Hyperbaric oxygen therapy for five days increases blood-brain barrier permeability

This study aimed to explore the effects of hyperbaric oxygen (HBO₂) on blood-brain barrier (BBB) integrity in rats, when administered for one (at 2.5 ATA, 3 HBO₂ sessions a day) and five days (at 2.5 ATA, 3 HBO₂ sessions a day for the first two days, and twice a day for the last three days). Horseradish peroxidase (HRP) was used to evaluate the BBB permeability. Superoxide dismutase (SOD) activity, glutathione (GSH) and malondialdehyde (MDA) levels were measured in the cerebral cortex and hippocampus regions. Frequent vesicles containing HRP reaction products were observed in capillary endothelial cells in the cerebral cortex and hippocampus of rats subjected to HBO₂. The accumulation of HRP reaction products in these brain regions was significantly higher than that of control animals (P ⟨ 0.01). In animals that received HBO₂, MDA levels (P ⟨ 0.01 for five days) and GSH (p ⟨ 0.05 for one day, and P ⟨ 0.01 for five days) were decreased in the cerebral cortex, whereas SOD activities slightly increased in this region. In animals that received HBO₂ significant decreases in MDA (P ⟨ 0.05 for one day; P ⟨ 0.01 for five days) and GSH (P ⟨ 0.05 for five days) levels were observed in the hippocampus region, but SOD activities decreased in this region. We showed that HBO₂ administered with the doses described above impaired BBB integrity in otherwise healthy rats. Therefore, we suggest that the results of this study should be taken into consideration when patients are exposed to HBO₂ with the same doses.