Local delivery of mutant CCL2 protein-reduced orthopaedic implant wear particle-induced osteolysis and inflammation in vivo

Ultra-High-Molecular-Weight Polyethylene in Hip and Knee Arthroplasties

Ultra-high-molecular-weight polyethylene (UHMWPE) wear and particle-induced osteolysis contribute to the failure of total hip arthroplasty (THA) and total knee arthroplasty (TKA). Highly crosslinked polyethylene (HXLPE) was developed in the late 1990s to reduce wear and has shown lower wear rates and loosening than conventional UHMWPE in THA. The irradiation dose for crosslinking is up to 100 kGy. However, during crosslinking, free radical formation induces oxidation. Using HXLPE in THA, the cumulative revision rate was determined to be significantly lower (6.2%) than that with conventional UHMWPE (11.7%) at a mean follow-up of 16 years, according to the Australian Orthopaedic Association National Joint Replacement Registry. However, HXLPE does not confer to TKA the same advantages it confers to THA. Several alternatives have been developed to prevent the release of free radicals and improve polymer mechanical properties, such as thermal treatment, phospholipid polymer 2-methacryloyloxyethyl phosphorylcholine grafting, remelting, and vitamin E addition. Among these options, vitamin E addition has reported good clinical results and wear resistance similar to that of HXLPE without vitamin E, as shown by short-term clinical studies of THA and TKA. This review aims to provide a comprehensive overview of the development and performance of UHMWPE in THA and TKA.

Involvement of NF-κB/NLRP3 axis in the progression of aseptic loosening of total joint arthroplasties: a review of molecular mechanisms

Particulate wear debris can trigger pro-inflammatory bone resorption and result in aseptic loosening. This complication remains major postoperative discomforts and complications for patients who underwent total joint arthroplasty. Recent studies have indicated that wear debris-induced aseptic loosening is associated with the overproduction of pro-inflammatory cytokines. The activation of osteoclasts as a result of inflammatory responses is associated with osteolysis. Moreover, stimulation of inflammatory signaling pathways such as the NF-κB/NLRP3 axis results in the production of pro-inflammatory cytokines. In this review, we first summarized the potential inflammatory mechanisms of wear particle-induced peri-implant osteolysis. Then, the therapeutic approaches, e.g., biological inhibitors, herbal products, and stem cells or their derivatives, with the ability to suppress the inflammatory responses, mainly NF-κB/NLRP3 signaling pathways, were discussed. Based on the results, activation of macrophages following inflammatory stimuli, overproduction of pro-inflammatory cytokines, and subsequent differentiation of osteoclasts in the presence of wear particles lead to bone resorption. The activation of NF-κB/NLRP3 signaling pathways within the macrophages stimulates the production of pro-inflammatory cytokines, e.g., IL-1β, IL-6, and TNF-α. According to in vitro and in vivo studies, novel therapeutics significantly promoted osteogenesis, suppressed osteoclastogenesis, and diminished particle-mediated bone resorption. Conclusively, these findings offer that suppressing pro-inflammatory cytokines by regulating both NF-κB and NLRP3 inflammasome represents a novel approach to attenuate wear-particle-related osteolytic diseases.

Chemerin/ChemR23 signaling mediates the effects of ultra-high molecular weight polyethylene wear particles on the balance between osteoblast and osteoclast differentiation

Background

Ultra-high molecular weight polyethylene (UHMWPE) is one of the favored materials for total joint replacement, but its wear particles cause osteolysis. This study aims to elucidate the signaling that mediates the effects of UHMWPE particles on bone cells.

Methods

RAW264.7 and MC3T3-E1 cells were treated with UHMWPE particles. Chemerin/ChemR23 signaling was manipulated by either overexpressing Rarres2 and Cmklr1 or silencing Cmklr1. The osteoblast and osteoclast differentiation was evaluated by Alizarin red and TRAP staining, respectively. The expression of osteogenic and osteoclastogenic markers was assessed with quantitative real time PCR and western blot.

Results

UHMWPE particles upregulated the expression of Rarres2 and Cmklr1 in both osteoblast and osteoclast precursor cells. UHMWPE particles induced osteoclast differentiation while inhibited osteoblast differentiation, and this effect was abrogated by silencing Cmklr1 but augmented by the overexpression of Rarres2 and Cmklr1. Similarly, the expression of osteogenic marker genes was inhibited while that of osteoclastogenic marker genes was activated by UHMWPE particles, and this effect was abolished by silencing Cmklr1 and enhanced by Rarres2 and Cmklr1 overexpression.

