Dataset Information

Association of Early β-Amyloid Accumulation and Neuroinflammation Measured With [¹¹C]PBR28 in Elderly Individuals Without Dementia.

ABSTRACT:

Objective

To examine whether early β-amyloid (Aβ) accumulation and metabolic risk factors are associated with neuroinflammation in elderly individuals without dementia.

Methods

We examined 54 volunteers (mean age 70.0 years, 56% women, 51% APOE ɛ4 carriers) with the translocator protein (TSPO) tracer [¹¹C]PBR28 to assess neuroinflammation and with [¹¹C] Pittsburgh compound B (PiB) to assess cerebral Aβ accumulation. [¹¹C]PBR28 and [¹¹C]PiB standardized uptake value ratios (SUVRs) were quantified in 6 regions of interests by using the cerebellar cortex as a pseudo-reference and reference region, respectively. Fasting venous glucose, insulin, and high-sensitivity C-reactive protein (hs-CRP) values were determined. Homeostatic model assessment of insulin resistance (HOMA-IR) was calculated. A subset of individuals (n = 11) underwent CSF sampling, and Aβ₄₀, Aβ₄₂, total tau, phospho-tau, soluble TREM2, and YKL-40 levels were measured.

Results

Among the whole study group, no significant association was found between [¹¹C]PiB and [¹¹C]PBR28 SUVR composite scores (slope 0.02, p = 0.30). However, higher [¹¹C]PiB binding was associated with higher [¹¹C]PBR28 binding among amyloid-negative ([¹¹C]PiB composite score ≤1.5) (TSPO genotype-, age- and sex-adjusted slope 0.26, p = 0.008) but not among amyloid-positive (slope -0.004, p = 0.88) participants. Higher CSF soluble TREM2 (r _s = 0.72, p = 0.01) and YKL-40 (r _s = 0.63, p = 0.04) concentrations were associated with a higher [¹¹C]PBR28 composite score. Higher body mass index, HOMA-IR, and hs-CRP were associated with higher [¹¹C]PBR28 binding in brain regions where Aβ accumulation is first detected in Alzheimer disease.

Conclusions

While there was no association between amyloid and neuroinflammation in the overall study group, neuroinflammation was associated with amyloid among the subgroup at early stages of amyloid pathology.

SUBMITTER: Toppala S

PROVIDER: S-EPMC8032368 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Alzheimer's disease is associated with chronic response of innate immune system, referred as neuroinflammation. PET radioligands binding to the 18 kDa translocator protein are potential biomarkers of neuroinflammation. Translocator protein PET studies in mild cognitive impairment and Alzheimer's disease have indicated controversial results, possibly reflecting interindividual variation and heterogeneity of study populations. We controlled for genetic and environmental effects by studying twin pairs discordant for episodic memory performance. Episodic memory impairment is a well-known cognitive hallmark of early Alzheimer's disease process. Eleven same-sex twin pairs (four monozygotic pairs, six female pairs, age 72-77 years) underwent [11C]N-acetyl-N-(2-methoxybenzyl)-2-phenoxy-5-pyridinamine ([11C]PBR28) PET imaging, structural magnetic resonance imaging and neuropsychological testing in 2014-17. Main PET outcome was the volume-weighted average standardized uptake value of cortical regions vulnerable to Alzheimer's disease pathology. Ten pairs were discordant for episodic memory performance. In the eight pairs with identical translocator protein genotype, twins with poorer episodic memory had ∼20% higher cortical [11C]PBR28 binding compared with their better-performing co-twins (mean intra-pair difference 0.21 standardized uptake value, 95% confidence interval 0.05-0.37, P = 0.017). The result remained the same when including all discordant pairs and controlling for translocator protein genotype. Increased translocator protein PET signal suggests that increased microglial activation is associated with poorer episodic memory performance. Twins with worse episodic memory performance compared with their co-twins had on average 20% higher uptake of the neuroinflammatory marker translocator protein PET tracer 11[11C]PBR28. The findings support a negative association between neuroinflammation and episodic memory and the use of translocator protein positron emission tomography as a useful indicator of Alzheimer's disease process.

