Comparison of multinucleated cells elicited in rats by particulate bone, polyethylene, or polymethylmethacrylate

Bone matrix regulates osteoclast differentiation and annexin A8 gene expression

While attachment to bone is required for optimal osteoclast function, the molecular events that underlie this fact are unclear, other than that the cell requires adhesion to mineralized matrix to assume a fully differentiated phenotype. To address this issue, we cultured murine bone marrow-derived osteoclasts on either cell culture plastic or devitalized mouse calvariae to identify the distinct genetic profile induced by interaction with bone. Among a number of genes previously unknown to be expressed in osteoclasts we found that Annexin A8 (AnxA8) mRNA was markedly up-regulated by bone. AnxA8 protein was present at high levels in osteoclasts present in human tissues recovered from sites of pathological bone loss. The presence of bone mineral was required for up-regulation of AnxA8 mRNA since osteoclasts plated on decalcified bone express AnxA8 at low levels as did osteoclasts plated on native or denatured type I collagen. Finally, AnxA8-regulated cytoskeletal reorganization in osteoclasts generated on a mineralized matrix. Thus, we used a novel approach to define a distinct bone-dependent genetic program associated with terminal osteoclast differentiation and identified Anxa8 as a gene strongly induced late in osteoclast differentiation and a protein that regulates formation of the cell's characteristic actin ring.

Volumetric analysis of osteoclastic bioresorption of calcium phosphate ceramics with different solubilities

Commonly, to determine osteoclastic resorption of biomaterials only the resorbed area is measured. The depth of the resorption pit, however, may also be important for the performance of a material. To generate such data we used two calcium phosphate ceramics (Ca(10) and Ca(2)). The solubility of the materials was determined according to DIN EN ISO 10993-14. They were scanned three-dimensionally using infinite focus microscopy and subsequently cultivated for 4 weeks in simulated body fluid without (control) or with human osteoclasts. After this cultivation period osteoclasts number was determined and surface changes were evaluated two- and three-dimensionally. Ca(10) and Ca(2) showed solubilities of 11.0+/-0.5 and 23.0+/-2.2 mgg(-1), respectively. Both materials induced a significant increase in osteoclast number. While Ca(10) did not show osteoclastic resorption, Ca(2) showed an increased pit area and pit volume due to osteoclastic action. This was caused by an increased average pit depth and an increased number of pits, while the average area of single pits did not change significantly. The deduced volumetric osteoclastic resorption rate (vORR) of Ca(2) (0.01-0.02 microm(3)microm(-2)day(-1)) was lower than the remodelling speed observed in vivo (0.08 microm(3)microm(-2)day(-1)), which is in line with the observation that implanted resorbable materials remain in the body longer than originally expected. Determination of volumetric indices of osteoclastic resorption might be valuable in obtaining additional information about cellular resorption of bone substitute materials. This may help facilitate the development of novel materials for bone substitution.

The relative timing of exposure to phagocytosable particulates and to osteoclastogenic cytokines is critically important in the determination of myeloid cell fate

During granulomatous inflammatory reactions, myeloid cells can differentiate into activated phagocytic macrophages, wound-healing macrophages, foreign body giant cells, and bone-resorbing osteoclasts. Although it is appreciated that a variety of stimuli, including cytokines, cell-matrix interactions, and challenge with foreign materials can influence myeloid cell fate, little is known of how these signals integrate during this process. In this study, we have investigated the cross talk between receptor activator of NF-kappaB ligand (RANKL)-induced osteoclastogenesis and particle phagocytosis-induced activation of human monocytes. Understanding interconnected signals is of particular importance to disorders, such as periprosthetic osteolysis, in which granulomatous inflammation is initiated by particle phagocytosis in proximity to bone and leads to inflammatory bone loss. Using cell-based osteoclastogenesis and phagocytosis assays together with expression analysis of key regulators of osteoclastogenesis, we show in this study that phagocytosis of disease-relevant particles inhibits RANKL-mediated osteoclastogenesis of human monocytes. Mechanistically, phagocytosis mediates this effect by downregulation of RANK and c-Fms, the receptors for the essential osteoclastogenic cytokines RANKL and M-CSF. RANKL pretreatment of monocytes generates preosteoclasts that are resistant to RANK downregulation and committed to osteoclast formation, even though they retain phagocytic activity. Thus, the relative timing of exposure to phagocytosable particulates and to osteoclastogenic cytokines is critically important in the determination of myeloid cell fate.

Differentiation of activated monocytes into osteoclast-like cells on a hydroxyapatite substrate: an in vitro study

BACKGROUND

Hydroxyapatite surface coatings of dental implants have been introduced to obtain more rapid and complete osteointegration. A possible complication associated with hydroxyapatite implant surface is the release of particles. Those particles may be phagocytosed by monocytes, the first cells to colonize the inflammatory sites. The activated monocytes produce cytokines that could cause osteoclast activation.

METHODOLOGY

In order to establish the biological effect of particles released on monocyte differentiation to an osteoclast phenotype, we have used the murine monocyte/macrophage cell line, RAW 264.7 clone CRL-2278 cultured on a hydroxyapatite substrate. The direct action of hydroxyapatite on monocyte differentiation was examined using tartrate-resistant acid phosphatase (TRAP), immunohistochemistry and transmission electron microscopy (TEM) and Western Blot analysis.

RESULTS

The present study demonstrated that hydroxyapatite substrate might be able to induce a self-production of RANKL cytokine that directly stimulates a different behaviour in terms of phenotype expression from monocyte/macrophage lineage to mature and functional osteoclasts without the addition of exogenous factors.

CONCLUSIONS

These studies were designed to test a model in which osteoclasts could be formed from HA-activated monocytes via positive feedback elicited by RANKL, allowing for identification of innovative targets for therapeutic approaches.

Synthetic bone scaffolds and fracture repair

Synthetic scaffolding has been used in the treatment of bone defects and fractures for over 100 years. They remain a critical tool in the treatment of large-volume bone defects, and their role as potential substitues for human bone graft continues to expand. Various materials are used commercially to produce osteoconductive scaffolds including ceramics (both bioactive and bioinert) and select polymers, all of which offer distinct advantages and dissadvantages. While currently used principally as osteoconductive conduits for growth, the role of bone-graft substitues in fracture treatment is likely to change, as biomaterial research moves towards utilizing current and future scaffold materials as delivery systems for biologic fracture treatments.

The role played by cell-substrate interactions in the pathogenesis of osteoclast-mediated peri-implant osteolysis

Prosthetic wear debris-induced peri-implant osteolysis is a major cause of aseptic loosening after total joint replacement. In this condition, wear particles released from the implant components induce a granulomatous inflammatory reaction at the interface between implant and adjacent bone, leading to progressive bone resorption and loss of fixation. The present study was undertaken to characterize definitively the phenotype of osteoclast-like cells associated with regions of peri-implant focal bone resorption and to compare the phenotypic features of these cells with those of mononucleated and multinucleated cells associated with polyethylene wear particles. Peri-implant tissues were obtained from patients undergoing hip revision surgery for aseptic loosening after total joint replacement. Cells were examined for the expression of several markers associated with the osteoclast phenotype using immunohistochemistry, histochemistry, and/or in situ hybridization. CD68 protein, a marker expressed by multiple macrophage lineage cell types, was detected in mononucleated and multinucleated cells associated with polyethylene particles and the bone surface. Cathepsin K and tartrate-resistant acid phosphatase were expressed highly in both mononucleated and multinucleated cells associated with the bone surface. Levels of expression were much lower in cells associated with polyethylene particles. High levels of β₃ integrin protein were detected in cells in contact with bone. Multinucleated cells associated with polyethylene particles exhibited faint positive staining. Calcitonin receptor mRNA expression was detected solely in multinucleated cells present in resorption lacunae on the bone surface and was absent in cells associated with polyethylene particles. Our findings provide further evidence that cells expressing the full repertoire of osteoclast phenotypic markers are involved in the pathogenesis of peri-implant osteolysis after total joint replacement. They also demonstrate that foreign body giant cells, although believed to be phenotypically and functionally distinct from osteoclasts, express many osteoclast-associated genes and gene products. However, the levels and patterns of expression of these genes in the two cell types differ. We speculate that, in addition to the role of cytokines and growth factors, the substrate with which these cells interact plays a critical role in their differential phenotypic and functional properties.

