Head-to-head comparison of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 postmortem binding across the spectrum of neurodegenerative diseases.

We and others have shown that [18F]-Flortaucipir, the most validated tau PET tracer thus far, binds with strong affinity to tau aggregates in Alzheimer's (AD) but has relatively low affinity for tau aggregates in non-AD tauopathies and exhibits off-target binding to neuromelanin- and melanin-containing cells, and to hemorrhages. Several second-generation tau tracers have been subsequently developed. [18F]-MK-6240 and [18F]-PI-2620 are the two that have garnered most attention. Our recent data indicated that the binding pattern of [18F]-MK-6240 closely parallels that of [18F]-Flortaucipir. The present study aimed at the direct comparison of the autoradiographic binding properties and off-target profile of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 in human tissue specimens, and their potential binding to monoamine oxidases (MAO). Phosphor-screen and high resolution autoradiographic patterns of the three tracers were studied in the same postmortem tissue material from AD and non-AD tauopathies, cerebral amyloid angiopathy, synucleopathies, transactive response DNA-binding protein 43 (TDP-43)-frontotemporal lobe degeneration and controls. Our results show that the three tracers show nearly identical autoradiographic binding profiles. They all strongly bind to neurofibrillary tangles in AD but do not seem to bind to a significant extent to tau aggregates in non-AD tauopathies pointing to their limited utility for the in vivo detection of non-AD tau lesions. None of them binds to lesions containing ß-amyloid, α-synuclein or TDP-43 but they all show strong off-target binding to neuromelanin and melanin-containing cells, as well as weaker binding to areas of hemorrhage. The autoradiographic binding signals of the three tracers are only weakly displaced by competing concentrations of selective MAO-B inhibitor deprenyl but not by MAO-A inhibitor clorgyline suggesting that MAO enzymes do not appear to be a significant binding target of any of them. These findings provide relevant insights for the correct interpretation of the in vivo behavior of these three tau PET tracers.

Projection of Care Partners' Preferences in the Proxy Assessments of Everyday Preferences for Persons With Cognitive Impairment.

OBJECTIVE: Bias in surrogate decision-making can occur when proxy decision-makers overestimate the degree to which their preferences are shared by others, resulting in a projection of their beliefs onto others. The purpose of this study is to assess projection of care partners' preferences onto surrogate assessments of everyday preferences for persons with cognitive impairment (CI) and to address clinical and demographic factors as predictors of projection. METHODS: The sample included 116 dyads of persons with CI (Clinical Dementia Rating Scale score ≥ 0.5) and their care partners. The Preferences for Everyday Living Inventory (PELI) was used to assess importance of preferences among persons with CI. Care partners completed two separate PELI assessments: one from the perspective of the persons with CI (i.e., acting as a surrogate decision-maker) and one from their own perspective. To assess for projection of care partners' preferences onto surrogate assessments of preferences for persons with CI, two-step regression with multivariable-adjusted general linear models was used. RESULTS: Significant projection was noted within the PELI domains of autonomous choice, personal growth, and keeping a routine (p < 0.005). More significant cognitive impairment was associated with increased projection within the PELI domains of autonomous choice and personal growth (p < 0.05). CONCLUSION: The results of this study suggest that projection of care partners' own preferences may be a significant source of bias in proxy decision-making regarding everyday preferences for persons with CI, particularly for those with more significant CI.

Potential impact of the COVID-19 pandemic on everyday preferences for persons with cognitive impairment.

The COVID-19 pandemic and subsequent social distancing guidelines and restrictions brought on changes in the everyday experiences of older adults. It is not clear, however, to what extent the pandemic has impacted the importance of everyday preferences for persons with cognitive impairment (CI) or the proxy ratings of those preferences. The sample of this study included 27 dyads of persons with CI and their care partners. The Preferences for Everyday Living Inventory was used to assess importance of preferences among persons with CI; care partners completed concurrent proxy assessments. Mixed random and fixed effects longitudinal models were used to evaluate changes in ratings and concordance levels between persons with CI and care partners prior to and during the COVID-19 pandemic. Persons with CI rated autonomous choice preferences as significantly more important during the COVID-19 pandemic than before; there was no association between the COVID-19 pandemic and change in other everyday preferences domains or discrepancy in proxy assessments of everyday preferences. Identifying avenues to support and provide for autonomy in the decision-making of older adults with CI may offer a way forward in mitigating the psychological and behavioral impacts of the COVID-19 pandemic in this population.

