The isolation and amino acid composition of senile plaque core protein

The past, present and future of Alzheimer's disease - part 1: the past

BACKGROUND

 Alzheimer's disease (AD) was described in 1907, and since then it changed from a relatively rare condition to one of the most prevalent diseases.

OBJECTIVE

 To describe the evolution of the notions of dementias and AD, and to investigate the reasons for the increase in scientific interest in AD.

METHODS

 A historical analysis was carried out on knowledge about dementia, the site of mental activity, the relationships between brain diseases and mental activity, and on the advances in research about AD, since its discovery until the publication of the amyloid cascade hypothesis in 1992. A search was carried out in the National Library of Medicine (PubMed) for scientific articles that included the terms dementia or AD over 50 years, from 1972 to 2021.

RESULTS

 The scientific research on AD increased from 615 papers with the term AD in the first decade (1972-1981), to 100,028 papers in the last decade (2012-2021): an increase of 162.6 times whereas publications with the term dementia increased 28.6 times in the same period. In the 1960s and 1970s, a consensus was reached that AD is responsible for the majority of cases of dementia previously known as senile dementia. In the 1980s, beta-amyloid peptide was identified in the core of the senile plaque, hyperphosphorylated tau protein was found in neurofibrillary tangles, and a mutation was discovered in a hereditary form of AD.

CONCLUSION

 The expansion of the concept of AD to include senile dementia, and the discoveries that occurred in the 1980s greatly expanded research in AD.

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.

Methods for the isolation and analysis of Aβ from postmortem brain

Amyloid β-protein (Aβ) plays an initiating role in Alzheimer's disease (AD), but only a small number of groups have studied Aβ extracted from human brain. Most prior studies have utilized synthetic Aβ peptides, but the relevance of these test tube experiments to the conditions that prevail in AD is uncertain. Here, we describe three distinct methods for studying Aβ from cortical tissue. Each method allows the analysis of different ranges of species thus enabling the examination of different questions. The first method allows the study of readily diffusible Aβ with a relatively high specific activity. The second enables the analysis of readily solubilized forms of Aβ the majority of which are inactive. The third details the isolation of true Aβ dimers which have disease-related activity. We also describe a bioassay to study the effects of Aβ on the neuritic integrity of iPSC-derived human neurons. The combined use of this bioassay and the described extraction procedures provides a platform to investigate the activity of different forms and mixtures of Aβ species, and offers a tractable system to identify strategies to mitigate Aβ mediated neurotoxicity.

Targeting the cannabinoid system to counteract the deleterious effects of stress in Alzheimer’s disease

Alzheimer’s disease is a progressive neurodegenerative disorder characterized histologically in postmortem human brains by the presence of dense protein accumulations known as amyloid plaques and tau tangles. Plaques and tangles develop over decades of aberrant protein processing, post-translational modification, and misfolding throughout an individual’s lifetime. We present a foundation of evidence from the literature that suggests chronic stress is associated with increased disease severity in Alzheimer’s patient populations. Taken together with preclinical evidence that chronic stress signaling can precipitate cellular distress, we argue that chronic psychological stress renders select circuits more vulnerable to amyloid- and tau- related abnormalities. We discuss the ongoing investigation of systemic and cellular processes that maintain the integrity of protein homeostasis in health and in degenerative conditions such as Alzheimer’s disease that have revealed multiple potential therapeutic avenues. For example, the endogenous cannabinoid system traverses the central and peripheral neural systems while simultaneously exerting anti-inflammatory influence over the immune response in the brain and throughout the body. Moreover, the cannabinoid system converges on several stress-integrative neuronal circuits and critical regions of the hypothalamic-pituitary-adrenal axis, with the capacity to dampen responses to psychological and cellular stress. Targeting the cannabinoid system by influencing endogenous processes or exogenously stimulating cannabinoid receptors with natural or synthetic cannabis compounds has been identified as a promising route for Alzheimer’s Disease intervention. We build on our foundational framework focusing on the significance of chronic psychological and cellular stress on the development of Alzheimer’s neuropathology by integrating literature on cannabinoid function and dysfunction within Alzheimer’s Disease and conclude with remarks on optimal strategies for treatment potential.

A History of Senile Plaques: From Alzheimer to Amyloid Imaging

Senile plaques have been studied in postmortem brains for more than 120 years and the resultant knowledge has not only helped us understand the etiology and pathogenesis of Alzheimer disease (AD), but has also pointed to possible modes of prevention and treatment. Within the last 15 years, it has become possible to image plaques in living subjects. This is arguably the single greatest advance in AD research since the identification of the Aβ peptide as the major plaque constituent. The limitations and potentialities of amyloid imaging are still not completely clear but are perhaps best glimpsed through the perspective gained from the accumulated postmortem histological studies. The basic morphological classification of plaques into neuritic, cored and diffuse has been supplemented by sophisticated immunohistochemical and biochemical analyses and increasingly detailed mapping of plaque brain distribution. Changes in plaque classification and staging have in turn contributed to changes in the definition and diagnostic criteria for AD. All of this information continues to be tested by clinicopathological correlations and it is through the insights thereby gained that we will best be able to employ the powerful tool of amyloid imaging.

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.

Progress toward Alzheimer's disease treatment: Leveraging the Achilles' heel of Aβ oligomers?

