Effect of Polyethylene on Osteocalcin, Alkaline Phosphatase and Procollagen Secretion by Human Osteoblastic Cells

We have studied the direct effects of polyethylene particles on osteoblastic function in primary human bone cell cultures. The cells were obtained from trabecular bone fragments of patients undergoing knee reconstructive surgery. When the cells reached confluency, they were subcultured into two flasks, one untreated (control culture) and the other treated with polyethylene particles, and incubated until confluency. Osteoblastic function was evaluated by assaying osteocalcin, alkaline phosphatase, and C-terminal procollagen type I, with and without 1,25(OH)2D stimulation, in the cell-conditioned medium. We found that addition of polyethylene to these osteoblastic cell cultures induced higher levels of secreted osteocalcin after 1,25(OH)2D stimulation. Alkaline phosphatase levels increased whereas C-terminal procollagen type I levels decreased in the cell conditioned medium after polyethylene was added to the cultures. Treatment of the control cultures with 1,25(OH)2D stimulated alkaline phosphatase levels and decreased C-terminal procollagen type I. However, these osteoblastic markers in 1,25(OH)2D-treated cells did not change in cultures with polyethylene. This study demonstrates that polyethylene particles have a direct effect on osteoblastic markers in human bone cells in culture.