Blood markers of osteoclastic differentiation in periparturient dairy cows at different parities, with and without milk fever

Osteoprotegerin (OPG) inhibits osteoclast (OC) differentiation. TRAP5b (tartrate-resistant acid phosphatase 5b) secreted by OCs reflects the numbers of mature OCs. This study assessed these OC-related markers around parturition in cows of different parities and in cows with milk fever (MF). The blood OPG and TRAP5b concentrations, as well as the ratio of OPG to TRAP5b (O/T), were measured beginning 3 weeks before (-21 d) and over a few days after calving in 49 Holstein Friesian cows at first (n = 8), second (n = 17), third (n = 12), and fourth or greater (n = 12) parities. The ratio of O/T at -21 d to O/T at calving (PreCOT) was also calculated. In the third and greater parities, seven cows developed MF (non-MF, n = 17). Regardless of the development of MF, the serum OPG started to decline in the last week of gestation only in the cows entering the second lactation, while the blood TRAP5b increased at calving in all cows. O/T decreased toward parturition only in multiparous cows. The decrease in O/T at caving was less pronounced in MF cows. PreCOT was negatively correlated with lactation number only in multiparous cows (n = 41, ρ = -0.50, P < .01). This study implied that OC differentiation toward calving was tapered in cows with advanced parities, and these indexes predict the risk of MF.

Characterization of osteoclasts derived from CD14+ monocytes isolated from peripheral blood

Bone resorption is solely mediated by osteoclasts. Therefore, a pure osteoclast population is of high interest for the investigation of biological aspects of the osteoclasts, such as the direct effect of growth factors and hormones, as well as for testing and characterizing inhibitors of bone resorption. We have established a pure, stable, and reproducible system for purification of human osteoclasts from peripheral blood. We isolated CD14-positive (CD14+) monocytes using anti-CD14-coated beads. After isolation, the monocytes are differentiated into mature osteoclasts by stimulation with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappaB ligand (RANKL). Osteoclast formation was only observed in the CD14+ population, not in the CD14- population, and only in the presence of both M-CSF and RANKL, confirming that the CD14+ system is a pure population of osteoclast precursors. No expression of osteoclast markers was observed in the absence of RANKL, whereas RANKL dose-dependently induced the expression of cathepsin K, tartrate-resistant acid phosphatase (TRACP), and matrix metallo proteinase (MMP)-9. Furthermore, morphological characterization of the cells demonstrated that actin rings were only formed in the presence of RANKL. Moreover, the osteoclasts were capable of forming acidic resorption lacunae, and inhibitors of lysosomal acidification attenuated this process. Finally, we measured the response to known bone resorption inhibitors, and found that the osteoclasts were sensitive to these and thereby provided a robust and valid method for interpretation of the effect of antiresorptive compounds. In conclusion, we have established a robust assay for developing osteoclasts that can be used to study several biological aspects of the osteoclasts and which in combination with the resorption marker CTX-I provides a useful tool for evaluating osteoclast function in vitro.

Changes of bone remodeling immediately after parathyroidectomy for secondary hyperparathyroidism

BACKGROUND

Successful parathyroidectomy for secondary hyperparathyroidism alleviates bone pain and is followed by the development of hypophosphatemia and hypocalcemia, as well as an increase in bone mineral density. An increase in osteoblast surface (Ob.S/BS) is not observed several months after surgery. In this study, we investigated early bone changes at 1 week after parathyroidectomy and the mechanism underlying an increase in bone mineral density.

METHODS

Fourteen patients with severe secondary hyperparathyroidism underwent iliac bone biopsy before and 1 week after parathyroidectomy. Changes in histomorphometric parameters, including osteoclast surface (Oc.S/BS), eroded surface (ES/BS), erosion depth (E.De), fibrosis volume (Fb.V/TV), Ob.S/BS, osteoid volume (OV/BV), osteoid surface (OS/BS), and osteoid thickness (O.Th), were investigated. Changes in texture of mineralized bone and osteoid seams were also investigated.

RESULTS

Oc.S/BS (P < 0.001), ES/BS (P < 0.01), and E.De (P < 0.001) decreased, but Fb.V/TV did not change at 1 week postoperatively. In particular, osteoclasts disappeared in almost all patients. Ob.S/BS (P < 0.001) increased, and cuboidal osteoblasts were proliferating on the trabecular surface where osteoclasts had existed before parathyroidectomy. As a result, newly developed osteoblasts coexisted with fibrous tissue after surgery. OV/BV (P < 0.005), OS/BS (P < 0.005), and O.Th (P < 0.005) increased, with lamellar osteoid volume showing a particular increase. Bone mineralization continued despite the low postoperative serum parathyroid hormone level.

