Accumulation of LPS by polyethylene particles decreases bone attachment to implants

Study on the preparation and properties of acellular matrix from the skin of silver carp (Hypophthalmichthys molitrix)

Acellular matrices are mainly composed of mammalian tissues, and aquatic tissues with lower biological risks and less religious restrictions are considered alternatives to mammalian tissues. The acellular fish skin matrix (AFSM) has been commercially available. Silver carp has the advantages of farmability, high yield and low price, but there are few studies on the silver carp acellular fish skin matrix (SC-AFSM). In this study, an acellular matrix with low DNA and endotoxin was prepared from the skin of silver carp. After treatment with trypsin/sodium dodecyl sulfate and Triton X-100 solutions, the DNA content in SC-AFSM reached 11.03 ± 0.85 ng/mg, and the endotoxin removal rate was 96.8%. The porosity of SC-AFSM was 79.64% ± 0.17%, which is favorable for cell infiltration and proliferation. The relative cell proliferation rate of SC-AFSM extract was 117.79% ± 15.26%. The wound healing experiment showed that SC-AFSM had no adverse acute pro-inflammatory response, which had a similar effect as commercial products in promoting tissue repair. Therefore, SC-AFSM has great application potential in biomaterials.

Suppression of NF-κB-induced chronic inflammation mitigates inflammatory osteolysis in the murine continuous polyethylene particle infusion model

Wear particle-associated bone loss (periprosthetic osteolysis) constrains the longevity of total joint arthroplasty (TJA). Wear particles induce a prolonged upregulation of nuclear factor kappa B (NF-κB) signaling in macrophages and osteoclasts. Synthetic double-stranded oligodeoxynucleotides (ODNs) can prevent the binding of NF-κB to the promoter regions of targeted genes and inhibit genetic activation. We tested the hypothesis that polyethylene-particle induced chronic inflammatory bone loss could be suppressed by local delivery of NF-κB decoy ODNs in murine in vivo model. Polyethylene particles were continuously infused into the medullary cavity of the distal femur for 6 weeks to induce chronic inflammation, and micro-computational tomography and immunohistochemical analysis were performed. Particle-induced chronic inflammation resulted in lower BMD values, an increase in osteoclastogenesis and nuclear translocation of p65, a prolonged M1 pro-inflammatory macrophage phenotype, and a decrease of M2 anti-inflammatory macrophage phenotype. Delayed timing of local infusion of NF-κB decoy ODN for the last 3 weeks reversed polyethylene-particle associated chronic inflammatory bone loss and facilitated bone healing. This study demonstrated that polyethylene-particle associated chronic inflammatory osteolysis can be effectively modulated via interference with the NF-κB pathway; this minimally invasive intervention could potentially be an efficacious therapeutic strategy for periprosthetic osteolysis after TJA.

IRAK-4 in macrophages contributes to inflammatory osteolysis of wear particles around loosened hip implants

TLRs recognizing PAMPS play a role in local immunity and participate in implant-associated loosening. TLR-mediated signaling is primarily regulated by IL-1 receptor associated kinase-M (IRAK-M) negatively and IRAK-4 positively. Our previous studies have proved that wear particles promote endotoxin tolerance in macrophages by inducing IRAK-M. However, whether IRAK-4 is involved in inflammatory osteolysis of wear particles basically, and the specific mechanism of IRAK-4 around loosened hip implants, is still unclear. IRAK-4 was studied in the interface membranes from patients in vivo and in particle-stimulated macrophages to clarify its role. Also, IL-1β and TNF-α levels were measured after particle and LPS stimulation in macrophages with or without IRAK-4 silenced by siRNA. Our results showed that the interface membranes around aseptic and septic loosened prosthesis expressed more IRAK-4 compared with membranes from osteoarthritic patients. IRAK-4 in macrophages increased upon particle and LPS stimulation. In the former, IL-1β and TNF-α levels were lower compared with those of LPS stimulation, and IRAK-4 siRNA could suppress production of pro-inflammatory cytokines. These findings suggest that besides IRAK-M, IRAK-4 also plays an important role in the local inflammatory reaction and contributes to prosthesis loosening.

Early changes in serum osteocalcin and body weight are predictive of implant fixation in a rat model of implant loosening

Biomarkers are of interest to identify patients at risk for peri-implant osteolysis and aseptic loosening. We used a rat model of particle-induced peri-implant osteolysis to investigate if early changes in biomarkers were associated with subsequent implant fixation strength. Implants were placed in rat femora, which were then challenged with intra-articular knee injections of either clean polyethylene, lipopolysaccharide-doped polyethylene, or cobalt-chromium alloy particles, with particle-free vehicle serving as control (n ≥ 8 per group). Rats were weighed weekly, blood was collected at weeks 0, 3, 5, and 6, and locomotor behavior was assessed 4 days before study conclusion. Rats were euthanized 6 weeks post surgery. Week 6 serum was analyzed for five bone remodeling markers, while longitudinal serum was assessed for osteocalcin. Bone-implant contact, peri-implant trabecular architecture, and implant fixation strength were measured. Rats challenged with cobalt-chromium particles had a significant reduction in implant fixation strength compared with the vehicle-control group (P = .034). This group also had elevated serum osteocalcin (P = .005), depressed weight gain (P = .001) and less frequent rearing behavior (P = .029). Regardless of group, change in serum osteocalcin at week 3 (r = -.368; P = .046), change in weight at week 2 (r = .586; P < .001), as well as weight change at all other time intervals were associated with fixation strength. The finding that early alterations in serum osteocalcin and body weight were predictive of subsequent implant fixation strength supports continued investigation of biomarkers for early detection of peri-implant osteolysis and implant loosening. Further, change in biomarker levels was found to be more indicative of implant fixation status than any single measurement.

Endotoxin Contributes to Artificial Loosening of Prostheses Induced by Titanium Particles

Background

Aseptic loosening of orthopedic implants caused by wear particles is a major cause of joint replacement failure. However, the mechanism of aseptic loosening has not yet been defined. The present study explored whether endotoxin adherent on the titanium (Ti) particles contributes to aseptic loosening.

