GPR119 as a fat sensor

Beyond the silence: A comprehensive exploration of long non-coding RNAs as genetic whispers and their essential regulatory functions in cardiovascular disorders

Long non-coding RNAs (lncRNAs) are RNA molecules that regulate gene expression at several levels, including transcriptional, post-transcriptional, and translational. They have a length of more than 200 nucleotides and cannot code. Many human diseases have been linked to aberrant lncRNA expression, highlighting the need for a better knowledge of disease etiology to drive improvements in diagnostic, prognostic, and therapeutic methods. Cardiovascular diseases (CVDs) are one of the leading causes of death worldwide. LncRNAs play an essential role in the complex process of heart formation, and their abnormalities have been associated with several CVDs. This Review article looks at the roles and relationships of long non-coding RNAs (lncRNAs) in a wide range of CVDs, such as heart failure, myocardial infarction, atherosclerosis, and cardiac hypertrophy. In addition, the review delves into the possible uses of lncRNAs in diagnostics, prognosis, and clinical treatments of cardiovascular diseases. Additionally, it considers the field's future prospects while examining how lncRNAs might be altered and its clinical applications.

Dietary Vitamin A Affects the Function of Incretin-Producing Enteroendocrine Cells in Male Mice Fed a High-Fat Diet

BACKGROUND

Retinol-binding protein 2 (RBP2) is an intracellular carrier for vitamin A in the absorptive enterocytes. Mice lacking RBP2 (Rbp2-/-) display an unexpected phenotype of obesity, glucose intolerance, and elevated glucose-dependent insulinotropic polypeptide (GIP) levels. GIP and glucagon-like peptide 1 (GLP-1) are incretin hormones secreted by enteroendocrine cells (EECs). We recently demonstrated the presence of RBP2 and other retinoid-related proteins in EECs.

OBJECTIVES

Given RBP2's role in intracellular retinoid trafficking, we aimed to evaluate whether dietary vitamin A affects incretin-secreting cell function and gene expression.

METHODS

Male Rbp2-/- mice and sex- and age-matched controls (n = 6-9) were fed a high-fat diet (HFD) for 18 wk containing normal (VAN, 4000 IU/kg of diet) or low (VAL, 25% of normal) vitamin A concentrations. Body weight was recorded biweekly. Plasma GIP and GLP-1 levels were obtained fasting and 30 min after an oral fat gavage at week 16. Glucose tolerance tests were also performed. Mice were killed at week 18, and blood and tissue samples were obtained.

RESULTS

Rbp2-/- mice displayed greater weight gain on the VAN compared with the VAL diet from week 7 of the intervention (P ≤ 0.01). Stimulated GIP levels were elevated in Rbp2-/- mice compared with their controls fed the VAN diet (P = 0.02), whereas their GIP response was lower when fed the VAL diet (P = 0.03). Although no differences in GLP-1 levels were observed in the VAN diet group, a lower GLP-1 response was seen in Rbp2-/- mice fed the VAL diet (P = 0.02). Changes in incretin gene expression and that of other genes associated with EEC lineage and function were consistent with these observations. Circulating and hepatic retinoid levels revealed no systemic vitamin A deficiency across dietary groups.

CONCLUSIONS

Our data support a role for RBP2 and dietary vitamin A in incretin secretion and gene expression in mice fed a HFD.

The 16α-hydroxylated Bile Acid, Pythocholic Acid Decreases Food Intake and Increases Oleoylethanolamide in Male Mice

Modulation of bile acid (BA) structure is a potential strategy for obesity and metabolic disease treatment. BAs act not only as signaling molecules involved in energy expenditure and glucose homeostasis, but also as regulators of food intake. The structure of BAs, particularly the position of the hydroxyl groups of BAs, impacts food intake partly by intestinal effects: (1) modulating the activity of N-acyl phosphatidylethanolamine phospholipase D, which produces the anorexigenic bioactive lipid oleoylethanolamide (OEA) or (2) regulating lipid absorption and the gastric emptying-satiation pathway. We hypothesized that 16α-hydroxylated BAs uniquely regulate food intake because of the long intermeal intervals in snake species in which these BAs are abundant. However, the effects of 16α-hydroxylated BAs in mammals are completely unknown because they are not naturally found in mammals. To test the effect of 16α-hydroxylated BAs on food intake, we isolated the 16α-hydroxylated BA pythocholic acid from ball pythons (Python regius). Pythocholic acid or deoxycholic acid (DCA) was given by oral gavage in mice. DCA is known to increase N-acyl phosphatidylethanolamine phospholipase D activity better than other mammalian BAs. We evaluated food intake, OEA levels, and gastric emptying in mice. We successfully isolated pythocholic acid from ball pythons for experimental use. Pythocholic acid treatment significantly decreased food intake in comparison to DCA treatment, and this was associated with increased jejunal OEA, but resulted in no change in gastric emptying or lipid absorption. The exogenous BA pythocholic acid is a novel regulator of food intake and the satiety signal for OEA in the mouse intestine.

First GPR119 PET Imaging Ligand: Synthesis, Radiochemistry, and Preliminary Evaluations

G-protein-coupled receptor 119 (GPR119) has emerged as a promising target for treating type 2 diabetes mellitus. Activating GPR119 improves glucose homeostasis, while suppressing appetite and weight gain. Measuring GPR119 levels in vivo could significantly advance GPR119-based drug development strategies including target engagement, occupancy, and distribution studies. To date, no positron emission tomography (PET) ligands are available to image GPR119. In this paper, we report the synthesis, radiolabeling, and preliminary biological evaluations of a novel PET radiotracer [18F]KSS3 to image GPR119. PET imaging will provide information on GPR119 changes with diabetic glycemic loads and the efficacy of GPR119 agonists as antidiabetic drugs. Our results demonstrate [18F]KSS3's high radiochemical purity, specific activity, cellular uptake, and in vivo and ex vivo uptake in pancreas, liver, and gut regions, with high GPR119 expression. Cell pretreatment with nonradioactive KSS3, rodent PET imaging, biodistribution, and autoradiography studies showed significant blocking in the pancreas showing [18F]KSS3's high specificity.

The emerging role of the endocannabinoidome-gut microbiome axis in eating disorders

Among the sources of chemical signals regulating food intake, energy metabolism and body weight, few have attracted recently as much attention as the expanded endocannabinoid system, or endocannabinoidome (eCBome), and the gut microbiome, the two systems on which this review article is focussed. Therefore, it is legitimate to expect that these two systems also play a major role in the etiopathology of eating disorders (EDs), in particular of anorexia nervosa, bulimia nervosa and binge-eating disorder. The major mechanisms through which, also via interactions with other endogenous signaling systems, the eCBome, with its several lipid mediators and receptors, and the gut microbiome, via its variety of microbial kingdoms, phyla and species, and armamentarium of metabolites, intervene in these disorders, are described here, based on several published studies in either experimental models or patients. Additionally, in view of the emerging multi-faceted cross-talk mechanisms between these two complex systems, we discuss the possibility that the eCBome-gut microbiome axis is also involved in EDs.

