Glucocorticoids and immunosuppressants do not change the prevalence of necrosis and regeneration in mdx skeletal muscles

Dimethyl fumarate modulates the dystrophic disease program following short-term treatment

New medicines are urgently required to treat the fatal neuromuscular disease Duchenne muscular dystrophy (DMD). Dimethyl fumarate (DMF) is a potent immunomodulatory small molecule nuclear erythroid 2-related factor 2 activator with current clinical utility in the treatment of multiple sclerosis and psoriasis that could be effective for DMD and rapidly translatable. Here, we tested 2 weeks of daily 100 mg/kg DMF versus 5 mg/kg standard-care prednisone (PRED) treatment in juvenile mdx mice with early symptomatic DMD. Both drugs modulated seed genes driving the DMD disease program and improved force production in fast-twitch muscle. However, only DMF showed pro-mitochondrial effects, protected contracting muscles from fatigue, improved histopathology, and augmented clinically compatible muscle function tests. DMF may be a more selective modulator of the DMD disease program than PRED, warranting follow-up longitudinal studies to evaluate disease-modifying impact.

Efficacy of Prednisolone in Generated Myotubes Derived From Fibroblasts of Duchenne Muscular Dystrophy Patients

Duchenne muscular dystrophy (DMD) is a recessive X-linked form of muscular dystrophy characterized by progressive muscle degeneration. This disease is caused by the mutation or deletion of the dystrophin gene. Currently, there are no effective treatments and glucocorticoid administration is a standard care for DMD. However, the mechanism underlying prednisolone effects, which leads to increased walking, as well as decreased muscle wastage, is poorly understood. Our purpose in this study is to investigate the mechanisms of the efficacy of prednisolone for this disease. We converted fibroblasts of normal human cell line and a DMD patient sample to myotubes by MyoD transduction using a retroviral vector. In myotubes from the MyoD-transduced fibroblasts of the DMD patient, the myotube area was decreased and its apoptosis was increased. Furthermore, we confirmed that prednisolone could rescue these pathologies. Prednisolone increased the expression of not utrophin but laminin by down-regulation of MMP-2 mRNA. These results suggest that the up-regulation of laminin may be one of the mechanisms of the efficacy of prednisolone for DMD.

Pharmacologic management of Duchenne muscular dystrophy: target identification and preclinical trials

Duchenne muscular dystrophy (DMD) is an X-linked human disorder in which absence of the protein dystrophin causes degeneration of skeletal and cardiac muscle. For the sake of treatment development, over and above definitive genetic and cell-based therapies, there is considerable interest in drugs that target downstream disease mechanisms. Drug candidates have typically been chosen based on the nature of pathologic lesions and presumed underlying mechanisms and then tested in animal models. Mammalian dystrophinopathies have been characterized in mice (mdx mouse) and dogs (golden retriever muscular dystrophy [GRMD]). Despite promising results in the mdx mouse, some therapies have not shown efficacy in DMD. Although the GRMD model offers a higher hurdle for translation, dogs have primarily been used to test genetic and cellular therapies where there is greater risk. Failed translation of animal studies to DMD raises questions about the propriety of methods and models used to identify drug targets and test efficacy of pharmacologic intervention. The mdx mouse and GRMD dog are genetically homologous to DMD but not necessarily analogous. Subcellular species differences are undoubtedly magnified at the whole-body level in clinical trials. This problem is compounded by disparate cultures in clinical trials and preclinical studies, pointing to a need for greater rigor and transparency in animal experiments. Molecular assays such as mRNA arrays and genome-wide association studies allow identification of genetic drug targets more closely tied to disease pathogenesis. Genes in which polymorphisms have been directly linked to DMD disease progression, as with osteopontin, are particularly attractive targets.

Microdystrophin ameliorates muscular dystrophy in the canine model of duchenne muscular dystrophy

