The Usefulness of Determining Plasma and Tissue Concentrations of Phosphorodiamidate Morpholino Oligonucleotides to Estimate Their Efficacy in Duchenne Muscular Dystrophy Patients.

Currently, four kinds of phosphorodiamidate morpholino oligomers (PMOs), such as viltolarsen, have been approved for the treatment of Duchenne muscular dystrophy (DMD); however, it is unclear whether human efficacy can be estimated using plasma concentrations. This study summarizes the tissue distribution of viltolarsen in mice and cynomolgus monkeys and evaluates the relationship between exposure and efficacy based on exon skipping. In the tissue distribution studies, all muscles in DMD-model mice showed higher concentrations of viltolarsen than those in wild-type mice and cynomolgus monkeys, and the concentrations in skeletal muscle were correlated with the exon-skipping efficiency in mice and cynomolgus monkeys. In addition, a highly sensitive bioanalytical method using liquid chromatography with tandem mass spectrometry shows promise for determining plasma concentrations up to a later time point, and the tissue (muscle)/plasma concentration ratio (Kp) in DMD-model mice was shown to be useful for predicting changes in pharmacodynamic (PD) markers in humans. Our results suggest that pharmacokinetic (PK)/PD analysis can be conducted by using the human PK profile or Kp values and skipping efficiency in DMD-model mice. This information will be useful for the efficient and effective development of PMOs as therapeutic agents. SIGNIFICANCE STATEMENT: We evaluated the relationship between the plasma or tissue concentrations and the efficiency of exon skipping for viltolarsen as an example phosphorodiamidate morpholino oligomers in the skeletal and cardiac muscle of mice and cynomolgus monkeys for pharmacokinetic/pharmacodynamic (PK/PD) analysis. The results suggest that PK/PD analysis can be conducted by using the human PK profile or tissue (muscle)/plasma concentration ratios and skipping efficiency in DMD-model mice.

Serum biomarkers associated with baseline clinical severity in young steroid-naïve Duchenne muscular dystrophy boys.

Duchenne muscular dystrophy (DMD) is caused by loss of dystrophin in muscle, and while all patients share the primary gene and biochemical defect, there is considerable patient-patient variability in clinical symptoms. We sought to develop multivariate models of serum protein biomarkers that explained observed variation, using functional outcome measures as proxies for severity. Serum samples from 39 steroid-naïve DMD boys 4 to <7 years enrolled into a clinical trial of vamorolone were studied (NCT02760264). Four assessments of gross motor function were carried out for each participant over a 6-week interval, and their mean was used as response for biomarker models. Weighted correlation network analysis was used for unsupervised clustering of 1305 proteins quantified using SOMAscan® aptamer profiling to define highly representative and connected proteins. Multivariate models of biomarkers were obtained for time to stand performance (strength phenotype; 17 proteins) and 6 min walk performance (endurance phenotype; 17 proteins) including some shared proteins. Identified proteins were tested with associations of mRNA expression with histological severity of muscle from dystrophinopathy patients (n = 28) and normal controls (n = 6). Strong associations predictive of both clinical and histological severity were found for ERBB4 (reductions in both blood and muscle with increasing severity), SOD1 (reductions in muscle and increases in blood with increasing severity) and CNTF (decreased levels in blood and muscle with increasing severity). We show that performance of DMD boys was effectively modeled with serum proteins, proximal strength associated with growth and remodeling pathways and muscle endurance centered on TGFß and fibrosis pathways in muscle.

Longitudinal metabolomic analysis of plasma enables modeling disease progression in Duchenne muscular dystrophy mouse models.

