Alendronate treatment for infants with osteogenesis imperfecta: demonstration of efficacy in a mouse model

Murine Animal Models in Osteogenesis Imperfecta: The Quest for Improving the Quality of Life

Osteogenesis imperfecta is a rare genetic disorder characterized by bone fragility, due to alterations in the type I collagen molecule. It is a very heterogeneous disease, both genetically and phenotypically, with a high variability of clinical phenotypes, ranging from mild to severe forms, the most extreme cases being perinatal lethal. There is no curative treatment for OI, and so great efforts are being made in order to develop effective therapies. In these attempts, the in vivo preclinical studies are of paramount importance; therefore, serious analysis is required to choose the right murine OI model able to emulate as closely as possible the disease of the target OI population. In this review, we summarize the features of OI murine models that have been used for preclinical studies until today, together with recently developed new murine models. The bone parameters that are usually evaluated in order to determine the relevance of new developing therapies are exposed, and finally, current and innovative therapeutic strategies attempts considered in murine OI models, along with their mechanism of action, are reviewed. This review aims to summarize the in vivo studies developed in murine models available in the field of OI to date, in order to help the scientific community choose the most accurate OI murine model when developing new therapeutic strategies capable of improving the quality of life.

Osteogenesis Imperfecta: Multidisciplinary and Goal-Centered Care

We describe a case of osteogenesis imperfecta (OI) in a late preterm female of 35-week gestation. The mother did have a history of substance abuse, poor prenatal care, and hypertension. On the day of delivery, an ultrasound revealed skeletal dysplasia and breech with nonreassuring fetal tracing, leading to an emergency cesarean. The clinical exam was concerning for OI, and postnatal care was focused on optimizing respiratory status and minimizing pain and discomfort during routine care. Genetics, endocrine, orthopaedics, and palliative care were all involved to diagnose and educate the family. Support and education were needed for bedside staff to minimize angst at performing routine care, given the high risk of fractures. While initially stable on minimal oxygen, once the diagnosis of type III OI was made, a progressively deforming condition with respiratory status decompensation, the family wished to minimize suffering, limited aggressive medical care, and focused on comfort. The infant eventually died from respiratory failure in the neonatal intensive care unit. We present this case to demonstrate the need for an interdisciplinary team approach to support both family and staff in cases of OI.

Osteogenesis Imperfecta: Multidisciplinary and Goal-Centered Care

We describe a case of osteogenesis imperfecta (OI) in a late preterm female of 35-week gestation. The mother did have a history of substance abuse, poor prenatal care, and hypertension. On the day of delivery, an ultrasound revealed skeletal dysplasia and breech with nonreassuring fetal tracing, leading to an emergency cesarean. The clinical exam was concerning for OI, and postnatal care was focused on optimizing respiratory status and minimizing pain and discomfort during routine care. Genetics, endocrine, orthopaedics, and palliative care were all involved to diagnose and educate the family. Support and education were needed for bedside staff to minimize angst at performing routine care, given the high risk of fractures. While initially stable on minimal oxygen, once the diagnosis of type III OI was made, a progressively deforming condition with respiratory status decompensation, the family wished to minimize suffering, limited aggressive medical care, and focused on comfort. The infant eventually died from respiratory failure in the neonatal intensive care unit. We present this case to demonstrate the need for an interdisciplinary team approach to support both family and staff in cases of OI.

Comparable Effects of Strontium Ranelate and Alendronate Treatment on Fracture Reduction in a Mouse Model of Osteogenesis Imperfecta

Alendronate (Aln) has been the first-line drug for osteogenesis imperfecta (OI), while the comparable efficacy of Aln and strontium ranelate (SrR) remains unclear. This study is aimed at comparing the effects of SrR and Aln treatment in a mouse model of OI. Three-week-old oim/oim and wt/wt female mice were treated with SrR (1800 mg/kg/day), Aln (0.21 mg/kg/week), or vehicle (Veh) for 11 weeks. After the treatment, the average number of fractures sustained per mouse was significantly reduced in both SrR- and Aln-treated oim/oim mice. The effect was comparable between these two agents. Both SrR and Aln significantly increased trabecular bone mineral density, bone histomorphometric parameters (bone volume, trabecular number, and cortical thickness and area), and biomechanical parameters (maximum load and stiffness) as compared with the Veh group. Both treatments reduced bone resorption parameters, with Aln demonstrating a stronger inhibitory effect than SrR. In contrast to its inhibitory effect on bone resorption, SrR maintained bone formation. Aln, however, also suppressed bone formation coupled with an inhibitory effect on bone resorption. The results of this study indicate that SrR has comparable effects with Aln on reducing fractures and improving bone mass and strength. In clinical practice, SrR may be considered an option for patients with OI when other medications are not suitable or have evident contraindications.

Sclerostin-Antibody Treatment Decreases Fracture Rates in Axial Skeleton and Improves the Skeletal Phenotype in Growing oim/oim Mice

In osteogenesis imperfecta (OI), vertebrae brittleness causes thorax deformations and leads to cardiopulmonary failure. As sclerostin-neutralizing antibodies increase bone mass and strength in animal models of osteoporosis, their administration in two murine models of severe OI enhanced the strength of vertebrae in growing female Crtap^-/- mice but not in growing male Col1a1^Jrt/+ mice. However, these two studies ignored the impact of antibodies on spine growth, fracture rates, and compressive mechanical properties. Here, we conducted a randomized controlled trial in oim/oim mice, an established model of human severe OI type III due to a mutation in Col1a2. Five-week-old female WT and oim/oim mice received either PBS or sclerostin antibody (Scl-Ab) for 9 weeks. Analyses included radiography, histomorphometry, pQCT, microcomputed tomography, and biomechanical testing. Though it did not modify vertebral axial growth, Scl-Ab treatment markedly reduced the fracture prevalence in the pelvis and caudal vertebrae, enhanced osteoblast activity (L4), increased cervico-sacral spine BMD, and improved the lumbosacral spine bone cross-sectional area. Scl-Ab did not impact vertebral height and body size but enhanced the cortical thickness and trabecular bone volume significantly in the two Scl-Ab groups. At lumbar vertebrae and tibial metaphysis, the absolute increase in cortical and trabecular bone mass was higher in Scl-Ab WT than in Scl-Ab oim/oim. The effects on trabecular bone mass were mainly due to changes in trabecular number at vertebrae and in trabecular thickness at metaphyses. Additionally, Scl-Ab did not restore a standard trabecular network, but improved bone compressive ultimate load with more robust effects at vertebrae than at metaphysis. Overall, Scl-Ab treatment may be beneficial for reducing vertebral fractures and spine deformities in patients with severe OI.

Biomechanical and Bone Material Properties of Schnurri-3 Null Mice

Schnurri‐3 (Shn3) is an essential regulator of postnatal skeletal remodeling. Shn3‐deficient mice (Shn3–/–) have high bone mass; however, their bone mechanical and material properties have not been investigated to date. We performed three‐point bending of femora, compression tests of L3 vertebrae. We also measured intrinsic material properties, including bone mineralization density distribution (BMDD) and osteocyte lacunae section (OLS) characteristics by quantitative backscatter electron imaging, as well as collagen cross‐linking by Fourier transform infrared microspectroscopy of femora from Shn3–/– and WT mice at different ages (6 weeks, 4 months, and 18 months). Moreover, computer modeling was performed for the interpretation of the BMDD outcomes. Femora and L3 vertebrae from Shn3–/– aged 6 weeks revealed increased ultimate force (2.2‐ and 3.2‐fold, p < .01, respectively). Mineralized bone volume at the distal femoral metaphysis was about twofold (at 6 weeks) to eightfold (at 4 and 18 months of age) in Shn3–/– (p < .001). Compared with WT, the average degree of trabecular bone mineralization was similar at 6 weeks, but increased at 4 and 18 months of age (+12.6% and +7.7%, p < .01, respectively) in Shn3–/–. The analysis of OLS characteristics revealed a higher OLS area for Shn3–/– versus WT at all ages (+16%, +23%, +21%, respectively, p < .01). The collagen cross‐link ratio was similar between groups. We conclude that femora and vertebrae from Shn3–/– had higher ultimate force in mechanical testing. Computer modeling demonstrated that in cases of highly increased bone volume, the average degree of bone matrix mineralization can be higher than in WT bone, which was actually measured in the older Shn3–/– groups. The area of 2D osteocyte lacunae sections was also increased in Shn3‐deficiency, which could only partly be explained by larger remnant areas of primary cortical bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Clinical pathologies of bone fracture modelled in zebrafish

