Induction of macrophage C-C chemokine expression by titanium alloy and bone cement particles

Friend or foe? Inflammation and the foreign body response to orthopedic biomaterials

The use of biomaterials and implants for joint replacement, fracture fixation, spinal stabilization and other orthopedic indications has revolutionized patient care by reliably decreasing pain and improving function. These surgical procedures always invoke an acute inflammatory reaction initially, that in most cases, readily subsides. Occasionally, chronic inflammation around the implant develops and persists; this results in unremitting pain and compromises function. The etiology of chronic inflammation may be specific, such as with infection, or be unknown. The histological hallmarks of chronic inflammation include activated macrophages, fibroblasts, T cell subsets, and other cells of the innate immune system. The presence of cells of the adaptive immune system usually indicates allergic reactions to metallic haptens. A foreign body reaction is composed of activated macrophages, giant cells, fibroblasts, and other cells often distributed in a characteristic histological arrangement; this reaction is usually due to particulate debris and other byproducts from the biomaterials used in the implant. Both chronic inflammation and the foreign body response have adverse biological effects on the integration of the implant with the surrounding tissues. Strategies to mitigate chronic inflammation and the foreign body response will enhance the initial incorporation and longevity of the implant, and thereby, improve long-term pain relief and overall function for the patient. The seminal research performed in the laboratory of Dr. James Anderson and co-workers has provided an inspirational and driving force for our laboratory's work on the interactions and crosstalk among cells of the mesenchymal, immune, and vascular lineages, and orthopedic biomaterials. Dr. Anderson's delineation of the fundamental biologic processes and mechanisms underlying acute and chronic inflammation, the foreign body response, resolution, and eventual functional integration of implants in different organ systems has provided researchers with a strategic approach to the use of biomaterials to improve health in numerous clinical scenarios.

A biodegradable magnesium surgical staple for colonic anastomosis: In vitro and in vivo evaluation

Staplers have been widely used in the clinical treatment of gastrointestinal reconstruction. However, the current titanium (Ti) staple will remain in the human body permanently, resulting in some adverse effects. In this study, we developed a type of biodegradable staple for colonic anastomosis using 0.3 mm diameter magnesium (Mg) alloy wires. The wire surface was modified by micro-arc oxidation treatment (MAO) and then coated with poly-l-lactic acid (PLLA) to achieve a moderate degradation rate matching the tissue healing process. The results of tensile tests on isolated porcine colon tissue anastomosed by Mg and Ti staples showed that the anastomotic property of Mg staples was almost equal to that of Ti staples. The in vitro degradation tests indicated the dual-layer coating effectively enhanced the corrosion resistance and maintained the tensile force of the coated staple stable after 14-day immersion in the simulated colonic fluid (SCF). Furthermore, 24 beagle dogs were employed to conduct a comparison experiment using Mg-based and clinical Ti staples for 90-day implantation by ent-to-side anastomosis of the colon. The integrated structure of Mg-based staples was observed after 7 days and completely degraded after 90 days. All animals did not have anastomotic leakage and stenosis, and 12 dogs with Mg-based staples fully recovered after 90 days without differences in visceral ion levels and other side effects. The favorable performance makes this Mg-based anastomotic staple an ideal candidate for colon reconstruction.

Worldwide Trends of Research on Periprosthetic Osteolysis: A Bibliometric Study Based on VOSviewer

BACKGROUND

Due to the increasing number of joint arthroplasty operations, surgeons have begun to devote more attention to the problem of periprosthetic osteolysis. In recent years, numerous studies have focussed on periprosthetic osteolysis, but there have been no relevant bibliometric studies.

METHODS

We searched the Web of Science database for relevant articles concerning periprosthetic osteolysis published from 1965 to 2021. The following data were extracted: authors' name, article title, publication journal, impact factor (IF) of the journal in the publication year, keywords, topic of the article, publication country/region, the sum of times cited, H-index and funding sources. VOSviewer and Excel 2019 were used to conduct the bibliometric study and visualise the analysis.

RESULTS

A total of 1255 publications were included. In all selected articles, "orthopaedics" became the dominant topic (662 of 1255, 52.75%). The most productive years were 2018 and 2019, with a total of 83 publications. The Journal of Arthroplasty published the most articles on periprosthetic osteolysis (110 publications). The United States of America published the most articles (525, 41.83%). The latest keywords "continuous intramedullary infusion", "erythromycin", "autophagy", "bone-resorbing cells" and "proinflammatory cytokines" both appeared in five articles in 2017.

CONCLUSION

This bibliometric study showed that there is a growing trend in published articles related to periprosthetic osteolysis. Journal of Arthroplasty was the top productive journal on periprosthetic osteolysis. The United States of America dominates studies of periprosthetic osteolysis. "Continuous intramedullary infusion", "erythromycin", "autophagy", "bone-resorbing cells" and "proinflammatory cytokines" may be new research hotspots in the field of periprosthetic osteolysis.

Changes in bone density, intraosseous pressure of distal femoral articular cartilage and subchondral bone after proximal femoral medullary cavity cement filling in rabbits

Bone cement is widely used, particularly in hip replacements, but the potential clinical complications of its use have been largely unrecognized. The purpose of the present study was to investigate the effects of bone cement in the proximal femoral medullary cavity (PFMC) on bone mineral density (BMD), intraosseous pressure (IOP), articular cartilage and subchondral bone in the distal femurs of rabbits. A total of 32 New Zealand white rabbits were randomly numbered and the left hind limb of the odd-numbered rabbits and the right hind limb of the even numbered rabbits were selected as the experimental side. For each rabbit, the non-experimental hind limb was labeled as the control side by the principal investigator. An intramedullary injection of polymethyl methacrylate was made into the experimental hindlimb of each rabbit and the PFMC filled with bone cement. BMD and IOP of the distal femur of the bilateral hindlimb were measured at 4 and 16 weeks after surgery, and histological and ultra-fine structural features were examined by light and transmission electron microscopy, respectively. At week 4 after the operation, IOP in the experimental limb was significantly higher and BMD lower compared with the control limb. At the 16th week after operation, the IOP in the experimental limb was lower than at the 4th week after operation, but still higher compared with controls, and the BMD was significantly higher than the controls. In the controls, IOP and BMD was not significantly different between the 4th and 16th week after operation. Compared with controls, the cartilage in the experimental group was thinner, the chondrocytes partially necrotic and the trabecular structure of the subchondral bone broken. Analysis of ultra-fine structural features in the experimental group showed chondrocytes with necrotic cytoplasm and pyknotic nuclei relative to controls. The results indicated that blockage of the PFMC with bone cement resulted in an increase in the IOP in the distal femur, a change in BMD and damage to the subchondral bone and articular cartilage.

Inflammatory responses to metal oxide ceramic nanopowders

Ceramic orthopaedic implants are increasingly popular due to the need for robust total joint replacement implants that have a high success rate long-term and do not induce biological responses in patients. This study was designed to investigate the biological effects of ceramic nanopowders containing aluminium oxide or zirconium oxide to activate the human macrophage THP-1 cell line. In vitro investigation of pro-inflammatory gene expression and chemokine secretion was performed studied using RT-qPCR and ELISA, respectively. TLR4 inhibition, using a small-molecule inhibitor, was used to determine whether ceramic-mediated inflammation occurs in a similar manner to that of metals such as cobalt. THP-1 macrophages were primed with ceramics or LPS and then treated with ATP or ceramics, respectively, to determine whether these nanopowders are involved in the priming or activation of the NLRP3 inflammasome through IL-1β secretion. Cells treated with ceramics significantly increased pro-inflammatory gene expression and protein secretion which was attenuated through TLR4 blockade. Addition of ATP to cells following ceramic treatment significantly increased IL-1β secretion. Therefore, we identify the ability of ceramic metal oxides to cause a pro-inflammatory phenotype in THP-1 macrophages and propose the mechanism by which this occurs is primarily via the TLR4 pathway which contributes to inflammasome signalling.

