Modulation of the production of cytokines in titanium-stimulated human peripheral blood monocytes by pharmacological agents. The role of cAMP-mediated signaling mechanisms

Immunomodulatory Effects of Fluoroquinolones in Community-Acquired Pneumonia-Associated Acute Respiratory Distress Syndrome

Community-acquired pneumonia is reported as one of the infectious diseases that leads to the development of acute respiratory distress syndrome. The innate immune system is the first line of defence against microbial invasion; however, its dysregulation during infection, resulting in an increased pathogen load, stimulates the over-secretion of chemokines and pro-inflammatory cytokines. This phenomenon causes damage to the epithelial-endothelial barrier of the pulmonary alveoli and the leakage of the intravascular protein into the alveolar lumen. Fluoroquinolones are synthetic antimicrobial agents with immunomodulatory properties that can inhibit bacterial proliferation as well as exhibit anti-inflammatory activities. It has been demonstrated that the structure of fluoroquinolones, particularly those with a cyclopropyl group, exerts immunomodulatory effects. Its capability to inhibit phosphodiesterase activity leads to the accumulation of intracellular cAMP, which subsequently enhances PKA activity, resulting in the inhibition of transcriptional factor NF-κB and the activation of CREB. Another mechanism reported is the inhibition of TLR and ERK signalling pathways. Although the sequence of events has not been completely understood, significant progress has been made in comprehending the specific mechanisms underlying the immunomodulatory effects of fluoroquinolones. Here, we review the indirect immunomodulatory effects of FQs as an alternative to empirical therapy in patients diagnosed with community-acquired pneumonia.

Fluoroquinolones Suppress TGF-β and PMA-Induced MMP-9 Production in Cancer Cells: Implications in Repurposing Quinolone Antibiotics for Cancer Treatment

BACKGROUND

Fluoroquinolones (FQs) are potent antimicrobials with multiple effects on host cells and tissues. Although FQs can attenuate cancer invasion and metastasis, the underlying molecular mechanisms remain unclear. Matrix metalloproteinase-9 (MMP-9) has functional roles in tumor angiogenesis, invasion, and metastasis, and is associated with cancer progression and poor prognosis, suggesting that inhibitors of MMP-9 activity and transcription are prime candidates for cancer therapy. Despite numerous preclinical data supporting the use of MMP-9 inhibitors as anticancer drugs, the few available examples are not therapeutically useful due to low specificity and off-target effects. We examined the effects of FQs on MMP-9 production in cancer cells following transforming growth factor beta (TGF-β) and phorbol 12-myristate 13-acetate (PMA) stimulation.

EXPERIMENTAL APPROACHES

Using confluent cultures of HepG2 and A549 cells, the effects of FQs (ciprofloxacin, levofloxacin, clinafloxacin, gatifloxacin, and enrofloxacin) on TGF-β and PMA-induced MMP-9 mRNA expression and production were studied in RNA extracts and culture supernatants, respectively. FQs specifically abrogated TGF-β and PMA-induced MMP-9 levels and activity in a concentration and time-dependent manner, without affecting other MMPs or proteins involved in epithelial-mesenchymal transition. Additionally, FQs inhibited TGF-β and PMA-induced cell migration via p38 and cyclic AMP signaling pathways.

CONCLUSIONS AND IMPLICATIONS

Overall, we demonstrated that FQs inhibit cancer cell migration and invasion by downregulating MMP-9 expression and revealed the cellular mechanisms underlying their potential value in cancer treatment.

Sophocarpine attenuates wear particle-induced implant loosening by inhibiting osteoclastogenesis and bone resorption via suppression of the NF-κB signalling pathway in a rat model

BACKGROUND AND PURPOSE

Aseptic prosthesis loosening, caused by wear particles, is one of the most common causes of arthroplasty failure. Extensive and over-activated osteoclast formation and physiological functioning are regarded as the mechanism of prosthesis loosening. Therapeutic modalities based on inhibiting osteoclast formation and bone resorption have been confirmed to be an effective way of preventing aseptic prosthesis loosening. In this study, we have investigated the effects of sophocarpine (SPC, derived from Sophora flavescens) on preventing implant loosening and further explored the underlying mechanisms.

EXPERIMENTAL APPROACH

The effects of SPC in inhibiting osteoclastogenesis and bone resorption were evaluated in osteoclast formation, induced in vitro by the receptor activator of NF-κB ligand (RANKL). A rat femoral particle-induced peri-implant osteolysis model was established. Subsequently, micro-CT, histology, mechanical testing and bone turnover were used to assess the effects of SPC in preventing implant loosening.

KEY RESULTS

In vitro, we found that SPC suppressed osteoclast formation, bone resorption, F-actin ring formation and osteoclast-associated gene expression by inhibiting NF-κB signalling, specifically by targeting IκB kinases. Our in vivo study showed that SPC prevented particle-induced prosthesis loosening by inhibiting osteoclast formation, resulting in reduced periprosthetic bone loss, diminished pseudomembrane formation, improved bone-implant contact, reduced bone resorption-related turnover and enhanced stability of implants. Inhibition of NF-κB signalling by SPC was confirmed in vivo.

CONCLUSION AND IMPLICATIONS

SPC can prevent implant loosening through inhibiting osteoclast formation and bone resorption. Thus, SPC might be a novel therapeutic agent to prevent prosthesis loosening and for osteolytic diseases.

Mechanism-based management for mucositis: option for treating side effects without compromising the efficacy of cancer therapy

Mucositis is a major side effect induced by chemotherapy and radiotherapy. Although mucositis is a leading cause of morbidity and mortality in cancer patients, management is largely limited to controlling symptoms, and few therapeutic agents are available for treatment. Since mucositis could be inhibited by the modulation of radiotherapy- or chemotherapy-induced pathways independently of cancer treatment, there is an opportunity for the development of more targeted therapies and interventions. This article examined potential therapeutic agents that have been investigated for the prevention and/or inhibition of mucositis induced by conventional chemotherapy and radiotherapy. They can be classified according to their mechanisms of action: scavenging reactive oxygen species, inhibition of specific cytokine production or inflammation, and inhibition of apoptosis. These early events may be good target pathways for preventing the pathogenesis of mucositis. Considering that both cancer therapy and therapeutic agents for mucositis act on both normal and cancer cells, agents that inhibit mucositis should act through mechanisms that selectively protect normal cells without compromising cancer treatment. Therefore, mechanism-based guidance for the treatment of mucositis is critical to prevent risky treatments for cancer patients and to relieve detrimental side effects effectively from cancer therapy.

Subinhibitory antibiotic therapy alters recurrent urinary tract infection pathogenesis through modulation of bacterial virulence and host immunity

The capacity of subinhibitory levels of antibiotics to modulate bacterial virulence in vitro has recently been brought to light, raising concerns over the appropriateness of low-dose therapies, including antibiotic prophylaxis for recurrent urinary tract infection management. However, the mechanisms involved and their relevance in influencing pathogenesis have not been investigated. We characterized the ability of antibiotics to modulate virulence in the uropathogens Staphylococcus saprophyticus and Escherichia coli. Several antibiotics were able to induce the expression of adhesins critical to urothelial colonization, resulting in increased biofilm formation, colonization of murine bladders and kidneys, and promotion of intracellular niche formation. Mice receiving subinhibitory ciprofloxacin treatment were also more susceptible to severe infections and frequent recurrences. A ciprofloxacin prophylaxis model revealed this strategy to be ineffective in reducing recurrences and worsened infection by creating larger intracellular reservoirs at higher frequencies. Our study indicates that certain agents used for antibiotic prophylaxis have the potential to complicate infections.

Antibiotics are the mainstay treatment for bacterial infections; however, evidence is emerging that argues these agents may have off-target effects if sublethal concentrations are present. Most studies have focused on changes occurring in vitro, leaving questions regarding the clinical relevance in vivo. We utilized a murine urinary tract infection model to explore the potential impact of low-dose antibiotics on pathogenesis. Using this model, we showed that subinhibitory antibiotics prime uropathogens for adherence and invasion of murine urothelial tissues. These changes in initial colonization promoted the establishment of chronic infection. Furthermore, treatment of chronically infected mice with subtherapeutic ciprofloxacin served to exacerbate infection. A part of these changes was thought to be due to suppression of mucosal immunity, as demonstrated through reductions in cytokine secretion and migration of leukocytes into the urinary tract. This work identifies novel risk factors associated with antibiotic therapy when dosing strategies fall below subtherapeutic levels.

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.

Impact of antibiotic therapy on systemic cytokine expression in pneumococcal pneumonia

The aim of this study was to compare the evolution of systemic cytokine levels over time in patients with pneumococal pneumonia treated either with β-lactam monotherapy or with combination therapy (β-lactam plus fluoroquinolone). Prospective observational study of hospitalized non-immunocompromised adults with PP. Concentrations of IL-6, IL-8, IL-10, and TNF-α were determined on days 0, 1, 2, 3, 5, and 7. Patients on β-lactam monotherapy were compared with those receiving combination therapy. Fifty-two patients were enrolled in the study. Concentrations of IL-6, IL-8, and IL-10 decreased rapidly in the first days after admission, in accordance with the mean time to defervescence. High levels of IL-6 were found in patients with the worst outcomes, measured by the need for intensive care unit admission and mortality. No major differences in demographic or clinical characteristics or severity of disease were found between patients treated with β-lactam monotherapy and those treated with combination therapy. IL-6 levels fell more rapidly in patients with combination therapy in the first 48 h (p = 0.016). Our data suggest that systemic expression of IL-6 production in patients with PP correlates with prognosis. Initial combination antibiotic therapy produces a faster decrease in this cytokine in the first 48 h.

