Acute and long-term effects of metformin on the function and insulin secretory responsiveness of clonal β-cells

2010 ◽  
Vol 391 (12) ◽  
Author(s):  
Joan M. McKiney ◽  
Nigel Irwin ◽  
Peter R. Flatt ◽  
Clifford J. Bailey ◽  
Neville H. McClenaghan
Keyword(s):  
Insulin Secretion ◽  
Cell Viability ◽  
Palmitic Acid ◽  
Insulin Release ◽  
Prolonged Exposure ◽  
Long Term Effects ◽  
Β Cell ◽  
Beneficial Effects ◽  
Intracellular Ca ◽  
Glucose Stimulated Insulin Secretion

Abstract Functional effects of acute and prolonged (48 h) exposure to the biguanide drug metformin were examined in the clonal pancreatic β-cell line, BRIN-BD11. Effects of metformin on prolonged exposure to excessive increased concentrations of glucose and palmitic acid were also assessed. In acute 20-min incubations, 12.5–50 μm metformin did not alter basal (1.1 mm glucose) or glucose-stimulated (16.7 mm glucose) insulin secretion. However, higher concentrations of metformin (100–1000 μm) increased (1.3–1.5-fold; p<0.001) insulin release at basal glucose concentrations, but had no effect on glucose-stimulated insulin secretion. There were no apparent acute effects of metformin on intracellular Ca2+ concentrations, but metformin enhanced (p<0.05 to p<0.01) the acute insulinotropic actions of GIP and GLP-1. Exposure for 48 h to 200 μm metformin improved aspects of β-cell insulin secretory function, whereas these benefits were lost at 1 mm metformin. Prolonged glucotoxic and lipotoxic conditions impaired β-cell viability and insulin release in response to glucose and to a broad range of insulin secretagogues. Concomitant culture with 200 μm metformin partially reversed many of the adverse effects of prolonged glucotoxic conditions. However, there were no beneficial effects of metformin under prolonged culture with elevated concentrations of palmitic acid. The results suggest that metformin exerts direct effects on β-cell viability, function and survival that could contribute to the use of this agent in the treatment of type 2 diabetes.

scholarly journals Glucose-regulated pulsatile insulin release from mouse islets via the K(ATP) channel-independent pathway

2001 ◽  
pp. 667-675 ◽  
Author(s):  
J Westerlund ◽  
H Ortsater ◽  
F Palm ◽  
T Sundsten ◽  
P Bergsten
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Prolonged Exposure ◽  
Pulse Frequency ◽  
Secretory Rate ◽  
Pulsatile Release ◽  
Glucose Signaling ◽  
K Concentration ◽  
Channel Dependent ◽  
Glucose Stimulated Insulin Secretion

OBJECTIVE: Regulation of insulin release by glucose involves dual pathways, including or not inhibition of ATP-sensitive K(+) channels (K(ATP) channels). Whereas the K(ATP) channel-dependent pathway produces pulsatile release of insulin it is not clear whether the independent pathway also generates such kinetics. DESIGN AND METHODS: To clarify this matter, insulin secretion and cytoplasmic Ca(2+) ([Ca(2+)](i)) were studied in perifused pancreatic islets from ob/ob mice. Insulin release was measured by ELISA technique and [Ca(2+)](i) by dual-wavelength fluorometry. RESULTS: Insulin secretion was pulsatile (0.2--0.3/min) at 3 mmol/l glucose when [Ca(2+)](i) was low and stable. Stimulation with 11 mmol/l of the sugar increased the amplitude of the insulin pulses with maintained frequency and induced oscillations in [Ca(2+)](i). Permanent opening of the K(ATP) channels with diazoxide inhibited glucose-stimulated insulin secretion back to basal levels with maintained pulsatility despite stable and basal [Ca(2+)](i) levels. Increase of the K(+) concentration to 30.9 mmol/l in the continued presence of diazoxide and 11 mmol/l glucose restored the secretory rate with maintained pulsatility and caused stable elevation in [Ca(2+)](i). Simultaneous introduction of diazoxide and elevation of K(+) augmented average insulin release almost 30-fold in 3 mmol/l glucose with maintained pulse frequency. Subsequent elevation of the glucose concentration to 11 and 20 mmol/l increased the release levels. After prolonged exposure to diazoxide, elevated K(+) and 20 mmol/l glucose, the pulse frequency decreased significantly. CONCLUSIONS: Not only glucose signaling via the K(ATP) channel-dependent but also that via the independent pathway generates amplitude-modulated pulsatile release of insulin from isolated islets.

