Abstract
The glucagon-like peptide 1 receptor (GLP-1R) is a promising target for the treatment of type II diabetes mellitus because of 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 signaling. 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 signaling (cAMP formation and intracellular Ca2+ mobilization) 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 hydroxyl flavonols with the ability to selectively augment calcium (Ca2+) signaling 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 (i.e., a flavonol) was essential for this activity, however insufficient on its own, to produce the allosteric effects. In contrast to hydroxyl flavonols, catechin had no effect on peptide-mediated Ca2+ signaling 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.
Footnotes
This work was funded in part by the National Health and Medical Research Council of Australia (NHMRC) [Program Grant 519461] (to P.M.S., A.C., and R.J.S.); a Principal Research Fellowship of the NHMRC (to P.M.S.); and a Senior Research Fellowship of the NHMRC (to A.C.).
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.176362.
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ABBREVIATIONS:
- GLP-1
- glucagon-like peptide-1
- GPCR
- G protein-coupled receptor
- GLP-1R
- glucagon-like peptide-1 receptor
- ERK
- extracellular signal-regulated kinase
- DMEM
- Dulbecco's modified Eagle's medium
- BSA
- bovine serum albumin
- SAR
- structure-activity relationship.
- Received October 18, 2010.
- Accepted November 10, 2010.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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