GPR120 suppresses adipose tissue lipolysis and synergizes with GPR40 in antidiabetic efficacy

Inverse agonism of the FFA4 free fatty acid receptor controls both adipogenesis and mature adipocyte function

Adipocyte disfunction is an important component of many metabolic disorders and there is a need for pharmacological approaches that can restore normal adipocyte function. The FFA4 receptor is a G protein coupled receptor (GPCR), activated by long chain free fatty acids (FFAs), that controls adipocyte function. Importantly, adipocytes produce FFAs, which may directly activate FFA4 and there is a need to better understand how FFAs produced by adipocytes interact with FFA4 signalling. In this study we have employed human and mouse adipocyte cell models to determine how pharmacological agonism or antagonism of FFA4 affects adipogenesis, lipolysis and glucose uptake. We show that a commonly used FFA4 antagonist, AH7614, is an inverse agonist and that treating adipocytes with this compound suppressed adipogenesis, inhibits glucose uptake and enhances isoprenaline stimulated lipolysis. In contrast, treatment with a synthetic FFA4 agonist, TUG-891, has only modest effects on adipogenesis and lipolysis, while showing no effect on glucose uptake. To explore the mechanism for why AH7614 but not TUG-891 affects adipocyte function, we demonstrate that during adipogenic differentiation sufficient FFAs are released into the culture medium to activate FFA4, suggesting AH7614 inhibits an autocrine feedback loop to suppress adipogenesis. In contrast, during lipolysis experiments, insufficient FFAs were released to activate the receptor, suggesting that AH7614 must enhance lipolysis by either inhibiting ligand independent FFA4 signalling, or FFA signalling that does not require the FFAs to be released from the cell. This study will help establish how FFA4 targeting therapeutics could be used to treat adipocyte dysfunction.

Assessing a Possibility of Divergent Metabolic Responses to Diet Adjustment and Changes of Eating Behaviours in Female Schizophrenia Patients

Background/Objectives: Individuals with schizophrenia are particularly susceptible to overweight, obesity, and metabolic disorders. This study was aimed at assessing the effects of approved diet adjustments, changed nutrition regimes, and eating behaviours on carbohydrate-lipid metabolism. Methods: This 3-year study involved 52 residents of a 24 h social welfare home for the chronically mentally ill. Diet adjustment involved balancing the diet energy content and nutrition value as well as changing the sources of basic nutrients. Both metabolic (concentrations of glucose, triglycerides, total cholesterol, and its HDL and LDL fractions) and anthropometric (body weight, waist circumference, hip circumference) parameters as well as body composition were monitored. Results: In almost all the subjects, including 12 female schizophrenia patients, diet adjustment and nutrition supervision resulted in beneficial changes in the parameters monitored. The exceptions were three women suffering from schizophrenia, who were sisters, in which glucose concentration declines (5.27 ± 0.22 mmol/L vs. 4.05 ± 0.36 mmol/L) were associated with increased concentrations of triglycerides (0.72 ± 0.17 mmol/L vs. 0.94 ± 0.32 mmol/L), total cholesterol (4.69 ± 0.70 mmol/L vs. 5.44 ± 0.38 mmol/L), and its LDL fraction (2.98 ± 0.65 mmol/L vs. 3.80 ± 0.41 mmol/L), as well as with a decreased HDL cholesterol fraction (1.38 ± 0.04 mmol/L vs. 1.30 ± 0.06 mmol/L). However, the observed changes were not statistically significant. Conclusions: It is concluded that diet adjustment and the improvement of nutrition regimes for people with schizophrenia does not always translate into improved parameters of carbohydrate-lipid metabolism.

Potential Therapeutic Exploitation of G Protein-Coupled Receptor 120 (GPR120/FFAR4) Signaling in Obesity-Related Metabolic Disorders

The increasing prevalence of overweight and obesity not only in adults but also among children and adolescents has become one of the most alarming health problems worldwide. Metabolic disorders accompanying fat accumulation during pathological weight gain induce chronic low-grade inflammation, which, in a vicious cycle, increases the immune response through pro-inflammatory changes in the cytokine (adipokine) profile. Obesity decreases life expectancy, largely because obese individuals are at an increased risk of many medical complications, often referred to as metabolic syndrome, which refers to the co-occurrence of insulin resistance (IR), impaired glucose tolerance, type 2 diabetes (T2D), atherogenic dyslipidemia, hypertension, and premature ischemic heart disease. Metabotropic G protein-coupled receptors (GPCRs) constitute the most numerous and diverse group of cell surface transmembrane receptors in eukaryotes. Among the GPCRs, researchers are focusing on the connection of G protein-coupled receptor 120 (GPR120), also known as free fatty acid receptor 4 (FFAR4), with signaling pathways regulating the inflammatory response and insulin sensitivity. This review presents the current state of knowledge concerning the involvement of GPR120 in anti-inflammatory and metabolic signaling. Since both inflammation in adipose tissue and insulin resistance are key problems in obesity, there is a rationale for the development of novel, GPR120-based therapies for overweight and obese individuals. The main problems associated with introducing this type of treatment into clinical practice are also discussed.

A phase IIb randomised-controlled trial of the FFAR1/FFAR4 agonist icosabutate in MASH

BACKGROUND & AIMS

Via regulation of glycaemic control and inflammation, free fatty receptor (FFAR)1 and 4 are potential targets for the treatment of metabolic dysfunction-associated steatohepatitis (MASH). In this study, we tested the efficacy and safety of icosabutate, a FFAR1/FFAR4 agonist, in patients with MASH.

METHODS

We performed a phase IIb, multicentre, 52-week, randomised, placebo-controlled trial (ICONA) testing the efficacy of icosabutate in patients with MASH and F1-F3 (mild to severe) fibrosis. Patients were randomised 1:1:1 to receive once-daily, oral icosabutate 300 mg, 600 mg or placebo for 52 weeks. The primary efficacy endpoint was the proportion of patients with MASH resolution with no worsening of fibrosis in the 600 mg arm.

