Abeta species removal after abeta42 immunization

Neuropathologic examination of 3 patients with Alzheimer disease in the Elan Pharmaceuticals trial using antibodies specific for different Abeta species showed in one case, 4 months after the immunization, evidence of a stage of active plaque clearance with "moth-eaten" plaques and abundant Abeta phagocytosis by microglia. At 1 to 2 years after immunization, 2 cases showed extensive areas cleared of plaques (69% and 86% of the temporal cortex was plaque-free). Cortex cleared of plaques in all 3 cases had a characteristic constellation of features, including a very low plaque burden, sparse residual dense plaque cores, and phagocytosed Abeta within microglia. There was resolution of tau-containing dystrophic neurites, although other features of tau pathology (tangles and neuropil threads) remained and cerebral amyloid angiopathy persisted. Although most antibodies generated by Abeta42 immunization in humans bind the intact N-terminus, immunohistochemistry with specific antibodies showed clearance of all major species of Abeta (Abeta40, Abeta42, and N-terminus truncated Abeta). Abeta immunotherapy can clear all Abeta species from the cortex. However, if it is to be used for treatment of established Alzheimer disease, then the residual tau pathology and cerebral amyloid angiopathy require further study.     

Cases of Alzheimer's disease due to deletion of exon 9 of the presenilin-1 gene show an unusual but characteristic beta-amyloid pathology known as 'cotton wool' plaques

The pattern of deposition of amyloid beta protein (Abeta) was investigated, using the monoclonal antibodies BA27 and BC05 detecting the C-terminal species Abeta40 and Abeta42(43), in six cases of Alzheimer's disease (AD) due to deletions in exon 9 of PS-1 gene. These cases are characterized histologically by the presence of very large rounded plaques within the frontal cortex, known as 'cotton wool' plaques, composed of both Abeta40 and Abeta42(43) that are relatively free from neuritic changes and glial cell components, and usually devoid of a compact amyloid core. In the cerebellum the plaques are almost entirely of a compact type, again composed of Abeta40 and Abeta42(43), with only few diffuse Abeta42(43) containing plaques. The area fraction of Abeta40, and the ratio between Abeta40 and Abeta42(43), in frontal cortex was significantly higher than that seen in other cases of AD due to different PS-1 mutations, or in cases of sporadic AD, all of similar APO E genotype. The area fractions of Abeta42(43), however, did not significantly differ between these three groups. The unusual nature of the Abeta deposition in these cases may reflect the uniqueness of the mutation, which results in a failure to constitutively cleave the PS-1 holoprotein into its active form, and the effect this might have on APP trafficking and catabolism.     

Association of increased cortical soluble abeta42 levels with diffuse plaques after severe brain injury in humans

BACKGROUND: Traumatic brain injury (TBI) is an environmental risk factor for developing Alzheimer disease. This may be due, in part, to changes associated with beta-amyloid (Abeta) plaque formation, which can occur within hours after injury, regardless of the patient's age. In addition to being precursors of toxic fibrils that deposit into plaques, soluble (nonfibrillar) Abeta peptides are posited to disrupt synaptic function and are associated with cognitive decline in Alzheimer disease. Changes in soluble Abeta levels and their relationship to Abeta plaque formation following TBI are unknown. OBJECTIVE: To quantify brain tissue levels of soluble Abeta peptides and their precursor protein in relation to Abeta plaque formation after TBI in humans. DESIGN: Surgically resected temporal cortex tissue from patients with severe TBI was processed for biochemical assays of soluble Abeta peptides with COOH-termini ending in amino acid 40 (Abeta(40)) or 42 (Abeta(42)) and Abeta precursor protein to compare patients with cortical Abeta plaques and those without. Patients Nineteen subjects admitted to the University of Pittsburgh Medical Center for treatment of severe closed head injury. RESULTS: Patients with severe TBI and cortical plaques had higher levels of soluble Abeta(1-42) but not Abeta(1-40); half of them were apolipoprotein E (APOE) epsilon4 allele carriers. The lowest Abeta levels were in 1 patient without plaques who was the only subject with an APOE epsilon2 allele. beta-Amyloid precursor protein levels were comparable in the 2 TBI groups. CONCLUSIONS: Selective increases in soluble Abeta(1-42) after TBI may predispose individuals with a brain injury to Alzheimer disease pathology. This may be influenced by the APOE genotype, and it may confer increased risk for developing Alzheimer disease later in life.     

