GLP-1 Receptor Expression Within the Human Heart

Cardioprotective benefits of metabolic surgery and GLP-1 receptor agonist-based therapies

Individuals with excessive adipose tissue and type 2 diabetes mellitus (T2DM) face a heightened risk of cardiovascular morbidity and mortality. Metabolic surgery is an effective therapy for people with severe obesity to achieve significant weight loss. Additionally, metabolic surgery improves blood glucose levels and can lead to T2DM remission, reducing major adverse cardiovascular outcomes (MACE). Glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RAs) are a class of medication that effectively reduce body weight and MACE in patients with T2DM. This review explores the potential mechanisms underlying the cardioprotective benefits of metabolic surgery and GLP-1RA-based therapies and discusses recent evidence and emerging therapies in this dynamic area of research.

The impact of GLP-1 signalling on the energy metabolism of pancreatic islet β-cells and extrapancreatic tissues

Glucagon-like peptide-1 signalling impacts glucose homeostasis and appetite thereby indirectly affecting substrate availability at the whole-body level. The incretin canonically produces an insulinotropic effect, thereby lowering blood glucose levels by promoting the uptake and inhibiting the production of the sugar by peripheral tissues. Likewise, GLP-1 signalling within the central nervous system reduces the appetite and food intake, whereas its gastric effect delays the absorption of nutrients, thus improving glycaemic control and reducing the risk of postprandial hyperglycaemia. We review the molecular aspects of the GLP-1 signalling, focusing on its impact on intracellular energy metabolism. Whilst the incretin exerts its effects predominantly via a Gs receptor, which decodes the incretin signal into the elevation of intracellular cAMP levels, the downstream signalling cascades within the cell, acting on fast and slow timescales, resulting in an enhancement or an attenuation of glucose catabolism, respectively.

Curbing the Obesity Epidemic: Should GLP-1 Receptor Agonists Be the Standard of Care for Obesity?

PURPOSE OF REVIEW

This article summarizes the medical management of obesity with an emphasis on incretin-based therapeutics that target the neuro-hormonal basis of obesity.

RECENT FINDINGS

Medications that mimic the effect of incretins, a group of peptide hormones released in response to nutrient intake that regulate appetite, result in potent and durable weight loss. Glucagon-like peptide 1 (GLP-1) agonists and glucose-dependent insulinotropic polypeptide (GIP) agonists such as semaglutide and tirzepatide are approved by the United States Food and Drug Administration (FDA) for the management of obesity. The SELECT trial demonstrated that semaglutide led to a reduction in major adverse cardiovascular events in patients without diabetes who were either overweight and had preexisting cardiovascular disease or obese.

SUMMARY

The treatment of obesity is critical to prevent the progression of cardiovascular-kidney-metabolic syndrome. Incretin-based therapies offer remarkable weight loss and reduce major cardiovascular adverse events.

Bridging the gap between GLP1-receptor agonists and cardiovascular outcomes: evidence for the role of tirzepatide

Tirzepatide is a new drug targeting glucagon-like peptide 1(GLP1) and gastric inhibitory polypeptide (GIP) receptors. This drug has demonstrated great potential in improving the clinical outcomes of patients with type 2 diabetes. It can lead to weight loss, better glycemic control, and reduced cardiometabolic risk factors. GLP1 receptor agonists have been proven effective antidiabetic medications with possible cardiovascular benefits. Even though they have been proven to reduce the risk of major adverse cardiovascular events, their effectiveness in treating heart failure is unknown. Unlike traditional GLP1 receptor agonists, tirzepatide is more selective for the GIP receptor, resulting in a more balanced activation of these receptors. This review article discusses the possible mechanisms tirzepatide may use to improve cardiovascular health. That includes the anti-inflammatory effect, the ability to reduce cell death and promote autophagy, and also its indirect effects through blood pressure, obesity, and glucose/lipid metabolism. Additionally, tirzepatide may benefit atherosclerosis and lower the risk of major adverse cardiac events. Currently, clinical trials are underway to evaluate the safety and efficacy of tirzepatide in patients with heart failure. Overall, tirzepatide's dual agonism of GLP1 and GIP receptors appears to provide encouraging cardiovascular benefits beyond glycemic control, offering a potential new therapeutic option for treating cardiovascular diseases and heart failure.

Semaglutide Concurrently Improves Vascular and Liver Indices in Patients With Type 2 Diabetes and Fatty Liver Disease

Context

The cardiovascular benefits of semaglutide are established; however, its effects on surrogate vascular markers and liver function are not known.

Objective

To investigate the effects of semaglutide on vascular, endothelial, and liver function in patients with type 2 diabetes (T2DM) and nonalcoholic fatty liver disease (NAFLD).

Methods

Overall, 75 consecutive subjects with T2DM and NAFLD were enrolled: 50 patients received semaglutide 1 mg (treatment group) and 25 patients received dipeptidyl peptidase 4 inhibitors (control group). All patients underwent a clinical, vascular, and hepatic examination with Fibroscan elastography at 4 and 12 months after inclusion in the study.

Results

Treatment with semaglutide resulted in a reduction of Controlled Attenuation Parameter (CAP) score, E fibrosis score, NAFLD fibrosis score, Fibrosis-4 (FIB-4) score and perfused boundary region (PBR) at 4 and at 12 months (P < .05), contrary to controls. Patients treated with semaglutide showed a greater decrease of central systolic blood pressure (SBP) (-6% vs -4%, P = .048 and -11% vs -9%, P = .039), augmentation index (AIx) (-59% vs -52%, P = .041 and -70% vs -57%, P = .022), and pulse wave velocity (PWV) (-6% vs -3.5%, P = .019 and -12% vs -10%, P = .036) at 4 and at 12 months, respectively. In all patients, ΔPWV and ΔPBR were correlated with a corresponding reduction of CAP, E fibrosis, NAFLD fibrosis, and FIB-4 scores.

Conclusion

Twelve-month treatment with semaglutide simultaneously improves arterial stiffness, endothelial function, and liver steatosis and fibrosis in patients with T2DM and NAFLD.

Glucagon-like peptide-1 receptor agonists and sodium-glucose cotransporter 2 inhibitors, anti-diabetic drugs in heart failure and cognitive impairment: potential mechanisms of the protective effects

Heart failure and cognitive impairment emerge as public health problems that need to be addressed due to the aging global population. The conditions that often coexist are strongly related to advancing age and multimorbidity. Epidemiological evidence indicates that cardiovascular disease and neurodegenerative processes shares similar aspects, in term of prevalence, age distribution, and mortality. Type 2 diabetes increasingly represents a risk factor associated not only to cardiometabolic pathologies but also to neurological conditions. The pathophysiological features of type 2 diabetes and its metabolic complications (hyperglycemia, hyperinsulinemia, and insulin resistance) play a crucial role in the development and progression of both heart failure and cognitive dysfunction. This connection has opened to a potential new strategy, in which new classes of anti-diabetic medications, such as glucagon-like peptide-1 receptor (GLP-1R) agonists and sodium-glucose cotransporter 2 (SGLT2) inhibitors, are able to reduce the overall risk of cardiovascular events and neuronal damage, showing additional protective effects beyond glycemic control. The pleiotropic effects of GLP-1R agonists and SGLT2 inhibitors have been extensively investigated. They exert direct and indirect cardioprotective and neuroprotective actions, by reducing inflammation, oxidative stress, ions overload, and restoring insulin signaling. Nonetheless, the specificity of pathways and their contribution has not been fully elucidated, and this underlines the urgency for more comprehensive research.

GLP-1 increases heart rate by a direct action on the sinus node

AIMS

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are increasingly used to treat type 2 diabetes and obesity. Albeit cardiovascular outcomes generally improve, treatment with GLP-1 RAs is associated with increased heart rate, the mechanism of which is unclear.

METHODS AND RESULTS

We employed a large animal model, the female landrace pig, and used multiple in-vivo and ex-vivo approaches including pharmacological challenges, electrophysiology and high-resolution mass spectrometry to explore how GLP-1 elicits an increase in heart rate. In anaesthetized pigs, neither cervical vagotomy, adrenergic blockers (alpha, beta or combined alpha-beta blockade), ganglionic blockade (hexamethonium) nor inhibition of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (ivabradine) abolished the marked chronotropic effect of GLP-1. GLP-1 administration to isolated perfused pig hearts also increased heart rate, which was abolished by GLP-1 receptor blockade. Electrophysiological characterization of GLP-1 effects in vivo and in isolated perfused hearts localized electrical modulation to the atria and conduction system. In isolated sinus nodes, GLP-1 administration shortened action potential cycle length of pacemaker cells and shifted the site of earliest activation. The effect was independent of HCN blockade. Collectively, these data support a direct effect of GLP-1 on GLP-1 receptors within the heart. Consistently, single nucleus RNA sequencing (snRNAseq) showed GLP-1 receptor expression in porcine pacemaker cells. Quantitative phosphoproteomics analyses of sinus node samples revealed that GLP-1 administration leads to phosphorylation changes of calcium cycling proteins of the sarcoplasmic reticulum, known to regulate heart rate.

