GLP-1 receptor signaling protects pancreatic beta cells in intraportal islet transplant by inhibiting apoptosis

Noninvasive quantitative evaluation of viable islet grafts using 111 In-exendin-4 SPECT/CT

Islet transplantation (IT) is an effective β-cell replacement therapy for patients with type 1 diabetes; however, the lack of methods to detect islet grafts and evaluate their β-cell mass (BCM) has limited the further optimization of IT protocols. Therefore, the development of noninvasive β-cell imaging is required. In this study, we investigated the utility of the ¹¹¹ Indium-labeled exendin-4 probe {[Lys12(111In-BnDTPA-Ahx)] exendin-4} (¹¹¹ In exendin-4) to evaluate islet graft BCM after intraportal IT. The probe was cultured with various numbers of isolated islets. Streptozotocin-induced diabetic mice were intraportally transplanted with 150 or 400 syngeneic islets. After a 6-week observation following IT, the ex-vivo liver graft uptake of ¹¹¹ In-exendin-4 was compared with the liver insulin content. In addition, the in-vivo liver graft uptake of ¹¹¹ In exendin-4 using SPECT/CT was compared with that of liver graft BCM measured by a histological method. As a result, probe accumulation was significantly correlated with islet numbers. The ex-vivo liver graft uptake in the 400-islet-transplanted group was significantly higher than that in the control and the 150-islet-transplanted groups, consistent with glycemic control and liver insulin content. In conclusion, in-vivo SPECT/CT displayed liver islet grafts, and uptakes were corroborated by histological liver BCM. ¹¹¹ In-exendin-4 SPECT/CT can be used to visualize and evaluate liver islet grafts noninvasively after intraportal IT.

Differentiation of Human-Induced Pluripotent Stem Cell-Derived Endocrine Progenitors to Islet-like Cells Using a Dialysis Suspension Culture System

The production of functional islet-like cells from human-induced pluripotent stem cells (hiPSCs) is a promising strategy for the therapeutic use and disease modeling for type 1 diabetes. However, the production cost of islet-like cells is extremely high due to the use of expensive growth factors for differentiation. In a conventional culture method, growth factors and beneficial autocrine factors remaining in the culture medium are removed along with toxic metabolites during the medium change, and it limits the efficient utilization of those factors. In this study, we demonstrated that the dialysis suspension culture system is possible to reduce the usage of growth factors to one-third in the differentiation of hiPSC-derived endocrine progenitor cells to islet-like cells by reducing the medium change frequency with the refinement of the culture medium. Furthermore, the expression levels of hormone-secretion-related genes and the efficiency of differentiation were improved with the dialysis suspension culture system, possibly due to the retaining of autocrine factors. In addition, we confirmed several improvements required for the further study of the dialysis culture system. These findings showed the promising possibility of the dialysis suspension culture system for the low-cost production of islet-like cells.

Implanted islet mass influences the effects of dipeptidyl peptidase-IV inhibitor LAF237 on transplantation outcomes in diabetic mice

Background

Previous studies showed inconsistent Results of the effects of dipeptidyl peptidase (DPP)-IV inhibitors on syngeneic mouse islet transplantation. We hypothesized that the implanted islet numbers are critical for the effects of DPP-IV inhibitors on the outcomes of transplantation.

Methods

One hundred and fifty or three hundred islets were syngeneically transplanted under the renal capsule of each streptozocin-diabetic C57BL/6 mouse and recipients were then treated without or with LAF237 (10 mg/kg/day, po) for 6 weeks. After transplantation, recipients’ blood glucose, body weight and intraperitoneal glucose tolerance test (IPGTT) were followed-up periodically. The graft was removed for the measurement of β-cell mass at 6 weeks.

Results

In recipients with 150 islets, it was not significantly different between the LAF237- treated group (n = 14) and control group (n = 14) in terms of the blood glucose, body weight, glucose tolerance at 2, 4 and 6 weeks or the graft β-cell mass at 6 weeks. In contrast, in recipients with 300 islets, the LAF237-treated group (n = 24) did have a lower area under the curve of the IPGTT at 4 weeks (p = 0.0237) and 6 weeks (p = 0.0113) as well as more graft β-cell mass at 6 weeks (0.655 ± 0.008 mg vs. 0.435 ± 0.006 mg, p = 0.0463) than controls (n = 24).

Conclusions

Our findings revealed 6-week treatment of LAF237 improves glucose tolerance and increases graft β-cell mass in diabetic mice transplanted with a sufficient number but not a marginal number of islets. These indicate that the effects of DPP-IV inhibitors are influenced by the implanted islet mass.

Liraglutide in combination with human umbilical cord mesenchymal stem cell could improve liver lesions by modulating TLR4/NF-kB inflammatory pathway and oxidative stress in T2DM/NAFLD rats

