Bone marrow-derived mesenchymal stem cells assembled with low-dose BMP-2 in a three-dimensional hybrid construct enhances posterolateral spinal fusion in syngeneic rats

BACKGROUND CONTEXT: The combination of potent osteoinductive growth factor, functional osteoblastic cells, and osteoconductive materials to induce bone formation is a well-established concept in bone tissue engineering. However, supraphysiological dose of growth factor, such as recom.binant human bone morphogenetic protein 2 (rhBMP-2), which is necessary in contemporary clinical application, have been reported to result in severe side effects. PURPOSE: We hypothesize that the synergistic osteoinductive capacity of low-dose bone morphogenetic protein 2 (BMP-2) combined with undifferentiated bone marrow-derived stromal cells (BMSCs) is comparable to that of osteogenically differentiated BMSCs when used in a rodent model of posterolateral spinal fusion. STUDY DESIGN/SETTING: A prospective study using a rodent model of posterolateral spinal fusion was carried out. PATIENT SAMPLE: Thirty-six syngeneic Fischer rats comprised the patient sample. METHODS: Six groups of implants were evaluated as follows (n=6): (1) 10 mu g BMP-2 with undifferentiated BMSCs; (2) 10 j.tg BMP-2 with osteogenic-differentiated BMSCs; (3) 2.5 j.tg BMP-2 with undifferentiated BMSCs; (4) 2.5 mu g BMP-2 with osteogenic-differentiated BMSCs; (5) 0.5 1 mu g IMP-2 with undifferentiated BMSCs; and (6) 0.5 mu g BMP-2 with osteogenic-differentiated BMSCs. Optimal in vitro osteogenic differentiation of BMSCs was determined by quantitative real-time polymerase chain reaction (qRT-PCR) gene analysis whereas in vivo bone formation capacity was evaluated by manual palpation, micro-computed tomography, and histology. RESULTS: Rat BMSCs cultured in fibrin matrix that was loaded into the pores of medical -grade poly epsilon caprolactone tricalcium phosphate scaffolds differentiated toward osteogenic lineage by expressing osterix, runt-related transcription factor 2, and osteocalcium mRNA when supplemented with dexamethasone, ascorbic acid, and paglycerophosphate. Whereas qRT-PCR revealed optimal increase in osteogenic genes expression after 7 days of in vitro culture, in vivo transplantation study showed that pre-differentiation of 13MSCs before transplantation failed to promote posterolateral spinal fusion when co-delivered with low-dose BMP-2 (1/6 or 17% fusion rate). In contrast, combined delivery of undifferentiated BMSCs with low dose BMP-2 (2.5 tag) demonstrated significantly higher fusion rate (4/6 or 67%) as well as significantly increased volume of new bone formation (p<.05). CONCLUSION: In sununary, this study supports the combination of undifferentiated BMSCs and low-dose BMP-2 for bone tissue engineering construct. (C) 2015 Elsevier Inc. All rights reserved.