CONCLUSION

GLP-1 has direct chronotropic effects on the heart mediated by GLP-1 receptors in pacemaker cells of the sinus node, inducing changes in action potential morphology and the leading pacemaker site through a calcium signaling response characterized by PKA-dependent phosphorylation of Ca2+ cycling proteins involved in pace making. Targeting the pacemaker calcium clock may be a strategy to lower heart rate in GLP-1 RA recipients.

The effect of GLP-1R agonists on the medical triad of obesity, diabetes, and cancer

Glucagon-like peptide-1 receptor (GLP-1R) agonists have garnered significant attention for their therapeutic potential in addressing the interconnected health challenges of diabetes, obesity, and cancer. The role of GLP-1R in type 2 diabetes mellitus (T2DM) is highlighted, emphasizing its pivotal contribution to glucose homeostasis, promoting β-cell proliferation, and facilitating insulin release. GLP-1R agonists have effectively managed obesity by reducing hunger, moderating food intake, and regulating body weight. Beyond diabetes and obesity, GLP-1R agonists exhibit a multifaceted impact on cancer progression across various malignancies. The mechanisms underlying these effects involve the modulation of signaling pathways associated with cell growth, survival, and metabolism. However, the current literature reveals a lack of in vivo studies on specific GLP-1R agonists such as semaglutide, necessitating further research to elucidate its precise mechanisms and effects, particularly in cancer. While other GLP-1R agonists have shown promising outcomes in mitigating cancer progression, the association between some GLP-1R agonists and an increased risk of cancer remains a topic requiring more profound investigation. This calls for more extensive research to unravel the intricate relationships between the GLP-1R agonist and different cancers, providing valuable insights for clinicians and researchers alike.

Cyclic Adenosine Monophosphate in Cardiac and Sympathoadrenal GLP-1 Receptor Signaling: Focus on Anti-Inflammatory Effects

Glucagon-like peptide-1 (GLP-1) is a multifunctional incretin hormone with various physiological effects beyond its well-characterized effect of stimulating glucose-dependent insulin secretion in the pancreas. An emerging role for GLP-1 and its receptor, GLP-1R, in brain neuroprotection and in the suppression of inflammation, has been documented in recent years. GLP-1R is a G protein-coupled receptor (GPCR) that couples to Gs proteins that stimulate the production of the second messenger cyclic 3',5'-adenosine monophosphate (cAMP). cAMP, acting through its two main effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), exerts several anti-inflammatory (and some pro-inflammatory) effects in cells, depending on the cell type. The present review discusses the cAMP-dependent molecular signaling pathways elicited by the GLP-1R in cardiomyocytes, cardiac fibroblasts, central neurons, and even in adrenal chromaffin cells, with a particular focus on those that lead to anti-inflammatory effects by the GLP-1R. Fully elucidating the role cAMP plays in GLP-1R's anti-inflammatory properties can lead to new and more precise targets for drug development and/or provide the foundation for novel therapeutic combinations of the GLP-1R agonist medications currently on the market with other classes of drugs for additive anti-inflammatory effect.

GLP-1 receptor agonists and atherosclerosis protection: the vascular endothelium takes center stage

Atherosclerotic cardiovascular disease is a chronic condition that often copresents with type 2 diabetes and obesity. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are incretin mimetics endorsed by major professional societies for improving glycemic status and reducing atherosclerotic risk in people living with type 2 diabetes. Although the cardioprotective efficacy of GLP-1RAs and their relationship with traditional risk factors are well established, there is a paucity of publications that have summarized the potentially direct mechanisms through which GLP-1RAs mitigate atherosclerosis. This review aims to narrow this gap by providing comprehensive and in-depth mechanistic insight into the antiatherosclerotic properties of GLP-1RAs demonstrated across large outcome trials. Herein, we describe the landmark cardiovascular outcome trials that triggered widespread excitement around GLP-1RAs as a modern class of cardioprotective agents, followed by a summary of the origins of GLP-1RAs and their mechanisms of action. The effects of GLP-1RAs at each major pathophysiological milestone of atherosclerosis, as observed across clinical trials, animal models, and cell culture studies, are described in detail. Specifically, this review provides recent preclinical and clinical evidence that suggest GLP-1RAs preserve vessel health in part by preventing endothelial dysfunction, achieved primarily through the promotion of angiogenesis and inhibition of oxidative stress. These protective effects are in addition to the broad range of atherosclerotic processes GLP-1RAs target downstream of endothelial dysfunction, which include systemic inflammation, monocyte recruitment, proinflammatory macrophage and foam cell formation, vascular smooth muscle cell proliferation, and plaque development.

Evidence that tirzepatide protects against diabetes-related cardiac damages

BACKGROUND

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are effective antidiabetic drugs with potential cardiovascular benefits. Despite their well-established role in reducing the risk of major adverse cardiovascular events (MACE), their impact on heart failure (HF) remains unclear. Therefore, our study examined the cardioprotective effects of tirzepatide (TZT), a novel glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) receptor agonist.

METHODS

A three-steps approach was designed: (i) Meta-analysis investigation with the primary objective of assessing major adverse cardiovascular events (MACE) occurrence from major randomized clinical trials.; (ii) TZT effects on a human cardiac AC16 cell line exposed to normal (5 mM) and high (33 mM) glucose concentrations for 7 days. The gene expression and protein levels of primary markers related to cardiac fibrosis, hypertrophy, and calcium modulation were evaluated. (iii) In silico data from bioinformatic analyses for generating an interaction map that delineates the potential mechanism of action of TZT.

RESULTS

Meta-analysis showed a reduced risk for MACE events by TZT therapy (HR was 0.59 (95% CI 0.40-0.79, Heterogeneity: r2 = 0.01, I2 = 23.45%, H2 = 1.31). In the human AC16 cardiac cell line treatment with 100 nM TZT contrasted high glucose (HG) levels increase in the expression of markers associated with fibrosis, hypertrophy, and cell death (p < 0.05 for all investigated markers). Bioinformatics analysis confirmed the interaction between the analyzed markers and the associated pathways found in AC16 cells by which TZT affects apoptosis, fibrosis, and contractility, thus reducing the risk of heart failure.

CONCLUSION

Our findings indicate that TZT has beneficial effects on cardiac cells by positively modulating cardiomyocyte death, fibrosis, and hypertrophy in the presence of high glucose concentrations. This suggests that TZT may reduce the risk of diabetes-related cardiac damage, highlighting its potential as a therapeutic option for heart failure management clinical trials. Our study strongly supports the rationale behind the clinical trials currently underway, the results of which will be further investigated to gain insights into the cardiovascular safety and efficacy of TZT.

The benefits of GLP1 receptors in cardiovascular diseases

Glucagon like peptide-1 (GLP-1) receptor agonists are well established drugs for the treatment of type 2 diabetes (T2D). In addition to glycemic control, GLP-1 receptor agonists have beneficial other effects. They act by binding to GLP-1 receptors, which are widely distributed in the body, including cardiomyocytes and blood vessels. The aim of this article is to provide a comprehensive review of GLP-1 receptor agonists impact on cardiovascular outcomes and risk reduction. In the last decade, several cardiovascular outcomes trials (CVOT) have been conducted in order to explore cardiovascular benefit of GLP-1 receptor agonists. CVOTs primarily proved cardiovascular safety and tolerability of different GLP-1 receptor agonists, but also showed cardiovascular benefit of specific drugs. CVOTs have shown that GLP-1 receptor agonists reduce MACE in patients with T2D compared to placebo. In addition, they have positive impact on several cardiovascular risk factors such as obesity by promoting weight loss, blood pressure and blood lipid levels. Also, they stimulate the endothelium to produce nitric oxide, reduce oxidative stress, and have antiatherogenic and antiinflammatory effects. Studies have shown their positive impact on kidney outcomes in patients with T2D compared to placebo. The results of previous trials are encouraging in terms of multiple positive effects of GLP-1 receptor agonists. However, further research is needed to understand their full potential and all details of their mechanism of action, which will enable to expand the therapeutic indications and to determine their optimal use in clinical practice.

