Vitamin C Inhibits NF-kB Activation by TNF Via the Activation of p38 Mitogen-Activated Protein Kinase1

The transcription factor NF-kB is a central mediator of altered gene expression during inflammation, and is implicated in a number of pathologies, including cancer, atherosclerosis, and viral infection. We report in this study that vitamin C inhibits the activation of NF-kB by multiple stimuli, including IL-1 and TNF in the endothelial cell line ECV304 and in primary HUVECs. The induction of a NF-kB-dependent gene, IL-8, by TNF was also inhibited. The effect requires millimolar concentrations of vitamin C, which occur intracellularly in vivo, particularly during inflammation. Vitamin C was not toxic to cells, did not inhibit another inducible transcription factor, STAT1, and had no effect on the DNA binding of NF-kB. Inhibition by vitamin C was not simply an antioxidant effect, because redox-insensitive pathways to NF-kB were also blocked. Vitamin C was shown to block IL-1-and TNF-mediated degradation and phosphorylation of I-kBa (inhibitory protein that dissociates from NF-kB), due to inhibition of I-kB kinase (IKK) activation. Inhibition of TNF-driven IKK activation was mediated by p38 mitogen-activated protein kinase, because treatment of cells with vitamin C led to a rapid and sustained activation of p38, and the specific p38 inhibitor SB203580 reversed the inhibitory effect of vitamin C on IKK activity, I-kBa phosphorylation, and NF-kB activation. The results identify p38 as an intracellular target for high dose vitamin C. The Journal of Immunology, 2000, 165: 7180–7188. V itamin C (ascorbic acid) is required in the diets of hu-mans and several other species that lack the terminalenzyme in its synthetic pathway, L-gulonolactone oxi-dase (1). It is involved in a number of vital functions within cells, including the hydroxylation reactions of collagen biosynthesis (2) and the facilitation of iron transport (3), as well as being one of the most important physiological antioxidants (4). The current recom-mended dietary allowance (1) for vitamin C is 60 mg/day for non-smoking adult males, which is sufficient to prevent scurvy (5). However, vitamin C has been suggested as having both a preven-tative and therapeutic role in a number of other pathologies when administered at much higher-than-recommended dietary allowance levels, including cancer (6), atherosclerosis (7), and viral infec