Pancreatic beta-cell growth and diabetes mellitus

Identification, measurement, and evaluation of blood concentrations of insulin glargine and insulin lispro by UPLC-MS-MS in a dead body suspected of insulin overdose

Insulin preparations, which are drug treatments for diabetes, cause fatal hypoglycemia when an overdose is administered. Cases of homicide and suicide using these preparations have been reported and are of great forensic interest. However, there are few reports assessing the postmortem concentration of insulin preparations, and it is often difficult to determine the cause of death. In the present study, we report a case of a suspected insulin glargine and insulin lispro overdose for suicide. A woman in her 30s had a history of mental illness and diabetes. The day before her death, she reported to her boyfriend that she had taken large doses of insulin preparations and prescription drugs. An autopsy revealed no fatal injuries or lesions. Drug screening tests revealed several prescription drugs, none of which showed toxic concentrations. Analysis using LC-MS/MS detected insulin glargine in the peripheral and cardiac blood at 429 μU/mL and 1362 μU/mL, respectively, whereas insulin lispro was detected in both the peripheral and cardiac blood at levels below the lower limit of quantification (LLOQ; <50 μU/mL). The cause of death was considered likely to be hypoglycemia caused by an overdose of insulin glargine. Insulin glargine is rapidly metabolized after subcutaneous administration and is rarely detected in the blood when used at therapeutic doses. There are no other reports on the quantification of insulin glargine parent compounds in postmortem samples, and this case provides important data on postmortem blood concentrations of insulin glargine intoxication.

Discrete and Continuous Glucose Monitoring Systems: The Point of View of a Patient Affected by Type-1 Diabetes

This work represents the point of view of a diabetic patient with an indirect experience in this specific field of research. As a chemical engineer and researcher in drug carrier production, he has always approached type-1 diabetes (T1D) in a scientific manner. Therefore, this work represents a description of almost 20 years of this illness treatment using a multi-injection insulin system, compared with the experience acquired with a newly adopted micro-infusion system, allowing automatized insulin administration. The use of the continuous system reduced significantly the Hb1Ac average values, from 8.8% to 6.6%, in less than 2 years. Moreover, a full 24 h control guaranteed the almost total elimination of the hypoglycemia risk, thanks to the automated control system, that can stop insulin administration in order to prevent critical situations. It is also important to note that the point of view underlined in this work does not presume to be that of a doctor or of a researcher who works closely in the field of medicine or diabetology. However, the author wants to highlight that doctors could try to educate patients to a scientific approach to treat illnesses correctly. The author experienced the very common difficulties related to the use of insulin with multi-injection administration for many years; then, he was proposed to start treatment with the automated pump mechanism. In this work, the author provides comments on the physical and psychological advantages and disadvantages of both insulin release systems, in order to define their impact on a patient’s daily life. This work may also represent a vademecum for patients during the beginning of diabetes treatment, helped by the constant support and advice of a medical doctor.

Insulin sensitivity in male sheep born to ewes treated with testosterone during pregnancy

In animal models, exposure to excess testosterone during gestation induces polycystic ovary syndrome (PCOS)-like reproductive and metabolic traits in female offspring, suggesting that the hyperandrogenemic intrauterine environment may have a role in the etiology of PCOS. Additionally, few studies have also addressed metabolic and reproductive outcomes in male offspring. In the present study, the intravenous glucose tolerance test (IGTT) was used to assess the insulin-glucose homeostasis at various ages during sexual development in male sheep born to testosterone-treated ewes. To further analyze the programming effect of testosterone on insulin-glucose homeostasis, indexes of insulin sensitivity were assessed in orchidectomized post-pubertal males born to testosterone-treated ewes (Torq-males) and orchidectomized post-puberal controls (Corq-males) before and 48 h after a testosterone injection. There was no difference in insulin sensitivity indexes between males born to testosterone-treated ewes (T-males) and control males born to control ewes (C-males) at 5, 10, 20 and 30 weeks of age, representing the infantile, early and late pre-pubertal, and early post-pubertal stage of sexual development, respectively. In orchidectomized males, basal levels of insulin and glucose were not different between both groups before and after the testosterone injection; however, Torq-males released more insulin before and after T challenge during the first 20 min of the test. Despite this, plasma glucose concentrations were not different in both groups during IVGTT, resulting in an insulin sensitivity index composite similar between groups. We concluded that the effect of prenatal exposure to excess testosterone may reprogram the pancreatic β-cells insulin release in ovine males, with effects more evident in castrated males versus intact males.

Hibiscus sabdariffa renews pancreatic β-cells in experimental type 1 diabetic model rats

This study evaluated the antidiabetic potentials of flavonoid-rich aqueous fraction of methanolic extract of Hibiscus sabdariffa calyx (HSCE) on the pancreatic β-cells of experimental type I diabetic model rats. Type 1 diabetes mellitus was induced in Wistar rats by a single intraperitoneal injection of 80mg/kg b/w streptozotocin (STZ) dissolved in 0.1M citrate buffer (pH 6.3). The rats were divided into five groups (n=12) including normal control group, test group I, diabetic negative control, test group II, and diabetic positive control. The test groups received 1.75g/kg b/w of HSCE by gavage for 15 days. Animals were sacrificed; the splenic portion of their pancreas and serum were evaluated for histopathological and biochemical parameters respectively. The regenerative effects of the extract on STZ-diabetes β-cells damage was evident from the results of the histopathological analysis and the biochemical parameters evaluated in the serum. Reduced levels of glutathione, catalase and superoxide dismutase in the serum of diabetic rats were significantly improved in the H. sabdariffa-treated rats (P<0.05). Histological examination of pancreatic islet sections revealed degenerative and necrotic changes (D) in the pancreatic islet of Langerhans, β-cell degranulation, pyknotic β-cell nuclei, decreased islet cellular density, and severe vacuolation (V) in the islet of STZ-diabetic negative control group. The morphology of the pancreas of HSCE-treated diabetic rats (test group II) revealed remarkable improvements in the islet of Langerhans. Stereological studies also revealed that HSCE-treatment remarkably improved volume of the pancreatic islets and the numerical density of β-cell (number of β-cells per unit area of islet) depleted by STZ diabetes. The study concluded that possible antidiabetic mechanism of Hibiscus sabdariffa in STZ diabetes is through induction of β-cell regeneration and its strong antioxidant potential.

Development and Characterization of Insulin-loaded Liposome-chitosan-Nanoparticle (LCS-NP) Complex and Investigation of Transport Properties Through a Pancreatic Beta Tc Cell Line

OBJECTIVES

In recent years, studies on oral use have increased rapidly due to the restrictive aspects of parenteral administration of indispensable peptide-structured insulin in the rapidly growing worldwide treatment of diabetes. The aim of the study was to examine the development of a novel insulin-loaded LCS-NP complex, and its characterization and efficacy on pancreatic cells responsible for insulin release.

