Organoplatinum‐Substituted Polyoxometalate Inhibits β‐amyloid Aggregation for Alzheimer's Therapy

Aggregated β‐amyloid (Aβ) is widely considered as a key factor in triggering progressive loss of neuronal function in Alzheimer's disease (AD), so targeting and inhibiting Aβ aggregation has been broadly recognized as an efficient therapeutic strategy for curing AD. Herein, we designed and prepared an organic platinum‐substituted polyoxometalate, (Me₄N)₃[PW₁₁O₄₀(SiC₃H₆NH₂)₂PtCl₂] (abbreviated as Pt^II‐PW₁₁) for inhibiting Aβ₄₂ aggregation. The mechanism of inhibition on Aβ₄₂ aggregation by Pt^II‐PW₁₁ was attributed to the multiple interactions of Pt^II‐PW₁₁ with Aβ₄₂ including coordination interaction of Pt²⁺ in Pt^II‐PW₁₁ with amino group in Aβ₄₂, electrostatic attraction, hydrogen bonding and van der Waals force. In cell‐based assay, Pt^II‐PW₁₁ displayed remarkable neuroprotective effect for Aβ₄₂ aggregation‐induced cytotoxicity, leading to increase of cell viability from 49 % to 67 % at a dosage of 8 μm . More importantly, the Pt^II‐PW₁₁ greatly reduced Aβ deposition and rescued memory loss in APP/PS1 transgenic AD model mice without noticeable cytotoxicity, demonstrating its potential as drugs for AD treatment.     

Metal–Organic Frameworks Harness Cu Chelating and Photooxidation Against Amyloid β Aggregation in Vivo

Recently, photooxygenation of amyloid β (Aβ) has emerged as an effective way to inhibit Aβ aggregation in Alzheimer's disease (AD) treatment. However, their further application has been highly obstructed by self-aggregation, no metal chelating ability, and poor protein-enrichment capacity. Herein, porphyrinic metal–organic frameworks (PMOFs) are utilized as a superior Cu^II chelating and photooxidation agent for inhibiting Aβ aggregation. We selected only four classical kinds of POMFs (Zr–MOF, Al–MOF, Ni–MOF, Hf–MOF) for further investigation in our study, which are stable in physiological conditions and exhibit excellent biocompatibility. Among them, Hf–MOF was the most efficient Aβ photooxidant. A possible explanation about the difference in capacity of ¹O₂ generation of these four PMOFs has been provided according to the experimental results and DFT calculations. Furthermore, Hf–MOFs are modified with Aβ-targeting peptide, LPFFD. This can not only enhance Hf–MOFs targeting cellular Aβ to decrease Aβ-induced cytotoxicity, but also improve Aβ photooxidation in the complicated living environment. More intriguingly, in vivo studies indicate that the well-designed LPFFD modified Hf–MOFs can decrease Aβ-induced neurotoxicity and extend the longevity of the commonly used transgenic AD model Caenorhabditis elegans CL2006. Our work may open a new avenue for using MOFs as neurotoxic-metal-chelating and photo-therapeutic agents for AD treatment.     

Solid‐Phase Synthesis and Characterization of N‐Terminally Elongated Aβ−3–x‐Peptides

In addition to the prototypic amyloid‐β (Aβ) peptides Aβ_1–40 and Aβ_1–42, several Aβ variants differing in their amino and carboxy termini have been described. Synthetic availability of an Aβ variant is often the key to study its role under physiological or pathological conditions. Herein, we report a protocol for the efficient solid‐phase peptide synthesis of the N‐terminally elongated Aβ‐peptides Aβ_?3–38, Aβ_?3–40, and Aβ_?3–42. Biophysical characterization by NMR spectroscopy, CD spectroscopy, an aggregation assay, and electron microscopy revealed that all three peptides were prone to aggregation into amyloid fibrils. Immunoprecipitation, followed by mass spectrometry, indicated that Aβ_?3–38 and Aβ_?3–40 are generated by transfected cells even in the presence of a tripartite β‐site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitor. The elongated Aβ peptides starting at Val(?3) can be separated from N‐terminally‐truncated Aβ forms by high‐resolution isoelectric‐focusing techniques, despite virtually identical isoelectric points. The synthetic Aβ variants and the methods presented here are providing tools to advance our understanding of the potential roles of N‐terminally elongated Aβ variants in Alzheimer's disease.     

