Efficacy and safety of the glucagon receptor antagonist PF-06291874: A 12-week, randomized, dose-response study in patients with type 2 diabetes mellitus on background metformin therapy

Glucagon-based therapy for people with diabetes and obesity: What is the sweet spot?

People with obesity and type 2 diabetes have a high prevalence of metabolic-associated steatotic liver disease, hyperlipidemia and cardiovascular disease. Glucagon increases hepatic glucose production; it also decreases hepatic fat accumulation, improves lipidemia and increases energy expenditure. Pharmaceutical strategies to antagonize the glucagon receptor improve glycemic outcomes in people with diabetes and obesity, but they increase hepatic steatosis and worsen dyslipidemia. Co-agonism of the glucagon and glucagon-like peptide-1 (GLP-1) receptors has emerged as a promising strategy to improve glycemia in people with diabetes and obesity. Addition of glucagon receptor agonism enhances weight loss, reduces liver fat and ameliorates dyslipidemia. Prior to clinical use, however, further studies are needed to investigate the safety and efficacy of glucagon and GLP-1 receptor co-agonists in people with diabetes and obesity and related conditions, with specific concerns regarding a higher prevalence of gastrointestinal side effects, loss of muscle mass and increases in heart rate. Furthermore, co-agonists with differing ratios of glucagon:GLP-1 receptor activity vary in their clinical effect; the optimum balance is yet to be identified.

Incretin and glucagon receptor polypharmacology in chronic kidney disease

Chronic kidney disease is a debilitating condition associated with significant morbidity and mortality. In recent years, the kidney effects of incretin-based therapies, particularly glucagon-like peptide-1 receptor agonists (GLP-1RAs), have garnered substantial interest in the management of type 2 diabetes and obesity. This review delves into the intricate interactions between the kidney, GLP-1RAs, and glucagon, shedding light on their mechanisms of action and potential kidney benefits. Both GLP-1 and glucagon, known for their opposing roles in regulating glucose homeostasis, improve systemic risk factors affecting the kidney, including adiposity, inflammation, oxidative stress, and endothelial function. Additionally, these hormones and their pharmaceutical mimetics may have a direct impact on the kidney. Clinical studies have provided evidence that incretins, including those incorporating glucagon receptor agonism, are likely to exhibit improved kidney outcomes. Although further research is necessary, receptor polypharmacology holds promise for preserving kidney function through eliciting vasodilatory effects, influencing volume and electrolyte handling, and improving systemic risk factors.

The Regulation and Secretion of Glucagon in Response to Nutrient Composition: Unraveling Their Intricate Mechanisms

Glucagon was initially regarded as a hyperglycemic substance; however, recent research has revealed its broader role in metabolism, encompassing effects on glucose, amino acids (AAs), and lipid metabolism. Notably, the interplay of glucagon with nutrient intake, particularly of AAs, and non-nutrient components is central to its secretion. Fasting and postprandial hyperglucagonemia have long been linked to the development and progression of type 2 diabetes (T2DM). However, recent studies have brought to light the positive impact of glucagon agonists on lipid metabolism and energy homeostasis. This review explores the multifaceted actions of glucagon, focusing on its regulation, signaling pathways, and effects on glucose, AAs, and lipid metabolism. The interplay between glucagon and other hormones, including insulin and incretins, is examined to provide a mechanistic understanding of its functions. Notably, the liver-α-cell axis, which involves glucagon and amino acids, emerges as a critical aspect of metabolic regulation. The dysregulation of glucagon secretion and its impact on conditions such as T2DM are discussed. The review highlights the potential therapeutic applications of targeting the glucagon pathway in the treatment of metabolic disorders.

Revisiting the role of glucagon in health, diabetes mellitus and other metabolic diseases

Insulin and glucagon exert opposing effects on glucose metabolism and, consequently, pancreatic islet β-cells and α-cells are considered functional antagonists. The intra-islet hypothesis has previously dominated the understanding of glucagon secretion, stating that insulin acts to inhibit the release of glucagon. By contrast, glucagon is a potent stimulator of insulin secretion and has been used to test β-cell function. Over the past decade, α-cells have received increasing attention due to their ability to stimulate insulin secretion from neighbouring β-cells, and α-cell-β-cell crosstalk has proven central for glucose homeostasis in vivo. Glucagon is not only the counter-regulatory hormone to insulin in glucose metabolism but also glucagon secretion is more susceptible to changes in the plasma concentration of certain amino acids than to changes in plasma concentrations of glucose. Thus, the actions of glucagon also include a central role in amino acid turnover and hepatic fat oxidation. This Review provides insights into glucagon secretion, with a focus on the local paracrine actions on glucagon and the importance of α-cell-β-cell crosstalk. We focus on dysregulated glucagon secretion in obesity, non-alcoholic fatty liver disease and type 2 diabetes mellitus. Lastly, the future potential of targeting hyperglucagonaemia and applying dual and triple receptor agonists with glucagon receptor-activating properties in combination with incretin hormone receptor agonism is discussed.

