Forearm bone mineral density and fracture incidence in postmenopausal women with osteoporosis: results from the ACTIVExtend phase 3 trial.

Abaloparatide increased ultradistal radius bone mineral density (BMD) in the Abaloparatide Comparator Trial in Vertebral Endpoints (ACTIVE) trial. Over the subsequent 24 months in ACTIVExtend, ultradistal radius BMD gains were maintained with alendronate. Conversely, 1/3 radius BMD remained stable during ALN treatment in ACTIVExtend after decreasing during ACTIVE. INTRODUCTION: Abaloparatide (ABL) increased femoral neck, total hip, and lumbar spine bone mineral density (BMD) in postmenopausal women with osteoporosis and decreased the risk of vertebral and nonvertebral fractures in ACTIVE. Effects on fracture risk and BMD were maintained subsequently with alendronate (ALN) in ACTIVExtend. In a prespecified subanalysis of ACTIVE, ABL also increased BMD at the ultradistal radius. Our objective was to determine the efficacy of ABL followed by ALN vs placebo (PBO) followed by ALN on forearm BMD and fracture risk over 43 months in ACTIVExtend. METHODS: Ultradistal and 1/3 radius BMD (ACTIVE baseline to month 43) were measured (ABL/ALN, n = 213; PBO/ALN, n = 233). Wrist fracture rates were estimated for the ACTIVExtend intent-to-treat population (ABL/ALN, n = 558; PBO/ALN, n = 581) by Kaplan-Meier (KM) method. RESULTS: At cumulative month 25, mean increase from ACTIVE baseline in ultradistal radius BMD was 1.1% (standard error, 0.49%) with ABL/ALN vs - 0.8% (0.43%) with PBO/ALN (P < 0.01). BMD increases with ABL were maintained with ALN through month 43 in ACTIVExtend. BMD decreases at the 1/3 radius in ACTIVE (similar with ABL and PBO) were maintained through 24 months of ALN treatment in ACTIVExtend. Wrist fractures over 43 months occurred in 15 women with ABL/ALN (KM estimate, 2.8%) and 20 with PBO/ALN (KM estimate, 3.6%) (HR = 0.77, 95% CI 0.39, 1.50; P = not significant). CONCLUSION: Ultradistal radius BMD gains following treatment with ABL in ACTIVE were maintained over 24 months of ALN treatment in ACTIVExtend. Conversely, 1/3 radius BMD remained stable during ALN treatment in ACTIVExtend after decreasing during ACTIVE. TRIAL REGISTRATION: ClinicalTrials.gov : NCT01657162 submitted July 31, 2012.

Correction to: Abaloparatide effect on forearm bone mineral density and wrist fracture risk in postmenopausal women with osteoporosis.

The original version of this article, published on 21 March 2019, unfortunately contains some typos in Figs. 2, 3, 4, and Supplemental Fig. 1. The corrected figures are given below.

Correction to: Abaloparatide effect on forearm bone mineral density and wrist fracture risk in postmenopausal women with osteoporosis.

The original version of this article, published on 21 March 2019, unfortunately contained a mistake.

Abaloparatide increases bone mineral density and bone strength in ovariectomized rabbits with glucocorticoid-induced osteopenia.

