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- Liu, Liehua, et al.
(författare)
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Dipeptidyl peptidase-4 (DPP-4): Localization and activity in human and rodent islets.
- 2014
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 453:3, s. 398-404
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Tidskriftsartikel (refereegranskat)abstract
- Dipeptidyl peptidase 4 (DPP-4) was recently found to be expressed in human and mouse islets with different expression patterns. However, whether species-dependent expression pattern is a generalized phenomenon and whether islet DPP-4 activity is regulated are not known. This study was conducted to investigate DPP-4 localization in several different species, and to examine the impact of glucose, incretin hormones, and insulin on islet DPP-4 activity. It was shown by immuofluorescent staining that there were two distinct species-specific expression patterns of islet DPP-4. The enzyme was expressed exclusively in α-cells in human and pig islets, but primarily in β-cells in mouse and rat islets. INS-1 832/13 cells also expressed DPP-4, and inhibition of DPP-4 enhanced insulin secretion in the presence of glucagon-like peptide-1 (GLP-1) in the cells. DPP-4 activity was remarkably robust when cultured with high glucose, incretin hormones, and insulin in mouse and human islets as well as INS-1 832/13 cells and islet DPP-4 activity and expression pattern was not altered in double incretin receptor knockout mice, compared to wild type mice. We conclude that islet DPP-4 is species-specifically expressed in α-cell and β-cell dominant patterns in several species and both patterns remained robust in enzyme activity during short-term metabolic challenge.
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| 3. |
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| 4. |
- Omar, Bilal, et al.
(författare)
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Fibroblast Growth Factor 21 (FGF21) and Glucagon Like-Peptide 1 Contribute to Diabetes Resistance in Glucagon Receptor Deficient Mice.
- 2014
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 63:1, s. 101-110
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Tidskriftsartikel (refereegranskat)abstract
- Mice genetically deficient in the glucagon receptor (Gcgr(-/-)) show improved glucose tolerance, insulin sensitivity and α-cell hyperplasia. In addition, Gcgr(-/-) mice do not develop diabetes after chemical destruction of β-cells. Since fibroblast growth factor 21 (FGF21) has insulin independent glucose lowering properties we investigated whether FGF21 was contributing to diabetes resistance in insulin deficient Gcgr(-/-) mice. Plasma FGF21 was 25 fold higher in Gcgr(-/-) mice than in wild type mice. FGF21 was found to be expressed in pancreatic β- and α-cells, with high expression in the hyperplastic α-cells of Gcgr(-/-) mice. FGF21 expression was also significantly increased in liver and adipose tissue of Gcgr(-/-) mice. To investigate the potential anti-diabetic actions of FGF21 in insulin deficient Gcgr(-/-) mice, an FGF21 neutralizing antibody was administered prior to oral glucose tolerance tests (OGTT). FGF21 neutralization caused a decline in glucose tolerance in insulin deficient Gcgr(-/-) mice during the OGTT. Despite this decline, insulin deficient Gcgr(-/-) mice did not develop hyperglycemia. Glucagon-like peptide (GLP-1) also has insulin independent glucose lowering properties and elevated circulating GLP-1 is a known characteristic of Gcgr(-/-) mice. Neutralization of FGF21 while concurrently blocking the GLP-1 receptor with the antagonist Exendin9-39 resulted in significant hyperglycemia in insulin deficient Gcgr(-/-) mice, while Exendin9-39 alone did not. In conclusion, FGF21 acts additively with GLP-1 to prevent insulinopenic diabetes in mice lacking glucagon action.
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| 5. |
- Omar, Bilal, et al.
(författare)
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Impact of glucose dosing regimens on modeling of glucose tolerance and β-cell function by intravenous glucose tolerance test in diet-induced obese mice.
- 2014
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Ingår i: Physiological Reports. - : Wiley. - 2051-817X. ; 2:5
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Tidskriftsartikel (refereegranskat)abstract
- Insulin sensitivity declines in overweight and obese individuals and, under normal conditions, insulin secretion adaptively increases which in healthy non-diabetic subjects maintains normal glycemia. This adaptation is best described by the disposition index derived from modeling of insulin and glucose data from an intravenous glucose tolerance testing (IVGTT). One caveat of the IVGTT is that basing the glucose dose on the individual total body weight can result in large differences in the amount of glucose given to lean and obese individuals. The effect this has on determination of insulin sensitivity and β-cell function is unknown. In this study, we therefore evaluated alternative glucose dosing regimens for determination of the impact of glucose dosing on measures of β-cell function in normal and diet-induced obese (DIO) mice. The glucose dosing regimens used for the IVGTT were 0.35 mg per kg total body weight (BW) or per kg lean BW or a fixed glucose dose based on the average BW for all experimental mice. Each regimen detected a similar decrease in insulin sensitivity in DIO mice. The different glucose dosing regimens gave, however, diverging results in regard to glucose elimination and the acute insulin response. Thus, the fixed-dose regimen was the only that revealed impairment of glucose elimination, whereas dosing according to total BW was the only regimen which showed significant increases in acute insulin response in DIO mice. The fixed-dose glucose dosing regimen was the only that revealed a significant decline in the disposition index value in DIO mice, which is characteristic of type 2 diabetes in humans. Our results therefore show that using different glucose dosing regimens during IVGTT in DIO mice one can model different aspects of physiology which are similar to prediabetes and type 2 diabetes in humans, with the fixed-dose regimen producing a phenotype that most closely resembles human type 2 diabetes.
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| 6. |
- Omar, Bilal, et al.
(författare)
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Pleiotropic Mechanisms for the Glucose-Lowering Action of DPP-4 Inhibitors.
- 2014
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 63:7, s. 2196-2202
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Tidskriftsartikel (refereegranskat)abstract
- Dipeptidyl peptidase (DPP)-4 inhibition is a glucose-lowering treatment for type 2 diabetes. The classical mechanism for DPP-4 inhibitors is that they inhibit DPP-4 activity in peripheral plasma, which prevents the inactivation of the incretin hormone glucagon-like peptide (GLP)-1 in the peripheral circulation. This in turn increases circulating intact GLP-1, which results in stimulated insulin secretion and inhibited glucagon secretion, in turn increasing glucose utilization and diminishing hepatic glucose production, which, through reduction in postprandial and fasting glucose, reduces HbA1c. However, recent experimental studies in mainly rodents but also to a limited degree in humans have found additional mechanisms for DPP-4 inhibitors that may contribute to their glucose-lowering action. These nonclassical mechanisms include 1) inhibition of gut DPP-4 activity, which prevents inactivation of newly released GLP-1, which in turn augments GLP-1-induced activations of autonomic nerves and results in high portal GLP-1 levels, resulting in inhibited glucose production through portal GLP-1 receptors; 2) inhibition of islet DPP-4 activity, which prevents inactivation of locally produced intact GLP-1 in the islets, thereby augmenting insulin secretion and inhibiting glucagon secretion and possibly preventing islet inflammation; and 3) prevention of the inactivation of other bioactive peptides apart from GLP-1, such as glucose-dependent insulinotropic polypeptide, stromal-derived factor-1α, and pituitary adenylate cyclase-activating polypeptide, which may improve islet function. These pleiotropic effects may contribute to the effects of DPP-4 inhibition. This Perspectives in Diabetes outlines and discusses these nonclassical mechanisms of DPP-4 inhibition.
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