Capillary electrophoresis of cytochrome P-450 epoxygenase metabolites of arachidonic acid. 2. Resolution of stereoisomers.

Each of the four regioisomers of epoxyeicosatrienoic acids (EETs) is a candidate for being an endothelial-dependent hyperpolarizing factor (EDHF). One regioisomer, 14,15-EET, stereospecifically blocks cyclooxygenases from converting arachidonic acid to prostaglandins and stereospecifically binds to cellular receptors. Both stereospecific actions emphasize the need to establish the tissue availability of the 14,15-EET enantiomers. The present work describes a method to quantitate picogram amounts of 14,15-EET enantiomers by capillary electrophoresis. The 14,15-EET enantiomers were baseline resolved (R = 1.3) using unsubstituted beta-cyclodextrin and 32% acetonitrile (v/v). When absorption at 194 nm was monitored using a photodiode array detector, 8 and 1 pg of underivatized 14,15-EET were readily quantitated and detected, respectively. Capillary electrophoresis accurately assessed chiral excesses up to 97:3 for either 14,15-EET enantiomer. Moreover, capillary electrophoresis with a photodiode array detector was sufficiently sensitive to detect and measure 14,15-EET enantiomers from murine liver. Thus, unlike chiral-phase high-performance liquid chromatography, capillary electrophoresis can be used to directly assess the chirality of trace amounts of underivatized eicosanoids.