IGF-I gene transfer by electroporation promotes regeneration in a muscle injury model

How can the adult zebrafish and neonatal mice teach us about stimulating cardiac regeneration in the human heart?

The proliferative capacity of mammalian cardiomyocytes diminishes shortly after birth. In contrast, adult zebrafish and neonatal mice can regenerate cardiac tissues, highlighting new potential therapeutic avenues. Different factors have been found to promote cardiomyocyte proliferation in zebrafish and neonatal mice; these include maintenance of mononuclear and diploid cardiomyocytes and upregulation of the proto-oncogene c-Myc. The growth factor NRG-1 controls cell proliferation and interacts with the Hippo-Yap pathway to modulate regeneration. Key components of the extracellular matrix such as Agrin are also crucial for cardiac regeneration. Novel therapies explored in this review, include intramyocardial injection of Agrin or zebrafish-ECM and NRG-1 administration. These therapies may induce regeneration in patients and should be further explored.

Intramuscular Stem Cell Injection in Combination with Bioengineered Nerve Repair or Nerve Grafting Reduces Muscle Atrophy

BACKGROUND

Peripheral nerve injuries represent a clinical challenge, especially when they are accompanied by loss of neural tissue. In this study, the authors attempted to attain a better outcome after a peripheral nerve injury by both repairing the nerve lesion and treating the denervated muscle at the same time.

METHODS

Rat sciatic nerves were transected to create 10-mm gaps. Repair was performed in five groups (n = 5 rats for each), as follows: group 1, nerve repair using poly-3-hydroxybutyrate strips to connect the proximal and distal stumps, in combination with control growth medium injection in the gastrocnemius muscle; group 2, nerve repair with poly-3-hydroxybutyrate strip seeded with Schwann cell-like differentiated adipose stem cells (differentiated adipose stem cell strip) in combination with growth medium intramuscular injection; group 3, differentiated adipose stem cell strip in combination with intramuscular injection of differentiated adipose stem cells; group 4, repair using autograft (reverse sciatic nerve graft) in combination with intramuscular injection of growth medium; and group 5, autograft in combination with intramuscular injection of differentiated adipose stem cells. Six weeks after nerve injury, the effects of the stem cells on muscle atrophy were assessed.

RESULTS

Poly-3-hydroxybutyrate strips seeded with differentiated adipose stem cells showed a high number of βIII-tubulin-positive axons entering the distal stump and abundant endothelial cells. Group 1 animals exhibited more muscle atrophy than all the other groups, and group 5 animals had the greatest muscle weights and muscle fibers size.

CONCLUSION

Bioengineering nerve repair in combination with intramuscular stem cell injection is a promising technique to treat nerve lesions and associated muscle atrophy.

CLINICAL RELEVANCE STATEMENT

Nerve injuries and resulting muscle atrophy are a clinical challenge. To optimize functional recovery after a nerve lesion, the authors treated the nerve and muscle at the same time by using regenerative medicine with adipose stem cells and obtained encouraging results for future clinical applications.

Needling on trigger point promotes muscle regeneration after bupivacaine injection induced injury

Dry needling treatment has a promising relieving effect on Myofascial Pain Syndrome (MPS). In China, acupuncture practitioners use acupuncture needle instead to insert the "A-Shi" acupoint to treat MPS which is defined as the same as the trigger point of dry needling. This method has been applied for thousands of years in China. In this study, bupivacaine injection induced gastrocnemius muscle injury in mice. We applied the clinical improved needling method on animal model by making the angle between the skin and needle less than 30 degree. Animals got needling treatment 24 h later at the point where the bupivacaine was injected. Results of muscle H.E. staining showed that, compared to bupivacaine injection group without needling, acupuncture treatment group showed more intact muscle fibers, less inflammatory cell infiltration and fractured muscle fibers. By RNA sequencing analysis, our work firstly demonstrated that the physical stimulation of needling changed the gene expression of muscle tissue to accelerate the muscular regeneration process. Therefore, our study proved that simple needling at "A-Shi" acupoint promoted muscle regeneration and revealed underlying mechanisms of the beneficial effects of acupuncture and dry needle treatments.

