Long-term treatment with naproxcinod significantly improves skeletal and cardiac disease phenotype in the mdx mouse model of dystrophy

Effects of Chronic, Maximal Phosphorodiamidate Morpholino Oligomer (PMO) Dosing on Muscle Function and Dystrophin Restoration in a Mouse Model of Duchenne Muscular Dystrophy

BACKGROUND

Phosphorodiamidate morpholino oligomer (PMO)-mediated exon skipping is currently used in clinical development to treat Duchenne muscular dystrophy (DMD), with four exon-skipping drugs achieving regulatory approval. Exon skipping elicits a truncated, but semi-functional dystrophin protein, similar to the truncated dystrophin expressed in patients with Becker Muscular dystrophy (BMD) where the disease phenotype is less severe than DMD. Despite promising results in both dystrophic animal models and DMD boys, restoration of dystrophin by exon skipping is highly variable, leading to contradictory functional outcomes in clinical trials.

OBJECTIVE

To develop optimal PMO dosing protocols that result in increased dystrophin and improved outcome measures in preclinical models of DMD.

METHODS

Tested effectiveness of multiple chronic, high dose PMO regimens using biochemical, histological, molecular, and imaging techniques in mdx mice.

RESULTS

A chronic, monthly regimen of high dose PMO increased dystrophin rescue in mdx mice and improved specific force in the extensor digitorum longus (EDL) muscle. However, monthly high dose PMO administration still results in variable dystrophin expression localized throughout various muscles.

CONCLUSIONS

High dose monthly PMO administration restores dystrophin expression and increases muscle force; however, the variability of dystrophin expression at both the inter-and intramuscular level remains. Additional strategies to optimize PMO uptake including increased dosing frequencies or combination treatments with other yet-to-be-defined therapies may be necessary to achieve uniform dystrophin restoration and increases in muscle function.

Cardioprotective effect of nicorandil on isoproterenol induced cardiomyopathy in the Mdx mouse model

BACKGROUND

Duchenne muscular dystrophy (DMD) associated cardiomyopathy is a major cause of morbidity and mortality. In an in vitro DMD cardiomyocyte model, nicorandil reversed stress-induced cell injury through multiple pathways implicated in DMD. We aimed to test the efficacy of nicorandil on the progression of cardiomyopathy in mdx mice following a 10-day treatment protocol.

METHODS

A subset of mdx mice was subjected to low-dose isoproterenol injections over 5 days to induce a cardiac phenotype and treated with vehicle or nicorandil for 10 days. Baseline and day 10 echocardiograms were obtained to assess cardiac function. At 10 days, cardiac tissue was harvested for further analysis, which included histologic analysis and assessment of oxidative stress. Paired student's t test was used for in group comparison, and ANOVA was used for multiple group comparisons.

RESULTS

Compared to vehicle treated mice, isoproterenol decreased ejection fraction and fractional shortening on echocardiogram. Nicorandil prevented isoproterenol induced cardiac dysfunction. Isoproterenol increased cardiac fibrosis, which nicorandil prevented. Isoproterenol increased gene expression of NADPH oxidase, which decreased to baseline with nicorandil treatment. Superoxide dismutase 2 protein expression increased in those treated with nicorandil, and xanthine oxidase activity decreased in mice treated with nicorandil during isoproterenol stress compared to all other groups.

CONCLUSIONS

In conclusion, nicorandil is cardioprotective in mdx mice and warrants continued investigation as a therapy for DMD associated cardiomyopathy.

Multi-Compartment, Early Disruption of cGMP and cAMP Signalling in Cardiac Myocytes from the mdx Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is the most frequent and severe form of muscular dystrophy. The disease presents with progressive body-wide muscle deterioration and, with recent advances in respiratory care, cardiac involvement is an important cause of morbidity and mortality. DMD is caused by mutations in the dystrophin gene resulting in the absence of dystrophin and, consequently, disturbance of other proteins that form the dystrophin-associated protein complex (DAPC), including neuronal nitric oxide synthase (nNOS). The molecular mechanisms that link the absence of dystrophin with the alteration of cardiac function remain poorly understood but disruption of NO-cGMP signalling, mishandling of calcium and mitochondrial disturbances have been hypothesized to play a role. cGMP and cAMP are second messengers that are key in the regulation of cardiac myocyte function and disruption of cyclic nucleotide signalling leads to cardiomyopathy. cGMP and cAMP signals are compartmentalised and local regulation relies on the activity of phosphodiesterases (PDEs). Here, using genetically encoded FRET reporters targeted to distinct subcellular compartments of neonatal cardiac myocytes from the DMD mouse model mdx, we investigate whether lack of dystrophin disrupts local cyclic nucleotide signalling, thus potentially providing an early trigger for the development of cardiomyopathy. Our data show a significant alteration of both basal and stimulated cyclic nucleotide levels in all compartments investigated, as well as a complex reorganization of local PDE activities.

