What are the local and systemic biologic reactions and mediators to wear debris, and what host factors determine or modulate the biologic response to wear particles?

Mutant MCP-1 protein delivery from layer-by-layer coatings on orthopedic implants to modulate inflammatory response

Total joint replacement (TJR) is a common and effective surgical procedure for hip or knee joint reconstruction. However, the production of wear particles is inevitable for all TJRs, which activates macrophages and initiates an inflammatory cascade often resulting in bone loss, prosthetic loosening and eventual TJR failure. Macrophage Chemoattractant Protein-1 (MCP-1) is one of the most potent cytokines responsible for macrophage cell recruitment, and previous studies suggest that mutant MCP-1 proteins such as 7ND may be used as a decoy drug to block the receptor and reduce inflammatory cell recruitment. Here we report the development of a biodegradable, layer-by-layer (LBL) coating platform that allows efficient loading and controlled release of 7ND proteins from the surface of orthopedic implants using as few as 14 layers. Scanning electron microscopy and fluorescence imaging confirmed effective coating using the LBL procedure on titanium rods. 7ND protein loading concentration and release kinetics can be modulated by varying the polyelectrolytes of choice, the polymer chemistry, the pH of the polyelectrolyte solution, and the degradation rate of the LBL assembly. The released 7ND from LBL coating retained its bioactivity and effectively reduced macrophage migration towards MCP-1. Finally, the LBL coating remained intact following a femoral rod implantation procedure as determined by immunostaining of the 7ND coating. The LBL platform reported herein may be applied for in situ controlled release of 7ND protein from orthopedic implants, to reduce wear particle-induced inflammatory responses in an effort to prolong the lifetime of implants.

A TNF variant that associates with susceptibility to musculoskeletal disease modulates thyroid hormone receptor binding to control promoter activation

Tumor necrosis factor (TNF) is a powerful pro-inflammatory cytokine and immuno-regulatory molecule, and modulates susceptibility to musculoskeletal diseases. Several meta-analyses and replicated association studies have implicated the minor 'A' variant within the TNF promoter single nucleotide polymorphism (SNP) rs361525 (-238A/G) as a risk allele in joint related disorders, including psoriatic and juvenile idiopathic arthritis, and osteolysis after joint arthroplasty. Here we characterized the effect of this variant on TNF promoter function. A transcriptional reporter, encoding the -238A variant of the TNF promoter, resulted in 2.2 to 2.8 times greater transcriptional activation versus the 'G' variant in murine macrophages when stimulated with pro-inflammatory stimuli. Bioinformatic analysis predicted a putative binding site for thyroid hormone receptor (TR) for the -238A but not the -238G allele. Overexpression of TR-α induced promoter expression 1.8-fold in the presence of the 'A' allele only. TR-α expression both potentiated and sensitized the -238A response to LPS or a titanium particulate stimulus, whilst siRNA knockdown of either THRA or THRB impaired transcriptional activation for the -238A variant only. This effect was independent of receptor-ligand binding of triiodothyronine. Immunohistochemical analysis of osteolysis interface membranes from patients undergoing revision surgery confirmed expression of TR-α within osteoclast nuclei at the resorption surface. The 'A' allele at rs361525 confers increased transcriptional activation of the TNF promoter and influences susceptibility to several arthritic conditions. This effect is modulated, at least in part, by binding of TR, which both sensitizes and potentiates transcriptional activation of the 'A' variant independent of its endogenous ligand.

Use of kernel-based Bayesian models to predict late osteolysis after hip replacement

We studied the relationship between osteolysis and polyethylene wear, age at surgery, body mass index and height in 463 subjects (180 osteolysis and 283 controls) after cemented Charnley total hip arthroplasty (THA), in order to develop a kernel-based Bayesian model to quantitate risk of osteolysis. Such tools may be integrated into decision-making algorithms to help personalize clinical decision-making. A predictive model was constructed, and the estimated posterior probability of the implant failure calculated. Annual wear provided the greatest discriminatory information. Age at surgery provided additional predictive information and was added to the model. Body mass index and height did not contain valuable discriminatory information over the range in which observations were densely sampled. The robustness and misclassification rate of the predictive model was evaluated by a five-times cross-validation method. This yielded a 70% correct predictive classification of subjects into osteolysis versus non-osteolysis groups at a mean of 11 years after THA. Finally, the data were divided into male and female subsets to further explore the relationship between wear rate, age at surgery and incidence of osteolysis. The correct classification rate using age and wear rate in the model was approximately 66% for males and 74% for females.