Impact of intramuscular administration of lipid-soluble and water-soluble vehicles into regenerating muscle at the distinct phases of skeletal muscle regeneration

Interpretation on the effectiveness of potential substances to enhance skeletal muscle regeneration is difficult if an inappropriate vehicle is administered, since vehicle administration can directly enhance or suppress regenerative capacity. In the current study, intramuscular administration of lipid-soluble and water-soluble vehicles into regenerating muscle at the distinct phases of skeletal muscle regeneration (regenerative vs. remodeling) were investigated. Tested vehicles included lipid-soluble [olive oil, (0.1, 1, 5, and 40%) dimethyl sulfoxide (DMSO), and 40% propylene glycol (PG)] and water-soluble [0.9% NaCl, PBS, 0.1% ethanol, and distilled water]. Skeletal muscle regeneration was induced by 1.2% BaCl2 injection to the tibialis anterior muscle of 10-week-old C57BL/6 male mice. Histological features, skeletal muscle stem cell activity, regenerating muscle fiber formation, angiogenesis, extracellular matrix remodeling, and macrophage infiltration were examined. The results revealed repeated administration of 40% DMSO and 40% PG causes significant recurrent muscle injury, which is pronounced during the remodeling phase compared to the regenerative phase. These findings were supported by (1) massive infiltration of F4/80+ macrophages; (2) significant increase of skeletal muscle stem cell re-activation and nascent regenerating muscle fiber formation; (3) excess fibrous formation; and (4) decreased regenerating muscle fiber cross-sectional area. These deleterious effects were comparable to 2% trypsin (degenerative substance) administration and less pronounced with a single administration. Nevertheless, recurrent muscle injury was still presented with 5% DMSO administration but it can be alleviated when 0.1% DMSO was administered during the remodeling phase. In contrast, none of the tested vehicles enhanced regenerative capacity compared with IGF-1 administration. Altogether, intramuscular administration of vehicle containing high concentration of DMSO or PG could impair skeletal muscle regenerative capacity and potentially affect validation of the investigational substance.

Optimizing IGF-I for skeletal muscle therapeutics

It is virtually undisputed that IGF-I promotes cell growth and survival. However, the presence of several IGF-I isoforms, vast numbers of intracellular signaling components, and multiple receptors results in a complex and highly regulated system by which IGF-I actions are mediated. IGF-I has long been recognized as one of the critical factors for coordinating muscle growth, enhancing muscle repair, and increasing muscle mass and strength. How to optimize this panoply of pathways to drive anabolic processes in muscle as opposed to aberrant growth in other tissues is an area that deserves focus. This review will address how advances in the bioavailability, potency, and tissue response of IGF-I can provide new potential directions for skeletal muscle therapeutics.

Medical interventions in the management of hamstring muscle injury

Acute muscle belly injuries to the semitendinosus, semimembranosus and biceps femoris (the 'hamstring' muscles) remain a common problem in the sporting population. Physiotherapy-led rehabilitation remains the mainstay of treatment, and the physician's input is often minimal. Anecdotally, many different topical, oral and injectable therapies are used around the world in an effort to accelerate the healing of these injuries and to prevent their recurrence. This article reviews the evidence available to support some of the most commonly used medical therapies and the pathophysiological basis for their use. It also presents the evidence behind some of the more promising future treatments for muscle injury, including stem cell therapy, growth factor delivery and potential novel uses of current medication not traditionally used in the musculoskeletal setting.

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.

Enhanced athletic performance on multisite AAV-IGF1 gene transfer coincides with massive modification of the muscle proteome

