Quantification of metal ion induced DNA damage with single cell array based assay

Under physiological and wear conditions, implanted orthopedic devices undergo undesired release of metal ions which cause DNA damage and inflammation of local tissue. However, individuals have personalized responses to identical devices due to varying susceptibility to DNA damage. The current one-size-fits-all approach is therefore not suitable to predict the response of patients to implanted devices. This paper describes a single cell array based method to quantify metal ion induced DNA damage that can potentially be used to predict the response to implanted devices in patients. Ions of several typical metals in implanted devices were used to treat human normal fibroblast cells. After patterning cells on a silicon substrate with cell-catching patches, cells were embedded in hydrogel and treated with alkaline buffer. Damaged DNAs diffuse out of the cell, and are stained to show a characteristic halo. All studied metal ions (Cu2+, Co2+, Ni2+, Cr2+, Fe2+, Al3+) induce DNA damage and have genotoxicity. Copper ions cause DNA damage at concentrations as low as 1 mu M. Cobalt and nickel ions damage DNA at 5 and 10 mu M, respectively. Aluminum, iron and chromium ions cause DNA damage at 50 mu M. The cytotoxicity assay shows that most ions, except cobalt and copper, are less toxic below 500 mu M. The fact that metal ions can cause genotoxicity at lower concentrations than that of cytotoxicity suggests: (1) a single cell based DNA damage assay is more sensitive than a membrane integrity based live/dead assay; and (2) metal ions preferentially induce DNA damage rather than cell membrane damage.