Characterization of the dehydroepiandrosterone (DHEA) metabolism via oxysterol 7alpha-hydroxylase and 17-ketosteroid reductase activity in the human brain.
Dehydroepiandrosterone and its sulphate are important factors for vitality, development and functions of the CNS. They were found to be subjects to a series of enzyme-mediated conversions within the rodent CNS. In the present study, we were able to demonstrate for the first time that membrane-associated dehydroepiandrosterone 7alpha-hydroxylase activity occurs within the human brain. The cytochrome P450 enzyme demonstrated a sharp pH optimum between 7.5 and 8.0 and a mean KM value of 5.4 micro m, corresponding with the presence of the oxysterol 7alpha-hydroxylase CYP7B1. Real-time RT-PCR analysis verified high levels of CYP7B1 mRNA expression in the human CNS. The additionally observed conversion of dehydroepiandrosterone via cytosolic 17beta-hydroxysteroid dehydrogenase activity could be ascribed to the activity of an enzyme with a broad pH optimum and an undetectably high KM value. Subsequent experiments with cerebral neocortex and subcortical white matter specimens revealed that 7alpha-hydroxylase activity is significantly higher in the cerebral neocortex than in the subcortical white matter (p < 0.0005), whereas in the subcortical white matter, 17beta-hydroxysteroid dehydrogenase activity is significantly higher than in the cerebral neocortex (p < 0.0005). No sex differences were observed. In conclusion, the high levels of CYP7B1 mRNA in brain tissue as well as in a variety of other tissues in combination with the ubiquitous presence of 7alpha-hydroxylase activity in the human temporal lobe led us to assume a neuroprotective function of the enzyme such as regulation of the immune response or counteracting the deleterious effects of neurotoxic glucocorticoids, rather than a distinct brain specific function such as neurostimulation or neuromodulation.
Steckelbroeck
Stephan
S
Department of Clinical Biochemistry, University of Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany. St_Steckelbroeck@hotmail.com
Watzka
Matthias
M
Lütjohann
Dieter
D
Makiola
Paul
P
Nassen
Alexander
A
Hans
Volkmar H J
VH
Clusmann
Hans
H
Reissinger
Annette
A
Ludwig
Michael
M
Siekmann
Lothar
L
Klingmüller
Dietrich
D
D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D002648:Child; D002675:Child, Preschool; D002855:Chromatography, Thin Layer; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D000072474:Cytochrome P450 Family 7; D003687:Dehydroepiandrosterone / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007223:Infant; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D009249:NADP / Q000378:metabolism; D009928:Organ Specificity; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013702:Temporal Lobe / Q000737:chemistry / Q000378:metabolism
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D003687:Dehydroepiandrosterone; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D015067:17-Hydroxysteroid Dehydrogenases; C044256:3 (or 17)-beta-hydroxysteroid dehydrogenase; D013250:Steroid Hydroxylases; C115867:oxysterol 7-alpha-hydroxylase; D000072474:Cytochrome P450 Family 7; C499571:CYP7B1 protein, human