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

Inflammation and Bone Repair: From Particle Disease to Tissue Regeneration

When presented with an adverse stimulus, organisms evoke an immediate, pre-programmed, non-specific innate immune response. The purpose of this reaction is to maintain the organism's biological integrity and function, mitigate or eradicate the injurious source, and re-establish tissue homeostasis. The initial stage of this protective reaction is acute inflammation, which normally reduces or terminates the offending stimulus. As the inflammatory reaction recedes, the stage of tissue repair and regeneration follows. If the above sequence of events is perturbed, reconstitution of normal biological form and function will not be achieved. Dysregulation of these activities may result in incomplete healing, fibrosis, or chronic inflammation. Our laboratory has studied the reaction to wear particles from joint replacements as a paradigm for understanding the biological pathways of acute and chronic inflammation, and potential translational treatments to reconstitute lost bone. As inflammation is the cornerstone for healing in all anatomical locations, the concepts developed have relevance to tissue engineering and regenerative medicine in all organ systems. To accomplish our goal, we developed novel in vitro and in vivo models (including the murine femoral continuous intramedullary particle infusion model), translational strategies including modulation of macrophage chemotaxis and polarization, and methods to interfere with key transcription factors NFκB and MyD88. We purposefully modified MSCs to facilitate bone healing in inflammatory scenarios: by preconditioning the MSCs, and by genetically modifying MSCs to first sense NFκB activation and then overexpress the anti-inflammatory pro-regenerative cytokine IL-4. These advancements provide significant translational opportunities to enhance healing in bone and other organs.

Human polyethylene granuloma tissues inhibit bone healing in a novel xenograft animal model

During revision of a conventional polyethylene joint replacement, surgeons usually remove the source of osteolysis (polyethylene) but cannot always remove all of the polyethylene granuloma tissues. We developed a human/rat xenograft model to investigate the effects of polyethylene granuloma tissues on bone healing. Human osteoarthritic and periprosthetic tissues collected during primary and revision hip arthroplasty surgeries were transplanted into the distal femora of athymic nude rats. After 3 weeks in vivo, there was a significant difference in the bone volume fraction (Vf ) between empty, primary, and revision defects (p = 0.02), with a lower Vf in defects with revision granuloma tissues compared to defects with primary osteoarthritic tissues. Polyethylene granuloma tissues in trabecular bone defects inhibited bone healing. Therefore, debridement around a metal-on-polyethylene hip replacement may shorten the time it takes to achieve secondary stability around a revision hip replacement.

Polyethylene and metal wear particles: characteristics and biological effects

This paper first presents a brief overview about the mechanism of wear particle formation as well as wear particle characteristics in metal-on-polyethylene and metal-on-metal artificial hip joints. The biological effects of such particles are then described, focusing on the inflammatory response induced by each type of particles as well as on how metal wear products may be the source of a T lymphocyte-mediated specific immune response, early adverse tissue responses, and genotoxicity. Finally, some of the current in vivo models used for the analysis of tissue response to various wear particles are presented.

New animal models of wear-particle osteolysis

Particle debris resulting from in vivo degradation of total joint replacement components are recognised as the major factor limiting the longevity of joint reconstruction and the overall success of the procedure. Better understanding the complex cellular and tissue mechanisms and interactions resulting in wear-particle osteolysis requires a number of experimental approaches, including radiological monitoring and analysis of retrieved tissues from clinical cases, in vitro experiments, and also animal-model investigations. In consideration of both their advantages and drawbacks, this paper provides an historical overview of numerous animal models that have been developed over the last three decades to investigate the pathogenesis of wear-particle osteolysis and to facilitate the preclinical testing of new treatment options. The authors also focus on recent studies in order to provide a better understanding of the current state of the art on this subject and propose some perspectives regarding technical and fundamental questions.