Enhanced dimethylarginine degradation improves coronary flow reserve and exercise tolerance in Duchenne muscular dystrophy carrier mice

Duchenne muscular dystrophy (DMD) is an X-linked disease caused by null mutations in dystrophin and characterized by muscle degeneration. Cardiomyopathy is common and often prevalent at similar frequency in female DMD carriers irrespective of whether they manifest skeletal muscle disease. Impaired muscle nitric oxide (NO) production in DMD disrupts muscle blood flow regulation and exaggerates postexercise fatigue. We show that circulating levels of endogenous methylated arginines including asymmetric dimethylarginine (ADMA), which act as NO synthase inhibitors, are elevated by acute necrotic muscle damage and in chronically necrotic dystrophin-deficient mice. We therefore hypothesized that excessive ADMA impairs muscle NO production and diminishes exercise tolerance in DMD. We used transgenic expression of dimethylarginine dimethylaminohydrolase 1 (DDAH), which degrades methylated arginines, to investigate their contribution to exercise-induced fatigue in DMD. Although infusion of exogenous ADMA was sufficient to impair exercise performance in wild-type mice, transgenic DDAH expression did not rescue exercise-induced fatigue in dystrophin-deficient male mdx mice. Surprisingly, DDAH transgene expression did attenuate exercise-induced fatigue in dystrophin-heterozygous female mdx carrier mice. Improved exercise tolerance was associated with reduced heart weight and improved cardiac β-adrenergic responsiveness in DDAH-transgenic mdx carriers. We conclude that DDAH overexpression increases exercise tolerance in female DMD carriers, possibly by limiting cardiac pathology and preserving the heart's responses to changes in physiological demand. Methylated arginine metabolism may be a new target to improve exercise tolerance and cardiac function in DMD carriers or act as an adjuvant to promote NO signaling alongside therapies that partially restore dystrophin expression in patients with DMD.NEW & NOTEWORTHY Duchenne muscular dystrophy (DMD) carriers are at risk for cardiomyopathy. The nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is released from damaged muscle in DMD and impairs exercise performance. Transgenic expression of dimethylarginine dimethylaminohydrolase to degrade ADMA prevents cardiac hypertrophy, improves cardiac function, and improves exercise tolerance in DMD carrier mice. These findings highlight the relevance of ADMA to muscular dystrophy and have important implications for therapies targeting nitric oxide in patients with DMD and DMD carriers.

Long-term human IgG treatment improves heart and muscle function in a mouse model of Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease caused by mutations in the dystrophin gene, which leads to structural instability of the dystrophin-glycoprotein-complex with subsequent muscle degeneration. In addition, muscle inflammation has been implicated in disease progression and therapeutically addressed with glucocorticosteroids. These have numerous adverse effects. Treatment with human immunoglobulin G (IgG) improved clinical and para-clinical parameters in the early disease phase in the well-established mdx mouse model. The aim of the present study was to confirm the efficacy of IgG in a long-term pre-clinical study in mdx mice.

METHODS

IgG (2 g/kg body weight) or NaCl solution as control was administered monthly over 18 months by intraperitoneal injection in mdx mice beginning at 3 weeks of age. Several clinical outcome measures including endurance, muscle strength, and echocardiography were assessed. After 18 months, the animals were sacrificed, blood was collected for analysis, and muscle samples were obtained for ex vivo muscle contraction tests, quantitative PCR, and histology.

RESULTS

IgG significantly improved the daily voluntary running performance (1.9 m more total daily running distance, P < 0.0001) and slowed the decrease in grip strength by 0.1 mN, (P = 0.018). IgG reduced fatigability of the diaphragm (improved ratio to maximum force by 0.09 ± 0.04, P = 0.044), but specific tetanic force remained unchanged in the ex vivo muscle contraction test. Cardiac function was significantly better after IgG, especially fractional area shortening (P = 0.012). These results were accompanied by a reduction in cardiac fibrosis and the infiltration of T cells (P = 0.0002) and macrophages (P = 0.0027). In addition, treatment with IgG resulted in a significant reduction of the infiltration of T cells (P ≤ 0.036) in the diaphragm, gastrocnemius, quadriceps, and a similar trend in tibialis anterior and macrophages (P ≤ 0.045) in gastrocnemius, quadriceps, tibialis anterior, and a similar trend in the diaphragm, as well as a decrease in myopathic changes as reflected by a reduced central nuclear index in the diaphragm, tibialis anterior, and quadriceps (P ≤ 0.002 in all).

CONCLUSIONS

The present study underscores the importance of an inflammatory contribution to the disease progression of DMD. The data demonstrate the long-term efficacy of IgG in the mdx mouse. IgG is well tolerated by humans and could preferentially complement gene therapy in DMD. The data call for a clinical trial with IgG in DMD.

Vamorolone targets dual nuclear receptors to treat inflammation and dystrophic cardiomyopathy

Cardiomyopathy is a leading cause of death for Duchenne muscular dystrophy. Here, we find that the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) can share common ligands but play distinct roles in dystrophic heart and skeletal muscle pathophysiology. Comparisons of their ligand structures indicate that the Δ9,11 modification of the first-in-class drug vamorolone enables it to avoid interaction with a conserved receptor residue (N770/N564), which would otherwise activate transcription factor properties of both receptors. Reporter assays show that vamorolone and eplerenone are MR antagonists, whereas prednisolone is an MR agonist. Macrophages, cardiomyocytes, and CRISPR knockout myoblasts show vamorolone is also a dissociative GR ligand that inhibits inflammation with improved safety over prednisone and GR-specific deflazacort. In mice, hyperaldosteronism activates MR-driven hypertension and kidney phenotypes. We find that genetic dystrophin loss provides a second hit for MR-mediated cardiomyopathy in Duchenne muscular dystrophy model mice, as aldosterone worsens fibrosis, mass and dysfunction phenotypes. Vamorolone successfully prevents MR-activated phenotypes, whereas prednisolone activates negative MR and GR effects. In conclusion, vamorolone targets dual nuclear receptors to treat inflammation and cardiomyopathy with improved safety.

