61 Interferon-Gamma Interplay With Serotonin Metabolism and Mucosal Permeability in Irritable Bowel Syndrome

Abstract

Background and aim: A variety of peripheral mechanisms may be involved in the pathophysiology of irritable bowel syndrome (IBS). These include alterations in serotonin metabolism, epithelial permeability, composition of microbiota and immune system. In vitro studies demonstrated that interferongamma (IFN-γ) enhanced paracellular permeability and decreased serotonin reuptake transporter (SERT) expression. In this study we assessed the potential role of IFN-γ in IBS pathophysiology. Material and methods: We included a total of 10 healthy controls (HC) and 26 patients with Rome III IBS. In all cases, we obtained 6 mucosal biopsies from the descending colon. Paraffin-embedded colonic biopsies were used to evaluate IFN-γ mRNA expression. Total RNA was retrotranscribed into cDNA and analysed in real-time PCR assays. Enzyme-linked immunosorbent assays (ELISA) were used to evaluate IFN-γ levels both in colonic biopsy homogenates and into supernatants of cultured biopsies. Supernatants of cultured biopsies were used to treat Caco-2 cell line to evaluate their effect on SERT expression level by real-time RT-PCR assays. Supernatants were also used to evaluate their effect on Caco-2 paracellular permeability. Results: IFN-γ mRNA expression was significantly higher in patients with IBS compared to HC (2-11Ct = 2.57±0.6 vs 2-11Ct = 0.66±0.1; P<0.05). In addition, we showed increased protein levels of IFN-γ in biopsy homogenates of patients with IBS vs HC (increase of 48% in IBS-D; P<0.05). Similarly, we demonstrated a higher concentration of IFN-γ protein in IBS supernatants. The treatment of Caco-2 cells with IBS supernatants induced a significant decrease in SERT expression compared to HC supernatants. IBS supernatants produced an increase in Caco-2 cell permeability. The effects of IBS supernatants on Caco-2 cells were mediated, at least in part, by IFN-γ. Conclusions: We demonstrated an increased expression of IFN-γ in the colonic mucosa of patients with IBS. We also showed increased IFN-γ amount both in biopsies and supernatants of patients with IBS. Epithelial permeability was enhanced by IBS supernatants which induced also a reduction of SERT expression, at least in part via IFN-γ. All together, these data suggest a potential role of IFN-γ in IBS pathophysiology.