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      Post-mortem correlates of in vivo PiB-PET amyloid imaging in a typical case of Alzheimer's disease

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          Abstract

          The positron emission tomography (PET) radiotracer Pittsburgh Compound-B (PiB) binds with high affinity to β-pleated sheet aggregates of the amyloid-β (Aβ) peptide in vitro. The in vivo retention of PiB in brains of people with Alzheimer's disease shows a regional distribution that is very similar to distribution of Aβ deposits observed post-mortem. However, the basis for regional variations in PiB binding in vivo, and the extent to which it binds to different types of Aβ-containing plaques and tau-containing neurofibrillary tangles (NFT), has not been thoroughly investigated. The present study examined 28 clinically diagnosed and autopsy-confirmed Alzheimer's disease subjects, including one Alzheimer's disease subject who had undergone PiB-PET imaging 10 months prior to death, to evaluate region- and substrate-specific binding of the highly fluorescent PiB derivative 6-CN-PiB. These data were then correlated with region-matched Aβ plaque load and peptide levels, [ 3H]PiB binding in vitro, and in vivo PET retention levels. We found that in Alzheimer's disease brain tissue sections, the preponderance of 6-CN-PiB binding is in plaques immunoreactive to either Aβ42 or Aβ40, and to vascular Aβ deposits. 6-CN-PiB labelling was most robust in compact/cored plaques in the prefrontal and temporal cortices. While diffuse plaques, including those in caudate nucleus and presubiculum, were less prominently labelled, amorphous Aβ plaques in the cerebellum were not detectable with 6-CN-PiB. Only a small subset of NFT were 6-CN-PiB positive; these resembled extracellular ‘ghost’ NFT. In Alzheimer's disease brain tissue homogenates, there was a direct correlation between [ 3H]PiB binding and insoluble Aβ peptide levels. In the Alzheimer's disease subject who underwent PiB-PET prior to death, in vivo PiB retention levels correlated directly with region-matched post-mortem measures of [ 3H]PiB binding, insoluble Aβ peptide levels, 6-CN-PiB- and Aβ plaque load, but not with measures of NFT. These results demonstrate, in a typical Alzheimer's disease brain, that PiB binding is highly selective for insoluble (fibrillar) Aβ deposits, and not for neurofibrillary pathology. The strong direct correlation of in vivo PiB retention with region-matched quantitative analyses of Aβ plaques in the same subject supports the validity of PiB-PET imaging as a method for in vivo evaluation of Aβ plaque burden.

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          Most cited references54

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          Imaging beta-amyloid burden in aging and dementia.

          To compare brain beta-amyloid (Abeta) burden measured with [(11)C]Pittsburgh Compound B (PIB) PET in normal aging, Alzheimer disease (AD), and other dementias. Thirty-three subjects with dementia (17 AD, 10 dementia with Lewy bodies [DLB], 6 frontotemporal dementia [FTD]), 9 subjects with mild cognitive impairment (MCI), and 27 age-matched healthy control subjects (HCs) were studied. Abeta burden was quantified using PIB distribution volume ratio. Cortical PIB binding was markedly elevated in every AD subject regardless of disease severity, generally lower and more variable in DLB, and absent in FTD, whereas subjects with MCI presented either an "AD-like" (60%) or normal pattern. Binding was greatest in the precuneus/posterior cingulate, frontal cortex, and caudate nuclei, followed by lateral temporal and parietal cortex. Six HCs (22%) showed cortical uptake despite normal neuropsychological scores. PIB binding did not correlate with dementia severity in AD or DLB but was higher in subjects with an APOE-epsilon4 allele. In DLB, binding correlated inversely with the interval from onset of cognitive impairment to diagnosis. Pittsburgh Compound B PET findings match histopathologic reports of beta-amyloid (Abeta) distribution in aging and dementia. Noninvasive longitudinal studies to better understand the role of amyloid deposition in the course of neurodegeneration and to determine if Abeta deposition in nondemented subjects is preclinical AD are now feasible. Our findings also suggest that Abeta may influence the development of dementia with Lewy bodies, and therefore strategies to reduce Abeta may benefit this condition.
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            Visualization of A beta 42(43) and A beta 40 in senile plaques with end-specific A beta monoclonals: evidence that an initially deposited species is A beta 42(43).

