Islet Amyloid Deposits Research Articles

Use of the PET ligand florbetapir for in vivo imaging of pancreatic islet amyloid deposits in hIAPP transgenic mice.

Islet amyloid deposits contribute to beta cell dysfunction and death in most individuals with type 2 diabetes but non-invasive methods to determine the presence of these pathological protein aggregates are currently not available. Therefore, we examined whether florbetapir, a radiopharmaceutical agent used for detection of amyloid-β deposits in the brain, also allows identification of islet amyloid in the pancreas. Saturation binding assays were used to determine the affinity of florbetapir for human islet amyloid polypeptide (hIAPP) aggregates in vitro. Islet amyloid-prone transgenic mice that express hIAPP in their beta cells and amyloid-free non-transgenic control mice were used to examine the ability of florbetapir to detect islet amyloid deposits in vitro, in vivo and ex vivo. Mice or mouse pancreases were subjected to autoradiographic, histochemical and/or positron emission tomography (PET) analyses to assess the utility of florbetapir in identifying islet amyloid. In vitro, florbetapir bound synthetic hIAPP fibrils with a dissociation constant of 7.9nmol/l. Additionally, florbetapir bound preferentially to amyloid-containing hIAPP transgenic vs amyloid-free non-transgenic mouse pancreas sections in vitro, as determined by autoradiography (16,475 ± 5581 vs 5762 ± 575 density/unit area, p < 0.05). In hIAPP transgenic and non-transgenic mice fed a high-fat diet for 1year, intravenous administration of florbetapir followed by PET scanning showed that the florbetapir signal was significantly higher in amyloid-laden hIAPP transgenic vs amyloid-free non-transgenic pancreases in vivo during the first 5min of the scan (36.83 ± 2.22 vs 29.34 ± 2.03 standardised uptake value × min, p < 0.05). Following PET, pancreases were excised and florbetapir uptake was determined ex vivo by γ counting. Pancreatic uptake of florbetapir was significantly correlated with the degree of islet amyloid deposition, the latter assessed by histochemistry (r = 0.74, p < 0.001). Florbetapir binds to islet amyloid deposits in a specific and quantitative manner. In the future, florbetapir may be useful as a non-invasive tool to identify islet amyloid deposits in humans.

Tissue Plasminogen Activator (tPA) Expression Is Increased by Islet Amyloid Formation In Vitro

Islet amyloid deposition is a pathologic hallmark of type 2 diabetes (T2D) resulting in β-cell loss. tPA, an activator of fibrinolysis, attenuates brain amyloid deposition associated with Alzheimer’s disease. Based on RNAseq analysis to identify genes upregulated by islet amyloid, we found tPA to be specifically increased in islets with amyloid deposition (FDR=6.23 E-40). We therefore determined whether tPA expression is explicitly regulated by islet amyloid formation and thus could impact islet pathology in T2D. Using a transgenic mouse expressing human islet amyloid polypeptide (hIAPP) in β cells, a model of islet amyloid formation, and mice expressing non-amyloidogenic mouse IAPP (mIAPP) as control, we measured tPA mRNA expression in islets during amyloid formation. Isolated islets were cultured for up to 7 days in 11.1 or 16.7 mM glucose, the latter to induce amyloid deposition in hIAPP islets. Under amyloidogenic conditions, tPA gene expression increased 2-fold after 2 days of culture and was further elevated at 7 days in hIAPP compared to mIAPP islets (7.6±1.4 vs. 1.2±0.1, n=4, p&amp;lt;0.001). This increase at 7 days was not observed in hIAPP islets cultured under non-amyloidogenic conditions (1.1±0.5 vs. 7.6±1.4 in 11.1 vs. 16.7 mM glucose, respectively, n=4, p&amp;lt;0.001). When cultured in 16.7 mM glucose with an amyloid inhibitor (200 μM Congo Red [CR]), tPA gene expression was abrogated in hIAPP transgenic islets (1.5±0.14 vs. 9.5±0.33 with or without CR, respectively, n=4, p&amp;lt;0.001), implying tPA gene expression is regulated downstream of amyloid formation. Immunoblot confirmed the presence of tPA protein in islets but not in a β-cell line, and islet immunohistochemistry showed it did not co-localize with insulin, suggesting it is likely that tPA is not produced in β cells. In summary, we identified the fibrinolytic activator tPA to be upregulated with amyloid formation in islets. Thus, modulating tPA expression could reduce the deleterious impact of islet amyloid on β-cell mass in T2D. Disclosure N. Esser: None. M.F. Hogan: None. A.T. Templin: None. M. Ziemann: None. A. El-Osta: None. S. Zraika: None. R.L. Hull: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company. S.E. Kahn: Advisory Panel; Self; Boehringer Ingelheim GmbH, Elcelyx Therapeutics, Inc., Eli Lilly and Company, Intarcia Therapeutics, Inc., Janssen Research &amp; Development, Merck &amp; Co., Inc., Novo Nordisk A/S.