Opposing effects of chronic glucagon receptor agonism and antagonism on amino acids, hepatic gene expression, and alpha cells

The pancreatic hormone, glucagon, is known to regulate hepatic glucose production, but recent studies suggest that its regulation of hepatic amino metabolism is equally important. Here, we show that chronic glucagon receptor activation with a long-acting glucagon analog increases amino acid catabolism and ureagenesis and causes alpha cell hypoplasia in female mice. Conversely, chronic glucagon receptor inhibition with a glucagon receptor antibody decreases amino acid catabolism and ureagenesis and causes alpha cell hyperplasia and beta cell loss. These effects were associated with the transcriptional regulation of hepatic genes related to amino acid uptake and catabolism and by the non-transcriptional modulation of the rate-limiting ureagenesis enzyme, carbamoyl phosphate synthetase-1. Our results support the importance of glucagon receptor signaling for amino acid homeostasis and pancreatic islet integrity in mice and provide knowledge regarding the long-term consequences of chronic glucagon receptor agonism and antagonism.

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Glucagon receptor agonism increases amino acid catabolism and hepatic CPS-1 activity

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Glucagon receptor signaling regulates the number of pancreatic alpha cells

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Glucagon regulates the hepatic transcription of genes involved in amino acid metabolism

Glucagon receptor signaling at white adipose tissue does not regulate lipolysis

Although the physiological role of glucagon receptor signaling in the liver is well defined, the impact of glucagon receptor (Gcgr) signaling on white adipose tissue (WAT) continues to be debated. Although numerous studies propose that glucagon stimulates WAT lipolysis, we lack evidence that physiological concentrations of glucagon regulate WAT lipolysis. In turn, we performed studies in both wild-type and WAT Gcgr knockout mice to determine if glucagon regulates lipolysis at WAT in the mouse. We assessed the effects of fasting and acute exogenous glucagon administration in wild-type C57BL/6J and Gcgr^Adipocyte+/+ versus Gcgr^Adipocyte-/- mice. Using an ex vivo lipolysis protocol, we further examined the direct effects of glucagon on physiologically (fasted) and pharmacologically stimulated lipolysis. We found that adipocyte Gcgr expression did not affect fasting-induced lipolysis or hepatic lipid accumulation in lean or diet-induced obese (DIO) mice. Acute glucagon administration did not affect serum nonesterified fatty acids (NEFA), leptin, or adiponectin concentration, but did increase serum glucose and FGF21, regardless of genotype. Glucagon did not affect ex vivo lipolysis in explants from either Gcgr^Adipocyte+/+ or Gcgr^Adipocyte-/- mice. Gcgr expression did not affect fasting-induced or isoproterenol-stimulated lipolysis from WAT explants. Moreover, glucagon receptor signaling at WAT did not affect body weight or glucose homeostasis in lean or DIO mice. Our studies have established that physiological levels of glucagon do not regulate WAT lipolysis, either directly or indirectly. Given that glucagon receptor agonism can improve dyslipidemia and decrease hepatic lipid accumulation, it is critical to understand the tissue-specific effects of glucagon receptor action. Unlike the crucial role of hepatic glucagon receptor signaling in maintaining glucose and lipid homeostasis, we observed no metabolic consequence of WAT glucagon receptor deletion.NEW & NOTEWORTHY It has been postulated that glucagon stimulates lipolysis and fatty acid release from white adipose tissue. We observed no metabolic effects of eliminating or activating glucagon receptor signaling at white adipose tissue.

