Fluconazole-Induced Protein Changes in Osteogenic and Immune Metabolic Pathways of Dental Pulp Mesenchymal Stem Cells of Osteopetrosis Patients

Osteopetrosis is a rare inherited disease caused by osteoclast failure, resulting in increasing bone density in humans. Patients with osteopetrosis possess several dental and cranial complications. Since carbonic anhydrase II (CA-II) deficiency is a major cause of osteopetrosis, CA-II activators might be an attractive potential treatment option for osteopetrosis patients. We conducted comprehensive label-free quantitative proteomics analysis on Fluconazole-treated Dental Pulp Mesenchymal Stem/Stromal Cells from CA-II-Deficient Osteopetrosis Patients. We identified 251 distinct differentially expressed proteins between healthy subjects, as well as untreated and azole-treated derived cells from osteopetrosis patients. Twenty-six (26) of these proteins were closely associated with osteogenesis and osteopetrosis disease. Among them are ATP1A2, CPOX, Ap2 alpha, RAP1B and some members of the RAB protein family. Others include AnnexinA1, 5, PYGL, OSTF1 and PGAM4, all interacting with OSTM1 in the catalytic reactions of HCO3 and the Cl- channel via CAII regulation. In addition, the pro-inflammatory/osteoclast regulatory proteins RACK1, MTSE, STING1, S100A13, ECE1 and TRIM10 are involved. We have identified proteins involved in osteogenic and immune metabolic pathways, including ERK 1/2, phosphatase and ATPase, which opens the door for some CA activators to be used as an alternative drug therapy for osteopetrosis patients. These findings propose that fluconazole might be a potential treatment agent for CAII- deficient OP patients. Altogether, our findings provide a basis for further work to elucidate the clinical utility of azole, a CA activator, as a therapeutic for OP.

Chloroquine increases osteoclast activity in vitro but does not improve the osteopetrotic bone phenotype of ADO2 mice

Autosomal Dominant Osteopetrosis type II (ADO2) is a bone disease of impaired osteoclastic bone resorption that usually results from heterozygous missense mutations in the chloride channel 7 (CLCN7) gene. We created mouse models of ADO2 by introducing a knock-in (p.G213R) mutation in the Clcn7 gene, which is analogous to one of the common mutations (G215R) found in humans. The mutation leads to severe osteopetrosis and lethality in homozygous mice but produces substantial phenotypic variability in heterozygous mice on different genetic backgrounds that phenocopy the human disease of ADO2. ADO2 is an osteoclast-intrinsic disease, and lysosomal enzymes and proteins are critical for osteoclast activity. Chloroquine (CQ) is known to affect lysosomal trafficking, intracellular signaling and the lysosomal and vesicular pH, suggesting it might improve ADO2 osteoclast function. We tested this hypothesis in cell culture studies using osteoclasts derived from wild-type (WT or ADO2+/+) and ADO2 heterozygous (ADO2+/-) mice and found that CQ and its metabolite desethylchloroquine (DCQ), significantly increased ADO2+/- osteoclasts bone resorption activity in vitro, whereas bone resorption of ADO2+/+ osteoclasts was increased only by DCQ. In addition, we exploited our unique animal model of ADO2 on 129 background to identify the effect of CQ for the treatment of ADO2. Female ADO2 mice at 8 weeks of age were treated with 5 doses of CQ (1, 2.5, 5, 7.5 and 10 mg/kg BW/day) via drinking water for 6 months. Bone mineral density and bone micro-architecture were analyzed by longitudinal in vivo DXA and micro-CT at baseline, 3 and 6 months. Serum bone biomarkers (CTX, TRAP and P1NP) were also analyzed at these time points. CQ treatment at the doses tested failed to produce any significant changes of aBMD, BMC (whole body, femur and spine) and trabecular BV/TV (distal femur) in ADO2 mice compared to the control group (water only). Further, levels of bone biomarkers were not significantly changed due to CQ treatment in these mice. Our findings indicate that while CQ increased osteoclast activity in vitro, it did not improve the osteopetrotic bone phenotypes in ADO2 heterozygous mice.

In silico experiments of bone remodeling explore metabolic diseases and their drug treatment

Bone structure and function are maintained by well-regulated bone metabolism and remodeling. Although the underlying molecular and cellular mechanisms are now being understood, physiological and pathological states of bone are still difficult to predict due to the complexity of intercellular signaling. We have now developed a novel in silico experimental platform, V-Bone, to integratively explore bone remodeling by linking complex microscopic molecular/cellular interactions to macroscopic tissue/organ adaptations. Mechano-biochemical couplings modeled in V-Bone relate bone adaptation to mechanical loading and reproduce metabolic bone diseases such as osteoporosis and osteopetrosis. V-Bone also enables in silico perturbation on a specific signaling molecule to observe bone metabolic dynamics over time. We also demonstrate that this platform provides a powerful way to predict in silico therapeutic effects of drugs against metabolic bone diseases. We anticipate that these in silico experiments will substantially accelerate research into bone metabolism and remodeling.

Biological Effects of Anti-RANKL Antibody and Zoledronic Acid on Growth and Tooth Eruption in Growing Mice

The anti-bone resorptive drugs denosumab, an anti-human-RANKL antibody, and zoledronic acid (ZOL), a nitrogen-containing bisphosphonate, have recently been applied for treatment of pediatric patients with bone diseases, though details regarding their effects in growing children have yet to be fully elucidated. In the present study, we administered these anti-resorptive drugs to mice from the age of 1 week and continued once-weekly injections for a total of 7 times. Mice that received the anti-RANKL antibody displayed normal growth and tooth eruption, though osteopetrotic bone volume gain in long and alveolar bones was noted, while there were nearly no osteoclasts and a normal of number osteoblasts observed. In contrast, ZOL significantly delayed body growth, tooth root formation, and tooth eruption, with increased osteoclast and decreased osteoblast numbers. These findings suggest regulation of tooth eruption via osteoblast differentiation by some types of anti-resorptive drugs.

Decompressive Cranioplasty in a Patient with Osteopetrosis

BACKGROUND

Osteopetrosis is a heterogeneous group of uncommon congenital disorders that causes bony sclerosis and remodeling. Patients who are symptomatic can show significant neurologic consequences with the involvement of cranial nerves and symptoms of increased intracranial pressure (ICP).

