Greater whole-body myofibrillar protein breakdown in cachectic patients with chronic obstructive pulmonary disease

Background: Experimental studies indicate that greater skeletal muscle protein breakdown is a trigger for the cachexia that often is prevalent in chronic obstructive pulmonary disease (COPD). Objective: We compared myofibrillar protein breakdown (MPB) with whole-body (WB) protein breakdown (PB) in 9 cachectic COPD patients [(x) over bar SEM forced expiratory Volume in 1 s (FEV1): 48 +/- 4% of predicted], 7 noncachectic COPD patients (FEV1: 53 +/- 5% of predicted), and 7 age-matched healthy control subjects, who were matched by body mass index with the noncachectic patients. Design: After the subjects fasted overnight (10 h) and discontinued the maintenance medication, a primed constant and continuous infusion protocol was used to infuse L-[ring-H-2(5)]-phenylalanine and L+[ring-H-2(2)]-tyrosine to measure WB protein turnover and L- [H-2(3)]- 3-methylhistidine to measure WB MPB. Three arterialized venous blood samples were taken between 80 and 90 min of infusion to measure amino acid concentrations and tracer enrichments. Results: Body composition, WB protein turnover, and WB MPB did not differ significantly between the noncachectic COPD and control subjects. Cachectic COPD patients had lower fat mass and fat-free mass values (both: P < 0.01) than did the noncachectic COPD patients. WB MPB was significantly (P < 0.05) higher in the cachectic COPD group (18 +/- 3 nmol (.) kg(-1) (.) min(-1)) than in the combined control and noncachectic COPD groups (10 +/- 1 nmol kg(-1) (.) min(-1)), but WB protein turnover did not differ significantly between the groups. Correlations with fat-free mass were significant (P < 0.05) for plasma glutamate and branched-chain amino acids, and that for WB MPEI trended toward significance (P = 0.07). Conclusion: Cachexia in clinically stable patients with moderate COPD is characterized by increased WB MPB, which indicates that myofibrillar protein wasting is an important target for nutritional and pharmacologic modulation.