Conclusions

These results demonstrated that chemerin/ChemR23 signaling plays a central role in the effects of UHMWPE particles on the balance of osteogenic and osteoclastogenic differentiation, which changes the course of bone remodeling and eventually results in osteolysis.

Real-Time Quantification of Cartilage Degeneration by GAG-Targeted Cationic Nanoparticles for Efficient Therapeutic Monitoring in Living Mice

One of the characterizations of degenerative cartilage disease is the progressive loss of glycosaminoglycans (GAGs). The real-time imaging method to quantify GAGs is of great significance for the biochemical analysis of cartilage and diagnosis and therapeutic monitoring of cartilage degeneration in vivo. To this end, a cationic photoacoustic (PA) contrast agent, poly-l-lysine melanin nanoparticles (PLL-MNPs), specifically targeting anionic GAGs was developed in this study to investigate whether it can image cartilage degeneration. PLL-MNP assessed GAG depletion by Chondroitinase ABC in vitro rat cartilage and intact ex vivo mouse knee joint. A papain-induced cartilage degenerative mice model was used for in vivo photoacoustic imaging (PAI). Oral cartilage supplement glucosamine sulfate was intragastrically administered for mice cartilage repair and the therapeutic efficacy was monitored by PLL-MNP-enhanced PAI. Histologic findings were used to further confirm PAI results. In vitro results revealed that the PLL-MNPs not only had a high binding ability with GAGs but also sensitively monitored GAG content changes by PAI. The PA signal was gradually weakened along with the depletion of GAGs in cartilage. Particularly, PLL-MNPs depicted the cartilage structure and the distribution of GAGs was demonstrated in PA images in ex vivo joints. Compared with the normal joint, a lower signal intensity was detected from degenerative joint at 3 weeks after papain injection, suggesting an early diagnosis of cartilage lesion by PLL-MNPs. Importantly, this PA-enhanced nanoprobe was suitable for monitoring in vivo efficacy of glucosamine sulfate, which effectively blocked cartilage degradation in a high dose manner. In vivo imaging findings correlated well with histological examinations. PLL-MNPs provided sensitive visualization of cartilage degeneration and promising monitoring of therapeutic response in living subjects.

Distinct macrophage populations and phenotypes associated with IL-4 mediated immunomodulation at the host implant interface

The host macrophage response to implants has shown to be affected by tissue location and physio-pathological conditions of the patient. Success in immunomodulatory strategies is thus predicated on the proper understanding of the macrophage populations participating on each one of these contexts. The present study uses an in vivo implantation model to analyze how immunomodulation via an IL-4 eluting implant affects distinct macrophage populations at the tissue-implant interface and how this may affect downstream regenerative processes. Populations identified as F4/80+, CD68+ and CD11b+ macrophages at the peri-implant space showed distinct susceptibility to polarize towards an M2-like phenotype under the effects of delivered IL-4. Also, the presence of the coating resulted in a significant reduction in F4/80+ macrophages, while other populations remained unchanged. These results suggests that the F4/80+ macrophage population may be predominant in the early stages of the host response at the surface of these implants, in contrast to CD11b+ macrophage populations which were either fewer in number or located more distant from the implant surface. Gene expression assays showed increased proteolytic activity and diminished matrix deposition as possible mechanisms explaining the decreased fibrotic capsule deposition and improved peri-implant tissue quality shown in previous studies using IL-4 eluting coatings. The pattern of M2-like gene expression promoted by IL-4 was correlated with glycosaminoglycan production within the site of implantation at early stages of the host response, suggesting a significant role in this response. These findings demonstrate that immunomodulatory strategies can be utilized to design and implement targeted delivery for improving biomaterial performance.

7ND protein exerts inhibitory effects on both osteoclast differentiation in vitro and lipopolysaccharide‑induced bone erosion in vivo

Excessive numbers of osteoclasts are responsible for inflammation-induced osteolysis. Identification of osteoclast-targeting agents may facilitate the development of a novel therapeutic approach for the treatment of pathological bone loss. Seven-amino acid truncated (7ND) protein, a mutant form of monocyte chemoattractant protein-1 (MCP-1), functions as a competitive inhibitor of MCP-1. However, the effects of 7ND protein on osteoclast differentiation remain unknown. Therefore, in the present study, the effects of 7ND protein on osteoclast differentiation induced by tumour necrosis factor superfamily member 11 were investigated. In the present study, 7ND protein inhibited the osteoclast differentiation of peripheral blood mononuclear cells without influencing cell proliferation. Furthermore, to evaluate the effects of 7ND protein in vivo, a lipopolysaccharide (LPS)-induced calvarial bone erosion animal model was established. The 7ND protein remarkably attenuated LPS-induced bone resorption, as assessed by micro-computed tomography and histological analysis. Taken together, the present results suggested the feasibility of local delivery of 7ND protein to mitigate osteoclast differentiation and LPS-induced osteolysis, which may represent a potential approach to treat inflammatory bone destruction.

