Secretion of the incretin hormones glucagon-like peptide-1 and gastric inhibitory polypeptide correlates with insulin secretion in normal man throughout the day

Dipeptidyl-peptidase 4 (DPP4) mediates fatty acid uptake inhibition by glucose via TAS1R3 and GLUT-2 in Caco-2 enterocytes

Both high glucose intake with a high-fat meal and inhibition of dipeptidyl peptidase-4 (DPP4) have been associated with plasma lipid-lowering effects, but mechanistic understanding linking glucose and fat absorption is lacking. We here hypothesized that glucose ameliorates intestinal fatty acid uptake via a pathway involving DPP4. A concentration of 50 mM glucose reduced mean DPP4 activity in differentiated Caco-2 enterocytes by 42.5 % and fatty acid uptake by 66.0 % via nutrient sensing by the sweet taste receptor subunit TAS1R3 and glucose transporter GLUT-2. No effect of the DPP4 substrates GLP-1 and GIP or of the cellular energy status on the reduced uptake of fatty acids was seen, but a direct interaction between DPP4 and fatty acid transporters is suggested. Conclusively we identified DPP4 as a regulator of fatty acid absorption in Caco-2 enterocytes that mediates the inhibition of intestinal fatty acid uptake by glucose via an interplay of GLUT-2 and TAS1R3.

A mathematical model of obesity-induced type 2 diabetes and efficacy of anti-diabetic weight reducing drug

The dominant paradigm for modeling the obesity-induced T2DM (type 2 diabetes mellitus) today focuses on glucose and insulin regulatory systems, diabetes pathways, and diagnostic test evaluations. The problem with this approach is that it is not possible to explicitly account for the glucose transport mechanism from the blood to the liver, where the glucose is stored, and from the liver to the blood. This makes it inaccurate, if not incorrect, to properly model the concentration of glucose in the blood in comparison to actual glycated hemoglobin (A1C) test results. In this paper, we develop a mathematical model of glucose dynamics by a system of ODEs. The model includes the mechanism of glucose transport from the blood to the liver, and from the liver to the blood, and explains how obesity is likely to lead to T2DM. We use the model to evaluate the efficacy of an anti-T2DM drug that also reduces weight.

Secretion of glucagon, GLP-1 and GIP may be affected by circadian rhythm in healthy males

BACKGROUND

Glucagon is secreted from pancreatic alpha cells in response to low blood glucose and increases hepatic glucose production. Furthermore, glucagon enhances hepatic protein and lipid metabolism during a mixed meal. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are secreted from gut endocrine cells during meals and control glucose homeostasis by potentiating insulin secretion and inhibiting food intake. Both glucose homeostasis and food intake have been reported to be affected by circadian rhythms and vice versa. In this study, we investigated whether the secretion of glucagon, GLP-1 and GIP was affected by circadian rhythms.

METHODS

A total of 24 healthy men with regular sleep schedules were examined for 24 h at the hospital ward with 15 h of wakefulness and 9 h of sleep. Food intake was standardized, and blood samples were obtained every third hour. Plasma concentrations of glucagon, GLP-1 and GIP were measured, and data were analyzed by rhythmometric statistical methods. Available data on plasma glucose and plasma C-peptide were also included.

RESULTS

Plasma concentrations of glucagon, GLP-1, GIP, C-peptide and glucose fluctuated with a diurnal 24-h rhythm, with the highest levels during the day and the lowest levels during the night: glucagon (p < 0.0001, peak time 18:26 h), GLP-1 (p < 0.0001, peak time 17:28 h), GIP (p < 0.0001, peak time 18:01 h), C-peptide (p < 0.0001, peak time 17.59 h), and glucose (p < 0.0001, peak time 23:26 h). As expected, we found significant correlations between plasma concentrations of C-peptide and GLP-1 and GIP but did not find correlations between glucose concentrations and concentrations of glucagon, GLP-1 and GIP.

CONCLUSIONS

Our results demonstrate that under meal conditions that are similar to that of many free-living individuals, plasma concentrations of glucagon, GLP-1 and GIP were observed to be higher during daytime and evening than overnight. These findings underpin disturbed circadian rhythm as a potential risk factor for diabetes and obesity.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT06166368. Registered 12 December 2023.

Dietary impact on fasting and stimulated GLP-1 secretion in different metabolic conditions - a narrative review

Glucagon-like peptide 1 (GLP-1), a gastrointestinal peptide and central mediator of glucose metabolism, is secreted by L cells in the intestine in response to food intake. Postprandial secretion of GLP-1 is triggered by nutrient-sensing via transporters and G-protein-coupled receptors (GPCRs). GLP-1 secretion may be lower in adults with obesity/overweight (OW) or type 2 diabetes mellitus (T2DM) than in those with normal glucose tolerance (NGT), but these findings are inconsistent. Because of the actions of GLP-1 on stimulating insulin secretion and promoting weight loss, GLP-1 and its analogs are used in pharmacologic preparations for the treatment of T2DM. However, physiologically stimulated GLP-1 secretion through the diet might be a preventive or synergistic method for improving glucose metabolism in individuals who are OW, or have impaired glucose tolerance (IGT) or T2DM. This narrative review focuses on fasting and postprandial GLP-1 secretion in individuals with different metabolic conditions and degrees of glucose intolerance. Further, the influence of relevant diet-related factors (e.g., specific diets, meal composition, and size, phytochemical content, and gut microbiome) that could affect fasting and postprandial GLP-1 secretion are discussed. Some studies showed diminished glucose- or meal-stimulated GLP-1 response in participants with T2DM, IGT, or OW compared with those with NGT, whereas other studies have reported an elevated or unchanged GLP-1 response in T2DM or IGT. Meal composition, especially the relationship between macronutrients and interventions targeting the microbiome can impact postprandial GLP-1 secretion, although it is not clear which macronutrients are strong stimulants of GLP-1. Moreover, glucose tolerance, antidiabetic treatment, grade of overweight/obesity, and sex were important factors influencing GLP-1 secretion. The results presented in this review highlight the potential of nutritional and physiologic stimulation of GLP-1 secretion. Further research on fasting and postprandial GLP-1 concentrations and the resulting metabolic consequences under different metabolic conditions is needed.

Advances in the Management of Diabetes and Overweight using Incretin-based Pharmacotherapies

Throughout the previous three decades, the secretion of glucagon-like peptide-1 hormone has attracted much attention to attain possible therapy goals for the treatment of both hypoglycaemic along type II diabetes militates and overweight. The pharmaceutical generation of peptides similar to hypoglycaemia-based medicines is exemplified by agonists of the GLP- 1R (Glucagon-like peptide-1 receptors). Pharmacokinetic profiles are continuously being improved, beginning with the native hormone with a two- to three-minute quarter and progressing through growth every day with once-drug combinations. Due to contradictory data that indicate stimulation or inhibition of the Glucagon-like peptide receptor, the Glucose-dependent insulin tropic peptide receptor offers favorable effects on systemic metabolism. The recent Glp-1R (Glucagon-like peptide-1 receptor-) targeting monomolecular drugs has demonstrated therapeutic effectiveness and has stoked interest in Glucose-dependent insulin tropic polypeptide antagonism as a treatment for overweight and diabetes mellitus. These drugs have been shown to dramatically improve carbohydrates with body weight management in sick people who have obesity and type II diabetes mellitus. In this study, recent breakthroughs in compelling therapeutic interventions are discussed, and the biology and pharmacology of the glucose-like peptide are reviewed.

Endogenous glucagon-like peptide (GLP)-1 as alternative for GLP-1 receptor agonists: Could this work and how?

In recent years, we have witnessed the many beneficial effects of glucagon-like peptide (GLP)-1 receptor agonists, including the reduction in cardiovascular risk in patients with type 2 diabetes, and the reduction of body weight in those with obesity. Increasing evidence suggests that these agents differ considerably from endogenous GLP-1 when it comes to their routes of action, although their clinical effects appear to be the same. Given the limitations of the GLP-1 receptor agonists, could it be useful to develop agents which stimulate GLP-1 release? Here we will discuss the differences and similarities between GLP-1 receptor agonists and endogenous GLP-1, and will detail how endogenous GLP-1-when stimulated appropriately-could have clinically relevant effects.

Pharmacological modulation of adaptive thermogenesis: new clues for obesity management?

