Glucagon-like peptide-1 receptor agonist treatment reduces beta cell mass in normoglycaemic mice

Incretin mimetics and acute pancreatitis: enemy or innocent bystander?

PURPOSE OF REVIEW

The incretin enhancers and mimetics, including dipeptidyl peptidase-4 (DPP-4) inhibitors, GLP-1 receptor agonists (GLP-1RA) and GLP-1/GIP co-agonists, have become mainstays in the treatment of type 2 diabetes (T2D). Recently, the approval of certain GLP-1RA and GLP-1/GIP co-agonists for the treatment of obesity has broadened their popularity and use. In this review, we summarize the evidence for an association of these drugs with acute pancreatitis and other adverse events of special interest to gastroenterologists.

RECENT FINDINGS

In addition to pancreatic islets, GLP-1 receptors are expressed in the exocrine cells of the pancreas. There is inconsistent evidence for an association of DPP-4 inhibitors, GLP-1RA and co-agonists with risk for acute pancreatitis in individual trials. Meta-analyses of long-term randomized controlled trials indicate a small risk of acute pancreatitis associated with DPP-4 inhibitors but not GLP-1RA or co-agonists. Cholecystitis and cholelithiasis may be more common among those treated with GLP-1RA and GLP-1/GIP co-agonists. There is no evidence that any of these drugs are associated with an increased risk of pancreatic cancer.

SUMMARY

While drugs that leverage the incretin system are increasingly being used for patients with T2D and obesity, caution in warranted in those with a history of pancreatitis and gallbladder disease.

Altered chronic glycemic control in a clinically relevant model of rat thoracic spinal contusion

The lifetime risk for Type 2 diabetes mellitus remains higher in people with spinal cord injuries (SCIs) than in the able-bodied population. However, the mechanisms driving this disparity remain poorly understood. The goal of the present study was to evaluate the impact of a palatable high-fat diet (HFD) on glycemic regulation using a rodent model of moderate thoracic contusion. Animals were placed on either Chow or HFD and tolerance to glucose, insulin, and ENSURE mixed meal were investigated. Important targets in the gut-brain axis were investigated. HFD consumption equally induced weight gain in SCI and naïve rats over chow (CH) rats. Elevated blood glucose was observed during intraperitoneal glucose tolerance test in HFD-fed rats over CH-fed rats. Insulin tolerance test (ITT) was unremarkable among the three groups. Gavage of ENSURE resulted in high glucagon-like peptide 1 (GLP-1) release from SCI rats over naïve controls. An elevation in terminal total GLP-1 was measured, with a marked reduction in circulating dipeptidyl peptidase 4, the GLP-1 cleaving enzyme, in SCI rats, compared with naïve. Increased glucagon mRNA in the pancreas and reduced immunoreactive glucagon-positive staining in the pancreas in SCI rats compared with controls suggested increased glucagon turnover. Finally, GLP-1 receptor gene expression in the ileum, the primary source of GLP-1 production and release, in SCI rats suggests the responsivity of the gut to altered circulating GLP-1 in the body. In conclusion, the actions of GLP-1 and its preprohormone, glucagon, are markedly uncoupled from their actions on glucose control in the SCI rat. More work is required to understand GLP-1 in the human.

An olive-derived elenolic acid stimulates hormone release from L-cells and exerts potent beneficial metabolic effects in obese diabetic mice

Insulin resistance and progressive decline in functional β-cell mass are two key factors for developing type 2 diabetes (T2D), which is largely driven by overweight and obesity, a significant obstacle for effective metabolic control in many patients with T2D. Thus, agents that simultaneously ameliorate obesity and act on multiple pathophysiological components could be more effective for treating T2D. Here, we report that elenolic acid (EA), a phytochemical, is such a dual-action agent. we show that EA dose-dependently stimulates GLP-1 secretion in mouse clonal L-cells and isolated mouse ileum crypts. In addition, EA induces L-cells to secrete peptide YY (PYY). EA induces a rapid increase in intracellular [Ca²⁺]_i and the production of inositol trisphosphate in L-cells, indicating that EA activates phospholipase C (PLC)-mediated signaling. Consistently, inhibition of (PLC) or Gα_q ablates EA-stimulated increase of [Ca²⁺]_i and GLP-1 secretion. In vivo, a single dose of EA acutely stimulates GLP-1 and PYY secretion in mice, accompanied with an improved glucose tolerance and insulin levels. Oral administration of EA at a dose of 50 mg/kg/day for 2 weeks normalized the fasting blood glucose and restored glucose tolerance in high-fat diet-induced obese (DIO) mice to levels that were comparable to chow-fed mice. In addition, EA suppresses appetite, reduces food intake, promotes weight loss, and reverses perturbated metabolic variables in obese mice. These results suggest that EA could be a dual-action agent as an alternative or adjuvant treatment for both T2D and obesity.

Safety of Glucagon-Like Peptide-1 Receptor Agonists: A Real-World Study Based on the US FDA Adverse Event Reporting System Database

BACKGROUND AND OBJECTIVE

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are used as adjunctive therapy to lifestyle intervention and metformin treatment in type 2 diabetes mellitus patients, as most GLP-1RAs have cardiovascular benefits; however, a number of adverse events (AEs) have been reported in postmarketing surveillance.

OBJECTIVE

The aim of this study was to describe the AEs associated with GLP-1RA monotherapy and identify important medical event (IME) signals for GLP-1RAs.

METHODS

Data from 1 April 2005 to 31 December 2021 from the US FDA Adverse Event Reporting System (FAERS) database were extracted to conduct disproportionality analysis and Bayesian analysis. AEs and IMEs were classified by system organ classes (SOCs) and preferred terms (PTs) according to the Medical Dictionary for Regulatory Activities (MedDRA^®). The reporting odds ratio (ROR) and information component (IC) were used to indicate the disproportionality.

RESULTS

A total of 71,515 records involving GLP-1RA monotherapy were submitted to the database, of which 16,350 records were GLP-1RA/IME pairs. Significant disproportionality emerged in five SOCs: 'gastrointestinal disorders' (n = 13,104; lower end of the 95% confidence interval (CI) of the IC [IC₀₂₅] = 1.34), 'investigations' (n = 6889; IC₀₂₅ = 0.64), 'metabolism and nutrition disorders' (n = 2943; IC₀₂₅ = 0.44), 'neoplasms benign/malignant' (n = 1989; IC₀₂₅ = 0.01), and 'hepatobiliary disorders' (n = 1497; IC₀₂₅ = 0.38). The most common AEs were pancreatitis, nausea, and weight decrease. Unexpected significant AEs were detected, such as ileus, osteomyelitis, renal cell carcinoma, nephrolithiasis, and drug-induced liver injury.

