Visfatin as a Novel Mediator Released by Inflamed Human Endothelial Cells

Background: Visfatin is a multifaceted adipokine whose circulating levels are enhanced in different metabolic diseases. Extracellular visfatin can exert various deleterious effects on vascular cells, including inflammation and proliferation. Limited evidence exists, however, on the capacity of human vascular cells to synthesize and release visfatin by themselves, under basal or pro-inflammatory conditions. Methods and Results: Intracellular visfatin was detected by Western blot in non-stimulated human umbilical vein endothelial cells (HUVEC). However, exposing HUVEC for 18 h to a series of pro-inflammatory stimulus, such as interleukin (IL)-1 beta (1 to 10 ng/mL), tumor necrosis factor-alpha (1 to 10 ng/mL) or angiotensin II (10 pmol/L to 1 mu mol/L) markedly enhanced intracellular visfatin content. Using IL-1 beta (10 ng/mL; 18 h), it was determined that the increase in intracellular visfatin, which was paralleled by enhanced visfatin mRNA levels, relied on a signalling mechanism involving both nuclear factor-kappa B and poly (ADP ribose) polymerase-1 activation. Moreover, IL-1 beta modified the subcellular localization of visfatin; while in non-stimulated HUVEC immunoreactive visfatin predominantly showed an intra-nuclear granular pattern, in IL-1 beta-inflamed cells an extra-nuclear filamentous staining, co-localising with F-actin fibers and suggesting a secretory pattern, was mainly found. Indeed, IL-1 beta promoted visfatin secretion, as determined by both ELISA and immunocytochemistry. Conclusions: Human endothelial cells synthesize and release visfatin, particularly in response to inflammation. We suggest that the inflamed endothelium can be a source of visfatin, which arises as a local inflammatory mediator and a potential therapeutic target to interfere with vascular inflammation.