Reduced bone quality or mineral density predict susceptibility to fracture and also attenuate subsequent repair. Bone regrowth is also compromised by bacterial infection, which exacerbates fracture site inflammation. Because of the cellular complexity of fracture repair, as well as genetic and environmental influences, there is a need for models that permit visualisation of the fracture repair process under clinically relevant conditions. To characterise the process of fracture repair in zebrafish, we employed a crush fracture of fin rays, coupled with histological and transgenic labelling of cellular responses; the results demonstrate a strong similarity to the phased response in humans. We applied our analysis to a zebrafish model of osteogenesis imperfecta (OI), which shows reduced bone quality, spontaneous fractures and propensity for non-unions. We found deficiencies in the formation of a bone callus during fracture repair in our OI model and showed that clinically employed antiresorptive bisphosphonates can reduce spontaneous fractures in OI fish and also measurably reduce fracture callus remodelling in wild-type fish. The csf1ra mutant, which has reduced osteoclast numbers, also showed reduced callus remodelling. Exposure to excessive bisphosphonate, however, disrupted callus repair. Intriguingly, neutrophils initially colonised the fracture site, but were later completely excluded. However, when fractures were infected with Staphylococcus aureus, neutrophils were retained and compromised repair. This work elevates the zebrafish bone fracture model and indicates its utility in assessing conditions of relevance to an orthopaedic setting with medium throughput.

This article has an associated First Person interview with the first author of the paper.

Summary: The effect of osteogenesis imperfecta, bisphosphonate treatment and bacterial infection on phases of bone fracture repair are determined using a zebrafish fracture model.

Sclerostin antibody reduces long bone fractures in the oim/oim model of osteogenesis imperfecta

Osteogenesis imperfecta type III (OI) is a serious genetic condition with poor bone quality and a high fracture rate in children. In a previous study, it was shown that a monoclonal antibody neutralizing sclerostin (Scl-Ab) increases strength and vertebral bone mass while reducing the number of axial fractures in oim/oim, a mouse model of OI type III. Here, we analyze the impact of Scl-Ab on long bones in OI mice. After 9 weeks of treatment, Scl-Ab significantly reduced long bone fractures (3.6 ± 0.3 versus 2.1 ± 0.8 per mouse, p < 0.001). In addition, the cortical thickness of the tibial midshaft was increased (+42%, p < 0.001), as well as BMD (+28%, p < 0.001), ultimate load (+86%, p < 0.05), plastic energy (+184%; p < 0.05) and stiffness (+172%; p < 0.01) in OI Scl-Ab mice compared to OI vehicle controls. Similar effects of Scl-Ab were observed in Wild type (Wt) mice. The plastic energy, which reflects the fragility of the tissue, was lower in the OI than in the Wt and significantly improved with the Scl-Ab treatment. At the tissue level by nanoindentation, Scl-Ab slightly increased the elastic modulus in bones of both OI and Wt, while moderately increasing tissue hardness (+13% compared to the vehicle; p < 0.05) in Wt bones, but not in OI bones. Although it did not change the properties of the OI bone matrix material, Scl-Ab reduced the fracture rate of the long bones by improving its bone mass, density, geometry, and biomechanical strength. These results suggest that Scl-Ab can reduce long-bone fractures in patients with OI.

Current concepts in osteogenesis imperfecta: bone structure, biomechanics and medical management

The majority of patients with osteogenesis imperfecta (OI) have mutations in the COL1A1 or COL1A2 gene, which has consequences for the composition of the bone matrix and bone architecture. The mutations result in overmodified collagen molecules, thinner collagen fibres and hypermineralization of bone tissue at a bone matrix level. Trabecular bone in OI is characterized by a lower trabecular number and connectivity as well as a lower trabecular thickness and volumetric bone mass. Cortical bone shows a decreased cortical thickness with less mechanical anisotropy and an increased pore percentage as a result of increased osteocyte lacunae and vascular porosity. Most OI patients have mutations at different locations in the COL1 gene. Disease severity in OI is probably partly determined by the nature of the primary collagen defect and its location with respect to the C-terminus of the collagen protein. The overall bone biomechanics result in a relatively weak and brittle structure. Since this is a result of all of the above-mentioned factors as well as their interactions, there is considerable variation between patients, and accurate prediction on bone strength in the individual patient with OI is difficult. Current treatment of OI focuses on adequate vitamin-D levels and interventions in the bone turnover cycle with bisphosphonates. Bisphosphonates increase bone mineral density, but the evidence on improvement of clinical status remains limited. Effects of newer drugs such as antibodies against RANKL and sclerostin are currently under investigation. This paper was written under the guidance of the Study Group Genetics and Metabolic Diseases of the European Paediatric Orthopaedic Society.

An update on the role of RANKL-RANK/osteoprotegerin and WNT-ß-catenin signaling pathways in pediatric diseases

BACKGROUND

Bone remodeling is a lifelong process due to the balanced activity of osteoclasts (OCs), the bone-reabsorbing cells, and osteoblasts (OBs), and the bone-forming cells. This equilibrium is regulated by numerous cytokines, but it has been largely demonstrated that the RANK/RANKL/osteoprotegerin and Wnt/β-catenin pathways play a key role in the control of osteoclastogenesis and osteoblastogenesis, respectively. The pro-osteoblastogenic activity of the Wnt/β-catenin can be inhibited by sclerostin and Dickkopf-1 (DKK-1). RANKL, sclerostin and DKKs-1 are often up-regulated in bone diseases, and they are the target of new monoclonal antibodies.

DATA SOURCES

The authors performed a systematic literature search in PubMed and EMBASE to June 2018, reviewed and selected articles, based on pre-determined selection criteria.

RESULTS

We re-evaluated the role of RANKL, osteoprotegerin, sclerostin and DKK-1 in altered bone remodeling associated with some inherited and acquired pediatric diseases, such as type 1 diabetes mellitus (T1DM), alkaptonuria (AKU), hemophilia A, osteogenesis imperfecta (OI), 21-hydroxylase deficiency (21OH-D) and Prader-Willi syndrome (PWS). To do so, we considered recent clinical studies done on pediatric patients in which the roles of RANKL-RANK/osteoprotegerin and WNT-ß-catenin signaling pathways have been investigated, and for which innovative therapies for the treatment of osteopenia/osteoporosis are being developed.

CONCLUSIONS

The case studies taken into account for this review demonstrated that quite frequently both bone reabsorbing and bone deposition are impaired in pediatric diseases. Furthermore, for some of them, bone damage began in childhood but only manifested with age. The use of denosumab could represent a valid alternative therapeutic approach to improve bone health in children, although further studies need to be carried out.

Low Dose of Bisphosphonate Enhances Sclerostin Antibody-Induced Trabecular Bone Mass Gains in Brtl/+ Osteogenesis Imperfecta Mouse Model

Osteogenesis imperfecta (OI) is a genetic disorder characterized by altered bone quality and imbalanced bone remodeling, leading to skeletal fractures that are most prominent during childhood. Treatments for OI have focused on restoring pediatric bone density and architecture to recover functional strength and consequently reduce fragility. Though antiresorptive agents like bisphosphonates (BPs) are currently the most common intervention for the treatment of OI, a number of studies have shown efficacy of sclerostin antibody (SclAb) in inducing gains in bone mass and reducing fragility in OI mouse models. In this study, the effects of the concurrent use of BP and SclAb were evaluated during bone growth in a mouse harboring an OI-causing Gly→Cys mutation on col1a1. A single dose of antiresorptive BP facilitated the anabolic action of SclAb by increasing availability of surfaces for new bone formation via retention of primary trabeculae that would otherwise be remodeled. Chronic effects of concurrent administration of BP and SclAb revealed that accumulating cycles conferred synergistic gains in trabecular mass and vertebral stiffness, suggesting a distinct advantage of both therapies combined. Cortical gains in mass and strength occurred through SclAb alone, independent of presence of BP. In conclusion, these preclinical results support the scientific hypothesis that minimal antiresorptive treatment can amplify the effects of SclAb during early stages of skeletal growth to further improve bone structure and rigidity, a beneficial outcome for children with OI. © 2018 American Society for Bone and Mineral Research.

