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. 2012;7(10):e46300.
doi: 10.1371/journal.pone.0046300. Epub 2012 Oct 9.

A Potent Class of GPR40 Full Agonists Engages the Enteroinsular Axis to Promote Glucose Control in Rodents

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Free PMC article

A Potent Class of GPR40 Full Agonists Engages the Enteroinsular Axis to Promote Glucose Control in Rodents

Jian Luo et al. PLoS One. .
Free PMC article

Abstract

Type 2 diabetes is characterized by impaired glucose homeostasis due to defects in insulin secretion, insulin resistance and the incretin response. GPR40 (FFAR1 or FFA1) is a G-protein-coupled receptor (GPCR), primarily expressed in insulin-producing pancreatic β-cells and incretin-producing enteroendocrine cells of the small intestine. Several GPR40 agonists, including AMG 837 and TAK-875, have been disclosed, but no GPR40 synthetic agonists have been reported that engage both the insulinogenic and incretinogenic axes. In this report we provide a molecular explanation and describe the discovery of a unique and potent class of GPR40 full agonists that engages the enteroinsular axis to promote dramatic improvement in glucose control in rodents. GPR40 full agonists AM-1638 and AM-6226 stimulate GLP-1 and GIP secretion from intestinal enteroendocrine cells and increase GSIS from pancreatic islets, leading to enhanced glucose control in the high fat fed, streptozotocin treated and NONcNZO10/LtJ mouse models of type 2 diabetes. The improvement in hyperglycemia by AM-1638 was reduced in the presence of the GLP-1 receptor antagonist Ex(9-39)NH(2).

Conflict of interest statement

Competing Interests: All authors were employed by and shareholders in Amgen during the study period. Patents filed or issued: U.S. Patent No. 7,649,110, U.S. Patent No. 7,816,367, U.S. Patent No. 8,030,354 and WO 2005/086661. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials.

