Review article: uptake of pepsin at pH 7 - in non-acid reflux -causes inflammatory, and perhaps even neoplastic, changes in the laryngopharynx

摘要

We describe herein how pepsin causes laryngeal epithelial cell damage at pH 7, and thus in non-acidic refluxate. Our data may help explain why some patients have refractory symptoms on maximal proton pump inhibitor therapy, and help explain the reported symptom association with non-acidic reflux events. We report mitochondrial and Golgi damage in laryngeal epithelial cells exposed to pepsin at pH 7. Cell toxicity was also demonstrated using the MTT cytoxicity assay. Pepsin at pH 7 significantly alters the expression levels of multiple genes implicated in stress and toxicity. We also report that pepsin (0.1 mg/mL, pH 7) induces a pro-inflammatory cytokine gene expression profile in hypopharyngeal FaDu epithelial cells in vitro similar to that which contributes to disease in gas-tro-oesophageal reflux patients. Moreover, using a Human Cancer PathwayFinder Super Array, we have shown that pepsin (0.1 mg/mL, pH 7) significantly alters the expression of 27 genes implicated in carcinogenesis. Collectively, these data suggest a mechanistic link between exposure to pepsin, even in non-acidic reflux-ate, and cellular changes that lead to laryngopharyngeal disease including cancer. In this context, our unexpected finding that pepsin is taken up by human laryngeal epithelial cells by receptor-mediated endocytosis is highly relevant. Pepsin has been previously assumed to cause damage by its proteolytic activity alone, but our discovery that pepsin is taken up by laryngeal epithelial cells by receptor-mediated endocytosis opens the door to a new mechanism for cell damage, and downstream, the development of new therapies for reflux disease - receptor antagonists and/or pepsin inhibitors.