Corticosteroids exert their effects by binding to a cytoplasmic glucocorticoid receptor (GR). The inactive GR is bound to a protein complex that includes heat shock protein hsp90, acting as molecular chaperones to prevent the nuclear localisation of unoccupied GR.
GR binding to the palindromic promotor induces the transcriptional induction of anti-inflammatory genes such as mitogen-activated protein kinase phosphatase-1 (MKP-1) and secretory leukocyte protease inhibitor (SLPI). GR-steroid complex also binds to negative GRE sequences, resulting in inhibition of pro-inflammatory mediators, such as IL-6. More importantly, GR binds transcription factor with recruitment of histone deacetylase (HDAC) and inhibits wide range of pro-inflammatory cytokines. By this process of transrepression, corticosteroids reduce such pro-inflammatory cytokines as tumour necrosis-alpha (TNF-alpha) and interleukin-8 (IL-8) in asthmatic patients whereas they are far less effective in chronic obstructive pulmonary disease (COPD) patients.
The combination of inhaled corticosteroids (ICS) and long acting beta 2-agonists (LABAs) has been shown to improve clinical effectiveness and anti-inflammatory properties in asthma. The addition of a LABA to low dose ICS has been shown to be more clinically beneficial in asthma than the use of high dose ICS, allowing a reduction in ICS dose and minimising and adverse side effects of corticosteroids. Recent evidence suggests that this may also be the case in COPD.
ICS such as budesonide, beclomethasone and fluticasone have been used in combination with LABA's such as formoterol and salmeterol. These combination treatments are established in national guidelines for treating patients with asthma and also, COPD. The combination of formoterol and budesonide (Symbicort ®, Astra Zeneca) will be studied in this project.
Evidence suggests that LABAs enhance GR function in vitro. In an asthmatics study, the combination of formoterol and budesonide (Symbicort ®, Astra Zeneca) was as effective as high dose ICS on GR activation, gene transactivation and transrepression. However, the precise mechanisms for this enhanced effectiveness are unknown, although priming of the steroid receptor (GR) by LABAs may be important.
Investigators have developed a novel method of measuring GR-GRE binding activity in sputum using an enzyme immunosorbent assay system. This method, together with the measurements of some functional readouts, will help us to understand some of the mechanisms of steroid and GR interactions using non-invasive methods of assessment of the airways. This may provide insight into the mechanisms of corticosteroid action and whether the addition of a LABA to ICS can alter molecular patterns, which may explain the observed beneficial action of combination therapy seen in patient studies in vivo. This may allow a scientific basis to explore future drug interactions that may be helpful in patients, particularly those patients whose disease tends to be severe and may be unresponsive to standard therapies for COPD and/or where high dose ICS have little beneficial clinical effect and have led to side-effects.
