Abstract 9161: NOX2 Inhibition Restores Contractility, Intracellular Calcium Handling and Reduces Arrhythmogenicity in Dystrophic Cardiomyopathy
Background. Dystrophic cardiomyopathy is the cardiac manifestation of three closely related diseases that include Duchenne and Becker muscular dystrophies, and X-linked dilated cardiomyopathy. Oxidative stress is characteristic of cardiomyopathies. Intracellular calcium ([Ca2+]i) handling is abnormal in the heart of the mdx mouse, a model of Duchenne muscular dystrophy. We tested the hypothesis that oxidative stress may be responsible of disturbances in Ca2+ handling and contractility in this model.
Methods and results. We used mdx mice with established cardiomyopathy: ejection fraction of 56.7 ± 0.5 % in mdx vs. 70.8 ± 2.4% in wild type. We found increased expression (fivefold) of the NADPH oxidase NOX2 in the mdx hearts compared to wild type, along with increased superoxide production, measured as intensity of dihydroethidium staining (p<0.05 vs. wild type). Treatment with apocyinin (30 min, 100 µmol/L), a NOX2 inhibitor, decreased superoxide in mdx (p<0.05 vs. untreated). Next, we studied the impact of NOX2 inhibition on contractility and calcium handling in isolated cardiomyocytes. Contractility, assessed as sarcomere shortening, was decreased in mdx myocytes compared to wild type (p<0.05). Pre-treatment with apocynin restored this response to normal levels. In addition, the amplitude of evoked [Ca2+]i transients (measured as fura-2 fluorescence) that was diminished in mdx myocytes (p<0.05), was also restored upon NOX2 inhibition. Total sarcoplasmic reticulum (SR) Ca2+ content (evaluated as caffeine-induced Ca2+ release) was reduced in mdx hearts (p<0.05). This content was normalized by apocynin treatment. At the same time, NOX2 inhibition decreased dramatically the production of spontaneous diastolic calcium release events in mdx myocytes (p<0.05, ANOVA).
Conclusions. These results indicate that in mdx hearts, NOX2 inhibition reduces oxidative stress, improving the SR [Ca2+] handling and contractility. Additionally, NOX2 inhibition reduced the sensitivity of the ryanodine receptor, reducing the incidence of diastolic Ca2+ waves. Targeting of NOX2 in may be therapeutically helpful to increase cardiac performance and avoid the incidence of ventricular arrhythmias in Duchenne and other dystrophic cardiomyopathies..
- © 2011 by American Heart Association, Inc.