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Administration of bacterial lipopolysaccharide (LPS) to laboratory animals and cultured macrophages induces tumor necrosis factor-alpha (TNF-alpha), a pro-inflammatory cytokine. Pretreatment with Ginkgo biloba extract (EGb 761) inhibited the in vivo production of TNF-alpha (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-alpha release, as measured by the L929 fibroblast assay. Northern blotting demonstrated that quercetin inhibited LPS-induced TNF-alpha mRNA, but did not alter its half-life. Activation of mitogen-activated protein kinases (MAPKs) and the redox-sensitive transcription factors, nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1), are key events in the signal transduction pathways mediating TNF-alpha 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-alpha 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-kappaB but has no effect on LPS-induced TNF-alpha transcription. Both EGb 761 and quercetin inhibited ERK1/2 phosphorylation and p38 MAPK activity, which are important in the post-transcriptional regulation of TNF-alpha mRNA.

Administration of bacterial lipopolysaccharide (LPS) to laboratory animals and cultured macrophages induces tumor necrosis factor-alpha (TNF-alpha), a pro-inflammatory cytokine. Pretreatment with Ginkgo biloba extract (EGb 761) inhibited the in vivo production of TNF-alpha (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-alpha release, as measured by the L929 fibroblast assay. Northern blotting demonstrated that quercetin inhibited LPS-induced TNF-alpha mRNA, but did not alter its half-life. Activation of mitogen-activated protein kinases (MAPKs) and the redox-sensitive transcription factors, nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1), are key events in the signal transduction pathways mediating TNF-alpha 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-alpha 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-kappaB but has no effect on LPS-induced TNF-alpha transcription. Both EGb 761 and quercetin inhibited ERK1/2 phosphorylation and p38 MAPK activity, which are important in the post-transcriptional regulation of TNF-alpha mRNA.

The beneficial effects of moderate red wine consumption have been attributed, in part, to the presence of antioxidant components. Oxidant stress is an activating stimulus for the NF (nuclear factor)-KB/Rel family of transcription factors, which have binding sites in the promoter regions of many genes involved in inflammatory and immune responses. The effect of lipopolysaccharide (LPS)-stimulated activation of NF-KB and the subsequent production of tumor necrosis factor alpha (TNF-alpha) and NO was determined in the macrophage cell line RAW 264.7. Unexpectedly, the wine polyphenolics quercetin and resveratrol and the antioxidant N-acetylcysteine (NAC) did not inhibit LPS-induced activation of the NF-KB complex p50/65, as determined by mobility shift. Quercetin inhibited LPS-induced p50/50. Northern blot analysis indicated that quercetin (0.1 and 0.2 mM) inhibited LPS-dependent production of inducible nitric oxide synthase (iNOS) mRNA and decreased NO release, as measured by the Griess reaction. This flavonoid had no effect on LPS-induced TNF-alpha mRNA, but decreased LPS-stimulated TNF-alpha release, as measured by ELISA. Resveratrol (0.05 and 0.1 mM) posttranscriptionally decreased LPS-induced nitrite release. It increased basal levels of TNF-alpha mRNA and protein and enhanced LPS-induced TNF-alpha mRNA and cytokine release. Our results do not support the view that wine antioxidants inhibit LPS-induced NF-KB activation but instead that they have a more selective action on genes activated by LPS.

In this study, using a combination of immunological and enzymatic characterizations, we compared the forms of cytochrome P-450 induced by ethanol and glutethimide in primary cultures of chicken embryo hepatocytes. Recently we purified a cytochrome P-450 of 50K molecular weight from chicken embryo liver using glutethimide as a prototypic inducer. Antibodies to both this chicken cytochrome P-450 and to rabbit cytochrome P-450 form 3a from the IIE subfamily detected microsomal proteins of 50K induced by either ethanol or glutethimide in cultured chick embryo hepatocytes, indicating the antigenic homology of these subfamilies of cytochromes P-450 among different animal species. However, the antibody to glutethimide-induced chick cytochrome P-450 of 50K inhibited p -nitrophenol hydroxylase and benzphetamine demethylase activities 85–90% in microsomes from both ethanol- and glutethimide-treated cells, indicating similar epitopes whose integrity is required for catalytic activity. In contrast, antibodies to rabbit cytochrome P-450 form 3a had little to no effect on these same microsomal activities. Both ethanol and glutethimide induced microsomal p -nitrophenol and aniline hydroxylase activities in cultured chick embryo hepatocytes. In microsomes from ethanol-treated cells, the turnover of p -nitrophenol per cytochrome P-450 was 2-fold greater than that induced by glutethimide treatment, suggesting that ethanol is inducing a form of cytochrome P-450 that has greater catalytic activity with this substrate than glutethimide-induced forms. Thus, in cultured chick embryo hepatocytes, ethanol may induce cytochromes P-450 from both the IIB and IIE subfamilies.

Immunoblot analysis of liver microsomes from nine patients demonstrated that each contained a cytochrome P-450 that reacted with an antibody directed against the ethanol-inducible rabbit liver cytochrome, P-450 3a. Two of the liver specimens exhibited high concentrations of the immunoreactive protein, high rates of aniline hydroxylation and N-nitrosodimethylamine demethylation, and extensive inhibition of activity in the presence of antibody to P-450 3a. One other liver specimen exhibited a very low rate of aniline hydroxylation with significantly less antibody inhibition. The variability witnessed was independent of the alcohol history of the individual patients, suggesting that the human cytochrome may be under some other environmental, dietary or genetic regulation. Its inducibility by ethanol was not directly studied in this investigation. However, we conclude that there is a cytochrome P-450 present in human liver which is immunochemically and catalytically similar to the ethanol-inducible P-450 of rabbit liver.