Glucose-dependent Insulinotropic Polypeptide Receptor Research Articles

Reduced Incretin Receptor Trafficking upon Activation Enhances Glycemic Control and Reverses Obesity in Diet-Induced Obese Mice.

Activation of incretin receptors by their cognate agonists augments sustained cAMP generation both from the plasma membrane as well as from the endosome. To address the functional outcome of this spatiotemporal signaling, we developed a non-acylated glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor dual agonist I-M-150847 that reduced receptor internalization following activation of the incretin receptors. The incretin receptor dual agonist I-M-150847 was developed by replacing the tryptophan cage of exendin-4 tyrosine substituted at the amino terminus with the C-terminal undecapeptide sequence of oxyntomodulin that placed lysine 30 of I-M-150847 in frame with the corresponding lysine residue of GIP. The peptide I-M-150847 is a partial agonist of GLP-1R and GIPR; however, the receptors, upon activation by I-M-150847, undergo reduced internalization that promotes agonist-mediated iterative cAMP signaling and augments glucose-stimulated insulin exocytosis in pancreatic beta cells. Chronic administration of I-M-150847 improved glycemic control, enhanced insulin sensitivity, and provided profound weight loss in diet-induced obese (DIO) mice. Our results demonstrated that despite being a partial agonist, I-M-150847, by reducing the receptor internalization upon activation, enhanced the incretin effect and reversed obesity.

Use of Tirzepatide in Adults with Type 2 Diabetes Mellitus: Scientific Evidence and Practical Aspects.

Tirzepatide is a novel antidiabetic medication a single-molecule, agonist to the glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptors. It is approved in the USA and EU for the treatment of type 2 diabetes mellitus (T2DM) and obesity. Due to the potential novelty represented by incorporating tirzepatide to clinical practice, we aim to review practical aspects of tirzepatide use in T2DM and the supporting scientific evidence. A group of ten endocrinologists involved as investigators in the phase 3 SURPASS clinical trial program followed a nominal group technique, a qualitative research methodology designed as a semi-structured group discussion to reach a consensus on the selection of a set of practical aspects. The scientific evidence for tirzepatide has been reviewed with respect to a number of patients' clinical profiles and care goals. Information of interest related to adverse events, special warnings and precautions, and other considerations for tirzepatide use has been included. Finally, information provided to the patients has been summarized. The practical aspects reported herein may be helpful in guiding physicians in the use of tirzepatide and contribute to optimizing the management of T2DM.

GIP receptor is expressed by human cumulus granulosa cells

GIP receptor is expressed by human cumulus granulosa cells

Healthcare professionals' perceptions and management of obesity & knowledge of glucagon, GLP-1, GIP receptor agonists, and dual agonists.

Anti-obesity medications (AOMs) have historically had limited weight-loss efficacy. However, newer glucagon-like peptide-1 receptor agonist (GLP-1 RA)-based therapies seem to be more effective, including dual agonists of GLP-1R and the glucagon receptor (GCGR) or glucose-dependent insulinotropic polypeptide receptor. To explore healthcare professionals' (HCPs) experience in obesity treatment and their understanding of agonists of GCGR, glucose-dependent insulinotropic polypeptide (GIP) RA, and GLP-1 RA. This cross-sectional online survey of HCPs prescribing AOMs was conducted in the United States in 2023 with a questionnaire designed to evaluate prescribing behavior and understanding of GCGR, GIP RA, and GLP-1 RA. The 785 respondents (251 primary-care physicians [PCPs], 263 endocrinologists, and 271 advanced practice providers [APPs]) reported 55% of their patients had obesity (body mass index ≥30kg/m2 or ≥27 with weight-related complications) and recommended AOMs to 49% overall, significantly more endocrinologists (57% of patients, p<0.0005) than PCPs (43%) or APPs (46%). The greatest barriers to treatment were medication cost/lack of insurance (mean 4.2 on 1-5 scale [no barrier-extreme barrier]), low patient engagement/adherence (3.3), and inadequate time/staff (3.1). Metformin was the type 2 diabetes (T2D) medication most commonly prescribed to treat obesity in T2D patients (92.5% of respondents). Most HCPs (65%) were very/extremely familiar with GLP-1 RA, but only 30% with GIP RA and 16% with GCGR. Most HCPs expected dual GCGR/GLP-1 RA to benefit many obesity-related conditions; however, only a minority of HCPs perceived that they would benefit non-cardiometabolic complications of obesity. Among HCPs prescribing AOMs, gaps exist in the management of people living with obesity as <50% are prescribed AOMs. Barriers to treatment indicate a need to improve access to AOMs. HCPs were less familiar with GCGR or GIP RA than GLP-1 RA but expect dual GCGR/GLP-1 RA may offer additional benefits, potentially addressing treatment barriers and access. Thus, there is a need for greater education among HCPs regarding the mechanism of action and therapeutic effects of GCGR agonists, and dual GCGR/GLP-1 RA, so that the full range of obesity-related complications can be effectively treated.

