The mineralocorticoid activity of progesterone derivatives depends on the nature of the C18 substituent.

Abstract

To investigate the role of the C18 substituents in the agonist/antagonist properties of mineralocorticoids, the activities of certain C18-substituted progesterone (P) derivatives were examined. These compounds were characterized by an unsaturated side-chain in the case of 18-vinylprogesterone (18VP) and 18-ethynylprogesterone (18EP) and by an enone group in the case of 18-oxo-18-vinylprogesterone (18OVP). P and its 18-substituted derivatives bind to the recombinant human MR (hMR) overexpressed in Sf9 cells with the following hierarchy of affinity: P > aldosterone > 18VP > 18EP >> 18OVP. Functional cotransfection assays in CV-1 cells, using mouse mammary tumor virus promoter as a steroid receptor-inducible DNA target sequence, indicated that the mineralocorticoid activity depends on the nature of the C18 substituent. 18VP and 18EP retained the antimineralocorticoid feature of P, with the following order of activity: P = 18VP > 18EP. The antagonist potency of 18VP was higher (IC50, approximately 10(-8) M) than that of spironolactone (IC50, approximately 7 x 10(-8) M), the most widely used aldosterone antagonist. Interestingly, introducing an oxo function at C18 conferred agonist mineralocorticoid properties; 18OVP behaves as a full agonist (ED50, approximately 10(-7) M) with no antagonist activity. In contrast to what was observed when the three 18-substituted P derivatives acted through hMR, they retained the agonist feature of P through the human P receptor, with the following order of potency: P > 18VP = 18OVP > 18EP. The activity of the 18-substituted P derivatives through the human glucocorticoid receptor was only detected at concentrations higher than 10(-6) M; P and 18VP displayed a partial antagonist activity, whereas 18OVP had a full agonist activity (ED50, approximately 2 x 10(-6) M). Thus, the presence of an oxo group at C18(18OVP) does not change the agonist feature of P through human P receptor, but confers to the ligand an agonist activity through hMR, suggesting that the C18 carbonyl group of aldosterone plays a crucial role in its agonist activity.

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

“…Several groups found a similar affinity of aldosterone and cortisol for hMR (1,6,8,9), and we confirmed these findings (Table 1; Fig. 1A).…”

“…In addition the discrepancies in K d and K i values between laboratories may be due to different incubation times and the fact that lipophilic steroids, e.g. progesterone, are absorbed easily by plastic and glass material (3,7,8,45).…”

“…Arriza et al (9) described a lower binding affinity for progesterone, but the incubation period was only 2.5 h, which is probably too short to achieve a steady state. Souque et al (8) showed that progesterone has a low agonist MC activity with , 24% of the maximum aldosterone-induced response at a progesterone concentration of 10 26 mol/l. We found a nearly identical agonist activity with 27% transactivation at 10 26 mol/l ( Fig.…”

“…Progesterone is probably not able to form a strong bond to helix H12 and to induce the conformational change described for aldosterone hMR activation. This greater instability of the antagonist -hMR complex could lead to faster dissociation of progesterone from the receptor (8). The antagonistic potency of progesterone has been described with IC 50 values ranging from 2 to 10 nmol/l (6,33,44).…”

11β-Hydroxyprogesterone Acts as a Mineralocorticoid Agonist in Stimulating Na+Absorption in Mammalian Principal Cortical Collecting Duct Cells

“…Progesterone binds to hMR with the same affinity as aldosterone and displays antagonist properties under in vitro conditions (Rupprecht et al, 1993;Souque et al, 1995;Myles and Funder, 1996). The antagonist activity of progesterone has been linked to its inability to establish contact with the Asn770 residue of hMR (Fagart et al, 1998).…”