| 1. |
- Banfi, C, et al.
(författare)
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Transcriptional regulation of plasminogen activator inhibitor type 1 gene by insulin: insights into the signaling pathway
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:7, s. 1522-1530
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Tidskriftsartikel (refereegranskat)abstract
- Impairment of the fibrinolytic system, caused primarily by increases in the plasma levels of plasminogen activator inhibitor (PAI) type 1, are frequently found in diabetes and the insulin-resistance syndrome. Among the factors responsible for the increases of PAI-1, insulin has recently attracted attention. In this study, we analyzed the effects of insulin on PAI-1 biosynthesis in HepG2 cells, paying particular attention to the signaling network evoked by this hormone. Experiments performed in CHO cells overexpressing the insulin receptor indicate that insulin increases PAI-1 gene transcription through interaction with its receptor. By using inhibitors of the different signaling pathways evoked by insulin-receptor binding, it has been shown that the biosynthesis of PAI-1 is due to phosphatidylinositol (PI) 3-kinase activation, followed by protein kinase C and ultimately by mitogen-activated protein (MAP) kinase activation and extracellular signal–regulated kinase 2 phosphorylation. We also showed that this pathway is Ras-independent. Transfection of HepG2 cells with several truncations of the PAI-1 promoter coupled to a CAT gene allowed us to recognize two major response elements located in the regions between −804 and −708 and between −211 and −54. Electrophoretic mobility shift assay identified three binding sites for insulin-induced factors, all colocalized with putative Sp1 binding sites. Using supershifting antibodies, the binding of Sp1 could only be confirmed at the binding site located just upstream from the transcription start site of the PAI-1 promoter. A construct comprising four tandem repeat copies of the −93/−62 region of the PAI-1 promoter linked to CAT was transcriptionally activated in HepG2 cells by insulin. These results outline the central role of MAP kinase activation in the regulation of PAI-1 induced by insulin.
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| 2. |
- Bavenholm, PN, et al.
(författare)
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Insulin sensitivity of suppression of endogenous glucose production is the single most important determinant of glucose tolerance
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:6, s. 1449-1454
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Tidskriftsartikel (refereegranskat)abstract
- Hyperglycemia results from an imbalance between endocrine pancreatic function and hepatic and extrahepatic insulin sensitivity. We studied 57 well-matched Swedish men with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or mild diabetes. Oral glucose tolerance and insulin release were assessed during an oral glucose tolerance test (OGTT). Insulin sensitivity and glucose turnover were determined during a two-step euglycemic insulin clamp (infusion 0.25 and 1.0 mU · kg–1 · min–1). High-performance liquid chromatography–purified [6-3H]glucose was used as a tracer. During low-insulin infusion, the rate of endogenous glucose production (EGP) decreased more in subjects with NGT than in subjects with IGT or diabetes (δ rate of appearance [Ra] 1.25 ± 0.10 vs. 0.75 ± 0.14 vs. 0.58 ± 0.09 mg · kg–1 · min–1, P < 0.001). The corresponding rates of glucose infusion during the high-dose insulin infusion (M values) were 8.3 ± 0.6 vs. 5.4 ± 0.9 vs. 4.7 ± 0.4 mg · kg–1 · min–1 (P < 0.001). A total of 56% of the variation in glucose area under the curve (AUC) during OGTT (glucose AUC) was mainly explained by δ Ra (increase in multiple R2 0.42) but also by δ Rd (rate of disapperance) (increase in multiple R2 0.05), and the early insulin response during OGTT contributed significantly (increase in multiple R2 0.07). When M value was included in the model, reflecting extrahepatic insulin sensitivity, it contributed to 20% of the variation in glucose AUC, and together with the incremental insulin response (increase in multiple R2 0.21), it explained 45% of the variation. In conclusion, insulin sensitivity of suppression of EGP plays the most important role in the determination of blood glucose response during OGTT.
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| 3. |
- Chandra, J, et al.