Longitudinal Changes in Neuropsychiatric Symptoms: Impact of Discrepancy in Everyday Preferences Between Persons With Cognitive Impairment and Their Care Partners.

OBJECTIVES: Neuropsychiatric symptoms (NPS) of dementia are common and may be driven by inability of persons with cognitive impairment (CI) to communicate needs. We addressed the relevance of this unmet-needs model to burden of NPS among persons with milder CI. METHODS: The sample included 48 dyads of persons with CI and their care partners. NPS were measured at baseline and follow-up (mean 486 days +/-107 SD). Mixed random and fixed effects longitudinal models were used to evaluate impact of discrepancies between persons with CI and their care partners in everyday preferences (baseline) on changes in NPS over time. RESULTS: Higher levels of underestimation of "social engagement" preferences of persons with CI by care partners were associated with a higher average burden of NPS across all follow-up. CONCLUSIONS: This study suggests that unmet-needs may be a useful construct for understanding etiology for NPS across the spectrum of severity of cognitive impairment.

Predictors of the importance of everyday preferences for older adults with cognitive impairment.

OBJECTIVES: Among older people with cognitive impairment and mild dementia, relatively little is known about the factors that predict preferences for everyday living activities and experiences and that influence the relative importance of those activities and experiences. DESIGN: Cross-sectional study. SETTING: Participants were recruited from the Massachusetts Alzheimer's Disease Research Center (MADRC) Clinical Core longitudinal cohort. PARTICIPANTS: The sample included 62 community-dwelling older adults with cognitive impairment (Clinical Dementia Rating global score ≥ 0.5). MEASUREMENTS: We used the Preferences for Everyday Living Inventory (PELI) to assess preferences for activities and lifestyle experiences among persons with cognitive impairment. Within-subjects analysis of variance was used to test for significant differences in the mean ratings of importance for four domains of the PELI ("autonomous choice," "social engagement," "personal growth," and "keeping a routine"). Multiple regression models were used to relate predictors, including neuropsychiatric symptoms, to importance ratings for each domain. RESULTS: Significant differences were noted in the mean importance ratings of the preferences domains: "social engagement" preferences were rated as most important, followed by "autonomous choice," "personal growth," and "keeping a routine." For the "social engagement" preferences domain, female sex was significantly associated with higher importance of "social engagement," while depressive symptoms (Geriatric Depression Scale-15 scores) were significantly associated with lower importance. CONCLUSIONS: This study adds novel insight into the everyday preferences of community-dwelling older adults with cognitive impairment and highlights the impact of a number of factors, particularly level of depression, on how important various everyday experiences are perceived.

Longitudinal differences in everyday preferences: Comparisons between people with cognitive impairment and their care partners.

OBJECTIVES: Persons with progressive cognitive impairment (CI) increasingly rely on surrogate decision-makers for everyday activities. Yet, little is known about changes in everyday preferences over time or about concordance between persons with CI and their care partners regarding longitudinal changes. METHODS: The sample included 48 dyads of persons with CI (Clinical Dementia Rating Scale score ≥0.5) and their care partners. The Preferences for Everyday Living Inventory was used to assess importance of preferences among persons with CI at baseline and follow-up (mean 486 days). Care partners separately completed concurrent proxy assessments. Mixed random and fixed effects longitudinal models were used to evaluate changes in ratings and concordance levels between persons with CI and care partners. RESULTS: There were significant gender differences regarding importance ratings of "autonomous choice" and "social engagement" preferences over time: women with CI rated these preferences as more important across time as a whole. Higher levels of neuropsychiatric symptoms were associated with less importance of "social engagement" preferences across time as a whole for persons with CI and a more negative discrepancy between persons with CI and care partner proxy assessments as time went on. CONCLUSION: This study yields new insights into predictors of longitudinal change in everyday preferences among persons with CI and their care partners. Although preferences were largely stable over time, there is increasing support for the relationship between differences in "social engagement" preferences and neuropsychiatric symptoms, which may have implications for monitoring and/or treatment in the context of cognitive impairment.

Distinct cytokine profiles in human brains resilient to Alzheimer's pathology.

