Changes In Β-cell Mass Research Articles

Insulin-Resistant Male LEW.1WR1 Rats Do Not Develop β-Cell Mass Expansion in Response to a Moderate Sucrose Diet

Characterizing changes in beta cell function during prolonged hyperinsulinemia and dietary stress is important to study to prevent diseases like metabolic dysfunction-associated steatotic liver disease and insulin resistance. This research investigates how a moderate sucrose (MS) diet affects insulin resistance and β-cell mass in two rat strains: LEW.1WR1 and Wistar Furth (WF). LEW.1WR1 rats seem to be sensitive to beta cell disruptions as weanlings. Twenty-one male LEW.1WR1 rats and sixteen male WF rats were studied over 18 weeks. The rats were divided into groups and given either the control or MS diet. Their body weight was monitored twice a week. Insulin tolerance tests (ITTs) and fasting blood glucose measurements were taken at intervals. Urine samples were analyzed to assess metabolic shifts, and pancreas tissue was examined to evaluate changes in β-cell mass. The LEW.1WR1 rats became overweight and showed higher insulin resistance than the WF rats. Both strains of rats on the MS diet displayed changes in urine metabolite profiles in terms of levels of lactic acid and alanine. This study highlights the impact or lack thereof of a moderate sucrose diet on body mass, insulin resistance, and β-cell mass, with notable effects observed specifically in LEW.1WR1 rats. These findings contribute to our understanding of how dietary sugar intake can affect metabolism when observed in models sensitive to metabolic defects.

234-OR: Succinate Potentiates Insulin Secretion through SUCNR1

Here, we examined the role of succinate, a metabolite that acts by engaging the succinate receptor 1 (SUCNR1), in regulating insulin secretion by β-cells. We found that glucose increases SUCNR1 expression in β-cells and that activating SUCNR1 with either extracellular succinate or a synthetic agonist boosts glucose-stimulated insulin secretion through the Gq and PKC signaling pathways. Also, we identified that SUCNR1 is essential for preserving insulin secretion in a diet-induced insulin-resistance model. Mice with β-cell-specific SUCNR1 deficiency had impaired glucose tolerance and reduced insulin secretion when fed a high-fat diet, without changes in β-cell mass or insulin sensitivity. To investigate the physiological significance of succinate as a secretagogue in humans, we studied the potential connection between circulating succinate levels and β-cell function in response to oral and intravenous glucose challenges in a cohort of patients with impaired glucose tolerance (IGT). These patients were characterized by presenting hyperinsulinemia during both oral and intravenous glucose tests, compared to normal glucose tolerance (NGT) individuals. Moreover, succinate levels were elevated in IGT patients in response to these challenges compared to NGT patients, whereas circulating GLP-1 levels during the tests were not different between groups. Remarkably, we found that circulating succinate levels are positively correlated with insulin secretion potentiation during intravenous glucose administration, indicating that this system is activated by high glucose levels and partially regulated by the β-cell in an autocrine fashion. These findings suggest that succinate may act as a hormone, potentiating insulin secretion in humans through SUCNR1- a compensatory mechanism particularly relevant in the hyperinsulinemia elicited by insulin resistance. Our work sheds new light on the role of the succinate-SUCNR1 axis as a potential therapeutic target for improving insulin secretion in metabolic disorders. Disclosure J.Sabadell-basallote: None. J.J.Vendrell: None. S.Fernandez-veledo: None. B.D.Astiarraga: None. M.Ejarque: None. M.Repollés-de-dalmau: None. F.X.Sureda: None. D.F.De jesus: None. C.Núñez roa: None. A.Mari: Consultant; Eli Lilly and Company. R.Kulkarni: Advisory Panel; Novo Nordisk, Inversago, Biomea Fusion, Inc., REDD Pharma, Research Support; Inversago. Funding Spanish Ministry of Science and Innovation (SAF2015-65019-R, RTI2018-093919-B-100); Instituto de Salud Carlos III (FI18/00151, CP10/00438, CPII16/00008); Spanish Biomedical Research Center in Diabetes and Associated Metabolic Disorders (CB07708/0012); Catalan Association of Diabetes (PV21039S)

Metabolic Adaptations to Pregnancy in Healthy and Gestational Diabetic Pregnancies: The Pancreas - Placenta Axis.

