BONE-INDUCTIVE EFFICACY OF RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2 EXPRESSED IN ESCHERICHIA COLI: AN EXPERIMENTAL STUDY IN RAT MANDIBULAR DEFECTS

Because to our knowledge the efficacy of prokaryotically expressed recombinant human bone morphogenetic proteins (rhBMP) to promote orthotopic osteogenesis has not previously been investigated, our aim was to test the efficacy of rhBMP-2 produced in Escherichia coli to promote bone healing in a standardised experimental bone healing model in rat mandibles. Different doses of rhBMP-2 were delivered in an absorbable collagen sponge carrier, and microporous barrier membranes were placed over half the number of defects in each treatment group, thereby making intraosseous cells the only recruitment source for new osteogenic cells. Results were evaluated by computerised image analysis after 12 and 24 days. The relative efficacy of rhBMP-2 preparations of different purity was also compared. E coli-produced rhBMP-2 stimulated bone healing, but its efficacy was estimated to be about one order of magnitude less than that of rhBMP-2 expressed in eukaryotic cells. We conclude that bacterially expressed rhBMP-2 is osteogenic in vivo, although higher doses will be required than of rhBMP-2 expressed in mammalian cell lines.     

异体DBM复合rhBMP-2修复兔桡骨缺损的实验研究

目的探讨异体脱钙骨基质（demineralized bonematrix，DBM）复合重组人骨形态发生蛋白2（reconstruction humn bonemorphology protein-2，rhBMP-2）修复节段性骨缺损的能力。方法48只新西兰大白兔采用桡骨15mm节段性骨缺损模型，随机分为3组，A组植入异体DBM与rhBMP-2复合材料，B组植入异体DBM，C组为空白对照组。术后4周、8周、12周、16周．进行放射学和组织学检查。结果A组：术后4周宿主结缔组织长入植骨材料内的骨小梁间，并有岛状新生软骨、骨组织形成；术后8周，新生软骨及骨形成并融合成片；术后12周，新骨改建成熟，但仍能见到植骨材料；术后16周，管状骨结构形成，髓腔再通。B组：术后4周，植骨材料周围有软骨形成；术后8周，大量软骨形成；术后12周，大片状骨形成；术后16周，有髓腔形成。C组：各时问点仅见有纤维结缔组织，只在两端有新骨形成。X片示A组成骨量大，新骨改建、成熟迅速，术后16周全部达骨性愈合。B组成骨量少，仅2例达骨性愈合。C组未见骨性愈合。结论异体DBM复合rhBMP-2材料通过骨诱导和骨传导两种方式修复骨缺损，是一种较理想、具有高效成骨活性的植骨材料。     

The healing of segmental bone defects, induced by recombinant human bone morphogenetic protein (rhBMP-2). A radiographic, histological, and biomechanical study in rats.

Subcutaneous implants of a recombinant human form of the bone-inducing protein rhBMP-2 (recombinant human bone morphogenetic protein-2) in rats have resulted in the local induction of endochondral bone formation. To test the osteoinductive activity of rhBMP-2 in an osseous location, we created five-millimeter segmental defects in the femora of forty-five adult male Sprague-Dawley rats. Two doses of lyophilized rhBMP-2 (1.4 or 11.0 micrograms) were implanted in each defect, together with guanidine-hydrochloride extracted demineralized rat-bone matrix as a carrier, and the results were compared with those in rats that had implantation of guanidine-hydrochloride extracted demineralized rat-bone matrix only. The formation and healing of bone were determined by radiographic, histological, and mechanical analysis. Both doses of rhBMP-2 induced formation of endochondral bone in the osseous defects in a dose-related manner. Implantation of 11.0 micrograms of rhBMP-2 yielded significant (p less than 0.05) bone formation, resulting in radiographic, histological, and mechanical evidence of union. Despite new-bone formation in the defects that had received 1.4 micrograms of rhBMP-2, no instances of union were observed.     

