Study Protocol for a Multicenter, Open-Label, Single-Arm Study of Tranilast for Cardiomyopathy of Muscular Dystrophy

We describe survival in Duchenne dystrophy by invasive and noninvasive ventilation vs. untreated. Patients were untreated prior to 1984 (Group 1), underwent tracheotomy from 1984 until 1991 (Group 2), and were managed by noninvasive mechanical ventilation and cardioprotective medications subsequently (Group 3). Symptoms, vital capacity, and blood gases were monitored for all and spirometry, cough peak flows, carbon dioxide tension, and oximetry for Group 3. Sleep nasal ventilation was initiated for symptomatic hypoventilation. An oximeter and mechanical cough assistance were prescribed for maximum assisted cough peak flow <300 L/m. Patients used continuous noninvasive ventilation and mechanically assisted coughing as needed to maintain pulse oxyhemoglobin saturation ≥95%. Survival was compared by Kaplan-Meier analysis. The 56 of Group 1 died at 18.6±2.9, the 21 Group 2 at 28.1±8.3 years of age with three still alive, and the 88 using noninvasive ventilation had 50% survival to 39.6 years, p<0.001, respectively. We conclude that noninvasive mechanical ventilation and assisted coughing provided by specifically trained physicians and therapists, and cardioprotective medication can result in more favorable outcomes and better survival by comparison with invasive treatment. Copyright © 2010 Elsevier B.V. All rights reserved.

Disruption of the dystrophin–glycoprotein complex caused by genetic defects of dystrophin or sarcoglycans results in muscular dystrophy and/or cardiomyopathy in humans and animal models. However, the key early molecular events leading to myocyte degeneration remain elusive. Here, we observed that the growth factor–regulated channel (GRC), which belongs to the transient receptor potential channel family, is elevated in the sarcolemma of skeletal and/or cardiac muscle in dystrophic human patients and animal models deficient in dystrophin or δ-sarcoglycan. However, total cell GRC does not differ markedly between normal and dystrophic muscles. Analysis of the properties of myotubes prepared from δ-sarcoglycan–deficient BIO14.6 hamsters revealed that GRC is activated in response to myocyte stretch and is responsible for enhanced Ca2+ influx and resultant cell damage as measured by creatine phosphokinase efflux. We found that cell stretch increases GRC translocation to the sarcolemma, which requires entry of external Ca2+. Consistent with these findings, cardiac-specific expression of GRC in a transgenic mouse model produced cardiomyopathy due to Ca2+ overloading, with disease expression roughly parallel to sarcolemmal GRC levels. The results suggest that GRC is a key player in the pathogenesis of myocyte degeneration caused by dystrophin–glycoprotein complex disruption.

Muscular dystrophy is a severe degenerative disorder of skeletal muscle characterized by progressive muscle weakness. One subgroup of this disease is caused by a defect in the gene encoding one of the components of the dystrophin-glycoprotein complex, resulting in a significant disruption of membrane integrity and/or stability and, consequently, a sustained increase in the cytosolic Ca(2+) concentration ([Ca(2+)](i)). In the present study, we demonstrate that muscular dystrophy is ameliorated in two animal models, dystrophin-deficient mdx mice and delta-sarcoglycan-deficient BIO14.6 hamsters by dominant-negative inhibition of the transient receptor potential cation channel, TRPV2, a principal candidate for Ca(2+)-entry pathways. When transgenic (Tg) mice expressing a TRPV2 mutant in muscle were crossed with mdx mice, the [Ca(2+)](i) increase in muscle fibers was reduced by dominant-negative inhibition of endogenous TRPV2. Furthermore, histological, biochemical and physiological indices characterizing dystrophic pathology, such as an increased number of central nuclei and fiber size variability/fibrosis/apoptosis, elevated serum creatine kinase levels, and reduced muscle performance, were all ameliorated in the mdx/Tg mice. Similar beneficial effects were also observed in the muscles of BIO14.6 hamsters infected with adenovirus carrying mutant TRPV2. We propose that TRPV2 is a principal Ca(2+)-entry route leading to a sustained [Ca(2+)](i) increase and muscle degeneration, and that it is a promising therapeutic target for the treatment of muscular dystrophy.