Involvement of reactive oxygen stress in cadmium-induced cellular damage in Euglena gracilis

Inorganic cadmium (Cd) causes cellular damage to eukaryotes and to tissues of higher organisms, including DNA strand breaks and intracellular membrane damage, as a result of reactive oxygen stress. We previously reported cadmium chloride (CdCl2)-induced abnormal cell morphologies in the unicellular eukaryote Euglena gracilis Z (a plant cell model) and its achlorophyllous mutant SMZ strain (an animal cell model). The present study was undertaken to examine whether exposure of both strains to CdCl2 would lead to similar cellular responses, especially with regard to reactive oxygen stress loading and cellular damage. The results indicate that CdCl2 exposure can induce morphological alteration, linked to reactive oxygen stress. Both E. gracilis Z and SMZ cells subjected to short-term, high-dose CdCl2 exposure showed long 'comet lengths' in the so-called 'Comet' assay, indicating DNA strand breaks. Similarly, short-term, high-dose CdCl(2)-exposed cells and CdCl(2)-induced morphologically altered cells showed intense fluorescence of dihydrofluorescein (HFLUOR) after incubation with dihydrofluorescein diacetate (HFLUOR-DA). Positive data on the generation and involvement of intracellular reactive oxygen species (ROS) were obtained from long-term, low-dose CdCl(2)-exposed E. gracilis Z and SMZ, by thiobarbituric acid (TBA)-malondialdehyde (MDA) complex analyses.