Effect of endogenous GLP-1 on insulin secretion in type 2 diabetes

The intricate relationship between circadian rhythms and gastrointestinal peptides in obesity

There are different molecular pathways that regulate appetite, particularly the role of the hypothalamus, circadian rhythms, and gastrointestinal peptides. The hypothalamus integrates signals from orexigenic peptides like neuropeptide Y (NPY) and agouti-related protein (AgRP), which stimulate appetite, and anorexigenic peptides such as pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART), which promote satiety. These signals are influenced by peripheral hormones like leptin, ghrelin, insulin, and cortisol, as well as gut peptides including glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and cholecystokinin (CCK). The circadian rhythm, regulated by proteins like circadian locomotor output cycles kaput (CLOCK) and brain and muscle ARNT-like 1 (BMAL1), modulates the secretion of these peptides, aligning feeding behaviors with the sleep-wake cycle. In obesity, these regulatory systems are disrupted, leading to leptin resistance, increased ghrelin sensitivity, and altered gut peptide secretion. This results in heightened appetite and impaired satiety, contributing to overeating and metabolic dysfunction. Additionally, circadian disruptions further impair metabolic processes, exacerbating obesity. The present article underscores the importance of understanding the molecular interplay between circadian rhythms and gastrointestinal peptides, particularly in the context of obesity. While some molecular interactions, such as the regulation of GLP-1 and PYY by reverberation of circadian rhythm α (REV-ERBα) and retinoic acid-related orphan receptor α (RORα), are well-established, clinical studies are scarce. Future research is expected to explore these pathways in obesity management, especially with the rise of incretin-based treatments like semaglutide. A deeper understanding of hypothalamic molecular mechanisms could lead to novel pharmacological and non-pharmacological therapies for obesity.

Effect of medium-chain triglycerides and whey protein isolate preloads on glycaemia in type 2 diabetes: a randomized crossover study

BACKGROUND

Small nutritional preloads can reduce postprandial glucose excursions in individuals with and without metabolic syndrome or type 2 diabetes (T2D). However, most studies have focused on preloads administered before single meals and have predominantly used protein-based preloads.

OBJECTIVES

To investigate the effects of sequential consumption of medium-chain triglycerides (MCT) and whey protein isolate (WPI) preloads before breakfast, lunch, and dinner on postprandial, diurnal, and 24-h glycaemia in individuals with T2D.

METHODS

Participants with T2D were studied over 3 randomized 24-h periods. They consumed either water before standardized breakfast, lunch, and dinner (CONTROL), 15 g MCT before breakfast and water before lunch and dinner (MCT), or 15 g MCT before breakfast and 10 g WPI before lunch and dinner (MCT + WPI). Diurnal (08:00-23:00 h) and 24 h (08:00-08:00 h) glycaemia (incremental AUC [iAUC]) and glycaemic variability (%coefficient of variation [%CV]) were evaluated by continuous glucose monitoring. Postprandial glycaemia (PPG) after breakfast and lunch was assessed by arterialized blood glucose iAUC.

RESULTS

In 21 enrolled patients (8 males/13 females, mean ± standard deviation age 55.1 ± 8.5 y, body mass index 31.7 ± 4.3 kg·m-2, glycated hemoglobin 59 ± 12 mmol·mol-1) diurnal and 24-h iAUC were similar across interventions, whereas 24-h %CV was lower in MCT (16.8 ± 0.8%, P = 0.033) and MCT + WPI (16.1 ± 0.9%, P = 0.0004) than CONTROL (18.7 ± 0.9%). PPG iAUC was ∼17% lower after breakfast in MCT and MCT + WPI compared with CONTROL, but only the MCT + WPI lowered glucose by 20% (P = 0.002) over the entire day (08:30-17:30 h). Gastric inhibitory polypeptide (GIP) (P = 0.00004), peptide YY (PYY) (P = 0.01), and β-hydroxybutyrate (P = 0.0001) were higher in MCT and MCT + WPI than CONTROL. Subjective appetite ratings were lower after breakfast and lunch in MCT + WPI (P = 0.001).

CONCLUSIONS

Sequential consumption of MCT and WPI preloads did not affect diurnal or 24-h glycaemia but lowered PPG and 24-h glycaemic variability in individuals with T2D. These effects were associated with increased circulating β-hydroxybutyrate, PYY, and GIP, and suppression of appetite. This trial was registered at clinicaltrials.gov as NCT04905589 (https://clinicaltrials.gov/study/NCT04905589).

GLP-1 enhances β-cell response to protein ingestion and bariatric surgery amplifies it

OBJECTIVE

The glycemic-independent actions of glucagon-like peptide-1 (GLP-1) in the prandial state in humans are unknown. We examined the contribution of GLP-1 to β-cell secretory response (primary endpoint) and glucose metabolism during protein ingestion under basal glycemia, as well as whether these responses are affected by rerouted gut after gastric bypass (GB) or sleeve gastrectomy (SG).

METHODS

Insulin secretion rate (ISR) and glucose fluxes during a 50-g oral protein load were compared among 10 nondiabetic individuals with GB, 9 with SG, and 7 non-operated controls (CN), with and without intravenous infusion of exendin(9-39) (Ex-9), a GLP-1 receptor (GLP-1R) antagonist.

RESULTS

Blocking GLP-1R increased glucose before and after protein ingestion and decreased β-cell sensitivity to glucose in the first 30 min of protein ingestion in all three groups (p < 0.05). Reduction in the premeal ISR by Ex-9 infusion was only observed in CN, whereas diminished prandial ISR3h by GLP-1R blockade was only observed in GB and SG (p < 0.05 for interaction). GLP-1R blockade enhanced post-protein insulin action in GB and SG, but not in CN, and exaggerated endogenous glucose production only GB (p < 0.05 for interaction).

CONCLUSIONS

These findings are consistent with both pancreatic and extra-pancreatic roles for GLP-1 during protein ingestion in humans that are exaggerated by bariatric surgery.

Improving insulin resistance by sulforaphane via activating the Bacteroides and Lactobacillus SCFAs-GPR-GLP1 signal axis

Background: Insulin resistance (IR) is closely associated with non-alcoholic fatty liver disease (NAFLD), and the gut microbiome contributes to the development of NAFLD. Sulforaphane (SFN) is a phytochemical in cruciferous vegetables that could improve lipid metabolism disorder. However, whether SFN can alleviate IR in NAFLD by regulating the intestinal flora remains unclear. Methods: SFN was administered to high fat diet (HFD)-fed Wistar rats for 10 weeks. Gut microbiota was analysed by 16S rRNA sequencing and the short chain fatty acids (SCFAs) by gas chromatography. The expression of tight junction protein and the numbers of Lactobacillus, Bacteroides and Bifidobacterium were determined by qPCR. The expression of G-protein-coupled receptor 41/43 (GPR41/43) was determined by western blot. A randomized controlled trial (RCT) was conducted in NAFLD patients with broccoli seed tablets (rich in SFN, 42 mg d-1) as intervention for 12 weeks. Thirty-six volunteers with abnormal glucose before the broccoli seed tablet treatment were selected in the intervention group to analyze their blood glucose, insulin, homeostasis model assessment-insulin resistance index (HOMA-IRI), homeostasis model assessment-insulin sensitivity index (HOMA-ISI) and glucagon-like peptide (GLP-1). Results: SFN reduced blood glucose and HOMA-IRI while increasing insulin sensitivity in HFD rats. SFN reduced glycogen synthase kinase 3 (GSK-3), phosphoenolpyruvate carboxykinase (PEPCK) activity, and phosphorylation of serine residues of IRS-2 induced by HFD. SFN reshaped the gut microbiota composition of HFD-induced rats and, especially, increased the content of Bacteroidaceae, Lactobacillaceae and Bifidobacteriaceae, which are related to the improvement from SFN of the blood glucose and HOMA-IRI. The increased numbers of Bacteroides and Lactobacillus were the targets of SFN to enhance the expression of tight junction proteins ZO-1 and occludin, thereby lowering lipopolysaccharide content to reduce inflammation, ultimately alleviating IR. Bacteroides and Lactobacillus produced SCFAs, which activated GPR41/43 to secrete GLP1. Moreover, it was also confirmed in RCT that SFN intervention increased the level of GLP1 in NAFLD patients, which was positively correlated with the reduction of blood glucose and HOMA-IR. Conclusions: SFN alleviated IR in NAFLD via the Bacteroides and Lactobacillus SCFAs-GPR41/43-GLP1 axis and protected the intestinal mucosal barrier to decrease inflammation.

