Inhibitory effects of Lactobacillus casei subsp rhamnosus on Salmonella lipopolysaccharide-induced inflammation and epithelial barrier dysfunction in a co-culture model using Caco-2/peripheral blood mononuclear cells

[[abstract]]In this study, we investigated the anti-inflammatory and reinforcing barrier effects of Lactobacillus casei subsp. rhamnosus (Lcr35) on Caco-2 intestinal epithelial cells already exposed to Salmonella LPS. Using the Transwell co-culture model, Salmonella LPS was apically added to polarized Caco-2 cells co-cultured with peripheral blood mononuclear cells (PBMCs) in the basolateral compartment. LPS-stimulated Caco-2 cells were incubated with Lcr35 for 1, 6, 24 or 48 h. Apical inoculation of Lcr35 after 48 h significantly inhibited the basolateral secretion of interleukin-8 (IL-8) in the Caco-2/PBMC co-culture. The PCR analysis showed that Lcr35 significantly downregulated mRNA expression of monocyte chemoattractant protein 1 (MCP-1) (P<0.05) and had a trend of decreasing mRNA expression of IL-8 (P=0.05), but did not alter mRNA expression of transforming growth factor-β1 in LPS-stimulated Caco-2 cells at 48 h after addition of Lcr35. Compared to non-LPS-pretreated controls, transepithelial electrical resistance (TEER) of the polarized Caco-2 cell monolayers pretreated with LPS for 48 h was decreased by 9.9% (P<0.05). Additionally, compared to those cells only treated with LPS, apical co-incubation with Lcr35 showed biphasic TEER levels increased by 12.1% (P<0.001), 5.7% (P<0.05) and 86.8% (P