Amyloid-beta peptides interact with plasma proteins and erythrocytes: implications for their quantitation in plasma.
Amyloid beta peptides are bound rapidly in the plasma complicating an accurate assessment of their in vivo abundance by immunoassay procedures. The extent of Abeta immunoassay interference was used to estimate the Abeta binding capacity of purified plasma proteins, erythrocytes and whole plasma. Human serum albumin bound Abeta peptides rapidly with a 1:1 stoichiometry and at physiological concentrations was capable of binding over 95% of an input of 5 ng/ml Abeta. Purified alpha2-macroglobulin was able to bind Abeta peptides and at physiological concentration bound 73% of 5 ng/ml of Abeta. Erythrocytes also sequestered the Abeta peptides, showing a preference for binding Abeta 1-42. Incubation of 5 ng/ml of Abeta in plasma revealed that about 30% of the peptides were still detectable by immunoassay, presumably reflecting the binding of Abeta peptides with albumin and other plasma molecules. Thus, our studies reveal that both the soluble and formed elements of the blood are capable of sequestering Abeta peptides. To avoid underestimating plasma Abeta values, we employed an improved column chromatography method under denaturing conditions to liberate Abeta from its associations with plasma proteins. Quantification of Abeta 40 and 42 levels in plasma from both normal and AD individuals after chromatography showed a large overlap between AD and control groups, despite the very large pool of Abeta present in the AD brains. The potential origins of the plasma Abeta pool are discussed.
Kuo
Y M
YM
Haldeman Laboratory for Alzheimer Disease Research, Sun Health Research Institute, 10515 West Santa Fe Drive, Sun City, Arizona 85351, USA.
Kokjohn
T A
TA
Kalback
W
W
Luehrs
D
D
Galasko
D R
DR
Chevallier
N
N
Koo
E H
EH
Emmerling
M R
MR
Roher
A E
AE
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000097:blood*; D016229:Amyloid beta-Peptides / Q000097:blood*; D001774:Blood Chemical Analysis; D001798:Blood Proteins / Q000378:metabolism*; D016022:Case-Control Studies; D004912:Erythrocytes / Q000378:metabolism*; D005260:Female; D006801:Humans; D007118:Immunoassay; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000097:blood; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000378:metabolism
D016229:Amyloid beta-Peptides; D001798:Blood Proteins; D010446:Peptide Fragments; D012709:Serum Albumin; D000511:alpha-Macroglobulins; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42)