Glucagon-like peptide 1 induces differentiation of islet duodenal homeobox-1-positive pancreatic ductal cells into insulin-secreting cells

Safety, tolerability, pharmacokinetic, pharmacodynamic and immunogenicity profiles of Exendin-4-IgG4-Fc in healthy subjects: A phase 1, single-centre, randomized, double-blind, dose escalation study

AIM

Novel long-acting drugs for type 2 diabetes mellitus may optimize patient compliance and glycaemic control. Exendin-4-IgG4-Fc (E4F4) is a long-acting glucagon-like peptide-1 receptor agonist. This first-in-human study investigated the safety, tolerability, pharmacokinetic, pharmacodynamic and immunogenicity profiles of a single subcutaneous injection of E4F4 in healthy subjects.

METHODS

This single-centre, randomized, double-blind, placebo-controlled phase 1 clinical trial included 96 subjects in 10 sequential cohorts that were provided successively higher doses of E4F4 (0.45, 0.9, 1.8, 3.15, 4.5, 6.3, 8.1, 10.35, 12.6 and 14.85 mg) or placebo (ChinaDrugTrials.org.cn: ChiCTR2100049732). The primary endpoint was safety and tolerability of E4F4. Secondary endpoints were pharmacokinetic, pharmacodynamic and immunogenicity profiles of E4F4. Safety data to day 15 after the final subject in a cohort had been dosed were reviewed before commencing the next dose level.

RESULTS

E4F4 was safe and well tolerated among healthy Chinese participants in this study. There was no obvious dose-dependent relationship between frequency, severity or causality of treatment-emergent adverse events. Cmax and area under the curve of E4F4 were dose proportional over the 0.45-14.85 mg dose range. Median Tmax and t1/2 ranged from 146 to 210 h and 199 to 252 h, respectively, across E4F4 doses, with no dose-dependent trends. For the intravenous glucose tolerance test, area under the curve of glucose in plasma from time 0 to 180 min showed a dose-response relationship in the 1.8-10.35 mg dose range, with an increased response at the higher doses.

CONCLUSION

E4F4 exhibited an acceptable safety profile and linear pharmacokinetics in healthy subjects. The recommended phase 2 dose is 4.5-10.35 mg once every 2 weeks.

Biochemical pancreatic β-cell lineage reprogramming: Various cell fate shifts

The incidence of pancreatic diseases has been continuously rising in recent years. Thus, research on pancreatic regeneration is becoming more popular. Chronic hyperglycemia is detrimental to pancreatic β-cells, leading to impairment of insulin secretion which is the main hallmark of pancreatic diseases. Obtaining plenty of functional pancreatic β-cells is the most crucial aspect when studying pancreatic biology and treating diabetes. According to the International Diabetes Federation, diabetes has become a global epidemic, with about 3 million people suffering from diabetes worldwide. Hyperglycemia can lead to many dangerous diseases, including amputation, blindness, neuropathy, stroke, and cardiovascular and kidney diseases. Insulin is widely used in the treatment of diabetes; however, innovative approaches are needed in the academic and preclinical stages. A new approach aims at synthesizing patient-specific functional pancreatic β-cells. The present article focuses on how cells from different tissues can be transformed into pancreatic β-cells.

Clinical significance of pancreatic ductal metaplasia

Pancreatic ductal metaplasia (PDM) is the stepwise replacement of differentiated somatic cells with ductal or ductal-like cells in the pancreas. PDM is usually triggered by cellular and environmental insults. PDM development may involve all cell lineages of the pancreas, and acinar cells with the highest plasticity are the major source of PDM. Pancreatic progenitor cells are also involved as cells of origin or transitional intermediates. PDM is heterogeneous at the histological, cellular, and molecular levels and only certain subsets of PDM develop further into pancreatic intraepithelial neoplasia (PanIN) and then pancreatic ductal adenocarcinoma (PDAC). The formation and evolution of PDM is regulated at the cellular and molecular levels through a complex network of signaling pathways. The key molecular mechanisms that drive PDM formation and its progression into PanIN/PDAC remain unclear, but represent key targets for reversing or inhibiting PDM. Alternatively, PDM could be a source of pancreas regeneration, including both exocrine and endocrine components. Cellular aging and apoptosis are obstacles to PDM-to-PanIN progression or pancreas regeneration. Functional identification of the cellular and molecular events driving senescence and apoptosis in PDM and its progression would help not only to restrict the development of PDM into PanIN/PDAC, but may also facilitate pancreatic regeneration. This review systematically assesses recent advances in the understanding of PDM physiology and pathology, with a focus on its implications for enhancing regeneration and prevention of cancer. © 2022 The Pathological Society of Great Britain and Ireland.

Valproic Acid Initiates Transdifferentiation of the Human Ductal Adenocarcinoma Cell-line Panc-1 Into α-Like Cells

Non-mesenchymal pancreatic cells are a potential source for cell replacement. Their transdifferentiation can be achieved by triggering epigenetic remodeling through e. g. post-translational modification of histones. Valproic acid, a branched-chain saturated fatty acid with histone deacetylase inhibitor activity, was linked to the expression of key transcription factors of pancreatic lineage in epithelial cells and insulin transcription. However, the potential of valproic acid to cause cellular reprogramming is not fully understood. To shed further light on it we employed next-generation RNA sequencing, real-time PCR, and protein analyses by ELISA and western blot, to assess the impact of valproic acid on transcriptome and function of Panc-1-cells. Our results indicate that valproic acid has a significant impact on the cell cycle, cell adhesion, histone H3 acetylation, and metabolic pathways as well as the initiation of epithelial-mesenchymal transition through acetylation of histone H3 resulting in α-cell-like characteristics. We conclude that human epithelial pancreatic cells can be transdifferentiated into cells with endocrine properties through epigenetic regulation by valproic acid favoring an α-cell-like phenotype.

Molecular signaling in pancreatic ductal metaplasia: emerging biomarkers for detection and intervention of early pancreatic cancer

Pancreatic ductal metaplasia (PDM) is the transformation of potentially various types of cells in the pancreas into ductal or ductal-like cells, which eventually replace the existing differentiated somatic cell type(s). PDM is usually triggered by and manifests its ability to adapt to environmental stimuli and genetic insults. The development of PDM to atypical hyperplasia or dysplasia is an important risk factor for pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma (PDA). Recent studies using genetically engineered mouse models, cell lineage tracing, single-cell sequencing and others have unraveled novel cellular and molecular insights in PDM formation and evolution. Those novel findings help better understand the cellular origins and functional significance of PDM and its regulation at cellular and molecular levels. Given that PDM represents the earliest pathological changes in PDA initiation and development, translational studies are beginning to define PDM-associated cell and molecular biomarkers that can be used to screen and detect early PDA and to enable its effective intervention, thereby truly and significantly reducing the dreadful mortality rate of PDA. This review will describe recent advances in the understanding of PDM biology with a focus on its underlying cellular and molecular mechanisms, and in biomarker discovery with clinical implications for the management of pancreatic regeneration and tumorigenesis.

Preproglucagon Products and Their Respective Roles Regulating Insulin Secretion

Historically, intracellular function and metabolic adaptation within the α-cell has been understudied, with most of the attention being placed on the insulin-producing β-cells due to their role in the pathophysiology of type 2 diabetes mellitus. However, there is a growing interest in understanding the function of other endocrine cell types within the islet and their paracrine role in regulating insulin secretion. For example, there is greater appreciation for α-cell products and their contributions to overall glucose homeostasis. Several recent studies have addressed a paracrine role for α-cell-derived glucagon-like peptide-1 (GLP-1) in regulating glucose homeostasis and responses to metabolic stress. Further, other studies have demonstrated the ability of glucagon to impact insulin secretion by acting through the GLP-1 receptor. These studies challenge the central dogma surrounding α-cell biology describing glucagon's primary role in glucose counterregulation to one where glucagon is critical in regulating both hyper- and hypoglycemic responses. Herein, this review will update the current understanding of the role of glucagon and α-cell-derived GLP-1, placing emphasis on their roles in regulating glucose homeostasis, insulin secretion, and β-cell mass.

