IMMUNOLOCALIZATION OF INHALED RECOMBINANT HUMAN MANGANESE SUPEROXIDE-DISMUTASE REVEALS A PROLONGED RETENTION IN LUNG SURFACE LINING FLUIDS

Oxygen-derived radicals play critical roles in many types of lung inju ries involving environmental pollutants. Recently, intranasal insuffla tion of recombinant human manganese superoxide dismutase (rh-MnSOD) wa s reported to be efficacious against a hyperoxia model of oxidant lung injury in mice. We employed immunocytochemistry to examine the distri bution, retention, and location of rh-MnSOD given to mice by intranasa l insufflation. Mice were given a single dose (20 mg/kg) of either rh- MnSOD or bovine serum albumin and killed at 0.25, 4, 24, 48, or 120 h after treatment. Lungs were fixed by vascular perfusion. lung sections from animals in the different time points and treatment groups were l abeled with rabbit anti-rh-MnSOD antibody and studied at both light an d electron microscopic levels, rh-MnSOD labeling was patchy but widely disseminated at the early time points and mainly localized in surface lining fluids and to a lesser extent on epithelial cell surfaces. The intensity of the labeling dropped off after 24 h and was virtually ab sent 120 h after treatment. There was little intracellular labeling of epithelial or interstitial cells or matrix labeling for rh-MnSOD. Alv eolar macrophages had heavy labeling for rh-MnSOD in vesicles and scat tered throughout their cytoplasm. rh-MnSOD appears to be cleared by a combination of mucociliary transport in the conducting airways and mac rophage endocytosis in the gas exchange regions. rh-MnSOD given by int ranasal insufflation delivered this protein to lung epithelial surface s and protected against hyperoxia-induced injury, which suggests that oxygen-derived radicals in this compartment are important mediators of oxidant-induced lung injury.