Investigating the binding interactions of galantamine with β-amyloid peptide

The anti-Alzheimer’s agent galantamine is known to possess anti-amyloid properties. However the exact mechanisms are not clear. We studied the binding interactions of galantamine with amyloid peptide dimer (Aβ_1–40) through molecular docking and molecular dynamics simulations. Galantamine’s binding site within the amyloid peptide dimer was identified by docking experiments and the most stable complex was analyzed by molecular dynamics simulation. These studies show that galantamine was interacting with the central region of the amyloid dimer (Lys16–Ala21) and the C-terminal region (Ile31–Val36) with minimum structural drift of Cα atom in those regions. Strikingly, a significant drift was observed at the turn region from Asp23-Gly29 (Cα atom RMSD = 9.2 Å and 11.6 Å at 50 fs and 100 fs respectively). Furthermore, galantamine’s binding mode disrupts the key pi–pi stacking interaction between aromatic rings of Phe19 (chain A) and Phe19 (chain B) and intermolecular hydrogen bonds seen in unbound peptide dimer. Noticeably, the azepine tertiary nitrogen of galantamine was in close proximity to backbone CO of Leu34 (distance <3.5 Å) to stabilize the dimer conformation. In summary, the results indicate that galantamine binding to amyloid peptide dimer leads to a significant conformational change at the turn region (Asp23–Gly29) that disrupts interactions between individual β-strands and promotes a nontoxic conformation of Aβ_1–40 to prevent the formation of neurotoxic oligomers.     

Small molecules that protect against β-amyloid-induced cytotoxicity by inhibiting aggregation of β-amyloid

Aggregated β-amyloid (Aβ) plays crucial roles in Alzheimer's disease (AD) pathogenesis, therefore blockade of Aβ aggregation is considered as a potential therapeutic target. We designed and synthesized small molecules to reduce Aβ-induced cytotoxicity by inhibiting Aβ aggregation. The small molecules were screened via ThT, MTT, and cell-based cytotoxicity assay (Aβ burden assay). Selected compounds 1c, 1d, 1e, and 1f were then investigated by evaluating their effects on cognitive impairment of acute AD mice model. Learning and memory dysfunction by injection of Aβ(1-42) was recovered by administration of these molecules. Especially, 1d showed the best recovery activity in Y-maze task, object recognition task, and passive avoidance task with dose dependent manner. These results suggest that 1d has high potential as a therapeutic agent for AD.     

Palmitoylethanolamide counteracts reactive astrogliosis induced by β-amyloid peptide

Emerging evidence indicates that astrogliosis is involved in the pathogenesis of neurodegenerative disorders. Our previous findings suggested cannabinoids and Autacoid Local Injury Antagonism Amides (ALIAmides) attenuate glial response in models of neurodegeneration. The present study was aimed at exploring palmitoylethanolamide (PEA) ability to mitigate β-amyloid (Aβ)-induced astrogliosis. Experiments were carried out to investigate PEA's (10(-7) M) effects upon the expression and release of pro-inflammatory molecules in rat primary astrocytes activated by soluble Aβ(1-42) (1 μg/ml) as well as to identify mechanisms responsible for such actions. The effects of Aβ and exogenous PEA on the astrocyte levels of the endocannabinoidsand of endogenous ALIAmides were also studied. The peroxisome proliferator-activated receptor (PPAR)-α (MK886, 3 μM) or PPAR-γ (GW9662, 9 nM) antagonists were co-administered with PEA. Aβ elevated endogenous PEA and d5-2-arachidonoylglycerol (2-AG) levels. Exogenous PEA blunted the Aβ-induced expression of pro-inflammatory molecules. This effect was reduced by PPAR-α antagonist. Moreover, this ALIAmide, like Aβ, increased 2-AG levels. These results indicate that PEA exhibits anti-inflammatory properties able to counteract Aβ-induced astrogliosis, and suggest novel treatment for neuroinflammatory/ neurodegenerative processes.     