Macrophagic response to human mesenchymal stem cell and poly(epsilon-caprolactone) implantation in nonobese diabetic/severe combined immunodeficient mice

Nonobese diabetic, severe combined immunodeficient (NOD/SCID) mice are extensively used to assess in vivo potentials for human cellular differentiation, development, and neophysiology. They are not only deficient in T and B cells, but also exhibit macrophage dysfunction and an absence of circulating complement. However, the survival of engrafted human mesenchymal stem cells (hMSCs) is limited and minimal mature bone tissue develops from implanted hMSCs in this model. The aim of the present study was to investigate the response to such implants in NOD/SCID mice. To this end, hMSCs genetically marked with enhanced green fluorescent protein, a biodegradable polymer, poly(epsilon-caprolactone) (PCL), and a bioconstruct incorporating the enhanced green fluorescent protein-labeled hMSCs with PCL after culture together for 3 weeks in vitro, were implanted into NOD/SCID mice and followed for up to 10 weeks. Monocytes/macrophages appeared to be the major invading cell type in all the implants and remained in the materials regardless of whether or not hMSCs were present over the time periods studied. When the hMSCs were implanted without the PCL scaffold, host macrophage invasion was also observed with the majority of hMSCs being eliminated within 2 weeks. Multinuclear giant cells or foreign body giant cells were seen in the cases of PCL implantation. These cells slowly infiltrated into the central core of the materials over a 10-week period of implantation with neutrophils and mast cells also being observed. In conclusion, in NOD/SCID mice, monocytes/macrophages still effectively respond to the implantation of xenografts and biopolymers with functional migration, phagocytosis, adhesion, foreign body recognition and formation of multinuclear giant cells, or foreign body giant cells. Thus, these animals still retain a level of innate immune responsiveness to these implantations and in addition may provoke a physiological environment that is unsuitable for extensive intramembranous ossification by engrafted hMSCs.

Ultrastructural cytochemical and ultrastructural morphological differences between human multinucleated giant cells elicited by wear particles from hip prostheses and artificial ligaments at the knee

The authors investigated the ultrastructural cytochemical features of multinucleated and mononuclear cells in periprosthetic tissues associated with bone resorption (osteolysis) and those in tissues adjoining failed artificial ligaments having no relation to bone resorption. Clinical specimens of granulation tissue of each type, respectively numbering 4 and 3, were stained for tartrate-resistant acid phosphatase (TRAP) reactions and examined by light and electron microscopy. Both periprosthetic granulation tissues and those adjoining artificial ligaments contained TRAP-positive multinucleated and mononuclear cells. Near joint prostheses, multinucleated cells, including some giant cells, showed TRAP activity and cytoplasmic features resembling osteoclasts, while others had features consistent with foreign-body giant cells, and still others showed degenerative changes. Near artificial ligaments, TRAP-positive multinucleated cells lacked osteoclastic features. At both sites, TRAP-positive multinucleated cells had phagocytised wear particles. TRAP-positive mononuclear cells at both sites also showed phagocytic cytoplasmic features, but not osteoclastic cytoplasmic features. Human mononuclear phagocytes and multinucleated giant cells induced by wear particles possess TRAP activity. Those multinucleated giant cells at sites of osteolysis developed osteoclastic cytoplasmic features and have a phagocytic function.

A preliminary report on the biocompatibility of photopolymerizable semi-interpenetrating anhydride networks

A new family of poly(anhydrides) (PA) has been developed which can be cured photochemically to produce degradable networks. These degradable anhydride networks may be useful in orthopaedics as bone cements and as matrices for drug delivery. This system, which is a semi-interpenetrating network (semi-IPN), has been evaluated for biocompatibility in subcutaneous tissue in rats and appears to undergo degradation primarily by surface erosion. The inflammatory response to the semi-IPN implants was minimal at both short (3 and 6 weeks) and long (28 weeks) time points and the fibrotic response was largely absent throughout the duration of this study. Furthermore, the OrthoCure implant material integrated well with the surrounding tissue and was invaded with vascularized connective tissue. For reference, linear PA controls were tested and showed a foreign body response culminating in the formation of relatively avascular fibrous capsule several cell layers thick, which became thicker over time, a response similar to what is typically observed in FDA approved implantable polymeric device systems.

Increase in expression of receptor activator of nuclear factor kappaB at sites of bone erosion correlates with progression of inflammation in evolving collagen-induced arthritis

OBJECTIVE

The receptor activator of nuclear factor kappaB (RANK)/RANK ligand (RANKL) pathway is critical in osteoclastogenesis and bone resorption and has been implicated in the process of focal bone erosion in arthritis. This study was undertaken to identify in vivo the hitherto-unknown origin and localization of RANK-expressing osteoclast precursor cells at sites of bone erosion in arthritis.

METHODS

DBA-1 mice were immunized with bovine type II collagen/Freund's complete adjuvant and were given an intraperitoneal booster injection of type II collagen on day 21. Arthritis was monitored visually, and joint pathology was examined histologically. RANK and RANKL expression were analyzed using specific immunohistochemistry, and tartrate-resistant acid phosphatase (TRAP) staining was performed. In addition, TRAP and cathepsin K messenger RNA expression were analyzed by in situ hybridization.

RESULTS

A marked increase in the number of cells expressing RANK correlated with the progression of synovial inflammation and clinical disease severity in evolving collagen-induced arthritis (CIA). Interestingly, RANK expression demonstrated a gradient pattern with increased numbers of RANK-positive cells within the synovial infiltrate in areas closer to periosteum and cortical bone. Cells expressing RANK included cells in synovial tissue, bone lining cells on the surface of trabecular bone at sites of erosion, and cells in periosteal areas adjacent to synovial inflammation. In areas where RANK-positive cells were abundant, TRAP-positive, multinucleated osteoclast-like cells were also present at sites of focal bone erosion, suggesting differentiation of synovially derived RANK-positive osteoclast precursor cells into osteoclasts. In addition, TRAP- and cathepsin K-double-positive osteoclast-like cells were detected on the synovial side of cortical bone at sites of early and advanced cortical bone erosion. Sites of RANK expression also correlated well with sites of RANKL expression, and there was a close correlation of the temporal expression of the receptor-ligand pair.

CONCLUSION

Cells expressing RANK increased in abundance with the progression of arthritis in evolving CIA, and sites of RANK-expressing cells correlated with sites of TRAP-positive, multinucleated osteoclast-like cells as well as with sites of RANKL expression. These data support the hypothesis that the RANK/RANKL pathway plays an important role in the process of bone erosion in CIA.

Pathogenesis of bone erosions in rheumatoid arthritis

Focal marginal joint erosions represent the radiographic hallmark of rheumatoid arthritis (RA). These bone changes are characteristically localized to the joint margins, but in addition, regions of focal bone resorption can be detected in the subchondral bone adjacent to the bone marrow space into which the synovial inflammatory tissues have extended. Because progressive destruction of the periarticular bone contributes significantly to joint dysfunction and disability in patients with RA, there is considerable interest in developing a better understanding of the pathologic mechanisms involved in this process and in developing therapies that can arrest these events. Previous analysis of joint tissues from patients with RA have provided morphologic evidence that osteoclasts are the cell types that mediate the focal bone resorption associated with the rheumatoid synovial lesion. Additional recent data from animal models have helped to further implicate these cells in the pathogenesis of focal bone erosions. Furthermore, analysis of RA synovium and joint tissues from animal models of inflammatory arthritis, as well as cell and tissues culture studies, have helped to define the cytokines and inflammatory mediators that are involved in the recruitment and activation of bone resorbing cells associated with focal bone erosions. These findings provide a rational framework for developing targeted therapies that can specifically inhibit or slow the progressive focal bone destruction associated with the rheumatoid synovial lesion.

