Discovery of a potent and selective GPR120 agonist

FFAR-mediated signaling drives migration of pancreatic cancer cells in hypoxic fibroblast co-cultures

The tumor microenvironment (TME) comprises cancer and non-cancerous stromal cells, including fibroblasts. Free fatty acids (FFAs) regulate various biological responses by binding to G protein-coupled FFA receptors (FFARs). In this study, we examined the impact of FFAR1 and FFAR4 on the cell migration of pancreatic cancer PANC-1 cells co-cultured with 3T3 fibroblast cells under hypoxic conditions. PANC-1 cells cultured at 1 % O2 exhibited elevated FFAR1 expression and decreased FFAR4 expression compared to those at 21 % O2. Cell migration of PANC-1 cells was reduced under 1 % O2 conditions. FFAR1 knockdown enhanced PANC-1 cell migration, whereas FFAR4 knockdown inhibited it. Co-culture of PANC-1 cells with 3T3 cells at 1 % O2 significantly increased FFAR4 expression, while FFAR1 expression remained unchanged. To evaluate the effects of FFAR1 and FFAR4 on PANC-1 cell migration in co-culture with 3T3 cells, we conducted a wound healing assay using the Culture-Insert 2 Well. PANC-1 and 3T3 cells were individually seeded into the two wells and incubated at both 21 % and 1 % O2 for 13 h. The cell migration of PANC-1 cells co-cultured with 3T3 cells at 1 % O2 was notably higher compared to 21 % O2. TUG-770 reduced and TUG-891 enhanced the cell migration of PANC-1 cells co-cultured with 3T3 cells under both 21 % and 1 % O2 conditions. These findings suggest that FFAR1 and FFAR4 play important roles in regulating the cell migration of PANC-1 cells co-cultured with 3T3 cells under hypoxic conditions.

Distinct binding hotspots for natural and synthetic agonists of FFA4 from in silico approaches

FFA4 has gained interest in recent years since its deorphanization in 2005 and the characterization of the Free Fatty Acids receptors family for their therapeutic potential in metabolic disorders. The expression of FFA4 (also known as GPR120) in numerous organs throughout the human body makes this receptor a highly potent target, particularly in fat sensing and diet preference. This offers an attractive approach to tackle obesity and related metabolic diseases. Recent cryo-EM structures of the receptor have provided valuable information for a potential active state although the previous studies of FFA4 presented diverging information. We performed molecular docking and molecular dynamics simulations of four agonist ligands, TUG-891, Linoleic acid, α-Linolenic acid, and Oleic acid, based on a homology model. Our simulations, which accumulated a total of 2 μs of simulation, highlighted two binding hotspots at Arg992.64 and Lys293 (ECL3). The results indicate that the residues are located in separate areas of the binding pocket and interact with various types of ligands, implying different potential active states of FFA4 and a highly adaptable binding intra-receptor pocket. This article proposes additional structural characteristics and mechanisms for agonist binding that complement the experimental structures.

Advancements in the management of obesity: a review of current evidence and emerging therapies

INTRODUCTION

Obesity is the modern world's current epidemic, with substantial health and economic impact. This study aimed to provide a narrative overview of the past, currently available, and future treatment options that offer therapeutic and preventive advantages for obesity management.

AREAS COVERED

Historically, rimonabant, and lorcaserin, were approved and used for managing non-syndromic obesity. Currently, orlistat, naltrexone/bupropion, glucagon-like peptide-1 receptor agonist (GLP-1 RA), and a few promising therapeutic agents are under investigation, including retatrutide, cagrilintide and orforglipron, which show promising weight reduction effects. We have developed a search string of the Medical Subject Headings (MeSH), including the terms GLP-1 RAs, obesity, and weight loss. This string was then used to perform a systematic literature search in the database including PubMed, EMBASE, MEDLINE, and Scopus up to January 31st, 2024.

EXPERT OPINION

Managing obesity often requires medical interventions, particularly in cases of severe obesity or obesity-related comorbidities. Thus, it is important to approach obesity management holistically, considering individual needs and circumstances. In our opinion, consulting with healthcare professionals is crucial to developing a personalized plan that addresses both weight loss and overall health improvement.

Structure-Activity Relationship Studies and Optimization of 4-Hydroxypyridones as GPR84 Agonists

GPR84 is a putative medium-chain fatty acid receptor that is implicated in regulation of inflammation and fibrogenesis. Studies have indicated that GPR84 agonists may have therapeutic potential in diseases such as Alzheimer's disease, atherosclerosis, and cancer, but there is a lack of quality tool compounds to explore this potential. The fatty acid analogue LY237 (4a) is the most potent GPR84 agonist disclosed to date but has unfavorable physicochemical properties. We here present a SAR study of 4a. Several highly potent agonists were identified with EC50 down to 28 pM, and with SAR generally in excellent agreement with structure-based modeling. Proper incorporation of rings and polar groups resulted in the identification of TUG-2099 (4s) and TUG-2208 (42a), both highly potent GPR84 agonists with lowered lipophilicity and good to excellent solubility, in vitro permeability, and microsomal stability, which will be valuable tools for exploring the pharmacology and therapeutic prospects of GPR84.

Transcriptional reprogramming during human osteoclast differentiation identifies regulators of osteoclast activity

Enhanced osteoclastogenesis and osteoclast activity contribute to the development of osteoporosis, which is characterized by increased bone resorption and inadequate bone formation. As novel antiosteoporotic therapeutics are needed, understanding the genetic regulation of human osteoclastogenesis could help identify potential treatment targets. This study aimed to provide an overview of transcriptional reprogramming during human osteoclast differentiation. Osteoclasts were differentiated from CD14+ monocytes from eight female donors. RNA sequencing during differentiation revealed 8 980 differentially expressed genes grouped into eight temporal patterns conserved across donors. These patterns revealed distinct molecular functions associated with postmenopausal osteoporosis susceptibility genes based on RNA from iliac crest biopsies and bone mineral density SNPs. Network analyses revealed mutual dependencies between temporal expression patterns and provided insight into subtype-specific transcriptional networks. The donor-specific expression patterns revealed genes at the monocyte stage, such as filamin B (FLNB) and oxidized low-density lipoprotein receptor 1 (OLR1, encoding LOX-1), that are predictive of the resorptive activity of mature osteoclasts. The expression of differentially expressed G-protein coupled receptors was strong during osteoclast differentiation, and these receptors are associated with bone mineral density SNPs, suggesting that they play a pivotal role in osteoclast differentiation and activity. The regulatory effects of three differentially expressed G-protein coupled receptors were exemplified by in vitro pharmacological modulation of complement 5 A receptor 1 (C5AR1), somatostatin receptor 2 (SSTR2), and free fatty acid receptor 4 (FFAR4/GPR120). Activating C5AR1 enhanced osteoclast formation, while activating SSTR2 decreased the resorptive activity of mature osteoclasts, and activating FFAR4 decreased both the number and resorptive activity of mature osteoclasts. In conclusion, we report the occurrence of transcriptional reprogramming during human osteoclast differentiation and identified SSTR2 and FFAR4 as antiresorptive G-protein coupled receptors and FLNB and LOX-1 as potential molecular markers of osteoclast activity. These data can help future investigations identify molecular regulators of osteoclast differentiation and activity and provide the basis for novel antiosteoporotic targets.

Structural basis for the ligand recognition and signaling of free fatty acid receptors

Free fatty acid receptors 1 to 4 (FFA1 to FFA4) are class A G protein-coupled receptors (GPCRs). FFA1 to FFA3 share substantial sequence similarity, whereas FFA4 is unrelated. However, FFA1 and FFA4 are activated by long-chain fatty acids, while FFA2 and FFA3 respond to short-chain fatty acids generated by intestinal microbiota. FFA1, FFA2, and FFA4 are potential drug targets for metabolic and inflammatory conditions. Here, we determined the active structures of FFA1 and FFA4 bound to docosahexaenoic acid, FFA4 bound to the synthetic agonist TUG-891, and butyrate-bound FFA2, each complexed with an engineered heterotrimeric Gq protein (miniGq), by cryo-electron microscopy. Together with computational simulations and mutagenesis studies, we elucidated the similarities and differences in the binding modes of fatty acid ligands to their respective GPCRs. Our findings unveiled distinct mechanisms of receptor activation and G protein coupling. We anticipate that these outcomes will facilitate structure-based drug development and underpin future research on this group of GPCRs.

