Background-We evaluated the amounts of amyloid-beta (Aβ) peptides in the central nervous system (CNS) and in reservoirs outside the CNS and their potential impact on Aβ plasma levels and Alzheimer's disease (AD) pathology.

We have undertaken an integrated chemical and morphological comparison of the amyloid-␤ (A␤) molecules and the amyloid plaques present in the brains of APP23 transgenic (tg) mice and human Alzheimer's disease (AD) patients. Despite an apparent overall structural resemblance to AD pathology, our detailed chemical analyses revealed that although the amyloid plaques characteristic of AD contain cores that are highly resistant to chemical and physical disruption, the tg mice produced amyloid cores that were completely soluble in buffers containing SDS. A␤ chemical alterations account for the extreme stability of AD plaque core amyloid. The corresponding lack of post-translational modifications such as N-terminal degradation, isomerization, racemization, pyroglutamyl formation, oxidation, and covalently linked dimers in tg mouse A␤ provides an explanation for the differences in solubility between human AD and the APP23 tg mouse plaques. We hypothesize either that insufficient time is available for A␤ structural modifications or that the complex species-specific environment of the human disease is not precisely replicated in the tg mice. The appraisal of therapeutic agents or protocols in these animal models must be judged in the context of the lack of complete equivalence between the transgenic mouse plaques and the human AD lesions. Alzheimer's disease (AD)1 is a progressive neurodegenerative disorder characterized by the presence of extracellular amyloid plaques composed principally of amyloid-␤ (A␤) surrounded by dystrophic neurites (1). This association and the realization that the basis of certain early-onset familial forms of AD seems to be the enhanced production of one or more A␤ peptides have led to the hypothesis that A␤ is intimately involved in the AD pathogenic process (2). A promising experimental approach to unraveling the role(s) of A␤ in AD pathology has been the construction and characterization of transgenic mice that overexpress the amyloid precursor protein (APP) (3-12). Several transgenic mouse lines have been described that produce A␤ deposits that accumulate in an agedependent fashion and morphologically resemble the senile plaques characteristic of human AD (3,6,8,12,37,38).The APP23 transgenic (tg) mice contain an APP751 cDNA with the Swedish familial AD mutation under the control of the neuron-specific Thy-1 promoter and express this human gene at levels 7-fold greater than endogenous murine APP (12). Longitudinal studies of these mice have revealed that extracellular amyloid deposits become evident as the APP23 tg mice age. These deposits exhibit, at their earliest appearance, the Congo red birefringence characteristic of the dense core plaques of human AD (12). A gradual progression from a diffuse deposit to a dense plaque is not a feature of the APP23 tg mouse pathology, paralleling our previous finding (13) that the diffuse amyloid deposits of AD do not represent a precursor developmental stage of senile plaques.A transgenic mouse model system that faithfully mimics every aspect of AD h...

Relative to the gray matter, there is a paucity of information regarding white matter biochemical alterations and their contribution to Alzheimer's disease (AD). Biochemical analyses of AD white matter combining size-exclusion, normal phase, and gas chromatography, immunoassays, and Western blotting revealed increased quantities of Abeta40 and Abeta42 in AD white matter accompanied by significant decreases in the amounts of myelin basic protein, myelin proteolipid protein, and 2',3'-cyclic nucleotide 3'-phosphodiesterase. In addition, the AD white matter cholesterol levels were significantly decreased while total fatty acid content was increased. In some instances, these white matter biochemical alterations were correlated with patient apolipoprotein E genotype, Braak stage, and gender. Our observations suggest that extensive white matter axonal demyelination underlies Alzheimer's pathology, resulting in loss of capacitance and serious disturbances in nerve conduction, severely damaging brain function. These white matter alterations undoubtedly contribute to AD pathogenesis and may represent the combined effects of neuronal degeneration, microgliosis, oligodendrocyte injury, microcirculatory disease, and interstitial fluid stasis. To accurately assess the success of future therapeutic interventions, it is necessary to have a complete appreciation of the full scope and extent of AD pathology.

Experiments with amyloid-␤ (A␤)-42-immunized transgenic mouse models of Alzheimer's disease have revealed amyloid plaque disruption and apparent cognitive function recovery. Neuropathological examination of patients vaccinated against purified A␤-42 (AN-1792) has demonstrated that senile plaque disruption occurred in immunized humans as well. Here, we examined tissue histology and quantified and biochemically characterized the remnant amyloid peptides in the gray and white matter and leptomeningeal/cortical vessels of two AN-1792-vaccinated patients, one of whom developed meningoencephalitis. Compact core and diffuse amyloid deposits in both vaccinated individuals were focally absent in some regions. Although parenchymal amyloid was focally disaggregated, vascular deposits were relatively preserved or even increased. Immunoassay revealed that total soluble amyloid levels were sharply elevated in vaccinated patient gray and white matter compared with Alzheimer's disease cases. Our experiments suggest that although immunization disrupted amyloid deposits, vascular capture prevented largescale egress of A␤ peptides. Trapped, solubilized amyloid peptides may ultimately have cascading toxic effects on cerebrovascular, gray and white matter tissues. Anti-amyloid immunization may be most effective not as therapeutic or mitigating measures but as a prophylactic measure when A␤ deposition is still minimal. This may allow A␤ mobilization under conditions in which drainage and degradation of these toxic peptides is efficient.

