Effects of Nandrolone Decanoate on Skeletal Muscle and Neuromuscular Junction of Sedentary and Exercised Rats

Background and Objectives: Nandrolone decanoate (ND) is the most widely used among the anabolic androgenic steroids (AAS), synthetic substances derived from testosterone, to improve muscular and health gains associated with exercises. The AAS leads to physical performance enhancement and presents anti-aging properties, but its abuse is associated with several adverse effects. Supraphysiological doses of AAS with or without physical exercise can cause morphological and functional alterations in neuromuscular interactions. This study aims to investigate the effects of ND supraphysiological doses in neuromuscular interactions, focusing on the soleus muscle and its neuromuscular junctions (NMJs) in rats, associated or not with physical exercise. Materials and Methods: Forty male Sprague Dawley rats were divided into four groups: sedentary and exercised groups, with or without ND at the dose of 10 mg/kg/week. The animals were treated for eight weeks, with intramuscular injections, and the soleus muscle was collected for morphological analyses. Results: The supraphysiological doses of ND in the sedentary group caused muscle degeneration, evidenced by splitting fibers, clusters of small fibers, irregular myofibrils, altered sarcomeres, an increase in collagen deposition and in the number of type I muscle fibers (slow-twitch) and central nuclei, as well as a decrease in fibers with peripheral nuclei. On the other hand, in the ND exercise group, there was an increase in the NMJs diameter with scattering of its acetylcholine receptors, although no major morphological changes were found in the skeletal muscle. Thus, the alterations caused by ND in sedentary rats were partially reversed by physical exercise. Conclusions: The supraphysiological ND exposure in the sedentary rats promoted an increase in muscle oxidative pattern and adverse morphological alterations in skeletal muscle, resulting from damage or post-injury regeneration. In the ND-exercised rats, no major morphological changes were found. Thus, the physical exercise partially reversed the alterations caused by ND in sedentary rats.

Biomarkers for Duchenne muscular dystrophy progression: impact of age in the mdx tongue spared muscle

BACKGROUND

Duchenne muscular dystrophy (DMD) is a severe form of muscular dystrophy without an effective treatment, caused by mutations in the DMD gene, leading to the absence of dystrophin. DMD results in muscle weakness, loss of ambulation, and death at an early age. Metabolomics studies in mdx mice, the most used model for DMD, reveal changes in metabolites associated with muscle degeneration and aging. In DMD, the tongue muscles exhibit unique behavior, initially showing partial protection against inflammation but later experiencing fibrosis and loss of muscle fibers. Certain metabolites and proteins, like TNF-α and TGF-β, are potential biomarkers for dystrophic muscle characterization.

METHODS

To investigate disease progression and aging, we utilized young (1 month old) and old (21-25 months old) mdx and wild-type tongue muscles. Metabolite changes were analyzed using 1H nuclear magnetic resonance, while TNF-α and TGF-β were assessed using Western blotting to examine inflammation and fibrosis. Morphometric analysis was conducted to assess the extent of myofiber damage between groups.

RESULTS

The histological analysis of the mid-belly tongue showed no differences between groups. No differences were found between the concentrations of metabolites from wild-type or mdx whole tongues of the same age. The metabolites alanine, methionine, and 3-methylhistidine were higher, and taurine and glycerol were lower in young tongues in both wild type and mdx (p < 0.001). The metabolites glycine (p < 0.001) and glutamic acid (p = 0.0018) were different only in the mdx groups, being higher in young mdx mice. Acetic acid, phosphocreatine, isoleucine, succinic acid, creatine, and the proteins TNF-α and TGF-β had no difference in the analysis between groups (p > 0.05).

CONCLUSIONS

Surprisingly, histological, metabolite, and protein analysis reveal that the tongue of old mdx remains partially spared from the severe myonecrosis observed in other muscles. The metabolites alanine, methionine, 3-methylhistidine, taurine, and glycerol may be effective for specific assessments, although their use for disease progression monitoring should be cautious due to age-related changes in the tongue muscle. Acetic acid, phosphocreatine, isoleucine, succinate, creatine, TNF-α, and TGF-β do not vary with aging and remain constant in spared muscles, suggesting their potential as specific biomarkers for DMD progression independent of aging.