After three decades of false hopes and failures, a pipeline of therapeutic drugs that target the actual root cause of Alzheimer's disease (AD) is now available. Challenging the old paradigm that focused on β-amyloid peptide (Aβ) aggregation in amyloid plaques, these compounds are designed to prevent the neurotoxicity of Aβ oligomers that form Ca²⁺ permeable pores in the membranes of brain cells. By triggering an intracellular Ca²⁺ overdose, Aβ oligomers induce a cascade of neurotoxic events including oxidative stress, tau hyperphosphorylation, and neuronal loss. Targeting any post-Ca²⁺ entry steps (e.g., tau) will not address the root cause of the disease. Thus, preventing Aβ oligomers formation and/or blocking their toxicity is by essence the best approach to stop any progression of AD. Three categories of anti-oligomer compounds are already available: antibodies, synthetic peptides, and small drugs. Independent in silico-based designs of a peptide (AmyP53) and a monoclonal antibody (PMN310) converged to identify a histidine motif (H13/H14) that is critical for oligomer neutralization. This "histidine trick" can be viewed as the Achilles' heel of Aβ in the fight against AD. Moreover, lipid rafts and especially gangliosides play a critical role in the formation and toxicity of Aβ oligomers. Recognizing AD as a membrane disorder and gangliosides as the key anti-oligomer targets will provide innovative opportunities to find an efficient cure. A "full efficient" solution would also need to be affordable to anyone, as the number of patients has been following an exponential increase, affecting every part of the globe.

An agnostic reevaluation of the amyloid cascade hypothesis of Alzheimer's disease pathogenesis: The role of APP homeostasis

OBJECTIVE

To reassess the role of amyloid beta (Aβ) and the amyloid precursor protein (APP) system in the pathogenesis of Alzheimer's disease (AD).

BACKGROUND

APP is a cell adhesion molecule that has been highly conserved over the course of phylogeny that has critical roles in brain development, synaptic plasticity, and the brain's intrinsic immune system. The amyloid cascade hypothesis describes a relatively linear, deterministic sequence of events triggered by a gain of Aβ peptide fragment toxicity that results in neurodegeneration and cognitive loss, yet well designed immunotherapy and beta secretase inhibitor trials that have successfully targeted Aβ have failed to have any consistent effects on the steady decline of cognition.

NEW/UPDATED HYPOTHESIS

Mutations of the APP and presenilin genes not only alter the ratio of longer to shorter Aβ fragments (resulting in a gain of Aβ toxicity), but also disrupt the normal homeostatic roles of their respective proteins. The evolutionary history, physiological importance, and complexity of the APP and presenilin systems, as well as other critical components including tau and apolipoprotein E (APOE) imply that altered function of such systems could have severe consequences that include but need not be limited to a gain of Aβ toxicity and would more generally result in altered homeostasis of APP-related functions.

MAJOR CHALLENGES ADDRESSED BY OUR HYPOTHESIS

Challenges that a loss of APP homeostasis addresses better than the more limited gain of Aβ toxicity model include the topographic mismatches between Aβ and tau pathology, the profile and chronology of cognitive and biomarker changes that precede the clinical expression of mild cognitive impairment and dementia, and the disappointments of Aβ targeted therapeutics among others.

LINKAGE TO OTHER MAJOR THEORIES

The importance of APP, α- and β-secretases, the presenilins and γ-secretase, as well as tau was recognized by the authors of the amyloid cascade hypothesis, and has since led multiple investigators to propose alternative, more balanced hypotheses including reduced homeostasis and frank loss-of-function of key components that include but go beyond the currently envisioned linear model of Aβ toxicity.

Bisphosphonates: Future perspective for neurological disorders

Neurodegenerative disorders and osteoporosis share some common underlying pathological features including calcium overload, accumulation of toxic chemicals, inflammation and impaired protein prenylation by isoprenoids (farnesyl pyrophosphate and geranylgeranyl pyrophosphate) appear later stage of life. Substantial number of pre-clinical and clinical reports as well as in vitro data univocally acknowledged the negative impact of altered post-translational modification (prenylation) of proteins like small GTPases (Rffhes, Rho, Rac etc.) and cholesterol levels in both serum and brain on CNS integrity. Bisphosphonates (BPs), referred to as gold standard for osteoporosis treatment, have well established role in attenuation of bone resorption and osteoclast apoptosis by inhibition of farnesyl pyrophosphate synthase enzyme (FPPS) in mevalonate pathway. BPs mainly nitrogen containing BPs (NBPs) have potential to offer new therapeutic targets for neurological disorders and received increasing attention in recent years. A year back clinical and pre-clinical studies revealed that NBPs have the potential to alleviate the symptoms of neurological disorders like brain calcification, Alzheimer's disease and Huntington's disease by targeting mevalonate pathway. Though these drugs have well developed role in inhibition of isoprenoids synthesis, these were demonstrated to inhibit acetyl cholinesterase enzyme and cholesterol synthesis in brain that are considered as the critical factors for impairment of cognitive functions which is the hallmark of several neurological disorders. Still the current understanding of BPs' effect in CNS is limited due to lack of studies focusing the molecular and cellular mechanism. The present review aims to reveal the updated discussion on the mechanism contributing BPs' effect in CNS disorders.

Aβ Amyloid Pathology Affects the Hearts of Patients With Alzheimer's Disease: Mind the Heart

BACKGROUND

Individually, heart failure (HF) and Alzheimer's disease (AD) are severe threats to population health, and their potential coexistence is an alarming prospect. In addition to sharing analogous epidemiological and genetic profiles, biochemical characteristics, and common triggers, the authors recently recognized common molecular and pathological features between the 2 conditions. Whereas cognitive impairment has been linked to HF through perfusion defects, angiopathy, and inflammation, whether patients with AD present with myocardial dysfunction, and if the 2 conditions bear a common pathogenesis as neglected siblings are unknown.

OBJECTIVES

Here, the authors investigated whether amyloid beta (Aβ) protein aggregates are present in the hearts of patients with a primary diagnosis of AD, affecting myocardial function.

