Bone morphogenetic proteins in open fractures: past, present, and future

Lysyl oxidase inhibits BMP9-induced osteoblastic differentiation through reducing Wnt/β-catenin via HIF-1a repression in 3T3-L1 cells

BACKGROUND

Bone morphogenetic protein 9 (BMP9) is a promising growth factor in bone tissue engineering, while the detailed molecular mechanism underlying BMP9-oriented osteogenesis remains unclear. In this study, we investigated the effect of lysyl oxidase (Lox) on the BMP9 osteogenic potential via in vivo and in vitro experiments, as well as the underlying mechanism.

METHODS

PCR assay, western blot analysis, histochemical staining, and immunofluorescence assay were used to quantify the osteogenic markers level, as well as the possible mechanism. The mouse ectopic osteogenesis assay was used to assess the impact of Lox on BMP9-induced bone formation.

RESULTS

Our findings suggested that Lox was obviously upregulated by BMP9 in 3T3-L1 cells. BMP9-induced Runx2, OPN, and mineralization were all enhanced by Lox inhibition or knockdown, while Lox overexpression reduced their expression. Additionally, the BMP9-induced adipogenic makers were repressed by Lox inhibition. Inhibition of Lox resulted in an increase in c-Myc mRNA and β-catenin protein levels. However, the increase in BMP9-induced osteoblastic biomarkers caused by Lox inhibition was obviously reduced when β-catenin knockdown. BMP9 upregulated HIF-1α expression, which was further enhanced by Lox inhibition or knockdown, but reversed by Lox overexpression. Lox knockdown or HIF-1α overexpression increased BMP9-induced bone formation, although the enhancement caused by Lox knockdown was largely diminished when HIF-1α was knocked down. Lox inhibition increased β-catenin levels and decreased SOST levels, which were almost reversed by HIF-1α knockdown.

CONCLUSION

Lox may reduce the BMP9 osteoblastic potential by inhibiting Wnt/β-catenin signaling via repressing the expression HIF-1α partially.

BMP-6 promotes type 2 immune response during enhancement of rat mandibular bone defect healing

Introduction

Bone morphogenetic proteins (BMPs) are used as key therapeutic agents for the treatment of difficult fractures. While their effects on osteoprogenitors are known, little is known about their effects on the immune system.

Methods

We used permutations of BMP-6 (B), vascular endothelial growth factor (V), and Hedgehog signaling pathway activator smoothened agonist (S), to treat a rat mandibular defect and investigated healing outcomes at week 8, in correlation with the cellular landscape of the immune cells in the fracture callus at week 2.

Results

Maximum recruitment of immune cells to the fracture callus is known to occur at week 2. While the control, S, V, and VS groups remained as nonunions at week 8; all BMP-6 containing groups - B, BV, BS and BVS, showed near-complete to complete healing. This healing pattern was strongly associated with significantly higher ratios of CD4 T (CD45⁺CD3⁺CD4⁺) to putative CD8 T cells (CD45⁺CD3⁺CD4^-), in groups treated with any permutation of BMP-6. Although, the numbers of putative M1 macrophages (CD45⁺CD3^-CD11b/c⁺CD38^high) were significantly lower in BMP-6 containing groups in comparison with S and VS groups, percentages of putative - Th1 cells or M1 macrophages (CD45⁺CD4⁺IFN-γ⁺) and putative - NK, NKT or cytotoxic CD8T cells (CD45⁺CD4^-IFN-γ⁺) were similar in control and all treatment groups. Further interrogation revealed that the BMP-6 treatment promoted type 2 immune response by significantly increasing the numbers of CD45⁺CD3^-CD11b/c⁺CD38^low putative M2 macrophages, putative - Th2 cells or M2 macrophages (CD45⁺CD4⁺IL-4⁺) cells and putative - mast cells, eosinophils or basophils (CD45⁺CD4^-IL-4⁺ cells). CD45^- non-haematopoietic fractions of cells which encompass all known osteoprogenitor stem cells populations, were similar in control and treatment groups.

Discussion

This study uncovers previously unidentified regulatory functions of BMP-6 and shows that BMP-6 enhances fracture healing by not only acting on osteoprogenitor stem cells but also by promoting type 2 immune response.