Duchenne muscular dystrophy is a severe pediatric neuromuscular disorder caused by the lack of dystrophin. Identification of biomarkers is needed to support and accelerate drug development. Alterations of metabolites levels in muscle and plasma have been reported in pre-clinical and clinical cross-sectional comparisons. We present here a 7-month longitudinal study comparing plasma metabolomic data in wild-type and mdx mice. A mass spectrometry approach was used to study metabolites in up to five time points per mouse at 6, 12, 18, 24 and 30 weeks of age, providing an unprecedented in depth view of disease trajectories. A total of 106 metabolites were studied. We report a signature of 31 metabolites able to discriminate between healthy and disease at various stages of the disease, covering the acute phase of muscle degeneration and regeneration up to the deteriorating phase. We show how metabolites related to energy production and chachexia (e.g. glutamine) are affected in mdx mice plasma over time. We further show how the signature is connected to molecular targets of nutraceuticals and pharmaceutical compounds currently in development as well as to the nitric oxide synthase pathway (e.g. arginine and citrulline). Finally, we evaluate the signature in a second longitudinal study in three independent mouse models carrying 0, 1 or 2 functional copies of the dystrophin paralog utrophin. In conclusion, we report an in-depth metabolomic signature covering previously identified associations and new associations, which enables drug developers to peripherally assess the effect of drugs on the metabolic status of dystrophic mice.

Serum Antibodies to N-Glycolylneuraminic Acid Are Elevated in Duchenne Muscular Dystrophy and Correlate with Increased Disease Pathology in Cmah-/-mdx Mice.

Humans cannot synthesize the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc) because of an inactivating deletion in the cytidine-5'-monophospho-(CMP)-N-acetylneuraminic acid hydroxylase (CMAH) gene responsible for its synthesis. Human Neu5Gc deficiency can lead to development of anti-Neu5Gc serum antibodies, the levels of which can be affected by Neu5Gc-containing diets and by disease. Metabolic incorporation of dietary Neu5Gc into human tissues in the face of circulating antibodies against Neu5Gc-bearing glycans is thought to exacerbate inflammation-driven diseases like cancer and atherosclerosis. Probing of sera with sialoglycan arrays indicated that patients with Duchenne muscular dystrophy (DMD) had a threefold increase in overall anti-Neu5Gc antibody titer compared with age-matched controls. These antibodies recognized a broad spectrum of Neu5Gc-containing glycans. Human-like inactivation of the Cmah gene in mice is known to modulate severity in a variety of mouse models of human disease, including the X chromosome-linked muscular dystrophy (mdx) model for DMD. Cmah-/-mdx mice can be induced to develop anti-Neu5Gc-glycan antibodies as humans do. The presence of anti-Neu5Gc antibodies, in concert with induced Neu5Gc expression, correlated with increased severity of disease pathology in Cmah-/-mdx mice, including increased muscle fibrosis, expression of inflammatory markers in the heart, and decreased survival. These studies suggest that patients with DMD who harbor anti-Neu5Gc serum antibodies might exacerbate disease severity when they ingest Neu5Gc-rich foods, like red meats.

Lipocalin 2 Influences Bone and Muscle Phenotype in the MDX Mouse Model of Duchenne Muscular Dystrophy.

Lipocalin 2 (Lcn2) is an adipokine involved in bone and energy metabolism. Its serum levels correlate with bone mechanical unloading and inflammation, two conditions representing hallmarks of Duchenne Muscular Dystrophy (DMD). Therefore, we investigated the role of Lcn2 in bone loss induced by muscle failure in the MDX mouse model of DMD. We found increased Lcn2 serum levels in MDX mice at 1, 3, 6, and 12 months of age. Consistently, Lcn2 mRNA was higher in MDX versus WT muscles. Immunohistochemistry showed Lcn2 expression in mononuclear cells between muscle fibres and in muscle fibres, thus confirming the gene expression results. We then ablated Lcn2 in MDX mice, breeding them with Lcn2-/- mice (MDXxLcn2-/-), resulting in a higher percentage of trabecular volume/total tissue volume compared to MDX mice, likely due to reduced bone resorption. Moreover, MDXxLcn2-/- mice presented with higher grip strength, increased intact muscle fibres, and reduced serum creatine kinase levels compared to MDX. Consistently, blocking Lcn2 by treating 2-month-old MDX mice with an anti-Lcn2 monoclonal antibody (Lcn2Ab) increased trabecular volume, while reducing osteoclast surface/bone surface compared to MDX mice treated with irrelevant IgG. Grip force was also increased, and diaphragm fibrosis was reduced by the Lcn2Ab. These results suggest that Lcn2 could be a possible therapeutic target to treat DMD-induced bone loss.

