Intestinal epithelial cells are confronted with many noxious stimuli which play an important role in the mucosal immune response. In the present study, Caco-2 cells treated with hydrogen peroxide were used as a model system for studying inflammatory responses and induction of cell death. Live lactobacilli and their concentrated spent culture supernatant (SCS) were applied for studying possible short- and long-term protective effects against hydrogen peroxide-mediated oxidative stress in Caco-2 cells. The secretion of pro-inflammatory cytokine interleukin-8 (IL-8) was investigated in non-filter grown Caco-2 cells, while transepithelial electrical resistance and cell death was studied in filter grown Caco-2 cells. Pre-incubation of Caco-2 cells with Lactobacillus plantarum 2142 did not decrease IL-8 levels induced by 1 mM hydrogen peroxide, nor did lactobacilli suppress IL-8 levels induced by hydrogen peroxide when Caco-2 cells were treated simultaneously with 1 mM hydrogen peroxide and L. plantarum 2142. Thus, lactobacilli did not exert a long-term protective effect against hydrogen peroxide in non-filter grown Caco-2 cells. However, the concentrated SCS of lactobacilli was able to reduce IL-8 levels by more than 6-fold, as determined 24 h after treatment. A short-term effect of lactobacilli was observed in filter grown Caco-2 cells, as they inhibited cell death induced by hydrogen peroxide in the concentration range 10-40 mM. Pre-incubation of epithelial cells with L. plantarum 2142 or simultaneous exposure to hydrogen peroxide and lactobacilli protected Caco-2 cells against cell death. In spite of the presence of lactobacilli, the permeability of membrane increased (transepithelial electrical resistance decreased), and exhibited a similar characteristic pattern as under treatment with hydrogen peroxide alone.
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