Newer pharmacological interventions directed at gut hormones for obesity

Molecular mapping and functional validation of GLP-1R cholesterol binding sites in pancreatic beta cells

G protein-coupled receptors (GPCRs) are integral membrane proteins which closely interact with their plasma membrane lipid microenvironment. Cholesterol is a lipid enriched at the plasma membrane with pivotal roles in the control of membrane fluidity and maintenance of membrane microarchitecture, directly impacting on GPCR stability, dynamics, and function. Cholesterol extraction from pancreatic beta cells has previously been shown to disrupt the internalisation, clustering, and cAMP responses of the glucagon-like peptide-1 receptor (GLP-1R), a class B1 GPCR with key roles in the control of blood glucose levels via the potentiation of insulin secretion in beta cells and weight reduction via the modulation of brain appetite control centres. Here, we unveil the detrimental effect of a high cholesterol diet on GLP-1R-dependent glucoregulation in vivo, and the improvement in GLP-1R function that a reduction in cholesterol synthesis using simvastatin exerts in pancreatic islets. We next identify and map sites of cholesterol high occupancy and residence time on active vs inactive GLP-1Rs using coarse-grained molecular dynamics (cgMD) simulations, followed by a screen of key residues selected from these sites and detailed analyses of the effects of mutating one of these, Val229, to alanine on GLP-1R-cholesterol interactions, plasma membrane behaviours, clustering, trafficking and signalling in INS-1 832/3 rat pancreatic beta cells and primary mouse islets, unveiling an improved insulin secretion profile for the V229A mutant receptor. This study (1) highlights the role of cholesterol in regulating GLP-1R responses in vivo; (2) provides a detailed map of GLP-1R - cholesterol binding sites in model membranes; (3) validates their functional relevance in beta cells; and (4) highlights their potential as locations for the rational design of novel allosteric modulators with the capacity to fine-tune GLP-1R responses.

Ventral tegmental area amylin / calcitonin receptor signaling suppresses feeding and weight gain in female rats

The pancreatic peptide amylin promotes negative energy balance in part through activation of amylin receptors (AmyRs) expressed in the ventral tegmental area (VTA), but studies have been limited to male rodents. We evaluated whether VTA amylin signaling governs feeding and body weight in female rats. Indeed, pharmacological VTA AmyR activation suppressed chow intake and body weight in females. Viral-mediated knockdown of VTA calcitonin receptor (GPCR of AmyR) supports the physiological relevance of VTA amylin signaling for energy balance control in females. Collectively, these data support the relevance of VTA amylin signaling for energy balance control in both sexes.

Incretin impact on gastric function in obesity: physiology, and pharmacological, surgical and endoscopic treatments

The aims of this review are to appraise the role of the stomach in satiation, the effects of incretin and other hormone agonists on weight loss and the role of altered gastric functions in their effects on obesity or glycaemic control. In addition to the gut in its role in enzymatic digestion and hormonal responses to nutrient ingestion, gastric motor functions include accommodation, trituration and emptying [gastric emptying (GE)] of food and elicitation of postprandial satiation and satiety. The postprandially released hormones most extensively studied and utilized therapeutically are glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). Their mechanisms of action include stimulation of pancreatic β cells to produce insulin. However, GLP-1 reduces glucagon and slows GE, whereas GIP increases glucagon and does not alter GE. Molecular modifications of GLP-1 (which has a T1/2 of 3 min) led to the development of long-acting subcutaneous or oral pharmacological agents that have been approved for the treatment of obesity, and their effects on gastric function are documented. Other medications in development target other molecular mechanisms, including glucagon and amylin. Small-molecule GLP-1 receptor agonists are promising for the treatment of obesity and may also slow GE. Bariatric surgery and endoscopy increase satiation by restricting gastric size; in addition Roux-en-Y gastric bypass and to a lesser extent sleeve gastrectomy (but not endoscopic gastroplasty) increase postprandial circulating incretins, reducing appetite. In conclusion the stomach's function is integral to the impact of the most effective pharmacological and procedural reversal of obesity related to the incretin revolution.

