Activity Of Pancreatic Beta-cells Research Articles

347-LB: MEA Technology as an Easy Electrophysiological Approach for Noninvasive Recordings of Intact Murine and Human Islets

Increase of blood glucose concentration leads to glucose-induced electrical activity of pancreatic beta-cells followed by insulin secretion. Electrical activity appears in glucose concentration-dependent oscillations easily recorded by microelectrode arrays (MEA). In comparison to other electrophysiological techniques MEAs can record non-invasively from intact islets and can be used for long term studies to investigate chronic effects of drugs. Murine islets or islets isolated from human biopsies were used for recordings. Electrical activity was quantified as fraction of plateau Phase (FOPP) or number of single spike activity. Islets were placed via suction or cultivated on MEAs. The glucose concentration response curve recorded with murine islets plotted as FOPP revealed a half-maximal activity of 12 ± 2 mM which is in line with traditional methods like e.g., with intracellular electrodes. Glucose-induced activity of cultured islets remains stable over a month. Application of well-known substances (like e.g., diazoxide, tolbutamide) matched regular results. Human islets displayed typical glucose-induced activity (10 mM). Validation studies showed the existence of functional KATP channels and TTX reduced spike activity from 1047 ± 314 to 199 ± 90 spikes/5min after the application of 300 nM TTX. The washout led to an increased spike activity of 779 ± 301 spikes/minutes. The glucose concentration response curve revealed an EC50 value of 8 ± 3 mM glucose. The glucose responsiveness recorded with the MEA Technology is in line with other reports showing that the EC50 value of human beta-cells (∼ 6 mM) is lower than in mouse beta-cells. MEA Technology allows medium throughput recordings from up to 40 intact islets simultaneously. While previous electrophysiological attempts failed MEAs offer large scale research in both academics and industry. The principle of function is not limited to rodent but is also applicable to human or stem cell derived islets of Langerhans. Disclosure S. Schönecker: None. M. Oza: Employee; Self; Multichannel Systems, Gmbh. U. Kraushaar: None.

Fibroblast growth factor receptor 5 (FGFR5) is a co-receptor for FGFR1 that is up-regulated in beta-cells by cytokine-induced inflammation

Fibroblast growth factor receptor-1 (FGFR1) activity at the plasma membrane is tightly controlled by the availability of co-receptors and competing receptor isoforms. We have previously shown that FGFR1 activity in pancreatic beta-cells modulates a wide range of processes, including lipid metabolism, insulin processing, and cell survival. More recently, we have revealed that co-expression of FGFR5, a receptor isoform that lacks a tyrosine-kinase domain, influences FGFR1 responses. We therefore hypothesized that FGFR5 is a co-receptor to FGFR1 that modulates responses to ligands by forming a receptor heterocomplex with FGFR1. We first show here increased FGFR5 expression in the pancreatic islets of nonobese diabetic (NOD) mice and also in mouse and human islets treated with proinflammatory cytokines. Using siRNA knockdown, we further report that FGFR5 and FGFR1 expression improves beta-cell survival. Co-immunoprecipitation and quantitative live-cell imaging to measure the molecular interaction between FGFR5 and FGFR1 revealed that FGFR5 forms a mixture of ligand-independent homodimers (∼25%) and homotrimers (∼75%) at the plasma membrane. Interestingly, co-expressed FGFR5 and FGFR1 formed heterocomplexes with a 2:1 ratio and subsequently responded to FGF2 by forming FGFR5/FGFR1 signaling complexes with a 4:2 ratio. Taken together, our findings identify FGFR5 as a co-receptor that is up-regulated by inflammation and promotes FGFR1-induced survival, insights that reveal a potential target for intervention during beta-cell pathogenesis.

Diminished Ca2+ Signaling, CaV1 Channel Expression, and Activity in Pancreatic Beta Cells Expressing Mutated DISC1 (Disrupted in Schizophrenia 1)

