Functional Metabolomics Reveals that Astragalus Polysaccharides Improve Lipids Metabolism through Microbial Metabolite 2-Hydroxybutyric Acid in Obese Mice

Polysaccharides are widely present in herbs with multiple activities, especially immunity regulation and metabolic benefits for metabolic disorders. However, the underlying mechanisms are not well understood. Functional metabolomics is increasingly used to investigate systemic effects on the host by identifying metabolites with particular functions. This study explores the mechanisms underlying the metabolic benefits of Astragalus polysaccharides (APS) by adopting a functional metabolomics strategy. The effects of APS were determined in eight-week high-fat diet (HFD)-fed obese mice. Then, gas chromatography–time-of-flight mass spectrometry (GC–TOFMS)-based untargeted metabolomics was performed for an analysis of serum and liver tissues, and liquid chromatography–tandem mass spectrometry (LC–MS/MS)-based targeted metabolomics was performed. The potential functions of the metabolites were tested with in vitro and in vivo models of metabolic disorders. Our results first confirmed the metabolic benefits of APS in obese mice. Then, metabolomics analysis revealed that APS supplementation reversed the HFD-induced metabolic changes, and identified 2-hydroxybutyric acid (2-HB) as a potential functional metabolite for APS activity that was significantly decreased by a HFD and reversed by APS. Further study indicated that 2-HB inhibited oleic acid (OA)-induced triglyceride (TG) accumulation. It was also found to stimulate the expression of proteins in lipid degradation in hepatocytes and TG lipolysis in 3T3-L1 cells. Moreover, it was found to reduce serum TG and regulate the proteins involved in lipid degradation in high-fat and high-sucrose (HFHS)-fed mice. In conclusion, our study demonstrates that the metabolic benefits of APS are at least partially due to 2-HB generation, which modulated lipid metabolism both in vitro and in vivo. Our results also highlight that functional metabolomics is practical for investigating the mechanism underlying the systemic benefits of plant polysaccharides.