Platelet-derived growth factor expression in normally healing human fractures

Temporal dynamics of immune-stromal cell interactions in fracture healing

Bone fracture repair is a complex, multi-step process that involves communication between immune and stromal cells to coordinate the repair and regeneration of damaged tissue. In the US, 10% of all bone fractures do not heal properly without intervention, resulting in non-union. Complications from non-union fractures are physically and financially debilitating. We now appreciate the important role that immune cells play in tissue repair, and the necessity of the inflammatory response in initiating healing after skeletal trauma. The temporal dynamics of immune and stromal cell populations have been well characterized across the stages of fracture healing. Recent studies have begun to untangle the intricate mechanisms driving the immune response during normal or atypical, delayed healing. Various in vivo models of fracture healing, including genetic knockouts, as well as in vitro models of the fracture callus, have been implemented to enable experimental manipulation of the heterogeneous cellular environment. The goals of this review are to (1): summarize our current understanding of immune cell involvement in fracture healing (2); describe state-of-the art approaches to study inflammatory cells in fracture healing, including computational and in vitro models; and (3) identify gaps in our knowledge concerning immune-stromal crosstalk during bone healing.

Efficacy of Platelet-Rich Plasma in the Treatment of Fractures: A Meta-Analysis

Background

Although numerous studies have reported the effectiveness of platelet-rich plasma (PRP) in promoting and enhancing bone healing, many orthopedic physicians remain skeptical of platelet-rich plasma in the treatment of fractures. The objective of this meta-analysis was to assess the efficacy of PRP in the treatment of fractures.

Methods

We search for research on PRP treatment of fractures in Pubmed, Embase, Medline, and Cochrane libraries. Two independent reviewers assessed included studies and met to develop a consensus on included studies. We also assessed the risk of bias using Review Manager 5.3 software.

Results

The present meta-analysis included 10 randomized controlled trials (RCT) containing 652 patients. In the fixed-effect meta-analysis of 10 RCTs, 8 RCTs found that fracture patients benefited from PRP treatment. The use of PRP reduced the time of fracture healing in 4 RCTs. Three RCTs found that PRP adjuvant therapy enhanced bone mineral density in the fracture trace and reduced the time of bone regeneration in mandibular fractures patients (standardized mean difference (SMD) = −1.99, 95%confidence interval (CI) = −2.64–−1.35). And 3 RCTs found that PRP adjuvant therapy decreased the risk of revision surgery in fracture patients (SMD = 1.83, 95%CI = 1.10–3.04).

Conclusion

PRP adjuvant therapy is beneficial for the treatment of fracture patients, particularly those with mandibular fractures, and decreased the risk of revision surgery in fracture patients.

The developing mouse coronal suture at single-cell resolution

Sutures separate the flat bones of the skull and enable coordinated growth of the brain and overlying cranium. The coronal suture is most commonly fused in monogenic craniosynostosis, yet the unique aspects of its development remain incompletely understood. To uncover the cellular diversity within the murine embryonic coronal suture, we generated single-cell transcriptomes and performed extensive expression validation. We find distinct pre-osteoblast signatures between the bone fronts and periosteum, a ligament-like population above the suture that persists into adulthood, and a chondrogenic-like population in the dura mater underlying the suture. Lineage tracing reveals an embryonic Six2+ osteoprogenitor population that contributes to the postnatal suture mesenchyme, with these progenitors being preferentially affected in a Twist1+/-; Tcf12+/- mouse model of Saethre-Chotzen Syndrome. This single-cell atlas provides a resource for understanding the development of the coronal suture and the mechanisms for its loss in craniosynostosis.

Effect of platelet-derived growth factor (PDGF-BB) and bone morphogenic protein 2 (BMP-2) transfection of rBMSCs compounded with platelet-rich plasma on adipogenic differentiation

The aim of this study was to inhibit adipogenic differentiation by transfecting two growth factors, platelet-derived growth factor (PDGF-BB) and bone morphogenic protein 2 (BMP-2), into modified rat bone marrow mesenchymal stem cells (rBMSCs) and then compounded with platelet-rich plasma (PRP). To achieve rBMSCs, the osteoporosis model of rats was established, and then the rBMSCs from the rats were isolated and identified. Co-transfection of rBMSCs with PDGF-BB-GFP and BMP-2 and detection of PDGF-BB/BMP-2 expression in transfected BMSCs was assessed by qRT-PCR and western blot, respectively. Moreover, the effect of the two growth factors transfection of rBMSCs on adipogenic differentiation was evaluated by oil red O staining and western blot, respectively. Finally, construction of the two growth factors transfection of rBMSCs compounded with PRP and detection of adipogenic differentiation were assessed by oil red O staining, CCK-8, and western blot, respectively. In vitro studies revealed that the two growth factors transfection of rBMSCs compounded with PRP promoted cell viability and inhibited adipogenic differentiation and could be promising for inhibiting adipogenic differentiation.

Local injections of β-NGF accelerates endochondral fracture repair by promoting cartilage to bone conversion

There are currently no pharmacological approaches in fracture healing designed to therapeutically stimulate endochondral ossification. In this study, we test nerve growth factor (NGF) as an understudied therapeutic for fracture repair. We first characterized endogenous expression of Ngf and its receptor tropomyosin receptor kinase A (TrkA) during tibial fracture repair, finding that they peak during the cartilaginous phase. We then tested two injection regimens and found that local β-NGF injections during the endochondral/cartilaginous phase promoted osteogenic marker expression. Gene expression data from β-NGF stimulated cartilage callus explants show a promotion in markers associated with endochondral ossification such as Ihh, Alpl, and Sdf-1. Gene ontology enrichment analysis revealed the promotion of genes associated with Wnt activation, PDGF- and integrin-binding. Subsequent histological analysis confirmed Wnt activation following local β-NGF injections. Finally, we demonstrate functional improvements to bone healing following local β-NGF injections which resulted in a decrease in cartilage and increase of bone volume. Moreover, the newly formed bone contained higher trabecular number, connective density, and bone mineral density. Collectively, we demonstrate β-NGF’s ability to promote endochondral repair in a murine model and uncover mechanisms that will serve to further understand the molecular switches that occur during cartilage to bone transformation.

