Cadmium Induces Apoptosis in the Human Osteoblast-like Cell Line Saos-2

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Human exposure to the heavy metal cadmium has been associated with the development of bone diseases, including osteoporosis and osteomalacia. The mechanisms by which cadmium exerts a direct effect on bone remain unclear. Bone cells go through apoptosis for proper bone remodeling; therefore, it was hypothesized that cadmium disrupts this normal balance by inducing apoptosis. Human osteoblast-like cells (Saos-2) were treated with 10–200 μM cadmium chloride (CdCl2) and evaluated by trypan blue staining and phase-contrast microscopy. Exposure to CdCl2 resulted in decreased cell viability and changes in cell morphology characteristic of apoptosis. The role of apoptosis in cadmium-induced toxicity was further evaluated using the fluorescent marker annexin V, which detects externalization of cell membrane phosphatidylserine. Nuclear changes associated with apoptosis were assessed by Hoechst staining and a DNA fragmentation assay. A significant increase in annexin V-positive cells was observed following CdCl2 treatment. Nuclear changes associated with apoptosis, including marginalization and condensing of chromatin and DNA fragmentation, were also observed following CdCl2 treatment. Cadmium-induced apoptosis in Saos-2 cells was also accompanied by an increase in caspase-3 activity. The addition of the caspase-3 inhibitor N-acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) or the known cadmium chelating agent potassium bis(2-hydroxyethy)dithiocarbamate, (K[bhedtc]), blocked caspase-3 activation induced by cadmium. Collectively, this study has identified a role for apoptosis in cadmium-induced toxicity in bone cells, and provides insight for future studies on mechanisms underlying the disruption of apoptotic signaling cascades in bone and the relationship to bone disease.