Reduced butyrate-producing bacteria could result in increased epithelial permeability particularly in the context of concomitant exposure to another stimulus that reduces mitochondria function. We speculate that prebiotics, the substrate for butyrate synthesis, is a valuable prophylaxis in the regulation of epithelial permeability and could be of benefit in preventing relapses in IBD.

Epithelial permeability is often increased in inflammatory bowel diseases. We hypothesized that perturbed mitochondrial function would cause barrier dysfunction and hence epithelial mitochondria could be targeted to treat intestinal inflammation. Mitochondrial dysfunction was induced in human colon-derived epithelial cell lines or colonic biopsy specimens using dinitrophenol, and barrier function was assessed by transepithelial flux of Escherichia coli with or without mitochondria-targeted antioxidant (MTA) cotreatment. The impact of mitochondria-targeted antioxidants on gut permeability and dextran sodium sulfate (DSS)-induced colitis in mice was tested. Mitochondrial superoxide evoked by dinitrophenol elicited significant internalization and translocation of E. coli across epithelia and control colonic biopsy specimens, which was more striking in Crohn's disease biopsy specimens; the mitochondria-targeted antioxidant, MitoTEMPO, inhibited these barrier defects. Increased gut permeability and reduced epithelial mitochondrial voltage-dependent anion channel expression were observed 3 days after DSS. These changes and the severity of DSS-colitis were reduced by MitoTEMPO treatment. In vitro DSS-stimulated IL-8 production by epithelia was reduced by MitoTEMPO. Metabolic stress evokes significant penetration of commensal bacteria across the epithelium, which is mediated by mitochondria-derived superoxide acting as a signaling, not a cytotoxic, molecule. MitoTEMPO inhibited this barrier dysfunction and suppressed colitis in DSS-colitis, likely via enhancing barrier function and inhibiting proinflammatory cytokine production. These novel findings support consideration of MTAs in the maintenance of epithelial barrier function and the management of inflammatory bowel diseases.

Analysis of parasite-host interactions can reveal the intricacies of immunity and identify ways to modulate immunopathological reactions. We assessed the ability of a phosphate-buffered saline-soluble extract of adult Hymenolepis diminuta to suppress macrophage (human THP-1 cell line, murine peritoneal macrophages) activity in vitro and the impact of treating mice with this extract on colitis induced by dinitrobenzene sulfonic acid (DNBS). A high-molecular-mass fraction of adult H. diminuta (HdHMW) or excretory/secretory products reduced macrophage activation: lipopolysaccharide (LPS)-induced interleukin-1β (IL-1β), IL-6, and tumor necrosis factor alpha (TNF-α) and poly(I:C)-induced TNF-α and IL-6 were suppressed by HdHMW. The active component in the HdHMW extract was minimally sensitive to boiling and trypsin digestion, whereas the use of sodium metaperiodate, as a general deglycosylation strategy, indicated that the immunosuppressive effect of HdHMW was at least partially dependent on a glycan: treating the HdHMW with neuraminidase and α-mannosidase failed to inhibit its blockade of LPS-induced TNF-α production by THP-1 macrophages. Mice treated with DNBS developed colitis, as typified by wasting, shortening of the colon, macroscopic and microscopic tissue damage, and an inflammatory infiltrate. Mice cotreated with HdHMW (three intraperitoneal injections) displayed significantly less inflammatory disease, and this was accompanied by reduced TNF-α production and increased IL-10 and IL-4 production by mitogen-stimulated spleen cells. However, cotreatment of mice with neutralizing anti-IL-10 antibodies had only a minor impact on the anticolitic effect of the HdHMW. We speculate that purification of the immunosuppressive factor(s) from H. diminuta has the potential to lead to the development of novel immunomodulatory drugs to treat inflammatory disease.

No abstract

Interferon-g (IFNg) is an important immunoregulatory cytokine that can also decrease intestinal epithelial barrier function. Little is known about the intracellular signalling events immediately subsequent to IFNg/IFNg receptor interaction that mediate increases in epithelial permeability; data that could be used to ablate this effect of IFNg while leaving its immunostimulatory effects intact. This study assessed the potential involvement of Src family kinases in IFNg-induced increases in epithelial permeability using confluent filter-grown monolayers of the human colon-derived T84 epithelial cell line. Inhibition of Src kinase with the pharmacologic PP1 and use of Fyn kinase-specific siRNA significantly reduced IFNg-induced increases in epithelial permeability as gauged by translocation of noninvasive E. coli (HB101 strain) and flux of horseradish peroxidase (HRP) across monolayers of T84 cells. However, the drop in transepithelial resistance elicited by IFNg was not affected by either treatment. Immunoblotting revealed that IFNg activated the transcription factor STAT5 in T84 cells, and immunoprecipitation studies identified an IFNg-inducible interaction between STAT5b and the PI3K regulatory subunit p85a through formation of a complex requiring the adaptor molecule Gab2. siRNA targeting STAT5b and Gab2 reduced IFNg-induced increases in epithelial permeability and phosphorylation of PI3K(p85a). PP1 and Fyn siRNA reduced IFNg-induced PI3K activity (indicated by decreased phospho-Akt) and the formation of the STAT5b/PI3K(p85a) complex. Collectively, the results suggest the formation of a Fyn-dependent STAT5b/Gab2/PI3K complex that links IFNg to PI3K signalling and the regulation of macromolecular permeability in a model enteric epithelium.