Spatial extent as a sensitive amyloid-PET metric in preclinical Alzheimer's disease.

INTRODUCTION: Spatial extent-based measures of how far amyloid beta (Aß) has spread throughout the neocortex may be more sensitive than traditional Aß-positron emission tomography (PET) measures of Aß level for detecting early Aß deposits in preclinical Alzheimer's disease (AD) and improve understanding of Aß's association with tau proliferation and cognitive decline. METHODS: Pittsburgh Compound-B (PIB)-PET scans from 261 cognitively unimpaired older adults from the Harvard Aging Brain Study were used to measure Aß level (LVL; neocortical PIB DVR) and spatial extent (EXT), calculated as the proportion of the neocortex that is PIB+. RESULTS: EXT enabled earlier detection of Aß deposits longitudinally confirmed to reach a traditional LVL-based threshold for Aß+ within 5 years. EXT improved prediction of cognitive decline (Preclinical Alzheimer Cognitive Composite) and tau proliferation (flortaucipir-PET) over LVL. DISCUSSION: These findings indicate EXT may be more sensitive to Aß's role in preclinical AD than level and improve targeting of individuals for AD prevention trials. HIGHLIGHTS: Aß spatial extent (EXT) was measured as the percentage of the neocortex with elevated Pittsburgh Compound-B. Aß EXT improved detection of Aß below traditional PET thresholds. Early regional Aß deposits were spatially heterogeneous. Cognition and tau were more closely tied to Aß EXT than Aß level. Neocortical tau onset aligned with reaching widespread neocortical Aß.

Associations of Physical Activity Engagement with Cerebral Amyloid-ß and Tau from Midlife.

Background: Higher midlife physical activity engagement has been associated with lower dementia risk in late life. However, the underlying mechanisms contributing to the protective effect remain unclear. Objective: The goal of the current study was to evaluate the associations of physical activity with cerebral amyloid-ß (Aß) and tau in a predominately middle-aged community-based cohort, as well as to explore whether the associations differ by sex or age. Methods: Participants from the Framingham Heart Study underwent 11C-Pittsburgh Compound B amyloid and 18F-Flortaucipir tau positron emission tomography (PET) imaging. Total physical activity levels were evaluated by self-report using the Physical Activity Index (PAI). Cross-sectional associations between total PAI with regional Aß and tau PET retention were evaluated using linear regression models adjusted for demographic and cardiovascular risk factors. Interactions with sex and age group were examined and stratified analyses were performed when significant. FDR-correction for multiple comparisons was applied. Results: The sample included 354 participants (mean age 53±8 years, 51% female). Higher total PAI scores were associated with lower entorhinal cortex tau PET binding (ß (SE) = -0.021(0.008), p = 0.049). There were significant interactions with sex. In men alone, total PAI inversely associated with entorhinal cortex (ß (SE) = -0.035(0.009), p = 0.001), inferior temporal (ß (SE) = -0.029(0.010), p = 0.012), and rhinal cortex tau(ß (SE) = -0.033(0.010), p = 0.002). Conclusions: The results suggest that higher midlife physical activity engagement may confer resistance to tau pathology. However, the effects may vary based on sex, highlighting the importance of better understanding and tailoring lifestyle interventions to address sex disparities.

Differential Vulnerability of Hippocampal Subfields to Amyloid and Tau Deposition in the Lewy Body Diseases.

