Nitric oxide release by macrophages in response to particulate wear debris

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

The Effect of Selected Dental Materials Used in Conservative Dentistry, Endodontics, Surgery, and Orthodontics as Well as during the Periodontal Treatment on the Redox Balance in the Oral Cavity

Oxidative stress (OS) is a redox homeostasis disorder that results in oxidation of cell components and thus disturbs cell metabolism. OS is induced by numerous internal as well as external factors. According to recent studies, dental treatment may also be one of them. The aim of our work was to assess the effect of dental treatment on the redox balance of the oral cavity. We reviewed literature available in PubMed, Medline, and Scopus databases, including the results from 2010 to 2020. Publications were searched according to the keywords: oxidative stress and dental monomers; oxidative stress and amalgam; oxidative stress and periodontitis, oxidative stress and braces, oxidative stress and titanium; oxidative stress and dental implants, oxidative stress and endodontics treatment, oxidative stress and dental treatment; and oxidative stress and dental composite. It was found that dental treatment with the use of composites, amalgams, glass-ionomers, materials for root canal filling/rinsing, orthodontic braces (made of various metal alloys), titanium implants, or whitening agents can disturb oral redox homeostasis by affecting the antioxidant barrier and increasing oxidative damage to salivary proteins, lipids, and DNA. Abnormal saliva secretion/composition was also observed in dental patients in the course of OS. It is suggested that the addition of antioxidants to dental materials or antioxidant therapy applied during dental treatment could protect the patient against harmful effects of OS in the oral cavity.

Free Radical Production, Inflammation and Apoptosis in Patients Treated With Titanium Mandibular Fixations-An Observational Study

Despite high biocompatibility of titanium and its alloys, this metal causes various side effects in the human body. It is believed that titanium biomaterials may induce an innate/adaptive immune response. However, still little is known about changes caused by titanium mandible implants, particularly with regard to bone healing. The latest studies showed disturbances in the antioxidant barrier, increased oxidative/nitrosative stress, as well as mitochondrial abnormalities in the periosteum covering titanium mandible fixations; nevertheless, the impact of titanium implants on free radical production, inflammation, and mandible apoptosis are still unknown. Because severe inflammation and apoptosis are among the main factors responsible for disturbances in osteointegration as well as implant rejection, this study is the first to evaluate pro-oxidant enzymes, cytokines as well as pro- and anti-apoptotic proteins in the periosteum of patients with a broken jaw, treated with titanium miniplates and miniscrews. The study group consisted of 29 patients with double-sided fracture of the mandible body requiring surgical treatment. We found significantly higher activity of NADPH oxidase and xanthine oxidase as well as enhanced rate of free radical production in the periosteum of patients in the study group compared to the control group. The markers of inflammation [interleukin 1 (IL-1), interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), transforming growth factor β (TGF-β) and β-glucuronidase (GLU)] as well as apoptosis [Bax, Bax/Bcl-2 ratio, caspase-3 (CAS-3) and nitric oxide (NO)] were significantly elevated in periosteum covering titanium fixations compared to the control group. In the study group, we also demonstrated an increased content of titanium on the periosteum surface, which positively correlated with CAS-3 activity. The study led us to the conclusion that titanium mandible implants increase the production of pro-inflammatory cytokines, and enhance free radical generation in the periosteum covering titanium miniplates and miniscrews. Additionally, exposure to Ti6Al4V titanium alloy induces apoptosis in the mandible periosteum. However, no clinical signs of the said phenomena have been observed.

Glutathione Metabolism, Mitochondria Activity, and Nitrosative Stress in Patients Treated for Mandible Fractures

The aim of the study was to evaluate the effect of titanium bone fixations on mitochondrial activity, reactive oxygen species (ROS) production, glutathione metabolism, and selected markers of oxidative/nitrosative stress in the periosteum-like tissue of patients treated with mandible fractures. The study group consisted of 30 patients with bilateral fractures of the mandible body eligible for surgical treatment. Our study is the first one that indicates disturbances of mitochondrial activity as well as a higher production of ROS in the periosteum-like tissue covering titanium fixations of the mandible. We also found significantly higher levels of reduced glutathione and enhanced activity of glutathione reductase in the periosteum homogenates of patients in the study group compared to the control group. Levels of nitrosative (S-nitrosothiols, peroxynitrite, nitrotyrosine) and oxidative stress biomarkers (malondialdehyde, protein carbonyls, dityrosine, kynurenine, and N-formylkynurenine) were statistically elevated in periosteum-like tissue covering titanium fixations. Although exposure to titanium fixations induces local antioxidant mechanisms, patients suffer oxidative damage, and in the periosteum-like tissue the phenomenon of metallosis was observed. Titanium implants cause oxidative/nitrosative stress as well as disturbances in mitochondrial activity.

