The effects of calcium regulating hormones on bone resorption by isolated human osteoclastoma cells

The role of magnesium in the pathogenesis of osteoporosis

Magnesium (Mg), a nutritional element which is essential for bone development and mineralization, has a role in the progression of osteoporosis. Osteoporosis is a multifactorial disease characterized by significant deterioration of bone microstructure and bone loss. Mg deficiency can affect bone structure in an indirect way through the two main regulators of calcium homeostasis (parathyroid hormone and vitamin D). In human osteoblasts (OBs), parathyroid hormone regulates the expression of receptor activator of nuclear factor-κ B ligand (RANKL) and osteoprotegerin (OPG) to affect osteoclast (OC) formation. In addition, Mg may also affect the vitamin D3 -mediated bone remodeling activity. vitamin D3 usually coordinates the activation of the OB and OC. The unbalanced activation OC leads to bone resorption. The RANK/RANKL/OPG axis is considered to be a key factor in the molecular mechanism of osteoporosis. Mg participates in the pathogenesis of osteoporosis by affecting the regulation of parathyroid hormone and vitamin D levels to affect the RANK/RANKL/OPG axis. Different factors affecting the axis and enhancing OC function led to bone loss and bone tissue microstructure damage, which leads to the occurrence of osteoporosis. Clinical research has shown that Mg supplementation can alleviate the symptoms of osteoporosis to some extent.

Osteoclasts and Probiotics Mediate Significant Expansion, Functional Activation and Supercharging in NK, γδ T, and CD3+ T Cells: Use in Cancer Immunotherapy

Our previous studies have introduced osteoclasts (OCs) as major activators of NK cells. It was found that OCs exhibit the capabilities of inducing cell expansion as well as increasing the cytotoxic activity of NK cells by granule release and increasing the secretion of TNF-α and TRAIL, leading to increased lysis of tumors in short-term as well as long-term periods, respectively. OC- induced expanded NK cells were named supercharged NK cells (sNK) due to their significantly high functional activity as well as their significantly higher cell expansion rate. It is, however, unclear whether the OC-mediated effect in NK cells is specific or whether other cytotoxic immune cells can also be expanded and activated by OCs. We chose to focus on γδ T cells and pan T cells, which also include CD8+ T cells. In this paper, we report that OCs are capable of expanding and functionally activating both γδ T cells and pan T cells. Expanded γδ T and pan T cells were capable of secreting high levels of INF-γ, albeit with different dynamics to those of NK cells, and, moreover, they are unable to kill NK-specific targets. Since we used humanized-BLT (hu-BLT) mice as a model of human disease, we next determined whether NK and T cell activation through OCs is also evident in cells obtained from hu-BLT mice. Similar to humans, OCs were capable of increasing the cell expansion and secretion of IFN-γ in the culture of either NK or T cells from hu-BLT mice, providing yet further evidence that these mice are appropriate models to study human disease. Therefore, these studies indicated that CD3+ T or γδ T cells can proliferate and be supercharged by OCs similar to the NK cells; thus, they can be used individually or in combination in the cell therapy of cancers.

Similarities and Differences between Osteoclast-Mediated Functional Activation of NK, CD3+ T, and γδ T Cells from Humans, Humanized-BLT Mice, and WT Mice

This study is focused on assessing the activation in NK, CD3+ T, and γδ T cells when they interact with osteoclasts (OCs) and monocytes in the presence or absence of zoledronate (ZOL), both in humans and WT mice. OCs resulted in increased IFN-γ secretion in NK, CD3+ T, and γδ T cells, however, the significantly highest increase was seen when cells were co-cultured with ZOL-treated OCs. Our previous studies have demonstrated increased IFN-γ secretion in the peripheral blood-derived immune cells of bisphosphonate-related osteonecrosis of the jaw (BRONJ) mice model. This could be due to increased OCs-induced activation of immune cells with ZOL treatment. We also observed increased IFN-γ secretion in humanized-BLT (hu-BLT) mice NK cells when were co-cultured with OCs or monocytes, and higher IFN-γ secretion levels were seen in the presence of OCs or ZOL-treated OCs. In addition, similar effects on IFN-γ secretion levels of NK, CD3+ T, and γδ T cells were seen whether cells were co-cultured with allogeneic OCs or autologous OCs.

Augmentation of IFN-γ by bone marrow derived immune cells in the presence of severe suppression of IFN-γ in gingivae induced by zoledronic acid and denosumab in Hu-BLT mice model of ONJ

Introduction

The potential mechanisms governing drug induced osteonecrosis of the jaw (ONJ) is not well understood, and is one of the objectives of this study. Thus, we tested the release of IFN-γ within different immune compartments including bone marrow and gingivae upon treatment with zoledronic acid (ZOL) and denosumab which are known to induce ONJ in susceptible individuals.

Methods

We used humanized-BLT mouse model for the in-vivo studies reported in this paper. To determine the effects of zoledronic acid and denosumab on IFN-γ secretion and NK cell-mediated cytotoxicity; peripheral blood, bone marrow, spleen and gingiva were obtained after the injection of ZOL and denosumab in mice.

Results

Percentages of B cells are much higher in wild-type mice whereas the proportions of immune subsets in humans and reconstituted hu-BLT peripheral-blood are similar. Therefore, hu-BLT mice are preferable model to study human disease, in particular, immune-pathologies induced by ZOL and denosumab. Both agents resulted in a severe suppression of IFN-γ in the gingiva, whereas they heightened the release of IFN-γ and NK cell-mediated cytotoxicity by the BM-derived immune cells. ZOL increased the IFN-γ secretion by the spleen and peripheral blood immune cells, whereas denosumab decreased the release IFN-γ by these cells significantly.

Discussion

ZOL and denosumab may likely suppress IFN-γ secretion in gingiva through different mechanisms. In addition, to the suppression of IFN-γ secretion, denosumab mediated effect could in part be due to the decrease in the bone resorptive function of osteoclasts due to the induction of antibody dependent cellular cytotoxicity and lysis of osteoclasts, whereas ZOL is able to mediate cell death of osteoclasts directly. Suppression of IFN-gamma in gingiva is largely responsible for the inhibition of immune cell function, leading to dysregulated osteoblastic and osteoclastic activities. Restoration of IFN-gamma in the local microenvironment may result in establishment of homeostatic balance in the gingiva and prevention of osteonecrosis of jaw.

Parathyroid Cell Differentiation from Progenitor Cells and Stem Cells: Development, Molecular Mechanism, Function, and Tissue Engineering

Parathyroid glands are endocrine organs which are located posterior to thyroid glands and control secretion of parathyroid hormone (PTH) in order to regulate blood calcium level. PTH maintains calcium homeostasis by acting on the bone, kidney, and small intestine. PTH deficiency leads to chronic hypocalcemia, organ calcinosis, kidney and heart failure, painful muscle spasms, neuromuscular problems, and memory problems. Since parathyroid cells have inadequate proliferation potential in culture conditions, their utilization as a cellular therapy option is very limited. Although studies conducted so far include parathyroid cell differentiation from various cell types, problems related to successful cellular differentiation and transplantation still remain. Recently, parathyroid tissue engineering has attracted attention as a potential treatment for the parathyroid-related diseases caused by hypoparathyroidism. Although major progression is made in the construction of tissue engineering protocols using parathyroid cells and biomaterials, PTH secretion to mimic its spontaneous harmony in the body is a challenge. This chapter comprehensively defines the derivation of parathyroid cells from various cell sources including pluripotent stem cells, molecular mechanisms, and tissue engineering applications.