Novel Approaches to Restore Pancreatic Beta-Cell Mass and Function

Beta-cell dysfunction and beta-cell death are critical events in the development of type 2 diabetes mellitus (T2DM). Therefore, the goals of modern T2DM management have shifted from merely restoring normoglycemia to maintaining or regenerating beta-cell mass and function. In this review we summarize current and novel approaches to achieve these goals, ranging from lifestyle interventions to N-methyl-D-aspartate receptor (NMDAR) antagonism, and discuss the mechanisms underlying their effects on beta-cell physiology and glycemic control. Notably, timely intervention seems critical, but not always strictly required, to maximize the effect of any approach on beta-cell recovery and disease progression. Conventional antidiabetic medications are not disease-modifying in the sense that the disease does not progress or reoccur while on treatment or thereafter. More invasive approaches, such as bariatric surgery, are highly effective in restoring normoglycemia, but are reserved for a rather small proportion of obese individuals and sometimes associated with serious adverse events. Finally, we recapitulate the broad range of effects mediated by peripheral NMDARs and discuss recent evidence on the potential of NMDAR antagonists to be developed as a novel class of antidiabetic drugs. In the future, a more refined assessment of disease risk or disease subtype might enable more targeted therapies to prevent or treat diabetes.

Proglucagon-Derived Peptides as Therapeutics

Initially discovered as an impurity in insulin preparations, our understanding of the hyperglycaemic hormone glucagon has evolved markedly over subsequent decades. With description of the precursor proglucagon, we now appreciate that glucagon was just the first proglucagon-derived peptide (PGDP) to be characterised. Other bioactive members of the PGDP family include glucagon-like peptides -1 and -2 (GLP-1 and GLP-2), oxyntomodulin (OXM), glicentin and glicentin-related pancreatic peptide (GRPP), with these being produced via tissue-specific processing of proglucagon by the prohormone convertase (PC) enzymes, PC1/3 and PC2. PGDP peptides exert unique physiological effects that influence metabolism and energy regulation, which has witnessed several of them exploited in the form of long-acting, enzymatically resistant analogues for treatment of various pathologies. As such, intramuscular glucagon is well established in rescue of hypoglycaemia, while GLP-2 analogues are indicated in the management of short bowel syndrome. Furthermore, since approval of the first GLP-1 mimetic for the management of Type 2 diabetes mellitus (T2DM) in 2005, GLP-1 therapeutics have become a mainstay of T2DM management due to multifaceted and sustainable improvements in glycaemia, appetite control and weight loss. More recently, longer-acting PGDP therapeutics have been developed, while newfound benefits on cardioprotection, bone health, renal and liver function and cognition have been uncovered. In the present article, we discuss the physiology of PGDP peptides and their therapeutic applications, with a focus on successful design of analogues including dual and triple PGDP receptor agonists currently in clinical development.

Glucagon-Like Peptide-1 Receptor Agonist Prevented the Progression of Hepatocellular Carcinoma in a Mouse Model of Nonalcoholic Steatohepatitis

Glucagon-like peptide-1 (GLP-1) receptor agonists are used to treat diabetes, but their effects on nonalcoholic steatohepatitis (NASH) and the development of hepatocellular carcinoma (HCC) remain unclear. In this study, mice with streptozotocin- and high-fat diet-induced diabetes and NASH were subcutaneously treated with liraglutide or saline (control) for 14 weeks. Glycemic control, hepatocarcinogenesis, and liver histology were compared between the groups. Fasting blood glucose levels were significantly lower in the liraglutide group than in the control group (210.0 ± 17.3 mg/dL vs. 601.8 ± 123.6 mg/dL), and fasting insulin levels were significantly increased by liraglutide (0.18 ± 0.06 ng/mL vs. 0.09 ± 0.03 ng/mL). Liraglutide completely suppressed hepatocarcinogenesis, whereas HCC was observed in all control mice (average tumor count, 5.5 ± 3.87; average tumor size, 8.1 ± 5.0 mm). Liraglutide significantly ameliorated steatosis, inflammation, and hepatocyte ballooning of non-tumorous lesions in the liver compared with the control findings, and insulin-positive β-cells were observed in the pancreas in liraglutide-treated mice but not in control mice. In conclusion, liraglutide ameliorated NASH and suppressed hepatocarcinogenesis in diabetic mice. GLP-1 receptor agonists can be used to improve the hepatic outcome of diabetes.

Farnesoid X receptor interacts with cAMP response element binding protein to modulate glucagon-like peptide-1 (7-36) amide secretion by intestinal L cell

Type II diabetes is a complex, chronic, and progressive disease. Glucagon-like peptide-1 (7-36) amide (GLP-1) is a gut hormone released from the L cells which stimulate insulin secretion and promotes insulin gene expression and β-cell growth and differentiation. Elevated levels of hormones secreted by L cells are an essential reason for diabetes improvement. GLP-1 secretion has been reported to be regulated by farnesoid X receptor (FXR), a transcriptional sensor for bile acids which also acts on glucose metabolism. Herein, we attempted to evaluate the effect of FXR on GLP-1 secretion in mouse enteroendocrine L cell line, namely STC-1, and to investigate the underlying mechanism. FXR inversely regulated GLP-1 secretion in STC-1. A total of 24 nonredundant human proteins were shown to be related to FXR by BioGRID; KEGG pathway analysis revealed that FXR was related to glucagon signaling pathway, particularly with the transcriptional activators CREB, PGC1α, Sirt1, and CBP. CREB could positively regulate GLP-1 secretion in STC-1 cells. FXR combined with CREB to inhibit its transcriptional activity, thus inhibiting proprotein convertase subtilisin/kexin type 1 protein level and GLP-1 secretion. In the present study, we demonstrated a negative regulation of GLP-1 secretion by FXR in L cell line, STC-1; FXR exerts its function in L cells through interacting with CREB, a crucial transcriptional regulator of cAMP-CREB signaling pathway, to inhibit its transcriptional activity. Targeting FXR to rescue GLP-1 secretion may be a promising strategy for type II diabetes.

Glucagon-Like Peptide 1 Increases β-Cell Regeneration by Promoting α- to β-Cell Transdifferentiation

Glucagon-like peptide 1 (GLP-1) can increase pancreatic β-cells, and α-cells could be a source for new β-cell generation. We investigated whether GLP-1 increases β-cells through α-cell transdifferentiation. New β-cells originating from non-β-cells were significantly increased in recombinant adenovirus expressing GLP-1 (rAd-GLP-1)-treated RIP-CreER;R26-YFP mice. Proliferating α-cells were increased in islets of rAd-GLP-1-treated mice and αTC1 clone 9 (αTC1-9) cells treated with exendin-4, a GLP-1 receptor agonist. Insulin⁺glucagon⁺ cells were significantly increased by rAd-GLP-1 or exendin-4 treatment in vivo and in vitro. Lineage tracing to label the glucagon-producing α-cells showed a higher proportion of regenerated β-cells from α-cells in rAd-GLP-1-treated Glucagon-rtTA;Tet-O-Cre;R26-YFP mice than rAd producing β-galactosidase-treated mice. In addition, exendin-4 increased the expression and secretion of fibroblast growth factor 21 (FGF21) in αTC1-9 cells and β-cell-ablated islets. FGF21 treatment of β-cell-ablated islets increased the expression of pancreatic and duodenal homeobox-1 and neurogenin-3 and significantly increased insulin⁺glucagon⁺ cells. Generation of insulin⁺glucagon⁺ cells by exendin-4 was significantly reduced in islets transfected with FGF21 small interfering RNA or islets of FGF21 knockout mice. Generation of insulin⁺ cells by rAd-GLP-1 treatment was significantly reduced in FGF21 knockout mice compared with wild-type mice. We suggest that GLP-1 has an important role in α-cell transdifferentiation to generate new β-cells, which might be mediated, in part, by FGF21 induction.

