Abstract 281: Long-Term Therapy with a Partial Adenosine A1-Receptor Agonist Upregulates mRNA and Protein Expression of Glucose Transporters in Left Ventricular Myocardium of Dogs with Chronic Heart Failure

Abstract

Background: Recruitment of glucose transport proteins GLUT-1 and -4 is a mechanism by which the heart increases glucose transport for metabolism in response to increased energy demands. In the failing LV, mRNA and protein levels of GLUT-1 and -4 are down-regulated and the response to increased demands is met by increased dependence on fatty acid oxidation. We previously showed that treatment with the partial adenosine A1-receptor agonist capadenoson (CAP) improves LV systolic function in dogs with advanced heart failure (HF). This study examined the effects of CAP on the regulation of GLUT-1 and -4 in LV myocardium of dogs with chronic HF. Methods: Studies were performed in LV tissue from 12 HF dogs randomized to 3 months oral therapy with the CAP (7.5 mg twice daily, n=6) or to no therapy at all (Control, n=6). LV tissue from 6 normal (NL) dogs was used for comparison. mRNA expression of GLUT-1 and -4 was measured in LV tissue homogenate using real time polymerase chain reaction (RT-PCR). Protein levels of GLUT-1 and -4 and calsequestrin (CSQ), a sarcoplasmic reticulum protein that does not change in HF (internal control), were measured in SDS-extract using Western blotting coupled with chemiluminescent method. Band intensity was quantified in densitometric units (du). Results: Compared to NL dogs, Control HF dogs showed a 3.6 fold decrease in mRNA expression of GLUT-1 and a 2.7 fold decrease in the expression of GLUT-4. CAP-treatment in HF dogs improved mRNA expression of GLUT-1 (1.38 fold decrease) and GLUT-4 (0.8 fold decrease). Similarly, compared to NL dogs, Control HF dogs showed a significant decrease of protein levels of GLUT-1 (0.64 ± 0.04 vs. 0.26 ± 0.04 du, p<0.05) and GLUT-4 (1.42 ± 0.06 vs. 0.40 ± 0.05 du, p<0.05). CAP treatment significantly increased protein levels of both GLUT-1 (0.49 ± 0.03 du) and GLUT-4 (0.82 ± 0.03) compared to Control HF dogs (p<0.05). CSQ levels were similar in all study groups. Conclusions: In dogs with chronic HF, long-term therapy with CAP improves mRNA and protein expression of GLUT-1 and -4. This improvement in expression of glucose transport proteins is likely to restore partial dependency of the failing heart to more efficient glucose metabolism, and therefore, lead to improved myocardial energetics and pump function.