Exendin-4, a new peptide from Heloderma suspectum venom, potentiates cholecystokinin-induced amylase release from rat pancreatic acini

Hepatic function of glucagon-like peptide-1 and its based diabetes drugs

Incretins are gut-produced peptide-hormones that potentiate insulin secretion, especially after food intake. The concept of incretin was formed more than 100 years ago, even before insulin was isolated and utilized in the treatment of subjects with type 1 diabetes. The first incretin, glucose-dependent insulinotropic polypeptide (GIP), was identified during later 1960's and early 1970's; while the second one, known as glucagon-like peptide-1 (GLP-1), was recognized during 1980's. Today, GLP-1-based therapeutic agents [also known as GLP-1 receptor (GLP-1R) agonists, GLP-1RAs] are among the first line drugs for type 2 diabetes. In addition to serving as incretin, extra-pancreatic functions of GLP-1RAs have been broadly recognized, including those in the liver, despite the absence of GLP-1R in hepatic tissue. The existence of insulin-independent or gut-pancreas-liver axis-independent hepatic function of GLP-1RAs explains why those therapeutic agents are effective in subjects with insulin resistance and their profound effect on lipid homeostasis. Following a brief review on the discovery of GLP-1, we reviewed literature on the exploration of hepatic function of GLP-1 and GLP-1RAs and discussed recent studies on the role of hepatic hormone fibroblast growth factor 21 (FGF21) in mediating function of GLP-1RAs in animal models. This was followed by presenting our perspective views.

Intramuscular injection of palmitic acid-conjugated Exendin-4 loaded multivesicular liposomes for long-acting and improving in-situ stability

BACKGROUND

Exendin-4 (Ex4) is a promising drug for diabetes mellitus with a half-life of 2.4 h in human bodies. Besides, the Ex4 formulations currently employed in the clinic or under development have problems pertaining to stability. In this study, palmitic acid-modified Ex4 (Pal-Ex4) was prepared and purified to extend the half-life of Ex4. In addition, Pal-Ex4-MVLs were further designed and optimized as a long-acting delivery system for intramuscular injection.

METHODS

Pal-Ex4 was encapsulated within multivesicular liposomes (MVLs) via a two-step double emulsification process. The formulated products were then assessed for their vesicle size, encapsulation efficiency, and in vitro and in vivo.

RESULTS

Pal-Ex4-MVLs with a notable encapsulation efficiency of 99.18% were successfully prepared. Pal-Ex4-MVLs, administered via a single intramuscular injection in Sprague-Dawley rats, sustained stable plasma concentrations for 168 h, presenting extended half-life (77.28 ± 12.919 h) and enhanced relative bioavailability (664.18%). MVLs protected Ex4 through providing stable retention and slow release. This approach considerably improved the in-situ stability of the drug for intramuscular administration.

CONCLUSIONS

The combination of palmitic acid modification process with MVLs provides dual protection for Ex4 and can be a promising strategy for other hydrophilic protein/polypeptide-loaded sustained-release delivery systems with high drug bioactivity.

Rational Design by Structural Biology of Industrializable, Long-Acting Antihyperglycemic GLP-1 Receptor Agonists

Glucagon-like peptide-1 (GLP-1) is easily degraded by dipeptidyl peptidase-4 (DPP-4) in the human body, limiting its therapeutic effect on type II diabetes. Therefore, improving GLP-1 receptor agonist (GLP-1RA) stability is a major obstacle for drug development. We analyzed human GLP-1, DPP-4, and GLP-1 receptor structures and designed three GLP-1RAs, which were introduced into fusion protein fragments and changed in the overall conformation. This modification effectively prevented GLP-1RAs from entering the DPP-4 active center without affecting GLP-1RAs’ ability to bind to GLP-1R, the new GLP-1RA hypoglycemic effect lasting for >24 h. Through molecular modeling, molecular dynamics calculation, and simulation, possible tertiary structure models of GLP-1RAs were obtained; molecular docking with DPP-4 and GLP-1R showed access to the fusion protein. The overall conformational change of GLP-1RAs prevented DPP-4 binding, without affecting GLP-1RAs’ affinity to GLP-1R. This study provides important drug design ideas for GLP-1RA development and a new example for application of structural biology-based protein design in drug development.

PET/MRI enables simultaneous in vivo quantification of β-cell mass and function

Non-invasive imaging of β-cells represents a desirable preclinical and clinical tool to monitor the change of β-cell mass and the loss of function during pre-diabetic stages. Although it is widely accepted that manganese (Mn) ions are actively gated by voltage-dependent calcium channels (VDCC) in response to glucose metabolism, little is known on its specificity in vivo for quantification of islet β-cell function using Mn and magnetic resonance imaging (MRI). On the other hand, glucagon-like-peptide-1 receptor (GLP-1R) represents a validated target for the estimation of β-cell mass using radiolabeled exendin-4 (Ex4) and positron emission tomography (PET). However, a multiparametric imaging workflow revealing β-cell mass and function quantitatively is still missing. Methods: We developed a simultaneous PET/MRI protocol to comprehensively quantify in vivo changes in β-cell mass and function by targeting, respectively, GLP-1R and VDCC coupled with insulin secretion. Differences in the spatial distribution of Mn and radiolabeled Ex4 were monitored overtime in native and transgenic pancreata, characterized by spontaneous pancreatic neuroendocrine tumor development. Follow-up with mass spectrometry imaging (MSI) and autoradiography allowed the ex vivo validation of the specificity of Mn and PET tracer uptake and the detection of endogenous biometals, such as calcium and zinc, throughout the endocrine and exocrine pancreas. Results: Our in vivo data based on a volumetric PET/MRI readout for native pancreata and insulinomas connects uptake of Mn measured at early imaging time points to high non-specific binding by the exocrine tissue, while specific retention was only found 24 h post injection. These results are supported by cross-validation of the spatial distribution of exogenous ⁵⁵Mn and endogenous ⁴⁴Ca and ⁶⁴Zn as well with the specific internalization of the radiolabeled peptide targeting GLP-1R. Conclusion: Simultaneous PET/MR imaging of the pancreas enabled the comprehensive in vivo quantification of β-cell function and mass using Mn and radiolabeled Ex4. Most important, our data revealed that only late time-point measurements reflect the Mn uptake in the islet β-cells, while early time points detect non-specific accumulation of Mn in the exocrine pancreas.

