Effects of controlled mechanical ventilation on sepsis-induced diaphragm dysfunction in rats.
OBJECTIVE
Diaphragm dysfunction develops during severe sepsis as a consequence of hemodynamic, metabolic, and intrinsic abnormalities. Similarly, 12 hours of controlled mechanical ventilation also promotes diaphragm dysfunction. Importantly, patients with sepsis are often treated with mechanical ventilation for several days. It is unknown if controlled mechanical ventilation exacerbates sepsis-induced diaphragm dysfunction, and this forms the basis for these experiments. We investigate the effects of 12-hour controlled mechanical ventilation on contractile function, fiber dimension, cytokine production, proteolysis, autophagy, and oxidative stress in the diaphragm of septic rats.


METHODS
Randomized controlled experiment.


METHODS
Animal research laboratory.


METHODS
Adult male Wistar rats.


METHODS
Treatment with a single intraperitoneal injection of either saline or Escherichia coli lipopolysaccharide (5 mg/kg). After 12 hours, the saline-treated animals (controlled mechanical ventilation) and half of the septic animals (lipopolysaccharide + controlled mechanical ventilation) were submitted to 12 hours of controlled mechanical ventilation while the remaining septic animals (lipopolysaccharide) were breathing spontaneously for 12 hours. They were compared to a control group. All animals were studied 24 hours after saline or lipopolysaccharide administration.


RESULTS
Twenty-four hours after saline or lipopolysaccharide administration, diaphragm contractility was measured in vitro. We also measured diaphragm muscle fiber dimensions from stained cross sections, and inflammatory cytokines were determined by proteome array. Activities of calpain, caspase-3, and proteasome, expression of 20S-proteasome α subunits, E2 conjugases, E3 ligases, and autophagy were measured with immunoblotting and quantitative polymerase chain reaction. Lipopolysaccharide and/or controlled mechanical ventilation independently decreased diaphragm contractility and fiber dimensions and increased diaphragm interleukin-6 production, protein ubiquitination, expression of Atrogin-1 and Murf-1, calpain and caspase-3 activities, autophagy, and protein oxidation. Compared with lipopolysaccharide alone, lipopolysaccharide + controlled mechanical ventilation worsened diaphragm contractile dysfunction, augmented diaphragm interleukin-6 levels, autophagy, and protein oxidation, but exerted no exacerbating effects on diaphragm fiber dimensions, calpain, caspase-3, or proteasome activation.


CONCLUSIONS
Twelve hours of controlled mechanical ventilation potentiates sepsis-induced diaphragm dysfunction, possibly due to increased proinflammatory cytokine production and autophagy and worsening of oxidative stress.
1Respiratory Muscle Research Unit, Laboratory of Pneumology and Respiratory Division, Katholieke Universiteit Leuven, Leuven, Belgium. 2Department of Critical Care Medicine, McGill University Health Centre and Meakins-Christie Laboratories, McGill University, Montréal, QC, Canada. 3Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL. 4Department of Kinesiology and Physical Education, McGill University, Montreal, QC, Canada. 5Medical Intensive Care Unit, General Internal Medicine, University Hospitals Leuven, Leuven, Belgium.
Karen
K
Maes
Angela
A
Stamiris
Debby
D
Thomas
Nele
N
Cielen
Ashley
A
Smuder
Scott K
SK
Powers
Felipe S
FS
Leite
Greet
G
Hermans
Marc
M
Decramer
Sabah N
SN
Hussain
Ghislaine
G
Gayan-Ramirez
D000818:Animals; D001343:Autophagy / Q000502:physiology*; D016207:Cytokines / Q000378:metabolism*; D003964:Diaphragm / Q000503:physiopathology*; D015151:Immunoblotting; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018384:Oxidative Stress / Q000502:physiology; D016133:Polymerase Chain Reaction; D059748:Proteolysis; D051381:Rats; D017208:Rats, Wistar; D012121:Respiration, Artificial / Q000009:adverse effects*; D018805:Sepsis / Q000503:physiopathology*; D013896:Thoracic Diseases / Q000503:physiopathology*
D016207:Cytokines; D008070:Lipopolysaccharides