Normal pregnancy is associated with increased insulin resistance as a metabolic adaptation to the nutritional demands of the placenta and fetus, and this is amplified in obese mothers. Insulin resistance is normally compensated for by an adaptive increase in pancreatic β-cell mass together with enhanced glucose-stimulated insulin release. Placentally-derived hormones and growth factors are central to the altered pancreatic morphology and function. A failure of β-cells to undergo adaptive change after the first trimester has been linked with gestational diabetes. In the pregnant mouse, an increase in β-cell replication contributes to a 2-3-fold increase in mass peaking in late gestation, depending on the proliferation of existing β-cells, the differentiation of resident progenitor β-cells, or islet cell transdifferentiation. Using mouse models and human studies placenta- and islet of Langerhans-derived molecules have been identified that are likely to contribute to the metabolic adaptations to pregnancy and whose physiology is altered in the obese, glucose-intolerant mother. Maternal obesity during pregnancy can create a pro-inflammatory environment that can disrupt the response of the β-cells to the endocrine signals of pregnancy and limit the adaptive changes in β-cell mass and function, resulting in an increased risk of gestational diabetes.

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

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

Biphasic Changes in β-Cell Mass Around Parturition Accompanied by Increased Serotonin Production

Pancreatic β-cell mass is known to be considerably altered during pregnancy and after parturition in rodents and humans. Although βcell mass is increased during pregnancy and starts to return toward its original level shortly after parturition, the cellular mechanisms by which β-cell mass during this period is regulated remains unclear. To address this issue in mice, we quantified β-cell mass and investigated the mechanisms underlying its regulation throughout the perinatal and postpartum period. The increased β-cell size and proliferation during pregnancy were significantly reduced shortly after parturition, whereas there was no evidence of β-cell reprogramming or increased apoptosis. Direct RNA sequencing of islets from pregnant and postpartum mice demonstrated dynamic changes in gene expression patterns, showing robust down-regulation of cell cycle-related genes 1 day after parturition, and the biphasic up-regulation of serotonin metabolism-related genes during pregnancy and at postpartum day 7. Serotonin synthesis was activated during lactation in human as well as in mice. Taken together, these findings demonstrate that β-cell mass is decreased shortly after parturition owing to reduced β-cell size and proliferation, and is subsequently increased, in association with lactation and serotonin biosynthesis. Funding Statement: This work was supported by research grant for Cross-disciplinary Collaboration, Juntendo University 2017 (29-35). Declaration of Interests: The authors stated: There is no conflict of interest on this study. Ethics Approval Statement: The study design was approved by the ethics committee of the Hirosaki University School of Medicine (approval number 2014-269), and the study conforms to the provision of the Declaration of Helsinki.

112-LB: Melatonin and DPP-IV Inhibitor: A Novel Combinatorial Approach for ß-Cell Regeneration

Progressive deterioration of β-cell function and mass is a central parameter to the development of type-1/2 diabetes (T1/2D). Over the last decade, many studies have explored the potential benefits of incretin-based therapies on β-cell preservation and/or regeneration. In this context, DPP-IV inhibitor is known to improve GLP-1 and GIP longevity besides increasing β-cell mass. Melatonin, a pineal hormone is shown to ameliorate oxidative stress and bring about insulin secretion via MT1 receptor activation. Our aim was to evaluate the additive therapeutic effect of melatonin and DPP-IV inhibitor (sitagliptin) on β-cell regeneration in chemically (streptozotocin) induced T1D young and old mouse models, and on insulin resistance in high-fat diet (HFD)-induced T2D mouse model. Our results on pancreatic β-cell regeneration in T1D young and old mice suggest that the combinatorial treatment significantly increased insulin levels thereby lowering FBG levels and increasing glucose tolerance. In young diabetic mice, sitagliptin and melatonin work in an additive manner by increasing β-cell mass (replication and neogenesis) and decreasing apoptosis thus, ameliorating TID manifestations. However, in old diabetic mice, melatonin treatment alone was not as effective as sitagliptin treatment but a significant additive effect was observed in S+M group on β-cell regeneration. In HFD-induced T2D mice the combination therapy was superior to monotherapies in reducing FBG levels, and increasing glucose tolerance. Further, the combination treatment showed increased glucose metabolism, glycogen synthesis, and insulin sensitivity. There was no significant change in β-cell mass in HFD-induced T2D mice. In conclusion, combinatorial therapy is able to ameliorate T1D and T2D in mouse models by β-cell regeneration and increasing insulin sensitivity. Melatonin promotes β-cell proliferation whereas sitagliptin promotes β-cell neogenesis and in concert, they enhance β-cell regeneration. Disclosure R. Patel: None. S. Pramanik: None. N.N. Rathwa: None. N.R. Parmar: None. H. Dhimmar: None. D.A. Pancholi: None. R. A.v.: None. R. Begum: None. Funding Department of Biotechnology, New Delhi, India (BT/PR12584/MED/31/289/2014)

