Comparative Study on the Antioxidative Effects and α-Glucosidase Inhibitory Potential In Vitro among Ellagic Acid and Its Metabolites Urolithins

The current study compared the radical scavenging and α-glucosidase inhibition potentials of ellagic acid (EA) and its metabolites, urolithins (Uros), and further explored the structure–activity relationship. The outcomes indicated that urolithin M5 (Uro-M5), EA, and urolithin M6 (Uro-M6) exhibited superior 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity; EA and urolithin D (Uro-D) expressed better ABTS scavenging ability, and EA and Uro-M5 showed preferable α-glucosidase inhibition activity. The results of CD spectra and fluorescence spectral analysis explained the interaction between Uros and α-glucosidase. Correlation analysis indicated that hydroxyl groups were crucial for the antioxidative effect, while C-8 OH contributed greatly to the α-glucosidase inhibition activity. Quantum mechanical analysis showed that both EA and Uros exhibited strong electrophilic properties. These comparative results showed a biological discrepancy between Uros and provided essential information for exploring the bioactive application of EA as a functional ingredient or dietary supplement.