Bisphosphonate Withdrawal: Effects on Bone Formation and Bone Resorption in Maturing Male Mice

Bisphosphonates are being increasingly used to treat pediatric patients with skeletal disorders. However, the effects of long-term bisphosphonate therapy and cessation of therapy during growth are unclear. Thus, studies were undertaken to determine the effects of alendronate discontinuation after treatment of C57Bl/6 mice during the period of rapid skeletal growth. Compared with vehicle-treated mice, 16 weeks of alendronate treatment starting at age 18 days resulted in a 3.7-fold increase in trabecular bone in the setting of suppressed bone formation. Alendronate therapy for 8 weeks followed by 8 weeks of vehicle treatment resulted in a more pronounced increase in trabecular bone compared with mice treated with alendronate for 16 weeks (1.7-fold) and to vehicle-treated controls (6.5-fold). Mice that received alendronate for 8 weeks followed by 8 weeks of vehicle exhibited increased osteoblast surface (2.5-fold), mineralizing surface (5.7-fold), and bone formation rate (5.1-fold) compared with mice treated continuously with alendronate. However, these parameters were not restored to the levels observed in the vehicle-treated mice. Thus, partial resumption of bone formation upon cessation of bisphosphonate therapy leads to a greater increase in trabecular bone than that found when bisphosphonates are administered continuously to growing mice. These data suggest that intermittent administration of bisphosphonates may optimize their beneficial effects on the growing skeleton. © 2017 American Society for Bone and Mineral Research.

Single dose of bisphosphonate preserves gains in bone mass following cessation of sclerostin antibody in Brtl/+ osteogenesis imperfecta model

Sclerostin antibody has demonstrated a bone-forming effect in pre-clinical models of osteogenesis imperfecta, where mutations in collagen or collagen-associated proteins often result in high bone fragility in pediatric patients. Cessation studies in osteoporotic patients have demonstrated that sclerostin antibody, like intermittent PTH treatment, requires sequential anti-resorptive therapy to preserve the anabolic effects in adult populations. However, the persistence of anabolic gains from either drug has not been explored clinically in OI, or in any animal model. To determine whether cessation of sclerostin antibody therapy in a growing OI skeleton requires sequential anti-resorptive treatment to preserve anabolic gains in bone mass, we treated 3week old Brtl/+ and wild type mice for 5weeks with SclAb, and then withdrew treatment for an additional 6weeks. Trabecular bone loss was evident following cessation, but was preserved in a dose-dependent manner with single administration of pamidronate at the time of cessation. In vivo longitudinal near-infrared optical imaging of cathepsin K activation in the proximal tibia suggests an anti-resorptive effect of both SclAb and pamidronate which is reversed after three weeks of cessation. Cortical bone was considerably less susceptible to cessation effects, and showed no structural or functional deficits in the absence of pamidronate during this cessation period. In conclusion, while SclAb induces a considerable anabolic gain in the rapidly growing Brtl/+ murine model of OI, a single sequential dose of antiresorptive drug is required to maintain bone mass at trabecular sites for 6weeks following cessation.

Animal models of osteogenesis imperfecta: applications in clinical research

Osteogenesis imperfecta (OI), commonly known as brittle bone disease, is a genetic disease characterized by extreme bone fragility and consequent skeletal deformities. This connective tissue disorder is caused by mutations in the quality and quantity of the collagen that in turn affect the overall mechanical integrity of the bone, increasing its vulnerability to fracture. Animal models of the disease have played a critical role in the understanding of the pathology and causes of OI and in the investigation of a broad range of clinical therapies for the disease. Currently, at least 20 animal models have been officially recognized to represent the phenotype and biochemistry of the 17 different types of OI in humans. These include mice, dogs, and fish. Here, we describe each of the animal models and the type of OI they represent, and present their application in clinical research for treatments of OI, such as drug therapies (ie, bisphosphonates and sclerostin) and mechanical (ie, vibrational) loading. In the future, different dosages and lengths of treatment need to be further investigated on different animal models of OI using potentially promising treatments, such as cellular and chaperone therapies. A combination of therapies may also offer a viable treatment regime to improve bone quality and reduce fragility in animals before being introduced into clinical trials for OI patients.

Impaired bone remodeling in children with osteogenesis imperfecta treated and untreated with bisphosphonates: the role of DKK1, RANKL, and TNF-α

In this study, we investigated the bone cell activity in patients with osteogenesis imperfecta (OI) treated and untreated with neridronate. We demonstrated the key role of Dickkopf-1 (DKK1), receptor activator of nuclear factor-κB ligand (RANKL), and tumor necrosis factor alpha (TNF-α) in regulating bone cell of untreated and treated OI subjects. These cytokines could represent new pharmacological targets for OI.

INTRODUCTION

Bisphosphonates are widely used in the treatment of children with osteogenesis imperfecta (OI) with the objective of reducing the risk of fractures. Although bisphosphonates increase bone mineral density in OI subjects, the effects on fracture incidence are conflicting. The aim of this study was to investigate the mechanisms underlying bone cell activity in subjects with mild untreated forms of OI and in a group of subjects with severe OI treated with cycles of intravenous neridronate.

METHODS

Sclerostin, DKK1, TNF-α, RANKL, osteoprotegerin (OPG), and bone turnover markers were quantified in serum of 18 OI patients (12 females, mean age 8.86 ± 3.90), 8 of which were receiving cyclic intravenous neridronate, and 21 sex- and age-matched controls. The effects on osteoblastogenesis and OPG expression of media conditioned by the serum of OI patients and anti-DKK1 neutralizing antibody were evaluated. Osteoclastogenesis was assessed in cultures from patients and controls.

RESULTS

DKK1 and RANKL levels were significantly increased both in untreated and in treated OI subjects with respect to controls. The serum from patients with high DKK1 levels inhibited both osteoblast differentiation and OPG expression in vitro. High RANKL and low OPG messenger RNA (mRNA) levels were found in lymphomonocytes from patients. High amounts of TNF-α were expressed by monocytes, and an elevated percentage of circulating CD11b-CD51/CD61+ osteoclast precursors was observed in patients.

CONCLUSIONS

Our study demonstrated the key role of DKK1, RANKL, and TNF-α in regulating bone cell activity of subjects with OI untreated and treated with bisphosphonates. These cytokines could represent new pharmacological targets for OI patients.

Strontium Ranelate Reduces the Fracture Incidence in a Growing Mouse Model of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a genetic bone dysplasia characterized by brittle bones with increased fracture risk. Although current treatment options to improve bone strength in OI focus on antiresorptive bisphosphonates, controlled clinical trials suggest they have an equivocal effect on reducing fracture risk. Strontium ranelate (SrR) is a promising therapy with a dual mode of action that is capable of simultaneously maintaining bone formation and reducing bone resorption, and may be beneficial for the treatment of OI. In this study, SrR therapy was investigated to assess its effects on fracture frequency and bone mass and strength in an animal model of OI, the oim/oim mouse. Three-week-old oim/oim and wt/wt mice were treated with either SrR or vehicle (Veh) for 11 weeks. After treatment, the average number of fractures sustained by SrR-treated oim/oim mice was significantly reduced compared to Veh-treated oim/oim mice. Micro-computed tomographic (μCT) analyses of femurs showed that both trabecular and cortical bone mass were significantly improved with SrR treatment in both genotypes. SrR significantly inhibited bone resorption, whereas bone formation indices were maintained. Biomechanical testing revealed improved bone structural properties in both oim/oim and wild-type (wt/wt) mice under the treatment, whereas no significant effects on bone brittleness and material quality were observed. In conclusion, SrR was able to effectively reduce fractures in oim/oim mice by improving bone mass and strength and thus represents a potential therapy for the treatment of pediatric OI. © 2015 American Society for Bone and Mineral Research.

