Quercetin Inhibits Inflammatory Response Induced by LPS<i> from Porphyromonas gingivalis</i> in Human Gingival Fibroblasts via Suppressing NF-<i>κ</i>B Signaling Pathway

Abstract

Quercetin, a natural flavonol existing in many food resources, has been reported to be an effective antimicrobial and anti-inflammatory agent for restricting the inflammation in periodontitis. In this study, we aimed to investigate the anti-inflammatory effects of quercetin on <i>Porphyromonas gingivalis</i> (<i>P. gingivalis</i>) lipopolysaccharide- (LPS-) stimulated human gingival fibroblasts (HGFs). HGFs were pretreated with quercetin prior to LPS stimulation. Cell viability was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. The levels of inflammatory cytokines, including interleukin-1<i>β</i> (IL-1<i>β</i>), interleukin-6 (IL-6), and tumor necrosis factor-<i>α</i> (TNF-<i>α</i>), along with chemokine interleukin-8 (IL-8), were determined by enzyme-linked immunosorbent assay (ELISA). The mRNA levels of IL-1<i>β</i>, IL-6, IL-8, TNF-<i>α</i>, I<i>κ</i>B<i>α</i>, p65 subunit of nuclear factor-kappa B (NF-<i>κ</i>B), peroxisome proliferator-activated receptor-<i>γ</i> (PPAR-<i>γ</i>), liver X receptor <i>α</i> (LXR<i>α</i>), and Toll-like receptor 4 (TLR4) were measured by real-time quantitative PCR (RT-qPCR). The protein levels of I<i>κ</i>B<i>α</i>, p-I<i>κ</i>B<i>α</i>, p65, p-p65, PPAR-<i>γ</i>, LXR<i>α</i>, and TLR4 were characterized by Western blotting. Our results demonstrated that quercetin inhibited the LPS-induced production of IL-1<i>β</i>, IL-6, IL-8, and TNF-<i>α</i> in a dose-dependent manner. It also suppressed LPS-induced NF-<i>κ</i>B activation mediated by TLR4. Moreover, the anti-inflammatory effects of quercetin were reversed by the PPAR-<i>γ</i> antagonist of GW9662. In conclusion, these results suggested that quercetin attenuated the production of IL-1<i>β</i>, IL-6, IL-8, and TNF-<i>α</i> in <i>P. gingivalis</i> LPS-treated HGFs by activating PPAR-<i>γ</i> which subsequently suppressed the activation of NF-<i>κ</i>B.