Transgenic mice with OIP-1/hSca overexpression targeted to the osteoclast lineage develop an osteopetrosis bone phenotype

Regulatory mechanisms operative in bone-resorbing osteoclasts are complex. We previously defined the Ly-6 gene family member OIP-1/hSca as an inhibitor of osteoclastogenesis in vitro; however, a role in skeletal development is unknown. In this study, we developed transgenic mice with OIP-1/hSca expression targeted to the osteoclast lineage that develop an osteopetrotic bone phenotype. Humeri from OIP-1 mice showed a significant increase in bone mineral density and bone mineral content. microCT analysis showed increased trabecular thickness and bone volume. OIP-1 mice have dense sclerotic cortical bone with absence of spongiosa and inadequate formation of marrow spaces compared to wild-type mice. Moreover, complete inhibition of osteoclasts and marrow cavities in calvaria suggests defective bone resorption in these mice. OIP-1 mouse bone marrow cultures demonstrated a significant decrease (41%) in osteoclast progenitors and inhibition (39%) of osteoclast differentiation/bone resorption. Western blot analysis further demonstrated suppression of TRAF-2, c-Fos, p-c-Jun, and NFATc1 levels in RANKL-stimulated osteoclast precursors derived from OIP-1 mice. Therefore, OIP-1 is an important physiological inhibitor of osteoclastogenesis and may have therapeutic value against bone loss in vivo.

IFN-gamma enhances osteoclast generation in cultures of peripheral blood from osteopetrotic patients and normalizes superoxide production

Interferon-gamma (IFN-gamma) treatment increases osteoclastic bone resorption in vivo in patients with malignant osteopetrosis (OP). The treatment effect was studied in vitro in osteoclasts generated by culturing peripheral white blood cells (PWBC) from OP patients and normal human control subjects. Osteoclasts were treated with or without IFN-gamma prior to the end of the culture period. Osteoclasts from normal subjects were large in size (161 +/- 18 microm in diameter) with >10 nuclei per osteoclast. These cells showed intense staining for tartrate-resistant acid phosphatase (TRAP), expressed abundant calcitonin receptors (CTR), and formed numerous resorption pits on bovine bone slices, indicative of authentic osteoclasts. In contrast, similarly cultured osteoclasts from OP patients were smaller in size (18 +/- 3 microm in diameter), with 2-3 nuclei per osteoclast, and stained lightly for TRAP. However, IFN-gamma treatment of osteoclasts from OP patients resulted in the formation of larger osteoclasts (171 +/- 33 microm in diameter) with >10 nuclei per cell, similar in appearance to osteoclasts from normal subjects. IFN-gamma stimulation increased the intensity of TRAP staining (p < 0.0001) to levels near that of the normal osteoclasts. Unstimulated osteoclasts from 6 OP patients had a significantly lower baseline level of superoxide production, as measured by nitroblue tetrazolium reduction (p < 0.0001), compared with normal osteoclasts. IFN-gamma markedly increased (p < 0.0001) superoxide production. Whereas there was a 3-fold increase in superoxide generation in OP patients' osteoclasts, osteoclasts from control subjects had only a small and insignificant increase in superoxide production after IFN-gamma treatment.

Superoxide generation and tyrosine kinase

NADPH oxidase is a multi-subunit enzyme complex responsible for superoxide generation in many cells, for example, B-lymphocytes and osteoclasts. NADPH oxidase is localized on the cell surface and generates superoxide extracellularly. After synthesis, components of this oxidase are transported to the cell membrane where the functional NADPH oxidase complex is assembled. The mechanism by which the membrane-bound components are transported to the cell surface of osteoclasts remains unclear. In this study, we examined the role of tyrosine kinase activity in the transport of NADPH oxidase components. When B-lymphocytes and osteoclasts were treated with herbimycin A, a specific inhibitor of tyrosine kinase, superoxide production was significantly decreased. The amount of p91, the catalytic subunit of NADPH oxidase, was decreased in the cellular membrane of herbimycin A treated cells compared to untreated controls. Similar results were obtained for the movement of a regulatory subunit of the NADPH oxidase complex, p47, in B-lymphocytes. Thus, inhibition of tyrosine kinase decreases superoxide production by disrupting the translocation of the NADPH oxidase complex.

Cranial MR imaging of osteopetrosis

BACKGROUND AND PURPOSE

The purpose of this study was to describe the cranial MR imaging manifestations of osteopetrosis. These features have not previously been reported in the literature.

METHODS

Cranial MR studies, obtained with a uniform imaging protocol, were reviewed in 47 patients with osteopetrosis. Thirty-four patients had autosomal recessive (malignant) osteopetrosis (AROP), seven had intermediate osteopetrosis (IOP), and six had either type I or type II autosomal dominant osteopetrosis (ADOP I or II). The prevalence of abnormalities was tabulated and compared with the specific osteopetrosis variants.

RESULTS

All patients with osteopetrosis had thickening and sclerosis of the calvaria. Ventriculomegaly, tonsillar herniation, proptosis, and dural venous sinus stenosis were observed in the majority of patients with AROP and ADOP I. Optic nerve sheath dilatation occurred in many of the patients with AROP and in all patients with ADOP I. Acquired cephaloceles were also observed only in these two groups. Optic nerve atrophy and optic canal stenosis were observed in a majority of patients with AROP, IOP, and ADOP II. Middle ear fluid was prevalent in AROP and IOP, present in over half the patients in each group. Features seen most prevalently, or exclusively, in AROP included stenosis of the internal carotid and vertebral arteries and extramedullary hematopoiesis.

CONCLUSION

The cranial MR imaging features of osteopetrosis are both shared and unique among the various subtypes of the disease. The specific cranial and intracranial manifestations reflect the predominant calvarial or skull base patterns of bone thickening. The unique features seen in patients with AROP probably reflect the early age of onset and the greater severity of this form of the disease.