Structural basis of C-terminal β-amyloid peptide binding by the antibody ponezumab for the treatment of Alzheimer's disease

Alzheimer's disease, the most common cause of dementia in the elderly and characterized by the deposition and accumulation of plaques, is composed in part of β-amyloid (Aβ) peptides, loss of neurons, and the accumulation of neurofibrillary tangles. Here, we describe ponezumab, a humanized monoclonal antibody, and show how it binds specifically to the carboxyl (C)-terminus of Aβ40. Ponezumab can label Aβ that is deposited in brain parenchyma found in sections from Alzheimer's disease casualties and in transgenic mouse models that overexpress Aβ. Importantly, ponezumab does not label full-length, non-cleaved amyloid precursor protein on the cell surface. The C-terminal epitope of the soluble Aβ present in the circulation appears to be available for ponezumab binding because systemic administration of ponezumab greatly elevates plasma Aβ40 levels in a dose-dependent fashion after administration to a mouse model that overexpress human Aβ. Administration of ponezumab to transgenic mice also led to a dose-dependent reduction in hippocampal amyloid load. To further explore the nature of ponezumab binding to Aβ40, we determined the X-ray crystal structure of ponezumab in complex with Aβ40 and found that the Aβ40 carboxyl moiety makes extensive contacts with ponezumab. Furthermore, the structure-function analysis supported this critical requirement for carboxy group of AβV40 in the Aβ-ponezumab interaction. These findings provide novel structural insights into the in vivo conformation of the C-terminus of Aβ40 and the brain Aβ-lowering efficacy that we observed following administration of ponezumab in transgenic mouse models.     

Modulation of β-amyloid precursor protein trafficking and processing by the low density lipoprotein receptor family

Selenium is an essential micronutrient that function through selenoproteins. Selenium deficiency results in lower concentrations of selenium and selenoproteins. The brain maintains it's selenium better than other tissues under low-selenium conditions. Recently, the selenium-containing protein selenoprotein P (Sepp) has been identified as a possible transporter of selenium. The targeted disruption of the selenoprotein P gene (Sepp1) results in decreased brain selenium concentration and neurological dysfunction, unless selenium intake is excessive However, the effect of selenoprotein P deficiency on the processes of memory formation and synaptic plasticity is unknown. In the present studies Sepp1(-/-) mice and wild type littermate controls (Sepp1(+/+)) fed a high-selenium diet (1 mg Se/kg) were used to characterize activity, motor coordination, and anxiety as well as hippocampus-dependent learning and memory. Normal associative learning, but disrupted spatial learning was observed in Sepp1(-/-) mice. In addition, severe alterations were observed in synaptic transmission, short-term plasticity and long-term potentiation in hippocampus area CA1 synapses of Sepp1(-/-) mice on a 1 mg Se/kg diet and Sepp1(+/+) mice fed a selenium-deficient (0 mg Se/kg) diet. Taken together, these data suggest that selenoprotein P is required for normal synaptic function, either through presence of the protein or delivery of required selenium to the CNS.     

Cholesterol promotes the interaction of Alzheimer β-amyloid monomer with lipid bilayer

Cholesterol in the plasma membrane plays an important role in the pathogenesis of Alzheimer's disease, but the exact function of cholesterol in the regulation of amyloid-β (Aβ) generation, aggregation, and toxicity remains elusive. To gain insight into the bioactivity of cholesterol, we investigate the effect of cholesterol levels on the interaction of Aβ(1-42) monomer with the zwitterionic 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) bilayer containing different mole fractions of cholesterol from χ=0, 0.2, to 0.4 using all-atom molecular dynamics simulations. Simulation results show that an increased cholesterol level alters the structure, dynamics, and surface chemistry of the lipid bilayer, leading to increased bilayer thickness, hydrophobic chain order, surface hydrophobicity, and decreased lipid mobility. All these effects significantly promote the binding of Aβ to the lipid bilayer. Mechanistically, the adsorption of Aβ on the bilayer is a cooperative process. First, charged residues act as anchors to establish the initial binding of Aβ to phosphate headgroups of the bilayer driven by electrostatic interactions, which further facilitates hydrophobic residues to reside on the bilayer. Once hydrophobic residues especially from C-terminus are locked on the bilayer, the interactions among charged residues, lipid bilayer, and calcium ions are optimized to provide additional attractive forces to stabilize Aβ adsorbed on or inserted into the lipid bilayer. Inclusion of cholesterol makes this binding process more energetically favorable. Upon adsorption on the bilayer, Aβ appears to preferentially adopt α-helical or unstructured conformation. This work supports that cholesterol acts as a promoter for Aβ--membrane interactions, which would facilitate Aβ aggregation and membrane insertion.     

