Peptide-based multi-agonists: a new paradigm in metabolic pharmacology

Cryo-electron microscopy for GPCR research and drug discovery in endocrinology and metabolism

G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors, with many GPCRs having crucial roles in endocrinology and metabolism. Cryogenic electron microscopy (cryo-EM) has revolutionized the field of structural biology, particularly regarding GPCRs, over the past decade. Since the first pair of GPCR structures resolved by cryo-EM were published in 2017, the number of GPCR structures resolved by cryo-EM has surpassed the number resolved by X-ray crystallography by 30%, reaching >650, and the number has doubled every ~0.63 years for the past 6 years. At this pace, it is predicted that the structure of 90% of all human GPCRs will be completed within the next 5-7 years. This Review highlights the general structural features and principles that guide GPCR ligand recognition, receptor activation, G protein coupling, arrestin recruitment and regulation by GPCR kinases. The Review also highlights the diversity of GPCR allosteric binding sites and how allosteric ligands could dictate biased signalling that is selective for a G protein pathway or an arrestin pathway. Finally, the authors use the examples of glycoprotein hormone receptors and glucagon-like peptide 1 receptor to illustrate the effect of cryo-EM on understanding GPCR biology in endocrinology and metabolism, as well as on GPCR-related endocrine diseases and drug discovery.

The dairy-derived peptide Miltin exerts anti-obesity effects by increasing adipocyte thermogenesis

Growing research has highlighted that the consumption of dairy products improves the metabolic health in obese individuals by functioning as regulatory modulators. However, the molecular basis of this effect remains largely unknown. Herein, we report a dairy-derived peptide, which we named Miltin, that activates the thermogenesis of brown adipocytes and increases white adipocyte browning. Previously, Miltin was merely identified for its antioxidant capacity, although it is commonly present in different dairy products. In this study, we revealed the effect of Miltin in modulating adipose thermogenesis and further explored its potential in treating obesity through in vivo and in vitro strategies. The administration of Miltin in mice fed with a high-fat diet resulted in enhanced thermogenesis, improved glucose homeostasis, and reduced body mass and lipid accumulation, indicating the anti-obesity effect of Miltin. Genomic analysis revealed that Miltin modulates thermogenesis by inducing the activation of the MAPK signaling pathway by preferentially interacting with GADD45γ to promote its stability. Together, our findings indicate that Miltin's role in initiating the thermogenesis of adipocytes makes it a potential anti-obesity therapy for future development.

Polyagonists in Type 2 Diabetes Management

PURPOSE OF THE REVIEW

This review summarizes the new developments in polyagonist pharmacotherapy for type 2 diabetes.

RECENT FINDINGS

Several dual- and triple-agonists targeting different pathogenic pathways of type 2 diabetes have entered clinical trials and have led to significant improvements in glycaemia, body weight, fatty liver, and cardio-renal risk factors, with variable adverse event profiles but no new serious safety concerns. Combining agents with complementary and synergistic mechanisms of action have enhanced efficacy and safety. Targeting multiple pathogenic pathways simultaneously has led to enhanced benefits which potentially match those of bariatric surgery. Tirzepatide, cotadutide, BI456906, ritatrutide, and CagriSema have entered phase 3 clinical trials. Outcomes from published clinical studies are reviewed. Efficacy-safety profiles are heterogeneous between agents, suggesting the potential application of precision medicine and need for personalized approach in pharmacological management of type 2 diabetes and obesity. Polyagonism has become a key strategy to address the complex pathogenesis of type 2 diabetes and co-morbidities and increasing number of agents are moving through clinical trials. Heterogeneity in efficacy-safety profiles calls for application of precision medicine and need for judicious personalization of care.

The secreted peptide BATSP1 promotes thermogenesis in adipocytes

Although brown adipose tissue (BAT) has historically been viewed as a major site for energy dissipation through thermogenesis, its endocrine function has been increasingly recognized. However, the circulating factors in BAT that play a key role in controlling systemic energy homeostasis remain largely unexplored. Here, we performed a peptidomic analysis to profile the extracellular peptides released from human brown adipocytes upon exposure to thermogenic stimuli. Specifically, we identified a secreted peptide that modulates adipocyte thermogenesis in a cell-autonomous manner, and we named it BATSP1. BATSP1 promoted BAT thermogenesis and induced browning of white adipose tissue in vivo, leading to increased energy expenditure under cold stress. BATSP1 treatment in mice prevented high-fat diet-induced obesity and improved glucose tolerance and insulin resistance. Mechanistically, BATSP1 facilitated the nucleocytoplasmic shuttling of forkhead transcription factor 1 (FOXO1) and released its transcriptional inhibition of uncoupling protein 1 (UCP1). Overall, we provide a comprehensive analysis of the human brown adipocyte extracellular peptidome following acute forskolin (FSK) stimulation and identify BATSP1 as a novel regulator of thermogenesis that may offer a potential approach for obesity treatment.