Evidence for Necroptosis as a Mechanism of Islet Amyloid–Induced Beta-Cell Death

Islet amyloid deposition occurs in the majority of individuals with type 2 diabetes (T2D) and contributes to beta-cell death by mechanisms which are not fully understood. Necroptosis is an immunogenic form of cell death dependent on tumor necrosis factor receptor 1 (TNFR1) signaling, receptor interacting protein kinase 3 (RIPK3) oligomerization, and mixed lineage kinase domain-like (MLKL) phosphorylation. We previously showed mRNA and protein levels of TNFa, a TNFR1 ligand, are increased in islets by amyloid deposition in vitro and in vivo, raising the possibility that amyloid formation induces necroptosis. Thus, we sought to determine whether the components of necroptosis are present in beta cells, and if islet amyloid-induced TNFa expression elicits beta-cell necroptosis. We observed protein expression of TNFR1, RIPK3, and MLKL in the INS-1 beta-cell line, indicating necroptosis components are present in beta cells. In human islet amyloid polypeptide (hIAPP) transgenic mouse islets cultured in 16.7 mM glucose, an in vitro model of islet amyloidosis, we found necroptosis signaling to be increased compared to amyloid-free wild type (WT) islets. This manifested as increased oligomerization of RIPK3 protein (trimers: 2.7 ± 0.2 [hIAPP] vs. 1.0 [WT], n=3, p&amp;lt;0.01) and phosphorylation of the RIPK3 target MLKL (1.8 ± 0.3 vs. 1.0, n=3, p=0.06), without a change in TNFR1 protein expression (1.1 ± 0.1 vs. 1.0, n=2, p=0.74). As further support that amyloid induces immunogenic cell death, immune cell mRNA abundance was increased in vivo in amyloid containing hIAPP transgenic islets vs. WT islets (macrophages: Emr1, 1.6 ± 0.2 [hIAPP] vs. 1.1 ± 0.1 [WT], n=4, p=0.04, T cells: Cd3, 2.7 ± 0.5 vs. 1.0 ± 0.2, n=4, p=0.03, and B cells: Cd20, 2.3 ± 0.2 vs. 1.2 ± 0.5, n=2, p=0.17). These data suggest that necroptosis may be a previously unrecognized mechanism of beta-cell death in response to islet amyloid formation. Further studies are needed to determine whether inhibition of necroptosis signaling may reduce beta-cell death in T2D. Disclosure A.T. Templin: None. M.F. Hogan: None. N. Esser: None. S. Zraika: None. R.L. Hull: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company. S.E. Kahn: Advisory Panel; Self; Boehringer Ingelheim GmbH, Elcelyx Therapeutics, Inc., Eli Lilly and Company, Intarcia Therapeutics, Inc., Janssen Research &amp; Development, Merck &amp; Co., Inc., Novo Nordisk A/S.

A pilot study of pancreatic islet amyloid PET imaging with [18F]FDDNP.

