Formation of cyclic products from the diepoxide of long-chain fatty esters by cytosolic epoxide hydrolase

Abstract

Since diepoxides are known metabolites of polyunsaturated fatty acids, the action of the cytosolic epoxide hydrolase purified from liver tissue was examined on these diepoxides. Diepoxymethylstearate was metabolized to the corresponding tetraol by high concentrations of affinity-purified cytosolic epoxide hydrolase. When the enzyme was diluted (1000- to 2000-fold), disappearance of the tetraol metabolite occurred simultaneously with formation of other hydration products with GC retention times and chromatographic mobilities different from those of the tetraol. The hydration products were identified as tetrahydrofuran diols based on comparison of chromatographic properties and mass spectral information with the properties and spectra of chemically generated products. Also, a mixture of diepoxymethylarachidonates was hydrated to tetraols using concentrated enzyme. As the enzyme was diluted (1000- to 2000-fold), a decrease in tetraol formation occurred along with the elevation of other hydration products whose mass spectra were consistent with tetrahydrofuran diol structures. These data are consistent with the epoxide hydrolase at low concentrations acting to open one epoxide followed by nonenzymatic cyclization to the tetrahydrofuran diols. The data also suggest that oxygenated lipids may be endogenous substrates for the cytosolic epoxide hydrolase. Since some oxylipins are known chemical mediators, the in vivo presence and role of these novel diols and tetrahydrofuran diols should be examined.