The omega-3 fatty acid, eicosapentaenoic acid (EPA), prevents the damaging effects of tumour necrosis factor (TNF)-alpha during murine skeletal muscle cell differentiation

Eicosapentaenoic acid-mediated activation of PGAM2 regulates skeletal muscle growth and development via the PI3K/AKT pathway

Eicosapentaenoic acid regulates glucose uptake in skeletal muscle and significantly affects whole-body energy metabolism. However, the underlying molecular mechanism remains unclear. Here we report that eicosapentaenoic acid activates phosphoglycerate mutase 2, which mediates the conversion of 2-phosphoglycerate into 3-phosphoglycerate. This enzyme plays a pivotal role in glycerol degradation, thereby facilitating the proliferation and differentiation of satellite cells in skeletal muscle. Interestingly, phosphoglycerate mutase 2 inhibits mitochondrial metabolism, promoting the formation of fast-type muscle fibers. Treatment with eicosapentaenoic acid and phosphoglycerate mutase 2 knockdown induced opposite transcriptomic changes, most of which were enriched in the PI3K-AKT signaling pathway. Phosphoglycerate mutase 2 activated the PI3K-AKT signaling pathway, which inhibited the phosphorylation of FOXO1, and, in turn, inhibited mitochondrial function and promoted the formation of fast-type muscle fibers. Our results suggest that eicosapentaenoic acid promotes skeletal muscle growth and regulates glucose metabolism by targeting phosphoglycerate mutase 2 and activating the PI3K/AKT signaling pathway.

RNA Sequencing Reveals the Inhibitory Effect of High Levels of Arachidonic Acid and Linoleic Acid on C2C12 Differentiation and Myogenic Biomarkers

Over the past three decades, studies have shown that consuming polyunsaturated fatty acids (PUFAs) can enhance animal and human health and welfare through biological, biochemical, pathological, and pharmacological impacts. Furthermore, omega-6 plays key roles in the cardiopulmonary system, including promoting airway relaxation and inhibiting atherosclerosis and hypertension. However, findings from investigations of the effects of omega-6 fatty acids on molecular and cellular activity and discussions on their influence on biomarkers are still unclear. Therefore, the present study aimed to evaluate omega-6 fatty acids, the arachidonic acid (AA), and linoleic acid (LA) effects on C2C12 proliferation, myogenesis morphology, and relative myogenic biomarker expression through the Wnt pathway. C2C12 cells were cultured with and without 25, 50, 100, and 150 µM of LA and AA and then subjected to CCK8, Giemsa staining, RT qPCR, Western blotting, and RNA Sequencing. The CCK8 Assay results showed that 25, 50, 100, and 150 µM LA significantly decreased the viability after 72 h for 25, 50, 100, and 150 µM concentrations. Also, AA supplementation decreased cell viability after 24 h for 150 µM, 48 h for 150 µM, and 72 h for 50, 100, and 150 µM concentrations. Moreover, the LA and AA inhibitory effects noticed through Gimesa staining were morphological changes during myoblast differentiation. Both LA and AA showed inhibiting IGF1, Cola1, Col6a2, Col6a1, Itga10, Itga11, SFRP2, DAAM2, and NKD2 effects; however, the depressing effect was higher for AA compared to LA. The previous results were confirmed through Western blotting, which showed that 50 µM LA and AA significantly reduced DAAM2 and SFRP2 protein levels compared to the control. Regarding RNA sequencing results, LA and AA increased the number of differentially expressed (DE) Mt-rRNA and snoRNA; however, the numbers of lncRNA detected decreased compared to the control. Our findings demonstrate that high and moderate LA and AA concentrations reduce primary myoblast proliferation and differentiation. Also, they highlight novel biomarkers and regulatory factors to improve our understanding of how the nutrition of fatty acids can control and modulate the myogenesis and differentiation process through different biomarker families.

Potential of Fatty Acids in Treating Sarcopenia: A Systematic Review

This paper presents a systematic review of studies investigating the effects of fatty acid supplementation in potentially preventing and treating sarcopenia. PubMed, Embase, and Web of Science databases were searched using the keywords 'fatty acid' and 'sarcopenia'. Results: A total of 14 clinical and 11 pre-clinical (including cell and animal studies) studies were included. Of the 14 clinical studies, 12 used omega-3 polyunsaturated fatty acids (PUFAs) as supplements, 1 study used ALA and 1 study used CLA. Seven studies combined the use of fatty acid with resistant exercises. Fatty acids were found to have a positive effect in eight studies and they had no significant outcome in six studies. The seven studies that incorporated exercise found that fatty acids had a better impact on elderlies. Four animal studies used novel fatty acids including eicosapentaenoic acid, trans-fatty acid, and olive leaf extraction as interventions. Three animal and four cell experiment studies revealed the possible mechanisms of how fatty acids affect muscles by improving regenerative capacity, reducing oxidative stress, mitochondrial and peroxisomal dysfunctions, and attenuating cell death. Conclusion: Fatty acids have proven their value in improving sarcopenia in pre-clinical experiments. However, current clinical studies show controversial results for its role on muscle, and thus the mechanisms need to be studied further. In the future, more well-designed randomized controlled trials are required to assess the effectiveness of using fatty acids in humans.

A Brief Narrative Review of the Underlying Mechanisms Whereby Omega-3 Fatty Acids May Influence Skeletal Muscle: From Cell Culture to Human Interventions

Skeletal muscle is essential for human locomotion as well as maintaining metabolic homeostasis. Age-related reduction in skeletal muscle mass, strength, and function (i.e., sarcopenia) is a result of pathophysiological processes that include inflammation, alteration of molecular signaling for muscle protein synthesis and degradation, changes in insulin sensitivity, as well as altered skeletal muscle satellite cell activity. Finding strategies to mitigate skeletal muscle loss with age is deemed paramount as the percentage of the population continues to shift towards having more older adults with sarcopenia. Recent research indicates omega-3 fatty acid supplementation can influence anabolic or catabolic pathways in skeletal muscle. Our brief review will provide a synopsis of some underlying mechanisms that may be attributed to omega-3 fatty acid supplementation's effects on skeletal muscle. We will approach this review by focusing on cell culture, animal (pre-clinical models), and human studies evaluating omega-3 fatty acid supplementation, with suggestions for future research. In older adults, omega-3 fatty acids may possess some potential to modify pathophysiological pathways associated with sarcopenia; however, it is highly likely that omega-3 fatty acids need to be combined with other anabolic interventions to effectively ameliorate sarcopenia.

Linoleic acid-induced ANGPTL4 inhibits C2C12 skeletal muscle differentiation by suppressing Wnt/β-catenin

Skeletal muscle differentiation is an essential process in embryonic development as well as regeneration and repair throughout the lifespan. It is well-known that dietary fat intake impacts biological and physiological function in skeletal muscle, however, understanding of the contribution of nutritional factors in skeletal muscle differentiation is limited. Therefore, the objective of the current study was to evaluate the effects of free fatty acids (FFAs) on skeletal muscle differentiation in vitro. We used C2C12 murine myoblasts and treated them with various FFAs, which revealed a unique response of angiopoietin-like protein-4 (ANGPTL4) with linoleic acid (LA) treatment that was associated with reduced differentiation. LA significantly inhibited myotube formation and lowered the protein expression of myogenic regulatory factors, including MyoD and MyoG and increased Pax7 during cell differentiation. Next, recombinant ANGPTL4 protein or siRNA knockdown of ANGPTL4 was employed to examine its role in skeletal muscle differentiation, and we confirmed that ANGPTL4 knockdown at day 2 and -6 of differentiation restored myotube formation in the presence of LA. RNA-sequencing analysis revealed that ANGPTL4-mediated inhibition of skeletal muscle differentiation at day 2 as well as LA at day 2 or -6 led to a reduction in Wnt/β-catenin signaling pathways. We confirmed that LA reduced Wnt11 and Axin2 while increasing expression of the Wnt inhibitor, Dkk2. ANGPTL4 knockdown increased β-catenin protein in the nucleus in response to LA and increased Axin2 and Wnt11 expression. Taken together, these results demonstrate that LA induced ANGPTL4 inhibits C2C12 differentiation by suppressing Wnt/β-catenin signaling.

