Pathological Role of Advanced Glycation End Products (AGEs) and their Receptor Axis in Atrial Fibrillation

Repurposing Metformin for the Treatment of Atrial Fibrillation: Current Insights

Metformin is an orally effective anti-hyperglycemic drug that despite being introduced over 60 years ago is still utilized by an estimated 120 to 150 million people worldwide for the treatment of type 2 diabetes (T2D). Metformin is used off-label for the treatment of polycystic ovary syndrome (PCOS) and for pre-diabetes and weight loss. Metformin is a safe, inexpensive drug with side effects mostly limited to gastrointestinal issues. Prospective clinical data from the United Kingdom Prospective Diabetes Study (UKPDS), completed in 1998, demonstrated that metformin not only has excellent therapeutic efficacy as an anti-diabetes drug but also that good glycemic control reduced the risk of micro- and macro-vascular complications, especially in obese patients and thereby reduced the risk of diabetes-associated cardiovascular disease (CVD). Based on a long history of clinical use and an excellent safety record metformin has been investigated to be repurposed for numerous other diseases including as an anti-aging agent, Alzheimer's disease and other dementias, cancer, COVID-19 and also atrial fibrillation (AF). AF is the most frequently diagnosed cardiac arrythmia and its prevalence is increasing globally as the population ages. The argument for repurposing metformin for AF is based on a combination of retrospective clinical data and in vivo and in vitro pre-clinical laboratory studies. In this review, we critically evaluate the evidence that metformin has cardioprotective actions and assess whether the clinical and pre-clinical evidence support the use of metformin to reduce the risk and treat AF.

Advanced Glycation End Products Downregulate Connexin 43 and Connexin 40 in Diabetic Atrial Myocytes via the AMPK Pathway

Purpose

Diabetes mellitus is an independent risk factor for atrial fibrillation (AF), which may be related to accumulation of advanced glycation end products (AGEs). However, the mechanisms involved are not completely clear. Abnormality of gap junction proteins, especially connexin 43 (Cx43) and connexin 40 (Cx40) in atrial myocytes, is an important cause of increased susceptibility of AF. The aim of our work is to investigate the mechanism of dysregulated Cx43 and Cx40 in atrial myocytes of diabetic rats.

Methods

We established a type 1 diabetic rat model by intraperitoneal injection of streptozotocin. HL-1 cells and primary rat atrial myocytes were treated with AGEs in vitro. Using Western blotting, immunofluorescence staining, immunohistochemistry, and lucifer yellow diffusion measurements, we investigated dysregulation of Cx43 and Cx40 and its mechanism in atrial myocytes of diabetic rats.

Results

Accumulation of AGEs was found in diabetic rats. The expression of Cx43 and Cx40 was reduced in the atrium of diabetic rats, accompanied by the decrease of phosphorylated Adenosine 5'-monophosphate-activated protein kinase (p-AMPK). Similar results were found in cultured HL-1 cells and primary rat atrial myocytes, suggesting a role of AGEs on gap junction proteins. An AMPK agonist, 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR), reversed the down-regulated Cx43 expression induced by AGEs stimulation. More importantly, lucifer yellow diffusion assay showed that AGEs significantly affected gap junctional function, and these changes were reversed by AICAR.

Conclusion

Thus, we conclude that AGEs cause dysregulation of Cx43 and Cx40 in diabetic atria via the AMPK pathway, thereby leading to gap junction dysfunction, which may contribute to the increased AF susceptibility in diabetes.

Accelerated AGEing: The Impact of Advanced Glycation End Products on the Prognosis of Chronic Kidney Disease

Advanced glycation end products (AGEs) are aging products. In chronic kidney disease (CKD), AGEs accumulate due to the increased production, reduced excretion, and the imbalance between oxidant/antioxidant capacities. CKD is therefore a model of aging. The aim of this review is to summarize the present knowledge of AGEs in CKD onset and progression, also focusing on CKD-related disorders (cardiovascular diseases, sarcopenia, and nutritional imbalance) and CKD mortality. The role of AGEs as etiopathogenetic molecules, as well as potential markers of disease progression and/or therapeutic targets, will be discussed.

