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- Amisten, Stefan, et al.
(författare)
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ADP mediates inhibition of insulin secretion by activation of P2Y13 receptors in mice.
- 2010
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Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; Jul 1, s. 1927-1934
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Tidskriftsartikel (refereegranskat)abstract
- AIMS/HYPOTHESES: To investigate the effects of extracellular purines on insulin secretion from mouse pancreatic islets. METHODS: Mouse islets and beta cells were isolated and examined with mRNA real-time quantification, cAMP quantification and insulin and glucagon secretion. ATP release was measured in MIN6c4 cells. Insulin and glucagon secretion were measured in vivo after glucose injection. RESULTS: Enzymatic removal of extracellular ATP at low glucose levels increased the secretion of both insulin and glucagon, while at high glucose levels insulin secretion was reduced and glucagon secretion was stimulated, indicating an autocrine effect of purines. In MIN6c4 cells it was shown that glucose does induce release of ATP into the extracellular space. Quantitative real-time PCR demonstrated the expression of the ADP receptors P2Y(1) and P2Y(13) in both intact mouse pancreatic islets and isolated beta cells. The stable ADP analogue 2-MeSADP had no effect on insulin secretion. However, co-incubation with the P2Y(1) antagonist MRS2179 inhibited insulin secretion, while co-incubation with the P2Y(13) antagonist MRS2211 stimulated insulin secretion, indicating that ADP acting via P2Y(1) stimulates insulin secretion, while signalling via P2Y(13) inhibits the secretion of insulin. P2Y(13) antagonism through MRS2211 per se increased the secretion of both insulin and glucagon at intermediate (8.3 mmol/l) and high (20 mmol/l) glucose levels, confirming an autocrine role for ADP. Administration of MRS2211 during glucose injection in vivo resulted in both increased secretion of insulin and reduced glucose levels. CONCLUSIONS/INTERPRETATION: In conclusion, ADP acting on the P2Y(13) receptors inhibits insulin release. An antagonist to P2Y(13) increases insulin release and could be evaluated for the treatment of diabetes.
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- Flodgren, Erik, et al.
(författare)
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GPR40 is expressed in glucagon producing cells and affects glucagon secretion.
- 2007
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 354:1, s. 240-245
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Tidskriftsartikel (refereegranskat)abstract
- The free fatty acid receptor, GPR40, has been coupled with insulin secretion via its expression in pancreatic beta-cells. However, the role of GPR40 in the release of glucagon has not been studied and previous attempts to identify the receptor in alpha-cells have been unfruitful. Using double-staining for glucagon and GPR40 expression, we demonstrate that the two are expressed in the same cells in the periphery of mouse islets. In-R1-G9 hamster glucagonoma cells respond dose-dependently to linoleic acid stimulation by elevated phosphatidyl inositol hydrolysis and glucagon release and the cells become increasingly responsive to fatty acid stimulation when overexpressing GPR40. Isolated mouse islets also secrete glucagon in response to linoleic acid, a response that was abolished by antisense treatment against GPR40. This study demonstrates that GPR40 is present and active in pancreatic alpha-cells and puts further emphasis on the importance of this nutrient sensing receptor in islet function. (c) 2006 Elsevier Inc. All rights reserved.
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- Jimenez, Javier, et al.
(författare)
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Abnormally decreased NO and augmented CO production in islets of the leptin-deficient ob/ob mouse might contribute to explain hyperinsulinemia and islet survival in leptin-resistant type 2 obese diabetes.
- 2011
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Ingår i: Regulatory Peptides. - : Elsevier BV. - 1873-1686 .- 0167-0115. ; 170, s. 43-51
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Tidskriftsartikel (refereegranskat)abstract
- The role of the gaseous messengers NO and CO for β-cell function and survival is controversial. We examined this issue in the hyperglycemic-hyperinsulinemic ob/ob mouse, an animal model of type 2 obese diabetes, by studying islets from obese vs lean mice regarding glucose-stimulated insulin release in relation to islet NO and CO production and the influence of modulating peptide hormones. Glucose-stimulated increase in ncNOS-activity in incubated lean islets was converted to a decrease in ob/ob islets associated with markedly increased insulin release. Both types of islet displayed iNOS activity appearing after ~60min in high-glucose. In ob/ob islets the insulinotropic peptides glucagon, GLP-1 and GIP suppressed NOS activities and amplified glucose-stimulated insulin release. The insulinostatic peptide leptin induced the opposite effects. Suppression of islet CO production inhibited, while stimulation amplified glucose-stimulated insulin release. Nonincubated isolated islets from young and adult obese mice displayed very low ncNOS and negligible iNOS activity. In contrast, production of CO, a NOS inhibitor, was impressively raised. Glucose injections induced strong activities of islet NOS isoforms in lean but not in obese mice and confocal microscopy revealed iNOS expression only in lean islets. Islets from ob/ob mice existing in a hyperglycemic in vivo milieu maintain elevated insulin secretion and protection from glucotoxicity through a general suppression of islet NOS activities achieved by leptin deficiency, high CO production and insulinotropic cyclic-AMP-generating hormones. Such a beneficial effect on islet function and survival might have its clinical counterpart in human leptin-resistant type 2 obese diabetes with hyperinsulinemia.
