Bupleuri radix extract ameliorates impaired lipid metabolism in high-fat diet-induced obese mice via gut microbia-mediated regulation of FGF21 signaling pathway

Abstract

BackgroundObesity and its comorbidities are associated with abnormal lipid metabolism and gut microbiota dysbiosis. Bupleuri Radix is a medicinal plant used in traditional Chinese medicine with the prevention and treatment of obesity-related diseases. In this study, we aim to validate the regulation of Bupleuri Radix Extract (BupE) on lipid metabolism in obese mice, and try to find out the potential active components and reveal the underlying mechanisms. MethodsIngredients in BupE, their circulating metabolites in mice and fecal biotransformation products were analyzed by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS). Western blotting, RT-PCR and ELISA were used for tests of objective genes and proteins. 16 s rRNA sequencing was performed to examine intestinal bacteria composition and microbes’ functional changes were predicted with PICRUSt software. An absolute quantification method was set up via the construction of recombinant plasmid for the assays of intestinal flora. Specific microbial strains were cultured in anaerobic conditions and oral administrated to mice for intestinal mono-colonization. ResultsBupE attenuated obesity, liver steatosis, and dyslipidemia in HFD-fed mice by up-regulating the expression of FGF21 in liver and white adipose tissue (WAT) as well as the downstream proteins of FGF21 signal pathway including β-klotho, GLUT1 and PGC-1α, etc. UPLC/Q-TOF-MS fingerprints showed no compounds from BupE or their metabolites or biotransformation products were detected in rodent serum samples. High-throughput pyrosequencing data indicated that BupE reversed obesity-induced constructional and functional alterations of intestinal flora. Two bacterial strains, Bacteroides acidifaciens (B. acidifaciens) and Ruminococcus gnavus (R. gnavus), were separated and identified from the feces of obese mice and by intestinal mono-colonization they were verified to intervene in the anti-obesity effects of BupE on mice. ConclusionThese data suggest that BupE protects against diet-induced obesity and counteracts metabolic syndrome features consistent with a mechanism involving the gut-liver axis that boosts hepatic FGF21 secretion and consequent down-stream proteins expression relating to lipid metabolism. And in this gut-liver axis, intestinal microbes such as B.acidifaciens and R.gnavus play an indispensable role.