Structural Characterization Of Different Short-chain Fatty Acid Acylated Starches And Their Research And Application In Metabolic Syndrome

Metabolic syndrome is becoming one of the major health-care problems of the twenty-first century and is associated with a wide spectrum of pathological disturbances in metabolic organs predisposed towards insulin resistance,as well as type 2 diabetes（T2D）and cardiovascular disease.T2D and its complications are the most concerned endocrine and metabolic diseases in the world.They are characterized by disorders of lipid,glucose metabolism and insulin efficacy,which ultimately lead to disorders of systemic homeostasis.The gut microbiota might affect the metabolic phenotype by fermenting indigestible dietary components and thereby producing short-chain fatty acids（SCFAs）.This study first studied the effects of different SCFAs on lipid metabolism in an in vitro liver steatosis model.Secondly,starting from the production characteristics of SCFAs,acylated starches with different degrees of substitution were prepared.The multi-scale structure,digestion characteristics,fermentation characteristics of acylated starches with different SCFAs under the same degree of substitution were studied,and their effects on T2D were studied.（1）The current study applied free fatty acid（FFA）-induced cell model of hepatic steatosis in an in vitro model of cultured rat hepatocytes（BRL 3A cells）,and measured the effects of SCFAs on oxidative stress,lipid accumulation and signal transduction pathways.The results indicated that a certain concentration of SCFAs increased the level of superoxide dismutase（SOD）and decreased the levels of malondialdehyde（MDA）,reactive oxygen species（ROS）,and cellular triglycerides（TG）,and these effects were characterized with concentration dependent.In addition,SCFAs inhibit the expression of lipid synthesis genes and up-regulate the expression of lipid oxidation-related genes by activating AMPK and PPAR signaling pathways.More importantly,either a mixture of SCFAs(M_{Na Ac}:M_{Na Pr}:M_{Na Bu}=3:1:1)or butyrate alone enhanced their corresponding inhibition of lipid accumulation compared to acetate or propionate,individually,and a higher in similarly differentially expressed genes profile was observed between SCFAs and Na Bu treatment groups compared to others,indicating the importance of the existence of butyrate for the regulation of lipids metabolism.（2）The effect of acylation with various short-chain fatty acids on starch fine structure,digestion and gut microbiota fermentation property was investigated.The presence of acyl protons was convinced by Nuclear magnetic resonance（NMR）spectra followed by the further support from Fourier transform infrared（FTIR）spectra with a carbonyl C=O vibration at 1730 cm^–1 into the acylated starch molecules.X-ray diffractometer（XRD）studies revealed that the acylation destroyed the internal structure for providing a chance of rearrangement of starch molecules,suggesting more ordered aggregation structures was formed inside the starch granules.Kinetics of in-vitro hydrolytic enzymatic model and Pearson correlation coefficients further confirmed the association between multi-scale structural order and digestion characters.Acyl groups introduced by acetylated,propionylated and butyrylated starch could be effectively released by the intestinal flora during the fermentation,specifically increasing their corresponding SCFAs production,respectively.（3）This study investigated the interventional effect of resistant starch（RS）,and acylated starch（SCFAs plus resistant starch,SCFA-RS）on liver function,lipid composition and oxidative stress in T2D rats.After acylated starch intervention,organ enlargement was reversed,liver lipids were significantly decreased,and oral glucose intolerance was improved in diabetic rats.Treatment with acylated starches（SCFAs-RS）significantly ameliorated hyperglycemia,hyperinsulinemia,hyperlipidemia,and oxidative stress in diabetic rats compared with HAMS.For the mechanism study,we have found that SCFAs-RS exhibited a significant protective effect on insulin resistance（IR）in T2DM rats through increasing expressions of insulin receptor substrate（IRS）,Akt,glucose transporters 2（Glut2）and decreasing the expressions of nuclear factor kappa-B（NFκB）.According to our present findings,we could conclude that SCFAs-RS possessed the potential anti-diabetic effects through activating NFκB and IRS-1/AKT/GLUT2 pathways.（4）This study investigated the correlations between the gut microbiota and type 2diabetes（T2D）indexes using either native resistant starch（from high amylose maize starch,HAMS）or acylated starch（SCFAs plus resistant starch,SCFA-RS）.The current results showed that,compared to HAMS,consumption of SCFA-RS achieved a greater impact on the improvement of T2D indexes in term of body weight loss,fasting blood glucose（FBG）,serum insulin level,and amino acid metabolism,indicating the importance of the dual function from both SCFAs and RS in the gut.The abundance of Butyricimonas was negatively significant with the level of serum FBG and glycated serum protein,and 10bacteria were positively significant with the HOMA-IR,which may indicate the association of some key microbiota with the pancreatic function.Insulin sensitivity may be related to the improvement of amino acids metabolism as well.All the acylated starch significantly enhanced the growth of SCFAs-producing bacteria compared to its native HAMS,and this change was highly consistent with their corresponding SCFAs concentration both in serum and fecal samples.The propionylated HAMS promoted the abundance of Bifidobacterium,while acetylated and butylated HAMS benefited the enrichment of Coprococcus,Butyricimonas and Blautia,which may indicate their different intervention pathway.In summary,the current study proves that acylated starch intervention is effective at improving HFD-STZ-induced T2D in term of the improved weight loss,glycemic control,and lipid metabolism,protected the tissue against oxidative stress injury.The hypoglycemic effects of acylated starch are related to the inhibition of the inflammatory response and oxidative stress,and the regulation of the imbalanced intestinal microbiota.Our research would promote the understanding of the efficacy of acylated starch in alleviating blood glucose,inflammation,oxidative stress,and metabolic disorders,and provide insights for the development of acylated starch-based treatment strategies for metabolic disorders.