Glucorticoid (GC) therapy is the commonest cause of secondary osteoporosis. Ovariectomized rabbits receiving the GC methylprednisolone for 6 weeks exhibited relatively lower vertebral and femoral bone mass. Treatment with the PTH receptor agonist abaloparatide for 12 weeks during ongoing methylprednisolone administration increased cortical and trabecular bone mass and femur bending strength. INTRODUCTION: Abaloparatide, an osteoanabolic PTHrP analog, increases bone mineral density (BMD) and reduces fracture risk in women with postmenopausal osteoporosis. This study assessed abaloparatide effects on BMD and bone strength in ovariectomized (OVX) rabbits with glucocorticoid (GC)-induced osteopenia. METHODS: Thirty-two rabbits underwent OVX and 8 underwent sham surgery. One day later, 24 OVX rabbits began daily s.c. GC injections (methylprednisolone, 1 mg/kg/day) for 6 weeks, while 8 OVX and 8 sham controls received no GC. GC-challenged rabbits (8/group) then received GC (0.5 mg/kg/day) along with daily s.c. vehicle (GC-OVX), abaloparatide 5 µg/kg/day (ABL5), or 25 µg/kg/day (ABL25) for 12 weeks, and the no-GC OVX and sham controls received daily vehicle. RESULTS: GC-OVX rabbits showed significant deficits in vertebral and proximal femur areal BMD, lower cortical area, thickness and volumetric BMD of the femur diaphysis, and reduced trabecular bone volume and volumetric BMD in the vertebra and distal femur versus sham controls. These deficits were significantly reversed in the ABL25 group, which also showed enhanced trabecular micro-architecture versus GC-OVX controls. Destructive bending tests showed significantly lower femur diaphysis ultimate load and bending rigidity of the femoral diaphysis in the GC-OVX group versus sham controls, whereas these parameters were similar in the ABL25 group vs sham controls. CONCLUSIONS: Abaloparatide 25 µg/kg/day mitigated the adverse effects of GC administration on cortical and trabecular bone and improved femoral strength in OVX rabbits. These results suggest potential promise for abaloparatide as an investigational therapy for glucocorticoid-induced osteoporosis.

Abaloparatide effect on forearm bone mineral density and wrist fracture risk in postmenopausal women with osteoporosis.

PURPOSE: Wrist fractures are common, contribute significantly to morbidity in women with postmenopausal osteoporosis, and occur predominantly at the ultradistal radius, a site rich in trabecular bone. This exploratory analysis of the phase 3 ACTIVE study evaluated effects of abaloparatide versus placebo and teriparatide on forearm bone mineral density (BMD) and risk of wrist fracture. METHODS: Forearm BMD was measured by dual energy X-ray absorptiometry in a subset of 982 women from ACTIVE, evenly distributed across the three treatment groups. Wrist fractures were ascertained in the total cohort (N = 2463). RESULTS: After 18 months, ultradistal radius BMD changes from baseline were 2.25 percentage points greater for abaloparatide compared with placebo (95% confidence interval (CI) 1.38, 3.12, p < 0.001) and 1.54 percentage points greater for abaloparatide compared with teriparatide (95% CI 0.64, 2.45, p < 0.001). At 18 months, 1/3 radius BMD losses (versus baseline) were similar for abaloparatide compared with placebo (-0.42; 95% CI -1.03, 0.20; p = 0.19) but losses with teriparatide exceeded those of placebo (-1.66%; 95% CI -2.27, -1.06; p < 0.001). The decline with abaloparatide was less than that seen with teriparatide (group difference 1.22%; 95% CI 0.57, 1.87; p < 0.001). The radius BMD findings, at both ultradistal and 1/3 sites, are consistent with the numerically lower incidence of wrist fractures observed in women treated with abaloparatide compared with teriparatide (HR = 0.43; 95% CI 0.18, 1.03; p = 0.052) and placebo (HR = 0.49, 95% CI 0.20, 1.19, p = 0.11). CONCLUSIONS: Compared with teriparatide, abaloparatide increased BMD at the ultradistal radius (primarily trabecular bone) and decreased BMD to a lesser extent at the 1/3 radius (primarily cortical bone), likely contributing to the numerically lower wrist fracture incidence observed with abaloparatide.

Bone mineral density response rates are greater in patients treated with abaloparatide compared with those treated with placebo or teriparatide: Results from the ACTIVE phase 3 trial.