Customizable Click Biochemistry Strategy for the Design and Preparation of Glucagon-like Peptide-1 Conjugates and Coagonists.

The development of oligomeric glucagon-like peptide-1 (GLP-1) and GLP-1-containing coagonists holds promise for enhancing the therapeutic potential of the GLP-1-based drugs for treating type 2 diabetes mellitus (T2DM). Here, we report a facile, efficient, and customizable strategy based on genetically encoded SpyCatcher-SpyTag chemistry and an inducible, cleavable self-aggregating tag (icSAT) scheme. icSAT-tagged SpyTag-fused GLP-1 and the dimeric or trimeric SpyCatcher scaffold were designed for dimeric or trimeric GLP-1, while icSAT-tagged SpyCatcher-fused GLP-1 and the icSAT-tagged SpyTag-fused GIP were designed for dual GLP-1/GIP (glucose-dependent insulinotropic polypeptide) receptor agonist. These SpyCatcher- and SpyTag-fused protein pairs were spontaneously ligated directly from the cell lysates. The subsequent icSAT scheme, coupled with a two-step standard column purification, resulted in target proteins with authentic N-termini, with yields ranging from 35 to 65 mg/L and purities exceeding 99%. In vitro assays revealed 3.0- to 4.1-fold increased activities for dimeric and trimeric GLP-1 compared to mono-GLP-1. The dual GLP-1/GIP receptor agonist exhibited balanced activity toward the GLP-1 receptor or the GIP receptor. All the proteins exhibited 1.8- to 3.0-fold prolonged half-lives in human serum compared to mono-GLP-1 or GIP. This study provides a generally applicable click biochemistry strategy for developing oligomeric or dual peptide/protein-based drug candidates.

Tirzepatide: A First-in-class Twincretin for the Management of Type 2 Diabetes

Background: Tirzepatide (LY3298176) was approved by U.S. Food and Drug Administration (FDA) on May 13th, 2022. The drug was developed by Eli Lilly and Co. and marketed under the trade name of ‘Mounjaro’, a first-in-class ‘Twincretin’, which is a dual activator of GIP and GLP-1 receptors, resulting in improved blood sugar control in type 2 diabetics The review covered the comprehensive insight on the drug discovery journey of tirzepatide. Methods: Using the keywords "Tirzepatide", "Twincretin", "Type 2 Diabetes", "GLP-1", and "GIP," data were gathered from Medline, PubMed, Google Scholar, and Science Direct. Results: The review covers comprehensive insight into the drug discovery journey of tirzepatide. The drug-target structural specialty has been discussed to establish the dual inhibition mechanism of action of tirzepatide. The results of in vitro studies, preclinical and clinical trial data, pharmacokinetic profile, dosing regimen, side effects, and toxicities of tirzepatide are reviewed to account for the potency, efficacy, and safety of the newly approved drug. The drug molecule may attain a privileged status in the antidiabetic market as the clinical data showed that it effectively reduces HbA1c level in monotherapy as well as in add-on therapy, compared to placebo, semaglutide, insulin degludec, and insulin glargine, and found effective in type 2 diabetes associated conditions like atherogenic dyslipidemia and non-alcoholic steatohepatitis. Conclusion: Tirzepatide is a clinically efficient drug, exhibiting a good safety profile as evident from the existing clinical data, and could be a new alternative to the currently available antidiabetics for the treatment of T2D.

