In vitro activation of human fibroblasts by retrieved titanium alloy wear debris

Cytokine expression of soft tissue cells cultured with titanium discs and their respective supernatants in vitro

OBJECTIVE

Titanium surface modifications improve osseointegration in dental and orthopedic implants. However, soft tissue cells can also reach the implant surface in immediate loading protocols. While previous research focused on osteogenic cells, the early response of soft tissue cells still needs to be better understood.

MATERIAL AND METHODS

We have established a bioassay to this aim where human gingival fibroblasts, HSC2 oral squamous carcinoma cells, and murine bone marrow cells were cultured onto titanium discs or exposed to the respective supernatants for overnight. Modifications were double acid-etching (SLA), and coating with simulated body fluid (SBF) with or without odanacatib (ODN), a selective cathepsin K inhibitor reducing bone resorption.

RESULTS

Our findings indicate that direct contact with titanium discs, with all surface modifications, slightly reduces cell viability. Growing gingival fibroblasts on discs consistently showed a trend toward increased IL8 expression. In HSC2 cells, this setting significantly increased IL1 and IL8 expression, confirmed by the immunoassay. Murine bone marrow macrophages also showed an increase in IL1 and IL6 expressions. Supernatants of the respective discs failed to cause these changes. Although ODN coating inhibited cathepsin K, osteoclastogenesis remained unchanged.

CONCLUSIONS

These findings suggest that titanium discs do not provide a favorable in vitro surface for oral soft tissue cells as they lose viability and respond with a moderately increased expression of inflammatory cytokines.

CLINICAL RELEVANCE

The soft tissue surrounding a dental implant can impact rehabilitation success. Understanding how soft tissue cells respond to titanium surface is potentially relevant to understand clinical outcomes.

Palatal soft tissue thickness around dental implants and natural teeth in health and disease: A cross sectional study

BACKGROUND

Previous studies focused on the influence of buccal mucosa thickness on peri-implant bone loss and inflammation, with inconclusive results. We observed substantially thicker palatal mucosal tissues at peri-implantitis sites. Therefore, we hypothesize that thick palatal peri-implant mucosa may be associated with deeper pockets and disease severity.

PURPOSE

To compare the thickness of the palatal tissue between natural teeth and implants in periodontal health and disease.

METHODS

Adult, non-smoker, healthy patients who visited our department for periodontal examination or treatment with restored implants in the posterior maxilla were recruited. Probing depth (PD), plaque index (PI), gingival index (GI) and radiographic measurements were recorded around implant and the contralateral tooth. Palatal tissue thickness was measured using a 30G needle that was inserted perpendicular into the mucosa at the bottom of the periodontal/peri-implant pocket and 3 mm coronally. Differences in the palatal tissue thickness between teeth and implants (in the same patient) was performed using t-test; as well as between peri-implantitis and non-peri-implantitis sites (among patients).

RESULTS

Sixty patients were included. Thirty-four implants were diagnosed with peri-implantitis and 26 healthy/mucositis implants with corresponding 24 healthy/gingivitis teeth and 36 teeth with attachment loss. Mean PD was higher around implants (4.47 ± 1.57 mm) than teeth (3.61 ± 1.23 mm, p = 0.001). The thickness of implants' palatal mucosa was higher than in teeth, at the base of the pocket and 3 mm coronally (4.58 ± 1.38 mm vs. 3.01 ± 1.11, p = 0.000; 3.58 ± 2.15 vs. 1.89 ± 1.11, p = 0.000, respectively). Mean palatal tissue thickness was 4.32 ± 2.35 mm for the peri-implantitis group while only 2.61 ± 1.39 in healthy implants, 3 mm coronal to the base of the pocket (p = 0.001). Palatal thickness at peri-implantitis sites was higher (4.32 ± 2.35) compared to periodontitis sites (2.23 ± 0.93), p = 0.000. Implant sites with palatal mucosa >4 mm (n = 32) had deeper mean pockets (5.58 ± 1.98) compared with thinner (≤4 mm) sites (n = 28) (4.48 ± 1.18, p = 0.018).

CONCLUSION

Thicker palatal tissue around implants is associated with deeper palatal pockets. Thick palatal tissue was found around implants diagnosed with peri-implantitis.

Systematic investigation of metallosis associated with magnetically controlled growing rod implantation for early-onset scoliosis

AIMS

To investigate metallosis in patients with magnetically controlled growing rods (MCGRs) and characterize the metal particle profile of the tissues surrounding the rod.

METHODS

This was a prospective observational study of patients with early onset scoliosis (EOS) treated with MCGRs and undergoing rod exchange who were consecutively recruited between February 2019 and January 2020. Ten patients were recruited (mean age 12 years (SD 1.3); 2 M:8 F). The configurations of the MCGR were studied to reveal the distraction mechanisms, with crucial rod parts being the distractable piston rod and the magnetically driven rotor inside the barrel of the MCGR. Metal-on-metal contact in the form of ring-like wear marks on the piston was found on the distracted portion of the piston immediately outside the barrel opening (BO) through which the piston rod distracts. Biopsies of paraspinal muscles and control tissue samples were taken over and away from the wear marks, respectively. Spectral analyses of the rod alloy and biopsies were performed to reveal the metal constituents and concentrations. Histological analyses of the biopsies were performed with haematoxylin and eosin staining.

RESULTS

Titanium (Ti), vanadium (V), and neodymium (Nd) concentrations in the biopsies taken near the wear marks were found to be significantly higher than those in the control tissue samples. Significantly increased Nd concentrations were also found in the tissues near the barrel of the MCGR. Chronic inflammation was revealed by the histological studies with fibrosis and macrophage infiltration. Black particles were present within the macrophages in the fibrotic tissues.

CONCLUSION

Ti and V were generated mainly at the BO due to metal-on-metal contact, whereas the Nd from the rotor of the MCGR is likely released from the BO during distraction sessions. Phagocytotic immune cells with black particles inside raise concern regarding the long-term implications of metallosis. Cite this article: Bone Joint J 2020;102-B(10):1375-1383.

Development of a stent capable of the controlled release of basic fibroblast growth factor and argatroban to treat cerebral aneurysms: In vitro experiment and evaluation in a rabbit aneurysm model

An ideal stent to treat cerebral aneurysms should have an antithrombotic effect on the inner stent blood-facing side and a tissue organization effect on the outer aneurysmal side of the stent. The objective of this study is to evaluate the feasibility of a drug containing stent in the in vivo treatment of cerebral aneurysms. Argatroban, an antithrombotic drug, is encapsulated in biodegradable poly (d,l-lactide-co-glycolide) (PLGA) microspheres for the controlled release with an in vitro study conducted to evaluate the drug release and anticoagulation behavior of released drug. Basic fibroblast growth factor (bFGF), an organization drug, is released from gelatin hydrogels. The stents are coated with gelatin hydrogels incorporating bFGF and PLGA microspheres containing argatroban, and applied to the carotid artery aneurysm of an elastase-induced rabbit model. Most of the aneurysm cavity is occupied by loose connective tissues in the group treated with drug-coated stents, whereas extensive massive hematomas are observed in the group treated with drug-free stents. The occurrence rate of in-stent thrombus is small in the drug-coated stents. The stent incorporating bFGF and PLGA microspheres containing argatroban is an effective device for cerebral aneurysm treatment. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2185-2194, 2019.

