Molecular Structure, Membrane Interactions, and Toxicity of the Islet Amyloid Polypeptide in Type 2 Diabetes Mellitus

Caillon, Lucie; Hoffmann, Anaïs R. F.; Botz, Alexandra; Khemtémourian, Lucie

doi:10.1155/2016/5639875

Cited by 61 publications

(46 citation statements)

References 127 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4,5 hIAPP is believed to play a key role in the control of gastric emptying, glucose homeostasis and suppression of glucagon release. 6 It has been found that the oligomeric and/or brillar amyloid species of hIAPP leads to the death of b-cells and pancreatic dysfunction, contributing to islet transplant failure and T2DM.…”

Section: Introductionmentioning

confidence: 99%

Brazilin inhibits fibrillogenesis of human islet amyloid polypeptide, disassembles mature fibrils, and alleviates cytotoxicity

Guo

Sun

et al. 2017

RSC Adv.

View full text Add to dashboard Cite

Fibrillogenesis of human islet amyloid polypeptide (hIAPP) is a pathological hallmark of type II diabetes mellitus (T2DM), and the inhibition of hIAPP fibrillogenesis is an important strategy for the prevention and treatment of T2DM. In this study, the inhibitory effects of brazilin on the fibrillization and cytotoxicity of hIAPP were examined using the thioflavin T fluorescence (ThT) assay, transmission electron microscopy (TEM), circular dichroism (CD) spectroscopy, cytotoxicity assays, and molecular dynamics simulations.Both the ThT and TEM results have shown that brazilin inhibits hIAPP fibrillogenesis in a dose-dependent manner. CD studies revealed that brazilin delays the conformational transition of hIAPP from its initial ahelical to the b-sheet form. As a result, brazilin greatly alleviates hIAPP-induced cytotoxicity. Moreover, we also found that brazilin disassembles preexisting hIAPP fibrils, and alleviates the cytotoxicity of hIAPP aggregates. The results of free energy decomposition studies calculated using molecular mechanicsPoisson-Boltzmann surface area analysis revealed that hydrophobic interactions contribute more than 75% of the free energy of binding in the brazilin-hIAPP complex, while electrostatic interactions (i.e., hydrogen bonds) play a secondary role (<25%). Two binding sites of brazilin on the hIAPP pentamer were identified, encompassing the N-terminal region and the turn region. There are 11 important residues of hIAPP that strongly interact with brazilin -Asn3, Thr4, Thr9, Arg11, Asn14, Phe15, His18, Ser19, Ser20, Asn21 and Phe23. The findings presented here will contribute to a comprehensive understanding of the inhibitory effect of brazilin on the fibrillogenesis of hIAPP, which is critical for the search for more effective agents that can inhibit hIAPP fibrillogenesis.

show abstract

Section: Introductionmentioning

confidence: 99%

Brazilin inhibits fibrillogenesis of human islet amyloid polypeptide, disassembles mature fibrils, and alleviates cytotoxicity

Guo

Sun

et al. 2017

RSC Adv.

View full text Add to dashboard Cite

show abstract

“…Aberrant aggregation of proteins into amyloid deposits is a hallmark of many human pathologies, for example, Alzheimer's disease, Parkinson's disease, and type 2 diabetes . Amyloid deposits contain amyloid fibrils characterized by cross‐β structure consisting of stacked β‐sheets held together by interpeptide hydrogen bonding along the long fibrillar axis .…”

Section: Introductionmentioning

confidence: 99%

Elucidation of insulin assembly at acidic and neutral pH: Characterization of low molecular weight oligomers

et al. 2017

View full text Add to dashboard Cite

Deficiency in insulin secretion and function that characterize type 2 diabetes often requires administration of extraneous insulin, leading to injection-site amyloidosis. Insulin aggregation at neutral pH is not well understood. Although oligomer formation is believed to play an important role, insulin oligomers have not been fully characterized yet. Here, we elucidate similarities and differences between in vitro insulin aggregation at acidic and neutral pH for a range of insulin concentrations (2.5-100 μM) by using kinetic thioflavin T fluorescence, circular dichroism, atomic force and electron microscopy imaging. Importantly, we characterize the size distribution of insulin oligomers at different assembly stages by the application of covalent cross-linking and gel electrophoresis. Our results show that at the earliest assembly stage, oligomers comprise up to 40% and 70% of soluble insulin at acidic and neutral pH, respectively. While the highest oligomer order increases with insulin concentration at acidic pH, the opposite tendency is observed at neutral pH, where oligomers up to heptamers are formed in 10 μM insulin. These findings suggest that oligomers may be on- and off-pathway assemblies for insulin at acidic and neutral pH, respectively. Agitation, which is required to induce insulin aggregation at neutral pH, is shown to increase fibril formation rate and fibrillar mass both by an order of magnitude. Insulin incubated under agitated conditions at neutral pH rapidly aggregates into large micrometer-sized aggregates, which may be of physiological relevance and provides insight into injection-site amyloidosis and toxic pulmonary aggregates induced by administration of extraneous insulin.