In addition to cognitive impairment, schizophrenics often suffer from non-obese T2D. Here, we examined whether similar cellular changes occur in pancreatic beta-cells as found in neurons from a genetic model of schizophrenia. Specifically we tested whether beta-cells exhibit disrupted excitation-secretion coupling when a truncated human DISC1 (thDISC1) gene, originally discovered in a Scottish family having high penetrance for schizophrenia, is expressed selectively in mouse beta-cells upon ingesting doxycycline (+DOX). Expression of thDISC1 significantly decreases blood insulin levels and GSIS from isolated mouse islets, revealing an independent role for DISC1 in beta-cells. In central neurons, DISC1 regulates Ca2+ CaV2 channel expression, Ca2+ influx and transmitter release. To determine whether DISC1 similarly regulates Ca2+ physiology in beta-cells, we tested thDISC1 DOX+ vs. DOX- beta-cells for changes in: i) intracellular Ca2+signaling using Fluo 3-AM; ii) CaV1 channel expression, the dominant channel class controlling GSIS; iii) and CaV1 channel activity using whole-cell recording methods. We found increases in [Ca2+]i following 20 mM glucose were delayed >2 min and diminished ∼50% in dissociated beta-cells expressing thDISC1. When sections of pancreas were stained with an anti-CaV1.2/1.3 antibody, thDISC1 DOX+ vs. DOX- insulin-positive cells exhibited decreased staining. Lastly, both peak inward Ba2+ current and FPL 64176 induced long-lasting L-type tail current decreased significantly in thDISC1 DOX+ vs. DOX- beta-cells. No obvious change in activation kinetics was observed. These changes in excitation-secretion coupling parallel those in neurons expressing truncated DISC1. Thus at the cellular level, truncated DISC1 precipitates disorders of secretion such as schizophrenia and T2D. Disclosure P. Lu: None. R.B. Sharma: None. L.C. Alonso: None. R. Zhuge: None. A.R. Rittenhouse: None. A. Jurczyk: None.

Arsenic-gene interactions and beta-cell function in the Strong Heart Family Study

We explored arsenic-gene interactions influencing pancreatic beta-cell activity in the Strong Heart Family Study (SHFS). We considered 42 variants selected for associations with either beta-cell function (31 variants) or arsenic metabolism (11 variants) in the SHFS. Beta-cell function was calculated as homeostatic model - beta corrected for insulin resistance (cHOMA-B) by regressing homeostatic model – insulin resistance (HOMA-IR) on HOMA-B and adding mean HOMA-B. Arsenic exposure was dichotomized at the median of the sum of creatinine-corrected inorganic and organic arsenic species measured by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS). Additive GxE models for cHOMA-B were adjusted for age and ancestry, and accounted for family relationships. Models were stratified by center (Arizona, Oklahoma, North Dakota and South Dakota) and meta-analyzed. The two interactions between higher vs. lower arsenic and SNPs for cHOMA-B that were nominally significant at P < 0.05 were with rs10738708 (SNP overall effect −3.91, P = 0.56; interaction effect with arsenic −31.14, P = 0.02) and rs4607517 (SNP overall effect +16.61, P = 0.03; interaction effect with arsenic +27.02, P = 0.03). The corresponding genes GCK and TUSC1 suggest oxidative stress and apoptosis as possible mechanisms for arsenic impacts on beta-cell function. No interactions were Bonferroni-significant (1.16 × 10−3). Our findings are suggestive of oligogenic moderation of arsenic impacts on pancreatic β-cell endocrine function, but were not Bonferroni-significant.

Nesfatin-1 inhibits voltage gated K+ channels in pancreatic beta cells

The anorexigenic neuropeptide NEFA/nucleobindin 2 (NUCB2)/nesfatin-1-containing neurons are distributed in the brain regions involved in feeding regulation. In spite of the growing knowledge of its physiological functions through extensive studies, its molecular mechanism of reaction, including its receptor, remains unknown. NUCB2/nesfatin-1 is also involved in various peripheral regulations, including glucose homeostasis. In pancreatic beta-cells, NUCB2/nesfatin-1 is reported to enhance glucose-stimulated insulin secretion (GSIS) but its exact mechanism remains unknown.To clarify this mechanism, we measured the effect of nesfatin-1 on the electrical activity of pancreatic beta-cells. Using mouse primary beta cells, we measured changes in the ATP-sensitive K+ (KATP) channel current, the voltage-gated K+ (Kv) channel current, and insulin secretion upon application of nesfatin-1.Nesfatin-1 inhibited the Kv channel, but KATP channel activity was unaffected. Nesfatin-1 enhanced insulin secretion to a same level as Kv channel blocker tetraethylammonium (TEA). The effect was not further enhanced when nesfatin-1 and TEA were applied simultaneously. The inhibition binding assay with [125I]nesfatin-1 in Kv2.1 channels, major contributor of Kv current in beta cell, expressing HEK239 cells indicated the binding of nesfatin-1 on Kv2.1 channel.Because Kv channel inhibition enhances insulin secretion under high glucose conditions, our present data suggest a possible mechanism of nesfatin-1 on enhancing GSIS through regulation of ion channels rather than its unidentified receptor.

