In vivo analysis of retroviral gene transfer to chondrocytes within collagen scaffolds for the treatment of osteochondral defects

Potential therapeutic strategies for osteoarthritis via CRISPR/Cas9 mediated gene editing

Osteoarthritis (OA) is an incapacitating and one of the most common physically degenerative conditions with an assorted etiology and a highly complicated molecular mechanism that to date lacks an efficient treatment. The capacity to design biological networks and accurately modify existing genomic sites holds an apt potential for applications across medical and biotechnological sciences. One of these highly specific genomes editing technologies is the CRISPR/Cas9 mechanism, referred to as the clustered regularly interspaced short palindromic repeats, which is a defense mechanism constituted by CRISPR associated protein 9 (Cas9) directed by small non-coding RNAs (sncRNA) that bind to target DNA through Watson-Crick base pairing rules where subsequent repair of the target DNA is initiated. Up-to-date research has established the effectiveness of the CRISPR/Cas9 mechanism in targeting the genetic and epigenetic alterations in OA by suppressing or deleting gene expressions and eventually distributing distinctive anti-arthritic properties in both in vitro and in vivo osteoarthritic models. This review aims to epitomize the role of this high-throughput and multiplexed gene editing method as an analogous therapeutic strategy that could greatly facilitate the clinical development of OA-related treatments since it's reportedly an easy, minimally invasive technique, and a comparatively less painful method for osteoarthritic patients.

New treatment for osteoarthr: pbad014itis: Gene therapy

Osteoarthritis is a complex degenerative disease that affects the entire joint tissue. Currently, non-surgical treatments for osteoarthritis focus on relieving pain. While end-stage osteoarthritis can be treated with arthroplasty, the health and financial costs associated with surgery have forced the search for alternative non-surgical treatments to delay the progression of osteoarthritis and promote cartilage repair. Unlike traditional treatment, the gene therapy approach allows for long-lasting expression of therapeutic proteins at specific sites. In this review, we summarize the history of gene therapy in osteoarthritis, outlining the common expression vectors (non-viral, viral), the genes delivered (transcription factors, growth factors, inflammation-associated cytokines, non-coding RNAs) and the mode of gene delivery (direct delivery, indirect delivery). We highlight the application and development prospects of the gene editing technology CRISPR/Cas9 in osteoarthritis. Finally, we identify the current problems and possible solutions in the clinical translation of gene therapy for osteoarthritis.

Scaffold-Mediated Gene Delivery for Osteochondral Repair

Osteochondral defects involve both the articular cartilage and the underlying subchondral bone. If left untreated, they may lead to osteoarthritis. Advanced biomaterial-guided delivery of gene vectors has recently emerged as an attractive therapeutic concept for osteochondral repair. The goal of this review is to provide an overview of the variety of biomaterials employed as nonviral or viral gene carriers for osteochondral repair approaches both in vitro and in vivo, including hydrogels, solid scaffolds, and hybrid materials. The data show that a site-specific delivery of therapeutic gene vectors in the context of acellular or cellular strategies allows for a spatial and temporal control of osteochondral neotissue composition in vitro. In vivo, implantation of acellular hydrogels loaded with nonviral or viral vectors has been reported to significantly improve osteochondral repair in translational defect models. These advances support the concept of scaffold-mediated gene delivery for osteochondral repair.

Chondrocyte Culture Parameters for Matrix-Assisted Autologous Chondrocyte Implantation Affect Catabolism and Inflammation in a Rabbit Model

