Oral rhein attenuate nonalcoholic steatohepatitis in mice through the modulation of gut microbiota and Th17 cell differentiation

Background Non-alcoholic steatohepatitis (NASH) is an important clinical issue and a challenge in the field of global public health. However, there are very few clinically approved drugs that can effectively treat NASH. Rhein is a natural organic compound with anti-inflammatory and antioxidant properties, but the specific role and mechanism on NASH remain unexplored. Purpose This study investigated the role and associated mechanism of rhein in NASH mice. Methods The effects of rhein on lipid accumulation were evaluated in NASH mice through systemic signs of obesity, biochemical parameters, and histological changes. Network pharmacology was employed to determine the main bioactive compounds and key targets of rhein for the NASH treatment. Additionally, antibiotics treatment and fecal microbiota transplantation (FMT) were performed to investigate the role of microbiota in the treatment of NASH with rhein. Bacterial 16S rRNA amplicon sequencing, LC-MS/MS analysis and flow cytometric were employed to investigate the mechanisms underlying rhein’s regulatory effects on gut microbiota, BA metabolism and immune balance. Finally, in vitro cell experiments were conducted to explore the effects of metabolites on Th17 cell differentiation. Results Our results showed that mice treated with rhein showed a significant alleviating effect from high-fat diet (HFD)-induced liver lipid accumulation and pathological changes compared to those in HFD group. The protective effects of rhein are gut microbiota dependent, as demonstrated by fecal microbiome transplantation and antibiotics treatment. Microbiota transferred from rhein-treated mice displayed a similar role in attenuating hepatic lipid deposition as rhein on NASH in mice, and depletion of the gut microbiota through antibiotics treatments diminished the protective effects of rhein on NASH mice. Moreover, the results from bacterial 16S rRNA sequencing suggested that rhein partially attenuated HFD-induced gut dysbiosis in NASH mice. Network pharmacology analyses was implemented and showed that Th17 cell differentiation might be the potential target in the treatment of rhein against NASH, which was confirmed by flow cytometric analysis showing markedly decrease of the percentage of Th17 cells, corresponded with upregulated Treg cells in rhein-treated NASH mice. Furthermore, targeted bile acid metabolomics analysis showed that supplement with rhein greatly increased the levels of primary bile acids β-MCA and AlloLCA, positively correlated with the relative abundances of Bifidobacterium_choerinum , which may play the key role by which rhein-altered gut microbiota promoted the restoration of Th17/Treg balance in NASH mice. Subsequent in vitro experiments confirmed that AlloLCA directly inhibits Th17 cell differentiation, with suppression of glycolysis potentially serving as the underlying mechanism for the immunomodulatory effects of AlloLCA. Conclusions Collectively, our results suggested that orally administrated rhein reduced hepatic lipid deposition through the modulation of dysregulated gut microbiota and bile acids metabolism, thus regulating Th17/Treg immune balance. This study uncovers a novel mechanistic axis in NASH pathogenesis and providing new research directions for microbiota-targeted clinical strategies.