TNF-α provokes electrical abnormalities in rat atrial myocardium via a NO-dependent mechanism

LNK/SH2B3 loss of function increases susceptibility to murine and human atrial fibrillation

AIMS

The lymphocyte adaptor protein (LNK) is a negative regulator of cytokine and growth factor signalling. The rs3184504 variant in SH2B3 reduces LNK function and is linked to cardiovascular, inflammatory, and haematologic disorders, including stroke. In mice, deletion of Lnk causes inflammation and oxidative stress. We hypothesized that Lnk-/- mice are susceptible to atrial fibrillation (AF) and that rs3184504 is associated with AF and AF-related stroke in humans. During inflammation, reactive lipid dicarbonyls are the major components of oxidative injury, and we further hypothesized that these mediators are critical drivers of the AF substrate in Lnk-/- mice.

METHODS AND RESULTS

Lnk-/- or wild-type (WT) mice were treated with vehicle or 2-hydroxybenzylamine (2-HOBA), a dicarbonyl scavenger, for 3 months. Compared with WT, Lnk-/- mice displayed increased AF duration that was prevented by 2-HOBA. In the Lnk-/- atria, action potentials were prolonged with reduced transient outward K+ current, increased late Na+ current, and reduced peak Na+ current, pro-arrhythmic effects that were inhibited by 2-HOBA. Mitochondrial dysfunction, especially for Complex I, was evident in Lnk-/- atria, while scavenging lipid dicarbonyls prevented this abnormality. Tumour necrosis factor-α (TNF-α) and interleukin-1 beta (IL-1β) were elevated in Lnk-/- plasma and atrial tissue, respectively, both of which caused electrical and bioenergetic remodelling in vitro. Inhibition of soluble TNF-α prevented electrical remodelling and AF susceptibility, while IL-1β inhibition improved mitochondrial respiration but had no effect on AF susceptibility. In a large database of genotyped patients, rs3184504 was associated with AF, as well as AF-related stroke.

CONCLUSION

These findings identify a novel role for LNK in the pathophysiology of AF in both experimental mice and humans. Moreover, reactive lipid dicarbonyls are critical to the inflammatory AF substrate in Lnk-/- mice and mediate the pro-arrhythmic effects of pro-inflammatory cytokines, primarily through electrical remodelling.

Abrogation of CC Chemokine Receptor 9 Ameliorates Ventricular Electrical Remodeling in Mice After Myocardial Infarction

Introduction: Myocardial infarction (MI) triggers structural and electrical remodeling. CC chemokine receptor 9 (CCR9) mediates chemotaxis of inflammatory cells in MI. In our previous study, CCR9 knockout has been found to improve structural remodeling after MI. Here, we further investigate the potential influence of CCR9 on electrical remodeling following MI in order to explore potential new measures to improve the prognosis of MI.

Methods and Results: Mice was used and divided into four groups: CCR9^+/+/Sham, CCR9^−/−/Sham, CCR9^+/+/MI, CCR9^−/−/MI. Animals were used at 1 week after MI surgery. Cardiomyocytes in the infracted border zone were acutely dissociated and the whole-cell patch clamp was used to record action potential duration (APD), L-type calcium current (I_Ca,L) and transient outward potassium current (I_to). Calcium transient and sarcoplasmic reticulum (SR) calcium content under stimulation of Caffeine were measured in isolated cardiomyocytes by confocal microscopy. Multielectrode array (MEA) was used to measure the conduction of the left ventricle. The western-blot was performed for the expression level of connexin 43. We observed prolonged APD₉₀, increased I_Ca,L and decreased I_to following MI, while CCR9 knockout attenuated these changes (APD₉₀: 50.57 ± 6.51 ms in CCR9^−/−/MI vs. 76.53 ± 5.98 ms in CCR9^+/+/MI, p < 0.05; I_Ca,L: −13.15 ± 0.86 pA/pF in CCR9^−/−/MI group vs. −17.05 ± 1.11 pA/pF in CCR9^+/+/MI, p < 0.05; I_to: 4.01 ± 0.17 pA/pF in CCR9^−/−/MI group vs. 2.71 ± 0.16 pA/pF in CCR9^+/+/MI, p < 0.05). The confocal microscopy results revealed CCR9 knockout reversed the calcium transient and calcium content reduction in sarcoplasmic reticulum following MI. MEA measurements showed improved conduction velocity in CCR9^−/−/MI mice (290.1 ± 34.47 cm/s in CCR9^−/−/MI group vs. 113.2 ± 14.4 cm/s in CCR9^+/+/MI group, p < 0.05). Western-blot results suggested connexin 43 expression was lowered after MI while CCR9 knockout improved its expression.

