Glucose-induced Insulin Release Research Articles

Protective effects of curcumin on desipramine-induced islet β-cell damage via AKAP150/PKA/PP2B complex.

Tricyclic antidepressants (TCAs) are widely used to treat depression and anxiety-related mood disorders. But evidence shows that TCAs elevate blood glucose levels and inhibit insulin secretion, suggesting that TCAs are a risk factor, particularly for individuals with diabetes. Curcumin is a bioactive molecule from the rhizome of the Curcuma longa plant, which has shown both antidepressant and anti-diabetic activities. In the present study, we investigated the protective effect of curcumin against desipramine-induced apoptosis in β cells and the underlying molecular mechanisms. In the mouse forced swimming test (FST), we found that lower doses of desipramine (5 and 10 mg/kg) or curcumin (2.5 mg/kg) alone did not affect the immobility time, whereas combined treatment with curcumin (2.5 mg/kg) and desipramine (5, 10 mg/kg) significantly decreased the immobility time. Furthermore, desipramine dose-dependently inhibited insulin secretion and elevated blood glucose levels, whereas the combined treatment normalized insulin secretion and blood glucose levels. In RIN-m5F pancreatic β-cells, desipramine (10 μM) significantly reduced the cell viability, whereas desipramine combined with curcumin dose-dependently prevented the desipramine-induced impairment in glucose-induced insulin release, most effectively with curcumin (1 and 10 μM). We demonstrated that desipramine treatment promoted the cleavage and activation of Caspase 3 in RIN-m5F cells. Curcumin treatment inhibited desipramine-induced apoptosis, increased mitochondrial membrane potential and Bcl-2/Bax ratio. Desipramine increased the generation of reactive oxygen species, which was reversed by curcumin treatment. Curcumin also inhibited the translocation of forkhead box protein O1 (FOXO1) from the cytoplasm to the nucleus and suppressed the binding of A-kinase anchor protein 150 (AKAP150) to protein phosphatase 2B (PP2B, known as calcineurin) that was induced by desipramine. These results suggest that curcumin protects RIN-m5F pancreatic β-cells against desipramine-induced apoptosis by inhibiting the phosphoinositide 3-kinase/AKT/FOXO1 pathway and the AKAP150/PKA/PP2B interaction. This study suggests that curcumin may have therapeutic potential as an adjunct to antidepressant treatment.

Hyperglycemia, pregnancy outcomes and maternal metabolic disease risk during pregnancy and lactation in a lean gestational diabetes mouse model.

Hyperglycemia in pregnancy (HIP) is a pregnancy complication characterized by mild to moderate hyperglycemia that negatively impacts short- and long-term health of mother and child. However, relationships between severity and timing of pregnancy hyperglycemia and postpartum outcomes have not been systemically investigated. We investigated the impact of hyperglycemia developing during pregnancy (gestational diabetes mellitus, GDM) or already present pre-mating (pre-gestational diabetes mellitus, PDM) on maternal health and pregnancy outcomes. GDM and PDM were induced in C57BL/6NTac mice by combined 60% high fat diet (HF) and low dose streptozotocin (STZ). Animals were screened for PDM prior to mating, all underwent an OGTT on gestational day (GD)15. Tissues were collected at GD18 or at postnatal day (PN)15. Among HFSTZ-treated dams, 34% developed PDM and 66% developed GDM, characterized by impaired glucose-induced insulin release and inadequate suppression of endogenous glucose production. No increased adiposity or overt insulin resistance was observed. Furthermore, markers of non-alcoholic fatty liver disease (NAFLD) were significantly increased in PDM at GD18 and were positively correlated with basal glucose levels at GD18 in GDM dams. By PN15, NAFLD markers were also increased in GDM dams. Only PDM affected pregnancy outcomes such as litter size. Our findings indicate that GDM and PDM, resulting in disturbances of maternal glucose homeostasis, increase the risk of postpartum NAFLD development, related to the onset and severity of pregnancy hyperglycemia. These findings signal a need for earlier monitoring of maternal glycemia and more rigorous follow-up of maternal health after GDM and PDM pregnancy in humans. KEY POINTS: We studied the impact of high-fat diet/streptozotocin induced hyperglycemia in pregnancy (HIP) in mice and found that this impaired glucose tolerance and insulin release. Litter size and embryo survival were compromised by pre-gestational, but not by gestational diabetes. Despite postpartum recovery from hyperglycemia in a majority of dams, liver disease markers were further elevated by PN15. Maternal liver disease markers were associated with the severity of hyperglycemia at GD18. The association between hyperglycemic exposure and NAFLD signal a need for more rigorous monitoring and follow-up of maternal glycemia and health in diabetic pregnancy in humans. Abstract figure legend Streptozotocin and high fat diet were used to induce GDM in female BL6/NTac mice. Pregnant dams underwent an OGTT at GD15 to confirm GDM diagnosis. By GD18, dams were hyperglycemic and showed a reduction in pancreatic beta cells. By PN15, dams additionally had developed an increase in NAFLD markers, despite the majority of the dams having recovered from hyperglycemia. This article is protected by copyright. All rights reserved.