Cartilage defects represent an increasing pathology among active individuals that affects the ability to contribute to sports and daily life. Cell therapy, such as autologous chondrocyte implantation (ACI), is a widespread option to treat larger cartilage defects still lacking standardization of in vitro cell culture parameters. We hypothesize that mRNA expression of cytokines and proteases before and after ACI is influenced by in vitro parameters: cell-passage, cell-density and membrane-holding time. Knee joint articular chondrocytes, harvested from rabbits (n = 60), were cultured/processed under varying conditions: after three different cell-passages (P1, P3, and P5), cells were seeded on 3D collagen matrices (approximately 25 mm³) at three different densities (2 × 10⁵/matrix, 1 × 10⁶/matrix, and 3 × 10⁶/matrix) combined with two different membrane-holding times (5 h and two weeks) prior autologous transplantation. Those combinations resulted in 18 different in vivo experimental groups. Two defects/knee/animal were created in the trochlear groove (defect dimension: ∅ 4 mm × 2 mm). Four identical cell-seeded matrices (CSM) were assembled and grouped in two pairs: One pair giving pre-operative in vitro data (CSM-i), the other pair was implanted in vivo and harvested 12 weeks post-implantation (CSM-e). CSMs were analyzed for TNF-α, IL-1β, MMP-1, and MMP-3 via qPCR. CSM-i showed higher expression of IL-1β, MMP-1, and MMP-3 compared to CSM-e. TNF-α expression was higher in CSM-e. Linearity between CSM-i and CSM-e values was found, except for TNF-α. IL-1β expression was higher in CSM-i at higher passage and longer membrane-holding time. IL-1β expression decreased with prolonged membrane-holding time in CSM-e. For TNF-α, the reverse was true. Lower cell-passages and lower membrane-holding time resulted in stronger TNF-α expression. Prolonged membrane-holding time resulted in increased MMP levels among CSM-i and CSM-e. Cellular density was of no significant effect. We demonstrated cytokine and MMP expression levels to be directly influenced by in vitro culture settings in ACI. Linearity of expression-patterns between CSM-i and CSM-e may predict ACI regeneration outcome in vivo. Cytokine/protease interaction within the regenerate tissue could be guided via adjusting in vitro culture parameters, of which membrane-holding time resulted the most relevant one.

Gene therapy for chondral and osteochondral regeneration: is the future now?

Gene therapy might represent a promising strategy for chondral and osteochondral defects repair by balancing the management of temporary joint mechanical incompetence with altered metabolic and inflammatory homeostasis. This review analysed preclinical and clinical studies on gene therapy for the repair of articular cartilage defects performed over the last 10 years, focussing on expression vectors (non-viral and viral), type of genes delivered and gene therapy procedures (direct or indirect). Plasmids (non-viral expression vectors) and adenovirus (viral vectors) were the most employed vectors in preclinical studies. Genes delivered encoded mainly for growth factors, followed by transcription factors, anti-inflammatory cytokines and, less frequently, by cell signalling proteins, matrix proteins and receptors. Direct injection of the expression vector was used less than indirect injection of cells, with or without scaffolds, transduced with genes of interest and then implanted into the lesion site. Clinical trials (phases I, II or III) on safety, biological activity, efficacy, toxicity or bio-distribution employed adenovirus viral vectors to deliver growth factors or anti-inflammatory cytokines, for the treatment of osteoarthritis or degenerative arthritis, and tumour necrosis factor receptor or interferon for the treatment of inflammatory arthritis.

An effective and efficient method of transfecting primary human chondrocytes in suspension

Human chondrocytes accumulate an ECM-rich matrix by secreting matrix macromolecules during monolayer culture, which makes them difficult to transfect efficiently. Here we report a non-viral based protocol to transfect the primary human chondrocytes with high efficiency in suspension. Chondrocyte cultures were digested using Pronase and Collagenase and transfected in suspension. Transfection efficiencies of more than 80% were achieved routinely using the protocol described. The viability of siRNA transfected or un-transfected chondrocytes was not affected and resulted in 80-90% knockdown of the target mRNA levels. This protocol may be useful in gene knockdown, and ectopic overexpression studies in chondrocytes.

