Polysaccharide PSLP-1 from Polygonatum sibiricum Stems and Leaves Alleviates Depressive-like Behaviors and Modulates Gut Microbiota and Tryptophan Metabolism along the Gut-Brain Axis.

The stems and leaves of Polygonatum sibiricum Red. are underused food byproducts whose polysaccharides and bioactivities remain poorly characterized. In this study, a novel homogeneous polysaccharide, PSLP-1 (4.287 kDa), was isolated and identified as a fructan-rich fraction with a →1)-β-d-Fruf-(2→ backbone and C6 side-chain substitution. In a chronic restraint stress mouse model, PSLP-1 showed clear antidepressant-like activity by reducing immobility time in both the forced swim and tail suspension tests. PSLP-1 was also associated with restoration of tryptophan metabolism, characterized by suppression of the indoleamine 2,3-dioxygenase 1-mediated kynurenine pathway and promotion of tryptophan hydroxylase-related 5-hydroxytryptamine synthesis. These effects were accompanied by gut microbiota remodeling, including increased Akkermansia and decreased Lactobacillus and Alistipes. These findings support P. sibiricum stems and leaves as a promising source of bioactive polysaccharides.