Chong Pyoung Chung

Platelet derived growth factor releasing chitosan sponge for periodontal bone regeneration

With an aim of improving bone regeneration, chitosan sponge containing platelet-derived growth factor-BB (PDGF-BB) were developed. For fabrication of chitosan sponge, chitosan solution was freeze-dried, crosslinked and freeze-dried again. PDGF-BB was incorporated into the chitosan sponge by soaking chitosan sponge into the PDGF-BB solution. Release kinetics of PDGF-BB, cell attachment, proliferation capacity and bony regenerative potentials of PDGF-BB-loaded chitosan sponge were investigated. Prepared chitosan sponge retained porous structure with 100 microm pore diameter that was suitable for cellular migration and growth. Release rate of PDGF-BB could be controlled by varying initial loading content of PDGF-BB to obtain optimal therapeutic efficacy. PDGF-BB-loaded chitosan sponge induced significantly high cell attachment and proliferation level, which indicated good cellular adaptability. PDGF-BB-loaded chitosan sponge demonstrated marked increase in new bone formation and rapid calcification. Degradation of the chitosan sponge was proceeded at defect site and subsequently replaced with new bone. Histomorphometric analysis confirmed that PDGF-BB-loaded chitosan sponge significantly induced new bone formation. These results suggested that chitosan sponge and PDGF-BB-loaded chitosan sponge may be beneficial to enhance periodontal bone regeneration.

Cell-penetrating chitosan/doxorubicin/TAT conjugates for efficient cancer therapy

In this study, a cell‐penetrating peptide, the transactivating transcriptional factor (TAT) domain from HIV, was linked to a chitosan/doxorubicin (chitosan/DOX) conjugate to form a chitosan/DOX/TAT hybrid. The synthesized chitosan/DOX/TAT conjugate showed a different intracellular distribution pattern from a conjugate without TAT. Unlike both free DOX and the conjugate without TAT, the chitosan/DOX/TAT conjugate was capable of efficient cell entry. The chitosan/DOX/TAT conjugate was found to be highly cytotoxic, with an IC50 value of approximately 480 nM, 2 times less than that of chitosan/DOX (980 nM). The chitosan/DOX/TAT provided decreases in tumor volume of 77.4 and 57.5% compared to free DOX and chitosan/DOX, respectively, in tumor‐bearing mice. Therefore, this study suggests that TAT‐mediated chitosan/DOX conjugate delivery is effective in slowing tumor growth.

Controlled release of platelet-derived growth factor-BB from chondroitin sulfate-chitosan sponge for guided bone regeneration.

Platelet-derived growth factor-BB (PDGF-BB) releasing porous chondroitin-4-sulfate (CS)-chitosan sponge was designed with an aim of controlling growth factor delivery in order to improve bone formation. Porous CS-chitosan sponge was fabricated by freeze drying and crosslinking aqueous CS-chitosan solution. PDGF-BB was incorporated into the CS-chitosan sponge by soaking CS-chitosan sponge into the PDGF-BB solution. CS-chitosan sponge retained a porous structure with a 150-200-microm pore diameter that was suitable for cellular migration and osteoid ingrowth. Release rate of PDGF-BB could be controlled by varying the composition of CS in the sponge or initial loading content of PDGF-BB. CS-chitosan sponge induced increased osteoblast migration and proliferation as compared with chitosan sponge alone. Furthermore, the release of PDGF-BB from CS-chitosan sponge significantly enhanced osteoblast proliferation. These results suggest that PDGF-BB-releasing CS-chitosan sponge may be beneficial to enhance bone cell adaptation and regenerative potential when applied in wound sites.

Immobilization of bone morphogenetic protein‐2 on a nanofibrous chitosan membrane for enhanced guided bone regeneration

BMP‐2 (bone morphogenetic protein‐2) has been used in promoting bone formation and, in combination with various delivery carriers, in bone regeneration or bone tissue‐engineering practice. In the present study, BMP‐2 was immobilized directly on a GBR (guided bone‐regenerative) membrane surface made of chitosan nanofibres, providing a bioactive surface that can enhance bone‐regeneration capacity. The BMP‐2‐conjugated membrane surface retained bioactivity for up to 4 weeks of incubation, as well as holding over 50% of the initial BMP‐2 attached. The BMP‐2‐conjugated surface increased osteoblastic cell attachment in accordance with the amount of BMP‐2 conjugated. In addition, the BMP‐2‐conjugated chitosan membrane significantly promoted cell proliferation, alkaline phosphatase activity, as well as calcium deposition when compared with BMP‐2‐adsorbed membrane, indicating a stable localization of BMP‐2 at the surface of the chitosan membrane. Taking these findings together, the conjugation of BMP‐2 on a chitosan nanofibrous membrane would seen to be applicable for inducing significant and localized bone formation in future GBR procedures.

