Mouse stool samples in response to antibiotic treatment

Background and Objectives: Antibiotic (ABx) therapy is associated with an increased risk for Crohn´s Disease but the underlying mechanisms are unknown. We observed high fecal serine protease activity (PA) to be a frequent side effect of ABx therapy in patients. The aim of the present study was to unravel whether this rise in PA may promote colitis development via detrimental effects on the large intestinal barrier. Design: Transwell experiments were used to assess the impact of high PA in ABx-treated patients or vancomycin/metronidazole (V/M)-treated mice on the epithelial barrier. Serine protease profiling was performed using LC-MS/MS analysis. The impact of high PA on the intestinal barrier in WT/IL10-/- mice and on colitis development in IL10-/- mice was investigated using V/M+/-oral serine protease inhibitor (AEBSF) treatment. Results: The ABx-induced high PA was found to be due to significantly increased levels of pancreatic proteases and to impair the epithelial barrier. In WT mice, the rise in PA caused a transient increase in intestinal permeability but did not affect susceptibility towards DSS-induced acute colitis. In IL10-/- mice, the rise in PA caused a lasting impairment of the intestinal barrier, which was associated with inflammatory activation of the large intestinal tissue. In the long term, the lasting increase in PA upon repeated V/M treatment aggravated colitis development in IL10-/-mice. Conclusion: High PA is a frequent adverse effect of ABx therapy which is detrimental to the large intestinal barrier and may contribute to the development of chronic inflammation in genetically susceptible individuals.