Dystrophin deficiency results in lethal Duchenne muscular dystrophy (DMD). Substituting missing dystrophin with abbreviated microdystrophin has dramatically alleviated disease in mouse DMD models. Unfortunately, translation of microdystrophin therapy has been unsuccessful in dystrophic dogs, the only large mammalian model. Approximately 70% of the dystrophin-coding sequence is removed in microdystrophin. Intriguingly, loss of ≥50% dystrophin frequently results in severe disease in patients. To test whether the small gene size constitutes a fundamental design error for large mammalian muscle, we performed a comprehensive study using 22 dogs (8 normal and 14 dystrophic). We delivered the ΔR2-15/ΔR18-19/ΔR20-23/ΔC microdystrophin gene to eight extensor carpi ulnaris (ECU) muscles in six dystrophic dogs using Y713F tyrosine mutant adeno-associated virus (AAV)-9 (2.6 × 10(13) viral genome (vg) particles/muscle). Robust expression was observed 2 months later despite T-cell infiltration. Major components of the dystrophin-associated glycoprotein complex (DGC) were restored by microdystrophin. Treated muscle showed less inflammation, fibrosis, and calcification. Importantly, therapy significantly preserved muscle force under the stress of repeated cycles of eccentric contraction. Our results have established the proof-of-concept for microdystrophin therapy in dystrophic muscles of large mammals and set the stage for clinical trial in human patients.

Recent advances in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), an allelic X-linked progressive muscle-wasting disease, is one of the most common single-gene disorders in the developed world. Despite knowledge of the underlying genetic causation and resultant pathophysiology from lack of dystrophin protein at the muscle sarcolemma, clinical intervention is currently restricted to symptom management. In recent years, however, unprecedented advances in strategies devised to correct the primary defect through gene- and cell-based therapeutics hold particular promise for treating dystrophic muscle. Conventional gene replacement and endogenous modification strategies have greatly benefited from continued improvements in encapsidation capacity, transduction efficiency, and systemic delivery. In particular, RNA-based modifying approaches such as exon skipping enable expression of a shorter but functional dystrophin protein and rapid progress toward clinical application. Emerging combined gene- and cell-therapy strategies also illustrate particular promise in enabling ex vivo genetic correction and autologous transplantation to circumvent a number of immune challenges. These approaches are complemented by a vast array of pharmacological approaches, in particular the successful identification of molecules that enable functional replacement or ameliorate secondary DMD pathology. Animal models have been instrumental in providing proof of principle for many of these strategies, leading to several recent trials that have investigated their efficacy in DMD patients. Although none has reached the point of clinical use, rapid improvements in experimental technology and design draw this goal ever closer. Here, we review therapeutic approaches to DMD, with particular emphasis on recent progress in strategic development, preclinical evaluation and establishment of clinical efficacy. Further, we discuss the numerous challenges faced and synergistic approaches being devised to combat dystrophic pathology effectively.

Inflammation in muscular dystrophy and the beneficial effects of non-steroidal anti-inflammatory drugs

INTRODUCTION

Glucocorticoids are the only drugs available for the treatment of Duchenne muscular dystrophy (DMD), but it is unclear whether their efficacy is dependent on their anti-inflammatory activity.

METHODS

To address this issue, mdx mice were treated daily with methylprednisolone and non-steroidal anti-inflammatory drugs (NSAIDs: aspirin, ibuprofen, parecoxib).

RESULTS

NSAID treatment was effective in ameliorating muscle morphology and reducing macrophage infiltration and necrosis. The percentage of regenerating myofibers was not modified by the treatments. The drugs were effective in reducing COX-2 expression and inflammatory cytokines, but they did not affect utrophin levels. The effects of the treatments on contractile performance were analyzed. Isometric tension did not differ in treated and untreated muscle, but the resistance to fatigue was decreased by treatment with methylprednisolone and aspirin.

CONCLUSIONS

NSAIDs have a beneficial effect on mdx muscle morphology, pointing to a crucial role of inflammation in the progression of DMD.

Glucocorticoid-treated mice are an inappropriate positive control for long-term preclinical studies in the mdx mouse

Background

Dmd^mdx (mdx) mice are used as a genetic and biochemical model of dystrophin deficiency. The long-term consequences of glucocorticoid (GC) treatment on dystrophin-deficient skeletal and heart muscle are not yet known. Here we used systematic phenotyping to assess the long-term consequences of GC treatment in mdx mice. Our investigation addressed not only the effects of GC on the disease phenotype but also the question of whether GCs can be used as a positive control for preclinical drug evaluations.

Methods and Findings

We performed nine pre-clinical efficacy trials (treated N = 129, untreated N = 106) of different durations in 9-to-50-week-old dystrophic mdx mice over a 3-year time period using standardized methods. In all these trials, we used either 1 mg/kg body weight of prednisone or 5 mg/kg body weight of prednisolone as positive controls to compare the efficacy of various test drugs. Data from untreated controls and GC-treated mice in the various trials have been pooled and analyzed to assess the effects of GCs on dystrophin-deficient skeletal and cardiac muscles of mdx mice. Our results indicate that continuous GC treatment results in early (e.g., at 50 days) improvements in normalized parameters such as grip strength, motor coordination and maximal in vitro force contractions on isolated EDL muscle, but these initial benefits are followed by a progressive loss of muscle strength after 100 days. We also found a significant increase in heart fibrosis that is reflected in a significant deterioration in cardiac systolic function after 100 days of treatment.

