Sputum Biomarkers in Wood and Tobacco Smoke Etiotypes of Chronic Obstructive Pulmonary Disease

Introduction: There is a need to better understand the etiotypes of chronic obstructive pulmonary disease (COPD) beyond the tobacco-smoke (TS-COPD). Wood smoke COPD (WS-COPD) is characterized by greater airway compromise, milder emphysema, and slower rate of lung function decline than TS-COPD. However, it is unclear if these two etiotypes of COPD have differences in sputum biomarker concentrations. Objective was to compare sputum levels of selected sputum biomarkers between WS-COPD and TS-COPD, and healthy controls. Methods: Eighty-eight women (69±12 years) were recruited and classified into: WS-COPD (n=31), TS-COPD (n=29) and controls (n=28). Using ELISA, we determined induced sputum levels of metalloproteinase 9 (MMP-9), chemokine ligand 5 (CCL5), interleukin-8 (IL-8), chemokine ligand 16 (CCL16/HCC-4) and vascular endothelial growth factor (VEGF-1). Differences were analyzed by Kruskal–Wallis and Mann–Whitney-U tests and correlation between airflow limitation and biomarkers by Spearman’s test. Results: At similar degree of airflow obstruction, anthropometrics and medications use, the level of sputum CCL5 was higher in TS-COPD than WS-COPD (p=0.03) without differences in MMP-9, IL-8, CCL16/HCC-4, and VEGF-1. Women with WS-COPD and TS-COPD showed significantly higher sputum levels of MMP-9, IL-8 and CCL5 compared with controls (p<0.001). FEV₁ % predicted correlated negatively with levels of MMP-9 (rho:-0.26; P=0.016), CCL5 (rho:-0.37; P=0.001), IL-8 (rho:-0.42; P<0.001) and VEGF (rho:-0.22; P=0.04). Conclusion: While sputum concentrations of MMP-9, IL-8, and CCL5 were higher in COPD women compared with controls, women with TS-COPD had higher levels of CCL5 compared with those with WS-COPD. Whether this finding relates to differences in pathobiological pathways remains to be determined.