Metabolism of monoepoxides of methyl linoleate: Bioactivation and detoxification

Leukotoxin (ltx) and isoleukotoxin (iltx) methyl esters, are metabolites of methyl linoleic acid, an essential fatty acid. They have been associated w ith acute respiratory distress syndrome. The observed toxicity of ltx and i ltx is, in fact, due to the metabolism of the epoxides to their correspondi ng diols by soluble epoxide hydrolase (sEH), Herein, we demonstrate that lt x/iltx are toxic in a time-dependent manner to human sEH expressing cells w ith a LT50 of 10.6 +/- 0.8 h and that ltx and iltx have K-M Of 6.15 +/- 1.0 and 5.17 +/- 0.56 mu M, respectively, and V-max of 2.67 +/- 0.04 and 1.86 +/- 0.06 mu mol/min/mg, respectively, which can be inhibited by sEH inhibit ors. We show that four major metabolites of ltx/iltx are formed in our syst em, including ltx/iltx free acid, ltxd/iltxd, free acid, and phosphotidylch oline and phosphotidylethanolamine containing the carboxylic acid forms of both ltx/iltx and ltxd/iltxd, but that the only metabolite associated with toxicity is the carboxylic acid form of ltxd/iltxd, suggesting the involvem ent of cellular esterases, We demonstrate that a serine esterase inhibitor provides some protection from the toxicity of epoxy fatty esters to sEH exp ressing cells as do intercellular free sulfhydryls, but that this protectio n is not due to glutathione conjugation, With these data, we have proposed an extension of the metabolic pathway for ltx/iltx in eukaryotic cells. (C) 2000 Academic Press.