Gene therapy and tissue engineering for sports medicine

Ethical Aspects of Human Genome Research in Sports-A Narrative Review

Human genome research in sports raises complex ethical considerations regarding the intersection of genetics and athletic performance. Pursuing genetic enhancements must uphold fairness, equality, and respect for human dignity. This narrative review explores the ethical dimensions of human genome research in sports, its potential implications on athletes, and the integrity of sports. As a narrative review, this study synthesizes the existing literature and expert insights to examine the ethical aspects of human genome research in sports. This study extensively examined the current literature on genetics, sports performance, ethical concerns, human rights, and legal regulations within the European context. The literature was searched using the SPORTDiscus, Scopus, Google Scholar, and PubMed databases. Exploring human genome research in sports reveals significant ethical implications, including potential genetic discrimination, impacts on human rights, and creating a genetic underclass of athletes. There are also definite benefits surrounding genetic testing. In conclusion, this review contends that integrating ethical considerations into developing and applying genetic technologies in sports is crucial to upholding fundamental principles of fairness, equality, and respect for human dignity. It stresses the importance of open and inclusive dialogue about the potential consequences of genetic advancements on athletic performance, future generations, and the integrity of sports.

Advanced Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

Arthroscopic utilization of ChondroFiller gel for the treatment of hip articular cartilage defects: a cohort study with 12- to 60-month follow-up

ChondroFiller gel is an absorbable collagen implant. It serves as a protective cover for the cartilage defects, allowing chondrocyte migration into the lesion. The implant consists of collagen (Type I) and is derived from veterinary monitored rats. This study evaluates the use of ChondroFiller gel in the treatment of cartilage lesions during hip joint arthroscopy. A prospective study was conducted on a group of 26 adult patients. All patients had an existing femoroacetabular impingement together with acetabular cartilage lesions >2 cm². All patients underwent hip arthroscopic surgery and the lesions were treated using ChondroFiller gel. The cartilage tissue healing was evaluated postoperatively using MRI. A total of 26 patients, including 5 females and 21 males, all with articular cartilage lesions, were included in the study. Cartilage healing conditions were evaluated for all patients, and the difference between pre- and post-surgery conditions was statistically significant. The follow-up scores have been acquired from 21 out of initial 26 patients (2 were disqualified after receiving THR, 3 could not be reached by researchers) after 3, 4 and 5 years consecutively with 17/21 patients having good/excellent results. The use of ChondroFiller gel during arthroscopy of the hip for acetabular cartilage lesions is an effective treatment technique. Encouraging long-term results have been observed, but further research on larger group of patient is required to better assess the full value of this technique. Patients with pre-existing osteoarthritis (Tönnis 2–3) have poor results.

Biophysical and Biochemical Cues of Biomaterials Guide Mesenchymal Stem Cell Behaviors

Mesenchymal stem cells (MSCs) have been widely used in the fields of tissue engineering and regenerative medicine due to their self-renewal capabilities and multipotential differentiation assurance. However, capitalizing on specific factors to precisely guide MSC behaviors is the cornerstone of biomedical applications. Fortunately, several key biophysical and biochemical cues of biomaterials that can synergistically regulate cell behavior have paved the way for the development of cell-instructive biomaterials that serve as delivery vehicles for promoting MSC application prospects. Therefore, the identification of these cues in guiding MSC behavior, including cell migration, proliferation, and differentiation, may be of particular importance for better clinical performance. This review focuses on providing a comprehensive and systematic understanding of biophysical and biochemical cues, as well as the strategic engineering of these signals in current scaffold designs, and we believe that integrating biophysical and biochemical cues in next-generation biomaterials would potentially help functionally regulate MSCs for diverse applications in regenerative medicine and cell therapy in the future.

Multidrug-loaded electrospun micro/nanofibrous membranes: Fabrication strategies, release behaviors and applications in regenerative medicine

Electrospun micro/nanofibrous membranes (EFMs) have been widely investigated as local drug delivery systems. Multiple drugs can be simultaneously incorporated into one EFM to create synergistic effects, reduce side effects, and play their respective roles in the complex physiological processes of tissue regeneration and postoperative adhesion prevention. Due to the versatile electrospinning techniques, sustained and programmed release behaviors of multiple drugs could be achieved by modulating the structure of the EFMs and the location of the drugs. In this review, various multidrug incorporation approaches based on electrospinning are overviewed. In particular, the advantages and limitations of each drug incorporation technique, the methods to control drug release and the effect of one drug release on another are discussed. Then the applications of multidrug-loaded EFMs in regenerative medicine, including wound healing, bone regeneration, vascular tissue engineering, nerve regeneration, periodontal regeneration and adhesion prevention are comprehensively reviewed. Finally, the future perspectives and challenges in the research of multidrug-loaded EFMs are discussed.

FGF2: a key regulator augmenting tendon-to-bone healing and cartilage repair

Ligament/tendon and cartilage injuries are clinically common diseases that perplex most clinicians. Because of the lack of blood vessels and nerves, their self-repairing abilities are rather poor. Therefore, surgeries are necessary and also widely used to treat ligament/tendon or cartilage injuries. However, after surgery, there are still many problems that affect healing. In recent years, it has been found that exogenous FGF2 plays an important role in the repair of ligament/tendon and cartilage injuries and exerts a synergistic effect with endogenous FGF2. Therefore, FGF2 can be used as a new type of biomolecule to accelerate tendon-to-bone healing and cartilage repair after injury.

Gene doping: Present and future

Being an elite athlete is an extremely coveted position, which can lead an individual to use doping. As knowledge is extended, doping techniques have become increasingly sophisticated, and the newest method of doping is gene doping. This article aims to present an updated bibliographic survey that addresses gene doping between 1983 and 2018. Anti-doping agencies have not yet approved any detection technique for this type of doping. The possibility of eradicating such doping is almost zero mainly because gene therapy advances rapidly. In this scenario, the future of gene doping must be discussed and decided before irreversible limits are exceeded.

