Abstract 649: Does Chronic Increase of Glucose Uptake Cause Cardiac “glycotoxicity”?

Abstract

A shift of substrate preference toward glucose in the heart is considered a reversion to fetal metabolic profile but its role in the pathogenesis of cardiac diseases is incompletely understood. We performed a 2-year follow-up study in transgenic mice with sustained high glucose uptake and utilization in the heart by cardiac-specific overexpression of the insulin-independent glucose transporter GLUT1 (GLUT1-TG). Compared to wildtype (WT) littermates, the GLUT1-TG mice showed normal survival rate and unaltered contractile function of the heart monitored by serial echocardiography and by pressure-volume studies in isolated perfused hearts in the 2-year period. When the hearts were subjected to ischemia-reperfusion, an age-related impairment in functional recovery was observed in WT; cardiac function recovered to 35% vs. 52% of the preischemic level in old (22 months) vs. young (3 months) WT hearts respectively (p<0.05). Ischemic tolerance was markedly enhanced in GLUT1-TG hearts, and importantly, the greater functional recovery in GLUT1-TG hearts was sustained at older age (83% vs. 86% for old and young GLUT1-TG, respectively, p=ns). 31 P NMR spectroscopic measurement showed delayed ATP depletion, reduced acidosis during ischemia and improved recovery of high energy phosphate content in old GLUT1-TG hearts (p<0.05 vs. old WT). These differences were found to be independent of alterations in the activations of Akt and AMPK by ischemia. During reperfusion, glucose oxidation was 3-fold higher while fatty acid oxidation was 45% lower in old GLUT1-TG hearts compared to old WT (p<0.05) suggesting that the deleterious effects of excessive fatty acid oxidation during reperfusion was prevented in old GLUT1-TG hearts. Thus, these results suggest that a normal heart is capable of adapting to chronic increases in basal glucose entry into cardiomyocytes without developing “glucotoxicity”, and furthermore, life-long increases in glucose uptake result in a favorable metabolic phenotype that affords protections against aging-associated increase of susceptibility to ischemic injury.