Mechanisms of action of incretin receptor based dual- and tri-agonists in pancreatic islets

Simultaneous activation of the incretin G-protein-coupled receptors (GPCRs) via unimolecular dual-receptor agonists (UDRA) has emerged as a new therapeutic approach for type 2 diabetes. Recent studies also advocate triple agonism with molecules also capable of binding the glucagon receptor. In this scoping review, we discuss the cellular mechanisms of action (MOA) underlying the actions of these novel and therapeutically important classes of peptide receptor agonists. Clinical efficacy studies of several UDRAs have demonstrated favorable results both as monotherapies and when combined with approved hypoglycemics. Although the additive insulinotropic effects of dual glucagon-like peptide-1 receptor (GLP-1R) and glucose-dependent insulinotropic peptide receptor (GIPR) agonism were anticipated based on the known actions of either glucagon-like peptide-1 (GLP-1) or glucose-dependent insulinotropic peptide (GIP) alone, the additional benefits from GCGR were largely unexpected. Whether additional synergistic or antagonistic interactions among these G-protein receptor signaling pathways arise from simultaneous stimulation is not known. The signaling pathways affected by dual- and tri-agonism require more trenchant investigation before a comprehensive understanding of the cellular MOA. This knowledge will be essential for understanding the chronic efficacy and safety of these treatments.

Efficacy and safety of tirzepatide, dual GLP-1/GIP receptor agonists, in the management of type 2 diabetes: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 are the main incretin hormones, and be responsible for the insulinotropic incretin effect. The addition of a GIP agonist to a GLP-1agonist has been hypothesized to significantly potentiate the weight-losing and glycemia control effect, which might offer a new therapeutic option in the treatment of type 2 diabetes. The current meta-analysis aims to synthesize evidence of primary efficacy and safety outcomes through clinically randomized controlled trials to evaluate integrated potency and signaling properties.

METHOD

We conducted comprehensive literature searches in Cochrane Library, Web of Science, Embase and PubMed for relevant literatures investigating the efficacy and/or safety of Tirzepatide published in the English as of May 30, 2023 was retrieved. We synthesized results using standardized mean differences (SMDs) and 95% confidence intervals (95 CIs) for continuous outcomes, and odds ratios (ORs) along with 95 Cis for dichotomous outcomes. All analyses were done using Revman version 5.3, STATA version 15.1 and the statistical package 'meta'.

RESULTS

Participants treated with weekly Tirzepatide achieved HbA1c and body weight target values significantly lower than any other comparator without clinically significant increase in the incidence of hypoglycemic events, serious and all-cause fatal adverse events. However, gastrointestinal adverse events and decreased appetite events were reported more frequently with Tirzepatide treatment than with placebo/controls.

CONCLUSION

The Tirzepatide, a dual GIP/GLP-1 receptor co-agonist, for diabetes therapy has opened a new era on personalized glycemia control and weight loss in a safe manner with broad and promising clinical implications.

Incretins and cardiovascular disease: to the heart of type 2 diabetes?

Major cardiovascular outcome trials and real-life observations have proven that glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1RAs), regardless of structural GLP-1 homology, exert clinically relevant cardiovascular protection. GLP-1RAs provide cardioprotective benefits through glycaemic and non-glycaemic effects, including improved insulin secretion and action, body-weight loss, blood-pressure lowering and improved lipid profile, as well as via direct effects on the heart and vasculature. These actions are likely combined with anti-inflammatory and antioxidant properties that translate into robust and consistent reductions in atherothrombotic events, particularly in people with type 2 diabetes and established atherosclerotic CVD. GLP-1RAs may also have an impact on obesity and chronic kidney disease, conditions for which cardiovascular risk-reducing options are limited. The available evidence has prompted professional and medical societies to recommend GLP-1RAs for mitigation of the cardiovascular risk in people with type 2 diabetes. This review summarises the clinical evidence for cardiovascular protection with use of GLP-1RAs and the main mechanisms underlying this effect. Moreover, it looks into how the availability of upcoming dual and triple incretin receptor agonists might expand the possibility for cardiovascular protection in people with type 2 diabetes.

The Molecular Pharmacology of Glucagon Agonists in Diabetes and Obesity

Within the past couple decades glucagon receptor agonism has drawn attention as a therapeutic tool for the treatment of type 2 diabetes and obesity. In both mice and humans glucagon-induced enhancements in energy expenditure and suppression of food intake suggest promising utility, therefore interest has advanced in the synthetic optimization of glucagon-based pharmacology to further resolve the physiological and cellular underpinnings. Modifications within the glucagon peptide sequence have allowed for greater solubility, stability, circulating half-life, and understanding of the structure-function potential behind partial and "super"-agonists. This knowledge gained from such modifications has provided a basis for the development of long-acting therapeutically useful glucagon analogues, chimeric unimolecular dual- and tri-agonists, and novel strategies for the targeting of nuclear hormones into glucagon receptor-expressing tissues. In this review, we summarize the peptide path leading to these glucagon-based developments in the field of anti-diabetes and anti-obesity pharmacology, while highlighting the associated biological and therapeutic effects.

Mechanisms and possible hepatoprotective effects of glucagon-like peptide-1 receptor agonists and other incretin receptor agonists in non-alcoholic fatty liver disease

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins that stimulate insulin secretion from pancreatic β cells in response to food ingestion. Modified GLP-1 and GIP peptides are potent agonists for their incretin receptors, and some evidence shows that the dual GLP-1 and GIP receptor agonist tirzepatide is effective in promoting marked weight loss. GLP-1 receptor agonists signal in the CNS to suppress appetite, increase satiety, and thereby decrease calorie intake, but many other effects of incretin signalling have been recognised that are relevant to the treatment of non-alcoholic fatty liver disease (NAFLD). This Review provides an overview of the literature supporting the notion that endogenous incretins and incretin-receptor agonist treatments are important not only for decreasing risk of developing NAFLD, but also for treating NAFLD and NAFLD-related complications. We discuss incretin signalling and related incretin-receptor agonist treatments, mechanisms in key relevant tissues affecting liver disease, and clinical data from randomised controlled trials. Finally, we present future perspectives in this rapidly developing field of research and clinical medicine.

