Platelet‐rich plasma/osteoblasts complex induces bone formation via osteoblastic differentiation following subcutaneous transplantation

Abstract

Platelet-rich plasma (PRP) has been shown to enhance the maturation of bone grafts following local application and to have biological effects on osteoblasts in vitro. However, PRP is not applied by itself clinically as a result of its poor benefits in large bone defects. The present study was undertaken to develop a clinical alternative to autologous bone, by investigating the application of PRP in combination with osteoblastic cells and evaluating its effects after transplantation. PRP and platelet-poor plasma (PPP) were prepared from blood, obtained from ddY mice, by two centrifugation steps. MC3T3-E1 cells were labeled with fluorescent carbocyanine just before transplantation. The combination of labeled cells and PRP gel was subcutaneously transplanted into the back of severe combined immunodeficient (SCID) mice, and the transplants were evaluated radiographically and immunohistologically after 4 wk. The effects of PRP were assessed by alkaline phosphatase (ALP) staining and von Kossa staining, and the expression of bone-related markers was analyzed by reverse transcription-polymerase chain reaction before transplantation. Before transplantation, PRP enhanced the expression of Osterix and bone sialoprotein mRNAs compared with PPP. Furthermore, PRP elevated ALP activity and induced the formation of mineralized nodules. After transplantation, the combination of labeled cells and PRP gel formed mineralized tissue, and the transplanted cells visualized in the tissue using fluorescence microscopy expressed osteocalcin and type I collagen. These results suggest that the application of a PRP/osteoblasts complex has beneficial effects for transplanting engineered cells into bone defects through the promotion of osteoblastic differentiation.