MATERIALS AND METHODS

Blank liposomes and insulin-loaded LCS-NPs were prepared using dry film hydration and ionotropic gelation methods, respectively. The LCS-NP complex was prepared by mixing liposomes/NPs in a 2:1 (w/w) ratio. The cytotoxic effects of the various concentrations of insulin and formulation components on the pancreatic cell line were determined using a 3-(4,5-dimethyldiazol-2-yl)-2,5 diphenyl tetrazolium bromide assay and quantities to be used in the formulation were determined. Particle size, zeta potential, encapsulation efficiency, in vitro release profile and release kinetics, and transport properties of the prepared complex were investigated.

RESULTS

The newly developed insulin-loaded LCS-NP complex had a particle size of 2.85±0.035 μm and zeta potential of 8.11±1.025 mV. The encapsulation yield was found as 48±1.1%. In vitro insulin release from the complex was 80.9±2.71%. Insulin transport from β Tc cells was 30.50%. Permeability coefficients (log k) were calculated as -1.280±0.070 for the insulin solution and -1.020±0.062 for the insulin-loaded complex.

CONCLUSION

This study suggests that insulin could be successfully loaded into the newly developed LCS-NP complex, and it is thought that this complex carries an effective formulation potential for long-term efficacy in the treatment of diabetes.

Insulin analogues in type 1 diabetes mellitus: getting better all the time

The treatment of type 1 diabetes mellitus consists of external replacement of the functions of β cells in an attempt to achieve blood levels of glucose as close to the normal range as possible. This approach means that glucose sensing needs to be replaced and levels of insulin need to mimic physiological insulin-action profiles, including basal coverage and changes around meals. Training and educating patients are crucial for the achievement of good glycaemic control, but having insulin preparations with action profiles that provide stable basal insulin coverage and appropriate mealtime insulin peaks helps people with type 1 diabetes mellitus to live active lives without sacrificing tight glycaemic control. Insulin analogues enable patients to achieve this goal, as some have fast action profiles, and some have very slow action profiles, which gives people with type 1 diabetes mellitus the tools to achieve dynamic insulin-action profiles that enable tight glycaemic control with a risk of hypoglycaemia that is lower than that with human short-acting and long-acting insulins. This Review discusses the established and novel insulin analogues that are used to treat patients with type 1 diabetes mellitus and provides insights into the future development of insulin analogues.

Suppressors of Cytokine Signaling in Sickness and in Health of Pancreatic β-Cells

Suppressors of cytokine signaling (SOCS) are a family of eight proteins that negatively regulate Janus kinase and signal transducers and activators of transcription signaling in cells that utilize this pathway to respond to extracellular stimuli. SOCS are best known for attenuating cytokine signaling in the immune system. However, they are also expressed in many other cell types, including pancreatic β-cells, where there is considerable interest in harnessing SOCS molecules to prevent cytokine-mediated apoptosis during diabetes and allogeneic transplantation. Apart from their potential as therapeutic targets, SOCS molecules play a central role for regulating important functions in β-cells, including growth, glucose sensing, and insulin secretion. This review will discuss SOCS proteins as central regulators for diverse cellular processes important for normal β-cell function as well as their protective anti-apoptotic effects during β-cell stress.

ALDH expression characterizes G1-phase proliferating beta cells during pregnancy

High levels of aldehyde dehydrogenase (ALDH) activity have been detected in various progenitor and stem cells. Thus, Aldefluor fluorescence, which represents precisely the ALDH activity, has been widely used for the identification, evaluation, and isolation of stem and progenitor cells. Recently, ALDH activity was detected in embryonic and adult mouse pancreas, specifically in adult centroacinar and terminal duct cells supposed to harbor endocrine and exocrine progenitor cells in the adult pancreas. Nevertheless, ALDH activity and aldeflour fluorescence have not been examined in beta cells. Here, we report a dynamic increase in the number of aldeflour+ beta cells during pregnancy. Interestingly, nearly all these aldeflour+ beta cells are positive for Ki-67, suggesting that they are in an active cell cycle (G1, S and M phases). To determine precisely at which phase beta cells activate ALDH activity and thus become aldeflour+, we co-stained insulin with additional proliferation markers, phosphohistone3 (PHH3, a marker for M-phase proliferating cells) and Bromodeoxyuridine (BrdU, a marker for S-phase proliferating cells). Our data show little aldeflour+ beta cells that were positive for either PHH3, or BrdU, suggesting that beta cells activate ALDH and become Aldefluor+ when they enter G1-phase of active cell cycle, but may downregulate ALDH when they leave G1-phase and enter S phase. Our data thus reveal a potential change in ALDH activity of proliferating beta cells during pregnancy, which provides a novel method for isolation and analysis of proliferating beta cells. Moreover, our data also suggest that caution needs to be taken on interpretation of Aldefluor lineage-tracing data in pancreas.

Chickens from lines artificially selected for juvenile low and high body weight differ in glucose homeostasis and pancreas physiology

Artificial selection of White Plymouth Rock chickens for juvenile (day 56) body weight resulted in two divergent genetic lines: hypophagic low weight (LWS) chickens and hyperphagic obese high weight (HWS) chickens, with the latter more than 10-fold heavier than the former at selection age. A study was designed to investigate glucose regulation and pancreas physiology at selection age in LWS chickens and HWS chickens. Oral glucose tolerance and insulin sensitivity tests revealed differences in threshold sensitivity to insulin and glucose clearance rate between the lines. Results from real-time PCR showed greater pancreatic mRNA expression of four glucose regulatory genes (preproinsulin, PPI; preproglucagon, PPG; glucose transporter 2, GLUT2; and pancreatic duodenal homeobox 1, Pdx1) in LWS chickens, than HWS chickens. Histological analysis of the pancreas revealed that HWS chickens have larger pancreatic islets, less pancreatic islet mass, and more pancreatic inflammation than LWS chickens, all of which presumably contribute to impaired glucose metabolism.

Relationship between insulin resistance and plasma vitamin D in adults

A recent relationship between vitamin D deficiency and the risk of type 2 diabetes mellitus (T2DM) and insulin resistance has been established through several studies. Research suggests a correlation between serum vitamin D and glycemic status measures. The aim of this study was to investigate the relationship between the plasma vitamin D levels (25[OH]D) and the factors linked to insulin resistance in a representative sample of Canadians ranging in age from 16-79 years. Data were used from the Canadian Health Measures Survey where direct measures of health and wellness were reported from 1,928 subjects. These data were gathered from March 2007-February 2009 at 15 sites selected through a multistage sampling strategy. An inverse relationship between insulin resistance and plasma vitamin D level in both men and women was observed. This study provides additional evidence for the role of vitamin D in T2DM. If causally associated, the supplementation of vitamin D may help in preventing insulin resistance and subsequent T2DM.