Systemic expression of cytokine production in patients with severe pneumococcal pneumonia: effects of treatment with a beta-lactam versus a fluoroquinolone

Bacterial alveolar invasion is followed by an inflammatory response. A systemic extension of the compartmentalized immune response has been described in patients with severe pneumonia. The data suggest that some antimicrobials may induce a differential release of cytokines. We conducted a prospective, randomized study in adult patients with severe pneumococcal pneumonia to measure the effects of ceftriaxone and levofloxacin in the systemic cytokine expression over time. Demographic, clinical characteristics, and severity scores were recorded. The serum concentrations of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, IL-8, IL-10, and IL-1 receptor agonist were measured at 0, 24, 72, and 120 h. A total of 32 patients were included in the study. Both groups were homogeneous in terms of age, comorbidities, severity of disease, and corticosteroid or statin use. With the single exception of IL-1beta, all cytokines were detected in venous blood. All of the cytokines studied showed a similar pattern of progressive decrease over time. No significant differences in the concentrations of any of the cytokines studied were found, with the exception of TNF-alpha, for which lower concentrations were obtained at 120 h in the levofloxacin group (P = 0.014). Basal oxygen saturation (P = 0.034) and heart rate (P = 0.029) returned to normal values earlier in the levofloxacin arm. We demonstrated that in patients with severe pneumococcal pneumonia pro- and anti-inflammatory responses could be detected in venous blood, representing a systemic extension of the compartmentalized response. Treatment with a beta-lactam agent or a fluoroquinolone has different effects on cytokine production and its systemic expression, impacting the clinical course of the disease.

Human macrophage response to UHMWPE, TiAlV, CoCr, and alumina particles: analysis of multiple cytokines using protein arrays

Aseptic loosening of total joint replacements is believed to be initiated by a macrophage response to prosthetic wear debris. To better characterize the early response to clinically relevant wear debris, we challenged primary human macrophages from four donors with ultra high molecular weight polyethylene (UHMWPE), TiAlV, CoCr, and alumina particles. After a 24-h culture, protein arrays were used to quantify the secretion of 30 different cytokines and chemokines. Macrophages secreted detectable levels of nine mediators in culture: Interleukin-1alpha (IL-1alpha), tumor necrosis factor-alpha (TNF-alpha), IL-1beta, MCP-1, IL-8, IL-6, GM-CSF, IL-10, and IL-12p40. TiAlV particles were the most stimulatory, causing 5- to 900-fold higher cytokine expression compared with nonstimulated cells and uniquely eliciting high levels of IL-1alpha, IL-6, IL-10, and GM-CSF. CoCr and alumina were mildly stimulatory and typically elicited two- to fivefold greater levels than nonstimulated cells. Surprisingly, UHMWPE did not elicit a significant increase in cytokine release. Our data suggests that IL-1alpha, TNF-alpha, IL-1beta, and MCP-1 are the primary initiators of osteolysis and implicates metallic debris as an important trigger for their release.

Enhanced osteolytic potential of monocytes/macrophages derived from bone marrow after particle stimulation

BACKGROUND

Total hip replacement can be complicated by periprosthetic osteolysis. Monocytes/macrophages play a major role in the formation of the foreign body granulomas induced by wear debris. We hypothesized that periprosthetic monocytes/macrophages do not only accelerate inflammatory and osteoclast-mediated osteolytic processes, but also resorb periprosthetic bone directly by themselves. This study was designed to evaluate the osteolytic potential in vitro of monocytes/macrophages derived from bone marrow.

METHODS

Monocytes/macrophages were produced by filtration of rat bone marrow cells, followed by culture in the presence of macrophage-colony stimulating factor (M-CSF). Monocyte/macrophage properties were ascertained using immunocytochemistry and phagocytic activity. Osteolytic cytokines and extracellular matrix degrading proteinases were quantified at the mRNA level.

RESULTS

Adherent cell fraction was immunoreactive for the monocyte/macrophage specific marker CD68 and active in the phagocytosis of carbon particles up to 72 h. They also showed immunoreactivity to cathepsin K, IL-1beta, IL-6, and M-CSF, but mostly did not react to TRAP. mRNA levels of osteolytic cytokines and extracellular matrix degrading proteinases were enhanced, but that of RANKL were not. Monocytes/macrophages resorbed dentine discs and carbonated calcium phosphate was very actively resorbed after stimulation with titanium particles.

DISCUSSION

Harvested bone marrow cells expressed monocyte/macrophage phenotype, but not osteoclastic markers. The capacity of these cathepsin-K-positive phagocytic cells to resorb dentine discs and carbonated calcium phosphate in vitro suggests a direct role of monocytes/macrophages in bone resorption and periprosthetic osteolysis. The finding supports our hypothesis and previous histomorphometric observations on the presence of such osteolytic macrophages in vivo around loosening prosthesis.

Statins attenuate polymethylmethacrylate-mediated monocyte activation

BACKGROUND

Periprosthetic osteolysis precipitates aseptic loosening of components, increases the risk of periprosthetic fracture and, through massive bone loss, complicates revision surgery and ultimately is the primary cause for failure of joint arthroplasty. The anti-inflammatory properties of HMG-CoA reductase inhibitors belonging to the statin family are well recognized. We investigated a possible role for status in initiating the first stage of the osteolytic cycle, namely monocytic activation.

METHODS

We used an in vitro model of the human monocyte/macrophage inflammatory response to poly-methylmethacrylate (PMMA) particles after pretreat-ing cells with cerivastatin, a potent member of the statin family. Cell activation based upon production of TNF-alpha and MCP-1 cytokines was analyzed and the intracellular Raf-MEK-ERK signal transduction pathway was evaluated using western blot analysis, to identify its role in cell activation and in any cerivastatin effects observed.

RESULTS

We found that pretreatment with cerivastatin significantly abrogates the production of inflammatory cytokines TNF-alpha and MCP-1 by human monocytes in response to polymethylmethacrylate particle activation. This inflammatory activation and attenuation appear to be mediated through the intracellular Raf-MEK-ERK pathway.

INTERPRETATION

We propose that by intervening at the upstream activation stage, subsequent osteoclast activation and osteolysis can be suppressed. We believe that the anti-inflammatory properties of statins may potentially play a prophylactic role in the setting of aseptic loosening, and in so doing increase implant longevity.

The biology of aseptic osteolysis

Total hip arthroplasty is one of the most commonly performed and successful elective orthopaedic procedures. However, numerous failure mechanisms limit the long-term success including aseptic osteolysis, aseptic loosening, infection, and implant instability. Aseptic osteolysis and subsequent implant failure occur because of a chronic inflammatory response to implant-derived wear particles. To reduce particulate debris and their consequences, implants have had numerous design modifications including high-molecular-weight polyethylene sockets and noncemented implants that rely on bone ingrowth for fixation. Surgical techniques have improved cementation with the use of medullary plugs, cement guns, lavage of the canal, pressurization, centralization of the stem, and reduction in cement porosity. Despite these advances, aseptic osteolysis continues to limit implant longevity. Numerous proinflammatory cytokines, such as interleukin-1, interleukin-6, tumor necrosis factor-alpha, and prostaglandin E2, have proosteoclastogenic effects in response to implant-derived wear particles. However, none of these cytokines represents a final common pathway for the process of particle-induced osteoclast differentiation and maturation. Recent work has identified the fundamental role of the RANKL-RANK-NF-kappaB pathway not only in osteoclastogenesis but also in the development and function the immune system. Thus, the immune system and skeletal homeostasis may be linked in the process of osteoclastogenesis and osteolysis.

Nonsurgical management of osteolysis: challenges and opportunities

Osteolysis remains a common mode of total hip arthroplasty failure. In vitro and animal models have been used to determine the pathophysiology of osteolysis by carefully dissecting the biochemical pathways leading to particulate wear debris and periprosthetic bone loss. Numerous cytokines and inflammatory mediators, including TNF-alpha and IL-1, are critical participants in this cascade and may represent prime targets for pharmacologic intervention. Osteoclasts, the end effector cells involved in the osteolytic process, also represent potential targets. Cell surface receptors on osteoclast precursors, such as receptor activator of NF-kappaB (RANK) (on osteoclasts) and RANK-ligand (RANKL) (on stromal cells), provide opportunities to arrest osteoclast maturation. Enhancing the naturally occurring osteoprotegerin is another recent attempt at modulating osteoclast behavior and a possible target for pharmacologic therapies. Other nonoperative strategies include intercepting tumor necrosis factor-alpha activity, interfering with the RANK-RANKL interaction necessary for osteoclast development and maturation, bisphosphonate therapy, and using viral vectors to deliver genes. Although each of these approaches has potential benefits, there are substantial challenges to effective implementation. Until there is convincing evidence of efficacy in human clinical trials, we recommend vigilant screening and appropriate surgery with component loosening or substantial likelihood of loosening, periprosthetic fracture, or major bone loss.

Aseptic loosening, not only a question of wear: a review of different theories

Today, aseptic loosening is the most common cause of revision of major arthroplasties. Aseptic loosening accounts for more than two-thirds of hip revisions and almost one-half of knee revisions in Sweden. Several theories on the cause of aseptic loosening have been proposed. Most of these theories, however, are based on empiric observations, experimental animal models or anecdotal cases. In this review, we discuss the most common theories concerning aseptic loosening. It emerges from this review that aseptic loosening has a multifactorial etiology and cannot be explained by a single theory.