Various pathways of zoledronic acid against osteoclasts and bone cancer metastasis: a brief review

Zoledronic acid (ZA) is one of the most important and effective class of anti-resorptive drug available among bisphosphonate (BP), which could effectively reduce the risk of skeletal-related events, and lead to a treatment paradigm for patients with skeletal involvement from advanced cancers. However, the exact molecular mechanisms of its anticancer effects have only recently been identified. In this review, we elaborate the detail mechanisms of ZA through inhibiting osteoclasts and cancer cells, which include the inhibition of differentiation of osteoclasts via suppressing receptor activator of nuclear factor κB ligand (RANKL)/receptor activator of nuclear factor κB (RANK) pathway, non-canonical Wnt/Ca2+/calmodulin dependent protein kinase II (CaMKII) pathway, and preventing of macrophage differentiation into osteoclasts, in addition, induction of apoptosis of osteoclasts through inhibiting farnesyl pyrophosphate synthase (FPPS)-mediated mevalonate pathway, and activation of reactive oxygen species (ROS)-induced pathway. Furthermore, ZA also inhibits cancer cells proliferation, viability, motility, invasion and angiogenesis; induces cancer cell apoptosis; reverts chemoresistance and stimulates immune response; and acts in synergy with other anti-cancer drugs. In addition, some new ways for delivering ZA against cancer is introduced. We hope this review will provide more information in support of future studies of ZA in the treatment of cancers and bone cancer metastasis.

Histopathology of giant cell tumors of the bone: With special emphasis on fibrohistiocytic and aneurysmal bone cyst like components

Objective

The aim of this study was to define histopathological features of giant cell tumor of bone, especially accompanying fibrohistiocytic or aneurysmal bone cyst like components, in the light of our institutions experience.

Methods

A total of 120 cases (64 females and 56 males; mean age: 36.2 (12–80)) with ‘GCT’ diagnosed between the years 1996–2016 were included in this retrospective analysis. Cases were evaluated according to clinical features such as age, gender, localization, recurrence, metastasis and histopathological features.

Results

Tumors were localized most frequently at proximal tibia and distal femur, respectively. In 11 cases areas rich in fibrohistiocytic component and in 20 cases aneurysmal bone cyst like component were observed. In 2 cases both components were present. Twenty three cases recurred. In 1 case which was primarily located at calcaneus, tumor metastasized to lung 4 years later during follow-up.

Conclusion

GCT can be confused with other tumor or tumor-like lesions involving giant cells. Secondary changes such as fibrohistiocytic or aneurysmal bone cyst-like components and coagulation necrosis were frequently seen in conventional giant cell tumor of bone. For tumors having prominent fibrohistiocytic and/or aneurysmal bone cyst-like components, in order to detect characteristic areas representing GCT, additional sampling is essential. Although secondary histopathological changes do not appear to affect clinical outcome, these features are important in differential diagnosis. Approximately one fifth of GCT cases show recurrence and sacrum and foot bones were the most frequent sites for recurrence.

Level of evidence

Level IV, diagnostic study.

The Influence of Chronic Kidney Disease on the Structural and Mechanical Properties of Canine Bone

Background

Chronic kidney disease (CKD) is common in companion animals. Secondary hyperparathyroidism is an inevitable consequence of the disease and may have deleterious effect on the bone; however, the information regarding CKD‐associated bone abnormalities in companion animals is scarce.

Hypothesis/Objectives

Dogs with CKD have decreased bone quality compared to dogs without CKD.

Animals

Nine dogs diagnosed with naturally occurring CKD for at least 6 months and 9 age‐matched controls.

Methods

Dogs with CKD were enrolled and compared to 9 age‐, weight‐, and sex‐matched control dogs with no evidence of CKD. Samples were assessed using light microscopy, mechanical testing, and microcomputed tomography. Variables evaluated included microstructural features such as number, size, and density of Haversian canals, resorption cavities and osteocytic lacunae, bone mineral density, porosity and Young's modulus.

Results

Median lacunae size was significantly smaller in the CKD group compared to the control group (P = 0.001). Resorption cavity density was higher in the CKD compared to the control group (10 [8–14] vs. 7 [4–9]/mm², respectively, P = 0.001). Overall porosity was significantly (2.3‐fold) higher in the CKD compared to the control group. There was no difference in Young's moduli between groups.

Conclusions and Clinical Importance

Naturally occurring CKD affects bone quality in dogs, but these changes are relatively mild and likely not to be manifested clinically. The duration of the disease in dogs evaluated here is short compared to cats and human patients, likely accounting for the more subtle changes in dogs compared to other species.

In Vitro Study of the Effects of Denosumab on Giant Cell Tumor of Bone: Comparison with Zoledronic Acid

Giant cell tumor of bone (GCTB) is a locally aggressive primary bone tumor that contains numerous osteoclasts formed from marrow-derived precursors through receptor activator of nuclear factor κ-B ligand (RANKL), an osteoclast differentiation factor expressed in neoplastic cells of GCTB. Denosumab, a fully human monoclonal antibody targeting RANKL, has recently been used for the treatment of GCTB, and superior treatment effects have been reported. The aim of this work was to elucidate the mechanism of action of denosumab, and the differences between denosumab and zoledronic acid at the level of GCTB cells. We isolated GCTB cells from 3 patients and separated them into osteoclasts, osteoclast precursors and proliferating spindle-shaped stromal cells (the true neoplastic component), and examined the action of denosumab on differentiation, survival and bone resorption activity of osteoclasts. Denosumab and zoledronic acid inhibited osteoclast differentiation from mononuclear cells containing osteoclast precursors. Zoledronic acid inhibited osteoclast survival, whereas an inhibitory effect of denosumab on osteoclast survival was not observed. The inhibitory effect on bone resorption by both agents was confirmed in culture on dentin slices. Furthermore, zoledronic acid showed dose-dependent inhibition of cell growth of neoplastic cells whereas denosumab had no inhibitory effect on these cells. Denosumab has an inhibitory effect on osteoclast differentiation, but no inhibitory effects on survival of osteoclasts or growth of neoplastic cells in GCTBs.

Pharmacological and surgical therapy for the central giant cell granuloma: A long-term retrospective cohort study

PURPOSE

This is a retrospective cohort study of patients with a central giant cell granuloma (CGCG) treated at a single center to assess and compare the different surgical and non-surgical approaches.

MATERIAL AND METHODS

A cohort with a single histologically proven non-syndrome-related CGCG was selected and reviewed. Patients were allocated to group I (surgery), group II (pharmacotherapy), and group III (pharmacotherapy and surgery). The primary outcome was long-term radiologic response using computed tomography. Secondary outcomes were intermediate radiologic responses and occurrence and severity of side effects.

RESULTS

Thirty-three subjects were included in the study. The surgical group (n = 4) included 1 patient with progression during follow-up and a relatively high post-surgical morbidity. Twenty-nine patients started on various pharmacological treatment regimens (groups II and III). Fourteen patients could be managed without additional surgery. One of these lesions showed progression during follow-up. The other 15 lesions underwent additional surgery, and none showed progression during follow-up. Interferon treatment was associated with the most side effects.

