Longitudinal analysis of osteogenic and angiogenic signaling factors in healing models mimicking atrophic and hypertrophic non-unions in rats

A comparative in vitro and in vivo analysis of the impact of copper substitution on the cytocompatibility, osteogenic, and angiogenic properties of a borosilicate bioactive glass

The 0106-B1-bioactive glass (BG) composition (in wt %: 37.5 SiO2, 22.6 CaO, 5.9 Na2O, 4.0 P2O5, 12.0 K2O, 5.5 MgO, and 12.5 B2O3) has demonstrated favorable processing properties and promising bone regeneration potential. The present study aimed to evaluate the biological effects of the incorporation of highly pro-angiogenic copper (Cu) in 0106-B1-BG in vitro using human bone marrow-derived mesenchymal stromal cells (BMSCs) as well as its in vivo potential for bone regeneration. CuO was added to 0106-B1-BG in exchange for CaO, resulting in Cu-doped BG compositions containing 1.0, 2.5 and 5.0 wt % CuO (composition in wt %: 37.5 SiO2, 21.6/ 20.1/17.6 CaO, 5.9 Na2O, 4.0 P2O5, 12.0 K2O, 5.5 MgO, 12.5 B2O3, and 1.0/ 2.5/ 5.0 CuO). In vitro, the BGs' impact on the viability, proliferation, and growth patterns of BMSCs was evaluated. Analyses of protein secretion, matrix formation, and gene expression were used for the assessment of the BGs' influence on BMSCs regarding osteogenic differentiation and angiogenic stimulation. The presence of Cu improved cytocompatibility, osteogenic differentiation, and angiogenic response when compared with unmodified 0106-B1-BG in vitro. In vivo, a critical-size femoral defect in rats was filled with scaffolds made from BGs. Bone regeneration was evaluated by micro-computed tomography. Histological analysis was performed to assess bone maturation and angiogenesis. In vivo effects regarding defect closure, presence of osteoclastic cells or vascular structures in the defect were not significantly changed by the addition of Cu compared with undoped 0106-B1-BG scaffolds. Hence, while the in vitro properties of the 0106-B1-BG were significantly improved by the incorporation of Cu, further evaluation of the BG composition is necessary to transfer these effects to an in vivo setting.

Biological effects of a zinc-substituted borosilicate bioactive glass on human bone marrow derived stromal cells in vitro and in a critical-size femoral defect model in rats in vivo

The borosilicate 0106-B1-bioactive glass (BG) composition (in wt%: 37.5 SiO2, 22.6 CaO, 5.9 Na2O, 4.0P2O5, 12.0 K2O, 5.5 MgO, 12.5 B2O3) has shown favorable processing characteristics and bone regeneration ability. This study investigated the addition of zinc (Zn) to 0106-B1-BG as an approach to improve this BG's biological properties. Different proportions of ZnO were substituted for CaO in 0106-B1-BG, resulting in three new BG-compositions: 1-Zn-BG, 2-Zn-BG, 3-Zn-BG (in wt%: 37.5 SiO2, 21.6/20.1/17.6 CaO, 4.0 P2O5, 5.9 Na2O, 12.0 K2O, 5.5 MgO, 12.5 B2O3 and 1.0/2.5/5.0 ZnO). Effects of the BG compositions on cytocompatibility, osteogenic differentiation, extracellular matrix deposition, and angiogenic response of human bone marrow-derived mesenchymal stromal cells (BMSCs) were evaluated in vitro. Angiogenic effects were assessed using a tube formation assay containing human umbilical vein endothelial cells. The in vivo osteogenic and angiogenic potentials of 3-Zn-BG were investigated in comparison to the Zn-free 0106-B1-BG in a rodent critical-size femoral defect model. The osteogenic differentiation of BMSCs improved in the presence of Zn. 3-Zn-BG showed enhanced angiogenic potential, as confirmed by the tube formation assay. While Zn-doped BGs showed clearly superior biological properties in vitro, 3-Zn-BG and 0106-B1-BG equally promoted the formation of new bone in vivo; however, 3-Zn-BG reduced osteoclastic cells and vascular structures in vivo. The acquired data suggests that the differences regarding the in vivo and in vitro results may be due to modulation of inflammatory responses by Zn, as described in the literature. The inflammatory effect should be investigated further to promote clinical applications of Zn-doped BGs.