The metal nanoparticle-induced inflammatory response is regulated by SIRT1 through NF-κB deacetylation in aseptic loosening

Aseptic loosening is the most common cause of total hip arthroplasty (THA) failure, and osteolysis induced by wear particles plays a major role in aseptic loosening. Various pathways in multiple cell types contribute to the pathogenesis of osteolysis, but the role of Sirtuin 1 (SIRT1), which can regulate inflammatory responses through its deacetylation, has never been investigated. We hypothesized that the downregulation of SIRT1 in macrophages induced by metal nanoparticles was one of the reasons for osteolysis in THA failure. In this study, the expression of SIRT1 was examined in macrophages stimulated with metal nanoparticles from materials used in prosthetics and in specimens from patients suffering from aseptic loosening. To address whether SIRT1 downregulation triggers these inflammatory responses, the effects of the SIRT1 activator resveratrol on the expression of inflammatory cytokines in metal nanoparticle-stimulated macrophages were tested. The results demonstrated that SIRT1 expression was significantly downregulated in metal nanoparticle-stimulated macrophages and clinical specimens of prosthesis loosening. Pharmacological activation of SIRT1 dramatically reduced the particle-induced expression of inflammatory cytokines in vitro and osteolysis in vivo. Furthermore, SIRT1 regulated particle-induced inflammatory responses through nuclear factor kappa B (NF-κB) acetylation. Thus, the results of this study suggest that SIRT1 plays a key role in metal nanoparticle-induced inflammatory responses and that targeting the SIRT1 pathway may lead to novel therapeutic approaches for the treatment of aseptic prosthesis loosening.

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.

Particle-induced osteolysis mediated by endoplasmic reticulum stress in prosthesis loosening

We hypothesized that endoplasmic reticulum (ER) stress in macrophages induced by wear particles was one of the reasons for particle-induced osteolysis (PIO) in total hip arthroplasty (THA) failure. In the present study, the expression of ER stress markers was examined by Western blot in macrophages treated with particles from materials used in prosthetics, specimens from PIO animal models and patients suffering from aseptic loosening. To address whether ER stress triggers these inflammatory responses, the effect of an ER stress blocker on the expression of inflammatory cytokines in particle-treated macrophages and PIO animal models was tested. The results demonstrated that ER stress markers were significantly upregulated in particle-treated macrophages, periosteum tissues from PIO animal models and clinical specimens of prosthesis loosening. Blocking ER stress with a specific inhibitor dramatically reduced the particle-induced expression of inflammatory cytokines in vitro and in vivo. Furthermore, in PIO animal models, this ER stress blocker dramatically suppressed the differentiation of osteoclasts and reduced the severity of osteolysis. Thus, the results of the present study suggest that ER stress plays a key role in particle-induced osteolysis and that targeting the ER stress pathway may lead to novel therapeutic approaches for the treatment of aseptic prosthesis loosening.

Regeneration of the periodontium using enamel matrix derivative in combination with an injectable bone cement

Objectives

Enamel matrix derivative (EMD) has proven to enhance periodontal regeneration; however, its effect is mainly restricted to the soft periodontal tissues. Therefore, to stimulate not only the soft tissues, but also the hard tissues, in this study EMD is combined with an injectable calcium phosphate cement (CaP; bone graft material). The aim was to evaluate histologically the healing of a macroporous CaP in combination with EMD.

Materials and methods

Intrabony, three-wall periodontal defects (2 × 2 × 1.7 mm) were created mesial of the first upper molar in 15 rats (30 defects). Defects were randomly treated according to one of the three following strategies: EMD, calcium phosphate cement and EMD, or left empty. The animals were killed after 12 weeks, and retrieved samples were processed for histology and histomorphometry.

Results

Empty defects showed a reparative type of healing without periodontal ligament or bone regeneration. As measured with on a histological grading scale for periodontal regeneration, the experimental groups (EMD and CaP/EMD) scored equally, both threefold higher compared with empty defects. However, most bone formation was measured in the CaP/EMD group; addition of CAP to EMD significantly enhanced bone formation with 50 % compared with EMD alone.

Conclusions

Within the limits of this animal study, the adjunctive use of EMD in combination with an injectable cement, although it did not affect epithelial downgrowth, appeared to be a promising treatment modality for regeneration of bone and ligament tissues in the periodontium.

Clinical relevance

The adjunctive use of EMD in combination with an injectable cement appears to be a promising treatment modality for regeneration of the bone and ligament tissues in the periodontium.

