Abstract 5360: A Nox-2 Containing NADPH Oxidase Plays a Critical Role in Cardiac Remodeling Associated with Doxorubicin Chemotherapy

Abstract

Anthracycline antibiotics, such as doxorubicin (DOX), are effective anti-cancer drugs, although their use is limited by a dose-dependent cardiotoxicity. Chronic anthracycline treatment is known to increase myocardial production of reactive oxygen species (ROS), which are implicated in the processes underlying cardiac remodeling. A Nox2-containing NADPH oxidase is an important source of ROS in the heart. Here, we investigated its role in DOX-induced cardiac remodeling using gene-modified mice lacking Nox2 (KO) and wild-type (WT) littermate controls. Adult male mice (8–10 weeks) were injected with DOX (12 mg/kg cumulative dose) or vehicle control and studied 8 weeks later ( n ≥ 7 per group). Echocardiography indicated that DOX caused significant systolic and diastolic dysfunction in WT mice compared to controls (fractional shortening: 25.3 ± 0.6 vs 34.3 ± 1.2 %; E/A ratio: 1.27 ± 0.05 vs 1.67 ± 0.05; P<0.05). In contrast, contractile function was preserved in KO mice subjected to DOX (fractional shortening: 34.2 ± 1.7 vs 34.8 ± 1.4 %; E/A ratio: 1.39 ± 0.04 vs 1.60 ± 0.09; P=NS). Furthermore, mRNA expression (real-time RT-PCR) of several pro-hypertrophic and pro-fibrotic genes was significantly increased by DOX in WT (eg ANP: 326 ± 63; β-MHC: 266 ± 68; procollagen III: 56 ± 18; MMP-9: 46 ± 11 %, P<0.05) but not KO mice (eg ANP: −6 ± 27; β-MHC: 23 ± 22; procollagen III: 4 ± 11; MMP-9: −11 ± 10 %, P=NS) compared to controls. Myocardial NADPH oxidase activity (lucigenin-enhanced chemiluminescence) was also significantly increased by DOX in WT but not KO mice (88 ± 28 vs −6 ± 13 %, P<0.05). This was associated with increased mRNA expression of Nox2 and Nox4 in WT DOX-treated mice (74 ± 33 and 106 ± 35 %, respectively; P<0.05), whereas Nox4 mRNA remained unchanged in KO mice (0.6 ± 15 %, P=NS). Isolated ventricular cardiomyocytes subjected to acute DOX treatment (0.5 μM for 3 h) demonstrated similar changes in superoxide production and Nox isoform and pro-hypertrophic/fibrotic gene expression, which were attenuated by the AT 1 antagonist, losartan (10 μM) in WT cells. Conclusion: These data suggest that ROS derived specifically from a Nox2-containing NADPH oxidase make a significant contribution to the processes underlying cardiac remodeling associated with doxorubicin chemotherapy.