Clinical investigation in Duchenne muscular dystrophy: penicillamine and vitamin E

Antioxidants to prevent respiratory decline in people with Duchenne muscular dystrophy and progressive respiratory decline

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterised by progressive muscle weakness beginning in early childhood. Respiratory failure and weak cough develop in all patients as a consequence of muscle weakness leading to a risk of atelectasis, pneumonia, or the need for ventilatory support. There is no curative treatment for DMD. Corticosteroids are the only pharmacological intervention proven to delay the onset and progression of muscle weakness and thus respiratory decline in DMD. Antioxidant treatment has been proposed to try to reduce muscle weakness in general, and respiratory decline in particular.  OBJECTIVES: To assess the effects of antioxidant agents on preventing respiratory decline in people with Duchenne muscular dystrophy during the respiratory decline phase of the condition.  SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, and two trials registers to 23 March 2021, together with reference checking, citation searching, and contact with study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs that met our inclusion criteria. We included male patients with a diagnosis of DMD who had respiratory decline evidenced by a forced vital capacity (FVC%) less than 80% but greater than 30% of predicted values, receiving any antioxidant agent compared with other therapies for the management of DMD or placebo.  DATA COLLECTION AND ANALYSIS: Two review authors screened studies for eligibility, assessed risk of bias of studies, and extracted data. We used standard methods expected by Cochrane. We assessed the certainty of the evidence using the GRADE approach. The primary outcomes were FVC and hospitalisation due to respiratory infections. Secondary outcomes were quality of life, adverse events, change in muscle function, forced expiratory volume in the first second (FEV1), and peak expiratory flow (PEF).  MAIN RESULTS: We included one study with 66 participants who were not co-treated with corticosteroids, which was the only study to contribute data to our main analysis. We also included a study that enrolled 255 participants treated with corticosteroids, which was only available as a press release without numerical results. The studies were parallel-group RCTs that assessed the effect of idebenone on respiratory function compared to placebo. The trial that contributed numerical data included patients with a mean (standard deviation) age of 14.3 (2.7) years at the time of inclusion, with a documented diagnosis of DMD or severe dystrophinopathy with clinical features consistent with typical DMD. The overall risk of bias across most outcomes was similar and judged as 'low'.  Idebenone may result in a slightly less of a decline in FVC from baseline to one year compared to placebo (mean difference (MD) 3.28%, 95% confidence interval (CI) -0.41 to 6.97; 64 participants; low-certainty evidence), and probably has little or no effect on change in quality of life (MD -3.80, 95% CI -10.09 to 2.49; 63 participants; moderate-certainty evidence) (Pediatric Quality of Life Inventory (PedsQL), range 0 to 100, 0 = worst, 100 = best quality of life). As a related but secondary outcome, idebenone may result in less of a decline from baseline in FEV1 (MD 8.28%, 95% CI 0.89 to 15.67; 53 participants) and PEF (MD 6.27%, 95% CI 0.61 to 11.93; 1 trial, 64 participants) compared to placebo. Idebenone was associated with fewer serious adverse events (RR 0.42, 95% CI 0.09 to 2.04; 66 participants; low-certainty evidence) and little to no difference in non-serious adverse events (RR 1.00, 95% CI 0.88 to 1.13; 66 participants; low-certainty evidence) compared to placebo. Idebenone may result in little to no difference in change in arm muscle function (MD -2.45 N, 95% CI -8.60 to 3.70 for elbow flexors and MD -1.06 N, 95% CI -6.77 to 4.65 for elbow extensors; both 52 participants) compared to placebo. We found no studies evaluating the outcome hospitalisation due to respiratory infection.  The second trial, involving 255 participants, for which data were available only as a press release without numerical data, was prematurely discontinued due to futility after an interim efficacy analysis based on FVC. There were no safety concerns. The certainty of the evidence was low for most outcomes due to imprecision and publication bias (the lack of a full report of the larger trial, which was prematurely terminated).

AUTHORS' CONCLUSIONS

Idebenone is the only antioxidant agent tested in RCTs for preventing respiratory decline in people with DMD for which evidence was available for assessment. Idebenone may result in slightly less of a decline in FVC and less of a decline in FEV1 and PEF, but probably has little to no measurable effect on change in quality of life. Idebenone is associated with fewer serious adverse events than placebo. Idebenone may result in little to no difference in change in muscle function. Discontinuation due to the futility of the SIDEROS trial and its expanded access programmes may indicate that idebenone research in this condition is no longer needed, but we await the trial data. Further research is needed to establish the effect of different antioxidant agents on preventing respiratory decline in people with DMD during the respiratory decline phase of the condition.