Speckle-Tracking Echocardiography in Children With Duchenne Muscular Dystrophy: A Prospective Multicenter Controlled Cross-Sectional Study

BACKGROUND

Prognosis of Duchenne muscular dystrophy (DMD) is related to cardiac dysfunction. Speckle-tracking echocardiographic (STE) imaging is emerging as a noninvasive functional biomarker to consider in the early detection of DMD-related cardiomyopathy. However, STE analysis has not been assessed in a prospectively controlled study, especially in presymptomatic children with DMD, and no study has used STE analysis in all three displacements (longitudinal, radial, and circumferential) and for both ventricles.

METHODS

This prospective controlled study enrolled 108 boys, 36 of whom had DMD (mean age, 11 ± 3.8 years) and 72 of whom were age-matched control subjects in a 1:2 case-control design. Conventional echocardiographic variables were collected for the left and right ventricles. STE analyses were performed in the longitudinal, radial, and circumferential displacements for the left ventricle and in the free wall longitudinal displacement for the right ventricle. The effect of age on the evolution of two-dimensional strain in children with DMD was studied by adding an interaction term, DMD × age, in the models.

RESULTS

Conventional echocardiographic measures were normal in both groups. Left ventricular (LV) ejection fraction ranged from 45% to 76% (mean, 63 ± 6%) in the DMD group and from 55% to 76% (mean, 64 ± 5%) in the control group. Global LV strain mean measures were significantly worse in the DMD group for the longitudinal (-16.8 ± 3.9% vs -20.6 ± 2.6%, P < .0001), radial (22.7 ± 11.3% vs 31.7 ± 14%, P = .002), and circumferential (-16.5 ± 3.8% vs -20.3 ± 3.1%, P < .0001) displacements. The decrease of global LV longitudinal strain with age in children with DMD was 0.34% per year more marked than that in control subjects. The LV inferolateral and anterolateral segments were specifically impaired, especially in the basal area. Right ventricular function evaluated using conventional echocardiography and STE analysis was normal and not different between children with DMD and control subjects.

CONCLUSIONS

The existence of altered LV strain despite normal LV function in children with DMD represents an important perspective for future pediatric drug trials in DMD-related cardiomyopathy prevention.

Dystrophin Cardiomyopathies: Clinical Management, Molecular Pathogenesis and Evolution towards Precision Medicine

Duchenne’s muscular dystrophy is an X-linked neuromuscular disease that manifests as muscle atrophy and cardiomyopathy in young boys. However, a considerable percentage of carrier females are often diagnosed with cardiomyopathy at an advanced stage. Existing therapy is not disease-specific and has limited effect, thus many patients and symptomatic carrier females prematurely die due to heart failure. Early detection is one of the major challenges that muscular dystrophy patients, carrier females, family members and, research and medical teams face in the complex course of dystrophic cardiomyopathy management. Despite the widespread adoption of advanced imaging modalities such as cardiac magnetic resonance, there is much scope for refining the diagnosis and treatment of dystrophic cardiomyopathy. This comprehensive review will focus on the pertinent clinical aspects of cardiac disease in muscular dystrophy while also providing a detailed consideration of the known and developing concepts in the pathophysiology of muscular dystrophy and forthcoming therapeutic options.

Role of neuronal nitric oxide synthase (nNOS) in Duchenne and Becker muscular dystrophies - Still a possible treatment modality?

Neuronal nitric oxide synthase (nNOS) is involved in nitric oxide (NO) production and suggested to play a crucial role in blood flow regulation of skeletal muscle. During activation of the muscle, NO helps attenuate the sympathetic vasoconstriction to accommodate increased metabolic demands, a phenomenon known as functional sympatholysis. In inherited myopathies such as the dystrophinopathies Duchenne and Becker muscle dystrophies (DMD and BMD), nNOS is lost from the sarcolemma. The loss of nNOS may cause functional ischemia contributing to skeletal and cardiac muscle cell injury. Effects of NO is augmented by inhibiting degradation of the second messenger cyclic guanosine monophosphate (cGMP) using sildenafil and tadalafil, both of which inhibit the enzyme phosphodiesterase 5 (PDE5). In animal models of DMD, PDE5-inhibitors prevent functional ischemia, reduce post-exercise skeletal muscle pathology and fatigue, show amelioration of cardiac muscle cell damage and increase cardiac performance. However, effect on clinical outcomes in DMD and BMD patients have been disappointing with minor effects on upper limb performance and none on ambulation. This review aims to summarize the current knowledge of nNOS function related to functional sympatholysis in skeletal muscle and studies on PDE5-inhibitor treatment in nNOS-deficient animal models and patients.

