Production of TNF-α and bone resorbing activity by macrophages in response to different types of bone cement particles

We have compared the capacity of clinically relevant wear debris from seven different cement types to activate macrophages to produce TNF-α, IL-1β, IL-6 and bone resorbing activity in vitro. The bone cements were: CMW 1 original (PMMA only); CMW 1RO (1 μm BaSO4; 9.2%); CMW copolymer bone cement 1 (10 μm BaSO4; 10%); CMW copolymer bone cement 2 (1 μm BaSO4; 10%); Palacos R (10 μm ZrO2; 15.6%); CMW Calcium phosphate cement 20% (10 μm tri-calcium phosphate; 20%) and CMW calcium phosphate cement 30% (10 μm tri-calcium phosphate; 30%). Cement debris was produced aseptically using a simple configuration wear test. The majority of particles were in the size range 0.1–0.5 μm for each cement type. The cement particles were co-cultured with the U937 macrophage cell line at ratios of 10 and 100 μm3 particle volumes to macrophage cell numbers for 24 h. At the 10 : 1 ratio the particles had no effect on the cells. At the 100 : 1 ratio, the major cytokine produced was TNF-α and there were no statistical differences between the different types of cement debris. The bone resorption activity of the co-culture supernatants was significantly greater than the control (U937 cells without particles) for particles of CMW 1RO, CMW copolymer bone cement 1, CMW copolymer bone cement 2 and Palacos R (P<0.05, ANOVA). However there were no statistical differences between the levels of bone resoprtion evoked by these four cement types. The CMW1 original and CMW calcium phosphate containing cements failed to induce the macrophages to elaborate bone resorption activity at the 100 : 1 ratio. These data suggest that the addition of radio-opaque additives to bone cement may increase the capacity of the debris to induce osteolysis.