Apolipoprotein E deposition and astrogliosis are associated with maturation of beta-amyloid plaques in betaAPPswe transgenic mouse: Implications for the pathogenesis of Alzheimer's disease

A transgenic mouse expressing the human beta-amyloid precursor protein with the 'Swedish' mutation, Tg2576, was used to investigate the mechanism of beta-amyloid (Abeta) deposition. Previously, we have reported that the major species of Abeta in the amyloid plaques of Tg2576 mice are Abeta1-40 and Abeta1-42. Moreover, Abeta1-42 deposition precedes Abeta1-40 deposition, while Abeta1-40 accumulates in the central part of the plaques later in the pathogenic process. Those data indicate that Abeta deposits in Tg2576 mice have similar characteristics to those in Alzheimer's disease. In the present study, to understand more fully the amyloid deposition mechanism implicating Alzheimer's disease pathogenesis, we examined immunohistochemically the distributions of apolipoprotein E (apoE) and Abeta in amyloid plaques of aged Tg2576 mouse brains. Our findings suggest that Abeta1-42 deposition precedes apoE deposition, and that Abeta1-40 deposition follows apoE deposition during plaque maturation. We next examined the relationship between apoE and astrogliosis associated with amyloid plaques using a double-immunofluorescence method. Extracellular apoE deposits were always associated with reactive astrocytes whose processes showed enhancement of apoE-immunoreactivity. Taken together, the characteristics of amyloid plaques in Tg2576 mice are similar to those in Alzheimer's disease with respect to apoE and astrogliosis. Furthermore, apoE deposition and astrogliosis may be necessary for amyloid plaque maturation.     

Fleecy amyloid deposits in the internal layers of the human entorhinal cortex are comprised of N-terminal truncated fragments of Abeta

The deposition of amyloid in the brain is a hallmark of Alzheimer disease (AD). Amyloid deposits consist of accumulations of beta-amyloid (Abeta), which is a 39-43 amino-acid peptide cleaved from the Abeta-protein precursor (APP). Another cleavage product of APP is the P3-peptide, which consists of the amino acids 17-42 of the Abeta-peptide. In order to study the deposition of N-terminal truncated forms of Abeta in the human entorhinal cortex, serial sections from 16 autopsy cases with AD-related pathology were immunostained with antibodies against Abeta1-40, Abeta1-42, Abeta17-23, and Abeta8-17, as well as with the Campbell-Switzer silver impregnation for amyloid. In the external entorhinal layers (pre-beta and pre-gamma), sharply delineated diffuse plaques were seen. They were labeled by silver impregnation and by all Abeta-antibodies used. By comparison, in the internal layers (pri-alpha, pri-beta, and pri-gamma) blurred, ill-defined clouds of amyloid existed, in addition to sharply delineated diffuse plaques. These clouds of amyloid were termed "fleecy amyloid." Immunohistochemically, fleecy amyloid was stained by Abeta17-23 and Abeta1-42 antibodies, but not with antibodies against Abeta8-17 and Abeta1-40. Using the Campbell-Switzer technique, the fleecy amyloid deposits were found to be fine argyrophilic amyloid fibrils. Thus, the internal entorhinal layers are susceptible to a distinct type of amyloid, namely fleecy amyloid. This fleecy amyloid obviously corresponds to N-terminal truncated fragments of Abeta1-42, probably representing the P3-peptide. These N-terminal truncated fragments of Abeta are capable of creating fine fibrillar "amyloid."     

