Glucagon-like Peptide-1 Receptor Blockade Research Articles

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

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are increasingly used to treat type 2 diabetes and obesity. Albeit cardiovascular outcomes generally improve, treatment with GLP-1 RAs is associated with increased heart rate, the mechanism of which is unclear. We employed a large animal model, the female landrace pig, and used multiple in-vivo and ex-vivo approaches including pharmacological challenges, electrophysiology and high-resolution mass spectrometry to explore how GLP-1 elicits an increase in heart rate. In anaesthetized pigs, neither cervical vagotomy, adrenergic blockers (alpha, beta or combined alpha-beta blockade), ganglionic blockade (hexamethonium) nor inhibition of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (ivabradine) abolished the marked chronotropic effect of GLP-1. GLP-1 administration to isolated perfused pig hearts also increased heart rate, which was abolished by GLP-1 receptor blockade. Electrophysiological characterization of GLP-1 effects in vivo and in isolated perfused hearts localized electrical modulation to the atria and conduction system. In isolated sinus nodes, GLP-1 administration shortened action potential cycle length of pacemaker cells and shifted the site of earliest activation. The effect was independent of HCN blockade. Collectively, these data support a direct effect of GLP-1 on GLP-1 receptors within the heart. Consistently, single nucleus RNA sequencing (snRNAseq) showed GLP-1 receptor expression in porcine pacemaker cells. Quantitative phosphoproteomics analyses of sinus node samples revealed that GLP-1 administration leads to phosphorylation changes of calcium cycling proteins of the sarcoplasmic reticulum, known to regulate heart rate. GLP-1 has direct chronotropic effects on the heart mediated by GLP-1 receptors in pacemaker cells of the sinus node, inducing changes in action potential morphology and the leading pacemaker site through a calcium signaling response characterized by PKA-dependent phosphorylation of Ca2+ cycling proteins involved in pace making. Targeting the pacemaker calcium clock may be a strategy to lower heart rate in GLP-1 RA recipients.

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.

Differential effect of endogenous glucagon-like peptide-1 on prandial glucose counterregulatory response to hypoglycaemia in humans with and without bariatric surgery.

To determine the effect of endogenous glucagon-like peptide 1 (GLP-1) on prandial counterregulatory response to hypoglycaemia after gastric bypass (GB). Glucose fluxes, and islet-cell and gut hormone responses before and after mixed-meal ingestion, were compared during a hyperinsulinaemic-hypoglycaemic (~3.2 mmol/L) clamp with and without a GLP-1 receptor (GLP-1R) antagonist exendin-(9-39) infusion in non-diabetic patients who had previously undergone GB compared to matched participants who had previously undergone sleeve gastrectomy (SG) and non-surgical controls. Exendin-(9-39) infusion raised prandial endogenous glucose production (EGP) response to insulin-induced hypoglycaemia in the GB group but had no consistent effect on EGP response among the SG group or non-surgical controls (p < 0.05 for interaction). The rates of systemic appearance of ingested glucose or prandial glucose utilization did not differ among the three groups or between studies with and without exendin-(9-39) infusion. Blockade of GLP-1R had no effect on insulin secretion or insulin action but enhanced prandial glucagon in all three groups. These results indicate that impaired post-meal glucose counterregulatory response to hypoglycaemia after GB is partly mediated by endogenous GLP-1, highlighting a novel pathogenic mechanism of GLP-1 in developing hypoglycaemia in this population.

Glucagon-like peptide-1 receptor blockade impairs islet secretion and glucose metabolism in humans.

BACKGROUNDProglucagon can be processed to glucagon-like peptide1 (GLP-1) within the islet, but its contribution to islet function in humans remains unknown. We sought to understand whether pancreatic GLP-1 alters islet function in humans and whether this is affected by type 2 diabetes.METHODSWe therefore studied individuals with and without type 2 diabetes on two occasions in random order. On one occasion, exendin 9-39, a competitive antagonist of the GLP-1 Receptor (GLP1R), was infused, while on the other, saline was infused. The tracer dilution technique ([3-3H] glucose) was used to measure glucose turnover during fasting and during a hyperglycemic clamp.RESULTSExendin 9-39 increased fasting glucose concentrations; fasting islet hormone concentrations were unchanged, but inappropriate for the higher fasting glucose observed. In people with type 2 diabetes, fasting glucagon concentrations were markedly elevated and persisted despite hyperglycemia. This impaired suppression of endogenous glucose production by hyperglycemia.CONCLUSIONThese data show that GLP1R blockade impairs islet function, implying that intra-islet GLP1R activation alters islet responses to glucose and does so to a greater degree in people with type 2 diabetes.TRIAL REGISTRATIONThis study was registered at ClinicalTrials.gov NCT04466618.FUNDINGThe study was primarily funded by NIH NIDDK DK126206. AV is supported by DK78646, DK116231 and DK126206. CDM was supported by MIUR (Italian Minister for Education) under the initiative "Departments of Excellence" (Law 232/2016).

