Abstract 12821: Short Interfering RNA-Mediated Knockdown Of Glucose-6-Phosphate Dehydrogenase Impairs Cardiac Contractile Performance and Efficiency in Conscious Dogs
The oxidative pentose phosphate pathway (oxPPP) generates cytosolic NADPH and has been found critically important for redox homeostasis and function of isolated cardiomyocytes. However, no studies have explored the functional consequences of oxPPP downregulation in the intact heart. We tested whether knocking down glucose-6-phosphate dehydrogenase (G6PD), the first and rate-limiting enzyme in the oxPPP, impairs cardiac performance, in vivo. In 5 conscious, chronically instrumented dogs, hemodynamics and cardiac oxygen consumption were measured at baseline and during beta-adrenergic stress (5, 10 and 15 µg/kg/min dobutamine, i.v.). A balloon-tip catheter was then inserted into the coronary sinus under fluoroscopy for cardio-selective delivery, in retrograde fashion, of 1013 p.f.u. adenoviral vectors carrying DNA encoding for anti-G6PD siRNA. Eight days after adenovirus delivery, dogs underwent the same protocol described above, with an additional infusion of [U-13C]-glucose. 13C-NMR spectroscopy was performed in frozen myocardial tissue samples. siRNA administration: 1) did not significantly alter heart rate and blood pressure at baseline and in response to dobutamine; 2) depressed LV stroke work, quantified as the pressure-diameter loop area (baseline: 422.2±26.4 vs 783.6±181.4 mm*mmHg, P<0.05); 3) consistent with the reduced contractile performance, caused also a decrease in MVO2/beat (baseline: 2.2±0.3 vs 3.6±0.5 ml/beat/100g, P<0.05). However, during dobutamine stress, the ratio stroke work/MVO2/beat, an index of mechanical efficiency, was significantly lower after siRNA administration compared to control (at 10 µg/kg/min dobutamine: 302.4±26.0 vs 228.8±27.2, P<0.05), indicating a performance/metabolism mismatch. In siRNA treated hearts, NMR analysis revealed a 28.8±4.1% reduction in 6-phospho-13C-gluconate, and a 32.2±2.7% reduction in 13C-ribose, two representative products of the oxPPP. No histological evidence of myocardial inflammation was found. To our knowledge, no prior studies have achieved siRNA-induced knockdown in large animal hearts and our results are the first to show that a partial interruption of the oxPPP impairs cardiac contractile performance and mechanical efficiency.
- © 2011 by American Heart Association, Inc.