Many
trypsin-like
serine proteases such as 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 probably 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 (5-isoxazoyl-Cha-Ile-spiro[
indene-1,4'-
piperidine]; GB88) was evaluated for the blockade of intracellular
calcium release in colonocytes and anti-inflammatory activity in acute (PAR2 agonist-induced) versus chronic [2,4,6-
trinitrobenzenesulfonic acid (TNBS)-induced] models of
colitis in Wistar rats.
Disease progression (disease activity index,
weight loss, and mortality) and postmortem colonic histopathology (
inflammation, bowel wall thickness, and
myeloperoxidase) were measured. PAR2 and
tryptase colocalization were investigated by using immunohistochemistry. GB88 was a more potent antagonist of PAR2 activation in colonocytes than another reported compound, N¹-3-methylbutyryl-N⁴-6-aminohexanoyl-piperazine (ENMD-1068) (IC₅₀ 8 μM versus 5 mM). Acute colonic
inflammation induced in rats by the PAR2 agonist
SLIGRL-NH₂ was inhibited by
oral administration of GB88 (10 mg/kg) with markedly reduced
edema,
mucin depletion,
PAR2 receptor internalization, and
mastocytosis. Chronic TNBS-induced
colitis in rats was ameliorated by GB88 (10 mg/kg/day p.o.), which reduced mortality and pathology (including colon obstruction, ulceration, wall thickness, and
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.