Project description:BackgroundUnderstanding the variation in uptake between different amyloid PET tracers is important to appropriately interpret data using different amyloid tracers. Therefore, we compared the uptake differences in [18F]Flutemetamol (FMT) and [11C]PiB (PiB) PET in the same people.MethodsStructural MRI, FMT PET and PiB PET were each performed in 30 young cognitively normal (yCN), 31 elderly cognitively normal (eCN) and 21 Alzheimer's disease dementia (AD) participants. PiB and FMT images for each participant were compared quantitatively using voxel- and region-based analyses. Region of interest (ROI) analyses included comparisons of grey matter (GM) regions as well as white matter (WM) regions. Regional comparisons of each tracer between different groups and comparisons of the two modalities within the different groups were performed. To compare mean SUVr between modalities, and between diagnostic groups, we used paired t-tests and Student's t-test, respectively. We also compared the ability of the two tracers to discriminate between diagnostic groups using AUROC estimates. The effect of using different normalization regions on SUVr values was also evaluated.ResultsBoth FMT and PiB showed greater uptake throughout GM structures in AD vs. eCN or yCN. In all dual-modality group comparisons (FMT vs. PiB in yCN, eCN, and AD), greater WM uptake was seen with FMT vs. PiB. In yCN and eCN greater diffuse GM uptake was seen with FMT vs. PiB. When comparing yCN to eCN within each tracer, greater WM uptake was seen in eCN vs yCN.ConclusionsFlutemetamol and PiB show similar topographical GM uptake in AD and CN participants and the tracers show comparable group discrimination. Greater WM accumulation with FMT suggests that quantitative differences vs. PiB will be apparent when using WM or GM as a reference region. Both imaging tracers demonstrate increased WM uptake in older people. These findings suggest that using different amyloid tracers or different methods of analyses in serial brain imaging in an individual may result in artifactual amyloid change measurements. Clinical use of several amyloid tracers in the same patient will have challenges that need to be carefully considered.

Project description:Importance:Aging is associated with excessive daytime sleepiness (EDS), which has been linked to cognitive decline in the elderly. However, whether EDS is associated with the pathologic processes of Alzheimer disease remains unclear. Objective:To investigate whether EDS at baseline is associated with a longitudinal increase in regional β-amyloid (Aβ) accumulation in a cohort of elderly individuals without dementia. Design, Setting, and Participants:This prospective analysis included participants enrolled in the Mayo Clinic Study of Aging, a longitudinal population-based study in Olmsted County, Minnesota. Of 2900 participants, 2172 (74.9%) agreed to undergo carbon 11-labeled Pittsburgh compound B positron emission tomography (PiB-PET). We included 283 participants 70 years or older without dementia who completed surveys assessing sleepiness at baseline and had at least 2 consecutive PiB-PET scans from January 1, 2009, through July 31, 2016, after excluding 45 (13.7%) who had a comorbid neurologic disorder. Main Outcomes and Measures:Excessive daytime sleepiness was defined as an Epworth Sleepiness Scale score of at least 10. The difference in Aβ levels between the 2 consecutive scans (ΔPiB) in Aβ-susceptible regions (prefrontal, anterior cingulate, posterior cingulate-precuneus, and parietal) was determined. Multiple linear regression models were fit to explore associations between baseline EDS and ΔPiB while adjusting for baseline age, sex, presence of the apolipoprotein E ε4 allele, educational level, baseline PiB uptake, global PiB positivity (standardized uptake value ratio ≥1.4), physical activity, cardiovascular comorbidities (obesity, hypertension, hyperlipidemia, and diabetes), reduced sleep duration, respiratory symptoms during sleep, depression, and interval between scans. Results:Of the initial 283 participants, mean (SD) age was 77.1 (4.8) years; 204 (72.1%) were men and 79 (27.9%) were women. Sixty-three participants (22.3%) had EDS. Baseline EDS was significantly associated with increased regional Aβ accumulation in the anterior cingulate (B coefficient = 0.031; 95% CI, 0.001-0.061; P = .04), posterior cingulate-precuneus (B coefficient = 0.038; 95% CI, 0.006-0.069; P = .02), and parietal (B coefficient = 0.033; 95% CI, 0.001-0.065; P = .04) regions. Association of EDS with longitudinal Aβ accumulation was stronger in participants with baseline global PiB positivity in the anterior cingulate (B coefficient = 0.065; 95% CI, 0.010-0.118; P = .02) and cingulate-precuneus (B coefficient = 0.068; 95% CI, 0.009-0.126; P = .02) regions. Conclusions and Relevance:Baseline EDS was associated with increased longitudinal Aβ accumulation in elderly persons without dementia, suggesting that those with EDS may be more vulnerable to pathologic changes associated with Alzheimer disease. Further work is needed to elucidate whether EDS is a clinical marker of greater sleep instability, synaptic or network overload, or neurodegeneration of wakefulness-promoting centers. Early identification of patients with EDS and treatment of underlying sleep disorders could reduce Aβ accumulation in this vulnerable group.

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