Antioxidants to prevent respiratory decline in people with Duchenne muscular dystrophy and progressive respiratory decline

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterised by progressive muscle weakness beginning in early childhood. Respiratory failure and weak cough develop in all patients as a consequence of muscle weakness leading to a risk of atelectasis, pneumonia, or the need for ventilatory support. There is no curative treatment for DMD. Corticosteroids are the only pharmacological intervention proven to delay the onset and progression of muscle weakness and thus respiratory decline in DMD. Antioxidant treatment has been proposed to try to reduce muscle weakness in general, and respiratory decline in particular.  OBJECTIVES: To assess the effects of antioxidant agents on preventing respiratory decline in people with Duchenne muscular dystrophy during the respiratory decline phase of the condition.  SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, and two trials registers to 23 March 2021, together with reference checking, citation searching, and contact with study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs that met our inclusion criteria. We included male patients with a diagnosis of DMD who had respiratory decline evidenced by a forced vital capacity (FVC%) less than 80% but greater than 30% of predicted values, receiving any antioxidant agent compared with other therapies for the management of DMD or placebo.  DATA COLLECTION AND ANALYSIS: Two review authors screened studies for eligibility, assessed risk of bias of studies, and extracted data. We used standard methods expected by Cochrane. We assessed the certainty of the evidence using the GRADE approach. The primary outcomes were FVC and hospitalisation due to respiratory infections. Secondary outcomes were quality of life, adverse events, change in muscle function, forced expiratory volume in the first second (FEV1), and peak expiratory flow (PEF).  MAIN RESULTS: We included one study with 66 participants who were not co-treated with corticosteroids, which was the only study to contribute data to our main analysis. We also included a study that enrolled 255 participants treated with corticosteroids, which was only available as a press release without numerical results. The studies were parallel-group RCTs that assessed the effect of idebenone on respiratory function compared to placebo. The trial that contributed numerical data included patients with a mean (standard deviation) age of 14.3 (2.7) years at the time of inclusion, with a documented diagnosis of DMD or severe dystrophinopathy with clinical features consistent with typical DMD. The overall risk of bias across most outcomes was similar and judged as 'low'.  Idebenone may result in a slightly less of a decline in FVC from baseline to one year compared to placebo (mean difference (MD) 3.28%, 95% confidence interval (CI) -0.41 to 6.97; 64 participants; low-certainty evidence), and probably has little or no effect on change in quality of life (MD -3.80, 95% CI -10.09 to 2.49; 63 participants; moderate-certainty evidence) (Pediatric Quality of Life Inventory (PedsQL), range 0 to 100, 0 = worst, 100 = best quality of life). As a related but secondary outcome, idebenone may result in less of a decline from baseline in FEV1 (MD 8.28%, 95% CI 0.89 to 15.67; 53 participants) and PEF (MD 6.27%, 95% CI 0.61 to 11.93; 1 trial, 64 participants) compared to placebo. Idebenone was associated with fewer serious adverse events (RR 0.42, 95% CI 0.09 to 2.04; 66 participants; low-certainty evidence) and little to no difference in non-serious adverse events (RR 1.00, 95% CI 0.88 to 1.13; 66 participants; low-certainty evidence) compared to placebo. Idebenone may result in little to no difference in change in arm muscle function (MD -2.45 N, 95% CI -8.60 to 3.70 for elbow flexors and MD -1.06 N, 95% CI -6.77 to 4.65 for elbow extensors; both 52 participants) compared to placebo. We found no studies evaluating the outcome hospitalisation due to respiratory infection.  The second trial, involving 255 participants, for which data were available only as a press release without numerical data, was prematurely discontinued due to futility after an interim efficacy analysis based on FVC. There were no safety concerns. The certainty of the evidence was low for most outcomes due to imprecision and publication bias (the lack of a full report of the larger trial, which was prematurely terminated).

AUTHORS' CONCLUSIONS

Idebenone is the only antioxidant agent tested in RCTs for preventing respiratory decline in people with DMD for which evidence was available for assessment. Idebenone may result in slightly less of a decline in FVC and less of a decline in FEV1 and PEF, but probably has little to no measurable effect on change in quality of life. Idebenone is associated with fewer serious adverse events than placebo. Idebenone may result in little to no difference in change in muscle function. Discontinuation due to the futility of the SIDEROS trial and its expanded access programmes may indicate that idebenone research in this condition is no longer needed, but we await the trial data. Further research is needed to establish the effect of different antioxidant agents on preventing respiratory decline in people with DMD during the respiratory decline phase of the condition.

Muscle and cardiac therapeutic strategies for Duchenne muscular dystrophy: past, present, and future

BACKGROUND

Duchenne muscular dystrophy (DMD) is a severe X-linked neuromuscular childhood disorder that causes progressive muscle weakness and degeneration and results in functional decline, loss of ambulation and early death of young men due to cardiac or respiratory failure. Although the major cause of the disease has been known for many years-namely mutation in the DMD gene encoding dystrophin, one of the largest human genes-DMD is still incurable, and its treatment is challenging.

