N-acetylcysteine Decreases Fibrosis and Increases Force-Generating Capacity of mdx Diaphragm

Abstract

Respiratory muscle weakness occurs due to dystrophin deficiency in Duchenne muscular dystrophy (DMD). The mdx mouse model of DMD shows evidence of impaired respiratory muscle performance with attendant inflammation and oxidative stress. We examined the effects of N-acetylcysteine (NAC) supplementation on respiratory system performance in mdx mice. Eight-week-old male wild type (n = 10) and mdx (n = 20) mice were studied; a subset of mdx (n = 10) received 1% NAC in the drinking water for 14 days. We assessed breathing, diaphragm, and external intercostal electromyogram (EMG) activities and inspiratory pressure during ventilatory and non-ventilatory behaviours. Diaphragm muscle structure and function, cytokine concentrations, glutathione status, and mRNA expression were determined. Diaphragm force-generating capacity was impaired in mdx compared with wild type. Diaphragm muscle remodelling was observed in mdx, characterized by increased muscle fibrosis, immune cell infiltration, and central myonucleation. NAC supplementation rescued mdx diaphragm function. Collagen content and immune cell infiltration were decreased in mdx + NAC compared with mdx diaphragms. The cytokines IL-1β, IL-6 and KC/GRO were increased in mdx plasma and diaphragm compared with wild type; NAC decreased systemic IL-1β and KC/GRO concentrations in mdx mice. We reveal that NAC treatment improved mdx diaphragm force-generating capacity associated with beneficial anti-inflammatory and anti-fibrotic effects. These data support the potential use of NAC as an adjunctive therapy in human dystrophinopathies.

Progressive Skeletal Muscle Atrophy in Muscular Dystrophies: A Role for Toll-Like Receptor-Signaling in Disease Pathogenesis

“…N-acetylcysteine-treated mdx mice also display improved grip strength, reduced hypertrophy of the extensor digitorum longus, increased mitochondrial function, and less severe inflammation in gastrocnemius muscle [ 85 ]. In addition, N-acetylcysteine supplementation rescues mdx diaphragm function, reducing fibrosis and inflammatory cell infiltration [ 86 ]. Though treated mdx mice display increased force, N-acetylcysteine supplements come with the important side effects of reduced muscle weight and impaired body weight gain in growing mice [ 87 ].…”

Tempol improves redox status in mdx dystrophic diaphragm muscle

“…34 A previous study has shown that NAC improved mdx diaphragm functional capacity, reduced fibrosis and immune cell infiltration in mdx diaphragm. 35 NAC also increased Nrf2 mRNA expression in mdx diaphragm and had no adverse effect on ventilation, inspiratory pressure and respiratory muscle EMG or growth measures in mdx mice. 35 NAC was also able to promote overexpression of SOD2, endothelial nitric oxide synthase (eNOS) and matrix metalloproteinase 3 (MMP3) in rat kidneys.…”

“…35 NAC also increased Nrf2 mRNA expression in mdx diaphragm and had no adverse effect on ventilation, inspiratory pressure and respiratory muscle EMG or growth measures in mdx mice. 35 NAC was also able to promote overexpression of SOD2, endothelial nitric oxide synthase (eNOS) and matrix metalloproteinase 3 (MMP3) in rat kidneys. 36 In agreement with our results, previous studies also showed that tempol upregulated SOD2 activity and that this increase was accompanied by oxidative stress reduction.…”

N-Acetylcysteine Reduces Skeletal Muscles Oxidative Stress and Improves Grip Strength in Dysferlin-Deficient Bla/J Mice

“…NAC (Sigma-Aldrich, St. Louis, MO, USA) was administered as a 1% ( w / v ) solution in drinking water ad libitum to 6 months old mice for 10 weeks, according to standard protocols [ 22 , 23 , 42 , 47 ]. NAC solutions were prepared every 5 days using autoclaved tap water (pH ~7.0), kept protected from light and refrigerated at 4 °C.…”

“…Most of the studies regarding the effect of NAC on muscular dystrophy have been performed in the mdx model of Duchenne muscular dystrophy pathology [22,23,42,46,47], and there are few in other models. One example is an animal model of chronic limb ischemia, where NAC attenuates inflammation [48].…”