Ginkgo biloba extract (EGb 761): Inhibitory effect on nitric oxide duction in the macrophage cell line RAW 264.7

The present study was conducted to evaluate the effect of Ginkgo biloba extract (EGb 761) on the synthesis of nitric oxide (NO) induced by lipopolysaccharide (LPS) plus interferon-γ (IFN-γ) in the mouse macrophage cell line RAW 264.7. EGb 761 inhibited nitrite and nitrate production, taken as an index for NO, in a concentration-dependent fashion. The IC₅₀ for inhibition of nitrite production by activated macrophages was about 100 μg/mL EGb 761. The inducible NO synthase (iNOS) enzyme activity of cytosolic preparations from activated RAW 264.7 cells was inhibited by treatment with EGb 761. In addition, reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that the expression of iNOS mRNA in activated macrophages was suppressed by high concentrations of EGb 761. However, NF-κB DNA binding activity induced by activation with LPS/IFN-γ was not inhibited by EGb 761. These findings indicate that not only does EGb 761 directly act as an NO scavenger but also that it inhibits NO production in LPS/IFN-γ-activated macrophages by concomitant inhibition of induction of iNOS mRNA and the enzyme activity of iNOS. Thus, EGb 761 may act as a potent inhibitor of NO production under tissue-damaging inflammatory conditions.