Agonistic and antagonistic properties of progesterone metabolites at the human mineralocorticoid receptor

Abstract

Objective: Progesterone binds to the human mineralocorticoid receptor (hMR) with nearly the same affinity as do aldosterone and cortisol, but confers only low agonistic activity. It is still unclear how aldosterone can act as a mineralocorticoid in situations with high progesterone concentrations, e.g. pregnancy. One mechanism could be conversion of progesterone to inactive compounds in hMR target tissues. Design: We analyzed the agonist and antagonist activities of 16 progesterone metabolites by their binding characteristics for hMR as well as functional studies assessing transactivation. Methods: We studied binding affinity using hMR expressed in a T7-coupled rabbit reticulocyte lysate system. We used co-transfection of an hMR expression vector together with a luciferase reporter gene in CV-1 cells to investigate agonistic and antagonistic properties. Results: Progesterone and 11b-OH-progesterone (11b-OH-P) showed a slightly higher binding affinity than cortisol, deoxycorticosterone and aldosterone. 20a-dihydro(DH)-P, 5a-DH-P and 17a-OH-P had a 3-to 10-fold lower binding potency. All other progesterone metabolites showed a weak affinity for hMR. 20a-DH-P exhibited the strongest agonistic potency among the metabolites tested, reaching 11.5% of aldosterone transactivation. The agonistic activity of 11b-OH-P, 11a-OH-P and 17a-OH-P was 9, 5.1 and 4.1% respectively. At a concentration of 100 nmol/l, progesterone, 17a-OH-P and 20a-DH-P inhibit nearly 75, 40 and 35% of the transactivation by aldosterone respectively. All other progesterone metabolites tested demonstrate weaker affinity, and agonistic and antagonistic potency. Conclusions: The binding affinity for hMR and the agonistic and antagonistic activity diminish with increasing reduction of the progesterone molecule at C20, C17 and at ring A. We assume that progesterone metabolism to these compounds is a possible protective mechanism for hMR. 17a-OH-P is a strong hMR antagonist and could exacerbate mineralocorticoid deficiency in patients with congenital adrenal hyperplasia.

Two Panels of Steroid Receptor Luciferase Reporter Cell Lines for Compound Profiling

“…Similarly both AR reporter cell lines respond to dihydrotestosterone in the picomolar range: EC 50 (U2OS-AR/3xGRE) = 4 pM and EC 50 (U2OS-AR/MMTV) = 3 pM (Table 1c ) and MR to aldosterone in the subnanomolar range: EC50(U2OS-MR/MMTV) = 88 pM (Table 1g ). We also compared data generated with our cell lines to values in the literature and found our data comparable to literature reports for all receptor/promoter combinations [11, 12, 14, 19-21]. …”

The ovarian cycle as a factor of variability in the laboratory screening for primary aldosteronism in women

“…24 Progesterone may affect aldosterone levels in several direct or indirect ways. In fact, progesterone (1) Is a natural precursor of aldosterone; (2) stimulates aldosterone secretion in vitro and in vivo; 24,29,30 (3) is a mineralocorticoid receptor antagonist; (4) has a direct natriuretic effect 24,29,31,32 that in turn may indirectly stimulate aldosterone secretion. Finally, the aldosterone increase in the luteal phase may be mediated by LH that, in addition to induce progesterone secretion in the ovary, may also stimulate aldosterone synthesis in the adrenal cortex.…”

Transactivation via the human glucocorticoid and mineralocorticoid receptor by therapeutically used steroids in CV-1 cells: a comparison of their glucocorticoid and mineralocorticoid properties

“…In general, one can conclude that receptor binding is only a prerequisite of the much more complex process of transactivation, and that a correlation between binding affinities and transactivation properties cannot be assumed a priori for all steroids. A good example for this notion is progesterone (Table 3), which has been shown to possess high affinity to the hMR but causes only minor transactivation at the MR (33,38) and acts as an antagonist in vivo (44).…”