Biomedical subjects

Kunio Takaoka

Publications and source records attributed to Kunio Takaoka.

At least 19 recordsLinked to original sources

PubMed2006

Repair of long intercalated rib defects using porous beta-tricalcium phosphate cylinders containing recombinant human bone morphogenetic protein-2 in dogs.

A new method to repair rib defects with biomaterials containing recombinant human bone morphogenetic protein-2 (rhBMP-2) is presented in this report. We had reported previously the successful regeneration of bony rib defects by placing a short chain of small beta-tricalcium phosphate (beta-TCP) cylinders on the intact periosteum. The multi-cylinder implants were ineffective in promoting rib repair when the periosteum was absent. By adding rhBMP-2 to the beta-TCP cylinders, we were able to promote rib bone regeneration in the presence or absence of the periosteum. The osteogenic capacity of the rhBMP-2/beta-TCP composite implant and the time required to complete regeneration were evaluated in a canine model. An 8cm long section of rib bone, including the periosteum, was removed and replaced with a chain of the rhBMP-2/beta-TCP cylinders. At 6 weeks after implantation, the ribs were restored to their original configuration and mechanical strength. The multi-cylinder beta-TCP implants were degraded and replaced by new bone in 12 weeks. This new degradable bone-inducing implant material has significant clinical potential for rib repair.

Absorbable Implants↗

PubMed2006

Heparin potentiates the in vivo ectopic bone formation induced by bone morphogenetic protein-2.

Although bone morphogenetic proteins (BMPs) are clinically useful for bone regeneration, large amounts are required to induce new bone formation in monkeys and humans. We found recently that heparin stimulates BMP activity in vitro (Takada, T., Katagiri, T., Ifuku, M., Morimura, N., Kobayashi, M., Hasegawa, K., Ogamo, A., and Kamijo, R. (2003) J. Biol. Chem. 278, 43229-43235). In the present study, we examined whether heparin enhances bone formation induced by BMPs in vivo and attempted to determine the molecular mechanism by which heparin stimulates BMP activity using C2C12 myoblasts. Heparin enhanced BMP-2-induced gene expression and Smad1/5/8 phosphorylation at 24 h and thereafter, although not within 12 h. Heparitinase treatment did not affect the response of cells to BMP-2. In the presence of heparin, degradation of BMP-2 was blocked, and the half-life of BMP-2 in the culture medium was prolonged by nearly 20-fold. Although noggin mRNA was induced by BMP-2 within 1 h regardless of the presence of heparin, noggin failed to inhibit BMP-2 activity in the presence of heparin. Furthermore, simultaneous administration of BMP-2 and heparin in vivo dose-dependently induced larger amounts of mineralized bone tissue compared with BMP-2 alone. These findings clearly indicate that heparin enhances BMP-induced osteoblast differentiation not only in vitro but also in vivo. This study indicates that heparin enhances BMP-induced osteoblast differentiation in vitro and in vivo by protecting BMPs from degradation and inhibition by BMP antagonists.

Alkaline Phosphatase↗

PubMed2006

Osteoblasts provide a suitable microenvironment for the action of receptor activator of nuclear factor-kappaB ligand.

Deficiency of osteoprotegerin (OPG), a soluble decoy receptor for receptor activator of nuclear factor-kappaB ligand (RANKL), in mice induces osteoporosis caused by enhanced bone resorption. Serum concentrations of RANKL are extremely high in OPG-deficient (OPG(-/-)) mice, suggesting that circulating RANKL is involved in osteoclastogenesis. RANKL(-/-) mice exhibit osteopetrosis, with the absence of osteoclasts. We examined the requirements for osteoclastogenesis using OPG(-/-) mice, RANKL(-/-) mice, and a system involving bone morphogenetic protein 2 (BMP-2)-induced ectopic bone formation. When collagen disks containing BMP-2 (BMP-2-disks) or vehicle were implanted into OPG(-/-) mice, osteoclast-like cells (OCLs) and alkaline phosphatase-positive OCLs appeared in BMP-2-disks but not the control disks. F4/80-positive osteoclast precursors were similarly distributed in both BMP-2- and control disks. Cells expressing RANKL were detected in the BMP-2-disks, and the addition of OPG to the disk inhibited OCL formation. Muscle cells in culture differentiated into alkaline phosphatase-positive cells in the presence of BMP-2 and accordingly expressed RANKL mRNA in response to PTH. This suggests that RANKL expressed by osteoblasts is a requirement for osteoclastogenesis. We then examined how osteoblasts are involved in osteoclastogenesis other than RANKL expression, using RANKL(-/-) mice. BMP-2- and control disks were implanted into RANKL(-/-) mice, which were injected with RANKL for 7 d. Many OCLs were observed in the BMP-2-disks and bone tissues but not the control disks. These results suggest that osteoblasts also play important roles in osteoclastogenesis through offering the critical microenvironment for the action of RANKL.