Evaluating the efficacy of GIPR agonists on non-alcoholic fatty liver disease: A Mediation Mendelian Randomization Study

ObjectiveNon-alcoholic fatty liver disease (NAFLD) is becoming the most common chronic liver disease worldwide while still lacks drugs for treatment or prevention. We aimed to investigate the causal role of glucose-dependent insulinotropic polypeptide receptor agonists (GIPRAs) on NAFLD and identify the mediated risk factors by which GIPRAs exert their therapeutic effects. MethodsGenetic proxies of GIPRAs were identified as cis-SNPs of GIPR associated with both the gene expression level and HbA1c and analyses including colocalization and linkage disequilibrium (LD) were performed for validation. We then performed two-sample two-step mendelian randomization to determine the causal effect of GIPRAs on NAFLD. ResultsThe MR analysis suggested genetic proxies of GIPRAs were causally associated with reduced risk of NAFLD (Odds ratio (OR): 0.46, 95 % confidence interval (95 % CI): 0.24–0.88, P = 0.02) and T2DM (OR: 0.10, 95 % CI: 0.07–0.13, P < 0.01). In addition, Mediation analysis showed evidence of indirect effect of GIPRAs on NAFLD via TRIG (0.88, [0.85–0.92], P < 0.01) and HDL-C (0.85, [0.80–0.90], P < 0.01). ConclusionsOur study provided strong evidence to support the causal role of GIPRAs on reducing the risk of NAFLD probably through improving lipid metabolism, especially TG and HDL-C, providing guidance for future clinical trials.

Incretin-Based Weight Loss Pharmacotherapy: Can Resistance Exercise Optimize Changes in Body Composition?

This narrative review highlights the degree to which new antiobesity medications based on gut-derived nutrient-stimulated hormones (incretins) cause loss of lean mass, and the importance of resistance exercise to preserve muscle. Glucagon-like peptide 1 receptor agonists (GLP-1RA) induce substantial weight loss in randomized trials, effects that may be enhanced in combination with glucose-dependent insulinotropic polypeptide (GIP) receptor agonists. Liraglutide and semaglutide (GLP-1RA), tirzepatide (GLP-1 and GIP receptor dual agonist), and retatrutide (GLP-1, GIP, and glucagon receptor triple agonist) are peptides with incretin agonist activity that induce ∼15-24% weight loss in adults with overweight and obesity, alongside beneficial impacts on blood pressure, cholesterol, blood glucose, and insulin. However, these agents also cause rapid and significant loss of lean mass (∼10% or ∼6 kg), comparable to a decade or more of aging. Maintaining muscle mass and function as humans age is crucial to avoiding sarcopenia and frailty, which are strongly linked to morbidity and mortality. Studies indicate that supervised resistance exercise training interventions with a duration >10 weeks can elicit large increases in lean mass (∼3 kg) and strength (∼25%) in men and women. After a low-calorie diet, combining aerobic exercise with liraglutide improved weight loss maintenance compared with either alone. Retaining lean mass during incretin therapy could blunt body weight (and fat) regain on cessation of weight loss pharmacotherapy. We propose that tailored resistance exercise training be recommended as an adjunct to incretin therapy to optimize changes in body composition by preserving lean mass while achieving fat loss.

Contemporary management of obesity: A comparison of bariatric metabolic surgery and novel incretin mimetic drugs.

The global prevalence of obesity has risen sharply during the past half-century, reaching pandemic proportions and creating a public health crisis. Obesity is a recognized risk factor for the development of diabetes, atherosclerosis, hypertension, hepatic steatosis, and many other cardiometabolic disorders with significant resultant morbidity and mortality. Though treatment of obesity can prevent or slow the progression of these aforementioned illnesses, efforts to help patients achieve reliable and sustainable weight loss have had limited success. While improving nutrition and increasing physical activity results in a host of health benefits, the weight loss achieved with lifestyle interventions alone is modest and difficult to sustain. Early attempts at medical and surgical treatment of obesity were plagued with adverse effects and complications. Moreover, these approaches failed to demonstrate long-term health benefits, even when weight loss was achieved. Recently, novel incretin-based therapies targeting glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors have gained popularity due to their effectiveness in achieving substantial weight loss in patients both with and without diabetes. After many successful clinical trials, there are now multiple GLP-1 and one dual GLP-1-GIP receptor agonists FDA approved for chronic weight management. Advancements in laparoscopic surgical technique and refinements in procedure selection have similarly improved the safety and efficacy of bariatric metabolic surgery for achieving weight reduction in overweight and obese patients. In this review, we discuss the advantages and disadvantages of contemporary pharmacologic and surgical weight management strategies. We review the data regarding expected weight loss, glycemic control, cardiometabolic benefits, and potential adverse effects of various treatment approaches. As obesity rates continue to rise worldwide, it is imperative that clinicians keep these considerations in mind in order to better care for patients.