METHODS

A comprehensive and systematic review of literature on the gene, cell, and pharmacological experimental therapies aimed at restoring functional dystrophin or to counteract the associated processes contributing to disease progression like inflammation, fibrosis, calcium signaling or angiogenesis was carried out.

RESULTS

Although some therapies lead to satisfying effects in skeletal muscle, they are highly ineffective in the heart; therefore, targeting defective cardiac and respiratory systems is vital in DMD patients. Unfortunately, most of the pharmacological compounds treat only the symptoms of the disease. Some drugs addressing the underlying cause, like eteplirsen, golodirsen, and ataluren, have recently been conditionally approved; however, they can correct only specific mutations in the DMD gene and are therefore suitable for small sub-populations of affected individuals.

CONCLUSION

In this review, we summarize the possible therapeutic options and describe the current status of various, still imperfect, strategies used for attenuating the disease progression.

Duchenne muscular dystrophy: an historical treatment review

In this review, we discuss the therapies used in the treatment of patients with Duchenne muscular dystrophy since the first description of the disease. A short description is given of the various theories based on disease pathogenesis, which give the substrates for the many therapeutic interventions. A brief review of the methods of evaluation used in therapeutic trials is made. Of all the treatments, the only drugs that are still considered able to modify the course of the disease are the corticosteroids (prednisone/prednisolone/deflazacort). Other drugs (coenzyme Q10 and creatine) have had a little effect in a few functions without adverse reactions. Idebenone seems to improve the respiratory function in the long term. The trials with mRNA transcription, through nonsense mutations or exon 51 skipping, show some beneficial results in a few functional tests, but they are limited to a small set of DMD patients.

(-)-Epicatechin improves mitochondrial-related protein levels and ameliorates oxidative stress in dystrophic δ-sarcoglycan null mouse striated muscle

Muscular dystrophies (MDs) are a group of heterogeneous genetic disorders characterized by progressive striated muscle wasting and degeneration. Although the genetic basis for many of these disorders has been identified, the exact mechanism of disease pathogenesis remains unclear. The presence of oxidative stress (OS) is known to contribute to the pathophysiology and severity of the MD. Mitochondrial dysfunction is observed in MD, and probably represents an important determinant of increased OS. Experimental antioxidant therapies have been implemented with the aim of protecting against disease progression, but results from clinical trials have been disappointing. In this study, we explored the capacity of the cacao flavonoid (-)-epicatechin (Epi) to mitigate OS by acting as a positive regulator of mitochondrial structure/function endpoints and redox balance control systems in skeletal and cardiac muscles of dystrophic, δ-sarcoglycan (δ-SG) null mice. Wild-type or δ-SG null 2.5-month-old male mice were treated via oral gavage with either water (controls) or Epi (1 mg·kg(-1) , twice daily) for 2 weeks. The results showed significant normalization of total protein carbonylation, recovery of the glutathione/oxidized glutathione ratio and enhanced superoxide dismutase 2, catalase and citrate synthase activities with Epi treatment. These effects were accompanied by increases in the protein levels of thioredoxin, glutathione peroxidase, superoxide dismutase 2, catalase, and mitochondrial endpoints. Furthermore, we found decreases in heart and skeletal muscle fibrosis, accompanied by an improvement in skeletal muscle function, with treatment. These results warrant further investigation of Epi as a potential therapeutic agent to mitigate MD-associated muscle degeneration.

Amplification of proinflammatory phenotype, damage, and weakness by oxidative stress in the diaphragm muscle of mdx mice

Duchenne muscular dystrophy (DMD) is a common and devastating type of childhood-onset muscular dystrophy, attributed to an X-linked defect in the gene that encodes dystrophin. Myopathy with DMD is most pronounced in the diaphragm muscle and fast-twitch limb muscles and is dependent upon susceptibility to damage, inflammatory cell infiltration, and proinflammatory signaling (nuclear factor-κB; NF-κB). Although recent papers have reawakened the notion that oxidative stress links inflammatory signaling with pathology in DMD in limb muscle, the importance of redox mechanisms had been clouded by inconsistent results from indirect scavenger approaches, including in the diaphragm muscle. Therefore, we used a novel catalytic mimetic of superoxide dismutase and catalase (EUK-134) as a direct scavenger of oxidative stress in myopathy in the diaphragm of the mdx mouse model. EUK-134 reduced 4-hydroxynonenal and total hydroperoxides, markers of oxidative stress in the mdx diaphragm. EUK-134 also attenuated positive staining of macrophages and T-cells as well as activation of NF-κB and p65 protein abundance. Moreover, EUK-134 ameliorated markers of muscle damage including internalized nuclei, variability of cross-sectional area, and type IIc fibers. Finally, impairment of contractile force was partially rescued by EUK-134 in the diaphragm of mdx mice. We conclude that oxidative stress amplifies DMD pathology in the diaphragm muscle.