Anandamide and other N-acylethanolamines: A class of signaling lipids with therapeutic opportunities

N-acylethanolamines (NAEs), including N-palmitoylethanolamine (PEA), N-oleoylethanolamine (OEA), N-arachidonoylethanolamine (AEA, anandamide), N-docosahexaenoylethanolamine (DHEA, synaptamide) and their oxygenated metabolites are a lipid messenger family with numerous functions in health and disease, including inflammation, anxiety and energy metabolism. The NAEs exert their signaling role through activation of various G protein-coupled receptors (cannabinoid CB₁ and CB₂ receptors, GPR55, GPR110, GPR119), ion channels (TRPV1) and nuclear receptors (PPAR-α and PPAR-γ) in the brain and periphery. The biological role of the oxygenated NAEs, such as prostamides, hydroxylated anandamide and DHEA derivatives, are less studied. Evidence is accumulating that NAEs and their oxidative metabolites may be aberrantly regulated or are associated with disease severity in obesity, metabolic syndrome, cancer, neuroinflammation and liver cirrhosis. Here, we comprehensively review NAE biosynthesis and degradation, their metabolism by lipoxygenases, cyclooxygenases and cytochrome P450s and the biological functions of these signaling lipids. We discuss the latest findings and therapeutic potential of modulating endogenous NAE levels by inhibition of their degradation, which is currently under clinical evaluation for neuropsychiatric disorders. We also highlight NAE biosynthesis inhibition as an emerging topic with therapeutic opportunities in endocannabinoid and NAE signaling.

Intestinal GPR119 activation by microbiota-derived metabolites impacts feeding behavior and energy metabolism

OBJECTIVE

The gastrointestinal tract affects physiological activities and behavior by secreting hormones and generating signals through the activation of nutrient sensors. GPR119, a lipid sensor, is indirectly involved in the secretion of incretins, such as glucagon-like peptide-1 and glucose-dependent insulinotropic peptide, by enteroendocrine cells, while it directly stimulates insulin secretion by pancreatic beta cells. Since GPR119 has the potential to modulate metabolic homeostasis in obesity and diabetes, it has attracted interest as a therapeutic target. However, previous studies have shown that the deletion of Gpr119 in mice does not affect glucose homeostasis and appetite in either basal or high-fat diet-fed conditions. Therefore, the present study aimed to explore the role of GPR119 signaling system in energy metabolism and feeding behavior in mice.

METHODS

Gpr119 knockout (KO) mice were generated using CRISPR-Cas9 gene-editing technology, and their feeding behavior and energy metabolism were evaluated and compared with those of wild type (WT) mice.

RESULTS

Upon inducing metabolic stress via food deprivation, Gpr119 KO mice exhibited lower blood glucose levels and a higher body weight reduction compared to WT mice. Although food intake in WT and KO mice were similar under free-feeding conditions, Gpr119 KO mice exhibited increased food intake when they were refed after 24 h of food deprivation. Further, food-deprived Gpr119 KO mice presented shorter post-meal intervals and lower satiety for second and later meals during refeeding, resulting in increased food intake. Associated with this meal pattern, levels of oleoylethanolamide (OEA), an endogenous agonist of GPR119, in the luminal contents of the distal gastrointestinal tract were elevated within 2 h after refeeding. The large-intestinal infusion of OEA prolonged post-meal intervals and increased satiety in the first meal, but not the second meal. On the other hand, infusion of oleic acid increased cecal OEA levels at 2 h from the beginning of infusion, while prolonging post-meal intervals and increasing satiety on the meals that occurred approximately 2 h after the infusion. Cecal OEA levels were low in antibiotic-treated mice, suggesting that the gut microbiota partially synthesizes OEA from oleic acid.

CONCLUSIONS

Collectively, our results indicate that the activation of gastrointestinal GPR119 by microbiota-produced OEA derived from oleic acid is associated with satiety control and energy homeostasis under energy shortage conditions.

Activation and signaling mechanism revealed by GPR119-Gs complex structures

Agonists selectively targeting cannabinoid receptor-like G-protein-coupled receptor (GPCR) GPR119 hold promise for treating metabolic disorders while avoiding unwanted side effects. Here we present the cryo-electron microscopy (cryo-EM) structures of the human GPR119-G_s signaling complexes bound to AR231453 and MBX-2982, two representative agonists reported for GPR119. The structures reveal a one-amino acid shift of the conserved proline residue of TM5 that forms an outward bulge, opening up a hydrophobic cavity between TM4 and TM5 at the middle of the membrane for its endogenous ligands-monounsaturated lipid metabolites. In addition, we observed a salt bridge between ICL1 of GPR119 and Gβ_s. Disruption of the salt bridge eliminates the cAMP production of GPR119, indicating an important role of Gβ_s in GPR119-mediated signaling. Our structures, together with mutagenesis studies, illustrate the conserved binding mode of the chemically different agonists, and provide insights into the conformational changes in receptor activation and G protein coupling.

2-Arachidonoyl glycerol suppresses gastric emptying via the cannabinoid receptor 1-cholecystokinin signaling pathway in mice

2-Monoacylglycerol (2-MAG) is one of the digestion products of dietary lipids. We recently demonstrated that a 2-MAG, 2-arachidonoyl glycerol (2-AG) potently stimulated cholecystokinin (CCK) secretion via cannabinoid receptor 1 (CB1) in a murine CCK-producing cell line, STC-1. CCK plays a crucial role in suppressing postprandial gastric emptying. To examine the effect of 2-AG on gastric emptying, we performed acetaminophen and phenol red recovery tests under oral or intraperitoneal administration of 2-AG in mice. Orally administered 2-AG (25 mg/kg) suppressed the gastric emptying rate in mice, as determined by the acetaminophen absorption test and phenol red recovery test. Intraperitoneal administration of a cholecystokinin A receptor antagonist (0.5 mg/kg) attenuated the gastric inhibitory emptying effect. In addition, both oral (10 mg/kg) and intraperitoneal (0.5 mg/kg) administration of a CB1 antagonist counteracted the 2-AG-induced gastric inhibitory effect. Furthermore, intraperitoneal 2-AG (25 mg/kg) suppressed gastric emptying. These results indicate that 2-AG exhibits an inhibitory effect on gastric emptying in mice, possibly mediated by stimulating both CCK secretion via CB1 expressed in CCK-producing cells and acting on CB1 expressed in the peripheral nerves. Our findings provide novel insights into the 2-MAG-sensing mechanism in enteroendocrine cells and the physiological role of 2-MAG.

