Pyroglutamation of amyloid-βx-42 (Aβx-42) followed by Aβ1-40 deposition underlies plaque polymorphism in progressing Alzheimer's disease pathology

Amyloid-β peptide signature associated with cerebral amyloid angiopathy in familial Alzheimer's disease with APPdup and Down syndrome

Alzheimer's disease (AD) is characterized by extracellular amyloid plaques containing amyloid-β (Aβ) peptides, intraneuronal neurofibrillary tangles, extracellular neuropil threads, and dystrophic neurites surrounding plaques composed of hyperphosphorylated tau protein (pTau). Aβ can also deposit in blood vessel walls leading to cerebral amyloid angiopathy (CAA). While amyloid plaques in AD brains are constant, CAA varies among cases. The study focuses on differences observed between rare and poorly studied patient groups with APP duplications (APPdup) and Down syndrome (DS) reported to have higher frequencies of elevated CAA levels in comparison to sporadic AD (sAD), most of APP mutations, and controls. We compared Aβ and tau pathologies in postmortem brain tissues across cases and Aβ peptides using mass spectrometry (MS). We further characterized the spatial distribution of Aβ peptides with MS-brain imaging. While intraparenchymal Aβ deposits were numerous in sAD, DS with AD (DS-AD) and AD with APP mutations, these were less abundant in APPdup. On the contrary, Aβ deposits in the blood vessels were abundant in APPdup and DS-AD while only APPdup cases displayed high Aβ deposits in capillaries. Investigation of Aβ peptide profiles showed a specific increase in Aβx-37, Aβx-38 and Aβx-40 but not Aβx-42 in APPdup cases and to a lower extent in DS-AD cases. Interestingly, N-truncated Aβ2-x peptides were particularly increased in APPdup compared to all other groups. This result was confirmed by MS-imaging of leptomeningeal and parenchymal vessels from an APPdup case, suggesting that CAA is associated with accumulation of shorter Aβ peptides truncated both at N- and C-termini in blood vessels. Altogether, this study identified striking differences in the localization and composition of Aβ deposits between AD cases, particularly APPdup and DS-AD, both carrying three genomic copies of the APP gene. Detection of specific Aβ peptides in CSF or plasma of these patients could improve the diagnosis of CAA and their inclusion in anti-amyloid immunotherapy treatments.

Integrated Spatial Multi-Omics Study of Postmortem Brains of Alzheimer's Disease

Pathological hallmark of Alzheimer's disease (AD) is characterized by the accumulation and aggregation of amyloid β (Aβ) peptides into extracellular plaques of the brain. Clarification of the process of how soluble Aβ starts to assemble into amyloid fibrils is an essential step in elucidating the pathogenesis of AD. In our previous study, Aβ proteoforms including full-length Aβ40 and Aβ42/43 with N- and C-terminal truncated forms were visualized in postmortem brains from AD patients with matrix-assisted laser desorption/ionization-based mass spectrometry imaging (MALDI-MSI). In this study, Aβ proteoforms were consistently visualized by an updated protocol, and uncharacterized peptides such as Aβ1-29 and Aβ10-40 in AD brains were also visualized. To decipher neurotoxic effects of Aβ in patients' brains, here we integrate liquid chromatography tandem mass spectrometry (LC-MS/MS) based shotgun proteomics with laser microdissection (LMD) excised tissue samples as well as direct tissue imaging with MALDI-MSI. With this approach, we have highlighted dynamic alterations of microtubule associating proteins (MAPs) including MAP1A, MAP1B and MAP2 as well as AD dominant proteins including APP, UCHL1, SNCA, and APOE. Of note, as lipid dysregulation has been implicated with AD pathology, we have challenged to integrate proteomics and lipid imaging for AD and control brain tissue. Spatial multi-omics is also valid to uncover molecular pathology of white matter as well as grey matter and leptomeningeal area, for example, by visualizing heme in patients' postmortem brains.

Search for unknown neural link between the masticatory and cognitive brain systems to clarify the involvement of its impairment in the pathogenesis of Alzheimer's disease

Brain degenerations in sporadic Alzheimer's disease (AD) are observed earliest in the locus coeruleus (LC), a population of noradrenergic neurons, in which hyperphosphorylated tau protein expression and β-amyloid (Aβ) accumulation begin. Along with this, similar changes occur in the basal forebrain cholinergic neurons, such as the nucleus basalis of Meynert. Neuronal degeneration of the two neuronal nuclei leads to a decrease in neurotrophic factors such as brain-derived neurotrophic factor (BDNF) in the hippocampus and cerebral cortex, which results in the accumulation of Aβ and hyperphosphorylated tau protein and ultimately causes neuronal cell death in those cortices. On the other hand, a large number of epidemiological studies have shown that tooth loss or masticatory dysfunction is a risk factor for dementia including AD, and numerous studies using experimental animals have also shown that masticatory dysfunction causes brain degeneration in the basal forebrain, hippocampus, and cerebral cortex similar to those observed in human AD, and that learning and memory functions are impaired accordingly. However, it remains unclear how masticatory dysfunction can induce such brain degeneration similar to AD, and the neural mechanism linking the trigeminal nervous system responsible for mastication and the cognitive and memory brain system remains unknown. In this review paper, we provide clues to the search for such "missing link" by discussing the embryological, anatomical, and physiological relationship between LC and its laterally adjoining mesencephalic trigeminal nucleus which plays a central role in the masticatory functions.

Integrative Single-Plaque Analysis Reveals Signature Aβ and Lipid Profiles in the Alzheimer's Brain

Cerebral accumulation of amyloid-β (Aβ) initiates molecular and cellular cascades that lead to Alzheimer's disease (AD). However, amyloid deposition does not invariably lead to dementia. Amyloid-positive but cognitively unaffected (AP-CU) individuals present widespread amyloid pathology, suggesting that molecular signatures more complex than the total amyloid burden are required to better differentiate AD from AP-CU cases. Motivated by the essential role of Aβ and the key lipid involvement in AD pathogenesis, we applied multimodal mass spectrometry imaging (MSI) and machine learning (ML) to investigate amyloid plaque heterogeneity, regarding Aβ and lipid composition, in AP-CU versus AD brain samples at the single-plaque level. Instead of focusing on a population mean, our analytical approach allowed the investigation of large populations of plaques at the single-plaque level. We found that different (sub)populations of amyloid plaques, differing in Aβ and lipid composition, coexist in the brain samples studied. The integration of MSI data with ML-based feature extraction further revealed that plaque-associated gangliosides GM2 and GM1, as well as Aβ1-38, but not Aβ1-42, are relevant differentiators between the investigated pathologies. The pinpointed differences may guide further fundamental research investigating the role of amyloid plaque heterogeneity in AD pathogenesis/progression and may provide molecular clues for further development of emerging immunotherapies to effectively target toxic amyloid assemblies in AD therapy. Our study exemplifies how an integrative analytical strategy facilitates the unraveling of complex biochemical phenomena, advancing our understanding of AD from an analytical perspective and offering potential avenues for the refinement of diagnostic tools.

Associations of Plasma Glutamatergic Metabolites with Alpha Desynchronization during Cognitive Interference and Working Memory Tasks in Asymptomatic Alzheimer's Disease

Electroencephalogram (EEG) studies have suggested compensatory brain overactivation in cognitively healthy (CH) older adults with pathological beta-amyloid(Aβ42)/tau ratios during working memory and interference processing. However, the association between glutamatergic metabolites and brain activation proxied by EEG signals has not been thoroughly investigated. We aim to determine the involvement of these metabolites in EEG signaling. We focused on CH older adults classified under (1) normal CSF Aβ42/tau ratios (CH-NATs) and (2) pathological Aβ42/tau ratios (CH-PATs). We measured plasma glutamine, glutamate, pyroglutamate, and γ-aminobutyric acid concentrations using tandem mass spectrometry and conducted a correlational analysis with alpha frequency event-related desynchronization (ERD). Under the N-back working memory paradigm, CH-NATs presented negative correlations (r = ~-0.74--0.96, p = 0.0001-0.0414) between pyroglutamate and alpha ERD but positive correlations (r = ~0.82-0.95, p = 0.0003-0.0119) between glutamine and alpha ERD. Under Stroop interference testing, CH-NATs generated negative correlations between glutamine and left temporal alpha ERD (r = -0.96, p = 0.037 and r = -0.97, p = 0.027). Our study demonstrated that glutamine and pyroglutamate levels were associated with EEG activity only in CH-NATs. These results suggest cognitively healthy adults with amyloid/tau pathology experience subtle metabolic dysfunction that may influence EEG signaling during cognitive challenge. A longitudinal follow-up study with a larger sample size is needed to validate these pilot studies.

