Honokiol attenuates diabetes by enriching Akkermansia muciniphila andregulating tryptophan metabolism in mice

Diabetes mellitus (DM) is a chronic disease influenced by gut microbiome disturbances. Honokiol (HON), a low oral bioavailability compound from Magnolia officinalis bark, has demonstrated potential as a treatment for DM. This research investigates the effects of HON on gut microbiota and host metabolism to elucidate its mechanism of action in DM. After 8 weeks of intervention through fecal microbiota transplantation (FMT) or antibiotic treatment, HON improved glucose tolerance and lipid metabolism in a gut microbiota-dependent manner. Specifically, HON administration significantly increased Akkermansia muciniphila (AKK) abundance and modulated tryptophan (TRP) metabolism, as evidenced by 16S ribosomal ribonucleic acid (rRNA) gene sequencing and untargeted/targeted metabolomics analysis. Notably, research revealed that AKK metabolized TRP into tryptamine (TA) and other metabolites in vitro. Both AKK and TA activated the aryl hydrocarbon receptor (AHR) pathway, increasing circulating glucagon-like peptide-1 (GLP-1) levels and ameliorating diabetes-related symptoms in DM mice. These findings indicate that HON's hypoglycemic effect primarily stems from AHR-GLP-1 pathway activation through targeted modulation of AKK and microbial TRP metabolite TA, potentially enhancing HON's clinical applications.