Delayed Titanium Hypersensitivity and Retained Foreign Body Causing Late Abdominal Complications

Titanium is a known metal used widely in the medical field and can cause allergic reactions with complications. Our case is about a 28-year-old female presenting with a spectrum of abdominal symptoms with a complicated medical history. The abdominal pain is associated with titanium allergy reaction from previously inserted titanium-based surgical clips. This patient is concurrently found to have a retained pigtail catheter in the cecum discovered incidentally through radiology. We discuss the presentation, investigations, and treatment of this unusual case. The case also unfolds rare differential diagnoses to keep in mind when encountering a patient with abdominal pain and associated nonspecific symptoms.

Host immune response to anti-cancer camptothecin conjugated cyclodextrin-based polymers

Introduction

Efficacy and safety are critical concerns when designing drug carriers. Nanoparticles are a particular type of carrier that has gained recent attention in cancer therapeutics.

Methods

In this study, we assess the safety profile of IT-101, a nanoparticle formed by self-assembly of camptothecin (CPT) conjugated cyclodextrin-based polymers. IT-101 delivers CPT to target cancer cells in animal models of numerous human cancers and in humans. Previous data from preclinical and clinical trials indicate that IT-101 has no notable immunological side effects. However, there have been no published studies focused on evaluating the effects of IT-101 on host immune systems.

Results

In this work, we demonstrate that IT-101 diminished initial host immune response following first injection of the nanopharmaceutical and induced NK cell activation and T cell proliferation upon further IT-101 exposure. Additionally, IT-101 could attenuate tumor growth more efficiently than CPT treatment only.

Conclusions

Drugs administration in whole-body circulation may lead to poorly bioavailable in central nervous system and often has toxic effects on peripheral tissues. Conjugated with cyclodextrin-based polymers not only reduce adverse effects but also modulate the immune responses to elevate drug efficacy. These immune responses may potentially facilitate actions of immune blockage, such as PD1/PDL1 in cancer treatment.

Polyethylene particles inserted over calvarium induce cancellous bone loss in femur in female mice

Focal bone resorption (osteolysis) induced by wear particles contributes to long-term orthopedic joint failure. However, the impact of focal osteolysis on remote skeletal sites has received less attention. The goal of this study was to determine the effects of polyethylene particles placed over calvaria on representative axial and appendicular skeletal sites in female mice. Because recent work has identified housing temperature as an important biological variable in mice, response to particle treatment was measured in animals housed at room (22 °C) and thermoneutral (32 °C) temperature. Osteolysis was evident in skeletal tissue adjacent to particle insertion. In addition, cancellous bone loss was observed in distal femur metaphysis. The bone loss was associated with lower osteoblast-lined perimeter and lower mineralizing perimeter in distal femur, lower osteocalcin gene expression in tibia, and lower serum osteocalcin, suggesting the response was due, at least in part, to reduced bone formation. Mild cold stress induced by sub-thermoneutral housing resulted in cancellous bone loss in distal femur and lumbar vertebra but did not influence skeletal response to particles. In summary, the results indicate that focal inflammation induced by polyethylene particles has the potential to result in systemic bone loss. This is significant because bone loss is a risk factor for fracture.

•

Wear particles contribute to orthopedic joint failure by promoting focal inflammation- mediated osteolysis.

•

Here we investigated effects of polyethylene particles placed over calvaria on remote skeletal sites in female mice.

•

Particles placed over calvaria resulted in focal inflammation and cancellous bone loss in distal femur metaphysis.

•

Lower osteoblast-lined perimeter suggests reduced bone formation contributed to bone loss in distal femur.

•

Our results suggest focal inflammation induced by polyethylene particles has the potential to result in systemic bone loss.

Disease-Associated Particulates and Joint Inflammation; Mechanistic Insights and Potential Therapeutic Targets

It is now well established that intra-articular deposition of endogenous particulates, such as osteoarthritis-associated basic calcium phosphate crystals, gout-associated monosodium urate crystals, and calcium deposition disease-associated calcium pyrophosphate crystals, contributes to joint destruction through the production of cartilage-degrading enzymes and pro-inflammatory cytokines. Furthermore, exogenous wear-debris particles, generated from prosthetic implants, drive periprosthetic osteolysis which impacts on the longevity of total joint replacements. Over the last few years, significant insight has been gained into the mechanisms through which these particulates exert their effects. Not only has this increased our understanding of the pathological processes associated with crystal deposition but it has also led to the identification of a number of therapeutic targets to treat particulate-associated disease. In this review, we discuss recent developments regarding the cellular events triggered by joint-associated particulates, as well as future directions in therapy for particulate-related arthropathies.

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

Osteolysis is a serious postoperative complication of total joint arthroplasty that leads to aseptic loosening and surgical revision. Osteolysis is a chronic destructive process that occurs when host macrophages recognize implant particles and release inflammatory mediators that increase bone-resorbing osteoclastic activity and attenuate bone-formation osteoblastic activity. Although much progress has been made in understanding the molecular responses of macrophages to implant particles, the pathways/signals that initiate osteolysis remain poorly characterized. Transcriptomics and gene-expression profiling of these macrophages may unravel key mechanisms in the pathogenesis of osteolysis and aid the identification of molecular candidates for therapeutic intervention. To this end, we analyzed the transcriptional profiling of macrophages exposed to ultra-high molecular weight polyethylene (UHMWPE) particles, the most common components used in bearing materials of orthopedic implants. Regulated genes in stimulated macrophages were involved in cytokine, chemokine, growth factor and receptor activities. Gene enrichment analysis suggested that stimulated macrophages elicited common gene expression signatures for inflammation and rheumatoid arthritis. Among the regulated genes, tumor necrosis factor superfamily member 15 (TNFSF15) and chemokine ligand 20 (CCL20) were further characterized as molecular targets involved in the pathogenesis of osteolysis. Treatment of monocyte cultures with TNFSF15 and CCL20 resulted in an increase in osteoclastogenesis and bone-resorbing osteoclastic activity, suggesting their potential contribution to loosening between implants and bone tissues.

STATEMENT OF SIGNIFICANCE

Implant loosening due to osteolysis is the most common mode of arthroplasty failure and represents a great challenge to orthopedic surgeons and a significant economic burden for patients and healthcare services worldwide. Bone loss secondary to a local inflammatory response initiated by particulate debris from implants is considered the principal feature of the pathogenesis of osteolysis. In the present study, we analyzed the transcriptional profiling of human macrophages exposed to UHMWPE particles and identified a large number of inflammatory genes that were not identified previously in macrophage responses to wear particles. Our data provide a new insight into the molecular pathogenesis of osteolysis and highlights a number of molecular targets with prognostic and therapeutic implications.

Mechanical instability and titanium particles induce similar transcriptomic changes in a rat model for periprosthetic osteolysis and aseptic loosening

Wear debris particles released from prosthetic bearing surfaces and mechanical instability of implants are two main causes of periprosthetic osteolysis. While particle-induced loosening has been studied extensively, mechanisms through which mechanical factors lead to implant loosening have been less investigated. This study compares the transcriptional profiles associated with osteolysis in a rat model for aseptic loosening, induced by either mechanical instability or titanium particles. Rats were exposed to mechanical instability or titanium particles. After 15 min, 3, 48 or 120 h from start of the stimulation, gene expression changes in periprosthetic bone tissue was determined by microarray analysis. Microarray data were analyzed by PANTHER Gene List Analysis tool and Ingenuity Pathway Analysis (IPA). Both types of osteolytic stimulation led to gene regulation in comparison to unstimulated controls after 3, 48 or 120 h. However, when mechanical instability was compared to titanium particles, no gene showed a statistically significant difference (fold change ≥ ± 1.5 and adjusted p-value ≤ 0.05) at any time point. There was a remarkable similarity in numbers and functional classification of regulated genes. Pathway analysis showed several inflammatory pathways activated by both stimuli, including Acute Phase Response signaling, IL-6 signaling and Oncostatin M signaling. Quantitative PCR confirmed the changes in expression of key genes involved in osteolysis observed by global transcriptomics. Inflammatory mediators including interleukin (IL)-6, IL-1β, chemokine (C-C motif) ligand (CCL)2, prostaglandin-endoperoxide synthase (Ptgs)2 and leukemia inhibitory factor (LIF) showed strong upregulation, as assessed by both microarray and qPCR. By investigating genome-wide expression changes we show that, despite the different nature of mechanical implant instability and titanium particles, osteolysis seems to be induced through similar biological and signaling pathways in this rat model for aseptic loosening. Pathways associated to the innate inflammatory response appear to be a major driver for osteolysis. Our findings implicate early restriction of inflammation to be critical to prevent or mitigate osteolysis and aseptic loosening of orthopedic implants.

