underlying mechanisms of obesity-related AF remain intricate and have yet to be fully elucidated. We have identified FPR2 as a potential hub gene involved in obesity-related AF through comprehensive analysis of four transcriptome datasets from AF patients and one transcriptome dataset from obese individuals, and its expression is up-regulated in both AF and obese individuals. Interestingly, ANXA1, the endogenous ligand of FPR2, was found to exhibit differential expression with AF and obesity. Specifically, it was observed to be down-regulated in AF patients but up-regulated in obese individuals. The susceptibility to AF in obese mice induced by high-fat diet (HFD) was increased following with the FPR2 blocker Boc-2.The administration of exogenous ANXA1 active peptide chain Ac2-26 can mitigate the susceptibility to AF in obese mice by attenuating atrial fibrosis, lipid deposition, oxidative stress injury, and myocardial cell apoptosis. However, this protective effect against AF susceptibility is reversed by AAV9-shAMPK-mediated AMPK specific knockdown in the myocardium. The vitro experiments demonstrated that silencing ANXA1 exacerbated lipid deposition, oxidative stress injury, and apoptosis induced by palmitic acid (PA) in cardiomyocytes. Additionally, Ac2-26 effectively mitigated myocardial lipid deposition, oxidative stress injury, and apoptosis induced by PA. These effects were impeded by FPR2 inhibitors Boc-2 and WRW4. The main mechanism involves the activation of AMPK by ANXA1 through FPR2 in order to enhance fatty acid oxidation in cardiomyocytes, thereby ultimately leading to a reduction in lipid accumulation and associated lipotoxicity. Our findings demonstrate that the ANXA1-FPR2 axis plays a protective role in obesity-associated AF by alleviating metabolic stress in the atria of obese mice, thereby emphasizing its potential as a promising therapeutic target for AF.

Electro-metabolic coupling in atrial fibrillation: A deeper understanding of the metabolic driver

Atrial fibrillation (AF), the most common sustained heart rhythm abnormality, disrupts the normal link between electrical activity and atrial muscle contraction; this disruption is termed "excitation-contraction uncoupling". It weakens atrial contractions and contributes to the development and persistence of AF. In addition to electrical dysfunction, AF is increasingly recognized as a metabolic disorder. Metabolic remodeling may reportedly precede electrophysiological, contractile, and structural changes in AF. Both clinical observations and experimental studies have underscored the critical importance of metabolic homeostasis, and its disturbance is considered a key initial factor in the development of AF. Research in this field has progressed, and a consensus has emerged that metabolic status (energy flux) and electrophysiological signaling (ion flux) are interactively regulated, highlighting the concept of "electro-metabolic coupling." Their uncoupling or decompensation constitutes a common pathological basis of AF. Despite growing recognition of the importance of metabolic balance, the role of electro-metabolic coupling in AF remains unclear. Thus, this review aimed to discuss 1) a comprehensive understanding of electro-metabolic alterations post-AF, 2) the pivotal role of metabolic homeostasis in AF pathogenesis, and 3) the mutual regulation of electro-metabolic signaling, along with potential therapeutic strategies targeting these imbalances.

SIRT3/AMPK Signaling Pathway Regulates Lipid Metabolism and Improves Vulnerability to Atrial Fibrillation in Dahl Salt-Sensitive Rats

BACKGROUND

Hypertension may result in atrial fibrillation (AF) and lipid metabolism disorders. The Sirtuins3 (SIRT3)/AMP-activated protein kinase (AMPK) signaling pathway has the capacity to regulate lipid metabolism disorders and the onset of AF. We hypothesize that the SIRT3/AMPK signaling pathway suppresses lipid metabolism disorders, thereby mitigating salt-sensitive hypertension (SSHT)-induced susceptibility to AF.

METHODS

The study involved 7-week-old male Dahl salt-sensitive that were fed either a high-salt diet (8% NaCl; DSH group) or a normal diet (0.3% NaCl; DSN group). Then DSH group was administered either oral metformin (MET, an AMPK agonist) or intraperitoneal injection of Honokiol (HK, a SIRT3 agonist). This experimental model allowed for the measurement of Systolic blood pressure (SBP), the expression levels of lipid metabolism-related biomarkers, pathological examination of atrial fibrosis, and lipid accumulation, as well as AF inducibility and AF duration.

RESULTS

DSH decrease SIRT3, phosphorylation-AMPK, and very long-chain acyl-CoA dehydrogenase, (VLCAD) expression, increased FASN and FABP4 expression and concentrations of free fatty acid and triglyceride, atrial fibrosis and lipid accumulation in atrial tissue, enhanced level of SBP, promoted AF induction rate and prolonged AF duration, which are blocked by MET and HK. Our results also showed that the degree of atrial fibrosis was negatively correlated with VLCAD expression, but positively correlated with the expression of FASN and FABP4.

