The glucagon-like peptide 1 receptor (GLP-1R) is a promising target for the treatment of type II diabetes mellitus due to its role in metabolic homeostasis. In recent years, difficulties with peptide therapies have driven the search for small molecule compounds to modulate the activity of this receptor. We recently identified quercetin, a naturally occurring flavonoid, as a probe-dependent, pathway-selective allosteric modulator of GLP-1R-mediated signalling. Using Chinese-hamster ovary cells expressing the human GLP-1R we have now extended this work to identify the structural requirements of flavonoids to modify GLP-1R binding and signalling (cAMP formation and intracellular Ca2+ mobilisation) of each of the GLP-1R endogenous agonists, as well as the clinically used exogenous peptide mimetic exendin-4. This study identified a chemical series of hydroxyflavonols with the ability to selectively augment calcium (Ca2+) signalling in a peptide agonist-specific manner, with effects only on truncated GLP-1 peptides (GLP-1(7-36)NH2 and GLP-1(7-37)) and exendin-4, but not on oxyntomodulin or full length GLP-1 peptides (GLP-1(1-36)NH2 and GLP-1(1-37)). In addition, the 3-hydroxyl group on the flavone backbone, ie a flavonol, was essential for this activity, however insufficient on its own to produce the allosteric effects. In contrast to hydroxyflavonols, catechin had no effect on peptide-mediated Ca2+ signalling, but negatively modulated peptide-mediated cAMP formation in a probe-dependent manner. These data represent a detailed examination of the action of different flavonoids on peptide agonists at the GLP-1R and may aid in the development of future small molecule compounds targeted at this receptor.
- G protein-coupled receptor
- allosteric modulation
- cell signalling
- glucagon-like peptide-1
- Received October 18, 2010.
- Revision received November 9, 2010.
- Accepted November 10, 2010.
- The American Society for Pharmacology and Experimental Therapeutics