Involvement of Nuclear Factor-κB in the Inhibition of Interleukin-12 Production from Mouse Macrophages by Baicalein, a Flavonoid inScutellaria baicalensis

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Abstract
Pharmacological inhibition of interleukin-12 (IL-12) production may be a therapeutic strategy for preventing development and progression of disease in experimental models of autoimmunity. In this study we investigated the effects of baicalein, a flavonoid present in the root of Scutellaria baicalensis, on the production of IL-12 from mouse macrophages stimulated with lipopolysaccharide (LPS). Baicalein potently inhibited the LPS-induced IL-12 production from both primary macrophages and RAW264.7 monocytic cell-line in a dose-dependent manner (the IC50 values were 43.7 and 17.4 μM, respectively). The effect of baicalein on IL-12 gene promoter activation was analyzed by transfecting RAW264.7 cells with IL-12 gene promoter/luciferase constructs. The repressive effect mapped to a region in the IL-12 gene promoter containing a binding site for NF-κB. Furthermore, activation of macrophages by LPS resulted in markedly enhanced binding activity to the NF-κB site, which significantly decreased upon addition of baicalein, indicating that baicalein inhibited IL-12 production in LPS-activated macrophages via inhibition of NF-κB binding activity. IL:interleukin LPS:lipopolysaccharide NK-κB:nuclear factor-κB Th1:T helper type 1 ELISA:enzyme-linked immunosorbent assay PCR:polymerase chain reaction

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