Glucagon-Like Peptide 1 and Atrial Natriuretic Peptide in a Female Mouse Model of Obstructive Pulmonary Disease

Glucagon-like peptide-1 (GLP-1) is protective in lung disease models but the underlying mechanisms remain elusive. Because the hormone atrial natriuretic peptide (ANP) also has beneficial effects in lung disease, we hypothesized that GLP-1 effects may be mediated by ANP expression. To study this putative link, we used a mouse model of chronic obstructive pulmonary disease (COPD) and assessed lung function by unrestrained whole-body plethysmography. In 1 study, we investigated the role of endogenous GLP-1 by genetic GLP-1 receptor (GLP-1R) knockout (KO) and pharmaceutical blockade of the GLP-1R with the antagonist exendin-9 to -39 (EX-9). In another study the effects of exogenous GLP-1 were assessed. Lastly, we investigated the bronchodilatory properties of ANP and a GLP-1R agonist on isolated bronchial sections from healthy and COPD mice.

Lung function did not differ between mice receiving phosphate-buffered saline (PBS) and EX-9 or between GLP-1R KO mice and their wild-type littermates. The COPD mice receiving GLP-1R agonist improved pulmonary function (P < .01) with less inflammation, but no less emphysema compared to PBS-treated mice. Compared with the PBS-treated mice, treatment with GLP-1 agonist increased ANP (nppa) gene expression by 10-fold (P < .01) and decreased endothelin-1 (P < .01), a peptide associated with bronchoconstriction. ANP had moderate bronchodilatory effects in isolated bronchial sections and GLP-1R agonist also showed bronchodilatory properties but less than ANP. Responses to both peptides were significantly increased in COPD mice (P < .05, P < .01).

Taken together, our study suggests a link between GLP-1 and ANP in COPD.

Exendin‑4 promotes osteogenic differentiation of adipose‑derived stem cells and facilitates bone repair

Inflammation-related bone defects pose a heavy burden on patients and orthopedic surgeons. Although stem-cell-based bone repair has developed rapidly, it is of great significance to characterize bio-active molecules that facilitate bone regeneration. It is reported that a glucagon-like peptide 1 receptor agonist, exendin-4, promoted bone regeneration mediated by the transplantation of adipose-derived stem cells in a metaphyseal defect mouse model of femur injury. However, the underlying mechanism is unclear. Bone imaging, immunohistochemistry real-time PCR and western blot analysis were used in the present study, and the results revealed that exendin-4 increased the transcription of the osteogenic differentiation-related genes and induced osteogenic differentiation in situ. Furthermore, the present data obtained from sorted adipose-derived stem cells revealed that exendin-4 promoted osteogenic differentiation and inhibited adipogenic differentiation in vitro. These findings indicated that exendin-4 facilitates osteogenic differentiation of transplanted adipose-derived stem cells for bone repair and illuminated clinical prospects of both adipose-derived stem cells and exendin-4 in stem-cell-based bone defect repair.

Nonglycemic Effects of GLP-1 Agonists: From a Starling to Lizards to People

With the approval of exenatide in 2005, physicians had a new class of hypoglycemic agents available for the treatment of type 2 diabetes-the glucagon-like peptide-1 receptor agonists (or GLP-1 receptor agonists). As of this writing, there are seven drugs in this class available in the United States. In addition to demonstrating either cardiovascular risk neutrality or overt benefit, as now mandated by the United States Food and Drug Administration (FDA), many of these drugs have other, unexpected actions. It is our goal to outline these actions, some beneficial, some not. We have reviewed English-language articles in this area, not for an exhaustive study, but rather a broad search to define current understanding and perhaps generate further investigation.

Insulin Release Mechanism Modulated by Toxins Isolated from Animal Venoms: From Basic Research to Drug Development Prospects

Venom from mammals, amphibians, snakes, arachnids, sea anemones and insects provides diverse sources of peptides with different potential medical applications. Several of these peptides have already been converted into drugs and some are still in the clinical phase. Diabetes type 2 is one of the diseases with the highest mortality rate worldwide, requiring specific attention. Diverse drugs are available (e.g., Sulfonylureas) for effective treatment, but with several adverse secondary effects, most of them related to the low specificity of these compounds to the target. In this context, the search for specific and high-affinity compounds for the management of this metabolic disease is growing. Toxins isolated from animal venom have high specificity and affinity for different molecular targets, of which the most important are ion channels. This review will present an overview about the electrical activity of the ion channels present in pancreatic β cells that are involved in the insulin secretion process, in addition to the diversity of peptides that can interact and modulate the electrical activity of pancreatic β cells. The importance of prospecting bioactive peptides for therapeutic use is also reinforced.

