Different BGMs associated to MSC: Can tissue engineering help GBR?

Abstract

Purpose: Bone augmentation in oral surgery relies on osteogenic andosteoconductive properties of bone graftmaterial (BGM). Several types of BGMs with different chemical compositions andmicrostructures are today available, including natural derived or artificially modified heterologous bone, and synthetically synthetized bioceramics. A further improvement is represented by the tissue engineering approach, where autologous mesenchymal stem cells (MSCs), expanded in vitro, are seeded on BGM prior implantation in the bone defect. In this study the effect of different bone substitutes on MSC differentiation when they were adopted as cell culture substrates has been evaluated. Methods andmaterials:HumanMSCwere cultured in vitro in the presence of BGMs of different origins (natural bone derived, synthetic and mixed). Cellular adhesion on BGMs were analyzed with SEM. Alkaline phosphatase (ALP – early marker of the osteogenic differentiation) gene expression was evaluated by real time PCR andALP enzyme activitywas determined at different culture time points (7, 14 and 28 days). In vivo osteogenic differentiation of implanted tissue constructs (BGM+MSC) was investigated taking advantage of an ectopic bone formation in an immunodeficient mouse model and analyzed by histology. Results: A good cell adhesion to all BGMs was observed already after 6h from plating and cells were successfully cultured for 28 days. ALP gene expression and enzymatic activity was detectable after 14 day culture. The ALP gene expression analysis indicated that the MSC cultured with BGM derived from natural bone (BioGen, Bio-Oss) presented a steady increase of the ALP expression reaching a significantly higher level at 28th day of osteoinduction compared to the other BGMs. Instead, cells cultured in the presence of BGMs of synthetic origin (Bonit, Skelite), presented themaximum level of ALP gene expression at day 14 with a subsequent stabilization in the expression at day 28. Interestingly the cells cultured in the presence of mixed origin (Pepgen P-15) BGM presented a peak in the gene expression at day 7. The in vivo osteogenic test showed a good bone formation at the periphery of all BGMsparticles seededwith BMSCs. Neo-formed bone progressively filled the gap between the particles bridging them after 8 weeks, maintaining a peripheral vasculature. Conclusion: All tested BGMs implemented bone formation in guided bone regeneration. BGMs of animal origin showed greater ALP expression at 28 days.