No correlation between time-linked plasma and CSF Aβ levels

Abstract

Plasma β-amyloid protein (Aβ) isoforms are considered potential biomarkers for Alzheimer's disease (AD) and dementia. The relation between plasma and cerebrospinal fluid (CSF) levels of Aβ isoforms remains unclear. In order to identify possible correlations between Aβ levels in plasma and CSF we determined Aβ levels in time-linked plasma and CSF samples. Aβ concentrations in plasma (Aβ 1–42 and Aβ N–42 ) and CSF (Aβ 1–42) samples from 49 AD patients, 47 non-Alzheimer's disease dementia (NONAD) patients, 39 MCI patients and 29 controls were determined using a multi-parameter fluorimetric bead-based immunoassay using xMAP ® technology (for plasma) and a conventional single-parameter ELISA (for CSF). Plasma Aβ 1–42 concentrations did not correlate with CSF Aβ 1–42 concentrations in the total study population, or in the different diagnostic groups. No correlations between plasma Aβ N–42 and CSF Aβ 1–42 levels were found either. The CSF/serum albumin index did not show any significant differences between AD, NONAD, MCI and controls. These results suggest that the Aβ levels in plasma are independent of the Aβ levels in CSF both in dementia and controls. The fact that CSF and plasma Aβ do not correlate in patients as well as controls and no significant differences in plasma Aβ 1–42 or Aβ N–42 between patients and controls can be detected hampers the diagnostic utility of the plasma Aβ levels as biomarkers for dementia.