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 K_m. 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.