ObjectivesPancreatic islet amyloid deposition occurs before β-cell damage in type 2 diabetes mellitus patients. The islet and Alzheimer’s disease β-amyloid shares similar secondary structures. The Alzheimer’s disease β-amyloid targeting tracer [18F]FDDNP could be used to image pancreatic islet amyloid with PET.Patients and methodsConsecutive pancreatic tissue sections from a 69-year-old male type 2 diabetes mellitus patient were stained by hematoxylin and eosin, anti-amylin antibody, Congo Red, periodic acid-Schiff, and [18F]FDDNP reference compound, respectively. The pancreatic tissue sections were also incubated with [18F]FDDNP with and without its reference compound for autoradiography. Subsequently, we performed control [18F]FDDNP pancreatic PET/CT imaging in four healthy individuals. The mean standardized uptake values of [18F]FDDNP uptake in the pancreatic head, neck, body, and tail, blood pool, liver, and vertebral bone from 5 to 120 min after injection were determined.ResultsIslet amyloid was observed in all four standard staining methods in the pancreas tissue. Similar islet amyloid distribution and phenotypes were observed clearly in the [18F]FDDNP reference compound-stained pancreas tissue. [18F]FDDNP was intensively accumulated in the same pancreatic tissue in autoradiography, which was largely blocked by its reference compound. In the PET/CT scans of control human participants, the mean standardized uptake values in pancreas decreased to the blood pool level in 30 min and all parts of the pancreas had similar [18F]FDDNP uptake. The pancreas could be distinguished clearly from the liver at all-time points.ConclusionThese results suggested that [18F]FDDNP is a potential tracer for pancreatic islet amyloid PET imaging.

Inhibition of Human Amylin Aggregation and Cellular Toxicity by Lipoic Acid and Ascorbic Acid.

More than 30 human degenerative diseases result from protein aggregation such as Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). Islet amyloid deposits, a hallmark in T2DM, are found in pancreatic islets of more than 90% of T2DM patients. An association between amylin aggregation and reduction in β-cell mass was also established by post-mortem studies. A strategy in preventing protein aggregation-related disorders is to inhibit the protein aggregation and associated toxicity. In this study, we demonstrated that two inhibitors, lipoic acid and ascorbic acid, significantly inhibited amylin aggregation. Compared to amylin (15 μM) as 100%, lipoic acid and ascorbic acid reduced amylin fibril formation to 42.1 ± 17.2% and 42.9 ± 12.8%, respectively, which is confirmed by fluorescence and TEM images. In cell viability tests, both inhibitors protected RIN-m5f β-cells from the toxicity of amylin aggregates. At 10:1 molar ratio of lipoic acid to amylin, lipoic acid with amylin increased the cell viability to 70.3%, whereas only 42.8% RIN-m5f β-cells survived in amylin aggregates. For ascorbic acid, an equimolar ratio achieved the highest cell viability of 63.3% as compared to 42.8% with amylin aggregates only. Docking results showed that lipoic acid and ascorbic acid physically interact with amylin amyloidogenic region (residues Ser20-Ser29) via hydrophobic interactions; hence reducing aggregation levels. Therefore, lipoic acid and ascorbic acid prevented amylin aggregation via hydrophobic interactions, which resulted in the prevention of cell toxicity in vitro.

Characterization of Dog, Cat, Guinea Pig, and Human IAPP toxicity in HeLa cells

Type 2 diabetes is one of the leading causes of death in the U.S. Type 2 Diabetes is the most generic form of diabetes, where your body suffers from insulin resistance. Islet Amyloid Polypeptide (IAPP) is a regulatory peptide which inhibits glucagon and insulin secretion. The aggregation of IAPP is present in pancreatic islet amyloid deposits seen especially in Type 2 diabetes in humans and other mammalian species. Our objective was to see how the changes in IAPP sequence correlates to the toxicity of IAPP on mammalian cells. Here, we focus on dog, cat, and guinea pig IAPP. Molecular techniques such as MTT assay and LDH Cytotoxicity assay were used to test the effect animal IAPP has on HeLa cells. As well as to see the effect mixing human and animal IAPP has on the HeLa cells. MTT assay results showed that the animal IAPP volumes had no significant effect on mammalian cell viability while the human IAPP was consistently toxic to the cells. Cell viability percentages stayed relatively constant despite increasing IAPP volume. In comparison, human IAPP showed a decreasing cell viability trend with increasing IAPP volume. However, when dog IAPP and human IAPP were mixed, cell viability was increased. The same effect occurred with the mixing of cat IAPP and human IAPP. LDH Cytotoxicity assay results showed that percent toxicity increased with increasing IAPP volumes for human, cat and guinea pig. Dog IAPP cell toxicity stayed constant as IAPP volume increased. When dog IAPP and cat IAPP were separately mixed with human IAPP, a decrease in cell toxicity is seen. Mixing guinea pig IAPP with human IAPP had no effect on cell viability or cell toxicity. Further experiments are necessary to determine a correlation between these specific animal IAPPs and cell toxicity.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The IAPP Toxicity on Rats, Raccoons and Degus in HeLa Cells