No evidence for β cell neogenesis in murine adult pancreas

Whether facultative β cell progenitors exist in the adult pancreas is a major unsolved question. To date, lineage-tracing studies have provided conflicting results. To track β cell neogenesis in vivo, we generated transgenic mice that transiently coexpress mTomato and GFP in a time-sensitive, nonconditional Cre-mediated manner, so that insulin-producing cells express GFP under control of the insulin promoter, while all other cells express mTomato (INSCremTmG mice). Newly differentiated β cells were detected by flow cytometry and fluorescence microscopy, taking advantage of their transient coexpression of GFP and mTomato fluorescent proteins. We found that β cell neogenesis predominantly occurs during embryogenesis, decreases dramatically shortly after birth, and is completely absent in adults across various models of β cell loss, β cell growth and regeneration, and inflammation. Moreover, we demonstrated upregulation of neurogenin 3 (NGN3) in both proliferating ducts and preexisting β cells in the ligated pancreatic tail after pancreatic ductal ligation. These results are consistent with some recent reports, but argue against the widely held belief that NGN3 marks cells undergoing endocrine neogenesis in the pancreas. Our data suggest that β cell neogenesis in the adult pancreas occurs rarely, if ever, under either normal or pathological conditions.

Islet neogenesis-associated protein (INGAP)-positive cell mass, β-cell mass, and insulin secretion: their relationship during the fetal and neonatal periods

OBJECTIVES

To study the chronological appearance of pancreatic islet neogenesis-associated protein (INGAP)-positive cells and its correlation with the increase in β-cell mass and function in fetal and neonatal rats.

METHODS

Normal Wistar rat embryos (E) at gestational days 15, 17, and 19 (E15, E17, E19) and 7-day-old postnatal rats (P7) were humanely killed to determine body and pancreas weight; blood glucose; glucose and arginine-induced insulin secretion; real-time polymerase chain reaction of Pdx1 and Ngn3; quantitative immunomorphometric analysis of β-cell replication and apoptosis rate, cytokeratin and INGAP cell mass, and Pdx-1- and Ngn3-positive cells.

RESULTS

Body and pancreas weight increased with age (P7 > E19 > E17 > E15; P < 0.05). Neonates had higher blood glucose concentrations than embryos (P < 0.05). We recorded a simultaneous and significant age-dependent trend of increase in the number of β- and Pdx-1-positive cells, β- and cytokeratin-positive cell mass and β-cell capacity to release insulin in response to glucose and arginine, and decreased β-cell apoptotic rate. These changes closely paralleled the increase in INGAP-positive cell mass.

CONCLUSIONS

These findings suggest that INGAP exerts a positive modulatory effect on β-cell mass and its secretory function in fetal and neonatal rats, thus becoming a new component in the multifactorial regulation of such processes.

Long-term treatment with EXf, a peptide analog of Exendin-4, improves β-cell function and survival in diabetic KKAy mice

EXf is a C-terminally truncated fragment of Exendin-4 with two amino acid substitutions. Previous studies showed that EXf controls plasma glucose level acting as a glucagon-like peptide 1 (GLP-1) receptor agonist. The purpose of this study was to evaluate the effects of EXf on β-cell function and survival in diabetic KKAy mice. EXf treatment significantly improved the glucose intolerance and reduced non-fasting and fasting plasma glucose levels, as well as plasma triglyceride levels in diabetic KKAy mice. In hyperglycemic clamp test, EXf-treated mice displayed an increased glucose infusion rate and first-phase insulin secretion. Treatment with EXf also led to a significant restoration of islet morphology, an increase in Ki67 expression in β-cells, and a reduction in the number of TUNEL positive β-cells. In the pancreas, comparative transcription analysis showed up-regulation of Akt1. The up-regulation of phosphorylated Akt1 was confirmed by Western blot, and changes in the protein levels of members of the Akt1 pathway, such as PI3K, Bim, Bcl-2, Bax, Caspase-3, and Caspase-9, PDX-1, were observed as well. Therefore, EXf treatment could improve β-cell function and survival in diabetic KKAy mice, likely as a result of islet morphology restoration, stimulation of β-cell proliferation, and inhibition of β-cell apoptosis.

Insulin-like growth factor and fibroblast growth factor expression profiles in growth-restricted fetal sheep pancreas

Placental insufficiency results in intrauterine growth restriction (IUGR), impaired fetal insulin secretion and less fetal pancreatic β-cell mass, partly due to lower β-cell proliferation rates. Insulin-like growth factors (IGFs) and fibroblast growth factors (FGFs) regulate fetal β-cell proliferation and pancreas development, along with transcription factors, such as pancreatic and duodenal homeobox 1 (PDX-1). We determined expression levels for these growth factors, their receptors and IGF binding proteins in ovine fetal pancreas and isolated islets. In the IUGR pancreas, relative mRNA expression levels of IGF-I, PDX-1, FGF7 and FGFR2IIIb were 64% (P < 0.01), 76% (P < 0.05), 76% (P < 0.05) and 52% (P < 0.01) lower, respectively, compared with control fetuses. Conversely, insulin-like growth factor binding protein 2 (IGFBP-2) mRNA and protein concentrations were 2.25- and 1.2-fold greater (P < 0.05) in the IUGR pancreas compared with controls. In isolated islets from IUGR fetuses, IGF-II and IGFBP-2 mRNA concentrations were 1.5- and 3.7-fold greater (P < 0.05), and insulin mRNA was 56% less (P < 0.05) than control islets. The growth factor expression profiles for IGF and FGF signaling pathways indicate that declines in β-cell mass are due to decreased growth factor signals for both pancreatic progenitor epithelial cell and mature β-cell replication.

Repression of malignant tumor progression upon pharmacologic IGF1R blockade in a mouse model of insulinoma

NVP-AEW541, a specific ATP-competitive inhibitor of the insulin-like growth factor-1 receptor (IGF1R) tyrosine kinase, has been reported to interfere with tumor growth in various tumor transplantation models. We have assessed the efficacy of NVP-AEW541 in repressing tumor growth and tumor progression in the Rip1Tag2 transgenic mouse model of pancreatic β-cell carcinogenesis. In addition, we have tested NVP-AEW541 in Rip1Tag2;RipIGF1R double-transgenic mice which show accelerated tumor growth and increased tumor malignancy compared with Rip1Tag2 single-transgenic mice. Previously, we have shown that high levels of IGF-2, a high-affinity ligand for IGF1R, are required for Rip1Tag2 tumor cell survival and tumor growth. Unexpectedly, treatment of Rip1Tag2 mice with NVP-AEW541 in prevention and intervention trials neither did affect tumor growth nor tumor cell proliferation and apoptosis. Yet, it significantly repressed progression to tumor malignancy, that is, the rate of the transition from differentiated adenoma to invasive carcinoma. Treatment of Rip1Tag2;RipIGF1R double-transgenic mice resulted in moderately reduced tumor volumes and increased rates of tumor cell apoptosis. Sustained expression of IGF-2 and of the IGF-2-binding form of insulin receptor (IR-A) in tumor cells suggests a compensatory role of IR-A upon IGF1R blockade. The results indicate that inhibition of IGF1R alone is not sufficient to efficiently block insulinoma growth and imply an overlapping role of IGF1R and insulin receptor in executing mitogenic and survival stimuli elicited by IGF-2. The reduction of tumor invasion upon IGF1R blockade on the other hand indicates a critical function of IGF1R signaling for the acquisition of a malignant phenotype.

