Tripeptide IRW Upregulates NAMPT Protein Levels in Cells and Obese C57BL/6J Mice.

Nicotinamide adenine dinucleotide (NAD) plays a vital role in cellular processes that govern human health and disease. Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in NAD biosynthesis. Thus, boosting NAD level via an increase in NAMPT levels is an attractive approach for countering the effects of aging and metabolic disease. This study aimed to establish IRW (Ile-Arg-Trp), a small tripeptide derived from ovotransferrin, as a booster of NAMPT levels. Treatment of muscle (L6) cells with IRW increased intracellular NAMPT protein levels (2.2-fold, < 0.05) and boosted NAD ( < 0.01). Both immunoprecipitation and recombinant NAMPT assays indicated the possible NAMPT-activating ability of IRW ( < 0.01). Similarly, IRW increased NAMPT mRNA and protein levels in the liver (2.6-fold, < 0.01) and muscle tissues (2.3-fold, < 0.05) of C57BL/6J mice fed with a high-fat diet (HFD). A significantly increased level of circulating NAD was also observed following IRW treatment (4.7 fold, < 0.0001). Dosing of with IRW elevated both D-NAAM (fly NAMPT) and NAD in vivo ( < 0.05). However, IRW treatment did not boost NAMPT levels in SIRT1 KO cells, indicating a possible SIRT1 dependency for the pharmacological effect. Overall, these data indicate that IRW is a novel small peptide booster of the NAMPT pool.