Is there any relationship between plasma antioxidant capacity and lung function in smokers and in patients with chronic obstructive pulmonary disease?

Background-It has been suggested that oxidative stress is an important fact or in the pathogenesis of chronic obstructive pulmonary disease (COPD). We have shown that an oxidant/antioxidant imbalance occurs in the distal air s paces of smokers and in patients with COPD which is reflected systemically in the plasma. A study was undertaken to determine whether plasma antioxida nt status correlated with lung function as assessed by forced expiratory vo lume in one second (FEV,) and forced vital capacity (FVC) in smokers and pa tients with COPD. Methods-Plasma antioxidant capacity, assessed by the Trolox equivalent anti oxidant capacity (TEAC) as an index of overall systemic oxidative stress, a nd protein thiol levels were measured in 95 patients with stable COPD, in 8 2 healthy smokers, and in 37 healthy non-smokers. Results-Mean (SE) plasma TEAC levels were significantly decreased in patien ts with COPD (0.81 (0.03) mmol/l, p<0.001) and in healthy smokers (0.87 (0. 04) mmol/l, p<0.001) compared with healthy nonsmokers (1.31 (0.11) mmol/l). The mean differences in plasma antioxidant capacity (mM) were (0.81, 95% c onfidence interval (CI) 0.22 to 1.48), (0.87, 95% CI 0.2 to 1.46), and (1.3 1, 95% CI 1.09 to 1.58) in patients with COPD, healthy smokers, and healthy non-smokers, respectively. This reduction was associated with a 29% (95% C I 18 to 38) and a 30% (95% CI 19 to 40) decrease in plasma protein thiol le vels in COPD patients and smokers, respectively. Current smoking was not th e main contributor to the reduction in antioxidant capacity in patients wit h COPD as those patients who were still smokers had similar TEAC levels (me an (SE) 0.78 (0.05); n = 25) to those who had stopped smoking (0.84 (0.02); n = 70). No significant correlations were found between spirometric data m easured as FEV1 % predicted or FEV1/FVC % predicted and the plasma levels o f TEAC in patients with COPD, healthy smokers, or healthy nonsmokers. Simil arly, there was no significant correlation between FEV1 % predicted or FEV1 /FVC % predicted and the levels of plasma protein thiols in the three group s. Conclusions-These data confirm decreased antioxidant capacity in smokers an d patients with COPD, indicating the presence of systemic oxidative stress. However, no relationship was found between protein thiols or TEAC levels a nd measurements of airflow limitation in either smokers or in patients with COPD.