Glibenclamide inhibits islet carnitine palmitoyltransferase 1 activity, leading to PKC-dependent insulin exocytosis

2003 ◽  
Vol 285 (2) ◽  
pp. E438-E446 ◽  
Author(s):  
Mikael Lehtihet ◽  
Nils Welsh ◽  
Per-Olof Berggren ◽  
George A. Cook ◽  
Åke Sjöholm
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Secretory Granules ◽  
Carnitine Palmitoyltransferase ◽  
Diabetic Patients ◽  
Β Cell ◽  
Type 2 Diabetic Patients ◽  
Insulin Exocytosis ◽  
Carnitine Palmitoyltransferase 1 ◽  
Stimulate Insulin Release

Hypoglycemic sulfonylureas such as glibenclamide have been widely used to treat type 2 diabetic patients for 40 yr, but controversy remains about their mode of action. The widely held view is that they promote rapid insulin exocytosis by binding to and blocking pancreatic β-cell ATP-dependent K+ (KATP) channels in the plasma membrane. This event stimulates Ca2+ influx and sets in motion the exocytotic release of insulin. However, recent reports show that >90% of glibenclamide-binding sites are localized intracellularly and that the drug can stimulate insulin release independently of changes in KATP channels and cytoplasmic free Ca2+. Also, glibenclamide specifically and progressively accumulates in islets in association with secretory granules and mitochondria and causes long-lasting insulin secretion. It has been proposed that nutrient insulin secretagogues stimulate insulin release by increasing formation of malonyl-CoA, which, by blocking carnitine palmitoyltransferase 1 (CPT-1), switches fatty acid (FA) catabolism to synthesis of PKC-activating lipids. We show that glibenclamide dose-dependently inhibits β-cell CPT-1 activity, consequently suppressing FA oxidation to the same extent as glucose in cultured fetal rat islets. This is associated with enhanced diacylglycerol (DAG) formation, PKC activation, and KATP-independent glibenclamide-stimulated insulin exocytosis. The fat oxidation inhibitor etomoxir stimulated KATP-independent insulin secretion to the same extent as glibenclamide, and the action of both drugs was not additive. We propose a mechanism in which inhibition of CPT-1 activity by glibenclamide switches β-cell FA metabolism to DAG synthesis and subsequent PKC-dependent and KATP-independent insulin exocytosis. We suggest that chronic CPT inhibition, through the progressive islet accumulation of glibenclamide, may explain the prolonged stimulation of insulin secretion in some diabetic patients even after drug removal that contributes to the sustained hypoglycemia of the sulfonylurea.

Myosin light-chain phosphorylation controls insulin secretion at a proximal step in the secretory cascade

1997 ◽  
Vol 273 (4) ◽  
pp. E782-E789 ◽  
Author(s):  
Yuji Iida ◽  
Takao Senda ◽  
Yoshihisa Matsukawa ◽  
Koji Onoda ◽  
Jun-Ichi Miyazaki ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Secretory Granules ◽  
Cam Kinase Ii ◽  
Cam Kinase ◽  
Β Cell ◽  
Cell Extracts

The aim of this study was to investigate how insulin secretion is controlled by phosphorylation of the myosin light chain (MLC). Ca2+-evoked insulin release from pancreatic islets permeabilized with streptolysin O was inhibited by different monoclonal antibodies against myosin light-chain kinase (MLCK) to an extent parallel to their inhibition of purified MLCK. Anti-MLCK antibody also inhibited insulin release caused by the stable GTP analog guanosine 5′- O-(3-thiodiphosphate), even at a substimulatory concentration (0.1 μM) of Ca2+. Free Ca2+ increased MLC peptide phosphorylation by β-cell extracts in vitro. In contrast to the phosphorylation by purified MLCK or by calmodulin (CaM) kinase II, the activity partially remained with the β-cell under nonstimulatory Ca2+ (0.1 μM) conditions. The MLCK inhibitor ML-9 inhibited the activity in the β-cell with both substimulatory and stimulatory Ca2+, whereas KN-62, an inhibitor of CaM kinase II, only exerted an influence in the latter case. ML-9 decreased intracellular granule movement in MIN6 cells under basal and acetylcholine-stimulated conditions. We propose that MLC phosphorylation may modulate translocation of secretory granules, resulting in enhanced insulin secretion.

