Regional dynamics of amyloid-β deposition in healthy elderly, mild cognitive impairment and Alzheimer's disease

A voxelwise PiB-PET longitudinal study

Nicolas Villain, Gaël Chételat, Blandine Grassiot, Pierrick Bourgeat, Gareth Jones, Kathryn A. Ellis, David Ames, Ralph N. Martins, Francis Eustache, Olivier Salvado, Colin L. Masters, Christopher C. Rowe, Victor L. Villemagne*

*Corresponding author for this work

Research output: Contribution to journalArticle

145 Citations (Scopus)

Abstract

Amyloid-β deposition in Alzheimer's disease is thought to start while individuals are still cognitively unimpaired and it is hypothesized that after an early phase of fast accumulation, a plateau is reached by the time of cognitive decline. However, few longitudinal Pittsburgh compound B-positron emission tomography studies have tested this hypothesis, and with conflicting results. The purpose of this work is to further our understanding of the dynamics of amyloid-b deposition in a large longitudinal cohort. A total of 32 patients with Alzheimer's disease, 49 subjects with mild cognitive impairment and 103 healthy controls underwent two Pittsburgh compound B-positron emission tomography scans 18 months apart. For each participant, a parametricmap of Pittsburgh compound B-positron emission tomography rate of change was created [(follow-up scan - baseline scan)/ follow-up duration] and entered in a voxelwise three-way analysis of covariance, with clinical status (healthy controls, mild cognitive impairment or Alzheimer's disease), disease progression (clinical conversion from healthy controls to mild cognitive impairment or Alzheimer's disease, or from mild cognitive impairment to Alzheimer's disease) and Pittsburgh compound B status (positive versus negative) as independent factors. Only a significant effect of the Pittsburgh compound B status was found: both Pittsburgh compound B-positive and -negative subjects showed a significant increase in amyloid-β deposition, with this increase being significantly higher in Pittsburgh compound B-positive individuals. This finding suggests either that Pittsburgh compound B-negative individuals have slower rates of amyloid-β accumulation than positive, or that the proportion of individuals showing significant increase in amyloid-β deposition, termed 'Pittsburgh compound B accumulators', is higher within the Pittsburgh compound B-positive group than within the Pittsburgh compound B-negative group. The bimodal distribution of the individual rates of neocortical amyloid-β accumulation observed support the existence of 'Pittsburgh compound B non-accumulators' and 'Pittsburgh compound B accumulators' and different clustering analyses led to a consistent threshold to separate these two subgroups (0.014-0.022 standardized uptake value ratiopons/year). The voxelwise three-way analysis of covariance was thus recomputed with the 'Pittsburgh compound B accumulators' only and the results were almost unchanged, with the Pittsburgh compound B-positive group showing higher accumulation than the Pittsburgh compound B-negative group. Finally, a significant negative correlation was found between Pittsburgh compound B rate of change and Pittsburgh compound B baseline burden, but only in the Pittsburgh compound B-positive group (r = -0.24; P = 0.025). Higher rates of amyloid- βdeposition are associated with higher amyloid-β burden suggesting that amyloid-β deposition does not reach a plateau when cognitive impairments manifest but is instead an ongoing process present even at the Alzheimer's disease stage. amyloid-βaccumulation also seems to slow down at the latest stages of the process, i.e. in participants with the highest amyloid burden. Furthermore, this study identified the existence of Pittsburgh compound 'accumulators' and 'non-accumulators', notably within the Pittsburgh compound B-negative group, which may be a relevant concept for future studies.

Original languageEnglish
Pages (from-to)2126-2139
Number of pages14
JournalBrain
Volume135
Issue number7
DOIs
Publication statusPublished - 2012
Externally publishedYes

Keywords

  • Alzheimer's disease
  • Amyloid-β imaging
  • Longitudinal imaging
  • Mild cognitive impairment
  • Normal ageing
  • Pittsburgh compound B
  • Positron emission tomography

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    Villain, N., Chételat, G., Grassiot, B., Bourgeat, P., Jones, G., Ellis, K. A., ... Villemagne, V. L. (2012). Regional dynamics of amyloid-β deposition in healthy elderly, mild cognitive impairment and Alzheimer's disease: A voxelwise PiB-PET longitudinal study. Brain, 135(7), 2126-2139. https://doi.org/10.1093/brain/aws125