NAMPT and obesity due to melanocortin 4 receptor deficiency: Visfatin/NAMPT exists in two forms: intracellular NAMPT (iNAMPT) that catalyzes NAD+ biosynthesis and modulates insulin sensitivity and lipid metabolism and extracellular eNAMPT/visfatin, an inflammatory cytokine that activates TLR4/NF-κB signaling in obesity and NAFLD [64].