Abeta42 gene vaccination reduces brain amyloid plaque burden in transgenic mice

OBJECTIVE: To demonstrate that in APPswe/PS1DeltaE9 transgenic mice, gene gun mediated Abeta42 gene vaccination elicits a high titer of anti-Abeta42 antibodies causal of a significant reduction of Abeta42 deposition in brain. METHODS: Gene gun immunization is conducted with transgenic mice using the Abeta42 gene in a bacterial plasmid with the pSP72-E3L-Abeta42 construct. Enzyme-linked immunoabsorbent assays (ELISA) and Western blots are used to monitor anti-Abeta42 antibody levels in serum and Abeta42 levels in brain tissues. Enzyme-linked immunospot (ELISPOT) assays are used for detection of peripheral blood T cells to release gamma-interferon. Immunofluorescence detection of Abeta42 plaques and quantification of amyloid burden of brain tissue were measured and sections were analyzed with Image J (NIH) software. RESULTS: Gene gun vaccination with the Abeta42 gene resulted in high titers of anti-Abeta42 antibody production of the Th2-type. Levels of Abeta42 in treated transgenic mouse brain were reduced by 60-77.5%. The Mann-Whitney U-test P=0.0286. INTERPRETATION: We have developed a gene gun mediated Abeta42 gene vaccination method that is efficient to break host Abeta42 tolerance without using adjuvant and induces a Th2 immune response. Abeta42 gene vaccination significantly reduces the Abeta42 burden of the brain in treated APPswe/PS1DeltaE9 transgenic mice with no overlap between treated and control mice.     

Occurrence of the diffuse amyloid beta-protein (Abeta) deposits with numerous Abeta-containing glial cells in the cerebral cortex of patients with Alzheimer's disease

Diffuse amyloid beta-protein (Abeta) deposits with numerous glial cells containing C-terminal Abeta fragments occur in the cerebral cortex of patients with Alzheimer's disease. By using a panel of antibodies specific for various epitopes in the Abeta peptide, we have investigated the immunohistochemical nature of the diffuse Abeta deposits. The extracellular material contains Abeta with a C-terminus at residue valine40 (Abeta40) as well as residues alanine42/threonine43 (Abeta42). The N-termini include aspartate1, pyroglutamate3, and pyroglutamate11, with pyroglutamate3 being dominant. Microglia and astrocytes in and around these deposits contain intensely staining granules. Most of these granules are negative for antibodies to the N-terminally located sequences of Abeta. These include 6E10 (Abeta1-17), 6F/3D (Abeta8-17), and the N-terminal antibodies specific to aspartate1, pyroglutamate3, and pyroglutamate11. The C-termini of intraglial Abeta are comparable with those of the extracellular deposits. The microglia and astrocytes have quiescent morphology compared with those associated with senile plaques and other lesions such as ischemia. Complement activation in these deposits is not prominent and often below the sensitivity of immunohistochemical detection. Although factors which may cause this type of deposit remain unclear, lack of strong tissue responses suggests that these deposits are a very early stage of Abeta deposition. They were found only inconsistently and were absent in a number of cases examined in this study. Further analysis of these deposits might provide important clues regarding the accumulation and clearance of Abeta in Alzheimer's disease brain.     

Tau load is associated with apolipoprotein E genotype and the amount of amyloid beta protein,Abeta40, in sporadic and familial Alzheimer's disease