BACKGROUND: Abaloparatide is a 34-amino acid peptide that selectively binds to the RG conformation of the parathyroid hormone receptor type 1. It was developed for the treatment of women with postmenopausal osteoporosis at high risk of fracture. In ACTIVE, an 18-month phase 3 study (NCT01343004), abaloparatide increased bone mineral density (BMD), decreased the risk of vertebral and nonvertebral fractures compared with placebo, and decreased the risk of major osteoporotic fractures compared with placebo and teriparatide. Here, we report a prospective, exploratory BMD responder analysis from ACTIVE. METHODS: Proportions of patients experiencing BMD gains from baseline of >0%, >3%, and >6% at the total hip, femoral neck, and lumbar spine at 6, 12, and 18 months of treatment were compared among the placebo, abaloparatide, and teriparatide groups in ACTIVE. Responders were defined prospectively as patients experiencing BMD gains at all 3 anatomic sites. RESULTS: At months 6, 12, and 18, there were significantly more >3% BMD responders in the abaloparatide group compared with placebo and teriparatide: month 6, 19.1% vs 0.9% for placebo and 6.5% for teriparatide; month 12, 33.2% vs 1.5% and 19.8%; month 18, 44.5% vs 1.9% and 32.0% (P < 0.001 for all comparisons of abaloparatide to placebo and to teriparatide). Findings were similar for the >0% and >6% responder thresholds. CONCLUSIONS: In postmenopausal women with osteoporosis, a significantly greater proportion of patients treated with abaloparatide experienced increases in BMD than did those treated with placebo or teriparatide.

Abaloparatide, a novel PTH receptor agonist, increased bone mass and strength in ovariectomized cynomolgus monkeys by increasing bone formation without increasing bone resorption.

Abaloparatide, a novel PTH1 receptor agonist, increased bone formation in osteopenic ovariectomized cynomolgus monkeys while increasing cortical and trabecular bone mass. Abaloparatide increased bone strength and maintained or enhanced bone mass-strength relationships, indicating preserved or improved bone quality. INTRODUCTION: Abaloparatide is a selective PTH1R activator that is approved for the treatment of postmenopausal osteoporosis. The effects of 16 months of abaloparatide administration on bone formation, resorption, density, and strength were assessed in adult ovariectomized (OVX) cynomolgus monkeys (cynos). METHODS: Sixty-five 9-18-year-old female cynos underwent OVX surgery, and 15 similar cynos underwent sham surgery. After a 9-month period without treatments, OVX cynos were allocated to four groups that received 16 months of daily s.c. injections with either vehicle (n = 17) or abaloparatide (0.2, 1, or 5 µg/kg/day; n = 16/dose level), while Sham controls received s.c. vehicle (n = 15). Bone densitometry (DXA, pQCT, micro-CT), qualitative bone histology, serum calcium, bone turnover markers, bone histomorphometry, and bone strength were among the key measures assessed. RESULTS: At the end of the 9-month post-surgical bone depletion period, just prior to the treatment phase, the OVX groups exhibited increased bone turnover markers and decreased bone mass compared with sham controls. Abaloparatide administration to OVX cynos led to increased bone formation parameters, including serum P1NP and endocortical bone formation rate. Abaloparatide administration did not influence serum calcium levels, bone resorption markers, cortical porosity, or eroded surfaces. Abaloparatide increased bone mass at the whole body, lumbar spine, tibial diaphysis, femoral neck, and femoral trochanter. Abaloparatide administration was associated with greater lumbar vertebral strength, and had no adverse effects on bone mass-strength relationships for the vertebrae, femoral neck, femoral diaphysis, or humeral cortical beams. CONCLUSIONS: Abaloparatide administration was associated with increases in bone formation, bone mass and bone strength, and with maintenance of bone quality in OVX cynos, without increases in serum calcium or bone resorption parameters.

Abaloparatide-SC improves trabecular microarchitecture as assessed by trabecular bone score (TBS): a 24-week randomized clinical trial.

