Introduction Patients with IBS-D have been reported to have increased faecal serine protease activity which could induce visceral hypersensitivity and increase gut permeability by activating proteinase activated receptor-2 (PAR-2). These proteases could be either endogenous (pancreatic or mast cell) or bacterial in origin.

Aim To define the type and origin of proteases using a proteomic method.

Methods Study 1: Serine protease activity in stool supernatant from 36 patients meeting the Rome III criteria for IBS-D and 9 healthy controls was evaluated using a previous published method.1 Patients completed a one week stool diary and a hospital anxiety and depression score. Study 2: Serine proteases from a subset of 8 pooled patient samples were purified using a combination of affinity chromatography and SDS-PAGE. Protease identification using proteolysis and mass-spectrometry was performed. Study 3: Assessment of stool amylase and elastase was performed using two commercially available ELISAs.

Results Study 1: Serine protease activity was significantly increased in patients, 621 ± 94 versus 211 ± 46 units of trypsin/mg protein in controls, p = 0.04. Serine protease activity was significantly correlated with anxiety r = 0.5 p = 0.002. Study 2: The predominant proteases were pancreatic in origin including trypsin, elastase and carboxypeptidase-B. Additionally there was abundant pancreatic amylase. Study 3: Stool amylase but not elastase was significantly increased in IBS-D 183 ± 35 103 units/ml versus controls 78 ± 44. Amylase also correlated with serine protease activity, r = 0.33, p < 0.05.

Conclusion We confirm previous reports of increased serine proteases in IBS-D but these appear to be of pancreatic origin and associated with increased anxiety. Anxiety may cause rapid transit which reduces degradation by colonic bacteria and increases fecal protease.