Neural regulation of glucagon-like peptide-1 secretion in pigs

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

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

A sympathetic brake on gut GLP-1 release

The brain-gut neurocircuitry is proving to be finely involved in a wide range of physiological functions. In this issue of Neuron, Ren et al.1 show that adrenergic signaling suppresses postprandial glucagon-like peptide 1 (GLP-1) secretion. This, in turn, raises circulating glucose levels and impairs brain glucose uptake and cognitive function.

The Sympathetic-Immune Milieu in Metabolic Health and Diseases: Insights from Pancreas, Liver, Intestine, and Adipose Tissues

Sympathetic innervation plays a crucial role in maintaining energy balance and contributes to metabolic pathophysiology. Recent evidence has begun to uncover the innervation landscape of sympathetic projections and sheds light on their important functions in metabolic activities. Additionally, the immune system has long been studied for its essential roles in metabolic health and diseases. In this review, the aim is to provide an overview of the current research progress on the sympathetic regulation of key metabolic organs, including the pancreas, liver, intestine, and adipose tissues. In particular, efforts are made to highlight the critical roles of the peripheral nervous system and its potential interplay with immune components. Overall, it is hoped to underscore the importance of studying metabolic organs from a comprehensive and interconnected perspective, which will provide valuable insights into the complex mechanisms underlying metabolic regulation and may lead to novel therapeutic strategies for metabolic diseases.

A Peptide in a Pill - Oral Semaglutide in the Management of Type 2 Diabetes

T2DM (type 2 diabetes mellitus) is a chronic and progressive illness with high morbidity and death rates. Oral semaglutide (Rybelsus®) is a combination of semaglutide, a glucagon-like peptide-1 receptor agonist (GLP-1 RA), and sodium N- (8- [2-hydroxybenzoyl] amino) caprylate (SNAC), an absorption enhancer that facilitates semaglutide absorption across the gastric epithelium in a concentration-dependent manner. This family of drugs apart from glucose lowering effects causes significant weight loss with lower risk of hypoglycemia, and some of them have been linked to a significant reduced major adverse cardiovascular events. GLP-1 RAs may assist persons with T2DM and chronic kidney disease (CKD), a major microvascular consequence of T2DM, in ways other than lowering blood sugar. Several large clinical studies, the bulk of which are cardiovascular outcome trials, show that GLP-1 RA treatment is safe and tolerated for persons with T2DM and impaired renal function and that it may potentially have renoprotective characteristics. This article focuses on the advances of oral GLP1-RA and describes the key milestones and predicted advantages.

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

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

Transvenous Right Greater Splanchnic Nerve Ablation in Heart Failure and Preserved Ejection Fraction: First-in-Human Study

BACKGROUND

Ablation of the right-sided greater splanchnic nerve (GSN) can reduce excessive splanchnic vasoconstriction, potentially improving the handling of volume shifts in patients with heart failure with preserved ejection fraction (HFpEF).

OBJECTIVES

The purpose of this study was to assess a novel catheter procedure of right-sided GSN ablation to treat HFpEF: splanchnic ablation for volume management.

METHODS

This trial included 11 HFpEF patients (8 women, age 70 ± 8 years) with New York Heart Association functional class II or III symptoms, ejection fraction ≥50%, and elevated pulmonary capillary wedge pressure at rest or with exercise. After splanchnic ablation for volume management, follow-up at 1, 3, 6, and 12 months included 6-minute walk test, Kansas City Cardiomyopathy Questionnaire (KCCQ), and echocardiography.

RESULTS

There were no device-related adverse cardiac events or clinical sequelae following right GSN ablation through 12 months. Patients experienced clinical improvements by 1 month that were sustained through 12 months. KCCQ score improved from baseline median 48 (IQR: 35-52) to 65 (IQR: 58-77) at 1 month and 80 (IQR: 77-88) at 12 months (P < 0.05). The 6-minute walk test distance increased from baseline 292 ± 82 m to 341 ± 88 m at 1 month and 359 ± 75 m at 12 months (P < 0.05). The NT-proBNP decreased from a baseline mean of 1,292 ± 1,186 pg/mL to 1,202 ± 797 pg/mL (P = 0.585) at 1 month, to 472 ± 226 pg/mL (P = 0.028) at 6 months, and to 379 ± 165 pg/mL (P = 0.039) at 12 months.

CONCLUSIONS

In this open-label, single-arm feasibility study, right-sided GSN ablation was safe and improved mostly subjective clinical metrics in patients with HFpEF over 12 months. (Endovascular GSN Ablation in Subjects With HFpEF; NCT04287946).

Circulating GLP-1 Levels in Patients with Pheochromocytoma/Paraganglioma

The sympathoadrenal system has been shown to stimulate the secretory activity of enteroendocrine cells, although the response is transient. Our aim was to investigate the effects of long-term catecholamine excess on circulating glucagon-likepeptide-1 (GLP-1) levels in patients with pheochromocytoma/paraganglioma (PPGL). Thirty patients diagnosed with PPGL were analyzed. A significant negative association was observed between fasting plasma GLP-1 levels and elevated plasma-free metanephrine (r = -0.407, p = 0.026). After adjustment for age, sex, body mass index (BMI), serum creatinine, and the presence of hyperglycemia, the negative association between plasma GLP-1 and metanephrine persisted by multiple linear regression analysis (β = -0.493, p = 0.013). Positive correlations between fasting glucose and plasma metanephrine (r = 0.380, p = 0.038) and normetanephrine levels (r = 0.450, p = 0.013) were also found. Mean fasting levels of total GLP-1 increased significantly from 25.81 to 39.01 pmol/L (p = 0.017) after PPGL resection. In conclusion, long-term overproduction of catecholamines appears to induce suppression of GLP-1 production compared to an acute response to a stress stimulus. Further studies are required to elucidate the mechanism of GLP-1 secretion with chronic exposure to catecholamine.

Danning tablets might improve glucose and lipid metabolism in asymptomatic T2MD patients after cholecystectomy: A cohort study

Considering the role of bile acids in glucose metabolism and the effect of farnesoid X receptor agonists on bile acids, we investigated the possible effect of Danning tablets (DNTs), a type of farnesoid X receptor agonist, on glucose and lipid metabolism in asymptomatic type 2 diabetes mellitus (T2DM) patients.A series of asymptomatic T2DM patients who underwent cholecystectomy at least 2 years prior and were regularly followed up in our hospital were included in our analysis. According to their choice, they were divided into 2 groups: the DNT group and the control group. Demographic data, body weight, food intake, effects on diabetes control, and biomedical variables were collected.After propensity score matching, a total of 64 T2DM patients (41 males and 23 females) were included in the analysis. The amount of daily food intake (kcals) and diet composition were little changed 6-months after DNT administration (P = .612). However, the average fasting glucose level of the DNT group decreased from 9.5 ± 1.4 mmol/L to 8.3 ± 1.6 mmol/L (P < .001), and the level of hemoglobin A1c decreased from 8.3 ± 1.1% to 7.6 ± 1.0% (P = .001). The total cholesterol level (P = .024) and low-density lipoprotein cholesterol level (P = .034) decreased significantly (P = .018). Moreover, the average level of total bile acids decreased from 6.05 ± 2.60 μmol/L to 5.10 ± 1.83 μmol/L in the DNT group (P = .037), and the level of glucagon-like peptide-1 significantly increased from 6.93 ± 4.94 pmol/L to 11.25 ± 5.88 pmol/L (P < .001).The results of our study show that DNT intake improved glucose and lipid metabolism and increased the level of glucagon-like peptide-1.Trial registration: registered in Chinese Clinical Trial Registry (No. ChiCTR1900027823).

