Inhibition of nuclear factor κB by direct modification in whole cells -: Mechanism of action of nordihydroguaiaritic acid, curcumin and thiol modifiers

This study was set up to investigate the mechanism of four inhibitors of interleukin-1 (IL-1)-alpha and tumor necrosis factor-(TNF)alpha activated nuclear factor kappa B (NF kappa B) in whole cells. The compounds fall into two classes: the first comprised two chain-breaking antioxidants, curcumin (diferulolylmethane) and nordihydroguaiaritic acid. The second class were two thiol-modifying agents, N-ethylmaleimide (NEM) and 2-chloro-1,3-dinitrobenzene (CDNB). Both sets of compounds were found to inhibit NF kappa B in tumour necrosis factor-activated Jurkat T lymphoma cells and interleukin 1-activated EL4.NOB-1 thymoma cells as determined by electrophoretic mobility shift assay using a specific NF kappa B DNA probe. In unstimulated cells the compounds were found to modify NF kappa B prior to chemical dissociation with sodium deoxycholate. They also inhibited DNA binding by NF kappa B when added to nuclear extracts from stimulated cells. Both of these effects occurred over a concentration range comparable to that which inhibited cytokine-activated NF kappa B in intact cells. All four agents were found to react directly with the p50 subunit of NF kappa B. However, only the antioxidants, curcumin and nordihydroguaiaritic acid (NDGA) were found to inhibit I kappa B alpha degradation activated by tumour necrosis factor-alpha. These results suggest that NF kappa B itself is susceptible to direct inhibition by a range of pharmacological agents. Furthermore, curcumin and nordihydroguaiaritic acid inhibit NF kappa B by interfering with I kappa B alpha degradation and reacting with p50 in the NF kappa B complex. These findings are likely to be useful in the attempt to develop agents which inhibit NF kappa B-dependent gene transcription. (C) 1998 Elsevier Science Inc.