CASE DESCRIPTION

We report an unusual case of a 26-year-old woman with an autosomal-dominant type of osteopetrosis who presented with headache and severe visual deterioration, both attributed to increased ICP. A hemicranioplasty was preformed, resulting in the resolution of her symptoms of ICP and stabilization of her vision. Postoperative imaging showed expansion of the ventricles and the subarachnoid spaces with an improvement of the associated cerebellar herniation.

CONCLUSIONS

In conclusion, in patients with symptomatic osteopetrosis, cranioplasty can be considered as an option to treat high ICP-related symptoms.

Ultrastructural Analyses of Alveolar Bone in a Patient With Osteomyelitis Secondary to Osteopetrosis: A Review of the Literature

Osteopetrosis is a generic term for generalized sclerotic conditions caused by rare genetic disorders. Decreased osteoclastic activities disturb bone remodeling, resulting in greater mineral density and greater compressive strength; therefore, bone fracture is a major physical symptom of osteopetrosis. Osteomyelitis of the maxilla or mandible is a common and well-documented complication of osteopetrosis. Local infection, such as odontogenic infection, is more likely to lead to osteomyelitis, and treatment strategies can be challenging. However, detailed ultrastructural analyses of bone from patients with osteopetrosis and odontogenic infection are limited. This report describes a case of osteomyelitis of the maxilla and mandible secondary to osteopetrosis in an adult patient and presents ultrastructural data of alveolar bone tissue analyzed by contact microradiography, electron probe microanalysis, and x-ray diffraction. Cases of osteomyelitis of the jaw secondary to osteopetrosis also are reviewed.

High dose calcitriol in osteopetrorickets

Osteopetrorickets is a rare autosomal recessive disorder of osteoclast function characterized by abnormally dense bone and failure of resorption of calcified cartilage. Rickets is a paradoxical complication of osteopetrosis, resulting from the inability of the osteoclasts to maintain a normal calcium-phosphorus balance in the extracellular fluid. We report a patient with an unusual case of infantile osteopetro-rickets who was admitted with anterior fontanel bulging and was treated with haploidentical bone marrow transplantation.

Assessment of osteoclast number and function: application in the development of new and improved treatment modalities for bone diseases

Numerous experimental and clinical observations suggest that overall changes in bone resorption during menopause or treatment with hormone replacement therapy (HRT) are combined effects of changes in osteoclast number and function. Moreover, due to a coupling between osteoclastic bone resorption and osteoblastic bone formation, pronounced alteration of osteoclast number will eventually lead to alteration of osteoblastic bone formation. Fragments of type I collagen, such as the C- and N-terminal telopeptides of collagen type I (CTX and NTX, respectively), are generated during bone resorption and hence can be used as surrogate markers of osteoclast function. Circulating levels of different enzymes in the serum, such as TRAP 5b and cathepsin K are proportional to the number of osteoclasts, and hence can be used as surrogate markers of osteoclast number. Since antiresorptive effects can be obtained in different ways, we felt it was timely to discuss the different scenarios, highlight differences specific to different pharmacological interventions with different mechanisms of action, and discuss how these bone markers can assist us in a deeper analysis of the pharmacodynamics and safety profile of existing and upcoming drug candidates.

Malignant infantile osteopetrosis: a rare cause of neonatal hypocalcemia

Malignant infantile osteopetrosis is a rare autosomal recessive disorder characterized by presentation in the first few months of life with manifestations relating to an underlying defect in osteoclastic bone resorption. This report describes a 10 day-old boy in whom neonatal hypocalcemia was present and whose brother had died with the diagnosis of osteopetrosis.

Interferon gamma-1b: new indication. Severe malignant osteopetrosis: too many unknowns

(1) Severe malignant osteopetrosis is a very rare disease. The principal manifestations are anaemia, infections, sensory disorders and fractures, due to generalised bone condensation. The disease is generally fatal in childhood. The only treatment capable of modifying the natural outcome is bone marrow transplantation. The benefits of high-dose steroids and calcitriol are usually modest and transient. (2) Severe malignant osteopetrosis is a new licensed indication for interferon gamma-1b, a drug known to reduce the incidence of severe infections in children with chronic septic granulomatosis. (3) An unblinded trial involving 15 children with a mean age of about one year compared calcitriol plus interferon gamma-1b with calcitriol alone. The time to treatment failure was longer with the combination, based on a combined endpoint chosen to make the statistical analysis more sensitive. (4) A clinical trial involving 15 patients, who were compared with a historical series of 94 untreated patients, provided ambiguous results. (5) In these trials the main adverse effect of interferon gamma-1b was a flu-like syndrome. (6) Given the gravity of severe malignant osteopetrosis, the limited available treatment options, and the rarity of serious adverse events with interferon gamma-1b, evaluation of this therapy should continue.

Therapeutic potential of vitamin D-binding protein

Vitamin D-binding protein (DBP) is a multi-functional plasma protein with many important functions. These include transport of vitamin D metabolites, control of bone development, binding of fatty acids, sequestration of actin and a range of less-defined roles in modulating immune and inflammatory responses. Exploitation of the unique properties of DBP could enable the development of important therapeutic agents for the treatment of a variety of diseases.

Autosomal malignant osteopetrosis. From diagnosis to therapy

Osteopetrosis is a heterogeneous family of rare human genetic disorders due to markedly decreased bone resorption. It is one among disorders causing osteosclerosis of the trabecular bone and/or hyperostosis of the cortical bone. Four types of human osteopetrosis have been clearly defined, but patients with atypical symptoms are frequent, suggesting that there are additional forms. The most severe expression of this condition in its malignant form is inherited as an autosomal recessive disorder and it is usually fatal before school age. It presents with failure to thrive, severe hepatosplenomegaly, pancytopenia and nerve compression leading to blindness and deafness during infancy. The case of a 2-month-old female child with severe hepatosplenomegaly, failure to thrive, nystagmus, pancytopenia, gengival hyperplasia, optic atrophy, absent evoked visual potential and increased bone density within the total skeleton, is reported. Diagnosis of autosomal recessive malignant osteopetrosis was established by transiliac bone biopsy. She underwent bone marrow transplantation, but died soon afterwards. This rare and mortal disorder of bone formation requires early diagnosis and immediate pharmacological treatment, consisting in administration of vitamin D, in order to enhance bone resorption and of prednisone to improve hematological indexes and, if possible, bone marrow transplantation in order to ameliorate quality of life and survival.