Temporal Pattern of micro-CT Angiography Vascular Parameters and VEGF mRNA Expression in Fracture Healing: a Radiograph and Molecular Comparison

Angiogenesis plays an important role in fracture healing with vascular endothelial growth factor (VEGF) as the main protein involved. Micro-computed tomography (CT) angiography may be used to analyze this revascularization with several parameters such as number of branches, total volume, and diameter. This systematic review is aimed to assess available studies on the temporal pattern of vascular imaging on micro-CT angiographs, especially in terms of the number of branches, total volume, and diameter as well as the temporal pattern of VEGF mRNA expression as the molecular comparison during bone fracture healing. This review was conducted according to the PRISMA guidelines. Electronic database searches were performed using PubMed, ProQuest, ScienceDirect, EBSCOhost, Taylor & Francis Online, and hand searching. The search strategy and keywords were adjusted to each database using the Boolean operators and other available limit functions to identify most relevant articles based on our inclusion and exclusion criteria. Screening and filtration were done in several stages by removing the duplicates and analyzing each title, abstract, and full-text in all included entries. Data extraction was done for syntheses to summarize the temporal pattern of each parameter. A total of 28 articles were eligible and met all criteria, 11 articles were synthesized in its angiograph's analysis, 16 articles were synthesized in its VEGF mRNA expression analysis, and 1 article had both parameters analyzed. The overall temporal pattern of both three micro-CT angiographic parameters and VEGF mRNA expression was in line qualitatively. The number of branches, total volume, and diameter of the blood vessels in micro-CT angiography showed an exponential rise at week 2 and decline at week 3 of fracture healing, with the VEGF mRNA expression concurrently showing a consistent pattern in the phase.

Non-union bone fractures

The human skeleton has remarkable regenerative properties, being one of the few structures in the body that can heal by recreating its normal cellular composition, orientation and mechanical strength. When the healing process of a fractured bone fails owing to inadequate immobilization, failed surgical intervention, insufficient biological response or infection, the outcome after a prolonged period of no healing is defined as non-union. Non-union represents a chronic medical condition not only affecting function but also potentially impacting the individual's psychosocial and economic well-being. This Primer provides the reader with an in-depth understanding of our contemporary knowledge regarding the important features to be considered when faced with non-union. The normal mechanisms involved in bone healing and the factors that disrupt the normal signalling mechanisms are addressed. Epidemiological considerations and advances in the diagnosis and surgical therapy of non-union are highlighted and the need for greater efforts in basic, translational and clinical research are identified.

Multivalent Presentation of Peptide Targeting Groups Alters Polymer Biodistribution to Target Tissues

Drug delivery to bone is challenging, whereby drug distribution is commonly <1% of injected dose, despite development of several bone-targeted drug delivery systems specific to hydroxyapatite. These bone-targeted drug delivery systems still suffer from poor target cell localization within bone, as at any given time overall bone volume is far greater than acutely remodeling bone volume, which harbors relevant cell targets (osteoclasts or osteoblasts). Thus, there exists a need to target bone-acting drugs specifically to sites of bone remodeling. To address this need, this study synthesized oligo(ethylene glycol) copolymers based on a peptide with high affinity to tartrate-resistant acid phosphatase (TRAP), an enzyme deposited by osteoclasts during the bone resorption phase of bone remodeling, which provides greater specificity relevant for bone cell drugging. Gradient and random peptide orientations, as well as polymer molecular weights, were investigated. TRAP-targeted, high molecular weight (M_n) random copolymers exhibited superior accumulation in remodeling bone, where fracture accumulation was observed for at least 1 week and accounted for 14% of tissue distribution. Intermediate and low M_n random copolymer accumulation was lower, indicating residence time depends on M_n. High M_n gradient polymers were cleared, with only 2% persisting at fractures after 1 week, suggesting TRAP binding depends on peptide density. Peptide density and M_n are easily modified in this versatile targeting platform, which can be applied to a range of bone drug delivery applications.

