Purification and molecular cloning of a novel group of BMPs and localization of BMP mRNA in developing bone

BMP-4 Extraction from Extracellular Matrix and Analysis of Heparin-Binding Properties

Recombinant human BMP-4 growth factor (GF) has significant commercial potential as therapeutic for regenerating bone and as cell culture supplement. However, its commercial utility has been limited as large-scale attempts to express and purify human BMP-4 GF have proved challenging. We have established a novel approach to obtain significant quantities of pure and bioactive BMP-4 GF from Chinese hamster ovary cell cultures by extracting the GF moiety from the extracellular matrix or cell pellet fraction. This approach increased yields approximately one 100-fold over BMP-4 GF purified from CM. The molecular activities of the two fractions are indistinguishable. We further analyzed binding of BMP-4 GF to the proteoglycan Heparin and showed that an N-terminal basic sequence is essential for this interaction. Taken together, these results provide novel insights into the purification, localization, and Heparin binding of human BMP-4 that have implications for its bioprocessing and biological function.

Emerging therapeutic targets for NASH: key innovations at the preclinical level

Introduction: nonalcoholic steatohepatitis (NASH) is a globally emerging health problem, mainly caused by increasing trends in the prevalence of obesity and metabolic syndrome. Patients with NASH are mainly affected by cardiovascular risk and extrahepatic cancer, but a significant proportion of patients will develop advanced liver disease, eventually resulting in liver failure or hepatocellular carcinoma. Recent research has yielded a better understanding of the underlying mechanisms and potential targetability for drug development.Areas covered: This review focuses on the role of fructose metabolism, de novo lipogenesis (DNL), endoplasmic reticulum (ER) stress, NLRP3 inflammasome, bone morphogenetic protein (BMP) signaling and platelets in the pathophysiology of NASH. We discuss the suitability of these substrates for targeting liver disease as well as cardiovascular health in patients with NASH. A non-systematic literature search was performed on PubMed and ClinicalTrials.gov.Expert opinion: Targeting fructose metabolism, DNL, ER stress, NLRP3 inflammasome, BMP signaling and platelets are promising therapeutic strategies, warranting further preclinical and clinical investigation. The discussed approaches might not only benefit liver-related outcomes but improve cardiovascular disease as well. Amidst the euphoria of advances in drug development for NASH, parallel endeavors need to address the underlying causes of obesity and metabolic syndrome to prevent NASH.

In Vitro Release of Bioactive Bone Morphogenetic Proteins (GDF5, BB-1, and BMP-2) from a PLGA Fiber-Reinforced, Brushite-Forming Calcium Phosphate Cement

Bone regeneration of sheep lumbar osteopenia is promoted by targeted delivery of bone morphogenetic proteins (BMPs) via a biodegradable, brushite-forming calcium-phosphate-cement (CPC) with stabilizing poly(l-lactide-co-glycolide) acid (PLGA) fibers. The present study sought to quantify the release and bioactivity of BMPs from a specific own CPC formulation successfully used in previous in vivo studies. CPC solid bodies with PLGA fibers (0%, 5%, 10%) containing increasing dosages of GDF5, BB-1, and BMP-2 (2 to 1000 µg/mL) were ground and extracted in phosphate-buffered saline (PBS) or pure sheep serum/cell culture medium containing 10% fetal calf serum (FCS; up to 30/31 days). Released BMPs were quantified by ELISA, bioactivity was determined via alkaline phosphatase (ALP) activity after 3-day exposure of different osteogenic cell lines (C2C12; C2C12BRlb with overexpressed BMP-receptor-1b; MCHT-1/26; ATDC-5) and via the influence of the extracts on the expression of osteogenic/chondrogenic genes and proteins in human adipose tissue-derived mesenchymal stem cells (hASCs). There was hardly any BMP release in PBS, whereas in medium + FCS or sheep serum the cumulative release over 30/31 days was 11-34% for GDF5 and 6-17% for BB-1; the release of BMP-2 over 14 days was 25.7%. Addition of 10% PLGA fibers significantly augmented the 14-day release of GDF5 and BMP-2 (to 22.6% and 43.7%, respectively), but not of BB-1 (13.2%). All BMPs proved to be bioactive, as demonstrated by increased ALP activity in several cell lines, with partial enhancement by 10% PLGA fibers, and by a specific, early regulation of osteogenic/chondrogenic genes and proteins in hASCs. Between 10% and 45% of bioactive BMPs were released in vitro from CPC + PLGA fibers over a time period of 14 days, providing a basis for estimating and tailoring therapeutically effective doses for experimental and human in vivo studies.

GDF5 significantly augments the bone formation induced by an injectable, PLGA fiber-reinforced, brushite-forming cement in a sheep defect model of lumbar osteopenia

BACKGROUND CONTEXT

Biodegradable calcium phosphate cement (CPC) represents a promising option for the surgical treatment of osteoporotic vertebral fractures. Because of augmented local bone catabolism, however, additional targeted delivery of bone morphogenetic proteins with the CPC may be needed to promote rapid and complete bone regeneration.

PURPOSE

In the present study, an injectable, poly(l-lactide-co-glycolide) acid (PLGA) fiber-reinforced, brushite-forming cement (CPC) containing the bone morphogenetic protein GDF5 was tested in a sheep lumbar osteopenia model.

STUDY DESIGN/SETTING

This is a prospective experimental animal study.

METHODS

Defined bone defects (diameter 5 mm) were placed in aged, osteopenic female sheep. Defects were treated with fiber-reinforced CPC alone (L4; CPC+fibers) or with CPC containing different dosages of GDF5 (L5; CPC+fibers+GDF5; 1, 5, 100, and 500 µg GDF5; n=5 or 6 each). The results were compared with those of untouched controls (L1). Three and 9 months postoperation, structural and functional effects of the CPC (±GDF5) were assessed ex vivo by measuring (1) bone mineral density (BMD); (2) bone structure, that is, bone volume/total volume (assessed by micro-computed tomography and histomorphometry), trabecular thickness, and trabecular number; (3) bone formation, that is, osteoid volume/bone volume, osteoid surface/bone surface, osteoid thickness, mineralized surface/bone surface, mineral apposition rate, and bone formation rate/bone surface; (4) bone resorption, that is, eroded surface/bone surface; and (5) compressive strength.

RESULTS

Compared with untouched controls (L1), both CPC+fibers (L4) and CPC+fibers+GDF5 (L5) numerically or significantly improved all parameters of bone formation, bone resorption, and bone structure. These significant effects were observed both at 3 and 9 months, but for some parameters they were less pronounced at 9 months. Compared with CPC without GDF5, additional significant effects of CPC with GDF5 were demonstrated for BMD and parameters of bone formation and structure (bone volume/total volume, trabecular thickness, and trabecular number, as well as mineralized surface/bone surface). The GDF5 effects were dose-dependent (predominantly in the 5-100 µg range) at 3 and 9 months.

CONCLUSIONS

GDF5 significantly enhanced the bone formation induced by a PLGA fiber-reinforced CPC in sheep lumbar osteopenia. The results indicated that a local dose as low as ≤100 µg GDF5 may be sufficient to augment middle to long-term bone formation. The novel CPC+GDF5 combination may thus qualify as an alternative to the bioinert, supraphysiologically stiff poly(methyl methacrylate) cement currently applied for vertebroplasty/kyphoplasty of osteoporotic vertebral fractures.

rhBMP-2 protects against reoperation for pseudoarthrosis and/or instrumentation failure: A matched case-control study of 448 patients

The objective of this independent study is to determine the impact of recombinant human bone morphogenetic protein 2 (rhBMP-2) on reoperation for pseudarthrosis and/or instrumentation failure. A nested case-control study of first-time posterolateral, instrumented fusion of the lumbar spine for degenerative spinal disease was undertaken. Cases of reoperation for pseudoarthrosis and/or instrumentation failure were assigned to controls, who did not experience the primary outcome measure at the time of reoperation. Cases and controls were matched on number of interspaces fused and inclusion of interbody. Predictors of reoperation for pseudoarthrosis and/or instrumentation failure were assessed with a conditional logistical regression controlling for rhBMP-2, age, obesity, and smoking. Of the 448 patients, 155 cases of reoperation for pseudoarthrosis and/or instrumentation were matched with 293 controls. Twenty-six percent of first-time surgeries included rhBMP-2, which was statistically more commonly used in the control cohort (33.11%) versus the case cohort (12.90%) (Unadjusted odds ratio [ORunadj]=0.28) (95% confidence interval [CI]: 0.16-0.49). Following a multivariate analysis controlling for age, obesity, and smoking, the rhBMP-2 recipients incurred a 73% lower odds of reoperation for pseudoarthrosis and/or instrumentation failure (95% CI, 0.15-0.48). Neither sarcomatous nor osseous neoplasm was detected in the study population. Mean follow up did not differ between the cases (81.57±standard deviation [SD] 4.98months) versus controls (74.75±2.49month) (ORunadj=1.01) (95% CI: 1.00-1.01). rhBMP-2 in lumbar fusion constructs protects against reoperation for pseudoarthrosis and/or instrumentation failure. However, the decision to include fusion supplements should be weighted between surgical determinants and clinical outcomes.

