Stabilization of nontoxic Aβ-oligomers: insights into the mechanism of action of hydroxyquinolines in Alzheimer's disease

Role of Oxidative Stress, Methionine Oxidation and Methionine Sulfoxide Reductases (MSR) in Alzheimer's Disease

A major contributor to dementia seen in aging is Alzheimer's disease (AD). Amyloid beta (Aβ), a main component of senile plaques (SPs) in AD, induces neuronal death through damage to cellular organelles and structures, caused by oxidation of important molecules such as proteins by reactive oxygen species (ROS). Hyperphosphorylation and accumulation of the protein tau in the microtubules within the brain also promote ROS production. Methionine, a residue of proteins, is particularly sensitive to oxidation by ROS. One of the enzyme systems that reverses the oxidative damage in mammalian cells is the enzyme system known as Methionine Sulfoxide Reductases (MSRs). The components of the MSR system, namely MSRA and MSRB, reduce oxidized forms of methionine (Met-(o)) in proteins back to methionine (Met). Furthermore, the MSRs scavenge ROS by allowing methionine residues in proteins to utilize their antioxidant properties. This review aims to improve the understanding of the role of the MSR system of enzymes in reducing cellular oxidative damage and AD pathogenesis, which may contribute to effective therapeutic approaches for AD by targeting the MSR system.

Computationally Designed Molecules Modulate ALS-Related Amyloidogenic TDP-43307-319 Aggregation

Abnormal cytosolic aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) is observed in multiple diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration, and Alzheimer's disease. Previous studies have shown that TDP-43307-319 located at the C-terminal of TDP-43 can form higher-order oligomers and fibrils. Of particular interest are the hexamers that adopt a cylindrin structure that has been strongly correlated to neurotoxicity. In this study, we use the joint pharmacophore space (JPS) model to identify and generate potential TDP-43 inhibitors. Five JPS-designed molecules are evaluated using both experimental and computational methods: ion mobility mass spectrometry, thioflavin T fluorescence assay, circular dichroism spectroscopy, atomic force microscopy, and molecular dynamics simulations. We found that all five molecules can prevent the amyloid fibril formation of TDP-43307-319, but their efficacy varies significantly. Furthermore, among the five molecules, [AC0101] is the most efficient in preventing the formation of higher-order oligomers and dissociating preformed higher-order oligomers. Molecular dynamics simulations show that [AC0101] both is the most flexible and forms the most hydrogen bonds with the TDP-43307-319 monomer. The JPS-designed molecules can insert themselves between the β-strands in the hexameric cylindrin structure of TDP-43307-319 and can open its structure. Possible mechanisms for JPS-designed molecules to inhibit and dissociate TDP-43307-319 oligomers on an atomistic scale are proposed.

Failure, Success, and Future Direction of Alzheimer Drugs Targeting Amyloid-β Cascade: Pros and Cons of Chemical and Biological Modalities

Alzheimer's disease (AD) is the most prevalent cause of dementia and has become a health concern worldwide urging for an effective therapeutic. The amyloid hypothesis, currently the most pursued basis of AD drug discovery, points the cause of AD to abnormal production and ineffective removal of pathogenic aggregated amyloid-β (Aβ). AD therapeutic research has been focused on targeting different species of Aβ in the amyloidogenic process to control Aβ content and recover cognitive decline. Among the different processes targeted, the clearance mechanism has been found to be the most effective, supported by the recent clinical approval of an Aβ-targeting immunotherapeutic drug which significantly slowed cognitive decline. Although the current AD drug discovery field is extensively researching immunotherapeutic drugs, there are numerous properties of immunotherapy in need of improvements that could be overcome by an equally performing chemical drug. Here, we review chemical and immunotherapy drug candidates, based on their mechanism of modulating the amyloid cascade, selected from the AlzForum database. Through this review, we aim to summarize and evaluate the prospect of Aβ-targeting chemical drugs.

Computationally Designed Small Molecules Disassemble Both Soluble Oligomers and Protofibrils of Amyloid β-Protein Responsible for Alzheimer's Disease

Alzheimer's disease (AD) is one of the world's most pressing health crises. AD is an incurable disease affecting more than 6.5 million Americans, predominantly the elderly, and in its later stages, leads to memory loss, dementia, and death. Amyloid β (Aβ) protein aggregates have been one of the pathological hallmarks of AD since its initial characterization. The early stages of Aβ accumulation and aggregation involve the formation of oligomers, which are considered neurotoxic and play a key role in further aggregation into fibrils that eventually appear in the brain as amyloid plaques. We have recently shown by combining ion mobility mass spectrometry (IM-MS) and atomic force microscopy (AFM) that Aβ42 rapidly forms dodecamers (12-mers) as the terminal oligomeric state, and these dodecamers seed the early formation of Aβ42 protofibrils. The link between soluble oligomers and fibril formation is one of the essential aspects for understanding the root cause of the disease state and is critical to developing therapeutic interventions. Utilizing a joint pharmacophore space (JPS) method, potential drugs have been designed specifically for amyloid-related diseases. These small molecules were generated based on crucial chemical features necessary for target selectivity. In this paper, we utilize our combined IM-MS and AFM methods to investigate the impact of three second-generation JPS small-molecule inhibitors, AC0201, AC0202, and AC0203, on dodecamer as well as fibril formation in Aβ42. Our results indicate that AC0201 works well as an inhibitor and remodeler of both dodecamers and fibril formation, AC0203 behaves less efficiently, and AC0202 is ineffective.

Role of Metal Cations of Copper, Iron, and Aluminum and Multifunctional Ligands in Alzheimer's Disease: Experimental and Computational Insights

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people around the world. Even though the causes of AD are not completely understood due to its multifactorial nature, some neuropathological hallmarks of its development have been related to the high concentration of some metal cations. These roles include the participation of these metal cations in the production of reactive oxygen species, which have been involved in neuronal damage. In order to avoid the increment in the oxidative stress, multifunctional ligands used to coordinate these metal cations have been proposed as a possible treatment to AD. In this review, we present the recent advances in experimental and computational works aiming to understand the role of two redox active and essential transition-metal cations (Cu and Fe) and one nonbiological metal (Al) and the recent proposals on the development of multifunctional ligands to stop or revert the damaging effects promoted by these metal cations.

Alzheimer's Drug PBT2 Interacts with the Amyloid β 1-42 Peptide Differently than Other 8-Hydroxyquinoline Chelating Drugs