Current and future approaches for in vitro hit discovery in diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a serious public health problem. In this review, we discuss current and promising future drugs, targets, in vitro assays and emerging omics technologies in T2DM. Importantly, we open the perspective to image-based high-content screening (HCS), with the focus of combining it with metabolomics or lipidomics. HCS has become a strong technology in phenotypic screens because it allows comprehensive screening for the cell-modulatory activity of small molecules. Metabolomics and lipidomics screen for perturbations at the molecular level. The combination of these data-intensive comprehensive technologies is enabled by the rapid development of artificial intelligence. It promises a deep cellular and molecular phenotyping directly linked to chemical information about the applied drug candidates or complex mixtures.

In vivo drug discovery for increasing incretin-expressing cells identifies DYRK inhibitors that reinforce the enteroendocrine system

Analogs of the incretin hormones Gip and Glp-1 are used to treat type 2 diabetes and obesity. Findings in experimental models suggest that manipulating several hormones simultaneously may be more effective. To identify small molecules that increase the number of incretin-expressing cells, we established a high-throughput in vivo chemical screen by using the gip promoter to drive the expression of luciferase in zebrafish. All hits increased the numbers of neurogenin 3-expressing enteroendocrine progenitors, Gip-expressing K-cells, and Glp-1-expressing L-cells. One of the hits, a dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) inhibitor, additionally decreased glucose levels in both larval and juvenile fish. Knock-down experiments indicated that nfatc4, a downstream mediator of DYRKs, regulates incretin+ cell number in zebrafish, and that Dyrk1b regulates Glp-1 expression in an enteroendocrine cell line. DYRK inhibition also increased the number of incretin-expressing cells in diabetic mice, suggesting a conserved reinforcement of the enteroendocrine system, with possible implications for diabetes.

Tirzepatide, a dual GIP/GLP-1 receptor co-agonist for the treatment of type 2 diabetes with unmatched effectiveness regrading glycaemic control and body weight reduction

Tirzepatide is the first dual GIP/GLP-1 receptor co-agonist approved for the treatment of type 2 diabetes in the USA, Europe, and the UAE. Tirzepatide is an acylated peptide engineered to activate the GIP and GLP-1 receptors, key mediators of insulin secretion that are also expressed in regions of the brain that regulate food intake. Five clinical trials in type 2-diabetic subjects (SURPASS 1–5) have shown that tirzepatide at 5–15 mg per week reduces both HbA_1c (1.24 to 2.58%) and body weight (5.4–11.7 kg) by amounts unprecedented for a single agent. A sizable proportion of patients (23.0 to 62.4%) reached an HbA_1c of < 5.7% (which is the upper limit of the normal range indicating normoglycaemia), and 20.7 to 68.4% lost more than 10% of their baseline body weight. Tirzepatide was significantly more effective in reducing HbA_1c and body weight than the selective GLP-1 RA semaglutide (1.0 mg per week), and titrated basal insulin. Adverse events related to tirzepatide were similar to what has been reported for selective GLP-1RA, mainly nausea, vomiting, diarrhoea, and constipation, that were more common at higher doses. Cardiovascular events have been adjudicated across the whole study program, and MACE-4 (nonfatal myocardial infarction, non-fatal stroke, cardiovascular death and hospital admission for angina) events tended to be reduced over up to a 2 year-period, albeit with low numbers of events. For none of the cardiovascular events analysed (MACE-4, or its components) was a hazard ratio > 1.0 vs. pooled comparators found in a meta-analysis covering the whole clinical trial program, and the upper bounds of the confidence intervals for MACE were < 1.3, fulfilling conventional definitions of cardiovascular safety. Tirzepatide was found to improve insulin sensitivity and insulin secretory responses to a greater extent than semaglutide, and this was associated with lower prandial insulin and glucagon concentrations. Both drugs caused similar reductions in appetite, although tirzepatide caused greater weight loss. While the clinical effects of tirzepatide have been very encouraging, important questions remain as to the mechanism of action. While GIP reduces food intake and body weight in rodents, these effects have not been demonstrated in humans. Moreover, it remains to be shown that GIPR agonism can improve insulin secretion in type 2 diabetic patients who have been noted in previous studies to be unresponsive to GIP. Certainly, the apparent advantage of tirzepatide, a dual incretin agonist, over GLP-1RA will spark renewed interest in the therapeutic potential of GIP in type 2 diabetes, obesity and related co-morbidities.

