OP-1/BMP-7 in cartilage repair

Three years ago we published a book chapter on the role of bone morphogenetic proteins (BMPs) in cartilage repair. Since that time our understanding of the function of osteogenic protein-1 (OP-1) or BMP-7 in cartilage homeostasis and repair has substantially improved and therefore we decided to devote a current review solely to this BMP. Here we summarise the information accumulated on OP-1 from in vitro and ex vivo studies with cartilage cells and tissues as well as from in vivo studies of cartilage repair in various animal models. The primary focus is on articular chondrocytes and cartilage, but data will also be presented on nonarticular cartilage, particularly from the intervertebral disc. The data show that OP-1 is a unique growth factor which, unlike other members of the same BMP family, exhibits in addition to its strong pro-anabolic activity very prominent anti-catabolic properties. Animal studies have demonstrated that OP-1 has the ability to repair cartilage in vivo in various models of articular cartilage degradation, including focal osteochondral and chondral defects and osteoarthritis, as well as models of degeneration in intervertebral disc cartilage. Together our findings indicate a significant promise for OP-1 as therapeutic in cartilage repair.     

BMPs and the muscle–bone connection

Muscle and bone are two intimately connected tissues. A coordinated interplay between these tissues at mechanical levels is required for their development, function and ageing. Evidence is emerging that several genes and molecular pathways exert a pleiotropic effect on both muscle and bone. Bone morphogenetic proteins (BMPs) are secreted signal factors belonging to the transforming growth factor β (TGFβ) superfamily. BMPs have an essential role during bone and cartilage formation and maintenance. Recently, we and others have demonstrated that the BMP pathway also has a role in controlling adult skeletal muscle mass. Thus, BMPs become crucial regulators of both bone and muscle formation and homeostasis. In this review we will discuss the signalling downstream BMP and its role in muscle–bone interaction.This article is part of a Special Issue entitled “Muscle Bone Interactions”.     

Absence of Correlation Between BMP-4 Polymorphism and Postmenopausal Osteoporosis in Italian Women

Several studies have demonstrated that bone has the power of regeneration and repair. BMPs (bone morphogenetic proteins) are involved in the determination of osteoblast phenotype and bone turnover, therefore genes coding for these proteins, like BMP-4, could be considered potential candidate genes for osteoporosis. We investigated the association of BMP-4 gene polymorphism with osteoporosis in a cohort of 72 osteoporotic, postmenopausal women and 82 unrelated controls. We failed to detect any significant association between this genetic marker and the disease. Received: 9 August 1999 / Accepted: 3 February 2000     

Distinct roles of bone morphogenetic proteins in osteogenic differentiation of mesenchymal stem cells.

Efficacious bone regeneration could revolutionize the clinical management of many bone and musculoskeletal disorders. Bone morphogenetic proteins (BMPs) can regulate the differentiation of mesenchymal stem cells into cartilage, bone, tendon/ligament, and fat lineages. Early data documented the osteogenic potential of rhBMP2 and rhBMP7/OP-1. However, prior to this work that summarized several of our recent studies, no comprehensive analysis had been undertaken to characterize relative osteogenic activity of all BMPs. Using recombinant adenoviruses expressing 14 BMPs, we have demonstrated that, besides BMP2 and BMP7, BMP6 and BMP9 exhibit the highest osteogenic activity both in vitro and in vivo. We further demonstrated that several BMPs may exert synergistic effect on osteogenic differentiation, and that osteogenic BMPs produce a distinct set of molecular fingerprints during osteogenic differentiation. The reported work should expand our current understanding of BMP functions during osteogenic differentiation. It is conceivable that osteogenic BMPs (i.e., BMP2, 4, 6, 7, and 9) may be used to formulate synergistic pairs among themselves and/or with other less osteogenic BMPs for efficacious bone regeneration in clinical settings.     