CONCLUSION

Pharmacological agents have a role in the treatment of aggressive and non-aggressive CGCGs by limiting the renewed progression during long-term follow up and the extent and morbidity of surgical treatment.

Bisphosphonate-induced differential modulation of immune cell function in gingiva and bone marrow in vivo: role in osteoclast-mediated NK cell activation

The aim of this study is to establish osteoclasts as key immune effectors capable of activating the function of Natural Killer (NK) cells, and expanding their numbers, and to determine in vivo and in vitro effect of bisphosphonates (BPs) during NK cell interaction with osteoclasts and on systemic and local immune function. The profiles of 27 cytokines, chemokines and growth factors released from osteoclasts were found to be different from dendritic cells and M1 macrophages but resembling to untreated monocytes and M2 macrophages. Nitrogen-containing BPs Zoledronate (ZOL) and Alendronate (ALN), but not non-nitrogen-containing BPs Etidronate (ETI), triggered increased release of pro-inflammatory mediators from osteoclasts while all three BPs decreased pit formation by osteoclasts. ZOL and ALN mediated significant release of IL-6, TNF-` and IL-1β, whereas they inhibited IL-10 secretion by osteoclasts. Treatment of osteoclasts with ZOL inhibited NK cell mediated cytotoxicity whereas it induced significant secretion of cytokines and chemokines. NK cells lysed osteoclasts much more than their precursor cells monocytes, and this correlated with the decreased expression of MHC class I expression on osteoclasts. Intravenous injection of ZOL in mice induced pro-inflammatory microenvironment in bone marrow and demonstrated significant immune activation. By contrast, tooth extraction wound of gingival tissues exhibited profound immune suppressive microenvironment associated with dysregulated wound healing to the effect of ZOL which could potentially be responsible for the pathogenesis of Osteonecrosis of the Jaw (ONJ). Finally, based on the data obtained in this paper we demonstrate that osteoclasts can be used as targets for the expansion of NK cells with superior function for immunotherapy of cancer.

Central Giant Cell Granuloma of the Mandible Requiring Multiple Treatment Modalities: A Case Report

Central giant cell granuloma (CGCG) is a relatively rare non-neoplastic, intraosseous lesion that exhibits a wide spectrum of clinical behavior, and its management can be particularly challenging even for experienced clinicians. The etiopathogenesis of this disease process remains unclear, although factors such as trauma, inflammatory foci, and a genetic predisposition have been implicated. Although multiple treatment modalities have been used with varying degrees of success, there is no accepted algorithm for therapeutic intervention and little is known about the reasons for success or failure of a given treatment. This article reviews the epidemiology, presentation, classification, and currently used therapies for CGCG while describing the clinical course and successful therapeutic outcome of a young female patient with an aggressive CGCG of the mandible.

Parathyroid hormone: anabolic and catabolic actions on the skeleton

Parathyroid hormone (PTH) is essential for the maintenance of calcium homeostasis through, in part, its actions to regulate bone remodeling. While PTH stimulates both bone formation and bone resorption, the duration and periodicity of exposure to PTH governs the net effect on bone mass, that is whether it is catabolic or anabolic. PTH receptor signaling in osteoblasts and osteocytes can increase the RANKL/OPG ratio, increasing both osteoclast recruitment and osteoclast activity, and thereby stimulating bone resorption. In contrast, PTH-induced bone formation is explained, at least in part, by its ability to downregulate SOST/sclerostin expression in osteocytes, permitting the anabolic Wnt signaling pathway to proceed. The two modes of administration of PTH, that is, continuous vs. intermittent, can regulate, in bone cells, different sets of genes; alternatively, the same sets of genes exposed to PTH in sustained vs. transient way, will favor bone resorption or bone formation, respectively. This article reviews the effects of PTH on bone cells that lead to these dual catabolic and anabolic actions on the skeleton.

Central giant cell granuloma: treatment with calcitonin, triamcinolone acetonide, and a cystic finding 3 years and 6 months after the primary treatment

BACKGROUND

Central giant cell granuloma is a benign condition of the jaws which may present an aggressive behavior.

CASE REPORT

A 9-year-old boy was complaining of swelling in the floor of the mouth. A solid swelling was observed in the area of the lower incisors. From the radiographic exam, we observed a radiolucent image in the mandibular bone with well-defined limits extending from the apical region of tooth 33 to the apical region of tooth 42.

DISCUSSION

Due to the diagnosis and the age of the patient, we chose a conservative treatment, administering subcutaneous injections of calcitonin. During this treatment, no reduction to the lesion was observed. Therefore, we chose to treat the lesion with triamcinolone acetonide. Monthly follow-ups demonstrated good lesion reduction and the absence of any clinical symptoms during the first 2 years. After a 3-year follow-up, the patient returned, presenting mobility of the lower incisors. A significant increase in the size of the lesion was observed. After a biopsy, with the removal of tissue which had the appearance of a cyst capsule, microscopic analyses were found to be compatible with a secondarily infected cyst. Two months following this procedure, the patient did not present tooth mobility anymore and the oral mucosa presented a normal aspect. Following a radiographic exam, full lesion repair was observed. These conservative treatments should be the first option in cases of central giant cell granuloma and the patient must be observed for a long period of time, until no further clinical or radiographic signs of lesions are observed.

Giant cell tumor of bone: a basic science perspective

Comprehending the pathogenesis of giant cell tumor of bone (GCT) is of critical importance for developing novel targeted treatments for this locally-aggressive primary bone tumor. GCT is characterized by the presence of large multinucleated osteoclast-like giant cells distributed amongst mononuclear spindle-like stromal cells and other monocytes. The giant cells are principally responsible for the extensive bone resorption by the tumor. However, the spindle-like stromal cells chiefly direct the pathology of the tumor by recruiting monocytes and promoting their fusion into giant cells. The stromal cells also enhance the resorptive ability of the giant cells. This review encompasses many of the attributes of GCT, including the process of giant cell formation and the mechanisms of bone resorption. The significance of the receptor activator of nuclear factor-κB ligand (RANKL) in the development of GCT and the importance of proteases, including numerous matrix metalloproteinases, are highlighted. The mesenchymal lineage of the stromal cells and the origin of the hematopoietic monocytes are also discussed. Several aspects of GCT that require further understanding, including the etiology of the tumor, the mechanisms of metastases, and the development of an appropriate animal model, are also considered. By exploring the current status of GCT research, this review accentuates the significant progress made in understanding the biology of the tumor, and discusses important areas for future investigation.

VEGF, FLT3 ligand, PlGF and HGF can substitute for M-CSF to induce human osteoclast formation: implications for giant cell tumour pathobiology

Giant cell tumour of bone (GCTB) is a primary bone tumour that contains numerous very large, hyper-nucleated osteoclastic giant cells. Osteoclasts form from CD14+ monocytes and macrophages in the presence of receptor activator of nuclear factor kappa B ligand (RANKL) and macrophage-colony stimulating factor (M-CSF). GCTB contains numerous growth factors, some of which have been reported to influence osteoclastogenesis and resorption. We investigated whether these growth factors are capable of substituting for M-CSF to support osteoclast formation from cultured human monocytes and whether they influence osteoclast cytomorphology and resorption. Vascular endothelial growth factor-A (VEGF-A), VEGF-D, FLT3 ligand (FL), placental growth factor (PlGF) and hepatocyte growth factor (HGF) supported RANKL-induced osteoclastogenesis in the absence of M-CSF, resulting in the formation of numerous TRAP+ multinucleated cells capable of lacunar resorption. Monocytes cultured in the presence of M-CSF, HGF, VEGF-A and RANKL together resulted in the formation of very large, hyper-nucleated (GCTB-like) osteoclasts that were hyper-resorptive. M-CSF and M-CSF substitute growth factors were identified immunohistochemically in GCTB tissue sections and these factors stimulated the resorption of osteoclasts derived from a subset of GCTBs. Our findings indicate that there are growth factors that are capable of substituting for M-CSF to induce human osteoclast formation and that these factors are present in GCTB where they influence osteoclast cytomorphology and have a role in osteoclast formation and resorption activity.