Crosstalk between beta-adrenergic and insulin signaling mediates mechanistic target of rapamycin hyperactivation in liver of high-fat diet-fed male mice

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease. While increased nutrient intake and sympathetic activity have been associated with the disease, the pathogenesis of NAFLD remains incompletely understood. We investigated the impact of the interaction of high dietary fat and sugar intake with increased beta-adrenergic receptor (β-AR) signaling on the activity of nutrient-sensing pathways and fuel storage in the liver. C57BL/6J mice were fed a standard rodent diet (STD), a high-fat diet (HFD), a high-fat/high-sugar Western diet (WD), a high-sugar diet with mixed carbohydrates (HCD), or a high-sucrose diet (HSD). After 6 week on diets, mice were treated with isoproterenol (ISO) and the activity of liver mTOR complex 1 (mTORC1)-related signaling analyzed by immunoblotting and correlated with tissue triglyceride and glycogen contents. ISO-stimulated AKT- and ERK-mediated activation of mTORC1 in STD-fed mice. Consumption of all four high-calorie diets exacerbated downstream activation of ribosomal protein S6 kinase beta-1 (S6K1) in response to ISO. S6K1 activity was greater with the fat-enriched HFD and WD and correlated with the presence of metabolic syndrome and a stronger activation of AKT and ERK1/2 pathways. Fat-enriched diets also increased triglyceride accumulation and inhibited glycogen mobilization under β-AR stimulation. In conclusion, crosstalk between β-AR and insulin signaling may contribute to HFD-induced hepatic steatosis through ERK1/2- and AKT-mediated hyperactivation of the mTORC1/S6K1 axis. The findings provide further rationale for the development of therapies aimed at targeting augmented β-AR signaling in the pathogenesis of NAFLD.

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

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

Role of the sympathetic nervous system in cardiometabolic control: implications for targeted multiorgan neuromodulation approaches

Sympathetic overdrive plays a key role in the perturbation of cardiometabolic homeostasis. Diet-induced and exercise-induced weight loss remains a key strategy to combat metabolic disorders, but is often difficult to achieve. Current pharmacological approaches result in variable responses in different patient cohorts and long-term efficacy may be limited by medication intolerance and nonadherence. A clinical need exists for complementary therapies to curb the burden of cardiometabolic diseases. One such approach may include interventional sympathetic neuromodulation of organs relevant to cardiometabolic control. The experience from catheter-based renal denervation studies clearly demonstrates the feasibility, safety and efficacy of such an approach. In analogy, denervation of the common hepatic artery is now feasible in humans and may prove to be similarly useful in modulating sympathetic overdrive directed towards the liver, pancreas and duodenum. Such a targeted multiorgan neuromodulation strategy may beneficially influence multiple aspects of the cardiometabolic disease continuum offering a holistic approach.

Combined renal and common hepatic artery denervation as a novel approach to reduce cardiometabolic risk: technical approach, feasibility and safety in a pre-clinical model

Background

Cardiovascular and metabolic regulation is governed by neurohumoral signalling in relevant organs such as kidney, liver, pancreas, duodenum, adipose tissue, and skeletal muscle. Combined targeting of relevant neural outflows may provide a unique therapeutic opportunity for cardiometabolic disease.

Objectives

We aimed to investigate the feasibility, safety, and performance of a novel device-based approach for multi-organ denervation in a swine model over 30 and 90 days of follow-up.

Methods

Five Yorkshire cross pigs underwent combined percutaneous denervation in the renal arteries and the common hepatic artery (CHA) with the iRF Denervation System. Control animals (n = 3) were also studied. Specific energy doses were administered in the renal arteries and CHA. Blood was collected at 30 and 90 days. All animals had a pre-terminal procedure angiography. Tissue samples were collected for norepinephrine (NEPI) bioanalysis. Histopathological evaluation of collateral structures and tissues near the treatment sites was performed to assess treatment safety.

Results

All animals entered and exited the study in good health. No stenosis or vessel abnormalities were present. No significant changes in serum chemistry occurred. NEPI concentrations were significantly reduced in the liver (− 88%, p = 0.005), kidneys (− 78%, p < 0.001), pancreas (− 78%, p = 0.018) and duodenum (− 95%, p = 0.028) following multi-organ denervation treatment compared to control animals. Histologic findings were consistent with favourable tissue responses at 90 days follow-up.

Conclusions

Significant and sustained denervation of the treated organs was achieved at 90 days without major safety events. Our findings demonstrate the feasibility of multi-organ denervation using a novel iRF Denervation System in a single procedure.

Alterations in Small Intestine and Liver Morphology, Immunolocalization of Leptin, Ghrelin and Nesfatin-1 as Well as Immunoexpression of Tight Junction Proteins in Intestinal Mucosa after Gastrectomy in Rat Model

The stomach is responsible for the processing of nutrients as well as for the secretion of various hormones which are involved in many activities throughout the gastrointestinal tract. Experimental adult male Wistar rats (n = 6) underwent a modified gastrectomy, while control rats (n = 6) were sham-operated. After six weeks, changes in small intestine (including histomorphometrical parameters of the enteric nervous plexuses) and liver morphology, immunolocalization of leptin, ghrelin and nesfatin-1 as well as proteins forming adherens and tight junctions (E-cadherin, zonula occludens-1, occludin, marvelD3) in intestinal mucosa were evaluated. A number of effects on small intestine morphology, enteric nervous system ganglia, hormones and proteins expression were found, showing intestinal enteroplasticity and neuroplasticity associated with changes in gastrointestinal tract condition. The functional changes in intestinal mucosa and the enteric nervous system could be responsible for the altered intestinal barrier and hormonal responses following gastrectomy. The results suggest that more complicated regulatory mechanisms than that of compensatory mucosal hypertrophy alone are involved.

Incretin Hormones and Type 2 Diabetes-Mechanistic Insights and Therapeutic Approaches

Simple Summary

When we ingest a meal, our intestine secretes hormones that are released into the bloodstream. Amongst these hormones are the incretins hormones which stimulate the release of insulin from the pancreas which is essential for the regulation of in particular postprandial glucose concentrations. In patients with type 2 diabetes, the effect of the incretins is diminished. This is thought to contribute importantly to the pathophysiology of the disease. However, in pharmacological amounts, the incretins may still influence insulin secretion and metabolism. Much research has therefore been devoted to the development of incretin-based therapies for type 2 diabetes. These therapies include compounds that strongly resemble the incretins, hereby stimulating their effects as well as inhibitors of the enzymatic degradation of the hormones, thereby increasing the concentration of incretins in the blood. Both therapeutic approaches have been implemented successfully, but research is still ongoing aimed at the development of further optimized therapies.

