Emerging Technologies in Bone Repair and Spine Fusion: Stem Cell Strategies
Kathleen F. Lundquist
Introduction. Spondylolisthesis is defined as the forward slippage of a vertebra without rupture of the posterior arc, usually inducing lumbar canal stenosis with a prevalence estimated at 2.7% in males and 8.1% in females2. Spondylolisthesis is frequently treated via a spinal fusion surgical procedure if the degree of slippage is severe or the patient presents with unmanageable back pain. The fusion is achieved by adding supplementary bone tissue, either an autograft or allograft, between the two vertebrae to achieve stability. There are several issues associated with each of these methods. Although autografts are currently the gold standard, there is increased morbidity associated with the harvest procedure. There are also concerns about immunogenicity and infectious disease transmission with the use of allografts. These reasons, as well as the rate of non-union, have prompted further research into new approaches for successful spinal fusions. Most notably, the use of bone marrow mesenchymal stem cells (BMSCs) transfected with Endothelin-1 (EDN-1) or bone morphogenic protein-7 (BMP-7) have been explored due to their great osteogenic potential1. EDN-1 plays an important role in bone development by enhancing the differentiation of osteoprogenitor cells into osteoblasts. Furthermore, BMP-7 is known to promote bone regeneration by facilitating BMSC differentiation and growth. Methods. In study one, BMSCs were transfected with either a vector containing EDN-1 or with a control. These cells were seeded into calcium phosphate cement (CPC) before implantation into the rat calvarium. Eight weeks post-operatively, the results were analyzed using micro CT-assay and histological evaluation3. In study two, BMSCs were isolated from rat femurs and infected with a vector encoding B2BMP-7. Rats then received control scaffolds, scaffolds seeded with BMSCs, or scaffolds seeded with BMP-7 BMSCs. The results were post-operatively analyzed with histology and immunohistochemistry4. Results. Although there was bone growth observed in both the control and EDN-1 BMSC groups of study one, there was a significantly greater amount of new bone area in the EDN-1 overexpressed group 8 weeks post operatively3. Similarly, in study two, fully mature new bone was observed in the BMP-7 MSC 12 weeks post operatively, where as the blank scaffold had poor formation of new bone4. Conclusion. Gene therapy with the induction of EDN-1 or BMP-7 into BMSCs showed increased osteogenic potential and greater bone formation. These results show a promising future for the use of BMSCs in spinal fusion procedures. Human trials will be necessary to further evaluate the effectiveness of this method.
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