Susan D. Neale

Human osteoclast formation and bone resorption by monocytes and synovial macrophages in rheumatoid arthritis.

OBJECTIVE: To determine whether synovial macrophages and monocytes isolated from patients with rheumatoid arthritis patients are capable of differentiating into osteoclastic bone resorbing cells; and the cellular and humoral conditions required for this to occur. METHODS: Macrophages isolated from the synovium and monocytes from the peripheral blood of rheumatoid arthritis patients were cultured on bone slices and coverslips, in the presence and absence of UMR 106 rat osteoblast-like cells, 1,25-dihydroxy vitamin D3 (1,25(OH)2D3) and macrophage colony stimulating factor (M-CSF), and assessed for cytochemical and functional evidence of osteoclast differentiation. RESULTS: Isolated calcitonin receptor (CTR), tartrate resistant acid phosphatase (TRAP), and vitronectin receptor (VNR) negative, CD11b and CD14 positive monocytes and macrophages differentiated into CTR, TRAP, and VNR positive multinucleated cells capable of extensive lacunar bone resorption when co-cultured for 14 d with UMR 106 cells in the presence 1,25(OH)2D3 and M-CSF. CONCLUSIONS: Mononuclear phagocytes (monocytes and macrophages) from rheumatoid arthritis patients are capable of differentiating into multinucleated cells showing all the cytochemical and functional criteria of mature osteoclasts. Synovial macrophage-osteoclast differentiation may represent an important cellular mechanism in the bone destruction associated with rheumatoid arthritis.

Human arthroplasty derived macrophages differentiate into osteoclastic bone resorbing cells.

OBJECTIVE In aseptic loosening, a heavy macrophage response to biomaterial wear particles is commonly found in arthroplasty tissues. The aim of this study was to discover if these cells contribute to the bone resorption of aseptic loosening by differentiating into osteoclasts. METHODS Macrophages were isolated from the pseudocapsule and pseudomembrane of loose cemented and uncemented hip arthroplasties at the time of revision surgery and then co-cultured on glass coverslips and dentine slices with UMR 106 rat osteoblast-like cells, both in the presence and absence of 1,25 dihydroxyvitamin D3 [1,25(OH)2D3]. Macrophages isolated from the synovial membrane of patients with osteoarthritis (OA) undergoing hip replacements were similarly studied as a control group. RESULTS After 24 hours incubation, most cells isolated from the above periprosthetic tissues strongly expressed macrophage (CD11b, CD14) but not osteoclast markers. However, after 14 days incubation, numerous multinucleated cells showing the phenotypic features of osteoclasts (that is, positive for tartrate resistant acid phosphatase, the vitronectin receptor, and capable of extensive lacunar resorption) formed in co-cultures of arthroplasty derived macrophages and UMR 106 cells, in the presence of 1,25(OH)2D3. The addition of an antibody to macrophage colony stimulating factor (M-CSF) considerably reduced macrophage-osteoclast differentiation and hence the lacunar resorption seen in these co-cultures. In contrast, OA synovial macrophage/UMR 106 co-cultures showed little or no evidence of macrophage-osteoclast differentiation and this was only seen when human M-CSF was added to the co-cultures. CONCLUSION This is the first report showing that human macrophages isolated directly from periprosthetic tissues surrounding loosened implants can differentiate into multinucleated cells showing all the functional and cytochemical characteristics of osteoclasts. In contrast with other macrophage populations, exogenous M-CSF is not required for this to occur. In the context of the heavy macrophage response to wear particles in periprosthetic tissues macrophage-osteoclast differentiation may represent an important cellular mechanism whereby osteolysis is effected in aseptic loosening.

Osteoclast differentiation from circulating mononuclear precursors in Paget’s disease is hypersensitive to 1,25-dihydroxyvitamin D3 and RANKL

A characteristic feature of Pagets disease is an increase in the number of osteoclasts in bone. Osteoclasts are formed from mononuclear phagocyte precursors that circulate in the monocyte fraction of peripheral blood. These cells require the presence of RANK ligand (RANKL)-expressing osteoblastic cells and human macrophage colony-stimulating factor (M-CSF) to form osteoclasts in vitro. To determine the role of osteoclast differentiation from circulating precursors in Pagets disease, we cultured monocytes from Pagets patients and gender- and age-matched normal controls with no evidence of bone disease for up to 21 days in the presence of UMR 106 cells and various concentrations of M-CSF (1-25 ng/mL) and 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] (10(-10) to 10(-7) mol/L). Relative to controls, there was a significant increase in the extent of osteoclast differentiation from pagetic monocytes as assessed by expression of tartrate-resistant acid phosphatase (TRAP), vitronectin receptor (VNR), and lacunar bone resorption. Serial dilution experiments (2 x 10(5) to 2 x 10(2) cells/well) showed no difference in the concentration of osteoclast precursors in the peripheral blood. In Pagets patients with high serum alkaline phosphatase (sAP) levels, increased sensitivity to the osteoclastogenic effect of 1,25(OH)(2)D(3) was noted. Osteoclast differentiation did not occur when M-CSF was substituted by interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6R), and these factors did not stimulate osteoclast differentiation in the presence of M-CSF. In this in vitro coculture system, osteoclast formation was inhibited by osteoprotegerin in a dose-dependent manner. In the presence of RANKL (5-30 ng/mL) and M-CSF (25 ng/mL), osteoclast formation and bone resorption were significantly increased in cultures of monocytes from patients with high and low sAP levels as compared with normal controls. Our findings suggest that the increase in osteoclast numbers seen in Pagets disease results not from an increase in the number of circulating precursors in peripheral blood but rather from an increased sensitivity of osteoclast precursors to the humoral factors, 1,25(OH)(2)D(3) and RANKL, which regulate osteoclast formation.