Ryanodine channel complex stabilizer compound S48168/ARM210 as a disease modifier in dystrophin-deficient mdx mice: proof-of-concept study and independent validation of efficacy

Muscle fibers lacking dystrophin undergo a long-term alteration of Ca2+ homeostasis, partially caused by a leaky Ca2+ release ryanodine (RyR) channel. S48168/ARM210, an RyR calcium release channel stabilizer (a Rycal compound), is expected to enhance the rebinding of calstabin to the RyR channel complex and possibly alleviate the pathologic Ca2+ leakage in dystrophin-deficient skeletal and cardiac muscle. This study systematically investigated the effect of S48168/ARM210 on the phenotype of mdx mice by means of a first proof-of-concept, short (4 wk), phase 1 treatment, followed by a 12-wk treatment (phase 2) performed in parallel by 2 independent laboratories. The mdx mice were treated with S48168/ARM210 at two different concentrations (50 or 10 mg/kg/d) in their drinking water for 4 and 12 wk, respectively. The mice were subjected to treadmill sessions twice per week (12 m/min for 30 min) to unmask the mild disease. This testing was followed by in vivo forelimb and hindlimb grip strength and fatigability measurement, ex vivo extensor digitorum longus (EDL) and diaphragm (DIA) force contraction measurement and histologic and biochemical analysis. The treatments resulted in functional (grip strength, ex vivo force production in DIA and EDL muscles) as well as histologic improvement after 4 and 12 wk, with no adverse effects. Furthermore, levels of cellular biomarkers of calcium homeostasis increased. Therefore, these data suggest that S48168/ARM210 may be a safe therapeutic option, at the dose levels tested, for the treatment of Duchenne muscular dystrophy (DMD).-Capogrosso, R. F., Mantuano, P., Uaesoontrachoon, K., Cozzoli, A., Giustino, A., Dow, T., Srinivassane, S., Filipovic, M., Bell, C., Vandermeulen, J., Massari, A. M., De Bellis, M., Conte, E., Pierno, S., Camerino, G. M., Liantonio, A., Nagaraju, K., De Luca, A. Ryanodine channel complex stabilizer compound S48168/ARM210 as a disease modifier in dystrophin-deficient mdx mice: proof-of-concept study and independent validation of efficacy.

A phase 3 randomized placebo-controlled trial of tadalafil for Duchenne muscular dystrophy

OBJECTIVE

To conduct a randomized trial to test the primary hypothesis that once-daily tadalafil, administered orally for 48 weeks, lessens the decline in ambulatory ability in boys with Duchenne muscular dystrophy (DMD).

METHODS

Three hundred thirty-one participants with DMD 7 to 14 years of age taking glucocorticoids were randomized to tadalafil 0.3 mg·kg^-1·d^-1, tadalafil 0.6 mg·kg^-1·d^-1, or placebo. The primary efficacy measure was 6-minute walk distance (6MWD) after 48 weeks. Secondary efficacy measures included North Star Ambulatory Assessment and timed function tests. Performance of Upper Limb (PUL) was a prespecified exploratory outcome.

RESULTS

Tadalafil had no effect on the primary outcome: 48-week declines in 6MWD were 51.0 ± 9.3 m with placebo, 64.7 ± 9.8 m with low-dose tadalafil (p = 0.307 vs placebo), and 59.1 ± 9.4 m with high-dose tadalafil (p = 0.538 vs placebo). Tadalafil also had no effect on secondary outcomes. In boys >10 years of age, total PUL score and shoulder subscore declined less with low-dose tadalafil than placebo. Adverse events were consistent with the known safety profile of tadalafil and the DMD disease state.

CONCLUSIONS

Tadalafil did not lessen the decline in ambulatory ability in boys with DMD. Further studies should be considered to confirm the hypothesis-generating upper limb data and to determine whether ambulatory decline can be slowed by initiation of tadalafil before 7 years of age.

CLINICALTRIALSGOV IDENTIFIER

NCT01865084.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that tadalafil does not slow ambulatory decline in 7- to 14-year-old boys with Duchenne muscular dystrophy.

A current approach to heart failure in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a genetic, progressive neuromuscular condition that is marked by the long-term muscle deterioration with significant implications of pulmonary and cardiac dysfunction. As such, end-stage heart failure (HF) in DMD is increasingly becoming the main cause of death in this population. The early detection of cardiomyopathy is often challenging, due to a long subclinical phase of ventricular dysfunction and difficulties in assessment of cardiovascular symptomatology in these patients who usually loose ambulation during the early adolescence. However, an early diagnosis of cardiovascular disease in patients with DMD is decisive since it allows a timely initiation of cardioprotective therapies that can mitigate HF symptoms and delay detrimental heart muscle remodelling. Echocardiography and ECG are standardly used for screening and detection of cardiovascular abnormalities in these patients, although these tools are not always adequate to detect an early, clinically asymptomatic phases of disease progression. In this regard, cardiovascular magnetic resonance (CMR) with late gadolinium enhancement is emerging as a promising method for the detection of early cardiac involvement in patients with DMD. The early detection of cardiac dysfunction allows the therapeutic institution of various classes of drugs such as corticosteroids, beta-blockers, ACE inhibitors, antimineralocorticoid diuretics and novel pharmacological and surgical solutions in the multimodal and multidisciplinary care for this group of patients. This review will focus on these challenges and available options for HF in patients with DMD.

