7alpha- and 7beta-hydroxy-epiandrosterone as substrates and inhibitors for the human 11beta-hydroxysteroid dehydrogenase type 1.
The human 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) catalyzes both the NADP(H)-dependent oxido-reduction of cortisol and cortisone and the inter-conversion of 7alpha- and 7beta-hydroxy-dehydroepiandrosterone (DHEA) through a 7-oxo-DHEA intermediate. As shown with human liver and intestine fractions, 7alpha-hydroxy-epiandrosterone (7alpha-hydroxy-EpiA) and 7beta-hydroxy-EpiA were readily inter-converted with no evidence for a 7-oxo-EpiA intermediate. Whether this inter-conversion resulted from action of the 11beta-HSD1 or from an unknown epimerase is unresolved. Furthermore, whether these steroids could inhibit the cortisol-cortisone oxido-reduction remains a question. The recombinant human 11beta-HSD1 was used to test these questions. NADP(+) supplementation only provided the production of 7beta-hydroxy-EpiA out of 7alpha-hydroxy-EpiA with a V(max)/K(M) ratio at 0.1. With NADPH supplementation, both 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA were formed in low amounts from 7beta-hydroxy-EpiA and 7alpha-hydroxy-EpiA, respectively. These inter-conversions occurred without a trace of the putative 7-oxo-EpiA intermediate. In contrast, the 7-oxo-EpiA substrate was efficiently reduced into 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA, with V(max)/K(M) ratios of 23.6 and 5.8, respectively. Competitive and mixed type inhibitions of the 11beta-HSD1-mediated cortisol oxidation were exerted by 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA, respectively. The 11beta-HSD1-mediated cortisone reduction was inhibited in a competitive manner by 7-oxo-EpiA. These findings suggest that the active site of the human 11beta-HSD1 may carry out directly the epimeric transformation of 7-hydroxylated EpiA substrates. The low amounts of these steroids in human do not support a physiological importance for modulation of the glucocorticoid status in tissues.
Hennebert
Olivier
O
Chaire de Génie Biologique, EA-3199, Conservatoire National des Arts et Métiers, 2 rue Conté, 75003 Paris, France.
Pernelle
Christine
C
Ferroud
Clotilde
C
Morfin
Robert
R
D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1 / Q000037:antagonists & inhibitors*; D000738:Androsterone / Q000378:metabolism*; D001483:Base Sequence; D003348:Cortisone / Q000378:metabolism; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D007700:Kinetics; D013379:Substrate Specificity
D017931:DNA Primers; D004791:Enzyme Inhibitors; D000738:Androsterone; D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1; D003348:Cortisone; D006854:Hydrocortisone