In a phase 2 trial of 222 postmenopausal women with osteoporosis aged 55 to 85 years randomized to one of three different doses of abaloparatide-SC, subcutaneous teriparatide, or placebo for 24 weeks, abaloparatide-SC resulted in improvements in skeletal microarchitecture as measured by the trabecular bone score. INTRODUCTION: Subcutaneous abaloparatide (abaloparatide-SC) increases total hip and lumbar spine bone mineral density and reduces vertebral and non-vertebral fractures. In this study, we analyzed the extent to which abaloparatide-SC improves skeletal microarchitecture, assessed indirectly by trabecular bone score (TBS). METHODS: This is a post hoc analysis of a phase 2 trial of 222 postmenopausal women with osteoporosis aged 55 to 85 years randomized to abaloparatide-SC (20, 40, or 80 µg), subcutaneous teriparatide (20 µg), or placebo for 24 weeks. TBS was measured from lumbar spine dual X-ray absorptiometry (DXA) images in 138 women for whom the DXA device was TBS software compatible. Assessments were made at baseline, 12 and 24 weeks. Between-group differences were assessed by generalized estimating equations adjusted for relevant baseline characteristics, and a pre-determined least significant change analysis was performed. RESULTS: After 24 weeks, TBS increased significantly by 2.27, 3.14, and 4.21% versus baseline in participants on 20, 40, and 80 µg abaloparatide-SC daily, respectively, and by 2.21% in those on teriparatide (p < 0.05 for each). The TBS in the placebo group declined by 1.08%. The TBS increase in each treatment group was significantly higher than placebo at 24 weeks (p < 0.0001 for each) after adjustment for age, BMI, and baseline TBS. A dose-response was observed at 24 weeks across the three doses of abaloparatide-SC and placebo (p = 0.02). The increase in TBS in the abaloparatide-SC 80 µg group was significantly greater than TPTD (p < 0.03). CONCLUSIONS: These results are consistent with an effect of abaloparatide-SC to improve lumbar spine skeletal microarchitecture, as assessed by TBS.

The localized expression of extracellular matrix components in healing tendon insertion sites: an in situ hybridization study.

The localized expression of a number of extracellular matrix genes was evaluated over time in a novel rat rotator cuff injury model. The supraspinatus tendons of rats were severed at the bony insertion and repaired surgically. The healing response was evaluated at 1, 2, 4, and 8 weeks post-injury using histologic and in situ hybridization techniques. Expression patterns of collagens (I, II, III, IX, X, XII), proteoglycans (decorin, aggrecan, versican, biglycan, fibromodulin), and other extracellular matrix proteins (elastin, osteocalcin, alkaline phosphatase) were evaluated at the healing tendon to bone insertion site. Histologic results indicate a poor healing response to the injury, with only partial recreation of the insertion site by 8 weeks. In situ hybridization results indicate a specific pattern of genes expressed in each zone of the insertion site (i.e., tendon, fibrocartilage, mineralized cartilage, bone). Overall, expression of collagen types I and XII, aggrecan, and biglycan was increased, while expression of collagen type X and decorin was decreased. Expression of collagen type I, collagen type XII, and biglycan decreased over time, but remained above normal at 8 weeks. Results indicate that the rat supraspinatus tendon is ineffective in recreating the original insertion site, even at 8 weeks post-injury, in the absence of biological or biomechanical enhancements.

Cloning and expression of the Wnt antagonists Sfrp-2 and Frzb during chick development.

The Wnt genes are known to play fundamental roles during patterning and development of a number of embryonic structures. Receptors for Wnts are members of the Frizzled family of proteins containing a cysteine-rich domain (CRD) that binds the Wnt protein. Recently several secreted frizzled-related proteins (Sfrps) that also contain a CRD have been identified and some of these can both bind and antagonise Wnt proteins. In this paper we report the expression patterns of the chick homologues of Frzb, a known Wnt antagonist, and Sfrp-2. Both genes are expressed in areas where Wnts are known to play a role in development, including the neural tube, myotome, cartilage, and sites of epithelial-mesenchymal interactions. Initially, Sfrp-2 and Frzb are expressed in overlapping areas in the neural plate and neural tube, whereas later, they have distinct patterns. In particular Sfrp-2 is associated with myogenesis while Frzb is associated with chondrogenesis, suggesting that they play different roles during development. Finally, we have used the early Xenopus embryo as an in vivo assay to show that Sfrp-2, like Frzb, is a Wnt antagonist. These results suggest that Sfrp-2 and Frzb may function in the developing embryo by modulating Wnt signalling.

A novel BMP expressed in developing mouse limb, spinal cord, and tail bud is a potent mesoderm inducer in Xenopus embryos.