Three-Dimensional Computational Model Simulating the Initial Callus Growth during Fracture Healing in Long Bones: Application to Different Fracture Types

Bone fractures are among the most common and potentially serious injuries to the skeleton, femoral shaft fractures being especially severe. Thanks to recent advances in the area of in silico analysis, several approximations of the bone healing process have been achieved. In this context, the objective of this work was to simulate the initial phase of callus formation in long bones, without a pre-meshed domain in the 3D space. A finite element approach was computationally implemented to obtain the values of the cell concentrations along the whole domain and evaluate the areas where the biological quantities reached the thresholds necessary to trigger callus growth. A voxel model was used to obtain the 3D domain of the bone fragments and callus. A mesh growth algorithm controlled the addition of new elements to the domain at each step of the iterative procedure until complete callus formation. The implemented approach is able to reproduce the generation of the primary callus, which corresponds to the initial phase of fracture healing, independently of the fracture type and complexity, even in the case of several bone fragments. The proposed approach can be applied to the most complex bone fractures such as oblique, severely comminuted or spiral-type fractures, whose simulation remains hardly possible by means of the different existing approaches available to date.

Current evidence on potential of adipose derived stem cells to enhance bone regeneration and future projection

Injuries to the postnatal skeleton are naturally repaired through successive steps involving specific cell types in a process collectively termed “bone regeneration”. Although complex, bone regeneration occurs through a series of well-orchestrated stages wherein endogenous bone stem cells play a central role. In most situations, bone regeneration is successful; however, there are instances when it fails and creates non-healing injuries or fracture nonunion requiring surgical or therapeutic interventions. Transplantation of adult or mesenchymal stem cells (MSCs) defined by the International Society for Cell and Gene Therapy (ISCT) as CD105+CD90+CD73+CD45-CD34-CD14orCD11b-CD79αorCD19-HLA-DR- is being investigated as an attractive therapy for bone regeneration throughout the world. MSCs isolated from adipose tissue, adipose-derived stem cells (ADSCs), are gaining increasing attention since this is the most abundant source of adult stem cells and the isolation process for ADSCs is straightforward. Currently, there is not a single Food and Drug Administration (FDA) approved ADSCs product for bone regeneration. Although the safety of ADSCs is established from their usage in numerous clinical trials, the bone-forming potential of ADSCs and MSCs, in general, is highly controversial. Growing evidence suggests that the ISCT defined phenotype may not represent bona fide osteoprogenitors. Transplantation of both ADSCs and the CD105^- sub-population of ADSCs has been reported to induce bone regeneration. Most notably, cells expressing other markers such as CD146, AlphaV, CD200, PDPN, CD164, CXCR4, and PDGFRα have been shown to represent osteogenic sub-population within ADSCs. Amongst other strategies to improve the bone-forming ability of ADSCs, modulation of VEGF, TGF-β1 and BMP signaling pathways of ADSCs has shown promising results. The U.S. FDA reveals that 73% of Investigational New Drug applications for stem cell-based products rely on CD105 expression as the “positive” marker for adult stem cells. A concerted effort involving the scientific community, clinicians, industries, and regulatory bodies to redefine ADSCs using powerful selection markers and strategies to modulate signaling pathways of ADSCs will speed up the therapeutic use of ADSCs for bone regeneration.

