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Li G, Qin S, Zhang D, Liu X. Preparation of antibacterial degummed silk fiber/nano-hydroxyapatite/polylactic acid composite scaffold by degummed silk fiber loaded silver nanoparticles. NANOTECHNOLOGY 2019; 30:295101. [PMID: 30917342 DOI: 10.1088/1361-6528/ab13df] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
In this study, an antibacterial degummed silk fiber (ADSF)/nano-hydroxyapatite/polylactic acid (ADSF/nHA/PLA) porous scaffold with antibacterial properties was prepared by using degummed silk fiber (DSF) loaded with silver nano-particles (Ag NPs) as a reinforcing material. In the experiment, ADSF and nHA were used as the main variables to investigate the effect of the change of the composition ratio on the performance of the composite scaffold, and a composite scaffold with excellent performance was obtained. Firstly, the DSFs were treated with dopamine (DA) and the silver ions were reduced to Ag NPs using the strong reducibility of polydopamine (PDA) to prepare ADSF loaded with Ag NPs. Finally, ADSF/nHA/PLA composite scaffolds with antibacterial properties were prepared using ADSF as a reinforcing material. In addition, samples were found to have good mineralization capacity in in vitro mineralization experiments. At the same time, in cell culture and antibacterial experiments, ADSF/nHA/PLA scaffolds were found to have good bioactivity, biocompatibility and antibacterial properties. All the results showed that the Ag NPs loaded DSF improved the performance of the nHA/PLA composite scaffold, while the ADSF/nHA/PLA had good bioactivity and antibacterial properties, making the antibacterial ADSF/nHA/PLA composite scaffold has a great potential for bone tissue engineering.
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Affiliation(s)
- Gang Li
- College of Materials Science and Metallurgy Engineering, Guizhou University, Guiyang 550025, People's Republic of China. National Engineering Research Center for Compounding and Modification of Polymeric Materials, Guiyang 550014, People's Republic of China
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Bae HW, Patel VV, Sardar ZM, Badura JM, Pradhan BB, Seim HB, Turner AS, Toth JM. Transient Local Bone Remodeling Effects of rhBMP-2 in an Ovine Interbody Spine Fusion Model. J Bone Joint Surg Am 2016; 98:2061-2070. [PMID: 28002369 DOI: 10.2106/jbjs.16.00345] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a powerful osteoinductive morphogen capable of stimulating the migration of mesenchymal stem cells (MSCs) to the site of implantation and inducing the proliferation and differentiation of these MSCs into osteoblasts. Vertebral end-plate and vertebral body resorption has been reported after interbody fusion with high doses of rhBMP-2. In this study, we investigated the effects of 2 rhBMP-2 doses on peri-implant bone resorption and bone remodeling at 7 time points in an end-plate-sparing ovine interbody fusion model. METHODS Twenty-one female sheep underwent an end-plate-sparing discectomy followed by interbody fusion at L2-L3 and L4-L5 using a custom polyetheretherketone (PEEK) interbody fusion device. The PEEK interbody device was filled with 1 of 2 different doses of rhBMP-2 on an absorbable collagen sponge (ACS): 0.13 mg (1×) or 0.90 mg (7×). Bone remodeling and interbody fusion were assessed via high-resolution radiography and histological analyses at 1, 2, 3, 4, 8, 12, and 20 weeks postoperatively. RESULTS Peri-implant bone resorption peaked between 3 and 8 weeks in both the 1× and the 7× rhBMP-2/ACS-dose group. Osteoclastic activity and corresponding peri-implant bone resorption was dose-dependent, with moderate-to-marked resorption at the 7×-dose level and less resorption at the 1×-dose level. Both dose (p < 0.0007) and time (p < 0.0025) affected bone resorption significantly. Transient bone-resorption areas were fully healed by 12 weeks. Osseous bridging was seen at all but 1 spinal level at 12 and at 20 weeks. CONCLUSIONS In the ovine end-plate-sparing interbody fusion model, rhBMP-2 dose-dependent osteoclastic resorption is a transient phenomenon that peaks at 4 weeks postoperatively. CLINICAL RELEVANCE Using the U.S. Food and Drug Administration (FDA)-approved rhBMP-2 concentration and matching the volume of rhBMP-2/ACS with the volume of desired bone formation within the interbody construct may limit the occurrence of transient bone resorption.
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Affiliation(s)
- Hyun W Bae
- 1Spine Center, Department of Surgery (H.W.B.), Cedars-Sinai Medical Center (Z.M.S.), Los Angeles, California 2Department of Orthopaedic and Spine Surgery, University of Colorado Health Sciences Center, Aurora, Colorado 3Medtronic Sofamor Danek, Inc., Memphis, Tennessee 4Risser Orthopaedic Group, Pasadena, California 5Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado 6Department of Orthopaedic Surgery, The Medical College of Wisconsin, Milwaukee, Wisconsin
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Zhu M, Zhu Y, Ni B, Xie N, Lu X, Shi J, Zeng Y, Guo X. Mesoporous silica nanoparticles/hydroxyapatite composite coated implants to locally inhibit osteoclastic activity. ACS APPLIED MATERIALS & INTERFACES 2014; 6:5456-5466. [PMID: 24666121 DOI: 10.1021/am405013t] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In an attempt to improve implant-bone integration and accelerate bone fracture healing from resisting osteoclastic resorption point of view, we have employed a novel procedure to develop a mesoporous silica nanoparticles/hydroxyapatite (MSNs/HA) composite coating onto stainless Kirschner wire substrate. Characterizations of the surface microstructures indicated enlarged specific surface area compared to HA-coated wires as control, thus the MSNs/HA composite coated implants are endowed with abilities to locally deliver biomedical substances and enhance fracture healing. Herein, zoledronic acid (ZOL) as a model drug, different doses of which were immobilized in the mesoporous coating toward decreasing osteoclastic resorption activity. The loading capacities of ZOL increased almost eight-folds to that of pure HA coating, and the introduction of MSNs obviously retarded ZOL release to achieve a more sustained release profile. After certain periods of osteoclast like cells co-culturing with ZOL contained wires, tartrat-resistant acid phosphatases (TRAP) staining of polynucleated cells and a pit formation assay were performed to investigate the ZOL dose-dependent anti-resorption activity. The promoted local effect on osteoclasts will be of clinical benefit to support implant integration and bone repair.