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- Lundquist, Ingmar, et al.
(författare)
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Metformin Ameliorates Dysfunctional Traits of Glibenclamide- and Glucose-Induced Insulin Secretion by Suppression of Imposed Overactivity of the Islet Nitric Oxide Synthase-NO System
- 2016
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- Metformin lowers diabetic blood glucose primarily by reducing hepatic gluconeogenesis and increasing peripheral glucose uptake. However, possible effects by metformin on beta-cell function are incompletely understood. We speculated that metformin might positively influence insulin secretion through impacting the beta-cell nitric oxide synthase (NOS)-NO system, a negative modulator of glucose-stimulated insulin release. In short-time incubations with isolated murine islets either glibenclamide or high glucose augmented insulin release associated with increased NO production from both neural and inducible NOS. Metformin addition suppressed the augmented NO generation coinciding with amplified insulin release. Islet culturing with glibenclamide or high glucose revealed pronounced fluorescence of inducible NOS in the beta-cells being abolished by metformin co-culturing. These findings were reflected in medium nitrite-nitrate levels. A glucose challenge following islet culturing with glibenclamide or high glucose revealed markedly impaired insulin response. Metformin co-culturing restored this response. Culturing murine islets and human islets from controls and type 2 diabetics with high glucose or high glucose + glibenclamide induced a pronounced decrease of cell viability being remarkably restored by metformin co-culturing. We show here, that imposed overactivity of the beta-cell NOS-NO system by glibenclamide or high glucose leads to insulin secretory dysfunction and reduced cell viability and also, importantly, that these effects are relieved by metformin inhibiting beta-cell NO overproduction from both neural and inducible NOS thus ameliorating a concealed negative influence by NO induced by sulfonylurea treatment and/or high glucose levels. This double-edged effect of glibenclamide on the beta-cellsuggests sulfonylurea monotherapy in type 2 diabetes being avoided.
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- Meidute, Sandra, et al.
(författare)
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Antagonistic and synergistic effects of fungal and bacterial growth in soil after adding different carbon and nitrogen sources
- 2008
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 40:9, s. 2334-2343
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Tidskriftsartikel (refereegranskat)abstract
- The effect of adding easily available and more complex carbon sources, with and without nitrogen, on fungal and bacterial growth and activity in soil were studied in the laboratory. Total microbial activity was estimated by measuring respiration, fungal growth with the acetate-in-ergosterol incorporation technique and bacterial growth with the thymidine and leucine incorporation techniques. The substrate additions consisted of glucose and cellulose, with and without nitrogen (as ammonium nitrate), and gelatine. The microbial development was followed over a 2-month period. The respiration rate increased within a few days after adding glucose, with and without nitrogen, and gelatine, initially by more than 10 but after 2 months no differences were seen compared with the control. Bacterial growth estimated, mated with the thymidine and leucine incorporation techniques gave similar results. Adding glucose with nitrogen, or gelatine, increased bacterial growth within a few days up to 10 times, but even after 2 months of incubation bacterial growth rates were still about 5 times higher than in the control. Adding only glucose increased bacterial growth rates by about twice over the whole incubation period. Fungal growth rates especially increased after adding cellulose and nitrogen, although a minor increase was found after adding cellulose alone. Fungal growth rates started to increase after 10 days of incubation with cellulose. There were indications of synergistic effects in that bacterial growth increased after the fungi had started to grow after adding cellulose. Treatments resulting in high bacterial growth rates (adding easily available carbon sources) led to decreased fungal growth rates compared with the control, indicating antagonistic effects of bacteria. (C) 2008 Elsevier Ltd. All rights reserved.
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| 8. |
- Meidute, Sandra, et al.
(författare)
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GPR40 protein levels are crucial to the regulation of stimulated hormone secretion in pancreatic islets. Lessons from spontaneous obesity-prone and non-obese type 2 diabetes in rats.