CONCLUSION

The majority of AEs have been listed in the prescribing information or reported in previous studies, however we found significant disproportionality in some specific tumor- and liver-related AEs. Clinicians should pay more attention to the newly detected disproportionality that may be triggered by GLP-1RAs, especially in the vulnerable population after long-term use. Considering the limitations of the FAERS database, there is a need for additional pharmacoepidemiological approaches to validate the results of this study.

Safety of Semaglutide

The glucagon-like peptide-1 receptor agonist (GLP-1RA) semaglutide is the most recently approved agent of this drug class, and the only GLP-1RA currently available as both subcutaneous and oral formulation. While GLP-1RAs effectively improve glycemic control and cause weight loss, potential safety concerns have arisen over the years. For semaglutide, such concerns have been addressed in the extensive phase 3 registration trials including cardiovascular outcome trials for both subcutaneous (SUSTAIN: Semaglutide Unabated Sustainability in Treatment of Type 2 Diabetes) and oral (PIONEER: Peptide InnOvatioN for the Early diabEtes tReatment) semaglutide and are being studied in further trials and registries, including real world data studies. In the current review we discuss the occurrence of adverse events associated with semaglutide focusing on hypoglycemia, gastrointestinal side effects, pancreatic safety (pancreatitis and pancreatic cancer), thyroid cancer, gallbladder events, cardiovascular aspects, acute kidney injury, diabetic retinopathy (DRP) complications and injection-site and allergic reactions and where available, we highlight potential underlying mechanisms. Furthermore, we discuss whether effects are specific for semaglutide or a class effect. We conclude that semaglutide induces mostly mild-to-moderate and transient gastrointestinal disturbances and increases the risk of biliary disease (cholelithiasis). No unexpected safety issues have arisen to date, and the established safety profile for semaglutide is similar to that of other GLP-1RAs where definitive conclusions for pancreatic and thyroid cancer cannot be drawn at this point due to low incidence of these conditions. Due to its potent glucose-lowering effect, patients at risk for deterioration of existing DRP should be carefully monitored if treated with semaglutide, particularly if also treated with insulin. Given the beneficial metabolic and cardiovascular actions of semaglutide, and the low risk for severe adverse events, semaglutide has an overall favorable risk/benefit profile for patient with type 2 diabetes.

Tolerance develops toward GLP-1 receptor agonists' glucose-lowering effect in mice

Glucagon-like peptide 1 (GLP-1) receptor agonists are popular antidiabetic drugs with potent glucose-lowering effects and low risk of hypoglycemia. Animal experiments and human data indicate that tolerance develops toward at least some of their effects, e.g., gastric motility. Whether tolerance develops toward the glucose-lowering effect of GLP-1 receptor agonists in mice has never been formally tested. The hypothesis of tolerance development in mice will be reported in this study. The direct glucose-lowering effect of the GLP-1 receptor agonists was measured in non-fasted mice and with intraperitoneal glucose tolerance test. Exenatide (10 μg/kg) and liraglutide (600 μg/kg) both substantially lost efficacy during the 18-day treatment as compared to the acute effect. We conclude that our results demonstrate development of tolerance toward GLP-1 receptor agonists' glucose-lowering effect in mice.

Pleiotropic Effects of GLP-1 and Analogs on Cell Signaling, Metabolism, and Function

The incretin hormone Glucagon-Like Peptide-1 (GLP-1) is best known for its "incretin effect" in restoring glucose homeostasis in diabetics, however, it is now apparent that it has a broader range of physiological effects in the body. Both in vitro and in vivo studies have demonstrated that GLP-1 mimetics alleviate endoplasmic reticulum stress, regulate autophagy, promote metabolic reprogramming, stimulate anti-inflammatory signaling, alter gene expression, and influence neuroprotective pathways. A substantial body of evidence has accumulated with respect to how GLP-1 and its analogs act to restore and maintain normal cellular functions. These findings have prompted several clinical trials which have reported GLP-1 analogs improve cardiac function, restore lung function and reduce mortality in patients with obstructive lung disease, influence blood pressure and lipid storage, and even prevent synaptic loss and neurodegeneration. Mechanistically, GLP-1 elicits its effects via acute elevation in cAMP levels, and subsequent protein kinase(s) activation, pathways well-defined in pancreatic β-cells which stimulate insulin secretion in conjunction with elevated Ca2+ and ATP. More recently, new studies have shed light on additional downstream pathways stimulated by chronic GLP-1 exposure, findings which have direct relevance to our understanding of the potential therapeutic effects of longer lasting analogs recently developed for clinical use. In this review, we provide a comprehensive description of the diverse roles for GLP-1 across multiple tissues, describe downstream pathways stimulated by acute and chronic exposure, and discuss novel pleiotropic applications of GLP-1 mimetics in the treatment of human disease.

Preventive treatment with liraglutide protects against development of glucose intolerance in a rat model of Wolfram syndrome

Wolfram syndrome (WS) is a rare autosomal recessive disorder caused by mutations in the WFS1 (Wolframin1) gene. The syndrome first manifests as diabetes mellitus, followed by optic nerve atrophy, deafness, and neurodegeneration. The underlying mechanism is believed to be a dysregulation of endoplasmic reticulum (ER) stress response, which ultimately leads to cellular death. Treatment with glucagon-like peptide-1 (GLP-1) receptor agonists has been shown to normalize ER stress response in several in vitro and in vivo models. Early chronic intervention with the GLP-1 receptor agonist liraglutide starting before the onset of metabolic symptoms prevented the development of glucose intolerance, improved insulin and glucagon secretion control, reduced ER stress and inflammation in Langerhans islets in Wfs1 mutant rats. Thus, treatment with GLP-1 receptor agonists might be a promising strategy as a preventive treatment for human WS patients.

Glucagon-like Peptide 1 Receptor Signaling in Acinar Cells Causes Growth-Dependent Release of Pancreatic Enzymes

Incretin-based therapies are widely used for type 2 diabetes and now also for obesity, but they are associated with elevated plasma levels of pancreatic enzymes and perhaps a modestly increased risk of acute pancreatitis. However, little is known about the effects of the incretin hormone glucagon-like peptide 1 (GLP-1) on the exocrine pancreas. Here, we identify GLP-1 receptors on pancreatic acini and analyze the impact of receptor activation in humans, rodents, isolated acini, and cell lines from the exocrine pancreas. GLP-1 did not directly stimulate amylase or lipase release. However, we saw that GLP-1 induces phosphorylation of the epidermal growth factor receptor and activation of Foxo1, resulting in cell growth with concomitant enzyme release. Our work uncovers GLP-1-induced signaling pathways in the exocrine pancreas and suggests that increases in amylase and lipase levels in subjects treated with GLP-1 receptor agonists reflect adaptive growth rather than early-stage pancreatitis.

