Abstract
Activation of FFA1 (GPR40), a member of G protein-coupling receptor family A, is mediated by medium- and long-chain fatty acids and leads to amplification of glucose-stimulated insulin secretion, suggesting a potential role for free fatty acid 1 (FFA1) as a target for type 2 diabetes. It was assumed previously that there is a single binding site for fatty acids and synthetic FFA1 agonists. However, using members of two chemical series of partial and full agonists that have been identified, radioligand binding interaction studies revealed that the full agonists do not bind to the same site as the partial agonists but exhibit positive heterotropic cooperativity. Analysis of functional data reveals positive functional cooperativity between the full agonists and partial agonists in various functional assays (in vitro and ex vivo) and also in vivo. Furthermore, the endogenous fatty acid docosahexaenoic acid (DHA) shows negative or neutral cooperativity with members of both series of agonists in binding assays but displays positive cooperativity in functional assays. Another synthetic agonist is allosteric with members of both agonist series, but apparently competitive with DHA. Therefore, there appear to be three allosterically linked binding sites on FFA1 with agonists specific for each of these sites. Activation of free fatty acid 1 receptor (FFAR1) by each of these agonists is differentially affected by mutations of two arginine residues, previously found to be important for FFAR1 binding and activation. These ligands with their high potencies and strong positive functional cooperativity with endogenous fatty acids, demonstrated in vitro and in vivo, have the potential to deliver therapeutic benefits.
Footnotes
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
The work was supported in part by the Medical Research Council, United Kingdom [Grant U117532193].
N.J.M.B. has been a paid consultant for AMGEN Inc.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- FFA
- free fatty acid
- GPC
- G protein-coupled fatty acid receptor
- TAK-875
- [(3S)-6-({2′,6′-dimethyl-4′-[3-(methylsulfonyl)propoxy]biphenyl-3-yl}methoxy)-2,3-dihydro-1-benzofuran-3-yl]acetic acid hemi-hydrate
- AMG 837
- (S)-3(-4-((4′-(trifluoromethyl)-[1,1′-biphenyl]-3-yl) methoxy) phenyl)hex-4-ynoic acid
- DHA
- docosahexaenoic acid
- FFAR1
- free fatty acid receptor 1
- AM 1638
- (S)-3-cyclopropyl-3-(3-((2-(5,5-dimethylcyclopent-1-en-1-yl)-2′-fluoro-5′-methoxy-[1,1′-biphenyl]-4-ylmethoxy) phenyl)propanoic acid
- AM 8182
- (S,E)-3-(4-((2′-fluoro-5′-methoxy-[1,1′-biphenyl]-4-yl)methoxy)phenyl)hex-4-enoic acid)
- AM 6331
- (S)-3-(4-((4′-chloro-2′-ethoxy-[1,1′-biphenyl]-4-yl)methoxy phenyl)hex-4-ynoic acid
- HBSS
- Hanks' buffered salt solution
- ERK
- extracellular signal-regulated kinase
- BSA
- bovine serum albumin
- HSA
- human serum albumin
- CHO
- Chinese hamster ovary
- hFFA
- human FFA
- FACS
- fluorescence-activated cell sorting
- STZ
- streptozotocin
- IP
- inositol phosphate
- SAR
- structure-activity relationship
- GPCR
- G protein-coupled receptor
- LA
- α-linolenic acid
- HF/STZ
- high-fat STZ-treated
- ANOVA
- analysis of variance
- GW9508
- 4-[[(3-phenoxyphenyl)methyl]amino]benzenepropanoic acid.
- Received April 26, 2012.
- Accepted August 2, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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