Prediction of gestational diabetes mellitus at 24 to 28 weeks of gestation by using first-trimester insulin sensitivity indices in Asian Indian subjects

The aim of the present study was to predict the development of gestational diabetes mellitus (GDM) after 24 weeks of gestation by using first-trimester insulin indices. A total of 298 nondiabetic pregnant women underwent 3-hour oral glucose tolerance test (OGTT) in the first trimester of pregnancy. The normoglycemic women underwent second OGTT between 24 and 28 weeks. Insulin sensitivity and resistance indices were calculated by using the Matsuda index (composite insulin sensitivity from OGTT), quantitative insulin sensitivity check index, and homeostasis model assessment for insulin resistance and sensitivity by using the results of the first-trimester OGTT. These indices were compared between subjects who were diagnosed as having GDM and subjects with normal glucose tolerance in the second OGTT. The overall prevalence of GDM was 15.49% (24 in the first trimester and 16 between 24 and 28 weeks). First-trimester fasting plasma insulin greater than 7.45 μU/mL was able to predict GDM with sensitivity and specificity of 80% and 57.4%, respectively. The negative predictive value for this parameter was 0.97. Values of first-trimester composite insulin sensitivity from OGTT less than 5.5 had sensitivity and specificity of 71.4% and 62.5% for the prediction of GDM. First-trimester hyperinsulinemia preceded the onset of hyperglycemia between 24 and 28 weeks of gestation and would predict the development of GDM with limited sensitivity and specificity.

A simple matter of life and death-the trials of postnatal Beta-cell mass regulation

Pancreatic beta-cells, which secrete the hormone insulin, are the key arbiters of glucose homeostasis. Defective beta-cell numbers and/or function underlie essentially all major forms of diabetes and must be restored if diabetes is to be cured. Thus, the identification of the molecular regulators of beta-cell mass and a better understanding of the processes of beta-cell differentiation and proliferation may provide further insight for the development of new therapeutic targets for diabetes. This review will focus on the principal hormones and nutrients, as well as downstream signalling pathways regulating beta-cell mass in the adult. Furthermore, we will also address more recently appreciated regulators of beta-cell mass, such as microRNAs.

Hepatocyte growth factor is constitutively produced by donor-derived bone marrow cells and promotes regeneration of pancreatic beta-cells

Recent studies have demonstrated that the transplantation of bone marrow cells following diabetes induced by streptozotocin can support the recovery of pancreatic b-cell mass and a partial reversal of hyperglycemia. To address this issue, we examined whether the c-Met/hepatocyte growth factor (HGF) signaling pathway was involved in the recovery of b-cell injury after bone marrow transplantation (BMT). In this model, donor-derived bone marrow cells were positive for HGF immunoreactivity in the recipient spleen, liver, lung, and pancreas as well as in the host hepatocytes. Indeed, plasma HGF levels were maintained at a high value.The frequency of c-Met expression and its proliferative activity and differentiative response in the pancreatic ductal cells in the BMT group were greater than those in the PBS-treated group, resulting in an elevated number of endogenous insulin-producing cells. The induction of the c-Met/HGF signaling pathway following BMT promotes pancreatic regeneration in diabetic rats.

Transforming growth factor-β induces epithelial to mesenchymal transition and suppresses the proliferation and transdifferentiation of cultured human pancreatic duct cells

Pancreatic duct cells are considered a potential source of β-cell regeneration, and transforming growth factor-β (TGF-β) has been suggested to perform an important role in these processes, but the underlying mechanism of the signal pathways, especially in humans, remains poorly understood. To evaluate the role of TGF-β1, pancreatic duct cells were isolated from three brain-dead organ donors. Pancreatic cell clusters harvested after islet isolation were dispersed to single cells and cultured in monolayers, then treated with TGF-β1. We analyzed the characteristics of the cultured cells, the TGF-β1 intracellular signaling pathway, the proliferation, and transdifferentiation rates of the duct cells. We also evaluated the genes and protein expression patterns after TGF-β1 treatment. After TGF-β1 treatment, typical morphologic changes representative of EMT were observed and Erk1/2, JNK, and AKT phosphorylation, Ras downstream effectors, were increased. β cell-specific transcription factors including PDX-1, Beta2/NeuroD, Ist-1, and NGN3 were markedly suppressed and the rate of transdifferentiation into β cells was also suppressed. Genomic and proteomic analyses suggested that TGF-β1 induces marked changes in a variety of structural genes and proteins associated with EMT. In conclusion, TGF-β1 induces EMT in cultured human pancreatic duct cells, but suppresses its proliferation and transdifferentiation into β cells. Our results are the first report of TGF-β1 effects for EMT and ductal cell transdifferentiation and proliferation at the protein level in human pancreatic duct cells.

Tissue-specificity of insulin action and resistance

Insulin resistance is the most important pathophysiological feature in many pre-diabetic states. Type 2 diabetes mellitus is a complex metabolic disease and its pathogenesis involves abnormalities in both peripheral insulin action and insulin secretion by pancreatic beta cells. The creation of monogenic or polygenic genetically manipulated mice models in a tissue-specific manner was of great help to elucidate the tissue-specificity of insulin action and its contribution to the overall insulin resistance. However, complete understanding of the molecular bases of the insulin action and resistance requires the identification of the intracellular pathways that regulate insulin-stimulated proliferation, differentiation and metabolism. Accordingly, cell lines derived from insulin target tissues such as brown adipose tissue, liver and beta islets lacking insulin receptors or sensitive candidate genes such as IRS-1, IRS-2, IRS-3, IR and PTP1B were developed. Indeed, these cell lines have been also very useful to understand the tissue-specificity of insulin action and inaction.

Adenoviruses Expressing PDX-1, BETA2/NeuroD and MafA Induces the Transdifferentiation of Porcine Neonatal Pancreas Cell Clusters and Adult Pig Pancreatic Cells into Beta-Cells

BACKGROUND

A limitation in the number of insulin-producing pancreatic beta-cells is a special feature of diabetes. The identification of alternative sources for the induction of insulin-producing surrogate beta-cells is a matter of profound importance. PDX-1/VP16, BETA2/NeuroD, and MafA overexpression have been shown to influence the differentiation and proliferation of pancreatic stem cells. However, few studies have been conducted using adult animal pancreatic stem cells.

METHODS

Adult pig pancreatic cells were prepared from the non-endocrine fraction of adult pig pancreata. Porcine neonatal pancreas cell clusters (NPCCs) were prepared from neonatal pigs aged 1-2 days. The dispersed pancreatic cells were infected with PDX-1/VP16, BETA2/NeuroD, and MafA adenoviruses. After infection, these cells were transplanted under the kidney capsules of normoglycemic nude mice.