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Affiliation(s)
- Min Zhu
- School of Materials Science and Engineering, University of Shanghai for Science and Technology , Shanghai, P. R. China
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Fong D, Bisson M, Laberge G, McManus S, Grenier G, Faucheux N, Roux S. Bone morphogenetic protein-9 activates Smad and ERK pathways and supports human osteoclast function and survival in vitro. Cell Signal 2013; 25:717-28. [PMID: 23313128 DOI: 10.1016/j.cellsig.2012.12.003] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Revised: 11/25/2012] [Accepted: 12/10/2012] [Indexed: 12/12/2022]
Abstract
BMP-9 is a potent osteogenic factor; however, its effects on osteoclasts, the bone-resorbing cells, remain unknown. To determine the effects of BMP-9 on osteoclast formation, activity and survival, we used human cord blood monocytes as osteoclast precursors that form multinucleated osteoclasts in the presence of RANKL and M-CSF in long-term cultures. BMP-9 did not affect osteoclast formation, but adding BMP-9 at the end of the culture period significantly increased bone resorption compared to untreated cultures, and reduced both the rate of apoptosis and caspase-9 activity. BMP-9 also significantly downregulated the expression of pro-apoptotic Bid, but only after RANKL and M-CSF, which are both osteoclast survival factors, had been eliminated from the culture medium. To investigate the mechanisms involved in the effects of BMP-9, we first showed that osteoclasts expressed some BMP receptors, including BMPR-IA, BMPR-IB, ALK1, and BMPR-II. We also found that BMP-9 was able to induce the phosphorylation of Smad-1/5/8 and ERK 1/2 proteins, but did not induce p38 phosphorylation. Finally, knocking down the BMPR-II receptor abrogated the BMP-9-induced ERK-signaling, as well as the increase in bone resorption. In conclusion, these results show for the first time that BMP-9 directly affects human osteoclasts, enhancing bone resorption and protecting osteoclasts against apoptosis. BMP-9 signaling in human osteoclasts involves the canonical Smad-1/5/8 pathway, and the ERK pathway.
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Affiliation(s)
- David Fong
- Division of Rheumatology, Faculty of Medicine, University of Sherbrooke, 3001, 12th Avenue North, Sherbrooke, Quebec, Canada
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Seeherman HJ, Li XJ, Smith E, Wozney JM. rhBMP-2/calcium phosphate matrix induces bone formation while limiting transient bone resorption in a nonhuman primate core defect model. J Bone Joint Surg Am 2012; 94:1765-76. [PMID: 23032587 DOI: 10.2106/jbjs.k.00523] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Transient bone resorption limits the use of recombinant human bone morphogenetic protein-2 (rhBMP-2)/absorbable collagen sponge in metaphyseal bone. The purpose of the present study was to evaluate the efficacy of rhBMP-2/calcium phosphate matrix (CPM) to induce bone formation while limiting transient bone resorption in nonhuman primate core defects. METHODS Metaphyseal core defects were created in eighteen cynomolgus monkeys. rhBMP-2 retention was evaluated in the distal part of the radius. Bone formation was evaluated at eight weeks following treatment with 1.5 or 4.5-mg/mL rhBMP-2/CPM, CPM alone, or no treatment in the distal part of the radius, the proximal part of the tibia, and the proximal part of the femur; at twenty-four weeks following treatment with 1.5-mg/mL rhBMP-2/CPM or CPM alone in the proximal part of the tibia; and at one, two, and four weeks following treatment with 1.5-mg/mL rhBMP-2/CPM or no treatment in the distal part of the radius. Bone resorption was evaluated at four weeks following treatment with 1.5, 2.0, 3.0, and 4.5-mg/mL rhBMP-2/CPM or CPM alone in the distal part of the femur. Evaluations were performed with use of scintigraphy, radiographs, histological analysis, and computed tomography. RESULTS Seventy-eight percent, 64%, 50%, 35%, and 12% of the rhBMP-2 was retained in the distal part of the radius at one, seven, fourteen, twenty-one, and forty-nine days after surgery. rhBMP-2/CPM increased bone formation within core defects and surrounding trabeculae compared with CPM alone or no treatment at all anatomic locations at eight weeks, and bone formation was ongoing in the rhBMP-2/CPM-treated proximal tibial sites at twenty-four weeks. Bone formation began in the trabeculae surrounding the core defects at one week and was observed adjacent to the resorbing CPM within the core defects and in the surrounding trabecular bone at two and four weeks in the rhBMP-2/CPM-treated distal radial sites. Bone formation was confined to the region immediately surrounding the core defects in the untreated distal radial sites at all time points. Transient bone resorption was only observed in the distal femoral sites treated with 4.5 mg/mL of rhBMP-2/CPM at two weeks. CONCLUSIONS Treatment of nonhuman primate metaphyseal core defects with 1.5 to 3.0-mg/mL rhBMP-2/CPM resulted in bone formation without transient bone resorption. CLINICAL RELEVANCE rhBMP-2/CPM may be useful to accelerate healing of metaphyseal bone defects in humans.