BACKGROUND AND OBJECTIVES: Alzheimer disease (AD) copathologies of ß-amyloid and tau are common in the Lewy body diseases (LBD), dementia with Lewy bodies (DLB) and Parkinson disease (PD), and target distinct hippocampal subfields compared with Lewy pathology, including subiculum and CA1. We investigated the hypothesis that AD copathologies impact the pattern of hippocampal subregion volume loss and cognitive function in LBD. METHODS: This was a cross-sectional and longitudinal, single-center, observational cohort study. Participants underwent neuropsychological testing and 3T-MRI with hippocampal segmentation using FreeSurferV7. PiB-PET and flortaucipir-PET imaging of comorbid ß-amyloid (A) and tau (T) were acquired. The association of functional cognition, ß-amyloid, and tau loads with hippocampal subregion volume was assessed. The contribution of subregion volumes to the relationship of AD-related deposits on functional cognition was examined with mediation analysis. The effects of AD-related deposits on the rate of subregion atrophy were evaluated with mixed-effects models. RESULTS: Of 103 participants (mean age: 70.3 years; 37.3% female), 52 had LBD with impaired cognition (LBD-I), 26 had normal cognition (LBD-N), and 25 were A- healthy controls (HCs). Volumes of hippocampal subregions prone to AD copathologies, including subiculum (F = 6.9, p = 0.002), presubiculum (F = 7.3, p = 0.001), and parasubiculum (F = 5.9, p = 0.004), were reduced in LBD-I compared with LBD-N and HC. Volume was preserved in CA2/3, Lewy pathology susceptible subregions. In LBD-I, reduced CA1, subiculum, and presubiculum volumes were associated with greater functional cognitive impairment (all p < 0.05). Compared with HC, subiculum volume was reduced in A+T+ but not A-T- participants (F = 2.62, p = 0.043). Reduced subiculum volume mediated the effect of amyloid on functional cognition (0.12, 95% CI: 0.005 to 0.26, p = 0.040). In 26 longitudinally-evaluated participants, baseline tau deposition was associated with faster CA1 (p = 0.021) and subiculum (p = 0.002) atrophy. DISCUSSION: In LBD, volume loss in hippocampal output subregions-particularly the subiculum-is associated with functional cognition and AD-related deposits. Tau deposition appears to accelerate subiculum and CA1 atrophy, whereas Aß does not. Subiculum volume may have value as a biomarker of AD copathology-mediated neurodegeneration and disease progression.

Contribution of extracerebral tracer retention and partial volume effects to sex differences in Flortaucipir-PET signal.

Clinically normal females exhibit higher 18F-flortaucipir (FTP)-PET signal than males across the cortex. However, these sex differences may be explained by neuroimaging idiosyncrasies such as off-target extracerebral tracer retention or partial volume effects (PVEs). 343 clinically normal participants (female = 58%; mean[SD]=73.8[8.5] years) and 55 patients with mild cognitive impairment (female = 38%; mean[SD] = 76.9[7.3] years) underwent cross-sectional FTP-PET. We parcellated extracerebral FreeSurfer areas based on proximity to cortical ROIs. Sex differences in cortical tau were then estimated after accounting for local extracerebral retention. We simulated PVE by convolving group-level standardized uptake value ratio means in each ROI with 6 mm Gaussian kernels and compared the sexes across ROIs post-smoothing. Widespread sex differences in extracerebral retention were observed. Although attenuating sex differences in cortical tau-PET signal, covarying for extracerebral retention did not impact the largest sex differences in tau-PET signal. Differences in PVE were observed in both female and male directions with no clear sex-specific bias. Our findings suggest that sex differences in FTP are not solely attributed to off-target extracerebral retention or PVE, consistent with the notion that sex differences in medial temporal and neocortical tau are biologically driven. Future work should investigate sex differences in regional cerebral blood flow kinetics and longitudinal tau-PET.

Association of Aortic Stiffness and Pressure Pulsatility With Global Amyloid-ß and Regional Tau Burden Among Framingham Heart Study Participants Without Dementia.

