Abstract:
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Communication n° 147 Introduction : An enhanced activity of calcium-dependent calpains and inflammation-related oxidative stress may contribute to dystrophin-deficient myofiber degeneration. Objective : To evaluate the benefit of an in-vivo treatment with a novel chimeric compound acting as anticalpain and antioxidant (BN82270) (Auvin et al., Bioorg Med Chem Lett. 2004), on the pathological signs of dystrophic mdx mice. Methods : BN82270 at 30 mg/kg, that acutely reduces calpain activity in mdx mouse diaphragm, was daily injected subcutaneously to mdx mice for 4-6 weeks in parallel with a chronic exercise that worsens the murine dystrophy. Drug effects were evaluated in-vivo (forelimb strength, FLS) and ex-vivo (electrophysiological and biochemical analyses). Results : The 4-weeks treated mdx mice were significantly stronger (FLS=0.145+/-0.01 kg) than untreated counterparts (0.138+/-0.005 kg). Current clamp microelectrode recordings showed that BN82270 significantly contrasted the decrease in chloride channel conductance (gCl) typical of spontaneously degenerating diaphragm, gCl being 1759+/-92 (treated, n=32) vs. 1278+/-60 microS/cm2 (control, n=23). The drug was weakly effective on both the exercise-induced decrease of gCl and the negative voltage threshold for contraction (index of calcium homeostasis) in the hind limb extensor digitorum longus (EDL) muscle fibers. However, the treatment significantly reduced by 46+/-14 % the elevated creatine kinase plasma level (~2000 U/L). The active form of the membrane permeable pro-drug BN82270 was detected at 3.74+/-0.6 microM in hind limb muscles by HPLC. The acute in-vitro exposure to 100 microM BN82270 for 75-90 min showed a significantly higher drug level in diaphragm (61+/-6.7%) than in EDL (39+/-2.8%), suggesting a greater ability of the former to activate BN82270. Conclusions : The beneficial effect of BN82270 on dystrophic progression of mdx mice reinforces the role of calpain/ROS in the pathology. Considering the drug/prodrug system and possible tissue specific activation, it may be anticipated that higher doses/different posology would result in a wider beneficial effect.
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