The bone morphogenetic proteins (BMPs) play critical roles in patterning the early embryo and in the development of many organs and tissues. We have identified a new member of this multifunctional gene family, BMP-11, which is most closely related to GDF-8/myostatin. During mouse embryogenesis, BMP-11 is first detected at 9.5 dpc in the tail bud with expression becoming stronger as development proceeds. At 10.0 dpc, BMP-11 is expressed in the distal and posterior region of the limb bud and later localizes to the mesenchyme between the skeletal elements. BMP-11 is also expressed in the developing nervous system, in the dorsal root ganglia, and dorsal lateral region of the spinal cord. To assess the biological activity of BMP-11, we tested the protein in the Xenopus ectodermal explant (animal cap) assay. BMP-11 induced axial mesodermal tissue (muscle and notochord) in a dose-dependent fashion. At higher concentrations, BMP-11 also induced neural tissue. Interestingly, the activin antagonist, follistatin, but not noggin, an antagonist of BMPs 2 and 4, inhibited BMP-11 activity on animal caps. Our data suggest that in Xenopus embryos, BMP-11 acts more like activin, inducing dorsal mesoderm and neural tissue, and less like other family members such as BMPs 2, 4, and 7, which are ventralizing and anti-neuralizing signals. Taken together, these data suggest that during vertebrate embryogenesis, BMP-11 plays a unique role in patterning both mesodermal and neural tissues.

Ectopic induction of tendon and ligament in rats by growth and differentiation factors 5, 6, and 7, members of the TGF-beta gene family.

Little is known about the regulatory signals involved in tendon and ligament formation, and this lack of understanding has hindered attempts to develop biologically based therapies for tendon and ligament repair. Here we report that growth and differentiation factors (GDFs) 5, 6, and 7, members of the TGF-beta gene superfamily that are most related to the bone morphogenetic proteins, induce neotendon/ligament formation when implanted at ectopic sites in vivo. Analysis of tissue induced by GDF-5, 6, or 7, containing implants by currently available morphological and molecular criteria used to characterize tendon and ligament, adds further evidence to the idea that these GDFs act as signaling molecules during embryonic tendon/ligament formation. In addition, comparative in situ localizations of the GDF-5, 6, and 7 mRNAs suggest that these molecules are important regulatory components of synovial joint morphogenesis.

Generation of osteoclast-inductive and osteoclastogenic cell lines from the H-2KbtsA58 transgenic mouse.

The development of osteoclastic cell lines would greatly facilitate analysis of the cellular and molecular biology of bone resorption. Several cell lines have previously been reported to be capable of osteoclastic differentiation. However, such cell lines form at best only occasional excavations, suggesting that osteoclastic differentiation is either incomplete or that osteoclasts represent a very small proportion of the cells present. We have used the recently developed H-2KbtsA58 transgenic mouse, in which the interferon-inducible major mouse histocompatibility complex H-2Kb promoter drives the temperature-sensitive (ts) immortalizing gene of simian virus 40 (tsA58), to develop cell lines from bone marrow with high efficiency. Bone marrow cells were incubated with gamma interferon at 33 degrees C, then cloned, and expanded. The cell lines were characterized at 39.5 degrees C in the absence of gamma interferon. First, stromal cell lines were established that induced osteclast formation (resorption of bone slices) when cocultured with hemopoietic spleen cells. Some of the stromal cell lines so generated were able to resorb approximately 30 mm2/cm2 of bone surface. We then established cell lines of hemopoietic origin, several of which possess osteoclastic potential. When these osteoclast-precursor cell lines were cocultured with stromal cell lines, extensive bone resorption was observed. Osteoclast formation did not occur if the precursor cell lines were incubated on bone slices without stromal cells; osteoclast formation was also dependent upon the presence of 1 alpha,25-dihydroxyvitamin D3. These cell lines represent a model for osteoclast formation and a valuable resource for identification of the mechanisms and factors that regulate osteoclast differentiation and function.

Derivation of osteoclasts from hematopoietic colony-forming cells in culture.