Lovastatin therapy for X-linked adrenoleukodystrophy: clinical and biochemical observations on 12 patients

X-linked adrenoleukodystrophy (X-ALD) is a progressive demyelinating disorder whose neurological signs and symptoms can manifest in childhood as cerebral ALD or in adulthood in the form of a progressive myelopathy (AMN). The consistent metabolic abnormality in all forms of X-ALD is an inherited defect in the peroxisomal beta-oxidation of very long chain (VLC) fatty acids (>C(22:0)) which may in turn lead to a neuroinflammatory process associated with demyelination of the cerebral white matter. The current treatment for X-ALD with Lorenzo's oil aims to lower the excessive quantities of VLC fatty acids that accumulate in the patients' plasma and tissues, but does not directly address the inflammatory process in X-ALD. We have previously demonstrated that lovastatin and other 3-HMG-CoA reductase inhibitors are capable of normalizing VLC fatty acid levels in primary skin fibroblasts derived from X-ALD patients. Lovastatin can block the induction of inducible nitric oxide synthase and proinflammatory cytokines in astrocytes, microglia, and macrophages in vitro. In a preliminary report, we demonstrated that lovastatin therapy can normalize VLC fatty acids in the plasma of patients with X-ALD. Here we report our clinical and biochemical observations on 12 patients with X-ALD who were treated with lovastatin for up to 12 months. Our results show that the high plasma levels of hexacosanoic acid (C(26:0)) showed a decline from pretreatment values within 1 to 3 months of starting therapy with 40 mg of lovastatin per day and stabilized at various levels during a period of observation up to 12 months. The percentage decline from pretreatment values varied and did not correlate with the type of ALD gene mutation (point mutation versus gene deletion). In 6 patients, in whom red cell membrane fatty acid composition was studied, a mean correction of 50% of the excess C(26:0) was observed after 6 months of therapy suggesting sustained benefit. In a few patients who discontinued lovastatin therapy plasma C(26:0) levels reverted to pretreatment values suggesting a cause and effect relationship between these events. Two patients dropped out of the study claiming no clinical benefit, 1 was withdrawn due to adverse effects, and an adult patient with cerebral involvement died during the study. A 10-year-old boy with severe cerebral involvement showed worsening of his neurological status. All patients with AMN remained neurologically stable or showed modest subjective improvement. All patients who did not have Addison's disease at the time of enrollment maintained normal adrenal function throughout the study. The implications of our findings for developing an effective therapy for X-ALD are discussed.

Superoxide generation in transformed B-lymphocytes from patients with severe, malignant osteopetrosis

Severe, malignant osteopetrosis is a disease characterized by osteoclasts that fail to resorb bone. Serious defects in the ability of white blood cells to eradicate infectious agents confound the clinical course. Defective superoxide generation by neutrophils, monocytes, and lymphocytes contributes to this inability to fight infection. To elucidate the mechanisms resulting in the defective superoxide generation observed in osteopetrotic leukocytes, gene expression, translocation, and phosphorylation of the major components that form the functional NADPH oxidase complex were studied in transformed B-lymphocytes. The expression of the p47 subunit of NADPH oxidase was reduced in B-lymphocytes collected from osteopetrotic patients compared to those from controls. Phosphorylation and translocation of p47 to the cell membrane after PMA stimulation was similar in B-lymphocytes from both patients and normal controls. However, total amount of p47 phosphorylation and translocation was reduced in patient samples. This was further supported by the experiment using p47 antisense oligonucleotide. The other major components of the oxidase (p91, p22, p67) were found to be present at normal levels. Thus, the reduction in p47 expression results in reduced ability to assemble a functional NADPH oxidase complex at the membrane of lymphocytes from osteopetrotic patients. This defect translates into reduced superoxide generation and an increased propensity for infection.

Nicotinamide adenine dinucleotide phosphate oxidase in the formation of superoxide in osteoclasts

Osteoclasts use a variety of chemical agents to degrade bone. One important component of this process is the generation of superoxide. It has been reported that nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is the enzyme responsible for superoxide production in phagocyte; however, the NADPH oxidase present in osteoclasts has not been studied in detail. One of the membrane-bound subunits of the NADPH oxidase is gp91(phox) which represents the rate-limiting component for the formation of the NADPH oxidase complex. This study was designed to demonstrate the presence of gp91(phox) in individual osteoclasts using the RT-PCR technique developed for limited numbers of cells. Compared with white cells, 1.8 times the amount of gp91(phox) mRNA was found in osteoclasts. This difference may be related to the size of the osteoclast and the multiple nuclei present. The presence of gp91(phox) in osteoclasts was confirmed at protein level by immunocytochemistry. Osteoclastic superoxide generation is inhibited by diphenylene iodonium, a specific inhibitor of the NADPH oxidase. These studies suggest that superoxide generation by osteoclasts correlates with the activity of NADPH oxidase.

Developmental spectrum of children with congenital osteopetrosis

This study reports on the developmental status of 23 children, ranging in age from 2 weeks to 11 years, with the severe form of autosomal recessive osteopetrosis. Results revealed widely scattered cognitive, adaptive, and language scores and delayed gross motor skills.

The effects of a high-protein, low-fat, ketogenic diet on adolescents with morbid obesity: body composition, blood chemistries, and sleep abnormalities

OBJECTIVE

To evaluate the efficacy and metabolic impact of a high-protein, low-carbohydrate, low-fat ketogenic diet (K diet) in the treatment of morbidly obese adolescents with initial weights of >200% of ideal body weight.

METHODS

Six adolescents, aged 12 to 15 years, weighing an average of 147.8 kg (range, 120.6-198.6 kg) and having an average body mass index of 50.9 kg/m (39.8-63.0 kg/m), consumed the K diet for 8 weeks. Daily intake consisted of 650 to 725 calories, which was substantively in the form of protein (80-100 g). The diet was very low in carbohydrates (25 g) and fat (25 g). This was followed by 12 weeks of the K diet plus two carbohydrates (30 g) per meal (K+2 diet).

MAIN OUTCOME MEASURES

Anthropometric data and blood and urine were collected at enrollment, during week 1, and at 4-week intervals throughout the course of the study. Resting energy expenditure was measured by indirect calorimetry. Body composition was estimated using dual-energy x-ray absorptiometry, bioelectrical impedance analysis, and urinary creatinine excretion at enrollment and on completion of each phase of the diet. Nocturnal polysomnography and multiple sleep latency testing were conducted at baseline and repeated after an average weight loss of 18.7 kg to determine sleep architecture, frequency and duration of apneas, and daytime sleepiness.