GPR120/FFAR4: A Potential New Therapeutic Target for Inflammatory Bowel Disease

Inflammatory bowel disease, whose major forms are Crohn's disease and ulcerative colitis, is characterized by chronic inflammation of the gut due to the loss of tolerance toward antigens normally contained in the gut lumen. G protein-coupled receptor (GPR) 120 has gained considerable attention as a potential therapeutic target for metabolic disorders due to its implication in the production of the incretin hormone glucagon-like peptide 1 and the secretion of cholecystokinin. Recent studies have also highlighted the role of GPR120 in regulating immune system activity and inflammation. GPR120, expressed by intestinal epithelial cells, proinflammatory macrophages, enteroendocrine L cells, and CD4+ T cells, suppresses proinflammatory and enhances anti-inflammatory cytokine production, suggesting that GPR120 might have a pivotal role in intestinal inflammation and represent a possible therapeutic target in inflammatory bowel disease. This narrative review aims at summarizing the role of GPR120 in the maintenance of intestinal homeostasis through the analysis of the most recent studies.

Structural basis for the ligand recognition and signaling of free fatty acid receptors

Free fatty acid receptors 1-4 (FFA1-4) are class A G protein-coupled receptors (GPCRs). FFA1-3 share substantial sequence similarity whereas FFA4 is unrelated. Despite this FFA1 and FFA4 are activated by the same range of long chain fatty acids (LCFAs) whilst FFA2 and FFA3 are instead activated by short chain fatty acids (SCFAs) generated by the intestinal microbiota. Each of FFA1, 2 and 4 are promising targets for novel drug development in metabolic and inflammatory conditions. To gain insights into the basis of ligand interactions with, and molecular mechanisms underlying activation of, FFAs by LCFAs and SCFAs, we determined the active structures of FFA1 and FFA4 bound to the polyunsaturated LCFA docosahexaenoic acid (DHA), FFA4 bound to the synthetic agonist TUG-891, as well as SCFA butyrate-bound FFA2, each complexed with an engineered heterotrimeric Gq protein (miniGq), by cryo-electron microscopy. Together with computational simulations and mutagenesis studies, we elucidated the similarities and differences in the binding modes of fatty acid ligands with varying chain lengths to their respective GPCRs. Our findings unveil distinct mechanisms of receptor activation and G protein coupling. We anticipate that these outcomes will facilitate structure-based drug development and underpin future research to understand allosteric modulation and biased signaling of this group of GPCRs.

Potential of omega-3 and conjugated fatty acids to control microglia inflammatory imbalance elicited by obesogenic nutrients

High-fat diet-induced obesity detrimentally affects brain function by inducing chronic low-grade inflammation. This neuroinflammation is, at least in part, likely to be mediated by microglia, which are the main immune cell population in the brain. Microglia express a wide range of lipid-sensitive receptors and their activity can be modulated by fatty acids that cross the blood-brain barrier. Here, by combining live cell imaging and FRET technology we assessed how different fatty acids modulate microglia activity. We demonstrate that the combined action of fructose and palmitic acid induce Ikβα degradation and nuclear translocation of the p65 subunit nuclear factor kB (NF-κB) in HCM3 human microglia. Such obesogenic nutrients also lead to reactive oxygen species production and LynSrc activation (critical regulators of microglia inflammation). Importantly, short-time exposure to omega-3 (EPA and DHA), CLA and CLNA are sufficient to abolish NF-κB pathway activation, suggesting a potential neuroprotective role. Omega-3 and CLA also show an antioxidant potential by inhibiting reactive oxygen species production, and the activation of LynSrc in microglia. Furthermore, using chemical agonists (TUG-891) and antagonists (AH7614) of GPR120/FFA4, we demonstrated that omega-3, CLA and CLNA inhibition of the NF-κB pathway is mediated by this receptor, while omega-3 and CLA antioxidant potential occurs through different signaling mechanisms.

Unsaturated bond recognition leads to biased signal in a fatty acid receptor

Individual free fatty acids (FAs) play important roles in metabolic homeostasis, many through engagement with more than 40G protein-coupled receptors. Searching for receptors to sense beneficial omega-3 FAs of fish oil enabled the identification of GPR120, which is involved in a spectrum of metabolic diseases. Here, we report six cryo-electron microscopy structures of GPR120 in complex with FA hormones or TUG891 and Gi or Giq trimers. Aromatic residues inside the GPR120 ligand pocket were responsible for recognizing different double-bond positions of these FAs and connect ligand recognition to distinct effector coupling. We also investigated synthetic ligand selectivity and the structural basis of missense single-nucleotide polymorphisms. We reveal how GPR120 differentiates rigid double bonds and flexible single bonds. The knowledge gleaned here may facilitate rational drug design targeting to GPR120.

Incretins play an important role in FFA4/GPR120 regulation of glucose metabolism by GW-9508

AIMS

To assess the role of GPR120 in glucose metabolism and incretin regulation from enteroendocrine L- and K-cells with determination of the cellular localisation of GPR120 in intestinal tissue and clonal Glucagon-Like Peptide-1 (GLP-1)/Gastric Inhibitory Polypeptide (GIP) cell lines.

MAIN METHODS

Anti-hyperglycaemic, insulinotropic and incretin secreting properties of the GPR120 agonist, GW-9508 were explored in combination with oral and intraperitoneal glucose tolerance tests (GTT) in lean, diabetic and incretin receptor knockout mice. Cellular localisation of GPR120 was assessed by double immunofluorescence.

KEY FINDINGS

Compared to intraperitoneal injection, oral administration of GW-9508 (0.1 μmol/kg body weight) together with glucose reduced the glycaemic excursion by 22-31 % (p < 0.05-p < 0.01) and enhanced glucose-induced insulin release by 30 % (p < 0.01) in normal mice. In high fat fed diabetic mice, orally administered GW-9508 lowered plasma glucose by 17-27 % (p < 0.05-p < 0.01) and augmented insulin release by 22-39 % (p < 0.05-p < 0.001). GW-9508 had no effect on the responses of GLP-1 receptor knockout mice and GIP receptor knockout mice. Consistent with this, oral GW-9508 increased circulating total GLP-1 release by 39-44 % (p < 0.01) and total GIP by 37-47 % (p < 0.01-p < 0.001) after 15 and 30 min in lean NIH Swiss mice. Immunocytochemistry demonstrated GPR120 expression on mouse enteroendocrine L- and K-cells, GLUTag cells and pGIP/Neo STC-1 cells.

SIGNIFICANCE

GPR120 is expressed on intestinal L- and K-cells and stimulates GLP-1/GIP secretory pathways involved in mediating enhanced insulin secretion and improved glucose tolerance, following oral GW-9508. These novel data strongly support the development of potent and selective GPR120 agonists as an effective therapeutic approach for diabetes.

