Visfatin (Nampt) is not an insulin-mimetic hormone and is detected differently by immunoassays

Objective: Visfatin has been described as an adipocytokine that exerts insulin-like effects through direct interaction with the insulin receptor. We evaluated various visfatin preparations, their molecular features and detection in immunoassays, and the biological action. Results: We did not observe phosphorylation of the insulin receptor or down-stream Akt in adipocytes, HepG2, or fibroblasts overexpressing the human insulin receptor. There was also no adipogenic effect of visfatin on the differentiation of adipocytes. Also, supernatants of transfected COS cells containing visfatin did not induce any of such in…