Intrahepatic cholestasis of pregnancy (ICP) is a common obstetric disorder characterized by pruritus and elevated serum bile acid levels, with a global prevalence of 1.5% to 4.0% of pregnancies (Hobson et al., 2022). Although the exact etiology remains unclear, ICP is thought to result from a complex interplay of genetic, hormonal, and environmental factors (Jamshidi Kerachi et al., 2025). The condition typically manifests in the second or third trimester of pregnancy and resolves spontaneously after delivery. Despite its transient nature, ICP is associated with adverse maternal and fetal outcomes, including preterm birth, fetal distress, and stillbirth, highlighting the importance of effective management strategies (Smith and Rood, 2020, Williamson and Geenes, 2014). Ursodeoxycholic acid (UDCA) is currently the most widely used treatment for ICP (Girling et al., 2022). It has been shown to alleviate pruritus and reduce serum alanine aminotransferase (ALT) levels (Fan et al., 2021). However, UDCA does not directly address the underlying disturbances in bile acid metabolism or the contribution of gut microbiota dysbiosis to ICP pathogenesis (Ovadia et al., 2021). This limitation highlights the need for novel therapeutic approaches that target these mechanisms more specifically.

Recent evidence suggests that the gut microbiota plays a pivotal role in ICP development. The gut microbiota participates in key metabolic processes, including bile acid metabolism, the production of short-chain fatty acids (SCFAs), and the regulation of other metabolites. These metabolites are essential for gut barrier function, immune regulation, and intestinal homeostasis (Dai et al., 2020). Studies have shown that the genus Ruminococcus (torques group) is a major producer of secondary bile acids, and reduced abundance of this bacterium is associated with an increased risk of ICP (Nishiwaki et al., 2022, Li et al., 2023).

The farnesoid X receptor (FXR), a nuclear receptor highly expressed in the liver and ileum, is central to bile acid homeostasis (Tang et al., 2023). FXR activation by bile acids suppresses bile acid synthesis by inhibiting cytochrome P450 family 7 subfamily A member 1 (CYP7A1) and cytochrome P450 family 8 subfamily B member 1 (CYP8B1) (Fan et al., 2021). In ICP, the function of FXR is impaired by sulfated progesterone metabolites, which disrupt bile acid metabolism (Wang et al., 2022). In addition, bile acid binding to intestinal FXR induces synthesis of the endocrine hormone fibroblast growth factor15 (FGF15) in mice (FGF19 in humans), which is secreted into the portal circulation (Keitel et al., 2019, Hartmann et al., 2018). Upon reaching the liver, FGF15 activates the fibroblast growth factor receptor 4 (FGFR4), leading to further suppression of CYP7A1 and CYP8B1 expression and thereby maintaining bile acid balance (Sun et al., 2023).

VSL#3 is a probiotic preparation containing multiple beneficial bacterial strains, including Lactobacillus and Bifidobacterium (Salim et al., 2013; Li et al., 2024). It exerts anti-inflammatory and immunomodulatory effects and has been widely applied in the treatment of ulcerative colitis (Chapman et al., 2006, Guandalini, 2010). At the genus level, VSL#3 promotes enrichment of butyrate-producing bacteria such as Ruminococcus and Faecalibacterium, which reduce hepatic lymphocyte infiltration in FXR knockout mice, lower hepatic fat accumulation, and restore bile acid homeostasis (Jena et al., 2020). However, the role and mechanism of VSL#3 in the context of ICP remain insufficiently understood.

Based on these observations, we hypothesize that VSL#3 can alleviate ICP by modulating gut microbiota composition and enhancing the FXR-FGF15/19 signaling axis, thereby restoring bile acid homeostasis. To test this hypothesis, we performed a comprehensive analysis of gut microbiota composition and bile acid metabolism in ICP patients and healthy pregnant women to evaluate the therapeutic efficacy of VSL#3 in animal models of ICP.