Osteogenic comparison of expanded and uncultured adipose stromal cells

Adipose stromal cells (ASC) are a promising alternative to progenitor cells from other tissue compartments because of their multipotential and capacity to retrieve significantly more progenitor cells. Initial cell samples are heterogeneous, containing a collection of cells that may contribute to tissue repair, but the sample becomes more homogeneous with each passage. Therefore, we hypothesized that the osteogenic potential of culture-expanded ASC would differ from uncultured ASC.

Adipose tissue was collected from a yearling colt, and ASC were isolated and expanded using standard protocols or prepared by a commercial vendor using proprietary technology (proprietary stromal vascular fraction, SVFp). Cells were seeded on collagen sponges and maintained in osteogenic culture conditions for up to 21 days to assess osteogenic potential. The ability of each population to stimulate neovascularization and bone healing was determined upon implanting cell-loaded sponges into a rodent calvarial bone defect. Neovascularization was measured 3 weeks post-implantation, while bone formation was monitored over 12 weeks using in vivo microcomputed tomography (microCT).

SVFp exhibited increased intracellular alkaline phosphatase activity compared with cultured ASC but proliferated minimally. Histologic analysis of explanted tissues demonstrated greater vascularization in defects treated with cultured ASC compared with SVFp. We detected increases in bone volume for defects treated with cultured cells while observing similar values for bone mineral density, regardless of cell type.

These results suggest that expanded ASC are advantageous for neovascularization and bone healing in this model compared with SVFp, and provide additional evidence of the utility of ASC in bone repair.