Gastric aspiration and lung transplantation

Abstract

Lung transplantation has become a viable therapeutic option for patients with end-stage lung disease, however, despite improvements in surgical techniques and post-operative management long term survival is poor when compared to those of other solid organ transplants. The long term success is limited by the onset of obliterative bronchiolitis (08) and its clinical correlate bronchiolitis obliterans syndrome (80S). Obliterative bronchiolitis is a chronic pathology involving inflammation and airway fibrosis causing allograft dysfunction. It is thought to occur as a response to both immunological and non-immunological mechanisms, and there is increasing evidence to suggest that gastro-oesophageal reflux with subsequent aspiration is a contributing factor. lhe aims of this project were to investigate whether gastric aspiration is occurring in lung transplant recipients and whether it can predispose a patient to the development of chronic rejection (08/80S). This was investigated using the gastric protease pepsin as a biomarker for gastric aspiration in the bronchoalveolar lavage (8AL) of lung transplant recipients. In addition, to further understand the link between aspiration and the development of OB/BOS the effects of pepsin on mucus and cytokine production from primary bronchial epithelial cells from lung transplant patients and goblet cells were investigated. From cross-sectional analyses pepsin levels were found to be elevated in lung transplant recipients compared to normal and disease controls, with the highest levels been found in the acute rejection (grade ~A2) group (normal: median, 1.1, range 0- 2.3ng/ml vs. all transplant: median 8.3, range 0-51.7ng/ml, P =0.02). Further analysis involving a longitudinal cohort of patients also confirmed that pepsin was present in the BAL of lung transplant recipients. A cut off value for a 'high' pepsin level was Prospectively determined using a separate and 'clinically well' stable transplant control group (75th percentile pepsin level, 10.4ng/ml). These subjects were documented to be free from rejection, infection or any clinical problems commonly associated with transplantation. Patients with early elevated levels of 8AL pepsin (Le. above 10.4ng/ml at 3 months post-transplant) were estimated to develop BOS at 3.0 times the rate of those with low early BAL pepsin. This is the first longitudinal study of BAL pepsin in lung transplant recipients which shows a trend for decreased survival in patients with early elevated BAL pepsin levels (60% BOS free in those with high early BAL pepsin vs. 80% BOS free in those with low early BAL pepsin at 3 years post-transplant). This shows a need for further investigations with increased patient numbers to reach statistical significance and confirm these results. The effect of pepsin and gastric juice on bronchial epithelial and goblet cell cultures was also investigated. The viability of the cells was not affected with the addition of pepsin, however the addition of whole gastric juice did cause a significant reduction in epithelial cell viability. In addition, mucin production from goblet cells was significantly increased at 72h on addition of 50l-lg/ml pepsin at pH 7.4 (median values pH 7.4; 163.4l-1g/ml and pH 7.4 & pepsin; 448.9I-1g/ml, P=0.038) and at pH 7.0 (median values pH 7.0; 55.3I-1g/ml and pH 7.0 & pepsin; 327.2I-1g/ml, P=0.016). Previous investigations from our group have shown that interleukin-8 (IL-8) can stimulate the production of mucin from goblet cells in vitro, therefore media from epithelial and goblet cells stimulated with pepsin was measured for IL-8, however there was no significant increase in production from either cell type. This suggests that the increase in mucin production in cells stimulated with pepsin is not mediated through an IL-8 pathway, therefore other mechanisms should be investigated. This thesis supports the hypothesis that gastric aspiration may be an important injury in lung transplantation and that pepsin is a potentially useful biomarker that may be associated with chronic allograft damage.