The Influence of n-3PUFA Supplementation on Muscle Strength, Mass, and Function: A Systematic Review and Meta-Analysis

The effects of omega 3 polyunsaturated fatty acids (n-3PUFA) supplementation on skeletal muscle are currently unclear. The purpose of this systematic review was to synthesize all available evidence regarding the influence of n-3PUFA supplementation on muscle mass, strength, and function in healthy young and older adults. Four databases were searched (Medline, Embase, Cochrane CENTRAL, and SportDiscus). Predefined eligibility criteria were determined according to Population, Intervention, Comparator, Outcomes, and Study Design. Only peer-reviewed studies were included. The Cochrane RoB2 Tool and the NutriGrade approach were used to access risk of bias and certainty in evidence. Effect sizes were calculated using pre-post scores and analyzed using a three-level, random-effects meta-analysis. When sufficient studies were available, subanalyses were performed in the muscle mass, strength, and function outcomes according to participant's age (<60 or ≥60 years), supplementation dosage (<2 or ≥2 g/day), and training intervention ("resistance training" vs. "none or other"). Overall, 14 individual studies were included, total 1443 participants (913 females; 520 males) and 52 outcomes measures. Studies had high overall risk of bias and consideration of all NutriGrade elements resulted in a certainty assessment of moderate meta-evidence for all outcomes. n-3PUFA supplementation had no significant effect on muscle mass (standard mean difference [SMD] = 0.07 [95% CI: -0.02, 0.17], P = 0.11) and muscle function (SMD = 0.03 [95% CI: -0.09, 0.15], P = 0.58), but it showed a very small albeit significant positive effect on muscle strength (SMD = 0.12 [95% CI: 0.006, 0.24], P = 0.04) in participants when compared with placebo. Subgroup analyses showed that age, supplementation dose, or cosupplementation alongside resistance training did not influence these responses. In conclusion, our analyses indicated that n-3PUFA supplementation may lead to very small increases in muscle strength but did not impact muscle mass and function in healthy young and older adults. To our knowledge, this is the first review and meta-analysis investigating whether n-3PUFA supplementation can lead to increases in muscle strength, mass, and function in healthy adults. Registered protocol: doi.org/10.17605/OSF.IO/2FWQT.

Coapplication of Magnesium Supplementation and Vibration Modulate Macrophage Polarization to Attenuate Sarcopenic Muscle Atrophy through PI3K/Akt/mTOR Signaling Pathway

Sarcopenia is an age-related geriatric syndrome characterized by the gradual loss of muscle mass and function. Low-magnitude high-frequency vibration (LMHFV) was shown to be beneficial to structural and functional outcomes of skeletal muscles, while magnesium (Mg) is a cofactor associated with better indices of skeletal muscle mass and strength. We hypothesized that LMHFV, Mg and their combinations could suppress inflammation and sarcopenic atrophy, promote myogenesis via PI3k/Akt/mTOR pathway in senescence-accelerated mouse P8 (SAMP8) mice and C2C12 myoblasts. Results showed that Mg treatment and LMHFV could significantly decrease inflammatory expression (C/EBPα and LYVE1) and modulate a CD206-positive M2 macrophage population at month four. Mg treatment also showed significant inhibitory effects on FOXO3, MuRF1 and MAFbx mRNA expression. Coapplication showed a synergistic effect on suppression of type I fiber atrophy, with significantly higher IGF-1, MyoD, MyoG mRNA (p < 0.05) and pAkt protein expression (p < 0.0001) during sarcopenia. In vitro inhibition of PI3K/Akt and mTOR abolished the enhancement effects on myotube formation and inhibited MRF mRNA and p85, Akt, pAkt and mTOR protein expressions. The present study demonstrated that the PI3K/Akt/mTOR pathway is the predominant regulatory mechanism through which LMHFV and Mg enhanced muscle regeneration and suppressed atrogene upregulation.

In vitro chemotherapy-associated muscle toxicity is attenuated with nutritional support, while treatment efficacy is retained

Purpose: Muscle-wasting and treatment-related toxicities negatively impact prognosis of colorectal cancer (CRC) patients. Specific nutritional composition might support skeletal muscle and enhance treatment support. In this in vitro study we assess the effect of nutrients EPA, DHA, L-leucine and vitamin D3, as single nutrients or in combination on chemotherapy-treated C2C12-myotubes, and specific CRC-tumor cells.

Materials and Methods: Using C2C12-myotubes, the effects of chemotherapy (oxaliplatin, 5-fluorouracil, oxaliplatin+5-fluorouracil and irinotecan) on protein synthesis, cell-viability, caspase-3/7-activity and LDH-activity were assessed. Addition of EPA, DHA, L-leucine and vitamin D3 and their combination (SNCi) were studied in presence of above chemotherapies. Tumor cell-viability was assessed in oxaliplatin-treated C26 and MC38 CRC cells, and in murine and patient-derived CRC-organoids.

Results: While chemotherapy treatment of C2C12-myotubes decreased protein synthesis, cell-viability and increased caspase-3/7 and LDH-activity, SNCi showed improved protein synthesis and cell viability and lowered LDH activity. The nutrient combination SNCi showed a better overall performance compared to the single nutrients. Treatment response of tumor models was not significantly affected by addition of nutrients.

Conclusions: This in vitro study shows protective effect with specific nutrition composition of C2C12-myotubes against chemotherapy toxicity, which is superior to the single nutrients, while treatment response of tumor cells remained.

A Review of free fatty acid-induced cell signaling, angiopoietin-like protein 4, and skeletal muscle differentiation

Postnatal skeletal muscle differentiation from quiescent satellite cells is a highly regulated process, although our understanding of the contribution of nutritional factors in myogenesis is limited. Free fatty acids (FFAs) are known to cause detrimental effects to differentiated skeletal muscle cells by increasing oxidative stress which leads to muscle wasting and insulin resistance in skeletal muscle. In addition, FFAs are thought to act as inhibitors of skeletal muscle differentiation. However, the precise molecular mechanisms underlying the effects of FFAs on skeletal muscle differentiation remains to be elucidated. There is a clear relationship between dietary FFAs and their ability to suppress myogenesis and we propose the hypothesis that the FFA-mediated increase in angiopoietin-like protein 4 (ANGPTL4) may play a role in the inhibition of differentiation. This review discusses the role of FFAs in skeletal muscle differentiation to-date and proposes potential mechanisms of FFA-induced ANGPTL4 mediated inhibition of skeletal muscle differentiation.

Nutritional Interventions to Improve Cachexia Outcomes in Cancer—A Systematic Review

Background and Objectives: The prevalence of cachexia has increased across all of the cancer types and accounts for up to 20% of cancer-related deaths. This paper is a systematic review of nutritional interventions aiming to improve cachexia outcomes in cancer, focusing on weight gain. Materials and Methods: A search in Medline and Elsevier databases for articles up until the 23 January 2022, was conducted. Results: Out of 5732 screened records, 26 publications were included in the final analysis. Four randomized clinical trials showed a significant body weight (BW) increase in patients treated with eicosapentaenoic acid (EPA), β-hydroxy-beta-methyl butyrate (β-HMB), arginine, and glutamine or marine phospholipids (MPL). An upward BW trend was observed in patients treated with L-carnitine, an Ethanwell/Ethanzyme (EE) regimen enriched with ω-3 fatty acids, micronutrients, probiotics, fish oil, a leucine-rich supplement, or total parental nutrition (TPN) with a high dose of a branched-chain amino acid (BCAA). Conclusions: Although clinical trials relating to large numbers of nutritional supplements present promising data, many trials provided negative results. Further studies investigating the underlying mechanisms of action of these nutritional supplements in cancer cachexia are needed. Early screening for cancer cachexia risk and nutritional intervention in cancer patients before aggravating weight loss may stabilize their weight, preventing cachexia syndrome. According to the GRADE methodology, no positive recommendation for these nutritional supplements may be expressed.