A new approach for initial callus growth during fracture healing in long bones

The incidence of bone fracture has become a major clinical problem on a worldwide scale. In the past two decades there has been an increase in the use of computational tools to analyse the bone fracture problem. In several works, various study cases have been analysed to compare human and animal bone fracture healing. Unfortunately, there are not many publications about computational advances in this field and the existing approaches to the problem are usually similar. In this context, the objective of this work is the application of a diffusion problem in the model of the bone fragments resulting from fracture, working together with a mesh-growing algorithm that allows free growth of the callus depending on the established conditions, without a pre-meshed domain. The diffusion problem concerns the different biological magnitudes controlling the callus growth, among which Mesenchymal Stem Cells and chondrocytes concentrations were chosen, together with Tumour Necrosis Factor α and Bone Morphogenetic Protein as the factors influencing the velocity in the callus formation. A Finite Element approach was used to solve the corresponding diffusion problems, obtaining the concentration values along the entire domain and allowing detecting the zones in which biological magnitudes reach the necessary thresholds for callus growth. The callus growth is guided by a geometrical algorithm which performs an additional mesh generation process (self-added mesh) at each step of the iterative procedure until complete callus formation. The proposed approach was applied to different types of diaphyseal femoral fractures treated by means of intramedullary nailing. Axisymmetric models based on triangular quadratic elements were used, obtaining results in good agreement with clinical evidence of these kinds of fractures. The algorithm proposed has the advantage of a natural callus growth, without the existence of a previous mesh that may affect the conditions and direction of growth. The approach is intended for the initial phase of callus growth. Future work will address the implementation of the corresponding formulations for tissue transformation and bone remodelling in order to achieve complete fracture healing.

Nerve growth factor promotes osteogenic differentiation of MC3T3-E1 cells via BMP-2/Smads pathway

BACKGROUND

Exogenous nerve growth factor (NGF) can induce osteogenic precursor cell differentiation and promote fracture healing. However, the molecular mechanism by which NGF induces osteogenesis is not well understood. BMP-2 has good osteogenic efficacy and is one of the most osteogenic-inducing growth factors known. Therefore, this study aimed to determine whether NGF induces osteogenic differentiation of mouse embryonic osteogenic precursor cell line MC3T3-E1 by BMP-2 and search further mechanisms of NGF on BMP-2.

METHODS

MC3T3-E1 cells were treated with NGF at a concentration gradient for indicated times, after which the cell viability was measured by CCK-8 kit. Osteogenic differentiation was detected with quantification of alkaline phosphatase (ALP) activity also visualized with ALP staining. The transcription and expression of relevant genes were detected by qPCR and western blotting, respectively. NGF's effect on BMP2 was studied with qPCR and luciferase reporter assay. The phosphorylation of Smads was probed with specific antibodies by western blotting, and the location of Smads was observed through immunofluorescence.

RESULTS

We found that NGF promoted proliferation and osteogenic differentiation of MC3T3-E1, increased the expression level of BMP-2, as well as the phosphorylation and nuclear translocation of Smad1/5/8. However, neutralization of BMP-2 with si-BMP-2 or BMP-2 signal inhibitors reversed NGF induced phosphorylation and nuclear translocation of Smad1/5/8, as well as the expression of Runx2, type I collagen, osteocalcin and osteopontin. In addition, si-BMP-2 abrogated NGF-induced ALP activity.

CONCLUSION

NGF induced osteogenic differentiation of MC3T3-E1 cells through BMP-2/Smads pathway and induction of Runx2. Our study would provide a theoretical basis for clinical treatment of fractures using NGF.

Optimized expression and purification of a soluble BMP2 variant based on in-silico design

Bone morphogenetic protein 2 (BMP2¹) is a highly interesting therapeutic growth factor due to its strong osteogenic/osteoinductive potential. However, its pronounced aggregation tendency renders recombinant and soluble production troublesome and complex. While prokaryotic expression systems can provide BMP2 in large amounts, the typically insoluble protein requires complex denaturation-renaturation procedures with medically hazardous reagents to obtain natively folded homodimeric BMP2. Based on a detailed aggregation analysis of wildtype BMP2, we designed a hydrophilic variant of BMP2 additionally containing an improved heparin binding site (BMP2-2Hep-7M). Consecutive optimization of BMP2-2Hep-7M expression and purification enabled production of soluble dimeric BMP2-2Hep-7M in high yield in E. coli. This was achieved by a) increasing protein hydrophilicity via introducing seven point mutations within aggregation hot spots of wildtype BMP2 and a longer N-terminus resulting in higher affinity for heparin, b) by employing E. coli strain SHuffle® T7, which enables the structurally essential disulfide-bond formation in BMP2 in the cytoplasm, c) by using BMP2 variant characteristic soluble expression conditions and application of l-arginine as solubility enhancer. The BMP2 variant BMP2-2Hep-7M shows strongly attenuated although not completely eliminated aggregation tendency.

