Pulse application of platelet-derived growth factor enhances formation of a mineralizing matrix while continuous application is inhibitory

Platelet-derived growth factor-BB regenerates functional periodontal ligament in the tooth replantation

Tooth ankylosis is a pathological condition of periodontal ligament (PDL) restoration after tooth replantation. Platelet-derived growth factor-BB (PDGF-BB) has been proposed as a promising factor for preventing tooth ankylosis. Using rat tooth replantation model, we investigated whether PDGF-BB accelerates the repair of PDL after tooth replantation without ankylosis, and its molecular mechanisms. In PDGF-BB pretreated replanted teeth (PDGF-BB group), ankylosis was markedly reduced and functionally organized PDL collagen fibers were restored; the mechanical strength of the healing PDL was restored to an average of 76% of that in non-replanted normal teeth at 21 days. The numbers of PDGF-Rβ- and BrdU-positive cells in the periodontal tissues of the PDGF-BB group were greater than those of atelocollagen pretreated replanted teeth (AC group). Moreover, in the PDGF-BB group, the periodontal tissues had fewer osteocalcin-positive cells and decreased number of nuclear β-catenin-positive cells compared to those in the AC group. In vitro analyses showed that PDGF-BB increased the proliferation and migration of human periodontal fibroblasts. PDGF-BB downregulated mRNA expressions of RUNX2 and ALP, and inhibited upregulatory effects of Wnt3a on β-catenin, AXIN2, RUNX2, COL1A1, and ALP mRNA expressions. These findings indicate that in tooth replantation, topical PDGF-BB treatment enhances cell proliferation and migration, and inhibits canonical Wnt signaling activation in bone-tooth ankylosis, leading to occlusal loading of the PDL tissues and subsequent functional restoration of the healing PDL. This suggests a possible clinical application of PDGF-BB to reduce ankylosis after tooth replantation and promote proper regeneration of PDL.

Comparison of Bone Formation After Sinus Membrane Lifting Without Graft or Using Bone Substitute "Histologic and Radiographic Evaluation"

PURPOSE

Sinus floor elevation without using autogenous bone graft or bone substitute will eliminate donor site morbidity and reduce the cost and the risk of infection. We evaluated the bone gain after sinus membrane elevation without graft or using bone substitute in the same maxilla. Dental implants were inserted simultaneously as a 1-stage procedure.

PATIENTS AND METHODS

In a split-mouth design, we conducted a randomized double-blinded clinical trial performing sinus lifts and simultaneous implant insertion in 10 healthy patients (n = 20). On the 1 site, we performed graft-less sinus lift (group 1) and on the other site Cerabone was used as bone substitute (group 2), respectively. The quantity and quality of bone gained in each sinus were evaluated and compared radiologically and histomorphometrically.

RESULTS

After 6 months, the average gain of bone height was 6.21 and 9.58 mm in group 1 and 2, respectively, as measured radiologically (P < .001, P < .001). Histomorphometric examination showed significantly higher thickness of trabeculae and bone formation in group 1 (P = .003 and P = .002). However, the neovascularization was higher, but not significantly (P = .288).

CONCLUSIONS

Radiological bone gain was similar in both groups. However, histomorphometric examination showed superior bone formation in graft-less group as compared to the Cerabone group. The blood clot seems to be an adequate filler and excellent medium for bone formation. More studies in split-mouth design are needed to compare different bone substitutes.

Local controlled release of simvastatin and PDGF from core/shell microspheres promotes bone regeneration in vivo

Simvastatin is demonstrated to be a potent stimulator for bone formation.

Gene Therapy for Bone Defects in Oral and Maxillofacial Surgery: A Systematic Review and Meta-Analysis of Animal Studies

Craniofacial bone defects are challenging problems for maxillofacial surgeons over the years. With the development of cell and molecular biology, gene therapy is a breaking new technology with the aim of regenerating tissues by acting as a delivery system for therapeutic genes in the craniofacial region rather than treating genetic disorders. A systematic review was conducted summarizing the articles reporting gene therapy in maxillofacial surgery to answer the question: Was gene therapy successfully applied to regenerate bone in the maxillofacial region? Electronic searching of online databases was performed in addition to hand searching of the references of included articles. No language or time restrictions were enforced. Meta-analysis was done to assess significant bone formation after delivery of gene material in the surgically induced maxillofacial defects. The search identified 2081 articles, of which 57 were included with 1726 animals. Bone morphogenetic proteins were commonly used proteins for gene therapy. Viral vectors were the universally used vectors. Sprague-Dawley rats were the frequently used animal model in experimental studies. The quality of the articles ranged from excellent to average. Meta-analysis results performed on 21 articles showed that defects favored bone formation by gene therapy. Funnel plot showed symmetry with the absence of publication bias. Gene therapy is on the top list of innovative strategies that developed in the last 10 years with the hope of developing a simple chair-side protocol in the near future, combining improvement of gene delivery as well as knowledge of the molecular basis of oral and maxillofacial structures.

Effect of sustained PDGF nonviral gene delivery on repair of tooth-supporting bone defects

Recombinant human platelet-derived growth factor-BB (rhPDGF-BB) promotes soft tissue and bone healing, and is Food and Drug Administration-approved for treatment of diabetic ulcers and periodontal defects. The short half-life of topical rhPDGF-BB protein application necessitates bolus, high-dose delivery. Gene therapy enables sustained local growth factor production. A novel gene activated matrix delivering polyplexes of polyethylenimine (PEI)-plasmid DNA encoding PDGF was evaluated for promotion of periodontal wound repair in vivo. PEI-pPDGF-B polyplexes were tested in human periodontal ligament fibroblasts and human gingival fibroblasts for cell viability and transfection efficiency. Collagen scaffolds containing PEI-pPDGF-B polyplexes at two doses, rhPDGF-BB, PEI vector or collagen alone were randomly delivered to experimentally induced tooth-supporting periodontal defects in a rodent model. Mandibulae were collected at 21 days for histologic observation and histomorphometry. PEI-pPDGF-B polyplexes were biocompatible to cells tested and enzyme-linked immunosorbent assay confirmed the functionality of transfection. Significantly greater osteogenesis was observed for collagen alone and rhPDGF-BB versus the PEI-containing groups. Defects treated with sustained PDGF gene delivery demonstrated delayed healing coupled with sustained inflammatory cell infiltrates lateral to the osseous defects. Continuous PDGF-BB production by nonviral gene therapy could have delayed bone healing. This nonviral gene delivery system in this model appeared to prolong inflammatory response, slowing alveolar bone regeneration in vivo.

Influence of platelet-derived growth factor on osseous remodeling properties of a variable-thread tapered dental implant in vivo

OBJECTIVES

To evaluate the effect of platelet-derived growth factor (rhPDGF-BB) on the promotion of osteogenesis around variable-thread tapered implants in an animal model.

MATERIAL AND METHODS

Twenty-four variable-thread tapered implants were inserted in the tibia of 12 rabbits. Twelve sites received additional rhPDGF-BB released from a presoaked xenogenic bone block that was fixed supracrestally. Primary outcomes were bone-to-implant contact (BIC; in % ± SD) and percentage of medullary bone fill around the implants (PMF; in % ± SD) after 3 weeks (PDGF n = 6, no PDGF n = 6) and 6 weeks (PDGF n = 6, no PDGF n = 6).

RESULTS

Considerable crestal and medullary bone remodeling could be found around all implants. After 3 weeks, both BIC and PMF values were higher in the no PDGF group (BIC: 63% ± 10 with PDGF vs. 85% ± 5 with no PDGF; PMF: 57% ± 10 with PDGF vs. 74% ± 4 with no PDGF). After 6 weeks, the BIC difference between the two groups was less distinct (BIC: 78% ± 17 with PDGF vs. 72% ± 25 with no PDGF), whereas the PDGF group showed higher PMF values (PMF: 77% ± 5 with PDGF vs. 56% ± 10 with no PDGF).

CONCLUSIONS

The addition of rhPDGF-BB decreases early osseous crestal and medullar healing properties around dental implants. In a later phase, an increase in the cortical area as well as an increased medullar bone formation was seen. This response is likely to provide stronger secondary stability and stability in suboptimal situations involving poor-quality bone.