Abstract

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are secreted from the gut upon nutrient stimulation and regulate postprandial metabolism. These hormones are known as classical incretin hormones and are responsible for a major part of postprandial insulin release. The incretin effect is severely reduced in patients with type 2 diabetes, but it was discovered that administration of GLP-1 agonists was capable of normalizing glucose control in these patients. Over the last decades, much research has been focused on the development of incretin-based therapies for type 2 diabetes. These therapies include incretin receptor agonists and inhibitors of the incretin-degrading enzyme dipeptidyl peptidase-4. Especially the development of diverse GLP-1 receptor agonists has shown immense success, whereas studies of GIP monotherapy in patients with type 2 diabetes have consistently been disappointing. Interestingly, both GIP-GLP-1 co-agonists and GIP receptor antagonists administered in combination with GLP-1R agonists appear to be efficient with respect to both weight loss and control of diabetes, although the molecular mechanisms behind these effects remain unknown. This review describes our current knowledge of the two incretin hormones and the development of incretin-based therapies for treatment of type 2 diabetes.

Effect of tasteless calorie-free gum chewing before meal on postprandial plasma glucose, insulin, glucagon, and gastrointestinal hormones in Japanese men without diagnosed glucose metabolism disorder: a pilot randomized crossover trial

This pilot study aimed to examine the effect of pre-meal tasteless calorie-free gum chewing on post-meal blood levels of glucose, insulin, glucagon, and gastrointestinal hormones. This was an open-label, randomized, 2-sequence, 3-period, 2-treatment crossover trial with a 1:1 allocation. Sixteen Japanese adult male volunteers aged between 30 and 49 years without diagnosed glucose metabolism disorder were enrolled. Ingestion of 200-g cooked rice after 15-min tasteless calorie-free gum chewing (GUM+ treatment) was compared to that without preceding gum chewing (GUM- treatment). Cooked rice was divided into twelve equally sized portions and consumed by chewing each portion 30 times before swallowing. Treatment sessions were separated by an at least 1-week interval and attended after an overnight fast. Circulating levels of glucose, insulin, glucagon, active glucagon-like peptide (GLP)-1 and ghrelin were measured at baseline (before treatment) and 0, 15, 30, 60, and 120 min after completion of the meal ingestion, and the postprandial change from baseline was assessed. As a result, the change in glucose levels at 0 min was significantly lower in the GUM+ treatment than in the GUM- treatment (P = 0.004). Furthermore, the GUM+ treatment demonstrated higher incremental insulin levels at 15 min (P = 0.041) and higher incremental active GLP-1 levels at 30 and 60 min (P = 0.018 and 0.021, respectively); whereas, postprandial glucagon and ghrelin levels were not significantly different. In conclusion, the current pilot study demonstrated that tasteless calorie-free gum chewing before rice eating had a significant but limited impact on the increase of postprandial active GLP-1 levels in male individuals without diagnosed glucose metabolism disorder.

Mycotoxins and the Enteric Nervous System

Mycotoxins are secondary metabolites produced by various fungal species. They are commonly found in a wide range of agricultural products. Mycotoxins contained in food enter living organisms and may have harmful effects on many internal organs and systems. The gastrointestinal tract, which first comes into contact with mycotoxins present in food, is particularly vulnerable to the harmful effects of these toxins. One of the lesser-known aspects of the impact of mycotoxins on the gastrointestinal tract is the influence of these substances on gastrointestinal innervation. Therefore, the present study is the first review of current knowledge concerning the influence of mycotoxins on the enteric nervous system, which plays an important role, not only in almost all regulatory processes within the gastrointestinal tract, but also in adaptive and protective reactions in response to pathological and toxic factors in food.

Pheochromocytoma With Adrenergic Biochemical Phenotype Shows Decreased GLP-1 Secretion and Impaired Glucose Tolerance

CONTEXT

Impaired glucose homeostasis is a common finding in pheochromocytoma (PHEO), especially with adrenergic phenotype. The possible contribution of incretin dysfunction to dysglycemia in PHEO patients has not been studied.

OBJECTIVE

To compare changes in pancreatic endocrine function and gut hormones' production during a liquid meal test before and 1 year after adrenalectomy.

METHODS

In a prospective study, we included 18 patients with PHEO (13 females) with adrenergic biochemical phenotype. A liquid meal test with predefined isocaloric enteral nutrition was performed to evaluate dynamic changes in pancreatic hormones and incretins.

RESULTS

During the meal test, insulin levels were significantly lower before adrenalectomy only in the early phase of insulin secretion, but changes in area under the curve (AUC) did not reach statistical significance (AUC = 0.07). Plasma glucagon (AUC < 0.01) and pancreatic polypeptide levels (AUC < 0.01) were suppressed in comparison with the postoperative state. Impaired response to the meal was found preoperatively for glucagon-like peptide-1 (GLP-1; AUC P < 0.05), but not glucose-dependent insulinotropic polypepide (GIP; AUC P = 0.21). No significant changes in insulin resistance indices were found, except for the homeostatic model assessment-beta index, an indicator of the function of islet β cells, which negatively correlated with plasma metanephrine (R = -0.66, P < 0.01).

CONCLUSIONS

Our study shows suppression of pancreatic α and β cell function and impaired GLP-1 secretion during a dynamic meal test in patients with PHEO, which is improved after its surgical treatment. These data demonstrate a novel and potentially significant interconnection between excessive catecholamine production and the secretion of glucoregulatory hormones.

Putting the Hindgut Hypothesis to the Test in a Diabetic Zucker Rat Model

BACKGROUND

The hindgut theory hypothesizes a key role of differential hindgut stimulation following metabolic procedures in ameliorating diabetes mellitus. We used two strategies to remove the hindgut from intestinal continuity in order to analyze its impact on diabetes mellitus.

METHODS

Loop duodeno-jejunostomy (DJOS) with exclusion of one-third of total intestinal length was performed in 3 groups of 9-week-old Zucker diabetic fatty rats. In group 1, no further alteration of the intestinal tract was made. Group 2 received additional ileal exclusion (IE). Group 3 underwent additional resection of 50% of the ileum with side-to-side ileocecal anastomosis (IR). One, 2, and 4 months after surgery, fasting blood glucose levels, oral glucose tolerance tests (OGTT), and glucose-stimulated hormone analyses were conducted, and bile acid blood levels were compared. Body weight was documented weekly.

RESULTS

In relation to DJOS, glucose control was not impaired in IR or IE. On the contrary, only IR could maintain preOP glucose values until 4 months. There were no significant weight differences between the groups. Confirming effective ileal diversion, bile acid blood levels were significantly higher in the DJOS group compared with both IR and IE (p = 0.0025 and p = 0.0047). Operative interventions had no impact on GLP-1 levels at any time point (ANOVA p > 0.05 for all). Insulin secretion was preserved in all groups.