The osteoclast is known to be derived from the hematopoietic stem cell, but its lineage remains controversial. There is evidence that osteoclastic differentiation is induced through a contact-dependent interaction between bone marrow stromal cells and hematopoietic precursors. To analyze osteoclastic lineage, colonies were generated in semisolid medium from mouse spleen cells in the presence of Wehi-conditioned medium, interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or macrophage colony-stimulating factor (M-CSF) with or without erythropoietin (epo). After 5-8 days colonies were picked and phenotyped and incubated with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on bone slices or coverslips with bone marrow-derived cell lines (ts8 or ST2) that induce osteoclastic differentiation. Cells of osteoclastic phenotype [as judged by calcitonin receptor (CTR) expression or bone resorption] were observed only in multilineage colonies. The ability of cells that generate macrophage colonies (CFU-M) to generate osteoclasts was tested by incubating alveolar or peritoneal macrophages on ts8 or ST2 cells. Despite colony formation, no osteoclastic differentiation was detectable. Last, individual cells from blast cell colonies were incubated (1 cell per culture well) on ts8 or ST2 cells in the presence of 1,25-(OH)2D3 and epo (to expose the lineage potential of the plated cell). We found CTR-positive (CTRP) cells in 6 of 66 macrophage colonies, 7 of 12 granulocyte-macrophage (GM) colonies, and 49 of 50 colonies containing multiple lineages other than GM colonies. No single-lineage CTRP colonies were observed. Although most macrophage colonies did not contain CTRP, no CTRP were observed in colonies from which macrophages were absent. These results suggest that osteoclasts are derived from a multilineage precursor rather than from CFU-M.

Prostaglandins in the kidney, urinary bladder and gills of the rainbow trout and European eel adapted to fresh water and seawater.

Prostaglandins in kidney, gills, and urinary bladder of freshwater-adapted and seawater-adapted rainbow trout, Oncorhynchus mykiss (= Salmo gairdneri), and European eel, Anguilla anguilla, were determined by solid-phase extraction of tissue homogenates and high-pressure liquid chromatography. Prostaglandins E2, E1, F1 alpha, F2 alpha, and D2 and the more stable metabolite of prostacyclin, 6-keto F1 alpha, occurred in these osmoregulatory tissues. In gill filaments and kidneys of both eel and trout, prostaglandins D2 and 6-keto F1 alpha were major prostaglandins. Concentrations of these prostaglandins were significantly lower in the eel after seawater adaptation, but not in the trout. The urinary bladder of the trout contained the highest levels of prostaglandins; bladders of seawater-adapted trout contained prostaglandin D2 at 6.7 ng/mg wet tissue, the highest level of any prostaglandin determined in the present studies. Prostaglandin D2 was not detected in bladders of freshwater-adapted trout.

Macrophage colony stimulating factor (M-CSF) is essential for osteoclast formation in vitro.

The op/op mouse, in which the M-CSF gene is mutated, has greatly reduced numbers of macrophages and osteoclasts. We assessed the ability of M-CSF to induce osteoclast and macrophage formation in op/op hemopoietic cells in vitro. Osteoclast production was undetectable in op/op cell cultures, but was restored by M-CSF at concentrations approximately an order of magnitude higher than those that induced macrophages. In normal hemopoietic tissue M-CSF similarly increased macrophage numbers, but inhibited osteoclast formation. Despite cure of the macrophage defect, neither interleukin 3 nor granulocyte-macrophage CSF were able to induce osteoclastic differentiation in op/op cells. The results suggest that M-CSF induces osteoclastic differentiation but that macrophages, which are also induced by M-CSF, suppress osteoclast differentiation. Macrophages induced by other cytokines seem unable to contribute to osteoclast-formation.

Effects of transforming growth factor beta 1 on the regulation of osteoclastic development and function.

Transforming growth factor (TGF) beta 1 is a multifunctional cytokine with powerful effects on osteoblastic cells. Its role in the regulation of osteoclast generation and function, however, is unclear. It has been reported both to stimulate and to inhibit resorption in organ culture and to inhibit multinuclear cell formation in bone marrow cultures. We tested the effects of TGF-beta 1 on bone resorption by osteoclasts isolated from neonatal rat long bones. We found potent stimulation of osteoclastic bone resorption, mediated by osteoblastic cells, with an EC50 of 10 pg/ml, considerably lower than that of well-documented osteotropic hormones. Stimulation was not mediated by Swiss mouse 3T3 cells, a nonosteoblastic cell line. TGF-beta 1 strongly inhibited the generation of calcitonin receptor (CTR)-positive cells in mouse bone marrow cultures, but as for isolated osteoclasts, bone resorption per CTR-positive cell was increased. The inhibition of CTR-positive cell formation was associated with suppression of maturation of other bone marrow derivatives and may be related more to the known ability of TGF-beta 1 to suppress the proliferation of primitive hematopoietic cells than to a specific role of TGF-beta 1 in osteoclast generation.

