Plasma protein thiols: an early marker of oxidative stress in asthma and chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease ( COPD ) and asthma are both characterized by heterogeneous chronic airway inflammation and obstruction as well as oxidative stress ( OS ). However, it is unknown whether OS occurs in early disease and how to best assess its presence. Plasma OS markers ( TBARS , PSH , taurine, GSH , ergothioneine and paraoxonase 1 activity) and lung function tests were measured in patients with mild stable asthma ( n = 24) and mild stable COPD ( n = 29) and in age‐ and sex‐matched controls. Forced expiratory volume in 1 s ( FEV 1 ) was associated with age both in patients and control groups. By contrast, FEV 1 was positively correlated with PSH only in COPD (ρ = 0·49, P = 0·007). In multiple logistic regression analysis, lower PSH was the only OS marker independently associated with increased odds of both asthma ( OR = 0·32, 95% CI 0·13–0·78, P = 0·01) and COPD ( OR = 0·50, 95% CI 0·26–0·95, P = 0·03). These findings suggest that proteins ‐SH are a sensitive OS marker in early COPD and asthma.