| 1. |
- Hals, Ingrid K., et al.
(författare)
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Investigating optimal β-cell-preserving treatment in latent autoimmune diabetes in adults : Results from a 21-month randomized trial
- 2019
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Ingår i: Diabetes, Obesity and Metabolism. - : Wiley. - 1462-8902 .- 1463-1326. ; 21:10, s. 2219-2227
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Tidskriftsartikel (refereegranskat)abstract
- Aims: To compare outcomes of glucagon-stimulated C-peptide tests (GSCTs) in people with latent autoimmune diabetes in adults (LADA) after a 21-month intervention with either insulin or the dipeptidyl peptidase-4 inhibitor sitagliptin. Research design and methods: We included 64 glutamic acid decarboxylase (GAD) antibody-positive individuals, who were diagnosed with diabetes <3 years before the study, aged 30 to 70 years, and without clinical need for insulin treatment. We stratified participants by age and body mass index (BMI) and evaluated β-cell function by GSCT after a 48-hour temporary withdrawal of study medication. Results: Age at randomization (mean 53 years), BMI (mean 27 kg/m2) and metabolic markers were similar between treatment arms. Glycated haemoglobin concentrations during intervention did not differ between arms. Fasting C-peptide concentrations after the intervention were similar, as were stimulated C-peptide levels (0.82 ± 0.63 nmol/L after insulin, 0.82 ± 0.46 nmol/L after sitagliptin; nonsignificant). Autoimmunity in the study population (estimated from GAD antibody titres and positivity/no positivity for zinc transporter 8 and islet antigen 2 antibodies) affected the evolution of the GSCT results significantly, which deteriorated in participants with high but not in those with low autoimmunity. Adjustment using analysis of covariance for the degree of autoimmunity did not alter the findings of no difference between treatment arms. Conclusions: β-cell function after intervention was similar in patients with insulin- and sitagliptin-treated LADA, regardless of the strength of autoimmunity. Further, participants with low levels of GAD antibodies did not experience progressive deterioration of β-cell function over a 21-month period. Taken together, these findings could be useful for clinicians' choices of treatment in people with LADA.
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| 2. |
- Krishnan, Kalaiselvan, et al.
(författare)
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Calcium Signaling in a Genetically Engineered Human Pancreatic beta-Cell Line
- 2015
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Ingår i: Pancreas. - 0885-3177 .- 1536-4828. ; 44:5, s. 773-777
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Tidskriftsartikel (refereegranskat)abstract
- Objectives The use of primary human -cells for studying Ca2+ signaling is limited by the scarcity of human pancreatic islets. Rodent insulinoma cell lines are widely used, but it is difficult to extrapolate results obtained from rodent cells to human. Recently, a genetically engineered human -cell line EndoC-BH1 has been developed. We have examined whether the EndoC-BH1 cells could be used as a model for studying Ca2+ signaling in the -cells. Methods We used microscope-based fluorometry to measure cytoplasmic-free Ca2+ concentration from fura-2-loaded single EndoC-BH1 cells cultured on glass cover slips. Ca2+ responses to different agonists of insulin secretion were studied. Insulin secretion was measured by radioimmunoassay. Results EndoC-BH1 cells secreted insulin in response to glucose in a dose-dependent manner, and the secretion was enhanced by GLP-1 (glucagon-like peptide 1). Glucose, potassium chloride, carbachol, l-arginine, and tolbutamide increased cytoplasmic-free Ca2+ concentration in the EndoC-BH1 cells. We found that GLP-1 was essential for Ca2+ response to glucose and tolbutamide. Conclusions We concluded that the EndoC-BH1 cells can be used as model cells to study Ca2+ signaling and stimulus-secretion coupling in the human -cells.
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| 3. |
- Krishnan, Kalaiselvan, et al.
