Zinc-induced heterodimer formation between metal-binding domains of intact and naturally modified amyloid-beta species: implication to amyloid seeding in Alzheimer’s disease?

Zinc ions and modified amyloid-beta peptides (Aβ) play a critical role in the pathological aggregation of endogenous Aβ in Alzheimer’s disease (AD). Zinc-induced Aβ oligomerization is mediated by the metal-binding domain (MBD) which includes N-terminal residues 1–16 (Aβ_1–16). Earlier, it has been shown that Aβ_1–16 as well as some of its naturally occurring variants undergoes zinc-induced homodimerization via the interface in which zinc ion is coordinated by Glu11 and His14 of the interacting subunits. In this study using surface plasmon resonance technique, we have found that in the presence of zinc ions Aβ_1–16 forms heterodimers with MBDs of two Aβ species linked to AD: Aβ containing isoAsp7 (isoAβ) and Aβ containing phosphorylated Ser8 (pS8-Aβ). The heterodimers appear to possess the same interface as the homodimers. Simulation of 200 ns molecular dynamic trajectories in two constructed models of dimers ([Aβ_1–16/Zn/Aβ_1–16] and [isoAβ_1–16/Zn/Aβ_1–16]), has shown that conformational flexibility of the N-terminal fragments of the dimer subunits is controlled by the structure of corresponding sites 6–8. The data suggest that isoAβ and pS8-Aβ can be involved in the AD pathogenesis by means of their zinc-dependent interactions with endogenous Aβ resulting in the formation of heterodimeric seeds for amyloid aggregation.     

Heat-shock protein HSP70 reduces the secretion of TNFα by neuroblastoma cells and human monocytes induced with beta-amyloid peptides

The progress of neurodegeneration in Alzheimer’s disease is closely associated with inflammatory processes in the brain tissues induced by beta-amyloid peptides (Aβ). In this paper, we showed that Aβ(1-42) and isoAβ(1-42) in human neuroblastoma cells SK-N-SH and promonocyte THP-1 activated the production of tumor necrosis factor (TNFα). Notably, isoAβ(1-42) had the strongest effect on the increase in the level of TNFα. The addition of recombinant heat-shock protein HSP70 reduces TNFα production induced by Aβ, which leads to a decrease in neuronal cell damage at the organism level.     

Hopeahainol A attenuates memory deficits by targeting β‐amyloid in APP/PS1 transgenic mice

Increasing evidence demonstrates that amyloid beta (Aβ) elicits mitochondrial dysfunction and oxidative stress, which contributes to the pathogenesis of Alzheimer's disease (AD). Identification of the molecules targeting Aβ is thus of particular significance in the treatment of AD. Hopeahainol A (HopA), a polyphenol with a novel skeleton obtained from Hopea hainanensis, is potentially acetylcholinesterase‐inhibitory and anti‐oxidative in H₂O₂‐treated PC12 cells. In this study, we reported that HopA might bind to Aβ_1–42 directly and inhibit the Aβ_1–42 aggregation using a combination of molecular dynamics simulation, binding assay, transmission electron microscopic analysis and staining technique. We also demonstrated that HopA decreased the interaction between Aβ_1–42 and Aβ‐binding alcohol dehydrogenase, which in turn reduced mitochondrial dysfunction and oxidative stress in vivo and in vitro. In addition, HopA was able to rescue the long‐term potentiation induction by protecting synaptic function and attenuate memory deficits in APP/PS1 mice. Our data suggest that HopA might be a promising drug for therapeutic intervention in AD.     