Chemical signatures delineate heterogeneous amyloid plaque populations across the Alzheimer's disease spectrum

Amyloid plaque deposition is recognized as the primary pathological hallmark of Alzheimer's disease(AD) that precedes other pathological events and cognitive symptoms. Plaque pathology represents itself with an immense polymorphic variety comprising plaques with different stages of amyloid fibrillization ranging from diffuse to fibrillar, mature plaques. The association of polymorphic Aβ plaque pathology with AD pathogenesis, clinical symptoms and disease progression remains unclear. Advanced chemical imaging tools, such as functional amyloid microscopy combined with MALDI mass spectrometry imaging (MSI), are now enhanced by deep learning algorithms. This integration allows for precise delineation of polymorphic plaque structures and detailed identification of their associated Aβ compositions. We here set out to make use of these tools to interrogate heterogenic plaque types and their associated biochemical architecture. Our findings reveal distinct Aβ signatures that differentiate diffuse plaques from fibrilized ones, with the latter showing substantially higher levels of Aβx-40. Notably, within the fibrilized category, we identified a distinct subtype known as coarse-grain plaques. Both in sAD and fAD brain tissue, coarse grain plaques contained more Aβx-40 and less Aβx-42 compared with cored plaques. The coarse grain plaques in both sAD and fAD also showed higher levels of neuritic content including paired helical filaments (PHF-1)/phosphorylated phospho Tau-immunopositive neurites. Finally, the Aβ peptide content in coarse grain plaques resembled that of vascular Aβ deposits (CAA) though with relatively higher levels of Aβ1-42 and pyroglutamated Aβx-40 and Aβx-42 species in coarse grain plaques. This is the first of its kind study on spatial in situ biochemical characterization of different plaque morphotypes demonstrating the potential of the correlative imaging techniques used that further increase the understanding of heterogeneous AD pathology. Linking the biochemical characteristics of amyloid plaque polymorphisms with various AD etiologies and toxicity mechanisms is crucial. Understanding the connection between plaque structure and disease pathogenesis can enhance our insights. This knowledge is particularly valuable for developing and advancing novel, amyloid-targeting therapeutics.

Thiophene-Based Ligands for Specific Assignment of Distinct Aβ Pathologies in Alzheimer's Disease

Aggregated species of amyloid-β (Aβ) are one of the pathological hallmarks in Alzheimer's disease (AD), and ligands that selectively target different Aβ deposits are of great interest. In this study, fluorescent thiophene-based ligands have been used to illustrate the features of different types of Aβ deposits found in AD brain tissue. A dual-staining protocol based on two ligands, HS-276 and LL-1, with different photophysical and binding properties, was developed and applied on brain tissue sections from patients affected by sporadic AD or familial AD associated with the PSEN1 A431E mutation. When binding to Aβ deposits, the ligands could easily be distinguished for their different fluorescence, and distinct staining patterns were revealed for these two types of AD. In sporadic AD, HS-276 consistently labeled all immunopositive Aβ plaques, whereas LL-1 mainly stained cored and neuritic Aβ deposits. In the PSEN1 A431E cases, each ligand was binding to specific types of Aβ plaques. The ligand-labeled Aβ deposits were localized in distinct cortical layers, and a laminar staining pattern could be seen. Biochemical characterization of the Aβ aggregates in the individual layers also showed that the variation of ligand binding properties was associated with certain Aβ peptide signatures. For the PSEN1 A431E cases, it was concluded that LL-1 was binding to cotton wool plaques, whereas HS-276 mainly stained diffuse Aβ deposits. Overall, our findings showed that a combination of ligands was essential to identify distinct aggregated Aβ species associated with different forms of AD.

Spatial neurolipidomics-MALDI mass spectrometry imaging of lipids in brain pathologies

Given the complexity of nervous tissues, understanding neurochemical pathophysiology puts high demands on bioanalytical techniques with respect to specificity and sensitivity. Mass spectrometry imaging (MSI) has evolved to become an important, biochemical imaging technology for spatial biology in biological and translational research. The technique facilitates comprehensive, sensitive elucidation of the spatial distribution patterns of drugs, lipids, peptides, and small proteins in situ. Matrix-assisted laser desorption ionization (MALDI)-based MSI is the dominating modality due to its broad applicability and fair compromise of selectivity, sensitivity price, throughput, and ease of use. This is particularly relevant for the analysis of spatial lipid patterns, where no other comparable spatial profiling tools are available. Understanding spatial lipid biology in nervous tissue is therefore a key and emerging application area of MSI research. The aim of this review is to give a concise guide through the MSI workflow for lipid imaging in central nervous system (CNS) tissues and essential parameters to consider while developing and optimizing MSI assays. Further, this review provides a broad overview of key developments and applications of MALDI MSI-based spatial neurolipidomics to map lipid dynamics in neuronal structures, ultimately contributing to a better understanding of neurodegenerative disease pathology.

Cryo-EM of Aβ fibrils from mouse models find tg-APPArcSwe fibrils resemble those found in patients with sporadic Alzheimer's disease

The use of transgenic mice displaying amyloid-β (Aβ) brain pathology has been essential for the preclinical assessment of new treatment strategies for Alzheimer's disease. However, the properties of Aβ in such mice have not been systematically compared to Aβ in the brains of patients with Alzheimer's disease. Here, we determined the structures of nine ex vivo Aβ fibrils from six different mouse models by cryogenic-electron microscopy. We found novel Aβ fibril structures in the APP/PS1, ARTE10 and tg-SwDI models, whereas the human type II filament fold was found in the ARTE10, tg-APPSwe and APP23 models. The tg-APPArcSwe mice showed an Aβ fibril whose structure resembles the human type I filament found in patients with sporadic Alzheimer's disease. A detailed assessment of the Aβ fibril structure is key to the selection of adequate mouse models for the preclinical development of novel plaque-targeting therapeutics and positron emission tomography imaging tracers in Alzheimer's disease.

Amyloid β Proteoforms Elucidated by Quantitative LC/MS in the 5xFAD Mouse Model of Alzheimer's Disease

Numerous Aβ proteoforms, identified in the human brain, possess differential neurotoxic and aggregation propensities. These proteoforms contribute in unknown ways to the conformations and resultant pathogenicity of oligomers, protofibrils, and fibrils in Alzheimer's disease (AD) manifestation owing to the lack of molecular-level specificity to the exact chemical composition of underlying protein products with widespread interrogating techniques, like immunoassays. We evaluated Aβ proteoform flux using quantitative top-down mass spectrometry (TDMS) in a well-studied 5xFAD mouse model of age-dependent Aβ-amyloidosis. Though the brain-derived Aβ proteoform landscape is largely occupied by Aβ1-42, 25 different forms of Aβ with differential solubility were identified. These proteoforms fall into three natural groups defined by hierarchical clustering of expression levels in the context of mouse age and proteoform solubility, with each group sharing physiochemical properties associated with either N/C-terminal truncations or both. Overall, the TDMS workflow outlined may hold tremendous potential for investigating proteoform-level relationships between insoluble fibrils and soluble Aβ, including low-molecular-weight oligomers hypothesized to serve as the key drivers of neurotoxicity. Similarly, the workflow may also help to validate the utility of AD-relevant animal models to recapitulate amyloidosis mechanisms or possibly explain disconnects observed in therapeutic efficacy in animal models vs humans.

Modulation of the Activity of the Insulin-Degrading Enzyme by Aβ Peptides

The insulin-degrading enzyme (IDE) is an evolutionarily conserved protease implicated in the degradation of insulin and amyloidogenic peptides. Most of the biochemical and biophysical characterization of IDE's catalytic activity has been conducted using solutions containing a single substrate, i.e., insulin or Aβ(1-40). IDE's activity toward a particular substrate, however, is likely to be influenced by the presence of other substrates. Here, we show by a kinetic assay based on insulin's helical circular dichroic signal and MALDI TOF mass spectrometry that Aβ peptides modulate IDE's activity toward insulin in opposing ways. Aβ(1-40) enhances IDE-dependent degradation of insulin, whereas Aβ(pyroE3-42), the most pathogenic pyroglutamate-modified Aβ peptide in AD, inhibits IDE's activity. Intriguingly, Aβ(pyroE3-42) also inhibits IDE's ability to degrade Aβ(1-40). Together, our results implicate Aβ peptides in the abnormal catabolism of IDE's key substrates.