Glucagon-like peptide-1 receptor agonists and pancreatic cancer: a meta-analysis with trial sequential analysis

We aimed to assess if GLP-1 agonists are associated with pancreatic cancer. Systematic review and meta-analysis of randomized trials with GLP-1 agonists as an intervention was performed. Trial sequential analysis (TSA) was performed to assess if the available information is sufficient to reject this association. Twelve trials met the study criteria, with a total of 36, 397 patients. GLP-1 analogues did not increase the risk for pancreatic cancer when compared to other treatments (OR 1.06; 95% CI 0.67 to 1.67; I² 14%). TSA confirmed that enough patients were randomized and again no association of the medications and pancreatic cancer was observed considering a NNH of 1000 and the short mean follow-up of the included trials (1.7 years). Larger studies with longer duration would be required to exclude a greater NNH and to aside concerns regarding possible influence of study duration and the outcome.

Incretin-based therapy for diabetic ulcers: from bench to bedside

INTRODUCTION

Diabetic foot ulcers are a serious complication of diabetes and are associated with pain, disability, and poor quality of life. Incretin-based therapy is available for type-2 diabetes. Aside from glucose control, such treatment can impart numerous beneficial effects.

AREAS COVERED

This review summarizes the preclinical and clinical evidence supporting incretin-based treatment approaches for diabetic ulcers.

EXPERT OPINION

Incretin-based therapy may have a role in the treatment of diabetic foot ulcers; the benefits of such treatment arise from attenuation of inflammatory response, improvement of keratinocyte migration, induction of angiogenesis, and the enhancement of tissue remodeling. Large-scale clinical trials are required to determine the advantages of GLP-1 receptor agonists and DPP4 inhibitors. Future research on the topical application of incretin-based therapy is necessary. Such therapeutic approaches may provide new hope in improving the treatment of impaired diabetic foot ulcers.

Toxins in Drug Discovery and Pharmacology

Venoms from marine and terrestrial animals (cone snails, scorpions, spiders, snakes, centipedes, cnidarian, etc.) can be seen as an untapped cocktail of biologically active compounds, being increasingly recognized as a new emerging source of peptide-based therapeutics.

Insulin resistance in Alzheimer's disease

The links between systemic insulin resistance (IR), brain-specific IR, and Alzheimer's disease (AD) have been an extremely productive area of current research. This review will cover the fundamentals and pathways leading to IR, its connection to AD via cellular mechanisms, the most prominent methods and models used to examine it, an introduction to the role of extracellular vesicles (EVs) as a source of biomarkers for IR and AD, and an overview of modern clinical studies on the subject. To provide additional context, we also present a novel analysis of the spatial correlation of gene expression in the brain with the aid of Allen Human Brain Atlas data. Ultimately, examining the relation between IR and AD can be seen as a means of advancing the understanding of both disease states, with IR being a promising target for therapeutic strategies in AD treatment. In conclusion, we highlight the therapeutic potential of targeting brain IR in AD and the main strategies to pursue this goal.

Non-insulin anti-diabetic drugs: An update on pharmacological interactions

Nowadays, the goal in the management of type 2 diabetes mellitus (T2DM) remains personalized control of glucose. Since less than 50% of patients with T2DM achieve glycemic treatment goal and most of them take medications for comorbidities associated to T2DM, drug interactions, namely pharmacokinetic and pharmacodynamic interactions, may enhance or reduce the effect of compounds involved in hyperglycemia. Hence, clinicians should be aware of the severe complications in T2DM patients in case of a concomitant use of these medications. It is within this context that this review aims to evaluate the effect of a second drug on the pharmacokinetic of these compounds which may lead, along with several pharmacodynamic interactions, to severe clinical complications, i.e., hypoglycemia. Available drugs already approved in Europe, USA and Japan have been included.

Imaging pancreatic islet cells by positron emission tomography

It was estimated that every year more than 30000 persons in the United States - approximately 80 people per day - are diagnosed with type 1 diabetes (T1D). T1D is caused by autoimmune destruction of the pancreatic islet (β cells) cells. Islet transplantation has become a promising therapy option for T1D patients, while the lack of suitable tools is difficult to directly evaluate of the viability of the grafted islet over time. Positron emission tomography (PET) as an important non-invasive methodology providing high sensitivity and good resolution, is able to accurate detection of the disturbed biochemical processes and physiological abnormality in living organism. The successful PET imaging of islets would be able to localize the specific site where transplanted islets engraft in the liver, and to quantify the level of islets remain alive and functional over time. This information would be vital to establishing and evaluating the efficiency of pancreatic islet transplantation. Many novel imaging agents have been developed to improve the sensitivity and specificity of PET islet imaging. In this article, we summarize the latest developments in carbon-11, fluorine-18, copper-64, and gallium-68 labeled radioligands for the PET imaging of pancreatic islet cells.

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.

