Normal Insulin Secretion Research Articles

Metabolic Effects of Selective Deletion of Group VIA Phospholipase A2 from Macrophages or Pancreatic Islet Beta-Cells.

To examine the role of group VIA phospholipase A2 (iPLA2β) in specific cell lineages in insulin secretion and insulin action, we prepared mice with a selective iPLA2β deficiency in cells of myelomonocytic lineage, including macrophages (MØ-iPLA2β-KO), or in insulin-secreting β-cells (β-Cell-iPLA2β-KO), respectively. MØ-iPLA2β-KO mice exhibited normal glucose tolerance when fed standard chow and better glucose tolerance than floxed-iPLA2β control mice after consuming a high-fat diet (HFD). MØ-iPLA2β-KO mice exhibited normal glucose-stimulated insulin secretion (GSIS) in vivo and from isolated islets ex vivo compared to controls. Male MØ-iPLA2β-KO mice exhibited enhanced insulin responsivity vs. controls after a prolonged HFD. In contrast, β-cell-iPLA2β-KO mice exhibited impaired glucose tolerance when fed standard chow, and glucose tolerance deteriorated further when introduced to a HFD. β-Cell-iPLA2β-KO mice exhibited impaired GSIS in vivo and from isolated islets ex vivo vs. controls. β-Cell-iPLA2β-KO mice also exhibited an enhanced insulin responsivity compared to controls. These findings suggest that MØ iPLA2β participates in HFD-induced deterioration in glucose tolerance and that this mainly reflects an effect on insulin responsivity rather than on insulin secretion. In contrast, β-cell iPLA2β plays a role in GSIS and also appears to confer some protection against deterioration in β-cell functions induced by a HFD.

Formation of βTC3 and MIN6 Pseudoislets Changes the Expression Pattern of Gpr40, Gpr55, and Gpr119 Receptors and Improves Lysophosphatidylcholines-Potentiated Glucose-Stimulated Insulin Secretion.

The impaired spatial arrangement and connections between cells creating islets of Langerhans as well as altered expression of G protein-coupled receptors (GPCRs) often lead to dysfunction of insulin-secreting pancreatic β cells and can significantly contribute to the development of diabetes. Differences in glucose-stimulated insulin secretion (GSIS) are noticeable not only in diabetic individuals but also in model pancreatic β cells, e.g., βTC3 and MIN6 β cell lines with impaired and normal insulin secretion, respectively. Now, we compare the ability of GPCR agonists (lysophosphatidylcholines bearing fatty acid chains of different lengths) to potentiate GSIS in βTC3 and MIN6 β cell models, cultured as adherent monolayers and in a form of pseudoislets (PIs) with pancreatic MS1 endothelial cells. Our aim was also to investigate differences in expression of the GPCRs responsive to LPCs in these experimental systems. Aggregation of β cells into islet-like structures greatly enhanced the expression of Gpr40, Gpr55, and Gpr119 receptors. In contrast, the co-culture of βTC3 cells with endothelial cells converted the GPCR expression pattern closer to the pattern observed in MIN6 cells. Additionally, the efficiencies of various LPC species in βTC3-MS1 PIs also shifted toward the MIN6 cell model.

HNF1α controls glucagon secretion in pancreatic α-cells through modulation of SGLT1

Hepatocyte nuclear factor 1α (HNF1α) is a transcription factor required for normal insulin secretion and maintenance of β-cell number in the pancreas. HNF1α is also expressed in pancreatic α-cells, but its role in these cells is unknown. The aim of this study was to clarify the role of HNF1α in α-cells. Male Hnf1a+/− mice with a mixed background were backcrossed to outbred ICR mice. Glucose tolerance, glucagon and insulin secretion, islet histology, and gene expression were investigated in ICR Hnf1a−/− and Hnf1a+/+ mice. Regulation of Slc5a1 (encoding sodium glucose cotransporter 1 [SGLT1]) expression by HNF1α and the effect of SGLT1 inhibition on glucagon secretion were also explored. ICR Hnf1a−/− mice were glucose intolerant and exhibited impaired glucose-stimulated insulin secretion. The β-cell area of ICR mice was decreased in Hnf1a−/− mice, but the α-cell area in the pancreas was similar between Hnf1a−/− and Hnf1a+/+ mice. Hnf1a−/− mice showed higher fasting glucagon levels and exhibited inadequate suppression of glucagon after glucose load. In addition, glucagon release in response to hypoglycemia was impaired in Hnf1a−/− mice, and glucagon secretion after 1.1 mM glucose administration, was also decreased in Hnf1a−/− islets. Slc5a1 expression was decreased in Hnf1a−/− islets, while HNF1α activated the Slc5a1 promoter in αTC1-6 cells. Inhibition of SGLT1 suppressed 1.1 mM glucose-stimulated glucagon secretion in islets and αTC1-6 cells, but SGLT1 inhibition had no additional inhibitory effect in HNF1α-deficient cells. Our findings indicate that HNF1α modulates glucagon secretion in α-cells through the regulation of Slc5a1.

