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

Stable Gastric Pentadecapeptide BPC 157 and Striated, Smooth, and Heart Muscle

First, we review the definitively severed myotendinous junction and recovery by the cytoprotective stable gastric pentadecapeptide BPC 157 therapy, its healing that might combine both transected and detached tendon and transected muscle, ligament and bone injuries, applied alone, as native peptide therapy, effective in rat injury, given intraperitoneally or in drinking water or topically, at the site of injury. As a follow up, we reviewed that with the BPC 157 therapy, its cytoprotective ability to organize simultaneous healing of different tissues of and full recovery of the myotendinous junction might represent the particular muscle therapy against distinctive etiopathology muscle disabilities and weakness. In this, BPC 157 therapy might recover many of muscle disabilities (i.e., succinylcholine, vascular occlusion, spinal cord compression, stroke, traumatic brain injury, severe electrolyte disturbances, neurotoxins, neuroleptics, alcohol, serotonin syndrome and NO-system blockade and tumor-cachexia). These might provide practical realization of the multimodal muscle-axis impact able to react depending on the condition and the given agent(s) and the symptoms distinctively related to the prime injurious cause symptoms in the wide healing concept, the concept of cytoprotection, in particular. Further, the BPC 157 therapy might be the recovery for the disabled heart functioning, and disabled smooth muscle functioning (various sphincters function recovery). Finally, BPC 157, native and stable in human gastric juice, might be a prototype of anti-ulcer cytoprotective peptide for the muscle therapy with high curing potential (very safe profile (lethal dose not achieved), with suited wide effective range (µg-ng regimens) and ways of application).

Potential Role of Insulin-Like Growth Factors in Myofascial Pain Syndrome: A Narrative Review

ABSTRACT

Insulin-like growth factors have diverse functions in skeletal muscles by acting through multiple signaling pathways, including growth regulation and differentiation, anti-inflammation, and antioxidation. Insulin-like growth factors have anti-inflammatory effects and also play roles in nociceptive pathways, determining pain sensitivity, in addition to their protective role against ischemic injury in both the nervous system and skeletal muscle. In skeletal muscle, insulin-like growth factors maintain homeostasis, playing key roles in maintenance, accelerating muscle regeneration, and repair processes. As part of their maintenance role, increased levels of insulin-like growth factors may be required for the repair mechanisms after exercise. Although the role of insulin-like growth factors in myofascial pain syndrome is not completely understood, there is evidence from a recent study that insulin-like growth factor 2 levels in patients with myofascial pain syndrome are lower than those of healthy individuals and are associated with increased levels of inflammatory biomarkers. Importantly, higher insulin-like growth factor 2 levels are associated with increased pain severity in myofascial pain syndrome patients. This may suggest that too low or high insulin-like growth factor levels may contribute to musculoskeletal disorder process, whereas a midrange levels may optimize healing without contributing to pain hypersensitivity. Future studies are required to address the mechanisms of insulin-like growth factor 2 in myofascial pain syndrome and the optimal level as a therapeutic agent.

Astragalosides Supplementation Enhances Intrinsic Muscle Repair Capacity Following Eccentric Exercise-Induced Injury

Astragalosides have been shown to enhance endurance exercise capacity in vivo and promote muscular hypertrophy in vitro. However, it remains unknown whether astragalosides supplementation can alter inflammatory response and enhance muscle recovery after damage in humans. We therefore aimed to evaluate the effect of astragalosides supplementation on muscle's intrinsic capacity to regenerate and repair itself after exercise-induced damage. Using a randomized double-blind placebo-controlled cross-over design, eleven male participants underwent 7 days of astragalosides supplementation (in total containing 4 mg of astragalosides per day) or a placebo control, following an eccentric exercise protocol. Serum blood samples and variables related to muscle function were collected prior to and immediately following the muscle damage protocol and also at 2 h, and 1, 2, 3, 5, and 7 days of the recovery period, to assess the pro-inflammatory cytokine response, the secretion of muscle regenerative factors, and muscular strength. Astragalosides supplementation reduced biomarkers of skeletal muscle damage (serum CK, LDH, and Mb), when compared to the placebo, at 1, 2, and 3 days following the muscle damage protocol. Astragalosides supplementation suppressed the secretion of IL-6 and TNF-α, whilst increasing the release of IGF-1 during the initial stages of muscle recovery. Furthermore, following astragaloside supplementation, muscular strength returned to baseline 2 days earlier than the placebo. Astragalosides supplementation shortens the duration of inflammation, enhances the regeneration process and restores muscle strength following eccentric exercise-induced injury.

Pegylated Insulin-Like Growth Factor 1 attenuates Hair Cell Loss and promotes Presynaptic Maintenance of Medial Olivocochlear Cholinergic Fibers in the Cochlea of the Progressive Motor Neuropathy Mouse

The progressive motor neuropathy (PMN) mouse is a model of an inherited motor neuropathy disease with progressive neurodegeneration. Axon degeneration associates with homozygous mutations of the TBCE gene encoding the tubulin chaperone E protein. TBCE is responsible for the correct dimerization of alpha and beta-tubulin. Strikingly, the PMN mouse also develops a progressive hearing loss after normal hearing onset, characterized by degeneration of the auditory nerve and outer hair cell (OHC) loss. However, the development of this neuronal and cochlear pathology is not fully understood yet. Previous studies with pegylated insulin-like growth factor 1 (peg-IGF-1) treatment in this mouse model have been shown to expand lifespan, weight, muscle strength, and motor coordination. Accordingly, peg-IGF-1 was evaluated for an otoprotective effect. We investigated the effect of peg-IGF-1 on the auditory system by treatment starting at postnatal day 15 (p15). Histological analysis revealed positive effects on OHC synapses of medial olivocochlear (MOC) neuronal fibers and a short-term attenuation of OHC loss. Peg-IGF-1 was able to conditionally restore the disorganization of OHC synapses and maintain the provision of cholinergic acetyltransferase in presynapses. To assess auditory function, frequency-specific auditory brainstem responses and distortion product otoacoustic emissions were recorded in animals on p21 and p28. However, despite the positive effect on MOC fibers and OHC, no restoration of hearing could be achieved. The present work demonstrates that the synaptic pathology of efferent MOC fibers in PMN mice represents a particular form of “efferent auditory neuropathy.” Peg-IGF-1 showed an otoprotective effect by preventing the degeneration of OHCs and efferent synapses. However, enhanced efforts are needed to optimize the treatment to obtain detectable improvements in hearing performances.

