Reoxygenation with 100% Oxygen Following Hypoxia in Mice Causes Apoptosis

After hypoxia, reoxygenation with air is the consensus treatment for full-term neonates; however, the effect of hyperoxic reoxygenation of adults is unknown. The present study was designed to investigate the effects of reoxygenation with 100% oxygen after hypoxia on inflammation and apoptosis in mice. Eight-week-old mice were either subjected to hypoxia in 8% oxygen for 30 min or air served as controls. Following hypoxia, mice underwent reoxygenation for 30 min with 21% or 100% oxygen. Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), caspase-3 and brain derived neurotrophic factor (BDNF) mRNA study and histopathological study were performed. Reoxygenation with 100% oxygen significantly increased TNF-α (2.5 h after hypoxia), IL-1β (5 h after hypoxia), caspase-3 (8 h after hypoxia) mRNA levels in the whole brain compared with 21% oxygen, and significantly decreased erythropoietin mRNA expression compared with 21% oxygen 9 h after reoxygenation. However, reoxygenation with 100% oxygen and 21% oxygen significantly decreased BDNF mRNA levels compared with control air group. There were no clear abnormal findings showing neuronal death among the three groups. Reoxygenation with 100% oxygen after hypoxia induced inflammation and apoptosis in adult mice. Therefore, these results suggest that the reoxygenation with 100% oxygen after hypoxia has harmful effects on adult brain as well as on neonatal brain.