The platelet-rich plasma and mesenchymal stem cell milieu: A review of therapeutic effects on bone healing

Platelet-rich plasma is autologous plasma that contains concentrated platelets compared to whole blood. It is relatively inexpensive to produce, can be easily isolated from whole blood, and can be administered while the patient is in the operating room. Further, because platelet-rich plasma is an autologous therapy, there is minimal risk for adverse reactions to the patient. Platelet-rich plasma has been used to promote bone regeneration due to its abundance of concentrated growth factors that are essential to wound healing. In this review, we summarize the methods for producing platelet-rich plasma and the history of its use in bone regeneration. We also summarize the growth factor profiles derived from platelet-rich plasma, with emphasis on those factors that play a direct role in promoting bone repair within the local fracture environment. In addition, we discuss the potential advantages of combining platelet-rich plasma with mesenchymal stem cells, a multipotent cell type often obtained from bone marrow or fat, to improve craniofacial and long bone regeneration. We detail what is currently known about how platelet-rich plasma influences mesenchymal stem cells in vitro, and then highlight the clinical outcomes of administering platelet-rich plasma and mesenchymal stem cells as a combination therapy to promote bone regeneration in vivo.

Unveiling diversity of stem cells in dental pulp and apical papilla using mouse genetic models: a literature review

The dental pulp, a non-mineralized connective tissue uniquely encased within the cavity of the tooth, provides a niche for diverse arrays of dental mesenchymal stem cells. Stem cells in the dental pulp, including dental pulp stem cells (DPSCs), stem cells from human exfoliated deciduous teeth (SHEDs) and stem cells from apical papilla (SCAPs), have been isolated from human tissues with an emphasis on their potential application to regenerative therapies. Recent studies utilizing mouse genetic models shed light on the identities of these mesenchymal progenitor cells derived from neural crest cells (NCCs) in their native conditions, particularly regarding how they contribute to homeostasis and repair of the dental tissue. The current concept is that at least two distinct niches for stem cells exist in the dental pulp, e.g., the perivascular niche and the perineural niche. The precise identities of these stem cells and their niches are now beginning to be unraveled thanks to sophisticated mouse genetic models, which lead to better understanding of the fundamental properties of stem cells in the dental pulp and the apical papilla in humans. The new knowledge will be highly instrumental for developing more effective stem cell-based regenerative therapies to repair teeth in the future.

Current and Future Concepts for the Treatment of Impaired Fracture Healing

Bone regeneration represents a complex process, of which basic biologic principles have been evolutionarily conserved over a broad range of different species. Bone represents one of few tissues that can heal without forming a fibrous scar and, as such, resembles a unique form of tissue regeneration. Despite a tremendous improvement in surgical techniques in the past decades, impaired bone regeneration including non-unions still affect a significant number of patients with fractures. As impaired bone regeneration is associated with high socio-economic implications, it is an essential clinical need to gain a full understanding of the pathophysiology and identify novel treatment approaches. This review focuses on the clinical implications of impaired bone regeneration, including currently available treatment options. Moreover, recent advances in the understanding of fracture healing are discussed, which have resulted in the identification and development of novel therapeutic approaches for affected patients.

Lesion Dynamics Under Varying Paracrine PDGF Signaling in Brain Tissue

Paracrine PDGF signaling is involved in many processes in the body, both normal and pathological, including embryonic development, angiogenesis, and wound healing as well as liver fibrosis, atherosclerosis, and cancers. We explored this seemingly dual (normal and pathological) role of PDGF mathematically by modeling the release of PDGF in brain tissue and then varying the dynamics of this release. Resulting simulations show that by varying the dynamics of a PDGF source, our model predicts three possible outcomes for PDGF-driven cellular recruitment and lesion growth: (1) localized, short duration of growth, (2) localized, chronic growth, and (3) widespread chronic growth. Further, our model predicts that the type of response is much more sensitive to the duration of PDGF exposure than the maximum level of that exposure. This suggests that extended duration of paracrine PDGF signal during otherwise normal processes could potentially lead to lesions having a phenotype consistent with pathologic conditions.

Cellular biology of fracture healing

The biology of bone healing is a rapidly developing science. Advances in transgenic and gene-targeted mice have enabled tissue and cell-specific investigations of skeletal regeneration. As an example, only recently has it been recognized that chondrocytes convert to osteoblasts during healing bone, and only several years prior, seminal publications reported definitively that the primary tissues contributing bone forming cells during regeneration were the periosteum and endosteum. While genetically modified animals offer incredible insights into the temporal and spatial importance of various gene products, the complexity and rapidity of healing-coupled with the heterogeneity of animal models-renders studies of regenerative biology challenging. Herein, cells that play a key role in bone healing will be reviewed and extracellular mediators regulating their behavior discussed. We will focus on recent studies that explore novel roles of inflammation in bone healing, and the origins and fates of various cells in the fracture environment. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Safety study: is there a pathologic IGF-1, PDGF and TGF-β cytokine expression caused by adjunct BMP-7 in tibial and femoral non-union therapy?

Background

In this prospective safety study, we investigated if the characteristic cytokine expression during bone regeneration is manipulated by the local application of bone morphogenetic protein-7 (BMP-7) in non-union surgery. Therefore, the levels of insulin like growth factor 1 (IGF-1), platelet-derived growth factor AB (PDGF-AB) and transforming growth factor beta (TGF-β) were compared between patients with the gold standard use of autologous bone graft (ABG) and those with additional application of BMP-7 as part of the diamond concept.