Generation of microRNA-378a-deficient hiPSC as a novel tool to study its role in human cardiomyocytes.

microRNA-378a (miR-378a) is one of the most highly expressed microRNAs in the heart. However, its role in the human cardiac tissue has not been fully understood. It was observed that miR-378a protects cardiomyocytes from hypertrophic growth by regulation of IGF1R and the expression of downstream kinases. Increased levels of miR-378a were reported in the serum of Duchenne muscular dystrophy (DMD) patients and female carriers of DMD gene-associated mutations with developed cardiomyopathy. In order to shed more light on the role of miR-378a in human cardiomyocytes and its potential involvement in DMD-related cardiomyopathy, we generated two human induced pluripotent stem cell (hiPSC) models; one with deletion of miR-378a and the second one with deletion of DMD exon 50 leading to the DMD phenotype. Our results indicate that lack of miR-378a does not influence the pluripotency of hiPSC and their ability to differentiate into cardiomyocytes (hiPSC-CM). miR-378a-deficient hiPSC-CM exhibited, however, significantly bigger size compared to the isogenic control cells, indicating the role of this miRNA in the hypertrophic growth of human cardiomyocytes. In accordance, the level of NFATc3, phosphoAKT, phosphoERK and ERK was higher in these cells compared to the control counterparts. A similar effect was achieved by silencing miR-378a with antagomirs. Of note, the percentage of cells with nuclear localization of NFATc3 was higher in miR-378a-deficient hiPSC-CM. Analysis of electrophysiological properties and Ca2+ oscillations revealed the decrease in the spike slope velocity and lower frequency of calcium spikes in miR-378a-deficient hiPSC-CM. Interestingly, the level of miR-378a increased gradually during cardiac differentiation of hiPSC. Of note, it was low until day 15 in differentiating DMD-deficient hiPSC-CM and then rose to a similar level as in the isogenic control counterparts. In summary, our findings confirmed the utility of hiPSC-based models for deciphering the role of miR-378a in the control and diseased human cardiomyocytes.

Elevation of fast but not slow troponin I in the circulation of patients with Becker and Duchenne muscular dystrophy.

INTRODUCTION: One of the hallmarks of injured skeletal muscle is the appearance of elevated skeletal muscle proteins in circulation. Human skeletal muscle generally consists of a mosaic of slow (type I) and fast (type IIa, IIx/d) fibers, defined by their myosin isoform expression. Recently, measurement of circulating fiber-type specific isoforms of troponin I has been used as a biomarker to suggest that muscle injury in healthy volunteers (HV) results in the appearance of muscle proteins from fast but not slow fibers. We sought to understand if this is also the case in severe myopathy patients with Becker and Duchenne muscular dystrophy (BMD, DMD). METHODS: An enzyme-linked immunosorbent assay (ELISA) that selectively measures fast and slow skeletal troponin I (TNNI2 and TNNI1) was used to measure a cross-section of patient plasma samples from HV (N = 50), BMD (N = 49), and DMD (N = 132) patients. Creatine kinase (CK) activity was also measured from the same samples for comparison. RESULTS: TNNI2 was elevated in BMD and DMD and correlated with the injury biomarker, CK. In contrast, TNNI1 levels were indistinguishable from levels in HV. There was an inverse relationship between CK and TNNI2 levels and age, but no relationship for TNNI1. DISCUSSION: We define a surprising discrepancy between TNNI1 and TNNI2 in patient plasma that may have implications for the interpretation of elevated muscle protein levels in dystrophinopathies.

Safety, feasibility, and efficacy of strengthening exercise in Duchenne muscular dystrophy.

