Selective blockade of interleukin 6 trans-signaling depresses atrial fibrillation

Interleukin-6: Molecular Mechanisms and Therapeutic Perspectives in Atrial Fibrillation

Atrial fibrillation (AF) is a prevalent cardiac arrhythmia with a multifactorial pathophysiology involving electrical, structural, and autonomic remodeling of the atria. AF is closely associated with elevated interleukin-6 (IL-6) levels, which contribute to atrial remodeling and the progression of AF. This review summarizes the mechanisms by which IL-6 promotes AF through inflammatory pathways, atrial fibrosis, electrical remodeling, and calcium mishandling. Experimental models have demonstrated that IL-6 neutralization reduces the incidence of AF, highlighting its potential as a therapeutic target. Future studies should focus on IL-6 blockade strategies to manage AF, aiming to improve patient outcomes.

Inhibition of IL-6 trans-signaling promotes post-stroke functional recovery in a sex and dose-dependent manner

INTRODUCTION

Elevated circulating IL-6 levels are associated with poorer outcomes after stroke, and increased serum IL-6 levels are linked to a higher risk of stroke. IL-6 binds to soluble IL-6 receptors (sIL-6R) and subsequently to ubiquitously expressed gp130, initiating proinflammatory trans-signaling. This study tested the hypothesis that inhibiting IL-6 trans-signaling by administering soluble (s) gp130 improves long-term functional outcomes in young mice after stroke.

METHODS

Recombinant mouse gp130Fc chimera (sgp130) was administered one hour after middle cerebral artery occlusion (MCAO) followed by twice-weekly administration for 2 weeks in mice (8-15 weeks old). Behavioral assessments were done on days 7 and 28 post-MCAO for chronic studies. Flow cytometry was performed on days 3 (blood) and 7 (spleen and brain) to assess IL-6, mIL-6R, and phosphorylated STAT3 expression.

RESULTS

Improved long-term functional outcomes were observed in male, but not female mice. To investigate the differential response in females, ELISA analyses revealed that plasma IL-6 levels increased in both sexes after MCAO, with a more pronounced induction in females. Additionally, circulating sIL-6R levels were significantly higher in females compared to males (p < 0.05) at 24 h post-MCAO. Administering a higher dose of sgp130 (1 mg/kg) to females improved long-term functional outcomes, suggesting that a higher dose is needed to inhibit IL-6 trans-signaling in females effectively. Mechanistically, sgp130 treatment reduced phosphorylated STAT3 expression in brain F4/80 macrophages and increased the expression of mIL-6R on splenic immune cells at day 7 post-MCAO in both sexes.

CONCLUSION

These findings demonstrate that inhibition of IL-6 trans-signaling with gp130Fc improves long-term functional outcomes in both male and female mice, albeit in a dose-dependent manner. This study provides novel insights into potential therapeutic strategies targeting IL-6 signaling pathways following stroke.

Causal association between varicose veins and atrial fibrillation: A 2-sample bidirectional Mendelian randomization study

This study selected genome-wide association study data from the FinnGen database and utilized a bidirectional 2-sample Mendelian randomization (MR) method to explore the causal association between varicose veins (VV) and atrial fibrillation (AF). Inverse variance weighted (IVW) was used as the primary analytical method to assess the causal relationship between VV and AF, supplemented by Weighted median, MR-Egger and Simple 1mode. Cochran's Q test, MR-Egger regression intercept and Mendelian randomization pleiotropy residual sum and outlier were used as sensitivity analyses to detect heterogeneity and multilevel pleiotropy. Additionally, reverse MR was conducted to analyze the causal association between AF and VV. The IVW method indicated a positive causal relationship between VV and AF (odds ratio = 1.1571, 95% confidence interval = 1.0810-1.2384, P = 2.59 × 10-5). Reverse MR analysis shows no potential reverse causal relationships. The results showed a significant causal effect of VV on AF, suggesting that VV may increase the risk of developing AF. It also elaborates on the common risk factors and pathophysiological conditions between VV and AF.

Immune cells and arrhythmias

Cardiac arrhythmias are a significant cause of morbidity and mortality worldwide. Emerging evidence has demonstrated that resident and infiltrating cardiac immune cells play direct, mechanistic roles in arrhythmia onset and progression. In this review, we provide a comprehensive summary and expert commentary on the role of each immune cell subtype in the pathogenesis of atrial and ventricular arrhythmias.

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.

