Dietary NaCl supplementation prevents muscle necrosis in a mouse model of Duchenne muscular dystrophy

Abstract

The mdx mouse is an animal model for Duchenne muscular dystrophy. Mdx mice fed a 12% NaCl diet from birth up to 20 days of age (mdx-Na mice) had an approximately 50% reduction in serum creatine kinase (CK) activity compared with mdx mice fed a standard diet. Most notably, necrotic fibers in tibialis anterior (TA) muscle of mdx-Na mice were reduced by 99% and were similar in control mice. These mdx mice displayed significantly elevated blood Ca2+ and Na+ levels, while the total calcium content of their TA muscle was reduced to the level of control mice. In addition, mdx-Na mice had elevated zinc and magnesium contents in their TA muscle. These results suggest that elevated serum Na+ leads to Ca2+ extrusion from muscle via the Na+/Ca2+ exchanger causing a decrease in intracellular Ca2+ levels and an increase in blood Ca2+ levels. Extracellular Ca2+ and, in addition, Zn2+ and Mg2+ might also contribute to the stabilization of the cell membrane. Other possibilities explaining the surprisingly efficacious beneficial effect of dietary sodium exist and are discussed.

Basal Bioenergetic Abnormalities in Skeletal Muscle from Ryanodine Receptor Malignant Hyperthermia-susceptible R163C Knock-in Mice

“…Considering that the R163C RyR1 mutation in skeletal muscle resulted in a significantly increased cytosolic Ca 2ϩ (about 2-fold of the normal resting concentration, this study and that by Yang et al (30), an activation of several calcium-dependent pathways was expected leading to the activation of a slow-twitch fiber program to increase the resistance to fatigue, the oxidative capacity, and the calcium buffering capacity of mitochondria. The values for total calcium contents of WT mitochondria evaluated in this study were within the range of those previously reported for rodent skeletal muscle using ICP-MS or other techniques (82)(83)(84)(85)(86). The significantly higher concentrations of mitochondrial calcium content in R163C reported here may stem from the chronically elevated (2-4-fold) resting intracellular Ca 2ϩ concentrations in intact MHS skeletal muscle from various species (76 -78).…”

“…Given that exposure of mitochondria to a sustained higher calcium concentration may lead to higher calcium uptake and net calcium accumulation, dissipation of the electrochemical gradient, decreased ATP production, and/or organelle swelling or bursting (79 -81), the calcium concentrations in mitochondrial and PM fractions were evaluated in WT and R163C skeletal muscle by ICP-MS. The values for total calcium contents of WT were within those reported for rodent skeletal muscle using ICP-MS or other techniques (690 -1500 nmol/g muscle wet weight) (82)(83)(84)(85)(86). Skeletal muscle mitochondria from R163C mice had 5.7 times more Ca 2ϩ than WT, and the Ca 2ϩ concentration in the cytosolic fraction was 1.8-fold higher than WT (Table 4).…”

Stretch-activated calcium channel protein TRPC1 is correlated with the different degrees of the dystrophic phenotype in mdx mice

“…Muscles (DIA, STN, TA, and BB) were excised, and the animals were euthanized with an overdose of the anesthetic mixture. The muscles were weighed and digested with 0.2 ml ultrapure HNO 3 at 100°C as previously described (25,45). The samples were diluted to a final volume of 10 ml with ultrapure water.…”

Preclinical drug trials in the mdx mouse: Assessment of reliable and sensitive outcome measures

“…Different treatment protocols, age groups, and endpoints have been used to assess the efficacy of drugs in mdx mice 2–4,6,8,9,11,14–16,20,21,31,33,37,39,42,45 (Table 1). Both trial design and endpoints should also consider data most attractive to the U.S. Food and Drug Administration in moving toward investigational new drug applications for initial human trials.…”