Our group has previously studied the brains of some unique individuals who are able to tolerate robust amounts of Alzheimer's pathological lesions (amyloid plaques and neurofibrillary tangles) without experiencing dementia while alive. These rare resilient cases do not demonstrate the patterns of neuronal/synaptic loss that are normally found in the brains of typical demented Alzheimer's patients. Moreover, they exhibit decreased astrocyte and microglial activation markers GFAP and CD68, suggesting that a suppressed neuroinflammatory response may be implicated in human brain resilience to Alzheimer's pathology. In the present work, we used a multiplexed immunoassay to profile a panel of 27 cytokines in the brains of controls, typical demented Alzheimer's cases, and two groups of resilient cases, which possessed pathology consistent with either high probability (HP, Braak stage V-VI and CERAD 2-3) or intermediate probability (IP, Braak state III-IV and CERAD 1-3) of Alzheimer's disease in the absence of dementia. We used a multivariate partial least squares regression approach to study differences in cytokine expression between resilient cases and both Alzheimer's and control cases. Our analysis identified distinct profiles of cytokines in the entorhinal cortex (one of the earliest and most severely affected brain regions in Alzheimer's disease) that are up-regulated in both HP and IP resilient cases relative to Alzheimer's and control cases. These cytokines, including IL-1ß, IL-6, IL-13, and IL-4 in HP resilient cases and IL-6, IL-10, and IP-10 in IP resilient cases, delineate differential inflammatory activity in brains resilient to Alzheimer's pathology compared to Alzheimer's cases. Of note, these cytokines all have been associated with pathogen clearance and/or the resolution of inflammation. Moreover, our analysis in the superior temporal sulcus (a multimodal association cortex that consistently accumulates Alzheimer's pathology at later stages of the disease along with overt symptoms of dementia) revealed increased expression of neurotrophic factors, such as PDGF-bb and basic FGF in resilient compared to AD cases. The same region also had reduced expression of chemokines associated with microglial recruitment, including MCP-1 in HP resilient cases and MIP-1α in IP resilient cases compared to AD. Altogether, our data suggest that different patterns of cytokine expression exist in the brains of resilient and Alzheimer's cases, link these differences to reduced glial activation, increased neuronal survival and preserved cognition in resilient cases, and reveal specific cytokine targets that may prove relevant to the identification of novel mechanisms of brain resiliency to Alzheimer's pathology.

Pathological correlations of [F-18]-AV-1451 imaging in non-alzheimer tauopathies.

OBJECTIVE: Recent studies have shown that positron emission tomography (PET) tracer AV-1451 exhibits high binding affinity for paired helical filament (PHF)-tau pathology in Alzheimer's brains. However, the ability of this ligand to bind to tau lesions in other tauopathies remains controversial. Our goal was to examine the correlation of in vivo and postmortem AV-1451 binding patterns in three autopsy-confirmed non-Alzheimer tauopathy cases. METHODS: We quantified in vivo retention of [F-18]-AV-1451 and performed autoradiography, [H-3]-AV-1451 binding assays, and quantitative tau measurements in postmortem brain samples from two progressive supranuclear palsy (PSP) cases and a MAPT P301L mutation carrier. They all underwent [F-18]-AV-1451 PET imaging before death. RESULTS: The three subjects exhibited [F-18]-AV-1451 in vivo retention predominantly in basal ganglia and midbrain. Neuropathological examination confirmed the PSP diagnosis in the first two subjects; the MAPT P301L mutation carrier had an atypical tauopathy characterized by grain-like tau-containing neurites in gray and white matter with heaviest burden in basal ganglia. In all three cases, autoradiography failed to show detectable [F-18]-AV-1451 binding in multiple brain regions examined, with the exception of entorhinal cortex (reflecting incidental age-related neurofibrillary tangles) and neuromelanin-containing neurons in the substantia nigra (off-target binding). The lack of a consistent significant correlation between in vivo [F-18]-AV-1541 retention and postmortem in vitro binding and tau measures in these cases suggests that this ligand has low affinity for tau lesions primarily made of straight tau filaments. INTERPRETATION: AV-1451 may have limited utility for in vivo selective and reliable detection of tau aggregates in these non-Alzheimer tauopathies. ANN NEUROL 2017;81:117-128.

Topological analyses in APP/PS1 mice reveal that astrocytes do not migrate to amyloid-ß plaques.

