Regulation of the action of hydrocortisone in airway epithelial cells by 11 beta-hydroxysteroid dehydrogenase

11 beta-hydroxysteroid dehydrogenase (11 beta HSD) reversibly converts hydr ocortisone, the predominant active endogenous glucocorticoid in humans, to its inactive metabolite cortisone by oxidizing the II-hydroxy group to an I I-keto group. Because this enzyme is highly expressed in human bronchial ep ithelial cells, we hypothesized that it regulates epithelial responses to g lucocorticoids by reducing levels of hydrocortisone available to bind to th e glucocorticoid receptor. Primary human bronchial epithelial cells (PBECs) were isolated from seven autopsy specimens and cultured in F12/Dulbecco's modified Eagle's medium with 5% fetal bovine serum until approximately 80% confluent. Cells were preincubated with 10(-9) M to 10(-5) M hydrocortisone for 24 h in the presence or absence of 10(-6) M of the 11 beta HSD inhibit or glycyrrhetinic acid, after which the cells were stimulated with 5 ng/ml interleukin-lp for 24 h. Granulocyte macrophage colony-stimulating factor ( GM-CSF) levels were quantitated in the resulting supernatants by enzyme-lin ked immunosorbent assay. Hydrocortisone inhibited GM-CSF release in stimula ted PBEC with a concentration that produces 50% inhibition of maximum effec t (IC(1/2)max) of 5.0 x 10(-8) M. In the presence of glycyrrhetinic acid, t he potency of hydrocortisone was increased approximately 33-fold (IC(1/2)ma x with glycyrrhetinic acid, 1.5 x 10-9 M). Hydrocortisone activity was maxi mally enhanced at concentrations between 10-9 M and 10-8 M, levels that are comparable to plasma levels of hydrocortisone not bound to plasma proteins . Glycyrrhetinic acid had no effect on the suppression of GM-CSF release by hydrocortisone in the transformed cell line BEAS-2B, which does not expres s the 11 beta HSD enzyme. Glycyrrhetinic acid also had no effect on the inh ibition of GM-CSF release in PBECs by the synthetic glucocorticoids budeson ide, beclomethasone dipropionate, fluticasone propionate, mometasone furoat e, and triamcinolone acetonide, steroids not metabolized by 11 beta HSD. To gether, these findings suggest that metabolism of hydrocortisone by 11 beta HSD may regulate glucocorticoid activity in human airway epithelial cells.