An LC/MS method for the quantitative determination of 7alpha-OH DHEA and 7beta-OH DHEA: an application for the study of the metabolism of DHEA in rat brain.

Dehydroepiandrosterone (DHEA) is an important neurosteroid with neuronal protection and memory enhancement functions. 7alpha-OH DHEA and 7beta-OH DHEA are the two important metabolites of DHEA in the brain. We have developed an LC/MS method to quantitatively analyze 7alpha-OH DHEA and 7beta-OH DHEA. Chromatographic separation was carried out on a C18 column with gradient elution using mobile phases of formic acid in acetonitrile and in water formic acid. Mass spectral detection was performed with a ThermoFinnigan LCQ advantage quadruple ion trap mass spectrometer with electrospray ionization. Positive ion chromatograms were acquired using single ion monitoring. The protonated molecule was 305 m/z, but the most abundant ion (269 m/z) was used for quantification. This method was validated and applied to investigate the 7-hydroxylation of DHEA. When incubating DHEA with rat brain microsomes, both 7alpha-OH DHEA and 7beta-OH DHEA were observed, but 7alpha-OH DHEA was the major metabolite.