gms | German Medical Science

Objectives: The brain derived neurotrophic factor (BDNF) is secreted by neurons where it stimulates axonal outgrowth and angiogenesis. BDNF is also synthesized by osteoblasts and up-regulated during human fracture healing [1]. In combination with bone substitute materials it enhanced the vitality of mesenchymal stem cells and osteoblasts but not of osteoclasts in vitro. Here we asked whether integration of BDNF into pasty calcium phosphate bone cement (pCPC) via coating of mesoporous bioactive glass (MBG) is able to stimulate fracture healing in a murine osteoporosis fracture model.

Methods: Female 16 week old knockout mice with a deletion of the muscarinic acetylcholine receptor M3 (KO) and their corresponding wild type mice (WT) were used in the present study that was approved by the regional authorities (Regierungspräsidium Gießen GI75/2014). The KO mice present a model for postmenopausal osteoporosis [2]. All mice (n=87) underwent an osteotomy, the fracture gap was filled with pCPC+MBG+BDNF (21 ng BDNF per mouse) in the experimental animal groups and without BDNF (pCPC+MBG) in the control groups. After a post operational duration of 35 days the femurs were extracted and analyzed by cell- and molecular biological methods, mass spectrometric imaging using time of flight secondary ion mass spectrometry (ToF-SIMS), scanning electron microscopy (SEM), and EDX. For the statistical evaluation, we used t-test, ANOVA, Kruskal-Wallis- and Mann-Whitney-test (SPSS, V23, IBM).

Results and conclusion: The implants were well integrated into the fracture gap and new built bone was localized at the interface of the bone substitute material. The silicon-rich MBG was detected by the combination ToF-SIMS, SEM, and EDX analysis and it could be observed that MBG was dissolved after reaching the implant interface by forming a pore that was subsequently filled with new built yet not fully mineralized bone tissue. In the fracture gap we measured an increase in new built bone in WT with pCPC+MBG+BDNF compared to WT without BDNF (p<0.05). In line with this we found an increase of new built bone tissue at the interface of the implants in WT with pCPC+MBG+BDNF compared to WT without BDNF (p<0.05). Additionally we measured a decrease in the amount of leucocytes in the KO with pCPC+MBG+BDNF compared to KO without application of BDNF (p<0.05).

Thus, the results demonstrated that pCPC+MBG+BDNF stimulates the formation of new bone tissue in bone healthy (WT) but not in osteoporotic (KO) mice. In osteoporotic (KO) mice BDNF seems to be involved in the regulation of the immune system during fracture healing which will be analyzed in up-coming studies.