Gastric Inhibitory Polypeptide Receptor (GIPR) Overexpression Reduces the Tumorigenic Potential of Retinoblastoma Cells.

Retinoblastoma (RB) is the most common malignant intraocular tumor in early childhood. Gene expression profiling revealed that the gastric inhibitory polypeptide receptor (GIPR) is upregulated following trefoil factor family peptide 1 (TFF1) overexpression in RB cells. In the study presented, we found this G protein-coupled transmembrane receptor to be co-expressed with TFF1, a new diagnostic and prognostic RB biomarker for advanced subtype 2 RBs. Functional analyses in two RB cell lines revealed a significant reduction in cell viability and growth and a concomitant increase in apoptosis following stable, lentiviral GIPR overexpression, matching the effects seen after TFF1 overexpression. In chicken chorioallantoic membrane (CAM) assays, GIPR-overexpressing RB cells developed significantly smaller CAM tumors. The effect of GIPR overexpression in RB cells was reversed by the GIPR inhibitor MK0893. The administration of recombinant TFF1 did not augment GIPR overexpression effects, suggesting that GIPR does not serve as a TFF1 receptor. Investigations of potential GIPR up- and downstream mediators suggest the involvement of miR-542-5p and p53 in GIPR signaling. Our results indicate a tumor suppressor role of GIPR in RB, suggesting its pathway as a new potential target for future retinoblastoma therapy.

Incretin-based investigational therapies for the treatment of MASLD/MASH

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), is the most common form of chronic liver disease. It exists as either simple steatosis or its more progressive form, metabolic dysfunction-associated steatohepatitis (MASH), formerly, non-alcoholic steatohepatitis (NASH). The global prevalence of MASLD is estimated to be 32% among adults and is projected to continue to rise with increasing rates of obesity, type 2 diabetes, and metabolic syndrome. While simple steatosis is often considered benign and reversible, MASH is progressive, potentially leading to the development of cirrhosis, liver failure, and hepatocellular carcinoma. Treatment of MASH is therefore directed at slowing, stopping, or reversing the progression of disease. Evidence points to improved liver histology with therapies that result in sustained body weight reduction. Incretin-based molecules, such as glucagon-like peptide-1 receptor agonists (GLP-1 RAs), alone or in combination with glucose-dependent insulinotropic polypeptide (GIP) and/or glucagon receptor agonists, have shown benefit here, and several are under investigation for MASLD/MASH treatment. In this review, we discuss current published data on GLP-1, GIP/GLP-1, GLP-1/glucagon, and GLP-1/GIP/glucagon RAs in MASLD/MASH, focusing on their efficacy on liver histology, liver fat, and MASH biomarkers.

Dual and Triple Incretin-Based Co-agonists: Novel Therapeutics for Obesity and Diabetes.

The discovery of long-acting incretin receptor agonists represents a major stride forward in tackling the dual epidemic of obesity and diabetes. Here we outline the evolution of incretin-based pharmacotherapy, from exendin-4 to the discovery of the multi-incretin hormone receptor agonists that look set to be our next step toward curing diabetes and obesity. We discuss the multiagonists currently in clinical trials and the improvement in efficacy each new generation of these drugs bring. The success of these agents in preclinical models and clinical trials suggests a promising future for multiagonists in the treatment of metabolic diseases, with the most recent glucose-dependent insulinotropic peptide receptor:glucagon-like peptide1 receptor:glucagon receptor (GIPR:GLP-1R:GCGR) triagonists rivaling the efficacy of bariatric surgery. However, further research is needed to fully understand how these therapies exert their effect on body weight and in the last section we cover open questions about the potential mechanisms of multiagonist drugs, and the understanding of how gut-brain communication can be leveraged to achieve sustained body weight loss without adverse effects.

