Fish oil positively regulates anabolic signalling alongside an increase in whole-body gluconeogenesis in ageing skeletal muscle

Expert consensus report on lipid mediators: Role in resolution of inflammation and muscle preservation

This meeting report presents a consensus on the biological aspects of lipid emulsions in parenteral nutrition, emphasizing the unanimous support for the integration of lipid emulsions, particularly those containing fish oil, owing to their many potential benefits beyond caloric provision. Lipid emulsions have evolved from simple energy sources to complex formulations designed to improve safety profiles and offer therapeutic benefits. The consensus highlights the critical role of omega-3 polyunsaturated fatty acids (PUFAs), notably eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), found in fish oil and other marine oils, for their anti-inflammatory properties, muscle mass preservation, and as precursors to the specialized pro-resolving mediators (SPMs). SPMs play a significant role in immune modulation, tissue repair, and the active resolution of inflammation without impairing host defense mechanisms. The panel's agreement underscores the importance of incorporating fish oil within clinical practices to facilitate recovery in conditions like surgery, critical illness, or immobility, while cautioning against therapies that might disrupt natural inflammation resolution processes. This consensus not only reaffirms the role of specific lipid components in enhancing patient outcomes, but also suggests a shift towards nutrition-based therapeutic strategies in clinical settings, advocating for the proactive evidence-based use of lipid emulsions enriched with omega-3 PUFAs. Furthermore, we should seek to apply our knowledge concerning DHA, EPA, and their SPM derivatives, to produce more informative randomized controlled trial protocols, thus allowing more authoritative clinical recommendations.

Potential nutritional strategies to prevent and reverse sarcopenia in aging process: Role of fish oil-derived ω-3 polyunsaturated fatty acids, wheat oligopeptide and their combined intervention

INTRODUCTION

Nutritional support is potentially considered an essential step to prevent muscle loss and enhance physical function in older adults.

OBJECTIVES

This study aimed to assess the role of potential nutritional strategies, i.e., fish oil-derived ω-3 polyunsaturated fatty acids (PUFAs), wheat oligopeptide and their combined intervention, in preventing and reversing sarcopenia in aging process.

METHODS

One hundred 25-month-old Sprague-Dawley rats were randomly divided into 10 groups, and 10 newly purchased 6-month-old rats were included in young control group (n = 10). Fish oil (200, 400 or 800 mg/kg body weight), wheat oligopeptide (100, 200 or 400 mg/kg body weight), fish oil + wheat oligopeptide (800 + 100, 400 + 200 or 200 + 400 mg/kg body weight) or the equal volume of solvent were administered daily by gavage for 10 weeks. The effects of these interventions on natural aging rats were evaluated.

RESULTS

All intervention groups had a significant increase in muscle mass and grip strength and reduction in perirenal fat weight when compared to the aged control group (P < 0.05). The results of biochemical parameters, magnetic resonance imaging, proteomics and western blot suggested that the combination of wheat oligopeptide and fish oil-derived ω-3 PUFA, especially group WFM 2 (400 + 200 mg/kg body weight fish oil + wheat oligopeptide), was found to be more effective against aging-associated muscle loss than single intervention. Additionally, the interventions ameliorated fatty infiltration, muscle atrophy, and congestion in the intercellular matrix, and inflammatory cell infiltration in muscle tissue. The interventions also improved oxidative stress, anabolism, hormone levels, and inflammatory levels of skeletal muscle.

CONCLUSIONS

The combination of fish oil-derived ω-3 PUFA and wheat oligopeptide was found to be a promising nutritional support to prevent and reverse sarcopenia. The potential mechanism involved the promotion of protein synthesis and muscle regeneration, as well as the enhancement of muscle strength.

Long-Chain Omega-3 Fatty Acid Supplementation and Exercise-Induced Muscle Damage: EPA or DHA?

PURPOSE

Long-chain omega-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) may enhance recovery from exercise-induced muscle damage (EIMD). However, it is unclear if the effects are due to EPA, DHA, or both. The purpose of this investigation was to examine the effect of EPA + DHA, EPA, and DHA compared with placebo (PL) on muscular recovery.

METHODS

Thirty males were randomized to 4 g·d -1 EPA + DHA ( n = 8), EPA ( n = 8), DHA ( n = 7), or PL ( n = 7). After 7-wk supplementation, a downhill running (20 min, 70% V̇O 2max , -16% gradient) plus jumping lunges (5 × 20 reps, 2-min rest intervals) muscle damage protocol was performed. Indices of muscle damage, soreness, muscle function, and inflammation were measured at baseline and throughout recovery. The omega-3 index (O3i; %EPA + %DHA in erythrocytes) was used to track tissue EPA and DHA status.

RESULTS

After supplementation, the O3i was significantly higher than PL in all experimental groups ( P < 0.001). Leg press performance was lower in the PL group at 24 h compared with EPA ( P = 0 .019) and at 72 h for EPA ( P = 0.004) and DHA ( P = 0 .046). Compared with PL, muscle soreness was lower in the DHA ( P = 0.015) and EPA ( P = 0.027) groups at 48 h. Albeit nonsignificant, EPA + DHA tended to attenuate muscle soreness ( d = 1.37) and leg strength decrements ( d = 0.75) compared with PL. Jump performance and power metrics improved more rapidly in the EPA and DHA groups (time effects: P < 0.001). Measures of inflammation, range of motion, and muscle swelling were similar between groups ( P > 0.05).

CONCLUSIONS

Compared with PL, 4 g·d -1 of EPA or DHA for 52 d improves certain aspects of recovery from EIMD. EPA + DHA did not clearly enhance recovery. Equivalent dosing of EPA + DHA may blunt the performance effects observed in EPA or DHA alone.

