Neutrophil elastase has been linked to inflammatory lung diseases such as chronic obstructive pulmonary disease, adult respiratory distress syndrome, emphysema, and cystic fibrosis. In guinea pigs, aerosol challenge with human neutrophil elastase causes bronchoconstriction, but the mechanism by which this occurs is not completely understood. Our laboratory previously showed that human neutrophil elastase releases tissue kallikrein (TK) from cultured tracheal gland cells. TK has been identified as the major kininogenase of the airway and cleaves both high- and low-molecular weight kininogen to yield lysyl-bradykinin. Because inhaled bradykinin causes bronchoconstriction and airway hyperresponsiveness in asthmatic patients and allergic sheep, we hypothesized that elastase-induced bronchoconstriction could be mediated by bradykinin. To test this hypothesis, we measured lung resistance (Rl) in sheep before and after inhalation of porcine pancreatic elastase (PPE) alone and after pretreatment with a bradykinin B2 antagonist (NPC-567), the specific human elastase inhibitor ICI 200,355, the histamine H1-antagonist diphenhydramine hydrochloride, the cysteinyl leukotriene 1 receptor antagonist montelukast, or the cyclooxygenase inhibitor indomethacin. Inhaled PPE (125–1,000 μg) caused a dose-dependent increase in Rl. Aerosol challenge with a single 500 μg dose of PPE increased Rlby 132 ± 8% over baseline. This response was blocked by pretreatment with NPC-567 and ICI-200,355 ( n = 6; P < 0.001), whereas treatment with dyphenhydramine hydrochloride, montelukast, or indomethacin failed to block the PPE-induced bronchoconstriction. Consistent with pharmacological data, TK activity in bronchial lavage fluid increased 134 ± 57% over baseline ( n = 5; P < 0.02). We conclude that, in sheep, PPE-induced bronchoconstriction is in part mediated by the generation of bradykinin. Our findings suggest that elastase-kinin interactions may contribute to changes in bronchial tone during inflammatory diseases of the airways.
Flavonoids as inhibitors of human neutrophil elastase