Glucocorticoids are the most effective treatment for asthma and other inflammatory diseases of the airways. New evidence now suggests that bronchoconstriction following experimental antigen challenge of asthmatic subjects is influenced by endogenous glucocorticoids (EG), and that antigen challenge induces an increase in circulating levels of EG. Exciting preliminary results indicate that the response of human airway epithelial cells to glucocorticoids is regulated by (11beta-HSD), a glucocorticoid-degrading enzyme which is highly expressed in airway epithelial cells. Studies described in Aim 1 of this proposal are designed to elucidate the mechanism of the increase of EG in allergic subjects following inhaled antigen challenge. Plasma cortisol, cortisone and corticotropin levels will be assayed and the influence of EG on the pulmonary early and late phase reactions will be explored. Whether bronchospasm causes the rise of EG after antigen challenge will be determined pharmacologically with drugs that modify bronchospasm (methacholine and salmeterol). Studies with metyrapone will assess the role of de novo synthesis of cortisol in the adrenal gland. Studies in Aim 2 are designed to establish the importance of 11beta-HSD in regulating the inflammatory response to intranasal antigen challenge using carbenoxolone, a potent 11beta-HSD inhibitor. In these studies we will monitor 11beta- HSD expression and function using RT-PCR and a highly sensitive and selective GC-MS assay for endogenous glucocorticoids in the airways. Studies in Aim 3 will test the hypothesis that 11beta- HSD reduces the access of cortisol to glucocorticoid receptors in airway epithelial cells. These studies will utilize epithelial cells that express 11beta-HSD and those that do not, and compare the ability of an 11beta-HSD inhibitor to potentiate the inhibitory effects of cortisol on the secretion of GM-CSF, RANTES and eotaxin. Mechanistic studies in this aim will utilize 11beta-HSD-transfected cells to establish specificity of observed effects. Studies of the influence of cortisol and 11beta-HSD on chemokine mRNA stability are planned. Since in vivo studies indicate that airway challenge increases EG, studies in Aim 4 will search for airway-derived factors that induce cortisol secretion from cultured human adrenal cells. Studies to confirm and elucidate the mechanism of exciting preliminary results showing that RANTES induces high levels of cortisol release are planned. There is clearly a dynamic interrelationship between airway inflammation and EG. An improved understanding of this relationship is likely to lead to new opportunities to exploit this system for therapeutic benefit.
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