Patients and methods

Between 2009 and 2014, of the 153 patients with tibial and femoral non-unions, a matched pair analysis was performed to compare the serological cytokine expressions. Blood samples were collected preoperatively, 1, 2 and 6 weeks as well as 3 and 6 months after non-union surgery. Matching criteria were smoking status, fracture location, gender, age and body mass index (BMI). Patients in G1 (n=10) were treated with ABG and local BMP-7 while their matching partners in G2 (n=10) received ABG only. The routine clinical and radiologic follow-up was 1 year.

Results

Although the IGF-1 quantification in G2 showed higher pre- and postoperative values compared to G1 (p<0.05), the courses of both groups were similar. Likewise, PDGF-AB and TGF-β expressions appeared similar in G1 and G2 with peaks in both groups at 2 weeks follow-up. Osseous consolidation was assessed in all operated non-unions. The adjunct application of BMP-7 did not cause any pathologic cytokine expression.

Conclusion

Similar expressions of the serum cytokines IGF-1, PDGF-AB and TGF-β were demonstrated in non-union patients treated with ABG and additional application of BMP-7 according to the diamond concept. Our findings indicate that the local application of BMP-7, which imitates the physiologic secretion of growth factors during bone regeneration, is safe and without the risk of abnormal systemic cytokine expression. Studies with higher patient numbers will have to validate these assumptions.

Loss of Dnmt3b in Chondrocytes Leads to Delayed Endochondral Ossification and Fracture Repair

Despite advanced understanding of signaling mediated by local and systemic factors, the role of epigenetic factors in the regulation of bone regeneration remains vague. The DNA methyltransferases (Dnmts) Dnmt3a and Dnmt3b have tissue specific expression patterns and create unique methylation signatures to regulate gene expression. Using a stabilized murine tibia fracture model we find that Dnmt3b is induced early in fracture healing, peaks at 10 days post fracture (dpf), and declines to nearly undetectable levels by 28 dpf. Dnmt3b expression was cell-specific and stage-specific. High levels were observed in chondrogenic lineage cells within the fracture callus. To determine the role of Dnmt3b in fracture healing, Agc1CreERT2 ;Dnmt3bf/f (Dnmt3bAgc1ER ) mice were generated to delete Dnmt3b in chondrogenic cells. Dnmt3bAgc1ER fracture displayed chondrogenesis and chondrocyte maturation defect, and a delay in the later events of angiogenesis, ossification, and bone remodeling. Biomechanical studies demonstrated markedly reduced strength in Dnmt3bAgc1ER fractures and confirmed the delay in repair. The angiogenic response was reduced in both vessel number and volume at 10 and 14 dpf in Dnmt3bAgc1ER mice. Immunohistochemistry showed decreased CD31 expression, consistent with the reduced angiogenesis. Finally, in vitro angiogenesis assays with human umbilical vein endothelial cells (HUVECs) revealed that loss of Dnmt3b in chondrocytes significantly reduced tube formation and endothelial migration. To identify specific angiogenic factors involved in the decreased callus vascularization, a protein array was performed using conditioned media isolated from control and Dnmt3b loss-of-function chondrocytes. Several angiogenic factors, including CXCL12 and osteopontin (OPN) were reduced in chondrocytes following loss of Dnmt3b. DNA methylation analysis further identified hypomethylation in Cxcl12 promoter region. Importantly, the defects in tube formation and cell migration could be rescued by administration of CXCL12 and/or OPN. Altogether, our findings establish that Dnmt3b positively regulates chondrocyte maturation process, and its genetic ablation leads to delayed angiogenesis and fracture repair. © 2017 American Society for Bone and Mineral Research.

Histological response to platelet-rich plasma added to polypropylene mesh implemented in rabbits

Introduction:

The platelet-rich plasma (PRP) is part of a set of biotechnologies, providing some growth factors that promote repair of different tissues. The polypropylene meshes (PPM) are applied in the correction of abdominal defects, pelvic floor and urinary incontinence, however, they induce many significant complications, as a result of an inappropriate inflammatory response.

Purpose:

To investigate the changes caused by PRP associated with the implantation of PPM in the abdomen of female rabbits, in the production of collagen I and III and the inflammatory infiltrate (ININ).

Materials and Methods:

We performed implant meshes with and without PRP in adult rabbits (n=30) and euthanasia at 7, 30 and 90 days. Two plates were prepared from each animal and analyzed in five different fields. The ININ was evaluated by quantification of inflammatory cells using hematoxylin-eosin and the collagen by Sirius red method. The results were analyzed applying the Wilcoxon, Kruskal-Wallis, Junckheere and Friedmann tests.

Results:

There was a significant difference in the number of inflammatory cells between the groups with and without PRP (p=0.01) at 90 days. There was increased production of collagen I, III and total with the use of PRP, at seven days.

Conclusion:

The PPM coating with PRP was associated with increased ININ at the implant area, and an increasing trend during the process of tissue repair. The PPM coated with PRP was related to increased concentration of collagen I, collagen III and the concentration of total collagen increased after seven days of implantation.

PDGFRβ+/c-kit+ pulp cells are odontoblastic progenitors capable of producing dentin-like structure in vitro and in vivo

Background

Successful pulp regeneration depends on identification of pulp stem cells capable of differentiation under odontoblastic lineage and producing pulp-dentinal like structure. Recent studies demonstrate that platelet-derived growth factor (PDGF) plays an important role in damage repair and tissue regeneration. The aim of this study was to identify a subpopulation of dental pulp cells responsive to PDGF and with dentin regeneration potential.

Methods

Pulp tissues were isolated from 12 freshly extracted human impacted third molars. Pulp cells were sorted by their expression of PDGFRβ and stem cell marker genes via flow cytometry. For the selected cells, proliferation was analyzed by a colorimetric cell proliferation assay, differentiation was assessed by real time PCR detection the expression of odontoblast marker genes, and mineralization was evaluated by Alizarin Red S staining. GFP marked PDGFRβ⁺/c-kit⁺ pulp cells were transplanted into emptied root canals of nude rat lower left incisors. Pulp-dentinal regeneration was examined by immunohistochemistry.