Although Alzheimer's disease (AD) was first described over a century ago, it remains the leading cause of age-related dementia. Innumerable changes have been linked to the pathology of AD; however, there remains much discord regarding which might be the initial cause of the disease. The "amyloid cascade hypothesis" proposes that the amyloid β (Aβ) peptide is central to disease pathology, which is supported by elevated Aβ levels in the brain before the development of symptoms and correlations of amyloid burden with cognitive impairment. The "metals hypothesis" proposes a role for metal ions such as iron, copper, and zinc in the pathology of AD, which is supported by the accumulation of these metals within amyloid plaques in the brain. Metals have been shown to induce aggregation of Aβ, and metal ion chelators have been shown to reverse this reaction in vitro. 8-Hydroxyquinoline-based chelators showed early promise as anti-Alzheimer's drugs. Both 5-chloro-7-iodo-8-hydroxyquinoline (CQ) and 5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline (PBT2) underwent unsuccessful clinical trials for the treatment of AD. To gain insight into the mechanism of action of 8HQs, we have investigated the potential interaction of CQ, PBT2, and 5,7-dibromo-8-hydroxyquinoline (B2Q) with Cu(II)-bound Aβ(1-42) using X-ray absorption spectroscopy (XAS), high energy resolution fluorescence detected (HERFD) XAS, and electron paramagnetic resonance (EPR). By XAS, we found CQ and B2Q sequestered ∼83% of the Cu(II) from Aβ(1-42), whereas PBT2 sequestered only ∼59% of the Cu(II) from Aβ(1-42), suggesting that CQ and B2Q have a higher relative Cu(II) affinity than PBT2. From our EPR, it became clear that PBT2 sequestered Cu(II) from a heterogeneous mixture of Cu(II)Aβ(1-42) species in solution, leaving a single Cu(II)Aβ(1-42) species. It follows that the Cu(II) site in this Cu(II)Aβ(1-42) species is inaccessible to PBT2 and may be less solvent-exposed than in other Cu(II)Aβ(1-42) species. We found no evidence to suggest that these 8HQs form ternary complexes with Cu(II)Aβ(1-42).

Modeling Alzheimer's Disease in Caenorhabditis elegans

Alzheimer’s disease (AD) is the most frequent cause of dementia. After decades of research, we know the importance of the accumulation of protein aggregates such as β-amyloid peptide and phosphorylated tau. We also know that mutations in certain proteins generate early-onset Alzheimer’s disease (EOAD), and many other genes modulate the disease in its sporadic form. However, the precise molecular mechanisms underlying AD pathology are still unclear. Because of ethical limitations, we need to use animal models to investigate these processes. The nematode Caenorhabditis elegans has received considerable attention in the last 25 years, since the first AD models overexpressing Aβ peptide were described. We review here the main results obtained using this model to study AD. We include works studying the basic molecular mechanisms of the disease, as well as those searching for new therapeutic targets. Although this model also has important limitations, the ability of this nematode to generate knock-out or overexpression models of any gene, single or combined, and to carry out toxicity, recovery or survival studies in short timeframes with many individuals and at low cost is difficult to overcome. We can predict that its use as a model for various diseases will certainly continue to increase.

Analysis of plasma proteins using 2D gels and novel fluorescent probes: in search of blood based biomarkers for Alzheimer's disease

BACKGROUND

The Australian Imaging and Biomarker Lifestyle (AIBL) study of aging is designed to aid the discovery of biomarkers. The current study aimed to discover differentially expressed plasma proteins that could yield a blood-based screening tool for Alzheimer's disease.

METHODS

The concentration of proteins in plasma covers a vast range of 12 orders of magnitude. Therefore, to search for medium to low abundant biomarkers and elucidate mechanisms of AD, we immuno-depleted the most abundant plasma proteins and pre-fractionated the remaining proteins by HPLC, prior to two-dimensional gel electrophoresis. The relative levels of approximately 3400 protein species resolved on the 2D gels were compared using in-gel differential analysis with spectrally resolved fluorescent protein detection dyes (Zdyes™). Here we report on analysis of pooled plasma samples from an initial screen of a sex-matched cohort of 72 probable AD patients and 72 healthy controls from the baseline time point of AIBL.

RESULTS

We report significant changes in variants of apolipoprotein E, haptoglobin, α1 anti-trypsin, inter-α trypsin inhibitor, histidine-rich glycoprotein, and a protein of unknown identity. α1 anti-trypsin and α1 anti-chymotrypsin demonstrated plasma concentrations that were dependent on APOE ε4 allele dose. Our analysis also identified an association with the level of Vitamin D binding protein fragments and complement factor I with sex. We then conducted a preliminary validation study, on unique individual samples compared to the discovery cohort, using a targeted LC-MS/MS assay on a subset of discovered biomarkers. We found that targets that displayed a high degree of isoform specific changes in the 2D gels were not changed in the targeted MS assay which reports on the total level of the biomarker.

CONCLUSIONS

This demonstrates that further development of mass spectrometry assays is needed to capture the isoform complexity that exists in theses biological samples. However, this study indicates that a peripheral protein signature has potential to aid in the characterization of AD.

Artificial Chiral Interfaces against Amyloid-β Peptide Aggregation: Research Progress and Challenges

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by an imbalance between the production and clearance of amyloid-β (Aβ) species. AD not only influences the life quality of the patients but also heavily burdens the families and society. Therefore, it is an urgent mission to research and develop some new anti-amyloid aggregation drugs. In recent years, there were research and development of engineered nanostructures as Aβ amyloid inhibitors have attracted extensive attention and become a new frontier in nanomedicine. The effects of nanostructural surface properties (e.g., morphology, charge, hydrophobicity) on inhibition of Aβ aggregation are modulated by adsorbed Aβ peptides. Nevertheless, chirality has been seldom considered in recognition of Aβ species and modulation of Aβ aggregations. Moreover, a more relevant question for chiral inhibitors is little known about the molecular mechanism of how to interface chiral effects Aβ targeting recognition and effective mitigation of amyloidosis at the molecular level. Herein, we review recent experimental and theoretical results acquired in the specific areas of artificial chiral nanostructure inhibitors. This article will be essential to provide a microlevel insight into the effects of chiral nanointerfaces on amyloidosis processes as well as the development of chiral inhibitor drugs against Aβ fibrillation.

Vitamin B12 Inhibits Aβ Fibrillation and Disaggregates Preformed Fibrils in the Presence of Synthetic Neuronal Membranes

The aggregation of amyloid β (Aβ) peptide with subsequent formation of fibrils which deposit in senile plaques is considered one of the key triggers of Alzheimer's disease (AD). Molecules targeting the inhibition of Aβ fibrillation and/or the disruption of Aβ fibrils are thus promising approaches for the medical prevention and treatment of AD. However, amyloid formation is a complex process strongly influenced by the cellular environment, such as cell membranes, which may affect the effectiveness of therapeutic molecules. In this study, the effect of the vitamin B12 (VB12) on the formation and disaggregation of Aβ_1-42 fibrils was investigated in the presence of artificial neuronal membranes mimicked by liposomes. Evidence showed that VB12 slows down the Aβ fibrillization and reduces the content of fibrils in aqueous solution. Moreover, the vitamin exhibited a strong ability to disrupt preformed fibrils. However, the presence of lipid vesicles compromised the VB12's antiamyloidogenic properties due to the competitive interaction of the vitamin with the lipid membrane and the Aβ peptide. Even so, VB12 was effective in inhibiting the fibril formation and disaggregating fibrils in the lipid membrane environment. Thereby, these results indicate that VB12 could be a promising molecule both for the prevention and cure of AD, thus warranting its study in animal models.

Surface Plasmon Resonance Assay for Identification of Small Molecules Capable of Inhibiting Aβ Aggregation

Toxic aggregates of amyloid-beta (Aβ) have importance in the pathology of Alzheimer's disease, and inhibition of aggregate formation is considered to be a promising strategy for drug development. Here, we report a simple and rapid surface plasmon resonance (SPR) assay method that can identify potential Aβ aggregation inhibitors. Our assay is based on the SPR shifting of the Aβ-gold nanoparticle (Aβ-GNP) aggregates by size under the influence of an Aβ aggregation inhibitor. This user-friendly assay features a short assay time with a low reagent consumption that can be easily adapted as a high-throughput screen. We demonstrated that an effective Aβ aggregation inhibitor induces the blue-shifted SPR peaks of the Aβ-GNP aggregates by hindering the formation of long fibrillar aggregates. Moreover, the blue shifting was correlated to the efficacy and concentrations of an Aβ aggregation inhibitor. Overall, our findings suggest that our simple SPR assay can be a powerful tool to screen small molecules targeting Aβ aggregation.