Effects of platelet-poor plasma, platelet-rich plasma, and platelet-rich fibrin on healing of extraction sockets with buccal dehiscence in dogs

Alveolar bone resorption generally occurs during healing after tooth extraction. This study aimed to evaluate the effects of platelet-poor plasma (PPP), platelet-rich plasma (PRP), and platelet-rich fibrin (PRF) on healing in a ridge-augmentation model of the canine socket with dehiscence of the buccal wall. The third mandibular premolars of 12 beagle dogs were extracted and a 3 mm buccal dehiscence from the alveolar crest to the buccal wall of the extraction socket was created. These sockets were then divided into four groups on the basis of the material used to fill the sockets: PPP, PRP, PRF, and control (no graft material) groups. Results were evaluated at 4 and 8 weeks after surgery. The ultrastructural morphology and constructs of each blood product were studied by a scanning electron microscope (SEM) or calculating concentrations of platelets, fibrinogen, platelet-derived growth factor, and transforming growth factor-β. A total of five microcomputed tomography images of specimens were selected for measurement, and the area occupied by the newly formed bone as well as the horizontal bone width were measured. Moreover, decalcified tissue specimens from each defect were analyzed histologically. The median area of new bone at 4 and 8 weeks and median horizontal bone width at 8 weeks were the highest in the PPP group. However, bone maturation in the PRF and the PRP groups was more progressed than that in the PPP and control groups. By SEM findings, the PRF group showed a more highly condensed fibrin fiber network that was regularly arranged when compared with the PPP and PRP groups. The growth factors released from platelets in PRP indicated higher concentrations than that in PRF. Under more severe conditions for bone formation, as in this experiment, the growth factors released from platelets had a negative effect on bone formation. This study showed that PPP is an effective material for the preservation of sockets with buccal dehiscence.

Sequential platelet-derived growth factor-simvastatin release promotes dentoalveolar regeneration

OBJECTIVES

Timely augmentation of the physiological events of dentoalveolar repair is a prerequisite for the optimization of the outcome of regeneration. This study aimed to develop a treatment strategy to promote dentoalveolar regeneration by the combined delivery of the early mitogenic factor platelet-derived growth factor (PDGF) and the late osteogenic differentiation factor simvastatin.

MATERIALS AND METHODS

By using the coaxial electrohydrodynamic atomization technique, PDGF and simvastatin were encapsulated in a double-walled poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) (PDLLA-PLGA) microspheres in five different modes: microspheres encapsulating bovine serum albumin (BB), PDGF alone (XP), simvastatin alone (SB), PDGF-in-core and simvastatin-in-shell (PS), and simvastatin-in-core and PDGF-in-shell (SP). The microspheres were characterized using scanning electronic microscopy, and the in vitro release profile was evaluated. Microspheres were delivered to fill large osteotomy sites on rat maxillae for 14 and 28 days, and the outcome of regeneration was evaluated by microcomputed tomography and histological assessments.

RESULTS

Uniform 20-μm controlled release microspheres were successfully fabricated. Parallel PDGF-simvastatin release was noted in the PS group, and the fast release of PDGF followed by the slow release of simvastatin was noted in the SP group. The promotion of osteogenesis was observed in XP, PS, and SP groups at day 14, whereas the SP group demonstrated the greatest bone fill, trabecular numbers, and thickest trabeculae. Bone bridging was evident in the PS and SP group, with significantly increased osteoblasts in the SP group, and osteoclastic cell recruitment was promoted in all bioactive molecule-treated groups. At day 28, osteogenesis was promoted in all bioactive molecule-treated groups. Initial corticalization was noted in the XP, PS, and SP groups. Osteoblasts appeared to be decreased in all groups, and significantly, a greater osteoclastic cell recruitment was noted in the SB and SP groups.

CONCLUSIONS

Both PDGF and simvastatin facilitate dentoalveolar regeneration, and sequential PDGF-simvastatin release (SP group) further accelerated the regeneration process through the enhancement of osteoblastogenesis and the promotion of bone maturation.

Dual delivery of rhPDGF-BB and bone marrow mesenchymal stromal cells expressing the BMP2 gene enhance bone formation in a critical-sized defect model

Bone tissue healing is a dynamic, orchestrated process that relies on multiple growth factors and cell types. Platelet-derived growth factor-BB (PDGF-BB) is released from platelets at wound sites and induces cellular migration and proliferation necessary for bone regeneration in the early healing process. Bone morphogenetic protein-2 (BMP-2), the most potent osteogenic differentiation inducer, directs new bone formation at the sites of bone defects. This study evaluated a combinatorial treatment protocol of PDGF-BB and BMP-2 on bone healing in a critical-sized defect model. To mimic the bone tissue healing process, a dual delivery approach was designed to deliver the rhPDGF-BB protein transiently during the early healing phase, whereas BMP-2 was supplied by rat bone marrow stromal cells (BMSCs) transfected with an adenoviral vector containing the BMP2 gene (AdBMP2) for prolonged release throughout the healing process. In in vitro experiments, the dual delivery of rhPDGF-BB and BMP2 significantly enhanced cell proliferation. However, the osteogenic differentiation of BMSCs was significantly suppressed even though the amount of BMP-2 secreted by the AdBMP2-transfected BMSCs was not significantly affected by the rhPDGF-BB treatment. In addition, dual delivery inhibited the mRNA expression of BMP receptor type II and Noggin in BMSCs. In in vivo experiments, critical-sized calvarial defects in rats showed enhanced bone regeneration by dual delivery of autologous AdBMP2-transfected BMSCs and rhPDGF-BB in both the amount of new bone formed and the bone mineral density. These enhancements in bone regeneration were greater than those observed in the group treated with AdBMP2-transfected BMSCs alone. In conclusion, the dual delivery of rhPDGF-BB and AdBMP2-transfected BMSCs improved the quality of the regenerated bone, possibly due to the modulation of PDGF-BB on BMP-2-induced osteogenesis.

Cellular re- and de-programming by microenvironmental memory: why short TGF-β1 pulses can have long effects

Background

Fibrosis poses a substantial setback in regenerative medicine. Histopathologically, fibrosis is an excessive accumulation of collagen affected by myofibroblasts and this can occur in any tissue that is exposed to chronic injury or insult. Transforming growth factor (TGF)-β1, a crucial mediator of fibrosis, drives differentiation of fibroblasts into myofibroblasts. These cells exhibit α-smooth muscle actin (α-SMA) and synthesize high amounts of collagen I, the major extracellular matrix (ECM) component of fibrosis. While hormones stimulate cells in a pulsatile manner, little is known about cellular response kinetics upon growth factor impact. We therefore studied the effects of short TGF-β1 pulses in terms of the induction and maintenance of the myofibroblast phenotype.

Results

Twenty-four hours after a single 30 min TGF-β1 pulse, transcription of fibrogenic genes was upregulated, but subsided 7 days later. In parallel, collagen I secretion rate and α-SMA presence were elevated for 7 days. A second pulse 24 h later extended the duration of effects to 14 days. We could not establish epigenetic changes on fibrogenic target genes to explain the long-lasting effects. However, ECM deposited under singly pulsed TGF-β1 was able to induce myofibroblast features in previously untreated fibroblasts. Dependent on the age of the ECM (1 day versus 7 days’ formation time), this property was diminished. Vice versa, myofibroblasts were cultured on fibroblast ECM and cells observed to express reduced (in comparison with myofibroblasts) levels of collagen I.

Conclusions

We demonstrated that short TGF-β1 pulses can exert long-lasting effects on fibroblasts by changing their microenvironment, thus leaving an imprint and creating a reciprocal feed-back loop. Therefore, the ECM might act as mid-term memory for pathobiochemical events. We would expect this microenvironmental memory to be dependent on matrix turnover and, as such, to be erasable. Our findings contribute to the current understanding of fibroblast induction and maintenance, and have bearing on the development of antifibrotic drugs.

PDGF-Simvastatin Delivery Stimulates Osteogenesis in Heat-induced Osteonecrosis

Heat generated during implant osteotomy might lead to osteonecrosis and delayed bone repair, thus resulting in impaired early osseointegration and fixation of bone-anchoring devices. In this study, we proposed to overcome heat-induced injury to bone by fabricating core-shell polymeric biodegradable microspheres encapsulating a mitogenic factor, platelet-derived growth factor (PDGF), and a differentiation factor, simvastatin, in a simultaneous or sequential release profile. Microspheres encapsulating bovine serum albumin (BSA), PDGF, simvastatin, PDGF-in-core with simvastatin-in-shell, and simvastatin-in-core with PDGF-in-shell were delivered to fill standardized osteotomy sites on edentulous ridges of rat maxillae under irrigated or non-irrigated conditions. In the absence of irrigation, significant reduction of cell viability and increase in inflammation and sequestrum formation without evidence of osteogenesis were observed. Both PDGF and simvastatin deliveries facilitated cell viability and reduced osteonecrosis. Localized osteogenesis was seen under simvastatin treatment, while generalized but primitive osteogenesis was noted in PDGF-treated osteotomy sites. In addition, sequential PDGF-simvastatin delivery further augmented osteogenesis and promoted bone maturation. The results suggested that sequential PDGF-simvastatin delivery was an effective modality to prevent heat-induced complications and facilitate bone apposition after implant osteotomy, potentially favoring the early fixation of bone-anchoring devices and oral implant osseointegration.

