Insulinoma with Hyperprocalcitoninemia and Hypercalcitoninemia Showing Coexpression of Insulin and Calcitonin in Its Tumor Cells

Neuroendocrine neoplasms can produce multiple hormones that are released into the bloodstream, causing symptoms that vary depending on the type and quantity of hormones involved. We herein report a 63-year-old asymptomatic patient with pancreatic insulinoma who showed marked elevations in circulating calcitonin and procalcitonin levels that returned to normal following surgery. Immunohistochemical analyses confirmed the co-staining of calcitonin and insulin immunoreactivity in the tumor cells, suggesting a calcitonin-producing insulinoma. This insulinoma released calcitonin and a considerable amount of its precursor peptide, procalcitonin, resulting in both hyperprocalcitoninemia and hypercalcitoninemia.

Purification of time-resolved insulin granules reveals proteomic and lipidomic changes during granule aging

Endocrine cells employ regulated exocytosis of secretory granules to secrete hormones and neurotransmitters. Secretory granule exocytosis depends on spatiotemporal variables such as proximity to the plasma membrane and age, with newly generated granules being preferentially released. Despite recent advances, we lack a comprehensive view of the molecular composition of insulin granules and associated changes over their lifetime. Here, we report a strategy for the purification of insulin secretory granules of distinct age from insulinoma INS-1 cells. Tagging the granule-resident protein phogrin with a cleavable CLIP tag, we obtain intact fractions of age-distinct granules for proteomic and lipidomic analyses. We find that the lipid composition changes over time, along with the physical properties of the membrane, and that kinesin-1 heavy chain (KIF5b) as well as Ras-related protein 3a (RAB3a) associate preferentially with younger granules. Further, we identify the Rho GTPase-activating protein (ARHGAP1) as a cytosolic factor associated with insulin granules.

TMEM219 regulates the transcription factor expression and proliferation of beta cells

Pancreatic beta cells replenishment is considered the next therapeutic option for type 1 diabetes; while stimulating endogenous beta cells proliferation is the "holy grail" for those patients with exhausted beta cell mass. Here we are demonstrating that the pro-apoptotic receptor TMEM219 is expressed in fetal pancreas, in beta cell precursors and in in vitro embryonic-derived endocrine progenitors. TMEM219 signaling negatively regulates beta cells at early stages and induces Caspase 8-mediated cell death. Pharmacological blockade of TMEM219 further rescued beta cell precursor and proliferation markers, and decreased cell death, both in islets and in in vitro-derived endocrine progenitors, allowing for beta cell preservation. While addressing the upstream controlling TMEM219 expression, we determined the TMEM219 miRNet; indeed, one of those miRNAs, miR-129-2, is highly expressed in human islets, particularly in patients at risk or with established type 1 diabetes. miR-129-2 mimic downregulated TMEM219 expression in islets, in in vitro embryonic-derived endocrine progenitors and in highly proliferating insulinoma-derived cells. Moreover, miR-129-2 inhibitor induced a TMEM219 overexpression in insulinoma-derived cells, which restored cell proliferation and functional markers, thus acting as endogenous regulator of TMEM219 expression. The TMEM219 upstream regulator miR129-2 controls the fate of beta cell precursors and may unleash their regenerative potentials to replenish beta cells in type 1 diabetes.

Exploring dual effects of dinutuximab beta on cell death and proliferation of insulinoma

Insulinoma INS-1 cells are pancreatic beta cell tumors. Dinutuximab beta (DB) is a monoclonal antibody used in the treatment of neuroblastoma. The aim of this study is to investigate the effects of DB on pancreatic beta cell tumors at the molecular level. DB (Qarziba®) was available from EUSA Pharma. Streptozotocin (STZ) was used induce to cell cytotoxicity. DB was applied to the cells before or after the STZ application. KCND3, KCNN4, KCNK1, and PTHrP gene expression levels were analyzed by q-RT-PCR, and protein levels were analyzed by Western blotting. Analysis of glucose-stimulated insulin secretion was performed. Ca+2 and CA19-9 levels were determined by the ELISA kit. PERK, CHOP, HSP90, p-c-Jun, p-Atf2, and p-Elk1 protein levels were analyzed by simple WES. Decreased KCND3, KCNK1, and PTHrP protein levels and increased KCND3, KCNN4, KCNK1, and PTHrP gene expression levels were observed with DB applied after STZ application. Cell dysfunction was detected with DB applied before and after STZ application. Ca19-9 and Ca+2 levels were increased with DB applied after STZ application. PERK, CHOP, and p-Elk1 levels decreased, while HSP90 levels increased with DB applied after STZ application. CHOP, p-Akt-2, and p-c-Jun levels increased in the DB group. As a result, INS-1 cells go to cell death via the ERK signaling pathway without ER stress and release insulin with the decrease of K+ channels and an increase in Ca+2 levels with DB applied after STZ application. Moreover, the cells proliferate via JNK signaling with DB application. DB holds promise for the treatment of insulinoma. The study should be supported by in vivo studies.

Immunohistochemical Glucagon-like Peptide-1 Receptor Expression in Human Insulinomas

Insulinomas are rare functional pancreatic neuroendocrine tumours, which metastasize in 10% of cases. As predicting the prognosis can be challenging, there is a need for the determination of clinicopathological factors associated with metastatic potential. The aim of this study is to evaluate the glucagon-like peptide-1 receptor (GLP-1R) expression in insulinomas and to analyse its association with clinicopathological features and patient outcome. This retrospective study involves pancreatic tumour tissue samples from fifty-two insulinoma patients. After histological re-evaluation, formalin-fixed paraffin-embedded tissue samples were processed into tissue microarrays and stained immunohistochemically with a monoclonal GLP-1R antibody. Forty-eight of the forty-nine (98%) non-metastatic tumours expressed GLP-1R, while one non-metastatic, multiple endocrine neoplasia type 1 (MEN1)-related tumour and all three of the metastatic tumours lacked GLP-1R expression. The lack of GLP-1R expression was associated with impaired overall survival, larger tumour diameter, higher Ki-67 PI and weaker insulin staining. Somatostatin receptor 1-5 expression did not differ between GLP-1R-positive and GLP-1R-negative insulinomas. In conclusion, the lack of GLP-1R expression is associated with metastatic disease and impaired survival in insulinoma patients. Thus, GLP-1R expression could be a useful biomarker in estimating the metastatic potential of the tumour and the prognosis of surgically treated patients.

Dibutyl phthalate affects insulin synthesis and secretion by regulating the mitochondrial apoptotic pathway and oxidative stress in rat insulinoma cells

Dibutyl phthalate (DBP) is a typical phthalate (PAEs). The environmental health risks of DBP have gradually attracted attention due to the common use in the production of plastics, cosmetics and skin care products. DBP was associated with diabetes, but its mechanism is not clear. In this study, an in vitro culture system of rat insulinoma (INS-1) cells was established to explore the effect of DBP on insulin synthesis and secretion and the potential mechanisms. INS-1 cells were cultured in RPMI-1640 medium containing 10% fetal bovine serum and treated with 15, 30, 60 and 120 μmol/L of DBP and dimethyl sulfoxide (vehicle, < 0.1%) for 24 h. The contents of insulin in the intracellular fluid and the extracellular fluid of the cells were measured. The results showed that insulin synthesis and secretion in INS-1 cells were significantly decreased in 120 μmol/L DBP group. The apoptosis rate and mitochondrial membrane potential of INS-1 cells were measured by flow cytometry with annexin V-FITC conjugate and PI, and JC-1, respectively. The results showed that DBP caused an increase in the apoptosis rate and a significant decrease in the mitochondrial membrane potential in INS-1 cells in 60 μmol/L and 120 μmol/L DBP group. The results of western blot showed that the expression of Bax/Bcl-2, caspase-3, caspase-9 and Cyt-C were significantly increased. Meanwhile, the level of oxidative stress in INS-1 cells was detected by fluorescent probes DCFH-DA and western blot. With the increase of DBP exposure, the oxidative stress levels (MDA, GSH/GSSG) were increased; and the antioxidant index (SOD) levels were decreased. Our experimental results provide reliable evidence that DBP induced apoptosis and functional impairment in INS-1 cells through the mitochondrial apoptotic pathway and oxidative stress. Therefore, we hypothesized that interference with these two pathways could be considered in the development of preventive protection measures.

In Vivo Imaging of Naked and Microencapsulated Islet Cell Transplantation

We describe step-by-step methods to label human pancreatic islet cells and murine insulinoma cells and their subsequent transplantation into type I diabetic mouse models with a focus on in vivo imaging using clinically applicable scanners. We also cover islets that are microencapsulated within alginate hydrogels loaded with imaging agents. By following these methods, it is possible to image cell grafts using T1-weighted and T2/T2*-weighted 1H magnetic resonance imaging (MRI), 19F MRI, computed tomography, ultrasound imaging, and bioluminescence imaging in vivo. Considering a myriad of factors that may affect the outcome of proper in vivo detection, we discuss potential issues that may be encountered during and after the process of labeling. The ultimate goal is to use these in vivo imaging approaches to determine and optimize naked and encapsulated islet cell survival, therapeutic function, and engraftment procedures.