Mechanical stimulation alters tissue differentiation and molecular expression during bone healing

Further understanding of how mechanical cues modulate skeletal tissue differentiation can identify potential means of enhancing repair following injury or disease. Prior studies examined the effects of mechanical loading on osteogenesis, chondrogenesis, and fibrogenesis in an effort to enhance bony union. However, exploring how mechanical stimuli can divert the bone healing process towards formation of other mesenchymal tissues, as an endpoint, may elucidate new avenues for repair and regeneration of tissues such as cartilage and fibrous tissue. This study investigated the use of mechanical stimulation to promote cartilage rather than bone formation within an osteotomy. Our overall goal was to define skeletal tissue distribution and molecular expression patterns induced by the stimulation. Retired breeder Sprague‐Dawley rats (n = 85) underwent production of a mid‐diaphyseal, transverse femoral osteotomy followed by external fixation. Beginning on postoperative day 10 and continuing for 1, 2, or 4 weeks, a cyclic bending motion (+35°/?25° at 1 Hz) was applied in the sagittal plane for 15 min/day for 5 consecutive days/week. Control animals experienced continuous rigid fixation. Histological and molecular analyses indicated that stimulation substantially altered normal bone healing. Stimulated specimens exhibited an increase in cartilage volume over time, while control specimens demonstrated bony bridging. Stimulation induced upregulation of cartilage‐related genes (COL2A1 and COL10A1) and downregulation of bone morphogenetic proteins (BMPs) ‐4, ‐6 and ‐7. However, BMP‐3 was upregulated with stimulation. These findings illustrate that mechanical cues can selectively modulate osteogenesis and chondrogenesis in vivo, and suggest a potential basis for treatment regimens for injured or diseased cartilaginous tissues. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

A new biotechnology for articular cartilage repair: subchondral implantation of a composite of interconnected porous hydroxyapatite, synthetic polymer (PLA-PEG), and bone morphogenetic protein-2 (rhBMP-2)

OBJECTIVE: Articular cartilage repair remains a major obstacle in tissue engineering. We recently developed a novel tool for articular cartilage repair, consisting of a triple composite of an interconnected porous hydroxyapatite (IP-CHA), recombinant human bone morphogenetic protein-2 (rhBMP-2), and a synthetic biodegradable polymer [poly-d,l-lactic acid/polyethylene glycol (PLA-PEG)] as a carrier for rhBMP-2. In the present study, we evaluated the capacity of the triple composite to induce the regeneration of articular cartilage. METHODS: Full-thickness cartilage defects were created in the trochlear groove of 52 New Zealand White rabbits. Sixteen defects were filled with the bone morphogenetic protein (BMP)/PLA-PEG/IP-CHA composite (group I), 12 with PLA-PEG/IP-CHA (group II), 12 with IP-CHA alone (group III), and 12 were left empty (group IV). The animals were killed 1, 3, and 6 weeks after surgery, and the gross appearance of the defect sites was assessed. The harvested tissues were examined radiographically and histologically. RESULTS: One week after implantation with the BMP/PLA-PEG/IP-CHA composite (group I), vigorous repair had occurred in the subchondral defect. It contained an agglomeration of mesenchymal cells which had migrated from the surrounding bone marrow either directly, or indirectly via the interconnecting pores of the IP-CHA scaffold. At 6 weeks, these defects were completely repaired. The regenerated cartilage manifested a hyaline-like appearance, with a mature matrix and a columnar organization of chondrocytes. CONCLUSIONS: The triple composite of rhBMP-2, PLA-PEG, and IP-CHA promotes the repair of full-thickness articular cartilage defects within as short a period as 3 weeks in the rabbit model. Hence, this novel cell-free implant biotechnology could mark a new development in the field of articular cartilage repair.     