CONCLUSION

This data supports the hypothesis that the mechanisms driving amelioration of diabetes mellitus are complex and cannot be reduced to the ileum.

Recent advances in understanding the role of glucagon-like peptide 1

The discovery that glucagon-like peptide 1 (GLP-1) mediates a significant proportion of the incretin effect during the postprandial period and the subsequent observation that GLP-1 bioactivity is retained in type 2 diabetes (T2D) led to new therapeutic strategies being developed for T2D treatment based on GLP-1 action. Although owing to its short half-life exogenous GLP-1 has no use therapeutically, GLP-1 mimetics, which have a much longer half-life than native GLP-1, have proven to be effective for T2D treatment since they prolong the incretin effect in patients. These GLP-1 mimetics are a desirable therapeutic option for T2D since they do not provoke hypoglycaemia or weight gain and have simple modes of administration and monitoring. Additionally, over more recent years, GLP-1 action has been found to mediate systemic physiological beneficial effects and this has high clinical relevance due to the post-diagnosis complications of T2D. Indeed, recent studies have found that certain GLP-1 analogue therapies improve the cardiovascular outcomes for people with diabetes. Furthermore, GLP-1-based therapies may enable new therapeutic strategies for diseases that can also arise independently of the clinical manifestation of T2D, such as dementia and Parkinson's disease. GLP-1 functions by binding to its receptor (GLP-1R), which expresses mainly in pancreatic islet beta cells. A better understanding of the mechanisms and signalling pathways by which acute and chronic GLP-1R activation alleviates disease phenotypes and induces desirable physiological responses during healthy conditions will likely lead to the development of new therapeutic GLP-1 mimetic-based therapies, which improve prognosis to a greater extent than current therapies for an array of diseases.

Glucose in the hypothalamic paraventricular nucleus regulates GLP-1 release

Glucokinase (GK) is highly expressed in the hypothalamic paraventricular nucleus (PVN); however, its role is currently unknown. We found that GK in the PVN acts as part of a glucose-sensing mechanism within the PVN that regulates glucose homeostasis by controlling glucagon-like peptide 1 (GLP-1) release. GLP-1 is released from enteroendocrine L cells in response to oral glucose. Here we identify a brain mechanism critical to the release of GLP-1 in response to oral glucose. We show that increasing expression of GK or injection of glucose into the PVN increases GLP-1 release in response to oral glucose. On the contrary, decreasing expression of GK or injection of nonmetabolizable glucose into the PVN prevents GLP-1 release. Our results demonstrate that gluco-sensitive GK neurons in the PVN are critical to the response to oral glucose and subsequent release of GLP-1.

Glucose Intolerance on Phaeochromocytoma and Paraganglioma-The Current Understanding and Clinical Perspectives

Half of the patients with phaeochromocytoma have glucose intolerance which could be life-threatening as well as causing postoperative hypoglycemia. Glucose intolerance is due to impaired insulin secretion and/or increased insulin resistance. Impaired insulin secretion is caused by stimulating adrenergic α2 receptors of pancreatic β-cells and increased insulin resistance is caused by stimulating adrenergic α1 and β3 receptors in adipocytes, α1 and β2 receptors of pancreatic α-cells and skeletal muscle. Furthermore, different affinities to respective adrenergic receptors exist between epinephrine and norepinephrine. Clinical studies revealed patients with phaeochromocytoma had impaired insulin secretion as well as increased insulin resistance. Furthermore, excess of epinephrine could affect glucose intolerance mainly by impaired insulin secretion and excess of norepinephrine could affect glucose intolerance mainly by increased insulin resistance. Glucose intolerance on paraganglioma could be caused by increased insulin resistance mainly considering paraganglioma produces more norepinephrine than epinephrine. To conclude, the difference of actions between excess of epinephrine and norepinephrine could lead to improve understanding and management of glucose intolerance on phaeochromocytoma.

Glucagon-like peptide 1 (GLP-1)

BACKGROUND

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

SCOPE OF REVIEW

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

MAJOR CONCLUSIONS

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

Anti-incretin effect: The other face of Janus in human glucose homeostasis

The provocative idea that type 2 diabetes (T2D) may be a surgically treated disorder is based on accumulating evidence suggesting impressive remission rates of obesity and diabetes following bariatric surgery interventions. According to the "anti-incretin" theory, ingestion of food in the gastrointestinal (GI) tract, apart from activating the well-described incretin effect, also results in the parallel stimulation of a series of negative feedback mechanisms (anti-incretin effect). The primary goal of these regulations is to counteract the effects of incretins and other postprandial glucose-lowering adaptive mechanisms. Disruption of the equilibrium between incretins and anti-incretins could be an additional pathway leading to the development of insulin resistance and hyperglycemia. This theory provides an alternative theoretical framework to explain the mechanisms behind the optimal effects of metabolic surgery on T2D and underlines the importance of the GI tract in the homeostatic regulation of energy balance in humans. The anti-incretin concept is currently based on a limited amount of evidence and certainly requires further validation by additional studies. The aim of the present review is to discuss and critically evaluate recent evidence on the anti-incretin theory, providing an insight into current state and future perspectives.

In vivo, ex vivo and in vitro evidence for atropine-mediated attenuation of glucagon-like peptide-1 secretion: findings from a systematic review

Glucagon-like peptide-1 (GLP-1) is involved in postprandial glucose homeostasis. Secretion of which involves a cholinergic pathway. Anticholinergic agent like atropine could act as a competitive antagonist of acetylcholine at muscarinic receptors. This review explores studies that assess the role of atropine in GLP-1 secretion. We selected published original articles from PubMed, Science Direct, The Cochrane Library, Trip, Google and the reference lists of the selected articles. Reporting was done according to the PRISMA statement. Relevant standard and previously published tools were used to assess the risk of bias of the selected articles. Twelve articles out of 185 search results fulfilled the review criteria. Eight were in vivo studies (six animal and two human studies), three were ex vivo studies and one was an in vitro study. Animal studies had rats, mice, pigs and monkeys as the subjects. Human studies involved healthy men and women. Majority of the studies reported an atropine-mediated attenuation of GLP-1 secretion and postprandial secretion of GLP-1 was mainly affected. However, atropine failed to significantly affect GLP-1 secretion when dipeptidyl peptidase-4 (DPP-4) enzyme was inhibited.

