Bile acids modulate glucocorticoid metabolism and the hypothalamic-pituitary-adrenal axis in obstructive jaundice

Abstract

Background & aims: Suppression of the hypothalamic-pituitary-adrenal axis occurs in cirrhosis and cholestasis and is associated with increased concentrations of bile acids. We investigated whether this was mediated through bile acids acting to impair steroid clearance by inhibiting glucocorticoid metabolism by 5beta-reductase.

Methods: The effect of bile acids on glucocorticoid metabolism was studied in vitro in hepatic subcellular fractions and hepatoma cells, allowing quantitation of the kinetics and transcript abundance of 5beta-reductase. Metabolism was subsequently examined in vivo in rats following dietary manipulation or bile duct ligation. Finally, glucocorticoid metabolism was assessed in humans with obstructive jaundice.

Results: In rat hepatic cytosol, chenodeoxycholic acid competitively inhibited 5beta-reductase (K(i) 9.19+/-0.40 microM) and reduced its transcript abundance (in H4iiE cells) and promoter activity (reporter system, HepG2 cells). In Wistar rats, dietary chenodeoxycholic acid (1% w/w chow) inhibited hepatic 5beta-reductase activity, reduced urinary excretion of 3alpha,5beta-tetrahydrocorticosterone and reduced adrenal weight. Conversely, a fat-free diet suppressed bile acid levels and increased hepatic 5beta-reductase activity, supplementation of the fat-free diet with CDCA reduced 5beta-reductase activity, and urinary 3alpha,5beta-reduced corticosterone. Cholestasis in rats suppressed hepatic 5beta-reductase activity and transcript abundance. In eight women with obstructive jaundice, relative urinary excretion of 3alpha,5beta-tetrahydrocortisol was significantly lower than in healthy controls.

Conclusion: These data suggest a novel role for bile acids in inhibiting hepatic glucocorticoid clearance, of sufficient magnitude to suppress hypothalamic-pituitary-adrenal axis activity. Elevated hepatic bile acids may account for adrenal insufficiency in liver disease.

Fig. 1

Inhibition of 5β-reductase by bile acids. 5β-Reduction of corticosterone in the presence of (A) CDCA, CA, DCA (B) CDCA, GCDCA, TCDCA. Velocity vs. Control (100%), without bile acids. (C) IC₅₀ of the reactions. (D) Lineweaver–Burke plots showing competitive inhibition of 5β-reductase by CDCA (open squares: 2.5 × 10^–6 M) (vs. vehicle (filled)). Mean ± SEM; n = 5. ^∗p <0.05 vs. CDCA; ^#p <0.05 DCA vs. CA.

Fig. 2

Effect of CDCA on transcription of steroid-metabolising enzymes. (A) Abundance of mRNAs of rat 5β-reductase and Cyp7a1 but not 3αHSD was suppressed in H4iiE cells by CDCA (100 μM), n = 5. (B) Activity of the promoter of human 5β-reductase was reduced by CDCA (50 μM). Data are fold induction of luciferase activity relative to control plasmid. (n = 3 triplicates), mean ± SEM; ^∗p <0.05, ^∗∗∗p <0.001 vs. vehicle.

Fig. 3

In vivoelevation of bile acids inhibits hepatic 5β-reductase in rats. (A) Hepatic 5β-reductase activity was inhibited in rats following dietary CDCA (filled) vs. Control (open) and (B) following BDL (filled) vs. sham operation (open). Mean ± SEM; ^∗p <0.05 vs. Control, ^#p <0.05 vs. Fat-free (FF) diet, ^∗∗∗p <0.001 vs. Sham.

Fig. 4

Dietary CDCA delays recovery from acute stress in rats. Following restraint (hatched), animals treated with CDCA (filled) had a delay in the return to basal levels of corticosterone (A) but not ACTH (B), compared to Controls (open). Mean ± SEM; ^∗p <0.05 vs. Control.