Long-chain n-3 PUFA ingestion for the stimulation of muscle protein synthesis in healthy older adults

This review aims to critically evaluate the efficacy of long-chain ո-3 PUFA ingestion in modulating muscle protein synthesis (MPS), with application to maintaining skeletal muscle mass, strength and function into later life. Ageing is associated with a gradual decline in muscle mass, specifically atrophy of type II fibres, that is exacerbated by periods of (in)voluntary muscle disuse. At the metabolic level, in otherwise healthy older adults, muscle atrophy is underpinned by anabolic resistance which describes the impaired MPS response to non-pharmacological anabolic stimuli, namely, physical activity/exercise and amino acid provision. Accumulating evidence implicates a mechanistic role for n-3 PUFA in upregulating MPS under stimulated conditions (post-prandial state or following exercise) via incorporation of EPA and DHA into the skeletal muscle phospholipid membrane. In some instances, these changes in MPS with chronic ո-3 PUFA ingestion have translated into clinically relevant improvements in muscle mass, strength and function; an observation evidently more prevalent in healthy older women than men. This apparent sexual dimorphism in the adaptive response of skeletal muscle metabolism to EPA and DHA ingestion may be related to a greater propensity for females to incorporate ո-3 PUFA into human tissue and/or the larger dose of ingested ո-3 PUFA when expressed relative to body mass or lean body mass. Future experimental studies are warranted to characterise the optimal dosing and duration of ո-3 PUFA ingestion to prescribe tailored recommendations regarding n-3 PUFA nutrition for healthy musculoskeletal ageing into later life.

The Effect of Long Chain n-3 Fatty Acid Supplementation on Muscle Strength in Older Adults: A Systematic Review and Meta-Analysis

The main objective of the current study was to perform a systematic literature review with the purpose of exploring the impact of long-chain n-3 polyunsaturated fatty acid (LCn-3 PUFA) relative to control oil supplementation on muscle strength, with secondary outcomes of muscle mass and physical function in older individuals under conditions of habitual physical activity/exercise. The review protocol was registered with PROSPERO (CRD42021267011) and followed the guidelines outlined in the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement. The search for relevant studies was performed utilizing databases such as PubMed, EMBASE, CINAHL, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL) up to June 2023. Randomized controlled trials (RCTs) in older adults comparing the effects of LCn-3 PUFA with a control oil supplement on muscle strength were included. Five studies involving a total of 488 participants (348 females and 140 males) were identified that met the specified inclusion criteria and were included. Upon analyzing the collective data from these studies, it was observed that supplementation with LCn-3 PUFA did not have a significant impact on grip strength (standardized mean difference (SMD) 0.61, 95% confidence interval [-0.05, 1.27]; p = 0.07) in comparison to the control group. However, there was a considerable level of heterogeneity among the studies (I2 = 90%; p < 0.001). As secondary outcomes were only measured in a few studies, with significant heterogeneity in methods, meta-analyses of muscle mass and functional abilities were not performed. Papers with measures of knee extensor muscle mass as an outcome (n = 3) found increases with LCn-3 PUFA supplementation, but studies measuring whole body lean/muscle mass (n = 2) and functional abilities (n = 4) reported mixed results. With a limited number of studies, our data indicate that LCn-3 PUFA supplementation has no effect on muscle strength or functional abilities in older adults but may increase muscle mass, although, with only a few studies and considerable heterogeneity, further work is needed to confirm these findings.

The Effect of Omega-3 Fatty Acids on Sarcopenia: Mechanism of Action and Potential Efficacy

Sarcopenia, a progressive disease characterized by a decline in muscle strength, quality, and mass, affects aging population worldwide, leading to increased morbidity and mortality. Besides resistance exercise, various nutritional strategies, including omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation, have been sought to prevent this condition. This narrative review summarizes the current evidence on the effect and mechanism of n-3 PUFA on musculoskeletal health. Despite conflicting evidence, n-3 PUFA is suggested to benefit muscle mass and volume, with more evident effects with higher supplementation dose (>2 g/day). n-3 PUFA supplementation likely improves handgrip and quadriceps strength in the elderly. Improved muscle functions, measured by walking speed and time-up-to-go test, are also observed, especially with longer duration of supplementation (>6 months), although the changes are small and unlikely to be clinically meaningful. Lastly, n-3 PUFA supplementation may positively affect muscle protein synthesis response to anabolic stimuli, alleviating age-related anabolic resistance. Proposed mechanisms by which n-3 PUFA supplementation improves muscle health include 1. anti-inflammatory properties, 2. augmented expression of mechanistic target of rapamycin complex 1 (mTORC1) pathway, 3. decreased intracellular protein breakdown, 4. improved mitochondrial biogenesis and function, 5. enhanced amino acid transport, and 6. modulation of neuromuscular junction activity. In conclusion, n-3 PUFAs likely improve musculoskeletal health related to sarcopenia, with suggestive effect on muscle mass, strength, physical performance, and muscle protein synthesis. However, the interpretation of the findings is limited by the small number of participants, heterogeneity of supplementation regimens, and different measuring protocols.

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.

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.

How to Increase Muscle Mass in Critically Ill Patients: Lessons Learned from Athletes and Bodybuilders

PURPOSE OF REVIEW

Decades of research on nutrition and exercise on athletes and bodybuilders has yielded various strategies to promote anabolism and improve muscle health and growth. We reviewed these interventions in the context of muscle loss in critically ill patients.

RECENT FINDINGS

For critically ill patients, ensuring optimum protein intake is important, potentially using a whey-containing source and supplemented with vitamin D and leucine. Agents like hydroxyl β-methylbutyrate and creatine can be used to promote muscle synthesis. Polyunsaturated fatty acids stimulate muscle production as well as have anti-inflammatory properties that may be useful in critical illness. Adjuncts like oxandralone promote anabolism. Resistance training has shown mixed results in the ICU setting but needs to be explored further with specific outcomes. Critically ill patients suffer from severe proteolysis during hospitalization as well as persistent inflammation, immunosuppression, and catabolism syndrome after discharge. High protein supplementation, ergogenic aids, anti-inflammatories, and anabolic adjuncts have shown potential in alleviating muscle loss and should be used in intensive care units to optimize patient recovery.

