Reduced Bone Resorption In Toothless (Osteopetrotic) Rats–An Abnormality of Osteoblasts Related to Their Inability to Activate Osteoclast Activity In Vitro

Osteopetrosis is a heterogeneous group of metabolic bone disorders characterized by reduced bone resorption. In the toothless (tl) osteopetrotic rat mutation there are few osteoclasts and mutants are not cured by bone marrow transplants. This suggests that the defect(s) in tl rats is within the skeletal microenvironment and not one of stem cell incompetence. Osteoblasts are known to play a role in bone resorption and abnormalities in these cells have been reported in tl rats. We explored the ability of osteoblasts from tl rats to activate resorption by normal osteoclasts when co-cultured in the presence of 1, 25-dihydroxyvitamin D (l, 25(OH)2D). Stimulation with l, 25(OH)2D produced a highly significant response in normal osteoblast co-cultures, but no response was observed in mutant cultures over a wide dose range. Ligand-binding studies demonstrated no abnormalities in vitamin D receptor (VDR) affinity, but mutant osteoblasts had reduced VDR numbers. Taken together with the demonstrated resistance of these mutants to the hypercalcemic effects of l, 25(OH)2D and parathyroid hormone in vivo, these data implicate osteoblasts in the pathogenesis of this mutation.     

Slipped capital femoral epiphysis in a patient with type II autosomal dominant osteopetrosis

We report on a 13-year-old boy who had a slipped capital femoral epiphysis and was found to have type II benign autosomal dominant osteopetrosis. This association has not previously been reported.     

Osteopetrosis-variable otorhinolaryngological manifestations

Osteopetrosis is a rare hereditary metabolic disease associated with a myriad of otolaryngological presentations. Three cases with varying otolaryngological presentations are described here. A brief review of the radiological changes of interest to the otorhinolaryngologist is being made.     

Osteopetrosis Complicated by Osteomyelitis of the Maxilla and Mandible: Light and Electron Microscopic Findings

This report presents a case of osteopetrosis in a 25-year-old male, which was complicated by the development of osteomyelitis in the maxilla and mandible following traumatic injury and tooth extractions. The osteomyelitis in the mandible was refractory to marginal resection and antibiotic therapy. Partial resection with mandible reconstruction was then carried out. Light and backscattered electron scanning microscopy revealed sclerosis of spongy bone and variations in mineral density of the bone matrix. There was also a prominent periosteal bone formation in regions affected by osteomyelitis. An 18-month follow-up showed absence of active infections in the face and oral structures, with a focal area of bone exposure in the right parasymphysis. However, development of anemia and bone marrow deficiency will likely affect prognosis. The importance of preventive oral health care and dental/periodontal managements in osteopetrosis is emphasized.     

Bone particles from osteopetrotic mice not cured by bone marrow transplants are resorbed in normal littermates

Osteosclerotic (oc/oc) and osteopetrotic (op/op) mice are not cured by bone marrow transplantation from normal littermates. The possibility that this is due to production of poorly resorbable bone was examined by comparing the fate of mutant and normal bone particles implanted subcutaneously in normal hosts. Bone, removed aseptically from calvarial and tibial sites of normal littermates and mutants, was cleaned of adherent soft tissue, ground and sieved to a particle size of 70–300 μm. Aliquots (17–20 mg) of bone from each phenotype of each stock were pelleted and implanted beneath the anterior thoracic skin of normal littermates for two weeks. Particle density in tissue sections was determined as percent of field by a point-counting method. Giant cell response was recorded as number per high-power field. Percent bone present initially was determined in pellets implanted for less than 24 hr. Bone particles were reduced in each pellet with time, about 25% of the original volume being removed in two weeks. No statistically significant differences were noted in the rates of disappearance of mutant and normal bone or in the percentage or number of giant cells in implants of mutant and normal bone in either stock. Furthermore, these values were not different from identical studies in microphthalmic mice, an osteopetrotic stock cured by bone marrow transplantation. These data suggest that the failure of osteopetrotic and osteosclerotic mice to be cured by bone marrow transplants from normal littermates is not due to the presence of unresorbable bone.     

Carbonic anhydrase isozymes of osteoclasts and erythrocytes of osteopetrotic microphthalmic mice

The content of carbonic anhydrase isozymes I (CA I) and II (CA II) in red blood cells and bone of osteopetrotic microphthalmic (mi/mi) mice was analyzed. Monospecific rabbit polyclonal antibodies against purified rat carbonic anhydrase I or II detected both isozymes in hemolysates of both normal and mi/mi mice. Total carbonic anhydrase activity measurements of hemolysates from normal or mi/mi mice were identical. A procedure based on bromopyruvate inactivation was devised to measure the relative contributions of CA I and II isozymes to the carbon dioxide hydration activity of hemolyzates. CA II dominates the observed activity of hemolysates of normal and mi/mi mice. Immunohistochemical studies showed that CA II was present in osteoclasts of tibial and calvarial bones of both normal and mi/mi mice. Thus, in contrast to the several cases of inherited osteopetrosis in humans, there is no lack of active CA II in erythrocytes of mi/mi mice. The absence of CA II, therefore, does not appear to play a role in the etiology of osteopetrosis in the mi/mi mouse.     