A novel nonviral gene delivery tool of BMP-2 for the reconstitution of critical-size bone defects in rats

The osseointegration of bone implants, implant failure, and the bridging of critical-size bone defects are frequent clinical challenges. Deficiencies in endogenous bone healing can be resolved through the local administration of suitable recombinant growth factors (GFs). In preclinical models, gene-therapy-supported bone healing has proven promising for overcoming certain limitations of GFs. We report the dose-dependent bridging of critical-size mandibular bone defects (CSDs) in a rat model using a non-viral BMP-2-encoding copolymer-protected gene vector (pBMP-2) embedded in poly(d, l-lactide) (PDLLA) coatings on titanium discs that were used to cover drill holes in the mandibles of 53 male Sprague Dawley rats. After sacrificing, the mandibles were subjected to micro-computed tomography (µCT), micro-radiography, histology, and fluorescence analyses to evaluate bone regeneration. pBMP-2 in PDLLA-coated titanium implants promoted partial bridging of bone defects within 14 days and complete defect healing within 112 days when the DNA dose per implant did not exceed 2.5 µg. No bridging was observed in untreated control CSDs. Thus, the delivery of plasmid DNA coding for BMP-2 appears to be a potent method for controlled new-bone formation with an inverse dose dependency. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2441-2455, 2016.

Enhanced chondrocyte culture and growth on biologically inspired nanofibrous cell culture dishes

Chondral and osteochondral defects affect a large number of people in which treatment options are currently limited. Due to its ability to mimic the natural nanofibrous structure of cartilage, this current in vitro study aimed at introducing a new scaffold, called XanoMatrix™, for cartilage regeneration. In addition, this same scaffold is introduced here as a new substrate onto which to study chondrocyte functions. Current studies on chondrocyte functions are limited due to nonbiologically inspired cell culture substrates. With its polyethylene terephthalate and cellulose acetate composition, good mechanical properties and nanofibrous structure resembling an extracellular matrix, XanoMatrix offers an ideal surface for chondrocyte growth and proliferation. This current study demonstrated that the XanoMatrix scaffolds promote chondrocyte growth and proliferation as compared with the Corning and Falcon surfaces normally used for chondrocyte cell culture. The XanoMatrix scaffolds also have greater hydrophobicity, three-dimensional surface area, and greater tensile strength, making them ideal candidates for alternative treatment options for chondral and osteochondral defects as well as cell culture substrates to study chondrocyte functions.

Matrix-assisted autologous chondrocyte transplantation for remodeling and repair of chondral defects in a rabbit model

Articular cartilage defects are considered a major health problem because articular cartilage has a limited capacity for self-regeneration (1). Untreated cartilage lesions lead to ongoing pain, negatively affect the quality of life and predispose for osteoarthritis. During the last decades, several surgical techniques have been developed to treat such lesions. However, until now it was not possible to achieve a full repair in terms of covering the defect with hyaline articular cartilage or of providing satisfactory long-term recovery (2-4). Therefore, articular cartilage injuries remain a prime target for regenerative techniques such as Tissue Engineering. In contrast to other surgical techniques, which often lead to the formation of fibrous or fibrocartilaginous tissue, Tissue Engineering aims at fully restoring the complex structure and properties of the original articular cartilage by using the chondrogenic potential of transplanted cells. Recent developments opened up promising possibilities for regenerative cartilage therapies. The first cell based approach for the treatment of full-thickness cartilage or osteochondral lesions was performed in 1994 by Lars Peterson and Mats Brittberg who pioneered clinical autologous chondrocyte implantation (ACI) (5). Today, the technique is clinically well-established for the treatment of large hyaline cartilage defects of the knee, maintaining good clinical results even 10 to 20 years after implantation (6). In recent years, the implantation of autologous chondrocytes underwent a rapid progression. The use of an artificial three-dimensional collagen-matrix on which cells are subsequently replanted became more and more popular (7-9). MACT comprises of two surgical procedures: First, in order to collect chondrocytes, a cartilage biopsy needs to be performed from a non weight-bearing cartilage area of the knee joint. Then, chondrocytes are being extracted, purified and expanded to a sufficient cell number in vitro. Chondrocytes are then seeded onto a three-dimensional matrix and can subsequently be re-implanted. When preparing a tissue-engineered implant, proliferation rate and differentiation capacity are crucial for a successful tissue regeneration (10). The use of a three-dimensional matrix as a cell carrier is thought to support these cellular characteristics (11). The following protocol will summarize and demonstrate a technique for the isolation of chondrocytes from cartilage biopsies, their proliferation in vitro and their seeding onto a 3D-matrix (Chondro-Gide, Geistlich Biomaterials, Wollhusen, Switzerland). Finally, the implantation of the cell-matrix-constructs into artificially created chondral defects of a rabbit's knee joint will be described. This technique can be used as an experimental setting for further experiments of cartilage repair.