Studies have shown that liraglutide, or human umbilical cord mesenchymal stem cell (hUC-MSCs) can improve non-alcoholic fatty liver disease (NAFLD). However there have been no studies on the combination of the two used to treat NAFLD. This study aimed to explore the therapeutic effects of combination of liraglutide and hUC-MSCs on liver injury in rats with type 2 diabetes mellitus (T2DM) and NAFLD, and further investigate their mechanisms. Sprague Dawley rats fed by a high fat and high sucrose diet were randomly divided into 5 groups, including NC group, T2DM/NAFLD group, liraglutide group (treated with liraglutide, 200 μg/kg, twice daily for 8 weeks), hUC-MSCs group (treated with hUC-MSCs at the first and fifth weeks), liraglutid＋hUC-MSCs group (treated with liraglutide and hUC-MSCs). Liver tissue was procured for histological examination, real-time qRT-PCR and Western blot analysis. After treatment, liraglutide and hUC-MSCs reduced serum ALT and AST levels, alleviate liver inflammation and improved liver histopathology. The expressions of inflammatory cytokines, TLR4 and NF-κB in serum and liver were significantly inhibited, particularly in the combination treatment group. Eight weeks after liraglutide or hUC-MSCs administration, FBG, HbA1c, HOMA-IR, ALT, AST, Liver wet eight and hepatic TLR4, NF-κB, IL-6, TNF-α, 8-OHdG mRNA and proteins were significantly decreased, and the levels of SOD expression were significantly increased in three treatment groups compared with T2DM/NAFLD group. This study suggests that liraglutide in combination with hUC-MSCs could significantly improve glycolipid metabolism, insulin resistance and liver injury in T2DM/NAFLD rats. Its mechanism may be related to the down-regulation of the TLR4/NF-κB inflammatory pathway and improvement in oxidative stress.

Microporous Polymer Scaffolds for the Transplantation of Embryonic Stem Cell Derived Pancreatic Progenitors to a Clinically Translatable Site for the Treatment of Type I Diabetes

Type I diabetes mellitus, which affects an estimated 1.5 million Americans, is caused by autoimmune destruction of the pancreatic beta cells that results in the need for life-long insulin therapy. Allogeneic islet transplantation for the treatment of type I diabetes is a therapy in which donor islets are infused intrahepatically, which has led to the transient reversal of diabetes. However, therapeutic limitations of allogeneic transplantation, which include a shortage of donor islets, long-term immunosuppression, and high risk of tissue rejection, have led to the investigation of embryonic or induced pluripotent stem cells as an unlimited source of functional beta-cells. Herein, we investigate the use of microporous scaffolds for their ability to promote the engraftment of stem cell derived pancreatic progenitors and their maturation toward mono-hormonal insulin producing β-cells at a clinically translatable, extrahepatic site. Initial studies demonstrated that microporous scaffolds supported cell engraftment, and their maturation to become insulin positive; however, the number of insulin positive cells and the levels of C-peptide secretion were substantially lower than what was observed with progenitor cell transplantation into the kidney capsule. The scaffolds were subsequently modified to provide a sustained release of exendin-4, which has previously been employed to promote maturation of pancreatic progenitors in vitro and has been employed to promote engraftment of transplanted islets in the peritoneal fat. Transplantation of stem cell derived pancreatic progenitors on scaffolds releasing exendin-4 led to significantly increased C-peptide production compared to scaffolds without exendin-4, with C-peptide and blood glucose levels comparable to the kidney capsule transplantation cohort. Image analysis of insulin and glucagon producing cells indicated that monohormonal insulin producing cells were significantly greater compared to glucagon producing and polyhormonal cells in scaffolds releasing exendin-4, whereas a significantly decreased percentage of insulin-producing cells were present among hormone producing cells in scaffolds without exendin-4. Collectively, a microporous scaffold, capable of localized and sustained delivery of exendin-4, enhanced the maturation and function of pluripotent stem cell derived pancreatic progenitors that were transplanted to a clinically translatable site.

Evaluation of 18F-labeled exendin(9-39) derivatives targeting glucagon-like peptide-1 receptor for pancreatic β-cell imaging

β-cell mass (BCM) is known to be decreased in subjects with type-2 diabetes (T2D). Quantitative analysis for BCM would be useful for understanding how T2D progresses and how BCM affects treatment efficacy and for earlier diagnosis of T2D and development of new therapeutic strategies. However, a noninvasive method to measure BCM has not yet been developed. We developed four ¹⁸F-labeled exendin(9-39) derivatives for β-cell imaging by PET: [¹⁸F]FB9-Ex(9-39), [¹⁸F]FB12-Ex(9-39), [¹⁸F]FB27-Ex(9-39), and [¹⁸F]FB40-Ex(9-39). Affinity to the glucagon-like peptide-1 receptor (GLP-1R) was evaluated with dispersed islet cells of ddY mice. Uptake of exendin(9-39) derivatives in the pancreas as well as in other organs was evaluated by a biodistribution study. Small-animal PET study was performed after injecting [¹⁸F]FB40-Ex(9-39). FB40-Ex(9-39) showed moderate affinity to the GLP-1R. Among all of the derivatives, [¹⁸F]FB40-Ex(9-39) resulted in the highest uptake of radioactivity in the pancreas 30 min after injection. Moreover, it showed significantly less radioactivity accumulated in the liver and kidney, resulting in an overall increase in the pancreas-to-organ ratio. In the PET imaging study, pancreas was visualized at 30 min after injection of [¹⁸F]FB40-Ex(9-39). [¹⁸F]FB40-Ex(9-39) met the basic requirements for an imaging probe for GLP-1R in pancreatic β-cells. Further enhancement of pancreatic uptake and specific binding to GLP-1R will lead to a clear visualization of pancreatic β-cells.

Liraglutide Compromises Pancreatic β Cell Function in a Humanized Mouse Model

Incretin mimetics are frequently used in the treatment of type 2 diabetes because they potentiate β cell response to glucose. Clinical evidence showing short-term benefits of such therapeutics (e.g., liraglutide) is abundant; however, there have been several recent reports of unexpected complications in association with incretin mimetic therapy. Importantly, clinical evidence on the potential effects of such agents on the β cell and islet function during long-term, multiyear use remains lacking. We now show that prolonged daily liraglutide treatment of >200 days in humanized mice, transplanted with human pancreatic islets in the anterior chamber of the eye, is associated with compromised release of human insulin and deranged overall glucose homeostasis. These findings raise concern about the chronic potentiation of β cell function through incretin mimetic therapy in diabetes.