Animals↗

PubMed2006

Ectopic bone formation in mice associated with a lactic acid/dioxanone/ethylene glycol copolymer-tricalcium phosphate composite with added recombinant human bone morphogenetic protein-2.

A new putty-like material with bone-inducing capacity was made by combining a block copolymer of poly d,l-lactic acid with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG) and beta-tricalcium phosphate (beta-TCP) powder with added recombinant human bone morphogenetic protein-2 (rhBMP-2). To optimize the material's efficacy for bone formation, we formulated the optimal composition ratio of the respective constituent that gives the greatest osteoinductive efficacy in a mouse model of ectopic bone formation. In this series of studies, we investigated the size of ectopic bone mass induced 3 and 6 weeks after implantation of the materials composed of 30 mg of PLA-DX-PEG with 2 microg of rhBMP-2 and 0, 15, 30, or 60 mg of beta-TCP powder. An additional experiment was designed to investigate how content ratios of beta-TCP powder in 30 mg-putty implants (0%, 16.7%, 33.3%, 50%, 66.7%, 83.3%, or 100%) for a fixed dose (5 microg) of the rhBMP-2 altered the size of the induced ossicle. The results from the first experiment indicated that the bone yields were linearly dependent on the amount of additional beta-TCP powder. In the second experiment, the largest ossicles induced by 5 microg of rhBMP-2 were obtained when the polymer/beta-TCP ratio was 1/2 in mice. The data provide important insights into the fabrication of implants that provide efficacious delivery of rhBMP-2. The new putty-like material may be valuable for repairing or regenerating bone in a clinical setting.

Absorbable Implants↗

PubMed2006

A biodegradable delivery system for antibiotics and recombinant human bone morphogenetic protein-2: A potential treatment for infected bone defects.

To produce an osteogenic and bacteriocidal biomaterial for the treatment of infected nonunions or bone defects, a synthetic degradable block copolymer of poly-D,L-lactic acid segments with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG) segments was mixed with recombinant human BMP-2 (rhBMP-2) and antibiotics at high concentration. We then examined the in vitro elution profile of an antibiotic (teicoplanin) from the polymer, the effects of antibiotics on the bone-inducing capacity of rhBMP-2 or on ectopic new bone formation induced by the rhBMP, and the ability of the polymer to repair bone in a rat cranial defect model. Approximately 40% of teicoplanin was released within the first 24 h, with the remaining amount released steadily over 21 days with no loss of antibacterial activity. The polymer had disappeared by degradation in the phosphate buffered saline (pH 7.4) at the end of the incubation period. The in vivo performance of pellets with antibiotics and rhBMP-2 revealed no significant change in bone yield within the ossicles after 3 weeks. Also, antibiotics had no inhibitory effect on the ability of rhBMP2 to repair cranial defects. Indeed, when the defect was filled by a polymer disc loaded with rhBMP-2 with or without teicoplanin, the defect was repaired by new bone, and normal anatomy was restored within 6 weeks. In conclusion, the PLA/DX/PEG polymer appears to work as effectively for antibiotics as it does for rhBMP-2. Additionally, the biological activity of rhBMP-2 was retained irrespective of the presence of antibiotics.

Absorbable Implants↗

PubMed2006

Efficacy and tolerability of once-weekly administration of 17.5 mg risedronate in Japanese patients with involutional osteoporosis: a comparison with 2.5-mg once-daily dosage regimen.