Effect of portal glucose sensing on incretin hormone secretion in a canine model

It is unknown whether activation of hepato-portal vein (PV) glucose sensors plays a role in incretin hormone amplification of oral glucose-stimulated insulin secretion (GSIS). In previous studies, PV glucose infusion increased GSIS through unknown mechanisms, perhaps neural stimulation of pancreatic β-cells and/or stimulation of gut incretin hormone release. Thus, there could be a difference in the incretin effect when comparing GSIS with portal rather than leg vein (LV) glucose infusion. Plasma insulin and incretin hormones were studied in six overnight-fasted dogs. An oral glucose tolerance test (OGTT) was administered, and then 1 and 2 wk later the arterial plasma glucose profile from the OGTT was mimicked by infusing glucose into either the PV or a LV. The arterial glucose levels were nearly identical between groups (AUCs within 1% of each other). Oral glucose administration increased arterial GLP-1 and GIP levels by more than sixfold, whereas they were not elevated by PV or LV glucose infusion. Oral glucose delivery was associated with only a small incretin effect (arterial insulin and C-peptide were 21 ± 23 and 24 ± 17% greater, respectively, during the 1st hour with oral compared with PV glucose and 14 ± 37 and 13 ± 35% greater, respectively, in oral versus LV; PV versus LV responses were not significantly different from each other). Thus, following an OGTT incretin hormone release did not depend on activation of PV glucose sensors, and the insulin response was not greater with PV compared with LV glucose infusion in the dog. The small incretin effect points to species peculiarities, which is perhaps related to diet.

Oxyntomodulin: Actions and role in diabetes

Oxyntomodulin is a product of the glucagon precursor, proglucagon, produced and released from the endocrine L-cells of the gut after enzymatic processing by the precursor prohormone convertase 1/3. It corresponds to the proglucagon sequence 33-69 and thus contains the entire glucagon sequence plus a C-terminal octapeptide, comprising in total 37 amino acids. As might have been expected, it has glucagon-like bioactivity, but also and more surprisingly also activates the receptor for GLP-1. This has given the molecule an interesting status as a glucagon-GLP-1 co-agonist, which is currently attracting considerable interest for its potential in the treatment of diabetes and obesity. Here, we provide an update on oxyntomodulin with a focus on its potential role in metabolic diseases.

Physiological and metabolic control of diet selection

The fact that most farm animals have no dietary choice under commercial practices translates the dietary decisions to the carers. Thus, a lack of understanding of the principles of dietary choices is likely to result in a high toll for the feed industry. In healthy animals, diet selection and, ultimately, feed intake is the result of factoring together the preference for the feed available with the motivation to eat. Both are dynamic states and integrate transient stimulus derived from the nutritional status, environmental and social determinants of the animal with hard-wired genetic mechanisms. Peripheral senses are the primary inputs that determine feed preferences. Some of the sensory aspects of feed, such as taste, are innate and genetically driven, keeping the hedonic value of feed strictly associated with a nutritional frame. Sweet, umami and fat tastes are all highly appetitive. They stimulate reward responses from the brain and reinforce dietary choices related to essential nutrients. In contrast, aroma (smell) recognition is a plastic trait and preferences are driven mostly by learned experience. Maternal transfer through perinatal conditioning and the individual’s own innate behaviour to try or to avoid novel feed (often termed as neophobia) are known mechanisms where the learning process strongly affects preferences. In addtition, the motivation to eat responds to episodic events fluctuating in harmony with the eating patterns. These signals are driven mainly by gastrointestinal hormones (such as cholecystokinin [CCK] and glucagon-like peptide 1 [GLP-1]) and load. In addition, long-term events generate mechanisms for a sustainable nutritional homeostasis managed by tonic signals from tissue stores (i.e. leptin and insulin). Insulin and leptin are known to affect appetite by modulating peripheral sensory inputs. The study of chemosensory mechanisms related to the nutritional status of the animal offers novel tools to understand the dynamic states of feed choices so as to meet nutritional and hedonic needs. Finally, a significant body of literature exists regarding appetite driven by energy and amino acids in farm animals. However, it is surprising that there is scarcity of knowledge regarding what and how specific dietary nutrients may affect satiety. Thus, a better understanding on how bitter compounds and excess dietary nutrients (i.e. amino acids) play a role in no-choice animal feeding is an urgent topic to be addressed so that right choices can be made on the animal’s behalf.

Effects of walking in water on gut hormone concentrations and appetite: comparison with walking on land

The effects of water exercise on gut hormone concentrations and appetite currently remain unclear. The aim of the present study was to investigate the effects of treadmill walking in water on gut hormone concentrations and appetite. Thirteen men (mean ± s.d. age: 21.6 ± 2.2 years, body mass index: 22.7 ± 2.8 kg/m², peak oxygen uptake (VO_2peak): 49.8 ± 7.8 mL/kg per min) participated in the walking in water and on land challenge. During the study period, ratings of subjective feelings of hunger, fullness, satiety and motivation to eat were reported on a 100-mm visual analog scale. A test meal was presented after walking, and energy intake (EI) was calculated. Blood samples were obtained during both trials to measure glucagon-like peptide-1 (GLP-1), peptide YY (PYY) and acylated ghrelin (AG) concentrations. Hunger scores (How hungry do you feel?) were significantly lower during the water trial than during the land trial (P < 0.05). No significant differences were observed in EI between water and land trials. GLP-1 concentrations were significantly higher in the water trial than in the land trial (P < 0.05). No significant differences were observed in PYY concentrations between water and land trials. AG concentrations were significantly lower in the water trial than in the land trial (P < 0.01). In conclusion, changes in gut hormone concentrations during walking in water contribute to the exercise-induced suppression of appetite and provide novel information on the influence of walking in water on the acute regulation of appetite.

Obstructive Sleep Apnea and Diabetes: A State of the Art Review

OSA is a chronic treatable sleep disorder and a frequent comorbidity in patients with type 2 diabetes. Cardinal features of OSA, including intermittent hypoxemia and sleep fragmentation, have been linked to abnormal glucose metabolism in laboratory-based experiments. OSA has also been linked to the development of incident type 2 diabetes. The relationship between OSA and type 2 diabetes may be bidirectional in nature given that diabetic neuropathy can affect central control of respiration and upper airway neural reflexes, promoting sleep-disordered breathing. Despite the strong association between OSA and type 2 diabetes, the effect of treatment with CPAP on markers of glucose metabolism has been conflicting. Variability with CPAP adherence may be one of the key factors behind these conflicting results. Finally, accumulating data suggest an association between OSA and type 1 diabetes as well as gestational diabetes. This review explores the role of OSA in the pathogenesis of type 2 diabetes, glucose metabolism dysregulation, and the impact of OSA treatment on glucose metabolism. The association between OSA and diabetic complications as well as gestational diabetes is also reviewed.

Feeding an Elemental Dietvsa Milk-Based Formula Does Not Decrease Intestinal Mucosal Growth in Infant Pigs

BACKGROUND

We previously showed that the level of enteral nutrient intake determines the rate of intestinal growth in piglets. Our objective was to determine whether providing enteral nutrition in the form of elemental nutrients (glucose, amino acids, lipid [ED]) rather than cow's milk formula (lactose, protein, lipid [FORM]) reduces small intestinal growth and lactase activity.

METHODS

Three-week-old piglets were fed either ED (n = 7) intragastrically or FORM (n = 6) orally for 6 days.