RESULTS

Subjects lost 15.4 +/- 1.4 kg (mean +/- SEM) during the K diet and an additional 2.3 +/- 2.9 kg during the K+2 diet. Body mass index decreased 5.6 +/- 0.6 kg/m(2) during the K diet and an additional 1.1 +/- 1.1 kg/m(2) during the K+2 diet. Body composition studies indicated that weight was lost equally from all areas of the body and was predominantly fat. Dual-energy x-ray absorptiometry showed a decrease from 51.1% +/- 2.1% body fat to 44.2% +/- 2.9% during the K diet and then to 41.6% +/- 4.5% during the K+2 diet. Lean body mass was not significantly affected. Weight loss was accompanied by a reduction in resting energy expenditure of 5.2 +/- 1.8 kcal/kg of fat-free mass per day. Blood chemistries remained normal throughout the study and included a decrease in serum cholesterol from 162 +/- 12 to 121 +/- 8 mg/dL in the initial 4 weeks of the K diet. An increase in calcium excretion was accompanied by a decrease in total-body bone mineral content. A paucity of rapid eye movement sleep and excessive slow-wave sleep were seen in all subjects at enrollment. Weight loss led to an increase in rapid eye movement sleep (P < .02) and a decrease in slow-wave sleep (P < .01) to near normal levels.

CONCLUSIONS

The K diet can be used effectively for rapid weight loss in adolescents with morbid obesity. Loss in lean body mass is blunted, blood chemistries remain normal, and sleep abnormalities significantly decrease with weight loss.

Defects of the testosterone biosynthetic pathway in boys with hypospadias

PURPOSE

We determined the incidence of defects in 3 enzymes, namely 3beta-hydroxysteroid dehydrogenase, 17alpha-hydroxylase and 17,20-lyase, on the testosterone biosynthetic pathway in boys with hypospadias.

MATERIALS AND METHODS

We evaluated 30 boys with a 46,XY karyotype, fully descended testes and penoscrotal or proximal shaft hypospadias. Serum concentrations of the metabolites mediated by these enzymes were measured, from which the precursor-to-product ratios were calculated. Seven patients underwent adrenocorticotropic hormone stimulation. Findings were compared to previously published data on age matched normal boys.

RESULTS

A total of 11 boys had evidence of impaired function of 3beta-hydroxysteroid dehydrogenase alone or in combination with impaired 17,20-lyase or 17alpha-hydroxylase activity. An additional 4 boys had evidence of isolated 17,20-lyase deficiency. Thus, of the 30 boys studied 15 (50%) had evidence of a testosterone biosynthetic defect. The effect of adrenocorticotropic hormone stimulation varied with widening of the precursor-to-product ratios in some boys and narrowing in others.

CONCLUSIONS

A high incidence of 3beta-hydroxysteroid dehydrogenase and 17,20-lyase deficiency was found in boys with proximal hypospadias. The response to adrenocorticotropic hormone stimulation suggests that enzymes in the adrenal glands and testes may be affected independently. Our findings support the hypothesis that hypospadias is the result of fetal endocrinopathy.

Cytophilic immunoglobulin G binding on neutrophils from a child with malignant osteopetrosis who developed fatal acute respiratory distress mimicking transfusion-related acute lung injury

A 16-month-old boy, diagnosed at age 3 months with osteopetrosis, was treated since age 6 months with rhIFN-gamma in combination with rhM-CSF. The child developed acute respiratory distress within 1 hr of a paternal platelet transfusion. Both the child and the father were blood group type O, and platelets were collected the previous day from the father. Chest X-ray revealed right pulmonary consolidation and a complete "whiteout" on the left. By 24 hr, the lungs had the appearance of adult respiratory distress syndrome (ARDS). Over the course of the next 11 days, the child remained intubated and hypotensive, and died of respiratory insufficiency 11 days later. ARDS was confirmed at autopsy. Pre- and posttransfusion patient's sera, as well as paternal serum, were tested by granulocyte agglutination and flow cytometry against granulocytes (PMN) from the patient, father, mother, and routine cell-panel donors and lymphocytes for the presence of neutrophil-specific and lymphocyte (HLA) antibodies, to rule out classical transfusion-related acute lung injury (TRALI). Both the patient's and the paternal sera were devoid of antibodies, but the patient's neutrophils demonstrated strong binding of cytophilic IgG accompanied by extremely low serum IgG and IgG1 levels. Since rhIFN-gamma is known to upregulate Fc gamma receptor type I (Fc(gamma)RI) with high affinity for IgG1, the binding of cytophilic IgG suggests that the patient's neutrophils may have been activated in vivo. The case report of another child with osteopetrosis has also been described. Although the blood specimen was not available for serological studies, this 4 1/2-year-old child treated with rhIFN-gamma and rhM-CSF also died of adult respiratory distress syndrome, with similar clinical presentations.

Petrous carotid canal stenosis in malignant osteopetrosis: CT documentation with MR angiographic correlation

PURPOSE

To study the association between petrous carotid canal (PCC) and internal carotid artery (ICA) stenoses in patients with malignant osteopetrosis.

MATERIALS AND METHODS

Mean and minimum PCC diameters obtained from cranial computed tomographic (CT) scans in 20 patients were compared with similar measurements in 52 control subjects. ICA caliber, evaluated with magnetic resonance (MR) arteriography, was correlated with age and PCC dimensions.

RESULTS

There was a statistically significant difference between patient and control PCC diameters. There was a strong positive correlation between age and PCC diameter in the control subjects, but only a weakly positive correlation in the patients. One or both ICAs were stenotic on all patient MR arteriograms. MR angiographic stenosis grade correlated positively with age but not with PCC diameters.

CONCLUSION

PCC and ICA stenoses occur frequently in patients with malignant osteopetrosis. Bony overgrowth or a "persistent fetal state" may produce the PPC stenoses. The findings do not support progressive PCC narrowing in these patients.

