Abstract 14950: Overexpression of Cardiomyocyte-specific Extracellular Superoxide Dismutase Increases Nitric Oxide Bioavailability and Reduces Infarct Size after Ischemia/ Reperfusion.
Background: Increased extracellular superoxide dismutase (ecSOD) with ischemic preconditioning or gene therapy protects hearts from myocardial ischemia reperfusion injury. The effect of increased reactive oxygen species (ROS) scavenging on nitrous oxide (NO) bioavailability has not been described.
Hypothesis: ecSOD overexpression increases NO bioavailability during reperfusion to induce cardioprotection.
Methods and Results: In mice overexpressing ecSOD under the direction of the αMyHC promoter, ecSOD expression was increased 6.2 fold resulting in a 27.5 fold increase in cardiac myocyte-specific ecSOD activity. Although ecSOD activity was increased, it did not significantly increase total cardiac SOD which includes the prominent CuZn- and MgSOD isoforms (TG: 45.0±6.5 vs. WT: 42.5±1.9 units/mg protein). By confocal microscopy, TG ecSOD was found to be localized to the sarcolemma and notably the cytoplasm of cardiac myocytes. Subcellular fractionation showed the cytoplasmic ecSOD to be localized to mitochondria. Ischemia reperfusion injury studied in isolated Langendorff perfused hearts, 30 min ischemia 90 min reperfusion, was attenuated in TG hearts where infarct size, measured by TTC staining, was decreased in TG hearts (TG 25±6% (n=8) vs WT 41±4% of LV (n=10), p<0.05) and recovery of LV function was increased in TG hearts with increased developed pressure (TG: 79±12 mmHg vs WT: 34±6 mmHg, p<0.05) and a decline in end-diastolic pressure (TG: 37±8 mmHg vs WT: 59±6 mmHg) at the end of reperfusion. Using the ROS spin trap, DMPO, electron spin resonance spectroscopy (ESR) demonstrated a significant decrease in ROS in TG hearts (TG 18.3±2.4x104 (n=7) vs WT 29.2±3.2 x104 AU (n=8) p<0.05) during the first 20 min of reperfusion. This decrease in ROS was accompanied by an increase in nitric oxide (NO) production in TG hearts determined by ESR using the NO spin trap, MGD, (TG: 1.0±0.3 AU vs. WT: 0.3±0.3 AU (n=6, p=0.001). NOS isoforms were similar in ecSOD TG and WT hearts demonstrating increased NO bioavailability.
Conclusions: Cardiac specific overexpression of ecSOD decreases ROS production leading to increased NO bioavailability in response to ischemia/reperfusion minimizing the degree of reperfusion injury.
- © 2010 by American Heart Association, Inc.