Osteoclastic resorption and osteoinduction in the highly purified B-tricalcium phosphate implanted in the rat subcutaneous tissue are promoted by autologous bone marrow cells.
Abstract
Sequential cellular events after highly purified β-tricalcium phosphate (β-TCP) implantation with or without rat bone marrow (BM) cells were investigated. β-TCP disks were soaked with BM cells harvested from femora of syngeneic rats and implanted into the subcutis of eight-week-old rats. Specimens were harvested at the intended stages, and histological examinations were performed.
In the BM-treated group, new bone formation was detected, and intense signals of the α1 chain of type I procollagen mRNA were expressed in osteoblasts after day 14. On day 56, the newly formed bone did not degenerate, and normal bone marrow tissue was observed. TRAP-positive multinucleated cells appeared after day 7, and cathepsin K–positive osteoclasts appeared after day 14, directly attached to β-TCP.
Conversely, in the BM non-treated group, new bone formation was not observed even on day 56, and neither TRAP- nor cathepsin K–positive osteoclasts were detected at any stage. Quantitative analysis showed that the β-TCP area decreased in a time-dependent manner in the BM-treated group, but not in the BM non-treated group.
In conclusion, these findings indicate that β-TCP loaded with BM cells has osteoinductive ability. β-TCP is resorbed mainly by osteoclasts, and this event promotes ectopic bone formation. BM cells play an important role in osteoinduction as well as in osteoclast differentiation and function.
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Introduction
For bone defects such as after malignant tumor resection, revision arthroplasty, trauma, and infection, autologous cancellous bone graft is the first choice because it provides scaffolding for osteoconduction, growth factors for osteoinduction, and progenitor stem cells for osteogenesis. However, due to its limited amounts of supply, this is not the perfect treatment method. A further disadvantage of allografts could be that allografts could cause host immune response or transfer disease. Instead, synthetic bone substitutes such as hydroxyapatite (HA), tricalcium phosphates (TCP), and combination of HA/TCP (biphasic calcium phosphate; BCP) have also been used [1-3] . The ideal character of biomaterial is to promote bone induction as well as bone conduction. It has been reported that calcium phosphate ceramics has osteoinductivity in the optimal condition [9-14], and various trials have been performed to achieve good bone induction in extra-skeletal sites in various animal species. Bone morphogenic protein-2 (BMP-2) and osteogenic protein-1 (OP-1) protein, and cultured bone marrow mesenchymal stem cell implantation are thought to be prominent candidates for further powerful bone induction [15-19]. However, these tools have disadvantages because they require a lot of processes or cost too much to maintain safely within the animal body. For example, it has been reported that long-term culture of mesenchymal stem cells leads to carcinogenesis [20,21]. Autologous bone marrow (BM) cells graft with -TCP is an alternative way that is readily available and relatively lower cost than other osteogenic proteins or ex vivo grafts that require mesenchymal stem cell cultures. We hypothesized that autologous BM cells promoted osteoinductive ability well.
Conclusion
β-tricalcium phosphate (β-TCP; OSferion®) is resorbed by osteoclasts and leads to new bone formation when implanted with syngeneic rat bone marrow cells into subcutaneous tissue. These cellular events follow the appearance of a large number of osteoclasts and their attachment to β-TCP.
The data from this study suggest that β-TCP implantation with autogenous bone marrow cells is a safe.