Modified amyloid variants in pathological subgroups of β-amyloidosis

Amyloid-beta antibody binding to cerebral amyloid angiopathy fibrils and risk for amyloid-related imaging abnormalities

Therapeutic antibodies have been developed to target amyloid-beta (Aβ), and some of these slow the progression of Alzheimer's disease (AD). However, they can also cause adverse events known as amyloid-related imaging abnormalities with edema (ARIA-E). We investigated therapeutic Aβ antibody binding to cerebral amyloid angiopathy (CAA) fibrils isolated from human leptomeningeal tissue to study whether this related to the ARIA-E frequencies previously reported by clinical trials. The binding of Aβ antibodies to CAA Aβ fibrils was evaluated in vitro using immunoprecipitation, surface plasmon resonance, and direct binding assay. Marked differences in Aβ antibody binding to CAA fibrils were observed. Solanezumab and crenezumab showed negligible CAA fibril binding and these antibodies have no reported ARIA-E cases. Lecanemab showed a low binding to CAA fibrils, consistent with its relatively low ARIA-E frequency of 12.6%, while aducanumab, bapineuzumab, and gantenerumab all showed higher binding to CAA fibrils and substantially higher ARIA-E frequencies (25-35%). An ARIA-E frequency of 24% was reported for donanemab, and its binding to CAA fibrils correlated with the amount of pyroglutamate-modified Aβ present. The findings of this study support the proposal that Aβ antibody-CAA interactions may relate to the ARIA-E frequency observed in patients treated with Aβ-based immunotherapies.

The Compartmentalization of Amyloid-β in Idiopathic Normal Pressure Hydrocephalus Brain Biopsies

Background

Amyloid-β (Aβ) is one of the hallmark lesions of Alzheimer's disease (AD). During the disease process, Aβ undergoes biochemical changes, producing toxic Aβ variants, proposed to be detected within the neurons. Idiopathic normal pressure hydrocephalus (iNPH) causes cognitive impairment, gait, and urinary symptoms in elderly, that can be reversed by a ventriculo-peritoneal shunt. Majority of iNPH subjects display different Aβ variants in their brain biopsies, obtained during shunting.

Objective

To study the cellular compartmentalization of different Aβ variants in brain biopsies from iNPH subjects.

Methods

We studied the cellular localization of different proteoforms of Aβ using antibodies towards different amino acid sequences or post-translational modifications of Aβ, including clones 4G8, 6F/3D, unmodified- (7H3D6), pyroglutamylated- (N3pE), phosphorylated-(1E4E11) Aβ and Aβ protein precursor (AβPP), in brain biopsies from 3 iNPH subjects, using immunohistochemistry and light microscopy (LM), light microscopy on semi-thin sections (LMst), and electron microscopy (EM).

Results

In LM all Aβ variants were detected. In LMst and EM, the Aβ 4G8, 6F/3D, and the pyroglutamylated Aβ were detected. The AβPP was visualized by all methods. The Aβ labelling was located extracellularly with no specific signal within the intracellular compartment, whereas the AβPP was seen both intra- and extracellularly.

Conclusions

The Aβ markers displayed extracellular localization when visualized by three assessment techniques, reflecting the pathological extracellular accumulation of Aβ in the human brain. No intracellular Aβ pathology was seen. AβPP was visualized in intra- and extracellularly, which corresponds to the localization of the protein in the membranes of cells and organelles.

Targeting protein kinases for the treatment of Alzheimer's disease: Recent progress and future perspectives

Alzheimer's disease (AD) is a serious neurodegenerative disease characterized by memory impairment, mental retardation, impaired motor balance, loss of self-care and even death. Among the complex and diverse pathological changes in AD, protein kinases are deeply involved in abnormal phosphorylation of Tau proteins to form intracellular neuronal fiber tangles, neuronal loss, extracellular β-amyloid (Aβ) deposits to form amyloid plaques, and synaptic disturbances. As a disease of the elderly, the growing geriatric population is directly driving the market demand for AD therapeutics, and protein kinases are potential targets for the future fight against AD. This perspective provides an in-depth look at the role of the major protein kinases (GSK-3β, CDK5, p38 MAPK, ERK1/2, and JNK3) in the pathogenesis of AD. At the same time, the development of different protein kinase inhibitors and the current state of clinical advancement are also outlined.

