Isobaric quantification of CSF amyloid beta peptides in Alzheimer`s disease – C-terminal truncation relates to early measures of neurodegeneration

Magnus Rogeberg* a,b, Ina Selseth Almdahl a, Marianne Wettergreen a,b, Lars N.G. Nilsson c, Tormod
Fladby a,d
a Department of Neurology, Akershus University Hospital, Lørenskog, Norway
b Department of Clinical Molecular Biology (EpiGen), Division of Medicine, Akershus University Hospital and University of Oslo, Norway
c Department of Pharmacology, University of Oslo and Oslo University Hospital, Oslo, Norway
d Department of Neurology, Faculty Division, Akershus University Hospital and University of Oslo, Lørenskog, Norway

J. Proteome Res.,  DOI: 10.1021/acs.jproteome.5b00668 • Publication Date (Web): 09 Oct 2015

Article: Isobaric quantification of CSF amyloid beta peptides in Alzheimer`s disease Rogeberg Faldby 2015

Abstract:

The amyloid beta (Aβ) peptide is the main constituent of the plaques characteristic of Alzheimer`s disease (AD). Measurement of Aβ1-42 in cerebrospinal fluid (CSF) is a valuable marker in AD research, where low levels indicate AD. Although the use of immunoassays measuring Aβ1-38 and Aβ1-40 in addition to Aβ1-42 has increased, quantitative assays of other Aβ peptides remains little explored. We recently discovered novel Aβ peptides in CSF using antibodies recognizing the Aβ mid-domain region. Here we have developed a method using both Aβ N-terminal and mid-domain antibodies for immunoprecipitation in combination with isobaric labeling and liquid chromatography – tandem mass spectrometry (LC-MS/MS) for relative quantification of endogenous Aβ peptides in CSF. The developed method was used in a pilot study to produce Aβ peptide profiles from 38 CSF samples. Statistical comparison between CSF samples from 19 AD patients and 19 cognitively healthy controls revealed no significant differences at group level. A significant correlation was found between several larger C-terminally truncated Aβ peptides and protein biomarkers for neuronal damage, particularly prominent in the control group. Comparison of the isobaric quantification With immunoassays measuring Aβ1-38 or Aβ1-40 showed good correlation (r2 = 0.84 and 0.85, respectively) between the two analysis methods. The developed method could be used to assess disease-modifying therapies directed at Aβ  production or degradation.