Mass Spectrometry Imaging in Alzheimer's Disease

Introduction: Amyloid-beta (Aβ) pathology is the precipitating histopathological characteristic of Alzheimer's disease (AD). Although the formation of amyloid plaques in human brains is suggested to be a key factor in initiating AD pathogenesis, it is still not fully understood the upstream events that lead to Aβ plaque formation and its metabolism inside the brains. Methods: Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) has been successfully introduced to study AD pathology in brain tissue both in AD mouse models and human samples. By using MALDI-MSI, a highly selective deposition of Aβ peptides in AD brains with a variety of cerebral amyloid angiopathy (CAA) involvement was observed. Results: MALDI-MSI visualized depositions of shorter peptides in AD brains; Aβ1-36 to Aβ1-39 were quite similarly distributed with Aβ1-40 as a vascular pattern, and deposition of Aβ1-42 and Aβ1-43 was visualized with a distinct senile plaque pattern distributed in parenchyma. Moreover, how MALDI-MSI covered in situ lipidomics of plaque pathology has been reviewed, which is of interest as aberrations in neuronal lipid biochemistry have been implicated in AD pathogenesis. Discussion: In this study, we introduce the methodological concepts and challenges of MALDI-MSI for the studies of AD pathogenesis. Diverse Aβ isoforms including various C- and N-terminal truncations in AD and CAA brain tissues will be visualized. Despite the close relationship between vascular and plaque Aβ deposition, the current strategy will define cross talk between neurodegenerative and cerebrovascular processes at the level of Aβ metabolism.

Advances and Emerging Medical Applications of Direct Mass Spectrometry Technologies for Tissue Analysis

Offering superb speed, chemical specificity, and analytical sensitivity, direct mass spectrometry (MS) technologies are highly amenable for the molecular analysis of complex tissues to aid in disease characterization and help identify new diagnostic, prognostic, and predictive markers. By enabling detection of clinically actionable molecular profiles from tissues and cells, direct MS technologies have the potential to guide treatment decisions and transform sample analysis within clinical workflows. In this review, we highlight recent health-related developments and applications of direct MS technologies that exhibit tangible potential to accelerate clinical research and disease diagnosis, including oncological and neurodegenerative diseases and microbial infections. We focus primarily on applications that employ direct MS technologies for tissue analysis, including MS imaging technologies to map spatial distributions of molecules in situ as well as handheld devices for rapid in vivo and ex vivo tissue analysis.

Thiophene-Based Ligands: Design, Synthesis and Their Utilization for Optical Assignment of Polymorphic-Disease-Associated Protein Aggregates

The development of ligands for detecting protein aggregates is of great interest, as these aggregated proteinaceous species are the pathological hallmarks of several devastating diseases, including Alzheimer's disease. In this regard, thiophene-based ligands have emerged as powerful tools for fluorescent assessment of these pathological entities. The intrinsic conformationally sensitive photophysical properties of poly- and oligothiophenes have allowed optical assignment of disease-associated protein aggregates in tissue sections, as well as real-time in vivo imaging of protein deposits. Herein, we recount the chemical evolution of different generations of thiophene-based ligands, and exemplify their use for the optical distinction of polymorphic protein aggregates. Furthermore, the chemical determinants for achieving a superior fluorescent thiophene-based ligand, as well as the next generation of thiophene-based ligands targeting distinct aggregated species are described. Finally, the directions for future research into the chemical design of thiophene-based ligands that can aid in resolving the scientific challenges around protein aggregation diseases are discussed.

Thiophene-Based Ligands for Histological Multiplex Spectral Detection of Distinct Protein Aggregates in Alzheimer's Disease

The aggregation and accumulation of proteins in the brain is the defining feature of many devastating neurodegenerative diseases. The development of fluorescent ligands that bind to these accumulations, or deposits, is essential for the characterization of these neuropathological lesions. We report the synthesis of donor-acceptor-donor (D-A-D) thiophene-based ligands with different emission properties. The D-A-D ligands displayed selectivity towards distinct disease-associated protein deposits in histological sections from postmortem brain tissue of individuals affected by Alzheimer's disease (AD). The ability of the ligands to selectively identify AD-associated pathological alterations, such as deposits composed of aggregates of the amyloid-β (Aβ) peptide or tau, was reduced when the chemical composition of the ligands was altered. When combining the D-A-D ligands with conventional thiophene-based ligands, superior spectral separation of distinct protein aggregates in AD tissue sections was obtained. Our findings provide the structural and functional basis for the development of new fluorescent ligands that can distinguish between aggregated proteinaceous species, as well as offer novel strategies for developing multiplex fluorescence detection of protein aggregates in tissue sections.

Correlative Chemical Imaging and Spatial Chemometrics Delineate Alzheimer Plaque Heterogeneity at High Spatial Resolution

We present a novel, correlative chemical imaging strategy based on multimodal matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI), hyperspectral microscopy, and spatial chemometrics. Our workflow overcomes challenges associated with correlative MSI data acquisition and alignment by implementing 1 + 1-evolutionary image registration for precise geometric alignment of multimodal imaging data and their integration in a common, truly multimodal imaging data matrix with maintained MSI resolution (10 μm). This enabled multivariate statistical modeling of multimodal imaging data using a novel multiblock orthogonal component analysis approach to identify covariations of biochemical signatures between and within imaging modalities at MSI pixel resolution. We demonstrate the method's potential through its application toward delineating chemical traits of Alzheimer's disease (AD) pathology. Here, trimodal MALDI MSI of transgenic AD mouse brain delineates beta-amyloid (Aβ) plaque-associated co-localization of lipids and Aβ peptides. Finally, we establish an improved image fusion approach for correlative MSI and functional fluorescence microscopy. This allowed for high spatial resolution (300 nm) prediction of correlative, multimodal MSI signatures toward distinct amyloid structures within single plaque features critically implicated in Aβ pathogenicity.

Tetramodal Chemical Imaging Delineates the Lipid-Amyloid Peptide Interplay at Single Plaques in Transgenic Alzheimer's Disease Models

Beta-amyloid (Aβ) plaque pathology is one of the most prominent histopathological feature of Alzheimer's disease (AD). The exact pathogenic mechanisms linking Aβ to AD pathogenesis remain however not fully understood. Recent advances in amyloid-targeting pharmacotherapies highlight the critical relevance of Aβ aggregation for understanding the molecular basis of AD pathogenesis. We developed a novel, integrated, tetramodal chemical imaging paradigm for acquisition of trimodal mass spectrometry imaging (MSI) and interlaced fluorescent microscopy from a single tissue section. We used this approach to comprehensively investigate lipid-Aβ correlates at single plaques in two different mouse models of AD (tgAPPSwe and tgAPPArcSwe) with varying degrees of intrinsic properties affecting amyloid aggregation. Integration of the multimodal imaging data and multivariate data analysis identified characteristic patterns of plaque-associated lipid- and peptide localizations across both mouse models. Correlative fluorescence microscopy using structure-sensitive amyloid probes identified intra-plaque structure-specific lipid- and Aβ patterns, including Aβ 1-40 and Aβ 1-42 along with gangliosides (GM), phosphoinositols (PI), conjugated ceramides (CerP and PE-Cer), and lysophospholipids (LPC, LPA, and LPI). Single plaque correlation analysis across all modalities further revealed how these distinct lipid species were associated with Aβ peptide deposition across plaque heterogeneity, indicating different roles for those lipids in plaque growth and amyloid fibrillation, respectively. Here, conjugated ceramide species correlated with Aβ core formation indicating their involvement in initial plaque seeding or amyloid maturation. In contrast, LPI and PI were solely correlated with general plaque growth. In addition, GM1 and LPC correlated with continuous Aβ deposition and maturation. The results highlight the potential of this comprehensive multimodal imaging approach and implement distinct lipids in amyloidogenic proteinopathy.

Unveiling the Potential of Polyphenols as Anti-Amyloid Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease that mostly affects the elderly population. Mechanisms underlying AD pathogenesis are yet to be fully revealed, but there are several hypotheses regarding AD. Even though free radicals and inflammation are likely to be linked with AD pathogenesis, still amyloid-beta (Aβ) cascade is the dominant hypothesis. According to the Aβ hypothesis, a progressive buildup of extracellular and intracellular Aβ aggregates has a significant contribution to the AD-linked neurodegeneration process. Since Aβ plays an important role in the etiology of AD, therefore Aβ-linked pathways are mainly targeted in order to develop potential AD therapies. Accumulation of Aβ plaques in the brains of AD individuals is an important hallmark of AD. These plaques are mainly composed of Aβ (a peptide of 39-42 amino acids) aggregates produced via the proteolytic cleavage of the amyloid precursor protein. Numerous studies have demonstrated that various polyphenols (PPHs), including cyanidins, anthocyanins, curcumin, catechins and their gallate esters were found to markedly suppress Aβ aggregation and prevent the formation of Aβ oligomers and toxicity, which is further suggesting that these PPHs might be regarded as effective therapeutic agents for the AD treatment. This review summarizes the roles of Aβ in AD pathogenesis, the Aβ aggregation pathway, types of PPHs, and distribution of PPHs in dietary sources. Furthermore, we have predominantly focused on the potential of food-derived PPHs as putative anti-amyloid drugs.