Response to growth hormone in children with chondrodysplasia

Theoretic concerns exist that children with chondrodysplasia will not grow in response to growth hormone (GH) therapy because of an inability of the abnormal growth cartilage to respond. Experience to date, however, suggests that there is an increase in growth velocity, especially during the first year of treatment, which may be beneficial. Growth has increased during the early phases of GH therapy in both patients with achondroplasia and patients with hypochondroplasia. Fourteen patients with achondroplasia in the National Cooperative Growth Study have been treated with an average dose of GH of 0.317 mg/kg per week for an average of 2.6 years and have gained an average of 0.7 SD in height. Twenty patients with hypochondroplasia in the National Cooperative Growth Study have been treated with an average dose of GH of 0.317 mg/kg per week for an average of 2.6 years and have gained an average of 0.7 SD in height. These data suggest that the abnormal growth cartilage in patients with chondrodysplasia responds to GH therapy. The effect on final height cannot be predicted with the currently available data.

Osteoclastic superoxide production and bone resorption: stimulation and inhibition by modulators of NADPH oxidase

Production of superoxide radicals by osteoclasts is necessary for normal bone degradation. White blood cell superoxide, needed for bacterial killing, is produced by activated NADPH oxidase. Since osteoclasts and white blood cells share a common hematopoietic origin, we initiated experiments to test the hypothesis that superoxide radicals at the osteoclast-bone interface are produced by NADPH oxidase. Diphenyl iodonium (IDP), an inhibitor of NADPH oxidase, blocked superoxide generation and decreased osteoclastic bone resorption in cultures of calvarial explants from normal mice. Interferon (IFN) gamma, a stimulant of NADPH oxidase activity, increased superoxide production and bone resorption in cultures of calvarial explants from osteopetrotic (microphthalmic) mice. IDP blocked the stimulatory effects of IFN in this bone resorption model. These data suggest that osteoclastic superoxide is produced by NADPH oxidase.

Functions of the M-CSF receptor on osteoclasts

Macrophage colony-stimulating factor (M-CSF) receptor has been previously reported to be present in osteoclasts both at mRNA and protein levels. However, the biochemical interactions between M-CSF and its receptor on osteoclasts are less well characterized than in mononuclear phagocytes. In this study, we show that (1) 125I-labeled M-CSF ligand specifically binds to the M-CSF receptor on osteoclasts by autoradiography; (2) binding of M-CSF to the receptor stimulates protein tyrosine phosphorylation in osteoclasts by immunostaining; (3) oxygen-derived free radicals produced by calvarial osteoclasts are increased by M-CSF stimulation (1.37 +/- 0.08, n = 10, P < 0.01); and (4) bone resorption in calvarial explants is enhanced by M-CSF (1.153 +/- 0.09, n = 10, p < 0.001). Thus, our data provide multiple lines of evidences that mouse calvarial osteoclasts are activated by M-CSF. These data suggest that under the conditions present in the calvarial model, M-CSF activates osteoclastic bone resorption.

Demonstration of a lack of racial difference in secretion of growth hormone despite a racial difference in bone mineral density in premenopausal women--a Clinical Research Center study

We previously found GH secretion to be higher in black than white men. Therefore, we performed studies to determine whether this racial difference in GH secretion also occurs in women. Measurements of GH were obtained at 20-min intervals over 24 h and analyzed by deconvolution in 12 healthy black and 12 healthy white premenopausal women. Bone mineral density (BMD) was determined by dual energy x-ray absorptiometry, and GM allotypes were measured as a genetic marker for race. Racial distribution of the groups, as determined by analysis of GM haplotypes, were typical for black and white American populations. Twenty-four-hour integrated GH concentration, GH secretory burst amplitude, burst frequency, half-duration, mass, and half-life were not different in the two groups. Serum testosterone was modestly, but significantly, greater in the black than in the white women (1.1 +/- 0.1 vs. 0.9 +/- 0.1 nmol/L; P < 0.05). Serum 17 beta-estradiol and insulin-like growth factor (IGF)-binding protein-3 were not different in the two groups. However, the IGF-I/IGF-binding protein-3 molar ratio was significantly greater in the black than the white women (2.0 +/- 0.1 vs. 1.6 +/- 0.1; P < 0.02). The BMD of total body (1.12 +/- 0.02 vs. 1.07 +/- 0.02 g/cm2; P < 0.05) and total hip (0.96 +/- 0.04 vs. 0.86 +/- 0.04 g/cm2, P < 0.05) were greater in the black (n = 13) than in the white (n = 12) women. There was a trend toward greater BMD of the forearm in the black women (0.58 +/- 0.01 vs. 0.56 +/- 0.01 g/cm2; P = 0.06) and no racial difference in the BMD of the spine. When examining all subjects together, the BMD of the total body, trochanter, and spine correlated with total integrated GH secretion. Thus, the racial difference in GH secretion that we had previously found in men does not occur in women despite the higher BMD values at several skeletal sites in black women.

Greater secretion of growth hormone in black than in white men: possible factor in greater bone mineral density--a clinical research center study

To determine why blacks have a higher bone mineral density (BMD) and lower incidence of osteoporosis and fractures than whites, we investigated whether the secretion of GH is higher in black than in white men. Measurements of GH were obtained at 20-min intervals over 24 h and analyzed by deconvolution. BMD was determined by dual energy x-ray absorptiometry in 16 normal black and 17 normal white men, aged 20-40 yr. The 24-h integrated GH concentration 942 +/- 174 vs. 602 +/- 104 micrograms/L; P = 0.0495) and GH secretory burst amplitude (0.499 +/- 0.163 vs. 0.169 +/- 0.027 micrograms/L.min; P = 0.0482) were higher in black than in white men. GH burst frequency, half-duration, mass, and half-life were not different in the 2 groups. The serum 17 beta-estradiol level (162 +/- 12 vs. 108 +/- 11 pmol/L; P = 0.0011) was higher, and the serum insulin-like growth factor-binding protein 3 level (2.2 +/- 0.1 vs. 2.8 +/- 0.1 microgram/mL; P = 0.0001) was lower in black than in white men. BMD values for total body (1.22 +/- 0.02 vs. 1.14 +/- 0.02 g/cm2; P = 0.0041), forearm (0.69 +/- 0.01 vs. 0.66 +/- 0.01 g/cm2; P = 0.0211), trochanter (0.91 +/- 0.03 vs. 0.77 +/- 0.03 g/cm2; P = 0.0003), and femoral neck (1.08 +/- 0.03 vs. 0.93 +/- 0.03 g/cm2; P = 0.0007) were higher in black than in white men. Thus, serum 17 beta-estradiol level, GH secretion, and BMD values for the total body, forearm, trochanter, and femoral neck are greater in black than in white men. As estrogen is known to increase GH secretion and GH to increase bone mass, increases in circulating 17 beta-estradiol may contribute to the higher GH secretion and bone mass in black men.