The impact of a single dose of whey protein on glucose flux and metabolite profiles in normoglycemic males: insights into glucagon and insulin biology

Protein ingestion concurrently stimulates euglycemic glucagon and insulin secretion, a response that is particularly robust with rapidly absorbing proteins. Previously, we have shown that ingestion of repeated doses of rapidly absorbing whey protein equally stimulated endogenous glucose production (EGP) and glucose disposal (Rd), thus explaining the preservation of euglycemia. Here, we aimed to determine if a smaller single dose of whey could elicit a large enough glucagon and insulin response to stimulate glucose flux. Therefore, in normoglycemic young adult males (n = 10; age ∼26; BMI ∼25), using [6,6-2H2] glucose tracing and quantitative targeted metabolite profiling, we determined the metabolic response to a single 25 g "standard" dose of whey protein. Whey protein ingestion did not alter glycemia, but increased circulating glucagon (peak 4-fold basal), insulin (peak 6-fold basal), amino acids, and urea while also reducing free fatty acid (FFA) and glycerol concentrations. Interestingly, the postprandial insulin response was driven by both a stimulation of insulin secretion and marked reduction in hepatic insulin clearance. Whey protein ingestion resulted in a modest stimulation of EGP and Rd, both peaking at ∼20% above baseline 1 h after protein ingestion. These findings demonstrate that the ingestion of a single standard serving of whey protein can induce a euglycemic glucagon and insulin response that stimulates glucose flux. We speculate on a theory that could potentially explain how glucagon and insulin synergistically provide hardwired control of nitrogen and glucose homeostasis.NEW & NOTEWORTHY Protein ingestion concurrently stimulates glucagon and insulin secretion. Here we show that in normoglycemic males, ingestion of a single "standard" 25 g serving of rapidly absorbing whey protein drives a sufficiently large glucagon and insulin response, such that it simultaneously increases endogenous glucose production and glucose disposal. We speculate on a novel theory that could potentially explain how the antagonistic/synergistic actions of glucagon and insulin simultaneously provide tight control of glucose and nitrogen homeostasis.

Effects of liraglutide on ANP secretion and cardiac dynamics

To observe the effects of liraglutide (analog of glucagon-like peptide 1 (GLP-1)) on atrial natriuretic peptide (ANP) secretion and atrial dynamics, an ex vivo isolated rat atrial perfusion model was used to determine atrial ANP secretion and pulse pressure. DPP-4-/- mice were also established in vivo. ANP levels were determined by radioimmunoassay; GLP-1 content was determined by Elisa. The expression levels of GLP-1 receptor (GLP-1R), PI3K/AKT/mTOR, piezo 1, and cathepsin K were analyzed by Western blot. In the clinical study, patients with acute coronary syndrome (ACS) had low levels of plasma GLP-1 but relatively high levels of plasma ANP. In ex vivo (3.2 nmol/L) and in vivo (30 μg/kg) models, liraglutide significantly decreased ANP levels and atrial pulse pressure. Exendin9-39 alone (GLP-1R antagonist) reversibly significantly increased ANP secretion, and the reduction effect of liraglutide on the secretion of ANP was significantly alleviated by Exendin9-39. Exendin9-39 demonstrated slightly decreased atrial pulse pressure; however, combined liraglutide and Exendin9-39 significantly decreased atrial pulse pressure. Ly294002 (PI3K/AKT inhibitor) inhibited the increase of ANP secretion by liraglutide for a short time, while Ly294002 didn't counteract the decrease in pulse pressure by liraglutide in atrial dynamics studies. Liraglutide increased the expression of GLP-1R and PI3K/AKT/mTOR in isolated rat atria and the hearts of mice in vivo, whereas Exendin9-39 reversibly reduced the expression of GLP-1R and PI3K/AKT/mTOR. Piezo 1 was significantly decreased in wild type and DPP-4-/- mouse heart or isolated rat atria after being treated with liraglutide. Cathepsin K expression was only decreased in in vivo model hearts. Liraglutide can inhibit ANP secretion while decreasing atrial pulse pressure mediated by GLP-1R. Liraglutide probably plays a role in the reduction of ANP secretion via the PI3K/AKT/mTOR signaling pathway. Piezo 1 and cathepsin K may be involved in the liraglutide mechanism of reduction.

The importance of glucose-dependent insulinotropic polypeptide receptor activation for the effects of tirzepatide

Tirzepatide is a unimolecular co-agonist of the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors recently approved for the treatment of type 2 diabetes by the US Food and Drug Administration and the European Medicine Agency. Tirzepatide treatment results in an unprecedented improvement of glycaemic control and lowering of body weight, but the contribution of the GIP receptor-activating component of tirzepatide to these effects is uncertain. In this review, we present the current knowledge about the physiological roles of the incretin hormones GLP-1 and GIP, their receptors, and previous results of co-targeting the two incretin hormone receptors in humans. We also analyse the molecular pharmacological, preclinical and clinical effects of tirzepatide to discuss the role of GIP receptor activation for the clinical effects of tirzepatide. Based on the available literature on the combination of GLP-1 and GIP receptor activation, tirzepatide does not seem to have a classical co-activating mode of action in humans. Rather, in vitro studies of the human GLP-1 and GIP receptors reveal a biased GLP-1 receptor activation profile and GIP receptor downregulation. Therefore, we propose three hypotheses for the mode of action of tirzepatide, which can be addressed in future, elaborate clinical trials.

Obesity and its comorbidities, current treatment options and future perspectives: Challenging bariatric surgery?

Obesity and its comorbidities, including type 2 diabetes mellitus, cardiovascular disease, heart failure and non-alcoholic liver disease are a major health and economic burden with steadily increasing numbers worldwide. The need for effective pharmacological treatment options is strong, but, until recently, only few drugs have proven sufficient efficacy and safety. This article provides a comprehensive overview of obesity and its comorbidities, with a special focus on organ-specific pathomechanisms. Bariatric surgery as the so far most-effective therapeutic strategy, current pharmacological treatment options and future treatment strategies will be discussed. An increasing knowledge about the gut-brain axis and especially the identification and physiology of incretins unfolds a high number of potential drug candidates with impressive weight-reducing potential. Future multi-modal therapeutic concepts in obesity treatment may surpass the effectivity of bariatric surgery not only with regard to weight loss, but also to associated comorbidities.

Current challenges in the treatment of cardiac fibrosis: Recent insights into the sex-specific differences of glucose-lowering therapies on the diabetic heart: IUPHAR Review 33

A significant cardiac complication of diabetes is cardiomyopathy, a form of ventricular dysfunction that develops independently of coronary artery disease, hypertension and valvular diseases, which may subsequently lead to heart failure. Several structural features underlie the development of diabetic cardiomyopathy and eventual diabetes-induced heart failure. Pathological cardiac fibrosis (interstitial and perivascular), in addition to capillary rarefaction and myocardial apoptosis, are particularly noteworthy. Sex differences in the incidence, development and presentation of diabetes, heart failure and interstitial myocardial fibrosis have been identified. Nevertheless, therapeutics specifically targeting diabetes-associated cardiac fibrosis remain lacking and treatment approaches remain the same regardless of patient sex or the co-morbidities that patients may present. This review addresses the observed anti-fibrotic effects of newer glucose-lowering therapies and traditional cardiovascular disease treatments, in the diabetic myocardium (from both preclinical and clinical contexts). Furthermore, any known sex differences in these treatment effects are also explored. LINKED ARTICLES: This article is part of a themed issue on Translational Advances in Fibrosis as a Therapeutic Target. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.22/issuetoc.

Glucagon-like peptide-1/glucose-dependent insulinotropic polypeptide receptor co-agonists for cardioprotection, type 2 diabetes and obesity: a review of mechanisms and clinical data

PURPOSE OF REVIEW

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are approved for the management of type 2 diabetes (T2D) and obesity, and some are recommended for cardiorenal risk reduction in T2D. To enhance the benefits with GLP-RA mono-agonist therapy, GLP-1/glucose-dependent insulinotropic polypeptide (GIP) receptor co-agonists are in development to capitalize on the synergism of GLP-1 and GIP agonism. We review the mechanisms of action and clinical data for GLP-1/GIP receptor co-agonists in T2D and obesity and their potential role in cardiovascular protection.

RECENT FINDINGS

Tirzepatide, a first-in-class unimolecular GLP-1/GIP receptor co-agonist, is approved for T2D and is awaiting approval for obesity management. Phase 3 trials in T2D cohorts revealed significant reductions in glycemia and body weight and superiority compared with GLP-1R mono-agonism with semaglutide. Tirzepatide has demonstrated significant body weight reductions in individuals with obesity but not diabetes. It enhances lipid metabolism, reduces blood pressure, and lowers liver fat content. Pooled phase 2/3 data showed cardiovascular safety in T2D while a post hoc analysis suggested tirzepatide slows the decline of kidney function in T2D.

SUMMARY

GLP-1/GIP receptor co-agonists are a novel addition to the diabetes and obesity armamentarium. The cardiorenal-metabolic benefits position them as promising multiprong tools for metabolically complex individuals with chronic vascular complications.

