Localization and activity of recombinant human CuZn superoxide dismutase after intratracheal administration

Hyperoxia and mechanical ventilation cause acute lung injury which may be mitigated by prophylactic intratracheal (IT) administration of recombinant human CuZn superoxide dismutase (rhSOD). However, little is known about the localization, activity, and metabolism of rhSOD after IT administration by instillation or nebulization. Twenty-six newborn piglets were intubated, mechanically ventilated, and given either saline or fluorescently labeled rhSOD (5 mg/kg IT) by instillation or nebulization. Animals were killed 1, 6, or 12 h later. Intact rhSOD (% total fluorescence still associated with macromolecules) and total SOD activity in lung tissue were then determined. Results indicate that, after 1 and 6 h of administration, the majority of rhSOD present in the lung was still associated with the fluorescent label. By 12 h, most of the rhSOD was no longer fluorescently labeled. At 1 h, lung SOD activity increased by 100% compared with untreated control values, with activity remaining elevated at 6 and 12 h. Laser confocal microscopy of lung tissue showed that at 1 h, labeled rhSOD was found throughout the lung, inside a variety of cell types of airways, respiratory bronchioles, and alveoli. Deposition was more homogeneous after nebulization. Negative controls had minimal background fluorescence. These data indicate that after IT administration, rhSOD is rapidly incorporated into cells in the lung and significantly increases lung SOD activity. These observations have important implications for the clinical use of rhSOD in human trials.