METHODS

The authors examined myocardial function in a retrospective cross-sectional study from a cohort of AD patients and age-matched controls. Imaging and proteomics approaches were used to identify and quantify Aβ deposits in AD heart and brain specimens compared with controls. Cell shortening and calcium transients were measured on isolated adult cardiomyocytes.

RESULTS

Echocardiographic measurements of myocardial function suggest that patients with AD present with an anticipated diastolic dysfunction. As in the brain, Aβ₄₀ and Aβ₄₂ are present in the heart, and their expression is increased in AD.

CONCLUSIONS

Here, the authors provide the first report of the presence of compromised myocardial function and intramyocardial deposits of Aβ in AD patients. The findings depict a novel biological framework in which AD may be viewed either as a systemic disease or as a metastatic disorder leading to heart, and possibly multiorgan failure. AD and HF are both debilitating and life-threatening conditions, affecting enormous patient populations. Our findings underline a previously dismissed problem of a magnitude that will require new diagnostic approaches and treatments for brain and heart disease, and their combination.

Effects of an amyloid-beta 1-42 oligomers antibody screened from a phage display library in APP/PS1 transgenic mice

We screened anti-Aβ1-42 antibodies from a human Alzheimer's disease (AD) specific single chain variable fragment (scFv) phage display library and assessed their effects in APP/PS1 transgenic mice. Reverse transcription-PCR was used to construct the scFv phage display library, and screening identified 11A5 as an anti-Aβ1-42 antibody. We mixed 11A5 and the monoclonal antibody 6E10 with Aβ1-42 and administered the mixture to Sprague-Dawley rats via intracerebroventricular injection. After 30 days, rats injected with the antibody/Aβ1-42 mixture and those injected with Aβ1-42 alone were tested on the Morris water maze. We also injected 11A5 and 6E10 into APP/PS1 transgenic mice and assessed the concentrations of Aβ in brain and peripheral blood by ELISA at 1-month intervals for 3 months. Finally we evaluated behavior changes in the Morris water maze. Rats injected with Aβ1-42 and mixed antibodies showed better performance in the Morris water maze than did rats injected with Aβ1-42 alone. In APP/PS1 transgenic mice, Aβ concentration was lower in the brains of the antibody-treated group than in the control group, but higher in the peripheral blood. The antibody-treated mice also exhibited improved behavioral performance in the Morris water maze. In conclusion, anti-Aβ1-42 antibodies (11A5) screened from the human scFv antibody phage display library promoted the efflux or clearance of Aβ1-42 and effectively decreased the cerebral Aβ burden in an AD mouse model.

The role and therapeutic targeting of α-, β- and γ-secretase in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly and its prevalence is set to increase rapidly in coming decades. However, there are as yet no available drugs that can halt or even stabilize disease progression. One of the main pathological features of AD is the presence in the brain of senile plaques mainly composed of aggregated β amyloid (Aβ), a derivative of the longer amyloid precursor protein (APP). The amyloid hypothesis proposes that the accumulation of Aβ within neural tissue is the initial event that triggers the disease. Here we review research efforts that have attempted to inhibit the generation of the Aβ peptide through modulation of the activity of the proteolytic secretases that act on APP and discuss whether this is a viable therapeutic strategy for treating AD.

Cerebrospinal fluid levels of amyloid precursor protein are associated with ventricular size in post-hemorrhagic hydrocephalus of prematurity

Background

Neurological outcomes of preterm infants with post-hemorrhagic hydrocephalus (PHH) remain among the worst in infancy, yet there remain few instruments to inform the treatment of PHH. We previously observed PHH-associated elevations in cerebrospinal fluid (CSF) amyloid precursor protein (APP), neural cell adhesion molecule-L1 (L1CAM), neural cell adhesion molecule-1 (NCAM-1), and other protein mediators of neurodevelopment.

Objective

The objective of this study was to examine the association of CSF APP, L1CAM, and NCAM-1 with ventricular size as an early step toward developing CSF markers of PHH.

Methods

CSF levels of APP, L1CAM, NCAM-1, and total protein (TP) were measured in 12 preterm infants undergoing PHH treatment. Ventricular size was determined using cranial ultrasounds. The relationships between CSF APP, L1CAM, and NCAM-1, occipitofrontal circumference (OFC), volume of CSF removed, and ventricular size were examined using correlation and regression analyses.

Results

CSF levels of APP, L1CAM, and NCAM-1 but not TP paralleled treatment-related changes in ventricular size. CSF APP demonstrated the strongest association with ventricular size, estimated by frontal-occipital horn ratio (FOR) (Pearson R = 0.76, p = 0.004), followed by NCAM-1 (R = 0.66, p = 0.02) and L1CAM (R = 0.57,p = 0.055). TP was not correlated with FOR (R = 0.02, p = 0.95).

Conclusions

Herein, we report the novel observation that CSF APP shows a robust association with ventricular size in preterm infants treated for PHH. The results from this study suggest that CSF APP and related proteins at once hold promise as biomarkers of PHH and provide insight into the neurological consequences of PHH in the preterm infant.

Inconsistencies and controversies surrounding the amyloid hypothesis of Alzheimer's disease

The amyloid hypothesis has driven drug development strategies for Alzheimer's disease for over 20 years. We review why accumulation of amyloid-beta (Aβ) oligomers is generally considered causal for synaptic loss and neurodegeneration in AD. We elaborate on and update arguments for and against the amyloid hypothesis with new data and interpretations, and consider why the amyloid hypothesis may be failing therapeutically. We note several unresolved issues in the field including the presence of Aβ deposition in cognitively normal individuals, the weak correlation between plaque load and cognition, questions regarding the biochemical nature, presence and role of Aβ oligomeric assemblies in vivo, the bias of pre-clinical AD models toward the amyloid hypothesis and the poorly explained pathological heterogeneity and comorbidities associated with AD. We also illustrate how extensive data cited in support of the amyloid hypothesis, including genetic links to disease, can be interpreted independently of a role for Aβ in AD. We conclude it is essential to expand our view of pathogenesis beyond Aβ and tau pathology and suggest several future directions for AD research, which we argue will be critical to understanding AD pathogenesis.