Long-term treatment of osteopetrosis with recombinant human interferon gamma

BACKGROUND

Congenital osteopetrosis is a rare osteosclerotic bone disease characterized by both a defect in osteoclastic function and reduced generation of superoxide by leukocytes. The disease is frequently fatal during the first decade of life. A six-month trial of therapy with recombinant human interferon gamma-1b in eight patients with osteopetrosis provided evidence of benefit, prompting this study of more prolonged therapy.

METHODS

We studied 14 patients with severe osteopetrosis treated with subcutaneous injections of recombinant human interferon gamma-1b (1.5 micrograms per kilogram of body weight per dose) three times per week for at least 6 months; 11 patients were treated for 18 months. We assessed the effect of therapy by evaluating the patients' clinical status, measuring blood counts and biochemical markers of bone turnover, and performing bone marrow imaging and bone biopsies.

RESULTS

After 6 months of therapy, all 14 patients had decreases in trabecular-bone area (determined by histomorphometric analysis of bone-biopsy specimens) and increases in bone marrow space (determined by marrow imaging), and the improvement was sustained in the 11 patients treated for 18 months. The mean (+SD) hemoglobin concentration increased from 7.5 +/- 2.9 to 10.5 +/- 0.3 g per deciliter (P = 0.05), and superoxide generation by granulocyte-macrophage colonies increased (P < 0.001) after 18 months of therapy. In six patients for whom pretreatment data were available, there was a 96 percent decrease in the frequency of infections requiring antibiotic therapy during interferon treatment. There were no side effects necessitating the discontinuation of therapy.

CONCLUSIONS

Long-term therapy with interferon gamma in patients with osteopetrosis increases bone resorption and hematopoiesis and improves leukocyte function.

Characterization of M-CSF and its receptor in microphthalmic mice

The macrophage colony-stimulating factor (M-CSF) gene expression in osteopetrotic mice (op/op) is defective due to a point-mutation in the M-CSF gene [1]. However, almost all osteopetrotic patients have been shown to have a normal or elevated circulating level of bioactive M-CSF [2]. To investigate the action of the M-CSF in mi/mi mice (microphthalmic; another osteopetrotic mouse mutant), M-CSF levels and its receptors were studied. We found that serum levels of M-CSF in mi/mi mice were not significantly different from normal control mice. The M-CSF receptor binding affinity of spleen-adherent cells was similar to that of control mice. In spleen cells from mi/mi mice, the receptor binding sites per cell (normalized to total spleen cells, M-CSF receptor positive cells, or M-CSF receptor RNA positive cells) were present in a greater number than in spleen cells from phenotypically normal siblings. Northern blot analysis showed that there is no significant difference in transcripts of the M-CSF receptor (c-fms) in the mi/mi and phenotypically normal mice. Unlike the op/op mutant, M-CSF levels, as well as the affinity and number of M-CSF receptors, do not explain the defect in osteoclastic function in the mi/mi mutation.

Effect of growth hormone on bone: bone mineral density, trabecular bone volume, and alkaline phosphatase improve or are restored in the dwarf rat treated with growth hormone

Studies were performed to determine whether serum total alkaline phosphatase (SAP), an index of bone formation; body weight; total body bone mineral density (BMD), measured by dual-energy X-ray absorptiometry; and tibial trabecular bone volume (TBV), measured by histomorphometry, are reduced in 2-week-old female sexually immature Lewis dwarf (dw/dw) rats (DW-CT, n = 9) with isolated growth hormone (GH) deficiency and, if so, whether recombinant human GH (rhGH), 200 micrograms/day subcutaneously for 4 weeks (DW-GH, n = 7), restores them. Studies were also performed to determine if 30% dietary restriction in 2-week-old female Lewis rats (LW-DR, n = 11) alters SAP, body weight, total BMD, or TBV compared with pair-fed controls (LW-CT, n = 7) given an ad libitum diet. Mean SAP (91 +/- 5 versus 109 +/- 5 U/l), body weight (102 +/- 11 versus 140 +/- 10 g), total BMD (88.5 +/- 0.3 versus 101.4 +/- 2.0 mg/cm2), and TBV (19.0 +/- 1.0 versus 27.0 +/- 1.4%) were significantly lower in DW-CT than in LW-CT animals, p < 0.05. In DW-GH, rhGH significantly increased mean SAP (130 +/- 7 U/l), body weight (133 +/- 10 g), total BMD (92.7 +/- 1.3), and TBV (24.0 +/- 1.9) compared with DW-CT animals. Compared with LW-CT rats, mean body weight and TBV were not different, but mean SAP was significantly higher (p < 0.01) and mean total BMD was significantly lower (p < 0.003) in DW-GH rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium needs of adolescents

Adolescents grow at the greatest rate of any age group after infancy and accumulate 37% of their total bone mass during this growth spurt. Because maximum bone mass is acquired during adolescence, the calcium deposited during adolescence determines the risk of osteoporosis and fracture in adulthood. Bone mass is dependent on calcium intake, growth and pubertal development, exercise, and genetic and racial factors. Unfortunately, during this time of tremendous calcium need, most adolescents eat a diet that is very deficient in calcium. Girls are twice as likely to be deficient as boys (85% vs 43%). Other factors contributing to poor bone mineralization include adolescent pregnancy, anorexia nervosa, excessive exercise, and various chronic medical conditions. To avoid osteoporosis in later life, adequate dietary calcium intake should be recommended and calcium supplementation considered in all adolescent patients.

Superoxide and bone resorption

The reaction of superoxide with nitroblue tetrazolium produces an electron-dense diformazan precipitate which can be used to localize areas of superoxide production. Transmission electron microscopy was used to demonstrate that diformazan granules formed by the reaction of nitroblue tetrazolium with excess superoxide are electron dense, whereas monoformazan granules generated by hydrogen peroxide were not. On the basis of these observations, superoxide formed along the osteoclast-bone interface was localized by demonstrating the electron-dense diformazan granules between the osteoclastic membrane and the bone surface. The formation of this reaction product was inhibited by a superoxide scavenger, the deferoxamine mesylate-manganese complex (the "green" complex), confirming the specificity of the reaction product. The scavenger also inhibited bone resorption. High concentrations of superoxide generated in vitro at a neutral pH degraded osteocalcin into numerous peptide fragments, demonstrating the ability of superoxide to break peptide bonds. These studies localize superoxide production to the ruffled border space and suggest that superoxide generated at the osteoclast-bone interface is involved in bone matrix degradation.