Alzheimer's protection effect of A673T mutation may be driven by lower Aβ oligomer binding affinity

Several mutations conferring protection against Alzheimer's disease (AD) have been described, none as profound as the A673T mutation, where carriers are four times less likely to get AD compared to noncarriers. This mutation results in reduced amyloid beta (Aβ) protein production in vitro and lower lifetime Aβ concentration in carriers. Better understanding of the protective mechanisms of the mutation may provide important insights into AD pathophysiology and identify productive therapeutic intervention strategies for disease modification. Aβ(1-42) protein forms oligomers that bind saturably to a single receptor site on neuronal synapses, initiating the downstream toxicities observed in AD. Decreased formation, toxicity, or stability of soluble Aβ oligomers, or reduction of synaptic binding of these oligomers, may combine with overall lower Aβ concentration to underlie A673T's disease protecting mechanism. To investigate these possibilities, we compared the formation rate of soluble oligomers made from Icelandic A673T mutant and wild type (wt) Aβ(1-42) synthetic protein, the amount and intensity of oligomer bound to mature primary rat hippocampal/cortical neuronal synapses, and the potency of bound oligomers to impact trafficking rate in neurons in vitro using a physiologically relevant oligomer preparation method. At equal protein concentrations, mutant protein forms approximately 50% or fewer oligomers of high molecular weight (>50 kDa) compared to wt protein. Mutant oligomers are twice as potent at altering the cellular vesicle trafficking rate as wt at equivalent concentrations, however, mutant oligomers have a >4-fold lower binding affinity to synaptic receptors (Kd  = 1,950 vs. 442 nM). The net effect of these differences is a lower overall toxicity at a given concentration. This study demonstrates for the first time that mutant A673T Aβ oligomers prepared with this method have fundamentally different assembly characteristics and biological impact from wt protein and indicates that its disease protecting mechanism may result primarily from the mutant protein's much lower binding affinity to synaptic receptors. This suggests that therapeutics that effectively reduce oligomer binding to synapses in the brain may be beneficial in AD.

Visualizing and trapping transient oligomers in amyloid assembly pathways

Oligomers which form during amyloid fibril assembly are considered to be key contributors towards amyloid disease. However, understanding how such intermediates form, their structure, and mechanisms of toxicity presents significant challenges due to their transient and heterogeneous nature. Here, we discuss two different strategies for addressing these challenges: use of (1) methods capable of detecting lowly-populated species within complex mixtures, such as NMR, single particle methods (including fluorescence and force spectroscopy), and mass spectrometry; and (2) chemical and biological tools to bias the amyloid energy landscape towards specific oligomeric states. While the former methods are well suited to following the kinetics of amyloid assembly and obtaining low-resolution structural information, the latter are capable of producing oligomer samples for high-resolution structural studies and inferring structure-toxicity relationships. Together, these different approaches should enable a clearer picture to be gained of the nature and role of oligomeric intermediates in amyloid formation and disease.

Copper Dyshomeostasis in Neurodegenerative Diseases-Therapeutic Implications

Copper is one of the most abundant basic transition metals in the human body. It takes part in oxygen metabolism, collagen synthesis, and skin pigmentation, maintaining the integrity of blood vessels, as well as in iron homeostasis, antioxidant defense, and neurotransmitter synthesis. It may also be involved in cell signaling and may participate in modulation of membrane receptor-ligand interactions, control of kinase and related phosphatase functions, as well as many cellular pathways. Its role is also important in controlling gene expression in the nucleus. In the nervous system in particular, copper is involved in myelination, and by modulating synaptic activity as well as excitotoxic cell death and signaling cascades induced by neurotrophic factors, copper is important for various neuronal functions. Current data suggest that both excess copper levels and copper deficiency can be harmful, and careful homeostatic control is important. This knowledge opens up an important new area for potential therapeutic interventions based on copper supplementation or removal in neurodegenerative diseases including Wilson's disease (WD), Menkes disease (MD), Alzheimer's disease (AD), Parkinson's disease (PD), and others. However, much remains to be discovered, in particular, how to regulate copper homeostasis to prevent neurodegeneration, when to chelate copper, and when to supplement it.

Copper Toxicity Links to Pathogenesis of Alzheimer's Disease and Therapeutics Approaches

Alzheimer's disease (AD) is an irreversible, age-related progressive neurological disorder, and the most common type of dementia in aged people. Neuropathological lesions of AD are neurofibrillary tangles (NFTs), and senile plaques comprise the accumulated amyloid-beta (Aβ), loaded with metal ions including Cu, Fe, or Zn. Some reports have identified metal dyshomeostasis as a neurotoxic factor of AD, among which Cu ions seem to be a central cationic metal in the formation of plaque and soluble oligomers, and have an essential role in the AD pathology. Cu-Aβ complex catalyzes the generation of reactive oxygen species (ROS) and results in oxidative damage. Several studies have indicated that oxidative stress plays a crucial role in the pathogenesis of AD. The connection of copper levels in AD is still ambiguous, as some researches indicate a Cu deficiency, while others show its higher content in AD, and therefore there is a need to increase and decrease its levels in animal models, respectively, to study which one is the cause. For more than twenty years, many in vitro studies have been devoted to identifying metals' roles in Aβ accumulation, oxidative damage, and neurotoxicity. Towards the end, a short review of the modern therapeutic approach in chelation therapy, with the main focus on Cu ions, is discussed. Despite the lack of strong proofs of clinical advantage so far, the conjecture that using a therapeutic metal chelator is an effective strategy for AD remains popular. However, some recent reports of genetic-regulating copper transporters in AD models have shed light on treating this refractory disease. This review aims to succinctly present a better understanding of Cu ions' current status in several AD features, and some conflicting reports are present herein.

Oral Immunization with Soybean Storage Protein Containing Amyloid-β 4-10 Prevents Spatial Learning Decline

 Amyloid-β (Aβ) plays a central role in the pathogenesis of Alzheimer’s disease (AD). Because AD pathologies begin two decades before the onset of dementia, prevention of Aβ amyloidosis has been proposed as a mean to block the pathological cascade. Here, we generate a transgenic plant-based vaccine, a soybean storage protein containing Aβ4–10, named Aβ+, for oral Aβ immunization. One mg of Aβ+ or control protein (Aβ–) was administered to TgCRND8 mice once a week from 9 weeks up to 58 weeks. Aβ+ immunization raised both anti-Aβ antibodies and cellular immune responses. Spatial learning decline was prevented in the Aβ+ immunized group in an extended reference memory version of Morris water maze test from 21 to 57 weeks. In Tris-buffered saline (TBS), sodium dodecyl sulfate (SDS), and formic acid (FA) serial extractions, all sets of Aβ species from Aβ monomer, low to high molecular weight Aβ oligomers, and Aβ smears had different solubility in TgCRND8 brains. Aβ oligomers decreased in TBS fractions, corresponding to an increase in high molecular weight Aβ oligomers in SDS extracts and Aβ smears in FA fraction of the Aβ+ treated group. There was significant inhibition of histological Aβ burden, especially in diffuse plaques, and suppression of microglial inflammation. Processing of amyloid-β protein precursor was not different between Aβ+ and Aβ– groups. No evidence of amyloid-related inflammatory angiopathy was observed. Thus, Aβ+ oral immunization could be a promising, cheap, and long-term safe disease-modifying therapy to prevent the pathological process in AD.

