Nuclear Factor B Is a Molecular Target for Sulforaphane-mediated Anti-inflammatory Mechanisms*

Sulforaphane (SFN), an aliphatic isothiocyanate, is a known cancer chemopreventive agent. Aiming to investigate anti-inflammatory mechanisms of SFN, we here report a potent decrease in lipopolysaccharide (LPS)induced secretion of pro-inflammatory and pro-carcinogenic signaling factors in cultured Raw 264.7 macrophages after SFN treatment, i.e. NO, prostaglandin E2, and tumor necrosis factor . SFN did not directly interact with NO, nor did it inhibit inducible nitric-oxide synthase enzymatic activity. Western blot analyses revealed timeand dose-dependent reduction of LPS-induced inducible nitric-oxide synthase as well as Cox-2 protein expression, which was suppressed at the transcriptional level. To reveal the target of SFN beyond its anti-inflammatory action, we performed electrophoretic mobility shift assay analyses of transcription factorDNA binding. Consequently, nuclear factor B (NFB), a pivotal transcription factor in LPS-stimulated proinflammatory response, was identified as the key mediator. SFN selectively reduced DNA binding of NFB without interfering with LPS-induced degradation of the inhibitor of NFB nor with nuclear translocation of NFB. Because SFN can interact with thiol groups by dithiocarbamate formation, it may impair the redoxsensitive DNA binding and transactivation of NFB. Sulforaphane could either directly inactivate NFB subunits by binding to essential Cys residues or interact with glutathione or other redox regulators like thioredoxin and Ref-1 relevant for NFB function. Our data provide novel evidence that anti-inflammatory mechanisms contribute to sulforaphane-mediated cancer chemoprevention.