Effects of cobalt and chromium ions on lymphocyte migration

A T cell-mediated hypersensitivity reaction has been reported in some patients with CoCrMo-based implants. However, the role of cobalt and chromium ions in this reaction remains unclear. The objective of the present study was to analyze the effects of Co²⁺ and Cr³⁺ in culture medium, as well as the effects of culture supernatants of macrophages exposed to Co²⁺ or Cr³⁺ , on the migration of lymphocytes. The release of cytokines/chemokines by macrophages exposed to Co²⁺ and Cr³⁺ was also analyzed. The migration of murine lymphocytes was quantified using the Boyden chamber assay and flow cytometry, while cytokine/chemokine release by J774A.1 macrophages was measured by ELISA. Results showed an ion concentration-dependent increase in TNF-α and MIP-1α release and a decrease in MCP-1 and RANTES release. Migration analysis showed that the presence of Co²⁺ (8 ppm) and Cr³⁺ (100 ppm) in culture medium increased the migration of T lymphocytes, while it had little or no effect on the migration of B lymphocytes, suggesting that Co²⁺ and Cr³⁺ can stimulate the migration of T but not B lymphocytes. Levels of T lymphocyte migration in culture medium containing Co²⁺ or Cr³⁺ were not statistically different from those in culture supernatants of macrophages exposed to Co²⁺ or Cr³⁺ , suggesting that the effects of the ions and chemokines were not additive, possibly because of ion interference with the chemokines and/or their cognate receptors. Overall, results suggest that Co²⁺ and Cr³⁺ are capable of stimulating the migration of T (but not B) lymphocytes in the absence of cytokines/chemokines, and could thereby contribute to the accumulation of more T than B lymphocytes in periprosthetic tissues of some patients with CoCrMo-based implants. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:916-924, 2017.

High-Purity Magnesium Staples Suppress Inflammatory Response in Rectal Anastomoses

Magnesium-based materials are promising biodegradable implants, although the impact of magnesium on rectal anastomotic inflammation is poorly understood. Thus, we investigated the inflammatory effects of high-purity Mg staples in rectal anastomoses by in vivo luciferase reporter gene expression in transgenic mice, hematoxylin-eosin staining, immunohistochemistry, and Western blotting. As expected, strong IL-1β-mediated inflammation and inflammatory cell infiltration were observed 1 day after rectal anastomoses were stapled with high-purity Mg or Ti. However, inflammation and inflammatory cell infiltration decreased more robustly 4-7 days postoperation in tissues stapled with high-purity Mg. This rapid reduction in inflammation was confirmed by immunohistochemical analysis of IL-6 and TNF-α. Western blot also suggested that the reduced inflammatory response is due to suppressed TLR4/NF-κB signaling. In contrast, MCP-1, uPAR, and VEGF were abundantly expressed, in line with the notion that expression of these proteins is regulated by feedback between the VEGF and NF-κB pathways. In vitro expression of MCP-1, uPAR, and VEGF was also similarly high in primary rectal mucosal epithelial cells exposed to extracts from Mg staples, as measured by antibody array. Collectively, the results suggest that high-purity Mg staples suppress the inflammatory response during rectal anastomoses via TLR4/NF-κB and VEGF signaling.

In vivo and in vitro assessment of the biocompatibility and degradation of high-purity Mg anastomotic staples

Titanium (Ti) staples are not biodegradable, and anastomotic complications related to Ti staples are reported frequently. In the present study, the biocompatibility and degradation behavior of high-purity magnesium (HP Mg) staples with the small intestine were investigated. HP Mg staples did not affect the relative growth rate, cell cycle and apoptosis of primary rectal mucosal epithelial cells (IEC-6) in vitro. At one, two and three days after immersion in intestinal juice, the weight of the 30 rinsed HP Mg staples reduced by 7.5 ± 1.6, 10.6 ± 2.2 and 13.5 ± 2.1 mg, respectively, and those in the Hanks' solution reduced by 3.9 ± 0.8, 6.1 ± 1.2 and 7.1 ± 2.4 mg. Extracts of HP Mg staples were bio-safe for IEC-6, and the corrosion rate of HP staples was faster in the small intestinal juice than in the Hanks' solution. In the in vivo experiments, the small intestine of the minipigs was anastomosed by HP Mg and Ti staples. HP Mg staples neither affected important bio-chemical parameters nor induced serious inflammation or necrosis in the anastomosis tissues. The residual weight of a HP Mg staples (0.81 ± 0.13 mg) was 89.7% of the original weight (9 ± 0.09 mg) one month after surgery. The in vivo corrosion rate for one HP Mg staple was determined to be∼0.007 ± 0.001 mm·month^-1. The preliminary results of the biocompatibility and degradation of high-purity Mg anastomotic staples are promising, and further studies will be initiated to study in more detail.

Chemokines Associated with Pathologic Responses to Orthopedic Implant Debris

Despite the success in returning people to health saving mobility and high quality of life, the over 1 million total joint replacements implanted in the US each year are expected to eventually fail after approximately 15-25 years of use, due to slow progressive subtle inflammation to implant debris compromising the bone implant interface. This local inflammatory pseudo disease state is primarily caused by implant debris interaction with innate immune cells, i.e., macrophages. This implant debris can also activate an adaptive immune reaction giving rise to the concept of implant-related metal sensitivity. However, a consensus of studies agree the dominant form of this response is due to innate reactivity by macrophages to implant debris danger signaling (danger-associated molecular pattern) eliciting cytokine-based and chemokine inflammatory responses. This review covers implant debris-induced release of the cytokines and chemokines due to activation of the innate (and the adaptive) immune system and how this leads to subsequent implant failure through loosening and osteolysis, i.e., what is known of central chemokines (e.g., IL-8, monocyte chemotactic protein-1, MIP-1, CCL9, CCL10, CCL17, and CCL22) associated with implant debris reactivity as related to the innate immune system activation/cytokine expression, e.g., danger signaling (e.g., IL-1β, IL-18, IL-33, etc.), toll-like receptor activation (e.g., IL-6, tumor necrosis factor α, etc.), bone catabolism (e.g., TRAP5b), and hypoxia responses (HIF-1α). More study is needed, however, to fully understand these interactions to effectively counter cytokine- and chemokine-based orthopedic implant-related inflammation.

Environmental Factors Impacting Bone-Relevant Chemokines

Chemokines play an important role in normal bone physiology and the pathophysiology of many bone diseases. The recent increased focus on the individual roles of this class of proteins in the context of bone has shown that members of the two major chemokine subfamilies-CC and CXC-support or promote the formation of new bone and the remodeling of existing bone in response to a myriad of stimuli. These chemotactic molecules are crucial in orchestrating appropriate cellular homing, osteoblastogenesis, and osteoclastogenesis during normal bone repair. Bone healing is a complex cascade of carefully regulated processes, including inflammation, progenitor cell recruitment, differentiation, and remodeling. The extensive role of chemokines in these processes and the known links between environmental contaminants and chemokine expression/activity leaves ample opportunity for disruption of bone healing by environmental factors. However, despite increased clinical awareness, the potential impact of many of these environmental factors on bone-related chemokines is still ill defined. A great deal of focus has been placed on environmental exposure to various endocrine disruptors (bisphenol A, phthalate esters, etc.), volatile organic compounds, dioxins, and heavy metals, though mainly in other tissues. Awareness of the impact of other less well-studied bone toxicants, such as fluoride, mold and fungal toxins, asbestos, and chlorine, is also reviewed. In many cases, the literature on these toxins in osteogenic models is lacking. However, research focused on their effects in other tissues and cell lines provides clues for where future resources could be best utilized. This review aims to serve as a current and exhaustive resource detailing the known links between several classes of high-interest environmental pollutants and their interaction with the chemokines relevant to bone healing.