The mitochondrial β-oxidation enzyme HADHA restrains hepatic glucagon response by promoting β-hydroxybutyrate production

Disordered hepatic glucagon response contributes to hyperglycemia in diabetes. The regulators involved in glucagon response are less understood. This work aims to investigate the roles of mitochondrial β-oxidation enzyme HADHA and its downstream ketone bodies in hepatic glucagon response. Here we show that glucagon challenge impairs expression of HADHA. Liver-specific HADHA overexpression reversed hepatic gluconeogenesis in mice, while HADHA knockdown augmented glucagon response. Stable isotope tracing shows that HADHA promotes ketone body production via β-oxidation. The ketone body β-hydroxybutyrate (BHB) but not acetoacetate suppresses gluconeogenesis by selectively inhibiting HDAC7 activity via interaction with Glu543 site to facilitate FOXO1 nuclear exclusion. In HFD-fed mice, HADHA overexpression improved metabolic disorders, and these effects are abrogated by knockdown of BHB-producing enzyme. In conclusion, BHB is responsible for the inhibitory effect of HADHA on hepatic glucagon response, suggesting that HADHA activation or BHB elevation by pharmacological intervention hold promise in treating diabetes.

Modulatory role of the endocannabinoidome in the pathophysiology of the gastrointestinal tract

Originating from Eastern Asia, the plant Cannabis sativa has been used for centuries as a medicinal treatment. The unwanted psychotropic effects of one of its major components, Δ⁹-tetrahydrocannabinol, discouraged its therapeutic employment until, recently, the discovery of cannabinoids receptors and their endogenous ligands endocannabinoids reignited the interest. The endocannabinoid system has lately been found to play an important role in the maintenance of human health, both centrally and peripherally. However, the initial idea of the endocannabinoid system structure has been quickly understood to be too simplistic and, as new receptors, mediators, and enzymes have been discovered to participate in a complex relationship, the new, more comprehensive term "expanded endocannabinoid system" or "endocannabinoidome", has taken over. The discovery of other endocannabinoid-like receptors, such as the G protein-coupled receptor 119 and G protein-coupled receptor 55, has opened the way to the development of potential therapeutic targets for the treatment of various metabolic disorders. In addition, recent findings have also provided evidence suggesting the potential therapeutic link between the endocannabinoidome and various inflammatory-based gut diseases, such as inflammatory bowel disease and cancer. This review will provide an introduction to the endocannabinoidome, focusing on its modulatory role in the gastrointestinal tract and on the interest generated by the link between gut microbiota, the endocannabinoid system and metabolic diseases such as inflammatory bowel disease, type-2 diabetes and obesity. In addition, we will look at the potential novel aspects and benefits of drugs targeting the endocannabinoid system.

Potentiation of microglial endocannabinoid signaling alleviates neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) isaprogressive neurodegenerative disorder characterized by chronic inflammation due to the presence of neurotoxic Aβ and tau proteins. Increased microglial activation and inflated immune response are the other factors to be considered in AD pathology. Microglial cells own biochemical machinery that synthesizes and release endocannabinoids. The exploitation of therapeutic actions of endocannabinoid system has newly emerged in the field of Alzheimer's disease. The activation of cannabinoid receptors/ cannabinoid system modulates inflammatory responses. This review assesses the association between the microglial endocannabinoid system and neuroinflammation in AD. The data supporting the anti-inflammatory role of pharmacological agents modulating cannabinoid system are also reviewed.

Pharmacological and structure-activity relationship studies of oleoyl-lysophosphatidylinositol synthetic mimetics

Metabolic diseases, such as obesity and type 2 diabetes, are relentlessly spreading worldwide. The beginning of the 21st century has seen the introduction of mechanistically novel types of drugs, aimed primarily at keeping these pathologies under control. In particular, an important family of therapeutics exploits the beneficial physiology of the gut-derived glucagon-like peptide-1 (GLP-1), with important clinical benefits, from glycaemic control to cardioprotection. Nonetheless, these protein-based drugs act systemically as exogenous GLP-1 mimetics and are not exempt from side effects. The food-derived lipid oleoyl-lysophosphatidylinositol (LPI) is a potent GPR119-dependent GLP-1 secreting agent. Here we present a structure-activity relationship (SAR) study of a synthetic library of oleoyl-LPI mimetics capable to induce the physiological release of GLP-1 from gastrointestinal enteroendocrine cells (EECs). The best lead compounds have shown potent and efficient release of GLP-1 in vitro from human and murine cells, and in vivo in diabetic db/db mice. We have also generated a molecular model of oleoyl-LPI, as well as its best performing analogues, interacting with the orthosteric site of GPR119, laying foundational evidence for their pharmacological activity.

Effects of Delayed-Release Olive Oil and Hydrolyzed Pine Nut Oil on Glucose Tolerance, Incretin Secretion and Appetite in Humans

BACKGROUND

To investigate the potential synergistic effects of olive oil releasing 2-oleoylglycerol and hydrolyzed pine nut oil containing 20% pinolenic acid on GLP-1 secretion, glucose tolerance, insulin secretion and appetite in healthy individuals, when delivered to the small intestine as potential agonists of GPR119, FFA1 and FFA4.

METHODS

Nine overweight/obese individuals completed three 6-h oral glucose tolerance tests (OGTTs) in a crossover design. At -30 min, participants consumed either: no oil, 6 g of hydrolyzed pine nut oil (PNO-FFA), or a combination of 3 g hydrolyzed pine nut oil and 3 g olive oil (PNO-OO) in delayed-release capsules. Repeated measures of glucose, insulin, C-peptide, GLP-1, GIP, ghrelin, subjective appetite and gastrointestinal tolerability were done.

RESULTS

PNO-FFA augmented GLP-1 secretion from 0-360 min compared to no oil and PNO-OO (p < 0.01). GIP secretion was increased from 240-360 min after both PNO-FFA and PNO-OO versus no oil (p < 0.01). Both oil treatments suppressed subjective appetite by reducing hunger and prospective food consumption and increasing satiety (p < 0.05).

CONCLUSIONS

In support of previous findings, 6 g of delayed-release hydrolyzed pine nut oil enhanced postprandial GLP-1 secretion and reduced appetite. However, no synergistic effect of combining hydrolyzed pine nut oil and olive oil on GLP-1 secretion was observed. These results need further evaluation in long-term studies including effects on bodyweight and insulin sensitivity.

2-Arachidonoyl glycerol potently induces cholecystokinin secretion in murine enteroendocrine STC-1 cells via cannabinoid receptor CB1

Cholecystokinin (CCK) is a peptide hormone secreted from enteroendocrine cells and regulates the exocrine pancreas, gastric motility, and appetite. Dietary triacylglycerols are hydrolyzed to fatty acids (FA) and 2-monoacylglycerols (2-MAG) in the small intestine. Although it is well known that FA stimulate CCK secretion, whether 2-MAG have the CCK-releasing activity remains unclear. We examined the CCK-releasing activity of four commercially available 2-MAG in a murine CCK-producing cell line, STC-1, and the molecular mechanism underlying 2-MAG-induced CCK secretion. CCK released from the cells was measured using ELISA. Among four 2-MAG (2-palmitoyl, 2-oleoyl, 2-linoleoyl, and 2-arachidonoyl monoacylglycerols) examined, 2-arachidonoyl glycerol (2-AG) potently stimulated CCK secretion in a dose-dependent manner. Structurally related compounds, such as 2-arachidonoyl glycerol ether and 1-arachidonoyl glycerol, did not stimulate CCK secretion. Both arachidonic acid and 2-AG stimulated CCK secretion at 100 μM, but only 2-AG did at 50 μM. 2-AG-induced CCK secretion but not arachidonic acid-induced CCK secretion was attenuated by treatment with a cannabinoid receptor 1 (CB1) antagonist. These results indicate that a specific 2-MAG, 2-AG, directly stimulates CCK secretion via CB1.

