The Pseudomonas aeruginosa secretory product pyocyanin inactivates α1 protease inhibitor:: Implications for the pathogenesis of cystic fibrosis lung disease

alpha(1) Protease inhibitor (alpha(1)PI) modulates serine protease activity in the lung. Reactive oxygen species inactivate alpha(1)PI, and this process has been implicated in the pathogenesis of a variety of forms of lung injury. An imbalance of protease-antiprotease activity is also detected in the airways of patients with cystic fibrosis-associated lung disease who are infected with Pseudomonas aeruginosa. P. aeruginosa secretes pyocyanin, which, through its ability to redox cycle, induces cells to generate reactive oxygen species. We tested the hypothesis that redox cycling of pyocyanin could lead to inactivation of alpha(1)PI. When alpha(1)PI was exposed to NADH and pyocyanin, a combination that results in superoxide production, alpha(1)PI lost its ability to form an inhibitory complex with both porcine pancreatic elastase (PPE) rind trypsin. Similarly, addition of pyocyanin to cultures of human airway epithelial cells to which alpha(1)PI was also added resulted in a loss of the ability of alpha(1)PI to form a complex with PPE or trypsin. Neither superoxide dismutase, catalase, nor dimethylthiourea nor depletion of the media of O-2 to prevent formation of reactive oxygen species blocked pyocyanin-mediated inactivation of alpha(1)PI. These data raise the possibility that a direct interaction between reduced pyocyanin and alpha(1)PI is involved in the process. Consistent with this possibility, pretreatment of alpha(1)PI with the reducing agent beta-mercaptoethanol also inhibited binding of trypsin to alpha(1)PI. These data suggest that pyocyanin could contribute to lung injury in the P. aeruginosa-infected airway of cystic fibrosis patients by decreasing the ability of alpha(1)PI to control the local activity of serine proteases.