Extracellular matrix inclusion in immunoisolating alginate-based microcapsules promotes longevity, reduces fibrosis, and supports function of islet allografts in vivo.

Immunoisolation of pancreatic-islets in alginate-microcapsules is applied to treat diabetes. However, long-term islet function is limited, which might be due to damaged and lack of contact with pancreatic extracellular matrix (ECM) components. Herein we investigated the impact of collagen IV combined with laminin sequences, either RGD, LRE, or PDSGR, on graft-survival of microencapsulated bioluminescent islets in vivo. Collagen IV with RGD had the most pronounced effect. It enhanced after 8-week implantation in immune-incompetent mice the bioluminescence of allogeneic islets by 3.2-fold, oxygen consumption rate by 14.3-fold and glucose-induced insulin release by 9.6-fold. Transcriptomics demonstrated that ECM enhanced canonical pathways involving insulin-secretion and that it suppressed pathways related to inflammation and hypoxic stress. Also, 5.8-fold fewer capsules were affected by fibrosis. In a subsequent longevity study in immune-competent mice, microencapsulated allografts containing collagen IV and RGD had a 2.4-fold higher functionality in the first week after implantation and remained at least 2.1-fold higher during the study. Islets in microcapsules containing collagen IV and RGD survived 211 ± 24.1 days while controls survived 125 ± 19.7 days. Our findings provide in vivo evidence for the efficacy of supplementing immunoisolating devices with specific ECM components to enhance functionality and longevity of islet-grafts in vivo. STATEMENT OF SIGNIFICANCE: Limitations in duration of survival of immunoisolated pancreatic islet grafts is a major obstacle for application of the technology to treat diabetes. Accumulating evidence supports that incorporation of extracellular matrix (ECM) molecules in the capsules enhances longevity of pancreatic islets. After selection of the most efficacious laminin sequence in vitro, we show in vivo that inclusion of collagen IV and RGD in alginate-based microcapsules enhances survival, insulin secretion function, and mitochondrial function. It also suppresses fibrosis by lowering proinflammatory cytokines secretion. Moreover, transcriptomic analysis shows that ECM-inclusion promotes insulin-secretion related pathways and attenuates inflammation and hypoxic stress related pathways in islets. We show that inclusion of ECM in immunoisolating devices is a promising strategy to promote long-term survival of islet-grafts.

Incretins play an important role in FFA4/GPR120 regulation of glucose metabolism by GW-9508

AimsTo assess the role of GPR120 in glucose metabolism and incretin regulation from enteroendocrine L- and K-cells with determination of the cellular localisation of GPR120 in intestinal tissue and clonal Glucagon-Like Peptide-1 (GLP-1)/Gastric Inhibitory Polypeptide (GIP) cell lines. Main methodsAnti-hyperglycaemic, insulinotropic and incretin secreting properties of the GPR120 agonist, GW-9508 were explored in combination with oral and intraperitoneal glucose tolerance tests (GTT) in lean, diabetic and incretin receptor knockout mice. Cellular localisation of GPR120 was assessed by double immunofluorescence. Key findingsCompared to intraperitoneal injection, oral administration of GW-9508 (0.1 μmol/kg body weight) together with glucose reduced the glycaemic excursion by 22–31 % (p < 0.05-p < 0.01) and enhanced glucose-induced insulin release by 30 % (p < 0.01) in normal mice. In high fat fed diabetic mice, orally administered GW-9508 lowered plasma glucose by 17–27 % (p < 0.05-p < 0.01) and augmented insulin release by 22–39 % (p < 0.05-p < 0.001). GW-9508 had no effect on the responses of GLP-1 receptor knockout mice and GIP receptor knockout mice. Consistent with this, oral GW-9508 increased circulating total GLP-1 release by 39–44 % (p < 0.01) and total GIP by 37–47 % (p < 0.01-p < 0.001) after 15 and 30 min in lean NIH Swiss mice. Immunocytochemistry demonstrated GPR120 expression on mouse enteroendocrine L- and K-cells, GLUTag cells and pGIP/Neo STC-1 cells. SignificanceGPR120 is expressed on intestinal L- and K-cells and stimulates GLP-1/GIP secretory pathways involved in mediating enhanced insulin secretion and improved glucose tolerance, following oral GW-9508. These novel data strongly support the development of potent and selective GPR120 agonists as an effective therapeutic approach for diabetes.