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.

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.

Nitroblue tetrazolium reduction and bone resorption by osteoclasts in vitro inhibited by a manganese-based superoxide dismutase mimic

Oxygen-derived free radicals are produced by osteoclasts. Oxygen radical formation occurs at the osteoclast/bone surface interface. This location next to bone implies that oxygen radicals, including but not limited to superoxide, are needed for bone resorption. Compounds that scavenge superoxide are being developed as pharmaceutical agents to inhibit the damaging effects of oxygen radical formation on tissues. One such scavenger is the Desferal-manganese complex (DMnC). DMnC reduced the amount of formazan staining produced by the interaction of oxygen radicals with nitroblue tetrazolium (NBT) in both individual mouse calvarial osteoclasts in tissue explants and isolated osteoclasts. As a result of the reduced concentrations of oxygen radicals, DMnC inhibited bone resorption by calvarial explants and isolated osteoclasts. Superoxide dismutase (SOD) inhibited NBT reduction and bone resorption by isolated osteoclasts but to a lesser degree than DMnC. Inhibition of bone resorption in the isolated osteoclast system increased in parallel to the concentration of DMnC in cultures. Desferal without Mn had no effect on bone resorption by isolated osteoclasts. These results support the hypothesis that osteoclasts produce oxygen radicals as part of the process of bone resorption.

Recombinant human interferon gamma therapy for osteopetrosis

A defect in leukocytic superoxide formation has been demonstrated in patients with congenital osteopetrosis. This leukocyte defect appears to be related to defective bone resorption. Because recombinant human interferon gamma therapy enhances superoxide production in patients with chronic granulomatous disease, we sought to determine whether a similar strategy could reverse the osteopetrotic condition. Interferon gamma, 1.5 micrograms/kg three times a week, was administered by subcutaneous injection for 6 months to eight patients with osteopetrosis. Urinary hydroxyproline and urinary calcium excretion increased markedly during therapy in parallel with a significant decrease in trabecular bone volume. Bone marrow scans demonstrated increased bone marrow production. The hemoglobin concentration, platelet count, and leukocyte production of superoxide increased significantly. No serious infections were encountered during the therapy. These data suggest that interferon gamma administration enhances bone resorption and leukocyte function in patients with osteopetrosis.

Cranial imaging in autosomal recessive osteopetrosis. Part I. Facial bones and calvarium

Cranial imaging studies (radiographs, computed tomographic [CT] scans, magnetic resonance [MR] images, and bone marrow scintigrams) in 13 infants and children with autosomally recessive osteopetrosis were reviewed to characterize patterns of facial and calvarial involvement at presentation and with progression of disease. In the mandible, a characteristic triangular opacity representing calcification within the secondary condylar cartilage ossification center was seen in 10 of the 13 patients. Defective dentition with incomplete enamel formation and/or caries was encountered in all patients. The paranasal sinuses were poorly pneumatized in all patients, but the ethmoid sinuses tended to be the least severely affected. Hypertelorism was present in five of the 13 patients, with a characteristic "space-alien" appearance on frontal radiographs. In younger patients, the calvarium demonstrated a high-attenuation inner table, a broad, low-attenuation diploic space, and a less high-attenuation outer table at CT. In three older children, a "hair-on-end" appearance was seen, which, at bone marrow scintigraphy, corresponded to areas of marked hematopoietic activity. Regions of sclerotic bone demonstrated low signal intensity on both T1- and T2-weighted MR images; areas containing marrow had intermediate signal intensity. These many new radiologic features of osteopetrosis are related to its pathophysiologic characteristics.

Six-year follow-up of a case of radiation injury following treatment for medulloblastoma

Recent reports in the literature have documented long-term sequelae of radiation treatment in children, the most notable of which are diminished endocrine functioning and decline in intellectual ability. A case is presented in which both these long-term effects were seen 7 years after radiation treatment for medulloblastoma. Growth hormone and thyroid hormone deficiencies were identified and treated. Full-Scale IQ dropped from the 79th percentile to the 3rd percentile, and neuropsychological functioning ranged from normal to impaired. However, magnetic resonance imaging reveals few direct imaging correlates of J.M.'s neuropsychological deficits. If identified, hormone deficiencies in such patients can be successfully treated; intellectual deficits may present more of a management problem. In this case, cognitive deficits have contributed to considerable difficulty in school; however, with special classes and modifications, the patient is making progress. Our findings indicate that the long-term outcome for children with radiation injury may be improved significantly with hormone therapy and appropriate academic intervention, and argue strongly for systematic, sequential follow-up of such children so that appropriate intervention can be implemented and continued as necessary.

Cranial imaging in autosomal recessive osteopetrosis. Part II. Skull base and brain

The authors reviewed cranial imaging studies (radiographs, computed tomographic scans, and magnetic resonance [MR] images) in 13 infants and children with the autosomal recessive form of osteopetrosis to characterize patterns of skull base, brain, and cranial nerve involvement at presentation and with progression of disease. Marked sclerosis and deposition of osteopetrotic bone was noted along the anterior (but not posterior) occipitomastoid suture (n = 8), at the basioccipital-exoccipital synchondrosis (n = 9), and along the sphenooccipital synchondrosis (n = 8). Endobones, presumably representing unresorbed primitive ossification centers, were seen in the sphenoidal body and basioccipital bone in 11 of the 13 patients. Marked cupping at the basioccipital-exoccipital synchondrosis was observed in three. Neurologic deficits included blindness (n = 11), conductive hearing loss (n = 11), and facial nerve palsies (n = 4). Delayed myelination was seen with MR imaging in two of five retarded infants, including one with a documented coexisting neuronal storage defect. Prominent extracerebral cerebrospinal fluid spaces were present over the frontal lobes in five of the eight developmentally normal patients, representing either subclinical parenchymal disease or a phenomenon related to discordant growth rates between skull and brain.

