Study On Mechanism Of Bacopaside Ⅰ In The Treatment Of Depression By Regulating Gut Microbiome And Host Metabolism

Objective:The aim of this study was to investigate the antidepressant effect of Bcopaside I（BSⅠ）on chronic unpredictable mild stress（CUMS）mice by regulating the microbiome-gut-brain axis and its molecular mechanisms of action.Methods:Different chronic stresses were applied to male C57BL/6 mice for 7 weeks to induce depressive phenotype.The antidepressant efficacy was observed with 45 mg·kg^-1BSI given by gavage during the last two weeks.Then,the collected blood,cecum contents,brain tissue and colon tissue were tested.Firstly,depression-like behaviors in CUMS-induced mice and antibiotic-treated mice after fecal microbiota transplantation were evaluated by behavioral methods,and levels of inflammatory cytokines,hypothalamic-pituitary-adrenal axis（HPA）-related hormones,and endotoxins were measured by ELISA kits and horseshoe crab kits,and then,histopathological sections were taken to observe pathological changes.Secondly,the effects of BSI on the intestinal microbial structure and short-chain fatty acids（SCFAs）content of CUMS-induced depression-like mice were analyzed by 16S r DNA gene sequencing and Gas chromatograph-Mass spectrometry（GC-MS）techniques,and the effects of lipid metabolism in CUMS-induced depressed mice were analyzed based on Liquid chromatograph-Mass spectrometer（LC-MS）techniques.Finally,the role of remodeling gut microbes on the microbiome-gut-brain axis in antibiotic-treated mice was analyzed by fecal microbiota transplantation.Results:1.The effect of BSⅠon depressive behavior of CUMS-induced mice was examined by behavioral experiments such as sucrose preference test,open field test,tail suspension test and forced swimming test,and it was found that CUMS mice showed obvious depression-like and anxiety-like behaviors,while BSⅠcould effectively alleviate the behavioral abnormalities of mice after two weeks of administration.2.The effect of BSⅠon inflammatory factors in brain and colon tissues of CUMS-induced mice was detected by ELISA kits,and it was found that the levels of inflammatory factors in brain and colon tissues of CUMS mice were significantly increased,while BSⅠcould improve the brain and colon inflammation of depressed mice after two weeks of administration.In addition,the endotoxin changes in mice were also detected by horseshoe crab kits,and it was found that endotoxin levels in the blood of CUMS mice were elevated,and after two weeks of treatment was able to significantly reduce endotoxin levels in the blood of CUMS mice.3.The effect of BSⅠon HPA axis-related hormones in the blood of CUMS-induced mice was detected by ELISA kit,and it was found that HPA axis-related hormones in the blood of CUMS mice were disordered,while BSⅠcould effectively modulate the levels of HPA axis-related hormones in the blood of depressed mice.4.The effects of BSⅠon the histopathological changes of brain and colon tissues of CUMS-induced mice were observed by histopathological sections,and it was found that hippocampal neurons were damaged,and microglia were significantly activated in the brain of CUMS-induced mice.The mechanical barrier and mucosal barrier were impaired to different degrees in the colon.In contrast,BSⅠcould effectively repair hippocampal neurons,stabilize microglia state,and alleviate colonic barrier damage.5.The effect of BSⅠon intestinal microbiome of CUMS-induced mice was analyzed by16S r DNA gene sequencing technology,and it was found that the intestinal microbial structure of CUMS-induced mice was significantly different from that of normal mice,and different degrees of disorder occurred at the phylum level and genus level.And BSⅠtreatment could significantly remodel the intestinal microbial structure,making it similar to that of the normal group,and significantly increase the content of probiotic bacteria such as Lactobacillus.6.The effect of BSⅠon the content of SCFAs in CUMS-induced mice was analyzed by GC-MS,and it was found that the contents of various SCFAs in the cecum contents of CUMS mice were disturbed to different degrees,while BSⅠcould effectively increase the contents of acetic acid,isobutyric acid and isovaleric acid.7.The effect of BSⅠon lipid metabolism in CUMS-induced mice was analyzed by LC-MS,and it was found that the lipid metabolism in the serum of CUMS mice was disturbed,while BSⅠcould significantly slow down the metabolic disorder state of CUMS mice,and it was found that it might play an antidepressant role by regulating neurotrophin signaling pathway and necroptosis pathway through regulating lipid metabolites.8.Through fecal microbiota transplantation,we found that the intestinal microbiota of CUMS mice can induce the depressive behavior of antibiotic-disturbed mice,cause colonic and brain damage,and induce intestinal and brain inflammation.In contrast,BSⅠtreatment of mice does not lead to the above symptoms.Conclusions:This study confirmed that BSI has antidepressant effect,and its antidepressant effect may be related to intestinal flora remodeling effect,and Lactobacillus and Streptococcus may be the key genera of BSI to remodel the intestinal flora.Acetic acid may be an important product of BSI affecting flora metabolism,and pathways such as necrotrophic apoptosis,neurotrophic factor signaling pathway,and sphingolipid signaling pathway may be the main pathways of gut microbes and their metabolites affecting host metabolism.In addition,BSI significantly alleviates gut-brain injury and maintains the HPA axis and immune homeostasis.In conclusion,BSI could exert antidepressant effects by regulating intestinal flora,SCFAs metabolism and lipid metabolism in CUMS mice.