Ethyl pyruvate attenuates myocardial ischemia-reperfusion injury exacerbated by hyperglycemia via retained inhibitory effect on HMGB1

Background Hyperglycemia (HG) exacerbates myocardial ischemia/reperfusion (I/R) injury and renders protective strategies ineffective by amplified inflammatory response via enhanced high-mobility group box-1 (HMGB1) release. This study investigated the role of ethyl pyruvate (EP) against myocardial I/R injury under a clinically relevant HG condition. Methods Sprague-Dawley rats (n = 76) were randomly assigned to 6 groups: normoglycemia (NG)-Sham, NG-I/R-control (C, saline), NG-I/R-EP treatment (50 mg/kg) upon reperfusion, HG-Sham, HG-I/R-C, and HG-I/R-EP treatment upon reperfusion. HG was induced by 1.2 g/kg dextrose. I/R was induced by ligation of the left anterior descending artery for 30 min followed by 4 h of reperfusion. Results HG resulted in exacerbation of myocardial infarct size by 19% with amplified activation of HMGB1–receptors of advanced glycation end products/toll like receptors–NF-κB pathway compared to NG following I/R, which all could be attenuated by EP. EP treatment was associated with diminished tumor necrosis factor-α interleukin-1β and interleukin-6 expressions. It also served to normalize the increase in pro-apoptotic Bax and the decrease in anti-apoptotic Bcl-2 protein levels. These effects were associated with decreased myocardial apoptosis and infarct size (by 30% and 36% in the NG and HG groups, respectively) regardless of the glycemic condition. Conclusion HG exacerbated myocardial I/R injury through amplified inflammatory response via increased HMGB1 level. EP treatment upon reperfusion conveyed significant myocardial protection against the I/R injury under both NG and HG conditions. Common to both glycemic conditions, associated mechanisms involved attenuated increase in HMGB1 level and suppression of its down-stream pathways.