Type 2 diabetes is the most common form of diabetes, where the body suffers from insulin resistance. The islet amyloid polypeptide (IAPP) is a secretory product of beta cells in pancreatic islets of Langerhans that also inhibits glucagon and insulin secretion. The aggregation of IAPP is present in pancreatic islet amyloid deposits seen especially in Type 2 diabetes, in humans and other mammalian species. The objective of this study was to determine the effects of the animal toxicity on mammalian cells. In this work, the human IAPP sequence and the effect on mammalian cells was compared to the IAPP from degu, rat, and raccoon. Molecular techniques such as MTT and LDH Cytotoxicity assay were used to test the effect of human and animal IAPP on HeLa cells. The MTT results show a consistent drop in cell viability as the concentration of IAPP from a human, degu, rat and raccoon increases. LDH cytotoxicity shows the highest toxicity in human IAPP compared to the rest of the studied animals. Although when mixing both the human and animal IAPPs, the toxicity of the human IAPP decreased whereas the viability had no significant effect. Further molecular analysis is necessary to determine the correlation between animal IAPP toxicity and the incidence of Type 2 diabetes.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Islet Interleukin-1β Immunoreactivity Is an Early Feature of Cystic Fibrosis That May Contribute to β-Cell Failure.

Cystic fibrosis-related diabetes (CFRD) is a common complication of cystic fibrosis (CF), increasing patient morbidity and mortality. Poor understanding of CFRD pathogenesis limits the development of targeted therapies to treat and/or prevent the disease. The aim of this study was to evaluate islet pathology, specifically, inflammation, amyloid deposition, and endocrine cell composition in subjects with CF with diabetes and with CF without diabetes. A retrospective analysis of archived pancreas tissue collected at autopsy was conducted using pancreas tissue from subjects with CF and diabetes (CFRD) (n = 18) and CF without diabetes (CF-no DM) (n = 17). Two cohorts of control non-CF subjects were identified, each matched to CFRD and CF-no DM subjects for age, sex, and BMI (non-CF older, n = 20, and non-CF younger, n = 20), respectively. Immunohistochemistry was performed to assess interleukin-1β (IL-1β) and islet hormone (insulin, glucagon, somatostatin, and pancreatic polypeptide) immunoreactivity; histochemistry was performed to quantify amyloid deposition. Islet IL-1β immunoreactivity was substantially increased in both CFRD and CF-no DM subjects compared with non-CF subjects and was common in young subjects with CF (≤10 years of age). In contrast, islet amyloid deposition was increased only in CFRD subjects. We also observe abnormal islet hormone immunoreactivity, characterized by increased glucagon immunoreactivity, in CF-no DM and CFRD subjects compared with non-CF subjects. These findings reveal novel molecular pathways and therapeutic targets underlying islet pathology in CF subjects and may be important in developing new approaches to treat CFRD.

Amyloid-induced β-cell dysfunction and islet inflammation are ameliorated by 4-phenylbutyrate (PBA) treatment.