Allergy or tolerance: reduced inflammatory cytokine response and concomitant IL-10 production of lymphocytes and monocytes in symptom-free titanium dental implant patients

Hypersensitivity reactions to titanium (Ti) are very rare. Thus, we assessed the proinflammatory response and also potential tolerance favoring in vitro reactivity of human blood lymphocytes and monocytes (PBMC) to Ti in healthy individuals (14 without, 6 with complication-free dental Ti implants). The proliferation index (SI) in lymphocyte transformation test (LTT) and production of cytokines linked to innate immune response (IL-1β, IL-6, and TNFα) or immune regulation (IL-10) were assessed in response to TiO₂ particles or Ti discs. In both groups, the Ti-LTT reactivity was not enhanced (e.g., SI < 3). The control antigen tetanus toxoid (TT) gave adequate reactivity (median SI individuals without/with implant: 20.6 ± 5.97/19.58 ± 2.99). Individuals without implant showed higher cytokine response to Ti materials than individuals with symptom-free implants; for example, TiO₂ rutile particle induced increase of IL-1β 70.27-fold/8.49-fold versus control medium culture. PBMC of 5 of the 6 individuals with complication-free Ti implants showed an ex vivo ongoing production of IL-10 (mean 4.18 ± 2.98 pg/mL)-but none of the 14 controls showed such IL-10 production. Thus in vitro IL-1β-, IL-6-, and TNF-α production reflects “normal” unspecific immune response to Ti. This might be reduced by production of tolerogenic IL-10 in individuals with symptom-free Ti dental implants.

Suppression of titanium particle-induced TNF-alpha expression and apoptosis in human U937 macrophages by siRNA silencing

Aseptic loosening of joint prosthetics is one of the most frequent reasons for the failure of total joint replacement surgeries. A major cause of the aseptic loosening is osteolysis caused by a periprosthetic inflammatory response to wear particles released from implanted prosthetics. Tumor necrosis factor (TNF)-α is thought to play a dominant role in wear-induced inflammation. It was shown previously by our group, as well as by other researchers, that macrophages produce abundant TNF-α when exposed to particulate titanium (Ti), which is widely used as a biomaterial in arthroplastic surgery. In the present study, we have tested the feasibility of using siRNA as a therapeutic intervention against wear-induced TNF-α production. Our data show that transfection of U937 macrophage cells with TNF-α siRNA inhibits Ti particle-induced expression of TNF-α mRNA and protein by >65%. Moreover, U937 cells transfected with TNF-α siRNA were significantly more resistant to Ti particle-induced apoptosis (>60%, p<0.05) and caspase-3 activation (>50%, p<0.05) compared with normal U937 cells. Collectively, our data show that siRNA can be an effective way to inhibit Ti particle-induced TNF-α expression and the activation of downstream pathways such as apoptosis in macrophages. These data provide a foundation for future studies to investigate the use of siRNA targeting inflammatory cytokines as a therapeutic modality for the treatment of aseptic loosening of prosthetic materials used in arthroplastic surgery.

Toll-like receptor 4 signaling pathway mediates proinflammatory immune response to cobalt-alloy particles

Metal orthopedic implant debris-induced osteolysis of hip bone is a major problem in patients with prosthetic-hips. Although macrophages are the principal targets for implant-wear debris, the receptor(s) and mechanisms underlying these responses are not fully elucidated. We examined whether the TLR4 pathway mediates immune response to metal-on-metal (MoM) implant-generated wear particles. Human monocytes (THP-1) were exposed to Co-alloy particles at increasing particle:cell ratio for 24 h. Challenge with particles caused up-regulation of IL-1β, TNF-α and IL-8, and mediated degradation of cytosolic I-κB and nuclear translocation of NF-κB. Blocking antibodies against TLR4 or gene silencing of MyD88 and IRAK-1 prevented particle-induced I-κB/NF-κB activation response and markedly inhibited IL-8 release. Particle-mediated IL-8 response was not observed in TLR4-negative HEK293T cells; whereas transfection-based TLR4-overexpression in HEK293T enabled particle-sensitivity, as observed by I-κB degradation and IL-8 expression in response to particles. Results demonstrate that Co-alloy particles trigger immune response via the TLR4-MyD88-dependent signaling pathway.

The basic science of periprosthetic osteolysis

Total joint arthroplasty has revolutionized the treatment of arthritic and degenerative conditions for many joints in the body; however, wear debris is continuously generated with day-to-day use of an artificial joint. Excessive production of wear by-products induces a foreign body and chronic inflammatory reaction that accelerates periprosthetic bone destruction and inhibits bone formation. The specific biologic reaction is dependent on the type, amount, and characteristics of the by-products of wear, along with individual genetic variations. For polymeric and ceramic particles, the inflammatory reaction is generally nonspecific and nonimmune; however, with metallic by-products, a type IV, T lymphocyte-mediated, antigen-dependent immune reaction can occur in some patients. The production of proinflammatory cytokines, chemokines, reactive oxygen species, and other mediators is upregulated by wear particles. Animal models have shown that the biologic reaction to wear particles is systemic in nature, not a localized event. Mechanical stimuli and the presence of endotoxin also appear to be important. Efficacious biologic treatments of periprosthetic osteolysis are not yet available. Research continues with the hope that viable strategies for preventing and treating particle-induced osteolysis will be introduced in the future, thus mitigating the need for revision surgery.