Discovery of the Once-Weekly Glucagon-Like Peptide-1 (GLP-1) Analogue Semaglutide

Liraglutide is an acylated glucagon-like peptide-1 (GLP-1) analogue that binds to serum albumin in vivo and is approved for once-daily treatment of diabetes as well as obesity. The aim of the present studies was to design a once weekly GLP-1 analogue by increasing albumin affinity and secure full stability against metabolic degradation. The fatty acid moiety and the linking chemistry to GLP-1 were the key features to secure high albumin affinity and GLP-1 receptor (GLP-1R) potency and in obtaining a prolonged exposure and action of the GLP-1 analogue. Semaglutide was selected as the optimal once weekly candidate. Semaglutide has two amino acid substitutions compared to human GLP-1 (Aib(8), Arg(34)) and is derivatized at lysine 26. The GLP-1R affinity of semaglutide (0.38 ± 0.06 nM) was three-fold decreased compared to liraglutide, whereas the albumin affinity was increased. The plasma half-life was 46.1 h in mini-pigs following i.v. administration, and semaglutide has an MRT of 63.6 h after s.c. dosing to mini-pigs. Semaglutide is currently in phase 3 clinical testing.

Potential side effects to GLP-1 agonists: understanding their safety and tolerability

INTRODUCTION

Glucagon-like peptide 1 receptor (GLP-1Rx) agonists might elicit unwelcome side effects and concerns have recently been raised about their safety.

AREAS COVERED

Available evidence about safety, tolerability and potential adverse events relative to GLP-1Rx agonists presently used. We searched the MEDLINE database using the terms: 'GLP-1 receptor agonists', 'Incretin therapy side effects', 'exenatide', ' liraglutide', 'exenatide long-acting release', 'lixisenatide'. Articles were selected on the basis of the study design and importance, in the light of authors' clinical experience and personal judgment. The main safety concern about GLP-1Rx agonists use is the possible association with increased risk of pancreatitis and/or tumors. This concern stems mainly from limited observations in animal models not confirmed in similar studies. Furthermore, clinical studies reporting association between GLP-1Rx agonist use and pancreatitis/cancer are marred by several biases and both clinical trials and post-marketing analyses failed to demonstrate a significant association.

EXPERT OPINION

As stated by both FDA and EMA, the safety concerns emerged so far about GLP-1RX agonists should not affect present prescribing habits. Thus, although a strict data monitoring must be encouraged, they should not prevent access to the benefits of an innovative treatment, such as GLP-1Rx agonists use, to a large diabetic population still confronted with unmet needs.

Mouse pancreas tissue slice culture facilitates long-term studies of exocrine and endocrine cell physiology in situ

Studies on pancreatic cell physiology rely on the investigation of exocrine and endocrine cells in vitro. Particularly, in the case of the exocrine tissue these studies have suffered from a reduced functional viability of acinar cells in culture. As a result not only investigations on dispersed acinar cells and isolated acini were limited in their potential, but also prolonged studies on pancreatic exocrine and endocrine cells in an intact pancreatic tissue environment were unfeasible. To overcome these limitations, we aimed to establish a pancreas tissue slice culture platform to allow long-term studies on exocrine and endocrine cells in the intact pancreatic environment. Mouse pancreas tissue slice morphology was assessed to determine optimal long-term culture settings for intact pancreatic tissue. Utilizing optimized culture conditions, cell specificity and function of exocrine acinar cells and endocrine beta cells were characterized over a culture period of 7 days. We found pancreas tissue slices cultured under optimized conditions to have intact tissue specific morphology for the entire culture period. Amylase positive intact acini were present at all time points of culture and acinar cells displayed a typical strong cell polarity. Amylase release from pancreas tissue slices decreased during culture, but maintained the characteristic bell-shaped dose-response curve to increasing caerulein concentrations and a ca. 4-fold maximal over basal release. Additionally, endocrine beta cell viability and function was well preserved until the end of the observation period. Our results show that the tissue slice culture platform provides unprecedented maintenance of pancreatic tissue specific morphology and function over a culture period for at least 4 days and in part even up to 1 week. This analytical advancement now allows mid -to long-term studies on the cell biology of pancreatic disorder pathogenesis and therapy in an intact surrounding in situ.

Development and evaluation of 18F-TTCO-Cys40-Exendin-4: a PET probe for imaging transplanted islets

Because islet transplantation has become a promising treatment option for patients with type 1 diabetes, a noninvasive imaging method is greatly needed to monitor these islets over time. Here, we developed an (18)F-labeled exendin-4 in high specific activity for islet imaging by targeting the glucagonlike peptide-1 receptor (GLP-1R).

METHODS

Tetrazine ligation was used to radiolabel exendin-4 with (18)F. The receptor binding of (19/18)F-tetrazine trans-cyclooctene (TTCO)-Cys(40)-exendin-4 was evaluated in vitro with INS-1 cell and in vivo on INS-1 tumor (GLP-1R positive) and islet transplantation models.

RESULTS

(18)F-TTCO-Cys(40)-exendin-4 was obtained in high specific activity and could specifically bind to GLP-1R in vitro and in vivo. Unlike the radiometal-labeled exendin-4, (18)F-TTCO-Cys(40)-exendin-4 has much lower kidney uptake. (18)F-TTCO-Cys(40)-exendin-4 demonstrated its great potential for transplanted islet imaging: the liver uptake value derived from small-animal PET images correlated well with the transplanted β-cell mass determined by immunostaining. Autoradiography showed that the localizations of radioactive signal indeed corresponded to the distribution of islet grafts in the liver of islet-transplanted mice.

CONCLUSION

(18)F-TTCO-Cys(40)-exendin-4 demonstrated specific binding to GLP-1R. This PET probe provides a method to noninvasively image intraportally transplanted islets.