scholarly journals Loss of Secretory Pathway Ca2+ ATPase (SPCA1) Impairs Insulin Secretion and Reduces Autophagy in the Pancreatic Islet

2021 ◽  
Author(s):  
Robert N. Bone ◽  
Xin Tong ◽  
Staci A. Weaver ◽  
Charanya Muralidharan ◽  
Preethi Krishnan ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Secretory Pathway ◽  
Cell Types ◽  
Β Cell ◽  
Human Organ ◽  
Altered Glucose ◽  
Intracellular Ca ◽  
Insulin Granule ◽  
Granule Maturation ◽  
Glucose Stimulated Insulin Secretion

AbstractThe β cell Golgi apparatus serves as a significant store of intracellular Ca2+ and an important site of proinsulin maturation. However, the contribution of Golgi Ca2+ to diabetes pathophysiology is unknown. The Golgi primarily utilizes the Secretory Pathway Ca2+ ATPase (SPCA1) to maintain intraluminal Ca2+ stores, and loss of SPCA1 has been linked to impaired Golgi function in other cell types. Here, we demonstrated that SPCA1 expression is decreased in islets from diabetic mice and human organ donors with type 2 diabetes, suggesting SPCA1 may impact diabetes development. INS-1 β cells lacking SPCA1 (SPCA1KO) showed reduced intraluminal Golgi Ca2+ levels, reduced glucose-stimulated insulin secretion (GSIS), and increased insulin content. Islets from SPCA1 haploinsufficient mice (SPCA1+/-) exhibited reduced GSIS, altered glucose-induced Ca2+ oscillations, and altered insulin granule maturation. Autophagy can regulate granule homeostasis, therefore we induced autophagy with Torin1 and found that SPCA1KO cells and SPCA1+/- islets had reduced levels of the autophagosome marker LC3-II. Furthermore, SPCA1KO LC3-II were unchanged after blocking autophagy initiation or autophagolysosome fusion and acidification. Thus, we concluded that β cell SPCA1 plays an important role in the maintenance of Golgi Ca2+ homeostasis and reduced Golgi Ca2+ impairs autophagy initiation and may impact insulin granule homeostasis.

scholarly journals Perilipin Is Present in Islets of Langerhans and Protects against Lipotoxicity When Overexpressed in the β-Cell Line INS-1

Endocrinology ◽  
2009 ◽  
Vol 150 (7) ◽  
pp. 3049-3057 ◽  
Author(s):  
Jörgen Borg ◽  
Cecilia Klint ◽  
Nils Wierup ◽  
Kristoffer Ström ◽  
Sara Larsson ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Cell Line ◽  
Islets Of Langerhans ◽  
Prolonged Exposure ◽  
Human Islets ◽  
Lipid Storage ◽  
Β Cells ◽  
Β Cell ◽  
Glucose Stimulated Insulin Secretion ◽  
In Cells

Lipids have been shown to play a dual role in pancreatic β-cells: a lipid-derived signal appears to be necessary for glucose-stimulated insulin secretion, whereas lipid accumulation causes impaired insulin secretion and apoptosis. The ability of the protein perilipin to regulate lipolysis prompted an investigation of the presence of perilipin in the islets of Langerhans. In this study evidence is presented for perilipin expression in rat, mouse, and human islets of Langerhans as well as the rat clonal β-cell line INS-1. In rat and mouse islets, perilipin was verified to be present in β-cells. To examine whether the development of lipotoxicity could be prevented by manipulating the conditions for lipid storage in the β-cell, INS-1 cells with adenoviral-mediated overexpression of perilipin were exposed to lipotoxic conditions for 72 h. In cells exposed to palmitate, perilipin overexpression caused increased accumulation of triacylglycerols and decreased lipolysis compared with control cells. Whereas glucose-stimulated insulin secretion was retained after palmitate exposure in cells overexpressing perilipin, it was completely abolished in control β-cells. Thus, overexpression of perilipin appears to confer protection against the development of β-cell dysfunction after prolonged exposure to palmitate by promoting lipid storage and limiting lipolysis.

