Acute hypoxia-induced diaphragm dysfunction is prevented by antioxidant pre-treatment

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O'Leary, Andrew J.
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University College Cork
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Diaphragm weakness is a strong predictor of poor outcome in patients. Acute hypoxia is a feature of respiratory conditions such as acute respiratory distress syndrome and ventilator-associated lung injury. However, the effects of acute hypoxia on the diaphragm are largely unknown despite the potential clinical relevance. C57BL6/J mice were exposed to 8hr of hypoxia (FiO2 = 0.10) or normoxia. A separate group of mice were administered N-acetyl cysteine (NAC; 200mg/kg, I.P.) immediately prior to acute hypoxia exposure. Ventilation was assessed using whole-body plethysmography. O2 consumption and CO2 production were measured as indices of metabolism. Diaphragm muscle contractile performance was determined ex-vivo. Gene expression was examined at 1, 4, and 8 hrs using qRT-PCR. Protein/phosphoprotein content was assessed using a sandwich immunoassay. Proteasome activity was measured using a spectrophotometric assay. Acute hypoxia decreased diaphragm force and fatigue. Ventilation during acute hypoxia was initially increased during the first 10 minutes, but quickly returned to normoxic levels for the duration of gas exposure. Metabolism was reduced by acute hypoxia, and gene expression driving mitochondrial uncoupling was increased. Acute hypoxia increased atrophic signalling, but not proteasome activity. Acute hypoxia increased hypertrophic and hypoxia protein signalling. NAC pre-treatment prevented the acute hypoxia-induced diaphragm weakness. Diaphragm weakness is reported in mechanically ventilated patients, which is primarily attributed to inactivity of the muscle, although this is controversial. The potential role of hypoxia in the development and/or exacerbation of ICU-related weakness is unclear. These data reveals that acute hypoxia is sufficient to cause diaphragm muscle weakness, likely relates to hypoxic stress. Muscle weakness was prevented by antioxidant supplementation, independent of the hypoxia-induced hypometabolic state. These findings highlight a potentially critical role for hypoxia in diaphragm muscle dysfunction observed in patients with acute respiratory diseases, and the potential benefits of NAC in preventing acute hypoxia-induced diaphragm dysfunction.
Diaphragm , Hypoxia , Weakness , Muscle , NAC , Antioxidant , Oxidative stress , ROS
O'Leary, A. J. 2016. Acute hypoxia-induced diaphragm dysfunction is prevented by antioxidant pre-treatment. PhD Thesis, University College Cork.
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