Selective monitoring of insulin secretion after CRISPR interference in intact pancreatic islets despite submaximal infection

ABSTRACT Virus-mediated gene knockdown in intact pancreatic islets is technically challenging due to poor infection of the center of the islet. Because the cells that do not have knockdown have normal insulin secretion, measuring changes in insulin secretion after gene knockdown is challenging. We describe a method to monitor insulin secretion from only the beta cells with knockdown of a gene of interest in intact islets using a single lentivirus containing a guide RNA, a luciferase insulin secretion reporter and a dCas9-KRAB cassette. This method allows rapid and inexpensive monitoring of insulin secretion from only those beta cells with knockdown, circumventing the problem of incomplete islet infection.

The pore-forming subunit MCU of the mitochondrial Ca2+ uniporter is required for normal glucose-stimulated insulin secretion in vitro and in vivo in mice

Aims/hypothesisMitochondrial oxidative metabolism is central to glucose-stimulated insulin secretion (GSIS). Whether Ca2+ uptake into pancreatic beta cell mitochondria potentiates or antagonises this process is still a matter of debate. Although the mitochondrial Ca2+ importer (MCU) complex is thought to represent the main route for Ca2+ transport across the inner mitochondrial membrane, its role in beta cells has not previously been examined in vivo.MethodsHere, we inactivated the pore-forming subunit of the MCU, encoded by Mcu, selectively in mouse beta cells using Ins1Cre-mediated recombination. Whole or dissociated pancreatic islets were isolated and used for live beta cell fluorescence imaging of cytosolic or mitochondrial Ca2+ concentration and ATP production in response to increasing glucose concentrations. Electrophysiological recordings were also performed on whole islets. Serum and blood samples were collected to examine oral and i.p. glucose tolerance.ResultsGlucose-stimulated mitochondrial Ca2+ accumulation (p< 0.05), ATP production (p< 0.05) and insulin secretion (p< 0.01) were strongly inhibited in beta cell-specific Mcu-null (βMcu-KO) animals, in vitro, as compared with wild-type (WT) mice. Interestingly, cytosolic Ca2+ concentrations increased (p< 0.001), whereas mitochondrial membrane depolarisation improved in βMcu-KO animals. βMcu-KO mice displayed impaired in vivo insulin secretion at 5 min (p< 0.001) but not 15 min post-i.p. injection of glucose, whilst the opposite phenomenon was observed following an oral gavage at 5 min. Unexpectedly, glucose tolerance was improved (p< 0.05) in young βMcu-KO (<12 weeks), but not in older animals vs WT mice.Conclusions/interpretationMCU is crucial for mitochondrial Ca2+ uptake in pancreatic beta cells and is required for normal GSIS. The apparent compensatory mechanisms that maintain glucose tolerance in βMcu-KO mice remain to be established.

Tcf19 Knockout Mouse Islets Have Increased Stress‐related Gene Expression and Reduced Proliferative Capacity