Progress in gene therapy has hinted at the potential misuse of gene transfer in sports to achieve better athletic performance, while escaping from traditional doping detection methods. Suitable animal models are therefore required in order to better define the potential effects and risks of gene doping. Here we describe a mouse model of gene doping based on adeno-associated virus (AAV)-mediated delivery of the insulin-like growth factor-I (IGF-I) cDNA to multiple muscles. This treatment determined marked muscle hypertrophy, neovascularization, and fast-to-slow fiber type transition, similar to endurance exercise. In functional terms, treated mice showed impressive endurance gain, as determined by an exhaustive swimming test. The proteomic profile of the transduced muscles at 15 and 30 days after gene delivery revealed induction of key proteins controlling energy metabolism. At the earlier time point, enzymes controlling glycogen mobilization and anaerobic glycolysis were induced, whereas they were later replaced by proteins required for aerobic metabolism, including enzymes related to the Krebs cycle and oxidative phosphorylation. These modifications coincided with the induction of several structural and contractile proteins, in agreement with the observed histological and functional changes. Collectively, these results give important insights into the biological response of muscles to continuous IGF-I expression in vivo and warn against the potential misuse of AAV-IGF1 as a doping agent.

Engineered insulin-like growth factor-1 for improved smooth muscle regeneration

Insulin-like growth factor-1 (IGF-1) has been shown to induce potent mitogenic responses in various cell types, yet its sustained local delivery is still an underdeveloped domain in the clinic. We report here an engineered IGF-1 that facilitates extended local delivery to a site through its immobilization capacity within fibrin. Through recombinant fusion with a substrate sequence tag derived from α(2)-plasmin inhibitor (α(2)PI(1-8)), the resulting variant, α(2)PI(1-8)-IGF-1, was covalently incorporated into fibrin matrices during normal thrombin/factor XIIIa-mediated polymerization. Bioactivity of the variant was confirmed to be equivalent to wild type (WT) IGF-1 via IGF-1 receptor phosphorylation and cell proliferation studies in urinary tract-derived cells in 2-D. Assessment of functional retention within 3-D fibrin matrices demonstrated that incorporation of α(2)PI(1-8)-IGF-1 induced a 1.3- and 1.5-fold more robust proliferative response in smooth muscle cells (SMCs) than WT IGF-1 and negative control matrices, respectively, when release was not contained. Sustained α(2)PI(1-8)-IGF-1 availability at bladder lesion sites in vivo evoked a considerable increase in SMC proliferation and a favorable host tissue response after 28 days in rats. We conclude that the sustained local IGF-1 availability from fibrin provided by our variant protein enhances smooth muscle regeneration better than the WT form of the protein.

Enhanced contractile force generation by artificial skeletal muscle tissues using IGF-I gene-engineered myoblast cells

The aim of this study was to investigate whether insulin-like growth factor (IGF)-I gene delivery to myoblast cells promotes the contractile force generated by hydrogel-based tissue-engineered skeletal muscles in vitro. Two retroviral vectors allowing doxycycline (Dox)-inducible expression of the IGF-I gene were transduced into mouse myoblast C2C12 cells to evaluate the effects of IGF-I gene expression on these cells. IGF-I gene expression stimulated the proliferation of C2C12 cells, and a significant increase in the growth rate was observed for IGF-I-transduced C2C12 cells with Dox addition, designated C2C12/IGF (Dox+) cells. Quantitative morphometric analyses showed that the myotubes induced from C2C12/IGF (Dox+) cells had a larger area and a greater width than control myotubes induced from normal C2C12 cells. Artificial skeletal muscle tissues were prepared from the respective cells using hydrogels composed of type I collagen and Matrigel. Western blot analyses revealed that the C2C12/IGF (Dox+) tissue constructs showed activation of a skeletal muscle hypertrophy marker (Akt) and enhanced expression of muscle-specific markers (myogenin, myosin heavy chain and tropomyosin). Moreover, the creatine kinase activity was increased in the C2C12/IGF (Dox+) tissue constructs. The C2C12/IGF (Dox+) tissue constructs contracted in response to electrical pulses, and generated a significantly higher physical force than the control C2C12 tissue constructs. These findings indicate that IGF-I gene transfer has the potential to yield functional skeletal muscle substitutes that are capable of in vivo restoration of the load-bearing function of injured muscle or acting as in vitro electrically-controlled bio-actuators.

Muscle atrophy in experimental cancer cachexia: is the IGF-1 signaling pathway involved?