Local injections of β-NGF accelerates endochondral fracture repair by promoting cartilage to bone conversion

There are currently no pharmacological approaches in fracture healing designed to therapeutically stimulate endochondral ossification. In this study, we test nerve growth factor (NGF) as an understudied therapeutic for fracture repair. We first characterized endogenous expression of Ngf and its receptor tropomyosin receptor kinase A (TrkA) during tibial fracture repair, finding that they peak during the cartilaginous phase. We then tested two injection regimens and found that local β-NGF injections during the endochondral/cartilaginous phase promoted osteogenic marker expression. Gene expression data from β-NGF stimulated cartilage callus explants show a promotion in markers associated with endochondral ossification such as Ihh, Alpl, and Sdf-1. Gene ontology enrichment analysis revealed the promotion of genes associated with Wnt activation, PDGF- and integrin-binding. Subsequent histological analysis confirmed Wnt activation following local β-NGF injections. Finally, we demonstrate functional improvements to bone healing following local β-NGF injections which resulted in a decrease in cartilage and increase of bone volume. Moreover, the newly formed bone contained higher trabecular number, connective density, and bone mineral density. Collectively, we demonstrate β-NGF’s ability to promote endochondral repair in a murine model and uncover mechanisms that will serve to further understand the molecular switches that occur during cartilage to bone transformation.

The Life of a Fracture: Biologic Progression, Healing Gone Awry, and Evaluation of Union

New knowledge about the molecular biology of fracture-healing provides opportunities for intervention and reduction of risk for specific phases that are affected by disease and medications. Modifiable and nonmodifiable risk factors can prolong healing, and the informed clinician should optimize each patient to provide the best chance for union. Techniques to monitor progression of fracture-healing have not changed substantially over time; new objective modalities are needed.

Recombinant Heparin-New Opportunities

Heparin and heparan sulfate (HS) are polydisperse mixtures of polysaccharide chains between 5 and 50 kDa. Sulfate modifications to discreet regions along the chains form protein binding sites involved in cell signaling cascades and other important cellular physiological and pathophysiological functions. Specific protein affinities of the chains vary among different tissues and are determined by the arrangements of sulfated residues in discreet regions along the chains which in turn appear to be determined by the expression levels of particular enzymes in the biosynthetic pathway. Although not all the rules governing synthesis and modification are known, analytical procedures have been developed to determine composition, and all of the biosynthetic enzymes have been identified and cloned. Thus, through cell engineering, it is now possible to direct cellular synthesis of heparin and HS to particular compositions and therefore particular functional characteristics. For example, directing heparin producing cells to reduce the level of a particular type of polysaccharide modification may reduce the risk of heparin induced thrombocytopenia (HIT) without reducing the potency of anticoagulation. Similarly, HS has been linked to several biological areas including wound healing, cancer and lipid metabolism among others. Presumably, these roles involve specific HS compositions that could be produced by engineering cells. Providing HS reagents with a range of identified compositions should help accelerate this research and lead to new clinical applications for specific HS compositions. Here I review progress in engineering CHO cells to produce heparin and HS with compositions directed to improved properties and advancing medical research.

Wnt11 promotes BMP9-induced osteogenic differentiation through BMPs/Smads and p38 MAPK in mesenchymal stem cells

