Elsevier

Biomaterials

Volume 25, Issue 18, August 2004, Pages 4037-4045
Biomaterials

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

https://doi.org/10.1016/j.biomaterials.2003.10.100Get rights and content

Abstract

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, TNFα, 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.

Introduction

Total hip replacement (THR), one of the greatest advances in orthopaedic surgery in the twentieth century, has considerably improved the quality of life of patients affected by osteoarthritis of the hip. However, a number of hip arthroplasties ultimately fail due to the loosening of their components, periprosthetic osteolysis standing as the major factor limiting the longevity of prosthetic implants. Bone loss around the implant is responsible for approximately 60–70% of failures due to aseptic loosening, predisposes to periprosthetic fracture, and markedly complicates subsequent revision surgery.

Most hip prostheses consist of a metal femoral head coupled with an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. Debris particles usually derive from the wear of the articulating components, and the particulate matter released from the UHMWPE component has been recognized as one of the major concerns for the long-term durability of THR. Phagocytosis of those particles is responsible for triggering a severe inflammatory reaction mediated by the release of cytokines and other soluble mediators. These factors favor osteoclast activity and, consequently, activate focal bone resorption. Once osteolysis ensues, it tends to progress and ultimately leads to implant failure [1], [2], [3].

Since the longevity of total joint prostheses is affected by the wear of their components, one of the main objectives of orthopaedic research is to validate different bearing surfaces with a reduced mechanical wear. Alumina (Al2O3) ceramic-on-ceramic hip prostheses offer as a good alternative to conventional metal-on-polyethylene coupling due to their low wear rate associated with satisfactory clinical results. A review of the authors’ experience with alumina-on-alumina bearings has shown that osteolysis is not a problem at a medium-term follow-up [4]. The alumina-on-alumina bearing has been compared with a cobalt chrome-on-polyethylene bearing in a multicentric, prospective, randomized study: in the short-term (48 months) the clinical performance of the two groups were comparable [5]. With alumina-on-alumina THR, minimal wear rates and limited osteolysis can be expected up to twenty years after the operation [6]. Wear particles released from ceramic-on-ceramic couplings are smaller than those released from conventional polyethylene-on-metal bearings, producing a similar active total surface area, which seems to be a crucial point for the entity of the cellular response. Several studies have shown that 0.1–1 μm particles are the most harmful to cells [2], [5], [7], [8], [9]. This kind of particles is easily phagocytosed by monocytes/macrophages and is able to induce an inflammatory reaction following cytokine release: at present the biological response of macrophages to the wear debris has been thoroughly explored, and their role in the pathogenesis of the periprosthetic osteolysis has been defined [1]. Although macrophages are the first cell type which respond to debris, direct contact of wear particles with bone cells may occur at the bone-implant interface [9].

In this study, an in vitro model was set up to investigate the osteoblast–osteoclast interaction in the presence of implant degradation products: human osteoblasts (HOB) were obtained from trabecular bone of patients undergoing primary THR, while osteoclasts were derived from circulating peripheral blood mononuclear cells (PBMC) of healthy donors. Wear debris consisted of pure Al2O3 or UHMWPE particles at different weight/volume concentrations. The ability of the particles to induce cells to release factors acting on the bone turnover was tested. Interleukin 6 (IL6), granulocyte-macrophage colony stimulating factor (GM-CSF), tumor necrosis factor alfa (TNFα, prostaglandins (PGE2) [9], and other mediators belonging to the TNF family have been suggested as key factors in the development and progression of osteolytic lesions [10], [11]. The TNF family includes the ‘receptor activator of NFkB’ ligand (RANKL) which binds two types of receptors. The first one, known as the ‘osteoclast differentiation and activation receptor’ (RANK), is expressed in pre-osteoclasts and its binding activates the cascade of intracellular events to complete osteoclast differentiation and activation. The second one is osteoprotegerin (OPG), also reported as an ‘osteoclastogenesis inhibitory factor’, a decoy receptor that is able to limit the biologic functions of RANKL. OPG suppresses the differentiation of osteoclasts, inhibits their activation and induces apoptosis [12]. TNFα promotes bone resorption, both in vitro and in vivo, by enhancing the proliferation and differentiation of osteoclast precursors [9]. Recent studies suggest that TNFα also acts directly on osteoclast precursors to potentiate RANKL-induced osteoclastogenesis, even in the absence of elevated levels of RANKL [13]. Sabokbar et al. demonstrated that, by a RANKL-independent mechanism and in the presence of M-CSF, TNFα supports osteoclast differentiation and lacunar resorption from macrophages isolated from the pseudomembrane of loosened THRs [14]. IL6 stimulates bone resorption either by recruiting mature osteoclasts or by activating them through an autocrine mechanism. More recently, Kudo et al. showed that IL6 induces human osteoclast formation from circulating precursors by a mechanism independent of the RANK/RANKL pathway [15]. GM-CSF was demonstrated to be a critical factor for osteoclast formation, but its effects are still controversial; some investigators have reported that GM-CSF is able to correct osteopetrosis stimulating osteoclast development [16], whereas others have shown that osteoclast differentiation was inhibited and dendritic cell differentiation was reciprocally stimulated by GM-CSF [17].

The main goal of the current study was to highlight the difference between Al2O3 and UHMWPE particles in influencing the osteoblast–osteoclast mechanism of cooperation. In this regard, our attention focused on the following aspects: (a) the ability of the particles to induce HOB to release soluble factors involved in bone resorption, and (b) the ability of these factors to promote osteoclast differentiation.

Section snippets

Preparation of wear particles

Particles of aluminium oxide, alpha 99.99% (on metal basis), surface area 14 m2/g, 1.0 μm average diameter, were obtained from Alpha Aesar (Johnson Matthey GmbH, Karlsruhe, Germany).

Medical grade UHMWPE particles were generated at the Institute of Biomechanics of Valencia (Spain), by using a Co–Cr vs. UHMWPE ball on a flat system, with a test length of 10 million cycles [18]. The lubricant solution was bovine serum (SIGMA-Aldrich) diluted to reach a total protein content of 20 mg/ml, which is

Cell viability

The highest concentrations of the particles, i.e. 1 and 0.1 mg/ml, did not show toxic effect, being the “index of cell viability” higher than 0.70. Nevertheless the results were not reliable because the excessive amount of debris interfered with morphological and spectrophotometric assays. For this reason the two concentrations were excluded in all the following spectrophotometric measurements, including the cytokine detection. Instead, the viability of HOB challenged with Al2O3 and UHMWPE

Discussion

Current ceramic-on-ceramic implants have been reported to undergo minimal wear, and ceramic wear particles are generally considered harmless [24]. Most attention has been paid to macrophage/particle interactions, but little is known about the effect of ceramic particles on bone cells. The main goal of this study was to highlight the difference between Al2O3 and UHMWPE particles in influencing the osteoblast–osteoclast mechanism of cooperation. The osteoclastogenesis may be influenced by changes

Conclusion

In the current study the Authors demonstrated that wear particles, according to their chemical composition or their physical characteristics influence differently the cell functions, namely the osteoblast–osteoclast cooperation. Our findings add information on the biological network around implants. The macrophage activation induced by wear particles has been recognized as the main biological mechanism leading to periprosthetic bone resorption. In addition to the macrophage-mediated foreign

Acknowledgments

The Research is supported by grants from Ministero della Salute, Ricerca Finalizzata and Ricerca Corrente.

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