Effect of dithiocarbamate pesticide zineb and its commercial formulation,azzurro: IV. DNA damage and repair kinetics assessed by single cell gel electrophoresis (SCGE) assay on Chinese hamster ovary (CHO) cells

Single cell gel electrophoresis (SCGE) was used to analyse dithiocarbamate zineb- and the zineb-containing technical formulation azzurro-induced DNA damage and repair in CHO cells. Cells were treated with zineb (50.0 μg/ml) or azzurro (100.0 μg/ml) for 80 min, washed and reincubated in pesticide-free medium for 0–12 h until SCGE. Viability of treated cells (0 h) did not differ from control remaining unchanged up to 6 h of incubation. After 12 h, viability decreased up to 70 and 54% in zineb- and azzurro-treated cultures, respectively. SCGE revealed at 0 h the absence of undamaged cells and an increase of slightly damaged and damaged cells in zineb-treated cultures or by an increase in damaged cells in azzurro-treated cultures. For both chemicals, a time-dependent repair of pesticide-induced DNA damage within a 0–12 h post-treatment incubation period was observed. Overall, damaged cells decreased as a function of the repair time for both pesticides while the slightly damaged cells decreased as a function of the repair time of zineb-induced DNA damage. Concomitantly, a time-dependent increase of undamaged cells was observed within the 0.5–12 h repair time for both pesticides. At 12 h after treatment, no differences in the frequencies of undamaged, slightly damaged and damaged cells were found between both zineb- or azzurro-treated cultures and control values as well as between zineb- and azzurro-treated cells. Immediately after exposure, nuclear DNA from zineb and azzurro-treated cells were larger and wider than nuclear DNA from untreated cells. When damaged cells were allowed to repair, a time-dependent decrease of the amount of free DNA migrating fragments was observed committed only to damaged cells but not in slightly or undamaged cells. On the other hand, no time-dependent alteration on nuclear DNA width within the 0–12 h repair period was observed.