Allogenic bone and cartilage morphogenesis. Rat BMP in vivo and in vitro

Effects of autogenous growth factors on heterotopic bone formation of osteogenic cells in small animal model

AIMS

This study used a new approach to investigate the effective concentrations of growth factors released from platelet concentrate (PC) on the bone formation capacity of osteogenically differentiated rat bone marrow stromal cells (rBMSCs).

MATERIALS AND METHODS

Rat BMSCs and whole blood were harvested from 40 adult male Spraque-Dawly rats. Rat BMSCs were expanded in an osteogenic medium and seeded on inert collagenous bovine bone matrix (ICBM). Growth factors released from degranulated PC (GFs) containing TGF-β1 1 (25ng/ml)-10ng (250ng/ml) and rhBMP-2 400ng (10μg/ml) were suspended in 40μl platelet poor plasma (PPP) and applied on the ICBM-rBMSC constructs or ICBM only, respectively. The constructs were then transplanted in autologous hosts for 4 weeks. Concurrently, osteoblastic differentiation of rBMSCs on ICBM-rBMSC-PPP constructs was characterized in vitro.

RESULTS

Rat BMSCs in osteogenic medium exhibited phenotypes of mature osteoblasts. The amount of newly formed bone among groups of ICBM-rBMSC-PPP with and without GFs was not significantly different (p>0.05) and was significantly lower than a group of ICBM-PPP-BMP-2 (p<0.05).

CONCLUSIONS

Autogenous GFs had no effect on the capacity of rBMSCs to form new bone. The ability to measure the bone formation capacity of transplanted autologous cells and growth factors in a small animal model was demonstrated.

Biocompatibility of individually designed scaffolds with human periosteum for use in tissue engineering

The aim of this study was to evaluate and compare the biocompatibility of computer-assisted designed (CAD) synthetic hydroxyapatite (HA) and tricalciumphosphate (TCP) blocks and natural bovine hydroxyapatite blocks for augmentations and endocultivation by supporting and promoting the proliferation of human periosteal cells. Human periosteum cells were cultured using an osteogenic medium consisting of Dulbecco's modified Eagle medium supplemented with fetal calf serum, Penicillin, Streptomycin and ascorbic acid at 37 degrees C with 5% CO(2). Three scaffolds were tested: 3D-printed HA, 3D-printed TCP and bovine HA. Cell vitality was assessed by Fluorescein Diacetate (FDA) and Propidium Iodide (PI) staining, biocompatibility with LDH, MTT, WST and BrdU tests, and scanning electron microscopy. Data were analyzed with ANOVAs.

RESULTS

After 24 h all samples showed viable periosteal cells, mixed with some dead cells for the bovine HA group and very few dead cells for the printed HA and TCP groups. The biocompatibility tests revealed that proliferation on all scaffolds after treatment with eluate was sometimes even higher than controls. Scanning electron microscopy showed that periosteal cells formed layers covering the surfaces of all scaffolds 7 days after seeding.

CONCLUSION

It can be concluded from our data that the tested materials are biocompatible for periosteal cells and thus can be used as scaffolds to augment bone using tissue engineering methods.

Gene therapy in orthopaedic surgery: the current status

The first successful gene therapy trial was reported in 1991. Since then, successful gene transfer in cultured cells and small animals has been reported by many studies, with achievement of at least transitory high levels of exogenous gene expression. Over 400 clinical protocols for gene therapy have been approved, involving over 4000 patients. However, publication of the results of these gene therapy trials has been limited, with only 80 published reports as of 2002. The majority of clinical gene therapy trials reported so far have been phase I or phase II trials, which are concerned mainly with safety issues and have focused on the treatment of malignancies and other potentially fatal conditions. The death of a patient in 1999 from systemic administration of an adenoviral vector and recent reports of leukaemia in two patients in a clinical gene therapy trial have led to a further re-evaluation of the safety of gene therapy and the role for gene therapy in clinical practice. This review outlines the current status of gene therapy as it relates to orthopaedic diseases and highlights the areas where progress is still to be made.