Matrix Development for the Detection of Phosphorylated Amyloid-β Peptides by MALDI-TOF-MS

Amyloid-β (Aβ) peptides, including post-translationally modified variants thereof, are believed to play a key role in the onset and progression of Alzheimer's disease. Suggested modified Aβ species with potential disease relevance include Aβ peptides phosphorylated at serine in position eight (pSer8-Aβ) or 26 (pSer26-Aβ). However, the published studies on those Aβ peptides essentially relied on antibody-based approaches. Thus, complementary analyses by mass spectrometry, as shown for other modified Aβ variants, will be necessary not only to unambiguously verify the existence of phosphorylated Aβ species in brain samples but also to reveal their exact identity as to phosphorylation sites and potential terminal truncations. With the aim of providing a novel tool for addressing this still-unresolved issue, we developed a customized matrix formulation, referred to as TOPAC, that allows for improved detection of synthetic phosphorylated Aβ species by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. When TOPAC was compared with standard matrices, we observed higher signal intensities but minimal methionine oxidation and phosphate loss for intact pSer8-Aβ(1-40) and pSer26-Aβ(1-40). Similarly, TOPAC also improved the mass spectrometric detection and sequencing of the proteolytic cleavage products pSer8-Aβ(1-16) and pSer26-Aβ(17-28). We expect that TOPAC will facilitate future efforts to detect and characterize endogenous phosphorylated Aβ species in biological samples and that it may also find its use in phospho-proteomic approaches apart from applications in the Aβ field.

Phosphorylation and Dephosphorylation of Beta-Amyloid Peptide in Model Cell Cultures: The Role of Cellular Protein Kinases and Phosphatases

Phosphorylation of beta-amyloid peptide (Aβ) at the Ser8 residue affects its neurotoxicity, metal-dependent oligomerisation, amyloidogenicity, and other pathogenic properties. Phosphorylated Aβ (pS8-Aβ) was detected in vivo in AD model mice and in the brains of patients with AD. However, the pS8-Aβ production and the regulation of its levels have not been previously studied in detail. In this paper, immunochemical methods together with radioactive labelling were used to study the Aβ phosphorylation by intracellular and surface protein kinases of HEK293 cells and brain endothelial cells (bEnd.3). It was found that HEK293 robustly phosphorylated Aβ, likely with contribution from casein kinase 2 (CK2), whereas in bEnd.3, the activity of Aβ phosphorylation was relatively low. Further, the study showed that both HEK293 and bEnd.3 could dephosphorylate pS8-Aβ, mainly due to the activity of protein phosphatases PP1 and PP2A. The Aβ dephosphorylation efficiency in bEnd.3 was three times higher than in HEK293, which correlated with the reduced abundance of pS8-Aβ in vascular amyloid deposits of patients with AD compared to senile plaques. These data suggest an important role of CK2, PP1, and PP2A as regulators of Aβ phosphorylation, and point to the involvement of the blood-brain barrier in the control of Aβ modification levels.

Hypertension and Alzheimer's disease pathology at autopsy: A systematic review

Hypertension is an important risk factor for Alzheimer's disease (AD) and all-cause dementia. The mechanisms underlying this association are unclear. Hypertension may be associated with AD neuropathological changes (ADNC), but reports are sparse and inconsistent. This systematic review included 15 autopsy studies (n = 5879) from observational cohorts. Studies were highly heterogeneous regarding populations, follow-up duration, hypertension operationalization, neuropathological methods, and statistical analyses. Hypertension seems associated with higher plaque and tangle burden, but results are inconsistent. Four studies (n = 3993/5879; 68%), reported clear associations between hypertension and ADNC. Another four suggested that antihypertensive medication may protect against ADNC. Larger studies with longer follow-up reported the strongest relationships. Our findings suggest a positive association between hypertension and ADNC, but effects may be modest, and possibly attenuate with higher hypertension age and antihypertensive medication use. Investigating interactions among plaques, tangles, cerebrovascular pathology, and dementia may be key in better understanding hypertension's role in dementia development.

