THE ENTEROGLIAL DERIVED-S100B PROTEIN MEDIATES THEPROTECTIVE EFFECT OF LACTOBACILLUS CASEI DG ON LPS-INDUCEDNITRIC OXIDE PRODUCTION IN HUMAN INTESTINAL BIOPSIES

INTRODUCTION: Probiotics are known to exert immunomodulatory effects within the gut, expecially by inhibiting the release of proinflammatory mediators, such as nitric oxide (NO). Enteroglial derived S100B protein plays an active role in NOdependent gut inflammation. Previous data show that pathogen bacteria are able to induce S100B release from enteroglial cells (EGCs). Whether probiotics are able to counteract these effects is not established yet. AIMS & METHODS: We aimed to study the effects of Lactobacillus Casei DG (LC-DG) on lipopolysaccharides (LPS)-induced iNOS protein expression, nitric oxide (NO) and S100B secretion from human intestinal biopsies. To achieve this goal, rectal biopsies from 6 healthy subjects undergoing screening for colorectal cancer were stimulated with LPS (10 ug/mL) and/or with LC-DG (108 bacteria/mL), as follows: experiment A) stimulation with LPS starts at 0h and end at 5h (0−5h); B) LC-DG 0−5h; C) LC-DG 0−5h + LPS 2.5−5h; D) LPS 0−5h + LC-DG 2.5−5h; E) LPS 0−5h + LC-DG 0−5h. To test EGCs stimulation, S100B release was evaluated by ELISA assay. Nitrite assay and Western Blot analysis were used to evaluate NO release and iNOS expression, respectively, in stimulated biopsies compared to unstimulated biopsies (control). Data are expressed as mean±SD of 6 independent experiments. RESULTS: In rectal biopsies, LPS, but not LC-DG, significantly increased S100B secretion (+1.8±0.5 fold increase vs control; p<0.05). When LC-DG was added to biopsy before, after or together LPS, S100B secretion was not increased respect to control. In parallel, incubation with LPS led to a significant increase of iNOS protein expression (+2.0±0.3 fold increase vs control; p<0.05) and of NO secretion (+2.9±0.7 fold increase vs control; p<0.05), that was not observed with LC-DG. When LC-DG was added to biopsy before, after or together LPS, iNOS expression and NO secretion were similar to control. CONCLUSION: We show that the probiotic LC-DG decreases LPS-induced NO secretion in human biopsies by inhibiting iNOS protein expression. This effect may be mediated by EGCs since LC-DG also decreases LPS-induced enteroglial-derived S100B protein secretion.