LBODP051 Relation Of The Quadrumvirate ― Hepatic Steatosis, High Normal Fasting Glucose, And Attenuated Whole Body-insulin Sensitivity And Glucose-stimulated Acute Insulin Secretion ― To Incident Prediabetes, The Beginning Of Type 2 Diabetes

Abstract Type 2 diabetes begins as conversion of normal glucose metabolism (NGM) to prediabetes, and 5-10% per year of people with prediabetes progress to diabetes. Therefore, understanding evolution of prediabetes is mandatory to know how type 2 diabetes starts. However, the process of conversion of NGM to prediabetes, which may be ethnicity-specific, has poorly been investigated. We analyzed 599 Japanese adults with NGM (fasting plasma glucose (FPG) &amp;lt;100 mg·dL-1 and 2-h PG at 75 g oral glucose tolerance (OGTT) &amp;lt;140 mg·dL-1) (male 62%, the mean age, body mass index (BMI), fasting IRI/FPG and 2-h IRI/PG, 52 years, 23.1 kg·m-2, 4.1 μU·mL-1/92 mg·dL-1 and 24.5 μU·mL-1/104 mg·dL-1, respectively). They received follow-up OGTTs at a mean of 3.7 years later (2,061 person-years observation). Prediabetes developed in 179 (impaired fasting glucose 102, impaired glucose tolerance 39, and impaired fasting glucose/impaired glucose tolerance 28). By the screening univariate analysis, Fatty Liver Index (FLI), FPG, ISIMATSUDA (index of basal and post-glucose whole body insulin sensitivity (Si) and Stumvoll's first phase (Stumvoll-1, an index of glucose-stimulated acute (∼10 min) insulin secretion (Isec) were robust risk factors for incident prediabetes. In contrast, indices of basal Si such as HOMA-IR, and basal, 30 min, or later phase index of Isec such as HOMAbeta and insulinogenic index, respectively, were not significant risk for prediabetes. In multivariate Cox model adjusted for age and sex, HR (95%CI) per 1 IQR increase were FLI 1.303 (1. 063-1.586), P &amp;lt;0. 01; FPG 1.400 (1. 076-1.840), P &amp;lt;0. 01; ISIMATSUDA 0.841 (0.712-0.963), P = 0. 03; Stumvoll-1 0.764 (0.622-0.935) P &amp;lt;0. 01. Note that FLI and FPG are risk factors and ISIMATSUDA and Stumvoll-1 are protective factors. Notably, FLI was a risk even after adjustment for BMI. The best cutoff values differentiating prediabetes Progressors from Nonprogressors obtained by the ROC curve using entire range of each risk factor was ≥12.4 for FLI, ≥95 mg·dL-1 for FPG, ≤11.99 for ISIMATSUDA and ≤486.3 for Stumvoll-1, and incidence of prediabetes was progressively high as 10/127 (6%), 34/153 (22%), 56/189 (30%), 53/106 (50%) and 16/24 (67%) among the participants with no, one, two, three and four unfavorable discriminating values for progression, respectively. AUC of ROC curve (AUROC) for the combination of the quadrumvirate was as large as 0.729 (0.661-0.788) with high precision as sensitivity 73.4% and specificity 63.8%. In conclusion, at the beginning of type 2 diabetes in the Japanese population who are non-obese and insulin-sensitive as shown, hepatic steatosis, the high normal FPG, attenuation of whole-body insulin sensitivity, lowered acute phase glucose-induced insulin release (the quadrumvirate) are synergistically and independently, with comparable strength each other, related to the development of prediabetes. Presentation: No date and time listed

