Modulation by prednisolone of calcium handling in skeletal muscle cells

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.

RhoA/ROCK inhibition improves the beneficial effects of glucocorticoid treatment in dystrophic muscle: implications for stem cell depletion

Glucocorticoid treatment represents a standard palliative treatment for Duchenne muscular dystrophy (DMD) patients, but various adverse effects have limited this treatment. In an effort to understand the mechanism(s) by which glucocorticoids impart their effects on the dystrophic muscle, and potentially reduce the adverse effects, we have studied the effect of prednisolone treatment in dystrophin/utrophin double knockout (dKO) mice, which exhibit a severe dystrophic phenotype due to rapid muscle stem cell depletion. Our results indicate that muscle stem cell depletion in dKO muscle is related to upregulation of mTOR, and that prednisolone treatment reduces the expression of mTOR and other pro-inflammatory mediators, consequently slowing down muscle stem cell depletion. However, prednisolone treatment was unable to improve the myogenesis of stem cells and reduce fibrosis in dKO muscle. We then studied whether glucocorticoid treatment can be improved by co-administration of an inhibitor of RhoA/ROCK signaling, which can be activated by glucocorticoids and was found in our previous work to be over-activated in dystrophic muscle. Our results indicate that the combination of RhoA/ROCK inhibition and glucocorticoid treatment in dystrophic muscle have a synergistic effect in alleviating the dystrophic phenotype. Taken together, our study not only shed light on the mechanism by which glucocorticoid imparts its beneficial effect on dystrophic muscle, but also revealed the synergistic effect of RhoA/ROCK inhibition and glucocorticoid treatment, which could lead to the development of more efficient therapeutic approaches for treating DMD patients.

Muscular response to the first three months of deflazacort treatment in boys with Duchenne muscular dystrophy

OBJECTIVE

Duchenne muscular dystrophy (DMD) patients are often treated with glucocorticoids; yet their precise molecular action remains unknown.

METHODS

We investigated muscle biopsies from nine boys with DMD (aged: 7,6±2,8 yrs.) collected before and after three months of deflazacort treatment and compared them to eight healthy boys (aged: 5,3±2,4 yrs.). mRNA transcripts involved in activation of satellite cells, myogenesis, regeneration, adipogenesis, muscle growth and tissue inflammation were assessed. Serum creatine kinase (CK) levels and muscle protein expression by immunohistochemistry of selected targets were also analysed.

RESULTS

Transcript levels for ADIPOQ, CD68, CDH15, FGF2, IGF1R, MYF5, MYF6, MYH8, MYOD, PAX7, and TNFα were significantly different in untreated patients vs. normal muscle (p⟨0.05). Linear tests for trend indicated that the expression levels of treated patients were approaching normal values (p⟨0.05) following treatment (towards an increase; CDH15, C-MET, DLK1, FGF2, IGF1R, MYF5, MYF6, MYOD, PAX7; towards a decrease: CD68, MYH8, TNFα). Treatment reduced CK levels (p⟨0.05), but we observed no effect on muscle protein expression.

CONCLUSIONS

This study provides insight into the molecular actions of glucocorticoids in DMD at the mRNA level, and we show that multiple regulatory pathways are influenced. This information can be important in the development of new treatments.

Dystrophic Cardiomyopathy-Potential Role of Calcium in Pathogenesis, Treatment and Novel Therapies

Duchenne muscular dystrophy (DMD) is caused by defects in the DMD gene and results in progressive wasting of skeletal and cardiac muscle due to an absence of functional dystrophin. Cardiomyopathy is prominent in DMD patients, and contributes significantly to mortality. This is particularly true following respiratory interventions that reduce death rate and increase ambulation and consequently cardiac load. Cardiomyopathy shows an increasing prevalence with age and disease progression, and over 95% of patients exhibit dilated cardiomyopathy by the time they reach adulthood. Development of the myopathy is complex, and elevations in intracellular calcium, functional muscle ischemia, and mitochondrial dysfunction characterise the pathophysiology. Current therapies are limited to treating symptoms of the disease and there is therefore an urgent need to treat the underlying genetic defect. Several novel therapies are outlined here, and the unprecedented success of phosphorodiamidate morpholino oligomers (PMOs) in preclinical and clinical studies is overviewed.

Corticosteroids for the treatment of Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy of childhood. Untreated, this incurable disease, which has an X-linked recessive inheritance, is characterised by muscle wasting and loss of walking ability, leading to complete wheelchair dependence by 13 years of age. Prolongation of walking is a major aim of treatment. Evidence from randomised controlled trials (RCTs) indicates that corticosteroids significantly improve muscle strength and function in boys with DMD in the short term (six months), and strength at two years (two-year data on function are very limited). Corticosteroids, now part of care recommendations for DMD, are largely in routine use, although questions remain over their ability to prolong walking, when to start treatment, longer-term balance of benefits versus harms, and choice of corticosteroid or regimen.We have extended the scope of this updated review to include comparisons of different corticosteroids and dosing regimens.

OBJECTIVES

To assess the effects of corticosteroids on prolongation of walking ability, muscle strength, functional ability, and quality of life in DMD; to address the question of whether benefit is maintained over the longer term (more than two years); to assess adverse events; and to compare efficacy and adverse effects of different corticosteroid preparations and regimens.

SEARCH METHODS

On 16 February 2016 we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, EMBASE, CINAHL Plus, and LILACS. We wrote to authors of published studies and other experts. We checked references in identified trials, handsearched journal abstracts, and searched trials registries.

SELECTION CRITERIA

We considered RCTs or quasi-RCTs of corticosteroids (e.g. prednisone, prednisolone, and deflazacort) given for a minimum of three months to patients with a definite DMD diagnosis. We considered comparisons of different corticosteroids, regimens, and corticosteroids versus placebo.

DATA COLLECTION AND ANALYSIS

The review authors followed standard Cochrane methodology.

MAIN RESULTS

We identified 12 studies (667 participants) and two new ongoing studies for inclusion. Six RCTs were newly included at this update and important non-randomised cohort studies have also been published. Some important studies remain unpublished and not all published studies provide complete outcome data.

PRIMARY OUTCOME MEASURE

one two-year deflazacort RCT (n = 28) used prolongation of ambulation as an outcome measure but data were not adequate for drawing conclusions.