Stem cell therapy: a promising biological strategy for tendon-bone healing after anterior cruciate ligament reconstruction

Tendon-bone healing after anterior cruciate ligament (ACL) reconstruction is a complex process, impacting significantly on patients' prognosis. Natural tendon-bone healing usually results in fibrous scar tissue, which is of inferior quality compared to native attachment. In addition, the early formed fibrous attachment after surgery is often not reliable to support functional rehabilitation, which may lead to graft failure or unsatisfied function of the knee joint. Thus, strategies to promote tendon-bone healing are crucial for prompt and satisfactory functional recovery. Recently, a variety of biological approaches, including active substances, gene transfer, tissue engineering and stem cells, have been proposed and applied to enhance tendon-bone healing. Among these, stem cell therapy has been shown to have promising prospects and draws increasing attention. From commonly investigated bone marrow-derived mesenchymal stem cells (bMSCs) to emerging ACL-derived CD34+ stem cells, multiple stem cell types have been proven to be effective in accelerating tendon-bone healing. This review describes the current understanding of tendon-bone healing and summarizes the current status of related stem cell therapy. Future limitations and perspectives are also discussed.

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.

Metal Ion Dependence of the Matrix Metalloproteinase-1 Mechanism

Matrix metalloproteinase-1 (MMP-1) plays crucial roles in disease-related physiologies and pathological processes in the human body. We report here solution studies of MMP-1, including characterization of a series of mutants designed to bind metal in either the catalytic site or the structural site (but not both). Circular dichroism and fluorescence spectroscopy of the mutants demonstrate the importance of the structural Zn(II) in maintaining both secondary and tertiary structure, while UV-visible, nuclear magnetic resonance, electron paramagnetic resonance, and extended X-ray absorption fine structure show its presence influences the catalytic metal ion's coordination number. The mutants allow us to demonstrate convincingly the preparation of a mixed-metal analogue, Co(C)Zn(S)-MMP-1, with Zn(II) in the structural site and Co(II) in the catalytic site. Stopped-flow fluorescence of the native form, Zn(C)Zn(S)-MMP-1, and the mixed-metal Co(C)Zn(S)-MMP-1 analogue shows that the internal fluorescence of a nearby Trp residue is modulated with catalysis and can be used to monitor reactivity under a number of conditions, opening the door to substrate profiling.

Overexpression of TGF-β via rAAV-Mediated Gene Transfer Promotes the Healing of Human Meniscal Lesions Ex Vivo on Explanted Menisci

BACKGROUND

Direct application of therapeutic gene vectors derived from the adeno-associated virus (AAV) might be beneficial to improve the healing of meniscal tears.

PURPOSE

To test the ability of recombinant AAV (rAAV) to overexpress the potent transforming growth factor-β (TGF-β) in primary cultures of human meniscal fibrochondrocytes, in human meniscal explants, and in experimental human meniscal lesions as a new tool to enhance meniscal repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

The effects of the candidate treatment on the proliferative and metabolic activities of meniscal cells were monitored in vitro for up to 21 days and in situ in intact and injured human menisci for up to 15 days using biochemical, immunohistochemical, histological, and histomorphometric analyses.

RESULTS

Efficient production of TGF-β via rAAV was achieved in vitro and in situ, both in the intact and injured meniscus. Application of the rAAV TGF-β vector stimulated the levels of cell proliferation and matrix synthesis (type I collagen) compared with control gene transfer in all systems tested, especially in situ in regions of poor healing capacity and in sites of meniscal injury. No adverse effects of the candidate treatment were observed at the level of osseous differentiation, as tested by immunodetection of type X collagen. Most remarkably, a significant reduction of the amplitude of meniscal tears was noted after TGF-β treatment, an effect that was associated with increased expression levels of the α-smooth muscle actin contractile marker.

CONCLUSION

Overexpression of TGF-β via rAAV gene transfer is capable of modulating the reparative activities of human meniscal cells, allowing for the healing of meniscal lesions by convenient injection in sites of injury.

CLINICAL RELEVANCE

Direct gene-based approaches using rAAV have strong potential to develop new therapeutic options that aim at treating human meniscal defects.

From gene engineering to gene modulation and manipulation: can we prevent or detect gene doping in sports?

During the last 2 decades, progress in deciphering the human gene map as well as the discovery of specific defective genes encoding particular proteins in some serious human diseases have resulted in attempts to treat sick patients with gene therapy. There has been considerable focus on human recombinant proteins which were gene-engineered and produced in vitro (insulin, growth hormone, insulin-like growth factor-1, erythropoietin). Unfortunately, these substances and methods also became improper tools for unscrupulous athletes. Biomedical research has focused on the possible direct insertion of gene material into the body, in order to replace some defective genes in vivo and/or to promote long-lasting endogenous synthesis of deficient proteins. Theoretically, diabetes, anaemia, muscular dystrophies, immune deficiency, cardiovascular diseases and numerous other illnesses could benefit from such innovative biomedical research, though much work remains to be done. Considering recent findings linking specific genotypes and physical performance, it is tempting to submit the young athletic population to genetic screening or, alternatively, to artificial gene expression modulation. Much research is already being conducted in order to achieve a safe transfer of genetic material to humans. This is of critical importance since uncontrolled production of the specifically coded protein, with serious secondary adverse effects (polycythaemia, acute cardiovascular problems, cancer, etc.), could occur. Other unpredictable reactions (immunogenicity of vectors or DNA-vector complex, autoimmune anaemia, production of wild genetic material) also remain possible at the individual level. Some new substances (myostatin blockers or anti-myostatin antibodies), although not gene material, might represent a useful and well-tolerated treatment to prevent progression of muscular dystrophies. Similarly, other molecules, in the roles of gene or metabolic activators [5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR), GW1516], might concomitantly improve endurance exercise capacity in ischaemic conditions but also in normal conditions. Undoubtedly, some athletes will attempt to take advantage of these new molecules to increase strength or endurance. Antidoping laboratories are improving detection methods. These are based both on direct identification of new substances or their metabolites and on indirect evaluation of changes in gene, protein or metabolite patterns (genomics, proteomics or metabolomics).

