Discovery of soluble epoxide hydrolase inhibitors from Inula britannica: Inhibition kinetics, molecular dynamics simulation, biochemical, and in vitro cell-based studies

Soluble epoxide hydrolase (sEH) is an enzyme involved in transforming epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs). EETs play a pivotal role in maintaining anti-inflammatory response and pain regulation, making sEH as an important target for therapeutic interventions. Based on our present study of discovery of sEH inhibitors, herein, six new (1-6) and fifteen known compounds (7-21) with inhibitory effects toward sEH were isolated from Inula britannica. Among them, compounds 5 (inulabritanthymol G) and 9 (bellidtfolin) possessed strongest inhibitory abilities with IC50 values of 3.87 and 2.85 mu M, respectively. Inhibition kinetics indicated that they were assigned as uncompetitive inhibitors, and their Ki values were 1.93 and 1.89 mu M, respectively. Molecular dynamics simulation demonstrated that the stability and interactions of inhibitors 5/ 9 with sEH were attributed to hydrogen bonds with amino acid residues of Asp335, Ser374, or Asn472. In addition, inhibitors 5 and 9 could exert anti-inflammatory effects through suppressing the NF-kappa B activation in LPS-exposed RAW264.7 cells, highlighting their potential as natural therapeutic agents for managing inflammatory diseases.