Interaction Of Amyloid-β Peptide Research Articles

Anionic lipids modulate little the reorganization effect of amyloid-beta peptides on membranes.

Amyloid-β peptide interactions with model lipid membranes have been studied by means of small angle neutron scattering and molecular dynamics simulations. These interactions had been indicated recently as an origin of the membrane structure reorganizations between spherical small unilamellar vesicles and planar bicelle-like structures. In present work, we investigate the influence of charge on the peptide-triggered morphological changes by introducing the anionic lipid DMPS to the underlying DMPC membrane. Changes to the membrane thickness and the overall membrane structure with and without Aβ25-35 incorporated have been investigated over a wide range of temperatures. Our results document the previously reported morphological reformations between bicelle-like structures present in gel phase and small unilamellar vesicles present in fluid phase to be independent from the charge existence in the system.

Amyloid β-Peptide Interaction with Membranes: Can Chaperones Change the Fate?

The understanding of amyloid β-peptide (Aβ) interactions with cellular membranes is a crucial molecular challenge against Alzheimer's disease. Indeed, Aβ prefibrillar oligomeric intermediates are believed to be the most toxic species, able to induce cellular damagesdirectly by membrane damage. We present a neutron-scattering study on the interaction of large unilamellar vesicles (LUV), as cell membrane models, with both freshly dissolved Aβ and early toxic prefibrillar oligomers, intermediate states in the amyloid pathway. In addition, we explore the effect of coincubating the Aβ-peptide with the chaperonin Hsp60, which is known to strongly interact with it in its aggregation pattern. In fact, the interaction of the LUV with coincubated Aβ/Hsp60, right after mixing and after following the aggregation protocol leading to the toxic intermediates in the absence of Hsp60, is studied. Neutron spin echo experiments show that the interaction with both freshly dissolved and aggregate Aβ species brings about an increase in membrane stiffness, whereas the presence of even very low amounts of Hsp60 (ratio Aβ/Hsp60 = 25:1) maintains unaltered the elastic properties of the membrane bilayer. A coherent interpretation of these results, related to previous literature, can be based on the ability of the chaperonin to interfere with Aβ aggregation, by the specific recognition oftheAβ-reactive transient species. In this framework, our results strongly suggest that early in a freshly dissolved Aβ solution are presentsomespecies able to modify the bilayer dynamics, and the chaperonin plays the role of an assistant in such stochastic "misfolding events", avoiding the insult on the membrane as well as the onset of the aggregation cascade.

Fe(II) formation after interaction of the amyloid β-peptide with iron-storage protein ferritin.

The interaction of amyloid β-peptide (Aβ) with the iron-storage protein ferritin was studied in vitro. We have shown that Aβ during fibril formation process is able to reduce Fe(III) from the ferritin core (ferrihydrite) to Fe(II). The Aβ-mediated Fe(III) reduction yielded a two-times-higher concentration of free Fe(II) than the spontaneous formation of Fe(II) by the ferritin itself. We suggest that Aβ can also act as a ferritin-specific metallochaperone-like molecule capturing Fe(III) from the ferritin ferrihydrite core. Our observation may partially explain the formation of Fe(II)-containing minerals in human brains suffering by neurodegenerative diseases.

Amyloid-β Peptide Interactions with Amphiphilic Surfactants: Electrostatic and Hydrophobic Effects.

The amphiphilic nature of the amyloid-β (Aβ) peptide associated with Alzheimer's disease facilitates various interactions with biomolecules such as lipids and proteins, with effects on both structure and toxicity of the peptide. Here, we investigate these peptide-amphiphile interactions by experimental and computational studies of Aβ(1-40) in the presence of surfactants with varying physicochemical properties. Our findings indicate that electrostatic peptide-surfactant interactions are required for coclustering and structure induction in the peptide and that the strength of the interaction depends on the surfactant net charge. Both aggregation-prone peptide-rich coclusters and stable surfactant-rich coclusters can form. Only Aβ(1-40) monomers, but not oligomers, are inserted into surfactant micelles in this surfactant-rich state. Surfactant headgroup charge is suggested to be important as electrostatic peptide-surfactant interactions on the micellar surface seems to be an initiating step toward insertion. Thus, no peptide insertion or change in peptide secondary structure is observed using a nonionic surfactant. The hydrophobic peptide-surfactant interactions instead stabilize the Aβ monomer, possibly by preventing self-interaction between the peptide core and C-terminus, thereby effectively inhibiting the peptide aggregation process. These findings give increased understanding regarding the molecular driving forces for Aβ aggregation and the peptide interaction with amphiphilic biomolecules.

