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Growing bone and cartilage

2006; British Editorial Society of Bone & Joint Surgery; Volume: 88-B; Issue: 4 Linguagem: Inglês

10.1302/0301-620x.88b4.17060

2044-5377

Ippokratis Pountos, Elena Jones, C. Tzioupis, Dennis McGonagle, Peter V. Giannoudis,

Hip disorders and treatments

The Journal of Bone and Joint Surgery. British volumeVol. 88-B, No. 4 EditorialFree AccessGrowing bone and cartilage THE ROLE OF MESENCHYMAL STEM CELLSI. Pountos, E. Jones, C. Tzioupis, D. McGonagle, P. V. GiannoudisI. PountosOrthopaedic SurgeonDepartment of Trauma & Orthopaedics, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK., E. JonesLecturer in RheumatologyChapel Allerton Hospital, Chapel Town Road, Leeds LS7 9SA, UK., C. TzioupisTrauma FellowDepartment of Trauma & Orthopaedics, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK., D. McGonagleRheumatologistChapel Allerton Hospital, Chapel Town Road, Leeds LS7 9SA, UK., P. V. GiannoudisProfessor of Trauma & Orthopaedic SurgeryDepartment of Trauma & Orthopaedics, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK.Published Online:1 Apr 2006https://doi.org/10.1302/0301-620X.88B4.17060AboutSectionsPDF/EPUB ToolsDownload CitationsTrack CitationsPermissionsAdd to Favourites ShareShare onFacebookTwitterLinked InRedditEmail The management of large bony defects and cartilage loss continues to be a challenge to trauma and orthopaedic surgeons. The treatment of these conditions has evolved over the years and has comprised of many techniques, such as autologous bone grafting, distraction osteogenesis and free fibular vascularised bone grafting. Advances in tissue engineering and regeneration have led to the development of new techniques and therapeutic options, while the introduction of pluripotent mesenchymal stem cells (MSCs) into the clinical setting opens new horizons. Autologous or allogenic MSCs can be expanded in monolayers and may then be loaded into a variety of scaffolds before implantation into a patient. This technique leads to regeneration of bone and cartilage by local induction of osteogenesis and chondrogenesis. This review article focuses on the latest advances in bone and cartilage regeneration using MSCs.The issues of 'growing' bone and restoring cartilage have been debated for centuries. In the past, extensive bone loss, as might occur in a large diaphyseal defect of a long bone, was thought to be incurable, with amputation often inevitable. In the early 19th century, the concept of autologous bone grafting was introduced, although it only proved successful for small defects.1In the mid-1950s, Ilizarov introduced a revolutionary method for salvaging limbs with severe bone loss. He used distraction osteogenesis, a technique which is still popular today.2,3 Subsequently, in the mid-1970s, the concept of free fibular vascularised bone grafting was introduced, thereby providing another dimension to the treatment of injuries associated with extensive bone loss.4 Also at this time the repair of joint cartilage defects was revolutionised,5 with the introduction of cartilage resurfacing perhaps becoming an alternative to joint replacement. While good results have been reported and these techniques have allowed many patients to retain their limbs, research into the development of more effective treatments has continued. Advances in all areas of medicine, including molecular medicine, molecular biology, tissue engineering and genetics have opened new horizons in both the philosophy and capability of growing tissue, in particular that of bone and cartilage.The discovery by Urist6 of bone morphogenetic protein (BMP) as well as a better understanding of the biological processes which govern the healing and repair of tissues, has led to the development of new strategies for the regeneration of tissues. In addition, the ability to isolate and culture MSCs has encouraged reexamination of the treatment of many musculoskeletal conditions.BiologyMSCs are non-haematopoetic, stromal cells that were isolated first from bone marrow and subsequently from other adult connective tissues.7 They exhibit a multilineage differentiation capacity and can develop into diverse cells, including adipocytes, osteoblasts, chondrocytes, myocytes, tenocytes, neural cells, and many others.8–29 In the laboratory, MSCs from bone marrow can be isolated and expanded using relatively simple protocols based on culture expansion of adherent cells (Figs 1 and 2). Expanded MSCs can be guided along specific differentiation pathways in culture, by using specific media that contain growth factors or other substances such as dexamethasone, indometacin, hydrocortisone and transforming growth factor β (TGFβ).8,30Bone marrow aspirates and trabecular bone have both been identified as sources of MSCs,31 although the quantity obtained from bone marrow aspirate is ≤ 0.01%.32 Recently, it has become clear that many tissues, other than bone, harbour MSCs able to be isolated from various skeletal sites, including articular cartilage, synovium, and periosteum among others.33–55 Other recent evidence suggests that adipose tissue, including the fat pad from the knee joint, can be a good source of MSCs,56–59 as are other sites, including artery walls.47 These observations might explain the pathological phenomenon of ectopic cartilage and