title: Cerebrospinal fluid amyloid beta peptide patterns in Alzheimer's disease patients and nondemented controls depend on sample pretreatment: indication of carrier-mediated epitope masking of amyloid beta peptides.
abstract: A quantitative urea-based amyloid beta (Abeta)-sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Western immunoblot (Abeta-SDS-PAGE/immunoblot) reveals highly conserved and disease-specific Abeta peptide patterns (Abeta 1-37, 1-38, 1-39, 1-40, 1-42) in Alzheimer's disease (AD) patients and nondemented controls. For further standardization of this method, we analyzed cerebrospinal fluid (CSF) of eight probable AD patients and seven nondemented controls using different preanalytical procedures for Abeta-SDS-PAGE/immunoblot and Abeta1-42-enzyme linked immunosorbent assay (ELISA). Both diagnostic groups were discriminated significantly by absolute levels of Abeta1-42 and ratios of Abeta1-42/40, 1-42/38, 1-42/39. Preanalytical freezing of CSF led to a highly significant loss of all Abeta peptide species. This effect was most pronounced for Abeta1-42 and completely prevented by SDS-heat denaturation prior to freezing. Prolonged storage of SDS-heat denatured CSF led to a selective loss of Abeta1-42 and impaired the discrimination of diagnostic groups as measured by Abeta-SDS-PAGE/immunoblot. Neither freezing nor storage significantly affected absolute Abeta1-42 levels as determined by Abeta1-42-ELISA, but both impaired the discrimination of diagnostic groups. Hence, we suggest immediate analysis of samples for Abeta1-42-ELISA, analysis after a short freezing interval for Abeta-SDS-PAGE/immunoblot, and avoidance of prolonged storage intervals. Remarkably, Abeta-SDS-PAGE/immunoblot measured threefold higher levels of Abeta1-42 in CSF than Abeta1-42-ELISA. In summary, our results indicate carrier-mediated epitope masking of Abeta1-42.
authors.affiliation: Department of Psychiatry, University of Göttingen, Göttingen, Germany.
authors.forename: Mirko
authors.initials: M
authors.lastname: Bibl
authors.forename: Hermann
authors.initials: H
authors.lastname: Esselmann
authors.forename: Markus
authors.initials: M
authors.lastname: Otto
authors.forename: Piotr
authors.initials: P
authors.lastname: Lewczuk
authors.forename: Lukas
authors.initials: L
authors.lastname: Cepek
authors.forename: Eckart
authors.initials: E
authors.lastname: Rüther
authors.forename: Johannes
authors.initials: J
authors.lastname: Kornhuber
authors.forename: Jens
authors.initials: J
authors.lastname: Wiltfang
mesh_terms: D000328:Adult; D000368:Aged; D000544:Alzheimer Disease / Q000134:cerebrospinal fluid* / Q000175:diagnosis*; D016229:Amyloid beta-Peptides / Q000134:cerebrospinal fluid*; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000134:cerebrospinal fluid; D006801:Humans; D008875:Middle Aged; D010446:Peptide Fragments / Q000134:cerebrospinal fluid; D012016:Reference Values
chemical_list: D016229:Amyloid beta-Peptides; D000939:Epitopes; D010446:Peptide Fragments