Anti-inflammatory benefits of semaglutide: State of the art

Individuals with diabetes often have chronic inflammation and high levels of inflammatory cytokines, leading to insulin resistance and complications. Anti-inflammatory agents are proposed to prevent these issues, including using antidiabetic medications with anti-inflammatory properties like semaglutide, a GLP-1 analogue. Semaglutide not only lowers glucose but also shows potential anti-inflammatory effects. Studies suggest it can modulate inflammatory responses and benefit those with diabetes. However, the exact mechanisms of its anti-inflammatory effects are not fully understood. This review aims to discuss the latest findings on semaglutide's anti-inflammatory effects and the potential pathways involved.

Semaglutide alters gut microbiota and improves NAFLD in db/db mice

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease associated with type 2 diabetes mellitus (T2D). NAFLD can progress to nonalcoholic steatohepatitis (NASH), cirrhosis, and even cancer, all of which have a very poor prognosis. Semaglutide, a novel glucagon-like peptide-1 (GLP-1) receptor agonist, has been recognized as a specific drug for the treatment of diabetes. In this study, we used a gene mutation mouse model (db/db mice) to investigate the potential liver-improving effects of semaglutide. The results showed that semaglutide improved lipid levels and glucose metabolism in db/db mice. HE staining and oil red staining showed alleviation of liver damage and reduction of hepatic lipid deposition after injection of semaglutide. In addition, semaglutide also improved the integrity of gut barrier and altered gut microbiota, especially Alloprevotella, Alistpes, Ligilactobacillus and Lactobacillus. In summary, our findings validate that semaglutide induces modifications in the composition of the gut microbiota and ameliorates NAFLD, positioning it as a promising therapeutic candidate for addressing hepatic steatosis and associated inflammation.

Cellular mechanisms of incretin hormone secretion

Enteroendocrine cells located along the gastrointestinal epithelium sense different nutrients/luminal contents that trigger the secretion of a variety of gut hormones with different roles in glucose homeostasis and appetite regulation. The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are involved in the regulation of insulin secretion, appetite, food intake and body weight after their nutrient-induced secretion from the gut. GLP-1 mimetics have been developed and used in the treatment of type 2 diabetes mellitus and obesity. Modulating the release of endogenous intestinal hormones may be a promising approach for the treatment of obesity and type 2 diabetes without surgery. For that reason, current understanding of the cellular mechanisms underlying intestinal hormone secretion will be the focus of this review. The mechanisms controlling hormone secretion depend on the nature of the stimulus, involving a variety of signalling pathways including ion channels, nutrient transporters and G-protein-coupled receptors.

The GLP-1R as a model for understanding and exploiting biased agonism in next-generation medicines

The glucagon-like peptide 1 receptor (GLP-1R) is a class B G protein-coupled receptor (GPCR) that emerged as a pharmacologic target in cardiometabolic disease, including diabetes and obesity, over 30 years ago. The subsequent widespread clinical use of GLP-1R agonists, including exenatide, liraglutide, and semaglutide, has made the GLP-1R a preeminent model for understanding basic GPCR biology, including the emergent field of biased agonism. Recent data demonstrate that the dual GLP-1R/glucose dependent insulinotropic polypeptide receptor (GIPR) agonist tirzepatide exhibits a biased signaling profile characterized by preferential Gαs activation over β-arrestin recruitment, which appears to contribute to its insulinotropic and body-weight reducing effects in preclinical models. This constitutes a major finding in which nuanced, mechanistic receptor signaling dynamics in vitro mediate real-world clinical differentiation within a drug class. Because of the striking bench-top-to-bed side relevance of this biased signaling phenomenon, we have undertaken a review of the emerging data detailing biased agonism at the GLP-1R. In this review, we introduce the core concept of biased agonism followed by a detailed consideration of the key mechanisms, including ligand-mediated bias, receptor-mediated bias, and systems/cell-type bias. Current industry programs are largely, if not entirely, focused on developing biased ligands, and so we have dedicated a section of the review to a brief meta-analysis of compounds reported to drive biased signaling, with a consideration of the structural determinants of receptor-ligand interactions. In this work, we aim to assess the current knowledge regarding signaling bias at the GLP-1R and how these ideas might be leveraged in future optimization.

Identification of glucagon like peptide-1 (GLP-1) in mice stomach

Glucagon like peptide-1 (GLP-1) is a peptide hormone encoded by the pre-proglucagon gene that serves multiple physiological functions, including incretin action. While GLP-1 is primarily synthesized in the L cells of the lower intestine, recent findings indicate its presence in the stomachs of both rats and humans. However, the role of gastric GLP-1 in other species remains unclear. In this study, we aimed to identify GLP-1-producing cells and examine the localization of GLP-1 production in the mouse stomach. We found that pre-proglucagon mRNA was higher in the corpus than that in the antrum of the stomach. In addition, GLP-1 immunoreactive cells were found in the gastric mucosa, and their cell number was higher in the corpus than that in the antrum. Double immunofluorescence showed that some GLP-1 immunoreactive cells displayed somatostatin immunoreactivity, whereas did not co-localize with ghrelin and gastrin. Moreover, transmembrane G protein-coupled Receptor 5 (TGR5) agonist decreased pre-proglucagon mRNA expression in SG-1 cells in a concentration-dependent manner, and in vivo experiments showed a decrease in its mRNA levels in the gastric corpus but not in the antrum. This study marks the first report of GLP-1 production in the mouse stomach. Our findings suggest that gastric pre-proglucagon mRNA expression is regulated by a distinct mechanism compared to the L cells of the lower intestine.

Positive interplay between FFAR4/GPR120, DPP-IV inhibition and GLP-1 in beta cell proliferation and glucose homeostasis in obese high fat fed mice

G-protein coupled receptor-120 (GPR120; FFAR4) is a free fatty acid receptor, widely researched for its glucoregulatory and insulin release activities. This study aimed to investigate the metabolic advantage of FFAR4/GPR120activation using combination therapy. C57BL/6 mice, fed a High Fat Diet (HFD) for 120 days to induce obesity-diabetes, were subsequently treated with a single daily oral dose of FFAR4/GPR120 agonist Compound A (CpdA) (0.1μmol/kg) alone or in combination with sitagliptin (50mg/kg) for 21 days. After 21-days, glucose homeostasis, islet morphology, plasma hormones and lipids, tissue genes (qPCR) and protein expression (immunocytochemistry) were assessed. Oral administration of CpdA improved glucose tolerance (34% p<0.001) and increased circulating insulin (38% p<0.001). Addition of CpdA with the dipeptidyl peptidase-IV (DPP-IV) inhibitor, sitagliptin, further improved insulin release (44%) compared to sitagliptin alone and reduced fat mass (p<0.05). CpdA alone (50%) and in combination with sitagliptin (89%) induced marked reductions in LDL-cholesterol, with greater effects in combination (p<0.05). All treatment regimens restored pancreatic islet and beta-cell area and mass, complemented with significantly elevated beta-cell proliferation rates. A marked increase in circulating GLP-1 (53%) was observed, with further increases in combination (38%). With treatment, mice presented with increased Gcg (proglucagon) gene expression in the jejunum (130% increase) and ileum (120% increase), indicative of GLP-1 synthesis and secretion. These data highlight the therapeutic promise of FFAR4/GPR120 activation and the potential for combined benefit with incretin enhancing DPP-IV inhibitors in the regulation of beta cell proliferation and diabetes.

Safety of native glucose-dependent insulinotropic polypeptide in humans

In this systematic review, we assessed the safety and possible safety events of native glucose-dependent insulinotropic polypeptide (GIP)(1-42) in human studies with administration of synthetic human GIP. We searched the PubMed database for all trials investigating synthetic human GIP(1-42) administration. A total of 67 studies were included. Study duration ranged from 30 min to 6 days. In addition to healthy individuals, the studies included individuals with impaired glucose tolerance, type 2 diabetes, type 1 diabetes, chronic pancreatitis and secondary diabetes, latent autoimmune diabetes in adults, diabetes caused by a mutation in the hepatocyte nuclear factor 1-alpha gene, end-stage renal disease, chronic renal insufficiency, critical illness, hypoparathyroidism, or cystic fibrosis-related diabetes. Of the included studies, 78% did not mention safety events, 10% of the studies reported that no safety events were observed in relation to GIP administration, and 15% of the studies reported safety events in relation to GIP administration with most frequently reported event being a moderate and transient increased heart rate. Gastrointestinal safety events, and changes in blood pressure were also reported. Plasma concentration of active GIP(1-42) increased linearly with dose independent of participant phenotype. There was no significant correlation between achieved maximal concentration of GIP(1-42) and reported safety events. Clearance rates of GIP(1-42) were similar between participant groups. In conclusion, the available data indicate that GIP(1-42) in short-term (up to 6 days) infusion studies is generally well-tolerated. The long-term safety of continuous GIP(1-42) administration is unknown.

Tirzepatide and exercise training in obesity

OBJECTIVES

The purpose of this study was to investigate the effects of 6 weeks of resistance training (RT) combined with aerobic training (AT) and Tirzepatide supplementation on lipid profiles, insulin resistance, anthropometric characteristics and physical fitness in prediabetic obese soldiers.

