Abstract
Flavonols possess several beneficial bioactivities in vitro and in vivo. In this study, two flavonols galangin and quercetin with or without heat treatment (100 °C for 15–30 min) were assessed for their anti-inflammatory activities in lipopolysaccharide (LPS)-stimulated rat intestinal epithelial (IEC-6) cells and whether the heat treatment caused activity changes. The flavonol dosages of 2.5–20 μmol/L had no cytotoxicity on the cells but could enhance cell viability (especially using 5 μmol/L flavonol dosage). The flavonols could decrease the production of prostaglandin E2 and three pro-inflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α, and simultaneously promote the production of two anti-inflammatory cytokines IL-10 and transforming growth factor-β. The Western-blot results verified that the flavonols could suppress the LPS-induced expression of TLR4 and phosphorylated IκBα and p65, while the molecular docking results also illustrated that the flavonols could bind with TLR4 and NF-κB to yield energy decreases of −(21.9–28.6) kJ/mol. Furthermore, an inhibitor BAY 11-7082 blocked the NF-κB signaling pathway by inhibiting the expression of phosphorylated IκBα/p65 and thus mediated the production of IL-6/IL-10 as the flavonols did, which confirmed the assessed anti-inflammatory effect of the flavonols. Consistently, galangin had higher anti-inflammatory activity than quercetin, while the heated flavonols (especially those with longer heat time) were less active than the unheated counterparts to exert these target anti-inflammatory effects. It is highlighted that the flavonols could antagonize the LPS-caused IEC-6 cells inflammation via suppressing TLR4/NF-κB activation, but heat treatment of the flavonols led to reduced anti-inflammatory efficacy.
Highlights
When the cells were treated with galangin and quercetin at these dosages for three time periods (6, 12, and 24 h), the results from the classic MTT assay indicated that the treated cells had viability values of
The previous results had revealed that a variety of food components could suppress intestinal inflammation and were regarded capable of maintaining the health of the body; for example, the peptide fractions from the dehydrated potatoes possessed anti-inflammatory activity to IEC-6 cells [21], while the polysaccharide from Schizophyllum commune could recover the DSS-induced colitis in the inflamed tissues, and showed an anti-inflammatory effect on the intestine [22]
The results demonstrated that the flavonols could exert anti-inflammatory activities against the LPS-induced inflammation in IEC-6 cells, via increasing the production of two anti-inflammatory mediators and decreasing the production of four inflammatory mediators
Summary
The intestinal epithelium, as an important element of the intestinal barrier, can protect the body from the entrance of various harmful substances including bacteria and endotoxins. LPS comes from the outer membrane of the Gram-negative bacteria and is well-known for its ability to induce food poisoning; LPS can impair the barrier function of the epithelial cells and induce cellular inflammation simultaneously [1]. It is known that the damaged intestinal lumen leads to an easier entrance of toxins into the body circulation, which thereby might promote the release of inflammatory factors, 4.0/). It is vital for us to maintain normal intestinal barrier function and alleviate the LPS-induced intestinal inflammation. There is growing evidence demonstrating the beneficial effects of natural polyphenols in the body, including their barrier protection and intestinal anti-inflammatory function
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