Skeletal Myosteatosis is Associated with Systemic Inflammation and a Loss of Muscle Bioenergetics in Stable COPD

Background: Common features among patients with more advanced chronic obstructive pulmonary disease (COPD) are systemic inflammation and a loss of both muscle mass and normal muscle composition. In the present study, we investigated COPD subjects to better understand how thigh muscle fat infiltration (MFI) and energy metabolism relate to each other and to clinical features of COPD with emphasis on systemic inflammation. Methods: Thirty-two Caucasians with stable COPD were investigated using questionnaires, lung function tests, blood analysis and magnetic resonance imaging (MRI) for analysis of body- and thigh muscle composition. Bioenergetics in the resting thigh muscle, expressed as the PCr/Pi ratio, were analysed using (31)phosphorus magnetic resonance spectroscopy ( (31)P-MRS). Results: Based on the combination of the MFI adjusted for sex ([MFI.sub.a]) and the thigh fat-tissue free muscle volume, expressed as the deviation from the expected muscle volume of a matched virtual control group ([FFMV.sub.vcg]), all COPD subjects displayed abnormally composed thigh muscles. Clinical features of increased COPD severity, including a decrease of blood oxygenation (r = -0.44, p < 0.05) and [FEV.sub.1]/FVC ratio, reflecting airway obstruction (r = -0.53, p < 0.01) and an increase of COPD symptoms (r = 0.37, p < 0.05) and breathing frequency at rest (r = 0.41, p < 0.05), were all associated with a raise of the PCr/Pi ratio in the thigh muscle. Increased [MFI.sub.a] of the thigh muscle correlated positively with markers of systemic inflammation (white blood cell count, r = 0.41, p < 0.05; fibrinogen, r = 0.44, p < 0.05), and negatively with weekly physical activity (r = -0.40, p < 0.05) and the PCr/Pi ratio in the resting thigh muscle (r = -0.41, p < 0.05). Conclusion: The present study implies a link between systemic inflammation, excessive MFI and a loss of bioenergetics in subjects with stable COPD. Keywords: adiposity, body composition, muscle fat infiltration, magnetic resonance imaging, (31)P-MRS, biomarkers