Determination of optimal concentration of vitamin E in polyethylene liners for producing minimal biological response to prosthetic wear debris.

The introduction of vitamin E-blended ultra-high molecular weight polyethylene (VE-UHMWPE) for use in prosthetic components of hip implants has resulted in the production of implants that have excellent mechanical properties and substantially less adverse cellular responses. Given the importance of a biological response to wear in the survival of a prosthesis, we generated wear debris from UHMWPE that had been prepared with different concentrations of vitamin E of 0.1, 0.3, 0.5, and 1% and evaluated their biological reaction in vitro and in vivo. All types of VE-UHMWPE debris promoted a significantly lower expression of Tnf-α in murine peritoneal macrophages than that induced by conventional UHMWPE debris. However, levels of Tnf-α were not significantly different among the macrophages that were stimulated with VE-UHMWPE wear at the concentrations tested. The ability of wear debris to induce inflammatory osteolysis was assessed in a mouse calvarial osteolysis model. The expressions of Tnf-α, Il-6, and Rankl in granulomatous tissue formed around the wear debris were significantly reduced in mice that had been implanted with 0.3%VE-UHMWPE debris as compared to the corresponding values for mice that had been implanted with UHMWPE debris. Consistent with this finding, 0.3%VE-UHMWPE debris showed the lowest osteolytic activity, as evidenced by the reduced bone resorption area, the degree of infiltration of inflammatory cells and the TRAP staining area. Our results suggested that a 0.3% vitamin E concentration is the most appropriate concentration for use in prosthetic components with a reduced adverse cellular response for prolonging the life-span of the implant.

Identification of IL-27 as potent regulator of inflammatory osteolysis associated with vitamin E-blended ultra-high molecular weight polyethylene debris of orthopedic implants.

Vitamin E-blended ultra-high molecular weight polyethylene (VE-UHMWPE) is a newly introduced material for prosthetic components that has proven a better mechanical performance with lesser adverse cellular responses than conventional polyethylene in experimental animal models. However, the mechanisms by which VE-UHMWPE particles trigger a reduced osteolytic activity are unclear and remain to be investigated. Therefore, the current study aims at exploring a possible anti-osteolytic mechanism associated with VE-UHMWPE particles. Transcriptional profiling and bioinformatic analyses of human macrophages stimulated by VE-UHMWPE particles revealed a distinct transcriptional program from macrophages stimulated with UHMWPE particles. Out of the up-regulated genes, IL-27 was found to be significantly elevated in macrophages cultured with VE-UHMWPE particles as compared to these with UHMWPE particles (p = 0.0084). Furthermore, we studied the potential anti-osteolytic function of IL-27 in osteolysis murine model. Interestingly, administration of recombinant IL-27 onto calvariae significantly alleviated osteolytic lesions triggered by UHMWPE particles (p = 0.0002). Likewise, IL-27 inhibited differentiation of osteoclasts (p = 0.0116) and reduced inflammatory response (p < 0.0001) elicited by conventional UHMWPE particles in vitro. This is the first study demonstrating the involvement of IL-27 in macrophage response to VE-UHMWPE particles and its regulatory role in osteolysis. Our data highlight a novel therapeutic agent for treatment of inflammatory osteolysis induced by polyethylene debris. STATEMENT OF SIGNIFICANCE: Aseptic loosening due to inflammatory osteolysis remains the major cause of arthroplasty failure and represents a substantial economic burden worldwide. Ideal approach to prevent this failure should be directed to minimize inflammatory response triggered by wear particles at the site of implant. Understanding the mechanism by which VE-UHMWPE particles triggers lesser cellular responses and reduced osteolysis as compared to conventional UHMWPE particles may aid in discovery of regulatory factors. In the current study, we reported that IL-27 is a potent regulator of inflammatory osteolysis involved in the reduced biologic activities and osteolytic potentials associated with VE-UHMWPE particles. Initiating the production IL-27 in vivo after total joint arthroplasties might be a novel strategy to prolong the life-spam of implant.

Transcriptional profile of human macrophages stimulated by ultra-high molecular weight polyethylene particulate debris of orthopedic implants uncovers a common gene expression signature of rheumatoid arthritis.

Osteolysis is a serious postoperative complication of total joint arthroplasty that leads to aseptic loosening and surgical revision. Osteolysis is a chronic destructive process that occurs when host macrophages recognize implant particles and release inflammatory mediators that increase bone-resorbing osteoclastic activity and attenuate bone-formation osteoblastic activity. Although much progress has been made in understanding the molecular responses of macrophages to implant particles, the pathways/signals that initiate osteolysis remain poorly characterized. Transcriptomics and gene-expression profiling of these macrophages may unravel key mechanisms in the pathogenesis of osteolysis and aid the identification of molecular candidates for therapeutic intervention. To this end, we analyzed the transcriptional profiling of macrophages exposed to ultra-high molecular weight polyethylene (UHMWPE) particles, the most common components used in bearing materials of orthopedic implants. Regulated genes in stimulated macrophages were involved in cytokine, chemokine, growth factor and receptor activities. Gene enrichment analysis suggested that stimulated macrophages elicited common gene expression signatures for inflammation and rheumatoid arthritis. Among the regulated genes, tumor necrosis factor superfamily member 15 (TNFSF15) and chemokine ligand 20 (CCL20) were further characterized as molecular targets involved in the pathogenesis of osteolysis. Treatment of monocyte cultures with TNFSF15 and CCL20 resulted in an increase in osteoclastogenesis and bone-resorbing osteoclastic activity, suggesting their potential contribution to loosening between implants and bone tissues. STATEMENT OF SIGNIFICANCE: Implant loosening due to osteolysis is the most common mode of arthroplasty failure and represents a great challenge to orthopedic surgeons and a significant economic burden for patients and healthcare services worldwide. Bone loss secondary to a local inflammatory response initiated by particulate debris from implants is considered the principal feature of the pathogenesis of osteolysis. In the present study, we analyzed the transcriptional profiling of human macrophages exposed to UHMWPE particles and identified a large number of inflammatory genes that were not identified previously in macrophage responses to wear particles. Our data provide a new insight into the molecular pathogenesis of osteolysis and highlights a number of molecular targets with prognostic and therapeutic implications.

Calcium phosphate crystallization on titania in a flowing Kokubo solution.

Dry titania layers on air-oxidized titanium substrates have been found to be active enough to cause apatite to be deposited in Kokubo's simulated body fluid (SBF) in narrow confined spaces, such as those in narrow grooves and thin gaps. Such in vitro apatite deposition is the basis of the GRAPE(®) technique. The aim of the present study is to determine why GRAPE conditions favor apatite deposition when laminar SBF flow (at 0.01-0.3 ml/min) passes through a shallow channel (0.5 mm) between a pair of titanium substrates each with a dry layer of titania. Assessing the factors that control the heterogeneous nucleation process led to the proposal of the working hypothesis that there are nucleation pre-embryos, ion assemblies that can be stabilized to form embryos, on the titania layer but that they are removed by the SBF flow. Specimens were subjected to different combinations of processes. One combination was that titania layers were exposed to still or flowing SBF, and the other was that half of a specimen, the inlet or outlet side, was exposed to still or flowing SBF with the other half being covered. The surface morphologies of the specimens were then compared in detail. The conclusion was that exposure to still SBF for 2 days before exposure to flowing SBF was required for apatite to be deposited. Some complicated apatite deposition modes were observed, e.g., apatite was deposited even on areas unexposed to still SBF. All of the results were successfully interpreted using the working hypothesis. The conclusion was that the GRAPE(®) technique depends on the confined space holding pre-embryo and embryo assemblies.