METHODS

61 obese men were randomly divided into six groups: Placebo; Tirzepatide 5 mg (T5); Tirzepatide 2.5 mg (T2.5); Hypertrophy, Strength, Power-Circuit Training+Placebo (Ex+P); Hypertrophy, Strength, Power-Circuit Training+Tirzepatide 5 mg (Ex+T5); Hypertrophy, Strength, Power-Circuit Training+Tirzepatide 2.5 mg (Ex+T2.5). All training groups performed aerobic training (AT) after resistance training. Subjects trained for six weeks, three sessions per week. Before and after the intervention period, the participants were evaluated for anthropometric measures, body composition [body weight, body mass index (BMI), waist circumference (WC), waist to hip ratio (WHR) and fat mass (FM)], cardiorespiratory fitness (VO2max), and muscle strength (chest press 1RM and leg press 1RM). Blood biochemistry evaluations included triglyceride (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), fasting blood glucose (FBG), insulin level and insulin resistance (HOMA-IR). To evaluate the differences between the groups, ANCOVA statistical method was used along with Bonferroni's post hoc test, and the significance level was P <  0.05.

RESULTS

Body weight, BMI, WC, FM, FBG, LDL-C, TC, TG and HOMA-IR were significantly decreased in Ex+P, Ex+T5 and Ex+T2.5 groups compared to Placebo, T5 and T2.5 groups. WHR significantly decreased in Ex+P, Ex+T5 and Ex+T2.5 groups compared to Placebo group. HDL-C, chest press and leg press significantly increased in Ex+P, Ex+T5 and Ex+T2.5 groups compared to Placebo, T5 and T2.5 groups. VO2max significantly increased and insulin significantly decreased in Ex+P group compared to Placebo, T5 and T2.5 groups. FM, FBG and TG were significantly decreased in both the T2.5 and T5 groups compared to Placebo group. HOMA-IR, LDL-C and TC significantly decreased in the T5 group compared to Placebo group. Also, leg press significantly increased in Ex+P group compared to all other groups.

CONCLUSIONS

Performing six weeks of combined resistance and aerobic training in the form of RT+AT alone is more effective than the simultaneous use of Tirzepatide on cardiorespiratory fitness, strength, and modulating insulin levels. Taking Tirzepatide in doses of 5 mg and 2.5 mg in combination with exercise training did not have a significant advantage over exercise training alone. Finally, taking Tirzepatide in doses of 5 mg or 2.5 mg in combination with exercise training is not significantly superior to each other.

GLP-1 modulated the firing activity of nigral dopaminergic neurons in both normal and parkinsonian mice

The spontaneous firing activity of nigral dopaminergic neurons is associated with some important roles including modulation of dopamine release, expression of tyrosine hydroxylase (TH), as well as neuronal survival. The decreased neuroactivity of nigral dopaminergic neurons has been revealed in Parkinson's disease. Central glucagon-like peptide-1 (GLP-1) functions as a neurotransmitter or neuromodulator to exert multiple brain functions. Although morphological studies revealed the expression of GLP-1 receptors (GLP-1Rs) in the substantia nigra pars compacta, the possible modulation of GLP-1 on spontaneous firing activity of nigral dopaminergic neurons is unknown. The present extracellular in vivo single unit recordings revealed that GLP-1R agonist exendin-4 significantly increased the spontaneous firing rate and decreased the firing regularity of partial nigral dopaminergic neurons of adult male C57BL/6 mice. Blockade of GLP-1Rs by exendin (9-39) decreased the firing rate of nigral dopaminergic neurons suggesting the involvement of endogenous GLP-1 in the modulation of firing activity. Furthermore, the PKA and the transient receptor potential canonical (TRPC) 4/5 channels are involved in activation of GLP-1Rs-induced excitatory effects of nigral dopaminergic neurons. Under parkinsonian state, both the exogenous and endogenous GLP-1 could still induce excitatory effects on the surviving nigral dopaminergic neurons. As the mild excitatory stimuli exert neuroprotective effects on nigral dopaminergic neurons, the present GLP-1-induced excitatory effects may partially contribute to its antiparkinsonian effects.

Semaglutide as a potential treatment for obesity in Smith-Kingsmore syndrome (SKS) patients: A mosaic mutation case report

We present for the first-time efficacy and tolerability of GLP-1-RA (Semaglutide) in Smith-Kingsmore syndrome (SKS). SKS is a rare genetic disorder characterized by intellectual disability, macrocephaly, seizures and distinctive facial features due to MTOR gene mutation. We present a 22-year-old woman with mosaic SKS and severe obesity (Body Mass Index ≥40 kg/m²), treated with semaglutide. She achieved a 9 kg (7.44%) weight loss over 12 months without adverse effects.This case highlights semaglutide's potential in managing obesity in SKS patients, emphasizing the need for further research in this rare genetic disorder.

Dual and Triple Incretin-Based Co-agonists: Novel Therapeutics for Obesity and Diabetes

The discovery of long-acting incretin receptor agonists represents a major stride forward in tackling the dual epidemic of obesity and diabetes. Here we outline the evolution of incretin-based pharmacotherapy, from exendin-4 to the discovery of the multi-incretin hormone receptor agonists that look set to be our next step toward curing diabetes and obesity. We discuss the multiagonists currently in clinical trials and the improvement in efficacy each new generation of these drugs bring. The success of these agents in preclinical models and clinical trials suggests a promising future for multiagonists in the treatment of metabolic diseases, with the most recent glucose-dependent insulinotropic peptide receptor:glucagon-like peptide 1 receptor:glucagon receptor (GIPR:GLP-1R:GCGR) triagonists rivaling the efficacy of bariatric surgery. However, further research is needed to fully understand how these therapies exert their effect on body weight and in the last section we cover open questions about the potential mechanisms of multiagonist drugs, and the understanding of how gut-brain communication can be leveraged to achieve sustained body weight loss without adverse effects.

Exploring the impact of lifestyle and environmental exposures on appetite hormone levels in children and adolescents: An observational study

BACKGROUND

Appetite hormones are considered a promising target in fighting obesity as impaired appetite hormone levels have already been associated with obesity. However, further insights in the drivers of appetite hormone levels are needed.

OBJECTIVES

In this study, we investigated the associations of fasting appetite hormone levels with lifestyle and environmental exposures in children and adolescents.

METHODS

A total of 534 fasting blood samples were collected from children and adolescents (4-16y,50% boys) and appetite hormone levels (glucagon-like peptide-1 (GLP-1), peptide YY (PYY), pancreatic polypeptide (PP), leptin and ghrelin) were measured. Exposures included dietary quality (fiber-rich food intake, sugar propensity, fat propensity), psychosocial stress (happiness, negative emotions, negative life events and emotional problems), sleep duration, physical activity and environmental quality (long term black carbon (BC), particulate matter <2.5 μM (PM2.5), nitrogen dioxide (NO2) exposure, and green space in a 100 m and 2000 m radius around the residence). A multi-exposure score was calculated to combine all the exposures at study in one measure. Associations of individual exposures and multi-exposure score with appetite hormone levels were evaluated using linear mixed regression models adjusting for sex, age, socioeconomic status, waist-to-height ratio and multiple testing.

RESULTS

GLP-1 was associated with air pollution exposure (NO2 β* = -0.13, BC β* = -0.15, PM2.5 β* = -0.16, all p < 0.001). Leptin was associated with green space in a 100 m radius around the residence (β* = -0.11; p = 0.002). Ghrelin was associated with negative emotions (active ghrelin β* = -0.16; p = 0.04, total ghrelin β* = -0.23; p = 0.0051) and happiness (active ghrelin β* = 0.25; p < 0.001, total ghrelin β* = 0.26; p < 0.001). Furthermore, total ghrelin levels were associated with the multi-exposure score, reflecting unhealthy exposures and lifestyle (β* = -0.22; p = 0.036).

DISCUSSION

Our findings provide new insights into the associations of exposures with appetite hormone levels, which are of high interest for preventive obesity research. Further research is crucial to reveal the underlying mechanisms of the observed associations.

Identification and utility exploration of a highly potent and long-acting bullfrog GLP-1 analogue in GLP-1 and amylin combination therapy

This study assesses the efficacy of an innovative therapeutic approach that combines GLP-1 and amylin analogues for weight reduction. Focusing on GLP-1 analogues from bullfrog (Rana catesbeiana), we designed ten bGLP-1 analogues with various modifications. Among them, bGLP-10 showed high potency in binding and activating GLP-1 receptors, with superior albumin affinity. In diet-induced obesity (DIO) mice fed a high-fat diet, bGLP-10 demonstrated significant superiority over semaglutide in reducing blood sugar and food intake at a dose of 10 nmol/kg (P < 0.001). Notably, in a chronic study involving DIO mice, the combination of bGLP-10 with the amylin analogue cagrilintide led to a more substantial weight loss (-38.4%, P < 0.001) compared to either the semaglutide-cagrilintide combination (-23.0%) or cagrilintide (-5.7%), bGLP-10 (-16.1%), and semaglutide (-10.9%) alone. Furthermore, the bGLP-10 and cagrilintide combination exhibited superior glucose control and liver lipid management compared to the semaglutide-cagrilintide combination (P < 0.001). These results highlight bGLP-10's potential in GLP-1 and amylin-based therapies and suggest exploring more GLP-1 analogues from natural sources for anti-obesity and anti-diabetic treatments.

