title: Effect of renal replacement therapy on retinol-binding protein 4 isoforms.
abstract: BACKGROUND
  Retinol-binding protein 4 (RBP4) levels are elevated in the serum of patients with kidney dysfunction. We recently showed that RBP4 isoforms including apo-RBP4 (RBP4 not bound to retinol) and RBP4 truncated at the C-terminus (RBP4-L, RBP4-LL) are increased in the serum of patients with kidney diseases but not in serum of patients with various liver diseases. The aim of this study was to investigate the effect of renal replacement therapy on RBP4 isoforms.
  
  
  METHODS
  We investigated serum levels of RBP4, apo-RBP4, holo-RBP4, RBP4-L, RBP4-LL, retinol and transthyretin (TTR) in 18 hemodialysis (HD) patients, 30 patients after renal transplantation (RTx) and in 35 healthy controls. RBP4 and TTR levels were measured by enzyme-linked immunosorbent assay, apo- and holo-RBP4 by native electrophoresis, retinol by high performance liquid chromatography and RBP4-L and RBP4-LL were analyzed by mass spectrometry.
  
  
  RESULTS
  HD and RTx patients had elevated RBP4, apo-RBP4 and RBP4-LL levels compared to controls. RTx patients had elevated amounts of RBP4-L compared to controls and elevated RBP4 and apo-RBP4 levels compared to HD patients.
  
  
  CONCLUSIONS
  The results demonstrate a strong correlation between kidney function and RBP4 isoforms and provide data for investigating the relation of RBP4 and insulin resistance in these patients.
authors.affiliation: Institute of Nutritional Science, University of Potsdam, Nuthetal Potsdam-Rehbrücke, Germany.
authors.forename: Simone K
authors.initials: SK
authors.lastname: Frey
authors.forename: Andrea
authors.initials: A
authors.lastname: Henze
authors.forename: Britta
authors.initials: B
authors.lastname: Nagl
authors.forename: Jens
authors.initials: J
authors.lastname: Raila
authors.forename: Alexandra
authors.initials: A
authors.lastname: Scholze
authors.forename: Martin
authors.initials: M
authors.lastname: Tepel
authors.forename: Florian J
authors.initials: FJ
authors.lastname: Schweigert
authors.forename: Walter
authors.initials: W
authors.lastname: Zidek
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000097:blood* / Q000628:therapy*; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged; D020033:Protein Isoforms / Q000096:biosynthesis / Q000097:blood; D006435:Renal Dialysis; D054839:Retinol-Binding Proteins, Plasma / Q000032:analysis / Q000096:biosynthesis*
chemical_list: D015415:Biomarkers; D020033:Protein Isoforms; C101326:RBP4 protein, human; D054839:Retinol-Binding Proteins, Plasma