Skeletal muscle wasting, one of the main features of cancer cachexia, is associated with marked protein hypercatabolism, and has suggested to depend also on impaired IGF-1 signal transduction pathway. To investigate this point, the state of activation of the IGF-1 system has been evaluated both in rats bearing the AH-130 hepatoma and in mice transplanted with the C26 colon adenocarcinoma. In the skeletal muscle of tumor hosts, the levels of phosphorylated (active) Akt, one of the most relevant kinases involved in the IGF-1 signaling pathway, were comparable to controls, or even increased. Accordingly, downstream targets such as GSK3beta, p70(S6K) and FoxO1 were hyperphosphorylated, while the levels of phosphorylated eIF2alpha were markedly reduced with respect to controls. In the attempt to force the metabolic balance toward anabolism, IGF-1 was hyperexpressed by gene transfer in the tibialis muscle of the C26 hosts. In healthy animals, IGF-1 overexpression markedly increased both fiber and muscle size. As a positive control, IGF-1 was also overexpressed in the muscle of aged mice. In IGF-1 hyperexpressing muscles the fiber cross-sectional area definitely increased in both young and aged animals, while, by contrast, loss of muscle mass or reduction of fiber size in mice bearing the C26 tumor were not modified. These results demonstrate that muscle wasting in tumor-bearing animals is not associated with downregulation of molecules involved in the anabolic response, and appears inconsistent, at least, with reduced activity of the IGF-1 signaling pathway.

BIOMECHANICAL AND HISTOLOGICAL ANALYSIS OF THE GASTROCNEMIUS IN RATS SUBJECTED TO MUSCLE INJURY AND TREATMENT WITH LOW-LEVEL LASER THERAPY

Objective: To mechanically and histologically evaluate the application of low-level laser therapy to the reparative process on lesions caused by impact on the gastrocnemius muscles of rats. Methods: 45 female Wistar rats were divided into three groups (n=15/ group): C (control, no lesion), ML (muscle lesion) and ML-L (muscle lesion and laser therapy). The experimental muscle lesion was produced by letting a 250 g load drop from a height of 30 cm, directly onto the muscle. The animals in the ML-L group were subjected to application of 960 nm laser, 2 J/cm², on the lesion site, for three days, twice a day. Mechanical tests were performed on an Emic^® universal testing machine. Results: The mean values for the maximum force were: 35.70 (± 2.69) N in group C, 31.77 (± 2.59) N in group ML and 34.36 (± 3.63) N in group ML-L, with a statistically significant difference between groups C and ML (p < 0.05). The mean values for relative stiffness were: 3.75 (± 0.98) N/mm in group C, 3.84 (± 0.32) N/mm in group ML and 4.43 (± 0.68) N/mm in group ML-L, with no statistically significant differences (p>0.05). Histological analysis showed the presence of blood vessels in group ML-L and hematomas during the repair process. Conclusion: Laser therapy had a positive effect on the regeneration process of the muscle injury.

Effect of nandrolone decanoate administration on recovery from bupivacaine-induced muscle injury

Although testosterone administration elicits well-documented anabolic effects on skeletal muscle mass, the enhancement of muscle regeneration after injury has not been widely examined. The purpose of this study was to determine whether anabolic steroid administration improves skeletal muscle regeneration from bupivacaine-induced injury. Male C57BL/6 mice were castrated 2 wk before muscle injury induced by an intramuscular bupivacaine injection into the tibialis anterior (TA) muscle. Control mice received an intramuscular PBS injection. Anabolic steroid [nandrolone decanoate (ND), 6 mg/kg] or sesame seed oil was administered at the time of initial injury and continued every 7 days for the study's duration. Mice were randomly assigned to one of four treatment groups for 5, 14, or 42 days of recovery, as follows: 1) control (uninjured); 2) ND only (uninjured + ND); 3) bupivacaine only (injured); or 4) bupivacaine + ND (injured + ND). TA morphology, protein, and gene expression were analyzed at 14 and 42 days after injury; protein expression was analyzed at 5 days after injury. After 14 days of recovery, the injury and injury + ND treatments induced small-diameter myofiber incidence and also decreased mean myofiber area. The increase in small-myofiber incidence was 65% greater in injury + ND muscle compared with injury alone. At 14 days, injury + ND induced a fivefold increase in muscle IGF-I mRNA expression, which was greater than injury alone. Muscle Akt activity and glycogen synthetase kinase-3beta activity were also induced by injury + ND at 14 days of recovery, but not by injury alone. ND had a main effect for increasing muscle MyoD and cyclin D1 mRNA expression at 14 days. After 42 days of recovery, injury + ND increased large-diameter myofiber incidence compared with injury only. Nandrolone decanoate (ND) administration can enhance castrated mouse muscle regeneration during the recovery from bupivacaine-induced injury.

