Platelet-derived growth factor (PDGF)-AA: a self-imposed cytokine in the proliferation of human fetal osteoblasts

Dental Pulp Stem Cell Conditioned Medium Enhance Osteoblastic Differentiation and Bone Regeneration

BACKGROUND

Cell-free approaches, utilizing mesenchymal stem cell secretome, have promising prospects in various fields of regenerative medicine. In this study, we examined in vitro and in vivo the potential of dental pulp stem cell-conditioned medium (DPSC-CM) for bone regeneration.

METHODS

The secretome of undifferentiated stem cells from dental pulp were collected, and the effects of this DPSC-CM were assessed for osteodifferentiation of osteoblast-like cells (MG-63) and osteoblasts deriving from DPSC. Cell proliferation, alkaline phosphatase (ALP) activity, gene expression of Runt-related transcription factor 2 (Runx2), Bone Sialoprotein (BSP), Osteocalcin (OCN), and extracellular matrix mineralization were evaluated. The rat caudal vertebrae critical size defect model was to investigate the effect of DPSC-CM in vivo.

RESULTS

Results showed that DPSC-CM induced cell growth, and increased ALP activity and the expression of key marker genes at an early stage of osteoblastic differentiation compared to control. A rat bone defect model was used to illustrate the effect of DPSC-CM in vivo. The bone density within the defects were improved using conditioned medium, even though there was no significant difference between the control and DPSC-CM groups. The analysis of DPSC-CM by human growth factor antibody array revealed the presence of several factors involved in osteogenesis.

CONCLUSION

Taken together, these findings indicate that DPSC-CM is a promising therapeutic candidate for bone regenerative therapy, accelerating the maturation of osteoblastic cells. And even though safety and efficiency of DPSC-CM have to be confirmed in preclinical studies, these results represent a first step toward clinical application.

Antifibrotic effects of sodium-glucose cotransporter-2 inhibitors: A comprehensive review

BACKGROUND AND AIMS

Scar tissue accumulation in organs is the underlying cause of many fibrotic diseases. Due to the extensive array of organs affected, the long-term nature of fibrotic processes and the large number of people who suffer from the negative impact of these diseases, they constitute a serious health problem for modern medicine and a huge economic burden on society. Sodium-glucose cotransporter-2 inhibitors (SGLT2is) are a relatively new class of anti-diabetic pharmaceuticals that offer additional benefits over and above their glucose-lowering properties; these medications modulate a variety of diseases, including fibrosis. Herein, we have collated and analyzed all available research on SGLT2is and their effects on organ fibrosis, together with providing a proposed explanation as to the underlying mechanisms.

METHODS

PubMed, ScienceDirect, Google Scholar and Scopus were searched spanning the period from 2012 until April 2023 to find relevant articles describing the antifibrotic effects of SGLT2is.

RESULTS

The majority of reports have shown that SGLT2is are protective against lung, liver, heart and kidney fibrosis as well as arterial stiffness. According to the results of clinical trials and animal studies, many SGLT2 inhibitors are promising candidates for the treatment of fibrosis. Recent studies have demonstrated that SGLT2is affect an array of cellular processes, including hypoxia, inflammation, oxidative stress, the renin-angiotensin system and metabolic activities, all of which have been linked to fibrosis.

CONCLUSION

Extensive evidence indicates that SGLT2is are promising treatments for fibrosis, demonstrating protective effects in various organs and influencing key cellular processes linked to fibrosis.

The effect of submucosal injection of platelet-rich fibrin vs. platelet-rich plasma on orthodontic tooth movement in rabbits; 28 days follow-up

OBJECTIVE

This study aimed to compare between the effects of submucosal injection of platelet rich fibrin (i-PRF) versus platelet rich plasma (PRP) on orthodontic tooth movement (OTM) in a rabbit model over a 28-day follow-up period.

MATERIALS AND METHODS

Sixty-three rabbits were assigned into 3 equal groups. Group I animals were subjected to the OTM without any treatments and considered as the control. Whereas groups II and III were handled as group I and instead i-PRF and PRP were injected submucosally in the buccal vestibular mucosa next to the mandibular 1st premolar, respectively. The distance of OTM was consecutively measured clinically after 7, 14 and 28 days. Seven rabbits from each group were euthanized after 7, 14 and 28 days for histological evaluation. Two-way ANOVA followed by LSD post-hoc statistical tests were used for comparison.

