| Summary: | Oxidative stress in the small intestine can lead to inflammation and barrier malfunction. The present study describes the effect of quercetin (Q), 3-o-methylquercetin (QM), and rhamnazin (R) on cell viability, paracellular permeability, production of intracellular reactive oxygen species (ROS), extracellular hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), and interleukin-6 (IL-6) after challenging jejunal cells (IPEC-J2) with different types (<i>Salmonella enterica</i> ser. Typhimurium, <i>Escherichia coli</i> O111:B4, and <i>E. coli</i> O127:B8) of lipopolysaccharides (LPS) applied in 10 µg/mL concentration. The intracellular ROS level increased after all LPS treatments, which could be decreased by all tested flavonoid compounds in 50 µM concentration. Extracellular H<sub>2</sub>O<sub>2</sub> production significantly increased after Q and R treatment (50 µM). <i>S</i>. Typhimurium LPS could significantly increase IL-6 production of enterocytes, which could be alleviated by Q, QM, and R (50 µM) as well. Using fluorescein isothiocyanate dextran (FD4) tracer dye, we could demonstrate that <i>S</i>. Typhimurium LPS significantly increased the permeability of the cell layer. The simultaneous treatments of <i>S.</i> Typhimurium LPS and the flavonoid compounds showed no alteration in FD4 penetration compared to untreated cells. These results highlight that Q, QM, and R are promising substances that can be used to protect intestinal epithelial cells from the deteriorating effects of oxidative stress.
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