Recent updates on GLP-1 agonists: Current advancements & challenges

Glucagon-like peptide (GLP)-1 is an incretin hormone exhibiting several pharmacological actions such as neuroprotection, increased cognitive function, cardio-protection, decreased hypertension, suppression of acid secretion, increase in lyposis, and protection from inflammation. The most potent actions are glucose-dependent insulinotropic and glucagonostatic actions, stimulation of β-cell proliferation, enhanced insulin secretion and reduced weight gain in patients with type-2 diabetes pertaining to blood glucose control. Despite all these actions, its short half-life (around 2∼min) and degradation by a dipeptidyl peptidase-4 enzyme (DPP-4) limits the therapeutic utility of GLP1. In this review, we have discussed DPP IV-resistant analogs of GLP-1 currently present in clinical trials such as Exenatide, Liraglutide, Semaglutide, Efpeglenatide, Exenatide ER, Ittca 650 (Intarcia), Dulaglutide, Albiglutide, and Lixisenatide. Moreover, we have also discussed in detail the pharmacology, signaling mechanisms, and pharmacokinetic properties (Cmax, Tmax, T_1/2, Vd, and Bioavailability) of DPP IV-resistant analogs of (GLP-1). Interestingly, GLP-1 agonist drugs have shown better potential to treat type-2 diabetes mellitus (T2DM) as compared to currently used drugs in clinics without causing the side effects of hypoglycemia and weight gain.

Vildagliptin Enhances Differentiation of Insulin Producing Cells from Adipose-Derived Mesenchymal Stem Cells

Objective

Type 1 diabetes is caused by destruction of beta cells of pancreas. Vildagliptin (VG), a dipeptidyl peptidase IV (DPP IV) inhibitor, is an anti-diabetic drug, which increases beta cell mass. In the present study, the effects of VG on generation of insulin-producing cells (IPCs) from adipose-derived mesenchymal stem cells (ASCs) is investigated.

Materials and Methods

In this experimental study, ASCs were isolated and after characterization were exposed to differentiation media with or without VG. The presence of IPCs was confirmed by morphological analysis and gene expression (Pdx-1, Glut-2 and Insulin). Newport Green staining was used to determine insulin-positive cells. Insulin secretion under different concentrations of glucose was measured using radioimmunoassay method.

Results

In the presence of VG the morphology of differentiated cells was similar to the pancreatic islet cells. Expression of Pdx-1, Glut-2 and Insulin genes in VG-treated cells was significantly higher than the cells exposed to induction media only. Insulin release from VG-treated ASCs showed a nearly 3.6 fold (P<0.05) increase when exposed to a high- glucose medium in comparison to untreated ASCs. The percentage of insulin-positive cells in the VG-treated cells was approximately 2.9-fold higher than the untreated ASCs.

Conclusion

The present study has demonstrated that VG elevates differentiation of ASCs into IPCs. Improvement of this protocol may be used in cell therapy in diabetic patients.

Treatment with specific soluble factors promotes the functional maturation of transcription factor-mediated, pancreatic transdifferentiated cells

Pancreatic lineage-specific transcription factors (TFs) display instructive roles in converting adult cells to endocrine pancreatic cells through a process known as transdifferentiation. However, little is known about potential factors capable of accelerating transdifferentiation following transduction to achieve the functional maturation of transdifferentiated cells. In this study, we demonstrated, using adult liver-derived progenitor cells, that soluble factors utilized in pancreatic differentiation protocols of pluripotent stem cells promote functional maturation of TFs-mediated transdifferentiated cells. Treatment with an N2 supplement in combination with three soluble factors (glucagon-like peptide-1 [GLP-1] receptor agonist, notch inhibitor, and transforming growth factor-β [TGF-β] inhibitor) enhanced liver-to-pancreas transdifferentiation based on the following findings: i) the incidence of c-peptide-positive cells increased by approximately 1.2-fold after the aforementioned treatment; ii) the c-peptide expression level in the treated cells increased by approximately 12-fold as compared with the level in the untreated cells; iii) the treated cells secreted insulin in a glucose-dependent manner, whereas the untreated cells did not; and iv) transplantation of treated-transdifferentiated cells into streptozotocin-induced immunodeficient diabetic mice led to the amelioration of hyperglycemia. These results suggest that treatment with specific soluble factors promotes the functional maturation of transdifferentiated cells. Our findings could facilitate the development of new modalities for cell-replacement therapy for patients with diabetes.

Glucagon Like Peptide 1 and MicroRNA in Metabolic Diseases: Focusing on GLP1 Action on miRNAs

Glucagon like peptide 1 (GLP1) is an incretin hormone released from the enteroendocrine L-type cells of the lower gastrointestinal tract. The active isoforms of GLP1 are rapidly degraded (<2 min) by protease dipeptidyl peptidase-4 (DPP-4) after their release. Among its functions, GLP1 exerts a pivotal role in regulating glucose and lipid metabolism. In particular, GLP1 increases glucose stimulated insulin secretion, functional pancreatic β-cell mass and decreases glucagon secretion from pancreatic α-cells. GLP1 can also be a regulator of lipid and lipoprotein metabolism ameliorating diabetic dyslipidemia, liver steatosis, and promoting satiety. Interestingly, it has been found that GLP1 and GLP1 agonists can modulate the expression of different microRNAs (miRNAs), a ~22 nucleotides small non-coding RNAs, key modulators of protein expression. In particular, in pancreas, GLP1 increases the expression levels of miRNA-212 and miRNA-132, stimulating insulin secretion. Similarly, GLP1 decreases miRNA-338 levels, leading to an increase of pancreatic β-cell function, followed by an improvement of diabetic conditions. Moreover, GLP1 modulation of miRNAs expression in the liver regulates hepatic lipid storage. Indeed, GLP1 down-regulates miRNA-34a and miRNA-21 and up-regulates miRNA-200b and miRNA-200c expression in liver, reducing intra hepatic lipid accumulation and liver steatosis. Clinical and pre-clinical studies, discussed in this review, suggest that modulation of GLP1/miRNAs pathway may be a useful and innovative therapeutic strategy for prevention and treatment of metabolic disorders, such as diabetes mellitus and liver steatosis.

FGF-2b and h-PL Transform Duct and Non-Endocrine Human Pancreatic Cells into Endocrine Insulin Secreting Cells by Modulating Differentiating Genes

Background: Diabetes mellitus (DM) is a multifactorial disease orphan of a cure. Regenerative medicine has been proposed as novel strategy for DM therapy. Human fibroblast growth factor (FGF)-2b controls β-cell clusters via autocrine action, and human placental lactogen (hPL)-A increases functional β-cells. We hypothesized whether FGF-2b/hPL-A treatment induces β-cell differentiation from ductal/non-endocrine precursor(s) by modulating specific genes expression. Methods: Human pancreatic ductal-cells (PANC-1) and non-endocrine pancreatic cells were treated with FGF-2b plus hPL-A at 500 ng/mL. Cytofluorimetry and Immunofluorescence have been performed to detect expression of endocrine, ductal and acinar markers. Bromodeoxyuridine incorporation and annexin-V quantified cells proliferation and apoptosis. Insulin secretion was assessed by RIA kit, and electron microscopy analyzed islet-like clusters. Results: Increase in PANC-1 duct cells de-differentiation into islet-like aggregates was observed after FGF-2b/hPL-A treatment showing ultrastructure typical of islets-aggregates. These clusters, after stimulation with FGF-2b/hPL-A, had significant (p < 0.05) increase in insulin, C-peptide, pancreatic and duodenal homeobox 1 (PDX-1), Nkx2.2, Nkx6.1, somatostatin, glucagon, and glucose transporter 2 (Glut-2), compared with control cells. Markers of PANC-1 (Cytokeratin-19, MUC-1, CA19-9) were decreased (p < 0.05). These aggregates after treatment with FGF-2b/hPL-A significantly reduced levels of apoptosis. Conclusions: FGF-2b and hPL-A are promising candidates for regenerative therapy in DM by inducing de-differentiation of stem cells modulating pivotal endocrine genes.