Inhibition of the MAP3 kinase Tpl2 protects rodent and human β-cells from apoptosis and dysfunction induced by cytokines and enhances anti-inflammatory actions of exendin-4

Proinflammatory cytokines exert cytotoxic effects on β-cells, and are involved in the pathogenesis of type I and type II diabetes and in the drastic loss of β-cells following islet transplantation. Cytokines induce apoptosis and alter the function of differentiated β-cells. Although the MAP3 kinase tumor progression locus 2 (Tpl2) is known to integrate signals from inflammatory stimuli in macrophages, fibroblasts and adipocytes, its role in β-cells is unknown. We demonstrate that Tpl2 is expressed in INS-1E β-cells, mouse and human islets, is activated and upregulated by cytokines and mediates ERK1/2, JNK and p38 activation. Tpl2 inhibition protects β-cells, mouse and human islets from cytokine-induced apoptosis and preserves glucose-induced insulin secretion in mouse and human islets exposed to cytokines. Moreover, Tpl2 inhibition does not affect survival or positive effects of glucose (i.e., ERK1/2 phosphorylation and basal insulin secretion). The protection against cytokine-induced β-cell apoptosis is strengthened when Tpl2 inhibition is combined with the glucagon-like peptide-1 (GLP-1) analog exendin-4 in INS-1E cells. Furthermore, when combined with exendin-4, Tpl2 inhibition prevents cytokine-induced death and dysfunction of human islets. This study proposes that Tpl2 inhibitors, used either alone or combined with a GLP-1 analog, represent potential novel and effective therapeutic strategies to protect diabetic β-cells.

Lixisenatide accelerates restoration of normoglycemia and improves human beta-cell function and survival in diabetic immunodeficient NOD-scid IL-2rg(null) RIP-DTR mice engrafted with human islets

OBJECTIVE

Glucagon-like peptide-1 induces glucose-dependent insulin secretion and, in rodents, increases proliferation and survival of pancreatic beta cells. To investigate the effects on human beta cells, we used immunodeficient mice transplanted with human islets. The goal was to determine whether lixisenatide, a glucagon-like peptide-1 receptor agonist, improves human islet function and survival in vivo.

METHODS

Five independent transplant studies were conducted with human islets from five individual donors. Diabetic human islet-engrafted immunodeficient mice were treated with lixisenatide (50, 150, and 500 µg/kg) or vehicle. Islet function was determined by blood glucose, plasma human insulin/C-peptide, and glucose tolerance tests. Grafts were analyzed for total beta- and alpha-cell number, percent proliferation, and levels of apoptosis.

RESULTS

Diabetic mice transplanted with marginal human islet mass and treated with lixisenatide were restored to euglycemia more rapidly than vehicle-treated mice. Glucose tolerance tests, human plasma insulin, and glucose-stimulation indices of lixisenatide-treated mice were significantly improved compared to vehicle-treated mice. The percentages of proliferating or apoptotic beta cells at graft recovery were not different between lixisenatide-treated and vehicle-treated mice. Nevertheless, in one experiment we found a significant twofold to threefold increase in human beta-cell numbers in lixisenatide-treated compared to vehicle-treated mice.

CONCLUSION

Diabetic human islet-engrafted immunodeficient mice treated with lixisenatide show improved restoration of normoglycemia, human plasma insulin, and glucose tolerance compared to vehicle-treated mice engrafted with the same donor islets. Because the proliferative capacity of human beta cells is limited, improved beta-cell survival coupled with enhanced beta-cell function following lixisenatide treatment may provide the greatest benefit for diabetic patients with reduced functional islet mass.

Enhancing human islet transplantation by localized release of trophic factors from PLG scaffolds

Islet transplantation represents a potential cure for type 1 diabetes, yet the clinical approach of intrahepatic delivery is limited by the microenvironment. Microporous scaffolds enable extrahepatic transplantation, and the microenvironment can be designed to enhance islet engraftment and function. We investigated localized trophic factor delivery in a xenogeneic human islet to mouse model of islet transplantation. Double emulsion microspheres containing exendin-4 (Ex4) or insulin-like growth factor-1 (IGF-1) were incorporated into a layered scaffold design consisting of porous outer layers for islet transplantation and a center layer for sustained factor release. Protein encapsulation and release were dependent on both the polymer concentration and the identity of the protein. Proteins retained bioactivity upon release from scaffolds in vitro. A minimal human islet mass transplanted on Ex4-releasing scaffolds demonstrated significant improvement and prolongation of graft function relative to blank scaffolds carrying no protein, and the release profile significantly impacted the duration over which the graft functioned. Ex4-releasing scaffolds enabled better glycemic control in animals subjected to an intraperitoneal glucose tolerance test. Scaffolds releasing IGF-1 lowered blood glucose levels, yet the reduction was insufficient to achieve euglycemia. Ex4-delivering scaffolds provide an extrahepatic transplantation site for modulating the islet microenvironment to enhance islet function posttransplant.

GLP-1 receptor agonist attenuates endoplasmic reticulum stress-mediated β-cell damage in Akita mice

Aims/Introduction:  Endoplasmic reticulum (ER) stress is one of the contributing factors in the development of type 2 diabetes. To investigate the cytoprotective effect of glucagon‐like peptide 1 receptor (GLP‐1R) signaling in vivo, we examined the action of exendin‐4 (Ex‐4), a potent GLP‐1R agonist, on β‐cell apoptosis in Akita mice, an animal model of ER stress‐mediated diabetes.

