Genomic and non-genomic actions of glucocorticoids in asthma

Abstract

Glucocorticoids are the mainstay of asthma therapy. They are primarily used to suppress airway inflammation, which is the central pathological change in asthmatic patients' airways. This is achieved by many different mechanisms. The classical mechanism is by suppression of the genetic transcription of many inflammatory cytokines that are key in asthma pathophysiology (transrepression). On the other hand, the transcription of certain inhibitory cytokines is activated by glucocorticoids (transactivation), a mechanism that also mediates many of the adverse effects of glucocorticoids. The onset of action through these mechanisms is often delayed (4-24 hours). Other mechanisms mediated through non-genomic pathways are increasingly appreciated. These are delivered in part by binding of glucocorticoids to nonclassical membrane-bound glucocorticoid receptors or by potentiating the α1-adrenergic action on the bronchial arterial smooth muscles, in addition to other mechanisms. These effects are characterized by their rapid onset and short duration of action. Understanding these different mechanisms will help in the development of new and better drugs to treat this common disease and to develop new improved strategies in our approach to its management. Here, the genomic and non-genomic mechanisms of actions of glucocorticoids in asthma are briefly reviewed, with special emphasis on the current updates of the non-genomic mechanisms.

Keywords: Asthma; genomic action; glucocorticoids; mechanism of action; non-genomic action.

Figure 1

Genomic actions are mediated through a) direct DNA binding (transactivation) or b) transcription factor inactivation (transrepression). Non-genomic actions are mediated by c) membrane-bound receptors, d) cytosolic receptors or e) interaction with cell membrane. cGR: cytosolic glucocorticoid receptor; mGR: membrane-bound glucocorticoid receptor; LBD: ligand-binding domain; DBD: DNA-binding domain; hsp 90: heat-shock protein 90; RE: response element; NFkB : nuclear factor kB; AP-1: activating protein-1. (Adopted from: Horvath, G and Wanner, A. Eur Respir J. 2006;27:172-187 with permission)

Figure 2

Glucocorticoids facilitate the noradrenergic neuromuscular signal transmission by rapidly (within 5 minutes) inhibiting the extraneuronal monoamine transporter (EMT) in vascular smooth muscle cells. (Adopted from: Horvath, G and Wanner, A. Eur Respir J. 2006;27:172-187 with permission)