Intestinal Perfusion of Unacylated Ghrelin Alleviated Metabolic Associated Fatty Liver Disease in Rat via a Central Glucagon-Like Peptide-1 Pathway

Unacylated ghrelin (UAG), the unacylated form of ghrelin, accounts for 80-90% of circulation. Accumulated studies have pointed out that UAG may be used to treat metabolic disorders. This study aimed to investigate the effect of intestinal perfusion of UAG on metabolic associated fatty liver disease (MAFLD) induced by a high-fat diet and its possible mechanism. Neuronal retrograde tracking combined with immunofluorescence, central administration of GLP-1R antagonist, and hepatic vagotomy were performed to reveal its possible mechanism involving a central glucagon-like peptide-1 pathway. The results showed that intestinal perfusion of UAG significantly reduced serum lipids, aminotransferases, and food intake in MAFLD rats. Steatosis and lipid accumulation in the liver were significantly alleviated and lipid metabolism-related enzymes in the liver were regulated. UAG upregulated the expression of GLP-1 receptor (GLP-1R) in the paraventricular nucleus (PVN) and GLP-1 in the nucleus tractus solitarii (NTS), as well as activated GLP-1 neurons in the NTS. Furthermore, GLP-1 fibers projected from NTS to PVN were activated by intestinal perfusion of UAG. However, hepatic vagotomy and GLP-1R antagonist delivered into PVN before intestinal perfusion of UAG partially attenuated its alleviation on MAFLD. In conclusion, intestinal perfusion of UAG showed a therapeutic effect on MAFLD, which might be related to its activating on GLP-1 neuronal pathway from NTS to PVN. The present results provide a new strategy for the treatment of MAFLD.

Long-acting exenatide does not prevent cognitive decline in mild cognitive impairment: a proof-of-concept clinical trial

PURPOSE

According to preclinical evidence, GLP-1 receptor may be an actionable target in neurodegenerative disorders, including Alzheimer's disease (AD). Previous clinical trials of GLP-1 receptor agonists were conducted in patients with early AD, yielding mixed results. The aim was to assess in a proof-of-concept study whether slow-release exenatide, a long-acting GLP-1 agonist, can benefit the cognitive performance of people with mild cognitive impairment (MCI).

METHODS

Thirty-two (16 females) patients were randomized to either slow-release exenatide (n = 17; 2 mg s.c. once a week) or no treatment (n = 15) for 32 weeks. The primary endpoint was the change in ADAS-Cog11 cognitive test score at 32 weeks vs baseline. Secondary endpoints herein reported included additional cognitive tests and plasma readouts of GLP-1 receptor engagement. Statistical analysis was conducted by intention to treat.

RESULTS

No significant between-group effects of exenatide on ADAS-Cog11 score (p = 0.17) were detected. A gender interaction with treatment was observed (p = 0.04), due to worsening of the ADAS-Cog11 score in women randomized to exenatide (p = 0.018), after correction for age, scholar level, dysglycemia, and ADAS-Cog score baseline value. Fasting plasma glucose (p = 0.02) and body weight (p = 0.03) decreased in patients randomized to exenatide.

CONCLUSION

In patients with MCI, a 32-week trial with slow-release exenatide had no beneficial effect on cognitive performance.

TRIAL REGISTRATION NUMBER

NCT03881371, registered on 21 July, 2016.

Newer pharmacological interventions directed at gut hormones for obesity

The objective is to review the newer pharmacological interventions for obesity, specifically single, dual and triple incretin receptor agonists that are either available or in the pipeline for treatment of obesity. The three incretin receptor targets are glucagon like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP) and glucagon. There are several approved single or dual incretin agonists which can be administered subcutaneously daily (e.g., liraglutide) or weekly (e.g., semaglutide, dulaglutide, and exenatide QW), and other experimental dual or triple incretin agonists. Analogues of amylin, peptide YY and oxyntomodulin, as well as the combination of a GLP1R agonist and GIPR antagonist also are in development. Oral semaglutide (administered daily) is approved for type 2 diabetes mellitus and is on track for regulatory review for obesity. The review includes specifically perspectives on the effects of these mechanisms and pharmacological agents on gastric emptying, which contribute to satiation and weight loss, in addition to the established evidence on effects on central mechanisms controlling appetite. In the future, it is anticipated that small molecule GLP-1 receptor agonists (e.g., oral danuglipron) will be developed for treating obesity. These pharmacological agents are having significant impact on glycaemic control and obesity and on their co-morbidities.

Gastrin: a new branch of the gastropancreatic axis that can explain the effect of sleeve gastrectomy on glucose metabolism

BACKGROUND

Among bariatric techniques, sleeve gastrectomy (SG) stands out owing to its efficiency. The role of the stomach as a secretory organ of many substances, such as gastrin, related to insulin secretion is well known. Gastrin induces insulin release in isolated pancreatic islets, limiting somatostatin-14 intraislet release, and has been associated with blood glucose level improvement in diabetic models after SG. SG involves gastric resection along the greater curvature. This study aimed to determine the role of gastrin in glucose metabolism improvement after SG with the aid of the gastrin antagonist netazepide.

METHODS

In 12 sham-operated, 12 SG-operated, and 12 SG-operated/netazepide-treated Wistar rats, we compared medium- and long-term plasma insulin, oral glucose tolerance test (OGTT) results, and plasma gastrin levels. In addition, gastrin expression was assessed in the gastric remnant, and the beta-cell mass was measured.

RESULTS

SG induced a medium-term elevation of the insulin response and plasma gastrin levels without modification of the OGTT results. However, long-term depletion of the insulin response with elevated OGTT areas under the curve and plasma gastrin levels appeared after SG. Netazepide prevented the SG effect on these parameters. Gastrin tissue expression was greater in SG animals than in SG/netazepide-treated or control animals. The beta-cell mass was lower in the SG group than in the control or SG/netazepide group.

CONCLUSION

Gastrin plays a central role in glucose improvement after SG. It stimulates a medium-term strong insulin response but also causes long-term beta-cell mass depletion and a loss of insulin response. These effects are prevented by gastrin antagonists such as netazepide.

Comparative effectiveness of sodium-glucose cotransporter-2 inhibitors versus glucagon-like peptide-1 receptor agonists in patients with type 2 diabetes and mild/moderate chronic kidney disease

AIM

To determine the comparative effectiveness regarding major cardiovascular events of glucagon-like peptide-1 (GLP-1) receptor agonists and sodium-glucose cotransporter-2 (SGLT-2) inhibitors in patients with type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD).

MATERIALS AND METHODS

We assembled a cohort of commercially insured adult patients with T2DM in the United States (derived from Optum Clinformatics DataMart 2003-2021) who were new users of GLP-1 receptor agonists or SGLT-2 inhibitors. We compared risks of non-fatal myocardial infarction or stroke in patients with and without CKD, and further categorized by CKD stage: stages G1 or G2 [estimated glomerular filtration rate (eGFR) ≥60 ml/min] and A2 (urine albumin to creatinine ratio 30 to <300 mg/g) or A3 (urine albumin to creatinine ratio ≥300 mg/g), stage G3a (eGFR 45 to <60 ml/min/1.73 m2 ) and stage G3b (eGFR 30 to <45 ml/min/1.73 m2 ). We used proportional hazards regression after inverse probability of treatment weighting to compute hazard ratios and 95% confidence intervals.

RESULTS

After accounting for the probability of treatment, patients with T2DM and CKD treated with SGLT-2 inhibitors experienced a 14% lower risk of non-fatal myocardial infarction or stroke (hazard ratio 0.86, 95% confidence interval 0.78-0.94) relative to those treated with GLP-1 receptor agonists.

CONCLUSIONS

Recognizing the potential for residual confounding, selection bias and immortal time bias, commercially insured patients in the United States with T2DM and CKD treated with SGLT-2 inhibitors experienced significantly lower risks of non-fatal myocardial infarction or stroke relative to those treated with GLP-1 receptor agonists.

Efficacy and safety of tirzepatide in people with type 2 diabetes by baseline body mass index: An exploratory subgroup analysis of SURPASS-AP-Combo

AIMS

To assess the efficacy and safety of tirzepatide versus insulin glargine in people with type 2 diabetes (T2D) by baseline body mass index (BMI).

MATERIALS AND METHODS

Participants with T2D from the Phase 3 SURPASS-AP-Combo trial (NCT04093752) were categorized into three BMI subgroups (normal weight [<25 kg/m2 ], overweight [≥25 and <30 kg/m2 ], and obese [≥30 kg/m2 ]) according to World Health Organization criteria. Exploratory outcomes including glycaemic control, body weight, cardiometabolic risk, and safety were compared among three tirzepatide doses (5, 10 or 15 mg) and insulin glargine.

RESULTS

Of 907 participants, 235 (25.9%) had a BMI <25 kg/m2 , 458 (50.5%) a BMI ≥25 to <30 kg/m2 , and 214 (23.6%) a BMI ≥30 kg/m2 at baseline. At Week 40, all tirzepatide doses led to a greater reduction in mean glycated haemoglobin (HbA1c; -2.0% to -2.8% vs. -0.8% to -1.0%, respectively) and percent change in body weight (-5.5% to -10.8% vs. 1.0% to 2.5%, respectively) versus insulin glargine, across the BMI subgroups. Compared with insulin glargine, a higher proportion of tirzepatide-treated participants achieved treatment goals for HbA1c and body weight reduction. Improvements in other cardiometabolic indicators were also observed with tirzepatide across all the BMI subgroups. The safety profile of tirzepatide was similar across all subgroups by BMI. The most frequent adverse events with tirzepatide were gastrointestinal-related events and decreased appetite, with relatively few events leading to treatment discontinuation.