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.

Dysregulation of Chemokine/Chemokine Receptor Axes and NK Cell Tissue Localization during Diseases

Chemokines are small chemotactic molecules that play key roles in physiological and pathological conditions. Upon signaling via their specific receptors, chemokines regulate tissue mobilization and trafficking of a wide array of immune cells, including natural killer (NK) cells. Current research is focused on analyzing changes in chemokine/chemokine receptor expression during various diseases to interfere with pathological trafficking of cells or to recruit selected cell types to specific tissues. NK cells are a heterogeneous lymphocyte population comprising several subsets endowed with distinct functional properties and mainly representing distinct stages of a linear development process. Because of their different functional potential, the type of subset that accumulates in a tissue drives the final outcome of NK cell-regulated immune response, leading to either protection or pathology. Correspondingly, chemokine receptors, including CXCR4, CXCR3, and CX₃CR1, are differentially expressed by NK cell subsets, and their expression levels can be modulated during NK cell activation. At first, this review will summarize the current knowledge on the contribution of chemokines to the localization and generation of NK cell subsets in homeostasis. How an inappropriate chemotactic response can lead to pathology and how chemokine targeting can therapeutically affect tissue recruitment/localization of distinct NK cell subsets will also be discussed.

The pathobiology and pathology of aseptic implant failure

Pathological assessment of periprosthetic tissues is important, not only for diagnosis, but also for understanding the pathobiology of implant failure. The host response to wear particle deposition in periprosthetic tissues is characterised by cell and tissue injury, and a reparative and inflammatory response in which there is an innate and adaptive immune response to the material components of implant wear. Physical and chemical characteristics of implant wear influence the nature of the response in periprosthetic tissues and account for the development of particular complications that lead to implant failure, such as osteolysis which leads to aseptic loosening, and soft-tissue necrosis/inflammation, which can result in pseudotumour formation. The innate response involves phagocytosis of implant-derived wear particles by macrophages; this is determined by pattern recognition receptors and results in expression of cytokines, chemokines and growth factors promoting inflammation and osteoclastogenesis; phagocytosed particles can also be cytotoxic and cause cell and tissue necrosis. The adaptive immune response to wear debris is characterised by the presence of lymphoid cells and most likely occurs as a result of a cell-mediated hypersensitivity reaction to cell and tissue components altered by interaction with the material components of particulate wear, particularly metal ions released from cobalt-chrome wear particles.Cite this article: Professor N. A. Athanasou. The pathobiology and pathology of aseptic implant failure. Bone Joint Res 2016;5:162-168. DOI: 10.1302/2046-3758.55.BJR-2016-0086.

Polysilicon-chromium-gold intracellular chips for multi-functional biomedical applications

The development of micro- and nanosystems for their use in biomedicine is a continuously growing field. One of the major goals of such platforms is to combine multiple functions in a single entity. However, achieving the design of an efficient and safe micro- or nanoplatform has shown to be strongly influenced by its interaction with the biological systems, where particle features or cell types play a critical role. In this work, the feasibility of using multi-material pSi-Cr-Au intracellular chips (MMICCs) for multifunctional applications by characterizing their interactions with two different cell lines, one tumorigenic and one non-tumorigenic, in terms of biocompatibility, internalization and intracellular fate, has been explored. Moreover, the impact of MMICCs on the induction of an inflammatory response has been assessed by evaluating TNFα, IL1b, IL6, and IL10 human inflammatory cytokines secretion by macrophages. Results show that MMICCs are biocompatible and their internalization efficiency is strongly dependent on the cell type. Finally as a proof-of-concept, MMICCs have been dually functionalized with transferrin and pHrodo™ Red, SE to target cancer cells and detect intracellular pH, respectively. In conclusion, MMICCs can be used as multi-functional devices due to their high biocompatibility, non-inflammatory properties and the ability of developing multiple functions.

The biological response to orthopedic implants for joint replacement. II: Polyethylene, ceramics, PMMA, and the foreign body reaction

Novel evidence-based prosthetic designs and biomaterials facilitate the performance of highly successful joint replacement (JR) procedures. To achieve this goal, constructs must be durable, biomechanically sound, and avoid adverse local tissue reactions. Different biomaterials such as metals and their alloys, polymers, ceramics, and composites are currently used for JR implants. This review focuses on (1) the biological response to the different biomaterials used for TJR and (2) the chronic inflammatory and foreign-body response induced by byproducts of these biomaterials. A homeostatic state of bone and surrounding soft tissue with current biomaterials for JR can be achieved with mechanically stable, infection free and intact (as opposed to the release of particulate or ionic byproducts) implants. Adverse local tissue reactions (an acute/chronic inflammatory reaction, periprosthetic osteolysis, loosening and subsequent mechanical failure) may evolve when the latter conditions are not met. This article (Part 2 of 2) summarizes the biological response to the non-metallic materials commonly used for joint replacement including polyethylene, ceramics, and polymethylmethacrylate (PMMA), as well as the foreign body reaction to byproducts of these materials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1685-1691, 2017.

Titanium: a review on exposure, release, penetration, allergy, epidemiology, and clinical reactivity

Exposure to titanium (Ti) from implants and from personal care products as nanoparticles (NPs) is common. This article reviews exposure sources, ion release, skin penetration, allergenic effects, and diagnostic possibilities. We conclude that human exposure to Ti mainly derives from dental and medical implants, personal care products, and foods. Despite being considered to be highly biocompatible relative to other metals, Ti is released in the presence of biological fluids and tissue, especially under certain circumstances, which seem to be more likely with regard to dental implants. Although most of the studies reviewed have important limitations, Ti seems not to penetrate a competent skin barrier, either as pure Ti, alloy, or as Ti oxide NPs. However, there are some indications of Ti penetration through the oral mucosa. We conclude that patch testing with the available Ti preparations for detection of type IV hypersensitivity is currently inadequate for Ti. Although several other methods for contact allergy detection have been suggested, including lymphocyte stimulation tests, none has yet been generally accepted, and the diagnosis of Ti allergy is therefore still based primarily on clinical evaluation. Reports on clinical allergy and adverse events have rarely been published. Whether this is because of unawareness of possible adverse reactions to this specific metal, difficulties in detection methods, or the metal actually being relatively safe to use, is still unresolved.

Novel Multifunctional Nanomatrix Reduces Inflammation in Dynamic Conditions in Vitro and Dilates Arteries ex Vivo

Inflammatory responses play a critical role in tissue-implant interactions, often limiting current implant utility. This is particularly true for cardiovascular devices. Existing stent technology does little to avoid or mitigate inflammation or to influence the vasomotion of the artery after implantation. We have developed a novel endothelium-mimicking nanomatrix composed of peptide amphiphiles that enhances endothelialization while decreasing both smooth muscle cell proliferation and platelet adhesion. Here, we evaluated whether the nanomatrix could prevent inflammatory responses under static and physiological flow conditions. We found that the nanomatrix reduced monocyte adhesion to endothelial cells and expression of monocyte inflammatory genes (TNF-α, MCP-1, IL-1β, and IL-6). Furthermore, the nitric-oxide releasing nanomatrix dramatically attenuated TNF-α-stimulated inflammatory responses as demonstrated by significantly reduced monocyte adhesion and inflammatory gene expression in both static and physiological flow conditions. These effects were abolished by addition of a nitric oxide scavenger. Finally, the nanomatrix stimulated vasodilation in intact rat mesenteric arterioles after constriction with phenylephrine, demonstrating the bioavailability and bioactivity of the nanomatrix, as well as exhibiting highly desired release kinetics. These results demonstrate the clinical potential of this nanomatrix by both preventing inflammatory responses and promoting vasodilation, critical improvements in stent and cardiovascular device technology.