Nogo-A Is Critical for Pro-Inflammatory Gene Regulation in Myocytes and Macrophages

Nogo-A (Rtn 4A), a member of the reticulon 4 (Rtn4) protein family, is a neurite outgrowth inhibitor protein that is primarily expressed in the central nervous system (CNS). However, previous studies revealed that Nogo-A was upregulated in skeletal muscles of Amyotrophic lateral sclerosis (ALS) patients. Additionally, experiments showed that endoplasmic reticulum (ER) stress marker, C/EBP homologous protein (CHOP), was upregulated in gastrocnemius muscle of a murine model of ALS. We therefore hypothesized that Nogo-A might relate to skeletal muscle diseases. According to our knocking down and overexpression results in muscle cell line (C2C12), we have found that upregulation of Nogo-A resulted in upregulation of CHOP, pro-inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α, while downregulation of Nogo-A led to downregulation of CHOP, IL-6 and TNF-α. Immunofluorescence results showed that Nogo-A and CHOP were expressed by myofibers as well as tissue macrophages. Since resident macrophages share similar functions as bone marrow-derived macrophages (BMDM), we therefore, isolated macrophages from bone marrow to study the role of Nogo-A in activation of these cells. Lipopolysaccharide (LPS)-stimulated BMDM in Nogo-KO mice showed low mRNA expression of CHOP, IL-6 and TNF-α compared to BMDM in wild type (WT) mice. Interestingly, Nogo knockout (KO) BMDM exhibited lower migratory activity and phagocytic ability compared with WT BMDM after LPS treatment. In addition, mice experiments data revealed that upregulation of Nogo-A in notexin- and tunicamycin-treated muscles was associated with upregulation of CHOP, IL-6 and TNF-α in WT group, while in Nogo-KO group resulted in low expression level of CHOP, IL-6 and TNF-α. Furthermore, upregulation of Nogo-A in dystrophin-deficient (mdx) murine model, myopathy and Duchenne muscle dystrophy (DMD) clinical biopsies was associated with upregulation of CHOP, IL-6 and TNF-α. To the best of our knowledge, this is the first study to demonstrate Nogo-A as a regulator of inflammation in diseased muscle and bone marrow macrophages and that deletion of Nogo-A alleviates muscle inflammation and it can be utilized as a therapeutic target for improving muscle diseases.

The Mouse Levator Auris Longus Muscle: An Amenable Model System to Study the Role of Postsynaptic Proteins to the Maintenance and Regeneration of the Neuromuscular Synapse

The neuromuscular junction (NMJ) is the peripheral synapse that controls the coordinated movement of many organisms. The NMJ is also an archetypical model to study synaptic morphology and function. As the NMJ is the primary target of neuromuscular diseases and traumatic injuries, the establishment of suitable models to study the contribution of specific postsynaptic muscle-derived proteins on NMJ maintenance and regeneration is a permanent need. Considering the unique experimental advantages of the levator auris longus (LAL) muscle, here we present a method allowing for efficient electroporation-mediated gene transfer and subsequent detailed studies of the morphology and function of the NMJ and muscle fibers. Also, we have standardized efficient facial nerve injury protocols to analyze LAL muscle NMJ degeneration and regeneration. Our results show that the expression of a control fluorescent protein does not alter either the muscle structural organization, the apposition of the pre- and post-synaptic domains, or the functional neurotransmission parameters of the LAL muscle NMJs; in turn, the overexpression of MuSK, a major regulator of postsynaptic assembly, induces the formation of ectopic acetylcholine receptor clusters. Our NMJ denervation experiments showed complete reinnervation of LAL muscle NMJs four weeks after facial nerve injury. Together, these experimental strategies in the LAL muscle constitute effective methods to combine protein expression with accurate analyses at the levels of structure, function, and regeneration of the NMJ.

Muscle wasting in the presence of disease, why is it so variable?

Skeletal muscle wasting is a common clinical feature of many chronic diseases and also occurs in response to single acute events. The accompanying loss of strength can lead to significant disability, increased care needs and have profound negative effects on quality of life. As muscle is the most abundant source of amino acids in the body, it appears to function as a buffer for fuel and substrates that can be used to repair damage elsewhere and to feed the immune system. In essence, the fundamentals of muscle wasting are simple: less muscle is made than is broken down. However, although well-described mechanisms modulate muscle protein turnover, significant individual differences in the amount of muscle lost in the presence of a given severity of disease complicate the understanding of underlying mechanisms and suggest that individuals have different sensitivities to signals for muscle loss. Furthermore, the rate at which muscle protein is turned over under normal conditions means that clinically significant muscle loss can occur with changes in the rate of protein synthesis and/or breakdown that are too small to be measurable. Consequently, the changes in expression of factors regulating muscle turnover required to cause a decline in muscle mass are small and, except in cases of rapid wasting, there is no consistent pattern of change in the expression of factors that regulate muscle mass. MicroRNAs are fine tuners of cell phenotype and are therefore ideally suited to cause the subtle changes in proteome required to tilt the balance between synthesis and degradation in a way that causes clinically significant wasting. Herein we present a model in which muscle loss as a consequence of disease in non-muscle tissue is modulated by a set of microRNAs, the muscle expression of which is associated with severity of disease in the non-muscle tissue. These microRNAs alter fundamental biological processes including the synthesis of ribosomes and mitochondria leading to reduced protein synthesis and increased protein breakdown, thereby freeing amino acids from the muscle. We argue that the variability in muscle loss observed in the human population arises from at least two sources. The first is from pre-existing or disease-induced variation in the expression of microRNAs controlling the sensitivity of muscle to the atrophic signal and the second is from the expression of microRNAs from imprinted loci (i.e. only expressed from the maternally or paternally inherited allele) and may control the rate of myonuclear recruitment. In the absence of disease, these factors do not correlate with muscle mass, since there is no challenge to the established balance. However, in the presence of such a challenge, these microRNAs determine the rate of decline for a given disease severity. Together these mechanisms provide novel insight into the loss of muscle mass and its variation in the human population. The involvement of imprinted loci also suggests that genes that regulate early development also contribute to the ability of individuals to resist muscle loss in response to disease.

Therapeutic effects of a mesenchymal stem cell‑based insulin‑like growth factor‑1/enhanced green fluorescent protein dual gene sorting system in a myocardial infarction rat model

The present study was conducted in order to improve gene expression efficiency of insulin‑like growth factor‑1 (IGF‑1)‑transfected mesenchymal stem cells (MSCs) using a non‑viral carrier and a simplified method of dual gene selection. The therapeutic efficacy of this MSC‑based IGF‑1/enhanced green fluorescent protein (EGFP) dual gene sorting system was evaluated in a rat myocardial infarction (MI) model. IGF‑1 and EGFP genes were expressed in MSCs in vitro. The purity of dual gene‑expressing MSCs was 95.1% by fluorescence‑activated cell sorting. Transfected MSCs injected into rats were identified based on green fluorescence, with an increased signal intensity observed in rats injected with sorted cells, compared with unsorted cells. IGF‑1 expression levels were additionally increased in the sorted group, and decreases in infarct size, fibrotic area and fraction of apoptotic cells were observed. These results demonstrated that IGF‑1 overexpression protects against fibrosis and apoptosis in the myocardium and reduces infarct size following MI. Additionally, the present vector sorting system may potentially be applied to other types of stem cell‑based gene therapy.

