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We report that intra-islet glucagon secreted from α-cells signals through β-cell glucagon and GLP-1 receptors (GcgR and GLP-1R), thereby conferring to rat islets their competence to exhibit first-phase glucose-stimulated insulin secretion (GSIS). Thus, in islets not treated with exogenous glucagon or GLP-1, first-phase GSIS is abolished by a GcgR antagonist (LY2786890) or a GLP-1R antagonist (Ex[9-39]). Mechanistically, glucose competence in response to intra-islet glucagon is conditional on β-cell cAMP signaling because it is blocked by the cAMP antagonist prodrug Rp-8-Br-cAMPS-pAB. In its role as a paracrine hormone, intra-islet glucagon binds with high affinity to the GcgR, while also exerting a "spillover" effect to bind with low affinity to the GLP-1R. This produces a right shift of the concentration-response relationship for the potentiation of GSIS by exogenous glucagon. Thus, 0.3 nM glucagon fails to potentiate GSIS, as expected if similar concentrations of intra-islet glucagon already occupy the GcgR. However, 10 to 30 nM glucagon effectively engages the β-cell GLP-1R to potentiate GSIS, an action blocked by Ex[9-39] but not LY2786890. Finally, we report that the action of intra-islet glucagon to support insulin secretion requires a step-wise increase of glucose concentration to trigger first-phase GSIS. It is not measurable when GSIS is stimulated by a gradient of increasing glucose concentrations, as occurs during an oral glucose tolerance test in vivo. Collectively, such findings are understandable if defective intra-islet glucagon action contributes to the characteristic loss of first-phase GSIS in an intravenous glucose tolerance test that is diagnostic of type 2 diabetes in the clinical setting. [ABSTRACT FROM AUTHOR]

Receptor activity-modulating proteins (RAMPs) are accessory molecules that form complexes with specific G protein-coupled receptors (GPCRs) and modulate their functions. It is established that RAMP interacts with the glucagon receptor family of GPCRs but the underlying mechanism is poorly understood. In this study, we used a bioluminescence resonance energy transfer (BRET) approach to comprehensively investigate such interactions. In conjunction with cAMP accumulation, G α q activation and β -arrestin1/2 recruitment assays, we not only verified the GPCR–RAMP pairs previously reported, but also identified new patterns of GPCR–RAMP interaction. While RAMP1 was able to modify the three signaling events elicited by both glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), and RAMP2 mainly affected β -arrestin1/2 recruitment by GCGR, GLP-1R and glucagon-like peptide-2 receptor, RAMP3 showed a widespread negative impact on all the family members except for growth hormone-releasing hormone receptor covering the three pathways. Our results suggest that RAMP modulates both G protein dependent and independent signal transduction among the glucagon receptor family members in a receptor-specific manner. Mapping such interactions provides new insights into the role of RAMP in ligand recognition and receptor activation. This study identified the interactome between RAMP and the glucagon receptor family of GPCRs. The interactions were further characterized by signaling profiles of cAMP accumulation, G α q activation and β -arrestin1/2 recruitment. [Display omitted] [ABSTRACT FROM AUTHOR]

The first intracellular loop (ICL1) of G protein-coupled receptors (GPCRs) has received little attention, although there is evidence that, with the 8th helix (H8), it is involved in early conformational changes following receptor activation as well as contacting the G protein β subunit. In class B1 GPCRs, the distal part of ICL1 contains a conserved R12.48KLRCxR2.46b motif that extends into the base of the second transmembrane helix; this is weakly conserved as a [R/H]12.48KL[R/H] motif in class A GPCRs. In the current study, the role of ICL1 and H8 in signaling through cAMP, iCa2+ and ERK1/2 has been examined in two class B1 GPCRs, using mutagenesis and molecular dynamics. Mutations throughout ICL1 can either enhance or disrupt cAMP production by CGRP at the CGRP receptor. Alanine mutagenesis identified subtle differences with regard elevation of iCa2+, with the distal end of the loop being particularly sensitive. ERK1/2 activation displayed little sensitivity to ICL1 mutation. A broadly similar pattern was observed with the glucagon receptor, although there were differences in significance of individual residues. Extending the study revealed that at the CRF1 receptor, an insertion in ICL1 switched signaling bias between iCa2+ and cAMP. Molecular dynamics suggested that changes in ICL1 altered the conformation of ICL2 and the H8/TM7 junction (ICL4). For H8, alanine mutagenesis showed the importance of E3908.49b for all three signal transduction pathways, for the CGRP receptor, but mutations of other residues largely just altered ERK1/2 activation. Thus, ICL1 may modulate GPCR bias via interactions with ICL2, ICL4 and the Gβ subunit. [ABSTRACT FROM AUTHOR]

Aim: To develop more effective and long‐lasting antiobesity and antidiabetic therapeutics by employing novel chemical modifications of glucagon‐like peptide‐1 receptor (GLP‐1R) agonists. Methods: We constructed novel unimolecular dual agonists of GLP‐1R and glucagon receptor prepared by linking sEx‐4 and native glucagon (GCG) via lysine or triazole [sEx4‐GCG(K) and sEx4‐GCG(T), respectively] and evaluated their antiobesity and antidiabetic efficacy in the diabetic and obese mouse model. Results: Both sEx4‐GCG(K) and sEx4‐GCG(T) showed the beneficial metabolic effects of GLP‐1 and glucagon: they promoted weight loss and ameliorated insulin resistance and hepatic steatosis. They also increased thermogenesis in brown adipose tissue, and lipolysis and β‐oxidation in white adipose tissue, with concomitant suppression of lipogenesis. Furthermore, both dual agonists activated the 5′‐AMP‐activated protein kinase signalling pathway and prevented palmitate‐induced oxidative stress in skeletal muscle cells. Conclusion: Through their complementary dual agonism, sEx4‐GCG(T) and sEx4‐GCG(K) induce more marked weight loss and metabolic improvements than conventional agonists, and could be developed as novel therapeutic agents for the treatment of obesity and associated metabolic disorders in humans. [ABSTRACT FROM AUTHOR]