Effects of the combination of low-level laser irradiation and recombinant human bone morphogenetic protein-2 in bone repair

Low-level laser irradiation (LLLI) and recombinant human bone morphogenetic protein type 2 (rhBMP-2) have been used to stimulate bone formation. LLLI stimulates proliferation of osteoblast precursor cells and cell differentiation and rhBMP-2 recruits osteoprogenitor cells to the bone healing area. This in vivo study evaluated the effects of LLLI and rhBMP-2 on the bone healing process in rats. Critical bone defects were created in the parietal bone in 42 animals, and the animals were divided into six treatment groups: (1) laser, (2) 7?μg of rhBMP-2, (3) laser and 7?μg of rhBMP-2, (4) 7?μg of rhBMP-2/monoolein gel, (5) laser and 7?μg rhBMP-2/monoolein gel, and (6) critical bone defect controls. A gallium-aluminum-arsenide diode laser was used (wavelength 780?nm, output power 60?mW, beam area 0.04?cm(2), irradiation time 80?s, energy density 120?J/cm(2), irradiance 1.5?W/cm(2)). After 15?days, the calvarial tissues were removed for histomorphometric analysis. Group 3 defects showed higher amounts of newly formed bone (37.89%) than the defects of all the other groups (P?相似文献   

Effect of Escherichia coli-produced recombinant human bone morphogenetic protein 2 on the regeneration of canine segmental ulnar defects

Because bone morphogenetic protein 2 gene transfected Escherichia coli (E-BMP-2) produce recombinant human BMP-2 (rhBMP-2) more efficiently than mammalian cells (Chinese hamster ovary [CHO]-BMP-2), they may be a more cost-effective source of rhBMP-2 for clinical use. However, use of E-BMP-2 for regenerating long bones in large animals has not been reported. In the current study, we evaluated the healing efficacy of E-BMP-2 in a canine model. We created 2.5-cm critical-size segmental ulnar defects in test animals, then implanted E-BMP-2 and 700 mg of artificial bone (beta-tricalcium phosphate; β-TCP) into the wounds. We examined the differential effects of 5 E-BMP-2 treatments (0, 35, 140, 560, and 2240 μg) across 5 experimental groups (control, BMP35, BMP140, BMP560, and BMP2240). Radiography and computed tomography were used to observe the regeneration process. The groups in which higher doses of E-BMP-2 were administered (BMP560 and BMP2240) displayed more pronounced bone regeneration; the regenerated tissues connected to the host bone, and the cross-sectional areas of the regenerated bone were larger than those of the originals. The groups in which lower doses of E-BMP-2 were administered (BMP35 and BMP140) experienced relatively less bone regeneration; furthermore, the regenerated tissues failed to connect to the host bone. In these groups, the cross-sectional areas of the regenerated bone were equal to or smaller than those of the originals. No regeneration was observed in the control group. These findings suggest that, like CHO-BMP-2, E-BMP-2 can be used for the regeneration of large defects in long bones and that its clinical use might decrease the cost of bone regeneration treatments.     

Reindeer BMP extract in the healing of critical-size bone defects in the radius of the rabbit

Background?Native BMP extracts from reindeer effectively induce ectopic new bone formation in vivo, but their bone healing properties have not yet been evaluated. We investigated the effect of reindeer BMP extracts on the healing of long bone defects.

Methods?The implants tested contained 5?mg or 10?mg of unsterilized BMP extract from reindeer and 10?mg of gamma-sterilized BMP extract administered with collagen carrier (Lyostypt, B. Braun, Germany). 70 μg of rhBMP-2 with collagen carrier (InductOs; Wyeth Europa) served as positive control, and collagen implants (Lyostypt) and untreated defects served as negative controls. New Zealand White rabbits with 1.5?cm of critical-size radius bone defects were used, with 8 weeks of follow-up.