BACKGROUND: This two-part study explored the safety, feasibility, and efficacy of a mild-moderate resistance isometric leg exercise program in ambulatory boys with Duchenne muscular dystrophy (DMD). METHODS: First, we used a dose escalation paradigm with varying intensity and frequency of leg isometric exercise to determine the dose response and safety in 10 boys. Second, we examined safety and feasibility of a 12-wk in-home, remotely supervised, mild-moderate intensity strengthening program in eight boys. Safety measures included T2 MRI, creatine kinase levels, and pain. Peak strength and function (time to ascend/descend four stairs) were also measured. RESULTS: Dose-escalation revealed no signs of muscle damage. Seven of the eight boys completed the 12-wk in-home program with a compliance of 84.9%, no signs of muscle damage, and improvements in strength (knee extensors P < .01; knee flexors P < .05) and function (descending steps P < .05). CONCLUSIONS: An in-home, mild-moderate intensity leg exercise program is safe with potential to positively impact both strength and function in ambulatory boys with DMD.

Kidney involvement and associated risk factors in children with Duchenne muscular dystrophy.

BACKGROUND: Kidney dysfunction is a common complication in adults with Duchenne muscular dystrophy (DMD); however, little attention has been paid to kidney function in pediatric patients. METHODS: Medical records of patients with DMD who were followed up for ≥ 12 months were retrospectively reviewed. Inclusion criteria were (i) aged 5-18 years, (ii) proven mutations in the dystrophin gene, and (iii) absence of structural anomalies of the kidney and urinary tract. Serum creatine kinase (CK) was used as an indirect marker of muscle destruction. RESULTS: Forty-four patients (mean age, 10.9 ± 3.3 years) were included. Blood pressure was evaluated by 24-h ambulatory blood pressure monitoring in 28 patients. Hypertension was found in 9 (32.1%), eight of whom were using steroids. Mild proteinuria, hypercalciuria, hypocalciuria, and hyperphosphaturia in 24-h urine collection (n = 36) were detected in 3 (8.3%), 5 (13.9%), 7 (19.7%), and 6 (16.7%) patients, respectively. Twenty-one (58.3%) demonstrated hyperuricosuria, associated with hyperuricemia in 4. Logarithmic cystatin C (CysC) had a positive correlation to creatinine (Cr) (p = 0.001, r = 0.54), CK (p = 0.048, r = 0.30), and parathormone (PTH) (p = 0.001, r = 0.49). Moreover, the patients were divided into two groups according to median CysC value: group 1 (n = 20, CysC ≤ 0.76 mg/l) and group 2 (n = 24, CysC > 0.76 mg/l). Mean CK, PTH, and Cr levels were significantly elevated in group 2 compared with group 1 (p = 0.010, 0.033, and 0.023, respectively). CONCLUSIONS: Long-term exposure to the excessive burden of intracellular components released from damaged muscles may be associated with an increased risk over time of chronic kidney impairment in pediatric DMD patients. Graphical abstract.

Evaluating RANKL and OPG levels in patients with Duchenne muscular dystrophy.

RANKL-OPG should be explored in DMD patients to potentially provide targeted therapy. We quantified RANKL and OPG levels in DMD patients compared with controls. RANKL, OPG, and RANKL:OPG significantly declined with age in DMD patients suggesting some bone turnover markers are difficult to assess or use as therapeutic indicators. INTRODUCTION: Osteoporosis in Duchenne muscular dystrophy (DMD) is multi-factorial in nature with high prevalence of fractures. RANKL-OPG should be explored to potentially provide targeted therapy for these patients. We quantified RANKL, OPG, and RANKL:OPG levels in DMD patients compared with controls and analyzed the influence of age, glucocorticoid use, ambulatory status, bone density, and fracture history. METHODS: DMD patients were enrolled at CHLA. Controls were recruited from general pediatric clinic and in collaboration with samples from a previously completed study. Free soluble RANKL and OPG levels were quantified using a sandwich ELISA. RESULTS: Fifty DMD patients and 50 controls were enrolled. DMD patients had a significant decline in RANKL, OPG, and RANKL:OPG with age (p = < 0.0001, p = 0.026, and p = 0.002, respectively) while healthy controls showed no significant change. RANKL trended lower in patients on glucocorticoids (p = 0.05), attributed to the significantly older age in the treatment group. RANKL and RANKL:OPG levels were significantly lower in the non-ambulatory group compared with the ambulatory group (p = 0.010 and 0.036 respectively), again likely due to their older age. There was no correlation of RANKL, OPG, or RANKL:OPG with DXA Z-score or presence of vertebral fractures. CONCLUSION: There was significant decline in RANKL, OPG, and RANKL:OPG with age in DMD patients compared with controls, potentially due to disease severity or worsening osteoblastic function. This suggests some bone turnover markers may be difficult to assess or use as therapeutic indicators in DMD patients. Larger studies are needed to evaluate the role of RANKL-OPG in DMD patients to provide better targeted therapy.