In vitro generation of mature human osteoclasts

Mononuclear precursors of human osteoclasts are found in the CD14(+) monocyte fraction of circulating peripheral blood mononuclear cells (PBMCs). It is possible to generate osteoclasts in vitro from PBMCs cultured with macrophage colony-stimulating factor and receptor activator for nuclear factor κB ligand. In these cultures, however, it is not possible to distinguish the effect of a specific agent on osteoclast resorption activity as opposed to osteoclast differentiation. To produce a population of mature human osteoclasts to study osteoclast lacunar resorption specifically, we cultured CD14(+) human monocytes on hydrophobic dishes in order to generate and maintain osteoclasts in suspension prior to culturing them on coverslips and dentine slices. Multinucleated cells formed in these cultures expressed vitronectin receptor, tartrate-resistant acid phosphatase, and cathepsin K. These cells also produced F-actin rings and were capable of extensive lacunar resorption on dentine slices after 24 h in culture. Lacunar resorption was inhibited by calcitonin and zoledronate but not by osteoprotegerin. This method of generating a highly enriched population of mature human osteoclasts should provide a valuable means of specifically assessing the effect of molecular factors (e.g., cytokines, growth factors, hormones) and therapeutic agents on osteoclast resorption activity.

Catabolic and anabolic actions of parathyroid hormone on the skeleton

PTH, an 84-amino acid peptide hormone synthesized by the parathyroid glands, is essential for the maintenance of calcium homeostasis.While in its traditional metabolic role, PTH helps to maintain the serum calcium concentration within narrow, normal limits and participates as a determinant of bone remodeling, more specific actions, described as catabolic and anabolic are also well known. Clinically, the catabolic effect of PTH is best represented by primary hyperparathyroidism (PHPT), while the osteoanabolic effect of PTH is best seen when PTH or its biological amino-terminal fragment [PTH(1-34)] is used as a therapy for osteoporosis. These dual functions of PTH are unmasked under very specific pathological (PHPT) or therapeutic conditions. At the cellular level, PTH favors bone resorption, mostly by affecting the receptor activator of nuclear factor κ-B (RANK) ligand (RANKL)-osteoprotegerin- RANK system, leading to an increase in osteoclast formation and activity. Increased bone formation due to PTH therapy is explained best by its ability to enhance osteoblastogenesis and/or osteoblast survival. The PTH-induced bone formation is mediated, in part, by a decrease in SOST/sclerostin expression in osteocytes. This review focuses on the dual anabolic and catabolic actions of PTH on bone, situations where one is enhanced over the other, and the cellular and molecular mechanisms by which these actions are mediated.

Calcitonin use in giant cell bone tumors

INTRODUCTION

As osteoclast, giant cell tumors express calcitonin receptors. The aim of this paper is to assess treatment using salmon calcitonin after curettage.

MATERIAL AND METHODS

We retrospectively reviewed 25 patients with giant cell tumor of the appendicular skeleton treated with a single protocol of calcitonin administration following curettage in order to assess the effectiveness of calcitonin in reducing the rate of local recurrence.

RESULTS

The mean duration follow-up was 68 months. Thirteen patients (52%) had local recurrence. Eight of them were treated successfully after repeated curettage and calcitonin. Four patients had bone resection and one patient had curettage and cement filling. All patients with cavity left empty had ossified and the functional score as assessed by the MSTS score was 28.02/30.

CONCLUSION

This study suggests that the use of calcitonin as adjuvant is not effective and that filling agents are not required after curettage of giant cell tumors.

LEVEL OF EVIDENCE

Level 4.

Combined treatment of aggressive central giant cell granuloma in the lower jaw

BACKGROUND

The aggressive type lesions of central giant cell granuloma (CGCG) require wide resection that leads to major defects in the jaws. This form of surgical treatment can be particularly disfiguring. A number of alternative non-surgical therapies have been advocated in recent years for the management of the central giant cell granuloma (CGCG). These include calcitonin injections and nasal spray, intralesional steroid injections and subcutaneous interferon injections.

MATERIALS AND METHODS

A large central giant cell granuloma aggressive type lesion in the mandible of a 24-year-old patient was treated successfully by intralesional injection of corticosteroid and nasal spray calcitonin that was followed by curettage with peripheral ostectomy with preservation of the continuity of the mandible and the teeth. At the 5-year clinical and radiological follow up there was no sign of recurrence.

CONCLUSIONS

This combined medical and surgical treatment is advantageous for large aggressive lesions in order to reduce the size of the lesion and thus minimize the need for extensive bone resection and loss of teeth that can result in functional and aesthetic defects.

Central Giant Cell Granuloma of the Jaws: A Clinical Study of 17 Cases and a Review of the Literature

Objectives:

The aim of this prospective study was to evaluate the outcome of treatment of a group of 17 patients with central giant cell granuloma (CGCG) who were treated in our clinic.

Methods:

A group of 17 patients with CGCG were treated in the Clinic of Oral and Maxillofacial Surgery of the “G. Papanikolaou” hospital in Thessaloniki. The age range was from 7 to 60 years. Eight patients were male and 9 patients were female. Because most of our patients (11) were less than 30 years old, the aim of the treatment was to eradicate the lesions without functional problems. All of the patients were treated by excision via curettage without a continuity defect and peripheral osteotomy. For 2 patients, the treatment was continued (after the first recurrence) with salmon calcitonin.

Results:

The follow-ups ranged from 1 to 15 years. All of the patients were free of the disease, without features of recurrence and without functional or aesthetic problems.

Conclusions:

Surgery has usually been considered to be the best method of treatment for CGCG. Most authors have proposed conservative surgical procedures (excision via curettage), especially for young patients. For aggressive lesions, supplementary treatment with calcitonin would provide good results.

Morphological Changes of Isolated Osteoclasts in Cell Culture Due to Different Biomaterials

Osteoclasts have been isolated in primary cell culture using femoral bone of laying hens being fed on an eight day calcium free diet. Placing these cells on the surface of fixed cortico-femoral chicken bone provoked the feature of resorption pits proving that they are able to resorb bone.

After placing osteoclasts on different biomaterials (Aluminumoxide ceramics, teflon, carbon fibre reinforced polysulphone, polymethylmethacrylate, polydioxanone) scanning electron microscopy was performed. Different materials provoke different morphological features of these cells, probably due to functional variations as a response to the changing surfaces. Adhesion was feasible on all the surfaces, uptake of small surface particles was possible and cell fusion took place on most materials suggesting acceptance of the tested biomaterials by the cells.

The results show that morphological changes of isolated osteoclasts in cell culture can be detected due to different functional challenges of the surfaces of different biomaterials.

