Visfatin is an adipokine, but it is not regulated by thiazolidinediones

Context: Visfatin was recently reported to be expressed in human adipose tissue and to exert insulin-mimicking effects. Objective: The objective of this study was to examine whether visfatin is a true adipokine and is expressed in isolated fat cells. We also examined whether visfatin is regulated by thiazolidinediones and, thus, can contribute to the ability of these agents to improve insulin sensitivity. Design: This was an open-labeled drug therapy trial. Setting: This study was performed at a university hospital. Patients: Seven newly diagnosed and previously untreated type 2 diabetic patients and six healthy individuals with reduced insulin sensitivity participated in the study. Intervention: Pioglitazone therapy (30-45 mg/d) was given for 3-4 wk. Main Outcome Measures: Serum and adipose tissue mRNA levels of visfatin and adiponectin were the main outcome measures. Results: Visfatin mRNA is expressed in both adipose tissue and isolated adipocytes. Treatment with thiazolidinediones for 3-4 wk did not alter the gene expression or circulating levels of visfatin in either nondiabetic or the diabetic individuals, whereas adiponectin increased significantly. Conclusion: The present study shows that visfatin is a true adipokine, but it is not regulated by TZD and, thus, is unlikely to contribute to the insulin-sensitizing actions of these drugs.