SECONDARY OUTCOME MEASURES

meta-analyses showed that corticosteroids (0.75 mg/kg/day prednisone or prednisolone) improved muscle strength and function versus placebo over six months (moderate quality evidence from up to four RCTs). Evidence from single trials showed 0.75 mg/kg/day superior to 0.3 mg/kg/day on most strength and function measures, with little evidence of further benefit at 1.5 mg/kg/day. Improvements were seen in time taken to rise from the floor (Gowers' time), timed walk, four-stair climbing time, ability to lift weights, leg function grade, and forced vital capacity. One new RCT (n = 66), reported better strength, function and quality of life with daily 0.75 mg/kg/day prednisone at 12 months. One RCT (n = 28) showed that deflazacort stabilised muscle strength versus placebo at two years, but timed function test results were too imprecise for conclusions to be drawn.One double-blind RCT (n = 64), largely at low risk of bias, compared daily prednisone (0.75 mg/kg/day) with weekend-only prednisone (5 mg/kg/weekend day), finding no overall difference in muscle strength and function over 12 months (moderate to low quality evidence). Two small RCTs (n = 52) compared daily prednisone 0.75 mg/kg/day with daily deflazacort 0.9 mg/kg/day, but study methods limited our ability to compare muscle strength or function.

ADVERSE EFFECTS

excessive weight gain, behavioural abnormalities, cushingoid appearance, and excessive hair growth were all previously shown to be more common with corticosteroids than placebo; we assessed the quality of evidence (for behavioural changes and weight gain) as moderate. Hair growth and cushingoid features were more frequent at 0.75 mg/kg/day than 0.3 mg/kg/day prednisone. Comparing daily versus weekend-only prednisone, both groups gained weight with no clear difference in body mass index (BMI) or in behavioural changes (low quality evidence for both outcomes, one study); the weekend-only group had a greater linear increase in height. Very low quality evidence suggested less weight gain with deflazacort than with prednisone at 12 months, and no difference in behavioural abnormalities. Data are insufficient to assess the risk of fractures or cataracts for any comparison.Non-randomised studies support RCT evidence in showing improved functional benefit from corticosteroids. These studies suggest sustained benefit for up to 66 months. Adverse effects were common, although generally manageable. According to a large comparative longitudinal study of daily or intermittent (10 days on, 10 days off) corticosteroid for a mean period of four years, a daily regimen prolongs ambulation and improves functional scores over the age of seven, but with a greater frequency of side effects than an intermittent regimen.

AUTHORS' CONCLUSIONS

Moderate quality evidence from RCTs indicates that corticosteroid therapy in DMD improves muscle strength and function in the short term (twelve months), and strength up to two years. On the basis of the evidence available for strength and function outcomes, our confidence in the effect estimate for the efficacy of a 0.75 mg/kg/day dose of prednisone or above is fairly secure. There is no evidence other than from non-randomised trials to establish the effect of corticosteroids on prolongation of walking. In the short term, adverse effects were significantly more common with corticosteroids than placebo, but not clinically severe. A weekend-only prednisone regimen is as effective as daily prednisone in the short term (12 months), according to low to moderate quality evidence from a single trial, with no clear difference in BMI (low quality evidence). Very low quality evidence indicates that deflazacort causes less weight gain than prednisone after a year's treatment. We cannot evaluate long-term benefits and hazards of corticosteroid treatment or intermittent regimens from published RCTs. Non-randomised studies support the conclusions of functional benefits, but also identify clinically significant adverse effects of long-term treatment, and a possible divergence of efficacy in daily and weekend-only regimens in the longer term. These benefits and adverse effects have implications for future research and clinical practice.

Quantitative and qualitative adaptations of muscle fibers to glucocorticoids

INTRODUCTION

The aim of this study was to understand the effects of short-term glucocorticoid administration in healthy subjects.

METHODS

Five healthy men received dexamethasone (8 mg/day) for 7 days. Vastus lateralis muscle biopsy and knee extension torque measurement were performed before and after administration. A large number of individual muscle fibers were dissected from the biopsy samples (pre-administration: n = 165, post-administration: n = 177).

RESULTS

Maximal knee extension torque increased after administration (∼ 13%), whereas both type 1 and type 2A fibers had decreased cross-sectional area (type 1: ∼ 11%, type 2A: ∼ 17%), myosin loss (type 1: ∼ 18%, type 2A: ∼ 32%), and loss of specific force (type 1: ∼ 24%, type 2A: ∼ 33%), which were preferential for fast fibers.

CONCLUSION

Short-term dexamethasone administration in healthy subjects elicits quantitative and qualitative adaptations of muscle fibers that precede (and may predict) the clinical appearance of myopathy in glucocorticoid-treated subjects.

Pregnancy-induced amelioration of muscular dystrophy phenotype in mdx mice via muscle membrane stabilization effect of glucocorticoid

Duchenne muscular dystrophy (DMD), the most common and severe type of dystrophinopathy, is an X-linked recessive genetic disease caused by the absence of dystrophin, which leads to fragility and vulnerability of the sarcolemma to mechanical stretching with increased membrane permeability. Currently, glucocorticoids such as prednisolone are the only medication available for DMD. However, molecular pathways responsible for this effect are still unclear. In addition, it remains unclear whether sex-related factors, including pregnancy and the postpartum period, affect the phenotype of dystrophinopathy. Here, we report the amelioration of muscle membrane permeability in the diaphragm muscle of pregnant and postpartum, but not in nulliparous, mdx mice, an animal model for DMD, during the physiological surge of corticosterone, the most abundant glucocorticoid in rodents. Cultures of single muscle fibers and myotubes isolated from mdx mouse diaphragm demonstrate resistance to hypo-osmotic shock when treated with corticosterone but not with estradiol or progesterone. This corticosterone-mediated resistance was diminished by an antagonist of corticosterone, indicating that the glucocorticoid-glucocorticoid receptor axis plays a role in this membrane stabilization effect on muscle. Moreover, subcutaneous injection of corticosterone into mdx mice showed decreased membrane permeability. This is the first report to demonstrate that pregnancy-related resistance to muscle fiber damage in mdx mice due to the membrane stabilization effect of corticosterone. We also propose that this membrane stabilization effect is exerted through annexin A1 up-regulation as the molecular mechanisms of glucocorticoid effects on DMD muscle. Furthermore, single muscle fiber culture studies provide a sensitive chemical screening platform for muscular dystrophies.