Exacerbation of pathology by oxidative stress in respiratory and locomotor muscles with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is the most devastating type of muscular dystrophy, leading to progressive weakness of respiratory (e.g. diaphragm) and locomotor muscles (e.g. gastrocnemius). DMD is caused by X-linked defects in the gene that encodes for dystrophin, a key scaffolding protein of the dystroglycan complex (DCG) within the sarcolemmal cytoskeleton. As a result of a compromised dystroglycan complex, mechanical integrity is impaired and important signalling proteins (e.g. nNOS, caveolin-3) and pathways are disrupted. Disruption of the dystroglycan complex leads to high susceptibility to injury with repeated, eccentric contractions as well as inflammation, resulting in significant damage and necrosis. Chronic damage and repair cycling leads to fibrosis and weakness. While the link between inflammation with damage and weakness in the DMD diaphragm is unresolved, elevated oxidative stress may contribute to damage, weakness and possibly fibrosis. While utilization of non-specific antioxidant interventions has yielded inconsistent results, recent data suggest that NAD(P)H oxidase could play a pivotal role in elevating oxidative stress via integrated changes in caveolin-3 and stretch-activated channels (SACs). Oxidative stress may act as an amplifier, exacerbating disruption of the dystroglycan complex, upregulation of the inflammatory transcription factor NF-B, and thus functional impairment of force-generating capacity.

Use of corticosteroids in a population-based cohort of boys with duchenne and becker muscular dystrophy

The use of corticosteroids for treatment of Duchenne and Becker muscular dystrophy in clinical practice from 1991 through 2005 was reviewed in a large population-based cohort (MD STARnet) of boys in 4 regional sites and 6 clinics of the United States. Corticosteroid use increased from 20% (11 of 56 individuals) in 1991 to 44% (93 of 218 individuals) in 2005. Average use varied by site and ranged from 15% to 49%. The median age of corticosteroid initiation was 6.9 years (range, 3.7-17.4 years). Dosage and growth information was available for 102 participants and showed a median dose as 0.729 mg/kg for prednisone and 0.831 mg/kg for deflazacort. T. The most common reasons that corticosteroids were discontinued included weight gain, behavioral side effects, and loss of ambulation, resulting in full-time wheelchair use. Substantial variations in clinical practice were identified among study sites.

Increased catalase expression improves muscle function in mdx mice

It has been well established that oxidative stress contributes to pathology associated with Duchenne muscular dystrophy (DMD). I hypothesized that overexpression of the antioxidant enzyme catalase would improve muscle function in the mdx mouse, the mouse model of DMD. To test this hypothesis, neonatal mdx mice were injected with a recombinant adeno-associated virus driving the catalase transgene. Animals were killed 4 or 6 weeks or 6 months following injection. Muscle function was generally improved by catalase overexpression. Four weeks following injection, extensor digitorum longus specific tension was improved twofold, while soleus was similar between groups. Resistance to contraction-induced injury was similar between groups; however, resistance to fatigue was increased 25% in catalase-treated soleus compared with control muscle. Six weeks following injection, extensor digitorum longus specific tension was increased 15%, while soleus specific tension was similar between treated and untreated limbs. Catalase overexpression reduced contraction-induced injury by 30-45% and fatigue by 20% compared with control limbs. Six months following injection, diaphragm specific tension was similar between groups, but resistance to contraction-induced injury was improved by 35% and fatigue by 25%. Taken together, these data indicate that catalase can improve a subset of parameters of muscle function in dystrophin-deficient skeletal muscle.

Oxidative stress regulation of stem and progenitor cells

In recent years, it has become clear that balanced regulation of reactive oxygen species is of critical significance for cell-fate determination as well as for stem cell development, function, and survival. Although many questions regarding intracellular redox status regulation of stem cell fate remain, we review here what is known regarding the impact of cell-fate signaling as shown with a variety of human cancer cells and more recently on cancer-initiating cells and on the regenerative capacity of skeletal muscle and hematopoietic tissue and their stem cells. We also discuss the role of altered intracellular redox status as a potential primary pathogenic mechanism in muscular dystrophy and hematopoietic pathologies. Studies discussed here illustrate how understanding altered redox regulation of stem cell behavior may contribute to the development of novel stem cell therapies.

Mechanisms of muscle degeneration, regeneration, and repair in the muscular dystrophies

To withstand the rigors of contraction, muscle fibers have specialized protein complexes that buffer against mechanical stress and a multifaceted repair system that is rapidly activated after injury. Genetic studies first identified the mechanosensory signaling network that connects the structural elements of muscle and, more recently, have identified repair elements of muscle. Defects in the genes encoding the components of these systems lead to muscular dystrophy, a family of genetic disorders characterized by progressive muscle wasting. Although the age of onset, affected muscles, and severity vary considerably, all muscular dystrophies are characterized by muscle necrosis that overtakes the regenerative capacity of muscle. The resulting replacement of muscle by fatty and fibrous tissue leaves muscle increasingly weak and nonfunctional. This review discusses the cellular mechanisms that are primarily and secondarily disrupted in muscular dystrophy, focusing on membrane degeneration, muscle regeneration, and the repair of muscle.