            To learn about the carboxy-terminal extent of amyloid beta-protein (A beta) composition of senile plaques (SPs) in the brain affected with Alzheimer's disease (AD), we employed two end-specific monoclonal antibodies as immunocytochemical probes: one is specific for A beta 40, the carboxyl terminus of A beta 1-40, while the other is specific for A beta 42(43). In the AD cortex, all SPs that were labeled with an authentic antibody were A beta 42(43) positive, while only one-third of which, on the average, were A beta 40 positive. There was a strong correlation between A beta 40 positivity and mature plaques. Two familial AD cortices with the mutation of beta-amyloid protein precursor 717 (beta APP717) (Val to Ile) showed a remarkable predominance of A beta 42(43)-positive, A beta 40-negative plaques. Diffuse plaques, representing the earliest stage of A beta deposition, were exclusively positive for A beta 42(43), but completely negative for A beta 40.
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              Correlation between elevated levels of amyloid beta-peptide in the brain and cognitive decline.

              Alzheimer disease (AD) is characterized neuropathologically by the presence of amyloid beta-peptide (Abeta)-containing plaques and neurofibrillary tangles composed of abnormal tau protein. Considerable controversy exists as to whether the extent of accumulation of Abeta correlates with dementia and whether Abeta alterations precede or follow changes in tau. To determine whether accumulation of Abeta correlates with the earliest signs of cognitive deterioration and to define the relationship between Abeta accumulation and early tau changes. Postmortem cross-sectional study of 79 nursing home residents with Clinical Dementia Rating (CDR) scale scores of 0.0 to 5.0 who died between 1986 and 1997, comparing the levels of Abeta variants in the cortices of the subjects with no (CDR score, 0.0 [n = 16]), questionable (CDR score, 0.5 [n = 11]), mild (CDR score, 1.0 [n = 22]), moderate (CDR score, 2.0 [n = 15]), or severe (CDR score, 4.0 or 5.0 [n = 15]) dementia. Levels of total Abeta peptides with intact or truncated amino termini and ending in either amino acid 40 (A(beta)x-40) or 42 (A(beta)x-42) in 5 neocortical brain regions as well as levels of tau protein undergoing early conformational changes in frontal cortex, as a function of CDR score. The levels of both A(beta)x-40 and A(beta)x-42 were elevated even in cases classified as having questionable dementia (CDR score = 0.5), and increases of both peptides correlated with progression of dementia. Levels of the more fibril-prone A(beta)x-42 peptide were higher than those of A(beta)x-40 in nondemented cases and remained higher throughout progression of disease in all regions examined. Finally, increases in A(beta)x-40 and A(beta)x-42 precede significant tau pathology at least in the frontal cortex, an area chosen for examination because of the absence of neuritic changes in the absence of disease. In this study, levels of total A(beta)x-40 and A(beta)x-42 were elevated early in dementia and levels of both peptides were strongly correlated with cognitive decline. Of particular interest, in the frontal cortex, Abeta was elevated before the occurrence of significant tau pathology. These results support an important role for Abeta in mediating initial pathogenic events in AD dementia and suggest that treatment strategies targeting the formation, accumulation, or cytotoxic effects of Abeta should be pursued.
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                Author and article information

                Journal
                Brain
                brainj
                brain
                Brain
                Oxford University Press
                0006-8950
                1460-2156
                June 2008
                12 March 2008
                12 March 2008
                : 131
                : 6
                : 1630-1645
                Affiliations
                1Department of Neurology, 2Department of Psychiatry, 3Department of Radiology and 4Department of Neuropathology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15213, USA
                Author notes
                Correspondence to: Steven T. DeKosky, MD, Department of Neurology, 3471 Fifth Avenue, Suite 811, Pittsburgh, PA 15213, USA E-mail: dekoskyst@ 123456upmc.edu
                Article
                awn016
                10.1093/brain/awn016
                2408940
                18339640
                8fe6759d-917f-4466-93d8-31158c8025f7
                © 2008 The Author(s)

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 28 October 2007
                : 29 December 2007
                : 21 January 2008
                Categories
                Original Articles

                Neurosciences
                amyloid imaging,plaques,pittsburgh compound-b,pib,pet imaging
                Neurosciences
                amyloid imaging, plaques, pittsburgh compound-b, pib, pet imaging

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