Recombinant human bone morphogenetic protein 2 and 7 inhibit the degeneration of intervertebral discs by blocking the Puma-dependent apoptotic signaling

Recombinant human bone morphogenetic proteins (rhBMPs) can stimulate bone formation and growth in the treatment of spinal fusions and nonunions. However, it is still unclear whether rhBMPs function in the prevention of intervertebral disc degeneration (IDD). Here, we discovered that BMP levels were decreased in IDD patients, which impaired the BMP/Smad (Mothers against decapentaplegic homologs) signaling. Conducting a microarray assay in Smad4-knockdown cells, we found that expression of PUMA (p53-upregulated modulator of apoptosis) was significantly induced. The molecular analysis revealed that Smad4 recruited HDAC1 (histone deacetylase 1) and the phosphorylated Smad1/5/8 to dock on the promoter of PUMA to repress its expression. The impairment of BMP/Smad signaling in IDD patients caused the significant induction of Puma-dependent apoptosis and resulted in the pathogenesis of IDD. In vitro knockdown of BMP receptors (BMPR1a and BMPR2) in nucleus pulposus (NP) cells could mimic the molecular changes of BMP/Smad signaling and Puma-dependent apoptotic signaling that were observed in IDD patients. Exposing NP cells to RITA (reactivating p53 and inducing tumor apoptosis) small molecule and rhBMP2 (or rhBMP7), we observed that rhBMP2/7 could significantly decrease protein levels of Puma and its downstream proapoptotic molecules, blocking cell apoptosis. Importantly, administration of rhBMPs in aged rats could inhibit the occurrence of IDD. Our results provide a link between BMP/Smad signaling and Puma-dependent apoptotic signaling, revealing a new mechanism of how BMPs contribute to IDD pathogenesis and providing evidence that rhBMPs may decrease apoptosis and improve the outcome of IDD.     

Delivery of recombinant bone morphogenetic proteins for bone regeneration and repair. Part A: Current challenges in BMP delivery

Recombinant human bone morphogenetic proteins (rhBMPs) have been extensively investigated for developing therapeutic strategies aimed at the restoration and treatment of orthopaedic as well as craniofacial conditions. In this first part of the review, we discuss the rationale for the necessary use of carrier systems to deliver rhBMP-2 and rhBMP-7 to sites of bone tissue regeneration and repair. General requirements for growth factor delivery systems emphasizing the distinction between localized and release-controlled delivery strategies are presented highlighting the current limitations in the development of an effective rhBMP delivery system applicable in clinical bone tissue engineering.     

Oral treatment with retinoic acid decreases bone mass in rats

13-cis-retinoic acid (13-cis-RA, isotretinoin) is used to treat severe recalcitrant acne. Other retinoids have adverse effects on bone. Recent studies of human patients treated with 13-cis-RA have had varying results, perhaps because of variability among patients and the lack of control groups. The effects of retinoids have been studied in rodents, but little information is available regarding the effects of clinically relevant retinoid doses as evaluated by use of bone densitometric techniques. We treated rats for 15 or 20 wk with 13-cis-RA, all-trans-RA, or soybean oil (control) by gavage. We used dual-energy X-ray absorptiometry, histomorphometry, and histologic evaluation to evaluate effects on bone. Spontaneous long bone fractures occurred in some rats treated with 15 mg/kg all-trans-RA daily. Bone mineral density, bone mineral content, bone diameter, and cortical thickness of the femur were reduced in rats treated daily with 10 or 15 mg/kg all-trans-RA or 30 mg/kg 13-cis-RA. The lumbar spine was not affected. Although the effects of 13-cis-RA were not as dramatic as those of all-trans-RA, further study of the effects of 13-cis-RA on long bones is warranted.     

Critical ages and stages of puberty in the accumulation of spinal and femoral bone mass: the validity of bone mass measurements

In growing children, lumbar and femoral areal bone mineral density (aBMD), as measured by dual-energy X-ray absorptiometry (DXA), is influenced by skeletal growth and bone size. Correction of lumbar bone mineral density (BMD) for bone volume (volumetric BMD [vBMD]), by the use of mathematical extrapolations, reduces the confounding effect of bone size, but vBMD remains dependent on age and bone size during growth. Femoral (neck and mid-shaft) vBMD, assessed by DXA, is independent of age prior to puberty, but a slight increase occurs in late puberty and after menarche. Femoral (mid-shaft) cortical bone density and radial cortical and trabecular bone densities, assessed by quantitative computed tomography (QCT), show no peak during childhood or adolescence. Bone strength index, calculated by peripheral QCT, increases with age and correlates with handgrip strength, bone cross-sectional area and cortical area. Puberty is one of the main factors that influences lumbar bone mineral content and aBMD accumulation, but a high incidence of fractures occurs during this period of life, which may be associated with a reduced aBMD.     