Although the clustering of GFAP immunopositive astrocytes around amyloid-ß plaques in Alzheimer's disease has led to the widespread assumption that plaques attract astrocytes, recent studies suggest that astrocytes stay put in injury. Here we reexamine astrocyte migration to plaques, using quantitative spatial analysis and computer modeling to investigate the topology of astrocytes in 3D images obtained by two-photon microscopy of living APP/PS1 mice and WT littermates. In WT mice, cortical astrocyte topology fits a model in which a liquid of hard spheres exclude each other in a confined space. Plaques do not disturb this arrangement except at very large plaque loads, but, locally, cause subtle outward shifts of the astrocytes located in three tiers around plaques. These data suggest that astrocytes respond to plaque-induced neuropil injury primarily by changing phenotype, and hence function, rather than location.

In Vivo Tau, Amyloid, and Gray Matter Profiles in the Aging Brain.

UNLABELLED: We provide a comparative in vivo examination of the brain network-based distribution of two hallmarks of Alzheimer's disease (AD) pathology in cognitively normal individuals: (1) Tau, detected with a novel positron emission tomography (PET) tracer known as (18)F-AV-1451; and (2) amyloid-ß, quantified with (11)C-PiB PET. We used a high-resolution graph-based approach to investigate local-to-local and local-to-distributed cortical associations between the maps of Tau, amyloid-ß, and gray matter intensity. Our study shows that Tau and amyloid-ß deposits are associated with distinctive spatial patterns of brain tissue loss. Moreover, Tau and amyloid-ß accumulations have strong network interdigitations in heteromodal and associative areas of the cortical mantle, particularly the inferior-lateral temporal lobe. These findings contribute significantly to our understanding of how these two main hallmarks of AD pathology propagate across the elderly human brain. SIGNIFICANCE STATEMENT: It has been postulated that Alzheimer's disease (AD) pathology interacts and resides within system-level circuits of the human brain, long before the onset of cognitive symptoms. However, a side-by-side comparison of tissue loss, amyloid-ß, and Tau deposition in early stages of the disease has been precluded until the recent advent of Tau tracer-based neuroimaging. In this study, we used Tau positron emission tomography and network analyses to disentangle these pathological relationships. We found that Tau and amyloid-ß deposits are associated with distinctive spatial patterns of brain tissue loss. Moreover, we uncovered the network interdigitations of Tau and amyloid-ß in the cortical mantle. These findings contribute significantly to our understanding of how two main hallmarks of AD pathology propagate across the elderly human brain.

Episodic memory of odors stratifies Alzheimer biomarkers in normal elderly.

OBJECTIVE: The objective of this study was to relate a novel test of identifying and recalling odor percepts to biomarkers of Alzheimer's disease (AD) in well-characterized elderly individuals, ranging from cognitively normal to demented. METHODS: One hundred eighty-three participants (cognitively normal: n = 70; subjective cognitive concerns: n = 74; mild cognitive impairment [MCI]: n = 29, AD dementia: n = 10) were administered novel olfactory tests: the Odor Percept IDentification (OPID) and the Percepts of Odor Episodic Memory (POEM) tests. Univariate cross-sectional analyses of performance across diagnoses; logistic regression modeling, including covariates of age, sex, education, APOE genotype, and neuropsychological test scores; and linear mixed modeling of longitudinal cognitive scores were performed. Amyloid deposition and MRI volumetrics were analyzed in a subset of participants. RESULTS: Accuracy of identification and episodic memory of odor percepts differed significantly across diagnosis and age, with progressively worse performance across degrees of impairment. Among the participants who were cognitively normal or had subjective cognitive concerns, poorer than expected performance on the POEM test (based on the same individual's performance on the OPID and odor discrimination tests) was associated with higher frequencies of the APOE ε4 allele, thinner entorhinal cortices, and worse longitudinal trajectory of Logical Memory scores. INTERPRETATION: Selective impairment of episodic memory of odor percepts, relative to identification and discrimination of odor percepts revealed by this novel POEM battery, is associated with biomarkers of AD in a well-characterized pre-MCI population. These affordable, noninvasive olfactory tests offer potential to identify clinically normal individuals who have greater likelihood of future cognitive decline. Ann Neurol 2016;80:846-857.

Tau positron emission tomographic imaging in aging and early Alzheimer disease.

