Biological repair of thyroid cartilage defects by osteogenic protein-1 (bone morphogenetic protein-7) in dog

Intradiscal application of rhBMP-7 does not induce regeneration in a canine model of spontaneous intervertebral disc degeneration

INTRODUCTION

Strategies for biological repair and regeneration of the intervertebral disc (IVD) by cell and tissue engineering are promising, but few have made it into a clinical setting. Recombinant human bone morphogenetic protein 7 (rhBMP-7) has been shown to stimulate matrix production by IVD cells in vitro and in vivo in animal models of induced IVD degeneration. The aim of this study was to determine the most effective dose of an intradiscal injection of rhBMP-7 in a spontaneous canine IVD degeneration model for translation into clinical application for patients with low back pain.

METHODS

Canine nucleus pulposus cells (NPCs) were cultured with rhBMP-7 to assess the anabolic effect of rhBMP-7 in vitro, and samples were evaluated for glycosaminoglycan (GAG) and DNA content, histology, and matrix-related gene expression. Three different dosages of rhBMP-7 (2.5 μg, 25 μg, and 250 μg) were injected in vivo into early degenerated IVDs of canines, which were followed up for six months by magnetic resonance imaging (T2-weighted images, T1rho and T2 maps). Post-mortem, the effects of rhBMP-7 were determined by radiography, computed tomography, and macroscopy, and by histological, biochemical (GAG, DNA, and collagen), and biomolecular analyses of IVD tissue.

RESULTS

In vitro, rhBMP-7 stimulated matrix production of canine NPCs as GAG deposition was enhanced, DNA content was maintained, and gene expression levels of ACAN and COL2A1 were significantly upregulated. Despite the wide dose range of rhBMP-7 (2.5 to 250 μg) administered in vivo, no regenerative effects were observed at the IVD level. Instead, extensive extradiscal bone formation was noticed after intradiscal injection of 25 μg and 250 μg of rhBMP-7.

CONCLUSIONS

An intradiscal bolus injection of 2.5 μg, 25 μg, and 250 μg rhBMP-7 showed no regenerative effects in a spontaneous canine IVD degeneration model. In contrast, intradiscal injection of 250 μg rhBMP-7, and to a lesser extent 25 μg rhBMP-7, resulted in extensive extradiscal bone formation, indicating that a bolus injection of rhBMP-7 alone cannot be used for treatment of IVD degeneration in human or canine patients.

The protective effect of OP-1 on articular cartilage in the development of osteoarthritis

OBJECTIVE

The purpose of this study was to determine whether osteogenic protein 1 (OP-1) would protect articular cartilage from degeneration during the development of osteoarthritis (OA) in the rabbit anterior cruciate ligament transection (ACLT) model. Previous studies have shown that OP-1 is vital to cartilage matrix integrity and repair, stimulates synthesis of cartilage matrix components, proteoglycans, and collagen, and has a protective effect against catabolic mediators like matrix metalloproteinases and interleukin-1.

METHODS

The rabbit ACLT model was used in which the anterior cruciate ligament was transected leading to OA. OP-1 was delivered to the joint surgically for approximately 6 weeks by implantation of an Alzet osmotic pump into the medial thigh with a catheter threaded from the pump into the knee joint. Forty rabbits (20 control and 20 experimental) had the ACLT surgery and implantation of the pump performed simultaneously. They were sacrificed after 9 weeks for analysis. The OA was graded using the Outerbridge classification with India Ink staining. Histological staining and histomorphometry with Hematoxylin & Eosin and Safranin O were performed to analyze OA progression and semi-quantitative polymerase chain reaction (PCR) was performed for anabolic and catabolic genes.

RESULTS

The experimental group had an average Outerbridge score of 1.8 vs 2.5 for the controls (P<0.05). Histomorphometry showed 10.9% surface deterioration or an average depression of 0.05mm vs 22.3% and 0.1mm for the controls (P<0.05). Semi-quantitative PCR showed a significantly greater expression of aggrecan and collagen type II in the OP-1 treated cartilage when compared to controls and less expression of aggrecanase, a catabolic mediator.

CONCLUSIONS

OP-1 may have a potential benefit in protecting articular cartilage during the development of OA.

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.

The effect of recombinant human osteogenic protein-1 on growth plate repair in a sheep model

Injuries to the growth plate in children can result in bone bridge formation, which ultimately lead to limb length and angular deformities. The histological and molecular changes associated with growth plate repair following the Langenskiöld procedure, a surgical technique used to remove impeding bone bridges, in conjunction with administration of recombinant human osteogenic protein-1 (rhOP-1) were examined using a sheep model. Following treatment with rhOP-1 there was an increase in the height of the growth plate immediately adjacent to the defect compared to untreated animals. The expression of type I collagen, osteopontin and decorin were observed in the growth plate adjacent to the defect in the untreated animals at day 56, but this response was accelerated in the rhOP-1 treated animals, with these molecules seen as early as day 7. Therefore, treatment with rhOP-1 initiated a complex response that was both chondrogenic and osteogenic in nature.