Identification and Validation of a New Peptide Targeting Pancreatic Beta Cells

Noninvasive targeted visualization of pancreatic beta cells or islets is becoming the focus of molecular imaging application in diabetes and islet transplantation studies. In this study, we aimed to produce the beta-cell-targeted peptide for molecular imaging of islet. We used phage display libraries to screen a beta-cell-targeted peptide, LNTPLKS, which was tagged with fluorescein isothiocyanate (FITC). This peptide was validated for targeting beta-cell with in vitro and in vivo studies. Immunocytochemistry (ICC) and fluorescence-activated cell sorting (FACS) analysis were used to validate the target specificity of the peptide. FITC-LNTPLKS displayed much higher fluorescence in beta cells vs. control cells in ICC. This discrimination was consistently observed using primary rodent islet. FACS analysis showed right shift of peak point in beta cells compared to control cells. The specific bind to in situ islet was verified by in vitro experiments using rodent and human pancreatic slices. The peptide also showed high affinity of islet grafts under the renal capsule. In the insulinoma animal model, we could find FITC-LNTPLKS accumulated specifically to the tumor, thus indicating a potential clinical application of molecular imaging of insulinoma. In conclusion, LNTPLKS showed a specific probe for beta-cells, which might be further utilized in targeted imaging/monitoring beta cells and theragnosis for beta-cells-related disease (diabetes, insulinoma, etc.).

Selenomethionine modulates insulin secretion in the MIN6-K8 mouse insulinoma cell line

Selenium is an essential trace element of interest for its potential role in glucose homeostasis. The present study investigated the impact of selenium supplementation as selenomethionine (SeMet) on insulin secretion in MIN6-K8 cells, a pancreatic β-cell model. We found that SeMet enhanced percent glucose-induced insulin secretion, while also increasing tolbutamide- and KCl-induced percent insulin secretion. RNA-sequencing showed that SeMet supplementation altered expression of several selenoproteins, including glutathione peroxidase 3 (Gpx3) and selenoprotein P (SelP). Targeted knockdown of Gpx3 increased both percent and total insulin release, while SelP knockdown increased insulin content and insulin release. Collectively, these studies support a putative role for selenium and selenoproteins in the regulation of insulin secretion, glucose homeostasis, and diabetes risk.

Cavβ3 Regulates Ca2+ Signaling and Insulin Expression in Pancreatic β-Cells in a Cell-Autonomous Manner

Voltage-gated Ca²⁺ (Cav) channels consist of a pore-forming Cavα1 subunit and auxiliary Cavα2-δ and Cavβ subunits. In fibroblasts, Cavβ3, independent of its role as a Cav subunit, reduces the sensitivity to low concentrations of inositol-1,4,5-trisphosphate (IP₃). Similarly, Cavβ3 could affect cytosolic calcium concentration ([Ca^{2 +}]) in pancreatic β-cells. In this study, we deleted the Cavβ3-encoding gene Cacnb3 in insulin-secreting rat β-(Ins-1) cells using CRISPR/Cas9. These cells were used as controls to investigate the role of Cavβ3 on Ca²⁺ signaling, glucose-induced insulin secretion (GIIS), Cav channel activity, and gene expression in wild-type cells in which Cavβ3 and the IP₃ receptor were coimmunoprecipitated. Transcript and protein profiling revealed significantly increased levels of insulin transcription factor Mafa, CaMKIV, proprotein convertase subtilisin/kexin type-1, and nitric oxide synthase-1 in Cavβ3-knockout cells. In the absence of Cavβ3, Cav currents were not altered. In contrast, CREB activity, the amount of MAFA protein and GIIS, the extent of IP₃-dependent Ca²⁺ release and the frequency of Ca²⁺ oscillations were increased. These processes were decreased by the Cavβ3 protein in a concentration-dependent manner. Our study shows that Cavβ3 interacts with the IP₃ receptor in isolated β-cells, controls IP₃-dependent Ca²⁺-signaling independently of Cav channel functions, and thereby regulates insulin expression and its glucose-dependent release in a cell-autonomous manner.

Oxidized LDL Downregulates ABCA1 Expression via MEK/ERK/LXR Pathway in INS-1 Cells

Impaired insulin secretion is one of the main causes of type 2 diabetes. Cholesterol accumulation-induced lipotoxicity contributes to impaired insulin secretion in pancreatic beta cells. However, the detailed mechanism in this process remains unclear. In this study, we proved that oxidized low-density lipoprotein (OxLDL) reduced insulin content, decreased PDX-1 expression, and impaired glucose-stimulated insulin secretion (GSIS) in INS-1 cells, which were rescued by addition of high-density lipoprotein (HDL). OxLDL receptors and cholesterol content were increased by OxLDL. Consistently, OxLDL suppressed cholesterol transporter ABCA1 expression and transcription in a dose-dependent and time-dependent manner. Inhibition of MEK by its specific inhibitor, PD98059, altered the effect of OxLDL on ABCA1 transcription and activation of ERK. Next, chromatin immunoprecipitation assay demonstrated that liver X receptor (LXR) could directly bind to ABCA1 promoter and this binding was inhibited by OxLDL. Furthermore, OxLDL decreased the nuclear LXR expression, which was prevented by HDL. LXR-enhanced ABCA1 transcription was suppressed by OxLDL, and the effect was cancelled by mutation of the LXR-binding sites. In summary, our study shows that OxLDL down-regulates ABCA1 expression by MEK/ERK/LXR pathway, leading to cholesterol accumulation in INS-1 cells, which may result in impaired insulin synthesis and GSIS.

Quercetin improves oxidative stress-induced pancreatic beta cell alterations via mTOR-signaling

Citrus flavonoids particularly quercetin which is abundant in grapefruit, onion, green tea, berries etc. are known to have a protective effect on oxidative stress. Pancreatic β cells which synthesize and secrete insulin are prone to oxidative stress induced damage because of low cellular antioxidant enzymes. To delineate the effects of quercetin on pancreatic β cells we evaluated the protective effect of quercetin on TC6 insulinoma cells subjected to oxidative stress induced by tert-butyl-hydrogen-peroxide (TBHP). Quercetin was found to reduce TBHP induced apoptosis and trigger insulin secretion in response to glucose, in a dose-dependent manner. Quercetin treatment increased mitochondrial biogenesis, caused hypertrophy in pancreatic β cells and activated mTOR signaling with a transient change in mitochondrial membrane potential and AMP/ATP. Activation of mTOR signaling resulted in enhanced insulin secretion in TC6 cells.

Optoacoustic Imaging of Glucagon-like Peptide-1 Receptor with a Near-Infrared Exendin-4 Analog

Limitations in current imaging tools have long challenged the imaging of small pancreatic islets in animal models. Here, we report the first development and in vivo validation testing of a broad-spectrum and high-absorbance near-infrared optoacoustic contrast agent, E4x12-Cy7. Our near-infrared tracer is based on the amino acid sequence of exendin-4 and targets the glucagon-like peptide-1 receptor (GLP-1R). Cell assays confirmed that E4x12-Cy7 has a high-binding affinity (dissociation constant, Kd, 4.6 ± 0.8 nM). Using the multispectral optoacoustic tomography, we imaged E4x12-Cy7 and optoacoustically visualized β-cell insulinoma xenografts in vivo for the first time. In the future, similar optoacoustic tracers that are specific for β-cells and combines optoacoustic and fluorescence imaging modalities could prove to be important tools for monitoring the pancreas for the progression of diabetes.

Lower threshold to NFκB activity sensitizes murine β-cells to streptozotocin

The β-cell response to injury may be as critical for the development of diabetes as the specific insult. In the current study, we used streptozotocin (STZ) to injure the β-cell in order to study the response with a focus on NFκB. MIN6 cells were exposed to STZ (0.5-8 mM, 0-24h) ±TNFα (100 ng/mL) and ±IκBβ siRNA to lower the threshold to NFκB activation. Cell viability was determined by trypan blue exclusion. NFκB activation was determined by the expression of the target genes Nos2 and Cxcl10, localization of the NFκB proteins p65 and p50, and expression and localization of the NFκB inhibitors, IκBβ and IκBα. There was no NFκB activation in MIN6 cell exposed to STZ (2 mM) alone. However, knocking down IκBβ expression using siRNA resulted in STZ-induced expression of NFκB target genes and increased cell death, while co-incubation with STZ and TNFα enhanced cell death compared to either exposure alone. Adult male IκBβ-/- and WT mice were exposed to STZ and monitored for diabetes. The IκBβ-/- mice developed hyperglycemia and diabetes more frequently than controls following STZ exposure. Based on these results we conclude that STZ exposure alone does not induce NFκB activity. However, lowering the threshold to NFκB activation by co-incubation with TNFα or lowering IκBβ levels by siRNA sensitizes the NFκB response to STZ and results in a higher likelihood of developing diabetes in vivo. Therefore, increasing the threshold to NFκB activation through stabilizing NFκB inhibitory proteins may prevent β-cell injury and the development of diabetes.