Establishing a Relationship between In Vitro Potency in Cell-Based Assays and Clinical Efficacious Concentrations for Approved GLP-1 Receptor Agonists

Background: Glucagon-like peptide-1 receptor agonists (GLP-1RAs) play an important role in the treatment of type 2 diabetes (T2D) and obesity. The relationship between efficacy and dosing regimen has been studied extensively for this class of molecules. However, a comprehensive analysis of the translation of in vitro data to in vivo efficacious exposure is still lacking. Methods: We collected clinical pharmacokinetics for five approved GLP-1RAs to enable the simulation of exposure profiles and compared published clinical efficacy endpoints (HbA1c and body weight) with in-house in vitro potency values generated in different cell-based assays. Additionally, we investigated the correlation with target coverage, expressed as a ratio between the steady state drug exposure and unbound potency, body weight, or HbA1c reduction in patients with T2D. Results: We found that the best correlation with in vivo efficacy was seen for in vitro potency data generated in cellular assays performed in the absence of any serum albumin or using ovalbumin. Residual variability was larger using in vitro potency data generated in endogenous cell lines or in the presence of human serum albumin. For the human receptor assay with no albumin, exposures above 100-fold in vitro EC50 resulted in >1.5% point HbA1c reduction, while a 5% BW reduction was related to approximately 3× higher exposures. A similar relationship was seen in the ovalbumin assay. Conclusions: Overall, the relationship established for in vitro potency and in vivo efficacy will help to increase confidence in human dose prediction and trial design for new GLP-1RAs in the discovery and early clinical phases.

Bitter-tasting drugs tune GDF15 and GLP-1 expression via bitter taste or motilin receptors in the intestine of patients with obesity

OBJECTIVE

Growth differentiation factor 15 (GDF15), a stress related cytokine, was recently identified as a novel satiety signal acting via the GFRAL receptor located in the hindbrain. Bitter compounds are known to induce satiety via the release of glucagon-like peptide 1 (GLP-1) through activation of bitter taste receptors (TAS2Rs, 25 subtypes) on enteroendocrine cells in the gut. This study aimed to investigate whether and how bitter compounds induce a stress response in intestinal epithelial cells to affect GDF15 expression in patients with obesity, thereby facilitating satiety signaling from the gut.

METHODS

The acute effect of oral intake of the bitter-containing medication Plaquenil (hydroxychloroquine sulfate) on plasma GDF15 levels was evaluated in a placebo-controlled, double-blind, randomized, two-visit crossover study in healthy volunteers. Primary crypts isolated from the jejunal mucosa from patients with obesity were stimulated with vehicle or bitter compounds, and the effect on GDF15 expression was evaluated using RT-qPCR or ELISA. Immunofluorescence colocalization studies were performed between GDF15, epithelial cell type markers and TAS2Rs. The role of TAS2Rs was tested by 1) pretreatment with a TAS2R antagonist, GIV3727; 2) determining TAS2R4/43 polymorphisms that affect taste sensitivity to TAS2R4/43 agonists.

RESULTS

Acute intake of hydroxychloroquine sulfate increased GDF15 plasma levels, which correlated with reduced hunger scores and plasma ghrelin levels in healthy volunteers. This effect was mimicked in primary jejunal cultures from patients with obesity. GDF15 was expressed in enteroendocrine and goblet cells with higher expression levels in patients with obesity. Various bitter-tasting compounds (medicinal, plant extracts, bacterial) either increased or decreased GDF15 expression, with some also affecting GLP-1. The effect was mediated by specific intestinal TAS2R subtypes and the unfolded protein response pathway. The bitter-induced effect on GDF15/GLP-1 expression was influenced by the existence of TAS2R4 amino acid polymorphisms and TAS2R43 deletion polymorphisms that may predict patient's therapeutic responsiveness. However, the effect of the bitter-tasting antibiotic azithromycin on GDF15 release was mediated via the motilin receptor, possibly explaining some of its aversive side effects.

CONCLUSIONS

Bitter chemosensory and pharmacological receptors regulate the release of GDF15 from human gut epithelial cells and represent potential targets for modulating metabolic disorders or cachexia.