Bisphosphonates: Pharmacokinetics, bioavailability, mechanisms of action, clinical applications in children, and effects on tooth development

Bisphosphonates (BPs) avidly bind to calcium crystals and inhibit osteoclastic bone resorption, making them useful for treatment of skeletal disorders such as osteoporosis, Paget's disease, osteogenesis imperfecta and metastatic bone diseases. BPs therapeutically act by causing toxic effects on osteoclasts or interfering with specific intracellular pathways in those cells. BPs that possess nitrogen in their composition are called nitrogen-containing BPs (NBPs) and include alendronate, pamidronate, risedronate, ibandronate, and zoledronate. Simple BPs or non-NBPs do not have nitrogen in their composition, include etiodronate and clodronate, and were the first to be tested in animals and clinically used. Because BPs may be administered to pregnant women or children during deciduous and permanent teeth development, it is expected that they might disturb tooth eruption and development. A review of current literature on pharmacokinetics, bioavailability, mechanisms of action, and clinical applications of BPs in children, and their effects on tooth eruption and development is presented.

Recent developments in osteogenesis imperfecta

Osteogenesis imperfecta (OI) is an uncommon genetic bone disease associated with brittle bones and fractures in children and adults. Although OI is most commonly associated with mutations of the genes for type I collagen, many other genes (some associated with type I collagen processing) have now been identified. The genetics of OI and advances in our understanding of the biomechanical properties of OI bone are reviewed in this article. Treatment includes physiotherapy, fall prevention, and sometimes orthopedic procedures. In this brief review, we will also discuss current understanding of pharmacologic therapies for treatment of OI.

Are Changes in Composition in Response to Treatment of a Mouse Model of Osteogenesis Imperfecta Sex-dependent?

BACKGROUND

Osteogenesis imperfecta (OI) is a genetic disease characterized by skeletal fragility and deformity. There is extensive debate regarding treatment options in adults with OI. Antiresorptive treatment reduces the number of fractures in growing oim/oim mice, an animal model that reproducibly mimics the moderate-to-severe form of OI in humans. Effects of long-term treatments with antiresorptive agents, considered for treatment of older patients with OI with similar presentation (moderate-to-severe OI) are, to date, unknown.

QUESTIONS/PURPOSES

Fourier transform infrared (FTIR) imaging, which produces a map of the spatial variation in chemical composition in thin sections of bone, was used to address the following questions: (1) do oim/oim mice show a sex dependence in compositional properties at 6.5 months of age; (2) is there a sex-dependent response to treatment with antiresorptive agents used in the treatment of OI in humans; and (3) are any compositional parameters in oim/oim mice corrected to wild-type (WT) values after treatment?

METHODS

FTIR imaging data were collected from femurs from four to five mice per sex per genotype per treatment. Treatments were 24 weeks of saline, alendronate, or RANK-Fc; and 12 weeks of saline+12 weeks RANK-Fc and 12 weeks of alendronate+RANK-Fc. FTIR imaging compositional parameters measured in cortical and cancellous bones were mineral-to-matrix ratio, carbonate-to-mineral ratio, crystal size/perfection, acid phosphate substitution, collagen maturity, and their respective distributions (heterogeneities). Because of the small sample size, nonparametric statistics (Mann-Whitney U- and Kruskal-Wallis tests with Bonferroni correction) were used to compare saline-treated male and female mice of different genotypes and treatment effects by sex and genotype, respectively. Statistical significance was defined as p<0.05.

RESULTS

At 6.5 months, saline-treated male cortical oim/oim bone had increased mineral-to-matrix ratio (p=0.016), increased acid phosphate substitution (p=0.032), and decreased carbonate-to-mineral ratio (p=0.016) relative to WT. Cancellous bone in male oim/oim also had increased mineral-to-matrix ratio (p=0.016) relative to male WT. Female oim/oim mouse bone composition for all cortical and cancellous bone parameters was comparable to WT (p>0.05). Only the female WT mice showed a response of mean compositional properties to treatment, increasing mineral-to-matrix after RANK-Fc treatment in cancellous bone (p=0.036) compared with saline-treated mice. Male oim/oim increased mineral-to-matrix cortical and cancellous bone heterogeneity in response to all long-term treatments except for saline+RANK-Fc (p<0.04); female oim/oim cortical mineral-to-matrix bone heterogeneity increased with ALN+RANK-Fc and all treatments increased cancellous female oim/oim bone acid phosphate substitution heterogeneity (p<0.04).

CONCLUSIONS

Both oim/oim and WT mice, which demonstrate sex-dependent differences in composition with saline treatment, showed few responses to long-term treatment with antiresorptive agents. Female WT mice appeared to be more responsive; male oim/oim mice showed more changes in compositional heterogeneity. Changes in bone composition caused by these agents may contribute to improved bone quality in oim/oim mice, because the treatments are known to reduce fracture incidence.

CLINICAL RELEVANCE

The optimal drug therapy for long-term treatment of patients with moderate-to-severe OI is unknown. Based on bone compositional changes in mice, antiresorptive treatments are useful for continued treatment in OI. There is a reported sexual dimorphism in fracture incidence in adults with OI, but to date, no one has reported differences in response to pharmaceutical intervention. This study suggests that such an investigation is warranted.

Effect of bisphosphonates on the rapidly growing male murine skeleton

Bisphosphonates are effective for preventing and treating skeletal disorders associated with hyperresorption. Their safety and efficacy has been studied in adults where the growth plate is fused and there is no longitudinal bone growth and little appositional growth. Although bisphosphonate use in the pediatric population was pioneered for compassionate use in the treatment of osteogenesis imperfecta, they are being increasingly used for the treatment and prevention of bone loss in children at risk of hyperresorptive bone loss. However, the effect of these agents on the growing skeleton in disorders other than osteogenesis imperfecta has not been systematically compared. Studies were, therefore, undertaken to examine the consequences of bisphosphonate administration on the growth plate and skeletal microarchitecture during a period of rapid growth. C57Bl6/J male mice were treated from 18 to 38 days of age with vehicle, alendronate, pamidronate, zoledronate, or clodronate at doses selected to replicate those used in humans. Treatment with alendronate, pamidronate, and zoledronate, but not clodronate, led to a decrease in the number of chondrocytes per column in the hypertrophic chondrocyte layer. This was not associated with altered hypertrophic chondrocyte apoptosis or vascular invasion at the growth plate. The effects of pamidronate on trabecular microarchitecture were less beneficial than those of alendronate and zoledronate. Pamidronate did not increase cortical thickness or cortical area/total area relative to control mice. These studies suggest that bisphosphonate administration does not adversely affect skeletal growth. Long-term investigations are required to determine whether the differences observed among the agents examined impact biomechanical integrity of the growing skeleton.

Gender-dependence of bone structure and properties in adult osteogenesis imperfecta murine model

Osteogenesis imperfecta (OI) is a dominant skeletal disorder characterized by bone fragility and deformities. Though the oim mouse model has been the most widely studied of the OI models, it has only recently been suggested to exhibit gender-dependent differences in bone mineralization. To characterize the impact of gender on the morphometry/ultra-structure, mechanical properties, and biochemical composition of oim bone on the congenic C57BL/J6 background, 4-month-old oim/oim, +/oim, and wild-type (wt) female and male tibiae were evaluated using micro-computed tomography, three-point bending, and Raman spectroscopy. Dramatic gender differences were evident in both cortical and trabecular bone morphological and geometric parameters. Male mice had inherently more bone and increased moment of inertia than genotype-matched female counterparts with corresponding increases in bone biomechanical strength. The primary influence of gender was structure/geometry in bone growth and mechanical properties, whereas the mineral/matrix composition and hydroxyproline content of bone were influenced primarily by the oim collagen mutation. This study provides evidence of the importance of gender in the evaluation and interpretation of potential therapeutic strategies when using mouse models of OI.

Bone properties by nanoindentation in mild and severe osteogenesis imperfecta

BACKGROUND

Osteogenesis imperfecta is a heterogeneous genetic disorder characterized by bone fragility. Previous research suggests that impaired collagen network and abnormal mineralization affect bone tissue properties, however, little data is yet available to describe bone material properties in individuals with this disorder. Bone material properties have not been characterized in individuals with the most common form of osteogenesis imperfecta, type I.

METHODS

Bone tissue elastic modulus and hardness were measured by nanoindentation in eleven osteotomy specimens that were harvested from children with osteogenesis imperfecta during routine surgeries. These properties were compared between osteogenesis imperfecta types I (mild, n=6) and III (severe, n=5), as well as between interstitial and osteonal microstructural regions using linear mixed model analysis.

FINDINGS

Disease severity type had a small but statistically significant effect on modulus (7%, P=0.02) and hardness (8%, P<0.01). Individuals with osteogenesis imperfecta type I had higher modulus and hardness than did those with type III. Overall, mean modulus and hardness values were 13% greater in interstitial lamellar bone regions than in osteonal regions (P<0.001).