Wear debris stimulates bone-resorbing factor expression in the fibroblasts and osteoblasts

Wear debris is believed to cause periprosthetic osteolysis and loosening of total joint arthroplasties. We investigated the wear debris-mediated osteolysis in wild-type mice and macrophage-deficient Csf1op/Csf1op (op/op) mice using high density polyethylene (HDP) particles transplanted on the parietal bone surface. Four weeks after surgery, phagocytosis of the HDP particles by F4/80-positive macrophages and tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts was observed in the normal mice, but not in the macrophage-deficient op/op mice. These results suggest that macrophages are implicated in wear debris-dependent osteoclast formation. However, HDP particles were phagocytosed not only by macrophages but also by F4/80-negative cells in both genotypes of mice. Electron microscopic observation identified these cells as fibroblasts. Cell culture studies demonstrated that fibroblasts cultured with HDP-particles showed upregulation of interleukin-6 (IL-6) expression compared with non-treated fibroblasts. When we examined the gene expression of osteoblasts that belong to the mesenchymal cell lineage as fibroblasts, we found that the expression of not only IL-6 but also interleukin-1 beta (IL-1ß), tumor necrosis factor-alpha (TNF-α) and cyclooxygenase2 (Cox2) were up-regulated by HDP particle-stimulation. These findings suggest the possibility that fibroblasts and osteoblasts are involved in wear debris-mediated osteolysis within the tissue surrounding artificial joints through the production of bone resorbing factors IL-6, IL-1ß, TNF-α, and Cox2.

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

BACKGROUND

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

QUESTIONS/PURPOSES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Influences of IL-6R antibody on PMMA bone cement-mediated expression of OPG and RANKL in synovial fibroblasts

Effect of interleukin-6 receptor (IL-6R) antibody on polymethyl methacrylate (PMMA) bone cement-mediated expression of osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand (RANKL) in synovial fibroblasts was investigated. Synovial tissue obtained from total knee arthroplasty was digested and cultured. Inverted microscope was employed to observe the synovial cells and immunocytochemistry (SABC method) staining was used to identify synovial fibroblasts. This experiment was divided into three groups according to different culture media: PMMA group (75 μg/mL PMMA bone cement particles), IL-6R antibody group (10 ng/mL IL-6R antibody+75 μg/mL PMMA bone cement particles), and control group (no IL-6R antibody or PMMA bone cement particles). Influence of IL-6R antibody and PMMA on proliferation of synovial fibroblasts was measured by cell counting kit-8 (CCK-8). ELISA method was used to measure OPG and RANKL levels in culture solution. Fluorescence quantitative real-time PCR (FQ-PCR) was used to detect the expression of OPG and RANKL mRNA. After three consecutive passages, more than 95% of the primary synovial cells became long spindle fibroblast-like cells. SABC staining results showed that the fibroblast-like cells were negative for anti-CD68 antibody and positive for anti-vimentin antibody, with brown madder stained. CCK-8 test demonstrated that the absorbance (A) value at 450 nm was significantly lower in IL-6R antibody group than in PMMA group and control group (P<0.01), but there was no statistically significant difference in A value at 450 nm between the control group and PMMA group (P>0.05). Results of ELISA indicated that the expression of OPG was significantly higher in IL-6R antibody group than in PMMA group and control group (P<0.01). The expression of RANKL was inhibited (P<0.05), and the ratio of OPG/RANKL was significantly increased in IL-6R antibody group as compared with PMMA group and control group. There was no significant difference in the expression of OPG between control group and PMMA group (P>0.05), but the expression of RANKL was higher in PMMA group than in control group (P<0.05), and there was a significant difference in the ratio of OPG/RANKL between them (P<0.05). Results of FQ-PCR revealed the expression of RANKL mRNA was significantly inhibited (P<0.01) and the expression of OPG mRNA was significantly increased (P<0.01) in IL-6R antibody group as compared with PMMA group and control group. The expression of RANKL mRNA was higher in PMMA group than in control group (P<0.05), but the expression of OPG mRNA had no significant difference between them (P>0.05). IL-6R antibody could significantly increase the expression of OPG, but inhibit the expression of RANKL, which might provide a theoretical basis of molecular biology for the prevention and treatment of aseptic loosening of prosthesis.

Extracellular matrix degradation and tissue remodeling in periprosthetic loosening and osteolysis: focus on matrix metalloproteinases, their endogenous tissue inhibitors, and the proteasome

The leading complication of total joint replacement is periprosthetic osteolysis, which often results in aseptic loosening of the implant, leading to revision surgery. Extracellular matrix degradation and connective tissue remodeling around implants have been considered as major biological events in the periprosthetic loosening. Critical mediators of wear particle-induced inflammatory osteolysis released by periprosthetic synovial cells (mainly macrophages) are inflammatory cytokines, chemokines, and proteolytic enzymes, mainly matrix metalloproteinases (MMPs). Numerous studies reveal a strong interdependence of MMP expression and activity with the molecular mechanisms that control the composition and turnover of periprosthetic matrices. MMPs can either actively modulate or be modulated by the molecular mechanisms that determine the debris-induced remodeling of the periprosthetic microenvironment. In the present study, the molecular mechanisms that control the composition, turnover, and activity of matrix macromolecules within the periprosthetic microenvironment exposed to wear debris are summarized and presented. Special emphasis is given to MMPs and their endogenous tissue inhibitors (TIMPs), as well as to the proteasome pathway, which appears to be an elegant molecular regulator of specific matrix macromolecules (including specific MMPs and TIMPs). Furthermore, strong rationale for potential clinical applications of the described molecular mechanisms to the treatment of periprosthetic loosening and osteolysis is provided.

Significance of nano- and microtopography for cell-surface interactions in orthopaedic implants

Cell-surface interactions play a crucial role for biomaterial application in orthopaedics. It is evident that not only the chemical composition of solid substances influence cellular adherence, migration, proliferation and differentiation but also the surface topography of a biomaterial. The progressive application of nanostructured surfaces in medicine has gained increasing interest to improve the cytocompatibility and osteointegration of orthopaedic implants. Therefore, the understanding of cell-surface interactions is of major interest for these substances. In this review, we elucidate the principle mechanisms of nano- and microscale cell-surface interactions in vitro for different cell types onto typical orthopaedic biomaterials such as titanium (Ti), cobalt-chrome-molybdenum (CoCrMo) alloys, stainless steel (SS), as well as synthetic polymers (UHMWPE, XLPE, PEEK, PLLA). In addition, effects of nano- and microscaled particles and their significance in orthopaedics were reviewed. The significance for the cytocompatibility of nanobiomaterials is discussed critically.