Amyloid beta: multiple mechanisms of toxicity and only some protective effects?

Amyloid beta (Aβ) is a peptide of 39–43 amino acids found in large amounts and forming deposits in the brain tissue of patients with Alzheimer's disease (AD). For this reason, it has been implicated in the pathophysiology of damage observed in this type of dementia. However, the role of Aβ in the pathophysiology of AD is not yet precisely understood. Aβ has been experimentally shown to have a wide range of toxic mechanisms in vivo and in vitro, such as excitotoxicity, mitochondrial alterations, synaptic dysfunction, altered calcium homeostasis, oxidative stress, and so forth. In contrast, Aβ has also shown some interesting neuroprotective and physiological properties under certain experimental conditions, suggesting that both physiological and pathological roles of Aβ may depend on several factors. In this paper, we reviewed both toxic and protective mechanisms of Aβ to further explore what their potential roles could be in the pathophysiology of AD. The complete understanding of such apparently opposed effects will also be an important guide for the therapeutic efforts coming in the future.

Atomic force microscopy to study molecular mechanisms of amyloid fibril formation and toxicity in Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by dementia and memory loss for which no cure or effective prevention is currently available. Neurodegeneration in AD is linked to formation of amyloid plaques found in brain tissues of Alzheimer's patients during post-mortem examination. Amyloid plaques are composed of amyloid fibrils and small oligomers - insoluble protein aggregates. Although amyloid plaques are found on the neuronal cell surfaces, the mechanism of amyloid toxicity is still not well understood. Currently, it is believed that the cytotoxicity is a result of the nonspecific interaction of small soluble amyloid oligomers (rather than longer fibrils) with the plasma membrane. In recent years, nanotechnology has contributed significantly to understanding the structure and function of lipid membranes and to the study of the molecular mechanisms of membrane-associated diseases. We review the current state of research, including applications of the latest nanotechnology approaches, on the interaction of lipid membranes with the amyloid-β (Aβ) peptide in relation to amyloid toxicity. We discuss the interactions of Aβ with model lipid membranes with a focus to demonstrate that composition, charge and phase of the lipid membrane, as well as lipid domains and rafts, affect the binding of Aβ to the membrane and contribute to toxicity. Understanding the role of the lipid membrane in AD at the nanoscale and molecular level will contribute to the understanding of the molecular mechanism of amyloid toxicity and may aid into the development of novel preventive strategies to combat AD.

Simultaneous determination of post-translational racemization and isomerization of N-terminal amyloid-β in Alzheimer's brain tissues by covalent chiral derivatized ultraperformance liquid chromatography tandem mass spectrometry

Typical markers of protein aging are spontaneous post-translational modifications such as amino acid racemization (AAR) and amino acid isomerization (AAI) during the degradation of peptides. The post-translational AAR and AAI could significantly induce the density and localization of plaque deposition in brain tissues. Alzheimer's disease (AD) is reliably related to the formation and aggregation of amyloid-β peptide (Aβ) plaques in the human brain. No current analytical methods can simultaneously determine AAR and AAI during the degradation of Aβ from AD patients. We now report a covalent chiral derivatized ultraperformance liquid chromatography tandem mass spectrometry (CCD-UPLC-MS/MS) method for the determination of post-translational AAR and AAI of N-terminal Aβ (N-Aβ1-5) in human brain tissues. When subjected to tryptic N-Aβ1-5 from post-translationally modified natural Aβ in focal brain tissues by the CCD procedure, it was monitored at m/z 989.6→637.0/678.9 during electrospray collision-induced dissociation. These N-Aβ1-5 fragments with l-aspartic acid (l-Asp), d-Asp, l-isoAsp, and d-isoAsp could be separated using the UPLC system with a conventional reversed-phase column and mobile phase. The quantification of these peptides was determined using a stable isotope [(15)N]-labeled Aβ1-40 internal standard. The CCD-UPLC-MS/MS assay of potential N-Aβ1-5 allowed for the discovery of the present and ratio levels of these N-Aβ1-5 sequences with l-Asp, d-Asp, l-isoAsp, and d-isoAsp.

[Genetic aspects of Alzheimer's disease (Review)]

Alzheimer's disease is a degenerative brain disorder, which concerns memory, cognition and behavior pattern. Its etiology is unknown, it is characterized by typical histological lesions: senile plaques and neuro-fibrillary tangles. Alzheimer's disease is a multifactorial pathology, characterized by interactions between genetic and environmental factors. Genetic factors concern first of all the exceptional monogenic forms, characterized by early onset (<60 years), autosomal dominant forms. Mutations of the genes coding for amyloid-ß precursor protein or preselinins 1 and 2 are involved. The much more frequent sporadic forms also have genetic factors, the best studied being the apolipoprotein E4 coding allele and some more recent genotypes which will be mentioned. No causal, only symptomatic treatments are available.

