Jeong-Ho Yun

The induction of bone formation in rat calvarial defects and subcutaneous tissues by recombinant human BMP-2, produced in Escherichia coli

We investigated the ability of recombinant human bone morphogenetic protein-2, produced from Escherichia coli (ErhBMP-2), to form orthotopic and ectopic bone in rat models. BMP-2 was expressed in E. coli and extracted from the inclusion bodies. Critical-sized calvarial defects and subcutaneous pouches were created in rats, and an absorbable collagen sponge (ACS) was loaded with different doses of ErhBMP-2 for implantation. ACS alone and sham surgery controls were also included. Implant sites were evaluated by histological and/or histometric analyses following a 2- or 8-week healing interval. In the calvarial defect model, enhanced bone formation was observed with all doses of ErhBMP-2, while only limited amounts of new bone were found in controls. In the ectopic subcutaneous implant model, bone formation was clearly observed in all animals treated with ErhBMP-2 at 2 weeks. However, at 8 weeks, less new bone formation was detected than at 2 weeks. Nevertheless, the remaining new bone showed an advanced degree of bone remodeling and more maturity than that observed at 2 weeks. These results showed that ErhBMP-2 was osteoinductive under controlled in vivo conditions. Thus, ErhBMP-2 has definite potential as an alternative to rhBMP-2 produced in a eukaryotic system for clinical use.

Osteoinductive activity of biphasic calcium phosphate with different rhBMP-2 doses in rats.

OBJECTIVE The aim of the current study was to determine whether a hydroxyapatite (HA)/beta-tricalcium phosphate (β-TCP) ratio of 20/80 impregnated with recombinant human bone morphogenetic protein (rhBMP-2) enhances new bone formation and to evaluate the dose-dependent response of rhBMP-2. STUDY DESIGN Critical-sized calvarial defects were made in rats, and biphasic calcium phosphate (BCP) with different rhBMP-2 doses was loaded into rat calvarial defects. The animals were allowed to heal for either 2 or 8 weeks. RESULTS The percentages of new bone after 2 and 8 weeks of healing were significantly greater in the rhBMP-2-treated groups (at all doses) than in the control groups. The percentage of remaining BCP was significantly lower at 8 weeks than at 2 weeks in all groups that included BCP. CONCLUSIONS rhBMP-2 administered using a BCP carrier significantly induces new bone formation. A dose-dependent response was not shown in the present study.

Sinus augmentation using absorbable collagen sponge loaded with Escherichia coli‐expressed recombinant human bone morphogenetic protein 2 in a standardized rabbit sinus model: a radiographic and histologic analysis

OBJECTIVES The purpose of this pilot study was to determine the osteoinductive effect of absorbable collagen sponge (ACS) loaded with Escherichia coli-expressed recombinant human bone morphogenetic protein 2 (ErhBMP-2) and evaluate structural stability of ACS in a standardized rabbit sinus model. MATERIAL AND METHODS The maxillary sinuses were prepared bilaterally in six male white rabbits. The windows were prepared using a 6 mm trephine bur, and circular bony windows were carefully removed. Following reflection of the sinus membrane, a saline-soaked ACS alone and an ErhBMP-2-loaded ACS were inserted into the left and right maxillary sinuses, respectively. After a healing period of 8 weeks, sections of the augmented sinus and surrounding bone were made and analyzed by microcomputed tomography and histologically for signs of window closure and bone augmentation. RESULTS Radiographic analysis revealed new bone formation in both groups of augmented sinus (i.e., with and without ErhBMP-2). The maximum augmented height did not differ significantly between the groups; however, window closure was significantly more advanced in the ErhBMP-2 group than in the control group (P=0.02). The defect was significantly deeper in the control group than in the ErhBMP-2-treated group (P=0.02). CONCLUSIONS In conclusion, ErhBMP-2-loaded ACS showed enhanced osteoinductive potential, particularly with regard to bone closure of a sinus window and facilitated maturation of the newly formed bone within the rabbit sinus cavity. However, the structural durability of ACS was not sufficient to maintain the augmented volume in the sinus.

Volumetric bone regenerative efficacy of biphasic calcium phosphate‐collagen composite block loaded with rhBMP‐2 in vertical bone augmentation model of a rabbit calvarium

Block-type biphasic calcium phosphate (BCP) carriers are more effective at delivering recombinant human bone morphogenetic protein-2 (rhBMP-2) in various clinical situations than are particle-type carriers, due to their potential for highly successful three-dimensional bone regeneration. The aim of this study was to confirm the bone-regenerative capabilities of three-dimensional BCP blocks with a low hydroxyapatite/β-tricalcium phosphate ratio (20/80) combined with collagen (10% wt) as an rhBMP-2 delivery system in a craniofacial vertical bone augmentation model. BCP blocks and BCP-collagen blocks (with average macropore sizes of 296 and 390 μm, respectively) with or without rhBMP-2 were fixed with osteosynthesis screws to the calvarial surface of rabbits. After 8 weeks, histologic and histomorphometric analyses were performed to evaluate the resulting new bone area, augmented area, bone density, and degree of integration. The area of new bone was significantly greater in specimens containing rhBMP-2 than in the control group (p < 0.05). Moreover, the area fractions of newly formed bone within the augmented area and a degree of integration between the regenerative bone and the calvarium were both significantly greater in the BCP-collagen/rhBMP-2 group than in the BCP/rhBMP-2 group (p < 0.05), whereas the two carrier systems exhibited similar rhBMP-2 release profiles, with sustained and linear release. The BCP and BCP/rhBMP-2 blocks exhibited excellent structural integrity, with large fragments of residual ceramic. In conclusion, the BCP-collagen composite block exhibited enhanced osteoinductive potential and could be a good candidate as a carrier of rhBMP-2 due to its characteristics of favorable volumetric stability, ease of handling, and excellent remodeling properties.