Material/Methods

Limulus amebocyte lysate detection was conducted to detect the levels of endotoxin adhered to the Ti particles. A mouse air pouches model was established and mice were divided into 4 groups and injected with phosphate-buffered saline (PBS) or Ti particles suspensions (0.1, 1, 10 mg/mL), following detection of the number of macrophages and the level of endotoxin. Scanning electron microscopy (SEM) was used to characterize the microstructures of Ti particles adhered with endotoxin.

Results

In vitro experiments showed that the level of endotoxin adhered to the Ti particles was significantly increased after adding LPS back to these “endotoxin-free” particles. In vivo experiments showed that Ti particles injection significantly increased the number of macrophages and the level of endotoxin.

Conclusions

In conclusion, these results suggest that adherent endotoxin may play an important role in aseptic loosening induced by Ti particles.

Immunobiology of periprosthetic inflammation and pain following ultra-high-molecular-weight-polyethylene wear debris in the lumbar spine

INTRODUCTION

Wear debris-induced osteolysis is a common cause of arthroplasty failure in several joints including the knee, hip and intervertebral disc. Debris from the prosthesis can trigger an inflammatory response that leads to aseptic loosening and prosthesis failure. In the spine, periprosthetic pain also occurs following accumulation of wear debris through neovascularization of the disc. The role of the immune system in the pathobiology of periprosthetic osteolysis of joint replacements is debatable. Areas covered: We discussed the stimulation of pro-inflammatory and pro-protective and pro-regenerative pathways due to debris from the prosthetics. The balance between the two pathways may determine the outcome results. Also, the role of cytokines and immune cells in periprosthetic inflammation in the etiology of osteolysis is critically reviewed. Expert commentary: Therapies targeting the inflammatory process associated with ultra-high-molecular-weight polyethylene wear debris could reduce implant failure. Additionally, therapies targeting neovascularization of discs following arthroplasty could mitigate periprosthetic pain.

NFκB sensing IL-4 secreting mesenchymal stem cells mitigate the proinflammatory response of macrophages exposed to polyethylene wear particles

Total joint replacement is a highly effective treatment for patients with end-stage arthritis. Proinflammatory macrophages (M1) mediate wear particle-associated inflammation and bone loss. Anti-inflammatory macrophages (M2) help resolve tissue damage and favor bone regeneration. Mesenchymal stem cell (MSC)-based therapy mitigates the M1 dominated inflammatory reaction and favorably modulates the bone remodeling process. In the current study, the immunomodulating ability of (1) unmodified MSCs, (2) MSCs preconditioned by NFκB stimulating ligands [lipopolysaccharide (LPS) plus TNFα], and (3) genetically modified MSCs that secrete IL-4 as a response to NFκB activation (NFκB-IL4) was compared in a macrophage/MSC co-culture system. Sterile or LPS-contaminated ultra-high molecular weight polyethylene particles were used to induce the proinflammatory responses in the macrophages. Contaminated particles induced M1 marker expression (TNFα, IL1β, and iNOS), while NFκB-IL4 MSCs modulated the macrophages from an M1 phenotype into a more favorable M2 phenotype (Arginase 1/Arg 1 and CD206 high). The IL4 secretion by NFκB-IL4 MSCs was significantly induced by the contaminated particles. The induction of Arg 1 and CD206 in macrophages via the preconditioned or naïve MSCs was negligible when compared with NFκB-IL4 MSC. Our findings indicated that NFκB-IL4 MSCs have the "on-demand" immunomodulatory ability to mitigate wear particle-associated inflammation with minimal adverse effects. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2744-2752, 2018.

Cloning, Expression, and Immunogenicity of Fimbrial-F17A Subunit Vaccine against Escherichia coli Isolated from Bovine Mastitis

There is a need to identify and select new promising immunodominant antigens that have the ability to provide protective immunity against E. coli causing bovine mastitis. Recently we showed that f17a was found to be the most prevalent and crucial virulent factor among the pathogenic E. coli isolated from bovine mastitis. Here, in this report, the recombinant F17A based subunit vaccine adjuvant with MF59 was tested for immunogenicity against E. coli in a murine model. The vaccinated mice did not show any abnormal behavioral changes and histopathological lesions after vaccination. The specific antibody level against F17A was significantly higher in MF59-adjuvant-group, and also lasted for longer duration with a significant (P < 0.01) production level of IgG1 and IgG2a. Moreover, we noted higher survival rate in mice injected with F17A-MF59-adjuvant group after challenging with the clinical E. coli strain. Our findings of bacterial clearance test revealed that elimination rate from liver, spleen, and kidney in MF59-adjuvant-group was significantly higher than the control group. Finally, the proportion of CD4+T cells was increased, while CD8+ was decreased in MF59-adjuvant group. In conclusion, the current study reveals the capability of F17A-MF59 as a potential vaccine candidate against pathogenic E. coli causing mastitis in dairy animals.

Arthrotomy-based preclinical models of particle-induced osteolysis: A systematic review

We completed a systematic literature review of in vivo animal models that use arthrotomy-based methods to study particle-induced peri-implant osteolysis. The purpose of the review was to characterize the models developed to date, to determine the questions addressed, to assess scientific rigor and transparency, and to identify gaps in knowledge. We probed three literature databases (Medline, Embase, and Scopus) and found 77 manuscripts that fit the search parameters. In the most recent 10 years, researchers mainly used rat and mouse models, whereas in the previous 20 years, large animal, canine, and rabbit models were more common. The studies have demonstrated several pathophysiology pathways, including macrophage migration, particle phagocytosis, increased local production of cytokines and lysosomal enzymes, elevated bone resorption, and suppressed bone formation. The effect of variation in particle characteristics and concentration received limited attention with somewhat mixed findings. Particle contamination by endotoxin was shown to exacerbate peri-implant osteolysis. The possibility of early diagnosis was demonstrated through imaging and biomarker approaches. Several studies showed that both local and systemic delivery of bisphosphonates inhibits the development of particle-induced osteolysis. Other methods of inhibiting osteolysis include the use of anabolic agents and altering the implant design. Few studies examined non-surgical rescue of loosened implants, with conflicting results with alendronate. We found that the manuscripts often lacked the methodological detail now advocated by the ARRIVE guidelines, suggesting that improvement in reporting would be useful to maximize rigor and transparency. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2595-2605, 2017.