Results

PDGFRβ⁺/c-kit⁺ pulp cells proliferated significantly faster than whole pulp cells. In mineralization media, PDGFRβ⁺/c-kit⁺ pulp cells were able to develop under odontoblastic linage as demonstrated by a progressively increased expression of DMP1, DSPP, and osteocalcin. BMP2 seemed to enhance whereas PDGF-BB seemed to inhibit odontoblastic differentiation and mineralization of PDGFRβ⁺/c-kit⁺ pulp cells. In vivo root canal transplantation study revealed globular dentin and pulp-like tissue formation by PDGFRβ⁺/c-kit⁺ cells.

Conclusions

PDGFRβ⁺/c-kit⁺ pulp cells appear to have pulp stem cell potential capable of producing dentinal like structure in vitro and in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12903-016-0307-8) contains supplementary material, which is available to authorized users.

Osteoblast-derived paracrine factors regulate angiogenesis in response to mechanical stimulation

Angiogenesis is a process by which new blood vessels emerge from existing vessels through endothelial cell sprouting, migration, proliferation, and tubule formation. Angiogenesis during skeletal growth, homeostasis and repair is a complex and incompletely understood process. As the skeleton adapts to mechanical loading, we hypothesized that mechanical stimulation regulates "osteo-angio" crosstalk in the context of angiogenesis. We showed that conditioned media (CM) from osteoblasts exposed to fluid shear stress enhanced endothelial cell proliferation and migration, but not tubule formation, relative to CM from static cultures. Endothelial cell sprouting was studied using a dual-channel collagen gel-based microfluidic device that mimics vessel geometry. Static CM enhanced endothelial cell sprouting frequency, whereas loaded CM significantly enhanced both frequency and length. Both sprouting frequency and length were significantly enhanced in response to factors released from osteoblasts exposed to fluid shear stress in an adjacent channel. Osteoblasts released angiogenic factors, of which osteopontin, PDGF-AA, IGBP-2, MCP-1, and Pentraxin-3 were upregulated in response to mechanical loading. These data suggest that in vivo mechanical forces regulate angiogenesis in bone by modulating "osteo-angio" crosstalk through release of paracrine factors, which we term "osteokines".

Growth factors and cytokines in patients with long bone fractures and associated spinal cord injury

BACKGROUND

The aim of the study was to test the effect of acute traumatic spinal cord injury of quadriplegia or paraplegia on bone healing in patients with associated long bone fractures and to investigate the molecular and cellular events of the underlying mechanism for a possible acceleration.

METHODS

Healing indicators of long bone fractures and growth factors, IGF-II, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), Activin-A, and cytokine I-L-1, in the patients' blood were calculated and measured for 21 patients with spinal cord injuries and associated long bone fractures in prospective controlled study and compared to 20 patients with only spinal cord injuries, 30 patients with only long bone fractures, and 30 healthy volunteers.

RESULTS

The study results showed that long bone fractures in patients with associated acute traumatic spinal cord injury of quadriplegia or paraplegia heal more expectedly, faster, and with exuberant florid union callus (P > 0.001) and show statistically significant higher levels of growth factors like PDGF, VEGF, Activin-A, and cytokine I-L-1, along the 3 weeks of follow-up (P > 0.005). I-IGF-II showed statistically significant subnormal level along the whole follow-up period in the same patients (P > 0.005).

CONCLUSION

We concluded that long bone fractures in spinal cord injury patients heal more expectedly, faster, and with exuberant and florid callus formation; growth factors like IGF-II, PDGF, VEGF, Activin-A, and cytokine I-L-I have roles as mediators, in molecular events and as byproducts of the subtle mechanism of accelerated osteogenesis in these patients and may represent therapeutic potentials to serve as agents to enhance bone repair.

The systemic influence of platelet-derived growth factors on bone marrow mesenchymal stem cells in fracture patients

BACKGROUND

Fracture healing is a complex process regulated by a variety of cells and signalling molecules which act both locally and systemically. The aim of this study was to investigate potential changes in patients' mesenchymal stem cells (MSCs) in the iliac crest (IC) bone marrow (BM) and in peripheral blood (PB) in relation to the severity of trauma and to correlate them with systemic changes reflective of inflammatory and platelet responses following fracture.

METHODS

ICBM samples were aspirated from two trauma groups: isolated trauma and polytrauma (n = 8 and 18, respectively) at two time-points post-fracture and from non-trauma controls (n = 7). Matched PB was collected every other day for a minimum of 14 days. BM MSCs were enumerated using colony forming-fibroblast (CFU-F) assay and flow cytometry for the CD45-CD271+ phenotype.

RESULTS

Regardless of the severity of trauma, no significant increase or decrease in BM MSCs was observed following fracture and MSCs were not mobilised into PB. However, direct positive correlations were observed between changes in the numbers of aspirated BM MSCs and time-matched changes in their serum PDGF-AA and -BB. In vitro, patients' serum induced MSC proliferation in a manner reflecting changes in PDGFs. PDGF receptors CD140a and CD140b were expressed on native CD45-CD271+ BM MSCs (average 12% and 64%, respectively) and changed over time in direct relationship with platelets/PDGFs.

CONCLUSIONS

Platelet lysates and other platelet-derived products are used to expand MSCs ex vivo. This study demonstrates that endogenous PDGFs can influence MSC responses in vivo. This indicates a highly dynamic, rather than static, MSC nature in humans.