BACKGROUND

Adaptive thermogenesis represents the main mechanism through which the body generates heat in response to external stimuli, a phenomenon that includes shivering and non-shivering thermogenesis. The non-shivering thermogenesis is mainly exploited by adipose tissue characterized by a brown aspect, which specializes in energy dissipation. A decreased amount of brown adipose tissue has been observed in ageing and chronic illnesses such as obesity, a worldwide health problem characterized by dysfunctional adipose tissue expansion and associated cardiometabolic complications. In the last decades, the discovery of a trans-differentiation mechanism ("browning") within white adipose tissue depots, leading to the generation of brown-like cells, allowed to explore new natural and synthetic compounds able to favour this process and thus enhance thermogenesis with the aim of counteracting obesity. Based on recent findings, brown adipose tissue-activating agents could represent another option in addition to appetite inhibitors and inhibitors of nutrient absorption for obesity treatment.

PURPOSE

This review investigates the main molecules involved in the physiological (e.g. incretin hormones) and pharmacological (e.g. β3-adrenergic receptors agonists, thyroid receptor agonists, farnesoid X receptor agonists, glucagon-like peptide-1, and glucagon receptor agonists) modulation of adaptive thermogenesis and the signalling mechanisms involved.

Whey Protein Premeal Lowers Postprandial Glucose Concentrations in Adults Compared with Water-The Effect of Timing, Dose, and Metabolic Status: a Systematic Review and Meta-analysis

BACKGROUND

Serving whey protein before a meal in order to lower postprandial blood glucose concentrations is known as a premeal. The underlying mechanisms are only partly understood but may involve stimulation of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and insulin secretion together with a slower gastric emptying rate.

OBJECTIVES

The objective of this systematic review and meta-analysis was to review all randomized clinical trials investigating premeals with whey protein in comparison with a nonactive comparator (control) that evaluated plasma glucose, GLP-1, GIP, insulin, and/or gastric emptying rate. Secondary aims included subgroup analyses on the timing and dose of the premeal together with the metabolic state of the participants [lean, obese, and type 2 diabetes mellitus (T2DM)].

METHODS

We searched EMBASE, CENTRAL, PUBMED, and clinicaltrials.gov and found 16 randomized crossover trials with a total of 244 individuals. The last search was performed on 9 August, 2022.

RESULTS

Whey protein premeals lowered peak glucose concentration by -1.4 mmol/L [-1.9 mmol/L; -0.9 mmol/L], and the area under the curve for glucose was -0.9 standard deviation (SD) [-1.2 SD; -0.6 SD] compared with controls (high certainty). In association with these findings, whey protein premeals elevated GLP-1 (low certainty) and peak insulin (high certainty) concentrations and slowed gastric emptying rate (high certainty) compared with controls. Subgroup analyses showed a more pronounced and prolonged glucose-lowering effect in individuals with T2DM compared with participants without T2DM. The available evidence did not elucidate the role of GIP. The protein dose used varied between 4 and 55 g, and meta-regression analysis showed that the protein dose correlated with the glucose-lowering effects.

CONCLUSIONS

In conclusion, whey protein premeals lower postprandial blood glucose, reduce gastric emptying rate, and increase peak insulin. In addition, whey protein premeals may elevate plasma concentrations of GLP-1. Whey protein premeals may possess clinical potential, but the long-term effects await future clinical trials.

Glucagon-like Peptide-1 Receptor Agonists for the Treatment of Type 2 Diabetes in Youth

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have gained traction for the management of type 2 diabetes and obesity. Unlike several classes of antidiabetic medications that contribute to weight gain, GLP-1RAs not only reduce haemoglobin A1c, but also promote weight loss. While there is a large body of evidence supporting its safety and efficacy in adults, paediatric clinical trial data have only emerged in recent years. This review will discuss the limited treatment options for paediatric type 2 diabetes and the mechanism of action of GLP-1RAs as it pertains to physiological pathways relevant for type 2 diabetes, obesity and their related comorbidities. The outcomes of paediatric trials evaluating liraglutide, exenatide, semaglutide and dulaglutide in paediatric type 2 diabetes and obesity will be closely examined, including differences compared with adult studies. Finally, potential barriers and strategies to expanding GLP-1RA access in adolescents will be discussed. Future studies are needed to determine if the cardio-and renal-protective benefits of GLP-1RAs apply to youth-onset type 2 diabetes.

Protective effects of Korean Red Ginseng against toxicity of endocrine-disrupting chemicals

Several chemicals have been developed owing to the progression of industrialization, among which endocrine-disrupting chemicals (EDCs; essential for plastic production) are used as plasticizers and flame retardants. Plastics have become an essential element in modern life because they provide convenience, thus increasing EDCs exposure to humans. EDCs cause adverse effects such as deterioration of reproductive function, cancer, and neurological abnormalities by disrupting the endocrine system and hence are classified as "dangerous substances." Additionally, they are toxic to various organs but continue to be used. Therefore, it is necessary to review the contamination status of EDCs, select potentially hazardous substances for management, and monitor the safety standards. In addition, it is necessary to discover substances that can protect against EDC toxicity and conduct active research on the protective effects of these substances. According to recent research, Korean Red Ginseng (KRG) exhibits protective effects against several toxicities caused by EDCs to humans. In this review, the effects of EDCs on the human body and the role of KRG in protection against EDC toxicity are discussed.

The postprandial actions of GLP-1 receptor agonists: The missing link for cardiovascular and kidney protection in type 2 diabetes

Recent clinical trials in people with type 2 diabetes have demonstrated beneficial actions on heart and kidney outcomes following treatment with GLP-1RAs. In part, these actions are consistent with improved glucose control and significant weight loss. But GLP-1RAs may also have additive benefits by improving postprandial dysmetabolism. In diabetes, dysregulated postprandial nutrient excursions trigger inflammation, oxidative stress, endothelial dysfunction, thrombogenicity, and endotoxemia; alter hormone levels; and modulate cardiac output and regional blood and lymphatic flow. In this perspective, we explore the actions of GLP-1RAs on the postprandial state and their potential role in end-organ benefits observed in recent trials.

A glucagon-like peptide-1 receptor antagonist reduces the insulin response to a glycemic meal in ponies

High plasma concentrations of insulin can cause acute laminitis. Ponies and horses with insulin dysregulation (ID) exhibit marked hyperinsulinemia in response to dietary hydrolyzable carbohydrates. Glucagon-like peptide-1 (GLP-1), an incretin hormone released from the gastrointestinal tract, enhances insulin release, and is increased postprandially in ponies with ID. The aim of this study was to determine whether blocking the GLP-1 receptor reduces the insulin response to a high glycemic meal. Five adult ponies were adapted to a cereal meal and then given two feed challenges 24 h apart of a meal containing 3 g/kg BW micronized maize. Using a randomized cross-over design all ponies received both treatments, where one of the feeds was preceded by the IV administration of a GLP-1 receptor blocking peptide, Exendin-3 (9-39) amide (80 µg/kg), and the other feed by a sham treatment of peptide diluent only. Blood samples were taken before feeding and peptide administration, and then at 30-min intervals via a jugular catheter for 6 h for the measurement of insulin, glucose, and active GLP-1. The peptide and meal challenge caused no adverse effects, and the change in plasma glucose in response to the meal was not affected (P = 0.36) by treatment: peak concentration 9.24 ± 1.22 and 9.14 ± 1.08 mmol/L without and with the antagonist, respectively. Similarly, there was no effect (P = 0.35) on plasma active GLP-1 concentrations: peak concentration 14.3 ± 1.36 pM and 13.7 ± 1.97 pM without and with the antagonist, respectively. However, the antagonist caused a significant decrease in the area under the curve for insulin (P = 0.04), and weak evidence (P = 0.06) of a reduction in peak insulin concentration (456 ± 147 μIU/mL and 370 ± 146 μIU/mL without and with the antagonist, respectively). The lower overall insulin response to the maize meal after treatment with the antagonist demonstrates that blocking the GLP-1 receptor partially reduced insulin production in response to a high starch, high glycemic index, diet. Using a different methodological approach to published studies, this study also confirmed that GLP-1 does contribute to the excessive insulin production in ponies with ID.

Glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 secretion in humans: Characteristics and regulation

AIMS/INTRODUCTION

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are important incretin hormones. They are released from the gut after meal ingestion and potentiate glucose-stimulated insulin secretion. Their release after meal ingestion and oral glucose are well established and have been characterized previously. During recent years, knowledge of other regulatory aspects that potentially may affect GIP and GLP-1 secretion after meal ingestion have also begun to emerge. Here, the results of human studies on these novel aspects of meal- and nutrient-stimulated incretin hormone secretion are reviewed.

MATERIALS AND METHODS

The human literature was revisited by identifying articles in PubMed using key words GIP, GLP-1, secretion, meal, and nutrients.

