Wendan Decoction exerts therapeutic effects on insomnia by regulating gut microbiota and tryptophan metabolism

Background: Insomnia has been a public problem threatening human health. Wendan Decoction (WDD) has good therapeutic effects on insomnia. However, its mechanism to improve sleep remains unclear. Purpose: To investigate the potential mechanism of WDD in treating insomnia from the perspective of gut microbiota and metabolism. Methods: The chemical composition of WDD was analyzed by UHPLC-Orbitrap Exploris/MS. The efficacy of WDD on PCPA-induced insomnia rats was evaluated through behavioral tests, ELISA, histopathological examination, immunofluorescence and western blotting. 16S rRNA sequencing, untargeted metabolomics, and network pharmacology were integrated to explore the mechanism of WDD in treating insomnia. The role of gut micro-biota in WDD treatment was validated by antibiotic treatment and fecal microbiota transplantation (FMT). Targeted metabolomics was used to detect changes in fecal tryptophan metabolites after FMT. Additionally, RTqPCR and western blotting were used to investigate the potential mechanisms. Results: WDD effectively shortened sleep latency, prolonged sleep duration, alleviated anxiety-like behaviors, attenuated neuronal damage, and modulated neurotransmitter levels in rats with insomnia. Moreover, WDD alleviated intestinal damage, reduced the number of Iba-1 positive cells, increased IL-10 levels and decreased IL-6, IL-1 beta, TNF-alpha and LPS levels in the colon, serum and hippocampus. It also increased the expression of Occludin, Claudin-1, and ZO-1 in both the colon and brain. 16S rRNA sequencing suggested that WDD improved gut microbiota disorders. Untargeted metabolomics and network pharmacology jointly suggested that WDD could regulate tryptophan metabolism. Antibiotic treatment and FMT confirmed the involvement of gut microbiota in the therapeutic effects of WDD in alleviating insomnia. Changes of tryptophan metabolites in feces, serum, and hippocampus confirmed the regulatory effect of WDD on tryptophan metabolism. Further mechanistic analysis suggested that WDD may correct the abnormal kynurenine pathway of tryptophan metabolism through inhibition of the expression of indoleamine 2,3-dioxygenase 1 and kynurenine-3-monooxygenase. Conclusion: WDD can modulate the neurotransmitter disorders, reduce inflammatory cytokine levels, and strengthen the intestinal barrier and blood-brain barrier by regulating gut microbiota and tryptophan metabolism, thereby improving sleep. This study provides evidence for the potential therapeutic effect of WDD on insomnia via the microbiota-gut-brain axis.