GLP-1 and GIP receptor signaling in beta cells - A review of receptor interactions and co-stimulation

Glucagon-like peptide 1 receptor (GLP-1R) and glucose-dependent insulinotropic polypeptide receptor (GIPR) are two class B1 G protein-coupled receptors, which are stimulated by the gastrointestinal hormones GLP-1 and GIP, respectively. In the pancreatic beta cells, activation of both receptors lead to increased cyclic adenosine monophosphate (cAMP) and glucose-dependent insulin secretion. Marketed GLP-1R agonists such as dulaglutide, liraglutide, exenatide and semaglutide constitute an expanding drug class with beneficial effects for persons suffering from type 2 diabetes and/or obesity. In recent years another drug class, the GLP-1R-GIPR co-agonists, has emerged. Especially the peptide-based, co-agonist tirzepatide is a promising candidate for a better treatment of type 2 diabetes by improving glycemic control and weight reduction. The mechanism of action for tirzepatide include biased signaling of the GLP-1R as well as potent GIPR signaling. Since the implications of co-targeting these closely related receptors concomitantly are challenging to study in vivo, the pharmacodynamic mechanisms and downstream signaling pathways of the GLP-1R-GIPR co-agonists in general, are not fully elucidated. In this review, we present the individual signaling pathways for GLP-1R and GIPR in the pancreatic beta cell with a focus on the shared signaling pathways of the two receptors and interpret the implications of GLP-1R-GIPR co-activation in the light of recent co-activating therapeutic compounds.

Melanocortin-4 receptor complexity in energy homeostasis,obesity and drug development strategies

The melanocortin-4 receptor (MC4R) has been critically investigated for the past two decades, and novel findings regarding MC4R signalling and its potential exploitation in weight loss therapy have lately been emphasized. An association between MC4R and obesity is well established, with disease-causing mutations affecting 1% to 6% of obese patients. More than 200 MC4R variants have been reported, although conflicting results as to their effects have been found in different cohorts. Most notably, some MC4R gain-of-function variants seem to rescue obesity and related complications via specific pathways such as beta-arrestin (ß-arrestin) recruitment. Broadly speaking, however, dysfunctional MC4R dysregulates satiety and induces hyperphagia. The picture at the mechanistic level is complicated as, in addition to the canonical G stimulatory pathway, the ß-arrestin signalling pathway and ions (particularly calcium) seem to interact with MC4R signalling to contribute to or alleviate obesity pathogenesis. Thus, the overall complexity of the MC4R signalling spectra has broadened considerably, indicating there is great potential for the development of new drugs to manage obesity and its related complications. Alpha-melanocyte-stimulating hormone is the major endogenous MC4R agonist, but structure-based ligand discovery studies have identified possible superior and selective agonists that can improve MC4R function. However, some of these agonists characterized in vitro and in vivo confer adverse effects in patients, as demonstrated in clinical trials. In this review, we provide a comprehensive insight into the genetics, function and regulation of MC4R and its contribution to obesity. We also outline new approaches in drug development and emerging drug candidates to treat obesity.

Structural insights into multiplexed pharmacological actions of tirzepatide and peptide 20 at the GIP, GLP-1 or glucagon receptors

Glucose homeostasis, regulated by glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1) and glucagon (GCG) is critical to human health. Several multi-targeting agonists at GIPR, GLP-1R or GCGR, developed to maximize metabolic benefits with reduced side-effects, are in clinical trials to treat type 2 diabetes and obesity. To elucidate the molecular mechanisms by which tirzepatide, a GIPR/GLP-1R dual agonist, and peptide 20, a GIPR/GLP-1R/GCGR triagonist, manifest their multiplexed pharmacological actions over monoagonists such as semaglutide, we determine cryo-electron microscopy structures of tirzepatide-bound GIPR and GLP-1R as well as peptide 20-bound GIPR, GLP-1R and GCGR. The structures reveal both common and unique features for the dual and triple agonism by illustrating key interactions of clinical relevance at the near-atomic level. Retention of glucagon function is required to achieve such an advantage over GLP-1 monotherapy. Our findings provide valuable insights into the structural basis of functional versatility of tirzepatide and peptide 20.

Multi-targeting agonists at GIPR, GLP-1R or GCGR are pursued vigorously. Here, the authors report cryo-EM structures of tirzepatide-bound GIPR and GLP-1R, peptide 20-bound GIPR, GLP-1R and GCGR, revealing the molecular basis of their multiplexed pharmacological actions.

The metabolic triad of non-alcoholic fatty liver disease, visceral adiposity and type 2 diabetes: Implications for treatment

Non-alcoholic fatty liver disease (NAFLD) is associated with visceral obesity, insulin resistance, type 2 diabetes (T2D) and has been often considered as the hepatic expression of the metabolic syndrome (MetS). Epidemiological studies highlight a bidirectional relationship of NAFLD with T2D in which NAFLD increases the risk of incident T2D and T2D increases the risk of severe non-alcoholic steatohepatitis (NASH) and liver fibrosis. Regarding the molecular determinants of NAFLD, we specifically focused in this review on adipocyte dysfunction as a key molecular link between visceral adipose tissue, MetS and NAFLD. Notably, the subcutaneous white adipose tissue expandability appears a critical adaptive buffering mechanism to prevent lipotoxicity and its related metabolic complications, such as NAFLD and T2D. There is a clinical challenge to consider therapeutic strategies targeting the metabolic dysfunction common to NASH and T2D pathogenesis. Strategies that promote significant and sustained weight loss (~10% of total body weight) such as metabolic and bariatric surgery or incretin-based therapies (GLP-1 receptor agonists or dual GLP-1/GIP or GLP-1/glucagon receptor co-agonists) are among the most efficient ones. In addition, insulin sensitizers such as PPARγ (pioglitazone) and pan-PPARs agonists (lanifibranor) have shown some beneficial effects on both NASH and liver fibrosis. Since NASH is a complex and multifactorial disease, it is conceivable that targeting different pathways, not only insulin resistance but also inflammation and fibrotic processes, is required to achieve NASH resolution.