Transcription factor 19 (Tcf19) is a putative transcription factor associated with both Type 1 and Type 2 diabetes. Tcf19 is expressed in human and rodent pancreatic β‐cells and is upregulated in proliferating islets and obesity. We generated a whole body knockout (wbKO) of Tcf19 and the resulting lean, 15‐week‐old mice have normal fasting glucose, insulin secretion, and glucose tolerance compared to control. RNASeq led to the identification of 733 upregulated and 763 downregulated genes in wbKO islets compared to control. Overrepresented GO terms include upregulated apoptotic process, and negative regulation of cell proliferation, and downregulated vesicle‐mediated transport. We verified markers of proliferation, β‐cell identity, cell stress, and pro‐apoptosis using RTqPCR. Ki67, Pdx1, Nkx6.1, and Nkx2.2 were significantly decreased while Chop, Bak, Gadd45α, and Dtx3l were significantly increased in islets from wbKO mice. Whole pancreas was harvested to measure β‐cell area and although total area is not different, wbKO mice have altered islet size distribution with an increased number of small islets. Next, β‐cell proliferation and apoptosis were measured in frozen pancreatic sections using Ki67 and TUNEL staining, which revealed significantly less proliferation with no change in apoptosis rates in wbKO mice. In adulthood, β‐cell mass expansion occurs due to proliferation as an early compensation for insulin resistance in response to obesity. To determine the role of Tcf19 in this adaptive response wbKO and control mice were put on a one‐week high fat diet (HFD). After one week on HFD, islets from wbKO do not appropriately upregulate Ki67 and cyclin D2 as measured by RTqPCR. In summary, Tcf19 is involved in proliferation and stress related processes both of which are involved in regulating β‐cell mass, which declines in Type 1 and Type 2 diabetes.Support or Funding InformationVA Merit Award 1I01BX001880VA Merit Award 1I01BX004715TL1 Award TR000429ICTR Clinical and Translational Science Award UL1TR000427NIDDK 5R01DK110324

A computational structural biology study to understand the impact of mutation on structure–function relationship of inward-rectifier potassium ion channel Kir6.2 in human

Type 2 diabetes (T2D) is clinically characterized via hyperglycemia. Polymorphism rs5219 in the KCNJ11 gene is a risk factor for developing T2D in humans. KCNJ11 encodes the ‘inward-rectifier potassium ion channel (Kir6.2)’. However, because of the absence of the complete crystal/NMR structures of Kir6.2 proteins, insight into its structure and function and its interaction with diverse ligands remain elusive to date. Therefore, a computational approach was employed for predicting the best plausible ‘three-dimensional’ structure of Kir6.2 as well as for studying the influence of mutation (p. GLU23LYS) on both architectures as well as the function of Kir6.2 employing simulation studies. Results obtained revealed that though, with increased time, ‘Gibbs free energy’ becomes positive, residues in wild type Kir6.2 experiences less random movement as compared to mutant Kir6.2. The less random movement of residues in wild type Kir6.2 represents the standard coupling between open and closing of ‘KATP channel’ and thus the normal secretion of insulin. The more dispersed motion of mutant Kir6.2 residues represents ‘overactivity’ of the ‘KATP channel’ and thus insulin ‘under-secretion’. Further, molecular docking and simulation studies identified two phytochemicals/drugs, namely, A-348441 and chushizisin I, which retains the wild type property of Kir6.2 after binding with mutant protein. Unlike A-348441, this is for the first time, the present study is reporting about the plausible anti-diabetic property of chushizisin I. As these two phytochemicals/drugs, namely, A-348441 and chushizisin I, have passed ADMET test, in the near future, they may be utilized as anti-diabetic drugs after further investigation. Communicated by Ramaswamy H. Sarma

Can Vitamin D Supplementation Reduce Insulin Resistance and Hence the Risks of Type 2 Diabetes?

The question of whether or not correction of vitamin D deficiency might reduce the risks of later type 2 diabetes mellitus (T2DM) has been under debate for many decades. The necessity of vitamin D for normal insulin secretion was first identified experimentally in the 1980s.

Rubicon in pancreatic beta cells plays a limited role in maintaining glucose homeostasis following increased insulin resistance.

Autophagy has been reported to play a crucial role in the maintenance of intracellular homeostasis, including in pancreatic beta cells. Rubicon, which interacts with the phosphoinositide 3-kinase (PI3K) complex, through autophagy-related 14 (ATG14), is among the few autophagy regulators that have been reported to inhibit autophagic flux to date and the deletion of Rubicon has been shown to increase autophagic flux. Based on previous results showing a causal relationship between autophagic dysfunction and pancreatic beta-cell impairment, we hypothesized that the deletion of Rubicon in pancreatic beta cells would improve cell integrity and confer protective effects. To test this hypothesis, we first confirmed that Rubicon knockdown (KD) promoted autophagic flux in βTC3 pancreatic beta-cell line. Next, we generated pancreatic beta-cell-specific Rubicon knockout (βKO) mice, by administering tamoxifen to Rubiconflox/flox:MIP-Cre-ERT mice, which showed normal glucose tolerance and insulin secretion under a normal chow diet, despite successful gene recombination. We also attempted to increase insulin resistance by feeding the mice with a high-fat diet for an additional 2 months to find little differences among the parameters evaluated for glucose metabolism. Finally, severe insulin resistance was induced with insulin receptor antagonist treatment, which resulted in comparable glucose homeostasis measurements between Rubicon βKO and control mice. In summary, these results suggest that in pancreatic beta cells, Rubicon plays a limited role in the maintenance of systemic glucose homeostasis.

