Use of Bortezomib in Golden Retriever Muscular Dystrophy (GRMD) Therapy viability validation and restructure of the muscle dystrophy

The Golden Retriever Muscular Dystrophy (GRMD) is a genetic myopathy homologue to Duchenne Muscular Dystrophy (DMD) in human. Use of canine model is the better because the disease development, clinical signs and body mass are closed to the sick children. It has been known muscle protein proteolysis and muscle atrophy are related with ubiquitin-proteasome pathway. Researches using mdx mice and human muscle (in vitro) treated with proteasome inhibitor (MG-132 and bortezomib) showing rescue of the dystrophin and associated proteins and improvement of histopatologycal phenotype. In this research, were analyzed five GRMD dogs, two dogs were treated with Bortezomib and three dogs were control. Muscle biopsies were collected before the treatment and after the treatment to histology, ultrastructure and immunohistochemical muscle analysis. Biochemistry analyses were made once a week and measurement of proteasome inhibition was analysed in each cycle of Bortezomib administration. In the first byopsy, all the dogs showing closed histophatological morphology of muscle fibers. At the end of treatment, the treated dogs had lower connective tissue deposition and inflammatory cells infiltration than untreated dogs by histology, collagen morphometry and ultrastructural analysis. We noted by ultrastructural analysis macrophages inside the fibers, degenerated products, activated fibroblasts and connective tissue deposition in edomisium and perimisium of the fibers. The dystrophin immunohistochemistry was not presence in sarcoplasmatic membrane in both groups. However, the treated dogs showing bigger expression of α and β-dystroglycan, this fact means improved of disease histopathology phenotype. The untreated dogs had bigger expression of phospho-NFκB and TGF-β1, suggesting bigger activation of pro-apoptotic factors, inflammatory molecules and bigger connective tissue deposition respectively. The proteasome inhibition tests indicated bigger inhibition in the blood cells one hour post doses of bortezomib and was dose-dependent pathway. In conclusion, the proteasome inhibitors may improve the appearance of GRMD muscle fibers, lowered the connective tissue deposition and infiltration of inflammatory cells, likewise to rescue the dystrophin- associated proteins in the muscle fiber membrane. (AU)