Tissue responses to nacreous implants in rat femur: an in situ hybridization and histochemical study

The interface of bone and aragonite nacre (Margaritifera, fresh water pearl mussel) was studied by in situ hybridization and a tartrate-resistant acid phosphatase (TRAP) histochemical assay. Columnar implants were inserted into rat femora for 4, 7, 14, 28 and 56 days. In medullary region, a burst of transient bone formation was observed, which propagated from the periphery towards the nacre implant. A fused interface of bone and nacre was observed at 14 days. Later, the new medullary bone was resorbed and bone marrow was re-established while a thin layer of bone tissue remained covering the implant surface. Expressions of collagen alpha1(I), osteocalcin, osteopontin mRNAs and TRAP in the surrounding tissue were monitored. Correlated with the histology events, a strong transient induction of collagen alpha1(I) and osteocalcin mRNAs as well as TRAP expression, exhibiting a peak signal intensity on day 7 and subsequent down-regulation after day 14 was observed. Osteopontin mRNA, in contrast, was expressed continuously. The degrading nacre surface appeared in direct contact with macrophages and multinucleated giant cells at both days 14 and 28. These cells expressed osteopontin mRNA intensively and some TRAP enzyme activity occasionally.

Phagocytosis of new cementum-like islets formed inside the gingival connective tissue in cyclosporin-A treated rats

Three control and 3 experimental rats were administered vehicle or cyclosporin-A solutions. Animals were anaesthetized, tissues fixed and jaws processed for Epon inclusion. Histological examination of serially cut areas revealed the presence inside the gingival connective tissue of new cementum-like islets (NCLIs) associated to or engulfed by voluminous multinucleated cells (MCs). These complexes were located adjacent to blood vessels, at 250-350 microns from the root surface. Histomorphometric study indicated that the volume of the NCLIs varied from 3900 to 72,900 microns 3 and that of the MCs from 822 to 56,190 microns 3. The latter bore up to 14 nuclear profiles. Comparative evaluation of the NCLI-MC associations to other complexes "multinucleated cell(s)-resorbed material" seems to indicate that the phagocytosis of the NCLIs is dictated by their ectopic location, rather than their nature (new cementum-like structures). Therefore the MCs should be considered as foreign body giant multinucleated cells rather than cementoclasts.

Cloning of the murine beta5 integrin subunit promoter. Identification of a novel sequence mediating granulocyte-macrophage colony-stimulating factor-dependent repression of beta5 integrin gene transcription

We previously noted that the initial receptor by which murine osteoclast precursors bind matrix is the integrin alphav beta5 and that granulocyte-macrophage colony-stimulating factor (GM-CSF) decreases expression of this heterodimer by suppressing transcription of the beta5 gene. We herein report cloning of the beta5 integrin gene promoter and identification of a GM-CSF-responsive sequence. A 13-kilobase (kb) genomic fragment containing part of the beta5 gene was isolated by screening a mouse genomic library with a probe derived from the most 5'-end of a murine beta5 cDNA. A combination of primer extension and S1 nuclease studies identifies two transcriptional start sites, with the major one designated +1. A 1-kb subclone containing sequence -875 to + 110 is transcriptionally active in a murine myeloid cell line. This 1-kb fragment contains consensus binding sequences for basal (Sp1), lineage-specific (PU.1), and regulatable (signal transducer and activator of transcription) transcription factors. Reflecting our earlier findings, promoter activity is repressed in transfected myeloid cells treated with GM-CSF. Using deletion mutants, we localized a 109-base pair (bp) promoter region responsible for GM-CSF-inhibited beta5 transcription. We further identified a 19-bp sequence within the 109-bp region that binds GM-CSF-induced nuclear proteins by gel shift/competition assays. Mutation of the 19-bp sequence not only ablates its capacity to bind nuclear proteins from GM-CSF-treated cells, in vitro, but the same mutation, when introduced in the 1-kb promoter, abolishes its ability to respond to GM-CSF treatment. Northern analysis demonstrates that cycloheximide treatment abrogates the capacity of GM-CSF to decrease beta5 mRNA levels. In summary, we have identified a 19-bp cis-element mediating GM-CSF-induced down-regulation of beta5 by a mechanism requiring protein synthesis.

Histopathological study of a newly developed root canal sealer containing tetracalcium-dicalcium phosphates and 1.0% chondroitin sulfate

We studied the possibility of the clinical use of a calcium phosphate-type newly developed sealer composed of tetracalcium phosphate, dicalcium phosphate dihydrate, and a modified McIlvain's buffer solution (TDM). Another sealer using the buffer solution, to which 2.5% chondroitin sulfate was added to promote wound healing (TDM-S), was also studied. TDM and TDM-S were histopathologically compared with another type of calcium phosphate sealer (ARS), which is commercially available in Japan, in the dorsal subcutaneous tissue and in the periapical tissue of rats. TDM and TDM-S caused no inflammatory reactions in the subcutaneous tissue. The periapical tissue reacted mildly to them. ARS caused severe inflammatory reactions in both the subcutaneous and the periapical tissue. These results indicate that TDM-S has excellent histocompatibility and potential as a root canal sealer.

Tissue ingrowth and differentiation in the bone-harvest chamber in the presence of cobalt-chromium-alloy and high-density-polyethylene particles

Particulate wear debris from joint replacements has been implicated in the etiology of periprosthetic bone resorption. However, the effect of high-density-polyethylene or cobalt-chromium-alloy particles on osteoclastic bone resorption in vivo has not been studied previously, to our knowledge. Therefore, we examined the effect of these particles on tissue ingrowth, net bone formation (per cent trabecular bone), and osteoclastic bone resorption (osteoclasts per unit of bone surface) with use of a bone-harvest chamber that had a transverse one-millimeter channel for tissue ingrowth. After an initial six-week period for incorporation of the chamber into the proximal part of the tibia of rabbits, the contents of the channel were harvested repeatedly at three-week intervals. The carrier solution, 1 per cent sodium hyaluronate, was implanted first. In subsequent implantations, the hyaluronate was mixed with high-density-polyethylene or cobalt-chromium particles at concentrations of 10(8) particles per milliliter. The tissue harvested from the chambers that contained no particles was composed of longitudinally oriented trabecular bone in a fibrovascular stroma. Particulate high-density polyethylene evoked a moderate foreign-body reaction and a chronic inflammatory response and decreased net bone formation. When cobalt-chromium particles had been implanted, the tissue exhibited a more florid foreign-body reaction and a chronic inflammatory response, often in a nodular arrangement, in a background of dense connective tissue. Bone was sparse, and areas of cell necrosis and hyaline degeneration were noted. Histomorphometric analyses were carried out to determine the amount of net bone formation and osteoclastic bone resorption in the presence or absence of high-density-polyethylene or cobalt-chromium particles. The amount of bone was greatest in the control specimens, moderately decreased in the presence of high-density-polyethylene particles, and greatly decreased in the presence of cobalt-chromium particles. The number of osteoclasts in Howship lacunae per unit of trabecular bone surface was increased in the presence of high-density polyethylene, indicating that these particles stimulate osteoclastic bone resorption.