Effects of TUG-891, a potent GPR120 agonist, on the physical and oral lipid- coating properties, and secretion of saliva

GPR120 agonists were recently shown to enhance the fatty orosensation in humans when added to vegetable oil or a low-fat food system, but did not evoke it by themselves. Furthermore, an emulsion prepared from vegetable oil had a stronger fatty orosensation than that prepared from mineral oil even though the physical properties of both emulsions were similar. To clarify the mechanisms underlying the enhancement of the fatty orosensation by GPR120 agonists, the present study investigated the effects of TUG-891, a potent GPR120 agonist, on physical and oral lipid-coating properties and the secretion of saliva. The addition of TUG-891 to a vegetable oil emulsion did not significantly change its physical properties, such as viscosity, particle distribution, interfacial tension, contact angle, frictional load, and ζ-electric potential, or the amount of the lipid coating remaining in the oral cavity. These results indicate that TUG-891 enhanced the fatty orosensation without changing the physical or oral lipid-coating properties of the emulsion. The addition of TUG-891 to a vegetable oil emulsion and whipped cream significantly increased the amount of saliva secreted. Therefore, TUG-891, a potent GPR120 agonist, may enhance the fatty orosensation by increasing the amount of saliva secreted.

Diphenyl Ether Derivatives as Novel GPR120 Agonists for the Treatment of Type 2 Diabetes Mellitus

Diabetes mellitus (DM) is a serious disease affecting human health. Numerous attempts have been made to develop safe and effective new antidiabetic drugs. Recently, a series of G protein-coupled receptors for free fatty acids (FFAs) have been described and characterized, and small molecule agonists and antagonists of these receptors show considerable promise for managing diabetes and related complications. FFA-activated GPR120 could stimulate the release of glucagon-like peptide-1(GLP-1), which can enhance the glucose-dependent secretion of insulin from pancreatic β cells. GPR120 is a promising target for treating type 2 DM (T2DM). Herein we designed and synthesized a series of novel GPR120 agonists based on the structure of TUG-891, which was the first potent and selective GPR120 agonist. Among the designed compounds, 18 f showed excellent GPR120 activation activity and high selectivity for GPR40 in vitro. Compound 18 f dose-dependently improved glucose tolerance in normal mice, and no hypoglycemic side effects were observed at high dose. In addition, compound 18 f increased insulin release and displayed good antidiabetic effect in diet-induced obese mice. Molecular simulations illustrated that compound 18 f could enter the active site of GPR120 and interact with Arg99. Based on these observations, compound 18 f may be a promising lead compound for the design of novel GPR120 agonists to treat T2DM.

Discovery of Novel and Selective G-Protein Coupled Receptor 120 (GPR120) Agonists for the Treatment of Type 2 Diabetes Mellitus

Diabetes mellitus (DM), a chronic metabolic disorder characterized by high blood glucose, not only poses a serious threat to human life and health, but also places an economic burden on society. Currently available antidiabetic pharmacological agents have some adverse effects, which have stimulated researchers to explore novel antidiabetic agents with different mechanisms of action. G-protein Coupled Receptor 120 (GPR120), also known as free fatty acid receptor 4 (FFAR4), which is activated by medium-chain and long-chain fatty acids, has emerged as an interesting potential target for the treatment of metabolic disorders. Herein, we designed and synthesized a series of novel GPR120 agonists based on the structure of TUG-891, which is susceptible to β-oxidation and loses its GPR120 agonistic activity in vivo. Among the designed compounds, 14d showed excellent agonistic activity and selectivity and could improve glucose tolerance in normal mice in a dose-dependent manner. In addition, the compound 14d displayed good antidiabetic effects in diet-induced obese (DIO) mice and elevated insulin levels. Molecular simulations illustrated that compound 14d could enter the active site of GPR120 and interact with ARG99, which plays an important role in GPR120 activation. Based on these observations, compound 14d may be a promising lead compound deserving of further biological evaluation and structural modifications.

How Arrestins and GRKs Regulate the Function of Long Chain Fatty Acid Receptors

FFA1 and FFA4, two G protein-coupled receptors that are activated by long chain fatty acids, play crucial roles in mediating many biological functions in the body. As a result, these fatty acid receptors have gained considerable attention due to their potential to be targeted for the treatment of type-2 diabetes. However, the relative contribution of canonical G protein-mediated signalling versus the effects of agonist-induced phosphorylation and interactions with β-arrestins have yet to be fully defined. Recently, several reports have highlighted the ability of β-arrestins and GRKs to interact with and modulate different functions of both FFA1 and FFA4, suggesting that it is indeed important to consider these interactions when studying the roles of FFA1 and FFA4 in both normal physiology and in different disease settings. Here, we discuss what is currently known and show the importance of understanding fully how β-arrestins and GRKs regulate the function of long chain fatty acid receptors.

Anti-inflammation and gut microbiota regulation properties of fatty acids derived from fermented milk in mice with dextran sulfate sodium-induced colitis

The by-products of milk fermentation by lactic acid bacteria provide potential health benefits to the balance of host intestinal microflora. In this study, the anti-inflammatory properties of fatty acids from monoculture-strain (Lactiplantibacillusplantarum A3) and multiple-strain (Streptococcus thermophilus, Lactobacillus bulgaricus, and L. plantarum A3 1:1:2) fermented milk were evaluated in a mouse model of dextran sulfate sodium-induced colitis, and the gut microbiota regulation properties of the fatty acids were also investigated. Results showed that fatty acids can attenuate the inflammatory response by inhibiting the expression of inflammatory factors IL-6 and tumor necrosis factor-α, and blocking the phosphorylation of the JNK in MAPK signal pathway. In addition, the relative abundance of the taxa Akkermansia and Lactobacillus were both enriched after the fatty acid intervention. This finding suggests that fatty acids from the milk fermentation with mixed lactic acid bacteria starters can reduce the severity of dextran sulfate sodium-induced colitis and enhance the abundance of the probiotics in the mice intestinal tract.

Ursodesoxycholic acid is an FFA4 agonist and reduces hepatic steatosis via FFA4 signaling

Ursodeoxycholic acid (UDCA) is a safe bile acid effective in reducing hepatic steatosis in non-alcoholic fatty liver disease (NAFLD). However, the mechanism of action linked to this effect is poorly defined. In the present study, we identified that UDCA acted as a free fatty acid receptor 4 (FFA4) agonist with EC50 of 10.4 ± 0.7 μM, and its activity was determined by dynamic mass redistribution, fluorometric imaging plate reader, inositol monophosphate and bioluminescence resonance energy transfer assays. Moreover, UDCA showed FFA4 selectivity over eleven other G protein-coupled receptors. Real-Time PCR and immunocytochemistry analyses showed that FFA4 was abundantly expressed in human hepatocytes HuH-7 cells. In an in vitro model of NAFLD induced by oleic acid (OA), UDCA downregulated lipid accumulation in HuH-7 cells and suppressed sterol-regulatory element binding protein-1c (SREBP-1c) mRNA expression. This suppression of SREBP-1c was restored when FFA4 expression was knocked down in siRNA assay. In a mouse model of hepatic steatosis, db/db mice were exposed to a high-fat diet (HFD), and treatment of UDCA or docosahexaenoic acid (DHA, an endogenous FFA4 agonist) effectively prevented body weight gain and hepatic fat deposition and reduced triglyceride (TG) levels in serum and liver. This study not only identified a new skeleton of FFA4 agonists, but also demonstrated that FFA4 signal was accounting for the protective effects of UDCA in the NAFLD treatment.

Fluorescent Ligand-Based Discovery of Small-Molecule Sulfonamide Agonists for GPR120

As a critical member of G protein-coupled receptors (GPCRs), G protein-coupled receptor 120 (GPR120) is a potential target for many physiological diseases, such as type 2 diabetes mellitus, inflammation, and obesity. Considering that small-molecule fluorescent ligands can combine the advantages of visualization, high sensitivity and selectivity, we initially undertook an effort to develop a series of fluorescent ligands to track GPR120 and establish a method to screen GPR120 agonists. The representative fluorescent ligand N1 possesses suitable optical property, equitable biological activity, and high fluorescence imaging feasibility, therefore, based on compound N1, we subsequently founded a bioluminescence resonance energy transfer (BRET) competition binding assay to screen three series of sulfonamide GPR120 agonists we developed herein. The activity evaluation results revealed that compound D5 was a potent GPR120 agonist with high activity and selectivity. Moreover, compound D5 exhibited a significant glucose-lowering effect in db/db mice, which indicates its potential application in the treatment of type 2 diabetes mellitus in vivo. It is anticipated that our fluorescent ligand-based method is a useful toolbox and will find broad applications in the discovery of small-molecule agonists for GPR120.

