The use of bone morphogenetic protein 7 in fracture non-unions

Bone Morphogenic Protein for Upper Extremity Fractures: A Systematic Review

BACKGROUND

This review discusses success, time to healing, and complications of bone morphogenic proteins (BMPs) 7 and 2 in treating upper extremity nonunions.

METHODS

Systematic review identified 26 of 479 studies that met inclusion criteria. Publications described application of BMPs to acute and chronic upper extremity delayed unions/nonunions. Unions, complications, patient demographics, and fracture/healing patterns were pooled and analyzed.

RESULTS

Nonunions treated with BMP-7 (n=302) involved the humerus (64%), forearm (22%), clavicle (11%), and hand/wrist (3%), with prior surgical correction attempted in 84%. Nonunions treated with BMP-2 (n=96) involved the humerus (58%), hand/wrist (27%), forearm (14%), and clavicle (1%), with prior surgical correction attempted in all. Most nonunions (80%) were present for over 12 months before BMP application. Union rates of BMP-7 varied according to site: hand/wrist (95%), humerus (74%), forearm (29%), and clavicle (6.2%) nonunions achieved union as defined by study authors in 232 days (confidence interval=96-369, Q<0.001) on average. While not significant across studies, BMP-2 union rates were 71% of hand/wrist and 75% of humerus nonunions. Comparison of the BMPs demonstrates different proportions of success in humerus and hand/wrist fractures (P<.001) but not forearm fractures (P<.77) and longer time to radiographic union with BMP-7 (P<.011).

CONCLUSIONS

Most hand/wrist and humerus nonunions treated with BMP-7 and BMP-2 achieved union, with significant similarity among BMP-7 studies not observed in BMP-2 studies. Nonunions treated with BMP-7 have longer healing times yet similar complication rates compared with BMP-2. Overall, BMPs are an effective adjunct to fracture healing with acceptable complication profile.

Improved Soluble expression in Escherichia coli and easily purified recombinant human bone morphogenetic 7-2 fusion protein

BACKGROUND

Bone morphogenetic protein (BMP) is a cysteine-rich growth factor, and plays a key role in early bone tissue development and bone defect repair. However, the low yield, high cost and complicated process in the production process of BMP significantly limit its clinical application.

OBJECTIVE

In this study, we developed an efficient method for soluble expression and preparation of recombinant human bone morphogenetic 7-2 fusion protein (rhBMP7-2) and determined its molecular weight and biological activity.

METHODS

The fusion gene for rhBMP-2 and rhBMP-7 was inserted into the pET-ELP expression vector. Correct DNA sequence was confirmed, the rhBMP7-2-ELP was transformed into Escherichia coli strain BL21 (DE3), and the rhBMP7-2 was produced in the recombinant E. coli. Recombinant BMP7-2 purify was identified using Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE). The cell proliferation and biological activity of rhBMP7-2 was measured by Cell Counting Kit-8 and Alkaline Phosphatase assay using C2C12 cells, respectively.

RESULTS

The result of digestion of NdeI, BamHI and XhoI enzymes showed that the rhBMP7-2-ELP was correctly constructed. The recombinat BMP7-2 was successfully expressed in soluble form; the purifed rhBMP7-2 showed biological activity and significantly promoted cell proliferation and differentiation in a dose-dependent manner.

CONCLUSION

The rhBMP7-2 fusion protein with osteogenic activity was prepared through a low-cost and time-efficient method. Our preparation method presents potential to be applied to the large-scale production of rhBMP7-2 and is expected to play a significant role in clinical treatment.

Assessment of the Defatting Efficacy of Mechanical and Chemical Treatment for Allograft Cancellous Bone and Its Effects on Biomechanics Properties of Bone

Objective

To assess the defatting efficacy of high pressure washing and gradient alcohol and biomechanical properties of defatted bone.

