Retinol-binding protein 4 and nicotinamide phosphoribosyltransferase/visfatin in rat obesity models

Retinol-binding protein 4 (RBP4) and nicotinamidephosphoribosyltransferase/visfatin(Nampt/ visfatin) are adipocyte-secreted proteins (adipokines) whose relevance to the metabolic syndrome and regulation in obesity remain controversial. Here, we tested the hypothesis that adipose tissue expression and circulating levels of these two adipokines are elevated in obesity by analyzing their changes in both a genetic and a diet-induced model of obesity in the rat (obese fa/fa Zucker rats and Wistar rats fed a cafeteria diet, respectively). Compared with lean controls, obese fa/fa rats were hyperleptinemic, hyperinsulinemic, and insulin resistant and had reduced RBP4 serum levels and mRNA levels in adipose depots, unchanged Nampt/visfatin serum levels, and reduced Nampt/visfatin mRNA levels selectively in the inguinal adipose depot. Cafeteria diet-induced obesity resulted in increased fed blood glucose levels, a variable degree of insulin resistance, unchanged serum Nampt/visfatin and RBP4 levels, and reduced mRNA levels of both adipokines in several adipose depots. Hence, increases in RBP4 or Nampt/visfatin do not accompany obesity and insulin resistance in the models examined.