1547-P: The Differential Effect of Glucagon-Like Peptide-1 Receptor Blockade on Glucose Metabolism in People With and Without Type 2 Diabetes

Glucagon-Like Peptide-1 (GLP-1) is present within the islet but the effects of GLP-1 Receptor (GLP1R) blockade on islet function in humans remains unknown. To address this, we studied 12 nondiabetic individuals (54 ± 2 years, 33 ± 1 kg/m2) and 11 people with type 2 diabetes (DM2 - 58 ± 2 years, 34 ± 2 kg/m2) on 2 occasions in random order. On each occasion, after an overnight fast, [3-3H] glucose was used to measure glucose turnover during fasting and a hyperglycemic clamp (~9 mmol/l) using the tracer dilution technique. On one occasion exendin-9,39 (300pmol/kg/min) was infused to block GLP1R, while on the other saline was infused. Exendin-9,39 increased fasting glucose concentrations in those without (4.6 ± 0.4 vs. 5.5 ± 0.1 mmol/l, saline vs. exendin-9,39 respectively, p = 0.04) and in those with DM2 (7.3 ± 0.5 vs. 8.3 ± 0.6 mmol/l, p = 0.03). Fasting islet hormone concentrations were unchanged, but inappropriate for the higher fasting glucose observed during exendin-9,39 infusion. The same pattern was seen in people with DM2 except that fasting glucagon concentrations increased (8.3 ± 0.5 vs. 10.2 ± 0.6 pmol/l, p &amp;lt; 0.01) and remained elevated throughout hyperglycemia (4.7 ± 0.4 vs. 7.7 ± 0.6 pmol/l, p &amp;lt; 0.02). Insulin secretion rate calculated by deconvolution of C-peptide concentrations was also decreased in DM2 (0.54 ± 0.08 vs. 0.51 ± 0.08 nmol/min, p = 0.02). Consequently, suppression of endogenous glucose production by hyperglycemia was impaired in people with DM2 (2.9 ± 0.4 vs. 5.7 ± 0.3 μmol/kg/min, p &amp;lt; 0.01). Intriguingly, 1st phase response to hyperglycemia was decreased in those without DM2 (3.5 ± 0.6 vs. 2.5 ± 0.5 nmol per 10 min, p = 0.04). These data show that in humans, GLP1R blockade impairs fasting α- and β-cell function resulting in fasting hyperglycemia. Subtle effects are also present in response to hyperglycemia. This implies that intra-islet GLP1R activation sustains islet responses to glucose and it does so to a greater degree in people with DM2. Disclosure A.A. Welch: None. R.A. Farahani: None. M. Zeini: None. A.M. Egan: None. M.C. Laurenti: None. C. Cobelli: None. C. Dalla Man: Research Support; Sanofi-Aventis Deutschland GmbH, Becton, Dickinson and Company. A. Vella: Other Relationship; Novo Nordisk. Advisory Panel; Rezolute, Inc. Consultant; Crinetics Pharmaceuticals, Inc., Hanmi Pharm. Co., Ltd., Zealand Pharma A/S. Funding National Institute of Diabetes and Digestive and Kidney Diseases (R01DK126206)

1646-P: The Effect of Glucagon-Like Peptide-1 Receptor Blockade and Acute Insulin Resistance on Islet Function and Glucose Metabolism in People without Diabetes