The multifaceted role of the vasculature in endochondral fracture repair

Fracture healing is critically dependent upon an adequate vascular supply. The normal rate for fracture delayed or non-union is estimated to be between 10 and 15%, and annual fracture numbers are approximately 15 million cases per year. However, when there is decreased vascular perfusion to the fracture, incidence of impaired healing rises dramatically to 46%. Reduction in the blood supply to the fracture can be the result of traumatic injuries that physically disrupt the vasculature and damage supportive soft tissue, the result of anatomical location (i.e., distal tibia), or attributed to physiological conditions such as age, diabetes, or smoking. The role of the vasculature during repair is multifaceted and changes during the course of healing. In this article, we review recent insights into the role of the vasculature during fracture repair. Taken together these data highlight the need for an updated model for endochondral repair to facilitate improved therapeutic approaches to promote bone healing.

Concentration of platelets and growth factors in platelet-rich plasma from Goettingen minipigs

In minipigs little is known about the concentration of growth factors in plasma, despite their major role in several patho-physiological processes such as healing of fractures. This prompted us to study the concentration of platelets and selected growth factors in plasma and platelet-rich plasma (PRP) preparation of sixteen Goettingen minipigs.

Platelet concentrations increased significantly in PRP in comparison to native blood plasma. Generally, significant increase in the concentration of all growth factors tested was observed in the PRP in comparison to the corresponding plasma or serum. Five of the plasma samples examined contained detectable levels of bone morphogenic protein 2 (BMP-2) whereas eleven of the plasma or serum samples contained minimal amounts of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF-bb) respectively. On the other hand variable concentrations of bone morphogenic protein 7 (BMP-7) and transforming growth factor β1 (TGF-β1) were measured in all plasma samples. In contrast, all PRP samples contained significantly increased amounts of growth factors. The level of BMP-2, BMP-7, TGF-β1, VEGF and PDGF-bb increased by 17.6, 1.5, 7.1, 7.2 and 103.3 fold, in comparison to the corresponding non-enriched preparations. Moreover significant positive correlations were found between platelet count and the concentrations of BMP-2 (r=0.62, p<0.001), TGF-β1 (r=0.85, p<0.001), VEGF (r=0.46, p<0.01) and PDGF-bb (r=0.9, p<0.001). Our results demonstrate that selected growth factors are present in the platelet-rich plasma of minipigs which might thus serve as a source of autologous growth factors.

Combined use of low-intensity pulsed ultrasound and rhBMP-2 to enhance bone formation in a rat model of critical size defect

BACKGROUND

Bone repair is regulated by biological factors and the local mechanical environment. We hypothesize that the combined use of low-intensity pulsed ultrasound (LIPUS) and recombinant human bone morphogenetic protein-2 (rhBMP-2) will synergistically or additively enhance bone regeneration in a model simulating the more difficult scenarios in orthopaedic traumatology.

METHODS

Femoral defects in rats were replaced with absorbable collagen sponges carrying rhBMP-2 (0, 1.2, 6, or 12 μg; n = 30). Each group was divided equally to receive daily treatment of either LIPUS or sham stimulation. At 4 weeks, new bone formation was assessed using quantitative (radiography and microcomputed tomography), qualitative (histology), and functional (biomechanical) end points.

RESULTS

LIPUS with 1.2 μg of rhBMP-2 significantly improved the radiographic healing as compared with its sham control starting as early as 2 weeks. Quantitatively, the use of LIPUS with 6 μg of rhBMP-2 significantly increased the bone volume. However, using LIPUS with 12 μg of rhBMP-2 indicated a reduction in callus size, without compromising the bone volume, which was also observable histologically, showing organized lamellar bone and repopulated marrow in the original defect region. Histologically, 1.2 μg of rhBMP-2 alone showed the presence of uncalcified cartilage in the defect, which was reduced with LIPUS treatment. Biomechanically, LIPUS treatment significantly increased the peak torsion and stiffness in the 6- and 12 μg rhBMP-2 groups.

CONCLUSIONS

LIPUS enhances rhBMP-2-induced bone formation at lower doses (1.2 and 6 μg) and callus maturation at 12-μg dose delivered on absorbable collagen sponge for bone repair in a rat critical-sized femoral segmental defect.

Effect of hyperbaric oxygen therapy combined with autologous platelet concentrate applied in rabbit fibula fraction healing

OBJECTIVES

The purpose is to study the effects of hyperbaric oxygen therapy and autologous platelet concentrates in healing the fibula bone of rabbits after induced fractures.

METHODS

A total of 128 male New Zealand albino rabbits, between 6-8 months old, were subjected to a total osteotomy of the proximal portion of the right fibula. After surgery, the animals were divided into four groups (n = 32 each): control group, in which animals were subjected to osteotomy; autologous platelet concentrate group, in which animals were subjected to osteotomy and autologous platelet concentrate applied at the fracture site; hyperbaric oxygen group, in which animals were subjected to osteotomy and 9 consecutive daily hyperbaric oxygen therapy sessions; and autologous platelet concentrate and hyperbaric oxygen group, in which animals were subjected to osteotomy, autologous platelet concentrate applied at the fracture site, and 9 consecutive daily hyperbaric oxygen therapy sessions. Each group was divided into 4 subgroups according to a pre-determined euthanasia time points: 2, 4, 6, and 8 weeks postoperative. After euthanasia at a specific time point, the fibula containing the osseous callus was prepared histologically and stained with hematoxylin and eosin or picrosirius red.

RESULTS

Autologous platelet concentrates and hyperbaric oxygen therapy, applied together or separately, increased the rate of bone healing compared with the control group.

CONCLUSION

Hyperbaric oxygen therapy and autologous platelet concentrate combined increased the rate of bone healing in this experimental model.