CONCLUSIONS

We have confirmed that a high-salt diet can result in hypertension, and associated atrial tissue lipid metabolism dysfunction. This condition is linked to the inhibition of the SIRT3/AMPK signaling pathway, which plays a significant role in the progression of susceptibility to AF in SSHT rats.

Exploring effects of melatonin supplementation on insulin resistance: An updated systematic review of animal and human studies

BACKGROUND

Insulin resistance (IR), defined as an impaired response to insulin stimulation of target tissues, is a substantial determinant of many metabolic disorders. This study aimed to update the findings of the previous systematic review evidence regarding the effect of melatonin on factors related to IR, including hyperinsulinemia, hyperglycemia, homeostasis model assessment of insulin resistance (HOMA-IR), and quantitative insulin sensitivity check index (QUICKI).

METHODS

We systematically reviewed the evidence on the impact of melatonin supplementation on IR indices, fasting insulin, and fasting plasma glucose. PubMed, ScienceDirect, SCOPUS, and Google Scholar databases were searched until March 2024.

RESULTS

We identified 6114 potentially relevant articles during the search. Eighteen animal studies and 15 randomized clinical trials met the inclusion criteria. The results indicated that melatonin supplementation reduced fasting plasma glucose (FPG, 14 out of 29 studies), fasting insulin (22 out of 28 studies), HOMA-IR (28 out of 33 studies), and increased QUICKI (7 out of 7 studies). According to RCT studies, melatonin treatment at a dosage of 10 mg reduced HOMA-IR levels in individuals with various health conditions.

CONCLUSION

According to most evidence, melatonin supplementation may decrease fasting insulin and HOMA-IR and increase QUICKI but may not affect FPG.

Exerkine β-aminoisobutyric acid protects against atrial structural remodeling and atrial fibrillation in obesity via activating AMPK signaling and improving insulin sensitivity

Moderate exercise decreases the risk for atrial fibrillation (AF), an effect which is probably mediated via exercise-stimulated release of exerkines. β-Aminoisobutyric acid (BAIBA), a novel exerkine, has been reported to provide protective benefits against many cardiovascular diseases, yet its role in AF remains elusive. Herein, using a mouse model of obesity-related AF through high-fat diet (HFD) feeding, we found that 12-week drinking administration of BAIBA (170 mg/kg/day) decreased AF susceptibility in obese mice. Atrial remodeling assessment showed that BAIBA attenuated obesity-induced atrial hypertrophy and interstitial fibrosis, thereby ablating the substrate for AF. Of note, to our knowledge, this is the first report of the direct association of BAIBA and hypertrophy. BAIBA has been reported to be a key regulator of glucose and lipid metabolism, and we found that BAIBA alleviated insulin resistance in obese mice. Transcriptional analysis of metabolism-related genes showed that BAIBA increased the transcription of fatty acids metabolism-related genes in the atria of lean mice but not in that of obese mice. Mechanistic investigation showed that BAIBA stimulated AMP-activated protein kinase (AMPK) signaling in the atria of obese mice and palmitic acid (PA)-treated neonatal rat cardiomyocytes (NRCM), whereas inhibition of AMPK via Compound C attenuated BAIBA-conferred cardioprotection against hypertrophy and insulin resistance in PA-treated NRCM. Collectively, BAIBA attenuates AF susceptibility in obese mice via activated AMPK signaling and resultant improvement of insulin sensitivity, thereby providing perspectives on the potential therapeutic role of BAIBA in AF treatment.

Recent advances in the study of circadian rhythm disorders that induce diabetic retinopathy

Diabetic retinopathy (DR) is a severe microvascular complication of diabetes mellitus and a major cause of blindness in young adults. Multiple potential factors influence DR; however, the exact mechanisms are poorly understood. Advanced treatments for DR, including laser therapy, vitrectomy, and intraocular drug injections, slow the disease's progression but fail to cure or reverse visual impairment. Therefore, additional effective methods to prevent and treat DR are required. The biological clock plays a crucial role in maintaining balance in the circadian rhythm of the body. Poor lifestyle habits, such as irregular routines and high-fat diets, may disrupt central and limbic circadian rhythms. Disrupted circadian rhythms can result in altered glucose metabolism and obesity. Misaligned central and peripheral clocks lead to a disorder of the rhythm of glucose metabolism, and chronically high sugar levels lead to the development of DR. We observed a disturbance in clock function in patients with diabetes, and a misaligned clock could accelerate the development of DR. In the current study, we examine the relationship between circadian rhythm disorders, diabetes, and DR. We conclude that: 1) abnormal function of the central clock and peripheral clock leads to abnormal glucose metabolism, further causing DR and 2) diabetes causes abnormal circadian rhythms, further exacerbating DR. Thus, our study presents new insights into the prevention and treatment of DR.