Lineage Reprogramming: A Promising Road for Pancreatic β Cell Regeneration

Cell replacement therapy is a promising method to restore pancreatic β cell function and cure diabetes. Distantly related cells (fibroblasts, keratinocytes, and muscle cells) and developmentally related cells (hepatocytes, gastrointestinal, and pancreatic exocrine cells) have been successfully reprogrammed into β cells in vitro and in vivo. However, while some reprogrammed β cells bear similarities to bona fide β cells, others do not develop into fully functional β cells. Here we review various strategies currently used for β cell reprogramming, including ectopic expression of specific transcription factors associated with islet development, repression of maintenance factors of host cells, regulation of epigenetic modifications, and microenvironmental changes. Development of simple and efficient reprogramming methods is a key priority for developing fully functional β cells suitable for cell replacement therapy.

Microfluidic perfusion systems for secretion fingerprint analysis of pancreatic islets: applications, challenges and opportunities

A secretome signature is a heterogeneous profile of secretions present in a single cell type. From the secretome signature a smaller panel of proteins, namely a secretion fingerprint, can be chosen to feasibly monitor specific cellular activity. Based on a thorough appraisal of the literature, this review explores the possibility of defining and using a secretion fingerprint to gauge the functionality of pancreatic islets of Langerhans. It covers the state of the art regarding microfluidic perfusion systems used in pancreatic islet research. Candidate analytical tools to be integrated within microfluidic perfusion systems for dynamic secretory fingerprint monitoring were identified. These analytical tools include patch clamp, amperometry/voltametry, impedance spectroscopy, field effect transistors and surface plasmon resonance. Coupled with these tools, microfluidic devices can ultimately find applications in determining islet quality for transplantation, islet regeneration and drug screening of therapeutic agents for the treatment of diabetes.

Pharmacological Modulators of Endoplasmic Reticulum Stress in Metabolic Diseases

The endoplasmic reticulum (ER) is the principal organelle responsible for correct protein folding, a step in protein synthesis that is critical for the functional conformation of proteins. ER stress is a primary feature of secretory cells and is involved in the pathogenesis of numerous human diseases, such as certain neurodegenerative and cardiometabolic disorders. The unfolded protein response (UPR) is a defense mechanism to attenuate ER stress and maintain the homeostasis of the organism. Two major degradation systems, including the proteasome and autophagy, are involved in this defense system. If ER stress overwhelms the capacity of the cell's defense mechanisms, apoptotic death may result. This review is focused on the various pharmacological modulators that can protect cells from damage induced by ER stress. The possible mechanisms for cytoprotection are also discussed.

Effects of Exendine-4 on The Differentiation of Insulin Producing Cells from Rat Adipose-Derived Mesenchymal Stem Cells

OBJECTIVE

To evaluate the effect of Exendine-4 (EX-4), a Glucagon-like peptide 1 (GLP-1) receptor agonist, on the differentiation of insulin-secreting cells (IPCs) from rat adipose-derived mesenchymal stem cells(ADMSCs).

MATERIALS AND METHODS

In this experimental study, ADMSCs were isolated from rat adi- pose tissue and exposed to induction media with or without EX-4. After induction, the existence of IPCs was confirmed by morphology analysis, expression pattern analysis of islet-specific genes (Pdx-1, Glut-2 and Insulin) and insulin synthesis and secretion.

RESULTS

IPCs induced in presence of EX-4 were morphologically similar to pancre- atic islet-like cells. Expression of Pdx-1, Glut-2 and Insulin genes in EX-4 treated cells was significantly higher than the cells exposed to differentiation media without EX-4. Compared to EX-4 untreated ADMSCs, insulin release from EX-4 treated ADMSCs showed a nearly 2.5 fold (P<0.05) increase when exposed to a high glucose (25 mM) medium. The percentage of insulin positive cells in the EX-4 treated group was ap- proximately 4-fold higher than in the EX-4 untreated ADMSCs.

CONCLUSION

The present study has demonstrated that EX-4 enhances the differen- tiation of ADMSCs into IPCs. Improvement of this method may help the formation of an unlimited source of cells for transplantation.

Chronic continuous exenatide infusion does not cause pancreatic inflammation and ductal hyperplasia in non-human primates

In this study, we aimed to evaluate the effects of exenatide (EXE) treatment on exocrine pancreas of nonhuman primates. To this end, 52 baboons (Papio hamadryas) underwent partial pancreatectomy, followed by continuous infusion of EXE or saline (SAL) for 14 weeks. Histological analysis, immunohistochemistry, Computer Assisted Stereology Toolbox morphometry, and immunofluorescence staining were performed at baseline and after treatment. The EXE treatment did not induce pancreatitis, parenchymal or periductal inflammatory cell accumulation, ductal hyperplasia, or dysplastic lesions/pancreatic intraepithelial neoplasia. At study end, Ki-67-positive (proliferating) acinar cell number did not change, compared with baseline, in either group. Ki-67-positive ductal cells increased after EXE treatment (P = 0.04). However, the change in Ki-67-positive ductal cell number did not differ significantly between the EXE and SAL groups (P = 0.13). M-30-positive (apoptotic) acinar and ductal cell number did not change after SAL or EXE treatment. No changes in ductal density and volume were observed after EXE or SAL. Interestingly, by triple-immunofluorescence staining, we detected c-kit (a marker of cell transdifferentiation) positive ductal cells co-expressing insulin in ducts only in the EXE group at study end, suggesting that EXE may promote the differentiation of ductal cells toward a β-cell phenotype. In conclusion, 14 weeks of EXE treatment did not exert any negative effect on exocrine pancreas, by inducing either pancreatic inflammation or hyperplasia/dysplasia in nonhuman primates.

Molecular mechanisms underlying physiological and receptor pleiotropic effects mediated by GLP-1R activation

The incidence of type 2 diabetes in developed countries is increasing yearly with a significant negative impact on patient quality of life and an enormous burden on the healthcare system. Current biguanide and thiazolidinedione treatments for type 2 diabetes have a number of clinical limitations, the most serious long-term limitation being the eventual need for insulin replacement therapy (Table 1). Since 2007, drugs targeting the glucagon-like peptide-1 (GLP-1) receptor have been marketed for the treatment of type 2 diabetes. These drugs have enjoyed a great deal of success even though our underlying understanding of the mechanisms for their pleiotropic effects remain poorly characterized even while major pharmaceutical companies actively pursue small molecule alternatives. Coupling of the GLP-1 receptor to more than one signalling pathway (pleiotropic signalling) can result in ligand-dependent signalling bias and for a peptide receptor such as the GLP-1 receptor this can be exaggerated with the use of small molecule agonists. Better consideration of receptor signalling pleiotropy will be necessary for future drug development. This is particularly important given the recent failure of taspoglutide, the report of increased risk of pancreatitis associated with GLP-1 mimetics and the observed clinical differences between liraglutide, exenatide and the newly developed long-acting exenatide long acting release, albiglutide and dulaglutide.

