Increased levels of N^ε-(carboxymethyl)lysine in epithelial lining fluid from peripheral airways in patients with chronic obstructive pulmonary disease: a pilot study

It has been reported that small airway inflammation is closely associated with the severity of airflow limitation in COPD (chronic obstructive pulmonary disease). We tested a new method of measurement of biochemical constituents in ELF (epithelial lining fluid) obtained separately from the central or peripheral airways using a bronchoscopic microsampling technique. The present study was designed to determine the validity of measuring CML [N^ε-(carboxymethyl)lysine] levels in ELF for the assessment of small airway inflammation in COPD. Ten non-smokers, ten current smokers and 16 COPD patients were included in the present study. Concentrations of CML, 8-isoprostane and IL-8 (interleukin-8) were measured in ELF separately from the central or peripheral airways. CML levels in central airways did not differ significantly, but were markedly higher in peripheral than in central airways in the three groups. However, CML levels in peripheral airways of COPD patients were significantly higher than those in non-smokers and current smokers. In COPD patients, the CML level in peripheral airways was significantly correlated with FEV₁ (forced expiratory volume in 1 s) (r=−0.82, P=0.002) and FEV₁/FVC (forced vital capacity) (r=−0.57, P=0.03). Moreover, CML levels in peripheral airways were significantly correlated with levels of both 8-isoprostane (r=0.76, P=0.003) and IL-8 (r=0.67, P=0.01). In conclusion, these findings suggest that elevated levels of CML in ELF from peripheral airways were observed in COPD patients, and this parameter was correlated with the severity of airflow limitation.