In this multicenter, randomized, double-blind controlled trial, the efficacy and safety of once-weekly dosing with 17.5 mg risedronate was compared with once-daily dosing with 2.5 mg risedronate in Japanese patients with involutional osteoporosis. A total of 496 patients were randomized to receive either once-weekly (n = 249) or once-daily (n = 247) treatment. All patients were supplemented with 200 mg/day calcium. Following 48 weeks of treatment, the mean (+/-SD) percent changes, from baseline, in the bone mineral density of the lumbar spine (L2-L4 BMD) in the once-weekly and once-daily treatment groups were 5.36 +/- 4.27% and 5.87 +/- 4.47%, respectively. The difference between the groups was -0.5% (95% confidence interval: -1.35% to 0.35%), demonstrating that the effect on BMD of once-weekly treatment was not inferior to that of once-daily treatment. The time-course reductions in biochemical markers of bone resorption (urinary N- and C-telopeptide of type I collagen) and bone formation (bone-specific alkaline phosphatase) were similar for the two dosing regimens. There were no differences in the incidence of new vertebral fractures or the worsening of existing fractures between the once-weekly (2.2%) and once-daily (2.7%) dosing regimens. No significant differences were observed between the two dosing regimens in the incidence or the type of adverse events. However, 10.1% of the patients in the once-daily group withdrew due to adverse events as compared to 5.2% in the once-weekly group. Moreover, drug-related adverse events, including upper gastrointestinal disorders and abnormal changes in laboratory parameters, tended to be less in the once-weekly dosing regimen than in the once-daily dosing regimen. In conclusion, once-weekly oral dosing with 17.5 mg risedronate was well tolerated in Japanese osteoporotic patients, and showed equivalent efficacy to once-daily oral dosing with 2.5 mg risedronate. This once-weekly regimen is expected to provide a more convenient therapeutic option as an alternative to daily dosing and to enhance patient compliance in long-term therapy for osteoporosis.

Aged↗

PubMed2006

Use of glycyrrhizin in prevention of tissue damage caused by ischemia-reperfusion in rabbit hind limbs.

BACKGROUND: Glycyrrhizin, an agent that can bind to selectins and inhibit their ability to bind neutrophils, was found to be effective in preventing tissue edema caused by ischemia-reperfusion in a rabbit model. METHODS: Complete ischemia was produced by applying a tight Esmarch tourniquet to the hind limbs of 24 Japanese white rabbits. Immediately before and 1 h after release of the tourniquet, 12 animals were given glycyrrhizin intravenously; 12 controls received saline. RESULTS: The mean relative increase in the circumference of the shins before and after ischemia-reperfusion with or without glycyrrhizin treatment was 4.6% +/- 2.4% and 9.6% +/- 4.2%, respectively, indicating that tissue edema caused by the ischemia-reperfusion was significantly attenuated by glycyrrhizin. Histological studies of cross sections of the anterior tibial muscle 24 h after reperfusion showed a significant reduction in the incidence of necrotic muscle fibers in the glycyrrhizin-treated animals compared with the controls that did not receive glycyrrhizin. The mRNA levels of P- and E-selectin 24 h after reperfusion were significantly higher in the ischemic anterior tibial muscle than in the nonischemic normal muscle. After 24 h of reperfusion, the mean activity of myeloperoxidase, a neutrophil-specific enzyme, in the anterior tibial muscles of the group given glycyrrhizin (0.0022 +/- 0.0013 absorbance units) was lower than that of the untreated group (0.027 +/- 0.026 absorbance units). CONCLUSIONS: These data suggest that glycyrrhizin treatment is effective in suppressing the acute inflammatory reaction or edema following ischemia-reperfusion and might be potentially useful in clinical practice for preventing ischemia-reperfusion injuries to the extremities.

Animals↗

PubMed2006

Accelerated repair of a bone defect with a synthetic biodegradable bone-inducing implant.

