11. THE USE OF ENDOTHELIAL PROGENITOR CELLS TO PROMOTE BONE HEALING: A DEFECT MODEL IN THE RAT FEMUR

Abstract

Purpose: Endothelial Progenitor Cells (EPCs) have been proven to contribute to formation of new blood vessels. The objective of this study was to evaluate the effects of local EPC therapy on the stimulation of angiogenesis at a fracture site and the promotion of bone healing by increasing osteogenesis and callus formation.

Method: Rat bone marrow EPCs were isolated and cultured. A segmental bone defect (4mm.) was created in the rat femur diaphysis and stabilized with a mini-plate. A gelfoam piece impregnated with a solution of EPCs (1x106) was placed into the fracture gap. Control animals received only saline-gelfoam with no cells. In total, 42 rats were studied: 21 in EPC and 21 in control groups. Seven animals were sacrificed from each group at one, two, and three weeks post-operatively. Plain radiographs of the operated femur were taken before sacrifice. Operated femurs were harvested and the specimens from the osteotomy site were collected for histological evaluation. The x-rays were scored in a scale from zero to five according to the percentage and the intensity of the bone filling at the osteotomy site. Hematoxylin-eosin stained slides were evaluated for new vessel formation and the amount of bone tissue.

Results: Radiographically, at three weeks, the mean score for the EPC group was 4.5 with five out of seven animals having bridging callus; whereas for the control group, the mean score was 2.2 with no bridging callus formation. At two weeks, EPC treated animals had a mean score of 2.4, and the control group had a score of 1. Bone formation was insignificant at one week in either group, however, the scores tended to be higher in the EPC group animals than the control; 0.6 to 0.3 respectively. Histological evaluation revealed that the specimens from EPC treated animals had abundant spicules of trabecular bone containing predominantly bone cells, osteoid, and new vessels. Conversely, control animals had scarce trabecular bone with markedly less bone cells and vessels.

Conclusion: Local EPC therapy stimulates angiogenesis and increases osteogenesis and callus formation post fracture. Our report encourages further investigation of the local use of EPCs as a potential therapy to promote bone regeneration.