Multinucleated giant cells elicited around hydroxyapatite particles implanted in craniotomy defects are not osteoclasts

BACKGROUND

The nature of the multinucleated giant cells (MNGC) elicited in contact with implantable biomaterials is still indecisive.

METHOD

In Wistar rats the MNGC recruited after the implantation of hydroxyapatite (HA) particles in standardized skull defects were examined morphologically (at both the light and electron microscope levels), enzymatically (tartrate-resistant acid phosphatase and non-specific esterase), and after a challenge with salmon calcitonin.

RESULTS

The MNGC were of great size and contained abundant mitochondria, vacuoles, and vesicles throughout the cytoplasm; they were either tightly apposed to the HA surface or had long and thin processes penetrating the material. When processed for tartrate-resistant acid phosphatase, only a few cells were weakly stained. The staining was totally suppressed when samples were pretreated with cyanuric chloride in the MNGC but not in the host osteoclasts. Calcitonin induced the withdrawal of the host osteoclasts from the bone surface while the MNGC remained in contact with the HA material.

CONCLUSION

The MNGC recruited to HA particles did not exhibit the morphologic, enzymatic and functional characteristics of the osteoclasts, and consequently must be regarded as macrophage polykaryons.

Histological, histocytochemical and ultrastructural study on the effects of surface charge on bone formation in the rabbit mandible

The osteogenic potential of different surface charges was studied by implanting uncharged, negatively changed and positively charged Sephadex beads subperiosteally on the buccal aspect of the mandible. The implant sites were examined 1, 2, and 4 weeks later. New bone formation was observed around the positively charged beads at 2 weeks. An amorphous collagen-free layer seen around the beads consisted of anionic substances and contained needle-like crystals. Tartrate-resistant acid phosphatase-positive, multinucleated giant cells, which had typical fine structural characteristics of osteoclast-like ruffled borders and a clear zone, were observed on the surface of positively charged beads, with osteoblastic cells juxtaposed to them. Bone formation was still going on at 4 weeks in this group. Around the uncharged or negatively charged beads, new bone formation and osteoclast-like cells were not observed at any time. The findings suggest that the surface charge of implant materials has a definite influence on the differentiation of osteoclastic cells and subsequent occurrence of osteoblastic cells leading to formation of bone.

Effects of particulate high-density polyethylene and titanium alloy on tissue ingrowth into bone harvest chamber in rabbits

The purpose of this study was to determine whether small, phagocytosable particles of titanium alloy (Ti) and high-density polyethylene (HDPE) have an adverse effect on bone ingrowth. The bone harvest chamber (BHC) was implanted bilaterally in the proximal tibial metaphysis of six mature rabbits. The BHC has a transverse 1-mm wide pore providing a continuous canal through the chamber for tissue ingrowth. After an initial 6-week period for osseointegration of the BHC, the contents of the canal were harvested repeatedly at 3 weekly intervals. This could be done with the chamber in place, without disturbing its exterior surface or the surrounding bone. The carrier solution, 1% sodium hyaluronate (Healon) was implanted first. In subsequent implantations, Healon was mixed with particles of HDPE or Ti averaging 4.7 +/- 2.1 and 3.0 +/- 2.6 microns, respectively. The contralateral chamber was left empty and served as a control. The chambers were harvested repeatedly, alternating experimental and control sides. The sections from the control side, and those containing Healon alone demonstrated extensive trabecular bone in a fibrovascular stroma. The sections containing Ti alloy particles were qualitatively and quantitatively similar to the control sections and those containing Healon, except for the presence of small black granules of Ti alloy, dispersed in the fibrovascular stroma or phagocytosed by scattered macrophages. The sections containing HDPE particles were infiltrated and engulfed by mononuclear and multinuclear histiocytic cells in a highly fibrous stroma. The majority of the multinucleated cells present were interpreted as being foreign body giant cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Osteoclast 121F antigen expression during osteoblast conditioned medium induction of osteoclast-like cells in vitro: relationship to calcitonin responsiveness, tartrate resistant acid phosphatase levels, and bone resorptive activity

Osteoclast differentiation from hematopoietic precursors into multinucleated cells uniquely capable of removing the organic and inorganic components of bone matrix occurs in multistep process, during which osteoclasts acquire the specialized characteristics necessary for bone resorptive activity and physiological regulation. Among those traits is a novel plasma membrane glycoprotein, reactive with the anti-osteoclast monoclonal antibody 121F, which is expressed during the course of osteoclast differentiation, shares structural and functional homologies with Mn2+/Fe2+ superoxide dismutase, and has been hypothesized to protect the osteoclast from the damaging effects of superoxide radicals generated during active bone resorption. We have reported previously that the expression of this membrane antigen is induced on multinucleated giant cells when the prefusion marrow mononuclear cells are cultured in conditioned medium from avian calvaria. The studies reported here were designed to investigate the relationship between expression of the 121F antibody-reactive osteoclast membrane antigen and tartrate resistant acid phosphatase levels, bone resorptive activity, calcitonin responsiveness, and ultrastructural features of avian bone marrow-derived multinucleated giant cells formed either in the presence or absence of diffusible osteoblast secreted factors. Parallel analyses of in vivo formed osteoclasts isolated from the same animals were performed for direct comparisons. In this report we demonstrate: (1) that the 121F monoclonal antibody-reactive osteoclast membrane antigen is stably induced in giant cells by soluble osteoblast-derived factors in a species nonrestricted but concentration- and temporal-dependent manner; (2) that osteoblast-mediated antigen induction is reflected in both increased numbers of cells and elevated expression of individual cells that are reactive with the 121F antibody, as determined by ELISA and histomorphometry; (3) that osteoblast conditioned medium, in addition to inducing this antigen in bone marrow cells, also elevates other defining osteoclast characteristics in these avian giant cells including their TRAP activity, cell retraction from the bone surface in response to calcitonin, bone resorptive function, and expression of a series of additional osteoclast antigenic markers; and (4) that secreted osteoblast products alone do not raise the levels of these traits for in vitro formed marrow giant cells to the extent associated with in vivo formed osteoclasts. Therefore, osteoblast soluble factors alone appear unable to promote the full differentiation of bone marrow cells in vitro into mature bone-resorbing osteoclasts.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of osteocytes on osteoinduction in the autogenous rib graft in the rat mandible

In order to clarify the influence of cell death of osteocytes on osteoinduction after bone grafting, autogenous fresh ribs, bone-marrow-removed fresh ribs, and frozen devitalized ribs were grafted after removal of the periosteum in a bridge manner in the rat mandible, and the process of bone remodeling was studied histologically, histochemically, and ultrastructurally in the central portion of the grafts. In the fresh bone group, osteocytes maintained normal morphology and grafted bones were undergoing resorption by osteoclasts with ruffled borders and strong tartrate-resistant acid phosphatase (TRACP) activity on the fifth day (Day 5). Alkalinephosphatase (ALP)-positive osteoblast-like cells were observed in close proximity of the osteoclasts. On Days 7 to 9, new bone formation occasionally accompanied by newly formed cartilage was observed in the grafted bones, and by Day 14, the majority of the grafted bones had been replaced by newly formed bone. In the marrow-removed fresh bone group, bone resorption by TRACP-positive cells and new bone formation similar to those seen in the fresh bone group were observed on Day 10. In the frozen devitalized bone group in which osteocytes had undergone necrosis, bone resorption and new bone formation were not observed even on Day 84, and grafted bones became surrounded by fibrous tissues. The TRACP activity was very weak and no ruffled border was observed ultrastructurally in multinucleated giant cells seen on Day 14. In conclusion, immediate bone resorption by osteocytes is essential for osteoinduction in the bone graft, and living osteocytes in the graft play an important roll in the differentiation and activation of osteocytes.