Correlation of Aβ oligomer levels in matched cerebrospinal fluid and serum samples

We recently reported a newly developed enzyme-linked immunosorbent assay (ELISA) for high molecular weight amyloid-β (Aβ) oligomers in which the same Aβ monoclonal antibody, BAN50, was used for both capture and detection in a single antibody sandwich enzyme linked immunosorbent assay (ELISA) system. Although our previous data have suggested that this assay will be useful for the early diagnosis of Alzheimer disease (AD) in cerebrospinal fluid (CSF) samples, the invasive CSF sampling procedure, with associated potential complications, limits use of these samples in routine clinical practice. In this study, we have demonstrated that our ELISA can detect signals in 60% of serum samples and in 80% of CSF samples obtained from non-demented subjects. Heterophilic antibodies that are reported to be a primary confounding factor in this type of ELISA system did not affect the signals obtained. Although the levels of serum Aβ oligomers were unexpectedly high, suggesting the possible detection of non-pathological Aβ complexes associated with serum carrier proteins, they did show a significant positive correlation with the levels obtained from matched CSF samples. This correlation between CSF and serum Aβ oligomer levels implies that the levels of serum Aβ oligomers measured with our ELISA might be useful as a marker for AD that reflects an intact system of Aβ transport across the blood brain barrier.

Biochemistry of amyloid β-protein and amyloid deposits in Alzheimer disease

Progressive cerebral deposition of the amyloid β-protein (Aβ) in brain regions serving memory and cognition is an invariant and defining feature of Alzheimer disease. A highly similar but less robust process accompanies brain aging in many nondemented humans, lower primates, and some other mammals. The discovery of Aβ as the subunit of the amyloid fibrils in meningocerebral blood vessels and parenchymal plaques has led to innumerable studies of its biochemistry and potential cytotoxic properties. Here we will review the discovery of Aβ, numerous aspects of its complex biochemistry, and current attempts to understand how a range of Aβ assemblies, including soluble oligomers and insoluble fibrils, may precipitate and promote neuronal and glial alterations that underlie the development of dementia. Although the role of Aβ as a key molecular factor in the etiology of Alzheimer disease remains controversial, clinical trials of amyloid-lowering agents, reviewed elsewhere in this book, are poised to resolve the question of its pathogenic primacy.

The levels of water-soluble and triton-soluble Aβ are increased in Alzheimer's disease brain

Although plaques composed of the amyloid β-protein (Aβ) are considered a defining feature of Alzheimer's disease (AD), they are also found in cognitively normal individuals and extensive evidence suggests that non-plaque, water-soluble forms of Aβ may play a role in AD pathogenesis. However, the relationship between the levels of water-soluble Aβ and the clinical severity of disease has never been investigated. Here, we present results of a pilot study designed to examine the levels of water-soluble forms of Aβ in brains of individuals who died at clinically distinct stages of AD. Using a serial extraction method, we also investigated the levels of triton-soluble and formic acid-soluble Aβ. We found that water-soluble and detergent-soluble Aβ monomer and SDS-stable dimer were elevated in AD and that the levels of water soluble Aβ did not increase with plaque pathology. These results support the notion that both water- and detergent-soluble Aβ are important in AD and are not simply released from plaques by mechanical disruption. Moreover, the fact that the levels of water- and triton-soluble Aβ were similar in very mild/mild AD and moderate/severe AD suggests that once a certain level of these species is attained, further accumulation is not necessary for the disease to progress. Consequently, therapeutic targeting of water-soluble Aβ should best benefit individuals in earliest phases of the disease process.

Pyroglutamate amyloid-β (Aβ): a hatchet man in Alzheimer disease

Pyroglutamate-modified amyloid-β (Aβ(pE3)) peptides are gaining considerable attention as potential key participants in the pathology of Alzheimer disease (AD) due to their abundance in AD brain, high aggregation propensity, stability, and cellular toxicity. Transgenic mice that produce high levels of Aβ(pE3-42) show severe neuron loss. Recent in vitro and in vivo experiments have proven that the enzyme glutaminyl cyclase catalyzes the formation of Aβ(pE3). In this minireview, we summarize the current knowledge on Aβ(pE3), discussing its discovery, biochemical properties, molecular events determining formation, prevalence in the brains of AD patients, Alzheimer mouse models, and potential as a target for therapy and as a diagnostic marker.

Aluminosilicates and the ageing brain: implications for the pathogenesis of Alzheimer's disease

Senile plaques are a neuropathological feature of the ageing brain and consist of abnormal neuritic and glial processes surrounding an extracellular core of material with fibrillary ultrastructure. Present at low densities in the cerebral cortex of most aged individuals, they occur in large numbers in Alzheimer's disease, the major form of senile dementia. Energy-dispersive X-ray microprobe analysis of isolated cores and plaques in situ from patients with Alzheimer's disease or Down's syndrome and from normal controls has shown co-localization of high concentrations of aluminium (4-19%) and silicon (6-24%) at the centre of the core. The presence of these elements as aluminosilicates has been confirmed using solid-state 27Al nuclear magnetic resonance. These findings provide a link with the other major neuropathological feature of Alzheimer's disease, the neurofibrillary tangle-bearing neurons, where high intracellular levels of Al and Si have also been reported. The focal deposition of these elements may be an early and essential factor in the pathogenesis of Alzheimer-type changes, reflecting an increased exposure to aluminium.

Neuronal origin of cerebral amyloidogenic proteins: their role in Alzheimer's disease and unconventional virus diseases of the nervous system

The protein component of Alzheimer's disease amyloid (neurofibrillary tangles, amyloid plaque cores and congophilic angiopathy) is an aggregated polypeptide with a subunit mass of approximately 4 kDa (the A4 monomer). The aggregational properties of this monomer may explain the amyloidogenic nature of the protein: the native monomer forms dimers, tetramers and higher oligomeric species which are dependent on pH, ionic strength and concentration; the synthetic peptide corresponding to residues 1-28 spontaneously forms fibrils in vitro. Based on the degree of N-terminal heterogeneity, the A4 monomer aggregates first in neurons and later in the extracellular space. Using antisera raised against synthetic peptides, we can demonstrate that the N-terminus contains an epitope for neurofibrillary tangles, and the inner region of the molecule contains an epitope for the extracellular amyloid fibrils. There is a non-protein component of the amyloid (inorganic residues of aluminium silicate) which may be important in the deposition of the amyloid fibrils. There are several intriguing similarities between the amyloid fibrils and proteins of Alzheimer's disease when compared to the scrapie-associated filaments and proteins of the unconventional virus diseases (scrapie, kuru, Creutzfeldt-Jakob disease). Although there is no sequence homology between the proteins, we suspect they are formed as a result of similar biochemical processes. If the scrapie proteins and filaments are an integral part of the infectious agent, it follows that Alzheimer's disease is also an infectious process similar to scrapie. As they are host-encoded proteins, it is still feasible that both types are pathological by-products of independent diseases.

