E.H. Burger

Use of recombinant human osteogenic protein-1 for the repair of subchondral defects in articular cartilage in goats

The objective of this pilot study was to examine in vivo the potential of recombinant human osteogenic protein-1 (rhOP-1, also called bone morphogenetic protein-7, BMP-7) for treatment of subchondral lesions by induction of new hyaline cartilage formation. Subchondral left knee defects in 17 mature goats were treated with fresh coagulated blood mixed with (1) rhOP-1 combined with collagen (OP-1 device, 400 microgram/mL); (2) rhOP-1 alone (OP-1 peptide, 200 microgram/mL); (3) OP-1 device with small particles of autologous ear perichondrium; (4) OP-1 peptide with small particles of autologous ear perichondrium; or (5) autologous ear perichondrium alone (controls). rhOP-1 was combined with either collagen (OP-1 device) or not (OP-1 peptide). The defects were closed with a periosteal flap. The formation of cartilage tissue was studied by histologic and biochemical evaluation at 1, 2, and 4 months after implantation. One and 2 months after implantation there were no obvious differences between control and rhOP-1-treated defects. Four months after implantation, only one out of three controls (without rhOP-1) showed beginning signs of cartilage formation while all four rhOP-1-treated defects were completely or partly filled with cartilage. A significant linear relationship was found between rhOP-1 concentration and the total amount of aggrecan in the defects. These results suggest that implantation of rhOP-1 promotes cartilage formation in subchondral defects in goats at 4 months after implantation. Therefore, rhOP-1 could be a novel factor for regeneration of cartilage in articular cartilage defects.

Effect of recombinant human osteogenic protein-1 on the healing of a freshly closed diaphyseal fracture

Osteogenic protein-1 (OP-1), or bone morphogenetic protein-7, is an osteoinductive morphogen that is involved in embryonic skeletogenesis and in bone repair. In bone defect models without spontaneous healing, local administration of recombinant human OP-1 (rhOP-1) induces complete healing. To investigate the ability of rhOP-1 to accelerate normal physiologic fracture healing, an experimental study was performed. In 40 adult female goats a closed tibial fracture was made, stabilized with an external fixator, and treated as follows: (1) no injection; (2) injection of 1 mg rhOP-1 dissolved in aqueous buffer; (3) injection of collagen matrix; and (4) injection of 1 mg rhOP-1 bound to collagen matrix. The test substances were injected in the fracture gap under fluoroscopic control. At 2 and 4 weeks, fracture healing was evaluated with radiographs, three-dimensional computed tomography (CT), dual-energy X-ray absorptiometry, biomechanical tests, and histology. At 2 weeks, callus diameter, callus volume, and bone mineral content at the fracture site were significantly increased in both rhOP-1 groups compared with the no-injection group. As signs of accelerated callus maturation, bending and torsional stiffness were higher and bony bridging of the fracture gap was observed more often in the group with rhOP-1 dissolved in aqueous buffer than in uninjected fractures. Treatment with rhOP-1 plus collagen matrix did not result in improved biomechanical properties or bony bridging of the fracture gap at 2 weeks. At 4 weeks there were no differences between groups, except for a larger callus volume in the rhOP-1 plus collagen matrix group compared with the control groups. All fractures showed an advanced stage of healing at 4 weeks. In conclusion, the healing of a closed fracture in a goat model can be accelerated by a single local administration of rhOP-1. The use of a carrier material does not seem to be crucial in this application of rhOP-1.

Transforming growth factor-β1 incorporated during setting in calcium phosphate cement stimulates bone cell differentiation in vitro

Growth stimulation of periimplant tissues by growth factors like transforming growth factor-beta1 (TGF-beta1) may increase the indication for and success of implant use. Calcium phosphate as a material for implants or for coating of implants is known for its good biologic interaction with bone. Therefore, calcium phosphate implants combined with TGF-beta1 might improve osseointegration. In this study we hypothesise that the addition of recombinant human TGF-beta1 (rhTGF-beta1) to calcium phosphate cement (CPC) affects the differentiation of bone cells growing on the cement layer. rhTGF-beta1 incorporated during setting in a CPC layer at 20 ng rhTGF-beta1/60 mg cement was found to be gradually released into tissue culturing medium leading to a 20% release after 24 h. Two cell populations were obtained from collagenase-treated fragments of adult rat long bones: preosteoblastic cells, which were released by the collagenase treatment, and osteoblastic cells, which grew from the collagenase-stripped bone fragments. Both cell populations were tested for their osteoblastic characteristic phenotype by measuring their alkaline phosphatase (ALP) activity after vitamin D treatment and cyclic AMP after parathyroid hormone stimulation. After preculture the cells were plated on a layer of CPC containing 0 (control), 10, or 20 ng rhTGF-beta1/60 mg CPC. Bone cell differentiation was analyzed after 10 days by measuring the ALP activity, as well as the protein content of the cell layer. Incorporation of rhTGF-beta1 in the CPC did not change the ALP activity in osteoblastic cells, but a significant (analyzed by multivariate analysis of variance) increase was observed in preosteoblastic cells. Incorporation of 10 ng of rhTGF-beta1 in 60 mg of CPC increased the ALP activity in preosteoblastic cells by threefold and 20 ng rhTGF-beta1/60 mg CPC increased it by fivefold. The total protein content was not affected by rhTGF-beta1 in either of the cell populations. We conclude that rhTGF-beta1 incorporated during setting in CPC stimulates the differentiation of preosteoblastic cells in vitro. These results provide a basis for further studies on the use of this combination as an implant material in vivo.

Bone and space flight: an overview

Even four centuries ago, Galileo Galile realized that the rigidity of the skeleton of terrestrial animals is related to its load bearing function, and is associated with the size and mass of the animal (Galilei 1974). This phenomenon of differences in mechanical properties also applies to the relatively small variations in the skeleton which occur between individuals of the same species, as well as to variations in bone properties within the same subject. Ward (1836) observed that the trabecular arrangement within the femoral head, the area now known as Ward’s triangle, showed patterns comparable to those found in the crossbeam structures of nineteenth century street lights. This very clearly illustrated natural mechanical engineering of the weight bearing properties of bone. Some 50 years later, Wolff postulated his law; ‘Das Gezetz der Transformation der Knochen’ (Wolff 1892). In this essay he discussed in more detail how the structure of bone reflects its mechanical usage history. The process of bone formation and bone remodeling according to its mechanical history is now generally known as functional adaptation, a term proposed by Roux (1895).

Osteoclastic Invasion and Mineral Resorption of Fetal Mouse Long Bone Rudiments are Inhibited by Culture Under Intermittent Compressive Force

To study the effect of low-magnitude mechanical stimuli on mineralized matrix metabolism, fetal mouse long bone rudiments were cultured for 5d in the absence or presence of intermittent (0.3 Hz) compressive force (ICF) of 132 g/cm2. ICF treatment stimulated mineralization of the diaphyseal bone collar as well as hypertrophic cartilage, but inhibited the release of 45Ca from prelabeled rudiments. ICF also inhibited the migration of osteoclasts and their precursors from the periosteum into the diaphysis and the subsequent excavation of a primitive marrow cavity. These data suggest that osteoclasts are sensitive to mechanical stimuli. Mechanical stimulation seems to protect the bone rudiment against osteoclastic attack and has a strong anabolic effect on mineral metabolism.