PTH and PTHrP signaling in osteoblasts

The striking clinical benefit of PTH in osteoporosis began a new era of skeletal anabolic agents. Several studies have been performed, new studies are emerging out and yet controversies remain on PTH anabolic action in bone. This review focuses on the molecular aspects of PTH and PTHrP signaling in light of old players and recent advances in understanding the control of osteoblast proliferation, differentiation and function.

Collagenase expression and activity in the stromal cells from giant cell tumour of bone

The characteristic bone destruction in giant cell tumour of bone (GCT) is largely attributed to the osteoclast-like giant cells. However, experimental analyses of bone resorption by cells from GCT often fail to exclude the neoplastic spindle-like stromal cells, and several studies have demonstrated that bone resorption by GCT cells is increased in the presence of stromal cells. The spindle-like stromal cells from GCT may therefore actively contribute to the bone resorption observed in the tumour. Type I collagen, a major organic constituent of bone, is effectively degraded by three matrix metalloproteinases (MMPs) known as the collagenases: MMP-1, MMP-8 and MMP-13. We established primary cell cultures from nine patients with GCT and the stromal cell populations were isolated in culture. The production of collagenases by primary cultures of GCT stromal cells was determined through real-time PCR, western blot analysis and a multiplex assay system. Results show that the cells produce MMP-1 and MMP-13 but not MMP-8. Immunohistochemistry confirmed the presence of MMP-1 and MMP-13 in paraffin-embedded GCT tissue samples. Medium conditioned by the stromal cell cultures was capable of proteolytic activity as determined by MMP-1 and MMP-13-specific standardized enzyme activity assays. The spindle-like stromal cells from GCT may therefore actively participate in the bone destruction that is characteristic of the tumour.

Central giant cell granuloma of the jaw: a review of the literature with emphasis on therapy options

Central giant cell granuloma (CGCG) is a benign lesion of the jaws with an unknown etiology. Clinically and radiologically, a differentiation between aggressive and non-aggressive lesions can be made. The incidence in the general population is very low and patients are generally younger than 30 years. Histologically identical lesions occur in patients with known genetic defects such as cherubism, Noonan syndrome, or neurofibromatosis type 1. Surgical curettage or, in aggressive lesions, resection, is the most common therapy. However, when using surgical curettage, undesirable damage to the jaw or teeth and tooth germs is often unavoidable and recurrences are frequent. Therefore, alternative therapies such as injection of corticosteroids in the lesion or subcutaneous administration of calcitonin or interferon alpha are described in several case reports with variable success. Unfortunately, randomized clinical trials are very rare or nonexistent. In the future, new and theoretically promising therapy options, such as imatinib and OPG/AMG 162, will be available for these patients.

Evolution of the CT/CGRP family: comparative study with new data from models of teleosts, the eel, and cephalopod molluscs, the cuttlefish and the nautilus

In mammals, alternative splicing of the calcitonin gene generates two distinct peptides: calcitonin (CT), synthesised in the thyroid C cells and involved in the regulation of calcium metabolism, and calcitonin gene-related peptide (CGRP), brain neuromediator synthesised in the peripheral and central nerves. CGRP is well represented and molecularly conserved during evolution whereas CT has not been detected in any of the invertebrates analysed so far. In order to better understand the evolution of this CT/CGRP peptide family we reviewed the major data concerning its evolution from the literature and our recent data obtained in models of teleosts and cephalopod molluscs. The presence of both CGRP-like molecules and its specific bindings sites in the central nervous system of eel, cuttlefish and nautilus, suggests that the brain neurotransmitter role of CGRP could represent an ancient role in metazoa, already present in cephalopods and conserved among vertebrates, as still observed in mammals. In contrast, the presence of CGRP specific binding sites, and not the peptide itself, in the gills suggests an endocrine role for CGRP, in cephalopods and teleosts, that may have been lost during the evolution of the tetrapod lineage. These data, and the absence of CT-like molecules that we observed in cephalopods, support the hypothesis that CGRP represents the ancestral molecule of the CT/CGRP family, appeared in metazoa before the vertebrate emergence. The distinction between CT and CGRP receptors appears to be an event posterior to the emergence of ecdysozoan and lophotrochozoan protostomes, probably in relation to the CT appearance. The evolution of the CT/CGRP peptide family is probably similar to the evolution of the CT/CGRP receptor family. In fact, the genic duplication that induced the appearance of the two separate molecules, CT and CGRP, may constitute an event close to that, which induced the appearance of the two specific receptors. These events remain to be further studied in order to better understand the peptide and receptor evolution of the CT/CGRP family.

Calcitonin therapy in central giant cell granuloma of the jaw: a randomized double-blind placebo-controlled study

The successful therapeutic use of calcitonin in patients with a central giant cell granuloma has been shown in several case reports. In a prospective, randomized, double-blinded, placebo-controlled clinical trial, 14 patients with a histologically confirmed central giant cell granuloma and normal calcium and parathyroid hormone serum levels were studied over 2 years. Patients were treated with intranasally administered salmon calcitonin (200 IU/day) or a placebo once a day. The placebo-controlled period was 3 months, after which all patients were treated with calcitonin for 1 year. Treatment response was assessed at the end of the placebo-controlled study phase (3 months), at the end of therapy (15 months' timepoint with patients being on calcitonin treatment for either 12 or 15 months) and at 6 months' follow-up. The chi(2)-test was used to compare the proportion of patients with a tumour reduction >/=10% of the pretreatment measurement between the 2 populations at the 3 timepoints: no differences were observed between the placebo group and the calcitonin group. At the 6-month follow-up timepoint, tumour volume had decreased by >/=10% in a total of 7 patients with a 37.9% (95% CI 31.3-44.5%) mean volume reduction in this subgroup. Complete remission was not observed.

Rapid growth of giant cell granuloma in pregnancy treated with calcitonin

The giant cell granuloma of the jaws is a benign osteolytic lesion that may be treated by curettage, intralesional corticosteroids, or calcitonin. These medical treatments may be particularly useful when lesions arise in the immature facial skeleton, recur, or enlarge very rapidly-the last two situations being recognized complications of pregnancy. In this study, a patient is presented with a central giant cell lesion of the maxilla that switched from a relatively indolent growth pattern to become a rapidly enlarging and destructive lesion in the maxilla almost immediately after the patient became pregnant. Although calcitonin treatment is normally avoided in pregnancy, it proved highly effective, caused no obstetric or fetal side effects, and was not contraindicated by renal failure due to lupus nephritis. Histologically, the lesion was converted to a fibro-osseous lesion-like appearance. On the basis of the results of this case, calcitonin appears to be a safe, effective, and conservative treatment for giant cell granulomas that enlarge rapidly during pregnancy.