Enalaprilat Inhibits Zinc-Dependent Oligomerization of Metal-Binding Domain of Amyloid-beta Isoforms and Protects Human Neuroblastoma Cells from Toxic Action of these Isoforms

Intact amyloid-β peptides (Aβ) may undergo prion-like aggregation when they interact with chemically or structurally modified variants of Aβ present in extracellular pathohistological inclusions (amyloid plaques). This aggregation is regarded as one of the key molecular mechanisms of Alzheimer’s disease (AD) pathogenesis. Zinc ions are involved in the pathological dimerization and oligomerization of natural Aβ isoforms, and zinc-induced oligomers can also initiate the pathological aggregation of Aβ. Based on the earlier found molecular mechanism of zinc-dependent oligomerization of Aβ, it has been suggested that the targeted inhibition of the 11EVHH14 site in one Aβ molecule from zinc-mediated interactions with the same site of another Aβ molecule can effectively inhibit the oligomerization and aggregation of Aβ. Taking into account the similarity in the structural organization of zinc-binding sites within Aβ and angiotensin-converting enzyme (ACE), we hypothesized that inhibitors of the ACE active sites could specifically interact with the 11EVHH14 site of Aβ. Using a surface plasmon resonance biosensor and nuclear magnetic resonance spectroscopy, we have found that the ACE inhibitor enalaprilat effectively inhibits zinc-dependent dimerization of the metal-binding domains of intact Aβ and Aβ with isomerized Asp7 (isoAβ). We have also found that enalaprilat protects SH-SY5Y human neuroblastoma cells from the toxic effects of Aβ(1–42) and isoAβ(1–42), which are among the most common components of amyloid plaques. The results confirm the role of zincdependent oligomerization of Aβ in AD pathogenesis and make it possible one to consider enalaprilat as a prototype of antiaggregation agents for treating AD.     

Multi-target-directed triazole derivatives as promising agents for the treatment of Alzheimer’s disease

A novel series of triazole-based compounds have been designed, synthesised and evaluated as multi-target-directed ligands (MTDLs) against Alzheimer disease (AD). The triazole-based compounds have been designed to target four major AD hallmarks that include Aβ aggregation, metal-induced Aβ aggregation, metal dys-homeostasis and oxidative stress. Among the synthesised compounds, 6n having o-CF₃ group on the phenyl ring displayed most potent inhibitory activity (96.89% inhibition, IC₅₀ = 8.065 ± 0.129 μM) against Aβ₄₂ aggregation, compared to the reference compound curcumin (95.14% inhibition, IC₅₀ = 6.385 ± 0.009 μM). Compound 6n disassembled preformed Aβ₄₂ aggregates as effectively as curcumin. Furthermore, 6n displayed metal chelating ability and significantly inhibited Cu²⁺-induced Aβ₄₂ aggregation and disassembled preformed Cu²⁺-induced Aβ₄₂ aggregates. 6n successfully controlled the generation of the reactive oxygen species (ROS) by preventing the copper redox cycle. In addition, 6n did not display cytotoxicity and was able to inhibit toxicity induced by Aβ₄₂ aggregates in SH-SY5Y cells. The preferred binding regions and key interactions of 6n with Aβ₄₂ monomer and Aβ₄₂ protofibril structure was evaluated with molecular docking. Compound 6n binds preferably to the C-terminal region of Aβ₄₂ that play a critical role in Aβ₄₂ aggregation. The results of the present study highlight a novel triazole-based compound, 6n, as a promising MTDL against AD.     

Design,synthesis, and evaluation of Trolox-conjugated amyloid-β C-terminal peptides for therapeutic intervention in an in vitro model of Alzheimer’s disease

Two hallmarks of Alzheimer’s disease (AD) observed in the brains of patients with the disease include oxidative injury and deposition of protein aggregates comprised of amyloid-β (Aβ) variants. To inhibit these toxic processes, we synthesized antioxidant-conjugated peptides comprised of Trolox and various C-terminal motifs of Aβ variants, TxAβ_x–n (x = 34, 36, 38, 40; n = 40, 42, 43). Most of these compounds were found to exhibit anti-aggregation activities. Among them, TxAβ_36–42 significantly inhibited Aβ_1–42 aggregation, showed potent antioxidant activity, and protected SH-SY5Y cells from Aβ_1–42-induced cytotoxicity. Thus, this method represents a promising strategy for developing multifunctional AD therapeutic agents.     