Bone formation of block and particulated biphasic calcium phosphate lyophilized with Escherichia coli-derived recombinant human bone morphogenetic protein 2 in rat calvarial defects.

The objective of this study was to evaluate bone formation in rat calvarial defects after surgical implantation of block or particulated biphasic calcium phosphate (BCP) lyophilized with Escherichia coli-derived recombinant human bone morphogenetic protein 2 (ErhBMP-2). Critical-size calvarial osteotomy defects were created in 5 groups of Sprague-Dawley rats. Each group received one of the following: 1) sham surgery control; 2) biphasic calcium phosphate particles (CPP); 3) biphasic calcium phosphate block (CPB); 4) ErhBMP-2-coated CPP; or 5) ErhBMP-2-coated CPB. ErhBMP was coated on BCP by a stepwise lyophilizing protocol. The new bone formation was significantly greater in ErhBMP-2-treated groups compared with the untreated group. In particular, the ErhBMP-2/CPB group showed stability of augmented areas during the period of healing, due to relevant space-providing capacity. Thus, it can be concluded that CPP and CPB lyophilized with ErhBMP-2 enhance the formation of new bone, and CPB appears to be a suitable carrier for ErhBMP-2 in which a 3-dimensional structural integrity is an important consideration factor.

Effects of bone marrow-derived mesenchymal stem cells and platelet-rich plasma on bone regeneration for osseointegration of dental implants: Preliminary study in canine three-wall intrabony defects

Tissue engineering has been applied to overcome the obstacles encountered with bone regeneration for the placement of dental implants. The purpose of this study was to determine the bone formation ability of human bone marrow-derived mesenchymal stem cells (BMMSCs) and platelet-rich plasma (PRP) when applied separately or together to the intrabony defect around dental implants with a porous hydroxyapatite (HA) scaffold. Standardized three-wall intrabony defects (4 × 4 × 4 mm) were created at the mesial of each dental implant site in four mongrel dogs. Defects were then grafted with the following materials: HA + BMMSCs (HS group), HA + PRP (HP group), HA + BMMSCs + PRP (HSP group), and HA scaffold alone (HA group). The level of bone formation (bone density) and osseointegration (bone-to-implant contact [BIC]) in bone defects around the implants were evaluated by histological and histometric analysis at 6 and 12 weeks after the placement of implants. HA, HS, HP, and HSP groups generally showed an increase in bone density and BIC between 6 and 12 weeks, except BIC in the HS group. Although no statistically significant differences were found among HA, HS, HP, and HSP groups (p > 0.05), the highest level of bone density and BIC were observed in the HSP group after the 12-week healing period. Furthermore, the level of bone maturation was higher in the HSP group than in the other groups as determined histologically. The findings of this preliminary study suggest that BMMSCs and PRP combined with HA scaffold may provide additional therapeutic effects on bone regeneration and improve osseointegration in bone defects around dental implants.

Induction of bone formation by Escherichia coli‐expressed recombinant human bone morphogenetic protein‐2 using block‐type macroporous biphasic calcium phosphate in orthotopic and ectopic rat models

BACKGROUND AND OBJECTIVE The potential of the Escherichia coli-expressed recombinant human bone morphogenetic protein-2 (ErhBMP-2) to support new bone formation/maturation using a block-type of macroporous biphasic calcium phosphate (bMBCP) carrier was evaluated in an orthotopic and ectopic rat model. MATERIAL AND METHODS Critical-size (Φ 8 mm) calvarial defects and subcutaneous pockets in 32 Sprague-Dawley rats received implants of rhBMP-2 (2.5 μg) in a bMBCP carrier or bMBCP alone (control). Implant sites were evaluated using histological and histometric analysis following 2- and 8-wk healing intervals (eight animals/group/interval). RESULTS   ErhBMP-2/bMBCP supported significantly greater bone formation at 2 and 8 wk (10.8% and 25.4%, respectively) than the control at 2 and 8 wk (5.3% and 14.0%, respectively) in calvarial defects (p < 0.01). Bone formation was only observed for the ErhBMP-2/bMBCP ectopic sites and was significantly greater at 8 wk (7.5%) than at 2 wk (4.5%) (p < 0.01). Appositional and endochondral bone formation was usually associated with a significant increase in fatty marrow at 8 wk. The bMBCP carrier showed no evidence of bioresorption. CONCLUSION ErhBMP-2/bMBCP induced significant bone formation in both calvarial and ectopic sites. Further study appears to be required to evaluate the relevance of the bMBCP carrier.