Apparent cure of a newborn with malignant osteopetrosis using prednisone therapy

A newborn girl with hemorrhagic purpura, suspected neonatal sepsis, and pale and dry skin was lethargic with remarkable hepatosplenomegaly, convergent strabismus, severe anemia, and elevated alkaline phosphatase activity. Radiographs showed a generalized increase in bone density, small medullary cavities, sclerosis of the skull and vertebrae, transverse wavy stripes of sclerotic bone in the metaphyses, and bone-in-bone appearance in phalanges of hands and feet. On this basis, she was diagnosed with malignant infantile osteopetrosis. On the first day of life, the infant was given a blood transfusion and vitamin K (1 mg intravenously [iv]). Corticosteroid therapy was started with prednisone (2 mg/kg per day). She showed marked improvement of symptoms. On the 26th day and 42nd day of life, she received additional blood transfusions. On the 49th day, the patient was discharged and corticosteroid therapy was continued at a regimen of 5 mg/day. Subsequent blood sample analyses revealed normal values for age. At 1 year of life, a bone marrow sample showed normal white and red cell lineages. X-ray confirmed attenuation of the bone sclerosis; therefore, bone marrow transplantation (BMT) was not implemented. At the age of 1.5 years, prednisone therapy was discontinued gradually and withdrawn before the age of 2 years. Subsequent follow-up showed normalization of all radiological and hematologic parameters. At present, the patient is 3 years old and appears healthy with apparently complete regression of the disease.

Histochemical examination of osteoblastic activity in op/op mice with or without injection of recombinant M-CSF

Osteopetrotic (op/op) mice do not exhibit bone remodeling because of defective osteoclast formation caused by the depletion of macrophage colony-stimulating factor (M-CSF). In the present study, we investigated tibial bones of op/op mice with or without prior injections of M-CSF to determine whether osteoclast formation and subsequent bone resorption could activate osteoblasts, which is known as a "coupling" phenomenon. In op/op mice, no osteoclasts were present, but the metaphyseal osteoblasts adjacent to the growth plate cartilage seemed to be active, revealing an intense alkaline phosphatase (ALPase) immunoreactivity. Consequently, primary trabecular bones were extended continuously to the diaphysis, indicating that bone modeling is well achieved in op/op mice. In contrast with the metaphysis, most of the diaphyseal osteoblasts were flattened and showed weak ALPase activity, and, as a result, they seemed to be less active. Osteopontin (OPN) was localized slightly at the interface between bone and cartilage matrices of the primary trabeculae. In contrast, in op/op mice injected with M-CSF, tartrate-resistant acid phosphatase-positive osteoclasts appeared, resorbing trabecular bones of the diaphyseal region. The diaphyseal osteoblasts in the vicinity of the active osteoclasts were cuboidal and exhibited strong ALPase immunoreactivity. OPN was observed not only at the bone-cartilage interface, but also significantly on the resorption lacunae beneath the bone-resorbing osteoclasts. These observations indicate that the activation of diaphyseal osteoblasts appears to be coupled with osteoclast formation and subsequent osteoclastic bone resorption. Alternatively, the metaphyseal osteoblasts at the chondro-osseous junction seemed to be less affected by osteoclastic activity.

Dual-energy x-ray absorptiometry in osteopetrosis

We have used dual-energy x-ray absorptiometry (DXA) in evaluation and follow-up of a patient with osteopetrosis, before and after cord blood transplantation. Other methods of follow-up in such cases have been described, but the use of DXA has not previously been reported. We have shown that DXA offers a safe means of assessing disease progression, the timing of treatment, and response after therapy for osteopetrosis.

The toothless osteopetrotic rat has a normal vitamin D-binding protein-macrophage activating factor (DBP-MAF) cascade and chondrodysplasia resistant to treatments with colony stimulating factor-1 (CSF-1) and/or DBP-MAF

The osteopetrotic rat mutation toothless (tl) is characterized by little or no bone resorption, few osteoclasts and macrophages, and chondrodysplasia at the growth plates. Short-term treatment of tl rats with colony-stimulating factor-1 (CSF-1) has been shown to increase the number of osteoclasts and macrophages, producing dramatic resolution of skeletal sclerosis at some, but not all, sites. Defects in production of vitamin D-binding protein-macrophage activating factor (DBP-MAF) have been identified in two other independent osteopetrotic mutations of the rat (op and ia), and two in the mouse (op and mi), in which macrophages and osteoclasts can be activated by the administration of exogenous DBP-MAF. The present studies were undertaken to examine the histology and residual growth defects in tl rats following longer CSF-1 treatments, to investigate the possibility that exogenous DBP-MAF might act synergistically with CSF-1 to improve the tl phenotype, and to assess the integrity of the endogenous DBP-MAF pathway in this mutation. CSF-1 treatment-with or without DBP-MAF-induced resorption of metaphyseal bone to the growth plate on the marrow side, improved slightly but did not normalize long bone growth, and caused no improvement in the abnormal histology of the growth plate. Injections of lysophosphatidylcholine (lyso-Pc) to prime macrophage activation via the DBP-MAF pathway raised superoxide production to similar levels in peritoneal macrophages from both normal and mutant animals, indicating no defect in the DBP-MAF pathway in tl rats. Interestingly, pretreatments with CSF-1 alone also increased superoxide production, although the mechanism for this remains unknown. In summary, we find that, unlike other osteopetrotic mutations investigated to date, the DBP-MAF pathway does not appear to be defective in the tl rat; that additional DBP-MAF does not augment the beneficial skeletal effects seen with CSF-1 alone; and that the growth plate chondrodystrophy seen in this mutation is unaffected by either molecule. Thus, the tl mutation intercepts the function of a gene required for both normal endochondral ossification and bone resorption, thereby uncoupling the coordination of skeletal metabolism required for normal long bone growth.