A comparative study of root defect coverage using an acellular dermal matrix with and without a recombinant human platelet-derived growth factor

BACKGROUND

The objective of this case series is to compare root defect coverage results and healing responses of bilateral recession defects treated with acellular dermal matrix (ADM) with and without recombinant human platelet-derived growth factor (rhPDGF).

METHODS

Seventeen patients with 40 bilateral gingival recession defects were compared. Each defect was ≥2 mm and treated with ADM and a coronally advanced flap. Using split-mouth design, the control-side ADM was hydrated in sterile saline, whereas the test-side ADM was hydrated in rhPDGF. The patients were evaluated at 1 week, 1 month, 3 months, and 6 months. Standardized measurements were taken preoperatively at 3 and 6 months. Healing was clinically assessed at 1 week and 1 month post-surgically.

RESULTS

Both test and control groups showed significant gain in root defect coverage over the 6-month period for all individuals, with the test group showing a 69.0% gain and the control group showing a 76.7% gain. Patients divided into Miller Class I and Class III defects were also found to have a significant gain in root defect coverage over 6 months. The test group showed 84.1% gain, and the control group showed 84.7% gain for Miller Class I defects. For Miller Class III defects, the test group showed 51.5% gain, and the control group showed a 60.8% gain. One week after surgery, 35% of the test group showed better healing, whereas 15% of the control group showed better healing. One month after surgery, 20% of the test group showed better healing, whereas 15% of the control group showed better healing.

CONCLUSION

Based on the results of this case series, there were no statistically or clinically significant differences in root defect coverage, keratinized tissue, clinical attachment level, or clinical healing for treatment of root recession with a coronally advanced flap and ADM with and without rhPDGF.

Exploitation of a novel polysaccharide nanogel cross-linking membrane for guided bone regeneration (GBR)

Cholesterol-bearing pullulan (CHP) nanogel is a synthetic degradable biomaterial for drug delivery with high biocompatibility. Guided bone regeneration (GBR) is a bone augmentation technique in which a membrane is used to create and keep a secluded regenerative space. The purpose of the present study was to evaluate the effects of the novel CHP nanogel membrane in GBR. Thirty-six adult Wistar rats were used and bilaterally symmetrical full-thickness parietal bone defects of 5 mm diameter were created with a bone trephine burr. Each defect was covered with the collagen membrane or the CHP nanogel membrane or untreated without any membrane. The animals were sacrificed at 2, 4 and 8 weeks and analysed radiologically and histologically. Furthermore, after incubating human serum with CHP nanogel or collagen, the amount of PDGF in the serum was measured using ELISA. New bone formation in terms of bone volume was higher in the nanogel group than in the control or collagen groups at 2 and 4 weeks. At 8 weeks, both membrane groups showed higher bone volumes than the control group. Notably, the newly-formed bone in the bone defect in the nanogel group was uniform and histologically indistinguishable from the original bone, whereas in the collagen group the new bone showed an irregular structure that was completely different from the original bone. After incubating with CHP nanogel, the amount of PDGF in the serum decreased significantly. CHP nanogel GBR membrane favourably stimulated bone regeneration, in which a unique characteristic of CHP nanogel, the storage of endogenous growth factors, was likely implicated.

Reduction of bone resorption by the application of platelet-rich plasma (PRP) in bone grafting of the alveolar cleft

OBJECTIVE

We evaluated the effectiveness of platelet-rich plasma (PRP) on the regeneration of autogenous cancellous bone and marrow grafted in the alveolar cleft.

DESIGN

Twenty patients with alveolar clefts were examined; 6 were the control group and received cancellous bone and marrow grafts without PRP, while the remaining 14 comprised the PRP group and received grafts with PRP. Prior to surgery, 50 ml of blood was withdrawn and 5 ml of PRP gel produced through centrifugal separation. The bone graft mixed with PRP was then packed into the alveolar cleft. Postoperative bone density was assessed as the aluminium-equivalent value on occlusal X-ray films in a qualitative analysis. Quantitative evaluation of regenerated bone was made with computed tomography and panoramic radiographs at 1 month, 6 months and 1 year after surgery.

RESULTS

Satisfactory bone bridging formation was observed in all patients without any complications. The bone density of the PRP group was lower than that of the control group at 1 week, but the same after 1 month. The added PRP reduced the resorption of regenerated bone postoperatively.

CONCLUSION

Autogenous cancellous bone grafting with PRP, which significantly reduces postoperative bone resorption, is a reliable technique for alveolar bone grafting of cleft patients.

Evaluation of functional dynamics during osseointegration and regeneration associated with oral implants

OBJECTIVES

The aim of this paper is to review current investigations on functional assessments of osseointegration and assess correlations to the peri-implant structure.

MATERIAL AND METHODS

The literature was electronically searched for studies of promoting dental implant osseointegration, functional assessments of implant stability, and finite element (FE) analyses in the field of implant dentistry, and any references regarding biological events during osseointegration were also cited as background information.

RESULTS

Osseointegration involves a cascade of protein and cell apposition, vascular invasion, de novo bone formation and maturation to achieve the primary and secondary dental implant stability. This process may be accelerated by alteration of the implant surface roughness, developing a biomimetric interface, or local delivery of growth-promoting factors. The current available pre-clinical and clinical biomechanical assessments demonstrated a variety of correlations to the peri-implant structural parameters, and functionally integrated peri-implant structure through FE optimization can offer strong correlation to the interfacial biomechanics.

CONCLUSIONS

The progression of osseointegration may be accelerated by alteration of the implant interface as well as growth factor applications, and functional integration of peri-implant structure may be feasible to predict the implant function during osseointegration. More research in this field is still needed.

Lysyl oxidase propeptide inhibits FGF-2-induced signaling and proliferation of osteoblasts

Pro-lysyl oxidase is secreted as a 50-kDa proenzyme and is then cleaved to a 30-kDa mature enzyme (lysyl oxidase (LOX)) and an 18-kDa propeptide (lysyl oxidase propeptide (LOX-PP)). The presence of LOX-PP in the cell layers of phenotypically normal osteoblast cultures led us to investigate the effects of LOX-PP on osteoblast differentiation. Data indicate that LOX-PP inhibits terminal mineralization in primary calvaria osteoblast cultures when added at early stages of differentiation, with no effects seen when present at later stages. LOX-PP was found to inhibit serum- and FGF-2-stimulated DNA synthesis and FGF-2-stimulated cell growth. Enzyme-linked immunosorbent assay and Western blot analyses show that LOX-PP inhibits FGF-2-induced ERK1/2 phosphorylation, signaling events that mediate the FGF-2-induced proliferative response. LOX-PP inhibits FGF-2-stimulated phosphorylation of FRS2alpha and FGF-2-stimulated DNA synthesis, even after inhibition of sulfation of heparan sulfate proteoglycans. These data point to a LOX-PP target at or near the level of fibroblast growth factor receptor binding or activation. Ligand binding assays on osteoblast cell layers with (125)I-FGF-2 demonstrate a concentration-dependent inhibition of FGF-2 binding to osteoblasts by LOX-PP. In vitro binding assays with recombinant fibroblast growth factor receptor protein revealed that LOX-PP inhibits FGF-2 binding in an uncompetitive manner. We propose a working model for the respective roles of LOX enzyme and LOX-PP in osteoblast phenotype development in which LOX-PP may act to inhibit the proliferative response possibly to allow cells to exit from the cell cycle and progress to the next stages of differentiation.

PDGF-B gene therapy accelerates bone engineering and oral implant osseointegration

Platelet-derived growth factor-BB (PDGF-BB) stimulates repair of healing-impaired chronic wounds such as diabetic ulcers and periodontal lesions. However, limitations in predictability of tissue regeneration occur due in part to transient growth factor bioavailability in vivo. Here, we report that gene delivery of PDGF-B stimulates repair of oral implant extraction socket defects. Alveolar ridge defects were created in rats and were treated at the time of titanium implant installation with a collagen matrix containing an adenoviral (Ad) vector encoding PDGF-B (5.5×10⁸ or 5.5×10⁹ pfu/ml), Ad encoding luciferase (Ad-Luc; 5.5×10⁹ pfu/ml; control) or recombinant human PDGF-BB protein (rhPDGF-BB, 0.3 mg/ml). Bone repair and osseointegration were measured via backscattered SEM, histomorphometry, microcomputed tomography, and biomechanical assessments. Further, a panel of local and systemic safety assessments was performed. Results demonstrated bone repair was accelerated by Ad-PDGF-B and rhPDGF-BB delivery compared to Ad-Luc, with the high dose of Ad-PDGF-B more effective than the low dose. No significant dissemination of the vector construct or alteration of systemic parameters was noted. In summary, gene delivery of Ad-PDGF-B demonstrates regenerative and safety capabilities for bone tissue engineering and osseointegration in alveolar bone defects comparable to rhPDGF-BB protein delivery in vivo.

