Use of recombinant human bone morphogenetic protein-2 to achieve posterolateral lumbar spine fusion in humans: a prospective, randomized clinical pilot trial: 2002 Volvo Award in clinical studies

Sustained delivery of PlGF-2123-144*-fused BMP2-related peptide P28 from small intestinal submucosa/polylactic acid scaffold material for bone tissue regeneration

Bone morphogenetic protein 2 (BMP-2) is one of the most important factors for bone tissue formation. However, its use over the past decade has been associated with numerous side effects. This is due to the fact that recombinant human (rh) BMP-2 has several biological functions, as well as that non-physiological high dosages were commonly administered. In this study, we synthesized a novel BMP-2-related peptide (designated P28) and fused a mutant domain in placenta growth factor-2 (PlGF-2123-144*) that allowed for the "super-affinity" of extracellular matrix proteins to P28, effectively controlling the release of low dosage P28 from small intestinal submucosa/polylactic acid (SIS/PLA) scaffolds. These have been shown to be excellent scaffold materials both in vivo and in vitro. The aim of this study was to determine whether these scaffolds could support the controlled release of P28 over time, and whether the composite materials could serve as structurally and functionally superior bone substitutes in vivo. Our results demonstrated that P28 could be released slowly from SIS/PLA to promote the adhesion, proliferation, and differentiation of bone marrow stromal cells (BMSCs) in vitro. In vivo, radiographic and histological examination showed that SIS/PLA/P28/PlGF-2123-144* completely repaired critical-size bone defects, compared to SIS/PLA, SIS/PLA/PlGF-2123-144*, or SIS/PLA/P28 alone. These findings suggest that this controlled release system may have promising clinical applications in bone tissue engineering.

Lipopolysaccharide (LPS) inhibits ectopic bone formation induced by bone morphogenetic protein-2 and TGF-β1 through IL-1β production

OBJECTIVES

In order to gain new insight into bacterial infection during bone-regenerative treatment using bone morphogenetic proteins (BMPs), we examined the effects of lipopolysaccharide (LPS) on ectopic bone formation induced by BMP-2 and transforming growth factor (TGF)-β1 in mice.

METHODS

We implanted collagen sponges containing BMP-2, TGF-β1, and various amounts of LPS into mouse muscle tissues. Lump-like masses in which ectopic bones developed in mice were processed for microcomputed tomography, DNA microarray, reverse-transcription PCR, and histological analyses.

RESULTS

LPS treatment caused a dose-dependent reduction in the volume of ectopic bone. The total volume of ectopic bone induced by BMP-2 + TGF-β1 treatment was reduced by more than 75% in the presence of LPS. Histological analysis of the ectopic bone tissues revealed a significant reduction in total bone volume and bone volume/total volume in response to LPS. LPS treatment significantly increased the osteoblast number and osteoid volume, while the osteoclast number did not change. Since LPS induced production of TNF-α and IL-1β in lump-like masses, we implanted collagen sponges containing BMP-2 and TGF-β1 with or without LPS into TNF-α- or IL-1α/β-deficient mice. LPS treatment reduced the volume of ectopic bones in TNF-α-deficient mice but not in IL-1α/β-deficient mice. Furthermore, collagen sponges containing IL-1β reduced ectopic bone formation by BMP-2 and TGF-β1 in wild-type mice to the same extent as LPS treatment did.

CONCLUSIONS

LPS suppresses the ectopic bone formation induced by BMP-2 and TGF-β1 through IL-1β production.

A meta-analysis of bone morphogenetic protein-2 versus iliac crest bone graft for the posterolateral fusion of the lumbar spine

The impact of autologous iliac crest bone graft versus BMP-2 to improve fusion rates for posterolateral fusion (PLF) of the lumbar spine remains unanswered. Single-institution-centered data dominate the literature, providing results that may be contradictory or inconclusive. The aim of this paper is to analyze data pooled from multiple well-controlled studies that examined both ICBG and BMP-2 for use in PLF. This meta-analysis also provides details of success in different subsets of patients with variable risk factors for delayed and non-unions. Six high-quality randomized clinical trials were selected. Efficacy, morbidity, quality of life, and safety were compared between the BMP-2 group and the ICBG group. A total of 908 patients were included in the study. At 24 months, 94% of patients achieved fusion in the BMP-2 group and 83% in the ICBG group. At 6 and 12 months, the fusion was also greater in the BMP-2 group (86% vs. 60% and 88% vs. 80%, respectively). Surgical time, intraoperative blood loss, and hospitalization days also showed significant differences in favor of the experimental group (p < 0.01). There were no differences between two groups in the Oswestry Disability Index, 36-Item Short Form Health Survey and Back Pain Score, whereas a greater number of additional surgical procedures were performed in the ICBG group (p = 0.001). In conclusion, the use of BMP-2 in PLF reduced the surgical morbidity and had more beneficial effects on the fusion rate. The quality of life based on clinical scores was the same in both groups.

Contained-Delivery Route and the Administration of Postoperative Steroids Following Anterior Cervical Spinal Fusion With Low-dose rhBMP-2 Reduces the Magnitude of Respiratory Compromise

STUDY DESIGN

Retrospective chart review of patients who underwent anterior cervical discectomy and fusion (ACDF) using low-dose recombinant human bone morphogenic protein (rhBMP)-2.

OBJECTIVE

Determine whether severity and incidence of respiratory complications after ACDF surgery are decreased when using a low-dose BMP-infused sponge within a constrained carrier and postoperative IV and oral steroids.

SUMMARY OF BACKGROUND DATA

Many physicians avoid using BMP in anterior cervical spine fusions because of concern for an increased incidence of dysphagia, significant prevertebral swelling, and airway edema compromise. Pilot studies have shown that the local application of steroids may decrease the incidence of postoperative airway edema and dysphagia. We performed a retrospective study to evaluate the safety of immediate postoperative tapered steroid use following low-dose rhBMP-2 completely contained inside either an allograft or PEEK cage in reducing the severity and incidence of respiratory complications following ACDF.

MATERIALS AND METHODS

Forty-seven patients between 33 and 74 years of age, undergoing 1-, 2-, 3-, or 4-level ACDFs augmented with a fraction of a small sponge of rhBMP-2 (0.525 mg/level) within an allograft or PEEK cage and prescribed IV and oral postoperative steroids between January 1, 2008 and November 1, 2016. The incidence of complications such as dyspnea, dysphagia, airway issues, edema ectopic bone osteolysis, radiculitis, and nonunion were collected using medical charts. Additional data regarding length of hospital stay and readmissions were also recorded.

RESULTS

No life-threatening respiratory events, such as prolonged intubation, re-intubation, or readmission for labored breathing, were observed. No complications referable to steroids such as delayed healing, uncontrollable blood sugar, or diabetes were encountered in this series.

CONCLUSIONS

This study provides evidence that a tapered dose of steroids and a contained delivery route significantly decreases postoperative respiratory compromise incidence and magnitude following anterior cervical spine fusion using low-dose rhBMP-2.

Local application of alendronate controls bone formation and β-tricalcium phosphate resorption induced by recombinant human bone morphogenetic protein-2

This study examined the ability of local alendronate (ALN) administration to control β-tricalcium phosphate (β-TCP) resorption as well as the induction of bone formation by recombinant human bone morphogenetic protein-2 (rhBMP-2). A 15-mm critical-sized bone defect was created in the diaphysis of rabbit ulnae. Nine female rabbits (4 to 5 months-old) were divided into 3 groups. Group 1 (n = 6 ulnae) animals received implants consisting of β-TCP granules and 25 μg of rhBMP-2 in 6.5% collagen gel. Group 2 (6 ulnae) and Group 3 (6 ulnae) animals received the same implants, but with 10^-6 M and 10^-3 M ALN-treated TCP granules, respectively. Two weeks postsurgery, tartrate-resistant acid phosphatase-positive cell counts, new bone formation, and residual β-TCP were evaluated. This study showed that a high dose of ALN strongly reduced osteoclastic resorption of β-TCP induced by rhBMP-2, resulting in decreased bone formation. In contrast, a low dose of ALN slightly reduced the bone resorptive effect but increased bone formation. These results suggest that osteoclast-mediated resorption plays an important role in bone formation and a coupling-like phenomenon could occur in the β-TCP-implanted area, and that administration of a low dose of ALN may solve clinical bone resorptive problems induced by rhBMP-2.

Reconstruction of Bone Defect Combined with Massive Loss of Periosteum Using Injectable Human Mesenchymal Stem Cells in Biocompatible Ceramic Scaffolds in a Porcine Animal Model

Clinically, in patients who sustain severe open fractures, there is not only a segmental bone defect needed to be reconstructed but also insufficient healing capacity due to concomitant damages to the periosteum and surrounding soft tissues. For studying the reconstruction of bone defects associated with massive loss of periosteum and surrounding soft tissues, there are no well-established preclinical models in large animals in the literature. The purpose of the study was to generate a large animal model of bone defect with massive periosteum loss and to adopt a tissue engineering approach to achieve rapid bony union with stem cells and biomaterials. In this study, a bone defect with massive periosteum stripping was generated in pigs, which was followed by emptying nearby canal marrow including fat and cancellous bone. The stripped periosteum was a mimic to the situation in the Gustilo type 3 open fractures. Bone defects were then reconstructed by impacting the biocompatible ceramic scaffold, morselized tricalcium phosphate (TCP) loaded with human adipose tissue-derived mesenchymal stem cells (hMSCs). Radiological and pathological assessments indicated that TCP and hMSCs synergistically promoted bone healing with increased lamination and ingrowth of vessels. Both bridging periosteum formation and gap filling were induced rapidly. In conclusion, a porcine model of segmental bone loss with damage of surrounding periosteum was created. Reconstruction of such defects with hMSCs and TCP achieved rapid union of bone defects associated with massive periosteal stripping.

