Background Bone has a capacity for self-repair without scar formation. Most fractures heal spontaneously or with the help of surgical procedures . However, despite the inherent ability of the bone to regenerate itself, there are a number of clinical situations in which complete bone healing fails to occur and requires cell therapy.
Objectives The purpose of this study was to determine optimal ratio of ASCs added to BMSCs for osteogenic differentiation and angiogenesis, and to find the optimal ratio of ASCs to BMSCs to promote these desired functions.
Methods In this study, we used transwell and mixed cocultures for the in vitro model and the subcutaneous ectopic ossification in nude mice for the in vivo model. In vitro segregated cocultures using transwell were carried out for 14 days in 4 ways using BMSCs and ASCs in passage 3: #1, 1x105 BMSCs and 0.25x105 ASCs; #2, 1x105 BMSCs and 0.5x105 ASCs; #3, 1x105 BMSCs and 0.75x105 ASCs; #4, 1x105 BMSCs and 1x105 ASCs. In vitro mixed cocultures were also performed in the same proportion. BMSCs, ASCs, or both were seeded in PLGA scaffold and implanted in the subcutaneous tissue of 25 nude mice for in vivo analysis of angiogenesis. To evaluate the orthotopic bone formation, critical size calvarial defects were created on 20 mice, and implanted with hydroxyapatite/β-tricalcium phosphate granules plus BMSCs, ASCs, or both.
Results From the transwell culture, 1x105 BMSCs cultured with 5x105 ASCs showed significantly greater osteogenic differentiation and mineralization as shown by alkaline phosphatase (ALP) activity and calcium deposition than BMSCs alone. In the mixed coculture model, ASC/BMSC coculture at a ratio of 0.5/1 showed a significantly greater level of ALP activity and calcium deposition as well as greater gene and protein expression of osteogenic markers compared with BMSCs alone. The mixed ASC/BMSC coculture at a ratio of 0.5/1 showed the highest level of vascular endothelial growth factor which was significantly greater than BMSCs alone, comparable to ASCs alone. The HUVEC tube formation assay also demonstrated that the mixed ASC/BMSC coculture of 0.5/1 enhanced tube formation to a level similar to ASCs alone. In vivo implantation studies, (PLGA)-ASCs-BMSCs had a number of vascular structures comparable to PLGA-ASCs and significantly greater than PLGA-BMSCs. Calvarial defects treated with ceramic/BMSCs/ASCs had greater area of repair and better reconstitution of osseous structure than the defects treated with ceramic/ASCs.
Conclusions A certain ratio of ASCs to BMSCs (0.5/1) seemed to be the optimal ratio for both osteogenesis and angiogenesis. The effect of mixed coculture on in vivo bone formation was evaluated by calvarial defect model in mice. Mixture of ASCs and BMSCs was more effective in inducing bone repair, and induced better restoration of osseous structure than BMSCs or ASCs alone. Further studies to prove the concept of this study will comprise an in vivo model of ONFH. In colclusion, ASCs added to BMSCs promoted osteogenesis and angiogenesis with the optimal ASCs/BMSCs ratio of 0.5/1.
Einhorn, TA. (2005) The science of fracture healing. J Orthop Trauma 19: S4-6.
Acknowledgements This work was supported by a grant from the Ministry of Health and Welfare in Korea (A111509).
Disclosure of Interest None declared