Local effect of IL-4 delivery on polyethylene particle induced osteolysis in the murine calvarium

Wear particles generated with use of total joint replacements incite a chronic macrophage-mediated inflammatory reaction, which leads to implant failure. Macrophage activation may be polarized into two states, with an M1 proinflammatory state dominating an alternatively activated M2 anti-inflammatory state. We hypothesized that IL-4, an activator of M2 macrophages, could modulate polyethylene (PE) particle-induced osteolysis in an experimental murine model. Four animal groups included (a) calvarial saline injection with harvest at 14 days (b) single calvarial injection of PE particles subcutaneously (SC) without IL-4 (c) PE particles placed as in (b), then IL-4 given SC for 14 consecutive days and (d) PE particles as in (b) then IL-4 beginning 7 days after particle injection for 7 days. The calvarial bone volume to total tissue volume was measured using microCT and histomorphometry. Calvaria were cultured for 24 h to assess release of RANKL, OPG, TNF-α, and IL-1ra and isolation and identification of M1 and M2 specific proteins. MicroCT and histomorphometric analysis showed that bone loss was significantly decreased following IL-4 administration to PE treated calvaria for both 7 and 14 days. Western blot analysis showed an increased M1/M2 ratio in the PE treated calvaria, which decreased with addition of IL-4. Cytokine analysis showed that the RANKL/OPG ratio and TNF-α/IL-1ra ratio decreased in PE-treated calvaria following IL-4 addition for 14 days. IL-4 delivery mitigated PE particle-induced osteolysis through macrophage polarization. Modulation of macrophage polarization is a potential treatment strategy for wear particle induced periprosthetic osteolysis.

Exogenous MC3T3 preosteoblasts migrate systemically and mitigate the adverse effects of wear particles

Understanding how relevant cell types respond to wear particles will reveal new avenues for treating osteolysis following joint replacements. In this study, we investigate the effects of ultrahigh molecular weight polyethylene (UHMWPE) particles on preosteoblast migration and function. We infused UHMWPE particles or saline into the left femur of mice and injected luciferase-expressing preosteoblasts (MC3T3 cells) into each left ventricle. Bioluminescence imaging (BLI) confirmed systemic administration of MC3T3 cells. BLI throughout the 28-day experiment showed greater MC3T3 migration to the site of particle infusion than to the site of saline infusion, with significant differences on days 0, 4, and 6 (p≤0.055). Immunostaining revealed a greater number of osteoblasts and osteoclasts in the particle-infused femora, indicating greater bone turnover. The bone mineralization of the particle-infused femora increased significantly when compared to saline-infused femora (an increase of 146.4±27.9 vs. 12.8±8.7 mg/mL, p=0.008). These results show that infused preosteoblasts can migrate to the site of wear particles. Additionally, as the migrated cells were associated with increased bone mineralization in spite of the presence of particles, increasing osteoblast recruitment is a potential strategy for combating bone loss due to increased osteoclast/macrophage number and decreased osteoblast function.

Biological responses of human mesenchymal stem cells to titanium wear debris particles

Wear debris-induced osteolysis is a major cause of orthopedic implant aseptic loosening, and various cell types, including macrophages, monocytes, osteoblasts, and osteoclasts, are involved. We recently showed that mesenchymal stem/osteoprogenitor cells (MSCs) are another target, and that endocytosis of titanium (Ti) particles causes reduced MSC proliferation and osteogenic differentiation. Here we investigated the mechanistic aspects of the endocytosis-mediated responses of MSCs to Ti particulates. Dose-dependent effects were observed on cell viability, with doses >300 Ti particles/cell resulting in drastic cell death. To maintain cell viability and analyze particle-induced effects, doses <300 particles/cell were used. Increased production of interleukin-8 (IL-8), but not IL-6, was observed in treated MSCs, while levels of TGF-β, IL-1β, and TNF-α were undetectable in treated or control cells, suggesting MSCs as a likely major producer of IL-8 in the periprosthetic zone. Disruptions in cytoskeletal and adherens junction organization were also observed in Ti particles-treated MSCs. However, neither IL-8 and IL-6 treatment nor conditioned medium from Ti particle-treated MSCs failed to affect MSC osteogenic differentiation. Among other Ti particle-induced cytokines, only GM-CSF appeared to mimic the effects of reduced cell viability and osteogenesis. Taken together, these results strongly suggest that MSCs play both responder and initiator roles in mediating the osteolytic effects of the presence of wear debris particles in periprosthetic zones.

Selective inhibition of the MCP-1-CCR2 ligand-receptor axis decreases systemic trafficking of macrophages in the presence of UHMWPE particles

The biological mechanisms leading to periprosthetic osteolysis involve both chemokines and the monocyte/macrophage cell lineage. Whether MCP-1 plays a major role in macrophage recruitment in the presence of wear particles is unknown. We tested two hypotheses: (1) that exogenous local delivery of MCP-1 induces systematic macrophage recruitment and (2) that blockade of the MCP-1 ligand-receptor axis decreases macrophage recruitment and osteolysis in the presence of ultra high molecular weight polyethylene (UHMWPE) particles. Six groups of nude mice were used. We used non-invasive imaging to assay macrophage recruitment and osteolysis. A murine macrophage cell line and primary wild type and CCR2 knockout murine macrophages were used as the reporter cells. Particles were infused into the femoral canal. Bioluminescence and immunohistochemical staining were used to confirm the migration of reporter cells. Locally infused MCP-1 induced systemic macrophage trafficking to bone. Injection of MCP-1 receptor antagonist significantly decreased reporter cell recruitment to bone infused with UHMWPE particles and decreased osteolysis. Systemic migration of reporter cells to infused particles was decreased when the reporter cells were deficient in the CCR2 receptor. Interruption of the MCP-1 ligand-receptor axis appears to be a viable strategy to mitigate trafficking of macrophages and osteolysis due to UHMWPE particles.