scholarly journals Decrement of postprandial insulin secretion determines the progressive nature of type-2 diabetes

2006 ◽  
Vol 155 (4) ◽  
pp. 615-622 ◽  
Author(s):  
Wan Sub Shim ◽  
Soo Kyung Kim ◽  
Hae Jin Kim ◽  
Eun Seok Kang ◽  
Chul Woo Ahn ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Insulin Secretion ◽  
Diabetic Patients ◽  
Β Cell ◽  
Type 2 Diabetic Patients ◽  
C Peptide ◽  
Duration Of Diabetes ◽  
Type 2 Diabetic ◽  
Postprandial Insulin

Objective: Type-2 diabetes is a progressive disease. However, little is known about whether decreased fasting or postprandial pancreatic β-cell responsiveness is more prominent with increased duration of diabetes. The aim of this study was to evaluate the relationship between insulin secretion both during fasting and 2 h postprandial, and the duration of diabetes in type-2 diabetic patients. Design: Cross-sectional clinical investigation. Methods: We conducted a meal tolerance test in 1466 type-2 diabetic patients and calculated fasting (M0) and postprandial (M1) β-cell responsiveness. Results: The fasting C-peptide, postprandial C-peptide, M0, and M1 values were lower, but HbA1c values were higher, in patients with diabetes duration > 10 years than those in other groups. There was no difference in the HbA1c levels according to the tertiles of their fasting C-peptide level. However, in a group of patients with highest postprandial C-peptide tertile, the HbA1c values were significantly lower than those in other groups. After adjustment of age, sex, and body mass index (BMI), the duration of diabetes was found to be negatively correlated with fasting C-peptide (γ = −0.102), postprandial C-peptide (γ = −0.356), M0 (γ = −0.263), and M1 (γ = −0.315; P < 0.01 respectively). After adjustment of age, sex, and BMI, HbA1c was found to be negatively correlated with postprandial C-peptide (γ = −0.264), M0 (γ = −0.379), and M1 (γ = −0.522), however, positively correlated with fasting C-peptide (γ = 0.105; P < 0.01 respectively). In stepwise multiple regression analysis, M0, M1, and homeostasis model assessment for insulin resistance (HOMA-IR) emerged as predictors of HbAlc after adjustment for age, sex, and BMI (R2 = 0.272, 0.080, and 0.056 respectively). Conclusions: With increasing duration of diabetes, the decrease of postprandial insulin secretion is becoming more prominent, and postprandial β-cell responsiveness may be a more important determinant for glycemic control than fasting β-cell responsiveness.

scholarly journals Dynamics of Insulin Secretion from EndoC-βH1 β-Cell Pseudoislets in Response to Glucose and Other Nutrient and Nonnutrient Secretagogues

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Hiroki Teraoku ◽  
Sigurd Lenzen
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Channel Blocker ◽  
Secretory Granules ◽  
Β Cell ◽  
Reserve Pool ◽  
Dynamics Of Insulin Secretion ◽  
Stimulation Period ◽  
Second Phases ◽  
Insulin Secretory Response

The dynamics of insulin secretion were characterized in response to a variety of physiological and pharmacological stimulators and other compounds in perifused pseudoislets generated from cells of the EndoC-βH1 β-cell line. Perifusion of EndoC-βH1 pseudoislets with the physiological stimulus glucose (16.7 mM) induced sustained insulin secretion, which was inhibited by mannoheptulose. The adenylate cyclase activators IBMX and forskolin strongly potentiated this secretion. Glibenclamide, a Kir 6.2 potassium channel blocker, and Bay K 8644, an opener of the voltage-sensitive Ca2+ channel, also potentiated glucose-induced insulin secretion. The dynamics of insulin secretion from EndoC-βH1 pseudoislets were characterized by an insulin secretory response to glucose starting within 1-2 min and passing over without interruption into a sustained phase of insulin release for the whole stimulation period. This lack of a transient decline between the first and the second phases of insulin release is an indication for a quick supply of insulin secretory granules from the reserve pool to the docking sites below the plasma membrane. Thereby, new secretory granules are directly made available for sustained exocytosis of insulin in EndoC-βH1 β-cells. The study shows that EndoC-βH1 β-cell pseudoislets are well suited for kinetic analyses of insulin secretion.