Mesenchymal stromal cells genetically engineered to overexpress IGF-I enhance cell-based gene therapy of renal failure-induced anemia

We previously demonstrated that erythropoietin (EPO)-secreting mesenchymal stromal cells (MSC) can be used for the long-term correction of renal failure-induced anemia. The present study provides evidence that coimplantation of insulin-like growth factor I (IGF-I)-overexpressing MSC (MSC-IGF) improves MSC-based gene therapy of anemia by providing paracrine support to EPO-secreting MSC (MSC-EPO) within a subcutaneous implant. IGF-I receptor RNA expression in murine MSC was demonstrated by RT-PCR. Functional protein expression was confirmed by immunoblots and MSC responsiveness to IGF-I stimulation in vitro. IGF-I was also shown to improve MSC survival following staurosporin-induced apoptosis in vitro. A cohort of C57Bl/6 mice was rendered anemic by right kidney electrocoagulation and left nephrectomy. MSC-EPO were subsequently admixed in a bovine collagen matrix and implanted, in combination with MSC-IGF or MSC null, by subcutaneous injection in renal failure mice. In mice receiving MSC-EPO coimplanted with MSC-IGF, hematocrit elevation was greater and enhanced compared with control mice; heart function was also improved. MSC-IGF coimplantation, therefore, represents a promising new strategy for enhancing MSC survival within implanted matrices and for improving cell-based gene therapy of renal anemia.

Systemic IL-12 gene therapy for treating malignancy via intramuscular electroporation

Interleukin 12 (IL-12) is effective in treating systemic microscopic malignancies by inducing T helper 1 (T(H)1) response, inhibiting angiogenesis, and triggering secondary cytokine production. Unfortunately, daily systemic administration of an acute dose of IL-12 protein is very costly and severely toxic. Here, a simple, economic, and less toxic approach, intramuscular administration of IL-12 gene, is provided for treating tumors in three tumor models. The results indicate that intramuscular administration of IL-12 encoding plasmid DNA via electroporation is a promising technology for treating systemic residual malignancies (less than 3-5 mm in diameter), as illustrated by the inhibition of tumor growth and lung metastases as well as the extension of survival rate. This approach is not effective in treating tumors larger than 3-5 mm in diameter.

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.

Enhancer of polycomb1, a novel homeodomain only protein-binding partner, induces skeletal muscle differentiation

Homeodomain only protein, Hop, is an unusual small protein that modulates target gene transcription without direct binding to DNA. Here we show that Hop interacts with Enhancer of Polycomb1 (Epc1), a homolog of a Drosophila polycomb group gene product that regulates transcription, to induce the skeletal muscle differentiation. Yeast two-hybrid assay with the human adult heart cDNA library revealed that Hop can associate with Epc1. The amino-terminal domain of Epc1 as well as full Epc1 physically interacted with Hop in mammalian cells and in yeast. Epc1 is highly expressed in the embryonic heart and adult skeletal muscles. Serum deprivation induced differentiation of H9c2, a myoblast cell line, into skeletal myocytes, and Epc1 was up-regulated. Differentiation of H9c2 was induced by Epc1 overexpression, although it was severely impaired in Epc1-knockdown cells. Co-transfection of Hop potentiated Epc1-induced transactivation of myogenin and myotube formation. Hop knock-out mice elicited a decrease in myosin heavy chain and myogenin expressions in skeletal muscle and showed delay in hamstring muscle healing after injury. Differentiation was impaired in skeletal myoblasts from Hop knock-out mice. These results suggest that Epc1 plays a role in the initiation of skeletal muscle differentiation, and its interaction with Hop is required for the full activity.