The role of reactive oxygen species in the hearts of dystrophin-deficient mdx mice

Duchenne muscular dystrophy (DMD) is caused by deficiency of the cytoskeletal protein dystrophin. Oxidative stress is thought to contribute to the skeletal muscle damage in DMD; however, little is known about the role of oxidative damage in the pathogenesis of the heart failure that occurs in DMD patients. The dystrophin-deficient (mdx) mouse is an animal model of DMD that also lacks dystrophin. The current study investigates the role of the antioxidant N-acetylcysteine (NAC) on mdx cardiomyocyte function, Ca(2+) handling, and the cardiac inflammatory response. Treated mice received 1% NAC in their drinking water for 6 wk. NAC had no effect on wild-type (WT) mice. Immunohistochemistry experiments revealed that mdx mice had increased dihydroethidine (DHE) staining, an indicator of superoxide production; NAC-treatment reduced DHE staining in mdx hearts. NAC treatment attenuated abnormalities in mdx cardiomyocyte Ca(2+) handling. Mdx cardiomyocytes had decreased fractional shortening and decreased Ca(2+) sensitivity; NAC treatment returned mdx fractional shortening to WT values but did not affect the Ca(2+) sensitivity. Immunohistochemistry experiments revealed that mdx hearts had increased levels of collagen type III and the macrophage-specific protein, CD68; NAC-treatment returned collagen type III and CD68 expression close to WT values. Finally, mdx hearts had increased NADPH oxidase activity, suggesting it could be a possible source of increased reactive oxygen species in mdx mice. This study is the first to demonstrate that oxidative damage may be involved in the pathogenesis of the heart failure that occurs in mdx mice. Therapies designed to reduce oxidative damage might be beneficial to DMD patients with heart failure.

MUSCLE DAMAGE IN MDX (DYSTROPHIC) MICE: ROLE OF CALCIUM AND REACTIVE OXYGEN SPECIES

1. Duchenne muscular dystrophy (DMD) is a lethal, degenerative muscle disease caused by a genetic mutation that leads to the complete absence of the cytoskeletal protein dystrophin in muscle fibres. 2. The present review provides an overview of some of the physiological pathways that may contribute to muscle damage and degeneration in DMD, based primarily on experimental findings in the mdx mouse, an animal model of this disease. 3. A rise in intracellular calcium is widely thought to be an important initiating event in the dystrophic pathogenesis. The pathway(s) leading to increased intracellular calcium in dystrophin deficient muscle is uncertain, but recent work from our laboratory provides evidence that stretch-activated channels are an important source of the calcium influx. Other possible routes of calcium entry are also discussed. 4. The consequences of elevated cytosolic calcium may include activation of proteases, such as calpain, and increased production of reactive oxygen species (ROS), which can cause protein and membrane damage. 5. Another possible cause of damage in dystrophic muscle involves inflammatory pathways, such as those mediated by neutrophils, macrophages and associated cytokines. There is recent evidence that increased ROS may be important in both the activation of and the damage caused by this inflammatory pathway in mdx muscle.

Nutritional inadequacy in adults with muscular dystrophy

Patients with muscular dystrophy may be prone to nutrient deficiency due to mobility limitations or oropharyngeal weakness. Patients with myotonic muscular dystrophy (DM1) may be particularly prone to nutritional deficiencies from associated dysmotility of the entire gastrointestinal tract. We prospectively evaluated nutritional intake, body composition, and muscle strength in adult patients with DM1 (n = 29) and other muscular dystrophies (n = 22) on two occasions separated by approximately 6 months. Handgrip was significantly lower and knee extension higher for DM1 compared to other dystrophies, with no between-group differences in nutritional intakes. Many patients in both groups demonstrated inadequate nutrient intake of protein, energy, vitamins (water and fat soluble), and minerals (calcium and magnesium). Significant correlations were found between measures of strength and certain individual nutrients (e.g., copper and water-soluble vitamins). These data indicate that a substantial number of adults with muscular dystrophy do not meet current dietary intake recommendations. The potential clinical implications of these findings are discussed.

Oxidative stress and the pathogenesis of muscular dystrophies

The muscular dystrophies represent a diverse group of diseases differing in underlying genetic basis, age of onset, mode of inheritance, and severity of progression, but they share certain common pathologic features. Most prominent among these features is the necrotic degeneration of muscle fibers. Although the genetic basis of many of the dystrophies has been known for over a decade and new disease genes continue to be discovered, the pathogenetic mechanisms leading to muscle cell death in the dystrophies remain a mystery. This review focuses on the oxidative stress theory, which states that the final common pathway of muscle cell death in these diseases involves oxidative damage.