The expanding incretin universe: from basic biology to clinical translation

Incretin hormones, principally glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1(GLP-1), potentiate meal-stimulated insulin secretion through direct (GIP + GLP-1) and indirect (GLP-1) actions on islet β-cells. GIP and GLP-1 also regulate glucagon secretion, through direct and indirect pathways. The incretin hormone receptors (GIPR and GLP-1R) are widely distributed beyond the pancreas, principally in the brain, cardiovascular and immune systems, gut and kidney, consistent with a broad array of extrapancreatic incretin actions. Notably, the glucoregulatory and anorectic activities of GIP and GLP-1 have supported development of incretin-based therapies for the treatment of type 2 diabetes and obesity. Here we review evolving concepts of incretin action, focusing predominantly on GLP-1, from discovery, to clinical proof of concept, to therapeutic outcomes. We identify established vs uncertain mechanisms of action, highlighting biology conserved across species, while illuminating areas of active investigation and uncertainty that require additional clarification.

Glucagon and Its Receptors in the Mammalian Heart

Glucagon exerts effects on the mammalian heart. These effects include alterations in the force of contraction, beating rate, and changes in the cardiac conduction system axis. The cardiac effects of glucagon vary according to species, region, age, and concomitant disease. Depending on the species and region studied, the contractile effects of glucagon can be robust, modest, or even absent. Glucagon is detected in the mammalian heart and might act with an autocrine or paracrine effect on the cardiac glucagon receptors. The glucagon levels in the blood and glucagon receptor levels in the heart can change with disease or simultaneous drug application. Glucagon might signal via the glucagon receptors but, albeit less potently, glucagon might also signal via glucagon-like-peptide-1-receptors (GLP1-receptors). Glucagon receptors signal in a species- and region-dependent fashion. Small molecules or antibodies act as antagonists to glucagon receptors, which may become an additional treatment option for diabetes mellitus. Hence, a novel review of the role of glucagon and the glucagon receptors in the mammalian heart, with an eye on the mouse and human heart, appears relevant. Mouse hearts are addressed here because they can be easily genetically modified to generate mice that may serve as models for better studying the human glucagon receptor.

Glucagon-Like Peptide-1 Protects Against Atrial Fibrillation and Atrial Remodeling in Type 2 Diabetic Mice

Atrial fibrillation (AF) is highly prevalent in type 2 diabetes where it increases morbidity and mortality. Glucagon-like peptide (GLP)-1 receptor agonists are used in the treatment of type 2 diabetes (T2DM), but their effects on AF in T2DM are poorly understood. The present study demonstrates type 2 diabetic db/db mice are highly susceptible to AF in association with atrial electrical and structural remodeling. GLP-1, as well as the long-acting GLP-1 analogue liraglutide, reduced AF and prevented atrial remodeling in db/db mice. These data suggest that GLP-1 and related analogues could protect against AF in patients with T2DM.

Glucagon-like peptide 1 receptor agonists: cardiovascular benefits and mechanisms of action

Type 2 diabetes mellitus (T2DM) and obesity are metabolic disorders characterized by excess cardiovascular risk. Glucagon-like peptide 1 (GLP1) receptor (GLP1R) agonists reduce body weight, glycaemia, blood pressure, postprandial lipaemia and inflammation - actions that could contribute to the reduction of cardiovascular events. Cardiovascular outcome trials (CVOTs) have demonstrated that GLP1R agonists reduce the rates of major adverse cardiovascular events in patients with T2DM. Separate phase III CVOTs of GLP1R agonists are currently being conducted in people living with heart failure with preserved ejection fraction and in those with obesity. Mechanistically, GLP1R is expressed at low levels in the heart and vasculature, raising the possibility that GLP1 might have both direct and indirect actions on the cardiovascular system. In this Review, we summarize the data from CVOTs of GLP1R agonists in patients with T2DM and describe the actions of GLP1R agonists on the heart and blood vessels. We also assess the potential mechanisms that contribute to the reduction in major adverse cardiovascular events in individuals treated with GLP1R agonists and highlight the emerging cardiovascular biology of novel GLP1-based multi-agonists currently in development. Understanding how GLP1R signalling protects the heart and blood vessels will optimize the therapeutic use and development of next-generation GLP1-based therapies with improved cardiovascular safety.

The effect of exenatide (a GLP-1 analogue) and sitagliptin (a DPP-4 inhibitor) on asymmetric dimethylarginine (ADMA) metabolism and selected biomarkers of cardiac fibrosis in rats with fructose-induced metabolic syndrome

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis, is a risk factor for endothelial dysfunction, a common pathophysiological denominator for both atherogenesis and cardiac fibrosis. We aimed to investigate whether the cardioprotective and antifibrotic effects of incretin drugs, exenatide and sitagliptin, may be associated with their ability to affect circulating and cardiac ADMA metabolism. Normal and fructose-fed rats were treated with sitagliptin (5.0/10 mg/kg) or exenatide (5/10 µg/kg) for 4 weeks. The following methods were used: LC-MS/MS, ELISA, Real-Time-PCR, colorimetry, IHC and H&E staining, PCA and OPLS-DA projections. Eight-week fructose feeding resulted in an increase in plasma ADMA and a decrease in NO concentration. Exenatide administration into fructose-fed rats reduced the plasma ADMA level and increased NO level. In the heart of these animals exenatide administration increased NO and PRMT1 level, reduced TGF-ß1, α-SMA levels and COL1A1 expression. In the exenatide treated rats renal DDAH activity positively correlated with plasma NO level and negatively with plasma ADMA level and cardiac α-SMA concentration. Sitagliptin treatment of fructose-fed rats increased plasma NO concentration, reduced circulating SDMA level, increased renal DDAH activity and reduced myocardial DDAH activity. Both drugs attenuated the myocardial immunoexpression of Smad2/3/P and perivascular fibrosis. In the metabolic syndrome condition both sitagliptin and exenatide positively modulated cardiac fibrotic remodeling and circulating level of endogenous NOS inhibitors but had no effects on ADMA levels in the myocardium.

Evidence for a lack of inotropic and chronotropic effects of glucagon and glucagon receptors in the human heart

BACKGROUND

Glucagon is thought to increase heart rate and contractility by stimulating glucagon receptors and increasing 3',5'-cyclic adenosine monophosphate (cAMP) production in the myocardium. This has been confirmed in animal studies but not in the human heart. The cardiostimulatory effects of glucagon have been correlated with the degree of cardiac dysfunction, as well as with the enzymatic activity of phosphodiesterase (PDE), which hydrolyses cAMP. In this study, the presence of glucagon receptors in the human heart and the inotropic and chronotropic effects of glucagon in samples of failing and nonfailing (NF) human hearts were investigated.

METHODS

Concentration‒response curves for glucagon in the absence and presence of the PDE inhibitor IBMX were performed on samples obtained from the right (RA) and left atria (LA), the right (RV) and left ventricles (LV), and the sinoatrial nodes (SNs) of failing and NF human hearts. The expression of glucagon receptors was also investigated. Furthermore, the inotropic and chronotropic effects of glucagon were examined in rat hearts.

RESULTS

In tissues obtained from failing and NF human hearts, glucagon did not exert inotropic or chronotropic effects in the absence or presence of IBMX. IBMX (30 µM) induced a marked increase in contractility in NF hearts (RA: 83 ± 28% (n = 5), LA: 80 ± 20% (n = 5), RV: 75 ± 12% (n = 5), and LV: 40 ± 8% (n = 5), weaker inotropic responses in the ventricular myocardium of failing hearts (RV: 25 ± 10% (n = 5) and LV: 10 ± 5% (n = 5) and no inotropic responses in the atrial myocardium of failing hearts. IBMX (30 µM) increased the SN rate in failing and NF human hearts (27.4 ± 3.0 beats min^-1, n = 10). In rat hearts, glucagon induced contractile and chronotropic responses, but only contractility was enhanced by 30 µM IBMX (maximal inotropic effect of glucagon 40 ± 8% vs. 75 ± 10%, in the absence or presence of IBMX, n = 5, P < 0.05; maximal chronotropic response 77.7 ± 6.4 beats min^-1 vs. 73 ± 11 beats min^-1, in the absence or presence of IBMX, n = 5, P > 0.05). Glucagon receptors were not detected in the human heart samples.

CONCLUSIONS

Our results conflict with the view that glucagon induces inotropic and chronotropic effects and that glucagon receptors are expressed in the human heart.

Epicardial fat links obesity to cardiovascular diseases

Patients with obesity have been historically associated with higher risk to develop cardiovascular diseases (CVD). However, regional, visceral, organ specific adiposity seems to play a stronger role in the development of those cardiovascular diseases than obesity by itself. Epicardial adipose tissue is the visceral fat depot of the heart with peculiar anatomy, regional differences, genetic profile and functions. Due to its unobstructed contiguity with heart and intense pro inflammatory and pro arrhythmogenic activities, epicardial fat is directly involved in major obesity-related CVD complications, such as coronary artery disease (CAD), atrial fibrillation (AF) and heart failure (HF). Current and developing imaging techniques can measure epicardial fat thickness, volume, density and inflammatory status for the prediction and stratification of the cardiovascular risk in both symptomatic and asymptomatic obese individuals. Pharmacological modulation of the epicardial fat with glucagon like peptide-1 receptor (GLP1R) analogs, sodium glucose transporter-2 inhibitors, and potentially dual (glucose-dependent insulinotropic polypeptide -GLP1R) agonists, can reduce epicardial fat mass, resume its original cardio-protective functions and therefore reduce the cardiovascular risk. Epicardial fat assessment is poised to change the traditional paradigm that links obesity to the heart.

