Purine Metabolism and Barrier Formation in Intestinal Epithelial Cells

Loss of epithelial barrier function is a hallmark in the pathogenesis of inflammatory bowel disease (IBD). Active inflammatory responses in the mucosa are characterized by fundamental shifts in energy supply and demand, although such metabolic changes are incompletely understood. Guided by an unbiased metabolomic screen of colonic tissue from healthy and actively colitic mice, we identified broad depletion of purine metabolites and cellular initiation of the energetically costly de novo synthesis of purines in response to metabolite loss. As barrier function is known to require high cellular energy, we pursued the hypothesis that protection against purine depletion will promote barrier function, with selective purine metabolites serving as predictable biomarkers of successful barrier formation. For these purposes, we profiled purine metabolism during the formation of intestinal epithelial barrier in vitro. These studies revealed that limiting purine loss through creatine supplementation enhanced barrier formation – a “top‐down” protection by increasing the phosphocreatine pool to limit ATP degradation. Additionally, we observed that hypoxanthine positively correlated with the magnitude and kinetics of barrier formation. As hypoxanthine‐guanine phosphoribosyltransferase (HGPRT) utilizes hypoxanthine in the first step of the purine salvage pathway, hypoxanthine may protect against purine degradation from the “bottom‐up.” Further studies with hypoxanthine and allopurinol (to inhibit hypoxanthine degradation by xanthine oxidase) supplementations supported the hypothesis by enhancing barrier, implicating the significance of purine salvage in barrier function. These findings are in agreement with the strategies employed by intestinal epithelial cells to preserve purine metabolites upon inflammatory insult and represent a potential therapeutic approach for the treatment of IBD.