Auditory ossicle abnormalities and hearing loss in the toothless (osteopetrotic) mutation in the rat and their improvement after treatment with colony-stimulating factor-1

Osteopetrosis describes a group of skeletal metabolic diseases of heterogeneous etiology and varied severity that produces a generalized accumulation of skeletal mass, the result of reduced bone resorption. Inherited in a variety of species including humans, the most severe forms are lethal. Among common features are progressive blindness and deafness of controversial etiologies for which there are no universally effective treatments. We have studied the auditory responsiveness and auditory ossicle quantitative histomorphology and temporal bone vasculature in the toothless (tl) rat, a lethal osteopetrotic mutation with few osteoclasts, very low bone turnover, and limited angiogenesis in the axial skeleton. Compared with normal littermates, 3-week-old mutants showed significantly reduced auditory responsiveness, a hearing loss due to abnormalities in both form and tissue composition of the stapes, and little capillary sprouting in the vascular bed of the temporal bone. Treatment of mutants with colony-stimulating factor 1 (CSF-1), known to greatly reduce sclerosis in the axial skeleton, significantly improved hearing, stapedial form and tissue composition, and angiogenesis in the temporal bone. In normal rats, the stapes consisted of 89.3% bone, 9.1% mineralized cartilage, and 0.8% porosity. In osteopetrotic rats, the stapes consisted of 48.3% bone, 35.9% mineralized cartilage, and 15.9% porosity, while after CSF-1 treatment, the bone content increased to 55.2%, cartilage was decreased to 21.7%, and porosity increased to 23.0%, respectively. This is the first demonstration of an auditory abnormality in an osteopetrotic animal mutation and shows that the hearing loss in tl rats can be significantly improved following treatment with CSF-1.

Granulocyte/macrophage colony-stimulating factor and interleukin-3 correct osteopetrosis in mice with osteopetrosis mutation

Although young mice homozygous for the osteopetrosis (op) mutation usually developed prominent osteopetrosis, its severity was markedly reduced in aged op/op mice. This age-associated reversal of osteopetrosis was accompanied by the expansion of bone marrow cavities and increased numbers of tartrate-resistant acid phosphatase (TRAP)-positive cells and of macrophages in the bone marrow. The TRAP-positive cells were mononuclear and developed ruffled borders and numerous vesicles, vacuoles, and granules. Enzyme-linked immunosorbent assay demonstrated a significant elevation of serum granulocyte/ macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-3 levels in the aged op/op mice. To examine whether GM-CSF and/or IL-3 could correct osteopetrosis in young op/op mice, 5 ng of recombinant murine (rm)GM-CSF and/or 100 ng of rmIL-3 were injected daily into young op/op mice. In these treated young op/op mice, the bone marrow cavities were expanded significantly at 2 weeks after administration, associated with significantly increased numbers of TRAP-positive cells and bone marrow macrophages. TRAP-positive cells increased in number with days after injection. These results suggest that GM-CSF and IL-3 induce the development of osteoclasts to correct osteopetrosis in the op/op mice with aging.

Normalization of periodontal tissues in osteopetrotic mib mutant rats, treated with CSF-1

The osteopetrotic mib mutation in rats causes defects in the skeletal bone tissue in young animals. These defects, i.e. slow bone remodelling, changes in both crystallinity and mineral content, are transient and undergo normalization, even without any treatment in 6-wk-old animals. Treatment with CSF-1 (colony stimulating factor-1) accelerates the normalization process in skeletal bones. The periodontal tissues around the apices of incisors show abnormalities caused by the slow remodelling process of the mandible bone tissue, the deficiency of osteoclasts and their abnormal morphology, as well as the disorganization of periodontal ligament fibres. In contrast to the skeletal tissues, these abnormalities would not undergo spontaneous normalization. Under treatment with colony stimulating factor 1 (CSF-1), the primitive bone trabeculae of mandible are resorbed and the normalization of the number of osteoclasts and their cytology occurs. The organization of the periodontal ligament fibres is partially restored, resembling the histological structure of the normal one.

Bone remodelling: a signalling system for osteoclast regulation

Two physiological regulators of osteoclast maturation have recently been identified: the secreted protein osteoprotegerin and the cell-surface ligand to which it binds. These proteins are likely to play an important part in the control of bone resorption, but are also likely to have important roles in other tissues.

Treatment with recombinant human macrophage colony-stimulating factor resorbs blood clot and restores osteoclastogenesis in heterotopic bone induced by partially purified native bone morphogenetic protein in osteopetrotic (op/op) mice

Native bone morphogenetic protein and associated noncollagenous proteins induced the formation of heterotopic bone in the hindquarter muscles of osteopetrotic (op/op) mice and those of their phenotypically normal littermates (+/?). In op/op mice, the heterotopic bone consisted of a disorganized, densely packed mixture of irregular calcified cartilage, osteoid, chondro-osteoid, and fibrous tissue. Injections of recombinant human macrophage colony-stimulating factor initiated bone resorption that began in the peripheral vascularized regions of the metaphyses and continued in central areas of uncalficified avascular chondro-osteoid. On vascularized surfaces, osteoclasts were stained with tartrate-resistant acid phosphatase. In op/op mice treated with macrophage colony-stimulating factor, the osteoclasts were small, with only two or three nuclei, and they did not exhibit tartrate-resistant acid phosphatase staining. In untreated op/op mice, surgical blood clots persisted in the heterotopic sites as late as 3 weeks after the operation, whereas in treated op/op mice, the blood clots were absorbed almost as rapidly as in normal mice. Histologically, recombinant human macrophage colony-stimulating factor restored normal macrophage functions: absorption and organization of blood clot, osteoclastogenesis, synthesis of tartrate-resistant acid phosphatase, bone remodeling, islands of myelopoiesis, and construction of an ossicle complete with a cortex and a medulla filled with functioning hematopoietic bone marrow.

Restoration of disturbed tooth eruption in osteopetrotic (op/op) mice by injection of macrophage colony-stimulating factor

Osteopetrotic (op/op) mice show severe osteosclerosis caused by an inherited deficiency of osteoclast and resultant failure of tooth eruption, which can be cured by the injection of macrophage colony-stimulating factor (M-CSF). The present study revealed that consecutive injections of M-CSF in these mutant mice brought about a recovery of bone resorption resulting in the resumption of growth of tooth root and periodontal ligament. Bone resorption at the inner surface of bony crypts was noted on the 5th day after the start of M-CSF injections. This activity was reduced with the progress of root and periodontal ligament formation, being confined to the basal and crestal portion of bony crypts by the 15th day of the experiment. Second molars emerged into the oral cavity on the 15th day, but no eruption of first molars was observed until the 20th day. Throughout the experiment, first molars exhibited appreciable root deformity, which was less severe in second molars. Delayed eruption of first molars was thought to be related to the severity of the disturbance of root formation.

