Effects Of Different Polysaccharides On Intestinal Immunity In Immunocompromised Mice

A variety of bioactive polysaccharides are considered to have intestinal immunomodulatory activity,but there are differences in the ways in which different polysaccharides modulate intestinal immunity.Since most of the current studies only report the bioactivity of a particular polysaccharide or compare the differences in bioactivity among a few polysaccharides,but few studies have systematically reported differences in the intestinal immunomodulatory activity and mechanisms of different typical polysaccharides,we selected 11 representative bioactive polysaccharides,including xanthan gum,apple pectin,inulin,guar gum,arabinogalactan,carrageenan,β-glucan,glucomannan,arabinoxylan,xylan and fucoidan,and compared their ways of modulating intestinal immunity.The study used cyclophosphamide(CTX)to induce the formation of an immunocompromised model in mice,and investigated the effects of polysaccharides on intestinal mucosal barrier,intestinal mucosal immune function,gut microbiota and intestinal metabolome to compare the differences of intestinal immunomodulatory activities of different polysaccharides,providing a theoretical basis for the development of excellent intestinal immunomodulatory polysaccharides.The main contents and results are as follows:(1)The effects of different polysaccharides on the intestinal mucosal barrier were compared.The results showed that most polysaccharides had differential effects on the ileal mucosal barrier in immunocompromised mice,among which arabinoxylan showed significant improvements on the height of the ileal villus,the depth of the crypt and the thickness of the bowel wall.Guar gum,arabinogalactan,carrageenan,glucomannan and xylan significantly promoted the expression of the tight junction proteins ZO-1 and Occludin,while having different degrees of improvement on ileal tissue morphology.(2)The effects of different polysaccharides on intestinal mucosal immunity were compared.It was shown that not all polysaccharides had good improvement on small intestinal mucosal immune depression.Guar gum,inulin and glucomannan had better intestinal mucosal immunomodulatory effects,and all three polysaccharides significantly restored the number of CD8~+T cells and CD4/CD8 values in the ileal mucosa.Among them,guar gum showed more significant improvements in the expression levels of immune-related genes and proteins,and it could significantly upregulate the expression of transcription factors RORγt,T-bet and Blimp-1 m RNA,as well as cytokines TNF-α,IFN-γ,IL-22 and IL-17.Therefore,guar gum can be found to have a better promotion effect on the immune function of intestinal mucosal T cells in immunocompromised mice.(3)The effects and differences of different polysaccharides on the regulation of gut microbiota disorders in intestinal immunocompromised mice were investigated.We found that fucoidan had the best improving ability to reverse the dysregulation of the relative abundance ratio of Bacteroidota/Firmicutes in intestinal immunocompromised mice,and that fucoidan significantly inhibited the intestinal immunocompromisedbiomarkerbacteriaHelicobacter,Lachnospiraceae＿NK4A136＿group and Lachnospiraceae＿UCG＿001 all exerted significant inhibition.In addition,the biomarker genera of different polysaccharides were different,the marker genera of fucoidan were Alloprevotella and Rikenella,the marker genus of inulin was the beneficial bacterium Lactobacillus,and the biomarker genera of arabinoxylan,carrageenan andβ-glucan were Incertae＿Sedis,Roseburia and Blautia,respectively.(4)The differences in the effects of different polysaccharides on intestinal metabolic disorders in intestinally immunocompromised mice were investigated.Among the polysaccharides,inulin and arabinogalactan had the strongest ability to promote the production of SCFAs.Fucoidan and carrageenan most significantly reversed the metabolic disorders in intestinal immunocompromised mice.Fucoidan and carrageenan improved the highest number of intestinal disordered metabolites and metabolic pathways,and the disordered metabolites they improved mainly included amino acid compounds such as L-Glutamine,L-Tryptophan and D-Arginine,there is also hyocholic acid,which has been reported to mark metabolic disorders in bile acids,and a large number of unsaturated fatty acids,glycerophospholipids and glycerolipids,etc.The main metabolic pathways improved are linoleic acid metabolism、alpha-linolenic acid metabolism、alanine,aspartate and glutamate metabolism和pentose and glucuronate interconversions,etc.Spearman correlation analysis showed that the abnormal enrichment of most amino acid-like and indole-like metabolites in the colon of intestinal immunocompromised mice was negatively correlated with the relative abundance of the normal mouse marker genera Eubacterium＿nodatum＿group and Clostridia＿UCG-014,the intestinal mucosal barrier,and immune indicators;in contrast,metabolites such as partial unsaturated fatty acids,glycerides and diglycerides,which were significantly downregulated in the colon of intestinal immunocompromised mice,were generally positively correlated with intestinal mucosal barriers and immune indicators,and mostly negatively correlated with the abundance of intestinal immunocompromised biomarker genera such as Helicobacter.In summary,different polysaccharides improve CTX-induced intestinal immune depression through different ways,among which inulin mainly promotes the production of large amounts of SCFAs by significantly promoting the colonization of beneficial bacteria Lactobacillus to repair the intestinal mucosal barrier and regulate the intestinal mucosal immune response;fucoidan were able to improve the disorder of intestinal flora structure well,significantly upregulating the relative abundance of Alloprevotella and Rikenella,while carrageenan significantly promoted the colonization of potentially beneficial bacteria Roseburia.Fucoidan and carrageenan also significantly decreased the relative abundance of harmful bacteria Helicobacter,thereby improving intestinal metabolic disorders,alleviating the abnormal accumulation of metabolites such as amino acids and indoles,upregulating the concentration of metabolite clusters such as unsaturated fatty acids,promoting the synthesis of tight junction proteins ZO-1 and Occludin,and relieving immunosuppression in the intestinal mucosa.The above research results can provide a reference for the development of polysaccharides with excellent intestinal immunomodulatory activity.