Regeneration of Large Rat Osteochondral Knee Fracture, Using the Recombinant Human Amelogenin Protein (rHAM⁺)

Osteochondral knee defects are common, painful and debilitating, leading with time to the development of joint degeneration. Regeneration of hyaline cartilage is very limited. Current surgical techniques most often induce fibrocartilaginous tissues, which do not consistently yield long term satisfactory clinical results. Previously, we have shown that application of our recombinant human amelogenin protein (rHAM⁺) alone induced in vivo regeneration of; (i) dog tooth supporting tissues; alveolar bone, periodontal ligament and cementum, lost due to chronic periodontitis, and (ii) transected rat skeletal ligament. In both models rHAM⁺ induced regeneration through recruitment of cells expressing mesenchymal stem cell (MSC) markers. Amelogenin is expressed in hyaline cartilage chondrocytes, in bone cells, and in MSCs. Hence, we assumed that application of rHAM⁺ could bring about functional regeneration of osteochondral knee fracture (OCF), through recruitment of MSCs. Large OCF was created in rat femoral trochlea. Different concentrations of rHAM⁺ dissolved in its carrier propylene glycol alginate (PGA) were applied to the experimental groups. To the control only the PGA carrier was applied. Three months after the operation, rHAM⁺ dose-dependently induced regeneration of the hyaline cartilage and the subchondral bone. The concentration which yielded the best results was 0.5mg/ml. Six months after operation and application of 0.5mg/ml rHAM⁺, the area of the defect was filled with normally arranged subchondral bone and hyaline cartilage, expressing normal extracellular matrix. Furthermore, application of rHAM⁺ prevented the severe post traumatic osteoarthritic changes seen in all controls rats. Four days after creation of OCF the number of cells expressing MSC markers in the experimental group was significantly higher than in the control. In conclusion, rHAM⁺ induces significant regeneration of the hyaline articular cartilage and the subchondral bone, through recruitment of MSCs.