Alteration of mineral crystallinity and collagen cross-linking of bones in osteopetrotic toothless (tl/tl) rats and their improvement after treatment with colony stimulating factor-1

A common feature of various types of mammalian osteopetroses is a marked increase in bone mass accompanied by spontaneous bone fractures. The toothless (tl/tl) rat osteopetrotic mutation is characterized by drastically reduced bone resorption due to a profound deficiency of osteoclasts and their precursors. An altered bone morphology has also been observed. The mutants cannot be cured by bone marrow transplantation, but skeletal defects are greatly reduced after treatment with colony stimulating factor 1 (CSF-1). The objectives of this study were to characterize mineral and collagen matrices in cancellous and compact bone isolated from long bones of 6-week-old normal littermates, tl/tl osteopetrotic mutants and mutants (tl/tl) treated with CSF-1. There were no differences in bone mineral content, but a significant decrease in the crystallinity of mineral evaluated by the method based on electron paramagnetic resonance spectrometry was observed in all bones of tl/tl mutants as compared to that of controls. Within the collagen matrix, slight decreases in the labile cross-links, but significant increases in the content of the stable cross-links, pyridinoline, and deoxypyridinoline, were observed in both cancellous and compact bone of osteopetrotic mutants. In tl/tl mutants treated with human recombinant CSF-1, the normalization of the crystallinity of bone mineral as well as collagen cross-links was found. Our results indicate that remodeling of bone matrix in tl/tl mutants is highly suppressed, but that after treatment with CSF-1, this activity recovers significantly. Taken together, these data provide further support for the hypothesis that CSF-1 is an essential factor for normal osteoclast differentiation and bone remodelling.

Macrophage differentiation and granulomatous inflammation in osteopetrotic mice (op/op) defective in the production of CSF-1

Since the osteopetrotic (op/op) mouse was demonstrated to have a mutation within the coding region of the CSF-1 gene itself, it serves as a model for investigating the differentiation mechanism of macrophage populations in the absence of functional CSF-1. The op/op mice were severely monocytopenic and showed marked reduction and abnormal differentiation of tissue macrophages. Osteoclasts as well as marginal metallophilic macrophages and marginal zone macrophages in the spleen were absent. Most of the tissue macrophages were reduced in number and ultrastructurally immature. However, the degree of reduction in numbers of macrophages in the mutant mice was variable among tissues, suggesting that the heterogeneity of macrophages was generated by their different dependency on CSF-1. After daily CSF-1 injection, the numbers of monocytes, tissue macrophages, and osteoclasts were remarkably increased, and the macrophages showed morphological maturation. However, the numbers of macrophages in the ovary, uterus, and synovial membrane were not increased. In the bone marrow, macrophage precursors detected by monoclonal antibody ER-MP58 proliferated and differentiated into preosteoclasts and osteoclasts. In the spleen, marginal metallophilic macrophages and marginal zone macrophages developed slowly. In this manner, CSF-1 plays an important role in the development, proliferation, and differentiation of certain tissue macrophage populations and osteoclasts. In the op/op mice, Kupffer cells proliferated, transformed into epithelioid cells and multinucleated giant cells, and participated in glucan-induced granuloma formation. In CSF-1-treated op/op mice, the process of granuloma formation was similar to that in normal littermates due to increased monocytopoiesis and monocyte influx into the granulomas. These results indicate that CSF-1 is a potent inducer of the development and differentiation of CSF-1-dependent monocyte/macrophages, and that CSF-1-independent macrophages also play an important role in granuloma formation.

Thrombocytopenia in the toothless (osteopetrotic) rat and its rescue by treatment with colony-stimulating factor-1

Osteopetrosis in toothless (tl) rats is characterized by reductions in bone resorption, osteoclasts, and macrophages, resistance to cure by bone marrow transplantation, and skeletal improvement after treatment with colony-stimulating factor-1 (CSF-1). Reductions in skeletal osteocalcin tl rats, together with the recent demonstration of osteocalcin expression in platelets and its possible role in bone turnover, prompted us to examine whether this rat mutation is associated with altered platelet numbers. Our prediction of a thrombocytopenia was confirmed by examination of tl rats, in which a profound reduction (32%) in platelets was accompanied by a significant elevation (62%) in megakaryocytes (MKC) compared to normal littermates. Light and transmission electron microscopy confirmed increases in both number and size of MKC in mutants without morphologic abnormalities of circulating platelets. CSF-1 treatment (10(6) U/48 hours for 10 days) of mutants restored platelet numbers to those found normal littermates and increased osteoclasts and the frequency of MKC in numbers. Preliminary studies of another mutation the rat, osteopetrosis (op), revealed a similar reduction (33%) in platelets. These data demonstrate the coexistence of osteopetrosis and thrombocytopenia in two osteopetrotic rat mutations and an increase in osteoclasts and platelets in one mutation after CSF-1 treatment. Together, these data suggest a potential functional interaction of MKC and osteoclasts in bone turnover.

Neonatal changes of osteoclasts in osteopetrosis (op/op) mice defective in production of functional macrophage colony-stimulating factor (M-CSF) protein and effects of M-CSF on osteoclast development and differentiation

In mice homozygous for the osteopetrosis (op) mutation, loss of osteoclasts in the postnatal period and their development, differentiation, and maturation following daily M-CSF administration in adult life were investigated. Histochemical, immunohistochemical, and ultrastructural approaches, as well as [3H]thymidine autoradiography, clarified the role of M-CSF on osteoclast development and differentiation. In op/op mice osteoclasts appeared normal at birth. However, osteoclast numbers were reduced within a few days after birth, and osteoclasts were undetectable by 3-4 days of age. In adult op/op mice there were no multinuclear osteoclasts; however, small numbers of mononuclear cells (so-called 'preosteoclasts') were observed on the endosteal surface of bone. These preosteoclasts expressed tartrate-resistant acid phosphatase and showed ultrastructural features of immature osteoclasts. After daily M-CSF administration in op/op mice, osteoclasts developed from the fusion of preosteoclasts and osteoclasts numbers increased to the levels of normal littermates at 3 days. Autoradiographic analysis with [3H]thymidine revealed no labeling in osteoclasts and preosteoclasts. In the mutant mice, M-CSF administration induced numerical increases of monocytes, promonocytes, and earlier precursor cells in bone marrow, ER-MP12- or, ER-MP58-positive granulocyte/macrophage colony-forming cells (GM-CFCs). Among these macrophage precursors, ER-MP58-positive cells were considered preosteoclast precursors, and possessed marked proliferative potential. These data suggest that an ER-MP58-positive cell subpopulation of GM-CFCs proliferates in response to M-CSF, differentiates into preosteoclasts which fuse with each other to develop into mature osteoclasts.