Results?Radiographic analysis showed bone formation (BF) to be higher in all groups containing BMPs than in the untreated controls. BF was also higher in the rhBMP-2 group, and marginally higher in the group treated with 10?mg of unsterilized reindeer BMP extract (p = 0.06) as compared to the collagen controls. Bone union (BU) was better in the unsterilized BMP extract groups and rhBMP-2 group than in the untreated controls. BU was also better in the implants with 10?mg of unsterilized reindeer BMP extract and rhBMP-2 than in the collagen-treated implants. The mean area of new bone at the site of the defect proved to be higher in all implants containing BMP than in the untreated defects. It was also higher in the groups with 10?mg of unsterilized reindeer BMP extract and rhBMP-2 than in the collagen-treated controls. Mechanical tests showed torsional stiffness of the bones to be higher in the group with 10?mg of unsterilized BMP extract than in the collagen group. The mean cross-sectional bone area measured by pQCT densitometry was higher in the rhBMP-2 group than in the collagen group. The mean bone density at the defect area was higher in the group with 10?mg of unsterilized BMP than in the rhBMP-2 group.

Interpretation?We conclude that both reindeer BMP extract and rhBMP-2 induced improved healing of the rabbit radius bone defects at the doses used. Gamma sterilization of reindeer BMP extract reduced osteoinductivity slightly, but not significantly.     

Effects of rhBMP-2 on cortical strut allograft healing to the femur in revision total hip arthroplasties: an experimental study

We have studied the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) on cortical strut allograft healing and remodelling in revision hip arthroplasty. Thirty adult New Zealand rabbits underwent bilateral onlay allograft strut procedures to the femur using wires. The left femur (experimental side) received the rhBMP-2 device (1.0-mg rhBMP-2/gelatin composites) interposed between the allograft and host bone, while the right side was grafted with an allograft strut as the control. The femurs and implants were retrieved at 4, 6, and 8 weeks postoperatively. The healing of cortical strut grafts to the femur was enhanced dramatically by the addition of the rhBMP-2 device in radiographic examination, contact radiographic examination, non-decalcification sections, fluorescence tag, and computer-aided image analysis. The remodelling of cortical strut allograft was also accelerated. The new bone formation ratio and radiographic scores of the experimental side were also much higher than the control side at all times. Strut healing with the rhBMP-2 device at 4 weeks postoperatively was superior to the healing in control sides at 8 weeks. Our findings showed that the rhBMP-2 device improved and accelerated the course of cortical strut allograft healing and remodelling with host bone.     

Calcium Phosphate Cement with BMP-2-loaded Gelatin Microspheres Enhances Bone Healing in Osteoporosis: A Pilot Study

Background

The capacity for bone healing reportedly is limited in osteoporosis with a less than ideal environment for healing of bone grafts. We therefore developed a composite bone substitute with rhBMP-2 loaded gelatin microsphere (GM) and calcium phosphate cement (CPC) to use in osteoporosis.

Questions/purposes

We asked whether (1) controlled release of rhBMP-2 could be improved in this composite bone substitute and (2) increasing factors released from the bone substitute could accelerate osteoporotic bone healing.

Methods

We soaked rhBMP-2/GM/CPC and rhBMP-2/CPC composites in simulated body fluid for 28 days and then determined the amount of rhBMP-2 released. Both composites were implanted in bone defects of osteoporotic goats and left in place for 45 and 140 days; the specimens then were evaluated mechanically (pushout test) and morphologically (CT scanning, histology).

Results

The in vitro study showed the new composite released more rhBMP-2 compared with rhBMP-2/CPC. CT showed the defects healed more quickly with new grafts. The bone mineralization rate was greater in rhBMP-2/GM/CPC than in rhBMP-2/CPC after 45 days of implantation and the pushout test was stronger after 45 and 140 days of implantation.

Conclusions

The new graft composite released more loaded factors and appeared to repair osteoporotic bone defects.