Mendelian Randomization Study Reveals Causal Pathways for Hypertrophic Cardiomyopathy, Cardiovascular Proteins, and Atrial Fibrillation

Aims/Background Research evidence has demonstrated a significant association between hypertrophic cardiomyopathy (HCM) and atrial fibrillation (AF), but the causality and pattern of this link remain unexplored. Therefore, this study investigated the causal relationship between HCM and AF using a two-sample and bidirectional Mendelian randomization (MR) approach. Additionally, this assessed the role of cardiovascular proteins (CPs) associated with cardiovascular diseases between HCM and AF by applying a two-step MR analysis. Methods Data for HCM, AF, and 90 CPs were obtained from the Finn Gen and IEU Open GWAS Project databases. MR-Egger, inverse variance weighting (IVW), weighted median estimator (WME), weighted mode, and simple mode were used to estimate causal inferences. Furthermore, Cochran's Q test, MR-Egger's intercept terms, and Leave-one-out methods determined the heterogeneity, horizontal pleiotropy, and sensitivity. Additionally, mediation effects were used to assess the role of CPs in the relationship between HCM and AF. Results Two-sample and bidirectional MR analysis revealed HCM as a risk factor for AF (odds ratio (OR) = 1.008, 95% confidence interval (CI): 1.001-1.016, p = 0.029) and AF was found to increase the risk of developing HCM (OR = 1.145, 95% CI: 0.963-1.361, p = 0.126). Moreover, Two-step MR analyses indicated that 5 CPs were causally associated with HCM; 12 CPs with AF and 1 CP (Melusin) with both HCM and AF. Additionally, Melusin was observed as a protective factor for both HCM and AF and may serve as a mediator variable for these two conditions (mediation effect 0.0004, mediation ratio 5.5178%, 95% CI: 5.4624-5.5731). Conclusion HCM may increase the risk of developing AF, with Melusin serving as a mediator for this risk.

Interleukin-6 Modulates the Expression and Function of HCN Channels: A Link Between Inflammation and Atrial Electrogenesis

Inflammatory cytokines, including interleukin 6 (IL6), are associated with ion channel remodeling and enhance the propensity to alterations in cardiac rhythm generation and propagation, in which the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels play a crucial role. Hence, we investigated the consequences of exposure to IL6 on HCN channels in cell models and human atrial biopsies. In murine atrial HL1 cells and in cardiomyocytes derived from human induced pluripotent stem cells (hiPS-CMs), IL6 elicited STAT3 phosphorylation, a receptor-mediated downstream signaling. Downregulation of HCN1,2,4 by IL6 was observed after 24-48 h; in hiPS-CMs, this effect was reverted by 24 h of application of tocilizumab, a human IL6 receptor antagonist. In parallel, hiPS-CM action potentials (APs) showed a reduced spontaneous frequency. Moreover, we assessed IL6 and HCN expression in dilated left atrial samples from patients with mitral valve disease, an AF-prone condition. IL6 levels were increased in dilated atria compared to controls and positively correlated with echocardiographic atrial dimensions. Interestingly, the highest IL6 transcript levels and the lowest HCN4 and HCN2 expression were in these samples. In conclusion, our data uncovered a novel link between IL6 and cardiac HCN channels, potentially contributing to atrial electrical disturbances and a higher risk of dysrhythmias in conditions with elevated IL6 levels.

Lipid-lowering drugs, circulating inflammatory factors, and atrial fibrillation: a mediation Mendelian randomization study

Background

Previous studies have shown an association between lipid-lowering drugs, circulating inflammatory factors, and atrial fibrillation (AF), but the specific effects of lipid-lowering drugs on AF and whether they can be mediated by circulating inflammatory factors remain unclear.

Methods

We collected 10 genetic variants encoding lipid-lowering drug targets (LDLR, HMGCR, PCSK9, NPC1L1, APOB, APOB, ABCG5, ABCG8, LPL, APOC3, and PPARA) and AF based on genome-wide association study (GWAS) summary statistics. Drug target Mendelian randomization (MR) was used to explore the causal relationship between lipid-lowering drugs and AF. In addition, we performed a mediation analysis of 91 circulating inflammatory factors to explore potential mediators. Sensitivity analyses were performed to verify the reliability of the MR Results by MR-Egger intercept test, Cochran's Q test and leave-one-out test.

Results

The results of IVW method showed that LPL agonist had a protective effect on AF(OR = 0. 854, 95%CI: 0.816-0.894, P = 1.844E-11). However, the other nine lipid-lowering drug targets had no significant effect on AF. Notably, we found a mediator role of Fibroblast Growth Factor 5 (FGF5) in the protective effect of LPL agonist on AF with a mediator ratio of 9.22%. Sensitivity analyses supported the robustness of our findings, indicating a possible mediating pathway by which LPL agonists affect the risk of AF.

Conclusion

Our study provides new insights into the complex interactions among lipid-lowering agents, circulating inflammatory factors and AF, and also identified a potential mediating role of FGF5 in the pathogenesis of AF. Our findings highlight the potential of LPL agonists and targeting specific inflammatory factors for therapeutic intervention in AF, providing promising avenues for future research and clinical strategies for the management and prevention of AF.

Pathophysiological Mechanisms of Psychosis-Induced Atrial Fibrillation: The Links between Mental Disorder and Arrhythmia

Atrial fibrillation (AF) is a common phenomenon of sustained arrhythmia leading to heart failure or stroke. Patients with mental disorders (MD), particularly schizophrenia and bipolar disorder, are at a high risk of AF triggered by the dysregulation of the autonomic nervous system, atrial stretch, oxidative stress, inflammation, and electrical or structural remodeling. Moreover, pathophysiological mechanisms underlying MD may also contribute to the genesis of AF. An overactivated hypothalamic-pituitary-adrenal axis, aberrant renin-angiotensin-aldosterone system, abnormal serotonin signaling, disturbed sleep, and genetic/epigenetic factors can adversely alter atrial electrophysiology and structural substrates, leading to the development of AF. In this review, we provide an update of our collective knowledge of the pathophysiological and molecular mechanisms that link MD and AF. Targeting the pathogenic mechanisms of MD-specific AF may facilitate the development of therapeutics that mitigate AF and cardiovascular mortality in this patient population.