Electroporation for targeted gene transfer

The utilisation of nonviral gene delivery methods has been increasing steadily, however, a drawback has been the relative low efficiency of gene transfer with naked DNA compared with viral delivery methods. In vivo electroporation, which has previously been used clinically to deliver chemotherapeutic agents, also enhances the delivery of plasmid DNA and has been used to deliver plasmids to several tissue types, particularly muscle and tumour. Recently, a large number of preclinical studies for a variety of therapeutic modalities have demonstrated the potential of electrically mediated gene transfer. Although clinical trials using gene transfer with in vivo electroporation have not as yet been realised, the tremendous growth of this technology suggests that the first trials will soon be initiated.

Comparative evaluation of IGF-I gene transfer and IGF-I protein administration for enhancing skeletal muscle regeneration after injury

Developing methodologies to enhance skeletal muscle regeneration and hasten the restoration of muscle function has important implications for minimizing disability after injury and for treating muscle diseases such as Duchenne muscular dystrophy. Although delivery of various growth factors, such as insulin-like growth factor-I (IGF-I), have proved successful in promoting skeletal muscle regeneration after injury, no study has compared the efficacy of different delivery methods directly. We compared the efficacy of systemic delivery of recombinant IGF-I protein via mini-osmotic pump (approximately 1.5 mg/kg/day) with a single electrotransfer-assisted plasmid-based gene transfer, to hasten functional repair of mouse tibialis anterior muscles after myotoxic injury. The relative efficacy of each method was assessed at 7, 21 and 28 days post-injury. Our findings indicate that IGF-I hastened functional recovery, regardless of the route of IGF-I administration. However, gene transfer of IGF-I was superior to systemic protein administration because in the regenerating muscle, this delivery method increased IGF-I levels, activated intracellular signals (Akt phosphorylation), induced a greater magnitude of myofiber hypertrophy and hastened functional recovery at an earlier time point (14 days) after injury than did protein administration (21 days). Thus, the relative efficacy of different modes of delivery is an important consideration when assessing the therapeutic potential of various proteins for treating muscle injuries and skeletal muscle diseases.

Prevention and treatment of cancer cachexia: new insights into an old problem

Cancer cachexia (CC) is a multifactorial paraneoplastic syndrome characterized by anorexia, body weight loss, loss of adipose tissue and skeletal muscle, accounting for at least 20% of deaths in neoplastic patients. CC significantly impairs quality of life and response to anti-neoplastic therapies, increasing morbidity and mortality of cancer patients. Muscle wasting is the most important phenotypic feature of CC and the principal cause of function impairment, fatigue and respiratory complications, mainly related to a hyperactivation of muscle proteolytic pathways. Most therapeutic strategies to CC have proven to be only partially effective . The inhibition of catabolic processes in muscle has been attempted pharmacologically with encouraging results in animal models. However, data in the clinical setting are still scanty and contradictory. Stimulation of muscle anabolism could represent a promising and valid therapeutic alternative for cancer-related muscle wasting. This goal may be currently achieved with the conventional, short-acting and adverse side effect-rich anabolic steroids. Insulin-like growth factor-1 (IGF-1) plays a critical role in muscle homeostasis, hypertrophy and regeneration. IGF-1 overexpression at the muscular level by gene therapy reverses muscle hypotrophy secondary to catabolic conditions and induces muscle hypertrophy increasing muscle mass and strength. This allows the speculation that this approach could also prove effective in modulating cancer-induced muscle wasting, while avoiding the potentially hazardous side effects of systemic IGF-1 administration. The present review will focus on the potential biochemical and molecular targets of CC therapy, and will define the rationale for a novel, gene therapy-based approach.

Muscle injuries: biology and treatment

Muscle injuries are one of the most common traumas occurring in sports. Despite their clinical importance, few clinical studies exist on the treatment of these traumas. Thus, the current treatment principles of muscle injuries have either been derived from experimental studies or been tested only empirically. Although nonoperative treatment results in good functional outcomes in the majority of athletes with muscle injuries, the consequences of failed treatment can be very dramatic, possibly postponing an athlete's return to sports for weeks or even months. Moreover, the recognition of some basic principles of skeletal muscle regeneration and healing processes can considerably help in both avoiding the imminent dangers and accelerating the return to competition. Accordingly, in this review, the authors have summarized the prevailing understanding on the biology of muscle regeneration. Furthermore, they have reviewed the existing data on the different treatment modalities (such as medication, therapeutic ultrasound, physical therapy) thought to influence the healing of injured skeletal muscle. In the end, they extend these findings to clinical practice in an attempt to propose an evidence-based approach for the diagnosis and optimal treatment of skeletal muscle injuries.