Clinical Relevance

These preliminary data suggest the new composite can be used as a bone substitute to accelerate healing of fractures and bone defects in osteoporosis.     

rhBMP-2在兔桡骨远端骨缺损模型中成骨效应研究

目的 评价大肠杆菌DH5α高度表达的重组人骨形态发生蛋白-2（rhBMP-2）促进兔桡骨远端骨缺损骨愈合的有效性和剂量-成骨关系.方法 72只成年雄性新西兰白兔按照所设rhBMP-2剂量随机等分为空白对照组、0.5mg组和1.0mg组,右桡骨远端截骨构建骨缺损模型,分别于骨缺损处植入吸附rhBMP-2的纤维胶原蛋白载体复合物.术后2周、4周和8周每组分别处死动物8只,根据钼钯X线摄片、微CT检测、三点弯曲最大承载力测定和组织细胞学检查评估rhBMP-2成骨效应及剂量-成骨关系.结果 3个rhBMP-2剂量组术后2周、4周、8周Lane-Merchant评分所示骨愈合率有统计学差异（P＜0.05）.根据微CT检测,所有标本正常骨密度无个体差异（P＞0.078）,3个rhBMP-2剂量组术后2周、4周、8周缺损区骨密度均有统计学差异（P＜0.05）;3个rhBMP-2剂量组术后2周、4周、8周三点弯曲最大承载力均有统计学差异（P＜0.05）.组织细胞学检查结果也符合以上结果.结论 rhBMP-2（0.5 mg、1.0 mg）能有效促进兔桡骨远端骨缺损愈合,其成骨能力在一定剂量范围内存在剂量依赖性.纤维胶原蛋白载体有着良好的生物相容性,但降解速度相对较快,对rhBMP-2缓释、提高局部有效浓度维持时间的作用有限.     

The use of recombinant human bone morphogenetic protein 2 (rhBMP-2) to promote spinal fusion in a nonhuman primate anterior interbody fusion model

STUDY DESIGN: A study on the efficacy of recombinant human bone morphogenetic protein 2 (rhBMP-2) in a nonhuman primate anterior interbody fusion model. OBJECTIVES: To investigate the efficacy of rhBMP-2 with an absorbable collagen sponge carrier to promote spinal fusion in a nonhuman primate anterior interbody fusion model. SUMMARY OF BACKGROUND DATA: RhBMP-2 is an osteoinductive growth factor capable of inducing new bone formation in vivo. Although dosage studies using rhBMP-2 have been performed on species of lower phylogenetic level, they cannot be extrapolated to the primate. Dosage studies on nonhuman primates are essential before proceeding with human primate application. METHODS: Six female adult Macaca mulatta (rhesus macaque) monkeys underwent an anterior L7-S1 interbody lumbar fusion. All six sites were assigned randomly to one of two fusion methods: 1) autogenous bone graft within a single freeze-dried smooth cortical dowel allograft cylinder (control) or 2) rhBMP-2-soaked absorbable collagen sponges within a single freeze-dried smooth cortical dowel allograft cylinder also soaked in rhBMP-2. The animals underwent a baseline computed tomography scan followed by 3- and 6-month postoperation scans. Anteroposterior and lateral radiographs of the lumbosacral spine were performed monthly. After the monkeys were killed, the lumbar spine fusion sites were evaluated. Histologic evaluation of all fusion sites was performed. RESULTS: The three monkeys receiving rhBMP-2-soaked collagen sponges with a freeze-dried allograft demonstrated radiographic signs of fusion as early as 8 weeks. The control animals were slower to reveal new bone formation. The computed tomography scans revealed extensive fusion of the L7-S1 lumbar vertebrae in the group with rhBMP-2. A pseudarthrosis was present in two of the control animals. CONCLUSIONS: This study was able to document the efficacy of rhBMP-2 with an absorbable collagen sponge carrier and a cortical dowel allograft to promote anterior interbody fusion in a nonhuman primate model at a dose of 0.4 mg per implant site (1.5 mg/mL concentration). The late of new bone formation and fusion with the use of rhBMP-2 and cortical dowel allograft appears to be far superior to that of autogenous cancellous iliac crest graft with cortical dowel allograft.     