Diagnosis and management of implant debris-associated inflammation

Introduction: Total joint replacement is one of the most common, safe, and efficacious operations in all of surgery. However, one major long-standing and unresolved issue is the adverse biological reaction to byproducts of wear from the bearing surfaces and modular articulations. These inflammatory reactions are mediated by the innate and adaptive immune systems.Areas covered: We review the etiology and pathophysiology of implant debris-associated inflammation, the clinical presentation and detailed work-up of these cases, and the principles and outcomes of non-operative and operative management. Furthermore, we suggest future strategies for prevention and novel treatments of implant-related adverse biological reactions.Expert opinion: The generation of byproducts from joint replacements is inevitable, due to repetitive loading of the implants. A clear understanding of the relevant biological principles, clinical presentations, investigative measures and treatments for implant-associated inflammatory reactions and periprosthetic osteolysis will help identify and treat patients with this issue earlier and more effectively. Although progressive implant-associated osteolysis is currently a condition that is treated surgically, with further research, it is hoped that non-operative biological interventions could prolong the lifetime of joint replacements that are otherwise functional and still salvageable.

Monocyte Chemoattractant Protein-1 (MCP-1/CCL2) Drives Activation of Bone Remodelling and Skeletal Metastasis

PURPOSE OF REVIEW

The purpose of this review is to explore the role of monocyte chemoattractant protein-1 (MCP-1 or CCL2) in the processes that underpin bone remodelling, particularly the action of osteoblasts and osteoclasts, and its role in the development and metastasis of cancers that target the bone.

RECENT FINDINGS

MCP-1 is a key mediator of osteoclastogenesis, being the highest induced gene during intermittent treatment with parathyroid hormone (iPTH), but also regulates catabolic effects of continuous PTH on bone including monocyte and macrophage recruitment, osteoclast formation and bone resorption. In concert with PTH-related protein (PTHrP), MCP-1 mediates the interaction between tumour-derived factors and host-derived chemokines to promote skeletal metastasis. In breast and prostate cancers, an osteolytic cascade is driven by tumour cell-derived PTHrP that upregulates MCP-1 in osteoblastic cells. This relationship between PTHrP and osteoblastic expression of MCP-1 may drive the colonisation of disseminated breast cancer cells in the bone. There is mounting evidence to suggest a pivotal role of MCP-1 in many diseases and an important role in the establishment of comorbidities. Coupled with its role in bone remodelling and the regulation of bone turnover, there is the potential for pathological relationships between bone disorders and bone-related cancers driven by MCP-1. MCP-1's role in bone remodelling and bone-related cancers highlights its potential as a novel anti-resorptive and anti-metastatic target.

Periprosthetic Osteolysis: Mechanisms, Prevention and Treatment

Clinical studies, as well as in vitro and in vivo experiments have demonstrated that byproducts from joint replacements induce an inflammatory reaction that can result in periprosthetic osteolysis (PPOL) and aseptic loosening (AL). Particle-stimulated macrophages and other cells release cytokines, chemokines, and other pro-inflammatory substances that perpetuate chronic inflammation, induce osteoclastic bone resorption and suppress bone formation. Differentiation, maturation, activation, and survival of osteoclasts at the bone-implant interface are under the control of the receptor activator of nuclear factor kappa-Β ligand (RANKL)-dependent pathways, and the transcription factors like nuclear factor κB (NF-κB) and activator protein-1 (AP-1). Mechanical factors such as prosthetic micromotion and oscillations in fluid pressures also contribute to PPOL. The treatment for progressive PPOL is only surgical. In order to mitigate ongoing loss of host bone, a number of non-operative approaches have been proposed. However, except for the use of bisphosphonates in selected cases, none are evidence based. To date, the most successful and effective approach to preventing PPOL is usage of wear-resistant bearing couples in combination with advanced implant designs, reducing the load of metallic and polymer particles. These innovations have significantly decreased the revision rate due to AL and PPOL in the last decade.

Inflammation time-axis in aseptic loosening of total knee arthroplasty: A preliminary study

OBJECTIVE

Aseptic loosening (AL) is the most frequent long-term reason for revision of total knee arthroplasty (TKA) affecting about 15-20% patients within 20 years after the surgery. Although there is a solid body of evidence about the crucial role of inflammation in the AL pathogenesis, scared information on inflammation signature and its time-axis in tissues around TKA exists.