The total amount of hyperphosphorylated tau protein (p-tau load), present as neurofibrillary tangles (NFTs), neuropil threads or plaque neurites, was quantified in the frontal cortex of 109 cases of sporadic Alzheimer's disease (AD) and 35 cases of familial AD due to missense mutations in the presenilin-1, presenilin-2 and amyloid precursor protein genes. p-tau load was inversely correlated with age at onset of illness in both sporadic and familial AD but not with duration of disease. There was no difference in p-tau load between cases of familial AD and others with sporadic AD, matching the familial cases for apolipoprotein E (APO E) genotype. However, p-tau was greater in cases of familial and sporadic AD in the presence of APO E epsilon4 allele and increased with gene dose. Conversely, p-tau load tended to be lower when epsilon2 allele was present. In sporadic AD, tau load was highly significantly correlated with amyloid beta40 (Abeta40), but not Abeta42(43), load. These data indicate that the burden of pathological tau deposited in the brain in both familial and sporadic AD is favoured in the presence of APO E epsilon4 allele and also related to the amount of Abeta40, this also being higher when epsilon4 allele is present. Abeta40 plaques are rich in microglial cells and it is possible that p-tau pathology in AD is triggered by reaction of microglial cells to the presence of Abeta40 and not this peptide directly.     

Immunohistochemical analysis of cerebral cortical and vascular lesions in the primate Microcebus murinus reveal distinct amyloid beta1-42 and beta1-40 immunoreactivity profiles

Recent reports have shown that amyloid beta deposits in the brains of Alzheimer's disease patients consist mainly of two distinct species of amyloid beta protein (Abeta) with different C-termini, Abeta1-42 (Abeta42) and Abeta1-40 (Abeta40). The nature of the Abeta species in Microcebus murinus brain was investigated immunocytochemically using polyclonal antibodies with clear specificity for the Abeta42 and Abeta40 C-termini. The cortical vascular deposits were immunopositive for both Abeta42 and Abeta40. However, most of the diffuse plaques were strongly positive for Abeta42 whereas only a subset of deposits were positive for Abeta40. Numerous cortical plaques were Abeta42-immunopositive but tested negative for Abeta40. This suggests that Abeta42 is probably associated with early stages of plaque maturation. This neuropathological feature reminiscent of that observed in brains affected by Alzheimer's disease further supports the idea that M. murinus could be used as a potential model of the early stages of this neurological disease.     

Microglial activation facilitates Abeta plaque removal following intracranial anti-Abeta antibody administration

The mechanisms by which anti-Abeta antibodies clear amyloid plaques in Abeta depositing transgenic mice are unclear. In the current study, we demonstrate that inhibition of anti-Abeta antibody-induced microglial activation with anti-inflammatory drugs, such as dexamethasone, inhibits removal of fibrillar amyloid deposits. We also show that anti-Abeta F(ab')(2) fragments fail to activate microglia and are less efficient in removing fibrillar amyloid than the corresponding complete IgG. Diffuse Abeta deposits are cleared by antibodies under all circumstances. These data suggest that microglial activation is necessary for efficient removal of compact amyloid deposits with immunotherapy. Inhibition of this activation may result in an impaired clinical response to vaccination against Abeta.     

Genetic associations between cathepsin D exon 2 C-->T polymorphism and Alzheimer's disease, and pathological correlations with genotype

Genetic variations represent major risk factors for Alzheimer's disease (AD). While familial early onset AD is associated with mutations in the amyloid precursor protein and presenilin genes, only the e4 allele of the apolipoprotein E (APOE) gene has so far been established as a genetic risk factor for late onset familial and sporadic AD. It has been suggested that the C-->T (224Ala-->Val) transition within exon 2 of the cathepsin D gene (CTSD) might represent a risk factor for late onset AD. The objective of this study was to investigate whether possession of the CTSD exon 2 T allele increases the risk of developing AD, and to determine whether this modulates the amyloid pathology of the disease in conjunction with, or independent of, the APOE e4 allele. Blood samples were obtained from 412 patients with possible or probable AD and brain tissues from a further 148 patients with AD confirmed by postmortem examination. CTSD and APOE genotyping were performed by PCR on DNA extracted from blood, or from frontal cortex or cerebellum in the postmortem cases. Pathological measures of amyloid beta protein (Abeta), as plaque Abeta40 and Abeta42(3) load and degree of cerebral amyloid angiopathy were made by image analysis or semiquantitative rating, respectively. CTSD genotype frequencies in AD were not significantly different from those in control subjects, nor did these differ between cases of early or late onset AD or between younger and older controls. There was no gene interaction between the CTSD T and APOE e4 alleles. The amount of plaque Abeta40 was greater in patients carrying the CTSD T allele than in non-carriers, and in patients bearing APOE e4 allele compared with non-carriers. Possession of both these alleles acted synergistically to increase levels of plaque Abeta40, especially in those individuals who were homozygous for the APOE e4 allele. Possession of the CTSD T allele had no effect on plaque Abeta42(3) load or degree of CAA. Possession of the CTSD T allele does not increase the risk of developing AD per se, but has a modulating effect on the pathogenesis of the disorder by increasing, in concert with the APOE e4 allele, the amount of Abeta deposited as senile plaques in the brain in the form of Abeta40.     