CONCLUSION

A rapid decrease in serum parathyroid hormone level after parathyroidectomy appears to suppress bone resorption, as well as cause a transient marked increase in bone formation and an increase in normal lamellar osteoid seams.

Cellular mechanisms of osteoclast formation and lacunar resorption in giant cell granuloma of the jaw

BACKGROUND

Giant cell granuloma (GCG) is an osteolytic tumour of the jaw which is characterised by the presence of both mononuclear and multinucleated (osteoclast-like) giant cell components. The nature of these component cells and the pathogenesis of the extensive osteolysis associated with this lesion is uncertain.

METHODS

Using cell culture techniques and immunohistochemistry, we defined the phenotypic characteristics of the mononuclear and multinucleated cells present in four cases of GCG of the jaw. We also analysed the cellular and humoral factors associated with osteoclast formation and osteolysis in these tumours and determined whether GCG stromal cells are capable of supporting osteoclast formation.

RESULTS

GCG-derived giant cells expressed the phenotypic characteristics of osteoclasts (TRAP+, VNR+, and calcitonin responsive) and were capable of lacunar resorption. In addition to macrophages, the mononuclear cell population contained numerous spindle-shaped stromal cells which proliferated in culture and expressed RANKL; these GCG-stromal cells were capable of supporting human osteoclast formation from circulating monocyte precursors.

CONCLUSION

Our findings indicate that the giant cells in GCG of the jaw are osteoclast-like and formed from monocyte/macrophage precursors which differentiate into osteoclasts under the influence of RANKL-expressing mononuclear stromal cells found in this lesion.

Novel mutations in the TCIRG1 gene encoding the a3 subunit of the vacuolar proton pump in patients affected by infantile malignant osteopetrosis

Fifty percent of the infantile malignant osteopetrosis (IMO) cases reported in the literature present mutations in the TCIRG1 gene encoding the 116-kDa osteoclast specific subunit of the vacuolar proton ATPase (ATP6I). In this study, we identified four novel mutations in a series of six IMO patients. All of these mutations correspond to single nucleotide changes and affect splice acceptor or donor sites, resulting in aberrant transcription products. We report also a missense mutation, G405R, previously described in several Costa Rican patients. This independent finding suggests that the highly conserved residue at amino acid 405 plays a critical role in the a3 subunit function. Finally, the results of this study were used to provide a prenatal diagnosis to one of the families.

A novel synthetic triazolotriazepine derivative JTT-606 inhibits bone resorption by down-regulation of action and production of bone resorptive factors

In the search for a new class of bone-sparing agents, we have conducted random screening of the domestic chemical library using 45Ca release assay from prelabeled cultured neonatal mouse calvariae and identified a novel synthetic triazolotriazepine JTT-606 as a candidate for a potent inhibitor of bone resorption. JTT-606 inhibited 45Ca release dose dependently not only in the control calvarial culture but also in the stimulated cultures by interleukin-1alpha (IL-1alpha), fibroblast growth factor 2 (FGF-2), and parathyroid hormone (PTH). JTT-606 also inhibited both basal and stimulated osteoclast-like (OCL) cell formation in the coculture of mouse osteoblastic cells and bone marrow cells dose dependently, indicating its inhibitory effect on osteoclast differentiation. Ex vivo OCL cell formation by cultured bone marrow cells collected from ovariectomized (OVX) mice also was decreased dose dependently by in vivo application of JTT-606 to a level similar to that from sham-operated mice. Furthermore, JTT-606 inhibited resorbed pit formation by isolated mature osteoclasts as well as by unfractionated bone cells derived from rabbit long bones in the control and FGF-2-stimulated cultures dose dependently, indicating both the direct and the indirect actions of JTT-606 on mature osteoclast function. In addition, JTT-606 reduced production of IL-1alpha, tumor necrosis factor alpha (TNF-alpha), IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF) in the human peripheral blood mononuclear cell culture. In vivo analyses of mature OVX rats revealed that the application of JTT-606 for 12 weeks increased the BMD of the lumbar spine and decreased the levels of serum osteocalcin and urine deoxypyridinoline to levels similar to those of 17beta-estradiol-treated OVX rats. We propose that JTT-606 may inhibit both osteoclast differentiation and function by down-regulating both the action and the production of bone resorptive factors. It is speculated that JTT-606 could be a potent agent for the treatment of osteopenic disorders with elevated osteoclastic bone resorption.