High Protein Diets Improve Liver Fat and Insulin Sensitivity by Prandial but Not Fasting Glucagon Secretion in Type 2 Diabetes

Glucagon (GCGN) plays a key role in glucose and amino acid (AA) metabolism by increasing hepatic glucose output. AA strongly stimulate GCGN secretion which regulates hepatic AA degradation by ureagenesis. Although increased fasting GCGN levels cause hyperglycemia GCGN has beneficial actions by stimulating hepatic lipolysis and improving insulin sensitivity through alanine induced activation of AMPK. Indeed, stimulating prandial GCGN secretion by isocaloric high protein diets (HPDs) strongly reduces intrahepatic lipids (IHLs) and improves glucose metabolism in type 2 diabetes mellitus (T2DM). Therefore, the role of GCGN and circulating AAs in metabolic improvements in 31 patients with T2DM consuming HPD was investigated. Six weeks HPD strongly coordinated GCGN and AA levels with IHL and insulin sensitivity as shown by significant correlations compared to baseline. Reduction of IHL during the intervention by 42% significantly improved insulin sensitivity [homeostatic model assessment for insulin resistance (HOMA-IR) or hyperinsulinemic euglycemic clamps] but not fasting GCGN or AA levels. By contrast, GCGN secretion in mixed meal tolerance tests (MMTTs) decreased depending on IHL reduction together with a selective reduction of GCGN-regulated alanine levels indicating greater GCGN sensitivity. HPD aligned glucose metabolism with GCGN actions. Meal stimulated, but not fasting GCGN, was related to reduced liver fat and improved insulin sensitivity. This supports the concept of GCGN-induced hepatic lipolysis and alanine- and ureagenesis-induced activation of AMPK by HPD.

Therapeutics for type-2 diabetes mellitus: a glance at the recent inclusions and novel agents under development for use in clinical practice

Diabetes mellitus (DM) is a chronic, progressive, and multifaceted illness resulting in significant physical and psychological detriment to patients. As of 2019, 463 million people are estimated to be living with DM worldwide, out of which 90% have type-2 diabetes mellitus (T2DM). Over the years, significant progress has been made in identifying the risk factors for developing T2DM, understanding its pathophysiology and uncovering various metabolic pathways implicated in the disease process. This has culminated in the implementation of robust prevention programmes and the development of effective pharmacological agents, which have had a favourable impact on the management of T2DM in recent times. Despite these advances, the incidence and prevalence of T2DM continue to rise. Continuing research in improving efficacy, potency, delivery and reducing the adverse effect profile of currently available formulations is required to keep pace with this growing health challenge. Moreover, new metabolic pathways need to be targeted to produce novel pharmacotherapy to restore glucose homeostasis and address metabolic sequelae in patients with T2DM. We searched PubMed, MEDLINE, and Google Scholar databases for recently included agents and novel medication under development for treatment of T2DM. We discuss the pathophysiology of T2DM and review how the emerging anti-diabetic agents target the metabolic pathways involved. We also look at some of the limiting factors to developing new medication and the introduction of unique methods, including facilitating drug delivery to bypass some of these obstacles. However, despite the advances in the therapeutic options for the treatment of T2DM in recent years, the industry still lacks a curative agent.

Treatment of type 2 diabetes: challenges, hopes, and anticipated successes

Despite the successful development of new therapies for the treatment of type 2 diabetes, such as glucagon-like peptide-1 (GLP-1) receptor agonists and sodium-glucose cotransporter-2 inhibitors, the search for novel treatment options that can provide better glycaemic control and at reduce complications is a continuous effort. The present Review aims to present an overview of novel targets and mechanisms and focuses on glucose-lowering effects guiding this search and developments. We discuss not only novel developments of insulin therapy (eg, so-called smart insulin preparation with a glucose-dependent mode of action), but also a group of drug classes for which extensive research efforts have not been rewarded with obvious clinical impact. We discuss the potential clinical use of the salutary adipokine adiponectin and the hepatokine fibroblast growth factor (FGF) 21, among others. A GLP-1 peptide receptor agonist (semaglutide) is now available for oral absorption, and small molecules activating GLP-1 receptors appear on the horizon. Bariatric surgery and its accompanying changes in the gut hormonal milieu offer a background for unimolecular peptides interacting with two or more receptors (for GLP-1, glucose-dependent insulinotropic polypeptide, glucagon, and peptide YY) and provide more substantial glycaemic control and bodyweight reduction compared with selective GLP-1 receptor agonists. These and additional approaches will help expand the toolbox of effective medications needed for optimising the treatment of well delineated subgroups of type 2 diabetes or help develop personalised approaches for glucose-lowering drugs based on individual characteristics of our patients.