Correlation between Abetax-40-, Abetax-42-, and Abetax-43-containing amyloid plaques and cognitive decline.

CONTEXT: Accumulation of senile plaques containing amyloid beta (Abeta)-protein is a pathologic hallmark of Alzheimer disease. Amyloid beta-peptide is heterogeneous, with carboxyterminal variants ending at residues Val40 (Abetax-40), Ala42 (Abetax-42), or Thr43 (Abetax-43). The relative importance of each of these variants in dementia or cognitive decline remains unclear. OBJECTIVE: To study whether Abeta deposition correlates with dementia and occurs at the earliest signs of cognitive decline. DESIGN, SETTING, AND PATIENTS: Postmortem cross-sectional study comparing the deposition of Abeta variants in the prefrontal cortex of 79 nursing home residents having no, questionable, mild, moderate, or severe dementia. MAIN OUTCOME MEASURES: Levels of staining of Abeta-peptides ending at amino acid 40, 42, or 43 in the frontal cortex, as a function of Clinical Dementia Rating score. RESULTS: There were significant deposits of all 3 Abeta species that strongly correlated with cognitive decline. Furthermore, deposition of Abetax-42 and Abetax-43 occurred very early in the disease process before there could be a diagnosis of Alzheimer disease. Levels of deposited Abetax-43 appeared surprisingly high given the low amounts synthesized. CONCLUSIONS: These data indicate that Abetax-42 and Abetax-43 are important species associated with early disease progression and suggest that the physiochemical properties of the Abeta species may be a major determinant in amyloid deposition. The results support an important role for Abeta in mediating initial pathogenic events in Alzheimer disease dementia and reinforce that treatment strategies targeting the formation, accumulation, or cytotoxic effects of Abeta should be pursued.     

Age-related plaque morphology and C-terminal heterogeneity of amyloid β in Dutch-type hereditary cerebral hemorrhage with amyloidosis

The evolvement of amyloid beta (Abeta) deposition in the frontal cerebral cortex of 24 patients of increasing age with Dutch-type hereditary cerebral hemorrhage with amyloidosis (HCHWA-D) was studied using end-specific monoclonal antibodies to Abetax-42 (Abeta42) or Abetax-40 (Abeta40) and markers for degenerating neurites. Abeta42 immunostaining revealed parenchymal Abeta deposits with a heterogeneous morphology and distribution, i.e., clouds, fine/dense diffuse, coarse, and homogeneous plaques. Clouds and diffuse plaques were associated with glial Abeta granules. Abeta40 labeling was absent in clouds/fine diffuse plaques, inconsistent and variably intense in dense diffuse/coarse plaques and consistent in homogeneous plaques. In a subset of Abeta40-positive plaques, degenerating neurites--without tauopathy--and/or amyloid cores were observed. Electron microscopy revealed no apparent amyloid fibrils in fine diffuse plaques, small bundles of fibrils in dense diffuse/homogeneous plaques, and amyloid masses in coarse plaques. The parenchymal Abeta pathology was age-related: the ratio of fine to dense diffuse plaques decreased with age, clouds were limited to younger patients; coarse plaques to the oldest old. Homogeneous/cored plaques were present most consistently in older patients. Plaque density did not increase with age. Vascular Abeta deposits stained for both Abeta species, but exclusively Abeta42-positive, presumably recent deposits were also observed. This study suggests that HCHWA-D is a model of plaque evolution in which clouds leave fine diffuse plaques, which may become dense diffuse and ultimately coarse or homogeneous plaques.     