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Affiliation(s)
- Howard J Seeherman
- Inflammation and Tissue Repair, Pfizer Discovery Research, 200 Cambridge Park Drive, Cambridge, MA 02140, USA.
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Zheng Y, Wang L, Zhang X, Zhang X, Gu Z, Wu G. BMP2/7 Heterodimer Can Modulate All Cellular Events of the In Vitro RANKL-Mediated Osteoclastogenesis, Respectively, in Different Dose Patterns. Tissue Eng Part A 2012; 18:621-30. [PMID: 21981321 DOI: 10.1089/ten.tea.2011.0366] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Affiliation(s)
- Yuanna Zheng
- School of Stomatology/Hangzhou Dental Hospital, Zhejiang Chinese Medical University, Hangzhou, People's Republic of China
- School/Hospital of Stomatology, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China
- Department of Oral Implantology and Prosthetic Dentistry, Academic Centre for Dentistry Amsterdam (ACTA), Research Institute MOVE, VU University and University of Amsterdam, Amsterdam, The Netherlands
| | - Linhong Wang
- Department of Stomatology, Zhejiang Provincial People's Hospital, Shangtang Road, Hangzhou, People's Republic of China
| | - Xiaodan Zhang
- School/Hospital of Stomatology, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China
| | - Xin Zhang
- School/Hospital of Stomatology, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China
| | - Zhiyuan Gu
- School of Stomatology/Hangzhou Dental Hospital, Zhejiang Chinese Medical University, Hangzhou, People's Republic of China
- School/Hospital of Stomatology, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China
| | - Gang Wu
- Department of Oral Implantology and Prosthetic Dentistry, Academic Centre for Dentistry Amsterdam (ACTA), Research Institute MOVE, VU University and University of Amsterdam, Amsterdam, The Netherlands
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Okamoto M, Murai J, Imai Y, Ikegami D, Kamiya N, Kato S, Mishina Y, Yoshikawa H, Tsumaki N. Conditional deletion of Bmpr1a in differentiated osteoclasts increases osteoblastic bone formation, increasing volume of remodeling bone in mice. J Bone Miner Res 2011; 26:2511-22. [PMID: 21786321 DOI: 10.1002/jbmr.477] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Bone undergoes remodeling consisting of osteoclastic bone resorption followed by osteoblastic bone formation throughout life. Although the effects of bone morphogenetic protein (BMP) signals on osteoblasts have been studied extensively, the function of BMP signals in osteoclasts has not been fully elucidated. To delineate the function of BMP signals in osteoclasts during bone remodeling, we deleted BMP receptor type IA (Bmpr1a) in an osteoclast-specific manner using a knock-in Cre mouse line to the cathepsin K locus (Ctsk(Cre/+);Bmpr1a(flox/flox), designated as Bmpr1a(ΔOc/ΔOc)). Cre was specifically expressed in multinucleated osteoclasts in vivo. Cre-dependent deletion of the Bmpr1a gene occurred at 4 days after cultivation of bone marrow macrophages obtained from Bmpr1a(ΔOc/ΔOc) with RANKL. These results suggested that Bmpr1a was deleted after formation of osteoclasts in Bmpr1a(ΔOc/ΔOc) mice. Expression of bone-resorption markers increased, thus suggesting that BMPRIA signaling negatively regulates osteoclast differentiation. Trabeculae in tibia and femurs were thickened in 3.5-, 8-, and 12-week-old Bmpr1a(ΔOc/ΔOc) mice. Bone histomorphometry revealed increased bone volume associated with increased osteoblastic bone-formation rates (BFR) in the remodeling bone of the secondary spongiosa in Bmpr1a(ΔOc/ΔOc) tibias at 8 weeks of age. For comparison, we also induced an osteoblast-specific deletion of Bmpr1a using Col1a1-Cre. The resulting mice showed increased bone volume with marked decreases in BFR in tibias at 8 weeks of age. These results indicate that deletion of Bmpr1a in differentiated osteoclasts increases osteoblastic bone formation, thus suggesting that BMPR1A signaling in osteoclasts regulates coupling to osteoblasts by reducing bone-formation activity during bone remodeling.
