Effect of G-CSF on the osteoinductive property of a BCP/blood clot composite

We previously reported that blood clot combined with biphasic calcium phosphate microparticles constitute a biomaterial (BRB) that can repair a bone critical defect in rat and induces subcutaneous bone formation in mice. The granulocyte colony-stimulating factor (G-CSF) is the agent most commonly used in human to enrich blood with hematopoietic stem and progenitor cells (HSPCs) as well as granulocytes (GCs). Moreover, recent data also suggest that it can mobilize mesenchymal stem cells (MSCs). Here, we asked whether the osteoinductive properties of the BRB could be further enhanced by G-CSF, either by replacing normal blood by G-CSF-mobilized blood (BRBe) or by treating the recipient animals with G-CSF. The experiments performed in C57BL/6 mice showed that G-CSF induces a marked increase of circulating HPCs and GCs, but not of MSCs. BRBe prepared with G-CSF-enriched blood induced a slight but significant decrease of subcutaneous bone formation compared to BRB prepared with normal blood. Additional injection of G-CSF to the recipient mice had no significant effect on the bone formation induced by BRB or BRBe. Altogether these results indicate that, in this model of ectopic implantation, cell mobilization induced by G-CSF has a negative effect on the osteoinductive property of this blood/BCP composite.