They have shaped Alzheimer disease: the protagonists, well known and less well known

This paper discusses the history of dementia and Alzheimer's disease (AD) with emphasis on the individuals who have shaped its development. In addition to the best known protagonists recognized as founders of the field, it will mention other figures who have provided important contributions but are sometimes overlooked. Many of these have also become famous for work unrelated to AD.

IGF-1-induced Processing of the Amyloid Precursor Protein Family Is Mediated by Different Signaling Pathways

The mammalian amyloid precursor protein (APP) protein family consists of the APP and the amyloid precursor-like proteins 1 and 2 (APLP1 and APLP2). The neurotoxic amyloid beta-peptide (Abeta) originates from APP, which is the only member of this protein family implicated in Alzheimer disease. However, the three homologous proteins have been proposed to be processed in similar ways and to have essential and overlapping functions. Therefore, it is also important to take into account the effects on the processing and function of the APP-like proteins in the development of therapeutic drugs aimed at decreasing the production of Abeta. Insulin and insulin-like growth factor-1 (IGF-1) have been shown to regulate APP processing and the levels of Abeta in the brain. In the present study, we show that IGF-1 increases alpha-secretase processing of endogenous APP and also increases ectodomain shedding of APLP1 and APLP2 in human SH-SY5Y neuroblastoma cells. We also investigated the role of different IGF-1-induced signaling pathways, using specific inhibitors for phosphatidylinositol 3-kinase and mitogen-activated protein kinase (MAPK). Our results indicate that phosphatidylinositol 3-kinase is involved in ectodomain shedding of APP and APLP1, but not APLP2, and that MAPK is involved only in the ectodomain shedding of APLP1.

Effects of chemical chaperones on oxidative stress and detergent-insoluble species formation following conditional expression of amyloid precursor protein carboxy-terminal fragment

Oxidative stress, protein misfolding, protein complex formation, and detergent insolubility are biochemical features of Alzheimer's disease (AD). We tested the cause-and-effect relationships among these using MC65 human neuroblastoma cells that exhibit toxicity upon conditional expression of carboxy-terminal fragments (CTFs) of the human amyloid precursor protein (APP). Treatments with three different antioxidants (alpha-tocopherol, N-acetyl cysteine, and alpha-lipoic acid) or three different compounds (glycerol, trimethylamine-N-oxide, and 4-phenylbutyric acid) that have been described to have a "chemical chaperone" function in promoting protein folding all had a protective effect on MC65 cells and decreased markers of oxidative damage and accumulation of high molecular weight amyloid (A) beta-immunoreactive (IR) species. However, chaperones partially reduced detergent insolubility of the remaining Abeta-IR species, while antioxidants did not. These results suggest that protein misfolding associated with overexpression of APP CTFs promotes oxidative stress and cytotoxicity and contributes to formation of detergent-insoluble species that appear unrelated to cytotoxicity.

Porcine APP cDNAs: Molecular cloning and characterization, expression analysis, chromosomal localization and SNP analysis

The human amyloid precursor protein (APP) is the precursor of Abeta, a peptide with the potential to create amyloid plaques in neurons. Mutations in the human APP gene are associated with the familial form of Alzheimer's disease. In addition, differential expression of three alternative pre-mRNA APP splicing variants of 695, 751, and 770 amino acids is linked to the pathogenesis. In this study, two novel transcript variants of porcine APP have been identified, producing isoforms of 695 and 751 amino acids, respectively. These are highly homologous to APP orthologues from other vertebrate species. Expression analyses revealed that the gene is expressed in all 30 examined porcine tissues and in a selected subset of these, differential representation of the three major APP transcript variants was observed. The APP isoform of 770 amino acids clearly predominates in non-neuronal tissues while in porcine cerebellum, the APP isoforms of 695 and 770 amino acids are expressed at equivalent levels. Employing a somatic cell hybrid panel, the APP gene was mapped to porcine chromosome 13 in either the 13q41 or 13q46-q49 region. A large pig population was screened for single nucleotide polymorphisms (SNPs) in APP exon 17 and flanking intron sequences. No missense mutations were detected; however, the allele frequencies of two silent mutations and two intron polymorphisms varied significantly among breeds.

The expression of wild-type human amyloid precursor protein affects the dendritic phenotype of neocortical pyramidal neurons in transgenic mice

The current study addresses the morphoregulatory effects of human amyloid precursor protein expression on neocortical pyramidal cells in vivo. For this purpose, a transgenic mouse line was used that expresses wild-type human amyloid precursor protein (APP) at levels similar to endogenous mouse APP. This strain does not develop Alzheimer's disease-related pathology which allowed to study effects of APP or APP cleavage products but excluded the influence of amyloid deposits. Commissural projecting pyramidal neurons of layers II/III within the primary somatosensory cortex were retrogradely labelled by injection of biotinylated dextran amine into the corpus callosum. In transgenic mice, computer-aided morphometric analysis revealed an increase in the surface area of proximal and intermediate basal dendritic segments resulting from an enlarged diameter. On the other hand, the length of the same segments was reduced. Both basal and apical dendrites were characterized by a higher dendritic density within the proximal and intermediate fields. Although the total spatial extension of basal and apical dendrites remained unchanged, a moderate withdrawal of arbors is suggested. The results implicate a physiological function for APP in regulatory mechanisms of neuronal morphogenesis.