A comparative study of osseointegration of Avana implants in a demineralized freeze-dried bone alone or with platelet-rich plasma

PURPOSE

The purpose of this study was to assess the efficacy of demineralized bone powder (DBP) alone or combined in a mixture with platelet-rich plasma (PRP) used to enhance osseointegration of dental implants in a dog model.

MATERIALS AND METHODS

Tissue integration was assessed using standard histomorphometric methods at 6 and 12 weeks after surgery. A total of 30 Avana dental implants (SooMin Synthesis Dental Materials Co, Busan, Korea) were inserted in the animals. They were self-tapping screw implants, 10 mm in length and 4 mm in diameter, made of commercially pure titanium. A titanium implant was then placed centrally in each defect. In each dog, the defects were treated with 1 of the following 3 treatment modalities:1) no treatment (control), 2) grafting with DBP, or 3) grafting with DBP and PRP.

RESULTS

Histologic analysis showed that all of the bone defects surrounding the implants that were treated with DBP, with and without PRP, were filled with new bone. The defects that were not treated (control) showed new bone formation only in the inferior threaded portion of the implants. Histomorphometric results revealed a higher percentage of bone contact with DBP and PRP compared with control and DBP.

CONCLUSION

These results suggested that bone defects around titanium implants can be treated successfully with DBP and that PRP may improve bone formation.

Inductive properties of recombinant human BMP-2 produced in a bacterial expression system

Recombinant human BMP-2, produced in E. coli, refolded and concentrated to a purity of more than 98%, has been demonstrated to be biologically active. In vitro, amounts of 0.4 microg BMP-2 or more induced new cartilage formation in 27 out of 47 samples of a neonatal muscle tissue assay, with chondroneogenesis occurring 14 days after a four-hour contact between BMP-2 and the muscle tissue. In vivo, BMP-2 was implanted in the thigh muscle of ICR mice for a period of three weeks. Amounts of 4 microg BMP-2 and more showed heterotopic bone formation in 15 out of 17 samples. When BMP-2 was combined with a collagen carrier, amounts of 0.4 microg protein or more induced heterotopic bone formation in 30 out of 33 samples four weeks after the implantation in the abdominal wall of Sprague-Dawley rats. The results show that the E. coli-derived BMP-2 was active in different assay systems in concentrations equal to those required with mammalian cell-expressed BMP-2. It could also be demonstrated that a single morphogen (BMP-2) is enough to initiate the differentiation process associated with bone induction. The presented bacterial expression system also offers the opportunity to produce large quantities of recombinant BMP-2 for clinical applications.

Proteínas morfogenéticas ósseas: terapêutica molecular no processo de reparo tecidual

As pesquisas biomoleculares sobre o desenvolvimento e a reparação óssea permitiram a descoberta de uma nova família de proteínas reguladoras da formação óssea e cartilaginosa in vivo. Capazes de iniciar a neoformação óssea quando implantadas em sítios extra-ósseos, estas proteínas são denominadas de proteínas ósseas morfogenéticas ou BMPs. A purificação e a caracterização das BMPs contribuíram para a fundamentação do conhecimento molecular e celular do processo de reparo ósseo. A resposta tecidual ao implante de BMPs ocorre de modo similar ao desenvolvimento ósseo embriológico, possibilitando a formação e o desenvolvimento da reparação na osteogênese pós-natal. A origem e a função das BMPs, entretanto, não estão limitadas ao tecido ósseo, sugerindo novos sítios de intervenções terapêuticas. O estádio atual de isolamento, as características, bem como as diversas possibilidades de aplicações clínicas das BMPs são relatados, analisando-se sua atuação.

[Osteoinduction and -reparation]

Traumata, diseases, developmental deformities, and tumor resections frequently cause bone defects and atrophies. In general, three different mechanisms exist by which bone restoration can be achieved: (1) osteogenesis initiated by vital, osteoblastic cells of autografts; (2) osteoconduction (or creeping substitution); and (3) osteoinduction. The latter mechanism means the differentiation of pluripotent, mesenchymal-type cells (located in a recipient bed with strong regenerative capacity) into cartilage- and bone-forming progenitor cells under the influence of inductive bone morphogenetic proteins (BMPs). Some BMPs are physiologically included in low concentrations as organic components in bone tissue. They can diffuse from demineralized bone implants into the recipient bed and induce a differentiation into new bone tissue. Nine different BMPs have been isolated, characterized, and cloned. Some of these possess inductive properties and can initiate new bone formation in muscle tissue or in bone defects. In the future recombinant BMPs will be available in unlimited quantities. This will lead to completely new therapeutic concepts in reconstructive bone surgery.

