Novel luciferase‐based glucagon‐like peptide 1 reporter assay reveals naturally occurring secretagogues

Background and PurposeGlucagon‐like peptide 1 (GLP‐1) is a hormone derived from preproglucagon. It is secreted by enteroendocrine cells in response to feeding and, in turn, acts as a critical regulator of insulin release. Modulating GLP‐1 secretion holds promise as a strategy for controlling blood glucose levels.Experimental ApproachTo dissect GLP‐1 regulation and discover specific secretagogues, we engineered a reporter cell line introducing a luciferase within the proglucagon sequence in GLUTag cells. The assay was validated using western blotting and ELISA. A focused natural compounds library was screened. We measured luminescence, glucose uptake and ATP to investigate the mechanism by which newly found secretagogues potentiate GLP‐1 secretion.Key ResultsThe newly created reporter cell line is ideal for the rapid, sensitive and quantitative assessment of GLP‐1 secretion. The small molecule screen identified non‐toxic GLP‐1 modulators. Quercetin is the most potent newly found GLP‐1 secretagogue, while other flavonoids also potentiate GLP‐1 secretion. Quercetin requires glucose and extracellular calcium to act as GLP‐1 secretagogue. Our results support a mechanism whereby flavonoids cause GLUTag cells to utilize glucose more efficiently, leading to elevated ATP levels, followed by KATP channel blockade and GLP‐1 exocytosis.Conclusion and ImplicationsOur methodology enabled finding of new GLP‐1 secretagogues. Quercetin is a potent, naturally occurring GLP‐1 secretagogue. Mechanistic studies of newly found secretagogues are possible in newly created reporter cell line. Further validation in more physiological systems, such as primary L‐cells or whole organisms, is needed. GLP‐1 secretagogues might serve as leads for developing alternative glucose‐lowering therapies.