| 1. |
- Abels, Mia, et al.
(author)
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CART is overexpressed in human type 2 diabetic islets and inhibits glucagon secretion and increases insulin secretion
- 2016
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In: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 59:9, s. 1928-1937
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Journal article (peer-reviewed)abstract
- Aims/hypothesis Insufficient insulin release and hyperglucagonaemia are culprits in type 2 diabetes. Cocaine- and amphetamine-regulated transcript (CART, encoded by Cartpt) affects islet hormone secretion and beta cell survival in vitro in rats, and Cart(-/-) mice have diminished insulin secretion. We aimed to test if CART is differentially regulated in human type 2 diabetic islets and if CART affects insulin and glucagon secretion in vitro in humans and in vivo in mice. Methods CART expression was assessed in human type 2 diabetic and non-diabetic control pancreases and rodent models of diabetes. Insulin and glucagon secretion was examined in isolated islets and in vivo in mice. Ca2+ oscillation patterns and exocytosis were studied in mouse islets. Results We report an important role of CART in human islet function and glucose homeostasis in mice. CART was found to be expressed in human alpha and beta cells and in a subpopulation of mouse beta cells. Notably, CART expression was several fold higher in islets of type 2 diabetic humans and rodents. CART increased insulin secretion in vivo in mice and in human and mouse islets. Furthermore, CART increased beta cell exocytosis, altered the glucose-induced Ca2+ signalling pattern in mouse islets from fast to slow oscillations and improved synchronisation of the oscillations between different islet regions. Finally, CART reduced glucagon secretion in human and mouse islets, as well as in vivo in mice via diminished alpha cell exocytosis. Conclusions/interpretation We conclude that CART is a regulator of glucose homeostasis and could play an important role in the pathophysiology of type 2 diabetes. Based on the ability of CART to increase insulin secretion and reduce glucagon secretion, CART-based agents could be a therapeutic modality in type 2 diabetes.
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| 2. |
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| 3. |
- Ahrén, Bo, et al.
(author)
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Disturbed alpha-cell function in mice with beta-cell specific overexpression of human islet amyloid polypeptide.
- 2008
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In: Experimental Diabetes Research. - : Hindawi Limited. - 1687-5214 .- 1687-5303. ; 2008
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Journal article (peer-reviewed)abstract
- Exogenous administration of islet amyloid polypeptide (IAPP) has been shown to inhibit both insulin and glucagon secretion. This study examined alpha-cell function in mice with beta-cell specific overexpression of human IAPP (hIAPP) after an oral protein gavage (75 mg whey protein/mouse). Baseline glucagon levels were higher in transgenic mice (41 +/- 4.0 pg/mL, n = 6) than in wildtype animals (19 +/- 5.1 pg/mL, n = 5, P = .015). In contrast, the glucagon response to protein was impaired in transgenic animals (21 +/- 2.7 pg/mL in transgenic mice versus 38 +/- 5.7 pg/mL in wildtype mice at 15 minutes; P = .027). Baseline insulin levels did not differ between the groups, while the insulin response, as the glucagon response, was impaired after protein challenge (P = .018). Glucose levels were not different between the groups and did not change significantly after protein gavage. Acetaminophen was given through gavage to the animals (2 mg/mouse) to estimate gastric emptying. The plasma acetaminophen profile was similar in the two groups of mice. We conclude that disturbances in glucagon secretion exist in mice with beta-cell specific overexpression of human IAPP, which are not secondary to changes in gastric emptying. The reduced glucagon response to protein challenge may reflect a direct inhibitory influence of hIAPP on glucagon secretion.
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| 4. |
- Ahrén, Bo, et al.
(author)
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Effects of conjugated linoleic acid plus n-3 polyunsaturated fatty acids on insulin secretion and estimated insulin sensitivity in men.
- 2009
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In: European Journal of Clinical Nutrition. - : Springer Science and Business Media LLC. - 1476-5640 .- 0954-3007. ; Sep 3, s. 778-786
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Journal article (peer-reviewed)abstract
- Background/Objectives:Dietary addition of either conjugated linoleic acid (CLA) or n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) has been shown to alter adiposity and circulating lipids, risk markers of cardiovascular diseases. However, CLA may decrease insulin sensitivity, an effect that may be reversed by n-3 LC-PUFA. Thus, the potential of CLA plus n-3 LC-PUFA to affect insulin secretion and sensitivity in non-diabetic young and old, lean and obese subjects was tested.Subjects/Methods:CLA (3 g daily) plus n-3 LC-PUFA (3 g daily) or control oil (6 g daily) was given to lean (n=12; BMI 20-26 kg/m(2)) or obese (n=10; BMI 29-35 kg/m(2)) young (20-37 years old) or lean (n=16) or obese (n=11) older men (50-65 years) for 12 weeks. The study had a double-blind, placebo-controlled randomized crossover design, and primary end points were insulin secretion and sensitivity during a standardized meal test, evaluated by modeling glucose, insulin and C-peptide data.Results:The combination was well tolerated. There was no significant difference in fasting levels of glucose, insulin or C-peptide after CLA/n-3 LC-PUFA treatment compared with control oil. Neither insulin secretion nor estimated sensitivity was affected by CLA/n-3 LC-PUFA in lean or obese young subjects or in older lean subjects. However, in older obese subjects, estimated insulin sensitivity was reduced with CLA/n-3 LC-PUFA compared with control (P=0.024).Conclusions:The results do not support beneficial effects of CLA/n-3 LC-PUFA for beta-cell dysfunction or insulin resistance in humans but suggest that insulin sensitivity in older obese subjects is reduced.European Journal of Clinical Nutrition advance online publication, 3 September 2008; doi:10.1038/ejcn.2008.45.
