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Glucose-induced Insulin Secretion (glucose-induced + insulin_secretion)
Selected AbstractsChanges in gene expression and morphology of mouse embryonic stem cells on differentiation into insulin-producing cells in vitro and in vivoDIABETES/METABOLISM: RESEARCH AND REVIEWS, Issue 5 2009Ortwin Naujok Abstract Background Embryonic stem (ES) cells have the potential to produce unlimited numbers of surrogate insulin-producing cells for cell replacement therapy of type 1 diabetes mellitus. The impact of the in vivo environment on mouse ES cell differentiation towards insulin-producing cells was analysed morphologically after implantation. Methods ES cells differentiated in vitro into insulin-producing cells according to the Lumelsky protocol or a new four-stage differentiation protocol were analysed morphologically before and after implantation for gene expression by in situ reverse transcription polymerase chain reaction and protein expression by immunohistochemistry and ultrastructural analysis. Results In comparison with nestin positive ES cells developed according to the reference protocol, the number of ES cells differentiated with the four-stage protocol increased under in vivo conditions upon morphological analysis. The cells exhibited, in comparison to the in vitro situation, increased gene and protein expression of Pdx1, insulin, islet amyloid polypeptide (IAPP), the GLUT2 glucose transporter and glucokinase, which are functional markers for glucose-induced insulin secretion of pancreatic beta cells. Renal sub-capsular implantation of ES cells with a higher degree of differentiation achieved by in vitro differentiation with a four-stage protocol enabled further significant maturation for the beta-cell-specific markers, insulin and the co-stored IAPP as well as the glucose recognition structures. In contrast, further in vivo differentiation was not achieved with cells differentiated in vitro by the reference protocol. Conclusions A sufficient degree of in vitro differentiation is an essential prerequisite for further substantial maturation in a beta-cell-specific way in vivo, supported by cell-cell contacts and vascularisation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Multi-Step Synthesis and Biological Evaluation of Analogues of Insulin Secretagogue (2S,3R,4S)-4-HydroxyisoleucineEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2009Kaïss Aouadi Abstract A series of stereochemically defined analogues of (2S,3R,4S)-4-hydroxyisoleucine and related ,-hydroxy acids have been prepared by multi-step routes from D -glucose, whereas ketolization between TBDMS-protected hydroxypropanone and ethyl isocyanoacetate led to racemic analogues. Bioassays showed that of eight newly synthesized compounds, two of them presented an interesting statistical trend to increase glucose-induced insulin secretion when tested in isolated rat pancreatic islets in the presence of 8.3 mM glucose and at a concentration of 200 ,M, which has previously been shown to be effective for (2S,3R,4S)-4-hydroxyisoleucine.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Rab11 and its effector Rip11 participate in regulation of insulin granule exocytosisGENES TO CELLS, Issue 4 2009Kenji Sugawara Rab GTPases and their effectors play important roles in membrane trafficking between cellular compartments in eukaryotic cells. In the present study, we examined the roles of Rab11B and its effectors in insulin secretion in pancreatic ,-cells. In the mouse insulin-secreting cell line MIN6, Rab11 was co-localized with insulin-containing granules, and over-expression of the GTP- or the GDP-bound form of Rab11B significantly inhibited regulated secretion, indicating involvement of Rab11B in regulated insulin secretion. To determine the downstream signal of Rab11-mediated insulin secretion, we examined the effects of various Rab11-interacting proteins on insulin secretion, and found that Rip11 is involved in cAMP-potentiated insulin secretion but not in glucose-induced insulin secretion. Analyses by immunocytochemistry and subcellular fractionation revealed Rip11 to be co-localized with insulin granules. The inhibitory effect of the Rip11 mutant was not altered in MIN6 cells lacking Epac2, which mediates protein kinase A (PKA)-independent potentiation of insulin secretion, compared with wild-type MIN6 cells. In addition, Rip11 was found to be phosphorylated by PKA in MIN6 cells. The present study shows that both Rab11 and its effector Rip11 participate in insulin granule