Increased oxidative stress is a known cause of cardiac dysfunction in animals and patients with diabetes, but the sources of
reactive oxygen species [e.g.,
superoxide anion (O(2)(-))] and the mechanisms underlying O(2)(-) production in diabetic hearts are not clearly understood. Our aim was to determine whether
NADPH oxidase (Nox) is a source of O(2)(-) and whether
glucose-6-phosphate dehydrogenase (G6PD)-derived
NADPH plays a role in augmenting O(2)(-) generation in diabetes. We assessed cardiac function, Nox and G6PD activities,
NADPH levels, and the activities of
antioxidant enzymes in heart homogenates from young (9-11 wk old) Zucker lean and obese (fa/fa) rats. We found that myocardial G6PD activity was significantly higher in fa/fa than in lean rats, whereas
superoxide dismutase and
glutathione peroxidase activities were decreased (P < 0.05). O(2)(-) levels were elevated (70-90%; P < 0.05) in the diabetic heart, and this elevation was blocked by the Nox inhibitor gp-91(ds-tat) (50 microM) or by the mitochondrial respiratory chain inhibitors
antimycin (10 microM) and
rotenone (50 microM). Inhibition of G6PD by
6-aminonicotinamide (5 mM) and dihydroepiandrosterone (100 microM) also reduced (P < 0.05) O(2)(-) production. Notably, the activities of Nox and G6PD in the fa/fa rat heart were inhibited by
chelerythrine, a
protein kinase C inhibitor. Although we detected no changes in stroke volume, cardiac output, or ejection fraction, left ventricular diameter was slightly increased during diastole and systole, and left ventricular posterior wall thickness was decreased during systole (P < 0.05) in Zucker fa/fa rats. Our findings suggest that in a model of severe hyperlipidema and
hyperglycemia Nox-derived O(2)(-) generation in the myocardium is fueled by elevated levels of G6PD-derived
NADPH. Similar mechanisms were found to activate O(2)(-) production and induce endothelial dysfunction in aorta. Thus G6PD may be a useful therapeutic target for treating the
cardiovascular disease associated with
type 2 diabetes, if second-generation drugs specifically reducing the activity of G6PD to near normal levels are developed.