Distinct inflammatory gene pathways induced by particles

The biologic response to particulate load after arthroplasty has not been fully characterized but is believed mediated by proinflammatory cytokines released from mononuclear cells in the periprosthetic region. To investigate the contribution of lymphocytes to expression of proinflammatory genes induced by metal particles, we compared gene expression of mononuclear cells in response to metal and polymethylmethacrylate particles using cDNA microarray profiling. Peripheral blood mononuclear cells and monocytes were stimulated with polymethylmethacrylate and titanium particles of clinically relevant sizes. Polymethylmethacrylate elicited a six- to 12-fold increase in gene expression of tumor necrosis factor alpha, interleukin 1alpha, interleukin 1beta, interleukin 6, and interleukin 8 in purified monocytes and unfractionated peripheral blood mononuclear cells. Although the effect of titanium on stimulation of purified monocytes was modest, stimulation of lymphocyte-containing peripheral blood mononuclear cells by titanium particles resulted in monocyte-derived proinflammatory cytokine expression. In contrast to polymethylmethacrylate, titanium particles stimulated increased expression of T lymphocyte-derived cytokines, including interleukin 2, interferon gamma, interleukin 9, and interleukin 22, in peripheral blood mononuclear cell cultures. The induction of T cell activation by titanium particles suggests lymphocytes may contribute to the inflammation that mediates osteolysis in patients with metallic particulate debris after total joint replacement.

Osteolysis after the use of a silicon-stabilized tricalcium phosphate-based bone substitute in a radius fracture: a case report

Skelite, a silicon-stabilized tricalcium phosphate-based bone substitute, is a synthetic alternative to the autogenous bone graft. We present a foreign body inflammatory reaction resulting in extensive osteolysis that occurred after use of Skelite as a void filler in the surgical reconstruction of a distal radius fracture.

Cobalt and chromium ions induce nitration of proteins in human U937 macrophagesin vitro

The in situ localization of nitrotyrosine, a product of the nitration of tyrosine residues by peroxynitrite, in the interface membranes from Co--Cr--Mo and Ti--Al--V prostheses provided evidence of nitric oxide-induced oxidative damage in the periprosthetic environment. In the present study, we compared the effects of different wear products from hip prostheses on the nitration of proteins in macrophages in vitro. Nitration of proteins was measured by Western blot using a polyclonal antibody directed against nitrotyrosines. Results showed that Co(2+) and Cr(3+) ions induced the nitration of a 79 +/- 4 kDa protein in a time- and dose-dependent manner. Indeed, the stimulation was significant (p < 0.05) after 24 h with 10 ppm Co(2+) and reached a plateau level between 48 and 72 h. With Cr(3+), the stimulation was significant (p < 0.05) only after 48 and 72 h. The effect of both Co(2+) and Cr(3+) ions was inhibited by glutathione monoethyl-ester that provides protection against oxidative stress. However, ultrahigh-molecular-weight-polyethylene and alumina ceramic particles had no significant effect on the nitration of proteins. Finally, the results showed that nitrated proteins are mainly found in the cytoplasmic fraction of cells and are absent from the nucleus. In conclusion, our results show that Co(2+) and Cr(3+) ions induce the nitration of cytoplasmic proteins in human U937 macrophages, suggesting that metal ions from MM prostheses have the potential to modify protein function in the periprosthetic environment and in circulating cells.

The effect of bisphosphonates and titanium particles on osteoblasts

In an attempt to increase the life of cementless prostheses, an hydroxyapatite-coated implant which releases a bisphosphonate has been suggested as a drug-delivery system. Our in vitro study was designed to determine the maximum dose to which osteoblasts could be safely exposed.

Our findings demonstrated that zoledronate did not impair the proliferation of human osteoblasts when used at concentrations below 1 μm. Murine cells can be exposed to concentrations as high as 10 μm.

A concentration of 0.01% of titanium particles did not impair the proliferation of either cell line. Zoledronate affected the alkaline phosphatase activity of murine osteoblasts through a chelation phenomenon. The presence of titanium particles strongly decreased the alkaline phosphatase activity of murine osteoblasts. We did not detect any synergic effect of zoledronate and titanium particles on the behaviour of both human and murine osteoblasts.

Response of intestinal cells and macrophages to an orally administered cellulose-PEG based polymer as a potential treatment for intractable edemas

The elimination of water from the body represents a fundamental therapeutic goal in those diseases in which oedemas occur. Aim of this work is the design of a material able to absorb large amount of water to be used, by oral administration, in those cases in which resistance to diuretics appears. Sorption and mechanical properties of the cellulose based superabsorbent hydrogel acting as a water elimination system have been modulated through the insertion of molecular spacers between the crosslinks. Starting polymers are the sodium salt of carboxymethylcellulose (CMCNa), a polyelectrolyte cellulose derivative, and the hydroxyethylcellulose (HEC), a non-polyelectrolyte derivative. Polyethyleneglycol (PEG) with various molecular weights, has been linked by its free ends at two divinylsulfone (DVS) crosslinker molecules, in order to increase the average distance between two crosslinking sites and thus acting as spacer. Both the effect of concentration and molecular weight of the spacer resulted to significantly affect the hydrogel final sorption properties and thus the efficiency of the body water elimination system. Biocompatibility studies have been performed to test the hydrogel compatibility with respect to intestinal and macrophages cell lines. To investigate the effects of intestinal cells conditioned media after the contact with the gel on macrophages nitric oxide release tests have been carried out.