Intra-islet Glucagon-Like Peptide-1 (GLP-1) is increased by islet inflammation and diabetes. GLP-1 Receptor (GLP1R) blockade with exendin-9,39 impairs fasting islet function in people with and without type 2 diabetes (DM2). In addition, it decreases insulin secretion and glucagon suppression in response to hyperglycemia in people with DM2. We sought to examine if free fatty acid (FFA) elevation to induce acute insulin resistance in people without DM2 replicated the effects of GLP1R blockade seen in DM2. We studied 6 nondiabetic individuals (54 ± 4 years, 33 ± 1 kg/m2) on 4 occasions in random order. Glucose metabolism was measured after an overnight fast and during a hyperglycemic clamp (~9 mmol/l) using [3-3H] glucose. On two occasions Intralipid® and heparin were infused to raise FFA. Exendin-9,39 (300pmol/kg/min) was infused to block GLP1R in the presence or absence of FFA elevation, while on the other days saline was infused. In the absence of FFA elevation, exendin-9,39 infusion increased fasting glucose concentrations (5.0 ± 0.1 vs. 5.4 ± 0.1 mmol/l, saline vs. exendin-9,39 respectively, p = 0.01). This pattern was also observed when FFA were elevated (5.3 ± 0.1 vs. 5.7 ± 0.2 mmol/l, p = 0.02). Fasting insulin, C-peptide (without FFA: 0.9 ± 0.1 vs. 0.8 ± 0.1 nmol/l, p = 0.17; with FFA: 1.1 ± 0.1 vs. 1.0 ± 0.1 nmol/l, p = 0.08) and glucagon concentrations were unchanged, but inappropriate for the higher fasting glucose observed during exendin-9,39 infusion. Exendin-9,39 infusion did not alter islet hormone secretion during the clamp in the presence or absence of FFA elevation. The magnitude of changes induced by exendin-9,39 did not differ in the presence or absence of FFA elevation (p &amp;gt; 0.10). These experiments confirm the effects of GLP1R blockade on fasting α- and β-cell function in people without DM2. However, FFA elevation does not replicate the abnormalities of islet function observed in people with DM2 when exendin-9,39 is infused. Disclosure M. Zeini: None. R.A. Farahani: None. A.A. Welch: None. M.C. Laurenti: None. C. Cobelli: None. C. Dalla Man: Research Support; Sanofi-Aventis Deutschland GmbH, Becton, Dickinson and Company. A.M. Egan: None. A. Vella: Other Relationship; Novo Nordisk. Advisory Panel; Rezolute, Inc. Consultant; Crinetics Pharmaceuticals, Inc., Hanmi Pharm. Co., Ltd., Zealand Pharma A/S. Funding National Institutes of Health (DK126206)

36-OR: The Effect of Glucagon-Like Peptide-1 Receptor Blockade on the ß-Cell Response to Glucagon Bolus in People With and Without Type 2 Diabetes

Glucagon acts as an insulin secretagogue in part via the glucagon-like peptide-1 receptor (GLP1R) expressed on β-cells. Type 2 diabetes (DM2) is characterized by increased (and inappropriate) glucagon secretion for the prevailing hyperglycemia. Increased islet glucagon staining has also been observed in DM2. This suggests that increased glucagon signaling via GLP1R is a mechanism to maintain β-cell secretion in DM2. To ascertain if this is the case, we quantified the relative contribution of GLP1R signaling to the insulin response to glucagon in the presence and absence of DM2. We studied 12 individuals without DM2 (54 ± 2 yrs, 33 ± 1 kg/m2) and 11 with DM2 (58 ± 2 yrs, 34 ± 2 kg/m2) on 2 occasions in random order. On one occasion Exendin-9,39 (300pmol/kg/min) was infused to block GLP1R, while on the other study day saline was infused. Following an overnight fast and a 3-hour hyperglycemic clamp (~9 mmol/L), 1 mg glucagon bolus was administered intravenously with subsequent measurement of insulin, and C-peptide over 30 minutes during hyperglycemia. Exendin-9,39 infusion decreased peak and integrated insulin and C-peptide concentrations in response to the glucagon bolus in both those with and without DM2. The symmetric % change in insulin (-49 ± 8 vs -32 ± 8, DM2 vs. subjects without diabetes respectively, p = 0.2) and C-peptide (-24 ± 5 vs -15 ± 4, p = 0.18) did not differ between groups. In addition, six of the subjects without DM2 completed two additional study days (± exendin-9,39) with infusion of Intralipid® and heparin to raise free fatty acids (FFA) and cause acute insulin resistance. Acute FFA elevation also did not alter the net contribution of GLP1R stimulation to the response to glucagon in individuals without DM2 (% change insulin: -34 ± 10, p = 0.42; C-peptide: -23 ± 7, p = 0.38). These data suggest that the % contribution of glucagon to the stimulation of β-cell secretion via GLP1R does not change significantly in the presence or absence of DM2 or of FFA elevation. Disclosure A.M.Egan: None. M.Zeini: None. A.A.Welch: None. R.A.Farahani: None. M.C.Laurenti: None. C.Cobelli: None. C.Dalla man: Research Support; Sanofi-Aventis Deutschland GmbH, Becton, Dickinson and Company. A.Vella: Advisory Panel; Rezolute, Inc., Consultant; Crinetics Pharmaceuticals, Inc., Hanmi Pharm. Co., Ltd., Zealand Pharma A/S, Other Relationship; Novo Nordisk. Funding National Institutes of Health (DK126206)