Conclusion: This study shows CCR9 knockout prevents the electrical remodeling by normalizing ion currents, the calcium homeostasis, and the gap junction to maintain APD and the conduction function. It suggests CCR9 is a promising therapeutic target for MI-induced arrhythmia, which warrants further investigation.

The relationship between adenosine deaminase and heart rate-corrected QT interval in type 2 diabetic patients

BACKGROUND

Prolonged heart rate-corrected QT (QTc) interval may reflect poor prognosis of patients with type 2 diabetes (T2D). Serum adenosine deaminase (ADA) levels are related to hyperglycemia, insulin resistance (IR) and inflammation, which may participate in diabetic complications. We investigated the association of serum ADA levels with prolonged QTc interval in a large-scale sample of patients with T2D.

METHODS

In this cross-sectional study, a total of 492 patients with T2D were recruited. Serum ADA levels were determined by venous blood during fasting. QTc interval was estimated from resting 12-lead ECGs, and prolonged QTc interval was defined as QTc > 440 ms.

RESULTS

In this study, the prevalence of prolonged QTc interval was 22.8%. Serum ADA levels were positively associated with QTc interval (r = 0.324, P < 0.0001). The proportion of participants with prolonged QTc interval increased significantly from 9.2% in the first tertile (T1) to 24.7% in the second tertile (T2) and 39.0% in the third tertile (T3) of ADA (P for trend < 0.001). After adjusting for other possible risk factors by multiple linear regression analysis, serum ADA level was still significantly associated with QTc interval (β = 0.217, t = 3.400, P < 0.01). Multivariate logistic regression analysis showed that female (OR 5.084, CI 2.379-10.864, P < 0.001), insulin-sensitizers treatment (OR 4.229, CI 1.290-13.860, P = 0.017) and ADA (OR 1.212, CI 1.094-1.343, P < 0.001) were independent contributors to prolonged QTc interval.

CONCLUSIONS

Serum ADA levels were independently associated with prolonged QTc interval in patients with T2D.

Risk of cardiomyopathy and cardiac arrhythmias in patients with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a common, progressive liver disease that affects up to one-quarter of the adult population worldwide. The clinical and economic burden of NAFLD is mainly due to liver-related morbidity and mortality (nonalcoholic steatohepatitis, cirrhosis or hepatocellular carcinoma) and an increased risk of developing fatal and nonfatal cardiovascular disease, chronic kidney disease and certain types of extrahepatic cancers (for example, colorectal cancer and breast cancer). Additionally, there is now accumulating evidence that NAFLD adversely affects not only the coronary arteries (promoting accelerated coronary atherosclerosis) but also all other anatomical structures of the heart, conferring an increased risk of cardiomyopathy (mainly left ventricular diastolic dysfunction and hypertrophy, leading to the development of congestive heart failure), cardiac valvular calcification (mainly aortic-valve sclerosis), cardiac arrhythmias (mainly atrial fibrillation) and some cardiac conduction defects. This Review focuses on the association between NAFLD and non-ischaemia-related cardiac disease, discusses the putative pathophysiological mechanisms and briefly summarizes current treatment options for NAFLD that might also beneficially affect cardiac disease.