β-Cell compensation concomitant with adaptive endoplasmic reticulum stress and β-cell neogenesis in a diet-induced type 2 diabetes model.

Insulin-secreting pancreatic β-cells adapt to obesity-related insulin resistance via increases in insulin secretion and β-cell mass. Failed β-cell compensation predicts the onset of type 2 diabetes (T2D). However, the mechanisms of β-cell compensation are not fully understood. Our previous study reported changes in β-cell mass during the progression of T2D in the Nile rat (NR; Arvicanthis niloticus) fed standard chow. In the present study, we measured other β-cell adaptive responses, including glucose metabolism and β-cell insulin secretion in NRs at different ages, thus characterizing NR at 2 months as a model of β-cell compensation followed by decompensation at 6 months. We observed increased proinsulin secretion in the transition from compensation to decompensation, which is indicative of impaired insulin processing. Subsequently, we compared adaptive unfolded protein response in β-cells and demonstrated a positive role of endoplasmic reticulum (ER) chaperones in insulin secretion. In addition, the incidence of insulin-positive neogenic but not proliferative cells increased during the compensation phase, suggesting nonproliferative β-cell growth as a mechanism of β-cell mass adaptation. In contrast, decreased neogenesis and β-cell dedifferentiation were observed in β-cell dysfunction. Furthermore, the progression of T2D and pathophysiological changes of β-cells were prevented by increasing fibre content of the diet. Novelty Our study characterized a novel model for β-cell compensation with adaptive responses in cell function and mass. The temporal association of adaptive ER chaperones with blood insulin and glucose suggests upregulated chaperone capacity as an adaptive mechanism. β-Cell neogenesis but not proliferation contributes to β-cell mass adaptation.

Pancreatic β-Cell Rest Replenishes Insulin Secretory Capacity and Attenuates Diabetes in an Extreme Model of Obese Type 2 Diabetes.

The onset of common obesity-linked type 2 diabetes (T2D) is marked by exhaustive failure of pancreatic β-cell functional mass to compensate for insulin resistance and increased metabolic demand, leading to uncontrolled hyperglycemia. Here, the β-cell-deficient obese hyperglycemic/hyperinsulinemic KS db/db mouse model was used to assess consequential effects on β-cell functional recovery by lowering glucose homeostasis and/or improving insulin sensitivity after treatment with thiazolidinedione therapy or glucagon-like peptide 1 receptor agonism alone or in combination with sodium/glucose cotransporter 2 inhibition (SGLT-2i). SGLT-2i combination therapies improved glucose homeostasis, independent of changes in body weight, resulting in a synergistic increase in pancreatic insulin content marked by significant recovery of the β-cell mature insulin secretory population but with limited changes in β-cell mass and no indication of β-cell dedifferentiation. Restoration of β-cell insulin secretory capacity also restored biphasic insulin secretion. These data emphasize that by therapeutically alleviating the demand for insulin in vivo, irrespective of weight loss, endogenous β-cells recover significant function that can contribute to attenuating diabetes. Thus, this study provides evidence that alleviation of metabolic demand on the β-cell, rather than targeting the β-cell itself, could be effective in delaying the progression of T2D.

