Xanthine Oxidase-Dependent Activation of NLPR3 Inflammasome in Epithelial Cells Sustains Inflammation in Inflammatory Bowel Disease

Xanthine oxidase (XO) plays a key role in purine metabolism, catalyzing the oxidation of hypoxanthine to xanthine, and xanthine to uric acid (UA) with the production of superoxide anions. The accumulation of UA has been shown to initiate the inflammatory process through NLRP3 inflammasome, and the production of reactive oxygen species (ROS) contributes to inflammation-related tissue damage in different organs. This study aimed to investigate the role of XO in the pathogenesis of Inflammatory Bowel Disease (IBD) and the anti-inflammatory potential of XO inhibition. XO expression and activity were assessed in the mucosa of moderately-to-severely active ulcerative colitis (UC) and Crohn's disease (CD) patients. The functional role of XO, the activation of NLRP3 inflammasome, and the expression of proinflammatory cytokines were investigated in ex vivo intestinal organ cultures in the presence or absence of XO inhibitors. In silico and in vitro analysis showed that XO mRNA and protein expression were upregulated in the UC and CD intestinal mucosa compared to controls. XO overexpression in the inflamed mucosa was associated with increased enzymatic activity, accumulation of UA and functionally linked to NLRP3-dependent IL1beta and IL18 expression. Accordingly, XO inhibitors, Allopurinol and Febuxostat, prevented NLRP3 activation, reduced Caspase1 activity and IL1beta and IL18 expression in ex vivo organ cultures of inflamed intestinal mucosa from both UC and CD patients. Overexpression of XO in IBD might contribute to inflammation by promoting NLRP3 inflammasome activation and proinflammatory cytokine production.