The intestinal mucosa serves to absorb nutrients, solutes and fluid, but simultaneously exclude luminal macromolecules and bacteria. The mucosal barrier is composed of epithelial cells and their tight junctions; failure of the mucosal barrier can lead to the dissemination of bacteria and ultimately, multiple organ failure syndrome. Also protecting the epithelium, is the mucus gel, composed of mucins, cellular debris, and adherent IgA. Maintenance of the mucus gel is accomplished by the baseline secretion of mucins from goblet cells. Numerous pathophysiologic conditions, including cystic fibrosis and ulcerative colitis, demonstrate altered mucin production/secretion; no physiologic significance,, however, has been assigned to these phenomena. We propose to characterize the role of mucins and an oxidant-generating enzyme of goblet cell origin, intestinal peroxidase (IPO), in the pathogenesis of ischemia/reperfusion (I/R), using the total occlusion of the superior mesenteric artery as our model. First, we will determine the role of luminal xanthine oxidase and IPO, as well as their oxidants, superoxide anion radical and hypohalous acid, in the progression of mucosal injury, using isotopic and morphological end-points. Second, we will characterize the response of goblet cells to I/R-induced mucosal injury, especially, the secretion of mucins and mucin species, as well as the secretion of IPO. We will also determine the ability of mucins to scavenge IPO-generated hypohalous acids to protect the epithelium. Third, we will characterize the chemistry and physiology of IPO, including: isolation and chemical composition; kinetic, bactericidal and cytotoxic analysis; and the binding affinity of IPO to a reconstituted mucin gel in vitro. Finally, we will use the information gained from the characterization of mucins and IPO to attempt to interrupt the pathogenesis of I/R-induced mucosal injury in vivo. Using the occlusion of the SMA as a model, we will attempt to ameliorate mucosal damage by inactivation of IPO activity with anti-IPO antibodies. We will also attempt to scavenge reactive oxygen species in vivo with mucins. Finally, we will attempt to mimic I/R -induced mucosal injury With exogenous IPO and substrate. We hypothesize that the mucus gel is far more versatile and bioactive than previously thought. That under normal conditions, mucin-IPO interactions result in an antimicrobial-barrier in the intestine, but that under conditions of ischemia/reperfusion, this defense system results in the initiation of I/R-induced mucosal damage.
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