RESULTS

The results show that all macronutrients individually stimulate GIP and GLP-1 secretion. However, there was no synergistic action when given in combination. A pre-load 30 min before a meal augments the GIP and GLP-1 response. GIP and GLP-1 secretion have a diurnal variation with a higher response to an identical meal in the morning than in the afternoon. There is no difference in GIP and GLP-1 secretion whether a meal is ingested slowly or rapidly. GIP and GLP-1 secretion after dinner are the same whether or not breakfast and lunch have been ingested. The temperature of the food may be of importance for the incretin hormone response.

CONCLUSIONS

These novel findings have increased our knowledge on the regulation of the complexity of the incretin system and are also important knowledge when designing future studies.

The effects of glucagon like peptide-1 (GLP-1) on cardiac remodeling: exploring the role of medication and physiological modulation after metabolic surgery

Obesity and associated comorbidities reach epidemic proportions nowadays. Several treatment strategies exist, but bariatric surgery has the only longstanding effects. Since a few years, there is increasing interest in the effects of gastro-intestinal hormones, in particular Glucagon-Like Peptide-1 (GLP-1) on the remission of Type 2 Diabetes (T2DM) and its effects on cardiac cardiovascular morbidity, cardiac remodeling, and mortality. In the past years several high quality multicenter randomized controlled trials were developed to assess the effects of GLP-1 receptor agonist therapy on cardiovascular morbidity and mortality. Most of the trials were designed and powered as non-inferiority trials to demonstrate cardiovascular safety. Most of these trials show a reduction in cardiovascular morbidity in patients with T2DM. Some follow-up studies indicate potential beneficial effects of GLP-1 receptor agonists on cardiovascular function in patients with heart failure, however the results are contradictory, and we need long-term studies to make firm conclusions about the pleiotropic properties of incretin-based therapies. However, it seems that GLP-1 receptor agonists have different effects than the increased GLP-1 production after bariatric surgery on cardiovascular remodeling. One of the hypotheses is that the blood concentrations of GLP-1 receptor agonists are three times higher compared to GLP-1 increase after bariatric and metabolic surgery. The purpose of this narrative review is to summarize the effects of GLP-1 on cardiovascular morbidity, mortality and remodeling due to medication but also due to bariatric and metabolic surgery. The second objective is to explain the possible differences in effects of GLP-1 agonists and bariatric and metabolic surgery.

GIP secretion after oral macronutrient ingestion-The human literature revisited and a systematic study in model experiments in mice

OBJECTIVES

The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) is secreted after meal ingestion. This study explored the relative influence of classes of macronutrients on GIP secretion.

METHODS

The human literature was revisited by identifying articles from Pubmed using key words GIP, macronutrients, carbohydrates, fat, protein, healthy subjects. In model experiments in anesthetized mice, glucose (25-125 mg), protein (15-120 mg), fat emulsion (6-100 mg) or saline was given orally with determination of GIP levels.

RESULTS

The literature survey revealed 15 studies in which glucose, protein or fat was administered to healthy subjects. All three classes of macronutrients stimulated GIP secretion with a 30-45 min peak after glucose and protein and a more prolonged release after fat. Limitation in study designs precludes firm conclusions on relative potency of the macronutrients. In mice, glucose was more potent to stimulate GIP secretion than fat and protein with no significant difference between protein and fat. By co-administration of the macronutrients at moderate caloric combinations, a synergistic stimulation of GIP secretion was observed. In contrast, when raising the glucose challenge together with protein and fat, no synergy but an additive effect was evident.

CONCLUSIONS

Glucose, protein and fat all stimulate GIP secretion in humans and mice. In mice, glucose is more potent than fat and protein and there is also a synergy between the macronutrients on GIP secretion at moderate caloric doses. Further studies are warranted in humans to explore the relative potency of macronutrients.

The Sensory Mechanisms of Nutrient-Induced GLP-1 Secretion

The enteroendocrine system of the gut regulates energy homeostasis through the release of hormones. Of the gut-derived hormones, GLP-1 is particularly interesting, as analogs of the hormone have proven to be highly effective for the treatment of type 2 diabetes mellitus and obesity. Observations on increased levels of GLP-1 following gastric bypass surgery have enhanced the interest in endogenous hormone secretion and highlighted the potential of endogenous secretion in therapy. The macronutrients and their digestive products stimulate the secretion of GLP-1 through various mechanisms that we have only begun to understand. From findings obtained from different experimental models, we now have strong indications for a role for both Sodium-Glucose Transporter 1 (SGLT1) and the K⁺_ATP channel in carbohydrate-induced GLP-1 secretion. For fat, the free fatty acid receptor FFA1 and the G-protein-coupled receptor GPR119 have been linked to GLP-1 secretion. For proteins, Peptide Transporter 1 (Pept1) and the Calcium-Sensing Receptor (CaSR) are thought to mediate the secretion. However, attempts at clinical application of these mechanisms have been unsuccessful, and more work is needed before we fully understand the mechanisms of nutrient-induced GLP-1 secretion.

Arterial responses to infusion of glucagon-like peptide-1 in humans: A randomized trial study

Glucagon-like-peptide-1 (GLP-1) is an incretin hormone implicated in several metabolic and neurological disorders. GLP-1 induces vasodilation and increases blood flow in the peripheral circulation. Whether GLP-1 alters cerebral hemodynamics in humans is yet to be elucidated. In a crossover, double-blind, placebo-controlled, and randomized design, 21 healthy volunteers were assigned to receive intravenous GLP-1 infusion (2.5 pmol/kg/min) or placebo over 20 min on two different days separated by at least one week. We used a noninvasive, well-validated transcranial doppler (TCD) and ultrasound dermascan to reveal the effect of GLP-1 on intra- and extracerebral arteries. The mean blood flow velocity in the middle cerebral artery (V_MCA), the diameter of the superficial temporal artery (STA) and radial artery (RA), and facial skin blood flow were measured. In addition, we documented headache and its associated symptoms during and after infusion. Twenty participants were included in the final analysis. We found no difference in the V_MCA (P = 0.227), diameter of the STA (P = 0.096) and the RA (P = 0.221) and facial blood flow (P = 0.814) after GLP-1 compared to placebo. There were no differences in HR, SAT, EtCO₂, or RF (P > 0.05) on the GLP-1 day compared to the placebo day. We found no differences in the incidence of headache after GLP-1 (n = 10) compared to placebo (n = 7) (P = 0.250). GLP-1 infusion did not affect cerebral hemodynamics and induce headache in humans. Further preclinical studies with validated methods are required to determine if intra - and extracerebral vasculature express GLP-1Rs in humans.

GLP-1 receptor agonists in diabetic kidney disease: current evidence and future directions

With the emergence of various classes of blood glucose-lowering agents, choosing the appropriate drug for each patient is emphasized in diabetes management. Among incretin-based drugs, glucagon-like peptide 1 (GLP-1) receptor agonists are a promising therapeutic option for patients with diabetic kidney disease (DKD). Several cardiovascular outcome trials have demonstrated that GLP-1 receptor agonists have beneficial effects on cardiorenal outcomes beyond their blood glucose-lowering effects in patients with type 2 diabetes mellitus (T2DM). The renal protective effects of GLP-1 receptor agonists likely result from their direct actions on the kidney, in addition to their indirect actions that improve conventional risk factors for DKD, such as reducing blood glucose levels, blood pressure, and body weight. Inhibition of oxidative stress and inflammation and induction of natriuresis are major renoprotective mechanisms of GLP-1 analogues. Early evidence from the development of dual and triple combination agents suggests that GLP-1 receptor agonists will probably become popular treatment options for patients with T2DM.

Recent Advances in Incretin-Based Pharmacotherapies for the Treatment of Obesity and Diabetes

The incretin hormone glucagon-like peptide-1 (GLP-1) has received enormous attention during the past three decades as a therapeutic target for the treatment of obesity and type 2 diabetes. Continuous improvement of the pharmacokinetic profile of GLP-1R agonists, starting from native hormone with a half-life of ~2-3 min to the development of twice daily, daily and even once-weekly drugs highlight the pharmaceutical evolution of GLP-1-based medicines. In contrast to GLP-1, the incretin hormone glucose-dependent insulinotropic polypeptide (GIP) received little attention as a pharmacological target, because of conflicting observations that argue activation or inhibition of the GIP receptor (GIPR) provides beneficial effects on systemic metabolism. Interest in GIPR agonism for the treatment of obesity and diabetes was recently propelled by the clinical success of unimolecular dual-agonists targeting the receptors for GIP and GLP-1, with reported significantly improved body weight and glucose control in patients with obesity and type II diabetes. Here we review the biology and pharmacology of GLP-1 and GIP and discuss recent advances in incretin-based pharmacotherapies.

