The case for soluble Aβ oligomers as a drug target in Alzheimer's disease

Aβ oligomers peak in early stages of Alzheimer's disease preceding tau pathology

INTRODUCTION

Soluble amyloid beta (Aβ) oligomers have been suggested as initiating Aβ related neuropathologic change in Alzheimer's disease (AD) but their quantitative distribution and chronological sequence within the AD continuum remain unclear.

METHODS

A total of 526 participants in early clinical stages of AD and controls from a longitudinal cohort were neurobiologically classified for amyloid and tau pathology applying the AT(N) system. Aβ and tau oligomers in the quantified cerebrospinal fluid (CSF) were measured using surface-based fluorescence intensity distribution analysis (sFIDA) technology.

RESULTS

Across groups, highest Aβ oligomer levels were found in A+ with subjective cognitive decline and mild cognitive impairment. Aβ oligomers were significantly higher in A+T- compared to A-T- and A+T+. APOE ε4 allele carriers showed significantly higher Aβ oligomer levels. No differences in tau oligomers were detected.

DISCUSSION

The accumulation of Aβ oligomers in the CSF peaks early within the AD continuum, preceding tau pathology. Disease-modifying treatments targeting Aβ oligomers might have the highest therapeutic effect in these disease stages.

Highlights

Using surface-based fluorescence intensity distribution analysis (sFIDA) technology, we quantified Aβ oligomers in cerebrospinal fluid (CSF) samples of the DZNE-Longitudinal Cognitive Impairment and Dementia (DELCODE) cohortAβ oligomers were significantly elevated in mild cognitive impairment (MCI)Amyloid-positive subjects in the subjective cognitive decline (SCD) group increased compared to the amyloid-negative control groupInterestingly, levels of Aβ oligomers decrease at advanced stages of the disease (A+T+), which might be explained by altered clearing mechanisms.

A Biomimic Nanobullet with Ameliorative Inflammatory Microenvironment for Alzheimer's Disease Treatments

Aβ oligomers, formed prior to diagnostic marker-amyloid β (Aβ) plaques, can damage neurons and trigger neuroinflammation, which accelerate the neuronal injury in Alzheimer's disease (AD). Herein, the combination of eliminating the Aβ oligomers and alleviating the inflammation is a promising therapeutic strategy for AD. However, the presence of the blood-brain barrier (BBB) and the intrinsic deficiencies of the drugs severely restrict their therapeutic effects. Inspired by the properties of rabies virus, a biomimic nanobullet (PBACR@NRs/SA) targeting neurons has been developed. The biomimic nanobullets possess the BBB penetrating character based on iron oxide nanorods; it can sequentially release rosmarinic acid and small interfering RNA targeting NF-κB triggered by microenvironment, which improve the microenvironment inflammation and realize the cure for AD. Compared with non-biomimic systems, the biomimic nanobullets exhibit a less caveolin-dependent internalization pathway, which reduces ROS production and mitochondrial fission in neurons. Therefore, the biomimic nanobullet is hopeful for the treatment of ADs and provides a promising platform for other brain diseases' treatments.

A single-domain antibody detects and neutralises toxic Aβ42 oligomers in the Alzheimer's disease CSF

BACKGROUND

Amyloid-β42 (Aβ42) aggregation consists of a complex chain of nucleation events producing soluble oligomeric intermediates, which are considered the major neurotoxic agents in Alzheimer's disease (AD). Cerebral lesions in the brain of AD patients start to develop 20 years before symptom onset; however, no preventive strategies, effective treatments, or specific and sensitive diagnostic tests to identify people with early-stage AD are currently available. In addition, the isolation and characterisation of neurotoxic Aβ42 oligomers are particularly difficult because of their transient and heterogeneous nature. To overcome this challenge, a rationally designed method generated a single-domain antibody (sdAb), named DesAb-O, targeting Aβ42 oligomers.

METHODS

We investigated the ability of DesAb-O to selectively detect preformed Aβ42 oligomers both in vitro and in cultured neuronal cells, by using dot-blot, ELISA immunoassay and super-resolution STED microscopy, and to counteract the toxicity induced by the oligomers, monitoring their interaction with neuronal membrane and the resulting mitochondrial impairment. We then applied this approach to CSF samples (CSFs) from AD patients as compared to age-matched control subjects.

RESULTS

DesAb-O was found to selectively detect synthetic Aβ42 oligomers both in vitro and in cultured cells, and to neutralise their associated neuronal dysfunction. DesAb-O can also identify Aβ42 oligomers present in the CSFs of AD patients with respect to healthy individuals, and completely prevent cell dysfunction induced by the administration of CSFs to neuronal cells.

CONCLUSIONS

Taken together, our data indicate a promising method for the improvement of an early diagnosis of AD and for the generation of novel therapeutic approaches based on sdAbs for the treatment of AD and other devastating neurodegenerative conditions.

A Hairpin Motif in the Amyloid-β Peptide Is Important for Formation of Disease-Related Oligomers

The amyloid-β (Aβ) peptide is associated with the development of Alzheimer's disease and is known to form highly neurotoxic prefibrillar oligomeric aggregates, which are difficult to study due to their transient, low-abundance, and heterogeneous nature. To obtain high-resolution information about oligomer structure and dynamics as well as relative populations of assembly states, we here employ a combination of native ion mobility mass spectrometry and molecular dynamics simulations. We find that the formation of Aβ oligomers is dependent on the presence of a specific β-hairpin motif in the peptide sequence. Oligomers initially grow spherically but start to form extended linear aggregates at oligomeric states larger than those of the tetramer. The population of the extended oligomers could be notably increased by introducing an intramolecular disulfide bond, which prearranges the peptide in the hairpin conformation, thereby promoting oligomeric structures but preventing conversion into mature fibrils. Conversely, truncating one of the β-strand-forming segments of Aβ decreased the hairpin propensity of the peptide and thus decreased the oligomer population, removed the formation of extended oligomers entirely, and decreased the aggregation propensity of the peptide. We thus propose that the observed extended oligomer state is related to the formation of an antiparallel sheet state, which then nucleates into the amyloid state. These studies provide increased mechanistic understanding of the earliest steps in Aβ aggregation and suggest that inhibition of Aβ folding into the hairpin conformation could be a viable strategy for reducing the amount of toxic oligomers.

Alzheimer's Disease: A Brief History of Immunotherapies Targeting Amyloid β

Alzheimer's disease (AD) is the most common form of dementia and may contribute to 60-70% of cases. Worldwide, around 50 million people suffer from dementia and the prediction is that the number will more than triple by 2050, as the population ages. Extracellular protein aggregation and plaque deposition as well as accumulation of intracellular neurofibrillary tangles, all leading to neurodegeneration, are the hallmarks of brains with Alzheimer's disease. Therapeutic strategies including active and passive immunizations have been widely explored in the last two decades. Several compounds have shown promising results in many AD animal models. To date, only symptomatic treatments are available and because of the alarming epidemiological data, novel therapeutic strategies to prevent, mitigate, or delay the onset of AD are required. In this mini-review, we focus on our understanding of AD pathobiology and discuss current active and passive immunomodulating therapies targeting amyloid-β protein.

