EARLY EFFECTS OF GLIADIN ON HUMAN INTESTINAL MUCOSA AND INTESTINAL CELL LINES

Background & Aims: The mechanism(s) of interaction of gliadin with intestinal epithelial cells are still largely unknown. Based on our recent discovery of zonulin, a modulator of intestinal tight junctions, and its up-regulation in celiac disease, we elected to establish whether gliadin has any immediate effect on the zonulin pathway. Methods: Both ex vivo human small intestines and intestinal cell monolayers were exposed to gliadin, and zonulin release and changes in paracellular permeability were monitored in the presence and absence of zonulin antagonism. Zonulin binding, cytoskeletal rearrangement, and zonula occludens-1 re-distribution were evaluated by immunofluorescence microscopy. Results: Zonulin receptor positive IEC6 and Caco 2 cells exposed to gliadin released zonulin with subsequent zonulin binding to the cell surface, rearrangement of the cell cytoskeleton, loss of occludin-ZO1 protein-protein interaction, and increased monolayer permeability. Pretreatment with the zonulin antagonist FZI/0 blocked these changes. When exposed to luminal gliadin, intestinal biopsies from celiac patients in remission expressed a sustained luminal zonulin release and increase in intestinal permeability that was blocked by FZI/0 pre-treatment. Conversely, biopsies from non-celiac patients demonstrated a limited, transient zonulin release which was paralleled by a reduction in intestinal TEER that never reached the level of permeability seen in CD tissues. Chronic gliadin exposure caused a down-regulation of both ZO-1 and occludin gene expression. Conclusions: Gliadin activates the zonulin system irrespective of the genetic predisposition to autoimmunity, leading to increased intestinal permeability to macromolecules.