Nuclear factor kappa B is a molecular target for sulforaphane-mediated anti-inflammatory mechanisms

Sulforaphane (SFN), an aliphatic isothiocyanate, is a known cancer chemopre ventive agent. Aiming to investigate anti-inflammatory mechanisms of SFN, w e here report a potent decrease in lipopolysaccharide (LPS)induced secretio n of pro-inflammatory and pro-careinogenic signaling factors in cultured Ra w 264.7 macrophages after SFN treatment, i.e. NO, prostaglandin E-2, and tu mor necrosis factor a. SFN did not directly interact with NO, nor did it in hibit inducible nitric-oxide synthase enzymatic activity. Western blot anal yses revealed time- and dose-dependent reduction of LPS-induced inducible n itric-oxide synthase as well as Cox-2 protein expression, which was suppres sed at the transcriptional level. To reveal the target of SFN beyond its an ti-inflammatory action, we performed electrophoretic mobility shift assay a nalyses of transcription factor-DNA binding. Consequently, nuclear factor k appaB (NF-kappaB), a pivotal transcription factor in LPS-stimulated proinfl ammatory response, was identified as the key mediator. SFN selectively redu ced DNA binding of NF-kappaB without interfering with LPS-induced degradati on of the inhibitor of NF-kappaB nor with nuclear translocation of NF-kappa B. Because SFN can interact with thiol. groups by dithiocarbamate formation , it may impair the redox-sensitive DNA binding and transactivation of NF-k appaB. Sulforaphane could either directly inactivate NF-kappaB subunits by binding to essential Cys residues or interact with glutathione or other red ox regulators like thioredoxin and Ref-1 relevant for NF-kappaB function. O ur data provide novel evidence that anti-inflammatory mechanisms contribute to sulforaphane-mediated cancer chemoprevention.