Previous work in insulinoma cell lines has established that calcineurin plays a critical role in the activation of Creb, a key transcription factor required for beta cell function and survival, by dephosphorylating the Creb coactivator Crtc2 at two regulatory sites, Ser171 and Ser275. Here we report that Crtc2 is essential both for glucose-stimulated insulin secretion and cell survival in the beta cell. Endogenous Crtc2 activation is achieved via increasing glucose levels to the physiological feeding range, indicating that Crtc2 is a sensor that couples ambient glucose concentrations to Creb activity in the beta cell. Immunosuppressant drugs such as CsA and FK506 that target the protein phosphatase calcineurin are commonly administered following organ transplantation. Chronic use is associated with reduced insulin secretion and new onset diabetes, suggestive of pancreatic beta cell dysfunction. Importantly, we show that overexpression of a Crtc2 mutant rendered constitutively active by introduction of non-phosphorylatable alanine residues at Ser171 and Ser275 permits Creb target gene activation under conditions when calcineurin is inhibited. Taken together, these data suggest promoting Crtc2-Creb activity is required for beta cell function and proliferation and promoting this pathway could ameliorate symptoms of new onset diabetes after transplantation (NODAT).

Insulinomas first presenting as refractory seizure disorders are well documented in adulthood but rarely found in children. Only a few cases of childhood insulinoma have been reported so far. We report on two adolescents with hyperinsulinaemic hypoglycaemia, initially misdiagnosed as epilepsy and migraine accompagnée, and compare those to other cases published. Localization of insulinoma was challenging and, in one patient, angiography with selective arterial calcium stimulation and hepatic venous sampling in addition to CT and MRI was necessary. In these patients, long-term recovery was achieved by laparoscopic distal pancreatic resection in one and by conventional enucleation in the pancreatic head in the second patient. In contrast to adults, macrosomy and a decrease in school performance were the main symptoms and, during fasting, impaired cognitive function occurred after a relatively short period and at a higher glucose threshold or lower insulin/glucose ratio, respectively. Neuroglycopenic signs may be attributed to behaviour abnormalities or seizure disorders but in children and adolescents may already be caused by insulinoma. In these cases, timely diagnosis as well as tumour resection ensure long-term cure.

The pathophysiology of type 2 diabetes is progressive pancreatic beta cell failure with consequential reduced insulin secretion. Glucotoxicity results in the reduction of beta cell mass in type 2 diabetes by inducing apoptosis. Autophagy is essential for the maintenance of normal islet architecture and plays a crucial role in maintaining the intracellular insulin content by accelerating the insulin degradation rate in beta cells. Recently more attention has been paid to the effect of autophagy in type 2 diabetes. The regulatory pathway of autophagy in controlling pancreatic beta cells is still not clear. The aim of our study was to evaluate whether liraglutide can inhibit apoptosis and modulate autophagy in vitro in insulinoma cells (INS-1 cells).INS-1 cells were incubated for 24 hours in the presence or absence of high levels of glucose, liraglutide (a long-acting human glucagon-like peptide-1 analogue), or 3-methyadenine (3-MA). Cell viability was measured using the Cell Counting Kit-8 (CCK8) viability assay. Autophagy of INS-1 cells was tested by monodansylcadaverine (MDC) staining, an autophagy fluorescent compound used for the labeling of autophagic vacuoles, and by Western blotting of microtubule-associated protein I light chain 3 (LC3), a biochemical markers of autophagic initiation.The viability of INS-1 cells was reduced after treatment with high levels of glucose. The viability of INS-1 cells was reduced and apoptosis was increased when autophagy was inhibited. The viability of INS-1 cells was significantly increased by adding liraglutide to supplement high glucose level medium compared with the cells treated with high glucose levels alone.Apoptosis and autophagy were increased in rat INS-1 cells when treated with high level of glucose, and the viability of INS-1 cells was significantly reduced by inhibiting autophagy. Liraglutide protected INS-1 cells from high glucose level-induced apoptosis that is accompanied by a significant increase of autophagy, suggesting that liraglutide plays a role in beta cell apoptosis by targeting autophagy. Thus, autophagy may be a new target for the prevention or treatment of diabetes.