OBJECTIVE: Detection of focal brain tau deposition during life could greatly facilitate accurate diagnosis of Alzheimer disease (AD), staging and monitoring of disease progression, and development of disease-modifying therapies. METHODS: We acquired tau positron emission tomography (PET) using (18)F T807 (AV1451), and amyloid-ß PET using (11)C Pittsburgh compound B (PiB) in older clinically normal individuals, and symptomatic patients with mild cognitive impairment or mild AD dementia. RESULTS: We found abnormally high cortical (18)F T807 binding in patients with mild cognitive impairment and AD dementia compared to clinically normal controls. Consistent with the neuropathology literature, the presence of elevated neocortical (18)F T807 binding particularly in the inferior temporal gyrus was associated with clinical impairment. The association of cognitive impairment was stronger with inferior temporal (18)F T807 than with mean cortical (11)C PIB. Regional (18)F T807 was correlated with mean cortical (11)C PiB among both impaired and control subjects. INTERPRETATION: These findings suggest that (18)F T807 PET could have value as a biomarker that reflects both the progression of AD tauopathy and the emergence of clinical impairment.

[F-18]-AV-1451 binding correlates with postmortem neurofibrillary tangle Braak staging.

[F-18]-AV-1451, a PET tracer specifically developed to detect brain neurofibrillary tau pathology, has the potential to facilitate accurate diagnosis of Alzheimer's disease (AD), staging of brain tau burden and monitoring disease progression. Recent PET studies show that patients with mild cognitive impairment and AD dementia exhibit significantly higher in vivo [F-18]-AV-1451 retention than cognitively normal controls. Importantly, PET patterns of [F-18]-AV-1451 correlate well with disease severity and seem to match the predicted topographic Braak staging of neurofibrillary tangles (NFTs) in AD, although this awaits confirmation. We studied the correlation of autoradiographic binding patterns of [F-18]-AV-1451 and the stereotypical spatiotemporal pattern of progression of NFTs using legacy postmortem brain samples representing different Braak NFT stages (I-VI). We performed [F-18]-AV-1451 phosphor-screen autoradiography and quantitative tau measurements (stereologically based NFT counts and biochemical analysis of tau pathology) in three brain regions (entorhinal cortex, superior temporal sulcus and visual cortex) in a total of 22 cases: low Braak (I-II, n = 6), intermediate Braak (III-IV, n = 7) and high Braak (V-VI, n = 9). Strong and selective [F-18]-AV-1451 binding was detected in all tangle-containing regions matching precisely the observed pattern of PHF-tau immunostaining across the different Braak stages. As expected, no signal was detected in the white matter or other non-tangle containing regions. Quantification of [F-18]-AV-1451 binding was very significantly correlated with the number of NFTs present in each brain region and with the total tau and phospho-tau content as reported by Western blot and ELISA. [F-18]-AV-1451 is a promising biomarker for in vivo quantification of brain tau burden in AD. Neuroimaging-pathologic studies conducted on postmortem material from individuals imaged while alive are now needed to confirm these observations.

Validating novel tau positron emission tomography tracer [F-18]-AV-1451 (T807) on postmortem brain tissue.

OBJECTIVE: To examine region- and substrate-specific autoradiographic and in vitro binding patterns of positron emission tomography tracer [F-18]-AV-1451 (previously known as T807), tailored to allow in vivo detection of paired helical filament-tau-containing lesions, and to determine whether there is off-target binding to other amyloid/non-amyloid proteins. METHODS: We applied [F-18]-AV-1451 phosphor screen autoradiography, [F-18]-AV-1451 nuclear emulsion autoradiography, and [H-3]-AV-1451 in vitro binding assays to the study of postmortem samples from patients with a definite pathological diagnosis of Alzheimer disease, frontotemporal lobar degeneration-tau, frontotemporal lobar degeneration-transactive response DNA binding protein 43 (TDP-43), progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies, multiple system atrophy, cerebral amyloid angiopathy and elderly controls free of pathology. RESULTS: Our data suggest that [F-18]-AV-1451 strongly binds to tau lesions primarily made of paired helical filaments in Alzheimer brains (eg, intraneuronal and extraneuronal tangles and dystrophic neurites), but does not seem to bind to a significant extent to neuronal and glial inclusions mainly composed of straight tau filaments in non-Alzheimer tauopathy brains or to lesions containing ß-amyloid, α-synuclein, or TDP-43. [F-18]-AV-1451 off-target binding to neuromelanin- and melanin-containing cells and, to a lesser extent, to brain hemorrhagic lesions was identified. INTERPRETATION: Our data suggest that [F-18]-AV-1451 holds promise as a surrogate marker for the detection of brain tau pathology in the form of tangles and paired helical filament-tau-containing neurites in Alzheimer brains but also point to its relatively lower affinity for lesions primarily made of straight tau filaments in non-Alzheimer tauopathy cases and to the existence of some [F-18]-AV-1451 off-target binding. These findings provide important insights for interpreting in vivo patterns of [F-18]-AV-1451 retention.