Current and future clinical applications of bone morphogenetic proteins in orthopaedic trauma surgery

Forty years after the discovery by Marshal R. Urist of a substance in bone matrix that has inductive properties for the development of bone and cartilage, there are now 15 individual human bone morphogenetic proteins (BMPs) that possess varying degrees of inductive activities. Two of these, BMP-2 and BMP-7, have become the subject of extensive research aimed at developing therapeutic strategies for the restoration and treatment of skeletal conditions. This has led to three different therapeutic preparations, each for a distinct clinical application. Non-union, open tibial fractures and spinal fusions are the three conditions for which there is clinical approval for use of BMPs. This article reviews the evidence supporting the therapeutic applications of BMPs as they are presently available and suggests future applications based on current research. Among the future directions discussed are percutaneous injections, protein carriers, advances in gene transfer technology and the use of BMPs to engineer the regeneration of skeletal parts.     

The family of bone morphogenetic proteins

The family of bone morphogenetic proteins. Bone morphogenetic proteins (BMPs) are secreted signaling molecules belonging to the transforming growth factor-beta (TGF-beta) superfamily of growth factors. The first BMPs were originally identified by their ability to induce ectopic bone formation when implanted under the skin of rodents. In this ectopic overexpression assay, there was a recapitulation of all the events occurring during skeletogenesis. This latter aspect indicated that these molecules could play important roles during development. More than 30 BMPs have been identified to date. The study of their expression pattern as well as the analysis of spontaneously mutated or genetically depleted mice have demonstrated a much broader range of function. These activities are mainly localized at sites of epithelial-mesenchymal interactions, including but not restricted to the skeleton. This review presents our current knowledge about the functions of BMPs during skeleton development as well as in many other biologic processes.     

骨形态发生蛋白在颅颌面外科的应用及展望

面部骨骼发育畸形、骨缺损、骨不连等的修复重建是颅面外科的主要内容。目前,颅面部骨骼修复重建治疗的手段不外乎手术截骨重排结合骨修复材料植入。随着细胞生物学研究的不断深入,及对颅面部骨骼生长发育的深入认识,越来越多的研究表明生长因子在骨骼修复重建中广泛参与骨骼组织再生重建的局部调节,其中骨形态发生蛋白家族(Bone Morphogenetic Proteins,BMPs)是研究热点之一。本文对BMPs概况、促成骨作用机制、动物实验、初步临床应用等方面进行综述,为今后BMPs在颅面骨骼修复重建领域的进一步研究和应用提供一定的理论依据。     

Long-term effects of bone morphogenetic protein- based treatments in humans

Bone morphogenetic proteins (BMPs) are low-molecular-weight proteins of the transforming growth factor-beta (TGF-β) superfamily. In recent years, these growth and differentiation factors have been extensively researched for their multifunctional properties ranging from embryonic development to postnatal homeostasis. The defining ability of BMPs is the role they play in skeletal development and maintenance, especially the powerful osteoinductive activity for which these proteins are currently sought after. There are over 20 BMPs that have been discovered, with BMP-2 and BMP-7 currently being the only proteins of the group that are approved by the US Food and Drug Administration for clinical use as an autograft substitute for lumbar spinal interbody fusion procedures and for open tibial fractures with intramedullary nail fixation. BMP-2 has also been approved for use in dental bone grafting indications. However, a significant amount of off-label usage of these proteins has been reported, which has led to an industry approaching a billion dollars annually. In this review, we examine the long-term effects of BMPs as evidenced from in vitro, preclinical, and clinical studies.     

Growth factors in bone

Bone contains several growth factors, including bone morphogenetic proteins (BMPs), transforming growth factor beta (TGF-beta), insulin-like growth factors I and II (IGF-I and IGF-II), platelet derived growth factor (PDGF) and basic and acidic fibroblast growth factor (bFGF and aFGF). Spatial and temporal variations in the expression and secretion of the various growth factors have been demonstrated in osteoblastic cultures and in various experimental and clinical in vivo models, including fracture healing in humans. Local application of various growth factors influences proliferation, differentiation and protein synthesis in osteoblastic cultures and bone formation in different animal models, including experimental fractures and skeletal defects. The BMPs are the only growth factors known to provoke bone formation heterotopically by making undifferentiated mesenchymal cells differentiate into osteoblasts (osteoinduction). BMPs and other growth factors, soon to become commercially available for clinical use, need a delivery system for their sustained release, as the factors are otherwise rapidly absorbed. Some existing systems inhibit bone formation by inducing chronic inflammation or physically by unresorbed carrier obstructing bone formation. New delivery systems are being investigated.     