ImmunoPET imaging of amyloid-beta in a rat model of Alzheimer's disease with a bispecific, brain-penetrating fusion protein

BACKGROUND

Hijacking the transferrin receptor (TfR) is an effective strategy to transport amyloid-beta (Aβ) immuno-positron emission tomography (immunoPET) ligands across the blood-brain barrier (BBB). Such ligands are more sensitive and specific than small-molecule ligands at detecting Aβ pathology in mouse models of Alzheimer's disease (AD). This study aimed to determine if this strategy would be as sensitive in rats and to assess how TfR affinity affects BBB transport of bispecific immunoPET radioligands.

METHODS

Two affinity variants of the rat TfR antibody, OX26, were chemically conjugated to a F(ab')₂ fragment of the anti-Aβ antibody, bapineuzumab (Bapi), to generate two bispecific fusion proteins: OX26₅-F(ab')₂-Bapi and OX26₇₆-F(ab')₂-Bapi. Pharmacokinetic analyses were performed 4 h and 70 h post-injection of radioiodinated fusion proteins in wild-type (WT) rats. [¹²⁴I]I-OX26₅-F(ab')₂-Bapi was administered to TgF344-AD and WT rats for in vivo PET imaging. Ex vivo distribution of injected [¹²⁴I]I-OX26₅-F(ab')₂-Bapi and Aβ pathology were assessed.

RESULTS

More [¹²⁵I]I-OX26₅-F(ab')₂-Bapi was taken up into the brain 4 h post-administration than [¹²⁴I]I-OX26₇₆-F(ab')₂-Bapi. [¹²⁴I]I-OX26₅-F(ab')₂-Bapi PET visualized Aβ pathology with significantly higher signals in the TgF344-AD rats than in the WT littermates without Aβ pathology. The PET signals significantly correlated with Aβ levels in AD animals.

CONCLUSION

Affinity to TfR affects how efficiently a TfR-targeting bispecific fusion protein will cross the BBB, such that the higher-affinity bispecific fusion protein crossed the BBB more efficiently. Furthermore, bispecific immunoPET imaging of brain Aβ pathology using TfR-mediated transport provides good imaging contrast between TgF344-AD and WT rats, suggesting that this immunoPET strategy has the potential to be translated to higher species.

Proteophenes - Amino Acid Functionalized Thiophene-based Fluorescent Ligands for Visualization of Protein Deposits in Tissue Sections with Alzheimer's Disease Pathology

Protein deposits composed of specific proteins or peptides are associated with several neurodegenerative diseases and fluorescent ligands able to detect these pathological hallmarks are vital. Here, we report the synthesis of a class of thiophene-based ligands, denoted proteophenes, with different amino acid side-chain functionalities along the conjugated backbone, which display selectivity towards specific disease-associated protein aggregates in tissue sections with Alzheimer's disease (AD) pathology. The selectivity of the ligands towards AD associated pathological hallmarks, such as aggregates of the amyloid-β (Aβ) peptide or tau filamentous inclusions, was highly dependent on the chemical nature of the amino acid functionality, as well as on the location of the functionality along the pentameric thiophene backbone. Finally, the concept of synthesizing donor-acceptor-donor proteophenes with distinct photophysical properties was shown. Our findings provide the structural and functional basis for the development of new thiophene-based ligands that can be utilized for optical assignment of different aggregated proteinaceous species in tissue sections.

Chemical traits of cerebral amyloid angiopathy in familial British-, Danish-, and non-Alzheimer's dementias

Familial British dementia (FBD) and familial Danish dementia (FDD) are autosomal dominant forms of dementia caused by mutations in the integral membrane protein 2B (ITM2B, also known as BRI2) gene. Secretase processing of mutant BRI2 leads to secretion and deposition of BRI2-derived amyloidogenic peptides, ABri and ADan that resemble APP/β-amyloid (Aβ) pathology, which is characteristic of Alzheimer's disease (AD). Amyloid pathology in FBD/FDD manifests itself predominantly in the microvasculature by ABri/ADan containing cerebral amyloid angiopathy (CAA). While ABri and ADan peptide sequences differ only in a few C-terminal amino acids, CAA in FDD is characterized by co-aggregation of ADan with Aβ, while in contrast no Aβ deposition is observed in FBD. The fact that FDD patients display an earlier and more severe disease onset than FBD suggests a potential role of ADan and Aβ co-aggregation that promotes a more rapid disease progression in FDD compared to FBD. It is therefore critical to delineate the chemical signatures of amyloid aggregation in these two vascular dementias. This in turn will increase the knowledge on the pathophysiology of these diseases and the pathogenic role of heterogenous amyloid peptide interactions and deposition, respectively. Herein, we used matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) in combination with hyperspectral, confocal microscopy based on luminescent conjugated oligothiophene probes (LCO) to delineate the structural traits and associated amyloid peptide patterns of single CAA in postmortem brain tissue of patients with FBD, FDD as well as sporadic CAA without AD (CAA+) that show pronounced CAA without parenchymal plaques. The results show that CAA in both FBD and FDD consist of N-terminally truncated- and pyroglutamate-modified amyloid peptide species (ADan and ABri), but that ADan peptides in FDD are also extensively C-terminally truncated as compared to ABri in FBD, which contributes to hydrophobicity of ADan species. Further, CAA in FDD showed co-deposition with Aβ x-42 and Aβ x-40 species. CAA+ vessels were structurally more mature than FDD/FBD CAA and contained significant amounts of pyroglutamated Aβ. When compared with FDD, Aβ in CAA+ showed more C-terminal and less N-terminally truncations. In FDD, ADan showed spatial co-localization with Aβ3pE-40 and Aβ3-40 but not with Aβx-42 species. This suggests an increased aggregation propensity of Aβ in FDD that promotes co-aggregation of both Aβ and ADan. Further, CAA maturity appears to be mainly governed by Aβ content based on the significantly higher 500/580 patterns observed in CAA+ than in FDD and FBD, respectively. Together this is the first study of its kind on comprehensive delineation of Bri2 and APP-derived amyloid peptides in single vascular plaques in both FDD/FBD and sporadic CAA that provides new insight in non-AD-related vascular amyloid pathology. Cover Image for this issue: https://doi.org/10.1111/jnc.15424.

Advances in the development of new biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is a complex, heterogeneous, progressive disease and is the most common type of neurodegenerative dementia. The prevalence of AD is expected to increase as the population ages, placing an additional burden on national healthcare systems. There is a large need for new diagnostic tests that can detect AD at an early stage with high specificity at relatively low cost. The development of modern analytical diagnostic tools has made it possible to determine several biomarkers of AD with high specificity, including pathogenic proteins, markers of synaptic dysfunction, and markers of inflammation in the blood. There is a considerable potential in using microRNA (miRNA) as markers of AD, and diagnostic studies based on miRNA panels suggest that AD could potentially be determined with high accuracy for individual patients. Studies of the retina with improved methods of visualization of the fundus are also showing promising results for the potential diagnosis of the disease. This review focuses on the recent developments of blood, plasma, and ocular biomarkers for the diagnosis of AD.

Protective Effects of Dendrobium nobile Lindl. Alkaloids on Alzheimer's Disease-like Symptoms Induced by High-methionine Diet

BACKGROUND

High methionine-diet (HMD) causes Alzheimer's disease (AD)-like symptoms. Previous studies have shown that Dendrobium nobile Lindle. alkaloids (DNLA) have potential benefits for AD Object: The objective of this study has been to explore whether DNLA can improve AD-like symptoms induced by HMD.

METHODS

Mice were fed with 2% HMD diet for 11 weeks; the DNLA20 control group (20 mg/kg), DNLA10 group (10 mg/kg), and DNLA20 group (20 mg/kg) were administered DNLA for 3 months. Morris water maze test was used to detect learning and memory ability. Neuron damage was evaluated by HE and Nissl staining. Levels of homocysteine (Hcy), beta-amyloid 1-42 (Aβ_1-42), S-adenosine methionine (SAM) and S-adenosine homocysteine (SAH) were detected by ELISA. Immunofluorescence and western blotting (WB) were used to determine the expression of proteins. CPG island methylation levels were accessed by Methylation-specific PCR (MSP) and MethylTarget methylation detection.

