title: Ex vivo18O-labeling mass spectrometry identifies a peripheral amyloid β clearance pathway.
abstract: Proteolytic degradation of amyloid β (Aβ) peptides has been intensely studied due to the central role of Aβ in Alzheimer's disease (AD) pathogenesis. While several enzymes have been shown to degrade Aβ peptides, the main pathway of Aβ degradation in vivo is unknown. Cerebrospinal fluid (CSF) Aβ42 is reduced in AD, reflecting aggregation and deposition in the brain, but low CSF Aβ42 is, for unknown reasons, also found in some inflammatory brain disorders such as bacterial meningitis.
  
  
  
  Using18O-labeling mass spectrometry and immune-affinity purification, we examined endogenous proteolytic processing of Aβ in human CSF.
  
  
  
  The Aβ peptide profile was stable in CSF samples from healthy controls but in CSF samples from patients with bacterial meningitis, showing increased leukocyte cell count,18O-labeling mass spectrometry identified proteolytic activities degrading Aβ into several short fragments, including abundant Aβ1-19 and 1-20. After antibiotic treatment, no degradation of Aβ was detected. In vitro experiments located the source of the proteolytic activity to blood components, including leukocytes and erythrocytes, with insulin-degrading enzyme as the likely protease. A recombinant version of the mid-domain anti-Aβ antibody solanezumab was found to inhibit insulin-degrading enzyme-mediated Aβ degradation.
  
  
  
  18O labeling-mass spectrometry can be used to detect endogenous proteolytic activity in human CSF. Using this technique, we found an enzymatic activity that was identified as insulin-degrading enzyme that cleaves Aβ in the mid-domain of the peptide, and could be inhibited by a recombinant version of the mid-domain anti-Aβ antibody solanezumab.
authors.affiliation: Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at University of Gothenburg, Mölndal, Sweden.|Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, University Hospital, SE-431 80, Mölndal, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Portelius
authors.affiliation: Clinical Memory Research Unit, Faculty of Medicine, Lund University, Lund, Sweden.|Department of Neurology, Skåne University Hospital, Lund, Sweden.
authors.forename: Niklas
authors.initials: N
authors.lastname: Mattsson
authors.affiliation: Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at University of Gothenburg, Mölndal, Sweden.|Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, University Hospital, SE-431 80, Mölndal, Sweden.
authors.forename: Josef
authors.initials: J
authors.lastname: Pannee
authors.affiliation: Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at University of Gothenburg, Mölndal, Sweden.|Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, University Hospital, SE-431 80, Mölndal, Sweden.|Department of Molecular Neuroscience, UCL Institute of Neurology, Queen Square, London, UK.
authors.forename: Henrik
authors.initials: H
authors.lastname: Zetterberg
authors.affiliation: Department of Infectious Diseases, Institute of Biomedicine, the Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Gisslén
authors.affiliation: ADx Neurosciences, Gent, Belgium.
authors.forename: Hugo
authors.initials: H
authors.lastname: Vanderstichele
authors.affiliation: Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at University of Gothenburg, Mölndal, Sweden.
authors.forename: Eleni
authors.initials: E
authors.lastname: Gkanatsiou
authors.affiliation: St. Vincent's Institute of Medical Research, Fitzroy, VIC, Australia.
authors.forename: Gabriela A N
authors.initials: GA
authors.lastname: Crespi
authors.affiliation: St. Vincent's Institute of Medical Research, Fitzroy, VIC, Australia.|Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC, Australia.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Parker
authors.affiliation: St. Vincent's Institute of Medical Research, Fitzroy, VIC, Australia.|Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC, Australia.
authors.forename: Luke A
authors.initials: LA
authors.lastname: Miles
authors.affiliation: Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at University of Gothenburg, Mölndal, Sweden. johan.gobom@neuro.gu.se.|Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, University Hospital, SE-431 80, Mölndal, Sweden. johan.gobom@neuro.gu.se.
authors.forename: Johan
authors.identifier: 0000-0001-6193-6193
authors.initials: J
authors.lastname: Gobom
authors.affiliation: Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at University of Gothenburg, Mölndal, Sweden.|Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, University Hospital, SE-431 80, Mölndal, Sweden.
authors.forename: Kaj
authors.initials: K
authors.lastname: Blennow
mesh_terms: D000544:Alzheimer Disease / Q000134:cerebrospinal fluid* / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000134:cerebrospinal fluid*; D016564:Amyloid beta-Protein Precursor / Q000134:cerebrospinal fluid*; D061067:Antibodies, Monoclonal, Humanized / Q000276:immunology; D001921:Brain / Q000378:metabolism; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods; D010103:Oxygen Isotopes; D010446:Peptide Fragments / Q000134:cerebrospinal fluid / Q000378:metabolism; D059748:Proteolysis
chemical_list: C545487:APP protein, human; D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D061067:Antibodies, Monoclonal, Humanized; D010103:Oxygen Isotopes; D010446:Peptide Fragments; C550616:solanezumab
keywords: Amyloid β; Cerebrospinal fluid; Insulin-degrading enzyme; Mass spectrometry; Stable isotope labeling