Reconstruct large osteochondral defects of the knee with hIGF-1 gene enhanced Mosaicplasty

OBJECTIVE

To investigate a compound technique including gene therapy, injectable tissue engineering and Mosaicplasty to reconstruct large osteochondral defect.

METHODS

Plasmid vector containing hIGF-1 cDNA was created and transfected into BMSCs in vitro with FuGene6. After gene expression determination, cells were mixed with calcium alginate gel. Osteochondral defects were created on the femoral condyle of goats in a diameter of 6mm. Osteochondral plugs were harvested from the intertrochlea groove and pressed into the recipient sites in a mosaic mode. Gene modified BMSCs-scaffold complex was applied to fill the residual defects. Control groups were also set up. At 4 and 16 weeks, specimens were investigated in gross and under microscopy, electromicroscopy and MRI detection.

RESULTS

hIGF-I gene was expressed effectively with the peak concentration at 34.75 ng/ml. Subchondral bone and cartilage were integrated well in gene enhanced Mosaicplasty group. The reconstructed tissue filled up the gaps between columns, which appeared better than other groups. The regenerated cartilage was integrated with neighbor tightly in regular arrange. Extracellular matrix distributed evenly and deeply stained by alcian blue. Quantitative histologic assessments showed higher score in gene enhanced Mosaicplasty group. Glycosaminoglycan assay revealed no difference between groups involving Mosaicplasty. MRI analysis demonstrated the healing process between the subchondral bone other than control groups.

CONCLUSIONS

hIGF-I gene enhanced tissue engineering can modify the outcome of Mosaicplasty to reconstruct large osteochondral defects in weight-bearing region.

Application of stem cells in orthopedics

Stem cell research plays an important role in orthopedic regenerative medicine today. Current literature provides us with promising results from animal research in the fields of bone, tendon, and cartilage repair. While early clinical results are already published for bone and cartilage repair, the data about tendon repair is limited to animal studies. The success of these techniques remains inconsistent in all three mentioned areas. This may be due to different application techniques varying from simple mesenchymal stem cell injection up to complex tissue engineering. However, the ideal carrier for the stem cells still remains controversial. This paper aims to provide a better understanding of current basic research and clinical data concerning stem cell research in bone, tendon, and cartilage repair. Furthermore, a focus is set on different stem cell application techniques in tendon reconstruction, cartilage repair, and filling of bone defects.

Future of local bone regeneration - Protein versus gene therapy

The most promising attempts to achieve bone regeneration artificially are based on the application of mediators such as bone morphogenetic proteins (BMPs) directly to the deficient tissue site. BMPs, as promoters of the regenerative process, have the ability to induce de novo bone formation in various tissues, and many animal models have demonstrated their high potential for ectopic and orthotopic bone formation. However, the biological activity of the soluble factors that promote bone formation in vivo is limited by diffusion and degradation, leading to a short half-life. Local delivery remains a problem in clinical applications. Several materials, including hydroxyapatite, tricalcium phosphate, demineralised bone matrices, poly-lactic acid homo- and heterodimers, and collagen have been tested as carriers and delivery systems for these factors in a sustained and appropriate manner. Unfortunately these delivery vehicles often have limitations in terms of biodegradability, inflammatory and immunological rejection, disease transmission, and most importantly, an inability to provide a sustained, continuous release of these factors at the region of interest. In coping with these problems, new approaches have been established: genes encoding these growth factor proteins can be delivered to the target cells. In this way the transfected cells serve as local "bioreactors", as they express the exogenous genes and secrete the synthesised proteins into their vicinity. The purpose of this review is to present the different methods of gene versus growth factor delivery in tissue engineering. Our review focuses on these promising and innovative methods that are defined as regional gene therapy and provide an alternative to the direct application of growth factors. Various advantages and disadvantages of non-viral and viral vectors are discussed. This review identifies potential candidate genes and target cells, and in vivo as well as ex vivo approaches for cell transduction and transfection. In explaining the biological basis, this paper also refers to current experimental and clinical applications.