The effect of TNFα secreted from macrophages activated by titanium particles on osteogenic activity regulated by WNT/BMP signaling in osteoprogenitor cells

Wear particles are the major cause of osteolysis associated with failure of implant following total joint replacement. During this pathologic process, activated macrophages mediate inflammatory responses to increase osteoclastogenesis, leading to enhanced bone resorption. In osteolysis caused by wear particles, osteoprogenitors present along with macrophages at the implant interface may play significant roles in bone regeneration and implant osteointegration. Although the direct effects of wear particles on osteoblasts have been addressed recently, the role of activated macrophages in regulation of osteogenic activity of osteoblasts has scarcely been studied. In the present study, we examined the molecular communication between macrophages and osteoprogenitor cells that may explain the effect of wear particles on impaired bone forming activity in inflammatory bone diseases. It has been demonstrated that conditioned medium of macrophages challenged with titanium particles (Ti CM) suppresses early and late differentiation markers of osteoprogenitors, including alkaline phosphatase (ALP) activity, collagen synthesis, matrix mineralization and expression of osteocalcin and Runx2. Moreover, bone forming signals such as WNT and BMP signaling pathways were inhibited by Ti CM. Interestingly, TNFα was identified as a predominant factor in Ti CM to suppress osteogenic activity as well as WNT and BMP signaling activity. Furthermore, Ti CM or TNFα induces the expression of sclerostin (SOST) which is able to inhibit WNT and BMP signaling pathways. It was determined that over-expression of SOST suppressed ALP activity, whereas the inhibition of SOST by siRNA partially restored the effect of Ti CM on ALP activity. This study highlights the role of activated macrophages in regulation of impaired osteogenic activity seen in inflammatory conditions and provides a potential mechanism for autocrine regulation of WNT and BMP signaling mediated by TNFα via induction of SOST in osteprogenitor cells.

Effect of a CCR1 receptor antagonist on systemic trafficking of MSCs and polyethylene particle-associated bone loss

Particle-associated periprosthetic osteolysis remains a major issue in joint replacement. Ongoing bone loss resulting from wear particle-induced inflammation is accompanied by continued attempts at bone repair. Previously we showed that mesenchymal stem cells (MSCs) are recruited systemically to bone exposed to continuous infusion of ultra high molecular weight polyethylene (UHMWPE) particles. The chemokine-receptor axis that mediates this process is unknown. We tested two hypotheses: (1) the CCR1 receptor mediates the systemic recruitment of MSCs to UHMWPE particles and (2) recruited MSCs are able to differentiate into functional mature osteoblasts and decrease particle-associated bone loss. Nude mice were allocated randomly to four groups. UHMWPE particles were continuously infused into the femoral shaft using a micro-pump. Genetically modified murine wild type reporter MSCs were injected systemically via the left ventricle. Non-invasive imaging was used to assay MSC migration and bone mineral density. Bioluminescence and immunohistochemistry confirmed the chemotaxis of reporter cells and their differentiation into mature osteoblasts in the presence of infused particles. Injection of a CCR1 antagonist decreased reporter cell recruitment to the UHMWPE particle infusion site and increased osteolysis. CCR1 appears to be a critical receptor for chemotaxis of MSCs in the presence of UHMWPE particles. Interference with CCR1 exacerbates particle-induced bone loss.

Calcineurin/nuclear factor of activated T cells (NFAT) signaling in cobalt-chromium-molybdenum (CoCrMo) particles-induced tumor necrosis factor-α (TNFα) secretion in MLO-Y4 osteocytes

Aseptic loosening is the devastating long term complication of total hip arthroplasty and orthopedic implant debris has been shown to trigger an intense inflammatory reaction leading to resorption of the bone matrix. Inflammatory cytokines, such as tumor necrosis factor-α (TNFα), have been implicated in this process and osteocytes may play a role in its production. We previously demonstrated that cobalt-chromium-molybdenum (CoCrMo) particles upregulate TNFα production by MLO-Y4 osteocytes in vitro, but the underlying mechanism has not been elucidated. Based on previous studies by others, we hypothesized that the calcineurin-nuclear factor of activated T cells (NFAT) pathway mediates CoCrMo particle-induced TNFα production in MLO-Y4 osteocytes. MLO-Y4 osteocytes exposed to CoCrMo particle treatment resulted in a rapid and significant increase in calcineurin activity. We also demonstrate that CoCrMo particle-induced upregulation of TNFα is reduced to control levels with calcineurin-NFAT inhibitors and this was also confirmed at mRNA level. Moreover, we demonstrate the localization of NFATs in MLO-Y4 osteocytes and that NFAT1 and 2 translocate to the nucleus upon CoCrMo particle treatment. Our results suggest that calcineurin-NFAT signaling is involved in TNFα production by MLO-Y4 osteocytes after CoCrMo particle treatment.

