INTRATRACHEAL INSTILLATION OF KERATINOCYTE GROWTH-FACTOR DECREASES HYPEROXIA-INDUCED MORTALITY IN RATS

Alveolar type II cell proliferation occurs after many forms of lung in jury and is thought to play a critical role in alveolar epithelial rep air. Keratinocyte growth factor/fibroblast growth factor 7 (KGF) has b een shown to promote alveolar type II cell growth in primary culture a nd alveolar epithelial hyperplasia in vivo. In this study, we used imm unohistochemical analysis to determine the intrapulmonary distribution and cellular localization of recombinant human KGF (rhKGF) instilled into the trachea of rats. 6 h after administration, immunoreactive KGF was observed within the lung parenchyma and along alveolar epithelial cell membranes. By 18-24 h, KGF was detected intracellularly in alveo lar epithelial cells and intraalveolar macrophages. Immunoreactive KGF was not demonstrable 48 h after delivery or in lung sections from PBS -treated animals. Intratracheal instillation of 5 mg/kg rhRGF stimulat ed a marked, time-dependent increase in the alveolar type II cell spec ific labeling index to a maximum level of 33+/-3% 48 h after rhKGF adm inistration compared with 1.3+/-0.3% after PBS instillation. In additi on, this increase in type II cell proliferation in vivo was documented by flow cytometric analysis of isolated type II cells which revealed a nearly fivefold increase in the proportion of cells traversing throu gh the S and G2/M phases of the cell cycle. To test the hypothesis tha t KGFs effects on type II cells in vivo might affect the response to l ung injury, rats were treated with rhKGF and exposed to hyperoxia. Ani mals that received 1 or 5 mg/kg rhKGF exhibited dramatically reduced m ortality (P < 0.001, for both doses). Survival for animals treated wit h 0.1 mg/kg rhKGF was not significantly different from either untreate d rats or animals treated with heat-denatured rhKGF. The lungs of rhKG E-treated animals that survived hyperoxia exposure had minimal hemorrh age and no exudate within the intraalveolar space. These experiments e stablished that intratracheal administration of rhKGF stimulated alveo lar type II cell proliferation in vivo and reduced hyperoxia-induced l ung injury in rats. Directed delivery of KGF to the lungs may provide a therapeutic strategy to preserve or restore the alveolar epithelium during exposure to hyperoxia or other injurious agents.