Beyond the pancreas: contrasting cardiometabolic actions of GIP and GLP1

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP1) exhibit incretin activity, meaning that they potentiate glucose-dependent insulin secretion. The emergence of GIP receptor (GIPR)-GLP1 receptor (GLP1R) co-agonists has fostered growing interest in the actions of GIP and GLP1 in metabolically relevant tissues. Here, we update concepts of how these hormones act beyond the pancreas. The actions of GIP and GLP1 on liver, muscle and adipose tissue, in the control of glucose and lipid homeostasis, are discussed in the context of plausible mechanisms of action. Both the GIPR and GLP1R are expressed in the central nervous system, wherein receptor activation produces anorectic effects enabling weight loss. In preclinical studies, GIP and GLP1 reduce atherosclerosis. Furthermore, GIPR and GLP1R are expressed within the heart and immune system, and GLP1R within the kidney, revealing putative mechanisms linking GIP and GLP1R agonism to cardiorenal protection. We interpret the clinical and mechanistic data obtained for different agents that enable weight loss and glucose control for the treatment of obesity and type 2 diabetes mellitus, respectively, by activating or blocking GIPR signalling, including the GIPR-GLP1R co-agonist tirzepatide, as well as the GIPR antagonist-GLP1R agonist AMG-133. Collectively, we update translational concepts of GIP and GLP1 action, while highlighting gaps, areas of uncertainty and controversies meriting ongoing investigation.

Short-term semaglutide treatment improves FGF21 responsiveness in primary hepatocytes isolated from high fat diet challenged mice

Metabolic functions of GLP-1 and its analogues have been extensively investigated. In addition to acting as an incretin and reducing body weight, we and others have suggested the existence of GLP-1/fibroblast growth factor 21 (FGF21) axis in which liver mediates certain functions of GLP-1 receptor agonists. In a more recent study, we found with surprise that four-week treatment with liraglutide but not semaglutide stimulated hepatic FGF21 expression in HFD-challenged mice. We wondered whether semaglutide can also improve FGF21 sensitivity or responsiveness and hence triggers the feedback loop in attenuating its stimulation on hepatic FGF21 expression after a long-term treatment. Here, we assessed effect of daily semaglutide treatment in HFD-fed mice for 7 days. HFD challenge attenuated effect of FGF21 treatment on its downstream events in mouse primary hepatocytes, which can be restored by 7-day semaglutide treatment. In mouse liver, 7-day semaglutide treatment stimulated FGF21 as well as genes that encode its receptor (FGFR1) and the obligatory co-receptor (KLB), and a battery of genes that are involved in lipid homeostasis. In epididymal fat tissue, expressions of a battery genes including Klb affected by HFD challenge were reversed by 7-day semaglutide treatment. We suggest that semaglutide treatment improves FGF21 sensitivity which is attenuated by HFD challenge.

Ischemia with Nonobstructive Coronary Artery Disease and Atrial Cardiomyopathy-Two Sides of the Same Story?

Ischemia with nonobstructive coronary artery disease (INOCA) is increasingly recognized as a significant cause of angina, myocardial remodeling, and eventually heart failure (HF). Coronary microvascular dysfunction (CMD) is a major endotype of INOCA, and it is caused by structural and functional alterations of the coronary microcirculation. At the same time, atrial cardiomyopathy (ACM) defined by structural, functional, and electrical atrial remodeling has a major clinical impact due to its manifestations: atrial fibrillation (AF), atrial thrombosis, stroke, and HF symptoms. Both these pathologies share similar risk factors and have a high comorbidity burden. CMD causing INOCA and ACM frequently coexist. Thus, questions arise whether there is a potential link between these pathologies. Does CMD promote AF or the reverse? Which are the mechanisms that ultimately lead to CMD and ACM? Are both part of a systemic disease characterized by endothelial dysfunction? Lastly, which are the therapeutic strategies that can target endothelial dysfunction and improve the prognosis of patients with CMD and ACM? This review aims to address these questions by analyzing the existing body of evidence, offering further insight into the mechanisms of CMD and ACM, and discussing potential therapeutic strategies.

Metabolic Messengers: glucagon

Plasma glucose is tightly regulated via the secretion of the two glucose-regulating hormones insulin and glucagon. Situated next to the insulin-secreting β-cells, the α-cells produce and secrete glucagon-one of the body's few blood glucose-increasing hormones. Diabetes is a bihormonal disorder, resulting from both inadequate insulin secretion and dysregulation of glucagon. The year 2023 marks the 100th anniversary of the discovery of glucagon, making it particularly timely to highlight the roles of this systemic metabolic messenger in health and disease.

Sirt3 activates autophagy to prevent DOX-induced senescence by inactivating PI3K/AKT/mTOR pathway in A549 cells

Sirtuin 3 (Sirt3), a mitochondrial deacetylase, regulates mitochondrial redox homeostasis and autophagy and is involved in physiological and pathological processes such as aging, cellular metabolism, and tumorigenesis. We here investigate how Sirt3 regulates doxorubicin (DOX)-induced senescence in lung cancer A549 cells. Sirt3 greatly reduced DOX-induced upregulation of senescence marker proteins p53, p16, p21 and SA-β-Gal activity as well as ROS levels. Notably, Sirt3 reversed DOX-induced autophagic flux blockage, as shown by increased p62 degradation and LC3II/LC3I ratio. Importantly, the autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ) partially abolished the antioxidant stress and antiaging effects of Sirt3, while the autophagy activator rapamycin (Rap) potentiated these effects of Sirt3, demonstrating that autophagy mediates the anti-aging effects of Sirt3. Additionally, Sirt3 inhibited the DOX-induced activation of the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway, which in turn activated autophagy. The PI3K inhibitor LY294002 promoted the antioxidant stress and antiaging effects of Sirt3, while the AKT activator SC-79 reversed these effects of Sirt3. Taken together, Sirt3 counteracts DOX-induced senescence by improving autophagic flux.

Revealing the tissue-level complexity of endogenous glucagon-like peptide-1 receptor expression and signaling

The glucagon-like peptide-1 receptor (GLP1R) is a class B G protein-coupled receptor (GPCR) involved in glucose homeostasis and food intake. GLP1R agonists (GLP1RA) are widely used in the treatment of diabetes and obesity, yet visualizing the endogenous localization, organization and dynamics of a GPCR has so far remained out of reach. In the present study, we generate mice harboring an enzyme self-label genome-edited into the endogenous Glp1r locus. We also rationally design and test various fluorescent dyes, spanning cyan to far-red wavelengths, for labeling performance in tissue. By combining these technologies, we show that endogenous GLP1R can be specifically and sensitively detected in primary tissue using multiple colors. Longitudinal analysis of GLP1R dynamics reveals heterogeneous recruitment of neighboring cell subpopulations into signaling and trafficking, with differences observed between GLP1RA classes and dual agonists. At the nanoscopic level, GLP1Rs are found to possess higher organization, undergoing GLP1RA-dependent membrane diffusion. Together, these results show the utility of enzyme self-labels for visualization and interrogation of endogenous proteins, and provide insight into the biology of a class B GPCR in primary cells and tissue.

Glucagon-like Peptide-1 Receptor-based Therapeutics for Metabolic Liver Disease

Glucagon-like peptide-1 (GLP-1) controls islet hormone secretion, gut motility, and body weight, supporting development of GLP-1 receptor agonists (GLP-1RA) for the treatment of type 2 diabetes (T2D) and obesity. GLP-1RA exhibit a favorable safety profile and reduce the incidence of major adverse cardiovascular events in people with T2D. Considerable preclinical data, supported by the results of clinical trials, link therapy with GLP-RA to reduction of hepatic inflammation, steatosis, and fibrosis. Mechanistically, the actions of GLP-1 on the liver are primarily indirect, as hepatocytes, Kupffer cells, and stellate cells do not express the canonical GLP-1R. GLP-1RA reduce appetite and body weight, decrease postprandial lipoprotein secretion, and attenuate systemic and tissue inflammation, actions that may contribute to attenuation of metabolic-associated fatty liver disease (MAFLD). Here we discuss evolving concepts of GLP-1 action that improve liver health and highlight evidence that links sustained GLP-1R activation in distinct cell types to control of hepatic glucose and lipid metabolism, and reduction of experimental and clinical nonalcoholic steatohepatitis (NASH). The therapeutic potential of GLP-1RA alone, or in combination with peptide agonists, or new small molecule therapeutics is discussed in the context of potential efficacy and safety. Ongoing trials in people with obesity will further clarify the safety of GLP-1RA, and pivotal studies underway in people with NASH will define whether GLP-1-based medicines represent effective and safe therapies for people with MAFLD.