Conclusion

Continuous administration of prednisone to mdx mice initially improves skeletal muscle strength, but further therapy result in deterioration of muscle strength and cardiac function associated with enhanced cardiac fibrosis. These results suggest that GCs may not serve as an appropriate positive control for long-term mdx mouse preclinical trials.

Motor performance of young dystrophic mdx mice treated with long-circulating prednisolone liposomes

For Duchenne muscular dystrophy (DMD), a common myopathy that leads to severe disability, no causal therapy is available. Glucocorticosteroids improve patients' muscle strength, but their long-term use is limited by negative side effects. Thus, pharmacological modifications of glucocorticosteroids are required to increase the efficacy by drug targeting. Liposomal encapsulation augments systemic half-life and local tissue concentrations of glucocorticosteroids and, at the same time, reduces systemic side effects. In this study, the efficacy of novel, long-circulating, polyethylene-glycol-coated liposomes encapsulating prednisolone was compared with free prednisolone in the treatment of mdx mice, a well-established animal model for DMD. Using an objective and sensitive computerized 24-hr detection system of voluntary wheel-running in single cages, we demonstrate a significant impairment of the running performance in mdx compared with black/10 control mice aged 3-6 weeks. Treatment with liposomal or free prednisolone did not improve running performance compared with saline control or empty liposomes. Histopathological parameters, including the rate of internalized nuclei and fiber size variation, and mRNA and protein expression levels of transforming growth factor (TGF)-β and monocytes chemotactic protein (MCP)-1 also remained unchanged. Bioactivity in skeletal muscle of liposomal and free prednisolone was demonstrated by elevated mRNA expression of muscle ring finger protein 1 (MuRF1), a mediator of muscle atrophy, and its forkhead box transcription factors (Foxo1/3). Our data support the assessment of voluntary running to be a robust and reproducible outcome measure of skeletal muscle performance during the early disease course of mdx mice and suggest that liposomal encapsulation is not superior in treatment efficacy compared with conventional prednisolone. Our study helps to improve the future design of experimental treatment in animal models of neuromuscular diseases.

Clinical use of immunosuppressants in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a degenerative disease primarily affecting voluntary muscles with secondary consequences on heart and breathing muscles. DMD is an X-linked recessive disease that results in the loss of dystrophin, a key muscle protein. Inflammation can play different roles in DMD; it can be a secondary response to muscle degeneration, a primary cause of degeneration, or can contribute to the disease progression. Several immunosuppressants have been used with the aim to reduce the inflammation associated with DMD. Most recently, myoblast transplantation has shown the possibility to restore the dystrophin lack in the DMD patient's muscle fibers and this evidence has emphasized the importance of the use of immunosuppressants and the necessity of studying them and their secondary effects. The aim of this review is to analyze the main immunosuppressants drugs starting from the mdx mice experiments and concluding with the most recent human clinical studies.

Quantitative assessment of the T2 relaxation time of the gluteus muscles in children with Duchenne muscular dystrophy: a comparative study before and after steroid treatment

OBJECTIVE

To determine the feasibility of using T2 mapping as a quantitative method to longitudinally follow the disease activity in children with Duchenne muscular dystrophy (DMD) who are treated with steroids.

MATERIALS AND METHODS

ELEVEN BOYS WITH DMD (AGE RANGE: 5-14 years) underwent evaluation with the clinical functional score (CFS), and conventional pelvic MRI and T2 mapping before and during steroid therapy. The gluteus muscle inflammation and fatty infiltration were evaluated on conventional MRI. The histograms and mean T2 relaxation times were obtained from the T2 maps. The CFS, the conventional MRI findings and the T2 values were compared before and during steroid therapy.

RESULTS

None of the patients showed interval change of their CFSs. On conventional MRI, none of the images showed muscle inflammation. During steroid treatment, two boys showed increased fatty infiltration on conventional MRI, and both had an increase of the mean T2 relaxation time (p < 0.05). The remaining nine boys had no increase in fatty infiltration. Of these, three showed an increased mean T2 relaxation time (p < 0.05), two showed no change and four showed a decreased mean T2 relaxation time (p < 0.05).