The use of platelet-rich plasma in bone reconstruction therapy

The use of platelet-rich plasma (PRP) in bone reconstruction therapy was introduced in the late 1990s. Since then, many scientists and clinicians have employed it in orthopaedic and oral surgeries. Unfortunately, studies that analyze the use of PRP are somewhat controversial as some conclude that the use of PRP may favor bone regeneration and others conclude that the use of PRP is irrelevant. By listing and analyzing the biological effect that each factor released by the activated platelets can have in bone regeneration, the present review answers the question of why PRP may be useful in bone reconstruction therapy. Subsequently, by examining the studies that have both successfully and unsuccessfully utilized PRP, it suggests how PRP might be used in order to achieve successful results in orthopaedic and dental bone reconstruction surgeries.

Assessment of the potential of growth factors for localized alveolar ridge augmentation: a systematic review

OBJECTIVE

To systematically assess the literature regarding the clinical, histological, and radiographic outcome of bone morphogenetic proteins (BMP-2, BMP-7), growth/differentiation factor-5 (GDF-5), platelet-derived growth factor (PDGF), and parathyroid hormone (PTH) for localized alveolar ridge augmentation.

MATERIAL AND METHODS

Five separate Medline searches were performed in duplicate for human and animal studies, respectively. The primary outcome of the included studies was bone regeneration of localized alveolar ridge defects or craniofacial defects.

RESULTS

In six human studies, BMP-2 affected local bone augmentation with increasing volume for higher doses. A majority (43 of 45) of animal studies using BMP-2 showed a positive effect in favour of the growth factor (GF). In six of eight studies, a positive effect was associated with the use of BMP-7. Only one animal study was included for GDF-5 revealing statistically significantly higher bone volume. Regarding PDGF, statistically significantly higher bone volume was observed in five of 10 included studies. Four animal studies using PTH revealed statistically significantly more bone regeneration compared with controls.

CONCLUSIONS

Differing levels and quantity of evidence were noted to be available for the GFs evaluated, revealing that BMP-2, BMP-7, GDF-5, PDGF, and PTH may stimulate local bone augmentation to various degrees. Human data for the potential of rhBMP-2 are supportive.

Molecular mechanisms controlling bone formation during fracture healing and distraction osteogenesis

Fracture healing and distraction osteogenesis have important applications in orthopedic, maxillofacial, and periodontal treatment. In this review, the cellular and molecular mechanisms that regulate fracture repair are contrasted with bone regeneration that occurs during distraction osteogenesis. While both processes have many common features, unique differences are observed in the temporal appearance and expression of specific molecular factors that regulate each. The relative importance of inflammatory cytokines in normal and diabetic healing, the transforming growth factor beta superfamily of bone morphogenetic mediators, and the process of angiogenesis are discussed as they relate to bone repair. A complete summary of biological activities and functions of various bioactive factors may be found at COPE (Cytokines & Cells Online Pathfinder Encyclopedia), http://www.copewithcytokines.de/cope.cgi.

Materials in particulate form for tissue engineering. 2. Applications in bone

Materials in particulate form have been the subjects of intensive research in view of their use as drug delivery systems. While within this application there are still issues to be addressed, these systems are now being regarded as having a great potential for tissue engineering applications. Bone repair is a very demanding task, due to the specific characteristics of skeletal tissues, and the design of scaffolds for bone tissue engineering presents several difficulties. Materials in particulate form are now seen as a means of achieving higher control over parameters such as porosity, pore size, surface area and the mechanical properties of the scaffold. These materials also have the potential to incorporate biologically active molecules for release and to serve as carriers for cells. It is believed that the combination of these features would create a more efficient approach towards regeneration. This review focuses on the application of materials in particulate form for bone tissue engineering. A brief overview of bone biology and the healing process is also provided in order to place the application in its broader context. An original compilation of molecules with a documented role in bone tissue biology is listed, as they have the potential to be used in bone tissue engineering strategies. To sum up this review, examples of works addressing the above aspects are presented.

Molecular Mechanisms Controlling Bone Formation during Fracture Healing and Distraction Osteogenesis

Fracture healing and distraction osteogenesis have important applications in orthopedic, maxillofacial, and periodontal treatment. In this review, the cellular and molecular mechanisms that regulate fracture repair are contrasted with bone regeneration that occurs during distraction osteogenesis. While both processes have many common features, unique differences are observed in the temporal appearance and expression of specific molecular factors that regulate each. The relative importance of inflammatory cytokines in normal and diabetic healing, the transforming growth factor beta superfamily of bone morphogenetic mediators, and the process of angiogenesis are discussed as they relate to bone repair. A complete summary of biological activities and functions of various bioactive factors may be found at COPE (Cytokines & Cells Online Pathfinder Encyclopedia), http://www.copewithcytokines.de/cope.cgi .

Osteoconductive effects of vinyl styrene microbeads in rat calvarial defects

PURPOSE

The aim of the present study was to evaluate the use of the nonresorbable vinyl styrene microbeads (VSM) alloplast as a delivery vehicle for platelet-derived growth factor (PDGF-BB) in rat calvarial critical size defects.

MATERIALS AND METHODS

Seventy-three Long-Evans male rats were divided into 4 groups; a negative control, vinyl styrene microbeads (VSM), PDGF-BB, and VSM plus PDGF-BB. Critical size calvarial defects were carried out and isolated with membranes sandwiching the defects with their fillers. Animals were sacrificed after 2, 4, and 16 weeks classifying each group into 3 subgroups. Calvarial specimens were radiographed for evaluation of regenerated bone volume and densitometry histogram analysis. Specimens were divided mid-sagittally and stained with hematoxylin and eosin (H&E) and trichrome stain for qualitative and histomorphometric analysis using an image analysis software.

RESULTS

The VSM groups showed statistically higher defect fills than the VSM-free groups at all sacrifice times except for the VSM/PDGF group that showed this difference after 2 weeks in relation to the PDGF group and the negative control after 4 and 16 weeks. For the radiographic analysis, the VSM/PDGF group showed the lowest bone volume compared with the other groups except when it was compared with the 4 weeks VSM group. In contrast, the PDGF showed the highest bone volumes at all sacrifice times that were only significant when compared with the 4 weeks VSM group and the 4 and 16 weeks VSM/PDGF group.

CONCLUSIONS

VSM enhances bone defect fill whereas the VSM/PDGF-BB is not able to improve bone regeneration capacity when compared with VSM alone.

Bone Formation at the Maxillary Sinus Floor Following Simultaneous Elevation of the Mucosal Lining and Implant Installation Without Graft Material: An Evaluation of 20 Patients Treated With 44 Astra Tech Implants

PURPOSE

Restoration of lost dentition in the severely artrophic posterior maxilla has for the last 2 decades been successfully treated with various sinus augmentation techniques and installation of dental implants. The use of graft material is anticipated to be necessary; however, recent studies have demonstrated that the mere lifting of the sinus mucosal lining and simultaneous placement of implants result in bone formation. This study was conducted in order to evaluate simultaneous sinus mucosal lining elevation and installation of dental implants without any graft material.

PATIENTS AND METHODS

Twenty patients were consecutively included from November 2001 to June 2004. Forty-four Astra ST dental implants (Astra Tech AB, Mölndal, Sweden) with a diameter of 4.5 mm or 5 mm were installed in 27 sinuses. A sinus lift was performed where a cortical window was removed from the maxillary anterior sinus wall. The sinus mucosal lining was elevated and implants installed in the residual subantral bone. The cortical window was thereafter replaced and the incision closed. The remaining bone height was recorded during surgery as well as perforations of the sinus mucosal lining. After 6 months of healing, abutments were connected (the series included 5 1-stage procedures). Clinical and radiological follow-up after loading was performed up to 4 years after implant installation.

RESULTS

Patients tolerated the procedure well as few complications were observed. Firm primary stability was achieved for all implants at installation with bone levels in residual bone of 2 to 9 mm. Perforations of the maxillary sinus mucosal lining occurred in 11 of the 27 operated sinuses (41%). One implant was lost during a mean follow-up of 27.5 months (range, 14 to 45 months) giving an implant survival rate of 97.7%. The average gain of bone at the sinus floor was 6.51 mm (SD = 2.49, 44 implants) including all measured implants after a minimum of 1 year follow-up. Marked bone formation was observed around long implants and also when the residual bone below the sinus was diminutive.

CONCLUSIONS

The present study including 20 patients showed consistent bone formation at the maxillary sinus floor following simultaneous mucosal lining elevation and installation of implants. It is suggested that the use of this technique can reduce the risk for morbidity related to harvesting of bone grafts and eliminate costs for grafting materials.