Activation of NF-kappaB signalling and TNFalpha-expression in THP-1 macrophages by TiAlV- and polyethylene-wear particles

Wear particles are believed to induce periprosthetic inflammation which contributes to periprosthetic osteolysis. TNFalpha plays a pivotal role in the pathogenesis of this process. The molecular mechanisms leading to the development of periprosthetic inflammation with upregulated TNFalpha expression in monocytic cells in response to different wear particles have yet to be defined. In this study we evaluated the effects of polyethylene- and TiAlV-particles on activation of NF-kappaB signalling pathways and TNFalpha biosynthesis and release in monocytic cells with respect to periprosthetic osteoclastogenesis. THP-1 monocytic cells were differentiated to macrophage-like cells and exposed to LPS-detoxified polyethylene and prosthesis-derived TiAlV-particles. TNFalpha release was analyzed in culture supernatant by ELISA. NF-kappaB activation was examined by electrophoretic mobility shift assay (EMSA), and NF-kappaB target promoter activities including transactivation of the TNFalpha promoter were determined by luciferase reporter gene assays. Differentiated THP-1 macrophages were exposed to increasing numbers of particles for 0, 60, 180 and 360 min. Both, polyethylene- and TiAlV-particles induced a significant activation of both NF-kappaB and TNFalpha promoters at 180 min. A significant TNFalpha release was detected after 360 min exposure to polyethylene- and TiAlV-particles in a dose dependent manner. In comparison, LPS induced a much greater activation of NF-kappaB and TNFalpha promoters, and TNFalpha secretion into the supernatant was strongly induced. These results provide evidence that induction of the NF-kappaB signal transduction pathway in macrophages plays a major role in initiating and mediating the inflammatory response leading to periprosthetic osteolysis.

Ciprofloxacin-releasing bioabsorbable polymer is superior to titanium in preventingStaphylococcus epidermidis attachment and biofilm formationin vitro

Antibiotic coating systems have been successfully used to prevent bacterial attachment and biofilm formation. Our purpose was to evaluate whether bioabsorbable polylactide-co-glycolide (PLGA) 80/20 on its own, and PLGA together with ciprofloxacin (PLGA+C) have any advantages over titanium in preventing Staphylococcus epidermidis attachment and biofilm formation in vitro. Cylindrical specimens of titanium, PLGA, and PLGA+C in triplicate were examined for S. epidermidis ATCC 35989 attachment and biofilm formation after incubation with a bacterial suspension of about 10(5) cfu/mL for 1, 3, 7, 14, and 21 days, using scanning electron microscopy. Growth inhibition properties of PLGA and PLGA+C cylinders were tested on agar plates. On days 1, 3, and 21, no bacterial attachment was seen in 19.5, 9.2, and 41.4% of the titanium specimens; in 18.4, 28.7, and 34.5% of the PLGA specimens; and in 57.5, 62.1, and 57.5% of the PLGA+C specimens, respectively. During the whole study period, no biofilm was observed on 74-93% of the titanium specimens, 58-78% of the PLGA specimens, and 93-100% of the PLGA+C specimens. PLGA+C showed clear bacterial growth inhibition on agar plates, while PLGA and titanium did not show any inhibition. PLGA+C bioabsorbable material was superior to titanium in preventing bacterial attachment and biofilm formation and may have clinical applicability, for example, in prevention of infection in trauma surgery or in the treatment of chronic osteomyelitis.

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.

Lumbar Intervertebral Body Fusion Cages: Histological Evaluation of Clinically Failed Cages Retrieved from Humans

The purpose of this study is to investigate the diagnostic value of evoked spinal cord potentials (ESCPs) and choline acetyltransferase (CAT) activity during exploration of injuries to the brachial plexus. We assessed 25 spinal roots in 19 patients. The results of the two investigations were consistent in all except two roots. Although assessment of ESCPs is easy and quick, it mainly records the nerve potentials along the sensory pathway. Although measurement of CAT activity needs a specimen of the nerve and the availability of a radioisotope laboratory, it gives direct information regarding the motor function of ventral spinal roots. These two techniques should be complementary to each other in order to achieve a more accurate diagnosis.

Effects of interleukin-10 on titanium particle-induced macrophage transcription factor activation and cytokine expressionin vitro

This study tests the hypothesis that transcription factor activation by exposure of macrophages to titanium particles can be modulated by the addition of the antiinflammatory cytokine, interleukin 10 (IL-10). The experiments were carried out with primary human monocyte/macrophages that were treated in the presence or absence of IL-10 with and without exposure to titanium particles. The time course for experiments varied from 1 h-5 h for analysis of nuclear protein and up to 48 h for analysis of cytokine release. Transcription factor translocation to the nucleus was analyzed using electrophoretic gel shift assays and cytokine release was quantified by enzyme-linked immunosorbent assay. Addition of titanium particles increased release of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-1 beta (IL-1 beta). In addition, titantium particle induced translocation of the transcription factors, NF-kappa B and NF-IL6, in the nucleus within 1 h. Treatment of macrophages with IL-10 prior to exposure to titanium particles decreased translocation of NF-IL6 but did not significantly alter nuclear levels of NF-kappa B. In addition, pretreatment of the cells with IL-10 decreased particle-induced cytokine release. These data show that antiinflammatory cytokines may provide a mechanism by which particle-induced inflammatory response may be modulated in vivo.

Use of volumetric computerized tomography as a primary outcome measure to evaluate drug efficacy in the prevention of peri-prosthetic osteolysis: a 1-year clinical pilot of etanercept vs. placebo

Although total hip replacement (THR) is amongst the most successful and beneficial medical procedures to date, long-term outcomes continue to suffer from aseptic loosening secondary to peri-prosthetic osteolysis. Extensive research over the last two decades has elucidated a central mechanism for osteolysis in which wear debris generated from the implant stimulates inflammatory cells to promote osteoclastogenesis and bone resorption. The cytokine tumor necrosis factor alpha (TNFalpha) has been demonstrated to be central to this process and is considered to be a leading target for intervention. Unfortunately, even though FDA approved TNF antagonists are available (etanercept), currently there are no reliable outcome measures that can be used to evaluate the efficacy of a drug to prevent peri-prosthetic osteolysis. To the end of developing an effective outcome measure, we evaluated the progression of lesion size in 20 patients with established peri-acetabular osteolysis (mean=29.99 cm(3), range=2.9-92.7 cm(3)) of an uncemented primary THR over 1-year, using a novel volumetric computer tomography (3D-CT) technique. We also evaluated polyethylene wear, urine N-telopeptides and functional assessments (WOMAC, SF-36 and Harris Hip Score) for comparison. At the time of entry into the study baseline CT scans were obtained and the patients were randomized to etanercept (25 mg s.q., twice/week) and placebo in a double-blinded fashion. CT scans, urine and functional assessments were also obtained at 6 and 12 months. No serious adverse drug related events were reported, but one patient had to have revision surgery before completion of the study due to aseptic loosening. No remarkable differences between the groups were observed. However, the study was not powered to see significant drug effects. 3D-CT data from the 19 patients was used to determine the mean increase in lesion size over 48 weeks, which was 3.19 cm(3) (p<0.0013). Analysis of the urine N-telopeptides and functional assessment data failed to identify a significant correlation with wear or osteolysis. In conclusion, volumetric CT was able to measure progression of osteolysis over the course of a year, thus providing a technology that could be used in therapeutic trials. Using the data from this pilot we provide a model power calculation for such a trial.

Spinal implant debris-induced osteolysis

STUDY DESIGN

Generally, implant-induced osteolysis is a manifestation of an adverse cellular response to phagocytosable particulate wear and corrosion debris. Initially termed "cement disease," particle-induced loosening was recognized by Charnley in the early 1960s. Despite the plethora of information gained over the last 40 years on the basic science of periprosthetic bone loss, much remains unanswered. The effect of unintended debris resulting from wear and corrosion (e.g., micromotion between the interconnection mechanisms in spinal implants) remains a clinical concern. The current study highlights what is known of particle-induced osteolysis and how the presence of spinal implant particulate debris deleteriously influences osseointegration of posterolateral bone graft or disrupts an established posterolateral fusion mass. Tissue explant, animal, and cell culture studies have revealed the complexity of cellular reactivity involved in aseptic particle-induced osteolysis.

OBJECTIVES

The objectives of this study are twofold: 1) to highlight the dominant cellular participants in total joint arthroplasty particle induced osteolysis, which are purportedly the macrophage, osteoblast, fibroblast, and osteoclast and several of the dominant chemical mediators have been identified as well, which include prostaglandin E2, tumor necrosis factor-alpha, interleukin-1, and interleukin-6; and 2) to demonstrate the potential deleterious effects of spinal implant debris using animal models and analysis of soft tissue surrounding spinal implants in symptomatic patients.

METHODS

There are a growing number of proinflammatory and anti-inflammatory cytokines, prostenoids, and enzymes that have been shown to play important roles in the pathology of particle-induced osteolysis. Reports that aseptic granulomatous inflammation typical of that associated with corrosion debris appear to correlate with the complexity of the implant. Titanium particulate material was used to induce effects in 34 New Zealand White rabbits where analysis included serological quantification of systemic cytokines. Postmortem microradiographic, immunocytochemical, and histopathologic assessment of the intertransverse fusion mass quantified the extent of osteolysis, local proinflammatory cytokines, osteoclasts and inflammatory infiltrates. Clinical analysis of 12 patients more than 0.4 years after spinal implants (mean 4.03, range 0.4 to 11 years) presented with late operative site pain.