RESULTS

Morris water maze test revealed that DNLA improved learning and memory dysfunction. HE, Nissl, and immunofluorescence staining showed that DNLA alleviated neuron damage and reduced the 5-methylcytosine (5-mC), Aβ_1-40) and Aβ_1-42) levels. DNLA also decreased the levels of Hcy and Aβ_1-42) in the serum, along with decreasing SAM/SAH level in the liver tissue. WB results showed that DNLA down-regulated the expression of amyloid-precursor protein (APP), presenilin-1 (PS1), beta-secretase-1 (BACE1), DNA methyltransferase1 (DNMT1), Aβ_1-40) and Aβ_1-42) proteins. DNLA also up-regulated the proteins expression of insulin-degrading enzyme (IDE), neprilysin (NEP), DNMT3a and DNMT3b. Meanwhile, DNLA increased CPG island methylation levels of APP and BACE1 genes.

CONCLUSION

DNLA alleviated AD-like symptoms induced by HMD via the DNA methylation pathway.

Impact of Anti-amyloid-β Monoclonal Antibodies on the Pathology and Clinical Profile of Alzheimer’s Disease: A Focus on Aducanumab and Lecanemab

Alzheimer’s disease (AD) is the most prevalent form of age-related dementia in the world, and its main pathological features consist of amyloid-β (Aβ) plaque deposits and neurofibrillary tangles formed by hyperphosphorylated tau protein. So far, only a few AD treatments approved have been applied in the clinic, but the effects of these drugs are limited only for partial symptomatic relief to patients with AD and are unable to alter AD progression. Later, all efforts for AD treatments with targeting the pathogenic factors were unsuccessful over the past decades, which suggested that the pathogenesis of AD is complex. Recently, disease-modifying therapies (DMTs) that can change the underlying pathophysiology of AD, with anti-Aβ monoclonal antibodies (mabs) (e.g., aducanumab, bapineuzumab, gantenerumab, solanezumab, and lecanemab) have been developed successively and conducted in clinical trials based on the theory that a systemic failure of cell-mediated Aβ clearance contributes to AD occurrence and progression. In the review, we summarized recent studies on the therapeutic effects and clinical trial results of these mabs in patients with AD. Specifically, we focused on the discussion of the impact of aducanumab and lecanemab on AD pathology and clinical profiles. The review provides a possible evidence for applying immunotherapy with anti-Aβ mabs in AD and analyzes lessons learned from these clinical trials in order to further study the therapeutic and adverse effects of these anti-Aβ mabs on AD.

Mass spectrometric studies of the variety of beta-amyloid proteoforms in Alzheimer's disease

This review covers the results of the application of mass spectrometric (MS) techniques to study the diversity of beta-amyloid (Aβ) peptides in human samples. Since Aβ is an important hallmark of Alzheimer's disease (AD), which is a socially significant neurodegenerative disorder of the elderly worldwide, analysis of its endogenous variations is of particular importance for elucidating the pathogenesis of AD, predicting increased risks of the disease onset, and developing effective therapy. MS approaches have no alternative for the study of complex samples, including a wide variety of Aβ proteoforms, differing in length and modifications. Approaches based on matrix-assisted laser desorption/ionization time-of-flight and liquid chromatography with electrospray ionization tandem MS are most common in Aβ studies. However, Aβ forms with isomerized and/or racemized Asp and Ser residues require the use of special methods for separation and extra sensitive and selective methods for detection. Overall, this review summarizes current knowledge of Aβ species found in human brain, cerebrospinal fluid, and blood plasma; focuses on application of different MS approaches for Aβ studies; and considers the potential of MS techniques for further studies of Aβ-peptides.

Inhibiting Autophagy Pathway of PI3K/AKT/mTOR Promotes Apoptosis in SK-N-SH Cell Model of Alzheimer's Disease

Alzheimer's disease is the most common dementia disease characterized by chronic progressive neurodegeneration. The incidence of Alzheimer's disease is on the rise as the population ages at an accelerating pace. According to epidemiological data, by 2050, the number of Alzheimer's patients in the United States will be three times higher than that in 2010, and a similar trend is occurring in China. To explore the effect and mechanism of let-7b by detecting the expression level of let-7b in Alzheimer's disease, fifty patients with Alzheimer's disease and thirty healthy controls were selected. The expression levels of let-7 families (let-7a, let-7b, let-7c, let-7d, let-7e, let-7f, let-7g, and let-7i) were detected by qPCR. Human neuroblastoma cell SK-N-SH were divided into control group (untreated), model group (treated with Aβ1-40), Aβ1-40+let-7b mimic group (treated with Aβ1-40 and transfected with let-7b mimic), and Aβ1-40+miR-NC group (treated with aβ1-40 and transfected with miR-NC). let-7b expression and cell survival rate were detected by qPCR and CCK-8, and the levels of caspase 3, LC3, beclin-1, PI3K, p-AKT, and p-mTOR were detected by Western blot. let-7b was significantly different between the case group and the control group (p < 0.001). CCK-8 showed a significant decrease in cell viability in Aβ1-40 treatment group compared with that in the control group (p < 0.01). Overexpression of let-7b significantly reduced the survival rate of the cells, and the expression of LC3II/LC3I and beclin-1 in the cells was significantly reduced by aβ1-40 treatment (p < 0.001). let-7b overexpression also inhibited autophagy via reducing the level of LC3II/LC3I and beclin-1 (p < 0.001). Aβ1-40 treatment and let-7b overexpression promoted apoptosis by increasing the expression of cleavage caspase 3. Western blot indicated that Aβ1-40 treatment and let-7b overexpression could increase the expression of PI3K, p-AKT, and p-mTOR. let-7b overexpression could inhibit autophagy and promote apoptosis in Alzheimer's cells by promoting PI3K/AKT/mTOR signaling pathway. PI3K/AKT/mTOR signaling pathway is involved in the imbalance between autophagy and apoptosis.

Structural amyloid plaque polymorphism is associated with distinct lipid accumulations revealed by trapped ion mobility mass spectrometry imaging

Understanding of Alzheimer's disease (AD) pathophysiology requires molecular assessment of how key pathological factors, specifically amyloid β (Aβ) plaques, influence the surrounding microenvironment. Here, neuronal lipids have been implicated in Aβ plaque pathology, though the lipid microenvironment in direct proximity to Aβ plaques is still not fully resolved. A further challenge is the microenvironmental molecular heterogeneity, across structurally polymorphic Aβ features, such as diffuse, immature, and mature, fibrillary aggregates, whose resolution requires the integration of advanced, multimodal chemical imaging tools. Herein, we used matrix-assisted laser desorption/ionization trapped ion mobility spectrometry time-of-flight based mass spectrometry imaging (MALDI TIMS TOF MSI) in combination with hyperspectral confocal microscopy to probe the lipidomic microenvironment associated with structural polymorphism of Aβ plaques in transgenic Alzheimer's disease mice (tgAPP_SWE ). Using on tissue and ex situ validation, TIMS MS/MS facilitated unambiguous identification of isobaric lipid species that showed plaque pathology-associated localizations. Integrated multivariate imaging data analysis revealed multiple, Aβ plaque-enriched lipid patterns for gangliosides (GM), phosphoinositols (PI), phosphoethanolamines (PE), and phosphatidic acids (PA). Conversely, sulfatides (ST), cardiolipins (CL), and polyunsaturated fatty acid (PUFA)-conjugated phosphoserines (PS), and PE were depleted at plaques. Hyperspectral amyloid imaging further delineated the unique distribution of PA and PE species to mature plaque core regions, while PI, LPI, GM2 and GM3 lipids localized to immature Aβ aggregates present within the periphery of Aβ plaques. Finally, we followed AD pathology-associated lipid changes over time, identifying plaque- growth and maturation to be characterized by peripheral accumulation of PI (18:0/22:6). Together, these data demonstrate the potential of multimodal imaging approaches to overcome limitations associated with conventional advanced MS imaging applications. This allowed for the differentiation of both distinct lipid components in a complex micro-environment as well as their correlation to disease-relevant amyloid plaque polymorphs.

Distinct conformers of amyloid beta accumulate in the neocortex of patients with rapidly progressive Alzheimer's disease

Amyloid beta (Aβ) deposition in the neocortex is a major hallmark of Alzheimer's disease (AD), but the extent of deposition does not readily explain phenotypic diversity and rate of disease progression. The prion strain-like model of disease heterogeneity suggests the existence of different conformers of Aβ. We explored this paradigm using conformation-dependent immunoassay (CDI) for Aβ and conformation-sensitive luminescent conjugated oligothiophenes (LCOs) in AD cases with variable progression rates. Mapping the Aβ conformations in the frontal, occipital, and temporal regions in 20 AD patients with CDI revealed extensive interindividual and anatomical diversity in the structural organization of Aβ with the most significant differences in the temporal cortex of rapidly progressive AD. The fluorescence emission spectra collected in situ from Aβ plaques in the same regions demonstrated considerable diversity of spectral characteristics of two LCOs-quatroformylthiophene acetic acid and heptaformylthiophene acetic acid. Heptaformylthiophene acetic acid detected a wider range of Aβ deposits, and both LCOs revealed distinct spectral attributes of diffuse and cored plaques in the temporal cortex of rapidly and slowly progressive AD and less frequent and discernible differences in the frontal and occipital cortex. These and CDI findings indicate a major conformational diversity of Aβ accumulating in the neocortex, with the most notable differences in temporal cortex of cases with shorter disease duration, and implicate distinct Aβ conformers (strains) in the rapid progression of AD.