Bone morphogenetic protein 9 (BMP9), as one of the most potent osteogenic factors, is a promising cytokine for bone tissue engineering. Wnt11 can regulate the development of the skeletal system and is related to high bone mass syndrome. However, the effect of Wnt11 on BMP9-induced osteogenic differentiation remains unknown. In this study, we investigated the relationship between Wnt11- and BMP9-induced osteogenic differentiation in mesenchymal stem cells (MSCs). We recapitulated the osteogenic potential of BMP9 in C3H10T1/2 cells. The messenger RNA expression of Wnt11 is detectable in the available progenitor cells, and BMP9 can obviously increase the protein level of Wnt11 in these cells. Exogenous Wnt11 potentiates the effect of BMP9 on increasing alkaline phosphatase (ALP) activities, the expression of osteopontin (OPN), and Runt-related transcription factor 2 (Runx2), so does matrix mineralization in C3H10T1/2 cells. Although Wnt11 cannot increase the BMP9-induced ectopic bone formation, it can increase the bone density induced by BMP9 apparently. Wnt11 increases the level of p-Smad1/5/8, as well as p-p38. Meanwhile, Wnt11 promotes the effect of BMP9 on increasing the levels of p-Smad1/5/8 and p-p38. Inhibition of p38 decreases the BMP9-induced ALP activities, the expression of OPN, and the mineralization in C3H10T1/2 cells. However, all of these effects of the p38 inhibitor on BMP9-induced osteogenic markers can be almost reversed by the overexpression of Wnt11. Our findings suggested that Wnt11 can enhance the osteogenic potential of BMP9 in MSCs, and this effect may be partly mediated through enhancing BMPs/Smads and the p38 MAPK signal, which was induced by BMP9.

Effects of Episodic Alcohol Exposure on BMP2 Signaling During Tibia Fracture Healing

OBJECTIVES

To explore how alcohol affects the BMP-2 signaling pathway, which is known to play a critical role in bone and cartilage formation during fracture healing.

METHODS

A rat model was used to demonstrate the detrimental effects of alcohol exposure on tibia fracture healing. Specific components of the BMP-2 pathway were analyzed in fracture callus on days 3, 7, 14, and 21 after fracture via western immunoassays and enzyme-linked immunosorbent assay.

RESULTS

Alcohol exposure before tibia fracture demonstrated attenuation of downstream BMP-2 signaling. The BMP-2 antagonist, Chordin, may be the central component of the BMP-2-related changes demonstrated in this study. Although alcohol affected BMP-related proteins at all time points, it seems that day 14 after fracture is a critical time point for alcohol-related modulation of callus formation in our model.

CONCLUSIONS

This study may provide the scientific basis for further studies addressing whether the application of exogenous BMP-2 in patients with a history of alcohol abuse who sustain long bone fractures may or may not be of benefit.

Biomaterials to Facilitate Delivery of RNA Agents in Bone Regeneration and Repair

Bone healing after traumatic injuries or pathological diseases remains an important worldwide problem. In search of safer and more effective approaches to bone regeneration and repair, RNA-based therapeutic agents, specifically microRNAs (miRNAs) and short interfering RNA (siRNA), are beginning to be actively explored. In this review, we summarize current attempts to employ miRNAs and siRNAs in preclinical models of bone repair. We provide a summary of current limitations when attempting to utilize bioactive nucleic acids for therapeutic purposes and position the unique aspects of RNA reagents for clinical bone repair. Delivery strategies for RNA reagents are emphasized and nonviral carriers (biomaterial-based) employed to deliver such reagents are reviewed. Critical features of biomaterial carriers and various delivery technologies centered around nanoparticulate systems are highlighted. We conclude with the authors' perspectives on the future of the field, outlining main critical issues important to address as RNA reagents are explored for clinical applications.

Bone morphogenetic proteins and their antagonists: current and emerging clinical uses

Bone morphogenetic proteins (BMPs) are members of the TGFβ superfamily of secreted cysteine knot proteins that includes TGFβ1, nodal, activins and inhibins. BMPs were first discovered by Urist in the 1960s when he showed that implantation of demineralized bone into intramuscular tissue of rabbits induced bone and cartilage formation. Since this seminal discovery, BMPs have also been shown to play key roles in several other biological processes, including limb, kidney, skin, hair and neuronal development, as well as maintaining vascular homeostasis. The multifunctional effects of BMPs make them attractive targets for the treatment of several pathologies, including bone disorders, kidney and lung fibrosis, and cancer. This review will summarize current knowledge on the BMP signalling pathway and critically evaluate the potential of recombinant BMPs as pharmacological agents for the treatment of bone repair and tissue fibrosis in patients.