DESIGN

The inflammation protein signatures in pseudosynovial tissues collected at revision surgery from patients with AL (AL, n = 12) and those with no clinical/radiographic signs of AL (non-AL, n = 9) were investigated by Proximity Extension Assay (PEA)-Immunoassay and immunohistochemistry.

RESULTS

AL tissues had elevated levels of TNF-family members sTNFR2, TNFSF14, sFasL, sBAFF, cytokines/chemokines IL8, CCL2, IL1RA/IL36, sIL6R, and growth factors sAREG, CSF1, comparing to non-AL. High interindividual variability in protein levels was evident particularly in non-AL. Levels of sTNFR2, sBAFF, IL8, sIL6R, and MPO discriminated between AL and non-AL and were associated with the time from index surgery, suggesting the cumulative character of inflammatory osteolytic response to prosthetic byproducts. The source of elevated inflammatory molecules was macrophages and multinucleated osteoclast-like cells in AL and histiocytes and osteoclast-like cells in non-AL tissues, respectively. All proteins were present in higher levels in osteoclast-like cells than in macrophages.

CONCLUSIONS

Our study revealed a differential inflammation signature between AL and non-AL stages of TKA. It also highlighted the unique patient's response to TKA in non-AL stages. Further confirmation of our preliminary results on a larger cohort is needed. Analysis of the time-axis of processes ongoing around TKA implantation may help to understand the mechanisms driving periprosthetic bone resorption needed for diagnostic/preventative strategies.

Distinct release strategies are required to modulate macrophage phenotype in young versus aged animals

The role of innate immunity and macrophages in the host response to biomaterials has received renewed attention. A context-dependent spectrum of macrophage phenotypes are shown to affect tissue integration and performance of implanted biomaterials and medical devices. Recent studies by our group demonstrated that the host response in aged animals was characterized by delayed macrophage recruitment, differences in marker expression and a shifted pro-inflammatory (M1) response, associated with an unresolved host response in the long-term. The present work sought to study the effects of single and sequential cytokine delivery regimens in aged mice to restore delayed recruitment of macrophages and shift the inflammatory host response towards an M2-like phenotype, using MCP-1 (macrophage chemotactic protein-1) and IL-4 (interleukin-4), respectively. Implantation of cytokine-eluting implants showed a preserved response to MCP-1 in both young and aged animals, restoring delayed macrophage recruitment in aged mice. However, the response elicited by IL-4, sequential delivery of MCP-1/IL-4 and coating components was distinct in young versus aged mice. While single delivery of IL-4 did not counteract the high inflammatory response observed in aged mice, the sequential delivery of MCP-1/IL-4 was capable of restoring both recruitment and shifting the macrophage response towards an M2-like phenotype, associated with decreased implant scarring in the long-term. In young mice, sequential delivery was not as effective as IL-4 alone at promoting an M2-like response, but did result in a reduction of M1 macrophages and capsule deposition downstream. These results demonstrate that a proper understanding of patient/context-dependent biological responses are needed to design biomaterial-based therapies with improved outcomes in the setting of aging.

Vx-11e protects against titanium-particle-induced osteolysis and osteoclastogenesis by supressing ERK activity

Wear particle-induced osteolysis around the prosthesis is the most common long-term complication after total joint replacement surgery which often leads to aseptic loosening of the prosthesis. Osteoclasts play key roles in the osteolytic process. Currently there is a lack of clinically effective measures to prevent or treat peri-prosthetic osteolysis and thus identification of new agents that can inhibit the enhanced osteoclastic bone resorption is warranted. Through this study, we discovered that the specific and potent ERK1/2 inhibitor, Vx-11e, can protect against calvarial osteolysis caused by titanium (Ti) particles in vivo. Low doses of Vx-11e mildly reduced osteoclast resorption whilst no calvarial osteolysis was observed with high dose Vx-11e treatment. Histological examination showed fewer osteoclasts and reduced bone erosion in the Vx-11e treated groups. In vitro cellular analyses showed that Vx-11e inhibited osteoclast formation from BMM precursors in response to RANKL, as well as bone resorption by mature osteoclasts. Mechanistically, Vx-11e impaired RANKL-induced ERK1/2 signaling by inhibiting its kinase activity thereby blocking the phosphorylation of downstream substrates. Moreover, Vx-11e significantly reduced the expression of RANKL-mediated genes such as ACP5/TRAcP, CTR, MMP-9, CTSK. Collectively, our data provides evidence for the potential therapeutic use of Vx-11e for the treatment of osteolysis diseases caused by extremely actived osteoclastogenesis.

