TY - JOUR
T1 - Effects of Ginkgo biloba extract (EGb 761) and quercetin on lipopolysaccharide-induced signaling pathways involved in the release of tumor necrosis factor-α
AU - Wadsworth, Teri L.
AU - McDonald, Tasha L.
AU - Koop, Dennis R.
N1 - Funding Information:
The authors thank Dr. T. Schmeller (Dr. Willmar Schwabe GmbH) for the gift of EGb 761 and Ms. Tanya Hudson for technical assistance. This work was supported by grants from the Oregon Wine Advisory Board and the National Institute on Alcohol Abuse and Alcoholism (AA08608).
PY - 2001/10/1
Y1 - 2001/10/1
N2 - Administration of bacterial lipopolysaccharide (LPS) to laboratory animals and cultured macrophages induces tumor necrosis factor-α (TNF-α), a pro-inflammatory cytokine. Pretreatment with Ginkgo biloba extract (EGb 761) inhibited the in vivo production of TNF-α (measured by ELISA) after challenge with LPS. To begin to understand the mechanism of this inhibition, we evaluated the in vitro effects of EGb 761 and its flavonoid component, quercetin, on LPS-treated RAW 264.7 macrophages. Pretreatment with EGb 761 or quercetin concentration-dependently inhibited TNF-α release, as measured by the L929 fibroblast assay. Northern blotting demonstrated that quercetin inhibited LPS-induced TNF-α mRNA, but did not alter its half-life. Activation of mitogen-activated protein kinases (MAPKs) and the redox-sensitive transcription factors, nuclear factor-κB (NF-κB) and activator protein 1 (AP-1), are key events in the signal transduction pathways mediating TNF-α induction. Phosphorylation of extracellular signal-related kinases 1 and 2 (ERK 1/2), p38 MAPK, and Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), members of the MAPK family, was analyzed by western blotting. Our results suggest that quercetin is unique in its ability to inhibit TNF-α transcription by inhibiting the phosphorylation and activation of JNK/SAPK and, therefore, suppressing AP-1-DNA binding [assessed by electrophoretic mobility shift analysis (EMSA)]. Results from western analysis, EMSA, and transient transfections suggest that EGb 761 diminishes LPS-induced NF-κB but has no effect on LPS-induced TNF-α transcription. Both EGb 761 and quercetin inhibited ERK1/2 phosphorylation and p38 MAPK activity, which are important in the post-transcriptional regulation of TNF-α mRNA.
AB - Administration of bacterial lipopolysaccharide (LPS) to laboratory animals and cultured macrophages induces tumor necrosis factor-α (TNF-α), a pro-inflammatory cytokine. Pretreatment with Ginkgo biloba extract (EGb 761) inhibited the in vivo production of TNF-α (measured by ELISA) after challenge with LPS. To begin to understand the mechanism of this inhibition, we evaluated the in vitro effects of EGb 761 and its flavonoid component, quercetin, on LPS-treated RAW 264.7 macrophages. Pretreatment with EGb 761 or quercetin concentration-dependently inhibited TNF-α release, as measured by the L929 fibroblast assay. Northern blotting demonstrated that quercetin inhibited LPS-induced TNF-α mRNA, but did not alter its half-life. Activation of mitogen-activated protein kinases (MAPKs) and the redox-sensitive transcription factors, nuclear factor-κB (NF-κB) and activator protein 1 (AP-1), are key events in the signal transduction pathways mediating TNF-α induction. Phosphorylation of extracellular signal-related kinases 1 and 2 (ERK 1/2), p38 MAPK, and Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), members of the MAPK family, was analyzed by western blotting. Our results suggest that quercetin is unique in its ability to inhibit TNF-α transcription by inhibiting the phosphorylation and activation of JNK/SAPK and, therefore, suppressing AP-1-DNA binding [assessed by electrophoretic mobility shift analysis (EMSA)]. Results from western analysis, EMSA, and transient transfections suggest that EGb 761 diminishes LPS-induced NF-κB but has no effect on LPS-induced TNF-α transcription. Both EGb 761 and quercetin inhibited ERK1/2 phosphorylation and p38 MAPK activity, which are important in the post-transcriptional regulation of TNF-α mRNA.
KW - EGb 761
KW - MAPK
KW - Macrophage
KW - Quercetin
KW - TNF-α
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U2 - 10.1016/S0006-2952(01)00734-1
DO - 10.1016/S0006-2952(01)00734-1
M3 - Article
C2 - 11543732
AN - SCOPUS:0035479909
SN - 0006-2952
VL - 62
SP - 963
EP - 974
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
IS - 7
ER -