Extracellular Amyloid β-protein (1-42) Oligomers Anchor Brain Cells and Make them inert as an Unconventional Integrin-Coupled Ligand

Neurotrophic and Neurotoxic Effects of Aβ42 and Its Oligomers on Neuronal Survival: Revealed by Their Opposite Influence on the Potency of Extracellular BDNF

Brain-derived neurotrophic factor (BDNF) is critical for neuronal survival. Amyloid-β monomers (Aβ42M) and oligomers (Aβ42O) have trophic and toxic effects on neuronal survival, respectively. Branched oligosaccharides (BOs) and catechins (CAs) can specifically bind to Aβ42M/Aβ42O, influencing both effects. However, whether and how Aβ42M/Aβ42O influences BDNF remains unknown. This study investigated the interaction between Aβ42M/Aβ42O and BDNF, the effects of Aβ42M and Aβ42O on BDNF binding to the TrkB/p75 receptor and their impact on BDNF-supported cell survival, and the roles of BOs and CAs in these processes. BDNF exhibited stronger binding affinity for Aβ42M and Aβ42O than BOs/CAs. Aβ42M increased neuronal viability by synergistically enhancing BDNF binding to TrkB and p75, whereas Aβ42O decreased neuronal viability by inactivating/consuming BDNF, thereby reducing its binding to these receptors. BDNF-Aβ42O binding appeared to mutually neutralize/counteract each other's biological effects; therefore, increasing BDNF levels might reduce Aβ42O's neurotoxicity. By competitively targeting Aβ42M/Aβ42O rather than BDNF or its receptors, BOs and CAs enhanced these effects. These findings suggest that Aβ42M's neurotrophicity was directly linked to its synergistic enhancement of BDNF activity, whereas Aβ42O's neurotoxicity was primarily due to its inactivation or consumption of BDNF. This study provided valuable insights for developing BOs/CAs-based neuroprotective therapeutics or nanomaterials against AD.

Neuroprotective Effects of Catechins by Differentially Affecting the Binding of Beta-amyloid and Its Aggregates to the Target Cells

Aggregation and deposition of amyloid-β protein (Aβ42) in extracellular spaces are key neuropathological features of Alzheimer's disease (AD). Extracellular Aβ42 aggregates not only impair the function of the extracellular matrix but also directly damage brain cells through binding interactions. Chemically, tea polyphenols are amphiphilic, similar to the Aβ42 molecule. This study found that catechin (CA) and epigallocatechin gallate (EGCG) effectively bound to Aβ42 monomers (Aβ42M) and oligomers (Aβ42O), preventing Aβ42 aggregation; in contrast, EGCG also showed some binding to protofibrils (Aβ42P) and fibrils (Aβ42F), slightly inhibiting their development. In the presence of Aβ42M and Aβ42 aggregates in vitro, CA and EGCG demonstrated considerable protective effects on neural and vascular endothelial cells. These effects corresponded with the ability of CA and EGCG (particularly CA) to preserve Aβ42M's targeting and binding to these cells, while they (especially EGCG) blocked or inhibited Aβ42O's targeting and binding. Molecular docking revealed that both CA and EGCG effectively maintained the active conformation of Aβ42M; in contrast, EGCG also effectively rendered Aβ42O units inactive, primarily by disrupting and covering the hydrophobic clusters. Furthermore, CA and EGCG improved the AD brain microenvironment, including reducing Aβ42 plaque burden and supporting brain cell populations. In conclusion, CA and EGCG inhibited the structure, bioactivity, and cell-targeting ability of Aβ42 aggregates; however, they protected these aspects of Aβ42M. These findings are essential for understanding the neuroprotective mechanisms of plant polyphenols.

Nano-Collision Electrochemistry for Real-Time Monitoring of Amyloid-β Oligomerization and Rapid Screening of Degrading Drugs

Toxic oligomers of amyloid-β (Aβ) are important in the pathology of Alzheimer's disease (AD), and degradation of Aβ oligomers (AβO) in the brain is considered a promising strategy for drug development. However, conventional drug screening techniques face challenges in the rapid and real-time assessment of AβO. Here, we report a simple and reliable nanocollision electrochemical method based on silver nanoparticles (AgNPs) "tagging" that can in situ monitor Aβ oligomerization and screen potential AβO-degrading drugs. The differences in collision signals between AgNPs-Aβ complexes and AgNPs were compared to achieve rapid identification of Aβ complexes with different aggregation degrees. The degradation effect following the addition of AβO-degrading drugs can be quickly evaluated by the recovery of collision frequency (f, number of peaks per unit time), which is effective if f > 0.15. Degradation efficiency was further quantified using current lifetimes (τ, the time required for the current to decay to 1/e of the original), based on the percentage of τ ≤ 10 ms. The practicability of the method was tested using Aβ-degrading protease and several small molecules, confirming the rapid screening of AβO-degrading drugs and offering a novel strategy to accelerate the development of drugs for AD treatment.