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.

Mutant monocyte chemoattractant protein-1 protein (7ND) inhibits osteoclast differentiation and reduces oral squamous carcinoma cell bone invasion

The seven-amino acid truncated (7ND) protein is an N-terminal deletion mutant of monocyte chemoattractant protein-1 (MCP-1) and it functions as a dominant-negative inhibitor. 7ND and wild-type MCP-1 form a heterodimer, which binds to MCP-1 receptors and inhibits monocyte chemotaxis. In the present study, the 7ND protein was cloned, expressed and purified. An MTT assay revealed that the proliferation of oral squamous cell carcinoma (OSCC) SCC25 cells was not affected following 3 days of treatment with synthetic 7ND protein. Serial dilutions of the 7ND protein were tested for monocyte migration and osteoclast differentiation, and tartrate-resistant acid phosphatase staining demonstrated that significantly fewer osteoclasts were differentiated from cluster of differentiation 14⁺ (CD14⁺) monocytes using magnetic activated cell sorting. Immunofluorescence confirmed these results and significantly less F-actin staining was observed in 7ND-treated osteoclasts. Furthermore, bone invasion was examined by subcutaneously injecting SCC25 cells into the area overlaying the calvariae of nude mice. The results demonstrated that the average tumor volume of SCC25 cells with 7ND protein was similar to the average volume of tumors formed by untreated SCC25 cells. Flow cytometric analysis suggested that the CD14⁺ subpopulation in the bone marrow of 7ND-treated mice was reduced compared with that of untreated mice. Micro-computed tomography imaging revealed significantly less bone resorption in the calvariae injected with SCC25 cells plus the 7ND protein. Taken together, the results of the present study demonstrated the potential therapeutic value of the 7ND protein. The 7ND MCP-1 variant not only functions in vitro to inhibit osteoclast differentiation, but also reduces the progression of bone invasion by OSCC cells in vivo.

* Murine Model of Progressive Orthopedic Wear Particle-Induced Chronic Inflammation and Osteolysis

Periprosthetic osteolysis and subsequent aseptic loosening of total joint replacements are driven by byproducts of wear released from the implant. Wear particles cause macrophage-mediated inflammation that culminates with periprosthetic bone loss. Most current animal models of particle-induced osteolysis are based on the acute inflammatory reaction induced by wear debris, which is distinct from the slowly progressive clinical scenario. To address this limitation, we previously developed a murine model of periprosthetic osteolysis that is based on slow continuous delivery of wear particles into the murine distal femur over a period of 4 weeks. The particle delivery was accomplished by using subcutaneously implanted osmotic pumps and tubing, and a hollow titanium rod press-fit into the distal femur. In this study, we report a modification of our prior model in which particle delivery is extended to 8 weeks to better mimic the progressive development of periprosthetic osteolysis and allow the assessment of interventions in a setting where the chronic particle-induced osteolysis is already present at the initiation of the treatment. Compared to 4-week samples, extending the particle delivery to 8 weeks significantly exacerbated the local bone loss observed with μCT and the amount of both peri-implant F4/80⁺ macrophages and tartrate-resistant acid phosphatase-positive osteoclasts detected with immunohistochemical and histochemical staining. Furthermore, systemic recruitment of reporter macrophages to peri-implant tissues observed with bioluminescence imaging continued even at the later stages of particle-induced inflammation. This modified model system could provide new insights into the mechanisms of chronic inflammatory bone loss and be particularly useful in assessing the efficacy of treatments in a setting that resembles the clinical scenario of developing periprosthetic osteolysis more closely than currently existing model systems.

tBHQ Suppresses Osteoclastic Resorption in Xenogeneic-Treated Dentin Matrix-Based Scaffolds

Extracellularmatrix (ECM)-based scaffolds are important for their potential therapeutic application. Treated dentin matrix (TDM), a kind of ECM, seeded with allogeneic dental follicle stem cells (TDM/aDFC) provides a suitable inductive microenvironment for tooth root regeneration. Considering the limited sources, xenogeneic TDM (xTDM) is a possible alternative to allogeneic TDM; however, xTDM-based scaffold presents severe osteolysis and resorption lacunae causing regenerated tooth root failure. Immune response-induced excessive osteoclastogenesis plays a critical role in xenogeneic scaffold osteolysis and resorption. The impact of antioxidant, tert-butylhydroquinone (tBHQ), on xTDM/aDFCs-induced osteoclastogenesis and osteoclastic resorption in vivo and in vitro are investigated. tBHQ upregulates heme oxygenase-1 release and downregulates high mobility group box 1 mRNA expression. mRNA expression of other osteoclast-related genes including nuclear factor-kappa Bp65, receptor activator of nuclear factor kappa-B, nuclear factor of activated T-cells cytoplasmic 1, cathepsin K, and integrin β3, also decreases significantly. Furthermore, tBHQ-treated xTDM/aDFCs scaffolds implanted into rhesus macaques show reduced osteolysis and osteoclastic resorption by microcomputed tomography and tartrate-resistant acid phosphatase staining. tBHQ-induced suppression of xTDM/aDFC-induced osteoclastogenesis and osteoclastic resorption presents a new strategy for the regeneration of biological tooth root and could be applied to the regeneration of other complex tissues and organs.

