Probucol prevents atrial ion channel remodeling in an alloxan-induced diabetes rabbit model

Atrial APD prolongation caused by the upregulation of RAGE and subsequent I NaL increase in diabetic patients

Diabetes mellitus (DM) is a risk factor for the development of atrial fibrillation (AF). The action potential duration (APD) has been demonstrated to be prolonged in the atrium of diabetic mice. In contrast, the APD is generally shortened in AF patients. It is unclear what change occurs in the atrial APD of diabetic patients. In this study, we explore the APD change of atrial myocytes from diabetic patients and the underlying molecular mechanisms. The whole-cell patch-clamp technique is used to detect single-cell electrical activity in diabetic and nondiabetic human samples. The results show that both APD 50 and APD 90, the APD at 50% and 90% repolarization, are increased in diabetic patients compared with those in nondiabetic controls. The density of late sodium current ( I NaL) in the atrial myocytes of diabetic patients is greater than that in the myocytes of nondiabetic patients. The expression of receptor for advanced glycation end products (RAGE) is increased in the atria of diabetic patients. In cultured HL-1 cells, high glucose (HG) treatment increases I NaL, and the expression of RAGE prolongs APD. The siRNA-mediated knockdown of RAGE reduces the I NaL and shortens the APD. The APD is prolonged in the atria of diabetic patients because of the upregulation of RAGE and the subsequent increase in I NaL. Our findings provide novel insights into atrial electrical remodeling in diabetic patients.

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

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

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

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

PKCβ/NF-κB pathway in diabetic atrial remodeling

Atrial remodeling in diabetes is partially attributed to NF-κB/TGF-β signal transduction pathway activation. We examined whether the hyperglycemia-induced increased expression of NF-κB/TGF-β was dependent upon protein kinase C-β (PKCβ) and tested the hypothesis that selective inhibition of PKCβ using ruboxistaurin (RBX) can reduce NF-κB/TGF-β expression and inhibit abnormal atrial remodeling in streptozotocin (STZ)-induced diabetic rats. The effects of PKCβ inhibition on NF-κB/TGF-β signal transduction pathway-mediated atrial remodeling were investigated in STZ-induced diabetic rats. Mouse atrial cardiomyocytes (HL-1 cells) were cultured in low- or high-glucose or mannitol conditions in the presence or absence of small interference RNA that targeted PKCβ. PKCβ inhibition using ruboxistaurin (RBX, 1 mg/kg/day) decreased the expression of NF-κBp65, p-IκB, P38MARK, TNF-α, TGF-β, Cav1.2, and NCX proteins and inducibility of atrial fibrillation (AF) in STZ-induced diabetic rats. Exposure of cardiomyocytes to high-glucose condition activated PKCβ and increased NF-κB/TGF-β expression. Suppression of PKCβ expression by small interference RNA decreased high-glucose-induced NF-κB and extracellular signal-related kinase activation in HL-1 cells. Pharmacological inhibition of PKCβ is an effective method to reduce AF incidence in diabetic rat models by preventing NF-κB/TGF-β-mediated atrial remodeling.

Chronic kidney disease predicts atrial fibrillation in patients with ST-segment elevation myocardial infarction treated by primary percutaneous coronary intervention

Background: Atrial fibrillation (AF) often complicates ST-segment elevation myocardial infarction (STEMI). Predictors of AF in this setting include factors related to the acute phase of STEMI and pre-existing conditions. More recently, novel AF predictors have been identified in the general population. We aimed to assess the ability of such novel factors to predict STEMI-related AF.Methods: Data were collected from STEMI patients treated by primary PCI. Factors related to the acute phase of STEMI (Killip class, heart rate, blood pressure on admission, post-PCI TIMI flow), classic (age, hypertension, heart failure, previous myocardial infarction), and more novel (body mass index [BMI], diabetes, chronic kidney disease [CKD], chronic obstructive pulmonary disease [COPD]) AF predictors were evaluated. The ability of these novel factors to predict STEMI-related AF was assessed.Results: Of the 629 studied patients, 10.5% presented STEMI-related AF. AF patients had higher Killip class on admission (p < .0001) and lower post-PCI TIMI flow (p < .01), they were older (p < .0001) and more likely to have a history of heart failure (p = .02) and myocardial infarction (p = .04). BMI, history of diabetes and COPD were similar between patients with and without AF (all p > .05), but CKD was more common in AF patients (p < .0001). In multiple regression analysis, CKD remained a strong independent predictor of STEMI-related AF (p < .0001).Conclusion: Irrespective of other factors, CKD was associated with increased risk of STEMI-related AF. CKD could be used to identify patients who will develop AF in this setting and who would benefit from closer follow-up and more intensive prophylactic strategies.

