title: LC-MS/MS quantification of Zn-alpha2 glycoprotein: a potential serum biomarker for prostate cancer.
abstract: BACKGROUND
  Zn-alpha2 glycoprotein (ZAG) is a relatively abundant glycoprotein that has potential as a biomarker for prostate cancer. We present a high-flow liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for measuring serum ZAG concentrations by proteolytic cleavage of the protein and quantification of a unique peptide.
  
  
  METHODS
  We selected the ZAG tryptic peptide (147)EIPAWVPEDPAAQITK(162) as the intact protein for quantification and used a stable isotope-labeled synthetic peptide with this sequence as an internal standard. Standards using recombinant ZAG in bovine serum albumin, 50 g/L, and a pilot series of patient sera were denatured, reduced, alkylated, and digested with trypsin. The concentration of ZAG was calculated from a dose-response curve of the ratio of the relative abundance of the ZAG tryptic peptide to internal standard.
  
  
  RESULTS
  The limit of detection for ZAG in serum was 0.08 mg/L, and the limit of quantification was 0.32 mg/L with a linear dynamic range of 0.32 to 10.2 mg/L. Replicate digests from pooled sera run during a period of 3 consecutive days showed intraassay imprecision (CV) of 5.0% to 6.3% and interassay imprecision of 4.4% to 5.9%. Mean (SD) ZAG was higher in 25 men with prostate cancer [7.59 (2.45) mg/L] than in 20 men with nonmalignant prostate disease [6.21 (1.65) mg/L, P = 0.037] and 6 healthy men [3.65 (0.71) mg/L, P = 0.0007].
  
  
  CONCLUSIONS
  This LC-MS/MS assay is reproducible and can be used to evaluate the clinical utility of ZAG as a cancer biomarker.
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA.
authors.forename: Olga P
authors.initials: OP
authors.lastname: Bondar
authors.forename: David R
authors.initials: DR
authors.lastname: Barnidge
authors.forename: Eric W
authors.initials: EW
authors.lastname: Klee
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Davis
authors.forename: George G
authors.initials: GG
authors.lastname: Klee
mesh_terms: D054392:Adipokines; D014408:Biomarkers, Tumor / Q000097:blood*; D002352:Carrier Proteins / Q000097:blood*; D002853:Chromatography, Liquid; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D006868:Hydrolysis; D008297:Male; D010455:Peptides / Q000097:blood; D010865:Pilot Projects; D011471:Prostatic Neoplasms / Q000175:diagnosis*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D044967:Serum; D053719:Tandem Mass Spectrometry; D000090203:Zn-Alpha-2-Glycoprotein
chemical_list: D054392:Adipokines; D014408:Biomarkers, Tumor; D002352:Carrier Proteins; D006023:Glycoproteins; D010455:Peptides; C488891:AZGP1 protein, human; D000090203:Zn-Alpha-2-Glycoprotein