Insulin- induced hypoglycemia is a major treatment barrier in type- 1 diabetes (T1D). Accordingly, it is important that we understand the mechanisms regulating the circulating levels of glucagon. Varying glucose over the range of concentrations that occur physiologically between the fed and fuel- deprived states (8 to 4 mM) has no significant effect on glucagon secretion in the perfused mouse pancreas or in isolated mouse islets (in vitro), and yet associates with dramatic increases in plasma glucagon. The identity of the systemic factor(s) that elevates circulating glucagon remains unknown. Here, we show that arginine- vasopressin (AVP), secreted from the posterior pituitary, stimulates glucagon secretion. Alpha- cells express high levels of the vasopressin 1b receptor (V1bR) gene (Avpr1b). Activation of AVP neurons in vivo increased circulating copeptin (the C- terminal segment of the AVP precursor peptide) and increased blood glucose; effects blocked by pharmacological antagonism of either the glucagon receptor or V1bR. AVP also mediates the stimulatory effects of hypoglycemia produced by exogenous insulin and 2- deoxy- D- glucose on glucagon secretion. We show that the A1/C1 neurons of the medulla oblongata drive AVP neuron activation in response to insulin- induced hypoglycemia. AVP injection increased cytoplasmic Ca2+ in alpha- cells (implanted into the anterior chamber of the eye) and glucagon release. Hypoglycemia also increases circulating levels of AVP/copeptin in humans and this hormone stimulates glucagon secretion from human islets. In patients with T1D, hypoglycemia failed to increase both copeptin and glucagon. These findings suggest that AVP is a physiological systemic regulator of glucagon secretion and that this mechanism becomes impaired in T1D. [ABSTRACT FROM AUTHOR]

The year 2023 brought reports of highly effective glucagon-like peptide 1 (GLP1) mono-agonists or combinations with amylin receptor agonists. Results for monomolecular co-agonists that added glucagon receptor and/or glucose-dependent insulinotropic polypeptide (GIP) receptor agonism to GLP1 receptor activation were also published in 2023. Interestingly, antagonistic GIP receptor antibodies conjugated with a GLP1 agonist were also shown to be effective. Key advances: Of particular interest are the SURMOUNT trials from 2023 of the GLP1–GIP co-agonist tirzepatide, which have shown weight loss of up to 25% of body weight in people with obesity4. A phase II trial with retatrutide, a GIP–GLP1–glucagon triple agonist, resulted in weight loss of 25% in patients with obesity3. A new long-acting amylin-based agonist, cagrilintide, has shown good efficacy in obesity, especially in combination with the highly effective GLP1 receptor agonist semaglutide, with potential for weight loss exceeding 20%5. Promising results of a small-molecule GLP1 receptor agonist (orforglipron)10 suggest that an orally active, effective agent will soon be made available, which is of huge interest in countries where injectable therapies are not immediately acceptable; positive results have also been reported for oral semaglutide2. AMG 133 combines GLP1 agonism with GIP antagonism, and has shown promising results7. [ABSTRACT FROM AUTHOR]

Pancreatic β-cell neogenesis in vivo holds great promise for cell replacement therapy in diabetic patients, and discovering the relevant clinical therapeutic strategies would push it forward to clinical application. Liraglutide, a widely used antidiabetic glucagon-like peptide-1 (GLP-1) analog, has displayed diverse β-cell-protective effects in type 2 diabetic animals. Glucagon receptor (GCGR) monoclonal antibody (mAb), a preclinical agent that blocks glucagon pathway, can promote recovery of functional β-cell mass in type 1 diabetic mice. Here, we conducted a 4-week treatment of the two drugs alone or in combination in type 1 diabetic mice. Although liraglutide neither lowered the blood glucose level nor increased the plasma insulin level, the immunostaining showed that liraglutide expanded β-cell mass through self-replication, differentiation from precursor cells, and transdifferentiation from pancreatic α cells to β cells. The pancreatic β-cell mass increased more significantly after GCGR mAb treatment, while the combination group did not further increase the pancreatic β-cell area. However, compared with the GCGR mAb group, the combined treatment reduced the plasma glucagon level and increased the proportion of β cells/α cells. Our study evaluated the effect of liraglutide, GCGR mAb monotherapy, or combined strategy in glucose control and islet β-cell regeneration and provided useful clues for the future clinical application in type 1 diabetes. [ABSTRACT FROM AUTHOR]

Glucagon receptor agonists show promise as components of next generation metabolic syndrome pharmacotherapies. However, the biology of glucagon action is complex, controversial, and likely context dependent. As such, a better understanding of chronic glucagon receptor (GCGR) agonism is essential to identify and mitigate potential clinical side-effects. Herein we present a novel, long-acting glucagon analogue (GCG104) with high receptor-specificity and potent in vivo action. It has allowed us to make two important observations about the biology of sustained GCGR agonism. First, it causes weight loss in mice by direct receptor signalling at the level of the liver. Second, subtle changes in GCG104-sensitivity, possibly due to interindividual variation, may be sufficient to alter its effects on metabolic parameters. Together, these findings confirm the liver as a principal target for glucagon-mediated weight loss and provide new insights into the biology of glucagon analogues. [ABSTRACT FROM AUTHOR]