CONCLUSIONS

In participants with T2D, regardless of baseline BMI, treatment with tirzepatide resulted in statistically significant and clinically meaningful glycaemic reductions and body weight reductions compared with insulin glargine, with a safety profile consistent with previous reports.

Effect of Food Consumption on the Pharmacokinetics, Safety, and Tolerability of Once-Daily Orally Administered Orforglipron (LY3502970), a Non-peptide GLP-1 Receptor Agonist

INTRODUCTION

We assessed the effect of the prandial state on the pharmacokinetics, safety, and tolerability of single and multiple doses of orforglipron (LY3502970), an oral, non-peptide glucagon-like peptide 1 receptor agonist (GLP-1 RA), in two studies (A and B).

METHODS

Study A and study B were phase 1, randomized, crossover studies in healthy adults aged 18-65 years and 21-70 years, respectively. Participants received single (3 mg, study A) or multiple (16 mg, study B) oral doses of orforglipron under fasted and fed conditions. Blood samples were collected pre- and postdose to assess area under the concentration-time curve (AUC), maximum observed drug concentration (Cmax), time of Cmax (tmax), and half-life (t1/2) associated with terminal rate constant. AUC and Cmax were analyzed using a linear mixed-effects model. Treatment differences were presented as ratios of geometric least squares means (GLSM). Treatment-emergent adverse events (TEAEs), adverse events of special interest, and serious adverse events were assessed.

RESULTS

Study A included 12 participants (mean age 45.0 years; male 66.7%); study B included 34 participants (mean age 42.8 years; male 88.2%). GLSM AUC and Cmax were lower by 23.7% and 23.2% in study A, and 17.6% and 20.9% in study B, in the fed versus fasted states, respectively. In both studies, t1/2 and median tmax were comparable between fed and fasted states. The majority of TEAEs in both studies were gastrointestinal tract-related conditions. No serious adverse events or deaths were reported in either study.

CONCLUSION

The observed pharmacokinetic differences due to the prandial state are unlikely to contribute to clinically meaningful differences in the efficacy of orforglipron. The safety profile was consistent with the known profiles of other GLP-1 RAs. Given the absence of prandial restrictions, orforglipron may emerge as a convenient oral treatment option for patients with type 2 diabetes or obesity.

TRIAL REGISTRATION

ClinicalTrials.gov identifiers, NCT03929744 and NCT05110794.

The effects of incretin-based therapies on weight reduction and metabolic parameters in children with obesity: A systematic review and meta-analysis

BACKGROUND

Growing evidence indicates that incretin-based therapies (IBTs), glucagon-like peptide-1 receptor agonists (GLP-1 RAs), and dipeptidyl peptidase-4 inhibitors (DPP4is) are effective and safe for treating pediatric obesity patients with or without type 2 diabetes. Therefore, we aimed to perform a systematic review and meta-analysis for updating current evidence.

METHODS

We searched the PubMed, the Cochrane Library, and the EMBASE database for articles published until September 15, 2023, and limited to randomized control trials. The primary outcomes were changed from baseline in weight metrics and the cardiometabolic profile. A random effects model will be used, as high heterogeneity is expected. All analyses were performed using STATA 17.0.

RESULTS

Fifteen trials with a total number of 1286 participants were included in our meta-analysis. Overall, the mean difference in weight change between the IBTs group and the control group was -2.89 kg (95% confidence interval, -5.12 to -0.65, p = 0.011). Additionally, IBTs significantly reduced the HbA1c level and fasting plasma glucose by 0.37% and 6.99 mg/dl, compared with control groups. IBTs showed a little increased risk of GI side effects and hypoglycemia events, but none of the severe hypoglycemia events were occurred in IBTs group.

CONCLUSIONS

Our study results have proved that GLP-1 RAs are safe, acceptable, and effective in weight reduction and sugar control for children with obesity. In addition, DPP-4is seems to have no effect on glycemic control and weight loss in childhood obesity. Further research is needed to confirm these findings, especially in younger children.

Transcranial Irradiation Mitigates Paradoxical Sleep Deprivation Effect in an Age-Dependent Manner: Role of BDNF and GLP-1

The growing prevalence of aged sleep-deprived nations is turning into a pandemic state. Acute sleep deprivation (SD) accompanies aging, changing the hippocampal cellular pattern, neurogenesis pathway expression, and aggravating cognitive deterioration. The present study investigated the ability of Near Infra Red (NIR) light laser to ameliorate cognitive impairment induced by SD in young and senile rats. Wistar rats ≤ 2 months (young) and ≥ 14 months (senile) were sleep-deprived for 72 h with or without transcranial administration of NIR laser of 830 nm. Our results showed that NIR photobiomodulation (PBM) attenuated cognitive deterioration made by SD in young, but not senile rats, while both sleep-deprived young and senile rats exhibited decreased anxiety (mania)-like behavior in response to PBM. NIR PBM had an inhibitory effect on AChE, enhanced the production of ACh, attenuated ROS, and regulated cell apoptosis factors such as Bax and Bcl-2. NIR increased mRNA expression of BDNF and GLP-1 in senile rats, thus facilitating neuronal survival and differentiation. The present findings also revealed that age exerts an additive factor to the cellular assaults produced by SD where hippocampal damages made in 2-month rats were less severe than those of the aged one. In conclusion, NIR PBM seems to promote cellular longevity of senile hippocampal cells by combating ROS, elevating neurotrophic factors, thus improving cognitive performance. The present findings provide NIR as a possible candidate for hippocampal neuronal insults accompanying aging and SD.

Comparison of A1c Reduction, Weight Loss, and Changes in Insulin Requirements With Addition of GLP-1 Agonists vs SGLT-2 Inhibitors in Patients Using Multiple Daily Insulin Injections

Objective: To determine whether Glucagon-Like Peptide 1 (GLP-1) agonists or Sodium Glucose Transporter 2 (SGLT-2) inhibitors result in greater A1c reduction, weight loss, and reduction of insulin requirements in veterans using multiple daily doses of insulin. Methods: This retrospective, single-site, cohort study included patients of VA Eastern Kansas Health Care System with a diagnosis of Type II Diabetes utilizing multiple daily dose insulin and an SGLT-2 inhibitor or GLP-1 agonist. SAS Enterprise Guide was utilized to complete a multivariate analysis of variance to evaluate all outcomes. Key Findings: 150 patients met selection criteria. The GLP-1 group averaged a .65% reduction in A1c compared to a 1.05% reduction in the SGLT-2 group (P = .1397). The Basal insulin dose was reduced by 5.5 units in the GLP-1 group vs 2.45 units in the SGLT-2 group (P = .3132), and 7.12 units vs 8.14 units respectively for short-acting insulin (P = .8170). The resulting weight reduction was 4.1 Kg in the GLP-1 group compared to 3.6 Kg in the SGLT-2 group (P = .6993). Conclusion: The results suggest there is not a statistically significant difference in changes to A1c, insulin requirements, or weight after 1 year of treatment with an SGLT-2 vs GLP-1 in patients using multiple daily insulin injections.

Elucidating the glucose-lowering effect of the bile acid sequestrant sevelamer

AIM

Bile acid sequestrants are cholesterol-lowering drugs, which also improve glycaemic control in people with type 2 diabetes. The mechanism behind the glucose-lowering effect is unknown but has been proposed to be mediated by increased glucagon-like peptide-1 (GLP-1) secretion. Here, we investigated the glucose-lowering effects of sevelamer including any contribution from GLP-1 in people with type 2 diabetes.

MATERIALS AND METHODS

In a randomized, double-blind, placebo-controlled, crossover study, 15 people with type 2 diabetes on metformin monotherapy underwent two 17-day treatment periods with the bile acid sequestrant sevelamer and placebo, respectively, in a randomized order and with an interposed wash-out period of minimum 6 weeks. On days 15 and 17 of each treatment period, participants underwent experimental days with 4-h liquid meal tests and application of concomitant infusion of exendin(9-39)NH2 or saline.

RESULTS

Compared with placebo, sevelamer improved insulin sensitivity (assessed by homeostatic model assessment of insulin resistance) and beta-cell sensitivity to glucose and lowered fasting and postprandial plasma glucose concentrations. In both treatment periods, exendin(9-39)NH2 increased postprandial glucose excursions compared with saline but without absolute or relative difference between the two treatment periods. In contrast, exendin(9-39)NH2 abolished the sevelamer-induced improvement in beta-cell glucose sensitivity.

CONCLUSIONS

The bile acid sequestrant sevelamer improved insulin sensitivity and beta-cell sensitivity to glucose, but using the GLP-1 receptor antagonist exendin(9-39)NH2 we were not able to detect a GLP-1-mediated glucose-lowering effect of sevelamer in individuals with type 2 diabetes. Nevertheless, the sevelamer-induced improvement of beta-cell sensitivity to glucose was shown to be GLP-1-dependent.