Self-Assembly of Amyloid Fibrils into 3D Gel Clusters versus 2D Sheets

The deposition of dense fibril plaques represents the pathological hallmark for a multitude of human disorders, including many neurodegenerative diseases. Fibril plaques are predominately composed of amyloid fibrils, characterized by their underlying cross beta-sheet architecture. Research into the mechanisms of amyloid formation has mostly focused on characterizing and modeling the growth of individual fibrils and associated oligomers from their monomeric precursors. Much less is known about the mechanisms causing individual fibrils to assemble into ordered fibrillar suprastructures. Elucidating the mechanisms regulating this "secondary" self-assembly into distinct suprastructures is important for understanding how individual protein fibrils form the prominent macroscopic plaques observed in disease. Whether and how amyloid fibrils assemble into either 2D or 3D supramolecular structures also relates to ongoing efforts on using amyloid fibrils as substrates or scaffolds for self-assembling functional biomaterials. Here, we investigated the conditions under which preformed amyloid fibrils of a lysozyme assemble into larger superstructures as a function of charge screening or pH. Fibrils either assembled into three-dimensional gel clusters or two-dimensional fibril sheets. The latter displayed optical birefringence, diagnostic of amyloid plaques. We presume that pH and salt modulate fibril charge repulsion, which allows anisotropic fibril-fibril attraction to emerge and drive the transition from 3D to 2D fibril self-assembly.

Amphiphilic stilbene derivatives attenuate the neurotoxicity of soluble Aβ42 oligomers by controlling their interactions with cell membranes

The misfolded proteins or polypeptides commonly observed in neurodegenerative diseases, including Alzheimer's disease (AD), are promising drug targets for developing therapeutic agents. To target the amyloid-β (Aβ) peptide plaques and oligomers, the hallmarks of AD, we have developed twelve amphiphilic small molecules with different hydrophobic and hydrophilic fragments. In vitro fluorescence binding assays demonstrate that these amphiphilic compounds show high binding affinity to both Aβ plaques and oligomers, and six of them exhibit selective binding toward Aβ oligomers. These amphiphilic compounds can also label the Aβ species in the brain sections of transgenic AD mice, as shown by immunostaining with an Aβ antibody. Molecular docking studies were performed to obtain structure-affinity relationships. To our delight, four amphiphilic compounds can alleviate the Cu2+-Aβ induced toxicity in cell viability assays. In addition, confocal fluorescence imaging studies provide evidence that two compounds, ZY-15-MT and ZY-15-OMe, can disrupt the interactions between Aβ oligomers and human neuroblastoma SH-SY5Y cell membranes. Overall, these studies strongly suggest that developing compounds with amphiphilic properties that target Aβ oligomers and modulate the Aβ oligomer-cell membrane interactions can be an effective strategy for the development of small molecule AD therapeutics.

MicroRNA-140-5p inhibitor attenuates memory impairment induced by amyloid-ß oligomer in vivo possibly through Pin1 regulation

AIMS

The peptidyl-prolyl cis/trans isomerase, Pin1, has a protective role in age-related neurodegeneration by targeting different phosphorylation sites of tau and the key proteins required to produce Amyloid-β, which are the well-known molecular signatures of Alzheimer's disease (AD) neuropathology. The direct interaction of miR-140-5p with Pin1 mRNA and its inhibitory role in protein translation has been identified. The main purpose of this study was to investigate the role of miRNA-140-5p inhibition in promoting Pin1 expression and the therapeutic potential of the AntimiR-140-5p in the Aß oligomer (AßO)-induced AD rat model.

METHODS

Spatial learning and memory were assessed in the Morris water maze. RT-PCR, western blot, and histological assays were performed on hippocampal samples at various time points after treatments. miRNA-140-5p inhibition enhanced Pin1 and ADAM10 mRNA expressions but has little effect on Pin1 protein level.

RESULTS

The miRNA-140-5p inhibitor markedly ameliorated spatial learning and memory deficits induced by AßO, and concomitantly suppressed the mRNA expression of inflammatory mediators TNFα and IL-1β, and phosphorylation of tau at three key sites (thr231, ser396, and ser404) as well as increased phosphorylated Ser473-Akt.

CONCLUSION

According to our results, Antimir-140-mediated improvement of AβO-induced neuronal injury and memory impairment in rats may provide an appropriate rationale for evaluating miR-140-5p inhibitors as a promising agent for the treatment of AD.

ACU193: An Immunotherapeutic Poised to Test the Amyloid β Oligomer Hypothesis of Alzheimer’s Disease

Alzheimer’s disease (AD) is an age-related neurodegenerative disease that affects 50 million people worldwide, with 10 million new cases occurring each year. The emotional and economic impacts of AD on patients and families are devastating. Approved treatments confer modest improvement in symptoms, and recently one treatment obtained accelerated approval from the United States Food and Drug Administration (FDA) and may have modest disease modifying benefit. Research over the past three decades has established a clear causal linkage between AD and elevated brain levels of amyloid β (Aβ) peptide, and substantial evidence now implicates soluble, non-fibrillar Aβ oligomers (AβOs) as the molecular assemblies directly responsible for AD-associated memory and cognitive failure and accompanying progressive neurodegeneration. The widely recognized linkage of elevated Aβ and AD spawned a comprehensive 20-year therapeutic campaign that focused primarily on two strategies – inhibition of the secretase enzymes responsible for Aβ production and clearance of Aβ peptide or amyloid plaques with Aβ-directed immunotherapeutics. Unfortunately, all clinical trials of secretase inhibitors were unsuccessful. Of the completed phase 3 immunotherapy programs, bapineuzumab (targeting amyloid plaque) and solanezumab (targeting Aβ monomers) were negative, and the crenezumab program (targeting Aβ monomers and to a small extent oligomers) was stopped for futility. Aducanumab (targeting amyloid plaques), which recently received FDA accelerated approval, had one positive and one negative phase 3 trial. More than 25 negative randomized clinical trials (RCTs) have evaluated Aβ-targeting therapeutics, yet none has directly evaluated whether selective blockage of disease-relevant AβOs can stop or reverse AD-associated cognitive decline. Here, we briefly summarize studies that establish the AD therapeutic rationale to target AβOs selectively, and we describe ACU193, the first AβO-selective immunotherapeutic to enter human clinical trials and the first positioned to test the AβO hypothesis of AD.

Yeast red pigment, protein aggregates, and amyloidoses: a review

Estimating the amyloid level in yeast Saccharomyces, we found out that the red pigment (product of polymerization of aminoimidazole ribotide) accumulating in ade1 and ade2 mutants leads to drop of the amyloid content. We demonstrated in vitro that fibrils of several proteins grown in the presence of the red pigment stop formation at the protofibril stage and form stable aggregates due to coalescence. Also, the red pigment inhibits reactive oxygen species accumulation in cells. This observation suggests that red pigment is involved in oxidative stress response. We developed an approach to identify the proteins whose aggregation state depends on prion (amyloid) or red pigment presence. These sets of proteins overlap and in both cases involve many different chaperones. Red pigment binds amyloids and is supposed to prevent chaperone-mediated prion propagation. An original yeast-Drosophila model was offered to estimate the red pigment effect on human proteins involved in neurodegeneration. As yeast cells are a natural feed of Drosophila, we could compare the data on transgenic flies fed on red and white yeast cells. Red pigment inhibits aggregation of human Amyloid beta and α-synuclein expressed in yeast cells. In the brain of transgenic flies, the red pigment diminishes amyloid beta level and the area of neurodegeneration. An improvement in memory and viability accompanied these changes. In transgenic flies expressing human α-synuclein, the pigment leads to a decreased death rate of dopaminergic neurons and improves mobility. The obtained results demonstrate yeast red pigment potential for the treatment of neurodegenerative diseases.

