Purpose Tryptophan metabolism is involved in the etiology and exacerbation of depressive disorders. Kai-Xin-San (KXS), a traditional Chinese medicine formula, has been widely used to treat depression and modulate serotonin simultaneously, but how it regulates depressive-like behavior by shifting the balance of the tryptophan-serotonin metabolism and kynurenine pathway remains vague. Patients and Methods Ten participants with mild to moderate depression treated with KXS (KXS preparation) were analyzed in this study. Depression rating scale score and the concentration of serum tryptophan, 5-hydroxytryptophan and kynurenine was measured at baseline and the endpoint of KXS treatment. To explore the specific regulatory mechanism of KXS in tryptophan metabolism, the chronic restraint stress (CRS) was used to induce depressive-like syndrome in rats and the hippocampus level of tryptophan, 5-hydroxytryptophan, kynurenine with downstream metabolites (kynurenic acid, quinolinic acid) and key enzymes (indoleamine 2,3-dioxygenase, kynurenine 3-monooxygenase, kynurenine aminotransferase) were analyzed by liquid chromatography–electros pray ionization tandem mass spectrometry, high performance liquid chromatography and enzyme-linked immunosorbent assay respectively. Results KXS significantly decreased depression rating scale scores and increased the serum tryptophan and kynurenine concentration in depressive patients compared to baseline. Also, it alleviated the depressive behavior in CRS rats obviously. Comparing with CRS group, KXS increased tryptophan, 5-hydroxytryptophan, kynurenine level in rat hippocampus. Furthermore, in kynurenine pathway, KXS decreased the expression of indoleamine 2,3-dioxygenase, increased kynurenic acid by upregulating the expression of kynurenine aminotransferase while decreased quinolinic acid level in hippocampus, which suggested that KXS more favored improving serotonin pathway, and neuroprotective kynurenic acid branch in the tryptophan metabolism. Conclusion This is the first tryptophan metabolomic study of patients with depression undergoing KXS treatment. Combining these clinical results with CRS induced rat model studies, it verified that KXS achieves an excellent antidepressant effect and balances tryptophan-kynurenine metabolic pathways by regulating some key metabolic products and enzymes.

Objectives. Kaixinsan (KXS), a traditional Chinese medicine formula, has been demonstrated to be effective in the treatment of depression. The present study applied a network pharmacology approach to dig out the new targets and mechanism of action of KXS and the active compounds in the treatment of depression. Methods. A network pharmacology approach based on public databases including ADME (absorption, distribution, metabolism, and excretion) evaluation, targets prediction, construction of networks, and molecule docking was used and validated the predicted new antioxidant targets and mechanisms in vitro. Based on an in vitro experiment, we verified the AKT1/Nrf2 pathway related to the thioredoxin (Trx) antioxidant mechanism. Results. The present study sorted 31 pharmacologically active components (kaempferol, ginsenoside rh2, ginsenoside rh4, stigmasterol, etc.) through the ADME algorithm from KXS. 136 potential molecular targets (AKT1, TNF, IL-1b, JUN, ESR1, NOS3, etc.) were predicted, of which there were 69 targets clearly related to depression. By compound-depression targets (C-DTs) network constructed, and protein-protein interaction networks (PPI) and KEGG pathway enrichment analyzed, we identified active compounds mediating depression-related targets to exert synergism on the predictive AKT1/Nrf2 pathway related to thioredoxin (Trx) antioxidant mechanism and other inflammation-related signaling pathways as well as neurotransmitter related signaling pathways. In the H2O2 induced SH-SY5Y cell damage model, this showed kaempferol and ginsenoside rh2 could enhance the activity of the Trx system by upregulation of AKT1 to activate Nrf2 in vitro. Conclusions. Taken together, by comprehensive systems pharmacology approach analysis, we found that KXS and its active compounds might exhibit antioxidant effects by stimulating the AKT1/Nrf2 pathway in the treatment of depression, which might shed new light on innovative therapeutic tactics for the new aspects for depression in traditional Chinese medicine in future studies.