GLP-1 response during pregnancy: variations between trimesters and associations with appetite sensations and usual energy intake

Further research is required to understand hormonal regulation of food intake during pregnancy and its association with energy intake. The objectives are to (i) compare postprandial responses of plasma glucagon-like peptide-1 (GLP-1) between trimesters, (ii) compare postprandial appetite sensations between trimesters, and (iii) examine trimester-specific associations between GLP-1 levels, appetite sensations, and usual energy intake. At each trimester, participants (n = 26) consumed a standard test meal following a 12 h fast. Plasma GLP-1 levels were measured by enzyme-linked immunosorbent assay method at fasting and at 30, 60, 120, and 180 min postprandial. A visual analogue scale assessing appetite sensations was completed at fasting and at 15, 30, 45, 60, 90, 120, 150, and 180 min postprandial. Mean energy intake was assessed using three web-based 24 h dietary recalls at each trimester. Lower postprandial GLP-1 responses were observed in the 2nd (p = 0.004) and 3rd trimesters (p < 0.001) compared to the 1st trimester. Greater postprandial sensations of desire to eat, hunger, and prospective food consumption were noted in the 3rd trimester compared to the 1st trimester (p < 0.04, for all). Fasting GLP-1 was negatively associated with fasting appetite sensations (except fullness) at the 2nd trimester (p < 0.02, for all). Postprandially, significant associations were observed for incremental areas under the curve from 0 to 30 min between GLP-1 and fullness at the 2nd (p = 0.01) and 3rd trimesters (p = 0.03). No associations between fasting or postprandial GLP-1 and usual energy intake were observed. Overall, GLP-1 and appetite sensation responses significantly differ between trimesters, but few associations were observed between GLP-1, appetite sensations, and usual energy intake.

Computational modelling of dynamic cAMP responses to GPCR agonists for exploration of GLP-1R ligand effects in pancreatic β-cells and neurons

The glucagon-like peptide-1 receptor (GLP-1R) is a class B G protein-coupled receptor (GPCR) which plays important physiological roles in insulin release and promoting fullness. GLP-1R agonists initiate cellular responses by cyclic AMP (cAMP) pathway signal transduction. Understanding of the potential of GLP-1R agonists in the treatment of type 2 diabetes may be advanced by considering the cAMP dynamics for agonists at GLP-1R in both pancreatic β-cells (important in insulin release) and neurons (important in appetite regulation). Receptor desensitisation in the cAMP pathway is known to be an important regulatory mechanism, with different ligands differentially promoting G protein activation and desensitisation. Here, we use mathematical modelling to quantify and understand experimentally obtained cAMP timecourses for two GLP-1R agonists, exendin-F1 (ExF1) and exendin-D3 (ExD3), which give markedly different signals in β-cells and neurons. We formulate an ordinary differential equation (ODE) model for the dynamics of cAMP signalling in response to G protein-coupled receptor (GPCR) ligands, encompassing ligand binding, receptor activation, G protein activation, desensitisation and second messenger generation. We validate our model initially by fitting to timecourse data for HEK293 cells, then proceed to parameterise the model for β-cells and neurons. Through numerical simulation and sensitivity studies, our analysis adds support to the hypothesis that ExF1 offers more potential glucose regulation benefit than ExD3 over long timescales via signalling in pancreatic β-cells, but that there is little difference between the two ligands in the potential appetite suppression effects offered via long-time signalling in neurons on the same timescales.

The bile-gut axis and metabolic consequences of cholecystectomy

Cholelithiasis and cholecystitis affect individuals of all ages and are often treated by surgical removal of the gallbladder (cholecystectomy), which is considered a safe, low-risk procedure. Nevertheless, recent findings show that bile and its regulated storage and excretion may have important metabolic effects and that cholecystectomy is associated with several metabolic diseases postoperatively. Bile acids have long been known as emulsifiers essential to the assimilation of lipids and absorption of lipid-soluble vitamins, but more recently, they have also been reported to act as metabolic signaling agents. The nuclear receptor, farnesoid X receptor (FXR), and the G protein-coupled membrane receptor, Takeda G protein-coupled receptor 5 (TGR5), are specific to bile acids. Through activation of these receptors, bile acids control numerous metabolic functions. Cholecystectomy affects the storage and excretion of bile acids, which in turn may influence the activation of FXR and TGR5 and their effects on metabolism including processes leading to metabolic conditions such as metabolic dysfunction-associated steatotic liver disease and metabolic syndrome. Here, with the aim of elucidating mechanisms behind cholecystectomy-associated dysmetabolism, we review studies potentially linking cholecystectomy and bile acid-mediated metabolic effects and discuss possible pathophysiological mechanisms behind cholecystectomy-associated dysmetabolism.

Colesevelam has no acute effect on postprandial GLP-1 levels but abolishes gallbladder refilling

OBJECTIVE

Colesevelam, a bile acid sequestrant approved for the treatment of hypercholesterolaemia, improves glycaemic control in type 2 diabetes. We hypothesised that single-dose colesevelam increases postprandial GLP-1 secretion, thus, reducing postprandial glucose excursions in individuals with type 2 diabetes. Further, we explored the effects of single-dose colesevelam on ultrasonography-assessed postprandial gallbladder motility, paracetamol absorption (proxy for gastric emptying), and circulating factors known to affect gallbladder motility.

METHODS

In a randomised, double-blind, placebo-controlled crossover study, 12 individuals with type 2 diabetes (mean ± SD: age 61 ± 8.8 years; body mass index 29.8 ± 3.0 kg/m2) were subjected to 4 mixed meal tests on separate days; 2 with orally administered colesevelam (3.75 g) and 2 with placebo, with intravenous infusion of the GLP-1 receptor antagonist exendin(9-39)NH2 or saline.

RESULTS

Single-dose colesevelam had no effect on postprandial concentrations of glucose (P = .786), C-peptide (P = .440), or GLP-1 (P = .729), and exendin(9-39)NH2 administration revealed no GLP-1-mediated effects of colesevelam. Colesevelam did not affect gallbladder emptying but abolished gallbladder refilling (P = .001), increased postprandial cholecystokinin (CCK) secretion (P = .010), and decreased postprandial serum concentrations of fibroblast growth factor 19 (FGF19) (P = .035) and bile acids (P = .043).

CONCLUSION

Single-dose colesevelam had no effect on postprandial GLP-1 responses or glucose tolerance but disrupted postprandial gallbladder refilling by increasing CCK secretion and reducing circulating concentrations of FGF19 and bile acids. These findings leave the antidiabetic actions of colesevelam unresolved but provide mechanistic insights into its effect on gallbladder motility.

Neurocircuitry underlying the actions of glucagon-like peptide 1 and peptide YY3-36 in the suppression of food, drug-seeking, and anxiogenesis

Obesity is a critical health condition worldwide that increases the risks of comorbid chronic diseases, but it can be managed with weight loss. However, conventional interventions relying on diet and exercise are inadequate for achieving and maintaining weight loss, thus there is significant market interest for pharmaceutical anti-obesity agents. For decades, receptor agonists for the gut peptide glucagon-like peptide 1 (GLP-1) featured prominently in anti-obesity medications by suppressing appetite and food reward to elicit rapid weight loss. As the neurocircuitry underlying food motivation overlaps with that for drugs of abuse, GLP-1 receptor agonism has also been shown to decrease substance use and relapse, thus its therapeutic potential may extend beyond weight management to treat addictions. However, as prolonged use of anti-obesity drugs may increase the risk of mood-related disorders like anxiety and depression, and individuals taking GLP-1-based medication commonly report feeling demotivated, the long-term safety of such drugs is an ongoing concern. Interestingly, current research now focuses on dual agonist approaches that include GLP-1 receptor agonism to enable synergistic effects on weight loss or associated functions. GLP-1 is secreted from the same intestinal cells as the anorectic gut peptide, Peptide YY3-36 (PYY3-36), thus this review assessed the therapeutic potential and underlying neural circuits targeted by PYY3-36 when administered independently or in combination with GLP-1 to curb the appetite for food or drugs of abuse like opiates, alcohol, and nicotine. Additionally, we also reviewed animal and human studies to assess the impact, if any, for GLP-1 and/or PYY3-36 on mood-related behaviors in relation to anxiety and depression. As dual agonists targeting GLP-1 and PYY3-36 may produce synergistic effects, they can be effective at lower doses and offer an alternative approach for therapeutic benefits while mitigating undesirable side effects.

GLP-1 Receptor Agonists: A New Treatment in Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Recent data highlight similarities between neurodegenerative diseases, including PD and type 2 diabetes mellitus (T2DM), suggesting a crucial interplay between the gut-brain axis. Glucagon-like peptide-1 receptor (GLP-1R) agonists, known for their use in T2DM treatment, are currently extensively studied as novel PD modifying agents. For this narrative review article, we searched PubMed and Scopus databases for peer-reviewed research, review articles and clinical trials regarding GLP-1R agonists and PD published in the English language with no time restrictions. We also screened the references of the selected articles for possible additional articles in order to include most of the key recent evidence. Many data on animal models and preclinical studies show that GLP1-R agonists can restore dopamine levels, inhibit dopaminergic loss, attenuate neuronal degeneration and alleviate motor and non-motor features of PD. Evidence from clinical studies is also very promising, enhancing the possibility of adding GLP1-R agonists to the current armamentarium of drugs available for PD treatment.