Advances in small-molecule insulin secretagogues for diabetes treatment

Diabetes, a metabolic disease caused by abnormally high levels of blood glucose, has a high prevalence rate worldwide and causes a series of complications, including coronary heart disease, stroke, peripheral vascular disease, end-stage renal disease, and retinopathy. Small-molecule compounds have been developed as drugs for the treatment of diabetes because of their oral advantages. Insulin secretagogues are a class of small-molecule drugs used to treat diabetes, and include sulfonylureas, non-sulfonylureas, glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase 4 inhibitors, and other novel small-molecule insulin secretagogues. However, many small-molecule compounds cause different side effects, posing huge challenges to drug monotherapy and drug selection. Therefore, the use of different small-molecule drugs must be improved. This article reviews the mechanism, advantages, limitations, and potential risks of small-molecule insulin secretagogues to provide future research directions on small-molecule drugs for the treatment of diabetes.

Molecular Mechanisms behind Obesity and Their Potential Exploitation in Current and Future Therapy

Obesity is a chronic disease caused primarily by the imbalance between the amount of calories supplied to the body and energy expenditure. Not only does it deteriorate the quality of life, but most importantly it increases the risk of cardiovascular diseases and the development of type 2 diabetes mellitus, leading to reduced life expectancy. In this review, we would like to present the molecular pathomechanisms underlying obesity, which constitute the target points for the action of anti-obesity medications. These include the central nervous system, brain-gut-microbiome axis, gastrointestinal motility, and energy expenditure. A significant part of this article is dedicated to incretin-based drugs such as GLP-1 receptor agonists (e.g., liraglutide and semaglutide), as well as the brand new dual GLP-1 and GIP receptor agonist tirzepatide, all of which have become "block-buster" drugs due to their effectiveness in reducing body weight and beneficial effects on the patient's metabolic profile. Finally, this review article highlights newly designed molecules with the potential for future obesity management that are the subject of ongoing clinical trials.

Pharmacovigilance study of GLP-1 receptor agonists for metabolic and nutritional adverse events

Aims: Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are employed extensively in the management of type 2 diabetes and obesity. However, there is a paucity of real-world data on their safety and tolerability for metabolic and nutritional adverse events in large sample populations. This study aimed to analyse the metabolic and nutritional safety signatures of different GLP-1 RAs by exploring the Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS). Methods: AEs data were extracted from the FDA Adverse Event Reporting System database for each GLP-1 RA from the time of its launch until the second quarter of 2023. The reported odds ratio (ROR), proportional reporting ratio (PRR), Empirical Bayesian Geometric Mean and Bayesian Confidence Propagation Neural Network were employed to identify AE signals. Results: A system organ class of metabolism and nutrition disorders was employed to filter AE reports, resulting in the identification of 10,450 reports for exenatide, 2,860 reports for liraglutide, 240 reports for albiglutide, 4,847 reports for dulaglutide, 2,905 reports for semaglutide, 1,089 reports for tirzepatide, and 13 reports for lixisenatide. Semaglutide (ROR, 3.34; 95%CI, 3.22), liraglutide (ROR, 2.78; 95%CI, 2.69), and exenatide (ROR, 2.15; 95%CI, 2.11) were associated with metabolism and nutrition disorders. The number of AE signals detected were as follows: albiglutide (n = 1), lixisenatide (n = 2), tirzepatide (n = 11), exenatide (n = 12), liraglutide (n = 16), semaglutide (n = 20), dulaglutide (n = 22). Dehydration was the most frequent AE contributing to serious outcomes for liraglutide (n = 318, 23.93%), dulaglutide (n = 434, 20.90%), semaglutide (n = 370, 25.10%) and tirzepatide (n = 70, 32.86%). The time to onset (TTO) of AE was statistically different between exenatide and the other GLP-1 RAs (p < 0.001), and the Weibull parameters for dehydration for liraglutide, dulaglutide, and semaglutide analyses all showed an early failure-type profile. Conclusion: Our study suggests that exenatide, liraglutide, and semaglutide are more susceptible to metabolic and nutritional AEs than other GLP-1 RAs. Liraglutide, dulaglutide, semaglutide, and tirzepaptide's potential to induce dehydration, necessitates special attention. Despite certain deficiencies, GLP-1 RAs have considerable potential for the treatment of eating disorders.