Human apolipoprotein A–I binds amyloid-β and prevents Aβ-induced neurotoxicity

Aggregates of the amyloid-β peptide (Aβ) play a central role in the pathogenesis of Alzheimer's disease (AD). Identification of proteins that physiologically bind Aβ and modulate its aggregation and neurotoxicity could lead to the development of novel disease-modifying approaches in AD. By screening a phage display peptide library for high affinity ligands of aggregated Aβ_1–42, we isolated a peptide homologous to a highly conserved amino acid sequence present in the N-terminus of apolipoprotein A–I (apoA-I). We show that purified human apoA-I and Aβ form non-covalent complexes and that interaction with apoA-I affects the morphology of amyloid aggregates formed by Aβ. Significantly, Aβ/apoA-I complexes were also detected in cerebrospinal fluid from AD patients. Interestingly, apoA-I and apoA-I-containing reconstituted high density lipoprotein particles protect hippocampal neuronal cultures from Aβ-induced oxidative stress and neurodegeneration. These results suggest that human apoA-I modulates Aβ aggregation and Aβ-induced neuronal damage and that the Aβ-binding domain in apoA-I may constitute a novel framework for the design of inhibitors of Aβ toxicity.     

Cholesterol ester hydrolase inhibitors reduce the production of synaptotoxic amyloid-β oligomers

The production of amyloid-β (Aβ) is the key factor driving pathogenesis in Alzheimer's disease (AD). Increasing concentrations of Aβ within the brain cause synapse degeneration and the dementia that is characteristic of AD. Here the factors that affect the release of disease-relevant forms Aβ were studied in a cell model. 7PA2 cells expressing the human amyloid precursor protein released soluble Aβ oligomers that caused synapse damage in cultured neurons. Supernatants from 7PA2 cells treated with the cholesterol synthesis inhibitor squalestatin contained similar concentrations of Aβ₄₂ to control cells but did not cause synapse damage in neuronal cultures. These supernatants contained reduced concentrations of Aβ₄₂ oligomers and increased concentrations of Aβ₄₂ monomers. Treatment of 7PA2 cells with platelet-activating factor (PAF) antagonists had similar effects; it reduced concentrations of Aβ₄₂ oligomers and increased concentrations of Aβ₄₂ monomers in cell supernatants. PAF activated cholesterol ester hydrolases (CEH), enzymes that released cholesterol from stores of cholesterol esters. Inhibition of CEH also reduced concentrations of Aβ₄₂ oligomers and increased concentrations of Aβ₄₂ monomers in cell supernatants. The Aβ monomers produced by treated cells protected neurons against Aβ oligomer-induced synapse damage. These studies indicate that pharmacological manipulation of cells can alter the ratio of Aβ monomer:oligomer released and consequently their effects on synapses.     

Asymmetric dimethylarginine exacerbates Aβ-induced toxicity and oxidative stress in human cell and Caenorhabditis elegans models of Alzheimer disease

Growing evidence suggests a strong association between cardiovascular risk factors and incidence of Alzheimer disease (AD). Asymmetric dimethylarginine (ADMA), the endogenous nitric oxide synthase inhibitor, has been identified as an independent cardiovascular risk factor and is also increased in plasma of patients with AD. However, whether ADMA is involved in the pathogenesis of AD is unknown. In this study, we found that ADMA content was increased in a transgenic Caenorhabditis elegans β-amyloid (Aβ) overexpression model, strain CL2006, and in human SH-SY5Y cells overexpressing the Swedish mutant form of human Aβ precursor protein (APPsw). Moreover, ADMA treatment exacerbated Aβ-induced paralysis and oxidative stress in CL2006 worms and further elevated oxidative stress and Aβ secretion in APPsw cells. Knockdown of type 1 protein arginine N-methyltransferase to reduce ADMA production failed to show a protective effect against Aβ toxicity, but resulted in more paralysis in CL2006 worms as well as increased oxidative stress and Aβ secretion in APPsw cells. However, overexpression of dimethylarginine dimethylaminohydrolase 1 (DDAH1) to promote ADMA degradation significantly attenuated oxidative stress and Aβ secretion in APPsw cells. Collectively, our data support the hypothesis that elevated ADMA contributes to the pathogenesis of AD. Our findings suggest that strategies to increase DDAH1 activity in neuronal cells may be a novel approach to attenuating AD development.     