Dual Effect of Palmitate on Voltage-Gated Calcium Channels and Insulin Secretion in Pancreatic Beta Cells of Rats

A variety of signaling molecules modify voltage-gated calcium channels activity in pancreatic beta cells, among them are, free fatty acids (FFA). Acute exposure to FFA increases glucose-stimulated insulin secretion, while chronic exposure increases basal insulin secretion, but decreases glucose-stimulated (Olofsson et al., 2004; Zhou and Grill, 1994). Preliminary studies in our laboratory showed that pre-incubation with 1 mM palmitate during 48-72 hours reduced barium currents in beta cells. In this work, we analyze the effect of different palmitate concentrations on calcium currents and insulin secretion in beta cells of adult male Wistar rats. Electrophysiological recordings were performed using whole-cell voltage clamp technique. Reverse hemolytic plaque assay measured insulin secretion by isolated beta cells. Pre-incubation with 0.25 and 0.5 mM palmitate during 48-72 h increased the high voltage-activated (HVA) calcium current without affecting the LVA current. An acute 5 min pre-incubation with 0.5 mM palmitate also increased HVA current. In contrast, 24 h pre-incubation with 1 mM decreased both, LVA and HVA currents. A similar effect was observed during an acute incubation. Chronic pre-incubation with 0.25, 0.5 and 1 mM palmitate decreased the percentage of insulin secretory cells, immunoplaque area and insulin secretion index in a glucose-stimulated condition (15.6 mM). Chronic pre-incubation with 0.5 and 1 mM palmitate, also decreased the secretion index at basal glucose (5.6 mM). However, acute pre-incubation with 1 mM palmitate increased the immunoplaque area in 5.6 mM glucose. Together these results show that palmitate has a dual effect, depending on time and concentration on the calcium currents and insulin secretion in beta cells. Partially supported by DGAPA PAPIIT-UNAM Grants: IN213114, M Hiriart; IV100116 to A. Frank and M Hiriart, and IN211416 to M Velasco-Torres.

Modulation of Ionic Channels and Insulin Secretion by Drugs and Hormones in Pancreatic Beta Cells.

Pancreatic beta cells, unique cells that secrete insulin in response to an increase in glucose levels, play a significant role in glucose homeostasis. Glucose-stimulated insulin secretion (GSIS) in pancreatic beta cells has been extensively explored. In this mechanism, glucose enters the cells and subsequently the metabolic cycle. During this process, the ATP/ADP ratio increases, leading to ATP-sensitive potassium (KATP) channel closure, which initiates depolarization that is also dependent on the activity of TRP nonselective ion channels. Depolarization leads to the opening of voltage-gated Na(+) channels (Nav) and subsequently voltage-dependent Ca(2+) channels (Cav). The increase in intracellular Ca(2+) triggers the exocytosis of insulin-containing vesicles. Thus, electrical activity of pancreatic beta cells plays a central role in GSIS. Moreover, many growth factors, incretins, neurotransmitters, and hormones can modulate GSIS, and the channels that participate in GSIS are highly regulated. In this review, we focus on the principal ionic channels (KATP, Nav, and Cav channels) involved in GSIS and how classic and new proteins, hormones, and drugs regulate it. Moreover, we also discuss advances on how metabolic disorders such as metabolic syndrome and diabetes mellitus change channel activity leading to changes in insulin secretion.

Higher expression level of Bat3 is associated with silencing of theMidn gene in primary mouse cardiomyocytes

Midnolin (Midn) is a developmentally regulated nucleolar protein that was originally identified in the mesencephalon of developing mouse embryos. Additionally, Midn expression was detected in various adult tissues and was associated with glucokinase activity in pancreatic beta cells and with the regulation of folliculogenesis in ovaries. In this study, our aim was to analyze the expression and function of the Midn gene in cardiomyocyte cells. We constructed a primary neonatal mouse cardiomyocyte cell culture and analyzed the expression of possible Midn-associated genes after short interfering RNA (siRNA)-mediated gene silencing for Midn. After 24 h of silencing, we observed that the expression level of Bat3 was significantly increased (1.69-fold, P = 0.04). As a result, we have detected a suggestive gene that might act in the common cellular pathways with Midn in cardiomyocyte cells.

