Abstract 1615: Suppression of TNF-α induction by insulin in the ischemic/reperfused rat hearts: Role of Akt-eNOS derived NO production
Objectives: Intensive insulin treatment protects injured myocardium and reduces mortality in critically ill patients but the mechanisms involved remain unclear. The aim of this study was to test the hypothesis that insulin attenuates inflammatory response, especially tumor necrosis factor (TNF)-α induction, in acute myocardial ischemia/reperfusion (MI/R) and to investigate the mechanism involved.
Methods: Anesthetized rats were subjected to MI/R (30 min/3 h), randomly received saline, glucose-insulin-potassium (GIK), or GK i.v. infusion respectively. In a separate study, cultured cardiomyocytes were subjected to simulated ischemia/reperfusion (SI/R) and the signaling pathway involved was investigated.
Results: In vivo treatment with GIK, but not GK, significantly decreased myocardial injury as evidenced by reduced infarct size (24.0%) and creatine kinase (CK) activity, and concurrently attenuated inflammatory response as evidenced by reduced TNF-α production (30.3%) and myeloperoxidase (MPO) activity in MI/R rat hearts compared with those in saline control (n=8, all P<0.01). In cultured cardiomyocytes subjected to SI/R, insulin (10−7 M) reduced TNF-α induction (18.32±2.07 vs. 32.63±2.89 pg/ml in vehicle, n=8, P<0.01), increased Akt and eNOS phosphorylation and subsequent NO production (16.4 ± 1.0 vs. 10.7 ± 0.8 μmol/L in vehicle, n=8, P<0.05). More importantly, inhibition of insulin-stimulated NO production by either wortmannin (PI3K inhibitor) or L-NAME (NOS inhibitor) significantly blocked the decrease of TNF-α induced by insulin. Furthermore, suppression of TNF-α by either insulin or neutralizing anti-TNF-α antibody showed cardioprotective effect as manifested by increased viability (36.5% and 20.3% respectively, n=8, P<0.05) and reduced apoptosis (47.2% and 27.8% respectively, n=5 independent experiments for bivariate flowcytometry, P<0.01) in SI/R myocytes.
Conclusions: Insulin treatment decreases TNF-α induction via an Akt-eNOS derived and NO dependent manner in MI/R rat hearts. The anti-inflammatory property of insulin may contribute to the insulin-elicited cardioprotection in the critically ill.