The Aggregation Pattern of Aβ1–40 is Altered by the Presence of N-Truncated Aβ4–40 and/or CuII in a Similar Way through Ionic Interactions

Alzheimer's disease (AD) is one of the most common of the multifactorial diseases and is characterized by a range of abnormal molecular processes, such as the accumulation of extracellular plaques containing the amyloid-β (Aβ) peptides and dyshomeostasis of copper in the brain. In this study, we have investigated the effect of Cu^II on the aggregation of Aβ_1–40 and Aβ_4–40, representing the two most prevalent families of Aβ peptides, that is, the full length and N-truncated peptides. Both families are similarly abundant in healthy and AD brains. For either of the studied peptides, substoichiometric Cu^II concentrations accelerated aggregation, whereas superstoichiometric Cu^II inhibited fibril formation, likely by stabilizing the oligomers. The addition of either Aβ_4–40 or substoichiometric Cu^II affected the aggregation profile of Aβ_1–40, by yielding shorter and thicker fibrils; amorphous aggregates were formed in the presence of a molar excess of Cu^II. The similarity of these two effects can be attributed to the increase in the positive charge on the Aβ N terminus, caused both by Cu^II complexation and N truncation at position 4. Our findings provide a better understanding of the biological Aβ aggregation process as these two Aβ species and Cu^II coexist and interact under physiological conditions.     

Application of an Electrochemical Method to Evaluation of Amyloid‐β Aggregation Inhibitors: Testing the RGKLVFFGR‐NH2 Peptide Antiaggregant

The aggregation of amyloid‐β peptide (Aβ) is believed to play a crucial role in the Alzheimer's disease (AD) pathogenesis and is considered as a therapeutic target for treating AD. The Aβ electrooxidation via a Tyr‐10 residue, sensitive to a depletion of a pool of Aβ monomers and oligomers in the course of Aβ aggregation, may be employed for testing natural and synthetic organic compounds (including short peptides) potentially able to inhibit the pathological Aβ aggregation (antiaggregants). In the present work, using the known peptide antiaggregant RGKLVFFGR‐NH₂ (OR2) and its scrambled variant KGLRVGFRF‐NH₂ as a control, we demonstrate that the electrochemical method based on electrooxidation of an Aβ42 Tyr‐10 residue, when combined with methods allowing for the evaluation of the Aβ42 aggregate structure and size, can provide essential information regarding the antiaggregant impact on Aβ42 aggregation. Electrochemical measurements were performed using square wave voltammetry on carbon screen printed electrodes whereas the Aβ42 aggregate structure and size were analyzed by means of the conventional thioflavin T (ThT) based fluorescence assay and dynamic light scattering. While inhibiting Aβ42 fibrillation as manifested by the unchanged level of ThT fluorescence, the OR2 peptide antiaggregant had no effect on the decrease of Aβ42 electrooxidation current in the course of Aβ42 aggregation. These observations suggest that OR2 does not stop the aggregation but redirects it into a pathway where amorphous rather than fibrillar aggregates are formed. Hence, the direct electrochemistry appears to offer a simple and cost‐effective approach for probing potential peptide antiaggregants, which is complementary to methods based on detecting Aβ aggregates.     

Characterization of the polymorphic states of copper(II)‐bound Aβ(1–16) peptides by computational simulations

Understanding the polymorphic states of metal amyloid β (Aβ) interactions helps to elucidate metal‐mediated events in the pathogenesis of Alzheimer's disease. Systematic investigations on the effects of metal ions such as Cu²⁺ and Zn²⁺ on the structural and thermodynamic properties of Aβ at the molecular lever seem desirable. In this study, a set of new AMBER force field parameters was developed to model various Cu²⁺ coordination spheres of Aβ. These parameters including force constants and partial charges obtained using restrained electrostatic potential method were then validated in replica‐exchange molecular dynamics simulations on six Cu²⁺‐Aβ(1–16) systems. The Cu²⁺ coordination geometry differs depending on the Cu²⁺ binding fashions. The structural analyses reveal that Aβ(1–16) prefers turn conformations, which provides a geometrical favor to establish multiple Cu²⁺ coordination modes in solution at physiological pH. The relative stability of different Cu²⁺‐Aβ(1–16) complexes was estimated by free energy calculations. The Cu²⁺ ligands in the most stable Cu²⁺‐Aβ(1–16) structure involve Glu³, His⁶, His¹³ and His¹⁴ in terms of MM/3D‐RISM (molecular mechanics/three‐dimensional reference interaction site model). The solvation free energy and conformational entropy calculated by 3D‐RISM method suggest that the binding of Cu²⁺ within Aβ(1–16) is a spontaneous process. The overlap of the preparation free energy distributions demonstrates the heterogeneous states of Aβ(1–16) conformations that are ready for Cu²⁺ binding whereas the populations of such polymorphic states may shift at differing pH. © 2013 Wiley Periodicals, Inc.     