Glucagon-like peptide-1 receptor agonist exendin-4 protects against interleukin-1β-mediated inhibition of glucose-stimulated insulin secretion by mouse insulinoma β cells

The aim of the present study was to investigate the protective effect of the glucagon-like peptide-1 receptor agonist exendin-4 on the interleukin (IL)-1β-induced impairment of glucose-stimulated insulin secretion (GSIS) in β-TC-6 cells. β-TC-6 cells were pretreated with various concentrations of IL-1β (0.15, 1.5 or 15 ng/ml) and exendin-4 (0.1 or 1 mM). Exendin-4 was administered to β-TC-6 cells prior to, during and following pretreatment. Cells were stimulated with various concentrations of glucose (0, 1.38, 5.5 and 11.1 mM), and insulin was measured via radioimmunoassay of the supernatant; furthermore, western blot analysis was used to detect phosphorylated extracellular receptor kinase (ERK)1/2. The insulin levels (151.08±14.34 µIU/ml) and ERK1/2 phosphorylation in β-TC-6 cells peaked in response to 1.38 mM glucose stimulation compared with 0, 5.5 and 11.1 mM glucose stimulation. IL-1β inhibited GSIS in a dose-dependent manner: Insulin levels were 83.76±1.16 µIU/ml when 0.15 ng/ml IL-1β was added under GSIS, 59.46±3.20 µIU/ml when 1.5 ng/ml IL-1β was added under GSIS, and 56.98±1.19 µIU/ml when 15 ng/ml IL-1β was added under GSIS. Exendin-4 exerted a protective effect against IL-1β-induced GSIS inhibition in a dose-dependent manner. The greatest protective effect was observed when exendin-4 was added prior to IL-1β pretreatment, which was statistically significant (P<0.05). These findings suggested that exendin-4 was able to reverse the IL-1β-induced inhibition of ERK1/2 phosphorylation and serves a protective role by impairing GSIS induced by IL-1β in β-TC-6 cells. This mechanism may be associated with the recovery of ERK1/2 activation.

Incretin Therapies Do Not Expand β-Cell Mass or Alter Pancreatic Histology in Young Male Mice

The impact of incretins upon pancreatic β-cell expansion remains extremely controversial. Multiple studies indicate that incretin-based therapies can increase β-cell proliferation, and incretins have been hypothesized to expand β-cell mass. However, disagreement exists on whether incretins increase β-cell mass. Moreover, some reports indicate that incretins may cause metaplastic changes in pancreatic histology. To resolve these questions, we treated a large cohort of mice with incretin-based therapies and carried out a rigorous analysis of β-cell turnover and pancreatic histology using high-throughput imaging. Young mice received exenatide via osmotic pump, des-fluoro-sitagliptin, or glipizide compounded in diet for 2 weeks (short-term) on a low-fat diet (LFD) or 4.5 months (long-term) on a LFD or high-fat diet (HFD). Pancreata were quantified for β-cell turnover and mass. Slides were examined for gross anatomical and microscopic changes to exocrine pancreas. Short-term des-fluoro-sitagliptin increased serum insulin and induced modest β-cell proliferation but no change in β-cell mass. Long-term incretin therapy in HFD-fed mice resulted in reduced weight gain, improved glucose homeostasis, and abrogated β-cell mass expansion. No evidence for rapidly dividing progenitor cells was found in islets or pancreatic parenchyma, indicating that incretins do not induce islet neogenesis or pancreatic metaplasia. Contrasting prior reports, we found no evidence of β-cell mass expansion after acute or chronic incretin therapy. Chronic incretin administration was not associated with histological abnormalities in pancreatic parenchyma; mice did not develop tumors, pancreatitis, or ductal hyperplasia. We conclude that incretin therapies do not generate β-cells or alter pancreatic histology in young mice.

Improvement of islet graft function using liraglutide is correlated with its anti-inflammatory properties

Background and Purpose

Liraglutide improves the metabolic control of diabetic animals after islet transplantation. However, the mechanisms underlying this effect remain unknown. The objective of this study was to evaluate the anti‐inflammatory and anti‐oxidative properties of liraglutide on rat pancreatic islets in vitro and in vivo.

Experimental Approach

In vitro, rat islets were incubated with 10 μmol·L⁻¹ liraglutide for 12 and 24 h. Islet viability functionality was assessed. The anti‐inflammatory properties of liraglutide were evaluated by measuring CCL2, IL‐6 and IL‐10 secretion and macrophage chemotaxis. The anti‐oxidative effect of liraglutide was evaluated by measuring intracellular ROS and the total anti‐oxidative capacity. In vivo, 1000 islets were cultured for 24 h with or without liraglutide and then transplanted into the liver of streptozotocin‐induced diabetic Lewis rats with or without injections of liraglutide. Effects of liraglutide on metabolic control were evaluated for 1 month.

Key Results

Islet viability and function were preserved and enhanced with liraglutide treatment. Liraglutide decreased CCL2 and IL‐6 secretion and macrophage activation after 12 h of culture, while IL‐10 secretion was unchanged. However, intracellular levels of ROS were increased with liraglutide treatment at 12 h. This result was correlated with an increase of anti‐oxidative capacity. In vivo, liraglutide decreased macrophage infiltration and reduced fasting blood glucose in transplanted rats.

Conclusions and Implications

The beneficial effects of liraglutide on pancreatic islets appear to be linked to its anti‐inflammatory and anti‐oxidative properties. These findings indicated that analogues of glucagon‐like peptide‐1 could be used to improve graft survival.

Effects of Noise Exposure on Systemic and Tissue-Level Markers of Glucose Homeostasis and Insulin Resistance in Male Mice

BACKGROUND

Epidemiological studies have indicated that noise exposure is associated with an increased risk of type 2 diabetes mellitus (T2DM). However, the nature of the connection between noise exposure and T2DM remains to be explored.

OBJECTIVES

We explored whether and how noise exposure affects glucose homeostasis in mice as the initial step toward T2DM development.

METHODS

Male ICR mice were randomly assigned to one of four groups: the control group and three noise groups (N20D, N10D, and N1D), in which the animals were exposed to white noise at 95 decibel sound pressure level (dB SPL) for 4 hr per day for 20 successive days, 10 successive days, or 1 day, respectively. Glucose tolerance and insulin sensitivity were evaluated 1 day, 1 week, and 1 month after the final noise exposure (1DPN, 1WPN, and 1MPN). Standard immunoblots, immunohistochemical methods, and enzyme-linked immunosorbent assays (ELISA) were performed to assess insulin signaling in skeletal muscle, the morphology of β cells, and plasma corticosterone levels.

RESULTS

Noise exposure for 1 day caused transient glucose intolerance and insulin resistance, whereas noise exposure for 10 and 20 days had no effect on glucose tolerance but did cause prolonged insulin resistance and an increased insulin response to glucose challenge. Akt phosphorylation and GLUT4 translocation in response to exogenous insulin were decreased in the skeletal muscle of noise-exposed animals.