Effects of n-3 EPA and DHA supplementation on fat free mass and physical performance in elderly. A systematic review and meta-analysis of randomized clinical trial

The most studied n-3 polyunsaturated fatty acids (n-3 PUFAs) are eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), and their intake seem to have a positive effect on skeletal muscle. This systematic review and meta-analysis aims to investigate the effect of n-3 EPA and DHA supplementation on fat free mass, and on different indexes of physical performance in the elderly. Eligible studies included RCT studies that investigated EPA and DHA intervention. Random-effects models have been used in order to estimate pooled effect sizes, the mean differences, and 95 % CIs. Findings from 14 studies (n = 2220 participants) lasting from 6 to 144 weeks have been summarized in this article. The meta-analyzed mean differences for random effects showed that daily n-3 EPA + DHA supplementation (from 0.7 g to 3.36 g) decreases the time of Time Up and Go (TUG) test of -0.28 s (CI 95 %-0.43, -0.13;). No statistically significant effects on physical performance indicators, such as 4-meter Walking Test, Chair Rise Test and Handgrip Strength, have been found. The fat free mass follows an improvement trend of +0.30 kg (CI 95 % -0.39, 0.99) but not statistically significant. N-3 EPA + DHA supplementation could be a promising strategy in order to enhance muscle quality and prevent or treat frailty.

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.

Beneficial Effects of a Mixture of Algae and Extra Virgin Olive Oils on the Age-Induced Alterations of Rodent Skeletal Muscle: Role of HDAC-4

Aging is associated with a progressive decline in skeletal muscle mass, strength and function (sarcopenia). We have investigated whether a mixture of algae oil (25%) and extra virgin olive oil (75%) could exert beneficial effects on sarcopenia. Young (3 months) and old (24 months) male Wistar rats were treated with vehicle or with the oil mixture (OM) (2.5 mL/kg) for 21 days. Aging decreased gastrocnemius weight, total protein, and myosin heavy chain mRNA. Treatment with the OM prevented these effects. Concomitantly, OM administration decreased the inflammatory state in muscle; it prevented the increase of pro-inflammatory interleukin-6 (IL-6) and the decrease in anti-inflammatory interleukin-10 (IL-10) in aged rats. The OM was not able to prevent aging-induced alterations in either the insulin-like growth factor I/protein kinase B (IGF-I/Akt) pathway or in the increased expression of atrogenes in the gastrocnemius. However, the OM prevented decreased autophagy activity (ratio protein 1A/1B-light chain 3 (LC3b) II/I) induced by aging and increased expression of factors related with muscle senescence such as histone deacetylase 4 (HDAC-4), myogenin, and IGF-I binding protein 5 (IGFBP-5). These data suggest that the beneficial effects of the OM on muscle can be secondary to its anti-inflammatory effect and to the normalization of HDAC-4 and myogenin levels, making this treatment an alternative therapeutic tool for sarcopenia.

Muscle Mass Loss in the Older Critically Ill Population: Potential Therapeutic Strategies

Skeletal muscle plays a critical role in everyday life, and its age-associated reduction has severe health consequences. The pre-existing presence of sarcopenia, combined with anabolic resistance, protein undernutrition, and the pro-catabolic/anti-anabolic milieu induced by aging and exacerbated in critical care, may accelerate the rate at which skeletal muscle is lost in patients with critical illness. Advancements in intensive care unit (ICU)-care provision have drastically improved survival rates; therefore, attention can be redirected toward other significant issues affecting ICU patients (e.g., length of stay, days on ventilation, nosocomial disease development, etc.). Thus, strategies targeting muscle mass and function losses within an ICU setting are essential to improve patient-related outcomes. Notably, loading exercise and protein provision are the most compelling. Many older ICU patients seldom meet the recommended protein intake, and loading exercise is difficult to conduct in the ICU. Nevertheless, the incorporation of physical therapy (PT), neuromuscular electrical stimulation, and early mobilization strategies may be beneficial. Furthermore, a number of nutrition practices within the ICU have been shown to improve patient-related outcomes ((e.g., feeding strategy [i.e., oral, early enteral, or parenteral]), be hypocaloric (∼70%-80% energy requirements), and increase protein provision (∼1.2-2.5 g/kg/d)). The aim of this brief review is to discuss the dysregulation of muscle mass maintenance in an older ICU population and highlight the potential benefits of strategic nutrition practice, specifically protein, and PT within the ICU. Finally, we provide some general guidelines that may serve to counteract muscle mass loss in patients with critical illness.

The Influence of Omega-3 Fatty Acids on Skeletal Muscle Protein Turnover in Health, Disuse, and Disease

Ingestion of omega-3 fatty acids is known to exert favorable health effects on a number of biological processes such as improved immune profile, enhanced cognition, and optimized neuromuscular function. Recently, data have emerged demonstrating a positive influence of omega-3 fatty acid intake on skeletal muscle. For instance, there are reports of clinically-relevant gains in muscle size and strength in healthy older persons with omega-3 fatty acid intake as well as evidence that omega-3 fatty acid ingestion alleviates the loss of muscle mass and prevents decrements in mitochondrial respiration during periods of muscle-disuse. Cancer cachexia that is characterized by a rapid involuntary loss of lean mass may also be attenuated by omega-3 fatty acid provision. The primary means by which omega-3 fatty acids positively impact skeletal muscle mass is via incorporation of eicosapentaenoic acid (EPA; 20:5n−3) and docosahexaenoic acid (DHA; 22:6n−3) into membrane phospholipids of the sarcolemma and intracellular organelles. Enrichment of EPA and DHA in these membrane phospholipids is linked to enhanced rates of muscle protein synthesis, decreased expression of factors that regulate muscle protein breakdown, and improved mitochondrial respiration kinetics. However, exactly how incorporation of EPA and DHA into phospholipid membranes alters these processes remains unknown. In this review, we discuss the interaction between omega-3 fatty acid ingestion and skeletal muscle protein turnover in response to nutrient provision in younger and older adults. Additionally, we examine the role of omega-3 fatty acid supplementation in protecting muscle loss during muscle-disuse and in cancer cachexia, and critically evaluate the molecular mechanisms that underpin the phenotypic changes observed in skeletal muscle with omega-3 fatty acid intake.