Endocannabinoid-Based Therapies

The endocannabinoids are lipid-derived messengers that play a diversity of regulatory roles in mammalian physiology. Dysfunctions in their activity have been implicated in various disease conditions, attracting attention to the endocannabinoid system as a possible source of therapeutic drugs. This signaling complex has three components: the endogenous ligands, anandamide and 2-arachidonoyl-sn-glycerol (2-AG); a set of enzymes and transporters that generate, eliminate, or modify such ligands; and selective cell surface receptors that mediate their biological actions. We provide an overview of endocannabinoid formation, deactivation, and biotransformation and outline the properties and therapeutic potential of pharmacological agents that interfere with those processes. We describe small-molecule inhibitors that target endocannabinoid-producing enzymes, carrier proteins that transport the endocannabinoids into cells, and intracellular endocannabinoid-metabolizing enzymes. We briefly discuss selected agents that simultaneously interfere with components of the endocannabinoid system and with other functionally related signaling pathways. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Slow digestion-oriented dietary strategy to sustain the secretion of GLP-1 for improved glucose homeostasis

Dysregulated glucose metabolism is associated with many chronic diseases such as obesity and type 2 diabetes mellitus (T2DM), and strategies to restore and maintain glucose homeostasis are essential to health. The incretin hormone of glucagon-like peptide-1 (GLP-1) is known to play a critical role in regulating glucose homeostasis and dietary nutrients are the primary stimuli to the release of intestinal GLP-1. However, the GLP-1 producing enteroendocrine L-cells are mainly distributed in the distal region of the gastrointestinal tract where there are almost no nutrients to stimulate the secretion of GLP-1 under normal situations. Thus, a dietary strategy to sustain the release of GLP-1 was proposed, and the slow digestion property and dipeptidyl peptidase IV (DPP-IV) inhibitory activity of food components, approaches to reduce the rate of food digestion, and mechanisms to sustain the release of GLP-1 were reviewed. A slow digestion-oriented dietary approach through encapsulation of nutrients, incorporation of viscous dietary fibers, and enzyme inhibitors of phytochemicals in a designed whole food matrix will be implemented to efficiently reduce the digestion rate of food nutrients, potentiate their distal deposition and a sustained secretion of GLP-1, which will be beneficial to improved glucose homeostasis and health.

Cannabinoids Drugs and Oral Health-From Recreational Side-Effects to Medicinal Purposes: A Systematic Review

Background: marijuana, the common name for cannabis sativa preparations, is one of the most consumed drug all over the world, both at therapeutical and recreational levels. With the legalization of medical uses of cannabis in many countries, and even its recreational use in most of these, the prevalence of marijuana use has markedly risen over the last decade. At the same time, there is also a higher prevalence in the health concerns related to cannabis use and abuse. Thus, it is mandatory for oral healthcare operators to know and deal with the consequences and effects of cannabis use on oral cavity health. This review will briefly summarize the components of cannabis and the endocannabinoid system, as well as the cellular and molecular mechanisms of biological cannabis action in human cells and biologic activities on tissues. We will also look into oropharyngeal tissue expression of cannabinoid receptors, together with a putative association of cannabis to several oral diseases. Therefore, this review will elaborate the basic biology and physiology of cannabinoids in human oral tissues with the aim of providing a better comprehension of the effects of its use and abuse on oral health, in order to include cannabinoid usage into dental patient health records as well as good medicinal practice. Methods: the paper selection was performed by PubMed/Medline and EMBASE electronic databases, and reported according to the PRISMA guidelines. The scientific products were included for qualitative analysis. Results: the paper search screened a total of 276 papers. After the initial screening and the eligibility assessment, a total of 32 articles were considered for the qualitative analysis. Conclusions: today, cannabis consumption has been correlated to a higher risk of gingival and periodontal disease, oral infection and cancer of the oral cavity, while the physico-chemical activity has not been completely clarified. Further investigations are necessary to evaluate a therapeutic efficacy of this class of drugs for the promising treatment of several different diseases of the salivary glands and oral diseases.

Targeting the GPR119/incretin axis: a promising new therapy for metabolic-associated fatty liver disease

In the past decade, G protein-coupled receptors have emerged as drug targets, and their physiological and pathological effects have been extensively studied. Among these receptors, GPR119 is expressed in multiple organs, including the liver. It can be activated by a variety of endogenous and exogenous ligands. After GPR119 is activated, the cell secretes a variety of incretins, including glucagon-like peptide-1 and glucagon-like peptide-2, which may attenuate the metabolic dysfunction associated with fatty liver disease, including improving glucose and lipid metabolism, inhibiting inflammation, reducing appetite, and regulating the intestinal microbial system. GPR119 has been a potential therapeutic target for diabetes mellitus type 2 for many years, but its role in metabolic dysfunction associated fatty liver disease deserves further attention. In this review, we discuss relevant research and current progress in the physiology and pharmacology of the GPR119/incretin axis and speculate on the potential therapeutic role of this axis in metabolic dysfunction associated with fatty liver disease, which provides guidance for transforming experimental research into clinical applications.

Roles of Endocannabinoids and Endocannabinoid-like Molecules in Energy Homeostasis and Metabolic Regulation: A Nutritional Perspective

The endocannabinoid system is involved in signal transduction in mammals. It comprises principally G protein-coupled cannabinoid receptors and their endogenous agonists, called endocannabinoids, as well as the enzymes and transporters responsible for the metabolism of endocannabinoids. Two arachidonic acid-containing lipid molecules, arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol, function as endocannabinoids. N-acylethanolamines and monoacylglycerols, in which the arachidonic acid chain is replaced with a saturated or monounsaturated fatty acid, are not directly involved in the endocannabinoid system but exhibit agonistic activities for other receptors. These endocannabinoid-like molecules include palmitoylethanolamide, oleoylethanolamide (OEA), and 2-oleoylglycerol. Endocannabinoids stimulate feeding behavior and the anabolism of lipids and glucose, while OEA suppresses appetite. Both central and peripheral systems are included in these nutritional and metabolic contexts. Therefore, they have potential in the treatment and prevention of obesity. We outline the structure, metabolism, and biological activities of endocannabinoids and related molecules, and focus on their involvement in energy homeostasis and metabolic regulation. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The specification and function of enteroendocrine cells in Drosophila and mammals: a comparative review

Enteroendocrine cells (EECs) in both invertebrates and vertebrates derive from intestinal stem cells (ISCs) and are scattered along the digestive tract, where they function in sensing various environmental stimuli and subsequently secrete neurotransmitters or neuropeptides to regulate diverse biological and physiological processes. To fulfill these functions, EECs are specified into multiple subtypes that occupy specific gut regions. With advances in single-cell technology, organoid culture experimental systems, and CRISPR/Cas9-mediated genomic editing, rapid progress has been made toward characterization of EEC subtypes in mammals. Additionally, studies of genetic model organisms-especially Drosophila melanogaster-have also provided insights about the molecular processes underlying EEC specification from ISCs and about the establishment of diverse EEC subtypes. In this review, we compare the regulation of EEC specification and function in mammals and Drosophila, with a focus on EEC subtype characterization, on how internal and external regulators mediate EEC subtype specification, and on how EEC-mediated intra- and interorgan communications affect gastrointestinal physiology and pathology.

