Vinegar-processed Schisandra Chinensis enhanced therapeutic effects on colitis-induced depression through tryptophan metabolism.

BACKGROUND

Ulcerative colitis (UC) is an inflammatory bowel disease characterized by its incurable nature and undefined etiology, which is often accompanied by a high prevalence of comorbid depression. The gut-brain axis has emerged as a promising treatment target in recent years.

PURPOSE

This study aimed to investigate how vinegar-processed Schisandra Chinensis (VSC) enhances therapeutic effects on depressive behavior in chronic UC mice.

METHODS

A chronic UC model was induced in mice using dextran sulfate sodium. The therapeutic effects of both raw and vinegar-processed Schisandra Chinensis on UC and associated depressive symptoms were assessed. Colonic mucosal damage was evaluated using hematoxylin and eosin (H&E) and Alcian blue staining. The integrity of the blood-brain barrier (BBB) and synaptic structures was visualized via transmission electron microscopy (TEM). Enzyme-linked immunosorbent assay (ELISA) was employed to quantify inflammatory cytokine levels in the colon, serum, and brain, while western blotting was performed for protein expression analysis. Additionally, metagenomic analysis was conducted to investigate gut microbiota composition. Nissl staining and immunofluorescence were used to assess hippocampal neuronal damage, and behavioral assessments including the morris water maze, open field test, forced swimming test and tail suspension test, were implemented to evaluate depressive states. Serum metabolites were analyzed using UPLC-MS/MS.

RESULTS

Both raw and vinegar-processed Schisandra Chinensis significantly upregulated aryl hydrocarbon receptor (AhR), inhibited NF-κB p-p65 activation, and reduced levels of pro-inflammatory cytokine. These treatments also enhanced the expression of tight junction proteins, restored colonic mucosal and BBB integrity, alleviated damage to hippocampal neurons, and improved synaptic structure. Behavioral assessments indicated that VSC was particularly effective in ameliorating depressive-like behaviors in chronic UC mice. In the gut, both treatments reshaped the gut microbial composition, restoring the relative abundance of Duncaniella, Candidatus_Amulumruptor, Alistipes, Parabacteroides, Lachnospiraceae_bacterium, uncultured_Bacteroides_sp., Candidatus_Amulumruptor_caecigallinarius, with VSC showing more pronounced effects. Serum metabolomics revealed an increase in tryptophan levels and a decrease in kynurenine and xanthurenic acid levels with VSC, indicating that tryptophan metabolism shifted from the kynurenine pathway to the 5-HT or indole pathway. However, this phenomenon did not occur with Schisandra Chinensis (SC).

CONCLUSION

This study demonstrated that the disruption of tryptophan metabolic balance served as a biological mechanism underlying the occurrence of depressive behaviors induced by UC. The application of SC following vinegar processing enhanced its regulatory effects on gut microbiota and tryptophan metabolism. This findings provided a new insight for the clinical management of gut-brain comorbidities.