Role of GIP receptor signaling in β-cell survival

Role of incretins and glucagon receptor agonists in metabolic dysfunction-associated steatotic liver disease: Opportunities and challenges

Metabolic dysfunction-associated steatotic liver disease (MASLD) has become the most common chronic liver disease worldwide, paralleling the rising pandemic of obesity and type 2 diabetes. Due to the growing global health burden and complex pathogenesis of MASLD, a multifaceted and innovative therapeutic approach is needed. Incretin receptor agonists, which were initially developed for diabetes management, have emerged as promising candidates for MASLD treatment. This review describes the pathophysiological mechanisms and action sites of three major classes of incretin/glucagon receptor agonists: glucagon-like peptide-1 receptor agonists, glucose-dependent insulinotropic polypeptide receptor agonists, and glucagon receptor agonists. Incretins and glucagon directly or indirectly impact various organs, including the liver, brain, pancreas, gastrointestinal tract, and adipose tissue. Thus, these agents significantly improve glycemic control and weight management and mitigate MASLD pathogenesis. Importantly, this study provides a summary of clinical trials analyzing the effectiveness and safety of incretin receptor agonists in MASLD management and provides an in-depth analysis highlighting their beneficial effects on improving liver function, hepatic steatosis, and intrahepatic inflammation. There are emerging challenges associated with the use of these medications in the real world, particularly adverse events, drug-drug interactions, and barriers to access, which are discussed in detail. Additionally, this review highlights the evolving role of incretin receptor agonists in MASLD management and suggests future research directions.

Glucagon-like Peptide 1, Glucose-Dependent Insulinotropic Polypeptide, and Glucagon Receptor Agonists in Metabolic Dysfunction-Associated Steatotic Liver Disease: Novel Medication in New Liver Disease Nomenclature

Glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins that regulate postprandial glucose regulation, stimulating insulin secretion from pancreatic β-cells in response to food ingestion. Modified GLP-1 receptor agonists (GLP-1RAs) are being administered for the treatment of obesity and type 2 diabetes mellitus (T2DM). Strongly related to those disorders, metabolic dysfunction-associated steatotic liver disease (MASLD), especially its aggressive form, defined as metabolic dysfunction-associated steatohepatitis (MASH), is a major healthcare burden associated with high morbidity and extrahepatic complications. GLP-1RAs have been explored in MASH patients with evident improvement in liver dysfunction enzymes, glycemic control, and weight loss. Importantly, the combination of GLP-1RAs with GIP and/or glucagon RAs may be even more effective via synergistic mechanisms in amelioration of metabolic, biochemical, and histological parameters of MASLD but also has a beneficial impact on MASLD-related complications. In this current review, we aim to provide an overview of incretins' physiology, action, and signaling. Furthermore, we provide insight into the key pathophysiological mechanisms through which they impact MASLD aspects, as well as we analyze clinical data from human interventional studies. Finally, we discuss the current challenges and future perspectives pertinent to this growing area of research and clinical medicine.

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.

Incretin and insulin signaling as novel therapeutic targets for Alzheimer's and Parkinson's disease

Despite an ever-growing prevalence and increasing economic burden of Alzheimer's disease (AD) and Parkinson's disease (PD), recent advances in drug development have only resulted in minimally effective treatment. In AD, along with amyloid and tau phosphorylation, there is an associated increase in inflammation/glial activation, a decrease in synaptic function, an increase in astrocyte activation, and a state of insulin resistance. In PD, along with α-synuclein accumulation, there is associated inflammation, synaptic dysfunction, dopaminergic neuronal loss, and some data to suggest insulin resistance. Therapeutic strategies for neurodegenerative disorders have commonly targeted individual pathological processes. An effective treatment might require either utilization of multiple drugs which target the individual pathological processes which underlie the neurodegenerative disease or the use of a single agent which could influence multiple pathological processes. Insulin and incretins are compounds with multiple effects on neurodegenerative processes. Preclinical studies have demonstrated that GLP-1 receptor agonists reduce neuroinflammation, reduce tau phosphorylation, reduce amyloid deposition, increase synaptic function, and improve memory formation. Incretin mimetics may act through the restoration of insulin signaling pathways, inducing further neuroprotective effects. Currently, phase 2 and phase 3 trials are underway in AD and PD populations. Here, we provide a comprehensive review of the therapeutic potential of incretin mimetics and insulin in AD and PD.