Characterization of endotoxins on orthopaedic fixation screws, using physicochemical surface analyses

The objective of this study was to determine if surface analysis techniques could be used to detect endotoxin on stainless steel malleolus screws. New malleolus screws were compared to ones that had been coated in purified lipopolysaccharide (LPS) or Artificial Test Soil (ATS) containing lipopolysaccharide. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and time-of flight secondary ion mass spectrometry (TOF-SIMS) were used to assess the fixation screws surface. Organic material was visualized on the LPS and ATS-LPS inoculated screws but not on the new unsoiled screws. This was further supported by the peaks observed at masses between 40 and 100 D in TOF-SIMS spectra of the LPS and ATS-LPS inoculated screws. After deconvolution of N1s high resolution XPS spectra, the LPS inoculated screws showed amide groups whereas the ATS-LPS inoculated screws showed predominantly nitroso groups (C-NO). Our data demonstrate that surface analysis can be used to detect organic residuals present on fixation screws. The XPS data confirmed that LPS reacted predominantly with positively charged surface metallic ions (Fe and Cr), whereas proteins reacted with the surface oxide layer of fixation screws, forming C-NO groups. The application of these surface analysis techniques will be helpful in determining if the reprocessing of such items results in an accumulation of organic material that might lead to aseptic loosening, when implanted. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:240-247, 2017.

Emperor's new clothes: Is particle disease really infected particle disease?

Aseptic loosening remains the most significant long-term complication of total hip replacement. The current paradigm points to an inflammatory response to wear particles as its main trigger. Recently, there have been increasing numbers of positive bacterial isolates reported among patients with clinically absent infection. This paper reviews existing evidence on possible involvement of bacteria and microbial-associated molecular patterns in the pathology of so-called "aseptic loosening." © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1497-1504, 2016.

Lipoteichoic acid modulates inflammatory response in macrophages after phagocytosis of titanium particles through Toll-like receptor 2 cascade and inflammasomes

Toll-like receptor 2 (TLR2) and nucleotide-binding and oligomerization domain-like receptors with a pyrin domain 3 (NLRP3) inflammasomes have been presumed to participate in the pathogenesis of aseptic implant loosening. The aim of this study is to analyze the cellular localization of TLR2 and NLRP3 inflammasomes in the periprosthetic tissue from aseptically loose hip implants as well as the expression of these molecules in macrophages stimulated in vitro with titanium particles (Ti) coated with lipoteichoic acid (LTA). Using immunohistochemistry, immunoreactivity of TLR2 and NLRP3 inflammasomes was found in macrophages within the foreign body granulomatosis. Using RAW264.7 cells, stimulation with Ti increased the messenger RNA (mRNA) levels of TLR2 and TNF-α. Stimulation with LTA-coated Ti enhanced mRNA levels of NLRP3 and IL-1β, whereas reinforced secretion of IL-1β was not detected in spite of marked release of TNF-α. Finally, the same cells with silenced Irak2, an adaptor protein in the TLR2 cascade, suppressed this NLRP3 upregulation. This study suggests that TLR2 and NLRP3 inflammasomes are factors involved in cross-talk mediating the foreign body type response to wear particles. In addition, discrepant behavior in the release between TNF-α and IL-1β release may explain the variable pathomechanisms of aseptic implant loosening without acute inflammatory reactions.

Innate immune reactions in septic and aseptic osteolysis around hip implants

According to the long-standing definition, septic and aseptic total joint replacement loosening are two distinct conditions with little in common. Septic joint replacement loosening is driven by bacterial infection whereas aseptic loosening is caused by biomaterial wear debris released from the bearing surfaces. However, recently it has been recognized that the mechanisms that drive macrophage activation in septic and aseptic total joint replacement loosening resemble each other. In particular, accumulating evidence indicates that in addition to mediating bacterial recognition and the subsequent inflammatory reaction, toll-like receptors (TLRs) and their ligands, pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPS), play a key role in wear debris-induced inflammation and macrophage activation. In addition, subclinical bacterial biofilms have been identified from some cases of seemingly aseptic implant loosening. Furthermore, metal ions released from some total joint replacements can activate TLR signaling similar to bacterial derived PAMPs. Likewise, metal ions can function as haptens activating the adaptive immune system similar to bacterial derived antigens. Thus, it appears that aseptic and septic joint replacement loosening share similar underlying pathomechanisms and that this strict dichotomy to sterile aseptic and bacterial-caused septic implant loosening is somewhat questionable. Indeed, rather than being two, well-defined clinical entities, peri-implant osteolysis is, in fact, a spectrum of conditions in which the specific clinical picture is determined by complex interactions of multiple local and systemic factors.

3-Dimensional cell-laden nano-hydroxyapatite/protein hydrogels for bone regeneration applications

The ability to encapsulate cells in three-dimensional (3D) protein-based hydrogels is potentially of benefit for tissue engineering and regenerative medicine. However, as a result of their poor mechanical strength, protein-based hydrogels have traditionally been considered for soft tissue engineering only. Hence, in this study we tried to render these hydrogels suitable for hard tissue regeneration, simply by incorporation of bioactive nano-hydroxyapatite (HAp) into a photocrosslinkable gelatin hydrogel. Different cell types were also encapsulated in three dimensions in the resulting composites to prepare cell-laden constructs. According to the results, HAp significantly improves the stiffness of gelatin hydrogels, while it maintains their structural integrity and swelling ratio. It was also found that while the bare hydrogel (control) was completely inert in terms of bioactivity, a homogeneous 3D mineralization occurs throughout the nanocomposites after incubation in simulated body fluid. Moreover, encapsulated cells readily elongated, proliferated, and formed a 3D interconnected network with neighboring cells in the nanocomposite, showing the suitability of the nano-HAp/protein hydrogels for cellular growth in 3D. Therefore, the hydrogel nanocomposites developed in this study may be promising candidates for preparing cell-laden tissue-like structures with enhanced stiffness and increased osteoconductivity to induce bone formation in vivo.

