Sugiyama M, Tsuzuki K, Ogura R
Department of Medical Biochemistry, Kurume University School of Medicine, Japan.
J Biol Chem. 1991 Feb 25;266(6):3383-6.
The effect of pretreatment with ascorbic acid (vitamin C) on chromate-induced DNA damage, cytotoxicity, and enzyme inhibition as well as on the cellular reduction of chromium(VI) was investigated using Chinese hamster V-79 cells. Cellular pretreatment with nontoxic levels of 1 mM ascorbic acid for 24 h prior to exposure resulted in a significant increase (1.7-fold) in cellular levels of this vitamin. Alkaline elution assays demonstrated that this pretreatment decreased cellular levels of Na2CrO4-induced alkali-labile sites while the numbers of DNA-protein crosslinks produced by chromate increased. In colony-forming assays, pretreatment with ascorbic acid enhanced the cytotoxicity of chromate. However, the inhibition of glutathione reductase attributed to Na2CrO4 was attenuated by this pretreatment. Under the same experimental condition, the uptake of chromate in pretreated cells was found to increase. ESR studies revealed that cellular pretreatment with ascorbic acid reduced the level of chromium(V) intermediate and increased the level of chromium(III) complex, indicating that cellular reduction of chromium(VI) to chromium(III) was accelerated by this vitamin. These results suggest that ascorbic acid decreases chromate-induced alkali-labile sites and chromium inhibition of glutathione reductase, but it enhances DNA-protein cross-links and cytotoxicity caused by this metal through its ability to directly reduce chromium(VI).
利用中国仓鼠V - 79细胞，研究了抗坏血酸（维生素C）预处理对铬酸盐诱导的DNA损伤、细胞毒性、酶抑制以及对铬（VI）细胞还原作用的影响。在暴露前用无毒水平的1 mM抗坏血酸对细胞进行24小时预处理，导致该维生素的细胞水平显著增加（1.7倍）。碱性洗脱试验表明，这种预处理降低了Na2CrO4诱导的碱不稳定位点的细胞水平，而铬酸盐产生的DNA - 蛋白质交联数量增加。在集落形成试验中，抗坏血酸预处理增强了铬酸盐的细胞毒性。然而，这种预处理减弱了由Na2CrO4引起的谷胱甘肽还原酶的抑制作用。在相同实验条件下，发现预处理细胞中铬酸盐的摄取增加。电子自旋共振研究表明，用抗坏血酸对细胞进行预处理降低了铬（V）中间体的水平并增加了铬（III）络合物的水平，表明这种维生素加速了铬（VI）向铬（III）的细胞还原。这些结果表明，抗坏血酸降低了铬酸盐诱导的碱不稳定位点和铬对谷胱甘肽还原酶的抑制作用，但通过其直接还原铬（VI）的能力增强了这种金属引起的DNA - 蛋白质交联和细胞毒性。
