Effect of chenodeoxycholic acid on 11β-hydroxysteroid dehydrogenase in various target tissues

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Article (peer-reviewed)

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Glucocorticoids are metabolized by isoforms of the enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD). There is some controversy concerning the bile acid, chenodeoxycholic acid (CDCA), as a potential endogenously produced inhibitor of 11β-HSD. The present experiments were designed to determine the relative specificity of CDCA for both isoforms of 11β-HSD and to assess the biological relevance of inhibition in vascular tissue. IC50 values (concentrations which inhibit 50% of the enzyme reaction) were calculated using rat liver microsomes as a source of 11β-HSD1 dehydrogenase, Leydig cells for 11β-HSD1 dehydrogenase and reductase, aorta for 11β-HSD1 dehydrogenase and reductase, and sheep kidney for 11β-HSD2 dehydrogenase. In each case, CDCA functioned as a potent inhibitor of 11β-HSD1 dehydrogenase with IC50 values of ranging from 0.2 to 7 μmol/L in contrast to 37 to 200 μmol/L for 11β-HSD1 reductase. CDCA exhibited relatively weak inhibitory activity against 11β-HSD2 from sheep kidney with an IC50 of 70 μmol/L. The effect of CDCA on vascular contraction was studied in aortic rings isolated from Spague-Dawley rats incubated in medium containing corticosterone 10 nmol/L ± CDCA (1 μmol/L) for 24 hours. Rings were stimulated with graded concentrations of phenylephrine (PE) (10 nmol/L, 100 nmol/L, and 1 μmol/L). Rings exposed to corticosterone and CDCA consistently demonstrated a greater contractile response at lower doses of PE (63% at PE 10 nmol/L, P < .001; 20% at PE 100 nmol/L, P < .025; and 10% at PE 1 μmol/L, not significant [NS]) compared to control preparations incubated with cortiosterone alone. These studies demonstrate (1) that CDCA preferentially affects 11β-HSD1 dehydrogenase; (2) CDCA does inhibit 11β-HSD2 dehydrogenase and 11β-HSD1 reductase but only at high(er) concentrations exceeding 70 μmol/L and 37 μmol/L, respectively; and (3) inhibition of 11β-HSD1 dehydrogenase in aortic rings by CDCA (1 μmol/L) enhances the contractile response of corticosterone plus PE.