<em>Lacticaseibacillus paracasei</em> LPB27 Ameliorates Depressive-like Behaviors in CUMS Rats by Inhibiting IDO-1 and Regulating Tryptophan Metabolism

It remains unclear whether probiotics could alleviate depression by regulating the tryptophan (Trp) metabolism and secretion of its metabolites <em>via</em> affecting indoleamine 2,3-dioxygenase (IDO-1). Therefore, this study was conducted to explore the underlying mechanism of <em>Lacticaseibacillus paracasei</em> LPB27 in resisting depression. Our results demonstrated that LPB27 intervention improved the depressive-like behavior in rats with depression and reversed the altered microbiota and decreased inflammatory factors. LPB27 intervention down-regulated the expression of HMGB1, RAGE and IDO-1 and regulated Trp metabolism of depression rats, manifested as an elevated concentration of 5-HT and 5-hydroxy-L-tryptophan (5-HTP) and a decreased level of L-kynurenine, kynurenate, picolinic acid and cinnavalininate. Moreover, LPB27 also significantly increased the level of dopamine (DA), norepinephrine (NE), glutamate (GLU), and gamma-aminobutyric acid (GABA). These results corroborated that LPB27 intervention could restore the disrupted homeostasis of certain gut microbiota, decrease the level of inflammation, HMGB1, RAGE and IDO-1, and regulate Trp metabolism, which collectively contributed to the improvement of depressive-like behavior.