RESULTS

After 28 days, the mean tooth movements were 4.36±0.04mm in the control group, 6.30±0.06mm in the group receiving PRP and, 6.85±0.09mm in the group receiving i-PRF. Statistical analysis for the values of teeth movements revealed highly significant differences between different groups (P=0.001) and between different time periods (P=0.001). Histological analysis showed that submucosal injection of PRP and i-PRF yielded significant differences in periodontal ligament width in compression and tension sides between different groups (P=0.001) and between different time periods (P=0.001).

CONCLUSION

Submucosal injection of either PRP or i-PRF is a minimally invasive and safe approach for accelerating OTM. In this rabbit model, the effect of i-PRF is significantly more pronounced than the effect of PRP.

Fibrotic Scar in CNS Injuries: From the Cellular Origins of Fibroblasts to the Molecular Processes of Fibrotic Scar Formation

Central nervous system (CNS) trauma activates a persistent repair response that leads to fibrotic scar formation within the lesion. This scarring is similar to other organ fibrosis in many ways; however, the unique features of the CNS differentiate it from other organs. In this review, we discuss fibrotic scar formation in CNS trauma, including the cellular origins of fibroblasts, the mechanism of fibrotic scar formation following an injury, as well as the implication of the fibrotic scar in CNS tissue remodeling and regeneration. While discussing the shared features of CNS fibrotic scar and fibrosis outside the CNS, we highlight their differences and discuss therapeutic targets that may enhance regeneration in the CNS.

Reduced PDGF-AA in subchondral bone leads to articular cartilage degeneration after strenuous running

To identify the effects of running on articular cartilage and subchondral bone remodeling, C57BL/6 mice were randomly divided into three groups: control, moderate-, and strenuous running. Magnetic resonance imaging showed bone marrow lesions in the knee subchondral bone in the strenuous-running group in contrast with the other two groups. The microcomputed tomography analysis showed promoted bone formation in the subchondral bone in mice subjected to strenuous running. Histological and immunohistochemistry results indicated that terminal differentiation of chondrocytes and degeneration of articular cartilage were enhanced but, synthesis of platelet-derived growth factor-AA (PDGF-AA) in the subchondral bone was suppressed after strenuous running. In vitro, excessive mechanical treatments suppressed the expression of PDGF-AA in osteoblasts, and the condition medium from mechanical-treated osteoblasts stimulated maturation and terminal differentiation of chondrocytes. These results indicate that strenuous running suppresses the synthesis of PDGF-AA in subchondral bone, leading to downregulated PDGF/Akt signal in articular cartilage and thus cartilage degeneration.

Evaluate the effects of platelet rich plasma (PRP) and zinc oxide ointment on skin wound healing

In this study efficiency of platelet rich plasma (PRP) and zinc oxide on full thickness wounds created on rabbits was researched. This study conducted on 24 New Zealand rabbits divided 2 groups. A circular of 1.5 × 1.5 cm (2.5 cm²) full thickness skin wound was created under the general anesthesia. 1 ml PRP (5.503106/mm³) was applied to the one of the wounds subcutaneously. To the other wound 1 mm³ zinc oxide ointment was applied once a day during the study. Wound contraction rates were measured, biopsy materials were collected and evaluated macroscopically and histopathologically postoperatively 3rd, 7th and 15th days. As a result it is determined that PRP and zinc oxide accelerated wound contraction rates between the groups were determined as 3rd day p = 0.007, 7th day p = 0.0002 and 15th day p = 0.002.

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Wound healing is inborn to all species and is the biologic procedure by which the body repairs itself after injury, whichever it be traumatic, complicated, infected and/or surgical.

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Platelet rich plasma (PRP) gel is measured to be progressive wound treatment for acute and chronic wounds. PRP gel has mainly been applied to improve or accelerate healing of wound.