The aroylhydrazone INHHQ prevents memory impairment induced by Alzheimer's-linked amyloid-β oligomers in mice

Converging evidence indicates that neurotoxicity and memory impairment in Alzheimer's disease is induced by brain accumulation of soluble amyloid-β oligomers (AβOs). Physiological metals are poorly distributed and concentrated in the senile plaques typical of Alzheimer's disease, where they may be coordinated to the amyloid-β peptide (Aβ). Indeed, zinc and copper increase Aβ oligomerization and toxicity. Metal-protein attenuating compounds represent a class of agents proposed for Alzheimer's disease treatment, as they reduce abnormal interactions of metal ions with Aβ, inhibit Aβ oligomerization and prevent deleterious redox reactions in the brain. The present work investigates the protective action of an isoniazid-derived aroylhydrazone, INHHQ, on AβO-induced memory impairment. Systemic administration of a single dose of INHHQ (1 mg/kg) prevented both short-term and long-term memory impairment caused by AβOs in mice. In-vitro studies showed that INHHQ prevents Cu(Aβ)-catalyzed production of reactive oxygen species. Although the mechanism of protection by INHHQ is not yet fully understood at a molecular level, the results reported herein certainly point to the value of aroylhydrazones as promising neuroprotective agents in Alzheimer's disease and related disorders.

Development of a brain-permeable peptide nanofiber that prevents aggregation of Alzheimer pathogenic proteins

Alzheimer's disease (AD) is proposed to be induced by abnormal aggregation of amyloidβ in the brain. Here, we designed a brain-permeable peptide nanofiber drug from a fragment of heat shock protein to suppress aggregation of the pathogenic proteins. To facilitate delivery of the nanofiber into the brain, a protein transduction domain from Drosophila Antennapedia was incorporated into the peptide sequence. The resulting nanofiber efficiently suppressed the cytotoxicity of amyloid βby trapping amyloid β onto its hydrophobic nanofiber surface. Moreover, the intravenously or intranasally injected nanofiber was delivered into the mouse brain, and improved the cognitive function of an Alzheimer transgenic mouse model. These results demonstrate the potential therapeutic utility of nanofibers for the treatment of AD.

High-resolution probing of early events in amyloid-β aggregation related to Alzheimer's disease

In Alzheimer's disease (AD), soluble oligomers of amyloid-β (Aβ) are emerging as a crucial entity in driving disease progression as compared to insoluble amyloid deposits. The lacuna in establishing the structure to function relationship for Aβ oligomers prevents the development of an effective treatment for AD. While the transient and heterogeneous properties of Aβ oligomers impose many challenges for structural investigation, an effective use of a combination of NMR techniques has successfully identified and characterized them at atomic-resolution. Here, we review the successful utilization of solution and solid-state NMR techniques to probe the aggregation and structures of small and large oligomers of Aβ. Biophysical studies utilizing the commonly used solution and 19F based NMR experiments to identify the formation of small size early intermediates and to obtain their structures, and dock-lock mechanism of fiber growth at atomic-resolution are discussed. In addition, the use of proton-detected magic angle spinning (MAS) solid-state NMR experiments to obtain high-resolution insights into the aggregation pathways and structures of large oligomers and other aggregates is also presented. We expect these NMR based studies to be valuable for real-time monitoring of the depletion of monomers and the formation of toxic oligomers and high-order aggregates under a variety of conditions, and to solve the high-resolution structures of small and large size oligomers for most amyloid proteins, and therefore to develop inhibitors and drugs.

Flavonoid-Derived Human Phenyl-γ-Valerolactone Metabolites Selectively Detoxify Amyloid-β Oligomers and Prevent Memory Impairment in a Mouse Model of Alzheimer's Disease

SCOPE

Amyloid-β oligomers (AβO) are causally related to Alzheimer's disease (AD). Dietary natural compounds, especially flavonoids and flavan-3-ols, hold great promise as potential AD-preventive agents but their host and gut microbiota metabolism complicates identification of the most relevant bioactive species. This study aims to investigate the ability of a comprehensive set of phenyl-γ-valerolactones (PVL), the main circulating metabolites of flavan-3-ols and related dietary compounds in humans, to prevent AβO-mediated toxicity.

METHODS AND RESULTS

The anti-AβO activity of PVLs is examined in different cell model systems using a highly toxic β-oligomer-forming polypeptide (β23) as target toxicant. Multiple PVLs, and particularly the monohydroxylated 5-(4'-hydroxyphenyl)-γ-valerolactone metabolite [(4'-OH)-PVL], relieve β-oligomer-induced cytotoxicity in yeast and mammalian cells. As revealed by atomic force microscopy (AFM) and other in vitro assays, (4'-OH)-PVL interferes with AβO (but not fibril) assembly and actively remodels preformed AβOs into nontoxic amorphous aggregates. In keeping with the latter mode of action, treatment of AβOs with (4'-OH)-PVL prior to brain injection strongly reduces memory deterioration as well as neuroinflammation in a mouse model of AβO-induced memory impairment.

CONCLUSION

PVLs, which have been validated as biomarkers of the dietary intake of flavan-3-ols, lend themselves as novel AβO-selective, candidate AD-preventing compounds.

Acetylation of Aβ40 Alters Aggregation in the Presence and Absence of Lipid Membranes

A hallmark of Alzheimer's disease (AD) is the formation of senile plaques comprised of the β-amyloid (Aβ) peptide. Aβ fibrillization is a complex nucleation-dependent process involving a variety of metastable intermediate aggregates and features the formation of inter- and intramolecular salt bridges involving lysine residues, K16 and K28. Cationic lysine residues also mediate protein-lipid interactions via association with anionic lipid headgroups. As several toxic mechanisms attributed to Aβ involve membrane interactions, the impact of acetylation on Aβ₄₀ aggregation in the presence and absence of membranes was determined. Using chemical acetylation, varying mixtures of acetylated and nonacetylated Aβ₄₀ were produced. With increasing acetylation, fibril and oligomer formation decreased, eventually completely arresting fibrillization. In the presence of total brain lipid extract (TBLE) vesicles, acetylation reduced the interaction of Aβ₄₀ with membranes; however, fibrils still formed at near complete levels of acetylation. Additionally, the combination of TBLE and acetylated Aβ promoted annular aggregates. Finally, toxicity associated with Aβ₄₀ was reduced with increasing acetylation in a cell culture assay. These results suggest that in the absence of membranes that the cationic character of lysine plays a major role in fibril formation. However, acetylation promotes unique aggregation pathways in the presence of lipid membranes.