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Affiliation(s)
- Mina Okamoto
- Department of Bone and Cartilage Biology, Osaka University Graduate School of Medicine, Osaka, Japan
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Biomimetic calcium phosphate coatings as bone morphogenetic protein delivery systems in spinal fusion. Spine J 2011; 11:560-7. [PMID: 20097616 DOI: 10.1016/j.spinee.2009.12.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2009] [Revised: 09/10/2009] [Accepted: 12/02/2009] [Indexed: 02/03/2023]
Abstract
BACKGROUND CONTEXT Use of recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to enhance spinal fusion rates. Case reports of soft-tissue swelling, ectopic bone formation, and osteolysis have recently surfaced. It is hypothesized that incorporation of rhBMP-2 within a calcium phosphate (CaP) coating may help to localize delivery and mitigate these complications. PURPOSE To compare the characteristics of posterolateral fusion between rabbits receiving rhBMP-2 delivered via physical adsorption to a collagen sponge or rhBMP-2 incorporated within the physical structure of a CaP coating on a collagen sponge. STUDY DESIGN/SETTING New Zealand white rabbit model of posterolateral lumbar fusion at L5-L6. METHODS Eighteen (18) New Zealand white rabbits underwent posterolateral spinal fusion at L5-L6. Rabbits received bilateral collagen sponges that were either coated with CaP (n=3), coated with CaP and dipped in rhBMP-2 (n=3), coated with a hybrid CaP-rhBMP-2 film (n=6), or coated with a hybrid CaP-rhBMP-2 film and dipped in rhBMP-2 (n=6). Animals were followed weekly with radiographs and were sacrificed at 6 weeks. Fusion masses were further characterized by manual palpation, computed tomography, and histology. RESULTS Radiographic evaluation showed that animals in Group 3 (incorporated BMP) fused at 4 weeks, whereas animals in Group 2 (adsorbed BMP) and Group 4 (incorporated and adsorbed BMP) fused by 6 weeks. Animals that received rhBMP-2 physically adsorbed to the collagen sponge showed extension of the fusion mass beyond the L5-L6 level in 56% of cases and bone resorption in 78%. Histology of fusion masses showed mature bone formation in animals belonging to Groups 2, 3, and 4 and extensive osteoclast recruitment in animals belonging to Groups 2 and 4. CONCLUSIONS Delivery of rhBMP-2 via incorporation within CaP coatings results in increased rates of radiographic fusion. The burst release profile of rhBMP-2 adsorbed to surfaces, although effective in achieving fusion, may result in increased osteoclast recruitment.
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Jensen ED, Pham L, Billington CJ, Espe K, Carlson AE, Westendorf JJ, Petryk A, Gopalakrishnan R, Mansky K. Bone morphogenic protein 2 directly enhances differentiation of murine osteoclast precursors. J Cell Biochem 2010; 109:672-82. [PMID: 20039313 DOI: 10.1002/jcb.22462] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Previous studies found that bone morphogenic proteins (BMPs) support osteoclast formation, but it is not clear whether this is a direct effect on osteoclasts or mediated indirectly through osteoblasts. We have shown that a mouse deficient for the BMP antagonist Twisted gastrulation suggested a direct positive role for BMPs on osteoclastogenesis. In this report, we further determine the significance of BMP signaling on osteoclast formation in vitro. We find that BMP2 synergizes with suboptimal levels of receptor activator of NF-kappaB ligand (RANKL) to enhance in vitro differentiation of osteoclast-like cells. The enhancement by BMP2 is not a result of changes in the rate of proliferation or survival of the bone marrow-derived cultures, but is accompanied by an increase in expression of genes involved in osteoclast differentiation and fusion. Treatment with BMP2 did not significantly alter expression of RANKL or OPG in our osteoclast cultures, suggesting that the enhancement of osteoclastogenesis is not mediated indirectly through osteoblasts or stromal cells. Consistent with this, we detected phosphorylated SMAD1,5,8 (p-SMAD) in the nuclei of mononuclear and multinucleated cells in osteoclast cultures. Levels of p-SMAD, BMP2, and BMP receptors increased during differentiation. RNAi suppression of Type II BMP receptor inhibited RANKL-stimulated formation of multinuclear TRAP-positive cells. The BMP antagonist noggin inhibited RANKL-mediated osteoclast differentiation when added prior to day 3, while addition of noggin on day 3 or later failed to inhibit their differentiation. Taken together, these data indicate that osteoclasts express BMP2 and BMP receptors, and that autocrine BMP signaling directly promotes the differentiation of osteoclasts-like cells.
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Affiliation(s)
- Eric D Jensen
- Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, Minnesota 55455, USA
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Seeherman HJ, Li XJ, Bouxsein ML, Wozney JM. rhBMP-2 induces transient bone resorption followed by bone formation in a nonhuman primate core-defect model. J Bone Joint Surg Am 2010; 92:411-26. [PMID: 20124069 DOI: 10.2106/jbjs.h.01732] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Bone resorption preceding bone formation has been reported following the administration of recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in an absorbable collagen sponge (ACS) in metaphyseal bone. This study characterizes treatment with rhBMP-2/ACS in metaphyseal bone with use of a nonhuman primate core-defect model. METHODS Unilateral proximal femoral core defects were treated with 360 microg of rhBMP-2/ACS or ACS alone or were left untreated in seven, five, and five adult male cynomolgus monkeys, respectively. Distal femoral core defects in seven of the above animals were treated with 360 microg of rhBMP-2/ACS in one limb and ACS alone in the contralateral limb. Retention of rhBMP-2 in the proximal part of the femora was determined with use of tracer amounts of (125)I-rhBMP-2 imaged with a gamma camera. The distal part of the femora was evaluated with in vivo computed tomography. Computed tomography and histological evaluation were performed on harvested segments in all animals at twenty-four weeks. The histological response in the proximal and distal parts of the femora containing core defects treated with 360 microg of rhBMP-2/ACS in one limb and ACS alone in the contralateral limb was evaluated at one, two, and four weeks in three animals per time point. RESULTS Approximately 39.9%, 24.2%, 3.4%, and 0.5% of the rhBMP-2 was retained in the proximal part of the femora at one, seven, fourteen, and twenty-one days, respectively. The mineral density and trabecular volume fraction of the core defects treated with rhBMP-2/ACS, those treated with ACS alone, and untreated core defects in the proximal part of the femora were 81%, 54%, and 20%, respectively, and 94%, 36%, and 31%, respectively, of the corresponding region in the contralateral limbs at twenty-four weeks. The mineral density and trabecular volume fraction of the region surrounding the core defects treated with rhBMP-2/ACS, those treated with ACS alone, and untreated core defects were 112%, 105%, and 104%, respectively, and 117%, 108%, and 107%, respectively, of the corresponding region in the contralateral limbs. Treatment with rhBMP-2/ACS increased the size of the proximal and distal core defects compared with treatment with ACS alone. Histological evaluation of the rhBMP-2/ACS-treated limbs demonstrated that bone resorption was initiated at one week in association with osteoclasts and receptor activator of nuclear factor-kappaB ligand-positive stained spindle-shaped cells and peaked at two weeks. Bone formation was observed at two weeks and was ongoing at twenty-four weeks. CONCLUSIONS Treatment of metaphyseal core defects with rhBMP-2/ACS resulted in bone resorption followed by bone formation in nonhuman primates.