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Zinc is a vital trace element in the human body and its significance in wellbeing and infection is valued. Zinc deficiency of genetic or dietary cause can prompt neurotic, pathologic and physiological changes and deferred wound healing.

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Topical treatment with autologous PRP can be used as clinical therapy and can enhance tissue healing and enhanced angiogenesis compared to zinc oxide treatments.

Pre-treatment of titanium alloy with platelet-rich plasma enhances human osteoblast responses

Osseointegration, the histological direct bone-to-implant contact, is the ultimate goal of implant healing and the first prerequisite for long-term success of endosseous implants. It is well-known that metal implants with rough surfaces achieve better osseointegration than those with smooth surfaces in vivo. The implantation of metal materials into bone is always accompanied by bleeding. The implant surface is initially coated with blood and these initial events could determine subsequent osseointegration. However, there is little concordance between in vitro results and in vivo findings regarding the effect of surface roughness on osseointegration. Here, we show that the osteoblast response to metal surfaces pre-treated with platelets and plasma proteins elucidates the superior osseointegration of rough surfaced implants in vivo. We found that osteoblast attachment, proliferation, and osteoblastic differentiation were significantly higher on a rough titanium surface pre-treated with platelet-rich plasma (PRP) than on the same surface without pretreatment. Furthermore, we found that the three-dimensional fibrillar network formed on the rough surface of the titanium by PRP pre-treatment might enhance osteoblast responses. Our results demonstrate why osseointegration is found to be most active on metal implants with a rough surface in vivo. We anticipate that our assay would be a useful tool for mimicking the in vivo model of osseointegration. Because cellular responses to the titanium implant that are pre-treated with platelet and plasma proteins on their surfaces after the biomimetic process in vitro, may be more similar to the events that occur in vivo.

PDGF-AA promotes osteogenic differentiation and migration of mesenchymal stem cell by down-regulating PDGFRα and derepressing BMP-Smad1/5/8 signaling

Platelet-derived growth factors (PDGFs) play important roles in skeletal development and bone fracture healing, yet how PDGFs execute their functions remains incompletely understood. Here we show that PDGF-AA, but not -AB or -BB, could activate the BMP-Smad1/5/8 pathway in mesenchymal stem cells (MSCs), which requires BMPRIA as well as PDGFRα. PDGF-AA promotes MSC osteogenic differentiation through the BMP-Smad1/5/8-Runx2/Osx axis and MSC migration via the BMP-Smad1/5/8-Twist1/Atf4 axis. Mechanistic studies show that PDGF-AA activates BMP-Smad1/5/8 signaling by feedback down-regulating PDGFRα, which frees BMPRI and allows for BMPRI-BMPRII complex formation to activate smad1/5/8, using BMP molecules in the microenvironment. This study unravels a physical and functional interaction between PDGFRα and BMPRI, which plays an important role in MSC differentiation and migration, and establishes a link between PDGF-AA and BMPs pathways, two essential regulators of embryonic development and tissue homeostasis.

Bone substitutes in orthopaedic surgery: from basic science to clinical practice

Bone substitutes are being increasingly used in surgery as over two millions bone grafting procedures are performed worldwide per year. Autografts still represent the gold standard for bone substitution, though the morbidity and the inherent limited availability are the main limitations. Allografts, i.e. banked bone, are osteoconductive and weakly osteoinductive, though there are still concerns about the residual infective risks, costs and donor availability issues. As an alternative, xenograft substitutes are cheap, but their use provided contrasting results, so far. Ceramic-based synthetic bone substitutes are alternatively based on hydroxyapatite (HA) and tricalcium phosphates, and are widely used in the clinical practice. Indeed, despite being completely resorbable and weaker than cortical bone, they have exhaustively proved to be effective. Biomimetic HAs are the evolution of traditional HA and contains ions (carbonates, Si, Sr, Fl, Mg) that mimic natural HA (biomimetic HA). Injectable cements represent another evolution, enabling mininvasive techniques. Bone morphogenetic proteins (namely BMP2 and 7) are the only bone inducing growth factors approved for human use in spine surgery and for the treatment of tibial nonunion. Demineralized bone matrix and platelet rich plasma did not prove to be effective and their use as bone substitutes remains controversial. Experimental cell-based approaches are considered the best suitable emerging strategies in several regenerative medicine application, including bone regeneration. In some cases, cells have been used as bioactive vehicles delivering osteoinductive genes locally to achieve bone regeneration. In particular, mesenchymal stem cells have been widely exploited for this purpose, being multipotent cells capable of efficient osteogenic potential. Here we intend to review and update the alternative available techniques used for bone fusion, along with some hints on the advancements achieved through the experimental research in this field.