Association Between Apelin and Atrial Fibrillation in Patients With High Risk of Ischemic Stroke

Background: Atrial fibrillation (AF) is associated with high risk of stroke preventable by timely initiation of anticoagulation. Currently available screening tools based on ECG are not optimal due to inconvenience and high costs. Aim of this study was to study the diagnostic value of apelin for AF in patients with high risk of stroke.

Methods: We designed a multicenter, matched-cohort study. The population consisted of three study groups: a healthy control group (34 patients) and two matched groups of 60 patients with high risk of stroke (AF and non-AF group). Apelin levels were examined from peripheral blood.

Results: Apelin was significantly lower in AF group compared to non-AF group (0.694 ± 0.148 vs. 0.975 ± 0.458 ng/ml, p = 0.001) and control group (0.982 ± 0.060 ng/ml, p < 0.001), respectively. Receiver operating characteristic (ROC) analysis of apelin as a predictor of AF scored area under the curve (AUC) of 0.658. Apelin's concentration of 0.969 [ng/ml] had sensitivity = 0.966 and specificity = 0.467. Logistic regression based on manual feature selection showed that only apelin and NT-proBNP were independent predictors of AF. Logistic regression based on selection from bivariate analysis showed that only apelin was an independent predictor of AF. A logistic regression model using repeated stratified K-Fold cross-validation strategy scored an AUC of 0.725 ± 0.131.

Conclusions: Our results suggest that apelin might be used to rule out AF in patients with high risk of stroke.

Advanced glycation end products predict long-term outcome of catheter ablation in paroxysmal atrial fibrillation

PURPOSE

Oxidative stress is an important contributor to the etiology of atrial fibrillation (AF). Our aim was to study oxidative stress biomarkers in patients undergoing pulmonary vein isolation (PVI) for paroxysmal AF with radiofrequency catheter ablation and to assess its prognostic value in predicting long-term PVI outcome.

METHODS

In this prospective cohort study, we included 62 patients (mean age 55±8 years, 12 females and 50 males) with paroxysmal AF and implanted ECG loop recorders who underwent PVI. Plasmatic concentrations of advanced glycation end-products (AGEs), fructosamine, advanced oxidation protein products, and thiobarbituric-acid reacting substances were measured before PVI. AF burden (percentage of time spent in AF) was continually assessed during the follow-up period (1063±271 days).

RESULTS

Nineteen patients (31%) were defined as optimal responders (oR) with AF burden < 0.5% after PVI. Remaining 43 patients (69%) were defined as sub-optimal responders. Concentration of AGEs was significantly lower in oR by 3.7 g/g (CI: -6.5 to -1.7; P=0.0003). After adjustment for age, sex, BMI, left atrial size, arterial hypertension, and AF burden before PVI, only low concentration of AGEs remained significantly associated with oR (odds ratio: 1.3; P=0.04). AGEs concentration achieved area under the curve of 0.78 for predicting optimal long-term PVI response.

CONCLUSIONS

AGEs concentration before PVI was associated with long-term PVI outcome in patients with paroxysmal AF. Further research will show if this biomarker could contribute to optimal patient selection for catheter ablation.

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

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

Advanced glycation end product levels were correlated with inflammation and carotid atherosclerosis in type 2 diabetes patients

Diabetes mellitus with atherosclerosis (AS) adds to the social burden. This study aimed to investigate whether advanced glycation end product (AGE) levels were correlated with inflammation and carotid AS (CAS) in type 2 diabetes mellitus (T2DM) patients. A total of 50 elderly T2DM patients and 50 age-matched senior healthy subjects were recruited in this study. T2DM patients were classified into two groups based on the intima–media thickness (IMT) of the carotid artery from color Doppler ultrasonography. Patients with IMT > 1 mm were classified into the T2DM + CAS group (n = 28), and patients with IMT < 1 mm were assigned as the T2DM + non-atherosclerosis (NAS) group (n = 22). The plasma levels of AGEs, receptor for AGE (RAGE), tumor necrosis factor alpha (TNF-α), and interferon gamma (IFN-γ) of all subjects were measured by enzyme-linked immunosorbent assay. The T-lymphocyte subsets were analyzed by a flow detector. T2DM + CAS patients showed significantly higher concentrations of AGEs, RAGE, TNF-α, and IFN-γ in the peripheral blood. The highest levels of CD4+ T cells were observed in the T2DM + CAS group. The AGE level was positively correlated with the concentrations of RAGE, TNF-α, IFN-γ, and CD4+. In summary, the results showed that the levels of AGEs may be correlated with the inflammatory status in T2DM patients with CAS.

