Cyclooxygenase 2 mediates post-inflammatory colonic secretory and barrier dysfunction

Background and aims: The colonic epithelium plays a key role in host defence. During colitis, epithelial function is impaired, leading to elevated bacterial translocation and exacerbation of inflammation. We previously documented perturbation of epithelial function, in terms of secretion and as a barrier to bacterial translocation, that persisted long after resolution of a bout of colitis in the rat. The mechanisms underlying the epithelial dysfunction are not completely understood. Methods: Given the ability of prostaglandin (PG) D-2 to suppress colonic epithelial secretion, we investigated the potential roles of this eicosanoid and of cyclooxygenase 2 (COX-2) in mediating postcolitis epithelial secretory and barrier dysfunction. Results: Six weeks after induction of colitis with trinitrobenzene sulphonic acid, there was marked elevated synthesis of PGD(2) and elevated COX-2 expression. Selective COX-2 inhibition abolished the increase in PGD(2) synthesis. Colonic chloride secretory responses ( in vitro) were significantly diminished relative to those in controls, a defect that was reversed by pre-exposure to a selective COX-2 inhibitor ( celecoxib) but not to a selective COX-1 inhibitor (SC-560). The hyporesponsiveness was mimicked by pre-exposure of normal colonic tissue to PGD(2), but not to its metabolite, 15-deoxy-Delta(12-14)PGJ(2). The post-colitis rats exhibited a 10-fold increase in bacterial colonisation of the colon, and >3-fold increase in bacterial translocation. Twice daily treatment for one week with a selective COX-2 inhibitor ( rofecoxib) did not affect bacterial colonisation but abolished the increase in bacterial translocation. Conclusions: These studies demonstrate an important role for COX-2, possibly via generation of PGD(2), in mediating the prolonged epithelial secretory and barrier dysfunction after a bout of colitis in the rat.