The Therapeutic and Diagnostic Potential of Amyloid β Oligomers Selective Antibodies to Treat Alzheimer's Disease

Improvements have been made in the diagnosis of Alzheimer’s disease (AD), manifesting mostly in the development of in vivo imaging methods that allow for the detection of pathological changes in AD by magnetic resonance imaging (MRI) and positron emission tomography (PET) scans. Many of these imaging methods, however, use agents that probe amyloid fibrils and plaques–species that do not correlate well with disease progression and are not present at the earliest stages of the disease. Amyloid β oligomers (AβOs), rather, are now widely accepted as the Aβ species most germane to AD onset and progression. Here we report evidence further supporting the role of AβOs as pathological instigators of AD and introduce promising anti-AβO diagnostic probes capable of distinguishing the 5xFAD mouse model from wild type mice by PET and MRI. In a developmental study, Aβ oligomers in 5xFAD mice were found to appear at 3 months of age, just prior to the onset of memory dysfunction, and spread as memory worsened. The increase of AβOs is prominent in the subiculum and correlates with concomitant development of reactive astrocytosis. The impact of these AβOs on memory is in harmony with findings that intraventricular injection of synthetic AβOs into wild type mice induced hippocampal dependent memory dysfunction within 24 h. Compelling support for the conclusion that endogenous AβOs cause memory loss was found in experiments showing that intranasal inoculation of AβO-selective antibodies into 5xFAD mice completely restored memory function, measured 30–40 days post-inoculation. These antibodies, which were modified to give MRI and PET imaging probes, were able to distinguish 5xFAD mice from wild type littermates. These results provide strong support for the role of AβOs in instigating memory loss and salient AD neuropathology, and they demonstrate that AβO selective antibodies have potential both for therapeutics and for diagnostics.

Evaluation of Amyloid Inhibitor Efficiency to Block Bacterial Survival

Amyloid inhibitors, such as the green tea compound epigallocatechin gallate EGCG, apomorphine or curlicide, have antibacterial properties. Conversely, antibiotics such as tetracycline derivatives or rifampicin also affect eukaryotic amyloids formation and may be used to treat neurodegenerative diseases. This opens the possibility for existing drugs to be repurposed in view of new therapy, targeting amyloid-like proteins from eukaryotes to prokaryotes and conversely. Here we present how to evaluate the effect of these amyloid-forming inhibitors on bacterial amyloid self-assemblies in vitro and on bacterial survival. The different approaches possible are presented.

Origin, toxicity and characteristics of two amyloid oligomer polymorphs

There is compelling evidence that small oligomeric aggregates, emerging during the assembly of amyloid fibrils and plaques, are important molecular pathogens in many amyloid diseases. While significant progress has been made in revealing the mechanisms underlying fibril growth, understanding how amyloid oligomers fit into the fibril assembly process, and how they contribute to the pathogenesis of amyloid diseases, has remained elusive. Commonly, amyloid oligomers are considered to be metastable, early-stage precursors to fibril formation that are either on- or off-pathway from fibril growth. In addition, amyloid oligomers have been reported to colocalize with late-stage fibrils and plaques. Whether these early and late-stage oligomer species are identical or distinct, and whether both are relevant to pathogenesis remains unclear. Here we report on the formation of two distinct oligomer species of lysozyme, formed either during the early or late-stages of in vitro fibril growth. We further observe that the pH change from in vitro growth conditions to cell media used for toxicity studies induced distinct mesoscopic precipitates, two of which resemble either diffuse or neuritic plaques seen in Alzheimer's histology. Our biophysical characterization indicates that both oligomer species share morphological and tinctorial features considered characteristic for amyloid oligomers. At the same time, their sizes, morphologies, their immunostaining, detailed tinctorial profiles and, most prominently, their biological activity are clearly distinct from each other. Probing the conditions promoting the formation of these two distinct oligomer species suggests distinct roles of charge interactions, hydrophobicity and monomer flexibility in directing oligomer assembly.

Discovery of Investigational Drug CT1812, an Antagonist of the Sigma-2 Receptor Complex for Alzheimer's Disease

An unbiased phenotypic neuronal assay was developed to measure the synaptotoxic effects of soluble Aβ oligomers. A collection of CNS druglike small molecules prepared by conditioned extraction was screened. Compounds that prevented and reversed synaptotoxic effects of Aβ oligomers in neurons were discovered to bind to the sigma-2 receptor complex. Select development compounds displaced receptor-bound Aβ oligomers, rescued synapses, and restored cognitive function in transgenic hAPP Swe/Ldn mice. Our first-in-class orally administered small molecule investigational drug 7 (CT1812) has been advanced to Phase II clinical studies for Alzheimer's disease.

On the Common Journey of Neural Cells through Ischemic Brain Injury and Alzheimer's Disease

Ischemic brain injury and Alzheimer's disease (AD) both lead to cell death in the central nervous system (CNS) and thus negatively affect particularly the elderly population. Due to the lack of a definitive cure for brain ischemia and AD, it is advisable to carefully study, compare, and contrast the mechanisms that trigger, and are involved in, both neuropathologies. A deeper understanding of these mechanisms may help ameliorate, or even prevent, the destructive effects of neurodegenerative disorders. In this review, we deal with ischemic damage and AD, with the main emphasis on the common properties of these CNS disorders. Importantly, we discuss the Wnt signaling pathway as a significant factor in the cell fate determination and cell survival in the diseased adult CNS. Finally, we summarize the interesting findings that may improve or complement the current sparse and insufficient treatments for brain ischemia and AD, and we delineate prospective directions in regenerative medicine.

Phosphorylated tau targeted small-molecule PROTACs for the treatment of Alzheimer's disease and tauopathies

Tau is a microtubule-stabilizing protein that plays an important role in the formation of axonal microtubules in neurons. Phosphorylated tau (p-Tau) has received great attention in the field of Alzheimer's disease (AD) as a potential therapeutic target due to its involvement with synaptic damage and neuronal dysfunction. Mounting evidence suggests that amyloid beta (Aβ)-targeted clinical trials continuously failed; therefore, it is important to consider alternative therapeutic strategies such as p-tau-PROTACs targeted small molecules for AD and other tauopathies. The present article describes the characteristics of tau biology, structure, and function in both healthy and pathological states in AD. It also explains data from studies that have identified the involvement of p-tau in neuronal damage and synaptic and cognitive functions in AD. Current article also covers several aspects, including small molecule inhibitors, and the development of p-tau-PROTACs targeted drug molecules to treat patients with AD and other tauopathies.