Human platelet lysate enhances the proliferative activity of cultured human fibroblast-like cells from different tissues

Several studies have shown the presence of fibroblast-like cells in the stromal fraction of different tissues with a high proliferative and differentiation potential. Platelet alpha granules contain growth factors released into the environment during activation. The effects of different supplements for culture medium (human serum, bovine serum and platelet lysate) on cultured human fibroblast-like cells from bone marrow, adipose tissue, trabecular bone and dental pulp have been compared. Expression of typical stromal and hematopoietic markers was analyzed and proliferative rates were determined. Flow cytofluorometry showed a homogenous pattern in serial-passaged cells, with a high level of stromal cell-associated markers (CD13, CD90, CD105). The presence of platelet lysate in culture media increased the number of cell generations obtained regardless of cell source. This effect was serum-dependent. Cell-based therapies can benefit by the use of products from human origin for "ex vivo" expansion of multipotent cells.

Starch-Based Microparticles as Vehicles for the Delivery of Active Platelet-Derived Growth Factor

In a previous work, we described the use of starch-based microparticles as vehicles for the controlled release of corticosteroids. The goal of the present work is to evaluate the potential of these microparticles to incorporate and release platelet-derived growth factor (PDGF). The loading efficiency and release profile were evaluated, and PDGF was incorporated into and released from the matrix of starch-based microparticles. The release profile shows rapid release of PDGF in the first 24 h, after which there was a slow but constant release for up to 8 weeks. The maintenance of the PDGF biological activity after incorporation and release was evaluated by its mitogenic effect over osteoblastic cells, and it was shown to be comparable to that of PDGF supplemented to the culture medium. This proves that the incorporation and release did not affect the biological activity of the growth factor (GF). The results clearly demonstrate that starch-based microparticles are suitable vehicles for the incorporation and release of GFs. When combined with previous results, these materials also suggest their ability to enhance the regenerating potential of tissue engineering hybrid constructs.

New technologies for the enhancement of skeletal repair

Although fracture healing is a well-optimized biological process that leads to healing, approximately 10-20% of fractures result in impaired or delayed healing and these fractures may benefit from the use of biotechnologies to enhance skeletal repair. Peptide signaling molecules such as the bone morphogenetic proteins have been shown to stimulate the healing of fresh fractures, nonunions, and spinal fusions and side effects from their use appear to be minimal. Other growth factors currently being studied for local application include growth and differentiation factor-5 (GDF-5), vascular endothelial growth factor (VEGF), transforming growth factor beta (TGFbeta), and platelet-derived growth factor (PDGF). Molecules such as prostaglandin E receptor agonists and the thrombin-related peptide, TP508, have shown promise in animal models of fracture repair. Gene therapy using various growth factors or combinations of factors might also aid in fracture repair, particularly as new methods for delivery that do not require viral vectors are developed. Systemic therapy with agents such as parathyroid hormone (PTH), growth hormone (GH), and the HMG-CoA reductase inhibitors are also under investigation. As these and other technologies are shown to be safe and effective, their use will become a part of the standard of care in managing skeletal injuries.

Platelet separation from whole blood in an aqueous two-phase system with water-soluble polymers

Platelet-rich plasma (PRP) stimulates tissue healing and centrifugation is the only method for PRP preparation. The purpose of the present study was to develop a method to separate platelets without centrifugation. We used 16 polymers of different chemical characteristics and mixed each polymer with fresh whole blood containing anticoagulant citrate-dextrose. Then, we observed blood cell separation. Focusing on the effective polymers and comparing our method with the conventional centrifugation method, we examined platelet recovery rate and P-selectin expression, which represents platelet activation. Poly-L-glutamic acid (PGA) and poly-L-aspartic acid (PAA) separated platelets efficiently; however, these polymers activated platelets. On the contrary, poly (2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB), which has phosphorylcholine residues mimicking a cellular membrane molecule, separated platelets moderately and the PMB-separated platelets were nearly inactive compared to the separation with the ordinary centrifugation and PGA. Conclusively, the present experiments demonstrated that without centrifugation platelets can be separated from whole blood with some water-soluble polymers, such as PGA, PAA, and PMB, and that PMB has an advantage not to activate platelets.

Osteogenic differentiation induced by bone morphogenetic proteins can be suppressed by platelet-released supernatant in vitro

Both bone morphogenetic proteins (BMPs) and growth factors released from activated platelets both occur at sites of bone regeneration but their functional relationship to regulate the temporal and spatial sequence of cellular events is not well defined. Here we investigated whether supernatants derived from activated platelets can modulate the response of the osteogenic cell line MC3T3-E1 to BMPs, and whether BMPs have an effect on MC3T3-E1 cells stimulated with platelet-released supernatant. Platelet-released supernatant suppressed BMP-2-, BMP-6-, and BMP-7-induced osteogenic differentiation of MC3T3-E1 cells, as indicated by the significant decrease in alkaline phosphatase activity and lower levels of osteocalcin transcripts, whereas BMP-2, BMP-6, and BMP-7 did not modulate migration and proliferation of MC3T3-E1 cells, which were stimulated with platelet-released supernatant. Osteogenic differentiation in response to BMPs was not affected after precultivation of MC3T3-E1 cells with platelet-released supernatant. These data suggest that activated platelets can provide a microenvironment that temporarily suppresses the differentiation of osteogenic cells in the presence of BMPs. Future strategies to stimulate bone regeneration should take the suppression of BMP-induced osteogenic differentiation during the existence of the blood clot into account.

Platelet-derived growth factor stimulates bone fill and rate of attachment level gain: results of a large multicenter randomized controlled trial

BACKGROUND

Growth factors are generally accepted to be essential mediators of tissue repair via well-established mechanisms of action that include stimulatory effects on angiogenesis and cellular proliferation, ingrowth, differentiation, and matrix biosynthesis. The aim of this study was to evaluate in a large-scale, prospective, blinded, and randomized controlled clinical trial the safety and effectiveness of purified recombinant human platelet-derived growth factor (rhPDGF-BB) mixed with a synthetic beta-tricalcium phosphate (beta-TCP) matrix for the treatment of advanced periodontal osseous defects at 6 months of healing.

METHODS

Eleven clinical centers enrolled 180 subjects, each requiring surgical treatment of a 4 mm or greater intrabony periodontal defect and meeting all inclusion and exclusion criteria. Subjects were randomized into one of three treatment groups: 1) beta-TCP + 0.3 mg/ml rhPDGF-BB in buffer; 2) beta-TCP + 1.0 mg/ml rhPDGF-BB in buffer; and 3) beta-TCP + buffer (active control). Safety data were assessed by the frequency and severity of adverse events. Effectiveness measurements included clinical attachment levels (CAL) and gingival recession (GR) measured clinically and linear bone growth (LBG) and percent bone fill (% BF) as assessed radiographically by an independent centralized radiology review center. The area under the curve (AUC), an assessment of the rate of healing, was also calculated for CAL measurements. The surgeons, clinical and radiographic evaluators, patients, and study sponsor were all masked with respect to treatment groups.

RESULTS

CAL gain was significantly greater at 3 months for group 1 (rhPDGF 0.3 mg/ml) compared to group 3 (beta-TCP + buffer) (3.8 versus 3.3 mm; P = 0.032), although by 6 months, this finding was not statistically significant (P = 0.11). This early acceleration of CAL gain led to group 1 exhibiting a significantly greater rate of CAL gain between baseline and 6 months than group 3 as assessed by the AUC (68.4- versus 60.1-mm weeks; P = 0.033). rhPDGF (0.3 mg/ml)-treated sites also had significantly greater linear bone gain (2.6 versus 0.9 mm, respectively; P < 0.001) and percent defect fill (57% versus 18%, respectively; P < 0.001) than the sites receiving the bone substitute with buffer at 6 months. There was less GR at 3 months in group 1 compared to group 3 (P = 0.04); at 6 months, GR for group 1 remained unchanged, whereas there was a slight gain in gingival height for group 3 resulting in comparable GR. There were no serious adverse events attributable to any of the treatments.

CONCLUSIONS

To our knowledge, this study is the largest prospective, randomized, triple-blinded, and controlled pivotal clinical trial reported to date assessing a putative periodontal regenerative and wound healing therapy. The study demonstrated that the use of rhPDGF-BB was safe and effective in the treatment of periodontal osseous defects. Treatment with rhPDGF-BB stimulated a significant increase in the rate of CAL gain, reduced gingival recession at 3 months post-surgery, and improved bone fill as compared to a beta-TCP bone substitute at 6 months.

The Effect of Sputtered Calcium Phosphate Coatings of Different Crystallinity on Osteoblast Differentiation

BACKGROUND

Coating titanium implants with hydroxyapatite (HA) has been suggested to increase osseointegration by stimulating early osteoblast function. The goal of this study was to determine the extent to which the crystalline content of the HA surface affected osteoblast function in vitro.