Regenerative Materials for Surgical Reconstruction: Current Spectrum of Materials and a Proposed Method for Classification

Chronic wound management is an enormous economic strain and quality-of-life issue for patients. Current treatments are ineffective or expensive and invasive. Materials (native and artificial) can act as the basis to enhance wound repair but often fall short of complete healing. The therapeutic index of materials have often been enhanced by combining them with drug or biologic elution technologies. Combination of materials with living drugs (cells) presents a new paradigm for enhancing therapy. Cell material interaction and therapeutic output will depend on variables ascribed to the living drug as well as variables ascribed to the underlying matrix. In this article, we review medical matrices currently approved by the US Food and Drug Administration (FDA) that would likely be the first generation of materials to be used in this manner. Currently there are hundreds of different materials on the market. Identification of the right combinations would benefit from a classification scheme to group materials with similar composition or derivation. We provide a classification scheme and FDA documentation references that should provide researchers and clinicians a starting point for testing these materials in the laboratory and rapidly transitioning cell therapies to the bedside.

A Bone Morphogenetic Protein (BMP)-derived Peptide Based on the Type I Receptor-binding Site Modifies Cell-type Dependent BMP Signalling

Bone morphogenetic proteins (BMPs) are multifunctional cytokines of the transforming growth factor β (TGFβ) superfamily with potential therapeutic applications due to their broad biological functionality. Designing BMP mimetics with specific activity will contribute to the translational potential of BMP-based therapies. Here, we report a BMP9 peptide mimetic, P3, designed from the type I receptor binding site, which showed millimolar binding affinities for the type I receptor activin receptor like kinase 1 (ALK1), ALK2 and ALK3. Although showing no baseline activity, P3 significantly enhanced BMP9-induced Smad1/5 phosphorylation as well as ID1, BMPR2, HEY1 and HEY2 gene expression in pulmonary artery endothelial cells (hPAECs), and this activity is dependent on its alpha helix propensity. However, in human dermal microvascular endothelial cells, P3 did not affect BMP9-induced Smad1/5 phosphorylation, but potently inhibited ALK3-dependent BMP4-induced Smad1/5 phosphorylation and gene expression. In C2C12 mouse myoblast cells, P3 had no effect on BMP9-induced osteogenic signalling, which is primarily mediated by ALK2. Interestingly, a previously published peptide from the knuckle region of BMP9 was found to inhibit BMP4-induced Smad1/5 phosphorylation. Together, our data identify a BMP9-derived peptide that can selectively enhance ALK1-mediated BMP9 signalling in hPAECs and modulate BMP9 and BMP4 signalling in a cell type-specific manner.

Polyelectrolyte Complexes between Polycarboxylates and BMP-2 for Enhancing Osteogenic Differentiation: Effect of Chemical Structure of Polycarboxylates

Bone morphogenetic protein 2 (BMP-2) has received considerable attention because of its osteoinductivity, but its use is limited owing to its instability and adverse effects. To reduce the dose of BMP-2, complexation with heparin is a promising approach, because heparin enhances the osteoinductivity of BMP-2. However, the clinical use of heparin is restricted because of its anticoagulant activity. Herein, to explore alternative polymers that show heparin-like activity, four polycarboxylates, poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), poly(aspartic acid) (PAsp), and poly(glutamic acid) (PGlu), were selected and their capability to modulate the osteoinductivity of BMP-2 was evaluated. Dynamic light scattering indicated that these polycarboxylates formed polyelectrolyte complexes with BMP-2. The osteogenic differentiation efficiency of MC3T3-E1 cells treated with the polycarboxylate/BMP-2 complexes was investigated in comparison to that of the heparin/BMP-2 complex. As a result, PGlu/BMP-2 complex showed the highest activity of alkaline phosphatase, which is an early-stage marker of osteogenic differentiation, and rapid mineralization. Based on these observations, PGlu could serve as an alternative to heparin in the regenerative therapy of bone using BMP-2.

Minimally Effective Dose of Bone Morphogenetic Protein in Minimally Invasive Lumbar Interbody Fusions: Six Hundred Ninety Patients in a Dose-Finding Longitudinal Cohort Study

STUDY DESIGN

Retrospective longitudinal cohort.

OBJECTIVE

We sought to demonstrate the minimally effective bone morphogenetic protein (BMP) dose to achieve fusion in minimally invasive transforaminal lumbar interbody fusions.

SUMMARY OF BACKGROUND DATA

Multiple studies have been conducted, which used a wide range of BMP doses for lumbar fusions highlighting associated risks and benefits. There is, however, a paucity in the literature in determining the minimally effective dose.

METHODS

Consecutive patients who underwent transforaminal lumbar interbody fusion from 2009 to 2014 were reviewed. Fusion was determined by a combination of computed tomography and dynamic x-ray by independent radiologists. We used backward stepwise multiple logistic regression with fusion as the dependent variable to determine whether BMP dose/level was a significant predictor for fusion. To determine the minimally effective dose of BMP/level, separate logistic regressions for different BMP dose ranges and sensitivity analyses were used. A P value ≤0.025 was considered significant.

RESULTS

There were 1102 interspaces among 690 patients. Average BMP dose was 1.28 mg/level. Overall fusion was 95.2% with a mean follow-up of 19 months. BMP dose/level was a significant predictor for fusion. Odds of fusion increased by 2.02 when BMP dose range was increased from (0.16-1 mg/level) to (1.0-2 mg/level), but fusion odds did not increase when BMP dose increased to more than 2 mg/level.

CONCLUSION

BMP dose/level was a significant predictor for fusion. There was a significant increase in odds of fusion when BMP dose increased from 0.16 to 1 mg/level to 1.0 to 2 mg/level. No benefit from increasing the dose more than 2 mg/level was found, suggesting 1.0 mg/level to be the minimally effective BMP dose.

LEVEL OF EVIDENCE

3.

Addition of an oligoglutamate domain to bone morphogenic protein 2 confers binding to hydroxyapatite materials and induces osteoblastic signaling

Nonautologous bone grafts have limited osteoinductive potential and thus there is substantial interest in reconstituting these graft materials with osteogenic factors such as bone morphogenic protein 2 (BMP2). However, one limitation of this approach is that BMP2 is typically weakly bound to the graft, which can lead to side effects associated with BMP2 dissemination. In the current study we added a hydroxyapatite (HA)-binding domain onto BMP2 to increase coupling to the graft surface. A sequence consisting of eight glutamate residues (E8) was inserted into the C-terminus of BMP2, and the recombinant protein (rBMP2-E8) was expressed in E. coli. Compared with rBMP2, rBMP2-E8 displayed markedly enhanced binding to HA disks and was better retained on the disks following exposure to vigorous wash steps. Furthermore, rBMP2-E8 was purified using a heparin column, and evaluated for its capacity to stimulate osteoblastic cell signaling. Treatment of SAOS2 cells with rBMP2-E8 induced SMAD 1/5 activation, confirming that the protein retains activity. Collectively these results suggest that the E8 domain serves as an effective tool for improving rBMP2 coupling to graft materials. The increased retention of rBMP2-E8 on the graft surface is expected to prolong BMP2's osteoinductive activity within the graft site, while simultaneously reducing off-target effects.

BMP2/7 heterodimer enhances osteogenic differentiation of rat BMSCs via ERK signaling compared with respective homodimers

Bone morphogenetic protein (BMP)2/7 heterodimer shows greater efficacy in enhancing bone regeneration. However, the precise mechanism and the role of mitogen-activated protein kinase (MAPK) signaling network in BMP2/7-driven osteogenesis remain ambiguous. In this study, we evaluated the effects of BMP2/7 heterodimers on osteoblastic differentiation in rat bone marrow mesenchymal stem cells (BMSCs), with the aim to elaborate how MAPKs might be involved in this cellular process by treatment of rat BMSCs with BMP2/-7 with a special signal-pathway inhibitor. We found that BMP2/7 heterodimer induced a much stronger osteogenic response in rat BMSCs compared with either homodimer. Most interestingly, extracellular signal-regulated kinase (ERK) demonstrated a highly sustained phosphorylation and activation in the BMP2/7 heterodimer treatment groups, and inhibition of ERK cascades using U0126 special inhibitor that significantly reduced the activity of ALP and calcium mineralization to a substantial degree in rat BMSCs treated with BMP2/7 heterodimers. Collectively, we demonstrate that BMP2/7 heterodimer shows a potent ability to stimulate osteogenesis in rat BMSCs. The activated ERK signaling pathway involved in this process may contribute partially to an increased osteogenic potency of heterodimeric BMP2/7 growth factors.

