Plasma Amyloid-β (Aβ42) Correlates with Cerebrospinal Fluid Aβ42 in Alzheimer's Disease

The 42 amino acid form of amyloid-beta (A beta(42)) plays a key role in the pathogenesis of Alzheimer's disease (AD) and is a core biomarker for the diagnosis of AD. Numerous studies have shown that cerebrospinal fluid (CSF) A beta(42) concentrations are decreased in AD, when measured by enzyme-linked immunosorbent assay (ELISA) and other conventional immunoassays. While most studies report no change in plasma A beta(42), independent studies using the immunomagnetic reduction (IMR) technique report an increase in plasma A beta(42)levels in AD. To confirm the opposite changes of A beta(42) levels in CSF and plasma for AD, we assayed the levels of A beta(42) in plasma of subjects with known CSF A beta(42) levels. In total 43 controls and 63 AD patients were selected at two sites: the VU University Medical Center (n = 55) and Sahlgrenska University Hospital (n = 51). IMR and ELISA were applied to assay A beta(42) in plasma and CSF, respectively. We found a moderately negative correlation between plasma and CSF A beta(42) levels in AD patients (r = -0.352), and a weakly positive correlation in controls (r = 0.186). These findings further corroborate that there are opposite changes of A beta(42) levels in CSF and plasma in AD. The possible causes for the negative correlation are discussed by taken assay technologies, A beta(42) transport from brain to peripheral blood, and sample matrix into account.