Increased kynurenine plasma concentrations and kynurenine-tryptophan ratio in mild-to-moderate chronic obstructive pulmonary disease patients

Aim: Since an increase in kynurenine (Kyn) plasma concentrations has been proposed as marker of immune system activation, we studied the associations between the Kyn levels and presence and severity of chronic obstructive pulmonary disease (COPD). Methods & results: Plasma Kyn, tryptophan (Trp) and Kyn/Trp ratio were measured in 43 COPD patients with clinically defined mild (n = 29) or moderate (n = 14) disease and 43 age-and sex-matched healthy controls. When compared with controls, COPD patients had significantly higher plasma Kyn concentrations and Kyn/Trp ratios. In multiple logistic regression analysis, after adjusting for clinical and demographic confounders, the Kyn/Trp ratio was independently associated with COPD severity. Discussion & conclusion: Kyn and Kyn/Trp ratio might represent a new, sensitive, biomarker of systemic inflammation in COPD patients.