Human islet amyloid polypeptide (hIAPP) aggregation is associated with β-cell dysfunction and death in type 2 diabetes (T2D). we aimed to determine whether in vivo treatment with chemical chaperone 4-phenylbutyrate (PBA) ameliorates hIAPP-induced β-cell dysfunction and islet amyloid formation. Oral administration of PBA in hIAPP transgenic (hIAPP Tg) mice expressing hIAPP in pancreatic β cells counteracted impaired glucose homeostasis and restored glucose-stimulated insulin secretion. Moreover, PBA treatment almost completely prevented the transcriptomic alterations observed in hIAPP Tg islets, including the induction of genes related to inflammation. PBA also increased β-cell viability and improved insulin secretion in hIAPP Tg islets cultured under glucolipotoxic conditions. Strikingly, PBA not only prevented but even reversed islet amyloid deposition, pointing to a direct effect of PBA on hIAPP. This was supported by in silico calculations uncovering potential binding sites of PBA to monomeric, dimeric, and pentameric fibrillar structures, and by in vitro assays showing inhibition of hIAPP fibril formation by PBA. Collectively, these results uncover a novel beneficial effect of PBA on glucose homeostasis by restoring β-cell function and preventing amyloid formation in mice expressing hIAPP in β cells, highlighting the therapeutic potential of PBA for the treatment of T2D.-Montane, J., de Pablo, S., Castaño, C., Rodríguez-Comas, J., Cadavez, L., Obach, M., Visa, M., Alcarraz-Vizán, G., Sanchez-Martinez, M., Nonell-Canals, A., Parrizas, M., Servitja, J.-M., Novials, A. Amyloid-induced β-cell dysfunction and islet inflammation are ameliorated by 4-phenylbutyrate (PBA) treatment.

Islet amyloid deposits preferentially in the highly functional and most blood-perfused islets.

Islet amyloid and beta cell death in type 2 diabetes are heterogeneous events, where some islets are affected early in the disease process, whereas others remain visibly unaffected. This study investigated the possibility that inter-islet functional and vascular differences may explain the propensity for amyloid accumulation in certain islets. Highly blood-perfused islets were identified by microspheres in human islet amyloid polypeptide expressing mice fed a high-fat diet for three or 10 months. These highly blood-perfused islets had better glucose-stimulated insulin secretion capacity than other islets and developed more amyloid deposits after 10 months of high-fat diet. Similarly, human islets with a superior release capacity formed more amyloid in high glucose culture than islets with a lower release capacity. The amyloid formation in mouse islets was associated with a higher amount of prohormone convertase 1/3 and with a decreased expression of its inhibitor proSAAS when compared to islets with less amyloid. In contrast, levels of prohormone convertase 2 and expression of its inhibitor neuroendocrine protein 7B2 were unaltered. A misbalance in prohormone convertase levels may interrupt the normal processing of islet amyloid polypeptide and induce amyloid formation. Preferential amyloid load in the most blood-perfused and functional islets may accelerate the progression of type 2 diabetes.

Residue specific effects of human islet polypeptide amyloid on self-assembly and on cell toxicity

Type 2 diabetes mellitus is characterized histopathologically by the presence of fibrillary amyloid deposits in the pancreatic islets of Langerhans. Human islet amyloid polypeptide (hIAPP), the 37-residue pancreatic hormone, is the major constituent of these amyloid deposits. The propensity of IAPP to form amyloid fibrils is strongly dependent on its primary sequence. An intriguing example is His at residue 18. Although H18 is located outside the amyloidogenic region, it has been suggested that this residue and its charge state play an important role in the kinetics of conformational changes and fibril formation as well as in mediating cell toxicity. To gain more insight into the importance of this residue, we have synthesized four analogues (H18R-IAPP, H18K-IAPP, H18A-IAPP and H18E-IAPP) and we performed a full biophysical study on the properties of these peptides. Kinetic experiments as monitored by thioflavin-T fluorescence, transmission electron microscopy, circular dichroism and cell toxicity assays revealed that all variants are less fibrillogenic and less toxic than native hIAPP both at neutral pH and at low pH. This demonstrates that the effect of H18 in native IAPP is not simply determined by its charge state, but rather that residue 18 is important for specific intra- and intermolecular interactions that occur during fibril formation and that may involve charge, size and hydrophobicity. Furthermore, our results indicate that H18R-IAPP has a strong inhibiting effect on native hIAPP fibril formation. Together these results highlight the large impact of modifying a single residue outside the amyloidogenic domain on fibril formation and cell toxicity induced by IAPP, opening up new avenues for design of inhibitors or modulators of IAPP aggregation.