Histomorphometric analysis of the intramedullary bone response to titanium particles in wild-type and IL-1R1 knock-out mice: a preliminary study

Aseptic loosening of implants following total joint arthroplasty remains a major cause of implant failure. Particulate debris generated primarily from wear results in inflammatory mediated periprosthetic osteolysis. Titanium is a commonly utilized metal in joint arthroplasty and titanium debris induces the production of the pro-inflammatory cytokine IL-1. To further elucidate the role of IL-1, this study examined the response of murine femora to the presence of titanium particles following implantation of an intramedullary rod in mice lacking the receptor for IL-1. We hypothesized that the inflammatory effects of wear debris on bone would be mitigated in IL-1R1 deficient mice with a resultant decrease in resorption. Femora receiving titanium particles demonstrated a marked inflammatory response in wild-type mice with increased endocortical resorption, periprosthetic membrane formation, and significant histomorphometric changes. Femora exposed to titanium particles in the knockout mice also demonstrated osteolysis with irregular deposition of trabecular bone and increased cortical porosity. The persistence of inflammation and osteolysis, despite the lack of functional IL-1R1, suggests a multi-factorial role for IL-1 in the proinflammatory cascade resulting from wear debris. This intramedullary murine model provides the ability to evaluate and quantify the proinflammatory cascade in an in vivo model approximating prosthesis failure.

Role of fibroblasts and fibroblast-derived growth factors in periprosthetic angiogenesis

The periprosthetic granulomatous soft tissue [designated iterfacial membrane (IFM) in this study] exhibits heterogeneous histopathological features, in which highly vascularized areas with dense cellularity alternate with fibrotic and pseudocapsule-like tissue structures. Although macrophage/monocyte activation is a prominent event in the periprosthetic environment, fibroblasts also phagocytose particulate wear debris both in vivo and in vitro. Particulate wear debris and/or cytokines/growth factors alone or in combination (e.g., in conditioned media of explant cultures of IFMs) stimulated normal synovial and IFM fibroblasts to express inflammatory mediators and growth factors such as interleukin (IL)-1beta, IL-6, IL-8, three isoforms of vascular endothelial growth factor (VEGF), monocyte/macrophage chemoattractant protein-1 (MCP-1), macrophage-colony-stimulating factor (M-CSF), cycloxygenases (Cox-1 and Cox-2), acid- and basic-fibroblast growth factors (FGF-1 and FGF-2), leukemia inhibitory factor-1 (LIF-1), transforming growth factor beta-1 (TGF-beta1), receptor activator of nuclear factor-kappa B ligand (RANKL), and osteoprotegerin (OPG). Thus, the fibroblast is capable of expressing a wide array of angiogenic and osteoclastogenic factors which are involved in the detrimental processes of the periprosthetic osteolysis.

The role of fibroblasts and fibroblast-derived factors in periprosthetic osteolysis

OBJECTIVE

This study was undertaken to investigate how fibroblasts respond to stimulation with particulate wear debris and/or conditioned media obtained from pathologic tissue, and whether these activated fibroblasts express compounds that are involved in bone resorption.

METHODS

Conditioned media from explant cultures of synovial tissue, periprosthetic soft tissue (interface membranes), titanium particles, and proinflammatory cytokines were used to stimulate fibroblasts. RNase protection assay was used to measure altered gene expression, and enzyme-linked immunosorbent assay, Western blot hybridization, and flow cytometry were used to determine fibroblast protein expression. Tartrate-resistant acid phosphatase staining was used to identify multinucleated osteoclast-like cells.

RESULTS

The most dominant compounds measured in the conditioned media from interface membranes were tumor necrosis factor alpha (TNFalpha), monocyte chemoattractant protein 1 (MCP-1), interleukin-1beta (IL-1beta), IL-6, IL-8, and vascular endothelial growth factor. Fibroblasts phagocytosed particulate wear debris and responded to cytokine/chemokine stimulation. The most prominent up-regulated genes and proteins secreted by fibroblasts in response to stimulation were matrix metalloproteinase 1, MCP-1, IL-1beta, IL-6, IL-8, cyclooxygenase 1 (COX-1), COX-2, leukemia inhibitory factor 1, transforming growth factor beta1 (TGFbeta1), and TGFbeta receptor type I. In addition, interface membrane fibroblasts expressed RANKL and osteoprotegerin in response to stimulation with conditioned media, TNFalpha, or IL-1beta. Stimulated fibroblasts cocultured with bone marrow cells in the presence of macrophage colony-stimulating factor induced osteoclastogenesis.

CONCLUSION

Interface membrane fibroblasts respond directly to particulate wear debris, possibly via phagocytosis, expressing proinflammatory cytokines and RANKL. Thus, these cells may be actively involved in osteoclastogenesis and pathologic (periprosthetic) bone resorption.

The central role of wear debris in periprosthetic osteolysis

Periprosthetic osteolysis remains the leading complication of total hip arthroplasty, often resulting in aseptic loosening of the implant, and a requirement for revision surgery. Wear-generated particular debris is the main cause of initiating this destructive process. The purpose of this article is to review recent advances in our understanding of how wear debris causes osteolysis, and emergent strategies for the avoidance and treatment of this disease. The most important cellular target for wear debris is the macrophage, which responds to particle challenge in two distinct ways, both of which contribute to increased bone resorption. First, it is well known that wear debris activates proinflammatory signaling, which leads to increased osteoclast recruitment and activation. More recently, it has been established that wear also inhibits the protective actions of antiosteoclastogenic cytokines such as interferon gamma, thus promoting differentiation of macrophages to bone-resorbing osteoclasts. Osteoblasts, fibroblasts, and possibly lymphocytes may also be involved in responses to wear. At a molecular level, wear particles activate MAP kinase cascades, NFkappaB and other transcription factors, and induce expression of suppressors of cytokine signaling. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties (such as metal-on-metal) should be balanced by awareness that reducing particle size may increase biological activity. Finally, although therapeutic agents against proinflammatory mediators [such as tumor necrosis factor (TNF)] and osteoclasts (bisphosphonates and molecules blocking RANKL signaling) have shown promise in animal models, no approved treatments are yet available to osteolysis patients. Considerable efforts are underway to develop such therapies, and to identify novel targets for therapeutic intervention.

Human fibroblast reactions to standard and electropolished titanium and Ti-6Al-7Nb, and electropolished stainless steel

Stainless steel (SS), titanium (cpTi), and Ti-6Al-7Nb (TAN) are frequently used metals in orthopedic internal fracture fixation. Although reactivity to SS and cpTi are noted in reference, the soft tissue compatibility of TAN has not been comprehensively studied. This study focuses on the in vitro soft tissue compatibility of TAN in comparison to SS and cpTi using a human fibroblast model. The industrial standard surface finishes of these three materials vary considerably in view of their use in similar applications. To distinguish between material parameters of topography and chemistry, we have included electropolished (e.p) counterparts of the standard preparations of cpTi and TAN in the study (standard SS is e.p). All materials were characterized using atomic force microscopy, profilometry, and scanning electron microscopy. Our findings demonstrate that cell morphology and growth rate was similar for SS, and e.p. cpTi and TAN, with cells well spread and forming a confluent monolayer by 10 days. Cell growth on standard cpTi was similar to the electropolished samples; however, they showed a less spread morphology with more filopodia and surface ruffling present. Cell morphology on standard TAN was rounded or elongated and proliferation was inhibited at all time points, with possible cell necrosis by day 10. We found evidence of endocytosis of beta-phase particles originating from the standard TAN surface. We believe that the particle uptake coupled with the characteristic surface topography contribute to the noncytocompatibility of fibroblasts on standard TAN.