The Metabolomic Effects of Tripeptide Gut Hormone Infusion Compared to Roux-en-Y Gastric Bypass and Caloric Restriction

CONTEXT

The gut-derived peptide hormones glucagon-like peptide-1 (GLP-1), oxyntomodulin (OXM), and peptide YY (PYY) are regulators of energy intake and glucose homeostasis and are thought to contribute to the glucose-lowering effects of bariatric surgery.

OBJECTIVE

To establish the metabolomic effects of a combined infusion of GLP-1, OXM, and PYY (tripeptide GOP) in comparison to a placebo infusion, Roux-en-Y gastric bypass (RYGB) surgery, and a very low-calorie diet (VLCD).

DESIGN AND SETTING

Subanalysis of a single-blind, randomized, placebo-controlled study of GOP infusion (ClinicalTrials.gov NCT01945840), including VLCD and RYGB comparator groups.

PATIENTS AND INTERVENTIONS

Twenty-five obese patients with type 2 diabetes or prediabetes were randomly allocated to receive a 4-week subcutaneous infusion of GOP (n = 14) or 0.9% saline control (n = 11). An additional 22 patients followed a VLCD, and 21 underwent RYGB surgery.

MAIN OUTCOME MEASURES

Plasma and urine samples collected at baseline and 4 weeks into each intervention were subjected to cross-platform metabolomic analysis, followed by unsupervised and supervised modeling approaches to identify similarities and differences between the effects of each intervention.

RESULTS

Aside from glucose, very few metabolites were affected by GOP, contrasting with major metabolomic changes seen with VLCD and RYGB.

CONCLUSIONS

Treatment with GOP provides a powerful glucose-lowering effect but does not replicate the broader metabolomic changes seen with VLCD and RYGB. The contribution of these metabolomic changes to the clinical benefits of RYGB remains to be elucidated.

New Phenol Esters for Efficient pH-Controlled Amine Acylation of Peptides, Proteins, and Sepharose Beads in Aqueous Media

This paper describes the discovery, synthesis, and use of novel water-soluble acylation reagents for efficient and selective modification, cross-linking, and labeling of proteins and peptides, as well as for their use in the effective modification of sepharose beads under pH control in aqueous media. The reagents are based on a 2,4-dichloro-6-sulfonic acid phenol ester core combined with a variety of linker structures. The combination of these motifs leads to an ideal balance between hydrolytic stability and reactivity. At high pH, good to excellent conversions (up to 95%) and regioselectivity (up to 99:1 N^ε/N^α amine ratio) in the acylation were realized, exemplified by the chemical modification of incretin peptides and insulin. At neutral pH, an unusually high preference toward the N-terminal phenylalanine in an insulin derivative was observed (>99:1 N^α/N^ε), which is up until now unprecedented in the literature for more elaborate reagents. In addition, the unusually high hydrolytic stability of these reagents and their ability to efficiently react at low concentrations (28 μM or 0.1 mg/mL) are exemplified with a hydroxy linker-based reagent and are a unique feature of this work.

Complementary and antagonistic effects of combined glucagon-like peptide-2 and glucagon-like peptide-1 receptor agonist administration on parameters relevant to short bowel syndrome

BACKGROUND

Short Bowel Syndrome (SBS) is characterized by debilitating malabsorption requiring parenteral nutrition. The intestinotrophic glucagon-like peptide-2 receptor agonist, h[Gly2]GLP2, is currently used to treat patients with SBS. Recent evidence suggests that GLP-1 receptor agonists such as Exendin-4 (Ex4) may also be beneficial in SBS given their ability to increase intestinal growth and delay gastric emptying (GE).

METHODS

Intestinal growth, body weight (BW), food intake (FI), GE, gastrointestinal (GI) transit, intestinal permeability, and glucose tolerance were investigated in male and female C57/BL6 mice following vehicle, h[Gly2]GLP2 or Ex4 treatment, alone or in combination at "low", "medium", and "high" doses (0.1, 0.5, 1.0 and 0.01, 0.05, 0.1 μg/g, respectively).

RESULTS

Only the h[Gly2]GLP2 low/Ex4 high-dose combination increased small intestinal (SI) weight, in an additive manner, compared to vehicle and both mono-agonists (P<0.01-0.001), via increases in villus height (P<0.01) and SI length (P<0.05), respectively. This combination had no effects on BW, FI and fat, liver, spleen, heart and kidney weights, but reduced GI transit (P<0.001) compared to low-dose h[Gly2]GLP2 mono-treatment, and abrogated the inhibitory effects of high-dose Ex4 on GE (P<0.01) and of low-dose h[Gly2]GLP2 on intestinal permeability (P<0.05). Ex4-induced improvements in glucose homeostasis were maintained upon combination with h[Gly2]GLP2 (P<0.001).

CONCLUSIONS

These findings suggest that combining specific doses of GLP-2-based therapies and GLP-1 receptor agonists additively improves SI growth and GI transit without detrimental effects on BW, FI, GE, and glucose homeostasis, and may therefore be a useful approach to the treatment of patients with SBS. This article is protected by copyright. All rights reserved.

