NAMPT and Insulin resistance: Correlation between visfatin concentration and insulin resistance, measured by the HOMA (Homeostatic Model Assessment for Insulin Resistance)-index was found in patients with ankylosing spondylitis, chronic inflammatory arthritis closely related to psoriatic arthritis (62). At the vascular level, visfatin upregulates vascular endothelial growth factor (VEGF) secretion and downregulates metalloproteins expression (63).