Materials and Methods:  Ex‐4, phosphate‐buffered saline (PBS) or phlorizin were injected intraperitoneally twice a day from 3 to 5 weeks‐of‐age. We evaluated the changes in blood glucose levels, bodyweights, and pancreatic insulin‐positive area and number of islets. The effect of Ex‐4 on the numbers of C/EBP‐homologous protein (CHOP)‐, TdT‐mediated dUTP‐biotin nick‐end labeling (TUNEL)‐ or proliferating cell nuclear antigen‐positive β‐cells were also evaluated.

Results:  Ex‐4 significantly reduced blood glucose levels and increased both the insulin‐positive area and the number of islets compared with PBS‐treated mice. In contrast, there was no significant difference in the insulin‐positive area between PBS‐treated mice and phlorizin‐treated mice, in which blood glucose levels were controlled similarly to those in Ex‐4‐treated mice. Furthermore, treatment of Akita mice with Ex‐4 resulted in a significant decrease in the number of CHOP‐positive β‐cells and TUNEL‐positive β‐cells, and in CHOP mRNA levels in β‐cells, but there was no significant difference between the PBS‐treated group and the phlorizin‐treated group. Proliferating cell nuclear antigen staining showed no significant difference among the three groups in proliferation of β‐cells.

Conclusions:  These data suggest that Ex‐4 treatment can attenuate ER stress‐mediated β‐cell damage, mainly through a reduction of apoptotic cell death that is independent of lowered blood glucose levels. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00075.x, 2010)

Modulation of the pancreatic islet-stress axis as a novel potential therapeutic target in diabetes mellitus

Loss of pancreatic islet function and insulin-producing beta cell mass is a central hallmark in the pathogenesis of both type 1 and type 2 diabetes. While in type 1 diabetes this phenomenon is due to an extensive destruction of beta cells caused by an autoimmune process, the mechanisms resulting in beta cell failure in type 2 diabetes are different and less clear. Also, beta cell destruction in type 1 diabetes occurs early and is the initial step in the pathogenetic process, while beta cell loss in type 2 diabetes after an initial phase of hyperinsulinemia due to the underlying insulin resistance occurs relatively late and it is less pronounced. Since diabetes mellitus is the most frequent endocrine disease, with an increasing high prevalence worldwide, huge efforts have been made over the past many decades to identify predisposing genetic, environmental, and nutritional factors in order to develop effective strategies to prevent the disease. In parallel, extensive studies in different cell systems and animal models have helped to elucidate our understanding of the physiologic function of islets and to gain insight into the immunological and non-immunological mechanisms of beta cell destruction and failure. Furthermore, currently emerging concepts of beta cell regeneration (e.g., the restoration of the beta cell pool by regenerative, proliferative and antiapoptotic processes, and recovery of physiologic islet function) apparently is yielding the first promising results. Recent insights into the complex endocrine and paracrine mechanisms regulating the physiologic function of pancreatic islets, as well as beta cell life and death, constitute an essential part of this new and exciting area of diabetology. For example, understanding of the physiological role of glucagon-like peptide 1 has resulted in the successful clinical implementation of incretin-based therapies over the last years. Further, recent data suggesting paracrine effects of growth hormone-releasing hormone and corticotropin-releasing hormone on the regulation of pancreatic islet function, survival, and proliferation as well as on local glucocorticoid metabolism provide evidence for a potential role of the pancreatic islet-stress axis in the pathophysiology of diabetes mellitus. In this chapter, we provide a comprehensive overview of current preventive and regenerative concepts as a basis for the development of novel therapeutic approaches to the treatment of diabetes mellitus. A particular focus is given on the potential of the pancreatic islet-stress axis in the development of novel regenerative strategies.

Dipeptidyl peptidase IV inhibition activates CREB and improves islet vascularization through VEGF-A/VEGFR-2 signaling pathway

Substitution of pancreatic islets is a potential therapy to treat diabetes and it depends on reconstitution of islet’s capillary network. In this study, we addressed the question whether stabilization of Glucagon-Like-Peptide-1 (GLP-1) by inhibiting Dipeptidyl Peptidase-IV (DPP-IV) increases β-cell mass by modulating vascularization. Mouse or porcine donor islets were implanted under kidney capsule of diabetic mice treated with DPP-IV inhibitor sitagliptin. Grafts were analyzed for insulin production, β-cell proliferation and vascularization. In addition, the effect of sitagliptin on sprouting and Vascular Endothelial Growth Factor (VEGF)-A expression was examined ex vivo. The cAMP response element-binding (CREB) and VEGF-A/ Vascular Endothelial Growth Factor Receptor (VEGFR)-2 signaling pathway leading to islet vascularization was explored. Sitagliptin increased mean insulin content of islet grafts and area of insulin-positive tissue as well as β-cell proliferation. Interestingly, sitagliptin treatment also markedly increased endothelial cell proliferation, microvessel density and blood flow. Finally, GLP-1 (7-36) stimulated sprouting and VEGF expression, which was significantly enhanced by sitagliptin- mediated inhibition of DPP-IV. Our in vivo data demonstrate that sitagliptin treatment phosphorylated CREB and induced islet vascularization through VEGF-A/VEGFR-2 signaling pathway. This study paves a new pathway for improvement of islet transplantation in treating diabetes mellitus.

Use of glucagon-like peptide-1 agonists to improve islet graft performance

Human islet transplantation is an effective and promising therapy for type I diabetes. However, long-term insulin independence is both difficult to achieve and inconsistent. De novo or early administration of incretin-based drugs is being explored for improving islet engraftment. In addition to its glucose-dependent insulinotropic effects, incretins also lower postprandial glucose excursion by inhibiting glucagon secretion, delaying gastric emptying, and can protect beta-cell function. Incretin therapy has so far proven clinically safe and tolerable with little hypoglycemic risk. The present review aims to highlight the new frontiers in research involving incretins from both in vitro and in vivo animal studies in the field of islet transplant. It also provides an overview of the current clinical status of incretin usage in islet transplantation in the management of type I diabetes.

