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 rec ombinant human CuZn superoxide dismutase (rhSOD). However, little is k nown about the localization, activity, and metabolism of rhSOD after I T administration by instillation or nebulization. Twenty-six newborn p iglets were intubated, mechanically ventilated, and given either salin e or fluorescently labeled rhSOD (5 mg/kg IT) by instillation or nebul ization. Animals were killed 1, 6, or 12 h later. Intact rhSOD (% tota l fluorescence still associated with macromolecules) and total SOD act ivity in lung tissue were then determined. Results indicate that, afte r 1 and 6 h of administration, the majority of rhSOD present in the lu ng was still associated with the fluorescent label. By 12 h, most of t he rhSOD was no longer fluorescently labeled. At 1 h, lung SOD activit y increased by 100% compared with untreated control values, with activ ity remaining elevated at 6 and 12 h. Laser confocal microscopy of lun g tissue showed that at 1 h, labeled rhSOD was found throughout the lu ng, inside a variety of cell types of airways, respiratory bronchioles , and alveoli. Deposition was more homogeneous after nebulization. Neg ative controls had minimal background fluorescence. These data indicat e that after IT administration, rhSOD is rapidly incorporated into cel ls in the lung and significantly increases lung SOD activity. These ob servations have important implications for the clinical use of rhSOD i n human trials.