Targeting BMP signalling in cardiovascular disease and anaemia

Bone morphogenetic proteins (BMPs) and their receptors, known to be essential regulators of embryonic patterning and organogenesis, are also critical for the regulation of cardiovascular structure and function. In addition to their contributions to syndromic disorders including heart and vascular development, BMP signalling is increasingly recognized for its influence on endocrine-like functions in postnatal cardiovascular and metabolic homeostasis. In this Review, we discuss several critical and novel aspects of BMP signalling in cardiovascular health and disease, which highlight the cell-specific and context-specific nature of BMP signalling. Based on advancing knowledge of the physiological roles and regulation of BMP signalling, we indicate opportunities for therapeutic intervention in a range of cardiovascular conditions including atherosclerosis and pulmonary arterial hypertension, as well as for anaemia of inflammation. Depending on the context and the repertoire of ligands and receptors involved in specific disease processes, the selective inhibition or enhancement of signalling via particular BMP ligands (such as in atherosclerosis and pulmonary arterial hypertension, respectively) might be beneficial. The development of selective small molecule antagonists of BMP receptors, and the identification of ligands selective for BMP receptor complexes expressed in the vasculature provide the most immediate opportunities for new therapies.

Structural insights into BMP receptors: Specificity, activation and inhibition

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β family (TGFβ), which signal through hetero-tetrameric complexes of type I and type II receptors. In humans there are many more TGFβ ligands than receptors, leading to the question of how particular ligands can initiate specific signaling responses. Here we review structural features of the ligands and receptors that contribute to this specificity. Ligand activity is determined by receptor-ligand interactions, growth factor prodomains, extracellular modulator proteins, receptor assembly and phosphorylation of intracellular signaling proteins, including Smad transcription factors. Detailed knowledge about the receptors has enabled the development of BMP-specific type I receptor kinase inhibitors. In future these may help to treat human diseases such as fibrodysplasia ossificans progressiva.

Phenotypic variability in a Hungarian patient with the 4q21 microdeletion syndrome

Background

Interstitial deletions of 4q21 (MIM 613509) have already been reported in more than a dozen patients with deletions ranging from 2 to 15.1 Mb delineating a common phenotype including marked growth restriction, hypotonia, severe developmental delay with absent or delayed speech and distinctive facial features. A minimal critical region of 1.37 Mb accounting for the common features with 5 known genes (PRKG2, RASGEF1B, HNRNPD, HNRPDL, and ENOPH1) has been described so far.

Results

Here we report on a 5 year-old Hungarian girl presenting with severe developmental delay, good receptive language but absent spoken speech, short stature, dystrophy, hypotonia, distinctive facies including broad forehead, frontal bossing, downward slanting palpebral fissures, hypertelorism, hypoplastic ear-lobes, anteverted nostrils, short philtrum, small mouth, higharched palate, short, small hands and feet, distally narrowing fingers and clinodactyly. Cerebral MRI showed ventricular dilation and an increase in periventricular signal intensity. After extensive metabolic tests and exclusion of subtelomeric deletions array CGH analysis was performed using the Agilent Human Genome G3 SurePrint 8x60K Microarray (Agilent Technologies, USA), which detected a 4,85 Mb de novo interstitial deletion of 4q21.21-4q21.23. The clinical symptoms only partly overlap with reported 4q21 microdeletion cases. Among multiple annotated genes our patient is also haploinsufficient for the following genes: RASGEF1B being a strong candidate for the neurodevelopmental features and PRKG2 for severe growth delay.

Conclusion

The first Hungarian case of 4q21 deletion adds to the phenotypic spectrum of this novel microdeletion syndrome and underlines the importance of array CGH to uncover the heterogeneous causes of intellectual disability.

Genetic association of ARHGAP21 gene variant with mandibular prognathism

Mandibular prognathism (MP) is a recognizable phenotype associated with dentoskeletal class III malocclusion. MP is a complex genetic trait, although familial recurrence also suggests the contribution of single inherited variations. To date, the genetic causes of MP have been investigated using linkage analysis or association studies in pooled families. Here for the first time, next-generation sequencing was used to study a single family with a large number of MP-affected members and to identify MP-related candidate genes. A 6-generation kindred with MP segregating as an autosomal dominant character was recruited. To identify family members affected by MP, a standard cephalometric procedure was used. In 5 MP subjects separated by the largest number of meioses, whole-exome sequencing was performed. Five promising missense gene variants (BMP3, ANXA2, FLNB, HOXA2, and ARHGAP21) associated with MP were selected and genotyped in most other family members. In this family, MP seemed to consist of 2 distinct genetic branches. Interestingly, the Gly1121Ser variant in the ARHGAP21 gene was found to be shared by all MP individuals in the larger branch of the family with nearly complete penetrance. This variant is rare in the Caucasian population (frequency 0.00034) and is predicted as damaging by all bioinformatic algorithms. ARHGAP21 protein strengthens cell-cell adhesions and may be regulated by bone morphogenetic factors, thus influencing mandibular growth. Further studies in both animal models and human patients are required to clarify the significance of this association.

The dynamic role of bone morphogenetic proteins in neural stem cell fate and maturation

The bone morphogenetic proteins (BMPs) are a group of powerful morphogens that are critical for development of the nervous system. The effects of BMP signaling on neural stem cells are myriad and dynamic, changing with each stage of development. During early development inhibition of BMP signaling differentiates neuroectoderm from ectoderm, and BMP signaling helps to specify neural crest. Thus modulation of BMP signaling underlies formation of both the central and peripheral nervous systems. BMPs secreted from dorsal structures then form a gradient which helps pattern the dorsal-ventral axis of the developing spinal cord and brain. During forebrain development BMPs sequentially induce neurogenesis and then astrogliogenesis and participate in neurite outgrowth from immature neurons. BMP signaling also plays a critical role in maintaining adult neural stem cell niches in the subventricular zone (SVZ) and subgranular zone (SGZ). BMPs are able to exert such diverse effects through closely regulated temporospatial expression and interaction with other signaling pathways.

B2A peptide induces chondrogenic differentiation in vitro and enhances cartilage repair in rats

This study investigated whether the synthetic peptide B2A (B2A2-K-NS) could induce in vitro chondrogenic differentiation and enhance the in vivo repair of damaged cartilage in an osteoarthritis model. In vitro, micromass cultures of murine and human stem cells with and without B2A were used as models of chondrogenic differentiation. Micromasses were evaluated for gene expression using microarray analysis and quantitative PCR; and for extracellular matrix production by Alcian blue staining for sulfated glycosaminoglycan and immunochemical detection of collagen type II. In vivo, osteoarthritis was chemically induced in knees of adult rats by an injection of mono-iodoacetate (MIA) into the synovial space. Treatment was administered at 7- and 14 days after the MIA by injection into the synovial space of B2A or saline and terminated at 21 days, after which knee cartilage damage was determined and scored by histological analysis. In murine C3H10T1/2 micromass culture, B2A induced the expression of more than 11 genes associated with growth factors/receptors, transcription, and the extracellular matrix, including PDGF-AA. B2A also significantly increased the sulfated glycosaminoglycan and collagen of murine- and human micromass cultures. In the knee osteoarthritis model, B2A treatment enhanced cartilage repair compared to untreated knees as determined histologically by a decrease in damage indicators. These findings suggest that B2A induces stem cells chondrogenic differentiation in vitro and enhances cartilage repair in vivo. The results suggest that B2A might be useful to promote cartilage repair.