Indirect Bactericidal Properties of Recombinant Human Bone Morphogenetic Protein 2 In Vitro

PURPOSE

Bone morphogenetic proteins (BMPs) are secreted cytokines and are involved in various metabolic functions and inflammatory processes in different organs. The purpose of this study was to investigate whether BMPs also possess antimicrobial properties in direct or indirect ways.

MATERIALS AND METHODS

Antibacterial properties of recombinant human BMP2 (rhBMP2) were tested on 4 bacteria species (Staphylococcus aureus, Escherichia coli, Streptococcus mitis, Streptococcus constellatus) to examine the potential synergism of rhBMP2 with antibiotics. Indirect antibacterial properties were tested by infecting neutrophils with rhBMP2 and bacteria to investigate bacterial survival. Reactive oxidative species (ROS) production in neutrophils in the presence of rhBMP2 also was tested.

RESULTS

RhBMP2 in cardboard disks or sponge collagen as carriers did not show antibacterial activity against all tested bacteria. Further, synergism of rhBMP2 with antibiotics was not evident. Survival of bacteria inoculated with neutrophils and rhBMP2 led to a marked decrease in bacterial survival compared with neutrophils without rhBMP2. Although rhBMP2 inoculation of neutrophils alone did not induce ROS, its presence with the bacterial infection showed augmented ROS production for all tested bacteria.

CONCLUSIONS

RhBMP2 did not show direct antibacterial properties but did exhibit an indirect bactericidal effect in the presence of neutrophils. ROS production indicated that rhBMP2 has a role as a priming agent for neutrophils by augmenting their bactericidal capabilities and suggests the importance of its presence in contaminated surgical bone augmentation sites.

Effects of BMP-2 dose and delivery of microvascular fragments on healing of bone defects with concomitant volumetric muscle loss

Traumatic composite bone-muscle injuries, such as open fractures, often require multiple surgical interventions and still typically result in long-term disability. Clinically, a critical indicator of composite injury severity is vascular integrity; vascular damage alone is sufficient to assign an open fracture to the most severe category. Challenging bone injuries are often treated with bone morphogenetic protein 2 (BMP-2), an osteoinductive growth factor, delivered on collagen sponge. Previous studies in a composite defect model found that a minimally bridging dose in the segmental defect model was unable to overcome concomitant muscle damage, but the effect of BMP dose on composite injuries has not yet been studied. Here, we test the hypotheses that BMP-2-mediated functional regeneration of composite extremity injuries is dose dependent and can be further enhanced via co-delivery of adipose-derived microvascular fragments (MVF), which have been previously shown to increase tissue vascular volume. Although MVF did not improve healing outcomes, we observed a significant BMP-2 dose-dependent increase in regenerated bone volume and biomechanical properties. This is the first known report of an increased BMP-2 dose improving bone healing with concomitant muscle damage. While high dose BMP-2 delivery can induce heterotopic ossification (HO) and increased inflammation, the maximum 10 μg dose used in this study did not result in HO and was associated with a lower circulating inflammatory cytokine profile than the low dose (2.5 μg) group. These data support the potential benefits of an increased, though still moderate, BMP-2 dose for treatment of bone defects with concomitant muscle damage. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res.

Peroxisome Proliferator-Activated Receptor-γ Knockdown Impairs Bone Morphogenetic Protein-2-Induced Critical-Size Bone Defect Repair

The Food and Drug Administration-approved clinical dose (1.5 mg/mL) of bone morphogenetic protein-2 (BMP2) has been reported to induce significant adverse effects, including cyst-like adipose-infiltrated abnormal bone formation. These undesirable complications occur because of increased adipogenesis, at the expense of osteogenesis, through BMP2-mediated increases in the master regulatory gene for adipogenesis, peroxisome proliferator-activated receptor-γ (PPARγ). Inhibiting PPARγ during osteogenesis has been suggested to drive the differentiation of bone marrow stromal/stem cells toward an osteogenic, rather than an adipogenic, lineage. We demonstrate that knocking down PPARγ while concurrently administering BMP2 can reduce adipogenesis, but we found that it also impairs BMP2-induced osteogenesis and leads to bone nonunion in a mouse femoral segmental defect model. In addition, in vitro studies using the mouse bone marrow stromal cell line M2-10B4 and mouse primary bone marrow stromal cells confirmed that PPARγ knockdown inhibits BMP2-induced adipogenesis; attenuates BMP2-induced cell proliferation, migration, invasion, and osteogenesis; and escalates BMP2-induced cell apoptosis. More important, BMP receptor 2 and 1B expression was also significantly inhibited by the combined BMP2 and PPARγ knockdown treatment. These findings indicate that PPARγ is critical for BMP2-mediated osteogenesis during bone repair. Thus, uncoupling BMP2-mediated osteogenesis and adipogenesis using PPARγ inhibition to combat BMP2's adverse effects may not be feasible.

Radiographic and CT Evaluation of Recombinant Human Bone Morphogenetic Protein-2-assisted Cervical Spinal Interbody Fusion

STUDY DESIGN

This was a retrospective study.

OBJECTIVE

To radiographically demonstrate the distinct fusion pattern of recombinant human bone morphogenetic protein-2 (rhBMP-2) in the setting of anterior cervical discectomy and fusion.

SUMMARY OF BACKGROUND DATA

Studies investigating spinal fusion assisted with rhBMP-2 have yielded promising results, suggesting rhBMP-2 is an efficacious alternative to iliac crest autografts. rhBMP-2-assisted spinal fusion both hastens healing and eliminates patient morbidity from iliac crest autograft. Unique to rhBMP-assisted spinal fusion is its distinct radiographic fusion pattern as fusion is achieved. Despite promising results and increased clinical use of rhBMP-2, there remains a paucity of literature documenting this radiographic process.

MATERIALS AND METHODS

This study included 26 patients who underwent single-level anterior cervical discectomy and fusion using rhBMP-2. All data used for this study was collected from a prior FDA Investigational Device Exemption study.

RESULTS

A polyetheretherketone cage was used as an interbody disk spacer in all 26 patients. Patients were evaluated between 2 and 6 weeks after surgery and subsequently at 3, 6, 12, and 24 months postoperative. All patients underwent plain radiography at every follow-up visit, and computed tomograhy evaluation was performed at 3, 6, 12, and 24 months as part of the study protocol. Earliest fusion was observed at 3 months in 38% of patients. Likely fusion was observed in all patients by 12 months postoperative.

CONCLUSIONS

rhBMP-2 leads to both successful interbody fusion and an enhanced fusion rate with unique imaging characteristics. Additional characteristics of BMP observed in 100% of patients included prevertebral soft-tissue swelling and early endplate resorption. Other common features included polyetheretherketone cage migration, heterotopic bone formation and cage subsidence.

Bone Regeneration by Controlled Release of Bone Morphogenetic Protein-2: A Rabbit Spinal Fusion Chamber Molecular Study

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been widely used in spine fusion surgery. However, high doses of rhBMP-2 delivered with absorbable collagen sponge (ACS) have led to inflammation-related adverse conditions. Polyelectrolyte complex (PEC) control release carrier can substantially reduce the rhBMP-2 dose and complication without compromising fusion. The molecular events underlying controlled release and their effects on spinal fusion remain unknown. In this study, a rabbit interbody spinal fusion chamber was designed to provide a controlled environment for profiling molecular events during the fusion process. Study groups included Group 1, PEC with 100 μg rhBMP-2; Group 2, ACS with 100 μg rhBMP-2; Group 3, ACS with 300 μg rhBMP-2; Group 4, autologous bone graft; and Group 5, empty chamber. Manual palpation, microcomputed tomography, and histological analysis showed that Group 1 and 3 achieved bone fusion, while the other groups showed no signs of fusion. Gene expression profiling showed robust induction of osteogenic markers in Groups 1 and 3, with modulated early induction of inflammatory genes in the PEC group. Delivery of 100 μg rhBMP-2 with ACS (Group 2) resulted in less upregulation of osteogenic genes, increased inflammatory genes expression, and upregulation of osteoclastic genes compared to Group 1. These results suggest that the manner of BMP-2 release at the interbody spinal defect site could dictate the balance of in-situ osteogenic and antiosteogenic activities, affecting fusion outcomes. The molecular evidence supports PEC for sustained release of BMP-2 for spinal interbody fusion, and the feasibility of employing this novel interbody spinal fusion chamber for future molecular studies. Impact Statement A radiolucent rabbit interbody spinal fusion chamber was developed to study the molecular events during spinal fusion process. The gene expression profile suggests that control release of bone morphogenetic protein-2 (BMP-2) resulted in lower inflammatory and osteoclastic activities, but elicited higher osteogenic activities, while burst release of BMP-2 resulted in predominantly inflammation and osteoclastogenesis with minimum osteogenic activity. This study provides the molecular evidence that underscores the regeneration outcomes from the two different BMP-2 delivery systems. This spinal fusion chamber could be used for future molecular studies to optimize carrier design for spinal fusion.

Highly Cited Works in Spinal Disorders: The Top 100 Most Cited Papers Published in Spine Journals

STUDY DESIGN

Bibliometric analysis.

OBJECTIVE

To identify, and summarize the key findings of, the top 100 most highly cited works published in spinal disorder topic-specific journals.