Novel advances in understanding fatty acid-binding G protein-coupled receptors and their roles in controlling energy balance

Diabetes, obesity, and other metabolic diseases have been recognized as the main factors that endanger human health worldwide. Most of these metabolic syndromes develop when the energy balance in the body is disrupted. Energy balance depends upon the systemic regulation of food intake, glucose homeostasis, and lipid metabolism. Fatty acid-binding G protein-coupled receptors (GPCRs) are widely expressed in various types of tissues and cells involved in energy homeostasis regulation. In this review, the distribution and biological functions of fatty acid-binding GPCRs are summarized, particularly with respect to the gut, pancreas, and adipose tissue. A systematic understanding of the physiological functions of the fatty acid-binding GPCRs involved in energy homeostasis regulation will help in identifying novel pharmacological targets for metabolic diseases.

GPR119 agonists: Novel therapeutic agents for type 2 diabetes mellitus

Diabetes mellitus type 2 (T2D) is a group of genetically heterogeneous metabolic disorders whose frequency has gradually risen worldwide. Diabetes mellitus Type 2 (T2D) has started to achieve a pandemic level, and it is estimated that within the next decade, cases of diabetes might get double due to increase in aging population. Diabetes is rightly called the 'silent killer' because it has emerged to be one of the major causes, leading to renal failure, loss of vision; besides cardiac arrest in India. Thus, a clinical requirement for the oral drug molecules monitoring glucose homeostasis appears to be unmet. GPR119 agonist, a family of G-protein coupled receptors, usually noticed in β-cells of pancreatic as well as intestinal L cells, drew considerable interest for type 2 diabetes mellitus (T2D). GPR119 monitors physiological mechanisms that enhance homeostasis of glucose, such as glucose-like peptide-1, gastrointestinal incretin hormone levels, pancreatic beta cell-dependent insulin secretion and glucose-dependent insulinotropic peptide (GIP). In this manuscript, we have reviewed the work done in the last five years (2015-2020) which gives an approach to design, synthesize, evaluate and study the structural activity relationship of novel GPR119 agonist-based lead compounds. Our article would help the researchers and guide their endeavours in the direction of strategy and development of innovative, effective GPR119 agonist-based compounds for the management of diabetes mellitus type 2.

Discovery of a potent G-protein-coupled receptor 119 agonist for the treatment of type 2 diabetes

The ever-growing prevalence of Type-2 diabetes in the world has an urgent need for multiple orally effective agents that can regulate glucose homeostasis. G-Protein coupled receptor 119 (GPR 119) agonists have demonstrated the glucose-dependent insulin secretion and showed beneficial effects on glycemic control in humans and/or relevant animal models. Herein, we describe our efforts towards identification of a potent and oral GPR 119 agonist 13c (ZY-G19), which showed in vitro potency in the cell-based assay and in vivo efficacy without exerting any significant signs of toxicity in relevant animal models.

The gut-brain axis: Identifying new therapeutic approaches for type 2 diabetes, obesity, and related disorders

BACKGROUND

The gut-brain axis, which mediates bidirectional communication between the gastrointestinal system and central nervous system (CNS), plays a fundamental role in multiple areas of physiology including regulating appetite, metabolism, and gastrointestinal function. The biology of the gut-brain axis is central to the efficacy of glucagon-like peptide-1 (GLP-1)-based therapies, which are now leading treatments for type 2 diabetes (T2DM) and obesity. This success and research to suggest a much broader role of gut-brain circuits in physiology and disease has led to increasing interest in targeting such circuits to discover new therapeutics. However, our current knowledge of this biology is limited, largely because the scientific tools have not been available to enable a detailed mechanistic understanding of gut-brain communication.

SCOPE OF REVIEW

In this review, we provide an overview of the current understanding of how sensory information from the gastrointestinal system is communicated to the central nervous system, with an emphasis on circuits involved in regulating feeding and metabolism. We then describe how recent technologies are enabling a better understanding of this system at a molecular level and how this information is leading to novel insights into gut-brain communication. We also discuss current therapeutic approaches that leverage the gut-brain axis to treat diabetes, obesity, and related disorders and describe potential novel approaches that have been enabled by recent advances in the field.

MAJOR CONCLUSIONS

The gut-brain axis is intimately involved in regulating glucose homeostasis and appetite, and this system plays a key role in mediating the efficacy of therapeutics that have had a major impact on treating T2DM and obesity. Research into the gut-brain axis has historically largely focused on studying individual components in this system, but new technologies are now enabling a better understanding of how signals from these components are orchestrated to regulate metabolism. While this work reveals a complexity of signaling even greater than previously appreciated, new insights are already being leveraged to explore fundamentally new approaches to treating metabolic diseases.

Multi-Target Approaches in Metabolic Syndrome

Metabolic syndrome (MetS) is a highly prevalent disease cluster worldwide. It requires polypharmacological treatment of the single conditions including type II diabetes, hypertension, and dyslipidemia, as well as the associated comorbidities. The complex treatment regimens with various drugs lead to drug-drug interactions and inadequate patient adherence, resulting in poor management of the disease. Multi-target approaches aim at reducing the polypharmacology and improving the efficacy. This review summarizes the medicinal chemistry efforts to develop multi-target ligands for MetS. Different combinations of pharmacological targets in context of in vivo efficacy and future perspective for multi-target drugs in MetS are discussed.

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.

GPCRs get fatty: the role of G protein-coupled receptor signaling in the development and progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), characterized by the abnormal deposition of lipids within the liver not due to alcohol consumption, is a growing epidemic affecting over 30% of the United States population. Both simple fatty liver and its more severe counterpart, nonalcoholic steatohepatitis, represent one of the most common forms of liver disease. Recently, several G protein-coupled receptors have emerged as targets for therapeutic intervention for these disorders. These include those with known hepatic function as well as those involved in global metabolic regulation. In this review, we highlight these emerging therapeutic targets, focusing on several common themes including their activation by microbial metabolites, stimulatory effect on insulin and incretin secretion, and contribution to glucose tolerance. The overlap in ligands, localization, and downstream effects of activation indicate the interdependent nature of these receptors and highlight the importance of this signaling family in the development and prevention of NAFLD.