RESULTS

Intestinal protein and DNA masses, villus height, and crypt depth were not different in ED and FORM pigs. Crypt cell proliferation, measured by in vivo bromodeoxyuridine labeling, was significantly (p < .05) higher (+37%) in ED than in FORM pigs. Rates of mucosal protein synthesis (%/d), measured by in vivo 2H-leucine incorporation, were higher (p < .05) in ED than FORM (147 vs 89) pigs. Circulating concentrations (pmol/L) of the intestinotrophic peptide, glucagon-like peptide-2 (GLP-2), were also higher (p < .05) in ED than in FORM (148 vs 87) pigs. The mean lactase-specific activity (micromol/min/g) in proximal and distal segments was higher (p < .05) in FORM than in ED (124 vs 58) pigs.

CONCLUSIONS

We conclude that intestinal mucosal growth and villus morphology are similar in pigs fed ED and FORM, despite higher cell proliferation and protein synthesis rates and lower lactase activity with ED. This implies that elemental diets may be as trophic as polymeric formulas to simultaneously provide nutrition and a stimulus for intestinal growth during bowel rest.

Roles of the Gut in Glucose Homeostasis

The gastrointestinal tract plays a major role in the regulation of postprandial glucose profiles. Gastric emptying is a highly regulated process, which normally ensures a limited and fairly constant delivery of nutrients and glucose to the proximal gut. The subsequent digestion and absorption of nutrients are associated with the release of a set of hormones that feeds back to regulate subsequent gastric emptying and regulates the release of insulin, resulting in downregulation of hepatic glucose production and deposition of glucose in insulin-sensitive tissues. These remarkable mechanisms normally keep postprandial glucose excursions low, regardless of the load of glucose ingested. When the regulation of emptying is perturbed (e.g., pyloroplasty, gastric sleeve or gastric bypass operation), postprandial glycemia may reach high levels, sometimes followed by profound hypoglycemia. This article discusses the underlying mechanisms.

The regulation of function, growth and survival of GLP-1-producing L-cells

Glucagon-like peptide-1 (GLP-1) is a peptide hormone, released from intestinal L-cells in response to hormonal, neural and nutrient stimuli. In addition to potentiation of meal-stimulated insulin secretion, GLP-1 signalling exerts numerous pleiotropic effects on various tissues, regulating energy absorption and disposal, as well as cell proliferation and survival. In Type 2 Diabetes (T2D) reduced plasma levels of GLP-1 have been observed, and plasma levels of GLP-1, as well as reduced numbers of GLP-1 producing cells, have been correlated to obesity and insulin resistance. Increasing endogenous secretion of GLP-1 by selective targeting of the molecular mechanisms regulating secretion from the L-cell has been the focus of much recent research. An additional and promising strategy for enhancing endogenous secretion may be to increase the L-cell mass in the intestinal epithelium, but the mechanisms that regulate the growth, survival and function of these cells are largely unknown. We recently showed that prolonged exposure to high concentrations of the fatty acid palmitate induced lipotoxic effects, similar to those operative in insulin-producing cells, in an in vitro model of GLP-1-producing cells. The mechanisms inducing this lipototoxicity involved increased production of reactive oxygen species (ROS). In this review, regulation of GLP-1-secreting cells is discussed, with a focus on the mechanisms underlying GLP-1 secretion, long-term regulation of growth, differentiation and survival under normal as well as diabetic conditions of hypernutrition.

Evidence for neural contribution to islet effects of DPP-4 inhibition in mice

It has been suggested that neural mechanisms may contribute to effects of the incretin hormones, and, therefore, also to the effects of dipeptidyl peptidase (DPP-4) inhibition. We therefore examined whether muscarinic mechanisms are involved in the stimulation of insulin secretion by DPP-4 inhibition. Fasted, anesthetized mice were given intraperitoneal saline or the muscarinic antagonist atropine (5mg/kg) before duodenal glucose (75mg/mouse), with or without the DPP-4 inhibitor NVPDPP728 (0.095mg/mouse), or before intravenous glucose (0.35g/kg) with or without co-administration with GLP-1 or glucose-dependent insulinotropic polypeptide (GIP) (both 3nmol/kg). Furthermore, isolated islets were incubated (1h) in 2.8 and 11.1mM glucose, with or without GIP or GLP-1 (both 100nM), in the presence or absence of atropine (100µM). Duodenal glucose increased circulating insulin and this effect was potentiated by DPP-4 inhibition. The increase in insulin achieved by DPP-4 inhibition was reduced by atropine by approximately 35%. Duodenal glucose also elicited an increase in circulating intact GLP-1 and GIP and this was augmented by DPP-4 inhibition, but these effects were not affected by atropine. Atropine did also not affect the augmentation by GLP-1 and GIP on glucose-stimulated insulin secretion from isolated islets. Based on these findings, we suggest that muscarinic mechanisms contribute to the stimulation of insulin secretion by DPP-4 inhibition through neural effects induced by GLP-1 and GIP whereas neural effects do not affect the levels of GLP-1 or GIP or the islet effects of the two incretin hormones.

Mechanisms for the cardiovascular effects of glucagon-like peptide-1

Over the past three decades, at least 10 hormones secreted by the enteroendocrine cells have been discovered, which directly affect the cardiovascular system through their innate receptors expressed in the heart and blood vessels or through a neural mechanism. Glucagon-like peptide-1 (GLP-1), an important incretin, is perhaps best studied of these gut-derived hormones with important cardiovascular effects. In this review, I have discussed the mechanism of GLP-1 release from the enteroendocrine L-cells and its physiological effects on the cardiovascular system. Current evidence suggests that GLP-1 has positive inotropic and chronotropic effects on the heart and may be important in preserving left ventricular structure and function by direct and indirect mechanisms. The direct effects of GLP-1 in the heart may be mediated through GLP-1R expressed in atria as well as arteries and arterioles in the left ventricle and mainly involve in the activation of multiple pro-survival kinases and enhanced energy utilization. There is also good evidence to support the involvement of a second, yet to be identified, GLP-1 receptor. Further, GLP-1(9-36)amide, which was previously thought to be the inactive metabolite of the active GLP-1(7-36)amide, may also have direct cardioprotective effects. GLP-1's action on GLP-1R expressed in the central nervous system, kidney, vasculature and the pancreas may indirectly contribute to its cardioprotective effects.