exocytosis and that Rip11, as a substrate of PKA, regulates the potentiation of exocytosis by cAMP in pancreatic ,-cells. [source] Perspective: Protein prenylation in glucose-induced insulin secretion from the pancreatic islet , cell: a perspectiveJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 1 2008Anjaneyulu Kowluru ,,Insulin secretion , a simplified view ,,Endogenous GTP and its binding proteins are important for GSIS ,,G-proteins undergo post-translational modifications ,,Data accrued from studies involving generic inhibitors of protein prenylation ,,Data accrued from studies involving site-specific inhibitors of protein prenylation -,Lovastatin (LOVA) -,Limonene -,Perillic acid (PA) -,Manumycin A ,,Data accrued from studies involving over-expression of inactive mutants of PPTases -,3-Allyl and-vinyl farnesols and geranylgeraniols ,,What are the functional consequences of prenylation in the islet , cell? ,,How are PPTases regulated by glucose in the islet? ,,Conclusions and future directions Abstract Insulin secretion from the pancreatic , cell is regulated principally by the ambient concentration of glucose. However, the molecular and cellular mechanisms underlying the stimulus , secretion coupling of glucose-stimulated insulin secretion (GSIS) remain only partially understood. Emerging evidence from multiple laboratories suggests key regulatory roles for GTP-binding proteins in the cascade of events leading to GSIS. This class of signalling proteins undergoes a series of requisite post-translational modifications (e.g. prenylation) at their C-terminal cysteines, which appear to be necessary for their targeting to respective membranous sites for optimal interaction with their respective effector proteins. This communication represents a perspective on potential regulatory roles for protein prenylation steps (i.e. protein farnesylation and protein geranylgeranylation) in GSIS from the islet , cell.Possible consequences of protein prenylation and potential mechanisms underlying glucose-induced regulation of prenylation, specifically in the context of GSIS, are also discussed. [source] Bimodal role of conventional protein kinase C in insulin secretion from rat pancreatic , cellsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2004Hui Zhang The present study was conducted to evaluate the role of conventional protein kinase C (PKC) in calcium-evoked insulin secretion. In rat , cells transfected with green fluorescent protein-tagged PKC-, (PKC-,,EGFP), a depolarizing concentration of potassium induced transient elevation of cytoplasmic free calcium ([Ca2+]c), which was accompanied by transient translocation of PKC-,,EGFP from the cytosol to the plasma membrane. Potassium also induced transient translocation of PKC-,,EGFP, the C1 domain of PKC-, and PKC-,,GFP. A high concentration of glucose induced repetitive elevation of [Ca2+]c and repetitive translocation of PKC-,,EGFP. Diazoxide completely blocked both elevation of [Ca2+]c and translocation of PKC-,,EGFP. We then studied the role of conventional PKC in calcium-evoked insulin secretion using rat islets. When islets were incubated for 10 min with high potassium, Gö-6976, an inhibitor of conventional PKC, and PKC-, pseudosubstrate fused to antennapedia peptide (Antp-PKC19,31) increased potassium induced secretion. Similarly, insulin release induced by high glucose for 10 min was enhanced by Gö-6976 and Antp-PKC19,31. However, when islets were stimulated for 60 min with high glucose, both Gö-6976 and Antp-PKC19,31 reduced glucose-induced insulin secretion. Similar results were obtained by transfection of dominant-negative PKC-, using adenovirus vector. Taken together, PKC-, is activated when cells are depolarized by a high concentration of potassium or glucose. Conventional PKC is inhibitory on depolarization-induced insulin secretion per se, but it also augments glucose-induced secretion. [source] Beneficial Effects of Desferrioxamine on Encapsulated Human Islets,In Vitro and In Vivo StudyAMERICAN JOURNAL OF TRANSPLANTATION, Issue 9 2010V. Vaithilingam As many as 2000 IEQs (islet equivalent) of encapsulated human islets are required to normalize glucose levels in diabetic mice. To reduce this number, encapsulated islets were exposed to 100 ,M desferrioxamine (DFO) prior to transplantation. Cell viability, glucose-induced insulin secretion, VEGF (Vascular endothelial growth factor), HIF-1, (Hypoxia inducible factor-1 alpha), caspase-3 and caspase-8 levels were assessed after exposure to DFO for 12, 24 or 72 h. Subsequently, 1000, 750 