Mechanisms of Cardiorenal Protection of Glucagon-Like Peptide-1 Receptor Agonists

The worldwide prevalence of type 2 diabetes (T2D) is steadily increasing, and it remains a challenging public health problem for populations in both developing and developed countries around the world. Despite the recent advances in novel antidiabetic agents, diabetic kidney disease and cardiovascular disease remain the leading causes of morbidity and mortality in T2D. Glucagon-like peptide-1 (GLP-1) receptor agonists (RAs), incretin hormones that stimulate postprandial insulin secretion, serve as a promising avenue for treatment of T2D as they result in a variety of antihyperglycemic effects including increased endogenous insulin secretion, decreased gluconeogenesis, inhibition of pancreatic α-cell glucagon production, decreased pancreatic β-cell apoptosis, and increased β-cell proliferation. GLP-1RAs have also been found to delay gastric emptying, promote weight loss, increase satiety, decrease hypertension, improve dyslipidemia, reduce inflammation, improve albuminuria, induce natriuresis, improve cardiovascular function, and prevent thrombogenesis. In this review, we will present risk factors for the development of cardiac and kidney disease in individuals with T2D and discuss possible mechanisms for the cardiorenal protective effects seen with GLP-1RAs. We will also present the possibility of dual- and tri-receptor agonist therapies with GLP-1, gastric inhibitory peptide, and glucagon RAs as an area of possible mechanistic synergy in the treatment of T2D and the prevention of cardiorenal complications.

A Metabolomic Signature of Glucagon Action in Healthy Individuals With Overweight/Obesity

Context

Glucagon is produced and released from the pancreatic alpha-cell to regulate glucose levels during periods of fasting. The main target for glucagon action is the liver, where it activates gluconeogenesis and glycogen breakdown; however, glucagon is postulated to have other roles within the body.

Objective

We sought to identify the circulating metabolites that would serve as markers of glucagon action in humans.

Methods

In this study (NCT03139305), we performed a continuous 72-hour glucagon infusion in healthy individuals with overweight/obesity. Participants were randomized to receive glucagon 12.5 ng/kg/min (GCG 12.5), glucagon 25 ng/kg/min (GCG 25), or a placebo control. A comprehensive metabolomics analysis was then performed from plasma isolated at several time points during the infusion to identify markers of glucagon activity.

Results

Glucagon (GCG 12.5 and GCG 25) resulted in significant changes in the plasma metabolome as soon as 4 hours following infusion. Pathways involved in amino acid metabolism were among the most affected. Rapid and sustained reduction of a broad panel of amino acids was observed. Additionally, time-dependent changes in free fatty acids and diacylglycerol and triglyceride species were observed.

Conclusion

These results define a distinct signature of glucagon action that is broader than the known changes in glucose levels. In particular, the robust changes in amino acid levels may prove useful to monitor changes induced by glucagon in the context of additional glucagon-like peptide-1 or gastric inhibitory polypeptide treatment, as these agents also elicit changes in glucose levels.

The Vicious Circle of Hepatic Glucagon Resistance in Non-Alcoholic Fatty Liver Disease

A key criterion for the most common chronic liver disease—non-alcoholic fatty liver disease (NAFLD)—is an intrahepatic fat content above 5% in individuals who are not using steatogenic agents or having significant alcohol intake. Subjects with NAFLD have increased plasma concentrations of glucagon, and emerging evidence indicates that subjects with NAFLD may show hepatic glucagon resistance. For many years, glucagon has been thought of as the counterregulatory hormone to insulin with a primary function of increasing blood glucose concentrations and protecting against hypoglycemia. However, in recent years, glucagon has re-emerged as an important regulator of other metabolic processes including lipid and amino acid/protein metabolism. This review discusses the evidence that in NAFLD, hepatic glucagon resistance may result in a dysregulated lipid and amino acid/protein metabolism, leading to excess accumulation of fat, hyperglucagonemia, and increased oxidative stress contributing to the worsening/progression of NAFLD.

The Role of Glucagon in the Acute Therapeutic Effects of SGLT2 Inhibition

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.

Repositioning Glucagon Action in the Physiology and Pharmacology of Diabetes

Glucagon is historically described as the counterregulatory hormone to insulin, induced by fasting/hypoglycemia to raise blood glucose through action mediated in the liver. However, it is becoming clear that the biology of glucagon is much more complex and extends beyond hepatic actions to exert control on glucose metabolism. We discuss the inconsistencies with the canonical view that glucagon is primarily a hyperglycemic agent driven by fasting/hypoglycemia and highlight the recent advances that have reshaped the metabolic role of glucagon. These concepts are placed within the context of both normal physiology and the pathophysiology of disease and then extended to discuss emerging strategies that incorporate glucagon agonism in the pharmacology of treating diabetes.