Therapeutic strategies to address neuronal nitric oxide synthase deficiency and the loss of nitric oxide bioavailability in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy is a rare and fatal neuromuscular disease in which the absence of dystrophin from the muscle membrane induces a secondary loss of neuronal nitric oxide synthase and the muscles capacity for endogenous nitric oxide synthesis. Since nitric oxide is a potent regulator of skeletal muscle metabolism, mass, function and regeneration, the loss of nitric oxide bioavailability is likely a key contributor to the chronic pathological wasting evident in Duchenne Muscular Dystrophy. As such, various therapeutic interventions to re-establish either the neuronal nitric oxide synthase protein deficit or the consequential loss of nitric oxide synthesis and bioavailability have been investigated in both animal models of Duchenne Muscular Dystrophy and in human clinical trials. Notably, the efficacy of these interventions are varied and not always translatable from animal model to human patients, highlighting a complex interplay of factors which determine the downstream modulatory effects of nitric oxide. We review these studies herein.

Attempting to Compensate for Reduced Neuronal Nitric Oxide Synthase Protein with Nitrate Supplementation Cannot Overcome Metabolic Dysfunction but Rather Has Detrimental Effects in Dystrophin-Deficient mdx Muscle

Duchenne muscular dystrophy arises from the loss of dystrophin and is characterized by calcium dysregulation, muscular atrophy, and metabolic dysfunction. The secondary reduction of neuronal nitric oxide synthase (nNOS) from the sarcolemma reduces NO production and bioavailability. As NO modulates glucose uptake, metabolism, and mitochondrial bioenergetics, we investigated whether an 8-week nitrate supplementation regimen could overcome metabolic dysfunction in the mdx mouse. Dystrophin-positive control (C57BL/10) and dystrophin-deficient mdx mice were supplemented with sodium nitrate (85 mg/l) in drinking water. Following the supplementation period, extensor digitorum longus and soleus were excised and radioactive glucose uptake was measured at rest (basal) and during contraction. Gastrocnemius was excised and mitochondrial respiration was measured using the Oroboros Oxygraph. Tibialis anterior was analyzed immunohistochemically for the presence of dystrophin, nNOS, nitrotyrosine, IgG and CD45+ cells, and histologically to assess areas of damage and regeneration. Glucose uptake in the basal and contracting states was normal in unsupplemented mdx muscles but was reduced following nitrate supplementation in mdx muscles only. The mitochondrial utilization of substrates was also impaired in mdx gastrocnemius during phosphorylating and maximal uncoupled respiration, and nitrate could not improve respiration in mdx muscle. Although nitrate supplementation reduced mitochondrial hydrogen peroxide emission, it induced mitochondrial uncoupling in red gastrocnemius, increased muscle fiber peroxynitrite (nitrotyrosine), and promoted skeletal muscle damage. Our novel data suggest that despite lower nNOS protein expression and likely lower NO production in mdx muscle, enhancing NO production with nitrate supplementation in these mice has detrimental effects on skeletal muscle. This may have important relevance for those with DMD.

Outside in: The matrix as a modifier of muscular dystrophy

Muscular dystrophies are genetic conditions leading to muscle degeneration and often, impaired regeneration. Duchenne Muscular Dystrophy is a prototypical form of muscular dystrophy, and like other forms of genetically inherited muscle diseases, pathological progression is variable. Variability in muscular dystrophy can arise from differences in the manner in which the primary mutation impacts the affected protein's function; however, clinical heterogeneity also derives from secondary mutations in other genes that can enhance or reduce pathogenic features of disease. These genes, called genetic modifiers, regulate the pathophysiological context of dystrophic degeneration and regeneration. Understanding the mechanistic links between genetic modifiers and dystrophic progression sheds light on pathologic remodeling, and provides novel avenues to therapeutically intervene to reduce muscle degeneration. Based on targeted genetic approaches and unbiased genomewide screens, several modifiers have been identified for muscular dystrophy, including extracellular agonists of signaling cascades. This review will focus on identification and possible mechanisms of recently identified modifiers for muscular dystrophy, including osteopontin, latent TGFβ binding protein 4 (LTBP4) and Jagged1. Moreover, we will review the investigational approaches that aim to target modifier pathways and thereby counteract dystrophic muscle wasting.

Nonsteroidal Anti-Inflammatory Therapy: A Journey Toward Safety

The efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) against inflammation, pain, and fever has been supporting their worldwide use in the treatment of painful conditions and chronic inflammatory diseases until today. However, the long-term therapy with NSAIDs was soon associated with high incidences of adverse events in the gastrointestinal tract. Therefore, the search for novel drugs with improved safety has begun with COX-2 selective inhibitors (coxibs) being straightaway developed and commercialized. Nevertheless, the excitement has fast turned to disappointment when diverse coxibs were withdrawn from the market due to cardiovascular toxicity. Such events have once again triggered the emergence of different strategies to overcome NSAIDs toxicity. Here, an integrative review is provided to address the breakthroughs of two main approaches: (i) the association of NSAIDs with protective mediators and (ii) the design of novel compounds to target downstream and/or multiple enzymes of the arachidonic acid cascade. To date, just one phosphatidylcholine-associated NSAID has already been approved for commercialization. Nevertheless, the preclinical and clinical data obtained so far indicate that both strategies may improve the safety of nonsteroidal anti-inflammatory therapy.