Platelet-derived growth factor and spatiotemporal cues induce development of vascularized bone tissue by adipose-derived stem cells

Vasculature is essential to the functional integration of a tissue-engineered bone graft to enable sufficient nutrient delivery and viability after implantation. Native bone and vasculature develop through intimately coupled, tightly regulated spatiotemporal cell-cell signaling. The complexity of these developmental processes has been a challenge for tissue engineers to recapitulate, resulting in poor codevelopment of both bone and vasculature within a unified graft. To address this, we cultured adipose-derived stromal/stem cells (ASCs), a clinically relevant, single cell source that has been previously investigated for its ability to give rise to vascularized bone grafts, and studied the effects of initial spatial organization of cells, the temporal addition of growth factors, and the presence of exogenous platelet-derived growth factor-BB (PDGF-BB) on the codevelopment of bone and vascular tissue structures. Human ASCs were aggregated into multicellular spheroids via the hanging drop method before encapsulation and subsequent outgrowth in fibrin gels. Cellular aggregation substantially increased vascular network density, interconnectivity, and pericyte coverage compared to monodispersed cultures. To form robust vessel networks, it was essential to culture ASCs in a purely vasculogenic medium for at least 8 days before the addition of osteogenic cues. Physiologically relevant concentrations of exogenous PDGF-BB (20 ng/mL) substantially enhanced both vascular network stability and osteogenic differentiation. Comparisons with the bone morphogenetic protein-2, another pro-osteogenic and proangiogenic growth factor, indicated that this potential to couple the formation of both lineages might be unique to PDGF-BB. Furthermore, the resulting tissue structure demonstrated the close association of mineral deposits with pre-existing vascular structures that have been described for developing tissues. This combination of a single cell source with a potent induction factor used at physiological concentrations can provide a clinically relevant approach to engineering highly vascularized bone grafts.

Growth factors in the treatment of early osteoarthritis

Regenerative medicine is the science that studies the regeneration of biological tissues obtained through use of cells, with the aid of support structures and with biomolecules such as growth factors. As regards the growth factors the PRP, or the platelet-rich plasma, obtained from a withdrawal of autologous blood, concentrating the platelets, represents a safe, economical, easy to prepare and easy to apply source of growth factors. Numerous growth factors are in fact within the platelets and in particular a large number of them have a specific activity on neo-proliferation, on cartilage regeneration and in particular also an antiapoptotic effect on chondroblasts: - The PDGF which regulates the secretion and synthesis of collagen;- The EGF that causes cellular proliferation, endothelial chemotaxis and angiogenesis;- The VEGF that increases angiogenesis and vascular permeability;- The TGF-beta that stimulates the proliferation of undifferentiated MSC, stimulates chemotaxis of endothelial cells and angiogenesis;- The bFGF that promotes the growth and differentiation of chondrocytes and osteoblasts stimulates mitogenesis of mesenchymal cells, chondrocytes and osteoblasts. These properties have led to the development of studies that evaluated the efficacy of treatment of infiltrations in the knee and hip with platelet-derived growth factors. Regarding the knee it was demonstrated that in patients with moderate degree of gonarthrosis, the PRP is able to significantly reduce the pain and improve joint function, both on placebo and towards infiltrations with hyaluronic acid. The success of the treatment was proportional to the age of and inversely proportional to the severity of osteoarthritis according to Kellgren and Lawrence classification. The possibility of infiltrations guided with ultrasound into the hip led us to extend the indications also to hip arthrosis, as already showed by Sanchez. Even in coxarthrosis preliminary results at 6 and 12 months show that a cycle of 3 infiltrations of PRP has significantly decreased the pain and increased range of motion and joint function.

Effects of the immobilization of heparin and rhPDGF-BB to titanium surfaces for the enhancement of osteoblastic functions and anti-inflammation

PURPOSE

This study was to investigate the effects of recombinant human platelet-derived growth factor (rhPDGF-BB) and heparin to titanium surfaces for enhancement of osteoblastic functions and inhibition of inflammation activity.

MATERIALS AND METHODS

The anodized titanium discs, not coated with any material, were used as a control group. In heparinized- Ti group, dopamine was anchored to the surface of Ti substrates, and coated with heparin. In PDGF-Ti group, rhPDGF-BB was immobilized onto heparinized Ti surface. The surface morphologies were investigated by the scanning electron microscope in each group. The release kinetics of rhPDGF-BB were analyzed, and cytotoxicity tests for each group were conducted. The biocompatibilities were characterized by measuring cell proliferation, alkaline phosphatase activity, and calcium deposition using MG-63 cells. Statistical comparisons were carried out by one-way ANOVA tests. Differences were considered statistically significant at ^*P<.05 and ^**P<.001.

RESULTS

The combination of rhPDGF-BB and heparin stimulated alkaline phosphatase activity and OCN mRNA expression in osteoblastic cells (^*P<.05 and ^**P<.001). MG-63 cells grown on PDGF-Ti had significantly higher amounts of calcium deposition than those grown on anodized Ti (^**P<.001). Heparinized Ti was more anti-inflammatory compared to anodized Ti, when exposed to lipopolysaccharide using the transcript levels of TNF-α and IL-6 of proinflammatory cytokine (^*P<.05 and ^**P<.001).

CONCLUSION

The result of this study demonstrated that the incorporation of rhPDGF-BB and heparin onto Ti surface enhanced osteoblastic functions and inhibited inflammation.

Comparison between the effects of platelet-rich plasma and bone marrow concentrate on defect consolidation in the rabbit tibia

OBJECTIVE

To perform a comparative analysis of the effects of platelet-rich plasma and centrifuged bone marrow aspirate on the induction of bone healing in rabbits.

METHOD

Twenty adult, male New Zealand rabbits were randomly separated into two equal groups, and surgery was performed to create a bone defect (a cortical orifice 3.3 mm in diameter) in the proximal metaphysis of each rabbit's right tibia. In the first group, platelet-rich plasma was implanted in combination with β-tricalcium phosphate (platelet-rich plasma group), and in the second group, centrifuged bone marrow in combination with β-tricalcium phosphate (centrifuged bone marrow group) was implanted. After a period of four weeks, the animals were euthanized, and the tibias were evaluated using digital radiography, computed tomography, and histomorphometry.