Nano-optogenetics for Disease Therapies

Optogenetic, known as the method of 21 centuries, combines optic and genetic engineering to precisely control photosensitive proteins for manipulation of a broad range of cellular functions, such as flux of ions, protein oligomerization and dissociation, cellular intercommunication, and so on. In this technique, light is conventionally delivered to targeted cells through optical fibers or micro light-emitting diodes, always suffering from high invasiveness, wide-field illumination facula, strong absorption, and scattering by nontargeted endogenous substance. Light-transducing nanomaterials with advantages of high spatiotemporal resolution, abundant wireless-excitation manners, and easy functionalization for recognition of specific cells, recently have been widely explored in the field of optogenetics; however, there remain a few challenges to restrain its clinical applications. This review summarized recent progress on light-responsive genetically encoded proteins and the myriad of activation strategies by use of light-transducing nanomaterials and their disease-treatment applications, which is expected for sparking helpful thought to push forward its preclinical and translational uses.

GLP-1 enhances beta-cell response to protein ingestion and bariatric surgery amplifies it

OBJECTIVE

Protein ingestion stimulates β-cell secretion and alters glucose flux. Enhanced action of glucagon-like peptide 1 (GLP-1) and increased plasma glucose excursion contribute to prandial hyperinsulinemia after gastric bypass surgery (GB) and sleeve gastrectomy (SG). We examined the contribution of endogenous GLP-1 to glucose kinetics and β-cell response to protein ingestion under basal glucose concentrations in humans, and whether these responses are affected by rerouted gut after GB or SG.

DESIGN

Glucose fluxes, insulin secretion rate (ISR), and incretin responses to a 50-gram oral protein load were compared between 10 non-diabetic individuals with GB, 9 matched subjects with SG and 7 non-operated controls (CN) with and without intravenous infusion of exendin-(9- 39) [Ex-9), a specific GLP-1 receptor (GLP-1R) antagonist.

RESULTS

Blocking GLP-1R increased the plasma glucose concentration before and after protein ingestion in all 3 groups (p<0.05) and decreased β-cell sensitivity to glucose in the first 30 minutes of protein ingestion (p<0.05). Reduction in the prandial ISR3h by Ex-9 infusion, however, only was observed in GB and SG (p<0.05 for interaction) and not in controls. Also, GLP-1R blockade increased post-protein insulin action in GB and SG, but not CN (p=0.09 for interaction). Endogenous glucose production (EGP) during the first 60 minutes after protein ingestion was increased in all 3 groups but EGP3h only was accentuated in GB by Ex-9 infusion (p<0.05 for interaction).

CONCLUSION

These findings are consistent with both a pancreatic and extrapancreatic role for GLP-1 during protein ingestion in humans, and GLP-1 actions are exaggerated by bariatric surgery.

Weight Loss-Independent Effect of Liraglutide on Insulin Sensitivity in Individuals With Obesity and Prediabetes

Metabolic effects of glucagon-like peptide 1 (GLP-1) receptor agonists are confounded by weight loss and not fully recapitulated by increasing endogenous GLP-1. We tested the hypothesis that GLP-1 receptor (GLP-1R) agonists exert weight loss-independent, GLP-1R-dependent effects that differ from effects of increasing endogenous GLP-1. Individuals with obesity and prediabetes were randomized to receive for 14 weeks the GLP-1R agonist liraglutide, a hypocaloric diet, or the dipeptidyl peptidase 4 (DPP-4) inhibitor sitagliptin. The GLP-1R antagonist exendin(9-39) and placebo were administered in a two-by-two crossover study during mixed-meal tests. Liraglutide and diet, but not sitagliptin, caused weight loss. Liraglutide improved insulin sensitivity measured by HOMA for insulin resistance (HOMA-IR), the updated HOMA model (HOMA2), and the Matsuda index after 2 weeks, prior to weight loss. Liraglutide decreased fasting and postprandial glucose levels, and decreased insulin, C-peptide, and fasting glucagon levels. In contrast, diet-induced weight loss improved insulin sensitivity by HOMA-IR and HOMA2, but not the Matsuda index, and did not decrease glucose levels. Sitagliptin increased endogenous GLP-1 and GIP values without altering insulin sensitivity or fasting glucose levels, but decreased postprandial glucose and glucagon levels. Notably, sitagliptin increased GIP without altering weight. Acute GLP-1R antagonism increased glucose levels in all groups, increased the Matsuda index and fasting glucagon level during liraglutide treatment, and increased endogenous GLP-1 values during liraglutide and sitagliptin treatments. Thus, liraglutide exerts rapid, weight loss-independent, GLP-1R-dependent effects on insulin sensitivity that are not achieved by increasing endogenous GLP-1.

ARTICLE HIGHLIGHTS

Metabolic benefits of glucagon-like peptide 1 (GLP-1) receptor agonists are confounded by weight loss and are not fully achieved by increasing endogenous GLP-1 through dipeptidyl peptidase 4 (DPP-4) inhibition. We investigated weight loss-independent, GLP-1 receptor (GLP-1R)-dependent metabolic effects of liraglutide versus a hypocaloric diet or the DPP-4 inhibitor sitagliptin. GLP-1R antagonism with exendin(9-39) was used to assess GLP-1R-dependent effects during mixed meals. Liraglutide improved insulin sensitivity and decreased fasting and postprandial glucose prior to weight loss, and these benefits were reversed by exendin(9-39). GLP-1R agonists exert rapid, weight loss-independent, GLP-1R-dependent effects on insulin sensitivity not achieved by increasing endogenous GLP-1.

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).

Assessment of the incretin effect in healthy subjects: concordance between clamp and OGTT methods

The incretin effect describes the insulin response to nutrient ingestion that exceeds the response to glycemia per se. It is mediated by gastrointestinal factors and is necessary to maintain postprandial glucose homeostasis. The incretin effect results in a more than twofold increase of the insulin response to a meal in healthy people and two different techniques have been used in the past to measure its magnitude. Most studies employ an OGTT on 1 day, followed by a matching glucose infusion on a separate day. Another study design employs a hyperglycemic glucose clamp that is maintained after oral ingestion of glucose. Both protocols allow quantification of the incretin effect by comparing the insulin response to an identical glycemic stimulus. Here we performed a within-subject comparison of both techniques to quantify the incretin effect and suggest different calculation methods to interpret the results derived from the clamp experiment in a cohort of healthy young adults (n = 10, age 33 ± 4 yr). All subjects participated on four different study days: 1) OGTT, 2) isoglycemic glucose infusion (Iso-IV), 3) hyperglycemic clamp with oral glucose ingestion (clamp-OGTT), and 4) hyperglycemic clamp (clamp). With the classic OGTT/Iso-IV method, the insulin response to glucose ingestion increased more than twofold and was 60 ± 6% and 49 ± 5% for insulin and c-peptide. Different estimates of the incretin effect based on the clamp method ranged from 58% to 79% for insulin and 38% to 61% for c-peptide, both significantly higher than values derived from the OGTT/isoglycemic infusion method. However, when the effect of continuous hyperglycemia on insulin secretion was accounted for, using extrapolation from early time points of the clamp, good agreement was noted between the two methods. Based on these results, both techniques seem to be equally suited to measure the incretin effect and should be employed according to the scientific questions, experimental contingencies, and investigator experience.NEW & NOTEWORTHY This proof-of-concept study shows that the incretin effect can be reliably assessed by two different methods with similar quantitative results. A single-day hyperglycemic clamp with oral glucose ingestion allows the determination of the incretin effect with fewer study days and less day-to-day variability.

GIPR/GLP-1R dual agonist therapies for diabetes and weight loss-chemistry, physiology, and clinical applications

The incretin system is an essential metabolic axis that regulates postprandial metabolism. The two incretin peptides that enable this effect are the glucose-dependent insulinotropic polypeptide (GIP) and the glucagon-like peptide 1 (GLP-1), which have cognate receptors (GIPR and GLP-1R) on islet β cells as well as in other tissues. Pharmacologic engagement of the GLP-1R is a proven strategy for treating hyperglycemia in diabetes and reducing body weight. Tirzepatide is the first monomeric peptide with dual activity at both incretin receptors now available for clinical use, and in clinical trials it has shown unprecedented effects to reduce blood glucose and body weight. Here, we discuss the foundational science that led to the development of monomeric multi-incretin receptor agonists, culminating in the development of tirzepatide. We also look to the future of this field and comment on how the concept of multi-receptor agonists will continue to progress for the treatment of metabolic disease.

Insight into Structure Activity Relationship of DPP-4 Inhibitors for Development of Antidiabetic Agents

This article sheds light on the various scaffolds that can be used in the designing and development of novel synthetic compounds to create DPP-4 inhibitors for the treatment of type 2 diabetes mellitus (T2DM). This review highlights a variety of scaffolds with high DPP-4 inhibition activity, such as pyrazolopyrimidine, tetrahydro pyridopyrimidine, uracil-based benzoic acid and esters, triazole-based, fluorophenyl-based, glycinamide, glycolamide, β-carbonyl 1,2,4-triazole, and quinazoline motifs. The article further explains that the potential of the compounds can be increased by substituting atoms such as fluorine, chlorine, and bromine. Docking of existing drugs like sitagliptin, saxagliptin, and vildagliptin was done using Maestro 12.5, and the interaction with specific residues was studied to gain a better understanding of the active sites of DPP-4. The structural activities of the various scaffolds against DPP-4 were further illustrated by their inhibitory concentration (IC50) values. Additionally, various synthesis schemes were developed to make several commercially available DPP4 inhibitors such as vildagliptin, sitagliptin and omarigliptin. In conclusion, the use of halogenated scaffolds for the development of DPP-4 inhibitors is likely to be an area of increasing interest in the future.