The effect of macrophage-colony stimulating factor and other humoral factors (interleukin-1, -3, -6, and -11, tumor necrosis factor-alpha, and granulocyte macrophage-colony stimulating factor) on human osteoclast formation from circulating cells.

Macrophage-colony stimulating factor (M-CSF) is an essential requirement for human osteoclast formation, but its effect on the proliferation and differentiation of circulating osteoclast precursor cells is unknown. Other growth factors and cytokines are also known to support/stimulate osteoclast formation from mouse marrow precursors, but it is not certain whether these factors similarly influence human osteoclast formation. In this study, human monocytes were cocultured with osteoblast-like UMR-106 cells on coverslips and dentine slices for up to 21 days in the presence of 1,25 dihydroxyvitamin D(3) (10(-7) mol/L), dexamethasone (10(-8) mol/L), and various concentrations of either M-CSF or other humoral factors (interleukin [IL]-1beta, IL-3, IL-6, and IL-11; tumor necrosis factor-alpha [TNF-alpha]; and granulocyte macrophage [GM]-CSF). The effect on osteoclast formation was assessed by tartrate-resistant acid phosphatase (TRAP) and vitronectin receptor staining and lacunar bone resorption. The results of time-course and proliferation studies showed that M-CSF stimulated both the proliferative and differentiation stages of human osteoclast formation from circulating osteoclast precursors in a dose-dependent manner. A high concentration of M-CSF (100 ng/mL) did not inhibit osteoclast formation. IL-3 and GM-CSF were also capable of stimulating human osteoclast formation, although these growth factors were much less potent than M-CSF. IL-3- and GM-CSF-stimulated osteoclast formation was inhibited by an antibody specific for human M-CSF. Osteoclast formation and lacunar resorption was not seen when either TNF-alpha, IL-1beta, IL-6 (+ soluble IL-6 receptor), or IL-11 was substituted for M-CSF during coculture. These results confirm that M-CSF is essential for human osteoclast formation from circulating mononuclear precursors, and also shows that IL-3 and GM-CSF may support osteoclast differentiation via the stimulation of M-CSF production by human monocytes.

Progression of acetabular periprosthetic osteolytic lesions measured with computed tomography.

BACKGROUND A better understanding of the factors associated with the size and/or progression of osteolytic lesions has been hampered by a lack of sensitivity of radiographic measurement techniques. METHODS We retrospectively analyzed quantitative computed tomography scans that had been made with use of a high-resolution multi-slice scanner with a metal artifact-suppression protocol. The scans had been made to determine the volume of osteolytic lesions around thirty-five cementless Harris-Galante acetabular components that had been in situ for at least ten years. Repeat scans of thirty hips allowed for the measurement of progression in the size of osteolytic lesions over a one-year period. Associations between the volume of osteolytic lesions, progression in the size of the lesions, polyethylene wear since the time of implantation, change in component position, and patient-related variables (age, gender, body mass index, activity level, walking limitations, joint pain, and function) were determined. RESULTS In sixteen of the thirty hips that had repeat computed tomography scans, the lesions progressed in size during the study period. The median size of the lesions in these sixteen hips was 10.3 cm(3) at the time of the initial scan, compared with 13.3 cm(3) at a median of fifteen months later (p = 0.001). Osteolytic lesions measuring >10 cm(3) in volume on the initial scan were 2.5 times (95% confidence interval 1.3 to 4.8 times) more likely to progress in size over one year than smaller lesions were. Patients with greater polyethylene wear rates, higher activity levels, no walking limitations, and larger prosthetic femoral head dimensions (26 or 28 mm) had significantly larger osteolytic lesions (p < 0.0001, p = 0.009, p = 0.006, and p = 0.028, respectively). Progression in the size of the osteolytic lesions over one year was significantly associated with larger initial osteolytic lesions (p = 0.002), greater polyethylene wear rates (p = 0.009), and larger (26 or 28-mm) prosthetic femoral head dimensions (p = 0.019). CONCLUSIONS There is considerable variation in the rates of progression of the size of osteolytic lesions around stable acetabular components. Lesion size and the progression of lesion size are generally related to polyethylene wear rates, higher patient activity levels, and larger-diameter femoral heads. Osteolytic lesions measuring >10 cm(3) in volume are associated with a high rate of progression.

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.

Progression of periacetabular osteolytic lesions.