The effects of 13 wk of liraglutide treatment on endocrine and exocrine pancreas in male and female ZDF rats: a quantitative and qualitative analysis revealing no evidence of drug-induced pancreatitis

A possible association between glucagon-like peptide-1 (GLP-1) analogs and incidences of pancreatitis has been suggested based on clinical studies. In male and female diabetic Zucker diabetic fatty (ZDF) rats, we investigated the effects of continuous administration of liraglutide and exenatide on biochemical [lipase, pancreatic amylase (P-amylase)] and histopathological markers of pancreatitis. Male and female ZDF rats were dosed for 13 wk with liraglutide (0.4 or 1.0 mg·kg(-1)·day(-1) sc once daily) or exenatide (0.25 mg·kg(-1)·day(-1) sc, Alzet osmotic minipumps). P-amylase and lipase plasma activity were measured, and an extended histopathological and stereological (specific cell mass and proliferation rate) evaluation of the exocrine and the endocrine pancreas was performed. Expectedly, liraglutide and exenatide lowered blood glucose and Hb A(1c) in male and female ZDF rats, whereas β-cell mass and proliferation rate were increased with greatly improved blood glucose control. Whereas neither analog affected lipase activity, small increases in P-amylase activity were observed in animals treated with liraglutide and exenatide. However, concurrent or permanent increases in lipase and P-amylase activity were never observed. Triglycerides were lowered by both GLP-1 analogs. The qualitative histopathological findings did not reveal adverse effects of liraglutide. The findings were mainly minimal in severity and focal in distribution. Similarly, the quantitative stereological analyses revealed no effects of liraglutide or exenatide on overall pancreas weight or exocrine and duct cell mass or proliferation. The present study demonstrates that, in overtly diabetic male and female ZDF rats, prolonged exposure to GLP-1 receptor agonists does not affect biochemical or histopathological markers of pancreatitis, and whereas both exenatide and liraglutide increase β-cell mass, they have no effect on the exocrine pancreas. However, clinical outcome studies and studies using primate tissues and/or studies in nonhuman primates are needed to further assess human risk.

The human GLP-1 analog liraglutide and the pancreas: evidence for the absence of structural pancreatic changes in three species

Glucagon-like peptide (GLP)-1 analogs have been implicated as a risk factor for pancreatitis in humans. We investigated whether liraglutide, the once-daily human GLP-1 analog, induces pancreatitis in rats, mice, and monkeys. Pancreata from mice, rats, and nonhuman primates were examined macro- and microscopically. Evaluation of preneoplastic proliferative lesions in the pancreata from nonhuman primates was performed. After 2 years of treatment, 3 of 79 male mice in the control group and 2, 1, 1, and 1 mice in the different liraglutide groups (of 67-79 mice per group) had pancreatitis based on microscopic criteria. For females, the numbers were 0 of 79 mice in the control group and 3 mice in all the liraglutide groups (of 66-76 mice per group). Pancreatitis was not the cause of death in any animals. There were no cases of pancreatitis, macroscopically or microscopically, in 400 rats. Neither pancreatitis nor preneoplastic proliferative lesions was found in monkeys dosed for 87 weeks, with plasma liraglutide exposure 60-fold higher than that observed in humans at the maximal clinical dose. In conclusion, liraglutide did not induce pancreatitis in mice, rats, or monkeys when dosed for up to 2 years and at exposure levels up to 60 times higher than in humans.

In vivo imaging of transplanted islets with 64Cu-DO3A-VS-Cys40-Exendin-4 by targeting GLP-1 receptor

Glucagon-like peptide 1 receptor (GLP-1R) is highly expressed in pancreatic islets, especially on β-cells. Therefore, a properly labeled ligand that binds to GLP-1R could be used for in vivo pancreatic islet imaging. Because native GLP-1 is degraded rapidly by dipeptidyl peptidase-IV (DPP-IV), a more stable agonist of GLP-1 such as Exendin-4 is a preferred imaging agent. In this study, DO3A-VS-Cys(40)-Exendin-4 was prepared through the conjugation of DO3A-VS with Cys(40)-Exendin-4. The in vitro binding affinity of DO3A-VS-Cys(40)-Exendin-4 was evaluated in INS-1 cells, which overexpress GLP-1R. After (64)Cu labeling, biodistribution studies and microPET imaging of (64)Cu-DO3A-VS-Cys(40)-Exendin-4 were performed on both subcutaneous INS-1 tumors and islet transplantation models. The subcutaneous INS-1 tumor was clearly visualized with microPET imaging after the injection of (64)Cu-DO3A-VS-Cys(40)-Exendin-4. GLP-1R positive organs, such as pancreas and lung, showed high uptake. Tumor uptake was saturable, reduced dramatically by a 20-fold excess of unlabeled Exendin-4. In the intraportal islet transplantation models, (64)Cu-DO3A-VS-Cys(40)-Exendin-4 demonstrated almost two times higher uptake compared with normal mice. (64)Cu-DO3A-VS-Cys(40)-Exendin-4 demonstrated persistent and specific uptake in the mouse pancreas, the subcutaneous insulinoma mouse model, and the intraportal human islet transplantation mouse model. This novel PET probe may be suitable for in vivo pancreatic islets imaging in the human.

