Cytokine profile in quadriceps muscles of patients with severe COPD.
BACKGROUND
Systemic proinflammatory cytokines and oxidative stress have been described in association with peripheral muscle wasting and weakness of patients with severe chronic obstructive pulmonary disease (COPD), but their expression in skeletal muscle is unknown. The objectives of the present study were to determine muscle protein levels of selected cytokines in patients with COPD and to study their relationships with protein carbonylation as a marker of oxidative stress, quadriceps function and exercise capacity.


METHODS
We conducted a cross sectional study in which 36 cytokines were detected using a human antibody array in quadriceps specimens obtained from 19 patients with severe COPD and seven healthy controls. Subsequently, selected cytokines (tumour necrosis factor (TNF)alpha, TNFalpha receptors I and II, interleukin (IL) 6, interferon gamma, transforming growth factor (TGF) beta and vascular endothelial growth factor (VEGF)), as well as protein carbonylation (oxidative stress index) were determined using an enzyme linked immunosorbent assay (ELISA) in all muscles.


RESULTS
Compared with controls, the vastus lateralis of patients with COPD showed significantly lower protein ELISA levels of TNFalpha, which positively correlated with their quadriceps function, TNFalpha receptor II and VEGF. Protein ELISA levels of IL6, interferon gamma and TGFbeta did not differ between patients and controls. Quadriceps protein carbonylation was greater in patients and inversely correlated with quadriceps strength among them.


CONCLUSIONS
These findings do not support the presence of a proinflammatory environment within the quadriceps muscles of clinically and weight stable patients with severe COPD, despite evidence for increased oxidative stress and the presence of muscle weakness.