Importance: Aortic stiffness is associated with clinical hallmarks of Alzheimer disease and related dementias and could be a modifiable target for disease prevention. Objective: To assess associations of aortic stiffness and pressure pulsatility with global amyloid-ß plaques and regional tau burden in the brain of middle-aged and older adults without dementia. Design, Setting, and Participants: The sample for this cross-sectional study was drawn from the Framingham Heart Study Third Generation Cohort at examination 3 (N = 3171; 2016-2019), of whom 3092 successfully underwent comprehensive hemodynamic evaluations. In a supplemental visit (2015-2021), a subset of 270 participants without dementia who represented the spectrum of vascular risk also underwent positron emission tomography. Thirteen participants were excluded for missing covariate data. The final sample size was 257 participants. Exposures: Three measures of aortic stiffness and pressure pulsatility (carotid-femoral pulse wave velocity, central pulse pressure [CPP], and forward wave amplitude [FWA]) were evaluated using arterial tonometry. Main Outcomes and Measures: Global amyloid-ß plaques and regional tau were assessed using 11C-Pittsburgh compound B and 18F-flortaucipir positron emission tomography tracers, respectively. Results: The mean (SD) age of the 257 participants was 54 (8) years, and 126 were women (49%). All participants were White Western European race. In multivariable models, higher CPP (ß per SD = 0.17; 95% CI, 0.00-0.35; P = .045) and FWA (ß per SD = 0.16; 95% CI, 0.00-0.31; P = .04) were associated with greater entorhinal tau burden. In similar models, higher CPP (ß per SD = 0.19; 95% CI, 0.02-0.36; P = .03) and FWA (ß per SD = 0.17; 95% CI, 0.01-0.32; P = .03) were associated with greater rhinal tau burden. Aortic stiffness and pressure pulsatility measures were not associated with amygdala, inferior temporal, precuneus tau burden, or global amyloid-ß plaques. Associations for entorhinal and rhinal tau outcomes were more prominent in older participants (≥60 years). For example, higher levels of all aortic stiffness and pressure pulsatility measures (ß per SD = 0.40-0.92; P = .001-.02) were associated with higher entorhinal tau burden among older but not younger participants in stratified analyses. Conclusions and Relevance: In this cross-sectional study, abnormal central vascular hemodynamics were associated with higher tau burden in specific brain regions. Findings suggest that aortic stiffness, which is potentially modifiable, may be a probable independent target for prevention of tau-related pathologies.

Association of Carotid Intima Media Thickening with Future Brain Region Specific Amyloid-ß Burden.

BACKGROUND: Carotid atherosclerosis is associated with cognitive impairment and dementia, though there is limited evidence of a direct link between carotid disease and amyloid-ß (Aß) burden. OBJECTIVE: We studied the association of baseline and progressive carotid intima media thickness (CIMT) with Aß on 11C-Pittsburgh Compound B (PiB) to determine if those with carotid atherosclerosis would have higher Aß burden. METHODS: We studied 47 participants from the Framingham Offspring cohort with carotid ultrasounds measuring CIMT at their 6th clinic examination (aged 49.5±5.7 years) and an average of 9.6 years later, and PiB imaging measuring Aß on average 22.1 years post baseline. We used multivariate linear regression analyses to relate baseline, follow-up, mean, and progression of internal carotid artery (ICA) and common carotid artery (CCA) CIMT to Aß in brain regions associated with Alzheimer's disease (AD) and related dementias (ADRD), adjusting for age, sex, and other vascular risk factors. RESULTS: Participants with higher mean ICA IMT had more Aß in the precuneus (beta±standard error [ß±SE]: 0.466±0.171 mm, p = 0.01) and the frontal, lateral, and retrosplenial regions (ß±SE: 0.392±0.164 mm, p = 0.022) after adjusting for age, sex, vascular risk factors, and medication use. We did not find an association between any CCA IMT measures and Aß or progression of ICA or CCA IMT and Aß. CONCLUSION: Carotid atherosclerosis, as measured by ICA IMT, is associated with increased Aß burden later in life. These findings support a link between vascular disease and AD/ADRD pathophysiology.

Non-Alcoholic Fatty Liver Disease, Liver Fibrosis, and Regional Amyloid-ß and Tau Pathology in Middle-Aged Adults: The Framingham Study.

