Potentiation by platelet-derived growth factor-BB of FGF-2-stimulated VEGF release in osteoblasts

Propolis extract and bovine bone graft combination in the expression of VEGF and FGF2 on the preservation of post extraction socket

Aim:

To determine the potential of propolis extract and BBG combination on the quantity of fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF), and osteoblasts in the preservation of tooth extraction socket on days 3 and 7.

Settings and Design:

Laboratory in vivo reseach using animal model.

Materials and Methods:

Fifty-six Cavia cobaya were divided into eight groups containing seven animals in each group. The extraction socket on the lower left incisor was filled with polyethylene glycol (PEG) at a concentration of 2% (Groups I and II) as a control; active materials consisted of propolis extract and PEG (Groups III and IV); active materials consisted of BBG and PEG (Groups V and VI); and active materials consisted of propolis extract, BBG, and PEG (Groups VII and VIII). Then, an examination was done using immunohistochemistry to perform an expression of VEGF, FGF2, as well as histology of osteoblasts.

Statistical Analysis Used:

The statistical analysis performed using a one-way ANOVA and Tukey's honestly significant difference test.

Results:

Propolis extract, BBG and PEG had the most significant result related to the formation of FGF2, VEGF, and osteoblasts.

Conclusion:

The combination of propolis extract with BBG and PEG in socket preservation is effective in increasing the expression of FGF2, VEGF, and osteoblasts.

Investigating the Osteoinductive Potential of a Decellularized Xenograft Bone Substitute

Bone grafting is the second most common tissue transplantation procedure worldwide. One of the alternative methods for bone repair under investigation is a tissue-engineered bone substitute. An ideal property of tissue-engineered bone substitutes is osteoinductivity, defined as the ability to stimulate primitive cells to differentiate into a bone-forming lineage. In the current study, we use a decellularization and oxidation protocol to produce a porcine bone scaffold and examine whether it possesses osteoinductive potential and can be used to create a tissue-engineered bone microenvironment. The decellularization protocol was patented by our lab and consists of chemical decellularization and oxidation steps using combinations of deionized water, trypsin, antimicrobials, peracetic acid, and triton-X100. To test if the bone scaffold was a viable host, preosteoblasts were seeded and analyzed for markers of osteogenic differentiation. The osteoinductive potential was observed in vitro with similar osteogenic markers being expressed in preosteoblasts seeded on the scaffolds and demineralized bone matrix. To assess these properties in vivo, scaffolds with and without preosteoblasts preseeded were subcutaneously implanted in mice for 4 weeks. MicroCT scanning revealed 1.6-fold increased bone volume to total volume ratio and 1.4-fold increase in trabecular thickness in scaffolds after implantation. The histological analysis demonstrates new bone formation and blood vessel formation with pentachrome staining demonstrating osteogenesis and angiogenesis, respectively, within the scaffold. Furthermore, CD31+ staining confirmed the endothelial lining of the blood vessels. These results demonstrate that porcine bone maintains its osteoinductive properties after the application of a patented decellularization and oxidation protocol developed in our laboratory. Future work must be performed to definitively prove osteogenesis of human mesenchymal stem cells, biocompatibility in large animal models, and osteoinduction/osseointegration in a relevant clinical model in vivo. The ability to create a functional bone microenvironment using decellularized xenografts will impact regenerative medicine, orthopedic reconstruction, and could be used in the research of multiple diseases.

A bio-inspired hybrid nanosack for graft vascularization at the omentum

For three-dimensional tissue engineering scaffolds, the major challenges of hydrogels are poor mechanical integrity and difficulty in handling during implantation. In contrast, electrospun scaffolds provide tunable mechanical properties and high porosity; but, are limited in cell encapsulation. To overcome these limitations, we developed a "hybrid nanosack" by combination of a peptide amphiphile (PA) nanomatrix gel and an electrospun poly (ε-caprolactone) (ePCL) nanofiber sheet with porous crater-like structures. This hybrid nanosack design synergistically possessed the characteristics of both approaches. In this study, the hybrid nanosack was applied to enhance local angiogenesis in the omentum, which is required of tissue engineering scaffolds for graft survival. The ePCL sheet with porous crater-like structures improved cell and blood vessel penetration through the hybrid nanosack. The hybrid nanosack also provided multi-stage fibroblast growth factor-2 (FGF-2) release kinetics for stimulating local angiogenesis. The hybrid nanosack was implanted into rat omentum for 14days and vascularization was analyzed by micro-CT and immunohistochemistry; the data clearly demonstrated that both FGF-2 delivery and porous crater-like structures work synergistically to enhance blood vessel formation within the hybrid nanosack. Therefore, the hybrid nanosack will provide a new strategy for engineering scaffolds to achieve graft survival in the omentum by stimulating local vascularization, thus overcoming the limitations of current strategies.