Gene expression clustering using self-organizing maps: analysis of the macrophage response to particulate biomaterials

The most common cause of total joint replacement failure is peri-implant bone loss causing pain and prosthesis loosening. This process, known as osteolysis or aseptic loosening, is characterized by macrophage phagocytosis of particulate implant wear debris. In an incompletely defined step, particulate biomaterial debris induces macrophages to release a variety of inflammatory mediators and signaling proteins that lead to bone loss. In an in vitro model of this process, we used microarray technology and data analysis techniques, including the use of self-organizing maps (SOMs), to understand the mRNA gene expression changes occurring in macrophages exposed to clinically relevant particles of ultra-high molecular weight polyethylene and TiAlV alloy. Earlier studies have been limited by technology that only allowed analysis of a few genes at a time, but the microarray techniques used in this paper generate the quantitative analysis of over a thousand genes simultaneously. Our microarray analysis utilized an SOM clustering to elucidate general patterns in the data, lists of top up- and down-regulated genes for each time point and genes with differential expression under different biomaterial exposures. The expression levels of the majority of genes (>95%) did not vary over time or with exposure to different biomaterials, but a few important genes, such as TNF-alpha, IL-1beta, IL-6, and MIP1alpha, proved to be highly regulated in response to biomaterial exposure. We also uncovered a novel set of genes, which not only validates and logically extends the current model of the pathogenesis of osteolysis and aseptic loosening, but also provides new targets for further research and therapeutics.

Analysis of polyethylene particles isolated from periprosthetic tissue of loosened hip arthroplasty and comparison with radiographic appearance

Aseptic loosening is the major problem associated with joint arthroplasty, but little is known about the precise mechanism of osteolysis. To elucidate this mechanism we analyzed polyethylene particles retrieved from granulation tissue around the stem of loosened hip arthroplasties. Granulation tissue was obtained from 35 patients at revision surgery for a loosened hip and digested with papain, followed by ultracentrifugation. The isolated particles were identified with ultra-high molecular weight polyethylene particles by Fourier transform infrared spectroscopy. The morphology and number of particles were analyzed by scanning electron microscopy. Most of the particles were granular, with 87.9% being less than 1 microm in equivalent circle diameter (mean 0.83 +/- 0.45 microm). The mean number of particles per gram of tissue was 1.48 x 10(9) (range 7.59 x 10(7) to 1.15 x 10(10)). We compared these data to the radiological appearance and found that focal-type osteolysis contained more particles than the linear type. The amount of submicron-sized particles is related to the development of osteolysis.

Particles of all sizes provoke inflammatory responses in vivo

The aim of this study was to investigate whether all sizes of wear particles are capable of provoking inflammatory responses and whether there are different responses among different particle sizes. The knees of 40 female Balb/c mice were injected with polystyrene particles of three different diameters, 0.5 microm, 2.0 microm, and 75 microm, using a 0.1% vol/vol concentration. Seven days after particle injection, assessment of the synovial microcirculation using intravital microscopy, and histologic examination, were done. All the mice injected with polystyrene particles had enhanced leukocyte-endothelial cell interactions and histologic scores regardless of particle size when compared with control animals injected with sterile phosphate buffered saline. Polystyrene particles 0.5 microm in size provoked stronger membrane thickening and increased leukocyte-endothelial cell interactions than 75-microm particles. The fraction of rolling leukocytes was enhanced in the 2.0-microm particle group when compared with the 75-microm particle group. These results indicate that polystyrene particles of all sizes (0.5 microm, 2.0 microm, and 75 microm) are capable of inducing an inflammatory response. Small particles (0.5 microm, 2.0 microm) seem to provoke a stronger inflammatory response than larger particles (75 microm) in conditions with equal particle volume.