The effects of micromotion and particulate materials on tissue differentiation. Bone chamber studies in rabbits

Motion at the interface between bone and implants for joint replacement may interfere with osseointegration and prosthesis stabilization. Particulate materials may cause foreign body and chronic inflammatory reactions resulting in bone resorption (osteolysis). The micromotion chamber (MC) and the bone harvest chamber (BHC) were implanted in the rabbit tibia, and the effects of micromotion and phagocytosable particulate materials on tissue formation within the chamber were assessed by studying bone ingrowth into a 1-mm pore. Using the MC, one short daily episode of motion (20 cycles/day, 0.5 mm amplitude) for three weeks decreased the amount of bone ingrowth. Using a different pore configuration, the same parameters of motion increased bone ingrowth. Increasing the amplitude of motion (from 0.5 to 0.75 mm), or the number of daily motion periods (from one to two per day) then decreased bone ingrowth. These studies suggest the existence of a window of externally applied strain: a small stimulus may facilitate and a large stimulus may discourage bone formation within the chamber. Cessation of a given set of motion parameters (producing primarily fibrous tissue) for an additional three weeks was accompanied by tissue differentiation into bone. Using the BHC, small, phagocytosable particles of bone cement, high density polyethylene and cobalt chrome alloy, at a concentration of 1.0 x 10(8) particles/mL, caused a foreign body reaction and inhibited the ingrowth of bone. Particles of titanium alloy had no effect on net bone formation. In studies using normal and immunodeficient rats, T lymphocytes were not a prerequisite for macrophages to phagocytose polyethylene particles. In the clinical situation, micromotion and particulate debris may be synergistic in producing prosthetic loosening. If an implant does not undergo osseointegration due to excessive micromotion, the fibrous tissue interface may provide a conduit for the subsequent migration of particles around the implant.

Biocompatibility and resorbability of a polylactic acid membrane for periodontal guided tissue regeneration

The biocompatibility and degradation processes of biomembranes made of a mixture of a high molecular weight racemic polylactic acid (PLA50P) with 0, 10, 20 and 30% w/w racemic polylactic acid oligomers (PLA50p) were assessed for morphological changes in subcutaneous abdominal membrane implantations after 15, 21, 30 and 60 d in 45 Wistar rats. These membranes, prepared for periodontal guided tissue regeneration, showed excellent tissue tolerance without an inflammatory reaction. The higher the content in low molecular weight polylactic acid, the higher the degradation rate. At 60 d, the resorption process was almost complete. This process was initiated by outgrowths of short vascular septa, which developed into lobular networks infiltrating the membranes, which were progressively replaced by normal fibrous connective tissue.

Human gingival tissue response to HTR polymer

Biopsies secured during reentry surgical evaluation of previously treated periodontal osseous defects were examined for gingival tissue response to HTR polymer. Eleven patients provided biopsies of HTR grafted sites 6-7 months after initial implantation. Minimal inflammation and infrequent foreign body giant cells were found. Bone was present in about half of the samples and osteogenesis associated with the HTR graft material was seen in about 20% of the biopsies. Serendipitously, biopsies of other graft materials or debridement only sites from 6-30 months post-treatment were also available for analysis and comparison, and showed similar tissue response. The results of this study suggest that HTR polymer (and other graft materials) is very biocompatible and elicits no untoward gingival tissue responses when placed in periodontal osseous defects.

Ultrastructural and ultracytochemical characteristics of multinucleated cells after hydroxyapatite implantation into rat periodontal tissue

Multinucleated cells (MNCs) that appeared after hydroxyapatite (HAP) implantation into experimentally-produced bone defects in rat periodontal tissues were investigated both ultrastructurally and ultracytochemically. At day 5 after implantation, MNCs first appeared along the HAP surface. They had no features of typical osteoclasts such as ruffled border and clear zone. By d 14, these cells acquired features similar to osteoclasts, including ruffled border and clear zone. With the appearance of ruffled borders in MNCs, new bone deposited around the implanted HAP. MNCs appeared to excavate both newly-formed bone and implanted HAP simultaneously. Ingested HAP particles were observed not only in MNCs but also in macrophages. MNCs contained both tartrate-resistant acid phosphatase (ACPase) and carbonic anhydrase (CAase). ACPase activity was detected along all the biosynthesizing pathways in MNCs. Extracellular ACPase activity around the ruffled border region was also demonstrable. CAase activity could be detected only in the cytosol, vesicles and mitochondrial cristae of the MNCs. These cytochemical characteristics were almost the same regardless of the time elapsed after implantation.

The biologic responses to orthopedic implants and their wear debris

The use of artificial materials in the treatment of orthopaedic conditions, most notably arthritis, over the past few decades has been increasing dramatically. Such use makes an understanding of the tissue responses to the various materials necessary to determine their effectiveness and acceptability. This review concentrates on the studies of the biological responses to the materials that are used mainly in joint replacements and fixation of fractures. In-vivo and in-vitro experimental studies of various metals, polymers and ceramics and their constituents are first presented with discussions regarding their clinical importance. Studies of clinically successful implants are then presented to illustrate the expected morphological features of incorporation and acceptance by the host tissues. The local and systemic effects complicating the use of the implanted materials as well as the failure of the implant are then presented.

Ultrastructural demonstration of the importance of crystal size of bioceramic powders implanted into human periodontal lesions

Stages in bone formation were studied ultrastructurally after the implantation of the following 3 bioceramic powders into human periodontal lesions: (1) beta-tricalcium phosphate whitlockite (Synthograft) consisting of particles with a mean length of 229 +/- 87 microns in SEM and appearing in TEM as crystals with a mean diameter 488 +/- 192 nm; (2) an hydroxyapatite (Bioapatite) which consisted of particles with a mean length of 283 +/- 87 microns in SEM and of crystals with a mean diameter of 146 +/- 47 nm in TEM; and finally (3), a microsized hydroxyapatite consisting of elongated platelets with a mean length of 32 +/- 4 microns in SEM, composed of small crystals with a mean diameter of 38 +/- 16 nm in TEM. In a preliminary experiment in rats, it appeared that the microsized hydroxyapatite implanted into the alveolar region after first molar extraction exhibited biocompatibility. In 6- and 12-month biopsies, it appeared that bone formation in association with the 3 bioceramics tested in human periodontal lesions occurred through similar mechanisms at the ultrastructural level. After the appearance of peripheral fibroblast-like or osteoblast-like cells with an interposed layer reminiscent of an osteoid tissue, collagen fibrils were observed in the intercrystalline spaces. These spaces subsequently underwent mineralization, with deposition of bone apatite crystals followed by the peripheral deposition of a thin inner bone layer with a granular appearance and an outer normal bone layer of either woven bone, lamellar bone or bone with parallel calcified collagen fibrils. These bone nodules, however, formed around the bioceramic particles at highly variable time intervals. Bone formation was observed around Synthograft and Bioapatite implants only in 12-month biopsies, and thicker layers of peripheral bone were observed with the latter hydroxyapatite implant. With microsized hydroxyapatite, a significant amount of peripheral bone formation had already occurred by 6 months, strongly suggesting an important effect of crystal size on bone formation.