Pre-Meal Whey Protein Alters Postprandial Insulinemia by Enhancing β-Cell Function and Reducing Insulin Clearance in T2D

CONTEXT

Treatments that reduce postprandial glycemia (PPG) independent of stimulating insulin secretion are appealing for the management of type 2 diabetes (T2D). Consuming pre-meal whey protein (WP) reduces PPG by delaying gastric emptying and increasing plasma insulin concentrations. However, its effects on β-cell function and insulin kinetics remains unclear.

OBJECTIVE

To examine the PPG-regulatory effects of pre-meal WP by modeling insulin secretion rates (ISR), insulin clearance, and β-cell function.

METHODS

This was a single-blind, randomized, placebo-controlled, crossover design study in 18 adults with T2D (HbA1c, 56.7 ± 8.8 mmol/mol) who underwent 2 240-minute mixed-meal tolerance tests. Participants consumed WP (15 g protein) or placebo (0 g protein) 10 minutes before a mixed-macronutrient breakfast meal. PPG, pancreatic islet, and incretin hormones were measured throughout. ISR was calculated by C-peptide deconvolution. Estimates of insulin clearance and β-cell function were modeled from glucose, insulin, and ISR. Changes in PPG incremental area under the curve (iAUC; prespecified) and insulin clearance (post hoc) were measured.

RESULTS

β-cell function was 40% greater after WP (P = .001) and was accompanied with a -22% reduction in postprandial insulin clearance vs placebo (P < .0001). Both the peak change and PPG iAUC were reduced by WP (-1.5 mmol/L and -16%, respectively; both P < .05). Pre-meal WP augmented a 5.9-fold increase in glucagon and glucagon-like peptide 1 iAUC (both P < .0001), and a 1.5-fold increase in insulin iAUC (P < .001). Although the plasma insulin response was greater following WP, ISR was unaffected (P = .133).

CONCLUSION

In adults with T2D, pre-meal WP reduced PPG by coordinating an enhancement in β-cell function with a reduction in insulin clearance. This enabled an efficient postprandial insulinemic profile to be achieved without requiring further β-cell stimulation.Trial registry ISRCTN ID: ISRCTN17563146 Website link: www.isrctn.com/ISRCTN17563146.

Role of Oxidative Stress and Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1 in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) has become a widely studied subject due to its increasing prevalence and links to diseases such as type 2 diabetes and obesity. It has severe complications, including nonalcoholic steatohepatitis, cirrhosis, hepatocellular carcinoma, and portal hypertension that can lead to liver transplantation in some cases. To better prevent and treat this pathology, it is important to understand its underlying physiology. Here, we identify two main factors that play a crucial role in the pathophysiology of NAFLD: oxidative stress and the key role of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1). We discuss the pathophysiology linking these factors to NAFLD pathophysiology.

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

CONTEXT

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).

OBJECTIVE

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.

METHODS

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).

RESULTS

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.

CONCLUSION

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.

Impact of Obesity on Postprandial Triglyceride Contribution to Glucose Homeostasis, Assessed with a Semimechanistic Model

The integrated glucose-insulin model is a semimechanistic model describing glucose and insulin after a glucose challenge. Similarly, a semiphysiologic model of the postprandial triglyceride (TG) response in chylomicrons and VLDL-V6 was recently published. We have developed the triglyceride-insulin-glucose-GLP-1 (TIGG) model by integrating these models and active GLP-1. The aim was to characterize, using the TIGG model, the postprandial response over 13 hours following a high-fat meal in 3 study populations based on body mass index categories: lean, obese, and very obese. Differential glucose and lipid regulation were observed between the lean population and obese or very obese populations. A population comparison revealed further that fasting glucose and insulin were elevated in obese and very obese when compared with lean; and euglycemia was achieved at different times postmeal between the obese and very obese populations. Postprandial insulin was incrementally elevated in the obese and very obese populations compared with lean. Postprandial chylomicrons TGs were similar across populations, whereas the postprandial TGs in VLDL-V6 were increased in the obese and very obese populations compared with lean. Postprandial active GLP-1 was diminished in the very obese population compared with lean or obese. The TIGG model described the response following a high-fat meal in individuals who are lean, obese, and very obese and provided insight into the possible regulation of glucose homeostasis in the extended period after the meal by utilizing lipids. The TIGG-model is the first model to integrate glucose and insulin regulation, incretin effect, and postprandial TGs response in chylomicrons and VLDL-V6.

Endogenous Lipid-GPR120 Signaling Modulates Pancreatic Islet Homeostasis to Different Extents

Long-chain fatty acids (LCFAs) are not only energy sources but also serve as signaling molecules. GPR120, an LCFA receptor, plays key roles in maintaining metabolic homeostasis. However, whether endogenous ligand-GPR120 circuits exist and how such circuits function in pancreatic islets are unclear. Here, we found that endogenous GPR120 activity in pancreatic δ-cells modulated islet functions. At least two unsaturated LCFAs, oleic acid (OA) and linoleic acid (LA), were identified as GPR120 agonists within pancreatic islets. These two LCFAs promoted insulin secretion by inhibiting somatostatin secretion and showed bias activation of GPR120 in a model system. Compared with OA, LA exerted higher potency in promoting insulin secretion, which is dependent on β-arrestin2 function. Moreover, GPR120 signaling was impaired in the diabetic db/db model, and replenishing OA and LA improved islet function in both the db/db and streptozotocin-treated diabetic models. Consistently, the administration of LA improved glucose metabolism in db/db mice. Collectively, our results reveal that endogenous LCFA-GPR120 circuits exist and modulate homeostasis in pancreatic islets. The contributions of phenotype differences caused by different LCFA-GPR120 circuits within islets highlight the roles of fine-tuned ligand-receptor signaling networks in maintaining islet homeostasis.

Pain relief and pain intensity response to GLP-1 receptor agonist ROSE-010 in irritable bowel syndrome; clinical study cross-analysis with respect to patient characteristics

BACKGROUND AND AIMS

Glucagon-like peptide-1 receptor agonist ROSE-010 has been studied for management of irritable bowel syndrome (IBS). ROSE-010 showed promising effects by reducing pain during attacks of IBS. In this exploratory substudy, we cross-analyzed earlier data to identify the most suitable subpopulation for treatment with ROSE-010.

METHODS

Data comprising 166 participants (116 females, 50 males) treated by subcutaneous injection with ROSE-010 at 100 µg and 300 µg versus placebo were broken down into subpopulations with recall of historical pain intensity, pain intensity immediately before treatment, gender, age, BMI, IBS subtype as well as pain intensity and pain relief of ROSE-010 with relationship to plasma glucose using visual analogue scores. Statistical cross-analysis was performed to detect optimal responders for adequate pain relief response.

RESULTS

ROSE-010 gave dose- and time-dependent effects with maximum pain relief at 300 µg relative 100 µg and placebo at 120 min post injection. Females had greater pain relief than males; age and BMI did not affect treatment response. IBS pain relief was greatest in constipation-dominant IBS (IBS-C) and mixed IBS (IBS-M) relative diarrhea-dominant and unspecified IBS.

CONCLUSIONS

Clinical trial data indicate that female participants are more likely than males to respond to ROSE-010 100 µg and 300 µg to achieve meaningful IBS pain relief. Maximum pain relief was achieved at 120 min with the higher dose, although this was accompanied with higher rates of nausea. Improvement of IBS pain attacks was most pronounced in IBS-C and IBS-M, suggesting these subgroups to be optimal ROSE-010 responders.

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

AIM

To present an overview of exendin(9-39)NH₂ usage as a scientific tool in humans and provide recommendations for dosage and infusion regimes.

METHODS

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.

RESULTS

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 ~2.5 hours 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.

CONCLUSIONS

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.

Phytochemicals modulate pancreatic islet β cell function through glucagon-like peptide-1-related mechanisms

Glucagon-like peptide-1 (GLP-1) receptor-based therapies have been developed and extensively applied in clinical practice. GLP-1 plays an important role in improving glycemic homeostasis by stimulating insulin biosynthesis and secretion, suppressing glucagon activity, delaying gastric emptying, and reducing appetite and food ingestion. Furthermore, GLP-1 has positive effects on β-cell function by promoting β-cell proliferation and neogenesis while simultaneously reducing apoptosis. Here, we summarize possible mechanisms of action of GLP-1 upon pancreatic islets as well as describe phytochemicals that modulate pancreatic islet β cell function through glucagon-like peptide-1-related mechanisms. Together, this information provides potential lead compound candidates against diabetes that function as GLP-1 receptor-based pharmacotherapy.