The influence of wear particles in the expression of osteoclastogenesis factors by osteoblasts

Orthopedic implant failures are often associated with peri-implant osteolysis. Particles generated from the wear process have been suspected to play an important role in this situation. Indeed, the peri-implant osteolysis could be due to the presence of particles stimulating the osteoclastogenesis process. We hypothesize then that the presence of a low particle concentration positively influences osteoblasts to produce osteoclastogenesis factors. If true, this hypothesis would then support the idea that the particles could be at the origin of the process leading to implant loosening. To check the validity of this hypothesis, we quantified in vitro the production of different genes involved in the osteoclastogenesis process using primary isolated human osteoblasts treated or not with particles. Results showed that low concentrations of particles might have a stimulating effect on osteoblasts to produce osteoclastogenesis factors as demonstrated by the increase of RANKL and CSF-1 gene expression in the particle group.

Particle bioreactivity and wear-mediated osteolysis

This review focuses on wear debris-mediated osteolysis, a major factor compromising the long-term success of total joint arthroplasty. Studies on retrieved implants and animal models, as well as in vitro studies on particle bioreactivity, suggest that wear-mediated periprosthetic osteolysis is unlikely to be caused solely by 1 particular cell type or particulate species, but is rather the cumulative consequence of a number of biological reactions. Our recent findings suggest 3 novel mechanisms of particle bioreactivity that may contribute to osteolysis: 1) exacerbated inflammation caused by elevated reactive oxygen species production by activated macrophages and osteoclasts, (2) impaired periprosthetic bone formation secondary to disrupted osteogenesis, and (3) compromised bone regeneration resulting from increased cytotoxic response of mesenchymal osteoprogenitor cells. Understanding the pathogenesis of wear-mediated osteolysis is needed to improve orthopedic implant biocompatibility and wear reduction, and to develop effective pharmacotherapies.

Aseptic loosening

Although total joint replacement surgery is one of the most successful clinical procedures performed today, bone loss around knee and hip implants (osteolysis), resulting in aseptic loosening of the prosthesis, remains a major problem for many patients. Over the last decade much has been learned about this process, which is caused by wear debris particles that simulate a local inflammatory response and osteoclastic bone resorption. Aseptic loosening cannot be prevented or treated by existing nonsurgical methods. Gene transfer, however, offers novel possibilities. Here, we review the current state of the field and the experimental gene therapy approaches that have been investigated toward a solution to aseptic loosening of prosthetic implants.

Influence of orthopedic particulate biomaterials on inflammation and synovial microcirculation in the murine knee joint

The purpose of the present study was to examine changes in the synovial microcirculation as well as synovial tissue responses to exposure to titanium, polymethylmethacrylate (PMMA), ceramic (Al(2)O(3)), cobalt-chromium alloy (Co-Cr), and polyethylene (PE) particles in an in vivo model. The particulate biomaterials were injected into the left knee joint of female Balb/c mice and assessment of the synovial microcirculation using intravital fluorescence microscopy as well as histological evaluation of the synovial tissue response were performed on day 7 after particle administration. Intravital microscopic measurements revealed that all tested biomaterials caused significantly (p < 0.05) enhanced leukocyte-endothelial cell interactions and an increase of functional capillary density compared to controls. In the histological examination PMMA, Al(2)O(3), PE, and Co-Cr particles provoked significantly (p < 0.05) enhanced inflammatory tissue responses in comparison to tissue from control animals. Titanium particles showed significantly (p < 0.05) less leukocyte-endothelial cell interactions than the other particulate biomaterials and caused significantly (p < 0.05) minor membrane thickening compared to PE and PMMA particles. In conclusion, all tested particulate biomaterials were capable of inducing inflammatory responses in the present study. Our data suggest that titanium particles may cause less leukocyte activation and inflammatory tissue responses than other particulate biomaterials used in total joint arthroplasty.

Expression of nitric oxide, peroxynitrite, and apoptosis in loose total hip replacements

Nitric oxide (NO) is an effector molecule associated with inflammation, immune function, bone metabolism, and the induction of apoptosis. This study examined the role of NO, peroxynitrite (ONOO(-)), and apoptosis in cases of revision total hip replacements (THRs). We hypothesized that apoptosis and excess production of NO contribute to the inflammatory reaction to orthopedic biomaterial wear debris that is associated with loosening and osteolysis. Periprosthetic membranous specimens were collected from revised cemented acetabular components with simple loosening and ballooning osteolysis. Synovial samples from patients undergoing primary THR were used as controls. The presence of macrophages (CD68(+)) and levels of inducible nitric oxide synthase (INOS), endothelial nitric oxide synthase (EcNOS), ONOO(-) (Nitro, assayed by the amount of nitrated tyrosine residues), and apoptosis (TUNEL staining) were examined using immunohistochemistry. Increased expression for INOS, EcNOS, and ONOO(-) in both the loose/osteolytic and the loose/non-osteolytic groups was observed when compared to the synovium group. There were no significant differences between the loose/osteolytic group and loose/non-osteolytic group for these biologic markers. TUNEL staining showed a significant increase in apoptosis in the loose/osteolytic group compared to the loose/non-osteolytic group and synovial tissues. These findings suggest that NO and NO-derived molecules, such as ONOO(-), may be involved in sustaining the foreign-body reaction to wear debris. NO and ONOO(-) may prove to be useful markers of prosthetic loosening whereas apoptosis may be a marker distinguishing ballooning from simple osteolysis.

