Angiotensin (ANG) II (AngII) and aldosterone contribute to the development of interstitial cardiac fibrosis. We investigated the potential role of a Nox2-containing NADPH oxidase in aldosterone-induced fibrosis and the involvement of this mechanism in AngII-induced effects. Nox2-/- mice were compared with matched wild-type controls (WT). In WT mice, subcutaneous (s.c.) AngII (1.1 mg/kg/day for 2 wk) significantly increased NADPH oxidase activity, interstitial fibrosis (11.5+/-1.0% vs. 7.2+/-0.7%; P<0.05), expression of fibronectin, procollagen I, and connective tissue growth factor mRNA, MMP-2 activity, and NF-kB activation. These effects were all inhibited in Nox2-/- hearts. The mineralocorticoid receptor antagonist spironolactone inhibited AngII-induced increases in NADPH oxidase activity and the increase in interstitial fibrosis. In a model of mineralocorticoid-dependent hypertension involving chronic aldosterone infusion (0.2 mg/kg/day) and a 1% Na Cl diet ("ALDO"), WT animals exhibited increased NADPH oxidase activity, pro-fibrotic gene expression, MMP-2 activity, NF-kB activation, and significant interstitial cardiac fibrosis (12.0+/-1.7% with ALDO vs. 6.3+/-0.3% without; P<0.05). These effects were inhibited in Nox2-/- ALDO mice (e.g., fibrosis 6.8+/-0.8% with ALDO vs. 5.8+/-1.0% without ALDO; P=NS). These results suggest that aldosterone-dependent activation of a Nox2-containing NADPH oxidase contributes to the profibrotic effect of AngII in the heart as well as the fibrosis seen in mineralocorticoid-dependent hypertension.

The Nox2 oxidase contributes to the development of cardiac contractile dysfunction and interstitial fibrosis during pressure overload, although it is not essential for development of morphologic hypertrophy per se. These data suggest divergent downstream effects of Nox2 on different components of the overall response to pressure overload.

Chronic heart failure, secondary to left ventricular hypertrophy or myocardial infarction, is a condition with increasing morbidity and mortality. Although the mechanisms underlying the development and progression of this condition remain a subject of intense interest, there is now growing evidence that redox-sensitive pathways play an important role. This article focuses on the involvement of reactive oxygen species derived from a family of superoxide-generating enzymes, termed NADPH oxidases (NOXs), in the pathophysiology of ventricular hypertrophy, the accompanying interstitial fibrosis and subsequent heart failure. In particular, the apparent ability of the different NADPH oxidase isoforms to define the response of a cell to a range of physiological and pathophysiological stimuli is reviewed. If confirmed, these data would suggest that independently targeting different members of the NOX family may hold the potential for therapeutic intervention in the treatment of cardiac disease.

Reactive oxygen species (ROS)‐mediated signaling is implicated in early ischemic preconditioning (PC). A NOX‐2‐containing NADPH oxidase is a recognized major source of ROS in cardiac myocytes, whose activity is augmented by preconditioning mimetics, such as angiotensin II. We hypothesized that this oxidase is an essential source of ROS in PC. Hearts from wild‐type (WT) and NOX‐2 knockout (KO) mice were Langendorff perfused and subjected to 35 min ischemia/reperfusion with or without preceding PC or drug treatment. Infarct size was measured by triphenyl tetrazolium chloride staining, and NADPH oxidase activity by lucigenin chemiluminescence. PC significantly attenuated infarct size in WT (26±2% vs. control, 38±2%, P<0.05) yet was ineffective in KO hearts (33±3% vs. control, 34±3%). Concomitantly, PC significantly increased NADPH oxidase activity in WT (+41±13%; P<0.05), but not in KO (−5±18%, P=NS). The ROS scavenger MPG (N‐2‐mercaptopropionyl glycine, 300 µmol/L) abrogated PC in WT (39±2% vs. control, 33±1%). CCPA (2‐chloro N6 cyclopentyl adenosine, 200 nmol/L), a putative ROS‐independent PC trigger, significantly attenuated infarct size in WT, MPG‐treated WT and KO hearts (24±2, 23±1, and 20±3%, respectively, P<0.05). Furthermore, CCPA did not augment NADPH oxidase activity over control (+22±11%, P=NS). Inhibition of protein kinase C (PKC) with chelerythrine (CHE, 2 µmol/L) completely abrogated both PC (38±2% vs. CHE alone, 35±2%) and associated increases in oxidase activity (+3±10%, P=NS). PKC‐dependent activation of a NOX‐2‐containing NADPH oxidase is pivotally involved in early ischemic PC. However, adenosine receptor activation can trigger a ROS and NOX‐2 independent PC pathway.