METHODS

Osteoblasts were isolated from fetal rat calvaria. Titanium coupons were sputter coated and analyzed. Mineralized nodule formation on plastic using von Kossa staining was compared to tetracycline and procion dye labeling. Cell proliferation, adhesion, alkaline phosphatase activity, morphology and spreading, and cytoskeletal arrangement were analyzed. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the expression of mRNA for specific proteins.

RESULTS

The percent crystallinity of coatings was 0% (HA1), 1.9% +/- 0.4% (HA2), and 66.4% +/- 2.8% (HA3). The nodule formation and cell number were greatest on titanium and HA3 compared to HA1 and HA2 (P < 0.01). At weeks 2 to 4, all samples showed strong alkaline phosphatase, osteocalcin, monocyte-colony stimulating factor (M-CSF), and receptor activator of nuclear factor kappa B ligand (RANKL) expression, but the specific activity of alkaline phosphatase decreased. Cell adherence was greater than 60% of applied cells for all surfaces except HA3. The cells were significantly more elongated on titanium, with no difference on the HA-coated surfaces. Actin filaments were arranged peripherally at 5 hours but arranged parallel to the long axis of the cell at 20 hours.

CONCLUSIONS

Procion labeling is a valid method for evaluating mineralized nodule formation on opaque surfaces. There were no major differences in osteoblast function using titanium or high-crystalline coatings, and most functions were decreased on amorphous or low-crystalline coatings.

Effects of platelet lysates on select bone cell functions

Although platelet-rich plasma and platelet concentrates have been used to promote bone healing in orthopaedic and maxillofacial surgery, the underlying cellular-level mechanisms remain poorly understood. The present in vitro study investigated the effects of human platelet lysate (PL) on selected functions of cultured bone cells. Cells from 18-day-old fetal rat calvaria were isolated by a collagenase digestion procedure. PL was added at different concentrations on pre- or post-confluent cell stage. After 1 day, bone cell proliferation was maximal and half-maximal in the presence of PL from 3 x 10(8) and 0.5 x 10(8) platelets/ml, respectively. During 17 h, the number of bone cells traversing the scrape border of a scrape wound model increased by 16-fold in the presence of PL from 3 x 10(8) platelets/ml. The presence of PL from 3 x 10(8) platelets/ml in pre-confluent bone cell cultures for 48 h resulted in a threefold decrease of alkaline phosphatase (ALP) specific activity. In the case of confluent bone cells, the presence of PL (from 1 x 10(6) to 3 x 10(8) platelets/ml) for 11 days, the ALP specific activity and total calcium content decreased in a PL dose-dependent manner and reached a minimum in the presence of PL from 3 x 10(8) platelets/ml. In summary, short-term PL exposure (up to 24 h) promotes the proliferative and chemotactic bone cell functions while long-term PL exposure results in a decrease of both ALP activity and mineral formation. These data show that the soluble components contained in PL may affect the bone healing process by modulating differently bone cell functions.

Effect of sustained gene delivery of platelet-derived growth factor or its antagonist (PDGF-1308) on tissue-engineered cementum

BACKGROUND

Cementum, a mineralized tissue lining the tooth root surface, is destroyed during the inflammatory process of periodontitis. Restoration of functional cementum is considered a criterion for successful regeneration of periodontal tissues, including formation of periodontal ligament, cementum, and alveolar bone. Short-term administration of platelet-derived growth factor (PDGF) has been shown to partially regenerate periodontal structures. Nonetheless, the role of PDGF in cementogenesis is not well understood. The aim of the present study was to determine the effect of sustained PDGF gene transfer on cementum formation in an ex vivo ectopic biomineralization model.

METHODS

Osteocalcin (OC) promoter-driven SV40 transgenic mice were used to obtain immortalized cementoblasts (OCCM). The OCCM cells were transduced with adenoviruses (Ad) encoding either PDGF-A, an antagonist of PDGF signaling (PDGF-1308), a control virus (green fluorescent protein, GFP), or no treatment (NT). The transduced cells were incorporated into polymer scaffolds and implanted subcutaneously into severe combined immunodeficient (SCID) mice. The implants were harvested at 3 and 6 weeks for histomorphometric analysis of the newly formed mineralized tissues. Northern blot analysis was performed to determine the expression levels of mineral-associated genes including bone sialoprotein (BSP), OC, and osteopontin (OPN) in the cell-implant specimens at 3 and 6 weeks.

RESULTS

The results indicated mineralization was significantly reduced in both the Ad/PDGF-A and Ad/PDGF-1308 treated specimens when compared to the NT or Ad/GFP groups at 3 and 6 weeks (P<0.01). In addition, the size of the implants treated with Ad/PDGF-A and Ad/PDGF-1308 was significantly reduced compared to implants from Ad/GFP and NT groups at 3 weeks (P<0.05). At 6 weeks, the size of implants and mineral formation increased in NT, Ad/GFP, and Ad/PDGF-A groups, while the Ad/PDGF-1308 treated implants continued to decrease in size and mineral formation (P<0.01). Northern blot analysis revealed that in the Ad/PDGF-A treated implants OPN was increased, whereas OC gene expression was downregulated at 3 weeks. In the Ad/PDGF-1308 treated implants, BSP, OC, and OPN were all downregulated at 3 weeks. At 3 weeks, the Ad/PDGF-A treated implants contained significantly higher multinucleated giant cell (MNGC) density compared to NT, Ad/GFP, and Ad/PDGF-1308 specimens. The MNGC density in NT, Ad/GFP, and Ad/PDGF-A treated groups reduced over time, while the Ad/PDGF-1308 transduced implants continued to exhibit significantly higher MNGC density compared with the other treatment groups at 6 weeks.

CONCLUSIONS

The results showed that continuous exposure to PDGF-A had an inhibitory effect on cementogenesis, possibly via the upregulation of OPN and subsequent enhancement of MNGCs at 3 weeks. On the other hand, Ad/PDGF-1308 inhibited mineralization of tissue-engineered cementum possibly due to the observed downregulation of BSP and OC and a persistence of stimulation of MNGCs. These findings suggest that continuous exogenous delivery of PDGF-A may delay mineral formation induced by cementoblasts, while PDGF is clearly required for mineral neogenesis.

Platelet-rich plasma for bone graft enhancement in sinus floor augmentation with simultaneous implant placement: patient series study

The use of autologous platelet-rich plasma (PRP) as a source for growth factors in bone grafting is a relatively new and promising technique. Early controlled studies indicate that combining PRP with autologous bone grafts significantly enhances the rate of bone formation and maturation. The study consisted of 105 patients who required sinus augmentation with crestal bone height of less than 5 mm in the posterior maxilla. All patients received a composite bone graft that consisted of 30% to 40% autogenous bone harvested from the lateral wall of the maxilla zygomatic-maxillary buttress and the tuberosity and 60% to 70% xenograft. A total of 50 mL of blood was obtained from each patient before the surgical treatment for preparation of 10 mL of PRP. The graft-PRP mixture was activated by human thrombin. All sinus augmentations were carried out simultaneously with dental implants. At 6 months postoperatively, implants were exposed showing no clinical evidence of crestal bone loss around the implants both clinically and radiographically. All implants were clinically osseointegrated and loaded with fixed porcelain fused to metal prosthesis. The use of PRP in augmenting the severely atrophic posterior maxilla has obvious clinical benefits in terms of reducing the healing period of bone maturation, better graft handling, and accelerated soft tissue healing.

Influence of platelet-rich plasma (PRP) on osteogenic differentiation of rat bone marrow stromal cells. An in vitro study

Recent clinical reports suggest that the application of an autologous blood plasma enriched with thrombocytes by centrifugal concentration (platelet-rich plasma: PRP) can enhance the formation of new bone. There are very fewin vitro or in vivo studies published on the efficiency of PRP. In this project a three dimensional cell culture system was used to compare PRP and rhBMP-2 in vitro. Marrow derived bone forming cells from Spraque-Dawley (SD) rats were seeded on porous collagenous carriers (d=5mm, h=3mm) at a density of 4 x 10(4) cells/carrier and exposed to different concentrations of PRP (platelet counts from 2.5 x 10(8)-1.6 x 10(7) platelets/culture), rhBMP-2 (300 ng) or plasma poor in thrombocytes (platelet-poor plasma, PPP). Cultures without additional supplements were used as controls. During a culture period of 21 days cell proliferation, alkaline phosphatase activity (ALP) and calcium content (days 18, 21) were measured in 3 day intervals.PRP showed a dose dependent stimulation of cell proliferation, while reducing ALP activity and calcium deposition in the culture. BMP-2 led to an opposite cell response and induced the highest ALP activity and mineral deposition. These data suggest that PRP inhibited osteogenic differentiation of marrow derived pre-osteoblasts in a dose dependent manner. PRP is not a substitute for BMP-2 in osteogenic induction.

