Am. J. Respir. Crit. Care Med., Volume 157, Number 5, May 1998, 1413-1417

Cytochrome Oxidase Activity and Mitochondrial Gene Expression in Skeletal Muscle of Patients with Chronic Obstructive Pulmonary Disease

JAUME SAULEDA, FRANCISCO GARCÍA-PALMER, RUDOLF J. WIESNER, SALVADOR TARRAGA, INGA HARTING, PURIFICACIÓN TOMÁS, CRISTINA GÓMEZ, CARLES SAUS, ANDREU PALOU, and ALVAR G. N. AGUSTÍ

Serveis de Pneumologia and Anatomia-Patològica, Hospital Univ. Son Dureta; Departament de Biologia Fonamental i Ciències de la Salut, Universitat Illes Balears, Institut Universitari Ciències de la Salut, Palma de Mallorca, Spain; and Physiologisches Institut, Universität Heidelberg, Heidelberg, Germany

Several recent studies have suggested that skeletal muscle bioenergetics are abnormal in patients with chronic obstructive pulmonary disease (COPD). This study investigates the activity of cytochrome oxidase (COX), the terminal enzyme in the mitochondrial electron transport chain, and the expression of two mitochondrial DNA genes related to COX (mRNA of subunit I of COX [COX-I] and the RNA component of the 12S ribosomal subunit [12S rRNA]), in quadriceps femoris muscle biopsies obtained from COPD patients with various degrees of arterial hypoxemia, and from healthy sedentary control subjects of similar age. The activity of COX was measured spectrophotometrically in fresh tissue at 37° C with excess substrate. RNA transcripts were measured using reverse transcription and polymerase chain reaction. The measurements of mRNA COX-I and 12S rRNA were normalized to the mRNA of actin, which is a housekeeping gene not influenced by hypoxia. We found that, compared with control subjects, COPD patients with chronic respiratory failure (Pa_O2 < 60 mm Hg) showed increased COX activity (p < 0.05). Further, the activity of COX was inversely related to arterial PO₂ value (Rho 0.59, p < 0.01). The COX-I mRNA content was not different between patients and control subjects but patients with chronic respiratory failure had higher levels of 12S rRNA (p < 0.05), which were again inversely related to Pa_O2 (Rho 0.49, p < 0.05). These results indicate that the activity of COX is increased in skeletal muscle of patients with COPD and chronic respiratory failure, and they suggest that this is likely regulated at the translational level by increasing the number of mitochondrial ribosomes.

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