Curcumin and Its Derivatives as Theranostic Agents in Alzheimer's Disease: The Implication of Nanotechnology

Curcumin is a polyphenolic natural compound with diverse and attractive biological properties, which may prevent or ameliorate pathological processes underlying age-related cognitive decline, Alzheimer's disease (AD), dementia, or mode disorders. AD is a chronic neurodegenerative disorder that is known as one of the rapidly growing diseases, especially in the elderly population. Moreover, being the eminent cause of dementia, posing problems for families, societies as well a severe burden on the economy. There are no effective drugs to cure AD. Although curcumin and its derivatives have shown properties that can be considered useful in inhibiting the hallmarks of AD, however, they have low bioavailability. Furthermore, to combat diagnostic and therapeutic limitations, various nanoformulations have also been recognized as theranostic agents that can also enhance the pharmacokinetic properties of curcumin and other bioactive compounds. Nanocarriers have shown beneficial properties to deliver curcumin and other nutritional compounds against the blood-brain barrier to efficiently distribute them in the brain. This review spotlights the role and effectiveness of curcumin and its derivatives in AD. Besides, the gut metabolism of curcumin and the effects of nanoparticles and their possible activity as diagnostic and therapeutic agents in AD also discussed.

Passive immunotherapies targeting Aβ and tau in Alzheimer's disease

Amyloid-β (Aβ) and tau proteins currently represent the two most promising targets to treat Alzheimer's disease. The most extensively developed method to treat the pathologic forms of these proteins is through the administration of exogenous antibodies, or passive immunotherapy. In this review, we discuss the molecular-level strategies that researchers are using to design an effective therapeutic antibody, given the challenges in treating this disease. These challenges include selectively targeting a protein that has misfolded or is pathological rather than the more abundant, healthy protein, designing strategic constructs for immunizing an animal to raise an antibody that has the appropriate conformational selectivity to achieve this end, and clearing the pathological protein species before prion-like cell-to-cell spread of misfolded protein has irreparably damaged neurons, without invoking damaging inflammatory responses in the brain that naturally arise when the innate immune system is clearing foreign agents. The various solutions to these problems in current clinical trials will be discussed.

Therapeutic Strategies Targeting Amyloid-β in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder linked to protein misfolding and aggregation. AD is pathologically characterized by senile plaques formed by extracellular Amyloid-β (Aβ) peptide and Intracellular Neurofibrillary Tangles (NFT) formed by hyperphosphorylated tau protein. Extensive synaptic loss and neuronal degeneration are responsible for memory impairment, cognitive decline and behavioral dysfunctions typical of AD. Amyloidosis has been implicated in the depression of acetylcholine synthesis and release, overactivation of N-methyl-D-aspartate (NMDA) receptors and increased intracellular calcium levels that result in excitotoxic neuronal degeneration. Current drugs used in AD treatment are either cholinesterase inhibitors or NMDA receptor antagonists; however, they provide only symptomatic relief and do not alter the progression of the disease. Aβ is the product of Amyloid Precursor Protein (APP) processing after successive cleavage by β- and γ-secretases while APP proteolysis by α-secretase results in non-amyloidogenic products. According to the amyloid cascade hypothesis, Aβ dyshomeostasis results in the accumulation and aggregation of Aβ into soluble oligomers and insoluble fibrils. The former are synaptotoxic and can induce tau hyperphosphorylation while the latter deposit in senile plaques and elicit proinflammatory responses, contributing to oxidative stress, neuronal degeneration and neuroinflammation. Aβ-protein-targeted therapeutic strategies are thus a promising disease-modifying approach for the treatment and prevention of AD. This review summarizes recent findings on Aβ-protein targeted AD drugs, including β-secretase inhibitors, γ-secretase inhibitors and modulators, α-secretase activators, direct inhibitors of Aβ aggregation and immunotherapy targeting Aβ, focusing mainly on those currently under clinical trials.

Role of tau protein in Alzheimer's disease: The prime pathological player

Alzheimer's disease (AD) is a prevalently found tauopathy characterized by memory loss and cognitive insufficiency. AD is an age-related neurodegenerative disease with two major hallmarks which includes extracellular amyloid plaques made of amyloid-β (Aβ) and intracellular neurofibrillary tangles of hyperphosphorylated tau. With population aging worldwide, there is an indispensable need for treatment strategies that can potentially manage this developing dementia. Despite broad researches on targeting Aβ in the past two decades, research findings on Aβ targeted therapeutics failed to prove efficacy in the treatment of AD. Tau protein with its extensive pathological role in several neurodegenerative diseases can be considered as a promising target candidate for developing therapeutic interventions. The abnormal hyperphosphorylation of tau plays detrimental pathological functions which ultimately lead to neurodegeneration. This review will divulge the importance of tau in AD pathogenesis, the interplay of Aβ and tau, the pathological functions of tau, and potential therapeutic strategies for an effective management of neuronal disorders.

Epigallocatechin-3-Gallate (EGCG) Improves Cognitive Deficits Aggravated by an Obesogenic Diet Through Modulation of Unfolded Protein Response in APPswe/PS1dE9 Mice

Epigallocatechin-3-gallate (EGCG), a catechin found in green tea, has been previously investigated for its neuroprotective effects in vitro and in vivo. In the present study, we aimed to evaluate its possible beneficial effects in a well-established preclinical mixed model of familial Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) based on the use of transgenic APPswe/PS1dE9 (APP/PS1) mice fed with a high fat diet (HFD). C57BL/6 wild-type (WT) and APP/PS1 mice were used in this study. APP/PS1 mice were fed with a palmitic acid-enriched HFD (APP/PS1 HFD) containing 45% of fat mainly from hydrogenated coconut oil. Intraperitoneal glucose tolerance tests (IP-GTT) and insulin tolerance tests (IP-ITT) were performed. Western blot analyses were performed to analyse protein expression, and water maze and novel object recognition test were done to evaluate the cognitive process. EGCG treatment improves peripheral parameters such as insulin sensitivity or liver insulin pathway signalling, as well as central memory deficits. It also markedly increased synaptic markers and cAMP response element binding (CREB) phosphorylation rates, as a consequence of a decrease in the unfolded protein response (UPR) activation through the reduction in the activation factor 4 (ATF4) levels and posterior downregulation of protein tyrosine phosphatase 1B (PTP1B). Moreover, EGCG significantly decreased brain amyloid β (Aβ) production and plaque burden by increasing the levels of α-secretase (ADAM10). Also, it led to a reduction in neuroinflammation, as suggested by the decrease in astrocyte reactivity and toll-like receptor 4 (TLR4) levels. Collectively, evidence suggests that chronic EGCG prevents distinct neuropathological AD-related hallmarks. This study also provides novel insights into the metabolic and neurobiological mechanisms of EGCG against cognitive loss through its effects on UPR function, suggesting that this compound may be a promising disease-modifying treatment for neurodegenerative diseases.

Modulation of Amyloid-β42 Conformation by Small Molecules Through Nonspecific Binding

Aggregation of amyloid-β (Aβ) peptides is a crucial step in the progression of Alzheimer's disease (AD). Identifying aggregation inhibitors against AD has been a great challenge. We report an atomistic simulation study of the inhibition mechanism of two small molecules, homotaurine and scyllo-inositol, which are AD drug candidates currently under investigation. We show that both small molecules promote a conformational change of the Aβ42 monomer toward a more collapsed phase through a nonspecific binding mechanism. This finding provides atomistic-level insights into designing potential drug candidates for future AD treatments.