Biochemical and histological effects of exendin-4 (exenatide) on the rat pancreas

AIMS/HYPOTHESIS

Exendin-4 is a 39 amino acid agonist of the glucagon-like peptide receptor and has been approved for treatment of type 2 diabetes. Many reports describe an increased incidence of acute pancreatitis in humans treated with exendin-4 (exenatide). Previous studies have evaluated the effect of exendin-4 on beta cells and beta cell function. We evaluated the histological and biochemical effects of exendin-4 on the pancreas in rats.

METHODS

We studied 20 Sprague-Dawley male rats, ten of which were treated with exendin-4 and ten of which were used as controls. The study period was 75 days. Serum and pancreatic tissue were removed for biochemical and histological study. Blood glucose, amylase, lipase, insulin and adipocytokines were compared between the two groups.

RESULTS

Animals treated with exendin-4 had more pancreatic acinar inflammation, more pyknotic nuclei and weighed significantly less than control rats. They also had higher serum lipase than control animals. Exendin-4 treatment was associated with lower insulin and leptin levels as well as lower HOMA values than in the untreated control group.

CONCLUSIONS/INTERPRETATION

Although the use of exendin-4 in rats is associated with decreased weight gain, lower insulin resistance and lower leptin levels than in control animals, extended use of exendin-4 in rats leads to pancreatic acinar inflammation and pyknosis. This raises important concerns about the likelihood of inducing acute pancreatitis in humans receiving incretin mimetic therapy.

Glucagon-like peptide-1 receptor activation modulates pancreatitis-associated gene expression but does not modify the susceptibility to experimental pancreatitis in mice

OBJECTIVE

Clinical reports link use of the glucagon-like peptide-1 receptor (GLP-1R) agonists exenatide and liraglutide to pancreatitis. However, whether these agents act on the exocrine pancreas is poorly understood.

RESEARCH DESIGN AND METHODS

We assessed whether the antidiabetic agents exendin (Ex)-4, liraglutide, the dipeptidyl peptidase-4 inhibitor sitagliptin, or the biguanide metformin were associated with changes in expression of genes associated with the development of experimental pancreatitis. The effects of Ex-4 when administered before or after the initiation of caerulein-induced experimental pancreatitis were determined. The importance of endogenous GLP-1R signaling for gene expression in the exocrine pancreas and the severity of pancreatitis was assessed in Glp1r(-/-) mice.

RESULTS

Acute administration of Ex-4 increased expression of egr-1 and c-fos in the exocrine pancreas. Administration of Ex-4 or liraglutide for 1 week increased pancreas weight and induced expression of mRNA transcripts encoding the anti-inflammatory proteins pancreatitis-associated protein (PAP) (RegIIIbeta) and RegIIIalpha. Chronic Ex-4 treatment of high-fat-fed mice increased expression of PAP and reduced pancreatic expression of mRNA transcripts encoding for the proinflammatory monocyte chemotactic protein-1, tumor necrosis factor-alpha, and signal transducer and activator of transcription-3. Sitagliptin and metformin did not significantly change pancreatic gene expression profiles. Ex-4 administered before or after caerulein did not modify the severity of experimental pancreatitis, and levels of pancreatic edema and serum amylase were comparable in caerulein-treated Glp1r(-/-) versus Glp1r(+/+) mice.

CONCLUSIONS

These findings demonstrate that GLP-1 receptor activation increases pancreatic mass and selectively modulates the expression of genes associated with pancreatitis. However, activation or genetic elimination of GLP-1R signaling does not modify the severity of experimental pancreatitis in mice.

Mechanisms of action of glucagon-like peptide 1 in the pancreas

Glucagon-like peptide 1 (GLP-1) is a hormone that is encoded in the proglucagon gene. It is mainly produced in enteroendocrine L cells of the gut and is secreted into the blood stream when food containing fat, protein hydrolysate, and/or glucose enters the duodenum. Its particular effects on insulin and glucagon secretion have generated a flurry of research activity over the past 20 years culminating in a naturally occurring GLP-1 receptor (GLP-1R) agonist, exendin 4 (Ex-4), now being used to treat type 2 diabetes mellitus (T2DM). GLP-1 engages a specific guanine nucleotide-binding protein (G-protein) coupled receptor (GPCR) that is present in tissues other than the pancreas (brain, kidney, lung, heart, and major blood vessels). The most widely studied cell activated by GLP-1 is the insulin-secreting beta cell where its defining action is augmentation of glucose-induced insulin secretion. Upon GLP-1R activation, adenylyl cyclase (AC) is activated and cAMP is generated, leading, in turn, to cAMP-dependent activation of second messenger pathways, such as the protein kinase A (PKA) and Epac pathways. As well as short-term effects of enhancing glucose-induced insulin secretion, continuous GLP-1R activation also increases insulin synthesis, beta cell proliferation, and neogenesis. Although these latter effects cannot be currently monitored in humans, there are substantial improvements in glucose tolerance and increases in both first phase and plateau phase insulin secretory responses in T2DM patients treated with Ex-4. This review will focus on the effects resulting from GLP-1R activation in the pancreas.

Drug discovery from natural sources

Organic compounds from terrestrial and marine organisms have extensive past and present use in the treatment of many diseases and serve as compounds of interest both in their natural form and as templates for synthetic modification. Over 20 new drugs launched on the market between 2000 and 2005, originating from terrestrial plants, terrestrial microorganisms, marine organisms, and terrestrial vertebrates and invertebrates, are described. These approved substances, representative of very wide chemical diversity, together with several other natural products or their analogs undergoing clinical trials, continue to demonstrate the importance of compounds from natural sources in modern drug discovery efforts.