Morphological characteristics of total joint arthroplasty-derived ultra-high molecular weight polyethylene (UHMWPE) wear debris that provoke inflammation in a murine model of inflammation

It is recognized that the chronic inflammation in peri-prosthetic tissue that contributes to implant failure frequently is provoked by the presence of wear debris. Some wear debris is inevitable because of the nature of the prosthesis, but not all patients develop severe inflammatory responses. The precise factors that mediate the severity of tissue inflammation to wear debris has yet to be fully defined. Because wear debris retrieved from peri-prosthetic tissue consists of a heterogeneous mixture of materials with various sizes and shapes, this study evaluated the influence of two major physical aspects of ultra-high molecular weight polyethylene (UHMWPE) wear debris (shape and surface texture) using a model of tissue inflammation. UHMWPE debris particulates recovered from 50 peri-prosthetic tissue samples were examined by scanning electron microscopy and categorized into four groups based upon aspect ratio and surface texture of the material. The four groups were defined as: 1) smooth and globular, 2) smooth and fibular, 3) rough and globular, and 4) rough and fibular. Histological analysis and ELISA assays were conducted to evaluate variations in cellular responses and cytokine production between the groups. The strongest expression of tumor necrosis factor alpha and interleukin-1 beta was found in tissues exposed to UHMWPE debris with both a rough surface texture and fibular shape, and this response was significantly elevated over debris particles with a smooth surface texture and globular shape. The data suggest that both shape and texture influence the severity of specific inflammatory responses and that rough debris surface texture exerts a marked effect on adverse tissue responses when combined with particles that have a sharp, elongated shape.

PMMA particles and pressure--a study of the osteolytic properties of two agents proposed to cause prosthetic loosening

Amongst the wear debris particles implicated in the particle hypothesis for prosthetic loosening are polymethylmethacrylate (PMMA), and particularly PMMA with barium sulphate contrast agent. Another suggested cause for loosening is hydrostatic pressure. PMMA particles were combined with hydrostatic pressure in a study to investigate whether there could be a synergistic or additive effect between these two factors. Titanium plates were fastened onto tibiae of 59 rats. After osseointegration, PMMA particles with barium sulphate were administered to the bone-implant interface. Further, PMMA particles were introduced into a previously published model for hydrostatic pressure induced osteolysis. There was measurable resorption in response to the PMMA particles but no additive or synergistic effect from introducing particles to the pressure model, and the effect of pressure was far greater than that of particles. These results suggest that, whereas particles can be shown to elicit an osteolytic response, the much less studied osteolytic effects of pressure could be far more important.

Nitric oxide synthase in tissues around failed hip prostheses

Nineteen patients who had undergone hip revision surgery for aseptic loosening of joint prostheses were studied. Tissue samples were harvested at the interface between bone and implant, either at the stem or at the cotyle level. Immunohistochemistry was performed on tissue sections to detect nitric oxide synthase (NOS), the enzyme which enables the synthesis of nitric oxide (NO), a molecule which can activate bone resorption. Quantitative analysis of the positive cells and correlation with the presence of particulate wear debris and radiological data were performed. The authors observed a trend towards a moderate increase in positive cells due to inducible NOS in tissues containing particulate wear debris, especially of a plastic material. This increase, however, did not achieve statistical significance. On the contrary, there was a statistical correlation between iNOS (inducible NOS) and the severity of osteolysis around the prosthetic implant. Pharmacological control of the biosynthesis of NO may be considered in the prevention or treatment of loosening.

The role of adsorbed endotoxin in particle-induced stimulation of cytokine release