Fast-Acting Insulin Aspart: The Rationale for a New Mealtime Insulin.

Attenuating postprandial hyperglycaemia is a critical factor in the achievement of optimal glucose control. Prandial insulin analogues have been developed to replicate the physiology of normal endogenous insulin secretion and action, with the aim of limiting postprandial glucose excursions. There is still, however, a significant unmet need, with many people failing to achieve desired glycaemic control targets despite the current armamentarium of prandial insulin analogues. Such insulins have a delayed onset and a longer duration of action than endogenous insulin production. There has been considerable focus on attempts to accelerate the time–action profile of prandial exogenous insulin in order to produce a more physiological profile. One such approach is to modify the insulin formulation. Fast-acting insulin aspart is a modified formulation of insulin aspart containing niacinamide and l-arginine. It has an earlier onset of action than aspart. In an extensive trial programme, this faster aspart demonstrated similar HbA1c reductions to those achieved with aspart but superior postprandial glucose reductions, with no increase in hypoglycaemia. Furthermore, administration of faster aspart up to 20 min after the start of a meal permitted similar glucose control to aspart given preprandially. These data, taken in totality, illustrate the potential role of faster insulin aspart in clinical practice.

Retraction: Muscle-derived Satellite Cells for Treating Type 1 Diabetes in Rats (Rattus norvegicus).

Diabetes mellitus(DM) is a complicated metabolic disease, with the fundamental treatment nowadays being diet control, insulin injections, slet or pancreas transplantation, which is limited because exogenous insulin injections fail to simulate normal insulin secretion in islet beta cells successfully and islet transplantation lacks organ donors. So far, stem cells with highly self-renewal and multi-directional differentiation potential have become a new hope for the treatment of diabetes. In this research, rat Muscle-derived satellite cells *MDSCs*were separated and cultivated in vitro and inducted into insulin-producing cells with observation and identification using dithizone staining and so on. T1D rat model was built with Streptozocin(STZ), then MDSCs and induced insulin-producing cells from MDSCs labeled by Dil were transplanted respectively. Transplantation of MDSCs (group 1) and the induced insulin-producing cells (group 2) into streptozotocin (STZ)-induced diabetic rats resulted in lower blood glucose, lower urine glucose, higher body weight, higher glucose tolerance and less water intake and urine output than control rats (P < 0.05). Among the male rats, the blood glucose levels of 50% of group 1 rats were <16.7 mmol/L, and 40% of group 2 rats yielded similar results (P < 0.01). Among the female rats, the blood glucose levels of 66.67% of group 1 rats were <16.7 mmol/L, and 33.33% of group 2 rats showed similar blood glucose levels (P < 0.01). Histological examination revealed that the transplanted cells reached the pancreas and repaired damaged tissues. The above research conclusions provide theoretical basis, cell selection and good prospect for the treatment of diabetes. This article is protected by copyright. All rights reserved.

The relationship between serum uric acid within the normal range and β-cell function in Chinese patients with type 2 diabetes: differences by body mass index and gender.

