Investigating cobalt toxicity in the context of joint replacement patients - cobalt uptake in primary cardiac fibroblasts and in 3T3 cells

Cobalt leaches out from cobalt/chromium metal-on-metal hip implants into patient blood, and its effects are thought to be toxic. There has been a 5% estimated incidence of adverse effects, including toxicity to the heart, in joint implant patients over the last 40 years. This was investigated by examination of the effects of CoCl2 on cell proliferation and viability performed using a range of assays. To assess effects on proliferation, MTT, neutral red and crystal violet assays were all used to compare effects of increasing concentrations of CoCl2 on the Swiss 3T3 fibroblast cell line (3T3s) and primary cardiac fibroblasts (CFs). CoCl2 induced toxicity in both 3T3s and CFs in a time- and dose-dependent manner with IC50 values for CoCl2 in the range of ~300 µM in both cells. Over 72h, increasing CoCl2 concentrations (up to 500 µM) resulted in decreased proliferation. Interestingly, in terms of proliferation, the 3T3s were more tolerant of CoCl2 than CFs. Uptake of CoCl2 into the 3T3s and CFs was measured by detecting intracellular metal content using ICP-MS. Cells were cultured and exposed to various concentrations of CoCl2 (0-72 ppm) and different exposure times (24, 48 and 72 h). Analysis of cobalt content of cells revealed that with increasing medium concentration of CoCl2 intracellular Co concentration on both 3T3s and CFs increased, to a range between 0-50 ppb and 0-120 ppb, respectively. Uptake into CFs was greater than into the 3T3s, and this at least partly explains the difference in toxicity between the two cell types.