Seeding, maturation and propagation of amyloid β-peptide aggregates in Alzheimer’s disease

Alzheimer’s disease is neuropathologically characterized by the deposition of the amyloid β-peptide (Aβ) as amyloid plaques. Aβ plaque pathology starts in the neocortex before it propagates into further brain regions. Moreover, Aβ aggregates undergo maturation indicated by the occurrence of post-translational modifications. Here, we show that propagation of Aβ plaques is led by presumably non-modified Aβ followed by Aβ aggregate maturation. This sequence was seen neuropathologically in human brains and in amyloid precursor protein transgenic mice receiving intracerebral injections of human brain homogenates from cases varying in Aβ phase, Aβ load and Aβ maturation stage. The speed of propagation after seeding in mice was best related to the Aβ phase of the donor, the progression speed of maturation to the stage of Aβ aggregate maturation. Thus, different forms of Aβ can trigger propagation/maturation of Aβ aggregates, which may explain the lack of success when therapeutically targeting only specific forms of Aβ.

TREM2 modulates differential deposition of modified and non-modified Aβ species in extracellular plaques and intraneuronal deposits

Progressive accumulation of Amyloid-β (Aβ) deposits in the brain is a characteristic neuropathological hallmark of Alzheimer’s disease (AD). During disease progression, extracellular Aβ plaques undergo specific changes in their composition by the sequential deposition of different modified Aβ species. Microglia are implicated in the restriction of amyloid deposits and play a major role in internalization and degradation of Aβ. Recent studies showed that rare variants of the Triggering Receptor Expressed on Myeloid cells 2 (TREM2) are associated with an increased risk for AD. Post-translational modifications of Aβ could modulate the interaction with TREM2, and the uptake by microglia. Here, we demonstrate that genetic deletion of TREM2 or expression of a disease associated TREM2 variant in mice lead to differential accumulation of modified and non-modified Aβ species in extracellular plaques and intraneuronal deposits. Human brains with rare TREM2 AD risk variants also showed altered deposition of modified Aβ species in the different brain lesions as compared to cases with the common variant of TREM2. These findings indicate that TREM2 plays a critical role in the development and the composition of Aβ deposits, not only in extracellular plaques, but also intraneuronally, that both could contribute to the pathogenesis of AD.

Differential interaction with TREM2 modulates microglial uptake of modified Aβ species

Rare coding variants of the microglial triggering receptor expressed on myeloid cells 2 (TREM2) confer an increased risk for Alzheimer's disease (AD) characterized by the progressive accumulation of aggregated forms of amyloid β peptides (Aβ). Aβ peptides are generated by proteolytic processing of the amyloid precursor protein (APP). Heterogeneity in proteolytic cleavages and additional post-translational modifications result in the production of several distinct Aβ variants that could differ in their aggregation behavior and toxic properties. Here, we sought to assess whether post-translational modifications of Aβ affect the interaction with TREM2. Biophysical and biochemical methods revealed that TREM2 preferentially interacts with oligomeric Aβ, and that phosphorylation of Aβ increases this interaction. Phosphorylation of Aβ also affected the TREM2 dependent interaction and phagocytosis by primary microglia and in APP transgenic mouse models. Thus, TREM2 function is important for sensing phosphorylated Aβ variants in distinct aggregation states and reduces the accumulation and deposition of these toxic Aβ species in preclinical models of Alzheimer's disease.