The Effects of Maternal Intake of EPA and DHA Enriched Diet During Pregnancy and Lactation on Offspring’s Muscle Development and Energy Homeostasis

EPA and DHA are n-3 long-chain polyunsaturated fatty acids with a diversity of health benefits on offspring. The objective of this study was to test the in vivo effect of maternal ingestion of EPA and DHA on fetal and offspring muscle development and energy balance. Two groups of female C57BL/6 mice were fed EPA and DHA enriched diet (FA) and diet devoid of EPA and DHA (CON) respectively throughout the entire period of gestation and lactation. Embryos at E13 and offspring at age of D1 and D21 were selected for sample collection and processing. No change in birth number and body weight were observed between groups at D1 and D21. Transient increase in the expression levels of myogenesis regulating genes was detected at D1 (p < 0.05) in FA group. Most of the expression of muscle protein synthesis regulating genes were comparable (p > 0.05) between FA and CON groups at D1 and D21. The significant increase in MHC4, and IGF-1 was not linked to increased muscle mass. A persistent increase in ISR expression (p < 0.05) but not in GLUT-4 (p > 0.05) was detected in offspring. Up-regulation of adipogenesis regulating genes was accompanied by increasing intramuscular fat accumulation in the offspring of FA group. Considerable increase in transcripts of genes regulating lipid catabolism and thermogenesis in liver (p < 0.05) was noticed in FA group at D21; whereas, only the levels of carnitine palmitoyl transferase 1A (Cpt1α) and Enoyl-CoA Hydratase And 3-Hydroxyacyl CoA Dehydrogenase (Ehhadh) increased at D1. Similarly, genes regulating lipolysis were highly expressed at D21 in FA group. EPA and DHA treatment promoted BAT development and activity by increasing the expression of BAT signature genes (p < 0.05). Also, maternal intake of EPA and DHA enriched diet enhanced browning of sWAT. Taken together, maternal ingestion of EPA/DHA may be suggested as a therapeutic option to improve body composition and counteract childhood obesity- related metabolic disorders and confer lifelong positive metabolic impact on offspring.

Surface-directed engineering of tissue anisotropy in microphysiological models of musculoskeletal tissue

Here, we present an approach to model and adapt the mechanical regulation of morphogenesis that uses contractile cells as sculptors of engineered tissue anisotropy in vitro. Our method uses heterobifunctional cross-linkers to create mechanical boundary constraints that guide surface-directed sculpting of cell-laden extracellular matrix hydrogel constructs. Using this approach, we engineered linearly aligned tissues with structural and mechanical anisotropy. A multiscale in silico model of the sculpting process was developed to reveal that cell contractility increases as a function of principal stress polarization in anisotropic tissues. We also show that the anisotropic biophysical microenvironment of linearly aligned tissues potentiates soluble factor-mediated tenogenic and myogenic differentiation of mesenchymal stem cells. The application of our method is demonstrated by (i) skeletal muscle arrays to screen therapeutic modulators of acute oxidative injury and (ii) a 3D microphysiological model of lung cancer cachexia to study inflammatory and oxidative muscle injury induced by tumor-derived signals.

Eicosapentaenoic acid enhances skeletal muscle hypertrophy without altering the protein anabolic signaling pathway

This study aimed to examine the effect of eicosapentaenoic acid (EPA) on skeletal muscle hypertrophy induced by muscle overload and the associated intracellular signaling pathways. Male C57BL/6J mice were randomly assigned to oral treatment with either EPA or corn oil for 6 weeks. After 4 weeks of treatment, the gastrocnemius muscle of the right hindlimb was surgically removed to overload the plantaris and soleus muscles for 1 or 2 weeks. We examined the effect of EPA on the signaling pathway associated with protein synthesis using the soleus muscles. According to our analysis of the compensatory muscle growth, EPA administration enhanced hypertrophy of the soleus muscle but not hypertrophy of the plantaris muscle. Nevertheless, EPA administration did not enhance the expression or phosphorylation of Akt, mechanistic target of rapamycin (mTOR), or S6 kinase (S6K) in the soleus muscle. In conclusion, EPA enhances skeletal muscle hypertrophy, which can be independent of changes in the AKT-mTOR-S6K pathway.

The regulatory role of dietary factors in skeletal muscle development, regeneration and function

Skeletal muscle plays a crucial role in motor function, respiration, and whole-body energy homeostasis. How to regulate the development and function of skeletal muscle has become a hot research topic for improving lifestyle and extending life span. Numerous transcription factors and nutritional factors have been clarified are closely associated with the regulation of skeletal muscle development, regeneration and function. In this article, the roles of different dietary factors including green tea, quercetin, curcumin (CUR), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and resveratrol (RES) in regulating skeletal muscle development, muscle mass, muscle function, and muscle recovery have been summarized and discussed. We also reviewed the potential regulatory molecular mechanism of these factors. Based on the current findings, dietary factors may be used as a potential therapeutic agent to treat skeletal muscle dysfunction as well as its related diseases.

MBNL1-Associated Mitochondrial Dysfunction and Apoptosis in C2C12 Myotubes and Mouse Skeletal Muscle

We explored the interrelationship between a tissue-specific alternative splicing factor muscleblind-like 1 (MBNL1) and peroxisome proliferator-activated receptor-γ coactivator 1-α (PGC-1α), B-cell lymphoma 2 (Bcl-2) or Bcl-2-associated X protein (Bax) in C2C12 myotubes and mouse skeletal muscle to investigate a possible physiological role of MBNL1 in mitochondrial-associated apoptosis of skeletal muscle. Expression level of PGC-1α and mitochondrial membrane potential evaluated by the fluorescence ratio of JC-1 aggregate to monomer in C2C12 myotubes were suppressed by knockdown of MBNL1. Conversely, the ratio of Bax to Bcl-2 as well as the apoptotic index in C2C12 myotubes was increased by MBNL1 knockdown. In plantaris muscle, on the other hand, not only the minimum muscle fiber diameter but also the expression level of MBNL1 and PGC-1α in of 100-week-old mice were significantly lower than that of 10-week-old mice. Furthermore, the ratio of Bax to Bcl-2 in mouse plantaris muscle was increased by aging. These results suggest that MBNL1 may play a key role in aging-associated muscle atrophy accompanied with mitochondrial dysfunction and apoptosis via mediating PGC-1α expression in skeletal muscle.

Omega-3 Polyunsaturated Fatty Acids Mitigate Palmitate-Induced Impairments in Skeletal Muscle Cell Viability and Differentiation

Accumulation of excess saturated free fatty acids such as palmitate (PAL) in skeletal muscle leads to reductions in mitochondrial integrity, cell viability and differentiation. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) counteract PAL-induced lipid accumulation. EPA and DHA, as well as the n-3 PUFA docosapentaenoic acid (DPA), may therefore mitigate PAL-induced lipotoxicity to promote skeletal muscle cell survival and differentiation. C2C12 myoblasts were treated with 50 μM EPA, DPA, or DHA in the absence or presence of 500 μM PAL for 16 h either prior to myoblast analysis or induction of differentiation. Myoblast viability and markers of apoptosis, endoplasmic reticulum (ER) stress and myotube differentiation capacity were investigated using fluorescence microscopy and immunoblotting. High-resolution respirometry was used to assess mitochondrial function and membrane integrity. PAL induced cell death via apoptosis and increased protein content of ER stress markers BiP and CHOP. EPA, DPA, and DHA co-treatment maintained cell viability, prevented PAL-induced apoptosis and attenuated PAL-induced increases in BiP, whereas only DPA prevented increases in CHOP. PAL subsequently reduced protein content of the differentiation marker myogenin and inhibited myotube formation, and all n-3 PUFAs promoted myotube formation in the presence of PAL. Furthermore, DPA prevented PAL-induced release of cytochrome c and maintained mitochondrial integrity. These findings demonstrate the n-3 PUFAs EPA, DPA and DHA elicit similar protective effects against PAL-induced impairments in muscle cell viability and differentiation. Mechanistically, the protective effects of DPA against PAL lipotoxicity are attributable in part to its ability to maintain mitochondrial respiratory capacity via mitigating PAL-induced loss of mitochondrial membrane integrity.

A novel transplantable model of lung cancer-associated tissue loss and disrupted muscle regeneration

BACKGROUND

Cancer-associated muscle wasting (CAW), a symptom of cancer cachexia, is associated with approximately 20% of lung cancer deaths and remains poorly characterized on a mechanistic level. Current animal models for lung cancer-associated cachexia are limited in that they (1) primarily employ flank transplantation methods, (2) have short survival times not reflective of the patient condition, and (3) are typically performed in young mice not representative of mean patient age. This study investigates a new model for lung cancer-associated cachexia that can address these issues and also implicates muscle regeneration as a contributor to CAW.

METHODS

We used tail vein injection as a method to introduce tumor cells that seed primarily in the lungs of mice. Body composition of tumor-bearing mice was longitudinally tracked using NMR-based, echo magnetic resonance imaging (echoMRI). These data were combined with histological and molecular assessments of skeletal muscle to provide a complete analysis of muscle wasting.

RESULTS

In this new lung CAW model, we observed (1) progressive loss in whole body weight, (2) progressive loss of lean and fat mass, (3) a circulating cytokine/inflammatory profile similar to that seen in other models of CAW, (4) histological changes associated with muscle wasting, and (5) molecular changes in muscle that implicate suppression of muscle repair/regeneration. Finally, we show that survival can be extended without lessening CAW by titrating injected cell number.