Callistephin inhibits amyloid-β protein aggregation and determined cytotoxicity against cerebrovascular smooth muscle cells as an in vitro model of cerebral amyloid angiopathy

It has been indicated that amyloid β (Aβ) plaques can be accumulated within the basement membranes of cerebrovascular smooth muscle cells (CVSMCs) and stimulate the induction of cerebral amyloid angiopathy (CAA). However, the exact mechanism(s) of which small molecules including callistephin mitigate the formation of Aβ aggregation and associated CAA is not well-understood. Therefore, in the present study, Aβ_1–42 samples in the aggregation buffer were co-incubated for 36 h without or with of callistephin and the protein aggregation features along with the associated cytotoxicity against CVSMCs as the core components of cerebral arterial wall were explored by different biochemical and cellular methods. Fluorescence (ThT, Nile red) and CD techniques indicated the inhibition of Aβ_1–42 fibrillization in the presence of callistephin. Cellular assays revealed that cytotoxicity of Aβ_1–42 samples aged in the aggregation buffer with callistephin was much less against CVSMCs than Aβ_1–42 amyloid alone through regulation of membrane leakage and downregulation of TNF-α and IL-6 at protein level. In conclusion, these data may provide useful information about the possible mechanisms by which callistephin can show its protective effect against CAA.     

Natural Compounds against Alzheimer’s Disease: Molecular Recognition of Aβ1–42 Peptide by Salvia sclareoides Extract and its Major Component,Rosmarinic Acid,as Investigated by NMR

Amyloid peptides, Aβ1–40 and Aβ1–42, represent major molecular targets to develop potential drugs and diagnostic tools for Alzheimer’s Disease (AD). In fact, oligomeric and fibrillar aggregates generated by these peptides are amongst the principal components of amyloid plaques found post mortem in patients suffering from AD. Rosmarinic acid has been demonstrated to be effective in preventing the aggregation of amyloid peptides in vitro and to delay the progression of the disease in animal models. Nevertheless, no information is available about its molecular mechanism of action. Herein, we report the NMR characterization of the interaction of Salvia sclareoides extract and that of its major component, rosmarinic acid, with Aβ1–42 peptide, whose oligomers have been described as the most toxic Aβ species in vivo. Our data shed light on the structural determinants of rosmarinic acid–Aβ1–42 oligomers interaction, thus allowing the elucidation of its mechanism of action. They also provide important information for the rational design of new compounds with higher affinity for Aβ peptides to generate new anti‐amyloidogenic molecules and/or molecular tools for the specific targeting of amyloid aggregates in vivo. In addition, we identified methyl caffeate, another natural compound present in different plants and human diet, as a good ligand of Aβ1–42 oligomers, which also shows anti‐amyloidogenic activity. Finally, we demonstrated the possibility to exploit STD‐NMR and trNOESY experiments to screen extracts from natural sources for the presence of Aβ peptide ligands.     

Rational Design and Identification of a Non‐Peptidic Aggregation Inhibitor of Amyloid‐β Based on a Pharmacophore Motif Obtained from cyclo[‐Lys‐Leu‐Val‐Phe‐Phe‐]

Inhibition of pathogenic protein aggregation may be an important and straightforward therapeutic strategy for curing amyloid diseases. Small‐molecule aggregation inhibitors of Alzheimer’s amyloid‐β (Aβ) are extremely scarce, however, and are mainly restricted to dye‐ and polyphenol‐type compounds that lack drug‐likeness. Based on the structure‐activity relationship of cyclic Aβ16–20 (cyclo‐[KLVFF]), we identified unique pharmacophore motifs comprising side‐chains of Leu², Val³, Phe⁴, and Phe⁵ residues without involvement of the backbone amide bonds to inhibit Aβ aggregation. This finding allowed us to design non‐peptidic, small‐molecule aggregation inhibitors that possess potent activity. These molecules are the first successful non‐peptidic, small‐molecule aggregation inhibitors of amyloids based on rational molecular design.     