Autosomal recessive osteopetrosis: bone marrow imaging

Technetium-99m sulfur colloid scintigraphy was performed prospectively in 12 infants and children with autosomal recessive osteopetrosis, to correlate the appearance of bone marrow stores with advancing age. Baseline images were obtained in all patients, and one to five follow-up images were obtained in eight patients after they began therapy with calcitriol, interferon-gamma, or both. Conventional radiography was performed along with the nuclear studies in all cases. Magnetic resonance (MR) images of the head or lower extremities were also obtained in six patients and were correlated with the scintigraphic findings. Patterns of abnormal distribution of bone marrow appeared to be age-dependent. In patients younger than 1 year, marrow stores were primarily in the skull base and at the ends of the long bones. In patients aged 3-5 years, marrow stores shifted to the diaphyseal regions of long bones and to the calvarium. In the appendicular skeleton, areas of greatest bone marrow activity corresponded to regions of relative decreased opacity on radiographs and areas of intermediate or high signal intensity on T2-weighted MR images. The skull base showed appreciable marrow activity in spite of densely sclerotic bone on radiographs.

Circulating macrophage colony-stimulating factor is not reduced in malignant osteopetrosis

Malignant osteopetrosis is a disorder characterized by a deficiency in osteoclast number or function. In one animal model of osteopetrosis, the op/op mouse, macrophage colony-stimulating factor (M-CSF) is absent, and the administration of M-CSF corrects the defects. We evaluated the serum of 13 patients with malignant osteopetrosis by an M-CSF radioimmunoassay to determine if a quantitative M-CSF deficiency existed in these patients. All patients had M-CSF present in levels equal to or higher than control serum. In addition, serum from 6 osteopetrotic patients was tested in a bioassay to determine if the M-CSF present is biologically active, and in all cases there was demonstrable activity in these samples. We provide evidence that deficiency of circulating M-CSF is unlikely to be a major contributor to the etiologic basis for the majority of children with malignant osteopetrosis.

The vitamin K-dependent carboxylation system in human osteosarcoma U2-OS cells. Antidotal effect of vitamin K1 and a novel mechanism for the action of warfarin

An osteoblast-like human osteosarcoma cell line (U2-OS) has been shown to possess a vitamin K-dependent carboxylation system which is similar to the system in human HepG2 cells and in liver and lung from the rat. In an 'in vitro' system prepared from these cells, vitamin K1 was shown to overcome warfarin inhibition of gamma-carboxylation carried out by the vitamin K-dependent carboxylase. The data suggest that osteoblasts, the cells involved in synthesis of vitamin K-dependent proteins in bone, can use vitamin K1 as an antidote to warfarin poisoning if enough vitamin K1 can accumulate in the tissue. Five precursors of vitamin K-dependent proteins were identified in osteosarcoma and HepG2 cells respectively. In microsomes (microsomal fractions) from the osteosarcoma cells these precursors revealed apparent molecular masses of 85, 78, 56, 35 and 31 kDa. When osteosarcoma cells were cultured in the presence of warfarin, vitamin K-dependent 14C-labelling of the 78 kDa precursor was enhanced. Selective 14C-labelling of one precursor was also demonstrated in microsomes from HepG2 cells and from rat lung after warfarin treatment. In HepG2 cells this precursor was identified as the precursor of (clotting) Factor X. This unique 14C-labelling pattern of precursors of vitamin K-dependent proteins in microsomes from different cells and tissues reflects a new mechanism underlying the action of warfarin.

Pituitary gland: MR imaging of physiologic hypertrophy in adolescence

The size and shape of pituitary glands in 169 children, adolescents, and young adults were analyzed with T1-weighted sagittal magnetic resonance (MR) images. In patients younger than 12 years old, no pituitary gland was found to be more than 6 mm in height. In adolescents, definite evidence for physiologic (pubertal) pituitary hypertrophy was seen in both sexes, although it was much more prominent in girls. The pituitary glands of four of 32 teenage girls measured 8-10 mm, but no teenage boy had a gland taller than 7 mm. Young adults aged 21-30 years had significantly (P less than .05) smaller glands than teenagers of the same sex. Significant (P = .0001) variations in the shape of the pituitary glands according to patient age and sex were also noted. Convex upper margins were seen in 56% of teenage girls, while this shape was noted in only 18% of the remaining patients of either sex. In eight of 32 teenage girls (25%) the pituitary glands were nearly spherical on sagittal images; this shape was not recorded in any other group. The normal maturation sequence of the pituitary gland apparently involves a period of physiologic hypertrophy in teenagers. This is manifest in girls by a significant change in both pituitary size and shape, while the glands of boys undergo a transformation in size only.

Oxygen derived free radicals in osteoclasts: the specificity and location of the nitroblue tetrazolium reaction

Oxygen derived free radicals are generated by osteoclasts. In a novel culture system, isolated rat osteoclasts were stained when nitroblue tetrazolium (NBT) was reduced by cellular oxidants to formazan, an insoluble precipitate. Superoxide dismutase (SOD) inhibited the accumulation of formazan by the isolated osteoclasts. Osteoclasts in mouse calvarial organ cultures also reduced NBT to formazan. The reaction products were localized to the area of the osteoclast-bone interface. At the light microscopic level, the formazan granules appeared to be concentrated within the cytoplasm. Formazan accumulation was significantly inhibited by calcitonin (hCT). The inhibition of NBT reduction by SOD indicates that the isolated osteoclasts were capable of producing superoxide. The localization of the formazan granules between the external osteoclastic membrane and the bone, and the inhibition of this reaction during hCT exposure suggests that oxygen derived free radicals may contribute to bone resorption.

Interleukin-2 stimulates osteoclastic activity: increased acid production and radioactive calcium release

Recombinant human interleukin-2 (IL-2) was studied to determine effects on acid production by individual osteoclasts in situ on mouse calvarial bones. This analysis was performed using a microspectrofluorimetric technique to quantify acid production in individual cells. Radioactive calcium release was determined using calvarial bones in a standard tissue culture system. This allowed us to correlate changes in acid production with a measure of bone resorption. IL-2 stimulated acid production and bone resorbing activity. Both effects were inhibited by calcitonin. No stimulation of bone resorption occurred when IL-2-containing test media was incubated with a specific anti-IL-2 antibody and ultrafiltered. Our data demonstrated a correlation between acid production and bone resorbing activity in mouse calvaria exposed to parathyroid hormone (PTH). The data obtained from cultured mouse calvaria exposed to IL-2 demonstrated similar stimulatory effects to those seen during PTH exposure. These data suggest that calvaria exposed to IL-2 in vitro have increased osteoclastic acid production corresponding with increased bone resorption.