Colonic Lactulose Fermentation Has No Impact on Glucagon-like Peptide-1 and Peptide-YY Secretion in Healthy Young Men

CONTEXT

The colon houses most of humans' gut microbiota, which ferments indigestible carbohydrates. The products of fermentation have been proposed to influence the secretion of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) from the many endocrine cells in the colonic epithelium. However, little is known about the colonic contribution to fasting or postprandial plasma levels of L-cell products.

OBJECTIVE

To determine the impact of colonic lactulose fermentation on gut peptide secretion and to evaluate whether colonic endocrine secretion contributes to gut hormone concentrations measurable in the fasting state.

METHODS

Ten healthy young men were studied on 3 occasions after an overnight fast. On 2 study days, lactulose (20 g) was given orally and compared to water intake on a third study day. For 1 of the lactulose visits, participants underwent a full colonic evacuation. Over a 6-h study protocol, lactulose fermentation was assessed by measuring exhaled hydrogen, and gut peptide secretion, paracetamol, and short-chain fatty acid levels were measured in plasma.

RESULTS

Colonic evacuation markedly reduced hydrogen exhalation after lactulose intake (P = 0.013). Our analysis suggests that the colon does not account for the measurable amounts of GLP-1 and PYY present in the circulation during fasting and that fermentation and peptide secretion are not acutely related.

CONCLUSION

Whether colonic luminal contents affect colonic L-cell secretion sufficiently to influence circulating concentrations requires further investigation. Colonic evacuation markedly reduced lactulose fermentation, but hormone releases were unchanged in the present study.

Chrono-communication and cardiometabolic health: The intrinsic relationship and therapeutic nutritional promises

Circadian rhythm, an innate 24-h biological clock, regulates several mammalian physiological activities anticipating daily environmental variations and optimizing available energetic resources. The circadian machinery is a complex neuronal and endocrinological network primarily organized into a central clock, suprachiasmatic nucleus (SCN), and peripheral clocks. Several small molecules generate daily circadian fluctuations ensuring inter-organ communication and coordination between external stimuli, i.e., light, food, and exercise, and body metabolism. As an orchestra, this complex network can be out of tone. Circadian disruption is often associated with obesity development and, above all, with diabetes and cardiovascular disease onset. Moreover, accumulating data highlight a bidirectional relationship between circadian misalignment and cardiometabolic disease severity. Food intake abnormalities, especially timing and composition of meal, are crucial cause of circadian disruption, but evidence from preclinical and clinical studies has shown that food could represent a unique therapeutic approach to promote circadian resynchronization. In this review, we briefly summarize the structure of circadian system and discuss the role playing by different molecules [from leptin to ghrelin, incretins, fibroblast growth factor 21 (FGF-21), growth differentiation factor 15 (GDF15)] to guarantee circadian homeostasis. Based on the recent data, we discuss the innovative nutritional interventions aimed at circadian re-synchronization and, consequently, improvement of cardiometabolic health.

Recombinant human GLP-1 beinaglutide regulates lipid metabolism of adipose tissues in diet-induced obese mice

GLP-1 analogs are a class of glucose-lowering agents with multiple benefits in diabetes, but its role in adipose tissues remains to be elucidated. The aim of this study was to determine the action of recombinant human GLP-1 (rhGLP-1) Beinaglutide (BN) in the insulin sensitivity and lipid metabolism of adipose tissues. We have shown that, after BN injection, obese mice displayed lower body weight, fat mass, and plasma lipid levels. In addition, BN promoted the insulin sensitivity in the white adipose tissues. Furthermore, we have found that the BN treatment caused significant changes in content and composition of different lipid classes, including glycerolipids, glycerophospholipids, and sphingolipids, as well as expression of genes in lipid metabolic pathways in the adipose tissues. Taken together, our data demonstrate that BN could resist HFD-induced obesity by targeting the composition of major lipid classes and the expression of genes in lipid metabolism of adipose tissues.

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Recombinant human GLP-1 Beinaglutide (BN) reduces high-fat-diet-induced obesity

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BN increases insulin sensitivity of adipocytes in vivo and in vitro

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BN alters lipidomic and transcriptomic profiles in adipose tissues of obese mice

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BN promotes thermogenic gene expression in adipose tissues

Glucagon-Like Peptide-1 Is Associated With Systemic Inflammation in Pediatric Patients Treated With Hematopoietic Stem Cell Transplantation

Patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) are challenged with severe side effects, which are propagated by mucosal barrier disruption, and the related microbial translocation and systemic inflammation. Glucagon-like peptide-1 (GLP-1), a well-known incretin hormone, possesses anti-inflammatory properties and promotes regeneration of damaged intestinal epithelium in animal studies. We hypothesized that the immense inter-individual variation in the degree of mucosal damage and systemic inflammation, seen after HSCT is influenced by endogenous GLP-1 and could be related to acute post-transplant complications. In this prospective study we measured serial weekly fasting plasma GLP-1, along with C-reactive protein (CRP), and citrulline in 82 pediatric patients during allogeneic HSCT together with a fasting plasma GLP-1 in sex- and age-matched healthy controls. Overall, GLP-1 levels were increased in the patients during the course of HSCT compared with the controls, but tended to decrease post-transplant, most pronounced in patients receiving high-intensity conditioning regimen. The increase in CRP seen in the early post-transplant phase was significantly lower from day +8 to +13 in patients with GLP-1 above the upper quartile (>10 pmol/L) at day 0 (all P ≤ 0.03). Similar findings were seen for peak CRP levels after adjusting for type of conditioning (-47.0%; 95% CI, -8.1 - -69.4%, P = 0.02). Citrulline declined significantly following the transplantation illustrating a decrease in viable enterocytes, most evident in patients receiving high-intensity conditioning regimen. GLP-1 levels at day 0 associated with the recovery rate of citrulline from day 0 to +21 (34 percentage points (pp)/GLP-1 doubling; 95% CI, 10 - 58pp; P = 0. 008) and day 0 to day +90 (48 pp/GLP-1 doubling; 95% CI, 17 - 79pp; P = 0. 004), also after adjustment for type of conditioning. This translated into a reduced risk of acute graft-versus-host disease (aGvHD) in patients with highest day 0 GLP-1 levels (>10 pmol/L) (cause-specific HR: 0.3; 95% CI, 0.2 - 0.9, P = 0.02). In conclusion, this study strongly suggests that GLP-1 influences regeneration of injured epithelial barriers and ameliorates inflammatory responses in the early post-transplant phase.

Glucagon-like peptide-1 (GLP-1) signalling in the brain: From neural circuits and metabolism to therapeutics

Glucagon‐like‐peptide‐1 (GLP‐1) derived from gut enteroendocrine cells and a discrete population of neurons in the caudal medulla acts through humoral and neural pathways to regulate satiety, gastric motility and pancreatic endocrine function. These physiological attributes contribute to GLP‐1 having a potent therapeutic action in glycaemic regulation and chronic weight management. In this review, we provide an overview of the neural circuits targeted by endogenous versus exogenous GLP‐1 and related drugs. We also highlight candidate subpopulations of neurons and cellular mechanisms responsible for the acute and chronic effects of GLP‐1 and GLP‐1 receptor agonists on energy balance and glucose metabolism. Finally, we present potential future directions to translate these findings towards the development of effective therapies for treatment of metabolic disease.

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.

Reappraising the role of the vagus nerve in GLP-1-mediated regulation of eating

Here, we provide a focused review of the evidence for the roles of the vagus nerve in mediating the regulatory effects of peripherally and centrally produced GLP-1 on eating behaviour and energy balance. We particularly focus on recent studies which have used selective genetic, viral, and transcriptomic approaches to provide important insights into the anatomical and functional organisation of GLP-1-mediated gut-brain signalling pathways. A number of these studies have challenged canonical ideas of how GLP-1 acts in the periphery and the brain to regulate eating behaviour, with important implications for the development of pharmacological treatments for obesity.

The physiological basis of insulin therapy in people with diabetes mellitus

Insulin therapy has been in use now for 100 years, but only recently insulin replacement has been based on physiology. The pancreas secretes insulin at continuously variable rates, finely regulated by sensitive arterial glucose sensing. Pancreatic insulin is delivered directlyin the portal blood to insulinize preferentially the liver. In the fasting state, insulin is secreted at a low rate to modulate hepatic glucose output. After liver extraction (50%), insulin concentrations in peripheral plasma are 2.4-4 times lower than in portal, but still efficacious to restrain lipolysis. In the prandial condition, insulin is secreted rapidly in large amounts to increase portal and peripheral concentrations to peaks 10-20 times greater vs the values of fasting within 30-40 min from meal ingestion. The prandial portal hyperinsulinemia fully suppresses hepatic glucose production while peripheral hyperinsulinemia increases glucose utilization, thus limitating the post-prandial plasma glucose elevation. Physiology of insulin indicates that insulin should be replaced in people with diabetes mimicking the pancreas, i.e. in a basal-bolus mode, for fasting and prandial state, respectively. Despite the presently ongoing limitations (subcutaneous and peripheral rather than portal and intravenous insulin delivery), basal-bolus insulin allows people with diabetes to achieve A1c in the range with minimal risk of hypoglycaemia, to prevent vascular complications and to ensure good quality of life.