Thiazolidinedione derivatives as novel GPR120 agonists for the treatment of type 2 diabetes

GPR120, also called FFAR4, is preferentially expressed in the intestines, and can be stimulated by long-chain free fatty acids to increase the secretion of glucagon-like peptide-1 (GLP-1) from intestinal endocrine cells. It is known that GLP-1, as an incretin, can promote the insulin secretion from pancreatic cells in a glucose-dependent manner. Therefore, GPR120 is a potential drug target to treat type 2 diabetes. In this study, thiazolidinedione derivatives were found to be novel potent GPR120 agonists. Compound 5g, with excellent agonistic activity, selectivity, and metabolic stability, improved oral glucose tolerance in normal C57BL/6 mice in a dose-dependent manner. Moreover, compound 5g exhibited anti-diabetic activity by promoting insulin secretion in diet-induced obese mice. In summary, compound 5g might be a promising drug candidate for the treatment of type 2 diabetes.

GPR120 has emerged as an attractive target for the treatment of type 2 diabetes and obesity. Thiazolidinedione derivatives were found to be novel potent GPR120 agonists.

Structure based prediction of a novel GPR120 antagonist based on pharmacophore screening and molecular dynamics simulations

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Hypothesis of the important residues in conserving the GPR120S “ionic-lock”.

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Computational model targeting W277 and N313 for virtual screening of GPR120S ligands.

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Cpd 9 emerged as a potential GPR120S antagonist and anti-cancer treatment.

The G-protein coupled receptor, GPR120, has ubiquitous expression and multifaceted roles in modulating metabolic and anti-inflammatory processes. Recent implications of its role in cancer progression have presented GPR120 as an attractive oncogenic drug target. GPR120 gene knockdown in breast cancer studies revealed a role of GPR120-induced chemoresistance in epirubicin and cisplatin-induced DNA damage in tumour cells. Higher expression and activation levels of GPR120 is also reported to promote tumour angiogenesis and cell migration in colorectal cancer. Some agonists targeting GPR120 have been reported, such as TUG891 and Compound39, but to date development of small-molecule inhibitors of GPR120 is limited.

Herein, following homology modelling of the receptor a pharmacophore hypothesis was derived from 300 ns all-atomic molecular dynamics (MD) simulations on apo, TUG891-bound and Compound39-bound GPR120S (short isoform) receptor models embedded in a water solvated lipid bilayer system. We performed comparative MD analysis on protein–ligand interactions between the two agonist and apo simulations on the stability of the “ionic lock” – a Class A GPCRs characteristic of receptor activation and inactivation. The detailed analysis predicted that ligand interactions with W277 and N313 are critical to conserve the “ionic-lock” conformation (R136 of Helix 3) and prevent GPR120S receptor activation. The results led to generation of a W277 and N313 focused pharmacophore hypothesis and the screening of the ZINC15 database using ZINCPharmer through the structure-based pharmacophore.

100 ns all-atomic molecular dynamics (MD) simulations were performed on 9 small molecules identified and Cpd 9, (2-hydroxy-N-{4-[(6-hydroxy-2-methylpyrimidin-4-yl) amino] phenyl} benzamide) was predicted to be a small-molecule GPR120S antagonist. The conformational results from the collective all-atomic MD analysis provided structural information for further identification and optimisation of novel druggable inhibitors of GPR120S using this rational design approach, which could have future potential for anti-cancer drug development studies.

Novel GPR120 Agonists with Improved Pharmacokinetic Profiles for the Treatment of Type 2 Diabetes

GPR120 is a promising target for the treatment of type 2 diabetes (T2DM), which is activated by free fatty acids (FFAs) and stimulates the release of glucagon-like peptide-1(GLP-1). GLP-1, as an incretin, can enhance glucose-dependent secretion of insulin from pancreatic beta cells and reduce blood glucose. In this study, a series of novel GPR120 agonists were designed and synthesized to improve the stability and hydrophilicity of the phenylpropanoic acid GPR120 agonist TUG-891. Compound 11b showed excellent GPR120 agonistic activity and pharmacokinetic properties, and could reduce the blood glucose of normal mice in a dose-dependent manner. In addition, no hypoglycemic side effects were observed even at a dose of 100 mg/kg. Moreover, 11b showed good anti-hyperglycemic effects in diet-induced obese (DIO) mice. Molecular simulation illustrated that compound 11b could enter the active site of GPR120 and interact with ARG99. Taken together, the results indicate that compound 11b might be a promising drug candidate for the treatment of T2DM.

The Anti-Atherosclerotic Action of FFAR4 Agonist TUG-891 in ApoE-Knockout Mice Is Associated with Increased Macrophage Polarization towards M2 Phenotype

Background: Over the past few years, a better understanding of the biology of G-protein coupled receptors (GPRs) has led to the identification of several receptors as novel targets for free fatty acids (FFAs). FFAR4 has received special attention in the context of chronic inflammatory diseases, including atherosclerosis, obesity and NAFLD, through to its anti-inflammatory effect. Methods: The present study investigates the influence of prolonged treatment with TUG-891-FFAR4 agonist on the development of atherosclerosis plaque in apoE-knockout mice, using morphometric and molecular methods. Results: TUG-891 administration has led to the reduction of atherosclerotic plaque size and necrotic cores in an apoE-knockout mice model. TUG-891-treated mice were administered subcutaneously at a dose of 20 mg/kg three times a week for 4 months. The FFAR4 agonist reduced the content of pro-inflammatory M1-like macrophages content in atherosclerotic plaques, as evidenced by immunohistochemical phenotyping and molecular methods. In atherosclerotic plaque, the population of smooth muscle cells increased as evidenced by α-SMA staining. We observed changes in G-CSF and eotaxin markers in the plasma of mice; changes in the levels of these markers in the blood may be related to macrophage differentiation. Importantly, we observed a significant increase in M2-like macrophage cells in atherosclerotic plaque and peritoneum. Conclusions: Prolonged administration of TUG-891 resulted in significant amelioration of atherogenesis, providing evidence that the strategy based on macrophage phenotype switching toward an M2-like activation state via stimulation of FFAR4 receptor holds promise for a new approach in the prevention or treatment of atherosclerosis.

The relevance of adhesion G protein-coupled receptors in metabolic functions

G protein-coupled receptors (GPCRs) modulate a variety of physiological functions and have been proven to be outstanding drug targets. However, approximately one-third of all non-olfactory GPCRs are still orphans in respect to their signal transduction and physiological functions. Receptors of the class of Adhesion GPCRs (aGPCRs) are among these orphan receptors. They are characterized by unique features in their structure and tissue-specific expression, which yields them interesting candidates for deorphanization and testing as potential therapeutic targets. Capable of G-protein coupling and non-G protein-mediated function, aGPCRs may extend our repertoire of influencing physiological function. Besides their described significance in the immune and central nervous systems, growing evidence indicates a high importance of these receptors in metabolic tissue. RNAseq analyses revealed high expression of several aGPCRs in pancreatic islets, adipose tissue, liver, and intestine but also in neurons governing food intake. In this review, we focus on aGPCRs and their function in regulating metabolic pathways. Based on current knowledge, this receptor class represents high potential for future pharmacological approaches addressing obesity and other metabolic diseases.