Recombinant bone morphogenetic protein-2 enhances bone healing,guided by osteopromotive e-PTFE membranes: An experimental study in rats

It has been shown earlier that it is possible to improve bone healing, to regenerate previously existing bone, and to create new bone by means of an osteopromotive membrane technique. The present study addresses the question of whether it is possible to combine this technique with a locally applied factor, stimulatory to osteogenesis. Circular transosseous critical size defects in mandibles of rats were either implanted with recombinant human bone morphogenetic protein type 2 (rhBMP-2) or were left empty; half the number of implanted and half the number of empty defects were covered with an expanded polytetrafluoroethylene (e-PTFE) membrane (GORE-TEX^®). Results were evaluated after 12 and 24 days of healing by a histomorphological scoring system. Implantation of rhBMP-2 alone resulted in bony bridging of the defect after only 12 days, but also in voluminous amounts of new bone outside the original defect area. When rhBMP-2 was combined with membrane, newly formed woven bone bridged the defect and the bone contour was maintained by the membrane. The combined treatment with membrane and rhBMP-2 demonstrated a significantly better bone healing than with e-PTFE membrane alone at both 12 days and 24 days of healing. It was concluded that rhBMP-2 has a strong osteoinductive potential and, in contrast to what was found earlier with other types of BMP preparations, this potential was retained when combining the rhBMP-2 with the osteopromotive membrane technique, yielding better bone healing than with the membrane alone, and at the same time maintaining the bone contour. This combination may have important therapeutic applications for osseous healing and in reconstructive surgery. The study also shows the importance of an appropriate carrier material when applying stimulatory substances to enhance bone formation in combination with a membrane.     

Recombinant human bone morphogenetic protein-2 enhances osteotomy healing in glucocorticoid-treated rabbits.

The objectives of this study were to evaluate the effect of chronic prednisolone treatment on osteotomy healing in rabbits and to determine whether recombinant human bone morphogenetic protein-2 (rhBMP-2) would enhance healing in the presence of chronic glucocorticoid therapy. Forty-nine skeletally mature, male rabbits were injected with either prednisolone (n = 26; 0.35 mg/kg per day, three times a week) or saline (n = 23). After a 6-week pretreatment period, bilateral ulnar osteotomies were created surgically. One osteotomy was treated with rhBMP-2 (0.2 mg/ml of rhBMP-2, 40 microg of rhBMP-2 total) delivered on an absorbable collage sponge (ACS), whereas the contralateral osteotomy remained untreated. Prednisolone or saline treatment was continued until the rabbits were killed either 6 weeks or 8 weeks after creation of the osteotomy. Osteotomy healing was evaluated by radiography, peripheral quantitative computed tomography (pQCT), torsional biomechanics, and undecalcified histology. Because we observed similar responses to both prednisolone and rhBMP-2/ACS treatment in the 6-week and 8-week cohorts, the results from these time points were combined. Serum osteocalcin and vertebral trabecular bone density were lower in the prednisolone-treated rabbits. Prednisolone treatment dramatically inhibited osteotomy healing. In the untreated ulnas, callus area and torsional strength were 25% and 55% less, respectively, in the prednisolone-treated rabbits than in the saline group (p < 0.001 for both). rhBMP-2/ACS enhanced healing in both the prednisolone- and the saline-treated groups, although the effect was larger in the prednisolone-treated rabbits. In the prednisolone-treated rabbits, callus area and torsional strength were 40% and 165% greater (p < 0.001 for both), respectively, in osteotomies treated with rhBMP-2/ACS compared with the contralateral, untreated osteotomies. Histological evaluation confirmed that osteotomy healing was inhibited by prednisolone and accelerated by rhBMP-2/ACS. In summary, a single application of rhBMP-2/ACS counteracted the inhibition of osteotomy healing caused by prednisolone exposure. These results suggest that rhBMP-2/ACS may be a useful treatment for enhancing fracture healing in patients who are undergoing chronic glucocorticoid therapy.     

