Trigonella foenum-graecum L. Extract Activates a Gβγ/PLC-Dependent Pathway to Promote GLP-1 Secretion and Improve Glucose Metabolism in T2DM

Objective: Trigonella foenum-graecum L. (fenugreek) is a characteristic bitter herb traditionally prepared as decoctions to treat diabetes. This study aimed to elucidate whether the traditional “bitter” property of fenugreek aqueous extract (FGE) exerts anti-diabetic effects by targeting the intestinal bitter taste receptor Tas2r138 (the murine functional ortholog of human TAS2R38) and modulating the GLP-1-mediated entero-pancreatic axis. Methods: Dried fenugreek seeds were extracted with distilled water and lyophilized. Following standardization via absolute quantitative HPLC, FGE was orally administered to type 2 diabetic (T2DM) mice at doses of 0.26 and 0.52 g/kg/day for four weeks. The underlying mechanisms were investigated using UPLC-MS/MS, network pharmacology, molecular dynamics (MD) simulations, and in vitro assays in STC-1 enteroendocrine cells. Results: FGE significantly reduced blood glucose levels and ameliorated hyperphagia, insulin resistance, and dyslipidemia in the T2DM model, exhibiting efficacy comparable to the positive control, metformin. Notably, FGE markedly elevated systemic total GLP-1 levels and restored pancreatic islet architecture. Mechanistically, FGE upregulated intestinal Tas2r138 expression and activated the PLCβ2/TRPM5 signaling pathway. HPLC quantification identified trigonelline (15.1 mg/g extract) as the primary bitter constituent, displaying favorable predicted docking interactions with the human TAS2R38 receptor. In STC-1 cells, trigonelline directly stimulated intracellular Ca2+ flux and GLP-1 secretion, effects that were significantly attenuated by Gβγ and PLC inhibitors, suggesting the involvement of a Gq-coupled GPCR signaling pathway. Conclusions: These findings provide a scientific rationale for the traditional use of fenugreek in metabolic disorders, demonstrating that FGE restores glucose and lipid homeostasis via a trigonelline-driven, Gβγ/PLC-dependent pathway, which is consistent with the modulation of the intestinal Tas2r138-GLP-1-pancreatic insulin axis.