TGF-beta isoform and receptor expression in giant cell tumor and giant cell lesions of bone

The authors examined the distribution of tumor growth factor-beta (TGF-beta) isoforms and receptors in 35 giant cell tumor (GCT) of bone in comparison with a group of benign giant cell-containing lesions of bone, including 5 aneurysmal bone cysts, 2 cases of brown tumor of hyperparathyroidism, 3 nonossifying fibromas, and 7 cases of giant cell reparative granuloma. The results of immunohistochemical analysis of GCT showed a complete absence of TGF-beta1 expression in both mononuclear tumor cells and giant cells. Only reactive bone present within the tumor showed an intense immunoreactivity. Transforming growth factor-beta2 and TGF-beta3 were detected in the majority of cases (97.1% and 82.8%, respectively), whereas TGF-beta receptor type I (TGF-beta RI) and type II (TGF-beta RII) were diffusely expressed in all cases. Reverse transcription-polymerase chain reaction (RT-PCR) analysis performed on 10 GCTs with specific oligonucleotide primers demonstrated the presence of mRNA transcripts for TGF-beta1, 2, 3, and for TGF-beta RI and RII. Quantitative measurements of TGF-beta1 in conditioned media from primary cultures of GCT showed undetectable or very low amounts of the cytokine (0-23 pg/mL). The results of immunohistochemical analysis showed that all giant cell-containing lesions of bone were at least focally positive for the 3 isoform of TGF-beta, with positivity present both in osteoclast-like giant cells and mononuclear cells, and diffusely positive for TGF-beta RI and RII. Reverse transcription-polymerase chain reaction analysis conducted on samples from 3 nonossifying fibromas and 1 giant cell reparative granuloma confirmed the expression of the corresponding mRNA. In conclusion, according to the current data, GCT of bone can be distinguished from other giant cell-containing lesions of bone on the basis of the absence of TGF-beta1 expression at the protein level, which appears to be the result of posttranslational regulation processes.

pH dependence of bone resorption: mouse calvarial osteoclasts are activated by acidosis

We examined the effects of HCO(3)(-) and CO(2) acidosis on osteoclast-mediated Ca(2+) release from 3-day cultures of neonatal mouse calvaria. Ca(2+) release was minimal above pH 7.2 in control cultures but was stimulated strongly by the addition of small amounts of H(+) to culture medium (HCO(3)(-) acidosis). For example, addition of 4 meq/l H(+) reduced pH from 7.12 to 7.03 and increased Ca(2+) release 3.8-fold. The largest stimulatory effects (8- to 11-fold), observed with 15-16 meq/l added H(+), were comparable to the maximal Ca(2+) release elicited by 1,25-dihydroxyvitamin D(3) [1, 25(OH)(2)D(3); 10 nM], parathyroid hormone (10 nM), or prostaglandin E(2) (1 microM); the action of these osteolytic agents was attenuated strongly when ambient pH was increased from approximately 7.1 to approximately 7.3. CO(2) acidosis was a less effective stimulator of Ca(2+) release than HCO(3)(-) acidosis over a similar pH range. Ca(2+) release stimulated by HCO(3)(-) acidosis was almost completely blocked by salmon calcitonin (20 ng/ml), implying osteoclast involvement. In whole mount preparations of control half-calvaria, approximately 400 inactive osteoclast-like multinucleate cells were present; in calvaria exposed to HCO(3)(-) acidosis and to the other osteolytic agents studied, extensive osteoclastic resorption, with perforation of bones, was visible. HCO(3)(-) acidosis, however, reduced numbers of osteoclast-like cells by approximately 50%, whereas 1,25(OH)(2)D(3) treatment caused increases of approximately 75%. The results suggest that HCO(3)(-) acidosis stimulates resorption by activating mature osteoclasts already present in calvarial bones, rather than by inducing formation of new osteoclasts, and provide further support for the critical role of acid-base balance in controlling osteoclast function.

Differential expression of transforming growth factor-alpha and macrophage colony-stimulating factor/colony-stimulating factor-1R (c-fins) by multinucleated giant cells involved in pathological bone resorption at the site of orthopaedic implants

The immunologic response to prosthetic biomaterial particles is characterized by macrophage-rich inflammatory infiltrate, formation of multinucleated giant cells, and aseptic loosening at the site of arthroplasty. We investigated the in vivo expression and tissue distribution of transforming growth factor alpha, macrophage colony-stimulating factor, and the receptor for colony-stimulating factor-1 at the site of bone erosion in patients with clinically failed orthopaedic implants (n = 30). The expression was further compared with that detected in the inflamed synovial membranes from patients with rheumatoid arthritis or osteoarthritis (n = 15) and one patient with osteoclastoma (giant cell tumour of bone). Immunostaining of the tissue demonstrated positivity for transforming growth factor alpha within the inflammatory macrophage and multinucleated giant cell infiltrate in the diseased synovial membrane and the bone-implant interface. A comparative analysis between the synovium and retrieval interface membranes (pseudosynovium) revealed a high level of expression of transforming growth factor alpha, with intense membrane staining on multinucleated giant cells in all failed arthroplasties with pseudosynovium. In addition, the frequency, antigenic phenotype, and pattern of transforming growth factor alpha expression on multinucleated giant cells in the interface were markedly similar to those observed for multinucleated giant cells in osteoclastoma. Multinucleated giant cells within the interface lacked the expression of macrophage colony-stimulating factor and colony-stimulating factor-1 receptor, whereas those at the bone surfaces exhibited strong immunoreactivity. The predominant expression of transforming growth factor alpha by multinucleated giant cells in the bone-implant interface and its similarity to osteoclastoma highlight the importance of assessing transforming growth factor alpha as a possible contributor to the development of bone-resorbing giant cells at the site of failed orthopaedic implants.

A new specialized cell-matrix interaction in actively resorbing osteoclasts

We have identified a novel cell-matrix interaction in activated osteoclasts. Resorbing osteoclasts maintain a barrier adjacent to the bone surface that prevents the leakage of secreted protons and proteases from the resorption area. Using a series of fluorescent dyes of known molecular mass and different surface charge we established that negatively charged molecules with M(r)up to 10,000 rapidly accumulate underneath actively resorbing osteoclasts. Live cell imaging shows that staining could be detected underneath the osteoclasts as early as 30 seconds after the addition of the low molecular mass markers. We provide evidence that the actin cytoskeleton and the adhesion substrate in contact with the cells are critically involved in the maintenance of the sealing barrier. These data taken together suggest that the accumulation under resorbing osteoclasts is by diffusion rather than transcytotic delivery. Our results indicate that the net concentration of secreted and resorbed components is a balance between generation rate and limited diffusion rather than the presence of an impermeable barrier as previously suggested. This dynamic osteoclast sealing zone may, thus, provide the mechanism by which osteoclast migration and resorption can occur simultaneously.

Gene expression of osteoprotegerin ligand, osteoprotegerin, and receptor activator of NF-kappaB in giant cell tumor of bone: possible involvement in tumor cell-induced osteoclast-like cell formation