PDGF regulates chondrocyte proliferation through activation of the GIT1- and PLCγ1-mediated ERK1/2 signaling pathway

Studies investigating the effects of cytokines on chondrocytes have significant application potential, since the culture of cartilage cells in vitro is a vital step for cartilage tissue engineering. Platelet-derived growth factor (PDGF), one of the growth factors occurring at the early stage of the healing process of damaged tissue, is critical in bone healing. The present study investigated the effects of the activation of PDGF on cell proliferation, apoptosis and the underlying mechanisms of chondrocytes in vitro. The results indicated that the stimulation of PDGF led to overexpression of the G-protein-coupled receptor kinase interacting protein-1 (GIT1) and promotion of the phosphorylation of phospholipase Cγ1 (PLCγ1). Furthermore, PDGF induced chondrocyte proliferation and inhibited apoptosis via activation of the extracellular signal-regulated kinase (ERK) 1/2 pathway. Following knocking down GIT1 expression by small interfering RNA, phosphorylation of PLCγ1 and activation of the ERK1/2 pathway was no longer promoted by PDGF. In addition, the effects of PDGF on proliferation and apoptosis were suppressed. The expression levels of GIT1 were not affected; however, the phosphorylation of ERK1/2 was suppressed through inhibition of the phosphorylation of PLCγ1 by U73122. The results demonstrated that GIT1 is upstream of PLCγ1. Although the ability of PDGF to induce cell proliferation was inhibited by the inhibition of the ERK1/2 pathway by PD98059, apoptosis was not suppressed. In conclusion, the present study demonstrated that PDGF was able to activate the GIT1‑PLCγ1‑mediated ERK1/2 pathway to control chondrocyte proliferation.

Platelet‑derived growth factor promotes osteoblast proliferation by activating G‑protein‑coupled receptor kinase interactor‑1

Platelet‑derived growth factor (PDGF) has been reported to stimulate bone fracture‑healing. Multiple studies have demonstrated that PDGF has a critical role in osteoblast or osteoprogenitor cell activation, although the underlying mechanism remains unclear. Studies have found that G‑protein‑coupled receptor kinase interactor‑1 (GIT1) is activated by PDGF and described as an important factor in bone metabolism. In the present study, the effects of PDGF and GIT1 on the proliferation and apoptosis of osteoblasts were investigated in cultured osteoblasts isolated from rat calvaria with PDGF stimulation and GIT1 small interfering RNA transfection. The results demonstrated that PDGF rapidly stimulated GTI1 expression in osteoblasts, increased osteoblast proliferation and inhibited cell apoptosis. Furthermore, cyclin D1 expression was significantly upregulated, the number of cells in the G0/G1 phase was decreased, while the number in the S phase was increased. In cells with knockdown of GIT1, the change stimulated by PDGF was not evident. The results indicate that, PDGF stimulated GIT1 activation of cyclin D1 expression, thereby promoting osteoblasts to enter the S phase from the stationary G0/G1 phase, leading to the proliferation of osteoblasts.

Regulation of chondrocyte proliferation through GIT1-Rac1-mediated ERK1/2 pathway by PDGF

There are many growth factors contributing to fracture healing after bone fractures. Platelet-derived growth factor (PDGF) released from platelets is a factor promoting cell division and proliferation, and first appears around the sites of fractures. Culture of chondrocytes in vitro are stimulated by PDGF to proliferation, its presence being upregulated in the extracellular matrix of cartilage; the main components include aggrecan and type II collagen. PDGF induces the expression of G the protein-coupled receptor kinase interacting protein 1 (GIT1), promoting Rac1 and ERK1/2 phosphorylation. Both knocking down GIT1 expression by siRNA and blocking phosphorylation of Rac1 inhibit this induced proliferation of chondrocyte. GIT1 and Rac1 control each other, having a synergistic effect on activation of the ERK1/2 pathway. The results suggest that PDGF regulates chondrocyte proliferation through activation of ERK1/2 pathway by upregulation of GIT1 expression and Rac1 phosphorylation.