Kinetic Transition in Amyloid Assembly as a Screening Assay for Oligomer-Selective Dyes

Assembly of amyloid fibrils and small globular oligomers is associated with a significant number of human disorders that include Alzheimer’s disease, senile systemic amyloidosis, and type II diabetes. Recent findings implicate small amyloid oligomers as the dominant aggregate species mediating the toxic effects in these disorders. However, validation of this hypothesis has been hampered by the dearth of experimental techniques to detect, quantify, and discriminate oligomeric intermediates from late-stage fibrils, in vitro and in vivo. We have shown that the onset of significant oligomer formation is associated with a transition in thioflavin T kinetics from sigmoidal to biphasic kinetics. Here we showed that this transition can be exploited for screening fluorophores for preferential responses to oligomer over fibril formation. This assay identified crystal violet as a strongly selective oligomer-indicator dye for lysozyme. Simultaneous recordings of amyloid kinetics with thioflavin T and crystal violet enabled us to separate the combined signals into their underlying oligomeric and fibrillar components. We provided further evidence that this screening assay could be extended to amyloid-β peptides under physiological conditions. Identification of oligomer-selective dyes not only holds the promise of biomedical applications but provides new approaches for unraveling the mechanisms underlying oligomer versus fibril formation in amyloid assembly.

Hippocampal neurons in direct contact with astrocytes exposed to amyloid β25-35 exhibit reduced excitatory synaptic transmission

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We exposed astrocytes to Aβ _25-35 and then co-cultured them with primary hippocampal neurons.

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The Aβ_25-35-exposed astrocytes lowered excitatory postsynaptic release and the size of the readily releasable synaptic pool.

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The number of excitatory synapses was reduced by direct contact between Aβ_25-35-exposed astrocytes and hippocampal neurons.

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The dendritic branching was decreased by direct contact between Aβ_25-35-exposed astrocytes and hippocampal neurons.

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The number of excitatory synapses and dendrite branches were conserved by putting distance from Aβ_25-35-exposed astrocytes.

Amyloid β protein (Aβ) is closely related to the progression of Alzheimer's disease because senile plaques consisting of Aβ cause synaptic depression and synaptic abnormalities. In the central nervous system, astrocytes are a major glial cell type that contribute to the modulation of synaptic transmission and synaptogenesis. In this study, we examined whether astrocytes exposed to Aβ fragment 25-35 (Aβ_25-35) affect synaptic transmission. We show that synaptic transmission by hippocampal neurons was inhibited by astrocytes exposed to Aβ_25-35. The Aβ_25-35-exposed astrocytes lowered excitatory postsynaptic release and the size of the readily releasable synaptic pool. The number of excitatory synapses was also reduced. However, the number of excitatory synapses was unchanged unless there was direct contact between Aβ_25-35-exposed astrocytes and hippocampal neurons. These data indicate that direct contact between Aβ_25-35-exposed astrocytes and neurons is critical for inhibiting synaptic transmission in the progression of Alzheimer’s disease.

Bone-Marrow-Derived Microglia-Like Cells Ameliorate Brain Amyloid Pathology and Cognitive Impairment in a Mouse Model of Alzheimer's Disease

Microglia, the primary immune cells in the brain, sense pathogens and tissue damage, stimulate cytokine production, and phagocytosis to maintain homeostasis. Accumulation of amyloid-β peptides (Aβ) in the brain triggers the onset of Alzheimer's disease (AD). Accordingly, promotion of Aβ clearance represents a promising strategy for AD therapy. We previously demonstrated that primary-cultured rat microglia phagocytose Aβ, and that transplantation of these cells ameliorates the Aβ burden in brains of Aβ-injected rats. In this study, we demonstrate that stimulation with colony-stimulating factor-1 efficiently differentiates mouse bone marrow cells into bone marrow-derived microglia-like (BMDML) cells that express markers for microglia, including the recently identified transmembrane protein 119. BMDML cells effectively phagocytose Aβ in vitro, with effects comparable to primary-cultured mouse microglia and greater than peritoneal macrophages. RT-qPCR analysis for cytokine mRNA levels revealed that BMDML cells polarize to a relatively anti-inflammatory state under non-stimulated and inflammatory conditions but exert a pro-inflammatory reaction after lipopolysaccharide treatment. Moreover, BMDML cells hippocampally injected into a mouse model of AD are morphologically similar to the ramified and amoeboid types of residential microglia. Comparisons with simulations assuming a uniform distribution of cells suggest that BMDML cells migrate directionally toward Aβ plaques. We also detected Aβ phagocytosis by BMDML cells, concomitant with a reduction in the number and area of Aβ plaques. Finally, we observed amelioration of cognitive impairment in a mouse model of AD after hippocampal injection of BMDML cells. Our results suggest that BMDML cells have potential as a cell-based disease-modifying therapy against AD.

Alzheimer's disease: Key developments support promising perspectives for therapy

Alzheimer's is the neurodegenerative disease affecting the largest number of patients in the world. In spite of the intense research of the last decades, progress about its knowledge and therapy was limited. In particular, various cytotoxic processes remained debated, while the few drugs approved for therapy were of only marginal relevance. Recent studies have identified key aspects of the disease, such as the mechanisms governing the development of pathology. In order to operate the Aβ peptide, known as the key factor, requires a complex assembled by its high affinity binding to PrP^c, a cell surface prion protein, and mGluR5, a metabotropic glutamate receptor. Aβ and its associates bind also phosphorylated tau transferred to the extracellular space, with final activation of intracellular cytotoxic signals. Pathology is further affected by factors (including genes, receptors and their agonists) and by glial cells governing (via vesicles, cytokines and enzymes) cell immunology, inflammation and oxidative stress. Concomitant to pathology studies, strong attempts have been made for the development of new, effective therapies. Critical for this are biomarkers, by which Alzheimer's patients are recognized even before appearance of their symptoms. The question was whether patients take advantage from drugs not yet approved. The latter, first identified in mice, were found effective also in men, however only before appearance or at early stage of the disease. In other words, the drugs not yet approved induce effective protection of patients still healthy or in a preliminary stage of the disease. In contrast, developed Alzheimer's disease is practically irreversible.

Chinese Herbal Medicine Xueshuantong Enhances Cerebral Blood Flow and Improves Neural Functions in Alzheimer's Disease Mice

Reduced cerebral blood flow in Alzheimer's disease (AD) may occur in early AD, which contributes to the pathogenesis and/or pathological progression of AD. Reversing this deficit may have therapeutic potential. Certain traditional Chinese herbal medicines (e.g., Saponin and its major component Xueshuantong [XST]) increase blood flow in humans, but whether they could be effective in treating AD patients has not been tested. We found that systemic XST injection elevated cerebral blood flow in APP/PS1 transgenic mice using two-photon time-lapse imaging in the same microvessels before and after injection. Subchronic XST treatment led to improved spatial learning and memory and motor performance in the APP/PS1 mice, suggesting improved neural plasticity and functions. Two-photon time lapse imaging of the same plaques revealed a reduction in plaque size after XST treatment. In addition, western blots experiments showed that XST treatment led to reduced processing of amyloid-β protein precursor (AβPP) and enhanced clearance of amyloid-β (Aβ) without altering the total level of AβPP. We also found increased synapse density in the immediate vicinity of amyloid plaques, suggesting enhanced synaptic function. We conclude that targeting cerebral blood flow can be an effective strategy in treating AD.