Association of glucagon-like peptide-1 receptor agonists with cardiac arrhythmias in patients with type 2 diabetes or obesity: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have been highly recommended for glycemic control and weight reduction. However, evidence has accumulated that GLP-1 RAs treatment is related to an increase in heart rate, which could potentially induce cardiac arrhythmias. This study aims to investigate the association of GLP-1 RAs therapy with incident arrhythmias in diabetic and obese patients.

METHODS

MEDLINE, EMBASE, Cochrane Library, and ClinicalTrials.gov were systematically searched from inception up to May 25, 2022. Randomized controlled trials (RCTs) comparing GLP-1 RAs with placebo or active control for adults with type 2 diabetes or obesity were included. The outcomes of interest were prespecified as incident atrial fibrillation (AF), atrial flutter (AFL), ventricular arrhythmias (VAs), and sudden cardiac death (SCD). Mantel-Haenszel relative risk (MH-RR) with a corresponding 95% confidence interval (95% CI) was estimated using a fixed-effects model.

RESULTS

A total of 56 RCTs involving 79,720 participants (44,028 GLP-1 RAs vs 35,692 control: mean age 57.3 years) were included from 7692 citations. GLP-1 RAs use overall did not significantly increase the risk of AF (RR 0.97, 95% CI 0.83-1.12), AFL (RR 0.83, 95% CI 0.59-1.17), VAs (RR 1.24, 95% CI 0.92-1.67), and SCD (RR 0.89, 95% CI 0.67-1.19), compared with controls. In further subgroup analyses, we observed an increasing trend toward incident AF with dulaglutide (RR 1.40, 95% CI 1.03-1.90) while an inverse trend with oral semaglutide (RR 0.43, 95% CI 0.21-0.87). Additionally, higher doses of GLP-1 RAs (RR 1.63, 95% CI 1.11-2.40) and higher baseline BMI (RR 1.60, 95% CI 1.04-2.48) might significantly increase the risk of VAs. No significant differences were identified in other subgroup analyses.

CONCLUSIONS

GLP-1 RAs therapy was not associated with an overall higher risk of arrhythmias, demonstrating an assuring cardiovascular safety profile. Further studies are required to determine whether the potential antiarrhythmic or arrhythmogenic effect of GLP-1 RAs is drug-specific and varies from doses or baseline BMI.

TRIAL REGISTRATION

PROSPERO Identifier: CRD42022339389.

Evaluation of commercially available glucagon receptor antibodies and glucagon receptor expression

Glucagon is a major regulator of metabolism and drugs targeting the glucagon receptor (GCGR) are being developed. Insight into tissue and cell-specific expression of the GCGR is important to understand the biology of glucagon and to differentiate between direct and indirect actions of glucagon. However, it has been challenging to localize the GCGR in tissue due to low expression levels and lack of specific methods. Immunohistochemistry has frequently been used for GCGR localization, but antibodies targeting G-protein-coupled-receptors may be inaccurate. We evaluated all currently commercially available GCGR antibodies. The antibody, ab75240 (Antibody no. 11) was found to perform best among the twelve antibodies tested and using this antibody we found expression of the GCGR in the kidney, liver, preadipocytes, pancreas, and heart. Three antibody-independent approaches all confirmed the presence of the GCGR within the pancreas, liver and the kidneys. GCGR expression should be evaluated by both antibody and antibody-independent approaches.

Glucagon-like Peptide-1 receptor Tie2+ cells are essential for the cardioprotective actions of liraglutide in mice with experimental myocardial infarction

OBJECTIVES

Glucagon-like peptide-1 receptor (GLP-1R) agonists reduce the rates of major cardiovascular events, including myocardial infarction in people with type 2 diabetes, and decrease infarct size while preserving ventricular function in preclinical studies. Nevertheless, the precise cellular sites of GLP-1R expression that mediate the cardioprotective actions of GLP-1 in the setting of ischemic cardiac injury are uncertain.

METHODS

Publicly available single cell RNA sequencing (scRNA-seq) datasets on mouse and human heart cells were analyzed for Glp1r/GLP1R expression. Fluorescent activated cell sorting was used to localize Glp1r expression in cell populations from the mouse heart. The importance of endothelial and hematopoietic cells for the cardioprotective response to liraglutide in the setting of acute myocardial infarction (MI) was determined by inactivating the Glp1r in Tie2+ cell populations. Cardiac gene expression profiles regulated by liraglutide were examined using RNA-seq to interrogate mouse atria and both infarcted and non-infarcted ventricular tissue after acute coronary artery ligation.

RESULTS

In mice, cardiac Glp1r mRNA transcripts were exclusively detected in endocardial cells by scRNA-seq. In contrast, analysis of human heart by scRNA-seq localized GLP1R mRNA transcripts to populations of atrial and ventricular cardiomyocytes. Moreover, very low levels of GIPR, GCGR and GLP2R mRNA transcripts were detected in the human heart. Cell sorting and RNA analyses detected cardiac Glp1r expression in endothelial cells (ECs) within the atria and ventricle in the ischemic and non-ischemic mouse heart. Transcriptional responses to liraglutide administration were not evident in wild type mouse ventricles following acute MI, however liraglutide differentially regulated genes important for inflammation, cardiac repair, cell proliferation, and angiogenesis in the left atrium, while reducing circulating levels of IL-6 and KC/GRO within hours of acute MI. Inactivation of the Glp1r within the Tie2+ cell expression domain encompassing ECs revealed normal cardiac structure and function, glucose homeostasis and body weight in Glp1r^Tie2-/- mice. Nevertheless, the cardioprotective actions of liraglutide to reduce infarct size, augment ejection fraction, and improve survival after experimental myocardial infarction (MI), were attenuated in Glp1r^Tie2-/- mice.

CONCLUSIONS

These findings identify the importance of the murine Tie2+ endothelial cell GLP-1R as a target for the cardioprotective actions of GLP-1R agonists and support the importance of the atrial and ventricular endocardial GLP-1R as key sites of GLP-1 action in the ischemic mouse heart. Hitherto unexplored species-specific differences in cardiac GLP-1R expression challenge the exclusive use of mouse models for understanding the mechanisms of GLP-1 action in the normal and ischemic human heart.

The Molecular Determinants of Glucagon-like Peptide Secretion by the Intestinal L cell

The intestinal L cell secretes a diversity of biologically active hormones, most notably the glucagon-like peptides, GLP-1 and GLP-2. The highly successful introduction of GLP-1-based drugs into the clinic for the treatment of patients with type 2 diabetes and obesity, and of a GLP-2 analog for patients with short bowel syndrome, has led to the suggestion that stimulation of the endogenous secretion of these peptides may serve as a novel therapeutic approach in these conditions. Situated in the intestinal epithelium, the L cell demonstrates complex relationships with not only circulating, paracrine, and neural regulators, but also ingested nutrients and other factors in the lumen, most notably the microbiota. The integrated input from these numerous secretagogues results in a variety of temporal patterns in L cell secretion, ranging from minutes to 24 hours. This review combines the findings of traditional, physiological studies with those using newer molecular approaches to describe what is known and what remains to be elucidated after 5 decades of research on the intestinal L cell and its secreted peptides, GLP-1 and GLP-2.

Liraglutide treatment attenuates inflammation markers in the cardiac, cerebral and renal microvasculature in streptozotocin-induced diabetic rats

BACKGROUND

Diabetes mellitus (DM) induces cardiac and cerebral microvascular dysfunction via increased glycation, oxidative stress and endothelial activation. Liraglutide, a glucagon-like peptide-1 analogue, inhibited NOX2 and adhesion molecules in isolated endothelial cells. Here, we have studied how Liraglutide affects advanced glycation, NOX expression and inflammation of the cardiac, cerebral and renal microvasculature in diabetic rats.

METHODS

DM was induced in Sprague-Dawley rats (n = 15) via intraperitoneal streptozotocin (STZ) injection (60 mg/kg bodyweight). Ten control rats remained nondiabetic. From day 9 post-STZ injection, Liraglutide (200 μg/kg bodyweight; n = 7) or vehicle (n = 8) was injected subcutaneously daily until termination on day 29. The advanced glycation endproduct N-ε-(carboxymethyl)lysine (CML), NOX2, NOX4, ICAM-1 and VCAM-1 were subsequently immunohistochemically analysed and quantified to compare Liraglutide treatment with placebo.

RESULTS

In the heart, Liraglutide treatment significantly reduced the DM-increased scores/cm² for CML in both ventricles (from 253 ± 53 to 72 ± 12; p = .003) and atria (343 ± 29 to 122 ± 8; p = .0001) and for NOX2, ICAM-1 and VCAM-1, but not for NOX4. Also in the cerebrum and cerebellum of the brain, Liraglutide significantly reduced the scores/cm² for CML (to 60 ± 7 (p = .0005) and 47 ± 13 (p = .02), respectively), and for NOX2 and NOX4. In the kidney, the DM-induced expression of ICAM-1 and VCAM-1 was decreased in the blood vessels and glomeruli by Liraglutide treatment. Liraglutide did not affect blood glucose levels or bodyweight.

