Mechanism of Mammalian Soluble Epoxide Hydrolase Inhibition by Chalcone Oxide Derivatives

A series of substituted chalcone oxides (1,3-diphenyl-2-oxiranyl propanones) and structural analogs was synthesized to investigate the mechanism by which they inhibit soluble epoxide hydrolases (sEH). The inhibitor potency and inhibition kinetics were evaluated using both murine and human recombinant sEH. Inhibition kinetics were well described by the kinetic models of A. R. Main (1982, in Introduction to Biochemical Toxicology, pp. 193-223, Elsevier, New York) supporting the formation of a covalent enzyme-inhibitor intermediate with a half-life inversely proportional to inhibitor potency. Structure-activity relationships describe active-site steric constraints and support a mechanism of inhibition consistent with the electronic stabilization of the covalent enzyme-inhibitor intermediate. The electronic effects induced by altering the ketone functionality and the para-substitution of the phenyl attached to the epoxy C1 (i.e., the alpha-carbon) had the greatest influence on inhibitor potency. The direction of the observed influence was reversed for the inhibitory potency of glycidol (1-phenyl-2-oxiranylpropanol) derivatives. Recent insights into the mechanism of epoxide hydrolase activity are combined with these experimental results to support a proposed mechanism of sEH inhibition by chalcone oxides.