Effect of strontium substituted ß-TCP associated to mesenchymal stem cells from bone marrow and adipose tissue on spinal fusion in healthy and ovariectomized rat

Despite alternatives to autogenous bone graft for spinal fusion have been investigated, it has been shown that osteoconductive materials alone do not give a rate of fusion comparable with autogenous bone. This study analyzed a strontium substituted beta-tricalcium phosphate (Sr-beta TCP) associated with syngeneic, unexpanded, and undifferentiated mesenchymal stem cells from bone marrow (BMSC) or adipose tissue (ADSC) as a new tissue engineering approach for spinal fusion procedures. A posterolateral fusion was performed in 15 ovariectomized (OVX) and 15 sham-operated (SHAM) Inbred rats. Both SHAM and OVX animals were divided into three groups: Sr-beta TCP, Sr-beta TCP+BMCSs, and Sr-beta TCP+ADSCs. Animals were euthanized 8 weeks after surgery and the spines evaluated by manual palpation, micro-CT, and histology. For both SHAM and OVX animals, the fusion tissue in the Sr-beta TCP+BMSCs group was more solid. This effect was significantly higher in OVX animals by comparing the Sr-beta TCP+BMCSs group with Sr-beta TCP+ADSCs. Radiographical score, based on micro-CT 2D image, highlighted that the Sr-beta TCP+BMCSs group presented a similar fusion to Sr-beta TCP and higher than Sr-beta TCP+ADSCs in both SHAM and OVX animals. Micro-CT 3D parameters did not show significant differences among groups. Histological score showed significantly higher fusion in Sr-beta TCP+BMSCs group than Sr-beta TCP and Sr-beta TCP+ADSCs, for both SHAM and OVX animals. In conclusion, our results suggest that addition of BMSCs to a Sr-beta TCP improve bone formation and fusion, both in osteoporotic and nonosteoporotic animal, whereas spinal fusion is not enhanced in rats treated with Sr-beta TCP+ADSCs. Thus, for conducting cells therapy in spinal surgery BMSCs still seems to be a better choice compared with ADSCs.