RESULTS

Currently the etiology of this inflammation around spinal implants resembles particle-induced osteolysis around joint arthroplasties where there typically is a self-perpetuating fibroinflammatory zone adjacent to the implant, where macrophage exhaustion, reactive oxygen intermediates, and pro-inflammatory cytokines affect a host of local cell types and induce a widening zone of soft tissue damage and inflammation. Animal model analysis indicated increased levels of local inflammatory cytokines typically associated with osteolysis-tumor necrosis factor-alpha. Osteoclast cell counts and regions of osteolytic resorption lacunas were higher in the titanium-treated versus autograft-alone groups (P < 0.05), and the extent of cellular apoptosis was markedly higher in the titanium-treated sites at both time intervals. Electron microscopy indicated definitive evidence of phagocytized titanium particles and foci of local, chronic inflammatory changes in the titanium-treated sites.

CLINICAL CASES

11 of 12 clinical cases demonstrated elevated tumor necrosis factor-alpha levels and an increased osteoclastic response in the vicinity of wear debris caused by dry frictional wear particles of titanium or stainless steel. Resection of the wear debris and surrounding fibroinflammatory zone resolved clinical symptoms in all 12 cases.

CONCLUSIONS

More basic science and clinical research is needed to develop novel strategies for gaining knowledge, and developing effective evaluation and treatment of patients with implant debris related osteolysis. Titanium debris simulating that produced by spinal implants introduced at the level of a spinal arthrodesis elicits an inflammatory cytokine mediated particulate-induced response through increased expression of intracellular TNF-alpha, increased osteoclastic activity and cellular apoptosis. This study highlighted the association between spinal implants particulate wear debris and increased potential for osteolysis. Aseptic osteolysis is among the primary reasons for failure of orthopedic implants. Increased awareness of this destructive process is becoming more important with the growing popularity of total disc arthroplasty and highly modular spinal implants.

Differential regulation of TNF-alpha, IL-6 and IL-10 in UVB-irradiated human keratinocytes via cyclic AMP/protein kinase A pathway

Pro-inflammatory cytokines are important mediators of cutaneous cellular activities during many skin diseases. In the present study, we investigated the production of tumor necrosis factor-alpha (TNF-alpha), IL-6 and IL-10 by UVB-irradiated human keratinocytes NCTC 2544 cell line in the presence of cAMP-elevating agents and we attempted to determine the implication of cyclic AMP/PKA pathway in the regulation of cytokine gene expression. Cytokine mRNA expression levels and cytokine concentrations were investigated by reverse transcription polymerase chain reaction and by ELISA method, respectively. Treatment of UVB-irradiated NCTC 2544 cells with drugs known to enhance cAMP concentration [dibutyryl cAMP, PGE(2) and cholera toxin] results in a significant decrease of TNF-alpha mRNA expression whereas IL-6 and IL-10 mRNAs were enhanced. In the same experimental conditions, treatment of irradiated keratinocytes with PKA inhibitors [H89 and PKA inhibitor (PKAi)] induced a significant inhibition of mRNA expression for all tested cytokines. Except for IL-10, the pharmacological effect of cAMP-elevating agents or PKA inhibitors on radiation-induced TNF-alpha and IL-6 mRNA expression was associated with a concomitant regulation of cytokine release. Taken together our results showed: (i) a differential regulation of TNF-alpha, IL-6 and IL-10 in UVB-irradiated human keratinocytes via cyclic AMP/protein kinase A pathway, and (ii) a possible reduction of deleterious inflammatory effects of cytokine following UVB-irradiation by using pharmacological agents that regulate both the intracellular cAMP levels and the cellular PKA activity.

Thalidomide blocking of particle-induced TNFalpha release in vitro

Tumor necrosis factor-alpha (TNFalpha) and interleukin-6 (IL-6), pleiotropic cytokines with osteotropic activities, are produced by multiple cells in the skeletal tissue, including macrophages and osteoblasts. They are thought to be pivotally involved in pathological bone resorption, such as that seen with aseptic loosening. Thalidomide is reported to have antiinflammatory, immunomodulatory effects in a number of inflammatory diseases. We investigated the effect of thalidomide on titanium (Ti) particle-induced TNFalpha and IL-6 production by both human macrophage U937 and osteoblast MG-63 cell lines. They were stimulated with 1 x 10(7) Ti particles/ml and treated simultaneously with or without various concentrations of thalidomide (from 2.5 ng/ml to 25 microg/ml) for 24, 48, or 72 h. Cell viability and proliferation were measured. TNFalpha and IL-6 in the supernatant of the culture media were also analyzed with an enzyme-linked immunosorbent assay. We found that with a concentration of thalidomide of less than 2.5 microg/ml the viability of the two cell lines did not differ significantly from that of controls treated simultaneously with 1 x 10(7) Ti particles/ml. Cell proliferation was inhibited to some extent when they were treated with thalidomide 2.5 microg/ml co-cultured with 1 x 10(7) Ti particles/ml. Thalidomide treatment was found to inhibit TNFalpha production in a dose-dependent manner in human macrophages exposed to Ti particles. At the clinically achievable drug dose of 2.5 microg/ml, 34.4% TNFalpha inhibition occurs. Thalidomide had no effect on IL-6 secretion in these cultures. These data support the idea that thalidomide may have potential for treating prosthetic loosening in humans.

Immunomodulatory effects of quinolones

We review data on the in-vitro, ex-vivo, in-vivo, and clinical effects of fluoroquinolones on the synthesis of cytokines and their mechanisms of immunomodulation. In general, most fluoroquinolone derivatives superinduce in-vitro interleukin 2 synthesis but inhibit synthesis of interleukin 1 and tumour necrosis factor (TNF)alpha; furthermore, they enhance significantly the synthesis of colony-stimulating factors (CSF). Fluoroquinolones affect in-vivo cellular and humoral immunity by attenuating cytokine responses. Interleukins 10 and 12 have an important role in the functional differentiation of immunocompetent cells and trigger the initiation of the acquired immune response. In addition, certain fluoroquinolones were seen to enhance haematopoiesis by increasing the concentrations of CSF in the lung as well as in the bone marrow and shaft. Those fluoroquinolones exerting significant effects on haematopoiesis were those with a cyclopropyl moiety at position N1 of their quinolone core structure. Mechanisms that could explain the various immunomodulatory effects of fluoroquinolones include: (1) an effect on intracellular cyclic adenosine-3',5'-monophosphate and phosphodiesterases; (2) an effect on transcription factors such as nuclear factor (NF)kappaB, activator protein 1, NF-interleukin-6 and nuclear factor of activated T cells; and (3) a triggering effect on the eukaryotic equivalent of bacterial SOS response with its ensuing intracellular events. Further studies are required, especially in the clinical setting to exploit fully the potential of the immunomodulatory effect of fluoroquinolones during, for example, immunosuppression, chronic airway inflammatory diseases, and sinusitis.

Human serum opsonization of orthopedic biomaterial particles: protein-binding and monocyte/macrophage activation in vitro

Wear particles generated after total joint arthroplasty activate monocyte/macrophages and incite formation of a granulomatous periprosthetic tissue associated with bone loss and implant loosening. This study tested the hypothesis that selective opsonization of orthopedic implant biomaterial wear particles by human serum proteins influences monocyte/macrophage activation. Serum protein binding to metallic, polymeric, and ceramic particles was determined by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Individual proteins bound to particles were subsequently identified using two-dimensional SDS-PAGE, microsequencing techniques, and SWISS-PROT analysis. Effects of selective protein opsonization on particle-induced monocyte/macrophage activation were assessed by quantification of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha release. Results from one-dimensional gel analyses revealed distinct serum protein-binding patterns specific for each material tested. Two-dimensional gel analysis together with amino acid sequencing of the prominent protein species confirmed the presence of albumin and alpha-1-antitrypsin bound to all particles tested. In contrast to the metallic particles, apolipoprotein was a major species associated with polymeric particles. Opsonization of PMMA particles with purified preparations of each of the identified proteins showed that albumin significantly enhanced particle-induced monocyte/macrophage activation. These data confirm orthopedic biomaterial specific binding of human serum proteins and demonstrate that albumin exacerbates particle-induced monocyte/macrophage activation. Alterations in the chemical and surface properties of orthopedic biomaterials to modulate protein interactions may improve implant longevity.

Roles of Rac and cytosolic phospholipase A2 in the intracellular signalling in response to titanium particles

Titanium (Ti) particle is one of the prosthetic materials commonly used in implantation and has frequently been implicated in pathogenesis such as periprosthetic osteolysis. In the present study, we undertook to understand the intracellular signalling pathway stimulated by exogenous Ti at Rat-2 fibroblasts. By reporter gene analysis following transient transfections, exogenous Ti was shown to stimulate c-fos serum response element (SRE)-dependent luciferase activities in a dose-dependent manner. In addition, Ti-induced SRE activation was shown to be dramatically repressed by RacN17, a dominant negative mutant of Rac1, suggesting that Rac GTPase is essential for the signalling of Ti to c-fos SRE. Furthermore, pretreatment with MAFP, an inhibitor of cytosolic phospholipase A(2) (cPLA(2)), MK886, an inhibitor of 5-lipoxygenase (5-LO), or indomethacin, a general inhibitor of cyclooxygenase (COX), also significantly repressed Ti-induced SRE activation, suggesting mediatory roles of cPLA(2) and subsequent arachidonic acid (AA) metabolisms to leukotrienes (LTs) and prostaglandins (PGs) in the Ti signalling to c-fos SRE. Consistent with these results, intracellular levels of leukotriene B(4) (LTB(4)) and prostaglandin E(2) (PGE(2)) were Rac-dependently elevated in cells exposed to Ti particles.

The effect of spinal instrumentation particulate wear debris. an in vivo rabbit model and applied clinical study of retrieved instrumentation cases

STUDY DESIGN

The current study was undertaken to determine if the presence of spinal instrumentation wear particulate debris deleteriously influences early osseointegration of posterolateral bone graft or disrupts an established posterolateral fusion mass.