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.

IGF-1-Overexpressing Mesenchymal Stem/Stromal Cells Promote Immunomodulatory and Proregenerative Effects in Chronic Experimental Chagas Disease

Mesenchymal stem/stromal cells (MSCs) have been investigated for the treatment of diseases that affect the cardiovascular system, including Chagas disease. MSCs are able to promote their beneficial actions through the secretion of proregenerative and immunomodulatory factors, including insulin-like growth factor-1 (IGF-1), which has proregenerative actions in the heart and skeletal muscle. Here, we evaluated the therapeutic potential of IGF-1-overexpressing MSCs (MSC_IGF-1) in a mouse model of chronic Chagas disease. C57BL/6 mice were infected with Colombian strain Trypanosoma cruzi and treated with MSCs, MSC_IGF-1, or vehicle (saline) six months after infection. RT-qPCR analysis confirmed the presence of transplanted cells in both the heart and skeletal muscle tissues. Transplantation of either MSCs or MSC_IGF-1 reduced the number of inflammatory cells in the heart when compared to saline controls. Moreover, treatment with MSCs or MSC_IGF-1 significantly reduced TNF-α, but only MSC treatment reduced IFN-γ production compared to the saline group. Skeletal muscle sections of both MSC- and MSC_IGF-1-treated mice showed a reduction in fibrosis compared to saline controls. Importantly, the myofiber area was reduced in T. cruzi-infected mice, and this was recovered after treatment with MSC_IGF-1. Gene expression analysis in the skeletal muscle showed a higher expression of pro- and anti-inflammatory molecules in MSC_IGF-1-treated mice compared to MSCs alone, which significantly reduced the expression of TNF-α and IL-1β. In conclusion, our results indicate the therapeutic potential of MSC_IGF-1, with combined immunomodulatory and proregenerative actions to the cardiac and skeletal muscles.

Skeletal muscle-specific overexpression of IGFBP-2 promotes a slower muscle phenotype in healthy but not dystrophic mdx mice and does not affect the dystrophic pathology

OBJECTIVE

The insulin-like growth factor binding proteins (IGFBPs) are thought to modulate cell size and homeostasis via IGF-I-dependent and -independent pathways. There is a considerable dearth of information regarding the function of IGFBPs in skeletal muscle, particularly their role in the pathophysiology of Duchenne muscular dystrophy (DMD). In this study we tested the hypothesis that intramuscular IGFBP-2 overexpression would ameliorate the pathology in mdx dystrophic mice.

DESIGN

4week old male C57Bl/10 and mdx mice received a single intramuscular injection of AAV6-empty or AAV6-IGFBP-2 vector into the tibialis anterior muscle. At 8weeks post-injection the effect of IGFBP-2 overexpression on the structure and function of the injected muscle was assessed.

RESULTS

AAV6-mediated IGFBP-2 overexpression in the tibialis anterior (TA) muscles of 4-week-old C57BL/10 and mdx mice reduced the mass of injected muscle after 8weeks, inducing a slower muscle phenotype in C57BL/10 but not mdx mice. Analysis of inflammatory and fibrotic gene expression revealed no changes between control and IGFBP-2 injected muscles in dystrophic (mdx) mice.

CONCLUSIONS

Together these results indicate that the IGFBP-2-induced promotion of a slower muscle phenotype is impaired in muscles of dystrophin-deficient mdx mice, which contributes to the inability of IGFBP-2 to ameliorate the dystrophic pathology. The findings implicate the dystrophin-glycoprotein complex (DGC) in the signaling required for this adaptation.

Relationship of anabolic and catabolic biomarkers with muscle strength and physical performance in older adults: a population-based cross-sectional study

Background

Previous studies have found inflammation, growth factors, and androgen signaling pathways all contribute to sarcopenia. However, few studies simultaneously have investigated the association between these potential risk factors and sarcopenia among older people. The aim of the study was to investigate whether elevated levels of inflammatory cytokines combined with low levels of anabolic hormone have a synergy effect on muscle strength and functional decline in older people.

Methods

We designed a cross-sectional study of 1,131 subjects aged 60 years and older. Concentrations of serum C-reactive protein, insulin-like growth factor 1 and dehydroepiandrosteronesulphate were assessed using chemiluminescent immunoassays. Handgrip strength was measured using a dynamometer, and physical performance was assessed using a four-meter gait speed and Timed Up and Go test. We defined poor physical performance as a 4-m gait speed <0.8 m/s or Timed Up and Go test ≥13.5 s.

Results

After adjustment for potential confounding factors, in multiple linear regression analysis, C-reactive protein levels are inversely related to handgrip strength (P <0.01), and in multiple logistic regression analysis, C-reactive protein levels are inversely related to poor physical performance (P for trend <0.05) in males, but not in females. After combining three biomarkers, no significant results were observed between biomarker scores and muscle strength or physical performance.

Conclusions

In older males, higher serum C-reactive protein levels, but not insulin-like growth factor 1 and dehydroepiandrosteronesulphate levels, are independently related to lower muscle strength and poor physical performance. In this study we did not observe that a combination of higher catabolic biomarkers and lower anabolic biomarkers were better predictors for muscle strength and physical performance.

Monocyte/Macrophage-derived IGF-1 Orchestrates Murine Skeletal Muscle Regeneration and Modulates Autocrine Polarization

Insulin-like growth factor 1 (IGF-1) is a potent enhancer of tissue regeneration, and its overexpression in muscle injury leads to hastened resolution of the inflammatory phase. Here, we show that monocytes/macrophages constitute an important initial source of IGF-1 in muscle injury, as conditional deletion of the IGF-1 gene specifically in mouse myeloid cells (ϕIGF-1 CKO) blocked the normal surge of local IGF-1 in damaged muscle and significantly compromised regeneration. In injured muscle, Ly6C+ monocytes/macrophages and CD206+ macrophages expressed equivalent IGF-1 levels, which were transiently upregulated during transition from the inflammation to repair. In injured ϕIGF-1 CKO mouse muscle, accumulation of CD206+ macrophages was impaired, while an increase in Ly6C+ monocytes/macrophages was favored. Transcriptional profiling uncovered inflammatory skewing in ϕIGF-1 CKO macrophages, which failed to fully induce a reparative gene program in vitro or in vivo, revealing a novel autocrine role for IGF-1 in modulating murine macrophage phenotypes. These data establish local macrophage-derived IGF-1 as a key factor in inflammation resolution and macrophage polarization during muscle regeneration.