N-Terminally Truncated and Pyroglutamate-Modified Aβ Forms Are Measurable in Human Cerebrospinal Fluid and Are Potential Markers of Disease Progression in Alzheimer's Disease

Alzheimer's disease (AD) is a pathology characterized by the accumulation in the brain of intracellular and extracellular amyloid-β (Aβ) aggregates, especially of Aβ1-40 and Aβ1-42 peptides. It is known that N-terminally truncated or modified Aβ forms also exist in AD brains and cerebrospinal fluid (CSF), and they play a key role in the pathogenesis of the disease. Herein, we developed an antibody-free method based on Solid-Phase Extraction and Electrospray Ionization Liquid Chromatography Mass Spectrometry for the identification and quantitation in human CSF of Aβ isoforms. In human CSF, we could detect and quantify a panel of 19 Aβ isoforms, including N-terminally truncated and pyroglutamate-modified forms, never quantified before in CSF. Among these, we identified novel N-terminally truncated Aβ species: four bound to copper and two phosphorylated forms, which were found to be the most common proteoforms in human CSF along with Aβ1-40, Aβ3-40, and AβpE11-42. We tested the newly developed and validated method in a pilot study on CSF from elderly individuals with subjective memory complaints (SMCs, n = 9), mild cognitive impairment (MCI, n = 18), and AD (n = 15); along with Aβ1-42, five N-terminally truncated forms (Aβ11-40, Aβ3-42, AβpE11-42, AβpE3-40, and Aβ4-40 Cu²⁺) are altered in AD/MCI. Thus, we demonstrated that N-terminally truncated and pyroglutamate-modified Aβ can be quantified in human CSF, and five of them, along with Aβ1-42, are potential markers of AD progression. The described method could represent a useful tool for patients' stratification and monitoring. Moreover, the newly identified Aβ CSF species might represent new potential therapeutic targets.

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.

Tau pathologies mediate the association of blood pressure with cognitive impairment in adults without dementia: The CABLE study

INTRODUCTION

This study delineated the interrelationships among blood pressure (BP), cerebrospinal fluid (CSF) core biomarkers of Alzheimer's disease (AD), and cognition.

METHODS

The linear regression analyses were conducted in 1546 non-demented participants (mean age of 61.58 years, range 40 to 89 years; 40% female; average days of BP measurement, 9.10 days). Mediation analyses with 10,000 bootstrapped iterations were used to explore the mediation effects.

RESULTS

A clear age-related pattern of BP was delineated. Mid-life hypertension (especially systolic BP), late-life lower diastolic BP, as well as mid- and late-life higher pulse pressure were associated with cognitive impairment and tau-related biomarkers. BP variability was associated only with cognition but not with CSF biomarkers. Overall, the associations between BP and cognition were partially mediated (proportion: 11% to 30%) by tau pathologies, independently of amyloid pathology.

DISCUSSION

Tau pathologies might play important roles in the relationship between BP and cognition, with significant age- and BP-type dependences.

In vivo Characterization of Biochemical Variants of Amyloid-β in Subjects with Idiopathic Normal Pressure Hydrocephalus and Alzheimer's Disease Neuropathological Change

Background:

Stepwise occurrence of biochemically modified amyloid-β (Aβ) in the brain of subjects with Alzheimer’s disease (AD) has been suggested to be of significance for cognitive impairment. Our previous reports have shown that Aβ is observed in 63% of all subjects with idiopathic normal pressure hydrocephalus (iNPH) suggesting that the majority of iNPH subjects with Aβ are indeed also suffering from AD.

Objective:

We assessed the occurrence of biochemically modified Aβ variants, in vivo, in subjects with iNPH and in a cohort of postmortem brain samples from patients with dementia.

Methods:

We assessed Aβ proteins in 127 diagnostic brain biopsies obtained from subjects with iNPH and in a cohort of subjects with dementia by means of immunohistochemistry.

Results:

The pyroglutamylated Aβ (pyAβ) precedes the aggregation of phosphorylated Aβ (pAβ) during the AD neuropathological change progression; moreover, these modified variants of Aβ correlate with hyperphosphorylated tau in the frontal cortical area of human brain. Our results confirm the existence of the suggested biochemical stages of Aβ aggregation that might be of significance for neurodegeneration leading to cognitive impairment.

Conclusion:

The observation that both pyAβ and pAβ are seen in vivo in iNPH subjects is intriguing. It has been reported that most of the iNPH subjects with Aβ in the brain biopsy indeed develop AD with time. Based on our current and previous results, it is clinically merited to obtain a diagnostic biopsy from a subject with iNPH. When Aβ is observed in the biopsy, the biochemical characterization is of interest.