The dependence of autologous chondrocyte transplantation on varying cellular passage, yield and culture duration

Matrix-assisted chondrocyte transplantation (m-ACI) still lacks any standardization in its execution in terms of cell passage (P), cell yield (C) and in vitro membrane-holding time (T). It was the goal of this study to analyze the effect of shifting cell culture parameters (P, C, T) on the in vitro as well as in vivo effort of a regulated animal m-ACI. Autologous rabbit knee articular chondrocytes were seeded within bilayer collagen I/III 3-D matrices in variation of P, C and T. Each time, 2 PCT-identical by 2 PCT-identical cell-matrix-constructs (CMC)/animal were created. Simultaneously 2 (PCT-distinct) were re-implanted (CMC-e) autologous into artificial trochlear pristine chondral defects in vivo to remain for 12 weeks while the remaining 2 were harvested (CMC-i) for immediate in vitro analysis at the time of transplantation of their identical twins. mRNA of both, CMC-e regenerates and CMC-i membranes, was analyzed for Collagen-1,-2,-10, COMP, Aggrecan, Sox9 expression by use of a mixed linear model, multiple regression analysis. Generally, CMC-i values were higher than CMC-e values for differentiation targets; the opposite was true for dedifferentiation targets. Regarding individual gene expression, in vivo regenerate cell-matrix properties were significantly dependent on initial cell-matrix in vitro values as a sign of linearity. The parameter membrane-holding time (T) had strongest effects on the resulting mRNA expression with slightly less impact of the parameter passage (P), whereas cell yield (C) had clearly less effects. Noting differences between in vitro and in vivo data, in general, optimal expression patterns concerning chondrogenic differentiation were achieved by few passages, medium cellular yield, short membrane-holding time. Clinical m-ACI may benefit from optimal orchestration of the cell culture parameters passage, yield and time.

In vitro and in vivo validation of human and goat chondrocyte labeling by green fluorescent protein lentivirus transduction

We investigated whether human articular chondrocytes can be labeled efficiently and for long-term with a green fluorescent protein (GFP) lentivirus and whether the viral transduction would influence cell proliferation and tissue-forming capacity. The method was then applied to track goat articular chondrocytes after autologous implantation in cartilage defects. Expression of GFP in transduced chondrocytes was detected cytofluorimetrically and immunohistochemically. Chondrogenic capacity of chondrocytes was assessed by Safranin-O staining, immunostaining for type II collagen, and glycosaminoglycan content. Human articular chondrocytes were efficiently transduced with GFP lentivirus (73.4 +/- 0.5% at passage 1) and maintained the expression of GFP up to 22 weeks of in vitro culture after transduction. Upon implantation in nude mice, 12 weeks after transduction, the percentage of labeled cells (73.6 +/- 3.3%) was similar to the initial one. Importantly, viral transduction of chondrocytes did not affect the cell proliferation rate, chondrogenic differentiation, or tissue-forming capacity, either in vitro or in vivo. Goat articular chondrocytes were also efficiently transduced with GFP lentivirus (78.3 +/- 3.2%) and maintained the expression of GFP in the reparative tissue after orthotopic implantation. This study demonstrates the feasibility of efficient and relatively long-term labeling of human chondrocytes for co-culture on integration studies, and indicates the potential of this stable labeling technique for tracking animal chondrocytes for in cartilage repair studies.

Why we need semisolid decalcification system in bone tissue engineering? A story begins with honeycomb

The repair of large segmental bone defects remains a tough problem disturbing surgeons and researchers. Bone tissue engineering brings some new sight in this field. However, it has not been effectively applied in clinics, for the reason that the involved mechanism is not well understood. Thus, we need to know the osteogenesis process of the tissue-engineered bone including distribution, proliferation and interaction among seed cells pre-inoculated in biomaterials as well as the function of surrounding tissues. As a matter of fact, the tissue-engineered bone or the biomaterials are solid and opaque, which makes the study difficult. Here, inspired by the structure of honeycomb and amber, we hypothesize a semisolid decalcification protocol to solve this problem.