Methods

Fresh cancellous bone was obtained from the femoral condyle and divided into six groups according to different defatting treatments, which were: high pressure washing for 10 s (10S group), 20 s (20S group), and 30 s (30S group), gradient alcohol immersion (Alcohol group), acetone immersion (Acetone group), and non‐defatted (Fresh group). The appearance of six groups was observed, and the appearance of defatted bone and fresh bone was compared. The residual lipid content and infrared spectrum were used to compare the efficacy of defatting, the DNA content was used to compare the cell content after defatting, and the maximum stress and elastic modulus were used to compare the effects of defatting treatment on biomechanical properties.

Results

The fresh bone was yellow and the pores contained a lot of fat. The defatted bone was white and the porous network was clear. There was no difference in residual lipid content among the three groups with high pressure washing (1.45% ± 0.16%, 1.40% ± 0.13%, and 1.46% ± 0.11%, respectively) (P = 0.828). There was no difference in residual lipid content among the 10S, alcohol, and acetone groups (1.45% ± 0.16%, 1.28% ± 0.07%, and 1.13% ± 0.22%, respectively) (P = 0.125). Infrared spectra showed that the fat content of the five defatting groups was significantly lower than that of the fresh group. There was no difference in residual lipid content among the three groups with high pressure washing (4.53 ± 0.23 ug/mL, 4.61 ± 0.18 ug/mL, and 4.66 ± 0.25 ug/mL, respectively) (P = 0.645). There was no difference in residual lipid content among the 10S, alcohol, and acetone groups (4.53 ± 0.23 ug/mL, 4.29 ± 0.24 ug/mL, and 4.27 ± 0.29 ug/mL, respectively) (P = 0.247). The maximum stress of the bone decreased significantly with the increase of the washing time (9.95 ± 0.31 Mpa, 9.07 ± 0.45 Mpa, and 8.17 ± 0.35 Mpa, respectively) (P = 0.003). The elastic modulus of the bone decreased significantly with the increase of the washing time (116.40 ± 3.54 Mpa, 106.10 ± 5.29 Mpa, and 95.63 ± 4.08 Mpa, respectively) (P = 0.003). There was no statistical difference in the maximum stress between the fresh group, the 10S group, the alcohol group, and the acetone group (10.09 ± 0.67 Mpa, 9.95 ± 0.31 Mpa, 10.11 ± 0.07 Mpa, and 10.09 ± 0.39 Mpa, respectively) (P = 0.963). There was no statistical difference in the maximum stress between the fresh group, the 10S group, the alcohol group and the acetone group (119.93 ± 4.94 Mpa, 116.40 ± 3.54 Mpa, 118.27 ± 0.85 Mpa, 118.10 ± 4.52 Mpa, respectively) (P = 0.737).

Conclusion

The defatting efficiency was satisfactory at a time of 10 s under high pressure washing. In terms of defatting efficiency and its effect on biomechanical properties of bone, high pressure washing and gradient alcohol were similar to conventional acetone solvent extraction defatting.

Clinical application of bone morphogenetic proteins for bone healing: a systematic review

PURPOSE

This paper documents the existing evidence on bone morphogenetic proteins (BMPs) use for the treatment of bone fractures, non-union, and osteonecrosis, through a review of the clinical literature, underlying potential and limitations in terms of cost effectiveness and risk of complications.

METHODS

A systematic review was performed on the PubMed database using the following string: (bone morphogenetic proteins OR BMPs) and (bone repair OR bone regeneration) including papers from 2000 to 2016. The search focused on clinical trials dealing with BMPs application to favor bone regeneration in bone fractures, non-union, and osteonecrosis, in English language, with level of evidence I, II, III, and IV. Relevant data (type of study, number of patients, BMPs delivery material, dose, site, follow-up, outcome, and adverse events) were extracted and analyzed.

