Dual Therapy Deflazacort/Doxycyclyne Is Better Than Deflazacort Monotherapy to Alleviate Cardiomyopathy in Dystrophin-Deficient mdx Mice

Sunitinib inhibits STAT3 phosphorylation in cardiac muscle and prevents cardiomyopathy in the mdx mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal X-linked genetic disorder affecting approximately 1 in 5000 male births worldwide. DMD is caused by mutations in the dystrophin gene. Dystrophin is essential for maintaining muscle cell membrane integrity and stability by linking the cytoskeleton to the extracellular matrix, which protects myofibers from contraction-induced damage. Loss of dystrophin leads to mechanically induced skeletal and cardiac muscle damage. Although the disease is not evident in DMD patients at birth, muscular dystrophy rapidly progresses and results in respiratory and cardiac muscle failure as early as the teenage years. Premature death in DMD patients is due to cardiac arrhythmias and left ventricular dysfunction. Currently, there is no effective treatment for DMD-related cardiac failure. Recently, we have shown that a Food and Drug Administration-approved small molecule, sunitinib, a multi-targeted tyrosine kinase inhibitor can mitigate skeletal muscle disease through an increase in myogenic capacity, cell membrane integrity, and improvement of skeletal muscle function via regulation of STAT3-related signaling pathway. Chronic activation of STAT3 has been shown to promote cardiac hypertrophy and failure. In this study, we examined the effects of long-term sunitinib treatment on cardiac pathology and function. Our results showed sunitinib treatment reduced STAT3 phosphorylation in the heart muscle of mdx mice, improved cardiac electrical function, increased cardiac output and stroke volume, decreased ventricular hypertrophy, reduced cardiomyocytes membrane damage, fibrotic tissue deposition and slightly decreased cardiac inflammation. Together, our studies support the idea that sunitinib could serve as a novel treatment to slow cardiomyopathy progression in DMD. One Sentence Summary In this study, we determined if sunitinib, a Food and Drug Administration-approved drug, could reduce the pathology and improve cardiac function in an animal model for DMD.

Angiotensin receptor-neprilysin inhibition by sacubitril/valsartan attenuates doxorubicin-induced cardiotoxicity in a pretreatment mice model by interfering with oxidative stress, inflammation, and Caspase 3 apoptotic pathway

OBJECTIVE

Doxorubicin (DOX) is a well-known cardiotoxic agent, whereas sacubitril/valsartan (Sac/Val) is an effective treatment option in heart failure. In this study, we aimed to evaluate the effect of Sac/Val on DOX-induced cardiotoxicity in pretreatment mice model.

METHODS

A total of 24 mice were equally classified into 4 groups; control group, DOX (20 mg/kg; fifth day), Sac/Val (80 mg/kg), and Sac/Val+DOX (Sac/Val was given from day one of the study before doxorubicin administration). Electrocardiography parameters, including durations of QRS, ST, QT, PP segment, and QT/PQ index were measured. Total antioxidant status (TAS), total oxidant status (TOS), tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β), IL-6, NT-proBNP concentrations, and Caspase 3 activity were evaluated.

RESULTS

At the end of the 9-day study duration, QRS, ST, QT intervals, QT/PQ index and TAS, TOS, TNF-α, IL-1β, IL-6 levels were significantly higher in the DOX group than in the control group (p<0.001). Moreover, there were significant differences only in the PP interval when comparing the Sac/Val+DOX and control groups (p<0.001). QRS, ST, QT intervals, and QT/PQ index, TAS, TOS, TNF-α, IL-1β, IL-6 levels were significantly lower in the Sac/Val+ DOX group compared with the DOX group (p<0.001). Furthermore, NT-proBNP levels were lower in the Sac/Val+DOX group compared with the DOX group along with less Caspase 3 apoptosis.

CONCLUSION

Sac/Val seems to be cardioprotective against DOX-induced cardiotoxicity in pretreatment mice model. These findings can be attributed to the antiarrhythmic, anti-inflammatory, antioxidant, and antiapoptotic effects of Sac/Val as shown in this study.

Skeletal Muscle Metabolism in Duchenne and Becker Muscular Dystrophy-Implications for Therapies

The interactions between nutrition and metabolism and skeletal muscle have long been known. Muscle is the major metabolic organ&mdash;it consumes more calories than other organs&mdash;and therefore, there is a clear need to discuss these interactions and provide some direction for future research areas regarding muscle pathologies. In addition, new experiments and manuscripts continually reveal additional highly intricate, reciprocal interactions between metabolism and muscle. These reciprocal interactions include exercise, age, sex, diet, and pathologies including atrophy, hypoxia, obesity, diabetes, and muscle myopathies. Central to this review are the metabolic changes that occur in the skeletal muscle cells of muscular dystrophy patients and mouse models. Many of these metabolic changes are pathogenic (inappropriate body mass changes, mitochondrial dysfunction, reduced adenosine triphosphate (ATP) levels, and increased Ca²⁺) and others are compensatory (increased phosphorylated AMP activated protein kinase (pAMPK), increased slow fiber numbers, and increased utrophin). Therefore, reversing or enhancing these changes with therapies will aid the patients. The multiple therapeutic targets to reverse or enhance the metabolic pathways will be discussed. Among the therapeutic targets are increasing pAMPK, utrophin, mitochondrial number and slow fiber characteristics, and inhibiting reactive oxygen species. Because new data reveals many additional intricate levels of interactions, new questions are rapidly arising. How does muscular dystrophy alter metabolism, and are the changes compensatory or pathogenic? How does metabolism affect muscular dystrophy? Of course, the most profound question is whether clinicians can therapeutically target nutrition and metabolism for muscular dystrophy patient benefit? Obtaining the answers to these questions will greatly aid patients with muscular dystrophy.

Calcium current properties in dystrophin-deficient ventricular cardiomyocytes from aged mdx mice

Duchenne muscular dystrophy (DMD), caused by mutations in the gene encoding for the cytoskeletal protein dystrophin, is linked with severe cardiac complications including cardiomyopathy development and cardiac arrhythmias. We and others recently reported that currents through L-type calcium (Ca) channels were significantly increased, and channel inactivation was reduced in dystrophin-deficient ventricular cardiomyocytes derived from the mdx mouse, the most commonly used animal model for human DMD. These gain-of-function Ca channel abnormalities may enhance the risk of Ca-dependent arrhythmias and cellular Ca overload in the dystrophic heart. All studies, which have so far investigated L-type Ca channel properties in dystrophic cardiomyocytes, have used hearts from either neonatal or young adult mdx mice as cell source. In consequence, the dimension of the Ca channel abnormalities present in the severely-diseased aged dystrophic heart has remained unknown. Here, we have studied potential abnormalities in Ca currents and intracellular Ca transients in ventricular cardiomyocytes derived from aged dystrophic mdx mice. We found that both the L-type and T-type Ca current properties of mdx cardiomyocytes were similar to those of myocytes derived from aged wild-type mice. Accordingly, Ca release from the sarcoplasmic reticulum was normal in cardiomyocytes from aged mdx mice. This suggests that, irrespective of the presence of a pronounced cardiomyopathy in aged mdx mice, Ca currents and Ca release in dystrophic cardiomyocytes are normal. Finally, our data imply that dystrophin- regulation of L-type Ca channel function in the heart is lost during aging.