Role of TLR4/NF-κB signaling pathway in hydrogen-rich water improving cognitive impairment induced by ionizing radiation in rats

Abstract

BackgroundIn the process of radiotherapy, when radiation kills tumor cells, it inevitably damages normal tissue cells. ObjectiveTo investigate the role of Toll-like receptor 4 (TLR4)/nuclear factor−kappa B (NF-κB) signaling pathway in the improvement of cognitive impairment induced by ionizing radiation by hydrogen-rich water before and after whole brain irradiation in rats. MethodsFifteen male SD rats were randomly divided into three groups: control group, irradiated group (IR group), and hydrogen-rich water intervention group (IR+HRW group), with 5 rats in each group. The control group was not irradiated, but was given purified water (20 mL·kg−1) by gavage every day, while the IR group and the IR+HRW group were irradiated with a single dose of 20 Gy. Three days before, 10 min before, and 30 days after irradiation, purified water/hydrogen-rich water (20 mL·kg−1) was given by continuous gavage every day. The general condition of the rats was observed every day, and the body weight were measured on the 7th, 14th, 21st, and 30th days after irradiation. On the 30th day after irradiation, the learning and memory ability of the rats was tested by Morris water maze; the pathological changes of hippocampus were detected by hematoxylin-eosin (HE) staining after sacrificing the rats; the contents of glutathione (GSH), malondialdehyde (MDA), interleukin-1β (IL-1β), and hydroxyl radicals in brain tissues were detected by enzyme linked immunosorbent assay (ELISA); the mRNA and protein expression levels of TLR4, NF-κB, NOD-like receptor pyrin domain 3 (NLRP3), and cysteinyl aspartate specific proteinase 1 (Caspase 1) were detected by quantitative real-time PCR (qRT-PCR) and Western blotting in the hippocampus of rats. ResultsAfter irradiation, the rats in the IR group showed symptoms such as head hair removal and salivation, while the symptoms of the rats in the IR+HRW group were milder. No animal died in the control and the IR+HRW groups, while one rat died in the IR group. From day 14 to day 30 after irradiation, the body weight of the rats in the IR+HRW group tended to be higher than that in the IR group, but the difference was not statistically significant (P>0.05). The Morris water maze results showed that the escape latency of the IR+HRW group was shortened compared with that of IR group from day 1 to day 5 except day 3, but the difference was not statistically significant (P>0.05). For the rats in the IR+HRW group, it took less time to reach the original location of the platform after removing the platform on day 6 and the number of crossing the platform and the residence time in the original platform quadrant increased (P0.05). The results of qRT-PCR showed that the mRNA expression levels of TLR4 and Caspase 1 in the hippocampus of the IR+HRW group were decreased compared with the IR group (P0.05). The results of Western blotting showed that the expression levels of TLR4 and Caspase 1 protein in the hippocampus of the IR+HRW group were decreased compared with the IR group (P0.05). ConclusionHydrogen-rich water can improve cognitive impairment induced by ionizing radiation in rats, and its mechanism may be related to regulating TLR4/NF-κB signaling pathway, inhibiting inflammatory factors, and attenuating oxidative stress.

Keywords

• hydrogen-rich water
• ionizing radiation
• tlr4/nf-κb signaling pathway
• cognitive impairment