Commercially-prepared allograft material has biological activity in vitro

The well-established finding that implantation of demineralized bone matrix at non-skeletal sites results in formation of cartilage and bone has been attributed to bone morphogenetic proteins/factors. Commercially-available demineralized bone allograft materials are being used currently to reconstruct/regenerate bone. The studies described here focused on establishing biological activity of protein extracts prepared from commercially obtained bone graft material in vitro. Furthermore, the biological activity of these protein extracts in vitro was compared with similar extracts prepared from freshly obtained human bone. Biological activities of bone matrix proteins examined included their ability to promote proliferation, attachment, and migration of gingival fibroblasts using an in vitro system. Guanidine followed by guanidine/EDTA was used to separate bone matrix proteins into proteins associated with soft tissues of bone and proteins retained within the mineral compartment, respectively. Two preparations of each starting material were tested and the biological activity of each preparation was evaluated in triplicate at least three times. Slot blot analysis revealed that commercially-prepared material contained type I collagen; fibronectin; BSP; and BMP-2, 4, and 7. However, the freshly prepared bone extracts appeared to have higher BMP concentrations. The ability of commercial extracts to promote cell proliferation, while significant, was limited and significantly less when compared with similar extracts prepared from freshly obtained bone. All extracts promoted cell attachment significantly, while none of the extracts promoted cell migration. Thus, commercially-prepared material retained proteins having the capacity to influence cell behavior in vivo. However, some biological activity as measured in vitro was lost as a result of tissue processing.

Powdered eggshell: a pilot study on a new bone substitute for use in maxillofacial surgery

The present study is a preliminary report on the use of hen's eggshell as a possible bone substitute. In the first part of the study, particles ranging from 400 microns to 600 microns in diameter were bioassayed in an intramuscular pouch in rodents. This material was found to be biocompatible, but appeared not to have osteoinductive capacities. In the second and third part of the study, this material was used as an interpositional graft material in critical-size defects of rat mandibles and rabbit skulls. At 2 months, a morphologic restoration was obtained using the graft, but the healing was only achieved by fibrous union. In the fourth part of the study, the material was experimented on as an onlay bone graft on rabbit mandibles. A 6-month follow-up of the implant confirmed its stability. In conclusion, the use of this safe and inexpensive material is suggested for filling limited bone defects in non-weight-bearing areas. The use of eggshell powder for bone augmentation may also be considered, after further studies, to assess its long-term stability.

Experimental study on demineralized bone matrix (DBM) and coral as bone graft substitutes in maxillofacial surgery

Three different bone substitutes were implanted in a standardized nasal bone defect in 30 Wistar rats. The results were assessed at 2 months by macroscopic examination, contact radiography, and histologic analysis. Demineralized osseous implants sterilized by ethylene oxide induced bone formation in 90% of the the cases, as no heat-treated graft showed any bone formation. Coralline grafts were osteointegrated in 50% of the cases, but osteoconduction was not sufficient to achieve complete bone repair. This study implies that ethylene oxide sterilization does not impair biologic properties of demineralized grafts, but further studies on more evolved animal species are necessary before human implantation.

IgG monoclonal antibodies that inhibit osteoinductivity of human bone matrix-derived proteins (hBMP/NCP)

Monoclonal hBMP/NCP (human bone morphogenetic protein and associated noncollagenous proteins) antibodies of the IgG class were produced. In vitro, 12 of 19 hBMP/NCP antibodies showed functional inhibition of hBMP/NCP-induced chondroneogenesis in a neonatal muscle tissue assay. Inducing factors were characterized by their inhibiting antibodies with immunoblotting. Several peptide factors seem to be involved in the cascade of induced chondro- and osteogenesis.

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.