Novel approaches to treat muscular dystrophies

Muscular dystrophies (MD) are a clinically and genetically heterogeneous group of skeletal muscle-wasting diseases. Mutations in the dystrophin gene result in dystrophin deficiency, which constitutes the pathogenic basis of Duchenne and Becker MD (DMD and BMD). Several MD are caused by mutations in other recently identified genes coding for proteins linked to the sarcolemma, the nuclear envelope or the contractile apparatus. In addition, several MD have been mapped to different chromosomal loci and for most of them, the identification of the molecular defect is underway. The immediate result is an ongoing reclassification of the MD into disorders defined not by clinical characteristics but specific genetic mutations. At present, therapy of MD is based on symptomatic treatment and supportive care. Convincing evidence for clinical efficacy is only available for corticosteroids that also suffer from frequent and severe side effects. Up to now, curative therapy is not available, although promising new molecular therapies are under investigation in animal models of MD. Current treatment strategies are discussed and a perspective for effective molecular therapy is given.

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is not treatable; there is no cure. More than a decade ago, randomized trials demonstrated that oral steroid therapy was of benefit to DMD patients by prolonging ambulation. Although few significant side effects were reported, study patients were followed for 18 months or less. However, when treating DMD with steroids, the clinician must consider beginning treatment in mid-childhood and continuing until adolescence or longer, a total of at least 10 years. There is no evidence that steroids are associated with prolonged life or with improved pulmonary or cardiac function in DMD. It is clear that the risk of side effects increases with duration of use of oral steroids. Therefore, oral steroids are not recommended for treatment of DMD on a routine basis. If, in certain cases, one does institute therapy, the patient should be monitored carefully for side effects, maintain dietary restriction, and exercise regularly.

Evidence of oxidative stress in mdx mouse muscle: studies of the pre-necrotic state

Considerable evidence indicates that free radical injury may underlie the pathologic changes in muscular dystrophies from mammalian and avian species. We have investigated the role of oxidative injury in muscle necrosis in mice with a muscular dystrophy due to a defect in the dystrophin gene (the mdx strain). In order to avoid secondary consequences of muscle necrosis, all experiments were done on muscle prior to the onset of the degenerative process (i.e. during the 'pre-necrotic' phase) which lasted up to 20 days of age in the muscles examined. In pre-necrotic mdx muscle, there was an induction of expression of genes encoding antioxidant enzymes, indicative of a cellular response to oxidative stress. In addition, the levels of lipid peroxidation were greater in mdx muscle than in the control. Since the free radical nitric oxide (NO*) has been shown to mediate oxidative injury in various disease states, and because dystrophin has been shown to form a complex with the enzyme nitric oxide synthase, we examined pre-necrotic mdx muscle for evidence of NO*-mediated injury by measuring cellular nitrotyrosine formation. By both immunohistochemical and electrochemical analyses, no evidence of increased nitrotyrosine levels in mdx muscle was detected. Therefore, although no relationship with NO*-mediated toxicity was found, we found evidence of increased oxidative stress preceding the onset of muscle cell death in dystrophin-deficient mice. These results lend support to the hypothesis that free radical-mediated injury may contribute to the pathogenesis of muscular dystrophies.

