Respiratory loading intensity and diaphragm oxidative stress: N-acetyl-cysteine effects

1 Muscle and Respiratory System Research Unit and Pneumology Department, Institut Municipal d'Investigacio Medica, Hospital del Mar, Pompeu Fabra University, Barcelona, Catalonia; 2 Pneumology Department and Research Unit, Cruces Hospital, Basque Country University, Barakaldo, Basque Country, Spain; and 3 Critical Care and Respiratory Divisions, Royal Victoria Hospital and Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada Submitted 1 July 2005 ; accepted in final form 26 September 2005 We hypothesized that resistive breathing of moderate to high intensity might increase diaphragm oxidative stress, which could be partially attenuated by antioxidants. Our objective was to assess the levels of oxidative stress in the dog diaphragm after respiratory muscle training of a wide range of intensities and whether N -acetyl-cysteine (NAC) might act as an antioxidant. Twelve Beagle dogs were anesthetized with 1% propophol, tracheostomized, and subjected to continuous inspiratory resistive breathing (IRB) (2 h/day for 2 wk). They were further divided into two groups ( n = 6): NAC group (oral NAC administration/24 h for 14 days) and control group (placebo). Diaphragm biopsies were obtained before (baseline biopsy) and after (contralateral hemidiaphragm) IRB and NAC vs. placebo treatment. Oxidative stress was evaluated in all diaphragm biopsies through determination of 3-nitrotyrosine immunoreactivity, protein carbonylation, hydroxynoneal protein adducts, Mn-SOD, and catalase, using immunoblotting and immunohistochemistry. Both protein tyrosine nitration and protein carbonylation were directly related to the amount of the respiratory loads, and NAC treatment abrogated this proportional rise in these two indexes of oxidative stress in response to increasing inspiratory loads. A post hoc analysis revealed that only the diaphragms of dogs subjected to high-intensity loads showed a significant increase in both protein tyrosine nitration and carbonylation, which were also significantly reduced by NAC treatment. These results suggest that high-intensity respiratory loading-induced oxidative stress may be neutralized by NAC treatment during IRB in the canine diaphragm. inspiratory loading; respiratory muscles; 3-nitrotyrosine; protein carbonylation; antioxidants Address for reprint requests and other correspondence: E. Barreiro, Muscle and Respiratory System Research Unit, IMIM, C/ Dr. Aiguader, 80, Barcelona, E-08003 Spain (e-mail: ebarreiro{at}imim.es