Cardioprotection Effect And Mechanism Of Glucose-insulin-potassium In Cardiac Surgery With Cardiopulmonary Bypass

Background and objectives Cardiopulmonary bypass(CPB) is widely used to maintain systemic perfusion and oxygenation during coronary artery bypass grafting and open heart surgeries, but it increases risk of cardiac failure, myocardial infarction and arrhythmia due to global ischemia-reperfusion injury and cardiac arrest. Cardiac procedures are becoming more complex, time consuming, and are performed in an older population, so the need to improve myocardial protection during CPB is of paramount importance. Since the first application of glucose-insulin-potassium(GIK) in the treatment of myocardial ischemia in the 1960 s, GIK therapy has gone through altering periods of varying attention because of mixed results from large clinical trials. Although there is a growing consensus supporting the utility of GIK in cardiac surgery(4), trials aboutGIK specific to the setting of cardiac surgery are limited in number and had a relative small sample size in the study groups Therefore, a randomized, double-blind, placebo-controlled study was designed to evaluate the effects of GIK, given intravenously before anesthesia, on major adverse cardiac events, mortality and postoperative complications in 930 patients undergoing cardiac surgery with CPB.. O-Linked β-N-acetylglucosamine(O-Glc NAc) glycosylation(O-Glc NAcylation) is a major factor in nutrient and stress responses. Altered function of these enzymes has been linked to diabetes, cancer, and cardiovascular disease. UDP-Glc NAc, the substrate for O-Glc NAcylation, is one of the end products of the hexosamine biosynthesis pathway(HBP). UDP-Glc NAc is the second most abundant high energy compound within the cell after ATP. Normally, 2–5% of total glucose is metabolized through the HBP, but this rate can be increased by an augmented supply of glucose or glucosamine. Laczy B et al demonstrated that acute increases in HBP flux and O-Glc NAc with glucosamine significantly decreased total carbohydrate oxidation, increased fatty acid oxidation in the heart, indicating the role of the HBP and O-Glc NAc in the regulation of cardiac metabolism. However, whether modification of serine and threonine residues in proteins by O-Glc NAc in involved in the cardioprotection of GIK, especially in cardiac surgery with CPB, remain speculative and unclear. Therefore, this study was designed to evaluate the effects of perioperative GIK infusion in patients undergoing cardiac surgery with CPB and the underlying mechanisms,especially the roles of of HBP and protein modification by O-Glc NAc.Methods 1. We performed a randomized, double-blind, controlled study in 930 patients admitted to our hospital who were receiving CPB. GIK(150 g glucose, 50 IU insulin, 4.5g KCl) or Placebo treatment was started at 10 min before anesthesia,running at 60 ml·h-1 for 12.5 hours. Clinical Trial Registration—clinicaltrials.gov Identifier: NCT01516138. The primary outcome was the incidence of major adverse cardiac events(MACE). Secondary outcomes were 30-day and 180-day mortality, length of stay in intensive care unit and hospital, and other serious postoperative complications including prolonged ventilation, reoperation, stroke, patients requiring epinephrine/the use of inotropes, sepsis/infection, and renal complications. 2. Eighteen male mini-pigs were anesthetized and subjected to 90 min CPB and for 30 min aortic cross clamp(AXC), and randomly assigned to one of the following treatments:(1) balanced salt solution;(2) GIK;(3)The GFAT inhibitor: glutamine analog 6-diazo-5-oxo-L-norleucine(DON)(40 μmol/L) 3. Blood samples in the mini-pigs were taken before CPB, 5 min after CPB, 5 min after aortic cross clamp(AXC), 5 min, 60 min and 120 min after the removal of AXC. Left ventricle biopsies were taken at before CPB, 5 min after CPB, 5 min after aortic cross clamp(AXC) and 5 min after the removal of AXC. 4. Left ventricular ejection fraction(LVEF(%)) was assessed by the M-mode, 2D and Doppler echocardiography before and after operation. Myocardial apoptosis was measured by TUNEL. The ultrastructure of the heart tissue was observed by the transmission electro-microscope. 5. Myocardial GFAT and OGT m RNA and protein expression were determined by the RT-PCR and western blot. Myocardial IRS-1, Akt, GSK3-β expression and phosphorylation and Glut-4 translocation in the membrane were determined by western blot. 6. Cardiac glucose uptake in the mini-pigs was determined by 18 Ffluorodeoxyglucose positron emission tomography(18F-FDG PET) imaging.Results:1. GIK therapy significantly reduced the incidence of MACE(25.8% in GIK versus 38.1% in Placebo, odds ratio, 0.57; 95% confidence interval, 0.43-0.75, P<0.001) without increasing perioperative blood glucose compared with Placebo group. Furthermore, GIK therapy was associated with decreased plasma lactate, improved echocardiographic left ventricular ejection fraction, reduced creatine kinase-MB and cardiac troponin I at 24 h after operation. 2. In addition, patients receiving GIK therapy were less likely to require prolonged ventilatory support and extended intensive care although no significant differences in mortality were found at 30-day(1.6% in GIK versus 2.7% in Placebo, P=0.37) and 180-day(2.2% in GIK versus 3.0% in Placebo, P=0.41) follow-up. 3. The incidence of redooperation, stroke and sepsis did not differ significantly between groups but the need for epinephrine use(48.0% in GIK versus 58.9% in Placebo, P=0.001) and the incidence of renal complications(4.9% in GIK versus 8.8% in Placebo, P=0.02) were significantly decreased in GIK group. 4. Compared with sham-operated group, blood glucose levels went up at 120 min after AXC release. Compared with control group, GIK treatment decreased blood glucose at 120 min after AXC release. 5. GIK treatment decreased myocardial apoptosis and improved myocardial dysfunction after CPB in the mini-pigs. Interestingly, GIK treatment was also associated with a substantial increase in GFAT activity(the rate-limiting enzyme for hexosamine biosynthesis) and a significant increase in protein O-Glc NAcylation in cardiac tissues(P<0.05, n=6). Moreover, pretreatment with DON blocked the increase in O-Glc NAcylation and ameliorated myocardial dysfunction after CPB. 6. Glucose uptake in heart dropped significantly as manifested by reduced cardiac 18F-FDG uptake by PET imaging. Furthermore, myocardial insulin signaling was blunted as manifested by decreased phosphorylation of Akt and GSK-3beta(P<0.01, n=6). GIK treatment promoted cardiac glucose uptake and increased phosphorylation of Akt and GSK-3beta during CPB.Conclusion: In patients undergoing cardiac surgery with CPB, perioperative GIK infusion significantly reduced the incidence of MACE and significantly improved heart function and reduced cardiac damage,but not benefit the mortality at 30-day and 180-day follow-up. Ninety minutes of CPB and thirty minutes of aortic cross clamp resulted in elevated hexosamine biosynthesis and protein O-glycosylation in minipigs. Perioperative GIK infusion activated Akt signaling but inhibited hexosamine biosynthesis and protein O-glycosylation, which might contribute to the decreased myocardial apoptosis and improved cardiac dysfunction afforded by GIK.