Modulating ALS-Related Amyloidogenic TDP-43307-319 Oligomeric Aggregates with Computationally Derived Therapeutic Molecules

TDP-43 aggregates are a salient feature of amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and a variety of other neurodegenerative diseases, including Alzheimer's disease (AD). With an anticipated growth in the most susceptible demographic, projections predict neurodegenerative diseases will potentially affect 15 million people in the United States by 2050. Currently, there are no cures for ALS, FTD, or AD. Previous studies of the amyloidogenic core of TDP-43 have demonstrated that oligomers greater than a trimer are associated with toxicity. Utilizing a joint pharmacophore space (JPS) method, potential drugs have been designed specifically for amyloid-related diseases. These molecules were generated on the basis of key chemical features necessary for blood-brain barrier permeability, low adverse side effects, and target selectivity. Combining ion-mobility mass spectrometry and atomic force microscopy with the JPS computational method allows us to more efficiently evaluate a potential drug's efficacy in disrupting the development of putative toxic species. Our results demonstrate the dissociation of higher-order oligomers in the presence of these novel JPS-generated inhibitors into smaller oligomer species. Additionally, drugs approved by the Food and Drug Administration for the treatment of ALS were also evaluated and demonstrated to maintain higher-order oligomeric assemblies. Possible mechanisms for the observed action of the JPS molecules are discussed.

Biological Evaluation of 8-Hydroxyquinolines as Multi-Target Directed Ligands for Treating Alzheimer's Disease

BACKGROUND

Accumulating evidence suggests that multi-target directed ligands have great potential for the treatment of complex diseases such as Alzheimer's Disease (AD).

OBJECTIVE

To evaluate novel chimeric 8-hydroxyquinoline ligands with merged pharmacophores as potential multifunctional ligands for AD.

METHODS

Nitroxoline, PBT2 and compounds 2-4 were evaluated in-vitro for their inhibitory potencies on cathepsin B, cholinesterases, and monoamine oxidases. Furthermore, chelation, antioxidative properties and the permeability of Blood-Brain Barrier (BBB) were evaluated by spectroscopy-based assays and the inhibition of Amyloid β (Aβ) aggregation was determined in immunoassay. Cell-based assays were performed to determine cytotoxicity, neuroprotection against toxic Aβ species, and the effects of compound 2 on apoptotic cascade.

RESULTS

Compounds 2-4 competitively inhibited cathepsin B β-secretase activity, chelated metal ions and were weak antioxidants. All of the compounds inhibited Aβ aggregation, whereas only compound 2 had a good BBB permeability according to the parallel artificial membrane permeability assay. Tested ligands 2 and 3 were not cytotoxic to SH-SY5Y and HepG2 cells at 10 μM. Compound 2 exerted neuroprotective effects towards Aβ toxicity, reduced the activation of caspase-3/7 and diminished the apoptosis of cells treated with Aβ1-42.

CONCLUSION

Taken together, our data suggest that compound 2 holds a promise to be used as a multifunctional ligand for AD.

Theories of Aging and the Prevalence of Alzheimer's Disease

OBJECTIVE

Aging and AD are associated in some way, then it is reasonable to ask whether or not it is possible to age without AD inexorably appearing at any moment, depending on the period of life. Therefore, the goal of this review is to verify, in light of some aging theories, the prevalence of AD.

METHODS

For the purpose of this manuscript, the indexers Alzheimer, aging, Alzheimer, and aging were considered; theories of aging were researched. The research was conducted using PubMed, Medline, Scopus, Elsevier, and Google Scholar.

RESULTS

The most common subjects in the papers analyzed for this manuscript were aging and Alzheimer's disease. The association between Alzheimer and theories of aging seems inconclusive.

CONCLUSIONS

Accordingly, the general idea is that AD is associated with aging in such a way that almost all people will present this disease; however, it is plausible to consider that the increase in life expectancy will generate a high prevalence of AD. In a general sense, it seems that the theories of aging explain the origin of AD under superlative and catastrophic considerations and use more biomolecular data than social or behavioral data as the bases of analysis, which may be the problem.

The Amyloid-β Oligomer Hypothesis: Beginning of the Third Decade

The amyloid-β oligomer (AβO) hypothesis was introduced in 1998. It proposed that the brain damage leading to Alzheimer’s disease (AD) was instigated by soluble, ligand-like AβOs. This hypothesis was based on the discovery that fibril-free synthetic preparations of AβOs were potent CNS neurotoxins that rapidly inhibited long-term potentiation and, with time, caused selective nerve cell death (Lambert et al., 1998). The mechanism was attributed to disrupted signaling involving the tyrosine-protein kinase Fyn, mediated by an unknown toxin receptor. Over 4,000 articles concerning AβOs have been published since then, including more than 400 reviews. AβOs have been shown to accumulate in an AD-dependent manner in human and animal model brain tissue and, experimentally, to impair learning and memory and instigate major facets of AD neuropathology, including tau pathology, synapse deterioration and loss, inflammation, and oxidative damage. As reviewed by Hayden and Teplow in 2013, the AβO hypothesis “has all but supplanted the amyloid cascade.” Despite the emerging understanding of the role played by AβOs in AD pathogenesis, AβOs have not yet received the clinical attention given to amyloid plaques, which have been at the core of major attempts at therapeutics and diagnostics but are no longer regarded as the most pathogenic form of Aβ. However, if the momentum of AβO research continues, particularly efforts to elucidate key aspects of structure, a clear path to a successful disease modifying therapy can be envisioned. Ensuring that lessons learned from recent, late-stage clinical failures are applied appropriately throughout therapeutic development will further enable the likelihood of a successful therapy in the near-term.

Tau Inclusions in Alzheimer's, Chronic Traumatic Encephalopathy and Pick's Disease. A Speculation on How Differences in Backbone Polarization Underlie Divergent Pathways of Tau Aggregation

Tau-related dementias appear to involve specific to each disease aggregation pathways and morphologies of filamentous tau assemblies. To understand etiology of these differences, here we elucidate molecular mechanism of formation of tau PHFs based on the PMO theory of misfolding and aggregation of pleiomorphic proteins associated with neurodegenerative diseases. In this model, fibrillization of tau is initiated by the coupled binding and folding of the MTB domains that yields antiparallel homodimers, in analogy to folding of split inteins. The free energy of binding is minimized when the antiparallel alignment brings about backbone-backbone H-bonding between the MTBD segments of similar "strand" propensities. To assess these propensities, a function of the NMR shielding tensors of the Cα atoms is introduced as the folding potential function FP i ; the Cα tensors are obtained by the quantum mechanical modeling of protein secondary structure (GIAO//B3LYP/D95**). The calculated FP i plots show that the "strand" propensities of the MBTD segments, and hence the homodimer's register, can be affected by the relatively small changes in the environment's pH, as a result of protonation of MBTD's conserved histidines. The assembly of the antiparallel tau dimers into granular aggregates and their subsequent conversion into the parallel cross-β structure of paired helical filaments is expected to follow the same path as the previously described fibrillization of Aβ. Consequently, the core structure of the nascent tau fibril is determined by the register of the tau homodimer. This model accounts for the reported differences in (i) fibril-core structure of in vivo and in vitro filaments, (ii) cross-seeding of isoforms, (iii) effects of reducing/non-reducing conditions, (iv) effects of PHF6 mutations, and (v) homologs' aggregation properties. The proposed model also suggests that in contrast to Alzheimer's and chronic traumatic encephalopathy disease, the assembly of tau prions in Pick's disease would be facilitated by a moderate drop in pH that accompanies e.g., transit in the endosomal system, inflammation response or an ischemic injury.