Apoptosis Repressor With Caspase Recruitment Domain Ameliorates Amyloid-Induced β-Cell Apoptosis and JNK Pathway Activation.

Islet amyloid is present in more than 90% of individuals with type 2 diabetes, where it contributes to β-cell apoptosis and insufficient insulin secretion. Apoptosis repressor with caspase recruitment domain (ARC) binds and inactivates components of the intrinsic and extrinsic apoptosis pathways and was recently found to be expressed in islet β-cells. Using a human islet amyloid polypeptide transgenic mouse model of islet amyloidosis, we show ARC knockdown increases amyloid-induced β-cell apoptosis and loss, while ARC overexpression decreases amyloid-induced apoptosis, thus preserving β-cells. These effects occurred in the absence of changes in islet amyloid deposition, indicating ARC acts downstream of amyloid formation. Because islet amyloid increases c-Jun N-terminal kinase (JNK) pathway activation, we investigated whether ARC affects JNK signaling in amyloid-forming islets. We found ARC knockdown enhances JNK pathway activation, whereas ARC overexpression reduces JNK, c-Jun phosphorylation, and c-Jun target gene expression (Jun and Tnf). Immunoprecipitation of ARC from mouse islet lysates showed ARC binds JNK, suggesting interaction between JNK and ARC decreases amyloid-induced JNK phosphorylation and downstream signaling. These data indicate that ARC overexpression diminishes amyloid-induced JNK pathway activation and apoptosis in the β-cell, a strategy that may reduce β-cell loss in type 2 diabetes.

Tat-biliverdin reductase A protects INS-1 cells from human islet amyloid polypeptide-induced cytotoxicity by alleviating oxidative stress and ER stress.

Human islet amyloid polypeptide (hIAPP), a major constituent of islet amyloid deposits, induces pancreatic β-cell apoptosis and eventually contributes to β-cell deficit in patients with type 2 diabetes mellitus (T2DM). In this study, Tat-mediated transduction of biliverdin reductase A (BLVRA) was investigated in INS-1 cells to examine whether exogenous supplementation of BLVRA prevented hIAPP-induced apoptosis and dysfunction in insulin secretion in β-cells. Tat-BLVRA fusion protein was efficiently delivered into INS-1 cells in a time- and dose-dependent manner. Exposure of cells to hIAPP induced apoptotic cell death, which was dose-dependently inhibited by pre-treatment with Tat-BLVRA for 1 h. Transduced Tat-BLVRA reduced hIAPP-evoked generation of reactive oxygen species, a crucial mediator of β-cell destruction. Immunoblot analysis showed that Tat-BLVRA suppressed hIAPP-induced increase in the levels of proteins involved in endoplasmic reticulum (ER) stress and apoptosis signaling. Transduced Tat-BLVRA also recovered hIAPP-induced dysfunction in basal and glucose-stimulated insulin secretions. These results suggested that transduced Tat-BLVRA enhanced the tolerance of β-cells against IAPP-induced cytotoxicity by alleviating oxidative stress and ER stress. Therefore, Tat-mediated transduction of BLVRA may provide a potential tool to ameliorate β-cell deficit in pancreas with T2DM.

Intraneuronal Amylin Deposition, Peroxidative Membrane Injury and Increased IL-1β Synthesis in Brains of Alzheimer's Disease Patients with Type-2 Diabetes and in Diabetic HIP Rats.