SUMMARY OF BACKGROUND DATA

There is an abundance of published articles pertaining to spine surgery and spinal disorders. The number of citations a work receives provides a useful measure of its scientific impact. An understanding of the most cited works in spine surgery can identify literature that surgeons and researchers should be familiar with, point to the most active areas of research, inform the design of educational curricula, and help guide future research efforts.

METHODS

Journals relating to spinal disorders were identified using the Journal Citation Reports database. We then searched the Web of Science database for articles appearing in each of these journals. The top 100 most cited works were selected for analysis.

RESULTS

The top 100 most cited articles appeared in seven of eight journals dedicated to spinal disorders, with 84 in Spine and seven in the European Spine Journal. The citation count for individual articles ranged from 343 to 1949. Most works (73) were published between 1990 and 2004. The greatest number of articles (22) focused on low back pain, followed by biomechanics (13), degenerative disc disease (12), and lumbar spinal stenosis/lumbar fusion (9). With regard to study design, laboratory investigations were the most common (12), followed by guideline documents (11), reviews (10), and retrospective cohort studies (10).

CONCLUSION

The most cited works in spinal disorder journals are guidelines for low back pain, descriptions of quality of life (QOL) metrics, or laboratory investigations into spinal biomechanics. A gap exists for work relating to neck pain or cervical spinal pathology (e.g., cervical myelopathy), representing opportunity for future work. Time of publication, topic of study, study design, and journal are possible determinants of likelihood of citation.

LEVEL OF EVIDENCE

N/A.

Enhancing the effects of exfoliated carbon nanofibers using bone morphogenetic protein in a rat spinal fusion model

Exfoliated carbon nanofibers (ExCNFs) are expected to serve as excellent scaffolds for promoting and guiding bone-tissue regeneration. We aimed to enhance the effects of ExCNFs using bone morphogenetic proteins (BMPs) and examined their feasibility and safety in clinical applications using a rat spinal fusion model. Group I (n = 15) animals were implanted with the control carrier; Group II (n = 16) animals were implanted with carrier containing 1 μg ExCNFs; Group III (n = 16) animals were implanted with carrier containing 1 μg recombinant human (rh) BMP-2; and Group IV (n = 17) animals were implanted with carrier containing 1 μg rhBMP-2 and 1 μg ExCNFs. The rats were euthanized after 4 or 8 weeks and their spines were explanted and assessed by manual palpation, radiographs, and high-resolution microcomputerized tomography (micro-CT); the spines were also subjected to histological analysis. The fusion rates in Group IV (25.0%: 4-week, 45.5%: 8-week) were considerably higher than in Groups I (0%: 4-week, 0%: 8-week), II (0%: 4-week, 15.0%: 8-week), and III (16.7%: 4-week, 30.0%: 8-week). These results demonstrated the enhancement of ExCNF bone fusion effects by BMP in a rat spinal fusion model. Our results suggest that the enhancement of ExCNFs effects by BMP makes this combination a possible attractive therapy for spinal fusion surgeries. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2892-2900, 2018.

A Computed Tomography Analysis of the Success of Spinal Fusion Using Ultra-Low Dose (0.7 mg per Facet) of Recombinant Human Bone Morphogenetic Protein 2 in Multilevel Adult Degenerative Spinal Deformity Surgery

Study Design

Retrospective cohort study.

Purpose

To report on spinal fusion assessment using computed tomography (CT) after adult spinal deformity (ASD) surgery using ultra-low dose recombinant human bone morphogenetic protein 2 (RhBMP-2).

Overview of Literature

The reported dose of RhBMP-2 needed for successful spinal posterolateral fusion in ASD ranges from 10 to 20 mg per spinal level. This study reports the use of ultra-low dose of RhBMP-2 (0.07 mg per facet) to achieve spinal fusion in multilevel ASD surgery.

Methods

Consecutive patients who underwent ASD surgery using ultra-low dose RhBMP-2 were recruited. Routine postoperative CT analysis for spinal fusion was performed by two spine surgeons. Inter-observer agreement was calculated for facet fusion (FF) and interbody fusion (IBF) at 6 and 12 months after the procedure.

Results

Six consecutive ASD patients with a mean age of 62 years (28–72 years) were examined. Each patient received a total dose of 12 mg with an average dose of 0.69±0.2 mg (0.42–1 mg) per single FF and 1.38±0.44 mg (0.85–2 mg) for IBF. Total 131 FF and 15 IBF were examined in the study, with 88 FFs and nine IBFs being analyzed specifically at 6 months after the surgery. FF and IBF reported by surgeons A and B at 6 months were 97.7% vs. 91.9% FF, respectively (κ=0.95) and 100% vs. 100% IBF, respectively (κ=1). Two patients underwent longitudinal follow-up CT at 12 months, and the FF rates reported by surgeons A and B were 100% vs. 95.8%, respectively (κ=0.96). Five out of nine facet (56%) non-unions were identified at the cross-links. The remaining four facet pseudarthrosis were noted at 1–2 spinal levels caudal to the cross-links. At the final clinical follow-up, there was no rod breakage, deformity progression, neurological deficit, or symptom recurrence. The Oswestry Disability Index improved by an average of 32.8±6.3, while the mental component summary of the 36-item Short-Form Health Survey improved by an average of 4.7±2.1, and physical component summary improved by an average of 10.5±2.1.

Conclusions

To our knowledge, this is the first study to report a CT that defined 92%–98% FF and 100% IBF using the lowest reported dose of RhBMP-2 in multilevel ASD surgery. The use of ultra-low dose RhBMP-2 reduces the RhBMP-2 related complications and healthcare costs.

All-trans retinoic acid can antagonize osteoblastogenesis induced by different BMPs irrespective of their dimerization types and dose-efficiencies

Introduction

Alcoholism can lead to low mineral density, compromised regenerative bone capacity and delayed osteointegration of dental implants. This may be partially attributed to the inhibitive effect of all-trans retinoic acid (ATRA), a metabolite of alcohol, on osteoblastogenesis. Our previous studies demonstrated that heterodimeric bone morphogenetic protein 2/7 (BMP2/7) was a more potent BMP than homodimeric BMP2 or BMP7, and could antagonize the inhibitive effect of ATRA to rescue osteoblastogenesis.

Materials and methods

In this study, we compared the effectiveness of BMP2/7, BMP2 and BMP7 in restoring osteoblastogenesis of murine preosteoblasts upon inhibition with 1 µM ATRA, and we further analyzed the potential mechanisms. We measured the following parameters: cell viability, ALP, OCN, mineralization, the expression of osteogenic differentiation marker genes (Collagen I, ALP and OCN) and the expression of BMP signaling key genes (Dlx5, Runx2, Osterix and Smad1).

Results

BMP2/7 treatment alone induced significantly higher osteoblastogenesis compared to BMP2 and BMP7. When cells were treated by ATRA, BMP2/7 was superior only in rescuing cell viability and ALP activity, compared to BMP2 or BMP7. However, BMP2/7 was not superior to BMP2 or BMP7 in restoring OCN expression and extracellular mineralized nodules, or in rescuing expression of two key osteogenic genes, Dlx5 and Runx2. Irrespective of their dimeric types or potency, the selected BMPs could antagonize the inhibitory effect of ATRA on osteoblastogenesis.

Conclusion

The presence of ATRA, BMP2/7 still induced significantly higher cell viability and early differentiation than the homodimers. However, ATRA significantly attenuated the advantages of BMP2/7 in inducing late and final osteoblastogenic differentiation over the homodimers.

Does Recombinant Human Bone Morphogenic Protein 2 Affect Perioperative Blood Loss after Lumbar and Thoracic Spinal Fusion?

STUDY DESIGN

Retrospective cohort design.

PURPOSE

This study aimed to determine whether recombinant human bone morphogenic protein 2 (rhBMP-2) reduces total perioperative blood loss during lumbar and thoracic fusion.

OVERVIEW OF LITERATURE

Previous studies on rhBMP-2 versus iliac crest bone grafting in thoracic and lumbar fusions have yielded mixed results regarding reductions in blood loss and have largely neglected the postoperative period when analyzing total blood loss. Additionally, these studies have been limited by heterogeneity and sample size.

METHODS

We analyzed the blood loss patterns of 617 consecutive adult patients undergoing lumbar and/or thoracic fusions requiring subfascial drain placement at a single institution from January 2009 to December 2016. Patients were divided into BMP and non-BMP cohorts, and a propensity score analysis was conducted to account for the differences between cohorts.

RESULTS

At a per-level fused basis, the BMP group exhibited a significant reduction in the intraoperative (66.1 mL per-level fused basis; 95% confidence interval [CI], 127.9 to 4.25 mL; p =0.036) and total perioperative blood loss (100.7 mL per-level fused basis; 95% CI, 200.9 to 0.5 mL; p =0.049). However, no significant differences were observed in an analysis when not controlling for the number of levels or when examining the postoperative drain output.

CONCLUSIONS

RhBMP-2 appears to reduce both intraoperative and total blood loss during lumbar and thoracic fusions on a per-level fused basis. This total reduction in blood loss was achieved via intraoperative effects because RhBMP-2 had no significant effect on the postoperative drain output.