Corticosteroid Treatment Impact on Spinal Deformity in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is a progressive disease with loss of ambulation at around 9-10 years of age, followed, if untreated, by development of scoliosis, respiratory insufficiency, and death in the second decade of life. This review highlights the natural history of the disease, in particular, with regard to the development of the spinal deformity and how this complication has been modified by surgical interventions and overall by corticosteroid treatment. The beneficial effect of corticosteroids may have also an impact on the clinical trial design of the new emerging causative therapies.

Effects of an immunosuppressive treatment in the GRMD dog model of Duchenne muscular dystrophy

The GRMD (Golden retriever muscular dystrophy) dog has been widely used in pre-clinical trials targeting DMD (Duchenne muscular dystrophy), using in many cases a concurrent immune-suppressive treatment. The aim of this study is to assess if such a treatment could have an effect on the disease course of these animals. Seven GRMD dogs were treated with an association of cyclosporine A (immunosuppressive dosage) and prednisolone (2 mg/kg/d) during 7 months, from 2 to 9 months of age. A multi-parametric evaluation was performed during this period which allowed us to demonstrate that this treatment had several significant effects on the disease progression. The gait quality as assessed by 3D-accelerometry was dramatically improved. This was consistent with the evolution of other parameters towards a significant improvement, such as the clinical motor score, the post-tetanic relaxation and the serum CK levels. In contrast the isometric force measurement as well as the histological evaluation argued in favor of a more severe disease progression. In view of the disease modifying effects which have been observed in this study it should be concluded that immunosuppressive treatments should be used with caution when carrying out pre-clinical studies in this canine model of DMD. They also highlight the importance of using a large range of multi-parametric evaluation tools to reliably draw any conclusion from trials involving dystrophin-deficient dogs, which reproduce the complexity of the human disease.

Urocortins improve dystrophic skeletal muscle structure and function through both PKA- and Epac-dependent pathways

In Duchenne muscular dystrophy, the absence of dystrophin causes progressive muscle wasting and premature death. Excessive calcium influx is thought to initiate the pathogenic cascade, resulting in muscle cell death. Urocortins (Ucns) have protected muscle in several experimental paradigms. Herein, we demonstrate that daily s.c. injections of either Ucn 1 or Ucn 2 to 3-week-old dystrophic mdx(5Cv) mice for 2 weeks increased skeletal muscle mass and normalized plasma creatine kinase activity. Histological examination showed that Ucns remarkably reduced necrosis in the diaphragm and slow- and fast-twitch muscles. Ucns improved muscle resistance to mechanical stress provoked by repetitive tetanizations. Ucn 2 treatment resulted in faster kinetics of contraction and relaxation and a rightward shift of the force-frequency curve, suggesting improved calcium homeostasis. Ucn 2 decreased calcium influx into freshly isolated dystrophic muscles. Pharmacological manipulation demonstrated that the mechanism involved the corticotropin-releasing factor type 2 receptor, cAMP elevation, and activation of both protein kinase A and the cAMP-binding protein Epac. Moreover, both STIM1, the calcium sensor that initiates the assembly of store-operated channels, and the calcium-independent phospholipase A(2) that activates these channels were reduced in dystrophic muscle by Ucn 2. Altogether, our results demonstrate the high potency of Ucns for improving dystrophic muscle structure and function, suggesting that these peptides may be considered for treatment of Duchenne muscular dystrophy.

Dexamethasone stimulates store-operated calcium entry and protein degradation in cultured L6 myotubes through a phospholipase A(2)-dependent mechanism

Muscle wasting in various catabolic conditions is at least in part regulated by glucocorticoids. Increased calcium levels have been reported in atrophying muscle. Mechanisms regulating calcium homeostasis in muscle wasting, in particular the role of glucocorticoids, are poorly understood. Here we tested the hypothesis that glucocorticoids increase intracellular calcium concentrations in skeletal muscle and stimulate store-operated calcium entry (SOCE) and that these effects of glucocorticoids may at least in part be responsible for glucocorticoid-induced protein degradation. Treatment of cultured myotubes with dexamethasone, a frequently used in vitro model of muscle wasting, resulted in increased intracellular calcium concentrations determined by fura-2 AM fluorescence measurements. When SOCE was measured by using calcium "add-back" to muscle cells after depletion of intracellular calcium stores, results showed that SOCE was increased 15-25% by dexamethasone and that this response to dexamethasone was inhibited by the store-operated calcium channel blocker BTP2. Dexamethasone treatment stimulated the activity of calcium-independent phospholipase A(2) (iPLA(2)), and dexamethasone-induced increase in SOCE was reduced by the iPLA(2) inhibitor bromoenol lactone (BEL). In additional experiments, treatment of myotubes with the store-operated calcium channel inhibitor gadolinium ion or BEL reduced dexamethasone-induced increase in protein degradation. Taken together, the results suggest that glucocorticoids increase calcium concentrations in myocytes and stimulate iPLA(2)-dependent SOCE and that glucocorticoid-induced muscle protein degradation may at least in part be regulated by increased iPLA(2) activity, SOCE, and cellular calcium levels.

Automated drug screening with contractile muscle tissue engineered from dystrophic myoblasts

Identification of factors that improve muscle function in boys with Duchenne muscular dystrophy (DMD) could lead to an improved quality of life. To establish a functional in vitro assay for muscle strength, mdx murine myoblasts, the genetic homologue of DMD, were tissue engineered in 96-microwell plates into 3-dimensional muscle constructs with parallel arrays of striated muscle fibers. When electrically stimulated, they generated tetanic forces measured with an automated motion tracking system. Thirty-one compounds of interest as potential treatments for patients with DMD were tested at 3 to 6 concentrations. Eleven of the compounds (insulin-like growth factor-1, creatine, beta-hydroxy-beta-methylbutyrate, trichostatin A, lisinopril, and 6 from the glucocorticoid family) significantly increased tetanic force relative to placebo-treated controls. The glucocorticoids methylprednisolone, deflazacort, and prednisone increased tetanic forces at low doses (EC(50) of 6, 19, and 56 nM, respectively), indicating a direct muscle mechanism by which they may be benefitting DMD patients. The tetanic force assay also identified beneficial compound interactions (arginine plus deflazacort and prednisone plus creatine) as well as deleterious interactions (prednisone plus creatine inhibited by pentoxifylline) of combinatorial therapies taken by some DMD patients. Since mdx muscle in vivo and DMD patients respond in a similar manner to many of these compounds, the in vitro assay will be a useful tool for the rapid identification of new potential treatments for muscle weakness in DMD and other muscle disorders.

