Pulsatilla chinensis saponins ameliorated murine depression by inhibiting intestinal inflammation mediated IDO1 overexpression and rebalancing tryptophan metabolism

Current antidepressant therapy remains unsatisfactory due to the complex pathogenesis. Emerging evidence suggested that depression is associated with inflammatory bowel disease (IBD), intestinal inflammation is an increasingly accepted factor that influences depression, but the mechanism is unclear.In the current study, we determined whether Pulsatilla chinensis saponins (PRS), a phytomedicine from Pulsatilla chinensis (Bunge) Regel with excellent anti-IBD effect, could improve the depression. Furthermore, we investigated the mechanisms to explore the relationship between IBD and depression and provide new source for the urgent development of antidepressants from phytomedicine.The antidepressant activity of PRS was accessed by behavioral test and multichannel technology in depression mice induced by Chronic Unpredictable Mild Stress (CUMS). 16S rDNA-based microbiota and RNA-seq in colon was used to explore potential intestinal metabolism affected by PRS. To illustrate the underlying mechanisms of anti-depression effect of PRS, targeted metabolomics, ELISA assay, immunofluorescence staining, Western Blot, and qPCR were carried out.The results clarified that CUMS induced depression with tryptophan (Trp) metabolism and intestinal inflammation. PRS effectively suppressed the depression and acted as a regulator of Trp/kynurenine (Kyn) metabolic and intestinal inflammation confirmed by analysis of microflora and colon RNA. Meanwhile PRS reduced interferon gamma (IFN-γ), inhibited JAK1-STAT1 phosphorylation, decreased IDO1 levels to protect against the overactivity of Trp/kyn path, suggesting that IFN-γ activated IDO1 probably a significant target for PRS to exert anti-depression effects. To further confirm the mechanism, this research expressed that PRS improved IDO1 activity and depressive behavior in mice with IFN-γ-induced depression. Furthermore, the therapeutic effect of 1-methyl-tryptophan (1-MT) well known as an IDO1 inhibitor in depression and clinically used anti-UC drug Mesalazine (MS) was demonstrated to confirm the potential mechanism.The study is the first to reveal the antidepressant effect of PRS and further demonstrate its potential therapeutic targets. In addition, it also clarifies that the Trp/kyn pathway is the crosstalk between IBD and depression and provides new choice for depression treatment. And it also provides an important basis for the follow-up development and exploration of anti-intestinal antidepressants.