Cyclooxygenase inhibitors modulate pro-fibrotic signalling mediated by TGFbeta in experimental colitis

Objectives. In extra-gastrointestinal sites, cyclooxygenase isoforms (COX-1, COX-2) have been implicated in fibrosis. In the setting of bowel inflammation, transforming growth factor beta (TGF-b has been identified as the main regulator of fibrotic remodelling. The present study evaluated the effects of cyclooxygenase inhibitors on profibrotic signalling mediated by TGF-b in experimental colitis. Methods. Colitis was induced in rats by intrarectal administration of 2,4-dinitrobenzenesulfonic acid (DNBS, 30 mg/rat in 0.25 ml ethanol 50%). After 6 days, systemic [body and spleen weight] and tissue inflammatory parameters [macroscopic and microscopic damage] were assessed. Three days before colitis assessment, the animals were treated daily with indomethacin (IND, non-selective COX-1/COX-2 inhibitor, 2 mg/kg), SC-560 (SC, selective COX-1 inhibitor, 2.5 mg/kg), or celecoxib (CEL, selective COX-2 inhibitor, 1 mg/kg), by intragastric gavage. At the time of sacrifice, COX-1, COX-2, collagen I and III, fibronectin, matrix metalloproteinase(MMP)-2 and MMP-9, TGF-b, RhoA, PCNA and phosphorylated p38, ERK1/2, Akt expression were analyzed by western blot. COX-2 was also analyzed by immunohistochemistry. Collagen fibers (Van Gieson) and elastic fibers (orcein) were detected by histochemistry. Results. Western blot analysis of inflamed colon showed an increased expression of COX-2, collagen I, collagen III, fibronectin, MMP-2, MMP-9, TGF-b, PCNA, p-Akt, p-p38, RhoA. COX-1 was not affected, while p-ERK1/2 was reduced. The enhanced expression of COX-2 was confirmed by immunohistochemistry. Histochemistry displayed an increased positivity for collagen fibers in concomitance with a dramatic decrease in elastic fibers. Based on western blot, IND, SC and CEL counteracted the increased expression of collagen III, fibronectin, collagen I, TGF-b, RhoA and p-p38. Histochemistry confirmed the inhibitory action of IND, SC and CEL on collagen deposition and showed their reverting effect on the loss of elastic fibers. Conclusions. In the DNBS model of colitis, bowel fibrosis is characterized by enhanced collagen/fibronectin deposition, by elastic fiber reduction, and TGF-b In this setting, the pharmacologiacal blockade of COX-1 and COX-2 is able to downregulate the fibrotic remodelling, and this action appears to depend on the modulation of TGF-b and its signalling pathways.