Insulin release transduction mechanism through acid glucan 1,4-α-glucosidase activation is Ca2+ regulated

1998 ◽  
Vol 274 (3) ◽  
pp. E459-E468 ◽  
Author(s):  
Albert Salehi ◽  
Henrik Mosén ◽  
Ingmar Lundquist
Keyword(s):  
Enzyme Activity ◽  
Insulin Secretion ◽  
Insulin Release ◽  
Similar Increase ◽  
Glucosidase Activity ◽  
Intracellular Ca ◽  
Low Glucose ◽  
Perifused Islets ◽  
Glucose Stimulated Insulin Secretion ◽  
Induced Changes

An important signal involved in glucose-stimulated insulin secretion is transduced through the action of a lysosomal acid, glucan 1,4-α-glucosidase. We investigated the Ca2+ dependency of this enzyme activity in relation to insulin release. In isolated islets, increased levels of extracellular Ca2+induced a large increase in acid glucan 1,4-α-glucosidase activity accompanied by a similar increase in insulin release at both substimulatory and stimulatory concentrations of glucose. At low glucose the Ca2+ “inflow” blocker nifedipine unexpectedly stimulated enzyme activity without affecting insulin release. However, nifedipine suppressed45Ca2+outflow from perifused islets at low glucose and at Ca2+ deficiency when intracellular Ca2+ was mobilized by carbachol. This nifedepine-induced retention of Ca2+ was reflected in increased acid glucan 1,4-α-glucosidase activity. Adding different physiological Ca2+ concentrations or nifedipine to islet homogenates did not increase enzyme activity. Neither selective glucan 1,4-α-glucosidase inhibition nor the ensuing suppression of glucose-induced insulin release was overcome by a maximal Ca2+ concentration. Hence, Ca2+-induced changes in acid glucan 1,4-α-glucosidase activity were intimately coupled to similar changes in Ca2+-glucose-induced insulin release. Ca2+ did not affect the enzyme itself but presumably activated either glucan 1,4-α-glucosidase-containing organelles or closely interconnected messengers.

scholarly journals FFAR1 Is Involved in Both the Acute and Chronic Effects of Palmitate on Insulin Secretion

Endocrinology ◽  
2013 ◽  
Vol 154 (11) ◽  
pp. 4078-4088 ◽  
Author(s):  
Hjalti Kristinsson ◽  
David M. Smith ◽  
Peter Bergsten ◽  
Ernest Sargsyan
Keyword(s):  
Insulin Secretion ◽  
Prolonged Exposure ◽  
Cell Function ◽  
Control Level ◽  
Insulin Content ◽  
Pancreatic Β Cell ◽  
Long Term Effects ◽  
Β Cell ◽  
Long Term Treatment

Free fatty acids (FFAs) have pleiotropic effects on the pancreatic β-cell. Although acute exposure to FFAs stimulates glucose-stimulated insulin secretion (GSIS), prolonged exposure impairs GSIS and causes apoptosis. FFAs exert their effects both via intracellular metabolism and interaction with the FFA receptor 1 (FFAR1/GPR40). Here we studied the role of FFAR1 in acute and long-term effects of palmitate on GSIS and insulin content in isolated human islets by using the FFAR1 agonist TAK-875 and the antagonist ANT203. Acute palmitate exposure potentiated GSIS approximately 3-fold, whereas addition of the antagonist decreased this potentiation to approximately 2-fold. In the absence of palmitate, the agonist caused a 40% increase in GSIS. Treatment with palmitate for 7 days decreased GSIS to 70% and insulin content to 25% of control level. These negative effects of long-term exposure to palmitate were ameliorated by FFAR1 inhibition and further aggravated by additional stimulation of the receptor. In the absence of extracellularly applied palmitate, long-term treatment with the agonist caused a modest increase in GSIS. The protective effect of FFAR1 inhibition was verified by using FFAR1-deficient MIN6 cells. Improved β-cell function by the antagonist was paralleled by the decreased apoptosis and lowered oxidation of palmitate, which may represent the potential mechanisms of protection. We conclude that FFAR1 in the pancreatic β-cell plays a substantial role not only in acute potentiation of GSIS by palmitate but also in the negative long-term effects of palmitate on GSIS and insulin content.

