Urolithin A (UroA) is a first-in-class natural compound derived from gut microbiota metabolites of ellagitannins. This research firstly evaluates the mechanisms of UroA inhibiting advanced glycation end-products (AGEs) formation by...

Quercetin (Que), kaempferol (Kaem), isorhamnetin (Irh), and myricetin (Myri) are typical flavonols that are abundant in plant resources. This research investigated their ability in attenuating harmful glycation product formation and the effect of hydroxyl substitution. The inhibition mechanisms were elucidated by fluorescence spectroscopy and nano-liquid chromatography Orbitrap tandem mass spectrometry. The results indicated that the 3′-OH on the B-ring is critical in alleviating harmful glycation product formation, methylation reduced its inhibition, and the 5′-OH showed much less contribution than the 3′-OH. Que showed the strongest suppression on initial product, 5-hydroxymethylfurfural, and advanced glycation end product formation, with the corresponding percentage inhibitions at 36.58 μM of 81.1, 56.9, and 95.4%. Que and Myri also clearly inhibited fructosamine and acrylaminde production, while no suppression was observed by Irh and Kaem. The number of glycated sites was reduced from ten to seven, five, six, and nine, respectively, when 36.58 μM Que, Myri, Kaem, and Irh was added. Suppressing the conformational changes of ovalbumin induced by glycation, trapping dicarbonyl compounds, altering the microenvironment around tryptophan, and reducing the glycation activity of potential sites were the major inhibition mechanisms. These results suggest that Que and Myri may be promising natural agents for inhibiting harmful glycation and provide theoretical support for the effective screening of natural antiglycation reagents.

Ovalbumin (OVA) is a common carrier with high efficiency to deliver flavonoids. The aim of this study was to investigate the interaction mechanism of OVA and four flavonoids (quercetin (Que), myricetin (Myri), isorhamnetin (Ish), and kaempferol (Kaem)) with similar structures by fluorescence spectra, SDS−PAGE, FT−IR, and molecular docking analysis, and the effect on the antioxidant abilities of flavonoids was also evaluated. Results indicated that the antioxidant activity of flavonoids was positively correlated to the number of phenolic hydroxyl groups of on the B-ring, and weakened when the C-3′ position was replaced by a methoxy group. The addition of OVA enhanced the antioxidant activity of Que/Kaem, while it masked the antioxidant activity of Myri. The formation of Que/Myri/Ish/Kaem−OVA complexes was a spontaneous exothermic process driven mainly by hydrogen bond and van der Waals force, which could result in the change in OVA conformation and induce the transformation of α-helix to β-sheet. Among these, Kaem exhibited the strongest binding ability with OVA, and showed the greatest impact on the secondary and conformational structure of OVA, followed by Que. The hydroxylation of C-3′ and methoxylation of C-5′ weaken the interaction of Kaem with OVA. Molecular docking analysis suggested that Que, Myri, Ish, and Kaem formed six, three, five, and four hydrogen bonds with OVA, and the number of hydrogen bonds was not positively correlated with their binding constants. Our findings can provide a theoretical basis for the application of OVA on improving the antioxidant activity of flavonoids, and may help to explain the delivery efficiency of OVA on different bioactive constituents.