The interplay of glucose-dependent insulinotropic polypeptide in adipose tissue.

Adipose tissue was once known as a reservoir for energy storage but is now considered a crucial organ for hormone and energy flux with important effects on health and disease. Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted from the small intestinal K cells, responsible for augmenting insulin release, and has gained attention for its independent and amicable effects with glucagon-like peptide 1 (GLP-1), another incretin hormone secreted from the small intestinal L cells. The GIP receptor (GIPR) is found in whole adipose tissue, whereas the GLP-1 receptor (GLP-1R) is not, and some studies suggest that GIPR action lowers body weight and plays a role in lipolysis, glucose/lipid uptake/disposal, adipose tissue blood flow, lipid oxidation, and free-fatty acid (FFA) re-esterification, which may or may not be influenced by other hormones such as insulin. This review summarizes the research on the effects of GIP in adipose tissue (distinct depots of white and brown) using cellular, rodent, and human models. In doing so, we explore the mechanisms of GIPR-based medications for treating metabolic disorders, such as type 2 diabetes and obesity, and how GIPR agonism and antagonism contribute to improvements in metabolic health outcomes, potentially through actions in adipose tissues.

DPP-4 inhibitors sitagliptin and PF-00734,200 mitigate dopaminergic neurodegeneration, neuroinflammation and behavioral impairment in the rat 6-OHDA model of Parkinson's disease.

Epidemiological studies report an elevated risk of Parkinson's disease (PD) in patients with type 2 diabetes mellitus (T2DM) that is mitigated in those prescribed dipeptidyl peptidase 4 (DPP-4) inhibitors. With an objective to characterize clinically translatable doses of DPP-4 inhibitors (gliptins) in a well-characterized PD rodent model, sitagliptin, PF-00734,200 or vehicle were orally administered to rats initiated either 7-days before or 7-days after unilateral medial forebrain bundle 6-hydroxydopamine (6-OHDA) lesioning. Measures of dopaminergic cell viability, dopamine content, neuroinflammation and neurogenesis were evaluated thereafter in ipsi- and contralateral brain. Plasma and brain incretin and DPP-4 activity levels were quantified. Furthermore, brain incretin receptor levels were age-dependently evaluated in rodents, in 6-OHDA challenged animals and human subjects with/without PD. Cellular studies evaluated neurotrophic/neuroprotective actions of combined incretin administration. Pre-treatment with oral sitagliptin or PF-00734,200 reduced methamphetamine (meth)-induced rotation post-lesioning and dopaminergic degeneration in lesioned substantia nigra pars compacta (SNc) and striatum. Direct intracerebroventricular gliptin administration lacked neuroprotective actions, indicating that systemic incretin-mediated mechanisms underpin gliptin-induced favorable brain effects. Post-treatment with a threefold higher oral gliptin dose, likewise, mitigated meth-induced rotation, dopaminergic neurodegeneration and neuroinflammation, and augmented neurogenesis. These gliptin-induced actions associated with 70-80% plasma and 20-30% brain DPP-4 inhibition, and elevated plasma and brain incretin levels. Brain incretin receptor protein levels were age-dependently maintained in rodents, preserved in rats challenged with 6-OHDA, and in humans with PD. Combined GLP-1 and GIP receptor activation in neuronal cultures resulted in neurotrophic/neuroprotective actions superior to single agonists alone. In conclusion, these studies support further evaluation of the repurposing of clinically approved gliptins as a treatment strategy for PD.