CONCLUSION

T2 mapping is a feasible technique to evaluate the longitudinal muscle changes in those children who receive steroid therapy for DMD. The differences of the mean T2 relaxation time may reflect alterations in disease activity, and even when the conventional MRI and CFS remain stable.

Glucocorticoid efficacy in asthma: is improved tissue remodeling upstream of anti-inflammation

Synthetic glucocorticoids (GCs), such as prednisone, are among the most widely prescribed drugs worldwide and are used to treat many acute and chronic inflammatory conditions. The current paradigm of GC efficacy is that they are potent anti-inflammatory agents. Decreased inflammation in many disorders is thought to lead to decreased pathological tissue remodeling. However, this model has never been validated. In particular, improvements in inflammation have not been shown to improve the rate of lung function decline in asthma. Herein, we present an alternative paradigm, where GC efficacy is mediated through more successful tissue remodeling, with reduction in inflammation secondary to successful regeneration.

Effects of prednisolone on skeletal muscle contractility in mdx mice

Current treatment for Duchenne muscular dystrophy (DMD) is chronic administration of the glucocorticoid prednisolone. Prednisolone improves muscle strength in boys with DMD, but the mechanism is unknown. The purpose of this study was to determine how prednisolone improves muscle strength by examining muscle contractility in dystrophic mice over time and in conjunction with eccentric injury. Mdx mice began receiving prednisolone (n = 23) or placebo (n = 16) at 5 weeks of age. Eight weeks of prednisolone increased specific force of the extensor digitorum longus muscle 26%, but other parameters of contractility were not affected. Prednisolone also improved the histological appearance of muscle by decreasing the number of centrally nucleated fibers. Prednisolone treatment did not affect force loss during eccentric contractions or recovery of force following injury. These data are of clinical relevance, because the increase in muscle strength in boys with DMD taking prednisolone does not appear to occur via the same mechanism in dystrophic mice.

Therapeutic possibilities in the autosomal recessive limb-girdle muscular dystrophies

Fourteen years ago, the first disease-causing mutation in a form of autosomal recessive limb-girdle muscular dystrophy was reported. Since then the number of genes has been extended to at least 14 and the phenotypic spectrum has been broadened. The generation of mouse models helped to improve our understanding of the pathogenesis of the disease and also served to study therapeutic possibilities. All autosomal recessive limb-girdle muscular dystrophies are rare diseases, which is one reason why there have been so very few controlled clinical trials. Other reasons are insufficient natural history data and the lack of standardized assessment criteria and validated outcome measures. Currently, therapeutic possibilities are mainly restricted to symptomatic treatment and the treatment of disease complications. On the other hand, new efforts in translational research and the development of molecular therapeutic approaches suggest that more promising clinical trials will be carried out in autosomal recessive limb-girdle muscular dystrophy in the next several years.

Steroid treatment causes deterioration of myocardial function in the {delta}-sarcoglycan-deficient mouse model for dilated cardiomyopathy

AIMS

As oral corticosteroids have a beneficial effect on muscle strength in Duchenne muscular dystrophy, it has been suggested that they may also be a useful treatment in the pathologically related sarcoglycanopathies. The delta-sarcoglycan-deficient mouse (Sgcd-null) is a model for both limb girdle muscular dystrophy 2F (LGMD2F) and dilated cardiomyopathy.

METHODS AND RESULTS

To study the effect of oral corticosteroids on cardiac function, we treated 8-week-old Sgcd-null mice with prednisolone (1.5 mg/kg body weight/day orally) for 8 weeks. In vivo cardiac function was assessed by pressure-volume loops using a conductance catheter. We found a well-compensated cardiomyopathy at baseline in Sgcd-null mice with decreased myocardial contractility, increased preload, and decreased afterload, maintaining a high cardiac output. Cardiac haemodynamics, surprisingly, did not improve in prednisolone-treated mice, but instead deteriorated with evidence of ventricular stiffening. On histology, after steroid treatment there was increased myocardial cell damage and increased myocardial fibrosis.

CONCLUSION

Prednisolone led to a decompensation of cardiac haemodynamics in Sgcd-null mice and induced additional cardiac damage. On the basis of these findings, although mouse models may not completely replicate the human situation for LGMD2F, we conclude that careful cardiac monitoring is clearly indicated in patients on long-term corticosteroids.

