Nicotinamide mononucleotide, a key NAD ⁺ intermediate, treats the pathophysiology of diet- and age-induced diabetes in mice

Type 2 diabetes (T2D) has become epidemic in our modern lifestyle, likely due to calorie-rich diets overwhelming our adaptive metabolic pathways. One such pathway is mediated by nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in mammalian NAD ⁺ biosynthesis, and the NAD ⁺-dependent protein deacetylase SIRT1. Here, we show that NAMPT-mediated NAD ⁺ biosynthesis is severely compromised in metabolic organs by high-fat diet (HFD). Strikingly, nicotinamide mononucleotide (NMN), a product of the NAMPT reaction and a key NAD ⁺ intermediate, ameliorates glucose intolerance by restoring NAD ⁺ levels in HFD-induced T2D mice. NMN also enhances hepatic insulin sensitivity and restores gene expression related to oxidative stress, inflammatory response, and circadian rhythm, partly through SIRT1 activation. Furthermore, NAD ⁺ and NAMPT levels show significant decreases in multiple organs during aging, and NMN improves glucose intolerance and lipid profiles in age-induced T2D mice. These findings provide critical insights into a potential nutriceutical intervention against diet- and age-induced T2D.