Background At present, radiation therapy is widely used in clinical treatment of tumors. However, while radiation therapy damages tumor cells, it also injures surrounding normal tissues. Studies have shown that hydrogen is a potential radiation-protective agent.

Objective To investigate the neuroprotective mechanisms of hydrogen-rich water activating phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/cysteinyl aspartate specificproteinase-9 (Caspase-9) signaling pathway in acute radiation-induced brain injury.

Methods Forty male SD rats were randomly divided into four groups: control group, irradiation only group (IR), high-dose hydrogen-rich water intervention group (IR+HHRW), and low-dose hydrogen-rich water intervention group (IR+LHRW), 10 rats in each group. Except for the control group, animals in each group received a single 20 Gy whole brain irradiation. Animals in all groups were gavaged once a day from 3 d before irradiation to 7 d after irradiation, pure water (20 mL·kg⁻¹) was given to the control and the IR groups, and hydrogen-rich water (20 mL·kg⁻¹, 10 mL·kg⁻¹) was given to the IR+HHRW and the IR+LHRW groups. After 7 d of intervention, 5 rats in each group were selected for the Morris water maze experiment for behavioral evaluation. Autopsies were conducted after anesthesia for the remaining animals and blood samples were collected for hematological analysis. Rat brains were harvested for TUNEL staining to observe neuronal apoptosis. HE staining was performed to observe histopathological changes, enzyme-linked immunosorbent assay was adopted to detect oxidative stress-related indicators, and real-time PCR and Western blotting were used to measure the expressions of PI3K/AKT/Caspase-9 pathway-related genes and proteins.

Results The body weight of rats receiving irradiation decreased after 7 d of irradiation compared with the control group (P<0.05), and the symptoms such as arched back and malaise occurred to varying degrees, and the symptoms of rats in the IR+HHRW group were significantly milder than those in the IR group. The behavioral test results showed that the escape latency of rats in the IR+HHRW group or the IR+LHRW group was shorter than that in the IR group from day 2 to day 5 (P<0.05), and it took less time for rats in the IR+HHRW group to reach the original position after removing the platform on day 6 (P<0.05). The hematological test results showed that red blood cell (RBC) count, hemoglobin (HGB) level, and white blood cell (WBC) count were significantly decreased in the IR group (P<0.05), and the changes in the IR+HHRW group were improved (P<0.05). The HE staining results showed that the number of abnormal nerve cells, broken and dissolved nuclei, and the degree of damage in the IR+HHRW group were significantly reduced than those in the IR group. The results of oxidative stress evaluation showed that the ability of the IR group to inhibit free radicals decreased, the level of malondialdehyde (MDA) increased (P<0.01); the MDA level decreased after LHRW intervention (P<0.05); the SOD activity was elevated after HHRW intervention (P<0.05). The TUNEL staining results showed that the apoptosis signals in the IR+HHRW group were sparser than those in the IR group (P<0.05). The real-time PCR results showed that compared with the IR group, the mRNA expression levels of PI3K and AKT in the IR+HHRW group and the IR+LHRW group increased (P<0.05), while the mRNA expression levels of Cytc and Caspase-9 decreased (P<0.05). The Western blotting results showed that compared with the IR group, the phospho-AKT (pAKT) protein expression level in the IR+HHRW group increased significantly (P<0.05), while the expression of Caspase-9 and Cytc proteins decreased significantly (P<0.05).

Conclusion Hydrogen-rich water can significantly reduce inflammation and oxidative stress caused by acute irradiation-induced brain injury, and decrease neuronal apoptosis. The mechanism may be related to the PI3K/AKT/Caspase-9 signaling pathway.