| Radiation-induced brain injury(RIBI)and radiation-induced cognitive impairment(RICD)are major issues closely related to the prognosis of primary and metastatic brain tumor patients.In recent years,the role of the gut-brain axis in the development of central nervous system diseases has received increasing attention.Intestinal damage caused by whole-brain irradiation(WBI)is one of the main reasons for post-irradiation systemic inflammation.Protecting the intestinal barrier and inhibiting intestinal inflammation are important for controlling excessive inflammatory response,reducing neural damage,and improving cognitive dysfunction.Studies have shown that the gut microbiota and its metabolites play an important role in regulating the gut-brain axis and can have an impact on the function of the central nervous system.Probiotics have been shown to improve cognitive and memory function in WBI mice by regulating the structure and composition of the gut microbiota,but the mechanism is not yet clear.Therefore,the purpose of this study is to investigate the effects of probiotics BB-12 and Bifico on RIBI and RICD after WBI,as well as to explore the role and mechanisms of the gut-brain axis in WBI,in order to elucidate their impact on disease progression and provide new avenues for improving intestinal and neural functional damage as well as cognitive impairment following WBI.In this study,60 C57BL/6J mice were randomly divided into four groups:Control+Saline group,IRR+saline group,BB-12+IRR group,and Bifico+IRR group.The BB-12+IRR group and the Bifico+IRR group were administered 0.2m L of BB-12suspension(containing 1×10~9CFU)or Bifico suspension(containing 1×10~7CFU)by gavage every day after whole-body irradiation(WBI)modeling.The IRR+saline group was administered 0.2m L of saline by gavage every day after WBI modeling.The control+saline group was only anesthetized and not irradiated,and was administered 0.2m L of saline by gavage every day at the same time as the other groups.The mice’s basic status and weight data were recorded every week.Starting from the third week after WBI,anxiety and short-and long-term learning and memory function of the mice in each group were tested using elevated plus maze(EPM),novel object recognition(NOR),Y-Maze,and Mirrors water maze(MWM)experiments.After 4 weeks of WBI,various techniques including immuno-fluorescence staining(IF),real-time quantitative polymerase chain reaction(RT-q PCR),Western blot(WB),and enzyme-linked immunosorbent assay(ELISA)were used to examine the number of neural cells,immature and mature neurons,glial cell activation,expression levels of inflammatory cytokine m RNA and protein,expression levels of neural plasticity-related proteins,and changes in hippocampal lipopolysaccharide(LPS)content in each group of mice.WB,RT-q PCR,and ELISA were also used to assess the expression levels of tight junction proteins and Toll-like receptor 4(TLR4)signaling pathway-related proteins,as well as the LPS content and expression levels of inflammatory cytokine m RNA and protein in colon tissues.The structure and composition of gut microbiota and changes in short-chain fatty acids(SCFAs)in each group of mice were observed using 16S r RNA gene sequencing and UPLC-MS/MS targeted metabolomics analysis.Furthermore,serum samples from each group of mice were collected to detect changes in LPS and inflammatory cytokine levels using ELISA.The main results and conclusions of the study are as follows:(1)Probiotics BB-12 and Bifico improve the neurological function of WBI mice.Compared with the Control+Saline group,mice in the IRR+Saline group showed obvious physical symptoms and slow recovery,including hair loss,decreased appetite,lethargy,and weight loss;anxiety behavior and learning and memory function also significantly decreased;different degrees of improvement of physical symptoms and cognitive function were observed after BB-12 and Bifico interventions.In addition,the number of neural cells in the hippocampus and the number of neurons were significantly reduced in the IRR+Saline group;the expression levels of post-synaptic density protein(PSD95)in hippocampal tissue significantly increased,while the protein expression levels of synaptophysin(Syn)and brain-derived neurotrophic factor(BDNF)significantly decreased;a large number of glial cells were accumulated in the hippocampus,and the expression levels of inflammatory cytokines interleukin-1β(IL-1β),interleukin-6(IL-6),and tumor necrosis factor-α(TNF-α)m RNA and protein were increased.BB-12 and Bifico interventions significantly improved the proliferation and differentiation of neural cells,increased the number of neurons in the hippocampus;significantly decreased the expression levels of PSD95protein,and significantly increased the expression levels of Syn and BDNF proteins;significantly decreased the total number of small glial cells and astrocytes in the hippocampus,and the expression levels of inflammatory cytokines IL-1β,IL-6,TNF-αm RNA,and protein significantly decreased.(2)Probiotics BB-12 and Bifico enhance the intestinal barrier function of WBI mice.Compared to the Control+Saline group,the IRR+Saline group of mice showed increased intestinal barrier permeability and significantly decreased expression of colonic tight junction proteins Claudin1,ZO-1,and Occludin;At the same time,intervention with BB-12 and Bifico significantly reduced intestinal barrier permeability and increased protein expression of Claudin1,ZO-1,and Occludin in mice after injury.In addition,the expression levels of TLR4 signaling pathway-related proteins and IL-1β,IL-6,and TNF-αm RNA and protein in the colon of IRR+Saline group mice were significantly increased.After intervention with BB-12 and Bifico,the expression levels of TLR4 signaling pathway-related proteins and IL-1β,IL-6,and TNF-αm RNA and protein were significantly decreased.(3)Probiotics BB-12 and Bifico affect the gut-brain axis of WBI mice.Compared to the Control+Saline group,the alpha and beta diversity,as well as the structure and composition of the gut microbiota,were significantly altered in the IRR+Saline mice after 4 weeks of WBI.After intervention with BB-12 and Bifico,the diversity and richness of the gut microbiota in mice were partially restored,and the structure of the microbiota tended to be similar to that of the Control+Saline group.Compared to the Control+Saline group,the IRR+Saline group of mice showed a significant decrease in the content of short-chain fatty acids(such as acetic acid,propionic acid,and butyric acid).Under the intervention of BB-12 and Bifico,the content of acetic acid and propionic acid in the BB-12+IRR group of mice significantly increased,and the content of propionic acid and butyric acid in the Bifico+IRR group of mice significantly increased.In addition,the levels of LPS in the hippocampus and serum and the levels of IL-1β,IL-6,and TNF-αin the serum were significantly increased in the IRR+Saline group mice.However,after intervention with BB-12 and Bifico,the levels of LPS in the hippocampus and serum and the levels of IL-1β,IL-6,and TNF-αin the serum significantly decreased.This study demonstrates that the probiotics BB-12 and Bifico promote recovery from brain injury and cognitive impairment in WBI mice by modulating the gut-brain axis. |