OBJECTIVES

Using an in vivo animal model, the first phase (basic science) of this study was to evaluate the effect(s) of titanium wear particulate on a posterolateral spinal arthrodesis based on serological, histological and immunocytochemical analyses. The second phase (clinical) was to perform the same analysis of soft tissue surrounding spinal instrumentation in 12 symptomatic clinical patients.

SUMMARY OF BACKGROUND DATA

The effect of unintended wear particulate resulting from micromotion between the interconnection mechanisms in spinal instrumentation remains a clinical concern.

METHODS

Thirty-four New Zealand White rabbits were randomized into two groups based on postoperative time periods of 2 months (Group 1, n=14) and 4 months (Group II, n=20). Group I underwent a posterolateral arthrodesis (PLF) at L5-L6 using tricortical iliac autograft or tricortical iliac autograft plus titanium particulate. Group 2 all received iliac autograft at the initial surgery and were reoperated on after 8 weeks and treated with PLF exposure alone or titanium particulate. Postoperative analysis included serological quantification of systemic cytokines. Postmortem microradiographic, immunocytochemical and histopathological assessment of the intertransverse fusion mass quantified the extent of osteolysis, local proinflammatory cytokines, osteoclasts and inflammatory infiltrates. Clinical aspect of study: Over the last 2 years, 12 patients more than 0.4 years after spinal instrumentation presented with painful paraspinal inflammation. At surgical exploration, the cultures were negative for infection and the surrounding soft tissue was examined for cytokine reactions. There was loosening of implants and osteolysis in the location of the wear debris in 8 of 12 patients.

RESULTS

Basic science phase: serological analysis of systemic cytokines indicated no significant differences in cytokine levels (p>.05) between the titanium or autograft treatments. Immunocytochemistry indicated increased levels of local cytokines: TNF-alpha at the titanium-treated PLF sites at both time periods (p<.05). Osteoclast cell counts and regions of osteolytic resorption lacunae were higher in the titanium-treated versus autograft-alone groups (p<.05), and the extent of cellular apoptosis was markedly higher in the titanium-treated sites at both time intervals. Electron microscopy indicated definitive evidence of phagocytized titanium particles and foci of local, chronic inflammatory changes in the titanium-treated sites. Clinical aspect: Eleven of 12 clinical cases demonstrated elevated TNF-alpha levels and an increased osteoclastic response in the vicinity of wear debris caused by dry frictional wear particles of titanium or stainless steel. Osteolysis most commonly involved loose transverse connectors. Resection of the wear debris and surrounding fibroinflammatory glycocalyx resulted in resolution of clinical symptoms in all 12 cases.

CONCLUSIONS

Titanium particulate debris introduced at the level of a spinal arthrodesis elicits a cytokine-mediated particulate-induced response favoring proinflammatory infiltrates, increased expression of intracellular TNF-alpha, increased osteoclastic activity and cellular apoptosis. This is the first basic scientific study and the first clinical study demonstrating associations of spinal instrumentation particulates wear debris and increased cytokines and increased osteoclastic activity. Osteolysis is the number one cause of failure of orthopedic implants in the appendicular skeleton. Spinal surgeons need to increase their awareness of this destructive process.

Modulation of IL-1beta, IL-6, TNF-alpha and PGE(2) by pharmacological agents in explants of membranes from failed total hip replacement

Introduction and goal Proinflammatory cytokines and prostaglandin E(2) (PGE(2)) play an important role in the pathophysiology of osteolysis and implant loosening. The aim of this study was to evaluate the role of pharmacological agents in the inhibition of Interleukin-1 (IL-1), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) and PGE(2) in explants of interface membranes from failed total hip replacements (fTHR). Material and methods Membranes from fTHR were retrieved (N=20) and explants were incubated for 72h in the absence or presence of tenidap at three different concentrations (5, 20 or 50 microg/ml) or diclofenac (125 microg/l). IL-1beta, IL-6, TNF-alpha, and PGE(2) levels were measured in the culture medium using ELISA Capture or EIA kits. Statistical analysis was done using the Mann-Whitney U-test. Results A statistically significant inhibition in IL-1beta synthesis was found at tenidap concentrations of 20 microg/ml (71.3%, P< 0.05) and 50 microg/ml (79.3%,P< 0.02). Tenidap reduced IL-6 levels by 90.4% at 20 microg/ml (P< 0.005) and 96.0% (P< 0.05) at 50 microg/ml. Tenidap also reduced the synthesis of TNF-alpha by 66.9% (P< 0.05) and 77.4% at concentrations of 20 microg/ml and 50 microg/ml. Tenidap had a marked suppressive effect of over 90% (P< 0.0001) on PGE(2) synthesis in all three concentrations. Diclofenac (125 microg/l) decreased PGE(2) production by 95% (P< 0.0001), but had no significant effect in IL-1beta, IL-6, and TNF-alpha levels in the culture medium. Conclusion The ability to simultaneously suppress the release of proinflammatory cytokines and PGE(2) may help control osteolysis and prevent aseptic loosening of THR. This effect could increase implant longevity and lead the way to the pharmacological treatment of this pathology.

The effect of titanium particulate on development and maintenance of a posterolateral spinal arthrodesis: an in vivo rabbit model

STUDY DESIGN

The current study was undertaken to determine if the presence of titanium wear particulate deleteriously influences early osseointegration of posterolateral bone graft or disrupts an established posterolateral fusion mass.

OBJECTIVES

Using an in vivo animal model to evaluate the effect(s) of titanium wear particulate on a posterolateral spinal arthrodesis based on serologic, histologic, and immunocytochemical analyses.

SUMMARY OF BACKGROUND DATA

The effect of unintended wear particulate resulting from micromotion between the interconnection mechanisms in spinal instrumentation remains a clinical concern.

METHODS

Thirty-four New Zealand White rabbits were randomized into two groups based on postoperative time periods of 2 months (Group 1, n = 14) and 4 months (Group 2, n = 20). Group 1 underwent a posterolateral arthrodesis at L5-L6 using tricortical iliac autograft or tricortical iliac autograft + titanium particulate. Group 2 received iliac autograft at the initial surgery and were reoperated on after 8 weeks and treated with posterolateral arthrodesis exposure alone or titanium particulate. Postoperative analysis included serologic quantification of systemic cytokines. Postmortem microradiographic, immunocytochemical, and histopathologic assessment of the intertransverse fusion mass quantified the extent of osteolysis, local pro-inflammatory cytokines, osteoclasts, and inflammatory infiltrates.

RESULTS

Serologic analysis of systemic cytokines indicated no significant differences in cytokine levels (P > 0.05) between the titanium or autograft treatments. Immunocytochemistry indicated increased levels of local cytokines (tumor necrosis factor-alpha) at the titanium-treated posterolateral arthrodesis sites at both time periods (P < 0.05). Osteoclast cell counts and regions of osteolytic resorption lacunas were higher in the titanium-treated versus autograft-alone groups (P < 0.05), and the extent of cellular apoptosis was markedly higher in the titanium-treated sites at both time intervals. Electron microscopy indicated definitive evidence of phagocytized titanium particles and foci of local, chronic, inflammatory changes in the titanium-treated sites.

CONCLUSION

Titanium particulate debris introduced at the level of a spinal arthrodesis elicits a cytokine-mediated particulate-induced response favoring pro-inflammatory infiltrates, increased expression of intracellular tumor necrosis factor-alpha, increased osteoclastic activity, and cellular apoptosis. The presence of titanium particulate debris, secondary to motion between spinal implants, may serve as the impetus for late-onset inflammatory-infectious complications and long-term osteolysis of an established posterolateral fusion mass in the clinical setting.

Macrophage exposure to particulate titanium induces phosphorylation of the protein tyrosine kinase lyn and the phospholipases Cgamma-1 and Cgamma-2

A frequent long-term complication of total joint arthroplasty is aseptic loosening, the end result of wear debris production, synovial macrophage activation, inflammatory mediator release, and osteolysis about the implant-bone or cement-bone interface. To elucidate the mechanisms of particle-induced macrophage activation and mediator production, we studied early signal transduction events using J774A.1 macrophages and 3 microm titanium particles. Treating macrophages with herbimycin A or genistein, two inhibitors of protein tyrosine kinases (PTKs), inhibited titanium phagocytosis as well as secretion of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin-E2 (PGE2) in a dose-dependent manner. Both processes therefore depend on a PTK signaling cascade. Specifically, macrophage exposure to titanium-induced phosphorylation of multiple proteins including the Src kinase Lyn and phospholipase Cgamma-1 and Cgamma-2. Phosphorylation peaked within 2 min and returned to baseline within 45 min. Similar but not identical phosphorylation patterns were obtained when cells were stimulated with titanium preincubated with serum or albumin, suggesting distinct signal transduction pathways dependent on particle coating.

Tumor necrosis factor-alpha mediates polymethylmethacrylate particle-induced NF-kappaB activation in osteoclast precursor cells

Tumor necrosis factor-alpha (TNF) is a potent osteoclastogenic cytokine that has a fundamental role in the pathogenesis of implant particle-induced osteolysis. The nuclear transcription factor NF-kappaB mediates TNF signaling and this transcription complex is necessary for osteoclastogenesis. Because polymethylmethacrylate (PMMA) particles cause osteolysis, we reasoned the PMMA would induce NF-kappaB activation. In fact, we find that exposure of osteoclast precursors, in the form of colony stimulating factor-1 (CSF-1) dependent murine bone marrow macrophages, to PMMA particles prompts nuclear translocation and activation of NF-kappaB. Supershift assays confirm the presence of the p50 and p65 NF-kappaB subunits in the activated transcription factor. Particle-induced NF-kappaB activation is equal in both wild type and LPS- hyporesponsive cells indicating that the phenomenon does not represent endotoxin contamination. A soluble, competitive inhibitor of TNF (huTNFr:Fc) dampens particle-directed NF-kappaB activation and this response is also abrogated in TNF-/- osteoclast precursors. Thus, PMMA particle activation of NF-kappaB is a secondary event resulting from enhanced TNF expression and is independent of LPS contamination.