Pathophysiological regulation of lung function by the free fatty acid receptor FFA4

Increased prevalence of inflammatory airway diseases including asthma and chronic obstructive pulmonary disease (COPD) together with inadequate disease control by current frontline treatments means that there is a need to define therapeutic targets for these conditions. Here, we investigate a member of the G protein-coupled receptor family, FFA4, that responds to free circulating fatty acids including dietary omega-3 fatty acids found in fish oils. We show that FFA4, although usually associated with metabolic responses linked with food intake, is expressed in the lung where it is coupled to G_q/11 signaling. Activation of FFA4 by drug-like agonists produced relaxation of murine airway smooth muscle mediated at least in part by the release of the prostaglandin E₂ (PGE₂) that subsequently acts on EP₂ prostanoid receptors. In normal mice, activation of FFA4 resulted in a decrease in lung resistance. In acute and chronic ozone models of pollution-mediated inflammation and house dust mite and cigarette smoke-induced inflammatory disease, FFA4 agonists acted to reduce airway resistance, a response that was absent in mice lacking expression of FFA4. The expression profile of FFA4 in human lung was similar to that observed in mice, and the response to FFA4/FFA1 agonists similarly mediated human airway smooth muscle relaxation ex vivo. Our study provides evidence that pharmacological targeting of lung FFA4, and possibly combined activation of FFA4 and FFA1, has in vivo efficacy and might have therapeutic value in the treatment of bronchoconstriction associated with inflammatory airway diseases such as asthma and COPD.

Anti-Atherosclerotic Potential of Free Fatty Acid Receptor 4 (FFAR4)

Fatty acids (FAs) are considered not only as a basic nutrient, but are also recognized as signaling molecules acting on various types of receptors. The receptors activated by FAs include the family of rhodopsin-like receptors: GPR40 (FFAR1), GPR41 (FFAR3), GPR43 (FFAR2), GPR120 (FFAR4), and several other, less characterized G-protein coupled receptors (GPR84, GPR109A, GPR170, GPR31, GPR132, GPR119, and Olfr78). The ubiquitously distributed FFAR4 can be activated by saturated and unsaturated medium- and long-chain fatty acids (MCFAs and LCFAs), as well as by several synthetic agonists (e.g., TUG-891). The stimulation of FFAR4 using selective synthetic agonists proved to be promising strategy of reduction of inflammatory reactions in various tissues. In this paper, we summarize the evidence showing the mechanisms of the potential beneficial effects of FFAR4 stimulation in atherosclerosis. Based partly on our own results, we also suggest that an important mechanism of such activity may be the modulatory influence of FFAR4 on the phenotype of macrophage involved in atherogenesis.

GPR120/FFAR4 Pharmacology: Focus on Agonists in Type 2 Diabetes Mellitus Drug Discovery

The G-protein coupled receptors (GPCRs) activated by free fatty acids (FFAs) have emerged as new and exciting drug targets, due to their plausible translation from pharmacology to medicines. This perspective aims to report recent research about GPR120/FFAR4 and its involvement in several diseases, including cancer, inflammatory conditions, and central nervous system disorders. The focus is to highlight the importance of GPR120 in Type 2 diabetes mellitus (T2DM). GPR120 agonists, useful in T2DM drug discovery, have been widely explored from a structure–activity relationship point of view. Since the identification of the first reported synthetic agonist TUG-891, the research has paved the way for the development of TUG-based molecules as well as new and different chemical entities. These molecules might represent the starting point for the future discovery of GPR120 agonists as antidiabetic drugs.

GPR120 agonists enhance the fatty orosensation when added to fat-containing system, but do not evoke it by themselves in humans

Dietary fat, an important macronutrient, has been considered to be perceived by texture and olfaction. Recently, fatty acid transporter, CD36, and fatty acid receptor, GPR120 are considered to be involved in human gustatory fatty acids perception in humans. However, limited information is currently available to show that agonists of CD36 and GPR120 evoke fatty oral sensations regarding to dietary fat in humans. Therefore, the role of GPR120 agonists in dietary fat perception in humans was investigated herein. An emulsion prepared from vegetable oil had a stronger fatty orosensation, an orosensation similar to an oily mouth-coating sensed 5 - 10 s after tasting, than that prepared from mineral oil; however, the physical properties of both emulsions, such as viscosity, particle distribution, interfacial tension, contact angle, frictional load, and ζ-electric potential were similar. The potent GPR120 agonist, TUG-891 enhanced the fatty orosensation when added to the emulsion prepared from vegetable oil, but not to that from mineral oil. All GPR120 agonists tested enhanced the fatty orosensation when added to a low-fat food system whereas they did not evoke any fatty sensation in aqueous solution at the concentrations tested in food system, and sensory activity positively correlated with GPR120 activity. These results suggest that GPR120 agonists enhance the fatty orosensation in humans when added to vegetable oil or a low-fat food system, but do not evoke it by themselves.

Pharmacology of Free Fatty Acid Receptors and Their Allosteric Modulators

The physiological function of free fatty acids (FFAs) has long been regarded as indirect in terms of their activities as educts and products in metabolic pathways. The observation that FFAs can also act as signaling molecules at FFA receptors (FFARs), a family of G protein-coupled receptors (GPCRs), has changed the understanding of the interplay of metabolites and host responses. Free fatty acids of different chain lengths and saturation statuses activate FFARs as endogenous agonists via binding at the orthosteric receptor site. After FFAR deorphanization, researchers from the pharmaceutical industry as well as academia have identified several ligands targeting allosteric sites of FFARs with the aim of developing drugs to treat various diseases such as metabolic, (auto)inflammatory, infectious, endocrinological, cardiovascular, and renal disorders. GPCRs are the largest group of transmembrane proteins and constitute the most successful drug targets in medical history. To leverage the rich biology of this target class, the drug industry seeks alternative approaches to address GPCR signaling. Allosteric GPCR ligands are recognized as attractive modalities because of their auspicious pharmacological profiles compared to orthosteric ligands. While the majority of marketed GPCR drugs interact exclusively with the orthosteric binding site, allosteric mechanisms in GPCR biology stay medically underexploited, with only several allosteric ligands currently approved. This review summarizes the current knowledge on the biology of FFAR1 (GPR40), FFAR2 (GPR43), FFAR3 (GPR41), FFAR4 (GPR120), and GPR84, including structural aspects of FFAR1, and discusses the molecular pharmacology of FFAR allosteric ligands as well as the opportunities and challenges in research from the perspective of drug discovery.

A novel GPR120-selective agonist promotes insulin secretion and improves chronic inflammation

AIMS

The present study aimed to disclose a potent and selective GPR120 agonist LXT34 and its anti-diabetic effects.

MAIN METHODS

Calcium mobilization assay was used to measure the agonistic potency and selectivity of LXT34 in GPR120 or GPR40-overexpression Chinese hamster ovary (CHO) cells. Glucagon-like peptide-1 (GLP-1) release and glucose-stimulated insulin secretion (GSIS) were evaluated in human colonic epithelial cell line NCI-H716 and mouse insulinoma cell line MIN6 by enzyme-linked immunosorbent assay (ELISA), respectively. The anti-inflammatory effect was determined in lipopolysaccharide (LPS)-induced murine macrophage cell line RAW264.7. Oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) were performed to assess the anti-diabetic effects of LXT34 in db/db mice, and chronic inflammation in liver and adipose tissues were investigated using histomorphology, immunoblot and gene expression analysis.

KEY FINDINGS

LXT34 was a potent GPR120 agonist with negligible activity toward human and mouse GPR40. LXT34 could potentiate GSIS and suppress LPS-induced inflammation in macrophages. LXT34 not only markedly improved glucose tolerance and insulin resistance, but also distinctly reduced macrophages infiltration, pro-inflammatory cytokines expression and JNK phosphorylation of both liver and adipose tissues in db/db mice.

SIGNIFICANCE

LXT34, a novel and potent GPR120-selective agonist, showed beneficial effects on improving glucose homeostasis in obesity-related type 2 diabetes.