scholarly journals Imeglimin lowers glucose primarily by amplifying glucose-stimulated insulin secretion in high-fat-fed rodents

2016 ◽  
Vol 311 (2) ◽  
pp. E461-E470 ◽  
Author(s):  
Rachel J. Perry ◽  
Rebecca L. Cardone ◽  
Max C. Petersen ◽  
Dongyan Zhang ◽  
Pascale Fouqueray ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Antidiabetic Activity ◽  
Diabetic Patients ◽  
Β Cell ◽  
Type 2 Diabetic Patients ◽  
Postprandial Glycemia ◽  
Hyperglycemic Clamp ◽  
Increase Insulin Secretion ◽  
Glucose Stimulated Insulin Secretion

Imeglimin is a promising new oral antihyperglycemic agent that has been studied in clinical trials as a possible monotherapy or add-on therapy to lower fasting plasma glucose and improve hemoglobin A1c (1–3, 9). Imeglimin was shown to improve both fasting and postprandial glycemia and to increase insulin secretion in response to glucose during a hyperglycemic clamp after 1-wk of treatment in type 2 diabetic patients. However, whether the β-cell stimulatory effect of imeglimin is solely or partially responsible for its effects on glycemia remains to be fully confirmed. Here, we show that imeglimin directly activates β-cell insulin secretion in awake rodents without affecting hepatic insulin sensitivity, body composition, or energy expenditure. These data identify a primary amplification rather than trigger the β-cell mechanism that explains the acute, antidiabetic activity of imeglimin.

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.

scholarly journals Reducing Glucokinase Activity Restores Endogenous Pulsatility and Enhances Insulin Secretion in Islets From db/db Mice

Endocrinology ◽  
2018 ◽  
Vol 159 (11) ◽  
pp. 3747-3760 ◽  
Author(s):  
Ishrat Jahan ◽  
Kathryn L Corbin ◽  
Avery M Bogart ◽  
Nicholas B Whitticar ◽  
Christopher D Waters ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Opposite Effect ◽  
Glucose Sensing ◽  
Β Cell ◽  
Left Shift ◽  
Low Glucose ◽  
Mouse Islets ◽  
Secretion Rates

Abstract An early sign of islet failure in type 2 diabetes (T2D) is the loss of normal patterns of pulsatile insulin release. Disruptions in pulsatility are associated with a left shift in glucose sensing that can cause excessive insulin release in low glucose (relative hyperinsulinemia, a hallmark of early T2D) and β-cell exhaustion, leading to inadequate insulin release during hyperglycemia. Our hypothesis was that reducing excessive glucokinase activity in diabetic islets would improve their function. Isolated mouse islets were exposed to glucose and varying concentrations of the glucokinase inhibitor d-mannoheptulose (MH) to examine changes in intracellular calcium ([Ca2+]i) and insulin secretion. Acutely exposing islets from control CD-1 mice to MH in high glucose (20 mM) dose dependently reduced the size of [Ca2+]i oscillations detected by fura-2 acetoxymethyl. Glucokinase activation in low glucose (3 mM) had the opposite effect. We then treated islets from male and female db/db mice (age, 4 to 8 weeks) and heterozygous controls overnight with 0 to 10 mM MH to determine that 1 mM MH produced optimal oscillations. We then used 1 mM MH overnight to measure [Ca2+]i and insulin simultaneously in db/db islets. MH restored oscillations and increased insulin secretion. Insulin secretion rates correlated with MH-induced increases in amplitude of [Ca2+]i oscillations (R2 = 0.57, P &lt; 0.01, n = 10) but not with mean [Ca2+]i levels in islets (R2 = 0.05, not significant). Our findings show that correcting glucose sensing can restore proper pulsatility to diabetic islets and improved pulsatility correlates with enhanced insulin secretion.

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