Acceleration of Aneurysm Healing by Hollow Fiber Enabling the Controlled Release of Basic Fibroblast Growth Factor

OBJECTIVE

The objective of this study was to develop an embolization material of hollow fiber combined with gelatin hydrogel for the controlled release of basic fibroblast growth factor (bFGF). We examined feasibility of the material in embolization healing aneurysm by bFGF-induced tissue organization.

METHODS

An aneurysm was prepared at the common carotid artery of 60 rabbits by the end-to-side anastomosis of jugular venous pouch. The hollow fibers combined with or without 100 microg free bFGF or gelatin hydrogel incorporating 0, 10, 50, or 100 microg bFGF were applied to the aneurysm. Tissue appearance or histological observation was performed 1, 2, 3, and 6 weeks after application to evaluate the area embolized by fibrous organization in the aneurysm and the neointima formation at the aneurysm orifice.

RESULTS

When applied with the hollow fibers combined with gelatin hydrogel containing 100 microg bFGF, the aneurysm was histologically occupied by fibrous tissue newly formed 3 weeks later, whereas neointima was formed at the aneurysm orifice. The histological area occupied by fibrous tissue was significantly larger than that of hollow fibers combined with 100 microg bFGF. No influence of bFGF dose on the aneurysm healing by the fibers combined with hydrogels incorporating bFGF was observed.

CONCLUSION

Local, controlled release of bFGF from the hollow fibers combined with gelatin hydrogel incorporating bFGF accelerated the aneurysm healing by tissue organization.

Alumina particles influence the interactions of cocultured osteoblasts and macrophages

The purpose of the current study was to evaluate the effects of alumina particles on secretion of several cytokines involved in bone resorption in cocultures of macrophages and osteoblasts. To distinguish the contribution of each individual cell type, we have established a heterologous in vitro system that makes use of mouse J774 cells and primary cultured human osteoblasts. J744 cells decreased the production of TNF-alpha when they were cocultured with osteoblasts. Treatment of J744 cells with alumina particles increased TNF-alpha secretion, but the induction was lower when cells were cocultured with osteoblasts. Secretion of IL-6 by J744 cells was very low, and increased in the presence of osteoblasts. Alumina particles were only able to stimulate the release of IL-6 by J744 cells when cells were cocultured with osteoblasts. On the other hand, incubation of osteoblasts with alumina particles enhanced the release of IL-6 and GM-CSF. Coculturing osteoblasts with J744 cells induced them to release IL-6 and GM-CSF, and treatment with alumina further increased the secretion of both mediators by osteoblasts. According to these in vitro results, it seems rather plausible that alumina particles are able to initiate an inflammatory response in vivo.

Chemokine IL-8 induction by particulate wear debris in osteoblasts is mediated by NF-kappaB

Chemokines, or chemotactic cytokines, are major regulators of the inflammatory response and have been identified as pathogenic factors in the periprosthetic soft tissue. Particulate wear debris induced NF-kappaB activation, the major transcriptional regulator of IL-8 and MCP-1 pro-inflammatory genes and, indeed, both IL-8 and MCP-1 chemokine gene expressions were upregulated in titanium particulate-stimulated human osteoblasts. Here, we demonstrate that phagocytosed particles activate the IL-8 gene promoter via a NF-kappaB-mediated mechanism. Transfection of a dominant negative mutant IkappaBalpha protein that cannot be serine phosphorylated led to suppression of IL-8 promoter activity. The p65/RelA NF-kappaB subunit activity was affected in both a time- and titanium particle concentration-dependent fashion. Titanium particles led to increased ERK, JNK, and p38 activation in MG-63 osteoblast cells, and IL-8 protein release was suppressed by specific inhibitors of the ERK and p38 MAPK pathways. Together, our results suggest that wear debris particles induce chemokine expression in osteoblasts via NF-kappaB-mediated transcriptional activation, which is controlled by the MAPK signal transduction pathway.

Electrochemical corrosion and metal ion release from Co-Cr-Mo prosthesis with titanium plasma spray coating

The corrosion behavior of CoCrMo implants with rough titanium coatings, applied by different suppliers by either sintering or vacuum plasma spraying, has been evaluated and compared with uncoated material. The open-circuit potential, corrosion current and polarization resistance were determined by electrochemical techniques. The Co, Cr and Ti ions released from the samples into the electrolyte during a potentiostatic extraction technique were analyzed using ICP-MS. The Ti coatings from the different suppliers showed a different porous morphology, and the implants exhibited a distinct corrosion activity, underlining the importance of the coating process parameters. Among the titanium coated samples, the one with the sintered overcoat turned out to be the most resistant. Yet, on an absolute scale, they all showed a corrosion resistance inferior to that of uncoated CoCrMo or wrought titanium.

Aseptic loosening

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

Acceleration of aneurysm healing by controlled release of basic fibroblast growth factor with the use of polyethylene terephthalate fiber coils coated with gelatin hydrogel

OBJECTIVE

The aims of this study were to develop an endovascular delivery system containing gelatin hydrogels for the controlled release of basic fibroblast growth factor (bFGF) with the use of polyethylene terephthalate fiber coils and to analyze whether such a system would promote healing in an experimental aneurysm.

METHODS

Carotid aneurysms were constructed in 66 rabbits with venous pouches. The polyethylene terephthalate fiber coils coated with and without gelatin hydrogels with different water volumes containing 0, 10, 50, and 100 microg bFGF were implanted into the aneurysms. Histological specimens were harvested at 1, 2, and 3 weeks and at 6 months after implantation. A histological evaluation was performed while the area occupied by the fibrosis in the aneurysms was calculated.

RESULTS

Three weeks after the application of the coils coated with gelatin hydrogels (95 vol%) containing 100 microg bFGF, all aneurysmal orifices were completely closed with neointima. When the coils coated with gelatin hydrogel (98 vol%) containing 100 microg bFGF were used, the orifices in three of the six aneurysms were closed. In contrast, the orifice of the aneurysm was not obliterated when other materials were used. After implanting the coils coated with gelatin hydrogel (95 vol%) containing 100 microg bFGF more than 3 weeks later, the aneurysm was histologically suffused with fibrous tissue, and the area occupied by fibrosis was significantly larger than that observed in the other groups (P < 0.05).

CONCLUSION

Local, controlled release of sufficient amounts of bFGF with polyethylene terephthalate fiber coils coated with gelatin hydrogel accelerated the organization of aneurysms.