INTERPRETATION

The current study presents the first dataset describing bone material properties in individuals with the most common form of osteogenesis imperfecta, i.e., type I. Results indicate that intrinsic bone tissue properties are affected by phenotype. Knowledge of the material properties of bones in osteogenesis imperfecta will contribute to the ability to develop models to assist in predicting fracture risk.

Ultra-structural defects cause low bone matrix stiffness despite high mineralization in osteogenesis imperfecta mice

Bone is a complex material with a hierarchical multi-scale organization from the molecule to the organ scale. The genetic bone disease, osteogenesis imperfecta, is primarily caused by mutations in the collagen type I genes, resulting in bone fragility. Because the basis of the disease is molecular with ramifications at the whole bone level, it provides a platform for investigating the relationship between structure, composition, and mechanics throughout the hierarchy. Prior studies have individually shown that OI leads to: 1. increased bone mineralization, 2. decreased elastic modulus, and 3. smaller apatite crystal size. However, these have not been studied together and the mechanism for how mineral structure influences tissue mechanics has not been identified. This lack of understanding inhibits the development of more accurate models and therapies. To address this research gap, we used a mouse model of the disease (oim) to measure these outcomes together in order to propose an underlying mechanism for the changes in properties. Our main finding was that despite increased mineralization, oim bones have lower stiffness that may result from the poorly organized mineral matrix with significantly smaller, highly packed and disoriented apatite crystals. Using a composite framework, we interpret the lower oim bone matrix elasticity observed as the result of a change in the aspect ratio of apatite crystals and a disruption of the crystal connectivity.

Comparable outcomes in fracture reduction and bone properties with RANKL inhibition and alendronate treatment in a mouse model of osteogenesis imperfecta

We report a direct comparison of receptor activator of nuclear factor kappa B ligand (RANKL) inhibition (RANK-Fc) with bisphosphonate treatment (alendronate, ALN) from infancy through early adulthood in a mouse model of osteogenesis imperfecta. Both ALN and RANK-Fc decreased fracture incidence to the same degree with increases in metaphyseal bone volume via increased number of thinner trabeculae.

INTRODUCTION

The potential therapeutic benefit of RANKL inhibitors in osteogenesis imperfecta (OI) is under investigation. We report a direct comparison of RANKL inhibition (RANK-Fc) with bisphosphonate treatment (ALN) from infancy through early adulthood in a model of OI, the oim/oim mouse.

METHODS

Two-week-old oim/oim, oim/+, and wildtype (+/+) mice were treated with RANK-Fc 1.5 mg/kg twice per week, ALN 0.21 mg/kg/week or saline (n = 12-20 per group) for 12 weeks.

RESULTS

ALN and RANK-Fc both decreased fracture incidence (9.0 ± 3.0 saline 4.4 ± 2.7 ALN, 4.3 ± 3.0 RANK-Fc fractures per mouse). Serum TRACP-5b activity decreased to 65% after 1 month in all treated mice, but increased sacrifice with RANK-Fc to 130-200% at sacrifice. Metaphyseal density was significantly increased with ALN in +/+ and oim/oim mice (p < 0.05) and tended to increase with RANK-Fc in +/+ mice. No changes in oim/oim femur biomechanical parameters occurred with treatment. Both ALN and RANK-Fc significantly increased trabecular number (3.73 ± 0.77 1/mm for oim/oim saline vs 7.93 ± 0.67 ALN and 7.34 ± 1.38 RANK-Fc) and decreased trabecular thickness (0.045 mm ± 0.003 for oim/oim saline vs 0.034 ± 0.003 ALN and 0.032 ± 0.002 RANK-Fc) and separation in all genotypes (0.28 ± 0.08 mm for oim/oim saline vs 0.12 ± 0.010 ALN and 13 ± 0.03 RANK-Fc)., with significant increase in bone volume fraction (BVF) with ALN, and a trend towards increased BVF in RANK-Fc.

CONCLUSION

Treatment of oim/oim mice with either a bisphosphonate or a RANK-Fc causes similar decreases in fracture incidence with increases in metaphyseal bone volume via increased number of thinner trabeculae.

Disruption of bone development and homeostasis by trisomy in Ts65Dn Down syndrome mice

Down syndrome (DS) is a genetic disorder resulting from trisomy 21 that causes cognitive impairment, low muscle tone and craniofacial alterations. Morphometric studies of the craniofacial and appendicular skeleton in individuals with DS suggest that bone development and homeostasis are affected by trisomy. The Ts65Dn mouse model has three copies of approximately half the genes found on human chromosome 21 and exhibits craniofacial skeletal and size differences similar to those observed in humans with DS. We hypothesized that Ts65Dn and euploid mice have distinct differences in bone development and homeostasis influencing both the craniofacial and appendicular skeletal phenotypes. Quantitative assessment of structural and mechanical properties of the femur in Ts65Dn and control mice at 6 and 16 weeks of age revealed significant deficiencies in trabecular and cortical bone architecture, bone mineral density, bone formation, and bone strength in trisomic bone. Furthermore, bone mineral density and dynamic dentin formation rate of the skull and incisor, respectively, were also reduced in Ts65Dn mice, demonstrating that trisomy significantly affects both the craniofacial and appendicular skeleton.

Transplantation of human fetal blood stem cells in the osteogenesis imperfecta mouse leads to improvement in multiscale tissue properties

Osteogenesis imperfecta (OI or brittle bone disease) is a disorder of connective tissues caused by mutations in the collagen genes. We previously showed that intrauterine transplantation of human blood fetal stem/stromal cells in OI mice (oim) resulted in a significant reduction of bone fracture. This work examines the cellular mechanisms and mechanical bone modifications underlying these therapeutic effects, particularly examining the direct effects of donor collagen expression on bone material properties. In this study, we found an 84% reduction in femoral fractures in transplanted oim mice. Fetal blood stem/stromal cells engrafted in bones, differentiated into mature osteoblasts, expressed osteocalcin, and produced COL1a2 protein, which is absent in oim mice. The presence of normal collagen decreased hydroxyproline content in bones, altered the apatite crystal structure, increased the bone matrix stiffness, and reduced bone brittleness. In conclusion, expression of normal collagen from mature osteoblast of donor origin significantly decreased bone brittleness by improving the mechanical integrity of the bone at the molecular, tissue, and whole bone levels.

Birefringence of the secretory-stage enamel organic extracellular matrix from rats submitted to successive injections of bisphosphonates

The aim of the present study was to assess birefringence of the secretory-stage enamel organic extracellular matrix (ECM) and mechanical properties of mature enamel from rats treated with bisphosphonates. Longitudinal sections were obtained from upper incisors of rats that had been submitted to injections of bisodic etidronate (8 mg/Kg/day), sodium alendronate (30 microg/Kg/day), or sodium chloride as control (8 mg/Kg/day) for 42 days. Sections were immersed in 80% glycerin for 30 min and optical retardation of birefringence brightness in the secretory-stage enamel organic ECM was determined in nanometers. Etidronate-treated rats exhibited extensive morphological changes in the secretory-stage enamel organic ECM inclusive nonbirefringent conspicuous incremental lines, but presented optical retardation values similar to those showed by control rats (p > 0.05). Birefringence of secretory enamel organic ECM from etidronate rats presented an irregular aspect. Alendronate-treated rats did not show morphological alterations in the secretory-stage enamel organic ECM, however, they presented significant reduction in optical retardation of birefringence brightness when compared with control and etidronate rats (p < 0.01). Alendronate and etidronate groups exhibited reductions of approximately 6-10% in mature enamel cross-sectional microhardness when compared with control group (p < 0.01). Scanning electron microscopy analysis showed extensive alterations in mature enamel only from etidronate group with absence of enamel rods. The present work shows that bisphosphonates can affect the birefringence of the secretory-stage enamel organic ECM. The results presented here suggest that alterations in the supramolecular organization of the secretory-stage enamel organic ECM are a plausible mechanism by which environmental factors may cause enamel defects.