Study of the interaction of Zn^2＋ with Aβ（10-21） by fluorescamine assay

Zinc may play a role as a co-factor in the pathogenesis of Alzheimer's disease(AD)through influencing the conformation and neurotoxicity of amyloidβ-protein(Aβ).Using the fluorescamine assay,we show for the first time that Zn~(2 )induced Aβ(10-21) aggregate in a concentration-dependent manner.These results indicate that Aβ(10-21)can be used as an in vitro model in Zn~(2 )- induced Aβaggregation and that the region 10-21 to be the minimal fragment of zinc-binding domain of full length Aβ(1-42).     

A Functional Role for Aβ in Metal Homeostasis? N‐Truncation and High‐Affinity Copper Binding

Accumulation of the β‐amyloid (Aβ) peptide in extracellular senile plaques rich in copper and zinc is a defining pathological feature of Alzheimer′s disease (AD). The Aβ1–x (x=16/28/40/42) peptides have been the primary focus of Cu^II binding studies for more than 15 years; however, the N‐truncated Aβ4–42 peptide is a major Aβ isoform detected in both healthy and diseased brains, and it contains a novel N‐terminal FRH sequence. Proteins with His at the third position are known to bind Cu^II avidly, with conditional log K values at pH 7.4 in the range of 11.0–14.6, which is much higher than that determined for Aβ1–x peptides. By using Aβ4–16 as a model, it was demonstrated that its FRH sequence stoichiometrically binds Cu^II with a conditional K_d value of 3×10⁻¹⁴ M at pH 7.4, and that both Aβ4–16 and Aβ4–42 possess negligible redox activity. Combined with the predominance of Aβ4–42 in the brain, our results suggest a physiological role for this isoform in metal homeostasis within the central nervous system.     

para‐Sulfonatocalix[n]arenes Inhibit Amyloid β‐Peptide Fibrillation and Reduce Amyloid Cytotoxicity

Amyloid β‐peptide (Aβ) fibrillation is a major hallmark of Alzheimer's disease (AD). Inhibition of Aβ fibrillation is thus considered to be an effective strategy for AD prevention and treatment. Here we show that para ‐sulfonatocalix[n ]arenes (SC[n ]A, n =4, 6, 8), a class of amphiphilic calixarene derivatives, can bind to Aβ₄₂ through nonspecific and multipoint hydrophobic interactions. Their binding leads to a pronounced delay in β‐sheet adoption and formation of multiple secondary structures of the peptide, accompanied by changes at the level of the fibrillary architecture. Furthermore, the ζ‐potential value of Aβ₄₂ incubated with SC[6/8]A decreased, which correlated with the reduction of amyloid cytotoxicity. Overall, the SC[n ]A effectively inhibits Aβ₄₂ fibrillation and reduces amyloid cytotoxicity, and SC[8]A showed the best performance among the three macrocycles, possibly owing to its having the strongest interactions with Aβ₄₂.     

A Functional Role for Aβ in Metal Homeostasis? N‐Truncation and High‐Affinity Copper Binding

Accumulation of the β‐amyloid (Aβ) peptide in extracellular senile plaques rich in copper and zinc is a defining pathological feature of Alzheimer′s disease (AD). The Aβ1–x (x=16/28/40/42) peptides have been the primary focus of Cu^II binding studies for more than 15 years; however, the N‐truncated Aβ4–42 peptide is a major Aβ isoform detected in both healthy and diseased brains, and it contains a novel N‐terminal FRH sequence. Proteins with His at the third position are known to bind Cu^II avidly, with conditional log K values at pH 7.4 in the range of 11.0–14.6, which is much higher than that determined for Aβ1–x peptides. By using Aβ4–16 as a model, it was demonstrated that its FRH sequence stoichiometrically binds Cu^II with a conditional K_d value of 3×10^?14 M at pH 7.4, and that both Aβ4–16 and Aβ4–42 possess negligible redox activity. Combined with the predominance of Aβ4–42 in the brain, our results suggest a physiological role for this isoform in metal homeostasis within the central nervous system.     

N‐Terminally Truncated Amyloid‐β(11–40/42) Cofibrillizes with its Full‐Length Counterpart: Implications for Alzheimer's Disease

Amyloid‐β peptide (Aβ) isoforms of different lengths and aggregation propensities coexist in vivo. These different isoforms are able to nucleate or frustrate the assembly of each other. N‐terminally truncated Aβ_(11–40) and Aβ_(11–42) make up one fifth of plaque load yet nothing is known about their interaction with full‐length Aβ_(1–40/42). We show that in contrast to C‐terminally truncated isoforms, which do not co‐fibrillize, deletions of ten residues from the N terminus of Aβ have little impact on its ability to co‐fibrillize with the full‐length counterpart. As a consequence, N‐terminally truncated Aβ will accelerate fiber formation and co‐assemble into short rod‐shaped fibers with its full‐length Aβ counterpart. This has implications for the assembly kinetics, morphology, and toxicity of all Aβ isoforms.     