Carboxymethyl-chitin promotes chondrogenesis by inducing the production of growth factors from immune cells

Many techniques have been tested for their ability to restore cartilage defects, but several problems still remain in the complete healing of injured cartilage. In our previous study, we found that a carboxymethyl-chitin/beta-tricalcium phosphate (CM-chitin/beta-TCP) composite induced cartilage regeneration in the osteochondral defects of rabbits in vivo. We also found that CM-chitin stimulated peritoneal exudate cells (PEC) in mice and induced several kinds of inflammatory cytokines and transforming growth factor beta-1 (TGF-beta1). In this study, we examined whether CM-chitin is responsible for the induction of chondrogenesis via the production of TGF-beta1 in vitro. The murine pluripotent cell line C3H10T1/2 was maintained as a micromass culture in conditioned medium prepared from PEC stimulated with and without CM-chitin. CM-chitin-conditioned medium induced RNA expression of the chondrogenic-factor Sox9 and the matrix proteins aggrecan, Col2a1, and Comp. Their expression levels were decreased in the presence of anti-TGF-beta1 antibody. The micromass tissues cultured in CM-chitin conditioned medium at day 21 were clearly stained by Toluidine blue or Alcian blue (histological staining) and collagen II antibody (immunohistological staining), showing the expression of acidic glycosaminoglycan and type II collagen. Similar results were observed in micromass tissue stimulated with TGF-beta1 as a positive control. However, no chondrogenesis occurred when CM-chitin was added directly to a C3H10T1/2 cell culture. These results indicated that CM-chitin is a potent inducer of chondrogenesis via the induction of TGF-beta1 in immune cells.

Effects of chitosan-coated pressed calcium sulfate pellets combined with recombinant human bone morphogenetic protein 2 on bone formation in femoral condyle-contained bone defects

Calcium sulfate has a rapid degradation rate and little osteoinductive capability. Chitosan-coated pressed calcium sulfate pellets combined with recombinant human bone morphogenetic protein 2 (rhBMP-2) have been developed that exhibit decreased resorption speed and increased compressive strength and osteoinduction. A rabbit femoral condyle-contained bone defect model was used to study the restoration of the defects treated with chitosan-coated pressed calcium sulfate pellets combined with rhBMP-2, chitosan-coated pressed calcium sulfate pellets, and uncoated pressed calcium sulfate pellets. No pellets were implanted in the control group. After 3 and 13 weeks, the results indicated that chitosan-coated pressed calcium sulfate pellets exhibited relatively slower resorption that closely coincides with the growth rate of new bone and enhanced osteogenesis when combined with rhBMP-2.

Repair of experimentally induced large osteochondral defects in rabbit knee with various concentrations of Escherichia coli-derived recombinant human bone morphogenetic protein-2

Effective therapies for the regeneration of large osteochondral defects are still lacking; however, various approaches have been used. We evaluated the efficacy of Escherichia coli-derived dimeric recombinant human BMP-2 (E-rhBMP-2) for the repair of large osteochondral defects in a rabbit model. Osteochondral defects made in the femoral patellar groove of the knee were treated by transplanting gelatin sponges onto which no or various doses of E-rhBMP-2 were loaded. The outcomes were compared with those of an untreated control group four, 12 and 24 weeks after transplantation. At early time points, the cartilage tissue was repaired in a dose-dependent manner, and bone repair was accelerated in the defects treated with high doses of E-rhBMP-2. At 24 weeks, the repair of cartilage tissue was better with E-rhBMP-2 treatment, even at low doses, than without E-rhBMP-2 treatment. Our findings suggest that the use of E-rhBMP-2 improves and accelerates the repair of osteochondral defects in a rabbit model.

Discovery and development of BMPs

In the early 1970s, the isolation and identification of bone morphogenetic proteins (BMPs) was a major breakthrough for the understanding of the distinct biological events occurring during bone formation. Not surprising, since their discovery, BMPs have been perhaps one of the most intensively studied group of factors in various physiological processes. The prompt development of recombinant BMPs and various delivery methods made BMPs currently available for clinical use. Research and clinical studies on BMPs are ongoing, aiming to refine further our understanding of their activities in vivo and to optimise and expand their clinical use in humans.

Morphing into cancer: the role of developmental signaling pathways in brain tumor formation

Morphogens play a critical role in most aspects of development, including expansion and patterning of the central nervous system. Activating germline mutations in components of the Hedgehog and Wnt pathways have provided evidence for the important roles morphogens play in the genesis of brain tumors such as cerebellar medulloblastoma. In addition, aberrant expression of transforming growth factor-beta (TGF-beta) superfamily members has been demonstrated to contribute to progression of malignant gliomas. This review summarizes our current knowledge about the roles of morphogens in central nervous system tumorigenesis.

The effect of host tissue irradiation on large-segment allograft incorporation

Therapeutic radiation delivered to bone and the adjacent local tissues before allograft limb-salvage surgery has been associated with poor graft incorporation and higher numbers of clinical complications. Our objective was to determine the effect of preoperative radiation therapy on specific histologic, molecular and structural parameters of large-segment, bone allograft incorporation in a canine model. Skeletally mature dogs received a total of 0, 25, or 50 Gy of radiation to the foreleg (radius and ulna) delivered in 2-Gy fractions during a 5-week period before reconstruction of a 3.5-cm defect in the radius. The dogs were sacrificed at postoperative day 150. Nondestructive four-point bending was done on the harvested allograft-host bone immediately after euthanasia and specimens were compared using biomechanical, histomorphometric, immunohistochemical, and in situ reverse transcription polymerase chain reaction techniques. Preoperative irradiation significantly impaired allograft incorporation as determined by radiographic healing scores, histomorphometry, and frequency of nonunions. Biochemical differences included diminished bone morphogenetic protein-2 and bone morphogenetic protein-4 protein levels and messenger ribonucleic acid expression. Vascular endothelial growth factor expression was not altered. These data suggest that bone morphogenetic protein-2 and bone morphogenetic protein-4 signaling at the allograft-host junction is altered after preoperative fractionated radiation and provides a plausible albeit partial mechanistic explanation for radiation-mediated delays in allograft incorporation.

Animal models for cartilage reconstruction

Animal models are widely used to develop and evaluate tissue-engineering techniques for the reconstruction of damaged human articular cartilage. For the purpose of this review, these model systems will include in vitro culture of animal cells and explants, heterotopic models of chondrogenesis, and articular cartilage defect models. The objectives for these preclinical studies are to engineer articular cartilage for the functional restoration of a joint surface that appears anatomically, histologically, biologically, biochemically, and mechanically to resemble the original joint surface. While no animal model permits direct application to humans, each is capable of yielding principles on which decisions can be made that might eventually translate into a human application. Clearly, the use of animal models has and will continue to play a significant role in the advancement of this field. Each animal model has specific advantages and disadvantages. The key issue in the selection of an appropriate animal model is to match the model to the question being investigated and the hypothesis to be tested. The purpose of this review is to discuss issues regarding animal model selection, the benefits and limitations of these model systems, scaffold selection with emphasis on polymers, and evaluation of the tissue-engineered articular cartilage.

Ne-Osteo bone growth factor for posterolateral lumbar spine fusion: results from a nonhuman primate study and a prospective human clinical pilot study

STUDY DESIGN

Prospective animal and human clinical pilot trial.

OBJECTIVES

The purpose of this study was to determine and test the dose of Ne-Osteo growth factor extract and carrier required for consistent radiographic bone induction in humans.

SUMMARY OF BACKGROUND DATA

Preclinical studies have demonstrated that Ne-Osteo, an extract-containing bone morphogenetic proteins, was successful at generating spine fusion in rabbits and rhesus monkeys. Consistent fusions have yet to be achieved in nonhuman primates and humans.

METHODS

Adult rhesus monkeys underwent single-level posterolateral intertransverse lumbar arthrodesis with either 3.0 mg (N = 4), 5.0 mg (N = 4), 12.5 mg (N = 4), or 25 mg (N = 4) of Ne-Osteo per side. Animals were killed after 24 weeks. In the human clinical trial, 22 patients (18 females, 4 males) had lumbar spinal stenosis and/or spondylolisthesis requiring spine arthrodesis. To minimize patient risk of nonunion, patients received autogenous bone graft from the posterior iliac crest on one side and Ne-Osteo growth factor on the other. The dose was 12.5 mg, 25 or 50 mg, or 25 mg Ne-Osteo per side performed in the three phases, respectively.