Biomarkers for Duchenne muscular dystrophy progression: impact of age in the mdx tongue spared muscle

Background: Duchenne muscular dystrophy (DMD) is a severe form of muscular dystrophy without an effective treatment, caused by mutations in the DMD gene, leading to the absence of dystrophin. DMD results in muscle weakness, loss of ambulation and death at an early age. Metabolomics studies in mdx mice, the most used model for DMD, reveal changes in metabolites associated with muscle degeneration and aging. In DMD, the tongue muscles exhibit unique behavior, initially showing partial protection against inflammation but later experiencing fibrosis and loss of muscle fibers. Certain metabolites and proteins, like TNF-α and TGF-β, are potential biomarkers for dystrophic muscle characterization. Methods: To investigate disease progression and aging, we utilized young (1-month old) and old (21-25 months old) mdx and wild-type mice. Metabolite changes were analyzed using 1-H Nuclear Magnetic Resonance, while TNF-α and TGF-β were assessed using Western blotting to examine inflammation, and fibrosis. Morphometric analysis was conducted to assess the extent of myofiber damage between groups. Results: The histological analysis of the tongue showed no differences between groups. No differences were found between the concentrations of metabolites from wild type or mdx animals of the same age. The metabolites alanine, methionine, 3-methylhistidine were higher, and taurine and glycerol were lower in young animals in both wild type and mdx (p < 0.001). The metabolites glycine (p < 0.001) and glutamic acid (p = 0.0018) were different only in the mdx groups, being higher in young mdx mice. Acetic acid, phosphocreatine, isoleucine, succinic acid, creatine and the proteins TNF-α and TGF-β had no difference in the analysis between groups (p > 0.05). Conclusions: Surprisingly, histological and protein analysis reveals that the tongue of young and old mdx animals is protected from severe myonecrosis observed in other muscles. The metabolites alanine, methionine, 3-methylhistidine, taurine, and glycerol may be effective for specific assessments, although their use for disease progression monitoring should be cautious due to age-related changes. Acetic acid, phosphocreatine, isoleucine, succinate, creatine, TNF-α, and TGF-β do not vary with aging and remain constant in spared muscles, suggesting their potential as specific biomarkers for DMD progression independent of aging.

Statin exposure during pregnancy promotes neuromuscular junction alterations in post-partum Wistar rats

INTRODUCTION/AIMS

The mechanisms that underlie the pathogenesis of statin-associated muscle symptoms (SAMS) remain unclear. Pregnancy is associated with increased cholesterol levels. Statins may be useful during pregnancy, but their safety is uncertain. Hence, we investigated the post-partum effects of exposure to rosuvastatin and simvastatin during pregnancy in Wistar Rats, targeting the neuromuscular structures.

METHODS

Twenty-one pregnant Wistar rats were divided into three groups: control (C) treated with vehicle (dimethylsulfoxide + dH20); simvastatin (S) 62.5 mg/kg/day; and rosuvastatin (R) 10 mg/kg/day. Gavage was performed daily from the 8th to the 20th gestational day. At weaning, the post-partum mother tissues were collected and subjected to morphological and morphometric analysis of the soleus muscle, associated neuromuscular junctions (NMJs), and the sciatic nerve; protein quantification; quantification of the cholesterol and creatine kinase in the serum; and intramuscular collagen analysis.

RESULTS

An increase in morphometric parameters (area, maximum and minimum diameter, Feret diameter and minimum Feret) was observed in NMJs from the S and R groups in comparison with the C group, and there was also a loss of common NMJ circularity. The number of myofibers with central nuclei was higher in S (17 ± 3.9 p = 0.0083) and R (18.86 ± 14.42 p = 0.0498) than in C (6.8 ± 2.6).

DISCUSSION

Gestational exposure to statins induced post-partum NMJ morphology alterations in soleus muscle, which may be caused by the remodeling of clusters of nicotinic acetylcholine receptors. This may be associated with the development and progression of SAMS observed in clinical practice. This article is protected by copyright. All rights reserved.

