Interactions of orthopaedic metals with an immortalized rat osteoblast cell line

The toxicity of nickel, chromium (III) and (VI), vanadium and aluminium was compared in an immortalized neonatal rat osteoblast cell line using the MTT assay and a novel index of cytotoxicity, alkaline phosphatase (ALP) activity. Where toxicity was observed, ALP was a consistently more sensitive detection method than the MTT assay. The toxicity of the metals increased in the order aluminium < chromium (III) < vanadium < nickel < chromium (VI). alpha-Tocopherol partially prevented nickel-induced toxicity (as assessed by ALP activity), whereas ascorbic acid had no protective effect. Chromium (VI) was more toxic than (III), with significant toxicity observed at 0.5 microM. It is thought that Cr (III) cannot readily penetrate the cell membrane and this may account for the lower toxicity. Aluminium had a stimulatory effect on cell growth at low concentrations (0.5 microM). The combination of immortalized rat osteoblasts and the ALP activity test provides a powerful tool for in vitro testing of orthopaedic materials.