Morphological and histochemical comparison of the cells elicited by ectopic bone implants and tibial osteoclasts

Pellets of mineralized and demineralized bone and a composite mixture of mineralized and demineralized, devitalized bone particles were implanted subcutaneously on the dorsal body wall of young adult rats. Two weeks post-implantation, the pellets were removed and processed for histochemical and morphological analyses. Rat proximal tibia was also processed for evaluation. The levels of tartrate-resistant acid phosphatase (TRAP) activity in the multinucleated giant cells (MNGCs) from each of the three implants and from osteoclasts were assessed using an image analyzer. The osteoclasts from the proximal tibia and the majority of MNGCs from the demineralized implants demonstrated high levels of TRAP activity. MNGCs from the mineralized implants showed either a low level or absence of TRAP activity. Most MNGCs from the composite implants exhibited a low level of TRAP activity; however, there was a population of cells that demonstrated a high level of reaction product, similar to that seen in the tibia and demineralized implant. Morphologically, osteoclasts from the proximal tibia and from the osteogenic demineralized implant exhibited ruffled borders. A small population of MNGCs from the composite implant also revealed osteoclastic features. In summary, MNGCs from the mineralized implant did not exhibit a level of TRAP reaction product or morphology similar to osteoclasts, while the majority of cells from the demineralized implant and a subpopulation of the MNGCs elicited by the composite implant did demonstrate TRAP expression and morphology similar to osteoclasts. The expression of osteoclastic characteristics in cells at an ectopic site may be dependent on accessory signals from the skeletal microenvironment; such signals appear to be absent from or incomplete in the mineralized implants but appear to be present when demineralized bone particles are implanted.

Normal bone particles are preferentially resorbed in the presence of osteocalcin-deficient bone particles in vivo

In an in vivo model of osteoclastic bone resorption, we previously showed that osteocalcin-deficient bone particles (BPs), derived from warfarin-treated rats, were resorbed 50% as well as normal BPs and that they recruited fewer osteoclastic cells with decreased tartrate-resistant acid phosphatase (TRAP) activity. In order to determine the specificity of the resorption response, we evaluated the fate of implanted mixtures of normal and osteocalcin-deficient BPs. Normal and warfarin-treated donor rats were prelabeled in vivo with oxytetracycline to permit identification of BPs from either source. Normal, osteocalcin-deficient, and 50:50 mixtures of BPs (either labeled or unlabeled) were implanted into normal rats and recovered 12 days later for enzymatic (TRAP) and nondecalcified histomorphometric analyses. The incorporated oxytetracycline had no significant effect on resorption of bone particles. The recovered osteocalcin-deficient BPs were surrounded by fewer osteoclastic cells, were resorbed less, and contained less extractable TRAP activity than normal BPs. In mixed BP implants with normal and osteocalcin-deficient BPs, each type of bone particle elicited the same tissue response as when implanted separately. Remarkably, the different particles evoked dissimilar osteoclastic responses and were resorbed to different extents, even when adjacent within the same implant. These data suggest that osteocalcin may act as a substrate signal for resorption and that osteocalcin in the normal BPs does not influence the cellular response to adjacent osteocalcin-deficient BPs.

The giant cells recruited by subcutaneous implants of mineralized bone particles and slices in rabbits are not osteoclasts

We have compared structural and functional characteristics of native osteoclasts and the multinucleated giant cells (MNGC) recruited by subcutaneous implants of mineralized bone particles and slices in normal rabbits. Weekly evaluation of the implants for 5 weeks showed distinct differences between MNGC and osteoclasts in the host with respect to morphology and the ability to stain for tartrate-resistant acid phosphatase and acid ATPase. An osteoclast-specific monoclonal antibody bound strongly to osteoclasts but not MNGC. Ground bone slices similarly implanted were surrounded by MNGC but did not show resorption pits by scanning electron microscopy. These data show that the MNGC recruited to subcutaneous implants of mineralized bone particles and slices lack the enzymatic, cell surface, and functional features of osteoclasts.

A role for osteocalcin in osteoclast differentiation

Specific cellular interactions with components of the extracellular matrix can influence cellular differentiation and development of many tissues. The extracellular matrix of bone is composed of organic constituents and a solid phase of calcium and inorganic phosphate (apatite). When implanted subcutaneously in rats, particles of bone matrix (BPs) recruit progenitors that differentiate into multinucleated cells with osteoclastic features. Because BPs deficient in osteocalcin, a bone matrix protein, were less efficient at promoting osteoclast formation than were normal BPs, we directly examined the influence of osteocalcin on osteoclast differentiation. We evaluated tissue responses to particles of synthetic crystalline apatite alone (Ap), having many of the features of native apatite of mature bone, or to apatite prepared with osteocalcin (Ap/OC), bovine serum albumin (Ap/BSA) or rat bone collagen (Ap/Col). Twelve days after subcutaneous implantation in normal rats, Ap, Ap/BSA, and Ap/Col particles generated a mild foreign body reaction with multinucleated cells in direct contact with the particles; these cells were negative for tartrate-resistant acid phosphatase (TRAP) activity and lacked ruffled borders. In contrast, Ap particles containing approximately 0.1% osteocalcin were partially resorbed and they generated more multinucleated cells that were TRAP-positive, were immunoreactive with an antibody against tartrate-resistant purple acid phosphatase, and displayed ultrastructural features of active osteoclasts including ruffled borders and clear zones. These data support the hypothesis that osteocalcin may function as a matrix signal in the recruitment and differentiation of bone-resorbing cells.

Bone particles from gallium-treated rats are resistant to resorption in vivo

Gallium nitrate is a clinically effective agent for the treatment of cancer related hypercalcemia. The mechanism of action of this agent was investigated following development of a quantitative in vivo bone resorption assay modified from the method of Glowacki. In a preliminary study, the time course of resorption of 50 mg subcutaneous implants of bone powder in growing rats was followed by chemical analysis of mineral (ash and Ca) contents, enzymatic and histochemical assay of tartrate resistant acid phosphatase (TRAP) activity, and image analysis of changes in particle size using von Kossa stained sections. Day 21 was chosen as a single time point for the comparison of the extent of resorption of gallium-containing and control bone particles. Resorption of bone particles containing 0.39 micrograms Ga/mg bone was significantly inhibited relative to control particles. Mineral content (6.7 vs. 3.6 mg), Ca content (1.72 vs. 1.37 mg), and the percentage of the field covered by bone particles (12 vs. 9%) were greater in the animals which received gallium-containing bone particles. Similarly, the number of osteoclast-like cells and the TRAP activity in the gallium-containing bone particle implants at 21 days were increased relative to controls. These data indicate that gallium incorporation into bone matrix confers resistance to resorption.

Osteoclasts: structure and function

Osteoclasts are multinucleated giant cells showing specialized membrane structures, clear zones and ruffled borders, which are responsible for the process of bone resorption. These cells arrive at the resorption site via the bloodstream as mononuclear cells, derived from haemopoietic precursors in the spleen or bone marrow, which fuse prior to resorption. The osteoclast may share an early progenitor cell, the granulocyte macrophage colony-forming unit (GM-CFU) with monocytes, macrophages and granulocytes, implying that osteoclasts share the pluripotent haemopoietic stem cell with all other haemopoietic cells. In the past, elucidation of the structure of these cells relied upon traditional ultrastructural techniques. Transmission electron microscopic studies revealed details of the unique ultrastructure of these cells and, in combination with stereological techniques, showed the response of cells to various hormonal stimuli. Scanning electron microscopy not only demonstrated the surface appearance of osteoclasts, and their predilection for spreading on various substratum components, but has also been used as an adjunct in resorption assays in which areas of resorption lacunae are measured as indicators of cell activity. Recent advances in fields such as immunocytochemistry and freeze fracture techniques have contributed towards a more detailed delineation of antigenic profile, cytoskeletal structure and localization of enzymatic pathways. The osteoclast is subject to extensive regulatory mechanisms and it has been established that the osteoblast plays a major rôle in mediating the effects of osteotropic hormones and local mediators on these cells. Hence, research aimed at elucidating the coupling mechanisms between these two cells may result in new therapies for bone disease.