Innate immunity sensors participating in pathophysiology of joint diseases: a brief overview

The innate immune system consists of functionally specialized "modules" that are activated in response to a particular set of stimuli via sensors located on the surface or inside the tissue cells. These cells screen tissues for a wide range of exogenous and endogenous danger/damage-induced signals with the aim to reject or tolerate them and maintain tissue integrity. In this line of thinking, inflammation evolved as an adaptive tool for restoring tissue homeostasis. A number of diseases are mediated by a maladaptation of the innate immune response, perpetuating chronic inflammation and tissue damage. Here, we review recent evidence on the cross talk between innate immune sensors and development of rheumatoid arthritis, osteoarthritis, and aseptic loosening of total joint replacements. In relation to the latter topic, there is a growing body of evidence that aseptic loosening and periprosthetic osteolysis results from long-term maladaptation of periprosthetic tissues to the presence of by-products continuously released from an artificial joint.

Macrophage responses to implants: prospects for personalized medicine

Implants, transplants, and implantable biomedical devices are mainstream solutions for a wide variety of human pathologies. One of the persistent problems around nondegradable metallic and polymeric implants is failure of macrophages to resolve the inflammation and their tendency to stay in a state, named "frustrated phagocytosis." During the initial phase, proinflammatory macrophages induce acute reactions to trauma and foreign materials, whereas tolerogenic anti-inflammatory macrophages control resolution of inflammation and induce the subsequent healing stage. However, implanted materials can induce a mixed pro/anti-inflammatory phenotype, supporting chronic inflammatory reactions accompanied by microbial contamination and resulting in implant failure. Several materials based on natural polymers for improved interaction with host tissue or surfaces that release anti-inflammatory drugs/bioactive agents have been developed for implant coating to reduce implant rejection. However, no definitive, long-term solution to avoid adverse immune responses to the implanted materials is available to date. The prevention of implant-associated infections or chronic inflammation by manipulating the macrophage phenotype is a promising strategy to improve implant acceptance. The immunomodulatory properties of currently available implant coatings need to be improved to develop personalized therapeutic solutions. Human primary macrophages exposed to the implantable materials ex vivo can be used to predict the individual's reactions and allow selection of an optimal coating composition. Our review describes current understanding of the mechanisms of macrophage interactions with implantable materials and outlines the prospects for use of human primary macrophages for diagnostic and therapeutic approaches to personalized implant therapy.

Endoplasmic reticulum stress-mediated inflammatory signaling pathways within the osteolytic periosteum and interface membrane in particle-induced osteolysis

Aseptic loosening secondary to periprosthetic inflammatory osteolysis results from the biological response to wear particles and is a leading cause of arthroplasty failure. The origin of this inflammatory response remains unclear. We aim to validate the definite link between endoplasmic reticulum (ER) stress and particle-induced inflammatory signaling pathways in periprosthetic osteolysis. We examine the histopathologic changes of osteolysis and the expression of specific biomarkers for ER-stress-mediated inflammatory signaling pathways (IRE1α, GRP78/Bip, c-Fos, NF-κB, ROS and Ca(2+)). Moreover, pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) and osteoclastogenic molecules (VEGF, OPG, RANKL and M-CSF) were assessed in clinical interface membranes and murine periosteum tissues. We found wear particles to be capable of inducing ER stress in macrophages within clinical osteolytic interface membranes and murine osteolytic periosteum tissues and to be associated with the inflammatory response and osteoclastogenesis. Blocking ER stress with sodium 4-phenylbutyrate (4-PBA) results in a dramatic amelioration of particle-induced osteolysis and a significant reduction of ER-stress intensity. Simultaneously, this ER-stress blocker also lessens inflammatory cell infiltration, diminishes the capability of osteoclastogenesis and reduces the inflammatory response by lowering IRE1α, GRP78/Bip, c-Fos, NF-κB, ROS and Ca(2+) levels. Thus, ER stress plays an important role in particle-induced inflammatory osteolysis and osteoclastogenic reactions. The pharmacological targeting of ER-stress-mediated inflammatory signaling pathways might be an appealing approach for alleviating or preventing particle-induced osteolysis in at-risk patients.

How has the introduction of new bearing surfaces altered the biological reactions to byproducts of wear and modularity?

BACKGROUND

Biological responses to wear debris were largely elucidated in studies focused on conventional ultrahigh-molecular-weight polyethylene (UHMWPE) and some investigations of polymethymethacrylate cement and orthopaedic metals. However, newer bearing couples, in particular metal-on-metal but also ceramic-on-ceramic bearings, may induce different biological reactions.

QUESTIONS/PURPOSES

Does wear debris from the newer bearing surfaces result in different biological responses compared with the known responses observed with conventional metal-on-UHMWPE bearings?

METHODS

A Medline search of articles published after 1996 supplemented by a hand search of reference lists of included studies and relevant conference proceedings was conducted to identify the biological responses to orthopaedic wear debris with a focus on biological responses to wear generated from metal-on-highly crosslinked polyethylene, metal-on-metal, ceramic-on-ceramic, and ceramic-on-polyethylene bearings. Articles were selected using criteria designed to identify reports of wear debris particles and biological responses contributing to prosthesis failure. Case reports and articles focused on either clinical outcomes or tribology were excluded. A total of 83 papers met the criteria and were reviewed in detail.

RESULTS

Biological response to conventional UHMWPE is regulated by the innate immune response. It is clear that the physical properties of debris (size, shape, surface topography) influence biological responses in addition to the chemical composition of the biomaterials. Highly crosslinked UHMWPE particles have the potential to alter, rather than eliminate, the biological response to conventional UHMWPE. Metal wear debris can generate elevated plasma levels of cobalt and chromium ions. These entities can provoke responses that extend to the elicitation of an acquired immune response. Wear generated from ceramic devices is significantly reduced in volume and may provide the impression of an "inert" response, but clinically relevant biological reactions do occur, including granulomatous responses in periprosthetic tissues.

CONCLUSIONS

The material composition of the device, the physical form of the debris, and disease pathophysiology contribute to complex interactions that determine the outcome to all wear debris. Metal debris does appear to increase the complexity of the biological response with the addition of immunological responses (and possibly direct cellular cytotoxicity) to the inflammatory reaction provoked by wear debris in some patients. However, the introduction of highly crosslinked polyethylene and ceramic bearing surfaces shows promising signs of reducing key biological mechanisms in osteolysis.

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.

Comparison of periprosthetic tissues in knee and hip joints: differential expression of CCL3 and DC-STAMP in total knee and hip arthroplasty and similar cytokine profiles in primary knee and hip osteoarthritis

OBJECTIVE

To identify expression profiles (EP) associated with aseptic loosening of total knee arthroplasty (TKA) and to compare them with EP observed in total hip arthroplasty (THA), and primary knee and hip osteoarthritis (OA).

DESIGN

Gene EP of TNF, IL-6, IL-8, CHIT1, BMP4, CCL3, CCL18, MMP9, RANKL, OPG, DC-STAMP and SOCS3 were assessed using quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) on tissues retrieved from patients with aseptically failed TKA (n = 21), THA (n = 41) and primary knee (n = 20) and hip (n = 17) OA. Immunohistochemistry was applied to localize the proteins.

RESULTS

When compared to knee OA, the pseudosynovial tissue in TKA exhibit (1) elevation of alternative macrophage activation marker (CHIT1), chemokine (IL-8), and a proteolytic enzyme (MMP9); (2) downregulation of pro-inflammatory cytokine (TNF), osteoclastic regulator (OPG) and a stimulator of bone formation (BMP4); (3) no difference in IL-6, CCL3, CCL18, RANKL, DC-STAMP and SOCS3. The EP in TKA differed from EP in aseptically failed THA by lower CCL3 and DC-STAMP mRNA and protein expression. EP of all studied inflammatory and osteoclastogenic molecules were similar in knee and hip OA.

