Mulberry leaf flavonoids alleviate type 2 diabetes by remodeling the gut microbiota-bile acid axis and activating FXR...

Mulberry leaf (Morus alba L.) has long been used in traditional Chinese medicine for treating "Xiaoke" (diabetes), as documented in "Compendium of Materia Medica" compiled by Li Shi-Zhen of the Ming Dynasty. Mulberry leaf flavonoids (MLF) are the major active components and have demonstrated anti-diabetic effects in modern studies. However, whether MLF alleviates type 2 diabetes mellitus (T2DM) by modulating the gut microbiota-bile acid axis and directly activating key metabolic receptors such as FXR remains unclear.

This study aimed to investigate whether MLF ameliorates T2DM through remodeling the gut microbiota-bile acid axis and activating FXR signaling, and to identify potential flavonoid constituents within MLF that directly interact with FXR.

db/db mice were treated with low- or high-dose MLF (300 or 600 mg/kg/day) or metformin for 10 weeks. Blood glucose, insulin sensitivity, lipid profiles, and hepatic pathology were assessed. Gut microbiota composition was analyzed by 16S rRNA sequencing, and bile acid profiles in serum, liver, ileum, and feces were quantified by targeted metabolomics. The expression of FXR/TGR5 signaling pathway components was determined by qRT-PCR and Western blot. Molecular docking was performed to screen for potential FXR modulator among MLF constituents, followed by in vitro validation using HepG2 and Caco-2 cells.

MLF treatment significantly reduced fasting blood glucose, improved glucose tolerance and insulin resistance, lowered serum and hepatic lipid levels, and alleviated hepatic steatosis in db/db mice. MLF reshaped the gut microbiota by increasing beneficial genera (e.g., Alloprevotella, Roseburia) and decreasing the Firmicutes/Bacteroidetes ratio. Concurrently, MLF reprogrammed bile acid profiles across multiple organs, elevating non-12-OH bile acids (e.g., CDCA) and reducing the FXR antagonist Tβ-MCA, thereby activating intestinal and hepatic FXR/TGR5 signaling, upregulating FGF15 and SHP, and increasing serum GLP-1. Molecular docking identified Morusin as a candidate FXR ligand, and in vitro assays confirmed that both MLF and Morusin activated FXR and modulated downstream targets (BSEP, NTCP, ASBT, CYP7A1) in hepatocytes and intestinal cells.

MLF alleviates T2DM by remodeling the gut microbiota-bile acid axis and activating FXR/TGR5 signaling. Morusin, a flavonoid constituent of MLF, is a potential FXR-modulating compound. These findings provide a modern mechanistic rationale for the traditional use of mulberry leaf in treating diabetes and support the development of MLF as a gut-targeted therapeutic strategy for T2DM.