(författare)
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Calcium signaling in a genetically engineered human pancreatic β-cell line
- 2015
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Ingår i: Pancreas. - 0885-3177 .- 1536-4828. ; 44:5, s. 773-777
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: The use of primary human β-cells for studying Ca2+ signalingis limited by the scarcity of human pancreatic islets. Rodent insulinomacell lines are widely used, but it is difficult to extrapolate results obtainedfrom rodent cells to human. Recently, a genetically engineered humanβ-cell line EndoC-BH1 has been developed. We have examined whetherthe EndoC-BH1 cells could be used as a model for studying Ca2+ signalingin the β-cells.Methods: We used microscope-based fluorometry to measure cytoplasmicfreeCa2+ concentration from fura-2–loaded single EndoC-BH1 cellscultured on glass cover slips. Ca2+ responses to different agonists of insulinsecretion were studied. Insulin secretion was measured by radioimmunoassay.Results: EndoC-BH1 cells secreted insulin in response to glucose ina dose-dependent manner, and the secretion was enhanced by GLP-1(glucagon-like peptide 1). Glucose, potassium chloride, carbachol, L-arginine,and tolbutamide increased cytoplasmic-free Ca2+ concentration in theEndoC-BH1 cells. We found that GLP-1 was essential for Ca2+ responseto glucose and tolbutamide.Conclusions: We concluded that the EndoC-BH1 cells can be used asmodel cells to study Ca2+ signaling and stimulus-secretion coupling inthe human β-cells.
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| 4. |
- Krishnan, Kalaiselvan, et al.
(författare)
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Role of Transient Receptor Potential Melastatin-like Subtype 5 Channel in Insulin Secretion From Rat beta-Cells
- 2014
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Ingår i: Pancreas. - 0885-3177 .- 1536-4828. ; 43:4, s. 597-604
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Tidskriftsartikel (refereegranskat)abstract
- Objective Several studies have reported that the transient receptor potential melastatin-like subtype 5 (TRPM5) channel, a Ca2+-activated monovalent cation channel, is involved in the stimulus-secretion coupling in the mouse pancreatic beta-cells. We have studied the role of the TRPM5 channel in regulating insulin secretion and cytoplasmic free Ca2+ concentration ([Ca2+](i)) in the rat beta-cells by using triphenylphosphine oxide, a selective inhibitor of the channel. Methods Insulin secretion from islets from Sprague-Dawley rats was measured in batch incubations. Cytoplasmic free Ca2+ concentration was measured from single beta-cells by fura-2-based microfluorometry. Results Triphenylphosphine oxide did not alter insulin secretion and [Ca2+](i) response triggered by KCl or fructose. It inhibited insulin secretion in response to glucose, l-arginine, and glucagon-like peptide 1. It also inhibited glucose-induced insulin secretion by mechanisms that are independent of the adenosine triphosphate-sensitive potassium channels and [Ca2+](i) increase. Conclusions Our results suggest that in the rat islets, TRPM5 is involved in mediating insulin secretion by glucose and l-arginine and in potentiating the glucose-induced insulin secretion by glucagon-like peptide 1.
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| 5. |
- Krishnan, Kalaiselvan, et al.
(författare)
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Role of TRPM5 channel in insulin secretion from rat β-cells. : TRPM5 and insulin secretion
- 2014
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Ingår i: Pancreas. - : Lippincott Williams & Wilkins. - 0885-3177 .- 1536-4828. ; 43:4, s. 597-604
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE:Several studies have reported that the transient receptor potential melastatin-like subtype 5 (TRPM5) channel, a Ca(2+)-activated monovalent cation channel, is involved in the stimulus-secretion coupling in the mouse pancreatic β-cells. We have studied the role of the TRPM5 channel in regulating insulin secretion and cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) in the rat β-cells by using triphenylphosphine oxide, a selective inhibitor of the channel.METHODS:Insulin secretion from islets from Sprague-Dawley rats was measured in batch incubations. Cytoplasmic free Ca(2+) concentration was measured from single β-cells by fura-2-based microfluorometry.RESULTS:Triphenylphosphine oxide did not alter insulin secretion and [Ca(2+)](i) response triggered by KCl or fructose. It inhibited insulin secretion in response to glucose, L-arginine, and glucagon-like peptide 1. It also inhibited glucose-induced insulin secretion by mechanisms that are independent of the adenosine triphosphate-sensitive potassium channels and [Ca(2+)](i) increase.CONCLUSIONS:Our results suggest that in the rat islets, TRPM5 is involved in mediating insulin secretion by glucose and l-arginine and in potentiating the glucose-induced insulin secretion by glucagon-like peptide 1.
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| 6. |
- Ma, Zuheng, et al.
(författare)
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A TRPM4 Inhibitor 9-Phenanthrol Inhibits Glucose- and Glucagon-Like Peptide 1-Induced Insulin Secretion from Rat Islets of Langerhans
- 2017
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Ingår i: Journal of Diabetes Research. - : Hindawi Limited. - 2314-6745 .- 2314-6753.