Amyloid beta40/42 clearance across the blood-brain barrier following intra-ventricular injections in wild-type,apoE knock-out and human apoE3 or E4 expressing transgenic mice

An important event in the pathogenesis of Alzheimer's disease (AD) is the deposition of the amyloid beta (Abeta)1-40 and 1-42 peptides in a fibrillar form, with Abeta42 typically having a greater propensity to undergo this conformational change. A major risk factor for late-onset AD is the inheritance of the apolipoprotein E (apoE) 4 allele [3,14,31]. We previously proposed that apoE may function as a "pathological chaperone" in the pathogenesis of AD (i.e. modulate the structure of Abeta, promoting or stabilizing a beta-sheet conformation), prior to the discovery of this linkage [7,40,41,42]. Data from apoE knockout / AbetaPP^(V717F) mice, has shown that the presence of apoE is necessary for cerebral amyloid formation [1,2], consistent with our hypothesis. However, in betaPP^(V717F) mice expressing human apoE3 or E4 early Abeta deposition at 9 months is suppressed, but by 15 months both human apoE expressing mice had significant fibrillar Abeta deposits with the apoE4 expressing mice having a 10 fold greater amyloid burden [8,9]. This and other data has suggested that apoE, in addition to having a facilitating role in fibril formation, may also influence clearance of Abeta peptides. In order to address if apoE affects the clearance of Abeta peptides across the blood-brain barrier (BBB) and whether there are differences in the clearance of Abeta40 versus Abeta42, we performed stereotactic, intra-ventricular micro-injections of Abeta40, Abeta42 or control peptides in wild-type, apoE knock-out (KO) or human apoE3 or apoE4 expressing transgenic mice. We found that consistent with other studies [5], Abeta40 is rapidly cleared from the brain across the BBB; however, Abeta42 is cleared much less effectively. This clearance of exogenous Abeta peptides across the BBB does not appear to be affected by apoE expression. This data suggests that Abeta42 production may favor amyloid deposition due to a reduced clearance across the BBB, compared to Abeta40. In addition, our experiments support a role of apoE as a pathological chaperone, and do not suggest an isotype specific role of apoE in exogenous Abeta peptide clearance from the CSF across the BBB.     

Alzheimer's pathology in human temporal cortex surgically excised after severe brain injury

Traumatic brain injury (TBI) is a risk factor for the development of Alzheimer's disease (AD). This immunohistochemical study determined the extent of AD-related changes in temporal cortex resected from individuals treated surgically for severe TBI. Antisera generated against Abeta species (total Abeta, Abeta(1-42), and Abeta(1-40)), the C-terminal of the Abeta precursor protein (APP), apolipoprotein E (apoE), and markers of neuron structure and degeneration (tau, ubiquitin, alpha-, beta-, and gamma-synuclein) were used to examine the extent of Abeta plaque deposition and neurodegenerative changes in 18 TBI subjects (ages 18-64 years). Diffuse cortical Abeta deposits were observed in one third of subjects (aged 35-62 years) as early as 2 h after injury, with only one (35-year old) individual exhibiting "mature", dense-cored plaques. Plaque-like deposits, neurons, glia, and axonal changes were also immunostained with APP and apoE antibodies. In plaque-positive cases, the only statistically significant change in cellular immunostaining was increased neuronal APP (P = 0.013). There was no significant correlation between the distribution of Abeta plaques and markers of neuronal degeneration. Diffuse tau immunostaining was localized to neuronal cell soma, axons or glial cells in a larger subset of individuals. Tau-positive, neurofibrillary tangle (NFT)-like changes were detected in only two subjects, both of more advanced age and who were without Abeta deposits. Other neurodegenerative changes, evidenced by ubiquitin- and synuclein-immunoreactive neurons, were abundant in the majority of cases. Our results demonstrate a differential distribution and course of intra- and extra-cellular AD-like changes during the acute phase following severe TBI in humans. Abeta plaques and early evidence of neuronal degenerative changes can develop rapidly after TBI, while fully developed NFTs most likely result from more chronic disease- or injury-related processes. These observations lend further support to the hypothesis that head trauma significantly increases the risk of developing pathological and clinical symptoms of AD, and provide insight into the molecular mechanisms that initiate these pathological cascades very early during severe brain injury.     