Calcium influx inhibition by steroids and analogs in C2C12 skeletal muscle cells

Glucocorticoids, namely alpha-methylprednisolone (PDN) and deflazacort, are the only drugs reported to have a beneficial effect on the degenerative course of Duchenne muscular dystrophy (DMD). Increased cytosolic calcium concentrations ([Ca2+]c) have been implicated as one of the pathological events responsible for the degeneration of dystrophic skeletal muscles. In previous studies, we have demonstrated that PDN treatment of both normal and dystrophic murine skeletal muscle cells was able to normalize elevated [Ca2+]c and improved myogenesis. Here we have investigated the mechanism underlying the effects of glucocorticoids on cellular Ca2+ influx into C2C12 skeletal muscle cells. Long-term incubation of C2C12 myocytes with PDN was necessary to observe a reduction of 45Ca2+ influx. PDN was most effective in inhibiting 45Ca2+ uptake when added for 4 days (at the time of fusion of myoblasts into myotubes) and to a lesser extent, when added after fusion. It was ineffective when added to C2C12 cells at the myoblast stage. Short PDN incubation times, at the time of fusion were insufficient to elicit a response. Several steroids were tested for their ability to inhibit 45Ca2+ influx in C2C12 myocytes. All four glucocorticoids examined were able to reduce Ca2+ influx, dexamethasone being the most potent (IC50 3.14+/-0.34 x 10(-8) M). Mineralocorticoids (aldosterone and 11-deoxycorticosterone) were also able to reduce Ca2+ influx. The vitamin E-derived lazaroid U-83836E and the glucocorticoid-derived lazaroid U-74389G also elicited a decrease in Ca2+ influx, but higher concentrations were necessary. Because both glucocorticoids and lazaroids display antioxidant properties, but U-83836E is devoid of glucocorticoid activity, the reduction in Ca2+ influx was suspected to be triggered via an antioxidant mechanism. To test this hypothesis, we assessed the action of several antioxidants, such as vitamin E, vitamin C, 2-tert.-butyl-4-methoxyphenol (BHA), 2,6-di-tert.-butyl-4-methyl-phenol (BHT) and nordihydroguaiaretic acid (NDGA), on 45Ca2+ influx. None of these agents had an effect on 45Ca2+ influx. In addition, several oxidants were tested (either acutely or chronically) for their ability to elicit 45Ca2+ influx in C2C12 myocytes and were found to be inactive. The involvement of the glucocorticoid receptor on the modulation of Ca2+ influx was investigated. The glucocorticoid receptor antagonist mifepristone (code name RU38486, 10(-6) M) caused a shift of two orders of magnitude of the PDN response. However, neither actinomycin D nor cycloheximide affected the response to PDN. Results with the phospholipase A2 inhibitor, manoalide, suggest that glucocorticoid-induced protein synthesis (e.g. enhanced stimulation of lipocortin) does not play a role in the reduction of calcium influx. Our results suggest that steroids elicit a decrease in calcium influx in C2C12 skeletal muscle cells. This decrease is not due to an antioxidant mechanism or to a mechanism which requires gene expression. Since mineralocorticoids and U-83836E also had similar effects, the mechanism could belong to the non-genomic effects of corticoids (e.g. membrane stabilization). The beneficial effect of glucocorticoids in DMD could be attributed to a reduction of the pathological increase in Ca2+ influx via an effect on the sarcolemma.

Muscle cells from mdx mice have an increased susceptibility to oxidative stress

Several lines of evidence suggest that free radical mediated injury and oxidative stress may lead to muscle necrosis in the muscular dystrophies, including those related to defects in the dystrophin gene. We have examined muscle cell death using an in vitro assay in which the processes that lead to myofiber necrosis in vivo may be amenable to investigation in a simplified cell culture system. Using myotube cultures from normal and dystrophin-deficient (mdx) mice, we have examined the susceptibilities of the cells to different metabolic stresses. Dystrophin-deficient cells were more susceptible to free radical induced injury when compared to normal cells, but the two populations were equally susceptible to other forms of metabolic stress. The differential response appeared to be specifically related to dystrophin expression since undifferentiated myoblasts (which do not express dystrophin) from normal and mdx mice were equally sensitive to oxidative stress. Thus, the absence of dystrophin appears to render muscle specifically more susceptible to free radical induced injury. These results support the hypothesis that oxidative stress may lead to myofiber necrosis in these disorders. Elucidating the mechanisms leading to cell death may help to explain the variabilities in disease expression that are seen as a function of age, among different muscles, and across species in animals with muscular dystrophy due to dystrophin deficiency.

Regeneration-blocked mdx muscle: in vivo model for testing treatments

We have refined the mdx mouse as a clinical model for Duchenne dystrophy. Our power estimates, primary measures, regular sacrifice intervals, and quality checks constitute a high-speed, low-cost system for preclinically testing therapies designed to slow muscle destruction in Duchenne dystrophy. Irradiated (18 Gy) and contralateral shielded anterior tibial muscles were studied in 21-day-old mdx and normal mice at the time of irradiation and 4, 8, 12, 16, and 20 weeks thereafter. Regeneration-blocked mdx (irradiated) muscle expressed muscular dystrophy as progressive wasting after a brief (4 week) period of growth. Regeneration-blocked normal muscle showed stunted growth but neither progressive wasting nor microscopic pathological changes.

Wheat kernel ingestion protects from progression of muscle weakness in mdx mice, an animal model of Duchenne muscular dystrophy

A simple, reproducible test was used to quantify muscle weakness in mdx mice, an animal model of Duchenne muscular dystrophy. The effect of bedding on wheat kernels and of dietary supplementation of alpha-tocopherol on the progression of muscle weakness was investigated in mdx mice. When measured during the first 200 d of life, mdx mice developed muscle weakness, irrespective of bedding and diet. When kept on wood shavings and fed a conventional rodent diet, mdx mice showed progressive muscle weakness over the consecutive 200 d, and eventually showed a significant weight loss during the next 200-d observation period. Progression of muscle weakness and weight loss were almost completely prevented in mdx mice that were kept on wheat kernel bedding. In contrast, only incomplete maintenance of muscle strength and body weight was observed in mdx mice kept on wood shavings and fed the alpha-tocopherol-supplemented diet. It is concluded from these experiments that a component of wheat kernels other than alpha-tocopherol is essential to prevent the progression of muscle weakness in mdx mice.

