Study On The Ameliorative Effect And Mechanism Of Glycerol Monolaurate On DSS-induced Colitis In Mice

Inflammatory bowel disease(IBD)is a type of immune-mediated chronic,nonspecific and relapsing inflammatory disease.At present,IBD cannot be completely cured and drugs are needed to extend the remission period of IBD.Glycerol monolaurate(GML)is a 12-carbon medium-chain fatty acid monoester which naturally found in breast milk,coconut oil and palm oil.GML is a ‘generally recognized as safe(GRAS)' food additive by the Food and Drug Administration(FDA)for topical use in human.Numerous studies have proven that GML has excellent antimicrobial,antiinflammatory,antiviral,and immunoregulatory functions.It's important to investigate the ameliorative effect of and mechanism of GML on IBD.In the present research,we investigated the effects of GML on the growth,intestinal barrier function,inflammatory response and gut microbiota in normal mice.Next,the effects of GML on alleviating the dextran sulfate sodium(DSS)induced colitis and dysbiosis of the gut microbiota was evaluated.Finally,fecal microbiota transplantation(FMT)experiment was performed to verify the role of gut microbiota on the ameliorative effect of GML on DSS-induced colitis.The main findings of the research were as followed.1.C57/BL6 mice were fed with or without different doses of GML(400,800 and1600 mg/kg)for 17 weeks.Results showed that different doses of GML can significantly promote the growth of mice,and high-dose GML(1600 mg/kg)decreased the ratio of low-density lipoprotein cholesterol and high-density lipoprotein cholesterol,and significantly increased gene expression levels of ileum antimicrobial proteins ?-defensin and reg3 g,and colonic anti-inflammatory cytokine tgfb1,also increased the secretion of serum immunoglobulins A(Ig A)and anti-inflammatory cytokines,including TGF-?1 and IL-22.Moreover,different doses of GML decreased the relative abundance of Anaeroplasma and Desulfovibrio.In addition,GML promoted the proliferation of Clostridium XIVa,Oscillibacter and Parasutterella in a dose-dependent manner,and 1600 mg/kg GML has the optimal effect.The findings provided new insights into the antimicrobial and anti-inflammatory activities of GML in vivo.2.The colitis model was induced by application of DSS and used to explore the effect of GML(6 mg/mice/day)on alleviating the colitis.Results suggested that GML pre-treatment before DSS-induced colitis or administration of GML at the initial period of colitis can effectively alleviate the body weight loss and the shortening the colon length caused by DSS.In addition,GML pre-treatment significantly alleviated DSSinduced increase in the disease activity index(DAI)and colonic histological scores.GML pre-treatment significantly reversed DSS-induced increase in the m RNA transcript levels of pro-inflammatory cytokines il6,tnfa and il23p19 in the colonic samples and the secretion of IL-6 in the serum.Transcriptomics analysis found that GML pre-treatment attenuated colitis by regulating IBD,circadian rhythm,and m TOR signaling pathway.Moreover,GML pre-treatment or co-treatment can counteract the reduction in microbial diversity caused by DSS.GML pre-treatment significantly decreased the relative abundance of Turicibacter and elevated the relative abundance of Romboutsia,Lactobacillus and Bifidobacterium.GML co-treatment significantly increased the relative abundance of Romboutsia and Chryseobacterium.Those differential microbes were closely related to the protective effect of GML pre-treatment on DSS-induced colitis.In addition,GML pre-treatment alleviated the decrease in the contents of fecal acetic acid and butyric acid caused by DSS,and significantly recovered the amount of total short-chain fatty acids(SCFAs).3.The role of gut microbiota on the ameliorative effect of GML on DSS-induced colitis were investigated based on fecal microbiota transplantation(FMT)in antibioticstreated mice.FMT experiment confirmed that,FMT from GML-treated donor mice have an advantage in achieving a faster induction of colitis remission,including earlier weight gain,declined DAI,less shortening of the colon length,deceased histological scores,increased production of anti-inflammatory cytokines(such as IL-10 and IL-22)and reduced levels of pro-inflammatory factors(such as IL-6 and IL-1?)at the gene or protein levels.At the same time,FMT from GML-treated donor mice significantly promoting the differentiation of regulatory T cells(Treg)and the m RNA transcript levels of foxp3 and rorgt,which are the functional markers of Treg and help to resist the inflammatory responses.Analysis of the gut microbiota revealed that the relative abundance of genera Bifidobacterium and Alistipes after GML(6 mg/mice/day)treatment for 4 weeks.After DSS induced colitis in ABX-treated mice,FMT from GML-treated donor mice significantly increased the relative abundance of Helicobacter and Helicobacter ganmani were,while decreased the relative abundance of genera Mucispirillum,Klebsiella,Cupriavidus,as well as species Mucispirillum schaedleri,Klebsiella pneumoniae and Cupriavidus metallidurans.Of note,the ameliorative effect of FMT from GML-treated donor mice on DSS-induced colitis in ABX-treated mice is closely associated with the structure of the gut microbiota after FMT.Together,results demonstrated that GML alleviated DSS-induced colitis based on its modulated effect on the gut microbiota.