CONCLUSIONS

Comparing to OA, aseptic loosening of TKA is associated with upregulated expression of CHIT1, IL-8 and MMP9, dysregulated RANKL:OPG ratio and low levels of inflammatory cytokines. Similar cytokine profiles were associated with primary knee and hip OA. Further research is required to explain the differences in CCL3 and DC-STAMP expression between failed TKA and THA.

Geraniin suppresses RANKL-induced osteoclastogenesis in vitro and ameliorates wear particle-induced osteolysis in mouse model

Wear particle-induced osteolysis and subsequent aseptic loosening remains the most common complication that limits the longevity of prostheses. Wear particle-induced osteoclastogenesis is known to be responsible for extensive bone erosion that leads to prosthesis failure. Thus, inhibition of osteoclastic bone resorption may serve as a therapeutic strategy for the treatment of wear particle induced osteolysis. In this study, we demonstrated for the first time that geraniin, an active natural compound derived from Geranium thunbergii, ameliorated particle-induced osteolysis in a Ti particle-induced mouse calvaria model in vivo. We also investigated the mechanism by which geraniin exerts inhibitory effects on osteoclasts. Geraniin inhibited RANKL-induced osteoclastogenesis in a dose-dependent manner, evidenced by reduced osteoclast formation and suppressed osteoclast specific gene expression. Specially, geraniin inhibited actin ring formation and bone resorption in vitro. Further molecular investigation demonstrated geraniin impaired osteoclast differentiation via the inhibition of the RANKL-induced NF-κB and ERK signaling pathways, as well as suppressed the expression of key osteoclast transcriptional factors NFATc1 and c-Fos. Collectively, our data suggested that geraniin exerts inhibitory effects on osteoclast differentiation in vitro and suppresses Ti particle-induced osteolysis in vivo. Geraniin is therefore a potential natural compound for the treatment of wear particle induced osteolysis in prostheses failure.

Contributions of human tissue analysis to understanding the mechanisms of loosening and osteolysis in total hip replacement

Aseptic loosening and osteolysis are the most frequent late complications of total hip arthroplasty (THA) leading to revision of the prosthesis. This review aims to demonstrate how histopathological studies contribute to our understanding of the mechanisms of aseptic loosening/osteolysis development. Only studies analysing periprosthetic tissues retrieved from failed implants in humans were included. Data from 101 studies (5532 patients with failure of THA implants) published in English or German between 1974 and 2013 were included. "Control" samples were reported in 45 of the 101 studies. The most frequently examined tissues were the bone-implant interface membrane and pseudosynovial tissues. Histopathological studies contribute importantly to determination of key cell populations underlying the biological mechanisms of aseptic loosening and osteolysis. The studies demonstrated the key molecules of the host response at the protein level (chemokines, cytokines, nitric oxide metabolites, metalloproteinases). However, these studies also have important limitations. Tissues harvested at revision surgery reflect specifically end-stage failure and may not adequately reveal the evolution of pathophysiological events that lead to prosthetic loosening and osteolysis. One possible solution is to examine tissues harvested from stable total hip arthroplasties that have been revised at various time periods due to dislocation or periprosthetic fracture in multicenter studies.

The pathology of orthopedic implant failure is mediated by innate immune system cytokines

All of the over 1 million total joint replacements implanted in the US each year are expected to eventually fail after 15–25 years of use, due to slow progressive subtle inflammation at the bone implant interface. This inflammatory disease state is caused by implant debris acting, primarily, on innate immune cells, that is, macrophages. This slow progressive pathological bone loss or “aseptic loosening” is a potentially life-threatening condition due to the serious complications in older people (>75 yrs) of total joint replacement revision surgery. In some people implant debris (particles and ions from metals) can influence the adaptive immune system as well, giving rise to the concept of metal sensitivity. However, a consensus of studies agrees that the dominant form of this response is due to innate reactivity by macrophages to implant debris where both danger (DAMP) and pathogen (PAMP) signalling elicit cytokine-based inflammatory responses. This paper discusses implant debris induced release of the cytokines and chemokines due to activation of the innate (and the adaptive) immune system and the subsequent formation of osteolysis. Different mechanisms of implant-debris reactivity related to the innate immune system are detailed, for example, danger signalling (e.g., IL-1β, IL-18, IL-33, etc.), toll-like receptor activation (e.g., IL-6, TNF-α, etc.), apoptosis (e.g., caspases 3–9), bone catabolism (e.g., TRAP5b), and hypoxia responses (Hif1-α). Cytokine-based clinical and basic science studies are in progress to provide diagnosis and therapeutic intervention strategies.

Novel biological strategies for treatment of wear particle-induced periprosthetic osteolysis of orthopaedic implants for joint replacement

Wear particles and by-products from joint replacements and other orthopaedic implants may result in a local chronic inflammatory and foreign body reaction. This may lead to persistent synovitis resulting in joint pain and swelling, periprosthetic osteolysis, implant loosening and pathologic fracture. Strategies to modulate the adverse effects of wear debris may improve the function and longevity of joint replacements and other orthopaedic implants, potentially delaying or avoiding complex revision surgical procedures. Three novel biological strategies to mitigate the chronic inflammatory reaction to orthopaedic wear particles are reported. These include (i) interference with systemic macrophage trafficking to the local implant site, (ii) modulation of macrophages from an M1 (pro-inflammatory) to an M2 (anti-inflammatory, pro-tissue healing) phenotype in the periprosthetic tissues, and (iii) local inhibition of the transcription factor nuclear factor kappa B (NF-κB) by delivery of an NF-κB decoy oligodeoxynucleotide, thereby interfering with the production of pro-inflammatory mediators. These three approaches have been shown to be viable strategies for mitigating the undesirable effects of wear particles in preclinical studies. Targeted local delivery of specific biologics may potentially extend the lifetime of orthopaedic implants.

In vitro biocompatibility assessment of Ti40Cu38Zr10Pd12 bulk metallic glass

The use of biocompatible materials has attained an increasing importance for tissue regeneration and transplantation. The excellent mechanical and corrosion properties of Ti40Cu38Zr10Pd12 bulk metallic glass (BMG) turn it into a potential candidate for its use in orthopaedic implants. Before being considered as a biomaterial, some biological parameters must be taken into account. In this study,mouse preosteoblasts were cultured in the presence or absence of the alloy at different times (24 h, 7 and 21 days) and no differences in cell viability were detected.Moreover, cells were able to adhere to the alloy surface by establishing focal contacts, and displayed a flattened polygonal morphology. After 14 days in culture, differentiation into osteoblasts was observed. Besides, the amount of Cu ions released and their potential toxic effects were analyzed, showing that the amount of Cu released did not increase cell death. Finally, the low levels of inflammatory cytokines secreted by THP-1 differentiated macrophages exposed to the alloy suggest the absence of an immunogenic response to the alloy. In conclusion, in vitro studies indicate that the Ti40Cu38Zr10Pd12 BMG could be considered as a biomaterial to be used in orthopaedic implants.

Mutant monocyte chemoattractant protein 1 protein attenuates migration of and inflammatory cytokine release by macrophages exposed to orthopedic implant wear particles

Wear particles generated from total joint replacements can stimulate macrophages to release chemokines, such as monocyte chemoattractant protein 1 (MCP-1), which is the most important chemokine regulating systemic and local cell trafficking and infiltration of monocyte/macrophages in chronic inflammation. One possible strategy to curtail the adverse events associated with wear particles is to mitigate migration and activation of monocyte/macrophages. The purpose of this study is to modulate the adverse effects of particulate biomaterials and inflammatory stimuli such as endotoxin by interfering with the biological effects of the chemokine MCP-1. In the current study, the function of MCP-1 was inhibited by the mutant MCP-1 protein called 7ND, which blocks its receptor, the C-C chemokine receptor type 2 (CCR2) on macrophages. Addition of 7ND decreased MCP-1-induced migration of THP-1 cells in cell migration experiments in a dose-dependent manner. Conditioned media from murine macrophages exposed to clinically relevant polymethylmethacrylate (PMMA) particles with/without endotoxin [lipopolysaccharide (LPS)] had a chemotactic effect on human macrophages, which was decreased dramatically by 7ND. 7ND demonstrated no adverse effects on the viability of macrophages, and the capability of mesenchymal stem cells (MSCs) to form bone at the doses tested. Finally, proinflammatory cytokine production was mitigated when macrophages were exposed to PMMA particles with/without LPS in the presence of 7ND. Our studies confirm that the MCP-1 mutant protein 7ND can decrease macrophage migration and inflammatory cytokine release without adverse effects at the doses tested. Local delivery of 7ND at the implant site may provide a therapeutic strategy to diminish particle-associated periprosthetic inflammation and 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.