Prediction of Cerebral Amyloid Pathology Based on Plasma Amyloid and Tau Related Markers

Background and Purpose: Pyroglutamate-modified β-amyloid peptide (Aβ_pE) is crucial for AD pathophysiological process. The potential associations of plasma Aβ_pE and total tau (t-tau) with brain Aβ burden and cognitive performance remain to be clarified.

Methods: Forty-six subjects with unimpaired cognition, mild cognitive impairment, or very mild dementia were enrolled. Plasma levels of Aβ_pE3−40, t-tau, and Aβ42 were quantified by immunomagnetic reduction (IMR) assays. We analyzed individual and combined biomarker correlations with neuropsychological scores and Aβ positivity determined by ¹⁸F-florbetapir positron emission tomography (PET).

Results: Both plasma Aβ_pE3−40 levels and Aβ_pE3−40/t-tau ratios correlated negatively with short-term memory and global cognition scores, while correlating positively with PET standardized uptake value ratios (SUVRs). Among the biomarkers analyzed, the combination of Aβ_pE3−40 in a ratio with t-tau had the best discriminatory ability for Aβ PET positivity. Likewise, logistic regression analysis showed that Aβ_pE3−40/t-tau was a highly robust predictor of Aβ PET positivity after controlling for relevant demographic covariates.

Conclusion: Plasma Aβ_pE3−40/t-tau ratios correlate with cognitive function and cerebral Aβ burden. The suitability of Aβ_pE3−40/t-tau as a candidate clinical biomarker of AD pathology in the brain should be examined further in larger studies.

Citrullination of Amyloid-β Peptides in Alzheimer's Disease

Protein citrullination (deimination of arginine residue) is a well-known biomarker of inflammation. Elevated protein citrullination has been shown to colocalize with extracellular amyloid plaques in postmortem AD patient brains. Amyloid-β (Aβ) peptides which aggregate and accumulate in the plaques of Alzheimer's disease (AD) have sequential N-terminal truncations and multiple post-translational modifications (PTM) such as isomerization, pyroglutamate formation, phosphorylation, nitration, and dityrosine cross-linking. However, no conclusive biochemical evidence exists whether citrullinated Aβ is present in AD brains. In this study, using high-resolution mass spectrometry, we have identified citrullination of Aβ in sporadic and familial AD brains by characterizing the tandem mass spectra of endogenous N-truncated citrullinated Aβ peptides. Our quantitative estimations demonstrate that ∼ 35% of pyroglutamate3-Aβ pool was citrullinated in plaques in the sporadic AD temporal cortex and ∼ 22% in the detergent-insoluble frontal cortex fractions. Similarly, hypercitrullinated pyroglutamate3-Aβ (∼ 30%) was observed in both the detergent-soluble as well as insoluble Aβ pool in familial AD cases. Our results indicate that a common mechanism for citrullination of Aβ exists in both the sporadic and familial AD. We establish that citrullination of Aβ is a remarkably common PTM, closely associated with pyroglutamate3-Aβ formation and its accumulation in AD. This may have implications for Aβ toxicity, autoantigenicity of Aβ, and may be relevant for the design of diagnostic assays and therapeutic targeting.

Postmortem Neocortical 3H-PiB Binding and Levels of Unmodified and Pyroglutamate Aβ in Down Syndrome and Sporadic Alzheimer's Disease

Individuals with Down syndrome (DS) have a genetic predisposition for amyloid-β (Aβ) overproduction and earlier onset of Aβ deposits compared to patients with sporadic late-onset Alzheimer’s disease (AD). Positron emission tomography (PET) with Pittsburgh Compound-B (PiB) detects fibrillar Aβ pathology in living people with DS and AD, but its relationship with heterogeneous Aβ forms aggregated within amyloid deposits is not well understood. We performed quantitative in vitro³H-PiB binding assays and enzyme-linked immunosorbent assays of fibrillar (insoluble) unmodified Aβ40 and Aβ42 forms and N-terminus truncated and pyroglutamate-modified AβNpE3-40 and AβNpE3-42 forms in postmortem frontal cortex and precuneus samples from 18 DS cases aged 43–63 years and 17 late-onset AD cases aged 62–99 years. Both diagnostic groups had frequent neocortical neuritic plaques, while the DS group had more severe vascular amyloid pathology (cerebral amyloid angiopathy, CAA). Compared to the AD group, the DS group had higher levels of Aβ40 and AβNpE3-40, while the two groups did not differ by Aβ42 and AβNpE3-42 levels. This resulted in lower ratios of Aβ42/Aβ40 and AβNpE3-42/AβNpE3-40 in the DS group compared to the AD group. Correlations of Aβ42/Aβ40 and AβNpE3-42/AβNpE3-40 ratios with CAA severity were strong in DS cases and weak in AD cases. Pyroglutamate-modified Aβ levels were lower than unmodified Aβ levels in both diagnostic groups, but within group proportions of both pyroglutamate-modified Aβ forms relative to both unmodified Aβ forms were lower in the DS group but not in the AD group. The two diagnostic groups did not differ by ³H-PiB binding levels. These results demonstrate that compared to late-onset AD cases, adult DS individuals with similar severity of neocortical neuritic plaques and greater CAA pathology have a preponderance of both pyroglutamate-modified AβNpE3-40 and unmodified Aβ40 forms. Despite the distinct molecular profile of Aβ forms and greater vascular amyloidosis in DS cases, cortical ³H-PiB binding does not distinguish between diagnostic groups that are at an advanced level of amyloid plaque pathology. This underscores the need for the development of CAA-selective PET radiopharmaceuticals to detect and track the progression of cerebral vascular amyloid deposits in relation to Aβ plaques in individuals with DS.

Challenges in Alzheimer's Disease Diagnostic Work-Up: Amyloid Biomarker Incongruences

BACKGROUND

Discordance among amyloid biomarkers is a challenge to overcome in order to increase diagnostic accuracy in dementia.

OBJECTIVES

1) To verify that cerebrospinal fluid (CSF) Aβ42/Aβ40 ratio (AβR) better agrees with Amyloid PET (Amy-PET) results compared to CSF Aβ42; 2) to detect differences among concordant positive, concordant negative, and discordant cases, basing the concordance definition on the agreement between CSF AβR and Amy-PET results; 3) to define the suspected underlying pathology of discordant cases using in vivo biomarkers.

METHOD

We retrospectively enrolled 39 cognitively impaired participants in which neuropsychological tests, apolipoprotein E genotype determination, TC/MRI, FDG-PET, Amy-PET, and CSF analysis had been performed. In all cases, CSF analysis was repeated using the automated Lumipulse method. In discordant cases, FDG-PET scans were evaluated visually and using automated classifiers.

RESULTS

CSF AβR better agreed with Amy-PET compared to CSF Aβ42 (Cohen's K 0.431 versus 0.05). Comparisons among groups did not show any difference in clinical characteristics except for age at symptoms onset that was higher in the 6 discordant cases with abnormal CSF AβR values and negative Amy-PET (CSF AβR+/AmyPET-). FDG-PET and all CSF markers (Aβ42, AβR, p-Tau, t-Tau) were suggestive of Alzheimer's disease (AD) in 5 of these 6 cases.

CONCLUSION

1) CSF AβR is the CSF amyloid marker that shows the better level of agreement with Amy-PET results; 2) The use of FDG-PET and CSF-Tau markers in CSFAβR+/Amy-PET-discordant cases can support AD diagnosis; 3) Disagreement between positive CSF AβR and negative Amy-PET in symptomatic aged AD patients could be due to the variability in plaques conformation and a negative Amy-PET scan cannot be always sufficient to rule out AD.