UHMWPE wear particles and dendritic cells promote osteoclastogenesis of RAW264.7 cells through RANK-activated NF-κB/MAPK/AKT pathways

Dendritic cells (DCs) were shown to enhance UHMWPE particle promoted osteoclastogenesis in RAW264.7 macrophages. This study aimed to elucidate the signaling network mediating the osteoclastogenic effects of UHMWPE particles and DCs. RAW264.7 cells were induced with UHMWPE particles and /or DC2.4 cells. The expression of Rank was silenced by shRNA. The activation of p38MAPK, AKT, and NF-κB was inhibited specific inhibitors. The osteoclasts were assessed by TRAP staining. The expression of osteoclastogenic genes and activation of p38MAPK, AKT, and NF-κB were analyzed by qPCR and/or Western blot. UHMWPE particles and DC2.4 cells cooperatively induced RAW264.7 macrophages to differentiate into osteoclasts, activated p38MAPK, AKT, and NF-κB pathways, and upregulated Nfatc1 and osteoclast markers, which was abolished by silencing Rank or inhibited by inhibitors of p38MAPK, AKT, and NF-κB in RAW264.7 cells. These data demonstrated the complexity of signaling network and cell-cell interactions involved in UHMWPE particles-induced osteolysis.

The Role of the Chemokine System in Tissue Response to Prosthetic By-products Leading to Periprosthetic Osteolysis and Aseptic Loosening

Millions of total joint replacements are performed annually worldwide, and the number is increasing every year. The overall proportion of patients achieving a successful outcome is about 80–90% in a 10–20-years time horizon postoperatively, periprosthetic osteolysis (PPOL) and aseptic loosening (AL) being the most frequent reasons for knee and hip implant failure and reoperations. The chemokine system (chemokine receptors and chemokines) is crucially involved in the inflammatory and osteolytic processes leading to PPOL/AL. Thus, the modulation of the interactions within the chemokine system may influence the extent of PPOL. Indeed, recent studies in murine models reported that (i) blocking the CCR2–CCL2 or CXCR2–CXCL2 axis or (ii) activation of the CXCR4–CXCL12 axis attenuate the osteolysis of artificial joints. Importantly, chemokines, inhibitory mutant chemokines, antagonists of chemokine receptors, or neutralizing antibodies to the chemokine system attached to or incorporated into the implant surface may influence the tissue responses and mitigate PPOL, thus increasing prosthesis longevity. This review summarizes the current state of the art of the knowledge of the chemokine system in human PPOL/AL. Furthermore, the potential for attenuating cell trafficking to the bone–implant interface and influencing tissue responses through modulation of the chemokine system is delineated. Additionally, the prospects of using immunoregenerative biomaterials (including chemokines) for the prevention of failed implants are discussed. Finally, this review highlights the need for a more sophisticated understanding of implant debris-induced changes in the chemokine system to mitigate this response effectively.

Titanium particle-induced osteogenic inhibition and bone destruction are mediated by the GSK-3β/β-catenin signal pathway

Wear debris-induced osteogenic inhibition and bone destruction are critical in the initiation of peri-prosthetic osteolysis. However, the molecular mechanism underlying this phenomenon is poorly understood. In this study, we analyzed the involvement of the GSK-3β/β-catenin signal pathway, which is important for bone formation in this pathological condition. We established a titanium (Ti) particle-stressed murine MC3T3-E1 cell culture system and calvariae osteolysis model to test the hypothesis that Ti particle-induced osteogenic inhibition and bone destruction are mediated by the GSK-3β/β-catenin signal pathway. Our findings showed that Ti particles reduced osteogenic differentiation induced by osteogenesis-related gene expression, alkaline phosphatase activity and matrix mineralization, as well as pSer9-GSK-3β expression and β-catenin signal activity. Downregulation of GSK-3β activity attenuated Ti particle-induced osteogenic inhibition, whereas the β-catenin inhibitor reversed this protective effect. Moreover, the GSK-3β/β-catenin signal pathway mediated the upregulation of RANKL and downregulation of OPG in Ti particle-stressed MC3T3-E1 cells. In addition, our in vivo results showed that Ti particles induced bone loss via regulating GSK-3β and β-catenin signals. Based on these results, we concluded that the GSK-3β/β-catenin signal pathway mediates the adverse effects of Ti particles on osteoblast differentiation and bone destruction, and can be used as a potential therapeutic target for the treatment of peri-prosthetic osteolysis.

