Immunolocalization of Inhaled Recombinant Human Manganese Superoxide Dismutase Reveals a Prolonged Retention in Lung Surface Lining Fluids

Abstract

Oxygen-derived radicals play critical roles in many types of lung injuries involving environmental pollutants. Recently, intranasal insufflation of recombinant human manganese superoxide dismutase (rh-MnSOD) was reported to be efficacious against a hyperoxia model of oxidant lung injury in mice. We employed immunocytochemistry to examine the distribution, retention, and location of rh-MnSOD given to mice by intranasal 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 labeled with rabbit anti-rh-MnSOD antibody and studied at both light and 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 absent 120 h after treatment. There was little intracellular labeling of epithelial or interstitial cells or matrix labeling for rh-MnSOD. Alveolar macrophages had heavy labeling for rh-MnSOD in vesicles and scattered throughout their cytoplasm. rh-MnSOD appears to be cleared by a combination of mucociliary transport in the conducting airways and macrophage endocytosis in the gas exchange regions. rh-MnSOD given by intranasal insufflation delivered this protein to lung epithelial surfaces and protected against hyperoxia-induced injury, which suggests that oxygen-derived radicals in this compartment are important mediators of oxidant-induced lung injury.