Poljsak B, Gazdag Z, Jenko-Brinovec S, Fujs S, Pesti M, Bélagyi J, Plesnicar S, Raspor P
University Polytechnic Nova Gorica, School of Environmental Science, Vipavska 13, 5000 Nova Gorica, Slovenia.
J Appl Toxicol. 2005 Nov-Dec;25(6):535-48. doi: 10.1002/jat.1093.
The effect of antioxidant ascorbic acid (vitamin C) pretreatment on chromium(VI)-induced damage was investigated using the yeast Saccharomyces cerevisiae as a model organism. The objective of this study was to pretreat yeast cells with the antioxidant ascorbic acid in an effort to increase cell tolerance against reactive chromium intermediates and reactive oxygen species formed during chromium(VI) reduction. Intracellular oxidation was estimated using the fluorescence indicators dihidro-2,7-dichlorofluorescein, dihydroethidium and dihydrorhodamine 123. The role of ascorbic acid pretreatment on chromium(VI) toxicity was determined by measuring mitotic gene conversion, reverse mutations, 8-OHdG, hydroxyl radical, superoxide anion and chromium(V) formation. The chromium content in the biomass was determined by flame atomic absorption spectrometry. In the absence of chromium, ascorbic acid effectively protected the cells against endogenous reactive oxygen species formed during normal cellular metabolism. In vitro measurements employing EPR and the results of supercoiled DNA cleavage revealed that the pro-oxidative action of ascorbic acid during Cr(VI) reduction was concentration-dependent and that harmful hydroxyl radical and Cr(V) had formed following Cr(VI) reduction. However, the in vivo results highlighted the important role of increased cytosol reduction capacity related to modification of Cr(V) formation, increased chromium accumulation, better scavenging ability of superoxide anions and hydrogen peroxide, and consequently decreased cytotoxicity and genotoxicity in ascorbic acid pretreated cells. Ascorbic acid influenced Cr(VI) toxicity both as a reducing agent, by decreasing Cr(V) persistence, and as an antioxidant, by decreasing intracellular superoxide anion and hydrogen peroxide formation and by quenching free radicals formed during Cr(VI) to Cr(III) reduction. Increased 8-OHdG and decreased reduced glutathione in ascorbic acid-treated cells might induce an endogenous antioxidant defense system and thus increase cell tolerance against subsequent Cr-induced stress.
以酿酒酵母作为模式生物，研究了抗氧化剂抗坏血酸（维生素C）预处理对六价铬诱导损伤的影响。本研究的目的是用抗氧化剂抗坏血酸预处理酵母细胞，以提高细胞对六价铬还原过程中形成的活性铬中间体和活性氧的耐受性。使用荧光指示剂二氢-2,7-二氯荧光素、二氢乙锭和二氢罗丹明123估计细胞内氧化。通过测量有丝分裂基因转换、回复突变、8-羟基脱氧鸟苷、羟基自由基、超氧阴离子和五价铬的形成，确定抗坏血酸预处理对六价铬毒性的作用。通过火焰原子吸收光谱法测定生物质中的铬含量。在没有铬的情况下，抗坏血酸有效地保护细胞免受正常细胞代谢过程中形成的内源性活性氧的影响。采用电子顺磁共振的体外测量结果和超螺旋DNA切割结果表明，抗坏血酸在六价铬还原过程中的促氧化作用是浓度依赖性的，并且在六价铬还原后形成了有害羟基自由基和五价铬。然而，体内结果突出了与五价铬形成的改变相关的胞质还原能力增加、铬积累增加、超氧阴离子和过氧化氢的清除能力增强的重要作用，因此抗坏血酸预处理细胞的细胞毒性和遗传毒性降低。抗坏血酸作为还原剂通过降低五价铬的持久性，以及作为抗氧化剂通过减少细胞内超氧阴离子和过氧化氢的形成以及淬灭六价铬还原为三价铬过程中形成的自由基，影响六价铬的毒性。抗坏血酸处理的细胞中8-羟基脱氧鸟苷增加和还原型谷胱甘肽减少可能诱导内源性抗氧化防御系统，从而提高细胞对随后铬诱导应激的耐受性。