Application of rhBMP-7 and platelet-rich plasma in the treatment of long bone non-unions: A prospective randomised clinical study on 120 patients

The purpose of this prospective randomised clinical study was to compare the efficacy of recombinant bone morphogenetic protein 7 (rhBMP-7) and platelet-rich plasma (PRP) as bone-stimulating agents in the treatment of persistent fracture non-unions.One hundred and twenty patients were randomised into two treatment groups (group rhBMP-7 vs. group PRP). Sixty patients with sixty fracture non-unions were assigned to each group (median age: 44 years, range 19–65, for the rhBMP-7 group and 41 years, range 21–62, for the PRP group, respectively). In the rhBMP-7 group, there were 15 tibial non-unions, 10 femoral, 15 humeral, 12 ulnar, and 8 radial non-unions. In the PRP group, there were 19 tibial non-unions, 8 femoral, 16 humeral, 8 ulnar, and 9 radial non-unions. The median number of operations performed prior to our intervention was 2 (range 1–5) and 2 (range 1–5) with autologous bone graft being used in 23 and 21 cases for the rhBMP-7 and PRP groups, respectively.Both clinical and radiological union occurred in 52 (86.7%) cases of the rhBMP-7 group compared to 41 (68.3%) cases of the PRP group, with a lower median clinical and radiographic healing time observed in the rhBMP-7 group (3.5 months vs. 4 months and 8 months vs. 9 months, respectively). This study supports the view that in the treatment of persistent long bone non-unions, the application of rhBMP-7 as a bone-stimulating agent is superior compared to that of PRP with regard to their clinical and radiological efficacy.     

Association of ex-vivo expanded human mesenchymal stem cells and rhBMP-7 is highly effective in treating critical femoral defect in rats

Mesenchymal stem cells (MSC), easily culture-expanded from bone marrow, can significantly enhance bone defect healing. Several proteins, such as the bone morphogenetic proteins (BMPs) and in particular BMP-7, are involved in bone formation in vitro and in vivo. In this preclinical study, we evaluated if the association of human MSC (hMSC) with BMP-7 had synergic action on bone healing. Rat femoral defects (n=12) were treated with: autoclaved bone and mononucleated cells (MNC) as control group G1; bone and hMSC, group G2; bone with BMP-7, group G3; bone and hMSC plus BMP-7, group G4. Defect regeneration was evaluated with plain radiographs after 2, 4, 8 and 12 weeks and with histological analysis. We observed organized trabeculae bridging between the osteotomic ends of the host bone in rats treated with the association of hMSC and rhBMP-7. These trabeculae, formed by a core of devitalized tissue surrounded by osteoblasts, osteocytes and osteoclasts, were continuous with a cortical-like structure of bony tissue. Such new bone formation of the group treated with the association of hMSC and rhBMP-7 (G4) was clearly superior compared to rats treated with rhBMP-7 (G2) or hMSC (G3) alone, as shown by radiographic analysis and histological study. The present study suggests that the association of hMSC and BMP-7 is more effective than hMSC or BMP-7 alone in the healing of femoral defects in rats. Further studies with larger samples are required to confirm these results and to evaluate the best dosage.     

rhBMP-2, rhVEGF(165), rhPTN and thrombin-related peptide, TP508 induce chemotaxis of human osteoblasts and microvascular endothelial cells.

Osteogenesis and angiogenesis are inter-linked and tightly regulated processes involved in growth, repair, and bone remodeling. Bone morphogenic protein 2 (BMP-2), vascular endothelial growth factor (VEGF), pleiotrophin (PTN) and thrombin-related peptide, TP508 have all been found to have the ability to promote bone fracture healing by enhancing both the osteogenesis and angiogenesis processes. One of the underlying mechanisms proposed is that mediators for osteogenesis may also be involved in mediating angiogenesis and vice versa. The aim of this study was to examine the chemotactic effects of rhBMP-2, rhVEGF(165), rhPTN and TP508 on human osteoblasts and endothelial cells. Using a direct-viewing chemotaxis assay system, we report for the first time, the direct quantitative observation of chemotaxis of both human osteoblastc cells and microvascular endothelial cells towards sources of rhBMP-2, rhVEGF(165), rhPTN and TP508. This study confirmed that rhBMP-2, rhVEGF(165), rhPTN and TP508 have chemotactic effects on both human osteoblastic and endothelial cells, indicating that these factors are directly involved in promoting angiogenesis and osteogenesis by recruiting osteoblasts and endothelial cells via chemotaxis.     