Emerging Applications of Stem Cell and Regenerative Medicine to Sports Injuries

Background:

The treatment of sports-related musculoskeletal injuries with stem cells has become more publicized because of recent reports of high-profile athletes undergoing stem cell procedures. There has been increased interest in defining the parameters of safety and efficacy and the indications for potential use of stem cells in clinical practice.

Purpose:

To review the role of regenerative medicine in the treatment of sports-related injuries.

Study Design:

Review.

Method:

Relevant studies were identified through a PubMed search combining the terms stem cells and cartilage, ligament, tendon, muscle, and bone from January 2000 to August 2013. Studies and works cited in these studies were also reviewed.

Results:

Treatment of sports-related injuries with stem cells shows potential for clinical efficacy from the data available from basic science and animal studies.

Conclusion:

Cell-based therapies and regenerative medicine offer safe and potentially efficacious treatment for sports-related musculoskeletal injuries. Basic science and preclinical studies that support the possibility of enhanced recovery from sports injuries using cell-based therapies are accumulating; however, more clinical evidence is necessary to define the indications and parameters for their use. Accordingly, exposing patients to cell-based therapies could confer an unacceptable risk profile with minimal or no benefit. Continued clinical testing with animal models and clinical trials is necessary to determine the relative risks and benefits as well as the indications and methodology of treatment.

Basic science of anterior cruciate ligament injury and repair

Injury to the anterior cruciate ligament (ACL) is one of the most devastating and frequent injuries of the knee. Surgical reconstruction is the current standard of care for treatment of ACL injuries in active patients. The widespread adoption of ACL reconstruction over primary repair was based on early perception of the limited healing capacity of the ACL. Although the majority of ACL reconstruction surgeries successfully restore gross joint stability, post-traumatic osteoarthritis is commonplace following these injuries, even with ACL reconstruction. The development of new techniques to limit the long-term clinical sequelae associated with ACL reconstruction has been the main focus of research over the past decades. The improved knowledge of healing, along with recent advances in tissue engineering and regenerative medicine, has resulted in the discovery of novel biologically augmented ACL-repair techniques that have satisfactory outcomes in preclinical studies. This instructional review provides a summary of the latest advances made in ACL repair. Cite this article: Bone Joint Res 2014;3:20-31.

Direct FGF-2 gene transfer via recombinant adeno-associated virus vectors stimulates cell proliferation, collagen production, and the repair of experimental lesions in the human ACL

BACKGROUND

Basic fibroblast growth factor (FGF-2) is a powerful stimulator of fibroblast proliferation and type I/III collagen production.

HYPOTHESIS

Overexpression of FGF-2 via direct recombinant adeno-associated virus (rAAV) vector-mediated gene transfer enhances the healing of experimental lesions to the human anterior cruciate ligament (ACL).

STUDY DESIGN

Controlled laboratory study.

METHODS

rAAV vectors carrying a human FGF-2 sequence or the lacZ marker gene were applied to primary human ACL fibroblasts in vitro and to intact or experimentally injured human ACL explants in situ to evaluate the efficacy and duration of transgene expression and the potential effects of FGF-2 treatment upon the proliferative, metabolic, and regenerative activities in these systems.

RESULTS

Sustained, effective dose-dependent lacZ expression was achieved in all systems tested (up to 96% ± 2% in vitro and 80%-85% in situ for at least 30 days). rAAV allowed for continuous FGF-2 production both in vitro and in the intact ACL in situ (32.7 ± 1.4 and 33.1 ± 0.8 pg/mL/24 h, respectively, ie, up to 41-fold more than in the controls at day 30; always P ≤ .001), leading to significantly and durably enhanced levels of proliferation and type I/III collagen production vis-à-vis lacZ (at least 3- and 4-fold increases at day 30, respectively; always P ≤ .001). Most notably, rAAV FGF-2 promoted a significant, long-term production of the factor in experimental ACL lesions (92.7 ± 3.9 pg/mL/24 h, ie, about 5-fold more than in the controls; P ≤ .001) associated with enhanced levels of proliferation and type I/III collagen synthesis (at least 2- and 4-fold increases at day 30, respectively; always P ≤ .001). Remarkably, the FGF-2 treatment allowed for a decrease in the amplitude of such lesions possibly because of the increased expression in contractile α-smooth muscle actin, ligament-specific transcription factor scleraxis, and nuclear factor-κB for proliferation and collagen deposition, which are all markers commonly induced in response to injury.

CONCLUSION

Efficient, stable FGF-2 expression via rAAV enhances the healing of experimental human ACL lesions by activating key cellular and metabolic processes.

CLINICAL RELEVANCE

This approach has potential value for the development of novel, effective treatments for ligament reconstruction.

Treatment of skeletal muscle injury: a review

Skeletal muscle injuries are the most common sports-related injuries and present a challenge in primary care and sports medicine. Most types of muscle injuries would follow three stages: the acute inflammatory and degenerative phase, the repair phase and the remodeling phase. Present conservative treatment includes RICE (rest, ice, compression, elevation), nonsteroidal anti-inflammatory drugs (NSAIDs) and physical therapy. However, if use improper, NSAIDs may suppress an essential inflammatory phase in the healing of injured skeletal muscle. Furthermore, it remains controversial whether or not they have adverse effects on the healing process or on the tensile strength. However, several growth factors might promote the regeneration of injured skeletal muscle, many novel treatments have involved on enhancing complete functional recovery. Exogenous growth factors have been shown to regulate satellite cell proliferation, differentiation and fusion in myotubes in vivo and in vitro, TGF-β1 antagonists behave as inhibitors of TGF-β1. They prevent collagen deposition and block formation of muscle fibrosis, so that a complete functional recovery can be achieved.

Doping genético e possíveis metodologias de detecção

O doping genético caracteriza-se pelo uso não terapêutico de células, genes e elementos gênicos, ou a modulação da expressão gênica com objetivo de aumentar o desempenho esportivo. Isto somente pode ser realizado através de manipulação gênica. Esta prática dopante caracteriza-se como virtualmente "indetectável", o que representa novos desafios analíticos para sua detecção. Esta revisão apresenta o doping genético e possíveis métodos de detecção para evitar futuras fraudes desportivas.