Immunomodulation and inflammation: Role of GLP-1R and GIPR expressing cells within the gut

Glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are peptide hormones produced by enteroendocrine cells in the small intestine. Despite being produced in the gut, the leveraging of their role in potentiating glucose-stimulated insulin secretion, also known as the incretin effect, has distracted from discernment of direct intestinal signaling circuits. Both preclinical and clinical evidence have highlighted a role for the incretins in inflammation. In this review, we highlight the discoveries of GLP-1 receptor (GLP-1R)+ natural (TCRαβ and TCRγδ) and induced (TCRαβ+CD4+ cells and TCRαβ+CD8αβ+) intraepithelial lymphocytes. Both endogenous signaling and pharmacological activation of GLP-1R impact local and systemic inflammation, the gut microbiota, whole-body metabolism, as well as the control of GLP-1 bioavailability. While GIPR signaling has been documented to impact hematopoiesis, the impact of these bone marrow-derived cells in gut immunology is not well understood. We uncover gaps in the literature of the evaluation of the impact of sex in these GLP-1R and GIP receptor (GIPR) signaling circuits and provide speculations of the maintenance roles these hormones play within the gut in the fasting-refeeding cycles. GLP-1R agonists and GLP-1R/GIPR agonists are widely used as treatments for diabetes and weight loss, respectively; however, their impact on gut homeostasis has not been fully explored. Advancing our understanding of the roles of GLP-1R and GIPR signaling within the gut at homeostasis as well as metabolic and inflammatory diseases may provide targets to improve disease management.

New Lessons from the gut: Studies of the role of gut peptides in weight loss and diabetes resolution after gastric bypass and sleeve gastrectomy

It has been known since 2005 that the secretion of several gut hormones changes radically after gastric bypass operations and, although more moderately, after sleeve gastrectomy but not after gastric banding. It has therefore been speculated that increased secretion of particularly GLP-1 and Peptide YY (PYY), which both inhibit appetite and food intake, may be involved in the weight loss effects of surgery and for improvements in glucose tolerance. Experiments involving inhibition of hormone secretion with somatostatin, blockade of their actions with antagonists, or blockade of hormone formation/activation support this notion. However, differences between results of bypass and sleeve operations indicate that distinct mechanisms may also be involved. Although the reductions in ghrelin secretion after sleeve gastrectomy would seem to provide an obvious explanation, experiments with restoration of ghrelin levels pointed towards effects on insulin secretion and glucose tolerance rather than on food intake. It seems clear that changes in GLP-1 secretion are important for insulin secretion after bypass and appear to be responsible for postbariatric hypoglycemia in glucose-tolerant individuals; however, with time the improvements in insulin sensitivity, which in turn are secondary to the weight loss, may be more important. Changes in bile acid metabolism do not seem to be of particular importance in humans.

Expression of glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide in the rat submandibular gland is influenced by pre- and post-natal high-fat diet exposure

Background: Incretins, i.e., glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) promote insulin secretion to reduce postprandial blood sugar. Previous studies found incretins in the salivary glands. However, the role of GLP-1 and GIP in the submandibular gland (SMG) is unclear. This study investigates the effects of a high-fat diet (HFD) on the expression of GLP-1 and GIP throughout the development of rat SMG. Methods: Pregnant 11-week-old Wistar rats were divided into two groups: those fed on a standard diet (n = 5) and those fed on a HFD (n = 5). From day 7 of pregnancy and throughout the lactation period, all the rats were fed on either a chow diet or HFD. The newborns were divided into four subgroups (n = 6): standard diet males (SM), HFD males (HM), standard diet females (SF), and HFD females (HF). The SMGs of 3- and 10-week-old rats from each subgroup were collected under general anesthesia. Moreover, body weight, food intake, and fasting blood sugar were measured. The mRNA expression of GLP-1 and GIP was quantified, and the localization was observed using immunohistochemistry (p < 0.05). Results: GLP-1 mRNA expression was statistically significantly more upregulated in HM than in HF at 3 weeks. Moreover, GLP-1 mRNA expression was significantly higher in HM than in both SM and HF at 10 weeks. Although a decreasing trend was observed in GIP mRNA expression in both 3- and 10-week-old rats fed on a HFD, a significant difference between HM and SM only occurred at 3 weeks. Furthermore, the GIP mRNA expression of HM was lower than that of HF at 10 weeks. Immunohistochemical staining revealed GLP-1 and GIP expression mainly in the SMG duct system. Moreover, vacuolated cytoplasm in the duct was observed in rats fed on a HFD. Conclusion: Exposure to HFD during pre- and post-natal periods increased GLP-1 mRNA expression in the SMGs of male rats. However, GIP expression decreased following the HFD in male newborns. Furthermore, a decreasing trend of GIP mRNA expression was observed in male newborns after HFD feeding. Sex influenced incretin hormones secretion and obesity-related conditions. HFD during pre- and post-natal periods reprograms the epigenome, contributing to subsequent disease development.

Regulation of energy metabolism through central GIPR signaling

In recent years, significant progress has been made to pharmacologically combat the obesity pandemic, particularly with regard to biochemically tailored drugs that simultaneously target the receptors for glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic polypeptide (GIP). But while the pharmacological benefits of GLP-1 receptor (GLP-1R) agonism are widely acknowledged, the role of the GIP system in regulating systems metabolism remains controversial. When given in adjunct to GLP-1R agonism, both agonism and antagonism of the GIP receptor (GIPR) improves metabolic outcome in preclinical and clinical studies, and despite persistent concerns about its potential obesogenic nature, there is accumulating evidence indicating that GIP has beneficial metabolic effects via central GIPR agonism. Nonetheless, despite growing recognition of the GIP system as a valuable pharmacological target, there remains great uncertainty as to where and how GIP acts in the brain to regulate metabolism, and how GIPR agonism may differ from GIPR antagonism in control of energy metabolism. In this review we highlight current knowledge on the central action of GIP, and discuss open questions related to its multifaceted biology in the brain and the periphery.

The Regulation Role of the Gut-Islets Axis in Diabetes

The gut-islets axis is an important endocrine signaling axis that regulates the function of islets by modulating the gut micro-environment and its endocrine metabolism. The discovery of intestinal hormones, such as GLP-1 and GIP, has established a preliminary link between the gut and the islet, paving the way for the development of GLP-1 receptor agonists based on the regulation theory of the gut-islets axis for diabetes treatment. This discovery has created a new paradigm for diabetes management and rapidly made the regulation theory of the gut-islets axis a focal point of research attention. Recent years, with in-depth study on gut microbiota and the discovery of intestinal-derived extracellular vesicles, the concept of gut endocrine and the regulation theory of the gut-islets axis have been further expanded and updated, offering tremendous research opportunities. The gut-islets axis refers to the complex interplay between the gut and the islet, which plays a crucial role in regulating glucose homeostasis and maintaining metabolic health. The axis involves various components, including gut microbiota, intestinal hormones, amino acids and ACE2, which contribute to the communication and coordination between the gut and the islet.

GLP-1R signaling modulates colonic energy metabolism, goblet cell number and survival in the absence of gut microbiota

OBJECTIVES

Gut microbiota increases energy availability through fermentation of dietary fibers to short-chain fatty acids in conventionally raised mice. Energy deficiency in germ-free (GF) mice increases glucagon-like peptide-1 (GLP-1) levels, which slows intestinal transit. To further analyze the role of GLP-1-mediated signaling in this model of energy deficiency, we re-derived mice lacking GLP-1 receptor (GLP-1R KO) as GF.

METHODS

GLP-1R KO mice were rederived as GF through hysterectomy and monitored for 30 weeks. Mice were subjected to rescue experiments either through feeding an energy-rich diet or colonization with a normal cecal microbiota. Histology and intestinal function were assessed at different ages. Intestinal organoids were assessed to investigate stemness.

RESULTS

Unexpectedly, 25% of GF GLP-1R KO mice died before 20 weeks of age, associated with enlarged ceca, increased cecal water content, increased colonic expression of apical ion transporters, reduced number of goblet cells and loss of colonic epithelial integrity. Colonocytes from GLP-1R KO mice were energy-deprived and exhibited increased ER-stress; mitochondrial fragmentation, increased oxygen levels and loss of stemness. Restoring colonic energy levels either by feeding a Western-style diet or colonization with a normal gut microbiota normalized gut phenotypes and prevented lethality.

CONCLUSIONS

Our findings reveal a heretofore unrecognized role for GLP-1R signaling in the maintenance of colonic physiology and survival during energy deprivation.

The effects of Fc fusion protein glucagon-like peptide-1 and glucagon dual receptor agonist with different receptor selectivity in vivo studies

BACKGROUND

Glucagon-like peptide-1 (GLP-1)/glucagon (GCG) dual receptor agonists with different receptor selectivity are under investigation and have shown significant improvement in both weight loss and glycemic control, but the optimal potency ratio between the two receptors to balance efficacy and safety remains unclear.

EXPERIMENTAL APPROACH

We designed and constructed several dual receptor agonists with different receptor potency ratios using Fc fusion protein technology. The long-term effects of the candidates on body weight and metabolic dysfunction-associated steatotic liver disease (MASLD) were evaluated in diet-induced obese (DIO) model mice, high-fat diet (HFD)-ob/ob mice and AMLN diet-induced MASLD mice. Repeat dose toxicity assays were performed to investigate the safety profile of the candidate (HEC-C070) in Sprague Dawley (SD) rats.