Lazaroids enhance skeletal myogenesis in primary cultures of dystrophin-deficient mdx mice

Growing evidence suggests a role for free radicals in the degeneration of dystrophin-deficient muscle (as observed in Duchenne muscular dystrophy). We therefore decided to test the action of the lazaroid antioxidant compounds on primary skeletal muscle cell cultures derived from an animal model of Duchenne muscular dystrophy, the mdx mouse. Both vitamin E-derived U-83836E and glucocorticoid-derived U-74389F enhanced myogenesis of dystrophin-deficient cultures as determined by the number of myotubes, the amount of nicotinic acetylcholine receptor, skeletal muscle alpha-actin levels and myosin light chain. U-83836E enhanced myogenesis of control congenic C57BL/10 mouse-derived muscle cultures whereas U-74389F had no detectable effect. This enhanced myogenesis was in most respects similar to the one triggered by alpha-methylprednisolone which is the only drug known to be beneficial in Duchenne muscular dystrophy.

Regulation of membrane-mediated chronic muscle degeneration in dystrophic hamsters by calcium-channel blockers: diltiazem, nifedipine and verapamil

Membrane-mediated excessive intracellular calcium accumulation (EICA) is a fundamental pathogenetic event associated with chronic muscle degeneration in patients with Duchenne muscular dystrophy (DMD), and in animals with hereditary muscular dystrophy (HMD). Because of potential Ca(2+)-channel blocking properties, we investigated the relative efficacies of chronic diltiazem (DTZM) (50 mg/kg/d), nifedipine (NFDN) (6 mg/kg/d), and verapamil (VPML) (25 mg/kg/d) therapies in reducing EICA and improving dystrophic pathobiology beginning in 30-day-old male BIO-14.6 strain dystrophic hamsters (DH). Each agent, and sterile distilled water as vehicle control, was given in a single daily oral dose for 180 days to four groups each of DH and BIO-F1B strain normal hamsters (NH). Plasma [Ca] and [Mg]; plasma aldolase (ALD), creatine kinase (CK), and lactate dehydrogenase (LDH) activities; relative cardiac hypertrophy and relative soleus hypertrophy; tissue [Ca] and [Mg] of the heart and rectus femoris muscle, histology of rectus femoris, and overall mortality rate were quantitated. Muscle Mg was not modified in DH, or by any of these agents. NFDN produced significant edema in the soleus and myocardium. During the 6-month therapeutic trial, 45% DH and 18% NH died on VPML, 27% DH and 9% NH on NFDN, and 20% DH controls on distilled water, but none on DTZM; suggesting that DTZM treated DH lived longer than DH controls. Relative efficacy in regulating EICA in both the cardiac and skeletal muscles; plasma ALD, CK, and LDH; and improving associated dystrophic pathobiology was found to be DTZM >>> NFDN > VPML. DTZM appears to be the most effective and safest agent in mitigating EICA in cardiac and skeletal muscles, efflux of intracellular enzymes, histopathology of dystrophic muscle with sporadic necrosis, and chronic muscle degeneration in DH with HMD. DTZM therapy also halted the high morbidity and mortality associated with the dystrophic pathobiology inherent in DH.

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

Therapeutic doses of methylprednisolone, azathioprine, cyclosporin A, and cyclophosphamide administered to mdx mice between 15 and 45 days of age failed to significantly influence the time course and prevalence of necrosis and regeneration or serum creatine kinase activity. This finding contrasts with previously reported findings of beneficial effects of glucocorticoids in Duchenne muscular dystrophy (DMD). This may indicate that, mechanisms upon which beneficial effects of glucocorticoids depend in DMD, do not operate (sufficiently) in mdx mice.

Randomized, double-blind trial of mazindol in Duchenne dystrophy

There is evidence that growth hormone may be related to the progression of weakness in Duchenne dystrophy. We conducted a 12-month controlled trial of mazindol, a putative growth hormone secretion inhibitor, in 83 boys with Duchenne dystrophy. Muscle strength, contractures, functional ability and pulmonary function were tested at baseline, and 6 and 12 months after treatment with mazindol (3 mg/d) or placebo. The study was designed to have a power of greater than 0.90 to detect a slowing to 25% of the expected rate of progression of weakness at P less than 0.05. Mazindol did not benefit strength at any point in the study. Side effects attributable to mazindol included decreased appetite (36%), dry mouth (10%), behavioral change (22%), and gastrointestinal symptoms (18%); mazindol dosage was reduced in 43% of patients. The effect of mazindol on GH secretion was estimated indirectly by comparing the postabsorptive IGF-I levels obtained following 3, 6, 9, and 12 months in the mazindol treated to those in the placebo groups. Although mazindol-treated patients gained less weight and height than placebo-treated patients, no significant effect on IGF-I levels was observed. Mazindol doses not slow the progression of weakness in Duchenne dystrophy.