Uptake of fluorescent D- and L-glucose analogues, 2-NBDG and 2-NBDLG, into human osteosarcoma U2OS cells in a phloretin-inhibitable manner

Mammalian cells take in d-glucose as an essential fuel as well as a carbon source. In contrast, l-glucose, the mirror image isomer of d-glucose, has been considered merely as a non-transportable/non-metabolizable control for d-glucose. We have shown that 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), a d-glucose analogue combining a fluorophore NBD at the C-2 position, is useful as a tracer for monitoring d-glucose uptake through glucose transporters (GLUTs) into mammalian cells. To more precisely evaluate the stereoselectivity of 2-NBDG uptake, we developed an l-glucose analogue 2-NBDLG, the mirror-image isomer of 2-NBDG. Interestingly, 2-NBDLG was taken up into mouse insulinoma MIN6 cells showing nuclear heterogeneity, a cytological feature of malignancy, while remaining MIN6 cells only exhibited a trace amount of 2-NBDLG uptake. The 2-NBDLG uptake into MIN6 cells was abolished by phloretin, but persisted under blockade of major mammalian glucose transporters. Unfortunately, however, no such uptake could be detected in other tumor cell lines. Here we demonstrate that human osteosarcoma U2OS cells take in 2-NBDLG in a phloretin-inhibitable manner. The uptake of 2-NBDG, and not that of 2-NBDLG, into U2OS cells was significantly inhibited by cytochalasin B, a potent GLUT inhibitor. Phloretin, but neither phlorizin, an inhibitor of sodium-glucose cotransporter (SGLT), nor a large amount of d/l-glucose, blocked the 2-NBDLG uptake. These results suggest that a phloretin-inhibitable, non-GLUT/non-SGLT, possibly non-transporter-mediated yet unidentified mechanism participates in the uptake of the fluorescent l-glucose analogue in two very different tumor cells, the mouse insulinoma and the human osteosarcoma cells.

Differentiation of insulinoma from accessory spleen by 99mTc-labelled heat-denaturated red blood cell scintigraphy: case report

BACKGROUND

Neuroendocrine tumors (NETs) are rare tumors harboring overexpression of somatostatin receptors (SSTRs) on their cell membrane. Because some organs, such as the spleen, adrenal glands and liver, physiologically express SSTR, it might be challenging to distinguish some pancreatic NETs located in the pancreatic tail from the accessory spleen next to the splenic hilum. In this manuscript, we report a case with hypoglycemia attack and 2 different masses displayed by Gallium 68-tetraazacyclododecane tetraacetic acid-octreotate (⁶⁸Ga-DOTATATE) positron emission tomography/computed tomography (PET/CT).

CASE PRESENTATION

A 63-year-old woman presented to the hospital with confusion and profuse sweating. Biochemical diagnosis of insulinoma was established. ⁶⁸Ga-DOTATATE PET/CT revealed two masses with increased tracer uptake located adjacent to the splenic hilum and inferior pole of the spleen which were initially reported as two separate accessory spleens. Then, ^99mTc-labelled heat-denaturated red blood cell (^99mTc-HDRBC) scintigraphy-single-photon emission computed tomography (SPECT)/CT was performed to distinguish a NET in the pancreatic tail from accessory spleen at the splenic hilum. Enhanced tracer uptake remained in the inferior pole of spleen, but not in the splenic hilum. The lesions were suggestive of insulinoma in the pancreatic tail and an accessory spleen adjacent to the inferior pole of the spleen.

CONCLUSION

Approximately 10% of the population have an accessory spleen which can show similar imaging characteristics with pancreatic NETs, especially if located in the pancreatic tail. In our presented case, ^99mTc-HDRBC scintigraphy-SPECT/CT is a useful nuclear medicine method to differentiate a NET in the pancreatic tail from accessory spleen at the splenic hilum which may avoid unnecessary surgeries in the presence of enhanced tracer uptake or vice versa.

[Pancreatic proinsulinoma]

OBJECTIVE

To report own experience in the treatment of patients with proinsulinoma.

MATERIAL AND METHODS

There were 10 patients with increased proinsulin production and normal insulin level since 2017. Most of them were young women.

RESULTS

Fasting hypoglycemia in all patients was severe (up to 0.7 mmol/l). Clinical picture consisted of typical symptoms similar to those in insulinoma. The main difference in the course of proinsulinoma was the absence of weight gain in 7 patients and rapid weight loss (from 210 to 90 kg within 9 months) in 1 patient. All patients with proinsulinoma underwent surgery. In most cases, minimally aggressive surgery was performed.

CONCLUSION

Proinsulinoma is an extremely rare endocrine-active neuroendocrine pancreatic tumor. Differential features of proinsulinoma are the absence of weight gain and normal insulin levels in the presence of hypoglycemia. Surgery is the only radical method of treatment.

Insulinoma induces a hyperinsulinemia-mediated decrease of GLUT2 and GLP1 receptor in normal pancreatic β-cells

There have been several clinical reports of transient postoperative hyperglycemia in patients with insulinoma, but the effect of insulinoma on normal β-cells has not been investigated. We examined the glucose transporter 2 (GLUT2) and glucagon-like peptide 1 receptor (GLP1R) expression in normal pancreatic β-cells of five patients with insulinoma and five patients with normal glucose tolerance (NGT) as controls. The positive rate of GLUT2-or GLP1R-positive islets in the nontumor area was calculated by the ratio with the analyzed islets. For functional in vitro analyses, q-PCR and Western blotting were performed after insulin loading on MIN6 cells. The expression rates of both GLUT2 and GLP1R were significantly lower in nontumor area islets of insulinoma patients than in patients with NGT (GLUT2: 31.6 ± 15.3% vs 95.9 ± 6.7%, p < 0.01, GLP1R: 66.8 ± 15.0% vs 96.7 ± 5.0%, p < 0.01). Exposure of MIN6 cells to high concentrations of insulin resulted in a significant decrease in GLUT2 protein for 12 h and GLP1R protein for 24 h (GLUT2; 1.00 ± 0.079 vs 0.81 ± 0.04. p = 0.02, GLP1R; 1.00 ± 0.10 vs 0.50 ± 0.24, p = 0.03) but not in those mRNAs. Our findings show that insulinoma is associated with the downregulation of GLUT2 and GLP1R expression in nontumor area islets. These phenomena may be caused by high levels of insulin.

Low-dose Selective Arterial Calcium Stimulation Test for Localizing Insulinoma: A Single-center Experience of Five Consecutive Cases

The selective arterial calcium stimulation test (SACST) is one of the most useful localization tests for insulinoma but can cause false-positive and/or unexpected multi arterial positive results that hamper clinical decisions. There are also several adverse effects, such as nausea and hypoglycemia, at the conventional dose (0.025 mEq/kg) of calcium injection. We herein report five consecutive insulinoma cases in which low-dose (0.005-0.007 mEq/kg) calcium injection for SACST led to successful insulinoma localization. No adverse effects of SACST were observed. In conclusion, a low-dose SACST can be a favorable option as an insulinoma localization test in terms of accuracy and safety.

Exposure to inorganic arsenic and its methylated metabolites alters metabolomics profiles in INS-1 832/13 insulinoma cells and isolated pancreatic islets

Inorganic arsenic (iAs) is an environmental diabetogen, but mechanisms underlying its diabetogenic effects are poorly understood. Exposures to arsenite (iAsIII) and its methylated metabolites, methylarsonite (MAsIII) and dimethylarsinite (DMAsIII), have been shown to inhibit glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells and isolated pancreatic islets. GSIS is regulated by complex mechanisms. Increase in ATP production through metabolism of glucose and other substrates is the ultimate trigger for GSIS in β-cells. In the present study, we used metabolomics to identify metabolites and pathways perturbed in cultured INS-1 832/13 rat insulinoma cells and isolated murine pancreatic islets by exposures to iAsIII, MAsIII and DMAsIII. We found that the exposures perturbed multiple metabolites, which were enriched primarily in the pathways of amino acid, carbohydrate, phospholipid and carnitine metabolism. However, the effects of arsenicals in INS-1 832/13 cells differed from those in the islets and were exposure specific with very few overlaps between the three arsenicals. In INS-1 832/13 cells, all three arsenicals decreased succinate, a metabolite of Krebs cycle, which provides substrates for ATP synthesis in mitochondria. Acetylcarnitine was decreased consistently by exposures to arsenicals in both the cells and the islets. Acetylcarnitine is usually found in equilibrium with acetyl-CoA, which is the central metabolite in the catabolism of macronutrients and the key substrate for Krebs cycle. It is also thought to play an antioxidant function in mitochondria. Thus, while each of the three trivalent arsenicals perturbed specific metabolic pathways, which may or may not be associated with GSIS, all three arsenicals appeared to impair mechanisms that support ATP production or antioxidant defense in mitochondria. These results suggest that impaired ATP production and/or mitochondrial dysfunction caused by oxidative stress may be the mechanisms underlying the inhibition of GSIS in β-cells exposed to trivalent arsenicals.

Identification of a small molecule that stimulates human β-cell proliferation and insulin secretion, and protects against cytotoxic stress in rat insulinoma cells

A key event in the development of both major forms of diabetes is the loss of functional pancreatic islet β-cell mass. Strategies aimed at enhancing β-cell regeneration have long been pursued, but methods for reliably inducing human β-cell proliferation with full retention of key functions such as glucose-stimulated insulin secretion (GSIS) are still very limited. We have previously reported that overexpression of the homeobox transcription factor NKX6.1 stimulates β-cell proliferation, while also enhancing GSIS and providing protection against β-cell cytotoxicity through induction of the VGF prohormone. We developed an NKX6.1 pathway screen by stably transfecting 832/13 rat insulinoma cells with a VGF promoter-luciferase reporter construct, using the resultant cell line to screen a 630,000 compound chemical library. We isolated three compounds with consistent effects to stimulate human islet cell proliferation, but not expression of NKX6.1 or VGF, suggesting an alternative mechanism of action. Further studies of the most potent of these compounds, GNF-9228, revealed that it selectively activates human β-cell relative to α-cell proliferation and has no effect on δ-cell replication. In addition, pre-treatment, but not short term exposure of human islets to GNF-9228 enhances GSIS. GNF-9228 also protects 832/13 insulinoma cells against ER stress- and inflammatory cytokine-induced cytotoxicity. GNF-9228 stimulates proliferation via a mechanism distinct from recently emergent DYRK1A inhibitors, as it is unaffected by DYRK1A overexpression and does not activate NFAT translocation. In conclusion, we have identified a small molecule with pleiotropic positive effects on islet biology, including stimulation of human β-cell proliferation and insulin secretion, and protection against multiple agents of cytotoxic stress.