RESULTS

The primary population for efficacy analysis comprised 187 patients (placebo [n = 62], 300 mg icosabutate [n = 58] or 600 mg icosabutate [n = 67]). The percentage of patients with MASH resolution favoured the icosabutate 600 mg arm without reaching statistical significance (23.9% vs. 14.5%; odds ratio 2.01; 95% CI 0.8-5.08; p = 0.13). A higher percentage of patients treated with icosabutate achieved a ≥1-stage improvement in fibrosis, with a response rate of 29.3% in the 300 mg arm (odds ratio 2.89; 95% CI 1.09-7.70) and 23.9% in the 600 mg arm (odds ratio 2.4; 95% CI 0.90-6.37) vs. 11.3% in the placebo arm. An improvement in fibrosis was observed using AI-assisted digital pathology. Marked decreases in biomarkers of liver damage were observed. Icosabutate was generally safe and well tolerated, with mild to moderate treatment-emergent adverse events and no reports of drug-induced liver injury.

CONCLUSION

Although the primary endpoint was not met, treatment with icosabutate was associated with encouraging fibrosis (as measured by both conventional and AI-assisted digital pathology) and non-invasive biomarker data, supporting further development in patients with MASH.

CLINICALTRIALS

GOV IDENTIFIER

NCT04052516.

IMPACT AND IMPLICATIONS

With expression on multiple cell types regulating both glycaemic control and liver inflammation, targeting free fatty acid receptors (FFAR)1 and 4 could offer an attractive approach for the treatment of both fibrosing metabolic dysfunction-assoicated steatohepatitis (MASH) and its comorbidities. Although treatment of patients with MASH and F1-F3 fibrosis with oral icosabutate (a FFAR1/FFAR4 agonist) did not meet the pre-defined primary endpoint (MASH resolution without worsening of fibrosis), the overall dataset (including AI-assisted digital pathology) suggest an improvement in fibrosis in treated patients. Improvements in multiple biomarkers of liver damage, inflammation and glycaemic control were observed in response to therapy. Icosabutate was generally safe and well tolerated, and the overall data support further testing of icosabutate in patients with MASH, in particular those with more advanced disease (F2-F3 fibrosis) and type 2 diabetes.

Implantation of engineered adipocytes suppresses tumor progression in cancer models

Tumors exhibit an increased ability to obtain and metabolize nutrients. Here, we implant engineered adipocytes that outcompete tumors for nutrients and show that they can substantially reduce cancer progression, a technology termed adipose manipulation transplantation (AMT). Adipocytes engineered to use increased amounts of glucose and fatty acids by upregulating UCP1 were placed alongside cancer cells or xenografts, leading to significant cancer suppression. Transplanting modulated adipose organoids in pancreatic or breast cancer genetic mouse models suppressed their growth and decreased angiogenesis and hypoxia. Co-culturing patient-derived engineered adipocytes with tumor organoids from dissected human breast cancers significantly suppressed cancer progression and proliferation. In addition, cancer growth was impaired by inducing engineered adipose organoids to outcompete tumors using tetracycline or placing them in an integrated cell-scaffold delivery platform and implanting them next to the tumor. Finally, we show that upregulating UPP1 in adipose organoids can outcompete a uridine-dependent pancreatic ductal adenocarcinoma for uridine and suppress its growth, demonstrating the potential customization of AMT.

Biased agonism at free-fatty acid receptor-4 (FFA4/GPR120)

Free-fatty acid receptor-4 (FFA4), previously known as GPR120, is a G protein-coupled receptor (GPCR) activated by medium-to-long chain free fatty acids (FFAs), including saturated, monounsaturated, and polyunsaturated fats, many of which (e.g., omega-3 fatty acids) are critical contributors to human health and disease. FFA4 is widely expressed across human tissues, and its activation supports a range of physiological functions, including the release of gastrointestinal incretin hormones like glucagon-like peptide-1 (GLP-1), regulation of pancreatic hormone secretion, peripheral glucose uptake, adipose regulation, and anti-inflammatory responses in macrophages. Due to its pivotal role in energy metabolism and inflammation, FFA4 has emerged as a major target in drug discovery. Historically, FFA4 signaling was linked to the Gαq/11 family of intracellular heterotrimeric G proteins, which mediate its GLP-1 releasing effects. However, emerging evidence indicates that FFA4 can signal through other Gα proteins in various cellular contexts. Notably, its anti-inflammatory effects are also dependent on interactions with β-arrestin proteins, further broadening the receptor's signaling versatility. This review explores the concept of biased agonism at FFA4, emphasizing how this receptor selectively signals through distinct transduction pathways, including Gα proteins and β-arrestins. We also examine the key structural elements of FFA4 that govern its interactions with different signaling partners, the elucidation of which has laid the groundwork for the development of biased agonists aimed at selectively modulating these FFA4-mediated pathways for therapeutic application.

Recent Developments in Drug Design of Oral Synthetic Free Fatty Acid Receptor 1 Agonists

Over the past two decades, synthetic FFAR1 agonists such as TAK-875 and TSL1806 have undergone meticulous design and extensive clinical trials. However, due to issues primarily related to hepatotoxicity, no FFAR1 agonist has yet received regulatory approval. Research into the sources of hepatotoxicity suggests that one potential cause lies in the molecular structure itself. These structures typically feature lipid-like carboxylic acid head groups, which tend to generate toxic metabolites. Strategies to mitigate these risks focus on optimizing chemical groups to reduce lipophilicity and prevent the formation of reactive metabolites. Recent studies have concentrated on developing low-molecular-weight compounds that more closely resemble natural products, with CPL207280 showing promising potential and liver safety, currently in Phase II clinical trials. Moreover, ongoing research continues to explore the potential applications of FFAR1 agonists in diabetes management, as well as in conditions such as non-alcoholic fatty liver disease (NAFLD) and cerebrovascular diseases. Utilizing advanced technologies such as artificial intelligence and computer-aided design, the development of compact molecules that mimic natural structures represents a hopeful direction for future research and development.

