| 1. |
- Abdel-Halim, SM, et al.
(författare)
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Mutations in the promoter of adenylyl cyclase (AC)-III gene, overexpression of AC-III mRNA, and enhanced cAMP generation in islets from the spontaneously diabetic GK rat model of type 2 diabetes
- 1998
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 47:3, s. 498-504
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Tidskriftsartikel (refereegranskat)abstract
- Glucose-induced insulin release is decreased in the spontaneously diabetic GK rat, a nonobese rodent model of type 2 diabetes. Forskolin restores the impaired insulin release in both the isolated perfused pancreas and isolated islets from these rats (Abdel-Halim et al., Diabetes 45:934-940, 1996). We demonstrate here that the insulinotropic effect of forskolin in the GK rat is due to increased generation of cAMP and that it is associated with overexpression of adenylyl cyclase (AC)-III mRNA and gene mutations. The AC-III mRNA overexpression was demonstrated by in situ hybridization using oligonucleotide probes binding to different regions of the rat AC-III mRNA. It was associated with the presence of two point mutations identified at positions -28 bp (A --> G) and -358 bp (A --> C) of the promoter region of the AC-III gene and was demonstrable in both GK rat islets and peripheral blood cells. Transfection of COS cells with a luciferase reporter gene system revealed up to 25-fold increased promoter activity of GK AC-III promoter when compared with normal rat promoter (P < 0.0001). In conclusion, forskolin restores the impaired insulin release in islets of the GK rat through enhanced cAMP generation. This is linked to overexpression of AC-III mRNA in GK islets due to two functional point mutations in the promoter region of the AC-III gene.
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| 2. |
- Bavenholm, PN, et al.
(författare)
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Fatty acid oxidation and the regulation of malonyl-CoA in human muscle
- 2000
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 49:7, s. 1078-1083
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Tidskriftsartikel (refereegranskat)abstract
- Questions concerning whether malonyl-CoA is regulated in human muscle and whether malonyl-CoA modulates fatty acid oxidation are still unanswered. To address these questions, whole-body fatty acid oxidation and the concentration of malonyl-CoA, citrate, and malate were determined in the vastus lateralis muscle of 16 healthy nonobese Swedish men during a sequential euglycemic-hyperinsulinemic clamp. Insulin was infused at rates of 0.25 and 1.0 mU x kg(-1) x min(-1), and glucose was infused at rates of 2.0 +/- 0.2 and 8.1 +/- 0.7 mg x kg(-1) x min(-1), respectively. During the low-dose insulin infusion, whole-body fatty acid oxidation, as determined by indirect calorimetry, decreased by 22% from a basal rate of 0.94 +/- 0.06 to 0.74 +/- 0.07 mg x kg(-1) x min(-1) (P = 0.005), but no increase in malonyl-CoA was observed. In contrast, during the high-dose insulin infusion, malonyl-CoA increased from 0.20 +/- 0.01 to 0.24 +/- 0.01 nmol/g (P < 0.001), and whole-body fatty acid oxidation decreased by an additional 41% to 0.44 +/- 0.06 mg x kg(-1) x min(-1) (P < 0.001). The increase in malonyl-CoA was associated with 30-50% increases in the concentrations of citrate (102 +/- 6 vs. 137 +/- 7 nmol/g, P < 0.001), an allosteric activator of the rate-limiting enzyme in the malonyl-CoA formation, acetyl-CoA carboxylase, and malate (80 +/- 6 vs. 126 +/- 9 nmol/g, P = 0.002), an antiporter for citrate efflux from the mitochondria. Significant correlations were observed between the concentration of malonyl-CoA and both glucose utilization (r = 0.53, P = 0.002) and the sum of the concentrations of citrate and malate (r = 0.52, P < 0.001), a proposed index of the cytosolic concentration of citrate. In addition, an inverse correlation between malonyl-CoA concentration and fatty acid oxidation was observed (r = -0.32, P = 0.03). The results indicate that an infusion of insulin and glucose at a high rate leads to increases in the concentration of malonyl-CoA in skeletal muscle and to decreases in whole-body and, presumably, muscle fatty acid oxidation. Furthermore, they suggest that the increase in malonyl-CoA in this situation is due, at least in part, to an increase in the cytosolic concentration of citrate. Because cytosolic citrate is also an inhibitor of phosphofructokinase, an attractive hypothesis is that changes in its concentration are part of an autoregulatory mechanism by which glucose modulates its own use and the use of fatty acids as fuels for skeletal muscle.
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| 3. |
- 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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| 4. |
- Cejvan, K, et al.