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.

CSF-1 treatment promotes angiogenesis in the metaphysis of osteopetrotic (toothless, tl) rats

It has recently been shown that following treatment with colony-stimulating factor-1 (CSF-1) the osteopetrotic condition in toothless (tl) rats greatly improves and growth is accelerated. We have examined the effects of such treatment on the microvasculature of the distal femoral chondro-osseous junction, a site where bone growth in length is coordinated with angiogenesis. Vascular casts and ultrastructural analyses of this region showed that, compared to untreated normal rats, untreated mutants showed little bone growth or angiogenesis. When mutants were treated with CSF-1 angiogenesis was markedly accelerated. These data show a remarkable effect of this growth factor on angiogenesis in this osteopetrotic mutation. Whether this effect of CSF-1 on angiogenesis is direct or indirect is not known and indicates that its effects on the normal microvasculature deserve further study.

Colony-stimulating factor-1 injections improve but do not cure skeletal sclerosis in osteopetrotic (op) mice

The osteopetrotic (op) mutation in mice is characterized by general skeletal sclerosis; reduced numbers of osteoclasts, macrophages, and monocytes; and failure to be cured by bone marrow transplantation. This mutation has been shown to result from an absence of colony-stimulating factor-1 (CSF-1) and reported to be cured by treatment with CSF-1. Contrary to previous reports, we have noted persistent metaphyseal sclerosis in op mice treated with CSF-1 at doses above physiological concentrations of circulating CSF-1. We pursued this observation by quantitating osteoclasts and macrophages in the first 500 microns (area A) and the subsequent 1000 microns (area B) in the proximal tibial metaphysis using tartrate-resistant acid phosphatase and F4/80 as cell markers. In untreated normal mice, osteoclasts and macrophages were found in areas A (9.1 and 13.8 cells/1000 microns2) and B (4.1 and 9.4 cells/1000 microns2), respectively. In untreated mutants, osteoclasts and macrophages as percentages of normal were, respectively, 0% and 2% (area A) and 30% and 13% (area B). After CSF-1 treatment (0.15, 0.3, 0.5, and 1.0 x 10(6) U/day) for 28 days, marrow cavity size and numbers of osteoclasts and macrophages increased significantly in area B. However, area A remained sclerotic, with few macrophages (3% to 20%), and although osteoclast numbers were normal, their distribution was not, being absent in subepiphyseal sites. High CSF-1 gene expression occurs at bone modeling sites, co-localizes with osteoblasts, and temporally correlates with their differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 1,25-dihydroxyvitamin D3 on bone resorption and natural immunity in osteopetrotic (ia) rats

Osteopetrois is an inherited bone disease characterized by an excessive accumulation of bone throughout the skeleton. The disease in the ia (incisors absent) rat is the result of reduced bone resorption caused by defective, although numerous osteoclasts. In addition to the bone defects, ia rats have suppressed natural immunity, even though these animals have excessive numbers of natural killer (NK) cells. The osteopetrotic condition also appears to have an associated abnormality in vitamin D metabolism. Because 1,25-dihydroxyvitamin D3[1,25-(OH)2D3] stimulates bone resorption and has a role in the immunoregulation of NK cells, mutant and normal rats were infused with 1,25-(OH)2D3 for 14 days in an attempt to correct the defects in this mutant. Serum levels of osteocalcin, 25-OHD3, and 1,25-(OH)2D3, as well as NK function and parameters of bone resorption, were evaluated after the infusion period. Serum levels of osteocalcin and 1,25-(OH)2D3 were elevated in both ia and normal rats treated with 1,25-(OH)2D3. Serum 25-OHD3 levels were significantly reduced in the treated animals. The elevated percentage of NK cells normally found in ia rats was reduced to normal in the treated mutants, and NK cell function was elevated to normal levels of lytic activity. The percentage of NK cells and NK function remained unchanged in the treated normal rats. The bone marrow cavity size was significantly increased in the 1,25-(OH)2D3-treated mutants, as was the percentage of osteoclasts exhibiting normal morphology. Radiographically, the mutant bones were less dense.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructure of macrophages and dendritic cells in osteopetrosis (op) mutant mice lacking macrophage colony-stimulating factor (M-CSF/CSF-1) activity

The ultrastructural features of macrophages and dendritic cells of mice homozygous for osteopetrosis (op/op) mutation were studied. The mutant mice are characterized by defective differentiation of osteoclasts, monocytes, and tissue macrophages due to the lack of functional macrophage colony stimulating factor (M-CSF/CSF-1) activity. In op/op mice, tissue macrophages were reduced in number and smaller than in normal littermates. Macrophages in op/op mice showed various degrees of phagocytosis but the development of intracytoplasmic organelles and microvillous projections was poor. After administration of CSF-1 daily for 2 weeks, macrophages in op/op mice developed lysosomes and microvillous projections. In the thymic medulla, T-cell zone of lymph nodes, splenic white pulp and epidermis of the op/op mice, the number of dendritic cells was similar to that in normal littermates and the dendritic cells developed a tubulovesicular system typical of interdigitating cells. Birbeck granules in epidermal Langerhans cells were detected in unmanipulated op/op mice, op/op mice injected with CSF-1, and normal littermates or control mice. However, in untreated op/op mice, dendritic cells projected shorter cytoplasmic processes than in normal littermates, normal control mice and CSF-1 injected op/op mice. These results indicate that the differentiation and maturation of tissue macrophages are mediated by CSF-1, but the dendritic cell differentiation is controlled by other factor(s) than CSF-1, most probably by GM-CSF.