A Prospective, Randomized, Multicenter Study Comparing Silicated Calcium Phosphate versus BMP-2 Synthetic Bone Graft in Posterolateral Instrumented Lumbar Fusion for Degenerative Spinal Disorders

STUDY DESIGN

A prospective, Phase IV, multicenter, randomized study.

OBJECTIVE

The aim of this study was to compare vertebral fusion success rates following posterolateral fusion [(PLF)/posterolateral intertransverse fusion (PITF)] surgery. The surgical procedure combined posterior lumbar interbody fusion (PLIF) and PLF with internal fixation over one or two levels using silicated calcium phosphate (SiCaP) or bone morphogenetic protein (BMP)-2 as graft material in patients with a degenerative disorder of the lumbar spine.

SUMMARY OF BACKGROUND DATA

Few controlled trials have evaluated the bone graft materials available to surgeons treating patients with spinal disorders, including degenerative disc disease, spondylolisthesis, and disc herniation.

METHODS

Following randomization, the surgical procedure consisting of PLIF and PLF with internal fixation over one or two levels was performed using SiCaP or BMP-2. No other osteoconductive/osteoinductive graft materials were permitted. Spinal fusion was assessed radiographically at ≤24 months. Clinical outcomes (pain on visual analog scale, Oswestry Disability Index, SF-36) and adverse events (AEs) were monitored.

RESULTS

One hundred three patients were enrolled. At 12 months, fusion was achieved in 25 of 35 (71.4%) of the SiCaP and 20 of 27 (74.1%) of the BMP-2 group, respectively (P = 1.000). At 24 months, the fusion rate was 78.6% and 84.8% for SiCaP and BMP-2, respectively (P = 0.5613). Clinical outcomes improved similarly in both groups over time. AEs were consistent with this surgical population.

CONCLUSION

SiCaP was safe and well tolerated in patients with degenerative spinal disorders requiring PLF and provided fusion rates similar to BMP-2.

LEVEL OF EVIDENCE

2.

Combination therapy with BMP-2 and psoralen enhances fracture healing in ovariectomized mice

The advantages of combining local delivery of bone morphogenetic protein (BMP)-2 with systemic or local anti-osteoporosis treatments have also been studied for enhancing osteoporotic fracture healing. The aim of the present study was to evaluate the effect of combination therapy with BMP-2 and psoralen on fracture repair in ovariectomized mice. At 6 weeks after bilateral ovariectomy, mice (n=30) underwent unilateral transverse osteotomy on the femur and were divided into 3 groups. In the model group (n=10), animals were implanted with an absorbable collagen sponge (ACS) alone and administered physiological saline intragastrically (i.g.). In the recombinant human (rh)BMP-2 group (n=10), animals were implanted with an ACS loaded with 2.5 µg rhBMP-2 and administered physiological saline i.g. In the psoralen + rhBMP-2 group (n=10) animals were implanted with an ACS loaded with 2.5 µg rhBMP-2 and administered psoralen i.g. The mice were euthanized after 21 days and their fractured femurs were assessed by micro computed tomography, histological analysis and biomechanical testing. Furthermore, the serum of the animals was analyzed. Psoralen + rhBMP-2 exerted more beneficial effects on callus consolidation and biomechanical strength. In addition, increased bone-specific alkaline phosphatase levels and decreased C-terminal telopeptide of type-1 collagen were observed in the Psoralen + rhBMP-2 group. However, no difference in estrogen levels was detected between the groups. In conclusion, the present study demonstrated that in ovariectomized mice, combination of locally delivered BMP-2 and systemically administered psoralen improved bone healing compared with BMP-2 alone.

The Induction of Bone Formation: The Translation Enigma

A paradigmatic shift in the way of thinking is what bone tissue engineering science requires to decrypt the translation conundrum from animal models into human. The deductive work of Urist (1965), who discerned the principle of bone induction from the pioneering works of Senn, Huggins, Lacroix, Levander, and other bone regenerative scientists, provided the basis that has assisted future bone tissue regenerative scientists to extend the bone tissue engineering field and its potential uses for bone regenerative medicine in humans. However, major challenges remain that are preventing the formation of bone by induction clinically. Growing experimental evidence is indicating that bone inductive studies are non-translatable from animal models into a clinical environment. This is preventing bone tissue engineering from reaching the next phase in development. Countless studies are trying to discern how the formation of bone by induction functions mechanistically, so as to try and solve this enigmatic problem. However, are the correct questions being asked? Why do bone inductive animal studies not translate into humans? Why do bone induction principles not yield the same extent of bone formation as an autogenous bone graft? What are bone tissue engineering scientists missing? By critically re-assessing the past and present discoveries of the bone induction field, this review article attempts to re-discover the field of bone formation by induction, identifying some key features that may have been missed. These include a detailed library of all proteins in bones and their arrangement in the 3D superstructure of the bone together with some other important criteria not considered by tissue engineering scientists. The review therefore not only re-iterates possible avenues of research that need to be re-explored but also seeks to guide present and future scientists in how they assess their own research in light of experimental design and results. By addressing these issues bone formation by induction without autografts might finally become clinically viable.

Postoperative pain following posterior iliac crest bone graft harvesting in spine surgery: a prospective, randomized trial

BACKGROUND CONTEXT

Postoperative pain at the site of bone graft harvest for posterior spine fusion is reported to occur in 6%-39% of cases. However, the area around the posterior, superior iliac spine is a frequent site of referred pain for many structures. Therefore, many postoperative spine patients may have pain in the vicinity of the posterior iliac crest that may not in fact be caused by bone graft harvesting. The literature may then overestimate the true incidence of postoperative iliac crest pain.

PURPOSE

We performed a prospective study testing the hypothesis that patients will not report significantly higher visual analog scores over the graft harvest site when compared with the contralateral, non-harvested side.

STUDY DESIGN/SETTING

This is a prospective, randomized cohort study.

PATIENT SAMPLE

Patients aged 18-75 years undergoing elective spinal fusion of one to two levels between L4 and S1 for spinal stenosis and spondylolisthesis were randomized to left-sided or right-sided iliac crest bone graft (ICBG) donor sites and blinded to the side of harvest.

OUTCOME MEASURES

Primary outcome was a 10-point visual analog scale (VAS) for pain over the left and right posterior superior iliac spine.

METHODS

Bone graft was harvested via spinal access incisions without making a separate skin incision over the crest. Each patient's non-harvested side served as an internal control. Data points were recorded by patients on their study visit sheets preoperatively and at 6 weeks, 3 months, 6 months, and 1 year postoperatively.

RESULTS

Forty patients were enrolled in the study (23 females) with an average follow-up of 8.1 months (1.5-12 months). Mean age was 51.7 years (23-77 years). Left- and right-side ICBG harvesting was performed equally between the 40 patients. The average volume of graft harvested from the left was 35.3 mL (15-70 mL) and 36.1 mL (15-60 mL) from the right. There was no statistical difference between preoperative VAS score on the harvested side compared with the non-harvested side (p=.415). Postoperatively, there were consistently higher VAS scores on the operative side; however, these differences were not statistically significant at 6 weeks (p=.111), 3 months (p=.440), 6 months (p=.887), or 12 months (p=.240). Both groups did, however, show statistically significant improvements in VAS scores over time within the operative and nonoperative sides (p<.05). Graft volume had no effect on the VAS scores (p=.382).

CONCLUSIONS

The current literature does not adequately illuminate the incidence of postoperative pain at the site of harvest and the relative magnitude of this pain in comparison with the patient's residual low back pain. This is the first study to blind the patient to the laterality of bone graft harvesting. Our randomized investigation showed that although pain on the surgical side was slightly higher, it was neither clinically nor statistically different from the nonsurgical side. Our conclusion supports surgeons' use of autologous bone graft, which offers a cost-effective, efficacious spinal fusion supplement.

The Influence of Geography, Time, and Payer Type on the Utilization of Bone Morphogenetic Protein (BMP) Between 2005 and 2015

Bone morphogenetic protein (BMP) is a critical compound for endochondral bone formation and is used as a bone graft substitute to promote spinal fusion and fracture healing. We sought to identify rate, type, and applications of use of BMP in spinal fusion surgery during 2005 to 2015. The Medicare 5% national sample (SAF5) database and the Humana Orthopaedics database (HORTHO) were searched for patients who underwent spinal fusion with BMP. Rate of use over time and influence of geographic region and payer type on utilization of BMP during 2005 to 2015 were analyzed. A total of 9879 and 12,598 patients were treated with BMP within the SAF5 database and HORTHO databases, respectively. There was a statistically significant variation in use of BMP among geographic regions. Rate of BMP usage for patients above 65 years old was 11.02 and 58.91 patients per 100,000 members for SAF5 and HORTHO databases, respectively (P<0.001). Rate of use of BMP did not vary significantly during 2005 to 2012 within the SAF5 database (P=0.153). There was a trend toward lower use of BMP in the HORTHO database between 2007 and 2015 (P=0.081). BMP use was higher for private pay than Medicare.

Human Spinal Bone Dust as a Potential Local Autograft: In Vitro Potent Anabolic Effect on Human Osteoblasts

STUDY DESIGN

In vitro Study.

OBJECTIVE

To evaluate the effect that factors released from human posterior spinal bone dust have on primary human osteoblast growth and maturation.