Anti-inflammatory strategies to enhance islet engraftment and survival

Early innate inflammatory reaction strongly affects islet engraftment and survival after intrahepatic transplantation. This early immune response is triggered by ischemia-reperfusion injury and instant blood mediated inflammatory reaction (IBMIR) occurring hours and days after islet infusion. Evidence in both mouse model and in human counterpart suggest the involvement of coagulation, complement system, and proinflammatory chemokines/cytokines. Identification and targeting of pathway(s), playing a role as "master regulator(s)" in post-transplant detrimental inflammatory events, is now mandatory to improve islet transplantation success. This review will focus on inflammatory pathway(s) differentially modulated by islet isolation and mainly associated with the early post-transplant events. Moreover, we will take into account anti-inflammatory strategies that have been tested at 2 levels: on the graft, ex vivo, during islet culture (i.e., donor) and/or on the graft site, in vivo, early after islet infusion (i.e., recipient).

Exendin-4 protects hypoxic islets from oxidative stress and improves islet transplantation outcome

Oxidative stress produced during pancreatic islet isolation leads to significant β-cell damage. Homeostatic cytokines secreted subsequently to islet transplantation damage β-cells by generating oxygen free radicals. In this study, exendin-4, a glucagon-like peptide-1 analog improved islet transplantation outcome by increasing the survival of diabetic recipient mice from 58% to 100%. We hypothesized that this beneficial effect was due to the ability of exendin-4 to reduce oxidative stress. Further experiments showed that it significantly reduced the apoptotic rate of cultured β-cells subjected to hypoxia or to IL-1β. Reduction of apoptotic events was confirmed in pancreatic islet grafts of exendin-4-treated mice. Exendin-4 enhanced Akt phosphorylation of β-cells and insulin released from them. It even augmented insulin secretion from islets cultivated at hypoxic conditions. Exposure to hypoxia led to a decrease in the activation of Akt, which was reversed when β-cells were pretreated with exendin-4. Moreover, exendin-4 increased the activity of redox enzymes in a hypoxia-treated β-cell line and reduced reactive oxygen species production in isolated pancreatic islets. Recovery from diabetes in mice transplanted with hypoxic islets was more efficient when they received exendin-4. In conclusion, exendin-4 rescued islets from oxidative stress caused by hypoxia or due to cytokine exposure. It improved the outcome of syngenic and xenogenic islet transplantation.

Liraglutide administration in type 2 diabetic patients who either received no previous treatment or were treated with an oral hypoglycemic agent showed greater efficacy than that in patients switching from insulin

Aims/Introduction

Liraglutide, a glucagon‐like peptide‐1 receptor agonist, is expected to provide a new treatment option for diabetes. However, the suitable timing of liraglutide administration in type 2 diabetic patients has not yet been clarified.

Materials and Methods

We reviewed type 2 diabetic patients (n = 155) who visited the Osaka Red Cross Hospital for glycemic control, with administration of liraglutide at a dose of 0.6 mg (average glycated hemoglobin [HbA_1c] level, 8.7 ± 0.1%). The effect of liraglutide based on the pretreatment status was compared. We also analyzed the background factors of both a successful and failed group of patients who switched to liraglutide from insulin.

Results

An improvement in blood glucose levels was confirmed in 122 of 155 patients. During the 4‐month observation period, the improvement in HbA_1c levels was significantly greater in the group of drug‐naïve/previous oral hypoglycemic agent (9.1 ± 0.2 to 7.2 ± 0.2%) than that in the group switching from insulin (8.6 ± 0.2 to 7.8 ± 0.2%). In addition, C‐peptide immunoreactivity levels (fasting > 2.2 ng/mL; delta >1.6 ng/mL; urine > 70 μg/day), younger age and a smaller number of insulin units used per day were considered important when deciding on switching to liraglutide from insulin.

Conclusions

Liraglutide was more effective in patients who had not been treated previously or received oral hypoglycemic agents than in patients switching from insulin. With respect to switching to liraglutide from insulin, the most important factors to be considered were C‐peptide immunoreactivity levels, age, and the number of insulin units used per day.

Exendin-4 increases the expression of hypoxia-inducible factor-1α in rat islets and preserves the endocrine cell volume of both free and macroencapsulated islet grafts

In this study, we evaluated the effects of exendin-4 on free and encapsulated islet grafts in a rodent model. We also investigated the role of a transcription factor, hypoxia-inducible factor-1 (HIF-1), in mediating the beneficial effects of exendin-4. Diabetic athymic mice were transplanted with free rat islets under the kidney capsule or with macroencapsulated rat islets SC with or without exendin-4, islet preculture (exendin-4 0.1 nM for 20 h), and/or recipient treatment (IP 100 ng/day, day 0-7). The mice were followed for 4 weeks and the graft function and β-cell volume were evaluated. The effects of exendin-4 on islet HIF-1α mRNA and protein expression and on ATP content in a rat insulinoma cell line (INS-1E) were also examined. Preculture with exendin-4 followed by recipient treatment improved the outcome of both free (73% graft function vs. 26% in controls, p = 0.03) and macroencapsulated islet grafts (100% vs. 25% in controls, p = 0.02). In macroencapsulated grafts, the exendin-4-treated group had significantly larger endocrine volume, less graft necrosis, and more blood vessels around the capsule. In rat islets cultured with exendin-4, HIF-1α mRNA and protein expression were significantly enhanced. ATP content was increased in exendin-4-treated INS-1E cells under hypoxic conditions. The improved functional outcome after transplantation of a marginal islet mass with a brief initial treatment with exendin-4 is related to a larger surviving endocrine cell volume. Exendin-4 may improve islet graft resistance to hypoxia during the peritransplant period by increasing the expression of HIF-1α.