The functioning side of the pancreas: a review on insulinomas

PURPOSE

Insulinomas are a rare type of neuroendocrine tumors, originating in the pancreas, difficult to diagnose and to treat. Due to its rarity, insulinomas are a not well-known pathological entity; thus, the diagnostic process is frequently a medical challenge with many possible differential diagnoses. The diagnostic process varies between non-invasive procedures, such as the fasting test or imaging techniques, and invasive ones. Insulinomas are rarely malignant, but the glycemic imbalance correlated with this tumor can frequently alter the quality of life of the patients and the consequent hypoglycemia can be extremely dangerous. Moreover, insulinomas can be associated with different genetic syndromes, such as Multiple Endocrine Neoplasia 1, accompanied by other specific symptoms. There are many different treatment strategies, depending on the need to control symptoms or control diseases progression, the only curative one being surgery.

METHODS AND RESULTS

We reviewed the evidences present in the literature on insulinomas and reported its main clinical characteristics and management strategies.

CONCLUSION

The aim of this review of the literature is to present the current knowledge on insulinomas, exploring the main clinical characteristics, the diagnostic tools, and the therapeutic strategies.

MiD51 Is Important for Maintaining Mitochondrial Health in Pancreatic Islet and MIN6 Cells

Background: Mitochondrial dynamics are important for glucose-stimulated insulin secretion in pancreatic beta cells. The mitochondrial elongation factor MiD51 has been proposed to act as an anchor that recruits Drp1 from the cytosol to the outer mitochondrial membrane. Whether MiD51 promotes mitochondrial fusion by inactivation of Drp1 is a controversial issue. Since both the underlying mechanism and the effects on mitochondrial function remain unknown, this study was conducted to investigate the role of MiD51 in beta cells. Methods: Overexpression and downregulation of MiD51 in mouse insulinoma 6 (MIN6) and mouse islet cells was achieved using the pcDNA expression vector and specific siRNA, respectively. Expression of genes regulating mitochondrial dynamics and autophagy was analyzed by quantitative Real-Time PCR, glucose-stimulated insulin secretion by ELISA, and cellular oxygen consumption rate by optode sensor technology. Mitochondrial membrane potential and morphology were visualized after TMRE and MitoTracker Green staining, respectively. Immunofluorescence analyses were examined by confocal microscopy. Results: MiD51 is expressed in insulin-positive mouse and human pancreatic islet and MIN6 cells. Overexpression of MiD51 resulted in mitochondrial fragmentation and cluster formation in MIN6 cells. Mitochondrial membrane potential, glucose-induced oxygen consumption rate and glucose-stimulated insulin secretion were reduced in MIN6 cells with high MiD51 expression. LC3 expression remained unchanged. Downregulation of MiD51 resulted in inhomogeneity of the mitochondrial network in MIN6 cells with hyperelongated and fragmented mitochondria. Mitochondrial membrane potential, maximal and glucose-induced oxygen consumption rate and insulin secretion were diminished in MIN6 cells with low MiD51 expression. Furthermore, reduced Mfn2 and Parkin expression was observed. Based on MiD51 overexpression and downregulation, changes in the mitochondrial network structure similar to those in MIN6 cells were also observed in mouse islet cells. Conclusion: We have demonstrated that MiD51 plays a pivotal role in regulating mitochondrial function and hence insulin secretion in MIN6 cells. We propose that this anchor protein of Drp1 is important to maintain a homogeneous mitochondrial network and to avoid morphologies such as hyperelongation and clustering which are inaccessible for degradation by autophagy. Assuming that insulin granule degradation frequently suppresses autophagy in beta cells, MiD51 could be a key element maintaining mitochondrial health.

Interplay Between Diabetes and Pancreatic Ductal Adenocarcinoma and Insulinoma: The Role of Aging, Genetic Factors, and Obesity

Epidemiologic analyses have shed light on an association between type 2 diabetes (T2D) and pancreatic ductal adenocarcinoma (PDAC). Recent data also suggest a potential relationship between T2D and insulinoma. Under rare circumstances, type 1 diabetes (T1D) can also be implicated in tumorigenesis. The biological mechanisms underlying such relationships are extremely complex. Some genetic factors contributing to the development of T2D are shared with pancreatic exocrine and endocrine tumors. Obesity and overweight can also contribute to the initiation and severity of T2D, while aging may influence both endocrine and exocrine tumors. Finally, pharmacological treatments of T2D may have an impact on PDAC. On the other hand, some treatments for insulinoma can trigger diabetes. In the present minireview, we discuss the cellular and molecular mechanisms that could explain these interactions. This analysis may help to define new potential therapeutic strategies.

Glucose-responsive Insulinoma with Insulin Hypersecretion Suppressed by Metformin

In type 2 diabetes mellitus, metformin suppresses excessive insulin secretion in relation to the intake of glucose. We herein report the case of a 45-year-old man with glucose-responsive insulinoma whose responsive hypoglycemia was alleviated by metformin. The patient had a history of a postprandial loss of consciousness, resulting in hospital admission. He refused surgery and diazoxide administration. A 75-g oral glucose tolerance test after metformin administration revealed the suppression of glucose-responsive insulin hypersecretion and responsive hypoglycemia. Pancreatic head duodenectomy was performed, which alleviated the symptoms. Metformin administration in patients with glucose-responsive insulinoma may therefore be effective for preventing responsive hypoglycemia and hyperinsulinemia.

Acute Deletion of METTL14 in β-Cells of Adult Mice Results in Glucose Intolerance

N6-Methyladenosine (m6A) is the most common and abundant mRNA modification that involves regulating the RNA metabolism. However, the role of m6A in regulating the β-cell function is unclear. Methyltransferase-like 14 (METTL14) is a key component of the m6A methyltransferase complex. To define the role of m6A in regulating the β-cell function, we generated β-cell METTL14-specific knockout (βKO) mice by tamoxifen administration. Acute deletion of Mettl14 in β-cells results in glucose intolerance as a result of a reduction in insulin secretion in β-cells even though β-cell mass is increased, which is related to increased β-cell proliferation. To define the molecular mechanism, we performed RNA sequencing to detect the gene expression in βKO islets. The genes responsible for endoplasmic reticulum stress, such as Ire1α, were among the top upregulated genes. Both mRNA and protein levels of IRE1α and spliced X-box protein binding 1 (sXBP-1) were increased in βKO islets. The protein levels of proinsulin and insulin were decreased in βKO islets. These results suggest that acute METTL14 deficiency in β-cells induces glucose intolerance by increasing the IRE1α/sXBP-1 pathway.

Linderane protects pancreatic β cells from streptozotocin (STZ)-induced oxidative damage

AIMS

Linderane, an important bioactive compound in Linderae, improved glucose and lipid metabolism in ob/ob mice. However, the effect of linderane on streptozotocin (STZ)-induced oxidative damage in INS-1 cells remains unclear.

MAIN METHODS

INS-1 cells were pre-treated with different doses of linderane for 2 h and then treated with 3 mM STZ for 12 h. Cell viability was determined by MTT assay. Cell apoptosis was detected using an Annexin V-FITC Apoptosis Detection Kit. The level of intracellular ROS was determined using dichlorofluorescein-diacetate (DCFH-DA). The activities of insulin secretion, SOD, catalase (CAT) and GPx were measured using ELISA kits. The expression levels of bax, bcl-2, p38, p-p38, nuclear Nrf2 and HO-1 were measured using western blot.

KEY FINDINGS

The results showed that STZ-caused inhibitory effects on cell viability and insulin secretion were mitigated by linderane. Furthermore, linderane inhibited apoptosis and oxidative stress in STZ-induced INS-1 cells. Finally, linderane suppressed the activation of p38 MAPK pathway, as well as enhanced the activation of Nrf2 pathway in STZ-induced INS-1 cells. Activation of p38 MAPK pathway or inhibition of Nrf2 significantly reversed the protective effects of linderane against STZ-induced ROS production and cell apoptosis.

SIGNIFICANCE

The protective effects of linderane on STZ-induced INS-1 cells might be attributed to the inhibition of p38 MAPK and activation of Nrf2 pathway.

Viscothionin purified from mistletoe (Viscum album var. coloratum Ohwi) induces insulin secretion from pancreatic beta cells

ETHNOPHARMACOLOGICAL RELEVANCE

Mistletoe (Viscum album), an evergreen parasitic plant, has been widely used as an oriental phytomedicine to treat diabetes mellitus. However, it is unknown which mistletoe constituent exerts the beneficial effect against the disease. In this study, we examined the hypoglycemic activity of mistletoe and investigated whether the polypeptide viscothionin, purified from mistletoe, was responsible for the activity.