CONCLUSIONS

Overall, this study describes a new model of CAW that could be useful for further studies of lung cancer-associated wasting and accompanying changes in the regenerative capacity of muscle. Additionally, this model addresses many recent concerns with existing models such as immunocompetence, tumor location, and survival time.

Divergent Regulation of Myotube Formation and Gene Expression by E2 and EPA during In-Vitro Differentiation of C2C12 Myoblasts

Estrogen (E2) and polyunsaturated fatty acids (n-3PUFA) supplements independently support general wellbeing and enhance muscle regeneration in-vivo and myotube formation in-vitro. However, the combined effect of E2 and n-3PUFA on myoblast differentiation is not known. The purpose of the study was to identify whether E2 and n-3PUFA possess a synergistic effect on in-vitro myogenesis. Mouse C2C12 myoblasts, a reliable model to reiterate myogenic events in-vitro, were treated with 10nM E2 and 50μM eicosapentaenoic acid (EPA) independently or combined, for 0-24 h or 0-120 h during differentiation. Immunofluorescence, targeted qPCR and next generation sequencing (NGS) were used to characterize morphological changes and differential expression of key genes involved in the regulation of myogenesis and muscle function pathways. E2 increased estrogen receptor α (Erα) and the expression of the mitogen-activated protein kinase 11 (Mapk11) within 1 h of treatment and improved myoblast differentiation and myotube formation. A significant reduction (p < 0.001) in myotube formation and in the expression of myogenic regulatory factors Mrfs (MyoD, Myog and Myh1) and the myoblast fusion related gene, Tmem8c, was observed in the presence of EPA and the combined E2/EPA treatment. Additionally, EPA treatment at 48 h of differentiation inhibited the majority of genes associated with the myogenic and striated muscle contraction pathways. In conclusion, EPA and E2 had no synergistic effect on myotube formation in-vitro. Independently, EPA inhibited myoblast differentiation and overrides the stimulatory effect of E2 when used in combination with E2.

EPA and DHA attenuate deoxynivalenol-induced intestinal porcine epithelial cell injury and protect barrier function integrity by inhibiting necroptosis signaling pathway

Deoxynivalenol (DON) is one of the most common mycotoxins that contaminates food or feed and cause intestinal damage. Long-chain n-3 polyunsaturated fatty acids (PUFA) such as EPA and DHA exert beneficial effects on intestinal integrity in animal models and clinical trials. Necroptosis signaling pathway plays a critical role in intestinal cell injury. This study tested the hypothesis that EPA and DHA could alleviate DON-induced injury to intestinal porcine epithelial cells through modulation of the necroptosis signaling pathway. Intestinal porcine epithelial cell 1 (IPEC-1) cells were cultured with or without EPA or DHA (6.25-25 μg/mL) in the presence or absence of 0.5 μg/mL DON for indicated time points. Cell viability, cell number, lactate dehydrogenase (LDH) activity, cell necrosis, transepithelial electrical resistance (TEER), fluorescein isothiocyanate-labeled dextran 4kDa (FD4) flux, tight junction protein distribution, and protein abundance of necroptosis related signals were determined. EPA and DHA promoted cell growth indicated by higher cell viability and cell number, and inhibited cell injury indicated by lower LDH activity in the media. EPA and DHA also improved intestinal barrier function, indicated by higher TEER and lower permeability of FD4 flux as well as increased proportions of tight junction proteins located in the plasma membrane. Moreover, EPA and DHA decreased cell necrosis demonstrated by live cell imaging and transmission electron microscopy. Finally, EPA and DHA downregulated protein expressions of necroptosis related signals including tumor necrosis factor receptor (TNFR1), receptor interacting protein kinase 1 (RIP1), RIP3, phosphorylated mixed lineage kinase-like protein (MLKL), phosphoglycerate mutase family 5 (PGAM5), dynamin-related protein 1 (Drp1), and high mobility group box-1 protein (HMGB1). EPA and DHA also inhibited protein expression of caspase-3 and caspase-8. These results suggest that EPA and DHA prevent DON-induced intestinal cell injury and enhance barrier function, which is associated with inhibition of the necroptosis signaling pathway.

A double-blind randomized controlled trial of the effects of eicosapentaenoic acid supplementation on muscle inflammation and physical function in patients undergoing colorectal cancer resection

BACKGROUND

Resection of colorectal cancer (CRC) initiates inflammation, mediated at least partly by NFĸB (nuclear factor kappa-light-chain-enhancer of activated B-cells), leading to muscle catabolism and reduced physical performance. Eicosapentaenoic acid (EPA) has been shown to modulate NFĸB, but evidence for its benefit around the time of surgery is limited.

OBJECTIVE

To assess the effect of EPA supplementation on muscle inflammation and physical function around the time of major surgery.

DESIGN

In a double-blind randomized control trial, 61 patients (age: 68.3 ± 0.95 y; 42 male) scheduled for CRC resection, received 3 g per day of EPA (n = 32) or placebo (n = 29) for 5-days before and 21-days after operation. Lean muscle mass (LMM) (via dual energy X-ray absorptiometry (DXA)), anaerobic threshold (AT) (via cardiopulmonary exercise testing (CPET)) and hand-grip strength (HG) were assessed before and 4-weeks after surgery, with muscle biopsies (m. vastus lateralis) obtained for the assessment of NF-ĸB protein expression.

RESULTS

There were no differences in muscle NFĸB between EPA and placebo groups (mean difference (MD) -0.002; 95% confidence interval (CI) -0.19 to 0.19); p = 0.98). There was no difference in LMM (MD 704.77 g; 95% CI -1045.6 g-2455.13 g; p = 0.42) or AT (MD 1.11 mls/kg/min; 95% CI -0.52 mls/kg/min to 2.74 mls/kg/min; p = 0.18) between the groups. Similarly, there was no difference between the groups in HG at follow up (MD 0.1; 95% CI -1.88 to 2.08; p = 0.81). Results were similar when missing data was imputed.

CONCLUSION

EPA supplementation confers no benefit in terms of inflammatory status, as judged by NFĸB, or preservation of LMM, aerobic capacity or physical function following major colorectal surgery.

CLINICAL TRIALS REFERENCE

NCT01320319.

Effect of dietary fish oil intake on ubiquitin ligase expression during muscle atrophy induced by sciatic nerve denervation in mice

Dietary fish oil intake improves muscle atrophy in several atrophy models however the effect on denervation-induced muscle atrophy is not clear. Thus, the aim of this study was to investigate the effects of dietary fish oil intake on muscle atrophy and the expression of muscle atrophy markers induced by sciatic nerve denervation in mice. We performed histological and quantitative mRNA expression analysis of muscle atrophy markers in mice fed with fish oil with sciatic nerve denervation. Histological analysis indicated that dietary fish oil intake slightly prevented the decrease of muscle fiber diameter induced by denervation treatment. In addition, dietary fish oil intake suppressed the MuRF1 (tripartite motif-containing 63) expression up-regulated by denervation treatment, and this was due to decreased tumor necrosis factor-alpha (TNF-α) production in skeletal muscle. We concluded that dietary fish oil intake suppressed MuRF1 expression by decreasing TNF-α production during muscle atrophy induced by sciatic nerve denervation in mice.

Modeling the Effect of TNF-α upon Drug-Induced Toxicity in Human, Tissue-Engineered Myobundles

A number of significant muscle diseases, such as cachexia, sarcopenia, systemic chronic inflammation, along with inflammatory myopathies share TNF-α-dominated inflammation in their pathogenesis. In addition, inflammatory episodes may increase susceptibility to drug toxicity. To assess the effect of TNF-α-induced inflammation on drug responses, we engineered 3D, human skeletal myobundles, chronically exposed them to TNF-α during maturation, and measured the combined response of TNF-α and the chemotherapeutic doxorubicin on muscle function. First, the myobundle inflammatory environment was characterized by assessing the effects of TNF-α on 2D human skeletal muscle cultures and 3D human myobundles. High doses of TNF-α inhibited maturation in human 2D cultures and maturation and function in 3D myobundles. Then, a tetanus force dose-response curve was constructed to characterize doxorubicin's effects on function alone. The combination of TNF-α and 10 nM doxorubicin exhibited a synergistic effect on both twitch and tetanus force production. Overall, the results demonstrated that inflammation of a 3D, human skeletal muscle inflammatory system alters the response to doxorubicin.

