Figure 3.

LABA/ICS combinations are both steroid-sparing and enhance GRE-dependent transcription. BEAS-2B cells stably expressing a GRE-reporter construct were treated concurrently with salmeterol (100 nM; a) or formoterol (10 nM; b) in the absence and presence of fluticasone and budesonide, respectively (10 pM–100 nM). After 6 h, cells were harvested for luciferase assay. The data show that the effect of formoterol/budesonide and salmeterol/fluticasone in combination promotes GRE-dependent transcription, above what can be achieved by the glucocorticoid alone, and is steroid sparing. Thus, in this simple system, neither LABA activated the GRE reporter construct (not shown), but markedly potentiated glucocorticoid-induced transcription (2.6- and 2.1-fold for salmeterol and formoterol respectively at the E_max). In addition, salmeterol and formoterol were glucocorticoid sparing in this model. Thus, both glucocorticoids at concentrations that evoked 90% of the maximum response produced a 12- to 15-fold induction of the luciferase gene. However, in the presence of salmeterol (100 nM) or formoterol (10 nM), which were inactive, the same degree of gene induction was achieved at a concentration of glucocorticoid that was significantly (∼10-fold) lower. Note: this measurement was made at the EC₉₀ concentration of glucocorticoid (as the upper asymptote, by definition, is never reached) and so the degree to which the LABAs are steroid sparing is underestimated. See text and Kaur et al. (2007) for further details. GRE, glucocorticoid response element; ICS, inhaled corticosteroid; LABA, long-acting β₂-adrenoceptor agonist.