Figures

Figure 1
Figure 1. In vitro characterization of AM-1638 and AM-6226 and comparison to AMG 837.
(A) Aequorin Ca2+ assay comparing AMG 837 to natural fatty acid ligands DHA, α-LNN and arachidonic acid. (B) Chemical structures of the key compounds synthesized during the medicinal chemistry effort that led to the discovery of AM-1638 and AM-6226. (C) Aequorin Ca2+ flux with key synthetic agonists and fatty acids. (D) Inositol phosphate assay with key synthetic agonists and fatty acids. (E–G) Plasmid titration experiments to examine agonist activity under conditions with reduced receptor levels, where either 5000 ng (E), 500 ng (F) or 50 ng (G) of GPR40 (FFAR1) expression plasmid was co-transfected with aequorin expression plasmids into CHO cells. (H) Competition binding experiment with 3H-AMG 837. (I) Competition binding experiment with 3H-AM-1638.
Figure 2
Figure 2. Activity of AM-1638 and AM-6226 in primary cells.
(A) GSIS assay in mouse islets incubated with a dose response of compounds in the presence of 16.7 mM glucose. (B) Mouse islet perifusion assay. The glucose concentration was raised from 3 mM to 16.7 mM at t = 20 minutes and returned to 3 mM glucose at t = 30 minutes. 10 µM compound was perifused through the entire experiment. (C) GSIS assay with islets from wild type or GPR40 knock-out mice. (D) Inositol phosphate assay with dispersed human islet cells. (E) GSIS assay with human islets incubated with GPR40 agonists and 12.5 mM glucose. (F) GLP-1 secretion assay with fetal rat intestinal cells. (G) GIP-1 secretion assay with fetal rat intestinal cells. (H) Inositol phosphate accumulation assay using the mouse GLUTag enteroendocrine L-cell line. Statistical significance is denoted by *(p<0.05), **(p<0.01), ***(p<0.001) and ****(p<0.0001), as determined by one-way or two-way ANOVA, and are color-coded to treatment in the figure legends. For (A), (B), (F), (G), and (H) statistical comparisons were made to AMG 837 treatment. For (C) and (E) statistical comparisons were made to vehicle treatment.
Figure 3
Figure 3. Enhanced in vivo efficacy of AM-1638 compared to AMG 837 in HF/STZ type 2 diabetic mice.
Drug treatment was administered 1-hour prior to an oral glucose bolus. (A) Glucose levels during an OGTT in high-fat fed, streptozotocin treated type 2 diabetic mice. (B) Glucose AUC values. (C) Change in plasma insulin levels from baseline during an OGTT (D) Insulin AUC (E) Unbound (free) plasma drug concentration in plasma 1-hour following drug dose, as determined by MS. Statistical significance compared to vehicle treatment is denoted by *(p<0.05), **(p<0.01), ***(p<0.001) and ****(p<0.0001), as determined by one-way or two-way ANOVA, and are color-coded to the treatment in the figure legends.
Figure 4
Figure 4. Engagement of the enteroendocrine axis in HF/STZ type 2 diabetic mice by AM-1638.
Following administration of a single dose of the indicated treatments at t = 0 minutes in HF/STZ mice, measurements of (A) GLP-1 (B) insulin (C) glucose and (D) GIP were taken at various timepoints. Statistical significance compared to vehicle treatment is denoted by *(p<0.05), **(p<0.01), ***(p<0.001) and ****(p<0.0001), as determined by one-way or two-way ANOVA, and are color-coded to the treatment in the figure legends.
Figure 5
Figure 5. During an OGTT in NONcNZO10/LtJ type 2 diabetic mice, AM-1638 lowers blood glucose levels through an increase in insulin and incretin secretion.
Vehicle (purple, n = 8) or 60 mg/kg AM-1638 (green, n = 8) was administered 1-hour prior to an oral glucose bolus. (A) Glucose levels at various timepoints. (B) Glucose AUC values. (C) Plasma insulin levels (D) GLP-1 levels and (E) GIP levels at baseline (-60 minutes) and 15 minutes after glucose challenge. Statistical significance compared to vehicle treatment is denoted by *(p<0.05), **(p<0.01), ***(p<0.001) and ****(p<0.0001), as determined by two-way ANOVA or student’s t-test.
Figure 6
Figure 6. Specificity of AM-1638 to GPR40 (FFAR1) in vivo and effect of the GLP-1R antagonist GLP-1(9–39)NH2.
An OGTT was performed in (A) wild type or (B) GPR40 null mice following a single oral dose of AM-1638 or sitagliptin. Glucose was dosed 1-hr post drug treatment. (C) Glucose AUC during OGTT. (D) GLP-1 secretion following a single oral dose of AM-1638 in wild type or GPR40 null mice. AM-1638 (60 mg/kg) was tested in an IPGTT in the presence or absence of the GLP-1R antagonist GLP-1(9–39)NH2 (300 µg/kg) as described in the Materials and Methods section. (E) Plasma glucose levels (F) Glucose AUC and (G) plasma insulin levels at the indicated timepoints during the experiment. Statistical significance compared to vehicle treatment is denoted by *(p<0.05), **(p<0.01), ***(p<0.001) and ****(p<0.0001), as determined by one-way or two-way ANOVA, and are color-coded to the treatment in the figure legends.
Figure 7
Figure 7. Model depicting the dual mechanism-of-action of GPR40 (FFAR1) full agonists to lower blood glucose levels.
GPR40 full agonists engage both the enteroendocrine axis as well as the pancreatic β-cell axis. These pathways both lead to augmentation of glucose stimulated insulin secretion on the pancreatic β-cell. Additionally, GLP-1 has multiple physiological and pharmacological roles, such as inhibition of glucagon secretion, that could further benefit type 2 diabetics. GPR40 partial agonists such as AMG 837 engage only the pancreatic pancreatic β-cell axis in vivo.

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Grant support

This study was supported by Amgen Inc., which played a role in study design, data collection and analysis, decision to publish, and preparation of the manuscript.
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