A Robust and Scalable High-Throughput Compatible Assay for Screening Amyloid-β-Binding Compounds

A robust fluorescent readout assay using topologically-sensitive dyes improves the screening of novel amyloid-binding molecules. One of the key components that make this assay more realistic is the use of endogenous amyloid obtained from 5XFAD mouse brains. The assay conditions were optimized for high throughput screening operation with Z-prime values >0.6. Using a combination of library of 3,500 compounds including known drugs, natural-derived molecules and random organic molecules, 8 unique molecules were identified as potential amyloid-binding agents.

Inhibiting and Remodeling Toxic Amyloid-Beta Oligomer Formation Using a Computationally Designed Drug Molecule That Targets Alzheimer's Disease

Alzheimer's disease (AD) is rapidly reaching epidemic status among a burgeoning aging population. Much evidence suggests the toxicity of this amyloid disease is most influenced by the formation of soluble oligomeric forms of amyloid β-protein, particularly the 42-residue alloform (Aβ42). Developing potential therapeutics in a directed, streamlined approach to treating this disease is necessary. Here we utilize the joint pharmacophore space (JPS) model to design a new molecule [AC0107] incorporating structural characteristics of known Aβ inhibitors, blood-brain barrier permeability, and limited toxicity. To test the molecule's efficacy experimentally, we employed ion mobility mass spectrometry (IM-MS) to discover [AC0107] inhibits the formation of the toxic Aβ42 dodecamer at both high (1:10) and equimolar concentrations of inhibitor. Atomic force microscopy (AFM) experiments reveal that [AC0107] prevents further aggregation of Aβ42, destabilizes preformed fibrils, and reverses Aβ42 aggregation. This trend continues for long-term interaction times of 2 days until only small aggregates remain with virtually no fibrils or higher order oligomers surviving. Pairing JPS with IM-MS and AFM presents a powerful and effective first step for AD drug development. Graphical Abstract.

Copper chelators promote nonamyloidogenic processing of AβPP via MT1/2 /CREB-dependent signaling pathways in AβPP/PS1 transgenic mice

Copper is essential for the generation of reactive oxygen species (ROS), which are induced by amyloid-β (Aβ) aggregation; thus, the homeostasis of copper is believed to be a therapeutic target for Alzheimer's disease (AD). Although clinical trials of copper chelators show promise when applied in AD, the underlying mechanism is not fully understood. Here, we reported that copper chelators promoted nonamyloidogenic processing of AβPP through MT_1/2 /CREB-dependent signaling pathways. First, we found that the formation of Aβ plaques in the cortex was significantly reduced, and learning deficits were significantly improved in AβPP/PS1 transgenic mice by copper chelator tetrathiomolybdate (TM) administration. Second, TM and another copper chelator, bathocuproine sulfonate (BCS), promoted nonamyloidogenic processing of AβPP via inducing the expression of ADAM10 and the secretion of sAβPPα. Third, the inducible ADAM10 production caused by copper chelators can be blocked by a melatonin receptor (MT_1/2 ) antagonist (luzindole) and a MT₂ inhibitor (4-P-PDOT), suggesting that the expression of ADAM10 depends on the activation of MT_1/2 signaling pathways. Fourth, three of the MT_1/2 -downstream signaling pathways, Gq/PLC/MEK/ERK/CREB, Gs/cAMP/PKA/ERK/CREB and Gs/cAMP/PKA/CREB, were responsible for copper chelator-induced ADAM10 production. Based on these results, we conclude that copper chelators regulate the balance between amyloidogenic and nonamyloidogenic processing of AβPP via promoting ADAM10 expression through MT_1/2 /CREB-dependent signaling pathways.

Beta-Site Amyloid Precursor Protein Cleaving Enzyme 1 Inhibition Impairs Synaptic Plasticity via Seizure Protein 6

BACKGROUND

Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is a promising drug target for the treatment of Alzheimer's disease. Prolonged BACE1 inhibition interferes with structural and functional synaptic plasticity in mice, most likely by altering the metabolism of BACE1 substrates. Seizure protein 6 (SEZ6) is predominantly cleaved by BACE1, and Sez6 knockout mice share some phenotypes with BACE1 inhibitor-treated mice. We investigated whether SEZ6 is involved in BACE1 inhibition-induced structural and functional synaptic alterations.

METHODS

The function of NB-360, a novel blood-brain barrier penetrant and orally available BACE1 inhibitor, was verified by immunoblotting. In vivo microscopy was applied to monitor the impact of long-term pharmacological BACE1 inhibition on dendritic spines in the cerebral cortex of constitutive and conditional Sez6 knockout mice. Finally, synaptic functions were characterized using electrophysiological field recordings in hippocampal slices.

RESULTS

BACE1 enzymatic activity was strongly suppressed by NB-360. Prolonged NB-360 treatment caused a reversible spine density reduction in wild-type mice, but it did not affect Sez6^-/- mice. Knocking out Sez6 in a small subset of mature neurons also prevented the structural postsynaptic changes induced by BACE1 inhibition. Hippocampal long-term potentiation was decreased in both chronic BACE1 inhibitor-treated wild-type mice and vehicle-treated Sez6^-/- mice. However, chronic NB-360 treatment did not alter long-term potentiation in CA1 neurons of Sez6^-/- mice.

CONCLUSIONS

Our results suggest that SEZ6 plays an important role in maintaining normal dendritic spine dynamics. Furthermore, SEZ6 is involved in BACE1 inhibition-induced structural and functional synaptic alterations.

Mechanistic analyses of the suppression of amyloid β42 aggregation by apomorphine

(R)-Apomorphine (1) has the potential to reduce the accumulation of amyloid β-protein (Aβ42), a causative agent of Alzheimer's disease (AD). Although the inhibition of Aβ42 aggregation by 1 is ascribable to the antioxidative effect of its phenol moiety, its inhibitory mechanism at the molecular level remains to be fully elucidated. LC-MS and UV analyses revealed that 1 is autoxidized during incubation to produce an unstable o-quinone form (2), which formed a Michael adduct with Lys 16 and 28 of Aβ42. A further autoxidized form of 1 (3) with o-quinone and phenanthrene moieties suppressed Aβ42 aggregation comparable to 1, whereas treating 1 with a reductant, tris(2-carboxyethyl)phosphine diminished its inhibitory activity. ¹H-¹⁵N SOFAST-HMQC NMR studies suggested that 1 interacts with Arg5, His13,14, Gln15, and Lys16 of the Aβ42 monomer. These regions form intermolecular β-sheets in Aβ42 aggregates. Since 3 did not perturb the chemical shift of monomeric Aβ42, we performed aggregation experiments using 1,1,1,3,3,3-hexafluoro-2-propanol-treated Aβ42 to investigate whether 3 associates with Aβ42 oligomers. Compounds 1 and 3 delayed the onset of the oligomer-driven nucleation phase. Despite their cytotoxicity, they did not exacerbate Aβ42-mediated neurotoxicity in SH-SY5Y neuroblastoma cells. These results demonstrate that extension of the conjugated system in 1 by autoxidation can promote its planarity, which is required for intercalation into the β-sheet of Aβ42 nuclei, thereby suppressing further aggregation.

Positional isomers of mannose–quinoline conjugates and their copper complexes: exploring the biological activity

Mannoconjugates show significant antibacterial activity. A regioisomer shows antiproliferative activity with copper(ii) ions.

