Oxidants affect permeability and repair of the cultured human tracheal epithelium

To examine the effects of oxidants on the airway epithelial barrier functions, human tracheal epithelial cells were cultured on porous filter membrane. Glucose oxidase (GO; 10 U/ml), hydrogen peroxide (H2O2; 4 x 10(-3) M), and xanthine (5 x 10(-4) M) plus xanthine oxidase (20 mU/ml) (X-XO) significantly increased electrical conductance across epithelial membrane (G), short-circuit current (Isc) measured with Ussing's chamber methods, and [3H]mannitol flux through the cultured epithelium. Increases in G and Isc induced by oxidants were significantly inhibited by catalase (1,000 U/ml) and the protein kinase C inhibitor staurosporine (10(-7) M), but superoxide dismutase (SOD; 100 U/ml) was without effect. GO, H2O2, and X-XO inhibited the epithelial cell growth, [3H]thymidine incorporation by the cells, and epithelial repair of artificially produced focal epithelial defects (1-2 mm diam) on plastic vessels. Catalase also inhibited effects induced by oxidants on cell growth and proliferation. These results suggest that oxidants reduce tracheal epithelial barrier functions by damaging tight junctions and inhibiting cell proliferation, and these effects of oxidants on epithelial cells may be mediated by H2O2 rather than superoxide anion and by activation of protein kinase C.