Alzheimer's disease (AD) is characterized by neurofibrillary tangles and by the accumulation of β-amyloid (Aβ) peptides in senile plaques and in the walls of cortical and leptomeningeal arteries as cerebral amyloid angiopathy (CAA). There also is a significant increase of interstitial fluid (ISF) in cerebral white matter (WM), the pathological basis of which is largely unknown. We hypothesized that the accumulation of ISF in dilated periarterial spaces of the WM in AD correlates with the severity of CAA, with the total Aβ load in the cortex and with Apo E genotype. A total of 24 AD brains and 17 nondemented age-matched control brains were examined. CAA was seen in vessels isolated from brain by using EDTA-SDS lysis stained by Thioflavin-S. Total Aβ in gray matter and WM was quantified by immunoassay, ApoE genotyping by PCR, and dilatation of perivascular spaces in the WM was assessed by quantitative histology. The study showed that the frequency and severity of dilatation of perivascular spaces in the WM in AD were significantly greater than in controls (P < 0.001) and correlated with Aβ load in the cortex, with the severity of CAA, and with ApoE ε4 genotype. The results of this study suggest that dilation of perivascular spaces and failure of drainage of ISF from the WM in AD may be associated with the deposition of Aβ in the perivascular fluid drainage pathways of cortical and leptomeningeal arteries. This failure of fluid drainage has implications for therapeutic strategies to treat Alzheimer's disease.

Objectives-We conducted a quantitative investigation of brain arterial atherosclerotic damage and its relationship to sporadic Alzheimer's disease (AD). Methods and Results-Fifty-four consecutive autopsy cases, 32 AD and 22 nondemented control subjects, were examined to establish the degree of arterial stenosis. Vessel external and lumenal area measurements were taken from 3-mm arterial cross-sections to calculate a stenosis index. AD patient circle of Willis arteries possessed a significant degree of stenosis as a consequence of multiple and severe atherosclerotic lesions. These lesions were significantly more severe in AD cases than in age-matched controls (PϽ0.0001), and the number of stenoses and the index of occlusion (Rϭ0.67; PϽ0.00001) were positively correlated. In addition, the index of stenosis significantly correlated with the following measures of AD neuropathological lesions: total plaque score, neuritic plaque score, neurofibrillary tangle score, Braak stage score, and white matter rarefaction score. Conclusions-Our study reveals an association between severe circle of Willis atherosclerosis and sporadic AD that should be considered a risk factor for this dementia. 38 and AD subjects exhibit positive correlations between brain A␤ n-42 levels and total serum cholesterol, LDL cholesterol, and apolipoprotein (Apo) B-100 and a negative correlation with HDL cholesterol levels. 38 Elevated total and LDL cholesterol have been reported in very old patients with AD. 39 Likewise, in a meta-analysis study, patients with probable or possible early-stage AD were found to possess elevated total cholesterol values compared with a ND population. 40 In addition to the wellestablished association between vascular disease risk factors and sporadic AD, the present study provides, for the first time, a rigorous and significant neuropathological association between circle of Willis atherosclerosis and sporadic AD. See page 1951 and cover MethodsSubjects were voluntary participants in the Brain Donation Program at Sun Health Research Institute (Sun City, Ariz). Rapid autopsies (2.5-hour average postmortem delay) were performed to remove and preserve the brain. All individuals examined were Caucasian. The degree and extent of arterial stenosis was quantified in 54 consecutive autopsy cases, in which neuropathologic examination indicated presence of either AD or normal aging changes only; the latter cases were considered ND controls if the neuropsychologic profile was within normal age limits.The sample subjected to computer-based quantitative analysis contained 22 ND control cases, consisting of 14 women and 8 men with mean ages of 87.1 and 82.6 years, respectively, and 32 AD cases, 18 women and 14 men with mean ages of 84.4 and 86.4 years, respectively. History of cardiovascular disease, in particular the presence or absence of hypertension, myocardial infarction, coronary artery disease, valvular heart disease, disorders of rhythm and conduction, cardiomyopathy, cardiorespiratory failure, and peripher-

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The amyloid (Abeta) peptides generated in Hsiao's APP Tg2576 transgenic (Tg) mice are physically and chemically distinct from those characteristic of Alzheimer's disease (AD). Transgenic mouse Abeta peptides were purified using sequential size-exclusion and reverse-phase chromatographic systems and subjected to amino acid sequencing and mass spectrometry analyses. The mouse Abeta peptides lacked the extensive N-terminal degradations, posttranslational modifications, and cross-linkages abundant in the stable Abeta peptide deposits observed in AD. Truncated Abeta molecules appear to be generated in vivo by hydrolysis at multiple sites rather than by post-mortem C-terminal degradation. In contrast to AD amyloid cores, the Tg mice peptides were soluble in Tris-SDS-EDTA solutions, revealing both monomeric and SDS-stable oligomeric species of Abeta. In contrast to our report on Novartis Pharma APP23 Tg mice [Kuo et al. (2001) J. Biol. Chem. 276, 12991], which maintain high levels of soluble Abeta early on with later development of extensive vascular amyloid, Tg2576 mice exhibited an age-related elevation of soluble Abeta with relatively limited vascular amyloid deposition. The transgenic mouse levels of carboxy-terminal (CT) APP fragments were nearly 10-fold greater than those of human brains, and this condition may contribute to the unique pathology observed in these animals. Immunization of transgenic mice may act to prevent the pathological effects of betaAPP overproduction by binding CT molecules or halting their processing to toxic forms, in addition to having any effects on Abeta itself. Thus, differences in disease evolution and biochemistry must be considered when using transgenic animals to evaluate drugs or therapeutic interventions intended to reduce the Abeta burden in Alzheimer's disease.