Amyloid pathology and synaptic loss in pathological aging

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive memory dysfunction and cognitive decline. Pathological aging (PA) describes patients who are amyloid-positive but cognitively unimpaired at time of death. Both AD and PA contain amyloid plaques dominated by amyloid β (Aβ) peptides. In this study, we investigated and compared synaptic protein levels, amyloid plaque load, and Aβ peptide patterns between AD and PA. Two cohorts of post-mortem brain tissue were investigated. In the first, consisting of controls, PA, AD, and familial AD (FAD) individuals, synaptic proteins extracted with tris(hydroxymethyl)aminomethane-buffered saline (TBS) were analyzed. In the second, consisting of tissue from AD and PA patients from three different regions (occipital lobe, frontal lobe, and cerebellum), a two-step extraction was performed. Five synaptic proteins were extracted using TBS, and from the remaining portion Aβ peptides were extracted using formic acid. Subsequently, immunoprecipitation with several antibodies targeting different proteins/peptides was performed for both fractions, which were subsequently analyzed by mass spectrometry. The levels of synaptic proteins were lower in AD (and FAD) compared with PA (and controls), confirming synaptic loss in AD patients. The amyloid plaque load was increased in AD compared with PA, and the relative amount of Aβ40 was higher in AD while for Aβ42 it was higher in PA. In AD loss of synaptic function was associated with increased plaque load and increased amounts of Aβ40 compared with PA cases, suggesting that synaptic function is preserved in PA cases even in the presence of Aβ.

The Uppsala APP deletion causes early onset autosomal dominant Alzheimer's disease by altering APP processing and increasing amyloid β fibril formation

Point mutations in the amyloid precursor protein gene (APP) cause familial Alzheimer's disease (AD) by increasing generation or altering conformation of amyloid β (Aβ). Here, we describe the Uppsala APP mutation (Δ690-695), the first reported deletion causing autosomal dominant AD. Affected individuals have an age at symptom onset in their early forties and suffer from a rapidly progressing disease course. Symptoms and biomarkers are typical of AD, with the exception of normal cerebrospinal fluid (CSF) Aβ42 and only slightly pathological amyloid-positron emission tomography signals. Mass spectrometry and Western blot analyses of patient CSF and media from experimental cell cultures indicate that the Uppsala APP mutation alters APP processing by increasing β-secretase cleavage and affecting α-secretase cleavage. Furthermore, in vitro aggregation studies and analyses of patient brain tissue samples indicate that the longer form of mutated Aβ, AβUpp1-42_Δ19-24, accelerates the formation of fibrils with unique polymorphs and their deposition into amyloid plaques in the affected brain.

Nilsson KP. Thiophene-Based Optical Ligands That Selectively Detect Aβ Pathology in Alzheimer's Disease

In several neurodegenerative diseases, the presence of aggregates of specific proteins in the brain is a significant pathological hallmark; thus, developing ligands able to bind to the aggregated proteins is essential for any effort related to imaging and therapeutics. Here we report the synthesis of thiophene-based ligands containing nitrogen heterocycles. The ligands selectively recognized amyloid-β (Aβ) aggregates in brain tissue from individuals diagnosed neuropathologically as having Alzheimer's disease (AD). The selectivity for Aβ was dependent on the position of nitrogen in the heterocyclic compounds, and the ability to bind Aβ was shown to be reduced when introducing anionic substituents on the thiophene backbone. Our findings provide the structural and functional basis for the development of ligands that can differentiate between aggregated proteinaceous species comprised of distinct proteins. These ligands might also be powerful tools for studying the pathogenesis of Aβ aggregation and for designing molecules for imaging of Aβ pathology.

Refining the amyloid β peptide and oligomer fingerprint ambiguities in Alzheimer's disease: Mass spectrometric molecular characterization in brain, cerebrospinal fluid, blood, and plasma

Since its discovery, amyloid-β (Aβ) has been the principal target of investigation of in Alzheimer's disease (AD). Over the years however, no clear correlation was found between the Aβ plaque burden and location, and AD-associated neurodegeneration and cognitive decline. Instead, diagnostic potential of specific Aβ peptides and/or their ratio, was established. For instance, a selective reduction in the concentration of the aggregation-prone 42 amino acid-long Aβ peptide (Aβ42) in cerebrospinal fluid (CSF) was put forward as reflective of Aβ peptide aggregation in the brain. With time, Aβ oligomers-the proposed toxic Aβ intermediates-have emerged as potential drivers of synaptic dysfunction and neurodegeneration in the disease process. Oligomers are commonly agreed upon to come in different shapes and sizes, and are very poorly characterized when it comes to their composition and their "toxic" properties. The concept of structural polymorphism-a diversity in conformational organization of amyloid aggregates-that depends on the Aβ peptide backbone, makes the characterization of Aβ aggregates and their role in AD progression challenging. In this review, we revisit the history of Aβ discovery and initial characterization and highlight the crucial role mass spectrometry (MS) has played in this process. We critically review the common knowledge gaps in the molecular identity of the Aβ peptide, and how MS is aiding the characterization of higher order Aβ assemblies. Finally, we go on to present recent advances in MS approaches for characterization of Aβ as single peptides and oligomers, and convey our optimism, as to how MS holds a promise for paving the way for progress toward a more comprehensive understanding of Aβ in AD research.

Critical Appraisal of Amyloid Lowering Agents in AD

PURPOSE OF REVIEW

According to the amyloid cascade hypothesis, removing amyloid beta (Aβ) should cure Alzheimer's disease (AD). In the past three decades, many agents have been tested to try to lower Aβ production, prevent Aβ aggregation, and dissolve Aβ deposits. However, the paucity in definitive preventative or curative properties of these agents in clinical trials has resulted in more avant-garde approaches to therapeutic investigations. Immunotherapy has become an area of focus for research on disease-modifying therapies for neurodegenerative diseases. In this review, we highlight the current clinical development landscape of monoclonal antibody (mAb) therapies that target Aβ plaque formation and removal in AD.

RECENT FINDINGS

Multiple potential disease-modifying therapeutics for AD are in active development. Targeting Aβ with mAbs has the potential to treat various stages of AD: prodromal, prodromal to mild, mild, and mild to moderate. Monoclonal antibodies discussed here include aducanumab, lecanemab, solanezumab, crenezumab, donanemab, and gantenerumab. The final decision by the FDA regarding the approval of aducanumab will offer valuable insight into the trajectory of drug development for mAbs in AD and other neurodegenerative diseases. Future directions for improving the treatment of AD will include more inquiry into the efficacy of mAbs as disease-modifying agents that specifically target Aβ peptides and/or multimers. In addition, a more robust trial design for AD immunotherapy agents should improve outcomes such that objective measures of clinical efficacy will eventually lead to higher chances of drug approval.

Following spatial Aβ aggregation dynamics in evolving Alzheimer's disease pathology by imaging stable isotope labeling kinetics

β-Amyloid (Aβ) plaque formation is the major pathological hallmark of Alzheimer's disease (AD) and constitutes a potentially critical, early inducer driving AD pathogenesis as it precedes other pathological events and cognitive symptoms by decades. It is therefore critical to understand how Aβ pathology is initiated and where and when distinct Aβ species aggregate. Here, we used metabolic isotope labeling in APP^NL-G-F knock-in mice together with mass spectrometry imaging to monitor the earliest seeds of Aβ deposition through ongoing plaque development. This allowed visualizing Aβ aggregation dynamics within single plaques across different brain regions. We show that formation of structurally distinct plaques is associated with differential Aβ peptide deposition. Specifically, Aβ1-42 is forming an initial core structure followed by radial outgrowth and late secretion and deposition of Aβ1-38. These data describe a detailed picture of the earliest events of precipitating amyloid pathology at scales not previously possible.

Passive immunotherapy with a novel antibody against 3pE-modified Aβ demonstrates potential for enhanced efficacy and favorable safety in combination with BACE inhibitor treatment in plaque-depositing mice

The imbalance between production and clearance of amyloid β (Aβ) peptides and their resulting accumulation in the brain is an early and crucial step in the pathogenesis of Alzheimer's disease (AD). Therefore, Aβ is strongly positioned as a promising and extensively validated therapeutic target for AD. Investigational disease-modifying approaches aiming at reducing cerebral Aβ concentrations include prevention of de novo production of Aβ through inhibition of β-site amyloid precursor protein cleaving enzyme 1 (BACE1), and clearance of Aβ deposits via passive Aβ immunotherapy. We have developed a novel, high affinity antibody against Aβ peptides bearing a pyroglutamate residue at amino acid position 3 (3pE), an Aβ species abundantly present in plaque deposits in AD brains. Here, we describe the preclinical characterization of this antibody, and demonstrate a significant reduction in amyloid burden in the absence of microhemorrhages in different mouse models with established plaque deposition. Moreover, we combined antibody treatment with chronic BACE1 inhibitor treatment and demonstrate significant clearance of pre-existing amyloid deposits in transgenic mouse brain, without induction of microhemorrhages and other histopathological findings. Together, these data confirm significant potential for the 3pE-specific antibody to be developed as a passive immunotherapy approach that balances efficacy and safety. Moreover, our studies suggest further enhanced treatment efficacy and favorable safety after combination of the 3pE-specific antibody with BACE1 inhibitor treatment.