- 2013
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Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 1872-8057 .- 0303-7207. ; 381:1-2, s. 150-159
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Tidskriftsartikel (refereegranskat)abstract
- The role of islet GPR40 protein in the pathogenesis of diabetes is unclear. We explored the influence of GPR40 protein levels on hormone secretion in islets from two rat models of spontaneous type 2 diabetes displaying either hyperlipidaemia or hyperglycaemia. GPR40 expression was analysed by confocal microscopy, Western blot and qPCR in islets from preobese Zucker (fa/fa) rats, diabetic Goto-Kakizaki (GK) rats, and controls. Confocal microscopy of control islets showed expression of GPR40 protein in insulin, glucagon and somatostatin cells. GPR40 expression was strongly increased in islets of hyperlipidaemic fa/fa rats and coincided with a concentration-related increase in palmitate-induced release of insulin and glucagon and its inhibition of somatostatin release. Conversely, hyperglycaemic GK islets displayed an extremely faint expression of GPR40 as did high-glucose-cultured control islets. This was reflected in abolished palmitate-induced hormone response in GK islets and high-glucose-cultured control islets. The palmitate antagonist rosiglitazone promoted reappearance of GPR40 in high-glucose-cultured islets and served as partial agonist in glucose-stimulated insulin release. GPR40 protein is abundantly expressed in pancreatic islets and modulates stimulated hormone secretion. Mild hyperlipidaemia in obesity-prone diabetes creates increased GPR40 expression and increased risk for an exaggerated palmitate-induced insulin response and lipotoxicity, a metabolic situation suitable for GPR40 antagonist treatment. Chronic hyperglycaemia creates abrogated GPR40 expression and downregulated insulin release, a metabolic situation suitable for GPR40 agonist treatment to avoid glucotoxicity. GPR40 protein is interactively modulated by both free fatty acids and glucose and is a promising target for pharmacotherapy in different variants of type 2 diabetes.
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| 9. |
- Meidute, Sandra, et al.
(författare)
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Imidazoline-induced amplification of glucose- and carbachol-stimulated insulin release includes a marked suppression of islet NO generation in the mouse.
- 2009
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 195:3, s. 375-383
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The role of islet nitric oxide (NO) production in insulin releasing mechanisms is unclear. We examined whether the beneficial effects of the imidazoline derivative RX 871024 (RX) on beta-cell function might be related to perturbations of islet NO production. Methods: Experiments were performed with isolated islets or intact mice challenged with glucose or carbachol with or without RX treatment. Insulin was determined with radioimmunoassay, NO generation with high-performance liquid chromatography and expression of inducible NO-synthase (iNOS) with confocal microscopy. Results: RX treatment, in doses lacking effects on basal insulin, greatly amplified insulin release stimulated by the NO-generating secretagogues glucose and carbachol both in vitro and in vivo. RX also improved the glucose tolerance curve. Islets incubated at high glucose (20 mmol/l) displayed increased NO production derived from both neuronal constitutive NO-synthase (ncNOS) and iNOS. RX abrogated this glucose-induced NO production concomitant with amplification of insulin release. Confocal microscopy revealed abundant iNOS expression in beta-cells after incubation of islets at high but not low glucose. This was abolished after RX treatment. Similarly, islets cultured for 24 h at high glucose showed intense iNOS expression in beta-cells. This was abrogated with RX and followed by an amplified glucose-induced insulin release. Conclusion: RX effectively counteracts the negative impact of beta-cell NO generation on insulin release stimulated by glucose and carbachol suggesting imidazoline compounds by virtue of NOS-inhibitory properties being of potential therapeutic value for treatment of beta-cell dysfunction in hyperglycaemia and type 2 diabetes.
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| 10. |
- Meidute, Sandra
(författare)
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Mechanisms underlying lipotoxicity and glucotoxicity in pancreatic islets
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although it has been known for many years that long-term exposure of pancreatic islets to a high level of free fatty acids (FFA) or glucose negatively modulates islet hormone release, the identities of signals mediating these effects are not yet fully clarified. The overall objective of this study was to investigate signal transduction pathways involved in FFA- and glucose-exerted effects on beta-cell function during both short-term as well as long-term exposure. The data presented here confirmed that the G-protein coupled receptor 40 (GPR40) is a functional FFA receptor expressed in pancreatic islets. We now show that both the acute stimulatory action of palmitate on IP3-generation, increased [Ca2+]i and insulin release as well as the long-term effects of palmitate on the activation of MAPKs (SAPK/JNK and p38), iNOS expression and caspase-3 activity is mediated via activation of GPR40. A modulated expression of GPR40 in the islets i.e. overexpression (fa/fa rats) was accompanied by an exaggerated secretion of insulin, glucagon and marked suppression of somatostatin release in response to palmitate. In contrast, a low expression pattern of islet GPR40 (GK rats) was associated with a negligible hormone response to palmitate. The islet expression of iNOS seems to be, at least in part, a common signalling pathway in both lipotoxicity and glucotoxicity. Rosiglitazone (ROZ) effectively counteracted the deleterious effects of palmitate but not that of high glucose on the islet function. Glucose-induced expression of iNOS with subsequent β-cell dysfunction was markedly counteracted by the imidazoline derivative RX871024. We conclude that, in addition to mediating acute stimulatory effects of FFA on insulin release, GPR40 is also an important mediator of dysfunctional effects of FFA overtime. The adverse effects of FFA and high glucose on the islet function involve different or at least partially different signal systems and the FFA signalling is counteracted by ROZ at GPR40, suggesting the thiazolidinediones are protective against beta-cell lipotoxicity.
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