Aims To investigate whether probiotics and/or prebiotics attenuate Salmonella typhimurium induced NF-κB activation via Smad7 and IκBα expression in the human colorectal epithelial CaCO₂ cells; to determine the molecular mechanisms of preventive effects of probiotics on intestinal infection.

Material and methods CaCO₂ cells were administered probiotic (Lactobicillus acidophilus) and/or prebiotic (inulin supplemented with oligofructose). Subsequently, the cells were infected with S. typhimurium. The culture supernatants and cell lysates were collected for cytokine determination and western blot analysis. The CaCO₂ cells were also transfected with plasmids containing Smads or NF-κB responsive reporter luciferase. After transfection, supernatants from cells were collected for luciferase assay. Involvement of miR-21 (Smad7 silencer) from supernatants of infected cells in the presence or absence of probiotics was determined.

Results The probiotics significantly suppressed NF-κB activation elevated by S. typhimurium. IL-8 mRNA was significantly lower in probiotics pretreated CaCO₂ cells compared with the cells infected with S. typhimurium alone. Synbiotics showed strongly suppressed effects on IL-8 and TNF-α gene transcriptions elevated by S. typhimurium. Pretreatment of probiotics increased IκBα expression level. Consistent with IκBα expression, pretreatment of probiotics increased 7 folds of Smad3/4 activity. The protein expressions of TGF-β and Smad7 in S. typhimurium infected cells with or without probiotics were determined by immunoblotting. Compared to S. typhimurium infection alone, pretreatment with probiotics and synbiotics induced 20 and 4 folds of miR 21 expressions, respectively.

Conclusions The experimental results showed that probiotics effectively attenuated Salmonella-induced intestinal inflammation in human intestinal CaCO₂ cells via TGF-β1/Smads and TGF-β1/miR21 signalling pathway.