Neuroprotective Effects of Molecular Hydrogen via Oxidative Stress and Neuroinflammation Regulation in a 5xFAD Mouse Model

Alzheimer's disease (AD) is a progressive neurodegenerative disorder in which amyloid-beta (Aβ) accumulation, oxidative stress (OS), and chronic inflammation drive synaptic dysfunction and cognitive decline. Molecular hydrogen (H₂) has emerged as a candidate neuroprotective gas with selective antioxidant and anti-inflammatory properties, although its efficacy in amyloid-driven pathology remains incompletely defined. In this study, 5xFAD transgenic mice harboring human amyloid precursor protein (APP) and presenilin-1 (PSEN1) mutations and age-matched C57BL/6 wild-type mice were exposed to 2% H₂ by inhalation for 1 h/day over 4 weeks. H₂ inhalation reduced hippocampal reactive oxygen species (ROS), increased systemic catalase activity, and enhanced hippocampal ATP levels. In serum, H₂ decreased tumor necrosis factor-α (TNF-α) and interleukin (IL)-1β, restored IL-10, and partially normalized IL-13, shifting the peripheral environment toward a less pro-inflammatory profile. In the hippocampus, H₂ upregulated nuclear factor erythroid 2-related factor 2 (NRF2), attenuated nuclear factor kappa B (NF-κB) activation, reduced the BAX/BCL-2 ratio, preserved neuronal nuclei (NEUN) expression, and decreased hippocampal Aβ42 burden. Collectively, these findings indicate that H₂ inhalation confers multi-faceted neuroprotection in 5xFAD mice by restoring redox homeostasis, suppressing inflammation, improving mitochondrial function, and limiting Aβ accumulation.