Long-chain n-3 fatty acids as an essential link between musculoskeletal and cardio-metabolic health in older adults

This narrative review aims to critically evaluate scientific evidence exploring the therapeutic role(s) of long-chain n-3 PUFA in the context of ageing, and specifically, sarcopenia. We highlight that beyond impairments in physical function and a lack of independence, the age-related decline in muscle mass has ramifications for cardio-metabolic health. Specifically, skeletal muscle is crucial in regulating blood glucose homeostasis (and by extension reducing type 2 diabetes mellitus risk) and providing gluconeogenic precursors that are critical for survival during muscle wasting conditions (i.e. AIDS). Recent interest in the potential anabolic action of n-3 PUFA is based on findings from experimental studies that measured acute changes in the stimulation of muscle protein synthesis (MPS) and/or chronic changes in muscle mass and strength in response to fish oil-derived n-3 PUFA supplementation. Key findings include a potentiated response of MPS to amino acid provision or resistance-based exercise with n-3 PUFA in healthy older adults that extrapolated to longer-term changes in muscle mass and strength. The key mechanism(s) underpinning this enhanced response of MPS remains to be fully elucidated, but is likely driven by the incorporation of exogenous n-3 PUFA into the muscle phospholipid membrane and subsequent up-regulation of cell signalling proteins known to control MPS. In conclusion, multiple lines of evidence suggest that dietary n-3 PUFA provide an essential link between musculoskeletal and cardio-metabolic health in older adults. Given that western diets are typically meagre in n-3 PUFA content, nutritional recommendations for maintaining muscle health with advancing age should place greater emphasis on dietary n-3 PUFA intake.

Comprehensive Analysis of lncRNAs and circRNAs Reveals the Metabolic Specialization in Oxidative and Glycolytic Skeletal Muscles

The biochemical and functional differences between oxidative and glycolytic muscles could affect human muscle health and animal meat quality. However, present understanding of the epigenetic regulation with respect to lncRNAs and circRNAs is rudimentary. Here, porcine oxidative and glycolytic skeletal muscles, which were at the growth curve inflection point, were sampled to survey variant global expression of lncRNAs and circRNAs using RNA-seq. A total of 4046 lncRNAs were identified, including 911 differentially expressed lncRNAs (p < 0.05). The cis-regulatory analysis identified target genes that were enriched for specific GO terms and pathways (p < 0.05), including the oxidation-reduction process, glycolytic process, and fatty acid metabolic. All these were closely related to different phenotypes between oxidative and glycolytic muscles. Additionally, 810 circRNAs were identified, of which 137 were differentially expressed (p < 0.05). Interestingly, some circRNA-miRNA-mRNA networks were found, which were closely linked to muscle fiber-type switching and mitochondria biogenesis in muscles. Furthermore, 44.69%, 39.19%, and 54.01% of differentially expressed mRNAs, lncRNAs, and circRNAs respectively were significantly enriched in pig quantitative trait loci (QTL) regions for growth and meat quality traits. This study reveals a mass of candidate lncRNAs and circRNAs involved in muscle physiological functions, which may improve understanding of muscle metabolism and development from an epigenetic perspective.

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.

Gene-based analysis of angiogenesis, mitochondrial and insulin-related pathways in skeletal muscle of older individuals following nutraceutical supplementation

Cocoa flavanols and fish oil omega-3 fatty acids are two bio-active nutrients that may improve muscle microvascular function, insulin sensitivity and mitochondrial function in older adults. We assessed changes in gene expression of these pathways in muscle from two nutritional intervention studies in older healthy volunteers: (i) 6-weeks daily fish oil supplementation in older females (3.4 g/d; age: 64.4 ± 0.8 y, BMI: 26.2 ± 0.7 kg/m²), and (ii) 7-day daily cocoa flavanol supplementation in older males (1050 mg/d; age: 70.1 ± 0.9 y, BMI: 25.7 ± 0.6 kg/m²). There was a main effect of 6-weeks fish oil supplementation on angiogenesis gene expression, with no overall changes in mitochondrial or insulin signaling genes. 7-day cocoa supplementation elicited changes in extracellular matrix (ECM) related genes. Thus, the effects of fish oil supplementation on vascular remodeling in skeletal muscle, and ECM remodeling with cocoa supplementation have emerged as areas for future study.

The impact of exercise and nutrition on the regulation of skeletal muscle mass

The maintenance of skeletal muscle mass and strength throughout life is a key determinant of human health and well-being. There is a gradual loss of both skeletal muscle mass and strength with ageing (a process termed sarcopenia) that increases the risk of functional dependence, morbidity and mortality. Understanding the factors that regulate the size of human muscle mass, particularly during the later years of life, has therefore become an area of intense scientific inquiry. The amount of muscle mass is determined by coordinated changes in muscle protein synthesis (MPS) and muscle protein breakdown (MPB). In this review, we assess both classical and contemporary work that has examined how resistance exercise and nutrition impact on MPS and MPB. Special consideration is given to the role of different sources of dietary protein (food vs. supplements) and non-protein nutrients such as omega-3 fatty acids in regulating MPS. We also critically evaluate recent studies that have employed novel 'omic' technologies such as dynamic protein profiling to probe for changes in rates of MPS and MPB at the individual protein level following exercise. Finally, we provide suggestions for future research that we hope will yield important information for the development of exercise and nutritional strategies to counteract muscle loss in a variety of clinical settings.