Receptor for Advanced Glycation End Products (RAGE) and Mechanisms and Therapeutic Opportunities in Diabetes and Cardiovascular Disease: Insights From Human Subjects and Animal Models

Obesity and diabetes are leading causes of cardiovascular morbidity and mortality. Although extensive strides have been made in the treatments for non-diabetic atherosclerosis and its complications, for patients with diabetes, these therapies provide less benefit for protection from cardiovascular disease (CVD). These considerations spur the concept that diabetes-specific, disease-modifying therapies are essential to identify, especially as the epidemics of obesity and diabetes continue to expand. Hence, as hyperglycemia is a defining feature of diabetes, it is logical to probe the impact of the specific consequences of hyperglycemia on the vessel wall, immune cell perturbation, and endothelial dysfunction-all harbingers to the development of CVD. In this context, high levels of blood glucose stimulate the formation of the irreversible advanced glycation end products, the products of non-enzymatic glycation and oxidation of proteins and lipids. AGEs accumulate in diabetic circulation and tissues and the interaction of AGEs with their chief cellular receptor, receptor for AGE or RAGE, contributes to vascular and immune cell perturbation. The cytoplasmic domain of RAGE lacks endogenous kinase activity; the discovery that this intracellular domain of RAGE binds to the formin, DIAPH1, and that DIAPH1 is essential for RAGE ligand-mediated signal transduction, identifies the specific cellular means by which RAGE functions and highlights a new target for therapeutic interruption of RAGE signaling. In human subjects, prominent signals for RAGE activity include the presence and levels of two forms of soluble RAGE, sRAGE, and endogenous secretory (es) RAGE. Further, genetic studies have revealed single nucleotide polymorphisms (SNPs) of the AGER gene (AGER is the gene encoding RAGE) and DIAPH1, which display associations with CVD. This Review presents current knowledge regarding the roles for RAGE and DIAPH1 in the causes and consequences of diabetes, from obesity to CVD. Studies both from human subjects and animal models are presented to highlight the breadth of evidence linking RAGE and DIAPH1 to the cardiovascular consequences of these metabolic disorders.

Role of Advanced Glycation Endproduct (AGE)-Receptor for Advanced Glycation Endproduct (RAGE) Axis in Cardiovascular Disease and Its Therapeutic Intervention

Despite the early loss of glycemic differences between the original intensive therapy group and conventional treatment in the DCCT/EDIC and UKPDS 80 trials, a continued reduction in microvascular risk and risk reductions for emergency myocardial infarction and all-cause death were observed 10-30 years after the end of these trials. These observations demonstrated that so-called "metabolic memory" could cause chronic abnormalities in diabetic vessels that are not easily reversed, even by subsequent improvement in blood glucose levels, thus suggesting a long-term beneficial influence of early metabolic control; that is, legacy effects on the risk of vascular complications and death in patients with both type 1 and type 2 diabetes. Formation and accumulation of advanced glycation endproducts (AGEs) are known to progress at an accelerated rate under diabetes. Furthermore, AGEs are hardly degraded and remain for a long time in diabetic vessels even after glycemic control is improved. Therefore, AGEs could explain why former cumulative diabetic exposure could contribute to current progression of vascular complications in diabetes. Here, the clinical utility of measurement of serum and tissue accumulation levels of AGEs for evaluating the prevalence and severity of numerous types of cardiovascular disease is reviewed and novel therapeutic strategies that could target the AGE-RAGE axis in CVD are discussed.