5α-Reduced Glucocorticoids, Novel Endogenous Activators of the Glucocorticoid Receptor

Abstract

Metabolism of glucocorticoids to A-ring-reduced dihydro-and tetrahydro-derivatives by means of hepatic 5␣-and 5␤-reductases has long been regarded as a pathway of irreversible inactivation. However, 5␣-reduced metabolites of other steroids, e.g. testosterone and aldosterone, have significant biological activity. We investigated whether 5␣-reduced metabolites of corticosterone are glucocorticoid receptor (GR) agonists. Corticosterone, 5␣-tetrahydrocorticosterone (5␣THB), and 5␣-dihydrocorticosterone (5␣DHB) were similarly effective in displacing tritiated dexamethasone from binding sites in hepatocytes, whereas 5␤-reduced metabolites were less effective in binding. 5␣THB had glucocorticoid receptor agonist effects in vitro and in vivo. After transient co-transfection of hGR and a murine mammary tumor virus-luciferase reporter into HeLa cells, 5␣THB was active to a comparable extent as corticosterone (28-fold versus 37-fold induction, respectively, at 1 M) and additive to the effect of corticosterone. 5␤-Reduced metabolites did not activate GR. In H4IIE hepatoma cells, both 5␣THB and corticosterone induced mRNA expression of tyrosine aminotransferase and phosphoenolpyruvate carboxykinase (6.0-versus 10.1-fold and 3.5-versus 3.9-fold at 1 M, respectively), an effect that was inhibited by RU486. To assess in vivo glucocorticoid activity, suppression of plasma ACTH was demonstrated in adrenalectomized rats after intraperitoneal administration of vehicle (ACTH trough 80.2 pM), corticosterone (5 mg/kg; 22 pM, p < 0.001) or 5␣THB (5 mg/kg; 51.3 pM, p < 0.005). Similar endogenous concentrations of corticosterone and 5␣THB were detected in rat liver homogenates by gas chromatography mass spectrometry. We conclude that 5␣-reduced glucocorticoids bind to and activate GR. Transcription of glucocorticoid-regulated genes in tissues that express 5␣-reductases will thus be influenced by intracellular levels of both corticosterone and its 5␣-reduced metabolites.The rate-limiting step in glucocorticoid metabolism is the reduction of the ⌬ 4.5 double bond in the A-ring of the steroid structure. This reaction is catalyzed by either 5␣-or 5␤-reductase. The resulting dihydro-metabolites are then reduced further by 3␣-hydroxysteroid dehydrogenases to form tetrahydrometabolites (Fig.

Microarray and real-time PCR analysis of adrenal gland gene expression in the 7-day-old rat: effects of hypoxia from birth

“…Two genes whose products are involved in further metabolism of corticosterone, Srd5a1 (steroid 5␣-reductase) and LOC191574 (3␣HSD), were significantly increased and decreased by hypoxia, respectively. An increase in plasma concentrations of 5␣-dihydrocorticosterone (5␣THB, the product of steroid 5␣-reductase) could influence physiological responses to hypoxia, since it has been shown that 5␣THB binds to and activates the glucocorticoid receptor (20). A decrease in the expression of Hsd11b2 (11␤HSD2) was also detected and may indicate decreased conversion of corticosterone to its inactive metabolite in the adrenal cortex.…”

Adrenocortical dysregulation as a major player in insulin resistance and onset of obesity

“…Indeed, adrenal gland weight is higher in rats fed a high-fat diet, which may reflect increased HPA axis activity (148). Although initially presumed to be inactive, 5␣-metabolites of GC are now known to bind and activate the GC receptors (125), which are also expressed in the adrenal cortex (142).…”

5α-Reduced glucocorticoids: a story of natural selection

“…a partial agonist) of TAT activity in hepatoma cells. These findings were supported by limited responses of other hepatic genes transactivated by GC (Danesch et al 1987, Ruppert et al 1990); 5aTHB induces PEPCK weakly (McInnes et al 2004), 5a-dihydrocortisol lacks efficacy to stimulate activity of tryptophan oxidase (Carlstedt-Duke et al 1977) and achieved sub-optimal induction of hepatocyte adhesion (Ballard & Tomkins 1969). Overall, the weak effects of these metabolites caused interest in their potential biological role to wane.…”

“…In similar experiments, even weaker displacement of tritiated dexamethasone by 5a-dihydrocorticosterone (5aDHB) was demonstrated by Carlstedt-Duke et al (1977). While McInnes et al (2004) concurred that 5a-DHB was a weak GR ligand, they also demonstrated that 5a-tetrahydrocorticosterone (5aTHB) could displace dexamethasone with a similar K d as corticosterone (Fig. 3A).…”

“…This lack of metabolic disruption has also been demonstrated in rats, where administration of 5a-reduced dihydroglucocorticoids (5a-dihydrocortisol and 5a-DHB) for a week actually lowered plasma insulin and hepatic PEPCK activity (Golf et al 1984). These latter effects may arise from suppression of synthesis of corticosterone, since, in both rats (McInnes et al 2004) and mice (Yang et al 2011), 5aTHB suppresses the HPA axis. Ex vivo, 5a-DHB impairs the development of long-term potential in neurones of the dentate gyrus (Dubrovsky et al 1987).…”