GPR40/GPR120 Agonist GW9508 Improves Metabolic Syndrome-Exacerbated Periodontitis in Mice

G protein-coupled receptor (GPR)40 and GPR120 are receptors for medium- and long-chain free fatty acids. It has been well documented that GPR40 and GPR120 activation improves metabolic syndrome (MetS) and exerts anti-inflammatory effects. Since chronic periodontitis is a common oral inflammatory disease initiated by periodontal pathogens and exacerbated by MetS, we determined if GPR40 and GPR120 activation with agonists improves MetS-associated periodontitis in animal models in this study. We induced MetS and periodontitis by high-fat diet feeding and periodontal injection of lipopolysaccharide, respectively, and treated mice with GW9508, a synthetic GPR40 and GPR120 dual agonist. We determined alveolar bone loss, osteoclast formation, and periodontal inflammation using micro-computed tomography, osteoclast staining, and histology. To understand the underlying mechanisms, we further performed studies to determine the effects of GW9508 on osteoclastogenesis and proinflammatory gene expression in vitro. Results showed that GW9508 improved metabolic parameters, including glucose, lipids, and insulin resistance. Results also showed that GW9508 improves periodontitis by reducing alveolar bone loss, osteoclastogenesis, and periodontal inflammation. Finally, in vitro studies showed that GW9508 inhibited osteoclast formation and proinflammatory gene secretion from macrophages. In conclusion, this study demonstrated for the first time that GPR40/GPR120 agonist GW9508 reduced alveolar bone loss and alleviated periodontal inflammation in mice with MetS-exacerbated periodontitis, suggesting that activating GPR40/GPR120 with agonist GW9508 is a potential anti-inflammatory approach for the treatment of MetS-associated periodontitis.

EPA and DHA differentially improve insulin resistance by reducing adipose tissue inflammation-targeting GPR120/PPARγ pathway

Insulin resistance (IR) is a global health challenge, often initiated by dysfunctional adipose tissue. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may have different effects on IR, but the mechanisms are unknown. This study aims to evaluate the protective effect of EPA and DHA against IR in a high-fat diet (HFD) mice model and investigate whether EPA and DHA alter IR modulate the G-protein-poupled receptor 120/peroxisome proliferator-activated receptor γ (GPR120/PPARγ) pathway in macrophages and adipocytes, which may affect IR in adipocytes. The findings of this study show that 4% DHA had a better effect in improving IR and reducing inflammatory cytokines in adipose tissue of mice. Additionally, in the cell experiment, the use of AH7614 (a GPR120 antagonist) inhibited the glucose consumption increase and the increasable expression of PPARγ and insulin signaling molecules mediated by DHA in adipocytes. Furthermore, GW9662 (a PPARγ antagonist) hindered the upregulation of glucose consumption and insulin signaling molecule expression induced by EPA and DHA in adipocytes. DHA exhibited significant effects in reducing the number of migrated cells and inflammation. The compounds AH7614 and GW9662 hindered the suppressive effects of EPA and DHA on macrophage-induced IR in adipocytes. These findings suggest that DHA has a stronger potential in improving IR in adipocytes through the GPR120/PPARγ pathway in macrophages, when compared to EPA.

Chronic administration of hydrolysed pine nut oil to mice improves insulin sensitivity and glucose tolerance and increases energy expenditure via a free fatty acid receptor 4-dependent mechanism

A healthy diet is at the forefront of measures to prevent type 2 diabetes. Certain vegetable and fish oils, such as pine nut oil (PNO), have been demonstrated to ameliorate the adverse metabolic effects of a high-fat diet. The present study investigates the involvement of the free fatty acid receptors 1 (FFAR1) and 4 (FFAR4) in the chronic activity of hydrolysed PNO (hPNO) on high-fat diet-induced obesity and insulin resistance. Male C57BL/6J wild-type, FFAR1 knockout (-/-) and FFAR4-/- mice were placed on 60 % high-fat diet for 3 months. Mice were then dosed hPNO for 24 d, during which time body composition, energy intake and expenditure, glucose tolerance and fasting plasma insulin, leptin and adiponectin were measured. hPNO improved glucose tolerance and decreased plasma insulin in the wild-type and FFAR1-/- mice, but not the FFAR4-/- mice. hPNO also decreased high-fat diet-induced body weight gain and fat mass, whilst increasing energy expenditure and plasma adiponectin. None of these effects on energy balance were statistically significant in FFAR4-/- mice, but it was not shown that they were significantly less than in wild-type mice. In conclusion, chronic hPNO supplementation reduces the metabolically detrimental effects of high-fat diet on obesity and insulin resistance in a manner that is dependent on the presence of FFAR4.

GPCRs involved in metabolic diseases: pharmacotherapeutic development updates

G protein-coupled receptors (GPCRs) are expressed in a variety of cell types and tissues, and activation of GPCRs is involved in enormous metabolic pathways, including nutrient synthesis, transportation, storage or insulin sensitivity, etc. This review intends to summarize the regulation of metabolic homeostasis and mechanisms by a series of GPCRs, such as GPR91, GPR55, GPR119, GPR109a, GPR142, GPR40, GPR41, GPR43 and GPR120. With deep understanding of GPCR's structure and signaling pathways, it is attempting to uncover the role of GPCRs in major metabolic diseases, including metabolic syndrome, diabetes, dyslipidemia and nonalcoholic steatohepatitis, for which the global prevalence has risen during last two decades. An extensive list of agonists and antagonists with their chemical structures in a nature of small molecular compounds for above-mentioned GPCRs is provided as pharmacologic candidates, and their preliminary data of preclinical studies are discussed. Moreover, their beneficial effects in correcting abnormalities of metabolic syndrome, diabetes and dyslipidemia are summarized when clinical trials have been undertaken. Thus, accumulating data suggest that these agonists or antagonists might become as new pharmacotherapeutic candidates for the treatment of metabolic diseases.