Age but not diagnosis is the main predictor of plasma amyloid beta-protein levels

BACKGROUND: Plasma amyloid beta-protein Abeta42 levels are increased in patients with familial Alzheimer disease (AD) mutations, and high levels reportedly identify individuals at risk to develop AD. OBJECTIVES: To determine whether there are characteristic changes in plasma Abeta40 and Abeta42 levels in sporadic AD, and to examine the relationship of plasma Abeta measures with clinical, demographic, and genetic variables in a prospectively characterized outpatient clinic population. PATIENTS: A total of 371 outpatients with sporadic AD (n = 146), mild cognitive impairment (n = 37), or Parkinson disease (n = 96) and nondemented control cases (n = 92). METHODS: We collected plasma samples and determined Abeta40 and Abeta42 levels by sandwich enzyme-linked immunosorbent assay with the use of the capture antibody BNT77 (anti-Abeta11-28) and the detector antibodies horseradish peroxidase-linked BA27 (anti-Abeta40) and BC05 (anti-Abeta42). RESULTS: Mean Abeta40 and Abeta42 levels increased significantly with age in each diagnostic group. When covaried for age, mean plasma levels of Abeta40 and Abeta42 did not differ significantly among the 4 diagnostic groups. Within the mild cognitive impairment and AD groups, Abeta40 and Abeta42 levels did not correlate with duration of memory impairment or with cognitive test scores. The Abeta measures were not influenced by family history of AD, apolipoprotein E genotype, or current medication use of cholinesterase inhibitors, vitamin E, statins, nonsteroidal anti-inflammatory drugs, or estrogen. CONCLUSIONS: Plasma Abeta measures increase with age, but, in contrast to reports on familial AD, plasma Abeta measures were neither sensitive nor specific for the clinical diagnosis of mild cognitive impairment or sporadic AD.     

Apolipoprotein E and beta-amyloid levels in the hippocampus and frontal cortex of Alzheimer's disease subjects are disease-related and apolipoprotein E genotype dependent.

The epsilon4 allele of apolipoprotein E (apoE) is associated with increased risk for the development of Alzheimer's disease (AD), possibly due to interactions with the beta-amyloid (Abeta) protein. The mechanism by which these two proteins are linked to AD is still unclear. To further assess their potential relationship with the disease, we have determined levels of apoE and Abeta isoforms from three brain regions of neuropathologically confirmed AD and non-AD tissue. In two brain regions affected by AD neuropathology, the hippocampus and frontal cortex, apoE levels were found to be decreased while Abeta(1-40) levels were increased. Levels of apoE were unchanged in AD cerebellum. Furthermore, levels of apoE and Abeta(1-40) were found to be apoE genotype dependent, with lowest levels of apoE and highest levels of Abeta(1-40) occurring in epsilon4 allele carriers. These results suggest that reduction in apoE levels may give rise to increased deposition of amyloid peptides in AD brain.     