Delta-6-desaturase (FADS2) inhibition and omega-3 fatty acids in skeletal muscle protein turnover

Polyunsaturated fatty acids (PUFAs) are essential dietary components. They are not only used for energy, but also act as signaling molecules. The delta-6 desaturase (D6D) enzyme, encoded by the FADS2 gene, is one of two rate limiting enzymes that convert the PUFA precursors – α-linolenic (n-3) and linoleic acid (n-6) to their respective metabolites. Alterations in the D6D enzyme activity alters fatty acid profiles and are associated with metabolic and inflammatory diseases including cardiovascular disease and type 2 diabetes. Omega-3 PUFAs, specifically its constituent fatty acids DHA and EPA, are known for their anti-inflammatory ability and are also beneficial in the prevention of skeletal muscle wasting, however the mechanism for muscle preservation is not well understood. Moreover, little is known of the effects of altering the n-6/n-3 ratio in the context of a high-fat diet, which is known to downregulate protein synthesis. Twenty C57BL6 male mice were fed a high-fat lard (HFL, 45% fat (mostly lard), 35% carbohydrate and 20% protein, n-6:n-3 PUFA, 13:1) diet for 6 weeks. Mice were then divided into 4 groups (n = 5 per group): HFL– , high-fat oil– (HFO, 45% fat (mostly Menhaden oil), 35% carbohydrate and 20% protein, n-6:n-3 PUFA, 1:3), HFL+ (HFL diet plus an orally administered FADS2 inhibitor, 100 mg/kg/day), and HFO+ (HFO diet plus an orally administered FADS2 inhibitor, 100 mg/kg/day). After 2 weeks on their respective diets and treatments, animals were sacrificed and gastrocnemius muscle harvested. Protein turnover signaling were analyzed via Western Blot. 4-EBP1 and ribosomal protein S6 expression were measured. A two-way ANOVA revealed no significant change in the phosphorylation of both 4EBP-1 and ribosomal protein S6 with diet or inhibitor. There was a significant reduction in STAT3 phosphorylation with the inhibition of FADS2 (p = 0.03). Additionally, we measured markers of protein degradation through levels of FOXO phosphorylation, ubiquitin, and LC3B expression; there was a trend towards increased phosphorylation of FOXO (p = 0.08) and ubiquitinated proteins (p = 0.05) with FADS2 inhibition. LC3B expression, a marker of autophagy, was significantly higher in the HFL plus FADS2 inhibition group from all other comparisons. Lastly, we analyzed activation of mitochondrial biogenesis which is closely linked with protein synthesis through PGC1-α and Cytochrome-C expression, however no significant differences were associated with either marker across all groups. Collectively, these data suggest that the protective effects of muscle mass by omega-3 fatty acids are from inhibition of protein degradation. Our aim was to determine the role of PUFA metabolites, DHA and EPA, in skeletal muscle protein turnover and assess the effects of n-3s independently. We observed that by inhibiting the FADS2 enzyme, the protective effect of n-3s on protein synthesis and proliferation was lost; concomitantly, protein degradation was increased with FADS2 inhibition regardless of diet.

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High fat omega-3 rich diets increase STAT3 signaling in a FADS2 dependent manner.

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Inhibition of FADS2 attenuates the protective effects of omega-3 rich diet.

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Inhibition of FADS2 increases protein degradation regardless of diet.

Metabolomics Biomarkers for Precision Psychiatry

The treatment of psychiatric disorders remains a significant challenge in part due to imprecise diagnostic criteria and incomplete understanding of the molecular pathology involved. Current diagnostic and pharmacological treatment guidelines use a uniform approach to address each disorder even though psychiatric clinical presentation and prognosis within a disorder are known to be heterogeneous. Limited therapeutic success highlights the need for a precision medicine approach in psychiatry, termed precision psychiatry. To practice precision psychiatry, it is essential to research and develop multiple omics-based biomarkers that consider environmental factors and careful phenotype determination. Metabolomics, which lies at the endpoint of the "omics cascade," allows for detection of alterations in systems-level metabolites within biological pathways, thereby providing insights into the mechanisms that underlie various physiological conditions and pathologies. The eicosanoids, a family of metabolites derived from oxygenated polyunsaturated fatty acids, play a key role in inflammatory mechanisms and have been implicated in psychiatric disorders such as anorexia nervosa and depression. This review (1) provides background on the current clinical challenges of psychiatric disorders, (2) gives an overview of metabolomics application as a tool to develop improved biomarkers for precision psychiatry, and (3) summarizes current knowledge on metabolomics and lipidomic findings in common psychiatric disorders, with a focus on eicosanoids. Metabolomics is a promising tool for precision psychiatry. This research has great potential for both discovering biomarkers and elucidating molecular mechanisms underlying psychiatric disorders.

New insights on the regulation of cancer cachexia by N-3 polyunsaturated fatty acids

Cancer cachexia is a multifactorial syndrome that develops during malignant tumor growth. Changes in plasma levels of several hormones and inflammatory factors result in an intense catabolic state, decreased activity of anabolic pathways, anorexia, and marked weight loss, leading to cachexia development and/or accentuation. Inflammatory mediators appear to be related to the control of a highly regulated process of muscle protein degradation that accelerates the process of cachexia. Several mediators have been postulated to participate in this process, including TNF-α, myostatin, and activated protein degradation pathways. Some interventional therapies have been proposed, including nutritional (dietary, omega-3 fatty acid supplementation), hormonal (insulin), pharmacological (clenbuterol), and nonpharmacological (physical exercise) therapies. Omega-3 (n-3) polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid, are recognized for their anti-inflammatory properties and have been used in therapeutic approaches to treat or attenuate cancer cachexia. In this review, we discuss recent findings on cellular and molecular mechanisms involved in inflammation in the cancer cachexia syndrome and the effectiveness of n-3 PUFAs to attenuate or prevent cancer cachexia.

Impact of Above-Average Proanabolic Nutrients Is Overridden by High Protein and Energy Intake in the Muscle-Tendon Unit Characteristics of Middle- to Older-Aged Adults

Background

The impact, within a single cohort, of independent modulators of skeletal muscle quality, including age, adiposity and obesity, habitual nutritional intake, and physical activity (PA), is unclear.

Objective

We examined the bivariate associations between age, adiposity, habitual nutritional intake, and PA against 11 key intrinsic muscle-tendon unit (MTU) characteristics to identify the strongest predictors. We also compared overall profile differences between MTU categories with the use of z scores shown in radar graphs.

Methods

Fifty untrained independently living men (n = 15) and women (n = 35) aged 43-80 y (mean ± SD: 64 ±9 y) were categorized by adiposity [men: normal adiposity (NA) <28%, high adiposity (HA) ≥28%; women: NA <40%, HA ≥40%] and body mass index [BMI (in kg/m2); normal: 18 to <25; overweight: ≥25 to <30; and obese: ≥30]. Group differences were examined by body composition assessed with the use of dual-energy X-ray absorptiometry, habitual nutritional intake through a 3-d food diary, PA (work, leisure, sport) using the Baecke questionnaire, 14 serum cytokine concentrations using multiplex luminometry, and 11 MTU characteristics of the gastrocnemius medialis using a combination of isokinetic dynamometry, electromyography, and ultrasonography.

Results

Interestingly, classification by BMI highlighted differences between normal and obese individuals in 6 of 11 MTU characteristics (P < 0.001 to P = 0.043). No significant differences were reported in serum cytokine concentrations between adiposity and BMI classifications. BMI predicted 8 of 11 (r = 0.62-0.31, P < 0.001 to P = 0.032), daily energy intake predicted 7 of 11 (r = 0.45-0.34, P = 0.002-0.036), age predicted 5 of 11 (r = -0.49-0.32, P < 0.001 to P = 0.032), work-based PA predicted 5 of 11 (r = 0.43-0.32, P = 0.003-0.048), and adiposity predicted 4 of 11 (r = 0.51-0.33, P < 0.001 to P = 0.022) MTU characteristics. Mathematical z scores and radar graphs showed how endocrine and dietary profiles, but not PA, differed between the top and bottom ∼20% of muscle unit size and specific force.

Conclusions

Given the number of factors associated with MTU, education should be targeted to both adequate food quantity and quality (especially protein intake) and increasing habitual moderate to vigorous PA while decreasing sedentary behavior. Specific endocrine variables are also proposed as key pharmaceutical targets.