Gene and cell therapy for muscle regeneration

Skeletal muscle injury and healing are multifactorial processes, involving three steps of healing: (1) degeneration and inflammation, (2) regeneration, and (3) fibrosis. Fibrous tissue hinders the muscle's complete recovery and current therapies fail in achieving total muscle recovery. Gene and cell therapy (or both) are potential future treatments for severe muscular injuries. Stem cells' properties associated with growth factors or/and cytokines can improve muscle healing and permit long-term recovery.

Gene therapy approaches to regenerating the musculoskeletal system

Injuries to the musculoskeletal system are common, debilitating and expensive. In many cases, healing is imperfect, which leads to chronic impairment. Gene transfer might improve repair and regeneration at sites of injury by enabling the local, sustained and potentially regulated expression of therapeutic gene products; such products include morphogens, growth factors and anti-inflammatory agents. Proteins produced endogenously as a result of gene transfer are nascent molecules that have undergone post-translational modification. In addition, gene transfer offers particular advantages for the delivery of products with an intracellular site of action, such as transcription factors and noncoding RNAs, and proteins that need to be inserted into a cell compartment, such as a membrane. Transgenes can be delivered by viral or nonviral vectors via in vivo or ex vivo protocols using progenitor or differentiated cells. The first gene transfer clinical trials for osteoarthritis and cartilage repair have already been completed. Various bone-healing protocols are at an advanced stage of development, including studies with large animals that could lead to human trials. Other applications in the repair and regeneration of skeletal muscle, intervertebral disc, meniscus, ligament and tendon are in preclinical development. In addition to scientific, medical and safety considerations, clinical translation is constrained by social, financial and logistical issues.

A novel isoform of met receptor tyrosine kinase blocks hepatocyte growth factor/Met signaling and stimulates skeletal muscle cell differentiation

Hepatocyte growth factor (HGF) and its receptor, Met, regulate skeletal muscle differentiation. In the present study, we identified a novel alternatively spliced isoform of Met lacking exon 13 (designated Δ13Met), which is expressed mainly in human skeletal muscle. Alternative splicing yielded a truncated Met having extracellular domain only, suggesting an inhibitory role. Indeed, Δ13Met expression led to a decrease in HGF-induced tyrosine phosphorylation of Met and ERK phosphorylation, as well as cell proliferation and migration via sequestration of HGF. Interestingly, in human primary myoblasts undergoing differentiation, Δ13Met mRNA and protein levels were rapidly increased, concomitantly with a decrease in wild type Met mRNA and protein. Inhibition of Δ13Met with siRNA led to a decreased differentiation, whereas its overexpression potentiated differentiation of human primary myoblasts. Furthermore, in notexin-induced mouse injury model, exogenous Δ13Met expression enhanced regeneration of skeletal muscle, further confirming a stimulatory role of the isoform in muscle cell differentiation. In summary, we identified a novel alternatively spliced inhibitory isoform of Met that stimulates muscle cell differentiation, which confers a new means to control muscle differentiation and/or regeneration.

Gene doping in sport - perspectives and risks

In the past few years considerable progress regarding the knowledge of the human genome map has been achieved. As a result, attempts to use gene therapy in patients' management are more and more often undertaken. The aim of gene therapy is to replace defective genes in vivo and/or to promote the long-term endogenous synthesis of deficient protein. In vitro studies improve the production of human recombinant proteins, such as insulin (INS), growth hormone (GH), insulin-like growth factor-1 (IGF-1) and erythropoietin (EPO), which could have therapeutic application. Unfortunately, genetic methods developed for therapeutic purposes are increasingly being used in competitive sports. Some new substances (e.g., antibodies against myostatin or myostatin blockers) might be used in gene doping in athletes. The use of these substances may cause an increase of body weight and muscle mass and a significant improvement of muscle strength. Although it is proven that uncontrolled manipulation of genetic material and/or the introduction of recombinant proteins may be associated with health risks, athletes are increasingly turning to banned gene doping. At the same time, anti-doping research is undertaken in many laboratories around the world to try to develop and refine ever newer techniques for gene doping detection in sport. Thanks to the World Anti-Doping Agency (WADA) and other sports organizations there is a hope for real protection of athletes from adverse health effects of gene doping, which at the same time gives a chance to sustain the idea of fair play in sport.

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.

Functional β-adrenoceptors are important for early muscle regeneration in mice through effects on myoblast proliferation and differentiation

Muscles can be injured in different ways and the trauma and subsequent loss of function and physical capacity can impact significantly on the lives of patients through physical impairments and compromised quality of life. The relative success of muscle repair after injury will largely determine the extent of functional recovery. Unfortunately, regenerative processes are often slow and incomplete, and so developing novel strategies to enhance muscle regeneration is important. While the capacity to enhance muscle repair by stimulating β₂-adrenoceptors (β-ARs) using β₂-AR agonists (β₂-agonists) has been demonstrated previously, the exact role β-ARs play in regulating the regenerative process remains unclear. To investigate β-AR-mediated signaling in muscle regeneration after myotoxic damage, we examined the regenerative capacity of tibialis anterior and extensor digitorum longus muscles from mice lacking either β₁-AR (β₁-KO) and/or β₂-ARs (β₂-KO), testing the hypothesis that muscles from mice lacking the β₂-AR would exhibit impaired functional regeneration after damage compared with muscles from β₁-KO or β₁/β₂-AR null (β₁/β₂-KO) KO mice. At 7 days post-injury, regenerating muscles from β₁/β₂-KO mice produced less force than those of controls but muscles from β₁-KO or β₂-KO mice did not exhibit any delay in functional restoration. Compared with controls, β₁/β₂-KO mice exhibited an enhanced inflammatory response to injury, which delayed early muscle regeneration, but an enhanced myoblast proliferation later during regeneration ensured a similar functional recovery (to controls) by 14 days post-injury. This apparent redundancy in the β-AR signaling pathway was unexpected and may have important implications for manipulating β-AR signaling to improve the rate, extent and efficacy of muscle regeneration to enhance functional recovery after injury.