AIM:

Malignant insulinoma is an infrequent functional endocrine tumor of the pancreas. Adequate therapy is a demanding challenge for oncologists and endocrinologists.

OBJECTIVE:

To evaluate the results of multidisciplinary management of malignant insulinoma.

MATERIALS AND METHODS:

Retrospective review of patients with malignant insulinoma treated from 1995 to 2011.

RESULTS:

Seven patients with malignant insulinoma were included: four males and three females; median age was 61.8 years (range 37-78). Six tumors were sporadic and one was diagnosed in a patient with a type 1 multiple endocrine neoplasia (MEN-1). Surgery was performed in six cases and one patient was considered unresectable. Hypoglycemias persisted in all cases and somatostatin analogs, glucocorticoids and diazoxide were used. Two patients received everolimus. Other techniques were chemoembolization and internal radiation therapy with yttrium-90. Successful liver transplant was done in the patient with MEN-1.

CONCLUSION:

Hypoglycemia management is complex and requires multiple therapies. Further evaluations will be necessary to determine the best treatment.

The diagnosis of insulinoma is based on universally defined clinical and laboratory parameters (Whipple triad and fasting test). Pre-operative tumor localization is the main challenge in the diagnostic management of insulinomas. The pre-operative and/or intra-operative localization of the tumor is required for the optimal surgical approach. We describe two cases of insulinoma characterized by a typical clinical presentation, a positive diagnosis on fasting test, and computerized tomography failure in localizing the tumor. In the first patient, angiography with hepatic venous sampling after calcium stimulation correctly localized pre-operatively the region of the pancreas where the tumor was and, following intra-operative investigations, the lesion was successfully enucleated. In the second patient, angiography with hepatic venous sampling after calcium stimulation failed to identify the region of the insulinoma, which was detected by intra-operative ultrasound and successfully enucleated. Invasive pre-operative procedures for tumor regionalization and/or localization (angiography with hepatic venous sampling after calcium stimulation, endoscopic ultrasound) should be performed in cases where the tumor cannot be localized with enough certainty by non-invasive imaging. However, a careful intra-operative study should be performed in all patients undergoing surgery to complete the information obtained pre-operatively and to exclude the presence of other smaller lesions.

A 68-year-old man presented to the accident and emergency department with a history of central chest pain associated with exertion. He was admitted for assessment and when an acute coronary syndrome was excluded, he underwent exercise stress testing. His exercise stress testing was discontinued due to lightheadedness. His capillary glucose was checked and it showed hypoglycaemia (2.2 mmol/l). In light of this, a 72 h supervised fast was performed and it became positive within 24 h with low plasma glucose, inappropriately high insulin and C peptide levels. Sulfonylurea screen was negative. CT, MRI and endoscopic ultrasound revealed a 2 cm pancreatic tail insulinoma. He underwent successful surgical enucleation of this lesion.

The small G-protein ras-related C3 botulinum toxin substrate 1 (RAC1) plays various roles in mammalian cells, such as in the regulation of cytoskeletal organisation, cell adhesion, migration and morphological changes. The present study examines the effects of RAC1 ablation on pancreatic beta cell function.Isolated islets from pancreatic beta cell-specific Rac1-knockout (betaRac1 (-/-)) mice and RAC1 knockdown INS-1 insulinoma cells treated with small interfering RNA were used to investigate insulin secretion and cytoskeletal organisation in pancreatic beta cells.BetaRac1 (-/-) mice showed decreased glucose-stimulated insulin secretion, while there were no apparent differences in islet morphology. Isolated islets from the mice had blunted insulin secretion in response to high glucose levels. In RAC1 knockdown INS-1 cells, insulin secretion was also decreased in response to high glucose levels, consistent with the phenotype of betaRac1 (-/-) mice. Even under high glucose levels, RAC1 knockdown INS-1 cells remained intact with F-actin, which inhibits the recruitment of the insulin granules, resulting in an inhibition of insulin secretion.In RAC1-deficient pancreatic beta cells, F-actin acts as a barrier for insulin granules and reduces glucose-stimulated insulin secretion.