Quantification of tartrate resistant acid phosphatase activity using a computerized image analysis system

Tartrate resistant acid phosphatase (TRAP) has been accepted as a marker for identification of osteoclasts. A method is reported here for quantitating TRAP using an image analysis system. The amount of the enzyme specific to osteoclasts can be used to differentiate osteoclasts from other cells capable of TRAP expression. TRAP expression characteristic of the osteoclast was compared with that of multi-nucleated giant cells (MNGC)s recruited to the site of subcutaneously implanted mineralized bone matrix. Two weeks post-implantation, the pellets were removed and processed for the demonstration of TRAP along with rat proximal tibiae. A large amount of TRAP was consistently expressed by the in situ osteoclasts. The MNGCs associated with the mineralized bone implants expressed little if any TRAP reaction product. Using this system, the amount of TRAP reaction product or any other enzyme reaction product expressed can be objectively and reproducibly quantitated.

Comparison of bone and parathyroid hormone as stimulators of osteoclast development and activity in calvarial cell cultures from normal and osteopetrotic (mi/mi) mice

Osteoclast development was studied in cell cultures prepared from calvaria of neonatal osteopetrotic (mi/mi) mice or their normal littermates, using tartrate-resistant acid phosphatase (TRAPase), as an osteoclast marker. In cultures from normal mice, treatment with 10 nM PTH for 4-5 days stimulated the formation of osteoclasts. However in cultures from mi/mi mice, this response was only 7% +/- 5% that of normal mice and they were significantly smaller than osteoclasts of normal mice. Mineralized bone particles elicited osteoclast development in cultures from both normal and mi/mi mice, and osteoclast size was identical for both genotypes. Seventy-eight to 96% of the TRAPase-positive cells bound 125I-CT, as demonstrated by autoradiography. 125I-CT binding characteristics were identical in cultures from both genotypes treated with bone particles, exhibiting a Kd of 3.3-3.6 x 10(-10) M. Addition of PTH stimulated 45Ca release from the added bone particles only in the case of cultures prepared from normal mice, and CT inhibited this response. Cells from normal mice were capable of excavating bone from the surface of smooth cortical bone wafers, but such excavations were rarely seen in the case of calvarial cells from mi/mi mice. Thus, PTH-driven differentiation of osteoclasts is arrested in calvarial cell cultures from mi/mi mice, but mi/mi preosteoclasts retain the ability to express certain osteoclast markers in response to bone derived signals. We hypothesize that the lack of activity of mi/mi osteoclasts is due to the failure of mi/mi preosteoclasts to respond appropriately to resorptive agents, or to cytokines elicited by these agents.

Recombinant murine interferon-gamma inhibits the fusion of mouse alveolar macrophages in vitro but stimulates the formation of osteoclastlike cells on implanted syngeneic bone particles in mice in vivo

Osteoclasts are multinucleated cells that originate from the fusion of mononuclear precursors and are responsible for bone resorption. Indirect evidence from in vitro studies suggests that IFN-gamma and TNF-alpha inhibit and stimulate bone resorption, respectively, but contradictory results have emerged from the literature regarding the effects of IFN-gamma on macrophage multinucleation. Using highly sensitive model systems, the present work demonstrates that, in mice, rMuIFN-gamma inhibits the fusion of alveolar macrophages in vitro but augments the number of osteoclastlike cells on implanted syngeneic bone particles in vivo. Although rMuTNF-alpha fails to stimulate macrophage multinucleation in either system, treatment of implanted animals with rMuIFN-gamma appears to limit the inflammatory reaction and favor tissue repair.

Correlation of an osteoclast antigen and ruffled border on giant cells formed in response to resorbable substrates

The osteoclast is the specialized multinucleated cell primarily responsible for the degradation of the organic and inorganic components of bone matrix. The functional and developmental relationship between osteoclasts and foreign body giant cells is unclear. The osteoclast plasma membrane ruffled border juxtaposed to the bone surface is a unique morphologic characteristic of active osteoclasts. In the studies reported here giant cell formation was induced in response to a variety of materials implanted onto the richly vascularized chick chorioallantoic membrane. Light and electron microscopic techniques were used to examine the morphologic characteristics of the giant cells. In addition, immunohistochemical methods were used to demonstrate the appearance of a 150 kD cell surface antigen on chicken osteoclasts recognized by monoclonal antibody 121F. Giant cells that formed in response to mineralized bone particles exhibited ruffled borders and stained positively with the 121F antibody. Many giant cells that formed in response to hydroxyapatite possessed ruffled borders similar to but not as extensive as those observed on giant cells formed on bone. Immunohistochemical localization of the 121F antigen on these cells suggested that the antigen was present, but staining intensity was reduced compared to that of bone-associated giant cells. The formation of mineral matrix complexes by the adsorption to hydroxyapatite of bone extract or osteocalcin enhanced ruffled borders and the presence of the 121F antigen on elicited giant cells. In contrast, giant cells that formed on non-resorbable materials, such as Sepharose beads, mica, and methacrylate, lacked ruffled borders and were negative for the 121F antigen. It appears that expression of the 121F osteoclast antigen correlates with the appearance and extent of ruffled membranes on giant cells. Furthermore, it appears that giant cell ruffled membrane development and the presence of the 121F osteoclast antigen are related to giant cell formation in response to resorbable materials that are subject to extracellular dissolution. Expression of this antigen may be indicative of the developmental and/or functional state of giant cells (osteoclasts) that form on resorbable substrates. In addition, components of the bone matrix, including osteocalcin, in association with bone mineral, lead to elevated levels of this osteoclast antigen.

Formation of multinucleated cells with osteoclast precursor features in human cord monocytes cultures

A common lineage between monocytes and osteoclasts has been suggested but not yet proved, and an osteoclast precursor might be an immature cell of the monocyte-macrophage family. We therefore compared the ability of cord blood and adult monocytes in long-term culture to differentiate toward osteoclasts. Both adult and cord monocytes were cultured for 3 weeks in the presence of 20% horse serum. The proportion of multinucleated cells formed was influenced by 1,25(OH)2D3 in cord, but not in adult monocyte cultures: 10(-9)M 1,25(OH)2D3 increased multinucleated cells from 13 +/- 2 to 26 +/- 1% of total cells in cord monocyte cultures. The formation of multinucleated cells in cord monocyte cultures, in the presence of 10(-9) M 1,25(OH)2D, was decreased by salmon calcitonin (dose dependently from 10(-8) to 10(-6) M) and increased by 1-34 parathormone (100 ng/ml). None of these hormones induced any modification of the proportion of multinucleated cells formed in adult monocytes culture. Specific antigens on the membrane of the cells obtained after 3 weeks culture in the presence of 10(-9) M 1,25(OH)2D3 were assessed by immunocytochemistry. The respective proportion of adult and cord labeled cells was 64 +/- 11 vs. 63 +/- 6% with Leu M5 (specific for monocyte) and 68 +/- 7 vs. 30 +/- 10% (P less than 0.05) with the anti-HLA DR antibody. The monoclonal antibody 23C6 is specific to the vitronectin receptor, which is highly expressed by osteoclasts--41 +/- 2% of the cells in cord monocyte cultures--but none in the adult monocytes culture were labeled with 23C6 at the end of the culture period.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural and histochemical study of beta-tricalcium phosphate resorbing cells in periodontium of dogs

beta-TCP was implanted in surgically prepared alveolar bone defects on the mesial side of the upper canine. The dogs that we used were sacrificed after 5 weeks, fixed by perfusion, and the beta-TCP resorbing cells were examined ultrastructurally and histochemically, with the following results: (1) beta-TCP was resorbed by macrophages and multinucleated giant cells. (2) Mitochondria, vacuoles and Golgi apparatus were abundant in beta-TCP-resorbing multinucleated giant cells that possessed neither ruffled borders nor clear zones. (3) The addition of tartric acid inhibited acid phosphatase activity in the cytoplasm of the multinucleated giant cells and macrophages.