The systemic delivery of siRNAs by a cell penetrating peptide, low molecular weight protamine

Small interfering RNAs (siRNAs), used for specific down-regulation of targeted genes, have garnered considerable interest as an attractive new class of drugs for broad clinical applications. The polyanionic charges carried by these siRNAs, however, restrain cellular uptake and consequently limit effects on gene regulation. Herein the authors describe a peptide/siRNA complex containing the cell penetrating peptide derived from natural protamine, termed low molecular weight protamine (LMWP), for the treatment of cancer. Fluorescently-tagged siRNAs were localized with the peptide in the cytoplasm shortly after incubation of LMWP/siRNA complex with carcinoma cells. The increased cell uptake of siRNA that was achieved using the LMWP resulted in significant down-regulation of model protein luciferase as well as therapeutic cancer target, vascular endothelial growth factor (VEGF) expression. In vivo studies with tumor-bearing mice further demonstrated that the peptide could carry and localize siRNA inside tumors and inhibit the expression of VEGF through systemic application of the peptide complex, thereby suppressing tumor growth. In addition, no detectable increase in the serum level of inflammatory cytokines including interferon (IFN)-alpha and interleukin (IL)-12 was observed under the LMWP/siRNA complex treatment, indicating systemic delivery of LMWP/siRNA did not exert measurable immunostimulatory effect. The LMWP-based systemic delivery method could be a reliable and safe approach to maximize effectiveness of therapeutic siRNA for treatment of cancer and other diseases.

Molded porous poly (L-lactide) membranes for guided bone regeneration with enhanced effects by controlled growth factor release

The aim of this study was to develop platelet-derived growth factor (PDGF-BB) loaded moldable porous poly (L-lactide) (PLLA)-tricalcium phosphate (TCP) membranes for guided bone regeneration (GBR) therapy. The membranes were designed to fit various types of bone defect sites. PDGF-BB-dissolved PLLA-TCP in methylene chloride-ethyl acetate solution was cast on a dome shaped metallic mold to fabricate a model membrane. The release rate of PDGF-BB, the osteoblast attachment test, and guided bone regeneration potential were evaluated with PDGF-BB-loaded PLLA-TCP membranes. Regular pores were generated throughout the membrane mainly due to phase inversion of PLLA-methylene chloride-ethyl acetate solution. A therapeutic amount of PDGF-BB was released from the membrane. The release rate could be controlled by varying the initial loading content of PDGF-BB. A significant amount of cells attached onto the PDGF-BB-loaded membrane rather than onto the unloaded membrane. Dome shaped bone formation was achieved in rabbit calvaria at 4 weeks. This indicated that restoration of bone defects to the bones original shape can be made possible by using molded membranes, which guide bone regeneration along with providing sufficient spaces. Bone forming efficiency was increased remarkably due to PDGF-BB release from PLLA-TCP membranes. These results suggested that the PDGF-BB releasing molded PLLA-TCP membrane may potentially improve GBR efficiency in various types of bone defects.

Controlled release of platelet-derived growth factor from porous poly(L-lactide) membranes for guided tissue regeneration

Platelet-derived growth factor-BB (PDGF-BB) was incorporated into porous poly (L-lactide) (PLLA) membranes with an aim of improving early bone healing in guided tissue regeneration (GTR) therapy. Porous PDGF-BB loaded membranes were fabricated by coating PDGF-BB-dissolved PLLA methylene chloride-ethyl acetate solutions on polyglycolic acid (PGA) meshes. Release kinetics of PDGF-BB, biologic activity, degradability and guided tissue regenerative potentials of the membranes were investigated. Release of PDGF-BB could be controlled by adding bovine serum albumin that may provide porous diffusion channels for PDGF-BB release and by varying initial loading content of PDGF-BB. Biologic activity of PDGF-BB in the membranes was ascertained by fibroblast chemotaxis. PDGF-BB loaded membranes maintained proper degradation property for periodontal application. PDGF-BB loaded membrane markedly increased new bone formation in rat calvarial defects, and completed bony reunion after 2 weeks of implantation period. These results suggested that PDGF-BB loaded PLLA membrane might potentially enhance guided tissue regenerative efficacy.

