calcitonin and Osteopetrosis

Malignant osteopetrosis is characterized by impaired osteoclast activity. Osteoclasts derive from hematopoietic stem cells. In osteopetrosis, marrow cavities fail to develop, resulting in extramedullary hematopoiesis and the presence of stem cells in the bloodstream. Resistance to 1,25-(OH)2D3 may be involved in the pathogenesis of the disease. Sensitivity to 1,25-(OH)2D3, calcitonin sensitivity, and expression of the osteoclast-associated vitronectin receptor (VR) was examined in cultures of circulating mononuclear cells of seven osteopetrotic infants (1.5-6 months old). Since peripheral blood from age-matched children contains few stem cells, umbilical cord blood was used as control. Mononucleated cells were isolated by the Ficoll-Hypaque method and cultured (10(6) cells per ml) in alpha-MEM containing 20% horse serum in presence or absence of added 1,25-(OH)2D3. VR was identified by immunochemical staining with MAb 23C6. 1,25-(OH)2D3 at 10(-8) M significantly stimulated the formation of multinucleated cells (MNC) in cultures from all osteopetrotic patients and cord blood samples. Cells from three of five patients responded to 10(-9) M 1,25-(OH)2D3, the minimal stimulatory concentration for cord blood. Salmon calcitonin (100 ng/ml) partially inhibited the 10(-8) M 1,25-(OH)2D3-induced MNC formation in cultures from three of six patients and in cultures of all cord blood samples. In both types of cultures mononuclear cells and MNC cross-reacted with MAb 23C6, and 1,25-(OH)2D3 concentration did not influence the number and percentage of these cells. This study does not support the hypothesis of 1,25-(OH)2D3 resistance in osteopetrotic infants and shows that mononuclear cells expressing VR, possibly osteoclast progenitors, develop in cultures of circulating mononuclear cells from these infants. 1,25-(OH)2D3 may not be closely involved in VR expression.

Topics: Bone Resorption; Calcitonin; Calcitriol; Cells, Cultured; Dentin; Humans; Infant; Leukocyte Count; Osteoclasts; Osteopetrosis; Receptors, Cytoadhesin; Receptors, Vitronectin

We have reported that osteoblastic cells are required for differentiation of osteoclast progenitors in splenic tissues into multinucleated osteoclasts. In the present study we examined the pathogenesis of the osteoclast deficiency in osteopetrotic (op/op) mice using a coculture system of spleen cells and osteoblastic cells. When spleen cells obtained from op/op or normal (+/?) littermates of op/+ parent mice were cocultured with osteoblastic cells obtained from calvaria of normal ddy strain mice, numerous tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNCs) were formed in the presence of 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3]. Most of the TRAP-positive MNCs bound [125I]salmon calcitonin. This suggests that there is no abnormality in the osteoclast progenitors present in the splenic tissues of op/op mice. When osteoblastic cells from +/? littermates were cocultured with normal spleen cells from ddy mice, TRAP-positive MNCs were similarly formed in response to 1 alpha,25(OH)2D3. In contrast, in cocultures of op/op osteoblastic cells with normal spleen cells, no TRAP-positive cells appeared, even in the presence of 1 alpha,25(OH)2D3. The op/op mutation was recently reported to exist in the coding region of the macrophage colony-stimulating factor (M-CSF) gene. Adding M-CSF and 1 alpha,25(OH)2D3 to the coculture with op/op osteoblastic cells induced the appearance of TRAP-positive MNCs with calcitonin receptors. These results clearly indicate that osteoclast deficiency in op/op mice is due to a defect in the local microenvironment in bone, in which M-CSF produced by osteoblastic cells plays a critical role in osteoclast development.

Topics: Acid Phosphatase; Animals; Calcitonin; Calcitriol; Cell Differentiation; Cells, Cultured; Female; Macrophage Colony-Stimulating Factor; Male; Mice; Osteoblasts; Osteoclasts; Osteopetrosis; Spleen; Stem Cells; Tartrates

A 3 year old girl presented with malignant osteopetrosis, which was treated by allogeneic bone marrow transplantation. Successful engraftment was complicated by prolonged hypercalcaemia, which was controlled by a combination of a bisphosphonate, phosphate infusions, vigorous resalination, and salmon calcitonin. She was alive and well 16 months after the transplant.

Topics: Bone Marrow Transplantation; Calcitonin; Child, Preschool; Diphosphonates; Female; Humans; Hypercalcemia; Osteopetrosis; Pamidronate; Phosphates; Postoperative Complications

Macrophages and osteoclasts derive from related cell lines. In osteopetrotic mutants the function of osteoclasts is greatly reduced compared to that in normal animals or children and macrophage function is variably affected depending upon the mutation. To further explore macrophage function in osteopetrosis we examined the regulation of cyclic AMP production in macrophages from mutants and normal littermates of the osteopetrotic stock incisors-absent (ia) in the rat. Surface stimulation by latex particles of elicited peritoneal macrophages from normal or osteopetrotic (ia) mutant rats caused an identical increase in the accumulation of cyclic AMP. This effect was inhibited in normal animals by coincubation of macrophages with calcitonin (CT) but this inhibition was either absent or less marked in macrophages from mutant littermates. In contrast to human monocytes preincubation of rat macrophages with pertussis toxin did not relieve this inhibition. This implies that rat peritoneal macrophages respond to CT by a different mechanism. These results demonstrate altered macrophage function in osteopetrotic animals and may be functionally related to the reduced CT binding previously described in ia osteoclasts. Furthermore, the coexistence of reduced function of macrophages and osteoclasts in the ia mutation suggests that macrophages and osteoclasts share a common progenitor.

Topics: Animals; Calcitonin; Cyclic AMP; Macrophage Activation; Macrophages; Microspheres; Osteopetrosis; Peritoneal Cavity; Pertussis Toxin; Rats; Rats, Mutant Strains; Virulence Factors, Bordetella