Background and aims: Oxidative stress is presumed to play an important role in Crohn's disease (CD) pathogenesis. Nevertheless, the evaluation of the intestinal antioxidant capacity through the analysis of glutathione peroxidase activity in CD remains to be determined. Methods: 20 CD outpatients and 16 volunteers going through colonic cancer screening were enrolled. Colonoscopy with biopsies was performed in all individuals. Samples from inflamed and non-inflamed mucosa were taken when there was CD endoscopic activity. Spectrophotometric assays were performed to measure tissue glutathione peroxidase (GPx) activity, and total (GSH T ) and oxidized (GSSG) glutathione in all samples. Demographics and clinical characteristics were collected from clinical charts. Results: Inflamed CD mucosa presented reduced GPx activity compared to non-inflamed CD mucosa (42.94 mU/mg protein vs 79.62 mU/mg protein, P b 0.05) and control mucosa (42.94 mU/mg protein vs 95.08 mU/mg protein, P b 0.001). GSH T concentration was reduced in inflamed mucosa when compared to non-inflamed CD mucosa (0.78 μmol/g vs 1.98 μmol/g, P b 0.01) and the control group (0.78 μmol/g vs 2.11 μmol/g, P b 0.001). A significant correlation was detected between GPx activity and GSSG (r = −0.599), disease duration (r = 0.546), and thiopurine treatment (r = −0.480) in non-inflamed CD mucosa. A v a i l a b l e o n l i n e a t w w w . s c i e n c e d i r e c t . c o m ScienceDirectJournal of Crohn's and Colitis (2013) 7, e358-e366Downloaded from https://academic.oup.com/ecco-jcc/article-abstract/7/9/e358/426937 by guest on 07 June 2019Conclusion: Our findings suggest that reduced GPx activity is present in inflamed CD mucosa. In addition, endoscopic activity, disease duration and thiopurine therapy could be associated with mucosal decreased antioxidant activity.