Comparison of the effects of recombinant human bone morphogenetic protein-2 and -9 on bone formation in rat calvarial critical-size defects

OBJECTIVES

Among bone morphogenetic protein (BMP) family members, BMP-2 and BMP-9 have demonstrated potent osteoinductive potential. However, in vivo differences in their potential for bone regeneration remain unclear. The present study aimed to compare the effects of recombinant human (rh) BMP-2 and rhBMP-9 on bone formation in rat calvarial critical-size defects (CSD).

MATERIALS AND METHODS

Twenty-eight Wistar rats surgically received two calvarial defects bilaterally in each parietal bone. Defects (n = 56) were allocated into four groups: absorbable collagen sponge (ACS) alone, rhBMP-2 with ACS (rhBMP-2/ACS), rhBMP-9/ACS, or sham surgery (control), on the condition that the treatments of rhBMP-2/ACS and rhBMP-9/ACS, or the same treatments were not included in the same animal. Animals were sacrificed at 2 and 8 weeks post-surgery. The calvarial defects were analyzed for bone volume (BV) by micro-computed tomography and for percentages of defect closure (DC/DL), newly formed bone area (NBA/TA), bone marrow area (BMA/NBA), adipose tissue area (ATA/NBA), central bone height (CBH), and marginal bone height (MBH) by histomorphometric analysis.

RESULTS

The BV in the rhBMP-2/ACS group (5.44 ± 3.65 mm³, n = 7) was greater than the other groups at 2 weeks post-surgery, and the rhBMP-2/ACS and rhBMP-9/ACS groups (18.17 ± 2.51 and 16.30 ± 2.46 mm³, n = 7, respectively) demonstrated significantly greater amounts of BV compared with the control and ACS groups (6.02 ± 2.90 and 9.30 ± 2.75 mm³, n = 7, respectively) at 8 weeks post-surgery. The rhBMP-2/ACS and rhBMP-9/ACS groups significantly induced new bone formation compared to the control and ACS groups at 8 weeks post-surgery. However, there were no statistically significant differences found between the rhBMP-2/ACS and rhBMP-9/ACS groups in any of the histomorphometric parameters. The ATA/NBA in the rhBMP-2/ACS group (9.24 ± 3.72%, n = 7) was the highest among the treatment groups at 8 weeks post-surgery.

CONCLUSIONS

Within the limits of this study, it can be concluded that rhBMP-2/ACS induced a slight early increase in new bone formation at 2 weeks and that rhBMP-9/ACS provided comparable new bone formation to rhBMP-2/ACS with less adipose tissues after a healing period of 8 weeks in rat CSD.

CLINICAL RELEVANCE

RhBMP-9/ACS treatment provided new bone formation with less adipose tissues compared with rhBMP-2/ACS.

Bioinformatics and Microarray Analysis of miRNAs in Aged Female Mice Model Implied New Molecular Mechanisms for Impaired Fracture Healing

Impaired fracture healing in aged females is still a challenge in clinics. MicroRNAs (miRNAs) play important roles in fracture healing. This study aims to identify the miRNAs that potentially contribute to the impaired fracture healing in aged females. Transverse femoral shaft fractures were created in adult and aged female mice. At post-fracture 0-, 2- and 4-week, the fracture sites were scanned by micro computed tomography to confirm that the fracture healing was impaired in aged female mice and the fracture calluses were collected for miRNA microarray analysis. A total of 53 significantly differentially expressed miRNAs and 5438 miRNA-target gene interactions involved in bone fracture healing were identified. A novel scoring system was designed to analyze the miRNA contribution to impaired fracture healing (RCIFH). Using this method, 11 novel miRNAs were identified to impair fracture healing at 2- or 4-week post-fracture. Thereafter, function analysis of target genes was performed for miRNAs with high RCIFH values. The results showed that high RCIFH miRNAs in aged female mice might impair fracture healing not only by down-regulating angiogenesis-, chondrogenesis-, and osteogenesis-related pathways, but also by up-regulating osteoclastogenesis-related pathway, which implied the essential roles of these high RCIFH miRNAs in impaired fracture healing in aged females, and might promote the discovery of novel therapeutic strategies.