Perforin Promotes Amyloid Beta Internalisation in Neurons

Studies on the mechanisms of neuronal amyloid-β (Aβ) internalisation are crucial for understanding the neuropathological progression of Alzheimer’s disease (AD). We here investigated how extracellular Aβ peptides are internalised and focused on three different pathways: (i) via endocytic mechanisms, (ii) via the receptor for advanced glycation end products (RAGE) and (iii) via the pore-forming protein perforin. Both Aβ₄₀ and Aβ₄₂ were internalised in retinoic acid differentiated neuroblastoma (RA-SH-SY5Y) cells. A higher concentration was required for Aβ₄₀ (250 nM) compared with Aβ₄₂ (100 nM). The internalised Aβ₄₀ showed a dot-like pattern of distribution whereas Aβ₄₂ accumulated in larger and distinct formations. By confocal microscopy, we showed that Aβ₄₀ and Aβ₄₂ co-localised with mitochondria, endoplasmic reticulum (ER) and lysosomes. Aβ treatment of human primary cortical neurons (hPCN) confirmed our findings in RA-SH-SY5Y cells, but hPCN were less sensitive to Aβ; therefore, a 20 (Aβ₄₀) and 50 (Aβ₄₂) times higher concentration was needed for inducing uptake. The blocking of endocytosis completely inhibited the internalisation of Aβ peptides in RA-SH-SY5Y cells and hPCN, indicating that this is a major pathway by which Aβ enters the cells. In addition, the internalisation of Aβ₄₂, but not Aβ₄₀, was reduced by 55 % by blocking RAGE. Finally, for the first time we showed that pore formation in cell membranes by perforin led to Aβ internalisation in hPCN. Understanding how Aβ is internalised sheds light on the pathological role of Aβ and provides further ideas of inhibitory strategies for preventing Aβ internalisation and the spreading of neurodegeneration in AD.     

Loss of proteostasis induced by amyloid beta peptide in brain endothelial cells

Abnormal accumulation of amyloid-β (Aβ) peptide in the brain is a pathological hallmark of Alzheimer's disease (AD). In addition to neurotoxic effects, Aβ also damages brain endothelial cells (ECs) and may thus contribute to the degeneration of cerebral vasculature, which has been proposed as an early pathogenic event in the course of AD and is able to trigger and/or potentiate the neurodegenerative process and cognitive decline. However, the mechanisms underlying Aβ-induced endothelial dysfunction are not completely understood. Here we hypothesized that Aβ impairs protein quality control mechanisms both in the secretory pathway and in the cytosol in brain ECs, leading cells to death. In rat brain RBE4 cells, we demonstrated that Aβ_1–40 induces the failure of the ER stress-adaptive unfolded protein response (UPR), deregulates the ubiquitin–proteasome system (UPS) decreasing overall proteasome activity with accumulation of ubiquitinated proteins and impairs the autophagic protein degradation pathway due to failure in the autophagic flux, which culminates in cell demise. In conclusion, Aβ deregulates proteostasis in brain ECs and, as a consequence, these cells die by apoptosis.     

Diazoxide Pretreatment Prevents Aβ1–42 Induced Oxidative Stress in Cholinergic Neurons Via Alleviating NOX2 Expression

The aggregation and accumulation of amyloid-β (Aβ) plays a significant role in the pathogenesis of Alzheimer’s disease. Aβ is known to increase free radical production in neuronal cells, leading to oxidative stress and cell death. Diazoxide (DZ), a highly selective drug capable of opening mitochondrial ATP-sensitive potassium channels, has neuroprotective effects against neuronal cell death. However, the mechanism through which DZ protects cholinergic neurons against Aβ-induced oxidative injury is still unclear. The present study was designed to investigate the effects of DZ pretreatment against Aβ_1–42 induced oxidative damage and cytotoxicity. Through measures of DZ effects on Aβ_1–42 induced cellular damage, reactive oxygen species (ROS) and MDA generation and expressions of gp91phox and p47phox in cholinergic neurons, new insights into the neuroprotective mechanisms can be derived. Aβ_1–42 significantly decreased 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide levels and increased ROS and MDA production; all effects were attenuated by pretreatment with DZ or diphenyleneiodonium chloride (a NOX2 inhibitor). Pretreatment with DZ also attenuated the upregulation of NOX2 subunits (gp91phox and p47phox) induced by Aβ_1–42. Since NOX2 is one of the main sources of free radicals, these results suggest that DZ can counteract Aβ_1–42 induced oxidative stress and associated cell death by reducing the level of ROS and MDA, in part, by alleviating NOX2 expression.     