Validation of 111In-Exendin SPECT for the Determination of the β-Cell Mass in BioBreeding Diabetes-Prone Rats.

The changes in β-cell mass (BCM) during the development and progression of diabetes could potentially be measured by radionuclide imaging using radiolabeled exendin. In this study, we investigated the potential of 111In-diethylenetriaminepentaacetic acid-exendin-3 (111In-exendin) in a rat model that closely mimics the development of type 1 diabetes (T1D) in humans: BioBreeding diabetes-prone (BBDP) rats. BBDP rats of 4-18 weeks of age were injected intravenously with 111In-exendin, and single-photon emission computed tomography (SPECT) images were acquired. The accumulation of the radiotracer was measured as well as the BCM and grade of insulitis by histology. 111In-exendin accumulated specifically in the islets, resulting in a linear correlation with the BCM (%) (Pearson r = 0.89, P < 0.0001, and r = 0.64 for SPECT). Insulitis did not have an influence on this correlation. These results indicate that 111In-exendin is a promising tracer to determine the BCM during the development of T1D, irrespective of the degree of insulitis.

Direct comparison of the abilities of bone marrow mesenchymal versus hematopoietic stem cells to reverse hyperglycemia in diabetic NOD.SCID mice

ABSTRACTBoth bone marrow-derived hematopoietic stem cells (HSC) and mesenchymal stem cells (MSC) improve glycemic control in diabetic mice, but their kinetics and associated changes in pancreatic morphology have not been directly compared. Our goal was to examine the time course of improvements in glucose tolerance and associated changes in β-cell mass and proliferation following transplantation of equivalent numbers of HSC or MSC from the same bone marrow into diabetic non-obese diabetic severe combined immune deficiency (NOD.SCID) mice. We used transgenic mice with a targeted expression of yellow fluorescent protein (YFP) driven by the Vav1 gene promoter to genetically tag HSC and progeny. HSC were separated from bone marrow by fluorescence-activated cell sorting and MSC following cell culture. Equivalent numbers of isolated HSC or MSC were transplanted directly into the pancreas of NOD.SCID mice previously made diabetic with streptozotocin. Glucose tolerance, serum insulin, β-cell mass and β-cell proliferation were examined up to 28 days following transplant. Transplantation with MSC improved glucose tolerance within 7 days and serum insulin levels increased, but with no increase in β-cell mass. Mice transplanted with HSC showed improved glucose tolerance only after 3 weeks associated with increased β-cell proliferation and mass. We conclude that single injections of either MSC or HSC transiently improved glycemic control in diabetic NOD.SCID mice, but with different time courses. However, only HSC infiltrated the islets and were associated with an expanded β-cell mass. This suggests that MSC and HSC have differing mechanisms of action.

Overexpression of Kinase-Dead mTOR Impairs Glucose Homeostasis by Regulating Insulin Secretion and Not β-Cell Mass.

Regulation of glucose homeostasis by insulin depends on β-cell growth and function. Nutrients and growth factor stimuli converge on the conserved protein kinase mechanistic target of rapamycin (mTOR), existing in two complexes, mTORC1 and mTORC2. To understand the functional relevance of mTOR enzymatic activity in β-cell development and glucose homeostasis, we generated mice overexpressing either one or two copies of a kinase-dead mTOR mutant (KD-mTOR) transgene exclusively in β-cells. We examined glucose homeostasis and β-cell function of these mice fed a control chow or high-fat diet. Mice with two copies of the transgene [RIPCre;KD-mTOR (Homozygous)] develop glucose intolerance due to a defect in β-cell function without alterations in β-cell mass with control chow. Islets from RIPCre;KD-mTOR (Homozygous) mice showed reduced mTORC1 and mTORC2 signaling along with transcripts and protein levels of Pdx-1. Islets with reduced mTORC2 signaling in their β-cells (RIPCre;Rictorfl/fl) also showed reduced Pdx-1. When challenged with a high-fat diet, mice carrying one copy of KD-mTOR mutant transgene developed glucose intolerance and β-cell insulin secretion defect but showed no changes in β-cell mass. These findings suggest that the mTOR-mediated signaling pathway is not essential to β-cell growth but is involved in regulating β-cell function in normal and diabetogenic conditions.