G protein-coupled receptors driven intestinal glucagon-like peptide-1 reprogramming for obesity: Hope or hype?

'Globesity' is a foremost challenge to the healthcare system. The limited efficacy and adverse effects of available oral pharmacotherapies pose a significant obstacle in the fight against obesity. The biology of the leading incretin hormone glucagon-like-peptide-1 (GLP-1) has been highly captivated during the last decade owing to its multisystemic pleiotropic clinical outcomes beyond inherent glucoregulatory action. That fostered a pharmaceutical interest in synthetic GLP-1 analogues to tackle type-2 diabetes (T2D), obesity and related complications. Besides, mechanistic insights on metabolic surgeries allude to an incretin-based hormonal combination strategy for weight loss that emerged as a forerunner for the discovery of injectable 'unimolecular poly-incretin-agonist' therapies. Physiologically, intestinal enteroendocrine L-cells (EECs) are the prominent endogenous source of GLP-1 peptide. Despite comprehending the potential of various G protein-coupled receptors (GPCRs) to stimulate endogenous GLP-1 secretion, decades of translational GPCR research have failed to yield regulatory-approved endogenous GLP-1 secretagogue oral therapy. Lately, a dual/poly-GPCR agonism strategy has emerged as an alternative approach to the traditional mono-GPCR concept. This review aims to gain a comprehensive understanding by revisiting the pharmacology of a few potential GPCR-based complementary avenues that have drawn attention to the design of orally active poly-GPCR agonist therapy. The merits, challenges and recent developments that may aid future poly-GPCR drug discovery are critically discussed. Subsequently, we project the mechanism-based therapeutic potential and limitations of oral poly-GPCR agonism strategy to augment intestinal GLP-1 for weight loss. We further extend our discussion to compare the poly-GPCR agonism approach over invasive surgical and injectable GLP-1-based regimens currently in clinical practice for obesity.

Palmitic acid-activated GPRs/KLF7/CCL2 pathway is involved in the crosstalk between bone marrow adipocytes and prostate cancer

BACKGROUND

Obesity-induced abnormal bone marrow microenvironment is one of the important risk element for bone metastasis in prostate cancer (PCa). The present study aimed to determine whether obesity-induced elevation in palmitic acid (PA), which is the most abundant of the free fatty acids (FFAs), increased CCL2 via the GPRs/KLF7 pathway in bone marrow adipocytes (BMA) to facilitate PCa growth and metastasis.

METHODS

We constructed a bone-tumor bearing mouse model with obesity through high-fat diet, and observed the tumor formation ability of PCa cells. In vitro, observe the effect of PA on the expression level of CCL2 in BMA through GPRs/KLF7 signaling pathway. After co-culture of BMA and PCa cells, CCK8 assay and transwell experiment were used to detect the changes in biological behavior of PCa cells stimulated by BMA.

RESULTS

The BMA distribution in the bone marrow cavity of BALB/c nude mice fed with the high-fat diet (HFD) was evidently higher than that in the mice fed with the normal diet (ND). Moreover, HFD-induced obesity promoted KLF7/CCL2 expression in BMA and PCa cell growth in the bone marrow cavity of the mice. In the vitro experiment, a conditioned medium with increased CCL2 obtained from the BMA cultured with PA (CM-BMA-PA) was used for culturing the PCa cell lines, which evidently enhanced the proliferation, invasion, and migration ability. KLF7 significantly increased the CCL2 expression and secretion levels in BMA by targeting the promoter region of the CCL2 gene. In addition, GPR40/120 engaged in the PA-induced high KLF7/CCL2 levels in BMA to facilitate the malignant progression of PC-3 cells.

CONCLUSIONS

PA-activated GPRs/KLF7/CCL2 pathway in BMA facilitates prostate cancer growth and metastasis.

HILPDA is a lipotoxic marker in adipocytes that mediates the autocrine negative feedback regulation of triglyceride hydrolysis by fatty acids and alleviates cellular lipotoxic stress

BACKGROUND

Lipolysis is a key metabolic pathway in adipocytes that renders stored triglycerides available for use by other cells and tissues. Non-esterified fatty acids (NEFAs) are known to exert feedback inhibition on adipocyte lipolysis, but the underlying mechanisms have only partly been elucidated. An essential enzyme in adipocyte lipolysis is ATGL. Here, we examined the role of the ATGL inhibitor HILPDA in the negative feedback regulation of adipocyte lipolysis by fatty acids.

METHODS

We exposed wild-type, HILPDA-deficient and HILPDA-overexpressing adipocytes and mice to various treatments. HILPDA and ATGL protein levels were determined by Western blot. ER stress was assessed by measuring the expression of marker genes and proteins. Lipolysis was studied in vitro and in vivo by measuring NEFA and glycerol levels.

RESULTS

We show that HILPDA mediates a fatty acid-induced autocrine feedback loop in which elevated intra- or extracellular fatty acids levels upregulate HILPDA by activation of the ER stress response and the fatty acid receptor 4 (FFAR4). The increased HILPDA levels in turn downregulate ATGL protein levels to suppress intracellular lipolysis, thereby maintaining lipid homeostasis. The deficiency of HILPDA under conditions of excessive fatty acid load disrupts this chain of events, leading to elevated lipotoxic stress in adipocytes.

