Metformin therapy confers cardioprotection against the remodeling of gap junction in tachycardia-induced atrial fibrillation dog model.

Abstract

OBJECTIVE: Metformin, introduced in 1957, is widely used as an anti-diabetic drug and has considerable benefits in cardiovascular disease reportedly, dependent or independent on its glucose-lowering effects. Aim of this study was to investigate the effect of metformin on gap junction and the inducibility of AF. METHODS: Beagle dogs were subjected to acute or chronic pacing at right atrial appendage by a pacemaker to develop an AF model and electrophysiological parameters were measured. In vitro study, a cell fast pacing model was developed by CardioExcyte 96. We performed Western blot, histology immunohistochemical staining and electron microscopy to detect the effect of metformin. RESULTS: In chronic AF model, the inducibility and duration of AF increased obviously after pacing for 6&#x202f;weeks compared with sham-operated group (Inducibility, 3.33&#x202f;&#xb1;&#x202f;5.77 vs. 85.33&#x202f;&#xb1;&#x202f;7.89%, P<0.0001; Duration, 0.8&#x202f;&#xb1;&#x202f;0.84 vs. 11&#x202f;&#xb1;&#x202f;2.67&#x202f;ms, P<0.0001). Effective refractory periods (ERP) decreased at left and right left atrium and atrial appendages compared with sham-operated group (123.95&#x202f;&#xb1;&#x202f;6.57 vs. 89.96&#x202f;&#xb1;&#x202f;7.39&#x202f;ms P<0.0001). Metformin attenuated the pacing-induced increase in EPR (89.96&#x202f;&#xb1;&#x202f;7.39 vs. 105.83&#x202f;&#xb1;&#x202f;7.45&#x202f;ms, P<0.05), AF inducibility and AF duration (Inducibility, 85.33&#x202f;&#xb1;&#x202f;7.89 vs. 64.17&#x202f;&#xb1;&#x202f;7.36%, Duration, 11&#x202f;&#xb1;&#x202f;2.67 vs. 8.62&#x202f;&#xb1;&#x202f;1.15&#x202f;ms, P<0.05). The expression of Cx43 shows a significant downregulation(about 38%, P<0.001) after chronic pacing and treating with metformin could alleviate this decrease(P<0.01). However, the effect of metformin in acute pacing model is limited. The immunohistochemical staining of cardiac tissue also shown that there is more lateralized Cx43 under pacing condition (87.67&#x202f;&#xb1;&#x202f;2.52 vs. 60.8&#x202f;&#xb1;&#x202f;9.13%, P<0.005). These pacing-induced lateralize Cx43 could be alleviated by the metformin (48.4&#x202f;&#xb1;&#x202f;8.62 vs. 60.8&#x202f;&#xb1;&#x202f;9.13%, P<0.05). Additionally, metformin could affect the interactions of ZO-1 with p-Src/Cx43 via decrease the abnormal cAMP level after pacing (84.04&#x202f;&#xb1;&#x202f;4.58 vs. 69.34&#x202f;&#xb1;&#x202f;4.5&#x202f;nmol/L, P<0.001). CONCLUSIONS: Metformin could alleviate the vulnerability of AF and attenuate the downregulation of gap junction under pacing condition via AMPK pathway and decreasing the P-Src level.