RESULTS

The adenovirus-mediated overexpression of PDX-1, BETA2/NeuroD and MafA induced insulin gene expression in NPCCs, but not in adult pig pancreatic cells. Immunocytochemistry revealed that the number of insulin-positive cells in NPCCs and adult pig pancreatic cells was approximately 2.6- and 1.1-fold greater than those in the green fluorescent protein control group, respectively. At four weeks after transplantation, the relative volume of insulin-positive cells in the grafts increased in the NPCCs, but not in the adult porcine pancreatic cells.

CONCLUSION

These data indicate that PDX-1, BETA2/NeuroD, and MafA facilitate the beta-cell differentiation of NPCCs, but not adult pig pancreatic cells. Therefore PDX-1, BETA2/NeuroD, and MafA-induced NPCCs can be considered good sources for the induction of pancreatic beta-cells, and may also have some utility in the treatment of diabetes.

Tissue specificity on insulin action and resistance: past to recent mechanisms

Insulin resistance is the most important pathophysiological feature in many pre-diabetic states. Type 2 diabetes mellitus is a complex metabolic disease and its pathogenesis involves abnormalities in both peripheral insulin action and insulin secretion by pancreatic β-cells. The creation of monogenic or polygenic genetically manipulated mice models in a tissue-specific manner was of great help to elucidate the tissue specificity of insulin action and its contribution to the overall insulin resistance. However, a complete understanding of the molecular bases of insulin action and resistance requires the identification of intracellular pathways that regulate insulin-stimulated proliferation, differentiation and metabolism. Accordingly, cell lines derived from insulin target tissues such as brown adipose tissue, liver and beta islets lacking insulin resistance or sensitive candidate genes such as IRS-1, IRS-2, IRS-3, IR and PTP1B have been developed. Indeed, these cell lines have also been very useful to understand the tissue specificity of insulin action and inaction. Obesity is a risk factor for several components of the metabolic syndromes such as type 2 diabetes, dyslipidaemia and systolic hypertension, because white and brown adipose tissues as endocrine organs express and secrete a variety of adipocytokines that can act at both local and systemic levels, modulating the insulin sensitivity. Recent studies revealed that the subjects with the highest transcription rates of genes encoding TNF-α and IL-6 were prone to develop obesity, insulin resistance and type 2 diabetes. Accordingly, we specifically focus in this review on the impact of those adipocytokines on the modulation of insulin action in skeletal muscle.

Silk fibroin has a protective effect against high glucose induced apoptosis in HIT-T15 cells

High glucose levels induce cell death in many cell types, including pancreatic β-cells. Although protective agents against glucotoxicity have been searched for extensively, so far none have been found. In this report, we tested silk fibroin (SF) as a candidate material for antiglucotoxicity in the pancreatic β-cell (HIT-T15 cell) line. Approximately 50% of cells were killed after treatment with 80 mg/mL glucose. This reduction of cell number was recovered by the addition of SF at 50 mg/mL. SF treatment also decreased cellular reactive oxygen species (ROS) and increased proliferating cellular nuclear antigen (PCNA) immunoreactivity. In addition, TUNEL assays demonstrated that SF protects against glucose-induced apoptosis of HIT-T15 cells, suggesting that SF might protect cells from cell death by lowering cellular ROS levels. SF also induced expression of the insulin-like growth factor-1 (IGF-1) gene, and IGF-1 expression may be the cause of SF-induced protection against glucose toxicity. Taken together, these results suggest that SF could serve as a potential therapeutic agent to treat the hyperglycemia-induced death of pancreatic β-cells.

A new look at established therapies: practical tools for optimizing insulin use

PURPOSE

Current evidence shows early initiation of insulin therapy in type 2 diabetes mellitus (T2DM) improves glycemic control, responsiveness to subsequent oral antidiabetic therapies, beta-cell function, and possible cardiovascular outcomes. The American Diabetes Association (ADA)/European Association for the Study of Diabetes (EASD) 2008 algorithm introduces insulin therapy earlier in the treatment of T2DM with prompt intensification to achieve therapeutic goals. Agent selection and insulin regimens are based on patient A1C levels and willingness to monitor blood glucose, use of previous medications, blood glucose patterns, diet, and lifestyle. Practical considerations offered for diabetes educators and clinicians include creating strategies for early initiation of insulin, addressing patients' psychosocial barriers and quality of life concerns, understanding pharmacokinetic properties of insulin formulations, selecting appropriate therapy and patient-based regimens, and intensifying therapy to achieve glycemic control.

CONCLUSIONS

Diabetes education, including intentional curriculum design, for patients with T2DM who are initiating or intensifying insulin therapy, addresses patient barriers to care, reduces the burden of treatment, improves adherence to treatment protocols, and helps optimize clinical outcomes.

Leucine metabolism in regulation of insulin secretion from pancreatic beta cells

Leucine, a branched-chain amino acid that must be supplied in the daily diet, plays an important role in controlling protein synthesis and regulating cell metabolism in various cell types. In pancreatic beta cells, leucine acutely stimulates insulin secretion by serving as both metabolic fuel and allosteric activator of glutamate dehydrogenase to enhance glutaminolysis. Leucine has also been shown to regulate gene transcription and protein synthesis in pancreatic islet beta cells via both mTOR-dependent and -independent pathways at physiological concentrations. Long-term treatment with leucine has been shown to improve insulin secretory dysfunction of human diabetic islets via upregulation of certain key metabolic genes. In vivo, leucine administration improves glycemic control in humans and rodents with type 2 diabetes. This review summarizes and discusses the recent findings regarding the effects of leucine metabolism on pancreatic beta-cell function.

Autologous stem cell transplantation for early type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is the result of the autoimmune response against pancreatic insulin producing beta cells. This autoimmune response begins months or even years before the first presentation of signs and symptoms of hyperglycemia and at the time of clinical diagnosis near 30% of beta-cell mass still remains. In daily clinical practice, the main therapeutic option for T1DM is multiple subcutaneous insulin injections that are shown to promote tight glucose control and reduce much of diabetic chronic complications, especially microvascular complications. Another important aspect related to long-term complications of diabetes is that patients with initially larger beta-cell mass suffer less microvascular complications and less hypoglycemic events than those patients with small beta-cell mass. In face of this, beta-cell preservation is another important target in the management of type 1 diabetes and its related complications. For many years, various immunomodulatory regimens were tested aiming at blocking autoimmunity against beta-cell mass and at promoting beta-cell preservation, mainly in secondary prevention trials. In this review, we summarize some of the most important studies involving beta-cell preservation by immunomodulation and discuss our preliminary data on autologous nonmyeloablative hematopoietic stem cell transplantation in newly-diagnosed T1DM.