Discrete Stretch Eliminates Electrophysiological Dose-Dependent Effects of Nitric Oxide Donor SNAP in Rat Atrium

Depolarization of cardiomyocytes triggered by stretch and activation of mechanically gated ion channels can lead to serious arrhythmias. However, stretch-induced signaling activating these channels remain little studied. This study tested the hypothesis on implication of NO in shaping the electrical abnormalities provoked by stretch of the right atrial myocardium in rat via a mechanism engaging a signaling cascade, where NO plays a significant role. This approach showed that in isolated right atrial preparation, NO donor SNAP induces the electrical abnormalities similar to those provoked by stretch, and the latter results from activation of NO synthase.

Cardiac Fibrosis and Arrhythmogenesis

Myocardial injury, mechanical stress, neurohormonal activation, inflammation, and/or aging all lead to cardiac remodeling, which is responsible for cardiac dysfunction and arrhythmogenesis. Of the key histological components of cardiac remodeling, fibrosis either in the form of interstitial, patchy, or dense scars, constitutes a key histological substrate of arrhythmias. Here we discuss current research findings focusing on the role of fibrosis, in arrhythmogenesis. Numerous studies have convincingly shown that patchy or interstitial fibrosis interferes with myocardial electrophysiology by slowing down action potential propagation, initiating reentry, promoting after-depolarizations, and increasing ectopic automaticity. Meanwhile, there has been increasing appreciation of direct involvement of myofibroblasts, the activated form of fibroblasts, in arrhythmogenesis. Myofibroblasts undergo phenotypic changes with expression of gap-junctions and ion channels thereby forming direct electrical coupling with cardiomyocytes, which potentially results in profound disturbances of electrophysiology. There is strong evidence that systemic and regional inflammatory processes contribute to fibrogenesis (i.e., structural remodeling) and dysfunction of ion channels and Ca2+ homeostasis (i.e., electrical remodeling). Recognizing the pivotal role of fibrosis in the arrhythmogenesis has promoted clinical research on characterizing fibrosis by means of cardiac imaging or fibrosis biomarkers for clinical stratification of patients at higher risk of lethal arrhythmia, as well as preclinical research on the development of antifibrotic therapies. At the end of this review, we discuss remaining key questions in this area and propose new research approaches. © 2017 American Physiological Society. Compr Physiol 7:1009-1049, 2017.

Cytokine Effects on Mechano-Induced Electrical Activity in Atrial Myocardium

The role of cytokines as regulators of stretch-related mechanisms is of special importance since mechano-sensitivity plays an important role in a wide variety of biological processes. Here, we elucidate the influence of cytokine application on mechano-sensitivity and mechano-transduction. The atrial myocardial stretch induces production of interleukin (IL)-2, IL-6, IL-13, IL-17A, and IL-18 with exception of tumor necrosis factor α (TNF-α), IL-1β, and vascular endothelial growth factor B (VEGF-B). Positive ionotropic effect was specific for VEGF-B, negative ionotropic effects were specific for TNF-α, IL-1β, IL-2, IL-6, IL-13, IL-17A and IL-18, while IL-1α doesn't show direct ionotropic effect. The IL-2, IL-6, IL-17A, IL-18, and VEGF-B cause elongation of the APD, in comparison with the reduced APD caused by the IL-13. The TNF-α, IL-1β, and IL-18 influences L-type Ca²⁺ channels, IL-2 has an inhibitory effect on the fast Na⁺ channels while IL-17A and VEGF-B were specific for Kir channels. With exception of the IL-1α, IL-2, and VEGF-B, all analyzed cytokines include nitric oxide dependent signaling with resultant combined effects on mechano-gated and Ca²⁺ channels. The relationships between these pathways and the time-dependence of their activation are of important considerations in the evaluation of cytokine-induced electrical abnormality, specific for cardiac dysfunctions. In general, the discussion presented in this review covers research devoted to counterbalance between different cytokines in the regulation of stretch-induced effects in rat atrial myocardium.

