title: Modification of the oxidative stress biomarker AOPP assay: application in uremic samples.
abstract: BACKGROUND
  The levels of advanced oxidation protein products (AOPP), a plasma protein biomarker used to assess oxidative stress, are elevated in patients with chronic kidney disease (CKD). However, this apparent elevation is to a large extent due to assay interference (mostly by triglycerides which are usually markedly elevated in CKD). We therefore developed and tested a modified version of the AOPP assay to minimize the impact of this interference.
  
  
  METHODS
  Plasma levels of AOPP, lipids, proteins and various biomarkers of inflammation and oxidative stress were analyzed in 218 prevalent hemodialysis patients and 13 healthy controls using the established original (oAOPP) assay and following precipitation of plasma lipids using dextran sulphate (modified assay, mAOPP). The modified results were validated against a lipid extraction procedure using ether/butanol.
  
  
  RESULTS
  The modified assay decreased the levels of triglycerides and AOPP by 87% and 38%, respectively. Whereas oAOPP values correlated strongly with triglycerides, no such correlation was seen with mAOPP. The mAOPP levels correlated significantly with the oxidative stress markers 8-oxo-dG and pentosidine, whereas no such correlations were found for oAOPP.
  
  
  CONCLUSIONS
  The oAOPP concentration is largely overestimated in plasma samples due to lipid interferences. Precipitation of triglycerides before analysis yields markedly lower mAOPP values which more accurately reflect oxidative stress. Based on these results we propose that AOPP should be analyzed using the modified assay, which is a cheap, simple and fast method.
authors.affiliation: Divisions of Renal Medicine and Baxter Novum, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden. bjorn.anderstam@ki.se
authors.forename: Björn
authors.initials: B
authors.lastname: Anderstam
authors.forename: Bragfors-Helin
authors.initials: BH
authors.lastname: Ann-Christin
authors.forename: Alessandro
authors.initials: A
authors.lastname: Valli
authors.forename: Peter
authors.initials: P
authors.lastname: Stenvinkel
authors.forename: Bengt
authors.initials: B
authors.lastname: Lindholm
authors.forename: Mohamed E
authors.initials: ME
authors.lastname: Suliman
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D014511:Uremia / Q000097:blood*
chemical_list: D015415:Biomarkers