Role of insulin-like growth factor-binding protein 5 (IGFBP5) in organismal and pancreatic beta-cell growth

A family of IGF-binding proteins (IGFBP) exerts biological actions both dependent on and independent of IGF-I. A major effector of the insulin/IGF-I signaling pathway, the serine/threonine protein kinase Akt, mediates cellular processes such as glucose uptake, protein synthesis, cell survival, and growth. IGF-I is required for normal organismal growth, and in the pancreatic beta-cell, the insulin/IGF-I signaling pathway is critical for normal and adaptive maintenance of beta-cell mass. Expression of myrAkt1, an activated form of Akt, in the endocrine pancreas drives beta-cell expansion through dramatic increases in both islet and beta-cell size and number. Herein we present a comparative expression profiling of myrAkt1 transgenic islets that demonstrates the increased abundance of transcripts encoding proteins associated with growth, suppression of apoptosis, RNA processing, and metabolism. Although IGFBP5 is identified as a gene induced by Akt1 activation in the beta-cell, Igfbp5 expression is not necessary for myrAkt1 to augment beta-cell size or mass in vivo. However, in the absence of Igfbp5, mice demonstrate an increase in size and mild glucose intolerance. This is accentuated during diet-induced obesity, when Igfbp5-deficient mice have increased adiposity compared with wild-type mice on the same diet. These studies reveal a novel role for Igfbp5 in the control of growth and metabolism.

Potential role of stem cell therapy in type 1 diabetes mellitus

Type 1 diabetes mellitus is the result of the autoimmune response against pancreatic beta-cell(s). At the time of clinical diagnosis near 70% of beta-cell mass is been destroyed as a consequence of the auto-destruction that begins months or even years before the clinical diagnosis. Although marked reduction of chronic complications was seen after development and progression of insulin therapy over the years for type 1 diabetic population, associated risks of chronic end-organ damage and hypoglycemia still remain. Besides tight glucose control, beta-cell mass preservation and/or increase are known to be other important targets in management of type 1 diabetes as long as it reduces chronic microvascular complications in the eyes, kidneys and nerves. Moreover, the larger the beta-cell mass, the lower the incidence of hypoglycemic events. In this article, we discuss some insights about beta-cell regeneration, the importance of regulation of the autoimmune process and what is being employed in human type 1 diabetes in regard to stem cell repertoire to promote regeneration and/or preservation of beta-cell mass.

Insulin glargine and its role in glycaemic management of Type 2 diabetes

BACKGROUND

Insulin glargine (Lantus) was the first recombinant-DNA long-acting insulin analogue to be licensed for use in the treatment of diabetes mellitus.

OBJECTIVE

This review considers the use of insulin glargine in the treatment of type 2 diabetes (T2DM).

METHODS

Medline, Cochrane and Embase databases were searched for relevant papers from the year 2000 onwards.

RESULTS/CONCLUSION

Overall glargine provides at least equivalent glycaemic control and is associated with less hypoglycaemia, especially nocturnal hypoglycaemia owing to its 24 h peakless profile, which allows more aggressive titration to achieve glycaemic targets. Glargine has been shown to be safely initiated both individually and within a group setting and titration algorithms self-managed by patients are effective in achieving diabetes control. Despite these advantages, caution is needed as clinical guidelines do not advocate its use in all people with T2DM until clinical efficacy and cost effectiveness have been proved. However, insulin glargine is a welcome addition to the plethora of treatment options available for T2DM.

Beta cells within single human islets originate from multiple progenitors

Background

In both humans and rodents, glucose homeostasis is controlled by micro-organs called islets of Langerhans composed of beta cells, associated with other endocrine cell types. Most of our understanding of islet cell differentiation and morphogenesis is derived from rodent developmental studies. However, little is known about human islet formation. The lack of adequate experimental models has restricted the study of human pancreatic development to the histological analysis of different stages of pancreatic development. Our objective was to develop a new experimental model to (i) transfer genes into developing human pancreatic cells and (ii) validate gene transfer by defining the clonality of developing human islets.

Methods and Findings

In this study, a unique model was developed combining ex vivo organogenesis from human fetal pancreatic tissue and cell type-specific lentivirus-mediated gene transfer. Human pancreatic progenitors were transduced with lentiviruses expressing GFP under the control of an insulin promoter and grafted to severe combined immunodeficient mice, allowing human beta cell differentiation and islet morphogenesis. By performing gene transfer at low multiplicity of infection, we created a chimeric graft with a subpopulation of human beta cells expressing GFP and found both GFP-positive and GFP-negative beta cells within single islets.

Conclusion

The detection of both labeled and unlabeled beta cells in single islets demonstrates that beta cells present in a human islet are derived from multiple progenitors thus providing the first dynamic analysis of human islet formation during development. This human transgenic-like tool can be widely used to elucidate dynamic genetic processes in human tissue formation.

Gamma-aminobutyric acid A receptor functional decrease in the hypothalamus during pancreatic regeneration in rats

OBJECTIVE

In the present study, we investigated the alteration of gamma-aminobutyric acid A (GABAA) receptors in the hypothalamus of rats during pancreatic regeneration.

METHODS

Three groups of rats were used for the study: sham operated, 72 hours partially pancreatectomized, and 7 days partially pancreatectomized. The GABA receptor assay was performed by using the [H]GABA as ligand to the Triton X-100-treated membranes, and displacement with unlabeled GABA and [H]bicuculline binding to the GABAA receptors was assayed in Triton X-100-treated synaptic membranes and displacement with unlabeled bicuculline.

RESULTS

The GABA content in the brain regions and pancreas of the sham and experimental rat groups was quantified by displacement method. In the hypothalamus, the high-affinity GABAA receptor binding showed a significant decrease in maximal binding (P < 0.01) and equilibrium dissociation constant (P < 0.05) in 72 hours and 7 days partially pancreatectomized rats. The content of GABA has significantly decreased in the hypothalamus during the regeneration of pancreas.

CONCLUSIONS

This effect of GABAA receptors in hypothalamus suggests a regulatory role during active regeneration of pancreas that will have significance in insulin secretion.

β-cell regeneration to treat Type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) results from the autoimmune destruction of the insulin-producing pancreatic β-cells. The autoimmune response begins years before the presentation of hyperglycemic symptoms. At the time of clinical diagnosis, less than 30% of β-cell mass still remains. The conventional therapeutic option to T1DM is daily insulin injections, which is shown to promote tight glucose control and reduce the majority of chronic diabetic complications. Subgroup analysis of the Diabetes Control and Complication Trial showed another important aspect related to long-term complications of diabetes, that is, patients with initially higher serum levels of C-peptide with sustained levels over the subsequent years suffered less microvascular complications and less hypoglycemic events than those patients with low or undetected C-peptide levels. In face of this, β-cell preservation is another important target in the management of T1DM and its related complications. Along the years, many efforts toward the identification of precursors of β-cells have been made, not only with the aim of understanding the physiology of β-cell preservation, but also as a potential source of β-cell replacement. In this review, we summarize the most important studies related to probable precursor cells implied in the process of regeneration, and the results of various immunomodulatory regimens aiming at blocking autoimmunity against pancreatic β-cells and at promoting β-cell preservation. Finally, we comment on the future perspective related to stem cell therapy in T1DM.

