Abstract
Reconstruction of bone due to surgical removal or disease-related bony defects is a clinical challenge. It is known that the immune system exerts positive immunomodulatory effects on tissue repair and regeneration. In this study, we evaluated the in vivo efficacy of autologous neutrophils on bone regeneration using a rabbit calvarial defect model. Methods: Twelve rabbits, each with two surgically created calvarial bone defects (10 mm diameter), were randomly divided into two groups; (i) single application of neutrophils (SA-NP) vs. SA-NP control, and (ii) repetitive application of neutrophils (RA-NP) vs. RA-NP control. The animals were euthanized at 4 and 8 weeks post-operatively and the treatment outcomes were evaluated by micro-computed tomography, histology, and histomorphometric analyses. Results: The micro-CT analysis showed a significantly higher bone volume fraction (bone volume/total volume) in the neutrophil-treated groups, i.e., median interquartile range (IQR) SA-NP (18) and RA-NP (24), compared with the untreated controls, i.e., SA-NP (7) and RA-NP (14) at 4 weeks (p < 0.05). Similarly, new bone area fraction (bone area/total area) was significantly higher in neutrophil-treated groups at 4 weeks (p < 0.05). Both SA-NP and RA-NP had a considerably higher bone volume and bone area at 8 weeks, although the difference was not statistically significant. In addition, immunohistochemical analysis at 8 weeks revealed a higher expression of osteocalcin in both SA-NP and RA-NP groups. Conclusions: The present study provides first hand evidence that autologous neutrophils may have a positive effect on promoting new bone formation. Future studies should be performed with a larger sample size in non-human primate models. If proven feasible, this new promising strategy could bring clinical benefits for bone defects to the field of oral and maxillofacial surgery.
Highlights
We examined the in vivo efficacy of autologous neutrophils on bone repair and regeneration using a rabbit calvarial defect model
The animals were randomly divided into two groups of six animals each viz. (i) single application of neutrophil group (SA-NP) (n = 3), where a single dose of neutrophils mixed with fibrin gel was added to the defect at once, while the contralateral defect was filled with phosphate-buffered saline (PBS) with fibrin gel as the control (SA-NP control) (n), and (ii) repetitive application of neutrophil group (RA-NP) (n = 3), where a single dose of neutrophils was added to the defect three times on day 0, 2, and 4
Day 0 was similar to SA NP group, where neutrophils mixed with fibrin gel was added to the defect, while the contralateral defect was filled with phosphate-buffered saline (PBS) with fibrin gel as the control
Summary
Reconstruction of large bone defects in the oral and maxillofacial region as a result of trauma, bone tumors, or congenital deformities remains a major clinical challenge [1]. Autologous bone or synthetic bone grafts have yielded satisfactory results for bone regeneration, they often possess significant limitations in terms of availability, efficacy, immunological reactions, and risk of disease transmission [2]. Additional surgery for bone harvesting causes pain and donor site morbidity. Bone tissue engineering has been considered a promising strategy to overcome foregoing challenges in the reconstruction of bone defects
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