Liposomal steroid nano-drug is superior to steroids as-is in mdx mouse model of Duchenne muscular dystrophy.

Glucocorticosteroids are the most efficacious anti-inflammatory agents and the gold standard treatment in Duchenne muscular dystrophy (DMD). However, their chronic use may lead to severe side effects. We evaluated the use of a novel injectable steroidal nano-drug in mdx mouse model of DMD by comparing the efficacy of nano-liposomes remotely loaded with the steroid prodrug, methylprednisolone hemisuccinate (MPS) with the same steroid as-is, in short (4-weeks) and long-term (58-weeks) treatments. Liposomal-MPS was selectively targeted to the mouse diaphragm, the most dystrophic muscle at early stage of the disease. The bioactivity of the steroidal nano-drug was evidenced by a significant decreased serum TGF-ß and reduced diaphragm macrophage infiltration after short-term treatment. In the long-term, the treatment with liposomal-MPS not only demonstrated improved muscle strength and mobility it also induced lower tibia and lumbar vertebrae osteoporosis indicating much lower bone related adverse effects.

miRNA Profiling for Early Detection and Treatment of Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder caused by out of frame mutations in the dystrophin gene. The hallmark symptoms of the condition include progressive degeneration of skeletal muscle, cardiomyopathy, and respiratory dysfunction. The most recent advances in therapeutic strategies for the treatment of DMD involve exon skipping or administration of minidystrophin, but these strategies are not yet universally available, nor have they proven to be a definitive cure for all DMD patients. Early diagnosis and tracking of symptom progression of DMD usually relies on creatine kinase tests, evaluation of patient performance in various ambulatory assessments, and detection of dystrophin from muscle biopsies, which are invasive and painful for the patient. While the current research focuses primarily on restoring functional dystrophin, accurate and minimally invasive methods to detect and track both symptom progression and the success of early DMD treatments are not yet available. In recent years, several groups have identified miRNA signature changes in DMD tissue samples, and a number of promising studies consistently detected changes in circulating miRNAs in blood samples of DMD patients. These results could potentially lead to non-invasive detection methods, new molecular approaches to treating DMD symptoms, and new methods to monitor of the efficacy of the therapy. In this review, we focus on the role of circulating miRNAs in DMD and highlight their potential both as a biomarker in the early detection of disease and as a therapeutic target in the prevention and treatment of DMD symptoms.

Cross-sectional serum metabolomic study of multiple forms of muscular dystrophy.

Muscular dystrophies are characterized by a progressive loss of muscle tissue and/or muscle function. While metabolic alterations have been described in patients'-derived muscle biopsies, non-invasive readouts able to describe these alterations are needed in order to objectively monitor muscle condition and response to treatment targeting metabolic abnormalities. We used a metabolomic approach to study metabolites concentration in serum of patients affected by multiple forms of muscular dystrophy such as Duchenne and Becker muscular dystrophies, limb-girdle muscular dystrophies type 2A and 2B, myotonic dystrophy type 1 and facioscapulohumeral muscular dystrophy. We show that 15 metabolites involved in energy production, amino acid metabolism, testosterone metabolism and response to treatment with glucocorticoids were differentially expressed between healthy controls and Duchenne patients. Five metabolites were also able to discriminate other forms of muscular dystrophy. In particular, creatinine and the creatine/creatinine ratio were significantly associated with Duchenne patients performance as assessed by the 6-minute walk test and north star ambulatory assessment. The obtained results provide evidence that metabolomics analysis of serum samples can provide useful information regarding muscle condition and response to treatment, such as to glucocorticoids treatment.