TGF-beta1 and high levels of glucose do not increase insulin cell proportions in the avian embryonic pancreas

TGF-beta1 is thought to decrease the proportion of embryonic pancreatic beta-cells with respect to alpha-cells, whereas glucose is thought to enhance beta-cell proportions in rats. However, chick pancreatic cells may respond in a dissimilar way to glucose. Thus, the effect of TGF-beta1 on the proportion of beta-cells in embryonic chick dorsal pancreatic buds (DPBs) in vitro was tested with short-term exposure to high levels of glucose. Five-day-old chick DPBs were cultured on growth factor-reduced Matrigel, which contains reduced levels of growth factors including TGF-beta1, and a variety of culture media with and without high levels of glucose. TGF-beta1 reduced the proportion of beta-cells, as expected. A similar decrease in the proportion of beta-cells occurred in the presence of high levels of glucose.

Proliferation, hyperplasia, neogenesis, and neoplasia in the islets of Langerhans

Pancreatic disease is responsible for significant morbidity and mortality as a result of pancreatic carcinoma and diabetes mellitus. Regulation of endocrine cell mass is thought to have a central role in the pathogenesis of both these diseases. Islet cell proliferation, hypertrophy, neogenesis, and apoptosis are the main determinants of endocrine cell mass in the pancreas, and their understanding has been improved by new clues of their genetic and molecular basis. Beta cells have attracted most research interest because of potential implications in the treatment of diabetes mellitus and hypoglycemic disorders. The processes that operate during pancreatic adaptation to a changing hormonal milieu are important in pancreatic carcinogenesis. There is evidence that somatostatin and its receptors are fundamental regulators of endocrine cell mass and are involved in islet tumorigenesis.

Regulation of pancreatic islet cell survival and replication by gamma-aminobutyric acid

AIMS/HYPOTHESIS

Pancreatic islets have evolved remarkable, though poorly understood mechanisms to modify beta cell mass when nutrient intake fluctuates or cells are damaged. We hypothesised that appropriate and timely adjustments in cell number occur because beta cells release proliferative signals to surrounding cells when stimulated by nutrients and 'bleed' these growth factors upon injury.

MATERIALS AND METHODS

In rat pancreatic islets, we measured DNA content, insulin content, insulin secretion after treatment, immunoblots of apoptotic proteins and the uptake of nucleoside analogues to assess the ability of gamma-aminobutyric acid (GABA), which is highly concentrated in beta cells, to act as a growth and survival factor. This focus is supported by work from others demonstrating that GABA increases cell proliferation in the developing nervous system, acts as a survival factor for differentiated neurons and, interestingly, protects plants under stress.

RESULTS

Our results show that DNA, insulin content and insulin secretion are higher in freshly isolated islets treated with GABA or GABA B receptor agonists. Exposure to GABA upregulated the anti-apoptotic protein B-cell chronic lymphocytic leukaemia XL and limited activation of caspase 3 in islets. The cellular proliferation rate in GABA-treated islets was twice that of untreated controls.

CONCLUSIONS/INTERPRETATION

We conclude that GABA serves diverse purposes in the islet, meeting a number of functional criteria to act as an endogenous co-regulator of beta cell mass.

Fatty acid-induced effect on glucagon secretion is mediated via fatty acid oxidation

BACKGROUND

While the effect of fatty acids and ectopic triglyceride storage in pancreatic beta cells has been well-defined, only limited information is available on alpha cells. This study evaluates the long-term impact of fatty acids on alpha cell function and proliferation as well as fatty acid oxidation.

METHODS

Clonal alpha cells were cultured with fatty acids in the presence of high glucose for up to 3 days. The influence of fatty acids on glucagon secretion, glucagon content and triglyceride accumulation from 24 to 72 h was investigated. After a - 72 h culture, cell proliferation, carnitine palmitoyl transferase-1 mRNA level and the effect of etomoxir were also elucidated.

RESULTS

Fatty acids stimulated glucagon secretion and increased triglyceride accumulation in a time- and dose-dependent manner, but inhibited alpha cell proliferation. Lower concentrations (0.125-0.25 mM) of fatty acids significantly increased glucagon secretion at 48 and 72 h, but did not affect triglyceride content. However, a marked increment in triglyceride accumulation occurred in the presence of 0.5 mM fatty acids. Fatty acids caused an up-regulation of the expression of carnitine palmitoyl transferase-1 gene. Etomoxir (1 microM) reversed fatty acid-induced glucagon hypersecretion, but did not inhibit carnitine palmitoyl transferase-1 mRNA level.

CONCLUSIONS

Our data indicates that compared with triglyceride accumulation, glucagon secretion is more sensitive to changes in fatty acid concentration. The effect of fatty acids on the glucagon response is mediated through their oxidation. The high carnitine palmitoyl transferase-1 gene expression and the accumulation of triglyceride may initially be a compensatory oxidation reaction to elevated fatty acids.

The role of AMPK and mTOR in nutrient sensing in pancreatic beta-cells

The AMP-activated protein kinase (AMPK) is a central regulator of the energy status of the cell, based on its unique ability to respond directly to fluctuations in the ratio of AMP:ATP. Because glucose and amino acids stimulate insulin release from pancreatic beta-cells by the regulation of metabolic intermediates, AMPK represents an attractive candidate for control of beta-cell function. Here, we show that inhibition of AMPK in beta-cells by high glucose inversely correlates with activation of the mammalian Target of Rapamycin (mTOR) pathway, another cellular sensor for nutritional conditions. Forced activation of AMPK by AICAR, phenformin, or oligomycin significantly blocked phosphorylation of p70S6K, a downstream target of mTOR, in response to the combination of glucose and amino acids. Amino acids also suppressed the activity of AMPK, and this at a minimum required the presence of leucine and glutamine. It is unlikely that the ability of AMPK to sense both glucose and amino acids plays a role in regulation of insulin secretion, as inhibition of AMPK by amino acids did not influence insulin secretion. Moreover, activation of AMPK by AICAR or phenformin did not antagonize glucose-stimulated insulin secretion, and insulin secretion was also unaffected in response to suppression of AMPK activity by expression of a dominant negative AMPK construct (K45R). Taken together, these results suggest that the inhibition of AMPK activity by glucose and amino acids might be an important component of the mechanism for nutrient-stimulated mTOR activity but not insulin secretion in the beta-cell.