Modulation of bone morphogenetic protein antagonists to stimulate clinical osteogenesis

Bone morphogenetic proteins (BMPs) are important for the development and functioning of a wide variety of tissues and organ systems. Their ability to induce bone formation has been harnessed for clinical application. Specifically, local application of BMPs into fractures and fusions has shown some efficacy in inducing bone formation. However, clinical success has not been as robust as might be expected from the results obtained using animal models. This difference may be due to a number of mechanisms regulating BMP activity in vivo. One class of major regulators is the extracellular antagonist (e.g. Noggin, Gremlin, DAN), the dysfunction of which has been shown to result in ectopic bone formation in animal models and human disease. We hypothesize that local application of BMPs at high concentrations induces increased production of BMP antagonists, thereby limiting BMP activity and clinical efficacy. Therapies blocking the function of BMP antagonists should therefore result in enhanced BMP activity and increased bone formation. Furthermore, titrated systemic regulation of BMP antagonist may potentially reverse osteoporosis. Our collective experience with the clinical use of BMP illustrates the importance of understanding mechanisms of endogenous antagonism and regulation in the exogenous application of a protein as a therapeutic.     

Biomechanical measurements on scaphoid bone screws in an experimental model

A number of screws commonly used for internal fixation in scaphoid bone fractures and nonunions are compared regarding biomechanical properties and clinical applicability. The experiments were carried out on models made of ash-wood, representing a reconstruction and fixation as is performed in a cortico-cancellous inlay bone graft for scaphoid non-union. For fixation use was made of 2.7 and 3.5 AO/ASIF cortical screws respectively, 4.0 AO/ASIF cancellous screws, Herbert screws, and a newly designed screw called the three components screw (D.K.S.). The models with implanted screws were tested for bending strength, tensile strength and torsion stability. No large differences between the various screws were found regarding the measured parameters, so that a small intra-osteal implant such as the Herbert screw and the D.K.S., which can be inserted easily and which gives a certain amount of interfragmentary compression, will be sufficient for osteosynthesis of the scaphoid bone. In case an intra-osteal implant is not available a single 3.5 AO/ASIF cortical screw, inserted following lag-screw principles, is recommended.     

A Challenge to Debate. III. The Inward and Outward Currents of a Space-Clamped Squid Axon

Fifteen patients with post-traumatic nonunions and a bone gap, eight of which were infected, were treated with bone grafting and electrostimulation using a stimulator connected to the external fixation pins. All nonunions healed with a median time of 9 months, and no recurrences of the osteomyelitis were observed.     

Emerging evidence that adaptive bone formation inhibition by non-steroidal anti-inflammatory drugs increases stress fracture risk

There is mounting evidence suggesting that the commonly used analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), may inhibit new bone formation with physical training and increase risk of stress fractures in physically active populations. Stress fractures are thought to occur when bones are subjected to repetitive mechanical loading, which can lead to a cycle of tissue microdamage, repair, and continued mechanical loading until fracture. Adaptive bone formation, particularly on the periosteal surface of long bones, is a concurrent adaptive response of bone to heightened mechanical loading that can improve the fatigue resistance of the skeletal structure, and therefore may play a critical role in offsetting the risk of stress fracture. Reports from animal studies suggest that NSAID administration may suppress this important adaptive response to mechanical loading. These observations have implications for populations such as endurance athletes and military recruits who are at risk of stress fracture and whose use of NSAIDs is widespread. However, results from human trials evaluating exercise and bone adaptation with NSAID consumption have been less conclusive. In this review, we identify knowledge gaps that must be addressed to further support NSAID-related guidelines intended for at-risk populations and individuals.     

Early experience with the Autophor prosthesis using a posterior approach

Twenty-eight Autophor hip prostheses have been implanted in 25 patients, using primarily a posterior approach. Complications have included two dislocations and two femoral shaft fractures. One dislocation required reoperation. The shaft fractures healed in three months with bone grafting and cerclage wiring. There were no infections and no cases of loosening or component failure. Radiological follow-up including bone scan suggests implant boney stabilization at six months. Our early experience suggests that this implant is quite successful, especially in the young patient and the patient with significant loss of bone stock from protrusio or revision surgery.     

Hydraulic resistance and permeability in human lumbar vertebral bodies

Hydraulic resistance (HR) was measured for ten intact human lumbar vertebrae to further understand the mechanisms of fluid flow through porous bone. Oil was forced through the vertebral bodies under various volumetric flow rates and the resultant pressure was measured The pressure-flow relationship for each specimen was linear. Therefore, HR was constant with a mean of 2.22 +/- 1.45 kPa*sec/ml. The mean permeability of the intact vertebral bodies was 4.90x10(-10) +/- 4.45x10(-10) m2. These results indicate that this methodology is valid for whole bone samples and enables the exploration of the effects of HR on the creation of high-speed fractures.     