Novel Therapies for Cardiometabolic Disease: Recent Findings in Studies with Hormone Peptide-Derived G Protein Coupled Receptor Agonists

The increasing prevalence of obesity and type 2 diabetes (T2DM) is provoking an important socioeconomic burden mainly in the form of cardiovascular disease (CVD). One successful strategy is the so-called metabolic surgery whose beneficial effects are beyond dietary restrictions and weight loss. One key underlying mechanism behind this surgery is the cooperative improved action of the preproglucagon-derived hormones, glucagon, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) which exert their functions through G protein-coupled receptors (GPCR). Great success has been reached with therapies based on the GLP-1 receptor monoagonism; therefore, a logical and rational approach is the use of the dual and triagonism of GCPC to achieve complete metabolic homeostasis. The present review describes novel findings regarding the complex biology of the preproglucagon-derived hormones, their signaling, and the drug development of their analogues, especially those acting as dual and triagonists. Moreover, the main investigations into animal models and ongoing clinical trials using these unimolecular dual and triagonists are included which have demonstrated their safety, efficacy, and beneficial effects on the CV system. These therapeutic strategies could greatly impact the treatment of CVD with unprecedented benefits which will be revealed in the next years.

Roux-en-Y gastric bypass alters intestinal glucose transport in the obese Zucker rat

INTRODUCTION

The gastrointestinal tract plays a major role in regulating glucose homeostasis and gut endocrine function. The current study examines the effects of Roux-en-Y gastric bypass (RYGB) on intestinal GLP-1, glucose transporter expression and function in the obese Zucker rat (ZR).

METHODS

Two groups of ZRs were studied: RYGB and sham surgery pair-fed (PF) fed rats. Body weight and food intake were measured daily. On post-operative day (POD) 21, an oral glucose test (OGT) was performed, basal and 30-minute plasma, portal venous glucose and glucagon-like peptide-1 (GLP-1) levels were measured. In separate ZRs, the biliopancreatic, Roux limb (Roux) and common channel (CC) intestinal segments were harvested on POD 21.

RESULTS

Body weight was decreased in the RYGB group. Basal and 30-minute OGT plasma and portal glucose levels were decreased after RYGB. Basal plasma GLP-1 levels were similar, while a 4.5-fold increase in GLP-1 level was observed in 30-minute after RYGB (vs. PF). The increase in basal and 30-minute portal venous GLP-1 levels after RYGB were accompanied by increased mRNA expressions of proglucagon and PC 1/3, GPR119 protein in the Roux and CC segments. mRNA and protein levels of FFAR2/3 were increased in Roux segment. RYGB decreased brush border glucose transport, transporter proteins (SGLT1 and GLUT2) and mRNA levels of Tas1R1/Tas1R3 and α-gustducin in the Roux and CC segments.

CONCLUSIONS

Reductions in intestinal glucose transport and enhanced post-prandial GLP-1 release were associated with increases in GRP119 and FFAR2/3 after RYGB in the ZR model. Post-RYGB reductions in the regulation of intestinal glucose transport and L cell receptors regulating GLP-1 secretion represent potential mechanisms for improved glycemic control.

Xenin and Related Peptides: Potential Therapeutic Role in Diabetes and Related Metabolic Disorders

Xenin bioactivity and its role in normal physiology has been investigated by several research groups since its discovery in 1992. The 25 amino acid peptide hormone is secreted from the same enteroendocrine K-cells as the incretin hormone glucose-dependent insulinotropic polypeptide (GIP), with early studies highlighting the biological significance of xenin in the gastrointestinal tract, along with effects on satiety. Recently there has been more focus directed towards the role of xenin in insulin secretion and potential for diabetes therapies, especially through its ability to potentiate the insulinotropic actions of GIP as well as utilisation in dual/triple acting gut hormone therapeutic approaches. Currently, there is a lack of clinically approved therapies aimed at restoring GIP bioactivity in type 2 diabetes mellitus, thus xenin could hold real promise as a diabetes therapy. The biological actions of xenin, including its ability to augment insulin secretion, induce satiety effects, as well as restoring GIP sensitivity, earmark this peptide as an attractive antidiabetic candidate. This minireview will focus on the multiple biological actions of xenin, together with its proposed mechanism of action and potential benefits for the treatment of metabolic diseases such as diabetes.