Potential mechanisms of a periosteum patch as an effective and favourable approach to enhance tendon-bone healing in the human body

Tendon-bone healing is a progressive and complex pathophysiological process after tendon graft transplantation into a bone tunnel. A fibrous scar tissue layer forms at the graft-bone interface, which means a weak bonding of the graft in the bone tunnel. Periosteum, a favourable autologous tissue, was confirmed to be effective in promoting tendon-bone healing in the human body. The advantages of a periosteum patch for tendon-bone repair include the fact that this tissue meets the three primary requirements for tissue engineering: a source of progenitor cells, a scaffold for recruiting cells and growth factors, and a source of local growth factors. Furthermore, the periosteum can prevent graft micromotion, alleviate inflammation and deter bone resorption. In this review, we highlight the role of progenitor cells in the periosteum, which contribute to the regeneration of new bone and/or fibrocartilage at the tendon-bone interface. In summary, the periosteum has shown significant potential for use in the enhancement of graft-bone healing. Our investigations may provoke further studies on the management of allograft-bone healing and artificial ligament graft healing using a periosteum patch in future.

Intracellular trafficking pathways involved in the gene transfer of nano-structured calcium phosphate-DNA particles

Nano-structured calcium phosphate (NanoCaP) particles have been proven to be a powerful means of non-viral gene delivery. In order to better understand the mechanisms through which NanoCaPs-mediated mammalian cell transfection is achieved, we have sought to define the intracellular trafficking pathways involved in the cellular uptake and intracellular processing of these particles. Previous work has indicated that NanoCaP-DNA complexes are most likely internalized via endocytosis, however the subsequent pathways involved have not been determined. Through the use of specific inhibitors, we show that endocytosis of NanoCaP particles is both clathrin- and caveolae-dependent, and suggest that the caveolaer mechanism is the major contributor. We demonstrate colocalization of NanoCaP-pDNA complexes with known markers of both clathrin-coated and caveolar vesicles. Furthermore, through the use of quantitative flow cytometry, we present the first work in which the percent internalization of CaP-DNA complexes into cells is quantified. The overall goal of this research is to foster the continued improvement of NanoCaP-based gene delivery strategies.

Gene Therapy for Cartilage Repair

The concept of using gene transfer strategies for cartilage repair originates from the idea of transferring genes encoding therapeutic factors into the repair tissue, resulting in a temporarily and spatially defined delivery of therapeutic molecules to sites of cartilage damage. This review focuses on the potential benefits of using gene therapy approaches for the repair of articular cartilage and meniscal fibrocartilage, including articular cartilage defects resulting from acute trauma, osteochondritis dissecans, osteonecrosis, and osteoarthritis. Possible applications for meniscal repair comprise meniscal lesions, meniscal sutures, and meniscal transplantation. Recent studies in both small and large animal models have demonstrated the applicability of gene-based approaches for cartilage repair. Chondrogenic pathways were stimulated in the repair tissue and in osteoarthritic cartilage using genes for polypeptide growth factors and transcription factors. Although encouraging data have been generated, a successful translation of gene therapy for cartilage repair will require an ongoing combined effort of orthopedic surgeons and of basic scientists.

Controlled delivery systems: from pharmaceuticals to cells and genes

During the last few decades, a fair amount of scientific investigation has focused on developing novel and efficient drug delivery systems. According to different clinical needs, specific biopharmaceutical carriers have been proposed. Micro- and nanoparticulated systems, membranes and films, gels and even microelectronic chips have been successfully applied in order to deliver biopharmaceuticals via different anatomical routes. The ultimate goal is to deliver the potential drugs to target tissues, where regeneration or therapies (chemotherapy, antibiotics, and analgesics) are needed. Thereby, the bioactive molecule should be protected against environmental degradation. Delivery should be achieved in a dose- and time-correct manner. Drug delivery systems (DDS) have been conceived to provide improvements in drug administration such as ability to enhance the stability, absorption and therapeutic concentration of the molecules in combination with a long-term and controlled release of the drug. Moreover, the adverse effects related with some drugs can be reduced, and patient compliance could be improved. Recent advances in biotechnology, pharmaceutical sciences, molecular biology, polymer chemistry and nanotechnology are now opening up exciting possibilities in the field of DDS. However, it is also recognized that there are several key obstacles to overcome in bringing such approaches into routine clinical use. This review describes the present state-of-the-art DDS, with examples of current clinical applications, and the promises and challenges for the future in this innovative field.

Baculovirus-mediated growth factor expression in dedifferentiated chondrocytes accelerates redifferentiation: effects of combinational transduction

Transduction of partially dedifferentiated rabbit chondrocytes with a baculovirus (Bac-CB) expressing bone morphogenetic protein-2 (BMP-2) reverses dedifferentiation and enhances matrix production. Hereby we examined whether transduction with Bac-CB in combination with another baculovirus expressing transforming growth factor-beta1 (TGF-beta1) or insulin-like growth factor-1 (IGF-1) synergistically augmented chondrogenic differentiation. Passage 3 rabbit articular chondrocytes were transduced by different baculovirus combinations: single transduction with Bac-CB, cotransduction with Bac-CB and Bac-CT (expressing TGF-beta1), cotransduction with Bac-CB and Bac-CI (expressing IGF-1), and transduction with Bac-CB followed by repeated transduction with Bac-CT, Bac-CI, or Bac-CB 5 days later. Transduced cells were encapsulated into alginate beads for culture. Among these strategies, only cotransduction with Bac-CB and Bac-CT led to improved redifferentiation when compared with Bac-CB single transduction, as evidenced by the enhanced expression of aggrecan and collagen IIB (Col IIB), suppressed expression of Col I and Col X, emergence of chondrocyte-specific lacunae, and elevated deposition of matrix molecules. The cotransduction also accelerated the expression of Sox9, Col IIB, and aggrecan. In summary, baculovirus-mediated coexpression of TGF-beta1 and BMP-2 synergistically accelerates the chondrocyte redifferentiation process and improves the maintenance of chondrocyte phenotype and accumulation of cartilage-specific matrix molecules.

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.