The relative importance of Endogenously Secreted incretin hormones, GLP‐1 and GIP for Postprandial Glucose Tolerance and β‐Cell Function After Roux‐en‐Y Gastric Bypass and Sleeve Gastrectomy Surgery

Bariatric surgery procedures, namely Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) is increasingly used worldwide, have been shown to be the most effective strategy to induce and maintain weight loss as well as inducing long-term remission from type 2 diabetes among people with significant obesity. The mechanism for diabetes remission remains unclear and multi-factorial, although increased secretion of endogenous glucagon-like peptide 1 (GLP-1) hormones to improve postprandial β-cell function is widely considered to be the main mechanism for diabetes remission following RYGB. However, recent studies have shown that rate of remission between the two types of bariatric surgery procedures are similar but yet, the mechanism for remission above and beyond weight loss per se following SG is less clear. Beyond GLP-1, the role of the other major incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), is relatively unexplored after bariatric surgery. A study published in Diabetes Care have therefore studied the effects of separate and combined GLP-1 receptor (GLP-1R) and GIP receptor (GIPR) blockade during mixed-meal tests in un-operated (CON), SG-operated, and RYGB-operated people with no history of diabetes. The investigator found that, as expected, postprandial GLP-1 concentrations were highest after RYGB but also higher after SG compared with CON. In contrast, postprandial GIP concentrations were lowest after RYGB. Interestingly, blockage of GLP-1R reduced β-cell glucose sensitivity and increased postprandial glucose responses in both surgical groups but had no effect in CON. Blockage of GIPR however reduced β-cell glucose sensitivity and increased postprandial glucose responses in the CON and SG groups but had no effect in the RYGB group. This study showed that while GLP-1 is the most important mediator of improved beta cell function after RYGB, both GLP-1 and GIP are equally important after SG. The combine benefits of GLP-1 and GIP following SG is interesting, given the recent emergence of the dual GLP-1 and GIP agonist for the treatment of diabetes and obesity. It would be interesting also to explore the relative role of Glucagon on beta cell function following both procedures.

The Importance of Endogenously Secreted GLP-1 and GIP for Postprandial Glucose Tolerance and β-Cell Function After Roux-en-Y Gastric Bypass and Sleeve Gastrectomy Surgery.

Enhanced secretion of glucagon-like peptide 1 (GLP-1) seems to be essential for improved postprandial β-cell function after Roux-en-Y gastric bypass (RYGB) but is less studied after sleeve gastrectomy (SG). Moreover, the role of the other major incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), is relatively unexplored after bariatric surgery. We studied the effects of separate and combined GLP-1 receptor (GLP-1R) and GIP receptor (GIPR) blockade during mixed-meal tests in unoperated (CON), SG-operated, and RYGB-operated people with no history of diabetes. Postprandial GLP-1 concentrations were highest after RYGB but also higher after SG compared with CON. In contrast, postprandial GIP concentrations were lowest after RYGB. The effect of GLP-1R versus GIPR blockade differed between groups. GLP-1R blockade reduced β-cell glucose sensitivity and increased or tended to increase postprandial glucose responses in the surgical groups but had no effect in CON. GIPR blockade reduced β-cell glucose sensitivity and increased or tended to increase postprandial glucose responses in the CON and SG groups but had no effect in the RYGB group. Our results support that GIP is the most important incretin hormone in unoperated people, whereas GLP-1 and GIP are equally important after SG, and GLP-1 is the most important incretin hormone after RYGB.

GLP-1 Receptor Blockade Reduces Stimulated Insulin Secretion in Fasted Subjects With Low Circulating GLP-1.

Glucagon-like peptide 1 (GLP-1), an insulinotropic peptide released into the circulation from intestinal enteroendocrine cells, is considered a hormonal mediator of insulin secretion. However, the physiological actions of circulating GLP-1 have been questioned because of the short half-life of the active peptide. Moreover, there is mounting evidence for localized, intra-islet mediation of GLP-1 receptor (GLP-1r) signaling including a role for islet dipeptidyl-peptidase 4 (DPP4). To determine whether GLP-1r signaling contributes to insulin secretion in the absence of enteral stimulation and increased plasma levels, and whether this is affected by DPP4. Single-site study conducted at an academic medical center of 20 nondiabetic subjects and 13 subjects with type 2 diabetes. This was a crossover study in which subjects received either a DPP4 inhibitor (DPP4i; sitagliptin) or placebo on 2 separate days. On each day they received a bolus of intravenous (IV) arginine during sequential 60-minute infusions of the GLP-1r blocker exendin[9-39] (Ex-9) and saline. The main outcome measures were arginine-stimulated secretion of C-Peptide (C-PArg) and insulin (InsArg). Plasma GLP-1 remained at fasting levels throughout the experiments and IV arginine stimulated both α- and β-cell secretion in all subjects. Ex-9 infusion reduced C-PArg in both the diabetic and nondiabetic groups by ~14% (P < .03 for both groups). Sitagliptin lowered baseline glycemia but did not affect the primary measures of insulin secretion. However, a significant interaction between sitagliptin and Ex-9 suggested more GLP-1r activation with DPP4i treatment in subjects with diabetes. GLP-1r activation contributes to β-cell secretion in diabetic and nondiabetic people during α-cell activation, but in the absence of increased circulating GLP-1. These results are compatible with regulation of β-cells by paracrine signals from α-cells. This process may be affected by DPP4 inhibition.

