Background: Chronic obstructive pulmonary disease (COPD) is associated with neutrophilic inflammation and excessive extracellular matrix (ECM) remodelling in the lungs. The heterogeneous nature of the disease necessitates the stratification of patients into sub-groups for optimal treatment. One such approach is the measurement of serological biomarkers. In this study we aimed to evaluate CPa9-HNE, a fragment of calprotectin released as a by-product of neutrophil elastase proteolytic activity, as a biomarker for COPD progression.  

Methods: Levels of CPa9-HNE were measured using ELISA in plasma from COPD patients (n=255) and control subjects (n=125). Unpaired t tests were used to compare CPa9-HNE plasma levels in COPD and control groups and to compare mild versus severe COPD patients.

Results: COPD and controls differed in sex distribution but not in age and smoking status. CPa9-HNE plasma levels were lower in COPD patients than in controls (p=0.016). Strikingly, higher levels of CPa9-HNE were associated with more severe COPD GOLD stages (p=0.011). Changes in CPa9-HNE were not correlated with the sex or smoking status of the patients.

Conclusions: Lower plasma levels of CPa9-HNE in COPD could be a result of differential fragmentation of calprotectin or higher retention of these fragments in COPD lungs compared to controls. Further investigation is required to understand the underlying disease mechanisms that result in higher levels of CPa9-HNE in more severe stages of COPD.