Evaluation of corrosion on plasma sprayed and anodized titanium implants, both with and without bone cement

The corrosion behavior of titanium with vacuum plasma sprayed titanium coatings and with anodized surfaces, both with and without polymeric bone cement were evaluated. Electrochemical extraction tests were carried out with subsequent analysis of the electrolyte by ICP-MS in order to verify our hypothesis of the ionic permeability of the polymer cement. The complexity of the situation resides in the existence of two interfaces: electrolyte-polymer and polymer-metal. The surface preparation (treatment of the surface) plays an important role in the corrosion resistance of titanium. The electrochemical magnitudes that were examined reveal that the plasma spray surfaces have the lowest corrosion resistance. The cement, in spite of having reduced electrical conductivity in comparison to metal, is an ionic transporter, and therefore capable of participating in the corrosion process. In the present study, we observed in fact crevice corrosion at the metal-cement interface. In the case of plasma spray surfaces, a process of diffusion of titanium particles in the electrolyte could accompany the crevice corrosion. In this study, we have shown that there is a corrosion process at the surface of the titanium through the cement which has as a consequence on the one hand the formation of titanium cations and on the other hand the growth of a passive layer on the titanium. In conclusion, we identified two principal factors that influence the corrosion process: [1] the type of surface treatment for the titanium, and [2] the ionic conductivity of the cement. There is indeed ionic transport through the cement; as evidenced by the presence of titanium in the electrolyte solution (ICP-MS analysis) and chloride at the surface of the titanium sample (EDX analysis). We show that the polymer cement is an ionic conductor and participates in the corrosion of the embedded titanium. We cannot deduce from our results, however, whether the polymer itself possesses corrosive properties. Long-term experiments will be necessary to study the degradation behavior of the polymer cement.

Particles and periimplant bone resorption

There is compelling evidence that the most important factor in late periprosthetic bone resorption is an inflammatory reaction to debris. Based on results from several laboratories, it seems likely that opsonized particles activate the macrophage nuclear factor-kappa B signal transduction system via membrane receptors, leading to release of tumor necrosis factor-alpha and other cytokines and growth factors. Tumor necrosis factor stimulates osteoblasts to release cytokines that recruit inflammatory cells and osteoclast precursors to the site and promote the differentiation of early osteoclasts. Tumor necrosis factor influences fibroblasts to release tissue metalloproteinases, and induces c-src in osteoclast precursors, the expression of which is necessary for additional bone resorption. Phagocytosis of debris by osteoblasts may reduce collagen synthesis, whereas phagocytosis by fibroblasts may induce chemokines that amplify inflammation. Bone has been partially protected from particle-induced resorption in animals with defective or inhibited tumor necrosis factor or nuclear factor-kappa B signaling. Many aspects of this inflammatory reaction require clarification, including identifying the factors that influence variability among patients, and testing the importance of costimulatory molecules such as bacterial endotoxin, but the fundamental importance of particles in most cases of aseptic loosening seems certain.

Animal model for evaluation of soft tissue ingrowth into various types of porous coating

Results from several studies have suggested that soft tissue ingrowth into porous coating can serve as a biologic containment mechanism to prevent particulate debris migration by sealing off the effective joint space. Therefore, a rabbit animal model was developed to investigate soft tissue ingrowth into various types of metallic rods. After implantation of several types of coated and smooth rods within the thigh musculature of rabbits, a thick encapsulation of soft tissue was observed around porous-coated rods whereas a nonadherent pseudosynovial-lined cavity was observed around smooth rods. Within 3 weeks, soft tissue had grown into the three different types of porous coating on the rods. Histologic evaluation verified that maturation of this ingrowth tissue occurred by 12 weeks. Incomplete soft tissue ingrowth occurred into the depths of large-bead (590-840 mm) porous-coated surfaces. Soft tissue separation from the bead surfaces was observed at 12 weeks in the porous-coated implants that also had been coated with a thin layer of tricalcium phosphate. These findings suggest that soft tissue ingrowth can be expected to occur into the porous coatings tested, but that tricalcium phosphate should not be used as an additional surface coating to obtain long-term adherence of circumferential soft tissue ingrowth.

Prosthetic metals have a variable necrotic threshold in human fibroblasts: an in vitro study

The generation of metal particles from prosthetic joints has been an evolving problem in orthopedics. Numerous factors have been involved including cells, metals, and responding cytokines, but determining roles of these factors or cascades of factors has been elusive. This laboratory has published threshold levels for commercially pure titanium (CpTi), which led to cell necrosis, but noted that cell viability differed among donor patients. To compliment the previous work we examined two other metals, Tantalum (Ta) and cobalt-chrome (CoCr), while making comparative measurements in these different donor patients. Retrieved human fibroblasts (superior medial plica) were cultured in a standard manner and exposed to various dosages of the three metals. Cell counts and interleukin (IL) 6 were used as dependent variables within a three-way analysis of variance. The data show that fibroblast necrosis was significantly affected by both type and mass of metal, with each metal having a distinct threshold (CpTi most necrotic, followed by Ta and CoCr). The cell counts and IL-6 at control levels varied significantly among all three donors. However, the response to the metals and dosages did not differ among tissue donors. Thus, although each patient had a different starting value for cell counts and IL-6, they responded to the metal particles in the same proportionate manner.

Effects of polyethylene and alpha-alumina particles on IL-6 expression and secretion in primary cultures of human osteoblastic cells

The effect of two biomaterials, polyethylene and alpha-alumina, on interleukin-6 (IL-6) secretion and expression has been studied in human osteoblasts in primary culture. Human osteoblastic cells were derived from fresh trabecular bone explants removed during total knee arthroplasty. On reaching confluence, cells were subcultured in 6 well plates; the resulting subcultures were incubated until confluence and polyethylene or alpha-alumina particles were added to some while the rest were left as controls. The IL-6 mRNA levels were assessed by reverse transcription (RT) followed by polymerase chain reaction (PCR). IL-6 secretion was measured in the conditioned medium. The IL-6 expression was higher in the presence of both biomaterials. Maximum expression occurred in response to a dose of 50 mg particles well with both biomaterials and was greater after polyethylene particle addition than after alpha-alumina particle addition at this dose. The maximum IL-6 secretion elicited by alpha-alumina was produced at 10 mg particles well while maximum response with polyethylene required 50 mg well. At a dose of 10 mg/well, alpha-alumina particles induced more secretion than 10 mg of polyethylene particles. Nevertheless, at a dose of 50 mg/well maximum secretion was produced with polyethylene particles. In conclusion and in our experimental conditions, polyethylene as well as alpha-alumina increased both the expression and the secretion of IL-6 in human osteoblastic cells in primary culture and stimulation from polyethylene appears stronger than that from alpha-alumina at the same dose.

Polyethylene particles from a hip simulator cause (45)Ca release from cultured bone

Periprosthetic osteolysis is a dominant factor in the success or failure of total hip prostheses. Polyethylene wear debris has been implicated in the process of bone resorption and subsequent implant loosening. The present study is the first to examine the effect of ultra high molecular weight polyethylene (UHMWPE) wear debris produced by a hip simulator on calvarial bone resorption in vitro. (45)Ca release was measured in cultured mouse calvarial bone samples. Although short-term exposure to UHMWPE particles (2 h) decreased (45)Ca release, longer-term exposure for 1-2 days increased release in a dose-dependent manner. After one-day exposure to 7.5 x 10(6) particles per mL, 18% more (45)Ca was released from cultured calvarial bone than from control samples. It was concluded that UHMWPE wear particles either directly or indirectly stimulated osteoclasts to activate bone resorption. Polyethylene wear debris contributes to the osteolytic process at the bone-implant interface.

Enhanced formation of fibrosis in a rabbit aneurysm by gelatin hydrogel incorporating basic fibroblast growth factor

OBJECTIVE

This study was undertaken to analyze whether the controlled release of basic fibroblast growth factor (bFGF) can promote intrasaccular thrombosis in an experimental aneurysmal model.

