Combination therapy with remote ischaemic conditioning and insulin or exenatide enhances infarct size limitation in pigs

AIMS: Remote ischaemic conditioning (RIC) has been shown to reduce myocardial infarct size in patients. Our objective was to investigate whether the combination of RIC with either exenatide or glucose-insulin-potassium (GIK) is more effective than RIC alone. METHODS AND RESULTS: Pigs were submitted to 40 min of coronary occlusion followed by reperfusion, and received (i) no treatment, (ii) one of the following treatments: RIC (5 min ischemia/5 min reperfusion × 4), GIK, or exenatide (at doses reducing infarct size in clinical trials), or (iii) a combination of two of these treatments (RIC + GIK or RIC + exenatide). After 5 min of reperfusion (n = 4/group), prominent phosphorylation of Akt and endothelial nitric oxide synthase (eNOS) was observed, both in control and reperfused myocardium, in animals receiving GIK, and mitochondria from these hearts showed reduced ADP-stimulated respiration. (1)H NMR-based metabonomics disclosed a shift towards increased glycolysis in GIK and exenatide groups. In contrast, oxidative stress (myocardial nitrotyrosine levels) and eNOS uncoupling were significantly reduced only by RIC. In additional experiments (n = 7-10/group), ANOVA demonstrated a significant effect of the number of treatments after 2 h of reperfusion on infarct size (triphenyltetrazolium, % of the area at risk; 59.21 ± 3.34, 36.64 ± 3.03, and 21.04 ± 2.38% for none, one, and two treatments, respectively), and significant differences between one and two treatments (P = 0.004) but not among individual treatments or between RIC + GIK and RIC + exenatide. CONCLUSIONS: GIK and exenatide activate cardioprotective pathways different from those of RIC, and have additive effects with RIC on infarct size reduction in pigs.