(författare)
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Role of apoptosis in pancreatic beta-cell death in diabetes
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 5050 Suppl 1, s. S44-S47
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Tidskriftsartikel (refereegranskat)abstract
- Apoptosis is a physiological form of cell death that occurs during normal development, and critical mediators of this process include caspases, reactive oxygen species, and Ca2+. Excessive apoptosis of the pancreatic beta-cell has been associated with diabetes. Consequently, apoptosis research has focused on how infiltrating macrophages or cytotoxic T-cells might kill pancreatic beta-cells using cytokines or death receptor triggering. Meanwhile, the intracellular events in the target beta-cell have been largely ignored. Elucidation of such targets might help develop improved treatment strategies for diabetes. This article will outline recent developments in apoptosis research, with emphasis on mechanisms that may be relevant to beta-cell death in type 1 and type 2 diabetes. Several of the models proposed in beta-cell killing converge on Ca2+ signaling, indicating that the pancreatic beta-cell may be an ideal system in which to carefully dissect the role of Ca2+ during apoptosis.
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| 4. |
- Efanov, AM, et al.
(författare)
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The novel imidazoline compound BL11282 potentiates glucose-induced insulin secretion in pancreatic beta-cells in the absence of modulation of K(ATP) channel activity
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:4, s. 797-802
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Tidskriftsartikel (refereegranskat)abstract
- The insulinotropic activity of the novel imidazoline compound BL11282 was investigated. Intravenous administration of BL11282 (0.3 mg · kg–1 · min–1) to anesthetized rats did not change blood glucose and insulin levels under basal conditions, but produced a higher increase in blood insulin levels and a faster glucose removal from the blood after glucose infusion. Similarly, in isolated Wistar rat pancreatic islets, 0.1–100 μmol/l BL11282 potently stimulated glucose-induced insulin secretion but did not modulate basal insulin secretion. Unlike previously described imidazolines, BL11282 did not block ATP-dependent K+ channels. Furthermore, the compound stimulated insulin secretion in islets depolarized with high concentrations of KCl or permeabilized with electric shock. Insulinotropic activity of BL11282 was dependent on activity of protein kinases A and C. In pancreatic islets from spontaneously diabetic GK rats, the imidazoline compound restored the impaired insulin response to glucose. In conclusion, the imidazoline BL11282 constitutes a new class of insulinotropic compounds that exerts an exclusive glucose-dependent insulinotropic activity in pancreatic islets by stimulating insulin exocytosis.
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| 5. |
- Grill, V, et al.
(författare)
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Overstimulation and beta-cell function
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 5050 Suppl 1, s. S122-S124
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Tidskriftsartikel (refereegranskat)abstract
- Previous and present evidence ascribes an important role to overstimulation of beta-cells for the secretory abnormalities associated with type 2 diabetes. The abnormality most clearly linked to overstimulation is the elevated ratio of circulating proinsulin to insulin. Evidence obtained in human pancreatic islets suggests that aberrations in insulin oscillations that occur in type 2 diabetes could at least in part be linked to abnormalities in cytoplasmic Ca2+ oscillations induced by overstimulation. Furthermore, in a transplantation model, we have obtained evidence for long-lasting, perhaps irreversible, effects of overstimulation, implying that this is a causative factor for the well-recognized deterioration of insulin secretion with increasing duration of type 2 diabetes. The mechanisms behind the effects of overstimulation are only partly clarified, but it is clear that reduced insulin secretion after overstimulation is only partly explained by decreased insulin stores. In cultured human pancreatic islets, overstimulation by high glucose leads to a rise in cytoplasmic Ca2+ levels, which persists after normalization of the glucose levels. Persistent elevation of cytoplasmic Ca2+ may trigger apoptosis, thus participating in long-term irreversible deterioration of beta-cell function. These data provide sufficient rationale for clinical studies to test the beneficial effects of relative beta-cell rest in type 2 diabetic patients.
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| 6. |
- Hagstrom-Toft, E, et al.
