The effect of particulate matter pollution on bronchial epithelial cell responses

Asthma is increasing in prevalence around the world. It is clinically characterised by shortness of breath, wheeze and cough and pathologically by increased Th2 inflammation, mucus hypersecretion and airway remodelling Epidemiological studies have linked inhalation of particulate matter (PM) with asthma, and although exposure has been shown to lead to acute airway inflammation, there is uncertainty regarding the mechanisms underlying the inflammatory response and the contribution of particulate matter to airway remodelling and asthma chronicity. In this study the effects of diesel exhaust particles (DEP) and residual oil fly ash (ROFA) on bronchial epithelial cell activation are investigated. It is postulated that DEP leads to inflammatory effects on bronchial epithelial cells as measured by the release of IL-8 via release of EGFR ligands and activation of the epidermal growth factor receptor (EGFR). In addition, it is further hypothesised that exposure of bronchial epithelial cells to DEP and ROFA leads to increased mucin gene expression. Recognising the contribution of IL-13 as a key allergic mediator in asthma it is postulated that DEP and IL-13 are synergistic in their effects on bronchial epithelial cells. Bronchial epithelial cells were cultured and exposed to DEP or ROFA. Methylene Blue assay was used to measure cell number, LDH assay to measure cell toxicity, TAQMAN RT-PCR to measure gene expression and ELISA to measure growth factor and cytokine release. In response to DEP > 50Jlgiml there was a modest increase in cytotoxicity in H292 cells and primary bronchial epithelial cells (PBEC) but not in 16HBEo - cells. DEP did not cause increased IL-8 release from H292 or 16HBEocells. Using PBEC there was significantly increased IL-8 gene and protein expression in response to DEP. IL-8 was released via activation of the EGFR. This was demonstrated by neutralisation of the EGFR and involved the shedding of the EGFR ligands Transforming Growth Factor a (TGFa) and Amphiregulin (AR). DEP and ROFA led to enhanced expression of gel forming and membrane bound mucin genes. DEP enhanced the gel forming mucin, MUC2 as well as the membrane bound mucins MUC1 and MUC4. ROFA led to enhanced induction of the gel forming mucins MUC5AC, MUC5B and MUC2 as well as the membrane bound mucin gene; MUC4. The inflammatory effects of DEP were enhanced in an additive fashion in the presence of the Th2 cytokines IL-4 and IL-13, suggesting that these effects of DEP may be more marked in asthmatic airways where Th2 cytokines are over-expressed. DEP activates bronchial epithelial cells through activation of the EGFR. This may contribute to inflammation and remodelling responses that are found in asthma. The increase in mucin gene expression may be a normal protective mechanism but may contribute to the symptoms and pathology of asthma. These changes may, in part, account for the recent epidemiological trends in asthma prevalence.