Evolving therapeutic strategies to improve nonsteroidal anti-inflammatory drug safety

Nonsteroidal anti-inflammatory drugs (NSAIDs) possess potent anti-inflammatory and analgesic properties through inhibition of cyclooxygenase enzymes (COX-1 and COX-2), which are responsible for synthesis of proinflammatory mediators. NSAIDs are frequently used for treatment of acute and chronic pain conditions. However, their use is associated with serious dose-dependent gastrointestinal (GI), cardiovascular, renal, and hepatic adverse effects, which pose a serious clinical concern for both patients and physicians. During the past 2 decades, approaches to improving the tolerability of NSAIDs were mainly directed toward discovery of COX-2 selective NSAIDs (coxibs), which were expected to minimize the risk of GI injury. Unfortunately, the results from multiple clinical studies have shown that treatment with coxibs may increase the risk for cardiovascular complications. This review summarizes current strategies used to reduce the toxicity of NSAIDs and outlines novel therapeutic approaches still in preclinical development. To minimize the risk of GI ulcerations and bleeding, combination therapies with gastroprotective agents are currently recommended. The new therapeutic agents anticipated to have similar effects include nitric oxide- and hydrogen sulfide-releasing NSAIDs. Novel manufacturing technologies enhance dissolution and absorption of NSAID products, allowing for their administration at low doses, which could lead to improved drug tolerability without diminishing the analgesic and anti-inflammatory efficacy of NSAIDs. This principle is in line with the current recommendation by the US Food and Drug Administration that NSAIDs should be used at the lowest effective dosage. Finally, NSAID formulations targeted directly to the site of inflammation are expected to reduce systemic drug exposure and thus decrease the risk of systemic adverse effects.

Deletion of Galgt2 (B4Galnt2) reduces muscle growth in response to acute injury and increases muscle inflammation and pathology in dystrophin-deficient mice

Transgenic overexpression of Galgt2 (official name B4Galnt2) in skeletal muscle stimulates the glycosylation of α dystroglycan (αDG) and the up-regulation of laminin α2 and dystrophin surrogates known to inhibit muscle pathology in mouse models of congenital muscular dystrophy 1A and Duchenne muscular dystrophy. Skeletal muscle Galgt2 gene expression is also normally increased in the mdx mouse model of Duchenne muscular dystrophy compared with the wild-type mice. To assess whether this increased endogenous Galgt2 expression could affect disease, we quantified muscular dystrophy measures in mdx mice deleted for Galgt2 (Galgt2(-/-)mdx). Galgt2(-/-) mdx mice had increased heart and skeletal muscle pathology and inflammation, and also worsened cardiac function, relative to age-matched mdx mice. Deletion of Galgt2 in wild-type mice also slowed skeletal muscle growth in response to acute muscle injury. In each instance where Galgt2 expression was elevated (developing muscle, regenerating muscle, and dystrophic muscle), Galgt2-dependent glycosylation of αDG was also increased. Overexpression of Galgt2 failed to inhibit skeletal muscle pathology in dystroglycan-deficient muscles, in contrast to previous studies in dystrophin-deficient mdx muscles. This study demonstrates that Galgt2 gene expression and glycosylation of αDG are dynamically regulated in muscle and that endogenous Galgt2 gene expression can ameliorate the extent of muscle pathology, inflammation, and dysfunction in mdx mice.

Phenylbutazone induces expression of MBNL1 and suppresses formation of MBNL1-CUG RNA foci in a mouse model of myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is caused by abnormal expansion of CTG repeats in the 3′ untranslated region of the DMPK gene. Expanded CTG repeats are transcribed into RNA and make an aggregate with a splicing regulator, MBNL1, in the nucleus, which is called the nuclear foci. The nuclear foci sequestrates and downregulates availability of MBNL1. Symptomatic treatments are available for DM1, but no rational therapy is available. In this study, we found that a nonsteroidal anti-inflammatory drug (NSAID), phenylbutazone (PBZ), upregulated the expression of MBNL1 in C2C12 myoblasts as well as in the HSA^LR mouse model for DM1. In the DM1 mice model, PBZ ameliorated aberrant splicing of Clcn1, Nfix, and Rpn2. PBZ increased expression of skeletal muscle chloride channel, decreased abnormal central nuclei of muscle fibers, and improved wheel-running activity in HSA^LR mice. We found that the effect of PBZ was conferred by two distinct mechanisms. First, PBZ suppressed methylation of an enhancer region in Mbnl1 intron 1, and enhanced transcription of Mbnl1 mRNA. Second, PBZ attenuated binding of MBNL1 to abnormally expanded CUG repeats in cellulo and in vitro. Our studies suggest that PBZ is a potent therapeutic agent for DM1 that upregulates availability of MBNL1.

Nicorandil, a Nitric Oxide Donor and ATP-Sensitive Potassium Channel Opener, Protects Against Dystrophin-Deficient Cardiomyopathy

BACKGROUND

Dystrophin-deficient cardiomyopathy is a growing clinical problem without targeted treatments. We investigated whether nicorandil promotes cardioprotection in human dystrophin-deficient induced pluripotent stem cell (iPSC)-derived cardiomyocytes and the muscular dystrophy mdx mouse heart.

