Hydrogen Gas Mitigates Acute Hypoxia-Induced Oxidative and Inflammatory Brain Injuries in Medaka (Oryzias latipes)

Hypoxia-induced oxidative stress and inflammation in the brain are critical contributors to neurological disorders. Hydrogen gas has emerged as a therapeutic agent with potent antioxidant and anti-inflammatory properties. In this study, we evaluated the protective effects of hydrogen against acute hypoxia-induced brain injuries in medaka. Fish were exposed to hypoxia and then recovered in water bubbled with air, hydrogen, or ozone. LOX-1 hypoxia probe imaging and HIF-1α immunostaining showed persistent tissue hypoxia in the air and ozone groups, which was significantly reduced by hydrogen treatment. Histological analysis revealed extensive vascular congestion in the midbrain after hypoxia, which was markedly alleviated by hydrogen. TUNEL assay demonstrated that hydrogen suppressed hypoxia-induced neuronal apoptosis. Immunohistochemistry and ELISA showed elevated levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and proinflammatory markers (COX-2, IL-6, TNF-α) in the brains of air- and ozone-treated fish; these increases were significantly attenuated by hydrogen. ORAC assay confirmed that hydrogen restored brain antioxidant capacity. Behavioral analysis further demonstrated that hydrogen treatment improved locomotor activity and stabilized respiratory function. These results indicate that hydrogen protects medaka against hypoxia-induced oxidative and inflammatory injuries and may represent a promising therapeutic strategy for hypoxia-related neurological disorders.