Balanced Diet-Fed Fat-1 Transgenic Mice Exhibit Lower Hindlimb Suspension-Induced Soleus Muscle Atrophy

The consequences of two-week hindlimb suspension (HS) on skeletal muscle atrophy were investigated in balanced diet-fed Fat-1 transgenic and C57BL/6 wild-type mice. Body composition and gastrocnemius fatty acid composition were measured. Skeletal muscle force, cross-sectional area (CSA), and signaling pathways associated with protein synthesis (protein kinase B, Akt; ribosomal protein S6, S6, eukaryotic translation initiation factor 4E-binding protein 1, 4EBP1; glycogen synthase kinase3-beta, GSK3-beta; and extracellular-signal-regulated kinases 1/2, ERK 1/2) and protein degradation (atrophy gene-1/muscle atrophy F-box, atrogin-1/MAFbx and muscle RING finger 1, MuRF1) were evaluated in the soleus muscle. HS decreased soleus muscle wet and dry weights (by 43% and 26%, respectively), muscle isotonic and tetanic force (by 29% and 18%, respectively), CSA of the soleus muscle (by 36%), and soleus muscle fibers (by 45%). Fat-1 transgenic mice had a decrease in the ω-6/ω-3 polyunsaturated fatty acids (PUFAs) ratio as compared with C57BL/6 wild-type mice (56%, p < 0.001). Fat-1 mice had lower soleus muscle dry mass loss (by 10%) and preserved absolute isotonic force (by 17%) and CSA of the soleus muscle (by 28%) after HS as compared with C57BL/6 wild-type mice. p-GSK3B/GSK3B ratio was increased (by 70%) and MuRF-1 content decreased (by 50%) in the soleus muscle of Fat-1 mice after HS. Balanced diet-fed Fat-1 mice are able to preserve in part the soleus muscle mass, absolute isotonic force and CSA of the soleus muscle in a disuse condition.

Sex differences in the effect of fish-oil supplementation on the adaptive response to resistance exercise training in older people: a randomized controlled trial

BACKGROUND

Resistance exercise increases muscle mass and function in older adults, but responses are attenuated compared with younger people. Data suggest that long-chain n-3 polyunsaturated fatty acids (PUFAs) may enhance adaptations to resistance exercise in older women. To our knowledge, this possibility has not been investigated in men.

OBJECTIVE

We sought to determine the effects of long-chain n-3 PUFA supplementation on resistance exercise training-induced increases in muscle mass and function and whether these effects differ between older men and women.

DESIGN

Fifty men and women [men: n = 27, mean ± SD age: 70.6 ± 4.5 y, mean ± SD body mass index (BMI; in kg/m2): 25.6 ± 4.2; women: n = 23, mean ± SD age: 70.7 ± 3.3 y, mean ± SD BMI: 25.3 ± 4.7] were randomly assigned to either long-chain n-3 PUFA (n = 23; 3 g fish oil/d) or placebo (n = 27; 3 g safflower oil/d) and participated in lower-limb resistance exercise training twice weekly for 18 wk. Muscle size, strength, and quality (strength per unit muscle area), functional abilities, and circulating metabolic and inflammatory markers were measured before and after the intervention.

RESULTS

Maximal isometric torque increased after exercise training to a greater (P < 0.05) extent in the long-chain n-3 PUFA group than in the placebo group in women, with no differences (P > 0.05) between groups in men. In both sexes, the effect of exercise training on maximal isokinetic torque at 30, 90, and 240° s-1, 4-m walk time, chair-rise time, muscle anatomic cross-sectional area, and muscle fat did not differ (P > 0.05) between groups. There was a greater (P < 0.05) increase in muscle quality in women after exercise training in the long-chain n-3 PUFA group than in the placebo group, with no such differences in men (P > 0.05). Long-chain n-3 PUFAs resulted in a greater decrease (P < 0.05) than the placebo in plasma triglyceride concentrations in both sexes, with no differences (P > 0.05) in glucose, insulin, or inflammatory markers.

CONCLUSION

Long-chain n-3 PUFA supplementation augments increases in muscle function and quality in older women but not in older men after resistance exercise training. This trial was registered at clinicaltrials.gov as NCT02843009.

Docosahexaenoic acid-supplementation prior to fasting prevents muscle atrophy in mice

BACKGROUND

Muscle wasting prevails in numerous diseases (e.g. diabetes, cardiovascular and kidney diseases, COPD,…) and increases healthcare costs. A major clinical issue is to devise new strategies preventing muscle wasting. We hypothesized that 8-week docosahexaenoic acid (DHA) supplementation prior to fasting may preserve muscle mass in vivo.

METHODS

Six-week-old C57BL/6 mice were fed a DHA-enriched or a control diet for 8 weeks and then fasted for 48 h.

RESULTS

Feeding mice a DHA-enriched diet prior to fasting elevated muscle glycogen contents, reduced muscle wasting, blocked the 55% decrease in Akt phosphorylation, and reduced by 30-40% the activation of AMPK, ubiquitination, or autophagy. The DHA-enriched diet fully abolished the fasting induced-messenger RNA (mRNA) over-expression of the endocannabinoid receptor-1. Finally, DHA prevented or modulated the fasting-dependent increase in muscle mRNA levels for Rab18, PLD1, and perilipins, which determine the formation and fate of lipid droplets, in parallel with muscle sparing.