Evidence against a Ca(2+)-induced potentiation of dehydrogenase activity in pancreatic beta-cells.

Pancreatic beta-cells respond to an unchanging stimulatory glucose concentration with oscillations in membrane potential (Vm), cytosolic Ca(2+) concentration ([Ca(2+)]c), and insulin secretion. The underlying mechanisms are largely ascertained. Some particular details, however, are still in debate. Stimulus-secretion coupling (SSC) of beta-cells comprises glucose-induced Ca(2+) influx into the cytosol and thus into mitochondria. It is suggested that this activates (mitochondrial) dehydrogenases leading to an increase in reduction equivalents and ATP production. According to SSC, a glucose-induced increase in ATP production would thus further augment ATP production, i.e. induce a feed-forward loop that is hardly compatible with oscillations. Consistently, other studies favour a feedback mechanism that drives oscillatory mitochondrial ATP production. If Ca(2+) influx activates dehydrogenases, a change in [Ca(2+)]c should increase the concentration of reduction equivalents. We measured changes in flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) autofluorescence in response to changes in glucose concentration or glucose-independent changes in [Ca(2+)]c. The FAD signal was altered by glucose but not by alterations in [Ca(2+)]c. NAD(P)H was increased by glucose but even decreased by Ca(2+) influx evoked by tolbutamide. The mitochondrial membrane potential ΔΨ was hyperpolarized by 4mM glucose. As adding tolbutamide then depolarized ΔΨ, we deduce that Ca(2+) does not activate mitochondrial activity but by contrast even inhibits it by reducing the driving force for ATP production. Inhibition of Ca(2+) influx reversed the Ca(2+)-induced changes in ΔΨ and NAD(P)H. The results are consistent with a feedback mechanism which transiently and repeatedly reduces ATP production and explain the oscillatory activity of pancreatic beta-cells at increased glucose concentrations.

Horizontal transfer of exosomal microRNAs transduce apoptotic signals between pancreatic beta-cells.

BackgroundDiabetes mellitus is a common metabolic disorder characterized by dysfunction of insulin-secreting pancreatic beta-cells. MicroRNAs are important regulators of beta-cell activities. These non-coding RNAs have recently been discovered to exert their effects not only inside the cell producing them but, upon exosome-mediated transfer, also in other recipient cells. This novel communication mode remains unexplored in pancreatic beta-cells. In the present study, the microRNA content of exosomes released by beta-cells in physiological and physiopathological conditions was analyzed and the biological impact of their transfer to recipient cells investigated.ResultsExosomes were isolated from the culture media of MIN6B1 and INS-1 derived 832/13 beta-cell lines and from mice, rat or human islets. Global profiling revealed that the microRNAs released in MIN6B1 exosomes do not simply reflect the content of the cells of origin. Indeed, while a subset of microRNAs was preferentially released in exosomes others were selectively retained in the cells. Moreover, exposure of MIN6B1 cells to inflammatory cytokines changed the release of several microRNAs. The dynamics of microRNA secretion and their potential transfer to recipient cells were next investigated. As a proof-of-concept, we demonstrate that if cel-miR-238, a C. Elegans microRNA not present in mammalian cells, is expressed in MIN6B1 cells a fraction of it is released in exosomes and is transferred to recipient beta-cells. Furthermore, incubation of untreated MIN6B1 or mice islet cells in the presence of microRNA-containing exosomes isolated from the culture media of cytokine-treated MIN6B1 cells triggers apoptosis of recipient cells. In contrast, exosomes originating from cells not exposed to cytokines have no impact on cell survival. Apoptosis induced by exosomes produced by cytokine-treated cells was prevented by down-regulation of the microRNA-mediating silencing protein Ago2 in recipient cells, suggesting that the effect is mediated by the non-coding RNAs.ConclusionsTaken together, our results suggest that beta-cells secrete microRNAs that can be transferred to neighboring beta-cells. Exposure of donor cells to pathophysiological conditions commonly associated with diabetes modifies the release of microRNAs and affects survival of recipient beta-cells. Our results support the concept that exosomal microRNAs transfer constitutes a novel cell-to-cell communication mechanism regulating the activity of pancreatic beta-cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s12964-015-0097-7) contains supplementary material, which is available to authorized users.