BackgroundElevated serum uric acid (SUA) has a positive correlation with insulin secretion and insulin resistance indexes. However, whether weight- and gender-specific differences regarding the relationship between SUA within the normal range and β-cell function and insulin resistance exist is unknown in type 2 diabetes mellitus (T2DM) patients.MethodsA total of 380 patients with type 2 diabetes were divided into two groups as overweight/obesity (n = 268) and normal weight (n = 112). Each group were again divided into low (LSUA) and high normal SUA (HSUA). The HbA1c, C-peptide, SUA, creatinine, and lipids profiles were measured. HOMA2IR and HOMA%2B were estimated using fasting glucose and C-peptide by homeostasis model assessment (HOMA). Pearson’s correlations and multiple linear regression analyses were conducted to assess the associations between SUA levels and islet function indexes.ResultsIn overweight/obesity subgroup, the levels of body mass index, fasting C-peptide (FCP), P2hCP, fasting CPI (FCPI), postprandial CPI (PPCPI), ΔC-peptide, HOMA2%B, and HOMA2IR were higher in HSUA group than in LSUA group. In contrast, the HbA1c, FBS, and P2hBS were lower in HSUA than in LSUA. In normal weight subgroup, there were no differences between the HSUA than LSUA group in terms of clinical characteristics. Pearson’s correlations indicated that there were no significant correlations between SUA and insulin secretory capacity in normal weight group, but in overweight/obesity group, SUA had positive significant correlations with P2hCP, FCPI, PPCPI, ΔC-peptide, and HOMA2%B. In the female group, there were no significant correlations between SUA and insulin secretory capacity. However, in the male group, SUA had positive significant correlations with insulin secretory capacity include P2hCP, FCPI, PPCPI, ΔC-peptide, and HOMA2%B. Multiple linear regression showed that SUA was significantly associated with HOMA2%B, but not with HOMA2IR in overweight/obesity and male group.ConclusionsOur study shows that SUA levels within normal range were associated with β-cell function in T2DM patients with overweight/obesity or male. This finding supports that the association between SUA within normal range and insulin secretion ability differs by weight and sex.

Comparing methods to normalize insulin secretion shows the process may not be needed.

Glucose-stimulated insulin secretion (GSIS) is a well-accepted method to investigate the physiological and pathophysiological function of islets. However, there is little consensus about which method is best for normalizing and presenting GSIS data. In this study, we evaluated the sufficiency of islet area, total protein, total DNA, and total insulin content as parameters to normalize GSIS data. First, we tested if there is a linear correlation between each parameter and the number of islets (10, 20, 30, and 40 islets). Islet area, total protein, and insulin content produced excellent linear correlations with islet number (R2 >0.9 for each) from the same islet material. Insulin secretion in 11mM glucose also correlated reasonably well for islet area (R2=0.69), protein (R2=0.49), and insulin content (R2=0.58). DNA content was difficult to reliably measure and was excluded from additional comparisons. We next measured GSIS for 18 replicates of 20 islets each, measuring 3mM and 11mM glucose to calculate the stimulation index and to compare each normalization parameter. Using these similar islet masses for each replicate, none of the parameters produced linear correlations with GSIS (R2<0.05), suggesting that inherent differences in GSIS dominate small differences in islet mass. We conclude that when comparing GSIS for islets of reasonably similar size (<50% variance), normalization does not improve the representation of GSIS data. Normalization may be beneficial when substantial differences in islet mass are involved. In such situations, we suggest that using islet cross-sectional area is superior to other commonly used techniques for normalizing GSIS data.

Protein SUMOylation regulates insulin secretion at multiple stages

Type-II Diabetes Mellitus (T2DM) is one of the fastest growing public health issues of modern times, consuming 12% of worldwide health budgets and affecting an estimated 400 million people. A key pathological trait associated with this disease is the failure of normal glucose-stimulated insulin secretion (GSIS) from pancreatic beta cells. Several lines of evidence suggest that vesicle trafficking events such as insulin secretion are regulated by the post-translational modification, SUMOylation, and indeed SUMOylation has been proposed to act as a ‘brake’ on insulin exocytosis. Here, we show that diabetic stimuli which inhibit GSIS are correlated with an increase in cellular protein SUMOylation, and that inhibition of deSUMOylation reduces GSIS. We demonstrate that manipulation of cellular protein SUMOylation levels, by overexpression of several different components of the SUMOylation pathway, have varied and complex effects on GSIS, indicating that SUMOylation regulates this process at multiple stages. We further demonstrate that inhibition of syntaxin1A SUMOylation, via a knockdown-rescue strategy, greatly enhances GSIS. Our data are therefore consistent with the model that SUMOylation acts as a brake on GSIS, and we have identified SUMOylation of syntaxin 1 A as a potential component of this brake. However, our data also demonstrate that the role of SUMOylation in GSIS is complex and may involve many substrates.

Rab8a is involved in membrane trafficking of Kir6.2 in the MIN6 insulinoma cell line.