Variable osteoclast appearance in human infantile osteopetrosis

A light and transmission electron microscopic (TEM) study of iliac crest metaphyseal bone from nine patients with infantile osteopetrosis demonstrates a variable spectrum of osteoclast abnormalities. All bone was obtained at biopsy before treatment. The average age at biopsy was 6 months with a range from 1 to 12 months. Osteoclast number was always increased and the cells were always appropriately positioned in relation to bone and cartilage. Osteoclast number, size, and nucleation varied from midly to markedly increased. In those with only a mild-to-moderate osteoclast increase, the marrow had an otherwise near-normal appearance with a good complement of hematopoietic cells. In those with markedly increased osteoclasts (hyperosteoclastic state) there were only scanty collections of hematopoietic cells. Light microscopic histomorphometry documented the percentage of bone and cartilage surfaces covered by osteoclasts. Controls from areas of greatest osteoclast presence documented a 5% coverage. One osteopetrotic patient registered a 4.8% value with all others elevated from 7.6 to 27.9%. Quantitative electron microscopy showed the ruffled border-clear zone complex to be absent or markedly diminished in seven of the nine patients. In two, however, osteoclast profiles had abundant ruffled border-clear zone complexes. Patients with the hyperosteoclastic bone marrow were more severely affected clinically. Light and TEM studies of marrow biopsies in initial assessment of osteopetrosis establish a baseline profile, may provide prognostic information, and allow for more meaningful treatment follow-up.

Vitamin D and retinoblastoma. The presence of receptors and inhibition of growth in vitro

The vitamin D receptor has been found in several human organs not involved in calcium metabolism and in several malignant neoplasms found in humans. The role of the receptor in these tissues is unclear. There is, however, a relationship between the presence and quantity of the vitamin D receptor in a malignant cell line and the antineoplastic effect of vitamin D on that cell line. We found that Y-79 retinoblastoma cells have receptors specific for calcitriol (1,25-dihydroxycholecalciferol). Scatchard analysis of the receptor data shows a quantity of 56,000 receptors per retinoblastoma cell. These receptors have a dissociation constant of 1.18 nmol/L. Retinoblastoma cells treated with 10(-9) mol/L of calcitriol for nine days had 15% less cell growth than the control cells. Further studies of the effect of vitamin D on retinoblastoma may warrant its inclusion in chemotherapeutic protocols for the treatment of this childhood affliction.

A link between calcitriol and bone resorption

Calcitriol exposure stimulated a human osteosarcoma cell line, U2-OS, to produce a factor(s) which stimulated bone degradation in human monocyte cultures and osteoclastic bone resorption in fetal rat long bone cultures. The factor(s) was elicited by as little as 10(-10) M calcitriol. The factor is effective in stimulating peripheral blood monocytes to degrade bone, suggesting a direct effect on cellular bone breakdown. The fetal long bone assays suggest that the osteoblast-like cells produce a factor(s) which stimulates osteoclasts. This is confirmed by the fact that human calcitonin added to the long bone cultures blocks the stimulation. The effect of PTH appears to be through the production of factors which stimulate osteoblasts. The present study suggests that a similar factor(s) may be responsible for the effect of calcitriol on bone resorption.

In vitro degradation of bone particles by human monocytes is decreased with the depletion of the vitamin K-dependent bone protein from the matrix

The bone vitamin K-dependent protein osteocalcin has been suggested to play a role in bone resorption. By administering sodium warfarin to rats, it is possible to inhibit the vitamin K-dependent addition of the their gamma-carboxyglutamic acid residues to osteocalcin. This results in reduced amounts of osteocalcin bone, probably because devoid of the calcium-binding Gla residues, the protein no longer accumulates in bone. Preparations of bone obtained from rats treated with sodium warfarin for 6 weeks contained only 0.2% of normal levels of osteocalcin and were 90% reduced in the concentration of Gla. This bone could not be degraded by human monocytes in vitro as well as control bone (only 54% of control; P less than 0.003). Defects in the movement of cells to the bone were documented by phase contrast microscopy. Only 60% as many monocytes attached to the osteocalcin-depleted bone as to control bone in an in vitro attachment assay. These effects do not appear to be related to direct cellular toxicity. The degradation of bone in this in vitro system appears to be dependent on the osteocalcin content in matrix. This may result from defective movement of cells to bone and/or attachment to the bone.

Monocyte bone degradation: in vitro analysis of monocyte activity in patients with juvenile rheumatoid arthritis

We examined the ability of the mononuclear phagocyte in vitro to degrade 45Ca-labeled bone particles to determine whether this assay allowed us to monitor disease activity in patients with juvenile rheumatoid arthritis. The monocytes from patients with juvenile rheumatoid arthritis receiving no anti-erosive therapy (n = 10) degraded significantly more bone than did cells obtained from normal controls (n = 10, P less than 0.001) or patients with juvenile rheumatoid arthritis receiving either gold thioglucose (n = 4, P less than 0.001) or D-penicillamine (n = 6, P less than 0.005). In two patients monitored for either 8 or 11 months, results of monocyte assays were found to parallel the clinical course. We conclude that in vitro monocyte bone degradation assays may provide a means of assessing joint activity in patients with juvenile rheumatoid arthritis. Further, this study and others indicate that mononuclear phagocytes are capable of causing erosive changes.

Platelet-derived growth factor stimulates bone resorption by monocyte monolayers

Resorption of devitalized bone particles by monocytes grown in culture was stimulated by platelet-derived growth factor (PDGF) in a dose-dependent manner. Bone resorption in response to PDGF was time-dependent with a significant increase over control cultures evident by 72 hours. These data are the first to demonstrate stimulation of bone resorption by PDGF in a specific cell type known to resorb bone in vivo and in vitro.