BACKGROUND The development of three-dimensional computed tomography (CT) imaging techniques has enabled the detection, accurate measurement, and monitoring of periprosthetic osteolytic lesions. The aim of this study was to track the progression in size of osteolytic lesions and to determine those factors that are associated with the risk of progression. A secondary aim was to investigate whether progression in size of osteolytic lesions could be monitored with use of radiographs. METHODS We retrospectively determined, with use of sequential CT scans, the progression of periacetabular osteolysis over a period of as much as nine years in a cohort of twenty-six patients (thirty acetabular components) in whom the cementless acetabular component or components had been in place for longer than ten years at the time of the initial CT scan. High-resolution CT scans with metal-artifact suppression were used to determine the volume of osteolytic lesions. Progression in the size of osteolytic lesions per year was calculated as the change in the volume of osteolytic lesions between serial CT scans. Associations were determined between the progression in size of osteolytic lesions, osteolysis rate at the initial CT, patient age, sex, walking limitations, and activity level. Progression in size of osteolytic lesions as determined with use of CT was compared with that determined with use of radiographs. RESULTS Mean progression in the size of osteolytic lesions, as determined with use of CT, was 1.5 cm(3)/yr (range, 0 to 7.5 cm(3)/yr). The amount of osteolysis at the initial CT scan and patient activity were good predictors of osteolytic lesion progression. The strongest predictor of osteolytic lesion progression occurred when these two risk factors were combined (p = 0.0019). The value of radiographs was limited to monitoring of larger lesions identified by CT. CONCLUSIONS This is the first study to report on the progression of osteolysis adjacent to cementless acetabular components from medium to long-term follow-up. The data suggest that the osteolysis rate at the initial CT and patient activity can be useful factors in predicting the progression in size of periacetabular osteolytic lesions.

Imaging Periprosthetic Osteolysis Around Total Knee Arthroplasties Using a Human Cadaver Model

We examined the sensitivity and accuracy of measuring osteolysis around total knee arthroplasty (TKA) on radiographs, computed tomography (CT), and magnetic resonance imaging (MRI) in a cadaver model. Fifty-four simulated osteolytic defects ranging from 0.7 to 14 cm(3) were created in 6 cadaver knees implanted with either a cemented or an uncemented TKA. Three blinded investigators assessed the presence, location, and volume of defects on radiographs and CT and MRI scans with metal reduction protocols. Both CT and MRI had significantly higher sensitivities and specificities than did plain radiographs (P < .005). Overall, there was no difference in the accuracy of defect volume measurements between CT and MRI (P = .574). This study demonstrates the limitations of radiographs and the high sensitivity and specificity of both CT and MRI in assessing osteolysis around TKA.

Circulating RANKL is inversely related to RANKL mRNA levels in bone in osteoarthritic males

IntroductionThe relationship of circulating levels of receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) with the expression of these molecules in bone has not been established. The objective of this study was to measure, in humans, the serum levels of RANKL and OPG, and the corresponding levels in bone of mRNA encoding these proteins.MethodsFasting blood samples were obtained on the day of surgery from patients presenting for hip replacement surgery for primary osteoarthritis (OA). Intraoperatively, samples of intertrochanteric trabecular bone were collected for analysis of OPG and RANKL mRNA, using real time RT-PCR. Samples were obtained from 40 patients (15 men with age range 50 to 79 years, and 25 women with age range 47 to 87 years). Serum total RANKL and free OPG levels were measured using ELISA.ResultsSerum OPG levels increased over the age range of this cohort. In the men RANKL mRNA levels were positively related to age, whereas serum RANKL levels were negatively related to age. Again, in the men serum RANKL levels were inversely related (r = -0.70, P = 0.007) to RANKL mRNA levels. Also in the male group, RANKL mRNA levels were associated with a number of indices of bone structure (bone volume fraction relative to bone tissue volume, specific surface of bone relative to bone tissue volume, and trabecular thickness), bone remodelling (eroded surface and osteoid surface), and biochemical markers of bone turnover (serum alkaline phosphatase and osteocalcin, and urinary deoxypyridinoline).ConclusionThis is the first report to show a relationship between serum RANKL and the expression of RANKL mRNA in bone.

Periprosthetic osteolysis after total hip replacement: molecular pathology and clinical management

AbstractPeriprosthetic osteolysis is a serious complication of total hip replacement (THR) in the medium to long term. Although often asymptomatic, osteolysis can lead to prosthesis loosening and periprosthetic fracture. These complications cause significant morbidity and require complex revision surgery. Here, we review advances in our understanding of the cell and tissue response to particles produced by wear of the articular and non-articular surfaces of prostheses. We discuss the molecular and cellular regulators of osteoclast formation and bone resorptive activity, a better understanding of which may lead to pharmacological treatments for periprosthetic osteolysis. We describe the development of imaging techniques for the detection and measurement of osteolysis around THR prostheses, which enable improved clinical management of patients, provide a means of evaluating outcomes of non-surgical treatments for periprosthetic osteolysis, and assist in pre-operative planning for revision surgery. Finally, there have been advances in the materials used for bearing surfaces to minimise wear, and we review the literature regarding the performance of these new materials to date.