Insoluble Vascular Amyloid Deposits Trigger Disruption of the Neurovascular Unit in Alzheimer's Disease Brains

Alzheimer's disease (AD) is a neurodegenerative disease, characterized histopathologically by intra-neuronal tau-related lesions and by the accumulation of amyloid β-peptide (Aβ) in the brain parenchyma and around cerebral blood vessels. According to the vascular hypothesis of AD, an alteration in the neurovascular unit (NVU) could lead to Aβ vascular accumulation and promote neuronal dysfunction, accelerating neurodegeneration and dementia. To date, the effects of insoluble vascular Aβ deposits on the NVU and the blood-brain barrier (BBB) are unknown. In this study, we analyze different Aβ species and their association with the cells that make up the NVU. We evaluated post-mortem AD brain tissue. Multiple immunofluorescence assays were performed against different species of Aβ and the main elements that constitute the NVU. Our results showed that there are insoluble vascular deposits of both full-length and truncated Aβ species. Besides, insoluble aggregates are associated with a decrease in the phenotype of the cellular components that constitute the NVU and with BBB disruption. This approach could help identify new therapeutic targets against key molecules and receptors in the NVU that can prevent the accumulation of vascular fibrillar Aβ in AD.

Novel Phosphorylation-State Specific Antibodies Reveal Differential Deposition of Ser26 Phosphorylated Aβ Species in a Mouse Model of Alzheimer's Disease

Aggregation and deposition of amyloid-β (Aβ) peptides in extracellular plaques and in the cerebral vasculature are prominent neuropathological features of Alzheimer's disease (AD) and closely associated with the pathogenesis of AD. Amyloid plaques in the brains of most AD patients and transgenic mouse models exhibit heterogeneity in the composition of Aβ deposits, due to the occurrence of elongated, truncated, and post-translationally modified Aβ peptides. Importantly, changes in the deposition of these different Aβ variants are associated with the clinical disease progression and considered to mark sequential phases of plaque and cerebral amyloid angiopathy (CAA) maturation at distinct stages of AD. We recently showed that Aβ phosphorylated at serine residue 26 (pSer26Aβ) has peculiar characteristics in aggregation, deposition, and neurotoxicity. In the current study, we developed and thoroughly validated novel monoclonal and polyclonal antibodies that recognize Aβ depending on the phosphorylation-state of Ser26. Our results demonstrate that selected phosphorylation state-specific antibodies were able to recognize Ser26 phosphorylated and non-phosphorylated Aβ with high specificity in enzyme-linked immunosorbent assay (ELISA) and Western Blotting (WB) assays. Furthermore, immunofluorescence analyses with these antibodies demonstrated the occurrence of pSer26Aβ in transgenic mouse brains that show differential deposition as compared to non-phosphorylated Aβ (npAβ) or other modified Aβ species. Notably, pSer26Aβ species were faintly detected in extracellular Aβ plaques but most prominently found intraneuronally and in cerebral blood vessels. In conclusion, we developed new antibodies to specifically differentiate Aβ peptides depending on the phosphorylation state of Ser26, which are applicable in ELISA, WB, and immunofluorescence staining of mouse brain tissues. These site- and phosphorylation state-specific Aβ antibodies represent novel tools to examine phosphorylated Aβ species to further understand and dissect the complexity in the age-related and spatio-temporal deposition of different Aβ variants in transgenic mouse models and human AD brains.