Potential Role of Chemokines in Fracture Repair

Chemokines are a family of small cytokines that share a typical key structure that is stabilized by disulfide bonds between the cysteine residues at the NH₂-terminal of the protein, and they are secreted by a great variety of cells in several different conditions. Their function is directly dependent on their interactions with their receptors. Chemokines are involved in cell maturation and differentiation, infection, autoimmunity, cancer, and, in general, in any situation where immune components are involved. However, their role in postfracture inflammation and fracture healing is not yet well established. In this article, we will discuss the response of chemokines to bone fracture and their potential roles in postfracture inflammation and healing based on data from our studies and from other previously published studies.

Targeting Toll-like receptor 4 prevents cobalt-mediated inflammation

Cobalt-chrome alloy is a widely used biomaterial in joint replacements, dental implants and spinal rods. Although it is an effective and biocompatible material, adverse reactions to metal debris (ARMD) have arisen in a minority of patients, particularly in those with metal-on-metal bearing hip replacements. There is currently no treatment for ARMD and once progressive, early revision surgery of the implant is necessary. Therapeutic agents to prevent, halt or reverse ARMD would therefore be advantageous.

Cobalt ions activate Toll-like receptor 4 (TLR4), an innate immune receptor responsible for inflammatory responses to bacterial lipopolysaccharide (LPS) resulting in the production of pro-inflammatory cytokines and chemokines. We hypothesised that anti-TLR4 neutralising antibodies, reported to inhibit TLR4-mediated inflammation, could prevent the inflammatory response to cobalt ions in an in vitro macrophagecell culture model.

This study shows that a monoclonal anti-TLR4 antibody inhibited cobalt-mediated increases in pro-inflammatory IL8, CCL20 and IL1A expression, as well as IL-8 secretion. In contrast, a polyclonal antibody did not prevent the effect of cobalt ions on either IL-8 or IL1A expression, although it did have a small effect on the CCL20 response. Interestingly, both antibodies inhibited cobalt-mediated neutrophil migration although the greater effect was observed with the monoclonal antibody.

In summary our data shows that a monoclonal anti-TLR4 antibody can inhibit cobalt-mediated inflammatory responses while a polyclonal antibody only inhibits the effect of specific cytokines. Anti-TLR4 antibodies have therapeutic potential in ARMD although careful antibody design is required to ensure that the LPS response is preserved.

Mutant CCL2 protein coating mitigates wear particle-induced bone loss in a murine continuous polyethylene infusion model

Wear particle-induced osteolysis limits the long-term survivorship of total joint replacement (TJR). Monocyte/macrophages are the key cells of this adverse reaction. Monocyte Chemoattractant Protein-1 (MCP-1/CCL2) is the most important chemokine regulating trafficking of monocyte/macrophages in particle-induced inflammation. 7ND recombinant protein is a mutant of CCL2 that inhibits CCL2 signaling. We have recently developed a layer-by-layer (LBL) coating platform on implant surfaces that can release biologically active 7ND. In this study, we investigated the effect of 7ND on wear particle-induced bone loss using the murine continuous polyethylene (PE) particle infusion model with 7ND coating of a titanium rod as a local drug delivery device. PE particles were infused into hollow titanium rods with or without 7ND coating implanted in the distal femur for 4 weeks. Specific groups were also injected with RAW 264.7 as the reporter macrophages. Wear particle-induced bone loss and the effects of 7ND were evaluated by microCT, immunohistochemical staining, and bioluminescence imaging. Local delivery of 7ND using the LBL coating decreased systemic macrophage recruitment, the number of osteoclasts and wear particle-induced bone loss. The development of a novel orthopaedic implant coating with anti-CCL2 protein may be a promising strategy to mitigate peri-prosthetic osteolysis.

