Painful interactions: Microbial compounds and visceral pain.

Visceral pain, characterized by abdominal discomfort, originates from organs in the abdominal cavity and is a characteristic symptom in patients suffering from irritable bowel syndrome, vulvodynia or interstitial cystitis. Most organs in which visceral pain originates are in contact with the external milieu and continuously exposed to microbes. In order to maintain homeostasis and prevent infections, the immune- and nervous system in these organs cooperate to sense and eliminate (harmful) microbes. Recognition of microbial components or products by receptors expressed on cells from the immune and nervous system can activate immune responses but may also cause pain. We review the microbial compounds and their receptors that could be involved in visceral pain development.

Multispecies probiotic protects gut barrier function in experimental models.

AIM: To investigate the effect of the probiotic combination Lactibiane Tolerance(®) (LT) on epithelial barrier function in vitro and in vivo. METHODS: The effect of the multispecies probiotic LT was assessed on several models of epithelial barrier function both in vitro (in basal and inflammatory conditions) and in vivo [visceral hypersensitivity induced by chronic stress or by colonic perfusion of a fecal supernatant (FSN) from patients with irritable bowel syndrome (IBS)]. In vitro, we measured the permeability of confluent T84 cell monolayers incubated with or without LT by evaluating the paracellular flux of macromolecules, in basal conditions and after stimulation with lipopolysaccharide (LPS) or with conditioned medium of colonic biopsies from IBS patients (IBS-CM). In vivo, male C57/Bl6 mice received orally NaCl or LT for 15 d and were submitted to water avoidance stress (WAS) before evaluating visceral sensitivity by measuring the myoelectrical activity of the abdominal muscle and the paracellular permeability with (51)Cr-EDTA. Permeability and sensitivity were also measured after colonic instillation of FSN. Tight-junctions were assessed by immunoblotting and TLR-4 expression was evaluated by immunohistochemistry RESULTS: Incubation of T84 cell monolayers with LT in basal conditions had no significant effect on permeability (P > 0.05 vs culture medium). By contrast, addition of LT bacterial bodies (LT) completely prevented the LPS-induced increase in paracellular permeability (P < 0.01 vs LPS 10 ng/mL (LPS 10); P < 0.01 vs LPS 100 ng/mL (LPS 100), P > 0.05 vs culture medium). The effect was dose dependent as addition of 10(9) LT bacterial bodies induced a stronger decrease in absorbance than 10(6) LT (10(9) LT + LPS 10: -20.1% ± 13.4, P < 0.01 vs LPS 10; 10(6) LT + LPS 10: -11.6% ± 6.2, P < 0.01 vs LPS 10; 10(9) LT + LPS 100: -14.4% ± 5.5, P < 0.01 vs LPS 100; 10(6) LT + LPS 100: -11.6% ± 7.3, P < 0.05 vs LPS 100). Moreover, the increase in paracellular permeability induced by culturing T84 cells with conditioned medium of colonic biopsies from IBS patients (IBS-CM) was completely inhibited in the presence of 10(9) LT (P < 0.01 vs IBS-CM). LT also significantly prevented the epithelial disruption induced by intracolonic infusion of fecal supernatant from IBS patients (P < 0.01 vs IBS FSN) or water avoidance stress P < 0.01 vs WAS) in C57/Bl6 mice and increased the expression of occludin in vitro and in vivo, as assessed by immnunoblotting. The WAS-induced effect on visceral sensitivity was prevented by LT treatment since values obtained for all steps of colorectal distension were significantly (P < 0.01) different from the WAS group. Finally, LT down-regulated the response mediated through TLR-4 in vitro (decrease in tumor necrosis factor α secretion in response to LPS: -65.8% for 10(9) LT and -52.5% for 10(6) LT, P < 0.01 vs LPS) and in vivo (inhibition of WAS induced an increase in TLR-4 expression in the LT treated mice colon, P < 0.01 vs WAS). CONCLUSION: The probiotic LT mix prevented the disruption to the epithelial barrier induced by LPS, stress or colonic soluble factors from IBS patients and prevented visceral hypersensitivity.