Quantification of amyloid-beta 40 in cerebrospinal fluid

Background: Truncated forms and full-length forms of the amyloid-beta 40 (A beta 40) are key molecules in the pathogenesis of dementia, and are detectable in CSF. Reliable methods to detect these biomarkers in CSF are of great importance for understanding the disease mechanisms and for diagnostic purposes. Methods: VU-alpha-A beta 40, a monoclonal antibody (mAb) specifically detecting A beta 40, was generated and characterized by solid and fluid phase ELISA, surface plasmon resonance spectroscopy (SPRS), immunoprecipitation (IP), immunohistochemical and Western blot (WB) analysis. In addition, an ELISA with VU-alpha-A beta 40 as catching and 6E10 as detecting mAbs was set up and validated. This ELISA was used to measure A beta 40 in CSF of controls (N = 27), patients with Alzheimer's disease (AD; N = 20), frontotemporal lobe dementia (FTLD; N = 14), noninflammatory (N = 15) and inflammatory (N = 15) neurological conditions. Results: VU-alpha-A beta 40 specifically recognizes A beta 40 with high affinity (K-A = 1.3 x 10(9) M-1) and detects A beta 40 in AD brain specimens. The developed sandwich ELISA has a detection limit of 0.21 ng/mL a mean recovery of 90%, and an intra- and inter-assay CV of 1.4% and 7.3%. FTLD patients had a lower mean level of A beta 40 (8.8 (1.9) ng/mL) than controls (12.0 (1.7) ng/mL): P<0.01). Conclusions: VU-alpha-A beta 40 was successfully implemented in an ELISA which enables us to measure A beta 40 accurately in human CSF. Clinical validation revealed lower levels of A beta 40 in FTLD patients. This finding opens new possibilities for early and differential diagnosis of dementia. (C) 2009 Elsevier B.V. All rights reserved.