Selection of multipotent cells and enhanced muscle reconstruction by myogenic macrophage-secreted factors

Skeletal muscle regeneration relies on satellite cells, a population of myogenic precursors. Inflammation also plays a determinant role in the process, as upon injury, macrophages are attracted by the damaged myofibers and the activated satellite cells and act as key elements of dynamic muscle supportive stroma. Yet, it is not known how macrophages interact with the more profound stem cells of the satellite cell niche. Here we show that in the presence of a murine macrophage conditioned medium (mMCM) a subpopulation of multipotent cells could be selected and expanded from adult rat muscle. These cells were small, round, poorly adhesive, slow-growing and showed mesenchymal differentiation plasticity. At the same time, mMCM showed clear myogenic capabilities, as experiments with satellite cells mechanically isolated from suspensions of single myofibers showed that the macrophagic factors inhibited their tendency to shift towards adipogenesis. In vivo, intramuscular administrations of concentrated mMCM in a rat model of extensive surgical ablation dramatically improved muscle regeneration. Altogether, these findings suggest that macrophagic factors could be of great help in developing therapeutic protocols with myogenic stem cells.

Matrix metalloproteinase-1 treatment of muscle fibrosis

The onset of scarring after injury may impede the regeneration and functional recovery of skeletal muscle. Matrix metalloproteinase-1 (MMP-1) hydrolyzes type I collagen and thus may improve muscle regeneration by resolving fibrotic tissue. We examined the effect of recombinant human MMP-1 on fibrosis in the lacerated gastrocnemius muscle of NOD/scid mice, allowing treatment potential to be ascertained in isolation from immune response. The efficacy of proMMP-1 and active MMP-1 were compared with or without poly(ethylene glycol) (PEG) modification, which was intended to increase the enzyme's stability. Active MMP-1 was most effective in reducing fibrosis, although treatment with proMMP-1 was also beneficial relative to controls. PEG-modified MMP-1 had minimal activity in vivo, despite retaining activity towards a thioester substrate. Moreover, the modified enzyme was inactivated by trypsin and subtilisin at rates comparable to that of native MMP-1. These results and those of computational structural studies suggest that modification occurs at the C-terminal hemopexin domain of MMP-1, which plays a critical role in collagen turnover. Site-specific modifications that spares catalytic and substrate binding sites while protecting susceptible proteolytic digestion sites may be beneficial. We conclude that active MMP-1 can effectively reduce muscle scarring and that its activity is related to the ability of the enzyme to digest collagen, thereby facilitating remodeling of the injured muscle.

Long term results after implantation of tissue engineered cartilage for the treatment of osteochondral lesions in a minipig model

In present study we determined the long term in vivo integration and histological modeling of an in vitro engineered cartilage construct. Tissue engineered autologous cartilagenous tissue was cultured on calcium phosphate cylinders and implanted into osteochondral defects into the femoral condyles in minipigs. Radiological follow-up was performed at 2, 8, 26 and 52 weeks, condyles were harvested 26 and 52 weeks post-implantation. Thickness of cultivated tissue (1.10 +/- 0.55 mm) was comparable to in situ cartilage and cells produced in vitro cartilage specific proteins. In vivo, 26 and 52 weeks post-implantation defects were resurfaced with hyaline-like tissue, the implants were well integrated with no gap at the interface between the engineered neocartilage and the adjacent articular cartilage. Synthesis of type II collagen was detected 26 and 52 weeks after implantation. The modified ICRS score increased from 26 to 52 weeks. Histomorphometric evaluation revealed a decrease in cellularity in tissue engineered cartilage from 2.2-fold of native cartilage after 26 weeks to 1.5-fold after 52 weeks. In conclusion, these findings demonstrate the integration and maturation of tissue engineered cartilage pellets attached on a bone substitute carrier implanted in osteochondral defects over a long time.

Genetic engineering for skeletal regenerative medicine

The clinical challenges of skeletal regenerative medicine have motivated significant advances in cellular and tissue engineering in recent years. In particular, advances in molecular biology have provided the tools necessary for the design of gene-based strategies for skeletal tissue repair. Consequently, genetic engineering has emerged as a promising method to address the need for sustained and robust cellular differentiation and extracellular matrix production. As a result, gene therapy has been established as a conventional approach to enhance cellular activities for skeletal tissue repair. Recent literature clearly demonstrates that genetic engineering is a principal factor in constructing effective methods for tissue engineering approaches to bone, cartilage, and connective tissue regeneration. This review highlights this literature, including advances in the development of efficacious gene carriers, novel cell sources, successful delivery strategies, and optimal target genes. The current status of the field and the challenges impeding the clinical realization of these approaches are also discussed.

Potential Use of Gene Transfer in Athletic Performance Enhancement

After only a short history of three decades from concept to practice, gene therapy has recently been shown to have potential to treat serious human diseases. Despite this success, gene therapy remains in the realm of experimental medicine, and much additional preclinical and clinical study will be necessary for proving the efficacy and safety of this approach in the treatment of diseases in humans. However, a potential complicating factor is that advances in gene transfer technology could be misused to enhance athletic performance in sports, in a practice termed "gene doping". Moreover, gene doping could be a precursor to a broader controversial agenda of human "genetic enhancement" with the potential for a significant long-term impact on society. This review addresses the possible ways in which knowledge and experience gained in gene therapy in animals and humans may be abused for enhancing sporting prowess. We provide an overview of recent progress in gene therapy, with potential application to gene doping and with the major focus on candidate performance-enhancement genes. We also discuss the current status of preclinical studies and of clinical trials that use these genes for therapeutic purposes. Current knowledge about the association between the natural "genetic make-up" of humans and their physical characteristics and performance potential is also presented. We address issues associated with the safety of gene transfer technologies in humans, especially when used outside a strictly controlled clinical setting, and the obstacles to translating gene transfer strategies from animal studies to humans. We also address the need for development and implementation of measures to prevent abuse of gene transfer technologies, and to pursue research on strategies for its detection in order to discourage this malpractice among athletes.