A multidisciplinary evaluation of the effectiveness of cyclosporine a in dystrophic mdx mice

Chronic inflammation is a secondary reaction of Duchenne muscular dystrophy and may contribute to disease progression. To examine whether immunosuppressant therapies could benefit dystrophic patients, we analyzed the effects of cyclosporine A (CsA) on a dystrophic mouse model. Mdx mice were treated with 10 mg/kg of CsA for 4 to 8 weeks throughout a period of exercise on treadmill, a protocol that worsens the dystrophic condition. The CsA treatment fully prevented the 60% drop of forelimb strength induced by exercise. A significant amelioration (P < 0.05) was observed in histological profile of CsA-treated gastrocnemius muscle with reductions of nonmuscle area (20%), centronucleated fibers (12%), and degenerating area (50%) compared to untreated exercised mdx mice. Consequently, the percentage of normal fibers increased from 26 to 35% in CsA-treated mice. Decreases in creatine kinase and markers of fibrosis were also observed. By electrophysiological recordings ex vivo, we found that CsA counteracted the decrease in chloride conductance (gCl), a functional index of degeneration in diaphragm and extensor digitorum longus muscle fibers. However, electrophysiology and fura-2 calcium imaging did not show any amelioration of calcium homeostasis in extensor digitorum longus muscle fibers. No significant effect was observed on utrophin levels in diaphragm muscle. Our data show that the CsA treatment significantly normalized many functional, histological, and biochemical endpoints by acting on events that are independent or downstream of calcium homeostasis. The beneficial effect of CsA may involve different targets, reinforcing the usefulness of immunosuppressant drugs in muscular dystrophy.

Prednisolone‐induced changes in dystrophic skeletal muscle

Although glucocorticoids delay the progression of Duchenne muscular dystrophy (DMD) their mechanism of action is unknown. Skeletal muscle gene expression profiles of mdx mice, an animal model of DMD, treated with prednisolone were compared with control mice at 1 and 6 wk. Of the 89 early differentially regulated genes and ESTs, delta-sarcoglycan, myosin Va, FK506-binding protein 51 (FKBP51), the potassium channel regulator potassium inwardly-rectifying channel Isk-like (IRK2) and ADAM 10 were overexpressed, whereas growth hormone-releasing hormone receptor (GHRHR) and Homer-2 were underexpressed. The 58 late differentially overexpressed genes included kallikreins (13, 16, and 26), FKBP51, PI3K alpha regulatory subunit, and IGFBP6, while underexpressed genes included NeuroD and nicotinic cholinergic receptor gamma. At both time points, overexpression of a cohort of genes relating to metabolism and proteolysis was apparent, alongside the differential expression of genes relating to calcium metabolism. Treatment did not increase muscle regeneration, reduce the number of infiltrating macrophages, or alter utrophin expression or localization. However, in the treated mdx soleus muscle, the percentage of slow fibers was significantly lower compared with untreated controls after 6 wk of treatment. These results show that glucocorticoids confer their benefit to dystrophic muscle in a complex fashion, culminating in a switch to a more normal muscle fiber type.

Evolving therapeutic strategies for Duchenne muscular dystrophy: targeting downstream events

Duchenne muscular dystrophy (DMD) is a progressive, lethal, muscle wasting disease that affects 1 of 3500 boys born worldwide. The disease results from mutation of the dystrophin gene that encodes a cytoskeletal protein associated with the muscle cell membrane. Although gene therapy will likely provide the cure for DMD, it remains on the distant horizon, emphasizing the need for more rapid development of palliative treatments that build on improved understanding of the complex pathology of dystrophin deficiency. In this review, we have focused on therapeutic strategies that target downstream events in the pathologic progression of DMD. Much of this work has been developed initially using the dystrophin-deficient mdx mouse to explore basic features of the pathophysiology of dystrophin deficiency and to test potential therapeutic interventions to slow, reverse, or compensate for functional losses that occur in muscular dystrophy. In some cases, the initial findings in the mdx model have led to clinical treatments for DMD boys that have produced improvements in muscle function and quality of life. Many of these investigations have concerned interventions that can affect protein balance in muscle, by inhibiting specific proteases implicated in the DMD pathology, or by providing anabolic factors or depleting catabolic factors that can contribute to muscle wasting. Other investigations have exploited the use of anti-inflammatory agents that can reduce the contribution of leukocytes to promoting secondary damage to dystrophic muscle. A third general strategy is designed to increase the regenerative capacity of dystrophic muscle and thereby help retain functional muscle mass. Each of these general approaches to slowing the pathology of dystrophin deficiency has yielded encouragement and suggests that targeting downstream events in dystrophinopathy can yield worthwhile, functional improvements in DMD.