Glucagon is required for early insulin-positive differentiation in the developing mouse pancreas

The embryonic pancreas is thought to develop from pluripotent endodermal cells that give rise to endocrine and exocrine cells. A key guidance mechanism for pancreatic development has previously been found to be epithelial-mesenchymal interaction. Interactions within the epithelium, however, have not been well studied. Glucagon is the earliest peptide hormone present at appreciable levels in the developing pancreatic epithelium (embryonic day [E]-9.5 in mouse). Insulin accumulation begins slightly later (E11 in mouse), followed by a rapid accumulation during the "second wave" of insulin differentiation ( approximately E15). Here we found that blocking early expression and function of glucagon, but not GLP-1, an alternate gene product of preproglucagon mRNA, prevented insulin-positive differentiation in early embryonic (E11) pancreas. These results suggest a novel concept and a key role for glucagon in the paracrine induction of differentiation of other pancreatic components in the early embryonic pancreas.

Glucagon-like peptide-1 does not mediate amylase release from AR42J cells

In this study, AR42J pancreatic acinar cells were used to investigate if glucagon-like peptide-1 (GLP-1) or glucagon might influence amylase release and acinar cell function. We first confirmed the presence of GLP-1 receptors on AR42J cells by reverse trasncriptase-polymerase chain reaction (RT-PCR), Western blotting, and partial sequencing analysis. While cholecystokinin (CCK) increased amylase release from AR42J cells, GLP-1, alone or in the presence of CCK, had no effect on amylase release but both CCK and GLP-1 increased intracellular calcium. Similar to GLP-1, glucagon increased both cyclic adenosine monophosphate (cAMP) and intracellular calcium in AR42J cells but it actually decreased CCK-mediated amylase release (n = 20, P < 0.01). CCK stimulation resulted in an increase in tyrosine phosphorylation of several cellular proteins, unlike GLP-1 treatment, where no such increased phosphorylation was seen. Instead, GLP-1 decreased such protein phosphorylations. Genestein blocked CCK-induced phosphorylation events and amylase secretion while vanadate increased amylase secretion. These results provide evidence that tyrosine phosphorylation is necessary for amylase release and that signaling through GLP-1 receptors does not mediate amylase release in AR42J cells. J. Cell. Physiol. 181:470-478, 1999. Published 1999 Wiley-Liss, Inc.

Glucagon-like peptide-1 is a physiological incretin in rat

Glucagon-like peptide-1 7-36 amide (GLP-1) has been postulated to be the primary hormonal mediator of the entero-insular axis but evidence has been indirect. The discovery of exendin (9-39), a GLP-1 receptor antagonist, allowed this to be further investigated. The IC50 for GLP-1 receptor binding, using RIN 5AH beta-cell membranes, was found to be 0.36 nmol/l for GLP-1 and 3.44 nmol/l for exendin (9-39). There was no competition by exendin (9-39) at binding sites for glucagon or related peptides. In the anaesthetized fasted rat, insulin release after four doses of GLP-1 (0.1, 0.2, 0.3, and 0.4 nmol/kg) was tested by a 2-min intravenous infusion. Exendin (9-39) (1.5, 3.0, and 4.5 nmol/kg) was administered with GLP-1 0.3 nmol/kg, or saline, and only the highest dose fully inhibited insulin release. Exendin (9-39) at 4.5 nmol/kg had no effect on glucose, arginine, vasoactive intestinal peptide or glucose-dependent insulinotropic peptide stimulated insulin secretion. Postprandial insulin release was studied in conditioned conscious rats after a standard meal. Exendin (9-39) (0.5 nmol/kg) considerably reduced postprandial insulin concentrations, for example by 48% at 15 min (431 +/- 21 pmol/l saline, 224 +/- 32 pmol/l exendin, P < 0.001). Thus, GLP-1 appears to play a major role in the entero-insular axis.

Exendin-4 and exendin-(9-39)NH2: agonist and antagonist, respectively, at the rat parietal cell receptor for glucagon-like peptide-1-(7-36)NH2

Exendin-4 is a novel peptide from Heloderma suspectum venom which is 53% homologous with glucagon-like peptide-1 GLP-1-(7-36)NH2, a stimulant of cAMP-dependent H+ production in rat parietal cells. It was the aim of the present study to determine whether this effect of GLP-1-(7-36)NH2 is shared by exendin-4, and whether the responses to either peptide are blocked by exendin-(9-39)NH2, a competitive specific exendin receptor antagonist. In enriched rat parietal cells H+ production was measured indirectly by [14C]aminopyrine accumulation. cAMP production was determined by radioimmunoassay. [125I]GLP-1-(7-36)NH2 was prepared using chloramine T followed by high pressure liquid chromatography (HPLC) purification. Exendin-4 (10(-12) - 10(-8) M) stimulated [14C]aminopyrine accumulation in a concentration-dependent manner (EC50 = 7.6 x 10(-11) M). At the maximally effective concentration (10(-9) M) exendin-4 was as effective as GLP-1-(7-36)NH2 reaching 70-80% of the response to 10(-4) M histamine. Likewise, exendin-4 (10(-11) - 10(-7) M) stimulated parietal cell cAMP production up to 2.8-fold. Maximal stimulation by exendin-4 of [14C]aminopyrine accumulation was not affected by ranitidine (10(-4) M), but was concentration-dependently reduced by exendin-(9-39)NH2 (10(-11) - 10(-7) M). At the maximal concentration, exendin-(9-39)NH2 completely abolished the responses to 10(-9) M exendin-4 and to 10(-9) M GLP-1-(7-36)NH2 while not altering stimulation by 10(-4) M histamine. Binding of [125I]GLP-1-(7-36)NH2 to enriched parietal cells was displaced by exendin-4 (Ki = 4.6 x 10(-10) M) as well as by exendin-(9-39)NH2 (Ki = 4.0 x 10(-9) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulus-secretion coupling and Ca2+ dynamics in pancreatic acinar cells