Sulforaphane Inhibits the Generation of Amyloid-β Oligomer and Promotes Spatial Learning and Memory in Alzheimer's Disease (PS1V97L) Transgenic Mice

Abnormal amyloid-β (Aβ) aggregates are a striking feature of Alzheimer's disease (AD), and Aβ oligomers have been proven to be crucial in the pathology of AD. Any intervention targeting the generation or aggregation of Aβ can be expected to be useful in AD treatment. Oxidative stress and inflammation are common pathological changes in AD that are involved in the generation and aggregation of Aβ. In the present study, 6-month-old PS1V97L transgenic (Tg) mice were treated with sulforaphane, an antioxidant, for 4 months, and this treatment significantly inhibited the generation and aggregation of Aβ. Sulforaphane also alleviated several downstream pathological changes that including tau hyperphosphorylation, oxidative stress, and neuroinflammation. Most importantly, the cognition of the sulforaphane-treated PS1V97L Tg mice remained normal compared to that of wild-type mice at 10 months of age, when dementia typically emerges in PS1V97L Tg mice. Pretreating cultured cortical neurons with sulforaphane also protected against neuronal injury caused by Aβ oligomers in vitro. These findings suggest that sulforaphane may be a potential compound that can inhibit Aβ oligomer production in AD.

Galectin-3 promotes Aβ oligomerization and Aβ toxicity in a mouse model of Alzheimer's disease

Amyloid-β (Aβ) oligomers largely initiate the cascade underlying the pathology of Alzheimer's disease (AD). Galectin-3 (Gal-3), which is a member of the galectin protein family, promotes inflammatory responses and enhances the homotypic aggregation of cancer cells. Here, we examined the role and action mechanism of Gal-3 in Aβ oligomerization and Aβ toxicities. Wild-type (WT) and Gal-3-knockout (KO) mice, APP/PS1;WT mice, APP/PS1;Gal-3^+/- mice and brain tissues from normal subjects and AD patients were used. We found that Aβ oligomerization is reduced in Gal-3 KO mice injected with Aβ, whereas overexpression of Gal-3 enhances Aβ oligomerization in the hippocampi of Aβ-injected mice. Gal-3 expression shows an age-dependent increase that parallels endogenous Aβ oligomerization in APP/PS1 mice. Moreover, Aβ oligomerization, Iba1 expression, GFAP expression and amyloid plaque accumulation are reduced in APP/PS1;Gal-3^+/- mice compared with APP/PS1;WT mice. APP/PS1;Gal-3^+/- mice also show better acquisition and retention performance compared to APP/PS1;WT mice. In studying the mechanism underlying Gal-3-promoted Aβ oligomerization, we found that Gal-3 primarily co-localizes with Iba1, and that microglia-secreted Gal-3 directly interacts with Aβ. Gal-3 also interacts with triggering receptor expressed on myeloid cells-2, which then mediates the ability of Gal-3 to activate microglia for further Gal-3 expression. Immunohistochemical analyses show that the distribution of Gal-3 overlaps with that of endogenous Aβ in APP/PS1 mice and partially overlaps with that of amyloid plaque. Moreover, the expression of the Aβ-degrading enzyme, neprilysin, is increased in Gal-3 KO mice and this is associated with enhanced integrin-mediated signaling. Consistently, Gal-3 expression is also increased in the frontal lobe of AD patients, in parallel with Aβ oligomerization. Because Gal-3 expression is dramatically increased as early as 3 months of age in APP/PS1 mice and anti-Aβ oligomerization is believed to protect against Aβ toxicity, Gal-3 could be considered a novel therapeutic target in efforts to combat AD.

Probing the Aggregation and Immune Response of Human Islet Amyloid Polypeptides with Ligand-Stabilized Gold Nanoparticles

The use of nanomaterials has recently become an emerging strategy against protein amyloidosis associated with a range of metabolic and brain diseases. To facilitate research in this area, here we first demonstrated the use of hyperspectral imaging (HSI) and COMSOL simulations for reporting the aggregation of human islet amyloid polypeptides (IAPPs), a hallmark of type 2 diabetes, as well as the physical interactions between the peptide and gold nanoparticles (AuNPs) grafted with citrate and poly(ethylene glycol) (PEG₄₀₀ and PEG₃₀₀₀). We found a distinct anticorrelation between increased IAPP aggregation and decreased spectral red shifts incurred in the AuNP plasmonic resonance. Moreover, Jurkat cells exposed to IAPP and AuNPs were characterized by quantifying their cytokine secretions with a localized surface plasmon resonance (LSPR) immunoassay, where a peak response was registered for the most toxic IAPP oligomers and most suppressed by citrate-coated AuNPs. This study demonstrated the potential of using HSI and LSPR as two new platforms for the facile examination of protein aggregation and their induced immune response associated with amyloid diseases.

9-Methylfascaplysin Is a More Potent Aβ Aggregation Inhibitor than the Marine-Derived Alkaloid, Fascaplysin, and Produces Nanomolar Neuroprotective Effects in SH-SY5Y Cells

β-Amyloid (Aβ) is regarded as an important pathogenic target for Alzheimer’s disease (AD), the most prevalent neurodegenerative disease. Aβ can assemble into oligomers and fibrils, and produce neurotoxicity. Therefore, Aβ aggregation inhibitors may have anti-AD therapeutic efficacies. It was found, here, that the marine-derived alkaloid, fascaplysin, inhibits Aβ fibrillization in vitro. Moreover, the new analogue, 9-methylfascaplysin, was designed and synthesized from 5-methyltryptamine. Interestingly, 9-methylfascaplysin is a more potent inhibitor of Aβ fibril formation than fascaplysin. Incubation of 9-methylfascaplysin with Aβ directly reduced Aβ oligomer formation. Molecular dynamics simulations revealed that 9-methylfascaplysin might interact with negatively charged residues of Aβ₄₂ with polar binding energy. Hydrogen bonds and π–π interactions between the key amino acid residues of Aβ₄₂ and 9-methylfascaplysin were also suggested. Most importantly, compared with the typical Aβ oligomer, Aβ modified by nanomolar 9-methylfascaplysin produced less neuronal toxicity in SH-SY5Y cells. 9-Methylfascaplysin appears to be one of the most potent marine-derived compounds that produces anti-Aβ neuroprotective effects. Given previous reports that fascaplysin inhibits acetylcholinesterase and induces P-glycoprotein, the current study results suggest that fascaplysin derivatives can be developed as novel anti-AD drugs that possibly act via inhibition of Aβ aggregation along with other target mechanisms.

Replica exchange molecular dynamics simulation of the coordination of Pt(ii)-Phenanthroline to amyloid-β

We report replica exchange molecular dynamics (REMD) simulations of the complex formed between amyloid-β peptides and platinum bound to a phenanthroline ligand, Pt(phen). After construction of an AMBER-style forcefield for the Pt complex, REMD simulation employing temperatures between 270 and 615 K was used to provide thorough sampling of the conformational freedom available to the peptide. We find that the full length peptide Aβ42, in particular, frequently adopts a compact conformation with a large proportion of α- and 3,10-helix content, with smaller amounts of β-strand in the C-terminal region of the peptide. Helical structures are more prevalent than in the metal-free peptide, while turn and strand conformations are markedly less common. Non-covalent interactions, including salt-bridges, hydrogen bonds, and π-stacking between aromatic residues and the phenanthroline ligand, are common, and markedly different from those seen in the amyloid-β peptides alone.