Modification of a Small β‐Barrel Protein,To Give Pseudo‐Amyloid Structures,Inhibits Amyloid β‐Peptide Aggregation

Aggregation of amyloid β‐peptide (Aβ) is closely related to the pathogenesis of Alzheimer’s disease (AD). Although much effort has been devoted to the construction of molecules that inhibit the aggregation of Aβ1‐42, high doses are needed for the inhibition of Aβ aggregation in many cases. Previously, we reported that designed green fluorescent protein (GFP) analogues that gives pseudo‐Aβ β‐sheet structures can work as an aggregation inhibitor against Aβ. To further test this design strategy, we constructed protein analogues that mimic Aβ β‐sheet structures of amyloids by using insulin‐like growth factor 2 receptor domain 11 (IGF2R‐d11) as a scaffold. A designed protein, named IG11KK, which has a parallel configuration of Aβ‐like β sheets, can bind more preferentially to oligomeric Aβ1‐42 than the monomer. Moreover, IG11KK suppressed the aggregation of Aβ1‐42 efficiently, even though lower concentrations of IG11KK than Aβ were used. The aggregation kinetics of Aβ in the presence of the designed proteins revealed that IG11KK can work as an inhibitor not only for the early to middle stages, but also in the latter stage of Aβ aggregation owing to its favorable binding to oligomeric structures of Aβ. The design strategy using β‐barrel proteins such as IGF2R‐d11 and GFP is useful in generating excellent inhibitors of protein misfolding and amyloid formation.     

Cryptotanshinone against vascular dementia through inhibition of Aβ aggregation and inflammatory responses in cerebrovascular endothelial cells

Abnormal aggregation of amyloid-β (Aβ) peptides and associated inflammation and apoptosis in cerebrovascular endothelial cells are prelude to inhibition of onset of vascular dementia (VaD). Although small molecules have been widely used to mitigate the cell damage induced by aggregated species of Aβ, its molecular mechanism based on anti-amyloid properties and corresponding mitigation of cytotoxicity against cerebrovascular endothelial cells have not been elucidated. Herein, we used cryptotanshinone as the major bioactive compound from the root of Salvia miltiorrhiza Bunge to effectively inhibit Aβ fibrillation and associated cytotoxicity. Thoflavin T (ThT) and 1-Anilino-8-naphthalene sulfonate (ANS) fluorescence, Congo red, and circular dichroism (CD) analyses indicted that cryptotanshinone potentially inhibit Aβ_1-42 aggregation through elongation of nucleation phase, apparent decrease in the slope of the growth phase, and the final fluorescence intensity in a concentration-dependent manner. Also, cell viability, inflammation and capsae-3 assays showed that co-incubation of Aβ_1-42 peptide with cryptotanshinone in the aggregation buffer not only mitigated their cytotoxicity, but also reduced the levels of TNF-α, IL-1β, IL-6 and caspase-3 activity in cerebrovascular endothelial cells induced by Aβ_1-42. This study suggested that cryptotanshinone may show a great promise in the development of small molecule-based platforms for the treatment of VaD.     

Studies on the cross‐interaction between hIAPP and Aβ25–35 and the aggregation process in binary mixture by electrospray ionization‐ion mobility‐mass spectrometry

