20(S/R)-Ginsenoside Rh1 Alleviates AOM/DSS-Induced Colorectal Cancer: Gut-Microbiota Modulation and Tryptophan-Metabolism-Mediated AhR/PXR Activation and IDO1.

Colorectal cancer (CRC) is intricately linked to gut microbiota dysbiosis and tryptophan (Trp) metabolic dysregulation. This study aimed to clarify the role and mechanisms of 20(S/R)-ginsenoside Rh1 in suppressing colorectal cancer through the regulation of gut microbiota and Trp metabolism. Azoxymethane/dextran sulfate sodium (AOM/DSS)was employed to induce a CRC mouse model, followed by treatment with 20(S/R)-ginsenoside Rh1 at 100 mg·kg-1·day-1 for 6 weeks. 20(S/R)-ginsenoside Rh1 significantly reduced the disease activity index (DAI) score, restored colon length, and decreased tumor count. 20(S/R)-Ginsenoside Rh1 ameliorated gut dysbiosis by increasing gut microbial diversity and elevating the prevalence of beneficial bacteria, including Lactobacillus, and stimulated the production of indole derivatives, including indole-3-propionic acid (IPA), indole-3-acetic acid (IAA), and indole-3-lactic acid (ILA) by enriching Trp -metabolizing bacteria such as Lactobacillus reuteri. These changes further activated the AhR/CYP1A1/IL-22 and PXR/TLR4 pathways, upregulated the expression of intestinal tight junction proteins, suppressed the secretion of proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and IFN-γ, and elevated the levels of the anti-inflammatory cytokine IL-10. Furthermore, 20(S/R)-ginsenoside Rh1 reduces the serum kynurenine (Kyn)/Trp ratio, downregulates the expression of forkhead box P3 (FoxP3), a marker of regulatory T (Treg) cells, and increases the number of CD8+ T cells by inhibiting the expression of indoleamine 2,3-dioxygenase 1 (IDO1) in colonic tissue. In conclusion, 20(S/R)-ginsenoside Rh1 showed potential anti-CRC activity, with our study observing links between its action and gut microbiota structure regulation, Trp metabolism modulation, AhR/PXR-mediated intestinal barrier activation, and IDO1-related immune suppression reversal.