(författare)
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Evidence for a major role of skeletal muscle lipolysis in the regulation of lipid oxidation during caloric restriction in vivo
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:7, s. 1604-1611
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Tidskriftsartikel (refereegranskat)abstract
- A lipolytic process in skeletal muscle has recently been demonstrated. However, the physiological importance of this process is unknown. We investigated the role of skeletal muscle lipolysis for lipid utilization during caloric restriction in eight obese women before and after 11 days of very low–calorie diet (VLCD) (2.2 MJ per day). Subjects were studied with indirect calorimetry and microdialysis of skeletal muscle and adipose tissue in order to analyze substrate utilization and glycerol (lipolysis index) in connection with a two-step euglycemic-hyperinsulinemic (12 and 80 mU/m2 · min) clamp. Local blood flow rates in the two tissues were determined with 133Xe-clearance. Circulating free fatty acids and glycerol decreased to a similar extent during insulin infusion before and during VLCD, and there was a less marked insulin-induced reduction in lipid oxidation during VLCD. Adipose tissue glycerol release was hampered by insulin infusion to the same extent (∼40%) before and during VLCD. Skeletal muscle glycerol release was not influenced by insulin before VLCD. However, during VLCD insulin caused a marked (fivefold) (P < 0.01) increase in skeletal muscle glycerol release. The effect was accompanied by a fourfold stimulation of skeletal muscle blood flow (P < 0.01). We propose that, during short-term caloric restriction, the reduced ability of insulin to inhibit lipids, despite a preserved antilipolytic effect of the hormone in adipose tissue, is caused by an augmented mobilization of fat from skeletal muscle, and that a physiological role of muscle lipolysis provides a local source of fatty acids.
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| 7. |
- Hoffstedt, J, et al.
(författare)
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A common hormone-sensitive lipase i6 gene polymorphism is associated with decreased human adipocyte lipolytic function
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:10, s. 2410-2413
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Tidskriftsartikel (refereegranskat)abstract
- Hereditary factors may be involved in the pathogenesis of type 2 diabetes. A polymorphism in the hormone-sensitive lipase (HSL) gene (HSLi6) is associated with obesity and diabetes, although it is unknown whether the polymorphism is functional and thereby influences lipolysis. We genotyped 355 apparently healthy nonobese male and female subjects for the HSLi6 polymorphism. Allele 5 was found to be the most common allele (allele frequency 0.57). In 117 of the subjects, we measured abdominal subcutaneous fat cell lipolysis induced by drugs acting at various steps in the lipolytic cascade. The lipolysis rate induced by norepinephrine isoprenaline (acting on β-adrenoceptors), forskolin (acting on adenylyl cyclase), and dibutyryl cyclic AMP (acting on HSL) were all decreased by ∼50% in allele 5 homozygotes, as compared with noncarriers. Heterozygotes showed an intermediate lipolytic rate. The difference in lipolysis rate between genotypes was more pronounced in men than in women. We conclude that allele 5 of the HSLi6 polymorphism is associated with a marked decrease in the lipolytic rate of abdominal fat cells. This may in turn contribute to the development of obesity.
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| 8. |
- Lin, JM, et al.
(författare)
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Phenotyping of individual pancreatic islets locates genetic defects in stimulus secretion coupling to Niddm1i within the major diabetes locus in GK rats
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 50:12, s. 2737-2743
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Tidskriftsartikel (refereegranskat)abstract
- The major diabetes quantitative trait locus (Niddm1), which segregates in crosses between GK rats affected with spontaneous type 2–like diabetes and normoglycemic F344 rats, encodes at least two different diabetes susceptibility genes. Congenic strains for the two subloci (Niddm1f and Niddm1i) have been generated by transfer of GK alleles onto the genome of F344 rats. Whereas the Niddm1f phenotype implicated insulin resistance, the Niddm1i phenotype displayed diabetes related to insulin deficiency. Individual islets from 16-week-old congenic rats were characterized for insulin release and oxygen tension (pO2). In the presence of 3 mmol/l glucose, insulin release from Niddm1f and Niddm1i islets was ∼5 pmol · g−1 · s−1 and pO2 was 120 mmHg. Similar recordings were obtained from GK and F344 islets. When glucose was raised to 11 mmol/l, insulin release increased significantly in Niddm1f and F344 islets but was essentially unchanged in islets from GK and Niddm1i. The high glucose concentration lowered pO2 to the same extent in islets from all strains. Addition of 1 mmol/l tolbutamide to the perifusion medium further increased pulsatile insulin release threefold in all islets. The pulse frequency was ∼0.4 min−1. α-Ketoisocaproate (11 mmol/l) alone increased pulsatile insulin release eightfold in islets from Niddm1f, Niddm1i, and control F344 rats but had no effect on insulin release from GK islets. These secretory patterns in response to α-ketoisocaproate were paralleled by reduction of pO2 in Niddm1f, Niddm1i, and control F344 islets and no change of pO2 in GK islets. The results demonstrate that Niddm1i carries alleles of gene(s) that reduce glucose-induced insulin release and that are amenable to molecular identification by genetic fine mapping.
