Daphnetin Preconditioning Decreases Cardiac Injury and Susceptibility to Ventricular Arrhythmia following Ischaemia-Reperfusion through the TLR4/MyD88/NF-Κb Signalling Pathway

Background/Aims: Daphnetin (7,8-dihydroxycoumarin, DAP) exhibits various bioactivities, such as anti-inflammatory and antioxidant activities. However, the role of DAP in myocardial ischaemia/reperfusion (I/R) injury and I/R-related arrhythmia is still uncertain. This study aimed to investigate the mechanisms underlying the effects of DAP on myocardial I/R injury and electrophysiological properties in vivo and in vitro. Methods: Myocardial infarct size was measured by triphenyltetrazolium chloride staining. Cardiac function was assessed by echocardiographic and haemodynamic analyses. The levels of creatine kinase-MB, lactate dehydrogenase, malondialdehyde, superoxide dismutase, interleukin-6 (IL-6), and tumour necrosis factor-alpha (TNF-α) were detected using commercial kits. Apoptosis was measured by terminal deoxynucleotidyl-transferase-mediated dUTP nick-end labelling staining and flow cytometry. The viability of H9c2 cells was determined by the Cell Counting Kit-8 assay. In vitro, the levels of IL-6 and TNF-α were measured by quantitative PCR. The expression levels of proteins associated with apoptosis, inflammation, and the Toll-like receptor 4/myeloid differentiation factor 88/nuclear factor kappa B (TLR4/MyD88/NF-κB) signalling pathway were detected by Western blot analysis. The RR, PR, QRS, and QTc intervals were assessed by surface ECG. The 90% action potential duration (APD 90 ), threshold of APD alternans, and ventricular tachycardia inducibility were measured by the Langendorff perfusion technique. Results: DAP preconditioning decreased myocardial I/R injury and hypoxia/reoxygenation (H/R) injury in cells. DAP preconditioning improved cardiac function after myocardial I/R injury. DAP preconditioning also suppressed apoptosis, attenuated oxidative stress, and inhibited inflammatory responses in vivo and in vitro. Furthermore, DAP preconditioning decreased the susceptibility to ventricular arrhythmia after myocardial I/R. Finally, DAP preconditioning inhibited the expression of TLR4, MyD88, and phosphorylated NF-κB (p-NF-κB)/P65 in mice subjected to I/R and cells subjected to H/R. Conclusions: DAP preconditioning protected against myocardial I/R injury and decreased susceptibility to ventricular arrhythmia by inhibiting the TLR4/MyD88/NF-κB signalling pathway.