The lysine demethylase KDM6A regulates pancreatic β cells function

Background and ObjectiveDiabetes mellitus refers to a group of metabolic disorders characterized by impaired glucose homeostasis. Both type 1 diabetes (T1D) and type 2 diabetes (T2D) are characterized by insulin insufficiency. β cell failure in diabetes are often due to posttranslational modifications of histones and transcription factors. Lysine demethylase 6A (KDM6A) belongs to the KDM6 family of histone H3 lysine 27 (H3K27) demethylases which is important for development of various organs. The objective of this study is to investigate whether KDM6A regulates pancreatic β cell function using targeted β cell‐specific deletion of KDM6Agene.Methods and ResultsBriefly, inducible insulin 1‐cre and KDM6A‐loxp mice were bed to generate cre‐loxp mice. Injection of tamoxifen induced deletion of KDM6A gene in β cells which led to increased H3K27me3 levels. KDM6A‐KO mice exhibited reduced baseline insulin levels compared with wild‐type mice. Interestingly, despite low baseline insulin levels, KDM6A‐KO mice demonstrated enhanced glucose tolerance. Insulin release was increased in KDM6A‐KO mice vs WT mice at 15 min following glucose challenge. Furthermore, ex vivo glucose‐induced insulin secretion was increased in cultured islets isolated from KDM6A‐KO mice. In cultured Min6 β cells, knockdown of KDM6A using KDM6A shRNA largely enhanced glucose‐induced insulin release. When challenged with high‐fat diet, KDM6A‐KO mice displayed similar weight gain vs wild‐type mice. However, the insulin sensitivity test showed that KDM6A‐KO enhanced peripheral insulin sensitivity as evidenced by the delayed recovery of glucose level in KDM6A‐KO mice fed with high‐fat diet.ConclusionOur results suggest a novel role of KDM6A in the regulation of pancreatic β cell function. KDM6A may be a potential therapeutic target for β cell dysfunction.

GPR40 Activation Abolishes Diabetes-Induced Painful Neuropathy by Suppressing VEGF-A Expression.

G-protein-coupled receptor 40 (GPR40) is a promising target to support glucose-induced insulin release in patients with type 2 diabetes. We studied the role of GPR40 in the regulation of blood-nerve barrier integrity and its involvement in diabetes-induced neuropathies. Because GPR40 modulates insulin release, we used the streptozotocin model for type 1 diabetes, in which GPR40 functions can be investigated independently of its effects on insulin release. Diabetic wild-type mice exhibited increased vascular endothelial permeability and showed epineural microlesions in sciatic nerves, which were also observed in naïve GPR40-/- mice. Fittingly, expression of vascular endothelial growth factor-A (VEGF-A), an inducer of vascular permeability, was increased in diabetic wild-type and naïve GPR40-/- mice. GPR40 antagonists increased VEGF-A expression in murine and human endothelial cells as well as permeability of transendothelial barriers. In contrast, GPR40 agonists suppressed VEGF-A release and mRNA expression. The VEGF receptor inhibitor axitinib prevented diabetes-induced hypersensitivities and reduced endothelial and epineural permeability. Importantly, the GPR40 agonist GW9508 reverted established diabetes-induced hypersensitivity, an effect that was blocked by VEGF-A administration. Thus, GPR40 activation suppresses VEGF-A expression, thereby reducing diabetes-induced blood-nerve barrier permeability and reverting diabetes-induced hypersensitivities.

ATP synthase inhibitory factor subunit 1 regulates islet β-cell function via repression of mitochondrial homeostasis

AbstractMitochondrial homeostasis is crucial for the function of pancreatic β-cells. ATP synthase inhibitory factor subunit 1 (IF1) is a mitochondrial protein interacting with ATP synthase to inhibit its enzyme activity. IF1 may also play a role in maintaining ATP synthase oligomerization and mitochondrial inner membrane formation. A recent study confirmed IF1 expresses in β-cells. IF1 knockdown in cultured INS-1E β-cells enhances glucose-induced insulin release. However, the role of IF1 in islet β-cells remains little known. The present study investigates islets freshly isolated from mouse lines with global IF1 knockout (IF1−/−) and overexpression (OE). The glucose-stimulated insulin secretion was increased in islets from IF1−/− mice but decreased in islets from IF1 OE mice. Transmitted Electronic Microscopic assessment of isolated islets revealed that the number of matured insulin granules (with dense core) was relatively higher in IF1−/−, but fewer in IF1 OE islets than those of controlled islets. The mitochondrial ultrastructure within β-cells of IF1 overexpressed islets was comparable with those of wild-type mice, whereas those in IF1−/− β-cells showed increased mitochondrial mass. Mitochondrial network analysis in cultured INS-1 β-cells showed a similar pattern with an increased mitochondrial network in IF1 knockdown cells. IF1 overexpressed INS-1 β-cells showed a compromised rate of mitochondrial oxidative phosphorylation with attenuated cellular ATP content. In contrast, INS-1 cells with IF1 knockdown showed markedly increased cellular respiration with improved ATP production. These results support that IF1 is a negative regulator of insulin production and secretion via inhibiting mitochondrial mass and respiration in β-cells. Therefore, inhibiting IF1 to improve β-cell function in patients can be a novel therapeutic strategy to treat diabetes.

