title: Protein profiling reveals inter-individual protein homogeneity of arachnoid cyst fluid and high qualitative similarity to cerebrospinal fluid.
abstract: BACKGROUND
  The mechanisms behind formation and filling of intracranial arachnoid cysts (AC) are poorly understood. The aim of this study was to evaluate AC fluid by proteomics to gain further knowledge about ACs. Two goals were set: 1) Comparison of AC fluid from individual patients to determine whether or not temporal AC is a homogenous condition; and 2) Evaluate the protein content of a pool of AC fluid from several patients and qualitatively compare this with published protein lists of cerebrospinal fluid (CSF) and plasma.
  
  
  METHODS
  AC fluid from 15 patients with temporal AC was included in this study. In the AC protein comparison experiment, AC fluid from 14 patients was digested, analyzed by LC-MS/MS using a semi-quantitative label-free approach and the data were compared by principal component analysis (PCA) to gain knowledge of protein homogeneity of AC. In the AC proteome evaluation experiment, AC fluid from 11 patients was pooled, digested, and fractionated by SCX chromatography prior to analysis by LC-MS/MS. Proteins identified were compared to published databases of proteins identified from CSF and plasma. AC fluid proteins not found in these two databases were experimentally searched for in lumbar CSF taken from neurologically-normal patients, by a targeted protein identification approach called MIDAS (Multiple Reaction Monitoring (MRM) initiated detection and sequence analysis).
  
  
  RESULTS
  We did not identify systematic trends or grouping of data in the AC protein comparison experiment, implying low variability between individual proteomic profiles of AC.In the AC proteome evaluation experiment, we identified 199 proteins. When compared to previously published lists of proteins identified from CSF and plasma, 15 of the AC proteins had not been reported in either of these datasets. By a targeted protein identification approach, we identified 11 of these 15 proteins in pooled CSF from neurologically-normal patients, demonstrating that the majority of abundant proteins in AC fluid also can be found in CSF. Compared to plasma, as many as 104 proteins in AC were not found in the list of 3017 plasma proteins.
  
  
  CONCLUSIONS
  Based on the protein content of AC fluid, our data indicate that temporal AC is a homogenous condition, pointing towards a similar AC filling mechanism for the 14 patients examined. Most of the proteins identified in AC fluid have been identified in CSF, indicating high similarity in the qualitative protein content of AC to CSF, whereas this was not the case between AC and plasma. This indicates that AC is filled with a liquid similar to CSF. As far as we know, this is the first proteomics study that explores the AC fluid proteome.
authors: Institute of Medicine, University of Bergen, 5021 Bergen, Norway. magnus.berle@med.uib.no.
authors: Magnus
authors: M
authors: Berle
authors: Ann C
authors: AC
authors: Kroksveen
authors: Oystein A
authors: OA
authors: Haaland
authors: Thin T
authors: TT
authors: Aye
authors: Jill A
authors: JA
authors: Opsahl
authors: Eystein
authors: E
authors: Oveland
authors: Knut
authors: K
authors: Wester
authors: Rune J
authors: RJ
authors: Ulvik
authors: Christian A
authors: CA
authors: Helland
authors: Frode S
authors: FS
authors: Berven
references: Cerebrospinal Fluid Res. 2010 Feb 26;7:6
references: 20187927
references: J Neurosurg. 2005 Nov;103(5 Suppl):427-32
references: 16302614
references: PLoS One. 2010 Jun 11;5(6):e10980
references: 20552007
references: Cerebrospinal Fluid Res. 2010 Jun 10;7:8
references: 20537169
references: Proteomics Clin Appl. 2007 Jul;1(7):699-711
references: 21136725
references: J Neurosurg. 2010 Nov;113(5):934-9
references: 20095787
references: Exp Neurol. 2010 Aug;224(2):424-8
references: 20471979
references: Proteomics. 2005 Aug;5(13):3226-45
references: 16104056
references: J Neurosurg. 1984 Apr;60(4):803-13
references: 6231356
references: N Engl J Med. 2007 Nov 1;357(18):1821-8
references: 17978290
references: Surg Neurol. 1982 May;17(5):363-9
references: 7089853
references: J Neuropathol Exp Neurol. 1981 Jan;40(1):61-83
references: 7205328
references: J Neurol Neurosurg Psychiatry. 2008 Jan;79(1):72-5
references: 17488784
references: J Biomed Biotechnol. 2010;2010:840518
references: 19911078
references: BMJ. 2009 Aug 17;339:b3016
references: 19687093
references: Neurosurgery. 1999 Oct;45(4):775-9
references: 10515470
references: Surg Neurol. 1978 Feb;9(2):139-44
references: 625699
references: Nat Protoc. 2009;4(6):870-7
references: 19444244