The metabolic fate and receptor interaction of 16α-hydroxyprogesterone and its 5α-reduced metabolite, 16α-hydroxy-dihydroprogesterone

- UHPLC-MS/MS analyses identifies novel 16OHP4 metabolites.
- 16OHP4 is 11β-hydroxylated by CYP11B2, and subsequently reduced by SRD5A.
- 16OHP4 is 5α- and 3α reduced by SRD5A and AKR1C2 to 16Pdione and 16Pdiol.
- 5α-reduced P4 exhibits partial agonist activity towards PR-A and PR-B.
- 16Pdione exhibits weak agonist activity towards AR and PRs.

16α-hydroxyprogesterone (16OHP4) is not well characterised in terms of metabolism and receptor interaction. We therefore investigated its metabolism by adrenal CYP11B and peripheral steroidogenic enzymes, SRD5A and AKR1C2. UHPLC-MS/MS analyses identified novel steroids: the biosynthesis of 4-pregnen-11β,16α-diol-3,20-dione catalysed by CYP11B2; the 5α-reduction of the latter and 16OHP4 catalysed by SRD5A yielding 5α-pregnan-11β,16α-diol-3,20-diovne and 5α-pregnan-16α-ol-3,20-dione (16OH-DHP4); and 16OH-DHP4 converted by AKR1C2 to 5α-pregnan-3α,16α-diol-20-one. Receptor studies showed 16OHP4, 16OH-DHP4, progesterone and dihydroprogesterone (DHP4) were weak partial AR agonists; 16OHP4, 16OH-DHP4 and DHP4 exhibited weak partial agonist activity towards PR-B with DHP4 also exhibiting partial agonist activity towards PR-A. Data showed that while the 5α-reduction of P4 decreased PR activation significantly, 16OHP4 and 16OH-DHP4 exhibited comparable receptor activation. Although the clinical relevance of 16OHP4 remains unclear the elevated 16OHP4 levels characteristic of 21OHD, CAH, PCOS, prostate cancer, testicular feminization syndrome and cryptorchidism likely contribute towards these clinical conditions, inducing receptor-activated target genes.