ß-TCP versus autologous bone for repair of alveolar clefts in a goat model.

OBJECTIVE: The aim of this study in goats was to test the hypothesis that a novel synthetic bone substitute beta tricalcium phosphate (ß-TCP) can work as well as autologous bone harvested from the iliac crest for grafting and repair of alveolar clefts. DESIGN: Ten adult Dutch milk goats (Capra hircus) were used in a split-mouth study design. MAIN OUTCOME MEASURES: Volumetric histologic assessment of new bone formation and radiographic measurement of orthodontic movement of teeth in a formerly created alveolar cleft. CONCLUSIONS: The synthetic bone substitute ß-TCP was shown to result in bone healing similar to that of iliac crest bone. The surgical, orthodontic, and histologic results now warrant the testing of ß-TCP in the human cleft situation.

Dexamethasone treatment during the expansion phase maintains stemness of bone marrow mesenchymal stem cells.

Human mesenchymal stem cells (hMSCs) can form various mesodermal tissues when grown under appropriate conditions. Dexamethasone (Dex) is regularly used to stimulate the osteogenic potential of hMSCs and it has recently been reported to increase the cell expansion rate. In this study we have investigated the effect of low-dose Dex treatment (10(-8) M) on the multipotency of expanded hMSCs, using histological, biochemical and molecular biological techniques. Early passage (P2-3) and late passage (P6) cells were positive (>90%) for mesenchymal adhesion cell markers (CD105/CD29/CD44/CD166/CD90) and negative (<10%) for haematopoietic markers (CD34/CD45/CD14). Dex did not change the overall expression pattern of these cell surface markers. Expanded hMSCs gave rise to specialized cell lineages when grown in differentiation-promoting medium. Depending on the donor, Dex treatment improved the potency for osteogenic, adipogenic and chondrogenic differentiation of expanded hMSCs. Dex also prevented the loss of proliferative potential of hMSCs upon sequential passaging and the loss of the typical hMSCs surface phenotype. hMSCs gene expression analysis showed that low-dose Dex negatively regulated transcription of genes correlated with apoptosis and differentiation, and positively regulated genes associated with cell proliferation. In conclusion, the collective data argue that low-dose Dex preserves the stemness of hMSCs during repeated passaging, as indicated by the maintenance of the stem cell phenotype, proliferative capacity and multi-lineage differentiation potential.

Growth, metabolism, and growth inhibitors of mesenchymal stem cells.

Most therapeutic applications of bone marrow stromal cells (MSCs), or mesenchymal stem cells, require expansion of these cells. This study aimed to obtain more information about human MSCs regarding their expansion characteristics: growth, metabolism, and growth inhibitors. In addition, the same expansion factors were examined for (model species) goat and rat MSCs to evaluate differences between MSCs of mammalian species. MSC proliferation, nutrient consumption, and metabolite production were determined for five donors per species. In addition, the growth inhibitory concentrations of lactate and ammonia (NH3) were established. Results showed that goat MSCs grew significantly faster than human and rat MSCs and that goat cells metabolized glucose more efficiently into energy (Ylac/glc=0.8) than human (Ylac/glc=2.0) and rat MSCs (Ylac/glc=1.9). In addition, human (qGlc= -9.2pmol cell(-1) day(-1) and rat MSCs (qGlc= -5.9pmol cell(-1) day(-1)) consumed more glucose than goat MSCs (qGlc= -2.6pmol cell(-1) day(-1)). Glutamine was shown not to be important as energy source for human, goat, and rat MSCs. Regarding growth inhibition by metabolites, rat MSCs were more sensitive to lactate and NH3 (growth inhibiting at 16mM lactate and at 1.9mM NH3) than goat (lactate: 28.4mM, NH3: 2.9mM) and human MSCs (lactate: 35.4mM, NH3: 2.4mM). Human MSCs did not lose their differentiation potential when their growth was inhibited by lactate or NH3.

cAMP/PKA pathway activation in human mesenchymal stem cells in vitro results in robust bone formation in vivo.

Tissue engineering of large bone defects is approached through implantation of autologous osteogenic cells, generally referred to as multipotent stromal cells or mesenchymal stem cells (MSCs). Animal-derived MSCs successfully bridge large bone defects, but models for ectopic bone formation as well as recent clinical trials demonstrate that bone formation by human MSCs (hMSCs) is inadequate. The expansion phase presents an attractive window to direct hMSCs by pharmacological manipulation, even though no profound effect on bone formation in vivo has been described so far using this approach. We report that activation of protein kinase A elicits an immediate response through induction of genes such as ID2 and FosB, followed by sustained secretion of bone-related cytokines such as BMP-2, IGF-1, and IL-11. As a consequence, PKA activation results in robust in vivo bone formation by hMSCs derived from orthopedic patients.