Osteoclast-like cells formed in long-term human bone marrow cultures express a similar surface phenotype as authentic osteoclasts

Long-term cultures of human bone marrow form multinucleated cells (MNC) with many functional characteristics of osteoclasts including: expression of tartrate-resistant acid phosphatase, appropriate responses to osteotropic hormones, calcitonin-induced contraction and formation of resorption lacunae on calcified matrices. However, it is unclear if these cells express similar surface antigens as expressed by authentic osteoclasts, since they form on plastic surfaces in the absence of bone. Bone may be required to complete the differentiation process for osteoclasts. Therefore, we have examined the surface phenotype of MNC and compared it with that of osteoclasts freshly isolated from bone, to determine if MNC express similar surface antigens, and if MNC express antigens which identify their cellular origin. Similar to bone-derived osteoclasts, MNC formed in long-term human bone marrow culture expressed osteoclast-specific antigens (detected by monoclonal antibodies 13c2 and 23c6) and did not express Fc receptors, T cell specific antigens, most myeloid antigens or mature macrophage antigens. In contrast to authentic osteoclasts, MNC reacted with a monoclonal antibody (Mol) which identifies an antigen present on myeloblasts, monocytes, granulocytes, and null cells from human peripheral blood and bone marrow. MNC also reacted with the monoclonal antibody My11, which is present on CFU-GM, the granulocyte-macrophage colony-forming cell, the probable precursor for MNC. These data demonstrate that MNC formed in long-term human marrow cultures express a similar surface phenotype to osteoclasts. This phenotype is different from that expressed by macrophage polykaryons. In addition, MNC also expressed monocyte-related antigens (My11, Mol), suggesting that are derived from or related to the monocytic lineage.

Bronchoscopic cytology of metastatic breast carcinoma with osteoclastlike giant cells

The cytologic appearance of bronchoscopic washings and brushings is reported in a rare case of pulmonary metastasis from breast carcinoma with osteoclastlike giant cells.

Investigation of the origin of the osteoclast by use of transplantation on chick chorioallantoic membrane

In recent years, it has become generally accepted that osteoblasts and osteoclasts are derived from separate stem cell lines: the osteoblasts from mesenchymal cells, and the osteoclasts from cells of hematopoietic origin. Principal evidence for this belief comes from experimental approaches, such as autoradiography, parabiosis, quail-chick nuclear markers, lysosomal markers in beige mice, and so forth. However, the problem remains unsolved. For further investigation of osteoclast origin, three experimental designs were employed: (1) six-day quail limb buds were directly implanted into chick chorioallantoic membrane; (2) viable or devitalized Dunn osteosarcomas were implanted onto chorioallantoic membrane; and (3) six-day quail limb buds in diffusion chambers were implanted onto chorioallantoic membrane by use of exogenous parathyroid hormone (PTH) stimulation. In these experiments, osteoblasts and osteoclasts were identified from host (chorioallantoic membrane) and implant (quail limb bud). Limb buds within diffusion chambers formed osteoclasts in response to PTH despite no blood circulation or bone marrow formation. These data indicate that the mesenchyme (perichondrium) plays an important role. Either osteoclast mononuclear precursors have migrated from hematopoietic sources to the perichondrium before transplantation of the limb buds or mesenchymal cells of developing bone can form osteoclasts. Thus, the origin of the osteoclasts should still be considered an unsettled question.

When is it an osteoclast?

Using acid phosphatase as a marker, osteoclasts were examined from single sections of undemineralised iliac crest biopsies from patients with renal failure and from normal controls. Eighty one per cent of the cells from controls and 56% of the cells from patients with renal failure appeared to be non-nucleated or mononucleated. Serial sections showed, however, that 73% of the control cells were actually multinucleated as were 91% of the patients' cells. Howship's lacunae were present in similar proportions in the controls whether the cells were multinucleated or not, suggesting that they should all be classed as osteoclasts. More multinucleated cells and lacunae were present in the patients with renal failure. It is concluded that all acid phosphatase cells adjacent to bone are osteoclasts and that the presence of more lacunae and multinucleated cells in renal failure is compatible with enhanced cellular resorption.