Antagonism of protease-activated receptor 2 protects against experimental colitis.

Many trypsin-like serine proteases like β-tryptase are involved in the pathogenesis of colitis and inflammatory bowel diseases. Inhibitors of individual proteases show limited efficacy in treating such conditions, but also likely disrupt digestive and defensive functions of proteases. Here we investigate whether masking their common target, protease activated receptor 2 (PAR2), is an effective therapeutic strategy for treating acute and chronic experimental colitis in rats. A novel PAR2 antagonist (GB88) was evaluated for blockade of intracellular calcium release in colonocytes, and for anti-inflammatory activity in acute (PAR2 agonistµinduced) versus chronic (TNBS-induced) models of colitis in Wistar rats. Disease progression (disease activity index, weight loss, mortality) and post-mortem colonic histopathology (inflammation, bowel wall thickness, myeloperoxidase) were measured. PAR2 and tryptase co-localization was investigated using immunohistochemistry. GB88 was a more potent antagonist of PAR2 activation in colonocytes than a reported compound ENMD-1068 (IC50 8 µM vs 5 mM). Acute colonic inflammation induced in rats by PAR2 agonist SLIGRL-NH2 was inhibited by oral administration of GB88 (10 mg/kg), with markedly reduced oedema, mucin depletion, PAR2 receptor internalisation and mastocytosis. Chronic TNBS-induced colitis in rats was ameliorated by GB88 (10mg/kg/day/p.o.), which reduced mortality and pathology (including colon obstruction, ulceration, wall thickness, myeloperoxidase release) more effectively than the clinically used drug sulfasalazine (100 mg/kg/day/p.o.). These disease-modifying properties for the PAR2 antagonist in both acute and chronic experimental colitis strongly support a pathogenic role for PAR2 and PAR2-activating proteases, and therapeutic potential for PAR2 antagonism, in inflammatory diseases of the colon.