Simultaneous resolution of underivatized regioisomers and stereoisomers of arachidonate epoxides by capillary electrophoresis

cis-Epoxyeicosatrienoic acids (EETs) and their hydrolysis products (threo-DHETs) have been proposed to be endothelial-dependent hyperpolarizing factors (EDHFs) which upregulate blood flow when tissue perfusion is impaired. Various EET regioisomers and enantiomers are formed from arachidonate by inducible cytochrome P450 epoxygenase isoforms, and tissue EET profiles may vary with diet, time, and disease. Because EET actions and metabolism may be regio- and stereospecific, convenient methods to measure profiles of EET isomers in tissues are needed. In the current studies, we describe two simple capillary electrophoretic methods for resolving EETs. The first method involves capillary electrophoresis with a mixture of neutral and anionic beta-cyclodextrins, which in one step baseline-resolves underivatized EET regioisomers and their enantiomers. Low picogram amounts of EET enantiomers were identified based on migration times and UV spectra. The method was also used to assess the antipode purity of EET standards, and to determine murine hepatic levels of EET enantiomers. The second method involves capillary electrochromatography, which also baseline-resolves underivatized EET and DHET regioisomers in one step. We conclude that in EET assays the major advantages of capillary electrophoresis over reversed-phase HPLC are improved peak efficiency, sensitivity, and resolution, plus precise coelution of deuterated and nondeuterated EETs.