RESULTS

Seven samples from each group were evaluated. The radiographic evaluation confirmed the absence of fractures in the postoperative limb and identified whether bone consolidation had occurred. The tomographic evaluation revealed a greater amount of consolidation and the formation of a greater cortical bone thickness in the platelet-rich plasma group. The histomorphometry revealed a greater bone density in the platelet-rich plasma group compared with the centrifuged bone marrow group.

CONCLUSION

After four weeks, the platelet-rich plasma promoted a greater amount of bone consolidation than the bone marrow aspirate concentrate.

Comparison between Platelet-Rich Plasma and Autologous Iliac Grafts for Tibial Osteotomy

OBJECTIVE

Platelet-rich plasma (PRP) has the capacity to improve the bone-healing process. The aim of this pilot study was to investigate the occurrence of bone healing and the time taken to achieve this in patients submitted to medial opening wedge high tibial osteotomy (MOWHTO), comparing platelet-rich plasma with bone marrow aspirate to autologous iliac graft.

DESIGN

Twenty-five patients who underwent tibial osteotomy were randomly divided into 2 groups: a control group, which received autologous iliac grafts (14 patients), and a study group, which received a compound of PRP and bone marrow aspirate (11 patients).

RESULTS

The bone-healing rates achieved were 100% in the control group and 91% in the study group. There was no difference in the time taken to achieve bone healing between the groups.

CONCLUSIONS

The use of a combination of PRP and bone marrow aspirate, as a bone substitute, did not demonstrate any advantage over the use of an autologous iliac graft in MOWHTO.

Occurrence and treatment of bone atrophic non-unions investigated by an integrative approach

Recently developed atrophic non-union models are a good representation of the clinical situation in which many non-unions develop. Based on previous experimental studies with these atrophic non-union models, it was hypothesized that in order to obtain successful fracture healing, blood vessels, growth factors, and (proliferative) precursor cells all need to be present in the callus at the same time. This study uses a combined in vivo-in silico approach to investigate these different aspects (vasculature, growth factors, cell proliferation). The mathematical model, initially developed for the study of normal fracture healing, is able to capture essential aspects of the in vivo atrophic non-union model despite a number of deviations that are mainly due to simplifications in the in silico model. The mathematical model is subsequently used to test possible treatment strategies for atrophic non-unions (i.e. cell transplant at post-osteotomy, week 3). Preliminary in vivo experiments corroborate the numerical predictions. Finally, the mathematical model is applied to explain experimental observations and identify potentially crucial steps in the treatments and can thereby be used to optimize experimental and clinical studies in this area. This study demonstrates the potential of the combined in silico-in vivo approach and its clinical implications for the early treatment of patients with problematic fractures.

In light of the ageing population, the occurrence of bone fractures is expected to rise substantially in the near future. In 5 to 10% of these cases, the healing process does not succeed in repairing the bone, leading to the formation of delayed unions or even non-unions. In this study we used a combination of an animal model mimicking a clinical non-union situation and a mathematical model developed for normal fracture healing to investigate both the causes of non-union formation and potential therapeutic strategies that can be applied to restart the healing process. After showing that the mathematical model is able to simulate key aspects of the non-union formation, we have used it to investigate several treatment strategies. One of these strategies, the treatment of a non-union involving a transplantation of cells from the bone marrow to the fracture site, was also tested in a pilot animal experiment. Both the simulations and the experiments showed the formation of a bony union between the fractured bone ends. In addition, we used the mathematical model to explain some unexpected experimental observations. This study demonstrates the added value of using a combination of mathematical modelling and experimental research as well the potential of using cell transplantation for the treatment of non-unions.

Altered relative expression of BMPs and BMP inhibitors in cartilaginous areas of human fractures progressing towards nonunion

The present study was conducted to evaluate the hypothesis that an imbalance in the local production of bone morphogenetic proteins (BMPs) and BMP inhibitors exists within the cartilaginous intermediate of nonhealing fractures. Biopsies were recovered intraoperatively from human fractures that, upon follow-up, were found to heal normally or become nonunions. The samples were examined by immunohistochemistry to determine the expression of BMP-2, BMP-14, and the BMP inhibitors noggin and chordin. Expression was determined semiquantitatively based on the area of positive staining per area of cartilage and by determining the number of positively staining cells and the intensity of staining. There was a significant reduction in BMP-2 and BMP-14 expression in cartilaginous areas of nonhealing fractures compared to healing fractures. However, there was no difference in the expression of the BMP inhibitors between the two groups of fractures. This imbalance in the expression of BMPs and BMP inhibitors within cartilaginous areas of developing nonunions may account for their reduced bone forming ability. These data suggest strategies for preventing the development of nonunions by altering levels of BMPs and their inhibitors within fracture sites.

Regional and cellular localisation of BMPs and their inhibitors' expression in human fractures

The objective of this study was to determine whether BMP-2 and -14, noggin, and chordin could be detected in human fractures and to assess their regional and cellular distribution. The expression of these proteins was detected by immunohistochemistry in an archive of human fractures. BMP-2 and BMP-14 expression was strongest in areas of cartilage formation and, to a lesser extent, in areas of bone formation. Within areas of cartilage formation, both BMP-2 and BMP-14 were expressed more strongly by the non-hypertrophic chondrocytes. The BMP inhibitors noggin and chordin were also expressed most intensely in areas of cartilage formation and there was no difference in their expression between the non-hypertrophic and hypertrophic chondrocytes. Our study demonstrates the expression of BMP-14 and the BMP inhibitors in human fractures for the first time, and our findings will contribute to an improved understanding of the physiological processes in bone repair.

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.

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 .