Influence of microenvironment on engraftment of transplanted β-cells

Pancreatic islet transplantation into the liver provides a possibility to treat selected patients with brittle type 1 diabetes mellitus. However, massive early β-cell death increases the number of islets needed to restore glucose homeostasis. Moreover, late dysfunction and death contribute to the poor long-term results of islet transplantation on insulin independence. Studies in recent years have identified early and late challenges for transplanted pancreatic islets, including an instant blood-mediated inflammatory reaction when exposing human islets to the blood microenvironment in the portal vein and the low oxygenated milieu of islets transplanted into the liver. Poor revascularization of remaining intact islets combined with severe changes in the gene expression of islets transplanted into the liver contributes to late dysfunction. Strategies to overcome these hurdles have been developed, and some of these interventions are now even tested in clinical trials providing a hope to improve results in clinical islet transplantation. In parallel, experimental and clinical studies have, based on the identified problems with the liver site, evaluated the possibility of change of implantation organ in order to improve the results. Site-specific differences clearly exist in the engraftment of transplanted islets, and a more thorough characterization of alternative locations is needed. New strategies with modifications of islet microenvironment with cells and growth factors adhered to the islet surface or in a surrounding matrix could be designed to intervene with site-specific hurdles and provide possibilities to improve future results of islet transplantation.

Effects of glucagon-like peptide 1 on glycemia control and its metabolic consequence after severe thermal injury--studies in an animal model

BACKGROUND

Hyperglycemia with insulin resistance is commonly seen in severely burned patients and tight glycemia control with insulin may be beneficial in this condition. The most potent insulinotropic hormone, glucagon-like peptide 1 (GLP-1), stimulates insulin secretion in a glucose-dependent manner. Because infusion of GLP-1 never reduces glucose levels to below ∼70 mg/dL, the risk of hypoglycemia by using insulin is reduced. In this study we investigated the metabolic effects of GLP-1 infusion after burn injury in an animal model.

METHODS

Male CD rats were divided in 3 groups: burn injury with saline, burn injury with GLP-1 treatment, and sham burn (SB). Burn injury was full thickness 40% total body surface area. The burn injury with GLP-1 treatment group received GLP-1 infusion via osmotic pump. Fasting blood glucose, plasma insulin, and plasma GLP-1 levels were measured during intraperitoneal glucose tolerance tests. Expressions of caspase 3 and bcl-2 were evaluated in pancreatic islets. In a subset of animals, protein metabolism and total energy expenditure were measured.

RESULTS

Fasting GLP-1 was reduced in burn injury with saline compared to SB or burn injury with GLP-1 treatment. Burn injury with GLP-1 treatment showed reduced fasting blood glucose, improved intraperitoneal glucose tolerance test results, with increased plasma insulin and GLP-1 responses to glucose. GLP-1 reduced protein breakdown and total energy expenditure in burn injury with GLP-1 treatment versus burn injury with saline, with improved protein balance. Increased expression of caspase 3 and decreased expression of bcl-2 in islet cells by burn injury were ameliorated by GLP-1.

CONCLUSION

Burn injury reduced plasma GLP-1 in association with insulin resistance. GLP-1 infusion improved glucose tolerance and showed anabolic effects on protein metabolism and reduced total energy expenditure after burn injury, possibly via insulinotropic and non insulinotropic mechanisms.

Sitagliptin prevents the development of metabolic and hormonal disturbances, increased β-cell apoptosis and liver steatosis induced by a fructose-rich diet in normal rats

The aim of the present study was to test the effect of sitagliptin and exendin-4 upon metabolic alterations, β-cell mass decrease and hepatic steatosis induced by F (fructose) in rats. Normal adult male Wistar rats received a standard commercial diet without (C) or with 10% (w/v) F in the drinking water (F) for 3 weeks; animals from each group were randomly divided into three subgroups: untreated (C and F) and simultaneously receiving either sitagliptin (CS and FS; 115.2 mg/day per rat) or exendin-4 (CE and FE; 0.35 nmol/kg of body weight, intraperitoneally). Water and food intake, oral glucose tolerance, plasma glucose, triacylglycerol (triglyceride), insulin and fructosamine concentration, HOMA-IR [HOMA (homoeostasis model assessment) for insulin resistance], HOMA-β (HOMA for β-cell function) and liver triacylglycerol content were measured. Pancreas immunomorphometric analyses were also performed. IGT (impaired glucose tolerance), plasma triacylglycerol, fructosamine and insulin levels, HOMA-IR and HOMA-β indexes, and liver triacylglycerol content were significantly higher in F rats. Islet β-cell mass was significantly lower in these rats, due to an increase in the percentage of apoptosis. The administration of exendin-4 and sitagliptin to F animals prevented the development of all the metabolic disturbances and the changes in β-cell mass and fatty liver. Thus these compounds, useful in treating Type 2 diabetes, would also prevent/delay the progression of early metabolic and tissue markers of this disease.