Development of Free Fatty Acid Receptor 4 (FFA4/GPR120) Agonists in Health Science

Till the 21^st century, fatty acids were considered as merely building blocks for triglycerides, phospholipids, or cholesteryl esters. However, the discovery of G protein-coupled receptors (GPCRs) for free fatty acids at the beginning of the 21^st century challenged that idea and paved way for a new field of research, merged into the field of receptor pharmacology for intercellular lipid mediators. Among the GPCRs for free fatty acids, free fatty acid receptor 4 (FFA4, also known as GPR120) recognizes long-chain polyunsaturated fatty acids such as DHA and EPA. It is significant in drug discovery because it regulates obesity-induced metaflammation and GLP-1 secretion. Our study reviews information on newly developed FFA4 agonists and their application in pathophysiologic studies and drug discovery. It also offers a potency comparison of the FFA4 agonists in an AP-TGF-α shedding assay.

New small molecule fluorescent probes for G protein-coupled receptors: valuable tools for drug discovery

G protein-coupled receptors (GPCRs) are essential signaling proteins and tractable therapeutic targets. To develop new drug candidates, GPCR drug discovery programs require versatile, sensitive pharmacological tools for ligand binding and compound screening. With the availability of new imaging modalities and proximity-based ligand binding technologies, fluorescent ligands offer many advantages and are increasingly being used, yet labeling small molecules remains considerably more challenging relative to peptides. Focusing on recent fluorescent small molecule studies for family A GPCRs, this review addresses some of the key challenges, synthesis approaches and structure-activity relationship considerations, and discusses advantages of using high-resolution GPCR structures to inform conjugation strategies. While no single approach guarantees successful labeling without loss of affinity or selectivity, the choice of fluorophore, linker type and site of attachment have proved to be critical factors that can significantly affect their utility in drug discovery programs, and as discussed, can sometimes lead to very unexpected results.

Synthesis and evaluation of 3-(4-(phenoxymethyl)phenyl)propanoic acid and N-phenylbenzenesulfonamide derivatives as FFA4 agonists

Free fatty acid receptor 4 (FFA4) has been recognized as an attractive target in metabolic diseases. To find potent and selective FFA4 agonist, 28 compounds of 3-(4-(phenoxymethyl)phenyl)propanoic acid and N-phenylbenzenesulfonamide derivatives were designed and synthesized, featuring OC and SO2-N linkage. For the OC linkage compounds, 1g showed the most potent FFA4 agonistic activity with a pEC₅₀ of 5.81 ± 0.04 and exhibited at least 64-fold selectivity against FFA1. For SO2-N linkage agonists, 2m had a pEC₅₀ of 5.66 ± 0.04 and displayed>46-fold selectivity against FFA1. Among these two series of compounds, 1g was the most potent agonist at FFA4 and the best selectivity against FFA1, demonstrated by docking simulation. Moreover, 1g showed receptor selectivity on other seven GPCRs. In anti-diabetic evaluation, 1g dose-dependently reduced blood glucose, which was better than a clinical phase III drug TAK875. This study provides guidance for FFA4 ligand design and drug optimization.

In silico and in vitro screening for potential anticancer candidates targeting GPR120

The G-protein coupled receptor - GPR120 has recently been implicated as a novel target for colorectal cancer (CRC) and other cancer managements. In this study, a homology model of GPR120S (short isoform) was generated to identify potential anti-cancer compounds targeting the GPR120 receptor using a combined in silico docking-based virtual screening (DBVS), structure-activity relationships (SAR) and in vitro screening approach. SPECS database of synthetic chemical compounds (~350,000) was screened using the developed GPR120S model to identify molecules binding to the orthosteric binding pocket followed by an AutoDock SMINA rigid-flexible docking protocol. The best 13 hit molecules were then tested in vitro to evaluate their cytotoxic activity against SW480 - human CRC cell line expressing GPR120. The test compound 1 (3-​(4-​methylphenyl)​-​2-​[(2-​oxo-​2-​phenylethyl)​sulfanyl]​-​5,6-​dihydrospiro(benzo[h]​quinazoline-​5,1'-​cyclopentane)​-​4(3H)​-​one) showed ~ 90% inhibitory effects on cell growth with micromolar affinities (IC₅₀ = 23.21-26.69 µM). Finally, SAR analysis of compound 1 led to the identification of a more active compound from the SPECS database showing better efficacy during cell-based cytotoxicity assay -5 (IC₅₀ = 5.89-6.715 µM), while a significant reduction in cytotoxic effects of 5 was observed in GPR120-siRNA pre-treated SW480 cells. The GPR120S homology model generated, and SAR analysis conducted by this work discovered a potential chemical scaffold, dihydrospiro(benzo[h]quinazoline-5,1'-cyclopentane)-4(3H)-one, which will aid future research on anti-cancer drug development for CRC management.

Identification and target-pathway deconvolution of FFA4 agonists with anti-diabetic activity from Arnebia euchroma (Royle) Johnst

FFA4 is a novel therapeutic target for the treatment of metabolic diseases, such as type II diabetes. However, there are still few ligands with structural diversity, selectivity and high potency, and the signaling pathway downstream of FFA4 remains to be poorly characterized. In this study, a high performance liquid chromatography-corona charged aerosol detector (HPLC-CAD) combined with label-free dynamic mass redistribution (DMR) method was introduced to guide the discovery of FFA4 agonists from Arnebia euchroma (Royle) Johnst. Ten compounds were identified as FFA4 agonists and structure-activity relationship was obtained. Among them, shikonin displayed the most potent activity with pEC₅₀ value of 6.02 ± 0.19. The activity of shikonin was confirmed by FLIPR (fluorometric imaging plate reader) assay. Signaling pathways of FFA4 were explored in HT-29 cells endogenously expressing FFA4 using shikonin and known FFA4 agonists α-linolenic acid (ALA) and TUG891. Multiple pathways included Gq/11-PLC-Ca²⁺-PKC, RohA, JNK, p38 MAPK, Gi/o and PI3K signaling but may not involve Gs signaling triggered by shikonin, ALA and TUG891. Besides, shikonin, TUG891 and ALA could induce ERK1/2 and AKT phosphorylation in HT-29 cells. Moreover, anti-diabetes effects of shikonin were evaluated on the glucose intolerance in diabetic db/db mice. Shikonin reduced plasma glucose level, suggesting that it had the potential in treatment of type II diabetes. The agonists identified in this study provided structure guidance for FFA4 drug design. This study was also useful for understanding FFA4 pharmacology and its biological function.

GPR120 agonists for the treatment of diabetes: a patent review (2014 present)

INTRODUCTION

G protein-coupled receptor 120 (GPR120) is a G_αq coupled GPCR specifically activated by long-chain fatty acids (LCFAs). Functionally, it has been identified as a member of a family of lipid-binding free fatty acid receptors including GPR40, GPR41, and GPR43. Upon stimulation by LCFAs, GPR120 can directly or indirectly modulate hormone secretion from the gastrointestinal tract and pancreas, and regulate lipid and/or glucose metabolism in adipose, liver, and muscle tissues. Additionally, GPR120 is postulated to mediate anti-inflammatory and insulin-sensitizing effects in adipose and macrophages. These benefits suggest that GPR120 agonists have the potential to be an effective treatment for obesity, type 2 diabetes mellitus (T2DM), and other metabolic syndromes.

AREA COVERED

This article highlights and reviews research advances in this field that have been published in patent literature and peer-reviewed journals since 2014.

EXPERT OPINION

Current development has been hindered by species differences in GPR120 distribution, differences in GPR120-mediated signaling in distinct tissue types, and lack of available ligands with suitable selectivity for GPR120 over GPR40 in both human and rodents. The discovery of β-arrestin biased GPR120 agonists will help elucidate the potential of selective therapeutics that may discriminate between desirable and undesirable pharmacological effects.

