Effects Of Inulin And Short Chain Fatty Acid Ester On Metabolism And Intestinal Microecology In Diabetic And Obese Mice

Type Ⅱ diabetes mellitus（T2DM）and obesity have become a worldwide epidemic of chronic disease,which serious threat people’s health.Lack of dietary fiber in the diet would influence the composition of intestinal bacterial community and cause chronic inflammatory diseases.Dietary fiber could be fermented by intestinal microorganisms to produce short chain fatty acids（SCFA）,including acetic acid,propionic acid and butyric acid,which plays an important role in regulating intestinal flora imbalance and improving body metabolism.Based on the role of dietary fiber and SCFA on the improvement of T2 DM and obesity,T2 DM mice model induced by streptozocin（STZ）and obese mice model induced by high-fat diet are build to investigate the effects of inulin,SCFA and short chain fatty acid esters on T2 DM and obese mice metabolism and intestinal microecology.The main research contents of this dissertation are as follows:（1）The STZ-induced T2 DM mice model were build to study the effects of inulin and SCFA on metabolism and intestinal microecology.The results are as follows:Inulin,sodium acetate（Ac）and sodium propionate（Pr）significantly reduced food intake（p < 0.05）and improved polyphagia symptoms in T2 DM mice,but had no significant effect on body weight（p > 0.05）.It may be related to the role of promoting the release of gastrointestinal hormone peptide YY（PYY）,which involved in appetite regulation.Inulin and sodium propionate significantly improved glucose tolerance and enhanced islet cell function.Fasting blood glucose（FBG）and insulin resistance（IR）were significantly improved in the sodium propionate group（p < 0.05）.The improvement in IR may be related to the promotion of glucagon-like peptide（GLP-1）secretion,which can promote insulin secretion and play an important role in glucose homeostasis regulation.The intervention of sodium propionate significantly reduced the liver index（liver-body ratio）.The HE staining results showed that sodium propionate significantly improved the liver swelling and liver tissue vacuolization of T2 DM mice（p < 0.05）,reduced the malondialdehyde（MDA）produced by lipid oxidation in the liver,and relieved the infiltration of liver cells caused by MDA.Sodium propionate significantly increased the amount of total fecal SCFA,especially acetic acid and propionic acid（p < 0.05）.The fecal microflora results showed that inulin and sodium propionate significantly reduced the relative abundance of Proteobacteria and Actinobacteria at the phylum level（p < 0.05）while Desulfovibrionales and Campylobacterales relative abundance significantly reduced at the order level（p < 0.05）.At the genus level,inulin and SCFA significantly reduced the relative abundance of diabetic pathogenic bacteria Lachnospiraceae_NK4A136,and increased the relative abundance of short chain fatty acid producing bacteria Weissella（p < 0.05）.Consequently,the improvement effect of inulin and propionic acid on T2 DM could be attributed to the role of reducing the relative abundance of pathogens that cause T2 DM and related inflammation and increasing the relative abundance of short chain fatty acid producing bacteria.（2）Effects of inulin propionate ester on metabolism and intestinal microecology of obese mice.Due to the unique structure,inulin could not degrade in the stomach and small intestine,it has been used as carrier or wrapping agent for oral drugs in biomedical and pharmaceutical fields,which could deliver medicine to the colon and then released through microbial action.In order to avoid the shortcomings of direct supplementation of SCFA and the excessive use of dietary fiber,which may cause gastrointestinal side reactions,and to ensure that SCFA is exactly delivered to the colon,we designed the new molecular carrier to prepare inulin acetate ester（IAE）,inulin propionate ester（IPE）and inulin butyrate ester（IBE）with the reaction of inulin and anhydride.To obtain the high degree of substitution（DS）of inulin short chain fatty acid esters,the single factor experiments and response surface methodology were used to optimize the three factors of anhydride to inulin molar ratio,inulin concentration and reaction temperature to determine the optimal preparation conditions.The in vitro fermentation activity of inulin short chain fatty acid esters were studied.The bifidobacteria was cultured with inulin and inulin short chain fatty acid esters to evaluate the effects on SCFA increment and bifidobacteria proliferation.The effects of promoting the growth of bifidobacteria were as follows: Inulin > IBE > IPE > IAE.The total SCFA content were as follows: IPE > IAE > IBE > Inulin.IAE and IPE significantly increased the ratio of acetic acid and propionic acid（p < 0.05）.By analyzing the in vitro fermentation activities,it is further proved that inulin short chain fatty acid esters can be used as SCFA carrier to increase the content of SCFA in the colon,which provides a theoretical basis for the development and application of inulin short chain fatty acid esters.The obesity mice model induced by high fat diet（HFD）were used to study the effects of inulin,sodium propionate and IPE on metabolism and intestinal microecology of obese mice.The results indicated that: high dose of inulin,high dose of sodium propionate,inulin propionate ester can significantly reduce the cumulative food intake,which may be related to the promotion of gastrointestinal hormones GLP-1 and PYY secretion.Glucose tolerance test（OGTT）showed that LIPE can improve glucose tolerance in obese mice,which may be related to the increase of intestinal propionic acid content that participate in intestinal gluconeogenesis metabolism.Inulin,sodium propionate,and LIPE significantly improved insulin resistance（IR）caused by high fat diet,and enhanced islet cell function.HPr and LIPE significantly reduced LDL-C（p < 0.05）.The results of liver index and oil red O staining showed that LIPE significantly reduced the liver index and fat accumulation in the liver of obese mice,which indicated that the fatty liver caused by high-fat diet was alleviated.LIPE significantly increased the faeces of propionic acid and butyric acid content（p < 0.05）,while sodium propionate intervention showed no significant effect on the increment,which showed that LIPE was more effective than direct adding sodium propionate in supplementing propionic acid in obese mice.The intestinal microflora results showed that Firmicutes/Bacteroidetes significantly increased at phylum level in the obesity model group and decreased in LIPE group（p < 0.05）.The significant increase in the relative abundance of Actinomycetes in inulin group（P < 0.05）could be ascribed to the significant increase of Bifidobacteriaceae and Coriobacteriaceae（P < 0.01）.The relative abundance of Ruminococcaceae and Bacteroidales_S24₇ were significantly increased while the relative abundance of Desulfovibrionaceae and Erysipelotrichaceae were significantly reduced by supplementation with LIPE.The improvement of obesity and related metabolic syndrome may be related to the decrease of pathogenic bacteria abundance with the supplementation of IPE,which increased the propionic acid in colon.This dissertation based on the improvement of SCFA on T2 DM and obesity,the methods by directly replenish SCFA and using inulin as the carrier,synthesis of inulin short chain fatty acid esters to supplement SCFA were employed to study the effects of SCFA on metabolism and intestinal microecology in T2 DM and obesity mice respectively.This study provides a theoretical basis for the application of SCFA and a new idea for the design of targeted drug delivery based on inulin.