GPR119 and GPR55 as Receptors for Fatty Acid Ethanolamides, Oleoylethanolamide and Palmitoylethanolamide

Oleoylethanolamide and palmitoylethanolamide are members of the fatty acid ethanolamide family, also known as acylethanolamides. Their physiological effects, including glucose homeostasis, anti-inflammation, anti-anaphylactic, analgesia, and hypophagia, have been reported. They have affinity for different receptor proteins, including nuclear receptors such as PPARα, channels such as TRPV1, and membrane receptors such as GPR119 and GPR55. In the present review, the pathophysiological functions of fatty acid ethanolamides have been discussed from the perspective of receptor pharmacology and drug discovery.

Role of cannabinoids in alcohol-induced neuroinflammation

Alcohol is a psychoactive substance highly used worldwide, whose harmful use might cause a broad range of mental and behavioural disorders. Underlying brain impact, the neuroinflammatory response induced by alcohol is recognised as a key contributing factor in the progression of other neuropathological processes, such as neurodegeneration. These sequels are determined by multiple factors, including age of exposure. Strikingly, it seems that the endocannabinoid system modulation could regulate the alcohol-induced neuroinflammation. Although direct CB1 activation can worsen alcohol consequences, targeting other components of the expanded endocannabinoid system may counterbalance the pro-inflammatory response. Indeed, specific modulations of the expanded endocannabinoid system have been proved to exert anti-inflammatory effects, primarily through the CB2 and PPARγ signalling. Among them, some endo- and exogeneous cannabinoids can block certain pro-inflammatory mediators, such as NF-κB, thereby neutralizing the neuroinflammatory intracellular cascades. Furthermore, a number of cannabinoids are able to activate complementary anti-inflammatory pathways, which are necessary for the transition from chronically overactivated microglia to a regenerative microglial phenotype. Thus, cannabinoid modulation provides cooperative anti-inflammatory mechanisms that may be advantageous to resolve a pathological neuroinflammation in an alcohol-dependent context.

What Is an L-Cell and How Do We Study the Secretory Mechanisms of the L-Cell?

Synthetic glucagon-like peptide-1 (GLP-1) analogues are effective anti-obesity and anti-diabetes drugs. The beneficial actions of GLP-1 go far beyond insulin secretion and appetite, and include cardiovascular benefits and possibly also beneficial effects in neurodegenerative diseases. Considerable reserves of GLP-1 are stored in intestinal endocrine cells that potentially might be mobilized by pharmacological means to improve the body's metabolic state. In recognition of this, the interest in understanding basic L-cell physiology and the mechanisms controlling GLP-1 secretion, has increased considerably. With a view to home in on what an L-cell is, we here present an overview of available data on L-cell development, L-cell peptide expression profiles, peptide production and secretory patterns of L-cells from different parts of the gut. We conclude that L-cells differ markedly depending on their anatomical location, and that the traditional definition of L-cells as a homogeneous population of cells that only produce GLP-1, GLP-2, glicentin and oxyntomodulin is no longer tenable. We suggest to sub-classify L-cells based on their differential peptide contents as well as their differential expression of nutrient sensors, which ultimately determine the secretory responses to different stimuli. A second purpose of this review is to describe and discuss the most frequently used experimental models for functional L-cell studies, highlighting their benefits and limitations. We conclude that no experimental model is perfect and that a comprehensive understanding must be built on results from a combination of models.

Metabolic Functions of G Protein-Coupled Receptors and β-Arrestin-Mediated Signaling Pathways in the Pathophysiology of Type 2 Diabetes and Obesity

Seven transmembrane receptors (7TMRs), often termed G protein-coupled receptors (GPCRs), are the most common target of therapeutic drugs used today. Many studies suggest that distinct members of the GPCR superfamily represent potential targets for the treatment of various metabolic disorders including obesity and type 2 diabetes (T2D). GPCRs typically activate different classes of heterotrimeric G proteins, which can be subgrouped into four major functional types: G_αs, G_αi, G_αq/11, and G_12/13, in response to agonist binding. Accumulating evidence suggests that GPCRs can also initiate β-arrestin-dependent, G protein-independent signaling. Thus, the physiological outcome of activating a certain GPCR in a particular tissue may also be modulated by β-arrestin-dependent, but G protein-independent signaling pathways. In this review, we will focus on the role of G protein- and β-arrestin-dependent signaling pathways in the development of obesity and T2D-related metabolic disorders.

Dietary fatty acid intake and gut microbiota determine circulating endocannabinoidome signaling beyond the effect of body fat

The endocannabinoidome encompasses several fatty acid (FA)-derived mediators, including the endocannabinoid anandamide (AEA) and 2-arachidonoyl-glycerol (2-AG), which served as targets for anti-obesity drug development, and their congener N-acyl-ethanolamines (NAEs) and 2-monoacyl-glycerols (2‑MAGs), which are involved in food intake and energy metabolism. Body weight and fat distribution have been suggested as determinants of peripheral endocannabinoid levels. We aimed at investigating factors, beyond body fat composition, that are associated with circulating NAE and 2-MAG levels in a heterogeneous human population. Plasma NAEs and 2-MAGs were measured using LC–MS/MS in a cross-sectional sample of healthy men and women (n = 195) covering a wide range of BMI and individuals before and after a 2-day Mediterranean diet (n = 21). Circulating levels of all 2-MAGs and NAEs, other than N-oleoyl-ethanolamine (OEA), correlated with body fat mass and visceral adipose tissue (0.26 < r < 0.54). NAE levels were elevated in individuals with elevated fat mass, while 2-MAGs were increased in individuals with predominantly visceral body fat distribution. Dietary intakes of specific FAs were associated with 2-AG and omega-3-FA-derived NAEs or 2-MAGs, irrespective of the body fat distribution. Some gut bacterial families (e.g. Veillonellaceae, Peptostreptococcaceae and Akkermansiaceae) were associated with variations in most NAEs or omega-3-FA-derived 2‑MAGs, independently of fat mass and dietary FA intake. Finally, a 2-day Mediterranean diet intervention increased circulating levels of NAEs and 2-MAGs in agreement with changes in FA intake (p < 0.01). Self-reported intake and short-term dietary intervention increased in oleic acid and EPA and DHA intake as well as certain gut microbiota taxa are associated to circulating NAEs and 2‑MAGs independently of adiposity measures, thus highlighting the potential importance of these variables in determining endocannabinoidome signaling in humans.