Platelet-rich plasma (PRP) in dental and oral surgery: from the wound healing to bone regeneration

Platelet-rich plasma (PRP) is a new approach to tissue regeneration and it is becoming a valuable adjunct to promote healing in many procedures in dental and oral surgery, especially in aging patients. PRP derives from the centrifugation of the patient's own blood and it contains growth factors that influence wound healing, thereby playing an important role in tissue repairing mechanisms. The use of PRP in surgical practice could have beneficial outcomes, reducing bleeding and enhancing soft tissue healing and bone regeneration. Studies conducted on humans have yielded promising results regarding the application of PRP to many dental and oral surgical procedures (i.e. tooth extractions, periodontal surgery, implant surgery). The use of PRP has also been proposed in the management of bisphosphonate-related osteonecrosis of the jaw (BRONJ) with the aim of enhancing wound healing and bone maturation. The aims of this narrative review are: i) to describe the different uses of PRP in dental surgery (tooth extractions and periodontal surgery) and oral surgery (soft tissues and bone tissue surgery, implant surgery and BRONJ surgery); and ii) to discuss its efficacy, efficiency and risk/benefit ratio. This review suggests that the use of PRP in the alveolar socket after tooth extractions is certainly capable of improving soft tissue healing and positively influencing bone regeneration but the latter effect seems to decrease a few days after the extraction. PRP has produced better results in periodontal therapy in association with other materials than when it is used alone. Promising results have also been obtained in implant surgery, when PRP was used in isolation as a coating material. The combination of necrotic bone curettage and PRP application seem to be encouraging for the treatment of refractory BRONJ, as it has proven successful outcomes with minimal invasivity. Since PRP is free from potential risks for patients, not difficult to obtain and use, it can be employed as a valid adjunct in many procedures in oral and dental surgery. However, further RCTs are required to support this evidence.

BLOOD-DERIVED, TISSUE ENGINEERING BIOMATERIALS

Fibrin sealant and platelet gels are human blood-derived, biodegradable, non toxic, surgical products obtained by mixing a fibrinogen concentrate or a platelet rich plasma with thrombin, respectively. Fibrin sealant is now a well known surgical tool increasingly used to stop or control bleeding, or to provide air and fluid tightness in many surgical situations. Platelet gels are newly developed preparations that are of specific interest because they contain numerous physiological growth factors and cytikines that are released upon the activation of blood platelets by thrombin. These growth factors, including PDGF, TGF-β 1, BMP, and VEGF have been shown to stimulate cell growth and differentiation with special clinical benefits for soft and bony tissue healing and regeneration. Platelet gels allow surgeons to manipulate the cellular environment of surgical sites and to guide tissue regeneration. A specific interest of such products is observed for the induction of osteogenesis and chondrogenesis. Advances in the preparation, clinical use, and safety of these two important classes of blood-derived biomaterials are reviewed.

Size effect of calcium phosphate coated with poly-DL-lactide- co-glycolide on healing processes in bone reconstruction

In this article, synthesis and application of calcium phosphate/poly-DL-lactide-co-glycolide (CP/PLGA) composite biomaterial in particulate form, in which each CP granule/particle is coated with PLGA, are described. Two types of the particulate material having different particle sizes were synthesized: one with an average particle diameter between 150 and 250 mum (micron-sized particles, MPs) and the other with an average particle diameter smaller than 50 nm (nanoparticles, NPs). A comparative in vivo analysis was done by reconstructing defects in osteoporotic alveolar bones using both composites. The material, CP granules/particles covered with polymer, was characterized using X-ray structural analysis, scanning electron microscopy, and atomic force microscopy. Changes in reparatory functions of tissues affected by osteoporosis were examined in mice in vivo, using these two kinds of composite materials, with and without autologous plasma. Having defined the target segment, histomorphometric parameters-bone area fraction, area, and mean density-were determined. The best results in the regeneration and recuperation of alveolar bone damaged by osteoporosis were achieved with the implantation of a mixture of nanoparticulate CP/PLGA composite and autologous plasma. After the implantation of microparticulate CP/PLGA, in the form of granules, mixed with autologous plasma, into an artificial defect in alveolar bone, new bone formation was also observed, although its formation rate was slower.