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

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

Changes in the expression of the type 2 diabetes-associated gene VPS13C in the β-cell are associated with glucose intolerance in humans and mice.

Single nucleotide polymorphisms (SNPs) close to the VPS13C, C2CD4A and C2CD4B genes on chromosome 15q are associated with impaired fasting glucose and increased risk of type 2 diabetes. eQTL analysis revealed an association between possession of risk (C) alleles at a previously implicated causal SNP, rs7163757, and lowered VPS13C and C2CD4A levels in islets from female (n = 40, P < 0.041) but not from male subjects. Explored using promoter-reporter assays in β-cells and other cell lines, the risk variant at rs7163757 lowered enhancer activity. Mice deleted for Vps13c selectively in the β-cell were generated by crossing animals bearing a floxed allele at exon 1 to mice expressing Cre recombinase under Ins1 promoter control (Ins1Cre). Whereas Vps13cfl/fl:Ins1Cre (βVps13cKO) mice displayed normal weight gain compared with control littermates, deletion of Vps13c had little effect on glucose tolerance. Pancreatic histology revealed no significant change in β-cell mass in KO mice vs. controls, and glucose-stimulated insulin secretion from isolated islets was not altered in vitro between control and βVps13cKO mice. However, a tendency was observed in female null mice for lower insulin levels and β-cell function (HOMA-B) in vivo. Furthermore, glucose-stimulated increases in intracellular free Ca2+ were significantly increased in islets from female KO mice, suggesting impaired Ca2+ sensitivity of the secretory machinery. The present data thus provide evidence for a limited role for changes in VPS13C expression in conferring altered disease risk at this locus, particularly in females, and suggest that C2CD4A may also be involved.

SPECT-OPT multimodal imaging enables accurate evaluation of radiotracers for β-cell mass assessments.

Single Photon Emission Computed Tomography (SPECT) has become a promising experimental approach to monitor changes in β-cell mass (BCM) during diabetes progression. SPECT imaging of pancreatic islets is most commonly cross-validated by stereological analysis of histological pancreatic sections after insulin staining. Typically, stereological methods do not accurately determine the total β-cell volume, which is inconvenient when correlating total pancreatic tracer uptake with BCM. Alternative methods are therefore warranted to cross-validate β-cell imaging using radiotracers. In this study, we introduce multimodal SPECT - optical projection tomography (OPT) imaging as an accurate approach to cross-validate radionuclide-based imaging of β-cells. Uptake of a promising radiotracer for β-cell imaging by SPECT, 111In-exendin-3, was measured by ex vivo-SPECT and cross evaluated by 3D quantitative OPT imaging as well as with histology within healthy and alloxan-treated Brown Norway rat pancreata. SPECT signal was in excellent linear correlation with OPT data as compared to histology. While histological determination of islet spatial distribution was challenging, SPECT and OPT revealed similar distribution patterns of 111In-exendin-3 and insulin positive β-cell volumes between different pancreatic lobes, both visually and quantitatively. We propose ex vivo SPECT-OPT multimodal imaging as a highly accurate strategy for validating the performance of β-cell radiotracers.

Pancreatic β‐cell imaging in humans: fiction or option?

Diabetes mellitus is a growing worldwide epidemic disease, currently affecting 1 in 12 adults. Treatment of disease complications typically consumes ∼10% of healthcare budgets in developed societies. Whilst immune-mediated destruction of insulin-secreting pancreatic β cells is responsible for Type 1 diabetes, both the loss and dysfunction of these cells underly the more prevalent Type 2 diabetes. The establishment of robust drug development programmes aimed at β-cell restoration is still hampered by the absence of means to measure β-cell mass prospectively in vivo, an approach which would provide new opportunities for understanding disease mechanisms and ultimately assigning personalized treatments. In the present review, we describe the progress towards this goal achieved by the Innovative Medicines Initiative in Diabetes, a collaborative public-private consortium supported by the European Commission and by dedicated resources of pharmaceutical companies. We compare several of the available imaging methods and molecular targets and provide suggestions as to the likeliest to lead to tractable approaches. Furthermore, we discuss the simultaneous development of animal models that can be used to measure subtle changes in β-cell mass, a prerequisite for validating the clinical potential of the different imaging tracers.