RANKL inhibition improves bone properties in a mouse model of osteogenesis imperfecta

Recently, a new class of agents targeting the receptor activator of nuclear factor-kappaB ligand (RANKL) pathway has been developed for the treatment of osteoporosis and other bone diseases. In the current study, inhibition of the RANKL pathway was evaluated to assess effects on "bone quality" and fracture incidence in an animal model of osteogenesis imperfect (OI), the oim/oim mouse. Juvenile oim/oim ( approximately 6 weeks old) and wildtype (+/+) mice were treated with either a RANKL inhibitor (RANK-Fc) or saline. After treatment, bone density increased significantly in the femurs of both genotypes. Femoral length decreased with RANK-Fc in +/+ mice. Geometric measurements at mid-diaphysis in the oim/oim groups showed increases in the ML periosteal and endosteal diameters and AP cortical thickness in the treated groups. Within +/+ groups, ML cortical thickness and ML femoral periosteal diameter were significantly increased with RANK-Fc. Biomechanical testing revealed increased stiffness in oim/oim and +/+ mice. Total strain was increased with treatment in the +/+ mice. Histologically, RANKL inhibition resulted in retained growth plate cartilage in both genotypes. The average number of fractures sustained by RANK-Fc-treated oim/oim mice was not significantly decreased compared to saline treated oim/oim mice. This preclinical study demonstrated that RANKL inhibition at the current dose improved density and some geometric and biomechanical properties of oim/oim bone, but it did not decrease fracture incidence. Further studies that address commencement of therapy at earlier time points are needed to determine whether this mode of therapy will be clinically useful in OI.

Alternative indications for bisphosphonate therapy

Bisphosphonates are currently used in the treatment of osteoporosis (postmenopausal and steroid-induced), hypercalcemia of malignancy, Paget's disease of bone, multiple myeloma, and skeletally related events associated with metastatic bone disease in breast, prostate, lung, and other cancers. There are, however, numerous other conditions where a decrease in bone remodeling by bisphosphonates might aid in disease management. The focus of this review will be to discuss a select group of conditions for which bisphosphonate therapy may be efficacious. In this review we present several cases where bisphosphonates have been used as a primary or adjunctive treatment for giant cell lesions of the jaws. Use of bisphosphonate therapy for giant cell tumors of the appendicular skeleton, pediatric osteogenesis imperfecta, fibrous dysplasia, Gaucher's disease, and osteomyelitis will be discussed. Finally, we will review previous in vivo studies on the use of bisphosphonates to augment integration and to treat osteolysis surrounding failing orthopedic implants.

Alendronate treatment of the brtl osteogenesis imperfecta mouse improves femoral geometry and load response before fracture but decreases predicted material properties and has detrimental effects on osteoblasts and bone formation

Long courses of bisphosphonates are widely administered to children with osteogenesis imperfecta (OI), although bisphosphonates do not block mutant collagen secretion and may affect bone matrix composition or structure. The Brtl mouse has a glycine substitution in col1a1 and is ideal for modeling the effects of bisphosphonate in classical OI. We treated Brtl and wildtype mice with alendronate (Aln; 0.219 mg/kg/wk, SC) for 6 or 12 wk and compared treated and untreated femora of both genotypes. Mutant and wildtype bone had similar responses to Aln treatment. Femoral areal BMD and cortical volumetric BMD increased significantly after 12 wk, but femoral length and growth curves were unaltered. Aln improved Brtl diaphyseal cortical thickness and trabecular number after 6 wk and cross-sectional shape after 12 wk. Mechanically, Aln significantly increased stiffness in wildtype femora and load to fracture in both genotypes after 12 wk. However, predicted material strength and elastic modulus were negatively impacted by 12 wk of Aln in both genotypes, and metaphyseal remnants of mineralized cartilage also increased. Brtl femoral brittleness was unimproved. Brtl osteoclast and osteoblast surface were unchanged by treatment. However, decreased mineral apposition rate and bone formation rate/bone surface and the flattened morphology of Brtl osteoblasts suggested that Aln impaired osteoblast function and matrix synthesis. We conclude that Aln treatment improves Brtl femoral geometry and load to fracture but decreases bone matrix synthesis and predicted material modulus and strength, with striking retention of mineralized cartilage. Beneficial and detrimental changes appear concomitantly. Limiting cumulative bisphosphonate exposure of OI bone will minimize detrimental effects.

Type I osteogenesis imperfecta and multiple osteochondromas in the same child

A male infant showed a humeral diaphysis fracture at 5 months of age and a distal tibial physis fracture at 2 years of age. A specialized consultant ruled out child abuse. This child had the characteristic features of type I osteogenesis imperfecta: blue sclerae, osseous fragility, and presumably autosomal dominant inheritance, as his father suffered from similar disorders. Later on, multiple painful osteochondromas were also found and some of these were surgically treated. The child's mother showed several peripheral osteochondromas. We describe the follow-up of this patient up to the age of 18 years. To our knowledge, the fortuitous association of these two inherited conditions has not been reported in medical literature.

Bisphosphonate treatment in the oim mouse model alters bone modeling during growth

Osteogenesis imperfecta (OI) is a heritable disease, which results from an abnormal amount or structure of Type I collagen. Bisphosphonates, a class of synthetic antiresorptive drugs, used in osteoporosis management, are also used to decrease fracture incidence and improve quality of life in children with OI. In this study, we used the oim mouse to test the hypotheses that pamidronate treatment during active growth (1) produces larger, stronger, stiffer long bone diaphyses without altering bone material properties, and (2) negatively impacts longitudinal bone growth. Our results indicate that femoral cross-sectional moment of inertia in the distal metaphysis tended to increase with pamidronate treatment and that the treated bones are thicker and structurally stiffer, but shorter than their control-dose counterparts.

Effects of alendronate and pamidronate on cultured rat metatarsal bones: failure to prevent dexamethasone-induced growth retardation

Bisphosphonates are widely used anti-resorptive drugs in the adult population. In children, their use has mainly been limited to patients with osteogenesis imperfecta. However, the powerful effects of bisphosphonates on bone turnover have raised concern about their long-term effects on the growing skeleton. We aimed to study the effects of two commonly used bisphosphonates, alendronate (Aln) and pamidronate (Pam) on normal bone growth as well as their potential to prevent glucocorticoid-induced growth retardation. Effects on bone growth were studied in fetal rat metatarsal bones (day E20) that were cultured for 5-47 days and measured every 2-7 days. Cellular mechanisms were investigated in metatarsal bones and also in the human chondrocytic cell line HCS-2/8. Chondrocyte viability (WST-1), proliferation (BrdU incorporation), differentiation (collagen type X immunohistochemistry) and apoptosis (TUNEL and Cell Death ELISA) were determined. At a clinically relevant concentration of bisphosphonates (1 microM), metatarsal bone growth was stimulated by both Aln (p<0.001 for length and p<0.05 for width) and Pam (p<0.05 for both length and width) from day 19 of culture. The growth-stimulatory effect was associated with increased chondrocyte proliferation (+21% with Aln and +24% with Pam), while cell differentiation and apoptosis were not affected. Despite the finding that both Aln and Pam (1 muM) rescued HCS-2/8 cells from undergoing dexamethasone-induced apoptosis, neither of them was able to prevent dexamethasone-induced growth retardation of fetal rat metatarsal bones. Aln and Pam have the capacity to stimulate the growth of cultured fetal rat metatarsal bones; an effect associated with increased proliferation of growth plate chondrocytes. Our experimental data suggest that bisphosphonates are ineffective in preventing glucocorticoid-induced growth retardation. Nevertheless, based on our in vitro data, both Aln and Pam appear safe to use in growing children, at least with regard to their effects on linear bone growth.

Quantitative second harmonic generation imaging of the diseased state osteogenesis imperfecta: experiment and simulation

We report the integrated use of 3D second harmonic generation (SHG) imaging microscopy and Monte Carlo simulation as a combined metric to quantifiably differentiate normal and diseased tissues based on the physical properties of the respective extracellular matrix. To achieve this, we have identified a set of parameters comprised of the SHG creation attributes and the bulk optical parameters, which are used collectively via comparative analysis. Monte Carlo simulations of the SHG axial directional and attenuation responses allow their decomposition into the underlying factors that are not readily obtainable through experimental techniques. Specifically, this approach allows for estimation of the SHG creation attributes (directionality and relative conversion efficiency) and separation of primary and secondary filter effects, collectively that form the observed SHG contrast. The quantitative metric is shown for the connective tissue disorder Osteogenesis Imperfecta (characterized by abnormal assembly of type I collagen) using a murine model that expresses the disease in the dermis layer of skin. Structural dissimilarities between the osteogenesis imperfecta mouse and wild-type tissues lead to significant differences in the SHG depth-dependent directionality and signal attenuation. The Monte Carlo simulations of these responses using measured bulk optical parameters reproduce the experimental data trends, and the extracted emission directionality and conversion efficiencies are consistent with independent determinations. The simulations also illustrate the dominance of primary filter affects on overall SHG generation and attenuation. Thus, the combined method of 3D SHG imaging and modeling forms an essential foundation for parametric description of the matrix properties that are not distinguishable by sole consideration of either bulk optical parameters or SHG alone. Moreover, due to the quasi-coherence of the SHG process in tissues, we submit that this approach contains unique information not possible by purely scattering based methods and that these methods will be applicable in the general case where the complex fibrillar structure is difficult to fully quantify via morphological analysis.

