Ethanol Extract of <i>Lilium</i> Bulbs Plays an Anti-Inflammatory Role by Targeting the IKKα/β-Mediated NF-κB Pathway in Macrophages

Abstract

Lilium bulbs have long been used as Chinese traditional medicines to alleviate the symptoms of various human inflammatory diseases. However, mechanisms of Lilium bulb-mediated anti-inflammatory activity and the bioactive components in Lilium bulbs remain unknown. In the present study, the anti-inflammatory activity of Lilium bulbs and the underlying mechanism of action were investigated in macrophages using Lilium bulb ethanol extracts (Lb-EE). In a dose-dependent manner, Lb-EE inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7 cells and bone marrow-derived macrophages (BMDMs) without causing significant cytotoxicity. Lb-EE also down-regulated mRNA expression of inflammatory genes in LPS-stimulated RAW264.7 cells, which included inducuble nitric oxide synthase (iNOS), cyclooxygenase-2 (COX2), and tumor necrosis factor-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> (TNF-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math>). Furthermore, Lb-EE markedly restored LPS-induced morphological changes in RAW264.7 cells to a normal morphology. HPLC analysis identified quercetin, luteolin, and kaempferol as bioactive components contained in Lb-EE. Mechanistic studies in LPS-stimulated RAW264.7 cells revealed that Lb-EE suppressed MyD88- and TRIF-induced NF-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math>B transcriptional activation and the nuclear translocation of NF-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math>B transcription factors. Moreover, Lb-EE inhibited IKK<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math>/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math>-induced activation of the NF-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math>B signaling pathway and IKK inhibition significantly reduced NO production in LPS-stimulated RAW264.7 cells. Taken together, these results suggest that Lb-EE plays an anti-inflammatory role by targeting IKK<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math>/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math>-mediated activation of the NF-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math>B signaling pathway during macrophage-mediated inflammatory responses.