Five Days Granulocyte Colony-Stimulating Factor Treatment Increases Bone Formation and Reduces Gap Size of a Rat Segmental Bone Defect: A Pilot Study

Abstract

Bone is an organ with high natural regenerative capacity and most fractures heal spontaneously when appropriate fracture fixation is provided. However, additional treatment is required for patients with large segmental defects exceeding the endogenous healing potential and for patients suffering from fracture non-unions. These cases are often associated with insufficient vascularization. Transplantation of CD34+ endothelial progenitor cells (EPCs) has been successfully applied to promote neovascularization of bone defects, however including extensive ex vivo manipulation of cells. Here, we hypothesized, that treatment with granulocyte colony-stimulating factor (G-CSF) may improve bone healing by mobilization of CD34+ progenitor cells into the circulation, which in turn may facilitate vascularization at the defect site. In this pilot study, we aimed to characterize the different cell populations mobilized by G-CSF and investigate the influence of cell mobilization on the healing of a critical size femoral defect in rats. Cell mobilization was investigated by flow cytometry at different time points after five consecutive daily G-CSF injections. In a pilot study, bone healing of a 4.5-mm critical femoral defect in F344 rats was compared between a saline-treated control group and a G-CSF treatment group. In vivo microcomputed tomography and histology were applied to compare bone formation in both treatment groups. Our data revealed that leukocyte counts show a peak increase at the first day after the last G-CSF injection. In addition, we found that CD34+ progenitor cells, including EPCs, were significantly enriched at day 1, and further increased at day 5 and day 11. Upregulation of monocytes, granulocytes and macrophages peaked at day 1. G-CSF treatment significantly increased bone volume and bone density in the defect, which was confirmed by histology. Our data show that different cell populations are mobilized by G-CSF treatment in cell specific patterns. Although in this pilot study no bridging of the critical defect was observed, significantly improved bone formation by G-CSF treatment was clearly shown.

Effectiveness of granulocyte colony stimulating factor to enhance healing on delayed union fracture model Sprague-Dawley rat

“…In this study, an increase in the percentage of cartilage formation in the treatment group with a combination of G-CSF and the antagonist CXCR4 [ 36 ]. Research conducted by Herrmann et al also showed similar results, where there was an increase in the formation of cartilage areas in the G-CSF treatment compared to controls [ 28 ].…”

“…therefore the fracture healing effect due to inducing osteoblast cells is not the answer to accelerating the healing process. As previously explained, G-CSF can increase the number of stem cells and it is these stem cells that will produce BMP-2 where BMP-2 expression will recruit stem cells at the fracture site [ [28] , [29] , [30] ]. In addition, from a clinical application point of view, Patients who presented with delayed union did not require surgery [ 31 ].…”

“…The results of the increase in woven bone which were found to be higher in the G-CSF group were supported by research by Herrmann et al which stated that on day 20, the size of the bone defect in the group of mice given G-CSF subcutaneously at a dose of 50 μg/kg body weight was smaller than the control group. Herrmann et al also stated that bone formation in mice in the G-CSF group was faster than in the control group [ 28 ].…”

Bone Complications in Allogenic Hematopoietic Stem Cell Transplantation

“…In children with severe chronic neutropenia, extended G-CSF use correlates significantly with lower BMD but this correlation is not seen in adults [54]. Contrasting this, a recent study in animals showed significantly improved bone formation with G-CSF treatment [55]. Together these data suggest a need for further study into the role of G-CSF in allogenic HSCTrelated loss of BMD.…”

“…Also, HRT can increase the possibility of cardiovascular complications such as thromboembolism and stroke, an important consideration in woman. Breast cancer risk needs to be discussed in detail when estrogen replacement therapy is considered [55]. Finally, bisphosphonate therapy should be started prophylactically in patients who are at high risk of bone loss and fracture or who already have developed osteoporosis [81].…”