Marginal zinc deficiency negatively affects recovery from muscle injury in mice

The aim of the present study was to elucidate whether the recovery from muscle injury is impaired in marginal zinc deficiency. C57BL/6 male mice were fed a marginally zinc-deficient diet (MZD: 8 mg Zn/kg diet), a zinc-adequate diet (ZA: zinc 35 mg Zn/kg diet), and a zinc-high diet (ZH: 190 mg Zn/kg diet) for 4 weeks. Muscle injury was induced in the gastrocnemius muscles using cardiotoxin. The gastrocnemius muscles of these mice were harvested at 3, 5, 7, 10, 14, and 20 days after injury. We evaluated the regeneration of the skeletal muscle with hematoxylin and eosin staining and developmental myosin heavy-chain (dMHC: implicated in regeneration) immunostaining. The rate of dMHC-positive cells was significantly low in MZD mice compared with ZA mice at 3 days after cardiotoxin injection. The peak dMHC expression was found at 3 days after injection in ZA mice, 5 days in ZH mice, and 7 days in MZD mice. These results suggest that recovery from muscle injury might be partly impaired and delayed in MZD mice. Therefore, we strongly suggest the appropriate zinc intake to prevent the impairment of skeletal muscle regeneration.

Pro-inflammatory mediation of myoblast proliferation

Skeletal muscle satellite cell function is largely dictated by the surrounding environment following injury. Immune cell infiltration dominates the extracellular space in the injured area, resulting in increased cytokine concentrations. While increased pro-inflammatory cytokine expression has been previously established in the first 3 days following injury, less is known about the time course of cytokine expression and the specific mechanisms of cytokine induced myoblast function. Therefore, the expression of IL-1β and IL-6 at several time points following injury, and their effects on myoblast proliferation, were examined. In order to do this, skeletal muscle was injured using barium chloride in mice and tissue was collected 1, 5, 10, and 28 days following injury. Mechanisms of cytokine induced proliferation were determined in cell culture using both primary and C2C12 myoblasts. It was found that there is a ∼20-fold increase in IL-1β (p≤0.05) and IL-6 (p = 0.06) expression 5 days following injury. IL-1β increased proliferation of both primary and C2C12 cells ∼25%. IL-1β stimulation also resulted in increased NF-κB activity, likely contributing to the increased proliferation. These data demonstrate for the first time that IL-1β alone can increase the mitogenic activity of primary skeletal muscle satellite cells and offer insight into the mechanisms dictating satellite cell function following injury.

Intramuscular administration of PEGylated IGF-I improves skeletal muscle regeneration after myotoxic injury

OBJECTIVE

Musculoskeletal injuries represent a major public health problem and drugs that can improve muscle repair and restore function are needed for patients with these conditions and other related muscular pathologies. Increasing insulin-like growth factor-I (IGF-I) levels in skeletal muscle improves regeneration after myotoxic injury and while administration of IGF-I has a potential for accelerating healing after trauma, optimizing its method of delivery and obviating potential side-effects currently associated with recombinant human (rh) IGF-I, remain a hurdle.

DESIGN

We compared the treatment efficacy of rhIGF-I with a polyethylene glycol modified IGF-I (PEG-IGF-I) analog to improve functional repair of mouse tibialis anterior muscles after myotoxic injury, testing the hypothesis that PEG-IGF-I would exert greater beneficial effects on regenerating skeletal muscles than rhIGF-I due to improved pharmacokinetic properties. We also examined the relative efficacy of systemic versus local delivery of these IGF-I variants for improving functional muscle regeneration.

RESULTS

Local delivery of PEG-IGF-I, but not rhIGF-I, at 4 days post-injury significantly improved early functional recovery as evident by a 27% increase in normalized force compared with saline control (P<0.05), whereas systemic application of either IGF-I variant was not effective. The improved function with intramuscular PEG-IGF-I administration was attributed to a greater and prolonged residence within the regenerating muscles, resulting in increased Akt activation and a 13% larger fiber cross-sectional area compared with rhIGF-I (P<0.05).

CONCLUSIONS

These data support the hypothesis that PEG-IGF-I is more efficacious than rhIGF-I in hastening early fiber regeneration and improving muscle function after injury, highlighting its therapeutic potential for muscular pathologies.

Current Challenges and Future Directions in Recombinant AAV-Mediated Gene Therapy of Duchenne Muscular Dystrophy

Various characteristics of adeno-associated virus (AAV)-based vectors with long-term safe expression have made it an exciting transduction tool for clinical gene therapy of Duchenne muscular dystrophy (DMD). Although host immune reactions against the vector as well as transgene products were detected in some instances of the clinical studies, there have been promising observations. Methods of producing AAV vectors for considerable in vivo experimentation and clinical investigations have been developed and a number of studies with AAV vector-mediated muscle transduction were attempted. Notably, an intravenous limb perfusion transduction technique enables extensive transgene expression in the skeletal muscles without noticeable adverse events. Furthermore, cardiac transduction by the rAAV9-microdystrophin would be promising to prevent development of cardiac dysfunction. Recent achievements in transduction technology suggest that long-term transgene expression with therapeutic benefits in DMD treatment would be achieved by the rAAV-mediated transduction strategy with an adequate regimen to regulate host immune response.

Paracrine effects of IGF-1 overexpression on the functional decline due to skeletal muscle disuse: molecular and functional evaluation in hindlimb unloaded MLC/mIgf-1 transgenic mice

Slow-twitch muscles, devoted to postural maintenance, experience atrophy and weakness during muscle disuse due to bed-rest, aging or spaceflight. These conditions impair motion activities and can have survival implications. Human and animal studies demonstrate the anabolic role of IGF-1 on skeletal muscle suggesting its interest as a muscle disuse countermeasure. Thus, we tested the role of IGF-1 overexpression on skeletal muscle alteration due to hindlimb unloading (HU) by using MLC/mIgf-1 transgenic mice expressing IGF-1 under the transcriptional control of MLC promoter, selectively activated in skeletal muscle. HU produced atrophy in soleus muscle, in terms of muscle weight and fiber cross-sectional area (CSA) reduction, and up-regulation of atrophy gene MuRF1. In parallel, the disuse-induced slow-to-fast fiber transition was confirmed by an increase of the fast-type of the Myosin Heavy Chain (MHC), a decrease of PGC-1α expression and an increase of histone deacetylase-5 (HDAC5). Consistently, functional parameters such as the resting chloride conductance (gCl) together with ClC-1 chloride channel expression were increased and the contractile parameters were modified in soleus muscle of HU mice. Surprisingly, IGF-1 overexpression in HU mice was unable to counteract the loss of muscle weight and the decrease of fiber CSA. However, the expression of MuRF1 was recovered, suggesting early effects on muscle atrophy. Although the expression of PGC-1α and MHC were not improved in IGF-1-HU mice, the expression of HDAC5 was recovered. Importantly, the HU-induced increase of gCl was fully contrasted in IGF-1 transgenic mice, as well as the changes in contractile parameters. These results indicate that, even if local expression does not seem to attenuate HU-induced atrophy and slow-to-fast phenotype transition, it exerts early molecular effects on gene expression which can counteract the HU-induced modification of electrical and contractile properties. MuRF1 and HDAC5 can be attractive therapeutic targets for pharmacological countermeasures and then deserve further investigations.