Hepatic hormone FGF21 and its analogues in clinical trials

Fibroblast growth factor 21 (FGF21) is a fasting or stress inducible metabolic hormone produced mainly in the liver. It plays important roles in regulating both glucose and lipid homeostasis via interacting with a heterodimeric receptor complex comprising FGF receptor 1 (FGFR1) and β‐klotho (KLB). For the past decade, great effort has been made on developing FGF21 derivatives or specific FGF21 receptor agonists into therapeutic agents for various metabolic disorders including type 2 diabetes (T2D), obesity, and more importantly, nonalcoholic fatty liver disease (NAFLD). Here we have reviewed FGF21 gene and protein structures, its expression pattern, cellular signaling cascades that mediate FGF21 production and function. We have then summarized the six clinical trials utilizing four FGF21 analogues. Finally, two recent literatures on the development of GLP‐1 and FGF21 dual agonists were presented briefly.

Gastrointestinal peptides in eating-related disorders

Food intake is tightly controlled by homeostatic signals sensitive to metabolic need for the regulation of body weight. This review focuses on the peripherally-secreted gastrointestinal peptides (i.e., ghrelin, cholecystokinin, glucagon-like peptide 1, and peptide tyrosine tyrosine) that contribute to the control of appetite and discusses how these peptides or the signals arising from their release are disrupted in eating-related disorders across the weight spectrum, namely anorexia nervosa, bulimia nervosa, and obesity, and whether they are normalized following weight restoration or weight loss treatment. Further, the role of gut peptides in the pathogenesis and treatment response in human weight conditions as identified by rodent models are discussed. Lastly, we review the incretin- and hormone-based pharmacotherapies available for the treatment of obesity and eating-related disorders.

Anti-diabetic drugs and NASH: from current options to promising perspectives

Introduction: Accumulating evidence supports a bidirectional association between nonalcoholic steatohepatitis (NASH) and type 2 diabetes (T2D). There is a clinical challenge to consider pharmaceutical strategies targeting the metabolic dysfunction common to NASH and T2D pathogenesis.Areas covered: By using PubMed, we performed a literature search to review the potential beneficial effect of anti-diabetic and metabolic investigational drugs on NASH.Expert opinion: Since insulin resistance is central in the pathophysiology of both T2D and NASH, there is an urgent need for new insulin sensitizers. Peroxisome proliferator-activated receptor (PPAR) agonists, especially PPARγ and pan-PPARs agonists, have shown some beneficial effects on both NASH and liver fibrosis, but their routine use should be limited by their safety profile. Incretin-based therapies, including glucagon-like peptide 1 receptor agonists (GLP-1 RAs) and the polyagonists (GLP-1, GIP, glucagon) under development are the most promising anti-diabetic drugs for NASH treatment, mainly due to their action on body weight loss. Preliminary, preclinical and early phase studies suggest that SGLT2 inhibitors and fibroblast growth factor (FGF)19 and FGF21-based therapies are promising targets for NASH and T2D treatment. The common weakness for all of these drugs is their limited effect on liver fibrosis, potentially due to short-term trial design.

The Function of Gastrointestinal Hormones in Obesity-Implications for the Regulation of Energy Intake

The global burden of obesity and the challenges of prevention prompted researchers to investigate the mechanisms that control food intake. Food ingestion triggers several physiological responses in the digestive system, including the release of gastrointestinal hormones from enteroendocrine cells that are involved in appetite signalling. Disturbed regulation of gut hormone release may affect energy homeostasis and contribute to obesity. In this review, we summarize the changes that occur in the gut hormone balance during the pre- and postprandial state in obesity and the alterations in the diurnal dynamics of their plasma levels. We further discuss how obesity may affect nutrient sensors on enteroendocrine cells that sense the luminal content and provoke alterations in their secretory profile. Gastric bypass surgery elicits one of the most favorable metabolic outcomes in obese patients. We summarize the effect of different strategies to induce weight loss on gut enteroendocrine function. Although the mechanisms underlying obesity are not fully understood, restoring the gut hormone balance in obesity by targeting nutrient sensors or by combination therapy with gut peptide mimetics represents a novel strategy to ameliorate obesity.

Proglucagon-Derived Peptides as Therapeutics

Initially discovered as an impurity in insulin preparations, our understanding of the hyperglycaemic hormone glucagon has evolved markedly over subsequent decades. With description of the precursor proglucagon, we now appreciate that glucagon was just the first proglucagon-derived peptide (PGDP) to be characterised. Other bioactive members of the PGDP family include glucagon-like peptides -1 and -2 (GLP-1 and GLP-2), oxyntomodulin (OXM), glicentin and glicentin-related pancreatic peptide (GRPP), with these being produced via tissue-specific processing of proglucagon by the prohormone convertase (PC) enzymes, PC1/3 and PC2. PGDP peptides exert unique physiological effects that influence metabolism and energy regulation, which has witnessed several of them exploited in the form of long-acting, enzymatically resistant analogues for treatment of various pathologies. As such, intramuscular glucagon is well established in rescue of hypoglycaemia, while GLP-2 analogues are indicated in the management of short bowel syndrome. Furthermore, since approval of the first GLP-1 mimetic for the management of Type 2 diabetes mellitus (T2DM) in 2005, GLP-1 therapeutics have become a mainstay of T2DM management due to multifaceted and sustainable improvements in glycaemia, appetite control and weight loss. More recently, longer-acting PGDP therapeutics have been developed, while newfound benefits on cardioprotection, bone health, renal and liver function and cognition have been uncovered. In the present article, we discuss the physiology of PGDP peptides and their therapeutic applications, with a focus on successful design of analogues including dual and triple PGDP receptor agonists currently in clinical development.