(författare)
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Intra-islet somatostatin regulates glucagon release via type 2 somatostatin receptors in rats
- 2003
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 52:5, s. 1176-1181
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Tidskriftsartikel (refereegranskat)abstract
- Exogenously administered somatostatin (SST) inhibits secretion of insulin and glucagon. Furthermore, it is hypothesized that islet SST regulates glucagon secretion by a local action. A number of studies utilizing SST antibodies have been performed to test this hypothesis, and their results have been conflicting. Five subtypes of SST receptor (SSTR1–5) mediate the effect of SST on target cells. In rodents, SST inhibits the release of glucagon, but not that of insulin, via SSTR2. A novel SSTR2-selective antagonist, DC-41-33, was synthesized recently. We have investigated the effects of this antagonist on arginine-stimulated glucagon and insulin release in batch incubations of isolated rat islets, perifused isolated rat islets, and isolated perfused rat pancreas. In batch incubations at 3.3 mmol/l glucose, DC-41-33 increased glucagon release in a dose-dependent manner. At the maximum dose tested (2 μmol/l), DC-41-33 enhanced the glucagon response by 4.3- to 5-fold. Similarly, this compound increased arginine-induced glucagon release in perifused islets at 3.3 mmol/l glucose (2.8-fold) and perfused pancreas at 3.3 and 5.5 mmol/l glucose (2.5- and 2.3-fold, respectively). In the two latter experimental systems, DC-41-33 had no significant effect on insulin release. In conclusion, our results strongly support the hypothesis that islet SST inhibits glucagon secretion via a local action.
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| 5. |
- Davani, B, et al.
(författare)
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Aged transgenic mice with increased glucocorticoid sensitivity in pancreatic beta-cells develop diabetes
- 2004
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 5353 Suppl 1, s. S51-S59
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Tidskriftsartikel (refereegranskat)abstract
- Glucocorticoids are diabetogenic hormones because they decrease glucose uptake, increase hepatic glucose production, and inhibit insulin release. To study the long-term effects of increased glucocorticoid sensitivity in β-cells, we studied transgenic mice overexpressing the rat glucocorticoid receptor targeted to the β-cells using the rat insulin I promoter. Here we report that these mice developed hyperglycemia both in the fed and the overnight-fasted states at 12–15 months of age. Progression from impaired glucose tolerance, previously observed in the same colony at the age of 3 months, to manifest diabetes was not associated with morphological changes or increased apoptosis in the β-cells. Instead, our current results suggest that the development of diabetes is due to augmented inhibition of insulin secretion through α2-adrenergic receptors (α2-ARs). Thus, we found a significantly higher density of α2-ARs in the islets of transgenic mice compared with controls, based on binding studies with the α2-AR agonist UK 14304. Furthermore, incubation of islets with benextramine, a selective antagonist of the α2-AR, restored insulin secretion in response to glucose in isolated islets from transgenic mice, whereas it had no effect on control islets. These results indicate that the chronic enhancement of glucocorticoid signaling in pancreatic β-cells results in hyperglycemia and impaired glucose tolerance. This effect may involve signaling pathways that participate in the regulation of insulin secretion via the α2-AR.
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| 6. |
- 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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| 7. |
- Efanova, IB, et al.
(författare)
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RX871024 induces Ca2+ mobilization from thapsigargin-sensitive stores in mouse pancreatic beta-cells
- 1998
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 47:2, s. 211-218
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Tidskriftsartikel (refereegranskat)abstract
- The effects of RX871024, a compound with an imidazoline structure, on cytoplasmic-free Ca2+ concentration ([Ca2+]i) in mouse pancreatic β-cells were studied. RX871024 modulates [Ca2+]i; by at least two mechanisms. One mechanism involves closure ofATPregulated K+ channels, resulting in membrane depolarization, opening of voltage-gated L-type Ca2+ channels, and a subsequent increase in [Ca2+]i. Another mechanism, reported here for the first time, deals with RX871024-induced mobilization of Ca2+ from nonmitochondrial thapsigargin-sensitive intracellular stores. Reduced glutathione, inhibitors of cytochrome P-450, and monoaminooxidases A and B blocked this Ca2+ mobilization. It is concluded that the mechanism of RX871024-induced Ca2+ mobilization from intracellular stores involves changes in the oxidation/reduction state of the pancreatic β-cell and may be controlled by cytochrome P-450.
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| 8. |
- Ekberg, K, et al.