Neuroendocrine Peptides of the Gut and Their Role in the Regulation of Food Intake

The regulation of food intake encompasses complex interplays between the gut and the brain. Among them, the gastrointestinal tract releases different peptides that communicate the metabolic state to specific nuclei in the hindbrain and the hypothalamus. The present overview gives emphasis on seven peptides that are produced by and secreted from specialized enteroendocrine cells along the gastrointestinal tract in relation with the nutritional status. These established modulators of feeding are ghrelin and nesfatin-1 secreted from gastric X/A-like cells, cholecystokinin (CCK) secreted from duodenal I-cells, glucagon-like peptide 1 (GLP-1), oxyntomodulin, and peptide YY (PYY) secreted from intestinal L-cells and uroguanylin (UGN) released from enterochromaffin (EC) cells. © 2021 American Physiological Society. Compr Physiol 11:1679-1730, 2021.

Exenatide, Metformin, or Both for Prediabetes in PCOS: A Randomized, Open-label, Parallel-group Controlled Study

CONTEXT

Up to 40% of patients with polycystic ovary syndrome (PCOS) have prediabetes; an optimal pharmacotherapy regimen for diabetes prevention in PCOS is yet to be established.

OBJECTIVE

To evaluate clinical efficacy of exenatide (EX), metformin (MET), or combination (COM) for prediabetes in PCOS.

DESIGN

Randomized, open-label, parallel-group controlled trial.

SETTING

Renji Hospital Affiliated to Shanghai Jiaotong University School of Medicine.

PATIENTS

PCOS with prediabetes (fasting plasma glucose 5.6-6.9 mmol/L and/or 2 hour post glucose 7.8-11.0 mmol/L on oral glucose tolerance test [OGTT]). A total of 150 out of 183 eligible enrollees completed the study.

INTERVENTION

EX (10-20μg daily), MET (1500-2000 mg daily), or COM (EX plus MET) for 12 weeks.

MAIN OUTCOME MEASURES

Sustained remission rate of prediabetes (primary endpoint, a normal OGTT after 12 weeks of treatment followed by 12 weeks of washout on no drug treatment) along with anthropometric, hormonal, metabolic, and pancreatic β-cell function parameters (secondary endpoints) and potential mechanisms were assessed.

RESULTS

Impaired glucose tolerance was found the dominant prediabetes phenotype. Overall sustained prediabetes remission rate was 50.7%. Remission rate of COM group (64%, 32/50) or EX group (56%, 28/50) was significantly higher than that of the MET group (32%, 16/50) (P = .003 and .027, respectively). EX was associated with superior suppression of 2-hour glucose increment in OGTT. A 2-step hyperglycemic clamp study revealed that EX had led to higher postprandial insulin secretion than MET, potentially explaining the higher remission rate.

CONCLUSIONS

Compared with MET monotherapy, EX or COM achieved higher rate of remission of prediabetes among PCOS patients by improving postprandial insulin secretion.

What Is an L-Cell and How Do We Study the Secretory Mechanisms of the L-Cell?

Synthetic glucagon-like peptide-1 (GLP-1) analogues are effective anti-obesity and anti-diabetes drugs. The beneficial actions of GLP-1 go far beyond insulin secretion and appetite, and include cardiovascular benefits and possibly also beneficial effects in neurodegenerative diseases. Considerable reserves of GLP-1 are stored in intestinal endocrine cells that potentially might be mobilized by pharmacological means to improve the body's metabolic state. In recognition of this, the interest in understanding basic L-cell physiology and the mechanisms controlling GLP-1 secretion, has increased considerably. With a view to home in on what an L-cell is, we here present an overview of available data on L-cell development, L-cell peptide expression profiles, peptide production and secretory patterns of L-cells from different parts of the gut. We conclude that L-cells differ markedly depending on their anatomical location, and that the traditional definition of L-cells as a homogeneous population of cells that only produce GLP-1, GLP-2, glicentin and oxyntomodulin is no longer tenable. We suggest to sub-classify L-cells based on their differential peptide contents as well as their differential expression of nutrient sensors, which ultimately determine the secretory responses to different stimuli. A second purpose of this review is to describe and discuss the most frequently used experimental models for functional L-cell studies, highlighting their benefits and limitations. We conclude that no experimental model is perfect and that a comprehensive understanding must be built on results from a combination of models.

DPP-4 Inhibitors: Renoprotective Potential and Pharmacokinetics in Type 2 Diabetes Mellitus Patients with Renal Impairment

The continuously increasing incidence of diabetes worldwide has attracted the attention of the scientific community and driven the development of a novel class of antidiabetic drugs that can be safely and effectively used in diabetic patients. Of particular interest in this context are complications associated with diabetes, such as renal impairment, which is the main cause of high cardiovascular morbidity and mortality in diabetic patients. Intensive control of glucose levels and other risk factors associated with diabetes and metabolic syndrome provides the foundations for both preventing and treating diabetic nephropathy. Dipeptidyl peptidase-4 (DPP-4) inhibitors represent a highly promising novel class of oral agents used in the treatment of type 2 diabetes mellitus that may be successfully combined with currently available antidiabetic therapeutics in order to achieve blood glucose goals. Beyond glycemic control, emerging evidence suggests that DPP-4 inhibitors may have desirable off-target effects, including renoprotection. All type 2 diabetes mellitus patients with impaired renal function require dose adjustment of any DPP-4 inhibitor administered except for linagliptin, for which renal excretion is a minor elimination pathway. Thus, linagliptin is the drug most frequently chosen to treat type 2 diabetes mellitus patients with renal failure.

The glucagon-like peptide-1 receptor agonist, exendin-4, reduces sexual interaction behaviors in a brain site-specific manner in sexually naïve male mice

Besides reducing food intake and controlling energy balance, glucagon-like peptide-1 (GLP-1) suppresses the reinforcing properties of palatable foods and addictive drugs. This reduction in reward involves activation of GLP-1 receptors (GLP-1R) within areas processing natural and artificial rewards, including the laterodorsal tegmental area (LDTg), ventral tegmental area (VTA) and nucleus accumbens (NAc) shell. These areas are part of a neurocircuitry mediating reward from addictive drugs and natural rewards including sexual behaviors. The male sexual encounter with a female includes three different stages: a pre-sexual interaction phase with social behaviors, which is followed by a sexual interaction phase with mounting and intromission of the female, and ends with a post-sexual interaction phase characterized by self-grooming behaviors. Albeit GLP-1 modulates reward, the influence of GLP-1R activation on sexual interaction is unknown. Thus, we infused the GLP-1R agonist, exendin-4 (Ex4), into sub-regions of the reward neurocircuitry in sexually naïve male mice and recorded their novel interaction with an estrus female. We found that Ex4 into the LDTg, posterior VTA or NAc shell reduces pre-sexual interaction behaviors and activation of GLP-1R in the LDTg or posterior VTA decreases sexual interaction behaviors. Contrarily, Ex4 infusion into anterior VTA does not influence these behaviors. Furthermore, self-grooming behaviors are not influenced by activation of GLP-1R in the aforementioned areas. These data highlight that activation of GLP-1R in reward-related areas reduces different aspects of the sexual interaction chain and further supports a role of the GLP-1R in social behaviors.

The Effects of Mutual Interaction of Orexin-A and Glucagon-Like Peptide-1 on Reflex Swallowing Induced by SLN Afferents in Rats

(1) Background: Our previous studies revealed that orexin-A, an appetite-increasing peptide, suppressed reflex swallowing via the commissural part of the nucleus tractus solitarius (cNTS), and that glucagon-like peptide-1 (GLP-1), an appetite-reducing peptide, also suppressed reflex swallowing via the medial nucleus of the NTS (mNTS). In this study, we examined the mutual interaction between orexin-A and GLP-1 in reflex swallowing. (2) Methods: Sprague–Dawley rats under urethane–chloralose anesthesia were used. Swallowing was induced by electrical stimulation of the superior laryngeal nerve (SLN) and was identified by the electromyographic (EMG) signals obtained from the mylohyoid muscle. (3) Results: The injection of GLP-1 (20 pmol) into the mNTS reduced the swallowing frequency and extended the latency of the first swallow. These suppressive effects of GLP-1 were not observed after the fourth ventricular administration of orexin-A. After the injection of an orexin-1 receptor antagonist (SB334867) into the cNTS, an ineffective dose of GLP-1 (6 pmol) into the mNTS suppressed reflex swallowing. Similarly, the suppressive effects of orexin-A (1 nmol) were not observed after the injection of GLP-1 (6 pmol) into the mNTS. After the administration of a GLP-1 receptor antagonist (exendin-4(5-39)), an ineffective dose of orexin-A (0.3 nmol) suppressed reflex swallowing. (4) Conclusions: The presence of reciprocal inhibitory connections between GLP-1 receptive neurons and orexin-A receptive neurons in the NTS was strongly suggested.