Glucagon-based therapy: Past, present and future

Diabesity and its related cardio-hepato-renal complications are of absolute concern globally. Last decade has witnessed a growing interest in the scientific community in investigating novel pharmaco-therapies employing the pancreatic hormone, glucagon. Canonically, this polypeptide hormone is known for its use in rescue treatment for hypoglycaemic shocks owing to its involvement in the counter-regulatory feedback mechanism. However, substantial studies in the recent past elucidated the pleiotropic effects of glucagon in diabesity and related complications like non-alcoholic steatohepatitis (NASH) and non-alcoholic fatty liver disease (NAFLD). Thus, the dual nature of this peptide has sparked the search for drugs that can modify glucagon signalling to combat hypoglycaemia or diabesity. Thus far, researchers have explored various pharmacological approaches to utilise this peptide in imminent modern therapies. The research endeavours in this segment led to explorations of stable glucagon formulations/analogues, glucagon receptor antagonism, glucagon receptor agonism, and incretin poly-agonism as new strategies for the management of hypoglycaemia or diabesity. This 'three-dimensional' research on glucagon resulted in the discovery of various drug candidates that proficiently modify glucagon signalling. Currently, several emerging glucagon-based therapies are under pre-clinical and clinical development. We sought to summarise the recent progress to comprehend glucagon-mediated pleiotropic effects, provide an overview of drug candidates currently being developed and future perspectives in this research domain.

Efficacy and Safety of the Glucagon Receptor Antagonist RVT-1502 in Type 2 Diabetes Uncontrolled on Metformin Monotherapy: A 12-Week Dose-Ranging Study

OBJECTIVE

Evaluate the safety and efficacy of RVT-1502, a novel oral glucagon receptor antagonist, in subjects with type 2 diabetes inadequately controlled on metformin.

RESEARCH DESIGN AND METHODS

In a phase 2, double-blind, randomized, placebo-controlled study, subjects with type 2 diabetes (n = 166) on a stable dose of metformin were randomized (1:1:1:1) to placebo or RVT-1502 5, 10, or 15 mg once daily for 12 weeks. The primary end point was change from baseline in HbA_1c for each dose of RVT-1502 compared with placebo. Secondary end points included change from baseline in fasting plasma glucose (FPG) and safety assessments.

RESULTS

Over 12 weeks, RVT-1502 significantly reduced HbA_1c relative to placebo by 0.74%, 0.76%, and 1.05% in the 5-, 10-, and 15-mg groups (P < 0.001), respectively, and FPG decreased by 2.1, 2.2, and 2.6 mmol/L (P < 0.001). The proportions of subjects achieving an HbA_1c <7.0% were 19.5%, 39.5%, 39.5%, and 45.0% with placebo and RVT-1502 5, 10, and 15 mg (P ≤ 0.02 vs. placebo). The frequency of hypoglycemia was low, and no episodes were severe. Mild increases in mean aminotransferase levels remaining below the upper limit of normal were observed with RVT-1502 but were reversible and did not appear to be dose related, with no other liver parameter changes. Weight and lipid changes were similar between RVT-1502 and placebo. RVT-1502-associated mild increases in blood pressure were not dose related or consistent across time.

CONCLUSIONS

Glucagon receptor antagonism with RVT-1502 significantly lowers HbA_1c and FPG, with a safety profile that supports further clinical development with longer-duration studies (NCT02851849).

Glucagon Receptor Signaling and Lipid Metabolism

Glucagon is secreted from the pancreatic alpha cells upon hypoglycemia and stimulates hepatic glucose production. Type 2 diabetes is associated with dysregulated glucagon secretion, and increased glucagon concentrations contribute to the diabetic hyperglycemia. Antagonists of the glucagon receptor have been considered as glucose-lowering therapy in type 2 diabetes patients, but their clinical applicability has been questioned because of reports of therapy-induced increments in liver fat content and increased plasma concentrations of low-density lipoprotein. Conversely, in animal models, increased glucagon receptor signaling has been linked to improved lipid metabolism. Glucagon acts primarily on the liver and by regulating hepatic lipid metabolism glucagon may reduce hepatic lipid accumulation and decrease hepatic lipid secretion. Regarding whole-body lipid metabolism, it is controversial to what extent glucagon influences lipolysis in adipose tissue, particularly in humans. Glucagon receptor agonists combined with glucagon-like peptide 1 receptor agonists (dual agonists) improve dyslipidemia and reduce hepatic steatosis. Collectively, emerging data support an essential role of glucagon for lipid metabolism.