Selective release of muscle-specific, extracellular microRNAs during myogenic differentiation.

MyomiRs are muscle-specific microRNAs (miRNAs) that regulate myoblast proliferation and differentiation. Extracellular myomiRs (ex-myomiRs) are highly enriched in the serum of Duchenne Muscular Dystrophy (DMD) patients and dystrophic mouse models and consequently have potential as disease biomarkers. The biological significance of miRNAs present in the extracellular space is not currently well understood. Here we demonstrate that ex-myomiR levels are elevated in perinatal muscle development, during the regenerative phase that follows exercise-induced myoinjury, and concomitant with myoblast differentiation in culture. Whereas ex-myomiRs are progressively and specifically released by differentiating human primary myoblasts and C2C12 cultures, chemical induction of apoptosis in C2C12 cells results in indiscriminate miRNA release. The selective release of myomiRs as a consequence of cellular differentiation argues against the idea that they are solely waste products of muscle breakdown, and suggests they may serve a biological function in specific physiological contexts. Ex-myomiRs in culture supernatant and serum are predominantly non-vesicular, and their release is independent of ceramide-mediated vesicle secretion. Furthermore, ex-myomiRs levels are reduced in aged dystrophic mice, likely as a consequence of chronic muscle wasting. In conclusion, we show that myomiR release accompanies periods of myogenic differentiation in cell culture and in vivo. Serum myomiR abundance is therefore a function of the regenerative/degenerative status of the muscle, overall muscle mass, and tissue expression levels. These findings have implications for the use of ex-myomiRs as biomarkers for DMD disease progression and monitoring response to therapy.

Identification of plasma interleukins as biomarkers for deflazacort and omega-3 based Duchenne muscular dystrophy therapy.

Duchenne muscular dystrophy (DMD) is a progressive and fatal disease, characterized by the absence of dystrophin, muscle degeneration and cardiorespiratory failure. Creatine kinase is the classic marker to screen for DMD. However, other markers are needed to follow disease progression and to evaluate the response to therapy over longer periods. In the present study, we aim to identify interleukins in the plasma of the mdx mice model of DMD that could serve as biomarkers to monitor dystrophy progression, at distinct stages of the disease (1, 3 and 8 months of age). We used deflazacort and omega-3 therapies to validate the biomarkers studied. Plasma levels of TNF-α and TGF-ß were increased in mdx mice in relation to control, at all times studied. Differences in IFN-γ and IL-10 contents, comparing mdx x CTRL, were detected only at the early stage (1 month). IL-6 decreased at 3 and 8 months and IL-13 increased at 8 months in the mdx compared to control. Deflazacort and omega-3 reduced the plasma levels of the pro-inflammatory (TNF-α, INF-γ, IL-6) and pro-fibrotic (IL-13 and TGF-ß) interleukins and increased the plasma levels of IL-10. It is suggested that TNF-α and TGF-ß in plasma would be the best markers to follow disease progression. IL-6, INF-γ and IL-10 would be suitable markers to the earlier stages of dystrophy and IL-13 a suitable marker to the later stages of dystrophy.

Results, meta-analysis and a first evaluation of UNOxR, the urinary nitrate-to-nitrite molar ratio, as a measure of nitrite reabsorption in experimental and clinical settings.