BACKGROUND: Nothing has ever had osteoinductive capacity and degradability equivalent to that of autogenous bone, although many types of biomaterials have been developed. To address this issue, we constructed a new bone graft substitute with osteogenic potential and degradability by using porous beta-tricalcium phosphate (beta-TCP) granules, bone morphogenetic protein (BMP), and a synthetic block copolymer composed of poly-D: ,L: -lactic acid with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG). In this experimental study, the bone-inducing capacity and degradation properties of the composite implant during the bone healing process were examined in vivo in a cortical and cancellous bone defect model in rabbits. METHODS: The advantages of this type of implant have been examined in a cortical bone defect model created in the distal femur of rabbits. The defects (6.5 x 5 mm) were filled with 30 mg of various implants: BMP-H [rhBMP-2, 0.0025% (w/w)], BMP-L [rhBMP-2, 0.000625% (w/w)], control A (beta-TCP alone), and control B (no implant). The distal femurs were harvested at scheduled intervals after surgery and examined for the evaluation of the bony repair of the defects by three-dimensional computed tomography and histology. RESULTS: The repair of both cortical and cancellous bone occurred predominantly in the BMP-H group, and only minor cortical bone repair and cancellous bone formation were noted in the BMP-L and control A groups. Most of the beta-TCP was resorbed in the BMP-H group at 6 weeks after surgery, whereas a significant amount of beta-TCP remained in the BMP-L and control A groups. CONCLUSIONS: beta-TCP granules coated with a BMP-retaining synthetic polymer appear to be effective in enhancing the repair of both cancellous and cortical bone defects. The early disappearance of the implanted beta-TCP and restoration of the normal anatomy of bone tissue are two notable features of this approach.

Absorbable Implants↗

PubMed2006

Low hepatic cytochrome P450 3A activity is a risk for corticosteroid-induced osteonecrosis.

BACKGROUND: Osteonecrosis of the femoral head (ONFH) is one of the major side effects of corticosteroid therapy. Because corticosteroids are metabolized by hepatic cytochrome P450 (CYP) 3A, a low endogenous activity of this enzyme may contribute to the pathogenesis of ONFH. The purpose of this study was to examine the possible association of hepatic CYP3A activity and the susceptibility to ONFH in patients treated with corticosteroids. METHODS: In this prospective controlled study we measured the clearance of intravenous midazolam (0.25 mg/kg) to estimate hepatic CYP3A activity in patients with steroid-induced ONFH (n = 26), patients with alcohol-related ONFH (n = 29), and non-ONFH control patients (n = 75) undergoing orthopedic surgery. Midazolam clearance was compared between the groups, and the relationship between the level of hepatic CYP3A activity and the prevalence of ONFH was evaluated by multivariate analysis. RESULTS: Midazolam clearance in patients with steroid-induced ONFH was significantly lower than that in control patients and patients with alcohol-related ONFH (7.7 +/- 1.8 mL x kg(-1) x min(-1) versus 11.4 +/- 3.5 mL x kg(-1) x min(-1) and 10.5 +/- 2.8 mL x kg(-1) x min(-1), respectively; P < .001). Patients with low midazolam clearance (<9.5 mL x kg(-1) x min(-1)) had a 9-fold greater risk for steroid-induced ONFH (adjusted odds ratio, 9.08 [95% confidence interval, 2.79-29.6]; P < .001). Midazolam clearance did not show a significant correlation with the prevalence of alcohol-related ONFH. CONCLUSIONS: Low hepatic CYP3A activity may significantly contribute to the risk for steroid-induced ONFH.

Adrenal Cortex Hormones↗

PubMed2006

Volar dislocation of the extensor carpi ulnaris tendon on magnetic resonance imaging is associated with extensor digitorum communis tendon rupture in rheumatoid wrists.

PURPOSE: Extensor tendon rupture in rheumatoid wrists is a common problem and causes immediate dysfunction of the digits. The best treatment for tendon rupture may be prophylactic management, although the factors associated with tendon rupture must first be identified. The purpose of this study was to evaluate structures around rheumatoid wrists using magnetic resonance imaging with forearm rotation and to identify factors associated with extensor tendon rupture as indications for prophylactic surgery. METHODS: The subjects were 34 patients (40 wrists) with active rheumatoid arthritis. The extensor digitorum communis (EDC) tendons were ruptured in 15 wrists. Magnetic resonance imaging of the wrists was performed in maximally pronated and supinated positions of the forearm. Axial images of the distal radioulnar joints (DRUJs) were selected to evaluate DRUJ synovitis, dorsal tenosynovitis, volar dislocation of the extensor carpi ulnaris (ECU) tendon, sigmoid notch angle, and the radioulnar ratio (RUR) (ie, the degree of DRUJ subluxation). RESULTS: No significant correlations were found between EDC tendon rupture and DRUJ synovitis, dorsal tenosynovitis, or RUR in pronation. Extensor digitorum communis tendon rupture correlated significantly with volar ECU tendon dislocation, sigmoid notch angle, and RUR in supination. Radioulnar ratio correlated significantly with volar ECU tendon dislocation only in supination and not in pronation. Thus, DRUJ subluxation was advanced even in the supinated wrist with volar ECU tendon dislocation. As a factor associated with EDC tendon rupture, volar ECU tendon dislocation had 87% sensitivity and 76% specificity. CONCLUSIONS: Volar ECU tendon dislocation is associated with increased RUR in supination and EDC tendon rupture. Volar ECU tendon dislocation can thus be considered a factor associated with EDC tendon rupture, and its presence may indicate the need for prophylactic surgical intervention in a subset of rheumatoid arthritis patients.

