Enhanced levels of whole-body protein turnover in patients with chronic obstructive pulmonary disease

Am J Respir Crit Care Med. 2000 Oct;162(4 Pt 1):1488-92. doi: 10.1164/ajrccm.162.4.2002045.


A substantial number of patients with chronic obstructive pulmonary disease (COPD) are characterized by fat-free mass wasting and altered muscle and plasma amino acid levels, suggesting changes in protein metabolism. In the present study, we examined whether whole-body protein breakdown (PB) and synthesis (PS) differ between 14 stable patients with COPD and 8 healthy controls. Whole-body PB, PS, and net PB (= PB-PS) were measured by the combined infusion of the stable isotopes L-[ring-(2)H(5)]phenylalanine (Phe) and L-[ring-(2)H(2)]tyrosine. Because there is evidence for specific disturbances in leucine (Leu) metabolism, the PB values were compared with those obtained when infusing L-[1-(13)C]Leu tracer. In arterialized-venous plasma and in vastus lateralis muscle, the isotope enrichment values and amino acid concentrations were measured. Whole-body PS and PB, assessed by Phe and Tyr tracer, were higher in the COPD group than in the control group (p < 0.05), indicating an elevated protein turnover. Net PB was increased in both groups, indicating a comparable degree of protein catabolism in the postabsorptive state. In contrast, whole-body PB determined by Leu tracer was not different between the groups. As a consequence, the ratio of Leu to Phe breakdown was reduced in the COPD group (p < 0.001). Moreover, in the COPD group a higher muscle-to-plasma gradient was found for Leu (p < 0.001) but not for Phe. The present study reveals elevated levels for protein turnover in patients with COPD, and indicates that infusion of the Leu tracer gives a reflection of Leu metabolism but not of whole-body protein metabolism in these patients.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Amino Acids / metabolism
  • Carbon Radioisotopes
  • Female
  • Humans
  • Leucine / metabolism
  • Lung Diseases, Obstructive / physiopathology*
  • Male
  • Middle Aged
  • Predictive Value of Tests
  • Proteins / metabolism*
  • Wasting Syndrome / physiopathology*
  • Whole-Body Counting


  • Amino Acids
  • Carbon Radioisotopes
  • Proteins
  • Leucine