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 CdCl₂-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.