We recently found that renal carbonic anhydrase (CA) is involved in the reabsorption of inorganic nitrite (NO2-), an abundant reservoir of nitric oxide (NO) in tissues and cells. Impaired NO synthesis in the endothelium and decreased NO bioavailability in the circulation are considered major contributors to the development and progression of renal and cardiovascular diseases in different conditions including diabetes. Isolated human and bovine erythrocytic CAII and CAIV can convert nitrite to nitrous acid (HONO) and its anhydride N2O3 which, in the presence of thiols (RSH), are further converted to S-nitrosothiols (RSNO) and NO. Thus, CA may be responsible both for the homeostasis of nitrite and for its bioactivation to RSNO/NO. We hypothesized that enhanced excretion of nitrite in the urine may contribute to NO-related dysfunctions in the renal and cardiovascular systems, and proposed the urinary nitrate-to-nitrite molar ratio, i.e., UNOxR, as a measure of renal CA-dependent excretion of nitrite. Based on results from clinical and experimental animal studies, here, we report on a first evaluation of UNOxR. We determined UNOxR values in preterm neonates, healthy children, and adults, in children suffering from type 1 diabetes mellitus (T1DM) or Duchenne muscular dystrophy (DMD), in elderly subjects suffering from chronic rheumatic diseases, type 2 diabetes mellitus (T2DM), coronary artery disease (CAD), or peripheral arterial occlusive disease (PAOD). We also determined UNOxR values in healthy young men who ingested isosorbide dinitrate (ISDN), pentaerythrityl tetranitrate (PETN), or inorganic nitrate. In addition, we tested the utility of UNOxR in two animal models, i.e., the LEW.1AR1-iddm rat, an animal model of human T1DM, and the APOE*3-Leiden.CETP mice, a model of human dyslipidemia. Mean UNOxR values were lower in adult patients with rheumatic diseases (187) and in T2DM patients of the DALI study (74) as compared to healthy elderly adults (660) and healthy young men (1500). The intra- and inter-variabilities of UNOxR were of the order of 50% in young and elderly healthy subjects. UNOxR values were lower in black compared to white boys (314 vs. 483, P = 0.007), which is in line with reported lower NO bioavailability in black ethnicity. Mean UNOxR values were lower in DMD (424) compared to healthy (730) children, but they were higher in T1DM children (1192). ISDN (3 × 30 mg) decreased stronger UNOxR compared to PETN (3 × 80 mg) after 1 day (P = 0.046) and after 5 days (P = 0.0016) of oral administration of therapeutically equivalent doses. In healthy young men who ingested NaNO3 (0.1 mmol/kg/d), UNOxR was higher than in those who ingested the same dose of NaCl (1709 vs. 369). In LEW.1AR1-iddm rats, mean UNOxR values were lower than in healthy rats (198 vs. 308) and comparable to those in APOE*3-Leiden.CETP mice (151).

Secondary Bone Defect in Neuromuscular Diseases in Childhood: A Longitudinal "Muscle-Bone Unit" Analysis.

To evaluate the potential bone defect in neuromuscular diseases, we conducted a longitudinal study including three groups of patients: 14 Duchenne muscular dystrophies (DMD) and 2 limb-girdle muscular dystrophies (LGMD); 3 Becker muscular dystrophies (BeMD) and 7 spinal muscular atrophies (SMA). Yearly osteodensitometries assessed body composition and bone mineral density (BMD) associated with bone markers and leptin. Along the 7-year study, 107 osteodensitometries showed that bone status evolved to osteopenia in most patients except BeMD. When analyzing the crude values, BMD improved with age in BeMD and SMA but not in DMD/LGMD. The correlation using the Z-scores displayed a decrease in BMD with age in DMD/LGMD for all regions, in SMA at total body less head, whereas BMD increased in BeMD at lumbar spine. As observed in healthy persons, muscular mass and bone tissue were significantly correlated. Glucocorticoids were deleterious on trabecular and cortical bone. Leptin was high in most patients and correlated to fat mass and bone parameters. This study confirms a secondary bone defect in neuromuscular diseases, further confirming the functional relationship between bone and muscle and arguing for regular bone follow-up in patients to prevent fracture risk. Adipose tissue seems to interfere with bone remodeling in neuromuscular diseases.

Large-scale serum protein biomarker discovery in Duchenne muscular dystrophy.