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Tidskriftsartikel (refereegranskat)abstract
- Pancreatic beta-cells express several ion channels of the transient receptor potential family, which play important roles in mediating the stimulus-secretion coupling. One of these channels, the TRPM4 is a Ca2+-activated monovalent cation channel. This channel is inhibited by 9-phenanthrol, which also inhibits the TMEM16a Cl- channel, and activates the Ca2+-activated K+ channel, K(ca)3.1. The net effects of ion-channel modulation by 9-phenantherol on the insulin secretion remain unclear. We tested the effects of 9-phenanthrol on glucose-and GLP-1-induced insulin secretion from isolated rat islets in static incubations. When applied to the islets in the presence of 3.3mM glucose, 9-phenanthrol caused a small increase in insulin secretion (similar to 7% of the insulin secretion stimulated by 10mM glucose). 10 mu M 9-phenanthrol did not inhibit glucose-or GLP-1-induced insulin secretion. 20 mu M and 30 mu M 9-phenanthrol inhibited glucose-induced insulin secretion by similar to 80% and similar to 85%, respectively. Inhibition of the GLP-1-induced insulin secretion by 20 mu M and 30 mu M 9-phenanthrol was 65% and 94%, respectively. Our study shows that the major effect of 9-phenanthrol on the islets is a strong inhibition of insulin secretion, and we speculate that compounds related to 9-phenanthrol may be potentially useful in treating the pancreatogenous hyperinsulinemic hypoglycemia syndromes.
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| 7. |
- Ma, Zuheng
(författare)
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Aspects on the modulation of potassium channels in insulin-producing beta-cells
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis attempts to further clarify mechanisms behind the negative effects of overstimulation and the beneficial effect of β-cell rest. For this purpose diazoxide - opener of K+-ATP channels, which reversibly inhibits glucose-induced insulin secretion, was used as a probe. Additionally, another type of potassium channel namely voltage dependent potassium channels (Kv-channels) specifically Kv1.1 has been tested for functional effects. Long-term (24 h) exposure of SD rat islets to elevated glucose (27 mmol/l) in vitro decreases glucoseinduced insulin response. The decrease is prevented by the co-culture with diazoxide. These effects were associated with reciprocal changes in certain exocytotic proteins (SNAP-25, syntaxin). Proteasomal inhibitors (MG132, ALLN and epoxomicin) but not a lysosomal inbitor (NH4Cl) blocked the inhibitory effects of diazoxide (tested for SNAP-25). This blocking effect was accompanied by a similar effect on glucose induced insulin secretion. The effects of short-term intermittent vs. continuous exposure to diazoxide in a high glucose environment appeared to have the same the benefit on K+-ATP dependent insulin secretion but not on K+-ATP independent insulin secretion. Intermittent and continuous diazoxide alike increased post-culture ATP-to-ADP ratios, failed to affect glucose oxidation, but decreased oleate oxidation. Continuous, but not intermittent, diazoxide decreased significantly mRNA for UCP-2. A 2 h exposure to 20 mmol/ll KCl or 10 µmol/l cycloheximide abrogated the postculture effects of intermittent, but not of continuous, diazoxide. Intermittent diazoxide islets levels of the SNARE protein SNAP-25, and KCl antagonized this effect. All in all, intermittent diazoxide exposure is sufficient to induce important functional changes in βcells. The overall effects by diazoxide on gene expression at high and low glucose were assessed by microarry. 114 genes were up-regulated (signal log2 ratio ≥0.5) and 173 genes down-regulated (signal log2 ratio ≤ -0.5) by diazoxide. 86% of diazoxide's effects (up and down regulation) were observed only after co-culture with 27 mmol/1 glucose. Up-regulation was to 3 1 % and down-regulation to 79 % contrary to effects of glucose per se. Diazoxide down-regulated genes of fatty acid oxidation and upregulated synthesis, whereas glucose per se had no effect. Irrespective of glucose concentration diazoxide up regulated certain genes which support β-cell functionality (nkx6.1 and pdx 1) and downregulated UCP-2, a potentially desensitizing gene. All in all, diazoxide effects were markedly glucose dependent and included genes known to be crucial for normal insulin secretion. The presence and functionality of Kv1.1 channels was assessed in BALB/cByJ mice and Kv1.1 truncated mceph/mceph mice islets. Gene expression (mRNA) was demonstrated in wild type and -as a smaller molecule- in mceph/mceph. Incremental glucose-induced insulin release was lower in BALB/cByJ than in mceph/mceph. Reciprocally, blocking Kvl.l by dendrotoxin-k increased secretion in BALB/cByJ but not in meeph/mceph mouse islets. These results strongly indicate the presence and functionality of Kv1.1 channels at least in mouse β-cells.
