PROTECTION AGAINST OXIDATIVE INJURY AND PERMEABILITY ALTERATION IN CULTURED ALVEOLAR EPITHELIUM BY TRANSFERRIN-CATALASE CONJUGATE

The successful prevention of hydrogen peroxide-induced alveolar permea bility alterations and cell injury by transferrin-catalase conjugate i s described in this study. Permeability alterations and cell injury we re induced in cultured alveolar epithelial monolayers by hydrogen pero xide. Transepithelial transport of a permeability marker, [C-14]mannit ol, and cellular nuclear fluorescence of a membrane integrity indicato r, propidium iodide, were used to quantitate epithelial permeability a nd damage respectively. Hydrogen peroxide (0.1-10 mM) induced a dose-d ependent increase in both alveolar permeability and cellular damage; h owever, the oxidant effect on monolayer permeability did not require p rior cell damage, Electron spin resonance measurements using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide indicated the formation of hydro xyl radicals in hydrogen peroxide-treated cells. Chelation of the cell ular pool of iron by deferoxamine inhibited radical formation and help ed protect the cells from oxidative changes. Prior treatment of the ce lls with catalase (0.1 U-10 U/ml) had minimal protective effects on ce ll injury and permeability alterations. In contrast, transferrin-catal ase conjugate, at the same concentration range, exhibited much improve d protective effects on the cells in response to oxidant stress. This enhanced protection was found to correlate well with an increase in ce llular uptake of the enzyme conjugate via the transferrin receptor end ocytosis pathway. Effective protection by the enzyme conjugate was sho wn to require both the antioxidant enzyme moiety and the cognate moiet y for the cell surface receptor. These findings indicate the potential therapeutic merit of transferrin-catalase conjugate for the treatment of pathological processes in the lung, whenever oxidative stress is i nvolved.