Type 2 diabetes is characterized by chronic hyperglycemia. Insulin, a hormone secreted from pancreatic β‐cells, decreases blood glucose levels, and glucagon, a hormone secreted from pancreatic α‐cells, increases blood glucose levels by counterregulation of insulin through stimulation of hepatic glucose production. In diabetic patients, dysregulation of glucagon secretion contributes to hyperglycemia. Thus, inhibition of the glucagon receptor is one strategy for the treatment of hyperglycemia in type 2 diabetes. In this paper, we report a series of biphenylsulfonamide derivatives that were designed, synthesized, and then evaluated by cAMP and hepatic glucose production assays as glucagon receptor antagonists. Of these, compound 7aB‐3 decreased glucagon‐induced cAMP production and glucagon‐induced glucose production in the in vitro assays. Glucagon challenge tests and glucose tolerance tests showed that compound 7aB‐3 significantly inhibited glucagon‐induced glucose increases and improved glucose tolerance. These results suggest that compound 7aB‐3 has therapeutic potential for the treatment of type 2 diabetes. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the safety and pharmacokinetics of cotadutide, a dual glucagon‐like peptide‐1 (GLP‐1) and glucagon receptor agonist, in overweight Asian participants with or without type 2 diabetes (T2D). Materials and Methods: In the phase 1, randomized, blinded, single‐ascending dose study, 24 Japanese and eight Chinese healthy adults (body mass index [BMI] 23‐40 kg/m2) received one subcutaneous dose of cotadutide (50‐150 or 100 μg, respectively) or placebo. The primary endpoint was safety. In the phase 2a, randomized, double‐blinded, parallel dose‐ranging study with forced uptitration, 61 Japanese adults with T2D (BMI 24‐40 kg/m2; HbA1c 7.0%‐10.5%) received cotadutide (100, 200, 300 μg) or placebo for 48 days. Co‐primary endpoints were safety/tolerability, change in glucose AUC0‐4h and body weight. Results: Significant reductions from baseline to day 48 were observed with cotadutide for glucose AUC0‐4h (33.6%‐42.1% reduction vs. +2.5% with placebo; 95% CIs: 100 μg −45.7%, −33.7%; 200 μg −35.6%, −23.7%; 300 μg −45.0%, −30.8%; placebo 3.4%, 8.3%) and body weight (1.3%‐2.5% decrease vs. +0.8% with placebo; 95% CIs: 100 μg −3.4%, −0.8%; 200 μg −4.7%, −2.0%; 300 μg −4.6%, −2.1%; placebo −2.1%, 0.4%). The most common adverse events with cotadutide were mild gastrointestinal symptoms with no serious adverse events. Increased pulse rate with cotadutide versus placebo is consistent with GLP‐1 monoagonists. Conclusions: Once‐daily cotadutide was effective and well tolerated up to 300 μg in overweight Japanese patients with T2D. Further evaluation in Asian populations is warranted. [ABSTRACT FROM AUTHOR]

The mammalian proglucagon gene (Gcg) encodes three glucagon like sequences, glucagon, glucagon-like peptide-1 (GLP-1), and glucagon-like peptide-2 that are of similar length and share sequence similarity, with these hormones having cell surface receptors, glucagon receptor (Gcgr), GLP-1 receptor (Glp1r), and GLP-2 receptor (Glp2r), respectively. Gcgr, Glp1r, and Glp2r are all class B1 G protein-coupled receptors (GPCRs). Despite their sequence and structural similarity, analyses of sequences from rodents have found differences in patterns of sequence conservation and evolution. To determine whether these were rodent-specific traits or general features of these genes in mammals I analyzed coding and protein sequences for proglucagon and the receptors for proglucagon-derived peptides from the genomes of 168 mammalian species. Single copy genes for each gene were found in almost all genomes. In addition to glucagon sequences within Hystricognath rodents (e.g., guinea pig), glucagon sequences from a few other groups (e.g., pangolins and some bats) as well as changes in the proteolytic processing of GLP-1 in some bats are suggested to have functional effects. GLP-2 sequences display increased variability but accepted few substitutions that are predicted to have functional consequences. In parallel, Glp2r sequences display the most rapid protein sequence evolution, and show greater variability in amino acids at sites involved in ligand interaction, however most were not predicted to have a functional consequence. These observations suggest that a greater diversity in biological functions for proglucagon-derived peptides might exist in mammals. [ABSTRACT FROM AUTHOR]

Sepsis is one of the most common comorbidities observed in diabetic patients, associated with a deficient innate immune response. Recently, we have shown that glucagon possesses anti-inflammatory properties. In this study, we investigated if hyperglucagonemia triggered by diabetes might reduce the migration of neutrophils, increasing sepsis susceptibility. 21 days after diabetes induction by intravenous injection of alloxan, we induced moderate sepsis in Swiss-Webster mice through cecum ligation and puncture (CLP). The glucagon receptor (GcgR) antagonist des-his1-[Glu9]-glucagon amide was injected intraperitoneally 24h and 1h before CLP. We also tested the effect of glucagon on CXCL1/KC-induced neutrophil migration to the peritoneal cavity in mice. Neutrophil chemotaxis in vitro was tested using transwell plates, and the expression of total PKA and phospho-PKA was evaluated by western blot. GcgR antagonist restored neutrophil migration, reduced CFU numbers in the peritoneal cavity and improved survival rate of diabetic mice after CLP procedure, however, the treatment did no alter hyperglycemia, CXCL1/KC plasma levels and blood neutrophilia. In addition, glucagon inhibited CXCL1/KC-induced neutrophil migration to the peritoneal cavity of non-diabetic mice. Glucagon also decreased the chemotaxis of neutrophils triggered by CXCL1/KC, PAF, or fMLP in vitro. The inhibitory action of glucagon occurred in parallel with the reduction of CXCL1/KC-induced actin polymerization in neutrophils in vitro , but not CD11a and CD11b translocation to cell surface. The suppressor effect of glucagon on CXCL1/KC-induced neutrophil chemotaxis in vitro was reversed by pre-treatment with GcgR antagonist and adenylyl cyclase or PKA inhibitors. Glucagon also increased PKA phosphorylation directly in neutrophils in vitro. Furthermore, glucagon impaired zymosan-A-induced ROS production by neutrophils in vitro. Human neutrophil chemotaxis and adherence to endothelial cells in vitro were inhibited by glucagon treatment. According to our results, this inhibition was independent of CD11a and CD11b translocation to neutrophil surface or neutrophil release of CXCL8/IL-8. Altogether, our results suggest that glucagon may be involved in the reduction of neutrophil migration and increased susceptibility to sepsis in diabetic mice. This work collaborates with better understanding of the increased susceptibility and worsening of sepsis in diabetics, which can contribute to the development of new effective therapeutic strategies for diabetic septic patients. [ABSTRACT FROM AUTHOR]