RESULTS

Three of four monkeys that received 12.5 mg Ne-Osteo per side and four of four that received 25 mg per side achieved solid fusions. In phase I of the human clinical trial, two of six patients showed radiographic bone induction (plain radiograph, CT scans-blindly evaluated) on the Ne-Osteo side (12.5-mg dose). In phase II, both sides were graded as fused in five of six patients. Although graded as fused, the 6-month scans demonstrated a ring of new bone with the center filling in slower (12-24 mo) than was predicted by nonhuman primate studies. As a result, phase III carrier was designed to have a more porous/open early fusion mass than with the dense DBM paste (used in phase I and II) by mixing in local bone or cancellous allograft chips. Results using the 25- and 50-mg doses were the same, so 25 mg was used in phase III. In phase III, 9 of 10 autograft were fused by 12 months. Five of five patients with Ne-Osteo plus local bone and four of five with allograft chips were fused by 6 months. The one patient in this group that did not heal on either the autograft or the Ne-Osteo side was a smoker.

CONCLUSIONS

A graft composite of Ne-Osteo bone growth factor with human DBM with or without cancellous allograft or local bone autograft was capable of achieving a contiguous spine fusion mass in 15 of 16 patients at a dose of at least 25 mg per side. This result was comparable with the results using iliac crest autograft (94%) in this side-by-side model. These results warrant confirmation in a definitive trial using Ne-Osteo on both sides of the spine and thus avoiding the need for iliac crest bone graft harvest.

Use of recombinant human bone morphogenetic protein-2 to achieve posterolateral lumbar spine fusion in humans: a prospective, randomized clinical pilot trial: 2002 Volvo Award in clinical studies

STUDY DESIGN

A prospective randomized clinical study was conducted.

OBJECTIVE

To determine whether the dose and carrier that were successful in rhesus monkeys could induce consistent radiographic spine fusion in humans.

SUMMARY OF BACKGROUND DATA

Preclinical studies have demonstrated that recombinant human bone morphogenetic protein-2 (rhBMP-2), an osteoinductive bone morphogenetic protein, is successful at generating spine fusion in rabbits and rhesus monkeys.

METHODS

For this study, 25 patients undergoing lumbar arthrodesis were randomized (1:2:2 ratio) based on the arthrodesis technique: autograft/Texas Scottish Rite Hospital (TSRH) pedicle screw instrumentation (n = 5), rhBMP-2/TSRH (n = 11), and rhBMP-2 only without internal fixation (n = 9). On each side, 20 mg of rhBMP-2 were delivered on a carrier consisting of 60% hydroxyapatite and 40% tricalcium phosphate granules (10 cm /side). The patients had single-level disc degeneration, Grade 1 or less spondylolisthesis, mechanical low back pain with or without leg pain, and at least 6 months failure of nonoperative treatment.

RESULTS

All 25 patients were available for follow-up evaluation (mean, 17 months; range 12-27 months). The radiographic fusion rate was 40% (2/5) in the autograft/TSRH group and 100% (20/20) with rhBMP-2 group with or without TSRH internal fixation ( = 0.004). A statistically significant improvement in Oswestry score was seen at 6 weeks in the rhBMP-2 only group (-17.6; = 0.009), and at 3 months in the rhBMP-2/TSRH group (-17.0; = 0.003), but not until 6 months in the autograft/TSRH group (-17.3; = 0.041). At the final follow-up assessment, Oswestry improvement was greatest in the rhBMP-2 only group (-28.7, < 0.001). The SF-36 Pain Index and PCS subscales showed similar changes.

DISCUSSION

This pilot study is the first with at least 1 year of follow-up evaluation to demonstrate successful posterolateral spine fusion using a BMP-based bone graft substitute, with radiographs and CT scans as the determinant. Consistently, rhBMP-2 was able to induce bone in the posterolateral lumbar spine when delivered at a dose of 20 mg per side with or without the use of internal fixation. Patients with spondylolisthesis classified higher than Meyerding Grade 1 or with more than 5 mm of translational motion may still require internal fixation. Some patients did smoke during the postoperative period, and all in the rhBMP-2 groups still obtained solid fusions.

CONCLUSIONS

Consistently, rhBMP-2 with the biphasic calcium phosphate granules induced radiographic posterolateral lumbar spine fusion with or without internal fixation in patients whose spondylolisthesis did not exceed Grade 1. Statistically greater and quicker improvement in patient-derived clinical outcome was measured in the rhBMP-2 groups.

Expression of bone morphogenetic protein in the course of osteoinduction by recombinant human bone morphogenetic protein-2

To clarify the mechanism of osteoinduction by recombinant human bone morphogenetic protein-2 (rhBMP-2), we examined the time-course localization of bone morphogenetic proteins (BMPs) immunostained by an anti-BMP-2 monoclonal antibody after implantation of pellets consisting of rhBMP-2 and collagen in rat calf muscle pouch. On day 3 after implantation, BMP was detected in the entire lump, and the intensity of staining for BMP around the implant on day 7 was weaker than that on day 3. The staining for BMP decreased with time and the region of staining for BMP remained more centralized in the implant. On day 10 after implantation, BMP was observed in part of the newly induced cartilage, especially around chondrocytes. On day 14 after implantation, BMP was localized in the newly induced woven bone. On day 21, BMP staining was found in osteoblasts at the surface of the newly induced bone. Especially, the staining for BMP decreased from day 10 to day 21. These results indicate that the woven bone was replaced with mature lamellar bone from day 14 to day 21. The present findings suggest that rhBMP-2 plays an important role in osteoinduction, especially at the early stage.

Gene expression profiling following BMP-2 induction of mesenchymal chondrogenesis in vitro

OBJECTIVE

This study aims to apply gene expression profiling technology to gain insight into the molecular regulation of mesenchymal chondrogenesis.

METHODS

The experimental system consists of micromass cultures of C3H10T1/2 cells, a murine multipotential embryonic cell line, treated with the chondroinductive growth factor, bone morphogenetic factor-2 (BMP-2). In this system, chondrogenic differentiation characterized by both morphological changes and cartilage matrix gene expression has been shown to be completely dependent upon BMP-2 treatment and the high cell plating density of micromass cultures. To identify candidate genes that may have key functional roles in chondrogenesis, we have applied subtractive hybridization to isolate genes whose expression is significantly up- or down-regulated during chondrogenesis. RNA was isolated from micromass cultures treated with BMP-2 for 24 h and analysed for representational differences by means of a subtractive hybridization screening method.

RESULTS

Sixteen different genes were identified whose expression was up-regulated between two- and 12-fold by B,P-2, and twelve different genes were identified whose expression was down-regulated between two- and seven-fold by BMP-2.

CONCLUSIONS

The potential of this screening methodology to identify new BMP-2 regulated genes is suggested by the fact that a majority of the identified genes are indeed novel. Identification and characterization of these genes should provide insight as to how chondrogenesis is regulated and also should provide important new markers for the study of osteoarthritis.

Efficient chondrogenic differentiation of mesenchymal cells in micromass culture by retroviral gene transfer of BMP-2

The multipotential murine embryonic C3H10T1/2 mesenchymal cell line is able to undergo chondrogenesis in vitro, in a high density micromass environment, following treatment with soluble human bone morphogenetic protein-2 (BMP-2). To enhance this process, the human BMP-2 cDNA was cloned into a retroviral expression vector and a high titer, infectious retrovirus (replication defective) was generated. Infection of C3HIOT1/2 cells with this retroviral construct resulted in an infection efficiency of 90-95% and was highly effective in converting cells in micromass culture to a chondrocyte phenotype, as assessed by positive Alcian blue staining for extracellular matrix proteoglycans, increased sulfate incorporation, increased expression of the cartilage marker genes collagen type II and aggrecan, and decreased expression of collagen type I. Interestingly, BMP-2 expression in the micromass cultures also induced the expression of the cell cycle inhibitory protein/differentiation factor p21/WAF1, suggesting its functional involvement in chondrogenesis. The chondrogenic effect of retrovirally expressed BMP-2 in these high-density cultures was limited to the infected cells, since uninfected cells did not chondrify when co-cultured as a nonoverlapping micromass adjacent to BMP-2 expressing cells. These data indicate that retrovirally expressed BMP-2 is highly effective at inducing a chondrocyte phenotype in a multipotential mesenchymal cell line in vitro, and its action is restricted to the infected cell population. These findings should provide a framework for the optimization of chondrogenesis in culture using mesenchymal stem cells and retroviral gene transfer.