Antibiotic prophylaxis for preventing infectious complications in orthognathic surgery

BACKGROUND

Orthognathic surgery (OS) is a term that refers to many elective surgical techniques to correct facial deformity; the associated malocclusion and functional disorders related to the stomatognathic system. Whilst such surgery is classed as "clean-contaminated", the usefulness of and the most appropriate regimen for antibiotic prophylaxis in these patients are still debated.

OBJECTIVES

To assess the effects of antibiotic prophylaxis for preventing surgical site infection (SSI) in people undergoing orthognathic surgery.

SEARCH METHODS

In June 2014, we searched the Cochrane Wounds Group Specialised Register; the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library); Ovid MEDLINE; Ovid MEDLINE (In-Process & Other Non-Indexed Citations); Ovid EMBASE; and EBSCO CINAHL. We also searched Google Scholar and performed manual searches in journals relevant to the topic, conference proceedings and lists of references of potentially included articles. We did not restrict the search and study selection with respect to language, date of publication or study setting.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) involving people undergoing orthognathic surgery comparing one regimen of antibiotic prophylaxis with any other regimen or placebo. The primary outcome was SSI, and secondary outcomes were systemic infections, adverse events, duration of hospital stay and health-related quality of life. Two review authors screened articles independently.

DATA COLLECTION AND ANALYSIS

Data were abstracted independently by two review authors, and agreement was checked. Risk of bias was assessed using the Cochrane risk of bias tool. Antibiotic regimens were classified as preoperative (one dose before surgery), short-term (before or during surgery and/or during the same day of surgery) and long-term (before or during surgery and longer than one day after surgery) antibiotic prophylaxis. Random-effects meta-analyses using inverse variance methods were undertaken when possible. We report risk ratios (RRs) and their corresponding 95% confidence intervals (CIs).

MAIN RESULTS

A total of 11 trials were included in this review. Most of the studies had an unclear risk of bias prompting us to downgrade the quality of evidence for our outcomes. Seven of these trials provided evidence for the main comparison and the primary outcome and these were pooled. Overall, long-term antibiotic prophylaxis probably reduces the risk of SSI (plausible effects range between a 76% to a 0.26% relative reduction in SSI with long-term antibiotic prophylaxis) (472 participants; RR 0.42, 95% CI 0.24 to 0.74; moderate-quality evidence). There is uncertainty surrounding the relative effects of short-term antibiotics compared with a single dose (220 participants; RR 0.34, 95% CI 0.09 to 1.22; low-quality evidence). No reports described adverse effects associated with the drugs in those trials that reported in this outcome. None of these trials assessed or reported data regarding other outcomes, and information was insufficient to show whether a specific antibiotic is better than another.

AUTHORS' CONCLUSIONS

For people undergoing orthognathic surgery, long term antibiotic prophylaxis decreases the risk of SSI compared with short-term antibiotic prophylaxis and the is uncertainty of whether short-term antibiotic prophylaxis decreases SSi risk relative to a single pre-operative dose of prophylactic antibiotics.

Do genetic susceptibility, Toll-like receptors, and pathogen-associated molecular patterns modulate the effects of wear?

Overwhelming evidence supports the concept that wear particles are the primary initiator of aseptic loosening of orthopaedic implants. It is likely, however, that other factors modulate the biologic response to wear particles. This review focuses on three potential other factors: genetic susceptibility, Toll-like receptors (TLRs), and bacterial pathogen-associated molecular patterns (PAMPs). WHERE ARE WE NOW?: Considerable evidence is emerging that both genetic susceptibility and TLR activation are important factors that modulate the biologic response to wear particles, but it remains controversial whether bacterial PAMPs also do so. WHERE DO WE NEED TO GO?: Detailed understanding of the roles of these other factors may lead to identification of novel therapeutic targets for patients with aseptic loosening. HOW DO WE GET THERE?: Highest priority should be given to polymorphism replication studies with large numbers of patients and studies to replicate the reported correlation between bacterial biofilms and the severity of aseptic loosening.

Interaction of Materials and Biology in Total Joint Replacement - Successes, Challenges and Future Directions

Total joint replacement (TJR) has revolutionized the treatment of end-stage arthritic disorders. This success is due, in large part, to a clear understanding of the important interaction between the artificial implant and the biology of the host. All surgical procedures in which implants are placed in the body evoke an initial inflammatory reaction, which generally subsides over several weeks. Thereafter, a series of homeostatic events occur leading to progressive integration of the implant within bone and the surrounding musculoskeletal tissues. The eventual outcome of the operation is dependent on the characteristics of the implant, the precision of the surgical technique and operative environment, and the biological milieu of the host. If these factors and events are not optimal, adverse events can occur such as the development of chronic inflammation, progressive bone loss due to increased production of degradation products from the implant (periprosthetic osteolysis), implant loosening or infection. These complications can lead to chronic pain and poor function of the joint reconstruction, and may necessitate revision surgery or removal of the prosthesis entirely. Recent advances in engineering, materials science, and the immunological aspects associated with orthopaedic implants have fostered intense research with the hope that joint replacements will last a lifetime, and facilitate pain-free, normal function.

