2,3-EPOXY-4-HYDROXYNONANAL, A POTENTIAL LIPID-PEROXIDATION PRODUCT FOR ETHENO ADDUCT FORMATION, IS NOT A SUBSTRATE OF HUMAN EPOXIDE HYDROLASE

Our previous studies have shown that 2,3-epoxy-4-hydroxynonanal, a rea ctive epoxy aldehyde capable of forming etheno adducts with DNA bases, is mutagenic and tumorigenic (Carcinogenesis, 14, 2073), The epoxy al dehyde can be generated from trans-4-hydroxy-2-nonenal, a lipid peroxi dation product of omega-6 polyunsaturated fatty acids, by autoxidation or by incubation with fatty acid hydroperoxides or hydrogen peroxides (Chem. Res. Toxicol., 9, 306), These are plausible in vivo pathways f or the formation of 2,3-epoxy-4-hydroxynonanal. The possibility that 2 ,3-epoxy-4-hydroxynonanal is a tumorigen of endogenous origin is sugge sted by recent observations that etheno bases are detected as backgrou nd DNA lesions in untreated rodents and humans. A metabolic pathway cr itical for detoxification of 2,3-epoxy-4-hydroxynonanal involves the r ing-opening by epoxide hydrolase, which abolishes its ability to form cyclic etheno DNA adducts, In this study, we examined whether 2,3-epox y-4-hydroxynonanal is a substrate of cDNA expressed human epoxide hydr olase, Human epoxide hydrolase was expressed in TK-143 cells (thymidin e kinase-deficient human embryoblast) infected with recombinant vaccin ia virus encoding human epoxide hydrolase cDNA, Controls consisted of the cells infected with vaccinia virus in the absence of human epoxide hydrolase cDNA, No hydrolysis occurred when [2,3-H-3]2,3-epoxy-4-hydr oxynonanal was incubated at 37 degrees C for 30 min at pH 7.4 with cel ls expressing human epoxide hydrolase, as indicated by the presence of a pair of radioactive peaks in reversed-phase HPLC chromatography, wh ich comigrated with the UV standards of the two diastereomers of the e poxy aldehyde, The identity of these compounds as the intact epoxy ald ehyde was further supported by derivatization to the 2,4-dinitrophenyl hydrazones followed by reversed phase HPLC analysis, Similar results w ere observed with the control cells or with the heat deactivated human epoxide hydrolase, The epoxide hydrolase activity in the expressed ce lls was demonstrated by their ability to convert benzo[a]pyrene-4,5-di hydroepoxide to benzo[a]pyrene-trans-4,5-dihydrodiol under the same co nditions. These results clearly indicate that 2,3-epoxy-4-hydroxynonan al is not a substrate of human epoxide hydrolase, and, thus strengthen its possible endogenous role in the formation of promutagenic exocycl ic etheno adducts in vivo.