Factors associated with GAD antibody titer in subtypes of type 1 diabetes

The objective of this study was to compare factors associated with glutamic decarboxylase antibody (GADAb) titer between acute-onset and slowly progressive type 1 diabetes. We used a cross-sectional study to investigate 90 cases of GADAb-positive type 1 diabetes, including 40 acute-onset and 50 slowly progressive cases, to clarify factors associated with GADAb positivity in the two disease subtypes. We performed multivariate linear regression analysis to clarify factors associated with GADAb titer. In acute-onset cases, positive insulinoma-associated antigen-2 antibody (IA-2Ab) was negatively correlated with GADAb titer (β = −1.29, p = 0.048). In slowly progressive cases, GADAb titer was positively correlated with age (β = 0.05, p = 0.035) and positive thyroid autoantibodies (β = 1.59, p = 0.023), and negatively correlated with duration of diabetes (β = −1.34, p = 0.003). In slowly progressive cases, female gender (β = 1.65, p = 0.009) and age (β = 0.05, p = 0.048) were positively correlated, and duration of diabetes (β = −1.34, p = 0.004) and IA-2Ab positivity (β = −1.92, p = 0.029) were negatively correlated with GADAb titer only in cases with high GADAb titer. GADAb titer was associated with autoimmune activity of pancreatic beta cells in acute-onset and slowly progressive cases with high GADAb titer, and duration of diabetes in slowly progressive cases.

Identification of the Ubiquitin-like Domain of Midnolin as a New Glucokinase Interaction Partner

Glucokinase acts as a glucose sensor in pancreatic beta cells. Its posttranslational regulation is important but not yet fully understood. Therefore, a pancreatic islet yeast two-hybrid library was produced and searched for glucokinase-binding proteins. A protein sequence containing a full-length ubiquitin-like domain was identified to interact with glucokinase. Mammalian two-hybrid and fluorescence resonance energy transfer analyses confirmed the interaction between glucokinase and the ubiquitin-like domain in insulin-secreting MIN6 cells and revealed the highest binding affinity at low glucose. Overexpression of parkin, an ubiquitin E3 ligase exhibiting an ubiquitin-like domain with high homology to the identified, diminished insulin secretion in MIN6 cells but had only some effect on glucokinase activity. Overexpression of the elucidated ubiquitin-like domain or midnolin, containing exactly this ubiquitin-like domain, significantly reduced both intrinsic glucokinase activity and glucose-induced insulin secretion. Midnolin has been to date classified as a nucleolar protein regulating mouse development. However, we could not confirm localization of midnolin in nucleoli. Fluorescence microscopy analyses revealed localization of midnolin in nucleus and cytoplasm and co-localization with glucokinase in pancreatic beta cells. In addition we could show that midnolin gene expression in pancreatic islets is up-regulated at low glucose and that the midnolin protein is highly expressed in pancreatic beta cells and also in liver, muscle, and brain of the adult mouse and cell lines of human and rat origin. Thus, the results of our study suggest that midnolin plays a role in cellular signaling of adult tissues and regulates glucokinase enzyme activity in pancreatic beta cells.

Modeling SK-Channels and Electrical Activity in Human Beta-Cells

Electrical activity in pancreatic beta-cells plays a pivotal role in glucose-stimulated insulin secretion by coupling metabolism to calcium-triggered exocytosis. Mathematical models based on rodent data have helped in understanding the mechanisms underlying the electrophysiological patterns observed in laboratory animals. However, human beta-cells differ in several aspects, and in particular in their electrophysiological characteristics, from rodent beta-cells. Hence, from a clinical perspective and to obtain insight into the defects in insulin secretion relevant for diabetes mellitus, it is important to study human beta-cells.To investigate the role of small conductance calcium-activated potassium SK-channels, we build on a recently developed mathematical model of electrical activity based entirely on detailed ion channel characteristics of human beta-cells.We show that the inclusion of SK-channels allows us to investigate various patterns of electrical activity, and interpret atypical and non-intuitive responses to ion channel blockers in human beta-cells. However, our simulations suggest that the effect on electrical activity of SK channel antagonists is minimal. This is supported by preliminary experimental data.

