Mechanical ventilation induces diaphragmatic mitochondrial dysfunction and increased oxidant production

Abstract

Mechanical ventilation (MV) is a life-saving intervention used in patients with acute respiratory failure. Unfortunately, prolonged MV results in diaphragmatic weakness, which is an important contributor to the failure to wean patients from MV. Our laboratory has previously shown that reactive oxygen species (ROS) play a critical role in mediating diaphragmatic weakness after MV. However, the pathways responsible for MV-induced diaphragmatic ROS production remain unknown. These experiments tested the hypothesis that prolonged MV results in an increase in mitochondrial ROS release, mitochondrial oxidative damage, and mitochondrial dysfunction. To test this hypothesis, adult (3-4 months of age) female Sprague-Dawley rats were assigned to either a control or a 12-h MV group. After treatment, diaphragms were removed and mitochondria were isolated for subsequent respiratory and biochemical measurements. Compared to control, prolonged MV resulted in a lower respiratory control ratio in diaphragmatic mitochondria. Furthermore, diaphragmatic mitochondria from MV animals released higher rates of ROS in both State 3 and State 4 respiration. Prolonged MV was also associated with diaphragmatic mitochondrial oxidative damage as indicated by increased lipid peroxidation and protein oxidation. Finally, our data also reveal that the activities of the electron transport chain complexes II, III, and IV are depressed in mitochondria isolated from diaphragms of MV animals. In conclusion, these results are consistent with the concept that diaphragmatic inactivity promotes an increase in mitochondrial ROS emission, mitochondrial oxidative damage, and mitochondrial respiratory dysfunction. KeywordsMitochondria; Superoxide; Antioxidants; Free radicals Mechanical ventilation (MV) is a life-saving measure used to maintain alveolar ventilation in patients incapable of doing so on their own (e.g., respiratory failure, coma, or spinal cord injury). Unfortunately, prolonged MV reduces the activity of the principal muscle of inspiration (i.e., diaphragm) and results in diaphragmatic wasting and contractile dysfunction [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Indeed, MV results in a rapid onset of diaphragmatic atrophy that is accompanied by oxidative stress [1,15,16]. Although extended periods of disuse also lead to locomotor skeletal muscle atrophy [13,[17][18][19][20][21][22][23][24][25][26], a unique characteristic of MV-induced diaphragmatic atrophy is the rapidity of the atrophic response [25,26]. Although the molecular steps that regulate MVinduced diaphragm atrophy remain unclear, growing evidence indicates that redox disturbances in diaphragmatic fibers play a key signaling role in this process. In this regard, our laboratory was the first to report that prolonged MV results in both protein oxidation and lipid peroxidation in the diaphragm [13,15]. Specifically, diaphragm unloading via MV is associated with a rapid onset of diaphragmatic oxidative stress that develops within 3-6 h after the initiation of MV [15]. Impor...

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“…For example, as few as 12 h of MV results in a large increase in ROS emission from rat diaphragm mitochondria during both state 3 and state 4 respiration (50,82). This increase in mitochondrial ROS production is associated with increased lipid peroxidation and protein oxidation within mitochondria (50).…”

“…For example, as few as 12 h of MV results in a large increase in ROS emission from rat diaphragm mitochondria during both state 3 and state 4 respiration (50,82). This increase in mitochondrial ROS production is associated with increased lipid peroxidation and protein oxidation within mitochondria (50). Moreover, the activities of the electron transport chain complexes II, III, and IV are depressed in mitochondria isolated from diaphragms of rats exposed to only 12 h of MV and prolonged MV in rats also promotes diaphragmatic mitochondrial uncoupling as indicated by a decrease in the respiratory control ratio (50).…”