SIRT1 and obesity due to melanocortin 4 receptor deficiency: This discrepancy may be attributed to the existence of two distinct forms of visfatin: intravisfatin (iNAMPT), which is positively correlated with obesity under caloric excess, and circulating extravisfatin (eNAMPT), which is associated with anti-aging and longevity effects induced by the suppression of age-related physiological decline through SIRT1-mediated deacetylation of iNAMPT [114,115].