STATEMENT OF SIGNIFICANCE

For three-dimensional tissue engineering scaffolds, the major challenges of hydrogels are poor mechanical integrity and difficulty in handling during implantation. In contrast, electrospun scaffolds provide tunable mechanical properties and high porosity; but, are limited in cell encapsulation. To overcome these limitations, we developed a "hybrid nanosack" by combination of a peptide amphiphile (PA) nanomatrix gel and an electrospun poly (ε-caprolactone) (ePCL) nanofiber sheet with porous crater-like structures. This design synergistically possessed the characteristics of both approaches. In this study, the hybrid nanosack was applied to enhance local angiogenesis in the omentum, which is required of tissue engineering scaffolds for graft survival. The hybrid nanosack was implanted into rat omentum for 14days and vascularization was analyzed by micro-CT and immunohistochemistry. We demonstrate that both FGF-2 delivery and porous crater-like structures work synergistically to enhance blood vessel formation within the hybrid nanosack. Therefore, the hybrid nanosack will provide a new strategy for engineering scaffolds to achieve graft survival in the omentum by stimulating local vascularization, thus overcoming the limitations of current strategies.

Interplay between VEGF-A and cMET signaling in human vestibular schwannomas and schwann cells

Vestibular schwannoma (VS), the fourth most common intracranial tumor, arises from the Schwann cells of the vestibular nerve. Although several pathways have been independently implicated in VS pathobiology, interactions among these pathways have not been explored in depth. We have investigated the potential cross-talk between hepatocyte growth factor (HGF) and vascular endothelial growth factor-A (VEGF-A) in human VS, an interaction that has been described in other physiological and pathological cell types. We affirmed previous findings that VEGF-A signaling is aberrantly upregulated in VS, and established that expression of HGF and its receptor cMET is also significantly higher in sporadic VS than in healthy nerves. In primary human VS and Schwann cell cultures, we found that VEGF-A and HGF signaling pathways modulate each other. siRNAs targeting cMET decreased both cMET and VEGF-A protein levels, and siRNAs targeting VEGF-A reduced cMET expression. Additionally, siRNA-mediated knockdown of VEGF-A or cMET and pharmacologic inhibition of cMET decreased cellular proliferation in primary human VS cultures. Our data suggest cross-talk between these 2 prominent pathways in VS and highlight the HGF/cMET pathway as an additional important therapeutic target in VS.

Platelet-derived growth factor (PDGF)-PDGF receptor interaction activates bone marrow-derived mesenchymal stromal cells derived from chronic lymphocytic leukemia: implications for an angiogenic switch

Malignant cells are capable of influencing the microenvironment in a manner that facilitates tumor cell survival. Bidirectional crosstalk between chronic lymphocytic leukemic (CLL) cells and marrow-derived mesenchymal stromal cells (MSCs) activates both cell types. In this study, we observed that the conditioned medium (CM) obtained from CLL cells was able to induce Akt activation in MSC. Subsequent studies investigated the mechanism of MSC activation mediated by CLL-CM. Platelet-derived growth factor receptors (PDGFRs) were selectively activated in MSCs by CLL-CM and found to be critical receptors for CLL-CM-driven MSC proliferation and MSC Akt activation. The known ligands of PDGFR, platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF), were detected in CLL-CM, but PDGF was the predominant ligand involved in the CM-mediated PDGFR activation. Both PDGF and VEGF were found to be elevated in the plasma of CLL patients with a positive association for high-risk factors and more advanced stage. Finally, we demonstrated that PDGF induced MSC VEGF production through a phosphatidylinositol 3-kinase (PI3K)-dependent mechanism. These results show that PDGF-PDGFR signaling influences at least the MSC in the microenvironment of CLL and may play a role in the induction of an angiogenic switch known to be permissive for disease progression.

Development of a fully human anti-PDGFRbeta antibody that suppresses growth of human tumor xenografts and enhances antitumor activity of an anti-VEGFR2 antibody