Endosomal damage and TLR2 mediated inflammasome activation by alkane particles in the generation of aseptic osteolysis

Ultra-high molecular weight polyethylene is widely used as a bearing surface in prosthetic arthroplasty. Over time the generation of implant-derived wear particles can initiate an inflammatory reaction characterized by periprosthetic inflammation and ultimately bone resorption at the prosthetic bone interface. Herein we present evidence that the different sized particles as well as the different length alkane polymers generated by implant wear leads to a two component inflammatory response. Polymeric alkane structures, with side chain oxidations, directly bind and activate the TLR-1/2 signaling pathway. Whereas micron- and nanometer-sized particulate debris are extensively phagocyted and induce enlargement, fusion and disruption of endosomal compartments. The resulting lysosomal damage and subsequent enzymatic leakage induces the NALP3 inflammasome activation as determined by cathepsins S and B cytosolic release, Caspase 1 activation and processing of pro-IL-1beta, and pro-IL-18. These two processes synergistically results in the initiation of a strong inflammatory response with consequent cellular necrosis and extracellular matrix degradation.

Immunogenecity of modified alkane polymers is mediated through TLR1/2 activation

BACKGROUND

With the advancement of biomedical technology, artificial materials have been developed to replace diseased, damaged or nonfunctional body parts. Among such materials, ultra high molecular weight alkane or modified alkyl polymers have been extensively used in heart valves, stents, pacemakers, ear implants, as well as total joint replacement devices. Although much research has been undertaken to design the most non-reactive biologically inert polyethylene derivatives, strong inflammatory responses followed by rejection and failure of the implant have been noted.

METHODOLOGY/PRINCIPAL FINDINGS

Purification of the alkane polymers from the site of inflammation revealed extensive "in vivo" oxidation as detected by fourier transformed infra-red spectroscopy. Herein, we report the novel observation that oxidized alkane polymers induced activation of TLR1/2 pathway as determined by ligand dependent changes in intrinsic tyrosine fluorescence intensity and NF-kappaB luciferase gene assays. Oxidized polymers were very effective in activating dendritic cells and inducing secretion of pro-inflammatory cytokines. Molecular docking of the oxidized alkanes designated ligand specificity and polymeric conformations fitting into the TLR1/2 binding grooves.

CONCLUSION/SIGNIFICANCE

This is the first report of a synthetic polymer activating immune responses through TLR binding.

What experimental approaches (eg, in vivo, in vitro, tissue retrieval) are effective in investigating the biologic effects of particles?

Understanding the complex cellular and tissue mechanisms and interactions resulting in periprosthetic osteolysis requires a number of experimental approaches, each of which has its own set of advantages and limitations. In vitro models allow for the isolation of individual cell populations and have furthered our understanding of particle-cell interactions; however, they are limited because they do not mimic the complex tissue environment in which multiple cell interactions occur. In vivo animal models investigate the tissue interactions associated with periprosthetic osteolysis, but the choice of species and whether the implant system is subjected to mechanical load or to unloaded conditions are critical in assessing whether these models can be extrapolated to the clinical condition. Rigid analysis of retrieved tissue from clinical cases of osteolysis offers a different approach to studying the biologic process of osteolysis, but it is limited in that the tissue analyzed represents the end-stage of this process and, thus, may not reflect this process adequately.

What other biologic and mechanical factors might contribute to osteolysis?

An overwhelming consensus exists that wear particles are the primary driving force in aseptic loosening of orthopaedic implants. Nonetheless, considerable evidence has emerged demonstrating that various other factors can modulate the biologic activity of orthopaedic wear particles. Two of the most studied modulating factors are bacterial endotoxins and implant motion.

Implant wear induces inflammation, but not osteoclastic bone resorption, in RANK(-/-) mice

Signaling of RANK (receptor activator of nuclear factor kappa B) through its ligand RANKL appears critical in osteolysis associated with aseptic loosening (AL). The purpose of this study was to investigate the role of RANK in a murine osteolysis model developed in RANK knockout (RANK(-/-)) mice. Ultra high molecular weight polyethylene (UHMWPE) debris was introduced into established air pouches on RANK(-/-) mice, followed by implantation of calvaria bone from syngeneic littermates. Wild type C57BL/6 (RANK(+/+)) mice injected with either UHMWPE or saline alone were included in this study. Pouch tissues were collected 14 days after UHMWPE inoculation for molecular and histology analysis. Results showed that UHMWPE stimulation induced strong pouch tissue inflammation in RANK(-/-) mice, as manifested by inflammatory cellular infiltration, pouch tissue proliferation, and increased gene expression of IL-1beta, TNFalpha, and RANKL. However, the UHMWPE-induced inflammation in RANK(-/-) mice was not associated with the osteoclastic bone resorption observed in RANK(+/+) mice. In RANK(+/+) mice subjected to UHMWPE stimulation, a large number of TRAP(+) cells were found on the implanted bone surface, where active osteoclastic bone resorption was observed. No TRAP(+) cells were found in UHMWPE-containing pouch tissues of RANK(-/-) mice. Consistent with the lack of osteoclastic activity shown by TRAP staining, no significant UHMWPE particle-induced bone resorption was found in RANK(-/-) mice. A well preserved bone collagen content (Van Gieson staining) and normal plateau surface contour [microcomputed tomography (microCT)] of implanted bone was observed in RANK(-/-) mice subjected to UHMWPE stimulation. In conclusion, this study provides the evidence that UHMWPE particles induce strong inflammatory responses, but not associated with osteoclastic bone resorption in RANK(-/-) mice. This indicates that RANK signaling is essential for UHMWPE particle-induced osteoclastic bone resorption, but does not participate in UHMWPE particle-induced inflammatory response.