RESULTS

Forty-four articles met the inclusion criteria: 10 randomized controlled trials (RCTs), 7 comparative studies, 18 case series, and 9 case reports. rhBMP-2 was documented mainly for the treatment of fractures, and rhBMP-7 mainly for non-unions and osteonecrosis. Mixed results were found among RCTs and comparative papers: 11 reported positive results for BMPs augmentation, 3 obtained no significant effects, and 2 showed negative results. The only study comparing the two BMPs showed a better outcome with rhBMP-2 for non-union treatment.

CONCLUSION

Clinical evidence on BMPs use for the treatment of fractures, non-union, and osteonecrosis is still controversial, with the few available reports being mainly of low quality. While positive findings have been described in many studies, mixed results are still present in the literature in terms of efficacy and adverse events. The difficulties in drawing clear conclusions are also due to the studies heterogeneity, mainly in terms of different BMPs applied, with different concomitant treatments for each bone pathology. Therefore, further research with well-designed studies is needed in order to understand the real potential of this biological approach to favour bone healing.

Expression and purification of recombinant human bone morphogenetic protein-7 in Escherichia coli

Bone morphogenetic protein-7 (BMP-7) is a multifunctional cytokine of the transforming growth factor β superfamily, which induces bone formation and plays an important role during bone tissue repair and embryonic development. In this study, human BMP-7 (hBMP-7) cDNA was cloned and expressed in Escherichia coli, and its yield was approximately 30% of the total bacterial protein. After the bacteria were lysed by ultrasonication and repeated washing, inclusion bodies were extracted and dissolved using a high-strength denaturant. The monomer of rhBMP-7 was purified by ion-exchange chromatography, and the purity coefficient was approximately 96%. The protein was renatured with refolding buffers at different pH values. The renatured rhBMP-7 dimer protein in this study increased the alkaline phosphatase activity of NIH3T3 cells. This study may be helpful for the in vitro production and biomedical application of rhBMP-7 protein expressed in an E. coli expression system.

Bone morphogenetic protein-2, -6, and -7 differently regulate osteogenic differentiation of human periodontal ligament stem cells

The utility of adult stem cells for bone regeneration may be an attractive alternative in the treatment of extensive injury, congenital malformations, or diseases causing large bone defects. To create an environment that is supportive of bone formation, signals from molecules such as the bone morphogenetic proteins (BMPs) are required to engineer fully viable and functional bone. We therefore determined whether BMP-2, -6, and -7 differentially regulate the (1) proliferation, (2) mineralization, and (3) mRNA expression of bone/mineralized tissue associated genes of human periodontal ligament stem cells (hPDLSCs), which were obtained from periodontal ligament tissue of human impacted third molars. hPDLSCs from six participants were isolated and characterized using histochemical and immunohistochemical methods. A real-time cell analyzer was used to evaluate the effects of BMP-2, -6, and -7 on the proliferation of hPDLSCs. hPDLSCs were treated with Dulbecco's modified Eagle's medium containing different concentrations of BMP-2, -6, and -7 (10, 25, 50, 100 ng/mL) and monitored for 264 hours. After dose-response experiments, 50 and 100 ng/mL concentrations of BMPs were used to measure bone/mineralized tissue-associated gene expression. Type I collagen, bone sialoprotein, osteocalcin, osteopontin, and osteoblastic transcription factor Runx2 mRNA expression of hPDLSCs treated with BMP-2, -6, and -7, were evaluated using quantitative RT-PCR. Biomineralization of hPDLSCs was assessed using von Kossa staining. This study demonstrated that BMPs at various concentrations differently regulate the proliferation, mineralization, and mRNA expression of bone/mineralized tissue associated genes in hPDLSCs. BMPs regulate hPDLSC proliferation in a time and dose-dependent manner when compared to an untreated control group. BMPs induced bone/mineralized tissue-associated gene mRNA expression and biomineralization of hPDLSCs. The most pronounced induction occurred in the BMP-6 group in the biomineralization of the hPDLSCs. Our data suggest that BMP-2, -6, and -7 are potent regulators of hPDLSC gene expression and biomineralization. Employing BMPs with hPDLSCs isolated from periodontal ligament tissues provides a promising strategy for bone tissue engineering.