Non-glucose modulators of insulin secretion in healthy humans: (dis)similarities between islet and in vivo studies

Optimal metabolic homeostasis requires precise temporal and quantitative control of insulin secretion. Both in vivo and in vitro studies have often focused on the regulation by glucose although many additional factors including other nutrients, neurotransmitters, hormones and drugs, modulate the secretory function of pancreatic β-cells. This review is based on the analysis of clinical investigations characterizing the effects of non-glucose modulators of insulin secretion in healthy subjects, and of experimental studies testing the same modulators in islets isolated from normal human donors. The aim was to determine whether the information gathered in vitro can reliably be translated to the in vivo situation. The comparison evidenced both convincing similarities and areas of discordance. The lack of coherence generally stems from the use of exceedingly high concentrations of test agents at too high or too low glucose concentrations in vitro, which casts doubts on the physiological relevance of a number of observations made in isolated islets. Future projects resorting to human islets should avoid extreme experimental conditions, such as oversized stimulations or inhibitions of β-cells, which are unlikely to throw light on normal insulin secretion and contribute to the elucidation of its defects.

Electronic Bypass for Diabetes: Optimization of Stimulation Parameters and Mechanisms of Glucagon-Like Peptide-1

OBJECTIVES

Intestinal electrical stimulation (IES) has been proposed for treating diabetes; however, its parameters need to be further systematically optimized. This study aimed to optimize the parameters of IES and investigate its possible mechanisms involving glucagon-like peptide-1 (GLP-1) in diabetic rats.

MATERIALS AND METHODS

Thirty-six high-fat diet-induced diabetic rats were chronically implanted with a pair of bipolar electrodes at the duodenum for IES. The oral glucose tolerance test (OGTT) was performed in a number of sessions with IES using different parameters and biphasic charge-balanced waveforms to derive the best values for train on-time, pulse frequency, and pulse width. Incretin hormones such as GLP-1 were assessed and the GLP-1 antagonist Exendin 9-39 was used to assess the role of GLP-1 in the ameliorating effect of IES on hyperglycemia.

RESULTS

The most effective IES parameters in reducing blood glucose (BG) during the OGTT were derived: 1.2 sec on, 0.3 sec off, 80 Hz, 3 msec. IES with these parameters reduced BG level by at least 29% from 15 min to 180 min (p < 0.05 for all points, N = 10). IES with these stimulation parameters increased plasma GLP-1 level at 30 min, 60 min, 90 min and gastric inhibitory peptide (GIP) level at 30 min (N = 8). Exendin 9-39 blocked the inhibitory effect of IES on BG (p > 0.05, IES + Exendin 9-39 vs. sham-IES, N = 8).

CONCLUSION

IES with the most effective parameters derived in this study improves hyperglycemia in diabetic rats. The ameliorating effect of IES on hyperglycemia is attributed to the enhanced release of GLP-1. IES has great potential for treating diabetes.

Cerebral effects of glucagon-like peptide-1 receptor blockade before and after Roux-en-Y gastric bypass surgery in obese women: A proof-of-concept resting-state functional MRI study

AIM

To assess the effects of Roux-en-Y gastric bypass surgery (RYGB)-related changes in glucagon-like peptide-1 (GLP-1) on cerebral resting-state functioning in obese women.

MATERIALS AND METHODS

In nine obese females aged 40-54 years in the fasted state, we studied the effects of RYGB and GLP-1 on five a priori selected networks implicated in food- and reward-related processes as well as environment monitoring (default mode, right frontoparietal, basal ganglia, insula/anterior cingulate and anterior cingulate/orbitofrontal networks).

RESULTS

Before surgery, GLP-1 receptor blockade (using exendin9-39) was associated with increased right caudate nucleus (basal ganglia network) and decreased right middle frontal (right frontoparietal network) connectivity compared with placebo. RYGB resulted in decreased right orbitofrontal (insula/anterior cingulate network) connectivity. In the default mode network, after surgery, GLP-1 receptor blockade had a larger effect on connectivity in this region than GLP-1 receptor blockade before RYGB (all P_FWE  < .05). Results remained similar after correction for changes in body weight. Default mode and right frontoparietal network connectivity changes were related to changes in body mass index and food scores after RYGB.

CONCLUSIONS

These findings suggest GLP-1 involvement in resting-state networks related to food and reward processes and monitoring of the internal and external environment, pointing to a potential role for GLP-1-induced changes in resting-state connectivity in RYGB-mediated weight loss and appetite control.

The altered enteroendocrine reportoire following roux-en-Y-gastric bypass as an effector of weight loss and improved glycaemic control

The alarming rise in obesity and relative lack of pharmacotherapies to treat, what is becoming a global epidemic, has necessitated that an increasing number of bariatric procedures be performed. Several surgical techniques have been developed during the last 50 years and the advent of laparoscopic surgery has increased the safety and efficacy of these procedures. Bariatric surgery is by a substantial margin, the most efficacious means of achieving sustained weight loss maintenance in patients with obesity. Roux-en-Y gastric bypass surgery (RYGB) elicits the most favourable metabolic outcomes with attendant benefits for type 2 diabetes and, cardiovascular disease as well as endocrine disorders and cancers in females. RYGB is the most extensively studied bariatric procedure regarding mechanism of action. In this review we catalogue the multiple alterations in secretion of gut hormones (ghrelin, obestatin, cholecystokinin, GLP-1, PYY, GIP, oxyntomodulin, glicentin and GLP-2) occurring after RYGB and summarise evidence indicating that these changes play a role in the reduction of food intake and improvements in glucose homeostasis.

Liraglutide Protects Against Brain Amyloid-β1-42 Accumulation in Female Mice with Early Alzheimer's Disease-Like Pathology by Partially Rescuing Oxidative/Nitrosative Stress and Inflammation

Alzheimer’s disease (AD) is the most common form of dementia worldwide, being characterized by the deposition of senile plaques, neurofibrillary tangles (enriched in the amyloid beta (Aβ) peptide and hyperphosphorylated tau (p-tau), respectively) and memory loss. Aging, type 2 diabetes (T2D) and female sex (especially after menopause) are risk factors for AD, but their crosslinking mechanisms remain unclear. Most clinical trials targeting AD neuropathology failed and it remains incurable. However, evidence suggests that effective anti-T2D drugs, such as the GLP-1 mimetic and neuroprotector liraglutide, can be also efficient against AD. Thus, we aimed to study the benefits of a peripheral liraglutide treatment in AD female mice. We used blood and brain cortical lysates from 10-month-old 3xTg-AD female mice, treated for 28 days with liraglutide (0.2 mg/kg, once/day) to evaluate parameters affected in AD (e.g., Aβ and p-tau, motor and cognitive function, glucose metabolism, inflammation and oxidative/nitrosative stress). Despite the limited signs of cognitive changes in mature female mice, liraglutide only reduced their cortical Aβ_1–42 levels. Liraglutide partially attenuated brain estradiol and GLP-1 and activated PKA levels, oxidative/nitrosative stress and inflammation in these AD female mice. Our results support the earlier use of liraglutide as a potential preventive/therapeutic agent against the accumulation of the first neuropathological features of AD in females.

Flavone Hispidulin Stimulates Glucagon-Like Peptide-1 Secretion and Ameliorates Hyperglycemia in Streptozotocin-Induced Diabetic Mice

SCOPE

Loss of functional β-cell mass is central for the deterioration of glycemic control in diabetes. The incretin hormone glucagon-like peptide-1 (GLP-1) plays a critical role in maintaining glycemic homeostasis via potentiating glucose-stimulated insulin secretion and promoting β-cell mass. Agents that can directly promote GLP-1 secretion, thereby increasing insulin secretion and preserving β-cell mass, hold great potential for the treatment of T2D.

METHODS AND RESULTS

GluTag L-cells, INS832/13 cells, and mouse ileum crypts and islets are cultured for examining the effects of flavone hispidulin on GLP-1 and insulin secretion. Mouse livers and isolated hepatocytes are used for gluconeogenesis. Streptozotocin-induced diabetic mice are treated with hispidulin (20 mg kg^-1 day^-1 , oral gavage) for 6 weeks to evaluate its anti-diabetic potential. Hispidulin stimulates GLP-1 secretion from the L-cell line, ileum crypts, and in vivo. This hispidulin action is mediated via activation of cyclic adenosine monophosphate/protein kinase A signaling. Hispidulin significantly improves glycemic control in diabetic mice, concomitant with improved insulin release, and β-cell survival. Additionally, hispidulin decreases hepatic pyruvate carboxylase expression in diabetic mice and suppresses gluconeogenesis in hepatocytes. Furthermore, hispidulin stimulates insulin secretion from β-cells.

CONCLUSION

These findings suggest that Hispidulin may be a novel dual-action anti-diabetic compound via stimulating GLP-1 secretion and suppressing hepatic glucose production.

