Submitted to: Journal of Molecular and Cellular Cardiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2006
Publication Date: 8/1/2006
Citation: Gupte, S.A., Levine, R.J., Gupte, R.S., Young, M.E., Lionetti, V., Labinskyy, V., Floyd, B.C., Ojaimi, C., Bellomo, M., Wolin, M.S., Recchia, F.A. 2006. Glucose-6-phosphate dehydrogenase-derived NADPH fuels superoxide production in the failing heart. Journal of Molecular and Cellular Cardiology. 41:340-349. Interpretive Summary: The prevalence of heart failure (a form of heart disease in which heart function is severely diminished) is increasing at an alarming rate in the United States. The mechanisms responsible for abnormal heart function during heart failure are currently poorly understood. Previous studies have suggested that the failing heart has increased oxidative stress (i.e., produces highly reactive oxidants, such as the free radical superoxide), which in turn damages the heart. The present study investigated the potential mechanisms by which the heart produces superoxide. The results strongly suggest that activation of specific proteins in the failing heart (such as glucose-6-phosphate dehydrogenase) causes production of superoxide.
Technical Abstract: In the failing heart, NADPH oxidase and uncoupled NO synthase utilize cytosolic NADPH to form superoxide. NADPH is supplied principally by the pentose phosphate pathway, whose rate-limiting enzyme is glucose 6-phosphate dehydrogenase (G6PD). Therefore, we hypothesized that cardiac G6PD activation drives part of the excessive superoxide production implicated in the pathogenesis of heart failure. Pacing-induced heart failure was performed in eight chronically instrumented dogs. Seven normal dogs served as control. End-stage failure occurred after 28 +/- 1 days of pacing, when left ventricular end-diastolic pressure reached 25 mm Hg. In left ventricular tissue homogenates, spontaneous superoxide generation measured by lucigenin (5 microM) chemiluminescence was markedly increased in heart failure (1338 +/- 419 vs. 419 +/- 102 AU/mg protein, P < 0.05), as were NADPH levels (15.4 +/- 1.5 vs. 7.5 +/- 1.5 micromol/gww, P < 0.05). Superoxide production was further stimulated by the addition of NADPH. The NADPH oxidase inhibitor gp91(ds-tat) (50 microM) and the NO synthase inhibitor L-NAME (1 mM) both significantly lowered superoxide generation in failing heart homogenates by 80% and 76%, respectively. G6PD was upregulated and its activity higher in heart failure compared to control (0.61 +/- 0.10 vs. 0.24 +/- 0.03 nmol/min/mg protein, P < 0.05), while superoxide production decreased to normal levels in the presence of the G6PD inhibitor 6-aminonicotinamide. We conclude that the activation of myocardial G6PD is a novel mechanism that enhances NADPH availability and fuels superoxide-generating enzymes in heart failure.