Reprint of: Recent Updates on Obesity Treatments: Available Drugs and Future Directions

In the last thirty years, obesity has reached epidemic proportions and is now regarded as a major health issue in contemporary society trending to serious economic and social burdens. The latest projections of the World Health Organization are alarming. By 2030, nearly 60% of the worldwide population could be either obese or overweight, highlighting the needs to find innovative treatments. Currently, bariatric surgery is the most effective way to efficiently lower body mass. Although great improvements in terms of recovery and patient care were made in these surgical procedures, bariatric surgery remains an option for extreme forms of obesity and seems unable to tackle obesity pandemic expansion. Throughout the last century, numerous pharmacological strategies targeting either peripheral or central components of the energy balance regulatory system were designed to reduce body mass, some of them reaching sufficient levels of efficiency and safety. Nevertheless, obesity drug therapy remains quite limited on its effectiveness to actually overcome the obesogenic environment. Thus, innovative unimolecular polypharmacology strategies, able to simultaneously target multiple actors involved in the obesity initiation and expansion, were developed during the last ten years opening a new promising avenue in the pharmacological management of obesity. In this review, we first describe the clinical features of obesity-associated conditions and then focus on the outcomes of currently approved drug therapies for obesity as well as new ones expecting to reach the clinic in the near future.

Gut-Pancreas-Liver Axis as a Target for Treatment of NAFLD/NASH

Non-alcoholic fatty liver disease (NAFLD) represents the most common form of chronic liver disease worldwide. Due to its association with obesity and diabetes and the fall in hepatitis C virus morbidity, cirrhosis in NAFLD is becoming the most frequent indication to liver transplantation, but the pathogenetic mechanisms are still not completely understood. The so-called gut-liver axis has gained enormous interest when data showed that its alteration can lead to NAFLD development and might favor the occurrence of non-alcoholic steatohepatitis (NASH). Moreover, several therapeutic approaches targeting the gut-pancreas-liver axis, e.g., incretins, showed promising results in NASH treatment. In this review, we describe the role of incretin hormones in NAFLD/NASH pathogenesis and treatment and how metagenomic/metabolomic alterations in the gut microbiota can lead to NASH in the presence of gut barrier modifications favoring the passage of bacteria or bacterial products in the portal circulation, i.e., bacterial translocation.

Sustained release of a GLP-1 and FGF21 dual agonist from an injectable depot protects mice from obesity and hyperglycemia

There is great interest in identifying a glucagon-like peptide-1 (GLP-1)-based combination therapy that will more effectively promote weight loss in patients with type 2 diabetes. Fibroblast growth factor 21 (FGF21) is a compelling yet previously unexplored drug candidate to combine with GLP-1 due to its thermogenic and insulin-sensitizing effects. Here, we describe the development of a biologic that fuses GLP-1 to FGF21 with an elastin-like polypeptide linker that acts as a sustained release module with zero-order drug release. We show that once-weekly dual-agonist treatment of diabetic mice results in potent weight-reducing effects and enhanced glycemic control that are not observed with either agonist alone. Furthermore, the dual-agonist formulation has superior efficacy compared to a GLP-1/FGF21 mixture, demonstrating the utility of combining two structurally distinct peptides into one multifunctional molecule. We anticipate that these results will spur further investigation into GLP-1/FGF21 multiagonism for the treatment of metabolic disease.

Insights into incretin-based therapies for treatment of diabetic dyslipidemia

Derangements in triglyceride and cholesterol metabolism (dyslipidemia) are major risk factors for the development of cardiovascular diseases in obese and type-2 diabetic (T2D) patients. An emerging class of glucagon-like peptide-1 (GLP-1) analogues and next generation peptide dual-agonists such as GLP-1/glucagon or GLP-1/GIP could provide effective therapeutic options for T2D patients. In addition to their role in glucose and energy homeostasis, GLP-1, GIP and glucagon serve as regulators of lipid metabolism. This review summarizes the current knowledge in GLP-1, glucagon and GIP effects on lipid and lipoprotein metabolism and frames the emerging therapeutic benefits of GLP-1 analogs and GLP-1-based multiagonists as add-on treatment options for diabetes associated dyslipidemia.

Regulatory peptides and systems biology: A new era of translational and reverse-translational neuroendocrinology

Recently, there has been a resurgence in regulatory peptide science as a result of three converging trends. The first is the increasing population of the drug pipeline with peptide-based therapeutics, mainly in, but not restricted to, incretin-like molecules for treatment of metabolic disorders such as diabetes. The second is the development of genetic and optogenetic tools enabling new insights into how peptides actually function within brain and peripheral circuits to accomplish homeostatic and allostatic regulation. The third is the explosion in defined structures of the G-protein coupled receptors to which most regulatory peptides bind and exert their actions. These trends have closely wedded basic systems biology to drug discovery and development, creating a "two-way street" on which translational advances travel from basic research to the clinic, and, equally importantly, "reverse-translational" information is gathered, about the molecular, cellular and circuit-level mechanisms of action of regulatory peptides, comprising information required for the fine-tuning of drug development through testing in animal models. This review focuses on a small group of 'influential' peptides, including oxytocin, vasopressin, pituitary adenylate cyclase-activating polypeptide, ghrelin, relaxin-3 and glucagon-like peptide-1, and how basic discoveries and their application to therapeutics have intertwined over the past decade.

