Nutr Res Pract.  2013 Dec;7(6):423-429.

Luteolin and luteolin-7-O-glucoside inhibit lipopolysaccharide-induced inflammatory responses through modulation of NF-kappaB/AP-1/PI3K-Akt signaling cascades in RAW 264.7 cells

Affiliations
  • 1Department of Clinical Laboratory Science, Dong-Eui University, Busan 614-714, Korea.
  • 2Department of Smart Foods and Drugs, Inje University, 607 Obang-dong, Gimhae, Gyeongnam 621-749, Korea. fdsnsong@inje.ac.kr

Abstract

Luteolin is a flavonoid found in abundance in celery, green pepper, and dandelions. Previous studies have shown that luteolin is an anti-inflammatory and anti-oxidative agent. In this study, the anti-inflammatory capacity of luteolin and one of its glycosidic forms, luteolin-7-O-glucoside, were compared and their molecular mechanisms of action were analyzed. In lipopolysaccharide (LPS)-activated RAW 264.7 cells, luteolin more potently inhibited the production of nitric oxide (NO) and prostaglandin E2 as well as the expression of their corresponding enzymes (inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) than luteolin-7-O-glucoside. The molecular mechanisms underlying these effects were investigated to determine whether the inflammatory response was related to the transcription factors, nuclear factor (NF)-kappaB and activator protein (AP)-1, or their upstream signaling molecules, mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K). Luteolin attenuated the activation of both transcription factors, NF-kappaB and AP-1, while luteolin-7-O-glucoside only impeded NF-kappaB activation. However, both flavonoids inhibited Akt phosphorylation in a dose-dependent manner. Consequently, luteolin more potently ameliorated LPS-induced inflammation than luteolin-7-O-glucoside, which might be attributed to the differentially activated NF-kappaB/AP-1/PI3K-Akt pathway in RAW 264.7 cells.

Keyword

Luteolin; luteolin-7-O-glucoside; NF-kappaB; AP-1; PI3K; RAW

MeSH Terms

Apium graveolens
Capsicum
Cyclooxygenase 2
Dinoprostone
Flavones
Flavonoids
Glucosides
Inflammation
Luteolin*
Mitogen-Activated Protein Kinases
NF-kappa B
Nitric Oxide
Nitric Oxide Synthase
Phosphorylation
Taraxacum
Transcription Factor AP-1
Transcription Factors
Cyclooxygenase 2
Dinoprostone
Flavones
Flavonoids
Glucosides
Luteolin
Mitogen-Activated Protein Kinases
NF-kappa B
Nitric Oxide
Nitric Oxide Synthase
Transcription Factor AP-1
Transcription Factors

Figure

  • Fig. 1 Luteolin and luteolin-7-O-glucoside inhibited NO (A) and PGE2 (B) production in LPS-stimulated RAW 264.7 cells without cytotoxicity (C). Data represent the mean ± SD of triplicate experiments. Values sharing the same superscript are not significantly different at P < 0.05 by Duncan's multiple range test. Lu: Luteolin, Lu-7-G: luteolin-7-O-glucoside.

  • Fig. 2 Luteolin and luteolin-7-O-glucoside inhibited protein expression of iNOS and COX-2 in LPS-stimulated RAW 264.7 cells. Panel A shows protein expression levels of iNOS and COX-2 in response to luteolin and luteolin-7-O-glucoside. All signals were normalized to protein levels of β-actin, an internal control, and expressed as a ratio (Panel B). Data represent the mean ± SD of triplicate experiments. Values sharing the same superscript are not significantly different at P < 0.05 by Duncan's multiple range test. Lu: Luteolin, Lu-7-G: luteolin-7-O-glucoside.

  • Fig. 3 Luteolin and luteolin-7-O-glucoside inhibited phosphorylation of transcription factors, NFκB and AP-1, in LPS-stimulated RAW 264.7 cells. Panel A shows phosphorylated status of p65 and c-jun in response to luteolin and luteolin-7-O-glucoside. All signals were normalized to protein levels of β-actin, an internal control, and expressed as a ratio (Panel B). Data represent the mean ± SD of triplicate experiments. Values sharing the same superscript are not significantly different at P < 0.05 by Duncan's multiple range test. Lu: Luteolin, Lu-7-G: luteolin-7-O-glucoside.

  • Fig. 4 Luteolin and luteolin-7-O-glucoside inhibited translocation of p65 and c-jun in LPS-stimulated RAW 264.7 cells. Panel A and C show translocation of p65 and c-jun in response to luteolin and luteolin-7-O-glucoside. All signals were normalized to protein levels of β-actin and PARP internal controls for cytosolic and nucleic extracts, and expressed as a ratio (Panel B and D). Data represent the mean ± SD of triplicate experiments. Values sharing the same superscript are not significantly different at P < 0.05 by Duncan's multiple range test. Lu-7-G: luteolin-7-O-glucoside.

  • Fig. 5 Luteolin and luteolin-7-O-glucoside inhibited phosphorylation of Akt in LPS-stimulated RAW 264.7 cells. Panel A shows protein expression levels of p-Akt, p-ERK, p-JNK and p-p38 in response to luteolin and luteolin-7-O-glucoside. All signals were normalized to protein levels of Akt, ERK, JNK and p38 internal controls, an expressed as a ratio (Panel B). Data represent the mean ± SD of triplicate experiments. Values sharing the same superscript are not significantly different at P < 0.05 by Duncan's multiple range test.

  • Fig. 6 Schematic diagram illustrating inhibitory mechanisms of luteolin and luteolin-7-O-glucoside on LPS-induced inflammatory cascades in RAW 264.7 cells Lu: Luteolin, Lu-7-G: luteolin-7-O-glucoside.


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