Distinct functional diversity of branched oligosaccharides as chaperones and inhibitory-binding partners of amyloid beta-protein and its aggregates

Aggregation and deposition of amyloid beta-protein 1-42 (Aβ42) in the brain, primarily owing to hydrophobic interactions between Aβ42 chains, is a common pathology in all forms of Alzheimer's disease (AD). Hydrophilic oligosaccharides are widely present in the extracellular matrix and on the cytoplasmic membrane. To determine if oligosaccharides bind to Aβ42 or its aggregates and consequently affect their aggregation and cellular function, this study examined the interaction of typical functional oligosaccharides with Aβ42 or its aggregates. Isomaltooligosaccharides (IMOs), particularly isomaltotriose, panose, and isomaltotetraose, functioned as molecular chaperones for Aβ42 by binding directly to Aβ42, preserving Aβ42's active conformation and cytotrophic activity. Oral IMOs reduced total plasma Aβ level and indirectly caused a slight reduction in the load of Aβ42 spots/plaques in the brain of AD model mice (male). Another branched oligosaccharide, bianntennary core pentasaccharide (BCP), had a relatively high binding specificity for Aβ42 oligomers (Aβ42O) and acted as an antagonistic binding partner for Aβ42O. Free BCP effectively blocked/prevented further assembly of Aβ42O and their toxicity to neural and vascular endothelial cell lines. Since BCP is also a signaling component of membrane targets (glycolipids, glycoproteins or receptors), it seemed that BCP had two opposing effects on the binding of Aβ42O to target cells. This study's findings suggest that these branched oligosaccharides may be potential candidates for blocking or preventing Aβ42 aggregation and Aβ42O cytotoxicity/neurotoxicity, respectively, and that IMO-like or free BCP-like oligosaccharide deficiencies in the brain may be one of the underlying mechanisms for Aβ42 aggregation and Aβ42O cytotoxicity.

Synergetic effect of matrine on the catalytic scFv antibody HS72 in vitro and in mice with Alzheimer disease pathology

Single-chain variable fragment (scFv) HS72 is a catalytic antibody that specifically degrades amyloid β-protein 1-42 (Aβ42) aggregates in vitro or reduces the level or burden of Aβ42 deposits/plaques in the brains of mice with Alzheimer disease pathology. Its efficacy has been shown in protecting neural cells in vitro and improving the morphology of the cell population in the brain of mice with AD pathology (AD mice). Matrine (Mat) is a natural product capable of binding to Aβ42 or its aggregates and blocking their neurotoxicity at concentrations of at least 10 μM or greater. However, this study revealed a synergistic effect of Mat on the catalytic effect of HS72 at low concentrations (0.01-2.5 μM). This is evidenced by the fact that Mat synergistically enhances HS72's ability to degrade Aβ42 aggregates and protect neural cells (SH-SY5Y and HT22 cells, and brain cells of AD mice). The molecular docking models and characterization of Mat's action both indicated that the mechanism of Mat's synergistic impact on HS72 catalysis is to increase the turnover number (or molecular activity) of HS72 by enhancing the catalytic power of the HS72's catalytic groups and encouraging the release of the degradation products (Aβ fragments). The study's results suggest a natural synergy between Mat-like small molecules and the catalytic anti-oligomeric Aβ42 antibody HS72, enabling more effective reduction or removal of Aβ42 aggregates or plaques than the antibody alone. These findings provide novel insights into the effectiveness of anti-oligomeric Aβ42 antibodies in AD immunotherapy.