Bisphosphonates in orthopedic applications

Bisphosphonates (BPs) exert potent effects on the skeleton. As such, there are important questions relating to how treatment with BPs for metabolic disorders might affect outcomes of orthopedic problems. A further question is what role, if any, might BPs play as adjunctive therapeutics for orthopedic problems. This article outlines the research thus far in the application of BPs to the management of osteonecrosis, bone repair, and joint arthroplasty. Many animal studies show a benefit to decreasing bone resorption in models of osteonecrosis. These include studies in both small and large animals, backed up by limited human data. Further clinical trials are underway for this indication. In bone repair, again, multiple studies exist. There are concerns that BPs could interfere with the normal processes of healing. Some of the controversy about benefits or adverse effects of BPs in this context can be distilled down to effects of dosing and administration. With some exceptions, longer intervals between dosing seem to be more beneficial while not producing adverse healing effects in animal studies. In joint arthroplasty, animal studies suggest a role for topical or systemic BPs for enhancing bone on-growth to implant surfaces and strength of mechanical fixation, although these are yet to be confirmed in clinical studies. Clinical studies show that BPs inhibit periprosthetic bone loss due to strain-adaptive remodeling and after impaction bone grafting, although an efficacy in inhibiting inflammatory bone loss due to wear particle-induced osteolysis has not been confirmed. Lastly, as anabolic drugs have become available, there is increasing interest in their combined use with BPs. From experimental data, manipulation of both the anabolic and catabolic responses is a powerful approach in models of bone repair.

Predictors of osteoclast activity in patients with sickle cell disease

BACKGROUND

Bone changes are common in sickle cell disease, but the pathogenesis is not fully understood. Tartrate-resistant acid phosphatase (TRACP) type 5b is produced by bone-resorbing osteoclasts. In other forms of hemolytic anemia, increased iron stores are associated with osteoporosis. We hypothesized that transfusional iron overload would be associated with increased osteoclast activity in patients with sickle cell disease.

DESIGN AND METHODS

We examined tartrate-resistant acid phosphatase 5b concentrations in patients with sickle cell disease and normal controls of similar age and sex distribution at steady state. Serum tartrate-resistant acid phosphatase 5b concentration was measured using an immunocapture enzyme assay and plasma concentrations of other cytokines were assayed using the Bio-Plex suspension array system. Tricuspid regurgitation velocity, an indirect measure of systolic pulmonary artery pressure, was determined by echocardiography.

RESULTS

Tartrate-resistant acid phosphatase 5b concentrations were higher in 58 adults with sickle cell disease than in 22 controls (medians of 4.4 versus 2.4 U/L, respectively; P=0.0001). Among the patients with sickle cell disease, tartrate-resistant acid phosphatase 5b independently correlated with blood urea nitrogen (standardized beta=0.40, P=0.003), interleukin-8 (standardized beta=0.30, P=0.020), and chemokine C-C motif ligand 5 (standardized beta=-0.28, P=0.031) concentrations, but not with serum ferritin concentration. Frequent blood transfusions (>10 units in life time) were not associated with higher tartrate-resistant acid phosphatase 5b levels in multivariate analysis. There were strong correlations among tartrate-resistant acid phosphatase 5b, alkaline phosphatase and tricuspid regurgitation velocity (r>0.35, P<0.001).

CONCLUSIONS

Patients with sickle cell disease have increased osteoclast activity as reflected by serum tartrate-resistant acid phosphatase 5b concentrations. Our results may support a potential role of inflammation rather than increased iron stores in stimulating osteoclast activity in sickle cell disease. The positive relationships among tartrate-resistant acid phosphatase 5b, alkaline phosphatase and tricuspid regurgitation velocity raise the possibility of a common pathway in the pulmonary and bone complications of sickle cell disease.

Effects of orthopedic polymer particles on chemotaxis of macrophages and mesenchymal stem cells

Wear particles generated from total joint arthroplasty (TJA) stimulate macrophages to release chemokines. The role of chemokines released from wear particle-stimulated macrophages on the migration of macrophages and osteoprogenitor cells in vitro has not been elucidated. In this study, we challenged murine macrophages (RAW 264.7) with clinically relevant polymethyl methacrylate (PMMA, 1-10 microm) and ultra high molecular weight polyethylene (UHMWPE, 2-3 microm) particles. The chemotactic effects of the conditioned media (CM) were tested in vitro using human macrophages (THP-1) and human mesenchymal stem cells (MSCs) as the migrating cells. CM collected from both particle types had a chemotactic effect on human macrophages, which could be eliminated by monocyte chemotactic protein-1 (MCP-1) neutralizing antibody. Blocking the CCR1 receptor eliminated the chemotactic effect, while CCR2 antibody only partially decreased THP-1 cell migration. CM from PMMA but not UHMWPE-exposed macrophages led to chemotaxis of MSCs; this effect could be eliminated by macrophage inflammatory protein-1 alpha (MIP-1alpha) neutralizing antibody. Neither CCR1 nor CCR2 blocking antibodies showed an effect on the migration of MSCs. Chemokines released by macrophages stimulated by wear particles can have an effect on the migration of macrophages and MSCs. This effect seems to be dependent on the particle type, and may be modulated by MCP-1 and MIP-1alpha, however, more than one chemokine may be necessary for chemotaxis.