The coarse-grained plaque: a divergent Aβ plaque-type in early-onset Alzheimer's disease

Alzheimer's disease (AD) is characterized by amyloid-beta (Aβ) deposits, which come in myriad morphologies with varying clinical relevance. Previously, we observed an atypical Aβ deposit, referred to as the coarse-grained plaque. In this study, we evaluate the plaque's association with clinical disease and perform in-depth immunohistochemical and morphological characterization. The coarse-grained plaque, a relatively large (Ø ≈ 80 µm) deposit, characterized as having multiple cores and Aβ-devoid pores, was prominent in the neocortex. The plaque was semi-quantitatively scored in the middle frontal gyrus of Aβ-positive cases (n = 74), including non-demented cases (n = 15), early-onset (EO)AD (n = 38), and late-onset (LO)AD cases (n = 21). The coarse-grained plaque was only observed in cases with clinical dementia and more frequently present in EOAD compared to LOAD. This plaque was associated with a homozygous APOE ε4 status and cerebral amyloid angiopathy (CAA). In-depth characterization was done by studying the coarse-grained plaque's neuritic component (pTau, APP, PrP^C), Aβ isoform composition (Aβ₄₀, Aβ₄₂, Aβ_N3pE, pSer8Aβ), its neuroinflammatory component (C4b, CD68, MHC-II, GFAP), and its vascular attribution (laminin, collagen IV, norrin). The plaque was compared to the classic cored plaque, cotton wool plaque, and CAA. Similar to CAA but different from classic cored plaques, the coarse-grained plaque was predominantly composed of Aβ₄₀. Furthermore, the coarse-grained plaque was distinctly associated with both intense neuroinflammation and vascular (capillary) pathology. Confocal laser scanning microscopy (CLSM) and 3D analysis revealed for most coarse-grained plaques a particular Aβ₄₀ shell structure and a direct relation with vessels. Based on its morphological and biochemical characteristics, we conclude that the coarse-grained plaque is a divergent Aβ plaque-type associated with EOAD. Differences in Aβ processing and aggregation, neuroinflammatory response, and vascular clearance may presumably underlie the difference between coarse-grained plaques and other Aβ deposits. Disentangling specific Aβ deposits between AD subgroups may be important in the search for disease-mechanistic-based therapies.

Phosphorylated Aβ peptides in human Down syndrome brain and different Alzheimer's-like mouse models

The deposition of neurotoxic amyloid-β (Aβ) peptides in extracellular plaques in the brain parenchyma is one of the most prominent neuropathological features of Alzheimer's disease (AD), and considered to be closely related to the pathogenesis of this disease. A number of recent studies demonstrate the heterogeneity in the composition of Aβ deposits in AD brains, due to the occurrence of elongated, truncated and post-translationally modified Aβ peptides that have peculiar characteristics in aggregation behavior and biostability. Importantly, the detection of modified Aβ species has been explored to characterize distinct stages of AD, with phosphorylated Aβ being present in the clinical phase of AD. People with Down syndrome (DS) develop AD pathology by 40 years of age likely due to the overproduction of Aβ caused by the additional copy of the gene encoding the amyloid precursor protein on chromosome 21. In the current study, we analysed the deposition of phosphorylated and non-phosphorylated Aβ species in human DS, AD, and control brains. In addition, deposition of these Aβ species was analysed in brains of a series of established transgenic AD mouse models using phosphorylation-state specific Aβ antibodies. Significant amounts of Aβ phosphorylated at serine residue 8 (pSer8Aβ) and unmodified Aβ were detected in the brains of DS and AD cases. The brains of different transgenic mouse models with either only human mutant amyloid precursor protein (APP), or combinations of human mutant APP, Presenilin (PS), and tau transgenes showed distinct age-dependent and spatiotemporal deposition of pSer8Aβ in extracellular plaques and within the vasculature. Together, these results demonstrate the deposition of phosphorylated Aβ species in DS brains, further supporting the similarity of Aβ deposition in AD and DS. Thus, the detection of phosphorylated and other modified Aβ species could contribute to the understanding and dissection of the complexity in the age-related and spatiotemporal deposition of Aβ variants in AD and DS as well as in distinct mouse models.