METHODS

Carotid aneurysms were constructed in 80 rabbits with venous pouches and treated by placing gelatin hydrogels into each aneurysm incorporating 0, 25, 50, or 100 microg of bFGF or incorporating 100 microg of bFGF with different water contents. In the controls, the venous pouches either were not treated or were treated with gauze alone. Gelatin hydrogel was used for the controlled release of bFGF into the aneurysms. The formation of fibrosis in the aneurysms was histologically viewed to assess the area occupied by the fibrous tissues at 3 and 6 weeks after the hydrogel application. The effect of the bFGF dose and water content on obliterating the aneurysm by the hydrogels incorporating bFGF was also investigated.

RESULTS

Six weeks after the application of gelatin hydrogels with a water content of 95 wt% incorporating 100 microg of bFGF, the lateral pouch orifice was completely closed, obliterating the aneurysm at the level of tissue appearance, in contrast to hydrogels incorporating lower doses of bFGF and other control agents. The venous pouch aneurysm was histologically occupied with the newly formed fibrous tissue, and the fibrous tissue area and percentage of the aneurysmal lumen occupied by the fibrosis-gauze complex were significantly larger than those of other hydrogel applications (P < 0.05). The neointima tissue was homogeneously covered with a monolayer of Factor VIII-positive cells. The fact that there was no difference in the water content in the fibrosis formation induced by the bFGF-incorporated gelatin hydrogels indicated that the hydrogel biodegradability did not affect the obliteration of the aneurysm.

CONCLUSION

Local controlled release of bFGF stimulated the formation of in vivo fibrosis, resulting in obliteration of the aneurysm. The long-term results of the fibrous organization remain speculative.

Fibroblast expression of C-C chemokines in response to orthopaedic biomaterial particle challenge in vitro

C-C chemokines are soluble mediators that occur in a periprosthetic granuloma and influence recruitment, localization and activation of inflammatory cells. This study tested effects of titanium and polymethylmethacrylate (PMMA) particles on expression of selected C-C chemokines in cultured human fibroblasts. The C-C chemokines analyzed included monocyte chemoattractant protein-1. 2 (MCP-1. 2), monocyte inflammatory protein-1 alpha (MIP-1 alpha), and regulated on activation, normal T-cell expressed and secreted protein (RANTES). Interleukin-1 beta (IL-1 beta) served as a known stimulator of chemokine release while interleukin-6 (IL-6) expression served as a marker for fibroblast activation. Protein and mRNA signal levels were determined by ELISA and RT-PCR, respectively. The results demonstrated that exposure of fibroblasts to titanium and PMMA particles resulted in increased release of MCP-1 in a dose- and time-dependent manner. After 24 h, titanium particles maximally upregulated MCP-1 release 7-fold while PMMA particles increased MCP-1 levels 2-fold, when compared to unchallenged fibroblasts. MCP-2, MIP-1 alpha and RANTES levels remained unchanged following exposure of fibroblasts to titanium or PMMA particles at any concentration or time point tested. However, IL-1 beta stimulated release of MCP-1, MCP-2, and RANTES, but not MIP-1 alpha from the fibroblasts. IL-1 beta, not particles, exhibited the most prominent effect on MCP-1 mRNA levels. Increased release of MCP-1 from fibroblasts exposed to titanium and PMMA particles coincided with increased release of IL-6. This study suggests that release of chemoattractant factors from fibroblasts localized in periprosthetic membranes enhances the chronic inflammatory process leading to bone resorption and implant loosening.

Osteoclast induction from bone marrow cells is due to pro-inflammatory mediators from macrophages exposed to polyethylene particles: a possible mechanism of osteolysis in failed THA

Polyethylene debris from joint replacements may be transported in synovial fluid and be phagocytosed by macrophages. The activation and migration of macrophages may play important roles in osteolysis and implant loosening. Tissues from the bone-implant interface do not always contain wear debris, which may mean that osteolysis may not require direct contact with wear debris. We hypothesized that the release of polyethylene debris from the implants induces macrophage activation in the joint space. Then the activated macrophages release humoral factors, such as inflammatory cytokines, into the joint fluid. These cytokines may be transported to the bone marrow tissues around the implants where they stimulate the differentiation of the bone marrow cells into osteoclasts. Finally, the activated osteoclasts resorb the surrounding bone. To test this hypothesis, macrophages were stimulated by polyethylene particles. The levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were determined by enzyme-linked immunosorbent assay and were increased significantly. To test humoral interaction between macrophages and bone-marrow cells, a co-culture system was used in an in vitro model. With this system, two kinds of cells can be cultured together with humoral contact without the two cell types having to contact each other. We stimulated the macrophages with 5 microm of polyethylene particles and observed whether the bone marrow cells differentiated into the osteoclasts without contact with the macrophages. The numbers of osteoclasts were assessed using tartrate-resistant acid phosphatase (TRAP) staining. The numbers of TRAP-positive cells in the polyethylene particle-stimulated group were higher than in the control group. The ability of the TRAP-positive cells to resorb bone was confirmed by dentine pit formation assay. The results of this study support our hypothesis and suggest that one mechanism of osteolysis in failed joint arthroplasty is the more distant effects of pro-inflammatory cytokine release on osteoclast differentiation and/or activity.

Effects of hydroxyapatite particulate debris on the production of cytokines and proteases in human fibroblasts

Cytokines and proteases are secreted by fibroblasts in response to particulate wear debris, and these proteins are felt to play an important role in the development of osteolysis and implant loosening. Although metallic and polyethlyene debris have been studied extensively, little is known about the cellular responses to hydroxyapatite, despite the wide clinical use of these materials. Therefore, the effects of hydroxyapatite (HA) and hydroxyapatite/beta-tricalciumphosphate (HA/TCP) on cellular proliferation, cytokine gene expression and protein secretion, protease synthesis, and gelatinolytic activity were investigated in human fibroblasts. HA and HA/TCP particles were synthesized, and their effects were compared to the responses elicited by titanium and cobalt chromium. Sample characterization by scanning electron microscopy and Coulter Counter demonstrated that the materials had a mean particle size of less than 10 microm, and all of the particles were compared using the same concentration ranges. Aliquots of particle suspensions were added to human fibroblasts maintained in tissue culture, and dose-response and time-course experiments were performed. Effects of the particles on fibroblast proliferation were assessed, and alterations in cytokine levels were determined by specific enzyme linked immunosorbent assays (ELISA). Cytokines that were evaluated included interleukin-1 (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha), all of which have been demonstrated to enhance bone resorption and are associated with osteolysis and implant loosening. Gene expression was determined using Northern blot analysis with cytokine-specific probes, while secretion of the proteases collagenase and stromelysin was determined by Western blot analysis. Functional gelatinolytic assay was assessed using zymogram gels. The particles were evaluated in a concentration range from 0.000021 to 0.021 vol%. All of the particles produced increases in cellular proliferation up to 0.0021 vol%, with the largest increases being seen at 0.021 vol% with HA/TCP and titanium. At the highest concentration, both cobalt chromium and HA samples decreased cellular proliferation relative to lower doses, possibly representing cytotoxicity. Hydroxyapatite particles yielded a 30-fold increase in interleukin-6 secretion compared to unstimulated controls, which was also greater than three times the levels produced by cobalt chromium, titanium, or HA/TCP. HA particles also tripled the secretion of IL-1beta at 0.00021 vol%, and doubled TNF-alpha secretion at 0.021 vol%. Addition of conditioned media prepared by incubation of the particles in culture medium in the absence of cells did not alter the secretion of any of the cytokines. Northern blot analysis using IL-6 probes also demonstrated strong increases with HA compared to the other materials, suggesting that the action of the HA particles was at the level of transcription. Secretion of the protease collagenase was increased by all of the samples including HA when compared to unstimulated controls. Stromelysin secretion into the culture medium was decreased by cobalt chromium, but increased by titanium, HA, and HA/TCP. All of the particles including HA increased the gelatinolytic activity of the fibroblasts. These findings demonstrate that HA and HA/TCP particles are capable of stimulating the expression and secretion of cytokines and proteases that enhance bone resorption, and suggest that particulate debris from implants using these coatings may also increase osteolysis and loosening.