CONCLUSIONS

Noise exposure at 95 dB SPL caused insulin resistance in male ICR mice, which was prolonged with longer noise exposure and was likely related to the observed blunted insulin signaling in skeletal muscle.

CITATION

Liu L, Wang F, Lu H, Cao S, Du Z, Wang Y, Feng X, Gao Y, Zha M, Guo M, Sun Z, Wang J. 2016. Effects of noise exposure on systemic and tissue-level markers of glucose homeostasis and insulin resistance in male mice. Environ Health Perspect 124:1390-1398; http://dx.doi.org/10.1289/EHP162.

Glucagon-Like Peptide 1 Analogs and their Effects on Pancreatic Islets

Glucagon-like peptide 1 (GLP-1) exerts many actions that improve glycemic control. GLP-1 stimulates glucose-stimulated insulin secretion and protects β cells, while its extrapancreatic effects include cardioprotection, reduction of hepatic glucose production, and regulation of satiety. Although an appealing antidiabetic drug candidate, the rapid degradation of GLP-1 by dipeptidyl peptidase 4 (DPP-4) means that its therapeutic use is unfeasible, and this prompted the development of two main GLP-1 therapies: long-acting GLP-1 analogs and DPP-4 inhibitors. In this review, we focus on the pancreatic effects exerted by current GLP-1 derivatives used to treat diabetes. Based on the results from in vitro and in vivo studies in humans and animal models, we describe the specific actions of GLP-1 analogs on the synthesis, processing, and secretion of insulin, islet morphology, and β cell proliferation and apoptosis.

An Update on the Effect of Incretin-Based Therapies on β-Cell Function and Mass

Type 2 diabetes mellitus (T2DM) is a multifactorial disease with a complex and progressive pathogenesis. The two primary mechanisms of T2DM pathogenesis are pancreatic β-cell dysfunction and insulin resistance. Pancreatic β-cell dysfunction is recognized to be a prerequisite for the development of T2DM. Therapeutic modalities that improve β-cell function are considered critical to T2DM management; however, blood glucose control remains a challenge for many patients due to suboptimal treatment efficacy and the progressive nature of T2DM. Incretin-based therapies are now the most frequently prescribed antidiabetic drugs in Korea. Incretin-based therapies are a favorable class of drugs due to their ability to reduce blood glucose by targeting the incretin hormone system and, most notably, their potential to improve pancreatic β-cell function. This review outlines the current understanding of the incretin hormone system in T2DM and summarizes recent updates on the effect of incretin-based therapies on β-cell function and β-cell mass in animals and humans.

GLP-1 based therapies: clinical implications for gastroenterologists

The gut-derived incretin hormone, glucagon-like peptide 1 (GLP-1) lowers postprandial blood glucose levels by stimulating insulin and inhibiting glucagon secretion. Two novel antihyperglycaemic drug classes augment these effects; GLP-1 receptor agonists and inhibitors of the GLP-1 degrading enzyme dipeptidyl peptidase 4. These so called GLP-1 based or incretin based drugs are increasingly used to treat type 2 diabetes, because of a low risk of hypoglycaemia and favourable effect on body weight, blood pressure and lipid profiles. Besides glucose control, GLP-1 functions as an enterogastrone, causing a wide range of GI responses. Studies have shown that endogenous GLP-1 and its derived therapies slow down digestion by affecting the stomach, intestines, exocrine pancreas, gallbladder and liver. Understanding the GI actions of GLP-1 based therapies is clinically relevant; because GI side effects are common and need to be recognised, and because these drugs may be used to treat GI disease.

Distinct effects of dipeptidyl peptidase-4 inhibitor and glucagon-like peptide-1 receptor agonist on islet morphology and function

Although the two anti-diabetic drugs, dipeptidyl peptidase-4 inhibitors (DPP4is) and glucagon-like peptide-1 (GLP-1) receptor agonists (GLP1RAs), have distinct effects on the dynamics of circulating incretins, little is known of the difference in their consequences on morphology and function of pancreatic islets. We examined these in a mouse model of β cell injury/regeneration. The model mice were generated so as to express diphtheria toxin (DT) receptor and a fluorescent protein (Tomato) specifically in β cells. The mice were treated with a DPP4i (MK-0626) and a GLP1RA (liraglutide), singly or doubly, and the morphology and function of the islets were compared. Prior administration of MK-0626 and/or liraglutide similarly protected β cells from DT-induced cell death, indicating that enhanced GLP-1 signaling can account for the cytoprotection. However, 2-week intervention of MK-0626 and/or liraglutide in DT-injected mice resulted in different islet morphology and function: β cell proliferation and glucose-stimulated insulin secretion (GSIS) were increased by MK-0626 but not by liraglutide; α cell mass was decreased by liraglutide but not by MK-0626. Although liraglutide administration nullified MK-0626-induced β cell proliferation, their co-administration resulted in increased GSIS, decreased α cell mass, and improved glucose tolerance. The pro-proliferative effect of MK-0626 was lost by co-administration of the GLP-1 receptor antagonist exendin-(9-39), indicating that GLP-1 signaling is required for this effect. Comparison of the effects of DPP4is and/or GLP1RAs treatment in a single mouse model shows that the two anti-diabetic drugs have distinct consequences on islet morphology and function.

Effects of liraglutide in hypothalamic arcuate nucleus of obese mice

OBJECTIVE

The neuroprotective effects of liraglutide (200 μg/kg, twice daily, subcutaneous administration) in the hypothalamic arcuate nucleus (ARC) of diet-induced obese mice were investigated.

METHODS

C57BL/6 mice were separated into groups: standard chow treated with vehicle or liraglutide and the respective liraglutide pair-fed group; high-fat diet treated with vehicle or liraglutide and the respective pair-fed group. Body mass (BM) evolution, carbohydrate metabolism, leptin resistance, proteins involved in energetic balance, apoptosis, and microglia in the ARC were studied.

RESULTS

Obese animals showed glucose intolerance, resistance to insulin and to anorexigenic effect of leptin, and microgliosis accompanied by elevated Bax/Bcl2 ratio in the ARC. Liraglutide improved the carbohydrate metabolism, BM loss, and the activation of pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART) in the ARC. The liraglutide enhanced leptin sensitivity and diminished the microgliosis with decrease in Bax/Bcl2 ratio.

CONCLUSIONS

Liraglutide activates central anorexigenic pathways, thereby diminishing the energy intake of obese mice and improving the metabolic parameters related to obesity. Liraglutide is a relevant neuroprotective agent, which can decrease the microgliosis and stimulate the anti-apoptotic pathway, a significant effect in the treatment of obesity and its comorbidities. Some benefits of liraglutide are independent of the BM loss, which usually accompanies the drug administration.

A systematic review of the safety of incretin-based therapies in type 2 diabetes

INTRODUCTION

Large randomized clinical trials have demonstrated that incretin-based therapies provide effective glycemic control in type 2 diabetes. Long-term safety assessments are ongoing.