Numerous in vitro models have demonstrated the capacity of wear particles to stimulate the release of soluble pro-inflammatory products with the ability to induce local bone resorption. Recent observations have demonstrated that binding of lipopolysaccharide (LPS) to particulate wear debris can significantly modulate the pattern of cell response in the in vitro models. These findings raise concerns over the possible role of LPS in the pathogenesis of aseptic loosening after total joint replacements, and also indicates the importance of controlling for possible confounding effects of LPS contamination in the in vitro models used to study the reactive nature of wear debris. Our studies were undertaken to rigorously analyze the effects of particle-associated LPS on cell responses and to assess the efficacy of different treatment protocols to inactivate LPS associated with different particulate materials. Particles of cobalt-chrome alloy, titanium-6-aluminum-4-vanadium, titanium nitride and silica were pretreated with LPS and exposed to multiple treatment protocols. When cells were treated with "as-received" particles prepared by washing in ethanol, small amounts of TNF-alpha, IL-1beta. and IL-1alpha were detected. In contrast, all particle species pretreated with LPS produced marked increases in TNF-alpha, IL-1alpha, and IL-1beta release, as well as upregulation of corresponding mRNA levels even after ethanol washing. Boiling the LPS-pretreated particles in 1% acetic acid or autoclaving and baking the particles also markedly reduced and in some instances abolished the effect of the LPS-pretreatment. This indicates that LPS binds to the surface of particles of diverse composition and that the bound LPS is biologically active. Treatment protocols to inactivate particle-associated LPS demonstrated significant differences in efficacy. When the most rigorous treatments were utilized, essentially all LPS activity could be eliminated. Particles treated with these methods retained some capacity to stimulate cytokine release, but activities were markedly reduced. These results provide further evidence indicating that LPS contamination of particulate materials can markedly enhance their biological activity. This potential confounding effect needs to be carefully monitored and controlled in the in vitro model systems used to evaluate wear particles. Furthermore, the presence of particle-associated endotoxin at the bone-implant interface in vivo could markedly enhance the adverse biological activity of particulate wear debris.

Adherent endotoxin mediates biological responses of titanium particles without stimulating their phagocytosis

Aseptic loosening of orthopaedic implants is thought to be primarily due to stimulation of cytokine production by wear particles from the implants. The cytokines increase osteoclast differentiation, leading to osteolysis and implant loosening. Accumulating evidence indicates that adherent endotoxin mediates the biological responses induced by the wear particles. One mechanism by which adherent endotoxin may act is by increasing phagocytosis of the wear particles. To test this hypothesis, the effect of adherent endotoxin on phagocytosis of titanium particles was determined. First, we developed reliable confocal and fluorescence microscopy methods to examine both the attachment and internalization steps of phagocytosis. Use of these methods showed that adherent endotoxin does not detectably alter the rate or the extent of phagocytosis of titanium particles by RAW 264.7 cells. Despite this lack of an effect on phagocytosis, adherent endotoxin dramatically increases the ability of RAW 264.7 cells to produce TNF-alpha and induce osteoclast differentiation. Thus, adherent endotoxin mediates these biological responses by a mechanism that does not rely on increased phagocytosis. These results also demonstrate that phagocytosis is not sufficient to induce cytokine production and osteoclast differentiation but do not rule out the possibility that phagocytosis is required for induction of these responses by titanium particles with adherent endotoxin.

Transmission electron microscopy of intracellular particles of polyethylene from joint replacement prostheses: size distribution and cellular response

The objectives of this transmission electron microscopy study of peri-implant tissues retrieved at revision arthroplasty were to (1) determine the size distribution of intracellular polyethylene particles, and (2) assess the cellular response to phagocytosed polyethylene particles as revealed by the condition of the cellular organelles. The frequency distributions of intracellular polyethylene particle sizes for 15 cases of total hip replacement showed that more than 75% of the particles had lengths of less than 0.5 microm. More than 90% of the particles were less than 1.0 microm in size. In comparison, the frequency distribution for the particles in cellscomprising tissue retrieved from three total knee replacement prostheses showed that only 43% of the particles were less than 0.5 microm in length and 72% were less than 1 microm in size. There was no statistically significant difference in the mean particle length between the specimens from the hip and knee patients. The majority of the cells containing polyethylene were without signs of degeneration. The cytoplasmic and nuclear membranes were intact. Several electron lucent voids which once contained polyethylene particles were seen surrounded by several healthy appearing mitochondria, which displayed sharp membranes and intact cristae. There were no signs of a cytotoxic response to polyethylene at the ultrastructural level.

Omega-3 polyunsaturated fatty acids and skeletal health

This minireview on skeletal biology describes the actions of prostaglandins and cytokines involved in the local regulation of bone metabolism, it documents the role of lipids in bone biology, and it presents relationships between fatty acids and other factors that impact skeletal metabolism. The data presented herein show consistent and reproducible beneficial effects of omega-3 (n-3) fatty acids on bone metabolism and bone/joint diseases. Polyunsaturated fatty acids modulate eicosanoid biosynthesis in numerous tissues and cell types, alter signal transduction, and influence gene expression. These effects have not been explored in the skeletal system. Future research on n-3 fatty acids in bone biology should focus on the following two aspects. First, the further elucidation of how n-3 fatty acids alter biochemical and molecular processes involved in bone modeling and bone cell differentiation, and second, the evaluation of the potential pharmaceutical applications of these nutraceutical fatty acids in maintaining bone mineral status and controlling inflammatory bone/joint diseases.