Physiology of proglucagon peptides: role of glucagon and GLP-1 in health and disease

The preproglucagon gene (Gcg) is expressed by specific enteroendocrine cells (L-cells) of the intestinal mucosa, pancreatic islet α-cells, and a discrete set of neurons within the nucleus of the solitary tract. Gcg encodes multiple peptides including glucagon, glucagon-like peptide-1, glucagon-like peptide-2, oxyntomodulin, and glicentin. Of these, glucagon and GLP-1 have received the most attention because of important roles in glucose metabolism, involvement in diabetes and other disorders, and application to therapeutics. The generally accepted model is that GLP-1 improves glucose homeostasis indirectly via stimulation of nutrient-induced insulin release and by reducing glucagon secretion. Yet the body of literature surrounding GLP-1 physiology reveals an incompletely understood and complex system that includes peripheral and central GLP-1 actions to regulate energy and glucose homeostasis. On the other hand, glucagon is established principally as a counterregulatory hormone, increasing in response to physiological challenges that threaten adequate blood glucose levels and driving glucose production to restore euglycemia. However, there also exists a potential role for glucagon in regulating energy expenditure that has recently been suggested in pharmacological studies. It is also becoming apparent that there is cross-talk between the proglucagon derived-peptides, e.g., GLP-1 inhibits glucagon secretion, and some additive or synergistic pharmacological interaction between GLP-1 and glucagon, e.g., dual glucagon/GLP-1 agonists cause more weight loss than single agonists. In this review, we discuss the physiological functions of both glucagon and GLP-1 by comparing and contrasting how these peptides function, variably in concert and opposition, to regulate glucose and energy homeostasis.

The role of gut adaptation in the potent effects of multiple bariatric surgeries on obesity and diabetes

Bariatric surgical procedures such as vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass (RYGB) are the most potent treatments available to produce sustained reductions in body weight and improvements in glucose regulation. While traditionally these effects are attributed to mechanical aspects of these procedures, such as restriction and malabsorption, a growing body of evidence from mouse models of these procedures points to physiological changes that mediate the potent effects of these surgeries. In particular, there are similar changes in gut hormone secretion, bile acid levels, and composition after both of these procedures. Moreover, loss of function of the nuclear bile acid receptor (FXR) greatly diminishes the effects of VSG. Both VSG and RYGB are linked to profound changes in the gut microbiome that also mediate at least some of these surgical effects. We hypothesize that surgical rearrangement of the gastrointestinal tract results in enteroplasticity caused by the high rate of nutrient presentation and altered pH in the small intestine that contribute to these physiological effects. Identifying the molecular underpinnings of these procedures provides new opportunities to understand the relationship of the gastrointestinal tract to obesity and diabetes as well as new therapeutic strategies to harness the effectiveness of surgery with less-invasive approaches.

Gut chemosensing mechanisms

The enteroendocrine system is the primary sensor of ingested nutrients and is responsible for secreting an array of gut hormones, which modulate multiple physiological responses including gastrointestinal motility and secretion, glucose homeostasis, and appetite. This Review provides an up-to-date synopsis of the molecular mechanisms underlying enteroendocrine nutrient sensing and highlights our current understanding of the neuro-hormonal regulation of gut hormone secretion, including the interaction between the enteroendocrine system and the enteric nervous system. It is hoped that a deeper understanding of how these systems collectively regulate postprandial physiology will further facilitate the development of novel therapeutic strategies.

Mosapride citrate increases postprandial glucagon-like peptide-1, insulin, and gene expression of sweet taste receptors

BACKGROUND AND AIM

Mosapride citrate-a prokinetic agent-improves hemoglobin A1c levels in diabetic patients; however, the underlying mechanism is unclear. We aimed to clarify this mechanism.

METHODS

Preprandial and postprandial (90 min after a meal) blood was obtained from 12 healthy men, and serum insulin and plasma active glucagon-like peptide-1 concentrations were measured. Measurements were also taken after the administration of 5 mg of mosapride citrate three times per day after every meal for 14 days. In addition, C57BL/6 mice were permitted free access to water containing 0.04 % domperidone (D group) or 0.02 % mosapride citrate (M group) for 2 weeks (four mice per group). T1r2 (taste receptor, type 1, member 2), T1r3, and Gnat3 (guanine nucleotide-binding protein, alpha transducing 3) mRNA expression levels of the stomach, duodenum, and proximal and mid-jejunum were evaluated.

RESULTS

In human subjects, postprandial plasma active glucagon-like peptide-1 and serum insulin concentrations after administration of mosapride citrate were significantly higher than those pre-administration (4.8 ± 2.2 pmol/L, 45.6 ± 41.6 μIU/mL, and 3.7 ± 1.2 pmol/L, 34.1 ± 28.4 μIU/mL, respectively). The mouse expression levels of T1r2 and Gnat3 in the proximal jejunum and mid-jejunum in the M group (4.1 ± 1.8-fold, 3.1 ± 1.6-fold, and 4.6 ± 0.8-fold, 3.1 ± 0.9-fold increases, respectively), were significantly higher than those of the control group.

CONCLUSIONS

The administration of mosapride citrate for 2 weeks enhanced postprandial plasma active glucagon-like peptide-1 and serum insulin concentration and increased the expression of sweet taste receptors in the upper intestine.

Molecular mechanisms of glucose-stimulated GLP-1 secretion from perfused rat small intestine

Glucose is an important stimulus for glucagon-like peptide 1 (GLP-1) secretion, but the mechanisms of secretion have not been investigated in integrated physiological models. We studied glucose-stimulated GLP-1 secretion from isolated perfused rat small intestine. Luminal glucose (5% and 20% w/v) stimulated the secretion dose dependently, but vascular glucose was without significant effect at 5, 10, 15, and 25 mmol/L. GLP-1 stimulation by luminal glucose (20%) secretion was blocked by the voltage-gated Ca channel inhibitor, nifedipine, or by hyperpolarization with diazoxide. Luminal administration (20%) of the nonmetabolizable sodium-glucose transporter 1 (SGLT1) substrate, methyl-α-D-glucopyranoside (α-MGP), stimulated release, whereas the SGLT1 inhibitor phloridzin (luminally) abolished responses to α-MGP and glucose. Furthermore, in the absence of luminal NaCl, luminal glucose (20%) did not stimulate a response. Luminal glucose-stimulated GLP-1 secretion was also sensitive to luminal GLUT2 inhibition (phloretin), but in contrast to SGLT1 inhibition, phloretin did not eliminate the response, and luminal glucose (20%) stimulated larger GLP-1 responses than luminal α-MGP in matched concentrations. Glucose transported by GLUT2 may act after metabolization, closing KATP channels similar to sulfonylureas, which also stimulated secretion. Our data indicate that SGLT1 activity is the driving force for glucose-stimulated GLP-1 secretion and that KATP-channel closure is required to stimulate a full-blown glucose-induced response.

