title: Evidence that kidney function but not type 2 diabetes determines retinol-binding protein 4 serum levels.
abstract: OBJECTIVE
  It has been suggested that retinol-binding protein 4 (RBP4) links adiposity, insulin resistance, and type 2 diabetes. However, circulating RBP4 levels are also affected by kidney function. Therefore, the aim of this study was to test whether RBP4 serum levels are primarily associated with kidney function or type 2 diabetes.
  
  
  METHODS
  RBP4 serum concentration was determined by enzyme-linked immunosorbent assay in 126 nondiabetic and 104 type 2 diabetic subjects. The study population was divided according to estimated glomerular filtration rate (eGFR) into the following groups: eGFR >90 ml/min per 1.73 m(2) (n = 53), 60-90 ml/min per 1.73 m(2) (n = 90), 30-60 ml/min per 1.73 m(2) (n = 38), and <30 ml/min per 1.73 m(2) (n = 49). Each group was subdivided into nondiabetic and type 2 diabetic subjects.
  
  
  RESULTS
  RBP4 serum concentration was elevated (2.65 vs. 2.01 micromol/l; P < 0.001) and eGFR was reduced (56 vs. 74 ml/min per 1.73 m(2); P < 0.001) in type 2 diabetic vs. nondiabetic subjects, respectively. By stratifying for eGFR, no more differences in RBP4 serum concentration were detectable between type 2 diabetic and nondiabetic subjects. A linear regression analysis revealed an influence of eGFR (r = -0.477; P < 0.001) but not A1C (r = 0.093; P = 0.185) on RBP4 serum concentration.
  
  
  CONCLUSIONS
  Existing human data showing elevated RBP4 levels in type 2 diabetic patients may be the result of moderate renal insufficiency rather than support for the suggestion that RBP4 links obesity to type 2 diabetes.
authors.affiliation: Department of Physiology and Pathophysiology of Nutrition, Institute of Nutritional Science, University of Potsdam, Potsdam, Germany. henze@rz.uni-potsdam.de
authors.forename: Andrea
authors.initials: A
authors.lastname: Henze
authors.forename: Simone K
authors.initials: SK
authors.lastname: Frey
authors.forename: Jens
authors.initials: J
authors.lastname: Raila
authors.forename: Martin
authors.initials: M
authors.lastname: Tepel
authors.forename: Alexandra
authors.initials: A
authors.lastname: Scholze
authors.forename: Andreas F H
authors.initials: AF
authors.lastname: Pfeiffer
authors.forename: Martin O
authors.initials: MO
authors.lastname: Weickert
authors.forename: Joachim
authors.initials: J
authors.lastname: Spranger
authors.forename: Florian J
authors.initials: FJ
authors.lastname: Schweigert
mesh_terms: D015415:Biomarkers / Q000097:blood; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology; D007677:Kidney Function Tests; D008297:Male; D009765:Obesity / Q000097:blood; D012016:Reference Values; D012044:Regression Analysis; D054839:Retinol-Binding Proteins, Plasma / Q000378:metabolism*
chemical_list: D015415:Biomarkers; C101326:RBP4 protein, human; D054839:Retinol-Binding Proteins, Plasma
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