On the role of hydroxyl radical and the effect of tetrandrine on nuclear factor-κB activation by phorbol 12-myristate 13-acetate

Nuclear factor κB (NF-κB) is considered to be an important target for therapeutic intervention because of its role in the regulation of proinflammatory and profibrotic mediators. The present study examined the role of hydroxyl (·OH) radical and the effect of tetrandrine, an alkaloid extracted from the Chinese medicinal herb Stephania tetrandra, on NF-κB activation by a tumor promoter, phorbol 12-myristate 13-acetate (PMA) in human lymphoid T cells (ie, Jurkat cells). Exogenous superoxide dismutase (SOD) enhanced the NF-κB activation by PMA, while catalase blocked it. Formate, a scavenger of ·OH radical, also was inhibitory, as was deferoxamine, a metal chelator. These data suggest an important role of ·OH radical in PMA-induced NF-κB activation. Incubation of the cells with tetrandrine prior to the stimulation of the cells was found to inhibit PMA- induced NF-κB activation. Tetrandrine activity was so potent that 50 μM of tetrandrine was sufficient to inhibit activation of NF-κB completely. Electron spin resonance (ESR) spin trapping was used to investigate the antioxidant action of tetrandrine using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap. Tetrandrine is an antioxidant for both ·OH and superoxide (O₂^-)radicals. The reaction rate constant of tetrandrine with ·OH is 1.4 x 10¹⁰ M^-1 sec^-1, which is comparable with several well established antioxidants, such as ascorbate, glutathione, and cysteine. The Fenton reaction (Fe(II) + H₂O₂ → Fe(III) + ·OH + OH^-) and xanthine/xanthine oxidase were used as sources of ·OH and O₂^- radicals. The free radical scavenging activity of tetrandrine is responsible for its inhibition of PMA-induced NF-κB activation.