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

AIMS

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

MATERIALS AND METHODS

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

KEY FINDINGS

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

SIGNIFICANCE

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

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

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

Urinary Biomarkers of Oxidative Stress in Atrial Fibrillation

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

Oxidative stress and atrial fibrillation: an update

Atrial remodelling involves electrophysiological and structural abnormalities that promote the development and perpetuation of atrial fibrillation. Experimental and clinical data indicate that oxidative stress is implicated in the pathophysiology of atrial remodelling. The mechanistic links between atrial remodelling and oxidative stress are complex with several underlying diseases and conditions may affect these pathways. Therefore, the development of antioxidant interventions in this setting remains difficult. Besides classical antioxidant compounds, several agents with pleiotropic effects, including anti-inflammatory and antioxidant, have been tested in experimental and clinical settings with variable results. Strategies applying conventional antioxidants in specific situations such as postoperative atrial fibrillation show beneficial effects, especially the two-step regimen of antioxidants combination. Of note, there are limited data on the development of strategies that target specific sources of reactive oxygen species implicated in atrial remodelling. Lifestyle, diet, and risk factors modification is a complementary promising approach. This updated review provides a concise and critical overview of all available data regarding oxidative stress and its modulation in atrial fibrillation. Future directions on this exciting field are also discussed.

Segmentation of histological images and fibrosis identification with a convolutional neural network

Segmentation of histological images is one of the most crucial tasks for many biomedical analyses involving quantification of certain tissue types, such as fibrosis via Masson's trichrome staining. However, challenges are posed by the high variability and complexity of structural features in such images, in addition to imaging artifacts. Further, the conventional approach of manual thresholding is labor-intensive, and highly sensitive to inter- and intra-image intensity variations. An accurate and robust automated segmentation method is of high interest. We propose and evaluate an elegant convolutional neural network (CNN) designed for segmentation of histological images, particularly those with Masson's trichrome stain. The network comprises 11 successive convolutional - rectified linear unit - batch normalization layers. It outperformed state-of-the-art CNNs on a dataset of cardiac histological images (labeling fibrosis, myocytes, and background) with a Dice similarity coefficient of 0.947. With 100 times fewer (only 300,000) trainable parameters than the state-of-the-art, our CNN is less susceptible to overfitting, and is efficient. Additionally, it retains image resolution from input to output, captures fine-grained details, and can be trained end-to-end smoothly. To the best of our knowledge, this is the first deep CNN tailored to the problem of concern, and may potentially be extended to solve similar segmentation tasks to facilitate investigations into pathology and clinical treatment.

Animal models of atherosclerosis

Atherosclerosis is a significant cause of morbidity and mortality globally. Many animal models have been developed to study atherosclerosis, and permit experimental conditions, diet and environmental risk factors to be carefully controlled. Pathophysiological changes can be produced using genetic or pharmacological means to study the harmful consequences of different interventions. Experiments using such models have elucidated its molecular and pathophysiological mechanisms, and provided platforms for pharmacological development. Different models have their own advantages and disadvantages, and can be used to answer different research questions. In the present review article, different species of atherosclerosis models are outlined, with discussions on the practicality of their use for experimentation.

Mouse models of atherosclerosis: a historical perspective and recent advances

Atherosclerosis represents a significant cause of morbidity and mortality in both the developed and developing countries. Animal models of atherosclerosis have served as valuable tools for providing insights on its aetiology, pathophysiology and complications. They can be used for invasive interrogation of physiological function and provide a platform for testing the efficacy and safety of different pharmacological therapies. Compared to studies using human subjects, animal models have the advantages of being easier to manage, with controllable diet and environmental risk factors. Moreover, pathophysiological changes can be induced either genetically or pharmacologically to study the harmful effects of these interventions. There is no single ideal animal model, as different systems are suitable for different research objectives. A good understanding of the similarities and differences to humans enables effective extrapolation of data for translational application. In this article, we will examine the different mouse models for the study and elucidation of the pathophysiological mechanisms underlying atherosclerosis. We also review recent advances in the field, such as the role of oxidative stress in promoting endoplasmic reticulum stress, mitochondrial dysfunction and mitochondrial DNA damage, which can result in vascular inflammation and atherosclerosis. Finally, novel therapeutic approaches to reduce vascular damage caused by chronic inflammation using microRNA and nano-medicine technology, are discussed.