CONCLUSIONS

These data suggest that 8-week DHA supplementation increased energy stores that can be efficiently mobilized, and thus preserved muscle mass in response to fasting through the regulation of Akt- and AMPK-dependent signalling pathways for reducing proteolysis activation. Whether a nutritional strategy aiming at increasing energy status may shorten recovery periods in clinical settings remains to be tested.

n-3 Fatty acids preserve muscle mass and insulin sensitivity in a rat model of energy restriction

In obese subjects, the loss of fat mass during energy restriction is often accompanied by a loss of muscle mass. The hypothesis thatn-3 PUFA, which modulate protein homoeostasis via effects on insulin sensitivity, could contribute to maintain muscle mass during energy restriction was tested in rats fed a high-fat diet (4 weeks) rich in 18 : 1n-9 (oleic acid, OLE-R), 18 : 3n-3 (α-linolenic acid, ALA-R) orn-3 long-chain (LC-R) fatty acid and then energy restricted (8 weeks). A control group (OLE-ad libitum(AL)) was maintained with AL diet throughout the study. Rats were killed 10 min after an i.v. insulin injection. All energy-restricted rats lost weight and fat mass, but only the OLE-R group showed a significant muscle loss. TheGastrocnemiusmuscle was enriched with ALA in the ALA-R group and with LC-PUFA in the ALA-R and LC-R groups. The proteolytic ubiquitin–proteasome system was differentially affected by energy restriction, with MAFbx and muscle ring finger-1 mRNA levels being decreased in the LC-R group (−30 and −20 %, respectively). RAC-αserine/threonine-protein kinase and insulin receptor substrate 1 phosphorylation levels increased in the LC-R group (+70 %), together with insulin receptor mRNA (+50 %). The ALA-R group showed the same overall activation pattern as the LC-R group, although to a lesser extent. In conclusion, dietaryn-3 PUFA prevent the loss of muscle mass associated with energy restriction, probably by an improvement in the insulin-signalling pathway activation, in relation to enrichment of plasma membranes inn-3 LC-PUFA.

Effects of high EPA and high DHA fish oils on changes in signaling associated with protein metabolism induced by hindlimb suspension in rats

The effects of either eicosapentaenoic (EPA)- or docosahexaenoic (DHA)-rich fish oils on hindlimb suspension (HS)-induced muscle disuse atrophy were compared. Daily oral supplementations (0.3 mL/100 g b.w.) with mineral oil (MO) or high EPA or high DHA fish oils were performed in adult rats. After 2 weeks, the animals were subjected to HS for further 2 weeks. The treatments were maintained alongside HS At the end of 4 weeks, we evaluated: body weight gain, muscle mass and fat depots, composition of fatty acids, cross-sectional areas (CSA) of the soleus muscle and soleus muscle fibers, activities of cathepsin L and 26S proteasome, and content of carbonylated proteins in the soleus muscle. Signaling pathway activities associated with protein synthesis (Akt, p70S6K, S6, 4EBP1, and GSK3-beta) and protein degradation (atrogin-1/MAFbx, and MuRF1) were evaluated. HS decreased muscle mass, CSA of soleus muscle and soleus muscle fibers, and altered signaling associated with protein synthesis (decreased) and protein degradation (increased). The treatment with either fish oil decreased the ratio of omega-6/omega-3 fatty acids and changed protein synthesis-associated signaling. EPA-rich fish oil attenuated the changes induced by HS on 26S proteasome activity, CSA of soleus muscle fibers, and levels of p-Akt, total p70S6K, p-p70S6K/total p70S6K, p-4EBP1, p-GSK3-beta, p-ERK2, and total ERK 1/2 proteins. DHA-rich fish oil attenuated the changes induced by HS on p-4EBP1 and total ERK1 levels. The effects of EPA-rich fish oil on protein synthesis signaling were more pronounced. Both EPA- and DHA-rich fish oils did not impact skeletal muscle mass loss induced by non-inflammatory HS.

Ratio of dietary ω-3 and ω-6 fatty acids-independent determinants of muscle mass-in hemodialysis patients with diabetes

OBJECTIVE

ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are essential nutrients in the human diet and possibly affect muscle mass. We evaluated the association between the dietary ratios of ω-3 and ω-6 PUFAs and muscle mass, indicated as skeletal muscle mass (SMM) and appendicular skeletal muscle mass (ASM), in patients with diabetes undergoing hemodialysis (HD).

METHODS

In this cross-sectional study, data on 69 patients with diabetes who underwent standard HD therapy were analyzed. For estimating muscle mass, anthropometric and bioelectrical impedance analyses were conducted following dialysis. In addition, routine laboratory and 3-d dietary data were obtained. The adequate intake (AI) cut-off for ω-3 PUFAs was 1.6 g/d and 1.1 g/d for male and female patients, respectively.

RESULTS

The average age of the participants was 63.0 ± 10.4 y. The mean ratios of ω-3/ω-6 PUFA intake, ω-6/ω-3 PUFA intake, SMM, and ASM of the patients were 0.13 ± 0.07, 9.4 ± 6.4, 24.6 ± 5.4 kg, and 18.3 ± 4.6 kg, respectively. Patients who had AI of ω-3 PUFAs had significantly higher SMM and ASM than did their counterparts. Linear and stepwise multivariable adjustment analyses revealed that insulin resistance and the ω-6/ω-3 PUFA ratio were the independent deleterious determinants of ASM normalized to height in HD patients.

CONCLUSIONS

Patients with AI of ω-3 PUFAs had total-body SMM and ASM that were more appropriate. A higher dietary ratio of ω-6/ω-3 PUFAs was associated with reduced muscle mass in HD patients.

Effect of dietary ALA on growth rate, feed conversion ratio, mortality rate and breast meat omega-3 LCPUFA content in broiler chickens

We have previously demonstrated that feeding chickens a diet containing high levels of the n-3 PUFA α-linolenic acid (ALA) significantly increases the content of the principal omega-3 long-chain polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaenoic acid, in their meat and eggs. However, the effect of the diet on production characteristics of the birds has not been assessed. This study aimed to determine the effect of feeding male and female Cobb 500 broilers (n = 3840) a high ALA diet (containing 2.5% flaxseed oil) compared with a standard commercial Control diet (containing 2.5% tallow) on growth, feed conversion ratio and mortality until 6 weeks of age. As expected the dietary flaxseed oil significantly increased breast meat levels of omega-3 polyunsaturated fatty acids (~4-fold), with most eicosapentaenoic acid and docosahexaenoic acid being deposited in the phospholipid fraction. Both male and female birds fed the high ALA diet were significantly heavier at 6 weeks of age (77 g heavier in females, 87 g heavier in males). They also had a significantly (10%) lower feed conversion ratio, and a mortality rate that was not different from the Control diet across the 6-week feeding period. These findings indicate that a high ALA diet has the potential to enrich chicken breast meat with eicosapentaenoic acid and docosahexaenoic acid without loss of growth rate or feed efficiency, or increase in fat content of breast meat.