Sustained Improvements in Glucose Metabolism Late After Roux-En-Y Gastric Bypass Surgery in Patients with and Without Preoperative Diabetes

To describe glucose metabolism in the late, weight stable phase after Roux-en-Y Gastric Bypass (RYGB) in patients with and without preoperative type 2 diabetes we invited 55 RYGB-operated persons from two existing cohorts to participate in a late follow-up study. 44 (24 with normal glucose tolerance (NGT)/20 with type 2 diabetes (T2D) before surgery) accepted the invitation (median follow-up 2.7 [Range 2.2–5.0 years]). Subjects were examined during an oral glucose stimulus and results compared to preoperative and 1-year (1 y) post RYGB results. Glucose tolerance, insulin resistance, beta-cell function and incretin hormone secretion were evaluated. 1 y weight loss was maintained late after surgery. Glycemic control, insulin resistance, beta-cell function and GLP-1 remained improved late after surgery in both groups. In NGT subjects, nadir glucose decreased 1 y after RYGB, but did not change further. In T2D patients, relative change in weight from 1 y to late after RYGB correlated with relative change in fasting glucose and HbA1c, whereas relative changes in glucose-stimulated insulin release correlated inversely with relative changes in postprandial glucose excursions. In NGT subjects, relative changes in postprandial nadir glucose correlated with changes in beta-cell glucose sensitivity. Thus, effects of RYGB on weight and glucose metabolism are maintained late after surgery in patients with and without preoperative T2D. Weight loss and improved beta-cell function both contribute to maintenance of long-term glycemic control in patients with type 2 diabetes, and increased glucose stimulated insulin secretion may contribute to postprandial hypoglycemia in NGT subjects.

The incretin system in healthy humans: The role of GIP and GLP-1

The incretin effect, the amplification of insulin secretion occurring when glucose is taken in orally as compared to infused intravenously, is one of the factors that help the body to tolerate carbohydrate/glucose ingestion. These include 1) amount and type of carbohydrates; 2) gastric emptying rate; 3) digestion and absorption of the carbohydrates; 4) secretion and effect of the incretin hormones; 5) disposition of absorbed nutrients/glucose. The incretin effect can also be viewed as the fraction of the ingested glucose load handled via gastrointestinal mechanisms (including the incretin effect); it is calculated by comparison of the amount of glucose required to copy, by intravenous infusion, the oral load. Typically, for 75 g of oral glucose, about 25 g are required. This means that the GastroIntestinal Glucose Disposal (GIGD) is 66%. Both the GIGD and the incretin effect depend on the amount of glucose ingested: for higher doses the GIGD may amount to 80%, which shows that this effect is a major contributor to glucose tolerance. The main mechanism behind it is stimulation of insulin secretion by a proportional secretion of the insulinotropic hormones GIP and GLP-1. Recently it has become possible to estimate their contributions in healthy humans using specific and potent receptor antagonists. Both hormones act to improve glucose tolerance (i.e. the antagonists impair tolerance) and their effects are additive. GIP seems to be quantitatively the most important, particularly regarding insulin secretion, whereas the action of GLP-1 is mainly displayed via inhibition of glucagon secretion.

Intestinal electrical stimulation attenuates hyperglycemia and prevents loss of pancreatic β cells in type 2 diabetic Goto-Kakizaki rats

BACKGROUND/OBJECTIVE

Recently, intestinal electrical stimulation (IES) has been reported to result in weight loss; however, it is unclear whether it has a therapeutic potential for diabetes. The aim of the present study was to explore the potential hypoglycemic effects of IES and its possible mechanisms involving β cells in diabetic rats.

SUBJECTS/METHODS

Diabetic Goto-Kakizaki (GK) rats were chronically implanted with one pair of electrodes in the duodenum. The oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) were performed with or without IES, and plasma glucagon-like peptide-1 (GLP-1) and insulin level were measured. In the other two OGTT sessions, rats were treated with either Exendin (9-39) (GLP-1 antagonist) or Exendin (9-39) plus IES to investigate the underlying mechanism involving GLP-1. Gastric emptying and small intestinal transit were also measured with or without IES. In a chronic study, GK rats were treated with IES or Sham-IES for 8 weeks. Blood glucose, plasma GLP-1 and insulin level, body weight, and food intake were measured. Pancreas weight, islet β-cell apoptosis, and proliferation were also analyzed.

RESULTS

Acute IES reduced blood glucose level from 60 to 120 min during OGTT by 16-20% (all p < 0.05, vs. Sham-IES). GLP-1 antagonist significantly blocked the inhibitory effect of IES on hyperglycemia from 15 to 120 min (all p < 0.05). IES accelerated the small intestinal transit by 15% (p = 0.004). After 8 weeks of chronic stimulation, IES significantly reduced blood glucose (p < 0.05) and body weight (p = 0.02) and increased the plasma GLP-1 concentration (p < 0.05). Furthermore, we observed that chronic IES reduced pancreatic β-cell apoptosis (p = 0.045), but showed no effects on β-cell proliferation.

CONCLUSIONS

Our study firstly proved the hypoglycemic effect of IES in a rodent model of type 2 diabetes, possibly attributed to the increasing GLP-1 secretion and improvement in β-cell functions.

The Role of Glucagon-Like Peptide-1 in Energy Homeostasis

Energy homeostasis is coordinated by bidirectional communication pathways between the brain and peripheral organs, including adipose tissue, muscle, the pancreas, liver, and gut. Disruption of the integrated chemical, hormonal, and neuronal signals that constitute the gut-brain axis significantly contributes to disorders of metabolism and body weight. Initial studies of glucagon-like peptide-1 (GLP-1), a gut hormone released in response to the ingestion of nutrients, focused on its incretin actions to improve postprandial glucose homeostasis by enhancing meal-induced insulin secretion. However, GLP-1 is also a key player in the gut-brain regulatory axis with multiple effects on appetite and energy metabolism outside of its peripheral glucoregulatory actions. In this review, we explore the function of GLP-1 as a component of the gut-brain axis in the regulation of energy homeostasis, and consider the implications of this role for the development of therapeutic treatment options for obesity.

Glucagon and insulin secretion, insulin clearance, and fasting glucose in GIP receptor and GLP-1 receptor knockout mice

It is not known whether GIP receptor and GLP-1 receptor knockout (KO) mice have perturbations in glucagon secretion or insulin clearance, and studies on impact on fasting glycemia have previously been inconsistent in these mice. We therefore studied glucagon secretion after oral whey protein (60 mg) and intravenous arginine (6.25 mg), insulin clearance after intravenous glucose (0.35 g/kg) and fasting glucose, insulin, and glucagon levels after standardized 5-h fasting in female GIP receptor and GLP-1 receptor KO mice and their wild-type (WT) littermates. Compared with WT controls, GIP receptor KO mice had normal glucagon responses to oral protein and intravenous arginine, except for an enhanced 1-min response to arginine, whereas glucagon levels after oral protein and intravenous arginine were enhanced in GLP-1 receptor KO mice. Furthermore, the intravenous glucose test revealed normal insulin clearance in both GIP receptor and GLP-1 receptor KO mice, whereas β-cell glucose sensitivity was enhanced in GIP receptor KO mice and reduced in GLP-1 receptor KO mice. Finally, GIP receptor KO mice had reduced fasting glucose (6.7 ± 0.1, n = 56, vs. 7.4 ± 0.1 mmol/l, n = 59, P = 0.001), whereas GLP-1 receptor KO mice had increased fasting glucose (9.1 ± 0.2, n = 44, vs. 7.7 ± 0.1 mmol/l, n = 41, P < 0.001). We therefore suggest that GIP has a limited role for glucagon secretion in mice, whereas GLP-1 is of importance for glucagon regulation, that GIP and GLP-1 are of importance for the regulation of β-cell function beyond their role as incretin hormones, and that they are both of importance for fasting glucose.

Remote ischemic conditioning protects against endothelial ischemia-reperfusion injury via a glucagon-like peptide-1 receptor-mediated mechanism in humans

BACKGROUND

Remote ischemic conditioning (RIC), i.e. short cycles of ischemia and reperfusion in remote tissue, is a novel approach to protect against myocardial ischemia-reperfusion injury in ST-elevation myocardial infarction. The nature of the factors transmitting the protective effect of RIC remains unknown, and both neuronal and hormonal mechanisms appear to be involved. A recent study indicated involvement of glucagon-like peptide-1 (GLP-1) regulated by the vagal nerve in RIC in rats. In the present study we aimed to investigate whether the protective effect of RIC is mediated by a GLP-1 receptor-dependent mechanism in humans.

METHODS

Endothelial function was determined from flow-mediated dilatation (FMD) of the brachial artery before and after 20 min of forearm ischemia and 20 min of reperfusion in twelve healthy subjects on three occasions: (A) ischemia-reperfusion without intervention, (B) ischemia-reperfusion + RIC and (C) iv administration of the GLP-1 receptor antagonist exendin(9-39) + ischemia-reperfusion + RIC.

RESULTS

Ischemia-reperfusion reduced FMD from 4.7 ± 0.8% at baseline to 1.5 ± 0.4% (p < 0.01). RIC protected from the impairment in FMD induced by ischemia-reperfusion (4.6 ± 1.1% at baseline vs. 5.0 ± 1.1% following ischemia-reperfusion). Exendin(9-39) abolished the protection induced by RIC (FMD 4.9 ± 0.9% at baseline vs. 1.4 ± 1.3% following ischemia-reperfusion; p < 0.01) but did not affect basal FMD. Plasma GLP-1 levels did not change significantly between examinations.