Increased processing of APLP2 and APP with concomitant formation of APP intracellular domains in BDNF and retinoic acid-differentiated human neuroblastoma cells

The amyloid precursor protein (APP) belongs to a conserved gene family, also including the amyloid precursor-like proteins, APLP1 and APLP2. We have previously shown that all members of the APP protein family are up-regulated upon retinoic acid (RA)-induced neuronal differentiation of SH-SY5Y neuroblastoma cells. Here, we demonstrate that RA also affects the processing of APLP2 and APP, as shown by increased shedding of both sAPLP2 and sAPPalpha, as well as elevated levels of the APP intracellular domains (AICDs). Brain-derived neurotrophic factor (BDNF) has been reported to induce APP promoter activity and RA induces expression of the tyrosine kinase receptor B (TrkB) in neuroblastoma cells. We show that the increase in shedding of both APLP2 and APP in response to RA is not mediated through the TrkB receptor. However, BDNF concomitant with RA increased the expression of APP even further. In addition, the secretion of sAPLP2 and sAPPalpha as well as the levels of AICDs were increased in response to BDNF. In contrast, the levels of membrane-bound APP C-terminal fragment C99 significantly decreased. Our results suggest that RA and BDNF shifts APP processing towards the alpha-secretase pathway. In addition, we show that RA and BDNF regulate N-linked glycosylation of APLP1.

N-terminal heterogenicity of amyloid protein examined in Alzheimer's disease

Alzheimer's disease is the major cause of dementia in humans. The affected brain shows characteristic abnormal filamentous proteins that accumulate intracellularly as neurofibrillary tangles, and extracellularly as senile plaques, as well as in cerebral blood vessels. The extracellular deposits are an amyloid protein, which is highly insoluble. In our study, we intended to show that the N-terminus of amyloid A4 protein can change in length and sequence in Alzheimer's disease, and possibly in other dementias.

Roles of amyloid precursor protein and its fragments in regulating neural activity, plasticity and memory

Amyloid-beta precursor protein (APP) is a membrane-spanning protein with a large extracellular domain and a much smaller intracellular domain. It is the source of the amyloid-beta (Abeta) peptide found in neuritic plaques of Alzheimer's disease (AD) patients. Because Abeta shows neurotoxic properties, and because familial forms of AD promote Abeta accumulation, a massive international research effort has been aimed at understanding the mechanisms of Abeta generation, catabolism and toxicity. APP, however, is an extremely complex molecule that may be a functionally important molecule in its full-length configuration, as well as being the source of numerous fragments with varying effects on neural function. For example, one fragment derived from the non-amyloidogenic processing pathway, secreted APPalpha (sAPPalpha), is neuroprotective, neurotrophic and regulates cell excitability and synaptic plasticity, while Abeta appears to exert opposing effects. Less is known about the neural functions of other fragments, but there is a growing interest in understanding the basic biology of APP as it has become recognized that alterations in the functional activity of the APP fragments during disease states will have complex effects on cell function. Indeed, it has been proposed that reductions in the level or activity of certain APP fragments, in addition to accumulation of Abeta, may play a critical role in the cognitive dysfunction associated with AD, particularly early in the course of the disease. To test and modify this hypothesis, it is important to understand the roles that full-length APP and its fragments normally play in neuronal structure and function. Here we review evidence addressing these fundamental questions, paying particular attention to the contributions that APP fragments play in synaptic transmission and neural plasticity, as these may be key to understanding their effects on learning and memory. It is clear from this literature that APP fragments, including Abeta, can exert a powerful regulation of key neural functions including cell excitability, synaptic transmission and long-term potentiation, both acutely and over the long-term. Furthermore, there is a small but growing literature confirming that these fragments correspondingly regulate behavioral learning and memory. These data indicate that a full account of cognitive dysfunction in AD will need to incorporate the actions of the full complement of APP fragments. To this end, there is an urgent need for a dedicated research effort aimed at understanding the behavioral consequences of altered levels and activity of the different APP fragments as a result of experience and disease.

Senile plaque composition and posttranslational modification of amyloid-beta peptide and associated proteins

Amyloid deposits are primarily composed of the amyloid-beta protein, although other proteins (and metal ions) also have been colocalized to these lesions. The pattern of oxidative modifications in amyloid plaques is very different to that associated with neurofibrillary tangles and neuronal cell bodies, likely reflecting the different composition of these structures, accessibility of oxidants, the generation of oxidants in and around these structures and the intrinsic antioxidant defense systems to protect these structures. Future studies directed at understanding Abeta interactions with other amyloid components, the role of oxidative modifications in stabilizing amyloid deposits and the determination of protease cleavage sites on Abeta may provide mechanistic insights regarding both amyloid formation and removal.

Lack of point mutation of the APP gene in sporadic Alzheimer's disease in Japanese

We investigated point mutations of the APP gene in 66 patients with sporadic Alzheimer's disease (AD) and 180 normal individuals by use of the PCR (polymerase chain reaction) method. Both the AD patients and the normal individuals were Japanese. We extracted DNA from blood samples using the phenol-chloroform method and amplified exons 16 and 17 of the APP gene by PCR. PCR products were digested by MBO-II (exon 16) and BCL-1(exon 17). Electrophoresis was carried out with 3% agarose gel and the separated fragments were stained with ethidium bromide. In addition we investigated other point mutations of exons 16 and 17 by use of the PCR-SSCP (single stranded conformation polymorphisms) method, and found no fragments that exhibited point mutations in the AD patients and normal individuals. These findings indicate that the presence of point mutation of the APP gene is not a major cause of AD in the Japanese population.

