Adipose tissue depots demonstrate variation in adipokine profile: a method to investigate the mechanisms underpinning arrhythmogenesis in obesity

Introduction: Obesity which is characterised by excess adipose tissue (AT) has been associated with increased risk of arrhythmia. AT functions as an endocrine organ and secretes adipokines which may induce a proarrhythmic substrate. Specifically, epicardial AT (EAT) has been associated with increased arrhythmic risk and a greater proinflammatory adipokine profile than subcutaneous AT (SAT). Culture of rat ventricular slices in EAT- and SAT- conditioned media containing adipokines may identify the mechanisms underpinning adverse electrophysiological remodelling associated with obesity. This requires culture of fresh AT to generate AT-conditioned media. However, the incubation time of AT in culture that yields maximum adipokine secretion, and whether adipokine protein expression varies temporally, remain unknown. Aims: To determine if there is a temporal variation in adipokine protein expression in human EAT and SAT culture, and thereby identify the incubation time yielding maximal adipokine concentrations. Additionally, to compare adipokine profiles between EAT and SAT. Methods: Paired samples of EAT and SAT were harvested from eleven patients undergoing elective coronary artery bypass graft or valve repair surgery. Samples were cultured for 24, 48, 72, or 96 hours, and adipokine protein expression in EAT- and SAT-conditioned media were analysed. Results: 12 pro- and anti-inflammatory adipokines were detected in EAT- and SAT-conditioned media. Expression of monocyte chemoattractant protein-1 (MCP-1) was significantly lower at 96 hours of SAT culture (669 ± 79 arbitrary units, au) compared with 24 hours (2459 ± 2037 au, p=0.0199) and 48 hours (2425 ± 2087 au, p=0.0448). When comparing adipokine profiles between EAT and SAT, resistin expression was significantly higher in EAT vs SAT at 24 hours (EAT: 4386 ± 1565 au vs SAT: 2561 ± 1053 au, p=0.0312). No other significant differences in adipokine expression were observed temporally during culture, or between EAT and SAT. Conclusion: EAT and SAT exhibited similar pro-inflammatory adipokine profiles in tissue culture over a 96-hour period. However, MCP-1 expression demonstrated temporal variation in SAT culture, and at 24 hours resistin was significantly higher in EAT vs SAT. Our findings suggest EAT and SAT cultured for 24 hours yields maximal adipokine concentrations, that can be utilised for co-culture with rat ventricular slices, to study the effect of AT on pro-arrhythmic myocardial remodelling. [Image Omitt