Porous poly(l-lactide) membranes for guided tissue regeneration and controlled drug delivery: membrane fabrication and characterization

Abstract With the aim of developing a new periodontal therapeutic modality, guided tissue regeneration (GTR), biodegradable barrier membranes composed of porous poly( l -lactide) (PLLA) films cast on poly(glycolide) (PGA) meshes were fabricated using an in-air drying phase inversion technique. PLLA was dissolved in methylene chloride-ethylacetate mixtures and cast on the knitted PGA meshes, followed by an air-drying process. The use of the three-component polymer solution (PLLA-methylene chloride-ethylacetate) was to generate porous substructures in the PLLA membranes during the solvent evaporation. The PGA meshes mechanically holding the PLLA membranes played an important role in forming the surface pores. Size and morphology of the pores were affected by the solvent composition of methylene chloride and ethylacetate. Regular pores were generated both at the surface and sublayer of the membranes. Flurbiprofen and tetracycline, used in periodontal therapy for their tissue regenerating effects, were incorporated in the membranes by adding the drugs in the PLLA solutions. The drug release kinetics mainly depended upon the hydrophobic-hydrophilic properties of the drugs and the porosity of the membranes regulated by the solvent composition of the PLLA solution. The release rate could be further controlled by loaded drug contents. The drug releasing porous PLLA membranes might be an effective therapeutic system in the treatment of periodontal disease.

Enhanced guided bone regeneration by controlled tetracycline release from poly(L‐lactide) barrier membranes

With the aim of providing effective periodontal therapeutic modality, drug-releasing membranes for guided tissue regeneration (GTR) were developed. As GTR membranes, biodegradable barrier membranes composed of porous poly(L-lactide) (PLLA) films cast on poly(glycolide) (PGA) meshes were fabricated using an in-air drying phase inversion technique. PLLA was dissolved in methylene chloride-ethylacetate mixtures, cast on knitted PGA mesh, and then air-dried. Tetracycline, which is used in periodontal therapy because of its antibacterial activity and tissue regenerating effects, including osteoblast chemotactic effect and anti-collagenolytic activity, was incorporated into the membranes by adding it to PLLA solutions. The guided bone regenerating potential of tetracycline-loaded membranes was evaluated using release kinetics both in vitro and in vivo, biodegradation tests, and cell attachment tests. Homogeneous pores were generated both at the surface and in a sublayer of the membranes. The release kinetics of tetracycline depended mainly upon the hydrophilicity of tetracycline and the porosity of the membrane. The release rate further could be controlled by loaded drug contents. The release of tetracycline was appropriate for maintaining anti-microbial activity and for its tissue-regenerating potential. The membranes retained a proper degradation property, maintaining their mechanical integrity for the barrier function for 4 weeks. Tetracycline-loaded membranes induced increased cell attachment levels compared with those of unloaded membranes. Tetracycline-loaded membranes markedly increased new bone formation in rat calvarial defects and induced bony reunion after 2 weeks of implantation. These results suggest that tetracycline-loaded PLLA membranes potentially enhance guided tissue regenerative efficacy.

Efficient labeling of mesenchymal stem cells using cell permeable magnetic nanoparticles.

For the purpose of successfully monitoring labeled cells, optimum labeling efficiency without any side effect is a prerequisite. Magnetic cellular imaging is a new and growing field that allows the visualization of implanted cells in vivo. Herein, superparamagnetic iron oxide (SPIO) nanoparticles were conjugated with a non-toxic protein transduction domain (PTD), identified by the authors and termed low molecular weight protamine (LMWP), to generate efficient and non-toxic cell labeling tools. The cells labeled with LMWP-SPIO presented the highest iron content compared to those labeled with naked SPIO and the complex of SPIO with poly-L-lysine, which is currently used as a transfection agent. In addition to the iron content assay, Prussian staining and confocal observation demonstrated the highest intracellular LMWP-SPIO presence, and the labeling procedure did not alter the cell differentiation capacity of mesenchymal stem cells. Taken together, cell permeable magnetic nanoparticles conjugated with LMWP can be suggested as labeling tools for efficient magnetic imaging of transplanted cells.