A wealth of epidemiological evidence indicates a strong link between type 2 diabetes (T2D) and Alzheimer's disease (AD). The fiber deposition with cross‐β‐sheet structure formed by self‐aggregation and misfolding of amyloidogenic peptides is a common hallmark of both diseases. For the patients with T2D, the fibrils are mainly found in the islets of Langerhans that results from the accumulation of human islet amyloid polypeptide (hIAPP). The major component of aggregates located in the brain of AD patients is amyloid‐β (Aβ). Many biophysical and physiological properties are shared by hIAPP and Aβ, and both peptides show similar cytotoxic mechanisms. Therefore, it is meaningful to investigate the possible cross‐interactions of hIAPP and Aβ in both diseases. In this article, the segment 25–35 of Aβ was selected because Aβ_25–35 was a core region in the process of amyloid formation and showed similar aggregation tendency and toxicity with full‐length Aβ. The electrospray ionization‐ion mobility‐mass spectrometry analysis and thioflavin T fluorescence kinetic analysis combined with transmission electron microscopy were used to explore the effects of the coexistence of Aβ_25–35 and hIAPP on the self‐aggregation of both peptides and whether there was co‐assembly in fibrillation. The results indicated that the aggregation of hIAPP and Aβ_25–35 had two nucleation stages in the binary mixtures. hIAPP and Aβ_25–35 had a high binding affinity and a series of hetero‐oligomers formed in the mixtures of hIAPP and Aβ_25–35 in the early stage. The cross‐reaction between hIAPP monomers and Aβ_25–35 monomers as well as a little of oligomers during primary nucleation stage could accelerate the aggregation of Aβ_25–35. However, owing to the obvious difference in aggregation ability between hIAPP and Aβ_25–35, this cross‐interaction had no significant impact on the self‐assembly of hIAPP. Our study may offer a better understanding for exploring the molecular mechanism of the association between AD and T2D observed in clinical and epidemiological studies and developing therapeutic strategies against amyloid diseases.     

Monomer Dynamics of Alzheimer Peptides and Kinetic Control of Early Aggregation in Alzheimer's Disease

The rate of reconfiguration—or intramolecular diffusion—of monomeric Alzheimer (Aβ) peptides is measured and, under conditions that aggregation is more likely, peptide diffusion slows down significantly, which allows bimolecular associations to be initiated. By using the method of Trp–Cys contact quenching, the rate of reconfiguration is observed to be about five times faster for Aβ₄₀, which aggregates slowly, than that for Aβ₄₂, which aggregates quickly. Furthermore, the rate of reconfiguration for Aβ₄₂ speeds up at higher pH, which slows aggregation, and in the presence of the aggregation inhibitor curcumin. The measured reconfiguration rates are able to predict the early aggregation behavior of the Aβ peptide and provide a kinetic basis for why Aβ₄₂ is more prone to aggregation than Aβ₄₀, despite a difference of only two amino acids.     

Gold‐Nanoparticle‐Based Multifunctional Amyloid‐β Inhibitor against Alzheimer’s Disease

Targeting amyloid‐β (Aβ)‐induced complex neurotoxicity has received considerable attention in the therapeutic and preventive treatment of Alzheimer’s disease (AD). The complex pathogenesis of AD suggests that it requires comprehensive treatment, and drugs with multiple functions against AD are more desirable. Herein, AuNPs@POMD‐pep (AuNPs: gold nanoparticles, POMD: polyoxometalate with Wells–Dawson structure, pep: peptide) were designed as a novel multifunctional Aβ inhibitor. AuNPs@POMD‐pep shows synergistic effects in inhibiting Aβ aggregation, dissociating Aβ fibrils and decreasing Aβ‐mediated peroxidase activity and Aβ‐induced cytotoxicity. By taking advantage of AuNPs as vehicles that can cross the blood–brain barrier (BBB), AuNPs@POMD‐pep can cross the BBB and thus overcome the drawbacks of small‐molecule anti‐AD drugs. Thus, this work provides new insights into the design and synthesis of inorganic nanoparticles as multifunctional therapeutic agents for treatment of AD.     

Resistance of Cu(Aβ4–16) to Copper Capture by Metallothionein‐3 Supports a Function for the Aβ4–42 Peptide as a Synaptic CuII Scavenger

Aβ4‐42 is a major species of Aβ peptide in the brains of both healthy individuals and those affected by Alzheimer's disease. It has recently been demonstrated to bind Cu^II with an affinity approximately 3000 times higher than the commonly studied Aβ1‐42 and Aβ1‐40 peptides, which are implicated in the pathogenesis of Alzheimer's disease. Metallothionein‐3, a protein considered to orchestrate copper and zinc metabolism in the brain and provide antioxidant protection, was shown to extract Cu^II from Aβ1‐40 when acting in its native Zn₇MT‐3 form. This reaction is assumed to underlie the neuroprotective effect of Zn₇MT‐3 against Aβ toxicity. In this work, we used the truncated model peptides Aβ1‐16 and Aβ4‐16 to demonstrate that the high‐affinity Cu^II complex of Aβ4‐16 is resistant to Zn₇MT‐3 reactivity. This indicates that the analogous complex of the full‐length peptide Cu(Aβ4‐42) will not yield copper to MT‐3 in the brain, thus supporting the concept of a physiological role for Aβ4‐42 as a Cu^II scavenger in the synaptic cleft.