Lipid-lowering Effects And Mechanism Of Apple Chlorogenic Acid-low Methylesterified Pectin Conjugate On High-fat Diet-induced Obese Mice

Obesity is a chronic metabolic disease caused by many factors,which seriously threatens human health.Recent studies have shown that obesity is closely related to lipid metabolism and intestinal microbiota.Chlorogenic acid(CGA)is a characteristic polyphenol in apples,which has varieties of bioactivity with regulation of lipid metabolism,and absorbed by the intestinal microbiota in the colon.Increasing the interaction of low methylesterified pectin(LMP)with CGA to extend the residence and fermentation time of CGA in the colon,which will improve the bioactivity of CGA,and promote the effective use of CGA in functional foods.In this study,CGA-LMP conjugate was characterized by FTIR,UV-vis,XRD,and SEM after preparation.Then,the effect of CGA-LMP conj ugate on lipid metabolism and intestinal microbiota in high-fat diet-induced mice was also explored.The main results obtained were as follows:(1)Preparation and characterization of CGA-LMP conjugate.Addition of CGA caused a significant shift in the infrared absorption spectrum of CGA-LMP conjugate,which may be due to the formation of a stable three-dimensional structure between CGA and LMP through hydrogen bonding.Then,the addition of CGA improved the crystal configuration.Furthermore,CGA-LMP conjugate has a more obvious porous and honeycomb structure and its smooth area is significantly increased from the SEM spectrum.Therefore,the CGA-LMP conjugate was selected for subsequent animal experiments.(2)CGA-LMP conjugate significantly prevented obesity in HFD mice.After administering CGA-LMP conjugate with 25,50,and 75 mg/(kg·d)CGA,the body weight of HFD-L,HFD-M,and HFDF-H groups decreased(P<0.05)by 25%,32%,and 37%respectively,relative to HFD mice.In addition,CGA-LMP conjugate reduced the Lee’s index and food efficiency ratio(FER)in obese mice,which confirmed that food intake was the main determinant of weight.In particularly,CGA-LMP conjugate reduced the epididymal fat index of mice in the HFD-L,HFD-M,and HFD-H groups by 22%,25%,and 35%,respectively(P<0.05),and decreased the pararenal fat index by 23%,26%and 35%(P<0.05),respectively,relative to HFD mice.But there was no significant effect on liver index.Then,CGA-LMP conjugate significantly reduced lipid accumulation and reduced the degree of steatosis of liver.Comparing with the HFD group,the area of adipocytes in HFD-L,HFD-M and HFD-H mice were reduced by 42%,63%,and 71%(P<0.05),respectively.Furthermore,CGA-LMP conjugate effectively prevented hyperlipidemia caused by high-fat diet.(3)Mechanism of CGA-LMP conjugate improved lipid metabolism in liver of highfat diet-induced obese mice.CGA-LMP conjugate lowered the mRNA and protein levels of lipogenesis related genes such as SREBP-1C,PPAR γ,FAS,ACC1,and LPL.Particularly,the protein levels of SREBP-1C,PPARy and FAS in the HFD-H group were reduced(P<0.05)by 76%,36%,and 22%in comparison with HFD mice,respectively.In addition,CGA-LMP conjugate elevated the mRNA and protein levels of lipolysis related genes in the liver of obese mice.The expression level of the two lipolytic proteins,PPARa and CPT1,increased(P<0.05)by 2.6-fold and 2.3-fold in the HFD-H mice,respectively,compared to the HFD mice.Furthermore,CGA-LMP conjugate promoted the expression of LXRa genes or proteins in liver to promote cholesterol metabolism.(4)CGA-LMP conjugate effectively regulated the composition of intestinal microbiota in obese mice.CGA-LMP conjugate effectively reduced the intestinal wall damage caused by high-fat diet in a dose-dependent manner.In addition,CGA-LMP conjugate significantly increased the content of SCFAs in fece.Furthermore,CGA-LMP conjugate regulated the structure of the intestinal microbiota,changed the diversity and richness,and effectively reduced the ratio of Firmicutes/Bacteroidetes via the sequence information of the V3-V4 region of the 16S rDNA.In particular,CGA-LMP conjugates significantly increased norank_f_Muribaculaceae and unclassified_f_lachnospiraceae at the genus level(P<0.05).CGA-LMP conjugates increased significantly,Uncultured_bacterium_g_norank_f_Muribaculaceae species and unclassified_g_norank_f_lachnospiraceae at the species level(P<0.05).In summary,CGA-LMP conjugate had a good effect on the preventation of obesity,which was reflected in reducing body weight,fat mass and blood lipids.In addition,CGALMP conjugate improved the expression of mRNA and proteins related to lipid metabolism and regulated the structure of intestinal microbiota.Therefore,it is speculated that the conjugation between CGA and LMP would effectively improve the biological activity of CGA,thus laying a theoretical foundation for the widespread application of CGA on functional foods.