No correlation between time-linked plasma and CSF Aβ levels

Plasma β-amyloid protein (Aβ) isoforms are considered potential biomarkers for Alzheimer's disease (AD) and dementia. The relation between plasma and cerebrospinal fluid (CSF) levels of Aβ isoforms remains unclear. In order to identify possible correlations between Aβ levels in plasma and CSF we determined Aβ levels in time-linked plasma and CSF samples. Aβ concentrations in plasma (Aβ_1–42 and Aβ_N–42) and CSF (Aβ_1–42) samples from 49 AD patients, 47 non-Alzheimer's disease dementia (NONAD) patients, 39 MCI patients and 29 controls were determined using a multi-parameter fluorimetric bead-based immunoassay using xMAP^® technology (for plasma) and a conventional single-parameter ELISA (for CSF). Plasma Aβ_1–42 concentrations did not correlate with CSF Aβ_1–42 concentrations in the total study population, or in the different diagnostic groups. No correlations between plasma Aβ_N–42 and CSF Aβ_1–42 levels were found either. The CSF/serum albumin index did not show any significant differences between AD, NONAD, MCI and controls.These results suggest that the Aβ levels in plasma are independent of the Aβ levels in CSF both in dementia and controls. The fact that CSF and plasma Aβ do not correlate in patients as well as controls and no significant differences in plasma Aβ_1–42 or Aβ_N–42 between patients and controls can be detected hampers the diagnostic utility of the plasma Aβ levels as biomarkers for dementia.     

Evaluation of Selenium,Redox Status and Their Association with Plasma Amyloid/Tau in Alzheimer’s Disease

The aim of the study was to evaluate blood selenium and antioxidants as possible oxidative stress markers in Alzheimer’s disease (AD) along with amyloid β42 (Aβ42) and tau by comparing them with vascular dementia (VD) and age-matched healthy controls. Selenium, total tau, Aβ42, glutathione (GSH) and malondialdehyde (MDA) levels and the activities of antioxidant enzymes were analysed in the blood of AD patients (n?=?30), VD patients (n?=?35) and controls (n?=?40) from South India. Plasma Aβ42 level was significantly higher (P?<?0.001) in both AD and VD compared to controls. Total tau and tau-to-amyloid ratio were significantly lower in both AD and VD (P?<?0.001), compared to controls, and a significant difference (P?<?0.01 and P?<?0.05, respectively) was also observed between AD and VD. The receiver operating characteristic (ROC) curve-derived cutoff values of <3.5 for tau-to-Aβ42 ratio and <520 pg/ml for total tau showed sensitivity and specificity of around 67–72 % for differentiating AD from VD and around 90 % for AD from controls, indicating that they could serve as reliable AD-specific markers. The MDA levels were significantly higher (P?<?0.001) in both dementia groups along with a significant decrease (P?<?0.001) in reduced GSH levels, indicating elevated oxidative stress and altered redox status in both forms of dementia. Selenium levels did not vary significantly between the three groups. The activity of glutathione peroxidase increased in both AD and VD compared to controls, with a concomitant decrease in glutathione reductase and glucose-6-phospate dehydrogenase (P?<?0.001) activity. The activity of thioredoxin reductase was significantly lower in both patient groups (P?<?0.001) compared to healthy controls. No correlation was observed between selenium and activities of selenoenzymes, tau, Aβ42 or tau-to-Aβ42 ratio, when analysing independently, indicating that blood selenium may not be directly involved in Aβ production and in regulating tau/Aβ42-mediated mechanism in AD. The present study emphasizes the enhanced oxidative stress in AD pathology and plasma tau and tau-to-amyloid ratio as possible markers to differentiate AD from VD. The study also points that blood selenium may not be involved in regulating oxidative stress in AD, and a longitudinal study correlating plasma and cerebrospinal fluid (CSF) selenium and selenoprotein levels is warranted.     

