Improvement Of Long- And Short-chain Inulin On High-fat Diet-induced Liver Injury And Intestinal Flora Disturbance In Mice And Its Mechanism Of Action

Inulin is a water-soluble polysaccharide,which is widely present in plants.Chicory and Jerusalem artichoke root are the most abundant sources of inulin.Because of its special?-(2,1)-glycosidic bond structure,inulin can only be decomposed by microorganisms in the colon,making inulin has a variety of effects such as regulating lipid metabolism,reducing blood sugar,promoting the absorption of vitamins and minerals,improving human intestinal function,preventing cancer and enhancing immunity.Due to the different degree of polymerization(DP)of inulin,the physicochemical properties and physiological effects also change.In this study,inulin with different degrees of polymerization was used,and mice induced by a high-fat diet(HFD)were used as animal models.Through the analysis of serum liver biochemical indexes and protein expression levels of mice and the analysis of intestinal flora and its metabolites of short-chain fatty acids(SCFAs),the effects of low-performance inulin(LPI,DP<9)and high-performance inulin(HPI,DP?23)on the improvement of liver injury and intestinal flora disorder in obese mice fed with high-fat diet and its mechanism were discussed.The research results are as follows:(1)The supplementation of HPI can more effectively improve the liver injury induced by HFD in mice.LPI and HPI can improve the disorder of the corresponding enzyme metabolism level caused by HFD in tissues,among which,HPI significantly reduces the concentration of aspartate aminotransferase(AST)and alanine aminotransferase(ALT),the markers of liver injury in serum of mice,demonstrating the protective effect of HPI on liver injury in mice.In addition,dietary HPI supplementation also significantly reduced the malondialdehyde(MDA)content in the liver of mice and enhanced the activity of glutathione peroxidase(GSH-Px)to prevent oxidative damage,further improving the liver damage caused by HFD.These results were more objectively confirmed by the observation of oil red O and H&E staining in pathological sections of mouse liver.Therefore,the liver protection effect of inulin is related to DP,and the effect of HPI is more significant.(2)For 8 consecutive weeks of HFD feeding,the mice exhibited the state of lipid metabolism disorder,insulin resistance,oxidative stress,and inflammation With the intervention of LPI and HPI,the abnormal increase in body weight and fat weight in various parts of the mouse was suppressed.Among them,HPI significantly reduced the level of total triglyceride(TG)in the serum of the mice,and effectively prevented the overexpression of fatty acid synthase(FAS).acetyl-CoA carboxylase(ACC)and sterol regulatory element binding protein 1(SREBP1)in the liver of the mice induced by HFD,indicating that HPI regulated the lipid metabolism level of the liver by down-regulating the key protein pathway of fat production,thus alleviating the obesity and liver injury caused by HFD in the mice.At the same time,we found that the intake of HPI was more effective in reducing fasting blood glucose,regulating glucose tolerance and insulin sensitivity by activating the IRS1/PI3K/Akt pathway in the liver of mice,thus improving insulin resistance in obese mice.In addition,the addition of LPI and HPI can up-regulate the expression of nuclear factor NF-E2 related factor(Nrf2)in mouse liver and improve the oxidative stress of liver.At the same time.HPI can effectively inhibit the expression of inflammatory nuclear factor-kappaB(NF-?B)and interleukin-6(IL-6)in the liver,thus preventing the inflammatory response caused by obesity.The above results show that HPI has a good regulatory effect on various factors inducing the occurrence of NAFLD.(3)The supplementation of LPI and HPI can effectively regulate the metabolism of short-chain fatty acids and intestinal flora disorder induced by HFD in mice.After 8 consecutive weeks supplementation,the content of short-chain fatty acids in the colon were changed,among which HPI significantly increased the concentrations of acetic acid.propionic acid and butyric acid.Analysis of important variable projection(VIP)analysis found that there was a correlation between SCFAs formation and various factors related to insulin sensitivity,inflammation,and de novo fat synthesis.which indicating that HPI can inhibit liver inflammation and insulin resistance by regulating the formation of SCFAs,thereby preventing NAFLD from occurring.Sequence analysis of 16S rDNA gene of microorganisms in the colon contents of mice showed that the intervention of LPI and HPI reversed the increase of Firmicutes abundance caused by HFD and the decrease of Bacleroideles abundance,and HPI more effectively reduced Firmicutes abundance from 72.1%to 34.5%and increased Bacteroides abundance from 19.8%to 57.1%.Meanwhile,at the genus level,the relative abundance of Barnesiella Lactobacillus(8.2%to 32.3%).Bucteroides(1.1%to 2.4%),AkkerMansia(0.5%to 2.1%)and Parabacteroides(0.1%to 1.4%)increased significantly.The relative abundance of Allobaculum and Clostridium ??a was significantly reduced.In addition.there is a correlation between the relative abundance of various microorganisms in the intestinal tract and the content of short-chain fatty acids.suggesting that the change in the abundance of intestinal flora may help to regulate the metabolism of SCFAs in HFD-fed mice.Accordingly,inulin can regulate the intestinal flora disorder and SCFAs metabolic balance induced by HFD in mice,and the effect of HPI is more prominent.This study suggests that inulin on liver injury in mice and the protection of the intestinal flora disturbance adjusting function related to the DP,and HPI in improving HFD mice induced accumulation of lipid,insulin resistance,inflammation,SCFAs metabolism,intestinal flora imbalance,etc,showing a better effect Furthermore,this study provides a new scientific understanding for the interaction between dietary prebiotics and gut microflora to regulate liver glucose and lipid metabolism,oxidative stress and inflammation,and provides a nutritional theory for the futher development of HPI as a new intestinal regulation and functional liver protection product.