Status of ghrelin as an islet hormone and paracrine/autocrine regulator of insulin secretion

Ghrelin is expressed in the pancreatic islet cells as well as the stomach. In the perfused pancreas and isolated islets, GHS-R antagonism, ghrelin immunoneutralization and ghrelin-knockout (Ghr-KO) all increase glucose-induced insulin release. Thus, pharmacological, immunological and genetic blockades of ghrelin in the pancreatic islets all markedly augment glucose-induced insulin release, showing that islet-derived ghrelin physiologically restricts insulin release in rodents. In this review, we focus on the current understanding of the following key questions: 1) from which islet cells ghrelin is released, 2) on which islet cells ghrelin acts, and 3) mechanisms by which the islet-derived ghrelin inhibits insulin secretion.

The Effects of Glucagon-Like Peptide-1 Receptor Agonists and Dipeptydilpeptidase-4 Inhibitors on Blood Pressure and Cardiovascular Complications in Diabetes.

Glucagon-like peptide-1 receptor (GLP-1R) agonists are a class of newly introduced antidiabetic medications that potentially lower blood glucose by several molecular pathways. DPP-4 inhibitors are the other type of novel antidiabetic medications which act by preventing GLP-1 inactivation and thereby increasing the activity levels of GLP-1, leading to more glucose-induced insulin release from islet β-cells and suppression of glucagon release. Most patients with diabetes have concurrent hypertension and cardiovascular disorder. If antihyperglycemic agents can attenuate the risk of hypertension and cardiovascular disease, they will amplify their overall beneficial effects. There is conflicting evidence on the cardiovascular benefits of GLP-1R induction in laboratory studies and clinical trials. In this study, we have reviewed the main molecular mechanisms by which GLP-1R induction may modulate the cardiovascular function and the results of cardiovascular outcome clinical trials.

Reduced glucose-induced first-phase insulin release is a danger signal that predicts diabetes.

During progression to both types 1 and 2 diabetes (T1D, T2D), there is a striking loss of glucose-induced first-phase insulin release (FPIR), which is known to predict the onset of T1D. The contribution of reduced β cell mass to the onset of hyperglycemia remains unclear. In this issue of the JCI, Mezza et al. report on their study of patients with pancreatic neoplasms before and after partial pancreatectomy to evaluate the impact of reduced β cell mass on the development of diabetes. The authors found that reduced FPIR predicted diabetes when 50% of the pancreas was removed. These findings suggest that low or absent FPIR indicates that β cell mass can no longer compensate for increased insulin needs. Notably, clinicians may use reduction of FPIR as a warning that progression to T2D is underway.

Age-dependent transition from islet insulin hypersecretion to hyposecretion in mice with the long QT-syndrome loss-of-function mutation Kcnq1-A340V

Loss-of-function (LoF) mutations in KCNQ1, encoding the voltage-gated K+ channel Kv7.1, lead to long QT syndrome 1 (LQT1). LQT1 patients also present with post-prandial hyperinsulinemia and hypoglycaemia. In contrast, KCNQ1 polymorphisms are associated with diabetes, and LQTS patients have a higher prevalence of diabetes. We developed a mouse model with a LoF Kcnq1 mutation using CRISPR-Cas9 and hypothesized that this mouse model would display QT prolongation, increased glucose-stimulated insulin secretion and allow for interrogation of Kv7.1 function in islets. Mice were characterized by electrocardiography and oral glucose tolerance tests. Ex vivo, islet glucose-induced insulin release was measured, and beta-cell area quantified by immunohistochemistry. Homozygous mice had QT prolongation. Ex vivo, glucose-stimulated insulin release was increased in islets from homozygous mice at 12–14 weeks, while beta-cell area was reduced. Non-fasting blood glucose levels were decreased at this age. In follow-up studies 8–10 weeks later, beta-cell area was similar in all groups, while glucose-stimulated insulin secretion was now reduced in islets from hetero- and homozygous mice. Non-fasting blood glucose levels had normalized. These data suggest that Kv7.1 dysfunction is involved in a transition from hyper- to hyposecretion of insulin, potentially explaining the association with both hypoglycemia and hyperglycemia in LQT1 patients.

