Effect of steroid on hyperoxia-induced ICAM-1 expression in pulmonary endothelial cells

Intercellular adhesion molecule-1 (ICAM-1) of the vascular endothelium plays a key role in the development of pulmonary oxygen toxicity. We studied the effect of steroid on hyperoxia-induced ICAM-1 expression using cultured endothelial cells in vitro. Human pulmonary artery endothelial cells (HPAECs) were cultured to confluence, and then the monolayers were exposed to either control (21% O₂-5% CO₂) or hyperoxic (90% O₂-5% CO₂) conditions with and without a synthetic glucocorticoid, methylprednisolone (MP). MP reduced hyperoxia-induced ICAM-1 and ICAM-1 mRNA expression in a dose-dependent manner. Neutrophil adhesion to hyperoxia-exposed endothelial cells was also inhibited by MP treatment. In addition, MP attenuated hyperoxia-induced H₂O₂ production in HPAECs as assessed by flow cytometry. An electrophoretic mobility shift assay demonstrated that hyperoxia activated nuclear factor-κB (NF-κB) but not activator protein-1 (AP-1) and that MP attenuated hyperoxia-induced NF-κB activation dose dependently. With Western immunoblot analysis, IκB-α expression was decreased by hyperoxia and increased by MP treatment. These results suggest that MP downregulates hyperoxia-induced ICAM-1 expression by inhibiting NF-κB activation via increased IκB-α expression.