New Modulators for IGF-I Activity within IGF-I Processing Products

Insulin-like growth factor I (IGF-I) is a key regulator of muscle development and growth. The pre-pro-peptide produced by the Igf1 gene undergoes several post-translational processing steps to result in a secreted mature protein, which is thought to be the obligate ligand for the IGF-I receptor (IGF-IR). However, the significance of the additional forms and peptides produced from Igf1 is not clear. For instance, the C-terminal extensions called the E-peptides that are part of pro-IGF-I, have been implicated in playing roles in cell growth, including cell proliferation and migration and muscle hypertrophy in an IGF-IR independent manner. However, the activity of these peptides has been controversial. IGF-IR independent actions suggest the existence of an E-peptide receptor, yet such a protein has not been discovered. We propose a new concept: there is no E-peptide receptor, rather the E-peptides coordinate with IGF-I to modulate activity of the IGF-IR. Growing evidence reveals that the presence of an E-peptide alters IGF-I activity, whether as part of pro-IGF-I, or as a separate peptide. In this review, we will examine the past literature on IGF-I processing and E-peptide actions in skeletal muscle, address the previous attempts to separate IGF-I and E-peptide effects, propose a new model for IGF-I/E-peptide synergy, and suggest future experiments to test if the E-peptides truly modulate IGF-I activity.

Insulin-like growth factor-I E-peptide activity is dependent on the IGF-I receptor

Insulin-like growth factor-I (IGF-I) is an essential growth factor that regulates the processes necessary for cell proliferation, differentiation, and survival. The Igf1 gene encodes mature IGF-I and a carboxy-terminal extension called the E-peptide. In rodents, alternative splicing and post-translational processing produce two E-peptides (EA and EB). EB has been studied extensively and has been reported to promote cell proliferation and migration independently of IGF-I and its receptor (IGF-IR), but the mechanism by which EB causes these actions has not been identified. Further, the properties of EA have not been evaluated. Therefore, the goals of this study were to determine if EA and EB possessed similar activity and if these actions were IGF-IR independent. We utilized synthetic peptides for EA, EB, and a scrambled control to examine cellular responses. Both E-peptides increased MAPK signaling, which was blocked by pharmacologic IGF-IR inhibition. Although the E-peptides did not directly induce IGF-IR phosphorylation, the presence of either E-peptide increased IGF-IR activation by IGF-I, and this was achieved through enhanced cell surface bioavailability of the receptor. To determine if E-peptide biological actions required the IGF-IR, we took advantage of the murine C2C12 cell line as a platform to examine the key steps of skeletal muscle proliferation, migration and differentiation. EB increased myoblast proliferation and migration while EA delayed differentiation. The proliferation and migration effects were inhibited by MAPK or IGF-IR signaling blockade. Thus, in contrast to previous studies, we find that E-peptide signaling, mitogenic, and motogenic effects are dependent upon IGF-IR. We propose that the E-peptides have little independent activity, but instead affect growth via modulating IGF-I signaling, thereby increasing the complexity of IGF-I biological activity.

Multifaceted role of insulin-like growth factors and mammalian target of rapamycin in skeletal muscle

This review describes the current literature on the interaction between insulin-like growth factors, endocrine hormones, and branched-chain amino acids on muscle physiology in healthy young individuals and during select pathologic conditions. Emphasis is placed on the mechanism by which physical and hormonal signals are transduced at the cellular level to either grow or atrophy skeletal muscle. The key role of the mammalian target of rapamycin and its ability to respond to hypertrophic and atrophic signals informs our understanding how a combination of physical, nutritional, and pharmacologic therapies may be used in tandem to prevent or ameliorate reductions in muscle mass.

Therapeutic potential of PEGylated insulin-like growth factor I for skeletal muscle disease evaluated in two murine models of muscular dystrophy

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a fatal monogenetic disease with affected males displaying severe and progressive muscle wasting and weakness eventually leading to premature death. Possible therapeutic benefits of insulin-like growth factor I (IGF-I) have been studied extensively in various models of muscle disease and DMD with IGF-I as a mediator of improved skeletal muscle regeneration by enhancing myoblast proliferation and differentiation.

DESIGN

We tested the efficacy of a novel IGF-I analogue, a polyethylene glycol modified IGF-I (PEG-IGF-I), to ameliorate the pathophysiology of muscular dystrophy in two mouse models of DMD. We used mdx mice which lack dystrophin (as in DMD) but exhibit only a relatively mild phenotype, and the dko mouse which is a transgenic model lacking utrophin in addition to dystrophin, and which exhibits a more severe, lethal phenotype like that in DMD.

RESULTS

In young mdx mice, twice-weekly PEG-IGF-I s.c. injections for 6 weeks protected the diaphragm muscle against fatigue and the tibialis anterior (TA) muscle against contraction-induced injury. However, this beneficial effect of PEG-IGF-I was less pronounced in mdx mice when treatment was initiated later in adulthood. In severely affected dko mice PEG-IGF-I treatment did not affect pathophysiological parameters including animal survival.

CONCLUSIONS

These data suggest a therapeutic benefit with PEG-IGF-I treatment only in mild muscle pathologies, since its potential to ameliorate the pathophysiology in models of severe muscular dystrophies was limited. Treatment should be initiated only for mild muscle pathologies if functional benefits are to be realised and therefore may be relevant as a short-term therapy to hasten the functional repair of otherwise healthy muscles after injury.

Early functional muscle regeneration after myotoxic injury in mice is unaffected by nNOS absence

Nitric oxide (NO) is an important signaling molecule produced in skeletal muscle primarily via the neuronal subtype of NO synthase (NOS1, or nNOS). While many studies have reported NO production to be important in muscle regeneration, none have examined the contribution of nNOS-derived NO to functional muscle regeneration (i.e., restoration of the muscle's ability to produce force) after acute myotoxic injury. In the present study, we tested the hypothesis that genetic deletion of nNOS would impair functional muscle regeneration after myotoxic injury in nNOS(-/-) mice. We found that nNOS(-/-) mice had lower body mass, lower muscle mass, and smaller myofiber cross-sectional area and that their tibialis anterior (TA) muscles produced lower absolute tetanic forces than those of wild-type littermate controls but that normalized or specific force was identical between the strains. In addition, muscles from nNOS(-/-) mice were more resistant to fatigue than those of wild-type littermates (P < 0.05). To determine whether deletion of nNOS affected muscle regeneration, TA muscles from nNOS(-/-) mice and wild-type littermates were injected with the myotoxin notexin to cause complete fiber degeneration, and muscle structure and function were assessed at 7 and 10 days postinjury. Myofiber cross-sectional area was lower in regenerating nNOS(-/-) mice than wild-type controls at 7 and 10 days postinjury; however, contrary to our original hypothesis, no difference in force-producing capacity of the TA muscle was evident between the two groups at either time point. Our findings reveal that nNOS is not essential for functional muscle regeneration after acute myotoxic damage.