Mild to moderate Alzheimer dementia with insufficient neuropathological changes.

Recently, ~16% of participants in an anti-Aß passive immunotherapy trial for mild-to-moderate Alzheimer disease (AD) had a negative baseline amyloid positron emission tomography (PET) scan. Whether they have AD or are AD clinical phenocopies remains unknown. We examined the 2005-2013 National Alzheimer's Coordinating Center autopsy database and found that ~14% of autopsied subjects clinically diagnosed with mild-to-moderate probable AD have no or sparse neuritic plaques, which would expectedly yield a negative amyloid PET scan. More than half of these "Aß-negative" subjects have low neurofibrillary tangle Braak stages. These findings support the implementation of a positive amyloid biomarker as an inclusion criterion in future anti-Aß drug trials.

Reversal of neurofibrillary tangles and tau-associated phenotype in the rTgTauEC model of early Alzheimer's disease.

Neurofibrillary tangles (NFTs), a marker of neuronal alterations in Alzheimer's disease (AD) and other tauopathies, are comprised of aggregates of hyperphosphorylated tau protein. We recently studied the formation of NFTs in the entorhinal cortex (EC) and their subsequent propagation through neural circuits in the rTgTauEC mouse model (de Calignon et al., 2012). We now examine the consequences of suppressing transgene expression with doxycycline on the NFT-associated pathological features of neuronal system deafferentation, NFT progression and propagation, and neuronal loss. At 21 months of age we observe that EC axonal lesions are associated with an abnormal sprouting response of acetylcholinesterase (AChE)-positive fibers, a phenotype reminiscent of human AD. At 24 months, NFTs progress, tau inclusions propagate to the dentate gyrus, and neuronal loss is evident. Suppression of the transgene expression from 18 to 24 months led to reversal of AChE sprouting, resolution of Gallyas-positive and Alz50-positive NFTs, and abrogation of progressive neuronal loss. These data suggest that propagation of NFTs, as well as some of the neural system consequences of NFTs, can be reversed in an animal model of NFT-associated toxicity, providing proof in principle that these lesions can be halted, even in established disease.

A phenotypic change but not proliferation underlies glial responses in Alzheimer disease.

Classical immunohistochemical studies in the Alzheimer disease (AD) brain reveal prominent glial reactions, but whether this pathological feature is due primarily to cell proliferation or to a phenotypic change of existing resting cells remains controversial. We performed double-fluorescence immunohistochemical studies of astrocytes and microglia, followed by unbiased stereology-based quantitation in temporal cortex of 40 AD patients and 32 age-matched nondemented subjects. Glial fibrillary acidic protein (GFAP) and major histocompatibility complex II (MHC2) were used as markers of astrocytic and microglial activation, respectively. Aldehyde dehydrogenase 1 L1 and glutamine synthetase were used as constitutive astrocytic markers, and ionized calcium-binding adaptor molecule 1 (IBA1) as a constitutive microglial marker. As expected, AD patients had higher numbers of GFAP(+) astrocytes and MHC2(+) microglia than the nondemented subjects. However, both groups had similar numbers of total astrocytes and microglia and, in the AD group, these total numbers remained essentially constant over the clinical course of the disease. The GFAP immunoreactivity of astrocytes, but not the MHC2 immunoreactivity of microglia, increased in parallel with the duration of the clinical illness in the AD group. Cortical atrophy contributed to the perception of increased glia density. We conclude that a phenotypic change of existing glial cells, rather than a marked proliferation of glial precursors, accounts for the majority of the glial responses observed in the AD brain.

Subjective cognitive concerns and neuropsychiatric predictors of progression to the early clinical stages of Alzheimer disease.