Synergistic effect of particles and cyclic pressure on cytokine production in human monocyte/macrophages: proposed role in periprosthetic osteolysis

Macrophages, activated by particulate wear debris, are important in the process of osteolysis, which occurs during joint implant loosening. We previously found increased levels of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha in cultured macrophages subjected to cyclical pressure of 0.138 MPa, suggesting that cyclic pressure may be another relevant cause of macrophage activation. The current study first investigated the effects of a range of cyclic pressures on cultured macrophages, including an investigation of the time course of cytokine expression. At 0.138 MPa, supernatant levels of TNF-alpha were maximal at 12 h, whereas IL-6 and IL-1beta were maximal at 24 h. All four cyclic pressure levels tested (without particles) resulted in increased production of all three cytokines relative to control. These increases were most marked at 0.069 and 0.035 MPa, and the increase in cytokine production at 0.017 MPa was not statistically significant. Further studies demonstrated that conditioned media from cyclically pressurized macrophages stimulated bone resorption in a neonatal mouse calvarial assay system. There were increased levels of calcium released from calvaria cultured in conditioned media from pressurised monocytes, and an increase in tartate-resistant acid phosphatase-positive osteoclasts was observed microscopically. As particulate wear debris is important in implant loosening, ultra high molecular weight polyethylene particles were also added to the pressurized cell cultures. The experiments compared the effect of atmospheric pressure, cyclic pressure alone, particles alone, and particles and cyclic pressure combined. A combination of ultra high molecular weight polyethylene particles and cyclic pressure at 0.017 MPa resulted in a dramatic synergistic elevation of levels of all three cytokines compared with the levels found with either pressure or particles alone. We propose that monocyte/macrophage activation by cyclic pressure plays a major role in the osteolysis seen in aseptic loosening of implants. The synergistic effect observed between particles and pressure could accelerate implant loosening, and implies that reduction in either cyclic pressure (by improving implant fixation) or wear debris load would reduce osteolysis.

The role of osteoclast differentiation in aseptic loosening

The major cause of orthopaedic implant loosening is thought to be accelerated osteoclastic bone resorption due to the action of cytokines produced in response to phagocytosis of implant-derived wear particles. This accelerated osteoclastic bone resorption could be due to increases in any of the following processes: recruitment of osteoclast precursors to the local microenvironment, differentiation of precursors into mature multinucleated osteoclasts. activation of mature osteoclasts, and/or survival of osteoclasts. Our studies have focused on differentiation and survival to complement work by others who have focused on recruitment of precursors and activation. Taken together, our studies and those of other investigators provide strong evidence that increased recruitment of osteoclast precursors and their subsequent differentiation play major roles in wear particle-induced osteolysis. In contrast, increased osteoclast activation and survival appear to play minor roles. These studies suggest that development of therapeutic interventions that reduce either recruitment or differentiation of osteoclast precursors would improve the performance of orthopaedic implants.

Bone graft incorporation in radiographically successful human intervertebral body fusion cages

STUDY DESIGN

Biopsies were obtained from within radiographically successful human intervertebral body fusion cages to document the histology of remodeling bone graft.

OBJECTIVES

The purpose of this study is to describe the tissue within successful human interbody cages with special reference to the viability of bone and the presence or absence of debris particles.

SUMMARY OF BACKGROUND DATA

The use of interbody fusion cages is gaining rapid acceptance, but there is little histologic documentation of the nature of tissue within successful human interbody fusion cages.

METHODS

Needle biopsies were obtained of tissue within radiographically successful intervertebral body fusion cages at the time of pedicle screw removal for back pain or fusion of adjacent spinal level in nine spinal levels of eight patients. Preoperative diagnoses of these eight adult patients included disease conditions in the sagittal plane: spondylosis (5), degenerative disc disease (6), failed laminectomy and discectomy (2), radiculopathy (1), and spondylolisthesis (1). In all cases the cages had been packed with autograft (iliac crest 7, local 1) at the time of insertion. Cage implantation was performed with anterior (anterior lumbar interbody fusion 4, corpectomy and plate fixation 1), and posterior (posterior lumbar interbody fusion 4), segmental instrumentation (plate 1, or pedicle screws 8). All cases except one cervical case had posterolateral fusion or bilateral facet fusion. The cages were composed of carbon fiber-reinforced polymer (Brantigan cage; DePuy AcroMed, Raynham, MA, n = 5) or titanium mesh (Harms Cage; DePuy AcroMed, Raynham, MA, n = 4). Cages had been in situ from 8 to 72 months (mean 28 months). All nine biopsies from eight patients were obtained from within the center of the cages. Specimens were decalcified, routinely embedded in paraffin, stained with hematoxylin and eosin, and viewed qualitatively with transmitted and polarized light.

RESULTS

All needle biopsies were obtained from within the center of the cages, and no patient developed spinal instability after the biopsy. All nine biopsies showed small fragments of necrotic bone associated with viable bone and restoration of hematopoietic bone marrow. Numerous cement lines demarcated the edges of previous cycles of remodeling. The ratio of necrotic to viable bone varied greatly among cases. Small particles of debris were associated with four of the five carbon-fiber cages and one of the four specimens from titanium cages, but there was no visible bone resorption or inflammation.

CONCLUSIONS

Autogenous bone graft was incorporated in these radiographically successful human intervertebral body fusion cages. A few debris particles were observed, but there was no histologic evidence of particle-induced bone resorption or inflammation.

Osteolysis: basic science

Since the recognition of aseptic loosening by Charnley in the early 1960s, much information has been gained on the basic science of periprosthetic bone loss. Initially termed cement disease, it now generally is accepted that, in most instances, osteolysis is a manifestation of an adverse cellular response to phagocytosable particulate wear and corrosion debris, possibly facilitated by local hydrodynamic effects. Tissue explant, animal, and cell culture studies have allowed us to compile an appreciation of the complexity of cellular interactions and chemical mediators involved in osteolysis. Cellular participants have been shown to include the macrophage, osteoblast, fibroblast, and osteoclast. The plethora of chemical mediators that are responsible for the cellular responses and effects on bone include prostaglandin E2, tumor necrosis factor-alpha, interleukin-1, and interleukin 6. However, an increasing number of other proinflammatory and antiinflammatory cytokines, prostenoids, and enzymes have been shown to play important roles in this process. The ultimate goal of basic research is to develop novel strategies for evaluation and treatment of patients with osteolysis. Although initial animal studies are promising for possible pharmacologic treatment and prevention of osteolysis, well-controlled human trials are required before agents such as bisphosphonates can be recommended for general clinical use.

Oral pentoxifylline inhibits release of tumor necrosis factor-alpha from human peripheral blood monocytes : a potential treatment for aseptic loosening of total joint components

BACKGROUND

Pentoxifylline (Trental) is a methylxanthine-derivative drug that has been used for more than twenty years in the treatment of peripheral vascular disease. Pentoxifylline is also a potent inhibitor of tumor necrosis factor-alpha (TNF-alpha) secretion, both in vitro and in vivo, and has demonstrated efficacy in the treatment of certain animal and human inflammatory diseases. Pentoxifylline has a potential therapeutic role in the treatment of aseptic loosening of total joint replacement components because it inhibits TNF-alpha secretion by particle-stimulated human peripheral blood monocytes. The purpose of our study was to determine whether the particle-stimulated secretion of TNF-alpha by peripheral blood monocytes was inhibited in volunteers who had received pentoxifylline orally.

METHODS

Human peripheral blood monocytes were harvested from eight healthy volunteers and were exposed to three different concentrations of titanium particles or to 500 ng/mL of lipopolysaccharide as a positive control. The same volunteers were then given pentoxifylline (400 mg, five times per day) for seven days. Their peripheral blood monocytes were again isolated and exposed to experimental conditions, and the TNF-alpha levels were measured.

RESULTS

The peripheral blood monocytes from all eight volunteers showed a significant reduction in TNF-alpha release following oral treatment with pentoxifylline. This reduction was observed at exposures of 10(7) and 10(6) titanium particles/mL and in the lipopolysaccharide-treated group, but not at 10(5) particles/mL.

CONCLUSIONS

To our knowledge, this is the first study to demonstrate the ability of an oral drug to decrease the release of TNF-alpha from human peripheral blood monocytes exposed ex vivo to particle debris. TNF-alpha is involved in the pathogenesis of osteolysis and subsequent loosening of total joint arthroplasty components. The ability to suppress the release of TNF-alpha in patients with a total joint replacement may help to control osteolysis and to reduce the development of aseptic loosening. This effect could increase implant longevity and decrease the need for revision arthroplasty.

