Reparative Osteogenesis during Transplantation of Mesenchymal Stem Cells

Is bone transplantation the gold standard for repair of alveolar bone defects?

New strategies to fulfill craniofacial bone defects have gained attention in recent years due to the morbidity of autologous bone graft harvesting. We aimed to evaluate the in vivo efficacy of bone tissue engineering strategy using mesenchymal stem cells associated with two matrices (bovine bone mineral and α-tricalcium phosphate), compared to an autologous bone transfer. A total of 28 adult, male, non-immunosuppressed Wistar rats underwent a critical-sized osseous defect of 5 mm diameter in the alveolar region. Animals were divided into five groups. Group 1 (n = 7) defects were repaired with autogenous bone grafts; Group 2 (n = 5) defects were repaired with bovine bone mineral free of cells; Group 3 (n = 5) defects were repaired with bovine bone mineral loaded with mesenchymal stem cells; Group 4 (n = 5) defects were repaired with α-tricalcium phosphate free of cells; and Group 5 (n = 6) defects were repaired with α-tricalcium phosphate loaded with mesenchymal stem cells. Groups 2-5 were compared to Group 1, the reference group. Healing response was evaluated by histomorphometry and computerized tomography. Histomorphometrically, Group 1 showed 60.27% ± 16.13% of bone in the defect. Groups 2 and 3 showed 23.02% ± 8.6% (p = 0.01) and 38.35% ± 19.59% (p = 0.06) of bone in the defect, respectively. Groups 4 and 5 showed 51.48% ± 11.7% (p = 0.30) and 61.80% ± 2.14% (p = 0.88) of bone in the defect, respectively. Animals whose bone defects were repaired with α-tricalcium phosphate and mesenchymal stem cells presented the highest bone volume filling the defects; both were not statistically different from autogenous bone.

Xenopus laevis as a novel model to study long bone critical-size defect repair by growth factor-mediated regeneration

We used the tarsus of an adult Xenopus laevis frog as an in vivo load-bearing model to study the regeneration of critical-size defects (CSD) in long bones. We found the CSD for this bone to be about 35% of the tarsus length. To promote regeneration, we implanted biocompatible 1,6 hexanediol diacrylate scaffolds soaked with bone morphogenetic proteins-4 and vascular endothelial growth factors. In contrast to studies that use scaffolds as templates for bone formation, we used scaffolds as a growth factor delivery vehicle to promote cartilage-to-bone regeneration. Defects in control frogs were filled with scaffolds lacking growth factors. The limbs were harvested at a series of time points ranging from 3 weeks to 6 months after implantation and evaluated using micro-computed tomography and histology. In frogs treated with growth factor-loaded scaffolds, we observed a cartilage-to-bone regeneration in the skeletal defect. Five out of eight defects were completely filled with cartilage by 6 weeks. Blood vessels had invaded the cartilage, and bone was beginning to form in ossifying centers. By 3 months, these processes were well advanced, and extensive ossification was observed in 6-month samples. In contrast, the defects in control frogs showed only formation of fibrous scar tissue. This study demonstrates the utility of a Xenopus model system for tissue engineering research and that the normal in vivo mechanism of endochondral bone development and fracture repair can be mimicked in the repair of CSD with scaffolds used as growth factor delivery mechanisms.

IMT504, the prototype of the immunostimulatory oligonucleotides of the PyNTTTTGT class, increases the number of progenitors of mesenchymal stem cells both in vitro and in vivo: potential use in tissue repair therapy

Bone marrow (BM)-derived adult mesenchymal stem cells (MSCs) have the capacity to differentiate in vitro into different cell lines. This makes them a likely source for application in tissue repair therapies. Here, we report evidence indicating that, both in vivo and in vitro, IMT504, the prototype of the PyNTTTTGT class of immunostimulatory oligonucleotides, significantly increases the number of fibroblast colony-forming units (CFU-Fs) that originate MSCs. When rat BM cells were cultured with IMT504, the mean number of CFU-Fs increased about three times as compared with untreated controls (CFU-F: 19 +/- 6.3 vs. 6.8 +/- 2.0/2 x 10(6) seeded BM cells, p = .03). Furthermore, rats inoculated with IMT504 had a significantly higher number of CFU-Fs both in BM (CFU-F: 124 +/- 33 vs. 38 +/- 17/femur, p = .04) and in peripheral blood (animals with detectable CFU-Fs in circulation 8/12 vs. 2/12, p = .04) as compared with untreated animals. On the other hand, BM-derived adherent cells either treated in vitro with IMT504 or obtained from animals injected with IMT504 possess the capacity to differentiate to the osteogenic and adipogenic cell lineages as regular MSCs. Finally, we found that repair of a bone defect was accelerated in rats injected with IMT504 as compared with control animals (area with consolidated bone: 80% +/- 6.4% vs. 49% +/- 3.5%, p = .03, n = 10 rats per group). Importantly, when two human BM were cultured in the presence of IMT504, the mean number of fibroblastic adherent colonies also increased as compared with controls. These results suggest the possibility of clinical use of IMT504 in bone, and presumably other, tissue repair therapies.