Effects Of Different Polysaccharides On Obesity And Study On The Anti-obesity Mechanism Of β-glucan

The composition and function of gut microbiota change with different dietary patterns and disease states of host.The evidence of frequent interactions between polysaccharides and gut microbiota has pushed the theory that polysaccharides participate in intestinal metabolism and regulate metabolic diseases through the function of gut microbiota to the forefront of research.However,the specific mechanisms by which polysaccharides interact with gut microbiota are still unclear,such as the pattern of the host gut microbiota response to the anti-obesity effect of polysaccharides,and how microbial composition and function affect gut metabolism and gut health.Therefore,in this study,based on high-fat diet induced obese rats,ten different sources of polysaccharides were selected,including β-glucan,arabinoxylan,glucomannan,xanthan gum,guar gum,apple pectin,carrageenan,arabinogalactan,inulin,xylan,compared their anti-obesity effects through combining the physiology,genomics,and metabolomics with the obese rat model.Then,based on the selected four polysaccharides with the significant effect on regulating obesity phenotype and the dominant abundant bacteria(Prevotella.copri,P.copri)in the gut,the anti-obesity effect of the combination of P.copri and four polysaccharides was verified by using high-fat diet(HFD)-induced obese mice model and germ-free mice model.Finally,based on the bile acid-gut-liver(FXR-FGF15 signaling)axis,the synergistic role of P.copri in polysaccharide regulating gut microbiota function and improving obesity was elucidated.The main study contents and results are summarized as follows:(1)Supplementation with β-glucan,arabinoxylan,xanthan gum,guar gum,apple pectin,carrageenan,inulin and xylan significantly reduced the bodyweight and dyslipidemia,whereas glucomannan and arabinogalactan did not affect serum lipids and bodyweight control in obese rats,respectively.Besides,apple pectin,β-glucan and arabinoxylan improved the greater biomarkers(15,17 and 18 kinds)which were relevant to obesity,and the bioactive dietary fibers associated with elevated glycerophospholipids levels and regulation of glycerophospholipid metabolism.Moreover,the abundance of beneficial bacteria Akkermansia,Butyricimonas,Oscillospira,Ruminococcus,Prevotella were enriched by dietary fibers with various degrees,furthering exhibited benefits on obesity.It was also found that increased Butyricimonas(including glucomannan,xanthan gum,guar gum,xylan,apple pectin,arabinogalactan)and Prevotella(except for xanthan gum and inulin)showed negative with dyslipidemia factors notably(TC,TG,LDL-C),positive with glycerophospholipids(like phosphatidylcholine),therefore promoted the improvement of host metabolism and relief in dyslipidemia.In brief,our study revealed that different dietary fibers have an impact on gut microbiota then mediating metabolic benefits in obese rats,and these interactions could be considered as targets for diet personalized.(2)Based on the dominant bacteria P.copri and four polysaccharides(β-glucan,arabinoxylan,apple gum,guar gum),we evaluated the degree of polysaccharide utilization by P.copri in vitro.Meanwhile,the anti-obesity effects of P.copri and the four polysaccharides were investigated with obese mice.Results showed that both P.copri and the four polysaccharides could regulate the phenotypes of obese mice.β-glucan,arabinoxylan,apple gum and guar gum could significantly reduce the body weight,epididymal fat and liver weight.P.copri also significantly down-regulated the body weight of obese mice and reduced the accumulation of TC,TG,LDL-C and NEFA.β-glucan,arabinoxylan,guar gum and P.copri decreased the concentration of TG by more than 20%,while β-glucan and P.copri significantly increased the concentration of HDL-C by 16.42% and 13.99%.P.copri combined with the four polysaccharides had certain anti-obesity effects,and the body weight of mice in the P.copri combined with β-glucan intervention group was the lowest,which was close to the normal group.Different polysaccharides can regulate the blood glucose of obese mice differently.β-glucan,arabinoxylan and apple gum only reduced the AUC(area under curve of oral glucose tolerance test)by 10-13%,but the intervention of P.copri and P.copri combined with β-glucan,arabinoxylan and guar gum could alleviate the impaired glucose tolerance of obese mice more effectively.The AUC was reduced by 20.28%,24.57%,22.64%,19.63% and 23.46%,respectively.These results suggested that P.copri combined with different polysaccharides could synergistically improve dietinduced obesity and abnormal glycemia.Polysaccharide has no significant effect on blood glucose regulation in obese mice,but P.copri combined with β-glucan,arabinoxylan and guar gum can alleviate impaired glucose tolerance in obese mice.These results suggested that P.copri could promote polysaccharide to improve high fat diet-induced obesity and abnormal glycemia.