Particle-induced osteolysis is not accompanied by systemic remodeling but is reflected by systemic bone biomarkers

Particle-induced osteolysis is caused by an imbalance in bone resorption and formation, often leading to loss of implant fixation. Bone remodeling biomarkers may be useful for identification of osteolysis and studying pathogenesis, but interpretation of biomarker data could be confounded if local osteolysis engenders systemic bone remodeling. Our goal was to determine if remote bone remodeling contributes to biomarker levels. Serum concentrations of eight biomarkers and bone remodeling rates at local (femur), contiguous (tibia), and remote (humerus and lumbar vertebra) sites were evaluated in a rat model of particle-induced osteolysis. Serum CTX-1, cathepsin K, PINP, and OPG were elevated and osteocalcin was suppressed in the osteolytic group, but RANKL, TRAP 5b, and sclerostin were not affected at the termination of the study at 12 weeks. The one marker tested longitudinally (CTX-1) was elevated by 3 weeks. We found increased bone resorption and decreased bone formation locally, subtle differences in contiguous sites, but no differences remotely at 12 weeks. Thus, the skeletal response to local particle challenge was not systemic, implying that the observed differences in serum biomarker levels reflect differences in local remodeling.

Orthopaedic implant failure: aseptic implant loosening–the contribution and future challenges of mouse models in translational research

Aseptic loosening as a result of wear debris is considered to be the main cause of long-term implant failure in orthopaedic surgery and improved biomaterials for bearing surfaces decreases significantly the release of micrometric wear particles. Increasingly, in-depth knowledge of osteoimmunology highlights the role of nanoparticles and ions released from some of these new bearing couples, opening up a new era in the comprehension of aseptic loosening. Mouse models have been essential in the progress made in the early comprehension of pathophysiology and in testing new therapeutic agents for particle-induced osteolysis. However, despite this encouraging progress, there is still no valid clinical alternative to revision surgery. The present review provides an update of the most commonly used bearing couples, the current concepts regarding particle–cell interactions and the approaches used to study the biology of periprosthetic osteolysis. It also discusses the contribution and future challenges of mouse models for successful translation of the preclinical progress into clinical applications.

Integrin-directed modulation of macrophage responses to biomaterials

Macrophages are the primary mediator of chronic inflammatory responses to implanted biomaterials, in cases when the material is either in particulate or bulk form. Chronic inflammation limits the performance and functional life of numerous implanted medical devices, and modulating macrophage interactions with biomaterials to mitigate this response would be beneficial. The integrin family of cell surface receptors mediates cell adhesion through binding to adhesive proteins nonspecifically adsorbed onto biomaterial surfaces. In this work, the roles of integrin Mac-1 (αMβ2) and RGD-binding integrins were investigated using model systems for both particulate and bulk biomaterials. Specifically, the macrophage functions of phagocytosis and inflammatory cytokine secretion in response to a model particulate material, polystyrene microparticles were investigated. Opsonizing proteins modulated microparticle uptake, and integrin Mac-1 and RGD-binding integrins were found to control microparticle uptake in an opsonin-dependent manner. The presence of adsorbed endotoxin did not affect microparticle uptake levels, but was required for the production of inflammatory cytokines in response to microparticles. Furthermore, it was demonstrated that integrin Mac-1 and RGD-binding integrins influence the in vivo foreign body response to a bulk biomaterial, subcutaneously implanted polyethylene terephthalate. A thinner foreign body capsule was formed when integrin Mac-1 was absent (~30% thinner) or when RGD-binding integrins were blocked by controlled release of a blocking peptide (~45% thinner). These findings indicate integrin Mac-1 and RGD-binding integrins are involved and may serve as therapeutic targets to mitigate macrophage inflammatory responses to both particulate and bulk biomaterials.

Chronic inflammation in biomaterial-induced periprosthetic osteolysis: NF-κB as a therapeutic target

Biomaterial-induced tissue responses in patients with total joint replacement are associated with the generation of wear particles, which may lead to chronic inflammation and local bone destruction (periprosthetic osteolysis). Inflammatory reactions associated with wear particles are mediated by several important signaling pathways, the most important of which involves the transcription factor NF-κB. NF-κB activation is essential for macrophage recruitment and maturation, as well as the production of pro-inflammatory cytokines and chemokines such as TNF-α, IL-1β, IL-6 and MCP1. In addition, NF-κB activation contributes to osteoclast differentiation and maturation via RANK/RANKL signaling, which increases bone destruction and reduces bone formation. Targeting individual downstream cytokines directly (such as TNF-α or IL-1β) may not effectively prevent wear particle induced osteolysis. A more logical upstream therapeutic approach may be provided by direct modulation of the core IκB/IKKα/β/NF-κB signaling pathway in the local environment. However, the timing, dose and strategy for administration should be considered. Suppression of chronic inflammation via inhibition of NF-κB activity in patients with malfunctioning joint replacements may be an effective strategy to mitigate wear particle induced periprosthetic osteolysis.

Macrophages-Key cells in the response to wear debris from joint replacements

The generation of wear debris is an inevitable result of normal usage of joint replacements. Wear debris particles stimulate local and systemic biological reactions resulting in chronic inflammation, periprosthetic bone destruction, and eventually, implant loosening, and revision surgery. The latter may be indicated in up to 15% patients in the decade following the arthroplasty using conventional polyethylene. Macrophages play multiple roles in both inflammation and in maintaining tissue homeostasis. As sentinels of the innate immune system, they are central to the initiation of this inflammatory cascade, characterized by the release of proinflammatory and pro-osteoclastic factors. Similar to the response to pathogens, wear particles elicit a macrophage response, based on the unique properties of the cells belonging to this lineage, including sensing, chemotaxis, phagocytosis, and adaptive stimulation. The biological processes involved are complex, redundant, both local and systemic, and highly adaptive. Cells of the monocyte/macrophage lineage are implicated in this phenomenon, ultimately resulting in differentiation and activation of bone resorbing osteoclasts. Simultaneously, other distinct macrophage populations inhibit inflammation and protect the bone-implant interface from osteolysis. Here, the current knowledge about the physiology of monocyte/macrophage lineage cells is reviewed. In addition, the pattern and consequences of their interaction with wear debris and the recent developments in this field are presented.

