Local Application of Mineral-Coated Microparticles Loaded With VEGF and BMP-2 Induces the Healing of Murine Atrophic Non-Unions.

M Orth,C Scheuer,B Ganse,Y Bullinger,T Pohlemann,J S Lee,T Fritz,M W Laschke,J Stutz,W L Murphy,M D Menger

doi:10.3389/fbioe.2021.809397

Abstract

Deficient angiogenesis and disturbed osteogenesis are key factors for the development of nonunions. Mineral-coated microparticles (MCM) represent a sophisticated carrier system for the delivery of vascular endothelial growth factor (VEGF) and bone morphogenetic protein (BMP)-2. In this study, we investigated whether a combination of VEGF- and BMP-2-loaded MCM (MCM + VB) with a ratio of 1:2 improves bone repair in non-unions. For this purpose, we applied MCM + VB or unloaded MCM in a murine non-union model and studied the process of bone healing by means of radiological, biomechanical, histomorphometric, immunohistochemical and Western blot techniques after 14 and 70 days. MCM-free non-unions served as controls. Bone defects treated with MCM + VB exhibited osseous bridging, an improved biomechanical stiffness, an increased bone volume within the callus including ongoing mineralization, increased vascularization, and a histologically larger total periosteal callus area consisting predominantly of osseous tissue when compared to defects of the other groups. Western blot analyses on day 14 revealed a higher expression of osteoprotegerin (OPG) and vice versa reduced expression of receptor activator of NF-κB ligand (RANKL) in bone defects treated with MCM + VB. On day 70, these defects exhibited an increased expression of erythropoietin (EPO), EPO-receptor and BMP-4. These findings indicate that the use of MCM for spatiotemporal controlled delivery of VEGF and BMP-2 shows great potential to improve bone healing in atrophic non-unions by promoting angiogenesis and osteogenesis as well as reducing early osteoclast activity.

Highlights

Despite growing knowledge about the process of bone healing, 5–10% of all fractures still fail to heal (Buza and Einhorn, 2016)
The elemental analysis by energy dispersive spectrometer (EDS) showed that the calcium to phosphorus ratio (Ca/P) of hydroxyapatite particles (1.74 ± 0.08) is similar to that of mineral-coated microparticles (MCM) (1.64 ± 0.05)
The intensity of carbonate peaks from MCM was slightly more prominent compared to those of uncoated hydroxyapatite particles. These results demonstrate that the coating of the MCM is plate-like, nanoporous, carbonate-substituted hydroxyapatite

Summary

Introduction

Despite growing knowledge about the process of bone healing, 5–10% of all fractures still fail to heal (Buza and Einhorn, 2016). VEGF+BMP-2-Loaded MCM and Bone Repair treatment of non-unions is still the transplantation of autologous bone tissue This procedure does not guarantee adequate bone healing and bears the risk of a number of complications, such as donor-site morbidity, infections and additional pain (Pelissier et al, 2003; Yoneda et al, 2005). To prevent patients from such complications and to improve the fusion rate of not healing fractures, artificial bone substitutes have been developed. These materials have been optimized by combining osteoconductive and osteoinductive properties in order to support natural bone growth and to induce new bone formation (Fillingham and Jacobs, 2016). MCM have been analyzed in detail regarding binding and release kinetics for vascular endothelial growth factor (VEGF) and bone morphogenetic protein (BMP)-2 (Yu et al, 2014)

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Results

Conclusion