Radix Bupleuri-Radix Paeoniae Alba herb pair (RB-RPA) is the fundamental medication combination of many classic antidepressant prescriptions, and RB-RPA's antidepressant effect is well established. For an extended period, the involvement of intestinal flora in the progression of depression has been widely acknowledged. However, it remains unclear whether RB-RPA could modulate intestinal microbiota disturbances and metabolic abnormalities induced by depression. The research explores the antidepressant mechanism of RB-RPA in chronic unpredictable mild stress (CUMS) rats in terms of intestinal flora and metabolites. We identified critical gut microbial species and metabolites associated with the antidepressant effects of RB-RPA using 16 S rRNA sequencing and Liquid Chromatography-Mass Spectrometry (LC-MS) metabolomics. And then, correlation analysis between critical microbiota and differential metabolites was conducted. The results demonstrate that RB-RPA significantly ameliorated depressive-like behavior in CUMS rats. RB-RPA improved intestinal flora disorders in depressed rats mainly by increasing the abundance of Lactobacillus (especially L. johnsonii), and ameliorated tryptophan synthesis and metabolism disorders in depressed rats and restored the levels of tryptophan and tryptophan microbial metabolites, such as indoleacrylic acid and 4-indoleacetaldehyde. Notably, correlation analysis showed that Lactobacillus had a significant positive correlation with tryptophan, indoleacrylic acid, and 4-indoleacetaldehyde. In conclusion, RB-RPA can improve the disorder of intestinal flora by increasing the abundance of Lactobacillus and improve the metabolic disorder of depressed rats by regulating tryptophan metabolism, thus exerting antidepressant effects.