Steroids in Duchenne muscular dystrophy: from clinical trials to genomic research

Steroids represent the only pharmacological palliative treatment for Duchenne muscular dystrophy. However, they do have side effects and despite a large number of published studies showing their efficacy, they are still not universally used. This is largely due to the lack of functional outcome and quality of life measures in most of the published studies and suggests that further trials might be required to answer some of the still unclear aspects of their role. Another important aspect of steroid therapy in Duchenne dystrophy is that we do not know how they work in dystrophic muscle. We have initiated a collaborative study on gene profiling using microarray in steroid-treated mdx mice. cDNA microarray studies were performed to examine the levels of skeletal muscle gene expression in a pool of mdx mice treated with prednisolone for 1 and 6 weeks. Interesting preliminary data on untreated mdx mice suggest that the gene profiling of young (7 weeks) versus older (12 weeks) mice is very significantly different. Furthermore, a large number of genes showed significant changes in expression at the mRNA level on treatment with prednisolone. These included structural protein genes; signalling genes and genes involved in immune response. Hopefully, analysis of this pattern of steroid-induced gene expression will provide some insight into understanding how glucocorticoids improve strength in Duchenne dystrophy, and may help in developing more effective and less toxic therapeutic approaches.

Systemic administration of the NF-kappaB inhibitor curcumin stimulates muscle regeneration after traumatic injury

Skeletal muscle is often the site of tissue injury due to trauma, disease, developmental defects or surgery. Yet, to date, no effective treatment is available to stimulate the repair of skeletal muscle. We show that the kinetics and extent of muscle regeneration in vivo after trauma are greatly enhanced following systemic administration of curcumin, a pharmacological inhibitor of the transcription factor NF-kappaB. Biochemical and histological analyses indicate an effect of curcumin after only 4 days of daily intraperitoneal injection compared with controls that require >2 wk to restore normal tissue architecture. Curcumin can act directly on cultured muscle precursor cells to stimulate both cell proliferation and differentiation under appropriate conditions. Other pharmacological and genetic inhibitors of NF-kappaB also stimulate muscle differentiation in vitro. Inhibition of NF-kappaB-mediated transcription was confirmed using reporter gene assays. We conclude that NF-kappaB exerts a role in regulating myogenesis and that modulation of NF-kappaB activity within muscle tissue is beneficial for muscle repair. The striking effects of curcumin on myogenesis suggest therapeutic applications for treating muscle injuries.

Characteristics of skeletal muscle in mdx mutant mice

We review the extensive research conducted on the mdx mouse since 1987, when demonstration of the absence of dystrophin in mdx muscle led to X-chromosome-linked muscular dystrophy (mdx) being considered as a homolog of Duchenne muscular dystrophy. Certain results are contradictory. We consider most aspects of mdx skeletal muscle: (i) the distribution and roles of dystrophin, utrophin, and associated proteins; (ii) morphological characteristics of the skeletal muscle and hypotheses put forward to explain the regeneration characteristic of the mdx mouse; (iii) special features of the diaphragm; (iv) changes in basic fibroblast growth factor, ion flux, innervation, cytoskeleton, adhesive proteins, mastocytes, and metabolism; and (v) different lines of therapeutic research.

Dystrophy and myogenesis in mdx diaphragm muscle

In order to determine why the diaphragm is more severely affected by progressive dystrophy than limb muscles in the mdx mouse, we examined how regional variations in diaphragm dystrophy, the measures of disease and repair, proliferation by committed myogenic cells, and the expression of mitogenic basic fibroblast growth factor (bFGF) could contribute to muscle-specific disease phenotypes. There were regional variations in new myotube formation in the diaphragm, with disease more severe in crural than costal leaflets. New repair increased in hyperthyroidism without changes in accumulated repair, probably due to fiber loss. General proliferation was nearly twofold higher in limb than diaphragm mononuclear cells. Since only 2.5-8.4% of committed muscle precursors were proliferating, the higher proliferation by myf5+ myogenic cells in diaphragm did not account for muscle-specific differences. Proliferation by bFGF+ mononuclear cells and an immunogold labeling index for bFGF protein in diaphragm myoblasts were lower in diaphragm than limb muscle. In culture, mixed limb myoblast and fibroblasts contained more S phase cells than diaphragm cells, although myoblasts cycled similarly between muscles. Therefore while muscle architecture and the formation and number of new myotubes certainly affect disease phenotype, the differential outcome of regeneration in mdx diaphragm and limb muscle appears to be contributed by both nonmyogenic and myogenic cells.