Bone morphogenetic proteins and bone morphogenetic protein gene therapy in neurological surgery: a review

OBJECTIVE: To review the uses of bone morphogenetic proteins (BMPs) and BMP gene therapy for the treatment of neurosurgical disorders. METHODS: Literature review. RESULTS: BMPs are members of the transforming growth factor beta superfamily, and they play an important role in the growth and development of numerous tissues, including bone, brain, and spinal cord. Although the majority of previous studies have focused on the regulatory functions of BMPs in the normal growth and differentiation of the skeletal system, BMPs also seem to be exquisitely involved in the regulation of cellular proliferation, survival, differentiation, apoptosis, and lineage commitment in the central nervous system. When specific BMPs are delivered on biological matrices, they have the capacity to induce bone, cartilage, ligament, and tendon at both heterotopic and orthotopic sites, suggesting that they may play a major role in the future treatment of spinal and craniofacial pathology. For example, recent studies have clearly demonstrated the usefulness of BMPs and BMP gene therapy for the induction of spinal arthrodesis in several animal models. In addition, several BMPs have been shown to have a neuroprotective effect in animal models of head injury, cerebral ischemia, and Parkinson's disease and may therefore have direct clinical applications for the treatment of central nervous system disorders. CONCLUSION: As the physiological activity of BMPs in the development and pathology of the central nervous system and spine are more fully elucidated, BMP therapeutics and gene therapy will probably have numerous applications in neurological surgery.     

Human autologous culture expanded bone marrow mesenchymal cell transplantation for repair of cartilage defects in osteoarthritic knees

OBJECTIVE: There is no widely accepted method to repair articular cartilage defects. Bone marrow mesenchymal cells have the potential to differentiate into bone, cartilage, fat and muscle. Bone marrow mesenchymal cell transplantation is easy to use clinically because cells can be easily obtained and can be multiplied without losing their capacity of differentiation. The objective of this study was to apply these cell transplantations to repair human articular cartilage defects in osteoarthritic knee joints. DESIGN: Twenty-four knees of 24 patients with knee osteoarthritis (OA) who underwent a high tibial osteotomy comprised the study group. Adherent cells in bone marrow aspirates were culture expanded, embedded in collagen gel, transplanted into the articular cartilage defect in the medial femoral condyle and covered with autologous periosteum at the time of 12 high tibial osteotomies. The other 12 subjects served as cell-free controls. RESULTS: In the cell-transplanted group, as early as 6.3 weeks after transplantation the defects were covered with white to pink soft tissue, in which metachromasia was partially observed. Forty-two weeks after transplantation, the defects were covered with white soft tissue, in which metachromasia was observed in almost all areas of the sampled tissue and hyaline cartilage-like tissue was partially observed. Although the clinical improvement was not significantly different, the arthroscopic and histological grading score was better in the cell-transplanted group than in the cell-free control group. CONCLUSIONS: This procedure highlights the availability of autologous culture expanded bone marrow mesenchymal cell transplantation for the repair of articular cartilage defects in humans.     

Bone morphogenetic protein 9 is a potent anabolic factor for juvenile bovine cartilage, but not adult cartilage.

