Impact of O-GlcNAc on cardioprotection by remote ischaemic preconditioning in non-diabetic and diabetic patients

Post-translational modification of proteins by O-linked -N-acetylglucosamine (O-GlcNAc) is cardioprotective but its role in cardioprotection by remote ischaemic preconditioning (rIPC) and the reduced efficacy of rIPC in type 2 diabetes mellitus is unknown. In this study we achieved mechanistic insight into the remote stimulus mediating and the target organ response eliciting the cardioprotective effect by rIPC in non-diabetic and diabetic myocardium and the influence of O-GlcNAcylation. The cardioprotective capacity and the influence on myocardial O-GlcNAc levels of plasma dialysate from eight healthy volunteers and eight type 2 diabetic patients drawn before and after subjection to an rIPC stimulus were tested on human isolated atrial trabeculae subjected to ischaemia/reperfusion injury. Dialysate from healthy volunteers exposed to rIPC improved post-ischaemic haemodynamic recovery (40 6 vs. 16 2; P 0.01) and increased myocardial O-GlcNAc levels. Similar observations were made with dialysate from diabetic patients before exposure to rIPC (43 3 vs. 16 2; P 0.001) but no additional cardioprotection or further increase in O-GlcNAc levels was achieved by perfusion with dialysate after exposure to rIPC (44 4 and 42 5 vs. 43 3; P 0.7). The glutamine:fructose-6-phosphate amidotransferase (GFAT) inhibitor azaserine abolished the cardioprotective effects and the increment in myocardial O-GlcNAc levels afforded by plasma from diabetic patients and healthy volunteers treated with rIPC. rIPC and diabetes mellitus per se influence myocardial O-GlcNAc levels through circulating humoral factors. O-GlcNAc signalling participates in mediating rIPC-induced cardioprotection and maintaining a state of inherent chronic activation of cardioprotection in diabetic myocardium, restricting it from further protection by rIPC.