Serum biomarkers in Duchenne muscular dystrophy (DMD) may provide deeper insights into disease pathogenesis, suggest new therapeutic approaches, serve as acute read-outs of drug effects, and be useful as surrogate outcome measures to predict later clinical benefit. In this study a large-scale biomarker discovery was performed on serum samples from patients with DMD and age-matched healthy volunteers using a modified aptamer-based proteomics technology. Levels of 1,125 proteins were quantified in serum samples from two independent DMD cohorts: cohort 1 (The Parent Project Muscular Dystrophy-Cincinnati Children's Hospital Medical Center), 42 patients with DMD and 28 age-matched normal volunteers; and cohort 2 (The Cooperative International Neuromuscular Research Group, Duchenne Natural History Study), 51 patients with DMD and 17 age-matched normal volunteers. Forty-four proteins showed significant differences that were consistent in both cohorts when comparing DMD patients and healthy volunteers at a 1% false-discovery rate, a large number of significant protein changes for such a small study. These biomarkers can be classified by known cellular processes and by age-dependent changes in protein concentration. Our findings demonstrate both the utility of this unbiased biomarker discovery approach and suggest potential new diagnostic and therapeutic avenues for ameliorating the burden of DMD and, we hope, other rare and devastating diseases.

Serum proteomic profiling reveals fragments of MYOM3 as potential biomarkers for monitoring the outcome of therapeutic interventions in muscular dystrophies.

Therapy-responsive biomarkers are an important and unmet need in the muscular dystrophy field where new treatments are currently in clinical trials. By using a comprehensive high-resolution mass spectrometry approach and western blot validation, we found that two fragments of the myofibrillar structural protein myomesin-3 (MYOM3) are abnormally present in sera of Duchenne muscular dystrophy (DMD) patients, limb-girdle muscular dystrophy type 2D (LGMD2D) and their respective animal models. Levels of MYOM3 fragments were assayed in therapeutic model systems: (1) restoration of dystrophin expression by antisense oligonucleotide-mediated exon-skipping in mdx mice and (2) stable restoration of α-sarcoglycan expression in KO-SGCA mice by systemic injection of a viral vector. Following administration of the therapeutic agents MYOM3 was restored toward wild-type levels. In the LGMD model, where different doses of vector were used, MYOM3 restoration was dose-dependent. MYOM3 fragments showed lower inter-individual variability compared with the commonly used creatine kinase assay, and correlated better with the restoration of the dystrophin-associated protein complex and muscle force. These data suggest that the MYOM3 fragments hold promise for minimally invasive assessment of experimental therapies for DMD and other neuromuscular disorders.

Characterization of a Blood Spot Creatine Kinase Skeletal Muscle Isoform Immunoassay for High-Throughput Newborn Screening of Duchenne Muscular Dystrophy.

BACKGROUND: Duchenne muscular dystrophy (DMD) is a progressive, lethal X-linked neuromuscular disorder with an average worldwide incidence of 1:5000. Blood spot creatine kinase (CK) enzyme assays previously used in newborn screening programs for DMD are nonspecific because measured CK enzyme activity is attributable to 3 isoenzyme forms of CK (CK-MM, CK-MB, and CK-BB) and it is the CK-MM isoform that is found predominantly in skeletal muscle. CK-MM is increased in boys with DMD owing to muscle damage. We describe a sensitive and specific automated immunoassay for CK-MM to screen for DMD in blood spots. METHODS: The prototype assay was developed on the PerkinElmer GSP® analyzer to enable high-throughput screening. CK-MM was assayed using a solid phase, 2-site immunofluorometric system. Purified human CK-MM was used to create calibrators and controls. RESULTS: The limit of blank (LOB), detection (LOD), and quantification (LOQ) values were <1, 3, and 8 ng/mL, respectively. The analytical measurement range was 4-8840 ng/mL. Interassay (n = 40) imprecision was <7% across the analytical range. Cross-reactivity was <5% for CK-MB and 0% for CK-BB. The mean recovery of CK-MM was 101% (range 87%-111%). Blood spots from newborn infants (n = 277) had a mean CK-MM concentration of 155 ng/mL and a 99th centile of 563 ng/mL. The mean blood spot CK-MM concentration from 10 cases of DMD was 5458 ng/mL (range 1217-9917 ng/mL). CONCLUSIONS: CK-MM can be reliably quantified in blood spots. The development of this CK-MM assay on a commercial immunoassay analyzer would enable standardized and high-throughput newborn blood spot screening of DMD.