Current application of β-tricalcium phosphate composites in orthopaedics

Presently, bioceramic materials have been extensively used in spinal surgery as bone grafts; however, there are some limitations for bioceramic materials. Calcium sulfate is rapidly absorbed in vivo, the degradation of which often occurs prior to the formation of new bones. Hydroxyapatite (HA) is hardly absorbed, which blocks the formation of new bones and remodeling, and results in poor local stability or permanent stress concentration. Only β-tricalcium phosphate (β-TCP) is relatively balanced between scaffold absorption and bone formation. And it is a good biodegradable ceramic material that could supply a large quantity of calcium ion and sulfate ion as well as scaffold structure for bone regeneration. However, the problem of single β-TCP is lack of osteoinductivity and osteogenicity, which restricts its application. Therefore β-TCP composite materials have been used in the field of orthopaedics in recent decades, which fully use excellent properties of other bone repairing materials, such as biodegradability, osteoinductivity, osteogenicity and osteoconductivity. These materials make up for the deficiencies of single β-TCP and endow β-TCP with more biological and physical properties.

The influence of environmental factors on bone tissue engineering

Bone repair and regeneration are dynamic processes that involve a complex interplay between the substrate, local and systemic cells, and the milieu. Although each constituent plays an integral role in faithfully recreating the skeleton, investigators have long focused their efforts on scaffold materials and design, cytokine and hormone administration, and cell-based therapies. Only recently have the intangible aspects of the milieu received their due attention. In this review, we highlight the important influence of environmental factors on bone tissue engineering.

Studies of bone morphogenetic protein-based surgical repair

Over the past several decades, recombinant human bone morphogenetic proteins (rhBMPs) have been the most extensively studied and widely used osteoinductive agents for clinical bone repair. Since rhBMP-2 and rhBMP-7 were cleared by the U.S. Food and Drug Administration for certain clinical uses, millions of patients worldwide have been treated with rhBMPs for various musculoskeletal disorders. Current clinical applications include treatment of long bone fracture non-unions, spinal surgeries, and oral maxillofacial surgeries. Considering the growing number of recent publications related to clincal research of rhBMPs, there exists enormous promise for these proteins to be used in bone regenerative medicine. The authors take this opportunity to review the rhBMP literature paying specific attention to the current applications of rhBMPs in bone repair and spine surgery. The prospective future of rhBMPs delivered in combination with tissue engineered scaffolds is also reviewed.

Osteogenic response to BMP-2 of hMSCs grown on apatite-coated scaffolds

Osteoconductive materials play a critical role in promoting integration with surrounding bone tissue and resultant bone repair in vivo. However, the impact of 3D osteoconductive substrates coupled with soluble signals on progenitor cell differentiation is not clear. In this study, we investigated the influence of bone morphogenetic protein-2 (BMP-2) concentration on the osteogenic differentiation of human mesenchymal stem cells (hMSCs) when seeded in carbonated apatite-coated polymer scaffolds. Mineralized scaffolds were more hydrophilic and adsorbed more BMP-2 compared to non-mineralized scaffolds. Changes in alkaline phosphatase (ALP) activity within stimulated hMSCs were dependent on the dose of BMP-2 and the scaffold composition. We detected more cell-secreted calcium on mineralized scaffolds at all time points, and higher BMP-2 concentrations resulted in increased ALP and calcium levels. RUNX2 and IBSP gene expression within hMSCs was affected by both substrate and soluble signals, SP7 by soluble factors, and SPARC by substrate-mediated cues. The present data indicate that a combination of apatite and BMP-2 do not simply enhance the osteogenic response of hMSCs, but act through multiple pathways that may be both substrate- and growth factor-mediated. Thus, multiple signaling strategies will likely be necessary to achieve optimal bone regeneration.