Platelet-enriched plasma and muscle strain injuries: challenges imposed by the burden of proof

OBJECTIVE

To review the evidence for the clinical utilization of autologous plasma products in the management of muscle strain injuries.

METHOD

Systematic review using EMBASE and MEDLINE (up to March 2010).

RESULTS

There is no level 1, 2, and 3 evidence for the use of autologous plasma products in muscle strain injuries. Furthermore, significant methodological limitations impact on the interpretation of the few published studies in this field.

CONCLUSIONS

Although basic science and the use of recombinant growth factors in animal models support the concept of applying growth factors to acute muscle injuries, it is unclear if this evidence can be directly translated to reflect outcomes from platelet-enriched plasma. There remain a large number of unanswered questions, including the principle questions regarding safety and efficacy, which require appropriate scientific investigation. It is incumbent on sports physicians wishing to enhance athlete care, together with researchers, to search for these answers.

Cationic and anionic lipoplexes inhibit gene transfection by electroporation in vivo

BACKGROUND

Nonviral gene therapy still suffers from low efficiency. Methods that would lead to higher gene expression level of longer duration would be a major advance in this field. Lipidic vectors and physical methods have been investigated separately, and both induced gene expression improvement.

METHODS

We sought to combine both chemical and physical methods. Cationic or anionic lipids can potentially destabilize the cell membrane and could consequently enhance gene delivery by a physical method such as electrotransfer. A plasmid model encoding luciferase was used, either free or associated with differently-charged lipoplexes before electrotransfer.

RESULTS

Electrotransfer alone strongly enhanced gene expression after intramuscular and intradermal injection of naked DNA. On the other hand, cationic and anionic lipoplex formulations decreased gene expression after electrotransfer, whereas poorly-charged thiourea-based complexes, brought no benefit. Pre-injection of the lipids, followed by administration of naked DNA, did not modified gene expression induced by electroporation in the skin.

CONCLUSIONS

The results obtained in the present study suggest that packing of DNA plasmid in lipoplexes strongly decreases the efficiency of gene electrotransfer, independently of the lipoplex charge. Non-aggregating complexes, such as poorly-charged thiourea-based complexes, should be preferred to increase DNA release.

Genetic ablation of TWEAK augments regeneration and post-injury growth of skeletal muscle in mice

Impairment in the regeneration process is a critical determinant for skeletal muscle wasting in chronic diseases and degenerative muscle disorders. Inflammatory cytokines are known to cause significant muscle wasting, however, their role in myofiber regeneration is less clear. In this study we have investigated the role of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) in skeletal muscle regeneration in vivo. Our results show that expression levels of TWEAK and its receptor Fn14 are significantly increased in skeletal muscles of mice after injury. Genetic deletion of TWEAK increased the fiber cross-sectional area and levels of embryonic isoform of myosin heavy chain in regenerating tibial anterior muscle. Conversely, muscle-specific transgenic overexpression of TWEAK reduced the fiber cross-sectional area and levels of the embryonic myosin heavy chain in regenerating muscle. TWEAK induced the expression of several inflammatory molecules and increased interstitial fibrosis in regenerating muscle. Genetic ablation of TWEAK suppressed, whereas overexpression of TWEAK increased, the activation of nuclear factor-kappa B without affecting the activation of Akt or p38 kinase in regenerating myofibers. Primary myoblasts from TWEAK-null mice showed enhanced differentiation in vitro, whereas myoblasts from TWEAK-Tg mice showed reduced differentiation compared with wild-type mice. Collectively, our study suggests that TWEAK negatively regulates muscle regeneration and that TWEAK is a potential therapeutic target to enhance skeletal muscle regeneration in vivo.

Measuring GLUT4 translocation in mature muscle fibers

Skeletal muscle is the major tissue for postprandial glucose disposal. Facilitated glucose uptake into muscle fibers is mediated by increases in surface membrane levels of the glucose transporter GLUT4 via insulin- and/or muscle contraction-mediated GLUT4 translocation. However, the regulatory mechanisms controlling GLUT4 translocation in skeletal muscle have been difficult to characterize at the cell biology level due to muscle tissue complexity. Muscle cell culture models have improved our understanding of GLUT4 translocation and glucose transport regulation, but in vitro muscle models lack many of the characteristics of mature muscle fibers. Thus, the molecular and cellular details of GLUT4 translocation in mature skeletal muscle are deficient. The objective of this review is to highlight how advances in recent experimental approaches translate into an enhanced understanding of the regulation of GLUT4 translocation and glucose transport in mature skeletal muscle.

The insulin-like growth factor (IGF)-I E-peptides are required for isoform-specific gene expression and muscle hypertrophy after local IGF-I production

Insulin-like growth factor I (IGF-I) coordinates proliferation and differentiation in a wide variety of cell types. The igf1 gene not only produces IGF-I, but also generates multiple carboxy-terminal extensions, the E-peptides, through alternative splicing leading to different isoforms. It is not known if the IGF-I isoforms share a common pathway for their actions, or if there are specific actions of each protein. Viral administration of murine IGF-IA, IGF-IB, and mature IGF, which lacked an E-peptide extension, was utilized to identify IGF-I isoform-specific responsive genes in muscles of young growing mice. Microarray analysis revealed responses that were driven by increased IGF-I regardless of the presence of E-peptide, such as Bcl-XL. In contrast, distinct expression patterns were observed after viral delivery of IGF-IA or IGF-IB, which included matrix metalloproteinase 13 (MMP13). Expression of Bcl-XL was prevented when viral administration of the IGF-I isoforms was performed into muscles of MKR mice, which lack functional IGF-I receptors on the muscle fibers. However, MMP13 expression persisted under the same conditions after viral injection of IGF-IB. At 4 mo after viral delivery, expression of IGF-IA or IGF-IB promoted muscle hypertrophy, but viral delivery of mature IGF-I failed to increase muscle mass. These studies provide evidence that local production of IGF-I requires the E-peptides to drive hypertrophy in growing muscle and that both common and unique pathways exist for the IGF-I isoforms to promote biological effects.