GRK2 regulates GLP-1R-mediated early phase insulin secretion in vivo

BackgroundInsulin secretion from the pancreatic β-cell is finely modulated by different signals to allow an adequate control of glucose homeostasis. Incretin hormones such as glucagon-like peptide-1 (GLP-1) act as key physiological potentiators of insulin release through binding to the G protein-coupled receptor GLP-1R. Another key regulator of insulin signaling is the Ser/Thr kinase G protein-coupled receptor kinase 2 (GRK2). However, whether GRK2 affects insulin secretion or if GRK2 can control incretin actions in vivo remains to be analyzed.ResultsUsing GRK2 hemizygous mice, isolated pancreatic islets, and model β-cell lines, we have uncovered a relevant physiological role for GRK2 as a regulator of incretin-mediated insulin secretion in vivo. Feeding, oral glucose gavage, or administration of GLP-1R agonists in animals with reduced GRK2 levels (GRK2+/− mice) resulted in enhanced early phase insulin release without affecting late phase secretion. In contrast, intraperitoneal glucose-induced insulin release was not affected. This effect was recapitulated in isolated islets and correlated with the increased size or priming efficacy of the readily releasable pool (RRP) of insulin granules that was observed in GRK2+/− mice. Using nanoBRET in β-cell lines, we found that stimulation of GLP-1R promoted GRK2 association to this receptor and that GRK2 protein and kinase activity were required for subsequent β-arrestin recruitment.ConclusionsOverall, our data suggest that GRK2 is an important negative modulator of GLP-1R-mediated insulin secretion and that GRK2-interfering strategies may favor β-cell insulin secretion specifically during the early phase, an effect that may carry interesting therapeutic applications.

Control of Insulin Release by Transient Receptor Potential Melastatin 3 (TRPM3) Ion Channels.

The release of insulin in response to increased levels of glucose in the blood strongly depends on Ca2+ influx into pancreatic beta cells by the opening of voltage-gated Ca2+ channels. Transient Receptor Potential Melastatin 3 proteins build Ca2+ permeable, non-selective cation channels serving as pain sensors of noxious heat in the peripheral nervous system. TRPM3 channels are also strongly expressed in pancreatic beta cells that respond to the TRPM3 agonist pregnenolone sulfate with Ca2+ influx and increased insulin release. Therefore, we hypothesized that in beta cells TRPM3 channels may contribute to pregnenolone sulfate- as well as to glucose-induced insulin release. We used INS-1 cells as a beta cell model in which we analysed the occurrence of TRPM3 isoformes by immunoprecipitation and western blotting and by cloning of RT-PCR amplified cDNA fragments. We applied pharmacological as well as CRISPR/Cas9-based strategies to analyse the interplay of TRPM3 and voltage-gated Ca2+ channels in imaging experiments (FMP, Fura-2) and electrophysiological recordings. In immunoassays, we examined the contribution of TRPM3 channels to pregnenolone sulfate- and glucose-induced insulin release. To confirm our findings, we generated beta cell-specific Trpm3-deficient mice and compared their glucose clearance with the wild type in glucose tolerance tests. TRPM3 channels triggered the activity of voltage-gated Ca2+ channels and both channels together contributed to insulin release after TRPM3 activation. Trpm3-deficient INS-1 cells lacked pregnenolone sulfate-induced Ca2+ signals just like the pregnenolone sulfate-induced insulin release. Both, glucose-induced Ca2+ signals and the glucose-induced insulin release were strongly reduced. Accordingly, Trpm3-deficient mice displayed an impaired decrease of the blood sugar concentration after intraperitoneal or oral administration of glucose. The present study suggests an important role for TRPM3 channels in the control of glucose-dependent insulin release.

Synthesis of Different Dipeptides From 4-Hydroxy Isoleucine and Evaluation of Their Anti-Diabetic Activity

