title: Excitatory amino acids display compartmental disparity between plasma and synovial fluid in clinical arthropathies.
abstract: BACKGROUND
  Previous studies have demonstrated elevated levels of excitatory amino acids (EAA) glutamate (Glu) and aspartate (Asp) in the synovial fluid (SF) of patients with active arthritis. The source of SF EAA concentrations are thought in large part to be secondary to passive diffusion from the plasma across synovial membranes and less so, reflective of local synovial pathology.
  
  
  OBJECTIVE
  This descriptive report assesses the hypothesis that the SF EAA levels reflect inflammatory processes of the joint and are not dependent on plasma levels.
  
  
  METHODS
  Simultaneously drawn plasma and SF samples were obtained from 14 recently deceased cadavers and 10 patients with active arthritis. Plasma and SF EAA and other amino acid (AA) levels were determined by HPLC. SF: Plasma compartment concentration ratios were calculated to assess if SF EAA levels were similar to plasma levels.
  
  
  RESULTS
  In the cadavers with no antemortem arthritis, the mean SF: Plasma ratios for Glu and Asp were 4-5-fold lower than the mean ratios seen for 9 other AAs, showing specific discrepancies of EAA levels between plasma and synovial fluid. In 9 patients with active arthritis, the SF: Plasma concentration ratios were higher in samples derived from inflammatory arthropathies.
  
  
  CONCLUSIONS
  Clinical samples demonstrated distinct, independent compartmental EAA concentrations between blood and joint compartments in support that local arthritic processes rather than plasma influence SF EAA concentrations. The SF EAA levels, whether from local cell production, local neurogenic sources, and/or transport-gradient mechanisms, parallel local pathology in the joint compartment and thus serve as surrogate biomarkers of local inflammatory processes.
authors: Department of Neuroscience and Cell Biology, University of Texas Medical Branch Galveston, TX, USA. tmcnearn@utmb.edu
authors: Terry A
authors: TA
authors: McNearney
authors: Karin N
authors: KN
authors: Westlund
mesh_terms: D000328:Adult; D000368:Aged; D001168:Arthritis / Q000378:metabolism* / Q000473:pathology; D001224:Aspartic Acid / Q000032:analysis / Q000378:metabolism*; D001774:Blood Chemical Analysis; D002102:Cadaver; D002851:Chromatography, High Pressure Liquid; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism*; D006801:Humans; D007596:Joints / Q000378:metabolism* / Q000473:pathology; D008875:Middle Aged; D013582:Synovial Fluid / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001224:Aspartic Acid; D018698:Glutamic Acid
keywords: Glutamate; arthritis; aspartate; biomarker; neurotransmitter; synovial fluid