濱 進

Tocopheryl succinate (TS), a succinyl ester of α-tocppherol (α-T), has been reported to have various biological activities. In this communication, we review the current findings about TS including our recent studies of its effects on nitric oxide (NO) and Superoxide (O2-) generations implicated in cancer and atherosclerosis. First, we investigated the effect of TS on NO production in vascular smooth muscle cells (VSMC) under atherosclerosis-like conditions using lipopolysaccharide (LPS) and interferon-γ (IFN). TS enhanced LPS/IFN-dependent NO production, but α-T itself did not. The enhancement by TS of NO production was inhibited by α-T but not by antioxidants such as ascorbic acid and 2[3]-t-butyl-4-hydroxy-anisole (BHA). TS enhanced the amount of protein kinase Cα (PKCα) in VSMC, and PKC inhibitors inhibited TS-enhanced NO production, suggesting that the enhancing effect of TS on NO production is caused by up-regulation of PKC. Second, we found that TS induced apoptosis in VSMC associated with increase in O2- generation via NADPH-dependent oxidase. We further observed that a mouse breast cancer cell line C127I was more susceptible for TS-induced apoptosis than a mouse breast normal cell line NmuMG, and that Superoxide dismutase, α-T, and BHA inhibited TS-caused morphological cell damage in C127I. From these results, O2- itself and/or other reactive oxygen species are assumed to associate with TS-induced cell toxicity, and antioxidative defense systems are supposed to be lowered in cancer cells. Finally, we found that intravenous injection of TS vesicles completely inhibited the growth of melanoma cells B16-F1 inoculated on the back of hairless mice and enhanced their survival time.

The effect of α-tocopheryl succinate (TS) on protein kinase C (PKC) activity was examined. TS increased the auto-phosphorylation of PKC in vascular smooth muscle cells. Furthermore TS activated isolated PKC-like phorbol 12-myristate 13-acetate (PMA), although it was required at a significantly higher concentration than PMA for PKC activation. Molecular superimposition of the TS on PMA by computation suggested that TS took an active binding conformation to the PKC-like PMA, but that the conformational population was about 1/1.000. Consequently, we conclude that TS interacts directly with PKC, and activates it by taking an active conformation like PMA.

We examined the effect of α-tocopheryl hemisuccinate (TS) on the growth of mouse melanoma cells B16-F1 inoculated on the back of hairless mice by two administration procedures of TS, i.p. administration of TS dissolved with dimethyl sulfoxide (TS i.p.) and i.v. administration of TS vesicles (TS-vesicle i.v.). TS i.p. significantly prevented the tumor growth of only half the mice in the group. However, TS-vesicle i.v. almost completely inhibited the tumor growth of all mice. Furthermore, the mean survival of the TS-vesicle i.v. group was 1.4-fold those of the control and TS i.p. groups. © 2002 Elsevier Science Ireland Ltd. All rights reserved.

α-Tocopheryl hemisuccinate (TS) has been reported to induce apoptosis in various cells, and to show higher toxicity to cancer cells than to normal cells. In this study, although TS induced apoptosis in both a mouse breast normal cell line NMuMG and a mouse breast cancer cell line C127I, the latter were more susceptible to TS. TS-induced apoptosis in C127I was inhibited by superoxide dismutase, α-tocopherol and butylated hydroxyanisol. From these results, superoxide (O2-) itself and reactive oxygen species derived from O2-and/or free radicals are assumed to be associated with TS toxicity, and the high toxicity of TS to cancer cells is suggested to be due to failure of their antioxidative defense systems. © 2002 Elsevier Science Ireland Ltd. All rights reserved.

The effect of α-tocopheryl hemisuccinate (TS) on lipopolysaccharide (LPS)/interferon-γ (IFN)-induced nitric oxide production in rat vascular smooth muscle cells (VSMC) was examined. The LPS/IFN-induced NO production was enhanced by TS but not by the other α-tocopherol (α-T) derivatives α-tocopheryl acetate (TA) and α-tocopheryl nicotinate (TN), or α-T itself. α-T, TA and TN inhibited the enhancement by TS of LPS/IFN-induced NO production. The enhancing effect of TS was observed in the presence of LPS, but not IFN, suggesting that TS participates in the LPS-stimulated signal pathway leading to NO production. Protein kinase C (PKC) inhibitors, but not protein kinase A inhibitors, inhibited the enhancing effect of TS on LPS/IFN-induced NO production. Furthermore, TS enhanced the amount of PKCα in VSMC. From these results, we concluded that the enhancing effect of LPS/IFN-induced NO production was caused by upregulation of PKC in VSMC.

We investigated the mechanism of cell toxicity of α-tocopheryl hemisuccinate (TS). TS concentration- and time-dependently induced the lactate dehydrogenase release and DNA fragmentation of rat vascular smooth muscle cells (VSMC). Exogenous addition of superoxide dismutase, but not catalase, significantly inhibited the cell toxicity of TS. The NADPH-dependent oxidase activity of VSMC was stimulated by TS treatment. The cell toxicity of TS was inhibited by NADPH oxidase inhibitor 4-(2-aminoethyl)-benzenesulfonyl fluoride. Consequently, TS-induced apoptosis of VSMC was suggested to be caused by exogenous O2- generated via the oxidase system activated with TS. © 2001 Elsevier Science B.V. All rights reserved.