OBJECTIVE: To examine neuropsychiatric and neuropsychological predictors of progression from normal to early clinical stages of Alzheimer disease (AD). METHODS: From a total sample of 559 older adults from the Massachusetts Alzheimer's Disease Research Center longitudinal cohort, 454 were included in the primary analysis: 283 with clinically normal cognition (CN), 115 with mild cognitive impairment (MCI), and 56 with subjective cognitive concerns (SCC) but no objective impairment, a proposed transitional group between CN and MCI. Two latent cognitive factors (memory-semantic, attention-executive) and two neuropsychiatric factors (affective, psychotic) were derived from the Alzheimer's Disease Centers' Uniform Data Set neuropsychological battery and Neuropsychiatric Inventory brief questionnaire. Factors were analyzed as predictors of time to progression to a worse diagnosis using a Cox proportional hazards regression model with backward elimination. Covariates included baseline diagnosis, gender, age, education, prior depression, antidepressant medication, symptom duration, and interaction terms. RESULTS: Higher/better memory-semantic factor score predicted lower hazard of progression (hazard ratio [HR] = 0.4 for 1 standard deviation [SD] increase, p <0.0001), and higher/worse affective factor score predicted higher hazard (HR = 1.3 for one SD increase, p = 0.01). No other predictors were significant in adjusted analyses. Using diagnosis as a sole predictor of transition to MCI, the SCC diagnosis carried a fourfold risk of progression compared with CN (HR = 4.1, p <0.0001). CONCLUSION: These results identify affective and memory-semantic factors as significant predictors of more rapid progression from normal to early stages of cognitive decline and highlight the subgroup of cognitively normal elderly with SCC as those with elevated risk of progression to MCI.

Dissecting phenotypic traits linked to human resilience to Alzheimer's pathology.

Clinico-pathological correlation studies and positron emission tomography amyloid imaging studies have shown that some individuals can tolerate substantial amounts of Alzheimer's pathology in their brains without experiencing dementia. Few details are known about the neuropathological phenotype of these unique cases that might prove relevant to understanding human resilience to Alzheimer's pathology. We conducted detailed quantitative histopathological and biochemical assessments on brains from non-demented individuals before death whose brains were free of substantial Alzheimer's pathology, non-demented individuals before death but whose post-mortem examination demonstrated significant amounts of Alzheimer's changes ('mismatches'), and demented Alzheimer's cases. Quantification of amyloid-ß plaque burden, stereologically-based counts of neurofibrillary tangles, neurons and reactive glia, and morphological analyses of axons were performed in the multimodal association cortex lining the superior temporal sulcus. Levels of synaptic integrity markers, and soluble monomeric and multimeric amyloid-ß and tau species were measured. Our results indicate that some individuals can accumulate equivalent loads of amyloid-ß plaques and tangles to those found in demented Alzheimer's cases without experiencing dementia. Analyses revealed four main phenotypic differences among these two groups: (i) mismatches had striking preservation of neuron numbers, synaptic markers and axonal geometry compared to demented cases; (ii) demented cases had significantly higher burdens of fibrillar thioflavin-S-positive plaques and of oligomeric amyloid-ß deposits reactive to conformer-specific antibody NAB61 than mismatches; (iii) strong and selective accumulation of hyperphosphorylated soluble tau multimers into the synaptic compartment was noted in demented cases compared with controls but not in mismatches; and (iv) the robust glial activation accompanying amyloid-ß and tau pathologies in demented cases was remarkably reduced in mismatches. Further biochemical measurements of soluble amyloid-ß species-monomers, dimers and higher molecular weight oligomers-in total brain homogenates and synaptoneurosomal preparations failed to demonstrate significant differences between mismatches and demented cases. Together, these data suggest that amyloid-ß plaques and tangles do not inevitably result in neural system derangement and dementia in all individuals. We identified distinct phenotypic characteristics in the profile of brain fibrillar and soluble amyloid-ß and tau accrual and in the glial response that discriminated demented and non-demented individuals with high loads of Alzheimer's pathology. Amyloid-ß deposition in the form of fibrillar plaques and intimately related oligomeric amyloid-ß assemblies, hyperphosphorylated soluble tau species localized in synapses, and glial activation emerged in this series as likely mediators of neurotoxicity and altered cognition, providing further insight into factors and pathways potentially involved in human susceptibility or resilience to Alzheimer's pathological changes.