GIP-derived GIP receptor antagonists – a review of their role in GIP receptor pharmacology

Surprisingly, agonists, as well as antagonists of the glucose-dependent insulinotropic polypeptide receptor (GIPR), are currently being used or investigated as treatment options for type 2 diabetes and obesity – and both, when combined with glucagon-like peptide 1 receptor (GLP-1R) agonism, enhance GLP-1-induced glycemia and weight loss further. This paradox raises several questions regarding not only the mechanisms of actions of GIP but also the processes engaged during the activation of both the GIP and GLP-1 receptors. Here, we provide an overview of studies of the properties and actions of peptide-derived GIPR antagonists, focusing on GIP(3-30)NH2, a naturally occurring N- and C-terminal truncation of GIP(1−42). GIP(3−30)NH2 was the first GIPR antagonist administered to humans. GIP(3−30)NH2 and a few additional antagonists, like Pro3-GIP, have been used in both in vitro and in vivo studies to elucidate the molecular and cellular consequences of GIPR inhibition, desensitization, and internalization and, at a larger scale, the role of the GIP system in health and disease. We provide an overview of these studies combined with recent knowledge regarding the effects of naturally occurring variants of the GIPR system and species differences within the GIP system to enhance our understanding of the GIPR as a drug target.

DR10627, a Novel Dual Glucagon‑like Peptide‑1 and Gastric Inhibitory Polypeptide Receptor Agonist for the Treatment of Obesity and Type 2 Diabetes Mellitus.

Diabetes and obesity are momentous risk factors threatening people's lives and health. Currently available incretin analogue glucagon-like peptide 1 (GLP-1) possesses huge hypoglycemic effect with the unsatisfactory effect of weight loss. Co-agonists targeting GLP-1R plus glucagon receptor (GCGR) or gastric inhibitory polypeptide receptor (GIPR) show synergistic benefits in glycaemic control and weight loss. Here, we describe a novel dual GIP and GLP-1 receptor agonist, DR10627, and performed a preclinical assessment of it. The agonistic ability of DR10627 was indirectly assessed by inducing cAMP accumulation in Chinese hamster ovary (CHO) cells transfected with GLP-1R or GIPR in vitro. The plasma pharmacokinetics of DR10627 were analysed in cynomolgus monkeys. The OGTTs were performed in Sprague‑Dawley (SD) rats. The glucose lowering effects were evaluated by repeated administration of DR10627 in diabetic (db/db) mice for 4 weeks. The effects of anti-obesity and improving metabolism of DR10627 were evaluated by repeated administration of DR10627 in diet-induced obesity (DIO) mice for 57 days. DR10627 had the capacity to activate both GLP-1R and GIPR in vitro. The terminal half-life of DR10627 was found to be approximately 4.19-5.8 h in cynomolgus monkeys. DR10627 had a great improvement in oral glucose tolerance in SD rats. Moreover, DR10627 had a potent glucose-lowering effect in db/db mice, and the hypoglycemic effect of 18 nmol/kg DR10627 was better than that of 50 nmol/kg liraglutide. In addition, 10 and 30 nmol/kg DR10627 possessed the ability of potentiating the weight-loss, lipid-lowing efficacy and improving metabolism to a greater extent than 80 nmol/kg liraglutide. Preclinical assessment demonstrated that administration of DR10627 resulted in glucose lowering in SD rats and db/db mice, and substantial body weight reduction and metabolism improvement in DIO mice. DR10627 is a promising agent deserving further investigation for the treatment of type 2 diabetes and obesity.

The antiemetic actions of GIP receptor agonism.

Nausea and vomiting are primitive aspects of mammalian physiology and behavior that ensure survival. Unfortunately, both are ubiquitously present side effects of drug treatments for many chronic diseases with negative consequences on pharmacotherapy tolerance, quality of life, and prognosis. One of the most critical clinical examples is the profound emesis and nausea that occur in patients undergoing chemotherapy, which continue to be among the most distressing side effects, even with the use of modern antiemetic medications. Similarly, antiobesity/diabetes medications that target the glucagon-like peptide-1 system, despite their remarkable metabolic success, also cause nausea and vomiting in a significant number of patients. These side effects hinder the ability to administer higher dosages for optimal glycemic and weight management and represent the major reasons for treatment discontinuation. Our inability to effectively control these side effects highlights the need to anatomically, molecularly, and functionally characterize novel neural substrates that drive and inhibit nausea and emesis. Here, we discuss clinical and preclinical evidence that highlights the glucose-dependent insulinotropic peptide receptor system as a novel therapeutic central target for the management of nausea and emesis.

