title: Pioglitazone lowers serum retinol binding protein 4 by suppressing its expression in adipose tissue of obese rats.
abstract: OBJECTIVE
  Pioglitazone, a peroxisome proliferator-activated receptor γ activator, is clinically used to treat insulin resistance. However, the underlying mechanism of pioglitazone's action remains unclear. We investigated whether, and how, pioglitazone modulates serum level of retinol binding protein 4 (RBP4), an adipocytokine associated with obesity and insulin resistance.
  
  
  METHODS
  Insulin sensitivity was determined by oral glucose tolerance test, and RBP4 expression was detected by RT-PCR and Western blotting.
  
  
  RESULTS
  Pioglitazone treatment significantly decreased serum RBP4 levels in obese rats, which was correlated with reduced body weight and increased insulin sensitivity. Moreover, pioglitazone greatly decreased RBP4 mRNA and protein levels in adipose tissue but not in the liver. Consistently, pioglitazone treatment significantly reduced RBP4 protein expression in 3T3-L1 adipocytes but not in HepG2 cells.
  
  
  CONCLUSIONS
  These results demonstrate that pioglitazone inhibits the level of serum RPB4 by suppressing RBP4 expression in adipose tissue of obese rats, suggesting that inhibiting RBP4 expression in adipocytes may provide a mechanism by which pioglitazone improves insulin sensitivity in insulin-resistant subjects.
authors: Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China.
authors: Chaoyu
authors: C
authors: Zhu
authors: Yuanyuan
authors: Y
authors: Xiao
authors: Xiaohua
authors: X
authors: Liu
authors: Junfeng
authors: J
authors: Han
authors: Jianmei
authors: J
authors: Zhang
authors: Li
authors: L
authors: Wei
authors: Weiping
authors: W
authors: Jia
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D059305:Diet, High-Fat / Q000009:adverse effects; D004195:Disease Models, Animal; D007004:Hypoglycemic Agents / Q000008:administration & dosage* / Q000494:pharmacology; D007333:Insulin Resistance; D050356:Lipid Metabolism / Q000187:drug effects; D008297:Male; D051379:Mice; D041681:NIH 3T3 Cells; D009765:Obesity / Q000097:blood* / Q000139:chemically induced / Q000235:genetics / Q000473:pathology; D000077205:Pioglitazone; D051381:Rats; D017207:Rats, Sprague-Dawley; D054839:Retinol-Binding Proteins, Plasma / Q000235:genetics / Q000378:metabolism*; D045162:Thiazolidinediones / Q000008:administration & dosage* / Q000494:pharmacology
chemical_list: D007004:Hypoglycemic Agents; C532035:Rbp4 protein, rat; D054839:Retinol-Binding Proteins, Plasma; D045162:Thiazolidinediones; D000077205:Pioglitazone