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Affiliation(s)
- Howard J Seeherman
- Musculoskeletal Therapies, Wyeth Discovery Research, Cambridge, MA 02140, USA.
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Schmidmaier G, Wildemann B. The role of BMPs in current orthopedic practice. ACTA ACUST UNITED AC 2009. [DOI: 10.1138/20090386] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Paul S, Lee JC, Yeh LCC. A comparative study on BMP-induced osteoclastogenesis and osteoblastogenesis in primary cultures of adult rat bone marrow cells. Growth Factors 2009; 27:121-31. [PMID: 19180354 DOI: 10.1080/08977190802707324] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Bone remodeling is a process consisting of bone formation and resorption. The present study compared the relative osteoclastic and osteoblastic potency of bone morphogenetic proteins (BMP)-2, -4, -5, -6, and -7 in primary murine bone marrow cultures. All five BMPs stimulated, to varying degree, formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells in a time- and protein concentration-dependent manner. The TRAP staining intensity correlated positively with the number of nuclei per TRAP-positive cell and the mRNA levels of colony-stimulating factor (CSF-1), receptor activator of nuclear factor kappaB ligand (RANKL), TRAP, and cathepsin K. Under osteogenic conditions, all five BMPs stimulated AP activity and mineralized bone nodule formation in a protein concentration-dependent manner in the same primary murine bone marrow cell culture system. These findings should be useful in designing treatment strategies for bone regeneration.
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Affiliation(s)
- Sangita Paul
- Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229-3900, USA
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Short-term osteoclastic activity induced by locally high concentrations of recombinant human bone morphogenetic protein-2 in a cancellous bone environment. Spine (Phila Pa 1976) 2009; 34:539-50. [PMID: 19240666 DOI: 10.1097/brs.0b013e3181952695] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN An experimental study investigating osteoclastic activity induced by rhBMP-2 in sheep. OBJECTIVE To examine the effects of increasing local rhBMP-2 concentration on osteoclastic response and peri-implant bone resorption. SUMMARY OF BACKGROUND DATA Level I clinical studies have established the safe and effective volume and concentration of rhBMP-2 delivered on an absorbable collagen sponge. However, peri-implant bone resorption appearing as decreased mineral density has been observed radiographically in rare instances after implantation of rhBMP-2 on an absorbable collagen sponge (rhBMP-2/ACS). METHODS Bilateral corticocancellous defects were created in the distal femora of 30 adult sheep. Combinations of rhBMP-2/ACS implant volume (V) (1V = normal fill or 2V = overfilled) and rhBMP-2 solution concentration (x) (1x = normal concentration or 3.5x = hyperconcentrated) resulted in local rhBMP-2 concentrations of 0x, 1x, 2x, 3.5x, and 7x the estimated effective concentration for this model. Faxitron radiography, quantitative CT, histology, and quantitative histomorphometry were conducted in a blinded fashion to analyze the effect of the treatments. RESULTS At 1 week, the normal fill-normal concentration implants (1x) produced the least transient osteoclastic activity resulting in limited peri-implant resorption. Overfilled-hyperconcentrated implants (2x, 3.5x) demonstrated moderate resorption zones. Overfilled-hyperconcentrated implants (7x) demonstrated extensive osteoclastic activity and marked resorption. Results at 4 and 8 weeks revealed dense osteoid and bone in the voids with progressive bony healing. Control defects showed no osteoclastic activity with little to no bony healing. CONCLUSION Increasing the local rhBMP-2 concentration by overfilling the defect with rhBMP-2/ACS or hyperconcentrating the rhBMP-2 solution on the absorbable collagen sponge led to a concentration-dependent osteoclastic resorption of peri-implant bone. The osteoclastic effect was transient, and progressive healing took place over the 8-week survival period.
