The influence of alumina and ultra-high molecular weight polyethylene particles on osteoblast-osteoclast cooperation

Particle-induced macrophage activation, mainly by UHMWPE wear, has been recognized as the biological mechanism leading to periprosthetic bone resorption, which is responsible for the loosening of the total hip replacements (THR). Ceramic-on-ceramic implants have been advocated as a means of reducing wear products. Many studies investigated the effect of alumina (Al2O3) particles on monocytes/macrophages, but only limited information are available on their participation to bone turnover. An in vitro model was performed to investigate how Al2O3 and UHMWPE particles may influence the osteoblast-osteoclast interaction: human osteoblasts (HOB) were obtained from trabecular bone, while osteoclasts were derived from peripheral blood mononuclear cells (PBMC) of healthy donors. The amount of IL6, TNFalpha, GM-CSF, and other factors acting on the bone turnover, i.e. the 'receptor activator of NFkB' ligand (RANKL) and osteoprotegerin (OPG), was detected in culture medium of particle-challenged HOB (HOB-CM). The Al2O3 and UHMWPE particles did not affect either cell viability or TNF and GM-CSF release, while the increase in IL6 release seemed to be dependent on the particle concentration. UHMWPE increased the release of RANKL from HOB, while OPG and OPG-to-RANKL ratio were significantly inhibited. The ability of HOB-CM to promote osteoclastogenesis was tested via osteoblast/monocyte cooperation: after seven days of culture UHMWPE HOB-CM induced a large amount of multinucleated TRAP-positive giant cells, as well as significantly reduced the amount of IL6, GM-CSF and RANKL in the supernatant. With regard to the inductive effect on the osteoclastogenesis, our results show that the Al2O3 wear debris are less active. (C) 2003 Elsevier Ltd. All rights reserved.