Effects of a Protease Inhibitor Camostat Mesilate on Gut Microbial Function in Patients with Irritable Bowel Syndrome: A Pilot Randomized Placebo-Controlled Study.

Introduction: Increased fecal protease activity, which may induce visceral hypersensitivity, has been observed in patients with irritable bowel syndrome (IBS). Serine proteases modulate FK506 binding protein (FKBP)-type peptidylprolyl cis-trans isomerase (PPIase) activity associated with immune and glucocorticoid receptor functions. The aim was to investigate whether camostat mesilate (CM), a serine protease inhibitor, modifies fecal bacterial function related to FKBP-type PPIases in patients with IBS.

Methods: Randomly assigned 16 patients with IBS received 200 mg po tid of CM and 16 patients received placebo for 14 days. Self-reported adequate relief (AR) as a primary endpoint, IBS Symptom Severity Scale (IBS-SSS), and colonic motor and pain thresholds to colorectal distention were assessed before and after treatment. The fecal bacterial content was inferred from 16S rRNA gene sequence data using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States and the Kyoto Encyclopedia of Genes and Genomes database.

Results: CM significantly increased the relative abundance of Streptococcus and the functional abundances of serine protease and FKBP-type PPIase FkpA, FklB and SlyD more than placebo after treatment. CM treatment was not superior to placebo in proportion of AR although colonic motor response partially changed.

Conclusion: CM modulated the fecal microbiome composition and functional potentials that are related to FKBP-type PPIase activity in IBS patients. These findings suggest that protease inhibitors may modify gut microbial function along with abnormal immunological and/or stress responses that underlie pathophysiology of IBS.