Gastrointestinal hormones and the regulation of β-cell mass

Type 2 diabetes occurs due to a relative deficit in β-cell mass or function. Glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), and gastrin are gastrointestinal hormones that are secreted in response to nutrient intake, regulating digestion, insulin secretion, satiety, and β-cell mass. In this review, we focus upon β-cell mass regulation. β-cell mass expands through β-cell proliferation and islet neogenesis; β-cell mass is lost via apoptosis. GLP-1 and GIP are well-studied gastrointestinal hormones and influence β-cell proliferation, apoptosis, and islet neogenesis. CCK regulates β-cell apoptosis and mitogenesis, and gastrin stimulates islet neogenesis. GLP-1 and GIP bind to G protein-coupled receptors and regulate β-cell mass via multiple signaling pathways. The protein kinase A pathway is central to this process because it directly regulates proliferative and anti-apoptotic genes and transactivates several signaling cascades, including Akt and mitogen-activated protein kinases. However, the signaling pathways downstream of G protein-coupled CCK receptors that influence β-cell mass remain unidentified. Gastrointestinal hormones integrate nutrient signals from the gut to the β-cell, regulating insulin secretion and β-cell mass adaptation.

FGF-21 enhances islet engraftment in mouse syngeneic islet transplantation model

To clarify the effect of fibroblast growth factor-21 (FGF-21) on islet transplantation, a suboptimal number of islets were transplanted into streptozotocin (STZ)-induced diabetic mice with or without FGF-21 treatment. Three-day treatment with FGF-21 contributed to restoration of normoglycemia by suppressing islet graft loss. The FGF-21-treated mice showed lower glycemic levels despite similar insulin content in the graft than that in untreated mice on day 3, indicating that FGF-21 not only has a cytoprotective effect but also decreases β-cell load by increasing insulin sensitivity. These results suggest that FGF-21 may be useful as a treatment to improve islet engraftment rates in clinical islet transplantation.

Glucagon-like peptide-1 receptor signalling selectively regulates murine lymphocyte proliferation and maintenance of peripheral regulatory T cells

AIMS/HYPOTHESIS

Glucagon-like peptide-1 receptor (GLP-1R) agonists improve glucose control in animals and humans with type 1 diabetes. However, there is little information on the role of the GLP-1R in the immune system. We studied the role of the GLP-1R in immune function in wild-type (WT) and nonobese diabetic (NOD) and Glp1r-/- mice.

METHODS

Glp1r mRNA expression was examined in sorted immune subpopulations by RT-PCR. The effects of GLP-1R activation were assessed on cAMP production and proliferation, migration and survival of primary immune cells from WT and NOD mice. The ability of primary cells from Glp1r-/- mice to proliferate, migrate or survive apoptosis was determined. Immunophenotyping studies were performed to assess the frequency of immune subpopulations in Glp1r-/- mice.

RESULTS

Ex vivo activation of the GLP-1R resulted in a modest but significant elevation of cAMP in primary thymocytes and splenocytes from both WT and NOD mice. GLP-1R activation did not increase proliferation of primary thymocytes, splenocytes or peripheral lymph node cells. In contrast, Glp1r-/- thymocytes exhibited a hypoproliferative response, whilst peripheral Glp1r-/- lymphocytes were hyperproliferative in response to mitogenic stimulation. Activation or loss of GLP-1R signalling did not modify apoptosis or chemotaxis in primary lymphocytes. Male Glp1r-/- mice exhibited a significantly lower percentage of peripheral regulatory T cells, although no differences were observed in the numbers of CD4+ and CD8+ T cells and B cells in the spleen and lymph nodes of Glp1r-/- mice.

CONCLUSIONS/INTERPRETATION

These studies establish that GLP-1R signalling may regulate lymphocyte proliferation and maintenance of peripheral regulatory T cells.

Effects of long-term dipeptidyl peptidase-IV inhibition on body composition and glucose tolerance in high fat diet-fed mice

AIM

Glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) are major incretins associated with body weight regulation. Dipeptidyl peptidase-IV (DPP-IV) inhibitor increases plasma active GLP-1 and GIP. However, the magnitude of the effects of enhanced GLP-1 and GIP signaling by long-term DPP-IV inhibition on body weight and insulin secretion has not been determined. In this study, we compared the effects of long-term DPP-IV inhibition on body composition and insulin secretion of high fat diet (HFD)-fed wild-type (WT) and GLP-1R knockout (GLP-1R(-/-)) mice.

MAIN METHODS

HFD-fed WT and GLP-1R(-/-) mice were treated with or without DPP-IV inhibitor by drinking water. Food and water intake and body weight were measured during 8 weeks of study. CT-based body composition analysis, Oral glucose tolerance test (OGTT), batch incubation study for insulin secretion and quantitative RT-PCR for expression of incretin receptors in isolated islets were performed at the end of study.

KEY FINDINGS

DPP-IV inhibitor had no effect on food and water intake and body weight, but increased body fat mass in GLP-1R(-/-) mice. DPP-IV inhibitor-treated WT and GLP-1R(-/-) mice both showed increased insulin secretion in OGTT. In isolated islets of DPP-IV inhibitor-treated WT and GLP-1R(-/-) mice, glucose-induced insulin secretion was increased and insulin secretion in response to GLP-1 or GIP was preserved, without downregulation of incretin receptor expression.

SIGNIFICANCE

Long-term DPP-IV inhibition may maintain body composition through counteracting effects of GLP-1 and GIP while improving glucose tolerance by increasing glucose-induced insulin secretion through the synergistic effects of GLP-1 and GIP.