Evidence for a direct role of cyclo-oxygenase 2 in implant wear debris-induced osteolysis

Aseptic loosening is a major complication of prosthetic joint surgery and is manifested as chronic inflammation, pain, and osteolysis at the bone implant interface. The osteolysis is believed to be driven by a host inflammatory response to wear debris generated from the implant. In our current study, we use a selective inhibitor (celecoxib) of cyclo-oxygenase 2 (COX-2) and mice that lack either COX-1 (COX-1-/-) or COX-2 (COX-2-/-) to show that COX-2, but not COX-1, plays an important role in wear debris-induced osteolysis. Titanium (Ti) wear debris was implanted surgically onto the calvaria of the mice. An intense inflammatory reaction and extensive bone resorption, which closely resembles that observed in patients with aseptic loosening, developed within 10 days of implantation in wild-type and COX-1-/- mice. COX-2 and prostaglandin E2 (PGE2) production increased in the calvaria and inflammatory tissue overlying it after Ti implantation. Celecoxib (25 mg/kg per day) significantly reduced the inflammation, the local PGE2 production, and osteolysis. In comparison with wild-type and COX-1-/- mice, COX-2-/- mice implanted with Ti had a significantly reduced calvarial bone resorption response, independent of the inflammatory response, and significantly fewer osteoclasts were formed from cultures of their bone marrow cells. These results provide direct evidence that COX-2 is an important mediator of wear debris-induced osteolysis and suggests that COX-2 inhibitors are potential therapeutic agents for the prevention of wear debris-induced osteolysis.

Efficacy of etanercept for wear debris-induced osteolysis

A major limitation of total joint arthroplasty is that up to 20% of patients require revision surgery to correct prosthetic loosening. Aseptic loosening is believed to result from the phagocytosis of wear debris particles by macrophages, which secrete proinflammatory cytokines that stimulate osteolysis. Tumor necrosis factor alpha (TNF-alpha) has been shown to be one of the prominent cytokines in this cascade and to be involved critically in the generation of particle-induced osteolysis. Etanercept is a soluble inhibitor of TNF-alpha, which is widely used for the treatment of rheumatoid arthritis. Here, we show this agent's ability to prevent wear debris-induced osteolysis. In vitro we show that Etanercept can inhibit directly osteoclastic bone resorption in a bone wafer pit assay, as well as cytokine production from titanium (Ti)-stimulated macrophages. Using a quantitative in vivo model of wear debris-induced osteolysis, we show that Etanercept prevents bone resorption and osteoclastogenesis. In mice treated with Etanercept at the time of osteolysis induction, bone resorption and osteoclast numbers were reduced to background levels in both normal and human TNF-alpha (hTNF-alpha) transgenic mice. In an effort to evaluate its effect on established osteolysis, Etanercept was administered 5 days after Ti implantation, and we observed that further osteolysis was prevented. These data support the concept that TNF-alpha is involved critically in osteoclastogenesis and bone resorption during periprosthetic osteolysis and suggest that soluble TNF-alpha inhibitors may be useful as therapeutic agents for the treatment of prosthetic loosening in humans.

The effects of particulate wear debris, cytokines, and growth factors on the functions of MG-63 osteoblasts

BACKGROUND

Particle-challenged cells release cytokines, chemokines, and eicosanoids, which contribute to periprosthetic osteolysis. The particle-induced activation of macrophages and monocytes has been extensively studied, but only limited information is available on the response of osteoblasts to particulate wear debris. This study examines the effects of particulate wear debris, proinflammatory cytokines, and growth factors on osteoblast functions.

METHODS

MG-63 osteoblasts were treated with metal particles (titanium, titanium alloy, and chromium orthophosphate) or polymeric particles (polyethylene and polystyrene) of phagocytosable sizes or were treated with exogenous cytokines and growth factors. The kinetics of particle phagocytosis and the number of engulfed particles were assessed with use of fluoresceinated particles. Cell proliferation was determined according to [3H]-thymidine incorporation, and cell viability was determined by either fluorescein diacetate uptake or trypan blue exclusion. Expressions of osteoblast-specific genes were quantified with Northern blot hybridization, and the secretions of osteoblast-specific proteins and cytokines were analyzed by enzyme-linked immunosorbent assays.

RESULTS

MG-63 osteoblasts phagocytosed particles and became saturated after twenty-four hours. A maximum of forty to sixty particles per cell were phagocytosed. Each type of particle significantly suppressed procollagen alpha1[I] gene expression (p<0.05), whereas other osteoblast-specific genes (osteonectin, osteocalcin, and alkaline phosphatase) did not show significant changes. Particle-stimulated osteoblasts released interleukin-6 (p<0.05) and a smaller amount of transforming growth factor-beta1. Particles reduced cell proliferation in a dose-dependent manner without affecting cell viability (p<0.05). Exogenous tumor necrosis factor-alpha also enhanced the release of interleukin-6 (p<0.01) and transforming growth factor-beta1 (p<0.05), whereas the secretion of transforming growth factor-beta1 was increased by insulin-like growth factor-I and prostaglandin E2 as well. Insulin-like growth factor-I and transforming growth factor-beta1 significantly increased procollagen alpha1[I] gene expression in osteoblasts (p<0.05), while tumor necrosis factor-alpha and prostaglandin E2 significantly suppressed procollagen alpha1[I] gene expression (p<0.01). In contrast, neither exogenous nor endogenous interleukin-6 had any effect on other cytokine secretion, on proliferation, or on procollagen alpha1[I] gene expression. The transcription inhibitor actinomycin D reduced both procollagen alpha1[I] transcription and interleukin-6 production. Inhibitors of protein synthesis (cyclohexamide) and intracellular protein transport (brefeldin A and monensin) blocked the release of interleukin-6, but none of these compounds influenced the suppressive effect of titanium on procollagen alpha1[I] gene expression.

CONCLUSIONS

MG-63 osteoblasts phagocytose particulate wear debris, and this process induces interleukin-6 production and suppresses type-I collagen synthesis. Osteoblast-derived interleukin-6 may induce osteoclast differentiation and/or activation, but the resorbed bone cannot be replaced by new bone because of diminished osteoblast function (reduced type-I collagen synthesis). Exogenous cytokines (tumor necrosis factor-alpha and interleukin-1beta), growth factors (insulin-like growth factor-I and transforming growth factor-beta1), and prostaglandin E2 can modify particulate-induced alterations of osteoblast functions.

Tumor necrosis factor has positive and negative self regulatory feed back cycles centered around cAMP

This paper reviews data that allow recognition of, (1) two opposing intracellular chains of events occurring subsequent to an increase in tumor necrosis factor, TNF, and (2) that these two chains have opposing effects on intracellular cyclic adenosine monophosphate, cAMP. The two chains - attenuation cycle, where TNF results in prostaglandin E mediated increased cAMP and, consequent to this, suppression of TNF levels; and an amplification cycle, where increased TNF increases intracellular cyclic adenosine phosphodiesterase, lowering cAMP, thereby raising TNF levels further. TNF is a central mediator in several inflammatory diseases. Understanding TNF control systems will allow better delineation of pathophysiology and clinical care.

Quantitative small-animal surrogate to evaluate drug efficacy in preventing wear debris-induced osteolysis

Individuals who suffer from severe joint destruction caused by the various arthritidies often undergo total joint arthroplasty. A major limitation of this treatment is the development of aseptic loosening of the prosthesis in as many as 20% of patients. The current paradigm to explain aseptic loosening proposes that wear debris generated from the prosthesis initiates a macrophage-mediated inflammatory response by resident macrophages, leading to osteoclast activation and bone resorption at the implant interface. No therapeutic interventions have been proved to prevent or inhibit aseptic loosening. The development of therapeutic strategies is limited due to the absence of a quantitative surrogate in which drugs can be screened rapidly in large numbers of animals. We have previously described a model in which titanium particles implanted on mouse calvaria induce an inflammatory response with osteolysis similar to that observed in clinical aseptic loosening. Here, we present new methods by which the osteolysis in this model can be quantified. We determined that 6-8-week-old mice in normal health have a sagittal suture area of 50 (+/-6) microm2, which contains approximately five osteoclasts. As a result of the titanium-induced inflammation and osteolysis, the sagittal suture area increases to 197 (+/-27) microm2, with approximately 30 osteoclasts, after 10 days of treatment. The sagittal suture area and the number of osteoclasts in the calvaria of sham-treated mice remained unchanged during the 10 days. We also determined the effects of pentoxifylline, a drug that blocks the responses of tumor necrosis factor-alpha to wear debris, and the osteoclast inhibitor alendronate. We found that both drugs effectively block wear debris-induced osteolysis but not osteoclastogenesis. In conclusion, we found the measurements made with this model to be reproducible and to permit quantitative analysis of agents that are to be screened for their potential to prevent aseptic loosening.

Alternate bearing surfaces in total joint arthroplasty: biologic considerations

The problem of periprosthetic osteolysis is currently the major limiting factor in joint arthroplasty longevity. Because this process has been shown to be primarily a biologic response to wear particles, corrosion products, or both, efforts to reduce particle generation are being undertaken. These efforts include the development of modified polyethylene and alternative articulating surfaces. These alternate bearing surfaces currently include ceramic-on-polyethylene, ceramic-on-ceramic, and metal-on-metal. Although these alternate bearings diminish or eliminate the generation of polyethylene particles, ceramic and metal particles are produced. The purpose of the current review is to discuss the literature that addresses the biologic response to these particles, locally and systemically.

