Pro-oxidative vs antioxidative properties of ascorbic acid in chromium(VI)-induced damage: anin vivo andin vitro approach

Abstract

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.

Effect of Chromium Picolinate and Melatonin either in Single or in a Combination in Alloxan Induced Male Wistar Rats

“…However, the compounds which act as antioxidants should have redox cycling character (the ability to undergo reduction and oxidation repeatedly) to reduce free radicals. Vitamins react with ROS and themselves become pro-oxidants [15]. Pro-oxidants react with superoxide to generate highly reactive hydroxyl radicals.…”

Extra-cellular chromate-reducing activity of the yeast cultures

“…The modified tolerance of the mu-tant cells to chromate is accompanied with the changes in Cr(VI) uptake and chromium bioaccumulation [22]. It was shown that ascorbic acid influenced Cr(VI) toxicity both as an antioxidant, by decreasing intracellular reactive oxygen species, and as a reducing agent, by decreasing the level of Cr(V), a highly toxic intermediate in chromate reduction [23]. The effects of chromate on cell growth and lethality were studied using DNA repair-deficient S. cerevisiae mutants [24].…”

The antioxidant and pro‐oxidant activity of vitamin C and trolox in vitro: a comparative study

“…The defense system is present in aqueous and membrane compartments of cells and can be enzymatic or non-enzymatic. A second category of natural antioxidants involves repair processes that remove damaged biomolecules before they can accumulate and before their Vitamin C can promote metal ion-dependent hydroxyl radical formation in biological fluids Poljsak et al, 2005;Rietjens et al, 2002;Stearns et al, 1995). Burkitt and Milne (1996) also reported hydroxyl radical formation from Cu(II)-trolox mixtures.…”