Exendin(9-39)NH2 : Recommendations for clinical use based on a systematic literature review.

To present an overview of exendin(9-39)NH2 usage as a scientific tool in humans and provide recommendations for dosage and infusion regimes. We systematically searched the literature on exendin(9-39)NH2 and included for review 44 clinical studies reporting use of exendin(9-39)NH2 in humans. Exendin(9-39)NH2 binds to the orthosteric binding site of the glucagon-like peptide-1 (GLP-1) receptor with high affinity. The plasma elimination half-life of exendin(9-39)NH2 after intravenous administration is ~30 minutes, requiring ~2.5hours of constant infusion before steady-state plasma concentrations can be expected. Studies utilizing infusions with exendin(9-39)NH2 in humans have applied varying regimens (priming with a bolus or constant infusion) and dosages (continuous infusion rate range 30-900 pmol/kg/min) with subsequent differences in effects. Administration of exendin(9-39)NH2 in healthy individuals, patients with diabetes, obese patients, and patients who have undergone bariatric surgery significantly increases fasting and postprandial levels of glucose and glucagon, but has inconsistent effects on circulating concentrations of insulin and C-peptide, gastric emptying, appetite sensations, and food intake. Importantly, exendin(9-39)NH2 induces secretion of all L cell products (ie, in addition to GLP-1, also peptide YY, glucagon-like peptide-2, oxyntomodulin, and glicentin) complicating use of exendin(9-39)NH2 as a tool to study the isolated effect of GLP-1. Exendin(9-39)NH2 is selective for the GLP-1 receptor, with numerous and complex whole-body effects. To obtain GLP-1 receptor blockade in humans, we recommend an initial high-dose infusion, followed by a continuous infusion rate aiming at a ratio of exendin(9-39)NH2 to GLP-1 of 2000:1. Highlights Exendin(9-39)NH2 is a competitive antagonist of the human GLP-1 receptor. Exendin(9-39)NH2 has been used as a tool to delineate human GLP-1 physiology since 1998. Exendin(9-39)NH2 induces secretion of GLP-1 and other L cell products. Reported effects of exendin(9-39)NH2 on insulin levels and food intake are inconsistent. Here, we provide recommendations for the use of exendin(9-39)NH2 in clinical studies.

Gastrointestinal Distension by Pectin-Containing Carbonated Solution Suppresses Food Intake and Enhances Glucose Tolerance via GLP-1 Secretion and Vagal Afferent Activation.

Diet-induced gastrointestinal distension is known to evoke satiation and suppress postprandial hyperglycemia; however, the underlying mechanisms remain poorly understood. This study explored how gastrointestinal distension regulates energy homeostasis by using inflating stomach formulation (ISF), the carbonated solution containing pectin that forms stable gel bubbles under acidic condition in the stomach. Here we show that, in mice, oral administration of ISF induced distension of stomach and proximal intestine temporarily, stimulated intestinal glucagon-like peptide-1 (GLP-1) secretion, and activated vagal afferents and brainstem. ISF suppressed food intake and improved glucose tolerance via enhancing insulin sensitivity. The anorexigenic effect was partially inhibited, and the beneficial glycemic effect was blunted by pharmacological GLP-1 receptor blockade and chemical denervation of capsaicin-sensitive sensory nerves. In HFD-fed obese mice showing arrhythmic feeding and obesity, subchronic ISF treatment at the light period (LP) onset for 10 days attenuated LP hyperphagia and visceral fat accumulation. These results demonstrate that gastrointestinal distension by ISF stimulates GLP-1 secretion and the vagal afferent signaling to the brain, thereby regulating feeding behavior and glucose tolerance. Furthermore, subchronic ISF treatment ameliorates HFD-induced visceral obesity. We propose the diet that induces gastrointestinal distension as a novel treatment of hyperphagic obesity and diabetes.