Elevation of plasma β-amyloid level by glucose loading in Alzheimer mouse models

With the emergence of a promising approach to treat Alzheimer disease (AD) targeting the β-amyloid (Aβ) pathway, it is necessary to establish new diagnostic biomarkers that enable the antemortem diagnosis of AD. Although plasma Aβ has been suggested as a non-invasive biomarker, its significance has been inconclusive. Thus, it is important to improve the diagnostic potential of plasma Aβ. One of the potential approaches is to modify plasma Aβ level using various modulators. In this study, we evaluated the influence of glucometabolic status on plasma Aβ level in two lines of AD transgenic mouse. The present study demonstrated that plasma Aβ level rapidly increased after glucose loading. More importantly, the magnitude of the increase in plasma Aβ was significantly larger in AD transgenic mice than in wild-type littermates. These findings might provide a novel diagnostic tool for AD using the elevation of plasma Aβ level after glucose loading.     

MEK inhibitors suppress β-amyloid production by altering the level of a β-C-terminal fragment of amyloid precursor protein in neuronal cells

β-Amyloid peptide (Aβ) is generated via sequential proteolysis of amyloid precursor protein (APP) by β- and γ-secretases. Cell-based screening experiments disclosed that the MEK (MAP kinase kinase) inhibitors, U0126 and PD184352, suppress Aβ secretion from human neuronal SH-SY5Y cells expressing Swedish mutant APP. These inhibitors did not affect the cellular levels of APP but significantly reduced those of the APP β-C-terminal fragment (β-CTF). Additionally, β-CTF levels were markedly reduced by these inhibitors in cells expressing the fragment in a γ-secretase-independent and proteasome-dependent manner. Our results suggest that MEK inhibitors reduce Aβ generation via secretase-independent alteration of β-CTF levels.     

Cross interaction of β-amyloid peptide and prion protein fragments

Summary This article presents kinetic studies of cross interaction of β-amyloid peptide and prion protein fragments. Syntheses of three peptides (β25-35, β22-35 and PrP 109–126) were performed. Those peptides were used for aggregation studies in PBS and TRIS buffers using HPLC with DAD detector. Comparison of aggregation of peptides alone and in combination with other fragments was investigated. In all cases aggregation was faster in PBS than in TRIS solution. Obtained results suggest that β-amyloid peptide and prion protein may interact to form macromolecular complexes with different ability for aggregation.     

Highly polymorphic repeat marker within the β-amyloid precursor protein gene

We have identified a polymorphic compound dinucleotide repeat sequence in intron 1 of the -amyloid precursor protein (APP) gene on chromosome 21. Using polymerase chain reaction (PCR) amplification of the locus, designated APPivsl, we detected 13 alleles in the CEPH family members (heterozygosity = 0.69). Lod score analysis showed complete linkage of the marker to the loci D21S210 and D21221.     

Methionine oxidation: Implications for the mechanism of toxicity of the β-amyloid peptide from Alzheimer's disease

Summary The amyloid β-peptide, Aβ is toxic to neurons and this toxicity plays a central role in the progression of Alzheimer's disease. The mechanism(s) by which Aβ exerts its toxicity has been hotly debated with several theories postulated. Here we discuss the role of oxidation of the sulfur atom of Met35 in Aβ42 (Met(O)Aβ), a modification that has significant implications for the mechanism of Aβ toxicity. Both Met(O)Aβ and its native form display toxicity to primary neuronal cells in culture which can be rescued by catalase, a H₂O₂ inhibitor and clioquinol a mild copper chelator. However both native Aβ and Met(O)Aβ differ substantially in primary and secondary structures, solubility, ability to penetrate lipid membranes, and oligomerization profiles. It is clearly evident that metals play an important role in the oxidation of Aβ to Met(O)Aβ via Fenton chemistry and that regulation of this pathway has a potential therapeutic application for the regulation of Alzheimer's disease.     