G-protein activity requirement for polymethylmethacrylate and titanium particle-induced fibroblast interleukin-6 and monocyte chemoattractant protein-1 release in vitro

Periprosthetic granulomatous membranes consisting of fibroblasts, macrophages, lymphocytes, foreign body giant cells, and abundant particulate debris occur at sites of implant loosening. Previous studies demonstrate that fibroblasts respond to particulate debris through the release of interleukin-6 (IL-6), prostaglandin E(2), and matrix metalloproteinases in vitro. C-C chemokines are observed in granulomatous tissue surrounding loosened prosthetic implants and are released by macrophages and fibroblasts in response to particle challenge in vitro. This study tested the hypothesis that G protein activity is required for fibroblast activation by titanium and polymethylmethacrylate (PMMA) particles, and that inhibition of G protein activity would alter IL-6 and and monocyte chemoattractant protein-1 (MCP-1) release from activated fibroblasts. The specific inhibitor of G protein activity, pertussis toxin, was added to the fibroblasts to examine the effects of G protein activity with respect to the production of IL-6 and MCP-1 by orthopedic biomaterial-challenged fibroblasts in vitro. Interleukin-1beta (IL-1beta), a proven activator of MCP-1 and interleukin-6, was used as a positive control. Exposure of fibroblasts to titanium and polymethylmethacrylate (PMMA) particles resulted in a dose-dependent release of MCP-1 and IL-6. Challenge with PMMA particles at doses of 0.150%, 0.300%, and 0.600% vol/vol increased the release of interleukin-6 by 7-, 19-, and 22-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone at 24 h. Challenge with PMMA particles at doses of 0.075%, 0.150%, 0.300%, and 0.600% vol/vol increased the release of MCP-1-6 by 2.5-, 3.6-, 4. 3-, and 4.5-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone. Challenge with titanium particles at concentrations of 0.075%, 0.150%, 0.300%, and 0.600% vol/vol increased the release of interleukin-6 by 2.6-, 6.4-, 9.6-, and 10. 0-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone at 24 h. Challenge with titanium particles at concentrations of 0.038%, 0.075%, 0.150%, 0.300%, and 0.600% vol/vol increased the release of MCP-1 by 2.9-, 3.1-, 5.8-, 5.4-, and 5. 8-fold, respectively, compared to fibroblasts exposed to serum-free culture medium alone. Pretreatment of fibroblasts with pertussis toxin inhibited the release of interleukin-6 and MCP-1 from PMMA and titanium particle challenged fibroblasts in a dose-dependent manner. PMMA particle induced fibroblast IL-6 release was inhibited by 23.6% and 35.3% with 20- and 200-ng/mL doses of pertussis toxin, respectively. Titanium particle induced fibroblast IL-6 release was inhibited by 48.2% and 56.3% with 20- and 200-ng/mL doses of pertussis toxin, respectively. PMMA particle-induced fibroblast MCP-1 release was inhibited by 36.0%, 50.4%, and 60.1% with 2-, 20- and 200-ng/mL doses of pertussis toxin, respectively. Titanium particle-induced fibroblast MCP-1 release was inhibited by 15.5%, 53.2%, and 64.6% with 2-, 20-, and 200-ng/mL doses of pertussis toxin, respectively. This study suggests that fibroblasts localized in periprosthetic membranes are a source of macrophage chemoattractant factors and proinflammatory mediators that may influence granuloma formation and lead to periprosthetic bone resorption. Furthermore, this study shows that G proteins are involved in particle-induced fibroblast activation, as evidenced by decrease levels of particle induced IL-6 and MCP-1 release following pertussis toxin treatment. (c) 2000 John Wiley & Sons, Inc.

Particulate wear debris activates protein tyrosine kinases and nuclear factor kappaB, which down-regulates type I collagen synthesis in human osteoblasts

Particulate wear debris generated mechanically from prosthetic materials is phagocytosed by a variety of cell types within the periprosthetic space including osteoblasts, which cells with an altered function may contribute to periprosthetic osteolysis. Exposure of osteoblast-like osteosarcoma cells or bone marrow-derived primary osteoblasts to either metallic or polymeric particles of phagocytosable sizes resulted in a marked decrease in the steady-state messenger RNA (mRNA) levels of procollagen alpha1[I] and procollagen alpha1[III]. In contrast, no significant effect was observed for the osteoblast-specific genes, such as osteonectin and osteocalcin (OC). In kinetic studies, particles once phagocytosed, maintained a significant suppressive effect on collagen gene expression and type I collagen synthesis for up to five passages. Large particles of a size that cannot be phagocytosed also down-regulated collagen gene expression suggesting that an initial contact between cells and particles can generate gene responsive signals independently of the phagocytosis process. Concerning such signaling, titanium particles rapidly increased protein tyrosine phosphorylation and nuclear transcription factor kappaB (NF-kappaB) binding activity before the phagocytosis of particles. Protein tyrosine kinase (PTK) inhibitors such as genistein and the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly reduced the suppressive effect of titanium on collagen gene expression suggesting particles suppress collagen gene expression through the NF-kappaB signaling pathway. These results provide a mechanism by which particulate wear debris can antagonize the transcription of the procollagen alpha1[I] gene in osteoblasts, which may contribute to reduced bone formation and progressive periprosthetic osteolysis.

Biological reactions to wear debris in total joint replacement

The vast majority of total hip prostheses currently implanted consist of a hard metal or ceramic femoral head articulating against an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. Over the last 10 years, evidence has accumulated to show that these prostheses are prone to failure due to late aseptic loosening and few survive beyond 25 years. With an increasing need to implant hip prostheses in the younger, more active patient the need to understand the mechanisms of failure and to develop artificial hip joints using alternative materials have become major issues in the orthopaedic community. This review focuses initially on our current understanding of the biological reactions to UHMWPE prosthetic wear debris in vivo and in vitro since this is believed to be the main cause of late aseptic loosening. While the precise mechanisms of osteolysis induced by UHMWPE wear debris have not been elucidated, the major message to emerge is that it is not the wear volume that determines the biological response to the debris, but the concentration of the wear volume that is within the critical size range (0.2-0.8 micron) for macrophage activation. The review then considers whether the problem of wear-debris-induced osteolysis may be overcome with the use of new generation metal-on-metal or ceramic-on-ceramic prostheses. For metal-on-metal prostheses, the prospects for increasing the osteolysis free life of the implant are good but additional biological problems associated with the nanometre size and reactivity of the wear particles in vivo may emerge. For the ceramic-on-ceramic prostheses, although initial prospects are encouraging, more data are needed on the characteristics of the wear particles generated in vivo before predictions can be made. It is concluded that the pre-clinical testing of any new materials for joint replacement must include an analysis of the wear particle characteristics and their biological reactivity in addition to the usual assessment of wear.

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.

Signaling pathways for tumor necrosis factor-alpha and interleukin-6 expression in human macrophages exposed to titanium-alloy particulate debris in vitro

BACKGROUND

Loosening of the implant after total joint arthroplasty remains a serious problem. The activation of macrophages by wear debris from implants, mediated by the release of cytokines that elicit bone resorption, may lead to loosening. The purpose of the present study was to elucidate the mechanisms of macrophage activation by titanium particles from the components of implants and to identify the signaling pathways involved in particle-mediated release of cytokines.

METHODS

Macrophages were isolated from mononuclear leukocytes obtained from healthy human donors and were exposed to titanium-alloy particles that had been obtained from periprosthetic membranes collected at revision total joint arthroplasties and then enzymatically prepared. The experimental protocols included examination of the effects of the inhibition of phagocytosis and the binding of antibodies to macrophage complement receptors on particle-induced macrophage activation. The release of the proinflammatory cytokines TNF-alpha (tumor necrosis factor-alpha) and IL-6 (interleukin-6) was used to assess macrophage activation. The signaling pathways involved in the induction of cytokine release were analyzed by identification of phosphorylated proteins with use of the Western blot technique and by translocation of the transcription factors nuclear factor-kappa B (NF-kappaB) and nuclear factor-interleukin-6 (NF-IL-6) into the nuclear protein fraction with use of electrophoretic mobility shift assays. The role of serine/threonine and tyrosine kinase pathways in the activation of nuclear factors and the release of cytokines was examined with use of selective pharmacological agents.

RESULTS

Exposure of macrophages to titanium-alloy particles in vitro for forty-eight hours resulted in a fortyfold increase in the release of TNF-alpha and a sevenfold increase in the release of IL-6 (p<0.01). Phagocytosis of particles occurred in approximately 73 percent of the macrophages within one hour of exposure. Pretreatment of the macrophages with cytochalasin B reduced phagocytosis by 95 percent but did not reduce the release of TNF-alpha or IL-6. Thus, phagocytosis of particles was not necessary for induction of the release of TNF-alpha or IL-6 in the cultured macrophages. Ligation of the macrophage CD11b/CD18 receptors by integrin-specific antibodies also increased the release of TNF-alpha and IL-6. Antibodies to CD11b/ CD18 receptors (macrophage Mac-1 receptors) reduced phagocytosis of particles by 50 percent (p<0.05). (The CD11b/CD18 macrophage receptor is the macrophage receptor for the complement component CR3bi. The CD11b/CD18 macrophage receptor can also bind to ICAM-1 and ICAM-2. CD is the abbreviation for cluster of differentiation, and ICAM is the abbreviation for intercellular adhesion molecule.) Inhibition of phagocytosis was not accompanied by a decrease in the release of TNF-alpha and IL-6. Blocking RNA synthesis with actinomycin D or preventing protein synthesis with cycloheximide abolished or decreased particle-induced release of TNF-alpha and IL-6 from the macrophages. Macrophage release of TNF-alpha and IL-6 in response to particles coincided with increased tyrosine phosphorylation and mitogen-activated protein kinase activation. Inhibition of tyrosine and serine/threonine kinase activity decreased the particle-induced release of cytokines. Exposure of macrophages to either titanium-alloy particles or to antibodies to the receptor proteins CD11b and CD18 for thirty minutes activated the transcription factors NF-kappaB and NF-IL-6. Inhibition of particle phagocytosis did not block activation of the transcription factors. However, inhibition of tyrosine and serine/threonine kinase activity decreased the activation of NF-kappaB and NF-IL-6.

CONCLUSIONS

These data suggest that particle induced macrophage release of TNF-alpha and IL-6 does not require phagocytosis but is dependent on tyrosine and serine/threonine kinase activity culminating in activation of