Effects of Growth Factors on Development of Fetal Islet B-Cells In Vitro

To investigate the role of growth factors (epidermal growth factor [EGF], betacellulin, and activin A) in the development of islet B cells of rat fetal pancreatic explants in vitro, pancreases from rat fetuses at day 18 of gestation were cultured for 96 hr, with or without these growth factors. Culture medium was changed every 24 hr, and the level of insulin released in the culture medium was measured. After 72 hr of culture, pancreases were examined histologically. As a result, EGF promoted cell proliferation, but reduced B cell volume. Whereas, betacellulin and activin A inhibited cell division, but promoted increased B cell volume and insulin secretion, especially activin A, which stimulated insulin release in a time dependent manner. These results suggest that EGF, betacellulin, and activin A promote pancreatic cell proliferation, islet B-cell differentiation, and islet B-cell differentiation and functional maturation, respectively, and that EGF, betacellulin, and activin A, in this order, regulate islet B-cell neogenesis.

Stem cells and diabetes treatment

Diabetes mellitus types 1 and 2 are characterized by absolute versus relative lack of insulin-producing beta cells, respectively. Reconstitution of a functional beta-cell mass by cell therapy--using organ donor islets of Langerhans--has been demonstrated to restore euglycaemia in the absence of insulin treatment. This remarkable achievement has stimulated the search for appropriate stem cell sources from which adequate expansion and maturation of therapeutic beta cells can be achieved. This recent activity is reviewed and presented with particular focus on directed differentiation from pluripotent embryonic stem cells (versus other stem/progenitor cell sources) based on knowledge from pancreatic beta-cell development and the parallel approach to controlling endogenous beta-cell neogenesis.

Differential mitogenic signaling in insulin receptor-deficient fetal pancreatic beta-cells

Insulin receptor (IR) may play an essential role in the development of beta-cell mass in the mouse pancreas. To further define the function of this signaling system in beta-cell development, we generated IR-deficient beta-cell lines. Fetal pancreata were dissected from mice harboring a floxed allele of the insulin receptor (IRLoxP) and used to isolate islets. These islets were infected with a retrovirus to express simian virus 40 large T antigen, a strategy for establishing beta-cell lines (beta-IRLoxP). Subsequently, these cells were infected with adenovirus encoding cre recombinase to delete insulin receptor (beta-IR(-/-)). beta-Cells expressed insulin and Pdx-1 mRNA in response to glucose. In beta-IRLoxP beta-cells, p44/p42 MAPK and phosphatidylinositol 3 kinase pathways, mammalian target of rapamycin (mTOR), and p70S(6)K phosphorylation and beta-cell proliferation were stimulated in response to insulin. Wortmannin or PD98059 had no effect on insulin-mediated mTOR/p70S(6)K signaling and the corresponding mitogenic response. However, the presence of both inhibitors totally impaired these signaling pathways and mitogenesis in response to insulin. Rapamycin completely blocked insulin-activated mTOR/p70S(6)K signaling and mitogenesis. Interestingly, in beta-IR(-/-) beta-cells, glucose failed to stimulate phosphatidylinositol 3 kinase activity but induced p44/p42 MAPKs and mTOR/p70S(6)K phosphorylation and beta-cell mitogenesis. PD98059, but not wortmannin, inhibited glucose-induced mTOR/p70S(6)K signaling and mitogenesis in those cells. Finally, rapamycin blocked glucose-mediated mitogenesis of beta-IR(-/-) cells. In conclusion, independently of glucose, insulin can mediate mitogenesis in fetal pancreatic beta-cell lines. However, in the absence of the insulin receptor, glucose induces beta-cell mitogenesis.

CART regulates islet hormone secretion and is expressed in the beta-cells of type 2 diabetic rats

Cocaine- and amphetamine-regulated transcript (CART) is an anorexigenic peptide widely expressed in the central, peripheral, and enteric nervous systems. CART is also expressed in endocrine cells, including beta-cells during rat development and delta-cells of adult rats. We examined the effect of CART 55-102 on islet hormone secretion, using INS-1(832/13) cells and isolated rat islets. In addition, islet CART expression was examined in two rat models of type 2 diabetes: Goto-Kakizaki (GK) rats and dexamethasone (DEX)-treated rats. At high glucose, CART potentiated cAMP-enhanced insulin secretion via the cAMP/protein kinase A-dependent pathway. In the absence of cAMP-elevating agents, CART was without effect on INS-1 cells but modestly inhibited secretion of insulin, glucagon, and somatostatin from isolated islets. CART was markedly upregulated in the beta-cells of both diabetes models. Thus, in DEX-treated rats, islet CART mRNA expression, and the number of CART-immunoreactive beta-cells were 10-fold higher than in control rats. In GK rats, the relative number of CART-expressing beta-cells was 30-fold higher than in control rats. We conclude that CART is a regulator of islet hormone secretion and that CART is upregulated in the beta-cells of type 2 diabetic rats.

Morphological changes in the rat endocrine pancreas within 12 h of intravenous streptozotocin administration

We examined early morphological changes in pancreatic endocrine cells within 12 h of intravenous streptozotocin (STZ) administration (60 mg/kg). Thirty rats were allocated either to a control group (vehicle alone) or to one of four experimental groups tested after 3, 6, 9 and 12 h. Karyopyknosis and cytoplasmic vacuoles were first observed in beta-cell cytoplasm 3 h after STZ administration (STZ-3 h), and the most severe damage was found in beta cells at STZ-12 h. Insulin-positive non-islet cells were observed near the intercalated duct (ICD) and/or centroacinar (CA) cells at STZ-6 h and their numbers peaked at STZ-6 h. The distribution patterns of the insulin-positive cells and those of nestin and insulin-like growth factor-1 were similar and their nuclei were positive for proliferating cell nuclear antigen. Thus, ICD cells and/or CA cells reacted immediately to transform into insulin-secreting cells to replace injured beta cells (or to compensate for the lack of beta cells) within 12 h of STZ administration.

Recovery in the fetal pancreatic islet following fetal administration of streptozotocin in the rat in vivo and in vitro

In our previous study, after direct administration of streptozotocin (STZ; 400 microg/g) to fetuses on day 19 of gestation, the B-cell volume in fetal pancreatic islets showed a marked decrease, but gradually recovered with electron microscopic confirmation of B-cell regeneration. However, STZ at this dose often caused fetal death. In this study, therefore, we determined whether B-cells are newly generated after treatment with STZ at a smaller dose in vivo and in vitro. For in vivo experiment, fetuses were administered STZ at 40 microg/g on day 19 of gestation. The B-cell volume in pancreatic islets decreased markedly 3 hr after the administration of STZ, but it began to increase after 6 hr. The fetal plasma insulin concentration decreased from 6 to 12 hr after the administration, but recovered after 48 hr. The cell division index in fetal pancreatic islets of the STZ-treated group began to be significantly larger after 6 hr. For in vitro experiment, fetal pancreases on day 18 of gestation were pretreated with 10 mM STZ for 6 hr and cultured for 98 hr. B-cells were completely destroyed with STZ treatment; however, as these pancreases were cultured in a medium free of STZ, B-cells began to appear and insulin secretion was detected after 48 hr. After 72 hr, the cell division index was significantly greater. These results suggest that the fetal pancreas treated with STZ has the ability to regenerate B-cells both in vivo and in vitro.