215-LB: The Role of GLP-1 in Glycemic Response to Protein Ingestion after Gastric Bypass Surgery or Sleeve Gastrectomy

Protein ingestion increases the plasma insulin and glucagon responses, but the enteral factors involved are entirely unknown. We hypothesized that glucagon-like peptide 1 (GLP-1) signaling regulates glucose metabolism after protein ingestion, and that this effect may be amplified after Roux-en Y gastric bypass (GB) and sleeve gastrectomy (SG). We examined the glucose and islet-cell secretory responses to 50 g protein ingestion with and without GLP-1 receptor antagonist, exendin-(9-39) [Ex-9], in 4 GB-treated subjects, 4 SG-treated, and 4 non-operated controls (CN). The groups were matched for age, BMI, fat-free mass, fasting glucose and insulin, and HbA1c. The surgical groups also were matched for weight loss and time post-surgery; none had diabetes. Protein ingestion resulted in an early rise in glycemia (AUCGlucose 1hr) in GB and SG compared to CN (p&amp;lt;0.05), whose glucose values remained at basal concentrations. Both β- and α-cell hormonal responses were enhanced by protein ingestion in all 3 groups. GLP-1 receptor blockade increased fasting and prandial glycemia in all 3 groups, but to a greater extent in GB (p&amp;lt;0.05, interaction). This glycemic effect of Ex-9 was associated with a ~25% reduction in prandial insulin secretion in GB and SG and ~25% increase in prandial insulin response in CN (p&amp;lt;0.05, interaction). The prandial glucagon responses were larger during studies with Ex-9 compared to those without (p&amp;lt;0.05). Blocking the GLP-1R increased prandial insulin clearance (p&amp;lt;0.05) in all groups, but to a much larger extent in surgical subjects (p=0.1, interaction). Our findings indicate that glucose metabolism after protein ingestion is altered after GB and SG. To our knowledge, this is the first report demonstrating that endogenous GLP-1 contributes to glucose and islet-cell secretory response to protein ingestion, and that GB and SG exaggerate GLP-1 contribution to insulin secretion and clearance after protein ingestion. Disclosure M. S. Rayas: Research Support; Self; National Center for Advancing Translational Sciences. H. Honka: None. R. A. Defronzo: Other Relationship; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Intarcia Therapeutics, Inc., Janssen Pharmaceuticals, Inc., Novo Nordisk, Research Support; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Merck &amp; Co., Inc., Speaker’s Bureau; Self; AstraZeneca, Novo Nordisk. A. Gastaldelli: Advisory Panel; Self; Boehringer Ingelheim International GmbH, Consultant; Self; Eli Lilly and Company, Inventiva Pharma, Research Support; Self; Gilead Sciences, Inc., Speaker’s Bureau; Self; Novo Nordisk. M. Salehi: None. Funding National Institutes of Health (DK105379)

Glucagon-like peptide-1 (GLP-1) receptor activation dilates cerebral arterioles, increases cerebral blood flow, and mediates remote (pre)conditioning neuroprotection against ischaemic stroke

Stroke remains one of the most common causes of death and disability worldwide. Several preclinical studies demonstrated that the brain can be effectively protected against ischaemic stroke by two seemingly distinct treatments: remote ischaemic conditioning (RIC), involving cycles of ischaemia/reperfusion applied to a peripheral organ or tissue, or by systemic administration of glucagon-like-peptide-1 (GLP-1) receptor (GLP-1R) agonists. The mechanisms underlying RIC- and GLP-1-induced neuroprotection are not completely understood. In this study, we tested the hypothesis that GLP-1 mediates neuroprotection induced by RIC and investigated the effect of GLP-1R activation on cerebral blood vessels, as a potential mechanism of GLP-1-induced protection against ischaemic stroke. A rat model of ischaemic stroke (90 min of middle cerebral artery occlusion followed by 24-h reperfusion) was used. RIC was induced by 4 cycles of 5 min left hind limb ischaemia interleaved with 5-min reperfusion periods. RIC markedly (by ~ 80%) reduced the cerebral infarct size and improved the neurological score. The neuroprotection established by RIC was abolished by systemic blockade of GLP-1R with a specific antagonist Exendin(9–39). In the cerebral cortex of GLP-1R reporter mice, ~ 70% of cortical arterioles displayed GLP-1R expression. In acute brain slices of the rat cerebral cortex, activation of GLP-1R with an agonist Exendin-4 had a strong dilatory effect on cortical arterioles and effectively reversed arteriolar constrictions induced by metabolite lactate or oxygen and glucose deprivation, as an ex vivo model of ischaemic stroke. In anaesthetised rats, Exendin-4 induced lasting increases in brain tissue PO2, indicative of increased cerebral blood flow. These results demonstrate that neuroprotection against ischaemic stroke established by remote ischaemic conditioning is mediated by a mechanism involving GLP-1R signalling. Potent dilatory effect of GLP-1R activation on cortical arterioles suggests that the neuroprotection in this model is mediated via modulation of cerebral blood flow and improved brain perfusion.