METHODS

This systematic review of incretin-based therapy safety is based on 112 randomized clinical trials of duration ≥26 weeks published between January 2000 and February 2015 in patients with type 2 diabetes.

RESULTS

As expected, hypoglycemia rates were lower with dipeptidyl peptidase-4 inhibitors (DPP-4is) and glucagon-like peptide-1 receptor agonists (GLP-1 RAs) versus other oral antidiabetic drugs and insulin. The most common adverse events were infection and infestation (DPP-4is) and gastrointestinal (GLP-1 RAs). Pancreatitis cases were rare across all studies and, in the SAVOR-TIMI and EXAMINE trials, pancreatitis rates were similar in DPP-4i- and placebo-treated patients. No thyroid tumors were reported, and increased risk of cardiovascular events was not associated with DPP-4is in SAVOR-TIMI and EXAMINE, albeit over a short follow-up period.

CONCLUSIONS

Overall, incretin-based therapies were well tolerated; however, their long-term safety profile should continue to be periodically assessed.

Molecular and cellular mechanisms of glucagon-like peptide-1 receptor agonist-mediated attenuation of cardiac fibrosis

BACKGROUND

Glucagon-like peptide-1 receptor agonists may have a role in modulation of cardiac fibrosis. Our study aimed to determine the effect of the glucagon-like peptide-1 receptor agonist liraglutide in obesity, hypertension and age-induced murine models of cardiac fibrosis and identify associated molecular mechanisms.

METHODS

C57Bl/6J mice on a high-fat diet and C57Bl/6J mice on a normal chow diet treated with angiotensin II were used to induce obesity and hypertension-mediated cardiac fibrosis, respectively. C57Bl/6J mice 20 months old were used to study age-induced cardiac fibrosis. Liraglutide treatment of 30 µg/kg/day-300 µg/kg s.c. twice daily was administered for 4 weeks.

RESULTS

Liraglutide treatment attenuated obesity, hypertension and age-induced increases in interstitial cardiac fibrosis and expression of inflammatory and oxidative stress markers.

CONCLUSIONS

These observations identify a potential role for liraglutide in the prevention of cardiac fibrosis and identify molecular mechanisms associated with these effects.

GLP-1 mimetic drugs and the risk of exocrine pancreatic disease: Cell and animal studies

BACKGROUND

Glucagon Like Peptide 1 (GLP-1) mimetic drugs or degradation inhibitors mimic the action of native GLP-1 as a incretin hormone and have become a common second line of therapy for Type 2 diabetes. However, an important clinical issue is whether these drugs increase the incidence of pancreatitis and pancreatic cancer.

OBJECTIVE

This paper reviews the physiology of GLP-1 including its synthesis, secretion and action of the peptide. Reported effects of the mimetic drugs on the exocrine pancreas in animal studies are also reviewed.

RESULTS

GLP-1 is synthesized in a specific class of enteroendocrine cell, the L-cell, by post-translational processing of proglucagon. It is released in response to the presence of nutrients in the small intestine and stimulates vagal afferent nerve endings as well as entering the blood where it is rapidly degraded by dipeptidyl peptidase IV. Its actions are mediated by specific G-protein coupled receptors. The major target tissues are the pancreatic islet beta cells, the brain and the heart but GLP-1 also affects gastrointestinal motility and secretion including the exocrine pancreas where its major systemic action is to inhibit secretion. In some animal, as well as human studies, the GLP-1 mimetic drugs are associated with pancreatitis or precursor lessions to pancreatic cancer but a mechanism is not clear. The most common occurrence of pathology in rodents is when the drugs are combined with a high fat diet.

CONCLUSIONS

There is nothing in the physiology of GLP-1 or animal toxicology studies to support a mechanism of action or a major concern about the action of GLP-1 mimetic drugs on the exocrine pancreas. Further studies are warranted using animal models of disease and high fat diets.

Loss of β-Cell Identity Occurs in Type 2 Diabetes and Is Associated With Islet Amyloid Deposits

Loss of pancreatic islet β-cell mass and β-cell dysfunction are central in the development of type 2 diabetes (T2DM). We recently showed that mature human insulin-containing β-cells can convert into glucagon-containing α-cells ex vivo. This loss of β-cell identity was characterized by the presence of β-cell transcription factors (Nkx6.1, Pdx1) in glucagon(+) cells. Here, we investigated whether the loss of β-cell identity also occurs in vivo, and whether it is related to the presence of (pre)diabetes in humans and nonhuman primates. We observed an eight times increased frequency of insulin(+) cells coexpressing glucagon in donors with diabetes. Up to 5% of the cells that were Nkx6.1(+) but insulin(-) coexpressed glucagon, which represents a five times increased frequency compared with the control group. This increase in bihormonal and Nkx6.1(+)glucagon(+)insulin(-) cells was also found in islets of diabetic macaques. The higher proportion of bihormonal cells and Nkx6.1(+)glucagon(+)insulin(-) cells in macaques and humans with diabetes was correlated with the presence and extent of islet amyloidosis. These data indicate that the loss of β-cell identity occurs in T2DM and could contribute to the decrease of functional β-cell mass. Maintenance of β-cell identity is a potential novel strategy to preserve β-cell function in diabetes.

Glucagon-like peptide-1 receptor agonist Liraglutide has anabolic bone effects in ovariectomized rats without diabetes

Recently, a number of studies have demonstrated the potential beneficial role for novel anti-diabetic GLP-1 receptor agonists (GLP-1RAs) in the skeleton metabolism in diabetic rodents and patients. In this study, we evaluated the impacts of the synthetic GLP-1RA Liraglutide on bone mass and quality in osteoporotic rats induced by ovariectomy (OVX) but without diabetes, as well as its effect on the adipogenic and osteoblastogenic differentiation of bone marrow stromal cells (BMSCs). Three months after sham surgery or bilateral OVX, eighteen 5-month old female Wistar rats were randomly divided into three groups to receive the following treatments for 2 months: (1) Sham + normal saline; (2) OVX + normal saline; and (3) OVX + Liraglutide (0.6 mg/day). As revealed by micro-CT analysis, Liraglutide improved trabecular volume, thickness and number, increased BMD, and reduced trabecular spacing in the femurs in OVX rats; similar results were observed in the lumbar vertebrae of OVX rats treated with Liraglutide. Following in vitro treatment of rat and human BMSCs with 10 nM Liraglutide, there was a significant increase in the mRNA expression of osteoblast-specific transcriptional factor Runx2 and the osteoblast markers alkaline phosphatase (ALP) and collagen α1 (Col-1), but a significant decrease in peroxisome proliferator-activated receptor γ (PPARγ). In conclusion, our results indicate that the anti-diabetic drug Liraglutide can exert a bone protective effect even in non-diabetic osteoporotic OVX rats. This protective effect is likely attributable to the impact of Liraglutide on the lineage fate determination of BMSCs.