The human glucagon‐like peptide‐1 receptor (GLP‐1R) and the glucagon receptor (GCGR) are class B G protein‐coupled receptors (GPCRs) that are activated by interactions with, respectively, the glucagon‐like peptide‐1 (GLP‐1) and glucagon (GCG). These polypeptide hormones are involved in the regulation of lipid and cholic acid metabolism, and thus play an important role in the pathogenesis of glucose metabolism and diabetes mellitus, which attracts keen interest of these GPCRs as drug targets. GLP‐1R and GCGR have therefore been extensively investigated by X‐ray crystallography and cryo‐electron microscopy (cryo‐EM), so that their structures are well known. Here, we present the groundwork for using nuclear magnetic resonance (NMR) spectroscopy in solution to complement the molecular architectures with information on intramolecular dynamics and on the thermodynamics and kinetics of interactions with physiological ligands and extrinsic drug candidates. This includes the generation of novel, near‐wild‐type constructs of GLP‐1R and GCGR, optimization of the solution conditions for NMR studies in detergent micelles and in nanodiscs, post‐translational chemical introduction of fluorine‐19 NMR probes, and sequence‐specific assignments of the 19F‐labels attached to indigenous cysteines. Addition of the negative allosteric modulator (NAM) NNC0640 was critically important for obtaining the long‐time stability needed for our NMR experiments, and we report on novel insights into the allosteric effects arising from binding of NNC0640 to the transmembrane domain of GLP‐1R (GLP‐1R[TMD]). [ABSTRACT FROM AUTHOR]

Therefore, we hypothesized that inhibition of GCGR signaling, a pathway that does not activate PI3K, would be an attractive strategy to normalize PI3K inhibitor-induced hyperglycemia without disrupting the antitumor PI3K blockade. Both compensatory endogenous insulin release as well as treatment of hyperglycemia with exogenous insulin/insulin mimetics activate INSR-associated PI3K signaling, ultimately limiting blockade of tumor-associated PI3K signaling [[2]]. Our study of the GCGR mAb REMD-477 as a novel strategy to counteract PI3K inhibitor-induced hyperglycemia is an advance that may allow for more effective and safer use of potent PI3K inhibitors in the treatment of aggressive lymphomas. [Extracted from the article]

Objective: Cotadutide, a dual GLP-1 and glucagon receptor agonist, is under development for nonalcoholic steatohepatitis (NASH) and chronic kidney disease with type 2 diabetes. The effects of cotadutide on hepatic and metabolic parameters were evaluated in participants with overweight/obesity and type 2 diabetes.Research Design and Methods: In this phase 2b study, 834 adults with BMI ≥25 kg/m2 and type 2 diabetes inadequately controlled with metformin (glycated hemoglobin A1c [HbA1c] of 7.0%-10.5% [53-91 mmol/mol]) were randomized to double-blind cotadutide 100 μg (n = 100), 200 μg (n = 256), or 300 μg (n = 256); placebo (n = 110); or open-label liraglutide 1.8 mg (n = 110)-all administered subcutaneously. Coprimary end points were changes in HbA1c and body weight at week 14. The originally randomized interventions were continued to week 54. Liver damage biomarkers and liver fibrosis algorithms were assessed.Results: Cotadutide significantly decreased HbA1c and body weight at weeks 14 and 54 versus placebo (all P < 0.001). Improvements in lipid profile, AST and ALT levels, propeptide of type III collagen level, fibrosis-4 index, and nonalcoholic fatty liver disease fibrosis score were observed with cotadutide 300 μg versus placebo, but not with liraglutide. Weight loss with cotadutide 200 μg was similar to that with liraglutide 1.8 mg and greater with cotadutide 300 μg versus liraglutide 1.8 mg. The most common adverse events with cotadutide (nausea, 35%; vomiting, 17%) decreased over time.Conclusions: Cotadutide treatment for 54 weeks improved glycemic control and weight loss in participants with overweight/obesity and type 2 diabetes. Ad hoc analyses demonstrated improvements in hepatic parameters and support further evaluation of cotadutide in NASH. [ABSTRACT FROM AUTHOR]