Influence of platelet-rich plasma on proliferation and osteogenic differentiation of skeletal muscle satellite cells: an in vitro study

OBJECTIVES

Platelet-rich plasma (PRP) is a new application of tissue engineering and a developing area for researchers and clinicians. The aim of this study was to assess the effect of PRP on the proliferation and osteogenic differentiation of skeletal muscle satellite cell (MSC) population and the ability of PRP to induce the production of some osteogeneic-related factors in vitro.

STUDY DESIGN

The PRP was obtained from Sprague-Dawley rats using 2 centrifugation techniques. Primary cultures of rat MSCs were exposed to various concentrations of PRP (0.16 × 10(8), 0.625 × 10(8), and 2.5 × 10(8) thrombocytes/carrier) on MSC proliferation using an MTT proliferation assay. Alkaline phosphatase (ALP) activity, Alizarin red S (AR) staining, calcium analyses and real-time reverse-transcription polymerase chain reaction (RT-PCR) of osteogenic-related genes were performed to study the effect of PRP on osteogenic differentiation of cultured MSCs population.

RESULTS

The platelet concentration and growth factors (GFs) in our PRP preparations were significantly higher than in the whole blood. PRP showed a dose-dependent stimulation of cell proliferation. The maximum effect was achieved with a concentration of 0.625 × 10(8) thrombocytes/carrier. ALP activity, AR staining, and calcium analyses showed enhanced cell osteogenic differentiation in the PRP group. The real-time RT-PCR results showed that PRP up-regulated osteocalcin at day 14 and type I collagen and osteopontin at day 7 compared with the control group.

CONCLUSIONS

The results of this study suggest that PRP containing osteoinductive GFs stimulates cell proliferation and osteogenic differentiation of rat-derived MSCs in vitro.

Effect of nicotine on gene expression of angiogenic and osteogenic factors in a rabbit model of bone regeneration

PURPOSE

This study aims to evaluate the influence of nicotine on the gene expression of osteogenic and angiogenic factors in bone regeneration by use of a nicotine-compromised rabbit model of mandibular lengthening.

MATERIALS AND METHODS

Thirty adult New Zealand white rabbits were randomly assigned to the nicotine group or the control group. The total nicotine or placebo exposure time for all animals was 7 weeks. Unilateral mandibular distraction osteogenesis was performed. Five animals in each group were sacrificed at day 5, day 11, and day 18, respectively, after commencement of active distraction. The distraction regenerate samples were harvested, and the messenger ribonucleic acid expression of bone transforming growth factor beta(1), platelet-derived growth factor A, and basic fibroblast growth factor was assayed by real-time polymerase chain reaction analysis.

RESULTS

The messenger ribonucleic acid expression of transforming growth factor beta(1), platelet-derived growth factor A, and basic fibroblast growth factor was significantly inhibited by nicotine exposure at a variety of time points.

CONCLUSIONS

The presence of nicotine inhibited the gene expression of angiogenic and osteogenic factors resulting in compromised bone regeneration.

The biology of platelet-rich plasma and its application in oral surgery: literature review

Platelet-rich plasma (PRP) is a new approach in tissue regeneration and a developing area for clinicians and researchers. It is used in various surgical fields, including oral and maxillofacial surgery. PRP is prepared from the patient's own blood and contains growth factors that influence wound healing. Of these growth factors, platelet-derived growth factor, transforming growth factor, insulin-like growth factor, and epidermal growth factor play a pivotal role in tissue repair mechanisms. Although the growth factors and mechanisms involved are still poorly understood, the easy application of PRP in the clinic and its possible beneficial outcome, including reduction of bleeding, rapid soft tissue healing, and bone regeneration, hold promise for new treatment approaches. However, animal studies and human trials demonstrate conflicting results regarding the application of PRP. Therefore the aim of this literature review is to evaluate the scientific evidence regarding the use of PRP in dentistry, to describe the different bioactive substances included in PRP and their participation in the healing process, to elucidate the different techniques and available technology for PRP preparation, to review animal and human studies, to clarify risks, and to provide guidance for future research.

