Yiqi Wenyang Formula ameliorates diabetic kidney disease via inhibiting inflammation and regulating the gut microbiota-bile acid axis in mice by FXR signaling pathway

BACKGROUND: Diabetic kidney disease (DKD) is a microangiopathic complication of diabetes. Yiqi Wenyang Formula (YQWYF) has been used to treat DKD in the clinic for many years. However, the underlying regulatory mechanisms of YQWYF on the gut microbiota and bile acids of DKD mice remain unclear. PURPOSE OF THE RESEARCH: This study aimed to investigate the mechanism of YQWYF on DKD mice using an integrative approach of network pharmacology, fecal 16S ribosomal RNA (rRNA) gene sequencing, and untargeted metabolomics. METHODS: The chemical composition of YQWYF was determined via ultrahigh-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). Common targets were identified between YQWYF and DKD, and a potential protein-protein interaction (PPI) network was constructed using network pharmacology. DKD mice were induced with streptozotocin (STZ) for 18 weeks. Twenty-four-hour urine was collected on the 9th and 18th weeks, and serum was collected on the 18th week to detect the biochemical measurements of urine and serum. Oxidative stress biomarkers and inflammatory cytokines in the kidney were detected via ELISA kits. The microstructure of the renal tissue was assessed by hematoxylin-eosin staining, periodic-acid Schiff staining, and Masson staining. Fresh fecal sample of mice were collected on the 18th week to detect the gut metabolites and microbiota using untargeted metabolomics and 16S rRNA sequencing. We analyzed the gut microbiota-bile acid (BA) axis for mechanism exploration. RESULTS: A total of 41 compounds were recognized in YQWYF. TNF and IL6 were the important core targets between YQWYF and DKD. The results of molecular docking revealed that astragaloside I, 16-meprednisone acetate, and astragaloside IV from YQWYF had strong affinities for TNF-α and IL-6. Animal experiments showed that YQWYF reduced glycemia and improved lipid metabolism abnormalities in DKD mice. Moreover, it had excellent anti-oxidant and anti-inflammatory effects to ameliorate renal injury in DKD mice. YQWYF improved the richness and evenness of the gut microbiota and increased bile acid levels in the feces of DKD mice. Importantly, 4 genus bacteria (christensenellaceae_R-7_group, oscillibacter, UCG-005, and [Eubacerium]_ xylanophilum_group) were closely related with 3 BAs (CA, GCA and DHCA). Meanwhile, YQWYF improved the protein expression of Farnesoid X receptor (FXR), CYP7A1 and CYP8B in the liver. CONCLUSION: These findings reveal that YQWYF ameliorates renal injury in DKD mice by inhibiting the inflammatory, increasing the FXR signaling, and regulating the gut microbiota disorder and bile acid dysregulation.