Terapia gênica, doping genético e esporte: fundamentação e implicações para o futuro

A busca pelo desempenho ótimo tem sido uma constante no esporte de alto rendimento. Para tanto, muitos atletas acabam utilizando drogas e métodos ilícitos, os quais podem ter importantes efeitos adversos. A terapia gênica é uma modalidade terapêutica bastante recente na medicina, cujos resultados têm, até o momento, indicado sua eficácia no tratamento de diversas doenças graves. O princípio da terapia gênica consiste na transferência vetorial de materiais genéticos para células-alvo, com o objetivo de suprir os produtos de um gene estruturalmente anormal no genoma do paciente. Recentemente, o potencial para uso indevido da terapia gênica entre atletas tem despertado a atenção de cientistas e de órgãos reguladores de esporte. A transferência de genes que poderiam melhorar o desempenho esportivo por atletas saudáveis, método proibido em 2003, foi denominado de doping genético. Os genes candidatos mais importantes para doping genético são os que codificam para GH, IGF-1, bloqueadores da miostatina, VEGF, endorfinas e encefalinas, eritropoetina, leptina e PPAR-delta. Uma vez inserido no genoma do atleta, o gene se expressaria gerando um produto endógeno capaz de melhorar o desempenho atlético. Assim, os métodos atuais de detecção de doping não são sensíveis a esse tipo de manipulação, o que poderia estimular seu uso indevido entre atletas. Além disso, a terapia gênica ainda apresenta problemas conhecidos de aplicação, como resposta inflamatória e falta de controle da ativação do gene. Em pessoas saudáveis, é provável que tais problemas sejam ainda mais importantes, já que haveria excesso do produto do gene transferido. Há também outros riscos ainda não conhecidos, específicos para cada tipo de gene. Em vista disso, debates sobre o doping genético devem ser iniciados no meio acadêmico e esportivo, para que sejam estudadas medidas de prevenção, controle e detecção do doping genético, evitando assim futuros problemas de uso indevido dessa promissora modalidade terapêutica.

Effect of transforming growth factor-beta and growth differentiation factor-5 on proliferation and matrix production by human bone marrow stromal cells cultured on braided poly lactic-co-glycolic acid scaffolds for ligament tissue engineering

Tissue engineering of ligaments based on biomechanically suitable biomaterials combined with autologous cells may provide a solution for the drawbacks associated with conventional graft material. The aim of the present study was to investigate the contribution of recombinant human transforming growth factor beta 1 (rhTGF-beta1) and growth differentiation factor (GDF)-5, known for their role in connective tissue regeneration, to proliferation and matrix production by human bone marrow stromal cells (BMSCs) cultured onto woven, bioabsorbable, 3-dimensional (3D) poly(lactic-co-glycolic acid) scaffolds. Cells were cultured for 12 days in the presence or absence of these growth factors at different concentrations. Human BMSCs attached to the suture material, proliferated, and synthesized extracellular matrix rich in collagen type I and collagen III. No differentiation was demonstrated toward cartilage or bone tissue. The addition of rhTGF-beta1 (1-10 ng/mL) and GDF-5 (10-100 ng/mL) increased cell content (p < 0.05), but only TGF-beta1 also increased total collagen production (p < 0.05) and collagen production per cell, which is a parameter indicating differentiation. In conclusion, stimulation with rhTGF-beta1, and to a lesser extent with GDF-5, can modulate human BMSCs toward collagenous soft tissue when applied to a 3D hybrid construct. The use of growth factors could play an important role in the improvement of ligament tissue engineering.

Baculovirus transduction of rat articular chondrocytes: roles of cell cycle

BACKGROUND

We have previously demonstrated highly efficient baculovirus transduction of primary rat articular chondrocytes, thus implicating the possible applications of baculovirus in gene-based cartilage tissue engineering. However, baculovirus-mediated gene expression in the chondrocytes is transient.

METHODS

In this study, we attempted to prolong the expression by supertransduction, but uncovered that after long-term culture the chondrocytes became more refractory to baculovirus transduction. Therefore, the correlation between baculovirus-mediated enhanced green fluorescent protein (EGFP) expression and cell cycle was investigated by comparing the cycling chondrocytes and chondrocytes rich in quiescent cells, in terms of EGFP expression, virus uptake, cell cycle distribution, nuclear import and methylation of viral DNA.

RESULTS

We demonstrated, for the first time, that baculovirus-mediated transduction of chondrocytes is correlated with the cell cycle. The chondrocytes predominantly in G2/M phase were approximately twice as efficient in EGFP expression as the cycling cells, while the cells in S and G1 phases expressed EGFP as efficiently as the cycling cells. Notably, the chondrocyte populations rich in quiescent cells resulted in efficient virus uptake, but less effective nuclear transport of baculoviral DNA and higher degree of methylation, and hence poorer transgene expression.

CONCLUSIONS

These findings unravel the practical limitations when employing baculovirus in cartilage tissue engineering. The implications and possible solutions are discussed.

Nanostructured calcium phosphates (NanoCaPs) for non-viral gene delivery: Influence of the synthesis parameters on transfection efficiency

Calcium phosphate (CaP) based approaches remain an attractive option for delivering plasmid DNA (pDNA) into cultured cells. However, despite their appeal, current synthesis methodologies typically yield lower, less consistent transfection efficiencies when compared to viral approaches. Therefore, we report here a novel method to consistently synthesize efficient, nano-sized, mono-dispersed CaP-pDNA particles; accomplished by optimizing both the stoichiometry (Ca/P ratio) of the CaP particles as well as the mode in which the calcium and phosphate precursor solutions are mixed. Our results indicate that calcium and phosphate precursors when mixed in a controlled and regulated manner reproducibly result in nano-sized particles that consistently yield higher transfection efficiencies when compared to particles synthesized via manual mixing (a two-fold increase was observed). Also, maximum transfection efficiencies in both HeLa and MC3T3-E1 cells lines were obtained when a Ca/P ratio between 100 and 300 was used. Particles synthesized within this optimum Ca/P ratio range were between 25 and 50 nm. Our data suggests that these maximized transfection efficiencies were obtained because these particles not only effectively condensed (70% efficient) but also efficiently bound (90% efficient) the pDNA. In addition, X-ray diffraction and Fourier transform infrared spectroscopy analyses confirmed that all of the synthesized CaP structures exhibited the hydroxyapatite phase.