Glucagon-like peptide-1 (GLP-1)/glucagon (GCG) dual receptor agonists with different receptor selectivity are under investigation and have shown significant improvement in both weight loss and glycemic control, but the optimal potency ratio between the two receptors to balance efficacy and safety remains unclear. We designed and constructed several dual receptor agonists with different receptor potency ratios using Fc fusion protein technology. The long-term effects of the candidates on body weight and metabolic dysfunction-associated steatotic liver disease (MASLD) were evaluated in diet-induced obese (DIO) model mice, high-fat diet (HFD)-ob/ob mice and AMLN diet-induced MASLD mice. Repeat dose toxicity assays were performed to investigate the safety profile of the candidate (HEC-C070) in Sprague Dawley (SD) rats. The high GCG receptor (GCGR) selectivity of HEC-C046 makes it more prominent than other compounds for weight loss and most MASLD parameters but may lead to safety concerns. The weight change of HEC-C052 with the lowest GCG agonism was inferior to that of selective GLP-1 receptor agonist (GLP-1RA) semaglutide in DIO model mice. The GLP-1R selectivity of HEC-C070 with moderate GCG agonism has a significant effect on weight loss and liver function in obese mice, and its lowest observed adverse effect level (LOAEL) was 30 nmol/kg in the repeat dose toxicity study. We compared the potential of the Fc fusion protein GLP-1/GCG dual receptor agonists with different receptor selectivity to provide the setting for future GLP-1/GCG dual receptor agonists to treat obesity and MASLD. [Display omitted] • A series of different ratios of GLP-1R/GCGR dual agonists were designed based on the sequence of human GCG. • GLP-1R/GCGR dual agonists improved body weight, fatty liver and glycaemic control in vivo. • GLP-1R/GCGR dual agonists have greater potential in the treatment ofmetabolic diseases than that of GLP-1R agonists. • The activity of GCG in GLP-1R/GCGR dual agonists can be enhanced as high as possible provided it is safe. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A study published in Nature Reviews Nephrology by Philipp Scherer and colleagues explores the role of kidney glucagon receptors (GCGRs) in kidney function and disease development. The researchers found that mice with knockout of Gcgr in the kidney showed evidence of kidney dysfunction and metabolic abnormalities, including altered glucose tolerance and insulin sensitivity, reduced kidney glucose output, and dysregulation of nitrogen, water, and electrolyte balance. These mice also exhibited hypertension, cardiac hypertrophy, and signs of kidney injury. The study suggests that downregulation of GCGRs may contribute to abnormal renal lipid disposition, oxidative stress, inflammation, and fibrosis, and promote the development of chronic kidney disease. [Extracted from the article]

Options for the treatment of type 2 diabetes mellitus (T2DM) and obesity have recently been expanded by the results of several large clinical trials with incretin-based peptide therapies. Most of these studies have been conducted with the glucagon-like peptide-1 (GLP-1) receptor agonist semaglutide, which is available as a once weekly subcutaneous injection and once daily tablet, and the once weekly injected dual agonist tirzepatide, which interacts with receptors for GLP-1 and glucose-dependent insulinotropic polypeptide (GIP). In individuals with T2DM these therapies have achieved reductions of glycated haemoglobin (HbA1c) by > 2% and lowered body weight by > 10%. In some studies, these agents tested in non-diabetic, obese individuals at much higher doses have lowered body weight by > 15%. Emerging evidence suggests these agents can also offer cardio-protective and potentially reno-protective effects. Other incretin-based peptide therapies in early clinical development, notably a triple GLP-1/GIP/glucagon receptor agonist (retatrutide) and a combination of semaglutide with the amylin analogue cagrilintide (CagriSema), have shown strong efficacy. Although incretin therapies can incur adverse gastrointestinal effects these are for most patients mild-to-moderate and transient but result in cessation of treatment in some cases. Thus, the efficacy of new incretin-based peptide therapies is enhancing the opportunity to control body weight and blood glucose and improve the treatment of T2DM and obesity. ● The GLP-1R agonist semaglutide achieved weight reduction of about 15% in the STEP trials. ● The GLP-1R/GIPR coagonist tirzepatide achieved weight reduction of about 20% in the SURMOUNT trials. ● Tirzepatide lowered HbA1c by about 2% and body weight by about 10-12 kg in the SURPASS trials. ● The GLP-1R/GIPR/GCGR triagonist, retatrutide achieved reductions in HbA1c by about 2% and weight by about 15 kg. ● Semaglutide with the amylin analogue, cagrilintide achieved similar reductions in HbA1c and weight as retatrutide. [ABSTRACT FROM AUTHOR]

Treatment with exogenous GLP-2 has been shown to accelerate the growth of intestinal adenomas and adenocarcinomas in experimental models of colonic neoplasia, however, the role of endogenous GLP-2 in tumor promotion is less well known. Mice with a global deletion of the glucagon receptor (Gcgr-/-) display an increase in circulating GLP-1 and GLP-2. Due to the intestinotrophic nature of GLP-2, we hypothesized that Gcgr-/- mice would be more susceptible to colonic dysplasia in a model of inflammation-induced colonic carcinogenesis. Female Gcgr-/- mice were first characterized for GLP-2 secretion and in a subsequent study they were given a single injection with the carcinogen azoxymethane (7.5 mg/kg) and treated with dextran sodium sulfate (DSS) (3%) for six days (n=19 and 9). A cohort of animals (n=4) received a colonoscopy 12 days following DSS treatment and all animals were sacrificed after six weeks. Disruption of glucagon receptor signaling led to increased GLP-2 secretion (p<0.0001) and an increased concentration of GLP-2 in the pancreas of Gcgr-/- mice, coinciding with an increase in small intestinal (p<0.0001) and colonic (p<0.05) weight. Increased villus height was recorded in the duodenum (p<0.001) and crypt depth was increased in the duodenum and jejunum (p<0.05 and p<0.05). Disruption of glucagon receptor signaling did not affect body weight during AOM/DSS treatment, neither did it affect the inflammatory score assessed during colonoscopy or the number of large and small adenomas present at the end of the study period. In conclusion, despite the increased endogenous GLP-2 secretion Gcgr-/- mice were not more susceptible to AOM/DSS-induced tumors. [ABSTRACT FROM AUTHOR]

Glucagon plays an important role in glucose homeostasis and amino acid metabolism. It regulates plasma amino acid levels which in turn modulate glucagon secretion from the pancreatic a-cell, thereby establishing a liver-a-cell axis described recently. We reported previously that the knock-in mice bearing homozygous V369M substitution (equivalent to a naturally occurring mutation V368M in the human glucagon receptor, GCGR) led to hypoglycemia with improved glucose tolerance. They also exhibited hyperglucagonemia, pancreas enlargement and a-cell hyperplasia. Here, we investigated the effect of V369M/V368M mutation on glucagon-mediated amino acidmetabolism. It was found that GcgrV369M+/+ mice displayed increased plasma amino acid levels in general, but significant accumulation of the ketogenic/glucogenic amino acids was observed in animals fed with a high-fat diet (HFD), resulting in deleterious metabolic consequence characteristic of a-cell proliferation and hyperglucagonemia. [ABSTRACT FROM AUTHOR]