KEY RESULTS

The high GCG receptor (GCGR) selectivity of HEC-C046 makes it more prominent than other compounds for weight loss and most MASLD parameters but may lead to safety concerns. The weight change of HEC-C052 with the lowest GCG agonism was inferior to that of selective GLP-1 receptor agonist (GLP-1RA) semaglutide in DIO model mice. The GLP-1R selectivity of HEC-C070 with moderate GCG agonism has a significant effect on weight loss and liver function in obese mice, and its lowest observed adverse effect level (LOAEL) was 30 nmol/kg in the repeat dose toxicity study.

CONCLUSION

We compared the potential of the Fc fusion protein GLP-1/GCG dual receptor agonists with different receptor selectivity to provide the setting for future GLP-1/GCG dual receptor agonists to treat obesity and MASLD.

Sympathetic nerve-enteroendocrine L cell communication modulates GLP-1 release, brain glucose utilization, and cognitive function

Glucose homeostasis is controlled by brain-gut communications. Yet our understanding of the neuron-gut interface in the glucoregulatory system remains incomplete. Here, we find that sympathetic nerves elevate postprandial blood glucose but restrict brain glucose utilization by repressing the release of glucagon-like peptide-1 (GLP-1) from enteroendocrine L cells. Sympathetic nerves are in close apposition with the L cells. Importantly, sympathetic denervation or intestinal deletion of the adrenergic receptor α2 (Adra2a) augments postprandial GLP-1 secretion, leading to reduced blood glucose levels and increased brain glucose uptake. Conversely, sympathetic activation shows the opposite effects. At the cellular level, adrenergic signaling suppresses calcium flux to limit GLP-1 secretion upon sugar ingestion. Consequently, abrogation of adrenergic signal results in a significant improvement in learning and memory ability. Together, our results reveal a sympathetic nerve-enteroendocrine unit in constraining GLP-1 secretion, thus providing a therapeutic nexus of mobilizing endogenous GLP-1 for glucose management and cognitive improvement.

Efficacy and Safety of Tirzepatide in Patients with Type 2 Diabetes: Analysis of SURPASS-AP-Combo by Different Subgroups

INTRODUCTION

Tirzepatide is a novel glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptor agonist. In the SURPASS-AP-Combo trial, once-weekly tirzepatide was associated with improved glycemic control and weight loss versus insulin glargine and was generally well tolerated in an Asia-Pacific, predominately Chinese, population with type 2 diabetes (T2D). This post hoc subgroup analysis of SURPASS-AP-Combo assessed the potential influence of patient baseline characteristics on the efficacy and safety of tirzepatide.

METHODS

Changes from baseline to week 40 in HbA1c, body weight, fasting serum glucose (FSG), and daily glucose average from self-measured blood glucose profiles were analyzed by potential influential factors including age (< 65, ≥ 65 years), sex, baseline HbA1c (≤ 8.5, > 8.5%), body mass index (BMI) (< 25, ≥ 25 kg/m2), body weight (< 75, ≥ 75 kg), duration of diabetes (< 10, ≥ 10 years), and concomitant oral antihyperglycemic medications (metformin, metformin plus sulphonylurea). Gastrointestinal adverse events and hypoglycemia were also evaluated.

RESULTS

At week 40, all tirzepatide doses were associated with reduced HbA1c, body weight, FSG, and daily glucose average from baseline in all subgroups. Greater HbA1c reductions were achieved in patients with higher baseline HbA1c across all tirzepatide doses, higher body weight with 10 mg and younger age with 15 mg tirzepatide. Greater reductions in body weight were observed in patients with higher body weight across all tirzepatide doses, lower baseline HbA1c with 5 mg and higher BMI with 5 mg tirzepatide.

CONCLUSIONS

In this post hoc analysis, tirzepatide was associated with reduced blood glucose and body weight in a predominantly Chinese population with T2D across different subgroups, consistent with previous reports for tirzepatide.

CLINICAL TRIAL REGISTRATION

NCT04093752.

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.

Loss of GIPR in LEPR cells impairs glucose control by GIP and GIP:GLP-1 co-agonism without affecting body weight and food intake in mice

OBJECTIVE

The glucose-dependent insulinotropic polypeptide (GIP) decreases body weight via central GIP receptor (GIPR) signaling, but the underlying mechanisms remain largely unknown. Here, we assessed whether GIP regulates body weight and glucose control via GIPR signaling in cells that express the leptin receptor (Lepr).

METHODS

Hypothalamic, hindbrain, and pancreatic co-expression of Gipr and Lepr was assessed using single cell RNAseq analysis. Mice with deletion of Gipr in Lepr cells were generated and metabolically characterized for alterations in diet-induced obesity (DIO), glucose control and leptin sensitivity. Long-acting single- and dual-agonists at GIPR and GLP-1R were further used to assess drug effects on energy and glucose metabolism in DIO wildtype (WT) and Lepr-Gipr knock-out (KO) mice.

RESULTS

Gipr and Lepr show strong co-expression in the pancreas, but not in the hypothalamus and hindbrain. DIO Lepr-Gipr KO mice are indistinguishable from WT controls related to body weight, food intake and diet-induced leptin resistance. Acyl-GIP and the GIPR:GLP-1R co-agonist MAR709 remain fully efficacious to decrease body weight and food intake in DIO Lepr-Gipr KO mice. Consistent with the demonstration that Gipr and Lepr highly co-localize in the endocrine pancreas, including the β-cells, we find the superior glycemic effect of GIPR:GLP-1R co-agonism over single GLP-1R agonism to vanish in Lepr-Gipr KO mice.

CONCLUSIONS

GIPR signaling in cells/neurons that express the leptin receptor is not implicated in the control of body weight or food intake, but is of crucial importance for the superior glycemic effects of GIPR:GLP-1R co-agonism relative to single GLP-1R agonism.

Incretin and Glucagon Receptor Polypharmacology in Chronic Kidney Disease

Chronic kidney disease (CKD) is a debilitating condition associated with significant morbidity and mortality. In recent years, the kidney effects of incretin-based therapies, particularly glucagon-like peptide-1 receptor agonists (GLP-1RAs), have garnered substantial interest in the management of type 2 diabetes (T2D) and obesity. This review delves into the intricate interactions between the kidney, GLP-1RAs, and glucagon, shedding light on their mechanisms of action and potential kidney benefits. Both GLP-1 and glucagon, known for their opposing roles in regulating glucose homeostasis, improve systemic risk factors affecting the kidney, including adiposity, inflammation, oxidative stress, and endothelial function. Additionally, these hormones and their pharmaceutical mimetics may have direct impact on the kidney. Clinical studies have provided evidence that incretins, including those incorporating glucagon receptor agonism, are likely to exhibit improved kidney outcomes. Although further research is necessary, receptor polypharmacology holds promise for preserving kidney function through eliciting vasodilatory effects, influence on volume and electrolyte handling, and improvement of systemic risk factors.

Fasting and post prandial pancreatic and enteroendocrine hormone levels in obese and non-obese participants

Circulating insulin levels are known to be increased in people with higher body mass index (BMI) due to effects of adiposity on insulin resistance, whilst gut hormones have a more complex relationship, with fasting peptideYY (PYY) reported to be inversely related to BMI. This study aimed to further explore fasting and post prandial pancreatic and gut hormone concentrations in plasma samples from obese and non-obese participants. Participants with healthy BMI (n=15), overweight BMI (n=29) and obesity (n=161) had samples taken fasting and 30 min post mixed liquid meal for analysis of glucagon-like peptide-1 (GLP-1), PYY, glucose-dependent insulinotropic polypeptide (GIP), insulin and glucagon. Data visualiation used linear discriminant analysis for dimensionality reduction, to visualise the data and assess scaling of each hormone. Fasting levels of insulin, GIP and PYY were shown to be key classifiers between the 3 groups on ANCOVA analysis, with an observation of increased GIP levels in overweight, but not obese participants. In non-obese subjects, fasting GIP, PYY and insulin correlated with BMI, whereas in subjects with obesity only the pancreatic hormones glucagon and insulin correlated with BMI. Concentrations of total GLP-1 in the fasting state correlated strongly with glucagon levels, highlighting potential assay cross-reactivities. The study, which included a relatively large number of subjects with severe obesity, supported previous evidence of BMI correlating negatively with fasting PYY and positively with fasting insulin. The observation of increased fasting GIP levels in overweight but not obese participants deserves further validation and mechanistic investigation.

Timosaponin A3 Induces Anti-Obesity and Anti-Diabetic Effects In Vitro and In Vivo

Obesity is a serious global health challenge, closely associated with numerous chronic conditions including type 2 diabetes. Anemarrhena asphodeloides Bunge (AA) known as Jimo has been used to address conditions associated with pathogenic heat such as wasting-thirst in Korean Medicine. Timosaponin A3 (TA3), a natural compound extracted from AA, has demonstrated potential therapeutic effects in various disease models. However, its effects on diabetes and obesity remain largely unexplored. We investigated the anti-obesity and anti-diabetic properties of TA3 using in vitro and in vivo models. TA3 treatment in NCI-H716 cells stimulated the secretion of glucagon-like peptide 1 (GLP-1) through the activation of phosphorylation of protein kinase A catalytic subunit (PKAc) and 5'-AMP-activated protein kinase (AMPK). In 3T3-L1 adipocytes, TA3 effectively inhibited lipid accumulation by regulating adipogenesis and lipogenesis. In a high-fat diet (HFD)-induced mice model, TA3 administration significantly reduced body weight gain and food intake. Furthermore, TA3 improved glucose tolerance, lipid profiles, and mitigated hepatic steatosis in HFD-fed mice. Histological analysis revealed that TA3 reduced the size of white adipocytes and inhibited adipose tissue generation. Notably, TA3 downregulated the expression of lipogenic factor, including fatty-acid synthase (FAS) and sterol regulatory element-binding protein 1c (SREBP1c), emphasizing its potential as an anti-obesity agent. These findings revealed that TA3 may be efficiently used as a natural compound for tackling obesity, diabetes, and associated metabolic disorders, providing a novel approach for therapeutic intervention.