Bone formation of Escherichia coli expressed rhBMP-2 on absorbable collagen block in rat calvarial defects

OBJECTIVES The aim of this study was to evaluate the osteogenic and space-providing effect of rhBMP-2 produced in an Escherichia coli expression system (ErhBMP-2) with absorbable collagen block (ACB) as the carrier system in the rat calvarial defect model. STUDY DESIGN Eight-millimeter diameter calvarial defects were created in 60 male Sprague-Dawley rats. The animals were divided into 6 groups containing 10 animals each that received sham-surgery control (no material applied), ACB control (ACB alone), or ErhBMP-2/ACB (ACB loaded with 0.025 mg/mL ErhBMP-2). Histological and histometric analysis was performed after 2- and 8-week healing intervals. RESULTS On histological observation, the level of bone formation in the defects was generally higher at 8 weeks than at 2 weeks. Surgical implantation of ErhBMP-2/ACB resulted in the enhanced bone regeneration compared with controls. Moreover, the collagen remnants of ACB appeared to be completely resorbed in ACB control and ErhBMP-2/ACB group after 8 weeks. Histometic analysis revealed that the ErhBMP-2/ACB group had a significantly greater augmented area, new bone area, and new bone ratio after 2 and 8 weeks than both control groups. However, there was no difference between 2 and 8 weeks in the ErhBMP-2/ACB group in all aspects of the augmented area, new bone area, and new bone ratio (P < .05). CONCLUSION ErhBMP-2 loaded on ACB can induce favorable bone formation in the rat calvarial defect model, but this collagen carrier in block type did not fulfill the space-maintaining expectations for bone formation by ErhBMP-2.

A short-term clinical study of marginal bone level change around microthreaded and platform-switched implants

Purpose The marginal bone levels around implants following restoration are used as a reference for evaluating implant success and survival. Two design concepts that can reduce crestal bone resorption are the microthread and platform-switching concepts. The aims of this study were to analyze the placement of microthreaded and platform-switched implants and their short-term survival rate, as well as the level of bone around the implants. Methods The subjects of this study were 27 patients (79 implants) undergoing treatment with microthreaded and platform-switched implants between October 2008 and July 2009 in the Dental Hospital of Yonsei University Department of Periodontology. The patients received follow-up care more than 6 months after the final setting of the prosthesis, at which time periapical radiographs were taken. The marginal bone level was measured from the reference point to the lowest observed point of contact between the marginal bone and the fixture. Comparisons were made between radiographs taken at the time of fixture installation and those taken at the follow-up visit. Results During the study period (average of 11.8 months after fixture installation and 7.4 months after the prosthesis delivery), the short-term survival rate of microthreaded and platform-switched implants was 100% and the marginal bone loss around implants was 0.16±0.08 mm, the latter of which is lower than the previously reported values. Conclusions This short-term clinical study has demonstrated the successful survival rates of a microthread and platform-switched implant system, and that this system is associated with reduced marginal bone loss.

Synergistic effect of bone marrow-derived mesenchymal stem cells and platelet-rich plasma on bone regeneration of calvarial defects in rabbits

Bone tissue regeneration techniques include tissue engineering approaches which employ mesenchymal stem cells as an osteogenic agent for bone repair. Recent studies have demonstrated that tissue engineering scaffolds and growth factors can support cell proliferation, bone formation, and bone tissue repair in lost bone tissue. Furthermore, many studies have suggested that platelet-rich plasma (PRP) can improve bone regeneration due to the numerous growth factors that it contains. This study was performed to investigate the influence of bone marrow-derived mesenchymal stem cells (BMMSCs) and PRP on bone regeneration of calvarial defects in rabbits. Hydroxyapatite (HA) was used as a scaffold for bone regeneration. There were three groups in this experiment: 1) HA loaded with BMMSCs (HS group), 2) HA loaded with PRP (HP group), and 3) HA loaded with BMMSCs and PRP (HSP group). Two circular bony defects (6 mm in diameter) were made in rabbit calvaria using a trephine bur. BMMSCs and PRP with a HA scaffold (diameter 5.5 mm, height 3 mm) were applied to each defect. The animals were sacrificed after 2 weeks, 4 weeks and 8 weeks. The level of their ability of osteogenesis was evaluated through histological and histomorphometric analyses. High-quality bone regeneration was observed in the HSP group. The percentage of new bone area around the scaffolds was higher in the HSP group than it was in the other groups (HS and HP group), especially at 8 weeks (HS, 72.5±15 %; HP, 85.8±14 %; HSP, 98.8±2.5%). In addition, the level of bone maturation was higher in the HSP group than in the other groups. The results of this study show that PRP has a positive effect on bone generation. HA with a combination of BMMSCs and PRP can enhance bone regeneration. In addition, the growth factor capacity of PRP may affect the differentiation of BMMSCs and promote bone formation.