Adolescent↗

PubMed2006

Endoscopic vertebroplasty for the treatment of chronic vertebral compression fracture. Technical note.

The authors describe a new vertebroplasty technique for the treatment of chronic painful vertebral compression fractures (VCFs). A urinary balloon catheter is introduced into the vertebral body (VB) via a bilateral transpedicular approach and inflated with contrast medium to obtain sufficient space for endoscopic observation. The granulation tissue occupying the VB is then removed using a punch or curette inserted through one pedicle, with the guidance of an endoscope introduced through the contralateral pedicle. After endoscopic resection of granulation tissue in the fractured VB, vertebroplasty is performed by injecting calcium phosphate cement (CPC) into the VB. Fourteen patients in whom chronic painful VCFs were diagnosed underwent surgery involving the aforementioned technique. In all cases, intractable pain and ambulatory function improved after surgery, and there were no significant systemic complications. On radiological evaluation in eight cases in which the follow-up period exceeded 1 year, the mean height of the fractured VB improved from 38% of that of adjacent intact VBs to 85%. Although a slight loss of correction was routinely observed at 1 month postoperatively, an additional loss of VB height was not noted up to 1 year later. Bone formation was commonly seen along the anterior wall of the involved vertebrae in all cases. Vertebroplasty involving the endoscopic removal of granulation tissue proved to be an efficacious procedure for the treatment of chronic painful VCFs. The osteoconductive capacity of CPC facilitated callus formation and ultimately restoration of vertebral bone structure.

Aged↗

PubMed2006

[Vertebroplasty for osteoporotic vertebral fracture].

Vertebroplasty for osteoporotic vertebral fracture has been published to enhance fractured vertebra and to reduce severe pain after the fracture. Bone cement such as Polymethylmethacrylate or calcium phosphate cement has been used for this procedure. However, serious neurological complication and pulmonary embolism might occur following the leakage of the cement. In order to avoid these serious complications, it seems to be important to make an enough space in the vertebral body before injecting bone cement. For this purpose, we utilized balloon inflation and endoscopic resection of connective tissue for pseudoarthrosis following osteoporotic vertebral fracture. With this procedure, severe pain after the fracture improved dramatically. So far, we did not have any serious systemic complications.

Bone Cements↗

PubMed2006

[Application of bone morphogenetic protein (BMP) in regenerative medicine of bone].

Main purpose of bone morphogenetic protein (BMP) related research in clinical setting is the development of new efficient technologies to regenerate bone tissue effectively by utilizing BMP's osteoinductivity. Problems to be solved for that purpose are the development of efficient career system for BMP and the exploitation of methods to promote efficacy of BMP's bone forming activity. These new technologies will enable orthopaedic surgeons to replace currently used autografts with BMP combined implants. Additionally, they are also applicable for the acceleration of bone healing, treatment of non-union, spinal fusion, reconstruction of bone defects after the resection of bone tumor or arthroplasty. Thus, these new technologies are expected for the breakthrough in clinical applications of BMP.

Bone Morphogenetic Proteins↗

PubMed2006

[Experimental spinal fusion in a rabbit model with new drug delivery system for BMP].

Bone morphogenic protein (BMP) is a powerful bone-inducing cytokine and has been used as a new bone graft substitute with bovine-derived collagen sponge as a delivery system. Excellent clinical results have been reported with use of these BMP-retaining implants. However, certain problems remain with use of them, such as the need for high doses of BMP to obtain new bone formation, resulting in high cost, and the potential risks for disease transmission (e.g., variant Creutzfeldt-Jacob disease). To avoid use of collagen, we have developed a synthetic polymer/beta-Tricalcium Phosphate composite as a new delivery system for BMP. This new material, when used in combination with low doses of BMP-2, consistently elicited new bone and was successfully used to achieve posterolateral spinal fusion in a rabbit model.