Deflazacort but not prednisone improves both muscle repair and fiber growth in diaphragm and limb muscle in vivo in the mdx dystrophic mouse

The effects of the glucocorticoids deflazacort and prednisone on mdx mouse dystrophy and muscle regeneration were evaluated in a 4.5-week double-blind study to test whether they would decrease dystrophy by anti-inflammatory effects [in intact diaphragm and left tibialis anterior (TA) muscle] and increase new muscle formation (after crush injury). In the left TA, fiber diameter was greater after deflazacort and prednisone compared to placebo. However, only deflazacort increased the centronucleation index of accumulated damage and repair, and myotube growth over the long term. In crush-injured TA, the fusion of proliferative muscle precursors to myotubes (by autoradiography) was increased only after deflazacort. Diaphragm muscle was much less inflamed, and fiber diameter was greater after deflazacort. Results suggest that glucocorticoids decreased the severe phenotype of dystrophy in the mdx diaphragm. Moreover, deflazacort uniquely promoted myogenic repair over short and longer terms, in addition to stimulating fiber growth. These first clues to the targets of deflazacort action on muscle repair have important positive implications for treating Duchenne dystrophy.

Modulation by prednisolone of calcium handling in skeletal muscle cells

1. Increased calcium (Ca2+) influx has been incriminated as a potential pathological mechanism in the chronic skeletal muscle degeneration exhibited by Duchenne muscular dystrophy (DMD) patients. We have studied the influence of the glucocorticoid alpha-methylprednisolone (PDN), the only drug known to have a beneficial effect on the degenerative course of DMD, on Ca2+ handling in the C2 skeletal muscle cell line. 2. PDN, when added 3 days (when myoblasts start to fuse into myotubes) after cell seeding, led to a 2 to 4 fold decrease in cellular Ca2+ uptake. This decrease was independent of the extracellular Ca2+ concentration applied to cells. The effect took at least 24 h in order to become established (PDN of 10(-5) M) and took longer for lower PDN concentrations (EC50 of ca. 10(-6) M at day 5, 10(-6.5) M at day 7 and 10(-7.5) M at day 9 in culture). 3. Cellular calcium accumulation was also decreased in PDN-treated myotubes exposed to 45Ca(2+)-containing medium for 1 to 6 days. 4. No effect of PDN was seen on 45Ca2+ efflux; a decrease in the amount of 45Ca2+ released was observed due to the reduction of cellular 45Ca2+ loading. 5. PDN treatment led to an approximately 2 fold decrease in basal cytosolic Ca2+ concentration. 6. Three antioxidant drugs (lazaroids), previously shown to enhance in vitro skeletal muscle cell differentiation to the same extent as PDN, induced a similar decrease in Ca2+ influx. 7. Our results suggest that long-term incubation of C2 cells with PDN leads to a decrease of the size of the cellular Ca2+ pools and to reduced resting cytosolic Ca2+ levels. Part of the beneficial effect of PDN in DMD patients could be attributed to a reduction of Ca2+ influx and of the size of Ca2+ pools in dystrophic muscle fibres.

Phenotype of dystrophinopathy in old mdx mice

BACKGROUND

Mdx mutant mice, like patients with Duchenne Muscular Dystrophy (DMD), lack dystrophin, a subsarcolemmal protein, that results in myofiber necrosis. However young mdx mice, in contrast to DMD children, exhibit a successful muscle regeneration and not an extensive fibrosis.

METHODS

Old mdx mice were monitored clinically up to their spontaneous death, and most of their organs were studied histologically to look for differences with those of the wild C57BL/10 mice strain.

RESULTS

In old mdx mice (at least 20 months of age), we report clinical and pathological features of muscular dystrophy, i.e., progressive motor weakness and loss of myofibers replaced by extensive connective tissue, similar to the phenotype of dystrophinopathy observed in DMD patients. Various degrees of dystrophic involvement were observed in cardiac, respiratory, postural, and hindlimb skeletal mdx muscles and also in smooth muscles of the digestive and urinary tracts. No gross histological abnormalities were found in other tissue than muscular tissue.

CONCLUSIONS

Late in life, mdx mice develop a muscular dystrophy close to DMD dystrophinopathy. We suggest that the study of the effects of ageing in mdx mice would give clues to better understand the pathophysiology of DMD.