EPA plays multiple roles in regulating lipid accumulation of grass carp Ctenopharyngodon idella adipose tissue in vitro and in vivo

This study was conducted to assess the effect of eicosapentaenoic acid (20:5n-3, EPA) on lipid accumulation in grass carp Ctenopharyngodon idella adipose tissue both in vitro and in vivo. EPA was observed to inhibit the adipocyte viability in a time and dose-dependent manner. EPA was also found to induce reactive oxygen species accumulation in vitro. The mRNA levels of caspase 3a and caspase 3b, as well as the activity of Caspase 3 increased significantly in vitro and in vivo, whereas the value of B cell leukemia 2-Bcl-2 associated X protein decreased significantly. Besides, the pro-apoptotic effect was relieved by α-tocopherol. Dietary 0.52% EPA had no apparent effect on intraperitoneal fat index. Moreover, EPA promoted the hydrolytic gene expressions in vitro and in vivo, including adipose triglyceride lipase and hormone sensitive lipase-a. Meanwhile, the lipogenic gene expressions of liver X receptor α, sterol regulatory element binding protein-1c and fatty-acid synthase were down-regulated by EPA in vitro and in vivo. However, EPA also acted to promote the marker gene expressions of adipogenesis, including peroxisome proliferator-activated receptor γ and lipoprotein lipase in vitro and in vivo. Contents of EPA increased significantly in the treatment groups in vitro and in vivo. These results support that EPA affects multiple aspects of lipid metabolism, including hydrolysis, lipogenesis, adipogenesis and apoptosis. However, it barely functioned in decreasing the lipid accumulation of Ctenopharyngodon idella under the current culture conditions.

Immune System Dysregulation During Spaceflight: Potential Countermeasures for Deep Space Exploration Missions

Recent studies have established that dysregulation of the human immune system and the reactivation of latent herpesviruses persists for the duration of a 6-month orbital spaceflight. It appears certain aspects of adaptive immunity are dysregulated during flight, yet some aspects of innate immunity are heightened. Interaction between adaptive and innate immunity also seems to be altered. Some crews experience persistent hypersensitivity reactions during flight. This phenomenon may, in synergy with extended duration and galactic radiation exposure, increase specific crew clinical risks during deep space exploration missions. The clinical challenge is based upon both the frequency of these phenomena in multiple crewmembers during low earth orbit missions and the inability to predict which specific individual crewmembers will experience these changes. Thus, a general countermeasure approach that offers the broadest possible coverage is needed. The vehicles, architecture, and mission profiles to enable such voyages are now under development. These include deployment and use of a cis-Lunar station (mid 2020s) with possible Moon surface operations, to be followed by multiple Mars flyby missions, and eventual human Mars surface exploration. Current ISS studies will continue to characterize physiological dysregulation associated with prolonged orbital spaceflight. However, sufficient information exists to begin consideration of both the need for, and nature of, specific immune countermeasures to ensure astronaut health. This article will review relevant in-place operational countermeasures onboard ISS and discuss a myriad of potential immune countermeasures for exploration missions. Discussion points include nutritional supplementation and functional foods, exercise and immunity, pharmacological options, the relationship between bone and immune countermeasures, and vaccination to mitigate herpes (and possibly other) virus risks. As the immune system has sentinel connectivity within every other physiological system, translational effects must be considered for all potential immune countermeasures. Finally, we shall discuss immune countermeasures in the context of their individualized implementation or precision medicine, based on crewmember specific immunological biases.

Potential Roles of n-3 PUFAs during Skeletal Muscle Growth and Regeneration

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), which are commonly found in fish oil supplements, are known to possess anti-inflammatory properties and more recently alter skeletal muscle function. In this review, we discuss novel findings related to how n-3 PUFAs modulate molecular signaling responsible for growth and hypertrophy as well as the activity of muscle stem cells. Muscle stem cells commonly known as satellite cells, are primarily responsible for driving the skeletal muscle repair process to potentially damaging stimuli, such as mechanical stress elicited by exercise contraction. To date, there is a paucity of human investigations related to the effects of n-3 PUFAs on satellite cell content and activity. Based on current in vitro investigations, this review focuses on novel mechanisms linking n-3 PUFA’s to satellite cell activity and how they may improve muscle repair. Understanding the role of n-3 PUFAs during muscle growth and regeneration in association with exercise could lead to the development of novel supplementation strategies that increase muscle mass and strength, therefore possibly reducing the burden of muscle wasting with age.

Free Fatty Acid Receptor 4 Mediates the Beneficial Effects of n-3 Fatty Acids on Body Composition in Mice

As populations continue to age worldwide, sarcopenic obesity has heightened interest due to its medical importance. Although much evidence now indicates that n-3 fatty acids (FAs) may have beneficial effects on body composition including fat and muscle, their exact mechanisms have not yet been elucidated. Because free FA receptor 4 (FFA4) has been reported to be a receptor for n-3 FAs, we hypothesized that the protective role of n-3 FAs on body composition could be mediated by FFA4. To test this possibility, we generated mice overexpressing n-3 FAs but lacking FFA4 by crossing fat-1 transgenic (fat-1 ^Tg+) and FFA4 knockout (Ffar4 ^-/-) mice. Because fat-1 ^Tg+ mice, in which n-6 is endogenously converted into n-3 FAs, contain high n-3 FA levels, they could be a good animal model for studying the effects of n-3 FAs in vivo. Male and female littermates were included in high-fat-diet- (HFD) and ovariectomy-induced models, respectively. In the HFD model, male fat-1 ^Tg+ mice had a lower percentage of fat mass and a higher percentage of lean mass than their wild-type littermates only when they had the Ffar4 ^+/+ not the Ffar4 ^-/- background. Female fat-1 ^Tg+ mice showed less increase of fat mass percentage and less decrease of lean mass percentage after ovariectomy than wild-type littermates. However, these effects on body composition were attenuated in the Ffar4 ^-/- background. Taken together, our results indicate that the beneficial effects of n-3 FAs on body composition were mediated by FFA4 and thus suggest that FFA4 may be a potential therapeutic target for modulating sarcopenic obesity.

Eicosapentaenoic acid abolishes inhibition of insulin-induced mTOR phosphorylation by LPS via PTP1B downregulation in skeletal muscle

Dietary n-3 polyunsaturated fatty acids (n-3 PUFAs) increase insulin signaling in skeletal muscle. In the current study, we investigated the effect of eicosapentaenoic acid (EPA) on insulin-induced mammalian target of rapamycin (mTOR) phosphorylation in myotubes. We showed that EPA did not affect basal and insulin-induced mTOR phosphorylation in myotubes. However, EPA abolished lipopolysaccharide (LPS) -induced deficiency in insulin signaling (P < 0.05). Pre-incubation of nuclear factor κB (NF-κΒ) and c-Jun N-terminal kinases (JNK) inhibitors prevented the decreased insulin-induced mTOR phosphorylation elicited by LPS (P < 0.05). In addition, in protein tyrosine phosphatase-1B (PTP1B) knockdown myotubes, LPS failed to decrease insulin-induced mammalian target of rapamycin (mTOR) phosphorylation in myotubes (P > 0.05). In myotubes, LPS stimulated PTP1B expression via NF-κB and activation protein-1 (AP1). Pre-incubation of 50 μM EPA prevented the LPS-induced activation of AP1 and NF-κΒ as well as PTP1B expression (P < 0.05). Interestingly, incubation of peroxisome proliferator-activated receptor γ (PPARγ) antagonist (GW9662) prior to EPA treatment, the effect of EPA on insulin-induced mTOR phosphorylation was blocked. Accordingly, EPA did not inhibit the LPS-induced activation of AP1 or NF-κΒ as well as PTP1B expression when incubation of GW9662 prior to EPA treatment. The in vivo study showed that EPA prevented LPS-induced PTPT1B expression and a decrease in insulin-induced mTOR phosphorylation in muscle of mice. In summary, EPA abolished LPS inhibition of insulin-induced mTOR phosphorylation in myotubes, and one of the key mechanisms was to inhibit AP1 and NF-κB activation and PTP1B transcription.

Omega-3 Fatty Acids and Vitamin D in Immobilisation: Part B- Modulation of Muscle Functional, Vascular and Activation Profiles

OBJECTIVES

This study set out to determine whether two potential protein-sparing modulators (eicosapentaenoic acid and vitamin D) would modulate the anticipated muscle functional and related blood vessels function deleterious effects of immobilisation.

DESIGN

The study used a randomised, double-blind, placebo-controlled design.

SETTING

The study took part in a laboratory setting.

PARTICIPANTS

Twenty-four male and female healthy participants, aged 23.0±5.8 years.