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

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

The role of macrophages in osteolysis of total joint replacement

The osteolysis associated with conventional polyethylene on metal total joint replacements is associated with the formation of an inflamed periprosthetic membrane rich in macrophages, cytokines and implant-derived wear particles. There is a wealth of evidence to indicate that the presence and activation of macrophages in the periprosthetic tissues around joint replacements is stimulated by UHMWPE particles. Particles within the size range 0.1-1.0 microm have been shown to be the most reactive. Animal studies have provided increasing evidence that, of the milieu of cytokines produced by particle-stimulated macrophages, TNF-alpha is a key cytokine involved in osteolysis. Recent advances in the understanding of the mechanisms of osteoclastogenesis and osteoclast activation at the cellular and molecular level have indicated that bone marrow-derived macrophages may play a dual role in osteolysis associated with total joint replacement. Firstly, as the major cell in host defence responding to UHMWPE particles via the production of cytokines and secondly as precursors for the osteoclasts responsible for the ensuing bone resorption.

Proinflammatory mediator expression in a novel murine model of titanium-particle-induced intramedullary inflammation

Wear debris from total joint replacement prostheses is implicated in periprosthetic osteolysis and implant loosening. The pathophysiology of this biological process remains unclear. Animal models of particle-induced osteolysis have proven useful in the study of specific tissue responses to wear debris. However, existing in vivo murine models of particle-mediated inflammation do not permit analysis of cortical bone degradation. This study describes a murine model of particle disease using an intramedullary rod in the mouse femur to parallel the clinical situation. The model consists of placing a 10-mm-long Kirschner wire retrograde in both femurs of C57b1/6 male mice via a medial parapatellar arthrotomy. Phagocytosable titanium particles were also implanted unilaterally to replicate generation of wear debris. Mice were sacrificed at 2, 10, and 26 weeks and whole femurs were cultured for 72 h. Levels of interleukin-6, monocyte chemotactic protein-1, and macrophage colony stimulating factor were assayed by ELISA. Transverse histological sections, at the level of the implant, were taken and stained with hematoxylin and eosin (H&E). Results demonstrated increased expression of proinflammatory mediators at 2 weeks in femora with rod and particles compared to femora with rods alone. Destruction of the endosteum was evident at 2, 10, and 26 weeks in the femora with titanium. This novel murine model of particle-induced intramedullary inflammation may facilitate cost-effective genetic studies and offers investigators a simple, clinically relevant intramedullary model to readily examine the pathogenesis of particle-mediated periprosthetic osteolysis.

In vitro assessment of proximal polyethylene contact surface areas and stresses in mobile bearing knees

Wear of the polyethylene (PE) insert in total knee arthroplasty remains a significant problem. The generation of biologically active wear particles may ultimately affect implant longevity through osteolysis or premature/catastrophic PE failure. The rate and pattern of wear is influenced by many factors, including component geometry and individual loading conditions, which determine the contact surface area and kinematics of the reconstructed knee. Contact areas and stresses at the proximal femoral-PE insert interface and distal PE-tibial interface contact surface areas were measured in nine mobile bearing total knee designs at 0, 30, 60, 90 and 110 degrees of flexion at 3600 N (5 x body weight) using a standardized test method. Proximal and, to a lesser degree, distal interface contact area footprints decreased significantly with increasing flexion angle based on the conformity of the designs, resulting in a corresponding increase in the mean and peak stresses.