scholarly journals Protective Effect of 2-Dodecyl-6-Methoxycyclohexa-2, 5-Diene-1, 4-Dione, Isolated from Averrhoa Carambola L., Against Palmitic Acid-Induced Inflammation and Apoptosis in Min6 Cells by Inhibiting the TLR4-MyD88-NF-κB Signaling Pathway

2016 ◽  
Vol 39 (5) ◽  
pp. 1705-1715 ◽  
Author(s):  
Qiuqiao Xie ◽  
Shijun Zhang ◽  
Chunxia Chen ◽  
Juman Li ◽  
Xiaojie Wei ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Inflammatory Response ◽  
Protective Effect ◽  
Cell Viability ◽  
Palmitic Acid ◽  
Signaling Pathway ◽  
Inflammatory Cytokines ◽  
Averrhoa Carambola ◽  
Min6 Cells ◽  
Glucose Stimulated Insulin Secretion

Background/Aims: Studies have demonstrated that 2-dodecyl-6-methoxycyclohexa-2, 5-diene-1, 4-dione (DMDD), isolated from the roots of Averrhoa carambola L., has significant therapeutic potential for the treatment of diabetes. However, the protective effect of DMDD against pancreatic beta cell dysfunction has never been reported. We investigated whether DMDD protected against palmitic acid-induced dysfunction in pancreatic β-cell line Min6 cells by attenuating the inflammatory response and apoptosis and to shed light on its possible mechanism. Methods: Cell viability was assessed by CCK-8. Glucose-stimulated insulin secretion levels and inflammatory cytokines levels were examined by ELISA. Apoptosis was assessed by Annexin V-FITC/PI Flow cytometry assay, Hoechst 33342/PI double-staining assay, and Transmission electron microscopy assay. Relative quantitative real-time PCR and western blot were used to determine the expressions of genes and proteins. Results: Cell viability and glucose-stimulated insulin secretion levels were increased in DMDD-pretreated Min6 cells. DMDD inhibited inflammatory cytokines IL-6, TNF-α and MCP-1 generations in palmitic acid (PA)-induced Min6 cells. Moreover, DMDD protected against PA-induced Min6 cells apoptosis and the expression of Cleaved-Caspase-3, -8 and -9 were down-regulated and the Bcl-2/Bax ratio was increased in DMDD-pretreated Min6 cells. In addition, the expression of TLR4, MyD88 and NF-κB were down-regulated in DMDD-pretreated Min6 cells and TAK-242-pretreated group cells. Conclusions: DMDD protected Min6 cells against PA-induced dysfunction by attenuating the inflammatory response and apoptosis, and its mechanism of this protection was associated with inhibiting the TLR4-MyD88-NF-κB signaling pathway.

scholarly journals Fatty Acid and Lipopolysaccharide Effect on Beta Cells Proteostasis and its Impact on Insulin Secretion

Cells ◽  
2019 ◽  
Vol 8 (8) ◽  
pp. 884 ◽  
Author(s):  
Paloma Acosta-Montaño ◽  
Eustolia Rodríguez-Velázquez ◽  
Esmeralda Ibarra-López ◽  
Héctor Frayde-Gómez ◽  
Jaime Mas-Oliva ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Insulin Secretion ◽  
Fatty Acid ◽  
Cell Viability ◽  
Insulin Release ◽  
Palmitoleic Acid ◽  
Cell Mass ◽  
Β Cells ◽  
Β Cell