Feasibility, safety, and efficacy of myoblast transfer therapy on Duchenne muscular dystrophy boys

Five billion normal myoblasts were injected into each of 21 Duchenne muscular dystrophy (DMD) boys aged 6-14 yr to assess the feasibility, safety, and efficacy of the Phase II myoblast transfer therapy (MTT). The Phase II study was designed to strengthen muscles of both lower limbs. Forty-eight intramuscular injections transferred the myoblasts into 22 major muscles at 55.6 x 10(6)/mL in 10 min under general anesthesia. Eleven boys had received 8 million myoblasts each 1 yr ago in the Phase I MTT. In the Phase II study, eight of them had their myoblasts subcultured from reserves frozen 1 yr ago. The donor myoblasts for each of the remaining boys were cultured from satellite cells derived from a 1-g muscle biopsy of a normal male who might or might not be histocompatible with the recipient. The immunosuppressant cyclosporine (Cy) is being administered to recipients for 6 mo after MTT to facilitate donor cell survival. There was no evidence of an adverse reaction to MTT or Cy as determined by serial laboratory evaluations including electrolytes, creatinine, and urea. Early objective functional tests using the KinCom Robotic Dynamometer were conducted on 13 subjects aged 6 to 13 before MTT and at 3 mo after MTT. Of the 69 muscle groups (knee extensors, knee flexors, plantar flexors) tested for isometric force generation in these subjects, 43% showed mean increase of 41.3% +/- 5.9 SEM, 38% showed no change, and 19% showed continuous force reduction of 23.4% +/- 3.1 SEM. The remaining subjects await the 3-mo post-MTT evaluation. The results indicate that 1) MTT is safe; 2) MTT increases muscle strength in DMD: 81% of the muscles tested showed either increase in strength or did not show continuous loss of strength; 3) more than 5 billion myoblasts can be cultured from 1 g normal muscle biopsy, providing unprecedented numbers of cells for MTT; 4) myoblasts, frozen over 1 yr, retain the ability to proliferate from 10 million to 5 billion, and to form normal myofibers; 5) injections of 5 billion myoblasts have not provoked any immunological rejection symptoms in the Phase II subjects, 11 of whom received 8 million myoblasts in the Phase I MTT a year ago; 6) it is safe to perform multiple injections of myoblasts into lower limb muscles without formation of emboli; and 7) donor cell rejection by the recipient can be prevented with Cy when properly managed.

Loss of cytoplasmic basic fibroblast growth factor from physiologically wounded myofibers of normal and dystrophic muscle

Using muscle as an in vivo model system, we have tested the hypothesis that basic fibroblast growth factor is released from a cytoplasmic storage site into the extra-cellular environment via diffusion through survivable, mechanically-induced plasma membrane disruptions. Normal and dystrophic (mdx) mouse muscle were studied. Strong immunostaining for bFGF was detected in the cytoplasm of myofibers of uninjured muscle fixed in situ by perfusion. By contrast, myofibers did not stain cytoplasmically for bFGF after suffering lethal disruptions of their plasma membranes caused by freezing and thawing followed by sectioning. Sub-lethal, transient disruptions of myofiber plasma membranes--termed plasma membrane ‘wounds’--were shown to be induced by needle puncture or exercise of muscle. Quantitative image analysis revealed that these wounded fibers contained significantly reduced levels of bFGF. Dystrophic exercised and unexercised muscle was found to possess an approximately 6-fold higher proportion of wounded myofibers than does normal muscle under equivalent conditions. Release of bFGF at a rate that is a direct function of the frequency of myofiber wounding may explain in part how a muscle adjusts its growth to meet changing mechanical demand as well as the pathological hypertrophy characteristic of certain stages of muscular dystrophy.

Prednisolone enhances myogenesis and dystrophin-related protein in skeletal muscle cell cultures from mdx mouse

The differentiation of skeletal muscle cells from mdx mice which lack dystrophin expression was examined after glucocorticoid treatment, namely alpha-methylprednisolone (PDN). Primary skeletal muscle cell cultures were established from newborn mdx, congenic C57BL/10, and allogenic BALB/C mice. We show that PDN promotes the myogenesis of both mdx- and control mice-derived cultures as determined by 1) the number of myotubes, 2) acetylcholine receptors, and 3) dystrophin and dystrophin-related protein levels. These results support the hypothesis that PDN could enhance the myogenesis of satellite cells and increase dystrophin-related protein expression in DMD treated patients.