Cortisol conversion to 20β-dihydrocortisol (20β-DHF) has been reported in many tissues and cells, including skin, muscle, thrombocytes and fibroblasts, although the enzyme responsible is poorly characterised. We have attributed 20β-DHF generation to carbonyl reductase 1 and shown increased activity of this pathway in adipose tissue in obesity in humans, horses and mice. This study addressed the hypothesis that 20β-DHF activates glucocorticoid receptors (GR) and mineralocorticoid receptors (MR).
Docking calculations were conducted to compare binding interactions formed by cortisol and 20β-DHF with the GR and MR ligand binding pockets. The ligands showed similar predicted interaction patterns with both receptors. However, the 20β-hydroxyl group of 20β-DHF seemed to be tolerated better tolerated by MR to retain activation than by GR. Using HEK293 cells transfected with GR or MR and a MMTV-luciferase reporter we compared receptor activation in the presence of increasing concentrations of cortisol or 20β-DHF (100 nM- 5 μM for 6 hours). We demonstrated that 20β-DHF induced significant activation of GR but only at much higher concentrations than cortisol (cortisol 100 nM: 2.6 ± 0.4 fold induction compared with vehicle, 20β-DHF 2.5 μM; 1.8 ± 0.2 fold induction, P<0.005 compared with vehicle). In contrast 20β-DHF induced MR activation equivalent to that of cortisol at much lower concentrations (cortisol 100 nM; 2.9 ± 0.3 fold induction, 20β-DHF 100 nM; 2.4 ± 0.2 fold induction, P<0.005 compared with vehicle). A Microarray Assay for Real-time Co-regulator-Nuclear Receptor Interaction (MARCoNI) of 20β-DHF as a GR or MR ligand supported these findings. On binding 20β-DHF GR recruited only 36% of co-regulators recruited by cortisol while MR recruited 77% of the co-regulators recruited by cortisol.
In conclusion, we have demonstrated that 20β-DHF is a weak endogenous GR agonist but a potent MR agonist. Increased production of 20β-DHF in obesity may contribute to dysregulation of glucocorticoid signalling with complex and likely tissue-specific consequences.