Chemical eluates from ultra-high molecular weight polyethylene and fibroblast proliferation

Although polyethylene wear particles have been implicated in osteolysis and implant loosening, this study is the first to test whether chemical eluates extracted from ultra-high molecular weight polyethylene (UHMWPE) could also be involved in this process. Eluates were prepared from UHMWPE bar stock and examined for their effects on (3)H-thymidine incorporation by human foreskin fibroblasts grown in 96-well culture plates. Low concentrations of eluates stimulated (3)H-thymidine uptake; whereas, high concentrations inhibited uptake in a dose-dependent manner. Maximum inhibition of proliferation for eluates (87+/-0.03% inhibition, n = 45 paired wells) was greater than that observed for particles (54+/-0.07% inhibition, n = 45 paired wells). Ethylene oxide sterilization of UHMWPE reduced (3)H-thymidine uptake at low eluate concentrations relative to sterilization by gamma-irradiation. It was concluded that leachable eluates from UHMWPE implantse contribute to the osteolytic process at the bone-implant interface.

Development and characteristics of a synovial-like interface membrane around cemented tibial hemiarthroplasties in a novel rat model of aseptic prosthesis loosening

OBJECTIVE

Aseptic prosthesis loosening (APL) is related to the formation and aggressive growth of a synovial-like interface membrane (SLIM) between prosthesis and bone. However, investigation of the early phases of SLIM development in humans presents major difficulties. This study was undertaken to develop and characterize the usefulness of a novel animal model of APL that is based on an established model of defined exercise in a running wheel by Wistar rats that have been subjected to intracranial self-stimulation (ICSS).

METHODS

Cemented tibial hemiarthroplasties were implanted into the left knees of 7 male Wistar rats. After 2 weeks, exercise in a running wheel was started in all rats, with a running-load of 2 hours/day for 5 days/week. Six months postoperatively, the knee joints were removed, decalcified, and embedded in paraffin. Histologic evaluation on hematoxylin and eosin-stained sections was performed to investigate the development of a SLIM and the presence of cement debris particles. To characterize the SLIM on a molecular level and investigate growth-regulating factors, the expression of transforming growth factor beta (TGFbeta) and the anti-apoptotic molecule Bcl-2 was analyzed by immunohistochemistry.

RESULTS

Although the prostheses appeared mechanically stable after 6 months, the development of SLIM with areas of bone resorption was seen in all samples. Resembling human SLIM, these membranes consisted of loose fibrous tissue, with cement debris particles located particularly at sites originally attached to the prostheses. Immunohistochemistry studies revealed the expression of TGFbeta and Bcl-2 in all specimens. Interestingly, staining for TGFbeta and Bcl-2 was restricted to areas where the SLIM were attached to bone. In contrast, there was only negligible expression of both proteins at sites adjacent to the prostheses.

CONCLUSION

Our findings demonstrate that the ICSS Wistar rat model constitutes a feasible tool for studying early stages of APL, and specifically the effect of defined running exercise on SLIM formation. The results further suggest that both cellular proliferation, as stimulated by TGFbeta, and altered apoptosis contribute to early stages of SLIM formation. The expression patterns of TGFbeta and Bcl-2 indicate that the growth of the SLIM is initiated and promoted from the bone rather than from the prosthesis.

Cutaneous metal sensitivity in patients with orthopaedic injuries

BACKGROUND

Manufactures of orthopaedic fracture implants have turned to titanium in a pure form and an alloy during the past ten to fifteen years. Although primarily because of the biomechanical properties of this metal, concern for allergy to nickel and chromium ions in stainless steel was a factor in these decisions.

OBJECTIVES

To document the incidence of baseline sensitivity to metal ions and the incidence of conversion to sensitivity to one of three ions in stainless steel in a population of trauma patients at a Level I trauma center.

DESIGN

Prospective, consecutive patient series.

SETTING

Level I trauma center.

PATIENTS

Patients eighteen years of age and older with no history of metallic implants were recruited for this study between October 1995 and July 1997. Four hundred ninety-three patients had a Finn chamber device with chromium, nickel, and cobalt ions, which were read using a photographic scale on day three. Two hundred forty-two of these patients had placement of a second patch, at a mean interval of 187 days (range 45 to 589 days).

INTERVENTION

Internal fixation of fracture or osteotomy with metal implant. MAIN OUTCOME MANAGEMENT: Cutaneous reactivity to metal ions.

RESULTS

Prevalence of sensitivity to chromium was 0.2 percent, to nickel 1.3 percent, and to cobalt 1.8 percent. Rates for conversion from a negative to positive status were 2.7 percent for chromium, 3.8 percent for nickel, and 3.8 percent for cobalt. Rates for desensitization (i.e., converting from a positive to negative status) were 2.1 percent for nickel and 3.8 percent for cobalt.

CONCLUSION

The prevalence of sensitivity to nickel, cobalt, and chromium is apparently low. Similarly, internal fixation devices composed of stainless steel appear to result in an equal incidence of conversion to metal ionic sensitivity and desensitization to metal ions. It is conceivable that cutaneous sensitivity is not representative of deep immune response.

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.

Cytokine receptor profile of arthroplasty macrophages, foreign body giant cells and mature osteoclasts

In the arthroplasty pseudomembrane surrounding a loose prosthesis there is a marked macrophage and foreign body giant cell (FBGC) response to implant-derived wear particles. These cells contribute to the osteolysis of loosening by releasing cytokines and growth factors which influence the formation and activity of osteoclasts. Using a panel of monoclonal antibodies directed against known cytokine/growth factor receptors, we have determined by immunohistochemistry whether arthroplasty macrophages, FB-GCs and osteoclasts express receptors for cytokines and growth factors that are known to modulate osteolysis. All these cell types reacted with antibodies directed against the following cytokine/growth factor receptors: gp130, IL-1R type 1, IL-2R, IL-4R, IL-6R, TNFR, M-CSFR, GM-CSFR and SCFR but not with antibodies directed against IL-3R and IL-8R. Arthroplasty macrophages, FBGCs and osteoclasts thus show a similar pattern of cytokine/growth factor receptor expression. This reflects the fact that arthroplasty macrophages are capable of osteoclast differentiation and that these cell types form part of the mononuclear phagocyte system. As regards the osteolysis of aseptic loosening, it also indicates that these cells are targets for numerous cytokines and growth factors which influence osteoclast formation and bone resorption.