Histomorphometric description of allograft bone remodeling and union in a canine segmental femoral defect model: a comparison of rhBMP-2, cancellous bone graft, and absorbable collagen sponge

The purpose of this study was to determine the effect of recombinant human bone morphogenetic protein type 2 (rhBMP-2) on the histomorphometry of femoral allograft-host bone union and allograft remodeling. A 6 cm mid-diaphyseal femoral defect was created and filled with an allograft stabilized with an interlocking nail in 21 dogs. Dogs were randomly divided into three equal groups and the allograft-host bone junctions and the mid-diaphyses of the allografts were treated with either an absorbable collagen sponge (ACS) loaded with rhBMP-2 (BMP group), an autogenous cancellous bone graft (CBG group), or ACS loaded with buffer solution (ACS group). All dogs received daily tetracycline until sacrifice at 24 weeks to label new bone formation. Histomorphometric analyses on sections of proximal and distal allograft-host bone junctions and the mid-diaphyseal portion of allografts were performed using fluorescent and regular light microscopy. Analyses of the host bone and junctions between allograft and host bone revealed significantly greater new bone formation and larger osteon radii in the BMP group compared to CBG and ACS groups and contralateral intact bone. Porosity in CBG and ACS groups was significantly higher than in the BMP group, which had similar values to intact bone. In transverse sections of allografts, the largest pore diameters were present in the CBG group. Based on all parameters measured, significantly higher bone turnover occurred in the outer cortical area of the allograft in all groups as compared to the inner cortical and mid-cortical areas. New bone formation and osteon radius/osteon width in allografts were similar for all three groups. Higher porosity and larger pore diameters in the CBG and ACS groups suggested higher bone resorption versus formation in these groups compared to the BMP group. The results of this study reveal more balanced allograft bone resorption and bone formation in the BMP group, with greater resorptive activity in the CBG and ACS groups. However, neither rhBMP-2 nor autogenous bone graft increased allograft incorporation when compared to the negative control (ACS group).

The effect of recombinant human bone morphogenetic protein-2 on femoral reconstruction with an intercalary allograft in a dog model

This study compared the effect of augmentation of allograft host bone junctions with recombinant human bone morphogenetic protein-2 (rhBMP-2) on an absorbable collagen sponge (ACS), autogenous cancellous bone graft (CBG), and a collagen sponge alone in a canine intercalary femoral defect model repaired with a frozen allograft. Outcome assessment included serial radiographs, dual energy X-ray absorptiometry scans, and gait analyses, and mechanical testing and histology of post-mortem specimens. The distal junction healed more quickly and completely with rhBMP-2 than ACS alone based on qualitative radiography and histologic evaluations. The primary tissue in the unhealed gaps in the ACS group was fibrous connective tissue. The proximal allograft host bone junction had complete bone union in the three treatment groups. There was significantly greater new bone callus formation at both junctions with rhBMP-2 than with CBG or ACS alone that resulted in increased bone density around the allograft host bone junctions. All dogs shifted their weight from the treated leg to the contralateral pelvic limb immediately after surgery. Weight bearing forces were redistributed equally between the pelvic limbs at 12 weeks after surgery with rhBMP-2, at 16 weeks after surgery with CBG, and at 24 weeks after surgery with ACS alone. Bending and compressive stiffnesses of the whole treated femora were equal to the contralateral control femora in all treatment groups, whereas torsional rigidities of the whole treated femora for the CBG and ACS groups were significantly less than the control. Both the proximal and distal junctions the treated with rhBMP-2 had torsional stiffnesses and strengths equal to intact control bones. Ultimate failure torques of the proximal junctions of the CBG group and of both junctions of the ACS group were significantly less than the BMP-treated bones. Augmentation of the allograft host bone junctions with rhBMP-2 on an ACS gave results for all parameters measured that equaled or exceeded autogenous graft in this canine intercalary femoral defect model.

Cartilage substitutes: overview of basic science and treatment options

Articular cartilage defects that are symptomatic and refractory to nonoperative treatment represent a clinical management challenge. Although there have been important advances in stimulating intrinsic repair mechanisms, cartilage regeneration, and other substitution techniques, to date none has unlocked the understanding necessary to duplicate normal articular cartilage. The objectives of treatment of cartilage lesions are to obtain pain relief, reduce effusions and inflammation, restore function, reduce disability, and postpone or alleviate the need for prosthetic replacement. As the field of articular cartilage repair continues to evolve rapidly, the most appropriate treatment option for an individual patient should be based on the pathologic characteristics of the lesion and the patient's symptoms and expectations. The orthopaedic surgeon needs to be familiar with both the existing and the newly emerging cartilage treatment techniques in order to best educate patients and meet their expectations for long-term benefits.

Cellular interactions and signaling in cartilage development

The long bones of the developing skeleton, such as those of the limb, arise from the process of endochondral ossification, where cartilage serves as the initial anlage element and is later replaced by bone. One of the earliest events of embryonic limb development is cellular condensation, whereby pre-cartilage mesenchymal cells aggregate as a result of specific cell-cell interactions, a requisite step in the chondrogenic pathway. In this review an extensive examination of historical and recent literature pertaining to limb development and mesenchymal condensation has been undertaken. Topics reviewed include limb initiation and axial induction, mesenchymal condensation and its regulation by various adhesion molecules, and regulation of chondrocyte differentiation and limb patterning. The complexity of limb development is exemplified by the involvement of multiple growth factors and morphogens such as Wnts, transforming growth factor-beta and fibroblast growth factors, as well as condensation events mediated by both cell-cell (neural cadherin and neural cell adhesion molecule) and cell-matrix adhesion (fibronectin, proteoglycans and collagens), as well as numerous intracellular signaling pathways transduced by integrins, mitogen activated protein kinases, protein kinase C, lipid metabolites and cyclic adenosine monophosphate. Furthermore, information pertaining to limb patterning and the functional importance of Hox genes and various other signaling molecules such as radical fringe, engrailed, Sox-9, and the Hedgehog family is reviewed. The exquisite three-dimensional structure of the vertebrate limb represents the culmination of these highly orchestrated and strictly regulated events. Understanding the development of cartilage should provide insights into mechanisms underlying the biology of both normal and pathologic (e.g. osteoarthritis) adult cartilage.

Bone morphogenetic protein excipients: comparative observations on poloxamer

Clinicians await the availability of synthetic bioimplants that will replace the need for autogeneic bone grafts in bone reconstructive surgery. For more than a decade, researchers have evaluated delivery vehicles for the tissue morphogen bone morphogenetic protein. The object of this investigation was to measure induced bone development when bone morphogenetic protein was delivered by human tendon collagen, human demineralized bone matrix, hydroxyapatite, a composite of human tendon collagen and human demineralized bone matrix (tendon collagen + demineralized bone matrix), Poloxamer 407, and a composite of human demineralized bone matrix and Poloxamer 407. Sixty-three adult male Swiss Webster mice (Harlan Sprague-Dawley, Indianapolis, Ind.) received 126 implants. The animals were divided into seven groups of nine animals, depending on carrier (six carriers plus the positive control group) used. Each animal received a bone morphogenetic protein-enhanced carrier in one hindquarter muscle mass, with the contralateral leg being implanted with the carrier alone. Implants were evaluated by quantitative radiomorphometry validated by histologic methods. Radiographically, no significant differences were identified among any of the implants evaluated (p > 0.05). Histomorphometric analysis demonstrated that Poloxamer 407 was significantly (p < 0.05) better at delivering bone morphogenetic protein than the other carriers involved in this investigation. The new bone developed in a tubular or spherical shape. Interaction of endogenous and exogenous delivery systems seems to be essential for optimal transmission of bone morphogenetic protein. The importance of the excipient to deliver bone morphogenetic protein and develop a bone morphogenetic protein concentration gradient has been emphasized by other investigators and confirmed by our research on poloxamer. With further research on the physicochemical mechanisms of localization and transmission of bone morphogenetic protein, it may be possible to avoid hazardous operations with autogeneic bone.

Experimental spinal fusion using sintered bovine bone coated with type I collagen and recombinant human bone morphogenetic protein-2

STUDY DESIGN

Posterolateral lumbar transverse process fusion using recombinant human bone morphogenetic protein (rhBMP)-2 carried by sintered bovine bone and Type I collagen complex was compared with fusion achieved using autogeneous bone graft or sintered bovine bone alone.

OBJECTIVES

This study examined the efficacy of sintered bovine bone coated with Type I collagen as a carrier of rhBMP-2 for lumbar intertransverse process arthrodesis.