Glucagon antagonism has been reported as a new therapeutic approach to hyperglycaemia. As the 14‐3‐3 protein YWHAB has been identified as a regulator of the glucagon receptor (GCGR) by affinity purification and mass spectrometry, we examined the role of YWHAB in vivo. Ywhab knockout mice display impaired blood glucose homeostasis only under pyruvate stimulation. Deletion of Ywhab in mouse primary hepatocytes (MPHs) increases hepatocyte glucose production by magnifying the effect of glucagon. Mechanistic analysis indicates that YWHAB forms a phosphorylation‐dependent complex with GCGR and directly interacts with forkhead box O1 (FOXO1). Together, these results reveal the inhibitory role of YWHAB in glucagon‐mediated hepatic glucose production, which may be a potential target for the control of gluconeogenesis and associated metabolic diseases. [ABSTRACT FROM AUTHOR]

Summary: Weight loss has been shown to improve metabolic parameters and cardiovascular risk in people with type 2 diabetes mellitus (T2DM). This phase 2 study evaluated the safety and efficacy of JNJ‐64565111, a dual agonist of GLP‐1 and glucagon receptors, in individuals with T2DM and class II/III obesity. In this randomized, double‐blind study, participants with T2DM (HbA1c 6.5%‐9.5%), body mass index of 35 to 50 kg/m2 and stable weight were randomly assigned (1:1:1:1) to placebo or JNJ‐64565111 (5.0 mg, 7.4 mg or 10.0 mg). The primary endpoint was percent change from baseline in body weight at week 12. Of 195 dosed participants, 144 (73.8%) completed treatment. At week 12, placebo‐subtracted body weight changes were −4.6%, −5.9% and −7.2% with JNJ‐64565111 5.0 mg, 7.4 mg and 10.0 mg, respectively. All JNJ‐64565111 doses were associated with no change in HbA1c and slight numerical elevation of fasting insulin. Numerical increases in fasting plasma glucose were observed with JNJ‐64565111 5.0 mg and 7.4 mg. Incidence of treatment‐emergent adverse events, especially nausea and vomiting, was higher with JNJ‐64565111 vs placebo. Overall, JNJ‐64565111 significantly reduced body weight in a dose‐dependent manner vs placebo but was associated with greater incidence of treatment‐emergent adverse events, no HbA1c reductions, and increased fasting plasma glucose and fasting insulin. [ABSTRACT FROM AUTHOR]

Glucagon is secreted by pancreatic α cells in response to hypoglycemia and increases hepatic glucose output through hepatic glucagon receptors (GCGRs). There is evidence supporting the notion of extrapancreatic glucagon but its source and physiological functions remain elusive. Intestinal tissue samples were obtained from patients undergoing surgical resection of cancer. Mass spectrometry analysis was used to detect glucagon from mucosal lysate. Static incubations of mucosal tissue were performed to assess glucagon secretory response. Glucagon concentration was quantitated using a highly specific sandwich enzyme-linked immunosorbent assay. A cholesterol uptake assay and an isolated murine colonic motility assay were used to assess the physiological functions of intestinal GCGRs. Fully processed glucagon was detected by mass spectrometry in human intestinal mucosal lysate. High glucose evoked significant glucagon secretion from human ileal tissue independent of sodium glucose cotransporter and KATP channels, contrasting glucose-induced glucagon-like peptide 1 (GLP-1) secretion. The GLP-1 receptor agonist Exendin-4 attenuated glucose-induced glucagon secretion from the human ileum. GCGR blockade significantly increased cholesterol uptake in human ileal crypt culture and markedly slowed ex vivo colonic motility. Our findings describe the human gut as a potential source of extrapancreatic glucagon and demonstrate a novel enteric glucagon/GCGR circuit with important physiological functions beyond glycemic regulation. [ABSTRACT FROM AUTHOR]

We evaluated the potential for a monoclonal antibody antagonist of the glucagon receptor (Ab-4) to maintain glucose homeostasis in type 1 diabetic rodents. We noted durable and sustained improvements in glycemia which persist long after treatment withdrawal. Ab-4 promoted β-cell survival and enhanced the recovery of insulin+ islet mass with concomitant increases in circulating insulin and C peptide. In PANIC-ATTAC mice, an inducible model of β-cell apoptosis which allows for robust assessment of β-cell regeneration following caspase-8-induced diabetes, Ab-4 drove a 6.7-fold increase in β-cell mass. Lineage tracing suggests that this restoration of functional insulin-producing cells was at least partially driven by α-cell-to-β-cell conversion. Following hyperglycemic onset in nonobese diabetic (NOD) mice, Ab-4 treatment promoted improvements in C-peptide levels and insulin+ islet mass was dramatically increased. Lastly, diabetic mice receiving human islet xenografts showed stable improvements in glycemic control and increased human insulin secretion. [ABSTRACT FROM AUTHOR]

Elevation of glucagon levels and increase in α-cell mass are associated with states of hyperglycemia in diabetes. Our previous studies have highlighted the role of nutrient signaling via mTOR complex 1 (mTORC1) regulation that controls glucagon secretion and α-cell mass. In the current studies we investigated the effects of activation of nutrient signaling by conditional deletion of the mTORC1 inhibitor, TSC2, in α-cells (αTSC2KO). We showed that activation of mTORC1 signaling is sufficient to induce chronic hyperglucagonemia as a result of α-cell proliferation, cell size, and mass expansion. Hyperglucagonemia in αTSC2KO was associated with an increase in glucagon content and enhanced glucagon secretion. This model allowed us to identify the effects of chronic hyperglucagonemia on glucose homeostasis by inducing insulin secretion and resistance to glucagon in the liver. Liver glucagon resistance in αTSC2KO mice was characterized by reduced expression of the glucagon receptor (GCGR), PEPCK, and genes involved in amino acid metabolism and urea production. Glucagon resistance in αTSC2KO mice was associated with improved glucose levels in streptozotocin-induced β-cell destruction and high-fat diet-induced glucose intolerance. These studies demonstrate that chronic hyperglucagonemia can improve glucose homeostasis by inducing glucagon resistance in the liver. [ABSTRACT FROM AUTHOR]