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| 9. |
- Lindgren, Cecilia M., et al.
(författare)
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Characterization of the annexin I gene and evaluation of its role in type 2 diabetes
- 2001
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 50:10, s. 2402-2405
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Tidskriftsartikel (refereegranskat)abstract
- In a previous study, we identified suggestive linkage between type 2 diabetes and a locus on chromosome 9p13-q21. This region contains the gene annexin I (ANXA1), encoding a protein suggested to be involved in both insulin secretion and insulin action. In this study, we sequenced the exon/intron boundaries of the human ANXA1 gene and performed mutation screening in 41 individuals from the initial linkage study. We identified five single nucleotide polymorphisms A58G, A401G, intronic variance sequence (IVS)8-28A/G, IVS11 +31A/G, and IVS12-11T/G, which were further tested for association to diabetes in 197 parent/offspring trios using the transmission disequilibrium test. No significant association with type 2 diabetes was observed, although the common A allele of the +58A/G variant gave a 22:12 transmission distortion (P = 0.12). This variant was further genotyped in 481 case and control subjects, but no difference in allele, genotype, or haplotype frequencies were observed between the groups. Further, a novel polymorphic (CA)(15-25) repeat in intron 11 was genotyped in the subjects included in the initial linkage study. No improvement of the original finding was observed. We therefore concluded that the ANXA1 gene is unlikely to harbor variants that contribute to risk of type 2 diabetes.
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| 10. |
- Musi, N., et al.
(författare)
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AMP-activated protein kinase (AMPK) is activated in muscle of subjects with type 2 diabetes during exercise
- 2001
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Ingår i: Diabetes. - Alexandria, VA, USA : American Diabetes Association Inc.. - 0012-1797 .- 1939-327X. ; 50:5, s. 921-927
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Tidskriftsartikel (refereegranskat)abstract
- Insulin-stimulated GLUT4 translocation is impaired in people with type 2 diabetes. In contrast, exercise results in a normal increase in GLUT4 translocation and glucose uptake in these patients. Several groups have recently hypothesized that exercise increases glucose uptake via an insulin-independent mechanism mediated by the activation of AMP-activated protein kinase (AMPK). If this hypothesis is correct, people with type 2 diabetes should have normal AMPK activation in response to exercise. Seven subjects with type 2 diabetes and eight matched control subjects exercised on a cycle ergometer for 45 min at 70% of maximum workload. Biopsies of vastus lateralis muscle were taken before exercise, after 20 and 45 min of exercise, and at 30 min postexercise. Blood glucose concentrations decreased from 7.6 to 4.77 mmol/l with 45 min of exercise in the diabetic group and did not change in the control group. Exercise significantly increased AMPK α2 activity 2.7-fold over basal at 20 min in both groups and remained elevated throughout the protocol, but there was no effect of exercise on AMPK α1 activity. Subjects with type 2 diabetes had similar protein expression of AMPK α1, α2, and β1 in muscle compared with control subjects. AMPK α2 was shown to represent approximately two-thirds of the total a mRNA in the muscle from both groups. In conclusion, people with type 2 diabetes have normal exercise-induced AMPK α2 activity and normal expression of the α1, α2 and β1 isoforms. Pharmacological activation of AMPK may be an attractive target for the treatment of type 2 diabetes.
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