Members of the bone morphogenetic protein (BMP) group of the TGF-beta superfamily have been shown to enhance matrix synthesis and maintain cartilage phenotype in long-term culture. These proteins have also been shown to augment cartilage repair in vivo, and may be of potential therapeutic benefit in the treatment of damaged articular cartilage. The present study was undertaken to examine the effects of BMP-9 on the metabolism of juvenile and adult bovine cartilage in vitro, and to compare the effects to those produced by two previously characterized BMPs: BMP-2 and 13 (CDMP-2). BMP-9 lead to a 7-8-fold stimulation of proteoglycan synthesis at the highest concentration tested, and a 6.4-fold stimulation of collagen synthesis at a concentration of 50 ng/mL in juvenile cartilage. BMP-2 also lead to a 7-8-fold increase in proteoglycan synthesis at the highest concentration tested, and was able to induce collagen synthesis 6.4-fold, but at a concentration of 1000 ng/mL. Proteoglycans isolated from BMP-9 treated cartilage exhibited an increased hydrodynamic size possibly due to increased glycosaminoglycan substitution or decreased C-terminal proteolysis. Consistent with the idea of limited C-terminal proteolysis, BMP-9 treatment lead to a significant reduction in the turnover rate of proteoglycans in juvenile explants. Interestingly, all three BMPs were unable to induce a measurable anabolic response in adult cartilage explants.     

Use of bone morphogenetic proteins in traumatology

An estimated 5–10% of all fractures show impaired healing, leading to delayed union, or non-union. Chemical, or physical methods to accelerate bone healing are of great interest to the orthopaedic and trauma community. Research over the last 20 years has established that successful fracture healing is steered by specific growth factors. Of these, the bone morphogenetic proteins (BMPs) are probably the most important. The signalling pathway of these proteins is tightly regulated, overseeing a finely orchestrated cascade of events that occur after a fracture. The promising results of BMPs in preclinical studies have recently cleared the way for their use in specific fractures, or non-unions in clinical practice. The purpose of this work is to give a brief overview of BMPs and to review the clinical data currently available on the use of BMPs in fracture healing.     

应用骨形态发生蛋白(BMP)修复关节软骨缺损的实验研究

目的探讨关节软骨全层缺损应用骨形态发生蛋白修复的效果。方法于2004年5月至2005年12月,30只新西兰种成年兔随机分为A,B,C三组,每只兔子左膝股骨髁间凹做一大小为4mm×5mm×2.5mm的全层关节软骨缺损。A,B组缺损内分别填充骨形态发生蛋白/纤维蛋白胶(BMP/FG)及FG,C组为空白。术后28周对缺损修复情况行大体形态、组织学和电镜观察。结果BMP/FG组,缺损组织以透明软骨修复,接近正常组织,而FG组和空白组则以纤维组织修复为主。结论BMP/FG能较好的完成关节骨软骨全层缺损的修复,并随着时间的延长修复的软骨越接近正常软骨,但修复软骨缺损的组织与邻近正常软骨组织连接性仍不是十分理想。     

Repair of articular cartilage defects one year after treatment with recombinant human bone morphogenetic protein-2 (rhBMP-2)