Gene therapy for cartilage defects

Focal defects of articular cartilage are an unsolved problem in clinical orthopaedics. These lesions do not heal spontaneously and no treatment leads to complete and durable cartilage regeneration. Although the concept of gene therapy for cartilage damage appears elegant and straightforward, current research indicates that an adaptation of gene transfer techniques to the problem of a circumscribed cartilage defect is required in order to successfully implement this approach. In particular, the localised delivery into the defect of therapeutic gene constructs is desirable. Current strategies aim at inducing chondrogenic pathways in the repair tissue that fills such defects. These include the stimulation of chondrocyte proliferation, maturation, and matrix synthesis via direct or cell transplantation-mediated approaches. Among the most studied candidates, polypeptide growth factors have shown promise to enhance the structural quality of the repair tissue. A better understanding of the basic scientific aspects of cartilage defect repair, together with the identification of additional molecular targets and the development of improved gene-delivery techniques, may allow a clinical translation of gene therapy for cartilage defects. The first experimental steps provide reason for cautious optimism.

Supplementation-time dependence of growth factors in promoting tendon healing

Growth factors potentially promote tendon healing. Understanding the right time to administer growth factors and the dosage of growth factors are prerequisites for designing effective cytokine therapy. We investigated the supplementation-time dependence of the effects of platelet-derived growth factor isoform B at various dosages on tendon healing, and the temporal responsiveness of healing tendon toward platelet-derived growth factor. Platelet-derived growth factor isoform B at various dosages (0, 10, 100, or 1000 ng) was delivered into the gap wound of rat patellar tendons via microsyringe injection on Day 3 or Day 7 after injury. Tendon specimens were harvested on Day 14 for measurement of cell proliferation, pyridinoline content, and mechanical properties. We found increased proliferative response only when the growth factor was supplemented on Day 3 after injury, whereas supplementation on Day 7 resulted in greater peak load, cross-sectional area, and pyridinoline content. The ultimate stress did not change. Our findings suggest supplementation of platelet-derived growth factor isoform B at Day 7 benefits the mechanical properties and maturation of healing tendons. We also found platelet-derived growth factor receptor beta expressing cells at the remodeling site as much as 6 months after injury, suggesting healing tendon also may be responsive to long-term delivery of platelet-derived growth factor.

Combination of baculovirus-mediated gene transfer and rotating-shaft bioreactor for cartilage tissue engineering

We have previously demonstrated efficient baculovirus transduction of rat chondrocytes in 6-well plates. To further explore the potential of baculovirus in cartilage tissue engineering, the baculovirus-transduced chondrocytes were seeded into porous scaffolds and cultivated in a rotating-shaft bioreactor (RSB) which was developed for two-phase cultivation of tissue engineered cartilage. The baculovirus transduction resulted in efficiencies up to 90%, and affected neither cell adhesion to the scaffolds nor cell survival in the RSB. After 4-week RSB cultivation, the transduced cells remained highly differentiated and grew into constructs that resembled the untransduced constructs with regard to gross appearance, construct size, cell morphology, cell spatial distribution, glycosaminoglycan and collagen production and deposition. Importantly, baculovirus transduction did not alter the expression of chondrocytic genes. These data confirmed that baculovirus transduction neither harms chondrocytes nor retards the formation of cartilage-like tissues in the RSB, thus implicating the potentials of combining baculovirus-mediated gene transfer with RSB cultivation in in vitro cartilage tissue engineering.

Tendon tissue engineering and gene transfer: the future of surgical treatment

Technologic improvements in the field of tissue engineering are leading to new potential developments in the currently used approaches to treat tendon injuries including difficult clinical scenarios such as zone II flexor tendon injuries of the hand and the mutilated hand with extensive tendon defects. A combination of mesenchymal (adult stem) cells, growth factors, and bioresorbable polymers can provide a solution for the treatment of difficult tendon injuries. Extensive research is needed to show that the extracellular matrix produced in response to the cell/growth factor/polymer composites in vivo is effective and functional as a regenerate tissue. Further exciting advances are foreseen in cell-based genetic engineering with the transfer of DNA to the site of tendon lacerations. These treatment modalities require improved safety precautions to reduce the risks and enhance the benefits of gene therapy.

Baculovirus vectors for gene therapy

Since the discovery that baculoviruses can efficiently transduce mammalian cells, baculoviruses have been extensively studied as potential vectors for both in vitro and in vivo gene therapy. This chapter reviews the history of this research area, cells permissive to baculovirus transduction, factors influencing transduction and transgene expression, efforts to improve transduction, mechanisms of virus entry and intracellular trafficking, applications for in vivo and ex vivo gene therapy, as well as advantages, limitations, and safety issues concerning use of baculoviruses as gene therapy vectors. Recent progress and efforts directed toward overcoming existing bottlenecks are emphasized.

Stem cell-based composite tissue constructs for regenerative medicine

A major task of contemporary medicine and dentistry is restoration of human tissues and organs lost to diseases and trauma. A decade-long intense effort in tissue engineering has provided the proof of concept for cell-based replacement of a number of individual tissues such as the skin, cartilage, and bone. Recent work in stem cell-based in vivo restoration of multiple tissue phenotypes by composite tissue constructs such as osteochondral and fibro-osseous grafts has demonstrated probable clues for bioengineered replacement of complex anatomical structures consisting of multiple cell lineages such as the synovial joint condyle, tendon-bone complex, bone-ligament junction, and the periodontium. Of greater significance is a tangible contribution by current attempts to restore the structure and function of multitissue structures using cell-based composite tissue constructs to the understanding of ultimate biological restoration of complex organs such as the kidney or liver. The present review focuses on recent advances in stem cell-based composite tissue constructs and attempts to outline challenges for the manipulation of stem cells in tailored biomaterials in alignment with approaches potentially utilizable in regenerative medicine of human tissues and organs.