Effect of deflazacort on cardiac and sternocleidomastoid muscles in Duchenne muscular dystrophy: a magnetic resonance imaging study

OBJECTIVE

To evaluate the involvement of cardiac and sternocleidomastoid muscles by magnetic resonance imaging (MRI) measurement of T2 relaxation time and the left ventricular systolic function in patients with Duchenne muscular dystrophy (DMD) on treatment with deflazacort and compare them with DMD patients without treatment.

SUBJECTS

Seventeen patients with DMD (aged 17-22 years) on treatment with deflazacort for at least 7 years and 17 boys with DMD of younger age (12-15 years) without steroid treatment. All patients were free of cardiac or respiratory symptoms and had normal ECG and Holter monitor examination.

METHODS

T2 relaxation time of the myocardium (H), left (SCM-L) and right sternocleidomastoid (SCM-R) muscles and left ventricular systolic function were evaluated by magnetic resonance imaging (MRI) in two groups of DMD patients. Myocardial and sternocleidomastoid muscles T2 relaxation time was calculated using 16 TEs (10-85 msec) and TR at least 2000 ms and T2 maps were created.

RESULTS

DMD on deflazacort had higher T2 relaxation time values of the heart and of both sternocleidomastoid muscles (T2H median (range): 47 (41-48) vs. 33 (31-37)ms, p<0.001, T2 SCM-L median (range): 35 (30-37) vs. 23 (20-26)ms, p<0.001, T2 SCM-R median (range): 35 (32-37) vs. 23 (20-27)ms, p<0.001) and left ventricular systolic function (LVEDV median (range): 95 (75-120) vs. 90 (80-105)ml, p=0.03, LVESV median (range): 45 (38-55) vs. 47 (41-51)ml, p=0.81(NS), LVEF median (range): 53% (51-57) vs. 48% (42-51), p<0.001) compared to DMD without treatment.

CONCLUSIONS

DMD patients on deflazacort are characterized by better preservation of the T2 relaxation time of myocardium and sternocleidomastoid muscles and better LV systolic function. The duration of this beneficial effect needs to be studied prospectively.

Investigation of Debio 025, a cyclophilin inhibitor, in the dystrophic mdx mouse, a model for Duchenne muscular dystrophy

BACKGROUND AND PURPOSE

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by the absence of the cytoskeletal protein dystrophin. This leads to muscle cell death accompanied by chronic inflammation. Cyclosporin A (CsA) is a powerful immunosuppressive drug, which has been proposed for DMD treatment. CsA also directly regulates the mitochondrial permeability transition pore (mPTP), which participates in cell death pathways through the inhibition of cyclophilin D. Here, we evaluated whether Debio 025, a cyclophilin inhibitor with no immunosuppressive activity, improves the dystrophic condition in a mouse model of DMD, through regulation of mPTP.

EXPERIMENTAL APPROACH

The potency of Debio 025 to protect mouse dystrophic cells against mitochondria-mediated death was assessed by caspase-3 activity and calcium retention capacity assays. Mdx(5Cv) mice (3-week-old) were treated daily by gavage for 2 weeks with Debio 025 (10, 30 or 100 mg kg(-1)), CsA (10 mg kg(-1)) or placebo. The effects on muscle necrosis and function were measured.

KEY RESULTS

In vitro investigations showed protective effect of low concentrations of Debio 025 against cell death. Histology demonstrated that Debio 025 partially protected the diaphragm and soleus muscles against necrosis (10 and 100 mg kg(-1), respectively). Hindlimb muscles from mice receiving Debio 025 at 10 mg kg(-1) relaxed faster, showed alteration in the stimulation frequency-dependent recruitment of muscle fibres and displayed a higher resistance to mechanical stress.

CONCLUSIONS AND IMPLICATIONS

Debio 025 partially improved the structure and the function of the dystrophic mouse muscle, suggesting that therapies targeting the mPTP may be helpful to DMD patients.

Glucocorticoid corticosteroids for Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy of childhood. This incurable disease is characterised by muscle wasting and loss of walking ability leading to complete wheelchair dependence by 13 years of age. Prolongation of walking is one of the major aims of treatment.

OBJECTIVES

The aim of this review was to assess whether glucocorticoid corticosteroids stabilize or improve muscle strength and walking in boys with DMD.

SEARCH STRATEGY

This is an update of the Cochrane systematic review first published in 2004 (Manzur 2004). We searched the Cochrane Neuromuscular Disease Group Trials Register (August 2006) using the term 'Duchenne muscular dystrophy'. We also searched MEDLINE (January 1966 to July 2007), EMBASE (January 1980 to August 2006), CINAHL and LILACS (January 1982 to August 2006). We wrote to authors of published studies and other experts in this disease to help identify other trials, checked the references in the identified trials and hand searched the abstracts of relevant journals.

SELECTION CRITERIA

Types of studies: randomised or quasi-randomised trials.

TYPES OF PARTICIPANTS

all patients with a definite diagnosis of Duchenne muscular dystrophy. Types of interventions: glucocorticoids such as prednisone, prednisolone, deflazacort or others, with a minimum treatment period of three months.

PRIMARY OUTCOME MEASURE

prolongation of walking (independent walking without long leg calipers).

SECONDARY OUTCOME MEASURES

strength outcome measures, manual muscle strength testing using Medical Research Council strength scores, functional outcome measures and adverse events.

DATA COLLECTION AND ANALYSIS

We identified six randomised controlled trials that met the inclusion criteria for our review, and one of these (Beenakker 2005) is a new addition to this update, as it was published subsequent to our first review (Manzur 2004). Two review authors independently selected the trials for the review and assessed methodological quality. Data extraction and inputting were double-checked.

PRIMARY OUTCOME MEASURE

data from one small study used prolongation of walking as an outcome measure and did not show significant benefit.