Metabolism of GIP and the contribution of GIP to the glucose-lowering properties of DPP-4 inhibitors

Glucose-dependent insulinotropic polypeptide (GIP) is a gastrointestinal hormone with insulinotropic and glucagonotropic actions, and is believed to be the more physiologically important incretin hormone in healthy humans. Together with the other incretin hormone, glucagon-like peptide-1 (GLP-1), it plays an important role in regulating glucose homeostasis. Both GLP-1 and GIP are substrates of the enzyme dipeptidyl peptidase-4 (DPP-4), and DPP-4 inhibitors, which potentiate their effects on glycaemic control, are now used to treat type 2 diabetes (T2D). This review describes how post-translational processing of the GIP precursor molecule and post-release degradation of the secretory products give rise to multiple isoforms of GIP, some, but not all of which are biologically active, and discusses how this impacts upon their measurement by immunological- and bioassay-based methods. DPP-4 inhibitors reduce degradation of GIP, and although the insulinotropic effects of GIP are impaired in patients with T2D, they can be at least partially restored if glycaemic control is improved. Therefore, given that studies with incretin receptor antagonists indicate that not all of the glucose-lowering effects of DPP-4 inhibition can be accounted for by GLP-1 alone, evidence supports the notion that GIP may play a role in mediating the anti-hyperglycaemic effects of DPP-4 inhibition, while its glucagonotropic actions at lower glucose levels may contribute to the low risk of hypoglycaemia associated with DPP-4 inhibitors.

Ghrelin Does Not Directly Stimulate Secretion of Glucagon-like Peptide-1

CONTEXT

The gastrointestinal hormone ghrelin stimulates growth hormone secretion and appetite, but recent studies indicate that ghrelin also stimulates the secretion of the appetite-inhibiting and insulinotropic hormone glucagon-like peptide-1 (GLP-1).

OBJECTIVE

To investigate the putative effect of ghrelin on GLP-1 secretion in vivo and in vitro.

SUBJECTS AND METHODS

A randomized placebo-controlled crossover study was performed in eight hypopituitary subjects. Ghrelin or saline was infused intravenously (1 pmol/min × kg) after collection of baseline sample (0 min), and blood was subsequently collected at time 30, 60, 90, and 120 minutes. Mouse small intestine was perfused (n = 6) and GLP-1 output from perfused mouse small intestine was investigated in response to vascular ghrelin administration in the presence and absence of a simultaneous luminal glucose stimulus. Ghrelin receptor expression was quantified in human (n = 11) and mouse L-cells (n = 3) by RNA sequencing and RT-qPCR, respectively.

RESULTS

Ghrelin did not affect GLP-1 secretion in humans (area under the curve [AUC; 0-120 min]: ghrelin infusion = 1.37 ± 0.05 min × nmol vs. saline infusion = 1.40 ± 0.06 min × nmol [P = 0.63]), but induced peripheral insulin resistance. Likewise, ghrelin did not stimulate GLP-1 secretion from the perfused mouse small intestine model (mean outputs during baseline/ghrelin infusion = 19.3 ± 1.6/25.5 ± 2.0 fmol/min, n = 6, P = 0.16), whereas glucose-dependent insulinotropic polypeptide administration, used as a positive control, doubled GLP-1 secretion (P < 0.001). Intraluminal glucose increased GLP-1 secretion by 4-fold (P < 0.001), which was not potentiated by ghrelin. Finally, gene expression of the ghrelin receptor was undetectable in mouse L-cells and marginal in human L-cells.

CONCLUSIONS

Ghrelin does not interact directly with the L-cell and does not directly affect GLP-1 secretion.

Glucagon-Like Peptide 1 and Atrial Natriuretic Peptide in a Female Mouse Model of Obstructive Pulmonary Disease

Glucagon-like peptide-1 (GLP-1) is protective in lung disease models but the underlying mechanisms remain elusive. Because the hormone atrial natriuretic peptide (ANP) also has beneficial effects in lung disease, we hypothesized that GLP-1 effects may be mediated by ANP expression. To study this putative link, we used a mouse model of chronic obstructive pulmonary disease (COPD) and assessed lung function by unrestrained whole-body plethysmography. In 1 study, we investigated the role of endogenous GLP-1 by genetic GLP-1 receptor (GLP-1R) knockout (KO) and pharmaceutical blockade of the GLP-1R with the antagonist exendin-9 to -39 (EX-9). In another study the effects of exogenous GLP-1 were assessed. Lastly, we investigated the bronchodilatory properties of ANP and a GLP-1R agonist on isolated bronchial sections from healthy and COPD mice.

Lung function did not differ between mice receiving phosphate-buffered saline (PBS) and EX-9 or between GLP-1R KO mice and their wild-type littermates. The COPD mice receiving GLP-1R agonist improved pulmonary function (P < .01) with less inflammation, but no less emphysema compared to PBS-treated mice. Compared with the PBS-treated mice, treatment with GLP-1 agonist increased ANP (nppa) gene expression by 10-fold (P < .01) and decreased endothelin-1 (P < .01), a peptide associated with bronchoconstriction. ANP had moderate bronchodilatory effects in isolated bronchial sections and GLP-1R agonist also showed bronchodilatory properties but less than ANP. Responses to both peptides were significantly increased in COPD mice (P < .05, P < .01).

Taken together, our study suggests a link between GLP-1 and ANP in COPD.

Glucagon-like peptide 1 (GLP-1)

BACKGROUND

The glucagon-like peptide-1 (GLP-1) is a multifaceted hormone with broad pharmacological potential. Among the numerous metabolic effects of GLP-1 are the glucose-dependent stimulation of insulin secretion, decrease of gastric emptying, inhibition of food intake, increase of natriuresis and diuresis, and modulation of rodent β-cell proliferation. GLP-1 also has cardio- and neuroprotective effects, decreases inflammation and apoptosis, and has implications for learning and memory, reward behavior, and palatability. Biochemically modified for enhanced potency and sustained action, GLP-1 receptor agonists are successfully in clinical use for the treatment of type-2 diabetes, and several GLP-1-based pharmacotherapies are in clinical evaluation for the treatment of obesity.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GLP-1 and its pharmacology and discuss its therapeutic implications on various diseases.

MAJOR CONCLUSIONS

Since its discovery, GLP-1 has emerged as a pleiotropic hormone with a myriad of metabolic functions that go well beyond its classical identification as an incretin hormone. The numerous beneficial effects of GLP-1 render this hormone an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, and neurodegenerative disorders.

Cardiac remodeling in obesity and after bariatric and metabolic surgery; is there a role for gastro-intestinal hormones?

Introduction: Obesity is associated with various diseases such as type 2 diabetes, hypertension, obstructive sleep apnea syndrome (OSAS), metabolic syndrome, and cardiovascular diseases. It affects several organ systems, including the pulmonary and cardiac systems. Furthermore, it induces pulmonary and cardiac changes that can result in right and/or left heart failure.Areas covered: In this review, authors provide an overview of obesity and cardiovascular remodeling, the individual actions of the gut hormones (like GLP-1 and PYY), the effects after bariatric/metabolic surgery and its influence on cardiac remodeling. In this review, we focussed and searched for literature in Pubmed and The Cochrane library (from the earliest date until April 2019), regarding cardiac function changes before and after bariatric surgery and literature regarding changes in gastrointestinal hormones.Expert opinion: Regarding the surgical treatment of obesity and metabolic diseases there is recognition of the importance of both weight loss (bariatric surgery) and improvement in metabolic milieu (metabolic surgery). A growing body of evidence further suggests that bariatric surgical procedures [like the Sleeve Gastrectomy (SG), Roux-en Y Gastric Bypass (RYGB), or One Anastomosis Gastric Bypass (OAGB)] have can improve outcomes of patients suffering from a number of cardiovascular diseases, including heart failure.

