Hesperetin and Naringenin promote GLP-1 secretion via TGR5 activation, alleviating type 2 diabetes in HFD mice.

Effective therapeutic strategies for type 2 diabetes often target the incretin system, particularly glucagon-like peptide-1 (GLP-1). GLP-1 is a potent insulin secretagogue that also suppresses glucagon, delays gastric emptying, and promotes satiety. While GLP-1 receptor agonists are established treatments, identifying novel GLP-1 secretagogues, especially from natural sources, remains a key research area. The Takeda G protein-coupled receptor 5 (TGR5), a bile acid receptor expressed on enteroendocrine L-cells, is known to stimulate GLP-1 release, presenting a promising target for new antidiabetic compounds.

Researchers screened a traditional Chinese medicine library using a GLUTag cell line (murine L-cells) engineered to report proglucagon activity via luciferase. Selected compounds were then tested for GLP-1 secretion in both GLUTag cells and primary mouse ileac epithelial cells. The underlying mechanisms were investigated by measuring intracellular cAMP levels and calcium flux, and TGR5 activation was confirmed using a dual-luciferase reporter assay. Compound binding to TGR5 was assessed via CETSA. In vivo efficacy was evaluated in high-fat-diet-induced diabetic mice through oral administration of Hesperetin or Naringenin.

Hesperetin and Naringenin significantly promoted GLP-1 secretion from L-cells in both GLUTag and primary mouse ileac cells. Mechanistically, both compounds increased cAMP accumulation and intracellular calcium influx in L-cells. These effects were largely absent in TGR5-deficient L-cells, strongly implicating TGR5 in their action. Dual-luciferase reporter assays further confirmed Hesperetin and Naringenin as direct TGR5 activators. CETSA provided evidence that each flavonoid forms a stable complex with TGR5. In the in vivo model, oral administration of either compound enhanced glucose-stimulated serum GLP-1 levels.

Furthermore, Hesperetin and Naringenin ameliorated both obesity and hyperglycemia under obese diabetic conditions in high-fat-diet-induced diabetic mice.