Plasma amyloid beta levels are associated with cerebral amyloid and tau deposition

Introduction We investigated the relationship of plasma amyloid beta (A beta) with cerebral deposition of A beta and tau on positron emission tomography (PET). Methods Forty-four participants (18 cognitively normal older adults [CN], 10 mild cognitive impairment, 16 Alzheimer's disease [AD]) underwent amyloid PET and a blood draw. Free and total plasma A beta 40 and A beta 42 were assessed using a validated assay. Thirty-seven participants (17 CN, 8 mild cognitive impairment, 12 AD) also underwent a [18F]flortaucipir scan. Scans were preprocessed by standard techniques, and mean global and regional amyloid and tau values were extracted. Free A beta 42/A beta 40 (A beta F42:F40) and total A beta 42/A beta 40 (A beta T42:T40) were evaluated for differences by diagnosis and relation to PET A beta positivity. Relationships between these measures and cerebral A beta and tau on both regional and voxel-wise basis were also evaluated. Results Lower A beta T42:T40 was associated with diagnosis and PET A beta positivity. Lower plasma A beta T42:T40 ratios predicted cerebral A beta positivity, both across the full sample and in CN only. Finally, lower plasma A beta T42:T40 ratios were associated with increased cortical A beta and tau in AD-related regions on both regional and voxel-wise analyses. Discussion Plasma A beta measures may be useful biomarkers for predicting cerebral A beta and tau. Additional studies in larger samples are warranted.