The biology of platelet-rich plasma and its application in trauma and orthopaedic surgery: a review of the literature

Although mechanical stabilisation has been a hallmark of orthopaedic surgical management, orthobiologics are now playing an increasing role. Platelet-rich plasma (PRP) is a volume of plasma fraction of autologous blood having platelet concentrations above baseline. The platelet alpha granules are rich in growth factors that play an essential role in tissue healing, such as transforming growth factor-beta, vascular endothelial growth factor, and platelet-derived growth factor. PRP is used in various surgical fields to enhance bone and soft-tissue healing by placing supraphysiological concentrations of autologous platelets at the site of tissue damage. The easily obtainable PRP and its possible beneficial outcome hold promise for new regenerative treatment approaches. The aim of this literature review was to describe the bioactivities of PRP, to elucidate the different techniques for PRP preparation, to review animal and human studies, to evaluate the evidence regarding the use of PRP in trauma and orthopaedic surgery, to clarify risks, and to provide guidance for future research.

Human bone marrow activates the Akt pathway in metastatic prostate cells through transactivation of the alpha-platelet-derived growth factor receptor

The factors regulating the bone tropism of disseminated prostate cancer cells are still vaguely defined. We report that prostate cancer cells that metastasize to the skeleton respond to human bone marrow with a robust stimulation of the phosphatidylinositol 3-kinase/Akt pathway, whereas prostate cells that lack bone-metastatic potential respond negligibly. The majority of this Akt activation is dependent on alpha-platelet-derived growth factor receptor (alpha-PDGFR) signaling, which was shown using the small-molecule inhibitor of PDGFR signaling AG1296. Low concentrations of PDGF-AA and PDGF-BB found in bone marrow aspirates, which were detected by ELISA, do not account for the high levels of alpha-PDGFR signaling. Additionally, neutralizing PDGF binding using a alpha-PDGFR-specific antibody (IMC-3G3) failed to produce a significant inhibition of bone marrow-induced Akt activation. However, the inhibitory effect of IMC-3G3 rivaled that of AG1296 when incubation was done under conditions that stimulated alpha-PDGFR internalization. We conclude that alpha-PDGFR is activated by multiple soluble factors contained within human bone marrow, in addition to its natural ligands, and this transactivation is dependent on receptor localization to the plasma membrane. Therefore, alpha-PDGFR expression may provide select prostate phenotypes with a growth advantage within the bone microenvironment.

Platelet-Rich Plasma: Quantification of Growth Factor Levels and the Effect on Growth and Differentiation of Rat Bone Marrow Cells

Platelet-rich plasma (PRP) is a new application of tissue engineering and a developing area for clinicians and researchers. It is a storage vehicle of growth factors (GFs) such as platelet-derived growth factor (PDGF)- AA, -BB, -AB; transforming growth factor (TGF)-beta1 and -2; platelet-derived epidermal growth factor (PDEGF); platelet-derived angiogenesis factor (PDAF); insulin growth factor-1 (IGF-1); and platelet factor- 4 (PF-4), which are known to influence bone regeneration. However, animal and clinical studies reveal different results with the use of PRP and its effect on bone healing. This could be due to the differences between species, that is, differences between species in GF concentrations or variation in presence of GFs between the various PRPs. In this study, rat bone marrow cells were cultured in PRP-coated wells or in uncoated wells for 16 days in osteogenic medium, and analyzed on cell growth (DNA content) and cell differentiation (alkaline phosphatase [ALP] activity, calcium content, scanning electron microscopy, and QPCR). The concentrations of TGF-beta1, PDGF-AA, PDGF-AB, and PDGF-BB in rat, goat, and human PRP were subsequently determined. The results showed that PRP stimulated initial cell growth and had no effect on ALP activity. The calcium measurements showed a significant increase in calcium at days 8, 12, and 16. The real-time PCR results showed that PRP upregulated osteocalcin at day 1 and collagen type I at day 8. Overall, the immunoassays revealed that human PRP contained higher concentrations of growth factors per platelet compared to rat and goat PRP. Goat PRP showed higher concentrations of growth factors per platelet as compared to rat PRP except for PDGF-BB, which had a higher concentration in rat PRP. TGF-beta1 was the most abundant growth factor in all 3 PRPs. On the basis of our results, we conclude that platelet-rich plasma contains osteo-inductive growth factors, which are probably species related. However, we cannot generalize the results because of large intraspecies variations. Further, we conclude that rat PRP gel stimulates initial growth and differentiation of rat bone marrow cells in vitro.