Lipids as modulators of bone remodelling

Bone remodelling processes are regulated by systemic hormones and a multitude of local and systemic factors, including prostaglandins, cytokines, and growth factors. Dietary fatty acids and their derivatives (eicosanoids) have been a recent focus of investigation on bone and cartilage metabolism. Specific fatty acids are recognized modulators of eicosanoid biosynthesis, signal transduction, and gene expression. The actions of polyunsaturated fatty acids have not been extensively examined in the skeletal system. Promising research on fatty acids and bone remodelling should evaluate the potential effects on pathways for osteoclastogenesis and osteoblastogenesis.

The effects of calcium phosphate cement particles on osteoblast functions

Calcium phosphate cements (CPC) are increasingly used in the orthopedic field. This kind of cement has potential applications in bone defect replacements, osteosynthetic screw reinforcements or drug delivery. In vivo studies have demonstrated a good osteointegration of CPC. However, it was also observed that the resorption of CPC could create particles. It is known from orthopedic implant studies that particles can be responsible for the peri-implant osteolysis. Biocompatibility assessment of CPC should then be performed with particles. In this study, we quantified the functions of osteoblasts in the presence of beta-TCP, brushite and cement particles. Two particle sizes were prepared. The first one corresponded to the critical diameter range 1-10 microm and the second one had a diameter larger than 10 microm. We found that CPC particles could adversely affect the osteoblast functions. A decrease in viability, proliferation and production of extracellular matrix was measured. A dose effect was also observed. A ratio of 50 CPC particles per osteoblast could be considered as the maximum number of particles supported by an osteoblast. The smaller particles had stronger negative effects on osteoblast functions than the larger ones. Future CPC development should minimize the generation of particles smaller than 10 microm.

Measurement and removal of adherent endotoxin from titanium particles and implant surfaces

Aseptic loosening is thought to be due primarily to osteolysis induced by cytokines and prostaglandins that are produced in response to implant-derived wear particles. Because endotoxin has many of the same effects as have been reported for wear particles, we hypothesized that adherent endotoxin may be responsible for the biological responses induced by wear particles. We demonstrated the presence of significant levels of adherent endotoxin on commonly used preparations of titanium particles as well as on titanium and titanium-alloy implant surfaces. In contrast, supernatants obtained by centrifugation of particle suspensions contained approximately 1% as much endotoxin as did the particles. Therefore, it is erroneous to assume that particles do not contain endotoxin on the basis of data that it cannot be detected in their supernatants or filtrates. These results emphasize the importance of considering the potential role of adherent endotoxin when examining the in vitro effects of wear particles and the in vivo performance of orthopaedic implants. We also developed a protocol that removed more than 99.94% of the adherent endotoxin from the titanium particles without detectably affecting their size or shape. The removal of adherent endotoxin will allow comparison of the biological responses induced by particles with or without adherent endotoxin.

The cytotoxic effect of titanium particles phagocytosed by osteoblasts

The cytotoxic effect of different concentrations of titanium particles on osteoblasts was studied in vitro. It was found that the viability of the osteoblasts was inversely proportional to the particle concentration. Phagocytosis of particles by the osteoblasts was evident and was demonstrated to be responsible for cell necrosis. Moreover, during and after phagocytosis, the osteoblasts released products that were cytotoxic for other osteoblasts, as established with a conditioned medium assay. The titanium particles thus had both a direct and an indirect effect on osteoblast viability. It also was observed that the titanium particles induced a process of programmed cell death (apoptosis) when co-cultured with osteoblasts. The results of this study suggest that not only is the amount of wear debris generated important, but the local accumulation of the debris also may have a significant impact on bone cell function.

Decontaminating particles exposed to bacterial endotoxin (LPS)

Lipopolysaccharide (LPS), which comes from the cell wall of gram-negative bacteria, can stimulate murine macrophage cells to produce nitric oxide (NO), cytokines, such as tumor necrosis factor-alpha, and interleukins, such as IL-6. When examining the biological effects of particles on macrophages, it is important to have no contaminating LPS associated with the particles and none with any cell culture media or supplies since even very low levels of LPS are stimulatory. The presence or absence of LPS was observed in two ways: (1) the amount of NO produced by RAW 264.7 murine macrophage cells, and (2) the Limulus amebocyte lysate (LAL) test. Treating particles with 70% ethanol at room temperature for 48 h, followed by washing the polymethylmethacrylate (PMMA) particles with endotoxin-free phosphate-buffered saline three times, decontaminated LPS and LPS-treated PMMA particles. When given LPS that had been treated with 70% ethanol for 48 h at room temperature or at 37 degrees C, cells did not produce NO above control levels. Negative LAL tests indicated the presence of extremely low levels or the complete absence of LPS in 70% ethanol-treated LPS.