Identification and evaluation of citrus peel-derived polymethoxyflavonoids as natural SIRT1 activators.

Sirtuin 1 (SIRT1), an NAD+-dependent deacetylase, regulates multiple age-related physiological processes, and its activation is associated with protection against metabolic and degenerative diseases. Citrus peel-derived polymethoxyflavonoids (PMFs) are abundant bioactive compounds with diverse pharmacological functions; however, their roles as SIRT1 activators remain underexplored. Using a non-fluorescence-based SIRT1 deacetylase assay coupled with ESI-TOF-MS, we screened peel extracts from 28 citrus cultivars. Extracts from kara mandarin, shiikuwasha, and dekopon significantly enhanced SIRT1 activity in a dose-dependent manner. Five PMFs-heptamethoxyflavone (HMF), 5-demethylnobiletin, tangeretin, nobiletin, and sinensetin-were identified as potent activators, with HMF exhibiting the strongest effect, surpassing that of resveratrol. Kinetic analyses revealed that HMF enhanced SIRT1 activity primarily by decreasing the substrate Km. Docking simulations indicated that HMF interacts with hydrophobic residues within the α2-loop-α3 motif of the SIRT1 N-terminal domain. These findings highlight citrus peels as a promising natural source of SIRT1 activators and suggest potential applications in health-promoting functional foods.