SUMMARY OF BACKGROUND DATA

Bone dust, created during spinal fusion surgeries, has the potential to be used as an autologous bone graft by providing a source of viable autologous osteoblasts and mesenchymal stem cells with osteogenic potential. Till date, no information is available on whether bone dust also provides a source of anabolic factors with the potential to enhance osteoblast proliferation and maturation, which would enhance its therapeutic potential.

METHODS

Bone dust was collected from consenting patients undergoing elective posterior spinal fusion surgeries, and primary human osteoblasts were cultured from patients undergoing elective hip or knee arthroplasty. Growth factors and cytokines released by bone dust were quantified using enzyme-linked immunosorbent assay. Primary human osteoblast proliferation and gene expression in response to bone dust were assessed using H-thymidine incorporation and real-time polymerase chain reaction, respectively.

RESULTS

Human bone dust released anabolic cytokines (IL-1β and IL-6) and growth factors (TGF-β, VEGF, FGF-Basic, and PDGF-BB) in increasing concentrations over a 7-day period. In vitro, the anabolic factors released by bone dust increased osteoblast proliferation by 7-fold, compared with osteoblasts cultured alone. In addition, the factors released from bone dust up-regulated a number of osteoblastic genes integral to osteoblast differentiation, maturation, and angiogenesis.

CONCLUSION

This study is the first to demonstrate that human posterior spinal bone dust released anabolic factors that potently enhance osteoblast proliferation and the expression of genes that favor bone healing and bone union. As bone dust is anabolic and its harvest is fast, simple, and safe to perform, spinal surgeons should be encouraged to 'recycle' bone dust and harness the regenerative potential of this free autologous bone graft.

LEVEL OF EVIDENCE

N/A.

Scaffolds for the repair of bone defects in clinical studies: a systematic review

Background

This systematic review aims to summarize the clinical studies on the use of scaffolds in the repair of bony defects.

Methods

The relevant articles were searched through PubMed database. The following keywords and search terms were used: “scaffolds,” “patient,” “clinic,” “bone repair,” “bone regeneration,” “repairing bone defect,” “repair of bone,” “osteanagenesis,” “osteanaphysis,” and “osteoanagenesis.” The articles were screened according to inclusion and exclusion criteria, performed by two reviewers.

Results

A total of 373 articles were obtained using PubMed database. After screening, 20 articles were identified as relevant for the purpose of this systematic review. We collected the data of biological scaffolds and synthetic scaffolds. There are eight clinical studies of biological scaffolds included collagen, gelatin, and cellular scaffolds for bone healing. In addition, 12 clinical studies of synthetic scaffolds on HAp, TCP, bonelike, and their complex scaffolds for repairing bone defects were involved in this systematic review.

Conclusions

There are a lot of clinical evidences showed that application of scaffolds had a good ability to facilitate bone repair and osteogenesis. However, the ideal and reliable guidelines are insufficiently applied and the number and quality of studies in this field remain to be improved.

BMP and Beyond: A 25-Year Historical Review of Translational Spine Research at Emory University

A high rate of symptomatic spinal pseudoarthrosis and a wide range of complications associated with the use of iliac crest bone graft (the gold standard) have prompted the spine surgery community to seek alternative options to promote spinal fusion. Emory University has been one of the global leaders in this endeavor. This invited review covers the last 25 years of Emory's contributions to translational spine research, focusing specifically on our work with bone morphogenetic proteins (BMP) and the BMP signaling pathway. As a result of this work, recombinant human BMP-2 is the only Food and Drug Administration approved biologic bone graft substitute. It has been shown to significantly increase spinal fusion rates across the spinal column because of its potent ability to stimulate local bone formation through the recruitment of mesenchymal stem cells. This review covers our development of animal models of spinal fusion, our body of work regarding the translation of BMP from the benchtop to the clinic, the discovery of LMP-1 and strategies to enhance cellular responsiveness to BMPs, and the design of various small molecule drugs that can enhance local bone formation.

Enhanced Bone Regeneration by Diabetic Cell-Based Adenoviral BMP-2 Gene Therapy in Diabetic Animals

The application of bone morphogenetic protein 2 (BMP-2) has been extensively investigated to improve diabetes-impaired bone healing; however, the delivery of BMP-2 by gene therapy for bone regeneration has rarely been investigated in diabetic animals. In this study, we aimed to evaluate which cells induce more new bone formation in diabetic animals when cell-based BMP2 gene therapy is applied. For this purpose, we harvested bone marrow stromal cells (BMSCs) twice in the same animal before (non-diabetic BMSCs; nBMSCs) and after diabetes induction (diabetic BMSCs; dBMSCs) using modified bone marrow ablation methods. And then, cells were transduced by adenoviral vectors carrying the BMP2 gene (AdBMP2). In in vitro, AdBMP2-transfected dBMSCs (B2/dBMSCs) produced higher BMP-2 mRNA levels over 48 h, whereas AdBMP2-transfected nBMSCs (B2/nBMSCs) exhibited a transient increase in BMP-2 mRNA followed by a decrease to the baseline level within 48 h. Both B2/dBMSCs and B2/nBMSCs induced secretion of BMP-2 for 3 weeks. However, B2/dBMSC BMP-2 secretion peaked from day 3 to 10, whereas B2/nBMSC BMP-2 secretion peaked from day 1 to 7. The analysis of osteogenic activity revealed that mineralization nodule formation and the expression levels of osteogenic genes were significantly higher in B2/dBMSCs than B2/nBMSCs and were accompanied by upregulation of canonical Wnt/β-catenin and Smad signaling. AdBMP2-transfected autologous cells were implanted into critical-sized calvarial defects in diabetic animals and induced significantly more bone regeneration than non-AdBMP2-transfected cells. In addition, B2/dBMSCs led to significantly more new bone formation than B2/nBMSCs. Thus, BMP2 gene therapy using diabetic cells effectively supported diabetic bone healing and it was related to the enhanced responses to AdBMP2 of dBMSCs.

Novel Osteobiologics and Biomaterials in the Treatment of Spinal Disorders

Spinal osteobiologics have evolved substantially in this century after the development of many product categories such as growth factors, allograft, and stem cells. The indications for the use of novel biologics within spine surgery are rapidly expanding as the mechanism of each is elucidated. While the knowledge base of bone morphogenetic protein increases with each subsequent year, the application of new nanotechnology and cell-based strategies are being reported. This review will discuss the most recent data in novel osteobiologics, and where we could use future study.

Osteogenic Potential of Tauroursodeoxycholic Acid as an Alternative to rhBMP-2 in a Mouse Spinal Fusion Model

The non-union rate after lumbar spinal fusion is potentially as high as 48%. To support efficient bone regeneration, recombinant human bone morphogenetic protein-2 (rhBMP-2) is commonly used as it is regarded as the most potent bone-inducing molecule. However, recently, there have been increasing concerns on the use of rhBMP-2 such as serious complications, including seroma and heterotopic ossification, and the low quality of bone at the center of fusion mass. Thus, many studies were conducted to find and to develop a potential alternative to rhBMP-2. In this study, we investigated the osteogenic potential of tauroursodeoxycholic acid (TUDCA) in the mouse fusion model and compared its effects with rhBMP-2. Twenty-four mice underwent bilateral posterolateral lumbar spinal fusion bone formation at L4-L5. Collagen sponge infused with saline, TUDCA, or rhBMP-2 was implanted at the fusion area. Two and 4 weeks postimplantation, bone formation and tissue regeneration were evaluated via micro-computed tomography and histological analysis. Compared with the TUDCA-treated group, the rhBMP-2 treatment produced a higher amount of bone fusion formation after 2 weeks but also showed higher resorption of the centralized bone after 4 weeks. Interestingly, the TUDCA-treated group developed higher trabecular thickness compared with rhBMP-2 after 4 weeks. Moreover, TUDCA treatment showed distinct angiogenic activity in human umbilical vein endothelial cells as confirmed by an in vitro tube formation assay. Our findings suggest that TUDCA is comparable to rhBMP-2 in supporting bone regeneration and spinal bone formation fusion by increasing trabecular thickness and promoting angiogenesis. Finally, our results indicate that TUDCA can be utilized as a potential alternative to rhBMP-2.

Comparison of the osteogenesis and fusion rates between activin A/BMP-2 chimera (AB204) and rhBMP-2 in a beagle's posterolateral lumbar spine model

BACKGROUND CONTEXT

Activin A/BMP-2 chimera (AB204) could promote bone healing more effectively than recombinant bone morphogenetic protein 2 (rhBMP-2) with much lower dose in a rodent model, but there is no report about the effectiveness of AB204 in a large animal model.

PURPOSE

The purpose of this study was to compare the osteogenesis and fusion rate between AB204 and rhBMP-2 using biphasic calcium phosphate (BCP) as a carrier in a beagle's posterolateral lumbar fusion model.

STUDY DESIGN

This is a randomized control animal study.

METHODS

Seventeen male beagle dogs were included. Bilateral posterolateral fusion was performed at the L1-L2 and L4-L5 levels. Biphasic calcium phosphate (2 cc), rhBMP-2 (50 µg)+BCP (2 cc), or AB204 (50 µg)+BCP (2 cc) were implanted into the intertransverse space randomly. X-ray was performed at 4 and 8 weeks. After 8 weeks, the animals were sacrificed, and new bone formation and fusion rate were evaluated by manual palpation, computed tomography (CT), and undecalcified histology.