ABBREVIATIONS

ALA: α-linolenic acid; AUC: area under the curve; BRET: bioluminescence resonance energy transfer; CCK: cholecystokinin; CHO-K1 cell: Chinese hamster ovary-K1 cell; db/db mouse: diabetic mouse; DHA: docosahexaenoic acid; DIO: diet-induced obesity; DMSO: dimethyl sulfoxide; DPP-4: dipeptidyl peptidase 4; EPA: eicosapentaenoic acid; FA(s): fatty acid(s); FFA(s): free fatty acid(s); FFAR: free fatty acid receptor; FLIPR: fluorescent imaging plate reader; GIR: glucose infusion rate; GLP-1: glucagon-like peptide 1; GP(C)R: G protein-coupled receptor; GSIS: glucose-stimulated insulin secretion; HEK293 cell: human embryonic kidney 293 cell; HOMA-IR: homeostatic measurement assessment of insulin resistance; IP1: inositol phosphate turnover; IPGTT: intraperitoneal glucose tolerance test; LCFA(s): long-chain fatty acid(s); MED_max: maximal efficacy; MIN6 cell: mouse insulin-secreting cell; NPY: neuropeptide Y; OGTT: oral glucose tolerance test; pERK: phosphorylated ERK; PPAR: peroxisome proliferator-activated receptor; QD: once daily; SAR: structure-activity relationship; siRNA: small interfering ribonucleic acid; STC-1: intestinal secretin tumor cell; T2DM: type 2 diabetes mellitus; U2OS cell: human bone osteosarcoma epithelial cell; uHTS: ultrahigh-throughput screening; ZDF: zucker diabetic fatty.

Effects of the juçara fruit supplementation on metabolic parameters in individuals with obesity: a double-blind randomized controlled trial

Adipose tissue inflammation has been proposed as a central mechanism connecting obesity with its metabolic and vascular complications due to the imbalance in the expression of several hormones and adipokines. Berries rich in polyphenols and unsaturated fatty acids have been able to prevent both obesity and adipose tissue inflammation, improving metabolic functions in human subjects and animal models of obesity. Juçara has been considered a super fruit owing to its nutritional composition and relevant biological activities with an interesting response in animals. Thus, we aimed to verify the potential antiobesogenic effect of juçara supplementation in humans. We conducted a double-blind, placebo-controlled, randomized trial with 35 adults with obesity of both sexes. They were assessed for resting metabolic rate, anthropometry and body composition, blood pressure, metabolic parameters and adipokines. Subsequently, they were randomized into two groups to use or not (placebo) 5 g lyophilized juçara for 6 weeks. Supplementation with juçara was significantly effective in reducing body fat, increasing high-density lipoprotein cholesterol and doubling serum adiponectin. Besides, juçara supplementation, high-density lipoprotein cholesterol and neck circumference were predictors to explain the enhancement in adiponectin. Juçara supplementation was determinant to improve adiponectin levels, and it may be considered a novel strategy for the treatment of obesity-related metabolic diseases.

Simultaneous determination of TUG-891 and its metabolites in rat plasma using LC-HRMS with application to preclinical pharmacokinetic study

In this study, a simple and reliable LC-MS/MS method was first proposed for the simultaneous determination of TUG-891 and its metabolites TUG-891-alcohol, TUG-891-aldehyde, and TUG-891-acid in rat plasma. The analytes and fasiglifam (internal standard) were extracted from plasma samples with acetonitrile and separated using an Acquity BEH C₁₈ column (1.7 μm, 2.1 × 50 mm) with water containing 0.05% ammonium hydroxide and acetonitrile containing 0.05% ammonium hydroxide as the mobile phase. A Q-Exactive Orbitrap mass spectrometer in full-scan mode was used for mass detection, and the data analysis was obtained using a mass extraction window of 5 ppm. The calibration curves exhibited excellent linearity (correlation coefficient > 0.9981) in the concentration range of 0.5-1000 ng/mL. The lower limit of quantification was 0.5 ng/mL for all analytes. The intra- and inter-day precision was less than 11.31%, and the accuracy ranged from -11.50 to 9.50%. The extraction recovery of the analytes from rat plasma was greater than 82.31%, and no obvious matrix effect was found. The established method was further applied to the pharmacokinetic study of TUG-891, TUG-891-alcohol, TUG-891-aldehyde, and TUG-891-acid in rat after a single dose of 5-mg/kg treatment of TUG-891. The results demonstrated that TUG-891 was rapidly metabolized into its metabolites and the systemic exposures of the metabolites were much higher than those of TUG-891.

Preference for dietary fat: From detection to disease

Recent advances in the field of taste physiology have clarified the role of different basic taste modalities and their implications in health and disease and proposed emphatically that there might be a distinct cue for oro-sensory detection of dietary long-chain fatty acids (LCFAs). Hence, fat taste can be categorized as a taste modality. During mastication, LCFAs activate tongue lipid sensors like CD36 and GPR120 triggering identical signaling pathways as the basic taste qualities do; however, the physico-chemical perception of fat is not as distinct as sweet or bitter or other taste sensations. The question arises whether "fat taste" is a basic or "alimentary" taste. There is compelling evidence that fat-rich dietary intervention modulates fat taste perception where an increase or a decrease in lipid contents in the diet results, respectively, in downregulation or upregulation of fat taste sensitivity. Evidently, a decrease in oro-sensory detection of LCFAs leads to high fat intake and, consequently, to obesity. In this article, we discuss recent relevant advances made in the field of fat taste physiology with regard to dietary fat preference and lipid sensors that can be the target of anti-obesity strategies.

Eicosapentaenoic acid prevents the progression of intracranial aneurysms in rats

Background

As subarachnoid hemorrhage due to rupture of an intracranial aneurysm (IA) has quite a poor outcome despite of an intensive medical care, development of a novel treatment targeting unruptured IAs based on the correct understanding of pathogenesis is mandatory for social health.

Methods

Using previously obtained gene expression profile data from surgically resected unruptured human IA lesions, we selected G-protein coupled receptor 120 (GPR120) as a gene whose expression is significantly higher in lesions than that in control arterial walls. To corroborate a contribution of GPR120 signaling to the pathophysiology, we used an animal model of IAs and examine the effect of a GPR120 agonist on the progression of the disease. IA lesion was induced in rats through an increase of hemodynamic stress achieved by a one-sided carotid ligation and induced hypervolemia. Eicosapentaenoic acid (EPA) was used as an agonist for GPR120 in this study and its effect on the size of IAs, the thinning of media, and infiltration of macrophages in lesions were examined.

Result

EPA administered significantly suppressed the size of IAs and the degenerative changes in the media in rats. EPA treatment also inhibited infiltration of macrophages, a hallmark of inflammatory responses in lesions. In in vitro experiments using RAW264.7 cells, pre-treatment of EPA partially suppressed lipopolysaccharide-induced activation of nuclear factor-kappa B and also the transcriptional induction of monocyte chemoattractant protein 1 (MCP-1), a major chemoattractant for macrophages to accumulate in lesions. As a selective agonist of GPR120, TUG-891, could reproduce the effect of EPA in RAW264.7 cells, EPA presumably acted on this receptor to suppress inflammatory responses. Consistently, EPA remarkably suppressed MCP-1 expression in lesions, suggesting the in vivo relevance of in vitro studies.

Conclusions

These results combined together suggest the potential of the medical therapy targeting GPR120 or using EPA to prevent the progression of IAs.

The GPR120 Agonist TUG-891 Inhibits the Motility and Phagocytosis of Mouse Alveolar Macrophages

Movement and phagocytosis characterize the fundamental actions of macrophages. Although it is known that the free fatty acid receptor GPR120 is expressed in macrophages and regulates cytokine expression to exert anti-inflammatory activities, the effects of GPR120 activation on the motility and phagocytosis of macrophages are not clear. In this study, mouse alveolar macrophages (AM) were stimulated with the GPR120 agonist TUG-891, and the changes in cell motility, intracellular Ca²⁺ concentration ([Ca²⁺]i), and the ability of phagocytosis were measured. Mouse AM in controls exhibited active movement in vitro, and TUG-891 significantly restrained AM movement. Meanwhile, TUG-891 stimulated a quick increase in [Ca²⁺]i in AM, which was blocked separately by the Gq protein inhibitor YM-254890, the phospholipase C (PLC) inhibitor U73122, or depletion of endoplasmic reticulum (ER) Ca²⁺ store by thapsigargin. The inhibition of AM movement by TUG-891 was eliminated by YM-254890, U73122, thapsigargin, and chelation of cytosolic Ca²⁺ by BAPTA. Moreover, TUG-891 inhibited AM phagocytosis of fluorescent microspheres, which was also blocked by YM-254890, U73122, thapsigargin, and BAPTA. In conclusion, GPR120 activation in mouse AM increases [Ca²⁺]i but inhibits the motility and phagocytosis via Gq protein/PLC-mediated Ca²⁺ release from ER Ca²⁺ store.