MATERIALS AND METHODS

Mistletoe extracts were prepared by heating mistletoe powder made of leaves and twigs in water for 3, 6, 9, and 12 h. Rat insulinoma RINm5F cells were used to test the cytotoxicity of the extracts and their effects on the secretion of insulin and its precursor, C-peptide. The inhibitory effects of a mistletoe extract on glucose absorption were measured using an α-glucosidase inhibition assay. To determine the component of mistletoe responsible for the observed effects, the mistletoe extract was precipitated with ethanol or hydrolyzed with a protease for further testing. A potential active constituent of mistletoe was isolated by chromatography and molecular weight cut-off fractionation, and its ability to induce insulin secretion was investigated.

RESULTS

A 12-h heat-treated mistletoe extract, showing no cytotoxicity, significantly increased the secretion of insulin and C-peptide by RINm5F cells and enhanced the expression of glucose transporter type 4 (GLUT-4), insulin receptor substrate 1 (IRS-1), and protein kinase B (also known as AKT) in differentiated C2C12 cells. The extract also inhibited α-glucosidase activity. After ethanol precipitation, the extract showed much stronger effects on insulin- and C-peptide-secreting activities of cells, whereas the enzyme-hydrolyzed extract was less effective than the original extract, suggesting that the effect was mediated by a proteinaceous constituent of mistletoe. Subsequent analysis showed that viscothionin, a heat-stable 6-kDa polypeptide isolated from mistletoe, increased the level of insulin secretion by more than 20-fold compared to that induced by the extract.

CONCLUSIONS

Our study indicates that the hypoglycemic effect of mistletoe is mediated by its insulinotropic action and α-glucosidase inhibitory activity, and the effect is due to viscothionin, one of the major bioactive constituents of mistletoe.

Menaquinone-4 Amplified Glucose-Stimulated Insulin Secretion in Isolated Mouse Pancreatic Islets and INS-1 Rat Insulinoma Cells

Vitamin K2 is indispensable for blood coagulation and bone metabolism. Menaquinone-4 (MK-4) is the predominant homolog of vitamin K2, which is present in large amounts in the pancreas, although its function is unclear. Meanwhile, β-cell dysfunction following insulin secretion has been found to decrease in patients with type 2 diabetes mellitus. To elucidate the physiological function of MK-4 in pancreatic β-cells, we studied the effects of MK-4 treatment on isolated mouse pancreatic islets and rat INS-1 cells. Glucose-stimulated insulin secretion significantly increased in isolated islets and INS-1 cells treated with MK-4. It was further clarified that MK-4 enhanced cAMP levels, accompanied by the regulation of the exchange protein directly activated by the cAMP 2 (Epac2)-dependent pathway but not the protein kinase A (PKA)-dependent pathway. A novel function of MK-4 on glucose-stimulated insulin secretion was found, suggesting that MK-4 might act as a potent amplifier of the incretin effect. This study therefore presents a novel potential therapeutic approach for impaired insulinotropic effects.

Heat shock protein B1 is a key mediator of prolactin-induced beta-cell cytoprotection against oxidative stress

Maintaining islet cell viability in vitro, although challenging, appears to be a strategy for improving the outcome of pancreatic islet transplantation. We have shown that prolactin (PRL) leads to beta-cell cytoprotection against apoptosis, an effect mediated by heat shock protein B1 (HSPB1). Since the role of HSPB1 in beta-cells is still unclear and the hormone concentration used is not compatible with clinical applications because of all the side effects displayed by the hormone in other tissues, we explored the molecular mechanisms by which HSPB1 mediates beta-cell cytoprotection. Lysates from PRL- and/or cytokine-treated MIN6 beta-cells were subjected to HSPB1 immunoprecipitation followed by identification through mass spectrometry. PRL-treated cells presented an enrichment of several proteins co-precipitating with HSPB1. Of note were oxidative stress resistance-, protein degradation- and carbohydrate metabolism-related proteins. Wild type, HSPB1 silenced or overexpressing MIN6 cells were exposed to menadione and hydrogen peroxide and analysed for several oxidative stress parameters. HSPB1 knockdown rendered cells more sensitive to oxidative stress and led to a reduced antioxidant capacity, while prolactin induced an HSPB1-mediated cytoprotection against oxidative stress. HSPB1 overexpression, however, led to opposite effects. PRL treatment, HSPB1 silencing or overexpression did not change the expression nor activities of antioxidant enzymes, it also did not lead to a modulation of total glutathione levels nor G6PD expression. However, HSPB1 levels are related to a modulation of GSH/GSSG ratio, G6PD activity and NADPH/NADP ⁺ ratio. We have shown that HSPB1 is important for pro-survival effects against oxidative stress-induced beta-cell death. These results are in accordance with PRL-induced enrichment of HSPB1-interacting proteins related to protection against oxidative stress. Finally, our results outline the need of further studies investigating the importance of HSPB1 for beta-cell viability, since this could lead to the mitigation of beta-cell death through the up-regulation of an endogenous protective pathway.

CD36 dependent redoxosomes promotes ceramide-mediated pancreatic β-cell failure via p66Shc activation

Altered metabolism is implicated in the pathogenesis of beta-cell failure in type 2 diabetes (T2D). Plasma and tissue levels of ceramide species play positive roles in inflammatory and oxidative stress responses in T2D. However, oxidative targets and mechanisms underlying ceramide signaling are unclear. We investigated the role of CD36-dependent redoxosome (redox-active endosome), a membrane-based signaling agent, in ceramide-induced beta-cell dysfunction and failure. Exposure of beta cells to C2-ceramide (N-acetyl-sphingosine) induced a CD36-dependent non-receptor tyrosine kinase Src-mediated redoxosome (Vav2-Rac1-NOX) formation. Activated Rac1-GTP-NADPH oxidase complex induced c-Jun-N-terminal kinase (JNK) activation and nuclear factor (NF)-kB transcription, which was associated with thioredoxin-interacting protein (TXNIP) upregulation and thioredoxin activity suppression. Upregulated JNK expression induced p66Shc serine36 phosphorylation and peroxiredoxin-3 hyperoxidation, causing beta-cell apoptosis via mitochondrial dysfunction. CD36 inhibition by sulfo-N-succinimidyl oleate (SSO) or CD36 siRNA blocked C2-ceramide-induced redoxosome activation, thereby decreasing JNK-dependent p66Shc serine36 phosphorylation. CD36 inhibition downregulated TXNIP expression and promoted thioredoxin activity via enhanced thioredoxin reductase activity, which prevented peroxiredoxin-3 oxidation. CD36 inhibition potentiated glucose-stimulated insulin secretion and prevented beta-cell apoptosis. Our results reveal a new role of CD36 during early molecular events that lead to Src-mediated redoxosome activation, which contributes to ceramide-induced pancreatic beta-cell dysfunction and failure.

Genetic obesity increases pancreatic expression of mitochondrial proteins which regulate cholesterol efflux in BRIN-BD11 insulinoma cells

Pancreatic β-cells are sensitive to fluctuations in cholesterol content, which can damage the insulin secretion pathway, contributing to the aetiology of type 2 diabetes mellitus. Cholesterol efflux to (apo)lipoproteins, via ATP-binding cassette (ABC) transporter A1 (ABCA1), can prevent intracellular cholesterol accumulation; in some peripheral cells, ABCA1-dependent efflux is enhanced by promotion of cholesterol trafficking to, and generation of Liver X receptor (LXR) ligands by, mitochondrial sterol 27-hydroxylase (Cyp27A1 (cytochrome P450 27 A1/sterol 27-hydroxylase)) and its redox partners, adrenodoxin (ADX) and ADX reductase (ADXR). Despite this, the roles of mitochondrial cholesterol trafficking (steroidogenic acute regulatory protein [StAR] and 18-kDa translocator protein [TSPO]) and metabolising proteins in insulin-secreting cells remain wholly uncharacterised. Here, we demonstrate an increase in pancreatic expression of Cyp27A1, ADXR, TSPO and LXRα, but not ADX or StAR, in obese (fa/fa) rodents compared with lean (Fa/?) controls. Overexpression of Cyp27A1 alone in BRIN-BD11 cells increased INS2 expression, without affecting lipid metabolism; however, after exposure to low-density lipoprotein (LDL), cholesterol efflux to (apo)lipoprotein acceptors was enhanced in Cyp27A1-overexpressing cells. Co-transfection of Cyp27A1, ADX and ADXR, at a ratio approximating that in pancreatic tissue, stimulated cholesterol efflux to apolipoprotein A-I (apoA-I) in both basal and cholesterol-loaded cells; insulin release was stimulated equally by all acceptors in cholesterol-loaded cells. Thus, genetic obesity increases pancreatic expression of Cyp27A1, ADXR, TSPO and LXRα, while modulation of Cyp27A1 and its redox partners promotes cholesterol efflux from insulin-secreting cells to acceptor (apo)lipoproteins; this response may help guard against loss of insulin secretion caused by accumulation of excess intracellular cholesterol.

Maternal resistin predisposes offspring to hypothalamic inflammation and body weight gain

Resistin promotes hypothalamic neuroinflammation and insulin resistance through Toll like receptor 4 (TLR4), this hormone is thought to be a link between obesity and insulin-resistance. Indeed, resistin plasma levels are higher in obese and insulin resistant subjects. However, the impact of maternal resistin on the predisposition of offspring to hypothalamic neuroinflammation is unknown. Here, female mice were treated with resistin during gestation/lactation periods, then hypothalamic neuroinflammation was investigated in male offspring at p28 and p90. At p28, resistin increased the expression of inflammation markers (IL6, TNFα and NFκB) and TLR4 in the hypothalamus and decreased both hypothalamic insulin and leptin receptors' expression. The hypothalamic up-regulation IL6, TNFα and TLR4 was sustained until p90 promoting most likely hypothalamic inflammation. Maternal resistin also increased IL6 and TNFα in the adipose tissue of offspring at p90 associated with a higher body weight gain. In contrast, liver and muscle were not affected. These findings reveal that the augmentation of maternal resistin during gestation and lactation promotes hypothalamic and adipose tissue inflammation of offspring as evidenced by sustained increase of inflammation markers from weaning to adulthood. Thus, maternal resistin programs offspring hypothalamic and adipose tissue inflammation predisposing then offspring to body weight gain.