Male gender, Charnley class C, and severity of bone defects predict the risk for aseptic loosening in the cup of ABG I hip arthroplasty

Background

We studied which factor could predict aseptic loosening in ABG I hip prosthesis with hydroxyapatite coating. Aseptic loosening and periprosthetic osteolysis are believed to be caused, at least in part, by increased polyethylene (PE) wear rate via particle disease. Based on it, increased PE wear rate should be associated with aseptic loosening regardless of the type of implant.

Methods

We analyzed data from 155 revisions of ABG I hip prostheses to examine the influence of patient, implant, surgery, and wear related factors on the rate of aseptic loosening at the site of the cup. This was calculated by stepwise logistic regression analysis. The stability of the implant and severity of bone defects were evaluated intraoperatively.

Results

We found that men (odds ratio, OR = 5.6; p = 0.004), patients with Charnley class C (OR = 6.71; p = 0.013), those having more severe acetabular bone defects (OR = 4 for each degree of severity; p = 0.002), and longer time to revision surgery (OR = 1.51 for each additional year; p = 0.012) had a greater chance of aseptic loosening of the cup. However, aseptic loosening was not directly predicted by polyethylene wear rate in our patients.

Conclusion

Severity of bone defects predicts the risk for aseptic loosening in ABG I cup. Factors potentially associated with the quality of bone bed and biomechanics of the hip might influence on the risk of aseptic loosening in this implant.

The relationship of polyethylene wear to particle size, distribution, and number: A possible factor explaining the risk of osteolysis after hip arthroplasty

The most critical factor in the development of periprosthetic osteolysis (OL) in total hip arthroplasty (THA) is the biological reaction to wear debris. This reaction is dependent, in part, on the size and concentration of particles, which are determined predominantly by the polyethylene (PE) wear rate. This implies that the risk for developing OL and prosthesis failure can be estimated from wear measurements. We developed a computational algorithm for calculating the total number of PE particles for volumetric wear when particle size and distribution are known. We found that: (i) total number of PE wear particles decreases up to 5 orders of magnitude if the average size of particles increases and the total volumetric wear remains constant; (ii) total amount of PE wear particles decreases up to 4 orders of magnitude if the width of the distribution increases and total volumetric wear remains constant; (iii) for the same volumetric wear, the number of particles significantly decreases/increases with the increase/decrease in their average size and range. These findings suggest that the risk for the development of OL in THA cannot be simply estimated from the volumetric wear alone.

Individual susceptibility to periprosthetic osteolysis is associated with altered patterns of innate immune gene expression in response to pro-inflammatory stimuli

Susceptibility to osteolysis after total hip arthroplasty (THA) varies between individuals. We examined whether patients susceptible to osteolysis (group I, n = 34 subjects) after cemented Charnley THA have quantitatively different innate immune responses to pro-inflammatory stimuli versus patients without this susceptibility (group II, n = 28 subjects) at a mean of 14 years after primary surgery. Extracted peripheral blood mononuclear cells were stimulated for 3 h using endotoxin (lipopolysaccharide-LPS, 100 ng/mL), endotoxin-stripped titanium particles (Ti) or endotoxin-stripped particles with adherent LPS added-back (TI + LPS). Subjects returned 1 week later and the experimental protocol was repeated. Assays for mRNA induction for interleukin (IL)-1alpha, IL-1beta, IL-1Ra, IL-6, IL-10, IL-18, and tumor necrosis factor (TNF) were made using quantitative real-time PCR. Although baseline levels of mRNA expression were slightly lower in group I, inducibility of mRNA expression was markedly greater in group I versus group II for all cytokines in response to LPS or Ti + LPS, and for IL-1alpha in response to Ti (P < 0.05). LPS or Ti + LPS stimulation also resulted in an increase in the IL-1/IL-1Ra mRNA ratio in group I versus group II (P < 0.05). mRNA induction was highly reproducible between subject visits (r > 0.7, P < 0.001). Osteolysis-susceptible patients show repeatable, quantitatively different patterns of innate cytokine gene expression in response to pro-inflammatory stimuli versus THA patients who do not display this susceptibility. These innate immune differences may contribute to the variation in osteolysis-susceptibility observed clinically between individuals.

