Plasma ß-amyloid in Alzheimer's disease and vascular disease.

ABSTRACT

Implementation of amyloid biomarkers in clinical practice would be accelerated if such biomarkers could be measured in blood. We analyzed plasma levels of Aß42 and Aß40 in a cohort of 719 individuals (the Swedish BioFINDER study), including patients with subjective cognitive decline (SCD), mild cognitive impairment (MCI), Alzheimer's disease (AD) dementia and cognitively healthy elderly, using a ultrasensitive immunoassay (Simoa platform). There were weak positive correlations between plasma and cerebrospinal fluid (CSF) levels for both Aß42 and Aß40, and negative correlations between plasma Aß42 and neocortical amyloid deposition (measured with PET). Plasma levels of Aß42 and Aß40 were reduced in AD dementia compared with all other diagnostic groups. However, during the preclinical or prodromal AD stages (i.e. in amyloid positive controls, SCD and MCI) plasma concentration of Aß42 was just moderately decreased whereas Aß40 levels were unchanged. Higher plasma (but not CSF) levels of Aß were associated with white matter lesions, cerebral microbleeds, hypertension, diabetes and ischemic heart disease. In summary, plasma Aß is overtly decreased during the dementia stage of AD indicating that prominent changes in Aß metabolism occur later in the periphery compared to the brain. Further, increased levels of Aß in plasma are associated with vascular disease.