Immunomodulation and inflammation: Role of GLP-1R and GIPR expressing cells within the gut

Glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are peptide hormones produced by enteroendocrine cells in the small intestine. Despite being produced in the gut, the leveraging of their role in potentiating glucose-stimulated insulin secretion, also known as the incretin effect, has distracted from discernment of direct intestinal signaling circuits. Both preclinical and clinical evidence have highlighted a role for the incretins in inflammation. In this review, we highlight the discoveries of GLP-1 receptor (GLP-1R)+ natural (TCRαβ and TCRγδ) and induced (TCRαβ+CD4+ cells and TCRαβ+CD8αβ+) intraepithelial lymphocytes. Both endogenous signaling and pharmacological activation of GLP-1R impact local and systemic inflammation, the gut microbiota, whole-body metabolism, as well as the control of GLP-1 bioavailability. While GIPR signaling has been documented to impact hematopoiesis, the impact of these bone marrow-derived cells in gut immunology is not well understood. We uncover gaps in the literature of the evaluation of the impact of sex in these GLP-1R and GIP receptor (GIPR) signaling circuits and provide speculations of the maintenance roles these hormones play within the gut in the fasting-refeeding cycles. GLP-1R agonists and GLP-1R/GIPR agonists are widely used as treatments for diabetes and weight loss, respectively; however, their impact on gut homeostasis has not been fully explored. Advancing our understanding of the roles of GLP-1R and GIPR signaling within the gut at homeostasis as well as metabolic and inflammatory diseases may provide targets to improve disease management.

Regulation of energy metabolism through central GIPR signaling

In recent years, significant progress has been made to pharmacologically combat the obesity pandemic, particularly with regard to biochemically tailored drugs that simultaneously target the receptors for glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic polypeptide (GIP). But while the pharmacological benefits of GLP-1 receptor (GLP-1R) agonism are widely acknowledged, the role of the GIP system in regulating systems metabolism remains controversial. When given in adjunct to GLP-1R agonism, both agonism and antagonism of the GIP receptor (GIPR) improves metabolic outcome in preclinical and clinical studies, and despite persistent concerns about its potential obesogenic nature, there is accumulating evidence indicating that GIP has beneficial metabolic effects via central GIPR agonism. Nonetheless, despite growing recognition of the GIP system as a valuable pharmacological target, there remains great uncertainty as to where and how GIP acts in the brain to regulate metabolism, and how GIPR agonism may differ from GIPR antagonism in control of energy metabolism. In this review we highlight current knowledge on the central action of GIP, and discuss open questions related to its multifaceted biology in the brain and the periphery.

Evaluating the Efficacy and Safety of Tirzepatide on Glycaemic and Non-glycaemic Outcomes in Diabetes: A Systematic Review of Meta-Analyses.

Tirzepatide is a novel once-a-week dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist, recently approved for type 2 diabetes mellitus (T2DM) and obesity. A systematic review of the literature published in multiple meta-analyses on Tirzepatide with emphasis on its effect on glycaemic and non-glycaemic parameters was conducted. We systematically searched the electronic databases PubMed and Google Scholar up to August 2023 for meta-analyses that compared Tirzepatide with placebo or active antihyperglycaemic drugs in subjects with T2DM. Various parameters for efficacy and safety, with their point estimates and confidence intervals, such as glycated haemoglobin (HbA1c), fasting serum glucose (FSG), body weight, lipid, and cardiovascular outcomes were assessed. Six meta-analyses fulfilled the pre-specified criteria and were included in the study. In all the studies, Tirzepatide treatment at different doses resulted in a significant reduction in HbA1c and FSG levels along with a significant reduction in weight compared with active control and placebo groups. Tirzepatide significantly reduced levels of triglycerides and increased high-density lipoprotein (HDL) cholesterol, whether used as monotherapy or add-on therapy. The studies suggested the cardiovascular safety ofTirzepatide as there was no increase in major adverse cardiovascular events(MACE). The drug shows lesser hypoglycemia but predominant gastrointestinal adverse effects such as nausea, vomiting, and diarrhoea. In conclusion, Tirzepatide shows superior glycaemic control and weight loss in patients with T2DM with beneficial effects on lipids, without an increased risk of hypoglycemia and cardiovascular events.