Dipeptidyl peptidase-4 (DPP-4): Localization and activity in human and rodent islets

Dipeptidyl peptidase 4 (DPP-4) was recently found to be expressed in human and mouse islets with different expression patterns. However, whether species-dependent expression pattern is a generalized phenomenon and whether islet DPP-4 activity is regulated are not known. This study was conducted to investigate DPP-4 localization in several different species, and to examine the impact of glucose, incretin hormones, and insulin on islet DPP-4 activity. It was shown by immuofluorescent staining that there were two distinct species-specific expression patterns of islet DPP-4. The enzyme was expressed exclusively in α-cells in human and pig islets, but primarily in β-cells in mouse and rat islets. INS-1 832/13 cells also expressed DPP-4, and inhibition of DPP-4 enhanced insulin secretion in the presence of glucagon-like peptide-1 (GLP-1) in the cells. DPP-4 activity was remarkably robust when cultured with high glucose, incretin hormones, and insulin in mouse and human islets as well as INS-1 832/13 cells and islet DPP-4 activity and expression pattern was not altered in double incretin receptor knockout mice, compared to wild type mice. We conclude that islet DPP-4 is species-specifically expressed in α-cell and β-cell dominant patterns in several species and both patterns remained robust in enzyme activity during short-term metabolic challenge.

Oxidative modification, inflammation and amyloid in the normal and diabetic cat pancreas

The pathogenesis of β-cell dysfunction leading to pancreatic β-cell failure seen in type 2 diabetes mellitus is incompletely understood. Pancreatic tissues were collected from nine control cats and nine diabetic cats and labelled immunohistochemically to examine expression of interleukin (IL)-1β, insulin, islet amyloid polypeptide (IAPP) and 4-hydroxynonenal (4-HNE). Thioflavin-S was used to stain for amyloid. All control cats showed positive labelling for IL-1β and 4-HNE. Diabetic cats showed varying degrees of inflammation and oxidative modification, owing in large part to the very small amount of islet structure remaining in the typical diabetic cat pancreas. Amyloid deposition was identified in 8/9 diabetic cats and 1/9 control cats. In order to validate these findings, paired biopsy samples taken from an additional group of cats enrolled in a study of obesity and hyperglycaemia (sampling at baseline and after 8-16 weeks of obesity and hyperglycaemia) were labelled for IL-1β and 4-HNE. A similar pattern of labelling was identified in the baseline samples to that seen in control cats. A significant increase in IL-1β and 4-HNE expression was seen after a period of hyperglycaemia and obesity. Taken together, these findings suggest that while present in normal cats, markers of inflammation and oxidative modification increase very early during the development of disease. Future studies focusing on these earlier time points are needed to understand the factors that function in protection of the islet β cell and the development of islet pathology in type 2 diabetes mellitus in the cat.

Incretins: their physiology and application in the treatment of diabetes mellitus

Therapies targeting the action of incretin hormones have been under close scrutiny in recent years. The incretin effect has been defined as postprandial enhancement of insulin secretion by gut-derived factors. Likewise, incretin mimetics and incretin effect amplifiers are the two different incretin-based treatment strategies developed for the treatment of diabetes. Although, incretin mimetics produce effects very similar to those of natural incretin hormones, incretin effect amplifiers act by inhibiting dipeptidyl peptidase-4 (DPP-4) enzyme to increase plasma concentration of incretins and their biologic effects. Because glucagon-like peptide-1 (GLP-1) is an incretin hormone with various anti-diabetic actions including stimulation of glucose-induced insulin secretion, inhibition of glucagon secretion, hepatic glucose production and gastric emptying, it has been evaluated as a novel therapeutic agent for the treatment of type 2 diabetes mellitus (T2DM). GLP-1 also manifests trophic effects on pancreas such as pancreatic beta cell growth and differentiation. Because DPP-4 is the enzyme responsible for the inactivation of GLP-1, DPP-4 inhibition represents another potential strategy to increase plasma concentration of GLP-1 to enhance the incretin effect. Thus, anti-diabetic properties of these two classes of drugs have stimulated substantial clinical interest in the potential of incretin-based therapeutic agents as a means to control glucose homeostasis in T2DM patients. Despite this fact, clinical use of GLP-1 mimetics and DPP-4 inhibitors have raised substantial concerns owing to possible side effects of the treatments involving increased risk for pancreatitis, and C-cell adenoma/carcinoma. Thus, controversial issues in incretin-based therapies under development are reviewed and discussed in this manuscript.

A fusion protein derived from plants holds promising potential as a new oral therapy for type 2 diabetes

The incretin hormone glucagon-like peptide-1 (GLP-1) is recognized as a promising candidate for the treatment of type 2 diabetes (T2D), with one of its mimetics, exenatide (synthetic exendin-4) having already been licensed for clinical use. We seek to further improve the therapeutic efficacy of exendin-4 (Ex-4) using innovative fusion protein technology. Here, we report the production in plants a fusion protein containing Ex-4 coupled with human transferrin (Ex-4-Tf) and its characterization. We demonstrated that plant-made Ex-4-Tf retained the activity of both proteins. In particular, the fusion protein stimulated insulin release from pancreatic β-cells, promoted β-cell proliferation, stimulated differentiation of pancreatic precursor cells into insulin-producing cells, retained the ability to internalize into human intestinal cells and resisted stomach acid and proteolytic enzymes. Importantly, oral administration of partially purified Ex-4-Tf significantly improved glucose tolerance, whereas commercial Ex-4 administered by the same oral route failed to show any significant improvement in glucose tolerance in mice. Furthermore, intraperitoneal (IP) injection of Ex-4-Tf showed a beneficial effect in mice similar to IP-injected Ex-4. We also showed that plants provide a robust system for the expression of Ex-4-Tf, producing up to 37 μg prEx-4-Tf/g fresh leaf weight in transgenic tobacco and 137 μg prEx-4-Tf/g freshweight in transiently transformed leaves of N. benthamiana. These results indicate that Ex-4-Tf holds substantial promise as a new oral therapy for type 2 diabetes. The production of prEx-4-Tf in plants may offer a convenient and cost-effective method to deliver the antidiabetic medicine in partially processed plant food products.

Anti-diabetic actions of glucagon-like peptide-1 on pancreatic beta-cells

Glucagon-like peptide-1 (GLP-1), an incretin hormone, is released from intestinal L-cells in response to nutrients. GLP-1 lowers blood glucose levels by stimulating insulin secretion from pancreatic beta-cells in a glucose-dependent manner. In addition, GLP-1 slows gastric emptying, suppresses appetite, reduces plasma glucagon, and stimulates glucose disposal, which are beneficial for glucose homeostasis. Therefore, incretin-based therapies such as GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase IV, an enzyme which inactivates GLP-1, have been developed for treatment of diabetes. This review outlines our knowledge of the actions of GLP-1 on insulin secretion and biosynthesis, beta-cell proliferation and regeneration, and protection against beta-cell damage, as well as the involvement of recently discovered signaling pathways of GLP-1 action, mainly focusing on pancreatic beta-cells.

Exendin-4 effects on islet volume and number in mouse pancreas

The aim of this study was to evaluate Exendin-4 (EX-4) effects on islet volume and number in the mouse pancreas. Thirty-two healthy adult male NMRI mice were randomly divided into control and experimental groups. EX-4 was injected intraperitoneally (i. p.) at doses of 0.25 (E1 group), 0.5 (E2 group), and 1 µg/kg (E3 group), twice a day for 7 consecutive days. One day after the final injection, the mice were sacrificed, and the pancreas from each animal dissected out, weighed, and fixed in 10% formalin for measurement of pancreas and islet volume, and determination of islet number by stereological assessments. There was a significant increase in the weight of pancreases in the E3 group. Islet and pancreas volumes in E1 and E2 groups were unchanged compared to the control group. The E3 group showed a significant increase in islet and pancreas volume (P < 0.05). There were no significant changes in the total number of islets in all three experimental groups. The results revealed that EX-4 increased pancreas and islet volume in non-diabetic mice. The increased total islet mass is probably caused by islet hypertrophy without the formation of additional islets.

Incretin hormones and beta-cell mass expansion: what we know and what is missing?