Receptors for the peptide hormones glucagon-like peptide-1 (GLP-1R), glucose-dependent insulinotropic polypeptide (GIPR), and glucagon (GCGR) are important regulators of insulin secretion and energy metabolism. GLP-1R agonists have been successfully deployed for the treatment of type 2 diabetes, but it has been suggested that their efficacy is limited by target receptor desensitization and downregulation due to recruitment of β-arrestins. Indeed, recently described GLP-1R agonists with reduced β-arrestin-2 recruitment have delivered promising results in preclinical and clinical studies. We therefore aimed to determine if the same phenomenon could apply to the closely related GIPR and GCGR. In HEK293 cells depleted of both β-arrestin isoforms the duration of G protein-dependent cAMP/PKA signaling was increased in response to the endogenous ligand for each receptor. Moreover, in wildtype cells, "biased" GLP-1, GCG, and GIP analogs with selective reductions in β-arrestin-2 recruitment led to reduced receptor endocytosis and increased insulin secretion over a prolonged stimulation period, although the latter effect was only seen at high agonist concentrations. Biased GCG analogs increased the duration of cAMP signaling, but this did not lead to increased glucose output from hepatocytes. Our study provides a rationale for the development of GLP-1R, GIPR, and GCGR agonists with reduced β-arrestin recruitment, but further work is needed to maximally exploit this strategy for therapeutic purposes. [ABSTRACT FROM AUTHOR]

The liver plays a critical role in maintaining ammonia homeostasis. Urea cycle defects, liver injury, or failure and glutamine synthetase (GS) deficiency result in hyperammonemia, serious clinical conditions, and lethality. In this study we used a mouse model with a defect in the urea cycle enzyme ornithine transcarbamylase (Otc spf-ash ) to test the hypothesis that glucagon receptor inhibition using a monoclonal blocking antibody will reduce the hyperammonemia and associated lethality induced by a high-protein diet, which exacerbates disease. We found reduced expression of glutaminase, which degrades glutamine and increased expression of GS in livers of Otc spf-ash mice treated with the glucagon receptor blocking antibody. The gene expression changes favor ammonia consumption and were accompanied by increased circulating glutamine levels and diminished hyperammonemia. Otc spf-ash mice treated with the glucagon receptor-blocking antibody gained lean and body mass and had increased survival. These data suggest that glucagon receptor inhibition using a monoclonal antibody could reduce the risk for hyperammonemia and other clinical manifestations of patients suffering from defects in the urea cycle, liver injury, or failure and GS deficiency. [ABSTRACT FROM AUTHOR]

The glucagon receptor (GCGR) activated by the peptide hormone glucagon is a seven-transmembrane G protein-coupled receptor (GPCR) that regulates blood glucose levels. Ubiquitination influences trafficking and signaling of many GPCRs, but its characterization for the GCGR is lacking. Using endocytic colocalization and ubiquitination assays, we have identified a correlation between the ubiquitination profile and recycling of the GCGR. Our experiments revealed that GCGRs are constitutively ubiquitinated at the cell surface. Glucagon stimulation not only promoted GCGR endocytic trafficking through Rab5a early endosomes and Rab4a recycling endosomes, but also induced rapid deubiquitination of GCGRs. Inhibiting GCGR internalization or disrupting endocytic trafficking prevented agonist-induced deubiquitination of the GCGR. Furthermore, a Rab4a dominant negative (DN) that blocks trafficking at recycling endosomes enabled GCGR deubiquitination, whereas a Rab5a DN that blocks trafficking at early endosomes eliminated agonist-induced GCGR deubiquitination. By down-regulating candidate deubiquitinases that are either linked with GPCR trafficking or localized on endosomes, we identified signaltransducing adaptor molecule-binding protein (STAMBP) and ubiquitin-specific protease 33 (USP33) as cognate deubiquitinases for the GCGR. Our data suggest that USP33 constitutively deubiquitinates the GCGR, whereas both STAMBP and USP33 deubiquitinate agonist-activated GCGRs at early endosomes. A mutant GCGR with all five intracellular lysines altered to arginines remains deubiquitinated and shows augmented trafficking to Rab4a recycling endosomes compared with the WT, thus affirming the role of deubiquitination in GCGR recycling. We conclude that the GCGRs are rapidly deubiquitinated after agonist- activation to facilitate Rab4a-dependent recycling and that USP33 and STAMBP activities are critical for the endocytic recycling of the GCGR. [ABSTRACT FROM AUTHOR]

Aim: The aim of this study was to evaluate amino acids as glucagon receptor (GCGR)‐specific biomarkers in rodents and cynomolgus monkeys in the presence of agonism of both glucagon‐like peptide‐1 receptor (GLP1R) and GCGR with a variety of dual agonist compounds. Materials and methods: Primary hepatocytes, rodents (normal, diet‐induced obese and GLP1R knockout) and cynomolgus monkeys were treated with insulin (hepatocytes only), glucagon (hepatocytes and cynomolgus monkeys), the GLP1R agonist, dulaglutide, or a variety of dual agonists with varying GCGR potencies. Results: A long‐acting dual agonist, Compound 2, significantly decreased amino acids in both wild‐type and GLP1R knockout mice in the absence of changes in food intake, body weight, glucose or insulin, and increased expression of hepatic amino acid transporters. Dulaglutide, or a variant of Compound 2 lacking GCGR agonism, had no effect on amino acids. A third variant with ~31‐fold less GCGR potency than Compound 2 significantly decreased amino acids, albeit to a significantly lesser extent than Compound 2. Dulaglutide (with saline infusion) had no effect on amino acids, but an infusion of glucagon dose‐dependently decreased amino acids on the background of GLP1R engagement (dulaglutide) in cynomolgus monkeys, as did Compound 2. Conclusions: These results show that amino acids are sensitive and translatable GCGR‐specific biomarkers. [ABSTRACT FROM AUTHOR]