Molecular-genetic verification and treatment of neonatal diabetes mellitus related to the defects in ATP-dependent potassium channels: Results of the observation of 9 patients and the first description of ABCC8 gene mutations in Russia

Introduction of the methods for molecular-genetic analysis into clinical practice has opened up new prospects for both diagnosis and pathogenetically sound therapy of neonatal diabetes mellitus. It is currently known that the overwhelming majority of the cases of diabetes mellitus developing in children during the first six month of life are associated with defects of the genes controlling formation, development, and functional activity of pancreatic beta-cells whereas type 1 diabetes mellitus of autoimmune origin accounts for less than 1% of this pathology. This paper reports the results of a molecular-genetic study of 14 patients presenting with neonatal diabetes mellitus. Nine cases are shown to have developed as a result of mutations in KCNJ11 and ABCC8 genes. ABCC8 mutations are described for the first time in Russia. Analysis of clinical forms of neonatal diabetes mellitus revealed correlation between the type of mutations, clinical features of the disease, and susceptibility of the patients to sulfonylurea drugs.

Visualization of Spatially Controlled Glucokinase Activation in Living Pancreatic Beta Cells using an Optimized FRET-Based Biosensor

Glucokinase (GCK) activity in pancreatic beta cells limits the rate of glucose metabolism and controls the glucose threshold for insulin secretion. Regulation of GCK activity by cell surface receptors can occur through activation of nitric oxide synthase (NOS) on insulin secretory granules, and subsequent S-nitrosation of GCK. It is thought that interaction between NOS and GCK is essential to the S-nitrosation reaction. Nonetheless, activation of an existing Förster resonance energy transfer (FRET)-based sensor suggests that the activation occurs diffusively. To examine whether GCK activation has a spatial regulatory component, we developed an improved GCK biosensor using cyan fluorescent protein derived from mCerulean3. Circularly permuted mCerulean3 proteins were constructed with the intent of optimizing rotational positioning of the FRET pair. Several cpmCer3 variants were constructed. The brightest variant, cpmCer174, retains a very high quantum yield (> 0.8) similar to mCerulean3, and produced the highest contrast sensor when incorporated into the FRET-GCK biosensor. Expression in pancreatic beta cells revealed evidence supporting tight spatial control over GCK activation at the insulin secretory granules. These results have numerous implications for the nature of post-translational regulation of glucose sensing in pancreatic beta cells.

Efficacy and safety of metformin-sitagliptin combination for the treatment of patients with diabetes mellitus and obesity

Aim. To elucidate therapeutic effect of metformin-sitaglitin combination on the dynamics of indices of insulin resistance and functional activity of pancreaticbeta-cells, lipid metabolism and body weight in patients with type 2 diabetes mellitus (DM2) and obesity. Materials and methods. The study included 32 patients treated by a combination of metformin (500-2550 mg/day) and sitagliptin (100 mg) for18 weeks. Standard parameters of carbohydrate and lipid metabolism, body mass index (BMI), blood adiponectin and leptin levels were measured, indices of insulin resistance and functional activity of pancreatic beta-cells were calculated. Results. Therapy with metformin-sitagliptin combination ensured compensation of fasting and postprandial hyperglycemia, reduced HbA1c level, increasedfunctional activity of beta-cells, decreased peripheral insulin resistance and BMI, had beneficial effect on lipid metabolism and hormonalactivity of adipose tissue. Conclusion. Metformin-sitagliptin combination can be recommended as a clinically efficacious modality for the treatment of patients with diabetesmellitus and obesity.

Pleiotropic effects of moxonidine

Background. Imidazoline receptor agonist moxonidine besides its antihypertensive effect, can increase insulin sensitivity, reduce leptin level, improve lipid metabolism. However, the efficacy, tolerability and pleiotropic effects of moxonidine in postmenopausal women with essential hypertension (EH) and metabolic syndrome (MS) are not well established, and it was the objective of this study. Design and methods. 30 postmenopausal women with EH and MS (52,5 ± 0,4 years old) were included. Moxonidine was administered (400-600 mkg/day) for 12 weeks. Waist circumference (WC), hip circumference (HC), WC/HC ratio, body mass index (BMI), insulin, leptin level, glucose, lipid profile of blood serum, index of insulin resistance (HOMA-IR) and index of functional activity of pancreatic beta cells (HOMA-FB), echocardiography, intima-media thickness (IMT) of common carotid arteries (CCA). Results. Moxonidine therapy was associated with blood pressure (BP) decrease, body weight and BMI decrease, high-density lipoprotein (HDL) cholesterol and HOMA-FB index increase. Left atrium diameter and volume decreased, left ventricular diastolic function improved. Conclusions. Moxonidine is an effective antihypertensive drug for the treatment of postmenopausal hypertensive women with MS, which improves a range of metabolic, hemodynamic parameters and leads to the decrease of left atrium volume and diameter.

