Bilateral femoral distraction was performed in rats to investigate whether
injections of marrow-derived mesenchymal progenitor cells could be used to
facilitate new bone formation. The cells were isolated from whole marrow of
2-6-month-old Sprague-Dawley rats. One-year-old recipient Sprague-Dawley r
ats were divided into five experimental groups. Rats in groups I, TI, and I
II received injections of mesenchymal progenitor cells on days 6 (beginning
), 12 (middle), and 18 (end of distraction) after surgery, respectively Tho
se in group IV received injections of serum and carrier gel alone, and thos
e in group V received no injections. Distraction zones were harvested at 36
days and analyzed for new bone volume within the distraction gap by three-
dimensional microcomputed tomography. Significant increases in new bone vol
ume were observed for femora injected with marrow-derived progenitor cells
compared with contralateral femora and controls (no injection). The timing
of the cell injections appeared to have no effect on the experimental outco
me. Histologic analyses demonstrated active formation of new trabecular bon
e with marked osteoblastic activity and osteoid production. No qualitative
differences in histologic appearances of new hone among rats in any of the
five groups were seen. The results of in vitro lysis assays indicated that
donor and recipient rats were not completely syngenic, leaving some doubt a
s to the reasons for observed increases in new bone formation. Future work
will focus on attempting to repeat these experiments in a fully syngenic ra
t model. This rat distraction model can be used to explore the molecular an
d cellular behavior of these progenitor cells in a clinically relevant ir?
vivo environment.