CONCLUSIONS

Our study implies that Liraglutide protects the cardiac, cerebral and renal microvasculature against diabetes-induced dysfunction, independent of lowering blood glucose in a type 1 diabetes rat model.

Genetic disruption of the Gipr in Apoe-/- mice promotes atherosclerosis

OBJECTIVE

The gut hormone glucose-dependent insulinotropic polypeptide (GIP) stimulates beta cell function and improves glycemia through its incretin actions. GIP also regulates endothelial function and suppresses adipose tissue inflammation through control of macrophage activity. Activation of the GIP receptor (GIPR) attenuates experimental atherosclerosis and inflammation in mice, however whether loss of GIPR signaling impacts the development of atherosclerosis is uncertain.

METHODS

Atherosclerosis and related metabolic phenotypes were studied in Apoe^-/-:Gipr^-/- mice and in Gipr^+/+ and Gipr^-/- mice treated with an adeno-associated virus expressing PCSK9 (AAV-PCSK9). Bone marrow transplantation (BMT) studies were carried out using donor marrow from Apoe^-/-:Gipr^-/-and Apoe^-/-:Gipr^+/+mice transplanted into Apoe^-/-:Gipr^-/- recipient mice. Experimental endpoints included the extent of aortic atherosclerosis and inflammation, body weight, glucose tolerance, and circulating lipid levels, the proportions and subsets of circulating leukocytes, and tissue gene expression profiles informing lipid and glucose metabolism, and inflammation.

RESULTS

Body weight was lower, circulating myeloid cells were reduced, and glucose tolerance was not different, however, aortic atherosclerosis was increased in Apoe^-/-:Gipr^-/- mice and trended higher in Gipr^-/- mice with atherosclerosis induced by AAV-PCSK9. Levels of mRNA transcripts for genes contributing to inflammation were increased in the aortae of Apoe^-/-:Gipr^-/- mice and expression of a subset of inflammation-related hepatic genes were increased in Gipr^-/- mice treated with AAV-PCSK9. BMT experiments did not reveal marked atherosclerosis, failing to implicate bone marrow derived GIPR + cells in the control of atherosclerosis or aortic inflammation.

CONCLUSIONS

Loss of the Gipr in mice results in increased aortic atherosclerosis and enhanced inflammation in aorta and liver, despite reduced weight gain and preserved glucose homeostasis. These findings extend concepts of GIPR in the suppression of inflammation-related pathophysiology beyond its classical incretin role in the control of metabolism.

Anti-Inflammatory Effects of GLP-1 Receptor Activation in the Brain in Neurodegenerative Diseases

The glucagon-like peptide-1 (GLP-1) is a pleiotropic hormone well known for its incretin effect in the glucose-dependent stimulation of insulin secretion. However, GLP-1 is also produced in the brain and displays a critical role in neuroprotection and inflammation by activating the GLP-1 receptor signaling pathways. Several studies in vivo and in vitro using preclinical models of neurodegenerative diseases show that GLP-1R activation has anti-inflammatory properties. This review explores the molecular mechanistic action of GLP-1 RAS in relation to inflammation in the brain. These findings update our knowledge of the potential benefits of GLP-1RAS actions in reducing the inflammatory response. These molecules emerge as a potential therapeutic tool in treating neurodegenerative diseases and neuroinflammatory pathologies.

Cardiovascular effects of incretins - focus on GLP-1 receptor agonists

GLP-1 receptor agonists (GLP-1 RAs) have been used to treat patients with type 2 diabetes since 2005 and have become popular because of the efficacy and durability in relation to glycaemic control in combination with weight loss in most patients. Today in 2022, seven GLP-1 RAs, including oral semaglutide are available for treatment of type 2 diabetes. Since the efficacy in relation to reduction of HbA1c and body weight as well as tolerability and dosing frequency vary between agents, the GLP-1 RAs cannot be considered equal. The short acting lixisenatide showed no cardiovascular benefits, while once daily liraglutide and the weekly agonists, subcutaneous semaglutide, dulaglutide, and efpeglenatide, all lowered the incidence of cardiovascular events. Liraglutide, oral semaglutide and exenatide once weekly also reduced mortality. GLP-1 RAs reduce the progression of diabetic kidney disease. In the 2019 consensus report from EASD/ADA, GLP-1 RAs with demonstrated cardio-renal benefits (liraglutide, semaglutide and dulaglutide) are recommended after metformin to patients with established cardiovascular diseases or multiple cardiovascular risk factors. European Society of Cardiology (ESC) suggests starting with a SGLT-2 inhibitor or a GLP-1 RA in drug naïve patients with type 2 diabetes and atherosclerotic CVD or high CV Risk. However, the results from cardiovascular outcome trials (CVOT) are very heterogeneous suggesting that some GLP-1RA are more suitable to prevent CVD than others. The CVOTs provide a basis upon which individual treatment decisions for patients with T2D and CVD can be made.

Semaglutide reduces vascular inflammation investigated by PET in a rabbit model of advanced atherosclerosis

BACKGROUND AND AIMS

The objective of this study was to investigate the effects of semaglutide, a long acting glucagon-like peptide-1 receptor agonist, on atherosclerotic inflammation and calcification using a multimodality positron emission tomography and computed tomography (PET/CT) approach.

METHODS

Atherosclerotic New Zealand White rabbits were randomized to an intervention- (n = 12) or placebo group (n = 11) receiving either semaglutide or saline-placebo. PET/CT imaging was done before and after 16-weeks of intervention. Three different radiotracers were used: [64Cu]Cu-DOTATATE for imaging of activated macrophages, [18F]FDG imaging cellular metabolism and [18F]NaF PET visualizing micro-calcifications. Tracer uptake was quantified by maximum standardized uptake value (SUVmax) and target-to-background-ratio (TBRmax). Animals were euthanized for autoradiographic imaging and histological analyses.

RESULTS

A reduction in activated macrophage tracer-uptake was observed in the semaglutide group (SUVmax: p = 0.001 and TBRmax: p = 0.029). When imaging cellular metabolism, an attenuation of SUVmax and TBRmax was observed in the semaglutide group (p = 0.034 and p = 0.044). We found no difference in uptake of the micro-calcification tracer between the two groups (SUVmax: p = 0.62 and TBRmax: p = 0.36). Values of macrophage density in the vessel wall were significantly correlated with SUVmax values of the activated macrophage (r = 0.54, p = 0.0086) and cellular metabolism tracers (r = 0.51, p = 0.013).

CONCLUSIONS

Semaglutide decreased vascular uptake of tracers imaging activated macrophages and cellular metabolism but not micro-calcifications compared to a saline placebo. This supports the hypothesis that semaglutide reduces atherosclerotic inflammation by means of decreased activated macrophage activity.

Effects of linagliptin on morphine dependence in larval zebrafish (Danio rerio)

Drug addiction is a chronic, recurrent disease of the central nervous system that leads to the development of comorbidities and premature death. Despite extensive scientific research concerning addiction, no effective method of addiction pharmacotherapy has been known so far. Glucagon-like peptide 1 has been suggested to play a role in the rewarding effect of addictive drugs. Linagliptin is a selective dipeptidyl peptidase-4 inhibitor that suppresses the rapid degradation of endogenous glucagon-like peptide-1. In clinical practice, it is used as an antidiabetic drug, but recent studies have confirmed its role in the activity of the central nervous system. This pilot study was conducted to ascertain whether linagliptin might influence morphine dependence – a locomotor activity test was carried out to assess the intensity of morphine withdrawal symptom. The obtained results clearly confirmed that linagliptin (0.01 and 0.1 mM) reduced the locomotor activity in morphine-dependent larval zebrafish. The undertaken experiments clearly indicates that linagliptin is involved in the addictive effects of morphine, thus, further studies on higher organisms should be carried out.

The risk of incident atrial fibrillation in patients with type 2 diabetes treated with sodium glucose cotransporter-2 inhibitors, glucagon-like peptide-1 receptor agonists, and dipeptidyl peptidase-4 inhibitors: a nationwide cohort study

Background

Although a few meta-analyses were conducted to compare the risk of incident atrial fibrillation (AF) between sodium-glucose cotransporter-2 inhibitor (SGLT2i), glucagon-like peptide-1 receptor agonists (GLP-1RA), and other anti-hyperglycemic agents using indirect or direct comparison, the above analyses showed conflicting results with each other. We aimed to evaluate the risk of new-onset AF associated with the use of SGLT2i, GLP-1RA, and dipeptidyl peptidase-4 inhibitor (DPP4i) among a large longitudinal cohort of diabetic patients.