Acetylcholine receptors of the neuromuscular junctions present normal distribution after peripheral nerve injury and repair through nerve guidance associated with fibrin biopolymer

Peripheral nerve injuries (PNI) lead to alterations in the Agrin-LRP4-MuSK pathway. This results in disaggregation of AChRs and change from epsilon (mature, innervated) to gamma (immature, denervated) subunit. Tubulization technique has been shown to be effective for PNI repair and it also allows the use of adjuvants, such as fibrin biopolymer (FB). This study evaluated the effect of the association of tubulization with FB after PNI on AChRs and associated proteins. Fifty-two adults male Wistar rats were used, distributed in 4 experimental groups: Sham Control (S), Denervated Control (D); Tubulization (TB) and Tubulization + Fibrin Biopolymer (TB+FB). Catwalk was performed every 15 days. Ninety days after surgery the right soleus muscles and ischiatic nerves were submitted to the following analyses: (a) morphological and morphometric analysis of AChRs by confocal microscopy; (b) morphological and morphometric analysis of the ischiatic nerve; (c) protein quantification of AChRs: alpha, gama, and epsilon, of Schwann cells, agrin, LRP4, MuSK, rapsyn, MMP3, MyoD, myogenin, MURF1 and atrogin-1. The main results were about the NMJs that in the TB+FB group presented morphological and morphometric approximation (compactness index; area of the AChRs and motor plate) to the S group. In addition, there were also an increase of S100 and AChRε protein expression and a decrease of MyoD. These positive association resulted in AChRs stabilization that potentiate the neuromuscular regeneration, which strengthens the use of TB for severe injuries repair and the beneficial effect of FB, along with tubulization technique.

Beta-hydroxy-beta-methylbutyrate associated with low-intensity exercise training improves skeletal muscle regeneration through the IGF-Akt pathway

The effect of beta-hydroxy-beta-methylbutyrate (HMB) supplementation associated with exercise training at different intensities and frequencies on skeletal muscle regeneration of muscle-injured rats was investigated. Male Wistar rats were divided into sedentary and trained groups. The sedentary groups were subdivided into non-injured (SED-Ct), non-injured supplemented with HMB (SED-Ct-HMB), injured (SED), and injured with HMB (SED-HMB), and the trained groups were injured, supplemented with HMB, and then divided into training three times a week without load (HT3) or with load (HT3L) and training five times a week without load (HT5) and with load (HT5L). The rats received a daily dose of HMB associated with 60 min of swimming with or without 5% body mass load for 14 days. On the 15th day, cryoinjury was performed in the right tibialis anterior muscle (TA), and 48 h later, supplementation and training continued for 15 days. After the last session, the TA was dissected and a cross-sectional area (CSA) of muscle fibers was used to determine the percentage of CSA fibers and connective tissue (%CT), as well as the total and phosphorylated protein contents. SED-HMB showed increased CSA and decreased %CT and TGF-β when compared to SED. HT3 showed increased CSA and reduced %CT accompanied by increased IGF-1/Akt, myogenin, and MuRF1, and decreased TGF-β. The CSA of HT5L also increased, but at the cost of a higher %CT compared to the other groups. Our results demonstrated that HMB associated with training without load and with lower frequency per week may be a valuable strategy for skeletal muscle regeneration.

High-fat diet suppresses the positive effect of creatine supplementation on skeletal muscle function by reducing protein expression of IGF-PI3K-AKT-mTOR pathway

High-fat (HF) diets in combination with sedentary lifestyle represent one of the major public health concerns predisposing to obesity and diabetes leading to skeletal muscle atrophy, decreased fiber diameter and muscle mass with accumulation of fat tissue resulting in loss of muscle strength. One strategy to overcome the maleficent effects of HF diet is resistance training, a strategy used to improve muscle mass, reverting the negative effects on obesity-related changes in skeletal muscle. Together with resistance training, supplementation with creatine monohydrate (CrM) in the diet has been used to improve muscle mass and strength. Creatine is a non-essential amino acid that is directly involved in the cross-bridge cycle providing a phosphate group to ADP during the initiation of muscle contraction. Besides its antioxidant and anti-inflammatory effects CrM also upregulates IGF-1 resulting in hyperthophy with an increase in muscle function. However, it is unknown whether CrM supplementation during resistance training would revert the negative effects of high-fat diet on the muscle performance. During 8 weeks we measured muscle performance to climb a 1.1m and 80° ladder with increasing load on trained rats that had received standard diet or high-fat diet, supplemented or not with CrM. We observed that the CrM supplementation up-regulated IGF-1 and phospho-AKT protein levels, suggesting an activation of the IGF1-PI3K-Akt/PKB-mTOR pathway. Moreover, despite the CrM supplementation, HF diet down-regulated several proteins of the IGF1-PI3K-Akt/PKB-mTOR pathway, suggesting that diet lipid content is crucial to maintain or improve muscle function during resistance training.