Increased adrenergic signaling is responsible for decreased glucose-stimulated insulin secretion in the chronically hyperinsulinemic ovine fetus.

Insulin may stimulate its own insulin secretion and is a potent growth factor for the pancreatic β-cell. Complications of pregnancy, such as diabetes and intrauterine growth restriction, are associated with changes in fetal insulin concentrations, secretion, and β-cell mass. However, glucose concentrations are also abnormal in these conditions. The direct effect of chronic fetal hyperinsulinemia with euglycemia on fetal insulin secretion and β-cell mass has not been tested. We hypothesized that chronic fetal hyperinsulinemia with euglycemia would increase glucose-stimulated insulin secretion (GSIS) and β-cell mass in the ovine fetus. Singleton ovine fetuses were infused with iv insulin to produce high physiological insulin concentrations, or saline for 7-10 days. The hyperinsulinemic animals also received a direct glucose infusion to maintain euglycemia. GSIS, measured at 133 ± 1 days of gestation, was significantly attenuated in the hyperinsulinemic fetuses (P < .05). There was no change in β-cell mass. The hyperinsulinemic fetuses also had decreased oxygen (P < .05) and higher norepinephrine (1160 ± 438 vs 522 ± 106 pg/mL; P < .005). Acute pharmacologic adrenergic blockade restored GSIS in the hyperinsulinemic-euglycemic fetuses, demonstrating that increased adrenergic signaling mediates decreased GSIS in these fetuses.

Synthesis and evaluation of 18F-labeled mitiglinide derivatives as positron emission tomography tracers for β-cell imaging

Measuring changes in β-cell mass in vivo during progression of diabetes mellitus is important for understanding the pathogenesis, facilitating early diagnosis, and developing novel therapeutics for this disease. However, a non-invasive method has not been developed. A novel series of mitiglinide derivatives (o-FMIT, m-FMIT and p-FMIT; FMITs) were synthesized and their binding affinity for the sulfonylurea receptor 1 (SUR1) of pancreatic islets were evaluated by inhibition studies. (+)-(S)-o-FMIT had the highest affinity of our synthesized FMITs (IC50=1.8μM). (+)-(S)-o-[18F]FMIT was obtained with radiochemical yield of 18% by radiofluorination of racemic precursor 7, hydrolysis, and optical resolution with chiral HPLC; its radiochemical purity was >99%. In biodistribution experiments using normal mice, (+)-(S)-o-[18F]FMIT showed 1.94±0.42% ID/g of pancreatic uptake at 5min p.i., and decreases in radioactivity in the liver (located close to the pancreas) was relatively rapid. Ex vivo autoradiography experiments using pancreatic sections confirmed accumulation of (+)-(S)-o-[18F]FMIT in pancreatic β-cells. These results suggest that (+)-(S)-o-[18F]FMIT meets the basic requirements for an radiotracer, and could be a candidate positron emission tomography tracer for in vivo imaging of pancreatic β-cells.

Long- But Not Short-Term Adult-Onset, Isolated GH Deficiency in Male Mice Leads to Deterioration of β-Cell Function, Which Cannot Be Accounted for by Changes in β-Cell Mass

