Petasites japonicus Leaves Alleviate Depression in Dextran Sulfate Sodium-Induced Colitis Mice Through the BDNF/TrkB Pathway and Modulation of Inflammation

Inflammatory bowel disease (IBD) is a chronic gastrointestinal disorder with a high incidence of anxiety and depression. However, the underlying mechanisms of these symptoms remain to be fully elucidated. This study investigated the effects and mechanisms of a 20% ethanolic extract of Petasites japonicus leaves (EPJ) on dextran sulfate sodium (DSS)-induced colitis and depression-like behaviors. The physiological compounds identified in the EPJ were citric acid, chlorogenic acid, caffeic acid, fukinolic acid, 3,5-dicaffeoylquinic acid, quercetin 3-O-β-D-glucose-6″-acetate, 4,5-dicaffeoylquinic acid, kaempferol-3-O-(6″-acetyl)-β-glucopyranoside, and pedunculoside. EPJ significantly alleviated DSS-induced colitis, as evidenced by improvements in body weight loss (87.41% vs. 76.02% in the DSS group), colon length (5.75 vs. 4.34 cm), intestinal permeability (52.80 vs. 163.01 μg/mL), and myeloperoxidase (MPO) activity (0.24 vs. 0.67 U/mg) (p < 0.05). Histological analysis further confirmed recovery of goblet cells and attenuation of muscle layer thickening. EPJ also reversed DSS-induced gut microbiota dysbiosis and contributed to the restoration of microbial homeostasis. Behavioral assessments showed that EPJ effectively ameliorated depression-like behaviors. EPJ improved antioxidant systems in colon and brain tissues by modulating malondialdehyde (MDA) levels and reduced glutathione (GSH) and superoxide dismutase (SOD) activity. EPJ further upregulated tight junction protein expression and suppressed TLR4/NF-κB inflammatory pathway activation in both colon and brain tissues. Moreover, EPJ modulated serum stress-related hormones, normalized hypothalamic–pituitary–adrenal (HPA) axis dysregulation, regulated the BDNF/TrkB signaling pathway, and modulated tryptophan–kynurenine metabolism. Collectively, these findings suggest that EPJ exerts protective effects against DSS-induced colitis and depression-like behaviors.