Congenital erythropoietic porphyria: skeletal manifestations and effect of pamidronate treatment

Congenital erythropoietic porphyria (CEP) is a rare disorder of heme biosynthesis. Skeletal abnormalities have been described in patients with this disease. We report a 25-year-old woman with osteodystrophy from CEP. On examination, mild hepatosplenomegaly, multiple hyperpigmented scars, hypertrichosis, erythrodontia and red coloration of urine were found. Biochemical studies showed increased serum levels of alkaline phosphatase, fasting and total 24-h urinary calcium excretion. Serum 250H vitamin-D concentration was low due to avoidance of sun exposure. Skeletal radiographs disclosed marked vertical and horizontal trabecular pattern and biconcavity of most of the dorsal and lumbar vertebral bodies. Several round sclerotic lesions (1-3 cm in diameter) were seen in the skull, pelvis and one lumbar vertebrae. The sclerotic lesions were augmented in size and number compared to X-rays obtained 8 years before. Bone mineral density (evaluated by DEXA) was markedly reduced at the spine and moderately diminished at the proximal femur and total skeleton. Treatment for 11 months with pamidronate (and the addition of hydrochlorotiazide for the last 6 months) reduced to normal values the serum levels of alkaline phosphatase and fasting urinary calcium. The 24-h urinary excretion of calcium and hydroxyproline were also decreased. The BMD increased in all the skeletal areas with presumably hyperactive bone marrow: spine, head, ribs and pelvis (and total skeleton), but did not change at the extremities and diminished at the femoral neck. Patients with CEP may present osteodystrophy characterized by sclerotic lesions and osteopenia, most likely due to accelerated bone turnover in areas of active bone marrow.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of calcitriol treatment in a patient with malignant osteopetrosis

In an attempt to stimulate bone resorption, a 10-week-old infant with malignant infantile osteopetrosis was treated with high doses of calcitriol, a potent bone resorption stimulatory agent, combined with a low calcium diet to prevent hypercalcaemia. Although calcitriol administration was initiated at this very young age, our patient did not show any clinical, radiological, or histological improvement. Despite reports of positive results of this treatment in the literature, our patient did not reveal any signs of bone resorption. She eventually died from the complications of osteopetrosis at the age of 6 months after 88 days of therapy.

Osteopetrosis. The pharmaco-physiologic basis of therapy

Medical treatments of osteopetrosis have attempted to improve hematologic function, reduce the osteosclerotic condition, and/or improve immune function. Prednisone therapy has improved hematologic function in some patients, but has not resulted in a reduction in bone mass. Calcium deficient diets have limited further sclerosis in some patients. High-dose calcitriol and parathormone infusions have stimulated osteoclastic activity. In some patients, high-dose calcitriol has resulted in clinical improvement. Newer treatments, such as interferon gamma and macrophage colony stimulating factor, may alter the osteoclastic and immune defects by stimulating cellular formation and function. These therapies, alone or in combination, ameliorate but do not cure the osteopetrotic condition.

The skeletal effects of colony-stimulating factor-1 in toothless (osteopetrotic) rats: persistent metaphyseal sclerosis and the failure to restore subepiphyseal osteoclasts

Toothless (tl), one of four osteopetrotic mutations in the rat, is characterized by few osteoclasts, undetectable bone resorption, and failure of correction by bone marrow transplantation. We recently reported that CSF-1 treatment improves these skeletal problems but that metaphyseal sclerosis persists. In the present study we demonstrate that optimal reduction of the skeletal sclerosis in tl rats following CSF-1 treatment has lower and upper dosage thresholds and that skeletal sclerosis returns after CSF-1 withdrawal. Osteoclasts increase significantly in tl rats after CSF-1 treatment, but compared to untreated normal littermates, histochemical staining for characteristic enzymes and osteoclast number is reduced and no osteoclasts appear in the subepiphyseal areas of long bones. These data are interpreted to mean that there are dosage limits to the beneficial skeletal effects of CSF-1, that persistent sclerosis is related to the failure to restore subepiphyseal osteoclasts, that osteoclast or progenitor populations may be deficient or differ in their responses to CSF-1, and that the defect in tl rats is not merely lack of a circulating, biologically active form of CSF-1.

Combination macrophage-colony stimulating factor and interferon-gamma administration ameliorates the osteopetrotic condition in microphthalmic (mi/mi) mice

Malignant osteopetrosis is a fatal congenital bone disorder characterized by defective osteoclastic function. Death frequently occurs within the first decade of life. The precise molecular defect(s) that causes osteopetrosis is not known. The possibility that osteoclasts, like macrophages, are controlled by interactions with cytokines suggests that these agents may provide a means of increasing osteoclastic function. Macrophage-colony stimulating factor (M-CSF), a cytokine known to enhance macrophage and osteoclast generation, and recombinant human interferon-gamma (rIFN), a cytokine known to stimulate superoxide generation by white cells, were administered to microphthalmic (mi/mi) mice in an attempt to improve the osteopetrotic condition. Each cytokine was administered separately and in combination to neonatal mi/mi mice for 7 consecutive d. Bone turnover, osteoclast numbers, superoxide generation by white cells, and hematocrit were assessed. rIFN, M-CSF, and a combination of the cytokines stimulates oxygen-derived free radical production by white cells and increased bone resorption. rIFN resulted in a reduction in the number of osteoclasts. This reduction in number was ameliorated by M-CSF. M-CSF alone and in combination with rIFN resulted in improved hematopoietic function, increased weight gain, and increased physical activity of the affected mutants.

[Early infantile malignant osteopetrosis. Experiences with drug therapy]

The autosomal recessive form of osteopetrosis becomes manifest in early infancy and often is lethal during the first decade of life. In an infant diagnosed at the age of eight weeks, a therapy with Calcitriol (Rocaltrol) was initiated with the intention to stimulate the osteoclast activity and to improve the bone marrow insufficiency. During therapy, a massive diarrhoea has been observed as potential and previously undescribed side effect of Calcitriol. Therefore the therapy had to be discontinued. A simultaneous trial with Ca-depleted diet did not show any effect. In the absence of a suitable donor, a bone-marrow transplantation could not be performed. The patient died at the age of five month.

