Phlorizin Alleviates Depression-like Behaviors via Gut Microbiota Reprogramming-Induced Methionine to Inhibit Neuroinflammation in Mice Hippocampus

Background: Depression is associated to gut microbiota imbalance. Our research examined the antidepressant potential of phlorizin (PHZ), a natural anti-inflammatory compound that influences gut microbiota, and explored its underlying mechanisms. Methods: A corticosterone (CORT)-induced depression mouse model was used for evaluating the ameliorative influences of PHZ on depressive phenotypes and central neuroinflammation through behavioral tests and biochemical assays. 16S rRNA sequencing and metabolomics were used to evaluate gut microbiota composition and metabolite levels in serum and hippocampal tissue, respectively. Spearman correlation and broad-spectrum antibiotic cocktail (ABx) treatment experiments verified the effect of gut microbes in the PHZ-mediated modulation of key metabolites. A lipopolysaccharide (LPS)-induced BV2 microglial inflammation model was established to evaluate the role of metabolites in PHZ’s antineuroinflammatory effects. Results: PHZ significantly alleviated depressive-like behaviors in CORT mice and suppressed hippocampal neuroinflammation by modulating microglial M1/M2 polarization. Furthermore, PHZ altered gut microbiota composition, influenced serum methionine (Met) metabolism, and significantly increased hippocampal L-methionine (L-Met) and S-adenosylmethionine (SAMe) levels. Cellular experiments confirmed that L-Met plays a critical role in PHZ-mediated antineuroinflammatory effects. Significant correlations were observed between Parabacteroides, Parasutterella, and Alistipes and serum Met levels. ABx treatment suppressed the increase in hippocampal L-Met levels, suggesting that PHZ regulates methionine metabolism via the microbiota. These findings indicate that PHZ alleviates depressive states in CORT mice by modulating the microbiota–gut–brain axis. Conclusions: PHZ modulates the gut microbiota (namely Parabacteroides, Parasutterella, and Alistipes) and increase L-Met and SAMe levels, thereby suppressing neuroinflammation and improving depressive phenotypes in mice.