Although ATP-sensitive K+ (KATP) channels play an important role in the secretion of insulin by pancreatic beta cells, the mechanisms that regulate the intracellular transport of KATP channel subunit proteins (i.e., Kir6.2 and sulfonylurea receptor 1 (SUR1)) to the plasma membrane remain uncharacterized. We investigated the possibility that an interaction between KATP channel subunit proteins and Rab8a protein, a member of the RAS superfamily, may be involved in the membrane trafficking of KATP channels. Co-immunoprecipitation and immunostaining experiments using co-expression systems with fluorescent protein-tagged Kir6.2 were carried out to identify the coupling of KATP channels and Rab8a proteins in the insulin-secreting cell line, MIN6. Rab8a protein co-localized with Kir6.2 protein, a channel pore subunit (in a granular pattern), and with insulin. Knockdown of the Rab8a gene with RNA interference using small interfering RNA systems caused reductions in the amount of total KATP and plasma membrane surface KATP channels without decreasing the messenger RNA transcription of the KATP channel subunits. Rab8a gene knockdown also enhanced glucose-induced insulin secretion. These results suggest that Rab8a may be involved in membrane trafficking of KATP channels and the maintenance of normal insulin secretion in the MIN6 pancreatic beta cell line.

Anti-diabetic activity of canophyllol from Cratoxylum cochinchinense (Lour.) Blume in type 2 diabetic mice by activation of AMP-activated kinase and regulation of PPARγ.

In the present study, the potential anti-diabetic activity of canophyllol (CNPL) and its mechanisms were investigated in vitro and in vivo. CNPL is a predominant friedelane-type triterpene extracted from young leaves of Cratoxylum cochinchinense ("Huang Niu Tea"). In vitro, CNPL increased GLUT4 translation in a L6-myotube model to 2.60-fold, and glucose uptake to 1.71-fold levels relative to untreated L6 myotubes. Moreover, compound C, an inhibitor of AMP-activated protein kinase (AMPK), completely suppressed the CNPL-induced GLUT4 translocation. In vivo, serum insulin levels, hyperglycemia, as well as other blood indexes of the KK-Ay diabetic mice were improved by a four-week oral administration of CNPL. Examination of its possible anti-diabetic mechanism showed that CNPL promoted the expression of p-AMPKα and GLUT4 in L6 myotubes. In KK-Ay mice treated with CNPL, GLUT4 expression was increased in skeletal muscle and white adipose tissue, and the levels of p-AMPKα were increased in the liver, skeletal muscle and white adipose tissue. Moreover, CNPL stimulated the expression of PPARγ to decrease and inhibited the activity of ACC by stimulating its phosphorylation in both liver and white adipose tissue, thereby indicating that CNPL also improved lipid metabolism disorders. Altogether, these results show that CNPL may improve glucose tolerance, reduce hyperglycemia, normalize insulin secretion, and ameliorate lipid metabolism disorders. The diverse anti-diabetic effects of CNPL may be attributed to the regulation of GLUT4, PPARγ, AMPK phosphorylation and ACC phosphorylation.

Normal Insulin Secretion from Immune-Protected Islets of Langerhans by PEGylation and Encapsulation in the Alginate-Chitosan-PEG.

BackgroundPancreatic islet transplantation is one of the most promising strategies for treating patients with type I diabetes mellitus.ObjectiveWe aimed to assess the immunoisolation properties of the multilayer encapsulated islets using alginate-chitosan-PEG for immunoprotection and insulin secretion from the encapsulated islets induced under different glucose concentrations in vitro.Materials and MethodsIn this study, the islets were isolated from Wistar rats. The biological function (insulin secretion) of the immunoisolated islets following to PEGylation and encapsulation in the alginate-chitosan-PEG, separately, in addition to their immuno-protection in a co-culturing with the lymphocytes isolated from the male C57BL/6 mice were investigated, respectively.ResultsAlginate-chitosan-PEG decreased IL-2 secretion from the lymphocytes co-cultured with islets. Also, insulin secretion from the encapsulated and PEGylated groups was stimulated by glucose (i.e., 5.6 and 16.7 mM of glucose, respectively); showed insulin secretion similar to the naked islets, without coating, after 30 and 60 min of incubation.ConclusionIn conclusion, encapsulation and PEGylation have no negative effect on the insulin secretion and glucose sensitivity of the islets for all of the groups. Also, encapsulation decreased IL-2 secretion from the lymphocytes.

