Abstract 4118084: Targeting Monoamine Oxidase B in Dystrophic <i>mdx</i> Hearts Dampens Inflammation and Fibrosis

Background: Cardiomyopathy is a major cause of death for Duchenne muscular dystrophy (DMD) patients. Current treatments cannot prevent cardiac tissue remodeling. Oxidative stress, inflammation and fibrosis are early events in DMD, preceding heart dysfunction. Monoamine Oxidase B (MAOB), which forms H 2 O 2 by oxidizing amines, is overactivated in inflammatory conditions and overcomes cell antioxidant defenses, thus altering redox homeostasis and eliciting harmful effects. We showed that targeting MAOB with inhibitors (iMAOB) improves skeletal muscle function in dystrophic mice by lowering oxidative stress, and reduces inflammation in murine models of sepsis and arthritis by dampening NF-kB, a redox-sensitive transcription factor. Aim: We explore the therapeutic potential of iMAOB to alleviate cardiomyopathy using dystrophin-deficient mdx mice. We hypothesize that iMAOB treatment could dampen oxidative stress, inflammation and fibrosis in dystrophic mdx hearts by modulating the phenotype of cells that are crucial in cardiac remodeling. Methods: Three-month-old mdx mice, that already show signs of fibrosis but no cardiac dysfunction, were orally treated with iMAOB or vehicle for one month (n≥ 6). Heart ventricular mononucleated cells were obtained by enzymatic digestion. Myeloid, endothelial and fibroblast cells were isolated by cell sorting by FACS and analysed by RT-PCR. Oxidative stress, inflammation and fibrosis were measured in whole tissue by immunohistochemistry. Results: The expression of proinflammatory and profibrotic genes was markedly increased in myeloid [Interleukin (Il)-1b, Il-6, Tgf-b and Spp1, the gene coding for osteopontin], endothelial [Il-1b, Il-6, mmp2 and nos3] and cardiac fibroblast cells [Tgf-b, Spp1, Timp1 and Col1] isolated from mdx hearts, as compared to wild type mice. All these genes were significantly dampened by iMAOB treatment. In parallel, once again iMAOB treatment blunted the increase in oxidative stress, inflammation and fibrosis observed in mdx cardiac sections. Of notice, the differences were not linked to changes in the percentage of the various cell types, as they were unmodified amongst wild type, mdx and iMAOB-treated mdx hearts. Conclusions: We show that iMAOB can positively affect the phenotype of cells that are important in cardiac tissue remodeling. Our data suggest that iMAOB can be a viable therapeutic tool in DMD cardiomyopathy. As iMAOB are already in clinical use, such approach could be easily translated to patients.