PROTEINASE-FREE MYELOPEROXIDASE INCREASES AIRWAY EPITHELIAL PERMEABILITY IN A WHOLE TRACHEA MODEL

In cystic fibrosis the bronchiectatic conducting airways have large nu mbers of neutrophils in their walls and in their luminal contents. The neutrophil's primary granule enzyme activities of elastase and peroxi dase are increased in the sputum of these patients. It has been postul ated that these enzymes-together or individually-act to damage the air way epithelium. However, only peroxidase activity has consistently cor related 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 w as designed to test whether human neutrophil-derived myeloperoxidase c an independently produce bronchial epithelial damage without the prese nce of proteases, as measured by increased permeability of the airway epithelium. Human peripheral blood neutrophils were purified, their pr imary granules isolated, and their peroxidase purified using affinity and ion exchange column chromatography. Activity of the proteinase-fre e peroxidase was measured using a chromogenic substrate. The effect of this peroxidase on the permeability of excised rat tracheas was measu red using radioactive and fluorescent-labeled non-ionic molecules of v arying molecular weight. Rat tracheas exposed to 15 minute treatments with either 130 U of peroxidase or hydrogen peroxide (10(-5) M) did no t show a significant increase in the permeability of the epithelium to [H-3]inulin, [C-14]sucrose, and fluorescein isothiocyanate dextran 20 compared with control tracheas. However, those tracheas exposed to 13 0 U peroxidase followed by 10(-5) M hydrogen peroxide showed an increa sed permeability to each of the three test solutes. We conclude that p roteinase-free myeloperoxidase, in the presence of non-toxic concentra tions of its substrates, hydrogen peroxide and halide, produced increa ses in permeability to non-ionic molecules in the rat trachea within 1 5 minutes. (C) 1997 Wiley-Liss, Inc.