MODULATION OF ICAM-1 EXPRESSION BY EXTRACELLULAR GLUTATHIONE IN HYPEROXIA-EXPOSED HUMAN PULMONARY-ARTERY ENDOTHELIAL-CELLS

To investigate the mechanisms regulating hyperoxia-induced intercellul ar adhesion molecule-1 (ICAM-1) expression, we studied the effects of antioxidants on ICAM-1 expression, and the relationship between ICAM-1 expression and extracellular glutathione levels in human pulmonary ar tery endothelial cells (HPAEC) and human umbilical vein endothelial ce lls (HUVEC). Cells were cultured to confluence and exposed to hyperoxi a (90% O-2) for 48 h with or without various antioxidants, including s uperoxide dismutase (SOD), catalase, N-acetylcysteine (NAC), and gluta thione. The levels of ICAM-1 expression in the endothelial cells and t he concentrations of reduced (GSH) and oxidized glutathione (GSSG) in the media were examined by flow cytometry and spectrophotometry, respe ctively. After exposure to hyperoxia, ICAM-1 expression was increased, and the supernatant total glutathione was decreased as compared with those at normoxia. SOD did not change ICAM-1 expression. The hyperoxia -induced increase in ICAM-1 expression was even greater with the addit ion of catalase. The ICAM-1 expression was decreased and the GSH conce ntration was increased with the addition of NAG. There were negative r elationships between the level of ICAM-1 expression and the supernatan t total glutathione concentration in catalase-treated HPAEC (R = 0.822 , P < 0.0005) and HUVEC (R = 0.567, P < 0.01). Negative relationships were also demonstrated between the level of ICAM-1 expression and the total extracellular glutathione concentrations in NAG-treated HPAEC (R = 0.877, P < 0.0005) and HUVEC (R = 0.727, P < 0.0005). Exogenous GSH decreased ICAM-1 expression in both hyperoxia-exposed HPAEC and HUVEC , while exogenous GSSG did not. These results suggest that extracellul ar GSH plays a role in regulating hyperoxia-induced ICAM-1 expression in HPAEC and HUVEC.