Enhanced meniscal repair by overexpression of hIGF-1 in a full-thickness model

The importance of the menisci to the well-being of the normal knee is well-documented. However, there is no ideal repair or reconstructive approach for damaged menisci. Gene therapy provides one promising alternative strategy, especially when combined with injectable tissue engineering to achieve minimally invasive clinical application. We asked whether the introduction of human insulin-like growth factor 1 (hIGF-1) gene could improve the repair of full-thickness meniscal defects. We created full-thickness meniscal defects in the "white area" of the anterior horn in 48 goats. Bone marrow stromal cells with the transfection of hIGF-1 gene and injectable calcium alginate gel were mixed together to repair the defects; three control groups included cells without transfection, gel without cells, and defects left empty. After 4, 8, and 16 weeks, the animals were euthanized and the excised defects were examined by macroscopic assessment, histological analysis, electron microscopy, proteoglycan determination, and MRI. Sixteen weeks after surgery the repaired meniscal defects were filled with white tissue similar to that in normal meniscal fibrocartilage. The repair tissue was composed of cells embedded within matrix that filled the spaces of the fibers. The proteoglycan content in the gene-enhanced tissue engineering group was higher than those in the control groups, and less than that in the normal meniscus. The results suggest full-thickness meniscal defects in regions without blood supply can be reconstructed with hIGF-1-enhanced injectable tissue engineering.

The possible use of stem cells in regenerative medicine: dream or reality?

Stem cells are one of the most fascinating areas in regenerative medicine today. They play a crucial role in the development and regeneration of human life and are defined as cells that continuously reproduce themselves while maintaining the ability to differentiate into various cell types. Stem cells are found at all developmental stages, from embryonic stem cells that differentiate into all cell types found in the human body to adult stem cells that are responsible for tissue regeneration. The general opinion postulates that clinical therapies based on the properties of stem cells may have the potential to change the treatment of degenerative diseases or important traumatic injuries in the "near" future. We here briefly review the literature in particularly for the liver, heart, kidney, cartilage, and bone regeneration.

Efficient non-viral transfection of primary human adult chondrocytes in a high-throughput format

OBJECTIVE

The development of a reliable high-throughput transfection protocol for primary human articular chondrocytes.

METHODS

Primary human chondrocytes were isolated from adult knee cartilage by an optimized enzymatic digestion protocol and cultivated in high-density monolayer culture for 3-5 days. Isolated chondrocytes were transfected with a green fluorescent protein (GFP)-expressing reporter construct using amaxa's Nucleofector 96-well Shuttle System. Transfection efficiencies were measured by fluorescence activated cell sorting and cell viability was determined by an adenosine-5'-triphosphate (ATP) assay. siRNA oligonucleotides (against glyceraldehyde-3-phosphate dehydrogenase (GAPDH)) were transfected into the cells using the optimized nucleofection protocol and mRNA knockdown values were determined by a branched-DNA assay.

RESULTS

Transfection efficiencies of more than 70% of surviving cells were achieved routinely with the nucleofection protocol presented in this article. Cell viability 24h post transfection was around 80%. The cell number used per transfection was reduced to 2x10(5) per sample. In addition, the protocol proved to be well suited for the transfer of siRNA molecules into primary human chondrocytes with suppression rates on the mRNA level of more than 95% (for GAPDH).

CONCLUSIONS

We present the successful use of nucleofection on primary human chondrocytes using a microtiter plate compatible format that for the first time allows the efficient transfection of up to 96 samples in parallel. The optimized nucleofection protocol is offering maximum substrate flexibility by allowing transfer of DNA and siRNA oligonucleotides with the same set of parameters. Moreover, the transfection procedure requires substantially lower cell numbers than single cuvette protocols and is therefore perfectly suited for applications requiring multiple experimental replicates.

