Investigation of the inhibitory activity of triterpenoids isolated from Actinidia polygama stems against β-glucuronidase via enzyme kinetics, molecular docking, and molecular dynamics analyses

Actinidia polygama, well-known for its traditional medicinal properties, has garnered significant attention due to its distinctive chemical composition. In this study, we isolated and structurally elucidated 11 known compounds, including a monoterpene glycoside (1), eight triterpenoids (2–9), and two lignan glycosides (10 and 11), from A. polygama stems. Notably, the inhibitory activity of these compounds on β-glucuronidase activity was evaluated for the first time. Our results show that 2α,3α,24-trihydroxyurs-12-en-28-oic acid (4), strongly inhibited β-glucuronidase (IC₅₀ = 14.36 ± 0.42 μM) to a degree much higher than that of the positive control (D-saccharic acid 1,4-lactone, DSA; IC₅₀ = 16.30 ± 0.21 μM). Furthermore, the results of an enzyme kinetics analysis indicate that compound 4 acts as a non-competitive inhibitor of β-glucuronidase. Finally, the findings from molecular docking and molecular dynamics simulations confirmed the inhibition mode of compound 4, its interaction with the allosteric site of β-glucuronidase, and the stability of the complex in the bound state.