Epithelial barrier dysfunction in ileal Crohn's disease

Abstract: The study aimed at investigating the intestinal barrier in Crohn's disease, with special reference to epithelial responses to luminal stimuli, and to permeation of proteins.Ileal mucosa from patients undergoing intestinal resection was studied in vitro in Ussing chambers. Intestinal permeability was also studied in vivo, by oral load of lactulose and mannitol.The Ussing chamber was evaluated for intestinal barrier studies. Normal ileal mucosa from patients with colon cancer was subjected to long-term experiments, and investigated in regard to various viability parameters. Mucosal permeability, structural integrity and metabolism were maintained for 90 minutes, and specimens with poor viability were detected by a low transepithelial potential difference. In rat ileal mucosa, luminal sodium caprate, a constituent of milk fat, induced dilatation of the tight junctions as visualised by electron microscopy, and a reversible increase in tight junction permeability. The findings indicate that the Ussing chamber is suitable for studies of the intestinal barrier, including tight junction regulation, provided that experiments are monitored by measurements of transepithelial potential difference and are limited in time.In vitro studies of human ileal mucosa showed that luminal sodium caprate caused uncoupling of oxidative phosphorylation, as shown by a fall in epithelial ATP contents, and mitochondrial swelling seen by electron microscopy, paralleled by an increased permeability. Non-inflamed Crohn's disease specimens had an exaggerated permeability increase and an augmented fall in transepithelial electrical resistance. Confocal microscopy revealed rearrangements of perijunctional filamentous actin, causing dilatation of the tight junctions. In Crohn's disease, a more pronounced reorganisation of actin filaments was seen, suggesting the tight junctions to be hyperreactive to luminal stimuli due to a disturbed cytoskeletal regulation.In vivo, an increased intestinal permeability was induced by ingestion of acetylsalicylic acid. One third of both Crohn's disease patients and their first-degree relatives showed an augmented permeability increase, whereas spouses were equal to controls, suggesting a genetically determined vulnerability of the intestinal barrier.In vitro, non-inflamed ileum from Crohn's disease patients had an increased permeation of ovalbumin. Confocal microscopy suggested this to be caused by an augmented transcytosis, a previously unrecognised defect in the epithelial barrier in Crohn's disease, with a subsequent exposure of antigenic proteins to the subepithelial immunocytes.The Crohn's disease patients without residual inflammation after surgery were followed with endoscopy within twelve months, and all revealed recurrent ileal inflammation.The study indicates a perturbed intestinal barrier in Crohn's disease, possibly genetically determined. The impaired barrier function is demonstrated both by an augmented epithelial transcytosis and by hyperreactive tight junctions. The epithelial barrier dysfunction precedes the recurrent intestinal inflammation in ileal Crohn's disease. The findings suggest an interplay between an impaired epithelial barrier and luminal factors in the initiation of intestinal inflammation.