Peptide receptor radionuclide therapy with 177Lu-DOTA-TATE as a promising treatment of malignant insulinoma: a series of case reports and literature review

INTRODUCTION

Insulinomas are a rare type of pancreatic neuroendocrine tumours characterized by insulin hypersecretion. They are considered malignant when metastases are present. Traditional therapies often promote only temporarily symptomatic relief and may be associated with severe adverse effects. There is scarce experience in treating malignant insulinomas with peptide receptors radionuclide therapy (PRRNT).

PATIENTS AND METHODS

We describe PRRNT results in four patients with inoperable malignant insulinomas with poorly controllable hypoglycaemia. All patients received therapy with ¹⁷⁷Lu-DOTA-TATE after conventional therapies failed in controlling disease progression and symptoms. The activity administered per cycle was 4.8-7.4 GBq. The interval between cycles was 10-16 weeks. Haematology, liver and kidney function tests were performed before treatment initiation and 5 and 10 weeks after each cycle.

RESULTS

Patient 1 presented significant clinical benefit for 13 months after PRRNT, with imaging improvement. Patient 2 obtained reduction of the number and severity of hypoglycaemic episodes during 15 months after therapy. Patient 3 is asymptomatic since PRRNT first cycle performed 23 months ago and revealed significant imaging improvement. Patient 4 had resolution of hypoglycaemia only 3 days after PRRNT first cycle and today, 16 months after therapy, the disease seems to be in remission and the patient maintains euglycaemic state. PRRNT was well tolerated, with only hematologic grade 2 toxicity in patient 1 and mild kidney toxicity in patient 3.

CONCLUSIONS

After the start of ¹⁷⁷Lu-DOTA-TATE all patients achieved hypoglycaemia symptomatic control and had evident improvement of their quality of life. Three patients showed imagiological improvement suggesting reduced tumour load.

Creation of versatile cloning platforms for transgene expression and dCas9-based epigenome editing

Genetic manipulation via transgene overexpression, RNAi, or Cas9-based methods is central to biomedical research. Unfortunately, use of these tools is often limited by vector options. We have created a modular platform (pMVP) that allows a gene of interest to be studied in the context of an array of promoters, epitope tags, conditional expression modalities, and fluorescent reporters, packaged in 35 custom destination vectors, including adenovirus, lentivirus, PiggyBac transposon, and Sleeping Beauty transposon, in aggregate >108,000 vector permutations. We also used pMVP to build an epigenetic engineering platform, pMAGIC, that packages multiple gRNAs and either Sa-dCas9 or x-dCas9(3.7) fused to one of five epigenetic modifiers. Importantly, via its compatibility with adenoviral vectors, pMAGIC uniquely enables use of dCas9/LSD1 fusions to interrogate enhancers within primary cells. To demonstrate this, we used pMAGIC to target Sa-dCas9/LSD1 and modify the epigenetic status of a conserved enhancer, resulting in altered expression of the homeobox transcription factor PDX1 and its target genes in pancreatic islets and insulinoma cells. In sum, the pMVP and pMAGIC systems empower researchers to rapidly generate purpose-built, customized vectors for manipulation of gene expression, including via targeted epigenetic modification of regulatory elements in a broad range of disease-relevant cell types.

Bacterial supernatants elevate glucose-dependent insulin secretion in rat pancreatic INS-1 line and islet β-cells via PI3K/AKT signaling

Diabetes and periodontitis are considered associated chronic diseases, and hyperinsulinemia in prediabetes has been shown to be present in normoglycemic animals with periodontitis. As periodontal bacterial species are significant sources of endotoxemia and may directly stimulate insulin secretion, we hypothesized that increased bacterial virulence may exert an adverse effect on rat pancreatic β-cell function via PI3K/AKT signaling. INS-1 cells and isolated pancreatic islets were cultured separately with the following supernatants: Streptococcus anginosus, Streptococcus mutans, Fusobacterium nucleatum, Prevotella intermedia, Porphyromonas gingivalis (P.g), and Treponema denticola (T.d). Supernatants were purified from single bacterial cultures and prepared at different dilutions (100 pg/ml, 50 ng/ml, 200 ng/ml, and 500 ng/ml) to challenge INS-1 and islets. Gene expression (IL-1β, TNFα, IL-6, TLR2, TLR4, Ins1, and Ins2) and insulin secretion were measured. The results showed upregulation of gene expression up to 5.5-fold, not only as a result of the different dilutions used, but also due to bacterial virulence (p < 0.05). P.g and T.d supernatants demonstrated an increase in insulin secretion to fivefold at hypo- and hyperglycemia, yet stimulation from hypo- to hyperglycemia stays in the same ratio. Activation of TLR4/PI3K/AKT signaling by supernatants in INS-1 cells resulted in increased IL-1β, TNFα, IL-6 gene expression levels, and AKT phosphorylation, which were abolished by TLR4 and PI3K/AKT signaling inhibitor. We demonstrated that bacterial supernatants derived from gram-negative species increasingly stimulate insulin secretion in β-cells and TLR4 may promote inflammation by activating the PI3K/AKT signaling pathway to induce pro-inflammatory molecules. Bacterial species, depending on their virulence, appear to play a role in the relationship between periodontitis and prediabetes by promoting insulin resistance and β-cell compensatory response.

Pro-inflammatory cytokines attenuate glucose-stimulated insulin secretion from INS-1E insulinoma cells by restricting mitochondrial pyruvate oxidation capacity - Novel mechanistic insight from real-time analysis of oxidative phosphorylation

Pro-inflammatory cytokines cause pancreatic beta cell failure during the development of type 2 diabetes. This beta cell failure associates with mitochondrial dysfunction, but the precise effects of cytokines on mitochondrial respiration remain unclear. To test the hypothesis that pro-inflammatory cytokines impair glucose-stimulated insulin secretion (GSIS) by inhibiting oxidative ATP synthesis, we probed insulin release and real-time mitochondrial respiration in rat INS-1E insulinoma cells that were exposed to a combination of 2 ng/mL interleukin-1-beta and 50 ng/mL interferon-gamma. We show that 24-h exposure to these cytokines dampens both glucose- and pyruvate-stimulated insulin secretion (P < 0.0001 and P < 0.05, respectively), but does not affect KCl-induced insulin release. Mirroring secretory defects, glucose- and pyruvate-stimulated mitochondrial respiration are lowered after cytokine exposure (P < 0.01). Further analysis confirms that cytokine-induced mitochondrial respiratory defects occur irrespective of whether fuel oxidation is coupled to, or uncoupled from, ATP synthesis. These observations demonstrate that pro-inflammatory cytokines attenuate GSIS by restricting mitochondrial pyruvate oxidation capacity. Interleukin-1-beta and interferon-gamma also increase mitochondrial superoxide levels (P < 0.05), which may reinforce the inhibition of pyruvate oxidation, and cause a modest (20%) but significant (P < 0.01) loss of INS-1E cells. Cytokine-induced INS-1E cell failure is insensitive to palmitoleate and linoleate, which is at odds with the cytoprotection offered by unsaturated fatty acids against harm caused by nutrient excess. Our data disclose a mitochondrial mechanism for cytokine-impaired GSIS in INS-1E cells, and suggest that inflammatory and nutrient-related beta cell failure emerge, at least partly, through distinct paths.

Biphasic voltage-dependent inactivation of human NaV 1.3, 1.6 and 1.7 Na+ channels expressed in rodent insulin-secreting cells

KEY POINTS

Na+ current inactivation is biphasic in insulin-secreting cells, proceeding with two voltage dependences that are half-maximal at ∼-100 mV and -60 mV. Inactivation of voltage-gated Na+ (NaV ) channels occurs at ∼30 mV more negative voltages in insulin-secreting Ins1 and primary β-cells than in HEK, CHO or glucagon-secreting αTC1-6 cells. The difference in inactivation between Ins1 and non-β-cells persists in the inside-out patch configuration, discounting an involvement of a diffusible factor. In Ins1 cells and primary β-cells, but not in HEK cells, inactivation of a single NaV subtype is biphasic and follows two voltage dependences separated by 30-40 mV. We propose that NaV channels adopt different inactivation behaviours depending on the local membrane environment.

