Aims. Cyclooxygenase isoforms (COX-1, COX-2) have been implicated in thedevelopment of fibrosis at gastrointestinal sites. Under bowel inflammation, transforming growth factor beta(TGF-beta) has been identified as the main regulator of fibrotic remodelling. The present study investigatedthe effects of cyclooxygenase inhibitors on pro-fibrotic signalling mediated by the TGF-beta/SMAD pathway inexperimental colitis.Methods. Colitis was induced in rats by intrarectal 2,4-dinitrobenzenesulfonic acid (DNBS, 30 mg/rat in 0.25ml 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 animalswere 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 intragastricgavage. At the time of sacrifice, functional and molecular tests were carried out. Peristaltic activity of controland inflamed colonic segments was studied in vitro by a modified Trendelenburg set-up. Collagen fibers (VanGieson) and elastic fibers (orcein) were examined by histochemistry. The expression of molecular factorsinvolved in TGF-beta signalling (TGF-beta, RhoA and SMAD6, as well as phosphorylated SMAD2, p38, ERKsand JNK), and cellular proliferation and apoptotis (PCNA, Akt and caspase-3) was analyzed by western blot.Results. Animals with colitis displayed an impairment of colonic peristalsis, as shown by a significant decreasein compliance and maximal ejection pressure, as well as an increase in the threshold pressure and luminalvolume required to trigger peristalsis. Moreover, histochemistry showed an increased deposition of collagenfibers in parallel with a dramatic decrease in elastic fibers. IND, SC and CEL inhibited collagen deposition, andreverted the loss of elastic fibers. In the inflamed/fibrotic colon, western blot analysis revealed an increasedexpression of TGF-beta, PCNA, caspase-3, pAkt, p-p38, RhoA and pSMAD2. By contrast, the expression ofSMAD6, pERKs and pJNK was reduced. In this setting, IND, SC and CEL counteracted the increasedexpression of TGF-beta, RhoA, pSMAD2 and p-p38, and partly reverted the reduced expression of SMAD6.Conclusions. In the DNBS model of colitis, bowel fibrosis is associated with impaired colonic peristalsis andalterations in the expression of factors driven by activation of TGF-beta signalling. The pharmacologicalblockade of COX-1 and COX-2 is able to counteract the fibrotic remodelling of inflamed colon, and this actionappears to depend on the modulation of TGF-beta-dependent SMAD signalling, particularly through aninduction of the inhibitory protein SMAD6 and a reduction of the phosphorylated status of SMAD2.
|Number of pages||2|
|Publication status||Published - 2013|