Biomarkers in obstructive respiratory diseases: an update

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation of the airways, with the involvement of many inflammatory cells and mediators. Traditionally, this inflammation is thought to spread to a systemic level, thus inducing damage of different organs. However, other pathogenetic mechanisms could take part to the above-described process, and some open questions need to be solved. Due to the burden and increasing prevalence of COPD, the opportunity to find biomarkers that can potentially be useful in identifying individuals with the disease, or better, prior to symptoms onset, to diagnose and properly manage the respiratory symptoms, as well as to evaluate the response to treatment and to select specific subtypes of patients for tailored treatments is strongly advocated. Several mediators, enzymes, hormones and cells have been claimed to adhere to this objective. Moreover, the presence of comorbid or concomitant diseases can variably influence the concentration of specific biomarkers in samples of individuals with COPD, and age-related functional and structural changes (inflammaging) can further confuse the biological pattern. Several observations have been performed in the last decades; nevertheless, no biomarker is currently considered as satisfying all the above-mentioned issues. The "Evaluation of COPD longitudinally to identify predictive surrogates and points (ECLIPSE)" study has specifically explored the possibility to identify novel biomarkers that correlate with clinically relevant COPD subtypes and with markers of disease progression. Among the thirty-four biomarkers considered, 15 resulted to be increased in COPD patients rather than in smoker and non-smoker controls. Specific lung proteins such as CC-16 and SPD are promising in detecting lung damage, exacerbation susceptibility or responsiveness to treatment. The ECLIPSE findings confirm that, to date, the use of a single biomarker is not sufficient, but the combination of novel biomarkers with the already existing tools could improve our skills in optimizing treatment of COPD patients.