Metabolic overload by saturated fatty acids (SFA), which comprises β-cell function, and impaired glucose-stimulated insulin secretion are frequently observed in patients suffering from obesity and type 2 diabetes mellitus. The increase of intracellular Ca2+ triggers insulin granule release, therefore several mechanisms regulate Ca2+ efflux within the β-cells, among others, the plasma membrane Ca2+-ATPase (PMCA). In this work, we describe that lipotoxicity mediated mainly by the saturated palmitic acid (PA) (16C) is associated with loss of protein homeostasis (proteostasis) and potentially cell viability, a phenomenon that was induced to a lesser extent by stearic (18C), myristic (14C) and lauric (12C) acids. PA was localized on endoplasmic reticulum, activating arms of the unfolded protein response (UPR), as also promoted by lipopolysaccharides (LPS)-endotoxins. In particular, our findings demonstrate an alteration in PMCA1/4 expression caused by PA and LPS which trigger the UPR, affecting not only insulin release and contributing to β-cell mass reduction, but also increasing reactive nitrogen species. Nonetheless, stearic acid (SA) did not show these effects. Remarkably, the proteolytic degradation of PMCA1/4 prompted by PA and LPS was avoided by the action of monounsaturated fatty acids such as oleic and palmitoleic acid. Oleic acid recovered cell viability after treatment with PA/LPS and, more interestingly, relieved endoplasmic reticulum (ER) stress. While palmitoleic acid improved the insulin release, this fatty acid seems to have more relevant effects upon the expression of regulatory pumps of intracellular Ca2+. Therefore, chain length and unsaturation of fatty acids are determinant cues in proteostasis of β-cells and, consequently, on the regulation of calcium and insulin secretion.

scholarly journals Quercetin Stimulates Insulin Secretion and Reduces the Viability of Rat INS-1 Beta-Cells

2016 ◽  
Vol 39 (1) ◽  
pp. 278-293 ◽  
Author(s):  
Michael Kittl ◽  
Marlena Beyreis ◽  
Munkhtuya Tumurkhuu ◽  
Johannes Fürst ◽  
Katharina Helm ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Cell Viability ◽  
Beta Cells ◽  
Insulin Release ◽  
Katp Channel ◽  
Annexin V ◽  
Long Term Effects ◽  
Mean Cell Volume ◽  
Channel Inhibition

Background/Aims: Previously we described insulinotropic effects of Leonurus sibiricus L. plant extracts used for diabetes mellitus treatment in Traditional Mongolian Medicine. The flavonoid quercetin and its glycoside rutin, which exert anti-diabetic properties in vivo by interfering with insulin signaling in peripheral target tissues, are constituents of these extracts. This study was performed to better understand short- and long-term effects of quercetin and rutin on beta-cells. Methods: Cell viability, apoptosis, phospho-protein abundance and insulin release were determined using resazurin, annexin-V binding assays, Western blot and ELISA, respectively. Membrane potentials (Vmem), whole-cell Ca2+ (ICa)- and ATP-sensitive K+ (IKATP) currents were measured by patch clamp. Intracellular Ca2+ (Cai) levels were measured by time-lapse imaging using the ratiometric Ca2+ indicator Fura-2. Results: Rutin, quercetin and the phosphoinositide-3-kinase (PI3K) inhibitor LY294002 caused a dose-dependent reduction in cell viability with IC50 values of ∼75 µM, ∼25 µM and ∼3.5 µM, respectively. Quercetin (50 µM) significantly increased the percentage of Annexin-V+ cells within 48 hrs. The mean cell volume (MCV) of quercetin-treated cells was significantly lower. Within 2 hrs, quercetin significantly decreased basal- and insulin-stimulated Akt(T308) phosphorylation and increased Erk1/2 phosphorylation, without affecting P-Akt(S473) abundance. Basal- and glucose-stimulated insulin release were significantly stimulated by quercetin. Quercetin significantly depolarized Vmem by ∼25 mV which was prevented by the KATP-channel opener diazoxide, but not by the L-type ICa inhibitor nifedipine. Quercetin significantly stimulated ICa and caused a 50% inhibition of IKATP. The effects on Vmem, ICa and IKATP rapidly reached peak values and then gradually diminished to control values within ∼1 minute. With a similar time-response quercetin induced an elevation in Cai which was completely abolished in the absence of Ca2+ in the bath solution. Rutin (50 µM) did not significantly alter the percentage of Annexin-V+ cells, MCV, Akt or Erk1/2 phosphorylation, insulin secretion, or the electrophysiological behavior of INS-1 cells. Conclusion: We conclude that quercetin acutely stimulates insulin release, presumably by transient KATP channel inhibition and ICa stimulation. Long term application of quercetin inhibits cell proliferation and induces apoptosis, most likely by inhibition of PI3K/Akt signaling.