Bile acid composition regulates GPR119-dependent intestinal lipid sensing and food intake regulation in mice

OBJECTIVES

Lipid mediators in the GI tract regulate satiation and satiety. Bile acids (BAs) regulate the absorption and metabolism of dietary lipid in the intestine, but their effects on lipid-regulated satiation and satiety are completely unknown. Investigating this is challenging because introducing excessive BAs or eliminating BAs strongly impacts GI functions. We used a mouse model (Cyp8b1^-/- mice) with normal total BA levels, but alterations in the composition of the BA pool that impact multiple aspects of intestinal lipid metabolism. We tested two hypotheses: BAs affect food intake by (1) regulating production of the bioactive lipid oleoylethanolamide (OEA), which enhances satiety; or (2) regulating the quantity and localisation of hydrolysed fat in small intestine, which controls gastric emptying and satiation.

DESIGN

We evaluated OEA levels, gastric emptying and food intake in wild-type and Cyp8b1^-/- mice. We assessed the role of the fat receptor GPR119 in these effects using Gpr119^-/- mice.

RESULTS

Cyp8b1^-/- mice on a chow diet showed mild hypophagia. Jejunal OEA production was blunted in Cyp8b1^-/- mice, thus these data do not support a role for this pathway in the hypophagia of Cyp8b1^-/- mice. On the other hand, Cyp8b1 deficiency decreased gastric emptying, and this was dependent on dietary fat. GPR119 deficiency normalised the gastric emptying, gut hormone levels, food intake and body weight of Cyp8b1^-/- mice.

CONCLUSION

BAs regulate gastric emptying and satiation by determining fat-dependent GPR119 activity in distal intestine.

The Physiological Importance of Bile Acid Structure and Composition on Glucose Homeostasis

PURPOSE OF REVIEW

Studies have identified several effects of bile acids (BAs) in glucose homeostasis, energy expenditure, and body weight control, through receptor-dependent and independent mechanisms. BAs are produced from cholesterol and characterized by their structures, which result from enzymes in the liver and the gut microbiota. The aim of this review is to characterize the effects of BA structure and composition on diabetes.

RECENT FINDINGS

The hydroxyl groups of BAs interact with binding pockets of receptors and enzymes that affect glucose homeostasis. Human and animal studies show that BA composition is associated with insulin resistance and food intake regulation. The hydroxylation of BAs and BA composition contributes to glucose regulation. Modulation of BA composition has the potential to improve glucose metabolism.

Lysophosphatidylcholine Containing Anisic Acid Is Able to Stimulate Insulin Secretion Targeting G Protein Coupled Receptors

Diabetes mellitus is a worldwide health problem with high rates of mortality and morbidity. Management of diabetes mellitus by dietary components is achievable especially at the initial stage of the disease. Several studies confirmed the antidiabetic activities of simple phenolic acids and lysophosphatidylcholine (LPC). The main goal of this study was to identify new potential insulin secretion modulators obtained by combining the structures of two natural compounds, namely O-methyl derivatives of phenolic acids and phospholipids. LPC and phosphatidylcholine bearing methoxylated aromatic carboxylic acids were tested as potential agents able to improve glucose-stimulated insulin secretion (GSIS) and intracellular calcium mobilization in MIN6 β pancreatic cell line. Our results show that LPC with covalently bonded molecule of p-anisic acid at the sn-1 position was able to induce GSIS and intracellular calcium flux. Notably, 1-anisoyl-2-hydroxy-sn-glycero-3-phosphocholine did not affect the viability of MIN6 cells, suggesting its potential safe use. Furthermore, we have shown that three G protein coupled receptors, namely GPR40, GPR55, and GPR119, are targeted by this LPC derivative.

Targeting Peripherally Restricted Cannabinoid Receptor 1, Cannabinoid Receptor 2, and Endocannabinoid-Degrading Enzymes for the Treatment of Neuropathic Pain Including Neuropathic Orofacial Pain

Neuropathic pain conditions including neuropathic orofacial pain (NOP) are difficult to treat. Contemporary therapeutic agents for neuropathic pain are often ineffective in relieving pain and are associated with various adverse effects. Finding new options for treating neuropathic pain is a major priority in pain-related research. Cannabinoid-based therapeutic strategies have emerged as promising new options. Cannabinoids mainly act on cannabinoid 1 (CB1) and 2 (CB2) receptors, and the former is widely distributed in the brain. The therapeutic significance of cannabinoids is masked by their adverse effects including sedation, motor impairment, addiction and cognitive impairment, which are thought to be mediated by CB1 receptors in the brain. Alternative approaches have been developed to overcome this problem by selectively targeting CB2 receptors, peripherally restricted CB1 receptors and endocannabinoids that may be locally synthesized on demand at sites where their actions are pertinent. Many preclinical studies have reported that these strategies are effective for treating neuropathic pain and produce no or minimal side effects. Recently, we observed that inhibition of degradation of a major endocannabinoid, 2-arachydonoylglycerol, can attenuate NOP following trigeminal nerve injury in mice. This review will discuss the above-mentioned alternative approaches that show potential for treating neuropathic pain including NOP.

Potential metabolic and behavioural roles of the putative endocannabinoid receptors GPR18, GPR55 and GPR119 in feeding

Endocannabinoids are ancient biomolecules involved in several cellular (e.g., metabolism) and physiological (e.g., eating behaviour) functions. Indeed, eating behaviour alterations in marijuana users have led to investigate the orexigen-ic/anorexigenic effects of cannabinoids in animal/human models. This increasing body of research suggests that the endo-cannabinoid system plays an important role in feeding control. Accordingly, within the endocannabinoid system, canna-binoid receptors, enzymes and genes represent potential therapeutic targets for dealing with multiple metabolic and behav-ioural dysfunctions (e.g., obesity, anorexia, etc.). Paradoxically, our understanding on the endocannabinoid system as a cel-lular mediator is yet limited. For example: (i) only two cannabinoid receptors have been classified, but they are not enough to explain the pharmacological profile of several experimental effects induced by cannabinoids; and (ii) several orphan G pro-tein-coupled receptors (GPCRs) interact with cannabinoids and we do not know how to classify them (e.g., GPR18, GPR55 and GPR119; amongst others).

On this basis, the present review attempts to summarize the lines of evidence supporting the potential role of GPR18, GPR55 and GPR119 in metabolism and feeding control that may explain some of the divergent effects and puzzling data re-lated to cannabinoid research. Moreover, their therapeutic potential in feeding behaviour alterations will be considered.