Poly(lactic-co-glycolide) polymer constructs cross-linked with human BMP-6 and VEGF protein significantly enhance rat mandible defect repair

We have previously shown that the combined delivery of mesenchymal stem cells (MSCs), vascular endothelial growth factor (VEGF) and bone morphogenetic protein 6 (BMP-6) induces significantly more bone formation than that induced by the delivery of any single factor or a combination of any two factors. We now determine whether the exogenous addition of VEGF and BMP-6 is sufficient for bone healing when MSCs are not provided. Poly(lactic-co-glycolic acid) (PLAGA) microsphere-based three-dimensional scaffolds (P) were fabricated by thermal sintering of PLAGA microspheres. The scaffolds were chemically cross-linked with 200 ng recombinant human VEGF (P(VEGF)) or BMP-6 (P(BMP-6)) or both (P(VEGF+BMP-6)) by the EDC-NHS-MES method. Release of the proteins from the scaffolds was detected for 21 days in vitro which confirmed their comparable potential to supply the proteins in vivo. The scaffolds were delivered to a critical-sized mandibular defect created in 32 Sprague Dawley rats. Significant bone regeneration was observed only in rats with P(VEGF+BMP-6) scaffolds at weeks 2, 8 and 12 as revealed by micro-computer tomography. Vascular ingrowth was higher in the P(VEGF+BMP-6) group as seen by microfil imaging than in other groups. Trichrome staining revealed that a soft callus formed in P(VEGF), P(BMP-6) and P(VEGF+BMP-6) but not in P. MSCs isolated from rat femurs displayed expression of the bone-specific marker osteocalcin when cultured with P(VEGF), P(BMP-6), or P(VEGF+BMP-6) but not with P. Robust mineralization and increased alkaline phosphatase gene expression were seen in rat MSCs when cultured on P(VEGF+BMP-6) but not on P, P(VEGF), or P(BMP-6). Thus, unlike the delivery of VEGF or BMP-6 alone, the combined delivery of VEGF and BMP-6 to the bone defect significantly enhanced bone repair through the enhancement of angiogenesis and the differentiation of endogenously recruited MSCs into the bone repair site.

Can OP-1 stimulate union in a rat model of pathological fracture post treatment for soft tissue sarcoma?

The goal of soft tissue sarcoma management in the extremities is limb preservation, often combining surgery and external beam radiation. In patients who have undergone this therapy in the thigh, pathologic fracture is a serious, late complication. Non-union rates of 80-90% persist. No reliable biologic solution exists. A rat model combining one 18 Gy dose of radiation and diaphyseal periosteal excision reliably generates atrophic non-union of femoral fractures. We hypothesized that augmentation with OP-1 would increase union rate. Female Sprague-Dawley retired breeder rats were randomized to Control, Disease (external beam radiotherapy and periosteal stripping), Control + OP-1 (80 µg) and Disease + OP-1 groups. Animals underwent prophylactic fixation and controlled left femur fracture. Twenty-eight, 35, and 42 days post-fracture were end-points. Femora were analyzed using MicroCT, Back Scattered Electron Microscopy, and Histomorphometry. We observed a 2% union rate in the Disease groups (±OP-1 treatment). The union rate in Control groups was 97%. MicroCT demonstrated a lack of callus volume in Disease groups. Heterotopic ossification was observed in some OP-1 treated animals. The ineffectiveness of OP-1 in stimulating fracture union in this model suggests the endogenous repair mechanism has been compromised beyond the capabilities of osteoinductive biologics.

Open tibial fractures grade IIIC treated successfully with external fixation, negative-pressure wound therapy and recombinant human bone morphogenetic protein 7

The aim of the therapy in open tibial fractures grade III was to cover the bone with soft tissue and achieve healed fracture without persistent infection. Open tibial fractures grade IIIC with massive soft tissue damage require combined orthopaedic, vascular and plastic-reconstructive procedures. Negative-pressure wound therapy (NPWT), used in two consecutive cases with open fracture grade IIIC of the tibia diaphysis, healed extensive soft tissue defect with exposure of the bone. NPWT eventually allowed for wound closure by split skin graft within 21-25 days. Ilizarov external fixator combined with application of recombinant human bone morphogenetic protein-7 at the site of delayed union enhanced definitive bone healing within 16-18 months.