CONCLUSION

The present study is the first to suggest that RIC protects against endothelial ischemia-reperfusion injury via a GLP-1 receptor-mediated mechanism in humans.

Islet prohormone processing in health and disease

Biosynthesis of peptide hormones by pancreatic islet endocrine cells is a tightly orchestrated process that is critical for metabolic homeostasis. Like neuroendocrine peptides, insulin and other islet hormones are first synthesized as larger precursor molecules that are processed to their mature secreted products through a series of proteolytic cleavages, mediated by the prohormone convertases Pc1/3 and Pc2, and carboxypeptidase E. Additional posttranslational modifications including C-terminal amidation of the β-cell peptide islet amyloid polypeptide (IAPP) by peptidyl-glycine α-amidating monooxygenase (Pam) may also occur. Genome-wide association studies (GWAS) have showed genetic linkage of these processing enzymes to obesity, β-cell dysfunction, and type 2 diabetes (T2D), pointing to their important roles in metabolism and blood glucose regulation. In both type 1 diabetes (T1D) and T2D, and in the face of metabolic or inflammatory stresses, islet prohormone processing may become impaired; indeed elevated proinsulin:insulin (PI:I) ratios are a hallmark of the β-cell dysfunction in T2D. Recent studies suggest that genetic or acquired defects in proIAPP processing may lead to the production and secretion of incompletely processed forms of proIAPP that could contribute to T2D pathogenesis, and additionally that impaired processing of both PI and proIAPP may be characteristic of β-cell dysfunction in T1D. In islet α-cells, the prohormone proglucagon is normally processed to bioactive glucagon by Pc2 but may express Pc1/3 under certain conditions leading to production of GLP-1(7-36_NH2 ). A better understanding of how β-cell processing of PI and proIAPP, as well as α-cell processing of proglucagon, are impacted by genetic susceptibility and in the face of diabetogenic stresses, may lead to new therapeutic approaches for improving islet function in diabetes.

Interleukin-6 Delays Gastric Emptying in Humans with Direct Effects on Glycemic Control

Gastric emptying is a critical regulator of postprandial glucose and delayed gastric emptying is an important mechanism of improved glycemic control achieved by short-acting glucagon-like peptide-1 (GLP-1) analogs in clinical practice. Here we report on a novel regulatory mechanism of gastric emptying in humans. We show that increasing interleukin (IL)-6 concentrations delays gastric emptying leading to reduced postprandial glycemia. IL-6 furthermore reduces insulin secretion in a GLP-1-dependent manner while effects on gastric emptying are GLP-1 independent. Inhibitory effects of IL-6 on gastric emptying were confirmed following exercise-induced increases in IL-6. Importantly, gastric- and insulin-reducing effects were maintained in individuals with type 2 diabetes. These data have clinical implications with respect to the use of IL-6 inhibition in autoimmune/inflammatory disease, and identify a novel target that could be exploited pharmacologically to delay gastric emptying and spare insulin, which may be beneficial for the beta cell in type 2 diabetes.

Altered glucose metabolism after bariatric surgery: What's GLP-1 got to do with it?

Bariatric surgery is an effective treatment for obesity. The two widely performed weight-loss procedures, Roux-en-Y gastric bypass (GB) and sleeve gastrectomy (SG), alter postprandial glucose pattern and enhance gut hormone secretion immediately after surgery before significant weight loss. This weight-loss independent glycemic effects of GB has been attributed to an accelerated nutrient transit from stomach pouch to the gut and enhanced secretion of insulinotropic gut factors; in particular, glucagon-like peptide-1 (GLP-1). Meal-induced GLP-1 secretion is as much as tenfold higher in patients after GB compared to non-surgical individuals and inhibition of GLP-1 action during meals reduces postprandial hyperinsulinemia after GB two to three times more than that in persons without surgery. Moreover, in a subgroup of patients with the late complication of postprandial hyperinsulinemic hypoglycemia after GB, GLP1R blockade reverses hypoglycemia by reducing meal stimulated insulin secretion. The role of enteroinsular axis activity after SG, an increasingly popular alternative to GB, is less understood but, similar to GB, SG accelerates nutrient delivery to the intestine, improves glucose tolerance, and increases postprandial GLP-1 secretion. This review will focus on the current evidence for and against the role of GLP-1 on glycemic effects of GB and will also highlight differences between GB and SG.

Regulation of glucose metabolism in nondiabetic, metabolically obese normal-weight Asians

Type 2 diabetes in Asia occurs largely in the absence of obesity. The metabolically obese normal-weight (MONW) phenotype refers to lean subjects with metabolic dysfunction that is typically observed in people with obesity and is associated with increased risk for diabetes. Previous studies evaluated MONW subjects who had greater body mass index (BMI) or total body fat than respective control groups, making interpretation of the results difficult. We evaluated insulin sensitivity (hyperinsulinemic-euglycemic clamp); insulin secretion (mixed meal with oral minimal modeling); intra-abdominal, muscle, and liver fat contents (magnetic resonance); and fasting and postprandial glucose and insulin concentrations in 18 MONW subjects and 18 metabolically healthy controls matched for age (43 ± 3 and 40 ± 3 yr; P = 0.52), BMI (both 22 ± 1 kg/m²; P = 0.69), total body fat (17 ± 1 and 16 ± 1 kg; P = 0.33), and sex (9 men and 9 women in each group). Compared with controls, MONW subjects had an approximately twofold greater visceral adipose tissue volume and an approximately fourfold greater intrahepatic fat content (but similar muscle fat), 20-30% lower glucose disposal rates and insulin sensitivity, and 30-40% greater insulin secretion rates (all P < 0.05). The disposition index, fasting glucose, and HbA1c concentrations were not different between groups, whereas postprandial glucose and insulin concentrations were ~15% and ~65% greater, respectively, in MONW than control subjects (both P < 0.05). We conclude that the MONW phenotype is associated with accumulation of fat in the intra-abdominal area and the liver, profound insulin resistance, but also a robust β-cell insulin secretion response that compensates for insulin resistance and helps maintain glucose homeostasis.

The effects of short-term continuous subcutaneous insulin infusion treatment on fasting glucagon-like peptide-1 concentrations in newly diagnosed type 2 diabetes

OBJECTIVE

Early short-term intensive insulin therapy in newly diagnosed type 2 diabetes patients shows benefit in glycemic control and β-cell function. Glucagon-like peptide-1 (GLP-1) plays an important role in glucose metabolism and development of type 2 diabetes. We did a study to observe the changes of GLP-1 and β-cell function after short-term continuous subcutaneous insulin infusion (CSII) treatment.

METHODS

A total of 66 subjects were enrolled, including 30 normal glucose tolerance controls (NGT) and 36 patients with newly diagnosed type 2 diabetes between October 2015 and July 2016. Fasting plasma glucose (FPG), insulin, and GLP-1 were measured in each subject. The patients underwent CSII treatment for 2 weeks, and then FBG, insulin, and GLP-1 were measured. HOMA-IR and HOMA-B were then calculated.

RESULTS

All patients achieved target glycemic control in two weeks. HOMA-IR and HOMA-B improved significantly after intensive interventions (p < 0.05). The GLP-1 concentration increased significantly in patients after treatment (p < 0.05). When grouped according to bodyweight and age in all patients, the HOMA-IR changed significantly in overweight and old age subgroups, the HOMA-B increased significantly in normal weight, overweight and middle age subgroups, and the GLP-1 concentration also increased significantly in overweight and middle age subgroups respectively (p < 0.05).

CONCLUSION

Short-term CSII treatment can obtain glycemic control target and recover β-cell function and GLP-1 secretion in newly diagnosed type 2 diabetes patients. The overweight and middle-aged patients may get more benefit from this treatment.

Liraglutide improves hepatic insulin resistance via the canonical Wnt signaling pathway

Liraglutide, a modified form of glucagon‑like peptide‑1 (GLP‑1), is used in the treatment of diabetes mellitus. However, the underlying mechanism by which liraglutide improves liver insulin resistance remains to be elucidated. The proto‑oncogene Wnt (Wnt) signaling pathway has been reported to be associated with glucose and lipid metabolism. Using in vivo and in vitro models of diabetes and insulin resistance, it was investigated whether the beneficial effects of liraglutide on liver glucose metabolism are mediated by the Wnt signaling pathway. The results of the present study demonstrate that body weight, fasting blood glucose, insulin levels and the homeostasis model assessment for insulin resistance were markedly decreased in db/db mice treated with liraglutide compared with control mice. Liraglutide also improved liver morphology and reduced the accumulation of lipid droplets. Furthermore, the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase was downregulated, whereas the expression of phosphorylated forkhead box O1, Wnt signaling pathway‑associated molecules, β‑catenin, transcription factor 7‑like 2 and phosphorylated glycogen synthase kinase-3β was upregulated in the liver of mice treated with liraglutide. In the in vitro study, increased gluconeogenesis and decreased glucose uptake rates were observed in insulin resistant hepatocytes; treatment with liraglutide significantly reversed this effect. Furthermore, transfection of insulin resistant hepatocytes with β‑catenin small interfering RNA attenuated the effects of liraglutide, suggesting that liraglutide improves insulin resistance via activating the β‑catenin/Wnt signaling pathway. The results of the present study suggest a novel mechanism underlying liraglutide‑mediated improvements in insulin resistance in the liver. The Wnt signaling pathway may be a potential therapeutic target for the treatment of altered hepatic physiology in insulin resistance.