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.

Fish oil supplemented for 9 months does not improve glycaemic control or insulin sensitivity in subjects with impaired glucose regulation: a parallel randomised controlled trial

The effects of fish oil (FO) supplementation on glycaemic control are unclear, and positive effects may occur only when the phospholipid content of tissue membranes exceeds 14 % asn-3 PUFA. Subjects (n36, thirty-three completed) were paired based on metabolic parameters and allocated into a parallel double-blind randomised trial with one of each pair offered daily either 6 g of FO (3·9 gn-3 PUFA) or 6 g of maize oil (MO) for 9 months. Hyperinsulinaemic–euglycaemic–euaminoacidaemic (HIEGEAA) clamps (with [6,62H2glucose]) were performed at the start and end of the intervention. Endogenous glucose production (EGP) and whole-body protein turnover (WBPT) were each measured after an overnight fast. The primary outcome involved the effect of oil type on insulin sensitivity related to glycaemic control. The secondary outcome involved the effect of oil type on WBPT. Subjects on FO (n16) had increased erythrocyten-3 PUFA concentrations >14 %, whereas subjects on MO (n17) had unalteredn-3 PUFA concentrations at 9 %. Type of oil had no effect on fasting EGP, insulin sensitivity or total glucose disposal during the HIEGEAA clamp. In contrast, under insulin-stimulated conditions, total protein disposal (P=0·007) and endogenous WBPT (P=0·001) were both increased with FO. In an associated pilot study (n4, three completed), althoughn-3 PUFA in erythrocyte membranes increased to >14 % with the FO supplement, the enrichment in muscle membranes remained lower (8 %;P<0·001). In conclusion, long-term supplementation with FO, at amounts near the safety limits set by regulatory authorities in Europe and the USA, did not alter glycaemic control but did have an impact on WBPT.

Mechanisms of enhanced insulin secretion and sensitivity with n-3 unsaturated fatty acids

The widespread acceptance that increased dietary n-3 polyunsaturated fatty acids (PUFAs), especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), improve health is based on extensive studies in animals, isolated cells and humans. Visceral adiposity is part of the metabolic syndrome, together with insulin resistance, dyslipidemia, hypertension and inflammation. Alleviation of metabolic syndrome requires normalization of insulin release and responses. This review assesses our current knowledge of the mechanisms that allow n-3 PUFAs to improve insulin secretion and sensitivity. EPA has been more extensively studied than either ALA or DHA. The complex actions of EPA include increased G-protein-receptor-mediated release of glucagon-like peptide 1 (GLP-1) from enteroendocrine L-cells in the intestine, up-regulation of the apelin pathway and down-regulation of other control pathways to promote insulin secretion by the pancreatic β-cells, together with suppression of inflammatory responses to adipokines, inhibition of peroxisome proliferator-activated receptor α actions and prevention of decreased insulin-like growth factor-1 secretion to improve peripheral insulin responses. The receptors involved and the mechanisms of action probably differ for ALA and DHA, with antiobesity effects predominating for ALA and anti-inflammatory effects for DHA. Modifying both GLP-1 release and the actions of adipokines by n-3 PUFAs could lead to additive improvements in both insulin secretion and sensitivity.

N-3 fatty acids improve body composition and insulin sensitivity during energy restriction in the rat

The hypothesis that n-3 polyunsaturated fatty acids (PUFA) could contribute to maintain muscle mass during energy restriction aiming to weight loss was tested in the rat, with special attention paid to insulin signalling. After 10 weeks on a diet rich in lipids and sucrose, male rats were energy restricted and fed diets rich in 18:1 n-9 (OLE), 18:3 n-3 (ALA) or n-3 long-chain (LC, >18 carbons) PUFA. After 4 weeks, they were killed after an insulin injection. Red blood cells, liver, and Gastrocnemius muscle were enriched in ALA in the ALA group, and in LC-PUFA in the ALA and LC groups. The LC diet resulted in a higher weight loss, without negative impact on the muscle weight. In parallel, hepatic phosphorylation of insulin receptor and IRS1 was the highest in this group. This suggests that the trend we observed in the preservation of protein homeostasis in the LC group is mediated, at least partly, by an enhancement of the early steps of insulin signalling resulting from cell membrane enrichment in n-3 PUFA.

SREBF1 gene variations modulate insulin sensitivity in response to a fish oil supplementation

BACKGROUND

An important inter-individual variability in the response of insulin sensitivity following a fish oil supplementation has been observed. The objective was to examine the associations between single nucleotide polymorphisms (SNPs) within sterol regulatory element binding transcription factor 1 (SREBF1) gene and the response of insulin sensitivity to a fish oil supplementation.

METHODS

Participants (n = 210) were recruited in the greater Quebec City area and followed a 6-week fish oil supplementation protocol (5 g/day: 1.9-2.2 g EPA; 1.1 g DHA). Insulin sensitivity was assessed by the quantitative insulin sensitivity check index (QUICKI). Three tag SNPs (tSNPs) within SREBF1 gene were genotyped according to TAQMAN methodology.

RESULTS

Three tSNPs (rs12953299, rs4925118 and rs4925115) covered 100% of the known genetic variability within SREBF1 gene. None of the three tSNPs was associated with either baseline fasting insulin concentrations (rs12953299, rs4925118 and rs4925115) (p = 0.29, p = 0.20 and p = 0.70, respectively) or QUICKI (p = 0.20, p = 0.18 and p = 0.76, respectively). The three tSNPs (rs12953299, rs4925118 and rs4925115) were associated with differences in the response of plasma insulin levels (p = 0.01, p = 0.005 and p = 0.004, respectively) and rs12953299 as well as rs4925115 were associated with the insulin sensitivity response (p = 0.009 and p = 0.01, respectively) to the fish oil supplementation, independently of the effects of age, sex and BMI.