CONCLUSION

Our data indicate that HILPDA is a lipotoxic marker in adipocytes that mediates a negative feedback regulation of lipolysis by fatty acids via ATGL and alleviates cellular lipotoxic stress.

Metabolite-sensing GPCRs controlling interactions between adipose tissue and inflammation

Metabolic disorders including obesity, diabetes and non-alcoholic steatohepatitis are a group of conditions characterised by chronic low-grade inflammation of metabolic tissues. There is now a growing appreciation that various metabolites released from adipose tissue serve as key signalling mediators, influencing this interaction with inflammation. G protein-coupled receptors (GPCRs) are the largest family of signal transduction proteins and most historically successful drug targets. The signalling pathways for several key adipose metabolites are mediated through GPCRs expressed both on the adipocytes themselves and on infiltrating macrophages. These include three main groups of GPCRs: the FFA4 receptor, which is activated by long chain free fatty acids; the HCA₂ and HCA₃ receptors, activated by hydroxy carboxylic acids; and the succinate receptor. Understanding the roles these metabolites and their receptors play in metabolic-immune interactions is critical to establishing how these GPCRs may be exploited for the treatment of metabolic disorders.

Implantation of engineered adipocytes that outcompete tumors for resources suppresses cancer progression

Tumors acquire an increased ability to obtain and metabolize nutrients. Here, we engineered and implanted adipocytes to outcompete tumors for nutrients and show that they can substantially reduce cancer progression. Growing cells or xenografts from several cancers (breast, colon, pancreas, prostate) alongside engineered human adipocytes or adipose organoids significantly suppresses cancer progression and reduces hypoxia and angiogenesis. Transplanting modulated adipocyte organoids in pancreatic or breast cancer mouse models nearby or distal from the tumor significantly suppresses its growth. To further showcase therapeutic potential, we demonstrate that co-culturing tumor organoids derived from human breast cancers with engineered patient-derived adipocytes significantly reduces cancer growth. Combined, our results introduce a novel cancer therapeutic approach, termed adipose modulation transplantation (AMT), that can be utilized for a broad range of cancers.

GPCR in Adipose Tissue Function-Focus on Lipolysis

Adipose tissue can be divided anatomically, histologically, and functionally into two major entities white and brown adipose tissues (WAT and BAT, respectively). WAT is the primary energy depot, storing most of the bioavailable triacylglycerol molecules of the body, whereas BAT is designed for dissipating energy in the form of heat, a process also known as non-shivering thermogenesis as a defense against a cold environment. Importantly, BAT-dependent energy dissipation directly correlates with cardiometabolic health and has been postulated as an intriguing target for anti-obesity therapies. In general, adipose tissue (AT) lipid content is defined by lipid uptake and lipogenesis on one side, and, on the other side, it is defined by the breakdown of lipids and the release of fatty acids by lipolysis. The equilibrium between lipogenesis and lipolysis is important for adipocyte and general metabolic homeostasis. Overloading adipocytes with lipids causes cell stress, leading to the recruitment of immune cells and adipose tissue inflammation, which can affect the whole organism (metaflammation). The most important consequence of energy and lipid overload is obesity and associated pathophysiologies, including insulin resistance, type 2 diabetes, and cardiovascular disease. The fate of lipolysis products (fatty acids and glycerol) largely differs between AT: WAT releases fatty acids into the blood to deliver energy to other tissues (e.g., muscle). Activation of BAT, instead, liberates fatty acids that are used within brown adipocyte mitochondria for thermogenesis. The enzymes involved in lipolysis are tightly regulated by the second messenger cyclic adenosine monophosphate (cAMP), which is activated or inhibited by G protein-coupled receptors (GPCRs) that interact with heterotrimeric G proteins (G proteins). Thus, GPCRs are the upstream regulators of the equilibrium between lipogenesis and lipolysis. Moreover, GPCRs are of special pharmacological interest because about one third of the approved drugs target GPCRs. Here, we will discuss the effects of some of most studied as well as "novel" GPCRs and their ligands. We will review different facets of in vitro, ex vivo, and in vivo studies, obtained with both pharmacological and genetic approaches. Finally, we will report some possible therapeutic strategies to treat obesity employing GPCRs as primary target.

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.

Comparison of two anti-diabetic monoestolides regarding effects on intact murine liver tissue

CONTEXT

Monoestolides belonging to the fatty acid-hydroxy fatty acid (FAHFA) family have recently emerged as promising insulin sensitizers.

OBJECTIVE

To investigate and compare impact of two selected FAHFA isomers, namely 9-hexadecanoyloxy-octadecanoic acid [9-PAHSA] and 9-(9Z-octadecenoyloxy)-octadecanoic acid [9-OAHSA], on intact livers in C57BL/6J mice.

MATERIALS AND METHODS

Short-term in vivo study with intragastric gavage of 13 mg/kg of substances. Morphological, biochemical and high-resolution respirometric assessment of plasma and liver tissue or homogenates thereof.

RESULTS

The 9-OAHSA-gavaged mice had the highest final total body weight, the lowest free fatty acid circulating levels and the highest plasma activities of both ALT and AST. No significant changes of ambient glycaemia were found, however 9-PAHSA-gavaged mice tended to have lower glycaemia than other animals. Respirometry proved no substance-dependent differences.

DISCUSSION AND CONCLUSION

9-PAHSA was more metabolically beneficial and less hepatotoxic than 9-OAHSA. Bioenergetic machinery of liver homogenates seemed unaffected at our FAHFA dose.