SECONDARY OUTCOME MEASURES

The meta-analysis of the results from four randomised controlled trials with altogether 249 participants showed that glucocorticoid corticosteroids improved muscle strength and function over six months. Improvements were seen in time taken to rise from the floor (Gowers' time), nine metres walking time, four-stair climbing time, ability to lift weights, leg function grade and forced vital capacity. One randomised controlled trial with altogether 28 participants showed that glucocorticoid corticosteroids stabilize muscle strength and function for up to two years. The most effective prednisolone regime appears to be 0.75 mg/kg/day, given in a daily dose regime. Not enough data were available to compare efficacy of prednisone with deflazacort. Adverse effects: Excessive weight gain, behavioural abnormalities, cushingoid appearance and excessive hair growth were all more common with glucocorticoid corticosteroids than placebo. Long-term adverse effects of glucocorticoid therapy could not be evaluated because of the short-term duration of the randomised studies.Non-randomised studies: A number of non-randomised studies with important efficacy and adverse effects data are tabulated and discussed.

AUTHORS' CONCLUSIONS

There is evidence from randomised controlled studies that glucocorticoid corticosteroid therapy in Duchenne muscular dystrophy improves muscle strength and function in the short-term (six months to two years). The most effective prednisolone regime appears to be 0.75 mg/kg/day, given daily. In the short term, adverse effects were significantly more common but not clinically severe. Long-term benefits and hazards of glucocorticoid treatment cannot be evaluated from the currently published randomised studies. Non-randomised studies support the conclusions of functional benefits but also identify clinically significant adverse effects of long-term treatment. These benefits and adverse effects have implications for future research studies and clinical practice.

Prednisolone in Duchenne muscular dystrophy with imminent loss of ambulation

An open controlled trial of 0.75 mg/Kg/day prednisolone was conducted at a stage when the patients had started falling several times in a day and stopped on their attaining a chair bound stage, thus minimising the total period of steroid therapy. Out of the 67 DMD patients enrolled in this study, 44 were put on prednisolone therapy and 23 served as controls. All patients were followed-up at two-monthly intervals for two years and thereafter they continued to take their respective medications till their chair-bound stage; then the drug was gradually withdrawn. In the treatment group 24 patients could not continue the trial because of adverse effects - 14 due to excessive obesity, 3 due to measles, 4 due to pulmonary tuberculosis, 2 due to recurrent throat and chest infection and 1 due to an unexplained high leukocyte count. Of the remaining 20 patients in the treatment group, steroid therapy was stopped in 5 patients as there was no improvement in power in six months. Fifteen patients in the treatment group and 19 patients in the control group could be followed regularly for 2 years and then up to chair-bound stage. Outcome parameters included fall frequency, peak expiratory flow rate, limb muscle power, ability to lift weights, time taken in getting up from squatting position, walking 9 metres and climbing 13 stairs. Maximum improvement was noted between 2 and 4 months while mild improvement in some parameters continued up to six months. All parameters remained stabilised for 1 year or so, after which there was slight deterioration. Deterioration at 2 years was, however, less than the natural course of events noted in control patients. Prednisolone treated patients and controls became chair bound at the mean age of 169 +/- 9 and 132 +/- 8 months respectively. Till the ideal stage of the disease and the type or dosage of starting steroid therapy is defined by specially designed studies, 0.75 mg/Kg/day prednisolone therapy may be started in DMD patients at the stage of frequent falls ( > 10 / day) on walking or increased get-up time ( > 10 s) as observed while testing Gowers' sign; this improves muscle power and timing of motor performance within 2-4 months of onset of therapy in about 75% of those who tolerate this therapy, with a possible gain of approximately 3 years in terms of independent walking.

Green tea extract and its major polyphenol (-)-epigallocatechin gallate improve muscle function in a mouse model for Duchenne muscular dystrophy

Duchenne muscular dystrophy is a frequent muscular disorder caused by mutations in the gene encoding dystrophin, a cytoskeletal protein that contributes to the stabilization of muscle fiber membrane during muscle activity. Affected individuals show progressive muscle wasting that generally causes death by age 30. In this study, the dystrophic mdx(5Cv) mouse model was used to investigate the effects of green tea extract, its major component (-)-epigallocatechin gallate, and pentoxifylline on dystrophic muscle quality and function. Three-week-old mdx(5Cv) mice were fed for either 1 or 5 wk a control chow or a chow containing the test substances. Histological examination showed a delay in necrosis of the extensor digitorum longus muscle in treated mice. Mechanical properties of triceps surae muscles were recorded while the mice were under deep anesthesia. Phasic and tetanic tensions of treated mice were increased, reaching values close to those of normal mice. The phasic-to-tetanic tension ratio was corrected. Finally, muscles from treated mice exhibited 30-50% more residual force in a fatigue assay. These results demonstrate that diet supplementation of dystrophic mdx(5Cv) mice with green tea extract or (-)-epigallocatechin gallate protected muscle against the first massive wave of necrosis and stimulated muscle adaptation toward a stronger and more resistant phenotype.

Drug–protein recognition processes investigated by NMR relaxation data

In this paper we investigated the interaction processes occurring at the protein-solvent interface for prednisolone-albumin and prednisone-albumin systems, using an approach based on the analysis of proton selective relaxation rate enhancements of the ligand in the presence of the macromolecule. The contribution from the bound ligand fraction to the observed relaxation rate in relation to protein concentration allowed the calculation of the affinity index[A]L(T) and the normalized affinity index [AI(N)]L(T) which removes the effects of motional anisotropies and different proton densities, and isolates the contribution due to a decrease in the ligand dynamics caused by the binding with the protein. This approach allowed the comparison of the binding ability of prednisolone and prednisone towards albumin.

Synthetic polymers as biomacromolecular models for studying ligand–protein interactions: A nuclear spin relaxation approach

In this paper, we applied an NMR methodology based on the analysis of selective spin-lattice relaxation rate enhancements of ligand protons induced by interaction processes between prednisolone and a synthetic copolymer, namely poly(N-isopropylacrylamide-co-N-acryloil-L-phenylalanine), in order to investigate this system as a model for studying drug-biomacromolecules interactions. The contribution from the bound ligand fraction to the observed relaxation rate in relation to macromolecule concentration allowed the calculation of the normalized affinity index [A(N)(I)](T)(L), in which the effects of motional anisotropies and different proton densities have been removed. This parameter, which represents the global affinity of the ligand towards the macromolecule, isolates the contribution due to a decrease in the ligand dynamics caused by the binding with the copolymer. The affinity index calculated for prednisolone-copolymer complex compared to that obtained for prednisolone-albumin system, suggested that synthetic polymers as models of biomacromolecules can play an important role in drug-protein interaction studies.