Pancreatic alpha-cells from female mice undergo morphofunctional changes during compensatory adaptations of the endocrine pancreas to diet-induced obesity

Obesity is frequently associated with insulin resistance. To compensate for this situation and maintain normoglycaemia, pancreatic beta-cells undergo several morphofunctional adaptations, which result in insulin hypersecretion and hyperinsulinaemia. However, no information exists about pancreatic alpha-cells during this compensatory stage of obesity. Here, we studied alpha-cells in mice fed a high-fat diet (HFD) for 12 weeks. These animals exhibited hyperinsulinaemia and normoglycaemia compared with control animals in addition to hypoglucagonaemia. While the in vivo response of glucagon to hypoglycaemia was preserved in the obese mice, the suppression of glucagon secretion during hyperglycaemia was impaired. Additionally, in vitro glucagon release at low glucose levels and glucagon content in isolated islets were decreased, while alpha-cell exocytosis remained unchanged. Assessment of morphological parameters revealed that alpha-cell area was reduced in the pancreas of the obese mice in association with alpha-cell hypotrophy, increased apoptosis and decreased proliferation. HFD feeding for 24 weeks led to significant deterioration in beta-cell function and glucose homeostasis. Under these conditions, the majority of alpha-cell changes were reversed and became comparable to controls. These findings indicate that pancreatic compensatory adaptations during obesity may also involve pancreatic alpha-cells. Additionally, defects in alpha-cell function during obesity may be implicated in progression to diabetes.

PKA Enhances the Acute Insulin Response Leading to the Restoration of Glucose Control

Diabetes arises from insufficient insulin secretion and failure of the β-cell mass to persist and expand. These deficits can be treated with ligands to Gs-coupled G-protein-coupled receptors that raise β-cell cAMP. Here we studied the therapeutic potential of β-cell cAMP-dependent protein kinase (PKA) activity in restoring glucose control using β-caPKA mice. PKA activity enhanced the acute insulin response (AIR) to glucose, which is a primary determinant of the efficacy of glucose clearance. Enhanced AIR improved peripheral insulin action, leading to more rapid muscle glucose uptake. In the setting of pre-established glucose intolerance caused by diet-induced insulin resistance or streptozotocin-mediated β-cell mass depletion, PKA activation enhanced β-cell secretory function to restore glucose control, primarily through augmentation of the AIR. Enhanced AIR and improved glucose control were maintained through 16 weeks of a high-fat diet and aging to 1 year. Importantly, improved glucose tolerance did not increase the risk for hypoglycemia, nor did it rely upon hyperinsulinemia or β-cell hyperplasia, although PKA activity was protective for β-cell mass. These data highlight that improving β-cell function through the activation of PKA has a large and underappreciated capacity to restore glucose control with minimal risk for adverse side effects.

Glucagon-like peptide-1 receptor agonists increase pancreatic mass by induction of protein synthesis

Glucagon-like peptide-1 (GLP-1) controls glucose homeostasis by regulating secretion of insulin and glucagon through a single GLP-1 receptor (GLP-1R). GLP-1R agonists also increase pancreatic weight in some preclinical studies through poorly understood mechanisms. Here we demonstrate that the increase in pancreatic weight following activation of GLP-1R signaling in mice reflects an increase in acinar cell mass, without changes in ductal compartments or β-cell mass. GLP-1R agonists did not increase pancreatic DNA content or the number of Ki67(+) cells in the exocrine compartment; however, pancreatic protein content was increased in mice treated with exendin-4 or liraglutide. The increased pancreatic mass and protein content was independent of cholecystokinin receptors, associated with a rapid increase in S6 phosphorylation, and mediated through the GLP-1R. Rapamycin abrogated the GLP-1R-dependent increase in pancreatic mass but had no effect on the robust induction of Reg3α and Reg3β gene expression. Mass spectrometry analysis identified GLP-1R-dependent upregulation of Reg family members, as well as proteins important for translation and export, including Fam129a, eIF4a1, Wars, and Dmbt1. Hence, pharmacological GLP-1R activation induces protein synthesis, leading to increased pancreatic mass, independent of changes in DNA content or cell proliferation in mice.

Effects of the glucagon-like peptide-1 receptor agonist liraglutide in juvenile transgenic pigs modeling a pre-diabetic condition

Background

The glucagon-like peptide-1 receptor (GLP1R) agonist liraglutide improves glycemic control and reduces body weight of adult type 2 diabetic patients. However, efficacy and safety of liraglutide in adolescents has not been systematically investigated. Furthermore, possible pro-proliferative effects of GLP1R agonists on the endocrine and exocrine pancreas need to be further evaluated. We studied effects of liraglutide in adolescent pigs expressing a dominant-negative glucose-dependent insulinotropic polypeptide receptor (GIPR^dn) in the beta-cells, leading to a pre-diabetic condition including disturbed glucose tolerance, reduced insulin secretion and progressive reduction of functional beta-cell mass.

Methods

Two-month-old GIPR^dn transgenic pigs were treated daily with liraglutide (0.6-1.2 mg per day) or placebo for 90 days. Glucose homeostasis was evaluated prior to and at the end of the treatment period by performing mixed meal and intravenous glucose tolerance tests (MMGTT and IVGTT). Finally animals were subjected to necropsy and quantitative-stereological analyses were performed for evaluation of alpha- and beta-cell mass, beta-cell proliferation as well as acinus-cell proliferation.

Results

MMGTT at the end of the study revealed 23% smaller area under the curve (AUC) for glucose, a 36% smaller AUC insulin, and improved insulin sensitivity, while IVGTT showed a 15% smaller AUC glucose but unchanged AUC insulin in liraglutide- vs. placebo-treated animals. Liraglutide led to marked reductions in body weight gain (-31%) and food intake (-30%) compared to placebo treatment, associated with reduced phosphorylation of insulin receptor beta (INSRB)/insulin-like growth factor-1 receptor beta (IGF1RB) and protein kinase B (AKT) in skeletal muscle. Absolute alpha- and beta-cell mass was reduced in liraglutide-treated animals, but alpha- and beta-cell mass-to-body weight ratios were unchanged. Liraglutide neither stimulated beta-cell proliferation in the endocrine pancreas nor acinus-cell proliferation in the exocrine pancreas, excluding both beneficial and detrimental effects on the pig pancreas.

Conclusions

Although plasma liraglutide levels of adolescent transgenic pigs treated in our study were higher compared to human trials, pro-proliferative effects on the endocrine or exocrine pancreas or other liraglutide-related side-effects were not observed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0431-2) contains supplementary material, which is available to authorized users.

