Quantification of sub-femtomole amounts of Alzheimer amyloid beta peptides.

We evaluated methods for the quantitative Western blot analysis of A beta 1-40 and A beta 1-42. Both chromogenic and chemiluminescent detection methods gave similar sensitivities (0.15 fmol of A beta 1-40 and 0.3 fmol of A beta 1-42); however, the chromogenic method was more rapid, simpler, less expensive and gave fewer background problems; consequently, it yielded more reliable results. Adsorption to various types of laboratory plasticware can greatly interfere with the accurate measurement of A beta, but this can be prevented by the addition of SDS or bovine serum albumin. Among several methods for concentrating A beta from biological materials, immunoadsorption to Sepharose-bound antibodies was the most efficient. It yielded 50% recovery of 1 pM A beta 1-42 or A beta 1-40 and so was a suitable method to measure A beta levels in human plasma. Through combined immunoadsorption and Western blotting we could determine the amounts of A beta isoforms secreted from 1 x 10(6) cells after a culture period as short as 1 h. This eliminates the need to use radiolabelling or over-expression to study A beta precursor processing Bovine serum contains subnanomolar A beta levels, similar to those that reportedly stimulate cell proliferation. That cultured cells quickly secrete these levels of A beta suggests that the peptide might exert an autocrine effect.