Bone-metastatic potential of human prostate cancer cells correlates with Akt/PKB activation by alpha platelet-derived growth factor receptor

Prostate adenocarcinoma metastasizes to the skeleton more frequently than any other organ. An underlying cause of this phenomenon may be the ability of bone-produced factors to specifically select disseminated prostate cancer cells that are susceptible to their trophic effects. Platelet-derived growth factor (PDGF), a potent mitogen for both normal and tumor cells, is produced in several tissues including bone, where it is synthesized by both osteoblasts and osteoclasts. Here, we show that PDGF causes a significantly stronger activation of the Akt/PKB survival pathway in bone-metastatic prostate cancer cells compared to nonmetastatic cells. Normal prostate epithelial cells and DU-145 prostate cells, originally derived from a brain metastasis, are not responsive to PDGF. In contrast, epidermal growth factor stimulates Akt to the same extent in all prostate cells tested. This difference in PDGF responsiveness depends on the higher expression of alpha-PDGFR in bone-metastatic compared to nonmetastatic prostate cells and the lack of alpha-PDGFR expression in normal and metastatic prostate cells derived from tissues other than bone. Thus, alpha-PDGFR expression might identify prostate cancer cells with the highest propensity to metastasize to the skeleton.

Osteoblasts respond to hydroxyapatite surfaces with immediate changes in gene expression

Bone mineral contains hydroxyapatite (HA). This is the surface that mature osteoblasts and osteocytes interact with. Synthetic HA is widely used in orthopedic surgeries as an implant or implant coating. The bone-like HA surfaces increase implant union and bone formation; however, the mechanisms accounting for this effect on osteoblasts are not known. In this study, we compared gene expression profiles of osteoblasts responding to HA or plastic surfaces for 24 h. Expression profiles were also compared between HA discs processed with gravity-sieved compared with combined gravity and air-jet-sieved HA powders. The latter, composed of smaller HA particles, exhibits an increase in grain boundary surface area. Discs made with either HA powder similarly up-regulated osteoblast expression of 10 genes (including proliferin 3, Glvr-1, DMP-1, and tenascin C) and down-regulated 15 genes (such as osteoglycin) by more than 2-fold compared with plastic surfaces. The overall changes are indicative of an immediate (24-h) response to the HA surface and a trend toward osteoblast differentiation. In addition, subsets of modulated genes exist that are unique to each HA subtype. Taken together, we identified HA responsive genes evident within 24 h of surface contact, indicating a critical role for extracellular mineral surfaces in the regulation of osteoblast gene expression and phenotype.

Treatment of Periapical Inflammatory Lesion with the Combination of Platelet-Rich Plasma and Tricalcium Phosphate: A Case Report

Periapical surgery is an important treatment alternative in the presence of a periapical inflammatory lesion. To achieve optimal healing and regeneration of the bone, different bone substitutes or barrier membranes can be used after degranulation of the lesion. Tricalcium phosphate (TCP) graft material is one of these substitutes. Platelet Rich Plasma (PRP) preparation is a new biotechnology and can be used in many different surgical procedures. It consists of thrombocyte concentrates and high amounts of growth factors (GFs), especially platelet derived growth factor (PDGF), insulin-like growth factor (IGF-I) and transforming growth factor (TGF-beta), which are important in wound healing and regeneration. In this case report, use of platelet gel in conjunction with TCP in the treatment of periapical inflammatory lesion and the results of 12 months has been reported.

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.