Giant cell tumor of bone (GCT) is a rare primary osteolytic tumor of bone that is characterized by massive tissue destruction at the epiphysis of long bones. There is no evidence that tumor cells themselves are capable of bone destruction; instead, it appears that the tumor cells of GCT act by promoting osteoclastogenesis and, as a consequence, osteoclastic bone resorption. However, the mechanism by which this is achieved is not understood. Here we attempted to determine whether osteoprotegerin ligand (OPGL), the factor that is necessary and essential for osteoclastogenesis, is involved in tumor cell-recruited osteoclast-like giant cell formation in GCT. Using fluorescence in situ hybridization, we sought to determine mRNA expression of OPGL, its receptor RANK, and its decoy receptor OPG in three major cell types of GCT. We demonstrated that OPG mRNA was expressed in all three cell types of GCT, OPGL transcripts were mainly detected in spindle-shaped stromal-like tumor cells, whereas RANK was expressed only in macrophage-like mononuclear cells and multinuclear osteoclast-like giant cells. By semiquantitative RT-PCR, we also showed that the level of OPGL mRNA in GCT is much higher than that in normal bone and osteogenic osteosarcoma. In contrast, a similar level of OPG transcripts was detected in these three kinds of tissues, and RANK mRNA was detectable only in GCT tissues. We have further examined the regulation of gene expression of OPGL and OPG in tumor cells in response to osteotropic hormones. Administration of 1,25(OH)(2)D(3) and dexamethasone resulted in maximum up-regulation of OPGL level and down-regulation of OPG level in cultured GCT stromal-like tumor cells and the mouse bone marrow-derived ST-2 stromal cell line. Furthermore, we have shown that tumor cells of GCT induce differentiation of RANK-expressing myeloid RAW(264.7) cells into osteoclast-like cells in the presence of 1,25(OH)(2)D(3) and dexamethasone. Our findings suggest that OPGL is involved in the tumor cell-induced osteoclast-like cell formation in GCT. The ratio of OPGL/OPG by tumor cells may contribute to the degree of osteoclastogenesis and bone resorption.

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

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

Development and characterization of a human in vitro resorption assay: demonstration of utility using novel antiresorptive agents

A human in vitro resorption assay has been developed using osteoclastoma-derived osteoclasts and used to evaluate novel antiresorptive agents including antagonists of the alphavbeta3 integrin, and inhibitors of cathepsin K and the osteoclast ATPase. The potency of novel compounds in the in vitro resorption assay correlates with functional assays for each class of inhibitor: the human alphavbeta3-mediated cell adhesion assay for the vitronectin receptor antagonists (r2 = 0.82), the chick osteoclast vacuolar ATPase enzyme assay for the H+-ATPase inhibitors (r2 = 0.77) and the recombinant human cathepsin K enzyme assay for the cathepsin K inhibitors (r2 = 0.80). Cell suspensions, rich in osteoclasts, are prepared by collagenase digestion of the tumor tissue. These cells can be stored long-term in liquid nitrogen and upon thawing maintain their bone-resorbing phenotype. The cryopreserved cells can be cultured on bovine cortical bone for 24-48 h and resorption can be measured by either confocal microscopy or biochemical assays. The resorptive activity of osteoclasts derived from a number of tumors can be inhibited reproducibly using a number of mechanistically unique antiresorptive compounds. In addition, the measurement of resorption pits by laser confocal microscopy correlates with the release of type I collagen C-telopeptides or N-telopeptides, as measured by enzyme-linked immunosorbent assay. Resorption can be measured reproducibly using a 48-h incubation of osteoclasts on bone slices, or a 24-h incubation with bone particles. This in vitro human osteoclast resorption assay provides a robust system for the evaluation of inhibitors of osteoclastic function that may be developed for the treatment of metabolic bone diseases such as osteoporosis.

Fra-1 potentiates osteoclastic differentiation in osteoclast-macrophage precursor cell lines

c-Fos, a component of the dimeric transcription factor AP-1, is necessary for osteoclast formation. To determine whether c-Fos can substitute for any or all of the stimuli needed for osteoclast induction, we infected osteoclast precursors with retroviral vectors expressing c-Fos or the Fos-related protein, Fra-1. The infected cells were incubated with or without osteoclast-inductive stimuli. Osteoclast formation from retroviral-infected precursors remained completely dependent on osteoclast-inductive stromal cells. Unexpectedly, infection of bipotential osteoclast-macrophage precursor cell lines with retroviruses expressing Fra-1 but not c-Fos caused a 10-100-fold increase in the number of precursors that developed calcitonin receptors associated with an increase in bone resorption. These observations suggest that, in the precursor cell lines, Fra-1 is a limiting factor for full responsiveness to the osteoclast-inductive environment. Fra-1 is therefore likely to play a role in osteoclast differentiation which is distinct from that of c-Fos.

Study of the cell biology and biochemistry of cherubism

AIMS

To establish whether the multinucleate cells in lesions of patients with cherubism are also osteoclasts and if this is the case whether they were responsive to calcitonin; to carry out cytogenetic studies on two members of the same family affected by cherubism in an attempt to identify any major chromosomal defects; and to perform an in-depth modern biochemical study of four children in the same family.

SUBJECTS AND METHODS

Four related children with cherubism were studied. Tissue taken from one of the children at elective decompression of an optic nerve was submitted to in vitro bone resorption studies. Cytogenetic studies were done on two of the children and biochemical studies on all four.

RESULTS

The multinucleate cells in the cherubic lesions were shown to be osteoclasts since they synthesised tartrate resistant acid phosphatase, expressed the vitronectin receptor, and resorbed bone. Bone resorption by the cultured multinucleate cells was significantly inhibited by calcitonin. High resolution cytogenetic studies failed to detect any chromosomal abnormalities in two children with cherubism. The biochemistry profile of all four children with cherubism showed that serum calcium, parathyroid hormone, parathyroid related hormone, calcitonin, and alkaline phosphatase were within normal levels. Urine analysis of pyridinium and deoxypyridinium cross links, hydroxyproline, and calcium in relation to urine creatinine were measured to assess bone resorption in these children, and the values were at the upper end of the normal range in all four.

CONCLUSIONS

Further studies are required to determine whether calcitonin treatment will control this grossly deforming disease until the time when the physiological changes that occur at puberty rectify the pathology. It is not recommended that biochemical markers of bone resorption are used in isolation to monitor the activity of cherubism in individuals because the results are based on a small number of children and because of reports of marked interindividual variation in the levels of these markers, particularly in children.

Prostaglandin E2, interleukin 1alpha, and tumor necrosis factor-alpha increase human osteoclast formation and bone resorption in vitro

Prostaglandin E2 (PGE2) and the cytokines interleukin (IL) 1alpha and tumor necrosis factor (TNF)alpha increase bone resorption in vivo, but the effect of these agents on osteoclastic bone resorption has never been studied in an in vitro human system. Our recently described human bone marrow culture system, in which osteoclasts are generated (vitronectin and calcitonin receptor-positive cells which resorb bone), was used to study the effects of these agents. Addition of indomethacin to macrophage colony-stimulating factor (M-CSF)-treated cultures nearly abolished osteoclast parameters, indicating that prostaglandins are virtually essential for human osteoclast formation. Additionally, PGE2 dose responsively increased osteoclast numbers and bone resorption. The effects of M-CSF and PGE2 are independent, as demonstrated by unaltered PGE2 concentrations in culture supernatants in spite of the dose-responsive increase in osteoclast parameters in response to M-CSF. The generation of osteoclasts in the presence of PGE2 occurred in favor of CD 14-positive macrophage formation. IL 1alpha and TNFalpha increased osteoclast parameters in a dose-responsive manner. Maximum stimulation yielded culture supernatant levels of PGE2 approximately the same as those concentrations of exogenous PGE2 that dramatically induced osteoclast formation. This osteoclast-inducing effect was inhibited both by indomethacin and by the specific inhibitor of inducible prostaglandin G/H synthase, NS398, and this was reversed by addition of exogenous PGE2. These results demonstrate unequivocally that IL 1alpha and TNFalpha enhance human osteoclast formation and suggest that they mediate their effects through PGE2.

