Background and aims: Previously we showed that the bioactive liquorice constituent glycyrrhetinic acid (GA) inhibits not only 11β-hydroxysteroid dehydrogenase enzymes but also the sulphation of corticosteroids by the enzyme sulphotransferase 2A1 (SULT2A1). Since pregnenolone, 17α-hydroxy-pregnenolone, deoxycorticosterone (DOC) and dehydroepiandrosterone (DHEA) are all prime substrates for SULT2A1, GA could have important effects in directing pathways of glucocorticoid, mineralocorticoid and androgen biosynthesis. This hypothesis has been investigated by comparing aldosterone, cortisol, cortisone, corticosterone, DOC, DHEA and testosterone output by human adrenocortical H295 cells treated with GA in the presence of added steroids.
Methods: Cells were incubated for 24 h in DMEM/F12, with 0, 3, 10, 25 or 100 μM GA and either 0.2 μM DOC or 1 μM DHEA. Free and conjugated steroids in the incubation medium were analysed by in-house ELISAs following extraction with Sep-Pak C18 cartridges and hydrolysis with Helix pomatia juice. SULT2A1 expression in cells was quantified by RTPCR.
Results and discussion: GA inhibited DHEA and DOC conjugation in a dose-dependent manner without affecting SULT2A1 transcription. However, total DOC (free + conjugated) was negatively correlated with GA-inhibition of sulphation in cells incubated in the presence of either DOC or DHEA (r=−0.74, P<0.02). We suggest that inhibition of pregnenolone sulphation (an early endogenous intermediate) channels steroidogenesis towards mineralocorticoid/glucocorticoid hormones. However, the total amounts of cortisol, cortisone and aldosterone were reduced rather than increased by GA; corticosterone levels were increased but not in line with DOC changes. Together, these results suggest that GA treatment affects the synthesis of 17α-hydroxylated steroid hormones (>75% reduction in cortisol:corticosterone ratios; P<0.01). DOC to aldosterone ratios were also reduced (P<0.001).
Conclusions: GA effects on steroid hormone profiles could be more complex than hitherto appreciated. It seems that GA can modulate adrenal steroidogenesis in vitro at multiple sites. The possibility of adrenocortical side-effects is, therefore, an important consideration in the development of 11β-HSD enzyme inhibitors to modulate glucocorticoid activity.