Endocrine Abstracts

It has been suggested that DHEA metabolites, especially 7-hydroxy and/or 7-keto derivatives could possess anti-inflammatory activity and enhance immune, cognitive and metabolic functions in rodents. It is thus important to elucidate the exact pathway (s) leading to the formation of these metabolites. While the role of cytochrome P450 CYP7B1 in the transformation of DHEA into 7α-OHDHEA is well recognized, the role of type 1 11β-hydroxysteroid dehydrogenase (11β-HSD1) in the transformation of 7α-OHDHEA into 7-ketoDHEA, as suggested by many authors, remains questionable. While 11β-HSD1 prefers NADPH as cofactor and is thus, essentially, a reductive enzyme, the transformation of 7β-OHDHEA into 7-ketoDHEA is an oxidative reaction. Since 11β-HSD2 prefers NAD+ as cofactor, and is the oxidative counterpart of 11β-HSD1, we hypothesized that 11β-HSD2 could rather be the enzyme responsible for the transformation of 7α-OHDHEA into 7-ketoDHEA.

To verify this hypothesis, we cloned the coding region of human CYP7B1, 11β-HSD1 and 11β-HSD2 genes into pCMV expression vectors and transfected them into transformed human embryonic kidney HEK-293 cells. Using transfected cells in culture, without addition of cofactor(s), thus better reproducing physiological conditions, and using [C14]DHEA as substrate, we have clearly observed that CYP7B1 catalyzes the conversion of DHEA into 7α-OHDHEA, while, upon the addition of 11β-HSD2, 7α-OHDHEA is oxidized readily into 7-ketoDHEA, a reaction which does not occur in the presence of 11β-HSD1. The present data indicate that 11β-HSD2, rather than 11β-HSD1, is the enzyme responsible for the conversion 7α-OHDHEA into 7-ketoDHEA (DHEA –-CYP7B1–» 7α-OHDHEA ––11β-HSD2 –» 7-ketoDHEA) in the biosynthetic pathway of 7-ketoDHEA formation.

Declaration of interest: I fully declare a conflict of interest. Details below:

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.