Updates in biological therapies for knee injuries: bone

Bone is a unique tissue because of its mechanical properties, ability for self-repair, and enrollment in different metabolic processes such as calcium homeostasis and hematopoietic cell production. Bone barely tolerates deformation and tends to fail when overloaded. Fracture healing is a complex process that in particular cases is impaired. Osteoprogenitor cells proliferation, growth factors, and a sound tridimensional scaffold at fracture site are key elements for new bone formation and deposition. Mechanical stability and ample vascularity are also of great importance on providing a proper environment for bone healing. From mesenchymal stem cells delivery to custom-made synthetic scaffolds, many are the biological attempts to enhance bone healing. Impaired fracture healing represents a real burden to contemporary society. Sound basic science knowledge has contributed to newer approaches aimed to accelerate and improve the quality of bone healing.

BMP-non-responsive Sca1+ CD73+ CD44+ mouse bone marrow derived osteoprogenitor cells respond to combination of VEGF and BMP-6 to display enhanced osteoblastic differentiation and ectopic bone formation

Clinical trials on fracture repair have challenged the effectiveness of bone morphogenetic proteins (BMPs) but suggest that delivery of mesenchymal stem cells (MSCs) might be beneficial. It has also been reported that BMPs could not increase mineralization in several MSCs populations, which adds ambiguity to the use of BMPs. However, an exogenous supply of MSCs combined with vascular endothelial growth factor (VEGF) and BMPs is reported to synergistically enhance fracture repair in animal models. To elucidate the mechanism of this synergy, we investigated the osteoblastic differentiation of cloned mouse bone marrow derived MSCs (D1 cells) in vitro in response to human recombinant proteins of VEGF, BMPs (-2, -4, -6, -9) and the combination of VEGF with BMP-6 (most potent BMP). We further investigated ectopic bone formation induced by MSCs pre-conditioned with VEGF, BMP-6 or both. No significant increase in mineralization, phosphorylation of Smads 1/5/8 and expression of the ALP, COL1A1 and osterix genes was observed upon addition of VEGF or BMPs alone to the cells in culture. The lack of CD105, Alk1 and Alk6 expression in D1 cells correlated with poor response to BMPs indicating that a greater care in the selection of MSCs is necessary. Interestingly, the combination of VEGF and BMP-6 significantly increased the expression of ALP, COL1A1 and osterix genes and D1 cells pre-conditioned with VEGF and BMP-6 induced greater bone formation in vivo than the non-conditioned control cells or the cells pre-conditioned with either VEGF or BMP-6 alone. This enhanced bone formation by MSCs correlated with higher CADM1 expression and OPG/RANKL ratio in the implants. Thus, combined action of VEGF and BMP on MSCs enhances osteoblastic differentiation of MSCs and increases their bone forming ability, which cannot be achieved through use of BMPs alone. This strategy can be effectively used for bone repair.

Simple signaling molecules for inductive bone regenerative engineering

With greater than 500,000 orthopaedic procedures performed in the United States each year requiring a bone graft, the development of novel graft materials is necessary. We report that some porous polymer/ceramic composite scaffolds possess intrinsic osteoinductivity as shown through their capacity to induce in vivo host osteoid mineralization and in vitro stem cell osteogenesis making them attractive synthetic bone graft substitutes. It was discovered that certain low crystallinity ceramics partially dissociate into simple signaling molecules (i.e., calcium and phosphate ions) that induce stem cells to endogenously produce their own osteoinductive proteins. Review of the literature has uncovered a variety of simple signaling molecules (i.e., gases, ions, and redox reagents) capable of inducing other desirable stem cell differentiation through endogenous growth factor production. Inductive simple signaling molecules, which we have termed inducerons, represent a paradigm shift in the field of regenerative engineering where they can be utilized in place of recombinant protein growth factors.