Novel aspects on the regulation of muscle wasting in sepsis

Muscle wasting in sepsis is associated with increased expression of messenger RNA for several genes in the ubiquitin-proteasome proteolytic pathway, indicating that increased gene transcription is involved in the development of muscle atrophy. Here we review the influence of sepsis on the expression and activity of the transcription factors activator protein-1, nuclear factor-kappaB (NF-kappaB), and CCAAT/enhancer binding protein, as well as the nuclear cofactor p300. These transcription factors may be important for sepsis-induced muscle wasting because several of the genes in the ubiquitin-proteasome proteolytic pathway have multiple binding sites for activating protein-1, nuclear factor-kappaB, and CCAAT/enhancer binding protein in their promoter regions. In addition, the potential role of increased muscle calcium levels for sepsis-induced muscle atrophy is reviewed. Calcium may regulate several mechanisms and factors involved in muscle wasting, including the expression and activity of the calpain-calpastatin system, proteasome activity, CCAAT/enhancer binding protein transcription factors, apoptosis and glucocorticoid-mediated muscle protein breakdown. Because muscle wasting is commonly seen in patients with sepsis and has severe clinical consequences, a better understanding of mechanisms regulating sepsis-induced muscle wasting may help improve the care of patients with sepsis and other muscle-wasting conditions as well.

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.

Glucocorticoid treatment alleviates dystrophic myofiber pathology by activation of the calcineurin/NF-AT pathway

Duchenne muscular dystrophy (DMD) is a progressive and ultimately fatal skeletal muscle disease. Currently, the most effective therapy is the administration of a subclass of glucocorticoids, most notably deflazacort. Although deflazacort treatment can attenuate DMD progression, extend ambulation, and maintain muscle strength, the mechanism of its action remains unknown. Prior observations have shown that activation of a JNK1-mediated signal transduction cascade contributes to the progression of the DMD phenotype, in part by phosphorylation and inhibition of a calcineurin sensitive NF-ATc1 transcription factor. Here, we observed that deflazacort treatment restored myocyte viability in muscle cells with constitutive activation of JNK1 and in dystrophic mdx mice. However, deflazacort treatment did not alter JNK1 activity itself, but rather led to an increase in the activity of the calcineurin phosphatase and an up-regulation of NF-ATc1-dependent gene expression. The prophylactic effect of deflazacort treatment was associated with increased expression of NF-ATc1 target genes such as the dystrophin homologue utrophin. Moreover, the muscle sparing effects of deflazacort were completely abolished when used in conjunction with the calcineurin inhibitor cyclosporine. Collectively, these results show that deflazacort attenuates loss of dystrophic myofiber integrity by up-regulating the activity of the phosphatase calcineurin, which in turn negates JNK1 inhibition of NF-ATc1-mediated phosphorylation and nuclear exclusion of NF-ATc1.

Prednisone reduces muscle degeneration in dystrophin-deficient Caenorhabditis elegans

Duchenne muscular dystrophy is a degenerative muscular disease caused by mutations in the dystrophin gene. There is no curative treatment against Duchenne muscular dystrophy. In several countries, the steroid prednisone (or analogs) is prescribed as a palliative treatment. In the model animal Caenorhabditis elegans, mutations of the dys-1 dystrophin-like gene lead to a muscular degenerative phenotype when they are associated with a mild MyoD mutation. This cheap and fast-growing model of dystrophinopathy may be used to screen for molecules able to slow muscle degeneration. In a blind screen of approximately 100 compounds covering a wide spectrum of targets, we found that prednisone is beneficial to the C. elegans dystrophin-deficient muscles. Prednisone reduces by 40% the number of degenerating cells in this animal. This result is a proof-of-principle for the use of C. elegans as a tool in the search for molecules active against the effects of dystrophin-deficiency. Moreover, since C. elegans is not susceptible to inflammation, this suggests that prednisone exerts a direct effect on muscle survival.

Glucocorticoid corticosteroids for Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy is the most common muscular dystrophy of childhood. This incurable disease is characterised by muscle wasting and loss of walking ability leading to complete wheelchair dependence by 13 years of age. Prolongation of walking is one of the major aims of treatment.

OBJECTIVES

The aim of this review was to assess whether glucocorticoid corticosteroids stabilize or improve muscle strength and walking in boys with DMD.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group specialised register (October 2003) using the term 'Duchenne muscular dystrophy'. We also searched MEDLINE (January 1966 to October 2003), EMBASE (January 1980 to October 2003), CINAHL and LILACS (January 1982 to October 2003). We wrote to authors of published studies and other experts in this disease to help identify other trials, checked the references in the identified trials and handsearched the abstracts of relevant journals.

SELECTION CRITERIA

Types of studies: randomised or quasi-randomised trials.

TYPES OF PARTICIPANTS

all patients with a definite diagnosis of Duchenne muscular dystrophy. Types of interventions: glucocorticoids such as prednisone, prednisolone, deflazacort or others, with a minimum treatment period of three months.

PRIMARY OUTCOME MEASURE

prolongation of walking (independent walking without long leg calipers).

SECONDARY OUTCOME MEASURES

strength outcome measures, manual muscle strength testing using Medical Research Council strength scores, functional outcome measures and adverse events.

DATA COLLECTION AND ANALYSIS

We identified five randomised controlled trials that met the inclusion criteria for our review. Two reviewers independently selected the trials for the review and assessed methodological quality. Data extraction and inputting were double-checked.

PRIMARY OUTCOME MEASURE

data from one small study used prolongation of walking as an outcome measure and did not show significant benefit.

SECONDARY OUTCOME MEASURES

The meta-analysis of the results from three randomised controlled trials showed that glucocorticoid corticosteroids improved muscle strength and function over six months. Improvements were seen in time taken to rise from the floor (Gowers' time), nine metres walking time, four-stair climbing time, ability to lift weights, leg function grade and forced vital capacity. One randomised controlled trial showed that glucocorticoid corticosteroids stabilize muscle strength and function for up to two years. The most effective prednisolone regime appears to be 0.75 mg/kg/day. Not enough data were available to compare efficacy of prednisone with deflazacort.Adverse effects: Excessive weight gain, behavioural abnormalities, cushingoid appearance and excessive hair growth were all more common with glucocorticoid corticosteroids than placebo. Long-term adverse effects of glucocorticoid therapy could not be evaluated because of the short-term duration of the randomised studies.Non-randomised studies: a number of non-randomised studies with important efficacy and adverse effects data are tabulated and discussed.

