Effect of size and dose on bone resorption activity of macrophages byin vitro clinically relevant ultra high molecular weight polyethylene particles

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Abstract
Polyethylene wear debris generated at the bearing surfaces of total artificial hip joints is thought to play an important role in the periprosthetic osteolysis and ultimately the aseptic loosening of these prostheses. The macrophage is believed to be central to this process by releasing various cytokines and other mediators of osteolysis upon phagocytosis of the polyethylene wear debris. This study evaluated the in vitro bone resorption response of C3H murine peritoneal macrophages to clinically relevant GUR 1120 polyethylene particles. Macrophages were co-cultured in vitro with GUR 1120 particles with a mean size of 0.24, 0.45, 1.71, and 7.62, and GUR 1120 polyethylene resin with a mean size of 88 μm at various particle volume (μm)3: macrophage ratios (0.1:1; 1:1; 10:1; and 100:1). The conditioned supernatants were incubated with 45calcium radio-labeled mouse calvariae, and bone resorption was measured as 45calcium release. The results showed that the 0.24 μm particles stimulated the macrophages to generate bone resorbing activity at a ratio of 10(μm)3 per macrophage. The 0.45 and 1.71μm particles were active at a ratio of 100(μm)3 per macrophage, and the 7.62 and 88 μm particles were inactive at all the doses tested. The co-culture supernatants were also assayed for TNF-α, IL-1β, IL-6, and PGE2. The results followed the same trend for particle size and volume dose to that observed for the bone resorbing activity. This study has demonstrated, for the first time, the importance of size and dose of clinically relevant polyethylene particles on the osteolytic response of macrophages in vitro. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 53: 490–497, 2000

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