Cellular chemotaxis induced by wear particles from joint replacements

The destruction of bone around joint replacements (periprosthetic osteolysis) is an adverse biological response associated with the generation of excessive wear particles. Wear debris from the materials used for joint replacements stimulate a chronic inflammatory and foreign body reaction that leads to increased osteoclast differentiation and maturation, and decreased bone formation. Wear debris induces both local and systemic trafficking of inflammatory cells to the site of particle generation. Recent studies have shown that this effect is mediated primarily by chemotactic cytokines (chemokines) including macrophage chemotactic protein-1 (MCP-1, also known as CCL2), macrophage inhibitory protein-1 (MIP-1), Interleukin-8 (IL-8 or CXCL8) and others. These ligands migrate along a concentration gradient to interact with G-protein-linked transmembrane receptors on the cell surface. Chemokines are involved in the innate and adaptive immune responses, angiogenesis, wound healing and tissue repair. In vitro, in vivo and tissue retrieval studies have shown that chemokine-directed systemic trafficking of polymorphonuclear leukocytes and cells of the monocyte/macrophage lineage to wear particles result in the release of pro-inflammatory factors and subsequent bone loss. Modulation of the chemokine ligand-receptor axis is a potential strategy to mitigate the adverse effects of wear particles from joint replacements.

Total ankle arthroplasty in the rheumatoid patient

Total ankle replacement in the rheumatoid patient is a feasible and effective treatment for ankle arthritis. The benefits of ankle prosthesis are good pain relief, acceptable function, and patient satisfaction. It is a joint-sparing procedure for restoring functionality. All investigators of total ankle replacement feel that, as clinicians gain experience with the procedure and related products, difficulties and risks associated with the procedure will decline. Following an early history of failure and poor patient satisfaction, more recent results have shown promise.

Functional variants of the P2RX7 gene, aseptic osteolysis, and revision of the total hip arthroplasty: a preliminary study

Periprosthetic osteolysis (OL) is a major long-term complication of the total hip arthroplasty (THA), which can result in aseptic loosening and revision surgery. Purinergic receptor P2X, ligand-gated ion channel 7 (P2RX7) is an important regulator of inflammation and bone turnover. We were therefore interested in whether functional variants of the P2RX7 gene may be associated with OL and risk of THA failure. A total of 205 unrelated Czech patients with cementless-type THA were stratified according to the severity of acetabular OL and revision of THA. Four "loss-of-function" P2RX7 single nucleotide polymorphisms (SNPs), namely Glu496Ala, Ile568Asn, Arg307Gln, and null allele (rs35933842), were genotyped by polymerase chain reaction with sequence-specific primers (PCR-SSP). No significant association of P2RX7 variants with severity of OL was observed. The carriers of rare variants P2RX7 568Asn, 307Gln and null allele, all causing complete loss of P2RX7 function, tended to be overrepresented among patients with THA revision (9.6%) by comparison with those with unrevised functional prosthesis (2.1%, p = 0.09). Furthermore, the carriage of the P2RX7 307Gln allele was associated with greater cumulative hazard of THA revision (p = 0.02). In this preliminary study, we could nominate but not clearly demonstrate rare P2RX7 loss-of-function variants being associated with THA failure. Investigation in large THA cohorts is therefore warranted.

Low dose metal particles can induce monocyte/macrophage survival

Aseptic loosening results in pain, loss of function, and ultimately prosthetic joint failure and revision surgery. The generation of wear particles from the prosthesis is a major factor in local osteolysis. We investigated the effects of such wear particles on the survival of monocytes and macrophages, populations implicated in wear particle-driven pathology. Particles from titanium aluminum vanadium (TiAlV) and cobalt chromium (CoCr) alloys were generated in-house and were equivalent in size (0.5-3 microm) to those seen in patients. Human CD14(+) monocytes and murine bone marrow-derived macrophages (BMM) were treated with TiAlV and CoCr particles in vitro, and cell survival was assayed. Both particles increased monocyte and macrophage survival in a dose-dependent manner, with an optimal concentration of around 10(7) particles/mL. Conditioned media from particle-treated BMM also increased macrophage survival. Studies with antibody blockade and gene-deficient mice suggest that particle-induced BMM survival is independent of endogenous CSF-1 (M-CSF), GM-CSF, and TNFalpha. These data indicate that wear particles can promote monocyte/macrophage survival in vitro possibly via an endogenous mediator. If this phenomenon occurs in vivo, it could mean that increased numbers of macrophages (and osteoclasts) would be found at a site of joint implant failure, which could contribute to the local inflammatory reaction and osteolysis.

Variation in cytokine genes can contribute to severity of acetabular osteolysis and risk for revision in patients with ABG 1 total hip arthroplasty: a genetic association study

BACKGROUND

The differences in total hip arthroplasty (THA) survivorship may be influenced by individual susceptibility to periprosthetic osteolysis. This may be driven by functional polymorphisms in the genes for cytokines and cytokine receptors involved in the development of osteolysis in THA, thereby having an effect on the individual's phenotype.

METHODS

We performed a study on 22 single-nucleotide polymorphisms (SNPs) for 11 cytokines and two cytokine receptor candidate genes for association with severity of acetabular osteolysis and risk to failure in THA. Samples from 205 unrelated Caucasian patients with cementless type THA (ABG 1) were investigated. Distribution of investigated SNP variants between the groups of mild and severe acetabular osteolysis was determined by univariate and multivariate analysis. Time-dependent output variables were analyzed by the Cox hazards model.

