Detection and inhibition of ENaC-activating proteases associated with airway dehydration in COPD

Abstract

Airways dehydration contributing to mucus obstruction is a hallmark of chronic airways diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) (Mall, Ann Am Thorac Soc 2016;13(2):S177-85). In CF the relationship between a reduced airways surface liquid and dysregulation of the epithelial sodium channel (ENaC) through the presence of elevated levels of trypsin-like channel activating proteases (TL-CAPs) is well established. In COPD airways dehydration is known to aggravate the disease however little is as yet known regarding the role of ENaC and associated TL-CAP activity. The objective of this study was to determine TL-CAP activity in primary COPD airway epithelial cells (AECs) and to assess the effectiveness of a highly novel in-house inhibitor, NAP858 compared to our established compound QUB-TL1 (Reihill et al, AJRCCM 2016;194(6):701-10). Secreted TL-CAP activity was determined in conditioned media recovered from primary differentiated COPD and healthy AECs treated in the presence and absence of QUB-TL1 and NAP858 by the hydrolysis of BOC-QAR-NH2Mec over 60 min. COPD AECs were found to secrete ~40% more TL-CAP activity than healthy cell controls. These activities were highly sensitive to QUB-TL1 and NAP858; with the latter eliciting a greater degree of inhibition. QUB-TL1 and NAP858 are effective inhibitors of the elevated TL-CAP activity observed in COPD primary AECs and have also been shown to increase mucociliary clearance in primary CF cultures. NAP858 is a novel compound which is more readily synthesised than QUB-TL1 therefore has significant potential as a TL-CAP inhibitor in future studies investigating the role of ENaC in chronic airways diseases.