Delayed Administration of the Glucagon-Like Peptide 1 Analog Liraglutide Promoting Angiogenesis after Focal Cerebral Ischemia in Mice

BACKGROUND

Glucagon-like peptide 1 (GLP-1) analogs administered before or after cerebral ischemia have been shown to provide neuroprotection. Here, we explored whether delayed administration of a GLP-1 analog, liraglutide, could improve long-term functional recovery and promote angiogenesis after stroke.

MATERIALS AND METHODS

In the present study, mice were established as a focal cerebral cortical ischemia model and were intraperitoneally administered liraglutide or normal saline (NS) daily for 14 consecutive days, starting 1 day after cerebral ischemia. The neurological deficits were evaluated using rotarod test. The microvessel density (MVD) and endothelial cell (EC) proliferation were assessed by immunohistochemical staining. The expression of vascular endothelial growth factor (VEGF) was assessed by Western blot analysis.

RESULTS

Liraglutide significantly reduced infarct volume and improved the rotarod test scores, compared with mice treated with NS. Liraglutide also greatly increased the MVD and EC proliferation and simultaneously upregulated the expression of VEGF in the cerebral ischemic area.

CONCLUSIONS

These results demonstrated that liraglutide promoted angiogenesis and long-term recovery of cerebral ischemia through increasing the expression of VEGF.

Dysregulated bile acid synthesis and dysbiosis are implicated in Western diet-induced systemic inflammation, microglial activation, and reduced neuroplasticity

The goal of this study was to identify the intrinsic links that explain the effect of a Western diet (WD) on cognitive dysfunction. Specific pathogen-free, wild-type mice were fed either a control diet (CD) or a high-fat, high-sucrose WD after weaning and were euthanized at 10 mo of age to study the pathways that affect cognitive health. The results showed that long-term WD intake reduced hippocampal synaptic plasticity and the level of brain-derived neurotrophic factor mRNA in the brain and isolated microglia. A WD also activated ERK1/2 and reduced postsynaptic density-95 in the brain, suggesting postsynaptic damage. Moreover, WD-fed mice had increased inflammatory signaling in the brain, ileum, liver, adipose tissue, and spleen, which was accompanied by microglia activation. In the brain, as well as in the digestive tract, a WD reduced signaling regulated by retinoic acid and bile acids (BAs), whose receptors form heterodimers to control metabolism and inflammation. Furthermore, a WD intake caused dysbiosis and dysregulated BA synthesis with reduced endogenous ligands for BA receptors, i.e., farnesoid X receptor and G-protein-coupled bile acid receptor in the liver and brain. Together, dysregulated BA synthesis and dysbiosis were accompanied by systemic inflammation, microglial activation, and reduced neuroplasticity induced by WD.-Jena, P. K., Sheng, L., Di Lucente, J., Jin, L.-W., Maezawa, I., Wan, Y.-J. Y. Dysregulated bile acid synthesis and dysbiosis are implicated in Western diet-induced systemic inflammation, microglial activation, and reduced neuroplasticity.

Liraglutide ameliorates cognitive decline by promoting autophagy via the AMP-activated protein kinase/mammalian target of rapamycin pathway in a streptozotocin-induced mouse model of diabetes

Diabetic cognitive dysfunction has gained widespread attention for its deleterious impact on individuals with diabetes. However, few clinical interventions are available to prevent the disorder. The glucagon-like peptide-1 analog liraglutide exerts neuroprotective effects in several models of neurodegenerative diseases. We investigated the effect of liraglutide pretreatment on diabetes-induced cognitive decline and explored the underlying mechanisms in vivo and in vitro. Liraglutide pretreatment prevented diabetes-induced cognitive impairment as assessed by the Morris Water Maze test, and alleviated neuronal injuries and ultrastructural damage to synapses in the hippocampal CA1 region. Furthermore, liraglutide promoted autophagy as indicated by enhanced expression of the autophagy markers Microtubule-associated protein 1 light chain 3 (LC3)-II and Beclin 1, decreased expression of p62, and increased formation of autophagic vacuoles and LC3-II aggregates. In vitro, liraglutide treatment elevated phosphorylated (p)-AMP-activated protein kinase (AMPK) levels and reduced p-mammalian target of rapamycin (p-mTOR) expression. Additionally, the AMPK inhibitor Compound C exhibited an inhibitory effect on liraglutide-induced increased LC3-II expression and p62 degradation. Liraglutide exhibits neuroprotective effects against diabetes-induced hippocampal neuronal injuries and cognitive impairment by promoting autophagy via the AMPK/mTOR pathway.

Pharmacotherapy of type 2 diabetes: An update

Type 2 diabetes (T2DM) is a leading cause of morbidity and mortality worldwide and a major economic burden. The prevalence of T2DM is rising, suggesting more effective prevention and treatment strategies are necessary. The aim of this narrative review is to summarize the pharmacologic treatment options available for patients with T2DM. Each therapeutic class is presented in detail, outlining medication effects, side effects, glycemic control, effect on weight, indications and contraindications, and use in selected populations (heart failure, renal insufficiency, obesity and the elderly). We also present representative cost for each antidiabetic category. Then, we provide an individualized guide for initiation and intensification of treatment and discuss the considerations and rationale for an individualized glycemic goal.

Exenatide exerts cognitive effects by modulating the BDNF-TrkB neurotrophic axis in adult mice

Modulation of insulin-dependent signaling is emerging as a valuable therapeutic tool to target neurodegeneration. In the brain, the activation of insulin receptors promotes cell growth, neuronal repair, and protection. Altered brain insulin signaling participates in the cognitive decline seen in Alzheimer's disease patients and the aging brain. Glucagon-like peptide-1 (GLP-1) regulates insulin secretion and, along with GLP-1 analogues, enhances neurotrophic signaling and counteracts cognitive deficits in preclinical models of neurodegeneration. Moreover, recent evidence indicates that GLP-1 modulates the activity of the brain-derived neurotrophic factor (BDNF). In this study, in adult wild-type mice, here employed as a model of mid-life brain aging, we evaluated the effects of a 2-month treatment with exenatide, a GLP-1 analogue. We found that exenatide promotes the enhancement of long-term memory performances. Biochemical and imaging analyses show that the drug promotes the activation of the BDNF-TrkB neurotrophic axis and inhibits apoptosis by decreasing p75NTR-mediated signaling. The study provides preclinical evidence for the use of exenatide to delay age-dependent cognitive decline.

The Dietary Furocoumarin Imperatorin Increases Plasma GLP-1 Levels in Type 1-Like Diabetic Rats

Imperatorin, a dietary furocoumarin, is found not only in medicinal plants, but also in popular culinary herbs, such as parsley and fennel. Recently, imperatorin has been shown to activate GPR119 in cells. Another GPR, GPR131, also called TGR5 or G-protein-coupled bile acid receptor 1 (GPBAR1), is known to regulate glucose metabolism. Additionally, TGR5 activation increases glucagon-like peptide (GLP-1) secretion to lower blood sugar levels in animals. Therefore, the present study aims to determine whether the effects of imperatorin on GLP-1 secretion are mediated by TGR5. First, we transfected cultured Chinese hamster ovary cells (CHO-K1 cells) with the TGR5 gene. Glucose uptake was confirmed in the transfected cells using a fluorescent indicator. Moreover, NCI-H716 cells, which secrete GLP-1, were used to investigate the changes in calcium concentrations and GLP-1 levels. In addition, streptozotocin (STZ)-induced type 1-like diabetic rats were used to identify the effects of imperatorin in vivo. Imperatorin dose-dependently increased glucose uptake in CHO-K1 cells expressing TGR5. In STZ diabetic rats, similar to the results in NCI-H716 cells, imperatorin induced a marked increase of GLP-1 secretion that was reduced, but not totally abolished, by a dose of triamterene that inhibited TGR5. Moreover, increases in GLP-1 secretion induced by imperatorin and GPR119 activation were shown in NCI-H716 cells. We demonstrated that imperatorin induced GLP-1 secretion via activating TGR5 and GPR119. Therefore, imperatorin shall be considered as a TGR5 and GPR119 agonist.

