Parthenolide promotes glucagon-like peptide-1 secreting in human Caco-2 cells via regulation of bitter taste receptor-induced of calcium signaling.

Bitter taste receptors (TAS2Rs), in addition to being expressed in oral tissues, are also present in the gastrointestinal tract and are promising targets for inducing glucagon-like peptide-1 (GLP-1) secretion and treating type 2 diabetes mellitus (T2DM). However, natural bitter agonists capable of enhancing endogenous GLP-1 secretion remain scarce. In this study, we aimed to identify natural bitter agonists with GLP-1-inducing potential through comprehensive screening of the BitterDB and BitterX databases, and to evaluate their effects and underlying mechanisms in human enteroendocrine Caco-2 cells. Parthenolide (PTL) was identified as a high-affinity TAS2R4 agonist candidate. Cellular thermal shift assays (CETSA) confirmed its direct binding to TAS2R4, enhancing its thermal stability. Molecular docking revealed strong interactions, including hydrogen bonding with ASN-65 and hydrophobic contacts with PHE-62 and PHE-88. Functionally, PTL promotes GLP-1 secretion in a dose-dependent manner. Mechanistically, PTL treatment enhances TAS2R4 expression and upregulates its key downstream signaling molecule, phospholipase C β2 (PLCβ2), which catalyzes the production of inositol trisphosphate (IP3). This indicates that PTL promotes secretion by activating the TAS2R4 signaling pathway. PTL treatment leads to increase in intracellular calcium ion (Ca2+) levels, and the induced GLP-1 secretion is a calcium-dependent vesicle fusion process. Moreover, calcium further activates the transient receptor potential channel melastatin 5 (TRPM5), amplifying calcium signaling. These findings suggest that PTL is a novel natural agonist of TAS2R4 that promotes GLP-1 secretion via TAS2R4 signaling, supporting its potential as a lead compound for the development of TAS2R4-targeted functional foods or nutraceuticals for T2DM.