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Greiner S, Kadow-Romacker A, Wildemann B, Schwabe P, Schmidmaier G. Bisphosphonates incorporated in a poly(D,L-lactide) implant coating inhibit osteoclast like cells in vitro. J Biomed Mater Res A 2008; 83:1184-1191. [PMID: 17595027 DOI: 10.1002/jbm.a.31444] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Nitrogen containing bisphosphonates such as zoledronic acid (ZOL) are clinically used to prevent osteoclast induced bone loss. Previous studies indicated that bisphosphonates prevent osteoclast formation, decreases their resorption activity and lead to osteoclast apoptosis. Aim of the study was to investigate the effect of ZOL on fusion and resorption activity of osteoclast like cells (OLC) derived from human peripheral blood mononuclear cells (PBMNC) in vitro. For application of ZOL a local drug delivery system based on a coating for medical devices was used. ZOL was incorporated in the coating based on Poly(D,L-Lactide) (PDLLA) in different concentrations (10-50 microM). Control groups were treated without ZOL or ZOL pure substance in corresponding concentrations. Human PBMNCs were isolated and stimulated to form OLCs. After an experimental period of 144 h, TRAP staining of polynucleated cells was performed and TRAP positive cells were counted. A pit formation assay was performed and resorption lacunas on dentin chips were counted. Results showed a significant dose dependent decrease in the number of TRAP positive cells after exposure to ZOL incorporated in the drug delivery system or applied as pure substance. The amount of resorption lacunas was also dose dependent decreased using both application methods. In conclusion, exposure to specific concentrations of ZOL incorporated in a drug delivery system showed a significant decrease in OLC formation and activity comparable to the effect of pure substance. The effect on osteoclasts might be of clinical benefit to reduce orthopedic implant loosening and to support fracture healing.
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Affiliation(s)
- Stefan Greiner
- Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Germany
| | - Anke Kadow-Romacker
- Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Germany
| | - Britt Wildemann
- Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Germany
| | - Philipp Schwabe
- Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Germany
| | - Gerhard Schmidmaier
- Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Germany
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15
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Wildemann B, Burkhardt N, Luebberstedt M, Vordemvenne T, Schmidmaier G. Proliferating and differentiating effects of three different growth factors on pluripotent mesenchymal cells and osteoblast like cells. J Orthop Surg Res 2007; 2:27. [PMID: 18093345 PMCID: PMC2234398 DOI: 10.1186/1749-799x-2-27] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Accepted: 12/20/2007] [Indexed: 12/03/2022] Open
Abstract
Growth factors are in clinical use to stimulate bone growth and regeneration. BMP-2 is used in long bone and spinal surgery, PDGFbb for the treatment of periodontal defects and children with growth hormone receptor deficiency are treated with IGF-I. Aim of the present study was the comparative analysis of the effect of these growth factors released from a local drug delivery system on cells of the osteogenic lineage at differing differentiation stages. The experiments with the mesenchymal cell line C2C12 revealed a proliferating effect of all three growth factors and a differentiating effect of BMP-2 with a dramatic increase in alkaline phosphatase activity. None of the growth factors stimulated cell migration. Human osteoblast like cells showed similar results with an increase in proliferation after stimulation with IGF-I or PDGFbb. The enzymatic activity of alkaline phosphatase was enhanced only in the cells stimulated with BMP-2. This group showed also more mineralized matrix compared to the other groups. In conclusion, the growth factors IGF-I and PDGFbb delivered with a local drug delivery system stimulated cell proliferation, whereas BMP-2 showed a dramatic effect on differentiation on osteoblast precursor cells and osteoblast like cells.
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Affiliation(s)
- Britt Wildemann
- Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Germany.
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16
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Giannoudis PV, Kanakaris NK, Einhorn TA. Interaction of bone morphogenetic proteins with cells of the osteoclast lineage: review of the existing evidence. Osteoporos Int 2007; 18:1565-81. [PMID: 17694399 DOI: 10.1007/s00198-007-0441-x] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2007] [Accepted: 07/17/2007] [Indexed: 11/25/2022]
Abstract
The present review evaluates the existing scientific proofs of this supplementary role of the BMPs and summarises its clinical implications. Bone regeneration is a process consisting of bone formation and bone resorption, two different but closely coupling pathways, which in most circumstances proceed simultaneously. Plenty of evidence has also characterised the bone morphogenetic proteins (BMPs) as inducing factors of bone formation. However, there is also evidence that these multifunctioning proteins affect bone resorption and the osteoclast homeostasis utilising various pathways. The present review evaluates the existing scientific evidence of this supplementary role of the BMPs, and summarises its clinical implications.
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Affiliation(s)
- P V Giannoudis
- Department of Trauma & Orthopaedics, School of Medicine, University of Leeds, Leeds, UK.
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17
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Abstract
Still a major problem in orthopedic and trauma surgery is the delayed healing or the non-union of long bone fractures. Demographic data reveal that due to the steadily rising age of the population, complications with the musculoskeletal system will increase during the next years. Bone morphogenetic proteins (BMPs) have successfully been applied in clinic for the treatment of delayed healing and non-unions. The broad difference concerning the indication, timing of treatment, dosage and application technique of BMPs calls for the need to perform further prospective studies in order to standardize the treatment and furthermore optimize the procedures or even develop new therapeutic strategies. For example, the application technique may be improved and in some cases injectable BMP preparations could be of use. Also the coating of implants with growth factors might be valuable in order to stimulate bone healing and to prevent delayed healing or non-union. This article tries to discuss some of the open questions, however can and will not reflect the absolute standard of care. To make the BMP treatment a standard of care, more clinical data and long time experiences are necessary. The intramedullary application of BMP in combination with autologous or allogenic bone grafts or bone substitutes after debridement and stabilization with implants seems to be an adequate procedure for treatment of atrophic non-unions. However, the total number of patients is too small to draw final conclusions. Further clinical studies need to be performed in the future.