CONCLUSIONS

The genetic variability within SREBF1 gene has an impact on the insulin sensitivity in response to a fish oil supplementation.

TRIAL REGISTRATION

clinicaltrials.gov: NCT01343342.

Role of n-3 fatty acids in muscle loss and myosteatosis

Image-based methods such as computed tomography for assessing body composition enables quantification of muscle mass and muscle density and reveals that low muscle mass and myosteatosis (fat infiltration into muscle) are common in people with cancer. Myosteatosis and low muscle mass have emerged as independent risk factors for mortality in cancer; however, the characteristics and pathogenesis of these features have not been resolved. Muscle depletion is associated with low plasma eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) in cancer and supplementation with n-3 fatty acids has been shown to ameliorate muscle loss and myosteatosis in clinical studies, suggesting a relationship between n-3 fatty acids and muscle health. Since the mechanisms by which n-3 fatty acids alter body composition in cancer remain unknown, related literature from other conditions associated with myosteatosis, such as insulin resistance and obesity is considered. In these noncancer conditions, it has been reported that n-3 fatty acids act by increasing insulin sensitivity, reducing inflammatory mediators, and altering adipokine profiles and transcription factors; therefore, the plausibility of these mechanisms of action in the neoplastic state are considered. The aim of this review is to summarize what is known about the effects of n-3 fatty acids with regards to muscle condition and to discuss potential mechanisms for effects of n-3 fatty acids on muscle health.

Long-chain n-3 DHA reduces the extent of skeletal muscle fatigue in the rat in vivo hindlimb model

Dietary fish oil modifies skeletal muscle membrane fatty acid composition and oxygen efficiency similar to changes in the myocardium. Oxygen efficiency is a key determinant of sustained force in mammalian skeletal muscle. Therefore, in the present study, we tested the effects of a fish-oil diet on skeletal muscle fatigue under the stress of contraction using the rat in vivo autologous perfused hindlimb model. For 8 weeks, male Wistar rats were fed a diet rich in saturated fat (SF), a diet rich in n-6 PUFA or a diet rich in long-chain (LC) n-3 PUFA DHA derived from fish oil. In anaesthetised, mechanically ventilated rats, with their hindlimbs perfused with arterial blood at a constant flow, the gastrocnemius–plantaris–soleus muscle bundle was stimulated via sciatic nerve (2 Hz, 6–12 V, 0·05 ms) to contract repetitively for 30 min. Rats fed the n-3 PUFA diet developed higher maximum twitch tension than those fed the SF and n-6 PUFA diets (P< 0·05) and sustained twitch tension through more repetitions before the tension declined to 50 % of the maximum twitch tension (P< 0·05). The n-3 PUFA group used less oxygen for tension developed and produced higher venous lactate concentrations with no difference in glycogen utilisation compared with the SF and n-6 PUFA groups. These results further support that incorporation of DHA into skeletal muscle membranes increases the efficiency of oxygen use over a range of contractile force and this is expressed as a higher sustained force and prolonged time to fatigue.

The effect of eicosapentaenoic and docosahexaenoic acid on protein synthesis and breakdown in murine C2C12 myotubes

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been found to stimulate protein synthesis with little information regarding their effects on protein breakdown. Furthermore whether there are distinct effects of EPA and DHA remains to be established. The aim of the current study was to determine the distinct effects of EPA and DHA on protein synthesis, protein breakdown and signalling pathways in C2C12 myotubes. Fully differentiated C2C12 cells were incubated for 24h with 0.1% ethanol (control), 50 μM EPA or 50 μM DHA prior to experimentation. After serum (4h) and amino acid (1h) starvation cells were stimulated with 2 mM L-leucine and protein synthesis measured using (3)H-labelled phenylalanine. Protein breakdown was measured using (3)H-labelled phenylalanine and signalling pathways (Akt, mTOR, p70S6k, 4EBP1, rps6 and FOXO3a) via Western blots. Data revealed that after incubation with EPA protein synthesis was 25% greater (P<0.05) compared to control cells, with no effect of DHA. Protein breakdown was 22% (P<0.05) lower, compared to control cells, after incubation with EPA, with no effect of DHA. Analysis of signalling pathways revealed that both EPA and DHA incubation increased (P<0.05) p70s6k phosphorylation, EPA increased (P<0.05) FOXO3a phosphorylation, with no alteration in other signalling proteins. The current study has demonstrated distinct effects of EPA and DHA on protein metabolism with EPA showing a greater ability to result in skeletal muscle protein accretion.

Allele-specific behavior of molecular networks: understanding small-molecule drug response in yeast

The study of systems genetics is changing the way the genetic and molecular basis of phenotypic variation, such as disease susceptibility and drug response, is being analyzed. Moreover, systems genetics aids in the translation of insights from systems biology into genetics. The use of systems genetics enables greater attention to be focused on the potential impact of genetic perturbations on the molecular states of networks that in turn affects complex traits. In this study, we developed models to detect allele-specific perturbations on interactions, in which a genetic locus with alternative alleles exerted a differing influence on an interaction. We utilized the models to investigate the dynamic behavior of an integrated molecular network undergoing genetic perturbations in yeast. Our results revealed the complexity of regulatory relationships between genetic loci and networks, in which different genetic loci perturb specific network modules. In addition, significant within-module functional coherence was found. We then used the network perturbation model to elucidate the underlying molecular mechanisms of individual differences in response to 100 diverse small molecule drugs. As a result, we identified sub-networks in the integrated network that responded to variations in DNA associated with response to diverse compounds and were significantly enriched for known drug targets. Literature mining results provided strong independent evidence for the effectiveness of these genetic perturbing networks in the elucidation of small-molecule responses in yeast.