scholarly journals Ontology of the apelinergic system in mouse pancreas during pregnancy and relationship with β-cell mass

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Brenda Strutt ◽  
Sandra Szlapinski ◽  
Thineesha Gnaneswaran ◽  
Sarah Donegan ◽  
Jessica Hill ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Insulin Secretion ◽  
Glucose Transporter ◽  
Cell Mass ◽  
Elevated Serum ◽  
Pancreatic Β Cell ◽  
Β Cells ◽  
Β Cell ◽  
Glucose Transporter 2 ◽  
Glucose Stimulated Insulin Secretion

AbstractThe apelin receptor (Aplnr) and its ligands, Apelin and Apela, contribute to metabolic control. The insulin resistance associated with pregnancy is accommodated by an expansion of pancreatic β-cell mass (BCM) and increased insulin secretion, involving the proliferation of insulin-expressing, glucose transporter 2-low (Ins+Glut2LO) progenitor cells. We examined changes in the apelinergic system during normal mouse pregnancy and in pregnancies complicated by glucose intolerance with reduced BCM. Expression of Aplnr, Apelin and Apela was quantified in Ins+Glut2LO cells isolated from mouse pancreata and found to be significantly higher than in mature β-cells by DNA microarray and qPCR. Apelin was localized to most β-cells by immunohistochemistry although Aplnr was predominantly associated with Ins+Glut2LO cells. Aplnr-staining cells increased three- to four-fold during pregnancy being maximal at gestational days (GD) 9–12 but were significantly reduced in glucose intolerant mice. Apelin-13 increased β-cell proliferation in isolated mouse islets and INS1E cells, but not glucose-stimulated insulin secretion. Glucose intolerant pregnant mice had significantly elevated serum Apelin levels at GD 9 associated with an increased presence of placental IL-6. Placental expression of the apelinergic axis remained unaltered, however. Results show that the apelinergic system is highly expressed in pancreatic β-cell progenitors and may contribute to β-cell proliferation in pregnancy.

scholarly journals PDX1LOW MAFALOW β-cells contribute to islet function and insulin release

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Daniela Nasteska ◽  
Nicholas H. F. Fine ◽  
Fiona B. Ashford ◽  
Federica Cuozzo ◽  
Katrina Viloria ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Metabolic Stress ◽  
Human Islets ◽  
Islet Function ◽  
Β Cells ◽  
Β Cell ◽  
Ionic Fluxes ◽  
Transcriptomic Level ◽  
Adult Islet

AbstractTranscriptionally mature and immature β-cells co-exist within the adult islet. How such diversity contributes to insulin release remains poorly understood. Here we show that subtle differences in β-cell maturity, defined using PDX1 and MAFA expression, contribute to islet operation. Functional mapping of rodent and human islets containing proportionally more PDX1HIGH and MAFAHIGH β-cells reveals defects in metabolism, ionic fluxes and insulin secretion. At the transcriptomic level, the presence of increased numbers of PDX1HIGH and MAFAHIGH β-cells leads to dysregulation of gene pathways involved in metabolic processes. Using a chemogenetic disruption strategy, differences in PDX1 and MAFA expression are shown to depend on islet Ca2+ signaling patterns. During metabolic stress, islet function can be restored by redressing the balance between PDX1 and MAFA levels across the β-cell population. Thus, preserving heterogeneity in PDX1 and MAFA expression, and more widely in β-cell maturity, might be important for the maintenance of islet function.

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