Mechanism Of Astragaloside Ⅳ Alleviating Diet-induced Obesity By Regulating Intestinal Flora

Obesity is a global epidemic characterized by excessive accumulation of body fat due to energy intake exceeding energy expenditure.Excessive lipid accumulation increases the risk of various diseases such as non-alcoholic fatty liver disease(NAFLD),cardiovascular disease,diabetes,hypertension,dyslipidemia and cancer.Intestinal flora and its related metabolite bile acids(BAs)play a vital role in the development of obesity and NAFLD.Astragaloside IV(AS-Ⅳ),as a low-permeability saponin extracted from Astragali radix,has been confirmed to have a variety of pharmacological activities,but its effect on obesity remains unclear.This study investigated the effect of AS-Ⅳ on diet-induced obesity and associated metabolic disorders in mice,as well as the changes of intestinal flora during this process.The main results of this study are as follows:1.AS-Ⅳ significantly inhibited the occurrence of obesity in mice.The mice were treated with AS-Ⅳ intragastric administration every day for 12 weeks.Body weight change and food intake of the mice were measured weekly,and obesity-related metabolic parameters were measured at the end of the experiment.Results showed that AS-Ⅳ treatment reduced diet-induced weight gain and improved systemic glucose and lipid metabolism disorders.In liver tissue,AS-Ⅳ alleviated hepatic steatosis by inhibiting(sterol regulatory element binding protein-1c)SREBP-1c.AS-Ⅳ did not significantly affect the metabolic level of mice fed with normal diet,nor did it significantly affect the food intake of mice.2.AS-Ⅳ remarkably affected the intestinal flora structure of mice.16 Sr RNA sequencing and untargeted metabolomics were performed using feces and intestinal contents of mice.The results showed that AS-Ⅳ reversed the reduction in Shannon index of the intestinal flora in mice caused by high fat diet(HFD)feeding,but there was no effect on the Chao1 index.In addition,Firmicutes and Bacteroides that were observably changed by HFD showed no marked change under AS-Ⅳ treatment.At the genus level,AS-Ⅳ significantly reduced the abundance of bile salt hydrolase(BSH)expressing bacteria compared with the HFD control group.These bacterial changes reduced BSH activity and thus inhibited the dissociation of conjugated BAs.Studies have shown that AS-Ⅳ affects the composition of BAs by regulating the intestinal flora,resulting in significant increases in tauro-β-muricholic acid,glycochenodeoxycholic acid,tauroursodeoxycholic acid and taurodeoxycholic acid in the conjugated bile acid and significant decrease in cholic acid and deoxycholic acid in unconjugated bile acid.3.AS-Ⅳ inhibited intestinal Farnesoid X receptor(FXR)signaling.PCR and immunofluorescence were used to detect the regulation of AS-Ⅳ on intestinal FXR signaling pathway.The results showed that AS-Ⅳ inhibited intestinal FXR signaling in HFD-fed mice,resulting in partial activation of hepatic bile acid synthase and compensatory activation of hepatic FXR signaling pathway.In addition,glucagon-like peptide-1(GLP-1)are also affected,AS-Ⅳ can activate the production of GLP-1 in intestine of HFD mice.These changes are involved in the regulation of SREBP-1c,which provides support for AS-Ⅳ to inhibit the occurrence of SREBP-1c-mediated lipogenesis.4.AS-Ⅳ alleviated the diet-induced obesity and associated metabolic disorders in mice via intestinal flora.Fecal transplantation confirmed that AS-Ⅳ receivers evidently reduced weight gain and improved lipid metabolism disorders.The intestinal flora of the recipient mice was similar to that of the donor mice,which showed that the relative abundance of Firmicutes and Bacteroides were almost unchanged in AS-Ⅳ receivers,while the relative abundance of BSH-expressing bacteria was reduced compared with HFD receivers.BSH activity as well as intestinal FXR signaling pathway were significantly inhibited in the AS-Ⅳ receptor group.These results imply that the importance of intestinal flora in the anti-obesity effects of AS-Ⅳ.In conclusion,this study confirmed that AS-Ⅳ can improve the occurrence of obesity,dyslipidemia and hepatic steatosis in mice.This beneficial effect of AS-Ⅳ is mainly achieved by the decreased intestinal BSH-expressing bacteria and BSH activity.As BSH activity decreased,AS-Ⅳ alters the composition of BAs,which ultimately inhibits intestinal FXR signaling pathway and thus SREBP-1c-related lipogenesis.These results indicate that the changes in intestinal flora and BAs play an essential role in the remission of obesity and hepatic steatosis by AS-Ⅳ,thereby suggesting that AS-Ⅳ may be used as a prebiotic agent to provide viable treatment for obesity and NAFLD.