Revisiting the concept of incretin and enteroendocrine L-cells as type 2 diabetes mellitus treatment

The significant growth in type 2 diabetes mellitus (T2DM) prevalence strikes a common threat to the healthcare and economic systems globally. Despite the availability of several anti-hyperglycaemic agents in the market, none can offer T2DM remission. These agents include the prominent incretin-based therapy such as glucagon-like peptide-1 receptor (GLP-1R) agonists and dipeptidyl peptidase-4 inhibitors that are designed primarily to promote GLP-1R activation. Recent interest in various therapeutically useful gastrointestinal hormones in T2DM and obesity has surged with the realisation that enteroendocrine L-cells modulate the different incretins secretion and glucose homeostasis, reflecting the original incretin definition. Targeting L-cells offers promising opportunities to mimic the benefits of bariatric surgery on glucose homeostasis, bodyweight management, and T2DM remission. Revising the fundamental incretin theory is an essential step for therapeutic development in this area. Therefore, the present review explores enteroendocrine L-cell hormone expression, the associated nutrient-sensing mechanisms, and other physiological characteristics. Subsequently, enteroendocrine L-cell line models and the latest L-cell targeted therapies are reviewed critically in this paper. Bariatric surgery, pharmacotherapy and new paradigm of L-cell targeted pharmaceutical formulation are discussed here, offering both clinician and scientist communities a new common interest to push the scientific boundary in T2DM therapy.

Metabolite G-Protein Coupled Receptors in Cardio-Metabolic Diseases

G protein-coupled receptors (GPCRs) have originally been described as a family of receptors activated by hormones, neurotransmitters, and other mediators. However, in recent years GPCRs have shown to bind endogenous metabolites, which serve functions other than as signaling mediators. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Naturally occurring mutations in G protein-coupled receptors associated with obesity and type 2 diabetes mellitus

G protein-coupled receptors (GPCRs) are the largest family of membrane receptors involved in the regulation of almost all known physiological processes. Dysfunctions of GPCR-mediated signaling have been shown to cause various diseases. The prevalence of obesity and type 2 diabetes mellitus (T2DM), two strongly associated disorders, is increasing worldwide, with tremendous economical and health burden. New safer and more efficacious drugs are required for successful weight reduction and T2DM treatment. Multiple GPCRs are involved in the regulation of energy and glucose homeostasis. Mutations in these GPCRs contribute to the development and progression of obesity and T2DM. Therefore, these receptors can be therapeutic targets for obesity and T2DM. Indeed some of these receptors, such as melanocortin-4 receptor and glucagon-like peptide 1 receptor, have provided important new drugs for treating obesity and T2DM. This review will focus on the naturally occurring mutations of several GPCRs associated with obesity and T2DM, especially incorporating recent large genomic data and insights from structure-function studies, providing leads for future investigations.

A new synthetic dual agonist of GPR120/GPR40 induces GLP-1 secretion and improves glucose homeostasis in mice

G-protein coupled receptors 40 and 120 (GPR40 and GPR120) are increasingly emerging as potential therapeutic targets for the treatment of altered glucose homeostasis, and their agonists are under evaluation for their glucagon-like peptide-1 (GLP-1)-mediated therapeutic effects on insulin production and sensitivity. Here, we characterized a new dual GPR40 and GPR120 agonist (DFL23916) and demonstrated that it can induce GLP-1 secretion and improve glucose homeostasis. Resulting from a rational drug design approach aimed at identifying new dual GPR120/40 agonists able to delay receptor internalization, DFL23916 had a good activity and a very high selectivity towards human GPR120 (long and short isoforms) and GPR40, as well as towards their mouse orthologous, by which it induced both Gαq/11-initiated signal transduction pathways with subsequent Ca2+ intracellular spikes and G protein-independent signaling via β-arrestin with the same activity. Compared to the endogenous ligand alpha-linolenic acid (ALA), a selective GPR120 agonist (TUG-891) and a well-known dual GPR40 and GPR120 agonist (GW9508), DFL23916 was the most effective in inducing GLP-1 secretion in human and murine enteroendocrine cells, and this could be due to the delayed internalization of the receptor (up to 3 h) that we observed after treatment with DFL23916. With a good pharmacokinetic/ADME profile, DFL23916 significantly increased GLP-1 portal vein levels in healthy mice, demonstrating that it can efficiently induce GLP-1 secretion in vivo. Contrary to the selective GPR120 agonist (TUG-891), DFL23916 significantly improved also glucose homeostasis in mice undergoing an oral glucose tolerance test (OGTT).

Fa(c)t checking: How fatty acids shape metabolism and function of macrophages and dendritic cells

In recent years there have been major advances in our understanding of the role of free fatty acids (FAs) and their metabolism in shaping the functional properties of macrophages and DCs. This review presents the most recent insights into how cell intrinsic FA metabolism controls DC and macrophage function, as well as the current evidence of the importance of various exogenous FAs (such as polyunsaturated FAs and their oxidation products—prostaglandins, leukotrienes, and proresolving lipid mediators) in affecting DC and macrophage biology, by modulating their metabolic properties. Finally, we explore whether targeted modulation of FA metabolism of myeloid cells to steer their function could hold promise in therapeutic settings.

Targeting lipid GPCRs to treat type 2 diabetes mellitus - progress and challenges

Therapeutic approaches to the treatment of type 2 diabetes mellitus that are designed to increase insulin secretion either directly target β-cells or indirectly target gastrointestinal enteroendocrine cells (EECs), which release hormones that modulate insulin secretion (for example, incretins). Given that β-cells and EECs both express a large array of G protein-coupled receptors (GPCRs) that modulate insulin secretion, considerable research and development efforts have been undertaken to design therapeutic drugs targeting these GPCRs. Among them are GPCRs specific for free fatty acid ligands (lipid GPCRs), including free fatty acid receptor 1 (FFA1, otherwise known as GPR40), FFA2 (GPR43), FFA3 (GPR41) and FFA4 (GPR120), as well as the lipid metabolite binding glucose-dependent insulinotropic receptor (GPR119). These lipid GPCRs have demonstrated important roles in the control of islet and gut hormone secretion. Advances in lipid GPCR pharmacology have led to the identification of a number of synthetic agonists that exert beneficial effects on glucose homeostasis in preclinical studies. Yet, translation of these promising results to the clinic has so far been disappointing. In this Review, we present the physiological roles, pharmacology and clinical studies of these lipid receptors and discuss the challenges associated with their clinical development for the treatment of type 2 diabetes mellitus.