Long-term in vivo gene expression via delivery of PEI-DNA condensates from porous polymer scaffolds

Nonviral delivery vectors are attractive for gene therapy approaches in tissue engineering, but suffer from low transfection efficiency and short-term gene expression. We hypothesized that the sustained delivery of poly(ethylenimine) (PEI)-condensed DNA from three-dimensional biodegradable scaffolds that encourage cell infiltration could greatly enhance gene expression. To test this hypothesis, a PEI-condensed plasmid encoding beta-galactosidase was incorporated into porous poly(lactide-co-glycolide) (PLG) scaffolds, using a gas foaming process. Four conditions were examined: condensed DNA and uncondensed DNA encapsulated into PLG scaffolds, blank scaffolds, and bolus delivery of condensed DNA in combination with implantation of PLG scaffolds. Implantation of scaffolds incorporating condensed beta-galactosidase plasmid into the subcutaneous tissue of rats resulted in a high level of gene expression for the entire 15-week duration of the experiment, as exemplified by extensive positive staining for beta-galactosidase gene expression observed on the exterior surface and throughout the cross-sections of the explanted scaffolds. No positive staining could be observed for the control conditions either on the exterior surface or in the cross-section at 8- and 15-week time points. In addition, a high percentage (55-60%) of cells within scaffolds incorporating condensed DNA at 15 weeks demonstrated expression of the DNA, confirming the sustained uptake and expression of the encapsulated plasmid DNA. Quantitative analysis of beta-galactosidase gene expression revealed that expression levels in scaffolds incorporating condensed DNA were one order of magnitude higher than those of other conditions at the 2- week time point and nearly two orders of magnitude higher than those of the control conditions at the 8- and 15-week time points. This study demonstrated that the sustained delivery of PEI-condensed plasmid DNA from PLG scaffolds led to an in vivo long-term and high level of gene expression, and this system may find application in areas such as bone tissue engineering.

Enhanced repair of the anterior cruciate ligament by in situ gene transfer: evaluation in an in vitro model

The inability of the ruptured anterior cruciate ligament (ACL) of the knee joint to heal spontaneously presents numerous clinical problems. Here we describe a novel, gene-based approach to augment ACL healing. It is based upon the migration of cells from the ruptured ends of the ligament into a collagen hydrogel laden with recombinant adenovirus. Cells entering the gel become transduced by the vector, which provides a basis for the local synthesis of gene products that aid repair. Monolayers of bovine ACL cells were readily transduced by first-generation, recombinant adenovirus, and transgene expression remained high after the cells were incorporated into collagen hydrogels. Using an in vitro model of ligament repair, cells migrated from the cut ends of the ACL into the hydrogel and were readily transduced by recombinant adenovirus contained within it. The results of experiments in which GFP was used as the transgene suggest highly efficient transduction of ACL cells in this manner. Moreover, during a 21-day period GFP+ cells were observed more than 6 mm from the severed ligament. This distance is ample for the projected clinical application of this technology. In response to TGF-beta1 as the transgene, greater numbers of ACL cells accumulated in the hydrogels, where they deposited larger amounts of type III collagen. These data confirm that it is possible to transduce ACL cells efficiently in situ as they migrate from the ruptured ACL, that transduction does not interfere with the cells' ability to migrate distances necessary for successful repair, and that ACL cells will respond in a suitable manner to the products of the transgenes they express. This permits optimism over a possible clinical use for this technology.

Inducible nonviral gene expression in the treatment of osteochondral defects

OBJECTIVE

The repair of osteochondral defects with chondrocytes genetically modified to express desired growth factors promises great potential in orthopaedic therapy. Controlled expression of the transgenes is required in many instances. The objective of the present study was to demonstrate the inducibility of tetracycline-responsive transgene expression in osteochondral defects in the knee joint filled with genetically modified chondrocyte implants.

METHODS

An expression plasmid containing the lacZ gene under the control of the minimal CMV promoter fused to the Tet-responsible element (TRE) as well as the reverse transactivator (rtTA2s-M2) was constructed and used to transfect isolated articular chondrocytes from New Zealand white rabbits. rtTA2s-M2 binds to the TRE in the presence of tetracycline and leads to the transcription of the transgene. Different concentrations of DNA and various DNA:lipid ratios were tested to determine best transfection conditions. Transfection efficiency and inducibility were analysed by histochemical analysis and flow-cytometry. To evaluate the system in vivo, collagen-sponges were seeded with transfected autologous chondrocytes and implanted in osteochondral defects in the knees of NZW-rabbits. Gene expression was induced by doxycycline and 3 weeks later, LacZ-expression in isolated knee joints was evaluated in histological sections by X-gal staining.

RESULTS

In vitro 13.5% (+/-1.32) of induced primary chondrocytes were LacZ-positive, while non-induced controls showed a background-staining in 0.6% (+/-0.2). In vivo, upon doxycycline treatment, induction of lacZ-gene-expression could be demonstrated in chondrocytes in 3-week-old, well-integrated implants.

CONCLUSION

For the first time, tetracycline-inducible gene expression is demonstrated to work in the treatment of osteochondral defects. This demonstrates the feasibility for a gene therapy-assisted approach using controlled expression of therapeutic growth factors from transplanted genetically modified chondrocytes.

The effect of the presence of muscle tissue in a bone healing site

PURPOSE

The recovery of a bone fracture is a process that is not yet fully understood. The literature conflicts on the results obtained by the interposition of foreign tissue inside a damaged bone. The objective of the present study was to ascertain the effect of placing muscle tissue between the stumps of a fractured bone.

METHOD

The study was carried out on 10 rabbits divided into 2 groups (n = 5): Group 1--partial fracture of the humerus and interposition of muscle tissue; Group 2--complete fracture of the humerus and interposition of muscle tissue. The fractured limb of all animals was immobilized for 8 weeks. At the end of this time, the rabbits were killed and their operated humeri were carefully removed for roentgenological and histological assessment.

RESULTS

All humeri of Group 1 recovered their integrity and normal aspect. However, the healing of the humeri of Group 2 was not perfect. Gross angulation of the bone diaphysis occurred in all animals, and immature trabecular bone, osteochondral tissue, and persistence of muscle tissue substituted normal bone.

CONCLUSIONS

Interposed muscle does not affect partial bone fracture healing but causes instability in a complete fracture.