RESULTS

The AB204 group showed significantly higher fusion rate (90%) than the rhBMP-2 group (15%) or the Osteon group (6.3%) by manual palpation. On x-ray and CT assessment, fusion rate and the volume of newly formed bone were also significantly higher in AB204 group than other groups. In contrast, more osteolysis was found in rhBMP-2 group (40%) than in AB204 group (10%) on CT study. In histologic results, new bone formation was sufficient between transverse processes in AB204 group, and obvious trabeculation and bone remodeling were observed. But in rhBMP-2 group, new bone formation was less than AB204 group and osteolysis was observed between the intertransverse spaces.

CONCLUSIONS

A low dose of AB204 with BCP as a carrier significantly promotes the fusion rate in a large animal model when compared with the rhBMP-2. These findings demonstrate that AB204 could be an alternative to rhBMP-2 to improve fusion rate.

Bone morphogenetic protein use in spine surgery in the United States: how have we responded to the warnings?

BACKGROUND CONTEXT

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been widely adopted as a fusion adjunct in spine surgery since its approval in 2002. A number of concerns regarding adverse effects and potentially devastating complications of rhBMP-2 use led to a Food and Drug Administration (FDA) advisory issued in 2008 cautioning its use, and a separate warning about its potential complications was published by The Spine Journal in 2011.

PURPOSE

To compare trends of rhBMP-2 use in spine surgery after the FDA advisory in 2008 and The Spine Journal warning in 2011.

STUDY DESIGN

Retrospective cross-sectional study using a national database.

PATIENT SAMPLE

All patients from 2002 to 2013 who underwent spinal fusion surgery at an institution participating in the Nationwide Inpatient Sample (NIS).

OUTCOME MEASURES

Proportion of spinal fusion surgeries using rhBMP-2.

METHODS

We queried the NIS from 2002 to 2013 and used International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) procedure codes to identify spinal fusion procedures and those that used rhBMP-2. Procedures were subdivided into primary and revision fusions, and by region of the spine. Cervical and lumbosacral fusions were further stratified into anterior and posterior approaches. The percentage of cases using BMP was plotted across time. A linear regression was fit to the data from quarter 3 of 2008 (FDA advisory) through quarter 1 of 2011, and a separate regression was fit to the data from quarter 2 of 2011 (The Spine Journal warning) onward. The slopes of these regression lines were statistically compared to determine differences in trends. No funding was received to conduct this study, and no authors had any relevant conflicts of interest.

RESULTS

A total of 4,167,079 patients in the NIS underwent spinal fusion between 2002 and 2013. We found a greater decrease in rhBMP-2 use after The Spine Journal warning compared with the FDA advisory for all fusion procedures (p=.006), primary fusions (p=.006), and revision fusions (p=.004). Lumbosacral procedures also experienced a larger decline in rhBMP-2 use after The Spine Journal article as compared with the FDA warning (p=.0008). This pattern was observed for both anterior and posterior lumbosacral fusions (p≤.0001 for both). Anterior cervical fusion was the only procedure that demonstrated a decline in rhBMP-2 use after the FDA advisory that was statistically greater than after The Spine Journal article (p=.02).

CONCLUSIONS

Warnings sanctioned through the spine literature may have a greater influence on practice of the spine surgery community as compared with advisories issued by the FDA.Comprehensive guidelines regarding safe and effective use of rhBMP-2 must be established.

Use of recombinant human bone morphogenetic protein-2 in spine surgery

Bone morphogenetic proteins are osteoinductive factors which have gained popularity in orthopaedic surgery and especially in spine surgery. The use of recombinant human bone morphogenetic protein-2 has been officially approved by the United States Food and Drug Administration only for single level anterior lumbar interbody fusion, nevertheless it is widely used by many surgeons with off-label indications. Despite advantages in bone formation, its use still remains a controversial issue and several complications have been described by authors who oppose their wide use.

Biologic Approaches to Problems of the Hand and Wrist

Orthobiologics are not used as frequently in the hand and wrist as in other sites. The most frequently reported is the use of bone morphogenetic protein for the treatment of Kienböck disease. Animal studies have described improved tendon healing with the use of platelet-rich plasma (PRP), but no clinical studies have confirmed these results. PRP has been reported to produce improvements in the outcomes of distal radial fractures and osteoarthritis of the trapeziometacarpal in small numbers of patients. The use of orthobiologics in the hand and wrist are promising, but clinical trials are necessary to establish efficacy and safety.

Competitive Protein Binding Influences Heparin-Based Modulation of Spatial Growth Factor Delivery for Bone Regeneration

Tissue engineering strategies involving the in vivo delivery of recombinant growth factors are often limited by the inability of biomaterials to spatially control diffusion of the delivered protein within the site of interest. The poor spatiotemporal control provided by porous collagen sponges, which are used for the clinical delivery of bone morphogenetic protein-2 (BMP-2) for bone regeneration, has necessitated the use of supraphysiological protein doses, leading to inflammation and heterotopic ossification. This study describes a novel tissue engineering strategy to spatially control rapid BMP-2 diffusion from collagen sponges in vivo by creating a high-affinity BMP-2 sink around the collagen sponge. We designed an electrospun poly-ɛ-caprolactone nanofiber mesh containing physically entrapped heparin microparticles, which have been previously demonstrated to bind and retain large amounts of BMP-2. Nanofiber meshes containing 0.05 and 0.10 mg of microparticles/cm2 demonstrated increased BMP-2 binding and decreased BMP-2 release in vitro compared with meshes without microparticles. However, when microparticle-containing meshes were used in vivo to limit the diffusion of BMP-2 delivered by using collagen sponges in a rat femoral defect, no differences in heterotopic ossification or biomechanical properties were observed. Further investigation revealed that, although BMP-2 binding to heparin microparticles was rapid, the presence of serum components attenuated microparticle-BMP-2 binding and increased BMP-2 release in vitro. These observations provide a plausible explanation for the results observed in vivo and suggest that competitive protein binding in vivo may hinder the ability of affinity-based biomaterials to modulate growth factor delivery.

Counting the Cost of Failed Spinal Fusion for Relief of Low Back Pain: Does Primary Fusion With Bone Morphogenetic Protein Make Economic Sense From a Primary Payer Perspective?

STUDY DESIGN

A retrospective cohort study.

OBJECTIVES

To investigate the unknown direct costs of failed instrumented lumbar fusion using iliac crest bone graft (ICBG) and subsequent reoperation utilizing recombinant human bone morphogenetic protein-2 (rhBMP-2) from a primary payer perspective.

SUMMARY OF BACKGROUND DATA

Recent evidence has demonstrated increased rates of instrumented lumbar fusion and utilization of rhBMP-2 to treat a range of conditions causing lower back pain. For health care providers with finite financial resources, there is an increasing demand to evaluate economic costs of available treatment modalities. The high cost of rhBMP-2 has often been cited as a leading reason for delaying its universal acceptance as a preferred substitute to ICBG. It has been hypothesized that rhBMP-2 may demonstrate cost-effectiveness if pseudarthrosis and reoperation rates are decreased, thus avoiding subsequent expenditure.

METHODS

This was a retrospective cohort study of patients who underwent instrumented lumbar fusions utilizing rhBMP-2. Hospital finance records were used to calculate direct total expenditure incurred by the primary payer for the procedure using rhBMP-2. For patients who received rhBMP-2 in a secondary lumbar fusion, additional total expenditure related to the patients' failed primary instrumented fusion with ICBG was also sought.

RESULTS

The mean total costs associated with failed instrumented lumbar fusion using ICBG and reoperation using rhBMP-2 totaled £47,734 per patient. The total direct costs of a policy of primary instrumented lumbar fusion with rhBMP-2 were less at £26,923 per patient; however, this was not significant.

CONCLUSIONS

To date, this is the first study to report the costs of failed primary instrumented lumbar fusions using ICBG and subsequent secondary fusions using rhBMP-2 from a primary payer perspective. On the basis of this evidence, a policy of using rhBMP-2 in all patients undergoing a primary instrumented lumbar fusion cannot be recommended.

Heterotopic ossification related to the use of recombinant human BMP-2 in osteonecrosis of femoral head

Despite the wide use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in bone defect, its application in treating osteonecrosis of femoral head (ONFH) is yet to be elucidated. The heterotopic ossification (HO) after rhBMP-2 usage in some orthopedic surgeries has been reported previously; however, only a few studies describe this complication in the treatment of ONFH.The present study investigated whether the rhBMP-2 application would increase the risk of HO formation in selected ONFH patients with nonvascularized bone grafting surgery and enhance the surgical results of nonvascularized bone grafting as compared to patients who did not receive intraoperative rhBMP-2.A retrospective analysis was performed on 94 patients (141 hips) who, with Association Research Circulation Osseous (ARCO) stages IIb, IIc, and IIIa ONFH, underwent nonvascularized bone grafting surgery. The first 46 patients (66 hips) received intraoperative rhBMP-2. The postoperative radiographic results (X-ray and CT scan) and Harris hip score (HHS) were reviewed in each patient to record the incidence of HO formation and evaluate the clinical efficacy of rhBMP-2, respectively.HO formation frequently occurred in patients receiving intraoperative rhBMP-2 (8/66 hips) than those not receiving the protein (1/75 hips) (P = .02). HHS improved from preoperatively at the final follow-up (P < .01) in the BMP-positive group, with a survival rate of 83.3%. In the BMP-negative group, the HHS improved from preoperatively at the end of the follow-up (P < .01), and the survival rate was 72.0%.rhBMP-2 has osteoinductive property and might serve as an adjuvant therapy in the surgical treatment of ONFH. However, the incidence of HO formation might increase when used in high doses.