Developmental models of GH deficiency (GHD) and excess indicate that GH is positively associated with β-cell mass. Therefore, the reduction in GH levels observed with age and weight gain may contribute to the age-related decline in β-cell function. To test this hypothesis, β-cell mass and function were assessed in a mouse model of adult-onset, isolated GHD (AOiGHD). β-Cell mass did not differ between low-fat (LF)-fed AOiGHD and controls. However, high fat-fed AOiGHD mice displayed impaired expansion of β-cell mass and a reduction of bromodeoxyuridine-labeled islet cells, whereas in vitro β-cell function (basal and glucose-stimulated insulin secretion [GSIS]) did not differ from controls. In contrast, duration of AOiGHD differentially altered in vitro β-cell function in LF-fed mice. Specifically, islets from young LF-fed AOiGHD mice showed significant reductions in insulin content and basal insulin secretion, but GSIS was similar to that of controls. A similar islet phenotype was observed in a developmental model of isolated GHD (GH-releasing hormone knockout). Given that LF- and high fat-fed AOiGHD mice, as well as GH-releasing hormone knockout mice, display improved insulin sensitivity, islet changes may be due to reduced insulin demand, rather than primary β-cell dysfunction. However, islets from older LF-fed AOiGHD mice exhibited impaired GSIS, associated with reduced expression of genes important to maintain glucose sensing, suggesting that factors secondary to AOiGHD can alter β-cell function with age. AOiGHD mice exhibited postprandial hypertriglyceridemia and increased pancreatic expression of lipid/inflammatory stress response genes (activating transcription factor 3 and peroxisome proliferator activator receptor β/δ). Therefore, we speculate that these changes may initially protect the AOiGHD β-cell, but with age, lipotoxicity may impair β-cell function.

Change in β-Cell Mass in Japanese Nondiabetic Obese Individuals

The aim of this study was to clarify the change in β-cell mass in Japanese obese individuals. We obtained the pancreas at autopsy from 39 lean and 33 obese Japanese nondiabetic individuals (aged 47 ± 13 vs 47 ± 12 y, P = .83, body mass index 20.4 ± 1.6 vs 28.5 ± 3.9 kg/m(2), P < .01). Pancreatic sections were stained for insulin, and β-cell area (%BCA) was measured as the fraction of the β-cell area to the total pancreas area. β-Cell mass was then calculated as the product of %BCA and estimated pancreas weight. β-Cell replication and apoptosis were assessed by double staining for insulin and Ki67 and insulin and single-stranded DNA, respectively. The frequencies of insulin-positive duct cells and scattered β-cells were assessed as the surrogate markers of β-cell neogenesis. The α-cell area (%ACA) was also measured, and the %ACA to %BCA ratio was determined. There was no increase in β-cell mass in obese individuals compared with lean individuals (0.6 ± 0.4 vs 0.7 ± 0.4 g, P = .12). β-Cell replication, β-cell neogenesis, and β-cell apoptosis were not significantly increased in the presence of obesity. There was no significant difference in %ACA to %BCA ratio between obese and lean individuals (0.91 ± 1.09 vs 0.75 ± 0.51, P = .47). There was no increase in β-cell mass and no detectable change in β-cell turnover in Japanese obese individuals.

Recovery from diabetes in neonatal mice after a low-dose streptozotocin treatment

Administration of streptozotocin (STZ) induces destruction of β-cells and is widely used as an experimental animal model of type I diabetes. In neonatal rat, after low-doses of STZ-mediated destruction of β-cells, β-cells regeneration occurs and reversal of hyperglycemia was observed. However, in neonatal mice, β-cell regeneration seems to occur much slowly compared to that observed in the rat. Here, we described the time dependent quantitative changes in β-cell mass during a spontaneous slow recovery of diabetes induced in a low-dose STZ mice model. We then investigated the underlying mechanisms and analyzed the cell source for the recovery of β-cells. We showed here that postnatal day 7 (P7) female mice treated with 50mg/kg STZ underwent the destruction of a large proportion of β-cells and developed hyperglycemia. The blood glucose increased gradually and reached a peak level at 500mg/dl on day 35–50. This was followed by a spontaneous regeneration of β-cells. A reversal of non-fasting blood glucose to the control value was observed within 150days. However, the mice still showed impaired glucose tolerance on day 150 and day 220, although a significant improvement was observed on day 150. Quantification of the β-cell mass revealed that the β-cell mass increased significantly between day 100 and day 150. On day 150 and day 220, the β-cell mass was approximately 23% and 48.5% of the control, respectively. Of the insulin-positive cells, 10% turned out to be PCNA-positive proliferating cells. Our results demonstrated that, β-cell duplication is one of the cell sources for β-cell regeneration.