Administration of insulin-like growth factor-1 (IGF-1) improves both structure and function of delta-sarcoglycan deficient cardiac muscle in the hamster

Dilated cardiomyopathies (DCM) are due to progressive dilatation of the cardiac cavities and thinning of the ventricular walls and lead unavoidably to heart failure. They represent a major cause for heart transplantation and, therefore, defining an efficient symptomatic treatment for DCM remains a challenge. We have taken advantage of the hamster strain CHF147 that displays progressive cardiomyopathy leading to heart failure to test whether stimulation of a hypertrophic pathway could delay the process of dilatation.Six month old CHF147 hamsters were treated with IGF-1 so that we could compare the efficacy of systemic administration of human recombinant IGF-1 protein (rh IGF-1) at low dose to that of direct myocardial injections of a plasmid DNA containing IGF-1 cDNA (pCMV-IGF1).IGF-1 treatment did not induce a significant variation of ventricle mass, but preserved left ventricular (LV) wall thickness and delayed dilatation of cardiac cavities when compared to non-treated hamsters. Together with this reduction of dilatation, we also noted a reduction in the amount of interstitial collagen. Furthermore, IGF-1 treatment induced beneficial effects on cardiac function since treated hamsters presented improved cardiac output and stroke volume, decreased end diastolic pressure when compared to nontreated hamsters and also showed a trend towards increased contractility (dP/dt(max)).This study provides evidence that IGF-1 treatment induces beneficial structural and functional effects on DCM of CHF147 hamsters, hence making this molecule a promising candidate for future gene therapy of heart failure due to DCM.

DNA electrotransfer: its principles and an updated review of its therapeutic applications

The use of electric pulses to transfect all types of cells is well known and regularly used in vitro for bacteria and eukaryotic cells transformation. Electric pulses can also be delivered in vivo either transcutaneously or with electrodes in direct contact with the tissues. After injection of naked DNA in a tissue, appropriate local electric pulses can result in a very high expression of the transferred genes. This manuscript describes the evolution in the concepts and the various optimization steps that have led to the use of combinations of pulses that fit with the known roles of the electric pulses in DNA electrotransfer, namely cell electropermeabilization and DNA electrophoresis. A summary of the main applications published until now is also reported, restricted to the in vivo preclinical trials using therapeutic genes.

Electroporation for gene transfer to skeletal muscles: current status

Naked plasmid DNA can be used to introduce genetic material into a variety of cell types in vivo. However, such gene transfer and expression is generally very low compared with that achieved with viral vectors and so is unsuitable for clinical therapeutic application in most cases. This difference in efficiency has been substantially reduced by the introduction of in vivo electroporation to enhance plasmid delivery to a wide range of tissues including muscle, skin, liver, lung, artery, kidney, retina, cornea, spinal cord, brain, synovium, and tumors. The precise mechanism of in vivo electroporation is uncertain, but appears to involve both electropore formation and an electrophoretic movement of the plasmid DNA. Skeletal muscle is a favored target tissue for three reasons: there is a pressing need to develop effective therapies for muscular dystrophies; skeletal muscle can act as an effective platform for the long-term secretion of therapeutic proteins for systemic distribution; and introduction of DNA vaccines into skeletal muscle promotes strong humoral and cellular immune responses. All of these applications are significantly improved by the application of in vivo electroporation. Importantly, the increased efficiency of plasmid delivery following electroporation is seen in larger species as well as rodents, in contrast to the decreasing efficiencies with increasing body size for simple intramuscular injection of naked plasmid DNA. As this electroporation-enhanced non-viral gene delivery system works well in larger species and avoids the vector-specific immune responses associated with recombinant viruses, the prospects for clinical application are promising.