Sublethal doses of β-amyloid peptide abrogate DNA-dependent protein kinase activity

Accumulation of DNA damage and deficiency in DNA repair potentially contribute to the progressive neuronal loss in neurodegenerative disorders, including Alzheimer disease (AD). In multicellular eukaryotes, double strand breaks (DSBs), the most lethal form of DNA damage, are mainly repaired by the nonhomologous end joining pathway, which relies on DNA-PK complex activity. Both the presence of DSBs and a decreased end joining activity have been reported in AD brains, but the molecular player causing DNA repair dysfunction is still undetermined. β-Amyloid (Aβ), a potential proximate effector of neurotoxicity in AD, might exert cytotoxic effects by reactive oxygen species generation and oxidative stress induction, which may then cause DNA damage. Here, we show that in PC12 cells sublethal concentrations of aggregated Aβ(25-35) inhibit DNA-PK kinase activity, compromising DSB repair and sensitizing cells to nonlethal oxidative injury. The inhibition of DNA-PK activity is associated with down-regulation of the catalytic subunit DNA-PK (DNA-PKcs) protein levels, caused by oxidative stress and reversed by antioxidant treatment. Moreover, we show that sublethal doses of Aβ(1-42) oligomers enter the nucleus of PC12 cells, accumulate as insoluble oligomeric species, and reduce DNA-PK kinase activity, although in the absence of oxidative stress. Overall, these findings suggest that Aβ mediates inhibition of the DNA-PK-dependent nonhomologous end joining pathway contributing to the accumulation of DSBs that, if not efficiently repaired, may lead to the neuronal loss observed in AD.     

Protective effect of ε-viniferin on β-amyloid peptide aggregation investigated by electrospray ionization mass spectrometry

Abnormal β-amyloid peptide accumulation and aggregation is considered to be responsible for the formation and cerebral deposition of senile plaques in the brains of patients with Alzheimer's disease (AD). Inhibition of the formation of β-amyloid (Aβ) fibrils would be an attractive therapeutic target for the treatment of AD. Resveratrol and its derivatives exhibit a broad range of pharmacological properties such as protection against cardiovascular diseases and cancers, as well as promoting antiaging effects. We reported previously that ε-viniferin glucoside (VG), a resveratrol-derived dimer, strongly inhibits Aβ (25-35) fibril formation in vitro. In this study, we investigated the effects of VG on the aggregation of the full-length peptides (Aβ (1-40) and Aβ (1-42)) and on the β-amyloid-induced toxicity in PC12 cells. VG inhibited Aβ cytotoxicity and the non-covalent complex between VG and Aβ was observed by electrospray ionization mass spectrometry.     

Bitterness Reduction of Citrus Fruits by β-Cyclodextrin

The levels of free amino acid, ammonia nitrogen and guanidino compounds were examined in renal failure rats induced by adenine. Among the essential amino acids in the serum, the marked reduction of lysine, valine, leucine and isoleucine was confirmed in the adenine-fed group as compared with the control group. Tyrosine and ornithine were also significantly reduced in the adenine-fed rats, while glycine, arginine and aspartic acid were significantly elevated. The urinary excretion of leucine, isoleucine and non-essential amino acids (glutamic acid, histidine, aspartic acid, citrulline, tyrosine, ornithine) was found to be high. On the other hand, adenine administered orally caused hyperammonemia. Furthermore, the results of the present study show that intake of adenine increased extraordinarily the level of guanidinosuccinic acid and methylguanidine in the serum, while the value of serum guanidinosuccinic acid and methylguanidine in rats fed on a control diet was not detectable.     

