Search

The effect of cadmium ion (Cd) and ascorbic acid (Asc) on the induction of oxidative DNA damage and on the activities of antioxidant enzymes were investigated in human lymphoblastoid cells (AHH-1 TK+/-). Cd at low concentrations of 5-35 microM induced the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and caused nuclear DNA strand breaks. The formation both of 8-OHdG and of DNA strand breaks was dose-dependent at the low Cd concentration; both parameters were linearly correlated with each other (R = 0.932 and P = 0.0209). 8-OHdG formation by Cd plateaued at a Cd concentration of 50 microM. Asc also induced 8-OHdG formation, but it had no synergistic effect with Cd on the formation of 8-OHdG or DNA strand breaks. Cd at the concentration of 50 microM induced the nuclear activity of the antioxidant enzymes, catalase and superoxide dismutase (SOD). Furthermore, Cd caused a decrease in the concentration of reduced glutathione (GSH) and an increase in concentration of the oxidized form (GSSG). While Asc had no observable effect on SOD activity, it did increase nuclear catalase activity in cells. This effect on catalase was synergistic with that of Cd. The linear correlation between 8-OHdG and DNA strand breaks induced by Cd at the lower Cd concentrations (< or = 50 microM), suggested that the extent of formation of DNA strand breaks induced by Cd may be offset by their induction of the formation of 8-OHdG and antioxidant enzyme activities.

The interactive effects of the anti-oxidant ascorbate (Asc) and the metals cadmium (Cd, as CdCl2) or nickel (Ni, as NiCl2) on the in vitro formation of breaks in double-stranded deoxyribonucleic acid (d/s DNA) were determined. Concentrations of 50 microM Cd or 200 microM Ni were dosed for 4 hours in factorial combinations with 500 microM Asc in RPMI 1640 medium (7 percent bovine serum) in which AHH-1 TK+/- cells (a spontaneously transformed human B lymphoblastoid cell line by Gentest Corp.) were replicating. In combination with Asc, Cd caused significant d/s DNA breaks (p < 0.01, n = 5), while Cd in the absence of Asc produced only a slight (but not significantly different) amount of d/s DNA damage when compared to the cells with no Cd added. The Asc alone was not damaging. The Cd caused damage to the d/s DNA only when Asc was present. The percent of d/s DNA remaining following the respective treatments was: +Cd+Asc, 13 +/- 3; +Cd-Asc, 46 +/- 8; -Cd+Asc, 54 +/- 5; -Cd-Asc, 55 +/- 7. Conversely, the presence of Ni resulted in increased amounts (percent) of d/s DNA compared to control values: +Ni+Asc, 63 +/- 5; +Ni-Asc, 58 +/- 5; -Ni+Asc, 52 +/- 1; -Ni-Asc, 51 +/- 4, (p < 0.05, n = 3). The contrasting results between Cd and Ni in the presence of Asc may reside in the point of action; while Cd acts directly on DNA, Ni is reported to act on heterochromatin. Although Asc is a recognized anti-oxidant, its presence in the media mixture potentiated d/s DNA damage from the Cd. This may be caused by a Fenton-type reaction in which an antioxidant in the presence of metal generates hydroxyl radicals and consequently d/s DNA breaks. Oxidative reactions between metals, oxygen, and antioxidants such as Asc may represent an important mechanism of cell death, toxicity, and transformation.

Magnesium, an essential metal that is important in the normal functioning of DNA, has been shown to interact with some of the toxic heavy metals in respect to biochemical and molecular mechanisms and in altering the tumorigenic process. This study examined the influence of magnesium in combination with nickel and cadmium in respect to damage of the DNA molecule. The purpose of this study was to evaluate the influence of magnesium on the amelioration of the toxic metals nickel and cadmium in respect to sustaining DNA damage. Two types of lymphocytes were used, i.e., primary Fischer 344 rat splenocytes and AHH-1 TK+/-, a human B-lymphoblastoid cell line that has been spontaneously transformed. These cells were grown in either a magnesium-free or magnesium-supplemented RPMI 1640 medium that was specifically formulated for this study. A 2 x 2 factorial design was employed with magnesium and either nickel or cadmium serving as the two factors. The experimental groups were as follows: +Mg+Ni, +Mg-Ni, -Mg+Ni, -Mg-Ni, with cadmium alternating for the nickel in the subsequent studies. The nickel or cadmium was added at a concentration of 50 mumol/L. The presence of double-stranded DNA was determined in each of the respective treatment groups with the two types of cell lines. Based on the results of this study, nickel is not directly toxic to DNA, whereas cadmium produces damage directly on the DNA molecule.(ABSTRACT TRUNCATED AT 250 WORDS)