Epicardial Adipose Tissue-Derived IL-1β Triggers Postoperative Atrial Fibrillation

Abstract

Background and aims: Post-operative atrial fibrillation (POAF), defined as new-onset AF in the immediate period after surgery, is associated with poor adverse cardiovascular events and a higher risk of permanent AF. Mechanisms leading to POAF are not completely understood and epicardial adipose tissue (EAT) inflammation could be a potent trigger. Here, we aim at exploring the link between EAT-secreted interleukin (IL)-1β, atrial remodeling, and POAF in a population of coronary artery disease (CAD) patients. Methods: We collected EAT and atrial biopsies from 40 CAD patients undergoing cardiac surgery. Serum samples and EAT-conditioned media were screened for IL-1β and IL-1ra. Atrial fibrosis was evaluated at histology. The potential role of NLRP3 inflammasome activation in promoting fibrosis was explored in vitro by exposing human atrial fibroblasts to IL-1β and IL-18. Results: 40% of patients developed POAF. Patients with and without POAF were homogeneous for clinical and echocardiographic parameters, including left atrial volume and EAT thickness. POAF was not associated with atrial fibrosis at histology. No significant difference was observed in serum IL-1β and IL-1ra levels between POAF and no-POAF patients. EAT-mediated IL-1β secretion and expression were significantly higher in the POAF group compared to the no-POAF group. The in vitro study showed that both IL-1β and IL-18 increase fibroblasts' proliferation and collagen production. Moreover, the stimulated cells perpetuated inflammation and fibrosis by producing IL-1β and transforming growth factor (TGF)-β. Conclusion: EAT could exert a relevant role both in POAF occurrence and in atrial fibrotic remodeling.

Keywords: atrial fibrillation; cardiac remodeling; cytokines; epicardial adipose tissue; fibrosis; inflammation.

FIGURE 1

IL-1β in POAF subgroups. (A) Boxplots denote IL-1β concentration distributions in conditioned media from EAT biopsies of subjects with the no-POAF outcome (“no-POAF”—green) and with POAF outcome (“POAF”—orange); IL-1β concentration is expressed as pg/ml. Box plots denote median and 25th–75th percentiles (boxes) and tukey whiskers. (B) Boxplots denote IL-1β absolute expression in EAT biopsies for 6 subjects with no POAF outcome (“no-POAF”—green) and 6 with POAF outcome (“POAF”—orange). Box plots denote median and 25th–75th percentiles (boxes) and min-to-max whiskers. (C) AUC of ROC analysis indicates the performance of IL-1β. p-value refers to the significant difference from the AUC basal level of 0.5 (red dotted line). *p < 0.05; **p < 0.01.

FIGURE 2

IL-1β and IL-18 effects on cardiac fibroblast proliferation and migration. (A–C) Relative confluence normalized on T0 and (B–D) relative proliferation with respect to the untreated (setted to 100%) and (E,F) relative wound healing density normalized on T0 of human immortalized fibroblasts exposed to different concentrations of (A,B–E) IL-1β and (C,D–F) IL-18 (n = 8). Data are expressed by mean ± SEM. *p < 0.05; **p < 0.01 vs. untreated.

FIGURE 3

IL-1β and IL-18 effects on pro-fibrotic and pro-inflammatory genes. Bar graphs reporting the relative gene expression of (A) collagen 1A1 (Col1A1), (B) collagen 3A1 (Col3A1), (C) transforming growth factor β1 (TGFβ1), and (D) interleukin 1β (IL-1β) of human cardiac fibroblasts under IL-1β, IL-18, and TGFβ1 (as positive control) treatments (n = 3). Data are expressed by mean ± SEM. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001 vs. untreated.