The Effects of Dual GLP-1/GIP Receptor Agonism on Glucagon Secretion-A Review

The gut-derived incretin hormones glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are secreted after meal ingestion and work in concert to promote postprandial insulin secretion. Furthermore, GLP-1 inhibits glucagon secretion when plasma glucose concentrations are above normal fasting concentrations while GIP acts glucagonotropically at low glucose levels. A dual incretin receptor agonist designed to co-activate GLP-1 and GIP receptors was recently shown to elicit robust improvements of glycemic control (mean haemoglobin A1c reduction of 1.94%) and massive body weight loss (mean weight loss of 11.3 kg) after 26 weeks of treatment with the highest dose (15 mg once weekly) in a clinical trial including overweight/obese patients with type 2 diabetes. Here, we describe the mechanisms by which the two incretins modulate alpha cell secretion of glucagon, review the effects of co-administration of GLP-1 and GIP on glucagon secretion, and discuss the potential role of glucagon in the therapeutic effects observed with novel unimolecular dual GLP-1/GIP receptor agonists. For clinicians and researchers, this manuscript offers an understanding of incretin physiology and pharmacology, and provides mechanistic insight into future antidiabetic and obesity treatments.

Development of therapeutic options on type 2 diabetes in years: Glucagon-like peptide-1 receptor agonist’s role intreatment; from the past to future

Diabetes mellitus (DM) is a chronic metabolic disease characterized by hypergly-cemia. Type 2 diabetes (T2DM) accounting for 90% of cases globally. The worldwide prevalence of DM is rising dramatically over the last decades, from 30 million cases in 1985 to 382 million cases in 2013. It’s estimated that 451 million people had diabetes in 2017. As the pathophysiology was understood over the years, treatment options for diabetes increased. Incretin-based therapy is one of them. Glucagon-like peptide-1 receptor agonist (GLP-1 RA) not only significantly lower glucose level with minimal risk of hypoglycemia but also, they have an important advantage in themanagement of cardiovascular risk and obesity. Thus, we will review here GLP-1 RAsrole in the treatment of diabetes.

Analysis of Patents Issued in China for Antihyperglycemic Therapies for Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is prevalent, with a dramatic increase in recent years. Moreover, its microvascular and macrovascular complications cause significant societal issues. The demand for new and effective antidiabetic therapies grows with each passing day and motivates organizations and individuals to pay more attention to such products. In this article, we focused on oral antihyperglycemic drugs patented in China and introduced them according to their antihyperglycemic mechanisms. By searching the website of State Intellectual Property Office of the People's Republic of China (http://www.sipo.gov.cn), 2,500 antihyperglycemic patents for T2DM were identified and analyzed. These consisted of 4 patents for derivatives of herbal extracts (0.2%), 162 patents for herbal extracts (6.5%), 61 compositions for traditional Chinese medicine (TCM) (2.4%), 2,263 patents for synthetic compounds (90.5%), and 10 (0.4%) patents of the combination of synthetic compounds and TCM. As the most common drugs for diabetes mellitus, synthetic compounds can also be classified into several categories according to their working mechanisms, such as insulin secretion promotor agents, insulin sensitizer agents, α-glucosidase inhibitors, and so forth. This article discussed the chemical structure, potential antihyperglycemic mechanism of these antihyperglycemic drugs in patents in China. Expert opinion: Insulin sensitivity and β-cell function could be improved by weight loss to prevent prediabetes into T2DM. However, 40-50% patients with impaired glucose tolerance (IGT) still progress to T2DM, even after successful long-term weight loss. Antihyperglycemic remedies provide a treatment option to improve insulin sensitivity and maintain β-cell function. Combination therapy is the best treatment for diabetes. Combination therapy can reduce the dosage of each single drug option, and avoid the side effects. Drugs with different mechanisms are complementary, and are better adapted to patients with changing conditions. Classical combination therapies include combinations such as sulfonylureas plus biguanides or glucosidase inhibitors, biguanide plus glucosidase inhibitors or insulin sensitizers, insulin treatment plus biguanides or glucosidase inhibitors. The general principle of combination therapy is that two drugs with different mechanisms are selected jointly, and the combination of three types of hypoglycemic drugs is not recommended. After reading a large amount of literature, we have rarely found a case of three oral hypoglycemic agents, which may mean that the combination of three oral hypoglycemic agents is unnecessary and has unpredictable risks. There is no objection to the idea of multi-drug therapy. But multiple drugs can only be used when it shows a significant benefit to the patients. Combined use of multiple antidiabetic drugs poses a risk to patients due to drug interactions and overtreatment.

Glucagon-Like Peptide-1 Is a Marker of Systemic Inflammation in Patients Treated with High-Dose Chemotherapy and Autologous Stem Cell Transplantation

Autologous stem cell transplantation (ASCT) is challenged by side effects that may be propagated by chemotherapy-induced mucositis, resulting in bacterial translocation and systemic inflammation. Because gastrointestinal damage appears as an early event in this cascade of reactions, we hypothesized that markers reflecting damage to the intestinal barrier could serve as early predictive markers of toxicity. Glucagon-like peptide-1 (GLP-1), a well-known regulator of blood glucose, has been found to promote intestinal growth and repair in animal studies. We investigated fasting GLP-1 plasma levels in 66 adults undergoing ASCT for lymphoma and multiple myeloma. GLP-1 increased significantly after chemotherapy, reaching peak levels at day +7 post-transplant (median, 8 pmol/L [interquartile range, 4 to 12] before conditioning versus 10 pmol/L [interquartile range, 6 to 17] at day +7; P = .007). The magnitude of the GLP-1 increase was related to the intensity of conditioning. GLP-1 at the day of transplantation (day 0) was positively associated with peak C-reactive protein (CRP) levels (46 mg/L per GLP-1 doubling, P < .001) and increase in days with fever (32% per GLP-1 doubling, P = .0058). Patients with GLP-1 above the median at day 0 had higher CRP levels from days +3 to +10 post-transplant than patients with lower GLP-1 (P ≤ .041) with peak values of 238 versus 129 mg/L, respectively. This study, which represents the first clinical investigation of fasting GLP-1 in relation to high-dose chemotherapy, provides evidence that GLP-1 plays a role in regulation of mucosal defenses. Fasting GLP-1 levels may serve as an early predictor of systemic inflammation and fever in patients receiving high-dose chemotherapy.

Systemic oscillator-driven and nutrient-responsive hormonal regulation of daily expression rhythms for gluconeogenic enzyme genes in the mouse liver

Gluconeogenesis is de novo glucose synthesis from substrates such as amino acids and is vital when glucose is lacking in the diurnal nutritional fluctuation. Accordingly, genes for hepatic gluconeogenic enzymes exhibit daily expression rhythms, whose detailed regulations under nutritional variations remain elusive. As a first step, we performed general systematic characterization of daily expression profiles of gluconeogenic enzyme genes for phosphoenolpyruvate carboxykinase (PEPCK), cytosolic form (Pck1), glucose-6-phosphatase (G6Pase), catalytic subunit (G6pc), and tyrosine aminotransferase (TAT) (Tat) in the mouse liver. On a standard diet fed ad libitum, mRNA levels of these genes showed robust daily rhythms with a peak or an elevation phase during the late sleep-fasting period in the diurnal feeding/fasting (wake/sleep) cycle. The rhythmicity was preserved in constant darkness, modulated with prolonged fasting, attenuated by Clock mutation, and entrained to varied photoperiods and time-restricted feedings. These results are concordant with the notion that gluconeogenic enzyme genes are under the control of the intrinsic circadian oscillator, which is entrained by the light/dark cycle, and which in turn entrains the feeding/fasting cycle and also drives systemic signaling pathways such as the hypothalamic-pituitary-adrenal axis. On the other hand, time-restricted feedings also showed that the ingestion schedule, when separated from the light/dark cycle, can serve as an independent entrainer to daily expression rhythms of gluconeogenic enzyme genes. Moreover, nutritional changes dramatically modified expression profiles of the genes. In addition to prolonged fasting, a high-fat diet and a high-carbohydrate (no-protein) diet caused modification of daily expression rhythms of the genes, with characteristic changes in profiles of glucoregulatory hormones such as corticosterone, glucagon, and insulin, as well as their modulators including ghrelin, leptin, resistin, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1). Remarkably, high-protein (60% casein or soy-protein) diets activated the gluconeogenic enzyme genes atypically during the wake-feeding period, with paradoxical up-regulation of glucagon, which frequently formed correlation networks with other humoral factors. Based on these results, we propose that daily expression rhythms of gluconeogenic enzyme genes are under the control of systemic oscillator-driven and nutrient-responsive hormones.

Impact on HbA1c and body weight of switching from other GLP-1 receptor agonists to semaglutide: A model-based approach

AIMS

Semaglutide is a glucagon-like peptide-1 (GLP-1) analogue approved for the treatment of type 2 diabetes. The impact of switching treatment from another GLP-1 receptor agonist (GLP-1RA) to semaglutide was investigated by analyses of exposure-response models.