Mechanisms of beneficial effects of metformin on fatty acid-treated human islets

Elevated levels of palmitate accentuate glucose-stimulated insulin secretion (GSIS) after short-term and cause beta-cell dysfunction after prolonged exposure. We investigated whether metformin, the first-line oral drug for treatment of T2DM, has beneficial effects on FFA-treated human islets and the potential mechanisms behind the effects. Insulin secretion, oxygen consumption rate (OCR), AMPK activation, endoplasmic reticulum (ER) stress and apoptosis were examined in isolated human islets after exposure to elevated levels of palmitate in the absence or presence of metformin. Palmitate exposure doubled GSIS after 2 days but halved after 7 days compared with control. Inclusion of metformin during palmitate exposure normalized insulin secretion both after 2 and 7 days. After 2-day exposure to palmitate, OCR and the marker of the adaptive arm of ER stress response (sorcin) were significantly raised, whereas AMPK phosphorylation, markers of pro-apoptotic arm of ER stress response (p-EIF2α and CHOP) and apoptosis (cleaved caspase 3) were not affected. Presence of metformin during 2-day palmitate exposure normalized OCR and sorcin levels. After 7-day exposure to palmitate, OCR and sorcin were not significantly different from control level, p-AMPK was reduced and p-EIF2α, CHOP and cleaved caspase 3 were strongly upregulated. Presence of metformin during 7-day culture with palmitate normalized the level of p-AMPK, p-EIF2α, CHOP and cleaved caspase 3 but significantly increased the level of sorcin. Our study demonstrates that metformin prevents early insulin hypersecretion and later decrease in insulin secretion from palmitate-treated human islets by utilizing different mechanisms.

Role of ROCK1 in Pancreatic ß Cells

Insulin signaling in pancreatic β-cell is critical for normal insulin secretion. ROCK1 plays an important role in the regulation of insulin and leptin signaling in the context of glucose and energy metabolism. However, the role of ROCK1 in pancreatic β-cell remains unknown. The current study was to determine whether deleting ROCK1 from β-cell affects insulin secretion and glucose metabolism in mice and cultured cell lines. Here we show that β-cell-specific deletion of ROCK1 results in a significant decrease insulin secretion in mice fed a normal chow diet, leading to hyperglycemia. These effects were independent of changes in adiposity. Consistent with this, in vitro studies with INS-1 and MIN6 cells indicated that inhibition of ROCK1 decreased insulin secretion in response to glucose without changes in β-cell proliferation and apoptosis. In addition, β-cell-ROCK1 deficient mice displayed glucose intolerance, as evidenced by the fact that the area under the glucose curve was increased 53% in β-cell-ROCK1 deficient mice compared with control mice. However, neither body weight, food intake nor insulin sensitivity was changed in theses mice. Upon insulin stimulation, proximal insulin signaling components, including p-IRS2, p-PI3K and p-Akt were impaired when ROCK1 expression was inhibited in INS-1 cells, suggesting a role for ROCK1 in insulin signaling. These data indicate that activation of ROCK1 in pancreatic β-cell is required for the maintenance of normal insulin secretion. Thus, pancreatic ROCK1 might be a key regulator of glucose homeostasis. Disclosure B. Sung: None. K. Hur: None. J. Kim: None. Y. Kim: None.M. Lee: None.

An Overview on the Insulin Preparations and Devices

Abstract: Insulin preparations are the mainstay in the management of type 1 along with various type 2 diabetes. Available insulin preparations are either short-acting or long-acting or mixture to mimic the physiological insulin secretion and their doses need to be individualized. Attempting to imitate normal secretion of insulin can be valuable paradigm for understanding and providing effective therapy. This review provides an outline about the composition, use, route of administration, injection site, pharmacokinetics, storage and handling of various insulin preparations. The efficacy and safety of various insulin preparations for the management of diabetes mellitus are discussed. In addition, the use and application of various insulin devices to improve adherence and provide optimum delivery are elaborated. Indeed, the patient awareness and adherence on these issues is crucial to achieve good glycemic control. Key words: Short-acting insulin, Long-acting insulin, Mixture, Analogues, Handling, Devices, Diabetes.