Nox2 NADPH oxidase promotes pathologic cardiac remodeling associated with Doxorubicin chemotherapy

Abstract

Doxorubicin is a highly effective cancer treatment whose use is severely limited by dose-dependent cardiotoxicity. It is well established that doxorubicin increases reactive oxygen species (ROS) production. In this study, we investigated contributions to doxorubicin cardiotoxicity from Nox2 NADPH oxidase, an important ROS source in cardiac cells, which is known to modulate several key processes underlying the myocardial response to injury. Nox2-deficient mice (Nox2-/-) and wild-type (WT) controls were injected with doxorubicin (12 mg/kg) or vehicle and studied 8 weeks later. Echocardiography indicated that doxorubicin-induced contractile dysfunction was attenuated in Nox2-/- versus WT mice (fractional shortening: 29.5±1.4 versus 25.7±1.0%; P<0.05). Similarly, in vivo pressure-volume analysis revealed that systolic and diastolic function was preserved in doxorubicin-treated Nox2-/- versus WT mice (ejection fraction: 52.6±2.5 versus 28.5±2.3%, LVdP/dtmin: -8,379±416 versus -5,198±527 mmHg s(-1); end-diastolic pressure-volume relation: 0.051±0.009 versus 0.114±0.012; P<0.001). Furthermore, in response to doxorubicin, Nox2-/- mice exhibited less myocardial atrophy, cardiomyocyte apoptosis, and interstitial fibrosis, together with reduced increases in profibrotic gene expression (procollagen IIIαI, transforming growth factor-β3, and connective tissue growth factor) and matrix metalloproteinase-9 activity, versus WT controls. These alterations were associated with beneficial changes in NADPH oxidase activity, oxidative/nitrosative stress, and inflammatory cell infiltration. We found that adverse effects of doxorubicin were attenuated by acute or chronic treatment with the AT1 receptor antagonist losartan, which is commonly used to reduce blood pressure. Our findings suggest that ROS specifically derived from Nox2 NADPH oxidase make a substantial contribution to several key processes underlying development of cardiac contractile dysfunction and remodeling associated with doxorubicin chemotherapy.

Figure 1

Effect of doxorubicin on LV pressure-volume relations in WT and Nox2^−/− mice. Representative (A, C) steady-state pressure-volume loops, (B, D) ESPVR after IVC occlusion.

Figure 2

Effect of doxorubicin on cardiomyocyte remodeling in WT and Nox2^−/− mice. (A) LV/tibial length (TL; n=13-20), (B) cardiomyocyte cross-sectional area (n=7), (C) GATA-4 mRNA expression (n=6-9), (D) TUNEL staining (n=8). Mean±SEM. **P<0.01, versus control; †P<0.05, Nox2^−/− doxorubicin versus WT doxorubicin.

Figure 3

Effect of doxorubicin on extracellular matrix remodeling in WT and Nox2^−/− mice. (A) cardiac interstitial fibrosis (n=7), (B-E) pro-fibrotic gene mRNA expression (n=10-14), (F) MMP-9 activity by gelatin zymography (n=6). Mean±SEM. *P<0.05, **P<0.01, ***P<0.001, versus control; ^†P<0.05, ^†††P<0.001, Nox2^−/− doxorubicin versus WT doxorubicin.

Figure 4

Effect of doxorubicin on NADPH oxidase activity/expression and oxidative/nitrosative stress in WT and Nox2^−/− mice. (A) NADPH-dependent superoxide production (relative light units, RLU; n=7-9), (B) effect of inhibitors on NADPH oxidase activity in WT mice (oxy=oxypurinol, rot=rotenone; n=6), (C-D) mRNA expression (N.D. = not detected; n=9-13), (E) 3-nitrotyrosine staining (n=6). Mean±SEM. *P<0.05, **P<0.01, ***P<0.001, versus control; ^††P<0.01, Nox2^−/− doxorubicin versus WT doxorubicin.

Figure 5

Effect of doxorubicin on leukocyte infiltration in WT and Nox2^−/− mice. (A-D) Representative LV sections stained for CD45, (E) positive spleen control, (F) negative secondary-only spleen control, (G) Mean quantification data±SEM, n=9, as CD45-positive cells per high-power field (HPF). *P<0.05, versus control.

Figure 6

Effect of losartan (Los) on doxorubicin cardiotoxicity in WT mice. Chronic treatment: (A-C) contractile function (n=5-10), (D) LV/tibial length (TL; n=9-11), (E) NADPH-dependent superoxide production (relative light units, RLU; n=5-8), (F-H) mRNA expression (n=5-8). Acute treatment in isolated cardiomyocytes: (I) NADPH-dependent superoxide production (n=6-7), (J-L) mRNA expression (n=6-7). Mean±SEM. *P<0.05, **P<0.01, ***P<0.001, versus vehicle; ^†P<0.05, ^††P<0.01, Los doxorubicin (DOX) versus doxorubicin; ^‡P<0.05, ^‡‡P<0.01, doxorubicin versus basal.