Maresin 1 attenuates pro-inflammatory activation induced by β-amyloid and stimulates its uptake

Alzheimer's disease (AD) is the most common dementia, characterized by pathological accumulation of β-amyloid (Aβ) and hyperphosphorylation of tau protein, together with a damaging chronic inflammation. The lack of effective treatments urgently warrants new therapeutic strategies. Resolution of inflammation, associated with beneficial and regenerative activities, is mediated by specialized pro-resolving lipid mediators (SPMs) including maresin 1 (MaR1). Decreased levels of MaR1 have been observed in AD brains. However, the pro-resolving role of MaR1 in AD has not been fully investigated. In the present study, human monocyte-derived microglia (MdM) and a differentiated human monocyte cell line (THP-1 cells) exposed to Aβ were used as models of AD neuroinflammation. We have studied the potential of MaR1 to inhibit pro-inflammatory activation of Aβ and assessed its ability to stimulate phagocytosis of Aβ₄₂. MaR1 inhibited the Aβ₄₂-induced increase in cytokine secretion and stimulated the uptake of Aβ₄₂ in both MdM and differentiated THP-1 cells. MaR1 was also found to decrease chemokine secretion and reduce the associated increase in the activation marker CD40. Activation of kinases involved in transduction of inflammation was not affected by MaR1, but the activity of nuclear factor (NF)-κB was decreased. Our data show that MaR1 exerts effects that indicate a pro-resolving role in the context of AD and thus presents itself as a potential therapeutic target for AD.     

Targeting NADPH Oxidase and Phospholipases A2 in Alzheimer’s Disease

Alzheimer’s disease (AD) is marked by an increase in the production of extracellular beta amyloid plaques and intracellular neurofibrillary tangles associated with a decline in brain function. Increases in oxidative stress are regarded as an early sign of AD pathophysiology, although the source of reactive oxygen species (ROS) and the mechanism(s) whereby beta amyloid peptides (Aβ) impact oxidative stress have not been adequately investigated. Recent studies provide strong evidence for the involvement of NADPH oxidase and its downstream oxidative signaling pathways in the toxic effects elicited by Aβ. ROS produced by NADPH oxidase activate multiple signaling pathways leading to neuronal excitotoxicity and glial cell-mediated inflammation. This review describes recent studies demonstrating the neurotoxic effects of Aβ in conjunction with ROS produced by NADPH oxidase and the downstream pathways leading to activation of cytosolic phospholipase A₂ (PLA₂) and secretory PLA₂. In addition, this review also describes recent studies using botanical antioxidants to protect against oxidative damage associated with AD. Investigating the metabolic and signaling pathways involving Aβ NADPH oxidase and PLA₂ can help understand the mechanisms underlying the neurodegenerative effects of oxidative stress in AD. This information should provide new therapeutic approaches for prevention of this debilitating disease.     

Anti-amyloidogenic effect of AA3E2 attenuates β-amyloid induced toxicity in SK-N-MC cells

β-Amyloid peptide (Aβ) is believed to play a recognized role in pathogenesis of Alzheimer's disease (AD). Self-association of Aβ peptide into amyloid fibrils causes neurotoxicity. Compounds capable of interfering with Aβ–Aβ interaction through binding to nucleation sites can inhibit Aβ amyloidogenesis and Aβ-induced cytotoxicity. AA3E2 is a triazine-derivative whose anti-amyloidogenic ability has previously been established. In the present study, we evaluated the protective effect of AA3E3 against Aβ_1–42-induced toxicity in SK-N-MC cell line. The cell exposure to the co-incubated Aβ_1–42 with AA3E2 decreased the cell viability loss dose-dependently, compared to cells exposed to Aβ_1–42 fibrils.Co-incubation with AA3E2 also attenuated the ROS production, activation of caspase-3 and the extent of apoptotic cell death induced by Aβ_1–42 fibril. Moreover, the 3D structure of the molecular associates between Aβ_1–42 and AA3E2 were theoretically determined by docking studies. Our docking data indicated that AA3E2 inhibits the formation of Aβ fibril likely via binding to the nucleation site within the hydrophobic region of Aβ (KLVFF). These observations provide the background for future design of more elegant β-breaking agents for dissolution of Aβ fibrillar aggregates.     