BACKGROUND:

The autoantibody to zinc transporter 8 (ZnT8A) is an independent marker for diagnosis of type 1 diabetes mellitus (T1DM). We investigated the distribution and clinical features of ZnT8A positive latent autoimmune diabetes in adult (LADA) patients, in order to explore the potential diagnostic application.

METHODS:

A total of 3062 phenotypic type 2 diabetes mellitus (T2DM) patients were randomly selected from a national multicenter study-the LADA China Study. Radioligand binding assays (RBA) were applied to detect the presence of ZnT8A, glutamic acid decarboxylase antibody (GADA) and insulinoma-associated protein-2 antibody (IA-2A) . HbA1c, fasting C peptide, serum lipid levels were followed up with ZnT8A positive patients.

RESULTS:

The positive prevalence of ZnT8A, GADA and IA-2A in phenotypic T2DM patients was 1.99%(61/3062), 6.43% (197/3062), 1.96% (60/3062), respectively. The ZnT8A positivity was lower than that of GADA(x(2)  = 74.8,P < 0.001), but was comparable to that of IA-2A(P > 0.05). The positivity of ZnT8A in IA-2A positive patients was higher than that in GADA positive patients(38.3% vs. 10.7%, x(2)  = 24.8,P < 0.001). Based on GADA and IA-2A positivity, the ZnT8A assay enhanced the diagnostic prevalence of LADA from 7.58% to 8.62%. The LADA patients who were positive for ZnT8A had higher systolic blood pressure when compared with GADA positive cases(P = 0.049), and higher total cholesterol(TC)levels when compared with antibody-negative T2DM patients(P = 0.035).

CONCLUSION:

The detection of ZnT8A at the basis of GADA and IA-2A, can improve diagnostic sensitivity of Chinese LADA. Copyright © 2013 John Wiley & Sons, Ltd.

It has been reported that peroxisome proliferator-activated receptor (PPAR)-γ and their synthetic ligands have direct effects on pancreatic β-cells. We investigated whether PPAR-γ activation stimulates insulin secretion through the up-regulation of GPR40 in pancreatic β-cells.Rat insulinoma INS-1 cells and primary rat islets were treated with rosiglitazone (RGZ) and/or adenoviral PPAR-γ overexpression. OLETF rats were treated with RGZ.PPAR-γ activation with RGZ and/or adenoviral PPAR-γ overexpression increased free fatty acid (FFA) receptor GPR40 expression, and increased insulin secretion and intracellular calcium mobilization, and was blocked by the PLC inhibitors, GPR40 RNA interference, and GLUT2 RNA interference. As a downstream signaling pathway of intracellular calcium mobilization, the phosphorylated levels of CaMKII and CREB, and the downstream IRS-2 and phospho-Akt were significantly increased. Despite of insulin receptor RNA interference, the levels of IRS-2 and phospho-Akt was still maintained with PPAR-γ activation. In addition, the β-cell specific gene expression, including Pdx-1 and FoxA2, increased in a GPR40- and GLUT2-dependent manner. The levels of GPR40, phosphorylated CaMKII and CREB, and β-cell specific genes induced by RGZ were blocked by GW9662, a PPAR-γ antagonist. Finally, PPAR-γ activation up-regulated β-cell gene expressions through FoxO1 nuclear exclusion, independent of the insulin signaling pathway. Based on immunohistochemical staining, the GLUT2, IRS-2, Pdx-1, and GPR40 were more strongly expressed in islets from RGZ-treated OLETF rats compared to control islets.These observations suggest that PPAR-γ activation with RGZ and/or adenoviral overexpression increased intracellular calcium mobilization, insulin secretion, and β-cell gene expression through GPR40 and GLUT2 gene up-regulation.

Pancreatic neuroendocrine tumors (PNET) are extremely rare, and although insulinomas are the commonest, less than 10% of insulinomas are malignant. Most patients with insulinomas present neuroglycopenic symptoms. Because of the rarity of the condition, we report the case of a 56-year-old man with malignant insulinoma, which was misdiagnosed as epilepsy. Timely diagnosis of this disease is of paramount importance to prevent neurologic sequelae of hypoglycemia. Insulinomas should be regarded from the beginning as potentially malignant, although the majority of malignant insulinomas progresses slowly.