SUMMARY OF BACKGROUND DATA

Posterolateral intertransverse process arthrodesis using osteoinductive growth factors is performed experimentally in the lumbar spine. The previous studies revealed the efficacy of osteoinductive factors applied to carriers having no bony structures, such as collagen sheet or polylactic acid polymer, for the spinal fusion. However, in their studies, a large amount of osteoinductive proteins have been applied for the spinal fusion. We used the sintered bovine bone "True Bone Ceramics" (TBC; Koken Co., Tokyo, Japan) coated with type I collagen as the carrier. True Bone Ceramics is the only biomaterial possessing a natural trabecular structure and an organized crystal of bone minerals.

METHODS

Twenty-two adult rabbits underwent bilateral lumbar intertransverse process arthrodesis at L4-L5. The animals were divided into four groups and had materials implanted as follows: autologous bone group, grafted autologous corticocancellous bone harvested from the posterior iliac crest; implanted TBC group; TBC collagen group, implanted TBC coated with Type I collagen infiltrating into the porous space; and BMP group, implanted sintered bovine bone coated with Type I collagen infiltrated with 100 micrograms of rhBMP-2. Spinal fusion was evaluated by radiographic analysis, manual palpation, biomechanical testing, and histologic examination 6 weeks after surgery.

RESULTS

Two rabbits were killed because of infection and lumbar plexus palsy. Radiographs of the BMP group showed a homogeneous fusion mass at the intertransverse area, and stability was confirmed by dynamic radiographs at 3 and 6 weeks after surgery. In the BMP group, a bony mass in the intertransverse area was more prominent than in the other groups. The BMP group had a higher fusion rate based on manual palpation than the-other groups, and BMP fusions showed significantly higher tensile strength and stiffer fusion. The histologic findings in the BMP group demonstrated membranous bone and endochondral bone formations between the transverse process and the fusion mass. In the other groups, continuous trabecular bone formation was observed in the area surrounding the transverse process, but gaps between grafted fragments and less mature bone formation were present in the intertransverse area.

CONCLUSIONS

Sintered bovine bone coated with Type I collagen and rhBMP-2 resulted in a higher fusion rate than the autograft and can be used as a carrier for rhBMP-2 in spinal fusion.

Collagen integrin receptors regulate early osteoblast differentiation induced by BMP-2

Studies in several cell types indicate that the actions of integrin receptors for extracellular matrix and receptors for growth factors are synergistic in regulating cellular differentiation and function. We studied the roles of the alpha1beta1 and alpha2beta1 integrin collagen receptors in regulating the differentiation of 2T3 osteoblastic cells in response to bone morphogenetic protein (BMP)-2. The immortalized 2T3 cell line was established from the calvaria of mice transgenic for a BMP-2 promoter driving SV40 T-antigen. These cells require exogenous BMP-2, as well as ascorbic acid and beta-glycerolphosphate, for expression of a mature osteoblast phenotype and formation of a mineralized matrix. To determine how integrin receptors for collagen-I affect BMP-2 signaling, function-perturbing anti-rat alpha1 and/or alpha2 integrin subunit, or anti-type I collagen (Col-I), antibodies were added to human recombinant (hr)BMP-2-treated 2T3 cultures at confluence (C0) or at 4 or 8 days postconfluence (C4, C8). After 4 days of exposure to the antibodies, cultures were assayed for alkaline phosphatase (ALP) mRNA levels and enzyme activity and for cAMP production in response to parathyroid hormone. Addition of anti-collagen-I or both anti-integrin-alpha1 and -alpha2 antibodies to C0 cultures blocked expression of these early osteoblast markers by more than 90%, and also blocked mineralization (0.5-1.8% control) of these cells. In all cases, adding anti-alpha1 or anti-alpha2 antibodies separately produced partial effects, while their combined effect approached that of anti-collagen-I. When antibodies were added to more differentiated 2T3 cells, the inhibitory effects decreased. 2T3 cells carrying constitutively active BMP receptor (caBMPR-IB) showed elevated ALP activity without hrBMP-2; this constitutive activity was also suppressed by alpha1 and alpha2 integrin antibodies and by anti-Col-I antibody. Together, our data suggest that a signal(s) from collagen integrin receptors regulates the response to BMP downstream of BMPR-IB and upstream of the regulation of ALP mRNA and other early markers of osteoblast differentiation.

Some basic factors essential to autogeneic nonvascularized onlay bone grafting to the craniofacial skeleton

The aim of this review is to provide a background on the experiences gained experimentally with autogeneic nonvascularized onlay bone transplantation, survey the most essential information in the medical literature, and to present modern trends and future expectations in bone graft science.

Chondrogenic differentiation of murine C3H10T1/2 multipotential mesenchymal cells: I. Stimulation by bone morphogenetic protein-2 in high-density micromass cultures

Chondrogenic differentiation of mesenchymal cells is generally thought to be initiated by the inductive action of specific growth factors and depends on intimate cell-cell interactions. In this study, we have used multipotential murine C3H10T1/2 cells to analyze the effect and mechanism of action of bone morphogenetic protein 2 (BMP-2) on chondrogenesis. C3H10T1/2 cells have been previously shown to undergo multiple differentiation pathways. While chondrogenesis, osteogenesis, myogenesis and adipogenesis have been observed, chondrocytes appear significantly less frequently than the other cell types, and the appearance of chondrocytes exclusive of the other cell types has not been observed. We report here that the appearance of chondrocytes in C3H10T1/2 cells is markedly enhanced as a result of culture under conditions favorable for chondrogenesis, i.e. plating as high-density micromass and treatment with BMP-2. Such cultures contain chondrocyte-like cells, elaborate an Alcian blue stained cartilage-like matrix, express link protein and type II collagen, both cartilage matrix markers, and show increased [35S]sulfate incorporation. The appearance of Alcian blue positive material and increased sulfate incorporation are dependent on the dose of BMP-2, culture time, and cell plating density of the micromass cultures. Differentiation of cells within the micromass was specific to the chondrogenic lineage, as alkaline phosphatase staining revealed only faint staining in the micromass at the highest BMP-2 concentration. The importance of enhanced cell-cell interaction in the chondroinductive effects of BMP-2 on high-density C3H10T1/2 cultures was further implicated by the additional promotion of chondrogenesis in the presence of the polycationic compound, poly-L-lysine, which has been previously reported to enhance cellular interactions and chondrogenesis in embryonic limb mesenchymal cells. Taken together, these findings suggest that chondrogenesis in C3H10T1/2 cells is inducible by BMP-2 and requires cell-cell interaction.

Effect of recombinant human bone morphogenetic protein-2 on fracture healing in a goat tibial fracture model

Bone morphogenetic proteins (BMPs) are considered to have important regulatory roles in skeletal embryogenesis and bone healing. Recombinant human BMPs (rhBMPs) have been shown to heal critical size defects and promote spinal fusion. We studied the effects of rhBMP-2 in an absorbable collagen sponge (ACS) on bone healing in a large animal tibial fracture model. Bilateral closed tibial fractures were created in 16 skeletally mature goats and reduced and stabilized using external fixation. In each animal, one tibia received the study device (0.86 mg of rhBMP-2/ACS or buffer/ACS), and the contralateral fracture served as control. The device was implanted as a folded onlay or wrapped circumferentially around the fracture. Six weeks following fracture, the animals were sacrificed and the tibiae harvested for torsional testing and histomorphologic evaluation. Radiographs indicated increased callus at 3 weeks in the rhBMP-2/ACS treated tibiae. At 6 weeks, the rhBMP-2/ACS wrapped fractures had superior radiographic healing scores compared with buffer groups and controls. The rhBMP-2/ACS produced a significant increase in torsional toughness (p = 0.02), and trends of increased torsional strength and stiffness (p = 0.09) compared with fracture controls. The device placed in a wrapped fashion around the fracture produced significantly tougher callus (p = 0.02) compared with the onlay application. Total callus new bone volume was significantly increased (p = 0.02) in the rhBMP-2/ACS fractures compared with buffer groups and controls regardless of the method of device application. The rhBMP-2/ACS did not alter the timing of onset of periosteal/endosteal callus formation compared with controls. Neither the mineral apposition rates nor bone formation rates were affected by rhBMP-2/ACS treatment. The increased callus volume associated with rhBMP-2 treatment produced only moderate increases in strength and stiffness.

Expression of BMP-4 mRNA during distraction osteogenesis in rabbits

We characterized the presence and localization of bone morphogenetic protein 4 (BMP-4) mRNA in the regenerating tissues produced by distraction osteogenesis following tibial osteotomy in the rabbit. The findings are consistent with previous reports on the localization of BMP-4 mRNA expression during fracture repair. The BMP-4 gene is expressed by less differentiated osteoprogenitor cells (fibroblastic mesenchymal cells and preosteoblasts), and not by fully differentiated osteoblasts. BMP-4 gene expression is localized in callus-forming tissue (muscle, periosteum) during callus formation. Our observations suggest that the BMP-4 gene product is one of the local contributing factors in regulating bone and cartilage formation in distraction osteogenesis.

The effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the healing of full-thickness defects of articular cartilage

Articular cartilage has a limited capacity for repair. We investigated the effect of rhBMP-2 (recombinant human bone morphogenetic protein-2) on the healing of full-thickness osteochondral defects in adult New Zealand White rabbits. A single defect, three millimeters wide by three millimeters deep, was created in the trochlear groove of the right femur in eighty-nine rabbits. The defect was either left empty, filled with a plain collagen sponge, or filled with a collagen sponge impregnated with five micrograms of rhBMP-2. The animals were killed at four, eight, or twenty-four weeks, and the repair tissue was examined histologically and evaluated with use of a grading scale. The defects also were examined immunohistochemically for the presence of type-II collagen at four and eight weeks. The rate of bone repair was evaluated with fluorescent labeling of bone at two and four weeks and with use of fluorescence microscopy at eight weeks. Treatment with rhBMP-2 greatly accelerated the formation of new subchondral bone and improved the histological appearance of the overlying articular surface. At twenty-four weeks, the thickness of the repair cartilage was 70 per cent that of the normal adjacent cartilage and a new tidemark usually had formed between the repair cartilage and the underlying subchondral bone. The average total scores on the histological grading scale were significantly better (p < 0.01) for the defects treated with rhBMP-2 than for the untreated defects (those left empty or filled with a plain collagen sponge) at all time-points. Immunostaining with an antibody against type-II collagen showed the diffuse presence of this cartilage-specific collagen throughout the repair cartilage in the treated defects. The untreated defects demonstrated minimum staining with this antibody.

Healing of experimentally created defects: a review

Within cranio-maxillofacial surgery and orthopedic surgery a bone graft or a bone substitute is required to recontour or assist bony healing in repair of osseous congenital deformities, or in repair of deformity due to trauma or to surgical excision after elimination of osseous disease processes exceeding a certain size. An autogenous bone graft is the optimal material of choice, however its use is problematic due to donor site morbidity, sparse amounts and uncontrolled resorption. Immunological responses and risk of viral contamination of allogenous and xenogenous bone materials make the use of these materials questionable. Healing and degradation of alloplastic materials are inconsistent with subsequent restricted use. The principle of guided tissue regeneration excluding soft tissue cells from a certain area is not alone sufficient to insure complete bony healing. Recombinant bone morphogenetic proteins have with success been added as adjuncts to already known biomaterials. In the future, inductive materials together with a suitable carrier and a biodegradable membrane may be the choice of bone substitute used within cranio-maxillofacial and orthopaedic surgery.

Immunolocalization and expression of bone morphogenetic proteins 2 and 4 in fracture healing

Recently, it has become increasingly evident that fracture healing involves a complex interaction of many local and systemic regulatory factors. The roles of some of these growth factors have been described; however, little is understood about the presence of the bone morphogenetic proteins in fracture repair, despite the fact that they are the most potent osteoinductive proteins known. This study defines and characterizes the physiologic presence, localization, and chronology of the bone morphogenetic proteins in fracture healing with an established rat fracture healing model. With use of a recently developed monoclonal antibody against bone morphogenetic proteins 2 and 4 developed with standard avidin-biotin complex/immunoperoxidase protocols, frozen undecalcified fracture calluses were analyzed semiquantitatively for the percentage of various types of fracture cells staining positively. During the early stages of fracture healing, only a minimum number of primitive cells stained positively in the fracture callus. As the process of endochondral ossification proceeded, the presence of bone morphogenetic proteins 2 and 4 increased dramatically, especially in the primitive mesenchymal and chondrocytic cells. While the cartilaginous component of the callus matured with a concomitant decrease in the number of primitive cells, there was a concomitant decrease in both the intensity and the number of positively staining cells. As osteoblasts started to lay down woven bone on the chondroid matrix, these osteoblastic cells exhibited strong positive staining. The intensity of this staining decreased, however, as lamellar bone replaced the primitive woven bone. A similar observation was noted for the areas of the callus undergoing intramembranous ossification. Initially, within several days after the fracture, periosteal cells and osteoblasts exhibited intense staining for bone morphogenetic proteins 2 and 4. As the woven bone was replaced with mature lamellar bone, this staining decreased. These data, and the awareness of the strong osteoinductive capacities of bone morphogenetic protein, suggest that bone morphogenetic proteins 2 and 4 are important regulators of cell differentiation during fracture repair.

Bone substitute with osteoinductive biomaterials--current and future clinical applications

In craniomaxillofacial surgery, possible indications for the use of osteo-inductive biomaterials are interposition in intraosseous defects, contour augmentation, and reconstruction of segmental defects. The experimental results in the field of bone morphogenetic protein (BMP) research within the last few years have shown that it is possible to combine osteoinductive proteins with suitable carrier materials to obtain new composite osteoinductive biomaterials. These carrier materials function as slow-delivery systems for BMP. By combination of BMP with different carrier materials such as various types of calcium phosphate ceramics, collagen or inactive collagenous bone matrix, and other organic and inorganic carriers, the biomaterial can be adapted to clinical demands in a wide range. In several experimental animal studies, we investigated nine different calcium phosphate ceramics and inactive rat bone matrix for their use as BMP carrier. All materials tested seem to be suitable carriers for BMP. The first clinical applications are discussed.

Transforming growth factor-beta and bone morphogenetic protein-2 act by distinct mechanisms to promote chick limb cartilage differentiation in vitro

A number of studies suggest that several members of the transforming growth factor-beta (TGF-beta) family of peptide growth factors may be involved in the regulation of cartilage differentiation. It has been previously reported that TGF-beta 1 and TGF-beta 2 promote the chondrogenic differentiation of chick limb mesenchymal cells in high density micromass cultures (Kulyk et al. [1989a] Dev. Biol. 135:424-430). In this study we report that chick limb mesenchymal cells express mRNA for chicken TGF-beta 1, TGF-beta 2, and TGF-beta 3 during cartilage differentiation in vitro. In addition, the time course of their expression during cartilage differentiation is consistent with their playing a role in the initiation of this differentiation process. We also report that two members of the TGF-beta family, TGF-beta 3 and bone morphogenetic protein-2 (BMP-2), are capable of promoting the accumulation of cartilage extracellular matrix molecules by differentiating chick limb mesenchymal cells in micromass culture. Significant differences, however, were noted between the specific effects on matrix production elicited by these two growth factors which suggest that they may be acting by distinct mechanisms to regulate cartilage matrix production. TGF-beta appears to be most effective on cells which have not yet undergone cell condensation, a critical event in early cartilage differentiation, whereas BMP-2 is most effective after cells have condensed or differentiated. These observations suggest that TGF-beta 3 and BMP-2 may be acting in a sequential manner to regulate chick limb mesenchymal cells through the different stages of cartilage differentiation.

Expression of bone morphogenetic proteins in human osteosarcoma. Immunohistochemical detection with monoclonal antibody

BACKGROUND

Bone morphogenetic proteins (BMP) induce ectopic bone formation in vivo and may play a role in normal bone development. In addition, bone morphogenetic activity, as measured in a bone-forming assay in immunodeficient, athymic nu/nu mice, is present in a proportion of osteosarcomas; this activity, which may be mediated by BMP, is correlated with a poor prognosis.

METHODS

The development of a monoclonal antibody against recombinant human BMP-2, AbH3b2/17, has allowed immunohistochemical localization of BMP in tumor tissues. Cryostat sections of osteosarcomas (21 tumor samples), chondrosarcomas (5 samples), and Ewing's sarcomas of bone (5 samples) were examined with AbH3b2/17 using the avidin-biotin-immunoperoxidase method.

RESULTS

The authors found AbH3b2/17 immunoreactivity in 12 of the 21 osteosarcoma samples (57% sensitivity) obtained from 20 patients. For one patient, samples of the primary lesion and a subsequent metastasis were tested, and only the latter showed AbH3b2/17 immunoreactivity. The chondrosarcomas and Ewing's sarcomas examined showed no immunoreactivity. In antigen-positive osteosarcomas, AbH3b2/17 immunostaining was localized predominantly in the cytoplasm of tumor cells. Moreover, the proportion of AbH3b2/17-reactive cells varied among osteosarcomas with disparate histologic features.

