Effect of PPAR-α and -γ agonist on the expression of visfatin, adiponectin, and TNF-α in visceral fat of OLETF rats

A variety of adipocytokines and peptides secreted from adipocytes have been considered to play a crucial role in obesity, insulin resistance, and type 2 diabetes. Recently, visfatin, a new adipocytokine, known as a pre-B cell colony-enhancing factor, has been isolated from visceral fat deposits. It has been shown to activate insulin receptors in a manner different from insulin. To understand the role of adipocytokines in improving insulin sensitivity via activation of the nuclear receptor peroxisome proliferator-activated receptor-α (PPAR-α) and -γ (PPAR-γ), we examined the expression of visfatin, adiponectin, and TNF-α in visceral fat depots of Otsuka Long-Evans Tokushima fatty (OLETF) rats from early to advanced diabetic stage (from 28 to 40 weeks of age). Serum glucose and insulin concentrations significantly (P < 0.05) decreased in rosiglitazone or fenofibrate-treated OLETF rats compared to untreated OLETF rats. Rosiglitazone significantly increased serum adiponectin concentration from 20 to 40 weeks of age (P < 0.05), whereas fenofibrate reduced TNF-α concentration. The expression of visfatin and adiponectin mRNA in visceral fat deposits was elevated by rosiglitazone or fenofibrate treatments when compared to untreated OLETF rats (P < 0.05), whereas, TNF-α mRNA was down-regulated by these drugs (P < 0.05). These results suggest that rosiglitazone and fenofibrate may prevent type 2 diabetes by regulating adipocytokines including visfatin, adiponectin, and TNF-α.