Mouse insulin cells expressing an inducible RIPCre transgene are functionally impaired

We used cre-lox technology to test whether the inducible expression of Cre minimize the deleterious effect of the enzyme on beta cell function. We studied mice in which Cre is linked to a modified estrogen receptor (ER), and its expression is controlled by the rat insulin promoter (RIP). Following the injection of tamoxifen (TM), CreER- migrates to the nucleus and promotes the appearance of a reporter protein, enhanced yellow fluorescent protein (EYFP), in cells. Immunocytochemical analysis indicated that 46.6 ± 2.1% insulin cells of adult RIPCreER- EYFP expressed EYFP. RIPCreER-EYFP (+TM) mice were normoglycemic throughout the study, and their glucose tolerance test results were similar to control CD-1 mice. However, an extended exposure to reagents that stimulate insulin synthesis was detrimental to the survival of IN+EYFP+cells. The administration of an inhibitor of the enzyme dipeptidyl-peptidase (DPP4i), which prevents the cleavage of glucagon-like peptide (GLP-1), to adult RIPCreER-EYFP mice lead to a decrease in the percentage of IN+EYFP+ to 17.5 ± 1.73 and a significant increase in apoptotic cells in islets. Similarly, a 2-week administration of the GLP-1 analog exendin 4 (ex-4) induced an almost complete ablation of IN+ expressing a different reporter protein and a significant decrease in the beta cell mass and rate of beta cell proliferation. Since normal beta cells do not die when induced to increase insulin synthesis, our observations indicate that insulin cells expressing an inducible RIPCre transgene are functionally deficient. Studies employing these mice should carefully consider the pitfalls of the Cre-Lox technique.

Rb and p107 are required for alpha cell survival, beta cell cycle control and glucagon-like peptide-1 action

AIMS/HYPOTHESIS

Diabetes mellitus is characterised by beta cell loss and alpha cell expansion. Analogues of glucagon-like peptide-1 (GLP-1) are used therapeutically to antagonise these processes; thus, we hypothesised that the related cell cycle regulators retinoblastoma protein (Rb) and p107 were involved in GLP-1 action.

METHODS

We used small interfering RNA and adenoviruses to manipulate Rb and p107 expression in insulinoma and alpha-TC cell lines. In vivo we examined pancreas-specific Rb knockout, whole-body p107 knockout and Rb/p107 double-knockout mice.

RESULTS

Rb, but not p107, was downregulated in response to the GLP-1 analogue, exendin-4, in both alpha and beta cells. Intriguingly, this resulted in opposite outcomes of cell cycle arrest in alpha cells but proliferation in beta cells. Overexpression of Rb in alpha and beta cells abolished or attenuated the effects of exendin-4 supporting the important role of Rb in GLP-1 modulation of cell cycling. Similarly, in vivo, Rb, but not p107, deficiency was required for the beta cell proliferative response to exendin-4. Consistent with this finding, Rb, but not p107, was suppressed in islets from humans with diabetes, suggesting the importance of Rb regulation for the compensatory proliferation that occurs under insulin resistant conditions. Finally, while p107 alone did not have an essential role in islet homeostasis, when combined with Rb deletion, its absence potentiated apoptosis of both alpha and beta cells resulting in glucose intolerance and diminished islet mass with ageing.

CONCLUSIONS/INTERPRETATION

We found a central role of Rb in the dual effects of GLP-1 in alpha and beta cells. Our findings highlight unique contributions of individual Rb family members to islet cell proliferation and survival.

Adverse drug reactions associated with the use of liraglutide in patients with type 2 diabetes--focus on pancreatitis and pancreas cancer

INTRODUCTION

The glucagon-like peptide-1 (GLP-1) receptor agonist, liraglutide , is a widely used drug for the treatment of type 2 diabetes. Liraglutide is one of several incretin-based agents that have been suggested to be associated with pancreatitis and pancreas cancer. The suspicion accelerated after publication of an autopsy study claiming increased incidences of several pathological changes in pancreata from patients with diabetes treated with incretin-based drugs.

AREAS COVERED

The aim of the present review is to give an overview of the pharmacology of liraglutide and provide a review of adverse reactions associated with liraglutide with a focus on the risk of pancreatitis and pancreas cancer.

EXPERT OPINION

When comprehensively reviewing the available literature, no clear and significant associations between liraglutide and pancreatitis and/or pancreas cancer seem evident. However, a recently published analysis suggests a trend toward a slightly elevated risk of pancreatitis with GLP-1 receptor agonists (including liraglutide), which may become statistical significant as more data become available. Well-established side effects are of gastrointestinal origin, typical mild-to-moderate and of transient character. The risk of hypoglycemia associated with liraglutide treatment is low.

Extended exenatide administration enhances lipid metabolism and exacerbates pancreatic injury in mice on a high fat, high carbohydrate diet

This study expanded upon a previous study in mice reporting a link between exenatide treatment and exocrine pancreatic injury by demonstrating temporal and dose responses and providing an initial mechanistic hypothesis. The design of the present study included varying lengths of exenatide exposure (3, 6 weeks to 12 weeks) at multiple concentrations (3, 10, or 30 µg/kg) with multiple endpoints (histopathology evaluations, immunoassay for cytokines, immunostaining of the pancreas, serum chemistries and measurement of trypsin, amylase, and, lipase, and gene expression profiles). Time- and dose-dependent exocrine pancreatic injury was observed in mice on a high fat diet treated with exenatide. The morphological changes identified in the pancreas involved acinar cell injury and death (autophagy, apoptosis, necrosis, and atrophy), cell adaptations (hypertrophy and hyperplasia), and cell survival (proliferation/regeneration) accompanied by varying degrees of inflammatory response leading to secondary injury in pancreatic blood vessels, ducts, and adipose tissues. Gene expression profiles indicated increased signaling for cell survival and altered lipid metabolism in exenatide treated mice. Immunohistochemistry supported gene expression findings that exenatide caused and/or exacerbated pancreatic injury in a high fat diet environment potentially by further increasing high fat diet exacerbated lipid metabolism and resulting oxidative stress. Further investigation is required to confirm these findings and determine their relevance to human disease.

Divergent effects of liraglutide, exendin-4, and sitagliptin on beta-cell mass and indicators of pancreatitis in a mouse model of hyperglycaemia

AIMS

Glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP4) inhibitors improve glucose tolerance by still incompletely understood mechanisms. Each class of antihyperglycemic drugs has also been proposed to increase pancreatitis risk. Here, we compare systematically the effects of two widely-used GLP-1 analogues, liraglutide and exendin-4, and the DPP4 inhibitor, sitagliptin, in the mouse.

METHODS

C57BL6 mice were maintained for 131 days on a normal diet (ND) or a diet comprising 60% fat (HFD) before measurements of fasting blood glucose and insulin, and intraperitoneal glucose tolerance. Beta- and alpha- cell volume, and Reg3b immunoreactivity, were measured by immunohistochemical analysis of pancreatic slices.