RESULTS

Univariate analysis showed: 1) TNF-238*A allele was associated with severe osteolysis (odds ratio, OR = 6.59, p = 0.005, population attributable risk, PAR 5.2%); 2) carriers of the IL6-174*G allele were 2.5 times more prone to develop severe osteolysis than non-carriers (OR = 2.51, p = 0.007, PAR = 31.5%); 3) the carriage of IL2-330*G allele was associated with protection from severe osteolysis (OR = 0.55, p = 0.043). Based on logistic regression, the alleles TNF-238*A and IL6-174*G were independent predictors for the development of severe acetabular osteolysis. Carriers of TNF-238*A had increased cumulative hazard of THA failure according to Cox model (p = 0.024). In contrast, IL2-330*G allele predicted lower cumulative hazard of THA failure (p = 0.019).

CONCLUSION

Genetic variants of proinflammatory cytokines TNF-alpha and IL-6 confer susceptibility to severe OL. In this way, presence of the minor TNF allele could increase the cumulative risk of THA failure. Conversely, SNP in the IL2 gene may protect carriers from the above THA complications.

Co-Cr-Mo alloy particles induce tumor necrosis factor alpha production in MLO-Y4 osteocytes: a role for osteocytes in particle-induced inflammation

Wear debris-induced osteolysis is purportedly the limiting problem affecting the long term results of joint arthroplasty. Pathogenic effects of wear debris in peri-implant cells such as macrophages, osteoblasts and osteoclasts have been well studied. In contrast, the effects of wear debris on osteocytes, which make up over 90% of all bone cells, remain unknown. We hypothesized that metal implant debris can induce the pro-inflammatory response in osteocytes. This study demonstrated the effects of cobalt-chromium-molybdenum alloy (Co-Cr-Mo) particles on a well-characterized MLO-Y4 osteocyte cell line. Co-Cr-Mo alloy particle treatment significantly (p<0.05) up-regulated tumor necrosis factor alpha (TNFalpha) gene expression after 3 and 6 h and TNFalpha protein production after 24 h, but down-regulated interleukin-6 (IL-6) gene expression after 6 h. Co-Cr-Mo alloy particle treatment also induced osteocyte apoptosis after 24 h. This apoptotic effect was partially (40%) dependent on TNFalpha. Therefore, our results suggest that osteocytes play a role in particle-induced inflammation and bone resorption following total joint arthroplasty by inducing pro-inflammatory cytokines and inducing osteocyte apoptosis.

Protective effects of dehydrocostus lactone against hydrogen peroxide-induced dysfunction and oxidative stress in osteoblastic MC3T3-E1 cells

Oxidative stress regulates cellular functions in multiple pathological conditions, including bone formation by osteoblasic cells. To elucidate the protective effects of dehydrocostus lactone on the response of osteoblast to oxidative stress, osteoblastic MC3T3-E1 cells were incubated with 0.3mM hydrogen peroxide (H(2)O(2)) and/or dehydrocostus lactone (0.1-10 microg/ml), and markers of osteoblast function and oxidative damage were examined. Dehydrocostus lactone (0.1-10 microg/ml) significantly increased osteoblast growth compared with control (P<0.05). H(2)O(2)-induced reduction of differentiation markers such as alkaline phosphatase (ALP), collagen content, and calcium deposition was recovered in the presence of dehydrocostus lactone (0.4-2 microg/ml). Treatment with dehydrocostus lactone (10 microg/ml) decreased the production of osteoclast differentiation-inducing factors such as interleukin (IL)-6 and receptor activator of nuclear factor-kB ligand (RANKL) in the presence of H(2)O(2). Moreover, dehydrocostus lactone (0.4-2 microg/ml) decreased the formation of protein carbonyl (PCO) and malondialdehyde (MDA) induced by H(2)O(2) in osteoblasts. Taken together, these results demonstrate that dehydrocostus lactone can protect osteoblasts against H(2)O(2)-induced cellular dysfunction. These results also suggest that dehydrocostus lactone may be valuable as a protective agent against oxidative damage in osteoblasts.

The basic science of periprosthetic osteolysis

Despite improvements in the techniques, materials, and fixation of total joint replacements, wear and its sequelae continue to be the main factors limiting the longevity and clinical success of arthroplasty. Since Charnley first recognized aseptic loosening in the early 1960s, a tremendous amount of information has been gained on the basic science of osteolysis. Tissue explant, animal, and cell culture studies have allowed development of an appreciation of the complexity of cellular interactions and chemical mediators involved in these processes. Cellular participants have been shown to include the macrophage, osteoblast, fibroblast, and osteoclast. The plethora of chemical mediators that are responsible for the cellular interactions and effects on bone primarily include PGE2, TNF-alpha, IL-1, and IL-6. Recent and ongoing work in the field of signaling pathways will continue to advance our understanding of the mechanisms of periprosthetic bone loss. Although initial animal studies are promising for the development of possible pharmacologic agents for the treatment and prevention of osteolysis, well controlled human trials are required.