Association of CYP19 Gene Polymorphism with Vertebral Fractures in Japanese Postmenopausal Women

This study investigates aromatase gene polymorphism, which might influence bone strength in terms of mineral density and quality. We explored the relationship between CYP19 polymorphisms and vertebral fractures in postmenopausal Japanese women. In addition, we compared estrogen and testosterone levels in Japanese postmenopausal women with and without fractures. Osteoporotic postmenopausal women showed higher incidences of vertebral fractures than osteopenic women or women with normal lumbar bone mineral density (L2-4 BMD). Estrogen concentrations in postmenopausal women were associated with BMD; however, no association was found between sex hormone levels and the presence of fractures. The C allele rs2470152 was significantly associated with increased risk of vertebral fractures (P = 0.04), whereas none of the CYP19 polymorphisms showed differences in sex steroid levels between subjects with and without fractures. Allelic variants of aromatase genes appear to interact to influence the risk of vertebral fractures in postmenopausal Japanese women.     

Extraordinarily low bone mineral density in an old female chimpanzee (<Emphasis Type="Italic">Pan troglodytes schweinfurthii</Emphasis>) from the Mahale Mountains National Park

We examined bone mineral density (BMD) of the femoral neck and lumbar vertebrae of four chimpanzee skeletons from Mahale Mountains National Park, Tanzania, and four captive ones, with a dual energy X-ray absorptiometer. The BMD of Wansombo, an old female chimpanzee from Mahale , was remarkably lower than the mean of the other six younger adult female chimpanzees and categorized as osteoporosis. Posture, locomotion, and trunk-sacral anatomy of chimpanzees may have prevented fractures in Wansombo, whose BMD was below human osteoporosis criteria. Electronic Publication     

Delivery of recombinant bone morphogenetic proteins for bone regeneration and repair. Part B: Delivery systems for BMPs in orthopaedic and craniofacial tissue engineering

Localized and release-controlled delivery systems for the sustained expression of the biologic potency of rhBMPs are essential. A substantial number of biomaterials have been investigated thus far. Most fail after implantation or administration mainly due to either being too soft, difficult to control and/or stabilize mechanically. In the second part of this review, we review a representative selection of rhBMP-2 and rhBMP-7 carrier materials and delivery systems ranging from simple nano/microparticles to complex 3-D scaffolds in sites of orthopaedic and craniofacial bone regeneration and repair.     

Local antibiotic delivery with demineralized bone matrix

A method of care for these infected nonunions is prolonged intravenous systemic antibiotic treatment and implantation of methyl methacrylate antibiotic carrier beads to delivery high local doses of antibiotics. This method requires a second surgery to remove the beads once the infection has cleared. Recent studies have investigated the use of biodegradable materials that have been impregnated with antibiotics as tools to treat bone infections. In the present study, human demineralized bone matrix (DBM) was investigated for its ability to be loaded with an antibiotic. The data presented herein demonstrates that this osteoinductive and biodegradable material can be loaded with gentamicin and release clinically relevant levels of the drug for at least 13 days in vitro. This study also demonstrates that the antibiotic loaded onto the graft has no adverse effects on the osteoinductive nature of the DBM as measured in vitro and in vivo. This bone void filler may represent a promising option for local antibiotic delivery in orthopedic applications.     

Craniosynostosis and multiple skeletal anomalies in humans and zebrafish result from a defect in the localized degradation of retinoic acid

Excess exogenous retinoic acid (RA) has been well documented to have teratogenic effects in the limb and craniofacial skeleton. Malformations that have been observed in this context include craniosynostosis, a common developmental defect of the skull that occurs in 1 in 2500 individuals and results from premature fusion of the cranial sutures. Despite these observations, a physiological role for RA during suture formation has not been demonstrated. Here, we present evidence that genetically based alterations in RA signaling interfere with human development. We have identified human null and hypomorphic mutations in the gene encoding the RA-degrading enzyme CYP26B1 that lead to skeletal and craniofacial anomalies, including fusions of long bones, calvarial bone hypoplasia, and craniosynostosis. Analyses of murine embryos exposed to a chemical inhibitor of Cyp26 enzymes and zebrafish lines with mutations in cyp26b1 suggest that the endochondral bone fusions are due to unrestricted chondrogenesis at the presumptive sites of joint formation within cartilaginous templates, whereas craniosynostosis is induced by a defect in osteoblastic differentiation. Ultrastructural analysis, in situ expression studies, and in vitro quantitative RT-PCR experiments of cellular markers of osseous differentiation indicate that the most likely cause for these phenomena is aberrant osteoblast-osteocyte transitioning. This work reveals a physiological role for RA in partitioning skeletal elements and in the maintenance of cranial suture patency.     

