Abstract 12689: Lack of NAD(P)H Oxidase Impairs Myocardial Energetics and Functional Recovery during Ischemia/Reperfusion
NAD(P)H oxidases (Nox) are major sources of reactive oxygen species (ROS), and Nox4 is a major isoform expressed in cardiomyocytes. Previous studies have shown that increased Nox4 expression in the heart during chronic stress contributes to a higher mitochondrial ROS production and an increase in cell death. Here we sought to test the hypothesis that a reduction of NAD(P)H oxidases mediated ROS generation protected the heart from ischemia/reperfusion (I/R) injury. We subjected mouse hearts with cardiac-specific expression of dominant negative Nox4 (DN-Nox4) which has a P437H mutation within the NAD(P)H binding site to 20 minutes of no-flow ischemia followed by 1 hour of reperfusion using isolated perfused heart preparations. Cardiac function assessed by rate pressure product was comparable between DN-Nox4 (n=12) and WT (n=14) hearts before ischemia (46816±2596 vs. 41099±1512 mmHg/min). ROS production post-ischemia was remarkably reduced in DN-Nox4 hearts compared to WT, as evidenced by dihydroethidium and 2′7′-dichlorofluorescein staining for in situ detection of superoxide and hydrogen peroxide respectively. Unexpectedly, DN-Nox4 hearts showed significantly impaired functional recovery (15±5% vs. 71±3% in WT, p<0.005, n=7/group) and increased infarct size/LV area (41±7 % vs.17±4% in WT, p<0.01, n=3/group) determined by TTC staining at the end of reperfusion. Using 31P NMR spectroscopy, we found that ATP depletion during ischemia was slightly delayed in DN-Nox4 hearts, whereas the recovery of phosphocreatine during reperfusion was compromised in DN-Nox4 hearts (49±5% vs. 88±3% in WT, p<0.01), suggesting that mitochondrial dysfunction was exacerbated in DN-Nox4 hearts upon reperfusion. The slight delay of ATP depletion during ischemia in DN-Nox4 hearts was likely attributive to increased endogenous glycogen consumption (1.7 fold of WT). Moreover, DN-Nox4 hearts showed a lower NAD/NADH ratio post-ischemia (67±7% of WT, p<0.05) and less HIF1-α activation following I/R (46±5% of WT, p<0.01). Taken together, our results suggest that endogenous Nox4 is indispensible for maintaining cardiac bioenergetics and survival during ischemia/reperfusion.
- Reactive oxygen intermediates
- Myocardial infarction
- Reperfusion injury
- Energy metabolism
- © 2010 by American Heart Association, Inc.