or 500 encapsulated IEQs were infused into peritoneal cavity of diabetic mice after 24 h exposure to DFO. Neither viability nor function in vitro was affected by DFO, and levels of caspase-3 and caspase-8 were unchanged. DFO significantly enhanced VEGF secretion by 1.6- and 2.5-fold at 24 and 72 h, respectively, with a concomitant increase in HIF-1, levels. Euglycemia was achieved in 100% mice receiving 1000 preconditioned IEQs, as compared to only 36% receiving unconditioned IEQs (p < 0.001). Similarly, with 750 IEQ, euglycemia was achieved in 50% mice receiving preconditioned islets as compared to 10% receiving unconditioned islets (p = 0.049). Mice receiving preconditioned islets had lower glucose levels than those receiving unconditioned islets. In summary, DFO treatment enhances HIF-1, and VEGF expression in encapsulated human islets and improves their ability to function when transplanted. [source] Uncoupling proteins: A complex journey to function discoveryBIOFACTORS, Issue 5 2009Federica Cioffi Abstract Since their discovery, uncoupling proteins have aroused great interest due to the crucial importance of energy-dissipating system for cellular physiology. The uncoupling effect and the physiological role of UCP1 (the first-described uncoupling protein) are well established. However, the reactions catalyzed by UCP1 homologues (UCPs), and their physiological roles are still under debate, with the literature containing contrasting results. Current hypothesis propose several physiological functions for novel UCPs, such as: (i) attenuation of reactive oxygen species production and protection against oxidative damage, (ii) thermogenic function, although UCPs do not generally seem to affect thermogenesis, UCP3 can be thermogenic under certain conditions, (iii) involvement in fatty acid handling and/or transport, although recent experimental evidence argues against the previously hypothesized role for UCPs in the export of fatty acid anions, (iv) fatty acid hydroperoxide export, although this function, due to the paucity of the experimental evidence, remains hypothetical, (v) Ca2+ uptake, although results for and against a role in Ca2+ uptake are still emerging, (vi) a signaling role in pancreatic beta cells, where it attenuates glucose-induced insulin secretion. From the above, it is evident that more research will be needed to establish universally accepted functions for UCPs. © 2009 International Union of Biochemistry and Molecular Biology, Inc. [source] Effects of T4 replacement therapy on glucose metabolism in subjects with subclinical (SH) and overt hypothyroidism (OH)CLINICAL ENDOCRINOLOGY, Issue 6 2008Ammon Handisurya Summary Objective To evaluate ,-cell function and insulin sensitivity in subjects with overt (OH) and subclinical hypothyroidism (SH) before and after T4 replacement therapy. Background Disturbances in glucose metabolism have been observed in hypothyroid states. However, the clinical significance and potential reversibility of these alterations by T4 replacement therapy remain to be elucidated especially in patients with SH. Design and patients Parameters of glucose metabolism have been investigated in subjects with OH (n = 12) and SH (n = 11). Insulin sensitivity has been assessed by the euglycaemic,hyperinsulinaemic clamp technique and ,-cell function by mathematical modelling of data derived from an oral glucose tolerance test. Results Fasting and dynamic glycaemia as assessed by the AUCGlucose remained unaltered following substitution therapy (P > 0·05). Insulin sensitivity significantly improved only in subjects with OH (P < 0·05). Fasting insulin and proinsulin concentrations increased proportionally in both groups (P < 0·05) with the proinsulin : insulin ratio remaining unchanged (P > 0·05). Total insulin secretion was higher in OH before initiation of therapy (P < 0·05). In both groups, dynamic parameters including total insulin secretion, hepatic insulin extraction and the adaptation index were significantly attenuated (P < 0·05) after restoration of thyroid function, whereas the disposition index and the basal insulin secretion rate remained unaltered (P > 0·05). Conclusion In summary, SH and OH are characterized by attenuated basal plasma insulin levels and increased glucose-induced insulin secretion. T4 replacement therapy partially ameliorates the insulin secretion profile and reduces the demand on pancreatic ,-cells after glucose challenge to an extent that exceeds any effect attributable to the improvement in insulin sensitivity. [source] | |||||||||||||