Introduction : Fenugreek is one of the oldest medicinal plants, originating in India and Northern Africa. The hypoglycemic effects of fenugreek have been attributed to several mechanisms. Under In vitro conditions, the amino acid 4-hydroxyisoleucine(4-OHIL) in fenugreek seeds increased glucose-induced insulin release in human and rat pancreatic islet cells. It was observed that 4-OHILextracted from fenugreek seeds has insulin tropic activity. This amino acid appeared to act only on pancreatic beta cells, since the levels of somatostatin and glucagon were not altered. Experimental: In order to separate amino acids from methanol extract of fenugreek seeds, ion exchange chromatography method containing 225H cationic resin was used. Five dipeptides were prepared from 4-OHILnamely; GLY-L-4-OHIL, ALA-L-4-OHIL, SER-L-4-OHIL, VAL-L-4-OHIL, THR-L-4-OHIL using cbZ-Cl in protecting step, DCC in peptide forming step and HBr in acetic acid in deprotection step. These five dipeptides are evaluated for invitro antidiabetic activity using non-enzymatic glycogenization heamoglobin assay method. Results: Five dipeptides were confirmed by spectral data like IR, MASS, NMR . Conclusion: In vitro antidiabetic studies showed that glycine l-4 hydroxy isoleucine showed improved activity compared to all other dipeptides and hence it is evaluated for invivo studies which showed remarkable anti diabetic activity compare to parent compound 4-hydroxy isoleucine.

Factors Influencing Mitochondrial Function as a Key Mediator of Glucose-Induced Insulin Release: Highlighting Nicotinamide Nucleotide Transhydrogenase.

Pancreatic β-cells recognize blood glucose changes and release insulin that is a peptide hormone responsible for stable glycemia. Diabetes, a chronic disorder of insulin insufficiency, leads to disturbed glucose homeostasis and multi-organ problems. Glucose and insulin are key markers in the follow-up and control of this disease. Mitochondrial metabolism of pancreatic beta cells is a crucial part of glucose-stimulated cascade of insulin secretion. Effective factors on β-cells mitochondrial function in production of compounds such as tricarboxylic acid intermediates, glutamate, nicotinamide adenine dinucleotide phosphate, and reactive oxygen species can have great effects on the secretion of insulin under diabetes. This review enhances our knowledge of factors influencing mitochondrial function as a key mediator of glucose-induced insulin release that accordingly will be helpful to further our understanding of the mechanisms implicated in the progressive beta cell failure that results in diabetes.

Perioperative Infusion of Glucagon-Like Peptide-1 Prevents Insulin Resistance After Surgical Trauma in Female Pigs.

Insulin resistance is an independent negative predictor of outcome after elective surgery and increases mortality among surgical patients in intensive care. The incretin hormone glucagon-like peptide-1 (GLP-1) potentiates glucose-induced insulin release from the pancreas but may also increase insulin sensitivity in skeletal muscle and directly suppress hepatic glucose release. Here, we investigated whether a perioperative infusion of GLP-1 could counteract the development of insulin resistance after surgery. Pigs were randomly assigned to three groups; surgery/control, surgery/GLP-1, and sham/GLP-1. Both surgery groups underwent major abdominal surgery. Whole-body glucose disposal (WGD) and endogenous glucose release (EGR) were assessed preoperatively and postoperatively using D-[6,6-2H2]-glucose infusion in combination with hyperinsulinemic euglycemic step-clamping. In the surgery/control group, peripheral insulin sensitivity (i.e., WGD) was reduced by 44% relative to preoperative conditions, whereas the corresponding decline was only 9% for surgery/GLP-1 (P < 0.05). Hepatic insulin sensitivity (i.e., EGR) remained unchanged in the surgery/control group but was enhanced after GLP-1 infusion in both surgery and sham animals (40% and 104%, respectively, both P < 0.05). Intraoperative plasma glucose increased in surgery/control (∼20%) but remained unchanged in both groups receiving GLP-1 (P < 0.05). GLP-1 diminished an increase in postoperative glucagon levels but did not affect skeletal muscle glycogen or insulin signaling proteins after surgery. We show that GLP-1 improves intraoperative glycemic control, diminishes peripheral insulin resistance after surgery, and suppresses EGR. This study supports the use of GLP-1 to prevent development of postoperative insulin resistance.

Effects of an enzymatically stable C-terminal hexapseudopeptide fragment peptide of xenin-25, ψ-xenin-6, on pancreatic islet function and metabolism