METHODS

HbA1c and body weight time-course models were developed, using up to 30 weeks of observations from four trials in the semaglutide phase 3 programme. Given the recommended dosing for each GLP-1RA, pharmacokinetic profiles were simulated based on published population pharmacokinetic models and exposure was adjusted by the relative potencies to ensure that model predictions matched the effects observed in clinical trials. After 26 weeks of simulated treatment with liraglutide, dulaglutide or exenatide extended-release, simulated semaglutide treatment was initiated 1 day after the last once-daily dose of liraglutide and 1 week after the last once-weekly doses of dulaglutide or exenatide extended-release.

RESULTS

The potency-adjusted total effective GLP-1RA concentration increased after switching from another GLP-1RA to semaglutide and was associated with reductions ranging from ~0.3% to ~0.8%-points for HbA1c and from ~2% to ~4% for body weight with semaglutide 1.0 mg. Temporary slight deteriorations in HbA1c were observed after switching to semaglutide 0.25 mg from liraglutide 1.2/1.8 mg or dulaglutide 1.5 mg.

CONCLUSIONS

Exposure-response modelling suggests that switching to semaglutide from liraglutide, dulaglutide or exenatide extended-release results in further reductions in HbA1c and body weight. Initial slight deterioration in outcome values when switching to semaglutide 0.25 mg could be avoided by initiating semaglutide treatment at a higher dose.

Thromboxane-Dependent Platelet Activation in Obese Subjects with Prediabetes or Early Type 2 Diabetes: Effects of Liraglutide- or Lifestyle Changes-Induced Weight Loss

Thromboxane (TX)-dependent platelet activation and lipid peroxidation, as reflected in vivo by the urinary excretion of 11-dehydro-TXB₂ and 8-iso-prostaglandin (PG)F_2α, play a key role in atherothrombosis in obesity and type 2 diabetes mellitus (T2DM) since the earlier stages. Thirty-five metformin-treated obese subjects with prediabetes or newly-diagnosed T2DM were randomized to the glucagon-like peptide receptor agonist (GLP-RA) liraglutide (1.8 mg/day) or lifestyle counseling until achieving a comparable weight loss (−7% of initial body weight), to assess whether changes in subcutaneous (SAT) and visceral (VAT) adipose tissue distribution (MRI), insulin sensitivity (Matsuda Index) and beta-cell performance (multiple sampling OGTT beta-index), with either intervention, might affect TX-dependent platelet activation, lipid peroxidation and inflammation. At baseline, Ln-8-iso-PGF_2α (Beta = 0.31, p = 0.0088), glycosylated hemoglobin (HbA1c) (Beta = 2.64, p = 0.0011) Ln-TNF-α (Beta = 0.58, p = 0.0075) and SAT (Beta = 0.14, p = 0.044) were significant independent predictors of 11-dehydro-TXB₂. After achievement of the weight loss target, a comparable reduction in U-11-dehydro-TXB₂ (between-group p = 0.679) and 8-iso-PGF-_2α (p = 0.985) was observed in both arms in parallel with a comparable improvement in glycemic control, insulin sensitivity, SAT, high-sensitivity C-reactive protein (hs-CRP). In obese patients with initial impairment of glucose metabolism, the extent of platelet activation is related to systemic inflammation, isoprostane formation and degree of glycemic control and abdominal SAT. Successful weight loss, achieved with either lifestyle changes or an incretin-based therapy, is associated with a significant reduction in lipid peroxidation and platelet activation.

Effects of liraglutide on gallbladder emptying: A randomized, placebo-controlled trial in adults with overweight or obesity

AIMS

Treatment with liraglutide 3.0 mg has been associated with gallbladder-related adverse events. To conduct a single-centre, double-blind, 12-week trial comparing the effect of 0.6 mg liraglutide and steady-state liraglutide 3.0 mg with placebo on gallbladder emptying in adults with body mass index (BMI) ≥27 kg/m² and without diabetes.

METHODS

Participants were randomized 1:1 to once-daily subcutaneous liraglutide (n = 26) or placebo (n = 26), starting at 0.6 mg with 0.6-mg weekly increments to 3.0 mg, with nutritional and physical activity counselling. A 600-kcal (23.7 g fat) liquid meal test was performed at baseline, after the first dose and after 12 weeks. The primary endpoint was the 12-week maximum postprandial gallbladder ejection fraction (GBEF_max ), measured over 240 minutes after starting the meal.

RESULTS

Baseline characteristics were similar between groups (mean ± SD overall age 47.6 ± 10.0 years, BMI 32.6 ±3.4 kg/m² , 50% women). Mean 12-week GBEF_max (treatment difference -3.7%, 95% confidence interval [CI] -13.1, 5.7) and area under the GBEF curve in the first 60 minutes (-390% × min, 95% CI -919, 140) did not differ for liraglutide 3.0 mg (n = 23) vs placebo (n = 24). The median (range) time to GBEF_max was 151 (11-240) minutes with liraglutide 3.0 mg and 77 (22-212) minutes with placebo. Similar findings were noted after the first 0.6-mg liraglutide dose. Gastrointestinal disorders, notably nausea and constipation, were the most frequently reported adverse events.

CONCLUSIONS

Treatment with liraglutide did not affect the GBEF_max but appeared to prolong the time to GBEF_max .

Endogenous glucagon-like peptide- 1 and 2 are essential for regeneration after acute intestinal injury in mice

Objective

Mucositis is a side effect of chemotherapy seen in the digestive tract, with symptoms including pain, diarrhoea, inflammation and ulcerations. Our aim was to investigate whether endogenous glucagon-like peptide -1 and -2 (GLP-1 and GLP-2) are implicated in intestinal healing after chemotherapy-induced mucositis.

Design

We used a transgenic mouse model Tg(GCG.DTR)(Tg) expressing the human diphtheria toxin receptor in the proglucagon-producing cells. Injections with diphtheria toxin ablated the GLP-1 and GLP-2 producing L-cells in Tg mice with no effect in wild-type (WT) mice. Mice were injected with 5-fluorouracil or saline and received vehicle, exendin-4, teduglutide (gly2-GLP-2), or exendin-4/teduglutide in combination. The endpoints were body weight change, small intestinal weight, morphology, histological scoring of mucositis and myeloperoxidase levels.

Results

Ablation of L-cells led to impaired GLP-2 secretion; increased loss of body weight; lower small intestinal weight; lower crypt depth, villus height and mucosal area; and increased the mucositis severity score in mice given 5-fluorouracil. WT mice showed compensatory hyperproliferation as a sign of regeneration in the recovery phase. Co-treatment with exendin-4 and teduglutide rescued the body weight of the Tg mice and led to a hyperproliferation in the small intestine, whereas single treatment was less effective.

Conclusion

The ablation of L-cells leads to severe mucositis and insufficient intestinal healing, shown by severe body weight loss and lack of compensatory hyperproliferation in the recovery phase. Co-treatment with exendin-4 and teduglutide could prevent this. Because both peptides were needed, we can conclude that both GLP-1 and GLP-2 are essential for intestinal healing in mice.

INSL5 activates multiple signalling pathways and regulates GLP-1 secretion in NCI-H716 cells

Insulin-like peptide 5 (INSL5) is a newly discovered gut hormone expressed in colonic enteroendocrine L-cells but little is known about its biological function. Here, we show using RT-qPCR and in situ hybridisation that Insl5 mRNA is highly expressed in the mouse colonic mucosa, colocalised with proglucagon immunoreactivity. In comparison, mRNA for RXFP4 (the cognate receptor for INSL5) is expressed in various mouse tissues, including the intestinal tract. We show that the human enteroendocrine L-cell model NCI-H716 cell line, and goblet-like colorectal cell lines SW1463 and LS513 endogenously express RXFP4. Stimulation of NCI-H716 cells with INSL5 produced phosphorylation of ERK1/2 (Thr²⁰²/Tyr²⁰⁴), AKT (Thr³⁰⁸ and Ser⁴⁷³) and S6RP (Ser^235/236) and inhibited cAMP production but did not stimulate Ca²⁺ release. Acute INSL5 treatment had no effect on GLP-1 secretion mediated by carbachol or insulin, but modestly inhibited forskolin-stimulated GLP-1 secretion in NCI-H716 cells. However, chronic INSL5 pre-treatment (18 h) increased basal GLP-1 secretion and prevented the inhibitory effect of acute INSL5 administration. LS513 cells were found to be unresponsive to INSL5 despite expressing RXFP4 Another enteroendocrine L-cell model, mouse GLUTag cells did not express detectable levels of Rxfp4 and were unresponsive to INSL5. This study provides novel insights into possible autocrine/paracrine roles of INSL5 in the intestinal tract.