Dual Efficacy of a Catalytic Anti-Oligomeric Aβ42 scFv Antibody in Clearing Aβ42 Aggregates and Reducing Aβ Burden in the Brains of Alzheimer's Disease Mice

One of the primary pathological mechanisms underlying Alzheimer's disease (AD) is the deposition of amyloid β-protein (Aβ42) aggregates in the brain. In this study, a catalytic anti-oligomeric Aβ42 scFv antibody, HS72, was identified by screening a human antibody library, its ability to degrade Aβ42 aggregates was defined, and its role in the reduction of Aβ burden in the AD mouse brain was evaluated. HS72 specifically targeted Aβ42 aggregates with an approximately 14-68 kDa range. Based on molecular docking simulations, HS72 likely catalyzed the hydrolytic cleavage of the His13-His14 bond of Aβ42 chains in an Aβ42 aggregate unit, releasing N/C-terminal fragments and Aβ42 monomers. Degradation of Aβ42 aggregates by HS72 triggered a considerable disassembly or breakdown of the Aβ42 aggregates and greatly reduced their neurotoxicity. Aβ deposit/plaque load in the hippocampus of AD mice was reduced by approximately 27% after 7 days (once daily) of intravenous HS72 administration, while brain neural cells were greatly restored and their morphology was drastically improved. The above efficacies of HS72 were all greater than those of HT7, a simple anti-oligomeric Aβ42 scFv antibody. Although a catalytic anti-oligomeric Aβ42 antibody may have a slightly lower affinity for Aβ42 aggregates than a simple anti-oligomeric Aβ42 antibody, the former may display a stronger overall efficacy (dual efficacy of induction and catalysis) than the latter (induction alone) in clearing Aβ42 aggregates and improving histopathological changes in AD brain. Our findings on the catalytic antibody HS72 indicate the possibility of functional evolution of anti-oligomeric Aβ42 antibodies and provide novel insights into the immunotherapy of AD.

Different Extracellular β-Amyloid (1-42) Aggregates Differentially Impair Neural Cell Adhesion and Neurite Outgrowth through Differential Induction of Scaffold Palladin

Extracellular amyloid β-protein (1-42) (Aβ42) aggregates have been recognized as toxic agents for neural cells in vivo and in vitro. The aim of this study was to investigate the cytotoxic effects of extracellular Aβ42 aggregates in soluble (or suspended, SAβ42) and deposited (or attached, DAβ42) forms on cell adhesion/re-adhesion, neurite outgrowth, and intracellular scaffold palladin using the neural cell lines SH-SY5Y and HT22, and to elucidate the potential relevance of these effects. The effect of extracellular Aβ42 on neural cell adhesion was directly associated with their neurotrophic or neurotoxic activity, with SAβ42 aggregates reducing cell adhesion and associated live cell de-adherence more than DAβ42 aggregates, while causing higher mortality. The reduction in cell adhesion due to extracellular Aβ42 aggregates was accompanied by the impairment of neurite outgrowth, both in length and number, and similarly, SAβ42 aggregates impaired the extension of neurites more severely than DAβ42 aggregates. Further, the disparate changes of intracellular palladin induced by SAβ42 and DAβ42 aggregates, respectively, might underlie their aforementioned effects on target cells. Further, the use of anti-oligomeric Aβ42 scFv antibodies revealed that extracellular Aβ42 aggregates, especially large DAβ42 aggregates, had some independent detrimental effects, including physical barrier effects on neural cell adhesion and neuritogenesis in addition to their neurotoxicity, which might be caused by the rigid C-terminal clusters formed between adjacent Aβ42 chains in Aβ42 aggregates. Our findings, concerning how scaffold palladin responds to extracellular Aβ42 aggregates, and is closely connected with declines in cell adhesion and neurite outgrowth, provide new insights into the cytotoxicity of extracellular Aβ42 aggregates in Alzheimer disease.

Conformational Essentials Responsible for Neurotoxicity of Aβ42 Aggregates Revealed by Antibodies against Oligomeric Aβ42

Soluble aggregation of amyloid β-peptide 1-42 (Aβ42) and deposition of Aβ42 aggregates are the initial pathological hallmarks of Alzheimer's disease (AD). The bipolar nature of Aβ42 molecule results in its ability to assemble into distinct oligomers and higher aggregates, which may drive some of the phenotypic heterogeneity observed in AD. Agents targeting Aβ42 or its aggregates, such as anti-Aβ42 antibodies, can inhibit the aggregation of Aβ42 and toxicity of Aβ42 aggregates to neural cells to a certain extent. However, the epitope specificity of an antibody affects its binding affinity for different Aβ42 species. Different antibodies target different sites on Aβ42 and thus elicit different neuroprotective or cytoprotective effects. In the present review, we summarize significant information reflected by anti-Aβ42 antibodies in different immunotherapies and propose an overview of the structure (conformation)-toxicity relationship of Aβ42 aggregates. This review aimed to provide a reference for the directional design of antibodies against the most pathogenic conformation of Aβ42 aggregates.