Methods

In this nationwide retrospective cohort study based on the Taiwan National Health Insurance Research Database, a total of 344,893, 44,370, and 393,100 consecutive patients with type 2 diabetes without preexisting AF receiving GLP-1RA, SGLT2i, and DPP4i, respectively, were enrolled from May 1, 2016, to December 31, 2019. We used 1:1 propensity score matching (PSM) to balance covariates across paired study groups. Patients were followed from the drug index date until the occurrence of AF, death, discontinuation of the index drug, or the end of the study period (December 31, 2020), whichever occurred first.

Results

After PSM, there were 245,442, 43,682, and 39,190 paired cohorts of SGLT2i-DPP4i, SGLT2i-GLP-1RA, and GLP-1RA-DPP4i, respectively. SGLT2i treatment was associated with lower risk of new-onset AF in participants with type 2 diabetes compared with either DPP4i [hazard ratio (HR):0.90; 95% confidential interval (CI) 0.84–0.96; P = 0.0028] or GLP-1RA [HR 0.74; 95% CI 0.63–0.88; P = 0.0007] treatment after PSM. There was no difference in the risk of incident AF between GLP-1RA and DPP4i users [HR 1.01; 95% CI 0.86–1.19; P = 0.8980]. The above findings persisted among several important subgroups. Dapagliflozin was specifically associated with a lower risk of new-onset AF compared with DPP4i (P interaction = 0.02).

Conclusions

Compared with DPP4i, SGLT2i but not GLP-1RA was associated with a lower risk of incident AF in patients with type 2 diabetes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01549-x.

Liraglutide stimulates the β-catenin signaling cascade in mouse epididymal fat tissue

Although canonical Wnt signaling pathway activation was shown to negatively regulate adipogenesis, recent investigations suggest that Wnt pathway effectors TCF7L2 and β-catenin (β-cat) in adipose tissues are also involved in energy homeostasis during adulthood. In assessing the metabolic beneficial effect of GLP-1-based diabetes drugs in high-fat diet (HFD)-challenged mice, we observed that liraglutide treatment affected the expression of a battery of adipose tissue-specific genes, including those that encode adiponectin and leptin, mainly in epididymal white adipose tissue (eWAT). Fourteen-week HFD challenge repressed TCF7L2 and β-cat S675 phosphorylation in eWAT, while such repression was reversed by liraglutide treatment (150 µg/kg body weight daily) during weeks 10-14. In Glp1r-/-mice, liraglutide failed in stimulating TCF7L2 or β-cat in eWAT. We detected Glp1r expression in mouse eWAT and its level is enriched in its stromal vascular fraction (SVF). Mouse eWAT-SVF showed reduced expression of Tcf7l2 and its Tcf7l2 level could not be stimulated by liraglutide treatment; while following adipogenic differentiation, rat eWAT-SVF showed elevated Tcf7l2 expression. Direct in vitro liraglutide treatment in eWAT-SVF stimulated CREB S133, β-cat S675 phosphorylation, and cellular cAMP level. Thus, cAMP/β-cat signaling cascade can be stimulated by liraglutide in eWAT via GLP-1R expressed in eWAT-SVF.

Discrepancy between the Actions of Glucagon-like Peptide-1 Receptor Ligands in the Protection of the Heart against Ischemia Reperfusion Injury

Tirzepatide is a dual glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist and a promising therapy for type 2 diabetes mellitus (T2DM). GLP-1 is an incretin hormone with therapeutic potential beyond type 2 diabetes mellitus. However, GLP-1 is rapidly degraded by dipeptdyl peptidase-IV (DPP-IV) to GLP-1 (9-36). Exendin-4 (Ex-4) is a DPP-IV-resistant GLP-1 receptor agonist which, when truncated to Ex-4 (9-39), acts as a GLP-1 receptor antagonist. In the present study, hearts isolated from Wistar rats (n = 8 per group) were perfused with a modified Langendorff preparation. Left ventricular (LV) contractility and cardiovascular hemodynamics were evaluated by a data acquisition program and infarct size was evaluated by 2,3,5-Triphenyl-2H-tetrazolium chloride (TTC) staining and cardiac enzyme levels. Hearts were subjected to 30 min regional ischemia, produced by ligation of the left anterior descending (LAD) coronary artery followed by 30 min reperfusion. Hearts were treated during reperfusion with either the non-lipidated precursor of tirzepatide (NLT), GLP-1, GLP-1 (9-36), or Ex-4 in the presence or absence of Ex-4 (9-39). Infusion of GLP-1 (9-36) or Ex-4 protected the heart against I/R injury (p > 0.01) by normalizing cardiac hemodynamic and enzyme levels. Neither GLP-1, NLT, nor Ex-4 (9-39) showed any protection. Interestingly, Ex-4 (9-39) blocked Ex-4-mediated protection but not that of GLP-1 (9-36). These data suggest that Ex-4-mediated protection is GLP-1-receptor-dependent but GLP-1 (9-36)-mediated protection is not.

Targeting appetite and satiety in diabetes and obesity, via G protein-coupled receptors

Type 2 diabetes and obesity have reached pandemic proportions throughout the world, so much so that the World Health Organisation coined the term "Globesity" to help encapsulate the magnitude of the problem. G protein-coupled receptors (GPCRs) are highly tractable drug targets due to their wide involvement in all aspects of physiology and pathophysiology, indeed, GPCRs are the targets of approximately 30% of the currently approved drugs. GPCRs are also broadly involved in key physiologies that underlie type 2 diabetes and obesity including feeding reward, appetite and satiety, regulation of blood glucose levels, energy homeostasis and adipose function. Despite this, only two GPCRs are the target of approved pharmaceuticals for treatment of type 2 diabetes and obesity. In this review we discuss the role of these, and select other candidate GPCRs, involved in various facets of type 2 diabetic or obese pathophysiology, how they might be targeted and the potential reasons why pharmaceuticals against these targets have not progressed to clinical use. Finally, we provide a perspective on the current development pipeline of anti-obesity drugs that target GPCRs.

The anti-inflammatory feature of glucagon-like peptide-1 and its based diabetes drugs—Therapeutic potential exploration in lung injury

Since 2005, GLP-1 receptor (GLP-1R) agonists (GLP-1RAs) have been developed as therapeutic agents for type 2 diabetes (T2D). GLP-1R is not only expressed in pancreatic islets but also other organs, especially the lung. However, controversy on extra-pancreatic GLP-1R expression still needs to be further resolved, utilizing different tools including the use of more reliable GLP-1R antibodies in immune-staining and co-immune-staining. Extra-pancreatic expression of GLP-1R has triggered extensive investigations on extra-pancreatic functions of GLP-1RAs, aiming to repurpose them into therapeutic agents for other disorders. Extensive studies have demonstrated promising anti-inflammatory features of GLP-1RAs. Whether those features are directly mediated by GLP-1R expressed in immune cells also remains controversial. Following a brief review on GLP-1 as an incretin hormone and the development of GLP-1RAs as therapeutic agents for T2D, we have summarized our current understanding of the anti-inflammatory features of GLP-1RAs and commented on the controversy on extra-pancreatic GLP-1R expression. The main part of this review is a literature discussion on GLP-1RA utilization in animal models with chronic airway diseases and acute lung injuries, including studies on the combined use of mesenchymal stem cell (MSC) based therapy. This is followed by a brief summary.

Pharmacokinetic and pharmacodynamic studies of supaglutide in rats and monkeys

We demonstrated recently that supaglutide, a novel GLP-1 mimetic generated by recombinant fusion protein techniques, exerted hypoglycemic effects in type 2 diabetes db/db mice and spontaneous diabetic monkeys. In this study, we investigated the pharmacokinetics and pharmacodynamics of supaglutide by single subcutaneous and intravenous injection(s) in rats and rhesus monkeys, as well as fourconsecutive subcutaneous injections in monkeys.We found the half-life (t1/2) of supaglutide was 39.7 hours and 35.8 hours at dosing 0.1 mg/kg upon subcutaneous or intravenous administration respectively, in rhesus monkeys. The plasma supaglutide peaked at 8-10 hours, while the plasma drug exposure levels increased with the increase of dose, showing approximately a linear pharmacokinetic characteristic. The elimination kinetics (Ke) were found to be similar between subcutaneous (∼0.025 in rats and ∼0.018 in monkeys) and intravenous administration (0.021 in rats and 0.020 in monkeys), whereas the bioavailability was found to be 31.1% in rats and 63.9% in monkeys. In monkeys, a single dose injection of supaglutide markedly decreased the random blood glucose levels that reaching the maxima effects in 14-16 hours, gradually recovered and returned to the baseline level approximately after 72 hours. 125I-supaglutide was found mainly distributed in the serum and organs rich in blood supply. Urine was found to be the primary excretion route of supaglutide, following by feces, but mostly not in bile.Our results show that supaglutide possess linear pharmacokinetic characteristics associated with prolonged hypoglycemic effects inanimals,suggestinga potential weekly dosing therapeutic reagent for the treatment of type 2 diabetes and metabolic diseases.