Consequences of Daily Administered Parathyroid Hormone on Myeloma Growth, Bone Disease, and Molecular Profiling of Whole Myelomatous Bone

Induction of osteolytic bone lesions in multiple myeloma is caused by an uncoupling of osteoclastic bone resorption and osteoblastic bone formation. Current management of myeloma bone disease is limited to the use of antiresorptive agents such as bisphosphonates.We tested the effects of daily administered parathyroid hormone (PTH) on bone disease and myeloma growth, and we investigated molecular mechanisms by analyzing gene expression profiles of unique myeloma cell lines and primary myeloma cells engrafted in SCID-rab and SCID-hu mouse models. PTH resulted in increased bone mineral density of myelomatous bones and reduced tumor burden, which reflected the dependence of primary myeloma cells on the bone marrow microenvironment. Treatment with PTH also increased bone mineral density of uninvolved murine bones in myelomatous hosts and bone mineral density of implanted human bones in nonmyelomatous hosts. In myelomatous bone, PTH markedly increased the number of osteoblasts and bone-formation parameters, and the number of osteoclasts was unaffected or moderately reduced. Pretreatment with PTH before injecting myeloma cells increased bone mineral density of the implanted bone and delayed tumor progression. Human global gene expression profiling of myelomatous bones from SCID-hu mice treated with PTH or saline revealed activation of multiple distinct pathways involved in bone formation and coupling; involvement of Wnt signaling was prominent. Treatment with PTH also downregulated markers typically expressed by osteoclasts and myeloma cells, and altered expression of genes that control oxidative stress and inflammation. PTH receptors were not expressed by myeloma cells, and PTH had no effect on myeloma cell growth in vitro.We conclude that PTH-induced bone formation in myelomatous bones is mediated by activation of multiple signaling pathways involved in osteoblastogenesis and attenuated bone resorption and myeloma growth; mechanisms involve increased osteoblast production of anti-myeloma factors and minimized myeloma induction of inflammatory conditions

Immunolocalization of receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) in Meckel's cartilage compared with developing endochondral bones in mice

We examined the immunolocalization of receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) in areas of resorption caused by osteoclasts/chondroclasts on embryonic days 14–16 (E14–16) in Meckel's cartilage, and compared the results with those in endochondral bones in mice. Intense RANKL and OPG immunoreactivity was detected in the chondrocytes in Meckel's cartilage. On E15, when the incisor teeth were closest to the middle portion of Meckel's cartilage, tartrate-resistant acid phosphatase (TRAP)-positive cells appeared on the lateral side of the cartilage. Furthermore, the dental follicle showed moderate immunoreactivity for RANKL and OPG, whereas osteoblasts derived from perichondral cells were immunonegative for RANKL and OPG in that area. On E16, cartilage resorption by TRAP-positive cells had progressed at the differential position, and intensely immunoreactive products of RANKL were overlapped on and found to exist next to TRAP-positive cells in the resorption area. In developing metatarsal tissue, OPG immunoreactivity was intense in periosteal osteoblasts, whereas RANKL was only faintly seen in some of the periosteal cells. In epiphyseal chondrocytes of the developing femur, RANKL immunoreactivity was moderate, and OPG scarcely detected. These results indicate a peculiarity of RANKL and OPG immunolocalization in resorption of Meckel's cartilage. Growth of the incisor teeth may be involved in the time- and position-specific resorption of Meckel's cartilage through local regulation of the RANKL/OPG system in dental follicular cells and periosteal osteoblasts, whereas RANKL and OPG in chondrocytes seem to contribute to resorption through regulation of the chondroclast function

Calcitonin impairs the anabolic effect of PTH in young rats and stimulates expression of sclerostin by osteocytes

The therapeutic goal of increasing bone mass by co-treatment of parathyroid hormone (PTH) and an osteoclast inhibitor has been complicated by the undefined contribution of osteoclasts to the anabolic activity of PTH. To determine whether active osteoclasts are required at the time of PTH administration, we administered a low dose of the transient osteoclast inhibitor salmon calcitonin (sCT) to young rats receiving an anabolic PTH regimen. Co-administration of sCT significantly blunted the anabolic effect of PTH as measured by peripheral quantitative computer tomography (pQCT) and histomorphometry in the femur and tibia, respectively. To determine gene targets of sCT, we carried out quantitative real time PCR and microarray analysis of metaphyseal samples 1.5, 4 and 6.5h after administration of a single injection of PTH, sCT or PTH+sCT. Known targets of PTH action, IL-6, ephrinB2 and RANKL, were not modified by co-administration with sCT. Surprisingly, at all time points, we noted a significant upregulation of sclerostin mRNA by sCT treatment, as well as down-regulation of two other osteocyte gene products, MEPE and DMP1. Immunohistochemistry confirmed that sCT administration increased the percentage of osteocytes expressing sclerostin, suggesting a mechanism by which sCT reduced the anabolic effect of PTH. Neither mRNA for CT receptor (Calcr) nor labeled CT binding could be detected in sclerostin-enriched cells differentiated from primary calvarial osteoblasts. In contrast, osteocytes freshly isolated from calvariae expressed a high level of Calcr mRNA. Furthermore immunohistochemistry revealed co-localization of CT receptor (CTR) and sclerostin in some osteocytes in calvarial sections. Taken together these data indicate that co-treatment with sCT can blunt the anabolic effect of PTH and this may involve direct stimulation of sclerostin production by osteocytes. These data directly implicate calcitonin as a negative regulator of bone formation through a previously unsuspected mechanism

A predator–prey based mathematical model of the bone remodelling cycle: Exploring the relationship between the model parameters and biochemical factors

© IMechE 2014. Bone remodelling is a vital process which enables bone to repair, renew and optimize itself. Disorders in the bone remodelling process are inevitably manifested in bone-related diseases, such as hypothyroidism, primary hyperparathyroidism and osteoporosis. In our previous work, a predator-prey based mathematical model was developed to simulate bone remodelling cycles under normal and two pathological conditions, hypothyroidism and primary hyperparathyroidism, for trabecular bone at a fixed point. However, the biochemical meanings of the model parameters were not fully explored. This article first extends the previous work by proposing relationships between the model parameters and biochemical factors involved in the bone remodelling process and by examining whether those relationships do predict the behaviours observed in vivo. The model is then applied to the simulation and investigation of bone remodelling of postmenopausal osteoporosis. The proposed connections are supported by good agreement between the model simulations and published experimental observations for the normal condition and all three pathological variations in bone remodelling