Effects of native and oxidation-resistant secretory leukoprotease inhibitor on cystic fibrosis sputum: inhibition of neutrophil elastase activity and of sputum-induced secretion from porcine tracheal submucosal glands.

Because the antiprotease defense in cystic fibrosis (CF) airways is overwhelmed by neutrophil elastase (NE), substitution of antiproteases such as secretory leukoprotease inhibitor (SLPI) seems to be a reasonable therapeutic approach. Knowing, however, that native antiproteases may be liable to rapid inactivation by the locally abundant oxidants, we comparatively investigated the interactions of CF sputum with recombinant native SLPI (rSLPI) and its partially oxidation-resistant variant (rSLPI-242), respectively, to estimate their therapeutic potentials. NE activity in supernatants from diluted CF sputum samples was dose-dependently inhibited by both rSLPI and rSLPI-242, with comparable potency. Addition of the oxidant N-chlorosuccinimide resulted in significant superiority of rSLPI-242 over rSLPI. When fresh neutrophil-rich CF sputum was incubated with rSLPI and rSLPI-242, respectively, rSLPI-242 inhibited sputum NE activity significantly more potently than did rSLPI; addition of the antioxidant superoxide dismutase significantly improved the effect of rSLPI. Furthermore, secretion of radiolabeled macromolecules from porcine tracheal glands induced by purified NE or by CF sputum was inhibited dose-dependently by rSLPI and even better by rSLPI-242. We conclude that both rSLPI and rSLPI-242 effectively inhibit NE activity and NE-induced gland hypersecretion in vitro. In vivo effects of CF remain to be analyzed; an advantage of the partially oxidation-resistant rSLPI-242 can be expected.