The effects of colony-stimulating factor-1 on tooth eruption in the toothless (osteopetrotic) rat in relation to the critical periods for bone resorption during tooth eruption

The toothless (tl) rat is an osteopetrotic mutation characterized by a generalized skeletal sclerosis, reduced bone resorption, few osteoclasts and a total absence of erupted teeth. This mutation is not cured by bone marrow transplants from normal littermates. It is known that the skeletal defects in tl rats are greatly improved after treatment with colony-stimulating factor-1 (CSF-1). This investigation concerns the effects of CSF-1 on the development and eruption of the dentition of tl rats. Untreated tl rats had no erupted teeth by 56 days after birth, and the roots of incisors and molars were severely distorted by compression against bone. The apex of the mandibular incisor did not extend past the first molar and continued growth of its apical end produced odontoma-like masses consisting of distorted dentine and enamel matrices. In addition, few osteoclasts were seen on alveolar bone surfaces surrounding the developing teeth. Mutants given CSF-1 were characterized by delayed eruption of all molars and sometimes incisors. The incidence of incisor eruption was related inversely to the age at which CSF-1 treatment began. Molars of treated tl rats had well-developed roots similar to those in normal rats. Treated mutants had numerous osteoclasts in alveolar bone and well-developed haemopoietic marrow spaces in the mandible. Histochemical staining for both tartrate-resistant acid phosphatase and tartrate-resistant acid ATPase was reduced or negligible in osteoclasts of untreated tl rats, heavy in normal osteoclasts and of intermediate intensity in CSF-1-treated mutants.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration of colony stimulating factor-1 corrects some macrophage, dental, and skeletal defects in an osteopetrotic mutation (toothless, tl) in the rat

The toothless (tl/tl) mutation in the rat results in a paucity of osteoclasts and osteopetrosis that cannot be corrected by bone marrow transplantation. In the present study we demonstrate that tl/tl rats also have profound deficiencies of femoral, peritoneal, and pleural cavity macrophages. Furthermore, the macrophage colony stimulating activity of post-endotoxin sera from tl/tl rats is substantially reduced, suggesting that, as in the case of the op mutation in mice, the basis of the tl mutation is a deficiency of the macrophage growth factor, colony stimulating factor-1 (CSF-1). Consistent with this suggestion, treatment of tl/tl rats from birth for up to six weeks with CSF-1 reduced the osteopetrosis, increased body weight, and permitted tooth eruption. In addition, CSF-1 treatment induced large numbers of osteoclasts in tl/tl bones and macrophages in the peritoneal cavity and bone marrow. Persistence of metaphyseal sclerosis, however, indicated that the disease was not totally corrected by this treatment. These studies indicate that the basis of the tl mutation is most likely another CSF-1 deficiency, and further emphasize the role of this growth factor in osteoclast differentiation.

Imaging rounds #110. Osteopetrosis

The following case is presented to illustrate the roentgenographic and clinical findings of a condition of interest to the orthopaedic surgeon. Initial history, physical findings, and roentgenographic examinations are found on this page. The next page presents the final clinical and roentgenographic differential diagnosis.

Correction by CSF-1 of defects in the osteopetrotic op/op mouse suggests local, developmental, and humoral requirements for this growth factor

Mice that are mutant at the op locus have a severe deficiency of mononuclear phagocytes due to an inactivating mutation in the CSF-1 (macrophage colony-stimulating factor, M-CSF) gene. op/op mice are toothless, possessing skeletal abnormalities, a low body weight, and compromised fertility; they are osteopetrotic due to a deficiency of osteoclasts. The congenital osteopetrosis, toothless phenotype, osteoclast deficit, and the defects in splenic and femoral macrophages were corrected by routes of administration of human recombinant CSF-1 that maintained normal circulating CSF-1 concentrations. Early restoration of circulating CSF-1 was required for rescue of the toothless phenotype, but only partially restored body weight. In contrast, the deficiencies of pleural and peritoneal cavity macrophages and the reduced female fertility were not corrected by restoration of circulating CSF-1. These results suggest that although circulating CSF-1 is required for osteoclast and macrophage production, local synthesis and action of the growth factor are important for certain target cell populations.

Treatment of congenital osteopetrosis in the rabbit with high-dose 1,25-dihydroxyvitamin D

Osteopetrosis is a congenital metabolic bone disease characterized by skeletal sclerosis resulting from defective osteoclast-mediated bone resorption. Osteopetrosis has been described in several animal species (mouse, rat, and rabbit) and in children. Bone marrow transplantation, originally shown to reverse the skeletal sclerosis in some animal mutations, has been effective in curing osteopetrosis in some children. Unfortunately, not all children with osteopetrosis are candidates for or respond to bone marrow transplantation. Recent studies have shown that several animal mutations and some children inheriting osteopetrosis have significantly elevated serum levels of 1,25-(OH)2D. Based on the possibility that there may be a resistance to 1,25-(OH)2D, high-dose calcitriol therapy has been used to treat some children and stimulated some parameters of resorption. In this study, we have examined the effects of high-dose calcitriol therapy on various serum and skeletal parameters in the osteopetrotic rabbit. Mutant rabbits and normal littermates were given continuous infusions of calcitriol via subcutaneously implanted osmotic minipumps for 2 weeks at a dose of 0.5, 2.5, or 25 micrograms/kg/per day. Untreated mutant rabbits are hypocalcemic and hypophosphatemic in the presence of elevated serum 1,25-(OH)2 levels in comparison with their normal littermates. Calcitriol infusions resulted in dose-dependent increases in circulating 1,25-(OH)2D levels in both normal and mutant rabbits. However, evaluation of other serum parameters and the skeletal response demonstrated significant differences between osteopetrotic and normal rabbits. At the highest dose, normal animals rapidly became hypercalcemic and osteoporotic, accompanied by weight loss and a failure to thrive; mutants remained hypocalcemic and osteopetrotic but did not exhibit the deleterious physical effects seen in treated normal littermates. Although the number of osteoclasts increased in both mutants and normals, osteoclast phenotype in the former remained abnormal. These data indicate that although very high levels of circulating 1,25-(OH)2D were achieved in osteopetrotic mutants, activation of osteoclast-mediated bone resorption with subsequent improvement of skeletal sclerosis was not observed.

Juvenile osteopetrosis: effects on blood and bone of prednisone and a low calcium, high phosphate diet

Four children with juvenile osteopetrosis are described who were treated with a combination of prednisone and a low calcium, high phosphate diet. One of the children, treated as a neonate, achieved complete clinical and radiological remission from the disease after nine months, at which point treatment was stopped. There have been no signs of recurrence for two years. Two who did not start treatment until over 24 months of age have shown a good clinical and radiological response but have remained on treatment for six years. The fourth child started treatment at 6 months and showed a good clinical response, but x ray films showed no change nine months later. He was then lost to follow up, stopped treatment, and died two years later of a septicaemia. These patients provide further evidence for the efficacy of steroids in juvenile osteopetrosis, and the combination with the low calcium, high phosphate diet described offers a potentially effective alternative treatment to marrow transplantation, both for the haematological and skeletal complications of the disorder.