Gene doping

Gene doping abuses the legitimate approach of gene therapy. While gene therapy aims to correct genetic disorders by introducing a foreign gene to replace an existing faulty one or by manipulating existing gene(s) to achieve a therapeutic benefit, gene doping employs the same concepts to bestow performance advantages on athletes over their competitors. Recent developments in genetic engineering have contributed significantly to the progress of gene therapy research and currently numerous clinical trials are underway. Some athletes and their staff are probably watching this progress closely. Any gene that plays a role in muscle development, oxygen delivery to tissues, neuromuscular coordination, or even pain control is considered a candidate for gene dopers. Unfortunately, detecting gene doping is technically very difficult because the transgenic proteins expressed by the introduced genes are similar to their endogenous counterparts. Researchers today are racing the clock because assuring the continued integrity of sports competition depends on their ability to develop effective detection strategies in preparation for the 2012 Olympics, which may mark the appearance of genetically modified athletes.

Validated treatments and therapeutics prospectives regarding pharmacological products for sarcopenia

Loss of physical function in older adults may be, at least in part, explained by sarcopenia, a phenomenon characterized by a reduction in number and size of muscle fibres and by increase in interstitial fat and connective tissue. Lifestyle intervention (i.e. physical activity and nutrition) have shown to impact on sarcopenia. However, several drugs were suggested, with various levels of scientific evidence, to have an impact on muscle outcomes. In this study we reviewed the effect of six classes of drugs on sarcopenia and muscular outcomes in older adults. We decided to focus our review on two commonly drugs which have recently showed promising effects on muscular outcomes in older adults (ACE inhibitors and statins) and on four drugs whose effect on skeletal muscle was already largely studied (creatine, Growth Hormone, testosterone, estrogens and tibolone).

The role of systemic inflammation in age-related muscle weakness and wasting

Ageing is associated with a slow, but progressive muscle weakness, which is largely attributable to muscle wasting. A diminished function of satellite cells at old age may hamper preservation and repair from (contraction)-induced injury and contribute to the age-related muscle wasting. Satellite cell function may be affected by circulating factors, as muscle regeneration in old mice sharing the circulation of young mice is not impaired. Chronic low-grade systemic inflammation in old organisms may be that environmental factor. Indeed, the inflammatory cytokine tumor necrosis factor-alpha (TNFalpha) negatively affects the muscle regenerating capacity. TNFalpha destabilizes MyoD, a muscle-specific transcription factor involved in satellite cell proliferation and differentiation, and induces apoptosis of satellite cells, particularly at old age. Here it is proposed that some of these effects are mediated by TNFalpha-induced expression of inhibitors of differentiation proteins. Yet, the increase in TNFalpha during the normal inflammatory response helps, rather than impairs, the repair process. This apparent contradiction may be resolved by the fact that the effects of TNFalpha are concentration and time dependent. Thus, the negative effect of systemic inflammation on muscle strength at old age may only become apparent when it exceeds a certain threshold and persists for a prolonged period.

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.

IGF-1-overexpressing mesenchymal stem cells accelerate bone marrow stem cell mobilization via paracrine activation of SDF-1alpha/CXCR4 signaling to promote myocardial repair

We hypothesized that mesenchymal stem cells (MSCs) overexpressing insulin-like growth factor (IGF)-1 showed improved survival and engraftment in the infarcted heart and promoted stem cell recruitment through paracrine release of stromal cell-derived factor (SDF)-1alpha. Rat bone marrow-derived MSCs were used as nontransduced ((Norm)MSCs) or transduced with adenoviral-null vector ((Null)MSCs) or vector encoding for IGF-1 ((IGF-1)MSCs). (IGF-1)MSCs secreted higher IGF-1 until 12 days of observation (P<0.001 versus (Null)MSCs). Molecular studies revealed activation of phosphoinositide 3-kinase, Akt, and Bcl.xL and inhibition of glycogen synthase kinase 3beta besides release of SDF-1alpha in parallel with IGF-1 expression in (IGF-1)MSCs. For in vivo studies, 70 muL of DMEM without cells (group 1) or containing 1.5x10(6) (Null)MSCs (group 2) or (IGF-1)MSCs (group 3) were implanted intramyocardially in a female rat model of permanent coronary artery occlusion. One week later, immunoblot on rat heart tissue (n=4 per group) showed elevated myocardial IGF-1 and phospho-Akt in group 3 and higher survival of (IGF-1)MSCs (P<0.06 versus (Null)MSCs) (n=6 per group). SDF-1alpha was increased in group 3 animal hearts (20-fold versus group 2), with massive mobilization and homing of ckit(+), MDR1(+), CD31(+), and CD34(+) cells into the infarcted heart. Infarction size was significantly reduced in cell transplanted groups compared with the control. Confocal imaging after immunostaining for myosin heavy chain, actinin, connexin-43, and von Willebrand factor VIII showed extensive angiomyogenesis in the infarcted heart. Indices of left ventricular function, including ejection fraction and fractional shortening, were improved in group 3 as compared with group 1 (P<0.05). In conclusion, the strategy of IGF-1 transgene expression induced massive stem cell mobilization via SDF-1alpha signaling and culminated in extensive angiomyogenesis in the infarcted heart.

Anabolic agents for improving muscle regeneration and function after injury

1. In the present review, we describe how muscles can be injured by external factors, internal factors or during the performance of some actions during sports. In addition, we describe the injury to a muscle that occurs when its blood supply is interrupted, an occurrence common in clinical settings. An overview of muscle regeneration is presented, as well as a discussion of some of the potential complications that can compromise successful muscle repair and lead to impaired function and permanent disability. 2. Improving muscle regeneration is important for hastening muscle repair and restoring muscle function and the present review describes ways in which this can be achieved. We describe recent advances in tissue engineering that offer considerable promise for treating muscle damage, but highlight the fact that these techniques require rigorous evaluation before they can become mainstream clinical treatments. 3. Growth-promoting agents are purported to increase the size of existing and newly regenerating muscle fibres and, therefore, could be used to improve muscle function if administered at appropriate times during the repair process. The present review provides an update on the efficacy of some growth-promoting agents, including anabolic steroids, insulin-like growth factor-I (IGF-I) and beta(2)-adrenoceptor agonists, to improve muscle function after injury. Although these approaches have clinical merit, a better understanding of the androgenic, IGF-I and b-adrenoceptor signalling pathways in skeletal muscle is important if we are to devise safe and effective therapies to enhance muscle regeneration and function after injury.