Monitoring pathological assembly of tau and beta-amyloid proteins in Alzheimer's disease

This double-labelling confocal microscopy study of the neuropathology of Alzheimer's disease (AD) reports the use of a fluorescent dye, thiazin red, which has staining properties similar to thioflavin-S. Thiazin red fluorescence can be visualised selectively in the red channel, and we have used this property to compare it with the labelling seen using monoclonal antibody (mAb) 423, which detects tau protein C-terminally truncated at Glu-391, and mAb 4G8, which detects beta-amyloid protein. Thiazin red is shown to recognized the typical histopathological deposits associated with both proteins. However, not all deposits containing these proteins are stained. Specifically, diffuse beta-amyloid plaques and severely degraded extracellular tangles are unlabelled. Likewise a characteristic mAb 423-reactive granular plaque-like structure, typically present in cases with abundant extracellular tangels, is unlabelled by thiazin red. Such plaques can be shown to be continuous with the basal dendrites of degraded tangle-bearing pyramidal cells. These findings suggest that paired helical filaments (PHFs) continue to undergo degradation in the extracellular space, which is associated with loss of thiazin red binding sites, but preservation of mAb 423 immunoreactivity. This epitope appears to be characteristic of a stable core element of the PHF which is highly resistant to proteolysis. Compounds such as thiazin red with high affinity for beta-pleated protein structures can be used to monitor the state of pathological assembly of amyloidogenic protein species found in AD.

Mechanical instability of Pick bodies and their isolation in an intact form using urea solution

Isolation of Pick bodies was attempted from an autopsied brain of a patient with Pick's disease following a modified method for isolation of senile plaques cores and neurofibrillary tangles in the brains of Alzheimer's disease. Pick bodies were mechanically less stable than senile plaque cores and neurofibrillary tangles since Pick bodies were destroyed by vigorous homogenization or treatment with 1% sodium dodecyl sulfate solution. Pick bodies were released out of mother neuronal cells in an intact form by treatment with 8 M urea solution for several hours at room temperature. Finally, fine structure of Pick filaments released from Pick bodies was compared with the filaments of neurofibrillary tangles.

Amyloid beta-protein precursor (APP) of cultured cells: secretory and non-secretory forms of APP

Overproduction or aberrant catabolism of the predicted amyloid beta-protein precursor (APP) is suspected as the cause of amyloid deposition in Alzheimer's disease and Down's syndrome brains. For possible in vitro experiments of amyloid formation, we have examined the expression of APP in various cultured cells. We found two types of APP producing cell lines. PC12h (rat pheochromocytoma) and HL-60 (human acute promyelocytic leukemia) cells produce a secretory form that is released into the culture medium, while Bu-17 (human glioma) cells synthesize only a non-secretory form that accumulates at the cell surface. APP immunoreactivity on the latter cells was detected at the tips of cell processes or growth cones. These observations indicate that the nonsecretory form of APP may play a role in cell contact or adhesion.

Subcellular distribution of acetylcholinesterase in Alzheimer's disease: abnormal localization and solubilization

AChE activity was detected mainly in membrane-bound fractions in the frontal cortex of autopsied control or Alzheimer brain as well as rat cerebral cortex. However, the distribution of AChE among various membrane fractions was different between control and Alzheimer brains. The highest specific activity was detected in the fraction enriched with senile plaque, which was obtained from the Alzheimer brain by sonication, solubilization with detergent and centrifugation on a sucrose density gradient. The senile plaque enriched fraction was incubated with purified collagenase or protease and centrifuged at 100,000 g for 60 min. More than 50% of AChE activity was detected in the supernatant fraction. AChE in the supernatant solution showed a property of G4 isozyme. AChE might probably be anchored to the senile plaque through its collagen tail and be solubilized with collagenase or protease, producing a G4 isozyme.

Alpha 1-antichymotrypsin is present together with the beta-protein in monkey brain amyloid deposits

The recent finding that the serine protease inhibitor, alpha 1-antichymotrypsin, is tightly associated with the amyloid deposits in brains of normal aged individuals and patients with Alzheimer's disease [Abraham C. R., Selkoe D. J. and Potter H. (1988) Cell 52, 487-501], suggests a role for this inhibitor in the progressive deposition of brain amyloid in humans. We have used immunocytochemistry to detect alpha 1-antichymotrypsin in the amyloid that accumulates in brains of aged monkeys, a naturally occurring animal model of Alzheimer-like neuropathology. In monkeys of increasing age, the earliest alpha 1-antichymotrypsin immunoreactivity was found in cortical perivascular cells, before the appearance of either Thioflavin S-detectable amyloid deposits or beta-protein reactivity in the vessel walls. Subsequently, amyloid deposits appeared in small meningeal blood vessels and cortical neuritic plaques. The oldest monkeys also showed microvascular amyloid in the cortical gray matter. Amyloid was never seen in white matter. The amyloid deposits in meningeal vessels were always positive for both beta-protein and alpha 1-antichymotrypsin, whereas in the cortex, alpha 1-antichymotrypsin immunoreactivity seemed to appear somewhat later than that of beta-protein. These findings demonstrate that two of the brain amyloid components of human senescence and Alzheimer's disease--the beta-protein and the protease inhibitor alpha 1-antichymotrypsin--are also present in the amyloid deposits of normal aged monkey brain. The extended molecular parallels between normal brain aging and Alzheimer's disease suggest that similar biochemical mechanisms may underlie progressive amyloid deposition in both situations.