INTERVENTION

The non-dominant arm was immobilised in a sling for a period of nine waking hours a day over two continuous weeks. Participants were randomly assigned to one of three groups: placebo (n=8, Lecithin, 2400 mg daily), omega-3 (ω-3) fatty acids (n=8, eicosapentaenoic acid (EPA); 1770 mg, and docosahexaenoic acid (DHA); 390 mg, daily) or vitamin D (n=8, 1,000 IU daily).

MEASUREMENTS

Isometric and isokinetic torque, antagonist muscle co-contraction (activation profile), muscle fatigability indices, and arterial resting blood flow were measured before, at the end of the immobilisation period, and two weeks after re-mobilisation.

RESULTS

Muscle elbow flexion and extension isometric and isokinetic torque decreased significantly with limb immobilisation in the placebo group (P<0.05). Despite no significant effect of supplementation, ω-3 and vitamin D supplementation showed trends (P>0.05) towards attenuating the decreases observed in the placebo group. There was no significant change in muscle fatigue parameters or co-contraction values with immobilisation and no effect of supplementation group (P>0.05). Similarly, this immobilisation model had no impact on the assessed blood flow characteristics. All parameters had returned to baseline values at the re-mobilisation phase of the study.

CONCLUSION

Overall, at the current doses, neither ω-3 nor vitamin D supplementation significantly attenuated declines in torque associated with immobilisation. It would appear that muscle function (described here in Part B) might not be as useful a marker of the effectiveness of a supplement against the impact of immobilisation compared to tissue composition changes (described in Part A).

Omega-3 Fatty Acids and Vitamin D in Immobilisation: Part A- Modulation of Appendicular Mass Content, Composition and Structure

OBJECTIVES

Muscle size decreases in response to short-term limb immobilisation. This study set out to determine whether two potential protein-sparing modulators (eicosapentaenoic acid and vitamin D) would attenuate immobilisation-induced changes in muscle characteristics.

DESIGN

The study used a randomised, double-blind, placebo-controlled design.

SETTING

The study took part in a laboratory setting.

PARTICIPANTS

Twenty-four male and female healthy participants, aged 23.0±5.8 years.

INTERVENTION

The non-dominant arm was immobilised in a sling for a period of nine waking hours a day over two continuous weeks. Participants were randomly assigned to one of three groups: placebo (n=8, Lecithin, 2400 mg daily), omega-3 (ω-3) fatty acids (n=8, eicosapentaenoic acid (EPA); 1770 mg, and docosahexaenoic acid (DHA); 390 mg, daily) or vitamin D (n=8, 1,000 IU daily).

MEASUREMENTS

Muscle and sub-cutaneous adipose thickness (B-mode ultrasonography), body composition (DXA) and arm girth (anthropometry) were measured before immobilisation, immediately on removal of the sling and two weeks after re-mobilisation.

RESULTS

Muscle thickness (-5.4±4.3%), upper and lower arm girth (-1.3±0.4 and -0.8±0.8%, respectively), lean mass (-3.6±3.7%) and bone mineral content (BMC) (-2.3±1.5%) decreased significantly with limb immobilisation in the placebo group (P<0.05). Despite no significant effect of group, ω-3 and vitamin D supplementation showed trends (p>0.05) towards attenuating the decreases in muscle thickness, upper/lower arm girths and BMC observed in the placebo group. The ω-3 supplementation group demonstrated a non-significant attenuation of the decrease in DXA quantified lean mass observed in the placebo group. Sub-cutaneous adipose thickness increased in the placebo group (P<0.05). ω-3 and vitamin D both blunted this response, with ω-3 having a greater effect (P<0.05). All parameters had returned to baseline values at the re-mobilisation phase of the study.

CONCLUSION

Overall, at the current doses, ω-3 and vitamin D supplementation only attenuated one of the changes associated with non-injurious limb immobilisation. These findings would necessitate further research into either a) supplementation linked to injury-induced immobilisation, or b) larger doses of these supplements to confirm/refute the physiological reserve potential of the two supplements.

Omega-3 fatty acid EPA improves regenerative capacity of mouse skeletal muscle cells exposed to saturated fat and inflammation

Sarcopenic obesity is characterised by high fat mass, low muscle mass and an elevated inflammatory environmental milieu. We therefore investigated the effects of elevated inflammatory cytokine TNF-α (aging/obesity) and saturated fatty acid, palmitate (obesity) on skeletal muscle cells in the presence/absence of EPA, a-3 polyunsaturated fatty acid with proposed anti-inflammatory, anti-obesity activities. In the present study we show that palmitate was lipotoxic, inducing high levels of cell death and blocking myotube formation. Cell death under these conditions was associated with increased caspase activity, suppression of differentiation, reductions in both creatine kinase activity and gene expression of myogenic factors; IGF-II, IGFBP-5, MyoD and myogenin. However, inhibition of caspase activity via administration of Z-VDVAD-FMK (caspase-2), Z-DEVD-FMK (caspase-3) and ZIETD-KMK (caspase 8) was without effect on cell death. By contrast, lipotoxicity associated with elevated palmitate was reduced with the MEK inhibitor PD98059, indicating palmitate induced cell death was MAPK mediated. These lipotoxic conditions were further exacerbated in the presence of inflammation via TNF-α co-administration. Addition of EPA under cytotoxic stress (TNF-α) was shown to partially rescue differentiation with enhanced myotube formation being associated with increased MyoD, myogenin, IGF-II and IGFBP-5 expression. EPA had little impact on the cell death phenotype observed in lipotoxic conditions but did show benefit in restoring differentiation under lipotoxic plus cytotoxic conditions. Under these conditions Id3 (inhibitor of differentiation) gene expression was inversely linked with survival rates, potentially indicating a novel role of EPA and Id3 in the regulation of apoptosis in lipotoxic/cytotoxic conditions. Additionally, signalling studies indicated the combination of lipo- and cyto-toxic effects on the muscle cells acted through ceramide, JNK and MAPK pathways and blocking these pathways using PD98059 (MEK inhibitor) and Fumonisin B1 (ceramide inhibitor) significantly reduced levels of cell death. These findings highlight novel pathways associated with in vitro models of lipotoxicity (palmitate-mediated) and cytotoxicity (inflammatory cytokine mediated) in the potential targeting of molecular modulators of sarcopenic obesity.

Skeletal muscle atrophy is attenuated in tumor-bearing mice under chemotherapy by treatment with fish oil and selenium

Chemotherapy can cause cachexia, which is manifested by weight loss, inflammation and muscle atrophy. However, the mechanisms of tumor and chemotherapy on skeletal muscle proteolysis, remained unclear. In this report, we demonstrated that tumor-induced myostatin in turn induced TNF-α, thus activating calcium-dependent and proteasomal protein degradation. Chemotherapy activated myostatin-mediated proteolysis and muscle atrophy by elevating IL-6. In tumor-bearing mice under chemotherapy, supplementation with fish oil and selenium prevented a rise in IL-6, TNF-α and myostatin and muscle atrophy. The findings presented here allow us to better understand the molecular basis of cancer cachexia and potentiate nutrition supplementation in future cancer chemotherapy.

Muscle wasting and aging: Experimental models, fatty infiltrations, and prevention

Identification of cost-effective interventions to maintain muscle mass, muscle strength, and physical performance during muscle wasting and aging is an important public health challenge. It requires understanding of the cellular and molecular mechanisms involved. Muscle-deconditioning processes have been deciphered by means of several experimental models, bringing together the opportunities to devise comprehensive analysis of muscle wasting. Studies have increasingly recognized the importance of fatty infiltrations or intermuscular adipose tissue for the age-mediated loss of skeletal-muscle function and emphasized that this new important factor is closely linked to inactivity. The present review aims to address three main points. We first mainly focus on available experimental models involving cell, animal, or human experiments on muscle wasting. We next point out the role of intermuscular adipose tissue in muscle wasting and aging and try to highlight new findings concerning aging and muscle-resident mesenchymal stem cells called fibro/adipogenic progenitors by linking some cellular players implicated in both FAP fate modulation and advancing age. In the last part, we review the main data on the efficiency and molecular and cellular mechanisms by which exercise, replacement hormone therapies, and β-hydroxy-β-methylbutyrate prevent muscle wasting and sarcopenia. Finally, we will discuss a potential therapeutic target of sarcopenia: glucose 6-phosphate dehydrogenase.

