Regeneration of Articular Cartilage Chondral Defects by Osteogenic Protein-1 (Bone Morphogenetic Protein-7) in Sheep

Abstract

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.

Articular cartilage repair by genetically modified bone marrow aspirate in sheep

“…Mesenchymal stromal cells (MSCs) present very attractive option for cell-based strategies as they can be readily isolated, expanded and, under appropriate conditions, differentiated into mesenchymal tissues such as cartilage, bone or muscle. 5 Numerous gene products such as transforming growth factor-b (TGF-b), 6 bone morphogenetic protein-7 (BMP-7), 7 insulin-like growth factor-1 (IGF-1) 8 and BMP-2 9 have shown potential in regulating the process of growth, repair and regeneration of cartilage in animal models, but their use is limited by delivery problems and rapid clearance from the joint. This issue can be addressed by gene therapy approaches for delivering therapeutic gene products specifically to the site of repair.…”

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

“…This dosage was the same as that used in the study by Johnstone et al [17], which reported an increase in growth plate height adjacent to the defect. This dosage is within the range of that used in other in vivo studies to regenerate articular and thyroid cartilages, doses of which have ranged from 11 pg to 500 pg f4, 16,18,24]. All of these studies have reported an induction of chondrogenesis, with cells taking on the chondrocyte phenotype and producing cartilage specific collagens and proteoglycans.…”

“…In addition to its powerful bone healing properties, the chondrogenic potential of OP-1 has been 0736 well documented [3,4,6,11,15,16,24]. In vitro studies in rat calvarial cells, ATDC5 cells, mouse embryonic long bone cultures, transplanted perichondrial cultures and articular cartilage cultures have reported an increase in the synthesis of type I1 collagen and proteoglycans following the administration of recombinant human OP-1 (rhOP-I); [l-3,5,6,13,19,20].…”

“…The repair of articular cartilage defects in vivo using rhOP-1 has been reported in rabbits, goats, sheep and dogs [4,11,16,24,25]. The defect is repaired through the infiltration of mesenchymal cells that differentiate into cells resembling articular cartilage chondrocytes.…”

“…In thyroid defects in dogs, bone, cartilage and ligament-like tissue have all been formed following the administration of OP-1 [IS]. The newly formed tissues integrated well with the host cartilage, indicating that the remodelling of the cartilage matrix is stimulated by the recombinant OP-1 [16,18]. A study by Mason et al reported the use of a combined gene therapy and tissue engineering approach to repair articular cartilage defects in rabbits [25], and complete or near complete regeneration of the bone and cartilage was seen in the grafts containing the OP-1 modified cells, compared to poor repair by the control grafts [25].…”