In vitro macrophage response to nanometer-size chromium oxide particles

An increasing number of studies have reported adverse tissue reactions around metal-on-metal (MM) hip implants. However, the origin and mechanisms of these reactions remain unclear. Moreover, the biological effects of nanometer-size chromium oxide particles, the predominant type of wear particles produced by MM implants, remain mostly unknown. The purpose of this study was to analyze the cytotoxic effects of clinically relevant nanometer-size chromium oxide particles on macrophage response in vitro. J774.A1 macrophages were cultured with either 60 nm or 700 nm commercially available Cr2 O3 particles at different concentrations. Two different particle sizes were analyzed to evaluate potential volume effects. Cell mortality was analyzed by light microscopy, flow cytometry (annexin V-fluorescein isothiocyanate and propidium iodide assay), and using a cell death detection enzyme-linked immunosorbant assay (ELISA). Tumor necrosis factor alpha (TNF-α), monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1 alpha (MIP-1α) release was measured by ELISA, and gene expression was analyzed by quantitative real-time PCR. Results showed that, at high concentrations, Cr2 O3 particles of both sizes can be cytotoxic, inducing significant decreases in total cell numbers and increases in necrosis. Results also suggested that these effects were dependent on particle volume. However, TNF-α, MCP-1, and MIP-1α cytokine release and gene expression remained low. Overall, this study demonstrates that nanometer-size particles of Cr2 O3 , a stable form of chromium oxide ceramic, have rather low cytotoxic effects on macrophages. Therefore, these particles may not be the main culprit in the initiation of the inflammatory reaction in MM periprosthetic tissues. However, other parameters (e.g., potential intracellular damage) remain to be investigated.

Characterization of wear debris in total elbow arthroplasty

BACKGROUND

The purpose of this study was to evaluate wear debris in periprosthetic tissues at the time of revision total elbow arthroplasty. Polyethylene, metallic, and bone cement debris were characterized, and the tissue response was quantified.

MATERIALS AND METHODS

Capsular and medullary tissue samples were collected during revision surgery. Polyethylene debris was characterized by scanning electron microscopy after tissue digestion. The concentrations of metal and cement debris were quantified by inductively coupled plasma mass spectrometry. Tissue response was graded with a semiquantitative histologic method.

RESULTS

Polyethylene particle size varied from the submicron range to over 100 μm. The mean diameter ranged from 0.6 μm to about 1 μm. Particles in the synovial tissues were larger and less abundant than those in tissues from the medullary canal. Cement, titanium alloy, and low levels of cobalt-chrome debris were also present, with cement predominating over metal debris. Histiocyte response was associated with small polyethylene particles (0.5-2 μm), and giant cells were associated with large polyethylene particles (>2 μm). Histiocyte scores positively correlated with the polyethylene particle number and the presence of metal.

DISCUSSION

We have shown that periprosthetic tissues of total elbow patients who have undergone revision for loosening and osteolysis contain polyethylene, cement, and metal debris. Although the polyethylene particles were of a size and shape that have been previously shown to result in activation of phagocytic cells, osteolysis after total elbow arthroplasty is a multimodal process. Because of the presence of multiple wear particle sources, a cause-and-effect relationship between polyethylene debris and osteolysis cannot be established with certainty.

Hypersensitivity to titanium: a less explored area of research

Titanium is considered as an excellent biocompatible metal and it is used in implant dentistry. Literature suggests that Ti can induce clinically relevant hypersensitivity and other immune dysfunctions in certain patients chronically exposed to this reactive metal. At the same time, no standard patch test for Ti has so far been developed, and positive reactions to Ti have therefore only rarely been demonstrated with skin testing. This article reports about the corrosion of dental implants, their significance when hypersensitivity is present, and the literature available till date regarding hypersensitivity of titanium.

The role of TLR and chemokine in wear particle-induced aseptic loosening

Wear particle-induced periprosthetic osteolysis remains the principal cause of aseptic loosening of orthopaedic implants. Monocytes/macrophages phagocytose wear particles and release cytokines that induce inflammatory response. This response promotes osteoclast differentiation and osteolysis. The precise mechanisms by which wear particles are recognized and induce the accumulation of inflammatory cells in the periprosthetic tissue have not been fully elucidated. Recent studies have shown that toll-like receptors (TLRs) contribute to the cellular interaction with wear particles. Wear particles are recognized by monocytes/macrophages through TLRs coupled with the adaptor protein MyD88. After the initial interaction, wear particles induce both local and systemic migration of monocytes/macrophages to the periprosthetic region. The cellular migration is mediated through chemokines including interleukin-8, macrophage chemotactic protein-1, and macrophage inhibitory protein-1 in the periprosthetic tissues. Interfering with chemokine-receptor axis can inhibit cellular migration and inflammatory response. This paper highlights recent advances in TLR, and chemokine participated in the pathogenesis of aseptic loosening. A comprehensive understanding of the recognition and migration mechanism is critical to the development of measures that prevent wear particle-induced aseptic loosening of orthopaedic implants.

Is monocyte chemotactic protein 1 elevated in aseptic loosening of TKA? A pilot study

BACKGROUND

Failure of TKA from aseptic loosening is a growing concern, as TKA is performed with increasing frequency. Loosening is multifactorial and may be associated with elevated inflammatory cytokines in addition to biomechanical failure.

QUESTIONS/PURPOSES

We asked whether proinflammatory cytokines and chemokines are elevated in synovial fluid from patients undergoing revision surgery as compared to those with osteoarthritis (OA) or rheumatoid arthritis (RA).

METHODS

We obtained synovial fluid samples from 20 patients: six with aseptic loosening of TKA (all with bone loss), 10 with primary OA, and four with RA. A panel of cytokines/chemokines was screened using a SearchLight(®) Array (Pierce Biotechnology, Rockford, IL, USA) in one revision sample. Using these data, we assayed the synovial fluids for monocyte chemotactic protein 1 (MCP-1) by ELISA.

RESULTS

We observed an increase in synovial MCP-1 levels in samples from patients planned for TKA revision compared to those with OA or RA. In patients undergoing revision arthroplasty, the mean (± SD) MCP-1 concentration was 21,233 ± 18,966 pg/mL (range, 1550-50,657 pg/mL; n = 6). In patients with OA, the mean MCP-1 level was 3012 ± 3321 pg/mL. In patients with RA, the mean MCP-1 concentration was 690 ± 561 pg/mL.

CONCLUSIONS

All patients undergoing revision TKA showed elevated concentrations of MCP-1 compared to patients with OA and RA, suggesting MCP-1 may serve as a potential marker or predictor of bone loss in patients undergoing revision surgery.

CLINICAL RELEVANCE

MCP-1 may be a novel biomarker in patients showing early symptoms of aseptic loosening of TKA.

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

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

Inhibitory effect of (-)-epigallocatechin gallate on titanium particle-induced TNF-α release and in vivo osteolysis

Tumor necrosis factor-α (TNF-α) and inflammatory cytokines released from activated macrophages in response to particulate debris greatly impact periprosthetic bone loss and consequent implant failure. In the present study, we found that a major polyphenolic component of green tea, (-)-epigallocatechin gallate (EGCG), inhibited Ti particle-induced TNF-α release in macrophages in vitro and calvarial osteolysis in vivo. The Ti stimulation of macrophages released TNF-α in a dose- and time-dependent manner, and EGCG substantially suppressed Ti particle-induced TNF-α release. Analysis of signaling pathway showed that EGCG inhibited the Ti-induced c-Jun N-terminus kinase (JNK) activation and inhibitory κB (IκB) degradation, and consequently the Ti-induced transcriptional activation of AP-1 and NF-κB. In a mouse calvarial osteolysis model, EGCG inhibited Ti particle-induced osteolysis in vivo by suppressing TNF-a expression and osteoclast formation. Therefore, EGCG may be a potential candidate compound for osteolysis prevention and treatment as well as aseptic loosening after total replacement arthroplasty.