Regulation of cell survival through free fatty acid receptor 1 (FFA1) and FFA4 induced by endothelial cells in osteosarcoma cells

Free fatty acid receptor 1 (FFA1) and FFA4 belong to a family of free fatty acid (FFA) receptors. FFA1- and FFA4-mediated signaling regulates a variety of malignant properties in cancer cells. It is known that stromal cells in the tumor microenvironment promote tumor progression. In the present study, to assess the roles of FFA1 and FFA4 in cellular functions modulated by endothelial cells, highly migratory MG63-CR7(F2) cells were generated from osteosarcoma MG-63 cells, using endothelial F2 cell supernatants. Expression levels of FFAR1 and FFAR4 genes in MG63-CR7(F2) cells were significantly higher than those of MG-63 cells. In cell survival assay, cells were treated with cisplatin (CDDP) every 24 h for 2 days. The cell survival rate of MG-63 cells was significantly elevated by an FFA1 agonist TUG-770 as well as an FFA4 agonist TUG-891. Moreover, the cell survival rate of MG63-CR7(F2) cells was higher than that of MG-63 cells in the presence of TUG-770 or TUG-891, correlating with FFAR1 and FFAR4 expression levels. To validate the effects of FFA1 and FFA4 on cell survival to CDDP, FFA1 and FFA4 knockdown cell were generated from MG-63 cells. The cell survival rate of MG-63 cells was markedly inhibited by FFA1 or FFA4 knockdown. These results suggest that FFA1 and FFA4 may play an important role in the modulation of cellular functions by endothelial cells in osteosarcoma cells.

Agonism of GPR120 prevents ox-LDL-induced attachment of monocytes to endothelial cells

Oxidized low-density lipoprotein (ox-LDL)-induced endothelial inflammation plays an important role in the development of cardiovascular diseases. G protein-coupled receptors (GPCR) are gaining traction as potential treatment targets due to their roles in mediating a wide range of physiological processes. GPR120 is a recently identified omega-3 fatty acid receptor. We hypothesized that agonism of GPR120 might attenuate ox-LDL-induced endothelial dysfunction. In the present study, we tested the effects of two GPR120 agonists-GW9508 and TUG-891-in mitigating endothelial insult induced by ox-LDL in human aortic endothelial cells (HAECs). Real-time PCR, western blot, and ELISA analyses were used in our experiments. Our findings demonstrate that GPR120 is downregulated by exposure to ox-LDL, suggesting a role for GPR120 in mediating ox-LDL insult. Furthermore, we found that agonism of GPR120 could suppress oxidative stress and inflammation by inhibiting the production of reactive oxygen species and the expression of proinflammatory cytokines. Importantly, we show that agonism of GPR120 prevents the attachment of monocytes to endothelial cells by suppressing the expression of VCAM-1 and E-selectin. Finally, we show that agonism of GPR120 exerts a remarkable atheroprotective effect by elevating the expression level of Krüppel-like factor 2 (KLF2). Together, our results demonstrate a potential role for specific agonism of GPR120 in the prevention of endothelial damages induced by ox-LDL.

Effect of GSK-137647A, the first non-carboxylic FFA4 agonist, on the osteogenic and adipogenic differentiation of bone mesenchymal stem cells in db/db mice

OBJECTIVE

To investigate the effect of GSK-137647A, the first non-carboxylic FFA4 agonist, on osteogenic and adipogenic differentiation of bone mesenchymal stem cells (BMSCs) of db/db mice.

METHODS

Bone mesenchymal stem cells were extracted from 8-week-old db/db mice. Cell Counting Kit-8 was used to evaluate the toxicity of GSK-137647A on BMSCs, and the optimal concentration of GSK-137647A was selected to investigate the osteogenic and adipogenic differentiation of BMSCs, and relevant indicators of osteoblasts and adipocytes were detected.

KEY FINDINGS

GSK-137647A had no significant toxicity on cell growth and proliferation. Moreover, GSK-137647A showed a significant increase in mineralization of BMSCs differentiated osteoblasts compared to the control group and elevated the alkaline phosphatase (ALP) activity in a time-dependent manner. Meanwhile, the treatment of GSK-137647A decreased the adipogenic differentiation of BMSCs. The expression levels of ALP, runt-related transcription factor 2, bone morphogenetic protein 4, osterix and β-catenin were significantly increased in GSK-137647A-treated group, while the gene and protein levels of peroxisome proliferator-activated receptor γ and CCAAT/enhancer binding protein α were significantly reduced.

CONCLUSIONS

All of these results demonstrated that GSK-137647A suppressed the adipogenic differentiation and promoted osteogenic differentiation of BMSCs, which is partly attributed to the increased expression of β-catenin in wingless/integrated signalling pathway.

Free Fatty Acid Receptors as new potential therapeutic target in inflammatory bowel diseases

Family of Free Fatty Acid Receptors (FFARs), specific G protein-coupled receptors comprises of four members: FFAR1-4, where each responds to different chain length of fatty acids (FAs). Over the years, FFARs have become attractive pharmacological targets in the treatment of type 2 diabetes, metabolic syndrome, cardiovascular diseases and asthma; recent studies also point to their role in inflammation. It is now well-established that activation of FFAR1 and FFAR4 by long and medium chain FAs may lead to reduction of inflammatory state; FFAR2 and FFAR3 are activated by short chain FAs, but only FFAR2 was shown to alleviate inflammation, mostly by neutrophil inhibition. All FFARs have thus been proposed as targets in inflammatory bowel diseases (IBD). Here we discuss current knowledge and future directions in FFAR research related to IBD.

Novel GPR120 agonist TUG891 modulates fat taste perception and preference and activates tongue-brain-gut axis in mice

GPR120 is implicated as a lipid receptor in the oro-sensory detection of dietary fatty acids. However, the effects of GPR120 activation on dietary fat intake or obesity are not clearly understood. We investigated to determine whether the binding of TUG891, a novel GPR120 agonist, to lingual GPR120 modulates fat preference in mice. We explored the effects of TUG891 on obesity-related hormones and conducted behavioral choice tests on mice to better understand the physiologic relevance of the action of TUG891. In cultured mouse and human taste bud cells (TBCs), TUG891 induced a rapid increase in Ca²⁺ by acting on GPR120. A long-chain dietary fatty acid, linoleic acid (LA), also recruited Ca²⁺ via GPR120 in human and mouse TBCs. Both TUG891 and LA induced ERK1/2 phosphorylation and enhanced in vitro release of glucagon-like peptide-1 from cultured human and mouse TBCs. In situ application of TUG891 onto the tongue of anesthetized mice triggered the secretion of pancreatobiliary juice, probably via the tongue-brain-gut axis. Furthermore, lingual application of TUG891 altered circulating concentrations of cholecystokinin and adipokines, associated with decreased circulating LDL, in conscious mice. In behavioral tests, mice exhibited a spontaneous preference for solutions containing either TUG891 or LA instead of a control. However, addition of TUG891 to a solution containing LA significantly curtailed fatty acid preference. Our study demonstrates that TUG891 binds to lingual GPR120 receptors, activates the tongue-brain-gut axis, and modulates fat preference. These findings may support the development of new fat taste analogs that can change the approach to obesity prevention and treatment.