title: Detection and quantification of plasma amyloid-β by selected reaction monitoring mass spectrometry.
abstract: Amyloid-β (Aβ) in human plasma was detected and quantified by an antibody-free method, selected reaction monitoring mass spectrometry (SRM-MS) in the current study. Due to its low abundance, SRM-based quantification in 10 μL plasma was a challenge. Prior to SRM analysis, human plasma proteins as a whole were digested by trypsin and high pH reversed-phase liquid chromatography (RPLC) was used to fractionate the tryptic digests and to collect peptides, Aβ(1-5), Aβ(6-16), Aβ(17-28) and Aβ(29-40(42)) of either Aβ(1-40) or Aβ(1-42). Among those peptides, Aβ(17-28) was selected as a surrogate to measure the total Aβ level. Human plasma samples obtained from triplicate sample preparations were analyzed, obtaining 4.20 ng mL(-1) with a CV of 25.3%. Triplicate measurements for each sample preparation showed CV of <5%. Limit of quantification was obtained as 132 pM, which corresponded to 570 pg mL(-1) of Aβ(1-40). Until now, most quantitative measurements of Aβ in plasma or cerebrospinal fluid have required antibody-based immunoassays. Since quantification of Aβ by immunoassays is highly dependent on the extent of epitope exposure due to aggregation or plasma protein binding, it is difficult to accurately measure the actual concentration of Aβ in plasma. Our diagnostic method based on SRM using a surrogate peptide of Aβ is promising in that actual amounts of total Aβ can be measured regardless of the conformational status of the biomarker.
authors.affiliation: Center for Theragnosis, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: Jun Seok
authors.initials: JS
authors.lastname: Kim
authors.affiliation: Center for Theragnosis, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea; Department of Biological Chemistry, University of Science and Technology, Daejeon 305-333, Republic of Korea.
authors.forename: Hee-Sung
authors.initials: HS
authors.lastname: Ahn
authors.affiliation: Center for Neuro-Medicine, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: Soo Min
authors.initials: SM
authors.lastname: Cho
authors.affiliation: Center for Theragnosis, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Lee
authors.affiliation: Center for Neuro-Medicine, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: YoungSoo
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Center for Theragnosis, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea; Department of Biological Chemistry, University of Science and Technology, Daejeon 305-333, Republic of Korea. Electronic address: clee270@kist.re.kr.
authors.forename: Cheolju
authors.initials: C
authors.lastname: Lee
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000097:blood* / Q000235:genetics; D000818:Animals; D015415:Biomarkers / Q000097:blood; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods* / Q000592:standards; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000097:blood* / Q000235:genetics
chemical_list: D016229:Amyloid beta-Peptides; D015415:Biomarkers; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42)
keywords: Alzheimer's disease; Amyloid-β; High pH reversed-phase liquid chromatography; Plasma; Selected reaction monitoring; Surrogate peptide