Therapeutic Potential for Aldosterone Inhibition in Duchenne Muscular Dystrophy

DMD is an X-linked disorder in which the sarcolemmal protein dystrophin is effectively absent. Males with DMD typically die in the third and fourth decades of life of cardiopulmonary disease. Mouse models of DMD, autopsy data, and in vivo human studies using magnetic resonance-based late gadolinium enhancement imaging (LGE) have shown that progressive myocardial damage is well underway before left ventricular ejection fraction (LV EF) becomes abnormal. Exertional symptoms and signs of myocardial disease are typically absent as skeletal muscle disease progressively limits functional capacity in affected boys. Thus, cardiac involvement can go undetected until LV dysfunction and myocardial fibrosis are advanced. While echocardiography remains a useful tool to evaluate LV dysfunction, CMR with LGE is advantageous for DMD patients since it identifies myocardial injury before decline in EF is apparent by echocardiography. Further, greater reproducibility affords efficient sample sizes for cardiomyopathy clinical trials in patients with rare diseases. CMR's increasing availability at DMD clinical centers has afforded earlier cardiomyopathy detection, and has helped refine current management to typically include agents such as angiotensin converting enzyme inhibitors (ACEI) once damage is evident. This strategy, however, may not be sufficient, with prior studies showing decline in systolic function with or without ACEI or angiotensin receptor blocker (ARB) therapy. The investigators previously tested mineralocorticoid receptor antagonism (MRA) added to ACEI while EF was still normal in a mouse model that mimics the myocardial damage seen in DMD patients. This combination significantly reduced myocardial injury and improved (made more negative) LV circumferential strain (Ecc), a sensitive and early marker of LV systolic dysfunction. Additionally, preliminary findings from a recently completed clinical trial suggests efficacy of eplerenone vs. placebo, while further preclinical data suggests greater benefit without concomitant steroid use. Thus, a non-inferiority trial comparing MRAs is needed.