Combined Deletion of Free Fatty-Acid Receptors 1 and 4 Minimally Impacts Glucose Homeostasis in Mice

The free fatty-acid receptors FFAR1 (GPR40) and FFAR4 (GPR120) are implicated in the regulation of insulin secretion and insulin sensitivity, respectively. Although GPR120 and GPR40 share similar ligands, few studies have addressed possible interactions between these 2 receptors in the control of glucose homeostasis. Here we generated mice deficient in gpr120 (Gpr120KO) or gpr40 (Gpr40KO), alone or in combination (Gpr120/40KO), and metabolically phenotyped male and female mice fed a normal chow or high-fat diet. We assessed insulin secretion in isolated mouse islets exposed to selective GPR120 and GPR40 agonists singly or in combination. Following normal chow feeding, body weight and energy intake were unaffected by deletion of either receptor, although fat mass increased in Gpr120KO females. Fasting blood glucose levels were mildly increased in Gpr120/40KO mice and in a sex-dependent manner in Gpr120KO and Gpr40KO animals. Oral glucose tolerance was slightly reduced in male Gpr120/40KO mice and in Gpr120KO females, whereas insulin secretion and insulin sensitivity were unaffected. In hyperglycemic clamps, the glucose infusion rate was lower in male Gpr120/40KO mice, but insulin and c-peptide levels were unaffected. No changes in glucose tolerance were observed in either single or double knock-out animals under high-fat feeding. In isolated islets from wild-type mice, the combination of selective GPR120 and GPR40 agonists additively increased insulin secretion. We conclude that while simultaneous activation of GPR120 and GPR40 enhances insulin secretion ex vivo, combined deletion of these 2 receptors only minimally affects glucose homeostasis in vivo in mice.

Autocrine negative feedback regulation of lipolysis through sensing of NEFAs by FFAR4/GPR120 in WAT

OBJECTIVES

Long-chain fatty acids (LCFAs) released from adipocytes inhibit lipolysis through an unclear mechanism. We hypothesized that the LCFA receptor, FFAR4 (GPR120), which is highly expressed in adipocytes, may be involved in this feedback regulation.

METHODS AND RESULTS

Liquid chromatography mass spectrometry (LC-MS) analysis of conditioned media from isoproterenol-stimulated primary cultures of murine and human adipocytes demonstrated that most of the released non-esterified free fatty acids (NEFAs) are known agonists for FFAR4. In agreement with this, conditioned medium from isoproterenol-treated adipocytes stimulated signaling strongly in FFAR4 transfected COS-7 cells as opposed to non-transfected control cells. In transfected 3T3-L1 cells, FFAR4 agonism stimulated Gi- and Go-mini G protein binding more strongly than Gq, effects which were blocked by the selective FFAR4 antagonist AH7614. In primary cultures of murine white adipocytes, the synthetic, selective FFAR4 agonist CpdA inhibited isoproterenol-induced intracellular cAMP accumulation in a manner similar to the antilipolytic control agent nicotinic acid acting through another receptor, HCAR2. In vivo, oral gavage with the synthetic, specific FFAR4 agonist CpdB decreased the level of circulating NEFAs in fasting lean mice to a similar degree as nicotinic acid. In agreement with the identified anti-lipolytic effect of FFAR4, plasma NEFAs and glycerol were increased in FFAR4-deficient mice as compared to littermate controls despite having elevated insulin levels, and cAMP accumulation in primary adipocyte cultures was augmented by treatment with the FFAR4 antagonist conceivably by blocking the stimulatory tone of endogenous NEFAs on FFAR4.

CONCLUSIONS

In white adipocytes, FFAR4 functions as an NEFA-activated, autocrine, negative feedback regulator of lipolysis by decreasing cAMP though Gi-mediated signaling.

n-3 polyunsaturated fatty acids regulate chemerin in cultured adipocytes: role of GPR120 and derived lipid mediators

Chemerin is a pro-inflammatory adipokine that is increased in obesity and associated with obesity-related comorbidities. The aim of this study was to investigate the effects of omega-3 polyunsaturated fatty acids, eicosapentaenoic and docosahexaenoic acids (EPA and DHA), on basal and tumor necrosis factor-α (TNF-α)-induced chemerin production in 3T3-L1 and human subcutaneous cultured adipocytes. The potential involvement of G protein-coupled receptor 120 (GPR120), as well as the actions of DHA-derived specialized proresolving lipid mediators (SPMs), resolvin D1 and D2 (RvD1 and RvD2) and maresin 1 (MaR1), were also evaluated. DHA significantly lowered both basal and TNF-α-stimulated chemerin production in 3T3-L1 and human adipocytes. EPA did not modify basal chemerin production, while it attenuated the induction of chemerin by TNF-α. Silencing of GPR120 using siRNA blocked the ability of DHA and EPA to reduce TNF-α-induced chemerin secretion. Interestingly, treatment with the DHA-derived SPMs RvD1, RvD2 and MaR1 also reversed the stimulatory effect of TNF-α on chemerin production in human adipocytes.

