N‐Acetyl cysteine improves dystrophic (mdx) mouse diaphragm muscle quality and strength

Abstract

Respiratory muscle weakness occurs as a consequence of dystrophin deficiency in Duchenne muscular dystrophy (DMD), with implications for breathing and airway protective behaviours. The mdx mouse model of DMD shows evidence of impaired respiratory muscle performance with attendant inflammation and oxidative stress. N‐Acetyl cysteine (NAC) is a dietary antioxidant commonly used in the treatment of respiratory disease. We sought to examine the effects of NAC intervention on respiratory system performance in the mdx mouse.Young adult male wild‐type and mdx mice were studied; a subset of mdx received 1% NAC in the drinking water for 14 days. Ventilation was assessed in conscious mice using whole‐body plethysmography. Inspiratory pressure and respiratory muscle (diaphragm and external intercostal) EMG activity were assessed in anaesthetised mice during ventilatory and non‐ventilatory behaviours. Diaphragm ex vivo force‐generating capacity, muscle structure, cytokine concentrations, glutathione status and mRNA expression were determined. Data were statistically compared by unpaired Student's t test.Diaphragm function was severely impaired in mdx, evidenced by reductions in force‐generating capacity (40–160Hz range), total muscle shortening and maximal shortening velocity compared to wild‐type. Extensive diaphragm myofibre remodelling and damage was observed for mdx, characterised by increased muscle fibrosis, immune cell filtration, muscle fibre central nucleation and embryonic myosin expression. The pro‐inflammatory cytokines IL‐1β and IL‐6 were elevated in mdx diaphragm and plasma samples. mRNA studies indicate an increase in gene expression related to muscle atrophy, regeneration and inflammation in mdx diaphragm, and a reduction in anti‐oxidant related gene expression. NAC supplementation increased mdx diaphragm force (60–160Hz), maximal shortening and shortening velocity. Collagen deposition and the infiltration of putative inflammatory cells in mdx diaphragm was decreased following NAC. Mdx diaphragm and plasma IL‐1β and IL‐6 concentrations were decreased following NAC. Glutathione reductase and peroxidase activities were increased in mdx diaphragm; both were unaffected by NAC. mRNA expression of Nrf2 was increased in mdx diaphragm and increased further with NAC supplementation. No adverse effects of NAC intervention were observed on ventilation, inspiratory pressure and EMG, and growth measures.We reveal that NAC treatment improved mdx diaphragm force‐generating capacity by way of beneficial anti‐inflammatory and anti‐fibrotic effects. These data support the potential use of NAC as an adjunctive therapy in the dystrophinopathies.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.