bone forming in vessel walls, as described by Virchow in 1863.59 MSCs have also been isolated from other extraskeletal sites, including the umbilical cord and fetal circulation, albeit at a lower frequency compared with bone marrow aspirates.45,46,48MSCs are thought to be reservoirs of reparative cells, which lack specific tissue characteristics and are ready, under different signals, to mobilise and differentiate into cells of a connective tissue lineage. These signals may include damage from trauma, fracture, inflammation, necrosis and tumours.60 The mobilisation and differentiation of MSCs can be influenced by both chemotaxis61 and interactions with the extracellular matrix through trans-membrane proteins such as integrins.62 However, in many cases MSCs appear to differentiate toward the local cell population under the influence of microenvironment.62 These issues are still poorly understood because basic research into MSCs is frequently performed on culture expanded cells, which may differ significantly from MSCs resident in vivo.8 Song and Tuan63 showed that fully differentiated osteoblasts with identifiable alkaline phosphatase activity are able to dedifferentiate into either fully functional lipid-producing adipocytes, or chondrocytes and vice versa. These phenomena, known as genetic reprogramming and transdifferentiation, suggest that a fully differentiated cell from one lineage may be able to switch into another mature cell type. The implication of this is that the main feature of MSCs could be their plasticity and ability to switch fates, instead of a high proliferative potential. Recently, it has also become clear that there is a pressing need to better understand the factors that govern the regulation of MSCs in vivo.Current evidenceSince the original work of Friedenstein, Piatetzky-Shapiro and Petrakova,64 many other papers have demonstrated the potential of MSCs to contribute to new bone formation and bone healing. Numerous data65 have suggested that MSCs can enhance the repair of experimentally-induced large bony defects in animals.Recently, several injectable carriers loaded with MSCs have been tested for their efficacy as an alternative to open surgical procedures.66,67 Goel et al68 evaluated the effect of percutaneous bone marrow grafting in patients with a tibial nonunion, resulting in union in most patients. Their technique was simple, less invasive, could be performed under local anaesthesia, and had few complications. Siwach et al69 treated 72 patients who had delayed or nonunion of a fracture or poor regeneration in segmental bone transportation or limb lengthening, with a percutaneous injection of autogenous bone marrow. They achieved union in 68 of 72 patients.69 Outcomes in these procedures seem to be influenced by the number of MSCs injected into a nonunion,70 as it has been reported that 20 ml of bone marrow are needed in order to generate 3 ml of new bone.71The treatment of large bony defects with the application of scaffolds loaded with bone marrow MSCs has also been undertaken. This technique appears capable of healing large defects although it can be further enhanced by the addition of several growth factors.72–78 Borden et al79 studied the effects of BMP-7 combined with bone marrow MSCs and a polymeric microsphere matrix, for large segmental defects in an animal model. The addition of BMP-7 seemed to induce penetration of new bone throughout the whole implant, therefore upregulating the osteogenic activity of MSCs and enhancing the healing of the defect. Similarly, Peterson et al57 have genetically enhanced MSCs in order to heal a femoral defect in rats. Human adipose tissue was the source for the MSCs which were grown in cultures and infected with BMP-2-carrying adenovirus. The MSCs were then applied to a collagen-ceramic carrier and implanted into the femoral defects. Within eight weeks, the defect had healed. In a limited number of human patients, where traditional treatments were difficult, the implantation of MSCs loaded into a porous ceramic scaffold have given positive results.80 Stabilisation of the fracture was obtained by external fixation, with complete consolidation between the implant and the host bone being seen between five and six months later.80In an animal model using tissue engineering approaches, Alhadlaq and Mao81 prepared an osteochondral construct in the shape of an articular condyle, by using bone marrow MSCs. They suggested that the technique could serve as an alternative to total joint replacement in the future.MSCs also play a crucial role in the repair of cartilage defects.82–84 In 1993, Shapiro, Koide and Glimcher85 showed that osteochondral defects could heal spontaneously because of the MSCs that invaded the defect, proliferating and differentiating towards chondrocytes. MSCs have also been used for in vivo cartilage formation in animal models. Murphy et al12 performed meniscectomy and resection of the anterior cruciate ligament in order to produce osteoarthritis in a caprine model. Simultaneously, caprine bone marrow was collected and MSCs were isolated following expansion in culture and were then labelled with green fluorescent protein. The MSCs were injected into the knee and retardation of further articular destruction as well as regeneration of meniscal tissue was observed.Tamai et al86 studied the healing