Interference of silica nanoparticles with the traditional Limulus amebocyte lysate gel clot assay

Endotoxin contaminations of engineered nanomaterials can be responsible for observed biological responses, especially for misleading results in in vitro test systems, as well as in vivo studies. Therefore, endotoxin testing of nanomaterials is necessary to benchmark their influence on cells. Here, we tested the traditional Limulus amebocyte lysate gel clot assay for the detection of endotoxins in nanoparticle suspensions with a focus on possible interference of the particles with the test system. We systematically investigated the effects of nanomaterials made of, or covered by, the same material. Different types of bare or PEGylated silica nanoparticles, as well as iron oxide-silica core shell nanoparticles, were tested. Detailed inhibition/enhancement controls revealed enhanced activity in the Limulus coagulation cascade for all particles with bare silica surface. In comparison, PEGylation led to a lower degree of enhancement. These results indicate that the protein-particle interactions are the basis for the observed inhibition and enhancement effects. The enhancement activity of a particle type was positively related to the calculated particle surface area. For most silica particles tested, a dilution of the sample within the maximum valid dilution was sufficient to overcome non-valid enhancement, enabling semi-quantification of the endotoxin contamination.

Severe impingement of lumbar disc replacements increases the functional biological activity of polyethylene wear debris

BACKGROUND

Wear, oxidation, and particularly rim impingement damage of ultra-high molecular weight polyethylene total disc replacement components have been observed following surgical revision. However, neither in vitro testing nor retrieval-based evidence has shown the effect(s) of impingement on the characteristics of polyethylene wear debris. Thus, we sought to determine (1) differences in polyethylene particle size, shape, number, or biological activity that correspond to mild or severe rim impingement and (2) in an analysis of all total disc replacements, regardless of impingement classification, whether there are correlations between the extent of regional damage and the characteristics of polyethylene wear debris.

METHODS

The extent of dome and rim damage was characterized for eleven retrieved polyethylene cores obtained at revision surgery after an average duration of implantation of 9.7 years (range, 4.6 to 16.1 years). Polyethylene wear debris was isolated from periprosthetic tissues with use of nitric acid and was imaged with use of environmental scanning electron microscopy. Subsequently, particle size, shape, number, biological activity, and chronic inflammation scores were determined.

RESULTS

Grouping of particles by size ranges that represented high biological relevance (&lt;0.1 to 1-μm particles), intermediate biological relevance (1 to 10-μm particles), and low biological relevance (&gt;10-μm particles) revealed an increased volume fraction of particles in the &lt;0.1 to 1-μm and 1 to 10-μm size ranges in the mild-impingement cohort as compared with the severe-impingement cohort. The increased volume fractions resulted in a higher specific biological activity per unit particle volume in the mild-impingement cohort than in the severe-impingement cohort. However, functional biological activity, which is normalized by particle volume (mm3/g of tissue), was significantly higher in the severe-impingement cohort. This increase was due to a larger volume of particles in all three size ranges. In both cohorts, the functional biological activity correlated with the chronic inflammatory response, and the extent of rim penetration positively correlated with increasing particle size, number, and functional biological activity.

CONCLUSIONS

The results of this study suggest that severe rim impingement increases the production of biologically relevant particles from motion-preserving lumbar total disc replacement components.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Endotoxins-the invisible companion in biomaterials research

Metal implants and polymeric devices for the application in the clinical treatment of orthopedic tissue injuries are increasingly coated with bioactive biomaterials derived from natural substances to induce desirable biological effects. Many metals and polymers used in biomaterials research show high affinity for endotoxins, which are abundant in the environment. Endotoxin contamination is indicated in the pathology of periodontitis and aseptic implant loosening, but may also affect the evaluation of a biomaterial's bioactivity by inducing strong inflammatory reactions. In this review, we discuss the high affinity of three commonly used implant biomaterials for endotoxins and how the contamination can affect the outcome of the orthopedic fixation. The chemical nature of bacterial endotoxins and some of the clinical health implications are described, as this knowledge is critically important to tackle the issues associated with the measurement and removal of endotoxins from medical devices. Commonly used methods for endotoxin testing and removal from natural substances are examined and the lack of standard guidelines for the in vitro evaluation of biomaterials is discussed.

Bone turnover markers correlate with implant fixation in a rat model using LPS-doped particles to induced implant loosening

Revision surgery for particle-induced implant loosening in total joint replacement is expected to increase dramatically over the next few decades. This study was designed to investigate if local tissue and serum markers of bone remodeling reflect implant fixation following administration of lipopolysaccharide (LPS)-doped polyethylene (PE) particles in a rat model. Twenty-four rats received bilateral implantation of intramedullary titanium rods in the distal femur, followed by weekly bilateral intra-articular injection of either LPS-doped PE particles (n = 12) or vehicle that contained no particles (n = 12) for 12 weeks. The group in which the particles were injected had increased serum C-terminal telopeptide of type I collagen (CTX-I), decreased serum osteocalcin (OC), increased peri-implant eroded surface, decreased peri-implant bone volume, and decreased mechanical pull-out strength compared to the controls. Implant fixation strength was positively correlated with peri-implant bone volume and serum OC and inversely correlated with serum CTX-I, while energy to yield was positively correlated with serum OC and inversely correlated with the number of tartrate-resistant acid phosphatase positive cells at the interface and the amount of peri-implant eroded surface. There was no effect on trabecular bone volume at a remote site. Thus, the particle-induced impaired fixation in this rat model was directly associated with local and serum markers of elevated bone resorption and depressed bone formation, supporting the rationale of exploring both anticatabolic and anabolic strategies to treat and prevent particle-related implant osteolysis and loosening, and indicating that serum markers may prove useful in tracking implant fixation.