BACKGROUND: Damaged articular cartilage has a limited ability to repair. Operative removal of damaged cartilage and penetration into the subchondral bone to allow population of the defect with progenitor cells can result in filling of the defect with repair tissue. However, this repair tissue often degenerates over time because of its inability to withstand the mechanical forces to which it is subjected. We previously reported that recombinant human bone morphogenetic protein-2 (rhBMP-2) improves the repair of full-thickness defects of cartilage as long as six months postoperatively. We have now extended that study to examine the quality of the repair tissue at one year. METHODS: Full-thickness defects of cartilage were created in the trochlear groove of twenty-five adult New Zealand White rabbits. Eight defects were left empty, eight were filled with a collagen sponge, and nine were filled with a collagen sponge impregnated with five micrograms of rhBMP-2. The animals were killed at fifty-two weeks postoperatively, and the gross appearance of the healed defect was assessed. The repair tissue was examined histologically and was evaluated, according to a grading scale, by four individuals who were blinded with respect to the treatment. The tissue sections were immunostained with antibodies against type-I collagen, type-II collagen, aggrecan, and link protein. The residence time of the rhBMP-2 in the cartilage defect was evaluated in vivo with use of scintigraphic imaging of radiolabeled protein. RESULTS: One year after a single implantation of a collagen sponge containing five micrograms of rhBMP-2, the defects had a significantly better histological appearance than the untreated defects (those left empty or filled with a collagen sponge). The histological features that showed improvement were integration at the margin, cellular morphology, architecture within the defect, and reformation of the tidemark. The total scores were also better for the defects treated with rhBMP-2 than for the untreated defects, but in no instance was the repair tissue identical to normal articular cartilage. The thickness of the cartilage in the defects treated with rhBMP-2 was 70 percent that of the normal cartilage, an observation that was identical to that at twenty-four weeks postoperatively. Immunostaining demonstrated significantly less type-I collagen in the defects treated with rhBMP-2 than in the untreated defects. Immunostaining for other matrix components showed no difference among the treatment groups. The mean residence time of rhBMP-2 in the cartilage defects was eight days with an elimination half-life of 5.6 days. Detectable amounts of rhBMP-2 were present as long as fourteen days after implantation. CONCLUSIONS: The problems associated with operative repair of cartilage include the formation of fibrocartilage rather than normal articular cartilage and the degeneration of that repair tissue over time. Our results demonstrate that the addition of rhBMP-2 to the operative site after creation of a full-thickness defect results in an improvement in the histological appearance and composition of the extracellular matrix at one year postoperatively. If these experimental results translate directly to the clinical situation, it is possible that the addition of rhBMP-2 to existing operative treatments for the repair of cartilage may improve the repair process and may help to maintain the integrity of the repair tissue.     

CDMP-2 induces bone or tendon-like tissue depending on mechanical stimulation.

Cartilage derived morphogenetic proteins (CDMPs, also known as growth and differentiation factors, GDFs) are a subgroup of the bone morphogenetic protein (BMP) gene family. As most BMPs, they are known to induce cartilage or bone formation when implanted subcutaneously or intramuscularly on an appropriate carrier. However, similar implantation experiments with CDMPs have also reported the formation of a tendon-like tissue, without any cartilage or bone. A solution to this apparent contradiction might be offered by the mechanical tissue differentiation theory, suggesting that tissue differentiation depends on the mechanical environment. This study analyzes the response to CDMP-2 implants at different sites and under different loading conditions in the rat. Collagen sponges carrying CDMP-2 were implanted subcutaneously, intramuscularly or inside a freshly created defect in the achilles tendon. Large amounts of bone were induced subcutaneously, smaller amounts intramuscularly, and in the tendons, only small amounts of bone or cartilage were seen in few animals. Thus, the amount of bone appeared inversely related to the degree of mechanical stimulus. To confirm this, CDMP was also injected into tendon defects that were either loaded or partially unloaded. All the unloaded tendons showed bone induction after one CDMP-2 injection, whereas only 4 of 10 loaded ones showed any cartilage or bone (p = 0.0005). Single injections of a similar dose of CDMP-2 have previously been shown to augment tendon repair by increasing the size of the tendon callus. This study suggests that the response to CDMP-2 is dependent on the mechanical situation at the site where it is applied.     

骨形态发生蛋白修复关节软骨的研究进展

【摘要】〓关节软骨损伤是一种常见疾病,其可导致关节炎的发生而严重影响人们的日常生活。但由于软骨缺乏血运,且不含祖干细胞,关节软骨的修复能力受到限制,至今临床上尚未有一个有效的方法来促进受损关节软骨的修复。目前,生长因子促进关节软骨修复和再生方面的研究日益受到重视,其中骨形态发生蛋白(BMP)是能够诱导骨组织形成的一个独特因子,对关节软骨的修复有促进作用。但是,BMP的作用尚处于研究阶段,仍有较多问题需解决,故有必要对BMP修复关节软骨作一综述。