Purification and characterisation of a tripeptidyl aminopeptidase I from rat spleen

A tripeptidyl aminopeptidase I with an M(r) of 47,000 Da has been purified from rat spleen. The N-terminal sequence of the enzyme and internal sequences did not resemble that of any known protein. The enzyme cleaves tripeptides from synthetic substrates provided that the N-terminus is unsubstituted and the amino acid in the P1 position is not charged. The enzyme also cleaves small peptides (angiotensin II and glucagon) releasing tripeptides but does not appear to demonstrate any preference for amino acids on either side of the cleavage site. The enzyme had maximum activity at pH 4 but was unstable above pH 7. Rat spleen tripeptidyl peptidase I was not inhibited by classical inhibitors of serine, cysteine, aspartate or metalloproteinases. The peptidase was potently inhibited by a series of substrate-based tripeptidyl chloromethyl ketones (Ki's of 10(-6)-10(-8) M). Inhibition was rapid and reversible. This mode of inhibition is different to the interaction between chloromethyl ketones and cysteine or serine peptidases. These tripeptidyl chloromethyl ketones were also inhibitors of bone resorption using an in vitro assay suggesting that a tripeptidyl peptidase is involved in the degradation of bone matrix proteins.

Osteoclasts are capable of particle phagocytosis and bone resorption

Osteoclasts are multinucleated cells specialized for the function of lacunar bone resorption. Although they are known to be capable of phagocytosis of inert particles, it is not known whether this abolishes their ability to respond to hormones or to form resorption lacunae. Human and rat osteoclasts were isolated from giant cell tumours of bone and rat long bones, respectively, and cultured on coverslips and cortical bone slices, both in the presence and in the absence of particles of latex (1 micron diameter) and polymethylmethacrylate (PMMA) (< 50 microns). By light microscopy, it was evident that osteoclasts which had phagocytosed both latex and PMMA particles remained responsive to calcitonin. Osteoclast phagocytosis of particles was also evident on scanning electron microscopy, where it could also be seen that these cells were associated with the formation of resorption lacunae. These findings underline the fact that the osteoclast is a true member of the mononuclear phagocyte system and that phagocytosis does not abrogate either its hormonal response to calcitonin or its highly specialized function of bone resorption. That osteoclasts which have phagocytosed biomaterial particles such as PMMA are still able to carry out lacunar bone resorption is of interest in clinical conditions such as aseptic loosening, where a heavy foreign body particle load is often associated with extensive bone resorption.

Human cord blood monocytes undergo terminal osteoclast differentiation in vitro in the presence of culture medium conditioned by giant cell tumor of bone

Osteoclasts (OCs), which form by fusion of hematopoietic precursor cells, are typically present in large numbers in giant cell tumors of bone (GCTBs). These tumors may, therefore, contain cells which secrete factors that stimulate recruitment and differentiation of OC precursors. Multinucleated cells resembling OCs also form in cultures of human cord blood monocytes (CBMs) stimulated by 1.25 dihydroxyvitamin D3, but these cells lack the ability to form bone resorption pits, the defining functional characteristic of mature OCs. CBMs may thus require additional stimulation to form OCs; we therefore investigated whether GCTBs are a source of such a stimulus. CBMs were stimulated in long term (21 day) culture by medium conditioned by explants of GCTBs; media collected within 15 days of explant (early-CM) and after 15 days (late-CM) were employed. We also cocultured CBMs with primary GCTB-derived stromal cells as well as immortalized bone marrow stroma-derived cells. CBMs stimulated by early-CM formed resorption pits on cortical bone slices; however, stimulation by late-CM resulted in virtually no resorption. Both early-CM and late-CM increased CBM proliferation, but not the proportion of vitronectin receptor positive or multinucleated cells. Coculture of CBMs with stromal cells of GCTBs or bone marrow did not result in bone resorption, although these stromal cells (most expressing alkaline phosphatase but progressively losing parathyroid hormone receptor expression) expressed mRNA for cytokines involved in OC differentiation, including macrophage-CSF, granulocyte-macrophage-CSF, IL-11, IL-6, and stem cell factor. Our results indicate that CBMs are capable of terminal OC differentiation in vitro, a process requiring 1,25 dihydroxyvitamin D3 as well as diffusible factor(s) which can be derived from GCTB. Stromal cells of GCTB may produce such factors in vivo, but do not support OC differentiation in vitro, possibly through phenotypic instability in culture.

Human osteoclast-like cells in primary culture

We describe a method for the isolation and culture of osteoclast-like cells from cancellous bone chips of iliac crests from patients undergoing reconstructive maxillofacial surgery. Under aseptic conditions, bone chips were cut into small pieces, incubated briefly with collagenase, and the isolated bone cells were separated from the bone chips by filtration using a nylon mesh. Bone cells were then cultured on a variety of surfaces for up to 10 days. Cell motility and fusion, together with the development of tartrate-resistant acid phosphatase activity, were seen in many cells soon after culture. The large osteoclast-like cells adhered to human cortical bone slices and produced resorption pits. These morphological and functional characteristics suggest that the cells we isolated and cultured were human osteoclasts and their precursors. Thus this method may provide a reliable means of obtaining human osteoclasts from normal tissue for short-term studies of their metabolism or from various skeletal diseases to study pathological aberrations and mechanisms.

Human osteoclasts, not osteoblasts, deposit osteopontin onto resorption surfaces: an in vitro and ex vivo study of remodeling bone

Osteopontin is a phosphorylated glycoprotein believed to be secreted by osteoblasts and deposited into the bone matrix to facilitate osteoclasts adhesion or to initiate osteoid mineralization. Previously we have presented contradictory evidence that osteoclasts express osteopontin mRNA in human remodeling bone. The aim of this study was to ascertain whether osteoclasts synthesize and deposit osteopontin in resorption lucunae. We characterized expression of osteopontin mRNA and protein expression in both intramembranous and endochondral ossification, as well as remodeling bone, in the human osteophyte. Osteopontin mRNA was expressed in osteoclast with tartrate-resistant acid phosphatase (TRAP) positivity within resorption lacunae. The osteoclasts and immediate resorption surfaces also expressed osteopontin. However, osteopontin mRNA and protein were weak (transient) or undetectable in osteoblasts at adjacent bone formation sites; no osteopontin expression was observed in the osteoid, although occasional reactivity was observed in osteocytes and the mineral-osteoid interface. In contrast, osteopontin was highly expressed in the osteoblasts and matrix of woven bone during intramembranous and endochondral ossification. The matrix expression correlated with mineralization; however, in some instances osteopontin deposition was observed prior to mineralization. Similarly, osteopontin expression was evident in cartilage matrix, solely at foci of mineralization. Chondroclasts expressed osteopontin mRNA and protein: the surfaces of resorbed calcified cartilage also expressed osteopontin. Abnormal, unmineralized matrices apparently lacked deposited osteopontin, but were nevertheless resorbed by osteoclasts; the osteoclasts and resorbed surfaces expressed no osteopontin protein. That osteoclasts are responsible for the deposition of osteopontin was confirmed in vitro, whereby resorption pits in whale dentine and bovine bone slices, produced by isolated human osteoclasts, contained deposited osteopontin. Osteopontin may facilitate the adhesion (or detachment) of the osteoclast to the bone surface. Alternatively, the possibility that osteopontin may act as a postresorptive signal to recruit osteoblasts, or to polarize and direct the mineralization of the formed osteoid, is discussed.