(författare)
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Contributions by kidney and liver to glucose production in the postabsorptive state and after 60 h of fasting
- 1999
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 48:2, s. 292-298
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Tidskriftsartikel (refereegranskat)abstract
- Contributions of renal glucose production to whole-body glucose turnover were determined in healthy individuals by using the arteriovenous balance technique across the kidneys and the splanchnic area combined with intravenous infusion of [U-13C6]glucose, [3-(3)H]glucose, or [6-(3)H]glucose. In the postabsorptive state, the rate of glucose appearance was 11.5 +/- 0.6 micromol x kg(-1) x min(-1). Hepatic glucose production, calculated as the sum of net glucose output (9.8 +/- 0.8 micromol x kg(-1) x min(-1)) and splanchnic glucose uptake (2.2 +/- 0.3 micromol x kg(-1) x min(-1)) accounted for the entire rate of glucose appearance. There was no net exchange of glucose across the kidney and no significant renal extraction of labeled glucose. The renal contribution to total glucose production calculated from the arterial, hepatic, and renal venous 13C-enrichments (glucose M+6) was 5 +/- 2%. In the 60-h fasted state, the rate of glucose appearance was 8.2 +/- 0.3 micromol x kg(-1) x min(-1). Hepatic glucose production, estimated as net splanchnic output (5.8 +/- 0.7 micromol x kg(-1) x min(-1)) plus splanchnic uptake (0.6 +/- 0.3 micromol x kg(-1) x min(-1)) accounted for 79% of the rate of glucose appearance. There was a significant net renal output of glucose (0.9 +/- 0.3 micromol x kg(-1) x min(-1)), but no significant extraction of labeled glucose across the kidney. The renal contribution to whole-body glucose turnover calculated from the 13C-enrichments was 24 +/- 3%. We concluded that 1) glucose production by the human kidney in the postabsorptive state, in contrast to recent reports, makes at most only a minor contribution (approximately 5%) to blood glucose homeostasis, but that 2) after 60-h of fasting, renal glucose production may account for 20-25% of whole-body glucose turnover.
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| 9. |
- Gu, HF, et al.
(författare)
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Quantitative trait loci near the insulin-degrading enzyme (IDE) gene contribute to variation in plasma insulin levels
- 2004
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 53:8, s. 2137-2142
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Tidskriftsartikel (refereegranskat)abstract
- Insulin-degrading enzyme (IDE) plays a principal role in the proteolysis of several peptides in addition to insulin and is encoded by IDE, which resides in a region of chromosome 10q that is linked to type 2 diabetes. Two recent studies presented genetic association data on IDE and type 2 diabetes (one positive and the other negative), but neither explored the fundamental question of whether polymorphism in IDE has a measurable influence on insulin levels in human populations. To address this possibility, 14 single nucleotide polymorphisms (SNPs) from a linkage disequilibrium block encompassing IDE have been genotyped in a sample of 321 impaired glucose tolerant and 403 nondiabetic control subjects. Analyses based on haplotypic genotypes (diplotypes), constructed with SNPs that differentiate common extant haplotypes extending across IDE, provided compelling evidence of association with fasting insulin levels (P = 0.0009), 2-h insulin levels (P = 0.0027), homeostasis model assessment of insulin resistance (P = 0.0001), and BMI (P = 0.0067), with effects exclusively evident in men. The strongest evidence for an effect of a single marker was obtained for rs2251101 (located near the 3′ untranslated region of IDE) on 2-h insulin levels (P = 0.000023). Diplotype analyses, however, suggest the presence of multiple interacting trait-modifying sequences in the region. Results indicate that polymorphism in/near IDE contributes to a large proportion of variance in plasma insulin levels and correlated traits, but questions of sex specificity and allelic heterogeneity will need to be taken into consideration as the molecular basis of the observed phenotypic effects unfolds.
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| 10. |
- Gu, HF, et al.
(författare)
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Single nucleotide polymorphisms in the proximal promoter region of the adiponectin (APM1) gene are associated with type 2 diabetes in Swedish caucasians
- 2004
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 5353 Suppl 1, s. S31-S35
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Tidskriftsartikel (refereegranskat)abstract
- Adiponectin (APM1) is an adipocyte-derived peptide. The APM1 gene is located on chromosome 3q27 and linked to type 2 diabetes. In patients with type 2 diabetes, the adiponectin level in plasma is decreased in comparison to healthy subjects. To identify genetic defects of the APM1 gene that contribute to the development of type 2 diabetes, we genotyped 13 single nucleotide polymorphisms (SNPs) in 106 patients with type 2 diabetes, 325 patients with impaired glucose tolerance (IGT), and 497 nondiabetic control subjects in Swedish Caucasians by using dynamic allele-specific hybridization (DASH). We found that SNPs −11426(A/G) and −11377(G/C) in the proximal promoter region had significant differences of allele frequencies between type 2 diabetic patients and nondiabetic control subjects (P = 0.02 and P = 0.04, respectively). SNP-11426(A/G) was significantly associated with fasting plasma glucose in type 2 diabetic patients (P = 0.02) and in IGT subjects (P = 0.04), while the patients carrying CC and CG genotypes for SNP-11377(G/C) had a higher BMI than the patients with the GG genotype (P = 0.03). Haplotype analysis of 13 SNPs in the APM1 gene showed that estimates of haplotype frequencies in Swedish Caucasians are similar to those estimated in French Caucasians. However, no significant association of haplotypes with type 2 diabetes and IGT was detected in our study. The present study provides additional evidence that SNPs in the proximal promoter region of the APM1 gene contribute to the development of type 2 diabetes.
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