NBD-BPEA regulates Zn2+- or Cu2+-induced Aβ40 aggregation and cytotoxicity

Abnormal interaction of amyloid-β peptide (Aβ) and metal ions is proved to be related to the etiology of Alzheimer's disease (AD). Using metal chelators to reverse metal-triggered Aβ aggregation has become one of the potential therapies for AD. In our work, the effect of metal chelator, NBD-BPEA, on Zn2+- or Cu2+-mediated Aβ40 aggregation and neurotoxicity has been systematically studied. NBD-BPEA exhibits the capability to inhibit the metal-mediated Aβ40 aggregation and disassemble performed Aβ40 aggregates. It also prevents the formation of the β-sheet structure and promotes the reversion of the β-sheet to the normal random coil conformation. Moreover, it can alleviate Zn2+- or Cu2+-Aβ40-induced neurotoxicity, suppress the intracellular ROS and protect against cell apoptosis. These preliminary findings indicate that NBD-BPEA has promising perspective of application in the treatment of AD, and therefore deserve further investigation as potential anti-AD agents.

On the possible structural role of single chain sphingolipids Sphingosine and Sphingosine 1-phosphate in the amyloid-β peptide interactions with membranes. Consequences for Alzheimer’s disease development

A strong interplay between the neurodegerative effects of the amyloid β (Aβ) peptides and the cell lipid composition or metabolism has been evidenced in Alzheimer’s disease. This appears to be, in part, related to Aβ-membrane interactions. Recently, an influence of the two cell fate-modulating single-chain sphingolipids, sphingosine (Sph) and sphingosine 1-phosphate (S1P), on AD-related mechanisms has been reported. We have investigated the influence of Sph and S1P on the interaction of Aβ(1–42) with lipid model membranes. A fluorescent Aβ(1–42) binds to egg phosphatidylcholine (EPC) giant unilamellar vesicles containing Sph or S1P. With Sph, gel microdomains are present at low temperature and Aβ(1–42) binds preferentially to these domains, especially at their boundaries. With S1P, which displays single lipid phase morphology, Aβ(1–42) binding is uniform. The binding of Aβ(1–42) to EPC/sphingolipid large unilamellar vesicles was investigated by spectrofluorimetry using the 2 probes Laurdan and di-ANEPPS. With most lipid compositions the binding of Aβ(1–42) to LUVs appears superficial. However, with Sph, a deeper membrane penetration is observed. This deeper interaction is reversed to superficial by the simultaneous presence of S1P. It is suggested that the influence of single-chain sphingolipids in AD might be related to a selective interaction of Aβ(1–42) with sphingosine in membranes, that is antagonized by S1P. Such interaction might occur intracellularly for Aβ(1–42) monomers or oligomers and/or extracellularly for Aβ still part of APP. Aβ(1–42) might also influence microdomains by binding to their boundaries. The influence of the Sph/S1P balance on the Alzheimer pathology might be related in part to the differential interactions of Aβ(1–42) with Sph and S1P and their effects on membrane domains.

Side Effect of Tris on the Interaction of Amyloid β-peptide with Cu(2+): Evidence for Tris-Aβ-Cu (2+) Ternary Complex Formation.

The interaction of amyloid β-peptide (Aβ) with Cu(2+) is crucial to the development of neurotoxicity in Alzheimer's disease (AD). Many recent studies show a variation on the dissociation constant of Aβ-Cu(2+) under different solvent conditions. Among various buffers, the Tris(hydroxymethyl)aminomethane (Tris) buffer is the most reliable chelator of Cu(2+). However, as a typical nucleophilic reagent capable of binding peptides, the behavior of Tris should be more complicated. In this work, the effect of Tris on the interaction of Aβ with Cu(2+) was investigated. Under acidic conditions, Tris-Aβ-Cu(2+) ternary complex was identified by electrospray ionization mass spectrometry and transmission electron microscopy. The results of surface plasmon resonance reveal that the formation of the ternary complex increases the dissociation constant by almost 1 order of magnitude. Consequently, the assessment of toxicity indicates that the generation of · OH induced by the Aβ-Cu(2+) complex was enhanced in the presence of Tris. The work reveals the significant side effect of Tris on the interaction of Aβ with Cu(2+), which will greatly improve the quantitative investigation on Aβ-Cu(2+) interaction and be helpful for the in-depth understanding of the roles of Aβ and Cu(2+) in AD neuropathology.

