Myricetin Amplifies Glucose-Stimulated Insulin Secretion via the cAMP-PKA-Epac-2 Signaling Cascade

Aim: Myricetin, a natural bioflavonoid, is reported as an anti-diabetic agent since it possesses the ability to inhibit α-glucosidase activity, stimulate insulin action and secretion, manage ROS, and prevent diabetes complications. Myricetin was identified as a new insulin secretagogue that enhances glucose-stimulated insulin secretion and seems like a better antidiabetic drug candidate. Here, we explored the insulinotropic mechanism(s) of myricetin in vitro in mice islets and in silico. Methods: Size-matched pancreatic islets were divided into groups and incubated in the presence or absence of myricetin and agonists/antagonists of major insulin signaling pathways. The secreted insulin was measured by ELISA. Molecular docking studies were performed with the key player of insulin secretory pathways. Results: Myricetin dose-dependently enhanced insulin secretion in isolated mice islets, and its insulinotropic effect was exerted at high glucose concentrations distinctly different from glibenclamide. Myricetin-induced insulin secretion was significantly inhibited using the diazoxide. Furthermore, myricetin amplified glucose-induced insulin secretion in depolarized and glibenclamide-treated islets. Myricetin showed an additive effect with forskolin- and IBMX-induced insulin secretion. Interestingly, H89, a PKA inhibitor, and MAY0132, an Epac-2 inhibitor, significantly inhibited myricetin-induced insulin secretion. The in silico molecular docking studies further validated these in vitro findings in isolated pancreatic islets. Conclusions: Myricetin, a potential natural insulin secretagogue, amplifies glucose-induced insulin secretion via the cAMP-PKA-Epac-2 signaling pathway.