Dehydroepiandrosterone 7α-hydroxylation in human tissues: Possible interference with type 1 11β-hydroxysteroid dehydrogenase-mediated processes

Dehydroepiandrosterone (DHEA) is 7α-hydroxylated by the cytochome P450 7B1 (CYP7B1) in the human brain and liver. This produces 7α-hydroxy-DHEA that is a substrate for 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) which exists in the same tissues and carries out the inter-conversion of 7α- and 7β-hydroxy-DHEA through a 7-oxo-intermediary. Since the role of 11β-HSD1 is to transform the inactive cortisone into active cortisol, its competitive inhibition by 7α-hydroxy-DHEA may support the paradigm of native anti-glucocorticoid arising from DHEA. Therefore, our objective was to use human tissues to assess the presences of both CYP7B1 and 11β-HSD1. Human skin was selected then and used to test its ability to produce 7α-hydroxy-DHEA, and to test the interference of 7α- and 7β-hydroxy-DHEA and 7-oxo-DHEA with the 11β-HSD1-mediated oxidoreduction of cortisol and cortisone. Immuno-histochemical studies showed the presence of both CYP7B1 and 11β-HSD1 in the liver, skin and tonsils. DHEA was readily 7α-hydroxylated when incubated using skin slices. A S9 fraction of dermal homogenates containing the 11β-HSD1 carried out the oxidoreduction of cortisol and cortisone. Inhibition of the cortisol oxidation by 7α-hydroxy-DHEA and 7β-hydroxy-DHEA was competitive with a K_i at 1.85 ± 0.495 and 0.255 ± 0.005 μM, respectively. Inhibition of cortisone reduction by 7-oxo-DHEA was of a mixed type with a K_i at 1.13 ± 0.15 μM. These findings may support the previously proposed native anti-glucocorticoid paradigm and suggest that the 7α-hydroxy-DHEA production is a key for the fine tuning of glucocorticoid levels in tissues.