Pancreatic beta-cell mass expands through beta-cell proliferation and neogenesis while it decreases mainly via apoptosis. The loss of balance between beta-cell death and regeneration leads to a reduction of beta-cell functional mass, thus contributing to the pathogenesis of type 2 diabetes mellitus (T2DM). The pathogenetic mechanisms causing T2DM are complex, and also include a significant reduction of the incretin effect. A better understanding of the role of incretin hormones in glucose homeostasis has led to the development of incretin-based therapies. Recently, incretin hormones have been shown to stimulate the beta-cell growth and differentiation from pancreas-derived stem/progenitor cells, as well as to exert cytoprotective, antiapoptotic effects on beta-cells. However, the role and the molecular mechanisms by which GLP-1 and its agonists regulate beta-cell mass have not been fully investigated. This review focuses the current findings and the missing understanding of the effects of incretin hormones on beta-cell mass expansion.

Glucagon-like peptide-1: modulator of β-cell dysfunction and death

Glucagon-like peptide-1 (GLP-1) is one of the hormones responsible for the incretin effect, a term that refers to the observation that orally administered glucose results in a larger increase in plasma insulin levels and insulin-dependent decrease in blood glucose concentration when compared to the same amount of glucose given intravenously. GLP-1 is secreted mainly by gut endocrine L-cells and is released under the control of carbohydrates, proteins and lipids. Upon secretion, GLP-1 targets different cell types and exerts a wide variety of actions such as potentiation of glucose-stimulated insulin secretion, reduction of appetite, delay of gastric emptying and increase in β-cell mass. These beneficial effects have resulted in the application of GLP-1-based therapies in patients with type 2 diabetes, but also exploitation of its effects in type 1 diabetes is being envisaged. In this review, we focus on the different, short- and long-term action mechanisms of GLP-1 with specific emphasis on its role as a modulator of β-cell function and survival.

The influence of matrix properties on growth and morphogenesis of human pancreatic ductal epithelial cells in 3D

A highly tunable synthetic biomimetic hydrogel platform was developed to study the growth and morphogenesis of pancreatic ductal epithelial cells (PDEC) under the influence of a myriad of instructive cues. A PDEC line, PANC-1, was used as a model system to illustrate the importance of matrix compositions on cell fate determination. PANC-1 is an immortalized ductal epithelial cell line widely used in the study of pancreatic tumor cell behaviors. PANC-1 cells are also increasingly explored as a potential cell source for endocrine differentiation. Thus far, most studies related to PANC-1, among other PDEC lines, are performed on 2D culture surfaces. Here, we evaluated the effect of matrix compositions on PANC-1 cell growth and morphogenesis in 3D. Specifically, PANC-1 cells were encapsulated in PEG-based hydrogels prepared by step-growth thiol-ene photopolymerization. It was found that thiol-ene hydrogels provided a cytocompatible environment for encapsulation and 3D culture of PANC-1 cells. In contrast to a monolayer morphology on 2D culture surfaces, PANC-1 cells formed clusters in 3D thiol-ene hydrogels within 4 days of culture. After culturing for 10 days, however, the growth and structures of these clusters were significantly impacted by gel matrix properties, including sensitivity of the matrix to proteases, stiffness of the matrix, and ECM-mimetic motifs. The use of matrix metalloproteinase (MMP) sensitive linker or the immobilization of fibronectin-derived RGDS ligand in the matrix promoted PANC-1 cell growth and encouraged them to adopt ductal cyst-like structures. On the other hand, the encapsulated cells formed smaller and more compact aggregates in non-MMP responsive gels. The incorporation of laminin-derived YIGSR peptide did not enhance cell growth and caused the cells to form compact aggregates. Immobilized YIGSR also enhanced the expression of epithelial cell markers including β-catenin and E-cadherin. These studies have established PEG-peptide hydrogels formed by thiol-ene photo-click reaction as a suitable platform for studying and manipulating pancreatic epithelial cell growth and morphogenesis in 3D.

Incretin-based therapy for type 2 diabetes mellitus: pancreatic and extrapancreatic effects

The prevalence of type 2 diabetes mellitus has increased at an alarming rate in recent years. Recent estimations project that 366 million people could have diabetes by 2030. The incretin system emerges as a new target for type 2 diabetes therapy, and new molecules are being approved for its use in humans since the year 2005. These agents could be divided into 2 main groups, glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 inhibitors. Endogenous GLP-1 is an incretin hormone composed by a 30-amino acid peptide and is secreted from L-cells in distal small intestine in response to calorie intake, causing a glucose-dependent β-cell response resulting in a restoration of the first-phase insulin response. Additionally, GLP-1 regulates glucagon production, which leads to inhibition of glucogenolysis and gluconeogenesis in the liver. Synthetic molecules such as exenatide and liraglutide have been developed to bind GLP-1 receptor and mimic GLP-1 effects in pancreatic cells and other target organs.

Vildagliptin preserves the mass and function of pancreatic β cells via the developmental regulation and suppression of oxidative and endoplasmic reticulum stress in a mouse model of diabetes

AIM

We investigated the molecular mechanisms by which vildagliptin preserved pancreatic β cell mass and function.

METHODS

Morphological, biochemical and gene expression profiles of the pancreatic islets were investigated in male KK-A(y) -TaJcl(KK-A(y) ) and C57BL/6JJcl (B6) mice aged 8 weeks which received either vildagliptin or a vehicle for 4 weeks.

RESULTS

Body weight, food intake, fasting blood glucose, plasma insulin and active glucagon-like peptide-1 were unchanged with vildagliptin treatment in both mice. In KK-A(y) mice treated with vildagliptin, increased plasma triglyceride (TG) level and islet TG content were decreased, insulin sensitivity significantly improved, and the glucose tolerance ameliorated with increases in plasma insulin levels. Furthermore, vildagliptin increased glucose-stimulated insulin secretion, islet insulin content and pancreatic β cell mass in both strains. By vildagliptin, the expression of genes involved in cell differentiation/proliferation was upregulated in both strains, those related to apoptosis, endoplasmic reticulum stress and lipid synthesis was decreased and those related to anti-apoptosis and anti-oxidative stress was upregulated, in KK-A(y) mice. The morphological results were consistent with the gene expression profiles.

CONCLUSION

Vildagliptin increases β cell mass by not only directly affecting cell kinetics but also by indirectly reducing cell apoptosis, oxidative stress and endoplasmic reticulum stress in diabetic mice.

N -acetyl-GLP-1: a DPP IV-resistant analogue of glucagon-like peptide-1 (GLP-1) with improved effects on pancreatic β-cell-associated gene expression

Glucagon-like peptide-1(7-36)amide (GLP-1) is a key insulinotropic hormone with the reported potential to differentiate non-insulin secreting cells into insulin-secreting cells. The short biological half-life of GLP-1 after cleavage by dipeptidylpeptidase IV (DPP IV) to GLP-1(9-36)amide is a major therapeutic drawback. Several GLP-1 analogues have been developed with improved stability and insulinotropic action. In this study, the N-terminally modified GLP-1 analogue, N-acetyl-GLP-1, was shown to be completely resistant to DPP IV, unlike native GLP-1, which was rapidly degraded. Furthermore, culture of pancreatic ductal ARIP cells for 72 h with N-acetyl-GLP-1 indicated a greater ability to induce pancreatic beta-cell-associated gene expression, including insulin and glucokinase. Further investigation of the effects of stable GLP-1 analogues on beta-cell differentiation is required to assess their potential in diabetic therapy.

Review article: a comparison of glucagon-like peptides 1 and 2

BACKGROUND

Recent advancements in understanding the roles and functions of glucagon-like peptide 1 (GLP-1) and 2 (GLP-2) have provided a basis for targeting these peptides in therapeutic strategies.

AIM

To summarise the preclinical and clinical research supporting the discovery of new therapeutic molecules targeting GLP-1 and GLP-2.