IRAK-M in macrophages around septically and aseptically loosened hip implants

The most common long-term complication of joint arthroplasty is loosening, which is mediated by chronic inflammatory cytokines produced by macrophages stimulated by implant-derived debris and eventually bacterial components adherent to such debris. In this study, antiinflammatory interleukin-1 receptor-associated kinase-M (IRAK-M) was studied in macrophages in interface membranes in vivo using immunohistochemical staining and in titanium particle-stimulated macrophages in vitro using reverse transcriptase-polymerase chain reaction. Results show that the interface membranes of septically and aseptically loosened prosthesis express more IRAK-M protein than control membranes from osteoarthritic patient and that IRAK-M mRNA-levels increase upon particle stimulation. These findings suggest that, the upregulation of IRAK-M in macrophages is involved in the local immunosuppression around implants, and may contribute to septic and aseptic implant loosening.

Macrophage response to high number of titanium particles is cytotoxic and COX-2 mediated and it is not affected by the particle's endotoxin content or the cleaning treatment

Periprosthetic osteolysis is a progressive deterioration of bone around prostheses resulting primarily from the presence of wear debris. Particulate material, number, and their interactions with environmental factors play important roles in macrophage activation around implants. We have previously shown that macrophages cultured in the presence of high numbers of cleaned titanium (Ti) particles released significant amounts of PGE₂ that is potentially detrimental for bone. Cleaning of particles has become routine in most studies of macrophage/particle interactions as contaminating endotoxin elicits a macrophage cytokine response and since numerous studies have suggested that endotoxins may be present on implant materials. However, the strenuous cleaning procedure itself represents a possible source of other contaminants (such as material by-products) that may be relevant to the prostanoid response of macrophages. To analyze this hypothesis, the macrophage response to high numbers of cleaned Ti particles was compared to that of unclean particles and to particles that were subjected to a short version of the cleaning procedure. It was found that neither the high amount of endotoxin on the unclean particles nor the duration of the cleaning procedure had an effect on the release of PGE₂ and the decrease in cell viability in response to high number of Ti particles. Evidence of a possible relationship between these two variables is presented.

Bacterial pathogen-associated molecular patterns stimulate biological activity of orthopaedic wear particles by activating cognate Toll-like receptors

Aseptic loosening of orthopaedic implants is induced by wear particles generated from the polymeric and metallic components of the implants. Substantial evidence suggests that activation of Toll-like receptors (TLRs) may contribute to the biological activity of the wear particles. Although pathogen-associated molecular patterns (PAMPs) produced by Gram-positive bacteria are likely to be more common in patients with aseptic loosening, prior studies have focused on LPS, a TLR4-specific PAMP produced by Gram-negative bacteria. Here we show that both TLR2 and TLR4 contribute to the biological activity of titanium particles with adherent bacterial debris. In addition, lipoteichoic acid, a PAMP produced by Gram-positive bacteria that activates TLR2, can, like LPS, adhere to the particles and increase their biological activity, and the increased biological activity requires the presence of the cognate TLR. Moreover, three lines of evidence support the conclusion that TLR activation requires bacterially derived PAMPs and that endogenously produced alarmins are not sufficient. First, neither TLR2 nor TLR4 contribute to the activity of "endotoxin-free" particles as would be expected if alarmins are sufficient to activate the TLRs. Second, noncognate TLRs do not contribute to the activity of particles with adherent LPS or lipoteichoic acid as would be expected if alarmins are sufficient to activate the TLRs. Third, polymyxin B, which inactivates LPS, blocks the activity of particles with adherent LPS. These results support the hypothesis that PAMPs produced by low levels of bacterial colonization may contribute to aseptic loosening of orthopaedic implants.

In vivo response to cross-linked polyethylene and polycarbonate-urethane particles

This study was undertaken to examine macrophage response to polycarbonate-urethane, a proposed alternative material to polyethylene in acetabular components of total hip arthroplasty. Polyethylene wear debris from total joint replacements has been linked to osteolysis and implant lifespan. It has been shown in vitro, that polyethylene particles cleaned of endotoxin generate less of an inflammatory cytokine response than endotoxin bound particles. Comparative particle induced effects on implant fixation were tested using endotoxin free cross-linked ultra-high molecular weight polyethylene (x-UHMWPE) and polycarbonate-urethane (PCU) particles with and without intraperitoneal injection (IP) of lipopolysaccharide (LPS) using a Ti-alloy femoral intramedullary nail rat model. MicroCT and mechanical testing assessment of peri-implant bone indicated significantly less bone and lower fixation strength, respectively, when the implant was surrounded by xUHMWPE particles compared to PCU particles (with and without LPS IP). This indicates particles of PCU may be less disruptive to bone-implant fixation than x-UHMWPE in vivo, under both LPS free and challenged conditions.

In vitro macrophage response to polyethylene and polycarbonate-urethane particles

This study was undertaken to compare macrophage response to polycarbonate-urethane (PCU), a proposed alternative material to polyethylene in acetabular components of total hip arthroplasty to cross-linked ultra-high molecular weight polyethylene (xUHMWPE) in the presence or absence of endotoxin. Polyethylene wear debris that is generated by total hip and knee replacements has been linked to osteolysis and limiting the lifespan of the implant. We added both lipopolysaccharide (LPS)-free and endotoxin-associated xUHMWPE and PCU particles to a human monocyte cell line (TH1) in culture and measured cell viability and tumor necrosis factor (TNF)alpha, interleukin (IL)-1beta, and prostaglandin E(2) (PGE(2)) in the medium after 24 h. Results indicate that particles (both xUHMWPE and PCU) free of endotoxin did not significantly induce secretion of TNFalpha, IL-1beta, or PGE(2) above basal levels. However, endotoxin-exposed PCU particles induced significantly less TNFalpha and IL-1beta than endotoxin-exposed xUHMWPE particles. This indicates that if endotoxin is available for binding to particles in vivo, then xUHMWPE may be more inflammatory to periprosthetic tissue and bone in part because of its affinity/reactivity with endotoxin when compared with PCU.

Toll-like receptors and aseptic loosening of hip endoprosthesis-a potential to respond against danger signals?

