Abstract
Background: Intestinal epithelial cells (IECs) are increasingly recognized as an essential player in the regulation of intestinal immune homeostasis. During inflammatory bowel diseases (IBDs) several chemokines have a dysregulated pattern of expression on IEC contributing to the sustained mucosal inflammation in IBD. Avoiding inappropriate activation of TLR4 via NF-kB inhibition, during IBD, might have a translational readout because epithelial cells are in constant contact with a dense and complex milieu of commensal microorganisms. In addition to the antimicrobial activity, rifaximin a poorly absorbed antibiotic, acts as a gut-specific human PXR ligand Aims. To investigate whether rifaximin regulates epithelial intestinal immune homeostasis through a PXR-dependent mechanism. Methods. CRL-1831 cells, a normal colonic human epithelial cell line (ATCC), were exposed to LPS (1 μg/ml for 20 h) alone and in combination with rifaximin (50 μM). Cytokines and chemokines generation wasmeasured by RT-PCR and ELISA. NF-kB binding activity by EMSA. Additional experiments were carried out in CRL-1831 cells in after PXR silencing (siPXR). Biopsy specimens obtained from CD patients, were cultured with LPS (100 mg/ml) alone or in combination with rifaximin (100 μM) for 18h. Results. CRL-1831 cells express PXR. In comparison to wild type cells, PXR silencing decreased the TGF-β and IP-10 production (P< 0.05) while generation of TNF-α, IL-8, RANTES, PGE2 and MIP-3α and IL-6 mRNA levels were increased (P< 0.05). LPS stimulation further enhanced the production of TNFα, IL-8, Rantes, PGE2, and MIP-3α mRNA levels in siPXR cells (P<0.05). LPS stimulation increased TGF-β production in cell line and siPXR cells. Rifaximin causes a robust attenuation of inflammatory response caused by LPS (P< 0.05), while increased TGF-β (P< 0.05) and IL-6 mRNA (P < 0.05). si PXR abrogated completely the ability of rifaximin to change the IEC's immune profile. Rifaximin cotreatment LPS induced NF-κB DNA binding activityin a PXR-dependent manner. Exposure of colon biopsies to rifaximin reduces the generation of IL-8, Rantes and TNFα caused by LPS and iboosted TGF-β production. Conclusions. Rifaximin regulates IEC immune functions by a PXR mediated mechanism. Attenuation of endotoxin-induced immune activation of epithelial cells might contribute to the immunomodulatory activities of rifaximin in IBDs.
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