Quantification of N-terminal amyloid-β isoforms reveals isomers are the most abundant form of the amyloid-β peptide in sporadic Alzheimer's disease

Plaques that characterize Alzheimer’s disease accumulate over 20 years as a result of decreased clearance of amyloid-β peptides. Such long-lived peptides are subjected to multiple post-translational modifications, in particular isomerization. Using liquid chromatography ion mobility separations mass spectrometry, we characterized the most common isomerized amyloid-β peptides present in the temporal cortex of sporadic Alzheimer’s disease brains. Quantitative assessment of amyloid-β N-terminus revealed that > 80% of aspartates (Asp-1 and Asp-7) in the N-terminus was isomerized, making isomerization the most dominant post-translational modification of amyloid-β in Alzheimer’s disease brain. Total amyloid-β_1–15 was ∼85% isomerized at Asp-1 and/or Asp-7 residues, with only 15% unmodified amyloid-β_1–15 left in Alzheimer’s disease. While amyloid-β_4–15 the next most abundant N-terminus found in Alzheimer’s disease brain, was only ∼50% isomerized at Asp-7 in Alzheimer’s disease. Further investigations into different biochemically defined amyloid-β-pools indicated a distinct pattern of accumulation of extensively isomerized amyloid-β in the insoluble fibrillar plaque and membrane-associated pools, while the extent of isomerization was lower in peripheral membrane/vesicular and soluble pools. This pattern correlated with the accumulation of aggregation-prone amyloid-β₄₂ in Alzheimer’s disease brains. Isomerization significantly alters the structure of the amyloid-β peptide, which not only has implications for its degradation, but also for oligomer assembly, and the binding of therapeutic antibodies that directly target the N-terminus, where these modifications are located.

Acute targeting of pre-amyloid seeds in transgenic mice reduces Alzheimer-like pathology later in life

Amyloid-β (Aβ) deposits are a relatively late consequence of Aβ aggregation in Alzheimer's disease. When pathogenic Aβ seeds begin to form, propagate and spread is not known, nor are they biochemically defined. We tested various antibodies for their ability to neutralize Aβ seeds before Aβ deposition becomes detectable in Aβ precursor protein-transgenic mice. We also characterized the different antibody recognition profiles using immunoprecipitation of size-fractionated, native, mouse and human brain-derived Aβ assemblies. At least one antibody, aducanumab, after acute administration at the pre-amyloid stage, led to a significant reduction of Aβ deposition and downstream pathologies 6 months later. This demonstrates that therapeutically targetable pathogenic Aβ seeds already exist during the lag phase of protein aggregation in the brain. Thus, the preclinical phase of Alzheimer's disease-currently defined as Aβ deposition without clinical symptoms-may be a relatively late manifestation of a much earlier pathogenic seed formation and propagation that currently escapes detection in vivo.

Computational Analysis of Alzheimer Amyloid Plaque Composition in 2D- and Elastically Reconstructed 3D-MALDI MS Images

MALDI mass spectrometry imaging (MSI) enables label-free, spatially resolved analysis of a wide range of analytes in tissue sections. Quantitative analysis of MSI datasets is typically performed on single pixels or manually assigned regions of interest (ROIs). However, many sparse, small objects such as Alzheimer's disease (AD) brain deposits of amyloid peptides called plaques are neither single pixels nor ROIs. Here, we propose a new approach to facilitate the comparative computational evaluation of amyloid plaque-like objects by MSI: a fast PLAQUE PICKER tool that enables a statistical evaluation of heterogeneous amyloid peptide composition. Comparing two AD mouse models, APP NL-G-F and APP PS1, we identified distinct heterogeneous plaque populations in the NL-G-F model but only one class of plaques in the PS1 model. We propose quantitative metrics for the comparison of technical and biological MSI replicates. Furthermore, we reconstructed a high-accuracy 3D-model of amyloid plaques in a fully automated fashion, employing rigid and elastic MSI image registration using structured and plaque-unrelated reference ion images. Statistical single-plaque analysis in reconstructed 3D-MSI objects revealed the Aβ_1-42Arc peptide to be located either in the core of larger plaques or in small plaques without colocalization of other Aβ isoforms. In 3D, a substantially larger number of small plaques were observed than that indicated by the 2D-MSI data, suggesting that quantitative analysis of molecularly diverse sparsely-distributed features may benefit from 3D-reconstruction. Data are available via ProteomeXchange with identifier PXD020824.

Correlation of pyroglutamate amyloid β and ptau Ser202/Thr205 levels in Alzheimer's disease and related murine models

Senile plaques frequently contain Aβ-pE(3), a N-terminally truncated Aβ species that is more closely linked to AD compared to other Aβ species. Tau protein is highly phosphorylated at several residues in AD, and specifically phosphorylation at Ser202/Thr205 is known to be increased in AD. Several studies suggest that formation of plaques and tau phosphorylation might be linked to each other. To evaluate if Aβ-pE(3) and ptau Ser202/Thr205 levels correlate in human and transgenic AD mouse models, we analyzed human cortical and hippocampal brain tissue of different Braak stages as well as murine brain tissue of two transgenic mouse models for levels of Aβ-pE(3) and ptau Ser202/Thr205 and correlated the data. Our results show that Aβ-pE(3) formation is increased at early Braak stages while ptau Ser202/Thr205 mostly increases at later stages. Further analyses revealed strongest correlations between the two pathologies in the temporal, frontal, cingulate, and occipital cortex, however correlation in the hippocampus was weaker. Evaluation of murine transgenic brain tissue demonstrated a slow but steady increase of Aβ-pE(3) from 6 to 12 months of age in the cortex and hippocampus of APP_SL mice, and a very early and strong Aβ-pE(3) increase in 5xFAD mice. ptau Ser202/Thr205 levels increased at the age of 9 months in APP_SL mice and at 6 months in 5xFAD mice. Our results show that Aβ-pE(3) and ptau Ser202/Thr205 levels strongly correlate in human as well as murine tissues, suggesting that tau phosphorylation might be amplified by Aβ-pE(3).

University College London/University of Gothenburg PhD course "Biomarkers in neurodegenerative diseases" 2019-course organisation

Biomarkers are increasingly employed for effective research into neurodegenerative diseases. They have become essential for reaching an accurate clinical diagnosis, monitoring disease, and refining entry criteria for participation in clinical treatment trials, and will be key in measuring target engagement and treatment outcome in disease-modifying therapies. Emerging techniques and research combining different biomarker modalities continue to strengthen our understanding of the underlying pathology and the sequence of pathogenic events. Given recent advances, we are now at a pivotal stage in biomarker research. PhD students working in the field of neurodegenerative disease require a working knowledge of a range of biomarkers available and their limitations, to correctly interpret scientific literature and to design and conduct successful research studies themselves. Here, we outline the University College London/University of Gothenburg "Biomarkers in neurodegenerative diseases course", the first initiative of its kind aimed to bring together both experts and PhD students from all areas within the field of neurodegeneration, to provide comprehensive knowledge of biomarker research for the next generation of scientists.

Fibrillation of human islet amyloid polypeptide and its toxicity to pancreatic β-cells under lipid environment

BACKGROUND

Previous studies suggested that fibrillar human IAPP (hIAPP) is more likely to deposit in β-cells, resulting in β-cell injury. However, the changes in the conformation of hIAPP in lipid environment and the mechanism involved in β-cell damage are unclear.

METHODS

Synthetic hIAPP was incubated with five types of free fatty acids and phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (POPS), which constitute the cell membrane. Thioflavin-T fluorescence assay was conducted to analyze the degree of hIAPP fibrosis, and circular dichroism spectroscopy was performed to detect the β-fold formation of hIAPP. Furthermore, INS-1 cells were infected with human IAPP delivered by a GV230-EGFP plasmid. The effects of endogenous hIAPP overexpression induced by sodium palmitate on the survival, endoplasmic reticulum (ER) stress, and apoptosis of INS-1 cells were evaluated.

RESULTS

The five types of free fatty acids can accelerate the fibrosis of hIAPP. Sodium palmitate also maintained the stability of fibrillar hIAPP. POPS, not POPC, accelerated hIAPP fibrosis. Treatment of INS-1 cells with sodium palmitate increased the expression of hIAPP, activated ER stress and ER stress-dependent apoptosis signaling pathways, and increased the apoptotic rate.

CONCLUSION

Free fatty acids and anionic phospholipid can promote β-fold formation and fibrosis in hIAPP. High lipid induced the overexpression of hIAPP and aggravated ER stress and apoptosis in INS-1 cells, which caused β-cell death in high lipid environment.

GENERAL SIGNIFICANCE

Our study reveals free fatty acids and hIAPP synergistically implicated in endoplasmic reticulum stress and apoptosis of islet β-cells.