Enhanced Dystrophic Progression in mdx Mice by Exercise and Beneficial Effects of Taurine and Insulin-Like Growth Factor-1

Abstract

A preclinical screening for prompt-to-use drugs that are safer than steroids and beneficial in Duchenne muscular dystrophy was performed. Compounds able to reduce calcium-induced degeneration (taurine or creatine 10% in chow) or to stimulate regeneration [insulin-like growth factor-1 (IGF-1); 50 or 500 g/kg s.c.] were administered for 4 to 8 weeks to mdx mice undergoing chronic exercise on a treadmill, a protocol to worsen dystrophy progression. ␣-Methyl-prednisolone (PDN; 1 mg/kg) was used as positive control. The effects were evaluated in vivo on forelimb strength and in vitro electrophysiologically on the macroscopic chloride conductance (gCl), an index of degeneration-regeneration events in mdx muscles, and on the mechanical threshold, a calcium-sensitive index of excitation-contraction coupling. The exercise produced a significant weakness and an impairment of gCl, by further decreasing the already low value of degenerating diaphragm (DIA) and fully hampering the increase of gCl typical of regenerating extensor digitorum longus (EDL) mdx muscle. The already negative voltage threshold for contraction of mdx EDL was also slightly worsened. Taurine Ͼ creatine Ͼ IGF-1 counteracted the exercise-induced weakness. The amelioration of gCl was drug-and muscle-specific: taurine was effective in EDL, but not in DIA muscle; IGF-1 and PDN were fully restorative in both muscles, whereas creatine was ineffective. An acute effect of IGF-1 on gCl was observed in vitro in untreated, but not in IGF-1-treated exercised mdx muscles. Taurine Ͼ PDN Ͼ IGF-1, but not creatine, significantly ameliorated the negative threshold voltage values of the EDL fibers. The results predict a potential benefit of taurine and IGF-1 for treating human dystrophy.

A Multidisciplinary Evaluation of the Effectiveness of Cyclosporine A in Dystrophic Mdx Mice

“…9,28 The training protocol started at the mouse age of 4 to 5 weeks. Approximately half of the mdx mice showed an avoidance behavior with respect to exercise, with a higher tendency to fatigue and had to be gently stimulated, or should be left resting, to complete the 30 minutes of running session.…”

“…Five measurements were taken from each animal within 2 minutes and the maximum values were used for statistical analysis. 9 The sedentary mice, both WT and mdx, were monitored for muscle strength every week. At the end of the fourth week of exercise the electrophysiological in vitro experiments were started.…”

“…In fact glucocorticoids, the sole drugs with a clinical interest for DMD until now, reduce symptoms and delay pathology in both patients and animal models of the disease. 8,9 The interest toward immunosuppressant drugs for treating DMD is reinforced by the need of immunosuppression to increase the transfection rate of gene and cell therapy in dystrophic subjects. 10 -13 Within this frame we focused our attention on cyclosporine A (CsA), a drug with a wide immunosuppressant action because of its ability to inhibit the calcium/calmodulindependent phosphatase calcineurin and consequently the NF-AT-induced transcription of interleukin-2 in activated T lymphocytes, finally inhibiting their clonal expansion.…”

“…[25][26][27] The CsA treatment has been performed on 4-to 5-weekold mdx mice for 4 to 8 weeks throughout a period of exercise on treadmill, a protocol that worsens the murine pathology by contrasting the spontaneous regeneration and allows to monitor the effectiveness of drug therapies both in vivo and ex vivo. 9,28,29 In vivo we evaluated the ability of CsA to prevent the exercise-induced forelimb muscle strength loss. Creatine kinase level, histological analysis, and markers of fibrosis as well as the level of utrophin expression were determined as indexes of the ability of CsA treatment to contrast muscle damage.…”

“…To gain insight in the mechanism of drug action, we recorded electrophysiologically the state of cellular parameters linked to the disease, such as the impairment of chloride channel function occurring spontaneously in diaphragm (DIA) muscle or induced by exercise in the hindlimb extensor digitorum longus (EDL) muscle. 9 In addition calcium homeostasis was monitored functionally by electrophysiological recordings of the voltage threshold for mechanical activation and by FURA-2 imaging. The data provided evidence that CsA treatment contrasts, in a calcium-independent manner, some of the functional and morphological disease-related alterations, suggesting that the CsA targets contribute to the pathology progression in muscular dystrophy.…”