CONCLUSIONS

The authors identified a rapid and widely applicable method for detecting BMP expression in intact tissues, which may complement and enhance the bone-forming assay in nu/nu mice as a prognostic procedure in osteosarcomas.

Osteoinductive, morphologic, and biomechanical properties of autolyzed, antigen-extracted, allogeneic human bone

Autolyzed, antigen-extracted, allogeneic (AAA) bone was prepared from human cortical bone and its morphologic, biomechanical, and osteoinductive properties were compared with untreated (frozen) as well as lyophilized human bone. Scanning electron microscopy revealed removal of inorganic calcium phosphates and persistence of shrunken collagen fibrils on the surface of AAA bone matrix. Biomechanical testing of differently prepared bone samples showed that lyophilization increased both the modulus of elasticity (P < .00001) and the compressive strength (P < .00001). Depending on the depth of decalcification in the preparation of AAA bone, both measured values decreased in rehydrated AAA bone compared with untreated bone (P < .00001). Completely demineralized and rehydrated AAA bone was soft, flexible, and showed very little compressive strength. Differences in biomechanical behavior between samples drilled longitudinally or perpendicularly to the diaphyseal bone axis were observed. Xenogeneic human bone samples were implanted in muscle pouches of Sprague-Dawley rats for 6 weeks. AAA bone implants showed chondrogenesis and osteogenesis in 50% of the cases, while untreated or lyophilized bone implants induced no new cartilage or bone formation. As decalcification exposed xenogeneic organic matrix components, AAA bone implants provoked the highest inflammatory reaction. When AAA bone samples were implanted in immunosuppressed rats, the inflammatory reaction was suppressed and 94% of the implants showed endochondral bone formation. The chondroinductivity of the bone samples also was tested in vitro using neonatal rat muscle tissue to avoid interference with inflammatory cells and secreted cytokines. In this assay, 68% of AAA bone samples induced chondroneogenesis, while untreated as well as lyophilized bone samples failed to induce any cartilage formation. The results clearly demonstrate that AAA bone has osteoinductive properties. Biomechanical stability of AAA bone implants depends on the degree of demineralization. Thus, they can be prepared in an appropriate manner for different indications in oral and maxillofacial surgery.

Initiation of bone regeneration in adult baboons by osteogenin, a bone morphogenetic protein

Osteogenin, and related bone morphogenetic proteins, induce endochondral bone differentiation through a cascade of events which include formation of cartilage, hypertrophy and calcification of the cartilage, vascular invasion, differentiation of osteoblasts, and formation of bone. These events have been studied in a postnatal model of bone development in rodents. Information concerning the morphogenetic potential of osteogenin in primates is a prerequisite for potential clinical application in man. The efficacy of allogeneic osteogenin in primates was investigated in both extraskeletal and skeletal sites in 19-Chacma baboons (Papio ursinus). Osteogenin was isolated from demineralized baboon bone matrix and purified by chromatography on heparin-Sepharose, hydroxyapatite, and Sephacryl S-200. Protein fractions with a molecular mass range of 26-42 kDa induced cartilage and bone differentiation in the subcutaneous space of rats. Final purification to homogeneity was obtained by electroendosmotic elution from a preparative sodium dodecyl sulphate (SDS) polyacrylamide gel, resulting in a single band on a SDS-polyacrylamide gel with an apparent molecular mass of 30-34 kDa, with biological activity in rats. The osteoinductive potential of osteogenin in primates was tested first in intramuscular sites in baboons and found to be active. The bone regeneration potential was investigated in nonhealing calvarial defects surgically prepared in adult male baboons. Baboon osteogenin induced complete regeneration of the cranial wound. These findings in adult primates establish a primary role for osteogenin in initiation and promotion of osteogenesis, and imply a potential therapeutic application based on cell biology of extracellular matrix-cell interactions.

The bone morphogenetic protein family and osteogenesis

The BMPs (bone morphogenetic proteins) are a group of related proteins originally identified by their presence in bone-inductive extracts of demineralized bone. By molecular cloning, at least six related members of this family have been identified and are called BMP-2 through BMP-7. These molecules are part of the TGF-beta superfamily, based on primary amino acid sequence homology, including the absolute conservation of seven cysteine residues between the TGF-betas and the BMPs. The BMPs can be divided into subgroups with BMP-2 and BMP-4 being 92% identical, and BMP-5, BMP-6, and BMP-7 being an average of about 90% identical. To examine the individual activities of these molecules, we are producing each BMP in a mammalian expression system. In this system, each BMP is synthesized as a precursor peptide, which is glycosylated, processed to the mature peptide, and secreted as a homodimer. These reagents have been used to demonstrate that single molecules, such as BMP-2, are capable of inducing the formation of new cartilage and bone when implanted ectopically in a rodent assay system. Whether each of the BMPs possesses the same inductive activities in an animal is the subject of ongoing research. Based on the chondrogenic and osteogenic abilities of the BMPs in the adult animal, the expression of the mRNAs for the BMPs has been examined in the development of the embryonic skeleton by in situ hybridization. These studies demonstrate that the BMP mRNAs are spatially and temporally expressed appropriately for the proteins involved in the induction and development of cartilage and bone in the embryonic limb bud.(ABSTRACT TRUNCATED AT 250 WORDS)

Primate dentine extracellular matrix induces bone differentiation in heterotopic sites of the baboon (Papio ursinus)

In rodents, demineralized dentine matrix induces local differentiation of endochondral bone. This study investigated the osteoinductive potential of primate dentine matrices when implanted extraskeletally in allogeneic recipients. Demineralized dentine cylinders prepared from adult baboon incisors and demineralized dentine matrix pulverized to a particle size of 74-420 microns were implanted into the rectus abdominis of 4 subadult male baboons (Papio ursinus). Specimens were harvested 30 and 90 d after implantation. Histological analysis on serial sections showed bone differentiation in demineralized dentine cylinders after partial resorption of the external demineralized layer, and in resorption lacunae and excavation chambers within the matrix. Implants of demineralized dentine matrix of 74-420 microns particle size showed no osteoinductive activity as determined biochemically (alkaline phosphatase activity) and histologically. The demonstration of bone induction by primate dentine prepared from fully erupted tooth matrix suggests that putative osteogenic proteins may be conserved after dentinogenesis and embryonic tooth development, and may play a role during healing after surface demineralization of exposed root surfaces during regenerative procedures in humans.

Growth and morphogenetic factors in bone induction: role of osteogenin and related bone morphogenetic proteins in craniofacial and periodontal bone repair

Bone has considerable potential for repair as illustrated by the phenomenon of fracture healing. Repair and regeneration of bone recapitulate the sequential stages of development. It is well known that demineralized bone matrix has the potential to induce new bone formation locally at a heterotopic site of implantation. The sequential development of bone is reminiscent of endochondral bone differentiation during bone development. The collagenous matrix-induced bone formation is a prototype model for matrix-cell interactions in vivo. The developmental cascade includes migration of progenitor cells by chemotaxis, attachment of cells through fibronectin, proliferation of mesenchymal cells, and differentiation of bone. The bone inductive protein, osteogenin, was isolated by heparin affinity chromatography. Osteogenin initiates new bone formation and is promoted by other growth factors. Recently, the genes for osteogenin and related bone morphogenetic proteins were cloned and expressed. Recombinant osteogenin is osteogenic in vivo. The future prospects for bone induction are bright, and this is an exciting frontier with applications in oral and orthopaedic surgery.

Effects of localized application of transforming growth factor beta 1 on developing chick limbs

The effects of exogenous transforming growth factor beta (TGF-beta) on chick limb development in vivo were studied by implanting carriers of TGF-beta 1 into developing wing buds. Agarose beads were soaked in solutions containing TGF-beta 1 and implanted into wing buds at stages 18 to 27. Localized application of TGF-beta 1 to distal regions of the wing bud caused specific skeletal elements in the limb to be reduced or absent. The particular proximal-distal limb element affected depended on the stage at which the bead was implanted. Position of the bead in the anterior-posterior axis also influenced the pattern of affected structures. Experiments in which TGF-beta 1 beads were implanted and then removed at 24- and 48-hr intervals indicate that there are specific periods during which a skeletal element appears to be sensitive to the effects of exogenous TGF-beta 1. In a few cases, beads placed in proximal positions in later staged limbs resulted in formation of ectopic cartilage near the bead. These results suggest that exposure to exogenous TGF-beta 1 in vivo influences the development of skeletal elements in the chick limb in a stage- and position-dependent manner.