REVIEWERS' CONCLUSIONS

There is evidence from randomised controlled studies that glucocorticoid corticosteroid therapy in Duchenne muscular dystrophy improves muscle strength and function in the short-term (six months to two years). The most effective prednisolone regime appears to be 0.75 mg/kg/day. In the short term, adverse effects were significantly more common but not clinically severe. Long-term benefits and hazards of glucocorticoid treatment cannot be evaluated from the currently published randomised studies. Non-randomised studies support the conclusions of functional benefits but also indicate clinically significant adverse effects of long-term treatment. These benefits and adverse effects have implications for future research studies and clinical practice.

Calcium homeostasis and glucose uptake of murine myotubes exposed to insulin, caffeine and 4-chloro-m-cresol

The modulation of glucose uptake by cytosolic calcium and the role of insulin on calcium homeostasis in insulin-target cells are incompletely understood and results are contradictory. To address this issue, we used the C2C12 murine skeletal muscle cell line model and examined the influence of caffeine and 4-chloro-m-cresol, two ryanodine receptor agonists known to mobilize intracellular calcium stores and increase cytosolic free calcium concentration. We followed 45calcium efflux, a validated indicator of cytosolic calcium concentration, and 3-O-methyl-[1-3H]-d-glucose uptake in parallel. We also determined if insulin incubation affected 45calcium influx rate. A 30-min treatment by 1 microm insulin highly significantly increased 45calcium efflux by 8.5% (P = 0.0014), despite a significant reduction of 45Ca2+ influx already measurable after 20 and 30 min of insulin stimulation (-16.6%, P = 0.0119 and -21.3%, P = 0.0047, respectively). Caffeine (1-20 mm) and 4-chloro-m-cresol (0.05-10 mm) concentration-dependently increased 45calcium efflux, the latter being more potent and efficacious. These agents, in a concentration-dependent manner, inhibited both basal and, more potently, insulin-stimulated glucose uptake. This resulted in a negative correlation of glucose uptake and 45calcium efflux (r > 0.95, P < 0.001). This effect was approximately 5 times greater for caffeine than for 4-chloro-m-cresol, suggesting a calcium-independent part of the glucose uptake inhibition by caffeine. In our in vitro model of cultured muscle cells, insulin appears to prevent calcium overload by both stimulating efflux and inhibiting cell storage. This effect, taken together with the observed inhibitory, inverse relationship between 45calcium efflux and glucose uptake, contributes to describing the complex insulin-calcium interplay involved in target cells.

Collaborative translational research leading to multicenter clinical trials in Duchenne muscular dystrophy: the Cooperative International Neuromuscular Research Group (CINRG)

Progress in the development of rationally based therapies for Duchenne muscular dystrophy has been accelerated by encouraging multidisciplinary, multi-institutional collaboration between basic science and clinical investigators in the Cooperative International Research Group. We combined existing research efforts in pathophysiology by a gene expression profiling laboratory with the efforts of animal facilities capable of conducting high-throughput drug screening and toxicity testing to identify safe and effective drug compounds that target different parts of the pathophysiologic cascade in a genome-wide drug discovery approach. Simultaneously, we developed a clinical trial coordinating center and an international network of collaborating physicians and clinics where those drugs could be tested in large-scale clinical trials. We hope that by bringing together investigators at these facilities and providing the infrastructure to support their research, we can rapidly move new bench discoveries through animal model screening and into therapeutic testing in humans in a safe, timely and cost-effective setting.

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.

Green tea extract decreases muscle necrosis in mdx mice and protects against reactive oxygen species

BACKGROUND

Duchenne muscular dystrophy is a severe X-linked congenital disorder characterized by lethal muscle wasting caused by the absence of the structural protein dystrophin.

OBJECTIVE

Because generation of reactive oxygen species appears to play an important role in the pathogenesis of this disease, we tested whether antioxidant green tea extract could diminish muscle necrosis in the mdx mouse dystrophy model.

DESIGN

A diet supplemented with 0.01% or 0.05% green tea extract was fed to dams and neonates for 4 wk beginning on the day of birth. Muscle necrosis and regeneration were determined in stained cryosections of soleus and elongator digitorum longus muscles. Radical scavenging by green tea extract was determined in differentiated cultured C2C12 cells treated with tert-butylhydroperoxide, with the use of 2',7'-dichlorofluorescin diacetate as a radical detector.

RESULTS

This feeding regimen significantly and dose-dependently reduced necrosis in the fast-twitch muscle elongator digitorum longus but at the doses tested had no effect on the slow-twitch soleus muscle. Green tea extract concentration-dependently decreased oxidative stress induced by tert-butylhydroperoxide treatment of cultured mouse C2C12 myotubes. The lower effective dose tested in mdx mice corresponds to approximately equal to 1.4 L (7 cups) green tea/d in humans.

CONCLUSION

Green tea extract may improve muscle health by reducing or delaying necrosis in mdx mice by an antioxidant mechanism.

Calcium influx through calcium leak channels is responsible for the elevated levels of calcium-dependent proteolysis in dystrophic myotubes

To estimate calpain proteolysis, we measured the hydrolysis rate of a fluorogenic calpain substrate in individual resting normal and dystrophic mdx mouse myotubes in culture. Hydrolysis rates were high during myoblast and myotube alignment and fusion. After alignment and fusion ceased, hydrolysis rates declined. For normal myotubes, hydrolysis remained low after the development of contractile activity. In contrast, after the development of contractile activity, dystrophic mdx myotubes had abnormally high levels of hydrolysis that were dependent on external calcium and that could be abolished by calpeptin, an inhibitor of calpain. We eliminated the direct effects of contraction during measurements of hydrolysis by the addition of tetrodotoxin. Substrate hydrolysis by lysosomes or proteosomes was controlled for using NH(4)Cl and clasto-lactacystin beta-lactone, respectively. Increased activity of the calcium-activated protease in mature mdx myotubes was linked to the abnormal activity of calcium-specific leak channels because an antagonist of these channels reduced the higher levels of hydrolysis in dystrophic myotubes to nearly normal levels. The abnormal activity of these channels is linked to an increased frequency of transient sarcolemmal disruptions in the more fragile mdx myotubes (, ). Treatment of mdx myotubes with a pro-drug of methylprednisolone also reduced calpain substrate hydrolysis to nearly normal levels. However, this inhibition only required 2.5 h of pretreatment, which was not long enough to act by the known effects of prednisolone on calcium homeostasis.