Replica exchange molecular dynamics are used to explore the conformational freedom of amyloid-βbound to Pt(phenanthroline), highlighting important differences in secondary and tertiary structure from the metal-free peptide.

The exploration of novel Alzheimer's therapeutic agents from the pool of FDA approved medicines using drug repositioning, enzyme inhibition and kinetic mechanism approaches

Novel drug development is onerous, time consuming and overpriced process with particularly low success and relatively high enfeebling rates. To overcome this burden, drug repositioning approach is being used to predict the possible therapeutic effects of FDA approved drugs in different diseases. Herein, we designed a computational and enzyme inhibitory mechanistic approach to fetch the promising drugs from the pool of FDA approved drugs against AD. The binding interaction patterns and conformations of screened drugs within active region of AChE were confirmed through molecular docking profiles. The possible associations of selected drugs with AD genes were predicted by pharmacogenomics analysis and confirmed through data mining. The stability behaviour of docked complexes (Drugs-AChE) were checked by MD simulations. The possible therapeutic potential of repositioned drugs against AChE were checked by in vitro analysis. Taken together, Cinitapride displayed a comparable results with standard and can be used as possible therapeutic agent in the treatment of AD.

Metal Binding to Amyloid-β1-42: A Ligand Field Molecular Dynamics Study

Ligand field molecular mechanics simulation has been used to model the interactions of copper(II) and platinum(II) with the amyloid-β_1-42 peptide monomer. Molecular dynamics over several microseconds for both metalated systems are compared to analogous results for the free peptide. Significant differences in structural parameters are observed, both between Cu and Pt bound systems as well as between free and metal-bound peptide. Both metals stabilize the formation of helices in the peptide as well as reducing the content of β secondary structural elements compared to the unbound monomer. This is in agreement with experimental reports of metals reducing β-sheet structures, leading to formation of amorphous aggregates over amyloid fibrils. The shape and size of the peptide structures also undergo noteworthy change, with the free peptide exhibiting globular-like structure, platinum(II) system adopting extended structures, and copper(II) system resulting in a mixture of conformations similar to both of these. Salt bridge networks exhibit major differences: the Asp23-Lys28 salt bridge, known to be important in fibril formation, has a differing distance profile within all three systems studied. Salt bridges in the metal binding region of the peptide are strongly altered; in particular, the Arg5-Asp7 salt bridge, which has an occurrence of 71% in the free peptide, is reduced to zero in the presence of both metals.

Pharmacophore-based models for therapeutic drugs against phosphorylated tau in Alzheimer's disease

Phosphorylated tau (P-tau) has received much attention in the field of Alzheimer's disease (AD), as a potential therapeutic target owing to its involvement with synaptic damage and neuronal dysfunction. The continuous failure of amyloid β (Aβ)-targeted therapeutics highlights the urgency to consider alternative therapeutic strategies for AD. The present review describes the latest developments in tau biology and function. It also explains abnormal interactions between P-tau with Aβ and the mitochondrial fission protein Drp1, leading to excessive mitochondrial fragmentation and synaptic damage in AD neurons. This article also addresses 3D pharmacophore-based drug models designed to treat patients with AD and other tauopathies.

'Evolutionary medicine' perspectives on Alzheimer's Disease: Review and new directions

Evolution by natural selection eliminates maladaptive traits from a species, and yet Alzheimer's Disease (AD) persists with rapidly increasing prevalence globally. This apparent paradox begs an explanation within the framework of evolutionary sciences. Here, I summarize and critique previously proposed theories to explain human susceptibility to AD, grouped into 8 distinct hypotheses based on the concepts of novel extension of the lifespan; lack of selective pressure during the post-reproductive phase; antagonistic pleiotropy; rapid brain evolution; delayed neuropathy by selection for grandmothering; novel alleles selected to delay neuropathy; by-product of selection against cardiovascular disease; and thrifty genotype. Subsequently, I describe a new hypothesis inspired by the concept of mismatched environments. Many of the factors that enhance AD risk today may have been absent or functioned differently before the modern era, potentially making AD a less common affliction for age-matched individuals before industrialization and for the majority of human history. Future research is needed to further explore whether changes in environments and lifestyles across human history moderate risk factors and susceptibility to AD.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

Remarkably Efficient Blood-Brain Barrier Crossing Polyfluorene-Chitosan Nanoparticle Selectively Tweaks Amyloid Oligomer in Cerebrospinal Fluid and Aβ1-40

Amyloid oligomers have emerged as a key neurotoxin in Alzheimer's dementia. Amyloid aggregation inhibitors and modulators have therefore offered potential applications in therapeutics and diagnosis. However, crossing the blood-brain barrier (BBB) and finding the toxic aggregates among aggregates of different sizes and shapes remain a challenge. The ability of identifying early aggregates can provide a new approach to find inhibitors of the initial nucleation events correlating presenile dementia. In this study, we have prepared polyfluorene nanoparticles using chitosan as an additive, which enables it to cross BBB efficiently and employed as a highly efficient amyloid oligomer modulator. The polymer conjugate, polyfluorene-chitosan (PC), shows no toxicity in MTT assay and precludes self-aggregation of Aβ1-40 and human cerebrospinal fluid oligomers to final fibril formation. This modulation strategy is supported by thioflavin T assay, circular dichroism studies, atomic force microscope images, and Fourier transform infrared analysis. The polymer-protein interface exhibits the presence of co-aggregates and responded with a stable optical response. The simple synthesis to get desired sizes and shapes with necessary photophysical behavior, biocompatibility, and most prominently BBB permeability makes this polymer conjugate very unique and highly attractive for modulation of amyloid oligomers selectively as well as for developing next generation nanotheranostic materials toward presenile dementia.

Antibody Engineering for Optimized Immunotherapy in Alzheimer's Disease

There are nearly 50 million people with Alzheimer's disease (AD) worldwide and currently no disease modifying treatment is available. AD is characterized by deposits of Amyloid-β (Aβ), neurofibrillary tangles, and neuroinflammation, and several drug discovery programmes studies have focussed on Aβ as therapeutic target. Active immunization and passive immunization against Aβ leads to the clearance of deposits in humans and transgenic mice expressing human Aβ but have failed to improve memory loss. This review will discuss the possible explanations for the lack of efficacy of Aβ immunotherapy, including the role of a pro-inflammatory response and subsequent vascular side effects, the binding site of therapeutic antibodies and the timing of the treatment. We further discuss how antibodies can be engineered for improved efficacy.