Development of the clinical candidate PBD-C06, a humanized pGlu3-Aβ-specific antibody against Alzheimer's disease with reduced complement activation

In clinical trials with early Alzheimer's patients, administration of anti-amyloid antibodies reduced amyloid deposits, suggesting that immunotherapies may be promising disease-modifying interventions against Alzheimer's disease (AD). Specific forms of amyloid beta (Aβ) peptides, for example post-translationally modified Aβ peptides with a pyroglutamate at the N-terminus (pGlu3, pE3), are attractive antibody targets, due to pGlu3-Aβ's neo-epitope character and its propensity to form neurotoxic oligomeric aggregates. We have generated a novel anti-pGlu3-Aβ antibody, PBD-C06, which is based on a murine precursor antibody that binds with high specificity to pGlu3-Aβ monomers, oligomers and fibrils, including mixed aggregates of unmodified Aβ and pGlu3-Aβ peptides. PBD-C06 was generated by first grafting the murine antigen binding sequences onto suitable human variable light and heavy chains. Subsequently, the humanized antibody was de-immunized and site-specific mutations were introduced to restore original target binding, to eliminate complement activation and to improve protein stability. PBD-C06 binds with the same specificity and avidity as its murine precursor antibody and elimination of C1q binding did not compromise Fcγ-receptor binding or in vitro phagocytosis. Thus, PBD-C06 was specifically designed to target neurotoxic aggregates and to avoid complement-mediated inflammatory responses, in order to lower the risk for vasogenic edemas in the clinic.

Different aspects of Alzheimer's disease-related amyloid β-peptide pathology and their relationship to amyloid positron emission tomography imaging and dementia

Alzheimer’s disease (AD)-related amyloid β-peptide (Aβ) pathology in the form of amyloid plaques and cerebral amyloid angiopathy (CAA) spreads in its topographical distribution, increases in quantity, and undergoes qualitative changes in its composition of modified Aβ species throughout the pathogenesis of AD. It is not clear which of these aspects of Aβ pathology contribute to AD progression and to what extent amyloid positron emission tomography (PET) reflects each of these aspects. To address these questions three cohorts of human autopsy cases (in total n = 271) were neuropathologically and biochemically examined for the topographical distribution of Aβ pathology (plaques and CAA), its quantity and its composition. These parameters were compared with neurofibrillary tangle (NFT) and neuritic plaque pathology, the degree of dementia and the results from [¹⁸F]flutemetamol amyloid PET imaging in cohort 3. All three aspects of Aβ pathology correlated with one another, the estimation of Aβ pathology by [¹⁸F]flutemetamol PET, AD-related NFT pathology, neuritic plaques, and with the degree of dementia. These results show that one aspect of Aβ pathology can be used to predict the other two, and correlates well with the development of dementia, advancing NFT and neuritic plaque pathology. Moreover, amyloid PET estimates all three aspects of Aβ pathology in-vivo. Accordingly, amyloid PET-based estimates for staging of amyloid pathology indicate the progression status of amyloid pathology in general and, in doing so, also of AD pathology. Only 7.75% of our cases deviated from this general association.

Amyloid precursor protein-fragments-containing inclusions in cardiomyocytes with basophilic degeneration and its association with cerebral amyloid angiopathy and myocardial fibrosis

Cardiomyopathies with intracellular inclusions are a distinct subset of cardiomyopathies whereas basophilic degeneration (BD) of the heart describes inclusions in cardiomyocytes of the aging heart, which have not yet been related to a specific disease condition or to a distinct type of protein inclusion. To address the question whether BD represents a specific pathological feature and whether it is linked to a distinct disease condition we studied 62 autopsy cases. BD inclusions exhibited an immunohistochemical staining pattern related to glycosylated, δ- or η-secretase-derived N-terminal cleavage products of the amyloid precursor protein (sAPPδ/η) or shorter fragments of sAPPη. BD aggregates were found in the myocardium of both ventricles and atria with highest amounts in the atria and lowest in the interventricular septum. The frequency of BD-lesions correlated with age, degree of myocardial fibrosis in individuals with arterial hypertension, and the severity of cerebral amyloid angiopathy (CAA). The intracytoplasmic deposition of N-terminal sAPPδ/η fragments in BD indicates a specific inclusion body pathology related to APP metabolism. The correlation with the severity of CAA, which is related to the APP-derived amyloid β-protein, supports this point of view and suggests a possible link between myocardial and cerebrovascular APP-related lesions.