ABBREVIATIONS

APs: action potentials; APD25: action potential durations to 25% of re-polarization; APD50: action potential durations to 50% of repolarization; APD90: action potential durations to 90% of repolarization; MGCs: mechanically gated channels.

Pathophysiology of cancer therapy-provoked atrial fibrillation

Atrial fibrillation (AF) occurs with increased frequency in cancer patients, especially in patients who undergo surgery or chemotherapy. AF disturbs the prognosis of cancer patients and challenges therapeutic outcomes of cancer treatment. Elucidating the mechanisms of cancer-induced AF would help identify specific strategies for preventing AF occurrence. In addition to concurrent risk factors of cancer and AF, cancer surgery, side effects of anticancer agents, and cancer-associated immune responses play critical roles in the genesis of AF. In this review, we provide succinct potential mechanisms of AF genesis in cancer patients.

A review of the literature on cardiac electrical activity between fibroblasts and myocytes

Myocardial injuries often lead to fibrotic deposition. This review presents evidence supporting the concept that fibroblasts in the heart electrically couple to myocytes.

Nonalcoholic Fatty Liver Disease Is Associated With QT Prolongation in the General Population

Background

Nonalcoholic fatty liver disease (NAFLD) is independently associated with QT prolongation among patients with diabetes. It has not yet been determined whether this association remains valid in the general population. We designed an observational study to explore this association.

Methods and Results

We conducted a cross-sectional analysis of 31 116 consecutive participants in our health management program. Heart rate–corrected QT (QTc) interval was derived from 12-lead electrocardiography and by Bazett’s formula. NAFLD was diagnosed by abdominal ultrasonography and classified as none, mild, moderate, or severe, according to the ultrasonographic criteria. A multivariable linear regression model was fitted for the association between QTc interval and potential predictors (including demographic, anthropometric, biochemical factors, and comorbidities). Multivariable logistic regression analyses were fitted to assess the association between the severity of NAFLD and QTc prolongation, with the adjustment of significant predictors derived from multivariable linear regression. The mean QTc interval was 421.3 ms (SD 45.4 ms). In the multivariable linear regression analyses, mild, moderate, and severe NAFLD were associated with increases of 2.55, 6.59, and 12.13 ms, respectively, in QTc interval compared with no NAFLD (all P<0.001). In the multivariable logistic regression analyses, mild, moderate, and severe NAFLD were associated with an increased risk for QTc prolongation, with odds ratios of 1.11 (95% CI: 1.01 to 1.21, P<0.05), 1.61 (95% CI: 1.36 to 1.9, P<0.001), and 1.31 (95% CI: 1.16 to 2.24, P<0.01), respectively, in women, and 1.11 (95% CI: 1.01 to 1.21, P<0.05), 1.39 (95% CI: 1.22 to 1.59, P<0.001), and 1.87 (95% CI: 1.16 to 2.24, P<0.001), respectively, in men, after adjusting for predictors known to be associated with the QTc interval. The association remained significant among subgroups with or without diabetes.

Conclusions

The severity of NAFLD was associated with a higher risk for QTc prolongation in the general population with and without diabetes.

Role of tumor necrosis factor alpha in the pathogenesis of atrial fibrillation: A novel potential therapeutic target?

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice and a major cause of morbidity and mortality. Although the fundamental mechanisms underlying AF remain incompletely understood, atrial remodeling, including structural, electrical, contractile, and autonomic remodeling, has been demonstrated to contribute to the substrate for AF maintenance. Accumulating evidence shows that tumor necrosis factor alpha (TNF-α) plays exceedingly important roles in atrial remodeling. This article reviews recent advances in the roles of TNF-α in the pathogenesis of AF, elucidates the related mechanisms, and exploits its potential usefulness as a novel therapeutic target.