Isoastragaloside II modulates PPAR-α/FXR signaling and bile acid metabolism to ameliorate cholestatic liver diseases (CLD).

Cholestatic liver disease (CLD) is a severe hepatobiliary disorder with limited treatment options. Although the natural compound Isoastragaloside II (IAS II) has been suggested to possess general hepatoprotective properties, its therapeutic efficacy against CLD has not been reported. In this study, the therapeutic potential and underlying mechanisms of IAS II for CLD were investigated using a murine model established by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) feeding. It was demonstrated that DDC-induced cholestatic liver injury was significantly alleviated by IAS II treatment, as indicated by the normalization of key serum biochemical parameters. An integrated analysis of histopathological, protein, and gene expression data demonstrated that IAS II treatment effectively suppressed the ductular reaction, inhibited hepatic fibrosis, and attenuated inflammation. Analysis of 16S rRNA sequencing data revealed that IAS II treatment was accompanied by alterations in gut microbiota composition, including an enrichment of Bacteroides and a reduction in Lachnospiraceae_NK4A136_group. Antibiotic depletion experiments demonstrated that the hepatoprotective effects of IAS II were abrogated by gut microbiota depletion, confirming the essential role of the gut microbiota in its pharmacological action. At the molecular level, IAS II activated both the PPAR-α pathway (as indicated by transcriptomic analysis) and the FXR pathway (as confirmed by subsequent validation), which collectively resulted in a significant reduction in the hepatic accumulation of toxic bile acids (BAs). In vitro studies in LCA-induced HepG2 cells further revealed that the restoration of PPAR-α, ACOX2, FXR, and BSEP protein expression by IAS II required receptor activation, as these effects were blocked by specific inhibitors. In summary, to our knowledge, this study provides the first demonstration that a protective effect against DDC-induced cholestatic liver injury is conferred by IAS II through coordinated regulation of PPAR-α and FXR signaling, restoration of BA homeostasis, and in a gut microbiota-dependent manner, with these effects requiring the activation of both PPAR-α and FXR pathways, thereby identifying IAS II as a novel and promising therapeutic candidate for CLD.