METHODS

This review is based on a comprehensive PubMed search, representing literature published during the past 30 years related to GLP-1 and GLP-2.

RESULTS

Although produced and secreted together primarily from L cells of the intestine in response to ingestion of nutrients, GLP-1 and GLP-2 exhibit distinctive biological functions that are governed by the expression of their respective receptors, GLP-1R and GLP-2R. Through widespread expression in the pancreas, intestine, nervous tissue, et cetera, GLP-1Rs facilitates an incretin effect along with effects on appetite and satiety. GLP-1 analogues resistant to degradation by dipeptidyl peptidase-IV and inhibitors of dipeptidyl peptidase-IV have been developed to aid treatment of diabetes and obesity. The GLP-2R is expressed almost exclusively in the stomach and bowel. The most apparent role for GLP-2 is its promotion of growth and function of intestinal mucosa, which has been targeted for therapies that promote repair and adaptive growth. These are used as treatments for intestinal failure and related conditions.

CONCLUSIONS

Our growing understanding of the biology and function of GLP-1, GLP-2 and corresponding receptors has fostered further discovery of fundamental biological function as well as new categories of potent therapeutic medicines.

Peripheral Pathways in the Food-Intake Control towards the Adipose-Intestinal Missing Link

In the physiological state a multitude of gut hormones are released into the circulation at the same time depending on the quality and quantity of the diet. These hormones interact with receptors at various points in the "gut-brain axis" to affect short-term and intermediate-term feelings of hunger and satiety. The combined effects of macronutrients on the predominant gut hormone secretion are still poorly understood. Besides, adipokines form an important part of an "adipoinsular axis" dysregulation which may contribute to β -cell failure and hence to type 2 diabetes mellitus (T2DM). Even more, gestational diabetes mellitus (GDM) and T2DM seem to share a genetic basis. In susceptible individuals, chronic exaggerated stimulation of the proximal gut with fat and carbohydrates may induce overproduction of an unknown factor that causes impairment of incretin production and/or action, leading to insufficient or untimely production of insulin, so that glucose intolerance develops. The bypass of the duodenum and jejunum might avoid a putative hormone overproduction in the proximal foregut in diabetic patients that might counteract the action of insulin, while the early presentation of undigested or incompletely digested food to the ileum may anticipate the production of hormones such as GLP1, further improving insulin action.

Micro/nanoscale technologies for the development of hormone-expressing islet-like cell clusters

Insulin-expressing islet-like cell clusters derived from precursor cells have significant potential in the treatment of type-I diabetes. Given that cluster size and uniformity are known to influence islet cell behavior, the ability to effectively control these parameters could find applications in the development of anti-diabetic therapies. In this work, we combined micro and nanofabrication techniques to build a biodegradable platform capable of supporting the formation of islet-like structures from pancreatic precursors. Soft lithography and electrospinning were used to create arrays of microwells (150-500 μm diameter) structurally interfaced with a porous sheet of micro/nanoscale polyblend fibers (~0.5-10 μm in cross-sectional size), upon which human pancreatic ductal epithelial cells anchored and assembled into insulin-expressing 3D clusters. The microwells effectively regulated the spatial distribution of the cells on the platform, as well as cluster size, shape and homogeneity. Average cluster cross-sectional area (~14000-17500 μm(2)) varied in proportion to the microwell dimensions, and mean circularity values remained above 0.7 for all microwell sizes. In comparison, clustering on control surfaces (fibers without microwells or tissue culture plastic) resulted in irregularly shaped/sized cell aggregates. Immunoreactivity for insulin, C-peptide and glucagon was detected on both the platform and control surfaces; however, intracellular levels of C-peptide/cell were ~60 % higher on the platform.

The global transcriptional response of isolated human islets of langerhans to glucagon-like Peptide-1 receptor agonist liraglutide

GLP-1 and its analog have been used in diabetes treatment; however, the direct alteration of gene expression profile in human islets induced by GLP-1 has not been reported. In present study, transcriptional gene expression in the liraglutide-treated human islets was analyzed with 12 human U133A chips including 23000 probe sets. The data compared between liraglutide and control groups showed a significant difference on glucose-induced insulin secretion, rather than viability. Microarray analysis identified 7000 genes expressed in human islets. Eighty genes were found to be modulated by liraglutide treatment. Furthermore, the products of these genes are proteins involved in binding capability, enzyme activity, transporter function, signal transduction, cell proliferation, apoptosis, and cell differentiation. Our data provides a set of information in the complex events, following the activation of the GLP-1 receptor in the islets of Langerhans.

Characterization of insulin-producing cells derived from PDX-1-transfected neural stem cells

Islet cell transplantation is a promising treatment strategy for type-1 diabetes. However, functional islet cells are hard to obtain for transplantation and are in short supply. Directing the differentiation of stem cells into insulin‑producing cells, which serve as islet cells, would overcome this shortage. Bone marrow contains hematopoietic stem cells and mesenchymal stem cells. The present study used bone marrow cells isolated from rats and neural stem cells (NSCs) that were derived from bone marrow cells in culture. Strong nestin staining was detected in NSCs, but not in bone marrow stromal cells (BMSCs). In vitro transfection of the pancreatic duodenal homeobox-1 (PDX-1) gene into NSCs generated insulin‑producing cells. Reverse transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) analysis confirmed that PDX-1-transfected NSCs expressed insulin mRNA and released insulin protein. However, insulin release from PDX-1-transfected NSCs did not respond to the challenge of glucose and glucagon-like peptide-1. These results support the use of bone marrow-derived NSCs as a renewable source of insulin-producing cells for autologous transplantation to treat type-1 diabetes.

Serum deprivation induces glucose response and intercellular coupling in human pancreatic adenocarcinoma PANC-1 cells

OBJECTIVE

This study aimed to investigate whether the previously described differentiating islet-like aggregates of human pancreatic adenocarcinoma cells (PANC-1) develop glucose response and exhibit intercellular communication.

METHODS

Fura 2-loaded PANC-1 cells in serum-free medium were assayed for changes in cytosolic free calcium ([Ca]i) induced by depolarization, tolbutamide inhibition of K(ATP) channels, or glucose. Dye transfer, assayed by confocal microscopy or by FACS, was used to detect intercellular communication. Changes in messenger RNA (mRNA) expression of genes of interest were assessed by quantitative real-time polymerase chain reaction. Proliferation was assayed by the MTT method.

RESULTS

Serum-deprived PANC-1 cell aggregates developed [Ca]i response to KCl, tolbutamide, or glucose. These responses were accompanied by 5-fold increase in glucokinase mRNA level and, to a lesser extent, of mRNAs for K(ATP) and L-type calcium channels, as well as increase in mRNA levels of glucagon and somatostatin. Trypsin, a proteinase-activated receptor 2 agonist previously shown to enhance aggregation, modestly improved [Ca]i response to glucose. Glucose-induced coordinated [Ca]i oscillations and dye transfer demonstrated the emergence of intercellular communication.

CONCLUSIONS

These findings suggest that PANC-1 cells, a pancreatic adenocarcinoma cell line, can be induced to express a differentiated phenotype in which cells exhibit response to glucose and form a functional syncytium similar to those observed in pancreatic islets.

Exendin-4 increases islet amyloid deposition but offsets the resultant beta cell toxicity in human islet amyloid polypeptide transgenic mouse islets

AIMS/HYPOTHESIS

In type 2 diabetes, aggregation of islet amyloid polypeptide (IAPP) into amyloid is associated with beta cell loss. As IAPP is co-secreted with insulin, we hypothesised that IAPP secretion is necessary for amyloid formation and that treatments that increase insulin (and IAPP) secretion would thereby increase amyloid formation and toxicity. We also hypothesised that the unique properties of the glucagon-like peptide-1 (GLP-1) receptor agonist exendin-4 to maintain or increase beta cell mass would offset the amyloid-induced toxicity.