A peptide that binds specifically to the β-amyloid of Alzheimer's disease: selection and assessment of anti-β-amyloid neurotoxic effects

The accumulation of the amyloid-β peptide (Aβ) into amyloid plaques, an essential event in Alzheimer''s disease (AD) pathogenesis, has caused researchers to seek compounds that physiologically bind Aβ and modulate its aggregation and neurotoxicity. In order to develop new Aβ-specific peptides for AD, a randomized 12-mer peptide library with Aβ_1-10 as the target was used to identify peptides in the present study. After three rounds of selection, specific phages were screened, and their binding affinities to Aβ_1-10 were found to be highly specific. Finally, a special peptide was synthesized according to the sequences of the selected phages. In addition, the effects of the special peptide on Aβ aggregation and Aβ-mediated neurotoxicity in vitro and in vivo were assessed. The results show that the special peptide not only inhibited the aggregation of Aβ into plaques, but it also alleviated Aβ-induced PC12 cell viability and apoptosis at appropriate concentrations as assessed by the cell counting kit-8 assay and propidium iodide staining. Moreover, the special peptide exhibited a protective effect against Aβ-induced learning and memory deficits in rats, as determined by the Morris water maze task. In conclusion, we selected a peptide that specifically binds Aβ_1-10 and can modulate Aβ aggregation and Aβ-induced neuronal damage. This opens up possibilities for the development of a novel therapeutic approach for the treatment of AD.     

Glycation exacerbates the neuronal toxicity of β-amyloid

Accumulation evidence shows that β-amyloid (Aβ) is a neurotoxic and accumulation of Aβ is responsible for the pathology of Alzheimer''s disease (AD). However, it is currently not fully understood what makes Aβ toxic and accumulated. Previous studies demonstrate that Aβ is a suitable substrate for glycation, producing one form of the advanced glycation endproducts (AGEs). We speculated that Aβ-AGE formation may exacerbate the neurotoxicity. To explore whether the Aβ-AGE is more toxic than the authentic Aβ and to understand the molecular mechanisms, we synthesized glycated Aβ by incubating Aβ with methylglyoxal (MG) in vitro and identified the formation of glycated Aβ by fluorescence spectrophotometer. Then, we treated the primary hippocampal neurons cultured 8 days in vitro with Aβ-AGE or Aβ for 24 h. We observed that glycation exacerbated neurotoxicity of Aβ with upregulation of receptor for AGE (RAGE) and activation of glycogen synthase kinase-3 (GSK-3), whereas simultaneous application of RAGE antibody or GSK-3 inhibitor reversed the neuronal damages aggravated by glycated Aβ. Thereafter, we found that Aβ is also glycated with an age-dependent elevation of AGEs in Tg2576 mice, whereas inhibition of Aβ-AGE formation by subcutaneously infusion of aminoguanidine for 3 months significantly rescued the early cognitive deficit in mice. Our data reveal for the first time that the glycated Aβ is more toxic. We propose that the glycated Aβ with the altered secondary structure may be a more suitable ligand than Aβ for RAGE and subsequent activation of GSK-3 that can lead to cascade pathologies of AD, therefore glycated Aβ may be a new therapeutic target for AD.     

Ab initio modelling of the structure and redox behaviour of copper(I) bound to a His–His model peptide: relevance to the β-amyloid peptide of Alzheimer’s disease

A contributing factor to the pathology of Alzheimer's disease is the generation of reactive oxygen species, most probably a consequence of the beta-amyloid (Abeta) peptide coordinating copper ions. Experimental and theoretical results indicate that His13 and His14 are the two most firmly established ligands in the coordination sphere of Cu(II) bound to Abeta. Abeta1-42 is known to reduce Cu(II) to Cu(I). The Abeta-Cu(II) complex has been shown to catalytically generate H(2)O(2) from reducing agents and O(2). Cu(II) in the presence of Abeta has been reported to have a formal reduction potential of +0.72-0.77 V (vs. the standard hydrogen electrode). Quantum chemical calculations using the B3LYP hybrid density functional method with the 6-31G(d) basis set were performed to model the reduction of previously studied Cu(II) complexes representing the His13-His14 portion of Abeta (Raffa et al. in J. Biol. Inorg. Chem. 10:887-902, 2005). The effects of solvation were accommodated using the CPCM method. The most stable complex between Cu(I) and the model compound, 3-(5-imidazolyl)propionylhistamine (1) involves tricoordinated Cu(I) in a distorted-T geometry, with the Npi of both imidazoles as well as the oxygen of the backbone carbonyl bound to copper. This model would be the most likely representation of a Cu(I) binding site for a His-His peptide in aqueous solution. A variety of possible redox processes are discussed.