Animals↗

PubMed2005

Optimized use of a biodegradable polymer as a carrier material for the local delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2).

To improve the efficacy of a block copolymer of poly-d, l-lactic acid with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG) as a drug delivery system for recombinant human bone morphogenetic proteins (rhBMPs), we examined the relationship between the volume of PLA-DX-PEG, the dose of rhBMP-2 and osteoinduction in a mouse model of ectopic bone formation. In a series of studies, we compared the size and bone mineral content (BMC) of ectopically induced bone by PLA-DX-PEG and collagen sponges carrying different quantities of rhBMP (0, 1, 2, 5, 10, 20 microg). An additional experiment was designed to investigate how a range of PLA-DX-PEG polymer volumes (15, 30, 60, 90 mg) with a fixed rhBMP concentration (0.01 wt%), altered the size and BMC of the induced ossicle. The influence of polymer volume was also examined in a further experiment wherein a fixed amount of rhBMP was placed in a range of PLA-DX-PEG copolymer volumes to give different concentrations of the protein per implant (0.02-0.0017 wt%). The results indicate that the bone yields were linearly dependent on the dose of rhBMP and also were proportional to the polymer volume above the minimal concentration of rhBMP-2 (0.0017 wt% in this series). The optimal concentration of rhBMP-2 in PLA-DX-PEG was 0.003 wt% in mice. The data provide important insights into the fabrication of implants that provide efficacious delivery of rhBMP-2 using the lowest possible dose of this expensive osteoinductive protein. This information will be of value for the clinical use of BMPs.

Animals↗

PubMed2005

Bone morphogenetic protein activities are enhanced by 3',5'-cyclic adenosine monophosphate through suppression of Smad6 expression in osteoprogenitor cells.

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor (TGF)-beta superfamily, and some display potent osteogenic activity both in vivo and in vitro. The BMP signaling cascade involving BMP receptors at the cell membrane and intracellular messengers (Smads) has been elucidated, but the regulatory mechanisms of BMP signaling have not been clarified. We previously found that pentoxifyline (PeTx), a nonspecific inhibitor of phosphodiesterase (PDE), and rolipram, a PDE-4-specific inhibitor, enhance BMP-4-induced osteogenic differentiation of mesenchymal cells, probably through the elevation of intracellular cyclic adenosine monophosphate (cAMP) accumulation and modulation of BMP signaling pathways as enhanced BMP-4 action was reproduced by addition of dibutylyl-cAMP (dbcAMP). However, the precise mechanisms underlying the enhancing effects of those agents on BMP signaling were not completely revealed. As already reported, BMPs utilize a specific intracellular signaling cascade to target genes via R-Smads (Smad1,5,8), Co-Smad (Smad4) and I-Smads (Smad6,7). One possibility for cAMP-mediated effects on BMP signaling might be suppression of I-Smads expression since these proteins form a negative feedback loop in BMP signaling. To examine this possibility, changes in I-Smad (Smad6) expression on addition of dbcAMP or PeTx were examined in a bone-marrow-derived osteogenic cell line (ST2). Alkaline phosphatase activity in ST2 cells was consistently induced by BMP-4 treatment (300 ng/ml), and Smad6 mRNA expression was also induced by BMP-4 treatment. Although concurrent treatment of ST2 cells with BMP-4 and dbcAMP elicited further activation of alkaline phosphatase, addition of dbcAMP reduced BMP-4-induced Smad6 expression in a dose-dependent manner. Furthermore, detection of phosphorylated Smad1/5/8 on Western blotting analysis was prolonged, suggesting prolonged kinase activity of BMP receptors through suppressed expression of Smad6. Elevated intracellular cAMP might thus enhance BMP signaling by suppressing Smad6 induction and prolonging intracellular BMP signaling.

Alkaline Phosphatase↗

PubMed2005

Experimental spinal fusion with recombinant human bone morphogenetic protein-2 delivered by a synthetic polymer and beta-tricalcium phosphate in a rabbit model.