Bone Morphogenic Protein Use in Spinal Surgery

Bone morphogenic protein (BMP) provides excellent enhancement of fusion in many spinal surgeries. BMP should be a cautionary tale about the use of industry-sponsored research, perceived conflicts of interest, and holding the field of spinal surgery to the highest academic scrutiny and ethical standards. In the case of BMP, not having a transparent base of literature as it was approved led to delays in allowing this superior technology to help patients.

Adenovirus-Mediated Gene Delivery: Potential Applications for Gene and Cell-Based Therapies in the New Era of Personalized Medicine

With rapid advances in understanding molecular pathogenesis of human diseases in the era of genome sciences and systems biology, it is anticipated that increasing numbers of therapeutic genes or targets will become available for targeted therapies. Despite numerous setbacks, efficacious gene and/or cell-based therapies still hold the great promise to revolutionize the clinical management of human diseases. It is wildly recognized that poor gene delivery is the limiting factor for most in vivo gene therapies. There has been a long-lasting interest in using viral vectors, especially adenoviral vectors, to deliver therapeutic genes for the past two decades. Among all currently available viral vectors, adenovirus is the most efficient gene delivery system in a broad range of cell and tissue types. The applications of adenoviral vectors in gene delivery have greatly increased in number and efficiency since their initial development. In fact, among over 2,000 gene therapy clinical trials approved worldwide since 1989, a significant portion of the trials have utilized adenoviral vectors. This review aims to provide a comprehensive overview on the characteristics of adenoviral vectors, including adenoviral biology, approaches to engineering adenoviral vectors, and their applications in clinical and pre-clinical studies with an emphasis in the areas of cancer treatment, vaccination and regenerative medicine. Current challenges and future directions regarding the use of adenoviral vectors are also discussed. It is expected that the continued improvements in adenoviral vectors should provide great opportunities for cell and gene therapies to live up to its enormous potential in personalized medicine.

Cyst-Like Osteolytic Formations in Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) Augmented Sheep Spinal Fusion

Multiple case reports using recombinant human bone morphogenetic protein-2 (rhBMP-2) have reported complications. However, the local adverse effects of rhBMP-2 application are not well documented. In this report we show that, in addition to promoting lumbar spinal fusion through potent osteogenic effects, rhBMP-2 augmentation promotes local cyst-like osteolytic formations in sheep trabecular bones that have undergone anterior lumbar interbody fusion. Three months after operation, conventional computed tomography showed that the trabecular bones of the rhBMP-2 application groups could fuse, whereas no fusion was observed in the control group. Micro-computed tomography analysis revealed that the core implant area's bone volume fraction and bone mineral density increased proportionately with rhBMP-2 dose. Multiple cyst-like bone voids were observed in peri-implant areas when using rhBMP-2 applications, and these sites showed significant bone mineral density decreases in relation to the unaffected regions. Biomechanically, these areas decreased in strength by 32% in comparison with noncystic areas. Histologically, rhBMP-2-affected void sites had an increased amount of fatty marrow, thinner trabecular bones, and significantly more adiponectin- and cathepsin K-positive cells. Despite promoting successful fusion, rhBMP-2 use in clinical applications may result in local adverse structural alterations and compromised biomechanical changes to the bone.

The Effects of Topical Vancomycin on Mesenchymal Stem Cells: More May Not Be Better

BACKGROUND

The use of topical vancomycin is increasingly popular in spine surgery. Large retrospective reviews suggest that topical vancomycin provides a cost-effective decrease in post-operative infection. Currently, there is little that is known about the maximum dose that can be applied locally. When 1 gram of vancomycin is mixed into the bone graft and another 1 gram applied freely in a spine wound, the local concentration of antibiotic ranges from 260-2900 μg/mL in the immediate post-op period and 50-730 μg/mL by the second post-operative day. We hypothesized that exuberant doses of vancomycin would be toxic to mesenchymal stem cells (MSCs).

METHODS

Bone marrow was obtained from the femoral canal of patients undergoing routine elective total hip arthroplasty. Mesenchymal stem cells were isolated using plastic adhesion. Cells were exposed to a wide range of doses of vancomycin for 24 hours and then assessed for viability. Osteogenic potential was assessed with alizarin red staining.

RESULTS

There was dose-dependent cell death with vancomycin use. MSC death was 9.43% at 400 μg/mL (p=0.047), 13.79% at 1600 μg/mL (p=0.0047), 19.35% at 3200 μg/mL (p<0.0001), 24.82% at 6400 μg/mL (p<0.0001) and 51.83% at 12800 μg/mL of vancomycin (p<0.0001) in comparison to the control group containing no vancomycin.

CONCLUSIONS

Our in vitro study suggests that vancomycin has toxic effects on hMSCs, a cell population particularly important for bone formation. In the absence of any clinical evidence suggesting that "more vancomycin is better," and our data suggesting that more vancomycin is harmful in vitro, surgeons electing to use topical vancomycin in spine surgery should restrict their use to the doses currently reported in the available published studies unless specific reasons exist otherwise. This study does not establish a contraindication to the use of topical vancomycin, nor does it suggest that pseudarthroses are attributable to vancomycin use.

Formulation, Delivery and Stability of Bone Morphogenetic Proteins for Effective Bone Regeneration

Bone morphogenetic proteins (BMPs) are responsible for bone formation during embryogenesis and bone regeneration and remodeling. The osteoinductive action of BMPs, especially BMP-2 and BMP-7, has led to their use in a range of insurmountable treatments where intervention is required for effective bone regeneration. Introduction of BMP products to the market, however, was not without reports of multiple complications and side effects. Aiming for optimization of the therapeutic efficacy and safety, efforts have been focused on improving the delivery of BMPs to lower the administered dose, localize the protein, and prolong its retention time at the site of action. A major challenge with these efforts is that the protein stability should be maintained. With this review we attempt to shed light on how the stability of BMPs can be affected in the formulation and delivery processes. We first provide a short overview of the current standing of the complications experienced with BMP products. We then discuss the different delivery parameters studied in association with BMPs, and their influence on the efficacy and safety of BMP treatments. In particular, the literature addressing the stability of BMPs and their possible interactions with components of the delivery system as well as their sensitivity to conditions of the formulation process is reviewed. In summary, recent developments in the fields of bioengineering and biopharmaceuticals suggest that a good understanding of the relationship between the formulation/delivery conditions and the stability of growth factors such as BMPs is a prerequisite for a safe and effective treatment.

Feasibility of Percutaneous Posterolateral Spinal Fusion With Recombinant Bone Morphogenetic Protein-2 (rhBMP-2): A Comparison With Standard Methods Using an Animal Model Study

BACKGROUND CONTEXT

The clinical application of recombinant bone morphogenetic protein in spinal surgery has been shown to be safe and effective. However, its use in minimally invasive spine surgery has been limited to anterior interbody fusion procedures. To date, no study has evaluated the feasibility of percutaneous posterolateral fusion in the spine utilizing recombinant bone morphogenetic protein-2 (rhBMP-2).

PURPOSE

To evaluate the feasibility of percutaneous posterolateral fusion in the spine utilizing rhBMP-2.

STUDY DESIGN

Animal study.

METHODS

This is an animal research model involving 32 New Zealand white rabbits stratified into 4 study groups: control, autogenous iliac crest bone graft (ICBG), demineralized bone matrix (DBM), and rhBMP-2 groups, with 8 study subjects per group. The rhBMP-2 group was subdivided into the open technique (right side) and the percutaneous technique groups (left side). Fusion was graded at 6 weeks and 3 months after plain radiography, computed tomography, and clinical assessment with the following grading system: grade A, no bone formation; grade B, non-bridging bone formation; grade C, fusion; and grade D, fusion with ectopic bone formation.

RESULTS

No fusion was noted in the placebo and the DBM groups. However, in the DBM group, bone formation occurred in 37.5% of the subjects. The rhBMP-2 group had a higher fusion rate compared with the ICBG group at 6 weeks and 3 months. The fusion rate for the ICBG, the rhBMP-2 (open), and the rhBMP-2 (percutaneous) groups were 37.5%, 87.5%, and 50.0% at 6 weeks and 50.0%, 100.0%, and 62.5% at 3 months, respectively. Ectopic bone formation occurred in 12.5% of the cases in the rhBMP-2 (percutaneous) group and in 25.0% of the cases in the rhBMP-2 (open) group.

CONCLUSIONS

Usage of rhBMP-2 is feasible for percutaneous posterolateral fusion of the lumbar spine in this animal model. However, a more precise delivery system might improve the fusion rate when the percutaneous technique is used. A significant rate of ectopic bone formation occurred when rhBMP-2 was used.