P091 Inflammation in relation to mucosal barrier function in chronic colitis: a study in time

Abstract

The pathogenesis of inflammatory bowel diseases (IBD) is multifactorial. Midst in the complex interaction between genetic, environmental and immunological factors is the intestinal barrier. IBD patients have been observed to have increased intestinal permeability which can partially explain the exaggerated immune response towards luminal antigens. Inflammatory mediators perpetuate this barrier defect by causing further damage to the intestinal barrier. Our aim is to investigate the interaction between permeability and inflammation in a chronic colitis mouse model. Colitis was induced in immunodeficient SCID mice by the adoptive transfer of naive T cells, isolated from BALB/c mice. Mice were sacrificed at fixed time points to study disease progression resulting in five groups: control mice (Week 0); colitis mice in week 1, 2, 4 and 6 of the experimental protocol (Week 1; Week 2; Week 4, Week 6; all n = 10). FITC-dextran was used to assess intestinal permeability, next to the messenger RNA of the tight junction proteins Claudin-1 and Occludin. After sacrifice, colonic inflammation was assessed by macro- and microscopic scoring, myeloperoxidase (MPO) activity and cytometric bead array (CBA) for TNF- α and IL-1β . Messenger RNA of transcription factors that regulate T helper (Th) cell differentiation including T-bet (Th1), GATA-3 (Th2), ROR- γt (Th17) were quantified using RT-qPCR technique. Mucosal inflammation appeared gradually in the colon of the diseased mice. Macroscopically there was a significant increase starting from Week 2 on, gradually increasing until Week 6. The same was true for the MPO activity. Microscopically, however, the first significant signs of inflammation were observed at Week 1, which then also gradually increased with the highest score at Week 6. The colonic inflammation was mainly Th1/Th2 driven, since the transcription factors T-bet and GATA-3 were significantly upregulated from respectively Week 2 and Week 4 on. TNF-α and IL-1β were significantly elevated starting from Week 1. Intestinal permeability was significantly elevated at Week 1 and remained elevated at Week 2, 4 and 6. Data are presented as mean±SEM and analysed by one-way ANOVA with multiple comparisons SNK posthoc testing. *<0.05 vs. WEEK 0 # <0.05 vs. WEEK 1. Our results show a gradual increase of intestinal inflammation over time which, for most parameters, started at Week 2. However, we observed an unexpectedly early increase in intestinal permeability at Week 1. This shows that the mucosal barrier function is of great importance in disease onset and could be an interesting therapeutic target or biomarker predicting flares.