The role of GLP-1 in postprandial glucose metabolism after bariatric surgery: a narrative review of human GLP-1 receptor antagonist studies.

The Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) bariatric procedures lead to remission or improvement of type 2 diabetes. A weight loss-independent augmentation of postprandial insulin secretion contributes to the improvement in glycemic control after RYGB and is associated with a ∼10-fold increase in plasma concentrations of the incretin hormone glucagon-like peptide-1 (GLP-1). However, the physiologic importance of the markedly increased postprandial GLP-1 secretion after RYGB has been much debated. The effect of GLP-1 receptor blockade after RYGB has been investigated in 12 studies. The studies indicate a shift toward a more prominent role for GLP-1 in postprandial β-cell function after RYGB. The effect of GLP-1 receptor antagonism on glucose tolerance after RYGB is more complex and is associated with important methodological challenges. The postprandial GLP-1 response is less enhanced after SG compared with RYGB. However, the effect of GLP-1 receptor blockade after SG has been examined in 1 study only and needs further investigation.

Continuous glucose monitoring reveals glycemic variability and hypoglycemia after vertical sleeve gastrectomy in rats

ObjectivePost–bariatric surgery hypoglycemia (PBH) is defined as the presence of neuroglycopenic symptoms accompanied by postprandial hypoglycemia in bariatric surgery patients. Recent clinical studies using continuous glucose monitoring (CGM) technology revealed that PBH is more frequently observed in vertical sleeve gastrectomy (VSG) patients than previously recognized. PBH cannot be alleviated by current medication. Therefore, a model system to investigate the mechanism and treatment is required. MethodsWe used CGM in a rat model of VSG and monitored the occurrence of glycemic variability and hypoglycemia in various meal conditions for 4 weeks after surgery. Another cohort of VSG rats with CGM was used to investigate whether the blockade of glucagon-like peptide-1 receptor (GLP-1R) signaling alleviates these symptoms. A mouse VSG model was used to investigate whether the impaired glucose counterregulatory system causes postprandial hypoglycemia. ResultsLike in humans, rats have increased glycemic variability and hypoglycemia after VSG. Postprandial hypoglycemia was specifically detected after liquid versus solid meals. Further, the blockade of GLP-1R signaling raises the glucose nadir but does not affect glycemic variability. ConclusionsRat bariatric surgery duplicates many features of human post–bariatric surgery hypoglycemia including postprandial hypoglycemia and glycemic variability, while blockade of GLP-1R signaling prevents hypoglycemia but not the variability.

Endogenous GLP-1 in lateral septum promotes satiety and suppresses motivation for food in mice

Glucagon-like peptide 1 receptors (GLP-1R) are expressed in the lateral septum (LS) of rats and mice, and we have published that endogenous LS GLP-1 affects feeding and motivation for food in rats. Here we asked if these effects are also observed in mice. In separate dose-response studies using male C57Bl6J mice, intra-LS GLP-1 or the GLP-1R antagonist Exendin 9 (Ex9) was delivered shortly before dark onset, at doses subthreshold for effect when injected intracerebroventricularly (icv). Intra-LS GLP-1 significantly suppressed chow intake early in the dark phase and tended to reduce overnight intake. However, blockade of LS GLP-1R with Ex9 had no effect on ad libitum dark onset chow intake. We then asked if LS GLP-1R blockade blunts nutrient preload-induced intake suppression. Mice were trained to consume Ensure immediately before dark onset, which suppressed subsequent chow intake, and intra-LS Ex9 attenuated that preload-induced intake suppression. We also found that restraint stress robustly activates hindbrain GLP-1-producing neurons, and that LS GLP-1R blockade attenuates 30-min restraint stress-induced hypophagia in mice. Furthermore, we have reported that in the rat, GLP-1R in the dorsal subregion of the LS (dLS) affect motivation for food. We examined this in food-restricted mice responding for sucrose pellets on a progressive ratio (PR) schedule. Intra-dLS GLP-1R stimulation significantly suppressed, and Ex9 significantly increased, operant responding, and the Ex9 effect remained after mice returned to ad libitum conditions. Similarly, we found that stimulation of dLS GLP-1 suppressed licking for sucrose and conversely, Ex9 increased licking under ad libitum feeding conditions. Together, our data suggest that endogenous activation of LS GLP-1R plays a role in feeding in mice under some but not all conditions, and that these receptors strongly influence motivation for food.