Plasma Membrane Injury Depends on Bilayer Lipid Composition in Alzheimer's Disease

Increasing evidence indicates that interaction of amyloid-β peptide (Aβ) with the cell membrane is a primary step in Alzheimer's disease (AD) neurotoxicity. In particular, it has been demonstrated that lipid rafts are key sites of Aβ production, aggregation, and interaction with the cell membrane. In this study we show that Aβ42 oligomers are recruited to lipid rafts, leading to plasma membrane perturbation and Ca2+ dyshomeostasis in primary fibroblasts from familial AD patients bearing APPVal717Ile, PS-1Leu392Val, or PS-1Met146Leu gene mutations. In contrast, a moderate increase in membrane cholesterol content precluded the interaction of Aβ42 oligomers with the plasma membrane and resulting cell damage. Moreover, the recruitment of amyloid assemblies to lipid raft domains of cholesterol-depleted fibroblasts was significantly increased, thus triggering an earlier and sharper increase in intracellular Ca2+ levels and plasma membrane permeabilization. Our findings suggest a protective role for raft cholesterol against amyloid toxicity in AD.

Erratum to: Probing of Various Physiologically Relevant Metals–Amyloid-β Peptide Interactions with a Lipid Membrane-Immobilized Protein Nanopore

Erratum to: Probing of Various Physiologically Relevant Metals–Amyloid-β Peptide Interactions with a Lipid Membrane-Immobilized Protein Nanopore

Probing of Various Physiologically Relevant Metals: Amyloid-β Peptide Interactions with a Lipid Membrane-Immobilized Protein Nanopore

One of the prevailing paradigms regarding the onset of Alzheimer's disease endows metal ions with key roles in certain steps of the amyloid-β (Aβ) peptide aggregation cascade, through peptide conformational changes induced by metal binding. Herein, we focused on the truncated, more soluble Aβ1-16 peptide fragment from the human Aβ1-40, and demonstrated the utility of a sensing element based on the α-hemolysin (α-HL) protein to examine and compare at single-molecule level the interactions between such peptides and various metals. By using the same approach, we quantified Cu(2+) and Zn(2+) binding affinities to the Aβ1-16 fragment, whereas the statistical analysis of blockages induced by a single Aβ1-16 peptide on the current flow through an open α-HL pore show that the metal propensity to interacting with the peptide and entailing conformational changes obey the following order: Cu(2+)>Zn(2+)>Fe(3+)>Al(3+).

Effect of trehalose on the interaction of Alzheimer's Aβ-peptide and anionic lipid monolayers

The interaction of amyloid β-peptide (Aβ) with cell membranes is believed to play a central role in the pathogenesis of Alzheimer's disease. In particular, recent experimental evidence indicates that bilayer and monolayer membranes accelerate the aggregation and amyloid fibril formation rate of Aβ. Understanding that interaction could help develop therapeutic strategies for treatment of the disease. Trehalose, a disaccharide of glucose, has been shown to be effective in preventing the aggregation of numerous proteins. It has also been shown to delay the onset of certain amyloid-related diseases in a mouse model. Using Langmuir monolayers and molecular simulations of the corresponding system, we study several thermodynamic and kinetic aspects of the insertion of Aβ peptide into DPPG monolayers in water and trehalose subphases. In the water subphase, the insertion of the Aβ peptide into the monolayer exhibits a lag time which decreases with increasing temperature of the subphase. In the presence of trehalose, the lag time is completely eliminated and peptide insertion is completed within a shorter time period compared to that observed in pure water. Molecular simulations show that more peptide is inserted into the monolayer in the water subphase, and that such insertion is deeper. The peptide at the monolayer interface orients itself parallel to the monolayer, while it inserts with an angle of 50° in the trehalose subphase. Simulations also show that trehalose reduces the conformational change that the peptide undergoes when it inserts into the monolayer. This observation helps explain the experimentally observed elimination of the lag time by trehalose and the temperature dependence of the lag time in the water subphase.

NMR Investigations of Amyloid-β Peptide Interactions with Propofol at Clinically Relevant Concentrations with and without Aqueous Halothane Solution

Oligomerization of amyloid-β peptide (Aβ) is an important stage in Alzheimer's disease. Recently, it has been shown that in an experimental model, smaller sized anesthetics (e.g., isoflurane, desflurane, etc.) induce Aβ oligomerization. Using state-of-the-art solution nuclear magnetic resonance, spectroscopic studies on Aβ interaction with propofol indicated that propofol does not interact with the G29, A30, and I31 residues of Aβ peptide at a clinically relevant concentration (0.083 mM), and no Aβ oligomerization was observed after 69 days. However, Aβ oligomerization was observed when treated with propofol (clinically relevant concentration) coadministered with aqueous halothane solution. Furthermore, dose dependence studies at various propofol concentrations (0.32 mM, 2.07 mM, and 53.4 mM) indicate the effect of propofol concentration on Aβ oligomerization revealing the hydrophobic nature of interactions between propofol with these critical residues (G29, A30, and I31). These experimental findings reaffirm that smaller molecular sized anesthetics (e.g., halothane) do play a leading role in Aβ oligomerization.