Expression of the GCG gene and secretion of active glucagon-like peptide-1 varies along the length of intestinal tract in horses

BACKGROUND

Active glucagon-like peptide-1 (aGLP-1) has been implicated in the pathogenesis of equine insulin dysregulation (ID), but its role is unclear. Cleavage of proglucagon (coded by the GCG gene) produces aGLP-1 in enteral L cells.

OBJECTIVES

The aim in vivo was to examine the sequence of the exons of GCG in horses with and without ID, where aGLP-1 was higher in the group with ID. The aims in vitro were to identify and quantify the expression of GCG in the equine intestine (as a marker of L cells) and determine intestinal secretion of aGLP-1.

STUDY DESIGN

Genomic studies were case-control studies. Expression and secretion studies in vitro were cross-sectional.

METHODS

The GCG gene sequence of the exons was determined using a hybridisation capture protocol. Expression and quantification of GCG in samples of stomach duodenum, jejunum, ileum, caecum and ascending and descending colon was achieved with droplet digital PCR. For secretory studies tissue explants were incubated with 12 mM glucose and aGLP-1 secretion was measured with an ELISA.

RESULTS

Although the median [IQR] post-prandial aGLP-1 concentrations were higher (p = 0.03) in animals with ID (10.2 [8.79-15.5]), compared with healthy animals (8.47 [6.12-11.7]), there was 100% pairwise identity of the exons of the GCG sequence for the cohort. The mRNA concentrations of GCG and secretion of aGLP-1 differed (p < 0.001) throughout the intestine.

MAIN LIMITATIONS

Only the exons of the GCG gene were sequenced and breeds were not compared. The horses used for the study in vitro were not assessed for ID and different horses were used for the small, and large, intestinal studies.

CONCLUSIONS

Differences in post-prandial aGLP-1 concentration were not due to a variant in the exons of the GCG gene sequence in this cohort. Both the large and small intestine are sites of GLP-1 secretion.

Weight loss and treatment patterns in a real-world population of adults receiving liraglutide 3.0 mg for weight management in routine clinical practice in Switzerland (ADDRESS study)

AIM

To assess weight loss associated with liraglutide 3.0 mg treatment in individuals with obesity (body mass index [BMI] ≥30 kg/m2 ) or overweight (BMI > 27 to <30 kg/m2 ) in a reimbursed, real-world setting in Switzerland.

MATERIALS AND METHODS

ADDRESS was a non-comparative, multicentre, retrospective exposure cohort study in Switzerland, examining weight loss in individuals with obesity or overweight whose treatment was reimbursed (divided into BMI subgroups) or non-reimbursed. The primary outcomes were proportions of participants in the reimbursed cohort achieving predefined weight loss targets with liraglutide 3.0 mg at Week 16 (≥5% and ≥7% for the lower BMI [28 to <35 kg/m2 with weight-related comorbidities] and higher BMI [≥35 kg/m2 ] subgroups, respectively) and Month 10 (additional ≥5% from Week 16; per Swiss reimbursement criteria).

RESULTS

The full analysis set comprised 258 individuals (195 reimbursed; 63 non-reimbursed). In the reimbursed cohort, 139 individuals (71.3%) achieved their weight loss targets at Week 16. Of individuals who met the Week-16 criteria, 43.2% attained an additional 5% weight loss at Month 10. In 162 individuals for whom data were recorded at Month 10, the mean (standard deviation) relative weight loss from baseline to Month 10 was -12.4% (6.4%).

CONCLUSIONS

Although reimbursement criteria may be difficult to achieve, particularly the additional weight loss of 5% from Week 16 to Month 10, a clinically relevant overall weight loss from baseline to Month 10 was shown in most individuals with obesity or overweight who received liraglutide 3.0 mg.

Effect of Teneligliptin 20 mg Twice Daily on Glucagon-Like Peptide-1 Levels and Its Influence on Non-Glycemic Components in Non-Diabetic Obese Individuals

Background and Aims: Teneligliptin is an oral antidiabetic agent, it can persevere glucagon-like peptide-1 (GLP-1) by inhibiting dipeptidyl peptidase enzyme. In addition, it has rare incidence of hypoglycemia. Hence, this study aimed to test the effect of teneligliptin 20 mg twice daily along with low carbohydrate diet and physical exercise on change of body weight and insulin resistance in nondiabetic obese subjects. Materials and Methods: It is a prospective, randomized, double-blind, placebo-controlled, parallel group study carried out at outpatient department of an endocrinology hospital over the period of 48 weeks. Teneligliptin 20 mg twice daily 30 min before food (low carbohydrate diet [LCD]) with regular physical exercise, and control group was kept with placebo twice daily 30 min before food LCD with regular physical exercise. This study was registered in clinical trial registry of India [CTRI/2020/02/023329]. Results: A total of 150 nondiabetic obese subjects were randomized into test (n = 75) and control groups (n = 75). At the end of 48 weeks there was significant improvement in GLP-1, simplified nutrition assessment questionnaire (SNAQ) score, homeostasis model assessment of insulin resistance (HOMA-IR), triglycerides (TG), and body weight. The mean difference and 95% confidence interval of GLP-1 (pg/mL) was 76.42 (44.42-148.41) (P = 0.37); SNAQ score, -1.64 (-2.48 to -0.81) (P = 0.000); HOMA-IR, -0.9 (-0.59 to -0.38) (P = 0.000); TG (mg/dL) -29.37 (-44.46 to -14.07) (P = 0.000); reduction of body weight (kilograms) -3.09 (-6.11 to -0.07) (P = 0.043). Conclusion: Findings of this study reveals that teneligliptin-treated group showed significant improvement in GLP-1 levels, reduced insulin resistance, body weight, TG, appetite, and metabolic syndrome. Teneligliptin is well tolerated, except in upper respiratory tract infections. CTR number: CTRI/2020/02/023329.

GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of mouse and human pancreatic islet glucagon secretion

AIMS/HYPOTHESIS

Diabetes mellitus is associated with impaired insulin secretion, often aggravated by oversecretion of glucagon. Therapeutic interventions should ideally correct both defects. Glucagon-like peptide 1 (GLP-1) has this capability but exactly how it exerts its glucagonostatic effect remains obscure. Following its release GLP-1 is rapidly degraded from GLP-1(7-36) to GLP-1(9-36). We hypothesised that the metabolite GLP-1(9-36) (previously believed to be biologically inactive) exerts a direct inhibitory effect on glucagon secretion and that this mechanism becomes impaired in diabetes.

METHODS

We used a combination of glucagon secretion measurements in mouse and human islets (including islets from donors with type 2 diabetes), total internal reflection fluorescence microscopy imaging of secretory granule dynamics, recordings of cytoplasmic Ca2+ and measurements of protein kinase A activity, immunocytochemistry, in vivo physiology and GTP-binding protein dissociation studies to explore how GLP-1 exerts its inhibitory effect on glucagon secretion and the role of the metabolite GLP-1(9-36).

RESULTS

GLP-1(7-36) inhibited glucagon secretion in isolated islets with an IC50 of 2.5 pmol/l. The effect was particularly strong at low glucose concentrations. The degradation product GLP-1(9-36) shared this capacity. GLP-1(9-36) retained its glucagonostatic effects after genetic/pharmacological inactivation of the GLP-1 receptor. GLP-1(9-36) also potently inhibited glucagon secretion evoked by β-adrenergic stimulation, amino acids and membrane depolarisation. In islet alpha cells, GLP-1(9-36) led to inhibition of Ca2+ entry via voltage-gated Ca2+ channels sensitive to ω-agatoxin, with consequential pertussis-toxin-sensitive depletion of the docked pool of secretory granules, effects that were prevented by the glucagon receptor antagonists REMD2.59 and L-168049. The capacity of GLP-1(9-36) to inhibit glucagon secretion and reduce the number of docked granules was lost in alpha cells from human donors with type 2 diabetes. In vivo, high exogenous concentrations of GLP-1(9-36) (>100 pmol/l) resulted in a small (30%) lowering of circulating glucagon during insulin-induced hypoglycaemia. This effect was abolished by REMD2.59, which promptly increased circulating glucagon by >225% (adjusted for the change in plasma glucose) without affecting pancreatic glucagon content.

CONCLUSIONS/INTERPRETATION

We conclude that the GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of glucagon secretion. We propose that the increase in circulating glucagon observed following genetic/pharmacological inactivation of glucagon signalling in mice and in people with type 2 diabetes reflects the removal of GLP-1(9-36)'s glucagonostatic action.