Laser de baixa intensidade favorece a regeneração muscular em modelo experimental desnutrido e recuperado

RESUMO A terapia por laser de baixa intensidade (Low-Level Laser Therapy - LLLT) é utilizada com frequência nas lesões musculares, mas precisa ser investigada em modelo de desnutrição. O objetivo desse estudo foi analisar os efeitos da LLLT na regeneração muscular de ratos submetidos à desnutrição e recuperação proteica. Foram utilizados 40 ratos Wistar, recém-desmamados, divididos em grupo controle (C), que consumiu ração normoproteica (14% caseína), e grupo desnutrido (D), que consumiu ração hipoproteica (6% caseína) por 45 dias e ração normoproteica até o final do experimento. Posteriormente, o músculo tibial anterior direito foi criolesado e tratado com LLLT (AsGaAl 830nm, 30mW, 20J/cm²), três vezes por semana, por 7 e 21 dias. Houve redução da área de inflamação/regeneração no grupo C21 comparado ao D21 (p<0,05), sendo mais evidente com a LLLT (C21L e D21L). O conteúdo de TNF-α foi reduzido após 21 dias da lesão. A área de densidade de tecido conjuntivo (ADTC) foi menor nos grupos C21 e C21L comparados aos respectivos grupos desnutridos (p<0,05). A LLLT reduziu a ADTC no grupo D21L quando comparado do D21 (p<0,05), porém o conteúdo de TGF-β1 não foi influenciado. A área de secção transversa (AST) da fibra muscular aumentou nos grupos 21 dias. A m-TOR apresentou maior conteúdo no grupo C21L quando comparado ao D21L (p<0,05). Concluiu-se que a LLLT favoreceu a regeneração muscular na fase tardia no modelo experimental de desnutrição pós-natal e posterior recuperação proteica.

Evaluation of skeletal muscle regeneration in experimental model after malnutrition

The aim of this study was to analyze muscle regeneration after cryoinjury in the tibialis anterior muscle of young rats that were malnourished and then recovered. Forty Wistar rats were divided into a nourished group that received a normal protein diet (14% casein) for 90 days and a malnourished and recovered rats group (MR) that was submitted to 45 days of malnutrition with a hypoproteic diet (6% casein) followed by 45 days of a normal protein diet (14% casein). After the recovery period, all of the animals underwent cryoinjury in the right tibialis anterior muscle and euthanasia after 7, 14 and 21 days. The amount of connective tissue and the inflammation area was higher in the malnutrition recovered injury MR group (MRI) at 14 days post-injury (p < 0.05). Additionally, the cross-sectional area (CSA) of the regenerated fibers was decreased in the MRI (p < 0.05). The MyoD and myogenin protein levels were higher in the nourished injury group. Similar levels of TGF-β1 were found between groups. The proposed malnutrition protocol was effective in showing delayed changes in the regeneration process of the tibialis anterior muscle of young rats. Furthermore, we observed a delay in muscle repair even after nutritional recovery.

Isobaric Tagging-Based Quantification for Proteomic Analysis: A Comparative Study of Spared and Affected Muscles from mdx Mice at the Early Phase of Dystrophy

Duchenne muscular dystrophy (DMD) is the most common childhood myopathy, characterized by muscle loss and cardiorespiratory failure. While the genetic basis of DMD is well established, secondary mechanisms associated with dystrophic pathophysiology are not fully clarified yet. In order to obtain new insights into the molecular mechanisms of muscle dystrophy during earlier stages of the disease, we performed a comparative proteomic profile of the spared extraocular muscles (EOM) vs. affected diaphragm from the mdx mice, using a label based shotgun proteomic approach. Out of the 857 identified proteins, 42 to 62 proteins had differential abundance of peptide ions. The calcium-handling proteins sarcalumenin and calsequestrin-1 were increased in control EOM compared with control DIA, reinforcing the view that constitutional properties of EOM are important for their protection against myonecrosis. The finding that galectin-1 (muscle regeneration), annexin A1 (anti-inflammatory) and HSP 47 (fibrosis) were increased in dystrophic diaphragm provides novel insights into the mechanisms through which mdx affected muscles are able to counteract dystrophy, during the early stage of the disease. Overall, the shotgun technique proved to be suitable to perform quantitative comparisons between distinct dystrophic muscles and allowed the suggestion of new potential biomarkers and drug targets for dystrophinopaties.

