Inhibition of NF-κB transcriptional activity by α-tocopheryl succinate

The role of vitamin E in cell regulation in addition to its function as an antioxidant has attracted attention. The effects of alpha-tocopherol (T) and alpha-tocopheryl succinate (TS) on transcriptional activation of the tumor necrosis factor alpha (TNF-alpha) gene and nuclear factor kappa B (NF-kappa B) activation were examined. Two stable transformants were used: TR-1 cells derived from THP-1 cells transfected with a vector contains the human TNF-alpha promoter (1.4-kb) joined to the human placental alkaline phosphatase (PLAP) coding sequence, and B164 cells derived from the same cell line but carrying the vector containing the human beta-actin promoter (4.3-kb) as a control. The transfectants were cultured in the presence of TS, followed by stimulation with lipopolysaccharide (LPS). After stimulation, PLAP activity secreted into the culture medium was measured. TS reduced TNF-alpha transcriptional activity in a concentration-dependent manner, while no effect was observed on that of the beta-actin promoter. Gel shift assay revealed that THP-1 cells pretreated with TS and then with LPS showed inhibition of NF-kappa B activity by 43% at 50 mu M versus the TS-untreated group. Since TS did not affect activator protein-1 (AP-1) activity under the same conditions, the inhibitory effect of TS on NF-kappa B activation might be specific. However, T had no effect on the results of the gel shift assay. Vitamin E transportation was analyzed by simultaneous determination of vitamin E and its derivatives using HPLC. The vitamin E recovered from culture pellets showed almost the same amounts of T and TS transferred and was recovered in unchanged form. These observations indicated that TS inhibited NF-kappa B activation and/or translocation to the nuclei in its unchanged form under the culture conditions used here. These results suggested that vitamin E is involved in signal transduction via an effect distinct from its antioxidant function. To explain the lack of activity with T, it remains to be clarified whether physiological incorporation of T occurred.