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18
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Gardner CR. Comparison of morphological effects of PGE2 and TGFbeta on osteoclastogenesis induced by RANKL in mouse bone marrow cell cultures. Cell Tissue Res 2007; 330:111-21. [PMID: 17694327 DOI: 10.1007/s00441-007-0450-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2007] [Accepted: 06/20/2007] [Indexed: 11/28/2022]
Abstract
RANKL, in the presence of M-CSF, induces the development and fusion of TRAP+ osteoclasts in mouse bone marrow cultures at 3-5 days. Early during culture (day 3), most cells are small (up to six nuclei). At lower cell densities, these osteoclasts exhibit a rounded morphology with cytoplasm extending around the cells but, at higher densities, this changes to a stellate morphology with the cytoplasm being retracted around the nuclei with numerous localised cytoplasmic extensions. Under optimal conditions, osteoclast fusion results in conglomerates of many cells, which become large cytoplasmic masses on day 4. PGE2 and TGFbeta have both been shown to increase osteoclast development in this model and their effects on the morphology of osteoclasts during fusion and differentiation have been compared under all these conditions. PGE2 or TGFbeta increase osteoclast numbers and size and also the number of nuclei, indicating increased osteoclast development and fusion. TGFbeta increases the size of rounded osteoclasts (with respect to the number of nuclei) more than PGE2, suggesting that TGFbeta increases cytoplasmic extension. TGFbeta increases the size and number of nuclei in stellate cells but particularly increases the number and length of the cytoplasmic extensions, in contrast to PGE2. Fusion of these extensions with other osteoclasts results in large networks of interconnected cells. On day 4, spreading cells develop but these are still interconnected by cytoplasmic links, a phenomenon not seen in control wells or after treatment with PGE2. TGFbeta is more effective than PGE2 in increasing fusion in the formation of cell conglomerates and cytoplasmic masses. PGE2 decreases overall cell density resulting in additional indirect effects on osteoclast numbers and morphology. However, PGE2 particularly promotes the formation of large mature spreading osteoclasts later during culture.
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Affiliation(s)
- Colin R Gardner
- Groupe de Recherche MERCI, Faculty of Medicine and Pharmacy, EA2122 Laboratoire DIFEMA, 7600, Rouen, France.
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19
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Yamaji K, Kawanami M, Matsumoto A, Odajima T, Nishitani Y, Iwasaka K, Yoshimitsu K, Yoshiyama M. Effects of Dose of Recombinant Human BMP-2 on Bone Formation at Palatal Sites in Young and Old Rats. Dent Mater J 2007; 26:481-6. [PMID: 17886450 DOI: 10.4012/dmj.26.481] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
This study was designed to examine the effects of dose of recombinant human BMP-2 (rhBMP-2) on bone formation at palatal sites in 10-week-old (10w) and 70-week-old (70w) rats, when combined with a polylactate-polyglycolate copolymer/gelatine sponge (PGS). New bone formation was observed at six weeks after implantation. In the 10w rats, thickness of new bone (TNB) increased as the dosage increased from 0 microg to 4 microg, and decreased significantly as the dosage increased from 8 microg to 24 microg. In contrast, in the 70w rats, TNB increased as the dosage increased from 0 microg to 16 microg, and did not significantly change as the dosage increased from 16 microg to 24 microg. These results suggest that the most effective dosage of rhBMP-2 for induction of bone formation varies according to age.
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Affiliation(s)
- Kozo Yamaji
- Department of Operative Dentistry, Field of Study of Biofunctional Recovery and Reconstruction, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1, Shikata-cho, Okayama 700-8525, Japan.
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20
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RHBMP-2 DELIVERED IN A CALCIUM PHOSPHATE CEMENT ACCELERATES BRIDGING OF CRITICAL-SIZED DEFECTS IN RABBIT RADII. J Bone Joint Surg Am 2006. [DOI: 10.2106/00004623-200607000-00017] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 04/05/2023]
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21
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Seeherman HJ, Azari K, Bidic S, Rogers L, Li XJ, Hollinger JO, Wozney JM. rhBMP-2 delivered in a calcium phosphate cement accelerates bridging of critical-sized defects in rabbit radii. J Bone Joint Surg Am 2006; 88:1553-65. [PMID: 16818982 DOI: 10.2106/jbjs.e.01006] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Treatment of segmental bone loss remains a challenge in skeletal repairs. This study was performed to evaluate the efficacy of the use of recombinant bone morphogenetic protein-2 (rhBMP-2) delivered in an injectable calcium phosphate cement (alpha bone substitute material [alpha-BSM]) to bridge critical-sized defects in the rabbit radius. METHODS Unilateral 20-mm mid-diaphyseal defects were created in the radii of thirty-six skeletally mature New Zealand White rabbits. The defects in twelve rabbits each were filled with 0.166 mg/mL rhBMP-2/alpha-BSM cement, 0.033 mg/mL rhBMP-2/alpha-BSM cement, or buffer/alpha-BSM cement. Six rabbits from each group were killed at four weeks, and six were killed at eight weeks. Serial radiographs were made to monitor defect-bridging and residual alpha-BSM carrier. A semiquantitative histological scoring system was used to evaluate defect-bridging. Histomorphometry was used to quantify residual alpha-BSM; trabecular bone area; trabecular bone volume fraction; and cortical length, width, and area. RESULTS At four weeks, there had been more rapid resorption of alpha-BSM and filling of the defects with trabecular bone in the group treated with 0.166 mg/mL rhBMP-2/alpha-BSM than in the other two groups. Histomorphometry confirmed an increased trabecular area and volume fraction in this group compared with the other two groups. In both rhBMP-2/alpha-BSM-treated groups, the majority of the trabecular bone was formed by a direct process adjacent to the resorbing alpha-BSM. At eight weeks, complete cortical bridging and regeneration of the marrow space were present in all of the defects treated with 0.166 mg/mL rhBMP-2/alpha-BSM. That group also had reduced residual alpha-BSM and trabecular area and volume, compared with the other two groups, at eight weeks as a result of a rapid remodeling process. CONCLUSIONS Treatment of a critical-sized defect in a rabbit radius with 0.166 mg/mL rhBMP-2/alpha-BSM injectable cement can result in bridging with cortical bone and a regenerated bone-marrow space by eight weeks. Site-specific remodeling appears to be responsible for corticalization and marrow regeneration. CLINICAL RELEVANCE RhBMP-2 delivered in a calcium phosphate cement may be useful to achieve bridging of critical-sized defects in patients. Its injectable properties may allow minimally invasive use. Delayed percutaneous administration would also be possible when augmentation is desired following an initial surgical procedure or when soft-tissue injuries preclude adequate initial treatment.
