THE RESPONSE OF PRIMARY RAT AND HUMAN OSTEOBLASTS AND AN IMMORTALIZEDRAT OSTEOBLAST CELL-LINE TO ORTHOPEDIC MATERIALS - COMPARATIVE SENSITIVITY OF SEVERAL TOXICITY INDEXES

When studying the biocompatibility of orthopaedic biomaterials it is o ften necessary to discriminate between responses which show mild cytot oxicity. It is therefore essential to use a very sensitive index of to xicity. We have compared the sensitivity of four well-established indi ces of toxicity: total cell protein content, leakage of lactate dehydr ogenase (LDH), reduced glutathione content and the MTT assay, with tha t of a novel index, alkaline phosphatase (ALP) activity. Comparisons w ere made by detecting nickel chloride toxicity in osteoblasts. ALP act ivity, the novel method, proved the most sensitive index of toxicity a nd it provides a convenient automated assay for assessing the interact ions of materials with osteoblasts. The responses to nickel chloride a nd to aqueous extracts prepared from carbon fibre reinforced epoxy and polyetheretherketone (peek), two candidate materials for orthopaedic implants, were compared in primary and immortalized rat osteoblasts, a nd in primary human osteoblasts. Although the immortalized rat osteobl ast cell line, FFC, was consistently the most sensitive cell type, the responses of the human cells and the FFC cell line were similar in te rms of ALP activity throughout the range of nickel concentrations stud ied. Neither peek nor epoxy material extracts showed a significant dec rease in the MTT or ALP responses in any of the three cell types. Our data suggest that immortalized rat osteoblasts may provide an in vitro model system for screening the biocompatibility of orthopaedic polyme rs.