The 7-hydroxylation of dehydroepiandrosterone in rat brain

Dehydroepiandrosterone (DHEA) is an important neurosteroid with multiple functions in the central nervous system including neuroprotection. How DHEA exerts its neuroprotection function has not been fully elucidated. One possible mechanism is via its active metabolites, 7 alpha-OH DHEA and 7 beta-OH DHEA. The purpose of this research is to understand how DHEA is metabolized to 7 alpha-OH DHEA and 7 beta-OH DHEA by brain tissue. DHEA was incubated with rat brain microsomes and mitochondria and the 7 alpha-OH DHEA and 7 beta-OH DHEA formed by these fractions were analyzed by LC/MS. For the first time, we observed that DHEA could be metabolized to 7 alpha-OH DHEA and 7 beta-OH DHEA in mitochondria but the formation of 7 alpha-OH DHEA and 7 beta-OH DHEA demonstrated different enzymatic kinetic properties. Adding NADPH, an essential cofactor, to mitochondria incubation mixtures increased only the formation of 7 alpha-OH DHEA, but not that of 7 beta-OH DHEA. Addition of estradiol to the incubation mixtures inhibited only the formation of 7 alpha-OH DHEA, but not that of 7 beta-OH DHEA. Western blot analysis showed that both microsomes and mitochondria contained cytochrome P450 7B. We also found that 7 alpha-OH DHEA could be converted to 7 beta-OH DHEA by rat brain homogenates. Our data suggest that 7 alpha-OH DHEA and 7 beta-OH DHEA are formed by different enzymes and that 7 beta-OH DHEA can be formed from both DHEA and 7 alpha-OH DHEA, although the overall level of 7 beta-OH DHEA was very low. (C) 2010 Elsevier Inc. All rights reserved.