The acute inflammatory response to intranigral α-synuclein differs significantly from intranigral lipopolysaccharide and is exacerbated by peripheral inflammation

Background

Activated microglia are a feature of the host response to neurodegeneration in Parkinson's disease (PD) and are thought to contribute to disease progression. Recent evidence suggests that extracellular α-synuclein (eSNCA) may play an important role in the pathogenesis of PD and that this may be mediated by a microglial response.

Methods

We wished to discover whether the host response to eSNCA would be sufficient to induce significant cytokine production. In vitro cultured BV-2 microglia were used to determine the basic inflammatory response to eSNCA. In vivo, 8-week old Biozzi mice were subjected to a single intranigral injection of either 3 μg SNCA, lipopolysaccharide (LPS) or serum protein (BSA) and allowed to recover for 24 hours. A second cohort of animals were peripherally challenged with LPS (0.5 mg/kg) 6 hours prior to tissue collection. Inflammation was studied by quantitative real-time PCR for a number of pro-inflammatory genes and immunohistochemistry for microglial activation, endothelial activation and cell death.

Results

In vitro data showed a robust microglial response to SNCA, including a positive NFĸB response and the production of pro-inflammatory cytokines. Direct injection of SNCA into the substantia nigra resulted in the upregulation of mRNA expression of proinflammatory cytokines, the expression of endothelial markers of inflammation and microglial activation. However, these results were significantly different to those obtained after direct injection of LPS. By contrast, when the animals were injected intracerebrally with SNCA and subsequently challenged with systemic LPS, the level of production of IL-1β in the substantia nigra became comparable to that induced by the direct injection of LPS into the brain. The injection of albumin into the nigra with a peripheral LPS challenge did not provoke the production of a significant inflammatory response. Direct injection of LPS into the substantia nigra also induces cell death in a more robust manner than direct injection of either SNCA or BSA.

Conclusion

These results suggest that the presence of eSNCA protein 'primes' microglia, making them susceptible to environmental proinflammatory challenge. For this reason, we hypothesise that where 'inflammation' contributes to the disease progression in PD, it does so in a punctuate manner (on-off) as a result of systemic events.

Role of polyethylene particles in peri-prosthetic osteolysis: A review

There is convincing evidence that particles produced by the wear of joint prostheses are causal in the peri-prosthetic loss of bone, or osteolysis, which, if it progresses, leads to the phenomenon of aseptic loosening. It is important to fully understand the biology of this bone loss because it threatens prosthesis survival, and loosened implants can result in peri-prosthetic fracture, which is disastrous for the patient and presents a difficult surgical scenario. The focus of this review is the bioactivity of polyethylene (PE) particles, since there is evidence that these are major players in the development and progression of osteolysis around prostheses which use PE as the bearing surface. The review describes the biological consequences of interaction of PE particles with macrophages, osteoclasts and cells of the osteoblast lineage, including osteocytes. It explores the possible cellular mechanisms of action of PE and seeks to use the findings to date to propose potential non-surgical treatments for osteolysis. In particular, a non-surgical approach is likely to be applicable to implants containing newer, highly cross-linked PEs (HXLPEs), for which osteolysis seems to occur with much reduced PE wear compared with conventional PEs. The caveat here is that we know little as yet about the bioactivity of HXLPE particles and addressing this constitutes our next challenge.

Synovial tissue-infiltrating natural killer cells in osteoarthritis and periprosthetic inflammation

OBJECTIVE

Infiltrating immune cells play a central role in degenerative joint disease associated with osteoarthritis (OA) and particle-mediated periprosthetic osteolysis. The goal of this study was to characterize a newly identified population of synovial tissue-infiltrating natural killer (NK) cells obtained from patients with OA or patients with periprosthetic joint inflammation.

METHODS

Synovial and interfacial tissue samples were collected from patients with OA who were undergoing primary or revision total joint replacement (TJR) surgery. The histologic features of OA synovium obtained from patients undergoing primary surgery and interfacial tissue obtained from patients undergoing revision surgery were determined by immunohistochemistry and immunofluorescence. Synovial tissue-infiltrating NK cells were evaluated for the expression of surface receptors, using flow cytometry. Chemoattractant and cytokine protein and RNA levels in synovial and interfacial tissue and fluid were assessed by Luminex assay and real-time quantitative polymerase chain reaction. Cytokine production and degranulation by stimulated synovial tissue versus normal blood NK cells were evaluated by intracellular cytokine staining.

RESULTS

NK cells comprised nearly 30% of the CD45+ mononuclear cell infiltrate in synovial tissue obtained from patients undergoing primary TJR and from patients undergoing revision TJR. NK cells from both groups expressed CXCR3, CCR5, L-selectin, α4 integrins, and cutaneous lymphocyte antigen. Synovial fluid from patients undergoing revision surgery contained elevated concentrations of the NK cell attractants CCL4, CCL5, CXCL9, and CXCL10; all levels in synovial fluid obtained from patients undergoing revision surgery were higher than those in synovial fluid from patients undergoing primary surgery. Cytokine-stimulated interferon-γ production was significantly impaired in NK cells derived from primary and revision TJRs compared with blood NK cells.

CONCLUSION

NK cells are a principal tissue-infiltrating lymphocyte subset in patients with OA and patients with periprosthetic inflammation and display a quiescent phenotype that is consistent with postactivation exhaustion.

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

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

Osteopontin deficiency impairs wear debris-induced osteolysis via regulation of cytokine secretion from murine macrophages

OBJECTIVE

To investigate the molecular mechanisms underlying particle-induced osteolysis, we focused on osteopontin (OPN), a cytokine and cell-attachment protein that is associated with macrophage chemoattractant and osteoclast activation.

METHODS

We compared OPN protein levels in human periprosthetic osteolysis tissues with those in osteoarthritis (OA) synovial tissues. To investigate the functions of OPN during particle-induced osteolysis in vivo, titanium particles were implanted onto the calvaria of OPN-deficient mice and their wild-type (WT) littermates. Mice were killed on day 10 and evaluated immunohistologically. The effects of OPN deficiency on the secretion of inflammatory cytokines were examined using cultured bone marrow-derived macrophages (BMMs). BMMs from OPN-deficient and WT mice were cultured with titanium particles for 12 hours, and the concentrations of inflammatory cytokines in the conditioned media were measured by enzyme-linked immunosorbent assay.

RESULTS

Expression of OPN protein was enhanced in human periprosthetic osteolysis tissues as compared with OA synovial tissues. In the particle-induced model of osteolysis of the calvaria, bone resorption was significantly suppressed by OPN deficiency via inhibition of osteoclastogenesis, whereas an inflammatory reaction was observed regardless of the genotype. Results of immunostaining indicated that OPN protein was highly expressed in the membrane and bone surface at the area of bone resorption in WT mice. When BMMs were exposed to titanium particles, the concentration of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1alpha (IL-1alpha), IL-1beta, and IL-6, as well as chemotactic factors, such as monocyte chemoattractant protein 1 and macrophage inflammatory protein 1alpha, in the conditioned medium were significantly reduced by OPN deficiency. Whereas phagocytic activity of BMMs was not attenuated by OPN deficiency, phagocytosis-mediated NF-kappaB activation was impaired in OPN-deficient BMMs. These data indicated that OPN was implicated in the development of particle-induced osteolysis via the orchestration of pro-/antiinflammatory cytokines secreted from macrophages.

CONCLUSION

OPN plays critical roles in wear debris-induced osteolysis, suggesting that OPN is a candidate therapeutic target for periprosthetic osteolysis.