Aspiration of Gastrointestinal Material and Induction of Fibronectin Expression in Lung Transplant Recipients: Implications for Early Airway Remodeling

Abstract

Background: Gastroesophageal reflux disease has been associated with allograft dysfunction in lung transplant (LTX) recipients. While the mechanisms are unclear it is postulated that microaspiration of gastrointestinal material (GIM) leads to inflammation and airway remodeling that culminates in obliterative bronchiolitis. Expression of the glycoprotein fibronectin has been shown to be an early marker of lung fibroproliferative disease, thus, its induction could suggest a causal mechanism for allograft dysfunction in LTX recipients experiencing microaspiration. Methods: De-identified bronchoalveolar lavage fluid (BALF) samples sequentially collected during surveillance bronchoscopies throughout the first post-transplant year were analysed. Microaspiration was defined by the detection of bile salts in the BALF via an ELISA assay. An in vitro bioassay then measured fibronectin expression as a marker of activation of airway remodeling via incorporation of murine NIH/3T3 fibroblasts transfected with the human fibronectin promoter connected to the luciferase reporter vector. Fibroblasts were cultured with BALF for 24 hours and the ability of the BALF to stimulate fibronectin induction was measured via luciferase activity units. Results: Sequential bronchoscopies on 15 LTX recipients yielded 101 BALF samples for analysis. Six recipients had at least one BALF ‘positive’ for bile salts indicating GIM aspiration while the remaining nine recipients had no ‘positive” analyses. Fibronectin induction in the recipients experiencing aspiration was significantly greater than in the samples from those recipients who did not aspirate (1.05 + 0.19 vs. 0.92 + 0.28 luciferase activity units/µg protein) [p< 0.02]. Furthermore, the amount of fibronectin induction correlated with the amount of bile salts recovered from the allografts (r2 =0.20, p=0.04) suggesting that the amount of aspirated material influenced the degree of fibronectin production in the lower airways. Conclusions: Fibronectin induction is increased in LTX recipients who experience microaspiration suggesting possible early airway remodeling that may lead to later allograft dysfunction.