Bioactive constituents from Inula japonica as soluble epoxide hydrolase inhibitors: Mechanistic insights and...

Soluble epoxide hydrolase (sEH) is implicated in the metabolism of epoxyeicosatrienoic acids (EETs) and is associated with neuroinflammation. Herein, based on sEH-mediated probe hydrolysis reaction, we obtained twenty-nine compounds from Inula japonica with the inhibition of sEH activities, including three new structures inulajaponines A-C (1-3) and twenty-six known structures (4-29). Among them, compounds 8-10 (3β,16β-dihydroxylup-20(29)-ene, maniladiol, and arnidiol), 25 (methyl [3-aryl-2-methoxycarbonyl-1-indanyl] acetate) and 27 (uncariarhyine A) presented strong inhibitory potentials to sEH with IC₅₀ values of 7.61, 8.58, 7.42, 6.96, and 8.38 μM, respectively. Inhibition kinetics indicated that uncompetitive inhibitors 8-10, 25, and 27 were defined as 8.15, 2.70, 6.03, 4.99, and 4.91 μM, respectively. In addition, we validated the interaction mechanism of compounds-sEH complex using compounds 9/10 as model inhibitors. Molecular dynamics simulations proved that amino acid residue Gln384 of sEH could effectively combine with inhibitors 9/10 through the hydrogen bond. The inhibitors 9 and 10 exerted anti-neuroinflammatory effects through MAPK/NF-κB in LPS-exposed BV2 cells. This study provided a useful insight to develop sEH inhibitors, showing their potency to treat neuroinflammatory diseases.