Caenorhabditis elegans as a model system for target identification and drug screening against neurodegenerative diseases

Over the past decades, Caenorhabditis elegans (C. elegans) has been widely used as a model system because of its small size, transparent body, short generation time and lifespan (~3 days and 3 weeks, respectively), completely sequenced genome and tractability to genetic manipulation. Protein misfolding and aggregation are key pathological features in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease and Amyotrophic lateral sclerosis. Animal models, including C. elegans, have been extensively used to discover and validate new drugs against neurodegenerative diseases. The well-defined and genetically tractable nervous system of C. elegans offers an effective model to explore basic mechanistic pathways of neurodegenerative diseases. Recent progress in high-throughput drug screening also provides a powerful approach for identifying chemical modulators of biological processes. Here, we summarize the latest progress of using C. elegans as a model system for target identification and drug screening in neurodegenerative diseases.

A randomized, exploratory molecular imaging study targeting amyloid β with a novel 8-OH quinoline in Alzheimer's disease: The PBT2-204 IMAGINE study

Introduction

We are developing a second generation 8-OH quinoline (2-(dimethylamino) methyl-5, 7-dichloro-8-hydroxyquinoline [PBT2, Prana Biotechnology]) for targeting amyloid β (Aβ) in Alzheimer's disease (AD). In an earlier phase IIa, 3 month trial, PBT2 lowered cerebrospinal fluid Aβ by 13% and improved cognition (executive function) in a dose-related fashion in early AD. We, therefore, sought to learn whether PBT2 could alter the Aβ-PET signal in subjects with prodromal or mild AD, in an exploratory randomized study over a 12-month phase in a double-blind and a 12-month open label extension phase trial design.

Methods

For inclusion, the usual clinical criteria for prodromal or probable AD, Mini–Mental State Examination ≥20, and global Pittsburgh compound B (PiB)-PET standardized uptake volume ratio (SUVR) >1.7 were used. As this was an exploratory study, we included contemporaneous matched control data from the Australian Imaging Biomarker and Lifestyle Study (AIBL). Other measures included fluorodeoxyglucose-positron emission tomography, magnetic resonance imaging volumetrics, blood Aβ biomarkers, and cognition and function.

Results

Forty subjects completed the first 12-month double-blind phase (placebo = 15, PBT2 = 25), and 27 subjects completed the 12-month open label extension phase (placebo = 11, PBT2 = 16). Overall, PTB2 250 mg/day was safe and well tolerated. The mean PiB-PET SUVR at baseline was 2.51 ± 0.59. After adjusting for baseline SUVR, in the double-blind phase, the placebo group showed a nonsignificant decline in PiB-PET SUVR, whereas the PBT2 group declined significantly (P = .048). Subjects who did not enter or complete the extension study had a significantly higher 12-month Aβ-PET SUVR (2.68 ± 0.55) compared with those who completed (2.29 ± 0.48). Both groups differed significantly from the rate of change over 12 months in the AIBL control group. In the open label 12-month extension study, the PiB-SUVR stabilized. There were no significant differences between PBT2 and controls in fluorodeoxyglucose-positron emission tomography, magnetic resonance imaging volumetrics, blood Aβ biomarkers, or cognition/function over the course of the double-blind phase.

Discussion

There was no significant difference between PBT2 and controls at 12 months, likely due to the large individual variances over a relatively small number of subjects. PBT2 was associated with a significant 3% PiB-PET SUVR decline in the double-blind phase and a stabilization of SUVR in the open-label phase. From this exploratory study, we have learned that the entry criterion of SUVR should have been set at ≥ 1.5 and <2.0, where we know from the AIBL study that subjects in this band are accumulating Aβ in a linear fashion and that subjects who withdrew from this type of study have much higher SUVRs, which if not taken into account, could distort the final results. Because of large individual variations in SUVR, future studies of PBT2 will require larger numbers of subjects (n > 90 per arm) over a longer period (18 months or more). Further evaluation of higher doses of PBT2 in earlier stages of AD is warranted.

Trial Registration

ACTRN 12611001008910 and ACTRN 12613000777796.

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Exploratory randomized controlled trial for Alzheimer's disease using novel 8-OH quinoline.

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Use of Aβ positron emission tomography molecular imaging as intake criterion.

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Small numbers, large variances, and higher than expected mean baseline standardized uptake volume ratio may have contributed to lack of demonstrable efficacy.

Protein folding, misfolding and aggregation: The importance of two-electron stabilizing interactions

Proteins associated with neurodegenerative diseases are highly pleiomorphic and may adopt an all-α-helical fold in one environment, assemble into all-β-sheet or collapse into a coil in another, and rapidly polymerize in yet another one via divergent aggregation pathways that yield broad diversity of aggregates’ morphology. A thorough understanding of this behaviour may be necessary to develop a treatment for Alzheimer’s and related disorders. Unfortunately, our present comprehension of folding and misfolding is limited for want of a physicochemical theory of protein secondary and tertiary structure. Here we demonstrate that electronic configuration and hyperconjugation of the peptide amide bonds ought to be taken into account to advance such a theory. To capture the effect of polarization of peptide linkages on conformational and H-bonding propensity of the polypeptide backbone, we introduce a function of shielding tensors of the C^α atoms. Carrying no information about side chain-side chain interactions, this function nonetheless identifies basic features of the secondary and tertiary structure, establishes sequence correlates of the metamorphic and pH-driven equilibria, relates binding affinities and folding rate constants to secondary structure preferences, and manifests common patterns of backbone density distribution in amyloidogenic regions of Alzheimer’s amyloid β and tau, Parkinson’s α-synuclein and prions. Based on those findings, a split-intein like mechanism of molecular recognition is proposed to underlie dimerization of Aβ, tau, αS and PrP^C, and divergent pathways for subsequent association of dimers are outlined; a related mechanism is proposed to underlie formation of PrP^Sc fibrils. The model does account for: (i) structural features of paranuclei, off-pathway oligomers, non-fibrillar aggregates and fibrils; (ii) effects of incubation conditions, point mutations, isoform lengths, small-molecule assembly modulators and chirality of solid-liquid interface on the rate and morphology of aggregation; (iii) fibril-surface catalysis of secondary nucleation; and (iv) self-propagation of infectious strains of mammalian prions.

The Case for Abandoning Therapeutic Chelation of Copper Ions in Alzheimer's Disease

The "therapeutic chelation" approach to treating Alzheimer's disease (AD) evolved from the metals hypothesis, with the premise that small molecules can be designed to prevent transition metal-induced amyloid deposition and oxidative stress within the AD brain. Over more than 20 years, countless in vitro studies have been devoted to characterizing metal binding, its effect on Aβ aggregation, ROS production, and in vitro toxicity. Despite a lack of evidence for any clinical benefit, the conjecture that therapeutic chelation is an effective approach for treating AD remains widespread. Here, the author plays the devil's advocate, questioning the experimental evidence, the dogma, and the value of therapeutic chelation, with a major focus on copper ions.

Aβ42 pentamers/hexamers are the smallest detectable oligomers in solution

Amyloid β (Aβ) oligomers may play a decisive role in Alzheimer's disease related neurodegeneration, but their structural properties are poorly understood. In this report, sedimentation velocity centrifugation, small angle neutron scattering (SANS) and molecular modelling were used to identify the small oligomeric species formed by the 42 amino acid residue long isoform of Aβ (Aβ42) in solution, characterized by a sedimentation coefficient of 2.56 S, and a radius of gyration between 2 and 4 nm. The measured sedimentation coefficient is in close agreement with the sedimentation coefficient calculated for Aβ42 hexamers using MD simulations at µM concentration. To the best of our knowledge this is the first report detailing the Aβ42 oligomeric species by SANS measurements. Our results demonstrate that the smallest detectable species in solution are penta- to hexamers. No evidences for the presence of dimers, trimers or tetramers were found, although the existence of those Aβ42 oligomers at measurable quantities had been reported frequently.