show abstract

“…It is well established that incubation of human IAPP with cells results in formation of IAPP oligomers that are cytotoxic (21), which is at least in part mediated by direct cell membrane disruption by the oligomers, because the effect was also observed with cell-free lipid bilayers (22). We used human erythrocytes as a model to study membrane disruption during incubation with IAPP monomers.…”

Section: Discussionmentioning

confidence: 99%

“…The raw data were summarized and normalized using the Robust Multi Average algorithm (21) in which raw intensities are background-corrected, log2-transformed, and quantile-normalized. Normalized data were found to be of excellent quality with sample to sample correlations Ͼ0.98 and normalized unscaled standard errors close to 1.…”

Section: Methodsmentioning

confidence: 99%

C4b-binding Protein Protects β-Cells from Islet Amyloid Polypeptide-induced Cytotoxicity

Sjölander

Byman

Kulak

et al. 2016

Journal of Biological Chemistry

View full text Add to dashboard Cite

C4BP (C4b-binding protein) is a polymer of seven identical ␣ chains and one unique ␤ chain synthesized in liver and pancreas. We showed previously that C4BP enhances islet amyloid polypeptide (IAPP) fibril formation in vitro. Now we report that polymeric C4BP strongly inhibited lysis of human erythrocytes incubated with monomeric IAPP, whereas no lysis was observed after incubation with preformed IAPP fibrils. In contrast, incubation with the monomeric ␣-chain of C4BP was less effective. These data indicate that polymeric C4BP with multiple binding sites for IAPP neutralizes lytic activity of IAPP. The present study focuses on C4BP 2 (C4b-binding protein), which is an essential inhibitor of the complement system (1). Complement has important roles in innate immunity and consists of more than 40 proteins involved in initiation and control of the system (2). C4BP is an abundant polymeric plasma protein that consists of seven identical ␣-chains with eight complement control protein (CCP) domains each, as well as one ␤-chain with three CCPs. The ␤-chain always carries anticoagulant PS (protein S) (3). Because of the high affinity of PS for negatively charged phospholipids, the C4BP-PS complex efficiently binds to apoptotic (4) and necrotic cells (5), ensuring controlled complement activation necessary for clearance of these cells. So far, C4BP has been characterized in detail as a complement inhibitor and is often employed by bacterial pathogens as a form of evasion strategy leading to decreased opsonization and phagocytosis (6). C4BP may have other immunomodulatory functions such as the induction of an antiinflammatory state in dendritic cells (7). Complete deficiency of C4BP has not been described, but non-synonymous polymorphisms causing impaired complement inhibitory activity were found in atypical hemolytic uremic syndrome (8) and recurrent, spontaneous pregnancy loss (9). C4BP is mainly secreted by hepatocytes but significant expression is also detected in lung and pancreatic islets. We found previously that C4BP interacts with various types of amyloid (10 -12), which similarly to in dying cells, allows a certain level of complement opsonization for clearance while preventing overt inflammation.In type 2 diabetes amyloid deposits are localized to the islets of Langerhans in the pancreas and mainly formed by islet amyloid polypeptide (IAPP). IAPP deposits are present in 90% of patients with type 2 diabetes and can cause apoptosis of ␤-cells (13). Apart from this cytotoxic effect IAPP also has a physiological role in regulating and stabilizing blood glucose levels. When insulin resistance develops in type 2 diabetes, so does the production and release of insulin and concomitantly IAPP in the ␤-cell (14, 15). Once IAPP reaches a critical concentration, it starts to aggregate. The small aggregates form ␤-sheet-rich proto-filaments that interact with each other and eventually form mature fibrils. Even though the exact cytotoxic form of IAPP (monomers, oligomers, or fibrils) is still discussed, there is a growing co...

show abstract

Molecular Structure, Membrane Interactions, and Toxicity of the Islet Amyloid Polypeptide in Type 2 Diabetes Mellitus

Cited by 61 publications

References 127 publications

Brazilin inhibits fibrillogenesis of human islet amyloid polypeptide, disassembles mature fibrils, and alleviates cytotoxicity

Brazilin inhibits fibrillogenesis of human islet amyloid polypeptide, disassembles mature fibrils, and alleviates cytotoxicity

Elucidation of insulin assembly at acidic and neutral pH: Characterization of low molecular weight oligomers

C4b-binding Protein Protects β-Cells from Islet Amyloid Polypeptide-induced Cytotoxicity

Contact Info

Product

Resources

About