Amylin is a hormone synthesized and co-secreted with insulin by pancreatic β-cells that crosses the blood-brain barrier and regulates satiety. Amylin from humans (but not rodents) has an increased propensity to aggregate into pancreatic islet amyloid deposits that contribute to β-cell mass depletion and development of type-2 diabetes by inducing oxidative stress and inflammation. Recent studies demonstrated that aggregated amylin also accumulates in brains of Alzheimer's disease (AD) patients, preponderantly those with type-2 diabetes. Here, we report that, in addition to amylin plaques and mixed amylin-Aβ deposits, brains of diabetic patients with AD show amylin immunoreactive deposits inside the neurons. Neuronal amylin formed adducts with 4-hydroxynonenal (4-HNE), a marker of peroxidative membrane injury, and increased synthesis of the proinflammatory cytokine interleukin (IL)-1β. These pathological changes were mirrored in rats expressing human amylin in pancreatic islets (HIP rats) and mice intravenously injected with aggregated human amylin, but not in hyperglycemic rats secreting wild-type non-amyloidogenic rat amylin. In cultured primary hippocampal rat neurons, aggregated amylin increased IL-1β synthesis via membrane destabilization and subsequent generation of 4-HNE. These effects were blocked by membrane stabilizers and lipid peroxidation inhibitors. Thus, elevated circulating levels of aggregated amylin negatively affect the neurons causing peroxidative membrane injury and aberrant inflammatory responses independent of other confounding factors of diabetes. The present results are consistent with the pathological role of aggregated amylin in the pancreas, demonstrate a novel contributing mechanism to neurodegeneration, and suggest a direct, potentially treatable link of type-2 diabetes with AD.

Inhibition of Insulin-Degrading Enzyme Does Not Increase Islet Amyloid Deposition in Vitro.

Islet amyloid deposition in human type 2 diabetes results in β-cell loss. These amyloid deposits contain the unique amyloidogenic peptide human islet amyloid polypeptide (hIAPP), which is also a known substrate of the protease insulin-degrading enzyme (IDE). Whereas IDE inhibition has recently been demonstrated to improve glucose metabolism in mice, inhibiting it has also been shown to increase cell death when synthetic hIAPP is applied exogenously to a β-cell line. Thus, we wanted to determine whether a similar deleterious effect is observed when hIAPP is endogenously produced and secreted from islets. To address this issue, we cultured hIAPP transgenic mouse islets that have the propensity to form amyloid for 48 and 144 hours in 16.7 mM glucose in the presence and absence of the IDE inhibitor 1. At neither time interval did IDE inhibition increase amyloid formation or β-cell loss. Thus, the inhibition of IDE may represent an approach to improve glucose metabolism in human type 2 diabetes, without inducing amyloid deposition and its deleterious effects.

Development of 99mTc-Labeled Pyridyl Benzofuran Derivatives To Detect Pancreatic Amylin in Islet Amyloid Model Mice

While islet amyloid deposition comprising amylin is one of pathological hallmarks of type 2 diabetes mellitus (T2DM), no useful amylin-imaging probe has been reported. In this study, we evaluated two (99m)Tc-labeled pyridyl benzofuran derivatives as novel amylin-imaging probes using the newly established islet amyloid model mouse. Binding experiments in vitro demonstrated that [(99m)Tc]1 displayed a higher affinity for amylin aggregates than [(99m)Tc]2. Autoradiographic studies using human pancreas sections with T2DM revealed that [(99m)Tc]1 clearly labeled islet amyloid in T2DM pancreatic sections, while [(99m)Tc]2 did not. Although the initial uptake of [(99m)Tc]1 by the normal mouse pancreas was low (0.74%ID/g at 2 min post-injection), [(99m)Tc]1 showed higher retention in the model mouse pancreas than that of the normal mouse, and exhibited strong binding to amylin aggregates in the living pancreas of the model mice. These results suggest that [(99m)Tc]1 is a potential imaging probe targeting islet amyloids in the T2DM pancreas.

Protein disulfide isomerase ameliorates β-cell dysfunction in pancreatic islets overexpressing human islet amyloid polypeptide

Human islet amyloid polypeptide (hIAPP) is the major component of amyloid deposits in islets of type 2 diabetic patients. hIAPP misfolding and aggregation is one of the factors that may lead to β-cell dysfunction and death. Endogenous chaperones are described to be important for the folding and functioning of proteins. Here, we examine the effect of the endoplasmic reticulum chaperone protein disulfide isomerase (PDI) on β-cell dysfunction. Among other chaperones, PDI was found to interact with hIAPP in human islet lysates. Furthermore, intrinsically recovered PDI levels were able to restore the effect of high glucose- and palmitate-induced β-cell dysfunction by increasing 3.9-fold the glucose-stimulated insulin secretion levels and restoring insulin content up to basal control values. Additionally, PDI transduction decreased induced apoptosis by glucolipotoxic conditions. This approach could reveal a new therapeutic target and aid in the development of strategies to improve β-cell dysfunction in type 2 diabetic patients.