Pharmacological characterization of mono-, dual- and tri-peptidic agonists at GIP and GLP-1 receptors

Glucose-dependent insulinotropic peptide (GIP) is an incretin hormone with physiological roles in adipose tissue, the central nervous system and bone metabolism. While selective ligands for GIP receptor (GIPR) have not been advanced for disease treatment, dual and triple agonists of GIPR, in conjunction with that of glucagon-like peptide-1 (GLP-1) and glucagon receptors, are currently in clinical trials, with an expectation of enhanced efficacy beyond that of GLP-1 receptor (GLP-1R) agonist monotherapy for diabetic patients. Consequently, it is important to understand the pharmacological behavior of such drugs. In this study, we have explored signaling pathway specificity and the potential for biased agonism of mono-, dual- and tri-agonists of GIPR using human embryonic kidney 293 (HEK293) cells recombinantly expressing human GIPR or GLP-1R. Compared to GIP(1-42), the GIPR mono-agonists Pro3GIP and Lys3GIP are biased towards ERK1/2 phosphorylation (pERK1/2) relative to cAMP accumulation at GIPR, whereas the triple agonist at GLP-1R/GCGR/GIPR is biased towards pERK1/2 relative to β-arrestin2 recruitment. Moreover, the dual GIPR/GLP-1R agonist, LY3298176, is biased towards pERK1/2 relative to cAMP accumulation at both GIPR and GLP-1R compared to their respective endogenous ligands. These data reveal novel pharmacological properties of potential therapeutic agents that may impact on diversity in clinical responses.

Recent Updates on Obesity Treatments: Available Drugs and Future Directions

In the last thirty years, obesity has reached epidemic proportions and is now regarded as a major health issue in contemporary society trending to serious economic and social burdens. The latest projections of the World Health Organization are alarming. By 2030, nearly 60% of the worldwide population could be either obese or overweight, highlighting the needs to find innovative treatments. Currently, bariatric surgery is the most effective way to efficiently lower body mass. Although great improvements in terms of recovery and patient care were made in these surgical procedures, bariatric surgery remains an option for extreme forms of obesity and seems unable to tackle obesity pandemic expansion. Throughout the last century, numerous pharmacological strategies targeting either peripheral or central components of the energy balance regulatory system were designed to reduce body mass, some of them reaching sufficient levels of efficiency and safety. Nevertheless, obesity drug therapy remains quite limited on its effectiveness to actually overcome the obesogenic environment. Thus, innovative unimolecular polypharmacology strategies, able to simultaneously target multiple actors involved in the obesity initiation and expansion, were developed during the last ten years opening a new promising avenue in the pharmacological management of obesity. In this review, we first describe the clinical features of obesity-associated conditions and then focus on the outcomes of currently approved drug therapies for obesity as well as new ones expecting to reach the clinic in the near future.

Peptide-Liganded G Protein-Coupled Receptors as Neurotherapeutics

Peptide-liganded G protein-coupled receptors (GPCRs) are a growing fraction of GPCR drug targets, concentrated in two of the five major GPCR structural classes. The basic physiology and pharmacology of some within the rhodopsin class, for example, the enkephalin (μ opioid receptor, MOR) and angiotensin (ATR) receptors, and most in class B, all the members of which are peptide receptors, are well-known, whereas others are less so. Furthermore, with the notable exception of opioid peptide receptors, the ability to translate from peptide to "drug-like" (i.e., low-molecular-weight nonpeptide) molecules, with desirable oral absorption, brain penetrance, and serum stability, has met with limited success. Yet, peripheral peptide administration in patients with metabolic disorders is clinically effective, suggesting that "drug-like" molecules for peptide receptor targets may not always be required for disease intervention. Here, we consider recent developments in GPCR structure analysis, intracellular signaling, and genetic analysis of peptide and peptide receptor knockout phenotypes in animal models. These lines of research converge on a better understanding of how peptides facilitate adaptive behaviors in mammals. They suggest pathways to translate this burgeoning information into identified drug targets for neurological and psychiatric illnesses such as obesity, addiction, anxiety disorders, and neurodegenerative diseases. Advances centered on the peptide ligands oxytocin, vasopressin, GLP-1, ghrelin, PACAP, NPY, and their GPCRs are considered here. These represent the spectrum of progress across the "virtual pipeline", of peptide receptors associated with many established drugs, those of long-standing interest for which clinical application is still under development, and those just coming into focus through basic research.

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.

Nonclassical Islet Peptides: Pancreatic and Extrapancreatic Actions

The pancreas has physiologically important endocrine and exocrine functions; secreting enzymes into the small intestine to aid digestion and releasing multiple peptide hormones via the islets of Langerhans to regulate glucose metabolism, respectively. Insulin and glucagon, in combination with ghrelin, pancreatic polypeptide and somatostatin, are the main classical islet peptides critical for the maintenance of blood glucose. However, pancreatic islets also synthesis numerous ‘nonclassical’ peptides that have recently been demonstrated to exert fundamental effects on overall islet function and metabolism. As such, insights into the physiological relevance of these nonclassical peptides have shown impact on glucose metabolism, insulin action, cell survival, weight loss, and energy expenditure. This review will focus on the role of individual nonclassical islet peptides to stimulate pancreatic islet secretions as well as regulate metabolism. In addition, the more recognised actions of these peptides on satiety and energy regulation will also be considered. Furthermore, recent advances in the field of peptide therapeutics and obesity-diabetes have focused on the benefits of simultaneously targeting several hormone receptor signalling cascades. The potential for nonclassical islet hormones within such combinational approaches will also be discussed.