on Free Fatty Acid Receptor 1 and Glucokinase Evaluated with a Dual Culture System with Epithelial, Pancreatic, and Liver Cells

The aim was to characterize a phenolic-rich water extract from the pericarp of an improved genotype of Apache red maize (RPE) and evaluate its ability to activate the type 2 diabetes markers free fatty acid receptor 1 (GPR40) and glucokinase (GK) in vitro. The extract contained mainly phenolic acids, anthocyanins, and other flavonoids. RPE inhibited α-amylase (IC₅₀ = 88.3 μg/mL), α-glucosidase (IC₅₀ = 169.3 μg/mL), and reduced glucose transport in a Caco-2 cell monolayer (up to 25%). Furthermore, RPE activated GPR40 (EC₅₀ = 77.7 μg/mL) in pancreatic INS-1E cells and GK (EC₅₀ = 43.4 μg/mL) in liver HepG2 cells, potentially through allosteric modulation. RPE activated GPR40-related insulin secretory pathway and activated the glucose metabolism regulator AMPK (up to 78%). Our results support the hypothesis that foods with a high concentration of anthocyanins and phenolic acids, such as in the selected variety of maize used, could ameliorate obesity and type 2 diabetes comorbidities.

Molecular dynamics-guided discovery of an ago-allosteric modulator for GPR40/FFAR1

Structures of G protein-coupled receptors (GPCRs) in complex with ligands mainly provide frozen pictures with little information about the actual molecular mechanism of action of the ligand in the normally highly dynamic receptor. Through computer-based molecular dynamics simulations of a receptor for long-chain fatty acids, free fatty acid receptor 1 (FFAR1), we discover that an unoccupied, solvent-exposed pocket closes on removal of the lipid-like agonist; that is, during a major conformational change of the receptor. Importantly, a compound designed to prevent closure of this previously unrecognized, dynamic pocket was identified through structure-based virtual screening and shown to function as an allosteric agonist for the receptor. The study demonstrates that molecular dynamics simulations can be used in drug discovery to identify different modes of stabilizing specific receptor states.

The long-chain fatty acid receptor FFAR1/GPR40 binds agonists in both an interhelical site between the extracellular segments of transmembrane helix (TM)-III and TM-IV and a lipid-exposed groove between the intracellular segments of these helices. Molecular dynamics simulations of FFAR1 with agonist removed demonstrated a major rearrangement of the polar and charged anchor point residues for the carboxylic acid moiety of the agonist in the interhelical site, which was associated with closure of a neighboring, solvent-exposed pocket between the extracellular poles of TM-I, TM-II, and TM-VII. A synthetic compound designed to bind in this pocket, and thereby prevent its closure, was identified through structure-based virtual screening and shown to function both as an agonist and as an allosteric modulator of receptor activation. This discovery of an allosteric agonist for a previously unexploited, dynamic pocket in FFAR1 demonstrates both the power of including molecular dynamics in the drug discovery process and that this specific, clinically proven, but difficult, antidiabetes target can be addressed by chemotypes different from existing ligands.

The Deletion of GPR40/FFAR1 Signaling Damages Maternal Care and Emotional Function in Female Mice

The free fatty acid receptor 1 (GPR40/FFAR1) is activated by polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acids (DHA). This receptor has been the focus of many studies regarding physiological functions of the central nervous system. PUFAs are essential for neuronal development and maintenance of neuronal function; thus, the decrease of PUFAs in the brain is closely related to the induction of psychiatric diseases associated with emotional disorder, such as anxiety, depression, and schizophrenia. However, details of the mechanisms remain unclear. In this study, we investigated changes of maternal and/or emotional behavior caused by a deficiency of GPR40/FFAR1 signaling. GPR40/FFAR1 deficient (FFAR1^-/-) female mice exhibited impaired maternal care such as retrieving behaviors and an increased rate of neglect and infanticide when compared to wild type (WT) female mice. Furthermore, FFAR1^-/- female mice showed increased time spent in the open arms in an elevated plus maze test, reduction of locomotor activity and social interaction behavior, and decreased sucrose intake, when compared to WT female mice. In conclusion, these findings suggest that PUFAs-GPR40/FFAR1 signaling might function, at least in part, as a regulatory factor of emotional and maternal behavior in mice.