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| 5. |
- Ahrén, Bo, et al.
(author)
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The augmenting effect on insulin secretion by oral versus intravenous glucose is exaggerated by high-fat diet in mice.
- 2008
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In: Journal of Endocrinology. - 1479-6805. ; 197:1, s. 181-187
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Journal article (peer-reviewed)abstract
- To study whether the incretin effect is involved in adaptively increased insulin secretion in insulin resistance, glucose was infused at a variable rate to match glucose levels after oral glucose (25 mg) in normal anesthetized C57BL/6J female mice or in mice rendered insulin resistant by 8 weeks of high-fat feeding. Insulin response was markedly higher after oral than i.v. glucose in both groups, and this augmentation was even higher in high-fat fed than normal mice. In normal mice, the area under the curve (AUC(insulin)) was augmented from 4.0+/-0.8 to 8.0+/-1.8 nmol/lx60 min by the oral glucose, i.e. by a factor of 2 (P=0.023), whereas in the high-fat fed mice, AUC(insulin) was augmented from 0.70+/-0.4 to 12.4+/-2.5 nmol/lx60 min, i.e. by a factor of 17 (P<0.001). To examine whether the incretin hormone glucagon-like peptide-1 (GLP-1) is responsible for this difference, the effect of i.v. GLP-1 was compared in normal and high-fat fed mice. The sensitivity to i.v. GLP-1 in stimulating insulin secretion was increased in the high-fat diet fed mice: the lowest effective dose of GLP-1 was 650 pmol/kg in normal mice and 13 pmol/kg in the high-fat diet fed mice. We conclude that 1) the incretin effect contributes by approximately 50% to insulin secretion by the oral glucose in normal mice, 2) this effect is markedly exaggerated in insulin-resistant mice fed a high-fat diet, and 3) this augmented incretin contribution in the high-fat fed mice may partially be explained by GLP-1.
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| 6. |
- Carr, Richard D., et al.
(author)
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Incretin and islet hormonal responses to fat and protein ingestion in healthy men
- 2008
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In: American Journal of Physiology: Endocrinology and Metabolism. - : American Physiological Society. - 1522-1555 .- 0193-1849. ; 295:4, s. 779-784
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Journal article (peer-reviewed)abstract
- Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) regulate islet function after carbohydrate ingestion. Whether incretin hormones are of importance for islet function after ingestion of noncarbohydrate macronutrients is not known. This study therefore examined integrated incretin and islet hormone responses to ingestion of pure fat (oleic acid; 0.88 g/kg) or protein (milk and egg protein; 2 g/kg) over 5 h in healthy men, aged 20-25 yr (n = 12); plain water ingestion served as control. Both intact (active) and total GLP-1 and GIP levels were determined as was plasma activity of dipeptidyl peptidase-4 (DPP-4). Following water ingestion, glucose, insulin, glucagon, GLP-1, and GIP levels and DPP-4 activity were stable during the 5-h study period. Both fat and protein ingestion increased insulin, glucagon, GIP, and GLP-1 levels without affecting glucose levels or DPP-4 activity. The GLP-1 responses were similar after protein and fat, whereas the early (30 min) GIP response was higher after protein than after fat ingestion (P < 0.001). This was associated with sevenfold higher insulin and glucagon responses compared with fat ingestion (both P < 0.001). After protein, the early GIP, but not GLP-1, responses correlated to insulin (r(2) = 0.86; P = 0.0001) but not glucagon responses. In contrast, after fat ingestion, GLP-1 and GIP did not correlate to islet hormones. We conclude that, whereas protein and fat release both incretin and islet hormones, the early GIP secretion after protein ingestion may be of primary importance to islet hormone secretion.
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| 7. |
- Fex, Malin, et al.
(author)
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{beta}-Cell Lipases and Insulin Secretion.