ABSTRACT

Pancreatic β-cells are equipped with voltage-gated Na+ channels that undergo biphasic voltage-dependent steady-state inactivation. A small Na+ current component (10-15%) inactivates over physiological membrane potentials and contributes to action potential firing. However, the major Na+ channel component is completely inactivated at -90 to -80 mV and is therefore inactive in the β-cell. It has been proposed that the biphasic inactivation reflects the contribution of different NaV α-subunits. We tested this possibility by expression of TTX-resistant variants of the NaV subunits found in β-cells (NaV 1.3, NaV 1.6 and NaV 1.7) in insulin-secreting Ins1 cells and in non-β-cells (including HEK and CHO cells). We found that all NaV subunits inactivated at 20-30 mV more negative membrane potentials in Ins1 cells than in HEK or CHO cells. The more negative inactivation in Ins1 cells does not involve a diffusible intracellular factor because the difference between Ins1 and CHO persisted after excision of the membrane. NaV 1.7 inactivated at 15--20 mV more negative membrane potentials than NaV 1.3 and NaV 1.6 in Ins1 cells but this small difference is insufficient to solely explain the biphasic inactivation in Ins1 cells. In Ins1 cells, but never in the other cell types, widely different components of NaV inactivation (separated by 30 mV) were also observed following expression of a single type of NaV α-subunit. The more positive component exhibited a voltage dependence of inactivation similar to that found in HEK and CHO cells. We propose that biphasic NaV inactivation in insulin-secreting cells reflects insertion of channels in membrane domains that differ with regard to lipid and/or membrane protein composition.

Nfe2l1-silenced insulinoma cells acquire aggressiveness and chemoresistance

The transcription factor nuclear factor erythroid 2-like 1 (NFE2L1 or NRF1) is involved in various critical cell processes such as maintenance of ubiquitin-proteasome system and regulation of the cellular antioxidant response. We previously determined that pancreatic β-cell-specific Nfe2l1-knockout mice had hyperinsulinemia and that silencing of Nfe2l1 in mouse islets or MIN6 insulinoma β-cells induced elevated basal insulin release and altered glucose metabolism. Hypoglycemia is a major issue with aggressive insulinomas, although a role of NFE2L1 in this pathology is not defined. In the present work, we studied the tumorigenicity of Nfe2l1-deficient insulinoma MIN6 cells (Nfe2l1-KD) and sensitivity to chemotherapy. Nfe2l1-KD cells grew faster and were more aggressive than Scramble cells in vitro In a mouse allograft transplantation model, insulinomas arising from Nfe2l1-KD cells were more aggressive and chemoresistant. The conclusion was amplified using streptozotocin (STZ) administration in an allograft transplantation model in diabetic Akita background mice. Furthermore, Nfe2l1-KD cells were resistant to damage by the chemotherapeutic drugs STZ and 5-fluorouracil, which was linked to binding of hexokinase 1 with mitochondria, enhanced mitochondrial membrane potential and closed mitochondrial potential transition pore. Overall, both in vitro and in vivo data from Nfe2l1-KD insulinoma cells provided evidence of a previously un-appreciated action of NFE2L1 in suppression of tumorigenesis. Nfe2l1 silencing desensitizes insulinoma cells and derived tumors to chemotherapeutic-induced damage, likely via metabolic reprograming. These data indicate that NFE2L1 could potentially play an important role in the carcinogenic process and impact chemosensitivity, at least within a subset of pancreatic endocrine tumors.

Identification of Components in Frog Skin Secretions with Therapeutic Potential as Antidiabetic Agents

Several peptides that were first identified on the basis of their antimicrobial or immunomodulatory properties have subsequently shown potential for development into agents for the treatment of patients with Type 2 diabetes. A strategy is presented for the isolation and characterization of such peptides in norepinephrine-stimulated skin secretions from a range of frog species. The methodology involves fractionation of the secretions by reversed-phase HPLC, identification of fractions containing components that stimulate the rate of release of insulin from BRIN-BD11 clonal β-cells without simultaneously stimulating the release of lactate dehydrogenase, identification of active peptides in the mass range 1-6 kDa by MALDI-TOF mass spectrometry, purification of the peptides to near homogeneity by further HPLC, and structural characterization by automated Edman degradation. The effect of synthetic replicates of the active peptides on glucose homeostasis in vivo may be evaluated in mice fed a high fat diet to produce obesity, glucose intolerance, and insulin resistance.

Optical Recording of Cellular Zinc Dynamics with Zinc-Finger-Based Biosensors

In addition to serving as an essential structural component, zinc is also involved in intracellular and intercellular signaling pathways to impact a number of cellular functions. Genetically encoded zinc sensors that are specifically targeted to various subcellular compartments (ER, mitochondria, nucleus, plasma membrane, and vesicles) have been proven to provide accurate and sensitive visualization and quantification of zinc. Here we describe the methods to utilize both ratiometric and intensiometric genetically encoded zinc sensors designed based on zinc fingers for imaging and quantification of cellular free, labile zinc concentrations, [Zn²⁺]_free. This chapter explains in detail how to quantify [Zn²⁺]_free in live cells as well as how to monitor zinc influx in INS-1 cells stimulated with high glucose.

[Over-expression of thioredoxin-interacting protein promotes apoptosis of MIN6 cells via activating p38MAPK pathway]

Objective To investigate the effect of thioredoxin interacting protein (TXNIP) over-expression on the apoptosis of MIN6 β-cells and the mechanism involved. Methods Lentivirus carrying TXNIP gene was used to infect MIN6 β-cells in logarithmic growth phase, and the infection efficiency was evaluated by fluorescence microscope and Western blotting. Then MIN6 β-cells were divided into three groups: control group, empty lentivirus vector (LV-GFP) group and TXNIP over-expression (LV-GFP-TXNIP) group. CCK-8 assay was used to detect cell proliferation. AnnexinV-FITC/PI double staining was utilized to measure the apoptosis of MIN6 cells. Western blotting was applied to detect the expressions of TXNIP protein, TRX, Bax, Bcl2, cleaved caspase-3 (c-caspase-3), p38 mitogen-activated protein kinase (p38MAPK), phospho-p38MAPK (p-p38MAPK) proteins in the MIN6 β-cells before and after treated with p38MAPK inhibitor SP169316. Results At 72 hours after the infection, the infection rate reached (87.10±2.30)% and (92.21±0.54)% in LV-GFP group and LV-GFP-TXNIP group, respectively, suggesting that lentivirus-mediated TXNIP over-expression was desirable. Compared with control group and LV-GFP group, the cell viability markedly decreased, and cell apoptosis, Bax/Bcl2 ratio, expression of c-caspased-3 and p38MAPK phosphorylation significantly increased in LV-GFP-TXNIP group. However, both the Bax/Bcl2 ratio and c-caspase-3 protein expression in LV-GFP-TXNIP group were obviously reduced after treated with p38MAPK inhibitor. Conclusion TXNIP over-expression might promote the apoptosis of MIN6 cells via activating the p38 MAPK pathway.

Evaluation of neurotensin receptor 1 as a potential imaging target in pancreatic ductal adenocarcinoma

Pancreatic cancer is one of the deadliest human malignancies and lack of effective diagnostic and therapeutic methods. Accumulating evidence suggests that the neurotensin (NT) and neurotensin receptors (NTRs) play key roles in pancreatic adenocarcinoma growth and survival. In this study, we not only evaluate the NTR1 expression in pancreatic cancer patient samples, but also explore the PET and fluorescence imaging of NTR1 expression in pancreatic cancer animal models. The NTR1 expression was evaluated by immunohistochemistry staining in clinical patient tissue samples with pancreatic ductal adenocarcinoma, insulinoma, and pancreatitis. The results showed 79.4% positive rate of NRT1 expression in pancreatic ductal adenocarcinoma, compared with 33.3 and 22.7% in insulinoma and pancreatitis samples, respectively. High NTR1 gene expression was also found in Panc-1 cells and confirmed by cell immunofluorescence. 64Cu-AmBaSar-NT and IRDye800-NT were synthesized as imaging probes and maintained the majority of NTR1-binding affinity. In vivo imaging demonstrated that 64Cu-AmBaSar-NT has prominent tumor uptake (3.76 ± 1.45 and 2.29 ± 0.10%ID/g at 1 and 4 h post-injection). NIR fluorescent imaging with IRDye800-NT demonstrated good tumor-to-background contrast (8.09 ± 0.38 × 108 and 6.67 ± 0.43 × 108 (p/s/cm2/sr)/(μW/cm2) at 30 and 60 min post-injection). Fluorescence guided surgery was also performed as a proof of principle experiment. In summary, our results indicated that NTR1 is a promising target for pancreatic ductal adenocarcinoma imaging and therapy. The imaging probes reported here may not only be considered for improved diagnosis of pancreatic ductal adenocarcinoma, but also has the potential to be fully integrated into patient screening and treatment monitoring of future NTR1 targeted therapies.

Embedded-Culture of Pancreatic β-Cells Derived from Transgenic Mouse Insulinoma as a Potential Source for Xenotransplantation using a Diffusion Chamber

Embedded-culture of pancreatic β-cells derived from a transgenic mouse insulinoma (MIN6 cells) was studied in vitro and in vivo. The MIN6 cells were enmeshed in an agarose-PVMA-collagen matrix for long-term maintenance. The cells formed islet-like cell clusters (ICCs) in the mixed matrix. When 10 mmol/L nicotinamide was added to these cultures the cells secreted insulin in response to various concentrations of glucose, whereas the untreated control cells were unresponsive. Both control and nicotinamide-treated MIN6 cells exhibited normal β-cell function for up to 35 days in the mixed matrix, and the cells were much better preserved with nicotinamide than without it. MIN6 cells were suspended in the mixed matrix with nicotinamide and transferred into diffusion chambers to create a bio-artificial endocrine pancreas (Bio-AEP). In streptozotocine-induced diabetic rats with implanted Bio-AEP but without any immunosuppressants, a return to normoglycaemia was observed for up to 12 wk or more after transplantation. Our results indicate that nicotinamide-treated MIN6 cells embedded in a mixed matrix should be useful for the study of xenotransplantation and the development of a bioartificial endocrine pancreas.