METHODS AND RESULTS

Dystrophin-deficient iPSC-derived cardiomyocytes had decreased levels of endothelial nitric oxide synthase and neuronal nitric oxide synthase. The dystrophin-deficient cardiomyocytes had increased cell injury and death after 2 hours of stress and recovery. This was associated with increased levels of reactive oxygen species and dissipation of the mitochondrial membrane potential. Nicorandil pretreatment was able to abolish these stress-induced changes through a mechanism that involved the nitric oxide-cyclic guanosine monophosphate pathway and mitochondrial adenosine triphosphate-sensitive potassium channels. The increased reactive oxygen species levels in the dystrophin-deficient cardiomyocytes were associated with diminished expression of select antioxidant genes and increased activity of xanthine oxidase. Furthermore, nicorandil was found to improve the restoration of cardiac function after ischemia and reperfusion in the isolated mdx mouse heart.

CONCLUSION

Nicorandil protects against stress-induced cell death in dystrophin-deficient cardiomyocytes and preserves cardiac function in the mdx mouse heart subjected to ischemia and reperfusion injury. This suggests a potential therapeutic role for nicorandil in dystrophin-deficient cardiomyopathy.

Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy

Becker muscular dystrophy (BMD) is a progressive X-linked muscle wasting disease for which there is no treatment. BMD is caused by in-frame mutations in the gene encoding dystrophin, a structural cytoskeletal protein that also targets other proteins to the sarcolemma. Among these is neuronal nitric oxide synthase mu (nNOSμ), which requires specific spectrin-like repeats (SR16/17) in dystrophin's rod domain and the adaptor protein α-syntrophin for sarcolemmal targeting. When healthy skeletal muscle is exercised, sarcolemmal nNOSμ-derived nitric oxide (NO) attenuates α-adrenergic vasoconstriction, thus optimizing perfusion. In the mdx mouse model of dystrophinopathy, this protective mechanism (functional sympatholysis) is defective, resulting in functional muscle ischaemia. Treatment with a NO-donating non-steroidal anti-inflammatory drug (NSAID) alleviates this ischaemia and improves the murine dystrophic phenotype. In the present study, we report that, in 13 men with BMD, sympatholysis is defective mainly in patients whose mutations disrupt sarcolemmal targeting of nNOSμ, with the vasoconstrictor response measured as a decrease in muscle oxygenation (near infrared spectroscopy) to reflex sympathetic activation. Then, in a single-arm, open-label trial in 11 BMD patients and a double-blind, placebo-controlled cross-over trial in six patients, we show that acute treatment with oral sodium nitrate, an inorganic NO donor without a NSIAD moiety, restores sympatholysis and improves post-exercise hyperaemia (Doppler ultrasound). By contrast, sodium nitrate improves neither sympatholysis, nor hyperaemia in healthy controls. Thus, a simple NO donor recapitulates the vasoregulatory actions of sarcolemmal nNOS in BMD patients, and constitutes a putative novel therapy for this disease.

Enhancement of Muscle T Regulatory Cells and Improvement of Muscular Dystrophic Process in mdx Mice by Blockade of Extracellular ATP/P2X Axis

Infiltration of immune cells and chronic inflammation substantially affect skeletal and cardiac muscle degeneration in Duchenne muscular dystrophy. In the immune system, extracellular adenosine triphosphate (ATP) released by dying cells is sensed as a danger associated molecular pattern through P2 purinergic receptors. Specifically, the P2X7 subtype has a prominent role in regulating immune system physiology and contributes to inflammasome activation also in muscle cells. Here, we show that in vivo blockade of the extracellular ATP/P2X purinergic signaling pathway by periodate-oxidized ATP delayed the progression of the dystrophic phenotype and dampened the local inflammatory response in mdx mice, a spontaneous mouse model of dystrophin deficiency. Reduced infiltration of leukocytes and macrophages and decreased expression of IL-6 were revealed in the muscles of periodate-oxidized ATP-treated mdx mice. Concomitantly, an increase in Foxp3(+) immunosuppressive regulatory T cells was observed and correlated with enhanced myofiber regeneration. Moreover, we detected reduced concentrations of profibrotic cytokines, including transforming growth factor-β and connective tissue growth factor, in muscles of periodate-oxidized ATP-treated mdx mice. The improvement of inflammatory features was associated with increased strength and reduced necrosis, thus suggesting that pharmacologic purinergic antagonism altering the adaptive immune component in the muscle infiltrates might represent a promising therapeutic approach in Duchenne muscular dystrophy.

Naproxcinod shows significant advantages over naproxen in the mdx model of Duchenne Muscular Dystrophy

Background

In dystrophin-deficient muscles of Duchenne Muscular Dystrophy (DMD) patients and the mdx mouse model, nitric oxide (NO) signalling is impaired. Previous studies have shown that NO-donating drugs are beneficial in dystrophic mouse models. Recently, a long-term treatment (9 months) of mdx mice with naproxcinod, an NO-donating naproxen, has shown a significant improvement of the dystrophic phenotype with beneficial effects present throughout the disease progression. It remains however to be clearly dissected out which specific effects are due to the NO component compared with the anti-inflammatory activity associated with naproxen. Understanding the contribution of NO vs the anti-inflammatory effect is important, in view of the potential therapeutic perspective, and this is the final aim of this study.

Methods

Five-week-old mdx mice received either naproxcinod (30 mg/kg) or the equimolar dose of naproxen (20 mg/kg) in the diet for 6 months. Control mdx mice were used as reference. Treatments (or vehicle for control groups) were administered daily in the diet. For the first 3 months the study was performed in sedentary animals, then all mice were subjected to exercise until the sixth month. Skeletal muscle force was assessed by measuring whole body tension in sedentary animals as well as in exercised mice and resistance to fatigue was measured after 3 months of running exercise. At the end of 6 months of treatment, animals were sacrificed for histological analysis and measurement of naproxen levels in blood and skeletal muscle.