Osteoclast kinetics in osteopetrotic (ia) rats cured by spleen cell transfers from normal littermates

Summary Excessive skeletal mass and reduced bone resorption characteristic of osteopetrosis in youngia rats can be corrected by irradiation and transfer of spleen cells from normal littermates. Cell population analyses and³H-thymidine (³H-TdR) autoradiographic methods were used to determine osteoclast population dynamics and kinetics of incorporation of nuclei following whole-body irradiation and spleen cell transfer inia/ia rats and in untreatedia rats and their (ia/+) normal littermates. The numbers of osteoclasts per metaphyseal area were greater inia rats than in (ia/+) normal littermates. Untreatedia rats had greater rates of incorporation of³H-TdR-labeled nuclei into osteoclasts but were reduced to near normal values following irradiation and spleen cell transfer. Labeled osteoclast nuclei were first seen in the primary spongiosa of the femoral metaphysis and with increasing time appeared at greater distances from the epiphyseal growth plate as the bones grew in length. These sites of osteoclast neogenesis correspond to sites where restoration of bone resorption is initially seen following bone marrow and splenic transplants in the treatment of osteopetrosis.     

Effects of vitamin D binding protein-macrophage activating factor (DBP-MAF) infusion on bone resorption in two osteopetrotic mutations

Osteopetrosis is a heterogeneous group of bone diseases characterized by an excess accumulation of bone and a variety of immune defects. Osteopetrosis (op) and incisors absent (ia) are two nonallelic mutations in the rat which demonstrated these skeletal defects as a result of reduced bone resorption. Osteopetrotic (op) rats have severe sclerosis as a result of reduced numbers of osteoclasts which are structurally abnormal. The sclerosis in ia rats is not as severe as in op mutants; they have elevated numbers of osteoclasts, but they are also morphologically abnormal, lacking a ruffled border. Both of these mutations have defects in the inflammation-primed activation of macrophages. They demonstrate independent defects in the cascade involved in the conversion of vitamin D binding protein (DBP) to a potent macrophage activating factor (DBP-MAF). Because this factor may also play a role in the pathogenesis of osteoclastic dysfunction, the effects of ex vivo-generated DBP-MAF were evaluated on the skeletal system of these two mutations. Newborn ia and op rats and normal littermate controls were injected with DBP-MAF or vehicle once every 4 days from birth until 2 weeks of age, at which time bone samples were collected to evaluate a number of skeletal parameters. DBP-MAF treated op rats had an increased number of osteoclasts and the majority of them exhibited normal structure. There was also reduced bone volume in the treated op animals and an associated increased cellularity of the marrow spaces. The skeletal sclerosis was also corrected in the ia rats; the bone marrow cavity size was significantly enlarged and the majority of the osteoclasts appeared normal with extensive ruffled borders. Superoxide production was enhanced to normal levels in the osteoclasts from the treated ia animals as well. These studies demonstrate that the skeletal defects in both mutations can be improved with exogenous DBP-MAF and that this protein is involved in the pathogenesis of the disease.     

Mineral and matrix alterations in the bones of incisors-absent (ia/ia) osteopetrotic rats

Summary The bones of incisors-absent (ia/ia) osteopetrotic rats differ from those of their normal littermates (ia/+) in histologic and radiographic appearance and in mechanical properties. This study examined how the mineral and matrices of osteopetrotic metaphyses and calvaria differed from normal controls. Bones of 11-day-old and 52-day-old osteopetrotic animals had higher ash (mineral) contents that age-matched controls; osteopetrotic metaphyses had elevated hexosamine contents, indicative of the persistence of cartilage. Calcium acidic phospholipid phosphate complexes, involved in initiation of hydroxyapatite formationin vivo andin vitro, were significantly reduced in content in all osteopetrotic bones. These results suggest that in the osteopetrotic rat, where osteoclast activity is defective, new mineral formation is reduced and replaced by accretion of mineral on existing crystals. Fractionation of osteopetrotic bone particles by density centrifugation demonstrated that the osteopetrotic bone was much more mineralized than that of age-matched controls. X-ray diffraction analysis of the mineralized fractions indicated a lack of growth of mineral crystals during maturation of the osteopetrotic animals. The absence of remodeling was apparent from the elevated Ca:P ratios of the highly mineralized osteopetrotic bone fractions, and from the high hexosamine content of these dense fractions. These observations may explain some of the unusual mechanical properties of osteopetrotic bone.     

Osteopetrosis--a review and report of two cases

We present a brief review of the rare condition of osteopetrosis together with two case reports of this disease in the same family affecting the jaws. The first in a 41-year-old woman, and the second in her 39-year-old brother. Plain films and computed tomography showed marked sclerosis of the affected bones with obliteration of the medullary cavities and thickening of the cortices as well as multiple absent and unerupted teeth. In addition radiographs showed discrete mixed radiopaque/radiolucent areas consistent with the appearance of fibro-cemento-osseous dysplasia, but which may also represent part of the overall spectrum of bone changes in osteopetrosis.