The influence of the stable expression of BMP2 in fibrin clots on the remodelling and repair of osteochondral defects

Growth factors like BMP2 have been tested for osteochondral repair, but transfer methods used until now were insufficient. Therefore, the aim of this study was to analyse if stable BMP2 expression after retroviral vector (Bullet) transduction is able to regenerate osteochondral defects in rabbits. Fibrin clots colonized by control or BMP2-transduced chondrocytes were generated for in vitro experiments and implantation into standardized corresponding osteochondral defects (n=32) in the rabbit trochlea. After 4 and 12 weeks repair tissue was analysed by histology (HE, alcian-blue, toluidine-blue), immunohistochemistry (Col1, Col2, aggrecan, aggrecan-link protein), ELISA (BMP2), and quantitative RT-PCR (BMP2, Col1, Col2, Col10, Cbfa1, Sox9). In vitro clots were also analysed by BMP2-ELISA, histology (alcian-blue), quantitative RT-PCR and in addition by electron microscopy. BMP2 increased Col2 expression, proteoglycan production and cell size in vitro. BMP2 transduction by Bullet was efficient and gene expression was stable in vivo over at least 12 weeks. Proteoglycan content and ICRS-score of repair tissue were improved by BMP2 after 4 and 12 weeks and Col2 expression after 4 weeks compared to controls. However, in spite of stable BMP2 expression, a complete repair of osteochondral defects could not be demonstrated. Therefore, BMP2 is not suitable to regenerate osteochondral lesions completely.

A fibrin glue composition as carrier for nucleic acid vectors

PURPOSE

Gene delivery from biomaterials has become an important tool in tissue engineering. The purpose of this study was to generate a gene vector-doted fibrin glue as a versatile injectable implant to be used in gene therapy supported tissue regeneration.

METHODS

Copolymer-protected polyethylenimine(PEI)-DNA vectors (COPROGs), naked DNA and PEI-DNA were formulated with the fibrinogen component of the fibrin glue TISSUCOL and lyophilized. Clotting parameters upon rehydration and thrombin addition were measured, vector release from fibrin clots was determined. Structural characterizations were carried out by electron microscopy. Reporter and growth factor gene delivery to primary keratinocytes and chondrocytes in vitro was examined. Finally,chondrocyte colonized clots were tested for their potency in cartilage regeneration in a osteochondral defect model.

RESULTS

The optimized glue is based on the fibrinogen component of TISSUCOL, a fibrin glue widely used in the clinics, co-lyophilized with copolymer-protected polyethylenimine(PEI)- DNA vectors (COPROGs). This material, when rehydrated, forms vector-containing clots in situ upon thrombin addition and is suitable to mediate growth factor gene delivery to primary keratinocytes and primary chondrocytes admixed before clotting. Unprotected PEI-DNA in the same setup was comparatively unsuitable for clot formation while naked DNA was ineffective in transfection. Naked DNA was released rapidly from fibrin clots (>70% within the first seven days) in contrast to COPROGs which remained tightly immobilized over extended periods of time (0.29% release per day). Electron microscopy of chondrocytecolonized COPROG-clots revealed avid endocytotic vector uptake. In situ BMP-2 gene transfection and subsequent expression in chondrocytes grown in COPROG clots resulted in the upregulation of alkaline phosphatase expression and increased extracellular matrix formation in vitro. COPROG-fibrinogen preparations with admixed autologous chondrocytes when clotted in situ in osteochondral defects in the patellar grooves of rabbit femura gave rise to luciferase reporter gene expression detectable for two weeks (n=3 animals per group). However, no significant improvement in cartilage formation in osteochondral defects filled with autologous chondrocytes in BMP-2-COPROG clots was achieved in comparison to controls (n=8 animals per group).

CONCLUSIONS

COPROGs co-lyophilized with fibrinogen are a simple basis for an injectable fibrin gluebased gene-activated matrix. The preparation can be used is complete analogy to fibrin glue preparations that are used in the clinics. However, further improvements in transgene expression levels and persistence are required to yield cartilage regeneration in the osteochondral defect model chosen in this study.