Periodontal Regeneration in Humans Using Recombinant Human Platelet- Derived Growth Factor-BB (rhPDGF-BB) and Allogenic Bone

BACKGROUND

Purified recombinant human platelet-derived growth factor BB (rhPDGF-BB) is a potent wound healing growth factor and stimulator of the proliferation and recruitment of both periodontal ligament (PDL) and bone cells. The hypothesis tested in this study was that application of rhPDGF-BB incorporated in bone allograft would induce regeneration of a complete new attachment apparatus, including bone, periodontal ligament, and cementum in human interproximal intrabony defects and molar Class II furcation lesions.

METHODS

Nine adult patients (15 sites) with advanced periodontitis exhibiting at least one tooth requiring extraction due to an extensive interproximal intrabony and/or molar Class II furcation defect were entered into the study. Eleven defects were randomly selected to receive rhPDGF-BB. Following full-thickness flap reflection and initial debridement, the tooth roots were notched at the apical extent of the calculus, the osseous defects were thoroughly debrided, and the tooth root(s) were planed/prepared. The osseous defects were then filled with demineralized freeze-dried bone allograft (DFDBA) saturated with one of three concentrations of rhPDGF-BB (0.5 mg/ml, 1.0 mg/ml, or 5.0 mg/ml). Concurrently, four interproximal defects were treated with a well accepted commercially available graft (anorganic bovine bone in collagen, ABB-C) and a bilayer collagen membrane. Radiographs, clinical probing depths, and attachment levels were obtained preoperatively (at baseline) and 9 months later. At 9 months postoperatively, the study tooth and surrounding tissues were removed en bloc. Clinical and radiographic data were analyzed for change from baseline by defect type and PDGF concentration. The histologic specimens were analyzed for the presence of regeneration of a complete new attachment apparatus coronal to the reference notch.

RESULTS

The post-surgical wound rapidly healed and was characterized by firm, pink gingivae within 7 to 10 days of surgery. There were no unfavorable tissue reactions or other safety concerns associated with the treatments throughout the course of the study. In rhPDGF/allograft sites, the vertical probing depth (vPD) reduction for interproximal defects was 6.42 +/- 1.69 mm (mean +/- SD) and clinical attachment level (CAL) gain was 6.17 +/- 1.94 mm (both P < 0.01). Radiographic fill was 2.14 +/- 0.85 mm. Sites filled with ABB-C had a PD reduction and CAL gain of 5.75 +/- 0.5 and 5.25 +/- 1.71, respectively. Furcation defects treated with rhPDGF/allograft exhibited a mean horizontal and vertical PD reduction of 3.40 +/- 0.55 mm (P < 0.001) and 4.00 +/- 1.58 mm (P < 0.005), respectively. The CAL gain for furcation defects was 3.2 +/- 2.17 mm (P < 0.030). Histologic evaluation revealed regeneration of a complete periodontal attachment apparatus, including new cementum, PDL, and bone coronal to the root notch in four of the six interproximal defects and all evaluable (four of four) furcation defects treated with PDGF. Two of the four interproximal intrabony defects treated with ABB-C and membrane exhibited regeneration.

CONCLUSIONS

Use of purified rhPDGF-BB mixed with bone allograft results in robust periodontal regeneration in both Class II furcations and interproximal intrabony defects. This is the first report of periodontal regeneration demonstrated histologically in human Class II furcation defects.

Triazolopyrimidine (trapidil), a platelet-derived growth factor antagonist, inhibits parathyroid bone disease in an animal model for chronic hyperparathyroidism

Parathyroid bone disease in humans is caused by chronic hyperparathyroidism (HPT). Continuous infusion of PTH into rats results in histological changes similar to parathyroid bone disease, including increased bone formation, focal bone resorption, and severe peritrabecular fibrosis, whereas pulsatile PTH increases bone formation without skeletal abnormalities. Using a cDNA microarray with over 5000 genes, we identified an association between increased platelet-derived growth factor-A (PDGF-A) signaling and PTH-induced bone disease in rats. Verification of PDGF-A overexpression was accomplished with a ribonuclease protection assay. Using immunohistochemistry, PDGF-A peptide was localized to mast cells in PTH-treated rats. We also report a novel strategy for prevention of parathyroid bone disease using triazolopyrimidine (trapidil). Trapidil, an inhibitor of PDGF signaling, did not have any effect on indexes of bone turnover in normal rats. However, dramatic reductions in marrow fibrosis and bone resorption, but not bone formation, were observed in PTH-treated rats given trapidil. Also, trapidil antagonized the PTH-induced increases in mRNA levels for PDGF-A. These results suggest that PDGF signaling is important for the detrimental skeletal effects of HPT, and drugs that target the cytokine or its receptor might be useful in reducing or preventing parathyroid bone disease.

Quantification and localization of platelet-derived growth factor in gingiva of periodontitis patients

BACKGROUND

Platelet-derived growth factor (PDGF) is a mitogen and chemoattractant for cells of mesenchymal origin. Over-expression of PDGF-B can promote formation of inflammatory lesions in the lungs of transgenic mice. Moreover, continuous exposure to PDGF inhibits collagen production by osteoblastic cells. Thus, the expression of mitogenic factors in an inflammatory context may limit the differentiated function of cells, and thereby limit repair following periodontal attachment and bone loss. The goals of the present study were to test whether PDGF is present at increased levels in inflamed gingiva and to localize its expression in gingival biopsies from individuals with chronic periodontitis.

METHODS

Tissues obtained during therapeutic procedures from inflamed and control sites of 9 patients were subjected to protein extraction, descriptive histology by hematoxylin and eosin, or immunohistochemistry assays. Quantification was calculated with an enzyme-linked immunosorbent assay (ELISA) kit specific for PDGF-AB. For the immunolocalization, anti-PDGF-A and -B antibodies were employed.

RESULTS

PDGF concentration in the total protein extract was approximately 3 times higher in the inflamed sites (0.60 +/- 0.18 ng/mg versus 0.20 +/- 0.05 ng/mg; P = 0.03). Immunohistochemistry revealed prominent expression of PDGF in the pocket epithelial cells as well as the adjacent connective tissue. In contrast, little or no expression was detected in control biopsies devoid of the pocket epithelium and granulation tissue.

CONCLUSIONS

PDGF is present in increased levels in the human inflamed gingiva and is mainly localized to the pocket epithelium. It is possible that chronic expression of PDGF contributes to the inflammatory changes that occur during periodontal diseases.

Bone growth factors in maxillofacial skeletal reconstruction

A literature review was performed to survey the available information on the potential of bone growth factors in skeletal reconstruction in the maxillofacial area. The aim of this review was to characterize the biological and developmental nature of the growth factors considered, their molecular level of activity and their osteogenic potential in craniofacial bone repair and reconstruction. A total of 231 references were selected for evaluation by the content of the abstracts. All growth factors considered have a fundamental role in growth and development. In postnatal skeletal regeneration, PDGF plays an important role in inducing proliferation of undifferentiated mesenchymal cells. It is an important mediator for bone healing and remodelling during trauma and infection. It can enhance bone regeneration in conjunction with other growth factors but is unlikely to provide entirely osteogenic properties itself. IGFs have an important role in general growth and maintenance of the body skeleton. The effect of local application of IGFs alone in craniofacial skeletal defects has not yet shown a clear potential for enhancement of bone regeneration in the reported dosages. The combination of IGF-I with PDGF has been effective in promoting bone regeneration in dentoalveolar defects around implants or after periodontal bone loss. TGFbeta alone in skeletal reconstruction appears to be associated with uncertain results. The presence of committed cells is required for enhancement of bone formation by TGFbeta. It has a biphasic effect, which suppresses proliferation and osteoblastic differentiation at high concentrations. BMPs, BMP2, BMP4 and BMP7 in particular, appear to be the most effective growth factors in terms of osteogenesis and osseous defect repair. Efficacy of BMPs for defect repair is strongly dependent on the type of carrier and has been subject to unknown factors in clinical feasibility trials resulting in ambiguous results. The current lack of clinical data may prolong the period until this factor is introduced into routine clinical application. PRP is supposed to increase proliferation of undifferentiated mesenchymal cells and to enhance angiogenesis. There is little scientific evidence about the benefit of PRP in skeletal reconstructive and preprosthetic surgery yet and it is unlikely that peri-implant bone healing or regeneration of local bone into alloplastic material by the application of PRP alone will be significantly enhanced.

