The inhibition of mammalian 15-lipoxygenases by the anti-inflammatory drugebselen: Dual-type mechanism involving covalent linkage and alteration of the iron ligand sphere

Mammalian lipoxygenases have been implicated in inflammation and atheroscle rosis and, thus, lipoxygenase inhibitors may be of pharmacological interest . In cells, lipoxygenases occur in a catalytically silent ground state that requires activation to become active. We found that the seleno-organic dru g ebselen [2-phenyl-1,2-benzisoselenazol-3(2H)-one], which exhibits anti-in flammatory properties, irreversibly inhibited pure rabbit 15-lipoxygenase,w ith an IC50 in the nM range when preincubated with the enzyme in the absenc e of fatty acid substrates. Subsequent dialysis, gel filtration, or substra te addition did not restore the enzyme activity, and experiments with [C-14 ]ebselen indicated a covalent linkage of the drug. The presence of sulfhydr yl compounds in the incubation mixture prevented both enzyme labeling and i nactivation, but we did not see any reactivation when sulfhydryl compounds were added afterward. X-ray absorption studies indicated that ebselen did a lter the geometry of the iron ligand sphere, and the data are consistent wi th an iron complexation by the drug. When fatty acid substrate was present during lipoxygenase-ebselen interaction, the inhibitory potency was strongl y reduced and a competitive mode of action was observed. These data suggest that ebselen inactivated the catalytically silent ground-state lipoxygenas e irreversibly by covalent linkage and alteration of the iron ligand sphere . In contrast, it functions as a competitive inhibitor of the catalytically active enzyme species. The pharmacological relevance of ebselen as a poten tial in vivo lipoxygenase inhibitor will be discussed.