Overview
The purpose of this study is to characterize and compare the molecular gene expression profile in endobronchial biopsies and cells recovered in bronchial washings from study subjects who have asthma of varying disease severity and who are on maintenance inhaled corticosteroid (ICS) treatment, with that for healthy control subjects. These studies will produce transcriptomic profiles of gene expression associated with asthma disease severity. The investigators will also culture epithelial cells from study participant endobronchial brushings, including those with asthma of varying disease severity and healthy control subjects, to examine differences in the response to corticosteroids (CS) in vitro. These studies will test whether intrinsic differences exist between the responses to ICS in each group.
60 participants will be recruited with 15 of each mild, moderate and severe asthma as defined by the Global Initiative for Asthma (GINA) guidelines, as well as 15 healthy controls. Participants will undergo an initial visit to obtain informed consent, bloodwork and to assess asthma control using the Asthma Control Questionnaire (ACQ); if >1.5, ICS dose will be increased, as per GINA strategy, for a 2 week 'stabilization' phase. Repeat ACQ, spirometry and sputum induction will be performed at visit 2. Bronchoscopy will be performed at visit 3, 2-4 weeks after visit 2. Mucosal biopsies, bronchial brushings and bronchial washings will be performed and processed as per our prior methods. Mucosal biopsies will be homogenized and processed for RNA, or fixed for later sectioning and histological examination. Biopsy RNA will be assessed for quality and subjected to RNA-sequencing of all human genes (mRNA-seq). Bronchial washing cells will be collected for differential cell counting and mRNA-seq analysis. Bronchial epithelial cells (BECs) from the brushings will be cultured. BECs treated with CS and inflammatory cytokines will allow comparative assessment of BEC responses.
Description
- Background
While inhaled corticosteroids (ICS), either as monotherapy or in combination with long-acting β2 agonists (LABA), provide effective control in mild to moderate asthma, they are less effective in severe asthma. Following a guideline-based stepwise approach of treatment escalation often results in extended periods during which both the underlying airway inflammation and the asthma symptoms remain uncontrolled in these patients with severe asthma. This can lead to permanent damage, often termed airway remodeling, which results in fixed airflow obstruction that is no longer amenable to pharmacological therapy. The ability to identify molecular phenotypes associated with severe asthma should enable a more direct transition to appropriate therapies.
The respiratory epithelium drives airway inflammation and represents a primary target for ICS, which act through the glucocorticoid receptor (GR) to inhibit inflammatory gene expression. In an effort to predict therapeutic responses, considerable work has gone into investigating the clinical and molecular phenotyping of asthmatic individuals. This has produced a focus on gene-expression profiles (in blood) of asthmatics that associates with Th2 inflammatory phenotypes. However, there remains a paucity of studies investigating transcriptomic differences in the airways of mild and severe asthmatics.
The investigators now submit that characterization of inflammatory gene expression that escapes repression by CS or, alternatively, induces further inflammation, even in the setting of increasing ICS exposure, is crucial to understanding the mechanisms underpinning severe asthma.
- Hypothesis
Rather than being merely an amplified version of mild asthma, the investigators hypothesize that severe asthma shows a distinct inflammatory gene expression profile, with specific genes escaping repression, or being enhanced in expression by CS. Such effects, as apparent in cell-based models, could contribute to a molecular phenotype that is inherently resistant to the anti-inflammatory effects of ICS.
Eligibility
Inclusion Criteria:
- Age 18-60
- Confirmed diagnosis of asthma by CTS criteria
- No contraindication to bronchoscopy
- No treatment with azithromycin
- No oral corticosteroid in the 4 weeks prior
- No participation in another drug study in the 4 weeks prior
- On stable doses of asthma inhaled therapies for 12 weeks prior to bronchoscopy
- FEV1 >80%
Exclusion Criteria:
- Current smokers (within past year)
- Subjects with ≥10 pack-year lifetime smoking history
- History of asthma exacerbation (requiring oral prednisone) in the 4 weeks prior to study entry