- 2006
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In: Diabetes. - 1939-327X. ; 55:Suppl 2, s. 24-31
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Journal article (peer-reviewed)abstract
- Lipids have been implicated in ß-cell stimulus-secretion coupling. Thus, lipases in ß-cells would be required to generate coupling factors from intracellular lipids. Indeed, we found that glucose stimulates lipolysis in rodent islets and clonal ß-cells. Lipolysis and diglyceride lipase activity in islets are abolished by orlistat, a pan-lipase inhibitor. Moreover, orlistat dose-dependently inhibits glucose- and forskolin-stimulated insulin secretion, while leaving glucose oxidation and the rise in ATP-to-ADP ratio intact. In an effort to identify ß-cell lipase(s), we found that hormone-sensitive lipase (HSL), the rate-limiting enzyme for acylglyceride hydrolysis in adipocytes, is active in rodent ß-cells. To further address the role of HSL, a global and ß-cell–specific inactivation, respectively, of the lipase has been created in mice. Whereas our line of HSL null mice is moderately glucose intolerant due to reduced peripheral insulin sensitivity, it exhibits normal islet metabolism and insulin secretion. Preliminary analysis of the ß-cell–specific HSL knockout has revealed no evidence for disturbed islet function. Thus, studies of ours and others indicate that there is a complex lipid regulatory component in ß-cell stimulus-secretion coupling. The role of HSL and other lipases needs to be further clarified to provide a balanced view of the role of lipids and lipolysis in ß-cells.
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| 8. |
- Flodgren, Erik, et al.
(author)
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GPR40 is expressed in glucagon producing cells and affects glucagon secretion.
- 2007
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In: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 354:1, s. 240-245
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Journal article (peer-reviewed)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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| 9. |
- Gunnarsson, Thomas, et al.
(author)
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Glucose-induced incretin hormone release and inactivation are differently modulated by oral fat and protein in mice.
- 2006
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In: Endocrinology. - : The Endocrine Society. - 0013-7227 .- 1945-7170. ; 147:7, s. 3173-3180
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Journal article (peer-reviewed)abstract
- Monounsaturated fatty acids, such as oleic acid (OA), and certain milk proteins, especially whey protein (WP), have insulinotropic effects and can reduce postprandial glycemia. This effect may involve the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). To explore this, we examined the release and inactivation of GIP and GLP-1 after administration of glucose with or without OA or WP through gastric gavage in anesthetized C57BL/6J mice. Insulin responses to glucose (75 mg) were 3-fold augmented by addition of WP (75 mg; P < 0.01), which was associated with enhanced oral glucose tolerance (P < 0.01). The insulin response to glucose was also augmented by addition of OA (34 mg; P < 0.05) although only 1.5-fold and with no associated increase in glucose elimination. The slope of the glucose-insulin curve was increased by OA (1.7-fold; P < 0.05) and by WP(4-fold; P < 0.01) compared with glucose alone, suggesting potentiation of glucose-stimulated insulin release. WP increased GLP-1 secretion (P < 0.01), whereas GIP secretion was unaffected. OA did not affect GIP or GLP-1 secretion. Nevertheless, WP increased the levels of both intact GIP and intact GLP-1 (both P < 0.01), and OA increased the levels of intact GLP-1 (P < 0.05). WP inhibited dipeptidyl peptidase IV activity in the proximal small intestine by 50% (P < 0.05), suggesting that luminal degradation of WP generates small fragments, which are substrates for dipeptidyl peptidase IV and act as competitive inhibitors. We therefore conclude that fat and protein may serve as exogenous regulators of secretion and inactivation of the incretin hormones with beneficial influences on glucose metabolism.
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| 10. |
- Lindgren, Ola, et al.
(author)
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Differential Islet and Incretin Hormone Responses in Morning vs. Afternoon after Standardized Meal in Healthy Men.
- 2009
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In: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 1945-7197 .- 0021-972X. ; 94:8, s. 2887-2892
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Journal article (peer-reviewed)abstract
- Context: The insulin response to meal ingestion is more rapid in the morning than in the afternoon. Whether this is explained by a corresponding variation in the incretin hormones is not known. Objective: Assess islet and incretin hormones after meal ingestion in the morning versus afternoon. Design, Settings and Participants: Ingestion at 8am and at 5pm of a standardized meal (524 kcal) in healthy lean males (n=12) at a University Clinical Research Unit. Main Outcome Measures: 1)Early (30 min) area under the curve (AUC30) of plasma levels of insulin and intact (i) and total (t) glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) after meal ingestion. 2)Estimation of ss-cell function by model analysis of glucose and C-peptide. Results: Peak glucose was lower in the morning than in the afternoon (6.1+/-0.2 vs. 7.4+/-0.3 mmol/l, P=0.001). AUC30insulin (4.9+/-0.6 vs 2.8+/-0.4 nmol/l*30 min; P=0.012), AUC30tGLP-1 (300+/-40 vs. 160+/-30 pmol/l*30 min, P=0.002), AUC30iGIP (0.7+/-0.1 vs. 0.3+/-0.1 nmol/l* 30 min, P=0.002) and AUC30tGIP (1.1+/-0.1 vs. 0.6+/-0.1nmol/l*min, P=0.007) were all higher in the morning. AUC30iGLP-1 (r=0.68, P=0.021) and AUC39iGIP (r=0.78, P=0.001) both correlated to AUC30insulin. Model analysis of ss-cell function showed a higher first hour potentiation factor in the morning (P=0.009). This correlated negatively with the 60 min glucose level (r=-0.63, P<0.001). Conclusions: The early release of GLP-1 and GIP are more pronounced in the morning than in the afternoon. This may contribute to the more rapid early insulin response, more pronounced potentiation of ss-cell function and lower glucose after the morning meal.
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