Fatty acid mimetic PBI-4547 restores metabolic homeostasis via GPR84 in mice with non-alcoholic fatty liver disease

Non-alcoholic Fatty Liver Disease (NAFLD) is the most common form of liver disease and is associated with metabolic dysregulation. Although G protein-coupled receptor 84 (GPR84) has been associated with inflammation, its role in metabolic regulation remains elusive. The aim of our study was to evaluate the potential of PBI-4547 for the treatment of NAFLD and to validate the role of its main target receptor, GPR84. We report that PBI-4547 is a fatty acid mimetic, acting concomitantly as a GPR84 antagonist and GPR40/GPR120 agonist. In a mouse model of diet-induced obesity, PBI-4547 treatment improved metabolic dysregulation, reduced hepatic steatosis, ballooning and NAFLD score. PBI-4547 stimulated fatty acid oxidation and induced gene expression of mitochondrial uncoupling proteins in the liver. Liver metabolomics revealed that PBI-4547 improved metabolic dysregulation induced by a high-fat diet regimen. In Gpr84^−/− mice, PBI-4547 treatment failed to improve various key NAFLD-associated parameters, as was observed in wildtype littermates. Taken together, these results highlight a detrimental role for the GPR84 receptor in the context of meta-inflammation and suggest that GPR84 antagonism via PBI-4547 may reflect a novel treatment approach for NAFLD and its related complications.

A Novel Model of Diabetic Complications: Adipocyte Mitochondrial Dysfunction Triggers Massive β-Cell Hyperplasia

Obesity-associated type 2 diabetes mellitus (T2DM) entails insulin resistance and loss of β-cell mass. Adipose tissue mitochondrial dysfunction is emerging as a key component in the etiology of T2DM. Identifying approaches to preserve mitochondrial function, adipose tissue integrity, and β-cell mass during obesity is a major challenge. Mitochondrial ferritin (FtMT) is a mitochondrial matrix protein that chelates iron. We sought to determine whether perturbation of adipocyte mitochondria influences energy metabolism during obesity. We used an adipocyte-specific doxycycline-inducible mouse model of FtMT overexpression (FtMT-Adip mice). During a dietary challenge, FtMT-Adip mice are leaner but exhibit glucose intolerance, low adiponectin levels, increased reactive oxygen species damage, and elevated GDF15 and FGF21 levels, indicating metabolically dysfunctional fat. Paradoxically, despite harboring highly dysfunctional fat, transgenic mice display massive β-cell hyperplasia, reflecting a beneficial mitochondria-induced fat-to-pancreas interorgan signaling axis. This identifies the unique and critical impact that adipocyte mitochondrial dysfunction has on increasing β-cell mass during obesity-related insulin resistance.

Mitochondrial 2,4-dienoyl-CoA reductase (Decr) deficiency and impairment of thermogenesis in mouse brown adipose tissue

A large number of studies have demonstrated significance of polyunsaturated fatty acids (PUFAs) for human health. However, many aspects on signals translating PUFA-sensing into body homeostasis have remained enigmatic. To shed light on PUFA physiology, we have generated a mouse line defective in mitochondrial dienoyl-CoA reductase (Decr), which is a key enzyme required for β-oxidation of PUFAs. Previously, we have shown that these mice, whose oxidation of saturated fatty acid is intact but break-down of unsaturated fatty acids is blunted, develop severe hypoglycemia during metabolic stresses and fatal hypothermia upon acute cold challenge. In the current work, indirect calorimetry and thermography suggested that cold intolerance of Decr^−/− mice is due to failure in maintaining appropriate heat production at least partly due to failure of brown adipose tissue (BAT) thermogenesis. Magnetic resonance imaging, electron microscopy, mass spectrometry and biochemical analysis showed attenuation in activation of lipolysis despite of functional NE-signaling and inappropriate expression of genes contributing to thermogenesis in iBAT when the Decr^−/− mice were exposed to cold. We hypothesize that the failure in turning on BAT thermogenesis occurs due to accumulation of unsaturated long-chain fatty acids or their metabolites in Decr^−/− mice BAT suppressing down-stream propagation of NE-signaling.

The current state of GPCR-based drug discovery to treat metabolic disease

One approach of modern drug discovery is to identify agents that enhance or diminish signal transduction cascades in various cell types and tissues by modulating the activity of GPCRs. This strategy has resulted in the development of new medicines to treat many conditions, including cardiovascular disease, psychiatric disorders, HIV/AIDS, certain forms of cancer and Type 2 diabetes mellitus (T2DM). These successes justify further pursuit of GPCRs as disease targets and provide key learning that should help guide identifying future therapeutic agents. This report reviews the current landscape of GPCR drug discovery with emphasis on efforts aimed at developing new molecules for treating T2DM and obesity. We analyse historical efforts to generate GPCR-based drugs to treat metabolic disease in terms of causal factors leading to success and failure in this endeavour.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

The HETE Is on FFAR1 and Pancreatic Islet Cells

It is known but generally unappreciated that the fatty acid receptor FFAR1 (GPR40) is responsible for a major part of glucose-induced insulin secretion. This puzzling fact is now explained by Tunaru et al. (2018), who demonstrate that glucose-induced 20-hydroxyeicosatetraenoic acid (20-HETE) amplifies insulin secretion through autocrine activation of FFAR1.

Dissecting the Physiology and Pathophysiology of Glucagon-Like Peptide-1

An aging world population exposed to a sedentary life style is currently plagued by chronic metabolic diseases, such as type-2 diabetes, that are spreading worldwide at an unprecedented rate. One of the most promising pharmacological approaches for the management of type 2 diabetes takes advantage of the peptide hormone glucagon-like peptide-1 (GLP-1) under the form of protease resistant mimetics, and DPP-IV inhibitors. Despite the improved quality of life, long-term treatments with these new classes of drugs are riddled with serious and life-threatening side-effects, with no overall cure of the disease. New evidence is shedding more light over the complex physiology of GLP-1 in health and metabolic diseases. Herein, we discuss the most recent advancements in the biology of gut receptors known to induce the secretion of GLP-1, to bridge the multiple gaps into our understanding of its physiology and pathology.