Impaired osteoclast differentiation in subcutaneous implants of bone particles in osteopetrotic mutants

Because of its synchrony and relative homogeneity, the subcutaneous model of the resorption of mineral-containing, devitalized bone particles (BPs) is useful to evaluate the recruitment, differentiation, and activity of bone-resorbing, osteoclastic cells. Bone particles were prepared from normal rats or mice and were implanted in normal and osteopetrotic rats (ia, tl, op strains) or mice (mi strain). In addition, particles of microcrystalline hydroxyapatite or polymethylmethacrylate were implanted into tl and op mutants and their unaffected littermates. Non-decalcified histomorphometry of elicited tissues after 12 days revealed significantly less resorption in each mutant. Enzyme histochemical assays revealed that only normal animals showed tartrate-resistant acid phosphatase-positive cells around the BPs. In agreement with this, only normal animals showed ruffled borders against the BPs. op and tl strains were tested for generation of foreign body giant cells in response to particulate hydroxyapatite or polymethylmethacrylate and no differences were found between mutant and normal animals. These mutants appear to have intact fusion of mononuclear progenitors. These data show impaired recruitment of osteoclasts by BP implants in several rodent strains of osteopetrotic mutants.

Effects of bone matrix components on osteoclast differentiation

When implanted subcutaneously in rats, devitalized bone particles (BP) elicit the differentiation of osteoclastic cells. Those cells can be distinguished from foreign body giant cells that form in response to particulate plastics. Osteoclast features include resorption of the bone substrate, ruffled borders, calcitonin receptors, tartrate-resistant acid phosphatase activity, and modulation by bone active agents. To determine whether expression of these features depends on specific components of the matrix, we characterized the multinucleated cells that developed in response to osteocalcin-deficient BPs, particulate microcrystalline hydroxyapatite (HA), and HA containing 0.1% osteocalcin, collagen, or bovine serum albumin. Only those particles that contained mineral and osteocalcin were associated with osteoclastic cells. These studies support the hypothesis that osteocalcin may function as a matrix signal in the differentiation of osteoclasts.

Bone cell biology: the regulation of development, structure, and function in the skeleton

Bone cells compose a population of cells of heterogeneous origin but restricted function with respect to matrix formation, mineralization, and resorption. The local, mesenchymal origin of the cells which form the skeleton contrasts with their extraskeletal, hemopoietic relatives under which bone resorption takes place. However, the functions of these two diverse populations are remarkably related and interdependent. Bone cell regulation, presently in its infancy, is a complicated cascade involving a plethora of local and systemic factors, including some components of the skeletal matrices and other organ systems. Thus, any understanding of bone cell regulation is a key ingredient in understanding not only the development, maintenance, and repair of the skeleton but also the prevention and treatment of skeletal disorders.

Migration and phenotypic transformation of osteoclast precursors into mature osteoclasts: the effect of a bisphosphonate

Osteoclast-devoid bone explants were cultured together with embryonic liver as a source of osteoclast precursors, but separated from each other by a filter. Cells migrated through the filter toward the calcified matrix and acquired the characteristics of mature, tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts upon contact with the bone explant. Migration and attachment could be visualized separately. Progressive reduction of filter pore size resulted in progressive reduction of resorption because the use of smaller pores made it increasingly difficult for cells to pass. Indeed, the use of 0.22-micron filters, through which no cells can pass, but which still allow full passage of medium, completely blocked the resorption. When migrating cells from fetal liver were arrested for 10 days by using a combination of filters with different pore sizes, the arrested cells showed a tendency to fuse just opposite the mineralized matrix. Furthermore, a great number of the arrested cells expressed the macrophage-specific cell-surface antigen F4/80 and showed acid phosphatase activity, but none of these cells were tartrate resistant. The acquisition of tartrate-resistant acid phosphatase activity upon contact with the bone explant and subsequent resorption of this explant could be prevented by exposure of the system to the bisphosphonate dimethyl-APD (Me2-APD), whereas migration of cells through the filter was not affected. We suggest that the bisphosphonate interferes with a matrix factor that is essential for the attachment and subsequent transformation of the osteoclast precursor into the mature phenotype.

Multinucleated cells elicited in response to implants of devitalized bone particles possess receptors for calcitonin

The introduction into soft tissues of particulate materials resistant to digestion results in the induction of a "foreign-body giant-cell reaction." We have examined the relation between osteoclasts and foreign-body giant cells by comparing the tissue responses elicited by subcutaneous implants of devitalized, mineral-containing bone particles (BP), nonresorbable plastics such as polymethylmethacrylate (PMMA), or both. Implantation of BP results in the recruitment of multinucleated cells with features of in osso osteoclasts including tartrate-resistant acid phosphatase activity, contact-mediated resorption of BP, membrane specializations (ruffled borders and clear zones), and inhibition of resorption by calcitonin treatment of animals. In the present study, an autoradiographic technique employing 125I-salmon calcitonin was used to demonstrate the presence of receptors for this hormone on multinucleated cells from BP implants. In contrast, outgrowth cells from PMMA implants lacked calcitonin receptors. Demonstration of features of the osteoclastic phenotype in multinucleated cells elicited in response to BP supports the hypothesis that the mineralized matrix of bone may be a requirement for acquisition of the osteoclast phenotype.

Role of mineralizing cartilage in osteoclast and osteoblast recruitment

Periost-free, live and/or devitalized cartilaginous long bone rudiments of fetal mice were transplanted under the renal capsule of adult syngeneic mice to study the role of cells and intercellular matrix in the recruitment and formation of osteoclasts and osteoblasts, both identified by means of enzyme- and immunohistochemical methods. Live bone rudiments recruited host-derived osteoclasts within 5 days after transplantation. Osteoblasts developed as rapidly as osteoclasts and participated in the modeling of the rudiments into hemopoietic bone marrow containing ossicles. Devitalized bone rudiments, killed before osteoclastic invasion had occurred, did not recruit osteoclasts or osteoblasts, and were not resorbed up till 35 days after transplantation. Co-transplantation of live and devitalized bone rudiments however resulted in osteoclastic resorption of the killed rudiments, starting 9 days after transplantation. Again the live rudiments were modeled into ossicles. Devitalized bone rudiments which had been invaded by osteoclasts before killing and transplantation, did recruit host osteoclasts, but at a slower rate than live rudiments, and depending on the number of resorption sites at the time of transplantation. Osteoblasts were not formed. These data suggest that in developing long bones chondrocyte activity is involved in the recruitment of osteoclasts as well as osteoblasts. Matrix components diffusing from resorbing surfaces seem to be involved in osteoclast recruitment.

Impaired recruitment and differentiation of osteoclast progenitors by osteocalcin-deplete bone implants

This is a report of an experimental system to study differentiation of bone-resorbing osteoclasts and demonstrates that osteocalcin, an extracellular bone-specific component, is necessary for the recruitment of osteoclast progenitor cells. The subcutaneous implantation of devitalized bone particles (BPs) elicits the recruitment and differentiation of osteoclasts that resorb the BPs. In a previous study, we showed by histomorphometric analysis that BPs that were deficient in osteocalcin were resorbed only 60% as well as normal BPs. In this study, the mechanism of this difference was investigated by measurements of recruitment, differentiation and activity of bone resorbing cells by normal and osteocalcin-deficient BP. Mononuclear cells were attracted to control BPs soon after implantation. In dramatic contrast, cellularity was depressed around osteocalcin-deficient BPs with very few mononuclear cells within the implant on day 5 (35% of control cellularity). In implants of normal BPs, tartrate-resistant acid phosphatase-positive multinucleated cells were evident by day 5; very few appeared in implants of osteocalcin-deplete BPs even by day 12. The amount of tartrate-resistant acid phosphatase activity in homogenates of the osteocalcin-deficient bone particle specimens not only lagged behind controls but never reached the maximum activity of control BP specimens. These data support the hypothesis that osteocalcin may function as a matrix signal in the recruitment and/or activation of cells for bone resorption.