Glascott P A, Gilfor E, Farber J L
Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Mol Pharmacol. 1995 Jul;48(1):80-8.
The relationship between the metabolism of alpha-tocopherol (alpha-T) (vitamin E) and that of ascorbic acid (vitamin C) was examined in cultured hepatocytes intoxicated with tert-butyl hydroperoxide (TBHP). Unlike vitamin E, the cellular content of vitamin C did not decline after overnight culturing of freshly prepared hepatocytes. In addition, this basal vitamin C content was not affected by the presence of alpha-T phosphate in the overnight culture medium. Supplementation of the overnight culture medium with vitamin C (10 microM to 10 mM) increased the cellular content of vitamin C by > 1 order of magnitude. Increasing the cellular content of ascorbate increased the protection against TBHP toxicity, with or without the presence of a physiological content of vitamin E. In vitamin E-supplemented cells, a loss of alpha-T occurred within 15 min of exposure to TBHP and before the decrease in cellular ascorbate content. The vitamin C content declined in parallel with the loss of cell viability. Supplementation of the overnight culture medium with increasing concentrations of ascorbate progressively spared the depletion of alpha-T while preventing the cell killing. Pretreatment with the ferric iron chelator deferoxamine or the antioxidant N,N'-diphenyl-1,4-phenylenediamine prevented the loss of ascorbate and the cell killing by TBHP in hepatocytes either sufficient or deficient in alpha-T. However, neither alpha-T nor ascorbate prevented the accumulation of DNA single-strand breaks caused by TBHP, indicating that these vitamins do not effectively scavenge the TBHP-derived radicals responsible for DNA damage. The data in the present study indicate that vitamins E and C act as independent antioxidants and that ascorbate does not regenerate alpha-T in cultured rat hepatocytes.
在经叔丁基过氧化氢（TBHP）处理的培养肝细胞中，研究了α-生育酚（α-T，维生素E）与抗坏血酸（维生素C）代谢之间的关系。与维生素E不同，新鲜制备的肝细胞过夜培养后，维生素C的细胞含量并未下降。此外，过夜培养基中α-T磷酸盐的存在并不影响这种基础维生素C含量。在过夜培养基中添加维生素C（10微摩尔至10毫摩尔）可使维生素C的细胞含量增加超过1个数量级。无论是否存在生理含量的维生素E，增加抗坏血酸的细胞含量均可增强对TBHP毒性的保护作用。在补充了维生素E的细胞中，暴露于TBHP后15分钟内且在细胞抗坏血酸含量下降之前，α-T就发生了损失。维生素C含量与细胞活力的丧失平行下降。在过夜培养基中添加浓度不断增加的抗坏血酸可逐渐减少α-T的消耗，同时防止细胞死亡。用铁螯合剂去铁胺或抗氧化剂N，N'-二苯基-1,4-苯二胺预处理可防止α-T充足或缺乏的肝细胞中抗坏血酸的损失以及TBHP引起的细胞死亡。然而，α-T和抗坏血酸均不能阻止TBHP引起的DNA单链断裂的积累，这表明这些维生素不能有效清除导致DNA损伤的TBHP衍生自由基。本研究中的数据表明，维生素E和C作为独立的抗氧化剂起作用，并且在培养的大鼠肝细胞中抗坏血酸不能再生α-T。