Germ-free mice exhibit profound gut microbiota-dependent alterations of intestinal endocannabinoidome signaling

The gut microbiota is a unique ecosystem of microorganisms interacting with the host through several biochemical mechanisms. The endocannabinoidome (eCBome), a complex signaling system including the endocannabinoid system, approximately 50 receptors and metabolic enzymes, and more than 20 lipid mediators with important physiopathologic functions, modulates gastrointestinal tract function and may mediate host cell-microbe communications there. Germ-free (GF) mice, which lack an intestinal microbiome and so differ drastically from conventionally raised (CR) mice, offer a unique opportunity to explore the eCBome in a microbe-free model and in the presence of a reintroduced functional gut microbiome through fecal microbiota transplant (FMT). We aimed to gain direct evidence for a link between the microbiome and eCBome systems by investigating eCBome alterations in the gut in GF mice before and after FMT. Basal eCBome gene expression and lipid profiles were measured in various segments of the intestine of GF and CR mice at juvenile and adult ages using targeted quantitative PCR transcriptomics and LC-MS/MS lipidomics. GF mice exhibited age-dependent modifications in intestinal eCBome gene expression and lipid mediator levels. FMT from CR donor mice to age-matched GF male mice reversed several of these alterations, particularly in the ileum and jejunum, after only 1 week, demonstrating that the gut microbiome directly impacts the host eCBome and providing a cause-effect relationship between the presence or absence of intestinal microbes and eCBome signaling. These results open the way to new studies investigating the mechanisms through which intestinal microorganisms exploit eCBome signaling to exert some of their physiopathologic functions.

Inhibition of MGAT2 modulates fat-induced gut peptide release and fat intake in normal mice and ameliorates obesity and diabetes in ob/ob mice fed on a high-fat diet

Monoacylglycerol O‐acyltransferase 2 (MGAT2) is one of the key enzymes responsible for triglyceride (TG) re‐synthesis in the small intestine. We have previously demonstrated that pharmacological inhibition of MGAT2 has beneficial effects on obesity and metabolic disorders in mice. Here, we further investigate the effects of MGAT2 inhibition on (a) fat‐induced gut peptide release and fat intake in normal mice and (b) metabolic disorders in high‐fat diet (HFD)‐fed ob/ob mice, a model of severe obesity and type 2 diabetes mellitus, using an orally bioavailable MGAT2 inhibitor Compound B (CpdB). CpdB inhibited elevation of plasma TG in mice challenged with an oil‐supplemented liquid meal. Oil challenge stimulated the secretion of two gut anorectic hormones (peptide tyrosine–tyrosine and glucagon‐like peptide‐1) into the bloodstream, and these responses were augmented in mice pretreated with CpdB. In a two‐choice test using an HFD and a low‐fat diet, CpdB selectively inhibited intake of the HFD in normal mice. Administration of CpdB to HFD‐fed ob/ob mice for 5 weeks suppressed food intake and body weight gain and inhibited elevation of glycated hemoglobin. These results indicate that pharmacological MGAT2 inhibition modulates fat‐induced gut peptide release and fat intake in normal mice and improves obesity and diabetes in HFD‐fed ob/ob mice and thus may have potential for development into a treatment of obesity and its related metabolic diseases.

Acyl ethanolamides in Diabetes and Diabetic Nephropathy: Novel targets from untargeted plasma metabolomic profiles of South Asian Indian men

The pathophysiology of diabetic nephropathy (DN) in type 2 diabetes (T2D) patients is minimally understood. We compared untargeted high-resolution accurate mass (HRAM) orbitrap-based plasma metabolomic profiles of 31 T2D-DN (with estimated glomerular filtration rate ≤80 mL/min/1.73 m²), 29 T2D and 30 normal glucose tolerance (NGT) Indian men. Of the 939 plasma metabolites that were differentially abundant amongst the NGT, T2D and T2D-DN (ANOVA, False Discovery Rate – FDR adjusted p-value < 0.05), 48 were associated with T2D irrespective of the renal function of the subjects. Acyl ethanolamides and acetylcholine were decreased while monoacylglycerols (MAGs) and cortisol were elevated in both T2D and T2D-DN. Sixteen metabolites, including amino acid metabolites Imidazolelactate and N-Acetylornithine, changed significantly between NGT, T2D and T2D-DN. 192 metabolites were specifically dysregulated in T2D-DN (ratio ≥2 or ≤0.5 between T2D-DN and T2D, similar abundance in NGT and T2D). These included increased levels of multiple acylcarnitine and amino acid metabolites. We observed a significant dysregulation of amino acid and fatty acid metabolism in South Asian Indian male T2D-DN subjects. Unique to this study, we report a reduction in acyl ethanolamide levels in both T2D and T2D-DN males. Those with dysregulation in acyl ethanolamides, which are endogenous agonists of GPR119, are likely to exhibit improved glycemic control with GPR119 agonists.

Glucagon-like peptide 1 (GLP-1)

BACKGROUND

The glucagon-like peptide-1 (GLP-1) is a multifaceted hormone with broad pharmacological potential. Among the numerous metabolic effects of GLP-1 are the glucose-dependent stimulation of insulin secretion, decrease of gastric emptying, inhibition of food intake, increase of natriuresis and diuresis, and modulation of rodent β-cell proliferation. GLP-1 also has cardio- and neuroprotective effects, decreases inflammation and apoptosis, and has implications for learning and memory, reward behavior, and palatability. Biochemically modified for enhanced potency and sustained action, GLP-1 receptor agonists are successfully in clinical use for the treatment of type-2 diabetes, and several GLP-1-based pharmacotherapies are in clinical evaluation for the treatment of obesity.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GLP-1 and its pharmacology and discuss its therapeutic implications on various diseases.

MAJOR CONCLUSIONS

Since its discovery, GLP-1 has emerged as a pleiotropic hormone with a myriad of metabolic functions that go well beyond its classical identification as an incretin hormone. The numerous beneficial effects of GLP-1 render this hormone an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, and neurodegenerative disorders.

Review: Chemosensing of nutrients and non-nutrients in the human and porcine gastrointestinal tract

The gastrointestinal tract (GIT) is an interface between the external and internal milieus that requires continuous monitoring for nutrients or pathogens and toxic chemicals. The study of the physiological/molecular mechanisms, mediating the responses to the monitoring of the GIT contents, has been referred to as chemosensory science. While most of the progress in this area of research has been obtained in laboratory rodents and humans, significant steps forward have also been reported in pigs. The objective of this review was to update the current knowledge on nutrient chemosensing in pigs in light of recent advances in humans and laboratory rodents. A second objective relates to informing the existence of nutrient sensors with their functionality, particularly linked to the gut peptides relevant to the onset/offset of appetite. Several cell types of the intestinal epithelium such as Paneth, goblet, tuft and enteroendocrine cells (EECs) contain subsets of chemosensory receptors also found on the tongue as part of the taste system. In particular, EECs show specific co-expression patterns between nutrient sensors and/or transceptors (transport proteins with sensing functions) and anorexigenic hormones such as cholecystokinin (CCK), peptide tyrosine tyrosine (PYY) or glucagon-like peptide-1 (GLP-1), amongst others. In addition, the administration of bitter compounds has an inhibitory effect on GIT motility and on appetite through GLP-1-, CCK-, ghrelin- and PYY-labelled EECs in the human small intestine and colon. Furthermore, the mammalian chemosensory system is the target of some bacterial metabolites. Recent studies on the human microbiome have discovered that commensal bacteria have developed strategies to stimulate chemosensory receptors and trigger host cellular functions. Finally, the study of gene polymorphisms related to nutrient sensors explains differences in food choices, food intake and appetite between individuals.