Identification of osteoclast precursors in multilineage hemopoietic colonies.

The osteoclast is known to be derived from the hemopoietic stem cell, but its lineage and the mechanisms by which its differentiation is regulated are largely unknown. There is evidence that osteoclastic differentiation is induced through a contact-dependent interaction between bone marrow stromal cells and hemopoietic precursors. To analyze osteoclastic lineage, colonies were generated in semi-solid medium from mouse spleen cells in the presence of erythropoietin with either Wehi 3B-conditioned medium or interleukin 3 (IL3). After 7 days, individual colonies were picked. Half of each colony was phenotyped by the morphology of cells in cytospin preparations; the second half of each was incubated for 7 days with a bone marrow-derived cell line (ts8) that induces osteoclastic differentiation from hemopoietic cells, on bone slices in the presence of 1,25-dihydroxyvitamin D3. After incubation, bone resorption was assessed by scanning electron microscopy. No resorption was induced in cells derived from single-lineage colonies, but resorptive cells differentiated in 17% of granulocyte-macrophage (GM) colonies and 38% of multilineage colonies. Since only a minority of GM colonies contained osteoclastic precursors, this suggests that the GM colonies that contained osteoclasts were not typical GM colonies but may have been a form of multilineage colony analagous to other multilineage colonies that contain granulocytes, macrophages, and a third cell type. No resorptive cells were formed when IL3-derived colonies were incubated on bone slices without ts8 cells. The results suggest that osteoclasts are derived from a multilineage precursor, upon which IL3 acts to generate cells capable of osteoclastic differentiation, which form resorptive cells upon incubation with bone marrow stromal cells in the presence of 1,25-dihydroxyvitamin D3.

Effects of interleukin 3 and of granulocyte-macrophage and macrophage colony stimulating factors on osteoclast differentiation from mouse hemopoietic tissue.

The effects of granulocyte-macrophage colony stimulating factor (GM-CSF), macrophage colony stimulating factor (M-CSF), and interleukin 3 (IL3) on osteoclast formation were tested by incubation of murine hemopoietic cells on plastic coverslips and bone slices with GM-CSF, M-CSF, or IL3, with or without 1,25(OH)2 vitamin D3 (1,25(OH)2D3). Osteoclastic differentiation was detected after incubation by scanning electron microscopical examination of bone slices for evidence of osteoclastic excavations, and by autoradiographic assessment of cells for 1,25(OH)2D3-calcitonin (CT) binding. The differentiation of CT-receptor-positive cells preceded bone resorption, but the number that developed correlated with the extent of bone resorption (r = 0.88). M-CSF and GM-CSF substantially reduced bone resorption and CT-receptor-positive cell formation. The degree of inhibition of bone resorption could not be attributed to effects on the function of mature cells, since M-CSF inhibits resorption by such cells only by 50%, and GM-CSF has no effect. GM-CSF inhibited the development of mature function (bone resorption) to a greater extent than it inhibited CT-receptor-positive cell formation. Since CT-receptor expression antedated resorptive function, this suggests that GM-CSF resulted in the formation of reduced numbers of relatively immature osteoclasts. This suggests that it may exert a restraining effect on the maturation of cells undergoing osteoclastic differentiation in response to 1,25(OH)2D3. Conversely, IL3, which also has no effect on mature osteoclasts, by itself induced CT-receptor expression but not bone resorption; in combination with 1,25(OH)2D3 it induced a threefold increase in bone resorption and CT-receptor-positive cells compared with cultures incubated with 1,25(OH)2D3 alone. IL3 did not induce CT-receptors in peritoneal macrophages, blood monocytes, or J 774 cells. The results suggest that IL3 induces only partial maturation of osteoclasts, which is augmented or completed by additional factors such as 1,25(OH)2D3.