The P21-activated kinase PAK4 is implicated in fatty-acid potentiation of insulin secretion downstream of free fatty acid receptor 1

Free fatty acid receptor 1 (FFA1/GPR40) plays a key role in the potentiation of glucose-stimulated insulin secretion by fatty acids in pancreatic β cells. We previously demonstrated that GPR40 signaling leads to cortical actin remodeling and potentiates the second phase of insulin secretion. In this study, we examined the role of p21 activated kinase 4 (PAK4), a known regulator of cytoskeletal dynamics, in GPR40-dependent potentiation of insulin secretion. The fatty acid oleate induced PAK4 phosphorylation in human islets, in isolated mouse islets and in the insulin secreting cell line INS832/13. However, oleate-induced PAK4 phosphorylation was not observed in GPR40-null mouse islets. siRNA-mediated knockdown of PAK4 in INS832/13 cells abrogated the potentiation of insulin secretion by oleate, whereas PAK7 knockdown had no effect. Our results indicate that PAK4 plays an important role in the potentiation of insulin secretion by fatty acids downstream of GPR40.

Novel FFA1 (GPR40) agonists containing spirocyclic periphery: polar azine periphery as a driver of potency

A series of nine compounds based on 3-[4-(benzyloxy)phenyl]propanoic acid core containing a 1-oxa-9-azaspiro[5.5]undecane periphery was designed, synthesized and evaluated as free fatty acid 1 (FFA1 or GPR40) agonists. The spirocyclic appendages included in these compounds were inspired by LY2881835, Eli Lilly’s advanced drug candidate for type II diabetes mellitus that was in phase I clinical trials. These polar spirocyclic, fully saturated appendages (that are themselves uncharacteristic of the known FFA1 ligand space) were further decorated with diverse polar groups (such as basic heterocycles or secondary amides). To our surprise, while seven of nine compounds were found to be inactive (likely due to the decrease in lipophilicity, which is known to be detrimental to FFA1 ligand affinity), two compounds containing 2-pyridyloxy and 2-pyrimidinyloxy groups were found to have EC₅₀ of 1.621 and 0.904 µM, respectively. This result is significant in the context of the worldwide quest for more polar FFA1 agonists, which would be devoid of liver toxicity effects earlier observed for a FFA1 agonist fasiglifam (TAk-875) in clinical studies.

Activation of free fatty acid receptor 1 improves hepatic steatosis through a p38-dependent pathway

Hepatic steatosis is highly correlated with insulin resistance and diabetes. Although, it has been demonstrated that activation of free fatty acid receptor 1 (FFAR1) by agonists showed benefits for the improvement of diabetes, the effects of FFAR1 agonists on hepatic steatosis were unknown. In this study, a high fat diet (HFD)-induced hepatic steatosis animal model was utilized to evaluate the effects of an FFAR1 agonist, GW9508, on hepatic lipid accumulation, and HepG2 hepatoma cells were also used to clarify the possible mechanisms. Administration of GW9508 significantly decreased the hepatic lipid accumulation with decreased expressions of lipogenesis-related proteins in HFD mice. Knockdown of hepatic Ffar1 by lentiviral vectors containing short hairpin RNA targeted to Ffar1 diminished the effect of GW9508 in HFD mice. In addition, GW9508 decreased oleic acid-induced lipid accumulation in HepG2 cells by decreases in the expression of lipogenesis-related proteins. Moreover, GW9508 downregulated the expression of sterol regulatory element-binding protein 1 (SREBP1) through a p38-dependent pathway, whereas knockdown of Ffar1 in HepG2 cells diminished the effect of GW9508 on the decrease in SREBP1. Considering all these results together, GW9508 exerts a therapeutic effect to improve hepatic steatosis through a p38-dependent pathway. Thus, investigation of chemicals that act on FFAR1 might be a new strategy for the treatment of hepatic steatosis.