Cytotoxicity of cobalt chloride in brain cell lines - a comparison between astrocytoma and neuroblastoma cells

High levels of circulating cobalt ions in blood have been reported to induce systemic reactions in patients with metal-on-metal (MoM) hip implants. We still lack information regarding these adverse effects, which may specifically impact on patients showing adverse neurological symptoms. To investigate this, we used a battery of in vitro viability and proliferation assays to identify toxic cobalt chloride (CoCl2) concentrations in two different brain cell types: SH-SY5Y neuroblastoma and U-373 astrocytoma cells. Cobalt cytotoxicity was characterised by MTT and Neutral Red (NR) assays at concentrations ranging from 0 to 500 μM after 24, 48, and 72 h exposure. MTT and NR showed a dose- and time-dependent toxicity with cobalt decreasing cell viability at high concentrations. IC50s for MTT at 72 h (astrocytes: 333.15 ± 22.88; neurons: 100.01 ± 5.91 μM) and for BrdU proliferation assays (astrocytes: 212.89 ± 9.84; neurons: 88.86 ± 19.03 μM) demonstrate that SH-SY5Y neurons are significantly more vulnerable to cobalt than astrocytes. Increased BrdU and MTT assay sensitivity suggested that DNA synthesis and metabolism disruption were involved in Co toxicity. Intracellular cobalt level measured by ICP-MS was significant after 100 μM treatment. Astrocytes displayed improved resistance to cobalt toxicity and higher uptake, which may reflect their neuroprotective nature. In summary, exposure to high concentrations of extracellular cobalt has deleterious effects in neurons and astrocytes, with neurons showing particular sensitivity.