IRRITABLE BOWEL SYNDROME Downregulation of epithelial apoptosis and barrier repair in active Crohn’s disease by tumour necrosis factor a antibody treatment

Background and aims: Barrier dysfunction is an important feature contributing to inflammation and diarrhoea in Crohn’s disease (CD). Recently, tumour necrosis factor a (TNF-a) antibodies were recognised as effective in steroid refractory CD. The aim of this study was to characterise the effects of this therapy on the epithelial barrier. Patients and methods: Forceps biopsies were obtained from the sigmoid colon before and 14 days after TNF-a antibody therapy in 11 patients treated for chronic active CD (Crohn’s disease activity index .150). Epithelial apoptoses were measured after terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labelling (TUNEL) and 49,6-diamidino-2-phenylindole staining. Epithelial resistance was determined by alternating current impedance analysis in miniaturised Ussing chambers. Occludin, claudin 1, and claudin 4 expression was quantified in immunoblots. Results: The epithelial apoptotic ratio was 2.1 (0.2)% in controls and increased to 5.3 (1.0)% in CD. TNF-a antibody therapy decreased the apoptotic ratio to 2.9 (1.0)% (normalised in 10 of 11 patients). In parallel, epithelial resistance was lower in CD than in controls (24 (3) v 42 (3) V6cm) and improved to 34 (3) V6cm after therapy. Occludin, claudin 1, and claudin 4 were not affected by TNF-a antibody therapy. In support of a functional role of epithelial apoptoses in CD, a similar decrease in resistance of 240% was observed when the apoptotic rate was selectively upregulated from 2.6% to 5.4% with camptothecin in HT-29/B6 cells. Conclusions: Epithelial apoptoses were upregulated in the colon in CD and restored to normal in 10 of 11 patients by TNF-a antibody therapy. This is the structural correlate of epithelial barrier dysfunction measured as epithelial resistance while expression of tight junction proteins did not contribute to this therapeutic effect.