Isolation and expansion of osteogenic cells from bone marrow and in vivo testing at ectopic sites
BACKGROUND: Cell therapy is a strategy to enhance bone formation in regenerative dentistry. Osteogenic cells can be isolated and expanded from total bone marrow by the use of biodegradable microcarriers. It remains, however, unknown whether the cells on the surface of microcarriers can provide bone substitutes with an osteogenic potential. METHODS: We therefore isolated and expanded rat bone marrow cells on the surface of CultiSpher G microcarriers in a spinner-flask bioreactor. Isolated cells were viable as determined by MTT assay and stained positive for alkaline phosphatase activity. CultiSpher G microcarriers loaded with osteogenic cells were mixed with two bone substitutes, natural bone mineral, and hydroxyapatite/tricalcium, phosphate before subcutaneous implantation into immunodeficient mice. RESULTS: Isolated cells showed positive formazan formation indicating cell viability. Alkaline phosphatase activity being a marker gene for osteogenic differentiation was detectable. However, implants recovered after eight weeks from ectopic sites failed to show bone formation, even though blood vessels were present. CONCLUSIONS: These results suggest that the presence of osteogenic cells on the surface of microcarriers is not sufficient to provide bone substitutes with a bone forming capacity. The lack of bone formation at ectopic sites does not rule out the possibility that supplementation of bone substitutes with cell-loaded microcarrier support bone regeneration at orthotopic sites. Moreover, our data do not exclude the possibility that the current concept can be optimized to achieve ectopic bone formation.