A Probiotic Mixture of Lactobacillus rhamnosus LR 32, Bifidobacterium lactis BL 04, and Bifidobacterium longum BB 536 Counteracts the Increase in Permeability Induced by the Mucosal Mediators of Irritable Bowel Syndrome by Acting on Zonula Occludens

Irritable Bowel Syndrome (IBS) is a disorder of gut- brain interaction characterized by recurrent abdominal pain associated with altered bowel habits. The therapeutic options for IBS patients include the use of probiotics. The aim of this study was to assess the effect of a multi-strain probiotic made up by <i>Lactobacillus rhamnosus</i> LR 32, <i>Bifidobacterium lactis</i> BL 04, and <i>Bifidobacterium longum</i> BB 536 (Serobioma, Bromatech s.r.l., Milano, Italy) on an in vitro model of the intestinal epithelial barrier in the presence of mucosal mediators that are released by IBS patients. IBS (n = 28; IBS with predominant diarrhea, IBS-D = 10; IBS with predominant constipation, IBS-C = 9; and IBS with mixed bowel habits, IBS-M = 9) patients, diagnosed according to the Rome IV criteria, and asymptomatic controls (ACs, n = 7) were enrolled. Mucosal mediators that were spontaneously released by colonic biopsies were collected (supernatants). Two doses of Serobioma were tested with/without IBS/AC mediators. RNA was extracted from Caco-2 cells to evaluate the tight junction (TJ) expression. Serobioma (10⁶ CFU/mL) significantly reinforced the Caco-2 monolayer compared to growth medium alone (<i>p</i> < 0.05). IBS supernatants significantly increased Caco-2 paracellular permeability compared to the AC supernatants. The co-incubation of Caco-2 cells with IBS supernatants and Serobioma (10⁶ CFU/mL) avoided the paracellular permeability alterations that were induced by IBS supernatants alone (<i>p</i> < 0.001), and, in particular, IBS-D and IBS-M ones. The co-incubation of Serobioma (10⁶ CFU/mL) and IBS-D supernatants significantly increased ZO-1 expression compared to Caco-2 cells incubated with supernatants alone (<i>p</i> < 0.05), as confirmed via qPCR analyses. Serobioma (10⁶ CFU/mL) counteracts the paracellular permeability changes that are induced by IBS supernatants, in particular IBS-D and IBS-M supernatants, likely modulating ZO-1 expression.