Xenin-25 undergoes rapid enzyme metabolism following secretion. Early studies demonstrated bioactivity of a C-terminal hexapeptide fragment of xenin-25, namely xenin-6, which were enhanced through introduction of a reduced N-terminal peptide bond, to yield Ψ-xenin-6. The present study was undertaken to define the biological actions and potential antidiabetic properties of Ψ-xenin-6. In vitro enzymatic stability, insulin and glucagon secretory activity, as well as effects on beta-cell survival were determined. Studies in mice were used to assess the impact of Ψ-xenin-6 on glucose homeostasis and satiety. Ψ-xenin-6 was resistant to murine plasma degradation. In BRIN-BD11 cells and isolated murine islets, Ψ-xenin-6 significantly stimulated insulin secretion, and prominently enhanced the insulinotropic actions of GIP. Xenin-6 and Ψ-xenin-6 had no impact on glucagon secretion, although xenin-6 partially reversed the glucagonotropic action of GIP. Further in vitro investigations revealed that, similar to GLP-1, Ψ-xenin-6 significantly augmented proliferation of human and rodent clonal beta-cells, whilst also fully protecting against cytokine-induced beta-cell cytotoxicity, with greater potency than xenin-25 and xenin-6. When administered to mice in combination with glucose, Ψ-xenin-6 significantly reduced glucose levels and enhanced glucose-induced insulin release, with a duration of biological action beyond 8 h. Ψ-xenin-6 also significantly enhanced the glucose-lowering action of GIP in vivo. In overnight fasted mice, Ψ-xenin-6 exhibited satiety actions at both 25 and 250 nmol/kg. These data demonstrates that Ψ-xenin-6 is a metabolically stable C-terminal fragment analogue of xenin-25, with a metabolic action profile that merits further study as a potential antidiabetic compound.

Increased uptake of oxLDL does not exert lipotoxic effects in insulin-secreting cells.

Modified lipoproteins can negatively affect beta cell function and survival. However, the mechanisms behind interactions of modified lipoproteins with beta cells - and in particular, relationships to increased uptake - are only partly clarified. By over-expressing the scavenger receptor CD36 (Tet-on), we increased the uptake of fluorescent low-density modified lipoprotein (oxLDL) into insulin-secreting INS-1 cells. The magnitude of uptake followed the degree of CD36 over-expression. CD36 over-expression increased concomitant efflux of 3H-cholesterol in proportion to the cellular contents of 3H-cholesterol. Exposure to concentrations of oxLDL from 20 to 100 µg/mL dose-dependently increased toxicity (evaluated by MTT) as well as apoptosis. However, the increased uptake of oxLDL due to CD36 over-expression did not exert additive effects on oxLDL toxicity - neither on viability, nor on glucose-induced insulin release and cellular content. Reciprocally, blocking CD36 receptors by Sulfo-N-Succinimidyl Oleate decreased the uptake of oxLDL but did not diminish the toxicity. Pancreatic islets of CD36-/- mice displayed reduced uptake of 3H-cholesterol-labeled oxLDL vs wild type but similar toxicity to oxLDL. OxLDL was found to increase the expression of CD36 in islets and INS-1 cells. In summary, given the experimental conditions, our results indicate that (1) increased uptake of oxLDL is not responsible for toxicity of oxLDL, (2) increased efflux of the cholesterol moiety of oxLDL counterbalances, at least in part, increased uptake and (3) oxLDL participates in the regulation of CD36 in pancreatic islets and in INS-1 cells.

Taurine supplementation in high-fat diet fed male mice attenuates endocrine pancreatic dysfunction in their male offspring.

Obesity in fathers leads to DNA damage and epigenetic changes in sperm that may carry potential risk factors for metabolic diseases to the next generation. Taurine (TAU) supplementation has demonstrated benefits against testicular dysfunction and pancreatic islet impairments induced by obesity, but it is not known if these protective actions prevent the propagation of metabolic disruptions to the next generation; as such, we hypothesized that paternal obesity may increase the probability of endocrine pancreatic dysfunction in offspring, and that this could be prevented by TAU supplementation in male progenitors. To test this, male C57Bl/6 mice were fed on a control diet (CTL) or a high-fat diet (HFD) without or with 5% TAU in their drinking water (CTAU and HTAU) for 4months. Subsequently, all groups of mice were mated with CTL females, and the F1 offspring were identified as: CTL-F1, CTAU-F1, HFD-F1, and HTAU-F1. HFD-fed mice were normoglycemic, but glucose intolerant and their islets hypersecreted insulin. However, at 90days of age, HFD-F1 offspring displayed normal glucose homeostasis and adiposity, but reduced glucose-induced insulin release. HFD-F1 islets also exhibited β- and α-cell hypotrophy, and lower δ-cell number per islet. Paternal TAU supplementation prevented the decrease in glucose-induced insulin secretion and normalized β-cell size and δ-cell number, and increased α-cell size/islet in HTAU-F1 mice. In conclusion, HFD consumption by male founders decreases β-cell secretion and islet-cell distribution in their offspring. TAU attenuates the deleterious effects of paternal obesity on insulin secretion and islet-cell morphology in F1 offspring.