Studies of barrier function in patients with ulcerative colitis and pouchitis

Abstract: Background and aim: The cause of ulcerative colitis (UC) is largely unknown. However, there is a presumed genetic component to susceptibility and altered intestinal barrier function has been implicated in the pathophysiology of ulcerative colitis. There is evidence that the increased intestinal permeability in IBD is partly controlled by delicate intercellular circuits in the colonic tissue linked to the enteric nervous system. Little is, however, known about how this is regulated in detail.Ileal pouch-anal anastomosis (IPAA) is a good surgical reconstructive option in UC patients after proctocolectomy. However 10-15% of IPAA patients develop a severe and recurrent inflammation in the constructed pouch. The standard treatment for pouchitis is long and/or frequent use of antibiotics. Probiotics have been shown to reduce the risk of recurrence of pouchitis after induction treatment with antibiotics.The aim was to characterize macromolecular permeability in non inflamed colon of UC and elucidate the role of cholinergic signaling, mast cells and eosinophils in the regulation of the human colonic permeability. Furthermore, we examine the mucosal barrier function in relation to pouchitis, before and after treatment with probiotics.Material and methods: In the first study 23 UC patients in remission and 53 healthy volunteers were included. Biopsies from the sigmoid colon were assed for macromolecular permeability (horseradish peroxidase (HRP) and 51CrEDTA) and electrophysiology during challenge with carbachol. Experiments were repeated with CRF receptor antagonists, carbachol receptor antagonists and mast cell stabilizers in Ussing chambers. Further, pouch biopsies from 16 IPAA patients with pouchitis and 13 IPAA controls were assed in Ussing chambers for macromolecular permeability and electrophysiology as above. In addition E. coli K12 were used to assess the barrier to bacteria. Biopsies were taken on three occasions; before treatment, after antibiotics and after probiotics. Pouchitis Disease Activity Index (PDAI) was used in all subjects.Results: Colonic tissues from UC patients had significant increase in permeability to protein antigens compared with controls. Permeability was normalized by atropine, α-helical CRF(9-41) and lodoxamide. Eosinophils were increased in number in UC tissues, expressed M2 and M3 muscarinic receptors and showed immunoreactivity to CRF. In pouchitis patients,  PDAI was significantly improved after treatment with antibiotics and probiotics. There was a significantly enhanced passage of E. coli K12 and HRP in patients with active pouchitis, which was unchanged during treatment with antibiotics, but significantly normalized by probiotics.Conclusions and discussion: We identified a neuroimmune intercellular circuit (from cholinergic nerves, via eosinophils to mast cells) that mediates colonic mucosal barrier dysfunction in UC patients. Furthermore we found that probiotics restored the increased permeation to E. coli and HRP in patients with pouchitis. Pouchitis, resembling symptoms in active UC, may well constitute a good model to study acquired intestinal barrier dysfunction in IBD.