Comparative study of sub-micrometer polymeric structures: Dot-arrays, linear and crossed gratings generated by UV laser based two-beam interference, as surfaces for SPR and AFM based bio-sensing

Two-dimensional gratings are generated on poly-carbonate films spin-coated onto thin gold–silver bimetallic layers by two-beam interference method. Sub-micrometer periodic polymer dots and stripes are produced illuminating the poly-carbonate surface by p- and s-polarized beams of a frequency quadrupled Nd:YAG laser, and crossed gratings are generated by rotating the substrates between two sequential treatments. It is shown by pulsed force mode atomic force microscopy that the mean value of the adhesion is enhanced on the dot-arrays and on the crossed gratings. The grating-coupling on the two-dimensional structures results in double peaks on the angle dependent resonance curves of the surface plasmons excited by frequency doubled Nd:YAG laser. The comparison of the resonance curves proves that a surface profile ensuring minimal undirected scattering is required to optimize the grating-coupling, in addition to the minimal modulation amplitude, and to the optimal azimuthal orientation. The secondary minima are the narrowest in presence of linear gratings on multi-layers having optimized composition, and on crossed structures consisting of appropriately oriented polymer stripes. The large coupling efficiency and adhesion result in high detection sensitivity on the crossed gratings. Bio-sensing is realized by monitoring the rotated-crossed grating-coupled surface plasmon resonance curves, and detecting the chemical heterogeneity by tapping-mode atomic force microscopy. The interaction of Amyloid-β peptide, a pathogenetic factor in Alzheimer disease, with therapeutical molecules is demonstrated.

Electrochemical impedance spectroscopy for study of amyloid β-peptide interactions with (−) nicotine ditartrate and (−) cotinine

Immobilization of amyloid β (Aβ) (1–40) peptide on Au-colloid modified gold electrodes has been studied. Colloidal Au was self-assembled onto gold electrodes through the thiol groups of 1,6-hexanedithiol monolayer. Next, buffered aqueous solution of Aβ (1–40) peptide existing in the β-sheet structure in the acidic media was dropped on the electrode surface. Each step of electrode modification has been confirmed with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The changes of the resistance of the layer with deposited Aβ (1–40) peptide, occurred under stimulation by different concentration of (−) nicotine ditartrate and (−) cotinine were measured with EIS and were used for the calculation of association constants. The gentle measuring conditions applied in electrochemical impedance spectroscopy, together with suitable environment for biomolecules immobilization created by Au-colloid, might be recommended as the analytical tool for assessing the effectiveness of potential drugs used in Alzheimer's disease (AD) therapy.

Amyloid beta-peptide interactions with neuronal and glial cell plasma membrane: binding sites and implications for Alzheimer's disease.

The extracellular accumulation of amyloid-beta (Abeta) in neuritic plaques is one of the characteristic hallmarks of Alzheimer's disease (AD), a progressive dementing neurodegenerative disorder of the elderly. By virtue of its structure, Abeta is able to bind to a variety of biomolecules, including lipids, proteins and proteoglycans. The binding of the various forms of Abeta (soluble or fibrillar) to plasma membranes has been studied with regard to the direct toxicity of Abeta to neurons, and the activation of a local inflammation phase involving microglia. The binding of Abeta to membrane lipids facilitates Abeta fibrillation, which in turn disturbs the structure and function of the membranes, such as membrane fluidity or the formation of ion channels. A subset of membrane proteins binds Abeta. The serpin-enzyme complex receptor (SEC-R) and the insulin receptor can bind the monomeric form of Abeta. The alpha7nicotinic acetylcholine receptor (alpha7nAChR), integrins, RAGE (receptor for advanced glycosylation end-products) and FPRL1 (formyl peptide receptor-like 1) are able to bind the monomeric and fibrillar forms of Abeta. In addition, APP (amyloid precursor protein), the NMDA-R (N-methyl-D-aspartate receptor), the P75 neurotrophin receptor (P75NTR), the CLAC-P/collagen type XXV (collagen-like Alzheimer amyloid plaque component precursor/collagen XXV), the scavenger receptors A, BI (SR-A, SR-BI) and CD36, a complex involving CD36, alpha6beta1-integrin and CD47 have been reported to bind the fibrillar form of Abeta. Heparan sulfate proteoglycans have also been described as cell-surface binding sites for Abeta. The various effects of Abeta binding to these membrane molecules are discussed.