STUDY DESIGN: An experimental animal study to achieve posterolateral intertransverse process spine fusion with recombinant bone morphogenetic protein in combination with a new delivery system. OBJECTIVE: To evaluate the efficacy of a new synthetic biodegradable bone-inducing material containing recombinant human bone morphogenetic protein-2 (rhBMP-2) as a bone-graft substitute for posterolateral intertransverse process fusion in a rabbit model. SUMMARY OF BACKGROUND DATA: rhBMP-2, a powerful bone-inducing cytokine, has been used as a bone graft substitute in combination with animal-derived collagen to achieve spinal fusion in animal models. However, the minimum dose of rhBMP-2 required to obtain solid posterolateral intertransverse process fusion was high on the basis of previous reports (>100 microg in rabbit models). To improve the efficacy, performance of rhBMP-2, and the safety of the delivery system for this protein, a more sophisticated system is required. METHODS: To fabricate one implant for one-side L4-L5 intertransverse process fusion, beta-tricalcium phosphate (beta-TCP) powder (300 microg), a polymer gel (PLA-DX-PEG block copolymer; 300 microg) and rhBMP-2 (7.5, 15, or 30 microg) were mixed and manually shaped to resemble a rod. Through a posterolateral approach, two implants were placed on both sides (1 per side) by surgery so as to bridge the transverse processes of adult New Zealand white rabbits (n = 27). In control animals, implants without rhBMP or autogenous cortico-cancellous bone chips from the iliaccrest were placed in a similar location. The lumbar vertebrae were recovered 6 weeks after surgery. The posterolateral fusion was examined by manual palpation, radiography, biomechanical testing, and histology. RESULTS: Rabbits that received 15 or 30 microg of rhBMP-2 showed consistent fusion. However, solid fusion was seen in 2 of 5 rabbits with autografting and rabbits that received 7.5 microg of rhBMP-2. Fusion was not observed in the rabbits that did not receive rhBMP-2. CONCLUSIONS: Consistent spinal fusion was obtained by implanting a biodegradable bone-inducing implant composed of beta-TCP, PLA-DX-PEG, and rhBMP-2 within a period of 6 weeks. The rhBMP-2 doses required for the spinal fusion were significantly lower than those reported previously.

Animals↗

PubMed2005

Hepatocyte growth factor contributes to fracture repair by upregulating the expression of BMP receptors.

UNLABELLED: Hepatocyte growth factor (HGF) is activated and the expression of BMP receptors (BMPRs) is induced around the fracture site during the early phase of fracture repair. HGF facilitates the expression of BMPRs in mesenchymal cells. This study suggests that HGF contributes to fracture repair by inducing the expression of BMPRs. INTRODUCTION: The precise mechanisms that control the upregulation of BMP, BMPRs, and other molecules involved in bone repair are not completely understood. In this study, we hypothesized that HGF, activated through the action of thrombin on the HGF activator, may enhance BMP action through the local induction of BMP or BMPRs. MATERIALS AND METHODS: Callus samples from tibial fractures in mice were harvested for immunohistochemical analysis of HGF and phosphorylated c-Met, for in situ hybridization of BMPRs, and for real-time RT-PCR analysis for the expression of HGF, c-Met, and BMPRs. To study the changes in gene expression of BMPRs in response to HGF, C3H10T1/2 cells were cultured with or without HGF and harvested for real-time RT-PCR and for Western blot analysis. To evaluate the contribution of HGF to the biological action of BMP2, C3H10T1/2 cells and primary muscle-derived mesenchymal cells were precultured with HGF and cultured with BMP2. In addition, the expression of the luciferase gene linked to the Id1 promoter containing the BMP responsive element and alkaline phosphatase (ALP) activity were assayed. RESULTS: Positive immunostaining of HGF and phosphorylated c-Met was detected around the fracture site at 1 day after the fracture was made. mRNA expression of BMPRs was increased 1 day after fracture and localized in mesenchymal cells at the fracture site. From an in vitro study, the expression of mRNA for BMPRs was elevated by treatment with HGF, but the expression of BMP4 did not change. Western blot analysis also showed the upregulation of BMPR2 by HGF treatment. The results from the luciferase and ALP assays indicated increased responsiveness to BMPs by treating with HGF. CONCLUSIONS: This study indicates that HGF is activated and expressed at the fracture site and that HGF induces the upregulation of BMPRs in mesenchymal cells. Furthermore, HGF may facilitate BMP signaling without altering the expression of BMP molecules.

Animals↗