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| 8. |
- Ma, Zuheng, et al.
(författare)
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Diabetes reduces beta-cell mitochondria and induces distinct morphological abnormalities, which are reproducible by high glucose in vitro with attendant dysfunction
- 2012
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Ingår i: ISLETS. - : Informa UK Limited. - 1938-2014 .- 1938-2022. ; 4:3, s. 233-242
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the impact of a diabetic state with hyperglycemia on morphometry of beta-cell mitochondria and modifying influence of a K+-ATP channel opener and we related in vivo findings with glucose effects in vitro. For in vivo experiments, islets from syngeneic rats were transplanted under the kidney capsule to neonatally streptozotocin-diabetic or nondiabetic recipients. Diabetic recipients received vehicle, or tifenazoxide (NN414), intragastrically for 9 weeks. Non-diabetic rats received vehicle. Transplants were excised 7 d after cessation of treatment (wash-out) and prepared for electron microscopy. Morphological parameters were measured from approx. 25,000 mitochondria. Rat islets were cultured in vitro for 2-3 weeks at 27 or 11 (control) mmol/l glucose. Transplants to diabetic rats displayed decreased numbers of mitochondria (-31%, p < 0.05), increased mitochondrial volume and increased mitochondrial outer surface area, p < 0.001. Diabetes increased variability in mitochondrial size with frequent appearance of mega-mitochondria. Tifenazoxide partly normalized diabetes-induced effects, and mega-mitochondria disappeared. Long-term culture of islets at 27 mmol/l glucose reproduced the in vivo morphological abnormalities. High-glucose culture was also associated with reduced ATP and ADP contents, reduced oxygen consumption, reduced signaling by MitoTracker Red and reduction of mitochondrial proteins (complexes I-IV), OPA 1 and glucose-induced insulin release. We conclude that (1) a long-term diabetic state leads to a reduced number of mitochondria and to distinct morphological abnormalities which are replicated by high glucose in vitro; (2) the morphological abnormalities are coupled to dysfunction; (3) K+-ATP channel openers may have potential to partly reverse glucose-induced effects.
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| 9. |
- Ma, Zuheng, et al.
(författare)
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Evidence for Presence and Functional Effects of Kv1.1 Channels in beta-Cells: General Survey and Results from mceph/mceph Mice
- 2011
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Voltage-dependent K+ channels (Kv) mediate repolarisation of beta-cell action potentials, and thereby abrogate insulin secretion. The role of the Kv1.1 K+ channel in this process is however unclear. We tested for presence of Kv1.1 in different species and tested for a functional role of Kv1.1 by assessing pancreatic islet function in BALB/cByJ (wild-type) and megencephaly (mceph/mceph) mice, the latter having a deletion in the Kv1.1 gene. Methodology/Principal Findings: Kv1.1 expression was detected in islets from wild-type mice, SD rats and humans, and expression of truncated Kv1.1 was detected in mceph/mceph islets. Full-length Kv1.1 protein was present in islets from wildtype mice, but, as expected, not in those from mceph/mceph mice. Kv1.1 expression was localized to the beta-cell population and also to alpha-and delta-cells, with evidence of over-expression of truncated Kv1.1 in mceph/mceph islets. Blood glucose, insulin content, and islet morphology were normal in mceph/mceph mice, but glucose-induced insulin release from batch-incubated islets was (moderately) higher than that from wild-type islets. Reciprocal blocking of Kv1.1 by dendrotoxin-K increased insulin secretion from wild-type but not mceph/mceph islets. Glucose-induced action potential duration, as well as firing frequency, was increased in mceph/mceph mouse beta-cells. This duration effect on action potential in beta-cells from mceph/mceph mice was mimicked by dendrotoxin-K in beta-cells from wild-type mice. Observations concerning the effects of both the mceph mutation, and of dendrotoxin-K, on glucose-induced insulin release were confirmed in pancreatic islets from Kv1.1 null mice. Conclusion/Significance: Kv1.1 channels are expressed in the beta-cells of several species, and these channels can influence glucose-stimulated insulin release.
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