Discovery of ethyl urea derivatives as inhibitors of islet amyloid polypeptide fibrillization and cytotoxicity

Islet amyloid polypeptide (IAPP) has been shown to form amyloid deposits in pancreatic islets, thereby furthering type 2 diabetes disease progression. Further discovery of new molecules is needed to create a diverse set of molecules that impede pancreatic amyloidosis. We have recently designed and synthesized N-phenyl-N'-(2-ethyl)ureas (EU) that are non-cytotoxic small molecules, to evaluate the role of the aryl-substituted moiety on the inhibition of hIAPP fibrillization. Several EUs were tested in vitro for their anti-amyloidogenic activity using the fluorometric ThT assay, the photo-induced cross-linking (PIUCP) assay, and cell survival assay in pancreatic MIN-6 cells. EU-362 and EU-418 were able to significantly inhibit the formation of hIAPP fibrils and protected cells from amyloid cytotoxic effects. Our results suggest that increasing the nucleophilic potency of the aryl moiety significantly enhances the anti-amyloidogenic activity of the molecules.

Hyaluronan: A Mediator of Islet Dysfunction and Destruction in Diabetes?

Hyaluronan (HA) is an extracellular matrix (ECM) component that is present in mouse and human islet ECM. HA is localized in peri-islet and intra-islet regions adjacent to microvessels. HA normally exists in a high molecular weight form, which is anti-inflammatory. However, under inflammatory conditions, HA is degraded into fragments that are proinflammatory. HA accumulates in islets of human subjects with recent onset type 1 diabetes (T1D), and is associated with myeloid and lymphocytic islet infiltration, suggesting a possible role for HA in insulitis. A similar accumulation of HA, in amount and location, occurs in non-obese diabetic (NOD) and DORmO mouse models of T1D. Furthermore, HA accumulates in follicular germinal centers and in T-cell areas in lymph nodes and spleen in both human and mouse models of T1D, as compared with control tissues. Whether HA accumulates in islets in type 2 diabetes (T2D) or models thereof has not been previously described. Here we show evidence that HA accumulates in a mouse model of islet amyloid deposition, a well-known component of islet pathology in T2D. In summary, islet HA accumulation is a feature of both T1D and a model of T2D, and may represent a novel inflammatory mediator of islet pathology.

Amylin at the interface between metabolic and neurodegenerative disorders.

The pancreatic peptide amylin is best known for its role as a satiation hormone in the control of food intake and as the major component of islet amyloid deposits in the pancreatic islets of patients with type 2 diabetes mellitus (T2DM). Epidemiological studies have established a clear association between metabolic and neurodegenerative disorders in general, and between T2DM and Alzheimer's disease (AD) in particular. Here, we discuss that amylin may be an important player acting at the interface between these metabolic and neurodegenerative disorders. Abnormal amylin production is a hallmark peripheral pathology both in the early (pre-diabetic) and late phases of T2DM, where hyperamylinemic (early phase) and hypoamylinemic (late phase) conditions coincide with hyper- and hypo-insulinemia, respectively. Moreover, there are notable biochemical similarities between amylin and β-amyloids (Aβ), which are both prone to amyloid plaque formation and to cytotoxic effects. Amylin's propensity to form amyloid plaques is not restricted to pancreatic islet cells, but readily extends to the CNS, where it has been found to co-localize with Aβ plaques in at least a subset of AD patients. Hence, amylin may constitute a “second amyloid” in neurodegenerative disorders such as AD. We further argue that hyperamylinemic conditions may be more relevant for the early processes of amyloid formation in the CNS, whereas hypoamylinemic conditions may be more strongly associated with late stages of central amyloid pathologies. Advancing our understanding of these temporal relationships may help to establish amylin-based interventions in the treatment of AD and other neurodegenerative disorders with metabolic comorbidities.