In vitro response of human fibroblasts to commercially pure titanium

The generation of metal particles through surface wear of prosthetic joints has been associated with biological reactions that may lead to prosthetic component loosening. The role of the macrophage in these reactions has been studied extensively, but that of the fibroblast has not. The few fibroblast studies that there have been have shown that particles of several metals, with sizes over a wide range, can promote cytokine release and may cause cell necrosis. The intent of this study was to determine if there are metal particle exposure threshold levels that result in morphological changes and cell necrosis of fibroblasts in peri-articular tissues. Retrieved human fibroblasts (superior medial plica) were cultured in standard fashion and then were exposed to various particle dosages of commercially pure Titanium (cpTi). Cell morphological changes and necrosis were observed to occur when the total mass of the particle dosage exceeded a threshold level. These data imply that these cell responses occur at threshold levels of wear particle exposure.

Effect of prosthetic titanium wear debris on mitogen-induced monocyte and lymphoid activation

Wear debris generated by joint implant components has been reported to activate inflammatory and immune cells. Particulate debris derived from prosthetic material induces monocytes/macrophages, lymphocytes, synoviocytes, and fibroblasts to secrete cellular products, such as cytokines, which mediate inflammation. It has been speculated that degradation products impair the ability of inflammatory and immune cells to mount a protective response against noxious agents and infectious organisms by interfering with cell activation. Recent in vitro studies suggest that soluble metal ions inhibit T and B cell activation, but it is not known whether insoluble metal particles generated by prosthetic wear in tissue have the same effect. The purpose of the present study was to determine whether titanium wear debris retrieved from periprosthetic tissues surrounding a failed knee prosthesis suppresses activation of human monocytic and lymphoid cells. Peripheral blood monocytes and lymphocytes were incubated with the nonspecific activator pokeweed mitogen (PWM) in the presence or absence of titanium particles. Cell proliferative capacity and production of interleukins IL-1beta and IL-2 were determined as measures of activation. Titanium wear debris induced monocyte secretion of IL-1beta at levels comparable to those induced by PWM alone. In combination with PWM, titanium wear debris stimulated monocytes to secrete higher concentrations of IL-1beta than is stimulated by titanium itself or by PWM alone. Titanium wear debris did not activate lymphocytes, as indicated by marginal changes in DNA synthesis and IL-2 secretion, nor did it suppress the PWM-induced stimulation of DNA synthesis and IL-2 secretion. Our study suggests that nonspecific mitogen activators in spite of exposure to titanium wear debris can stimulate monocytic and lymphoid cells.

Macrophage colony-stimulating factor and interleukin-6 release by periprosthetic cells stimulates osteoclast formation and bone resorption

Periprosthetic bone loss is an important contributory factor for aseptic loosening of total joint replacements. It has recently been shown that osteoclast precursor cells are present in the wear particle-associated macrophage infiltrate found in the membrane surrounding loose implants and that these cells are capable of differentiating into osteoclastic bone-resorbing cells. Long-term co-culture of arthroplasty-derived macrophages and the rat osteoblast-like cell line, UMR-106, in the presence of 1,25(OH)2D3 results in the formation of numerous multinucleated cells that are positive for tartrate-resistant acid phosphatase and vitronectin receptor and capable of extensive lacunar bone resorption. The aim of this study was to determine the effect of cytokines/growth factors, known to be present in the arthroplasty membrane, on this process of osteoclast differentiation. During osteoclast formation, increased levels of macrophage colony-stimulating factor, interleukin-6, and to a lesser extent, interleukin-1beta, but not tumour necrosis factor alpha, were detected in the co-culture supernatants. Addition of neutralising antibodies to human interleukin-1beta or tumour necrosis factor alpha to the co-culture system did not inhibit osteoclast formation. In contrast, co-cultures to which neutralising antibodies to human macrophage colony-stimulating factor or interleukin-6 were added contained fewer cells positive for tartrate-resistant acid phosphatase and vitronectin receptor and formed significantly fewer resorption pits. Time-course studies showed that macrophage colony-stimulating factor and interleukin-6 increase osteoclast formation mainly in the early stages of osteoclast differentiation. These results indicate that the release of macrophage colony-stimulating factor and interleukin-6 by activated cells in the arthroplasty membrane is likely to contribute to pathological bone resorption associated with aseptic loosening by stimulating differentiation of mononuclear phagocyte osteoclast precursors into mature bone-resorbing cells.

Proinflammatory mediator release in response to particle challenge: studies using the bone harvest chamber

This study reports on the effects of phagocytosable particles on proinflammatory mediator release in an animal model. Bone harvest chambers (BHCs) were implanted bilaterally into mature rabbits; phagocytosable ultrahigh molecular weight polyethylene (UHMWPE) and polystyrene (PS) particles, and the carrier sodium hyaluronate (HE) were tested for their ability to stimulate proinflammatory mediator release. Tissues were harvested after 3, 4, or 6 weeks. Retrieved tissues were placed into culture medium. The release of the proinflammatory mediators interleukin-6 (IL-6), interleukin-1beta (IL-1beta), and tumor necrosis factor alpha (TNF-alpha) into the culture medium was assessed using bioassays. DNA content and dry weights were also measured. The maximal biological response to the PE particles with respect to TNF-alpha and IL-1beta was observed at three weeks with 11- and fivefold stimulations over controls, respectively. The maximal response to PE particles with respect to IL-6 was observed at 4 weeks with a twofold stimulation over controls. Similar patterns were seen with PS particles; however, PE particles stimulated higher cytokine release. PE particles stimulated the expression of IL-1beta, IL-6, and TNF-alpha in the BHC model. Cell culture and human retrieval studies also implicate these proinflammatory mediators in loosening and osteolysis of total joint replacements. Thus, the BHC is a useful in vivo model to document the effects of particles on the evolution of biological responses to particulate debris.

Procollagen-positive fibroblasts predominantly express fibrogenic growth factors and their receptors in human encapsulation process against foreign body

This paper addresses the in situ expression of transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), and their receptors in the encapsulation process against a foreign body, using 20 cases of the titanium miniplate as a model of the foreign body, used clinically to fix a fractured mandible. Fibrous tissue formed during the encapsulation process was composed of scar-like and fibrogenic layers, with the former directly facing the foreign body. By immunohistochemistry using pre-fixed frozen sections, only the fibrogenic layer was characterized by expression of type I procollagen (PC-I). Spindle-shaped mesenchymal cells in the fibrogenic layer expressed TGF-beta isoforms and receptors, PDGF isoforms, and PDGF beta-receptor. In contrast, the scar-like layer had few such cells. In both layers, spindle-shaped cells did not express Ki-67 in their nuclei. Double immunofluorescence microscopy for cell identification revealed that most PC-I-positive fibroblasts expressed both isoforms and receptors of TGF-beta and PDGF in the fibrogenic layer, while in contrast, they were expressed by only a small number of CD68-positive macrophages. These results suggest that in the maintenance stage of the human encapsulation process against a foreign body, both TGF-beta and PDGF function cooperatively via their receptors in the fibrogenic layer, with such stimuli markedly diminished in the scar-like layer.