The normal equilibrium between CSF and plasma amyloid beta levels is disrupted in Alzheimer's disease

Amyloid-beta (A beta) with 40 (A beta 40) and 42 (A beta 42) amino acids, the main components of amyloid plaques in the Alzheimer's disease (AD) brain, can be measured in human cerebrospinal fluid (CSF) and plasma. Whereas CSF A beta 42 is decreased in AD, some studies have reported changed plasma A beta levels in AD and in subjects with mild cognitive impairment (MCI). To this date it is unclear if and how CSF and plasma levels of A beta correlate with each other in healthy individuals, albeit earlier studies on AD patients found no correlation between CSF and plasma A beta. We have measured A beta 40 and A beta 42 in paired CSF and plasma samples from patients with AD (n=39), MCI (n=29) and healthy control subjects (n= 18). We observed a clear correlation between CSF and plasma levels for both A beta 40 and A beta 42 in healthy individuals, whereas no such correlation could be seen for AD or MCI cases. Similarly to other studies we also found low levels of A beta 42 in AD CSF, whereas there were no significant differences in plasma A beta levels between the diagnostic groups. Our findings suggest that the normal equilibrium between CSF and plasma A beta may be disrupted with the initiation of amyloid deposition in the brain. (c) 2007 Elsevier Ireland Ltd. All rights reserved.