Animal models of gastrointestinal and liver diseases. Animal models of infant short bowel syndrome: translational relevance and challenges

Intestinal failure (IF), due to short bowel syndrome (SBS), results from surgical resection of a major portion of the intestine, leading to reduced nutrient absorption and need for parenteral nutrition (PN). The incidence is highest in infants and relates to preterm birth, necrotizing enterocolitis, atresia, gastroschisis, volvulus, and aganglionosis. Patient outcomes have improved, but there is a need to develop new therapies for SBS and to understand intestinal adaptation after different diseases, resection types, and nutritional and pharmacological interventions. Animal studies are needed to carefully evaluate the cellular mechanisms, safety, and translational relevance of new procedures. Distal intestinal resection, without a functioning colon, results in the most severe complications and adaptation may depend on the age at resection (preterm, term, young, adult). Clinically relevant therapies have recently been suggested from studies in preterm and term PN-dependent SBS piglets, with or without a functional colon. Studies in rats and mice have specifically addressed the fundamental physiological processes underlying adaptation at the cellular level, such as regulation of mucosal proliferation, apoptosis, transport, and digestive enzyme expression, and easily allow exogenous or genetic manipulation of growth factors and their receptors (e.g., glucagon-like peptide 2, growth hormone, insulin-like growth factor 1, epidermal growth factor, keratinocyte growth factor). The greater size of rats, and especially young pigs, is an advantage for testing surgical procedures and nutritional interventions (e.g., PN, milk diets, long-/short-chain lipids, pre- and probiotics). Conversely, newborn pigs (preterm or term) and weanling rats provide better insights into the developmental aspects of treatment for SBS in infants owing to their immature intestines. The review shows that a balance among practical, economical, experimental, and ethical constraints will determine the choice of SBS model for each clinical or basic research question.

Therapies for inter-relating diabetes and obesity - GLP-1 and obesity

INTRODUCTION

The dramatic rise in the prevalence of obesity and type 2 diabetes mellitus (T2DM) is associated with increased mortality, morbidity as well as public health care expenses worldwide. The need for effective and long-lasting pharmaceutical treatment is obvious. The record of anti-obesity drugs has been poor so far and the only efficient treatment today is bariatric surgery. Research has indicated that appetite inhibiting hormones from the gut may have a therapeutic potential in obesity. The gut incretin hormone, glucagon-like peptide-1 (GLP-1), appears to be involved in both peripheral and central pathways mediating satiety. Clinical trials have shown that two GLP-1 receptor agonists exenatide and liraglutide have a weight-lowering potential in non-diabetic obese individuals. Furthermore, they may also hold a potential in preventing diabetes as compared to other weight loss agents.

AREAS COVERED

The purpose of this review is to cover the background for the GLP-1-based therapies and their potential in obesity and pre-diabetes. Up-to-date literature on incretin-based therapies will be summarized with a special mention of their weight-lowering properties. The literature updated to August 2014 from PubMed was identified using the combinations: GLP-1, GLP-1 receptor agonists, incretins, obesity and pre-diabetes.

EXPERT OPINION

The incretin impairment, which seems to exist in both obesity and diabetes, may link these two pathologies and underlines the potential of GLP-1-based therapies in the prevention and treatment of these diseases.

Vagal afferents are not necessary for the satiety effect of the gut lipid messenger oleoylethanolamide

The endogenous lipid messenger oleoylethanolamide (OEA) inhibits eating and modulates fat metabolism supposedly through the activation of peroxisome proliferator-activated receptor-α (PPARα) and vagal sensory fibers. We tested in adult male rats whether OEA stimulates fatty acid oxidation (FAO) and ketogenesis and whether it increases plasma levels of the satiating gut peptides glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). We also explored whether OEA still inhibits eating after subdiaphragmatic vagal deafferentation (SDA). We found that intraperitoneally injected OEA (10 mg/kg body wt) reduced ( P < 0.05) food intake mainly by increasing meal latency and that this effect was stronger in rats fed a 60% high-fat diet (HFD) than in chow-fed rats. OEA increased ( P < 0.05) postprandial plasma nonesterified fatty acids and β-hydroxybutyrate (BHB) in the hepatic portal vein (HPV) and vena cava (VC) 30 min after injection, which was more pronounced in HFD- than in chow-fed rats. OEA also increased the protein expression of the key ketogenetic enzyme, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase, in the jejunum of HFD-fed rats, but not in the liver or duodenum of either diet group. Furthermore, OEA decreased GLP-1 and PYY concentrations ( P < 0.05) in the HPV and VC 30 min after administration. Finally, OEA reduced food intake in SDA and sham-operated rats similarly. Our findings indicate that neither intact abdominal vagal afferents nor prandial increases in GLP-1 or PYY are necessary for the satiety effect of OEA. The enhanced FAO and ketogenesis raise the possibility of an involvement of intestine-derived BHB in OEA's satiety effect under certain conditions.

Association of obstructive sleep apnea in rapid eye movement sleep with reduced glycemic control in type 2 diabetes: therapeutic implications

OBJECTIVE

Severity of obstructive sleep apnea (OSA) has been associated with poorer glycemic control in type 2 diabetes. It is not known whether obstructive events during rapid eye movement (REM) sleep have a different metabolic impact compared with those during non-REM (NREM) sleep. Treatment of OSA is often limited to the first half of the night, when NREM rather than REM sleep predominates. We aimed to quantify the impact of OSA in REM versus NREM sleep on hemoglobin A1c (HbA1c) in subjects with type 2 diabetes.

RESEARCH DESIGN AND METHODS

All participants underwent polysomnography, and glycemic control was assessed by HbA1c.

RESULTS

Our analytic cohort included 115 subjects (65 women; age 55.2 ± 9.8 years; BMI 34.5 ± 7.5 kg/m(2)). In a multivariate linear regression model, REM apnea-hypopnea index (AHI) was independently associated with increasing levels of HbA1c (P = 0.008). In contrast, NREM AHI was not associated with HbA1c (P = 0.762). The mean adjusted HbA1c increased from 6.3% in subjects in the lowest quartile of REM AHI to 7.3% in subjects in the highest quartile of REM AHI (P = 0.044 for linear trend). Our model predicts that 4 h of continuous positive airway pressure (CPAP) use would leave 60% of REM sleep untreated and would be associated with a decrease in HbA1c by approximately 0.25%. In contrast, 7 h of CPAP use would cover more than 85% of REM sleep and would be associated with a decrease in HbA1c by as much as 1%.

CONCLUSIONS

In type 2 diabetes, OSA during REM sleep may influence long-term glycemic control. The metabolic benefits of CPAP therapy may not be achieved with the typical adherence of 4 h per night.

Meal induced gut hormone secretion is altered in aerobically trained compared to sedentary young healthy males

Postprandial insulin release is lower in healthy aerobically trained (T) compared to untrained (UT) individuals. This may be mediated by a lower release of the two incretin hormones [glucagon like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP)] in T. The aim of this study was to assess and compare gut hormone response and satiety changes after a liquid meal intake in young, healthy T and UT males. Postprandial gut hormone release and subjective feelings of hunger, satiety, fullness and prospective food consumption were assessed before and frequently for the following 3 h after a 200 ml liquid meal (1,260 kJ and 27, 41 and 32 energy % as protein, carbohydrates and fat, respectively) in ten T and ten UT young, healthy male subjects. The insulin and GIP responses were markedly lower in T than UT and correlated during the first 30 min after the liquid meal. Baseline GLP-1 concentration was higher in T versus UT, but the response in the following 3 h after a liquid meal was similar in T and UT. Satiety measures did not differ between groups throughout the test. It is possible that in aerobically T subjects, a lower GIP release is partly responsible for a lower postprandial incretin stimulated insulin secretion.