The effects of RANKL inhibition on fracture healing and bone strength in a mouse model of osteogenesis imperfecta

Currently, the standard treatment for osteogenesis imperfecta (OI) is bisphosphonate therapy. Recent studies, however, have shown delayed healing of osteotomies in a subset of OI patients treated with such agents. The current study sought to determine the effects of another therapy, RANKL inhibition, on bone healing and bone strength in the growing oim/oim mouse, a model of moderate to severe OI. Mice [73 oim/oim and 69 wild-type (WT)] were injected twice weekly with either soluble murine RANK (RANK-Fc) (1.5 mg/kg) or saline beginning at 6 weeks of age. At 8 weeks of age, the animals underwent transverse mid-diaphyseal osteotomies of the right femur. Therapy was continued until sacrifice at 2, 3, 4, or 6 weeks postfracture. At 6 weeks post-fracture, greater callus area (6.59 +/- 3.78 mm(2) vs. 2.67 +/- 2.05 mm(2), p = 0.003) and increased radiographic intensity (mineral density) (0.48 +/- 0.14 vs. 0.30 +/- 0.80, p = 0.005) were found in the RANK-Fc versus saline oim/oim group, indicating a delay in callus remodeling. Despite this delay, mechanical tests at 6 weeks postfracture revealed no significant differences in whole bone properties of stiffness and failure moment. Further, RANKL inhibition resulted in a greater failure moment and greater work to failure for the nonfractured contralateral WT bones compared to the nonfractured saline WT bones. Together, these results demonstrate that RANKL inhibition does not adversely affect the mechanical properties of healing bone in the oim/oim mice, and is associated with increased strength in intact bone in the WT mice.

Intrauterine transplantation of human fetal mesenchymal stem cells from first-trimester blood repairs bone and reduces fractures in osteogenesis imperfecta mice

The inherited skeletal dysplasia osteogenesis imperfecta (OI) results in multiple fractures and is currently treated empirically. We transplanted human first-trimester fetal blood mesenchymal stem cells (MSCs) into homozygous oim mice in utero. This resulted in a two-thirds reduction in long bone fractures (P < .01), with fewer fractures per mouse (median 1, range 0-2 in mice that received transplants vs median 3, range 1-5 in mice that did not receive transplants by 12 weeks, P < .01). Nearly all mice that did not receive transplants had fractures (47 [97.9%] of 48), in contrast to 17 (58.6%) of 29 4- to 12-week-old mice that received transplants (P < .01). Transplantation was associated with increased bone strength (P < .01), thickness (P < .01), and length (P < .01), and normalization/reduction of growth plate height in 4- to 12-week-old oim was reduced in mice that underwent transplantion (P < .001). More donor cells were found in bone tissues compared with other organs (P < .001), with cells clustered in areas of active bone formation and remodeling, and at sites of fracture healing. Donor cells found in the bone expressed osteoblast lineage genes, and produced the extracellular bone structural protein osteopontin. Finally, MSC transplantation decreased bone hydroxyproline content. In conclusion, intrauterine transplantation of fetal MSCs markedly reduced fracture rates and skeletal abnormalities in a mouse model of the intermediate severity type III OI, suggesting a scientific basis for MSC treatment of affected human fetuses.

Alendronate treatment promotes bone formation with a less anisotropic microstructure during intramembranous ossification in rats

There are safety concerns regarding administration of bisphosphonates to children. Little is known about the effects of bisphosphonates on bone matrix organization during bone modeling. The present study examined the effects of alendronate (ALN) on bone matrices formed by intramembranous ossification in the appendicular growing skeleton. ALN was administered to 1-week-old Sprague-Dawley rats at a dose of 0, 35, or 350 microg/kg/week for 4 or 8 weeks. The position of femoral diaphysis formed exclusively by intramembranous ossification was identified, and cross sections of cortical bone at this position were analyzed. Bone mineral density (BMD) and geometric parameters were evaluated using peripheral quantitative computed tomography. The preferential orientation degree of biological apatite (BAp) crystals in the bone longitudinal direction, which shows the degree of bone matrix anisotropy, was evaluated using microbeam X-ray diffraction analysis. We analyzed bone histomorphometrical parameters and performed bone nanomechanical tests to examine the material properties of newly developing cortical bone. The preferential orientation degree of BAp crystals significantly decreased in 35 microg/kg/week ALN-treated groups compared with vehicle-treated groups, although there were no significant differences in BMD between the two groups. The periosteal mineral apposition rate significantly increased in the 35 microg/kg/week ALN-treated group. We found a high negative correlation between bone matrix anisotropy and the regional periosteal mineral apposition rate (r = -0.862, P < 0.001). Nanomechanical tests revealed that 35 microg/kg/week ALN administration caused deterioration of the material properties of the bone microstructure. These new findings suggest that alendronate affects bone matrix organization and promotes bone formation with a less anisotropic microstructure during intramembranous ossification.

Abnormal mineral-matrix interactions are a significant contributor to fragility in oim/oim bone

The presence of abnormal type I collagen underlies the tissue fragility in the heritable disease osteogenesis imperfecta (OI), though the specific mechanism remains ill-defined. The current study addressed the question of how an abnormal collagen-based matrix contributes to reduced bone strength in OI by comparing the material properties of mineralized and demineralized bone from the oim/oim mouse, a model of OI that contains homotrimeric (alpha1(3)(I)) type I collagen, with the properties of bone from wildtype (+/+) mice. Femoral three-point bend tests combined with geometric analyses were conducted on intact (mineralized) 14-week-old oim/oim and +/+ mice. To investigate the bone matrix properties, tensile tests combined with geometric analyses were conducted on demineralized femora. The majority of the properties of the mineralized oim/oim bone were inferior to those of the +/+ bone, including greater brittleness (+78.6%) and lower toughness (-69.2%). In contrast, tensile measurements on the demineralized bone revealed no significant differences between the oim/oim and +/+ bone, indicating that the matrix itself was not brittle. These results support the concept that deficient material properties of the demineralized bone matrix itself are not the principal cause of the severe fragility in this model of OI. It is likely the abnormal collagen scaffold serves as a template for abnormal mineral deposition, resulting in an incompetent mineral-matrix interaction that contributes significantly to the inferior material properties of bone in oim/oim mice.

Infantile hypophosphatasia: transplantation therapy trial using bone fragments and cultured osteoblasts

BACKGROUND

Hypophosphatasia (HPP) is a rare, heritable, metabolic bone disease due to deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase. The infantile form features severe rickets often causing death in the first year of life from respiratory complications. There is no established medical treatment. In 1997, an 8-month-old girl with worsening and life-threatening infantile HPP improved considerably after marrow cell transplantation.

OBJECTIVE

Our aim was to better understand and to advance these encouraging transplantation results.

DESIGN

In 1999, based on emerging mouse transplantation models involving implanted donor bone fragments as well as osteoblast-like cells cultured from bone, we treated a 9-month-old girl suffering a similar course of infantile HPP.

RESULTS

Four months later, radiographs demonstrated improved skeletal mineralization. Twenty months later, PCR analysis of adherent cells cultured from recipient bone suggested the presence of small amounts of paternal (donor) DNA despite the absence of hematopoietic engraftment. This patient, now 8 yr old (7 yr after transplantation), is active and growing, and has the clinical phenotype of the more mild, childhood form of HPP.

CONCLUSIONS

Cumulative experience suggests that, after immune tolerance, donor bone fragments and marrow may provide precursor cells for distribution and engraftment in the skeletal microenvironment in HPP patients to form tissue-nonspecific isoenzyme of alkaline phosphatase-replete osteoblasts that can improve mineralization.