METHODS

Islets from amyloid-forming human IAPP transgenic and control non-transgenic mice were cultured for 48 h in 16.7 mmol/l glucose alone (control) or with exendin-4, potassium chloride (KCl), diazoxide or somatostatin. Human IAPP and insulin release, amyloid deposition, beta cell area/islet area, apoptosis and AKT phosphorylation levels were determined.

RESULTS

In control human IAPP transgenic islets, amyloid formation was associated with increased beta cell apoptosis and beta cell loss. Increasing human IAPP release with exendin-4 or KCl increased amyloid deposition. However, while KCl further increased beta cell apoptosis and beta cell loss, exendin-4 did not. Conversely, decreasing human IAPP release with diazoxide or somatostatin limited amyloid formation and its toxic effects. Treatment with exendin-4 was associated with an increase in AKT phosphorylation compared with control and KCl-treated islets.

CONCLUSIONS/INTERPRETATION

IAPP release is necessary for islet amyloid formation and its toxic effects. Thus, use of insulin secretagogues to treat type 2 diabetes may result in increased islet amyloidogenesis and beta cell death. However, the AKT-associated anti-apoptotic effects of GLP-1 receptor agonists such as exendin-4 may limit the toxic effects of increased islet amyloid.

Activation of the GLP-1 receptor signalling pathway: a relevant strategy to repair a deficient beta-cell mass

Recent preclinical studies in rodent models of diabetes suggest that exogenous GLP-1R agonists and DPP-4 inhibitors have the ability to increase islet mass and preserve beta-cell function, by immediate reactivation of beta-cell glucose competence, as well as enhanced beta-cell proliferation and neogenesis and promotion of beta-cell survival. These effects have tremendous implication in the treatment of T2D because they directly address one of the basic defects in T2D, that is, beta-cell failure. In human diabetes, however, evidence that the GLP-1-based drugs alter the course of beta-cell function remains to be found. Several questions surrounding the risks and benefits of GLP-1-based therapy for the diabetic beta-cell mass are discussed in this review and require further investigation.

Differentiation of rat pancreatic duct-derived stem cells into insulin-secreting cells in vitro

AIM: To isolate and identify rat pancreatic duct-derived stem cells (PDSCs) and to induce their differentiation into insulin-secreting cells in vitro.

METHODS: The pancreas of rats underwent in situ collagenase digestion, and PDSCs were obtained by adherent cultivation. The morphology and phenotypes of PDSCs were characterized. PDSCs were then cultured in serum-free medium containing Matrigel and exendin-4 to induce their differentiation into insulin-secreting cells. The morphology, phenotypes, and functions of the obtained insulin-secreting cells were then characterized.

RESULTS: Rat PDSCs had a typical fibroblast-like shape, grew rapidly in an adherent manner in serum-containing medium, and belonged to mesenchymal stem cells (MSCs) which expressed PDX-1 and nestin. Serum-free cultivation could induce PDSCs to differentiate into islet-like cell clusters (ICCs) that possessed the capability of secreting insulin.

CONCLUSION: Rat PDSCs belong to MSCs which express PDX-1 and nestin and could differentiate into insulin-secreting cells in vitro.

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.

Exenatide Use in the Management of Type 2 Diabetes Mellitus

Exenatide is a GLP-1 (glucagon-like peptide-1) agonist that has been approved in the UK for use in the management of Type 2 Diabetes Mellitus (T2DM) since 2006. It acts by increasing glucose-induced insulin release and by reducing glucagon secretion postprandially. It therefore increases insulin secretion and reduces glucose levels, especially postprandially. It also reduces gastric emptying and acts centrally to promote satiety. In clinical practice it reduces HbA1c (range; -0.4% to -1.3%), fasting and postprandial blood glucose levels and is the only antidiabetic agent (together with liraglutide; a human GLP-1 analogue) to promote weight loss (range; -1.5 kg to -5.5 kg). It can be used as monotherapy or in combination with metformin and/or sulphonylureas (SU) and/or thiazolinediones (TZD). When compared with insulin it causes similar reductions in HbA1c and glucose levels, but unlike insulin it has the advantage of inducing weight loss. Its main side effect is gastrointestinal (GI) disturbances; nausea is the commonest GI adverse effect, albeit usually mild and transient. Hypoglycaemia is uncommon, especially when used as monotherapy or in combination with metformin. In this review article we scrutinize the currently available evidence for use of exenatide in the management of T2DM.

Roux-en-Y gastric bypass promotes expression of PDX-1 and regeneration of β-cells in Goto-Kakizaki rats

AIM: To study the effects of Roux-en-Y gastric bypass (RYGB) on the expression of pancreatic duodenal homeobox-1 (PDX-1) and pancreatic β-cell regeneration/ neogenesis, and their possible mechanisms in diabetics.

METHODS: Three groups of randomly selected non-obese diabetic Goto-Kakizaki (GK) rats were subjected to RYGB, sham-RYGB and sham-operation (sham-op) surgery, respectively. The rats were euthanized at post-operative 1, 2, 4 and 12 wk. Their pancreases were resected and analyzed using reverse transcription polymerase chain reaction to detect the mRNA of PDX-1. Anti-PDX-1 immunohistochemical (IHC) staining and Western blotting were used to detect the protein of PDX-1. Double IHC staining of anti-Brdu and -insulin was performed to detect regenerated β-cells. The index of double Brdu and insulin positive cells was calculated.

RESULTS: In comparison with sham-RYGB and sham-op groups, a significant increase in the expressions of PDX-1 mRNA in RYGB group was observed at all experimental time points (1 wk: 0.378 ± 0.013 vs 0.120 ± 0.010, 0.100 ± 0.010, F = 727.717, P < 0.001; 2 wk: 0.318 ± 0.013 vs 0.110 ± 0.010, 0.143 ± 0.015, F = 301.509, P < 0.001; 4 wk: 0.172 ± 0.011 vs 0.107 ± 0.012, 0.090 ± 0.010, F = 64.297, P < 0.001; 12 wk: 0.140 ± 0.007 vs 0.120 ± 0.010, 0.097 ± 0.015, F = 16.392, P < 0.001); PDX-1 protein in RYGB group was also increased significantly (1 wk: 0.61 ± 0.01 vs 0.21 ± 0.01, 0.15 ± 0.01, F = 3031.127, P < 0.001; 2 wk: 0.55 ± 0.00 vs 0.15 ± 0.01, 0.17 ± 0.01, F = 3426.455, P < 0.001; 4 wk: 0.39 ± 0.01 vs 0.18 ± 0.01, 0.22 ± 0.01, F = 882.909, P < 0.001; 12 wk: 0.41 ± 0.01 vs 0.20 ± 0.01, 0.18 ± 0.01, F = 515.833, P < 0.001). PDX-1 mRNA and PDX-1 protein production showed no statistical significance between the two sham groups. Many PDX-1 positive cells could be found in the pancreatic islets of the rats in RYGB group at all time points. In addition, the percentage of Brdu-insulin double staining positive cells was higher in RYGB group than in the other two groups (1 wk: 0.22 ± 0.13 vs 0.03 ± 0.06, 0.03 ± 0.06, P < 0.05; 2 wk: 0.28 ± 0.08 vs 0.00 ± 0.00, 0.03 ± 0.06, P < 0.05; 4 wk: 0.24 ± 0.11 vs 0.07 ± 0.06, 0.00 ± 0.00, P < 0.001; 12 wk: 0.20 ± 0.07 vs 0.03 ± 0.06, 0.00 ± 0.00, P < 0.05).

CONCLUSION: RYGB can increase the expression of pancreatic PDX-1 and induce the regeneration of β-cells in GK rats. The associated regeneration of islet cells may be a possible mechanism that how RYGB could improve type 2 diabetes mellitus.