potential of full-thickness articular defects in an animal model by combining porous hydroxyapatite with recombinant human BMP-2 and a synthetic biodegradable polymer. This triple composite produced an agglomeration of MSCs which had migrated from the surrounding bone marrow, leading to complete repair of the defect at six weeks.Patients with non-traumatic osteonecrosis of the femoral head could benefit from the properties of MSCs in promoting osteogenesis and angiogenesis.87,88 Gangji and Hauzeur,88 when investigating the management of osteonecrosis of the femoral head, compared the effects of core decompression and implantation of autologous bone marrow cells with a control group that was treated by decompression alone. Their results showed a large difference in the rate of deterioration between the two groups, with the implantation of autologous bone marrow cells having a more favourable outcome. Similarly, Hernigou and Beaujean89 found a better outcome when a greater number of progenitor cells was transplanted into the affected hip.Table I illustrates recent evidence which supports the use of MSCs in both clinical and experimental studies.ConclusionsConventional forms of treatment for loss of bone or cartilage as a result of trauma or degenerative disease are not always successful. Treatment involving MSC engineering may give better results. Questions concerning the biology and survival of MSCs and their capacity to populate host tissues, are of great importance, as are issues such as the effectiveness of topical implantation of MSCs as well as their systemic application. The best method of implantation for MSCs should be identified. The use of scaffolds and growth factors and the type and number of MSCs required also needs to be defined. In addition, there are many issues concerning a suitable scaffold matrix. This should be biodegradable, have adequate survival, and permit cell infiltration, proliferation, differentiation and integration with existing bone. It should also produce minimal side effects. Current results from many laboratories, both in animal models and clinical studies, suggest that important developments in the therapeutic uses of MSCs lie ahead for clinical problems which were once considered untreatable.Table I. Evidence to support the therapeutic use of mesenchymal stem cells (MSCs)Type of defectSource of MSCsModelResultReference(s)* OA, osteoarthritis† BMP, bone morphogenetic proteinTibial nonunionBone marrowHumanUnion in most patients68Nonunion, delayed union, poor regeneration after bone transportBone marrowHumanUnion in 68 of 72 patients69NonunionBone marrowHumanBone union obtained in 53 of 60 patients with the number of injected MSCs possibly affecting outcome70Large femoral defectAdipose tissue (human)RatHealing of defect in eight weeks57Cranial bone defectBone marrow (human)RatAcceleration of healing75Segmental bone defectBone marrowRabbitBMP†-7 and bone-marrow loaded into a porous matrix had the most favourable outcome79Segmental bone defectBone marrowHumanComplete consolidation between the implant and bone at six months80Large bone defectBone marrowRabbitIncreased osteogenesis, bone union and resorption of the coral scaffold90Osteochondral defectBone marrowRatThe defect was repaired by hyaline cartilage and subchondral bone although the humber of injected MSCs decreased with time83Articular cartilage defectAutologous chondrocytesPigGeneration of hyaline cartilage84Full thickness osteochondral defectBone marrowRabbitComplete healing of the defect91Physeal defectBone marrowRabbitEnhancement of physeal defect82Partial growth arrestBone marrow, periosteum, fatRabbitBone marrow and periosteum have more homogeneous MSCs and provides better correction of a physeal defect than fat92Full-thickness articular defectBone marrowRabbitJoint destruction, collagen gel and MSC transplantation enhanced the repair93Articular defectPeriosteal graftGoatEarly treatment of articular defects had more favourable results94OA*and meniscal injuryBone marrowGoatRetardation of destruction of the joint and regeneration of meniscal tissue12Large scale osteoarticular constructBone marrowRatConstruction of articular condyle81Prevention of loosening of total ankle arthroplastyBone marrowHumanPreliminary study: bone-prosthesis interface was established, no inflammatory reaction76Spinal fusionBone marrowDogImproved bone grafting77Spinal fusionBone marrowRabbitMSCs loaded into a porous ceramic seemed to enhance outcome95Femoral head osteonecrosisBone marrowHumanLow rates of deterioration85–87Unicameral bone cystsBone marrowHumanBone marrow can be used in the treatment of unicameral bone cysts but has a high failure rate; no difference compared with steroid injection96Fig. 1 Expansion and differentiation of bone marrow derived mesenchymal stem cells (MSCs) in vitro. a) single freshly purified MSC, b) small MSC colony early in expansion, c) confluent MSC monolayer following extensive expansion in culture, d) osteogenesis from MSCs (alkaline phosphatase stain), e) chondrogenesis from MSCs (toluidine blue stain), f) adipogenesis from MSCs (Nile red stain), and g) chondrogenesis from MSCs (collagen II stain).Fig. 2 Outline of the culture, collection and implantation of bone marrow-divided mesenchymal stem cells (MSCs).References1 Young MH. 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