Preconditioning Effect of Hydrogen Gas on Traumatic Brain Injury

Abstract

Traumatic brain injury (TBI) affects approximately 1% of the global population annually. In Japan, sports-related head injuries are recognized as one of the most common causes. There have been reports suggesting that TBI sustained during sports activities may become more severe because of the added oxidative stress compared with injuries at rest, but there are still few reports on the actual changes in oxidative stress following TBI. Therefore, we first examined the changes in oxidative stress immediately post-sports-related TBI. No pharmacological treatment has been established to effectively prevent TBI, and preconditioning approaches aimed at enhancing endogenous tolerance prior to injury have attracted attention. However, existing methods often involve invasive procedures, limiting their clinical applicability. Prior studies demonstrated the therapeutic potential of hydrogen gas, which possesses antioxidant properties in TBI. Therefore, we examined whether hydrogen administration prior to TBI could attenuate secondary brain injury in a model incorporating exercise-induced oxidative stress before trauma. Male C57BL/6 mice (6 weeks old) were subjected to treadmill exercise at 15 m/min for 90 min to induce oxidative stress. During exercise, 1.3% hydrogen gas was delivered into the chamber for preconditioning. Moderate TBI was induced using a controlled cortical impact (CCI) device immediately postexercise. Four groups were evaluated: resting controls, exercise alone, exercise followed by TBI induced by CCI (ExCCI), and hydrogen-preconditioned exercise followed by TBI. Oxidative stress was assessed using hippocampal malondialdehyde (MDA) levels, and antioxidant capacity was evaluated using manganese superoxide dismutase (MnSOD) activity. Brain edema was quantified using brain water content, and vasogenic edema was assessed using Evans Blue extravasation. Histological analysis of the pericontusional cortex included glial fibrillary acidic protein (GFAP) and aquaporin-4 (AQP4) immunofluorescence. MDA levels increased 3 h postexercise and remained elevated for 24 h when TBI was induced. Hydrogen preconditioning significantly reduced MDA levels and enhanced MnSOD activity, which peaked 24 h postinjury. At the same time point, ExCCI mice showed significant brain and vasogenic edema, both of which were attenuated by hydrogen. GFAP and AQP4 were increased in ExCCI mice and suppressed by hydrogen. Although hydrogen is known to disappear from the blood within approximately 1 h postinhalation, MnSOD activity remained elevated for up to 24 h postinjury, indicating endogenous antioxidant defense activation. Hydrogen is considered to mitigate blood–brain barrier vulnerability to oxidative stress, thereby reducing vasogenic edema. These findings indicate that hydrogen gas may be effective as a treatment and a preventive intervention for TBI.