Bacterial remnants and subclinical biofilms residing on prosthesis surfaces have been speculated to play a role in hip implant loosening by opsonizing otherwise relatively inert wear particles. The innate immune system recognizes these microbial pathogen-associated molecular patterns (PAMPs) using Toll-like receptors (TLRs). Our objective was to evaluate the possible presence of TLRs in aseptic synovial membrane-like interface tissue. Bacterial culture-negative, aseptic (n = 4) periprosthetic synovial membrane-like tissue was compared to osteoarthritis synovial membrane (n = 5) for the presence of cells positive for all known human functional TLRs, stained using specific antibodies by immunohistochemistry, and evaluated using morphometry. In comparison to osteoarthtritic synovium, the number of TLR-positive cells was found to be increased in the aseptic setting, reflecting the considerable macrophage infiltration to the tissues investigated. Thus aseptic periprosthetic tissue seems to be very reactive to PAMPs. It has been recently recognized that TLR do not only respond to traditional PAMPs, but also to endogenous alarmings or danger signals released from necrotic and activated cells. Alarming-TLR interaction in the periprosthetic tissue might be a novel mechanism of aseptic loosening of endoprosthesis.

Highly crosslinked vs conventional polyethylene particles: relative in vivo inflammatory response

Crosslinked polyethylenes have been introduced to reduce wear and osteolysis. The osteolysis rate depends on many factors including the biologic activity of the wear particles. This study examines the relative inflammatory potential of highly crosslinked and non-crosslinked polyethylene particles. Polyethylene particles were crosslinked and characterized. Dose-response curves were generated for endotoxin-positive and endotoxin-negative particles at each degree of cross-linking using an in vivo model. The 10-MRad crosslinked polyethylene was more inflammatory than an identical dose (25 mg/mL) of non-crosslinked polyethylene (P = .05). Endotoxin increased the inflammatory response to crosslinked and non-crosslinked polyethylene in a similar fashion. These data suggest that the improved wear characteristics of highly crosslinked polyethylenes may be offset somewhat by the modestly increased inflammatory profile of the highly crosslinked compared with non-crosslinked particles.

What other biologic and mechanical factors might contribute to osteolysis?

An overwhelming consensus exists that wear particles are the primary driving force in aseptic loosening of orthopaedic implants. Nonetheless, considerable evidence has emerged demonstrating that various other factors can modulate the biologic activity of orthopaedic wear particles. Two of the most studied modulating factors are bacterial endotoxins and implant motion.

Titanium particles that have undergone phagocytosis by macrophages lose the ability to activate other macrophages

Titanium particles derived from the wear of the orthopaedic implant surfaces can activate macrophages to secrete cytokines and stimulate osteoclastic bone resorption, causing osteolysis around orthopaedic implants. However, what happens to the titanium particles after being phagocytosed by macrophages is not known. We prepared titanium particles (as received, clean, and LPS-coated), and exposed them to macrophages in culture. Free particles were washed away after 24 h and the intracellular particles were kept in culture for additional 48 h until being harvested by lysing the cells. Particles that had been cell treated or noncell treated were examined by scanning electronic microscopy to analyze the shape, size, and concentration of the particles. The cell treated and noncell treated particles were exposed to macrophages in culture with a particle to cell ratio of 300:1. After 18 h, the levels of TNF-alpha in culture medium and the viability of the cells were examined. Clean particles did not stimulate TNF-alpha secretion by macrophages, while LPS-coated particles dramatically increased that response. Phagocytosis by macrophages did not change the shape and size of the particles, but depleted the ability of the particles to stimulate TNF-alpha secretion by macrophages. This indicates that macrophages are capable of rendering titanium particles inactive without degrading the particles, possibly by altering the surface chemistry of the particles.

Administration of pamidronate alters bone-titanium attachment in the presence of endotoxin-coated polyethylene particles

Bisphosphonates are promising in the treatment of periprosthetic osteolysis induced by particulate wear debris. The in vivo effects of pamidronate with different doses and durations of administration on bone-titanium attachment in the presence of endotoxin-coated polyethylene particles were examined in a rat model in this study. Titanium pins and endotoxin-coated polyethylene particles were introduced into rat femoral canals followed by intraperitoneal injection of pamidronate every other day. The treatment varied in the dose from 0 to 40 microg/kg and the duration of either 10 days or 6 weeks. Bilateral femurs were harvested after 6 weeks and examined by bone densitometer and MicroCT scan. Pamidronate increased the bone density of the left, unoperated femurs in a dose and duration dependent manner. Bone-titanium attachment significantly increased in all treatment groups compared to the control group. When pamidronate was administered for 10 days, the increase of bone-titanium attachment was significantly dose-dependent. However, when pamidronate was given for 6 weeks at 4 microg/kg, the bone-titanium attachment was significantly (p < 0.001) lower compared to the 10 day treatment of the same dose, although it was significantly higher than controls. Our results suggest that pamidronate effectively increase bone-titanium attachment even in the presence of endotoxin-coated polyethylene particles. However, long-term administration may reduce its efficacy.

The balance between endotoxin accumulation and clearance during particle-induced osteolysis in murine calvaria

Bacterial endotoxin may contribute to aseptic loosening of orthopedic implants even in the absence of clinical or microbiological evidence of infection. One potential source of endotoxin during aseptic loosening is systemically circulating endotoxin, derived from intestinal flora, minor infections, or dental procedures, that may bind to wear particles. The current study demonstrates that systemically derived endotoxin accumulates when 'endotoxin-free' titanium and polyethylene particles are implanted on murine calvaria. Time-course experiments and experiments using germ-free mice rule out the possibility that the observed endotoxin accumulation may be due to bacterial contamination. In contrast, endotoxin is cleared from titanium particles that originally carry high amounts of adherent endotoxin. The mechanism of endotoxin clearance is not dependent on induction of a respiratory burst. Taken together, these results indicate that a balance between endotoxin accumulation and endotoxin clearance controls the steady-state level of endotoxin surrounding orthopedic wear particles implanted on murine calvaria. This balance may regulate the rate of osteolysis in the murine calvaria model as well as in patients with aseptic loosening.