Retrovirally Transferred Genes Inhibit Apoptosis in an Insulin-Secreting Cell Line: Implications for Islet Transplantation

The transplantation of pancreatic islets for the treatment of type I diabetes is hindered by the enormous loss of cells due to early apoptotic events. Genetic engineering of islets with cytoprotective genes is an important strategy aimed to enhance the survival of these cells in the transplant setting. The present study was designed to evaluate and compare the effects of five genes on a cell line derived from insulin-producing β-cells, NIT-1. Cells were transduced using a Maloney murine leukemia virus (MLV) vector coding for yellow fluorescent protein (YFP) and for one of the following antiapoptotic genes: cFLIP, FADD-DN, BcL-2, PI-9, and ICAM-2. These genes were able to protect NIT-1 cells from cytokine-induced apoptosis to varying degrees ranging from no protection to significant protection equivalent to an optimal dose of a chemical caspase inhibitor. The data demonstrate that cFLIP, FADD-DN, and PI-9 are significantly more effective in protecting NIT-1 cells than BcL-2 and ICAM-2. Additionally, the data show that despite its weak in vitro inhibition of caspase-3, PI-9 affords significant protection against TNF-α-induced apoptosis in these cells. These genes may be ideal candidates to augment islet survival following transplantation.

Intrasplenic Transplantation of Encapsulated Genetically Engineered Mouse Insulinoma Cells Reverses Streptozotocin-Induced Diabetes in Rats

Pancreatic islet transplantation is limited by shortage of donor organs. Although β-cell lines could be used, their secretion of insulin is characteristically glucose independent and immunoisolation is required. Here we show that intrasplenic transplantation of encapsulated glucose-responsive mouse insulinoma cells reversed streptozotocin (STZ)-induced diabetes in rats. MIN-6 cells derived from a transgenic mouse expressing SV 40 large T antigen in pancreatic β-cells were transfected with minigene encoding for human glucagon-like-peptide-1 under the control of rat insulin promoter. The cells were encapsulated in alginate/poly-L-lysine and used for cell transplantation in STZ-diabetic rats. Rats with nonfasting blood glucose (n-FBG) greater than 350 mg/dl were used. In group I rats (n = 6) 20 million encapsulated cells were injected into the spleen. Group II rats (n = 6) received empty capsules. n-FBG was measured biweekly. After 4 and 8 weeks, an intraperitoneal glucose tolerance test (IPGTT) was performed in group I; normal rats served as controls. Plasma insulin level was measured every other week (RIA). After 8 weeks, spleens were removed 1 day before sacrifice. In rats transplanted with cells the n-FBG was 100—150 mg/dl until the end of the study. After splenectomy, all cell recipients became diabetic (glucose 400 ± 20 mg/dl). Transplanted rats showed increase in body weight and insulin production (3.3 ± 1.0 ng/ml versus 0.92 ± 0.3 ng/ml; p < 0.01) and had normal IPGTT. Spleens contained capsules with insulin-positive cells. Overall, data from this work indicate that intrasplenic transplantation of xenogeneic encapsulated insulin-producing cells without immunosuppression reversed diabetes in rats. Excellent survival and function of the transplanted cells was due to the fact that the cells were separated from the bloodstream by the immunoisolatory membrane only and insulin was delivered directly to the liver (i.e., in a physiological manner).

ANTHROPOMETRIC FEATURES ARE NOT PREDICTIVE OF 72-HOUR FAST DURATION IN INSULINOMAS

OBJECTIVE

The 72-hour fast is used to document Whipple's triad and understand the mechanism of hypoglycemia. Although hypoglycemia develops within 24 hours in the majority of fasts, identifying possible determinants of fast duration may help to predict the need for admission. Therefore, we determined the relation between anthropometric features on fast duration and assessed end of fast parameters on maximal tumor size, extent of disease, or tumor recurrence.

METHODS

A retrospective analysis of patients with insulinoma in the past 25 years who underwent a 72-hour fast was conducted. Electronic medical records were reviewed to obtain anthropometric patient data and tumor characteristics.

RESULTS

A total of 233 patients underwent the 72-hour fast. The mean age at diagnosis was 50 ± 16 years, with a body mass index (BMI) of 29 ± 7 kg/m², and 66% (153 of 233) were female. Duration of fast was not associated with gender (P = .2), age (P = .3), or BMI (P = .7). A shorter fast duration was inversely related to end of fast C-peptide (P = .0075) but not insulin (P = .13) or proinsulin (P = .28) concentration. End of fast C-peptide was associated with increased tumor size (P = .036) and multiplicity (P =.01). Proinsulin was associated with increased tumor size (P<.01) and malignancy (P = .018).

CONCLUSION

Duration of fast was not significantly related age, gender, weight, or BMI, although end-of-fast C-peptide and proinsulin may provide some information regarding tumor characteristics. Consequently, the duration of fast cannot be predicted a priori and should be allowed to run for the planned length unless hypoglycemia develops. Abbreviation: BMI = body mass index.

Geniposide accelerates proteasome degradation of Txnip to inhibit insulin secretion in pancreatic β-cells

PURPOSE

To analyze the role of geniposide in the protein degradation of Txnip and to determine the impact of Txnip on geniposide-regulated GSIS in pancreatic INS-1 cells.

METHODS

The content of Txnip protein was measured by western blot; insulin content and glucose uptake were determined by ELISA; and knockdown of Txnip was the method of RNA interference.

RESULTS

Glucose induces a rapid increase in Txnip protein, and geniposide accelerates the degradation of Txnip via proteasome pathway in the presence of high glucose (25 mM) in INS-1 pancreatic β-cells. And MG132, a proteasomal inhibitor, potentiates glucose uptake, metabolism (ATP production) and glucose-stimulated insulin secretion (GSIS) in high-glucose (25 mM)-treated INS-1 cells, but geniposide significantly prevents these effects. Furthermore, the combination of geniposide and Txnip knockdown shows substantial synergistic effects to reduce glucose uptake, metabolism and GSIS in high-glucose (25 mM)-treated INS-1 cells.

CONCLUSIONS

Txnip protein played an essential role in glucose uptake, metabolism and GSIS, and geniposide could accelerate the degradation via proteasome pathway in high-glucose-treated pancreatic INS-1 cells.

Baicalein protects rat insulinoma INS-1 cells from palmitate-induced lipotoxicity by inducing HO-1

Objective

β-Cell dysfunction plays a central role in the pathogenesis of type 2 diabetes (T2D), and the identification of novel approaches to improve β-cell function is essential to treat this disease. Baicalein, a flavonoid originally isolated from the root of Scutellaria Baicalensis, has been shown to have beneficial effects on β-cell function. Here, the authors investigated the molecular mechanism responsible for the protective effects of baicalein against palmitate (PA)-induced impaired β-cell function, and placed focus on the role of heme oxygenase (HO)-1.

Methods

Rat pancreatic β-cell line INS-1 cells or mouse pancreatic islets were cultured with PA (500 μM) to induce lipotoxicity in the presence or absence of baicalein (50 μM), and the expressions of the ER stress markers, ATF-3, CHOP and GRP78 were detected by Western blotting and/or qPCR. The involvement of HO-1 was evaluated by HO-1 siRNA transfection and using the HO-1 inhibitor ZnPP.

Results

Baicalein reduced PA-induced ER stress and inflammation and enhanced insulin secretion, and these effects were associated with the induction of HO-1. Furthermore, these protective effects were attenuated by ZnPP and by HO-1 siRNA. Pretreatment of PD98059 (an ERK inhibitor) significantly inhibited the protective effects of baicalein and blocked HO-1 induction. On the other hand, CO production by RuCO (a CO donor) ameliorated PA-induced ER stress, suggesting that CO production followed by HO-1 induction may contribute to the protective effects of baicalein against PA-induced β-cell dysfunction.

Conclusion

Baicalein protects pancreatic β-cells from PA-induced ER stress and inflammation via an ERK-HO-1 dependent pathway. The authors suggest HO-1 induction in pancreatic β-cells appears to be a promising therapeutic strategy for T2D.

DPP-4 (CD26) inhibitor sitagliptin exerts anti-inflammatory effects on rat insulinoma (RINm) cells via suppressing NF-κB activation

Dipeptidyl peptidase-4 (CD26), a cell surface glycoprotein, is expressed by a variety of cells. It has been shown that dipeptidyl peptidase-4 (CD26) is involved in T cell activation. Nonetheless, its role in inflammatory effects in islet β cells has not been well investigated. In this study, we used sitagliptin, a classic inhibitor of dipeptidyl peptidase-4 (CD26), to research the effect of dipeptidyl peptidase-4 (CD26) on the activation of NF-κB, the expression of inflammatory cytokines, and cell apoptosis in rat insulinoma cells. Results showed that dipeptidyl peptidase-4 (CD26) was expressed on the surface of rat insulinoma cells. Lipopolysaccharide-induced NF-κB activation and expression of inflammatory cytokines were suppressed by sitagliptin treatment in rat insulinoma cells. Furthermore, sitagliptin treatment reduced cell apoptosis stimulated by lipopolysaccharide. Taken together, this study showed for the first time that sitagliptin suppressed NF-κB activation and inflammatory cytokines expression in rat insulinoma cells, suggesting that the dipeptidyl peptidase-4 inhibitor may exert direct anti-inflammatory effects in islet β cells.