Skeletal muscle regeneration and impact of aging and nutrition

After skeletal muscle injury a regeneration process takes place to repair muscle. Skeletal muscle recovery is a highly coordinated process involving cross-talk between immune and muscle cells. It is well known that the physiological activities of both immune cells and muscle stem cells decline with advancing age, thereby blunting the capacity of skeletal muscle to regenerate. The age-related reduction in muscle repair efficiency contributes to the development of sarcopenia, one of the most important factors of disability in elderly people. Preserving muscle regeneration capacity may slow the development of this syndrome. In this context, nutrition has drawn much attention: studies have demonstrated that nutrients such as amino acids, n-3 polyunsaturated fatty acids, polyphenols and vitamin D can improve skeletal muscle regeneration by targeting key functions of immune cells, muscle cells or both. Here we review the process of skeletal muscle regeneration with a special focus on the cross-talk between immune and muscle cells. We address the effect of aging on immune and skeletal muscle cells involved in muscle regeneration. Finally, the mechanisms of nutrient action on muscle regeneration are described, showing that quality of nutrition may help to preserve the capacity for skeletal muscle regeneration with age.

Potential Role of Omega-3 Fatty Acids on the Myogenic Program of Satellite Cells

Skeletal muscle loss is associated with aging as well as pathological conditions. Satellite cells (SCs) play an important role in muscle regeneration. Omega-3 fatty acids are widely studied in a variety of muscle wasting diseases; however, little is known about their impact on skeletal muscle regeneration. The aim of this review is to evaluate studies examining the effect of omega-3 fatty acids, α-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid on the regulation of SC proliferation and differentiation. This review highlights mechanisms by which omega-3 fatty acids may modulate the myogenic program of the stem cell population within skeletal muscles and identifies considerations for future studies. It is proposed that minimally three myogenic transcriptional regulatory factors, paired box 7 (Pax7), myogenic differentiation 1 protein, and myogenin, should be measured to confirm the stage of SCs within the myogenic program affected by omega-3 fatty acids.

Omega-3 Fatty Acids and Skeletal Muscle Health

Skeletal muscle is a plastic tissue capable of adapting and mal-adapting to physical activity and diet. The response of skeletal muscle to adaptive stimuli, such as exercise, can be modified by the prior nutritional status of the muscle. The influence of nutrition on skeletal muscle has the potential to substantially impact physical function and whole body metabolism. Animal and cell based models show that omega-3 fatty acids, in particular those of marine origin, can influence skeletal muscle metabolism. Furthermore, recent human studies demonstrate that omega-3 fatty acids of marine origin can influence the exercise and nutritional response of skeletal muscle. These studies show that the prior omega-3 status influences not only the metabolic response of muscle to nutrition, but also the functional response to a period of exercise training. Omega-3 fatty acids of marine origin therefore have the potential to alter the trajectory of a number of human diseases including the physical decline associated with aging. We explore the potential molecular mechanisms by which omega-3 fatty acids may act in skeletal muscle, considering the n-3/n-6 ratio, inflammation and lipidomic remodelling as possible mechanisms of action. Finally, we suggest some avenues for further research to clarify how omega-3 fatty acids may be exerting their biological action in skeletal muscle.

GH-Releasing Hormone Promotes Survival and Prevents TNF-α-Induced Apoptosis and Atrophy in C2C12 Myotubes

Skeletal muscle atrophy is a consequence of different chronic diseases, including cancer, heart failure, and diabetes, and also occurs in aging and genetic myopathies. It results from an imbalance between anabolic and catabolic processes, and inflammatory cytokines, such as TNF-α, have been found elevated in muscle atrophy and implicated in its pathogenesis. GHRH, in addition to stimulating GH secretion from the pituitary, exerts survival and antiapoptotic effects in different cell types. Moreover, we and others have recently shown that GHRH displays antiapoptotic effects in isolated cardiac myocytes and protects the isolated heart from ischemia/reperfusion injury and myocardial infarction in vivo. On these bases, we investigated the effects of GHRH on survival and apoptosis of TNF-α-treated C2C12 myotubes along with the underlying mechanisms. GHRH increased myotube survival and prevented TNF-α-induced apoptosis through GHRH receptor-mediated mechanisms. These effects involved activation of phosphoinositide 3-kinase/Akt pathway and inactivation of glycogen synthase kinase-3β, whereas mammalian target of rapamycin was unaffected. GHRH also increased the expression of myosin heavy chain and the myogenic transcription factor myogenin, which were both reduced by the cytokine. Furthermore, GHRH inhibited TNF-α-induced expression of nuclear factor-κB, calpain, and muscle ring finger1, which are all involved in muscle protein degradation. In summary, these results indicate that GHRH exerts survival and antiapoptotic effects in skeletal muscle cells through the activation of anabolic pathways and the inhibition of proteolytic routes. Overall, our findings suggest a novel therapeutic role for GHRH in the treatment of muscle atrophy-associated diseases.

Interleukin-10 limits intense acute swimming-induced muscle mechanical hyperalgesia in mice

NEW FINDINGS

What is the central question of this study? This study investigated the role of the endogenous anti-inflammatory cytokine interleukin-10 in intense acute swimming-induced muscle mechanical hyperalgesia in mice. What is the main finding and its importance? Endogenous interleukin-10 has a key role in limiting exercise-induced muscle pain in a model presenting similarities to delayed-onset muscle soreness in mice. Interleukin-10 reduced muscle pain by diminishing leucocyte recruitment, hyperalgesic cytokine production, oxidative stress and myocyte damage. Interleukin-10 (IL-10) is an antihyperalgesic cytokine. In this study, IL-10-deficient (IL-10(-/-) ) mice were used to investigate the role of endogenous IL-10 in intense acute swimming-induced muscle mechanical hyperalgesia, which presents similarities with delayed-onset muscle soreness. An intense acute swimming session of 1 or 2 h induced significant muscle mechanical hyperalgesia in a time-dependent manner in wild-type mice compared with the sham group 24 h after the session, which was further increased in IL-10(-/-) mice (P ˂ 0.05). Intraperitoneal treatment of wild-type mice with IL-10 (1-10 ng) reduced muscle mechanical hyperalgesia in a dose-dependent manner and reversed the enhanced muscle hyperalgesia in IL-10(-/-) mice (P ˂ 0.05). The 2 h swimming session induced increases in tumour necrosis factor-α, interleukin-1β and IL-10 production in the soleus muscle. However, tumour necrosis factor-α and interleukin-1β production in the soleus muscle were even higher in IL-10(-/-) mice between 2 and 6 h after the stimulus (P ˂ 0.05). There was no statistical difference in the levels of the antihyperalgesic cytokines interleukin-4, interleukin-5, interleukin-13 and transforming growth factor-β between wild-type and IL-10(-/-) mice (P ˃ 0.05). Interleukin-10 deficiency also resulted in increased myeloperoxidase activity, greater depletion of reduced glutathione levels, increased superoxide anion production and the maintenance of high plasma concentrations of creatine kinase (until 24 h after the swimming session) in soleus muscle (P ˂ 0.05). These results demonstrate that endogenous IL-10 controls intense acute swimming-induced muscle mechanical hyperalgesia by limiting oxidative stress and cytokine production.

Hypo-activity induced skeletal muscle atrophy and potential nutritional interventions: A review

Periods of hypo-activity result in profound changes in skeletal muscle morphology and strength. This review primarily addresses the differential impact of de-training, bed-rest, limb immobilisation and unilateral lower limb suspension on muscle morphology, strength and fatigability. The degree of muscle atrophy differs depending on the hypo-activity model and the muscles in question, with the leg and postural muscles being the most susceptible to atrophy. Hypo-activity also results in the dramatic loss of strength that often surpasses the loss of muscle mass, and consequently, the nervous system and contractile properties adapt to adjust for this excessive loss of strength. In addition, the degree of muscle strength loss is different depending on the hypo-activity model, with immobilisation appearing to have a greater impact on strength than unloaded models. There is a step-wise difference in the magnitude of muscle loss so that, even after accounting for differential durations of interventions immobilisation ≥ unilateral lower limb suspension ≥ bed-rest ≥ de-training. Muscle fatigability varies between hypo-activity models but the results are equivocal and this may be due to task-specific adaptations. This review also addresses potential nutritional interventions for attenuating hypo-activity induced muscle atrophy and strength declines, in the absence of exercise. Essential amino acid supplementation stands as a strong candidate but other supplements are good contenders for attenuating hypo-activity induced atrophy and strength losses. Several potential nutritional supplements are highlighted that could be used to combat muscle atrophy but extensive research is needed to determine the most effective.