Platelet Proteomic Analysis Revealed Differential Pattern of Cytoskeletal- and Immune-Related Proteins at Early Stages of Alzheimer’s Disease

Platelets are considered a good model system to study a number of elements associated with neuronal pathways as they share biochemical similarities. Platelets represent the major source of amyloid-β (Aβ) in blood contributing to the Aβ accumulation in the brain parenchyma and vasculature. Peripheral blood platelet alterations including cytoskeletal abnormalities, abnormal cytoplasmic calcium fluxes or increased oxidative stress levels have been related to Alzheimer’s disease (AD) pathology. Therefore, platelets can be considered a peripheral model to study metabolic mechanisms occurring in AD. To investigate peripheral molecular alterations, we examined platelet protein expression in a cohort of 164 subjects, including mild cognitive impairment (MCI), and AD patients, and healthy aged-matched controls. A two-dimensional difference gel electrophoresis (2D-DIGE) discovery phase revealed significant differences between patients and controls in five proteins: talin, vinculin, moesin, complement C3b and Rho GDP, which are known to be involved in cytoskeletal regulation including focal adhesions, inflammation and immune functions. Western blot analysis verified that talin was found to be increased in mild and moderate AD groups versus control, while the other three were found to be decreased. We also analysed amyloid precursor protein (APP), amyloid-β 1-40 (Aβ₄₀) and 1-42 (Aβ₄₂) levels in platelets from the same groups of subjects. Upregulation of platelet APP and Aβ peptides was found in AD patients compared to controls. These findings complement and expand previous reports concerning the morphological and functional alterations in AD platelets, and provide more insights into possible mechanisms that participate in the multifactorial and systemic damage in AD.     

Unveiling Amyloid-β<Subscript>1–42</Subscript> Interaction with Zinc in Water and Mixed Hexafluoroisopropanol Solution in Alzheimer’s Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder caused by overproduction and accumulation of amyloid beta-peptide (Aβ). The hallmarks associated with this AD are the presence of Aβ plaques between the nerve cell in the brain which leading to synaptic loss in memory. The amyloid plaques contain of transition metals like zinc, copper and iron. In a healthy brain, the metal ions are present in balance concentration. High concentrations of Zn are normally released during neurotransmission process. The release of Zn might cause the aggregation of Aβ leading to AD. Amyloid-β_1–42 is the main type of Aβ in amyloid plaque. There still have limited explanation on how Aβ_1–42 interaction with Zn metal, as well as the effect of Zn metal on the Aβ structure in different solvents in atomic detail. Therefore, we investigated the structural changes of Aβ_1–42 in water (Aβ-H₂O) and the mixed hexafluoroisopropanol (HFIP) with water (Aβ-HFIP/H₂O). The mixed solvent consisted of hexafluoroisopropanol (HFIP) and water was used with the ratio of HFIP:H₂O (80:20). The effect of zinc ion was also examined for the interaction of Aβ peptide with zinc in water (Aβ-Zn-H₂O) and mixed solvent (Aβ-Zn-HFIP/H₂O) using all atom level molecular dynamics (MD) calculations for 1 μs. We found that Aβ-Zn-HFIP/H₂O contained more α-helix compared to Aβ-HFIP/H₂O while Aβ-H₂O and Aβ-Zn-H₂O produced well-dissolved structure and they contained more β-sheets. β-turns are possible to bind with the receptor proteins and may induce the aggregation process in AD. Thus, Aβ-H₂O and Aβ-Zn-H₂O have higher possibility leading to AD compared to Aβ-Zn-HFIP/H₂O and Aβ-HFIP/H₂O models.