Potential Role of DARC-Chemokine Interaction in the Recruitment of Osteoclast Precursors in Response to Bacterial Lipopolysaccharide Challenge

Duffy antigen receptor for chemokines (DARC) binds to a number of pro-inflammatory chemokines, and since chemokines are known to regulate trafficking of osteoclast (OC) precursors, we predicted that DARC would regulate OC recruitment to sites of inflammation by modulating chemokine activity. To test this hypothesis, we evaluated the mRNA expression of Darc and the chemokines known to bind to DARC, in endothelial cells treated with bacterial lipopolysaccharide (LPS). The mRNA expression of Mcp-1, Rantes, Darc and Ccr5 was significantly increased in endothelial cells in response to LPS treatment. Blocking the function of DARC with neutralizing antibody partially abrogated the effect of LPS on the mRNA expression of Mcp-1 and Rantes. In vivo, mice with targeted disruption of Darc gene (Darc-KO) and control wild-type (WT) mice were used to assess the role of DARC in response to single LPS application on the top of parietal bones. Five hours post-LPS injection, local expression of Cd14 mRNA (a marker of inflammatory monocytes) was significantly increased in both lines of mice. However, the magnitude of increase was greater in WT mice compared with Darc-KO mice suggesting a role for DARC in mediating the recruitment of monocytes in response to LPS. Histological staining for tartrate-resistant acid phosphatase (TRAP) in calvaria sections taken from the injection sites revealed a significant reduction in TRAP-labeled surface per bone surface in response to LPS in Darc-KO mice compared with WT mice. Based on these findings, we concluded that DARC regulates recruitment of OC precursors at the inflammation site, probably through regulation of chemokines transcytosis across endothelial cell barrier.

Recent advances in the understanding of molecular mechanisms of cartilage degeneration, synovitis and subchondral bone changes in osteoarthritis

Osteoarthritis (OA), the most common form of degenerative joint disease, is linked to high morbidity. It is predicted to be the single greatest cause of disability in the general population by 2030. The development of disease-modifying therapy for OA currently face great obstacle mainly because the onset and development of the disease involve complex molecular mechanisms. In this review, we will comprehensively summarize biological and pathological mechanisms of three key aspects: degeneration of articular cartilage, synovial immunopathogenesis, and changes in subchondral bone. For each tissue, we will focus on the molecular receptors, cytokines, peptidases, related cell, and signal pathways. Agents that specifically block mechanisms involved in synovial inflammation, degeneration of articular cartilage, and subchondral bone remodeling can potentially be exploited to produce targeted therapy for OA. Such new comprehensive agents will benefit affected patients and bring exciting new hope for the treatment of OA.

The effect of local IL-4 delivery or CCL2 blockade on implant fixation and bone structural properties in a mouse model of wear particle induced osteolysis

Modulation of macrophage polarization and prevention of CCL2-induced macrophage chemotaxis are emerging strategies to reduce wear particle induced osteolysis and aseptic total joint replacement loosening. In this study, the effect of continuous IL-4 delivery or bioactive implant coating that constitutively releases a protein inhibitor of CCL2 signaling (7ND) on particle induced osteolysis were studied in the murine continuous femoral intramedullary particle infusion model. Polyethylene particles with or without IL-4 were infused into mouse distal femurs implanted with hollow titanium rods using subcutaneous infusion pumps. In another experimental group, particles were infused into the femur through a 7ND coated rod. After 4 weeks, fixation of the implant was assessed using a pullout test. The volume of trabecular bone and the geometry of the local cortical bone were assessed by µCT and the corresponding structural properties of the cortical bone determined by torsional testing. Continuous IL-4 delivery led to increased trabecular bone volume as well as enhanced local bone geometry and structural properties, while 7ND implant coating did not have effect on these parameters. The results suggest that local IL-4 treatment is a promising strategy to mitigate wear particle induced osteolysis. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2255-2262, 2016.

Nanocoating for biomolecule delivery using layer-by-layer self-assembly

Since its introduction in the early 1990s, layer-by-layer (LbL) self-assembly of films has been widely used in the fields of nanoelectronics, optics, sensors, surface coatings, and controlled drug delivery. The growth of this industry is propelled by the ease of film manufacture, low cost, mild assembly conditions, precise control of coating thickness, and versatility of coating materials. Despite the wealth of research on LbL for biomolecule delivery, clinical translation has been limited and slow. This review provides an overview of methods and mechanisms of loading biomolecules within LbL films and achieving controlled release. In particular, this review highlights recent advances in the development of LbL coatings for the delivery of different types of biomolecules including proteins, polypeptides, DNA, particles and viruses. To address the need for co-delivery of multiple types of biomolecules at different timing, we also review recent advances in incorporating compartmentalization into LbL assembly. Existing obstacles to clinical translation of LbL technologies and enabling technologies for future directions are also discussed.