Compressive fatigue behavior of human vertebral trabecular bone

Damage accumulation under compressive fatigue loading is believed to contribute significantly to non-traumatic, age-related vertebral fractures in the human spine. Only few studies have explored trabecular bone fatigue behavior under compressive loading and none examined the influence of trabecular architecture on fatigue life. In this study, trabecular bone samples of human lumbar and thoracic vertebrae (4 donors from age 29 to 86, n=29) were scanned with a microCT system prior to compressive fatigue testing to determine morphology-mechanical relationships for this relevant loading mode. Inspired from previous fabric-based relationships for elastic properties and quasi-static strength of trabecular bone, a simple power relationship between volume fraction, fabric eigenvalue, applied stress and the number of cycles to failure is proposed. The experimental results demonstrate a high correlation for this relationship (R2=0.95) and detect a significant contribution of the degree of anisotropy towards prediction of fatigue life. Step-wise regression for total and residual strains at failure suggested a weak, but significant correlation with volume fraction. From the obtained results, we conclude that the applied stress normalized by volume fraction and axial fabric eigenvalue can estimate fatigue life of human vertebral trabecular bone in axial compressive loading.     

Site specific effects of zoledronic acid during tibial and mandibular fracture repair

Numerous factors can affect skeletal regeneration, including the extent of bone injury, mechanical loading, inflammation and exogenous molecules. Bisphosphonates are anticatabolic agents that have been widely used to treat a variety of metabolic bone diseases. Zoledronate (ZA), a nitrogen-containing bisphosphonate (N-BP), is the most potent bisphosphonate among the clinically approved bisphosphonates. Cases of bisphosphonate-induced osteonecrosis of the jaw have been reported in patients receiving long term N-BP treatment. Yet, osteonecrosis does not occur in long bones. The aim of this study was to compare the effects of zoledronate on long bone and cranial bone regeneration using a previously established model of non-stabilized tibial fractures and a new model of mandibular fracture repair. Contrary to tibial fractures, which heal mainly through endochondral ossification, mandibular fractures healed via endochondral and intramembranous ossification with a lesser degree of endochondral ossification compared to tibial fractures. In the tibia, ZA reduced callus and cartilage formation during the early stages of repair. In parallel, we found a delay in cartilage hypertrophy and a decrease in angiogenesis during the soft callus phase of repair. During later stages of repair, ZA delayed callus, cartilage and bone remodeling. In the mandible, ZA delayed callus, cartilage and bone remodeling in correlation with a decrease in osteoclast number during the soft and hard callus phases of repair. These results reveal a more profound impact of ZA on cartilage and bone remodeling in the mandible compared to the tibia. This may predispose mandible bone to adverse effects of ZA in disease conditions. These results also imply that therapeutic effects of ZA may need to be optimized using time and dose-specific treatments in cranial versus long bones.     

Atypical femoral fracture in a metastatic bone disease patient six months after discontinuation of denosumab received sequentially to previous bisphosphonate therapy - A case report

Although, both bisphosphonates and denosumab are effective in reducing the risk of skeletal-related events in patients with metastatic bone disease, many concerns were being raised about the possible association between their use and atypical femoral fractures. A case of an atypical femoral fracture in a metastatic bone disease patient, six months after discontinuation of long-term zoledronic acid therapy and sequential treatment with denosumab is reported. After extensive laboratory and imaging examination, the fracture was classified as atypical and it was finally treated with discontinuation of denosumab, long cephalomedullary interlocking nailing and vitamin D administration. Sequential treatment with bisphosphonates and denosumab in patients with metastatic bone disease, may lead to an overlapping treatment effect, increasing bone suppression and the risk of atypical femoral fracture. In addition, discontinuation of denosumab may activate bone remodeling units in an area with microdamage accumulation in cortical bone caused by the previous bone suppression from the antiresorptive treatment. The activation of bone remodeling units may accelerate the occurrence of the atypical femoral fractures.     

Fractures of the Calcaneus—Diagnosis and Treatment

Good lateral, Anthonsen oblique, anterior-posterior, and axial roentgenograms are necessary to define the extent of fractures of the calcaneus. Roentgenograms of the lumbar spine, including the thoracolumbar junction, are recommended whenever a fall has occurred sufficient to fracture the calcaneus.The great majority of calcaneal fractures are compression shearing fractures. Significant disruption of articular surfaces and spreading of the body beneath the fibula are major surgical problems and require careful treatment. In a series of 50 fractures treated by four methods, open reduction with stabilization by bone grafts, followed by active motion at six to eight weeks, gave the best results.