Deletion of the glucagon receptor gene before and after experimental diabetes reveals differential protection from hyperglycemia

ObjectiveMice with congenital loss of the glucagon receptor gene (Gcgr−/− mice) remain normoglycemic in insulinopenic conditions, suggesting that unopposed glucagon action is the driving force for hyperglycemia in Type-1 Diabetes Mellitus (T1DM). However, chronic loss of GCGR results in a neomorphic phenotype that includes hormonal signals with hypoglycemic activity. We combined temporally-controlled GCGR deletion with pharmacological treatments to dissect the direct contribution of GCGR signaling to glucose control in a common mouse model of T1DM. MethodsWe induced experimental T1DM by injecting the beta-cell cytotoxin streptozotocin (STZ) in mice with congenital or temporally-controlled Gcgr loss-of-function using tamoxifen (TMX). ResultsDisruption of Gcgr expression, using either an inducible approach in adult mice or animals with congenital knockout, abolished the response to a long-acting Gcgr agonist. Mice with either developmental Gcgr disruption or inducible deletion several weeks before STZ treatment maintained normoglycemia. However, mice with inducible knockout of the Gcgr one week after the onset of STZ diabetes had only partial correction of hyperglycemia, an effect that was reversed by GLP-1 receptor blockade. Mice with Gcgr deletion for either 2 or 6 weeks had similar patterns of gene expression, although the changes were generally larger with longer GCGR knockout. ConclusionsThese findings demonstrate that the effects of glucagon to mitigate diabetic hyperglycemia are not through acute signaling but require compensations that take weeks to develop.

Endogenous GLP-1 in lateral septum contributes to stress-induced hypophagia.

Glucagon-like peptide 1 (GLP-1) neurons of the caudal brainstem project to many brain areas, including the lateral septum (LS), which has a known role in stress responses. Previously, we showed that endogenous GLP-1 in the LS plays a physiologic role in the control of feeding under non-stressed conditions, however, central GLP-1 is also involved in behavioral and endocrine responses to stress. Here, we asked whether LS GLP-1 receptors (GLP-1R) contribute to stress-induced hypophagia. Male rats were implanted with bilateral cannulas targeting the dorsal subregion of the LS (dLS). In a within-subjects design, shortly before the onset of the dark phase, rats received dLS injections of saline or the GLP-1R antagonist Exendin (9-39) (Ex9) prior to 30 min restraint stress. Food intake was measured continuously for the next 20 h. The stress-induced hypophagia observed within the first 30 min of dark was not influenced by Ex9 pretreatment, but Ex9 tended to blunt the effect of stress as early as 1 and 2 h into the dark phase. By 4-6 h, there were significant stress X drug interactions, and Ex9 pretreatment blocked the stress-induced suppression of feeding. These effects were mediated entirely through changes in average meal size; stress suppressed meal size while dLS Ex9 attenuated this effect. Using a similar design, we examined the role of dLS GLP-1R in the neuroendocrine response to acute restraint stress. As expected, stress potently increased serum corticosterone, but blockade of dLS GLP-1Rs did not affect this response. Together, these data show that endogenous GLP-1 action in the dLS plays a role in some but not all of the physiologic responses to acute stress.

Palmitic Acid Hydroxystearic Acids Activate GPR40, Which Is Involved in Their Beneficial Effects on Glucose Homeostasis

Palmitic acid hydroxystearic acids (PAHSAs) are endogenous lipids with anti-diabetic and anti-inflammatory effects. PAHSA levels are reduced in serum and adipose tissue of insulin-resistant people and high-fat diet (HFD)-fed mice. Here, we investigated whether chronic PAHSA treatment enhances insulin sensitivity and which receptors mediate PAHSA effects. Chronic PAHSA administration in chow- and HFD-fed mice raises serum and tissue PAHSA levels ∼1.4- to 3-fold. This improves insulin sensitivity and glucose tolerance without altering body weight. PAHSA administration in chow-fed, but not HFD-fed, mice augments insulin and glucagon-like peptide (GLP-1) secretion. PAHSAs are selective agonists for GPR40, increasing Ca+2 flux, but not intracellular cyclic AMP. Blocking GPR40 reverses improvements in glucose tolerance and insulin sensitivity in PAHSA-treated chow- and HFD-fed mice and directly inhibits PAHSA augmentation of glucose-stimulated insulin secretion in human islets. In contrast, GLP-1 receptor blockade in PAHSA-treated chow-fed mice reduces PAHSA effects on glucose tolerance, but not on insulin sensitivity. Thus, PAHSAs activate GPR40, which is involved in their beneficial metabolic effects.