Factors in the fracture microenvironment induce primary osteoblast angiogenic cytokine production

Neoangiogenesis is essential for successful wound repair. Platelets are among the earliest cells recruited to a site of skeletal injury and are thought to provide numerous factors critical to successful repair. The release of platelet-derived growth factor (PDGF) after skeletal injury increases osteoblast proliferation, chemotaxis, and collagen synthesis; however, its angiogenic effect on osteoblast biology remains unknown. The purpose of this study was to investigate the effect of recombinant human (rh)PDGF-BB on the synthesis of vascular endothelial growth factor (VEGF) by primary neonatal rat calvarial osteoblasts. Furthermore, the authors investigated whether PDGF works in concert with hypoxia, another component of the fracture microenvironment, to additively or synergistically induce VEGF production. Osteoblast cultures were stimulated with varying concentrations of rhPDGF-BB (1, 10, 50, and 100 ng/ml) in normoxic and hypoxic (<1% oxygen) conditions for 0, 3, 6, 12, and 24 hours, and VEGF gene expression was analyzed by Northern blot analysis. To determine whether rhPDGF-BB-induced VEGF messenger RNA (mRNA) expression was transcriptionally mediated or required de novo protein synthesis, transcription, and translation, studies were performed using actinomycin D and cycloheximide, respectively. Treatment with 50 ng/ml rhPDGF-BB resulted in a 2.4-fold increase in VEGF mRNA expression after 3 hours. Interestingly, rhPDGF-BB and hypoxia seemed to have an additive effect, resulting in a 3.7-fold increase in VEGF mRNA expression after 6 hours in primary neonatal rat calvarial osteoblasts. Furthermore, by using actinomycin D and cycloheximide, the authors demonstrated that the rhPDGF-BB-induced VEGF mRNA expression was transcriptionally mediate and not dependent on de novo protein synthesis. These data demonstrate that rhPDGF-BB transcriptionally increases osteoblasts VEGF mRNA expression in vitro. Furthermore, the semiquantitative results suggest that rhPDGF-BB and hypoxia act additively to increase VEGF mRNA expression. It is postulated that similar mechanisms may occur in vivo, at a site of skeletal injury, to induce neoangiogenesis and promote fracture repair.

Platelet-derived growth factor (PDGF) gene delivery for application in periodontal tissue engineering

BACKGROUND

A challenge in the reconstruction of periodontal structures is the targeted delivery of growth-promoting molecules to the tooth root surface. Polypeptide growth factors such as platelet-derived growth factor (PDGF) stimulate both cementogenesis and osteogenesis. Recent advances in gene therapy offer the advantage of delivering recombinant proteins to tissues for extended periods of time in vivo.

METHODS

Recombinant adenoviral vectors encoding for the PDGF-A gene were constructed to allow delivery of PDGF transgenes to cells. The recombinant adenoviruses were assembled using the viral backbone of Ad2/CMV/EGFP and replacing GFP (reporter gene encoding green fluorescent protein driven by the cytomegalovirus promoter [CMV] within adenovirus type 2) with the PDGF-A gene. Root lining cells (cloned cementoblasts) were transduced with Ad2/PDGF-A and evaluated for gene expression, DNA synthesis, and cell proliferation. PDGF-inducible genes, c-myc and osteopontin, were also evaluated following gene delivery of Ad2/PDGF-A.

RESULTS

The results revealed high level transduction of cementoblasts by gene transfer for 7 days as evidenced by flow cytometry and Northern blotting. Cementoblast DNA synthesis and subsequent proliferation were stimulated by Ad2/PDGF-A at levels equal to or greater than continuous rhPDGF-AA application. Strong message for the PDGF-A gene and protein as evidenced by Northern blotting and immunocytochemistry was noted. Furthermore, the potent induction of c-myc and osteopontin mRNA was found after PDGF gene delivery to cementoblasts.

CONCLUSIONS

These findings demonstrate that gene delivery of platelet-derived growth factor stimulates cementoblast activity that is sustained above that of rhPDGF-AA application. The use of gene therapy as a mode of growth factor delivery offers a novel approach to periodontal tissue engineering.

Gene transfer and expression of platelet-derived growth factors modulate periodontal cellular activity

Platelet-derived growth factor (PDGF) is a potent stimulator of wound healing. PDGF gene therapy may promote greater periodontal regeneration than local protein application, due to sustained growth factor delivery to the target tissue. This investigation tested the ability of recombinant adenoviruses (rAds) encoding PDGF-A or PDGF-1308 (a PDGF-A dominant-negative mutant that disrupts endogenous PDGF bioactivity) to affect cells derived from the periodontium. Osteoblasts, periodontal ligament fibroblasts, and gingival fibroblasts were transduced with rAds, and gene expression, DNA synthesis, and cell proliferation were evaluated. The results revealed strong message for the PDGF-A gene for 7 days following gene delivery. Ad2/PDGF-A enhanced the mitogenic and proliferative response in all cell types, while Ad2/PDGF-1308 potently inhibited mitogenesis and proliferation. In conclusion, Ad2/PDGF can effectively transduce cells derived from the periodontium and promote biological activity equivalent to PDGF-AA. These studies support the potential use of gene therapy for sustained PDGF release in periodontal tissues.

Enamel factors regulate expression of genes associated with cementoblasts

BACKGROUND

In order to design predictable periodontal regenerative therapies, it is important to understand the responsiveness of cells within the local environment to factors considered attractive candidates. The aim of this study was to determine the effect of an enamel matrix derivative (EMD) on cementoblast behavior in vitro and in vivo.

METHODS

Osteocalcin (OC) promoter SV40 transgenic mice were used to obtain cementoblasts. For comparison, preosteoblasts from these mice, as well as another murine pre-osteoblast cell line, MC3T3-E1 cells, were used. Cells exposed to EMD were evaluated for changes in: 1) proliferation over an 8-day period by cell counting; 2) gene expression using Northern blot analysis; and 3) biomineralization by von Kossa stain, in vitro and by preparing histological samples from implants retrieved from immunodeficient (SCID) mice, where cementoblasts were treated with EMD prior to implantation.

RESULTS

EMD promoted proliferation of all cell types. EMD down-regulated osteocalcin transcripts in cementoblasts and MC3T3-E1 cells and up-regulated osteopontin gene expression markedly in MC3T3-E1 cells and slightly in cementoblasts at day 8. In vitro, EMD decreased cementoblast-mediated biomineralization. In contrast, mineralization was noted in implants retrieved from SCID mice, where cells were pretreated with EMD.

CONCLUSION

These results indicate that EMD can influence activities of cementoblasts and osteoblasts, and thus may be able to regulate cell activities at a periodontal regenerative site.

Growth factors regulate expression of mineral associated genes in cementoblasts

BACKGROUND

Knowledge of the responsiveness of cells within the periodontal region to specific bioactive agents is important for improving regenerative therapies. The aim of this study was to determine the effect of specific growth factors, insulin-like growth factor-I (IGF-I), platelet-derived growth factor-BB (PDGF-BB), and transforming growth factor-beta (TGF-beta) on cementoblasts in vitro and ex vivo.

METHODS

Osteocalcin (OC) promoter driven SV40 transgenic mice were used to obtain immortalized cementoblasts. Growth factor effects on DNA synthesis were assayed by [3H]-thymidine incorporation. Northern analysis was used to determine the effects of growth factors on gene expression profile. Effects of growth factors on cementoblast induced biomineralization were determined in vitro (von Kossa stain) and ex vivo (re-implantation of cells in immunodeficient (SCID) mice).

RESULTS

All growth factors stimulated DNA synthesis compared to control. Twenty-four hour exposure of cells to PDGF-BB or TGF-beta resulted in a decrease in bone sialoprotein (BSP) and osteocalcin (OCN) mRNAs while PDGF-BB also increased osteopontin (OPN) mRNA. Cells exposed to IGF-I for 24 hours exhibited decreased transcripts for OCN and OPN with an upregulation of BSP mRNA noted at 72 hours. In vitro mineralization was inhibited by continuous application of PDGF-BB or TGF-beta, while cells exposed to these factors prior to implantation into SCID mice still promoted biomineralization.

CONCLUSIONS

These data indicate IGF-I, PDGF-BB, and TGF-beta influence mitogenesis, phenotypic gene expression profile, and biomineralization potential of cementoblasts suggesting that such factors alone or in combination with other agents may provide trigger factors required for regenerating periodontal tissues.

Quantification of growth factor levels using a simplified method of platelet-rich plasma gel preparation

PURPOSE

This study compared two methods of preparing platelet-rich plasma (PRP) gel and the levels of PDGF and TGFbeta in each preparation.

MATERIALS AND METHODS

Platelet-rich plasma gel was prepared by centrifugation and clotted using the ITA gelling agent (Natrex Technologies Inc, Greenville, NC) or by the addition of thrombin and calcium chloride. The levels of platelet-derived growth factor (PDGF) and transforming growth factor beta (TGFbeta) generated by clot formation were assayed by enzyme-linked immunoassay (ELISA).

RESULTS

Both methods of preparation yielded PRP gel in less than 30 minutes. However, the ITA preparation did not require thrombin to achieve adequate gel formation. The levels of PDGF and TGFbeta were similar regardless of which method was used for initiation of clot formation.

CONCLUSION

Use of ITA for gel preparation is equivalent to using calcium chloride and thrombin, without the need for special equipment and the risk of coagulopathy.