Proteinase-free myeloperoxidase increases airway epithelial permeability in a whole trachea model

In cystic fibrosis the bronchiectatic conducting airways have large numbers of neutrophils in their walls and in their luminal contents. The neutrophil's primary granule enzyme activities of elastase and peroxidase are increased in the sputum of these patients. It has been postulated that these enzymes-together or individually-act to damage the airway epithelium. However, only peroxidase activity has consistently correlated with the degree of structural and functional airway disease in these patients with leakage of plasma protein into the airway lumen (Regelmann et al., Pediatr Pulmonol. 1995; 19:1-9). The present study was designed to test whether human neutrophil-derived myeloperoxidase can independently produce bronchial epithelial damage without the presence of proteases, as measured by increased permeability of the airway epithelium. Human peripheral blood neutrophils were purified, their primary granules isolated, and their peroxidase purified using affinity and ion exchange column chromatography. Activity of the proteinase-free peroxidase was measured using a chromogenic substrate. The effect of this peroxidase on the permeability of excised rat tracheas was measured using radioactive and fluorescent-labeled non-ionic molecules of varying molecular weight. Rat tracheas exposed to 15 minute treatments with either 130 U of peroxidase or hydrogen peroxide (10^-5 M) did not show a significant increase in the permeability of the epithelium to [³H]inulin, [¹⁴C]sucrose, and fluorescein isothiocyanate dextran 20 compared with control tracheas. However, those tracheas exposed to 130 U peroxidase followed by 10^-5 M hydrogen peroxide showed an increased permeability to each of the three test solutes. We conclude that proteinase-free rnyeloperoxidase, in the presence of non-toxic concentrations of its substrates, hydrogen peroxide and halide, produced increases in permeability to non-ionic molecules in the rat trachea within 15 minutes.