Platelet-derived growth factor receptor beta (PDGFRbeta) is upregulated in most of solid tumors. It is expressed by pericytes/smooth muscle cells, fibroblast, macrophage, and certain tumor cells. Several PDGF receptor-related antagonists are being developed as potential antitumor agents and have demonstrated promising antitumor activity in both preclinical and clinical settings. Here, we produced a fully human neutralizing antibody, IMC-2C5, directed against PDGFRbeta from an antibody phage display library. IMC-2C5 binds to both human and mouse PDGFRbeta and blocks PDGF-B from binding to the receptor. IMC-2C5 also blocks ligand-stimulated activation of PDGFRbeta and downstream signaling molecules in tumor cells. In animal studies, IMC-2C5 significantly delayed the growth of OVCAR-8 and NCI-H460 human tumor xenografts in nude mice but failed to show antitumor activities in OVCAR-5 and Caki-1 xenografts. Our results indicate that the antitumor efficacy of IMC-2C5 is primarily due to its effects on tumor stroma, rather than on tumor cells directly. Combination of IMC-2C5 and DC101, an anti-mouse vascular endothelial growth factor receptor 2 antibody, resulted in significantly enhanced antitumor activity in BxPC-3, NCI-H460, and HCT-116 xenografts, compared with DC101 alone, and the trend of additive effects to DC101 treatment in several other tumor models. ELISA analysis of NCI-H460 tumor homogenates showed that IMC-2C5 attenuated protein level of vascular endothelial growth factor and basic fibroblast growth factor elevated by DC101 treatment. Finally, IMC-2C5 showed a trend of additive effects when combined with DC101/chemotherapy in MIA-PaCa-2 and NCI-H460 models. Taken together, these results lend great support to the use of PDGFRbeta antagonists in combination with other antiangiogenic agents in the treatment of a broad range of human cancers.

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

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

Platelet-derived growth factor-BB reflects clinical, inflammatory and angiogenic disease activity and oxidative stress in inflammatory bowel disease

OBJECTIVES

The goal of the studies was the evaluation of platelet-stored (serum) and circulating (plasma) pools of platelet-derived growth factor (PDGF)-BB in inflammatory bowel disease (IBD) and the assessment of a possible application of PDGF as the disease marker.

DESIGN AND METHODS

Serum and plasma PDGF-BB were measured in 134 IBD patients and 81 controls and evaluated with respect to the disease status, endoscopic, inflammatory, and angiogenic activity. The diagnostic utility was evaluated using ROC analysis.

RESULTS

PDGF was increased exclusively in active IBD regardless the disease type and associated with its clinical and endoscopic activity. Serum- and plasma-PDGF were poorly interrelated. Plasma-PDGF better reflected oxidative stress whereas serum-PDGF reflected inflammation and angiogenesis. In multivariate analysis, platelets alone explained about 30% in the PDGF variability and seemed to mediate most of the observed relationships.

CONCLUSIONS

IBD is associated with the increases in platelet-stored and circulating PDGF, which correspond with the disease clinical, endoscopic, inflammatory, and angiogenic activity and IBD-associated oxidative stress. However, PDGF as an active-IBD marker was not better than currently applied C-reactive protein, erythrocyte sedimentation rate and platelets.

Regulation of human bone sialoprotein gene transcription by platelet-derived growth factor-BB

Platelet-derived growth factor (PDGF) is produced by mesenchymal cells and released by platelets following aggregation and is synthesized by osteoblasts. In bone, PDGF stimulates proliferation and differentiation of osteoblasts. PDGF also increases bone resorption, most likely by increasing the number of osteoclasts. Bone sialoprotein (BSP) is thought to function in the initial mineralization of bone, selectively expressed by differentiated osteoblast. To determine the molecular mechanisms PDGF regulation of human BSP gene transcription, we have analyzed the effects of PDGF-BB on osteoblast-like Saos2 and ROS17/2.8 cells. PDGF-BB (5 ng/ml) increased BSP mRNA and protein levels at 12 h in Saos2 cells, and induced BSP mRNA expression at 3 h, reached maximal at 12 h in ROS17/2.8 cells. Transient transfection analyses were performed using chimeric constructs of the human BSP gene promoter linked to a luciferase reporter gene. Treatment of Saos2 cells with PDGF-BB (5 ng/ml, 12 h) increased luciferase activities of all constructs between -184LUC to -2672LUC including the human BSP gene promoter. Effects of PDGF-BB abrogated in constructs included 2 bp mutations in the two cAMP response elements (CRE1 and CRE2), activator protein 1(3) (AP1(3)) and shear stress response element 1 (SSRE1). Luciferase activities induced by PDGF-BB were blocked by protein kinase A inhibitor H89 and tyrosine kinase inhibitor herbimycin A. Gel mobility shift analyses showed that PDGF-BB increased binding of CRE1, CRE2, AP1(3) and SSRE1 elements. CRE1- and CRE2-protein complexes were supershifted by CREB1 and phospho-CREB1 antibodies. Notably, AP1(3)-protein complexes were supershifted by c-Fos and JunD, and disrupted by CREB1, phospho-CREB1, c-Jun and Fra2 antibodies. These studies, therefore, demonstrate that PDGF-BB stimulates human BSP transcription by targeting the CRE1, CRE2, AP1(3) and SSRE1 elements in the human BSP gene promoter.