The effect of methylprednisolone on intracellular calcium of normal and dystrophic human skeletal muscle cells

Clinical trials have shown that a glucocorticoid, the methyiprednisolone (PDN), has a beneficial effect on muscle strength and function in Duchenne muscular dystrophy (DMD) patients. The aim of this study was to test if the effect of PDN could be mediated via a possible action on intracellular calcium. The intracellular calcium activity, at rest and during calcium mobilizing drug superfusion protocols was recorded in normal and dystrophic human cocultured muscle cells. PDN (10 microM) pretreatment induced an elevation of the resting calcium concentration of 51, 34 and 38% in proliferating normal myoblasts, DMD myoblasts and DMD myotubes, respectively, while normal myotubes resting [Ca2+]i was not altered.

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.

Increased calcium entry into dystrophin-deficient muscle fibres of MDX and ADR-MDX mice is reduced by ion channel blockers

1. Single fibres were enzymatically isolated from interosseus muscles of dystrophic MDX mice, myotonic-dystrophic double mutant ADR-MDX mice and C57BL/10 controls. The fibres were kept in cell culture for up to 2 weeks for the study of Ca2+ homeostasis and sarcolemmal Ca2+ permeability. 2. Resting levels of intracellular free Ca2+, determined with the fluorescent Ca2+ indicator fura-2, were slightly higher in MDX (63 +/- 20 nM; means +/- s.d.; n = 454 analysed fibres) and ADR-MDX (65 +/- 12 nM; n = 87) fibres than in controls (51 +/- 20 nM; n = 265). 3. The amplitudes of electrically induced Ca2+ transients did not differ between MDX fibres and controls. Decay time constants of Ca2+ transients ranged between 10 and 55 ms in both genotypes. In 50 % of MDX fibres (n = 68), but in only 20 % of controls (n = 54), the decay time constants were > 35 ms. 4. Bath application of Mn2+ resulted in a progressive quench of fura-2 fluorescence emitted from the fibres. The quench rate was about 2 times higher in MDX fibres (3.98 +/- 1.9 % min-1; n = 275) than in controls (2.03 +/- 1.4 % min-1; n = 204). The quench rate in ADR-MDX fibres (2.49 +/- 1.4 % min-1; n = 87) was closer to that of controls. 5. The Mn2+ influx into MDX fibres was reduced to 10 % by Gd3+, to 19 % by La3+ and to 47 % by Ni2+ (all at 50 microM). Bath application of 50 microM amiloride inhibited the Mn2+ influx to 37 %. 6. We conclude that in isolated, resting MDX muscle fibres the membrane permeability for divalent cations is increased. The presumed additional influx of Ca2+ occurs through ion channels, but is well compensated for by effective cellular Ca2+ transport systems. The milder dystrophic phenotype of ADR-MDX mice is correlated with a smaller increase of their sarcolemmal Ca2+ permeability.

Creatine supplementation improves intracellular Ca2+ handling and survival in mdx skeletal muscle cells

Dystrophic skeletal muscle cells from Duchenne muscular dystrophy (DMD) patients and mdx mice exhibit elevated cytosolic Ca2+ concentrations ([Ca2+]c). Pretreatment of mdr myotubes for 6-12 days with creatine (20 mM) decreased the elevation in [Ca2+]c induced by either high extracellular Ca2+ concentrations or hypo-osmotic stress to control levels. 45Ca2+ influx measurements suggest that creatine lowered [Ca2+]c by stimulating sarcoplasmic reticulum Ca2+-ATPase. Creatine pretreatment increased levels of phosphocreatine but not ATP. Furthermore, myotube formation and survival were significantly enhanced by creatine pretreatment. Therefore, creatine supplementation may be useful for treatment of DMD.

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.

Regulation of cytosolic calcium in skeletal muscle cells of the mdx mouse under conditions of stress

1. In Duchenne muscular dystrophy (DMD) dysregulation of cytosolic calcium appears to be involved in the degeneration of skeletal muscle fibres. Therefore, we have studied the regulation of the free cytosolic calcium concentration ([Ca2+]c) under specific stress conditions in cultured myotubes isolated from the hind limbs of wild-type (C57BL10) and dystrophin-deficient mutant mdx mice. [Ca2+]c in the myotubes was estimated by the use of the Ca(2+)-sensitive fluorescent dye, fura-2. 2. Resting [Ca2+]c was similar in mdx and normal myotubes (35 +/- 9 nM and 38 +/- 11 nM, respectively). However, when mdx myotubes were exposed to a high extracellular calcium concentration ([Ca2+]c) of 40 mM, the [Ca2+]c was elevated to 84 +/- 29 nM, compared to 49 +/- 7 nM in normal myotubes. 3. Lowering the osmolarity of the superfusion solution from 300 mOsm to 100 mOsm resulted also in a rise in [Ca2+]c which was about two times higher for mdx (243 +/- 65 nM) than for C57BL10 (135 +/- 37 nM). Replacing extracellular Ca2+ by EGTA (0.2 mM) prevented the rise in [Ca2+]c in both mdx and normal myotubes when exposed to the low osmolarity solution. 4. Gadolinium ion (50 microM), an inhibitor of Ca2+ entry, antagonized the rise in [Ca2+]c of myotubes superfused with 40 mM [Ca2+]c by 20-40% for both mdx and C57BL10 cells, but did not significantly reduce the rise in [Ca2+]c when the cells were exposed to the hypo-osmotic buffer (100 mOsm). 5. Incubation of the cell culture for 3-5 days from the onset of induction of myotube formation with the membrane permeable protease inhibitor, calpeptin (50 microM) abolished the rise in [Ca2+]c in mdx myotubes upon exposure to hypo-osmotic shock. 6. Treatment of the cell culture for 3-5 days with alpha-methylprednisolone (PDN, 10 microM) attenuated the rise in [Ca2+]c following hypo-osmotic stress for both normal and mdx myotubes by about 50%. 7. The results described here suggest an increased permeability of mdx myotubes to Ca2+ under specific stress conditions. The ameliorating effect of PDN on [Ca2+]c could explain, at least partly, the beneficial effect of this drug on DMD patients.