Quantitation of apoE domains in Alzheimer disease brain suggests a role for apoE in Abeta aggregation

Apolipoprotein E (apoE) and apoE-derived proteolytic fragments are present in amyloid deposits in Alzheimer disease (AD) and cerebral amyloid angiopathy (CAA). In this study, we examined which apoE fragments are most strongly associated with amyloid deposits and whether apoE receptor binding domains were present. We found that both apoE2- and apoE4-specific residues were present on plaques and blood vessels in AD and CAA. We quantified Abeta plaque burden and apoE plaque burdens in 5 AD brains. ApoE N-terminal-specific and C-terminal-specific antibodies covered 50% and 74% of Abeta plaque burden, respectively (p < 0.003). Double-labeling demonstrated that the plaque cores contained the entire apoE protein, but that outer regions contained only a C-terminal fragment, suggesting a cleavage in the random coil region of apoE. Presence of N- and C-terminal apoE cleavage fragments in brain extracts was confirmed by immunoblotting. The numbers of plaques identified by the apoE N-terminal-specific antibodies and the apoE C-terminal-specific antibody were equal, but were only approximately 60% of the total Abeta plaque number (p < 0.0001). Analysis of the size distribution of Abeta and apoE deposits demonstrated that most of the Abeta-positive, apoE-negative deposits were the smallest deposits (less than 150 microm2). These data suggest that C-terminal residues of apoE bind to Abeta and that apoE may help aid in the progression of small Abeta deposits to larger deposits. Furthermore, the presence of the apoE receptor binding domain in the center of amyloid deposits could affect surrounding cells via chronic interactions with cell surface apoE receptors.     

Cerebrospinal fluid levels of beta-amyloid(42) in patients with Alzheimer's disease are related to the exon 2 polymorphism of the cathepsin D gene

The intracellular aspartyl protease cathepsin D (catD) is involved in such Alzheimer's disease (AD)-related processes as the activation of the endosomal/lysosomal system and the cleavage of the amyloid precursor protein into amyloidogenic components, which may initiate neurodegeneration. A non-synonymous polymorphism (exon 2, C to T exchange leading to ala-->val substitution) of the gene encoding catD (CTSD) was previously associated with AD, in that the T allele increased the risk for AD. To investigate whether the T allele is associated with disease-related traits, we measured the concentration of the amyloid beta-peptide 1-42 (Abeta(42)) and 1-40 (Abeta(40)) in patients and control subjects. The T allele of the CTSD genotype was associated with a 50% decrease in Abeta(42) levels in the cerebrospinal fluid. Thus, we demonstrate a significant impact of the CTSD genotype on Abeta(42) levels in the cerebrospinal fluid of AD patients and underpin the importance of the validation of susceptibility genes by examining their potential pathophysiological relevance.     

The nucleation growth and reversibility of Amyloid-beta deposition in vivo

The amyloid-beta (Abeta) peptide is a major constituent of the brain senile plaques that characterize Alzheimer's disease (AD). Converging observations led to the formulation of the amyloid hypothesis whereby the accumulation of soluble aggregates and insoluble Abeta deposits is the primary event in AD pathogenesis. Furthermore, the apoE4 isoform of apolipoprotein E, a major prevalent genetic risk factor of AD, is associated with increased Abeta deposition. To investigate the initial stages of the amyloid cascade in vivo and how this is affected by apoE4, we studied the effects of prolonged inhibition and subsequent reactivation of the Abeta-degrading enzyme, neprilysin, on aggregation and deposition of Abeta in apoE transgenic and control mice. The results revealed that Abeta deposition in vivo is initiated by aggregation of Abeta42, which is followed by reversible deposition of both Abeta42 and Abeta40, along with growth of the deposits, and by their subsequent irreversible fibrillization. The initiation of Abeta42 deposition is accelerated isoform-specifically by apoE4, whereas the growth and dissolution of the Abeta deposits as well as their fibrillization are similarly stimulated by the various apoE isoforms. Interestingly, Abeta deposition was associated with increased gliosis, which may reflect early pathological interactions of beta with the brain's parenchyma.