Modulation of bone ingrowth and tissue differentiation by local infusion of interleukin-10 in the presence of ultra-high molecular weight polyethylene (UHMWPE) wear particles

Interleukin-10 (IL-10) is a cytokine that plays a major role in suppressing the inflammatory response, particularly cell-mediated immunity that is characteristic of the TH1 response. The purpose of this study was to determine whether local infusion of IL-10 could mitigate the suppression of bone ingrowth associated with polyethylene wear particles. Drug test chambers were implanted in the proximal tibia of 20 mature New Zealand White rabbits. The DTC provided a continuous 1 x 1 x 5-mm canal for tissue ingrowth. After a 6-week period for osseointegration, the DTC was then connected to an osmotic diffusion pump. IL-10 at doses of 0.1-100 ng/mL (0.25 microL/h) was infused with or without ultra-high molecular weight polyethylene particles (0.5 +/- 0.2 microm diameter, 10(12) particles/mL) present in the chamber for a 3- or 6-week period. The tissue in the chamber was harvested after each treatment; sections were stained with hematoxylin and eosin for morphometric analysis. Osteoclast-like cells were identified by immunohistochemical staining using a monoclonal antibody directed against the alpha chain of the vitronectin receptor, CD51. Osteoblasts were identified using alkaline phosphatase staining. In dose-response studies, infusion of 1 ng/mL IL-10 yielded the greatest bone ingrowth in the presence of particles. The addition of polyethylene particles evoked a marked foreign body reaction and fibrosis; bone ingrowth was significantly suppressed (p = 0.0003). Bone ingrowth was increased by over 48% with infusion of IL-10 for the final 3 weeks of a 6-week ultra-high molecular weight polyethylene particle exposure compared with particles alone (p = 0.027). IL-10 is a cytokine that plays a major role in suppressing the inflammatory response, especially cell-mediated immunity that is characteristic of the TH1 response. Local infusion of immune-modulating cytokines such as IL-10 may prove to be useful in abating particle-induced periprosthetic osteolysis.

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

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

Interleukin-10 inhibits polymethylmethacrylate particle induced interleukin-6 and tumor necrosis factor-alpha release by human monocyte/macrophages in vitro

Periprosthetic membranes commonly observed at sites of total joint implant loosening exhibit abundant macrophages and particulate debris. Macrophages phagocytose orthopedic debris and release the pro-inflammatory mediators interleukin-1, interleukin-6, tumor necrosis factor-alpha, and prostaglandin E2. Populations of activated lymphocytes are often seen in periprosthetic membranes. These lymphocytes may modulate the monocyte/macrophage response to particulate debris and influence aseptic loosening. In addition, other immunologic agents, such as interleukin-10, are present in tissues harvested from the bone-implant interface of failed total joint arthroplasties. The present study examined the effects of interleukin-10 on polymethylmethacrylate (PMMA) particle challenged human monocyte/macrophages in vitro. Human monocyte/macrophages isolated from buffy coats of five healthy individuals were exposed to 1-10 microm PMMA particles. Interleukin-10 was added to the monocyte/macrophages with and without the addition of PMMA particles. Interleukin-10-induced alterations in monocyte/macrophage metabolism were determined measuring interleukin-6 and tumor necrosis factor-alpha release by the cells following exposure to PMMA particles. Exposure of the monocyte/macrophages to PMMA particles resulted in a dose-dependent release of interleukin-6 and tumor necrosis factor-alpha at 48 h. Interleukin-10 reduced the levels of interleukin-6 and tumor necrosis factor-alpha release by macrophages in response to PMMA particles in a dose-dependent manner. At 48 h, particle-induced interleukin-6 release was inhibited by 60 and 90% with 1.0 and 10.0 ng/ml treatments of interleukin-10, respectively. At 48 h, particle-induced tumor necrosis factor-alpha release was inhibited by 58 and 88% with 1.0 and 10.0 ng/ml treatments of interleukin-10, respectively. Interleukin-10 challenge alone did not significantly alter basal interleukin-6 or tumor necrosis factor-alpha release relative to control cultures. The data presented in this study demonstrate that the anti-inflammatory cytokine, interleukin-10, inhibits monocyte/macrophage release of the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor-alpha in response to PMMA particle challenge in vitro.

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.