Epoxyeicosatrienoic acids (EETs) are potent lipid mediators formed by cytochrome 
P450 epoxygenases from arachidonic acid. They consist of four regioisomers of 
cis-epoxyeicosatrienoic acids: 5,6-, 8,9-, 11,12- and 14,15-EET. Here we 
investigated whether these triene epoxides are electrophilic enough to form 
covalent adducts with DNA in vitro. Using the thin-layer chromatography (TLC) 
(32)P-postlabelling method for adduct detection we studied the reaction of 
individual deoxynucleoside 3'-monophosphates and calf thymus DNA with the four 
racemic EETs. Under physiological conditions (pH 7.4) only ±11,12-EET11,12-EET 
formed adducts with DNA in a dose dependent manner detectable by the 
(32)P-postlabelling method. However, when pre-incubated at pH 4 all four racemic 
EETs were capable to bind to DNA forming several adducts. Under these conditions 
highest DNA adduct levels were found with ±11,12-EET followed by ±5,6-EET, 
±8,9-EET, and ±14,15-EET, all of them two orders of magnitude higher (between 3 
and 1 adducts per 10(5) normal nucleotides) than those obtained with ±11,12-EET 
at pH 7.4. Similar DNA adduct patterns consisting of up to seven spots were 
observed with all four racemic EETs the most abundant adducts being derived from 
the reaction with deoxyguanosine and deoxyadenosine. In summary, when analysed 
by the (32)P-postlabelling method all four racemic EETs formed multiple DNA 
adducts after activation by acidic pH, only ±11,12-EET produced DNA adducts in 
aqueous solution at neutral pH. Therefore, we conclude from our in vitro studies 
that EETs might be endogenous genotoxic compounds.