Impact of small-molecule glucokinase activator on glucose metabolism and beta-cell mass

We investigated the effect of glucokinase activator (GKA) on glucose metabolism and beta-cell mass. We analyzed four mouse groups: wild-type mice and beta-cell-specific haploinsufficiency of glucokinase gene (Gck(+/-)) mice on a high-fat (HF) diet. Each genotype was also treated with GKA mixed in the HF diet. Rodent insulinoma cells and isolated islets were used to evaluate beta-cell proliferation by GKA. After 20 wk on the above diets, there were no differences in body weight, lipid profiles, and liver triglyceride content among the four groups. Glucose tolerance was improved shortly after the GKA treatment in both genotypes of mice. beta-Cell mass increased in wild-type mice compared with Gck(+/-) mice, but a further increase was not observed after the administration of GKA in both genotypes. Interestingly, GKA was able to up-regulate insulin receptor substrate-2 (Irs-2) expression in insulinoma cells and isolated islets. The administration of GKA increased 5-bromo-2-deoxyuridine (BrdU) incorporation in insulinoma cells, and 3 d administration of GKA markedly increased BrdU incorporation in mice treated with GKA in both genotypes, compared with those without GKA. In conclusion, GKA was able to chronically improve glucose metabolism for mice on the HF diet. Although chronic GKA administration failed to cause a further increase in beta-cell mass in vivo, GKA was able to increase beta cell proliferation in vitro and with a 3-d administration in vivo. This apparent discrepancy can be explained by a chronic reduction in ambient blood glucose levels by GKA treatment.

Long-term insulin independence and improvement in insulin secretion after supplemental islet infusion under exenatide and etanercept

BACKGROUND

Progressive graft dysfunction (GDF) and loss of insulin independence (II) have been invariably observed in islet transplant recipients under the "Edmonton protocol." To reestablish II, we performed supplemental islet infusions (SI) in recipients of allogeneic islet transplant alone, displaying GDF. To improve the engraftment and long-term graft function of SI, exenatide (EXN) and etanercept treatment at islet infusion, and long-term EXN treatment were tested in a non-randomized pilot clinical trial.

METHODS

Patients with GDF received SI under Edmonton-like immunosuppression with daclizumab induction, either without interventions (SI-control; n=5) or with EXN and etanercept treatment (SI-EXN; n=4). Clinical and metabolic profiles were assessed during 18-month follow-up.

RESULTS

Long-term II (18 months) was observed in 100% of SI-EXN and in 20% of SI-control (P=0.04). SI-EXN subjects demonstrated restoration of function better than that seen after initial islet infusions. Comparison of SI-EXN and SI-control groups demonstrated better responses in SI-EXN subjects at 3 months post-SI. During the 18 months of follow-up, function was sustained in the SI-EXN subjects better than in SI-controls. Acute effects of EXN during mixed meal tolerance test and intravenous glucose tolerance test results in improved first and second phase insulin release in response to intravenous glucose tolerance test and suppressed postprandial hyperglucagonemia after mixed meal tolerance test.

CONCLUSION

These results suggest that the combination of EXN and etanercept improve engraftment and long-term islet survival and function in subjects undergoing SI. This data, however, must be interpreted with some caution because of small sample size, lack of randomization, and sequential comparison with historical controls.

An update on preventive and regenerative therapies in diabetes mellitus

Type 1A (immune-mediated) and type 2 diabetes mellitus are two of the most common severe chronic illnesses, affecting over 230 million people worldwide with an estimated global prevalence of 5.1%. Although type 1 and type 2 diabetes differ greatly in modes of pathogenesis, these illnesses share a common pathology and consequences characterized by loss of functional beta-cell mass and subsequent dysregulation of carbohydrate and lipid metabolism. Since therapy for diabetes and the associated complications poses enormous public health and economic burdens, novel preventive and regenerative therapies have emerged in the past decade with the aim to preserve beta-cell mass and delay the onset of diabetes. The goal of this review is to provide a comprehensive overview of current efforts in the fight against diabetes, and attempts to document all strategies that have emerged in clinical studies within the past 25 years. First, strategies to identify individuals at risk, ranging from whole-genome scans to autoantibody screening, will be discussed. Second, novel approaches to prevent or delay the onset of disease will be covered. Particular focus is given on emerging strategies for individuals at risk for type 1 diabetes that target T-cell regulation and induction of tolerance, while new pharmaceutical concepts in combination with lifestyle interventions are discussed within the scope of type 2 diabetes prevention. Lastly, important efforts to halt disease progression with emphasis on beta-cell regeneration are presented.

The glucagon-like peptide-1 receptor agonist oxyntomodulin enhances beta-cell function but does not inhibit gastric emptying in mice

The proglucagon gene gives rise to multiple peptides that play diverse roles in the control of energy intake, gut motility, and nutrient disposal. Glucagon-like peptide-1 (GLP-1), a 30-amino-acid peptide regulates glucose homeostasis via control of insulin and glucagon secretion and by inhibition of gastric emptying and food intake. Oxyntomodulin (OXM) a 37-amino-acid peptide also derived from the proglucagon gene, binds to both the glucagon and GLP-1 receptor (GLP-1R); however, a separate OXM receptor has not yet been identified. Here we show that OXM, like other GLP-1R agonists, stimulates cAMP formation and lowers blood glucose after both oral and ip glucose administration, actions that require a functional GLP-1R. OXM also directly stimulates insulin secretion from murine islets and INS-1 cells in a glucose- and GLP-1R-dependent manner. Moreover, OXM ameliorates hyperglycemia and significantly reduces apoptosis in murine beta-cells after streptozotocin administration and directly reduces apoptosis in thapsigargin-treated INS-1 cells. Unexpectedly, OXM, but not the GLP-1R agonist exendin-4, increased plasma levels of insulin after oral glucose administration. Moreover, OXM administered at doses that potently lower blood glucose had no effect on inhibition of gastric emptying but reduced food intake in WT mice. Taken together, these findings illustrate that although structurally distinct proglucagon-derived peptides such as GLP-1 and OXM engage the GLP-1R, OXM mimics some but not all of the actions of GLP-1R agonists in vivo. These findings may have implications for therapeutic efforts using OXM as a long-acting GLP-1R agonist for the treatment of metabolic disorders.