The Mitochondrial Phenotype of Peripheral Muscle in Chronic Obstructive Pulmonary Disease Disuse or Dysfunction?

Rationale Peripheral muscle alterations have been recognized to contribute to disability in chronic obstructive pulmonary disease (COPD). Objectives: To describe the mitochondrial phenotype in a moderate to severe COPD population and age-matched controls. Methods: Three primary aspects of mitochondrial function were assessed in permeabilized locomotor muscle fibers. Measurements and Main Results: Respiration rates per milligram of fiber weight were significantly lower in COPD muscle compared with healthy age-matched control muscle under various respiratory states. However, when variations in mitochondrial volume were taken into account by normalizing respiration per unit of citrate synthase activity, differences between the two groups were abolished, suggesting the absence of specific mitochondrial respiratory impairment in COPD. H2O2 production per mitochondrion was higher both under basal and ADP-stimulated states, suggesting that mitochondria from COPD muscle have properties that potentiate H2O2 release. Direct assessment of mitochondrial sensitivity to Ca2+-induced opening of the permeability transition pore (PTP) indicated that mitochondria from patients with COPD were more resistant to PTP opening than their counterparts in control subjects. Conclusions: Comparison of these results with those of studies comparing healthy glycolytic with oxidative muscle suggests that these differences may be attributable to greater type 11 fiber expression in COPD muscle, as mitochondria within this fiber type have respiratory function similar to that of mitochondria from type I fibers, and yet are intrinsically prone to greater release of H2O2 and more resistant to PTP opening. These results thus argue against the presence of pathological mitochondrial alterations in this category of patients with COPD.