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Affiliation(s)
- Howard J Seeherman
- Department of Surgery, School of Medicine, Oregon Health Sciences University, Portland, Oregon, USA.
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22
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Boyan BD, Ranly DM, Schwartz Z. Use of growth factors to modify osteoinductivity of demineralized bone allografts: lessons for tissue engineering of bone. Dent Clin North Am 2006; 50:217-28, viii. [PMID: 16530059 DOI: 10.1016/j.cden.2005.11.007] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Biologically active bone graft substitute materials are needed for repair and regeneration of skeletal tissues. Current approaches are focused on the use of osteoinductive agents, including bone morphogenetic proteins (BMP) in combination with biodegradable carriers. Demineralized freeze-dried bone allograft (DFDBA) can provide an osteoconductive surface and, at the same time, function as a time-release carrier for BMP. Donor variability, however, limits the predictability of DFDBA as an osteoinductive material. This article examines the use of growth factors, including platelet-rich plasma, platelet-derived growth factor, enamel matrix derivatives, and BMP-2, to enhance the osteoinductive properties of human DFDBA.
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Affiliation(s)
- Barbara D Boyan
- Georgia Institute of Technology, Atlanta, GA 30332-0363, USA.
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23
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Graziani F, Ivanovski S, Cei S, Ducci F, Tonetti M, Gabriele M. The in vitro effect of different PRP concentrations on osteoblasts and fibroblasts. Clin Oral Implants Res 2006; 17:212-9. [PMID: 16584418 DOI: 10.1111/j.1600-0501.2005.01203.x] [Citation(s) in RCA: 343] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVES The aim of this study was to assess the biological rationale for the use of platelet-rich plasma (PRP) by evaluating the effect of different concentrations of PRP on osteoblasts (OB) and fibroblasts (FB) function in vitro. MATERIAL AND METHODS PRP was obtained from volunteer donors using standard protocols. Primary human cultures of oral FBs and OBs were exposed to both activated and non-activated plasma as well as various concentrations of PRP (2.5 x, 3.5 x and max (4.2-5.5 x)). Cell proliferation was evaluated after 24 and 72 h using an MTT proliferation assay. Production of osteocalcin (OCN), osteoprotegerin (OPG) and transforming growth factor beta1 (TGF-beta1) was evaluated in OB after 24 and 72 h. Statistical analysis was performed using one-way ANOVA. RESULTS PRP-stimulated cell proliferation in both OBs and FBs. The effect of different PRP concentrations on cell proliferation was most notable at 72 h. The maximum effect was achieved with a concentration of 2.5 x, with higher concentrations resulting in a reduction of cell proliferation. Upregulation of OCN levels and downregulation of OPG levels were noted with increasing PRP concentrations at both 24 and 72 h. TGF-beta1 levels were stimulated by increasing concentrations of PRP, with the increased levels being maintained at 72 h. CONCLUSIONS PRP preparations exert a dose-specific effect on oral FBs and OBs. Optimal results were observed at a platelet concentration of 2.5 x, which was approximately half of the maximal concentrate that could be obtained. Increased concentrations resulted in a reduction in proliferation and a suboptimal effect on OB function. Hence, different PRP concentrations may have an impact on the results that can be obtained in vivo.
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Affiliation(s)
- Filippo Graziani
- Department of Neurosciences, Section of Oral Surgery, University of Pisa, Pisa, Italy.
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24
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Fox SW, Lovibond AC. Current insights into the role of transforming growth factor-beta in bone resorption. Mol Cell Endocrinol 2005; 243:19-26. [PMID: 16219413 DOI: 10.1016/j.mce.2005.09.008] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 09/05/2005] [Indexed: 01/25/2023]
Abstract
Transforming growth factor-beta (TGF-beta) elicits a variety of effects on cellular proliferation and differentiation. The major repository for TGF-beta is bone, where it possesses separate facilitative and suppressive actions on osteoclast differentiation and bone resorption. Without a direct enabling stimulus from TGF-beta monocytes cannot form osteoclasts but instead follow macrophage differentiation pathways. This facilitative action depends on an ability to promote a state in which precursors are resistant to anti-osteoclastic inflammatory signals. Following the initiation of resorption TGF-beta is released from bone matrix. This acts on osteoblasts to reduce the availability of the osteoclast differentiation factor, RANKL (receptor activator of NFkappaB ligand) and thereby indirectly limits further osteoclast formation. Thus TGF-beta has a fundamental role in the control of bone resorption having actions that first allow monocytes to develop into osteoclasts then subsequently limiting the extent and duration of resorption after its release from the bone matrix.
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Affiliation(s)
- Simon W Fox
- Ecotoxicology and Stress Biology Research Group, Room A413 Portland Square, School of Biological Science, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK.
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