Iron-sulfur cluster biosynthesis and trafficking - impact on human disease conditions

Iron-sulfur clusters (Fe-S) are one of the most ancient, ubiquitous and versatile classes of metal cofactors found in nature. Proteins that contain Fe-S clusters constitute one of the largest families of proteins, with varied functions that include electron transport, regulation of gene expression, substrate binding and activation, radical generation, and, more recently discovered, DNA repair. Research during the past two decades has shown that mitochondria are central to the biogenesis of Fe-S clusters in eukaryotic cells via a conserved cluster assembly machinery (ISC assembly machinery) that also controls the synthesis of Fe-S clusters of cytosolic and nuclear proteins. Several key steps for synthesis and trafficking have been determined for mitochondrial Fe-S clusters, as well as the cytosol (CIA - cytosolic iron-sulfur protein assembly), but detailed mechanisms of cluster biosynthesis, transport, and exchange are not well established. Genetic mutations and the instability of certain steps in the biosynthesis and maturation of mitochondrial, cytosolic and nuclear Fe-S cluster proteins affects overall cellular iron homeostasis and can lead to severe metabolic, systemic, neurological and hematological diseases, often resulting in fatality. In this review we briefly summarize the current molecular understanding of both mitochondrial ISC and CIA assembly machineries, and present a comprehensive overview of various associated inborn human disease states.

Astrocytic glutamatergic transporters are involved in Aβ-induced synaptic dysfunction

In Alzheimer's disease (AD), dementia severity correlates most strongly with decreased synapse density in the hippocampus and cerebral cortex. Although studies in rodents have established that hippocampal long-term potentiation (LTP) is inhibited by soluble oligomers of beta-amyloid (Aβ), the synaptic mechanisms remain unclear. Here, field excitatory postsynaptic potentials (fEPSP) recordings were made in the CA1 region of mouse hippocampal slices. The medium of APP-expressing CHO cells, which contain soluble forms of Aβ including small oligomers, inhibited LTP and facilitated long-term depression (LTD), thus making the LTP/LTD curve shift toward the right. This phenomenon could be mimicked by the non-selective glutamate transporter inhibitor, DL-TBOA. More specifically, the Aβ impaired LTP and facilitated LTD were occluded by the selective astrocytic glutamate transporter inhibitors, TFB-TBOA. In cultured astrocytes, the Aβ oligomers also decrease astrocytic glutamate transporters (EAAT1, EAAT2) expression. We conclude that soluble Aβ oligomers decrease the activation of astrocytic glutamate transporters, thereby impairing synaptic plasticity.

To What Extent Are the Terminal Stages of Sepsis, Septic Shock, Systemic Inflammatory Response Syndrome, and Multiple Organ Dysfunction Syndrome Actually Driven by a Prion/Amyloid Form of Fibrin?

A well-established development of increasing disease severity leads from sepsis through systemic inflammatory response syndrome, septic shock, multiple organ dysfunction syndrome, and cellular and organismal death. Less commonly discussed are the equally well-established coagulopathies that accompany this. We argue that a lipopolysaccharide-initiated (often disseminated intravascular) coagulation is accompanied by a proteolysis of fibrinogen such that formed fibrin is both inflammatory and resistant to fibrinolysis. In particular, we argue that the form of fibrin generated is amyloid in nature because much of its normal α-helical content is transformed to β-sheets, as occurs with other proteins in established amyloidogenic and prion diseases. We hypothesize that these processes of amyloidogenic clotting and the attendant coagulopathies play a role in the passage along the aforementioned pathways to organismal death, and that their inhibition would be of significant therapeutic value, a claim for which there is considerable emerging evidence.

Components of Goutengsan in Rat Plasma by Microdialysis Sampling and Its Protection on Aβ1-42-Induced PC12 Cells Injury

Goutengsan, a Chinese herbal formula, potential protection on Alzheimer's disease (AD) has been less reported. In current study, we investigated the protection of Goutengsan on Aβ_1–42-induced pheochromocytoma-derived cells (PC12). Furthermore, the components from Goutengsan in rat plasma were identified by microdialysis (MD) for in vivo sampling. Meanwhile, the protection of components identified was also verified. At last, we found that Goutengsan has a potential protective effect on Aβ_1–42-induced PC12 cells via reducing cells damage and increasing cells vitality as well as six components (pachymic acid, liquiritin, rhynchophylline, isorhynchophylline, corynoxeine, and isocorynoxeine) which may be effective components. This study helps to understand the treatment of Goutengsan for AD and would facilitate the clinical and further studies for this formula.

Berberine improves cognitive impairment by promoting autophagic clearance and inhibiting production of β-amyloid in APP/tau/PS1 mouse model of Alzheimer's disease

This study investigates the neuroprotective properties of berberine (a natural isoquinoline alkaloid isolated from the Rhizoma coptidis) and finds that berberine could promote β-amyloid (Aβ) clearance and inhibit Aβ production in the triple-transgenic mouse model of Alzheimer's disease (3×Tg-AD). During the study, berberine was first administrated to treat 3×Tg-AD mice and primary neurons. Morris water maze assay, western blotting, enzyme-linked immunosorbent assay (ELISA), immunofluorescence staining and histological analysis, transmission electron microscopic analysis were then used to evaluate the effects of the berberine administration. The result showed that berberine significantly improved 3×Tg-AD mice's spatial learning capacity and memory retention, promoted autophagy activity identified by the enhancement of brain LC3-II, beclin-1, hVps34, and Cathepsin-D levels as well as the reduction of brain P62 and Bcl-2 levels in AD mice, facilitated reduction of Aβ and APP levels, reduced Aβ plaque deposition in the hippocampus of AD mice, and inhibited b-site APP cleavage enzyme 1 (BACE1) expression. Similar results were also found in 3×Tg-AD primary hippocampal neurons: berbernine treatment decreased the levels of extracellular and intracellular Aβ1-42, increased the protein levels of LC3-II, beclin-1, hVps34, and Cathepsin-D, and decreased the levels of P62, Bcl-2, APP and BACE1 levels. In summary, berberine shows neuroprotective effects on 3×Tg-AD mice and may be a promising multitarget drug in the preventionand protection against AD.

The neurotoxicity of amyloid β-protein oligomers is reversible in a primary neuron model

Alzheimer’s disease (AD) is characterized by the accumulation of extracellular amyloid β-protein (Aβ) and intracellular hyperphosphorylated tau proteins. Recent evidence suggests that soluble Aβ oligomers elicit neurotoxicity and synaptotoxicity, including tau abnormalities, and play an initiating role in the development of AD pathology. In this study, we focused on the unclarified issue of whether the neurotoxicity of Aβ oligomers is a reversible process. Using a primary neuron culture model, we examined whether the neurotoxic effects induced by 2-day treatment with Aβ42 oligomers (Aβ-O) are reversible during a subsequent 2-day withdrawal period. Aβ-O treatment resulted in activation of caspase-3 and eIF2α, effects that were considerably attenuated following Aβ-O removal. Immunocytochemical analyses revealed that Aβ-O induced aberrant phosphorylation and caspase-mediated cleavage of tau, both of which were mostly reversed by Aβ-O removal. Furthermore, Aβ-O caused intraneuronal dislocation of β-catenin protein and a reduction in its levels, and these alterations were partially reversed upon Aβ-O withdrawal. The dislocation of β-catenin appeared to reflect synaptic disorganization. These findings indicate that removal of extracellular Aβ-O can fully or partially reverse Aβ-O-induced neurotoxic alterations in our neuron model. Accordingly, we propose that the induction of neurotoxicity by Aβ oligomers is a reversible process, which has important implications for the development of AD therapies.