Dapagliflozin/Saxagliptin Fixed-Dose Tablets: A New Sodium-Glucose Cotransporter 2 and Dipeptidyl Peptidase 4 Combination for the Treatment of Type 2 Diabetes

Objective: To review the pharmacology, pharmacokinetics, efficacy, safety, and place in therapy of the fixed-dose combination (FDC) product, QTERN (dapagliflozin/saxagliptin) tablets. Data Sources: Searches of MEDLINE (1946 to July 1, 2017) were conducted using the keywords QTERN, saxagliptin, and dapagliflozin. Additional data were obtained from the prescribing information, the product dossier, and Clinicaltrials.gov . Study Selection and Data Extraction: All English language articles related to pharmacology, pharmacokinetics, efficacy, or safety of the combination therapy in human subjects were reviewed. Data Synthesis: The pharmacokinetics of saxagliptin and dapagliflozin were not affected significantly when administered as an FDC product. Saxagliptin may suppress the increased secretion of glucagon associated with dapagliflozin. The combination dapagliflozin/saxagliptin has been studied as add-on therapy to metformin in patients with uncontrolled type 2 diabetes mellitus (T2DM). The difference in hemoglobin A1C (A1C) between saxagliptin + dapagliflozin + metformin (triple therapy) and saxagliptin + metformin was −0.59 (95% CI = −0.81 to −0.37, P < 0.0001), and the difference between triple therapy and dapagliflozin + metformin was −0.27 (95% CI = −0.48 to −0.05, P = 0.0166). The combination was well tolerated when added to metformin. Conclusion: QTERN (dapagliflozin/saxagliptin) tablets are a reasonable option for patients with T2DM not controlled on metformin, but cost, insurance coverage, and a lackluster reduction in A1C will likely limit its use until more data regarding its effects on complications of diabetes and cardiovascular outcomes become available.

The Role of Pancreatic Preproglucagon in Glucose Homeostasis in Mice

Glucagon-like peptide 1 (GLP-1) is necessary for normal gluco-regulation, and it has been widely presumed that this function reflects the actions of GLP-1 released from enteroendocrine L cells. To test the relative importance of intestinal versus pancreatic sources of GLP-1 for physiological regulation of glucose, we administered a GLP-1R antagonist, exendin-[9-39] (Ex9), to mice with tissue-specific reactivation of the preproglucagon gene (Gcg). Ex9 impaired glucose tolerance in wild-type mice but had no impact on Gcg-null or GLP-1R KO mice, suggesting that Ex9 is a true and specific GLP-1R antagonist. Unexpectedly, Ex-9 had no effect on blood glucose in mice with restoration of intestinal Gcg. In contrast, pancreatic reactivation of Gcg fully restored the effect of Ex9 to impair both oral and i.p. glucose tolerance. These findings suggest an alternative model whereby islet GLP-1 also plays an important role in regulating glucose homeostasis.

Once-weekly dulaglutide 1.5 mg restores insulin secretion in response to intravenous glucose infusion

AIMS

To evaluate the effects of dulaglutide 1.5 mg on first- and second-phase insulin secretion in response to an intravenous (i.v.) glucose bolus challenge, in subjects with type 2 diabetes mellitus (T2DM; primary objective) and in healthy subjects.

MATERIALS AND METHODS

In this randomized, double-blind, placebo-controlled, 2-period crossover study, subjects received a single subcutaneous injection of dulaglutide 1.5 mg or placebo on day 1 of each period. On day 3, subjects underwent a 6-hour insulin infusion, followed by an i.v. glucose bolus and a glucagon challenge during hyperglycaemia. Areas under the concentration-time curve and maximum concentrations for first- (AUC_0-10 and C_max0-10 ) and second-phase secretion (AUC_10-180 and C_max10-180 ) were calculated for insulin and C-peptide. The glucose disappearance constant (K_g ) and homeostasis model assessment of β-cell function (HOMA-β) were assessed.

RESULTS

In 20 subjects with T2DM, dulaglutide increased mean insulin AUC_0-10 by 7.92-fold and C_max0-10 by 5.40-fold vs placebo, and mean AUC_10-180 and C_max10-180 by 2.44- and 3.78- fold, respectively. In 10 healthy subjects, dulaglutide increased the mean insulin AUC_0-10 by 3.09-fold and C_max0-10 by 2.96-fold vs placebo, and mean AUC_10-180 and C_max10-180 by 2.04- and 4.15-fold, respectively. The corresponding C-peptide values also increased. Mean K_g and HOMA-β were higher after dulaglutide compared with placebo.

CONCLUSIONS

In subjects with T2DM, a single dulaglutide 1.5-mg dose restored the first-phase insulin secretion in response to an i.v. glucose bolus, increased the second-phase insulin response and enhanced β-cell function.

Short-term administration of the GLP-1 analog liraglutide decreases circulating leptin and increases GIP levels and these changes are associated with alterations in CNS responses to food cues: A randomized, placebo-controlled, crossover study

BACKGROUND

GLP-1 agonists, including liraglutide, have emerged as effective therapies for type 2 diabetes (DM) and obesity. Here, we attempted to delineate how liraglutide, at doses approved for DM, may impact circulating hormones influencing energy homeostasis in diabetics.

BASIC PROCEDURES

Using a randomized, placebo-controlled, double-blind, cross-over trial of 20 patients with type 2 diabetes, we examined the effects of liraglutide as compared to placebo on fasting levels of circulating hormones important to energy homeostasis, including leptin, ghrelin, PYY, and GIP. After 17days (0.6mg for 7days, 1.2mg for 7days and 1.8mg for 3days) of treatment, we also studied changes in fMRI responses to food cues.

MAIN FINDINGS

By design, to avoid any confounding by weight changes, subjects were studied for 17days, i.e. before body weight changed. Participants on liraglutide had significantly increased GLP-1 levels (p<0.001), decreased percent change in leptin levels (p<0.01) and increased GIP levels (p<0.03) in comparison to placebo treated subjects. Whole brain regressions of functional activity in response to food cues reveal that increased GIP levels were associated with deactivation of the attention- and reward-related insula. Decreases in leptin levels were associated with activations in the reward-related midbrain, precuneus, and dorsolateral prefrontal cortex (DLPFC), and sensorimotor-related motor cortex and with deactivations in the attention-related parietal cortex and the cognitive control-related thalamus and pre-SMA.

PRINCIPAL CONCLUSIONS

We demonstrate herein short-term changes to circulating levels of GIP and leptin in response to GLP-1 agonist liraglutide therapy. These findings suggest that liraglutide may alter the circulating levels of hormones important in energy homeostasis that, in turn, influence CNS perception of food cues. This could possibly lead to compensatory changes in energy homeostasis that could over time limit the efficacy of liraglutide to decrease body weight. These novel findings, which, pointing to the potential advantages of combination therapies, may have therapeutic implications, will need to be confirmed by larger and longer-term trials.

Mechanisms of surgical control of type 2 diabetes: GLP-1 is the key factor-Maybe

Bariatric surgery is the most effective treatment for obesity and diabetes. The 2 most commonly performed weight-loss procedures, Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy, improve glycemic control in patients with type 2 diabetes independent of weight loss. One of the early hypotheses raised to explain the immediate antidiabetic effect of RYGB was that rapid delivery of nutrients from the stomach pouch into the distal small intestine enhances enteroinsular signaling to promote insulin signaling. Given the tenfold increase in postmeal glucagon-like peptide-1 (GLP-1) response compared to unchanged integrated levels of postprandial glucose-dependent insulinotropic peptide after RYGB, enhanced meal-induced insulin secretion after this procedure was thought to be the result of elevated glucose and GLP-1 levels. In this contribution to the larger point-counterpoint debate about the role of GLP-1 after bariatric surgery, most of the focus will be on RYGB.

The Neuroprotection of Liraglutide Against Ischaemia-induced Apoptosis through the Activation of the PI3K/AKT and MAPK Pathways

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that increases glucose-dependent insulin secretion to reduce the glucose level. Liraglutide, a long-acting GLP-1 analogue, has been found to have neuroprotective action in various experimental models. However, the protective mechanisms of liraglutide in ischaemic stroke remain unclear. Here, we demonstrated that liraglutide significantly decreased the infarct volume, improved neurologic deficits, and lowered stress-related hyperglycaemia without causing hypoglycaemia in a rat model of middle cerebral artery occlusion (MCAO). Liraglutide inhibited cell apoptosis by reducing excessive reactive oxygen species (ROS) and improving the function of mitochondria in neurons under oxygen glucose deprivation (OGD) in vitro and MCAO in vivo. Liraglutide up-regulated the phosphorylation of protein kinase B (AKT) and extracellular signal-regulated kinases (ERK) and inhibited the phosphorylation of c-jun-NH2-terminal kinase (JNK) and p38. Moreover, the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and/or the ERK inhibitor U0126 counteracted the protective effect of liraglutide. Taken together, these results suggest that liraglutide exerts neuroprotective action against ischaemia-induced apoptosis through the reduction of ROS and the activation of the PI3K/AKT and mitogen-activated protein kinase (MAPK) pathways. Therefore, liraglutide has therapeutic potential for patients with ischaemic stroke, especially those with Type 2 diabetes mellitus or stress hyperglycaemia.