Comparison of nanoindentation measurements between osteogenesis imperfecta Type III and Type IV and between different anatomic locations (femur/tibia versus iliac crest)

Nanoindentation was used to compare the intrinsic mechanical properties of bone tissue (iliac crest biopsy) from children with type III and type IV osteogenesis imperfecta (OI). Young's modulus and hardness values were not significantly different between the two clinical severity groups on either cortical or trabecular measurement. In comparing the ratio of modulus over hardness (E/H) between OI type III and IV. The type III bone showed a marginally significant decrease for cortical bone and significant decrease for trabecular bone, which indicated that the OI type III bone was more brittle than OI type IV bone at the tissue level. In addition, nanoindentation measurements of the bone tissue harvested at femur/tibia from the same patients were compared with the results from the iliac crest biopsy. Young's modulus and hardness values were not significantly different between the two anatomic locations in either cortical or trabecular measurements. The ratio of E/H was not significantly different between the two groups. Results indicate that intrinsic modulus, hardness, and indentation deformation pattern (E/H) of OI bone tissues are not significantly different at long bone (midshaft of femur/tibia) and iliac crest. We observed that age (1.9 to 13.2 years) did not influence OI bone tissue intrinsic mechanical properties.

Density and structural changes in the bone of growing rats after weekly alendronate administration with and without a methotrexate challenge

Alendronate (ALN) and other bisphosphonates have been used successfully in pediatric patients with osteopenia secondary to connective tissue diseases. Loss of growth in height has not been reported, but concerns remain regarding the effect of these potent antiresorptive agents when used in children and adolescents. High-dose methotrexate (MTX) and other chemotherapy drugs have been implicated in osteoporosis and a high fracture incidence in survivors of childhood cancers and are also associated with osteopenia in adult animals. The effect of high dose MTX on bone density during rapid skeletal growth, however, has not been widely studied, nor has the potentially therapeutic effect of bisphosphonates in this setting. We examined the effects of ALN and MTX administration, alone and in combination, on bone density, morphology, mechanical strength, and longitudinal growth in normal growing rats. Sprague-Dawley rats were given ALN once weekly (0.3 mg/kg) from 5 to 11 weeks of age, with and without a course of methotrexate (MTX) given daily in weeks 1 and 3 (0.75 mg/kg/day). Twenty-four animals were randomly divided into four groups: Control (vehicle), ALN alone, ALN + MTX, and MTX alone. After 6 weeks, the femora, tibiae, and lumbar spine were studied by dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, mechanical strength testing, microradiography, light microscopy, and by determination of ash weights and bone lengths. ALN treatment increased bone mineral density (BMD) by 23% to 68%. The largest increases in the femur occurred in the distal third where endochondral bone growth was greatest and included large increases in trabecular bone and total cross-sectional area. ALN + MTX produced similar effects to ALN alone. MTX only reduced BMD by 8% in the vertebrae, but not significantly at other sites. MTX also led to femoral length reductions of 2.9%. The small reductions in BMD due to MTX were overwhelmed by the increases due to ALN, whereas the length loss was unaffected. Transverse density banding corresponding to weekly ALN administrations were clearly evident radiographically throughout the growing skeleton, likely due to decreased resorption and possibly increased mineralization in the bands. ALN or ALN + MTX treatment also led to increases in mechanical strength in the femora. Although MTX administration during growth leads to some BMD reduction, ALN given with MTX eliminates this reduction and in fact bone density and strength increase above control levels.

Impact of alendronate on quality of life in children with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a debilitating clinical condition characterized by fragile bone and skeletal deformity. Over the past decade frequent reports have suggested that the cyclical administration of intravenous pamidronate has a positive impact on bone density and skeletal fractures; however, the impact of such therapy on the quality of life (QOL) has rarely been reported. Alendronate, an oral bisphosphonate, is widely used to treat osteoporosis. The purpose of this study was to evaluate the impact of daily alendronate on QOL and bone parameters in children with OI. A prospective double-blind crossover study was designed in which placebo was alternated with daily alendronate. Twenty children with types I, III, and IV OI were recruited. Seventeen patients completed the study. Markers of QOL were measured in children with type III and IV OI (n = 15) using total mobility (PEDI), self-care (WeeFIM), well-being, pain, and use of analgesic scores. After 1 year of alendronate therapy, vertebral bone mineral density (BMD) improved from a change in standard deviation score (z-score) of 0.89 +/- 0.19 to -0.12 +/- 0.14 after 1 year of placebo (P < 0.001). All QOL markers, except for mobility score, improved in response to alendronate therapy. Change in height z-score also improved in response to 1 year of alendronate therapy (0.41 +/- 0.21 vs. -0.09 +/- 0.11, P < 0.05). Alendronate therapy did not alter serum levels of calcium, osteocalcin, parathyroid hormone (PTH), 1, 5 (OH)2 vitamin D, cholesterol, or urinary hydroxyproline or any other biochemical marker evaluated. Alendronate decreased by 56% urinary cross-linked N-telopeptide of type 1 collagen divided by urinary creatinine (uNTX/uCr). Daily alendronate therapy was well tolerated. Only two patients had mild gastrointestinal discomfort, responding to minor adjustments in alendronate intake. Daily alendronate therapy is safe and effective in improving QOL in children with OI.

Immunocytochemical Study of Amelogenin Deposition during the Early Odontogenesis of Molars in Alendronate-treated Newborn Rats

Newborn rats were treated with sodium alendronate to study how enamel is formed and the effect of alendronate during early odontogenesis. Ultrastructural analysis combined with high-resolution immunocytochemistry for amelogenin was carried out. Twelve rats were subjected to daily SC injections of sodium alendronate (2.5 mg/kg/day) for 3 days on their dorsal region, whereas three rats were daily injected with saline solution as a control. Molar tooth germs from 3-day-old rats were fixed under microwave irradiation in 0.1% glutaraldehyde + 4% formaldehyde buffered at pH 7.2 with 0.1 M sodium cacodylate. The specimens were left undecalcified, postfixed with osmium tetroxide, dehydrated, and embedded in LR White resin. Ultrathin sections were incubated with a chicken anti-24-kDa rat amelogenin antibody, a secondary antibody, and finally with a protein A-gold complex. Large patches of amelogenin were present over the unmineralized mantle dentin and at early secretory ameloblasts. At more advanced stages, they were also detected at the enamel matrix, as well as in the mineralized dentin, at the periodontoblastic space of the dentinal tubules, and at the predentin. It is likely that the main effect of alendronate at early stages of odontogenesis is the increase of synthesis/secretion of amelogenin, promoting its deposition within the forming dentin and enamel.

Mechanical properties of OI type III bone tissue measured by nanoindentation

Nanoindentation was used to characterize the intrinsic mechanical properties of bone tissue from eight (8) children with type III Osteogenesis Imperfecta (OI). The bone samples were harvested from the cortex portion at the site of bowing (the mid 2/3 of the shaft of the tibia/femur). Unlike normal bone tissue, OI type III cortical bone exhibited more isotropic material properties. Young's modulus and hardness values measured in the longitudinal direction did not show significant differences from the transverse measurements. No differences were observed in modulus or hardness in an analysis of the cortical and trabecular samples. The deformation patterns of the OI type III bone during nanoindentation were found to be similar to those of normal adult bone in an analysis of the ratio of modulus to hardness. No correlation was found between nanoindentation measurement and age in an analysis of regression.

Efficacy of oral alendronate in children with osteogenesis imperfecta

The purpose of this study was to investigate the efficacy of oral alendronate for children with osteogenesis imperfecta. Nine boys and seven girls of average age 9.5 years were given oral alendronate for an average of 4 years. Fracture frequency decreased, and in more than half of the patients the ambulatory/mobility status improved. Bone mineral density improved significantly, and restoration of collapsed vertebral bodies was observed. Urinary excretion of calcium and a bone resorption marker decreased significantly. Iliac crest physis biopsy showed an expanded primary spongiosa area with numerous multinucleated cells. This study reveals that oral alendronate caused biochemical, radiologic, and histologic changes along with clinical improvement. Oral alendronate treatment, which is convenient for the school-age group, was found to be a tolerable and efficacious treatment for children with moderate or severe osteogenesis imperfecta.