Inhibitory Effects of Flavonoids from Citrus reticulata 'Chachi' Peel on the Formation of Advanced Glycation End-products

This study investigated the inhibitory effects of extracts from Citrus reticulata 'Chachi' peels at different growth stages and the primary flavonoid components (nobiletin, hesperetin, and hesperidin) on fluorescent AGEs using the bovine serum albumin-glucose (BSA-Glu) model. To elucidate the underlying mechanisms, the interactions between flavonoids and BSA were analyzed using multi-spectral techniques and computer molecular docking. Results showed that extracts from Citrus reticulata 'Chachi' peels at four growth stages significantly inhibited AGEs formation. The extracts obtained in December (2.5 mg/mL) showed maximum inhibition rates of 76.33% for fluorescent AGEs and 71.78%, 62.73%, and 66.07% for the protein glycoxidation products dityrosine, kynurenine, and N'-formylkynurenine, respectively. Fluorescence spectroscopy revealed that the fluorescence quenching mechanism of BSA by nobiletin, hesperetin, and hesperidin was via a static quenching procedure. Synchronous fluorescence spectroscopy revealed that these flavonoids slightly altered the conformation of BSA and the microenvironment of tryptophan (TRP) and tyrosine (TYR) residues. Molecular docking studies showed that the flavonoids bound to a hydrophobic pocket near the TRP-213 residue of BSA, forming a complex and disrupting glucose binding to glycation sites on BSA through hydrogen bonds and hydrophobic interactions. In conclusion, flavonoids derived from Citrus reticulata 'Chachi' peels effectively inhibited the formation of AGEs by reducing the combination of arginine and lysine residues with reducing sugars, and had potential for use in developing natural AGEs inhibitors.