The safety and utility of recombinant human bone morphogenetic protein-2 for cranial procedures in a nonhuman primate model

OBJECT: The goal of this study was to evaluate the safety and efficacy of recombinant human bone morphogenetic protein 2 (rhBMP-2) in cranial applications. METHODS: Critical-sized calvarial defects were created bilaterally in four rhesus monkeys, and bilateral rectangular bone flaps were created in six others. Control and rhBMP-2-treated sides were randomly chosen for each animal, and an absorbable collagen sponge was used to deliver the growth factor. Over a 6-month period postoperatively, the animals were serially evaluated for bone healing and adverse BMP-related consequences by using the following methods: computerized tomography (CT) scanning, magnetic resonance (MR) imaging, electroencephalography, histological investigations, and cerebrospinal fluid (CSF) analysis. The critical-sized defects for the rhBMP-2-treated and control sides attained 71 +/- 12% and 28 +/- 11% closure, respectively (four animals; p = 0.04). The CT scans demonstrated that the bone flaps treated with rhBMP-2 had complete osteointegration in five of six animals, whereas scans of the untreated bone flaps demonstrated uniformly poor osteointegration with the intact skull. Histological analysis confirmed well-formed bridges of bone on the rhBMP-2-treated sides. No epileptogenic activity was detected in any of the animals, and MR imaging revealed no evidence of adverse effects on the brain parenchyma. Meningitic irritation was not found on postoperative CSF sample analysis. CONCLUSIONS: Treatment of bone flaps and critical-sized cranial defects with rhBMP-2 leads to improved bone formation and osteointegration in nonhuman primates. Initial evaluation of rhBMP-2 appears to indicate a good safety profile for use in cranial procedures in primates.     

Vancomycin-bearing Synthetic Bone Graft Delivers rhBMP-2 and Promotes Healing of Critical Rat Femoral Segmental Defects

Background

Bone grafts simultaneously delivering therapeutic proteins and antibiotics may be valuable in orthopaedic trauma care. Previously, we developed a poly(2-hydroxyethyl methacrylate)-nanocrystalline hydroxyapatite (pHEMA-nHA) synthetic bone graft that, when preabsorbed with 400-ng rhBMP-2/7, facilitated the functional repair of critical-size rat femoral defects. Recently, we showed that pHEMA-nHA effectively retains/releases vancomycin and rhBMP-2 in vitro. The success of such a strategy requires that the incorporation of vancomycin does not compromise the structural integrity of the graft nor its ability to promote bone healing.

Questions/purposes

(1) To evaluate the ability of pHEMA-nHA-vancomycin composites in combination with 3-µg rhBMP-2 to repair 5 mm rat femoral segmental defects, and (2) To determine if the encapsulated vancomycin impairs the graft/rhBMP-2-assisted bone repair.

Methods

pHEMA-nHA-vancomycin, pHEMA-nHA, or collagen sponge control with/without 3-µg rhBMP-2 were press-fit in 5 mm femoral defects in SASCO-SD male rats (289–300 g). Histology, microcomputed tomography, and torsion testing were performed on 8- and 12-week explants to evaluate the extent and quality of repair. The effect of vancomycin on the temporal absorption of endogenous BMP-2 and stromal cell-derived factor-1 was evaluated by immunohistochemistry. These factors are important for bone healing initiation and stem cell recruitment, respectively.

Results

Partial bridging of the defect with bony callus by 12 weeks was observed with pHEMA-nHA-vancomycin without rhBMP-2 while full bridging with substantially mineralized callus and partial restoration of torsional strength was achieved with 3-µg rhBMP-2. The presence of vancomycin changed the absorption patterns of endogenous proteins on the grafts, but did not appear to substantially compromise graft healing.

Conclusions

The composite pHEMA-nHA-vancomycin preabsorbed with 3-µg rhBMP-2 promoted repair of 5 mm rat femoral segmental defects. With the sample sizes applied, vancomycin encapsulation did not appear to have a negative effect on bone healing.

Clinical Relevance

pHEMA-nHA-vancomycin preabsorbed with rhBMP-2 may be useful in the repair of critical-size long bone defects prone to infections.