RESULTS

Whereas liraglutide (200 µg/kg) and exendin-4 (10 µg/kg) treatment reduced body weight and/or improved glucose tolerance, sitagliptin (10 mg/kg) was without effect on either parameter. Liraglutide caused a sharp reduction in beta-cell mass in both ND and HFD mice, whereas exendin-4 exerted no effect. By contrast, sitagliptin unmasked an action of high fat diet to increase beta-cell mass. Reg3B positive area was augmented by all three agents in normal chow-fed mice, whilst sitagliptin and exendin-4, but not liraglutide, affected this parameter in HFD animals. Correspondingly sitagliptin, but not the GLP-1 analogues, increased circulating amylase levels in ND and HFD mice.

CONCLUSIONS

Liraglutide improves glucose tolerance in the mouse whilst exerting relatively modest effects on pancreatitis risk. Conversely, exendin-4 and sitagliptin, at doses which exert, respectively, minor or no effects on metabolic parameters, lead to signs of pancreatitis.

The novel GLP-1-gastrin dual agonist ZP3022 improves glucose homeostasis and increases β-cell mass without affecting islet number in db/db mice

Antidiabetic treatments aiming to preserve or even to increase β-cell mass are currently gaining increased interest. Here we investigated the effect of chronic treatment with the novel glucagon-like peptide-1 (GLP-1)-gastrin dual agonist ZP3022 (HGEGTFTSDLSKQMEEEAVRLFIEWLKN-8Ado-8Ado-YGWLDF-NH2) on glycemic control, β-cell mass and proliferation, and islet number. Male db/db mice were treated with ZP3022, liraglutide, or vehicle for 2, 4, or 8 weeks, with terminal assessment of hemoglobin A1c, basal blood glucose, and plasma insulin concentrations. Pancreata were removed for immunohistochemical staining and stereological quantification of β-cell mass, islet numbers, proliferation, and apoptosis. Treatment with ZP3022 or liraglutide led to a significant improvement in glycemic control. ZP3022 treatment resulted in a sustained increase in β-cell mass after 4 and 8 weeks of treatment, whereas the effect of liraglutide was transient. The expansion in β-cell mass observed in the ZP3022-treated mice appeared to be driven by increased β-cell proliferation in existing islets rather than by formation of new islets, as mean islet mass increased but the number of islets remained constant. Our data demonstrate that the GLP-1-gastrin dual agonist ZP3022 causes a sustained improvement in glycemic control accompanied by an increase in β-cell mass, increased proliferation, and increased mean islet mass. The results highlight that the GLP-1-gastrin dual agonist increases β-cell mass more than liraglutide and that dual agonists could potentially be developed into a new class of antidiabetic treatments.

Hope and fear for new classes of type 2 diabetes drugs: is there preclinical evidence that incretin-based therapies alter pancreatic morphology?

Incretin-based therapies appear to offer many advantages over other approaches for treating type 2 diabetes. Some preclinical studies have suggested that chronic activation of glucagon-like peptide 1 receptor (GLP1R) signalling in the pancreas may result in the proliferation of islet β-cells and an increase in β-cell mass. This provided hope that enhancing GLP1 action could potentially alter the natural progression of type 2 diabetes. However, to date, there has been no evidence from clinical trials suggesting that GLP1R agonists or dipeptidyl peptidase-4 (DPP4) inhibitors can increase β-cell mass. Nevertheless, while the proliferative capacity of these agents remains controversial, some studies have raised concerns that they could potentially contribute to the development of pancreatitis and hence increase the risk of pancreatic cancer. Currently, there are very limited clinical data to directly assess these potential benefits and risks of incretin-based therapies. However, a review of the preclinical studies indicates that incretin-based therapies probably have only a limited capacity to regenerate pancreatic β-cells, but may be useful for preserving any remaining β-cells in type 2 diabetes. In addition, the majority of preclinical evidence does not support the notion that GLP1R agonists or DPP4 inhibitors cause pancreatitis.

Long-term ketogenic diet causes glucose intolerance and reduced β- and α-cell mass but no weight loss in mice

High-fat, low-carbohydrate ketogenic diets (KD) are used for weight loss and for treatment of refractory epilepsy. Recently, short-time studies in rodents have shown that, besides their beneficial effect on body weight, KD lead to glucose intolerance and insulin resistance. However, the long-term effects on pancreatic endocrine cells are unknown. In this study we investigate the effects of long-term KD on glucose tolerance and β- and α-cell mass in mice. Despite an initial weight loss, KD did not result in weight loss after 22 wk. Plasma markers associated with dyslipidemia and inflammation (cholesterol, triglycerides, leptin, monocyte chemotactic protein-1, IL-1β, and IL-6) were increased, and KD-fed mice showed signs of hepatic steatosis after 22 wk of diet. Long-term KD resulted in glucose intolerance that was associated with insufficient insulin secretion from β-cells. After 22 wk, insulin-stimulated glucose uptake was reduced. A reduction in β-cell mass was observed in KD-fed mice together with an increased number of smaller islets. Also α-cell mass was markedly decreased, resulting in a lower α- to β-cell ratio. Our data show that long-term KD causes dyslipidemia, a proinflammatory state, signs of hepatic steatosis, glucose intolerance, and a reduction in β- and α-cell mass, but no weight loss. This indicates that long-term high-fat, low-carbohydrate KD lead to features that are also associated with the metabolic syndrome and an increased risk for type 2 diabetes in humans.

High-fat diet action on adiposity, inflammation, and insulin sensitivity depends on the control low-fat diet

Animal studies using a high-fat diet (HFD) have studied the effects of lipid overconsumption by comparing a defined HFD either with a natural-ingredient chow diet or with a defined low-fat diet (LFD), despite the dramatic differences between these control diets. We hypothesized that these differences in the control diet could modify the conclusions regarding the effects that an increase of fat in the diet has on several metabolic parameters. For 11 weeks, C57bl6/J mice were fed a low-fat chow diet (8% energy from fat), a typical semisynthetic LFD (12%), or a semisynthetic HFD (sy-HF) (40%). Conclusions about the effect of sy-HF on body weight gain, subcutaneous adipose tissue, insulin sensitivity, and adipose tissue inflammation were modified according to the control LFD. Conversely, conclusions about epididymal and retroperitoneal adipose tissue; fat intake effects on liver and muscular lipids, cholesterol, free fatty acids, and markers of low-grade inflammation; and of adipose tissue macrophage infiltration were the same regardless of the use of low-fat chow diet or semisynthetic LFD. For some physiological outcomes, conflicting conclusions were even reached about the effects of increased fat intake according to the chosen low-fat control. Some deleterious effects of sy-HF may not be explained by lipid overconsumption but rather by the overall quality of ingredients in a semisynthetic diet. According to the control LFD chosen, conclusions on the lipid-related effects of HFDs must be formulated with great care because some end points are profoundly affected by the ingredient composition of the diet rather than by fat content.