Bone morphogenetic protein-7 (osteogenic protein-1) promotes tendon graft integration in anterior cruciate ligament reconstruction in sheep

BACKGROUND

Bone morphogenetic proteins induce new bone both in patients with bone defects and at extraskeletal sites in animals. After anterior cruciate ligament rupture, tendon graft fixation into a bone tunnel is a widely used method for anterior cruciate ligament reconstruction.

HYPOTHESIS

Bone morphogenetic protein-7 applied to the bone-tendon interface enables better integration of a free tendon graft into the surrounding bone.

STUDY DESIGN

Controlled laboratory study.

METHODS

The anterior cruciate ligament was reconstructed using a free tendon graft in the right rear knees of 30 one-year-old male sheep. Recombinant human bone morphogenetic protein-7 (25 microg) was applied randomly to the bone-tendon interface in 15 animals, and a vehicle was applied in 15 control animals. At 3 weeks, 10 animals from each group were sacrificed, and the remaining sheep were sacrificed at 6 weeks after surgery. Subsequently, histologic analysis and mechanical testing were performed. In another group of 20 sheep, the same procedure was used and mechanical testing was performed after 3 weeks.

RESULTS

More new bone was formed at the bone-tendon interface in the knees treated with bone morphogenetic protein-7 as compared histologically with similar areas in control animals, creating areas of dense trabecular network with significantly greater invasion of the tendon fibrous tissue into the bone marrow space. Mechanical testing showed greater strain resistance to force (368 N) in the knees treated with bone morphogenetic protein-7 than in control specimens (214 N). There was no difference between mechanical testing of samples from 3 and 6 weeks after surgery.

CONCLUSION

Bone morphogenetic protein-7 promotes complete tendon graft integration into the newly formed surrounding trabecular bone in the reconstruction of the anterior cruciate ligament.

CLINICAL RELEVANCE

Bone morphogenetic protein-7 in tendon graft integration might be successfully used in reconstructive surgery of ligaments.

Recombinant human bone morphogenetic protein-2 enhances experimental laryngotracheal reconstruction in rabbits

OBJECTIVE

Bone morphogenetic protein-2 offers potential benefits for cartilage regeneration. We investigated the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the regeneration of laryngeal cartilage and respiratory epithelium in a rabbit model.

MATERIAL AND METHODS

We used a cricoid defect rabbit model. Twenty-four rabbits were randomly divided into four equal groups. Two groups were treated with 5 microg of rhBMP-2 delivered on an absorbable collagen sponge and the other two groups were used as controls. One group of treated rabbits and one group of control rabbits were euthanized 1 week after surgery, while the others were euthanized 4 weeks after surgery. The healing pattern of the laryngeal wound was evaluated by means of histomorphometry.

RESULTS

Regeneration of both the epithelial layer and cartilage was significantly better in rabbits treated with rhBMP-2. Four weeks after surgery, the cricoid cartilage defect was completely repaired by new cartilage and new bone in rabbits treated with rhBMP-2. Furthermore, the lining respiratory epithelium healed more rapidly in treated rabbits.

CONCLUSION

rhBMP-2, delivered via an absorbable collagen sponge, induces complete regeneration and repair of rabbit cricoid cartilage defects. It also induces faster relining and regeneration of airway epithelium than in control rabbits.

Regeneration of articular cartilage chondral defects by osteogenic protein-1 (bone morphogenetic protein-7) in sheep

The efficacy of osteogenic protein-1 (OP-1; BMP-7) in regeneration of articular cartilage was examined by creating knee chondral defects in sheep. With a specially designed instrument in both knees, two 10 mm (diameter) chondral defects were created: one in the trochlea and the other on the femoral condyle. The recombinant BMP was delivered via an extra-articulary positioned mini-osmotic pump, which was fixed to the femoral diaphysis above the knee joint, and connected by a polyethylene tubing to the articular space. Prior to use, the compatibility of OP-1 with mini-osmotic pumps was tested in vitro by measuring aggregation/precipitation and modification of the released protein by size exclusion and reversed phase HPLC. The average amount of aggregation was 15% and about 5% of OP-1 was modified. However, the biological activity of OP-1 released from pumps over a period of 2 weeks at 37 degrees C was equal to ROS cell assay OP-1 standard. Following surgery, a total of 55 microg (low dose) or 170 microg (high dose) OP-1 in acetate buffer (pH 4.5) was slowly released from the pump over a period of 2 weeks. The pumps connected to control knees were filled with acetate buffer as a vehicle. Twelve animals were operated, six of which were treated with the low OP-1 dose, and six with the high OP-1 dose. Three sheep of each group were killed either at 3 or 6 months following surgery, based on arthroscopical evaluation. The chondral defects in the control knees remained empty during the observation period. At 3 months following surgery, defects treated with both OP-1 doses were filled with connective tissue and cartilage. At 6 months following surgery, both doses of OP-1 stimulated regeneration in treated knees. The boundaries between new and old cartilage were well fused and mechanically resisted animals' weight bearing. The regenerated cartilage was rich in proteoglycans and type II collagen, as demonstrated by toluidine blue staining and immunohistochemistry. No signs of endochondral bone formation above the bony tidemark were observed. We suggest that a recombinant bone morphogenctic protein stimulates ingrowth of mesenchymal cells into the chondral defects which then transform into newly formed articular cartilage-like tissue.