Effects of propofol on renal ischemia/reperfusion injury in rats

Renal ischemia/reperfusion injury (IRI) is a major cause of acute renal failure. The aim of this study was to investigate whether propofol pretreatment in a rat model protects kidney tissue against IRI. Thirty-two Wistar rats were equally divided into four groups: a sham-operated group, untreated renal IRI group, and low-dose (5 mg/kg) and high-dose (10 mg/kg) propofol-treated groups which were treated with propofol prior to the induction of IRI. The rats were subjected to renal ischemia by bilateral clamping of the pedicles for 50 min, followed by reperfusion. The low-dose and high-dose propofol treatment groups were pretreated via femoral vein injection with a propofol suspension prior to the induction of ischemia/reperfusion. The untreated IRI group showed significantly higher serum creatinine (SCr), blood urea nitrogen (BUN), interleukin 6 (IL-6), IL-8, tumor necrosis factor-α (TNF-α), and malondialdehyde (MDA) levels compared with the sham-operated rats. Superoxide dismutase (SOD) levels were significantly reduced following IRI; however, they significantly increased following propofol administration. Bone morphogenetic protein 2 (BMP2) levels were significantly increased in the propofol-treated groups compared with the untreated IRI group. These results suggest that propofol reduces renal oxidative injury and facilitates repair following IRI. Propofol may play a protective role by regulating BMP2 expression in renal IRI.

Affinity-selected heparan sulfate for bone repair

Bone morphogenetic protein (BMP)-2 is a potent bone healing compound produced at sites of bone trauma. Here we present a therapeutic strategy to harness the activity of endogenously produced BMP-2 by delivery of an affinity-matched heparan sulfate (HS) glycos aminoglycan biomaterial that increases the bioavailability, bioactivity and half-life of this growth factor. We have developed a robust, cost effective, peptide-based affinity platform to isolate a unique BMP-2 binding HS variant from commercially available preparations of HS, so removing the manufacturing bottleneck for their translation into the clinic. This affinity-matched HS enhanced BMP-2-induced osteogenesis through improved BMP-2 kinetics and receptor modulation, prolonged pSMAD signaling and reduced interactions with its antagonist noggin. When co-delivered with a collagen implant, the HS was as potent as exogenous BMP-2 for the healing of critical-sized bone defects in rabbits. This affinity platform can be readily tuned to isolate HS variants targeted ata range of clinically-relevant growth and adhesive factors.

Bone morphogenetic protein-7 accelerates fracture healing in osteoporotic rats

BACKGROUND

Osteoporosis is characterized by low bone mass, bone fragility and increased susceptibility to fracture. Fracture healing in osteoporosis is delayed and rates of implant failure are high with few biological treatment options available. This study aimed to determine whether a single dose of bone morphogenetic protein-7 (BMP-7) in a collagen/carboxy-methyl cellulose (CMC) composite enhanced fracture healing in an osteoporotic rat model.

MATERIALS AND METHODS

An open femoral midshaft osteotomy was performed in female rats 3 months post-ovarectomy. Rats were randomized to receive either BMP-7 composite (n = 30) or composite alone (n = 30) at the fracture site during surgery. Thereafter calluses were collected on days 12, 20 and 31. Callus cross-sectional area, bone mineral density, biomechanical stiffness and maximum torque, radiographic bony union and histological callus maturity were evaluated at each time point.

RESULTS

There were statistically significant increases in bone mineral density and callus cross-section area at all time points in the BMP-7 group as compared to controls and biomechanical readings showed stronger bones at day 31 in the BMP-7 group. Histological and radiographic evaluation indicated significant acceleration of bony union in the BMP-7 group as compared to controls.

CONCLUSION

This study demonstrated that BMP-7 accelerates fracture healing in an oestrogen-deficient environment in a rat femoral fracture healing model to scientific relevance level I. The use of BMP-7 composite could offer orthopedic surgeons an advantage over oestrogen therapy, enhancing osteoporotic fracture healing with a single, locally applied dose at the time of surgery, potentially overcoming delays in healing caused by the osteoporotic state.

Growth factors: beyond bone morphogenetic proteins

The current landscape of growth factors in orthopaedic trauma is dominated by the BMPs, as they are the most extensively studied growth factors in clinical applications pertaining to orthopaedic trauma. Despite this, their application and indications for use in trauma remain controversial. This article highlights a number of selected growth factors, other than BMPs, that are currently being investigated in orthopaedic trauma applications. These growth factors have shown significant promise in preclinical and early clinical investigation.