1. Unique spatiotemporal dynamics in cytosolic Ca2+ concentration, [Ca2+]c, were characterized in various cell types. In pancreatic acinar cells, physiological concentrations of cholecystokinin octapeptide, CCK-8, (< 10 pM) induce repetitive [Ca2+]c spikes commonly termed Ca2+ oscillation, whereas relatively higher concentrations (30 pM-1 nM) evoke biphasic [Ca2+]c dynamics; a rapid transient peak followed by a sustained increase. Much higher concentrations (> 1 nM) induce a large transient followed by a steep decay. 2. These [Ca2+]c dynamics correspond to secretory responses. Repetitive [Ca2+]c change is attributable to the upstroke of the bell-shaped dose-response relationship and the biphasic change is responsible for the downstroke of the relation (so called high-dose inhibited secretion). The large transient [Ca2+]c increase is associated with morphological changes such as bleb formation. 3. Possible interrelation between dose of secretagogues, secretory responses, [Ca2+]c dynamics, IP3 production, receptor occupation and morphological change will be discussed from both pharmacological and physiological points of view.

Use of 125I-[Y39]exendin-4 to characterize exendin receptors on dispersed pancreatic acini and gastric chief cells from guinea pig

We synthesized and iodinated an exendin-4 analogue, [Y39]exendin-4 (700 Ci/mmol), for use as a radioligand to characterize exendin receptors on dispersed pancreatic acini and gastric chief cells from guinea pig. Binding of this bioactive radioligand was rapid, temperature-dependent and specific (not inhibited by other pancreatic or gastric secretagogues). Measurement of the ability of exendin-4 to inhibit the binding of 125I-[Y39]exendin-4 indicated the presence of two classes of receptors. Pancreatic acini had 12.5.10(10) binding sites/mg acinar protein of which 6% were high affinity (Kd = 0.5 nM) and 94% were low affinity (Kd = 0.1 microM). Chief cells had 3370 binding sites/cell of which 9% were high affinity (Kd = 0.3 nM) and 91% were low affinity (Kd = 0.2 microM). Washing with 0.2 M acetic acid (pH 2.5), 0.2 M glycine (pH 10.5), or trypsin (100 micrograms/ml) after 30 min incubation at 37 degrees C, indicated that 63 and 49% of radioligand was internalized in acini and chief cells, respectively. Truncated glucagon-like peptide-1 (tGLP-1), a mammalian peptide sharing 53% homology with exendin-4, inhibited radioligand binding at the same concentrations that altered secretion from acini and chief cells. Glucagon, GLP-1 and GLP-2 inhibited 125I-[Y39]exendin-4 binding only at concentrations > or = 100 nM. Exendin(9-39)NH2, a specific exendin-receptor antagonist, potently inhibited 125I-[Y39] exendin-4 binding (IC50 = 6.1 and 3.5 nM in acini and chief cells, respectively). In pancreatic acini and gastric chief cells from guinea pig, exendin-3, exendin-4 and tGLP-1 increase cellular cAMP and modulate enzyme secretion by interacting with high-affinity exendin receptors. 125I-[Y39] exendin-4 is a useful radioligand for studying exendin receptors.

Stable expression of the rat GLP-I receptor in CHO cells: activation and binding characteristics utilizing GLP-I(7-36)-amide, oxyntomodulin, exendin-4, and exendin(9-39)

Glucagon-like peptide-I (GLP-I) is a potent insulinotropic peptide that mediates its actions at pancreatic B-cells via specific receptors. In the present study we stably expressed the rat B-cell GLP-I receptor in CHO cells and studied binding characteristics and receptor activation utilizing the naturally occurring receptor agonist GLP-I(7-36)-amide (GLP-I), the proglucagon-derived GLP-I-related peptide oxyntomodulin, the GLP-I receptor agonist exendin-4, and the specific antagonist exendin(9-39). The potencies to displace [125I]GLP-I from the receptor were GLP-I > exendin-4 > exendin(9-39) > oxyntomodulin, and to displace [125I]exendin-4 GLP-I = exendin-4 > exendin(9-39) > oxyntomodulin. cAMP production was stimulated equally by GLP-I and exendin-4. Oxyntomodulin was less potent to stimulate cAMP generation. Exendin(9-39) blocked the stimulatory action of GLP-I and exendin-4 on cAMP production, but not that of oxyntomodulin. This study shows that GLP-I and exendin-4 are potent agonists at the transfected rat B-cell GLP-I receptor whereas oxyntomodulin is only a weak GLP-I receptor agonist. Furthermore, exendin(9-39) is a potent GLP-I receptor antagonist. This peptide is a valuable tool to further study the physiological actions of GLP-I.