Obesity Arrhythmias: Role of IL-6 Trans-Signaling

Obesity is a chronic disease that is rapidly increasing in prevalence and affects more than 600 million adults worldwide, and this figure is estimated to increase by at least double by 2030. In the United States, more than one-third of the adult population is either overweight or obese. The global obesity epidemic is a major risk factor for the development of life-threatening arrhythmias occurring in patients with long QT, particularly in conditions where multiple heart-rate-corrected QT-interval-prolonging mechanisms are simultaneously present. In obesity, excess dietary fat in adipose tissue stimulates the release of immunomodulatory cytokines such as interleukin (IL)-6, leading to a state of chronic inflammation in patients. Over the last decade, increasing evidence has been found to support IL-6 signaling as a powerful predictor of the severity of heart diseases and increased risk for ventricular arrhythmias. IL-6's pro-inflammatory effects are mediated via trans-signaling and may represent a novel arrhythmogenic risk factor in obese hearts. The first selective inhibitor of IL-6 trans-signaling, olamkicept, has shown encouraging results in phase II clinical studies for inflammatory bowel disease. Nevertheless, the connection between IL-6 trans-signaling and obesity-linked ventricular arrhythmias remains unexplored. Therefore, understanding how IL-6 trans-signaling elicits a cellular pro-arrhythmic phenotype and its use as an anti-arrhythmic target in a model of obesity remain unmet clinical needs.

Nonspecific Inhibition of IL6 Family Cytokine Signalling by Soluble gp130

IL6 is a proinflammatory cytokine that binds to membrane-bound IL6 receptor (IL6R) or soluble IL6R to signal via gp130 in cis or trans, respectively. We tested the hypothesis that sgp130Fc, which is believed to be a selective IL6 trans-signalling inhibitor, is in fact a non-specific inhibitor of gp130 signalling. In human cancer and primary cells, sgp130Fc inhibited IL6, IL11, OSM and CT1 cis-signalling. The IC50 values of sgp130Fc for IL6 and OSM cis-signalling were markedly (20- to 200-fold) lower than the concentrations of sgp130Fc used in mouse studies and clinical trials. sgp130 inhibited IL6 and OSM signalling in the presence of an ADAM10/17 inhibitor and the absence of soluble IL6R or OSMR, with effects that were indistinguishable from those of a gp130 neutralising antibody. These data show that sgp130Fc does not exclusively block IL6 trans-signalling and reveal instead that broad inhibition of gp130 signalling likely underlies its therapeutic effects. This proposes global or modular inhibition of gp130 as a therapeutic approach for treating human disease.

Circulating IL-6 and not its circulating signaling components sIL-6R and sgp130 demonstrate clinical significance in NSCLC patients treated with immune checkpoint inhibitors

Introduction: Clinical roles of plasma IL-6 levels have been reported in patients with various cancers, including non-small cell lung cancer (NSCLC), treated with immune checkpoint inhibitors (ICIs). However, the roles of other IL-6 signaling components, soluble IL-6 receptor (sIL-6R) and soluble gp130 (sgp130), in the plasma have not been elucidated. Methods: Blood was collected from 106 patients with NSCLC before initiation of ICI treatment (anti-PD-1 or anti-PD-L1 antibody). Plasma levels of IL-6, sIL-6R, sgp130, and their complexes were assessed by Cox regression hazard model to evaluate their clinical significance. The clinical role of IL-6 or IL-6R genetic polymorphisms was also analyzed. Results: Cox regression analysis showed that higher plasma IL-6 levels significantly predicted unfavorable overall survival (OS; hazard ratio [HR] 1.34, 95% confidence interval [CI] 1.05-1.68, p = 0.012) in NSCLC patients treated with ICIs. However, plasma sIL-6R and sgp130 levels showed no prognostic significance (p = 0.882 and p = 0.934, respectively). In addition, the estimated concentrations of binary IL-6:sIL-6R and ternary IL-6:sIL-6R:sgp130 complexes and their ratios (binary/ternary complex) were not significantly associated with OS (p = 0.647, p = 0.727, and p = 0.273, respectively). Furthermore, the genetic polymorphisms of IL-6 (-634G>C) and IL-6R (48892A>C) showed no clinical role by Kaplan-Meier survival analysis (p = 0.908 and p = 0.639, respectively). Discussion: These findings demonstrated the clinical significance of plasma levels of IL-6, but not of other IL-6 signaling components, sIL-6R and sgp130, suggesting that classical IL-6 signaling, but not trans-signaling, may be related to anti-tumor immune responses in cancer patients treated with ICIs.