Effect of 25-HydroxyVitamin D Deficiency and Its Interaction with Prednisone Treatment on Musculoskeletal Health in Growing Mdx Mice

Combined growth hormone and insulin-like growth factor-1 rescues growth retardation in glucocorticoid-treated mdxmice but does not prevent osteopenia

Short stature and osteoporosis are common in Duchenne muscular dystrophy (DMD) and its pathophysiology may include an abnormality of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis, which is further exacerbated by long-term glucocorticoid (GC) treatment. Hence, an agent that has anabolic properties and may improve linear growth would be beneficial in this setting and therefore requires further exploration. A 5-week-old x-linked muscular dystrophy (mdx) mice were used as a model of DMD. They were treated with prednisolone ± GH + IGF-1 for 4 weeks and then compared to control mdx mice to allow the study of both growth and skeletal structure. GC reduced cortical bone area, bone fraction, tissue area and volume and cortical bone volume, as assessed by micro computed tomography (CT) In addition, GC caused somatic and skeletal growth retardation but improved grip strength. The addition of GH + IGF-1 therapy rescued the somatic growth retardation and induced additional improvements in grip strength (16.9% increase, P < 0.05 compared to control). There was no improvement in bone microarchitecture (assessed by micro-CT and static histomorphometry) or biomechanical properties (assessed by three-point bending). Serum bone turnover markers (Serum procollagen 1 intact N-terminal propeptide (P1NP), alpha C-terminal telopeptide (αCTX)) also remained unaffected. Further work is needed to maximise these gains before proceeding to clinical trials in boys with DMD.

Meclozine ameliorates skeletal muscle pathology and increases muscle forces in mdx mice

We screened pre-approved drugs for the survival of the Hu5/KD3 human myogenic progenitors. We found that meclozine, an anti-histamine drug that has long been used for motion sickness, promoted the proliferation and survival of Hu5/KD3 cells. Meclozine increased expression of MyoD, but reduced expression of myosin heavy chain and suppressed myotube formation. Withdrawal of meclozine, however, resumed the ability of Hu5/KD3 cells to differentiate into myotubes. We examined the effects of meclozine on mdx mouse carrying a nonsense mutation in the dystrophin gene and modeling for Duchenne muscular dystrophy. Intragastric administration of meclozine in mdx mouse increased the body weight, the muscle mass in the lower limbs, the cross-sectional area of the paravertebral muscle, and improved exercise performances. Previous reports show that inhibition of phosphorylation of ERK1/2 improves muscle functions in mouse models for Emery-Dreifuss muscular dystrophy and cancer cachexia, as well as in mdx mice. We and others previously showed that meclozine blocks the phosphorylation of ERK1/2 in cultured cells. We currently showed that meclozine decreased phosphorylation of ERK1/2 in muscles in mdx mice but not in wild-type mice. This was likely to be one of the underlying mechanisms of the effects of meclozine on mdx mice.

Effects of chronic treatment with gold nanoparticles on inflammatory responses and oxidative stress in Mdx mice

Duchenne muscular dystrophy (DMD) is an X-linked recessive hereditary myopathy characterised by progressive muscle degeneration in male children. As a consequence of DMD, increased inflammation and oxidative stress occur in muscle tissue along with morphological changes. Several studies have reported anti-inflammatory and antioxidant effects of gold nanoparticles (GNP) in muscle injury models. The objective of this study was to evaluate these effects along with the impacts of the disease on histopathological changes following chronic administration of GNP to Mdx mice. Two-month-old Mdx mice were separated into five groups of eight individuals each, as follows: wild-type (WT), Mdx-modified without treatment, Mdx + 2.5 mg/kg GNP, Mdx + 7.0 mg/kg GNP and Mdx + 21 mg/kg GNP. GNP with a mean diameter of 20 nm were injected subcutaneously at concentrations of 2.5, 7.0 and 21 mg/kg. Treatments continued for 30 d with injections administered at 48-h intervals. Twenty-four hours after the last injection, the animals were killed and the central region of the gastrocnemius muscle was surgically removed. Chronic administration of GNP reduced inflammation in the gastrocnemius muscle of Mdx mice and reduced morphological alterations due to inflammatory responses to muscular dystrophy. In addition, GNP also demonstrated antioxidant potential by reducing the production of reactive oxygen and nitrogen species, reducing oxidative damage and improving antioxidant activity.

Increased Rates of Vitamin D Insufficiency in Boys With Duchenne Muscular Dystrophy Despite Higher Vitamin D3 Supplementation

Vitamin D supplementation is important for many chronic pediatric conditions to help maintain bone health; however, there is little evidence about how disease-related factors affect vitamin D status. The objective was to compare 25-hydroxyvitamin D (25(OH)D) concentrations in 3 pediatric cohorts (Duchenne muscular dystrophy [DMD], systemic lupus erythematosus [SLE], and osteogenesis imperfecta [OI]). In a retrospective study of 367 subjects, children with DMD had increased prevalence of vitamin D insufficiency (25% vs 14% [SLE] and 10% [OI], P = .002), despite higher vitamin D₃ supplementation doses. Boys with DMD also had higher weight, fat mass, and lower lean mass percentage Z scores. DMD was associated with having higher rates of vitamin D insufficiency than other comparable pediatric chronic disease cohorts, the effect of which may be modulated by clinical factors such as increased adiposity. While corroboration of these results is needed given baseline differences between the patient groups, greater vitamin D supplementation doses may be required to achieve optimal serum 25(OH)D concentrations in boys with DMD.

Pre-treatment with Pamidronate Improves Bone Mechanical Properties in Mdx Mice Treated with Glucocorticoids

Duchenne muscular dystrophy (DMD) is an X-linked disease of progressive muscle deterioration and weakness. Patients with DMD have poor bone health which is partly due to treatment with glucocorticoids, a standard therapy to prolong muscle function that also induces bone loss. Bisphosphonates are used to treat adults at risk of glucocorticoid-induced osteoporosis but are not currently used in DMD patients until after they sustain fractures. In this study, C57BL/10ScSn-mdx mice, a commonly used DMD animal model, received continuous glucocorticoid, prednisone treatment (0.083 mg/day) from 5 to 10 weeks of age. Pre-treatment with the bisphosphonate pamidronate started at 4 weeks of age over a period of 2 weeks or 6 weeks (cumulative dose 8 mg/kg for both) to assess the effectiveness of the two dosing regimens in ameliorating glucocorticoid-induced bone loss. Mdx mice treated with prednisone had improved muscle function that was not changed by pamidronate treatment. Glucocorticoid treatment caused cortical bone loss and decreased cortical bone strength. Both 2 and 6 week pamidronate treatment increased cortical thickness and bone area compared to prednisone-treated Mdx mice, however, only 2 week pamidronate treatment improved the strength of cortical bone compared to that of glucocorticoid-treated Mdx mice. In the trabecular bone, both pamidronate treatments significantly increased the amount of bone, and increased the ultimate load but not the energy to fail. These results highlight the importance of when and how much bisphosphonate is administered prior to glucocorticoid exposure.