BACKGROUND: Liver steatosis and fibrosis are emerging as risk factors for multiple extrahepatic health conditions; however, their relationship with Alzheimer's disease pathology is unclear. OBJECTIVE: To examine whether non-alcoholic fatty liver disease (NAFLD) and FIB-4, a non-invasive index of advanced fibrosis, are associated with brain amyloid-ß (Aß) and tau pathology. METHODS: The study sample included Framingham Study participants from the Offspring and Third generation cohorts who attended exams 9 (2011-2014) and 2 (2008-2011), respectively. Participants underwent 11C-Pittsburgh Compound-B amyloid and 18F-Flortaucipir tau positron emission tomography (PET) imaging and abdomen computed tomography, or had information on all components of the FIB-4 index. Linear regression models were used to assess the relationship of NAFLD and FIB-4 with regional tau and Aß, adjusting for potential confounders and multiple comparisons. RESULTS: Of the subsample with NAFLD information (N = 169; mean age 52±9 y; 57% males), 57 (34%) had NAFLD. Of the subsample with information on liver fibrosis (N = 177; mean age 50±10 y; 51% males), 34 (19%) had advanced fibrosis (FIB-4 > 1.3). Prevalent NAFLD was not associated with Aß or tau PET. However, FIB-4 index was significantly associated with increased rhinal tau (ß= 1.03±0.33, p = 0.002). Among individuals with prevalent NAFLD, FIB-4 was related to inferior temporal, parahippocampal gyrus, entorhinal and rhinal tau (ß= 2.01±0.47, p < 0.001; ß= 1.60±0.53, p = 0.007, and ß= 1.59±0.47, p = 0.003 and ß= 1.60±0.42, p = 0.001, respectively) and to Aß deposition overall and in the inferior temporal and parahippocampal regions (ß= 1.93±0.47, p < 0.001; ß= 1.59±0.38, p < 0.001, and ß= 1.52±0.54, p = 0.008, respectively). CONCLUSION: This study suggests a possible association between liver fibrosis and early Alzheimer's disease pathology, independently of cardio-metabolic risk factors.

Association of Midlife Depressive Symptoms with Regional Amyloid-ß and Tau in the Framingham Heart Study.

BACKGROUND: Depressive symptoms predict increased risk for dementia decades before the emergence of cognitive symptoms. Studies in older adults provide preliminary evidence for an association between depressive symptoms and amyloid-ß (Aß) and tau accumulation. It is unknown if similar alterations are observed in midlife when preventive strategies may be most effective. OBJECTIVE: The study aim was to evaluate the association between depressive symptoms and cerebral Aß and tau in a predominately middle-aged cohort with examination of the apolipoprotein (APOE) ɛ4 allele as a moderator. METHODS: Participants included 201 adults (mean age 53±8 years) who underwent 11C-Pittsburgh Compound B amyloid and 18F-Flortaucipir tau positron emission tomography (PET) imaging. Depressive symptoms were evaluated with the Center for Epidemiological Studies Depression Scale (CES-D) at the time of PET imaging, as well as eight years prior. Associations between depressive symptoms at both timepoints, as well as depression (CES-D≥16), with regional Aß and tau PET retention were evaluated with linear regression adjusting for age and sex. Interactions with the APOE ɛ4 allele were explored. RESULTS: Depressive symptoms and depression were not associated with PET outcomes in the overall sample. However, among APOE ɛ4 allele carriers, there was a significant cross-sectional association between depressive symptoms and increased tau PET uptake in the entorhinal cortex (ß= 0.446, SE = 0.155, p = 0.006) and amygdala (ß= 0.350, SE = 0.133, p = 0.012). CONCLUSION: Although longitudinal studies are necessary, the results suggest that APOE ɛ4 carriers with depressive symptoms may present with higher susceptibility to early tau accumulation in regions integral to affective regulation and memory consolidation.