Mechanical, biochemical and morphometric alterations in the femur of mdx mice

The bone tissue abnormalities observed in patients with Duchenne muscular dystrophy are frequently attributed to muscle weakness. In this condition, bones receive fewer mechanical stimuli, compromising the process of bone modeling. In the present study we hypothesize that other factors inherent to the disease might be associated with bone tissue impairment, irrespective of the presence of muscle impairment. Mdx mice lack dystrophin and present cycles of muscle degeneration/regeneration that become more intense in the third week of life. As observed in humans with muscular dystrophy, bone tissue abnormalities were found in mdx mice during more intense muscle degeneration due to age. Under these circumstances, muscle deficit is probably one of the factors promoting these changes. To test our hypothesis, we investigated the changes that occur in the femur of mdx mice at 21 days of age when muscle damage is still not significant. The mechanical (structural and material) and biochemical properties and morphometric characteristics of the femur of mdx and control animals were evaluated. The results demonstrated a lower strength, stiffness and energy absorption capacity in mdx femurs. Higher values for structural (load and stiffness) and material (stress, elastic modulus and toughness) properties were observed in the control group. Mdx femurs were shorter and were characterized by a smaller cortical area and thickness and a smaller area of epiphyseal trabecular bone. The hydroxyproline content was similar in the two groups, but there was a significant difference in the Ca/P ratios. Thermogravimetry showed a higher mineral matrix content in cortical bone of control animals. In conclusion, femurs of mdx mice presented impaired mechanical and biochemical properties as well as changes in collagen organization in the extracellular matrix. Thus, mdx mice developed femoral osteopenia even in the absence of significant muscle fiber degeneration. This weakness of the mdx femur is probably due to genetic factors that are directly or indirectly related to dystrophin deficiency.

Calcium-binding proteins in skeletal muscles of the mdx mice: potential role in the pathogenesis of Duchenne muscular dystrophy

Duchenne muscular dystrophy is one of the most common hereditary diseases. Abnormal ion handling renders dystrophic muscle fibers more susceptible to necrosis and a rise in intracellular calcium is an important initiating event in dystrophic muscle pathogenesis. In the mdx mice, muscles are affected with different intensities and some muscles are spared. We investigated the levels of the calcium-binding proteins calsequestrin and calmodulin in the non-spared axial (sternomastoid and diaphragm), limb (tibialis anterior and soleus), cardiac and in the spared extraocular muscles (EOM) of control and mdx mice. Immunoblotting analysis showed a significant increase of the proteins in the spared mdx EOM and a significant decrease in the most affected diaphragm. Both proteins were comparable to the cardiac muscle controls. In limb and sternomastoid muscles, calmodulin and calsequestrin were affected differently. These results suggest that differential levels of the calcium-handling proteins may be involved in the pathogenesis of myonecrosis in mdx muscles. Understanding the signaling mechanisms involving Ca(2+)-calmodulin activation and calsequestrin expression may be a valuable way to develop new therapeutic approaches to the dystrophinopaties.

Alterations in the permeability of dystrophic fibers during neuromuscular junction development

In the mdx mice, lack of dystrophin leads to increases in calcium influx and myonecrosis, followed by muscle regeneration. Synapse elimination is faster in mdx than in controls, suggesting that increases in calcium influx during development could be involved. In the present study, we evaluated whether dystrophic fibers display changes in permeability to Evans Blue Dye (EBD) during development of the neuromuscular junction. EBD is a sensitive label for the early detection of increased myofiber permeability and sarcolemmal damage. After intraperitoneal injection of EBD, sternomastoid (STN) and tibialis anterior (T. anterior) muscles were analyzed with fluorescence microscopy. At 01, 07 and 14 days of age, STN and TA mdx myofibers were not stained with EBD. At 21 days of age, positive labeling of TA and STN mdx myofibers was seen, suggesting permeability modification and myonecrosis. Adult muscles showed a decrease (T. anterior) or no changes (STN) in the amount of EBD-positive fibers. These results suggest that there is no sarcolemmal damage detected by EBD during development of dystrophic neuromuscular junctions and other factors may contribute to the earlier synapse elimination seen in dystrophic muscle.