Results

Naproxcinod significantly ameliorated skeletal muscle force and resistance to fatigue in sedentary as well as in exercised mice, reduced inflammatory infiltrates and fibrosis deposition in both cardiac and diaphragm muscles. Conversely, the equimolar dose of naproxen showed no effects on fibrosis and improved muscle function only in sedentary mice, while the beneficial effects in exercised mice were lost demonstrating a limited and short-term effect.

Conclusion

In conclusion, this study shows that NO donation may have an important role, in addition to anti-inflammatory activity, in slowing down the progression of the disease in the mdx mouse model therefore positioning naproxcinod as a promising candidate for treatment of DMD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-015-0311-0) contains supplementary material, which is available to authorized users.

Drug Discovery of Therapies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a genetic, lethal, muscle disorder caused by the loss of the muscle protein, dystrophin, leading to progressive loss of muscle fibers and muscle weakness. Drug discovery efforts targeting DMD have used two main approaches: (1) the restoration of dystrophin expression or the expression of a compensatory protein, and (2) the mitigation of downstream pathological mechanisms, including dysregulated calcium homeostasis, oxidative stress, inflammation, fibrosis, and muscle ischemia. The aim of this review is to introduce the disease, its pathophysiology, and the available research tools to a drug discovery audience. This review will also detail the most promising therapies that are currently being tested in clinical trials or in advanced preclinical models.

Physical exercise associated with NO production: signaling pathways and significance in health and disease

Here we review available data on nitric oxide (NO)-mediated signaling in skeletal muscle during physical exercise. Nitric oxide modulates skeletal myocyte function, hormone regulation, and local microcirculation. Nitric oxide underlies the therapeutic effects of physical activity whereas the pharmacological modulators of NO-mediated signaling are the promising therapeutic agents in different diseases. Nitric oxide production increases in skeletal muscle in response to physical activity. This molecule can alter energy supply in skeletal muscle through hormonal modulation. Mitochondria in skeletal muscle tissue are highly abundant and play a pivotal role in metabolism. Considering NO a plausible regulator of mitochondrial biogenesis that directly affects cellular respiration, we discuss the mechanisms of NO-induced mitochondrial biogenesis in the skeletal muscle cells. We also review available data on myokines, the molecules that are expressed and released by the muscle fibers and exert autocrine, paracrine and/or endocrine effects. The article suggests the presence of putative interplay between NO-mediated signaling and myokines in skeletal muscle. Data demonstrate an important role of NO in various diseases and suggest that physical training may improve health of patients with diabetes, chronic heart failure, and even degenerative muscle diseases. We conclude that NO-associated signaling represents a promising target for the treatment of various diseases and for the achievement of better athletic performance.

Nitric oxide synthase deficiency and the pathophysiology of muscular dystrophy

The secondary loss of neuronal nitric oxide synthase (nNOS) that occurs in dystrophic muscle is the basis of numerous, complex and interacting features of the dystrophic pathology that affect not only muscle itself, but also influence the interaction of muscle with other tissues. Many mechanisms through which nNOS deficiency contributes to misregulation of muscle development, blood flow, fatigue, inflammation and fibrosis in dystrophic muscle have been identified, suggesting that normalization in NO production could greatly attenuate diverse aspects of the pathology of muscular dystrophy through multiple regulatory pathways. However, the relative importance of the loss of nNOS from the sarcolemma versus the importance of loss of total nNOS from dystrophic muscle remains unknown. Although most current evidence indicates that nNOS localization at the sarcolemma is not required to achieve NO-mediated reductions of pathology in muscular dystrophy, the question remains open concerning whether membrane localization would provide a more efficient rescue from features of the dystrophic phenotype.

Arginine butyrate per os protects mdx mice against cardiomyopathy, kyphosis and changes in axonal excitability

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by lack of dystrophin, a sub-sarcolemmal protein, which leads to dramatic muscle deterioration. We studied in mdx mice, the effects of oral administration of arginine butyrate (AB), a compound currently used for the treatment of sickle cell anemia in children, on cardiomyopathy, vertebral column deformation and electromyographic abnormalities. Monthly follow-up by echocardiography from the 8th month to the 14th month showed that AB treatment protected the mdx mice against drastic reduction (20-23%) of ejection fraction and fractional shortening, and also against the ≈20% ventricular dilatation and 25% cardiac hypertrophy observed in saline-treated mdx mice. The phenotypic improvement was corroborated by the decrease in serum CK level and by better fatigue resistance. Moreover, AB treatment protected against the progressive spinal deformity observed in mdx mice, another similarity with DMD patients. The value of the kyphosis index in AB-treated mice reached 94% of the value in C57BL/10 mice. Finally, axonal excitability parameters such as the membrane resting potential, the threshold and amplitude of the action potential, the absolute and relative refractory periods and the supernormal and subnormal periods, recorded from caudal and plantar muscles in response to excitability tests, that were modified in saline-treated mdx mice were not significantly changed, compared with wild-type animals, in AB-treated mdx mice. All of these results suggest that AB could be a potential treatment for DMD patients.