Multitarget trehalose-carnosine conjugates inhibit Aβ aggregation, tune copper(II) activity and decrease acrolein toxicity

Increasing evidence is accumulating, showing that neurodegenerative disorders are somehow associated with the toxicity of amyloid aggregates, metal ion dyshomeostasis as well as with products generated by oxidative stress. Within the biological oxidation products, acrolein does have a prominent role. A promising strategy to deal with the above neurogenerative disorders is to use multi-functions bio-molecules. Herein, we show how a class of bio-conjugates takes advantage of the antiaggregating, antioxidant and antiglycating properties of trehalose and carnosine. Their ability to sequester acrolein and to inhibit both self- and metal-induced aggregation is here reported. The copper(II) coordination properties of a new trehalose-carnosine conjugate and the relative antioxidant effects have also been investigated.

Iron, Copper, and Zinc Concentration in Aβ Plaques in the APP/PS1 Mouse Model of Alzheimer's Disease Correlates with Metal Levels in the Surrounding Neuropil

The metal ions of iron, copper, and zinc have long been associated with the aggregation of β-amyloid (Aβ) plaques in Alzheimer's disease; an interaction that has been suggested to promote increased oxidative stress and neuronal dysfunction. We examined plaque metal load in the hippocampus of APP/PS1 mice using X-ray fluorescence microscopy to assess how the anatomical location of Aβ plaques was influenced by the metal content of surrounding tissue. Immunohistochemical staining of Aβ plaques colocalized with areas of increased X-ray scattering power in unstained tissue sections, allowing direct X-ray based-assessment of plaque metal levels in sections subjected to minimal chemical fixation. We identified and mapped 48 individual plaques in four subregions of the hippocampus from four biological replicates. Iron, Cu, and Zn areal concentrations (ng cm^-2) were increased in plaques compared to the surrounding neuropil. However, this elevation in metal load reflected the local metal makeup of the surrounding neuropil, where different brain regions are enriched for different metal ions. After correcting for tissue density, only Zn levels remained elevated in plaques. This study suggests that the in vivo binding of Zn to plaques is not simply due to increased protein deposition.

Modulation of Amyloid Aggregates into Nontoxic Coaggregates by Hydroxyquinoline Appended Polyfluorene

Inhibitory modulation toward de novo protein aggregation is likely to be a vital and promising therapeutic strategy for understanding the molecular etiology of amyloid related diseases such as Alzheimer's disease (AD). The building up of toxic oligomeric and fibrillar amyloid aggregates in the brain plays host to a downstream of events, causing damage to axons, dendrites, synapses, signaling, transmission, and finally cell death. Herein, we introduce a novel conjugated polymer (CP), hydroxyquinoline appended polyfluorene (PF-HQ), which has a typical "amyloid like" surface motif and exhibits inhibitory modulation effect on amyloid β (Aβ) aggregation. We delineate inhibitory effects of PF-HQ based on Thioflavin T (ThT) fluorescence, atomic force microscopy (AFM), circular dichroism (CD), and Fourier transform infrared (FTIR) studies. The amyloid-like PF-HQ forms nano coaggregates by templating with toxic amyloid intermediates and displays improved inhibitory impacts toward Aβ fibrillation and diminishes amyloid cytotoxicity. We have developed a CP based modulation strategy for the first time, which demonstrates beneficiary amyloid-like surface motif to interact efficiently with the protein, the pendant side groups to trap the toxic amyloid intermediates as well as optical signal to acquire the mechanistic insight.

A Novel Multifunctional Compound Camellikaempferoside B Decreases Aβ Production, Interferes with Aβ Aggregation, and Prohibits Aβ-Mediated Neurotoxicity and Neuroinflammation

Accumulating evidence suggested that soluble oligomeric β-amyloid protein (Aβ) exerts diverse roles in neuronal cell death, neuroinflammation, oxidative stress, and the eventual dementia associated with Alzheimer's disease (AD). Developing an agent with multiple properties may be a reasonable strategy for the treatment of AD. In this study, we isolated a novel multifunctional compound named camellikaempferoside B (YCF-2) from Fuzhuan brick tea. YCF-2 consists of kaempferol backbone, p-coumaric acid (p-CA) group, and a novel structure of rhamnopyranosyl group at the C-4' position, possessing the properties of both kaempferol and p-CA. YCF-2 significantly inhibited Aβ production by decreasing β-secretase activity. Moreover, YCF-2 suppressed Aβ42 fibrillation and facilitated nontoxic oligomer formation by binding to Aβ42 oligomers and by blocking the conformational transition to β-sheet. Furthermore, YCF-2 ameliorated Aβ-induced neuronal cell death, ROS production, inflammatory factor release, and microglia activation by blocking the NF-κB signaling pathway in microglia. These findings indicated that YCF-2 with a novel lead structure has potential applications for drug development for AD treatment.

New Hydroxyquinoline-Based Derivatives as Potent Modulators of Amyloid-β Aggregations

Copper and zinc have been found to contribute to the burden of amyloid-β (Aβ) aggregations in neurodegenerative Alzheimer's disease (AD). Dysregulation of these metals leads to the generation of reactive oxygen species (ROS) and eventually results in oxidative damage and accumulation of the Aβ peptide, which are the key elements of the disease. Aiming to pursue the discovery of new modulators for the disease, we here rationally focused on conjugating the core hydroxyquinoline of the metal-protein attenuating compound PBT2 and the N-methylanilide analogous moiety of the Aβ imaging agent to build a new type of multi-target modulators of Aβ aggregations. We found that the N,N-dimethylanilinyl imines 7a, 8a, and the corresponding amines 7b, 8b exerted efficient inhibition of Cu(2+) - or Zn(2+) -induced Aβ aggregations and significant disassembly of metal-mediated Aβ aggregated fibrils. Further, 7a and 7b also exhibited significant ROC scavenging effects compared to PBT2. The results suggested that 7a and 7b are promising lead compounds for the development of a new therapy for AD.

Effects of Neonatal Iron Feeding and Chronic Clioquinol Administration on the Parkinsonian Human A53T Transgenic Mouse

Increased nigral iron (Fe) is a cardinal feature of Parkinson's disease, as is the accumulation of aggregates comprising α-synuclein. We used wild-type mice and transgenic mice overexpressing the human A53T mutation to α-synuclein to examine the influence of increased Fe (days 10-17 postpartum) on the parkinsonian development phenotype of these animals (including abnormal nigral Fe levels and deficits in both cell numbers and locomotor activity), and to explore the impact of the Fe chelator clioquinol in the model. Both untreated and Fe-loaded A53T mice showed similar levels of nigral cell loss, though 5 months of clioquinol treatment was only able to prevent the loss in the non-Fe-loaded A53T group. Iron levels in the Fe-loaded A53T mice returned to normal at 8 months, though effects of dopamine denervation remained, demonstrated by limited locomotor activity and sustained neuron loss. These data suggest that Fe exposure during a critical developmental window, combined with the overexpression mutant α-synuclein, presents a disease phenotype resistant to intervention using clioquinol later in life.