(3)Based on genomic analysis,the effects of P.copri and four polysaccharides on the composition and function of gut microbiota were evaluated.The diversity of gut microbiota in obese mice was reduced by high-fat diet.The ratio of Firmicutes/Bacteroidetes(F/B)was significantly increased in model group,the ratio was 1.57,which was about 4-fold higher than that in the normal group.β-glucan,arabinoxylan,apple gum and P.copri significantly reduced the ratio of F/B(to 0.84,0.91,0.72,and 1.0 respectively).The intervention of the three polysaccharides and P.copri promoted the proliferation of beneficial bacteria Bacteroides.The proportion of Bacteroides in β-glucan,arabinoxylan,and apple gum groups was more than 15%,while the proportion of Bacteroides in P.copri intervention group increased to 15.05%,about 2.5-times that of the model group.In addition,Parabacteroides was significantly enriched in P.copri group,which may be related to the regulation of bile acid metabolism.The relative abundance of Lactobacillus and Lactococcus(expressing bile salt hydrolase(BSH)function)was significantly down-regulated in the β-glucan,arabinoxylan,and P.copri combined with β-glucan intervention groups.These results suggested that β-glucan,arabinoxylan and P.copri may regulate bile acid metabolism through gut microbiota function,then further exert anti-obesity effects.(4)To compare the effects of polysaccharides on bile acid metabolism in obese mice based on targeted metabolomics.We explored the anti-obesity mechanisms of β-glucan and P.copri in the FXR-FGF15 signaling pathway.The results showed that β-glucan reduced the accumulation of cholesterol,which was close to the normal liver TC concentration(0.35 ± 0.02 mmol/gprot),while P.copri promoted β-glucan and arabinoxylan to reduce cholesterol level.Meanwhile,P.copri,and P.copri combined with β-glucan increased the concentration of conjugated BAs including TCDCA and TUDCA,and decreased the concentration of non-conjugated BAs(such as CDCA and UDCA)in the intestine of mice.The concentration of BSH in intestinal bacteria of obese mice showed a downward trend with β-glucan and P.copri intervention.P.copri also promoted the down-regulation of non-conjugated BAs(CDCA)in β-glucan,and the expression of FXR-FGF15 signal axis in the intestine was decreased accordingly.The expression of CYP7A1,CYP8B1(the classical biosynthetic pathway)and CYP27A1,CYP7B1(the alternative biosynthetic pathway)of hepatic bile acid synthesis pathway were significantly increased.These results suggested that β-glucan may alleviate HFD-induced hepatic cholesterol accumulation via reducing gut microbiota BSH function,inhibiting the activation of FXR-FGF15 signaling axis,and promoting hepatic BA synthesis and fecal BA excretion.And P.copri promoted the effect of β-glucan on FXR-FGF15 signaling axis to increase hepatic cholesterol consumption and alleviate obesity.(5)A “pseudo germ-free” mouse model was constructed using antibiotics to verify the anti-obesity effect of P.copri and investigate whether β-glucan exert anti-obesity effect in a microbiota-dependent manner completely.The results showed that P.copri colonization reduced the body weight gain by 37.61% compared with obese mice,and the levels of TC,LDL-C and HDL-C were significantly improved(p < 0.05),suggesting that P.copri is beneficial to improve lipid disorders in obese mice under “pseudo-germfree” mode.The body weight gain of β-glucan group decreased by 47.50%,suggesting that β-glucan could not completely rely on gut microbiota to reduce body weight,whileβ-glucan reduced serum lipid TG,LDL-C and HDL-C in a microbiota-dependent manner.Moreover,P.copri combined with β-glucan significantly reduced bodyweight gain(decreased by 64.04% compared with the model group).In addition,P.copri promoted β-glucan improving the impaired glucose tolerance in obese mice.The results of gut microbiota showed that P.copri combined with β-glucan increased the abundance of Bacteroidetes(16.61%),more than 2 times to the model group(7.71%).However,Lactobacillus and Lactococcus that expressed BSH function did not change significantly in the pseudo-germ-free” model.These results suggested that P.copri has anti-obesity effect,and promotes the hypolipidemic effect of β-glucan.