OASIS/CREB3L1 Induces Expression of Genes Involved in Extracellular Matrix Production But Not Classical Endoplasmic Reticulum Stress Response Genes in Pancreatic β-Cells

Old astrocyte specifically induced substance (OASIS) has previously been shown to be a putative endoplasmic reticulum (ER) stress sensor in astrocytes with a mechanism of activation that is similar to ATF6. In this study we investigated the expression and activation of endogenous and overexpressed OASIS in pancreatic beta-cells. OASIS mRNA expression was detected in pancreatic beta-cell lines and rodent islets, and the expression level was up-regulated by ER stress-inducing compounds. Endogenous OASIS protein, however, is expressed at low levels in pancreatic beta-cell lines and rodent islets, possibly due to abundant levels of the micro-RNA miR-140 present in these cells. In contrast, expression of both full-length and cleaved (active) OASIS was readily detectable in the developing mouse pancreas (embryonic d 15.5). Microarray analysis after expression of an active nuclear-localized version of OASIS in an inducible INS-1 beta-cell line resulted in the up-regulation of many genes implicated in extracellular matrix production and protein transport but not classical ER stress response genes. Consistent with this, expression of active OASIS failed to induce glucose-regulated protein 78 kDa promoter activity in pancreatic beta-cells. These results suggest that the repertoire of genes induced by OASIS is cell type-dependent and that the OASIS protein may have a role in pancreas development.

Mechanisms of Impaired Glucose Tolerance and Insulin Secretion during Isoflurane Anesthesia

Volatile anesthetics impair insulin secretion and glucose utilization; however, the precise mechanism of action that underlies these effects is unknown. The authors hypothesized that isoflurane inhibits glucose-induced inhibition of adenosine triphosphate-sensitive potassium channel activity in pancreatic beta cells, which could result in impaired insulin secretion and glucose tolerance. Intravenous glucose tolerance tests were performed on 28 male Japanese White rabbits anesthetized with sodium pentobarbital. Glibenclamide (50 microg/kg + 33.5 microg x kg x h) or vehicle was administered 75 min before intravenous administration of 0.6 g/kg glucose. Half of the animals (n = 7) in the vehicle and glibenclamide groups received isoflurane at 1.0 minimum alveolar concentration 30 min before administration of glucose, and the other half received a vehicle control. Hemodynamics, blood glucose, and plasma insulin were measured. A cell-attached patch clamp configuration was used to record single channel currents in the pancreas from male Swiss-Webster mice. Isoflurane alone or a combination of isoflurane and glibenclamide inhibited the insulinogenic index to a greater extent than in the vehicle and glibenclamide groups. In the patch clamp experiments, channel activity was significantly decreased as the glucose concentration was increased from 0 to 10 mm. The subsequent application of 0.5 mm isoflurane reversed the effects of glucose on channel activity. These results show that isoflurane impairs insulin secretion and glucose utilization. The mechanism of action responsible for these effects may involve a decrease in glucose-induced inhibition of adenosine triphosphate-sensitive potassium channel activity in pancreatic beta cells.

Modeling of oscillatory bursting activity of pancreatic beta-cells under regulated glucose stimulation

A mathematical model to describe the oscillatory bursting activity of pancreatic beta-cells is combined with a model of glucose regulation system in this work to study the bursting pattern under regulated extracellular glucose stimulation. The bursting electrical activity in beta-cells is crucial for the release of insulin, which acts to regulate the blood glucose level. Different types of bursting pattern have been observed experimentally in glucose-stimulated islets both in vivo and in vitro, and the variations in these patterns have been linked to changes in glucose level. The combined model in this study enables us to have a deeper understanding on the regime change of bursting pattern when glucose level changes due to hormonal regulation, especially in the postprandial state. This is especially important as the oscillatory components of electrical activity play significant physiological roles in insulin secretion and some components have been found to be lost in type 2 diabetic patients.