Nuclear factor κB 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-careinogenic signaling factors in cultured Raw 264.7 macrophages after SFN treatment, i.e. NO, prostaglandin E-2, and tumor necrosis factor a. SFN did not directly interact with NO, nor did it inhibit inducible nitric-oxide synthase enzymatic activity. Western blot analyses revealed time- and 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 factor-DNA binding. Consequently, nuclear factor kappaB (NF-kappaB), a pivotal transcription factor in LPS-stimulated proinflammatory response, was identified as the key mediator. SFN selectively reduced DNA binding of NF-kappaB without interfering with LPS-induced degradation of the inhibitor of NF-kappaB nor with nuclear translocation of NF-kappaB. Because SFN can interact with thiol. groups by dithiocarbamate formation, it may impair the redox-sensitive DNA binding and transactivation of NF-kappaB. Sulforaphane could either directly inactivate NF-kappaB subunits by binding to essential Cys residues or interact with glutathione or other redox regulators like thioredoxin and Ref-1 relevant for NF-kappaB function. Our data provide novel evidence that anti-inflammatory mechanisms contribute to sulforaphane-mediated cancer chemoprevention.