Sodium–glucose cotransporter 2 inhibitors (SGLT2i) effectively lower plasma glucose (PG) concentration in patients with type 2 diabetes, but studies have suggested that circulating glucagon concentrations and endogenous glucose production (EGP) are increased by SGLT2i, possibly compromising their glucose-lowering ability. To tease out whether and how glucagon may influence the glucose-lowering effect of SGLT2 inhibition, we subjected 12 patients with type 2 diabetes to a randomized, placebo-controlled, double-blinded, crossover, double-dummy study comprising, on 4 separate days, a liquid mixed-meal test preceded by single-dose administration of either 1) placebo, 2) the SGLT2i empagliflozin (25 mg), 3) the glucagon receptor antagonist LY2409021 (300 mg), or 4) the combination empagliflozin + LY2409021. Empagliflozin and LY2409021 individually lowered fasting PG compared with placebo, and the combination further decreased fasting PG. Previous findings of increased glucagon concentrations and EGP during acute administration of SGLT2i were not replicated in this study. Empagliflozin reduced postprandial PG through increased urinary glucose excretion. LY2409021 reduced EGP significantly but gave rise to a paradoxical increase in postprandial PG excursion, which was annulled by empagliflozin during their combination (empagliflozin + LY2409021). In conclusion, our findings do not support that an SGLT2i-induced glucagonotropic effect is of importance for the glucose-lowering property of SGLT2 inhibition. [ABSTRACT FROM AUTHOR]

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Aims: To test specific mono‐agonists to the glucagon‐like peptide‐1 receptor (GLP‐1R), glucagon receptor (GCGR) and glucose‐dependent insulinotropic peptide receptor (GIPR), individually and in combination, in a mouse model of diet‐induced non‐alcoholic steatohepatitis (NASH) and fibrosis in order to decipher the contribution of their activities and potential additive effects to improving systemic and hepatic metabolism. Materials and methods: We induced NASH by pre‐feeding C57BL/6J mice a diet rich in fat, fructose and cholesterol for 36 weeks. This was followed by 8 weeks of treatment with the receptor‐specific agonists 1‐GCG (20 μg/kg twice daily), 2‐GLP1 (3 μg/kg twice daily) or 3‐GIP (30 μg/kg twice daily), or the dual (1 + 2) or triple (1 + 2 + 3) combinations thereof. A dual GLP‐1R/GCGR agonistic peptide, 4‐dual‐GLP1/GCGR (30 μg/kg twice daily), and liraglutide (100 μg/kg twice daily) were included as references. Results: Whereas low‐dose 1‐GCG or 3‐GIP alone did not influence body weight, liver lipids and histology, their combination with 2‐GLP1 provided additional weight loss, reduction in liver triglycerides and improvement in histological disease activity score. Notably, 4‐dual‐GLP‐1R/GCGR and the triple combination of selective mono‐agonists led to a significantly stronger reduction in the histological non‐alcoholic fatty liver disease activity score compared to high‐dose liraglutide, at the same extent of body weight loss. Conclusions: GCGR and GIPR agonism provide additional, body weight‐independent improvements on top of GLP‐1R agonism in a murine model of manifest NASH with fibrosis. [ABSTRACT FROM AUTHOR]

Unimolecular dual agonists of the glucagon (GCG) receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R) are a new class of drugs that are potentially superior to GLP-1R–specific agonists for the management of metabolic disease. The dual-agonist, peptide 15 (P15), is a glutamic acid 16 analog of GCG with GLP-1 peptide substitutions between amino acids 17 and 24 that has potency equivalent to those of the cognate peptide agonists at the GCGR and GLP-1R. Here, we have used cryo-EM to solve the structure of an active P15-GCGR-Gs complex and compared this structure to our recently published structure of the GCGR-Gs complex bound to GCG. This comparison revealed that P15 has a reduced interaction with the first extracellular loop (ECL1) and the top of transmembrane segment 1 (TM1) such that there is increased mobility of the GCGR extracellular domain and at the C terminus of the peptide compared with the GCG-bound receptor. We also observed a distinct conformation of ECL3 and could infer increased mobility of the far N-terminal His-1 residue in the P15-bound structure. These regions of conformational variance in the two peptide-bound GCGR structures were also regions that were distinct between GCGR structures and previously published peptide-bound structures of the GLP-1R, suggesting that greater conformational dynamics may contribute to the increased efficacy of P15 in activation of the GLP-1R compared with GCG. The variable domains in this receptor have previously been implicated in biased agonism at the GLP-1R and could result in altered signaling of P15 at the GCGR compared with GCG [ABSTRACT FROM AUTHOR]

We report on a combined activation mechanism for a class B G-protein–coupled receptor (GPCR), the glucagon receptor. By computing the conformational free-energy landscape associated with the activation of the receptor–agonist complex and comparing it with that obtained with the ternary complex (receptor–agonist–G protein) we show that the agonist stabilizes the receptor in a preactivated complex, which is then fully activated upon binding of the G protein. The proposed mechanism contrasts with the generally assumed GPCR activation mechanism, which proceeds through an opening of the intracellular region allosterically elicited by the binding of the agonist. The mechanism found here is consistent with electron cryo-microscopy structural data and might be general for class B GPCRs. It also helps us to understand the mode of action of the numerous allosteric antagonists of this important drug target. [ABSTRACT FROM AUTHOR]