Based on current knowledge a working definition of the disease is;
“A preventable and treatable disease with some significant extrapulmonary effects that may contribute to the severity in individual patients. Its pulmonary component is characterised by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and associated with an abnormal inflammatory response of the lung to noxious particles and gases” .
Cigarette smoking is the most significant risk factor for COPD with over 90% of patients reported to have a history of smoking . The slow and progressive decline in lung function results largely from chronic lung inflammation, structural changes, narrowing of the small airways, hypersecretion of airway mucus and tissue destruction .
We are developing and seeking to validate in vitro models that address inflammation, airway remodeling, mucin production and oxidative stress, key processes and mechanisms involved in the development of COPD. Currently we are working with a variety of models ranging from simple cell lines (NCI-H292) to more complex primary cell cultures (HBEC, MuCilAir™ and lung slices) and with the aim of publishing this work in the open literature [4-9].
We are evaluating the response of this simple model of the lung epithelium to cigarette smoke total particulate matter (TPM). The model is being assessed against a range of positive agents known to initiate an inflammatory response in man. Further studies on the robustness and repeatability of agent and reference TPM exposure are being conducted. Once developed, the model will be used to test TPM from several different cigarette designs and future studies with whole cigarette smoke and vapour phase are also planned. Changes in disease related mediators at the protein and gene level will be measured using ELISA, MSD (Meso Scale Discovery®) platform, RT-PCR and Affymetrix® Gene Chip technologies.
Studies using primary cell culture systems are being developed to ensure that the response to TPM and cigarette smoke are more representative of what may occur in situ. We are therefore assessing the potential of two primary airway culture systems, the human bronchial epithelial cell (HBEC) culture, prepared in house, and the commercially available MuCilAir™ culture.
HBEC cultures are grown for 28 days at the air liquid interface and form a pseudostratified columnar epithelium with basal, goblet and ciliated epithelial cells (see picture below). This culture system can be exposed to TPM  and cigarette smoke [5, 10] either during the differentiation process or at day 28 when the culture is fully differentiated. The morphological, biochemical, structural and functional alterations of the culture system are being monitored through in house research activities and through external collaborations. The commercially available human epithelial airway culture system, MuCilAir™, can be kept in culture for up to 12 months and offers the opportunity to undertake repeated smoke exposure studies. The COPD team is currently assessing the utility of this culture system in studies following exposure to cigarette smoke.
The picture above shows transmission (A and B) and scanning (C) electron micrographs of HBEC air-liquid interface cultures at day 1 (A) and day 28 (B and C). At day 1 HBECs appear as simple epithelial cells, whereas at day 28 cultures have developed into a psuedostratified columnar epithelium containing basal cells (B), mucus containing goblet cells (G) and ciliated cells (C).
Studies involve measuring the inflammatory response of the MuCilAir™ and HBEC culture systems at the protein and gene level . Such responses include mediator release and changes in gene expression levels specific to inflammation, tissue remodelling, mucin production and oxidative stress. In addition the antioxidant and proteomic profile of the air surface liquid, a complex mixture of mucins and proteins secreted on the apical surface, is also being measured.
The development of squamous cell metaplasia (SCM) in long term cigarette smokers is a characteristic feature of COPD. Through external collaborations we are currently developing a model of SCM and identifying key biomarkers which will help assess the role of cigarette smoke in driving primary epithelial cell culture systems towards this cellular morphology.
The study of airway remodeling in the lower respiratory tract in vitro with respect to tobacco smoke exposure is a complex issue. Although experiments utilising single cell cultures systems are convenient from the point of view of ease of culture, availability, manipulation and measurement, the extrapolation and interpretation of the data with respect to the in vivo consequences is often difficult. These simple cultures do not take into account the complex interplay between the different cell populations and as such we are currently trying to overcome this problem through the use of organotypic cultures such as the lung slice.
These slices of lung tissue, obtained from commercial sources, contain the majority of the cells involved in the development of injury and remodeling following cigarette smoke exposure. These cultures can be maintained on microporous inserts, fed from below and using the BAT exposure chamber slices can be exposed to cigarette smoke. Histopathological, biochemical and gene expression analysis of the slices are being undertaken, specifically to assess the parenchymal response to cigarette smoke at low exposure levels .