Callus mineralization and maturation are delayed during fracture healing in interleukin-6 knockout mice

IL-6 is a pleiotropic cytokine involved in cell signaling in the musculoskeletal system, but its role in bone healing remains uncertain. The purpose of this study was to examine the role of IL-6 in fracture healing. Eight-week-old male C57BL/6 and IL-6 -/- mice were subjected to transverse, mid-diaphyseal osteotomies on the right femora. Sacrifice time points were 1, 2, 4, or 6 weeks post-fracture (N=14 per group). Callus tissue properties was analyzed by microcomputed tomography (micro-CT) and Fourier transform infrared imaging spectroscopy (FT-IRIS). Cartilage and collagen content, and osteoclast density were measured histologically. In intact unfractured bone, IL-6 -/- mice had reduced crystallinity, mineral/matrix ratio, tissue mineral density (TMD), and bone volume fraction (BVF) compared to wildtype mice. This suggests that there was an underlying deficit in baseline bone quality in IL-6 -/- mice. At 2 weeks post-fracture, the callus of IL-6 -/- mice had reduced crystallinity and mineral/matrix ratio. These changes were less evident at 4 weeks. At 2 weeks, the callus of the IL-6 -/- mice had an increased tissue mineral density (TMD), an increased cartilage and collagen content, and reduced osteoclast density compared to these parameters in wildtype mice. By 4 and 6 weeks, these parameters were no longer different between the two strains of mice. In conclusion, IL-6 -/- mice had delayed callus maturity, mineralization, and remodeling compared with the callus of the wildtype mice. These effects were transient indicating that the role of IL-6 appears to be most important in the early stages of fracture healing.

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.

Expression of the gene encoding the matrix gla protein by mature osteoblasts in human fracture non-unions

BACKGROUND

Osteoblast phenotypic abnormality, namely the expression of collagen type III, has been shown previously in fracture non-union woven bone.

AIMS

To investigate osteoblasts from fracture non-unions for evidence of gene expression of non-collagenous bone matrix proteins that have been implicated in mineralisation, namely matrix gla protein (MGP), osteonectin, osteopontin, and osteocalcin. MGP is a consistent component of bone matrix, but there are no reports of osteoblasts in the skeleton expressing the gene for MGP, and the site of synthesis of skeletal MGP (perhaps the liver) has yet to be determined.

METHODS

Biopsies from normally healing human fractures and non-unions were examined by means of in situ hybridisation, using 35S labelled probes and autoradiography to disclose levels of gene expression.

RESULTS

In normally healing fractures, mature osteoblasts on woven bone were negative for MGP mRNA, but positive for osteonectin, osteopontin, and osteocalcin mRNA molecules. In non-unions, osteoblasts displayed a novel phenotype: they were positive for MGP mRNA, in addition to osteonectin, osteopontin, and osteocalcin mRNA molecules.

CONCLUSIONS

Mature osteoblasts in slowly healing fractures have an unusual phenotype: they express the gene encoding MGP, which indicates that control of osteoblast gene expression in non-unions is likely to be abnormal. This might be of importance in the pathogenesis of non-uniting human fractures, and is of current interest given the emerging status of MGP as an inhibitor of mineralisation.

Gene expression of matrix metalloproteinases 1, 3, and 9 by chondrocytes in osteoarthritic human knee articular cartilage is zone and grade specific

OBJECTIVES

Matrix metalloproteinases (MMPs) are thought to be major mediators of cartilage destruction. Osteoarthritis (OA) is characterised by cartilage degradation. This study explores gene expression of three MMPs in articular chondrocytes during the histological development of the cartilage lesion of OA.

METHODS

Biopsy specimens of human normal and OA cartilage, classified into four grades on the basis of histology, were probed for MMPs 1, 3, and 9 using 35S-labelled cDNA probes. The signal was measured at four different depths (zones) using an automated image analyser and compared with signal from sections probed with lambda DNA. Rheumatoid synovium was used as a positive control for MMP gene expression.

RESULTS

Rheumatoid tissue contained mRNA for all three MMPs. Expression in chondrocytes varied with the depth of the chondrocyte in the cartilage and the histomorphological extent of the OA changes. There was no detectable mRNA signal for these three MMPs in normal cartilage. In general, in OA, MMP-1 gene expression was greatest in the superficial cartilage in established disease. By contrast mRNAs for MMP-3 and 9 were expressed deeper in the cartilage, MMP-9 early in disease and MMP-3 with a biphasic pattern in early and late stage disease, most pronounced in the latter. This was a consequence of differential expression in single cells and chondrocyte clusters in late disease.

CONCLUSION

The data indicate that expression of genes for MMPs 1, 3, and 9 is differentially regulated in human articular chondrocytes and, in individual cells, is related to the depth of the chondrocyte below the cartilage surface and the nature and extent of the cartilage lesion.

Mature osteoblasts in human non-union fractures express collagen type III

AIMS

High levels of collagen type III are biochemically detectable in biopsies of non-uniting fractures, and in the serum of patients suffering from this condition. The aim of this study was to determine whether the expression of collagen type III was limited to fibrous tissue in non-unions, or whether some was present in bone.

METHODS

Biopsies from normally healing human fractures and non-unions were examined using in situ hybridisation and immunohistochemistry.

RESULTS

The mesenchymal cell population, which includes fibroblast and osteoblast precursors, expressed mRNA for collagen type III. However, mature osteoblasts on the surface of woven bone varied profoundly between normally healing fractures (in which they were negative or occasionally weakly positive) and non-unions (in which they were strongly positive). Areas of woven bone that had osteoblasts positive for collagen type III mRNA also immunostained positively for the protein.

CONCLUSIONS

This study shows that non-union fracture callus osteoblasts on the surfaces of woven bone exhibit an unusual phenotype: they express collagen type III, a molecule characteristic of an earlier stage of osteoblast differentiation, which is not expressed by osteoblasts on woven bone surfaces of bone that develops normally. This finding may be useful in developing an early clinical test for impending non-union.